0680 air pollution engineering manual part1 1973

AIR POLLUTION

ENGINEERING MANUAL

SECOND EDIT ION

Compiled and Edi ted

b y

John A. Donie l ron

A IR P O L L U T I O N CONTROL DISTRICT

C O U N T Y OF LOS ANGELES

ENVIRONMENTAL PROTECTION AGENCY Office of Air ond Water Programs

Office of Air Quality Planning and Standards

Research Triangle P a r k N.C. 27711

M a y 1973

The AP ser ies of reports i s published by the Technical Publications Branch of the Information Services Division of the Office of Administration for the Office of Air and Water Programs, Environmental Protection Agency, to report the results of scientific and engineering studies, and information of general interest in the field of a i r pollution. Information reported in this ser ies includes coverage of intramural activities and of cooperative studies conducted in conjunction with state and local agencies, research institutes, and industrial organizations. Copies of A P reports a r e available f r ee of charge to Federal employees, current contractors and grantees, andnonprofit organizations - as supplies permit - from the Air Pollution Technical Information Center, Environmental Protection Agency, Research Triangle Park, North Carolina 27711 o r from the Superintendent of Documents.

Publication No. AP-40

FOREWORD

As concern for the quality of the atmosphere has grown, so also has the response to that concern. Federal, State, andlocal programs a r e assuming increasingly greater responsibility in the development and practice of the many disciplines that contribute to understanding and resolution of the a i r pollution problem.

Rapid program expansion imposes even greater demands for the dissemination of knowledge in the field of a i r pollution control. Much work has been accomplished by competent scientists and engineers. However, in many instances, the experience gained has not been transcribed and organized into a form readily accessible to those most in need of id'ormation.

We a r e pleased, therefore, to have the opportunity to make available this second edition of the Air Pollution Engineering Manual. Distilling as i t does the equivalent of hundreds of man-years of painstaking engineering innovation in the a i r pollution control field under one cover, it has become a valuable-if not indispensable-tool,

The manual is an outgrowth of the practical knowledge gained by the technical personnel of the Los Angeles County Air Pollution Control District, long recognized a s outstanding in the field. District personnel have worked closely with industry to develop emission controls where none formerly existed.

It will be noted that there a r e categories of industrial emissions that a re not discussed. The reason is that engineering controlapplications a re described for only those industries located in Los Angeles County.

Realizing the value of this manual to the field of a i r pollution, Mr. Robert L. Chass, Air Pollution ControlOfficer of Los Angeles County, has authorized the up-dating of the manual into this second edition. The editorial and technical content were developed exclusively by the District. The staff, in turn, was supervised during the development of the manual by Mr. Robert G. Lunche, Chief Deputy Air Pollution Control Officer, and Mr. Er ic Lemke, Director of Engineering. Mr. John A. Danielson, Senior Air Pollution Engineer, has again served a s editor.

The Environmental Protection Agency, recognizing the need for such a manual, is pleased to serve as publisher.

The f i r s t edition of the Air PollutionEngineering Manualwas acknowledged by its readers to be an outstanding and practical manual on the control of a i r pollution. It has been in wide demand throughout the United States and in many other parts of the world. Recog- nizing the need for an up-dated version, Editor John A. Danielson and the engineers of the Los Angeles County Air Pollution Control District have prepared this second edition.

The f i rs t edition was written in the early sixties. Since that time, many changes have occurred inthe field of a i r pollution control, and this second edition reflects these changes. The control of photochemically reactive organic solvent emissions is but one example, and a new chapter is devoted to this subject. Reducing the formation of oxides of nitrogen in combustion processes by improved burner and furnace designs i s another new innovation. Improved versions of afterburner control devices a re included. This second edition also contains a comprehensive index to aid the reader in locating quickly the subject of his choice.

The manual deals with the control of a i r pollution a t specific sources. This approach emphasizes the practical engineering problems of design and operation associated with the many sources of a i r pollution. These sources include metallurgical, mechanical, incineration, combustion, petroleum, chemical, and organic-solvent-emitting processes.

The manual consists of 12 chapters, each by different authors, and 5 appendices. The f i rs t five chapters treat the history of a i r pollution in Los Angeles County, the types of contaminants, and the design of a i r pollution control devices. The remaining chapters discuss the control of a i r pollution from specific sources. A reader interested in controlling a i r pollutionfrom a specific source can gainthe information needed by referring only to the chapter of the manual dealing with that source. If he then desires more general information about an a i r pollution control device, he can refer to other chapters. It is suggested that Chapter 1 be read since it cites Los Angeles County prohibitory rules that

regulated the degree of control efficiency required when the manual was written in 1971.

It is recognized that a i r pollution problems of one area can be quite different from those of another area. The a i r pollution problems presented in this manual originate in indus- t r ia l and commercial sources in the Los Angeles area. Consequently, some processes, e. g., the burning of coal in combustion equipment, a re not mentioned. Furthermore, the degree of a i r pollution control strived for in this manual corresponds to the degree of control demanded by a i r pollution statutes of the Los Angeles County Air Pollution Control District. Many other areas require less stringent control and permit less efficient control devices.

Sole responsibilityforthe information is borneby the District, which presents this second edition of the manual fo r the advancement of national understanding of the control of a i r pollution from stationary sources.

Robert L. Chass Air Pollution Control Officer County of Los Angeles

ACKNOWLEDGMENT

Under the p rov i s ions of the Cal i fornia l a w c rea t ing the L o s Angeles County A i r Pollution Control Dis t r i c t , the Board of Superv i sors is empowered t o a c t a s the A i r Po l lu t ionCon- t r o l Board. Responsible f o r superv i s ion and pol icy de te rmina t ion f o r the Dis t r i c t , t h e i r f i r m suppor t of needed a i r pollution control m e a s u r e s h a s advanced engineer ing capabili ty i n th i s field t o a high degree . The informat ion gained i n L o s Angeles County is applicable t o the improvement of a i r quali ty w h e r e v e r a i r pollution is exper ienced. Without the sup- p o r t of t h i s Board, the informat ion p resen ted h e r e would not have been possible.

KENNETHHAHN Second D i s t r i c t

ERNEST E. DEBS T h i r d D i s t r i c t

THE BOARD O F SUPERVISORS O F LOS ANGELES COUNTY

P E T E R F. SCHABARUM, Cha i rman First D i s t r i c t

JAMES A. HAYES F o u r t h D i s t r i c t

BAXTER WARD Fif th D i s t r i c t

EDITORIAL REVIEW COMMITTEE

Rober t L. Chass William B. K r e n z

E r i c E. Lemke Rober t G. Lunche

Rober t J. M a c Knight John L. Mi l l s

TECHNICAL ASSISTANCE

Ivan S. Decker t William F. Hammond

John L. McGinnity Rober t C. M u r r a y Ar thur B. Netzley

H e r b e r t Simon Rober t T. Walsh

Sanford M. Weiss John E. Wil l iamson

EDITORIAL ASSISTANCE

J e r o m e D. Beale Eugene Hochman George Thomas

Edwin J. Vincent Wayne E. Zwiacher

GRAPHIC ART

Lewis K. Smith

PHOTOGRAPHY

John A. Danielson

v i i

CONTENTS

CHAPTER 1 . I N T R O D U C T I O N

THE LOS ANGELES BASIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . RULES AND REGULATIONS IN LOS ANGELES COUNTY . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Regulation 11: Pe rmi t s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Regulation IV: Prohibitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rule 50: The Ringelmann Chart Rule 51: Nuisance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rule 52: Part iculate Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rule 53: Specific Contaminants Rules 53.1. 53.2. and 53 . 3: Sulfur Production and Sulfuric Acid Plants . . . . . . . . . . . . Rule 54: Dust and Fumes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rule 56: Storage of Petroleum Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rules 57 and 58: Open F i r e s and Incinerators . . . . . . . . . . . . . . . . . . . . . . . . . . Rule 59: Oil-Effluent Water Separators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rule 61: Gasoline Loading Into Tank Trucks and Tra i le rs . . . . . . . . . . . . . . . . . . . . Rules 62. 62.1. and 62.2. Sulfur Content of Fuels . . . . . . . . . . . . . . . . . . . . . . . Rule 63: Gasoline Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rule 64: Reduction of Animal Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rule 65: Gasoline Loading Jnto Tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rule 66: Organic Solvents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rule 66 . 1: Architectural Coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rule 66 . 2: Disposal and Evaporation of Solvents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rule 67: Fuel-Burning Equipment

. . . . . . . . . . . . . . . . . . . . . . Rule 68: Fuel-Burning Equipment Oxides of Nitrogen ROLE OF THE AIR POLLUTION ENGINEER . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Accomplishments of the P e r m i t System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . USE OF THIS MANUAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

General Design Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Specific Air Pollution Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CHAPTER 2 . AIR C O N T A M I N A N T S

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FACTORS IN AIR POLLUTION PROBLEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TYPES OF AIR CONTAMINANTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Organic Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Current Sources in Los Angeles County . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Hydrocarbons . 12 . . . Hydrocarbon derivatives . 12 Significance in Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Inorganic Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Current Sources in Los Angeles County

Oxides of nitrogen . 14 . . Oxides of sulfur . 15 . carbon monoxide . 15 Significance in Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Oxides of nitrogen . 15 . Oxides of sulfur . 15 . Carbon monoxide . 16 . . . Miscellaneous inorganic gases . 16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aerosols

Current Sources in Los Angeles County . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carbon o r soot particles . 16 . . Metallic oxides and sal ts . 17 . Oily or t a r r y drop-

. . . le ts . 17 . . . Acid droplets . 17 . . . Silicates and other inorganic dusts . 17 Metallic fumes . 18

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Significance in Air Pollution Problem AIR POLLUTION CONTROLS ALREADY IN EFFECT . . . . . . . . . . . . . . . . . . . . . . . . CONTROL MEASURES STILL NEEDED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Motor Vehicle Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 'Additional Controls Over Stationary Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Organic Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oxides of Nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Other Contaminants

i i x

x CONTENTS

C H A P T E R 3 . DESIGN O F L O C A L E X H A U S T S Y S T E M S

FLUID FLOW FUNDAMENTALS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bernoulli 's Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pitot Tube for Flow Measurement Correction Fac tors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

HOOD DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Continuity Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Flow Into a Duct . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nul lpoin t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design of Hoods for Cold P roces se s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Spray Booths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Abrasive Blasting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Open-Surface Tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Design of Hoods for Hot P roces se s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Canopy Hoods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Circular high-canopy hoods - 34 . . . Rectangular high-canopy hoods - 38 . . . Circular low-canopy hoods . 39 . . Rectangular low-canopy hoods . 40 . . . Enclosures - 41

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Specific Problems Steaming tanks - 42 . . . Preventing leakage . 42

Hood Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . High-Temperature Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Corrosion-Resistant Materials

Design Proportions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transition to Exhaust Duct . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

DUCT DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General Layout Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types of Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Inert ia Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Orifice Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Straight-Duct Friction Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Elbow and Branch Entry Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Exhaust sys tem calculator . 45 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Contraction and Expansion Losses

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Collection Equipment Design Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methods of Calculation Methods of Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Calculation Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fan Static P r e s s u r e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Balanced-Duct Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Blast Gate Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Checking an Exhaust System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Illustrative Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fan Curve Calculator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Corrections for Temperature and Elevation . . . . . . . . . . . . . . . . . . . . . . . . . . . . Duct Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FANDESIGN Centrifugal Fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Axial . Flow Fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fan Character is t ics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Influence of Blade Shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Geometrically Similar Fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Multirating Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

F a n L a w s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SeIecting a Fan F r o m Multirating Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Construction Proper t ies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Heat Resistance

Explosive-Proof Fans and Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F a n D r i v e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CONTENTS

VAPOR COMPRESSORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types of Compressors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Positive-Displacement Compressors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dynamic Compressors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reciprocating Compressors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Use m Air Pollution Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CHECKING O F EXHAUST SYSTEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Theory of Field Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Quantity Meters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Velocity Meters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pi to tTubes Pitot Tube Traversing Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Altitude and Temperature Corrections for Pitot Tubes . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Swinging-Vane Velocity Meter Calibrating the Velocity Meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Uses of the Velocity Meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

COOLING O F GASEOUS EFFLUENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methods of Cooling Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Dilution With Ambient Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Quenching With Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Natural Convection and Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Forced-Draft Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Factors Determining Selection of Cooling Device . . . . . . . . . . . . . . . . . . . . . . . . . . C H A P T E R 4 A I R P O L L U T I O N C O N T R O L E Q U I P M E N T FOR P A R T I C U L A T E M A T T E R

INERTLAL SEPARATORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Single-Cyclone Separators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Separation Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . P r e s s u r e Drop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Other Types of Cyclone Separators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . High-Efficiency Cyclone Separators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Multiple-Cyclone Separators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mechanical. Centrifugal Separators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Predicting Efficiency of Cyclones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Method of Solving a Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

WET COLLECTION DEVICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Theory of Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mechanisms for Wetting the Par t ic le . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types of Wet Collection Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Spray Chambers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cyclone-Type Scrubbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Orifice-Type Scrubbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mechanical Scrubbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mechanical. Centrifugal Collector With Water Sprays . . . . . . . . . . . . . . . . . . . . . . High-pressure Sprays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Venturi Scrubbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Packed Towers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . W e t F i l t e r s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The Role of Wet Collection Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . BAGHOUSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fil t rat ion P roces s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Direct intercept ion . 108 . . Impingement . 109 . . Diffusion - 110 . . Electrostat ics - 110 Baghouse Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . Clean cloth res i s tance - 110 Resistance of dust m a t 111 Effect of resis tance on design - 115

Fi l ter ing Velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fil ter ing Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fibe r s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cotton - 118 . . . Wool . 118 . . . Nylon - 118 . . Dyne1 - 118 . . . Orlon and Dacron - . . . 118 . . . Teflon - 119 Glass - 119

xii CONTENTS

Yarn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 Filament ya rns . 119 . . . Staple ya rns . 119

Weave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 Plain weave . 120 . . . Twill weave . 120 . . . Satin weave . 120

Finish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 Size and Shape of F i l t e r s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

Diameters of tubular fil tering elements . 121 . . . Length of tubular bags . 121 . . . Length-to-diameter rat io . 121 . . Multiple-tube bags . 122 . . Envelope type . 122

Installation of F i l te rs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 Arrangement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 Bag Spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 Bag Attachment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

Bottom attachments . 123 . Top support . 123 Cleaning of F i l t e r s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 Manual cleaning . 124 . . . Mechanical shakers . 125 . . Pneumatic shakers . 125 . . . Bag collapse . 127 . . Sonic cleaning . 127 . Reverse airflow . 128 . . . Reverse-a i r jets . 128

Cleaning Cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 Manually initiated cycles . 130 . . . Semiautomatic cycles . 131 . . . Fully automatic cycles . 131 . . Continuous cleaning . 131

Disposal of Collected Dust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 Baghouse Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132

Pushthrough versus Pullthrough . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 StructuralDesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 Hoppers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132

Size . 132 . . Slope of hopper s ides . 133 . . . Gage of meta l . 133 . . . Use of vibrators and rappers . 133 . . . Discharge . 134

Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Service 134

Bag Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 Precoating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

SINGLE-STAGE ELECTRICAL PRECIPITATORS . . . . . . . . . . . . . . . . . . . . . . . . . . 135 History of Electrostatic Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

Origins of Electrostat ic Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 Ear ly Experiments With Electrostat ics on Air Contaminants . . . . . . . . . . . . . . . . . . . 137 Development of the F i r s t Successful Precipi tator . . . . . . . . . . . . . . . . . . . . . . . . . 137 Improvements in Design. and Acceptance by Industry . . . . . . . . . . . . . . . . . . . . . . 138

Advantages and Disadvantages of Electr ical Precipitation . . . . . . . . . . . . . . . . . . . . . 138 Mechanisms Involved in Electr ical Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . 139 Diverse Applications of Electr ical Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . 141

Construction Details of Electr ical Precipi tators . . . . . . . . . . . . . . . . . . . . . . . . . 141 Discharge electrodes . 141 . Collecting electrodes . 141 . . . Tubular collecting electrodes . 141 . . Removal of dust f rom collecting electrodes . 143 . . Precipi tator shells and hoppers . 144

High Voltage for Successful Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 Tube-type rect i f iers . 145 . . Solid-state rect i f iers . 145

Effects of Wave F o r m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 Controlled Sparking Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 Operating Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 Uniform Gas Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 Cast of Electr ical Precipi tator Installations . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 Theoretical Analysis of Precipi tator Per formance . . . . . . . . . . . . . . . . . . . . . . . . 147

Par t ic le charging . 147 . . . Par t ic le migration . 148 Theoretical Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

. . . . . . . . . . . . . . . . . Deficiencies in Theoretical Approach to Precipi tator Efficiency 150 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~ f f ~ ~ t ~ of Resistivity 150

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methods of Reducing Reentrainment 152 . . . . . . . . . . . . . . . . . . . Prac t ica l Equations for Precipi tator Design and Efficiency 153

Effects of Nonuniform Gas Velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 . . . . . . . . . . . . . . . . . . . . . . . . Important Fac tors in the Design of a Precipi tator 156

Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

CONTENTS xi i i . .

TWO-STAGE ELECTRICAL PRECIPITATORS . . Theoretical Aspects . . . . . . . . . . . . . . .

Theory of Dust Separation . . . . . . . . . . . Par t ic le Charging . . . . . . . . . . . . . . . Drif t Velocity . . . . . . . . . . . . . . . . . . Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Fac tors Electr ical Requirements . . . . . . . . . . . . Air Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Distribution Auxiliary Controls . . . . . . . . . . . . . . .

Construction and Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Assembly

. . . . . . . . . . . . . . . . . . Maintenance Safety . . . . . . . . . . . . . . . . . . . . . .

Application . . . . . . . . . . . . . . . . . . . . Two-Stage Precipi tators of Special Design . . Equipment Selection . . . . . . . . . . . . . .

OTHER PARTICULATE-COLLECTING DEVICES . . . . . . . . . . . . . . . . Settling Chambers

Impingement Separators . . . . . . . . . . . . . Panel F i l t e r s . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . Prec leaners

C H A P T E R 5 . CONTROL E Q U I P M E N T FOR GASES A N D VAPORS

AFTERBURNERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Direct-Flame Afterburners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Afterburner Chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Gas Burners for Afterburners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Mixing-Plate Burners - . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Multi-Port B u r n e r s

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nozzle Mixing and.. Premixing Burners Sources of Combus6on Air for Gas Burners . . . . . . . . . . . . . . . . . . . . . . Oil Fir ing of Afterburners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Afterburner Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Direct-Flame Afterburner Efficiency i Direct-Flame Afterburner Design Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . Catalytic Afterburners . . . . . . . . . . . . . . . . . . . '. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Operation

Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Recovery of Heat F r o m Afterburner Exhaust Gases . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preheating of Afterburner Inlet Gases BOILERS USED AS AFTERBURNERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Conditions for Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Manner of Venting Contaminated Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Adaptable Types of Equipment . . . . . . . . . . . . . . . . . . .I . . . . . . . . . . . . . . . . . .

Boilers and Fi red Heaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Burners

Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Procedure

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . T e s t D a t a ADSORPTION EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Types of Adsorbents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Use of Activated Carbon in Ai r Pollution Control

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Saturation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Retentivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Breakpoint

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Adsorption of Mixed Vapors Heat of Adsorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carbon Regeneration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Equipment Design I

xiv CONTENTS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F i x e d - B e d A d s o r b e r Conical fixed-bed a d s o r b e r . 196

Continuous A d s o r b e r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . P r e s s u r e Drop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Operat ional P r o b l e m s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . P a r t i c u l a t e Mat te r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Corros ion P o l a r and Nonpolar Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

VAPOR CONDENSERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types of Condensers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sur face and Contact Condensers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Typical Ins ta l la t ions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Condensers in Control Sys tems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Subcooling Condensate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Contact Condensers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sizing Contact Condensers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

S u r f a c e Condensers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C h a r a c t e r i s t i c s of Condensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design of Sur face Condensers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GAS ABSORPTION EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Genera l Types of A b s o r b e r s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Packed Tower Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Packing Mate r ia l s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Liquid Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tower Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tower Diamete r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Number of T r a n s f e r Units (NTU) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Height of a T r a n s f e r Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . P r e s s u r e Drop Through Packing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I l lus t ra t ive P r o b l e m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

P l a t e o r T r a y Towers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types of P l a t e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Bubble Cap P l a t e Tower Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Liquid Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . P l a t e Design and Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flooding Liquid Gradient on P l a t e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . P l a t e Spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tower Diamete r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Number of Theore t i ca l P l a t e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I l lus t ra t ive P r o b l e m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Comparison of Packed and P l a t e Towers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V e s s e l s fo r Dispers ion of Gas in Liquid

Spray Towers and Spray Chambers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ventur i A b s o r b e r s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

NOTATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . FURNACE TYPES R e v e r b e r a t o r y F u r n a c e . . . Cupola F u r n a c e . . . . . . . . . . . . . . Combustion A i r

Methods of Charging . . . . Prehea t ing Combustion A i r

E l e c t r i c F u r n a c e . . . . . . . D i r e c t - A r c F u r n a c e . . . . Ind i rec t -Arc F u r n a c e . . . Induction F u r n a c e . . . . . Res i s tance F u r n a c e . . .

Crucible F u r n a c e . . Tilt ing F u r n a c e . . . .

C H A P T E R 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

M E T A L L U R G I C A L E Q U I P M E N T

. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . .

CONTENTS xv

P i t Crucible . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238 Stationary Crucible . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238

Po t Furnace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238 STEEL-MANUFACTURING PROCESSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239

Open-Hearth Furnaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 The Ai r Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241 Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242 A i r Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244

Elec t r ic -Arc Furnaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245 The Air Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246 Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246 A i r Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252

Baghouse dust col lectors . 252 . . Elec t r ica l precipi ta tors . 252 . . Water s c rubbe r s . 253 Electric-Induction Furnace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254

The Ai r Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254 Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255 A i r Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255

IRON CASTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CupolaFurnaces 256

The A i r Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258 Ai r Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258

Af te rburners - 259 . . Baghouse dust col lectors . 260 . . Elec t r ica l precipi ta tors . 260 I l lustrat ive P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262

Elec t r ic -Arc Furnaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 The A i r Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 Ai r Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267

. Baghouse dust col lectors . 267 . . Elec t r ica l precipi ta tors 267 Jnduction Furnaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 Reverbera tory Furnaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267

. . . . . . . . . . . . . . . . . . . . SECONDARY BRASS- AND BRONZE-MELTING PROCESSES 269 Furnace Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269

The Ai r Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269 Charac te r i s t i cs of emiss ions - 269 . . Fac to r s causing la rge concentrations of zinc fumes - 270 Crucible furnace.- pit and t i l t type . 272 . . Elec t r ic furnace-lo w.frequency induction type . 272 Cupola furnace - 273

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements 273 Reverbera tory furnace.-ope n-hear th type . 273 . . Reverbera tory furnace- -cyl indrical type . 275 Reverberatory furnace.. tilting type . 275 . . Reverbera toryfurnace- . r o t a ry ti l t ingtype . 275 . . Crucible- typefurnaces - 278 . . Low-frequency induction furnace - 278 . . Cupolafurnace - 279

A i r Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 . . . Baghouses - 279 . . . Elec t r ica l precipi ta tors - 280 Scrubbers - 282

. . . . . . . . . . . . . . . . . . . . . . . . . . SECONDARY ALUMINUM-MELTING PROCESSES 283 Types of P r o c e s s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283

Crucible Fu rnaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reverbera tory Fu rnaces 284

Fue l -F i red Fu rnaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electr ical ly Heated Furnaces 284

Charging P rac t i c e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 Pouring P rac t i c e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fluxing 285

. . . . . Cover fluxes - 286 . Solvent fluxes 286 Degassing fluxes - 286 . . . Magnesium-reducing fluxes 286 Magnesium reduction with chlor ine 287

The A i r Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pa r t i c l e Size of Fumes F r o m Fluxing 288 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements 288

A i r Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SECONDARY ZINC-MELTING PROCESSES 293 Zinc Melting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293

The Ai r Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293

z i n c vaporizat ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293

xvi CONTENTS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reduction Retor t Furnaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reduction in Belgian Retorts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Distillation Retort Furnaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Muffle Furnaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . LEAD REFINING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reverberatory Furnaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lead Blast Furnaces

The Alr Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hoodlng and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pot-Type Furnaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Barton P roces s

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . METAL SEPARATION PROCESSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aluminum Sweating . . . . . . . . . . . . . . . . . . . . Zinc. Lead. Tin . Solder. and LOW- elt tin^ Alloy Sweating

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem Contaminants f r o m aluminum-separating processes . 306 . . . Contaminants f rom low-temperature sweating . 306

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment Aluminum-separating processes . 308 . . . Low-temperature sweating . 308 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CORE OVENS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Typeso fOvens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Heating Core Ovens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Core Binders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FOUNDRY SAND-HANDLING EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types of Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements Shakeout grates . 317 . Other sand-handling equipment . 317

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HEAT TREATING SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Heat Treating Equipment The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment

CHAPTER 7 . M E C H A N I C A L E Q U I P M E N T

. . . . . . . . . . . . . . . . . . . . . . . . . . . HOT-MIX ASPHALT PAVING BATCH PLANTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Raw Materials Used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Basic Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plant Operation The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment

CONTENTS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Variables Affecting Scrubber Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Collection Efficiencies Attained

Future Trends in Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CONCRETE-BATCHING PLANTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wet-Concrete-Batching Plants

The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . Cement-receiving and storage sys tem 335 Cement weigh hopper 336 Gathering hoppers . 336

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dry-Concrete-Batching Plants The Air Pollution Probiem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment Dust created by truck movement . 337

Central Mix Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment CEMENT-HANDLING EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Receiving Hoppers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Storage and Receiving Bins

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Elevators and Screw Conveyors

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hopper Truck and Car Loading

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ROCK AND GRAVEL AGGREGATE PLANTS

The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements

Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MINERAL WOOL FURNACES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types and Uses of Mineral Wool Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mineral Wool Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . Baghouse Collection and Cupola Air Contaminants

. . . . . . . . . . . . . . . . . . . . . . Afterburner Control of Curing Oven Air Contaminants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reducing Blowchamber Emissions

Controlling Asphalt Fumes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PERLITE-EXPANDING FURNACES

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Uses

Mining Sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Per l i te Expansion Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Expansion Furnaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GasandProductCool ing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Product Collectors and Classif iers

The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements

-Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FEED AND GRAIN MILLS - -

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Receiving. Handling. ands tor ing Operations

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Feed-Manufacturing P rocesses The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . Receiving. Handling. and Storing Operations . . . . Feed-Manufacturing Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements

. . . . . . . . . . . . . . . . . . . . . . . . . . . Receiving. Handling. and Storing Operations Feed-Manufacturing P rocesses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

xvii .

xviii CONTENTS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . Receiving. Handling. and Storing Operations Feed-Manufacturing P roces se s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fi l te r Vents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cyclones

Baghouses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PNEUMATIC CONVEYING EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types of Pneumatic Conveying Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types of Air-Moving Used in Conveying

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pre l iminary Design Calculations The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment DRIERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rotary Dr i e r s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flash Dr i e r s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Spray Dr i e r s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Other Types of Dr i e r s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dus tcon t ro l

Drying With Solvent Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Smoke and Odor Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . WOODWORKING EQUIPMENT

Exhaust Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Construction of Exhaust Systems

The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Disposal of Collected Wastes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . RUBBER-COMPOUNDING EQUIPMENT

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Additives Employed in Rubber Compounding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements ; . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ASPHALT ROOFING F E L T SATURATORS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Description and Operation Asphalt Coating of Fe l t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Roof Capping Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements

Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Afterburners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Scrubbers Electr ical Precipi tators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Baghouses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Glass F iber Mats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PIPE COATING EQUIPMENT

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction Methods of Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pipe Dipping

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pipe Spinning Pipe Wrapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preparat ion of Enamel

The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ABRASIVE BLAST CLEANING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction

CONTENTS xix

Abrasive Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Method of Propelling the Abrasive 397

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Equipment Used to Confine the Blast 398 The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401 Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401 Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401

ZINC-GALVANIZING EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402

Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402 Cover Fluxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402 Foaming Agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403 Dusting Fluxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403

The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403 Physical and Chemical Composition of the Contaminants . . . . . . . . . . . . . . . . . . . . . 404

Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404 Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406

Baghouses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406 Electr ical Precipi tators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409

TIRE BUFFING EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410 The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411 Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411 Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412

Cyclones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412 Cyclones With Afterburners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413 Cyclones With Dry F i l t e r s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413 Cyclones With Baghouses and Dry F i l t e r s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413

Other Tread Removal Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413 Cutting Type Detreader . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413 Water Spray at Rasp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414

Cost of Pollution Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414 WOOD TREATLNG EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414 Methods of Treating Wood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415 The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418 Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419 Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419

CERAMIC SPRAYING AND METAL DEPOSITION EQUIPMENT . . . . . . . . . . . . . . . . . . . 421 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421 Ceramic Spraying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422

The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422 Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423

Metal Deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429 The Air Pollution P rob lem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431 Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432

CHAPTER 8 . I N C I N E R A T I O N

. . . . . . . . . . . . . . . . DESIGN PRINCIPLES FOR MULTIPLE-CHAMBER INCINERATORS 437 Retort Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437 In-Line Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437 Description of the P roces s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 439 Design Types and Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440

Comparison of Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440 Principles of Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440 Design Fac tors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441

Design Precepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441 GENERAL-REFUSE INCINERATORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 443

The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444 Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Procedure 445

General Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446 Refractories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A47

CONTENTS XX

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grates and Hearths A i r h l e t s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Induced-Draft System Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Illustrative Problem

MOBILE MULTIPLE-CHAMBER INCINERATORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stack Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Induced-Draft Fan System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Standards of Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Refractories Grates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . AirInle ts Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Auxiliary Burners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stack Ernissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Illustrative Problem

MULTIPLE-CHAMBER INCINERATORS FOR BURNING WOOD WASTE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Description of the Refuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipmenr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Incinerator Arrangements Design Procedure for Mechanical Feed Systems . . . . . . . . . . . . . . . . . . . . . . . . . .

SurgeBin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Screw or Drag Conveying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pneumatic Conveying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Standards for Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Refractories Grates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Exterior Walls A i r p o r t s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Operation of Incinerators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Illustrative Problem

FLUE-FED APARTMENT INCINERATORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Description of Refuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stack Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Installation of Afterburner on a Roof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Procedure Draft control . 473 . . . Chute door locks . 474 . . . Design parameters . 474 . . . Limitations . 474 . . . Typical installations . 475 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Standards for Construction

. . . Mounting and supports . 476 . . . Metals . 476 . . . Castable refractories 476 , Firebrick . 476 . . . Insulating firebrick . 476 . . . Burners . 476 . . . Draft control damper . 477 . . . Chute door locks . 477 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stack Emissions

Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Basement Afterburner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Procedure Design parameters . 478 . Typical installation . 478 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Standards for Construction Hot-zone refractory . 479 . . . Draft control damper . 479 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stack Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Operation . . . . . . . . . . . . . . . . . . . . . . . Multiple-Chamber Incinerator. Basement Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Procedure

. . . . . Draft control 480 Typical installation 480

CONTENTS xxi

Standards for Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stack Emissions Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Illustrative Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

PATHOLOGICAL-WASTE INCINERATORS . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Design Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ignition chamber . 487 . . . Secondary combustion zone . 488 . . . Stack design

Piping requirements . 489 . . . Crematory design . 489 . . . Incinerator design configuration . 489

Standards for Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stack Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Illustrative Problem

DEBONDING OF BRAKE SHOES AND RECLAMATION OF ELECTRICAL EQUIPMENT WINDINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Debonding of Brake Shoes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reclamation of Electrical Equipment Winding . . . . . . . . . . . . . . . . . . . . . The Air Pollution Froblem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollutiog Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Primary Ignition Chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Secondary Combustion Chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Typical Reclamation Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . Standards for Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Illustrative Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

DRUM RECLAMATION FURNACES . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Description of the Furnace Charge . . . . . . . . . . . . . . . . . . . . . . . . . . Description of the Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Primary Ignition Chamber. Batch Type . . . . . . . . . . . . . . . . . . . . . . . . Primary Ignition Chamber. Continuous Type . . . . . . . . . . . . . . . . . . . . . Afterburner (Secondary Combustion Chamber) . . . . . . . . . . . . . . . . . . . . Draft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Standards for Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Illustrative Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

WIRE RECLAMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Descriptionof the Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~ e s c r i p t i o n of the Charge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Primary Ignition Chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Secondary Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Draft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Equipment Arrangement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Refractories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Charge Door . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Combustion Air Por ts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gas Burners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .,. . . Illustrative Problem . . . . . . . . . . . . . . . . . . . . i . . . . . . . . . . . . . .

C H A P T E R 9 . COMBUSTION EQUIPMENT GASEOUS AND LIQUID FUELS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . .E_ i.. . , . . .

xxii CONTENTS

Gaseous Fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oi lFue l s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Blacksmoke . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Whitesmoke Particulate Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sulfur in Fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sulfur Oxides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oxides of Nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Methods Prohibitions Against Sulfur Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Removal of Sulfur and Ash F r o m Fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Illustrative Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

GAS AND OIL BURNERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Draft Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gas Burners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Partially Aerated Burners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Multiple-Port Gas Burners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Forced-Draft Gas Burners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gas Flow Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oil Burners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Viscosity and Oil Preheaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Smoke and Unburned Contaminants . . . . . . . . . . . . . . . . . . . . . . . . . . Ash and Sulfur Oxides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oxides of Nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . BOILERS. HEATERS. AND STEAM GENERATORS . . . . . . . . . . . . . . . . . . . . . . . . .

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Industrial Boilers and Water Heaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Power Plant Steam Generators Refinery Heaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hot Oil Heaters and Boilers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fireboxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SootBlowing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Solid Particulate Emission During Normal Oil Fir ing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Soot-Blowing Particulates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sulfur Dioxide Sulfur Trioxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Excessive Visible Emissions :

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oxides of Nitrogen p Estimating NOx Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Methods .. w . ..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Combustible Particulates

.. : .. Soot Collectors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Collection of Sulfur Oxides . . . . . . . . . . . . Wet absorption 569 Dry absorption 569 Wet adsorption 570 ;

. . . . . Catalytic oxidation 570 Other processes for removing SO2 f rom stack gases 570 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Controlling Oxides of Nitrogen . . . . Reduction of NOxby modification of boiler operation 571 Removal of NOx by:

treatment of flue gas . 576 ...

CHAPTER 1 0 . PETROLEUM EQUIPMENT j .$

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GENERAL INTRODUCTION Crude Oil Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Refining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fla res and Blowdown Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pressu re Relief Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Storage Vessels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bulk-Loading Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Catalyst Regeserators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CONTENTS xxiii

Effluent-Waste Disposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584 Pumps and Compressors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584 Air-Blowing Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584 Pipeline Valves and Flanges. Blind Changing. Process Drains . . . . . . . . . . . . . . . . . 584 Cooling Towers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584 Vacuum Jets and Barometric Condensers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584

Effective Air Pollution Control Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 585 Marketing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 585

WASTE-GAS DISPOSAL SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 585 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 585

Design of Pressure Relief System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 588 Safety Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 589 Rupture Discs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 590

Sizing rupture discs . 592 . . . Sizing liquid safety valves . 593 . . . Sizing vapor and gas relief and safety valves . 594 . . .

. . . . Installing relief and safety valves and rupture discs . 595 . . . Knockout vessels 596 Sizing a blowdown line . 598

The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 604 Smoke From Flares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 604 Noise From Flares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 604 Other Air Contaminants F rom Flares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 605

Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 605 Types of Flares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 605

. . . Elevated flares . 605 . . . Ground level f lares . 610 . . . Effect of steam injection 613 Design of a smokeless f lare . 614 . . . Pilot ignition system . 616 . . .

. . . Instrumentation and control of steam and gas . 617 . . . Supply and control of steam 618 Design of water-injection-type ground flares . 623 . . .

. . . Design of venturi-type ground flares 624 Maintenance of f lares 626 STORAGE YESSELS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 626

Types of Storage Vessels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 626 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pressure Tanks and Fixed-Roof Tanks 627 Floating-Roof Tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627 Conservation Tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 628 . . . . . . . . . . . . . . . . . . . . . . . . . Open-Top Tanks. Reservoirs . Pits. and Ponds , 631

The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 631 . . . . . . . . . . . . . . . . . . . . . . . . . Factors Affecting Hydrocarbon Vapor Emissions 631 Hydrocarbon Emissions From Floating-Roof Tanks . . . . . . . . . . . . . . . . . . . . . . . 632

Withdrawal emissions . 634 . . . Application of results . 634 Hydrocarbon Emissions From Low-Pressure Tanks . . . . . . . . . . . . . . . . . . . . . . . 634 Hydrocarbon Emissions From Fixed-Roof Tanks . . . . . . . . . . . . . . . . . . . . . . . . . 638 Aerosol Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 642 Odors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 642

Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643 Seals for Floating-Roof Tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 644 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Floating Plastic Blankets 644 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plastic Microspheres 645 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vapor Balance Systems 647 Vapor Recovery Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 647 Miscellaneous Control Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 648 Masking Agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649 Costs of Storage Vessels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649

LOADING FACILITIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649

Loading Racks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 652 Marine Terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 652 Loading Arm Assemblies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 652 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem 653

Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 655 . . . . . . . . . . . . . . . . . . . . Types of Vapor Collection Devices for Overhead Loading 655 Collection of Vapors F r o m Bottom Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . 658 . . . . . . . . . . . . . . . . . . . . . Factors Affecting Design of Vapor Collection Apparatus 659 Methods of Vapor Disposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 660

xxiv CONTENTS

CATALYST REGENERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types of Catalysts Loss of Catalyst Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Regeneration P roces se s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FCC Catalyst Regenerators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TCC Catalyst Regenerators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Catalyst Regeneration in Catalytic Reformer Units . . . . . . . . . . . . . . . . . . . . . . . .

The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Wet- and Dry.Type. Centrifugal Dust Collectors . . . . . . . . . . . . . . . . . . . . . . . . . Electr ical Precipi tators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carbon Monoxide Waste-Heat Boilers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Economic Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OIL-WATER EFFLUENT SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Functions of Systems

Handling of Crude-Oil Production Effluents . . . . . . . . . . . . . . . . . . . . . . . . . . . . Handling of Refinery Effluents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Treatment of Effluents by Oil-Water Separators . . . . . . . . . . . . . . . . . . . . . . . . . Clarification of Final-Effluent Water S t reams . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . Effluent Wastes F r o m Marketing Operations The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Hydrocarbons F r o m Oil-Water Separators . . . . . . . . . . . . . . . . . . . . . . . . . . . . Treatment of Refinery Liquid Wastes a t Their Source . . . . . . . . . . . . . . . . . . . . . .

Oil-in-water emulsions . 677 . . . Sulfur-bearing waters . 677 . . . Acid sludge . 678 . . . Spent caustic wastes . 679

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PUMPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types of Pumps

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Positive-Displacement Pumps Centrifugal Pumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Results of Study to Measure Losses F r o m Pumps

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . AIRBLOWN ASPHALT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Recovery of Asphalt F r o m Crude Oil Airblowing of Asphalt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VALVES

Types of Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Manual and Automatic Flow Control Valves.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . P r e s s u r e Relief and Safety Valves The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Total Emissions F r o m Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment

COOLING TOWERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Character is t ics of Cooling Tower Operation

The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment

MISCELLANEOUS SOURCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Airblowing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Blind Changing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Equipment Turnarounds Tank Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Use of Vacuum Je ts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Use of Compressor Engine Exhausts

C H A P T E R 1 1 . C H E M I C A L P R O C E S S I N G E Q U I P M E N T

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . RESIN KETTLES

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types of Resins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Phenolic Resins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Amino Resins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Polyester and Alkyd Resins

CONTENTS xxv

. . , " . r:> .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Polyurethane ........ ..-. ... ..:. .. . . . . Thermoplast ic Resins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ;,

. . . . . . . - ..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Polyvinyl Resins ;. ..... Polystyrene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pet ro leum and Coal T a r Res ins

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Resin- Manufacturing Equipment The Ai r Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ai r Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

VARNISH COOKERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Definitions Produc ts and P r o c e s s e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Major Types of Varnish Cooking Equipment

. , . ~ , The A i r Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .- ...

Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ai r Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Scrubbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Condensers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Afterburners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . SULFURIC ACID MANUFACTURING , . . . . . . . . . . . . . . . . . . . . . . Contact P r o c e s s . . . . . . . . . . . . . . . . . . . . ,

The A i r Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment "

Sulfur Dioxide Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acid Mist Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . Elec t r ica l precipi ta tors - 720 Packed-bed s epa ra to r s -. 720 . . . . Wire m e s h m i s t e l iminators - 721 Ceramic f i l t e r s - 72.2 Sonic agglomeration - 722 . . . Miscellaneous devices - 722

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SULFUR SCAVENGER PLANTS Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sulfur in Crude Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Removal of H2S F r o m Refinery Waste Gases . . . . . . . . . . . . . . . . . . . . , . . . . . . . The Ai r Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ai r Pollution Control Equipment ,

Incineration Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stack Dilution Ai r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ,

Incinerator Stack Height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plan t Operational P rocedu re s

Tai l Gas Trea tment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PHOSPHORIC ACLD MANUFACTURING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Phosphoric Acid P r o c e s s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ,

The A i r Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment , . . . . . . . . . . . . . SOAP, FATTY ACID, AND GLYCERINE MANUFACTURING EQUIPMENT

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Raw Mater ia ls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fat ty Acid Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Glycerine Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Soap Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Soap Finishing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Ai r Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . SYNTHETIC DETERGENT SURFACTANT MANUFACTURING EQUIPMENT

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Raw Mater ia ls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . P r o c e s s e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Oleum Sulfonation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Ai r Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ole- Sulfonation and Sulfation

P r o c e s s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Ai r Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

xxvi CONTENTS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sulfur Trioxide Vapor Sulfonation The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sulfur Trioxide Liquid Sulfonation '

The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chlorosulfuric Acid Sulfation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sulfoalkylation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment SYNTHETIC DETERGENT PRODUCT MANUFACTURING EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Raw Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Proces ses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Slurry Preparat ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Spray Drying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Granule Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GLASS MANUFACTURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types of Glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Glass-Manufacturing P roces s . . . . . . . . . . . . . . . . . . . . Handling . Mixing. and Storage Systems f o r Raw Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . Continuous Soda-Lime Glass-Melting Furnaces

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem Source t e s t data - 770 . Opacity of stack emissions . 771

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Methods

Control of r aw mater ia l s - 775 . Batch preparation - 775 . Checkers . 777 . . . Prehea ters - 777 . . Refractories and insulation - 778 . . . Combustion of fuel . 778 . . . Electr ic melting - 779 . . . Baghouses and centrifugal sc rubbers . 779 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Glass-Forming Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FRIT SMELTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Raw Materials

Types of Smel te rs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F r i t Manufacturing

. . . . . . . . . . . . . . . . . . . . . . . . . . . . Application. Firing. and Uses of Enamels The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FOOD PROCESSING EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Coffee Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Batch Roasting

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . An Integrated Coffee Plant ., .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Smokehouses The Smoking P roces s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Atmospheric Smokehouses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Recirculating Smokehouses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Smoking by Immers ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Smoking by Elec t r ica l Precipi ta t ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Ai r Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Afterburners . 796 . Elec t r ica l precipi ta tors . 797 Elec t r ica l precipitation ve r su s incineration . 797 Bypassing control devices during nonsmoking per iods . 798

Deep F a t Frying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Ai r Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Livestock Slaughtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Ai r Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Edible-Lard and Tallow Rendering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dry Rendering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Batchwise rendering . 803 . Continuous low-temperature rendering . 8 0 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wet Rendering

The Ai r Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

FISH CANNERIES AND FISH REDUCTION PLANTS . . . . . . . . . . . . . . . . . . . . . . . . . Wet-Fish Canning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tuna Canning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cannery Byproducts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fi sh Meal Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F i s h Solubles and F i sh Oil Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Digestion P roces se s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Ai r Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Odors F r o m Meal D r i e r s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Smoke F r o m D r i e r s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dust F r o m D r i e r s and Conveyors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Odors F r o m Reduction Cookers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Odors F r o m Digesters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Odors F r o m Evaporators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Odors F r o m Edibles Cookers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Controlling F i sh Meal D r i e r s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Incinerating Dr i e r Gase s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chlorinating and Scrubbing D r i e r Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Controlling Reduction Cookers and Auxiliary Equipment . . . . . . . . . . . . . . . . . . . . . Controlling Diges te rs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Controlling Evaporators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Collecting Dust Controlling Edible-Fish Cookers . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

REDUCTION O F INEDIBLE ANIMAL MATTER . . . . . . . . . . . . . . . . . . . . . . . . . . . Batchwise Dry Rendering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Continuous Dry Rendering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wet Rendering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Refining Rendered Produc ts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Drying Blood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . P r o c e s s i n g F e a t h e r s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rotary A i r D r i e r s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Ai r Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cookers a s Prominent Odor Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Odors F r o m Air D r i e r s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Odors and Dust F r o m Rendered-Product Systems . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grease-Process ing Odors Raw-Mater ia ls Odors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

xxviii CONTENTS . . L..7

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Emission Rates F r o m Cookers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Emission Rates F r o m Driers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Controlling High-Moisture S t reams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Subcooling Condensate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Condenser Tube Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Interceptors in Cooker Vent Lines

Vapor Incinerator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Condensation-Incineration Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carbon Adsorption of Odors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Odor Scrubbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Odor Masking and Counteraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ELECTROPLATING The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilating Requirements

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Scrubbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mist Inhibitors

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . INSECTICIDE MANUFACTURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methods of Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Solid-Insecticide Production Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Liquid-Insecticide Production Methods

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HAZARDOUS RADIOACTIVE MATERIAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hazards in the Handling of Radioisotopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . Characteris t ics of Solid. Radioactive Waste . . . . . . . . . . . . . . . . . . . . . . . . . . . Characteris t ics of Liquid. Radioactive Waste . . . . . . . . . . . . . . . . . . . . . . . Problems in Control of Airborne. Radioactive Waste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements

Hooding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ventilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment Reduction of Radioactive. Particulate Matter a t Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design of Suitable Air-Cleaning Equipment

. . . Reverse-jet baghouse - 841 Wet collectors - 841 . . . Electr ical precipitators - 842 . . . Glass fiber f i l te rs - 842 Paper f i l ters - 843

. . . . . . . . . . . . . . . . . . . . . . . . . Disposal and Control of Solid . Radioactive Waste . . . . . . . . . . . . . . . . . . . . . . . . Disposal and Control of Liquid. Radioactive Waste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OIL AND SOLVENT RE-REFINING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Re-refining P rocess for Oils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Re-refining Process for Organic Solvents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution F r o m Oil Re-refining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution F r o m Solvent Re-refining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oil Re-refining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Solvent Re -refining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CHEMICAL MILLING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Description of the P rocess . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Etchant Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air Pollution Problem

Mists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vapors Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . e e

Solvents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and VentilationsRequirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Corrosion Problems

CONTENTS

CHAPTER 12 . ORGANIC SOLVENT E M I T T I N G E Q U I P M E N T

SOLVENTS AND THEIR USES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lntroduction

R u l e 6 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Limitations on the Use of Photochemically Reactive Solvents Baking and Curing Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Air Pollution Control Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SURFACE COATING OPERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types of Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Spray Booths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flowcoating Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dip Tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ..... Roller Coating Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

" .z..vw .! The A i r Pollution P rob l em . . . . . . A ..&.A > . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Ai r Contaminants F r o m Pa in t Spray Booths . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ai r Contaminants F r o m Other Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Requirements fo r Pa in t Spray Booths

Requirements for Other Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Control of Pa in t Spray Booth Part iculates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Control of Organic Vapors F r o m Surface Coating Operations

. . . . . . . . . . . . . . . . PA1NT:BAKING OVENS AND OTHER SOLVENT-EWTTING OVENS Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bake Oven Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Batch Type Ovens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Continuous Ovens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Heating of Ovens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oven Circulating and Exhaust Sys tems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A i r s e a l s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The Ai r Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements

A i r Pollution Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Other Ovens Emitting Air Contaminants . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Can Lithograph Oven . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Print ing Sys tem Ovens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SOLVENT DEGREASERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Design and Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types of Solvent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The A i r Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . Air Pollution Control Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ; Methods of Minimizing Solvent Emiss ions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tank Covers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Controlling Vaporized Solvent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

DRY CLEANING EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Wash Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Combination Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ext rac tors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tumblers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fi l t e r s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Muck Rec la imers The A i r Pollution P rob l em . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Solvents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Hooding and Ventilation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ai r Pollution Control Methods . . . . . . . . . . . . . . . . . . . . . . . .- . . . . . . . . . . .

xxx CONTENTS

A d s a r b e r s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 883 L i n t T r a p s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 884

REFERENCES

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 885

A P P E N D I X E S

APPENDIX A: RULES AND REGULATIONS O F T H E AIR POLLUTION CONTROL DISTRICT. COUNTY O F LOS ANGELES

APPENDIX B: ODOR-TESTING TECHNIQUES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Odor P a n e l The Odor Evaluation Room . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sampling Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Evaluation of Odor Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Determinat ion of Odor Concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

APPENDIX C: HYPOTHETICAL AVAILABLE HEATS FROM NATURAL GAS . . . . . . . . . APPENDIX D: MISCELLANEOUS DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . APPENDIX E: EMISSION SURVEYS. INVENTORIES. AND FACTORS . . . . . . . . . . . . .

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Values of Surveys

Need fo r Continuing Surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conduc t~ng the Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S o u r c e s of Survey Informat ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Detailed V e r s u s "Short-Cut" Surveys

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Elements of a Survey Developing a L i s t of Surveyees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Developing Emiss ion F a c t o r s . . . . . . . . . . . . . . . . . . . . . . . Determining and P h r a s l n g Appropr ia te Questions

Designing Effective Questionnaires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Trea t ing and Evaluating the Data. Reporting Resu l t s . and Recommending Action

SUBJECT I N D E X

SUBJECT INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 969

C H A P T E R 1

INTRODUCTION

JOHN A. DANIELSON, Senior Air Po l lu t ion Engineer

ROBERT L. CHASS, A L ~ Pol lut lon Control Off lcer

ROBERT G. LUNCHE, Chlef Deputy Alr Pol lut lon Control Offlcer

CHAPTER 1

INTRODUCTION

The pas t two decades have witnessed remarkable p rog re s s in the development of reasonable engineering solutions for controlling industr ia l and commerc ia l sources of a i r pollution. This man- ua lpresen ts theprac t ica l technical knowledge a c - quired through m o r e than 25 y e a r s of experience by the Engineering Division of the Los Angeles County Air Pollution Control Distr ic t . With the r i ch backgroundof experience attained by government and industry, this engineering knowledge can now be applied to solving specific community a i r pollution problems throughout the world.

THE LOS ANGELES BASlN

Los Angeles and i t s environs have special prob- l ems peculiar to the a r ea . Los Angeles County i s the la rges t heavily industrialized, semitropical a r e a in the world. It compr ises 4, 083 square mi les and contains m o r e than 75 incorporated ci t ies and l a rge sca t te red unincorporated a r e a s . I ts population has m o r e than doubled since 1939, and industry has expanded f r o m approximately 6, 000 establishments in 1939 to about 25, 000 in 1970.

Topographical and meteorological conditions ag - gravate the effects of the pollution produced by this populationand this industry in the Los Angeles Basin. The average wind velocity t he r e i s l e s s than 6 mi les pe r hour. The light winds that do develop a r e relatively ineffective in car ry ing off the polluted a i r because of the tempera ture inversions that prevai l approximately 260 days of the yea r . The height of the inversion base v a r - - i e s f r o m ground level to 3, 000 feet. These in- vers ions have been mos t noticeable during the summer months, but in the l a s t few y e a r s ex- t r e m e inversions have occur red in the November -

operations of industry, because these operations have been mos t frequently associated with com-

munity a i r pollution problems. Accordingly, the Los Angeles County control p rog ram was f i rs t

directed to industr ia l operations.

Although the exac tyear when smogwas f i r s t r e c - ognized in Los Angeles i s not known, the f i r s t public demands for relief f r o m a i r pollution appear to have been made immediately a f te r World War I1 (Weisburd, 1962). Newspapers, in par t icular , beganto expose the problemin thepublic interest . As a consequence, a i r pollution control groups we re formed under health department jurisdiction - f i r s t by the city of Los Aneeles, and then - by the county of Los Angeles in the unincorporated a r e a s . These control efforts failed, however, because of the multiplicity and inadequacy of the control jurisdictions. It was soon apparent that adequate control could he exercised only by a single authority with jurisdiction over the en t i re pollution zone - the incorporated and unincorpo- ra ted a r e a s of Los Angeles County. As a resul t , Assembly Bill No. 1 was presented to the 1947 sess ion of the California Legislature. This Bill proposedconsolidation of cont ro lmeasures . The Legislature voted toadd Chapter 2, "Air Pollution Control Distr ic t , ' I to Division 20 of the Health and Safety Code relat ing to the control and sup- press ion of a i r pollution. Thus, the f i r s t s ta te - wide a i r pollution control statute was enacted. This statute, The California Act, i s an enabling type of legislation that legal izes the establishment o f a i r pollution control d i s t r ic t s on a local option basis by the counties of California.

RULES AND REGULATIONS IN LOS ANGELES COUNTY

Decemberpe r iodas well. Their effect i s to l imit ver t ica l distributionof atmospheric pollutionwhile Under authority of the Health and Safety Code, the

Board of Supervisors of Los Angeles County en- localwinds f r o m the wes t a r e moving the a i r over the a r e a during the day. acted, on December 30, 1947, the f i r s t r u l e s and

regulations guiding the conduct of the Los Angeles

In Los Angeles County, the complex mixture of County Air Pollution Control Distr ic t . Additional smoke, dusts , fumes, gases , and other solid and ru l e s and regulations w e r e enacted a s the need l iquidpart ic les is called "smog. " This smog may a rose . The ru l e s a r e contained i n eight regula- produce a single effect o r a combination of effects, tions, a s follows: (I) "General Provisions, I ' (11) such a s i r r i t a t ion of eyes, i r r i t a t ion of throats , "Permi ts , " (111) "Fees , ' I (IV) "Prohibitions, " (V) reduction of visibility, damage to vegetation, "Procedure Before theHearing Board, I ' (VI) "Or - cracking of rubber , local nuisances, and a host chard o r Citrus Grove Heaters , " (VII) "Emergen- of other effects , r e a l and fancied. c ies , " (VILI) "Orders for Abatement. "

Any community suffering f r o m a n a i r pollution It i s important that the reader realize that most of the problem must inevitably tu rn i t s attention to the revisions of the second edition of this manual were

4 INTRODUCTION

written in 1971. The degree of air pollution control system i s a positive means of controlling a i r achieved, therefore, relates to 1971 rules and regu- pollution. lations. Since that time, there have been many In using this regulation, the members of the En- changes, particularly to the prohibition rules. For gineering Division of the Air Pollution Control example, Rule 50, which limited emissions to Number District have reviewed the design and approved 2 on the Ringelmann Chart in 1971, now limits emis- or denied the construction or operation of thou- sions to Number 1. The rules summarized in this sands of industrial and commercial enterprises chapter are those which were effective as of January in Los Angeles County. These 25 years of ex- 1, 1971. The current rules, i . e . , those which were perience provide the background for much of the effective January 1, 1973, are shown in Appendix 4. data in this manual. In using this manual, the reader should be aware of certain provisions of the 1971 rules. Of most R E G U L A T I O N I V : P R O H I B I T I O N S importance a r e Regulations I1 and IV, "Permits" The rules in Regulation IV prohibit the emission and "Prohibitions, ' I respectively. of certain a i r contaminants and regulate certain

types of equipment, Because these rules apply to R E G U L A T I O N I I : P E R M I T S encineering problems and touch upon many sci- .

The permit system of the Los Angeles County Air ences, they require extraordinary care for their

Pollution Control District i s one of the most im- framing. The prohibitions that were in effect a t

portant features of the air pollution control pro- the time this manual was written (1971) and that

e r a . A diaeram of the oermit svstem and how a r e pertinent to readers of this manual will now - - i t operates i s given in Figure 1. In general, the be discussed.

system requires owners, operators, or lessees R u l e 50: T h e R i n g e l m a n n C h a r t to apply for permits to construct and operate any - - . equipment capable of emitting a i r contaminants. If the applicant's plans, specifications, and field tests show that the equipment can operate within the limits allowed by law, then a permit i s granted. If the equipment i s capable of emitting contaminants that create a public nuisance or violate any section of the State Health or Safety Code or the rules and regulations of the Air Pollution Con- trol District, then a permit i s denied.

This permit system i s effective because it elimi- nates use of equipment that emits excessive a i r contaminants or reduces emissions to within allowable limits by requiring that the design of the equipment or of the process be modified or that adequate control equipment be used. The construction or operation of control equipment must also be authorized by permit. Thus, the permit

Rule 50 sets standards for reading densities and opacities of visible emissions in determining vi- olation of, or compliance with, the law. It limits to 3 minutes in any hour the discharge, f rom any single source, of any a i r contaminant that i s (1) a s da rkas or darker than that designated as Num- ber 2 on the Ringelmann Chart, or (2) of such opacity as to obscure an observer 's view to a degree equal to or greater than that to which smoke described in (1) does.

R u l e 51: N u i s a n c e

According to Rule 51, whatever tends to endanger life or property or whatever affects the health of the community i s a public nuisance. Thenuisance must, however, affect the community at large and not merely one or a few persons. A nuisance

E n g i n e e r i n g - Enforcement m.mmrnrn.~n8#

SUBMISSION OF CONSTRUCTION PLANS

I , AUTHORITY TO C0N:TRUCT ISSUED , AUTHORITY 1 0 CONSTRUCT DENIED

PERMIT 2 0 OPERATE GRANTED PERMIT TO OPERATE DENIED I

APPEAL OF DENIAL - - - - +-I

To h e a r i n q b o a r d , or new p l a n s r u b m i t t e d .

I N S P E C T ~ O N OF EQUIPMENT A C o n t i n u i n g P r o c e s s

APPEAL OF DENIAL PETITION FOR VARIANCE REVOCATION OF PERMIT To h e a r i n q board. S u b m i t t e d t o h e a r i n q b o a r d t o p e r m i t or a c t i o n i n c r i m i n a l o r c i v i l I o p e r a t i o n f o r l i m i t e d t i m e w h i l e c o n t r o l c o u r t . i f i n s p e c t i o n d i r c l o s e r equipment i r d e v e l o p e d o r i n s t a l l e d . d e f e c t r o r improper o p e r a t i o n . I

F i g u r e 1 . T h e p e r m i t s y s t e m and how i t o p e r a t e s when i n d u s t r y s e e k s t o i n s t a l l e q u i p m e n t t h a t may p o l l u t e t h e a i r .

- Rules and R e d a t i o n s 5

. . becomes a crime if it contributes seriouslyto the per hour. The maximum allowable weight in pounds discomfort of an area. per hour i s graduated according to the weights of

materials processed per hour. The maximum R u l e 5 2 : P a r t i c u l a t e M a t t e r emission allowed i s 40 pounds per hour where

Rule 52 establishes the maximum allowable limits 60,000 or more pounds areprocessedinthe equip-

for the discharge of particulate matter. It limits ment in any given hour.

the discharge of this contaminant f rom any source - to a maximum concentrationof 0. 3 grainper cubic - foot of gas at standard conditions of 60° F and 14. 7 psia. This rule does not, however, apply

~ ~~~~

when the particulate matter i s a combustion contaminant. * Rule 5 3 : Specif ic Contaminants

Rule 53 establishes the maximum allowable limits for the discharge of sulfur compounds and combustion contaminants a s follows:

Rule 53a: Sulfur compounds calculatedas sulfur dioxide (SOL): 0.2 percent, by volume.

Rule 53b: Cornbustioncontaminants: 0. 3 grain per cubic foot of gas calculated to 12 percent of carbondioxide (COZ) at standard conditions. Inmeasuring thecombustioncontaminants from incinerators used to dispose of combustible refuse by burning, the C02 produced by combus- tionof any liquid or gaseous fuels shall be ex- cluded from the calculation to 12 percent of COZ.

Rules 5 3 . 1 , 5 3 . 2 , a n d 5 3 . 3 : S u l f u r P r o d u c t i o n

a n d S u l f u r i c A c i d P l a n t s

These rules set maximum allowable concentrations of sulfur dioxide in the effluent gases from the sulfur production and sulfuric acid plants a t 500parts per million. The standards further limit the total weight of sulfur dioxide emissions from theseplants to no more than 200 pounds per hour. In the case of sulfuricproductionplants, a further limitation in the maximum allowable concentrations of hydrogen sulfide of 10 parts per million was set. Sulfur production plants must meet the new emissionstandards by June 30, 1973. Sulfuric acid plants must meet the new standards by December 31, 1973.

Rule 54: Dust and Fumes

Rule 54 establishes the maximum allowable lim- i ts for the discharge of dusts and fumes according to the process weightst of materials processed

P d r t l c - l a t e m d l t e r 1 5 any a a - . e r i a l , escep: .racJlro>nea ,are,. c n ~ t exlrrs i n a fmnely a l r l a e c rorn a s a l ~ o ~ l a or s o l l a a t I L ~ ~ O > ~ O ~ o i l ~ l t i ~ n s . i L X T Y I L I ~ I O ~ c m : d ~ i n a n r i s p r r t l c . l ~ t e mairer alrcndrgea i n t o tne arnorpoere t r m rne o-roing of any < in0 O l m d f r r l d l ;onrrhnlng c4roun in a f r e e or comotnea r t J i e .

t ~ r o c e s r weight i s the rota1 weight o f a l l mate r ia ls i n r r o - duced i n r o any spec i f i c process tha t i s capable o f causing any discharge i n t o the atrmrphere. S o l i d fuels charged are considered par t of the process weight, b u t l i q u i d and gaseous fuels and cwnburrion a i r are no t . The "process weight per hour" i s derived by d iv id ing the t o t a l process weighr by the number of hours i n one complete operarion from the beginning of any given process co rhe completion thereof, ex- c luding any rime during which the equipment i s i d l e .

Rule 5 6 : Storage of Petroleum Products

Rule 56 sets forth the type of equipment that can be used for the control of hydrocarbons arising f rom the storage of gasoline and certain petroleum distillates. Rule 56 provides that any tank of more than 40,000-gallon capacity used for storing gasoline or any petroleum distillate having a vapor pressure of 1-112psia or greater mustbe equipped witha vapor loss control device suchas apontoon- type or double-deck-type floating roof or a vapor recovery system capable of collecting all emissions.

R u l e s 5 7 a n d 5 8 : O p e n F i r e s a n d I n c i n e r a t o r s

Rules 57 and 58 ban the burning of combustible refuse in openfires and single-chamber incinerators in the Los Angeles Basin.

R u l e 5 9 : O i l - E f f l u e n t W a t e r S e p a r a t o r s

Rule 59 regulates the type of equipment that can be used for the control of hydrocarbons from oil- water separators. Itprovidesthat this equipment must either be covered, or provided with a floating roof, or equipped with a vapor recovery system, or fitted with other equipment of equal efficiency if the effluent handled by the separator contains a minimum of 200 or more gallons of petroleum products per day.

R u l e 61: G a s o l i n e L o a d i n g i n t o T a n k T r u c k s

a n d T r a i l e r s

Rule 61 sets forth the type of control equipment that can be used for the control of hydrocarbons resulting from the loading of gasoline into tank trucks. It provides for the installation of vapor collection and disposal systems on bulk gasoline- loading facilities where more than 20, 000 gallons of gasoline a r e loaded per day and requires that the loading facilities be equippedwith a vapor collection and disposal system. The disposal system employed must have a minimum recovery efficiency of 90 percent o r a variable vapor space tankcompressor and fuel gas systemof suchcapac - ity a s to handle all vapors and gases displaced f rom the trucks being loaded.

6 INTRODUCTION

R u l e s 6 2 , 6 2 . 1 , a n d 6 2 . 2 : S u l f u r C o n t e n t o f F u e l s R u l e 6 6 . 2 : D i s p o s a l a n d E v a p o r a t i o n o f S o l v e n t s

Rules 62, 62. 1, and 62. 2 prohibit the burning in Rule 66.2 prohibits the disposal of more than

the Los Angeles Basin of any gaseous fuel contain- 1-112 gallons per day of any photochemically r e -

ing sulfur compounds in excess of 50 grains per active solvent by any means that will permit the

100 cubic feetof gaseous fuel (calculated a s hydro- evaporation of such solvent into the atmosphere.

gen sulfide a t standard conditions) or any liquid or solid fuel having a sulfur content in excess of 0. 5 percent by weight.

R u l e 6 7 : F u e l - B u r n i n g E q u i p m e n t

R u l e 6 3 : G a s o l i n e S p e c i f i c a t i o n s

Rule 67 requires that a person shall not build, erect, install, or expand any fuel-burning equipment unless the discharge of contaminants will not exceed 200 pounds per hour of sulfur dioxide,

Rule 63 prohibits the sale anduse of fuel for motor or 140 pounds per hour of nitrogen oxides, or

vehicles having a degree of unsaturation exceeding a bromine number of 30. 10 pounds per hour of combustion contaminants.

R u l e 6 4 : R e d u c t i o n o f A n i m o l M a t t e r R u l e 6 8 : F u e l - B u r n i n g E q u i p m e n t - O x i d e s o f

N i t r o g e n

Rule 64 requires that malodors from all equip- Rule 68 requires that a person shall not discharge

ment used for reduction of animal matter either into the atmosphere from any fuel-bearing equip-

be incinerated at temperatures of not less than ment having a heat input of more than 1775 x 106

1, 200° F for a period of not l e s s than 0.3 second Btu per hour, flue gas having a concentration of

or processed in an odor-free manner under con- nitrogen oxides at 3 percent oxygen in excess of

ditions stated in the rule. the following:

Effective date

December 31, December 3 1, R u l e 65: G a s o l i n e L o a d i n g i n t o T a n k s Fuel 1971 1974

Rule 65 prohibits the loading of gasoline into any stationary tank with a capacity of 250 gallons or more from any tank truck or trai ler , except through a permanent submerged fill pipe, unless such tank is equipped with a vapor loss control device a s described in Rule 56, or i s a pressure tank a s described in Rule 56.

R u l e 66: O r g a n i c S o l v e n t s

Rule 66 requlres that photochemically reactive organic solvent emissions in excess of 40 pounds per day (or 15 pounds per day from processes involving contact with a flame or baking, heat- curing or heat polymerizing, in the presence of oxygen) shall not be emitted unless controlled by incineration, adsorption, or in an equally efficient manner.

R u l e 66.1: A r c h i t e c t u r a l C o a t i n g s

Rule 66.1 prohibits the sale of architectural coatings containing photochemically reactive solvents in containers larger than 1-quart capacity. It also prohibits diluting any architectural coating with a photochemically reactive solvent.

Liquid or 325 225 solid, ppm

ROLE O F THE AIR POLLUTION E N G I N E E R

Clearly, as indicated by this impressive l is t of prohibitions, the rules and regulations affect the operation of nearly every industry in Los Angeles County. Through their enforcement, controls have been applied to such diverse sources and operations as incinerators, open fires, rendering cook- e r s , coffeeroasters, petroleumrefineries, chemical plants, rock crushers, and asphalt plants. From the smelting of metals to the painting of manufactured goods, industrial and commercial operations have been brought within the scope of the controlprogram. This control has beenaccom- plished through the use of the permit system.

A C C O M P L I S H M E N T S O F T H E P E R M I T S Y S T E M

Under the permit system every source capable of emitting a i r contaminants and constructed since February 1948 has needed an authorization to be constructed and a permit to be operated f rom the

Use of This Manual 7

Engineering Division of the Air Pollution Control in the development of a i r pollution control sys- District. From April 1948 through April 1969, tems. Specifically, chapter 2 describes the types 109,332permits were issued byDistrict engineers. of a i r contaminants encounteredandchapter 3 pre- The estimated value of the basic equipment was sents design problems of hoods and exhaust sys- $1,363,400,000 and that of the control equipment tems. Types of control devices, and their gen- was an additiona1$152,200,000. During this same era1 design features a r e discussed in chapters 4 period, 6, 045 applications for basic and control and 5. equipment were denied.

This wealth of engineeringexperience is reflected in the contents of this manual. Nearly all the data . S P E C I F I C A l R P O L L U T l O N S O U R C E S presented were acquired through the experience and work of the District 's Air Pollution engineers and of engineers in industry. ~ h ~ i ~ pioneering Chapters 6 through 12 discuss the control of a i r

efforts to stay at least one pace ahead of the prob- pollutionfrom specific sources. Each solution of

lem have produced many engineering f i rs ts in the an a i r pollution problem represents a separate

control of a i r pollution. sectionof the text. Manyprocesses a r e discussed: metallurgical andmechanicalprocesses, process-

USE OF THIS MANUAL

Users of this manual should remember that the degree of air pollution control discussed herein i s based upon the prohibitions as set forth by the rules and regulations of the Los Angeles County Air Pollution Control District in effect as of Jan- uary 1, 1971. In many areas , a i r pollution regulations a r e less stringent, and control devices of lower efficiency may be permitted.

G E N E R A L D E S I G N P R O B L E M S

This manual consists of 12 chapters and 5 appen- dixes. Chapters 2 through 5 present general design problems confronting a i r pollution engineers

es of incineration and combustion, and processes associated with petroleum, chemical equipment, and organic solvents, each in a separate chapter and in that order. Usually the process i s described and then the a i r pollution problem associated with it i s discussed, together with the characteristics of the a i r contaminants and the unique design features of the a i r pollution control equipment.

By this arrangement, thereader can, if hewishes, refer only to that section discussing the specific process in which he is interested. If he wants to know more about the general designfeatures of the air pollution control device serving that process, he can refer to chapters 4 and 5 on controlequip- ment.

CHAPTER 2

AIR CONTAMINANTS

J A N E T DICKINSON, Ass i s t an t Chief A i r Pollution Analyst

ROBERT L. CHASS, Air Pollution Control Officer

W. J. HAMMING, Chief A i r Pollution Analyst

JOHN A . DANIELSON, Senior A i r Pollution Engineer

CHAPTER 2

AIR CONTAMINANTS

INTRODUCTION

Thepurpose of this chapter is to describe briefly the parameters of an a i r pollution problem, particularly the problem of Los Angeles County; the measures taken to eliminate the problem; and those still needed. Other chapters will delineate, in detail, the methods and equipment successfully used in the control of emissions of a i r contaminants from a variety of stationary sources.

Thecontrolprogramin the County of Los Angeles duringthe past 25 years has been the most effective ever attempted anywhere. During the same ~ e r i o d , however, the countyhas had a phenomenal population explosion that has caused the emissions f rom motor vehicles to overtake and surpass the gains made by control over stationary sources. The net effect has been the more frequent occurrence of smog symptoms over anincreasinglylarg- e r area.

Since control over motor vehicle emissions i s the responsibility of the state and federal govern- ments rather than of the local agency, substantial improvement in the situation in Los Angeles will probablyhave to await the successful implementa- tion of their programs. In the interim, however, the Air Pollution Control District of Los Angeles Countv will continue its efforts to reduce emis-

Air pollution problems may exist over a small a rea as a result of just one emission source or group of sources or they may be widespread and cover a whole community or urban complex involving avarietyof sources. The effects that cause the situation to be regarded as a problem may be limitedin scope and associated with a single kind of contaminantor theymay be the variable results of complexatrnospheric interactionof a number of contaminants.

The factors that contribute to the creation of an a i r pollution problem a r e both natural and man made. The natural factors a r e primarily meteorological, sometimes geographical, andare generally beyond man's sphere of control, whereas the manmade factors involve tErk emission of a i r contaminants in quantities sufficient to produce deleterious effects and a r e within man's sphere of codtrol. The natural factors that res t r ic t the normaldilutionof codtaminant emissions include: temperature inversions, which prevent diffusion upwards; very low wind speeds, which do little to move emitted substances away f rom their points of origin; and geographical terrain, which causes the flow to follow certain patterns and c a r r y f rom one a r e a to another whatever the a i r contains. The manmade factors involve the contaminant emissions resulting from some human activity.

sions of a i r contaminants from stationary sources The predominant kind of a i r pollution problem in-

wherever possible within its jurisdiction. volves simply the overloading of the atmosphere with harmful o r unpleasant materials. his is

FACTORS I N AIR POLLUTION PROBLEMS

Literally, any substance not normally present in the atmosphere, o r measured there ingreater than normal concentrations, should he considered an a i r contaminant. More practically, however,a substance is not s o labeled until i ts presence and concentration produce or contribute to the produc - tion of some deleterious effect.

Many foreign substances find theirway into the atmosphere as the result of some human activity. Under normal circumstances, they diffuse throughout a rather large volume of a i r and do not accumulate to potentially harmful concentrations. Under less favorable conditions, however, the a i r volume available for this diffusion becomes inade- quate. The concentrations of some foreign substances then may reach a level a t which an a i r pollution problem i s created.

the problem usually associated with an industrial area , and the type that has been responsible for al l the killer a i r pollution incidents of the past. I t i s also the type of problem most readily solved, if the need and desire to do so a r e great enough. Contaminants frequently associated with this kind of problem include: Sulfur compounds (sulfur oxides, sulfates, sulfides, mercaptans); fluorides; metallic oxides; odors; smoke; and all types of dusts andfumes. The harmful effects may be such a s to cause illness and death to persons and animals, darnagetovegetation, or just annoyance and displeasure to persons in affected areas.

During the past 25 years, however, another kind of a i r pollution problem has evolved--that produced by the photochemical reaction of organic chemicals and oxides of nitrogen in the presence of sunlight. The effects of this type of a i r pollution were f i r s t noted in the Los Angeles a rea in themid-1940's. hutthe cause was not then known.

12 AIR CONTAMINANTS

nor was there any apparent relationship between in connection withthese processes and in connec- the initial effects and a i r pollution. tion with their manufacture and use. They can

even be formed in the atmosphere as the result The effect f i rs t noted was damage to vegetation. of certain photochemical reactions. This was followed bv irritation of the eves, marked - - -

reductioninvisibilitynot related to unusual quan- C u r r e n t S o u r c e s i n Lor A n g e l e s C o u n t y

tities of atmospheric moisture o r dust, and later , unexplained acceleration Of the aging rubber

M~~~ specifically, the principal current sources products as evidenced by cracking. Early research of organic gases inLos Angeles County are listed demonstrated and additional research confirmed in Table 1. that al l these effects were produced by the reaction in the atmosphere of organic compounds, principally hydrocarbons, and nitrogen dioxide, and that the cracking of rubber products was caused specificallyby one of the products of these reactions, ozone.

Initially, only a relatively small portion of the Los Angeles Basin was affected, but a tremendous influx of new residents and new industrial growth during the past 20 years have caused acontinuous enlargement of the affected area. Within this area, certain local problems related to single sources and groups of sources also exist, but they a re of less significance than the overall problem of photochemical smog.

TYPES OF AIR CONTAMINANTS Substances considered a i r contaminants in Los Angeles Countyfall into three classes onthe basis of their chemical composition and physical state. These are (1) organic gases, (2) inorganic gases, and (3) aerosols. Each class may include many different compounds, emanate f rom several different sources, and contribute to the production of a number of characteristic smog effects. A brief summary of some of the contaminants, their principal sources, and their significance i s presented in Table 1.

O R G A N I C G A S E S

The f i rs t group, organic gases, consists entirely of compounds of carbon and hydrogen and their derivatives. These include all classes of hydrocarbons (olefins, paraffins, and aromatics) and the compounds formed when some of the hydrogen in the original compounds is replaced by oxygen, halogens, nitro or other substituent groups. The latter a re the hydrocarbon derivatives.

The principal origin of hydrocarbons i s petroleum, and the principal sources of emissions of hydrocarbons and their derivatives a r e those related to the processing _and use of petroleum and i ts products. Hydrocarbons a re released to the atmosphere during the refining of petroleum, during the txansfer and storage of petroleum products, and during the use of products such a s fuels, lu- bricants, and solvents. Derivatives of hydrocarbons can also be released into the atmosphere

Hydrocarbons

The most important source, by far , of emission of hydrocarbons is the use of gasoline for the operation of 4-114million motor vehicles. This source alone accounts for approximately 1,610 tons per day, or 65 percent of the total emissions. Of this quantity, about 73 percent is attributed to exhaust emissions; 5 percent, t o crankcase emissions ; and 22 percent, to evaporation of fuel f rom car- buretors and gasoline tanks. Except for about 2 percent of the total, the balance of the hydrocarbon emissions a re divided between the petroleum industry and industrial and commercial uses of organic solvents.

Kinds of hydrocarbons contributed by these sources vary considerably. Auto exhaust, for example, is the principal source of olefins and other photochemically reactive hydrocarbons, though other sources connected with the operation of motor vehicles and with the processing and handling of gasoline contribute indirectproportionto the ole- fin content of the gasoline marketed here. All these sources contribute paraffins andaromatics, and emissions of hydrocarbons f rom solvent usage a re composedalmostentirely of these twoclasses.

Hydrocarbon derivatives

Of the 300 tons of hvdrocarbonderivatives (or substituted hydrocarbons) emitted to the atmosphere of Los Angeles County eachday, aboutthree-fourths results fromsolvent uses such a s surface coating, degreasing, anddry cleaning, and other industrial and commercial processes. The balance is included in the products of combustion of various petroleum fuels &dof incineration of refuse. The substitutedhydrocarbons emitted to the atmosphere by industrial and commercial use of organic solvents include oxygenates, such as aldehydes, ketones, andalcohols; organic acids; and chlorinated hydrocarbons. Most hydrocarbon derivatives associatedwith surface coating a r e oxygenates whose presence canbe relatedeither to the solvent itself o r to the products of the partial oxidation involved in the drying of the coated objects. The hydro- carbonderivatives associatedwith degreasing and dry cleaning a r e mostly chlorinated hydrocarbons. The derivatives associatedwith combustion, either

Types of Contaminants 13

Table 1. AIR CONTAMINANTS IN LOS ANGELES COUNTY, THER PRINCIPAL SOURCES AND SIGNIFICANCE (JANUARY 1971)

Significant effects

Emitted contaminant Principal sources

Processing and transfer of gasoline; motor vehicles 1

Organic gases

Hydrocarbons Paraffins

Aromatics Same as for paraffins X (Atypical)

0

Processing and transfer of petroleum products; use of solvents: motor vehicles

'Iant damage

Others Oxygenated hydrocarbons (Aldehydes, ketones, alcohols, acids)

Odors

Odors

Eye irritation

Use of solvents; motor vehicles

Halogenated hydrocarbons (Carbon tetrachlo- ride, trichloroethylene, etc)

Use of solvents

Oxidant formation

Inorganic gases

Oxides of nitrogen (Nitric oxide, nitrogen dioxide)

Carbon monoxide Motor vehicles; petroleum refining; metals industry; pismn-driven aircraft

Oddee of sulfur (Sulfur dioxide, sulfur trioxide)

Visibility reduction

Combustion of fuels; motor vehicles

Combustion of fuels: chemical industry

Aerosols

Solid particles Carbon or soot particles X

(Under special

circumstances)

Danger to

health

X

Combustion of fuels; motor vehicles

Metal oxides and salts

Silicates and mineral dusts

Metallic fumes

Other

X

X (Specific type)

Catalyst dusts from refineries; motor vehicle exhaust: combustion of fuel oil; metals industry

Minerals industry; construction

Metals industry

roperty k e

X

Liquid particles Acid droplets

Oily o r tarry droplets

Paints and surface coatins3

Combustion of fue1s:plating battery manufacture

Motor vehicles; asphalt paving and roofing; asphalt saturators; petroleum refining

Various industries

14 ALP. CONTAMINANTS

of fuels or of refuse, a re products of incomplete of the aldehydes and nitro derivatives are , them- combustion and are almost entirely oxygenates. selves, lachrymators and some of the chlorinated Thus, the composition of atmospheric emissions hydrocarbons a r e rather toxic. Except for the of hydrocarbon derivatives i s currently about one- peroxyacyl nitrates, these compounds a re not, fourth to one-third chlorinated hydrocarbons and however, generally associated with production of two-thirds to three-fourths oxygenates. plant damage.

In addition to the hydrocarbon derivatives contributed by direct emissions, the atmosphere of photochemical smog contains similar compounds formed there as a result of the reactions that produced the smog. These substituted hydrocarbons include oxygenates, such as aldehydes, ketones, alcohols. and oreanic acids, and nitroeen-contain- - - ing compounds, such as the peroxyacyl nitrates and, perhaps, nitro olefins. These compounds a re the products of partial oxidation of hydrocarbons and some derivatives in the atmosphere and of atmospheric reactions between oxides of nitrogen and organic gases in sunlight, but not in the dark.

S i g n i f i c a n c e i n A i r P o l l u t i o n P r o b l e m

Hydrocarbons and their derivatives a r e important factors inthe a i r pollution problem inLos Angeles County because of their ability to participate in the atmospheric reactions thatproduce effects associated with photochemical smog. Not all hydrocarbons and their derivatives have the same potential for smog formation. The most reactive group, the olefins (unsaturated hydrocarbons), can react with atomic oxygen, formed f rom the dissociation of nitrogen dioxide in sunlight, or with ozone to produce plant damage, eye irritation, visibility- reducing aerosols, oxidants, andadditional ozone. Branched paraffinic hydrocarbons can also react when nitrogen dioxide is present in sunlight to produce some oxidants or ozone, but the reaction depends specifically upon the concentration ratio of nitrogen oxides and paraffins. In Los Angeles this ratio in the atmosphere is not conducive to this formation for normal straight-chainparaffins. Eye irritation andplantdamage a re not caused by paraffinic hydrocarbons in general.

The secondmostimportant group of hydrocarbons is the aromatic hydrocarbons, particularly those having various substituent groups. These compounds can also react with atomic oxygen formed from the sunlight dissociation of nitrogen dioxide to produce all the same types and kinds of smog effects. Sometimes, however, depending uppn a high ratio of nitrogen oxides to hydrocarbon, a different kind of plant damage results f rom these reactions.

The hydrocarbon derivatives, particularly some of the aldehydes and ketones, and even some of the chlorinated hydrocarbons, can also react with nitrogendioxide inthe atmosphere to produce eye irritation, aerosols, and ozone. Further, some

The hydrocarbons a re further indicted because photochemical reactions in which they participate sometimes produce hydrocarbon derivatives such as aldehydes, ketones, and nitro-substituted or- ganics, which can in turn react to increase the production of smog effects.

I N O R G A N I C GASES

Inorganic gases constitute the second major group of a i r contaminants in Los Angeles County. They include oxides of nitrogen, oxides of sulfur, carbon monoxide, and much smaller quantities of ammonia, hydrogen sulfide, and chlorine.

The principal source of al l the oxides listed above is the combustion of fuelfor industrial, commercial, and domestic uses; fo r transportation; for space heating; and for generation of power. Addi- tionally, small quantities of sulfur oxides and carbon monoxide, and the total of the minor constituents, ammonia, hydrogen sulfide, and chlorine, a re emitted in connection with certain indus- t r ia l processes.

C u r r e n t S o u r c e s i n L o r A n g e l e s C o u n t y

The principal sources currently responsible for atmospheric emissions of each of the important inorganic gaseous a i r contaminants will now be discussed.

Oxides of nitrogen

A number of compounds must be classified as oxides of nitrogen, but only two, nitric oxide (NO) and nitrogen dioxide (NOZ), are important as a i r contaminants. The f i rs t , nitric oxide, is formed through the direct combination of nitrogenand oxygen f rom the a i r in the intense heat of any combustion process. Nitric oxide in the atmosphere is then able, in the presence of sunlight, to combine with additional oxygen to form nitrogen dioxide.

Usually the concentrations of nitric oxide in the combustioneffluents constitute 90percent or more of the total nitrogen oxides. Nonetheless, since every mole of nitric oxide emitted to the atmosphere has the potential to produce a mole of nitrogen dioxide, one may not be considered without the other. In fact, measurement of their concentrations often provides only a sum of the two reported a s the dioxide.

Types of Conf

Of the total quantities of these contaminants currently being emitted each day in Los Angeles County, approximately 70 percent, or 740 tons, must be attributed to the exhaust effluents from gasoline-powered motor vehicles. Almost the entire balance is produced as the result of combustion of fuel fo r space heating and power generation.

Oxides of sulfur

Air contaminants classified a s oxides of sulfur consist essentially of only two compounds, sulfur dioxide (S02) and sulfur trioxide (SO3). The primary source of both is the combination of atmospheric oxygen with the sulfur in certain fuels during their combustion. The total emitted quantities of these substances are, therefore, directly related to the sulfur content and total quantities of the principal fuels used in a community. Normally, the dioxide i s emitted in much greater quantities than the trioxide, the latter being formed only under rather unusual conditions. In fact, the t r i - oxide i s normally a finely divided aerosol rather than a gas.

In Los Angeles County, the emissions of sulfur oxides have shown a marked decrease during the winter months with thepromulgation of Rule 62.2. This rule places a limitation of 0. 5 percent, by weight, on the sulfur content of the liquid fuels. P r io r to the adoption of this rule, high-sulfur oils, often a s high as 1.6 percent sulfur, were allowed to be burned when natural gas was not available.

~ u r i n ~ t h e period November 15 to April 15, emissions of sulfur oxides a r e 290 tons per day, of which 85 tons per day is from the combustion of fuels. Ninety tons per day a r e f r o m sulfur recov- e ry plants and 25 tons per day occur f rom sulfuric acid plants. The remainder i s f rom petroleum refining and metallurgical plants.

During the period April 15 to November 15, the total emissions of sulfur oxides i s 220 tons per day. The 70-ton reduction is mainly a result of burning natural gas instead of low-sulfur oil in steam power plants.

Carbon monoxide

Carbon monoxide (CO) is a single contaminant formed during incomplete oxidation of any carbo- naceous fueland currently has only one significant source in Los Angeles County-the incomplete combustion of gasoline in motor vehicles. Of a total of 9,100 tons of this contaminantemitted per day, 98 percent i s attributable to this source. About 1.5 percent i s attributable to the emissions fromaircraft , andthe balancefromdieselengines, metallurgical processes, and petroleum refining operations.

S i g n i f i c a n c e i n A i r P o l l u t i o n P r o b l e m

The importance of the inorganic gases in an a i r pollution problem varies with the gas in question. Each will, therefore, he discussed separately.

Oxides of nitrogen

The oxides of nitrogen have far greater significance in photochemical smog than any of the other inorganic gaseous contaminants. Research has demonstrated that upon absorbing sunlight energy nitroaen dioxide undergoes several reactions, - - depending uponthe wavelength or frequency of the light. The near-ultraviolet wavelengths a r e the most effective in producing atomic oxygen from the nitrogen dioxide, and this oxygen reacts with a number of organic compounds to produce all the effects associated with photochemical smog. In fact, this type of a i r pollution was named photochemical smog because of the manner in which i t i s generated. The presence of the dioxide has been shown to be a necessary condition for these reactions. This does not, however, diminish the need for adequate consideration of nitric oxide as a i r contaminant, since this i s the form in which the oxides of nitrogen normally enter the atmosphere.

In communities not affected by photochemical smog, the oxides of nitrogen st i l lmust be considered i f only for their inherent ability to produce deleterious effects bythemselves. The only effect that must seriously be considered in this regard is their toxicity, though the reddish-brown color of the dioxide and its sharp odor could cause problems inareas near a nylon plant, nitric acid plant, or nitrate fertilizer plant. Nitric oxide is considerably less toxic than the dioxide. It acts as an asphyxiant when in concentrations great enough to reduce the normal oxygen supply f rom the a i r . Nitrogen dioxide, on the other hand, in concentrations of approximately 10 ppm for 8 hours, can ~ r o d u c e lung injury and edema, and in greater concentrations, i. e . , 20 to 30 ppm for 8 hours can produce fatal lung damage.

The dioxide, then, i s heavily indicted a s an undesirable constituent of the atmosphere, regard- less of the type of a i r pollutionproblem under consideration. Nitric oxide i s indicted, too, because of i ts ability to produce the dioxide by atmospheric oxidation.

Oxides of sulfur

During the past few years, information in the lit- erature has indicated that the presence of sulfur dioxide in the photochemical-smog reaction en- hances the formation of visibility-reducing aerosols. The mechanism responsible for this effect

I

16 AIR CONTAMINANTS

has notbeendescribed, andi t i s not known whether sulfur dioxide enters into the organic photochemical reactions or whether the additional aerosols ob- served represent simply a combination of sulfur dioxide and moisture.

Primarily, gaseous oxides of sulfur in the atmosphere a r e significant because of their toxicity. Both the dioxide and trioxide a r e capable of producing illness and lung injury even a t small concentrations, from 5 to 10 ppm. Further, each can combine with water in the a i r to form toxic acid aerosols thatcancorrode metal surfaces, fabrics, and the leaves of plants. Sulfur dioxide by itself also produces a characteristic type of damage to vegetation whereby portions of the plants' leaves a r e bleached in a specific pattern. In concentrations as small as 5 ppm, sulfur dioxide is i r r i - tating to the eyes and respiratory system.

Both the dioxide and trioxide can combine with particles of soot and other aerosols to produce contaminants more toxic than either alone. The combination of the dioxide and trioxide with their acid aerosols has also been found to exert a syn- ergistic effect on their individual toxicities. These mixtures were apparently responsible for the illness anddeathassociatedwithtbe famous air pol- lutionincidents thatoccurred in the Meuse Valley, Belgium; in Donora, Pennsylvania; and, more r e - cently, in London, England.

Carbon monoxide

Carbonmonoxide plays no part in the formation of photochemical smog though i t i s almost invariably emitted to the atmosphere along with the most po- tent of smog formers--hydrocarbons and oxides of nitrogen. At concentrations of 200 ppm and greater , itproducesillness anddeathby depriving the blood of its oxygen-carrying capacity. It has been detected in the atmosphere of various urban centers of the world a t concentrations from 10 to 100ppm. Greater concentrations have occasion- ally been measured in confined spaces such as tunnels andlarge, poorly ventilated garages. At- mospheric concentrations havenot yet been linked to fatalities but have sometimes been implicated in short-term illnesses of traffic officers.

Miscellaneous inorganic gases

A few additional gases were listed among those

odors. Hydrogen sulfide can cause discoloration of certain kinds of paint; ammonia and chlorine candiscolor certain fabric dyes; fluorine and fluo- I r ides, especially hydrogen fluoride, a r e highly !

toxic, corrosive, and capable of causing damage ! to vegetation, and illness and injury to humans and animals.

Many other inorganic gases maybe individually o r locally objectionable o r toxic. These a r e of relatively minor importance and will not be discussed here.

AEROSOLS

Aerosols (also called particulate matter) present inthe atmosphere may be organic or inorganic in composition, and in liquidor solid physical state. By definition, they mustbe particles of very small size or theywillnot remaindispersed in the atmosphere. Among the most common a r e carbon or soot particles; metallic oxides and salts; oily o r tar ry droplets; acid droplets; 'silicates and other inorganic dusts; and metallic fumes.

The quantities of aerosols emitted in Los Angeles i ! i County, a t present, a r e relatively small but in- !

cludeatleastsome amounts of al l the types listed 1 above. Part icles of larger than aerosol size a r e I

a lso emitted but, because of their weight, do not ! i

long remain airborne. Additionally, however, ! vast auantities of aerosols a r e formed in the at- 4 mosphere a s the result of photochemical reactions among emitted contaminants. Total quantities of these aerosols may easily exceed those of emitted aerosols, a t leas t in terms of particle numbers.

C u r r e n t S o u r c e s i n L o r A n g e l e s C o u n t y

The most important current sources of aerosol emissions inLos Angeles County, by type of aerosol, will now be discussed.

Carbon or soot particles

Probablythemost commonly emitted kind of particle anywhere i s carbon. Carbon particles a r e nearly always present among the products of com- bustionfrom all types of fuels, even f rom operations inwhich the combustionis apparently complete.

emitted to the atmosphere fromvarious operations in Los Angeles County. They include ammonia, In Los Angeles County, the principal sources of

hvdroeen sulfide, chlorine. and fluorine or fluo- emissions containing carbon or soot particles a r e , -

rides. Althoughnone has been detected in greater the exhaust effluents , from motor vehicles, and I than trace quantities Los Angeles atmosphere the combustion. of fuels for power generation and

space heating, though not al l the particulates and none is known to have any significance in the 1 emitted from these sources a r e carbon. Emis- formationof pbotocbemical smog, these contami-

sions from the latter group of sources vary with . . ~ . nants can be important in other types of a i r pollu-

theRule 62 period* since these particles occur in tionproblems. Al lare toxic in small to moderate concentrations, and the f i rs t three have unpleasant 'April 15 to November 15.

Types of Contaminants 17

greater quantities in the effluent fromthe burning of fuel oil than in that f rom the burning of natural gas. During Rule 62 periods, then, the combustion of fuel for space heating and generation of power accountsfor about one-fourth of the carbon particles emitted to the atmosphere, and during non-Rule 62 periods, about one-half. The portion contributed by auto exhaust varies, therefore, duringcomparableperiods f rom one-half to three- fourths of the total.

The actual total of emitted carbon particles cannot be estimated withmuch accuracy, but they probably represent about one-third to one-half of the total aerosol emissions.

The only other sources from which significant quantities of carbon particles might be emitted are incineration of refuse, operation of piston-driven aircraft, and operation of ships and railroads. Eventhe total of particulate emissions from these sources does not, however, comprise 5 percent of the total carbon emissions.

Metallic oxides and salts

Metallic oxides and salts can be found in small quantities in the emissions from many sources. These sources include catalystdustsfrom refinery operations, emissions f rom the metals industry, effluents f rom combustion of fuel oil, and even exhaust f rom motor vehicles. The total quantity of these emissions i s , however, small and probably does not constitute more than 5 to 10 percent of the total particulate emitted to the atmosphere.

Thematerials emitted as catalyst dusts a re mostly oxides. Small quantities of metallic oxides may also result f rom the combustion of fuel oil and perhaps from metal-working operations. These oxides might include those of vanadium, aluminum, titanium, molybdenum, calcium, iron, barium, lead, mangenese, zinc, copper, nickle, magnesium, chromium, and silver.

Metallic salts a re emitted from essentially the same sources - again, in small concentrations. Most emissions of particulate lead in auto exhaust, for example, a re present a s oxides and complex salts, usually chlorides, bromides, and sulfates. Metallic oxides a re emitted from certain metals operations, and small quantities of sulfates a re emitted from some industrial operations.

Oily o r t a r ry droplets

Small droplets of oily a r t a r r y materials a re f r e - quently found in combustion effluents from many types of sources. The most common sources a re

probably the emissions associated with the operation of motor vehicles, particularly crankcase emissions; exhaust emissions from gasoline- and diesel-powered vehicles; effluents from asphalt manufacturing, saturating, paving, and roofing operations; and effluents from inefficient combus- tionof fuels in stationary sources. Smallamounts might alsobe foundin the effluents from aircraft, ships, and locomotives and from incineration of refuse. Oily or t a r ry particles also appear to be among the products of the photochemical reactions that produce smog. Emitted quantities of these materials probably comprise 10 to 20 percent of the total particulate emissions.

Althoughthe composition of these materials is not well established, they appear to he predominantly organic. They undoubtedly have relatively high molecular weights and probably contain at least some aromatics. The polycyclic hydrocarbons, which currently cause somuch concern, probably occur in a liquid phase in the atmosphere.

Acid droplets

Smalldroplets of acid, bothorganic and inorganic, are emitted f rom a number of sources in Los Angeles County under certain conditions. These sources include stack effluents f rom power plants, especially during combustion of fuel oil; effluents f rom industrial operations such as certain metal- working and plating operations, and storage battery reclamation; effluents from waste rendering and incineration; and even effluents from motor vehicle exhaust. Under some circumstances, these acid droplets are also formed in the atmosphere. Like the other kinds of particulate matter, the total emitted quantities of these droplets are small, probably 5 to 10 percent of the total particulate emissions. Even the quantities of thesematerials formed in the atmosphere are small relative to the total.

The inorganic acids emitted to the atmosphere include, primarily, sulfuric and nitric acids; the organic acids include probably acetic, propionic, and butyric acids. The acids formed inthe atmos - phere through combination of gases with water include sulfurous, sulfuric, nitrous, and nitric acids. Acid droplets formed through oxidation of organic emissions may not include any but acetic acid, if that.

Silicates and other inorganic dusts

Emissions of inorganic dusts inLos Angeles County consist primarily of silicates, carbonates, and

18 ALR CONTAM

oxides and a r e probably associated most commonly withquarryingoperations, sand and gravel plants, and other phases of the minerals industry. They can also result from highway construction and landfilloperations. Their quantity may represent about 5 to 10 percent of the totalparticulate emissions.

Metallic fumes

The metals industry i s responsible for 8 percent of the total aerosol emissions, and metal fumes probably constitute less than half of this portion. Metal fumes a r e generally considered to be minute particles created by the condensation of metals that have vaporized or sublimed from the molten state.

S i g n i f i c a n c e i n A i r P o l l u f i o n P r o b l e m

The significance of aerosols, and of all airborne particulatematter, varies with the type of a i r pollutionproblem inwhich they a r e involved. In most situations, particulate emissions represent a major portionof the total quantity of a i r contaminants andwould be important for their soiling and and nuisance properties alone, if for no other. Even in a i r pollution problems of the type produced by coal burning, which involves only carbon particles, ash, andoxides of sulfur, there a r e in- dications thatthe toxic effect of the sulfur dioxide and trioxide i s enhanced by the concomitant particulatematter. This kindof effect has been noted in other cases involving aerosols and toxic gases or liquids and has given r ise to the theory that other contaminants can adsorb on the surface of the particles and thus come into contact with inner surfaces of the lungs and mucous membranes in much greater concentrations than would otherwise be possible.

Particulate emissions a r e also associatedwith re - duction of visibility. In some instances, this i s the simple physical phenomenon of obscuration of visibility by the quantity of interfering material. In those instances associated with photochemical smog, however, the visibility reduction is due to refractionandscattering of light, and the number and size of the particles involved a r e much more important than their identities. The smaller the particles (maximumreductionofvisibilityat 0.7 mi- cron) and the larger their number, the greater their collective effect on visibility.

It has also been suggested that the presence of minute particles promotes the photochemical r e - actions that produce smog. Furthermore, small aerosolparticles a r e among the products of these reactions and add to the visibility reduction produced by the emitted contaminants.

AIR POLLUTION CONTROLS ALREADY I N EFFECT

When the a i r pollution problem inLos Angeles County was recognized, an agency was immediately provided to study the problem and t ry to solve it. The f i rs t Air Pollution Control District in Californiawas formedand charged with responsibility for the elimination o r , a t least,significant reduction of a i r pollution in Los Angeles County.

Duringits f irst 10 years, theDistrict concentrated its efforts on control of emissions from stationary sources. Experience of other agencies in this field had shown that certain kinds of industrial emissions were most commonly responsible for a i r pollution problems. Mobile equipment was ex- empted from control and not a t that time considered a serious source of contaminants.

Continuous study and diligence have since led to the promulgation of the most stringent and complete rules and regulations in force anywhere in theworld and to the most effective control program currently feasible. Both a r e frequently copied and studied. Table 2 concisely summarizes what has been accomplished. Other sections of this manual explain in detail the methods and equipment used.

Perhaps themost graphic evidence of the success of this control effort i s the almost complete ahsence of emissions from stacks and chimneys anywhere in the Los Angeles Basin. Any source of visible emissions immediately calls attention to itself.

CONTROL MEASURES STILL NEEDED

Despite a n almost incredibly successful program of control over stationary-source emissions , the persistence of unpleasant effects of a i r pollution and the concentrations of atmospheric contaminants still being measured did not properly reflect these dramatic reductions. A research program undertakenconcurrentlywith the programs of control and enforcementhad revealed that the a i r pollution problem in the Los Angeles a rea was dif- ferentfromthatusually encountered. It had shown also that the hydrocarbons and oxides of nitrogen primarily responsible for the effects associated with smog inLos Angeles were likely to be emitted only in connectionwith the processing and handling of ~ e t r o l e u m and the combustion of fuels.

AS soonas hydrocarbons were recognized to be of great significance in this kind of a i r pollution problem, measures were undertaken to control the emissions from their principal stationary sources, the refineries. Although these measures failed to eliminate smog effects throughout the basin, they

Control Measures Needed 19

20 AIR CONTAMINANTS

diminished these effects and reduced the atmospheric hydrocarbon concentrations in the refinery a r e a of the county. At the same time, however, damage to plants, irritation of eyes, and reduction in visibility were more widespread and increasing in severity in suburban areas that had previously been almost smog free. Obviously, some important source of the contaminants that produce photochemical smog had not been adequately taken into account. This source proved to be the most prevalent consumer of petroleum products, the gasoline-powered motor vehicle.

Although no feasible means for control of motor vehicle emissions were yet known, assessment of

enable the distr ict to encourage the development ofnecessarycontroldevices and require their use when they became available. Additional study, plus the increasing occurrence of the effects of photochemical smog in other areas of California, suggested that control of mobile sources a t the local, or district, levelprobablywouldnot be adequate. In 1959, therefore, the state government formallyoccupied this particul.ar field of a i r pollution control in California. Although the Los Angeles County Air PollutionControl District continued i ts participation in research on vehicular emissions, i ts primary responsibility reverted to control of emissions from stationary sources.

the relative importance of this source of emissions was clearly mandatory. Investigation of exhaust A D D I T I O N A L C O N T R O L S O V E R S T A T I O N A R Y S O U R C E S

emissions revealed that. althoueh each individual - vehicle was negligible as a source, the vast number of vehicles could have great significance. Further study demonstrated how the phenomenal postwar growth of the Los Angeles a rea had so increased the sources of a i r contaminants that the gains made by the control of stationary sources had been almost nullified. From 1945 to 1955, for example the pollution of Los Angeles County increased by almost 50 percent; motor vehicle registration and gasoline consumption increased about loopercent; and the number of industrial establishments increased by nearly 80 percent. The district had had to "run a t great speed to stay in one place, " and the picture of what the situation might have been without a controlprogramwas almost unimag- inable.

Estimating the total quantities of a i r pollution in Los Angeles County, the distr ict was able to determine that hydrocarbon emissions from motor vehicles as a fraction of the total for the county had probably increased from about one-eighth in 1940 to one-third in 1950 and to one-half to two- thirds in 1955. Oxides of nitrogen emissions from - motor vehicles probably constituted about 50 percent of the total in 1940 and 1950, and 50 to 60 percent in 1955. During the entire period, motor vehicle emissions probably accounted for 85 to 95 percent of the total of carbon monoldde emitted to the atmosphere. These estimates represent the net effect of both growth and control measures and illustrate the change in emphasis that has grad- ually taken place. Probably this would, however, be less true of areas that had little or no control over emissions from stationary sources.

The principal areas in which additional controls will be needed involve reduction of emissions of organic gases and oxides of nitrogen. Present control measures have so far brought about only 67 and 53 percent control, respectively, of these emissions from stationary sources. Obviously, control of these emissions from motor vehicles also i s necessary, but this i s no longer the Dis- tr ict 's responsibility.

The State of California has adopted str ict ambient a i r quality standards for specific contaminants; these standards a r e exceededon many days of the year inLos Angeles County. Because these standards a r e being exceeded, new rules must be adopted to reduce these contaminants. Of particular concern, in addition to organic gases and oxides of nitrogen as mentioned above, a r e sulfur dioxide and particulate matter.

O r g a n i c G a s e s

On a tonnage basis, only 67 percent control of organic gases from stationary sources has been achieved. The full benefits from Rule 66 pertain- ing to organic solvents have not yet been realized. Many of these organic solvent processes a r e now undergoing modifications; afterburners a r e being installed on existing basic equipment, and processes are being revamped to substitute solvents that do not react photochemically, A new rule, to he effective September 1, 1974, also will prevent large use r s of non-photochemically-reactive solvents f rom discharging these contaminants into

M O T O R V E H I C L E E M I S S I O N S the atmosphere. In petroleum processes, asphalt ForLos Angeles County, this gradual change and air-blowing and release of oreanic eases and va- - - - - - I i ts effecton the solution of the a i r pollution prob- pors from vacuum-producing devices or systems lem had to be carefully evaluated, and the probable (including hot wells and accumulators) also will necessity for control of motor vehicle emissions, be controlled under new rules. Other new rules prudentlyconsidered. In 1957, though no controls will require that pumps and compressors be e - were available, appropriate steps were taken to quippedwithmechanical seals and that safety pres-

Control Measures Needed 21

sure rellef valves be vented to a vapor recovery O t h e r C o n i a m i n a n f s or dlsposal system.

O x i d e s o f N i t r o g e n

Oxides of nitrogen f rom stationary sources will be reduced significantly during the next 3 years by the provisions of Rule 68. Future single large sources of oxides of nitrogen will no longer be allowed in Los Angeles County because of the limitations imposed by Rule 67. Most of the future reduction inoxides ofnitrogen will be achieved by the electric power generating plants. In anticipa- tion of Rule 68, which was adopted early in 1971, much work already has been accomplished and measurable reductions were achieved in 1969 and 1970. In fact, the design changes and operational changes brought about during those 2 years re - duced oxides of nitrogen about one-half from the power utilities.

If the str ict ambient a i r quality standards of the State of California a r e to be met, additional rules must be adopted to further control sulfur dioxide and particulate matter. Recently adopted Rules 53.1, 53.2, and 53. 3 will reduce substantially the emissions of sulfur dioxide f rom sulfur scavenger plants and sulfuric acid plants. Several new rules a r e in effect to further reduce particulate emissions.

Continued surveillance of all contaminant emis - sions will be maintained. If any emissions a r e found to have increased to the extent that more stringent control i s necessary, or if means a r e discovered to make certain additional controls feasible, then new rules will be adopted immediately.

CHAPTER 3

D E S I G N OF LOCAL EXHAUST S Y S T E M S

FLUID FLOW F U N D A M E N T A L S

HERBERT SIMON, Senior A i r Pollution Engineer

JOHN L. McGINNITY, Intermediate A i r Pollution Engineer*

JOHN L. SPINKS, A i r Pollution Engineer

HOOD DESIGN

HERBERT SIMON, Senior Air Pol lut ion Engineer

JOHN L. McGINNITY, In te rmedia te Air Po l lu t ion Engineer"

JOHN L. SPINKS, Senior A i r Pollution Engineer

DUCT DESIGN

EDWIN J. VINCENT, In te rmedia te Air Pollution Engineer"

FAN DESIGN

EDWIN J. VINCENT, Intermediate A i r Pollution Engineer':

LEWIS K. SMITH, A i r Pollution ~ n g i n e e r t

VAPOR COMPRESSORS

GEORGE THOMAS, Senior Air Pol lut ion Engineer

CHECKING A N EXHAUST SYSTEM

JOSEPH D'IMPERIO, A i r Pollution ~ n ~ i n e e r t

COOLING OF GASEOUS EFFLUENTS

GEORGE THOMAS, Senior Air Pol lut ion Engineer

*Now with Environmental P ro tec t ion Agency, Research T r ~ a n g l e P a r k , N. C.

t ~ o w deceased

CHAPTER 3

D E S I G N O F LOCAL EXHAUST SYSTEMS

F L U I D F L O W F U N D A M E N T A L S

Local exhaust sy s t ems a r e devices used t o cap- tu re dusts and fumes o r other contaminants a t the i r source and prevent the discharge of these contaminants into the atmosphere. Close-fitting hoods a r e u s e d to capture the contaminants f r o m one or more locations s o that the laden gases can. byconveyed through a sy s t em of ducts by onc o r m o r e exhaust fans. An a i r pollution control device can then be used to collect the a i r contaminants and discharge the cleansed a i r into the a t - mosphere.

Lndesigningalocal exhaust sys tem, sufficient a i r m u s t be provided for essent ia l ly complete pickup of the contaminants. Conversely, too much a i r can r e su l t in excessive construction and opera- t ioncos t s . I t i s , the re fore , nece s sa ry f o r the de- s igner to understand cer ta in ~ h ~ s i c a l pr inciples that a r e useful in analyzing the ventilation needs and in selecting the hooding devices.

Thena ture of flow of a r e a l fluid i s ve ry complex. The basic laws describing the complete motion ol a fluid a r e , in general , unknown. Some s imple cases of l aminar flow, however, m a y be computed analytically. F o r turbulent flow, onthe other hand, only a par t ia l analysis can be made by using the principles olmechanics . The flow in exhaust s y s - t ems i s always turbulent; therc iore , the f inal solu- t lon to these problems depends upon experimental data.

BERNOULLI 'S EQUATION

The bas ic energy equation of a f r i c t ion less , In- compress ib le fluid f o r the case of s teady flow along a single s t reaml ine i s given by Bernoulli a s

where

h = elevation above any a r b i t r a r y datum, f t

p = p r e s s u r e , l b l f t 2

3 y = specific weight, lb / f t

v = velocity, f t l s e c 2

g = accelerat ion due t o gravity, 32.17 f t / s e c

C = a constant, di f ferent f o r each s t reamline.

2 5

Each t e r m i n Bernoul l i ' s equationhas the units foot- pounds pe r pound of fluid o r feet of fluid. These t e r m s a r e frequently r e f e r r e d t o a s elevation head, p r e s su rehead , andvelocityhead. They a l so rep- r e s en t t he potential energy, p r e s s u r e energy, and velocity energy, respectively.

When Bernoul l i ' s equation i s applied t o industr ia l exhaust sys tems , the elevation t e r m i s usually omitted, s ince only relat ively sma l l changes in e l - evation a r e involved. Since al l s t reaml ines or ig- i n a t e f r o m a r e se rvo i r of constant energy (the atmosphere) , the constant i s the s a m e f o r a l l s t reaml ines , and the res t r i c t ion of the equation t o a single s t reaml ine canbe removed. Fu r the rmore , s ince the p r e s s u r e changes in near ly a l l exhaust sy s t ems a r e a t m a s t only a few percen t of the absolute p r e s s u r e , the assumption of incompress i - b i l i tymaybe made withnegligible e r r o r . Although steady-[low conditions do not always exis t in exhaust sys tems , i t i s safe t o make the assumption of s teady flow if the wors t possible case i s con- s idered. A n y e r r o r w i l l then he on the s a f e side.

All r e a l fluids have a property called viscosity. Viscosity accounts f o r energy l o s se s , which a r e the resu l t of shea r s t r e s s e s duringflow. The magnitude of the l o s se s mus t be determined exper i - mentally, but once established, the values can be applied t o dynamically s im i l a r configurations. Bernoul l i ' s equat ionmayhe applied t o a r e a l fluid by adding an energy l o s s t e rm . Letting l b e a n ups t ream point and 2 a downstream point, the energy pe r unit weight a t i s equal to the energy per unitweight a t 2 plus a l l energy l o s se s between point and point 2.

P I T O T TUBE FOR FLOW MEASUREMENT

The velocity of a fluid (liquid) (lowing i n an open channel m a y be measu red by means of a s imple pitottube, a s shown in F igure 2 (Streeter , 1951). Although this instrument i s s imple, usually con- sisting of a g lass tube with a right-angle bend, i t i s one of the m o s t accura te means of measur ing velocity. When the tube opening i s directed up- s t r e am, the fluidflows into the tube until the p r e s - su r e intensitybuilds up within the tube sufficiently to withstand the impact of velocity against i t . The fluid a t a point d i rec t ly in f ront of the tube (stag- nationpoint) i s then a t res t . The p r e s s u r e a t the stagnation point i s known f r o m the height of the liquid column in the tube. The velocity of the fluid

,j

2 6 DESIGN O F LOCAL EXHAUST SYSTEMS j

F i g u r e 2 . S i m p ! e p i t o : t u b e ( S t r ~ e t e r , 1 9 5 1 ) .

i n the s t r e a m m a y be evaluated by writing Be r - noulli 's equation between point ups t ream of the stagnation point and point 2 the stagnation point. Note that h i = h2 and v2 = 0. Therefore

solving for the velocity,

A simple pitot tube measu re s the total head o r total p r e s s u r e , which i s composed of two pa r t s , a s shown inF igu re 2. These a r e the s ta t ic p res - s u r e R, and the dynamic o r velocity p r e s s u r e h,. In open-channel flow, hv i s measu red f rom the f r ee surface. When the liquid is in a pipe o r conduit in which it flows full , a s imple pitot tube

wil lagain indicate the total p r e s s u r e , but now the portion of the total headcaused by velocity cannot be distinguished. The s ta t ic p r e s s u r e i n th i s c a se can he measu red by a piezometer o r s ta t ic tube, a s shown inF igu re 3. The total p r e s s u r e H con- s i s t s of rhe sum of the static p r e s s u r e hS and the velocity p r e s s u r e hv, o r

The velocity can be determined, therefore , f r o m the difference between the total and s ta t ic heads.

In p rac t ice , measurement of total p r e s s u r e and s ta t ic p r e s s u r e i s combined into a single ins t rument (pi tot-s ta t ic tube, F igure 4), which permi t s d i rec t measurement of velocity head since the s ta t ic head is automatically subtracted f rom the total head. An inclined manometer (El l ison guage) i s par t icular ly useful when the heads a r e smal l a s i n exhaust sys tems . U s e of this device to measu re the flow of a gas introduces, however, a n additional factor , which i s the conversion of readings in inches ofmanometer fluid into mean- ingful velocity t e rms . This relationship, when wate r i s used a s the manometer fluid to measu re the velocity of a i r , i s

where

h = velocity p r e s s u r e o r head, inches of v

wate r

4005 = 1096.2 Volume in f t 3 of 1 lb of a i r ' a t 7 0 ° F and 14.7 ps ia

v = velocity of a i r , fpm. a

F ~ g u r e 3. S t a t ~ c t u b e ( S t r e e t e r , 1 9 5 1 ) F ~ g u r e 4. P ~ t o t - s t a t i c t u b e ( S t r e e t e r , 1951).

Hood Design 27

Correct ion F a c t o r s

The relationship expressed in equation 5 i s exact onlyfor a i r at standard temperature and pressure, 7 0 ° F and 14.7 psia, respectively. A correction must be applied for other than standard conditions. Ifthe a i r in the duct departs f rom 7 0 ° F by more than about 50°F , a correction i s required:

where

ta = the temperature of the air , "F.

For smaller temperature deviations, the e r r o r i s not significant and maybe neglected. E the gas i s other than a i r , a correction for the difference in density may be applied:

in the path of the high-velocity dust particles. Inertial forces ca r ry the a i r contaminants into the hood.

Exterior hoods must capture a i r contaminants that a r e being generated f rom a point outside the hood itself, sometimes some distance away. Exterior hoods a r e the most difficult to design, require the most a i r to control a given process, and a r e most sensitive to external conditions. For example, a hood that works well in a still atmosphere may be rendered completely inef- fectual by even a slight draft through the area. The b,,t rule to follow in hood design is to plac. the hood where the a i r contaminants a r e generated. Since this i s not always physically possible, it is important to consider the design criteria for external hoods.

CONTINUITY E Q U A T I O N

density of as The volume of a i r flow is dependentu~on the cross-

= (AT (density of a i r STP v sectional area and the average ve' :city. of the air. The relationshipmaybe representedby the familiar equation

where the density of the gas under conditions ac- tually existing at the time of the measurement in- Vt = Av cludes the effects of temperature, pressure, and

(8

molecular weight. where

H O O D DESIGN Hoods a r e devices used toventilate process equipment by capturing emissions of heat or a i r contaminants, whlch are then conveyed through exhaust system ductwork to a more convenient discharge point or to a i r pollution control equipment. The quantity of air required to capture and convey the air contaminants depends upon the size and shape of the hood, its position relative t o the points of emission, and the nature and quantity of the a i r contaminants.

Hoods can generallybe classified into three broad groups: enclosures, receivinghoods, andexterior hoods. Enclosures usually surround the point of emission, thoughsometimes one face may he partially or even completely open. Examples of this type a r e paint spray booths, abrasive blasting cabinets, totally enclosed bucket elevators, and enclosures for conveyor belt t ransfer points, mul- l e r s , vibrating screens, crushers, and so forth.

V = total a i r volume, cfm t

2 A = cross-sectional area, ft

v = velocity, fpm.

The cont~nuity equation (equation 8 ) shows that, for agiven quantity of fluid, the velocity must increase i f the area decreases. Imagine that a i r i s being withdrawn f rom a point at the center of a i

large room. Since an imaginary point has no di- 4 mensions, there will be no interference with the flowof a i r toward the point. The a i r will, therefore,approach this point radially and at a uniform rate from all directions. The velocity of the a i r must increase as it passes through a succession of diminishing areas represented by spherical surfaces in its approach to the imaginary point, according to the relationship

Receiving hoods a r e those wherein the air con- where taminants a r e injected into the hoods. For example, the hood for a grinder i s designed to be r = the distance from the imaginary point, it.

28 DESIGN OF LOCAL EXHAUST SYSTEMS

AIR FLOW INTO A DUCT

If a circular duct opening, representing a simple hood, i s substituted for the imaginary point, the pattern of flow into the end of the duct, or hood, will be modified as shown in Figure 5 because of the interference f rom the duct. The velocity of the a i r approaching aplain, circular opening along the axis of the duct i s given by Dalla Valle (1952) as approximately

where

Y = the percent of the velocity at the opening found a t a point x on the axis

x = the distance outward along the axis f rom the opening, f t

k = the area of the opening, ft2.

The velocity a t the opening is computed from the continuity equation.

The actual flow pattern is found to he a s shown inFigure 5from studies by Dalla Valle and others. The lines of constant velocity a r e called contour iines, while those perpendicular to them a r e s t r eamlines, which r epr esent the dir ection of flow. The addition of a flange improves the efficiency of the duct a s a hood for a distance of about one diameter from the duct face. Beyond this point, flanging the duct improves the efficiency only slightly. Figure 6 illustrates flow patterns for several sizes of square hoods. Because there i s little difference in the center line velocity of hoods of equal a i r volume at a distance of one or two hooddiameters f romthe hoodface, Hemeon (1955) recommends using one equation for all shapes-- square, circular, and rectangular up to about 3:l length-to-width ratio. He also does not distinguish between flanged and unflanged hoods, which appears justified when these hoods a r e used only at distances of one diameter or more from the hood face. At close distances, flanged hoods a r e f a r superior at the same volume. By rearranging terms in equation 10 and combining with equation 8 , the iollowing is obtained:

where

Vt = the volume of a i r entering the hood, cfm

v = the velocity at point x, fpm X

x = the distance to any point x on the axis or center line of the hood measured f rom the hood lace. it

2 Af = the area of the hood face, f t

Analysis of equatton 11 shows that at the hood face x = 0 and the equation becomes identical to equation 8. F o r large values of x, the Af t e rm becomes less significant, a s the evidence shows i t should. To use equation 11, select a value of vx that i s sufficient to assure complete capture of the a i r contaminants a t point x. From the physical dimensions and location of the hood, Af and x a r e determined. The volume required may then be calculated.

Whileequation 11 applies to a freestanding or un- obstructed hood, i t can also be applied to a rec- tangularhoodbounded on one side by a plane su r - face, as showninFigure 7. Thehoodis considered to he twice i ts actual size, the additional portion beingthe mi r ro r image of the actual hood and the bounding plane being the bisector. Equation 11 then becomes

where the t e rms have the same meaning as before.

NULL POINT

Air contaminants a r e often released into the atmosphere withconsiderablevelocity a t their point of generation. Because the mass i s essentially small, however, the momentum is scan spent and the particles a r e then easily captured. Hemeon (1955) refers to a null point, shown in Figure 8, as the distance within which the initial energy of an emitted a i r contaminant has been dissipated or nullifiedinovercomingair resistance. If an adequate velocity toward the hood i s provided at the farthestnull point from the hood, all the a i r contaminants released from the process will be captured. What constitutes an adequate velocity towards the hood depends upon drafts in the area and cannot, therefore, be determined precisely.

Establishing the null point in advance for a new process i s not always easy or even possible. For existing equipment, however, direct observation will usually establish a locus ol null points. Ob- viously, in the ahsence of external disturbances, any positive velocity toward the hood at the farthest null poxnt will give assurance of complete capture. When this i s put into practice, however, the r e - sults a r e disappointing. Even closed rooms have drafts and thermal currents that destroy the hood's effectivenessunless a substantial velocity toward thehoodis created at the farthest null point. Ex- perience has shown that a velocity of less than 100 fpm at a null point can seldom, ii ever, be toleratedwithoutaloss in the hood's effectiveness.

Draft velocities in industrial situations may almost always be expected to bc 200 to 300 fpm

Hood Design 29

DISTANCE FROM O P E N I N G , n c h e s

D I S T A N C E FROM O P E N I N G , i n c h e s

F i g u r e 5. A c t u a l f l o w c o n t o u r s and s t r e a m l i n e s f o r f l o w i n t o c i r c u l a r open ings . C o n t o u r s a r e e x p r e s s e d a s p e r c e n t a g e o f o p e n i n g v e l o c i t y ( D a l l a V a l l e , 1952) .

3 0 DESIGN O F LOCAL EXHATST SYSTEMS

O l S i l N C E OUTWARD FROM OPENING. InchLr

F i g u r e 6. A c t u a l v e l o c i t i e s f o r s q u a r e o p e n i n g s o f d i f f e r e n t s i z e s . A i r f l o w t h r o u g h each o p e n i n g i s 500 c f m (Da l l a Va l l e , 1952 ) .

F i g u r e 7 . R e c t a n g u l a r hood Sounded by a p l a n e s u r f a c e (Hemeon. 1955 ) .

or more periodically, and draft velocities of 500 to600fpmare not unusual in many cases. Drafts such as these mayprevent capture of a i r contaminants by exterior hoods, a s illustrated in Figure 9 for the case of ahigh-canopyhood, unless adequate baffling i s provided or hood volume is increased tounreasonable values. Baffling provides, in effect, an enclosure that i s almost always the most efficient hooding.

DESIGN OF HOODS FOR COLD PROCESSES

Alarge body of recommendedventilation rates has beenbuilt up over the years by various groups and organizations who a r e concerned with the control of a i r contaminants. This type of da ta is illustrated in Table 3. Theuse of these recommended values

Figure 8. Locat ion o f n u l l po i n t and x-distance (Hemeon, 1955).

F i g u r e 3. D r a f t s d i v e r t t h s r i s i n g co lumn o f a i r and p r e v e n t i t s c a p t u r e b y t h e hood (Hemeon, 1955) .

greatlysimplifies hoodingdesignforthe control of many common a i r pollution problems. Note that almost all published recommendations have specified complete or nearly complete enclosure. These published data provide a reliable guide fo r the design engineer. The recommended values must, however, be adjusted to specific applications that depart f rom the assumed normal conditions.

Hood Design

Table 3. EXHAUST REQUIREMENTS FOR VARIOUS OPERATIONS

Operation Exhaust arrangement Remarks

Abrasive blast rooms

Abrasive blast cabinets

Baggingmachines

Belt conveyors

Bucket elevator

Foundry screens

Foundry shakeout

Foundry shakeoutside

Grinders, disc and portable

Grinders and crushers

Mixer ,

Packaging machines

Paint spray

Rubber rol ls (calendars)

Welding (arc)

Tight enclosures with a i r inlets (generally in roof)

Tight enclosure

Booth or enclosure

Hoods at t ransfer points enclosed a s much as possible

Tight casing

Enclosure

Enclosure

hood (with side shields when possible)

Downdraft grilles in bench or floor

Enclosure

Enclosure

Booth Downdraft Enclosure

Booth

Enclosure

Booth

For 60 to 100 fpm downdraft or 100 fpm crossdraft in room

For 500 fpm through all openings, and a minimum of 20 a i r changes per minute

For 100 fpm through a l l openings fo r paper bags; 200 fpm for cloth bags

For belt speeds l e s s than 200 fpm, V = 350 cfmlft belt width with a t least 150 fpm through openings. For belt speeds greater than 200 fpm, V = 500 cfm/ft belt width with at least 200 fpm through remaining openings

2 F o r 100 cfmlf t of elevator casing cross-section (exhaust near elevator top and also vent at bottom i f over 35 f t high)

Cylindrical--400 fpm through openings, and not l e s s than 100 cfm/ft2 of cross- section; flat deck--200 fpm through openings, and not less than 25 c f ~ l f t 2

of screen area

For 200 fpm through all openings, and not less than 200 cfm/ft2 of grate area with hot castings and 150 cfm/ft2 with cool castings

For 400 to 500 cfm/f t2 grate area with hot castings and 350 to 400 cfm/ft2with cool castings

For 200 to 400 fprn through open face, but at least 150 cfm/ft2 of plan working area

For 200 fpm through openings

For 100 to 200 fpm through openings

For 50 to 100 fpm For 75 to 150 fpm For 100 to 400 fpm

For 100 to 200 fpm indraft, depending upon size of work, depth of booth, etc.

For 75 to 100 fpm through openings

F o r 100 fpm through openings

3 2 DESIGN OF LOCAL EXHAUST SYSTEMS

S p r a y B o o t h s

Spray booths of the open-face type a r e generally designed to have a face Indraft velocity of 100 to 200fpxn. This is usually adequate to assure complete capture of all overspray, provided the spraying is done within the confines of the booth, and the spray gun i s always directed towards the interior. It is a common practice, especially with largeworkpieces, toplace the work a short distance in front of the booth face. The overspray deflectedfrom the workmay easily escape capture, particularlywith a careless or inexperienced operator. If this si tuat~on is anticipated, the equipment deslgner can provlde a yelocity of 100 fpm at the farthest point to be controlled, as in the following illustrative problem.

Example 1

Given:

A paint spray booth 10 feet wide by 7 feet high. Work may be 5 feet in front of the booth face a t times. Nearly draftless area requires 100 fpm at point of spraying.

Problem:

Determine the exhaust rate required.

Solution:

F r o m equation 12, volume required is

2

- Vt - X

F r o m equation 8, face velocity is

When the spraying area is completely enclosed to formapaint spray room, the ventilation requirements a re not greatly reduced over those for spraying inside an open-face booth. This is necessary because a velocity of approximately 100 fprn must be provided through the room for the comfort and health of the operator.

A b r a s i v e B l a s t i n g

Abrasvve blasting booths a r e similar to spray booths exceptthat a complete enclosure i s always required. In addition, particularlyfor small booths (benchtype), the ventilation rate must sometimes be increased to accommodate the a i r used for blasting. The volume of blasting a i r can be determined from the manufacturer's specifications. For a small blasting booth, this will usually be about 50 to 150 cfm. The following illustrative problem shows how the ventilation rate is calculated.

Example 2

Given:

A small abrasive blasting enclosure 4 feet wide by 3 feet high by 3 feet deep. Total open area equals 1.3 it2.

Pr oblem:

Determine the exhaust rate required.

Solution:

F rom Table 3, ventilation required = 500 fprn through all openings but not less than 20 a i r changes per minute.

Volume at 500 fpm through all openings:

Vt = 500 x 1.3 = 650 cfm

Volume required for 20 a i r changes per minute:

Vt = 20 x volume of booth

Vt = 2 0 ~ 4 x 3 ~ 3 = 720 cfm

O p e n - S u r f a c e T a n k s

Open-surface tanks may be controlled by canopy hoods or by slothoods, as illustratedin Figure 10. The latter a r e more commonly employed. The ventilation rates required for open-surface tanks may be taken from Table 4, which i s a modification of the American Standards Association code Z 9.1. Thesevalues shouldbe considered a s min- imumunder conditions where no significant drafts will interfere with the operation of the hood. When slot hoods a re employed the usual practice is to provide a slot along eachlong side of the tank. The slots a r e designed for a velocity of 2, 000 fprn through the slot face a t the required ventilation rate. Fora tank with two parallel slot hoods, the ventilation rate required and the slot width b, may be taken directly from Figure 11, which graphs the American Standards Association code Z 9.1.

Hood Design 33

Figure 10. Slot b o d for eOntr0l of emissions from open-surface tanks (Adapted from l n d ~ ~ s t r i a l Venti lat ipn, 1960).

be used by assuming the tank to be half of a tank twice a s wide having slothoods on both sides. This procedure i s illustrated below.

Example 4

Given:

The same tank a s in Example 3, but a slot hood is to be installed along one side only. The other side i s flush with a vertical wall.

Problem:

Determine the total exhaust rate and slot width required.

Solution:

The ventilation ra te in cfrn per foot of tank length

Neither the code nor Figure 11 makes allowance is taken as half the rate for a tank twice a s wide

fordraf ts . The use of baffles i s strongly recom- f;om Figure 11. Use width of 4 feet.

mended wherever possible to minimize the effect of drafts. If baffles cannot be used or arenot suf- - - Vt - 880 -

L 2 = 440 cfm per foot

ficiently effective, theventilation rate must be increased. The slot width i s also increased to hold the slot face velocity in the range of 1,800 to Total exhaust volume required 2,400 fpm.

The use of Figure 11 i s illustrated in the follow- Vt = 440 x 3 = 1,320 cfm ing problem:

Slot width i s read directly from Figure 11 fo r twice Example 3 the width bs = 2-518 inches.

Given:

A chrome plating tank, 2 feet wide by 3 feet long, to be controlled by parallel slot hoods along each of the 3-foot-long sides.

Problem:

Determine the total exhaust rate required and the slot width.

Solution:

F r o m Figure 11, the ventilation ra te required i s 390 cfm per foot of tank length.

Vt = 390 x 3 = 1, 170 cfm

1 . F r o m Figure 11, the slot width i s 1- mches. 8

Ifa slot hood i s used on only one side of a tank to capture emissions, and the opposite side of the tank is bounded by a vert ical wall, Figure 11 can

Figure 1 1 . Minimum v e n t i l a t i o n ra tes requ i red f o r tanks.


Table 4. VENTILATION RATES FOR OPEN-SURFACE TANKS (American Ai r F i l t e r Company, Inc. , 1964)

Minimurn ventilation rate, Minimum ventilation ra te , a c f m pe r ft2 of c fm pe r f t2 of tank a r ea . hood opening L a t e r a l exhaust

P r o c e s s Enclosing Canopy tank width hood hood

W/L = ra t io tank length

One Two Three F o u r W/L W/L W / L open open open open 00 t o 0.24 0.25 to 0 .49 0.50 t o 1 . 0 s ide s ides s ides s ides A B A B A B

Plat ing Chromium (chromic acid m i s t ) 75 100 125 175 1 2 5 1 7 5 150 200 175 225 Arsen ic (a r s ine) 65 90 100 150 90 130 110 150 130 170 Hydrogen cyanide 75 100 125 175 1 2 5 1 7 5 150 200 175 225 Cadmium 75 100 125 175 1 2 5 1 7 5 150 200 175 225 Anodizing 75 100 125 175 125 175 150 200 175 225

Metal cleaning (pickling) Cold acid Hot acid Nitric and sulfur ic acids Nitr ic and hydrofluoric acids

Metal cleaning (degreasing) Trichloroethylene Ethylene dichloride Carbon te t rachlor ide

Metal cleaning (caustic o r e lectrolyt ic) Not boiling Boiling

Bright dip (ni t r ic acid) Stripping

Concentrated n i t r i c acid Concentratednitricandsulfuricacids

Salt baths (molten sa l t ) Salt solution (Parker i se ,Bonder i se , etc.)

Not boiling Boiling

Hot wate r (if vent. des i red) Not boiling Boiling

aColumn A r e f e r s to tank with hood along one s ide o r two para l le l s ides when one hood i s against a wall o r a baffle running length of tank and a s high a s tank i s wide; a l so t o tanks with exhaust mani - fold along center l ine with W/2 becoming tank width i n W/L ratio.

'Column B r e f e r s to f reestanding tank with hood along one s ide o r two para l le l sides.

D E S I G N O F H O O D S FOR H O T PROCESSES of the hoodand the ventilation r a t e provided m u s t take th i s t he rma l d r a f t into consideration.

C a n o p y H o o d s As the heated a i r s t r e a m r i s ing f r o m a hot s u r -

Ci rcu la r high-canopy hoods f ace moves upward, i t m ixes turbulently with the surrounding a i r . The higher the a i r column r i s e s

Hooding f o r hot p roce s se s r equ i r e s the application the l a r g e r i t becomes and the m o r e diluted with of different pr inciples than tha t f o r cold p roce s se s ambient a i r . Sutton (1950) investigated the turbu- because of the t he rma l effect. Whensignif icant l en t mixing of a r i s ing column of hot a i r above a quantit ies of hea t a r e t r an s f e r r ed t o the surround- heat source. Using data f r o m experiments by ing a i r by conduction and convectiolqa t he rma l d ra f t Schmidt published in Germany, and h i s own ex- i s c r ea t ed tha tmay cause a r i s ing a i r cu r r en t with per iments wi thmi l i t a ry smoke genera tors , Sutton velocities somet imes over 400 fpm. T h e design developed equations that descr ibe the velocity and

I 65 75 75 75

75 75 75

65 75 75

75 75 50

90 75

50 75

90 100 100 100

100 100 100

90 100 100

100 100

75

90 100

75 100

100 125 125 125

125 125 125

100 125 125

125 125

75

100 125

75 125

150 175 175 175

175 175 175

150 175 175

175 175 125

150 175

125 175

90 130 1 2 5 1 7 5 1 2 5 1 7 5 1 2 5 1 7 5

125 175 125 175 125 175

90 130 1 2 5 1 7 5 125 175

125 175 125 175

60 90

90 130 1 2 5 1 7 5

60 90 1 2 5 1 7 5

110 150 150 200 150 200 150 200

150 200 150 200 150 200

110 150 150 200 150 200

150 200 150 200

75 100

110 150 150 200

75 100 150 200

130 170 175 225 175 225 175 225

175 225 175 225 175 225

130 170 175 225 175 225

175 225 175 225

90 110

130 170 175 225

90 110 175 225

Hood Design 35

diameter of a hot rising jet at any height above a hypotheticalpoint source located a distance z he- low the actual hot surface. Hemeon adapted Sutton's equations to the design of high-canopy hoods for the control of a i r contaminants f r o m hot sources. The rising a i r column illustrated in Figure 12 expands approximately according to the empirical formula

where

D = the diameter of the hot column of a i r a t the levei of the hood face, ft

x = the distance f r o m the hypothetical point source to the hood face, ft.

F r o m Figure 12 it i s apparent that xf i s the s u m of y, the distancefromhot source to the hood face, and z the distance below the hot source to the hypothetical point source. Values of z may be taken f r o m Figure 13. According to Hemeon, the velocity of the rising column of a i r into the hood may be calculated f rom

where

F i g u r e 13. Va lue o f z f o r use w i t h h i g h - c a n o p y hood equa t i ons ;

100

- Y 5 0

4 0

u N 30 " - z

.s: 2 0 w = 3

C 0 0 w

= C

2 5 , o = 0 L a

u 2 " < = " < - C C 5

u, - r 4 0 C 0

:

D f .

Y

Z . . . . . . . . : : : .

HYPOTHETICAL . : . . . .

POINT SOURCE \;

= 2 2

v = the velocity of the hot a i r jet at the level of the hood face, fpm

2 3 4 5 10 7 0 3C

x = the height of the hood face above the f

theoretical point source = y t z, i t

DIAMETER OF HOT SOURCE ( O s l . f e e t

q, = the rate a t which heat i s t ransferred to the rising column of a i r , Btulmin.

The rate at which heat i s absorbed by the rising column may be calculated f rom the appropriate natural convection heat loss coefficient qL listed in Table 5 and from the relationship

where

qc = the total heat absorbed by the rising air column, Btulmin

qL = the natural convection heat loss coefficient listed in Table 5, ~ t u l h r - i t 2 - " F

A = the area of the hot source, i t2 F ~ g u r e 1 2 . D lmens lons used t o d e s ~ g n h l g h - c a n o p y hoods f o r h o t At = the temperature difference between the hot s o u r c e s (Hemeon. 1955). source and the ambient a i r , "F.


Table 5. COEFFICIENTS FOR CALCULATING SENSIBLE HEAT LOSS BY NATURAL CONVECTION (Hemeon, 1955)

Natural convection Shape or disposition of heat surface

heat loss (ar ) coefficienta

Vertical plates, over 2 f t high / 0.3 ( a t ) 114

I 114 Vertical plates, less than 2 ft high 0.28 (9

(X = height in ft)

Horizontal plates, facing upward I 0.38 (At) 114

Horizontal plates, facing down- 0.2 (At) 114

ward

Single horizontal cylinders At 114

0. 42 (T) (where d is diameter in inches)

Vertical cylinders, over 2 ft high At I14

0.4 (T) (same a s horizontal)

Vertical cylinders less than 2 ft high. Multiply q~ from formula above by appropriate factor below:

Height, ft Factor -

0.1 3.5 0.2 2.5 0.3 2.0 0.4 1. 7 0.5 1. 5 1.0 1 .1

aHeat loss coefficient, q i s related to q a s follows: L

Schmidt's experimentswere conducted in a closed laboratory environment designed tominimize drafts and other disturbances. Nevertheless, Sutton r e - ports that there was a considerable amount of waver and fluctuation in the rising a i r column. In developinghis equations, Sutton defined the hori- zontallimits of the rising a i r column a s the locus of points having a temperature difference relative to the ambient atmosphere equal to 10 percent of that at the center of the column.

In view of the facts that this arb i t rary definition doesnottruly define the outer limits of the rising a i r column and that greater effects of waver and drafts may be expected in an industrial environment, a safety factor should be applied in calculating the size of the hood required and the minimum ventilation rate to assure complete capture of the emissions. Since high-canopyhoods usually control emissions arising f r o m horizontal-plane

surfaces, a simplification can be derived by combining equations 14 and 15 with the heat t ransfer coefficient f o r horizontal-plane surfaces and allowing a 15 percent safety factor.

Although the mean diameter of the rising a i r column in the plane of the hood face i s determined f rom equation 13, the hood must be made somewhat la rger in order to assure complete capture of the rising column of contaminated a i r a s it wavers back and forth and is deflected by drafts . The

exact amount of allowance cannot be calculated precisely, but factors that must be considered include thehorizontalvelocity of the a i r currents in the area, the size and velocity of the rising a i r jet, and tne distance y of the hood above the hot

source. Other factors being equal, i t appears Diameter of rising a i r s t ream at the hood face most likely that the additional allowance for the f rom Equation 13: hood size must he a function of the distance y. Increasing the diameter of the hood by a factor of

D = 0 . 5 ~ 0.88 0.8 yhas been recommended (Industrial Ventila- f tion, 1960). The totalvolume ior the hood can he calculated f rom D = 0. 5 (21) 0. 85 = 7. 3 feet

where

Vt = v A t v ( A - A ) f c r f c (17)

Area of rising a i r s t r eam a t the hood face:

. Vt = the total volume entering the hood,cfm

vf = the velocity of the rising a i r column at the hood face, fpm

A = the a rea of the rising column of con- C

taminated a i r at the hood face, f t2

v = the required velocity through the re - maining area of the hood, A - A,, fpm f

A* = the total a rea of the hood face, ft2.

The value of v, selected will depend upon the draftiness, height of the hood above the source, and the seriousness of permitting some of the contaminated a i r to escape capture. The value of this velocity i s usually taken in the range of 100 to 200 fpm. It i s recommended that a value less than 100 fpm not he used except under ex- ceptional circumstances. The following problem illustrates the use of this methodtodesign a high- canopy hood to control the emissions f rom a metal-melting furnace.

A = (0. 7554)(7.3) 2

C

= 42 squarefeet

Hood size required--including increase to allowfor waver of jet and effect of drafts:

Df = D t 0.Sy C

Df = 7. 3 t (0. 8)(10) = 15.3

Use 15-foot-4-inch-diameter hood

Area of hood face:

Af = (0. 7854)(15. 33) 2

= 185 squarefeet

Velocity of rising a i r jet at hood face: Example 5

Given:

A z'inc-melting pot 1 feet in diameter with metal temperature 550°F. A high-canopy hood is to he used to capture emissions. Because of interference, the hood must be located 10 feet above the pot. Ambient a i r temperature i s 80°F.

Problem: = 143 fpm

Total volume required f o r hood: Determine the size of hood and exhaust rate required.

Tt = v A t 1 0 0 ( A f - A ) f c C

Solution: Vt = (143)(42) t (100)(155-42)

z = 11 feet f rom Figure 13 f o r 4-foot-diameter Source = 20, 300 cfm

x = z + y f

If the hood could be lowered, the volume required to capture the emissions would be reduced suh-

x = 11 t 10 f

= 21 feet stantially a s illustrated below:


Example 6

Given:

The same furnace a s in example problem No. 5, but the hood i s lowered to 6 fee t above the pot.

Problem:

Determine the s ize of hood and exhaust rate required.

Solution:

z = 11 feet f r o m Figure 13 for 4-foot-diameter Source

x = 1 1 + 6 f

= 17 feet

Diameter of rising a i r s t r eam a t the hood face f r o m equation 13.

D = 0. 5 (17) O' 88 = 6.1 fee t

Area of the rising a i r s t r eam a t the hood face:

C A = (0.7854)(6. I ) = 29. 2 square fee t

C

Hood size required:

D = D t 0 . 8 y f

Df = (6.1) + (0.8)(6) = 10.9 feet

Use 10-foot-11 -inch-diameter hood

Area of the hood face:

Af = (0 .7854) (10 .9~)~ = 93.7 square feet

Velocity of rising a i r jet a t hood face:

( 8 ) ( 1 2 . 5 7 ) ~ / ~ (800) 5/12 v = f

( 1 7 ) ~ ~ ~ = 149 fpm

Total volume required f o r hood:

vt = v A + 100 (Af - A=)

f c

Vt = (149)(29. 2) + (100)(93.7-29.2)

= 10,800 cfm

Rectangular high-canopy hoods

The control of emissions f rom sources with other than circular shape may best be handled by hoods of appropriate shape. Thus, a rectangular source would require a rectangular hood in order to minimize the ventilation requirements. A circular hoodused to controla rectangular source of emission would require an excessive volume. The method used t o design a hood fo r a rectangular source is il lustrated in example 7.

Example 7

Given:

A rectangular lead-melting furnace 2 feet 6 inches wide by 4 feet long. Metal temperature 700'F. A high-canopy hood i s t o be used located 8 fee t .hove furnace. Assume 80°F ambient a i r .

Problem:

Determine the dimensions of the hood and the exhaust ra te required.

Solution:

z = 6.2 f rom Figure 13 for 2. 5-foot source

The width of the r is ing a i r jet a t the hood may be calculated f r o m

D = 0. 5 (14. 2) 0.88 = 5.2 fee t

The length of the rising a i r jet may be assumed to be increased over that of the source the same amount a s the width

D = (4) t (5.2 - 2. 5) = 6.7 feet C

Hood Design 3 9

The area of the rising a i r jet i s

A = (5.2)(6. 7) = 35 square feet C

The hood must be larger than the rising a i r s t ream to allow for waver and drafts. By allowing 0. 8 y for both width and length, the hood size i s

Width = (5. 2) + (0.8)(8) = 11. 6 feet

Length = (6. 7) + (0. 8)(8) = 13. 1 feet

U s e hood 11 feet 7 inches wide by 13 feet 1 inch long

Area of hood:

Af = (11.58)(13. 083) = 152 square feet

Velocity of rising a i r jet:

( 8 ) ( l 0 ) ~ / ~ (620) 5/12 v =

f 114 = 130 fpm

(14.2)

Total volume require&for hood:

Vt = (130)(35) + (200)(152-35) = 28, 000 cfm

Note that in this problema velocity of 200 fpm was usedthrough the area of the hood in excess of the a rea of the rising a i r column. A larger value was selected for this case because lead fumes must be captured completelyto protect the health of the workers in the area.

Circular low-canopy hoods

The design of low-canopy hoods is somewhat different f rom that for high-canopy hoods. A hood may be considered a low-canopy hood when the distancehetweenthe hood and the hot source does not exceed approximately the diameter of the source, or 3 feet, whichever i s smaller . A rigid distinction between low-canopy hoods and high- canopy hoods i s not intended oy neces8a~jf;:' The

. .

important distinction i s that the hood i s close enough to the source that very little mixing between the rising a i r column and the surrounding atmosphere occurs. The diameter of the a i r column may, therefore, be considered essentially equal to the diameter of the hot source. The hood needbelarger by only a small amount than the hot sourcetoprovide for the effects of waver and de- flectlonduetodrafts. Whendrafts a r e not a ser i - ous problem, extending the hood 6 inches on all sides s k u l d he sufficient. This means that the hoodface diameter mustbe taken a s 1 foot greater than the diameter of the source. For rectangular sources, a rectangular hood would be provided withdimensions 1 foot wider and 1 foot longer than the source. Under more severe conditions of draft or toxic emissions, or both, a greater safetyfactor i s required, which can be provided by increasing the size of the hood an additional foot or more or byproviding a complete enclosure. A solution to the problem of designing low-canopy hoods fo r hot sources has been proposed by Hemeon (1955).

Although the hoodis usually larger than the source, little e r r o r occurs i f they a r e considered equal. The total volume fo r the hood may then be determined frornthe following equation obtained by rearranging terms in Hemeon's equation and apply- ing a 15 percent safety factor.

where

Vt = total volume for the hood, cfm

Df = the diameter of the hood, f t

a t = the difference between the temperature of the hot source and the ambient a t - mosphere, OF.

A graphical solution to equation 18 is shown in Figure 14. To use this graph, select a hood size 1 or 2 feet la rger than the source. The total volume required for a hood Df feet in diameter may then be read directly f rom the graph for the actual temperature difference At between the hot source and the surrounding atmosphere.

Example 8

Given:

A low-canopy hood is to be used to capture the emissions during fluxing and slagging of brass in a 20-inch-diameter ladle. The metal temperature during this operation will not exceed 2,350-F. The hood will be located 24 inches above the metal surface. Arnbient temperature may be a s s u m e d t o ~ b e 80°F.


10

TOTAL V E N T I L A T I O N R A T E ( V t ) , c f m

F ~ g u r e 14. Mlnlmum v e n t 1 l a t ~ o n r a t e s r e q u i r e d f o r C I r c u l a r low-canopy hooas.

. . ! Problem: *.., I (19)

L Determine the size of hood and exhaust rate required. where

Vt = the total volume for a low-canopy rec- Solution: tangular hood, cfm

Temperature difference between hot source and amblent a l r :

L = the length of the rectangular hood (usually 1 to 2 feet la rger than the source), f t

b = width of the rectangular hood (usually 1 to 2 feet la rger than the source), f t

Use a hood diameter 1 foot la rger than the hot At = the temperature difference between the

source: hot source and the surrounding atmosphere, O F .

Df = 1.67 t 1.0 = 2 . 6 7 f e e t Figure 15 i s a graphical solution of equation 19. The use of this graph to design a low-canopy rec -

Total exhaust rate required f rom Flgure 14: tangular hood for a rectangular source i s illustrated m example 9.

Vt = 1, 150 cfrn Example 9

Rectangular low-canopy hoods Given:

In a similar manner, Hemeon's equations for A zinc die-casting machine with a 2-foot-wide by low-canopy hoods may be modified and simpli- 3-foot-long holding pot for the molten zinc. A

. . fied for application to rectangular hoods. With low-canopy hood is to be provided 30 inches above a 15 percent safety factor, the equation then the pot. The meta*&@erature i s 820°F. Am- becomes bient a i r temperature i s 9O'F. !

Hood Design 4 1

40 6 0 8 0 100 150 200 300 400 500 600 800 1.000 1,500

MINIMUM VENTILATION RATE (Vt/L), c fm/ f t O f hood length

F I g u r e 1 5 . Minimum v e n t 1 l a t r on r a t e s f o r r e c t a n g u l a r l o w - c a n o p y h o o d s . 1

Problem: Total exhaust rate required for hood: I I

Determine hood size and exhaust rate required. Vt = 430 x 4 = 1,720 cfm

i 1

Solution: Enclosures !

Use a hood 1 foot wider and 1 foot longer than the source.

Hood size = 3 feet wide by 4 feet long.

Temperature difference between the hot source and ambient a i r :

Exhaust rate required per foot of hood length f rom Figure 15:

A low-canopy hood with baffles is essentially the 1 same as a complete enclosure. The exhaust rate 1 for anenclosure arounda hot source must, there- 1

I fore, be based on the same principles a s that for 1 alow-canopyhood. Enclosures for hot processes j cannot, however, be designed in the same manner a s for cold processes. Here again, the thermal draft must be accommodated by the hood. Fail- ure to do so will certainly result in emissions escaping f rom the hood openings. After determining the exhaust rate required to accommodate the thermal draft, calculate the hood face velocity or indraft through all openings. The indraft through all openings inthehood should not be less than 100 fpmunder any circumstances. When a i r contaminants a r e releasedwithconsiderableforce, a min-

I imurn indraft velocity of 200 fpm should be provided. When the. a i r contaminants a r e released with extremely great force as , for example, in a 1


direct-arc electric steel-melting furnace, an in- draftof 500 to 800 fpm through all openings in the hood is required.

S p e c i f i c P r o b l e m s

Steaming tanks

When the hot source is a steaming tank of water, Hemeon (1955)develops a special equation by assuming a latent heat of 1, 000 Btu per pound of water evaporated. He derives the following equation for the totalvolume required fo r a low-canopy hood venting a tank of steaming hot water.

where

Vt = the total hood exhaust rate, cfm

Ws = the rate a t which steam i s released, lb/min

Af r the area of the hood face, assumed approximately equal to the tank area, ft2

Dt = the diameter for circular tanks or the width for rectangular tanks, ft.

Preventing leakage

Hoods for hot processes must be airtight. When leaks or openings in the hood above the level of the hood face occur, a s illustrated in Figure 16, they will be a source of leakage owing to a -effect, unless the volumevented f rom the hood is substantially increased. Since openings may sometimes be unavoidable in the upper portions of an enclosure or canopy hood, a means of determining the amount of the leakage and the increase in the volume required to eliminate the leakage i s necessary. Hemeon (1955) has devel- opedanequation to determine the volume of leak- agef roma sharp-edge orifice in a hood a t a point above the hood face.

where

v = the velocity of escape through orifices e

in the upper portions of a hood, fpm

10 = the vertical distance above the hood

face to the location of the orifice, f t

qc = the rate at which heat i s transferred

to the a i r in the hood f rom the hot source, Btulmin

A. = the a rea of the orifice, f t 2

t = the average temperature of the a i r in- m

side the hbod. "F.

F i g u r e 1 6 . I l l u s t r a t i o n o f l eakage f r o m t o p o f hood (Hemeon, 1955 ) .

A small amount of leakage can often be tolerated; however, if the emissions a r e toxic or malodorous, the leakage must be prevented completely. If all the cracks or openings in the upper portion of the hood cannot be eliminated, the volume vented f rom the hood must be increased s o that the minimum indraft velocity through all openings including the hoodiace is in excess of the escape velocity through the orifice calculated bymeans of equation 21. The value of q, may be determined by using the appropriate heat transfer coefficient from Table 5 together with equation 15 or by any other appropriate means. This method is illustrated in example 10.

Example 10

Given:

Several oil-fired crucible furnaces a r e hooded and vented as illustrated in Figure 16. The enclosure i s 20 feet long. It i s not possible to prevent leakage a t the top of the enclosure. Total area of the leakage openings is 1 square foot. The fuel rate i s 30 gallons per hour and the heating value is 140, 000 Btu per gallon. Assume 80°F ambient a i r and 150°F average temperature of gases in the hood.

\Hood Design 43

Problem: H O O D C O N S T R U C T I O N

Oetermine the minimum face velocity and total exhaust ra te required to prevent leakage' of contaminated a i r through the upper openings by assuming al l openings a r e sharp-edge orifices.

Solution:

The rate of heat generation:

Btu = 30 x 140,000 - 1

9, gal 60

Total open area:

A. = (20 x 7) t 1 = 141 ft 2

The escape velocity through the leakage orifice:

If a i r temperature and corrosion problems a r e not severe, hoods a r e usually constructed of galva- nized sheetmetal. As with elbows and transitions, thernetal should be a t least 2 gauges heavier than the connecting duct. Reinforcement with angle ironandother devices is required except f o r very small hoods.

H i g h - T e m p e r a t u r e M a t e r i a l s

F o r elevated temperatures up to approximately 900°F, blackironmay be employed, the thickness of the metal being increased in proportion to the temperature. For temperatures i n the range of 400 to 5006F, 10-gauge metal i s most commonly used. When the temperature of the hood is as high as 900 "F, the thickness of the metal may be increased up to 114 inch. Over 900qF, up to about 1, 600 to 1, 800DF, stainless steel must be employed. If the hood temperature periodically exceeds 1 ,800-F or i s in excess of 1, 600'F for a substantial amount of the time, refractory materials a r e required.

C o r r o s i o n - R e s i s t a n t M a t e r i a l s 11)(70, 000 = (141 ((460 + 150; = 420 fpm

e A varietvof materials a r e available for corrosive

The required exhaust rate:

Vt = Ve A.

= 59,000 cfm

conditions. Plywood is sometimes employed for relatively light duty or for temporary installations. A rubber or plastic coating may sometimes be applied on steel. Some of these coatings canbe appliedlike ordinary paint. If severe corrosion problems exist, hoods must be con- structpd of sheets of P V C (polyvinyl chloride), glass fiber, or transite.

Check mean hood a i r temperature:

D e s i g n P r o p o r t i o n s qc = Vt P CnAt

- r Although the items of primary importance in de-

where signinghoods a r e the size, shape, and location of the hood face, and the exhaust rate, the depth of

p = average density of mixture, 0. 075 lb/f t3 the hood and the transition to the connecting duct must also be considered. A hood that i s too shal- c = average specific heat of mixture, 0.24

Btullb per " F low is nothing more than a flanged-duct opening. On the other hand, excessive deoth increases the

A t = average hood temperature minus ambient cost without serving a useful purpose. a i r temperature.

T r a n s i t i o n t o E x h a u s t D u c t Solving for At in the equation:

It i s desirable to have a transition piece between 70,000 = 66°F the hoodand the exhaust system ductwork that i s

At = (59, O O O ) ( O . 075)(0. 24) cone shapedwith an included angle of 60" or less.

= 80 C 66 = 146°F This can often be made a part of the hood itself. The exact shape of the transition is the most important factor in determining the hood orifice

This adequately approximates the original assump- losses. Examples of good practice inthis regard tion. a r e illustrated in Figure 17.

4 ~ _ IDESIGN OF LOCAL

POURING STATION FOR SL1ALL MOLDS

TOP 8AFFLE TRANSITION

SPACE

V = 2 0 0 ( 1 0 ~ ~ t A )

where V = minimum v e n t i l a t i o n r a t e , c fm X = d i s t a n c e between hood and l a d l e , f t A = face area o f hood, f t z

ENCLOSURE FOR FOUNCRY SHAKEOUT

TRANSITION

P r o v i d e a minimum i n d r a f t o f 200 c fm pe r square f o o t o f open ing b u t n o t l e s s t h a n 200 c fm per squa te f o o t o f g r a t e a rea f o r h o t c a s t i n g s .

F i g u r e 1 7 . E x a m p l e s o f g o o d h o o d d e s i g n . N o t e u s e o f e n c l o s u r e , f l a n g e s , a n d t r a n s i t ~ o n s ( I n d u s t r i a l V e n t i l a t i o n , 1960)

DUCT DESIGN

The design of hoods and thr determination of exhaust volumes have been considered. Now the design of the ductwork required to conduct the contaminants to a collection device will be discussed. Calculations of pressure drop, system resistance, system balance, and duct construction will be covered.

GENERAL L A Y O U T C O N S I D E R A T I O N S

Beforedesigningand installing an exhaust system, t ry to group together the equipment to be served in order to make the system as small and compact as possible and thereby reduce the resistance load and power required. Extending an exhaust system to reach an isolated hood or enclosure is usually costly in regard to power consumption, and if the isolated hood cannot be located close to the mainexhaust system, the installation of a separate systemto careforthe isolated equipment is probably preferable, in terms of operating economy.

Whenlongrows of equipment must be served, the main header duct should be located as near as possible to the center of the group of equipment in order td equalize runs of branch duct. Where necessary, the equipment should be divided into sub- groups and subheaders located to provide good distribution of airflow in the duct system, and proper velocities a t the hood and enclosure inlets.

Air flowing in ducts encounters resistance due to frictionand dynamic losses. Friction losses occur from the rubbing of the a i r along the surface of the duct, whereas dynamic losses occur from a i r turbulence due to rapid changes in velocity or direction. F rom Bernoulli's theorem, the sum of the static and velocity pressure upstream i s equal to the sum of the static and velocity pressure plus the friction and dynamic losses downstream. A fan i s normally required to provide sufficient static pressure to overcome the res is- tance of the system.

TYPES OF LOSSES I The losses inan exhaust system may be expressed a s inertia losses, orifice losses, straight-duct friction losses, elbow and branch entry losses, and contraction and expansion losses. In addition to losses fromthe ductwork, there a r e also pressure losses through the a i r pollution collection equipment.

I n e r t i a L o s s e s i i

Lnertia losses may be defined a s the energy re - quired to accelerate the a i r from res t to the ve- locityinthe duct. In effect, they a re the velocity pressure. Many other losses a r e expressed in terms of velocity pressure, but velocity pressure itself represents the energy of acceleration. It is calculated by equation 5, set forth earlier. By this equation, values of velocity pressure versus velocityhave beencalculated, as shown in Table 6 .

O r i f i c e L o s s e s I

Thepressure or energy losses a t the hood or duct entrances vary widely depending on the shape of the entrance. The losses a r e due mainly to the vena contracta a t the hood throat. They a r e usually expressedas apercentage of thevelocitypres- sure corresponding to the velocity a t the hood throat. Thelossesvary from 1.8 hy for a sharp- edge orifice tonearly zero for a well-rounded bell- mouth entry. Losses for common shapes of en- t r ies a r e given in Figure 18. Most complicated entries canbebroken do- into two or more simple entries, and the total entry loss computed by adding the individual losses.

Table 6. TABLE FOR CONVERSION OF VELOCITY (v,)

TO VELOCITY PRESSURE (hv)

v,, va, fpm I h,, in. WC

a r e added to the actual lengths of straight duct, and the resis tance for eachrun computedfro~nFigure 19. Equivalentlengths oielbows and entr ies a r e given in Table 7.

Exhaust system calculator

Most of the charts , tables, and equations have been incorporated into a single sliderule device, a s illustrated in Figure 20. The upper scales on the front side will give friction losses just a s in Figure 19. Velocity p re s su re can be read f rom the same scales by setting 4, 000 on the velocity scale opposite 1. 00 on the friction scale. Then, opposite any other velocity, the friction scale will give the correctveloci ty p re s su re . The lower scales perform volume and velocity calculations for a given duct diameter. Temperature cor rec- tion scales and a duct condition correction scale a r e provided. On the reverse side (not shown in Figure ZO), equivalent lengths for elbows, branch entr ies , and weather caps a r e given. On the low- e r portion of each side, hood entry losses a r e given for al l the usual entry shapes.

5,500 1.886 PLAIN DUCT FLANGED DUCT TRAP OR S E T L I N G W E R 5,600 1.955 END

HE = 0 . 9 H "

HE = 1 . 5 H

STANDARD GRINDER HWD ORIFICE FLANGED W C T PLUS

YIARP-EDGE ORIFICE 7 1

S t r a i g h t - D u c t F r i c t i o n Losses + 0 .5Hy DUCT

Many charts have been developed that give the H E = 0 .65Hy

friction losses in straight ducts. Most of these charts a r e based on new, clean duct. A r e s i s - FLARED ENTRY D l RECT BRANCH BELL-MXml ENlRY tance chart in which allowance has been made f o r BOOTH

moderate roughness of the duct i s shown inFigure 19. T d - Most exhaust systems collecting appreciable a -

HE = 0 . 1 5 H " -

mounts of a i r contaminants a r e believed to reach i

a t least this degree of roughness in a relatively 3 H E = 0 . 5 H y iB- H~ = 0 . 0 2 5 H y

short time after being placed in operation. F r i c -

t ionloss in inches of water per 100 fee t of duct i s plotted in t e rms of duct diameter , velocity, and TAPERED H W S

volurne. If any two of these quantities a r e given, the other two can be read f r o m the chart .

0 . 0 8 8 " o . , a " "

Elbow a n d B r o n r h En t r y Losses

The simplest wayto express resis tance of elbows andbranchentr ies i s in equivalent fee t of s traight ductof the same diameter that will have the same F i g u r e 1 8 . Hood e n t r y l o s s e s (Adap ted f r o m pres su re loss a s the fitting. The equivalent lengths I n d u s t r i a l V e n t i l a t i o n , 1956) .


FRICTION, inches of water/lOO feet

Figure 19. Friction loss chart

Duct Desjgn- 47

Table 7. AIR FLOW RESISTANCE CAUSED BY ELBOWS AND BRANCH ENTRLES EXPRESSED AS EQUIVALENT FEET OF STRAIGHT DUCT

(Adapted f rom Industrial Ventilation, 1956)

I I

- Diameter

C o n f r o c f i o n a n d E x p a n s i o n L o s s e s

kD.1

w 9 0 " Elbow Branch entrv of duct,

in.

Whenthe cross-sectional a rea of a channel through whicha gas i s flowing contracts, a pressure loss is encountered. The magnitude of the loss depends upon the abruptness of the contraction. Whenthe cross-sectional a rea expands, a portion of the decrease in velocity pressure may be con- vertedinto static pressure. The increase or decrease inpressure fromexpansionand contraction can be calculatedfrom the diagrams and formulas

Throat radius (R) / Throat radius (NI Throat radius ( ~ ) / ~ n g l e of entry (8) l .OD/ l . 5 D 1 2 . O D l l . O D 1 1 . 5 D I 2 . O D I l . O D I l . 5 D l 2 . O D 1 4 5 " / 3 0 " 1 1 5 "

data, resistances a r e usually estimated by com- paring them with known values fo r similar equipment. In collectors such as cyclones and scrubbers where the velocities a r e high, pressure varies approximately with the square of the velocity. If the loss i s known at one velocity, the loss at any other velocity i s computed by multiplying by the square of the ratio of the velocities. In cloth fil- ter dust collectors, however, the flow is laminar, and pressure drop varies approximately as the f i r s t power of the velocity ratios.

given in Tables 8 and 9. Losses f rom small changes in velocity can be neglected. D E S I G N P R O C E D U R E S

C o l l e c t i o n E q u i p m e n t M e t h o d s o f C o l r u l o f i o n

Pressure through collection equipment varies The f i r s t step in iesigning an exhaust system is widely. Mostmanufacturers supply data on pres- to determine the volwne of a i r required at each sure drop for their equipment. In the absence of hood or enclosure to ensure complete collection

Figure 20. E x h a u s t s y s t e m c a l c u l a t o r

of the a i r contaminants, by using the principles givenpreviously. The required conveying velocity i s then determined from the nature of the contaminant. Table 10 can be used in determining CDnveying velocities.

The branch duct and header diameters a r e then calculated to give the minimum conveying velocity. When the calculated diameter lies between two available diameters, the smaller diamete; should be chosen to ensure an adequate conveying velocity. The duct layout i s then completed, and the lengths of ducts and number and kinds of fittings determined. The system resistance can then be computed. The calculations can be most easily accomplished byusing a tabular fo rm such as those shown later .

M e t h o d s o f D e s i g n

In designing a system of ductwork with multiple branches, the resistance of each branch must be adjusted so that the static pressure balance, which exists at the junction of two branches, will give the desired volume in each branch. In general, twomethods of accomplishing this result a re used:

1. The balanced-duct or static pressure balance method, inwhich duct sizes are chosen so that the static-pressure balance at each junctionwill achieve the desired a i r volume in each branch duct.

2 . The blast gate adjustment method, in which calculations beginatthe branch of greatest r e s i s - tance. The other branches a r e merely sized

Duct Design 49

to glve the minimum required velocity at the desired volume. Blast gates a r e provided in eachbranch, and after construction, the gates a r e ad~us ted to give the desired volume in each branch duct.

The balanced-duct system is less flexible and more tedious to calculate, but it has no blast gates thatmight collect deposits or be tampered withbyunauthorized persons. Layout must be in complete detail and construction must follow layout exactly.

The blast gate system has more flexibility for future changes and i s easier to calculate; volumes can be adjusted within certain ranges,

. . . . . . . .~ . .

and duct location i s not s o critical. . ~

C a l c u l a t i o n P r o c e d u r e s

T I ~ c b ~ l a n c r ~ k l u c t mzthoi: Tile calculat~ons fo r a balance.1-duct sysrein s tar t at t h c hranci' oigrentesr resistance. Using the duct size that will give the required volume a t the minimum conveying velocity, calculate the static pressureup to the junction with the next branch. The static pressure i s then calculated along this next branch to the same junction. If the two calculations agree within 5 percent, the branches may be considered in balance.

Table 8 . DUCTWORK DESIGN DATA SHOWING STATIC PRESSURE LOSSES AND REGAINSa

THROUGH ENLARGING DUCT TRANSITIONS (Industrial Ventilation, 1962)

e

Taper I Regain factor (R) /Logs factor (L) deerces D2 - DI

3-11.? 5

10 15 20 25 30

over 30

=The ==gain and loss factors are expressed as a fraction of the velocity pressure difference between points (1) and (2). In calculating the static pressure changes through an enlarging duct transition, select R from the table and aub- stitute in the equation

sP2 = SP1 t R(hv - h2)

1

where hv i s (t) SP is (t) in discharge duct from fan S P is ( - ) in inlet duct to fan

Table 9. DUCTWORK DESIGN DATA SHOWING CONTRACTION PRESSURE LOSSES THROUGH DECREASING DUCT TRANSITIONS

(Industrial Ventilation, 1956)

e L

Taperangle (e), Loss fraction (L) For abrupt contraction (9 > 60") of hv difference Ratio D2/D1 1 Factor K

I

5 10 15 2 0 2 5 3 0 45 6 0

SP change:


Table 10. RECOMMENDED MINIMUM DUCT VELOCITIES (Brandt, 1947)

Heavy dusts

Average industrial dust

Lead, and foundry 5,000 shakeout dusts; metal turnings

Duct velocity, fpm

2,000

3,000

Nature of contaminant

Gases, vapors, smokes, furnes, and very light dusts

Medium-density dry dust

If the difference in static pressure i s more than 20 percent, a smaller diameter duct normally should he used for economy reasons in the branch with the lower pressure drop to increase its resistance. Branch sizes smaller than 3 inches indiameter should be avoided. When the difference in pressure loss in the two branches i s between 5 and 20 percent, balance can be obtained hy increasing the flow in the branch with the lower loss. Since pressure losses increase with the square ' of the volume, the increased volume can be readily calculated as:

Examples

All vapors, gases, and smokes; zinc and aluminum oxide fumes; wood, flour, and cotton lint

Buffing lint; saw- dust; grain, rubber, and plastic dust

Sandblast and grinding dust, wood shavings, cement dust

Corrected cfm = h lower (Original cfm) (22)

4,000

Thepressureloss in the header i s then calculated to the next branch. This branch i s then sized to achieve a static pressure balance a t this junction with the required volume (or slightly greater) in the branchduct. This procedure i s continued until the discharge point of the system is reached.

The blast gate adjustment method: The calculations fo r a systemto be balanced by blast gate adjustment also s tar t at the branch of greatest r e s i s - tanceandproceedtothe header. P ressure losses are then calculated only along the header. P r e s - suredrops inthe remaining branches i r e not calculated except when calculationis deemedadvisable inordertocheck a branch to be sure its pressure drop does not exceed the static pressure a t i ts junction with the header.

F a n S l o f i c P r e s s u r e

The preceding calculations a r e based on static pressure; that i s , the balancing or governing pressures at the duct junctions a r e static pressures. Most fan-rating tables a r e given in terms of fan static pressure. The National Association of Fan Manufacturers defines the fan static pressure as the total pressure diminished by the velocity pressure a t the fan outlet, or

fan h = fan H - h fan outlet S v (23;

On the absolute pressure scale,

fan H = H outlet - H inlet (24)

Combining the two equations

fan h = H outlet - H inlet - h outlet S v

= h outlet + h outlet - (h inlet + hv inlet) S v S

- h outlet V

= hs outlet - h inlet - h inlet S Y

(25)

Stat icpressures arenear ly always measured re l - ative to atmospheric pressure, and static pressure a t the fan inlet i s negative. In ordinary usage, only thenumerical values a r e considered, in which case, equation 25 becomes

In evaluating the performance of a fan, examine the tables to determine whether they a r e based on fan static pressure o r on total pressure.

B a l a n c e d - D u c t C a l c u l a f i o n s

Aproblemillustrating calculationby the balanced- duct method is worked out as follows. The given operation involves the blending of dry powdered materials. A sketch of the equipment is given in Figure 21. The equipment andventilation requirements a r e presented in Tables 11 and 12.

A minimum conveying velocity of 3, 500 fpm is to be maintained in al l ducts. Elbows have a throat radius of 2 D. The balanced-duct method is to be used in the duct design. The detailed calculations a r e shown in Table 13. Calculations start at branch A. A 6-inch-diameter duct gives the nearest velocity to 3, 500 fpm a t the required volume of 750 cfm. The actual velocity of 3, 800 fpm is entered in column 5, and the corresponding velocitypressure, in column6. From Figure 18, the entry loss i s 50 percent hv, which is entered in column 7 left. The length of straight duct i s entered in column 8. The equivalent length for the elbows i s found in Table 7, and the sum is entered in column 9 right. The total equivalent length is then found by adding column 8 and umn 9 right and entering the sum in columnl l . The resistance per 100 feet of duct i s then read f romFigure 20 at 6-inchdiameter and 3, 800 fpm, and is entered in column 12. The resistance pressure (hr) i s calculated by multiplying column 11 by column 12 anddividing by 100. This value i s entered in column 13. The static p res - sure i s then the sum of the velocity pressure and the hood loss plus the resistance pressure, & umn 6 t column 7 right t column 13.

Jnbranch B, a volume of 200 cfm i s required. A 3-112-inchduct would give a velocity of 3,000 fpm, which is below the minimum. Hence the branch was calculated with a 3-inch duct a t 4, 000 fpm. The resulting hs (column 14 left) was more than 2Opercent greater thanthat for branch A. A 3-112- inchduct must, therefore, be used and the volume increased to 240 cfm to maintain the minimum velocity. At these conditions, the hs values for the twobranches a r e within 5 percent and may be considered in balance.

In section C, a 7-inch duct will ca r ry the combined volumefrom branches A and B_ at the nearest velocity above the minimum. The onlypressure drop

F i g u r e 21. Sketch o f e x h a u s t system used i n T a b l e 1 1 showing d u c t d e s i g n c a l c u l a - t i o n s by t h e b a l a n c e d - d u c t method.

Dump hopper ( I ) , 125-fpm indraft 2 - by 3-it opening through opening

1 750

Table 11. EQUIPMENT AND VENTILATION REQUIREMENTS FOR SAMPLE PROBLEM

Bucket elevator (2), 100 cfm per f t 2 1- by 2-ft casing of casing a rea

1 200

Equipment

Ribbon blender (3), 150-fpm indraft 1- by 2-ft opening through opening

1 300

Drum-filling booth (4), 200-fpm indraft 1- by 3-ft opening through opening

1 600

Ventilation requirement

Cloth f i l ter dust collector (5) maximum resistance, 4 in. wg

Volume, cfm


1, 30 The preceding example problem illustrates the calculations for designing an exhaust system. In checking plans for an exhaust system, use similar

1, 30 calculations but take a different approach. A sys- temaf ductworkwith a specific exhauster is given

1, 30 and the problem is to determine the flow conditions that will exist.

Table 12. DUCT LENGTHS AND FITTINGS with the main. No adjustments a r e made in the REQUIRED IN SAMPLE PROBLEM volumes. Blast gates will be installed in each of

these branches to provide the required increase

The objectives of checking an exhaust system are:

Branch

A

is due to the friction in the 7 feet of straight duct. This hr i s added to the hs a t the f i rs t junction. In branch D, 300 cfrn i s required, and this volume will give approximately 3,450 fpm in a 4-inch duct. The resulting hs is, however, about 20 percent lower than the hs a t the main. The cfrn must, therefore, beincreased by the ratio of the square roots of the stat icpressures,or from 300 to 350 cfm.

Inmainduct E, an 8-inch diameter duct will handle a volume of 1, 340 cfrn a t a velocity of 3, 800 fpm. An hr of 0.10 inch WC is recorded in column 13, giving an hs of 2.87 inches WC to the iunction EF.

Length, f t

14

Calculation procedures for branch F a r e similar to those for branch E, and the required 600 cfrn for the drum-filling booth must be increased to 640 cfrn to obtain a static pressure balance a t junction EF.

Elbows, No. Entries, No. in resistance. and degree and degree

2, 90 C H E C K I N G A N E X H A U S T S Y S T E M

The total volume of 1, 980 cfrn gives a velocity of 3, 600 fpm in a 10-inch-diameter main duct G to the baghouse. This runof duct and two 90" elbows have a resistance pressure of 0.88 inch WC, giv- ingatotalinlet static pressure of 7. 75 inches WC, afterthegivenresistance of the baghouse is added. The outlet static pressure i s calculated similarly by calculating the resistance of the straight run of duct. This static pressure of 0.21 inch WC i s addedtothe inlet static pressure. The velocity pressure of 0. 81 inch WC (one h, a t a velocity of 3, 600 fpm at the fan inlet) i s subtracted f rom the above total static pressure to yield a fan static pressure of 7. 15 inches WC.

B l a s t G a t e M e t h o d

The same system can be designed by the blast gate adjustment method. The calculations a r e shown in Table 14. Branch A i s calculated a s before. Branches B, _D, and _F a r e calculated a t or near the minimum conveying velocity so that the hs dropin each does not exceed the hs a t the junction

1. To determine the exhaust volume and indraft velocity a t each pickup point and evaluate the adequacy of contaminant pickup;

2. to determine the total exhaust volume and eval- .uate the size and performance of the collector o r control device;

3. todetermine the system's static pressure and evaluate the fan capacity, speed, and horsepower required;

4. to determine the temperature a t all points in the system in order to evaluate the materials of construction of the ductworkand the collector.

I l l u s t r a t i v e P r o b l e m

To illustrate amethod of checking an exhaust system, another problem i s worked. A line drawing of the ductworkis given in Figure 22. None of the calculations used in designing the system a r e given. Since no blast gates a r e shown, assume that the systemwas designed by the balanced-duct method.

Resistance calculations a r e presented in Table 15. This form was designed for maximum facility in checking an exhaust system. Calculations s tar t at=A with an assumed velocity (or volume) of 3,500fpm. The static pressure drop i s then com- putedtojunctionc. Branch B-C is then computed withanassumed velocity of 3,500 fpm. Since the h, from this branch does not match that f rom branch A-C, the second velocity i s corrected by multiplying by the square root of h, U / h s B A . The correctedvelocityis entered in column 14 and i s used to compute the cfm, which is entered in col- 15. The other branches a r e calculated in the same manner, that i s , assume a velocity at the hood and correct i t by the square root of the h, ratio. Thus, all the calculations a r e related to the original assumption of velocity in the f i r s t branch.

Table 13. EXHAUST SYSTEM CALCULATIONS BY BALANCED-DUCT METHOD

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

b ~ ~ . of Gas Yolume, cfm. loss h n g t h Branch entry ~ o t a ~ ~ e s i e t a n c e Static p ressurea Velocity, No. hr in.WC Branch

Cor. Tempin ranch

diam, t e m p . Branch Main a t ,,, in, WC

st ra ight ~ ~ ~ i ~ ~ l ~ ~ t ~ ~ ~ i ~ ~ ~ ~ ~ i per br. main, No. and or

in. ' F 70.F duct, f t length, ft l eng th f i t and

angle length, ff

angle 100 f t at 70mF

a t 70'FI at T D F Main 'F

h difference g rea te r than 20%: inc rease B t o 3 I d i a m e t e r 2

C 7 990 3.700 7 3 .6 0.25 2.77

D 4 300 3.450 0.74 50 0.37 6 1'90' 1.30' 3 16 5 .6 0.90 2.01 2.77 1 , 6 0 e

350 ha difference about 20%; increase cfm to: 300 @ = 350 2.77 2.77

E 8 1,340 3.800 3 3 3 . 4 0. 10 2. 87

1 F 5 2 600 3,600 0.81 50 0.40 11 15 1.30' 4 30 4.4 1.32 2.53 2.87

640 hs difference i s between 5 and 20%; increase cfm to: 6 O O E = 640 2.87 2.87

Cloth f i l ter dust collector resist*nce = 4 in.

H 10 1,980 3,600 8 8 2.6 0.21

Fan s t a t i c pressure = h inlet t h outlet - h inlet

= 7.75 t 0.21 - 0.81 = 7.15 in. WC

Table 14. EXHAUST SYSTEM CALCULATIONS BY THE BLAST-GATE METHOD

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

No. of Duct Volume, cfm One%

Hood loss . Length

Elbows Branch entry branch Velocity,

at Total Reeistance h, in WC - Static pressurea

Cor. diam, temp,

%hV m, WC straight

No' Equivalent and Angle quivalent equivalent per 100

a t Branch or Branch Main fpm br.

main 70-F duct. ft length, ft length, f t length, ft ft 70.F at 70°F at T'F Main "el. angle

A 6 750 3,800 0.90 50 0.45 14 2.90' 12 26 4.5 1.17 2.52

Cloth fi l ter dust collector resistance = 4 in. 7.62

H 10 1,885 3,500 8 8 2.2 0.18

Fan static preasure = ha inlet t h, outlet - hy inlet

= 7.62 t 0.18 - 0.76 = 7.04 in. WC

%se highest h, at junction of branches.

A-C 4 70' 3.500 0.76 65 0. 50 22 2 ,90° 8 30 5.5 1.65 2.91

B-C 5 3,500 0.76 65 0.50 20 2.90' 10 30' 4 34 4 . 4 1.50 2.76

C-G 6 4.100 12 12 5.0 .60

D-F 3 3.500 0.76 65 0. 50 12 2.90' 6 18 7.3 1.31 2. 57

E - T 4 3.500 0.76 65 0.50 16 l . 6 0 0 30' 3 30 5.5 1.65 2.91 2 90' 8

F -G 5 3,400 14 1 , 6 0 e 4 30' 4 22 4.1 0.90 3.47

G-I 8 3,600 12 12 2.9 0.35

H-I 4 3,500 0.76 65 0.50 34 5.5 1.87 3.13 2 ,90° 8 30. 1.60' 3

I -J 9 3.600 0.81 22 9 10 32 2. 6 0.83

1

NO. of branch

or main

Cyclone12-in. x 6-m. 3.200 0.64 150 0.96 5.65 1.600 en t ry

3

Gas temp, 'F

5

One h, at

70'F

2

Duct diam.

in.

F a n h = 5.65 - 0.81 = 4.84 in. WC

ah a duct on the lnlet side of a fan, h8 = 0. L. + 1 h., t hr. On the outlet sxde, hs = h,.. For fans ra ted under the NAFM-ASHYE and ASME codes, fan h, '= h, inlet + he outlet - h" ,"let.

7

Length nf=ight duct,

4

velocity,

fpm

6

Hood loss

% h,

8

Elbows

in. WC

9

Branch

Equivalent length,

No, and

angle E ~ u ~ v ~ ~ c ~ ~ length, f t

10

Total equivalent length, ft

11

Resietance

pe r 100 f t

12

h r in.WC at 70'F

13

Static pressurea

14

Corrected branch velocity.

fpm

Branch

a t 7 0 e F l a t T e F Main

16

Ternp in main,

OF

15

Volume, cfm

Branch Main

56 DESIGN OF LOCAL EXHAITST SYSTEMS

F i g u r e 22 . L a y o u t o f d u c t w o r k used i n example s h o w ~ n g p r o c e d u r e i n c h e c k i n g an exhaus t system.

Fan hs i s used in computing this curve because the fan, a Chicago No. 25 Steel Plate Exhauster, i s rated by the methods of the National Associa- tion of Fan Manufacturers (NAFM). The fan

Since assumed values of volume a r e used in the calculations, thefinal result i s the system's res is - tance a t a given totalvolume. The system's res is - tance willincrease with increase in volume by the square of the ratio of the increase in volume. On the other hand, the capacity of an exhauster decreases with increase in resistance. The one point that satisfies both system and fan can best be found by plotting the characteristic curves of the system and the fan. The operating point i s the point of intersection of the two curves. The system's characteristic curve is that curve established by the static pressure losses through the exhaust system fo r various a i r volumes. It i s computed by starting with the resistance and volume from Table 15 and calculating the res is - tance a t other volumes by using the square of the ratio of the volume change. The curve f o r the sample problem is computed from Table 16.

0

characteristic curves a r e families of curves at differentfan speeds defining static pressures developedfor various volumes of a i r handled through

A horsepower versus a i r volume curve can also be plotted f r o m Table 17.

Table 16. CALCULATIONS FOR CHARACTERISTIC CURVE

Table 17. FAN CAPACITY AT VARIOUS I STATIC PRESSURES !

I

E D

F r o m Chicago Bulletin

rpm cfm hs hp I I I

the fan. These data a r e available f rom fan manu-

New hs

4. 84

6. 12

7. 56

3. 71

2. 72

1.89

0. 47

Volume, cfm

1,600

1,800

2,000

1,400

1,200

1,000

500

Corrected to 2 - Multiplying factor

(1 ,80011 ,600)~ x 4.84

(2, 00011, 6 0 0 ) ~ x 4. 84

(1, 40011,600)~ x 4. 84

(1,20011, 6 0 0 ) ~ x 4.84

(1, 00011 ,600)~ x 4.84

(50011, 6 0 0 ) ~ x 4. 84

600 rpm

hp

4 .3

3.8

3.4

3.0

2.5

r * i n .

The system curve, fan curve, and horsepower !

curve a r e plotted in Figure 23. The fan and sys- !~ temcurves intersect at 1, 860 cfm and 6. 5 inches

hs. The horsepower required i s 3.2.

s i n . ALL MilOnI 111 111.a11a 611101"a M r n D I . facturers. Data for the single fan curve a t 2, 600

O l l i l C E LOII = 0.65 1," E L B ~ mm.7 mstw ~ 2 a rpm as specified bythis example a r e obtained from allrLr rrrllr~ = la "0 a m ~ c ~ s OR SUST WTES us- Chicago Blower Corporation Bulletin SPE-102.

5 in. Fan capacities at various static pressures and at the given speednearest to 2, 600 rpm a r e tabulated

Since the volume obtained f rom the curves of Fig- u re 23 i s appreciably higher than the total volume f rom Table 15, the volume a t each hood must be corrected. The correction factor i s obtained by dividing the volume from the curve by the total volume f rom Table 15. Corrections a r e made in Table 18.

ontheleft in Table 17; on the right the figures a re 4 i " . C 6 in. B in. I B in. 9 i n . m . - 3 correctedto 2, 600 rpm by use of the fan laws, a s

follows:

VOLUME. cfm

F ~ g u r e 23. C h a r a c t e r i s t ~ c c u r v e s o f an

e x h a u s t sys tem.

Fan C u r v e C o l c u l a f o r

The calculations required to produce a fan curve from catalog data have been incorporated in a slide rule-type calculator (Fig- ure 24). A calculator of this type will reduce the time re - quired to plot characteristic curves such as shown in Figure 2 3 .

C O R R E C T I O N S FOR T E M P E R A T U R E

A N D E L E V A T I O N

Fan tables, resistance charts, and exhaust volume requirements a re based on standard atmospheric conditions of 70°F and average barometric pressure at sea level. Under these conditions the density of a i r i s 0.075 pound per cubic foot. Where conditions vary appreciably from standard conditions, the change in ai r density must be considered.

F i g u r e 24. Fan c u r v e c a l c u l a t o r .


Table 18. CORRECTIONS FOR HOOD VOLUME Acentr ifugalfan connected to a given sys tem will , . ,

exhaust the s ame volume regard less of gas density. ; The weight of a i r exhausted will, however, be di- !

Hood I I I

stat ic p re s su re developed and the horsepower

proceed a s follows:

The density of a i r var ies inversely with absolute

rect lyproport ional to the density, 'and s o will the

A B D E

. . .

temperature a n d direct ly with barometr ic p r e s - 1. Read the density correct ion factor f rom

sure . Both effects a r e combined in the density Table 19.

correct ion fac tors given in Table 19.

Velocity p re s su re , s tat ic p re s su re , and r e s i s - 2. Multiplythe given hs bythe correct ion factor. tance p re s su re vary direct ly with gas density. In

320 48 0

p re s su re and a t a given tempera ture and altituze,

176: . ; .: i9p., -.. ,. -.\j.40

calculat ' inga system, i f the tempera tures i n all , the ducts are~approximatelythe s a m e (within 25'F), 3. Select thefan s ize a n d r p m based on the given

he ent ire sys tem's resis tance a s a t stan- volume and the cor rec ted static pressure . nditions and co r r ec t the final sys tem's

ie$&-e by multiplying by the density cor- ctor. If the tempera tures in the different 4. Multiply the horsepower (given by the above

branches vary, the s tat ic p r e s s u r e i n each branch selection) by the density correct ion factor to

mus t be corrected. obtain the required horsepower.

Table 19. DENSITY CORRECTION FACTORS=

1,860/1,600 1,86011,600 1,86011,600 1,860/1,600 1,860/1,600

370 consumed. 560 200 340 In selecting an exhauster f r o m multirating tables

390 t o move a given volume of a i r a t a given stat ic

"F

02: 4 e 7 0

L q @ .GO S60

7180 ::-.200

250 300 350 .

i - 400 s.. :- 450

500 550 600 650 700 750 800 850 900 950

1, 000

aDensity

6,000

0.92 0.84 0.80

----0.75

0.72 0. 70 0.68 0.66 0.64 0.60 0.56 0.52 0.49 0.46 0.44 0.42 0.40 0.38 0.37 0.35 0.33 0.32 0.31 0. 30 0.29

0

- .*

1. 15 1. 06 1.00 0. 96 0.92 0.88 0.85 0.83 0.80 0.75 0.70 0.65 0.62 0.58 0.55 0.53 0.50 0.48 0.46 0.44 0.42 0.40 0.39 0.38 0.36

in

7,000

0.88 0.81 0.78 0. 72 0.70 0. 68 0.65 0.63 0.61 0.58 0.54 0.50 0.47 0.44 0.42 0.40 0.38 0.36 0.35 0.33 0.32 0.31 0.30 0.29 0.28

above s e a

4,000

0. 99 0. 91 0.86 0. 81 0.78 0 .76 0.74 0.71 0.68 0.64 0.60 0.56 0.53 0.50 0.47 0.45 0.43 0.41 0.39 0.38 0.36 0.34 0.33 0.32 0.31

factor .

level

5,000

0.95 0.88 0.83 0. 78- 0.75 0.73 0.70 0.68 0.66 0.62 0.58 0.54 0.51 0.48 0.45 0.44 0.41 0.40 0.38 0.36 0.35 0.33 0.32 0.31 0.30

1,000

1.10 1. 02 0.96 0. 91 0.88 0. 85 0. 82 0 . 7 9 0.77 0.72 0.67 0.62 0.60 0.56 0.53 0.51 0.48 0.46 0.44 0.42 0.40 0.38 0.37 0 .36 0.35

l b / f t 3 =

Altitude,

2,000

1.06 0. 98 0.93 0. 88 0.85 0.82 0.79 0.77 0.74 0.70 0.65 0.60 0.57 0.54 0.51 0.49 0.46 0.44 0.43 0.41 0.39 0.37 0.36 0. 35 0. 33

0.075 x

f t

3,000

1.04 0.94 0.89 0. 84 0.81 0.79 0.76 0.74 0.71 0.67 0.62 0.58 0.55 0.52 0.49 0.47 0.45 0.43 0.41 0.39 0.37 0.36 0.35 0.34 0.32

density

Duct Desien c o

The procedure for plotting the fan's character is ti^ curve a t other than standard conditions is a s follows:

1. Correct the values of cfm, hs, and hp f rom the tables tot the given rpm.

2. Multiply the values of hs and hp by the density , . . correction factor.. . . . . . , ... . .- - .. .. :..

3. Plot values of hs and Ep f rom Step 2 against values of cfm from Step I .

DUCT CONSTRUCTION

Correct designand competent installation of sheet steel ducts andhoods a r e necessary for the proper functioning of an exhaust system. The following construction and installation practices a r e recommended (Industrial Ventilation, 1956):

1. All exhaust systems should be constructed of new materials and installed in a permanent and workmanlike manner. Interior of all ducts should be smooth and f ree f rom obstructions, with joints either welded or soldered airtight.

2. Ducts should be constructed of galvaniied sheet steel riveted and soldered or black iron welded, except where corrosive gases or mists or other factors ,make. such materials impractical. Gal- vanized construction i s not recommended for temperatures above 400°F. Welding of black iron of 18 gauge and lighter i s not recommended for field fabrication.

3. For average exhaust on noncorrosive application, the following gauges should be used for straight duct:

U. S. Standard gage Duct diameter Class I Class 11 Class III

To 8 in. 24 22 2 0 1

8- to 18 in. 2 22 20 18

19 to 30 in. 20 18 16

Over 30 in. 18 16 14

Class I. Includes nonabrasive applications, such as paint spraying, woodworking, food products, and discharge ducts f rom dust collectors.

Class 11. Includes nonabrasive material in large concentration, moderately abrasive material in small to moderate concentrations, and highly abrasive material in small concentration.

Class 111. Includes al l highly abrasive material in inoderate to heavy concentrations and

moderately abrasive material in heavy concentration.

Brown and Sharpe gage numbers a r e used toindicate thickness. of aluminum sheet as compared with U. S. Standard gages for steel sheet. When aluminum duct i s indicated, the following equivalent B and S ~, , ~ , , ... . . . . , ,. gages should be used:. . .

Steel - U. S. Standard gage: 26 24 22 20 18 16 14

Aluminum - B and S gage 24 22 -20 18 16 14 12

4. Elbows and angles should be a minimum of two gauges heavier than straight sections of the same diameter.

5. Longitudinal joints of the ducts should be lapped and riveted or spot-welded on 3-inch centers or less.

6. Girth joints of ducts should be made with the lap in the direction of airflow. A l-inch lap should be used for ducts to 19-inch diameters and 1 -114-inch laps for diameters over 19 inches.

7. All bends should have an inside or throat r a - dius of two pipe diameters whenever possible, but never less than one diameter. Large ra - dii bends a r e recommended for heavy concentrations of highly abrasive dust. Ninety degree elbows not over 6 inches in diameter should be constructed of a t least five sections, and over 6-inch diameter of a t least seven sections.

8. The duct should be connected to the fan inlet by means of a split-sleeve drawband a t least one pipe diameter long, but not less than 5 inches.

9. Transition in main and submains should be tapered, with a taper of about 5 inches for each 1-inch change in diameter.

10. All branches should enter main a t the large end of transition at an angle not to exceed 45', preferably 30" or less. Branches should be connected only to the top or sides of main, never to the bottom. Two branches should never enter a main at diametrically opposite points.

11. Dead-end caps should be provided on mains and submains about 6 inches f rom the last branch.

12. Cleanout openings should be provided every 10 or 12 feet and near each bend or duct junction.


13. The ducts should be supported sufficiently so 2. that no load i s ever placed on connecting e- quipment. Ducts 8 inches or smaller should be supported a t leas t every 12 feet, and larg- e r ducts, a t least every 20 feet.

14. A minimum clearance of 6 inches should be provided between the ducts and ceilings, walls, or floors.

3.

15. Blast gates used fo r adjusting a systemshould be placed near the connection of branch to main, and means provided for locking them in place after the system has been balanced.

16. Round ducts should be used wherever possible. Where clearances prevent the use of round ducts, rectangular ducts a s nearly square as possible may be used.

F A N DESIGN

Fans areusedtomove a i r f rom one point to anoth- e r . In the control of a i r pollution, the fan, blower, o r exhauster imparts movement to an a i r mass and conveys the a i r contaminants from the source of generation to a control device in which the a i r contaminants a r e separated and collected, allowing cleaned a i r to be exhausted to the atmosphere.

Fans a r e divided into two main classifications: (1) radial-flow or centrifugal type, in which the airflowis at right angles to the axis of rotation of the rotor, and (2) axial-flow or propeller type, in which the airflow i s parallel to the axis of rotation of the rotor.

C E N T R I F U G A L F A N S

A centrifugal fan consists of a wheel or rotor mounted on a shaft that rotates in a scroll-shaped housing. Air enters at the eye of the rotor, makes a right-angle turn, andis forced through the blades of the rotor by centrifugal force into the scroll- shaped housing. The centrifugal force imparts static pressure to the a i r . The diverging shape of the scroll also converts a portion of the velocity pressure into static pressure.

Centrifugal fans may be divided into three main classifications as follows:

1. Forward-curved-blade type. The rotor ofthe forward-curved-blade fan i s known a s the squirrel-cage rotor. A solid steel backplate holds one end of the blade, and a shroud ring supports the other end. The blades a r e shal- low with the leading edge curved towards the direction of rotation. The usual number of blades i s 20 to 64.

Backward-curved-blade type. In the backward-curved-blade fan , the blades are i n - clined in a direction opposite to the direction of rotation, and the blades are larger than those of the forward-curved-blade fan. The usual number of blades i s 14 to 24, and they are supported by a solid steel backplate and shroud ring.

Straight-blade type. The blades of the straight-blade fan may be attached to the rotor by a solid steel hackplate or a spider built up f rom the hub. The rotors a r e of comparatively large diameter. The usual number of blades i s 5 to 12. This classifi- cation includes a number of modified designs whose characteristics a re , in part, similar to those of the forward- and backward-curved blade types.

A X I A L - F L O W F A N S

Axial-flow fans include all those wherein the a i r flows through the impellers substantially parallel with the shaft upon which the impeller i s mounted. Axial-flow fans depend upon the action of the r e - volvingairfoil-typeblades to pull the a i r in by the leading edge and discharge i t f rom the trailing edge in ahelicalpattern of flow. Stationary vanes may be installed on the suction side or the discharge side of the rotor, or both. These vanes convert the centrifugal force and the helical-flow pattern to static pressure.

Axial fans may be divided into three main classifications:

1. Propeller type. Propeller fans have large, disc-like blades or narrow, airfoil-type blades. The number of blades i s 2 to 16. The propeller fan blades may be mounted on a large or small hub, depending upon the use of the fan. The propeller fan i s distinguished f rom the tube-axial and vane-axial fans inthat i t is equipped with a mounting ring only.

2. Tube-axial type. The tube-axial fan is simi- l a r to the propeller fan except i t i s mounted in a tube or cylinder. It i s more efficientthan the propeller fan and, depending upon the design of the rotor and hub, may develop medium pressures. A two-stage, tube-axial fan, with one rotor revolving clockwise and the second, counter-clockwise, will recover a large portion of the centrifugal force as static pressure, which would otherwise be lost in turbulence. Two-stage, tube-axial fans approach vane-axial fans in efficiency.

3. Vane-axial type. The vane-axial fan i s simi- l a r in design to a tube-axial fan except that air-straightening vanes a r e installed on the

Fan Design 61

suction side or discharge side of the rotor. Vane-axial fans a r e readily adaptable to mul- tistaging, and fans have been designed that will operate at a pressure of 16 inches water column a t high volume and efficiency.

F A N C H A R A C T E R I S T I C S

The performance of a fan is characterized by the volume of gas flow, the pressure a t which this flow isproduced, the speed of rotation, the power r e - quired, and the efficiency. The relationships of VOLUME thesequantities aremeasuredby the fan manufac- tu re r with testing methods sponsored by the Na- tional Association of Fan Manufacturers or thk American Society of Mechanical Engineers. Brief- ly, the method consists of mounting a duct on the fan outlet, operating the fan with various sized orifices in the duct, and measuring the volume, pressure, velocity, and power input. About 10 tests a r e run, with the duct opening varied from wide open to completely closed. The test results arethenplotted against volume on the abscissa to provide the characteristic curves of the fan, such a s those shown in Figure 25. VULUMt

BACKWARD-CURVED-BLADE FAN . . - . . . . . -

STRA IGHT-BLADE FAN

VOLUME

F i g u r e 26. C e n t r i f u g a l f a n t y p i c a l c h a r a c t e r i s t i c c u r v e s ( H i c k s . 1951).

. . . . . . 0 0 2C 30 10 5C SO 70 80 90 10C

s/ll/r*, OF l l D t O P L I lOLUUi

These curves a r e shown for comparison purposes F i g u r e 25. T y p i c a l f a n c h a r a c t e r i s t i c c u r v e s only; they a r e not applicable for fan selection but, ( A i r M o v i n g and C o n d i t i o n i n g A s s n . , l n c . , 1 5 6 3 ) . do indicate variations in the operating character-

istics of a specific type of fan.

1. Forward-Curved-Blade Fans. This type of . . fan i s normally referred to as a volume fan. . . Fromthe volume andpressure, the airhorsepower ! In this fan, the static pressure r i ses sharply i s computed, either the real power based on total f rom free delivery to a point at approximate pressure or the fictitious static power based on

fan s ta t icpressure . The efficiency based on total maximum efficiency, then drops to point 5 i pressure i s called mechanical efficiency. shown in Figure 26, before rising to static

pressure a t no delivery. Horsepower input rxses rapidlyfromno delivery to f ree delivery.

I N F L U E N C E O F B L A D E S H A P E Soundlevelis leas t a t rnaxirnum efficiency and greatest a t f ree delivery. Forward-curved-

The size, shape, and number of blades in a cen- Dlade fans a r e designed to handle large vol- trifugal fan have a considerable influence on the umes of a i r a t low pressures. They rotate at operating character is t~cs of the fan. The general relatively low speeds, which results in quiet effects a r e indicated by the curves in Figure 26. operation. Initial cost of such a fan is low.


Resistance of a system to be served by this type of fanmust be constant and must be determined accurately in advance because of sharply rising power demand. This type of fan should notbeusedfor gases containingdusts or fumes because deposits will accumulate on the short curved blades resulting in an unbalanced wheel and excessive maintenance. The pressure produced by a forward-curved-blade fan is not normally sufficient to meet the pressure requirements for the majority of a i r pollution control devices. They are , however, used extensively in heating, ventilating, and a i r conditioning work. Also, they a r e commonly used for exhausting a i r f rom one enclosed space to another without the use of ductwork.

2. Backward-Curved-Blade Fans. The static pressure of this type fan r ises sharply f rom free delivery almost to the point of no delivery. Maximum efficiencies occur at maximum horsepower input. The horsepower requirement i s self-limiting; i t r i ses to a maximum a s the capacity increases and then decreases withadditional capacity. Thus, when the r e - sistance of a complex exhaust system i s f r e - quently changed because of production demands, the self-limiting power requirements prevent overloading the motor.

This type of fandevelops higher pressure than the forward-curved-blade type. Sound level i s least a t maximum efficiency and increases slightly at f ree delivery. The physical sizes of backward-curved-blade fans for givenduties a r e large, but for most industrial work this may be unimportant. The operating efficiency is high, but initial cost i s also high. Blade shape is conducive to buildup of material and should not be used on gases containing dusts or fumes.

The backward-curved-multiblade fan is used extensively in heatihg, ventilating, and a i r conditioning work and fo r continuous service where a large volume of a i r i s to be handled. I t i s commonlyfound on forced-draft combustion processes. It may be used on some a i r pollution control devices, out must oe installed on the clean a i r discharge as an induced system.

3. Straight-Blade Fans. The static pressure of this type fan r i ses sharply f rom free delivery to a maximum point near no delivery, where it falls off. Maximum static efficiency occurs near maximum pressure. Mechanical efficiency r i ses rapidly f rom no delivery to a maximum near maximum pressure, then drops slowly as the fan capacity approaches f r e e delivery.

This type fan is utilized fo r exhaust systems handling gas streams that a r e contaminated with dusts and fumes. Various blades and scroll designs have been developedfor specific dust-handling and pneumatic -conveying problems. This fan is too large for some duties, but for most industrial work this may be unimportant. Initial cost of this type fan is less than that of the backward-curved-blade type, but efficiency i s also less. Fan blades may be made of an abrasive resistant alloy or covered with rubber to prevent high maintenance in systems handling abrasive or corrosive materials.

Anumber of modifieddesigns of straight-blade fans have been sveciticallv develowed for handling contaminated a i r or gas streams.

4. Axial Fans. For this type fan, the horsepower curve may be essentiallyflat and self-limiting, dependingupon the design of the blades, or it may fall f rom a maximum a t no delivery as capacity increases. The type oi vanes in the vane-axialkansmeasurablyaffects the horsepower curve and efficiency. Maximum efficiencies occur a t a higher percent delivery than with the centrifugal-type fan.

Space requirements for a specific fan duty are exceptionally low. Available fans can be installed directly in circular ducts (vane-axial or tube-axial type). Initial cost of the fan is low.

The axial-type fan i s best adapted for handling large volumes of a i r against low res i s - tance. Thepropellertype, which is equipped only with a mounting ring, i s commonly used for ventilation and is mounted directly in a wall. Although the vane-axial and tube-axial fans can deliver large volumes of a i r a t rela- tivelyhigh resistances, they a r e best suited for handling clean a i r only. Any solid material in the a i r being handled causes rapid erosion of impellers, guidevanes, hubs, andthe inner wall of the cylindrical fan housing. This results f rom the high tip speed of the fan and the high a i r velocity through the fan homing.

G e o m e t r i c a l l y S i m i l a r F a n s

Fan manufacturers customarily produce a ser ies of fans characterized by constant ratios of linear dimensions and constant angles between various fanparts. These fans a r e saidto be geometrically similar or of a homologous series. The drawings - of all the fans in the ser ies a r e identical in all views except for scale.

Fan Design 63

It i s usual for a manufacturer to produce homol- equating exponents for like terms, ogous series of fans with diameters increasing by afactor of about 1. 10. Each is designated by the m : O = c impeller diameter or by anarbi t rary symbol, often a number proportional to the diameter. L : 3 = a - 3c

t : - 1 = -b

M u l t i r a f i n g T a b l e s and solving the equations simultaneously

The performance of each fan in a homologous a = 3 ; b = l ; c = 0 ser ies i s usually given in a ser ies of tables called

multirating tables. Values of static pressure a r e usually arranged as headings of columns, which hence:

contain the fan speed and horsepower required to 3 produce various volume flows. The point of maxi- V t = k D N (28) mum efficiency at each static pressure i s usually indicated.

Repeating fo r the system resistance developed and noting that hr i s fundamentally force per

FAN L A W S unit a rea = mass x acceleration per area,

Certain relationships have been established among the variables affecting the performance of fans of a homologous ser ies or a single fan operating at varying speedin a constant system. The quantity, Vt,and the power, p, a r e controlled by four inde- pendent variables: (1) Fan size, wheel diameter, D, (2) fan speed, N, (3) gas density, p, and (4) system resistance, hr. Since all dimensions of homologous fans a r e proportional, any dimen- sion could De used to designate the size. The wheel diameter i s , however, nearly always used.

In order to develop these relationships, the effects of system resistancemust be fixed by limiting the comparisons to the same points of rating. For twofans of different size, the same point of rating is obtained when the respective volumes a r e the same percentage of wide open volume, and the s ta t icpressure is the same percentage of shut-off stat icpressure. For the same fan, the same point of rating is obtained when the system is held constant and the fan speed i s varied.

For homologous fans (or the same fan) operating a t the same point of rating, the quantity (Vt) and the power (P) will depend upon the fan size (D), fan speed (N), and gas density ( p ) . The flow through a fan i s always in the turbulent region, and the effect of viscosity i s ignored. The fo rm of dependence can oe derived f rom dimensional analysis by the equation

a b c hr = k D N p

And repeating again for the power required:

a b c P = k D N p

5 3 P = k D ~ p (30)

By substituting fundamental dimensional units,

Equations 28, 29, and 30 for Vt, h,, and P define the relationships among all the variables, within the limitations originally stated. The equations can be simplified, combined, or modifiedto yield


a large number of relationships. The following relationships derived from them a r e usually refer red to as the Fan Laws.

1. Change in Fan Speed.

Fan siz?, gas density, and system constant.

a. Vt varies as fan speed.

b. h varies as fan speed squared. r

c. P varies as fan speed cubed.

2. Change in Fan Size.

Fan speed and gas density constant.

a . V varies as cube of wheel diameter. t

b. hr varies as square of wheel diameter.

c. P varies as fifth power of wheel diameter.

d. Tipspeed varies as wheel diameter.

3. Change in Fan Size.

Tip speed and gas density constant.

a. V varies as square of wheel diameter. t

b. h remains constant.

6. Change in Gas Density.

Constant weight of gas, constant system, fixed fan size, and variable fan speed.

a. V varies inversely as gas density. t

b. h varies inversely a s gas density. r

c . Fan speed varies inversely as gas density.

d. P varies inversely as square gas density.

The fan laws enable a manufacturer to calculate the operating characteristics for al l the fans in a homologous ser ies f rom test data obtained from a single fan in the series. The laws also enable use r s of fans to make many needed computations. A few of the more important cases a r e illustrated as follows.

Example 11

A fan operating a t 830 rpm delivers 8, 000 cfm at 6 inches static pressure and requires 11. 5 horsepower. It i s desired to increase the output to . 10,000 cfm in the same system. What should be the increased speed and what will be the horsepower required and the new static pressure?

Solution:

Use fan law 1 a , b , c :

c. P varies as square of wheel diameter.

d. rpm varies inversely as wheel diameter. 2

h. = 7 [*] = 9.35 in. wc 4. Change in Gas Density.

i System, fan speed, and fan size constant. P1 = 11.5 [ = 22.4hp !

i . a. V i s constant. 1

t j

b. h varies as density. Example 12 j

c. P varies as density.

5. Change in Gas Density.

Constant pressure and system, fixed fan size, and variable fan speed.

a. V varies inversely as square root of density. t

b. Fan speed varies inversely a s square root of density.

c. P varies inversely as square root of density.

A fan i s exhausting 12,000 cfm of a i r at bOO-F. (density = 0.0375 pound per cubic foot a t 4 inches static pressure f rom a dr ier ) . Speed is 630 rpm, and 13 horsepower is required. What will be the required horsepower if a i r at 70°F (density 0.075 pound per cubic foot) is pulled through the system7

Solution:

Use fan law 4 c :

Fan Desien i c

If a 15-horsepower motor were used in this installation, i t would be necessary to use a damper when starting up cold to prevent overloading the fan motor.

Example 13

A 30-inch-diameter fan operating at 1, 050 rpm delivers 4, 600 cfm a t 5 inches static pressure. What size fan of the same ser ies would deliver 11, 000 cfm a t the same static pressure?

Solution:

Use fan law 2 a .

( 1 1 , 0 0 0 ~ ' ~ (30) = 40. 0 in. 4,600

S e l e c t i n g o F o n F r o m M u l t i r a t i n g T o b l e s

A typical multirating table i s given in Table 20. The datainthis table a r e for a paddle wheel-type industrial exhauster. Inusingmultirating tables, use linear interpolation to find values between those given in the table. For instance, f rom Table 20 i t is desired to find the fan speed that will deliver 6, 300 cfrn a t 6-112 inches static pressure. The nearest capacities a r e 6,040 and 6,550.

At 6 in. h the speed is s

6' 300-63 040 (1, 095 - 1. 088) = 1, 092 rpm. Oa8 ' 6,550-6,040

At 7 in. h the speed is S

6,300-63040 (1, 171 - 1, 160) = 1,167 rpm. 160 ' 6,550-6,040

The required speed a t 6-112 inches static pressure and 6,300 cfm is halfway between 1,092 and 1 , lb7 or 1,129 rpm.

C O N S T R U C T I O N P R O P E R T I E S

Specialmaterials of construction must be used for tans handling corrosive gases. Certain alloys that have been used have proved very satisfactory. Bronze alloys a r e used for handling sulfuric acid fumes and other sulfates, halogen acids, various organic gases, and mercury compounds. These alloys a r e particularly applicable to low-temperature installations. Stainless steel i s the most commonlyusedmetal for corrosion-resistant impellers and fan housings. It has proved satisfac- toryfor exhausting the fumes of many acids. P ro -

tective coatings on standard fan housing and impellers such as bisonite, cadmium plating, hot galvanizing, and rubber covering have proved satisfactory. Cadmiumplating and hot galvanizing are oftenusedin conjunction with a zinc chromate primer, with which they form a chemical bond. The zinc chromate primer may then be covered with various types of paints. This combination has proved iavorable in atmospheres near the ocean.

The increasing use oi rubber for coating fan impellers and housings deserves special mention. Rubber i s one of the least porous materials and, whenvulcanized to the metal, surrounds and pro- tects the metal from corrosive gases or fumes. Depending upon the particular application, soft, medium, or i i r m ruboer i s oonded to the metal. A good bond will yield an adhesive strength of 7OOpounds per square inch. When pure, live rubber i s so bonded, i t i s capable of withstanding the high s t resses set up in the fan and i s sufficiently flexible to res is t cracking. Rubber-covered fans have proved exceptionally durable and a r e found throughout the chemical industry.

H e a t R e s i s t a n c e

Standard construction fans with ball bearings can withstand temperatures up to 250'F. Water- cooled bearings, shaft coolers, and heat gaps permi t operation up to 800°F. A shaft cooler is a separate, small, centrifugal fan that is mounted betweenthefanhousing and the inner bearing and that circulates cool a i r over the bearing and shaft. A heat gap, which is merely a space of 1-112 to 2 inches between the bearing pedestal andfanhousing, reduces heattransfer to the bearings by conduction.

Certaintypes of stainless steel will withstand the high temperatures encountered in the induced- draft fan f rom furnaces or comoustion processes Stainless steelfans have been known to withstand temperatures a s high as 1, 100°F without excess warping.

E x p l o s i v e - P r o o f F a n s a n d M o t o r s

When an exhaust system is handling an explosive mixture of a i r and gas or powder, a material to oe used in the construction of the fan must generally be specified to be one that will not produce a spark if accidentally struck by another metal. Normally, thefan impeller and housing a r e constructed of bronze or aluminum alloys, whichpre- cludes sparkformation. Aluminum is frequently used on some of the narrower or smaller fans, especially those overhung on the motor shaft. Aluminumreduces the weight and vibration of the motor shaft andprotects the motor hearing f rom excessive wear.

Volume c fm

velocity, p r e s su re ,

1,000 0.063 1,200 0.090 1,400 0.122 t

Table 20. TYPICAL FAN MULTIRATING TABLE (New York Blower Company, 1948) I . SP ( 3 in. SP / 4 in. SP 1 5 in. SP 1 6 in. S P 1 7 in. S P 1 8 in. S P 1 9 in. SP

I I I I I I I I I I I I I I S P

bhp

0.63 0.85610 1.05

1.33 1.61 2.00688

2.36712 2.79746 3.27

3.81 4.42

2 i

rpn

595

626

642 666

762

795 833 8 66

900

bhp

1.27 1.55 1.87

rprn

728 735 746

bhp

2.00 2.30 2. 72

rprn

837 842 847

bhp

2.66 3. 10 3.57

rprn

943

bhp

4.60

rprn bhp r p m bhp rprn bhp rprn

Vapor Compressors 67

Explosive-prooi motors and fan wheels a r e r e - 3. to evacuate enclosed volumes; quired by law for installation in places where an explosive mixture may be encountered. Ex- 4. to transport gases or vapors;

haust systems such as those used in paint spray booths usually consist of an aiuminurn or bronze 5. to store compressible fluids as gases or

tube-axial fan and an explosive-proof motor that liquids under pressure and ass is t in recov-

drives the fan wheel by indirect drive. ering them f rom storage or tank cars ;

6. to convert mechanical energy to fluid energy for F a n D r i v e s operating instruments, a i r agitation, fluidiza-

tion, solid transport, blowcases, a i r tools, and All types of fans may be obtained with either direct motors. drive or belt drive. Directly driven exhausters offer the advantage of a more compact assembly and ensure constant fan speed. Theyarenottrou- bled by the belt slippage that occurs when belt- driven fan drives a r e not properly maintained. Fan speeds a re , however, limited to the available motor speeds, which results in inflexibility ex- ceptin direct-current application. A quick change in fan speed, which is possible with belt-driven fans, i s a definite advantage in many applications.

V A P O R C O M P R E S S O R S

Compressors a r e widely used in industry to increase the pressure of gases or vapors fo r a variety of reasons. They a r e used:

1. To provide the desired pressure for chemical and physical reactions;

2. to control Doiling points oi fluids, a s in gas separation, refrigeration, and evaporation;

Compressors normally take suction near atmospheric pressure and deliver fluids at pressures ranging upward to 40, 000 psig in commercial applications and even higher in experimental uses. The capacity of commerically available compresso r s ranges iromlow volumes up to 3 million cim.

T Y P E S OF C O M P R E S S O R S

Vapors or gases canbecompressed by either positive displacement or dynamic action. The positive- displacement compressors produce pressure by physically reducing the gas volume. The dynamic compressors increase pressure by accelerating the gas and converting the velocity into pressure in a receiving chamber. Positive-displacement compressors a r e of reciprocating- or rotary-displacement types. The dynamic compressors a r e centrifugal- or axial-flow machines. Figure 27 shows general compressor applications, and Table 21 gives general limits of compressors.

COMPRESSOR INLET CAPACITY. cfm

F i g u r e 27. Genera l a r e a s o f cbmpressor a p p l i c a t i o n s (Des J a r d i n s . 1 9 5 6 )


Table 21. GENERAL LDAITS OF COMPRESSORS (Des Jardins, 1956)

Approximate maximum limits of commercially

available compressors

I ~ s i a I stage / cfm

Reciprocating 35,000 10 13,000 Centrifugal 1 4, :ig 1 : 1 18,000 Rotary displace- 7.000

ment Axial flow 1 9O 1 1.2 1 3,000,000

P o r i t i v e - D i s p l a c e m e n t C o m p r e s s o r s

A reciprocating compressor ra ises the pressure of the a i r or gas by the forced reduction of i ts volume through the movement of a piston within the confines of a cylinder. These compressors a r e commercially designed for volumes up to 15,000 cfmandpressuresupto 40,000psig. They a r e by f a r the most common type in use both for process systems and a i r pollution control systems (Cumiskey, 1956).

Rotary sliding-vane compressors have longitudinal vanes that slide radially in a rotor mounted eccen- trically in a cylinder. The rotor i s supported at each end by antifriction bearings mounted in the heads, which, in turn, a r e bolted and doweled to the cylinder. Figure 28 shows a cross-sectional view of a sliding-vane compressor.

In a sliding-vane unit, pressure i s increased by reducingthe size of the compression cell while it rotates f rom the suction to the discharge ports.

F i g u r e 28. S l i d i n g - v a n e compresso r ( B r u c e and S c h u b e r t , 1956).

As the unit rotates, each compression cell reaches maximum sizewhenitpasses the inlet ports. Fur- ther rotation of this cell reduces i ts size, and compression i s completedupon reaching the discharge ports (Bruce and Schubert, 1956). In general, single-stage, rotary, sliding-vane compressors a r e suitable for pressures up to 50 psig. Multi- stagedmachines a r e designed for pressures up to 250psig, and booster units a r e available for pressure up to 400 psig. These machines can deliver up to 6,000 cfm.

Rotary-lobe compressors have two mating, lobed impellers that revolve within a cylinder. Timing gears, mounted outside the cylinder, prevent the impellers fromcontacting each other. The lobes a r e mounted on shafts supported by antifriction bearings. Figure 29 shows a cross-sectional view of a rotary-lobe compressor. Flow through the rotary-lobe compressor i s accomplished by the lobes' pushing the a i r or gas from the suction to thedischarge. Essentially, no compression takes place within the unit; rather, compression takes place against system back pressure (Bruce and Schubert, 1956). Rotary-lobe compressors a r e available in sizes up to 50, 000 cfm and pressures upto30psig. Single-stage machines a r e usually good for pressures up to 15 psig, and vacuums to 22 inches of mercury.

F i g u r e 29. R o t a r y - l o b e compresso r ( B r u c e and S c h u b e r t , 1956).

Rotary liquid-piston compressors use water or other liquids, usually in a sinzle rotating element to displace the a i r or gas being handled. A rotating element i s mounted on a shaft and supported a t each end by antifriction bearings. Figure 30 shows a cross-sectional view of a rotary liquid- piston compressor. In the rotary liquid-piston compressor, flow of compressed a i r or gas i s discharged in a uniform, nonpulsating stream. Compression is obtained in this machine by rotating a round, multiblade rotor freely in an ellip-

Vapor Cox

Dl SCHARGE PO

. . .. . . . . F igure 30. Rotary l i q u i d - p i s t o n compresso~

. . . . . . . . . . (Bruce and Schubert. 1956).

. . . . . . . . . .

tical casing partially filled with liquid. The rotating force of the multiblade rotor causes the liquidtofollow the inside contour of the elliptical casing. As theliquid recedes f romthe rotor blades a t the inlet port, the space between buckets fills with the a i r or gas. As the liquid reaches the narrow point of the elliptical casing, the a i r or gas i s compressedand forced out through the discharge ports (Bruce and Schubert, 1956). Rotary liquid-piston compressors a r e available in sizes uptoapproximately 5, 000 cfm. Standard single- stageunitsareusedforpressures to 35 psig, and special single-stageunits, for pressures up to 75

psig. Units a r e staged above 75 psig.

D y n a m i c C o m p r e s s o r s

Centrifugal compressors a r e similar to centrifugal pumps and fans. An impeller rotates in a case, imparting a high velocity and a centrifugal motion to the gas being compressed. The impeller i s mounted on a shaft supported by bearings in each end of the case. Ln multiple-stage compressors, several impellers a r e mounted on a single shaft. Passages conduct the gas from one stage to the next. Guide vanes in the passages direct the gas flow from one impeller to the next at the proper angle for efficient operation. Figure 31 shows a cross-sectional view of a typical four-stage compressor.

Since the flow of gas tothe centrifugal compressor i s continuous, the fundamental concepts of fluid flow apply. The gas enters at the eye of the impeller, passes through the impeller, changing in velocity and direction, and exits into the diffuser or volute, where the kinetic energy i s converted to pressure (Leonard, 1956).

The centrifugal compressor generally handles a large volume of gas a t relatively low pressures, hut some commercially used centrifugal compressors have discharge pressures of up to 4,200 psig. These compressors a re , of course, multistaged. Generally, the single- stage centrifugal compressor produces pressures up to 35 psig.

The axial-flow compressor, shown in Figure 32 is another type of dynamic compressor. It i s distinguished bythe multiplicity of its rotor and stator blades. These a r e either forged, machined, or precision cast into airfoil shapes. The compresso r casingis made of cast iron, or fabricated out of steel, depending upon inlet volume, pressure ratio, and temperature conditions. Stator blades a r e attached to the casing to direct the flow of gas through the case.

The rotor i s a drum with blades mounted around i ts periphery. The drum is mounted on the shaft supported by bearings in each end of the case. As the rotor turns, the bladed force a i r through the compressor inau action similar to that of the propeller fan. The stator blades control the direction of the a i r a s i t leaves the rotor blades. Pressure i s increased owing to the kinetic energy given to the gas, and the action of the gas on the stator blades. Axial-flowcompressors a r e high-speed high-volwne machines. The pressures attained a r e relatively low, withamaximum commercially used discharge pressure of 90 psig. These compressors a r e rarely used for inlet capacities below 5,000 cfm (Claude, 1956).

R e c i p r o c a t i n g C o m p r e s s o r s

Reciprocating compressors a r e positive-displace- mentmachinesused to increase the pressure of a definite volume of gas by volume reduction (Case, 1956). Most reciprocating compressors used in heavy industrial production and continuous chemical processing a r e stationary, water-cooled, double-acting units (see Figure 33). The basic running-gear mechanism is of the crank-and-fly- wheel type enclosed in a caet-iron frame. The crosshead construction permits complete separation of the compression cylinder f rom the crankcase, an ideal feature for handling combustible, toxic, or corrosivegases. Generally, the cylinder i s double acting, that i s , compression occurs al- ternatelyinthe head and crank end of the cylinder. The cylinder and i t s heads a r e usuallywater cooled to reduce thermal s t resses and dissipate par t of the heat developed during compression. Com- pression rings on the pistons seal one end of the cylinder f rom the other. The piston rod is sealed in the cylinder by highly effective packing, and any slight leakage may be collected in a vent gland for return to suction or for venting to the atmosphere.

:

7 0 DESIGN O F LOCAL EXHAUST SYSTEMS j

F i g u l e 31. C r a s s - s e c t i o n o f a t y p i c a l f o u r - s t a g e c e n t r i f u g a l c o m p r e s s o r ( C l a r k B r o s . Co., O l e a n , N.Y. . f r o m L e o n a r d , 1 9 5 6 ) .

Gas being compressed enters and leaves the cylinder through the voluntary valves, which a r e actuated entirely bythe difference in pressure between the interior of the cylinder and the outside system. Uponenteringthe cylinder, the gas may be compressed f rom the initial to the desired final pressure in one continuous step, that i s , single- stage compression. Alternatively, multistage com- pressiondivides the compression into a s e r i e s of steps or s tages, each occurring in an individual cylinder. Here the gas i s usually cooled between the various stages of compression.

considered a s efficiencies related to the isentropic base. Thermaldynamiclosses within the cylindex, including fluid friction losses through the valves, heating of the gas on admission to the cylinder, andirreversibi l i ty ofthe process , may be grouped under the single t e r m compression efficiency. Mechanical friction losses encountered in the piston rings, rod packings, and f rame bearings a r e grouped under the termmechanical efficiency. Thus, the overall efficiency of the compressor is the product of compression and mechanical efficiency.

The compression process i s fundamentally isen- Fo r given service, the actual brake horsepower requirementofthe compressor i s normally about 1 tropic (perfectly reversible adiabatic), with ce r -

tain actual modifications or losses that may be 18 to 33 percent grea ter than the calculated ideal

!

Vapor Cornpressors 7 1 ! 1

F i g u r e 32. A x i a i - f l o w c o m p r e s s o r ( A l l i s - C h a l m e r s M a n u f a c t u r i n g Company. M i l w a u k e e , W i s c o n s i n , f r o m C l a u d e , 1956 ) .

F i g u r e 33. F o u r - c y l i n d e r , h o r i z o n t a l , b a l a n c e d , o p p o s e d , s y n c h r o n o u s ~ m o t o r c o m p r e s s o r ( W o r t h i n g t o n C o r p o r a t i o n , H a r r i s o n , N . J . , f r o m Case , 1 9 5 6 ) .


iseatropic horsepower. Or , s ta ted another way, V e l o c i t y M e t e r s the overal l efficiency of m o s t compre s so r s i s i n the range of 75 to 85 percent . Velocity m e t e r s a r e m o r e commonly used in the

field f o r determining a i r velocities. The mos t

U S E I N A I R P O L L U T I O N C O N T R O I

Conlpressors areusedtotransportvapors o r gases f r o m the i r source and del iver them to a control device o r sy s t em under p r e s s u r e . In some ca se s , the vapors o r gases can be p r e s su r i z ed direct ly to a holding ve s se l and then a compre s so r is used to send the vapors to control equipment.

The vapors c rea ted f r o m the refining, s tor ing, and bulkloading of volatile petroleum products a r e being controlled by the u s e of compre s so r s . The compres so r s deliver the vapors under p r e s s u r e s ranging f r o m 5 to 200 psig to plant fuel sy s t ems , p roce s s s t r e a m s , or absorption sys tems .

Centrilugal, reciprocat ing, and rotary- lobe com- p r e s s o r s a r e being used for controlling a i r contaminants . Single-stage reciprocat ing machines a r e the mos t common. Two-stage compres so r s developing p r e s su re s up to 200 psig a r e i n u se .

C H E C K I N G OF E X H A U S T S Y S T E M

Air flow measurements and t e s t data a r e nece s - s a r y to determine whether an exhaust sy s t em i s functioning properly and in compliance with de- a inn snecilications. Co r r ec t testing procedures

accura te and widely accepted in engineering p r a c - t i ces a r e the pitot tube and the swinging-vane velocity me t e r .

P I T O T T U B E S

F o r determining a i r velocity, the s tandard pitot tube, namedfo r t h e m a n who discovered the pr in - ciple, i s considered rel iable and i s general ly a c - cepted i n engineering prac t ice . It i s the m o s t widely used field method fo r determining a i r velocity.

A s tandard pitot tube (Figure 34) consis ts ol two concentr ic tubes: the inner tube measu re s the impact p r e s s u r e , which i s the sum of the s ta t ic and kinetic p r e s s u r e s , while the outer tube mea - s u r e s onlythe s ta t i c p r e s su re . When the two tubes a r e connected a c r o s s a U-tube manometer o r other suitable p ressure -measur ing device, the s ta t ic p r e s su re i s nullified automatically and only the velocity p r e s s u r e (kinetic p r e s s u r e ) i s reg i s te red . The velocity i s cor re la ted t o the velocity p r e s s u r e by the equation

where . . - - ~ - . mus t be established to obtain measurements f o r v = velocity, fprn determining whether an cxhaust sy s t em has s u f - i icient capacity f o r additional hoods, and a l so t o h v =

velocity p r e s s u r e (manometer reading) ,

obtain operational data f r o m existing installations in. WC

lor designing iuturc exhaust sys tems . 3

p = density of a i r , l b l i t

T H E O R Y O F F I E L D T E S T I N G Clearly, below 1, 266 fprn, the velocity p r e s s u r e becomes ex t remely low and i s , the re fore , difficult t o read accurately on a manometer . With a

F o r most purposes the m o s t important factor i s the accura te measurement of a i r quantity. Most field

IMPACT PRESSURE CONNECTION m e t e r s m e a s u r e velocity r a t he r than quantity. This necess i ta tes equatingvelocity to quantity. By T U B I N G ADAPTER

-- <--~ -- --p using equation 8 and a velocity me t e r , the quantity S l A l N L E s s S T E E L ol a i r flowing through an exhaust sy s t em can be accurately measured .

S T d T i C PRESSURE CONNECTION S T A T I C PRESSURE HOLES S T A I N L E S S STEEL P I P E N I P P L E S OUTER P I P E ONLY

Q u a n t i t y M e t e r s !I ' I M P A C T PRESSURE O P E H I N G Some examples of quantity m e t e r s a r e thin-plate o r i f i c e s , sharp-edged or i f i ces , and ven tu r ime t e r s . F i g u r e 34. S t a n d a r d p i t o t t u b e ( W e s t e r n These m e t e r s a r e used extensively in laboratory P r e c i p i t a t i o n , D i v i s i o n o f J o y M a n u f a c t u r i n g studies, but infrequently in industr ia l exhaust Co., L o s A n g e l e s , C a l i f . , f r o m ASHRAE G u i d e sys tems . and D a t a Book , 1963).

Checking of Exhaust System 7 3

U-tubemanometer , t heaccu racy i s low f o r veloc- p' = re la t ive density of a i r , a t the mea. i t ies below 2, 500 fpm. With a careful ly made, sured condition, lb/f t3 . accurately leveled, inclined manometer , veloci- t i es a s low as 600 fom can be determined s a t i s - factor i ly , but field conditions ordinar i ly make this procedure difficult (ASHRAE Guide and Data Book, 1963). -

P i t o t T u b e T r a v e r s i n g P r o c e d u r e / I n \ / Since the velocity in a duct i s seldom uniform a c r o s s any c r o s s sec t ionands ince each pitot tube reading determines the velocity a t only one local- ized point, a t r a v e r s e of the duct i s nece s sa ry i n o rder to compute the average velocity and thus determine a i r flow accurately. Suggested pitot tubelocations for t ravers ing round and rectangu- l a r ducts a r e shown in F igu re 35.

The velocity in a dud: va r i e s great ly . It i s gen- e ra l ly lowest nea r the edges o r co rne r s and grea tes t i n the central portion. Because of th i s fluctuation, a l a rge number of readings mus t be

taken to de te rmine the t r u e average velocity. I n round ducts, not l e s s than eight readings should be taken along two d i ame te r s a t cen te rs of equal annular a r e a s . Additional readings a r e nece s sa ry w l ~ e n d u c t s a r e l a rge r than 1 foot in d iameter . In rectangular ducts , the readings should be taken in the center ol equal a r e a s over the c r o s s section of the duct. The number of space s should be taken a s depicted i n F igure 35. In determining the av- e r age velocity in the duct, the velocity p r e s s u r e readings a r e converted t o velocities; the veloci- t i e s , not the velocity p r e s s u r e s , a r e averaged to compute the average duct veloci t ies .

Disturbedflow will give e r roneous resu l t s ; t he r e - f o r e , whenever possible , the pitot tube t r a v e r s e shouldbe made a t l e a s t 7. 5 duct d i ame t e r s down- s t r e a m f r o m any ma jo r a i r s t r e a m dis turbances such a s a branch entry, f i t t ing, o r supply opening (ASHRAE Guide and Data Book, 1963).

A l t i t u d e a n d T e m p e r a t u r e Cor rec t ions f o r

P i t o t Tubes

If the tempera ture of the a i r s t r e a m i s more than 30" above o r below the s tandard tempera ture of 70"F, o r if the alti tude i s m o r e than 1 , 000 fee t , o r if both conditions hold t r ue , make a correct ion fo r density change a s follows:

1 Cor rec ted velocity p r e s s u r e = measu red h x -, v P

( 3 2 )

where

h = velocity p r e s s u r e , a s determined by v

pitot tube, in. WC

Cross s e c t i o n o f a c i r c u l a r s t a c k d i v i d e d i n t a t h r e e c o n c e n t r i c , equa l a r e a s , shoiri ng l o c a t i o n o f t r a v e r s e p o i n t s . .The l o c a t i o n and number o f these p o i n t s f o r a stack o f g i v e n d i a m e t e r can be d e t e r m i n e d from T a b l e s 2 2 and 23.

Cross s e c t i o n of a r e c t a n g u l a r s t a c k d i v i d e d i n t o 12 equa l areas, w i t h t r a v e r s e p a i n t s l o c a t e d a t t h e cen- t e r of each a r i a . The minimum number of t e s t p o i n t r i s shown i n T a b l e 29.

F i g u r e 3 5 . P i t o t t u b e t r a v e r s e f o r r o u n d a n d r e c t a n g u l a r d u c t s .

S W I N G I N G - V A N E V E L O C I T Y M E T E R

The f ac to r s that make the swinging-vane velocity m e t e r an extensivelyused field instrument a r e i t s portabili ty, instantaneous reading fea tures , and

74 DESIGN O F LOCAL EXHAUST SYSTEMS

Table 22. SUGGESTED NUMBER r e s i s t e d by a h a i r sp r ing and damping magnet .

O F EQUAL AREAS The ins t rument gives ins tantaneous readings of

FOR VELOCITY MEASUREMENT direct ional veloci t ies on the indicating sca le .

IN CIRCULAR STACKS C o l i b r o t i n g t h e V e l o c i t y M e t e r

Stack d i a m e t e r , f t

1 o r l e s s 1 t o 2 2 to 4 4 to 6 over 6

Number of equal a r e a s

2 3 4 5

6 o r m o r e

Table 23. PERCENT O F CLRCULAR STACK DIAMETER FROM INSIDE

WALL TO TRAVERSE POINT

- --

number

1 2 3 4

Table 24. MINIMUM NUMBER O F TEST POINTS

FORRECTANGULARDUCTS

wide-range s c a l e . The ins t rument is f a i r l y rug-

ged, and its a c c u r a c y is sui table f o r m o s t field velocity determinat ions .

The m e t e r cons i s t s of a pivoted vane enclosed in a c a s e , aga ins t which a i r e x e r t s a p r e s s u r e a s i t p a s s e s through the i n s t r m e n t f r o m a n u p s t r e a m t o a downs t ream opening; movement of the vane is

Before us ing a m e t e r , check the z e r o sett ing. If the pointer does not come t o r e s t a t the z e r o posit ion, t u r n t h e z e r o ad jus te r to m a k e the n e c e s s a r y c o r - r ec t ions . The m e t e r w i t h i t s f i t t ings i s cal ibrated a s a u n i t ; the re fo re , f i t t ings cannothe interchanged f r o m o n e m k t e r toano ther . The s e r i a l number on the fi t t ings and on the m e t e r m u s t a g r e e . If a m e t e r was or iginal ly cal ibrated f o r a f i l t e r , it m u s t always b e used . Only connecting tubing of the s a m e length and ins ide d i a m e t e r a s that o r i g - inal ly supplied with the m e t e r should be used, s i n c e changes i n tubing a f fec t the cal ibrat ion of the m e t e r ( Industr ia l Ventilation, 1956).

When the t e m p e r a t u r e of a n a i r s t r e a m v a r i e s m o r e than 30' f r o m the s t andard t e m p e r a t u r e of 70"F , o r the alt i tude i s m o r e than 1, 000 feet , o r when both conditions a r e ful f i l led , it i s advisable to m a k e a c o r r e c t i o n f o r t e m p e r a t u r e and p r e s - s u r e . Other cor rec t ion f a c t o r s , a s shown i n Table 25 should a l s o b e used ( Industr ia l Ventila- t ion, 1956). -

Table 25. SOME CORRECTION FACTORS FOR THE SWINGING-VANE VELOCITY M E T E R

(Industri&Y_ntilation, 1960) -- --

Opening

P r e s s u r e openinga Hold m e t e r jet aga ins t g r i l l e (use g r o s s a r c a ) m o r e than 4 i n , wide and up to 600 in. 2

a r c a , f r e e opening 70% o r m o r e of g r o s s a r e a . Hold m e t e r jet aga ins t g r i l l e (use f ree -open a r e a )

Hold m e t e r jet 1 inch in f r o n t of g r i l l e (use g r o s s a r e a )

Suction opening b

Square punched g r i l l e (use f ree -open a r e a ) B a r g r i l l e (use g r o s s a r e a ) S t r ip g r i l l e (use g r o s s a r e a ) F r e e open, no g r i l l e

a

Cor rec t ion factor

0 .93

1 .00

0. 88 0. 78 0 . 7 3 1 . 0 0

F o r p r e s s u r e openings, i t is advisable to u s e the g r i l l e m a n u f a c t u r e r ' s coeff ic ient of d i scharge .

b ~ o r auction openings, hold m e t e r jet perpendicu- l a r to the opening, with the t ip in the s a m e plane a s the opening. This i s v e r y impor tan t because veloci t ies a r e changing v e r y rapidly in f ron t of a suct ion opening.

Note: volume, cfm = a r e a , f t2 x a i r velocity, f p m x cor rec t ion fac to r .

Checking of Exhaust System 7 5

U s e s o f t h e V e l o c ~ t y M e t e r the me te r or fitting should be held between 1 and 2 inches in front of the grille.

Someuses of the me te r and fittings a r e illustrated in Figure 36. On la rge (at leas t 3 i t2) supply openings, where the instrument itself willnot s e r i - ously block the opening and where the velocities a r e low, hold the instrument itself in the a i r s t ream, the a i r impinging directly in the left-hand port. When the opening is smal le r than 3 square feet, o r the velocities a r e above the no-jet scale, o r when both conditions hold true, appropriate fittings mustbeused . On modernair-conditioning gri l les ,

E X H A U S T S Y S T E M GRINDER

If the exhaust opening i s la rge (at least 3 i tZ) and the a i r velocities a r e low, as in spray booths, chemicalhoods, and soforth, the meter itself can he held in the a i r s t ream. The instrument should be held s o that the left-hand port of the me te r i s flushwith the exhaust opening. When the opening i s smal le r than 3 square feet, o r the velocities a r e above the no-jet scale, or whenboth conditions hold true, appropriate fittings must be used (In- dustr ial Ventilation, 1956).

P L A T I N G T A N K

SPRAY BOOTH (NO-JET RANGE)

F i g u r e 3 6 . Some s w i n g i n g - v a n e v e l o c i t y m e t e r a p p l i c a t i o n s ( I n d u s t r i a l V e n t i l a t i o n , 1960 ) .


COOLING OF GASEOUS EFFLUENTS When designing an a i r pollution control system, the designer must know the temperatures of the gases to be nandled before he can specify the materials of construction for the system, the s ize of ductwork, the s ize of the blower, and the type of a i r pollution control device. Olten, hot gases must be cooled before being admitted to the con- t ro l device. The cooling equipment will add to the resis tance of the flow of gases through the exhaust system and may affect the volume and composition of the gases. Since the gases must pass through the cooling device, i t must be designed as an integral par t of the exhaust system.

M E T H O D S O F C O O L I N G G A S E S

Although there a r e severalmethods of cooling hot Eases, those most commonly used in a i r pollution control systems are : (1) Dilutionwithambient a i r , ( 2 ) quenching with water, and (3) natural convec- tionand radiation f rom ductwork. In a few cases, forced-dral thcat exchangers, a i r cooled and water cooled, have been used.

Withthe dilution method, the hot gaseous eflluent f r o m the process equipment i s cooled by adding sufficient ambient a i r to resu l t in a mixture ol gases a t the desired temperature. Natural convection and radiation occur whenever there i s a temperature diflerence between the gases inside a dud: and the atmosphere surrounding it. Cooling hot gases by this method requires only the pro- vision of enough heat t ransfer a r ea to obtain the desired amount of cooling. The water quench method uses the heat of vaporization of water to cool the gases. Water i s sprayed into the hot gas - e s under conditions conducive to evaporation, the heat in the gases evaporates the water, and this cools the gases. In forced-draft heat exchangers, the hot gases a r c cooled by forcing cooling fluid past the ba r r i e r separating the fluid f r o m the hot gases.

D i l u t i o n W i t h A m b i e n t A i r

The cooling of gases by dilution with ambient a i r i s the most simple method that can he employed. Essentially i t involves the mixing of ambient a i r with a gas 01 known volume and temperature to produce a low-temperature mixture that can be admitted to an a i r pollution control device. In designing such a system, f i r s t determine the volume and temperature of a i r necessary to capture and convey the a i r contaminants f rom a given source. Then calculate the amount of ambient a i r required to provide a mixture of the desired temperature. The a i r pollution control device i s then sized to handle the combined mixture.

Althoughlittle instrumentation i s required, a gas temnerature indicator with a warning device. a t the very least , should be used ahead of the a i r pollution control device to ensure that no damage occurs owing to sudden, unexpected surges ol temperature. The instrmnentation may he expanded to control either the fuel input to the process or the volume of ambient a i r to the exhaust system.

This method of cooling hot gases i s used extensively where the 'riot gases a r e discharged f rom process equipment in such a way that an external hood must be used to capture the a i r contaminants. The amount of a i r needed to ensure complete cap- t u re of the a i r contaminants i s generally sufficient to cool the eases to appro xi mat el^ 500°F, which permits the use of high-temperature a i r pollution control devices. When the volume of hot gases i s small , this method may be used econo'mically even when much more a i r i s needed to achieve the de- s i red cooling than that needed for zdequate capture of a i r contaminants.

When la rge volumes of hot gases require cooling, the s ize of the exhaust system and control device becomes excessively la rge fo r dilution cooling. Inanycase , compare the costs of installation and operation ol the various cooling methods before deciding which method to use .

The following examples i l lustrate (1) a method of determining the resultant temperature of the mixture of the hot furnace gases and the ambient a i r induced a t the turnace hood, and (2) a method of determining the volume of a i r needed to corl the hot furnace gases to a selected temperature.

Example 14

Given:

Yellow-brass-melting crucible furnace. Fuel burned: 1,750 cfh natural gas with 20 percent excess a i r .

Maximum gas temperature a t furnace outlet: 2 ,500-F.

Volume of dilution a i r drawn in a t the furnace hood: 4, 000 cfm.

Maximum temperature of dilution a i r : 100°F.

Fo r this problem, neglect the heat losses due to radiation and natural convection f r o m the hood and ductwork. Assume complete combus-

tion of the fuel.

C o o l p g of Gaseous Eff luents 7 7

TEMP. = 7 10 CONTROL DEVICE

F l g u r e 37. P r o b l e m : Determine t h e t e m p e r a - t u r e o f t h e g a s e s e n t e r l n g t h e c o n t r o l d e v l c e .

Solution:

1. De te rmine the weight (W) and heat ( 0 ) above 6 0 ° F in the products of combustion (PC) :

a. = wl hi

where

W. = weight of individual gas flowing, l b l m i n

hi = enthalpy above 6 0 ° F of each gas , B tu / lh

Qi = heat above 6 0 ° F in each g a s , B t u l m i n

1 750 Conver t fue l r a t e t o c f m - = 29. 17 c f m 60

R e f e r r i n g t o the calculation data of Table 26, Wi = 29. 14 l b l m i n and Qi = 21,470 Btu lmin

2. Heat above 6 0 ° F i n 4, 000 cfrn of dilution a i r

enter ing hood a t 1 0 0 ° F :

3 Densi ty of a i r a t 100°F = 0. 0708 1bIft ( f rom Table D l , Appendix D )

Enthalpy oi a i r a t 100°F = 9. 6 Btu l lb ( f r o m Table D3, Appendix D )

Weight of dilution a i r = (4, 000)(0. 0705) = 283. 2 l b l m i n

Heat above 6 0 ° F in dilution a i r = (9 . 6)(283. 2) = 2 , 720 Btu lmin

3 . Enthalpy of mix tu re of P C and dilution a i r :

Total weight o i mix tu re = 29. 14 f 253. 2 = 312 . 3 l b l m i n

Heat above 6 0 ° F in mix tu re 21, 470 t 2 , 720 = 24, 190

24 190 Enthalpy of mix tu re = = 77. 4 Btu / lb

312. 3

4. T e m p e r a t u r e ol mix tu re :

To de te rmine the t e m p e r a t u r e of the mix tu re , de te rmine the enthalpy of the m i x t u r e a t two t e m p e r a t u r e s , p r e f e r a b l y above and belowthe calcula ted enthalpy of 77. 4 Btu l lb .

Table 26. CONVERSION VALUES FOR ITEM 1, EXAMPLE 14

P C p e r cubic foot of fue l

To ta l s 1 1 2 9 . 1 4 ( 1 21 ,470

I I I

a F r o m Table D7, Appendix D.

b w i = (0. 132 lb/ft3)(29. 17 f t3 /min) = 3. 85 l b l m i n 'F rom Table D3, Appendix D. d ~ . = (3. 85 lb/rnin)(690.2 Btu/ lb) = 2, 660 B t u l m i n

P C f r o m furnace

Component

Enthalpy of

component

Weight, lb / f t3

Heat above 6 0 ° F in

component

Wi, l b l m i n

h i a t 2, 500°F , B tu l lb

Qi, B tu lmin


Then, by interpolat ion, the t e m p e r a t u r e c o r - Example 15 responding to 77. 4 Btu l lb can be determined. Since the mix tu re contains mos t ly ni t rogen, P r o b l e m : the enthalpies should be c lose to those of ni - trogen. F r o m Table D3 it a p p e a r s that the Using the s a m e given data i n P r o b l e m No. 1 ,de- mix tu re t e m p e r a t u r e will be between 350°F t e r m i n e the amount 01 dilution a i r r equ i red t o r e - and 400°F. The enthalpy of the m i x t u r e , H m ' duce the t e m p e r a t u r e of P C to 300°F. is:

Qm h = -- a t d e s i r e d t e m p e r a t u r e s m

W m where

The O2 and N2 f r o m the dilution a i r m u s t beadded to the O2 and N2 f r o m the P C ,

Weight of dilution a i r = 253. 2 I b l m i n

0 2 content = (283. 2)(0.23) = 65. 0 l b / m i n N2 content = (283. 2)(0.77) = 218 l b / m i n

R e f e r r i n g to the calculation data of Tahle 27:

a t 4 0 0 ° F = 26 ,150

hm 312.3 = 83. 6 Btul lb .

Solution:

1. Heat above 6 0 ° F in P C a t 2, 5 0 0 ° F = 21, 470 B t u l m i n ( F r o m Table 26)

2. Heat l o s t by P C i n cooling f r o m 2, 5 0 0 ° F to 300°F: F r o m Table 26 obtain the weight (Wi) of each component of P C d i scharged f r o m the furnace. F r o m Table D3, obtain t h e enthalpy (hi) of e a c h component a t 300°F. Refe r r ing to the calculation data of Table 28: Heat to be los t = 21,470 - 1 ,847 = 19,623 B t u l m i n

3 . Volume of a i r needed to cool P C t o 3 0 0 ° F :

Air inlet t e m p e r a t u r e = 100'F (given) F ina l a i r t e m p e r a t u r e = 3 0 0 ° F

h a t 100'F = 9 . 6 Btu/ lb ( f r o m Table D3)

h , a t 3 0 0 ° F = 57. 8 Btu l lb ( f r o m Table D3)

By interpolation the mix tu re t e m p e r a t u r e = 373°F Ah = 45. 2 B t u l l b

T h e r e f o r e , the exhaust s y s t e m and control device m u s t be designed t o handle g a s e s a t 373°F . Weight of a i r needed = ---- 19' 623 - - 408 lb /min

45.2

Tahle 27. CONVERSION VALUES FOR ITEM 4, EXAMPLE 14

d d Q. -. h . ~ . Q. = h . ~ . I w i h i / h i 1 - 1 1 1 1 1

Component lblmin a t 3 5 0 " E a t 400°F, a t 350°F, a t 400°F , B tu l lh Btu l lb B t u l m i n B t u l m i n

Tota l s

a Wi of N2 i s s u m of N2 f r o m P C and dilution a i r .

b ~ o t a l s a r e rounded off to four significant f igures . 'Wi of O2 is s u m of O2 f r o m P C and dilution a i r .

d ~ r o m Table D3, Appendix D. eQ. = (3. 85 lb/min)(63. 1 Btu l lb ) = 242. 9 Btulmin.

1

312. 3b 22, 530 26, 150

Volume of dilution a i r a t 100 " F

Cool~ng of G a s e o ~

Table 28. CONVERSION VALUES

3 p a t 100°F = 0. 0708 l b / f t ( F r o m Table D l )

408 Volume = ----- = 5,760 c fm

0.0708

-- -- Qi = hiWi, a t

300' F Btulmin

197.7

312.5

1,279. 0

57.5

1, 846. 7

Gaseous components

C02

H20

N2

0 2

Totals

The exhaust sys tem m u s t be designed t o handle a sufficient volume of ga se s a t 300°F to p ro- vide an indraf t of dilution a i r of 5 ,760 cfm in addition t o the products of combustion.

Total heat above 60°F in P C a t 300" F = 1,847 Btu/

Q u e n c h i n g W i t h W a f e r

Wi, l b lmin

3. 85

2. 89

21. 32

1. 08

29. 14

When a l a rge volume of hot gas i s to be cooled and only a sma l l quantity of dilution a i r i s needed to capture the a i r contaminants, some methods of cooling other than dilution with ambient a i r should be used. Since the evaporation of water requ i res a large amount of heat , the gas can be cooled s i m - ply by spraying water into the hot gas .

h i a t 300" F, Btu/ lb

51. 3

108.2

59. 8

53.4

F o r e f f ic ie ,~ t evaporation of water in a gas s t r e a m , i t has been determined that the gas velocity should be f r o m 500 t o 700 ipm and the ent i re c r o s s s e c - tion of the s t r e a m should he covered with a fine sp r ay o i water . I€, however, wate r ca r ryover i s undesirable , a s in a baghouse, sat isfactory s e t - tling of the water droplets m u s t be attained; hence, lower velocities a r e employed. El iminator plates a r e seldom used in installations where excessive maintenance due to cor ros ion o r fouling i s expected To reduce fur ther the likelihood of water droplet ca r ryover , place the water sp r ay chamber a s f a r f r o m the haghouse a s p rac t ica l .

Water s p r a y p r e s s u r e s genera l ly range f r o m 50 t o 150 psig: however, to reduce the amount of mois ture collected, some installations have e m - ployed p r e s s u r e s a s high a s 400 psig. Since the mois ture collected in s p r a y chambers readi ly c o r - rodes s tee l , the charnbers a r e f requent ly l inedwith ma te r i a l s res i s tan t to corrosion.

If the gases discharged f r o m the basic equipment a re exceptionally hot, a s a r e those f r o m the cupo- l a furnace, the f i r s t portion of the duct should be

1s Effluents 79

re f rac tory lined o r made f r o m stainless s teel . In some ca se s , stail l less s teel ilucts with water sprays have been used hctween the furnace anrl the quench chamber . 4,

F o r controlling the gas t empera ture lcaving the quench chamber , a t empera ture coiltroller i s general ly used to regulate the amount or water sprayed into thc clucnch charnbcr. F o r ernergen- cy conditions, a seconrl t empera ture control ler can be used lo d iver t excessively hot gases away f r o m the a i r pollution control device.

Cooling hot gascs with a wate r quench is re la t ive- l y s imple and requi res very li t t le spacc. Figure 3 5 shows a quench chamber u s e d to cool the gas -

F i g u r e 3 8 . A quench chamber i n a baghouse c o n t r o l s y s t e m s e r v i n g a c u p o l a f u r n a c e ( H a r s e l ! E n g i n e e r i n g Company, I n g l e w o o d . C a l i f o r n i a ) .


eous effluent f r o m a cupola fu rnace . Quench cham- b e r s a r e l i t t le m o r e than enlarged portions of the ductwork equipped with wate r sp r ays . They a r e easy to op?rate and, with automatic t empera ture controls , only that amount of wate r i s used that i s needed to maintain the des i red tempera ture of the ga se s a t the discharge. Their installationand operating costs a r e general ly considered to be l e s s than f o r other cooling methods. Quench chambers should not be used when the gases to be cooled contain a l a rge amount of gases o r fumes that become highly cor ros ive when wet. This c r ea t e s addition- a l maintenance problems, not only in the quench chamber , but in the remainder of the ductwork, the control device, and the blower.

The following example will i l lus t ra te some of the fac tors that m u s t be considered when designing a quench chamber to cool the gaseous c f f luen t f rom a gray-iron-melting cupola.

Example 16

Given:

32-in.-I. D. cupola. Maximum tempera ture of gaseous effluent a t cupola outlet - 2, 000°F.

Weight ol gaseous effluent a t cupola outlet z 216 lb lmin .

Volume of gaseous effluent a t cupola outlet = 13,280 cfm a t 2, 000'F. This volume of effluent includes indraft a i r a t the charging door of the cupola. The tempera ture of 2, 000°F i s a maximum tempera ture .

Assume the effluent gases have the s a m e proper - t i es a s a i r . Cmsidera t ion of the enthalpies of the gaseous constituents in the effluent gas s t r e a m will show that this i s a valid assumption. Any co r r ec -

t ions would introduce an insignificant refinement to the calculations when considered with r e spec t t o the accuracy of other design fac tors .

VOL - 1 3 . 280 cfn

E V A P O R 4 T I V E

ATEF S P R A Y O N O I T I O N I N S CHIIIABEI)

I I I

U CUPOLA

FURNACE

COOL N G l A T E R

0 UT

F ~ g u r e 39. P r o b l e m : D e t e r m ~ n e t h e w a t e r needed t o c o o l t h e g a s e o u s e f f l u e n t t o 22s°F and t h e t o t a l v o l u m e o f g a s e s d ~ s c h a r g e d f r o m t h e quench chamber.

Solution:

1: Cooling requi red :

Entllalpy of ga s a t 2, 000°F = 509. 5 Btuf lb Enthalpy of g a s a t 225°F = 39. 6 Btuf lb

Ah = 469. 9 Btuf lb

(216)(469. 9) = 101, 300 Btufmin

2: Water to be evaporated:

Heat absorbed p e r l b of water :

Q = h (225"F, 14.7 psig) -hf (60°F) g

= 1, 156. 5 - 29. 06 = 1, 129. 7 Btuf lb

101, 300 Water requ i red = = 90 l b imin

1, 128. 7

3. Volume of water evaporated a t 225 "F:

4. Total volume vented f r o m sp ray chamber a t ! 225°F: 8 !

( 225 + '") = 3,700 c fm Cupola = (13,230) 2, 000 ,. 460 1 Water = 2 , 510 c l m

Total = 6, 210 cfm

P rob l em Note: In this example, the calculated amount of water required to cool the ga se s , 90 I

I I h fmin o r 10. 9 ga l imin , i s only the wate r that m u s t be evaporated. Since a l l the water sprayed into a quench chamber does not evaporate, the ! ! pump and sp r ay sy s t em should be s ized to supply m o r e wate r than that calculated. The amount of excess water needed will depend on fac tors such I a s the inlet t empera ture of the gases , the tern- i

pe ra ture drop requi red , the fineness of the wate r I I

sp r ay , and the a r rangement of sp r ay heads. I t

i s not uncommon to s ize the pump to give 200 p e r - cent of the water needed f o r evaporation. The ac -

tual amount of wate r used should h e controlled hy the tempera ture of the gases discharged f r o m the quench chamber .

The loss of heat by radiation and convection f r o m the ducts was neglected. With long duct runs, how- eve r , a considerable t empera ture d rop in the gas -