api rec 536, post-combustion nox control for fired equipment

Post-Combustion NO, Control for Fired Equipment in General Refinery Services

API RECOMMENDED PRACTICE 536 FIRST EDITION, MARCH 1998

American Petroleum

1_ Institute

COPYRIGHT 2002; American Petroleum Institute

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Manufacturing, Distribution and Marketing Department

API RECOMMENDED PRACTICE 536 FIRST EDITION, MARCH 1998

American Petroleum Institute



STD-API/PETRO RP 53b-ENGL L97h 9 1732270 Ob08505 37

SPECIAL NOTES

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Copyright Q 1998 American Pemleum institute



FOREWORD

API publications may be used by anyone desiring to do so. Every effort has been made by the Institute to assure the accuracy and reliability of the data contained in them; however, the Institute makes no representation, warranty, or guarantee in connection with this publication and hereby expressly disclaims any liability or responsibility for loss or damage resulting from its use or for the violation of any federal, state, or municipal regulation with which this publication may conflict.

Suggested revisions are invited and should be submitted to the director of the Manufactur- ing, Distribution and Marketing Department, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005.



CONTENTS

Page

............................................................... 1 SCOPE 1

2 APPLICABLE ENVIRONMENTAL REGULATIONS AND REFERENCES . . . . . 1 2.1 Environmental Regulations .......................................... 1

U.S. Federal Regulations ............................................ 1 Environmental Protection Agency (EPA) References ...................... 1 National Ambient Air Quality Standards ............................... 1 National Standards & Publications .................................... 2

2.2 2.3 2.4 2.5

3 DEFINITIONS AND ABBREVIATIONS ................................... 2

Units of Reporting Emissions ........................................ 3

GUIDELINES FOR SELECTION ......................................... 3 Selective Non-Catalytic Reduction (SNCR) ............................. 3 Selective Catalytic Reduction ........................................ 4

4.4 Applications ...................................................... 5

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

3.1 Definitions 2 3.2 Abbreviations 2 3.3

4 4.1 4.2 4.3 Considerations 5 ....................................................

5 DESIGN CONSIDERATIONS ........................................... 6

SNCR Systems Overview ........................................... 6 SCR Systems Overview ............................................ 17 Reactant Control and Dilution System Components ..................... 17 Reactant Injection System .......................................... 18

5.6 CatalystlReactor .................................................. 18 Structures and Appurtenances ....................................... 19 Refractories and Insulation ......................................... 19 Instrumentation and Electrical Systems ............................... 19

Instrument and Auxiliary Connections ................................ 20 5.12 Shop Fabrication and Field Erection .................................. 20 5.13 Inspection. Examination and Testing .................................. 20

.......................................................... 5.1 General 6 5.2 5.3 5.4 5.5

5.7 5.8 5.9 5.10 Induced Draft Fan (IDF) .......................................... 20 5.1 1

6 OPERATIONS DESCRIPTION .......................................... 20 Selective Non-Catalytic Reduction ................................... 20 Selective Catalytic NOx Reduction ................................... 21

6.1 6.2

APPENDIX A APPENDIX B

POST-COMBUSTION NO, CONTROL DATA SHEETS . . . . . . . . . . 25

NO, MEASUREMENT ...................................... 41 CALCULATION METHOD FOR CORRECTING

Figures 1 2 3 4 5

SNCR System Schematics Aqueous Ammonia ............................ 7 SNCR System Schematics Anhydrous Ammonia .......................... 9 SNCR System Schematics Urea Injection ............................... 11 SCR System Schematics Aqueous Ammonia ............................. 13 SCR System Schematics Anhydrous Ammonia ........................... 15

V



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6

7

8

9

10

Formation Temperature of Ammonium Sulfate and Ammonium Bisulfate for Various Concentrations of NH, and SO3 ................................ 21 Catalyst Activity Profile versus Time -An Example for a Paricular Situation ................................................. 22 NO, Reduction versus Temperature for Different SCR Catalysts- Typical Example ................................................... 23 NO, Reduction Efficiency versus Catalyst Space Velocity- An Example Situation. .............................................. 23 ?Lpical NO, Reduction Efficiency and Ammonia Slip ..................... 24

Tables 1 Comparison of Typical SNCR and SCR Systems .......................... 1

vi



STD*API/PETRO RP 53b-ENGL 1778 R 0732270 0b085[17 482 I


1 Scoee ing of the reactant, but is often suitable for retrofitting existing - . equipment for low or moderate NO, reduction. SCR systems operate at a high reduction efficiency at a lower temperature window than a SNCR system and are usually selected for lowest NO, emission.

'" description, operation, maintenance, and test procedures of post-combustion NO, control equipment for fired equipment in general refinery service. It does not cover reduced NO, for-

This recommended practice covers the

mation through burner design techniques, such as flue gas recirculation (FGR) and staged combustion. 2 Applicable Environmental Regulations

and References 1.2 This document covers two of the methods of post combustion NO, reduction: 2.1 ENVIRONMENTAL REGULATIONS

a. Selective Non-Catalytic Reduction (SNCR). b, Selective Catalytic Reduction (SCR).

1.3 SNCR is a process where the addition of ammonia or urea into the flue gas stream causes the oxides of nitrogen to convert to nitrogen and water vapor. The basis for the selection and limitations of the SNCR systems are described in Section 4.1.

a. Local. b. State. c. National.

2.2 u.s. FEDERAL REGULATIONS a. CleanAirAct. b. Code of Federal Regulations (CFR).

1.4 SCR is a process where the addition of ammonia into the flue gas stream in the presence of a suitable catalyst causes the oxides of nitrogen to convert to nitrogen and water vapor,

2.3 ENVIRONMENTAL PROTECTION AGENCY (EPA) REFERENCES

I

The basis for the selection of the variois catalyst types-are described in Section 4.2.

1.5 Table 1 indicates the typical operating performance and Units* limitations of both types of NO, duct ion systems. The

gas temperature range and difficulty in achieving proper mix-

a. New Source perfomance Standuds 40 CFR 60 SubPm Db, Industrial Commercial-Institutional Steam Generating

b. Alternative Control Techniques Documents 1993 NO, k~iss ions from Process I-katers- c. National Ambient Air Quality Standards.

1 reduction efficiency of SNCR is limited because of the flue

Table 1 -Comparison of Typical SNCR and SCR Systems

Design Criteria SNCR SCR NO, Reduction Efficiency 40 - 75% O-%% Temperature Window 870" - 1200C 165" - 600C

(1 600" - 2200F) (325" - 1100F) Reactant Ammonia or Urea Ammonia Reactor None Catalytic Waste Disposal None Spent catalyst Therma Efficiency Debit O - 0.3% 0% Energy Consumption LOW High-I.D. fan Capitai investment Costs LOW High Plot Requirements Minor Major Maintenance LOW 3 to 5 years Ammonia 1 NO, (Molar Ratio)

Urea / NO, (Molar Ratio) 0.5 - 0.75 Not applicable Ammonia Slip 5 to 20 ppmvd 5 to 10 ppmvd

Mechanical Draft Not required

1.0 - 1.5 (typical catalyst life) 0.8 to 1.2

Remfit E=Y Difficult Required

1



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2 API PUEUCATION 536

2.4 NATIONAL STANDARDS & PUBLICATIONS

API Std 560 Pub1 534 Pub1 535

ASME Section V U B 31.3

Fired Heater for General Rejnery Services Heat Recovev Steam Generators Burners for Fired Heaters

Boiler & Pressure Vessel Code Chemical Plant & Petroleum Refinery Piping

3 Definitions and Abbreviations 3.1 DEFINITIONS

3.1.1 ammonium bisulfate and sulfate: Injecting ammonia or urea into a flue gas stream containing sulfur trioxide forms these compounds and causes fouling of heat transfer surface and increases particulate emissions.

3.1.2 ammonia breakthrough: The point at which increasing the NHJNO, molar ratio does not significantly reduce the amount of NO,.

3.1.3 ammonia/NO, ratio: The molar ratio indicating the amount of injected ammonia required to reduce the inlet NO, in the flue gas stream.

3.1.4 ammonia slip: The amount of unreacted ammonia in the flue gas stream after the reduction of the NO,, measured in ppmvd corrected to the standard oxygen level.

3.1.5 catalyst activity: Measurement of the NO, reduction performance (with time).

3.1.6 catalyst handling facilities: Device used for loading and unloading of catalyst modules, usually a mono- rail and hoist.

3.1.7 catalyst matrix or substrate: Device coated or impregnated by the active ingredients of the catalyst. The catalyst matrix can be made from ceramic honeycomb, pellets, metal plates or mesh.

3.1.8 catalyst module: A number of catalyst elements make up one module.

3.1.9 catalyst space velocity: The quantity of flue gas (at standard conditions) flowing per volume of catalyst per hour.

3.1.10 catalyst support: Structure within the reactor housing to support the catalyst modules.

3.1.11 catalyst types: Active ingredients are vanadium oxide, titanium oxide, platinum, or zeolite.

American Society for Mechanical Engineers, 345 East 47th Street, New York, NY 10017.

3.1.12 cell density: Measurement of hole density in a honeycomb catalyst matrix (cells per sq. cm [sq.ins.]).

3.1.13 dilution medium: Fluid (usually air, steam, or water) used to disperse the reactant within the flue gas stream-also referred to as a carrier.

3.1.14 injection grid: Consists of a series of distribution pipes and injection nozzles located in the flue gas stream to permit the correct mixing of the reactant and flue gas.

3.1.15 injection skid: Contains the equipment necessary for the control and injection of the reactant (ammonia or urea), including vaporizer or atomizer, dilution air fan, mixer, and control valves.

3.1.16 NO,: General term used to describe all oxides of nitrogen including nitric oxide (NO), nitrogen dioxide (NO,), and nitrous oxide (N,O) For the purpose of emission calcula- tions NO, is assumed to be nitrogen dioxide MW = 46.01.

3.1.17 reactant-ammonia anhydrous or aqueous: Used in the majority of post combustion NO, reduction systems. Industrial anhydrous ammonia contains 99.5%.minimum by volume ammonia and is injected as a vapor. Aqueous contains about 20 to 30% by weight ammonia solution mixed with water and has to be vaporized or atomized before injecting into the gas stream.

3.1.18 reactant urea: Used in some SNCR processes. Urea is normally used as an aqueous solution containing about 50% urea by weight.

3.1.1 9 reactor: The equipment housing including the cataiyst modules and support structure.

3.1.20 reduction efficiency: The percentage of NO, removed from the flue gas by the reduction process.

3.1.21 residence time: The time period the reactant is in contact with the nitrogen oxides or catalyst.

3.1.22 temperature window: The flue gas temperature range that is most effective for NO, reduction for a given process.

3.1.23 trilobe: A pellet type catalyst substrate used in low flue gas temperature applications.

!

3.2 ABBREVIATIONS

ACDS AIG AIS BACT CEMS JXS FGR IDF IGCI

Ammonia Control and Dilution System Ammonia Injection Grid Ammonia Injection System Best Available Control Technology Continuous Emissions Monitoring System Distributed Control System Flue Gas Recirculation Induced Draft Fan Industrial Gas Cleaning Institute



STD-APIIPETRO RP 53b-ENGL L77a 0732270 Ob085Li O30

POST-COMBUSTION NO, CONTROL FOR FIRED EQUIPMENT IN GENERAL REFINERY SERVICES 3

ppmvd RCDS RIS Reagent Injection System RMS Root Mean Square SCR Selective Catalytic Reduction SIP State Implementation Plans SNCR Selective Non Catalytic Reduction

parts per million by volume (dry) Reactant Control and Dilution System

3.3 UNITS OF REPORTING EMISSIONS

3.3.1 Analysis of NO, and other emissions are normally measured in ppmvd. Since some sampling instruments mea- sure the wet sample, care should be taken when analyzing results.

3.3.2 The performance of equipment must be compared on a common basis. The amount of NO, and ammonia slip should be corrected back to the standard oxygen levels. For boilers and fired heaters the standard is 3 percent oxygen (volume dry) in the flue gas, and for gas turbines the standard is 15 percent oxygen (volume dry). The calculation method for correcting the NO, values is given in Appendix B.

3.3.3 In the United States, the most common unit of reporting emissions is lb/MM Btu liberated. The heat liberation is based upon the Higher Heating Value (HHV) of the fuel. As API standard basis for heat liberation in process heaters is the Lower Heating Value (LHV) of the fuel, care should be used in expressing the emissions on the correct basis.

3.3.4 In other countries, the units of reporting emissions can be milligrams per Normal cubic meter (mg/Nm3) or parts per million (ppmvd) based on a different flue gas oxygen reference. See Appendix B for methods of converting the various units.

4 Guidelines for Selection 4.1 SELECTIVE NON-CATALYTIC REDUCTION

(SNCR)

4.1.1 General Description

These processes use a reactant (ammonia or urea) to react with NO, to form water and inert gas (nitrogedcarbon dioxide). To be effective in reducing NO, emission, the reducing agent must be injected into the fired equipment at a desired temperature point. Although the NO, reduction takes place in the 870"-1200C ( 1600"-2200"F) temperature range, the temperature window in the SNCR process can be extended down to approximately 700C (1300F) by the injection of hydrogen or enhanced chemicals along with the reducing agents. The complex fluid dynamics and chemical reactions involved generally limit the SNCR process to less than 75% NO, reduction in the fired equipment application.

At least two SNCR technologies are commercially available. One is an ammonia-based process, the other is a urea-

based process. Both processes require a series of injector nozzles and a reducing agent distribution and storage system. The following are general considerations for selecting a SNCR process for a specific NO, reduction requirement:

a. NO, reduction efficiency required. b. Allowable NH, slip to meet requirements. c. Physical configuration of the fired equipment and the flue gas temperature profiles at various loads. d. Available potential location for injection. e. Performance at various loads and different modes of operation. f. Side reactions and corrosiodfouling on the downstream equipment. g. Safety hazards on storage, processing, transportation and distribution of the reactants and enhancers. h. Operating cost, as well as the initial capital investment.

In general, the NO, reduction efficiency decreases as the initial NO, value decreases. High NO, reductions become more difficult to achieve when the initial NO, value is below 1 O0 ppmvd.

4.1.2 Ammonia-Based Process

In this SNCR process, ammonia vapor carried by an air stream or steam is injected into the flue gas at the appropriate temperature zone 870"-1200C ( 1600"-2200F) effecting a reduction of NO, to nitrogen and water.

The injection of ammonia into flue gas leads to a complexity of intermediate chain branching reactions. The following two simplified chemical equations summarize the overall process:

2N0 + 4NH, + 20, + 3N2 + 6H20 (1) 4NH, + 50, + 4NO + 6H20 (2)

Equation (1) is the NO, reduction reaction which occurs in the 870"-1200"C (1600"-2200F) temperature range by the injection of ammonia alone. NO, reduction effectiveness can be enhanced down to 700C (1300F) by injection of hydrogen (H2 along with NH,). However, as indicated by Equation (2), the injection of NH, into high temperature flue gas results in increased NO, formation and is thus counterproductive.

For initial NO, levels of 200 ppmvd or less, " 0 0 , molar ratios of about 1.5 are commonly used.

4.1.3 Urea-Based Process

This SNCR process uses urea, CO (NH,), as a reducing agent. it injects an aqueous urea solution into the path of the NO, laden combustion products. The urea thermally decom- poses to produce chemical species which react with NO, to form nitrogen, carbon dioxide, and water.

CO ("~, + 2N0 + I/, O, + 2N, + CO, + 2H20 (3) 4NH, + 50, +4NO +6H20 (4)



.. ~~

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4 API PUBLICATION 536

From Equation (3) it follows that the stoichiometric molar rate of urea relative to NO in the combustion products is 0.5 since one mole of urea potentially has two moles of NH, available to react with NO. The urea injection process for NO, control is also temperature sensitive. The urea solution, therefore, must be injected in the temperature range of 870"- 1200C ( 1600-2200"F).

4.1.4 NO, Reduction Efficiency Factors

depends on the following factors:

a. Flue gas temperature in reaction zone. b. Uniformity of flue gas temperature in the reaction zone. c. Normal flue gas temperature variation with load. d. Residence time. e. Distribution and mixing of ammonidurea into the flue gases. f. Initial NO, concentration. g. Arnmonidurea injection rate. h. Heater configuration, which affects location and design of injection nozzles.

The NO, reduction efficiency of both SNCR processes

4.2 SELECTIVE CATALYTIC REDUCTION 4.2.1 Process Description

Selective Catalytic Reduction Process removes nitrogen oxides (NO,) from flue gases by injecting ammonia (NH,) into the flue gas and passing the well mixed gases through a catalyst bed. NO, reacts with NH, in the presence of the catalyst to produce nitrogen (N2) and water (H20) as shown in the following equations.

4NO + 4NH3 + O2 + 4N, + 6H,O (5) 6N0 + 4NH3 + 5N, + 6H20 (6) 2N02 + 4NH, + O, + 3N2 + 6H20 (7) 6N02 + 8NH, + 7 N , + 12H2O (8) NO + NO, + 2NH, + 2N2 + 3H20 (9)

Note that the first reaction for refinery applications generally dominates since 90% of the NO, is NO.

A wide variety of available cataiysts can operate at flue gas temperature windows ranging from 165"-600C (325"- 1 lOO"(F). High NO, reduction efficiencies can be achieved if the parameters such as residence time, space velocity, and the correct temperature window are controlled. For SCR technology, the NHJ NO, molar ratio of 1 .O is commonly used.

4.2.2 Catalyst Types

4.2.2.1 Low Temperature Catalysts

effect when using platinum catalysts is that a significant part of the SOz is converted to SO3.

SO, combines with water vapors, forming acid which is corrosive to the downstream equipment. Vanadium-based catalysts also convert SO, to SO, but to a lesser extent.

The ideal temperature range for the platinum-based catalyst to effect optimum NO, reduction is 230"-285C (450"- 55Oo(F).

For lower temperature applications, vanadium-titanium catalyst or trilobe substrate is available. The temperature range for this substrate is 165"-345"C (325"-65OoF).

4.2.2.2 Medium Temperature Catalyst

Vanaium-titanium-based catalysts use a vanadidtitania catalytic coating on a ceramic honeycomb or metallic plate substrate. They can also be a homogeneous monolithic honeycomb. The cell density of the honeycomb and the plate spacing can be varied to meet the application requirements.

The ideal temperature range for this catalyst to effect optimum NO, reduction is 290"40O"C (550"-750"F).

4.2.2.3 High Temperature Catalyst

Zeolite catalysts use zeolitic materials rather than heavy metals for their catalytic activity. These catalysts have optimum performance at a higher temperature range than the heavy metal catalysts.

The ideal temperature range for this catalyst to effect optimum NO, reduction is 455"-51 1C (850"-950"F).

4.2.2.4 Efkct of Flue Gas Temperature and Effect of Catalyst Poisons

A platinum-based SCR system will generate proportion- ally more nitrous oxide (N,O) at lower temperatures than other types. Depending on the caaiyst substrate material, the cataiyst may be quickly damaged due to thermal stresses at temperatures in excess of 450C (850F). It is also important to have stable operations and uniform flue gas temperature across the catalyst.

'Avo general classes of poisoning, selective and non-selective, can result in catalyst deactivation.

Selective poisoning occurs when a component of the flue gases, such as SO, or SO,, gets adsorbed on the active surfaces of the catalyst and renders it inactive. SO, gets selec- tively absorbed on platinum.

Non-selective poisoning is caused by the accumulation of foreign substances on both the carrier and the catalytic component. Dust, soot, oil mist, and phosphorous components forming a polymeric glaze can ail block the pres . "Masking" is the term used when the outer surfaces of the cataiyst are

Platinum based catalysts can be used for NO, reduction in lower temperature applications. Platinum catalysts are also used to oxidize unbumt hydrocarbons and CO. One side

covered with such foreign material rendering the inner active surfaces inaccessible for NO, reduction. Pellet-type catalysts aremorepronetomasking.



~

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POST-COMSUSTION NO, CONTROL FOR FIRED EQUIPMENT IN GENERAL REFINERY SERVICES 5

Arsenic compounds and heavy metal compounds, such as zinc dithiophosphate, tend to accumulate on the periphery of the catalyst. They tend to decompose with time, producing Eree heavy metals, which then react with the catalytic compounds to produce less active material.

4.3 CONSIDERATIONS

4.3.1 Effect of Flue Gas Components

The dominant factors for NO, reduction utilizing either of these processes are the flue gas temperature and temperature profile, rather than the fuel type or its products of combustion. However the SNCR process is affected by the concentrations of O,, H,O, and CO in the flue gas. High CO concentrations are reported to shift the temperature window at the low end, so that NO, removal is effective at relatively lower temperatures, Le., 800C (1470F). Conversely, the SNCR process may retard the oxidation of CO in the flue gas, resulting in slightly higher CO emissions.

The presence of HCl or HF in the flue gas in excess of 500 ppmvd may also retard the effectiveness of the SNCR process. The other flue gas components, such as CO,, N,, SO,, etc., appear to have no effect on the NO, reduction process.

4.3.2 NO, Reduction from Initial NO, Values

4.3.2.1 SNCR Technology

Whether urea or ammonia based, SNCR is most cost effective in achieving moderate NO, reduction in the 40-75% range from initial NO, values of 100 ppmvd or greater.

The ammonia slip in either of these process technologies typically ranges between 5-20 ppmvd.

4.3.2.2 SCR Technology

Applications of SCR NO, reduction are reported for each of the catalyst types listed above for inlet NO, concentrations up to 300 ppmvd. However, most applications of SCR are for inlet NO, concentrations in the range of 50 to 150 ppmvd. In this range, NO, reductions of 90% or more are possible with an ammonia slip of no more than 5 ppmvd.

While very high NO, reduction is possible (approaching loo%), this is likely to be at the expense of increasing the ammonia slip (above 5 ppmvd) which adds to the operating costs and may be unacceptable for environmental reasons.

4.3.3 Excess Reactants

Some NH, exits the reaction zone unreackd. This is refend to as ammonia slip. As a result of the complexity of the reactions, ammonia slip must be evaluated for each individual application; so very few generalizations can be made. Because slip is linked to a certain degree to NO, reduction performance, fired equipment in which the time-temperature rela-

tionship is favorable to achieving high NO, reduction will also exhibit low NH, slip. in cases where favorable conditions exist, it has been possible for NH, slip to be held below 5 ppmvd. The placement of the injectors and injection mixing effectiveness are of prime importance in minimizing NH, slip.

Other than the reactions outlined in equations earlier in this section, there are no significant reactions between ammonia and other compounds in high temperature flue gas. However, at low temperatures, ammonia can combine with sulfur or chlorine compounds to form complex salts. These reactions can be minimized, in many cases to negligible amounts, by limiting the ammonia slip level from the process.

Depending on the process, as combustion gases cool, ammonia can react with sulfur trioxide (SO,) and water vapor to form ammonium bisulfate and ammonium sulfate. Ammonium bisulfate is a sticky corrosive liquid which can foul heat transfer surfaces. Ammonium sulfae, on the other hand, is a dry solid, forms as solid particles, and may increase particulate emissions.

At flue gas temperatures below 120C (25OoF), ammonia can react with hydrochloric acid (ici) to form ammonium chloride (&I). ,Cl is a dry, neutral white salt, which can contribute to a visible plume if present in sufficient quantities.

4.4 APPLICATIONS

4.4.1 SNCR PROCESSES

SNCR processes are effective at relatively high temperatures, so their applications are more numerous with industrial and power boilers. SNCR also finds extensive applications in units with relatively high residence times (e.g., 2 to 3 sec- onds), such as incinerators. These processes are more effi- cient in reducing NO, from high levels to moderate levels (i.e., 200 to 50-75 ppmvd).

These processes do not find many applications in gas fired process heaters where modem burner technology offers extremely low NO, emissions. Refer to API Publication 535, Burners for Fired Heaters.

4.4.2 SCR Processes

The SCR processes find ideal application in heaters, boilers, and gas turbine exhaust heat recovery equipment where the initial NO, levels are in the moderate range of 50 to 150 ppmvd and the permit requirements demand a reduction by 80 to 90% of such values.

4.4.3 Combination of SNCR, SCR, and Low NO, Burner Technologies

Each of these technologies has its ideal range for achieving NO, reduction. There may be industrial applications where ail three technologies can be combined to bring the NO, level from initial values in the 200 ppmvd range to final values in the 5 ppmvd range.



STD-API/PETRO RP 53b-ENGL 1598 0732270 Ob08514 8qT D


5 Design Considerations 5.1 GENERAL 5.1.1 Typical Design Considerations

The SNCWSCR System design should yield an Industrial Quality system with the flexibility and reliability to operate continuously between unit turnarounds (typically 2-3 years). Such expectations will q u i r e the equipment supplier to consider (at least) the following in the system design:

The codes, industry standards, and reference publications noted in Section 2.

All appropriate site specific seismic, wind, snow, and thermal loading conditions.

All appropriate job specific operating and environmental requirements.

The peculiarities of operation, maintenance and performance in the selection of injector location, orientation and design (SCR and SNCR Systems), and in the selection of reactor location, orientation, and design (SCR Systems).

Provisions for one future layer of catalyst (SCR Systems). Such provisions should include the incremental system pressure drop in the system process design, and the incremental system loadings in the mechanical design.

Insulation and heat tracing should be provided as required on vaporized ammonia systems to avoid condensation upstream of the injectors.

Freeze protection may be required for aqueous ammonia and urea-based systems, depending on location.

5.1.2 Typical Purchasing Considerations

should be addressed

a. Adequate system definition and scope delineation. b. System commissioning advisor from equipment supplier. c. Spares for commissioning and two-year operation. d. Performance Guarantee(s) for NO, reduction efficiency. e. Catalyst life.

In the development of a Job Scope, the following items

5.2 SNCR SYSTEMS OVERVIEW 5.2.1 Ammonia-Based SNCR Systems

There are two types of ammonia-based SNCR systems: Aqueous Ammonia and Anhydrous Ammonia Systems. The difference between the two systems lies in the processes used in the Reactant Control and Dilution Systems (RCDS) to vaporize the ammonia and mix it with a carrier gas to obtain the reactant charge. The primary components of ammonia- based SNCR systems are (select either a or b):

through vaporizer before mixing with either an air or steam carrier. The primary components in this system are as follows, and as illustrated on typical schematic (Figure 1).

1. Aqueous ammonia storage tank. 2. Carrier air supply: two air blowers (or compressors) or one blower and a backup air source; or a source of carrier steam. 3. Ammonia supply pump. 4. Two cartridge filters and/or strainers. 5. Air heater with ammonia-air vaporizer or ammonia vaporizer. 6. Insrumentation and interconnecting piping for a fully functional system. 7. The recommended features noted in Section 5.4.

b. RCDS-Anhydrous Ammonia: Vaporized anhydrous ammonia is mixed directly with either an air or steam carrier. A vaporizer usually supplies heat to the storage tank to maintain pressure, and the ammonia vapor is drawn from the vapor space in the tank. The primary components in this system are as follows, and as illustrated on typical schematic (Figure 2).

1. Pressurized anhydrous ammonia storage tank. 2. Carrier gas supply: two air blowers, or one blower and a backup air source; or a source of carrier steam. 3. Ammonia vaporizer. 4. A m m o n i a 4 static mixer (if required). 5. Instrumentation and interconnecting piping for a fully functional system. 6. The recommended features noted in Section 5.4.

1. How distribution manifold with a series of injector nozzles that introduce the vaporized ammonidcarrier gas mixture to the flue gas stream. 2. The recommended features noted in Sections 5.5 and 5.7.

d. System controls, provided by either a local control panel or the plants DCS.

c. Reactant Injection System (RIS), consisting of:

5.2.2 Urea-Based SNCR Systems

The primary components of a urea-based SNCR system are as follows, and as illustrated on typical schematic Figure 3).

a. Urea Reactant Control and Dilutions System (RCDS), consisting of:

1. A reactant storage tank. 2. bo cartridge filters and/or strainers. 3. A reactant metering pump. 4. A water pump, or dilution water source connection. 5. An in-line static mixer as required. 6. A series of flow indicators and regulating valves, as

a. RCDS-Aqueous Ammonia: Aqueous ammonia is required, to balance the flow of reactant to each reactant pumped from the storage tanks and is commonly mixed with injector. a heated carrier air stream in an ammonia vaporizer/mixer. 7. All pertinent instrumentation and interconnecting p ip Alternatively, the ammonia can be vaporized in a once- ing for a fully functional system.



F-XAB E-X c-x T-X P- AQUEOUS AMMONIA FILTERS AQUEOUS AMMONIA VAPORIZER AIR COMPRESSOR AQUEOUS AMMONIA TANK AQUEOUS A;

, - . . - , . - . . - . . - . . - . . - . . - . . - . . - . . - . . - . . - . . - . . - . . - . . - I Process Signal >-----

(Note 2) I -@--

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Notes: 1. May use steam in lieu of air compressor. 2. Process signai for feed forward, as needed. 3. Either Zone 1 or Zone 2 in operation.

This schematic is o used as a 5



:ONIA PUMP

I

I

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I

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I

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- --

I Combustion Zone

I

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Zone 2 1, ;:; ~

- E --

typical system and is intended to be de, actual design might vary.

Figure 1-SNCR System Schematics Aqueous Ammonia

7



c-x T-X AIR COMPRESSOR ANHYDROUS AMMONIA TANK

Ammonia Con , - , . - . . - . . - . . - . . - . . - . . - . . - . . - , , - , . - . . - . . - . . - . . - . . - . . - I

- TSO

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v c-x SeeNote1

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H-1 This schemati

used :

Notes: 1. May use steam in lieu of air compressor. 2. Process signal for feed forward, as needed. 3. Either Zone 1 or Zone 2 in operation.



~

S T D * A P I / P E T R O R P 53b-ENGL 1778 0732290 Ob08518 '495

I

--

Zone 1 (Note 3) I

. . - .

I

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L

I 7 LI .- Zone 2

J I

s of a typical system and is intended to be a guide, actual design might vary.

L

/ Combustion Zone -

Figure 2-SNCR System Schematics Anhydrous Ammonia

9



F-1 A/B WATER FILTERS

I I

F-2A/B UREA FILTERS

T-X UREA TANK

(Note 3)

P-1 WATER PUMP

AtomizingX=ooling I

>-I Air

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l

I F-1 B

P-1

I - - - A I

I r -

Y 1

1 P-3 Notes : 1. Static mixer, use as needed. 2. Process signal for feedforward control. 3. Tank heat traced if urea is 50% or greater solution 4. All urea piping to be stainless steel.

T-X

This schematir used E



STD*API/PETRO RP 53b-ENGL 1998 9

P-2 P-3 UREA PUMP CIRCULATION PUMP

Control A- i = I I

- - (Note 1)

. - . . - . . -

I

I ----

0732290 Ob08522 71b M

C

--@-

of a typical system and is intended to be a guide, actual design might vary.

I Combustion Zone

I I

Figure 3-SNCR System Schematics Urea Injection

11



F-XA/B AMMONIA FILTER

v-x AMMONIA VAPORIZOR ELEC

I %

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F-XB

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To IA Users j l I

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I 4 c

Notes: 1. Inlet NO, is optional and should be used when large load variation on fired equipment is expected 2. Expanded view of ammonia injection grid.

P-x - T-X



STD-APIIPETRO R P 53b-ENGL 1778 D 0732290 Ob08524 799

6-XA/B DILUTION AIR BLOWERS

P-x T-X AQUEOUS AMMONIA PUMP AQUEOUS AMMONIA TANK

API 620

i

9 +'V B-XA

Q +\I '

6-XB

3 Aqueous Ammonia Injection Skid

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iis schematic is of a typical system and is intended to be used as a guide, actual design might vary.

Figure 4-SCR System Schematics Aqueous Ammonia

13



STD*API/PETRO R P 53b-ENGL 1998 0732290 Ob08525 b25 W

B-XA/B DILUTION AIR BLOWERS

x-1 STATIC MIXER

. - . , - . . - . , - . . - , . - . , - . . - . . - . . - . . - , , - , . - . . - . . - . . - . . -

(Note 1)

ANH

TSO

B-XA

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H-i Note 2

Notes: 1. Inlet NOx is optional and should be used when large load variation on fired equipment is expected. 2. Thermosiphon ammonia vaporizer. 3. Expanded view of ammonia injection grid.

. .. .. .gdrouc Ammonia In , - . . - . . - . . - . . - . . - . .

Th



STD*API/PETRO R P 53b-ENGL 1778 0732270 ObOB52b 5bL = T- 1

!?OUS AMMONIA TANK

1

tion Skid . < - . .

schematic is of a typical system and is intended to be used as a guide, actual design might vary.

Figure 5-SCR System Schematics Anhydrous Ammonia

15



S T D - A P I I P E T R O RP 53b-ENGL L77 I O 7 3 2 2 7 0 O b 0 8 5 2 7 4T


b. Reactant Injection System (RIS), consisting of: 1. An atomizing chamber. 2. Interconnecting tubing. 3. Injector nozzles that introduce the atomized reactanif carrier air mixture into the flue gas stream.

c. System controls, provided by either a local control panel and/or the plants DCS.

5.3 SCR SYSTEMS OVERVIEW

There are two major types of SCR systems: Aqueous Ammonia and Anhydrous Ammonia systems. The differences between the two systems lie in the processes used in the Reactant Control and Dilution System @CDS) to vaporize the ammonia and mix it with the carrier air stream to obtain the reactant charge. The primary components of an SCR system are (select either a or b):

a. RCDS-Aqueous Ammonia: Aqueous ammonia is pumped from the storage tanks and is commonly mixed with a heated carrier air stream in an ammonia vaporizer/mixer. Alternatively, the ammonia can be vaporized in a once- through vaporizer before mixing with either an air or steam carrier. The primary components in this system are as follows, and as illustrated on typical schematic (Figure 4).

1. Aqueous ammonia storage tank. 2. Carrier air supply: two air blowers, or one blower and a backup air source; or a source of carrier steam. 3. Ammonia supply pump. 4. Two cartridge filters and/or strainers. 5. Air heater and ammonia-air vaporizer or ammonia vaporizer. 6. All instrumentation and interconnecting piping for a fully functional system. 7. The recommended features noted in Section 5.4.

b. RCDS-Anhydrous Ammonia: Vaporized anhydrous ammonia is mixed directly with carrier air or steam. A vaporizer usually supplies heat to the storage tank to maintain pressure, and the ammonia vapor is drawn from the vapor space in the tank. The primary components in this system are as follows, and as illustrated on typical schematic. (Figure 5.)

1. Pressurized anhydrous ammonia storage tank. 2. Carrier air supply: two air blowers or one blower and a backup air source, or a source of carrier steam. 3. Ammonia vaporizer. 4. AmmoniaAr static mixer (if required). 5. Instrumentation and interconnecting piping for a fully functional system. 6. The recommended features noted in Section 5.4.

1. A flow distribution manifold with a series of flow indicators and regulating valves. 2. A set of internal elements, with injection nozzles, capable of accommodating the entire range of temperatures.

c. Reactant Injection System (RIS), consisting of:

d. A Selective Catalytic Reactor, consisting of:

1. Insulated housing, with at least one catalyst access door. 2. Catalyst support structure. 3. Catalyst module(s). 4. Appropriate ladders and platforms. 5. Recommended features noted in Sections 5.6 through 5.8.

e. Induced Draft Fan, if required, which should be designed and purchased in accordance with Section 5.10. f. System Controls, provided by either a local control panel or the plants DCS.

5.4 REACTANT CONTROL AND DILUTION SYSTEM COMPONENTS

5.4.1 Dilution Air Blower System

Dilution air blowers should be industrial quality and of a design suitable for the intended application. The following features should be included in the system:

a. An isolation valve downstream of each blower, to provide the means to positively isolate either blower from the operating system, which permits the safe maintenance of the idle blower. b. A check valve, to prevent the flow of air through the idle blower. c. An inlet air filter-silencer. d. A ducting design, that may be constructed of pipe, that allows the removal of either blower without the removal of adjacent ducting.

5.4.2 Air Heater

a. Electric Air Heater-Heating elements will require peri- odic replacement. The electnc air heater should be constructed for ease of maintenance and long term reliability, and contain the following recommended features:

1. Elements should provide a minimum mean-time between-failure of 60 months. 2. Heating elements should be designed for easy replacement. 3. The heater control should be a silicon controlled recti- fied type, with a 4-20 mA control input.

b. Other air heater types, such as a once-through exchanger heated by a fluid such as flue gas or steam, may be used.

5.4.3 Am mon ia VaporizerNlixer

Boiler and Pressure Vessel Code, Section VIII, Division 1. This vessel should be designed in accordance with ASME

5.4.4 Filterfltrainers

Filters and/or strainers should be an industrial quality and of a design suitable for the intended application. It is recommended that two in-line cartridge filters and/or strainers be



~

STD.API/PETRO RP 53b-ENGL 1998 0732290 Ob08528 33Li m


piped in parallel, and valved to permit quick and safe switch- ing (on-line vs. off-line).

5.4.5 Skid Design

Some system components may be prefabricated and mounted on skids. Based on industry experience, the following features are recommended:

a. The skid should have a solid checker plate floor with a minimum 50 mm (2") high curb seal-welded to the floor, and a drain line connection. The floor should be sloped to the drain. b. The skid equipment layout should provide easy access for operation and maintenance. c. The design and placement of piping, conduit and mechanical members should permit the removal of skid components, without the removal of piping, conduit or members. d. The skid structural design should be sufficient for a four- point lift without temporary bracing.

5.4.6 Control and Dilution System Piping

It is recommended that the piping between the system inlet and the RIS be in accordance with the foilowing minimum design practices:

a. Piping design, fabrication, inspection and testing should be in accordance with the job specifications and ASWANSI B31.3. b. Skid piping should be properly supported and terminated with flanged connections at the skid edge. c. Skid terminals should be designed to accept reasonable forces, moments and movements from the interconnecting piping per M I Standard 560. d. Piping should not obstruct any access openings. e. Piping should be properly supported and protected to prevent damage from vibration, operation and maintenance. f. Piping should be designed to minimize the use of flanges and fittings. g. All piping should be of seamless construction. h. Corrosion allowances for carbon steel materials should not be less than 3.0 mm (0.125"). Stainless steel materiais may be designed without a corrosion allowance. i. Flange bolt holes should straddle vertical centerlines. j. Connections 1.50" NPS and smaller should be socket welded. k. Connections 2" NPS and larger should be butt-welded or flanged. 1. instrument connections and stubs, including root valves, should not be less than 3/4'' NPS. m. Vents and drains should be provided to completely vent and drain pressure parts. High or low point pockets should be avoided. n. Components made of, or containing, copper, brass, and cast iron should be avoided.

o. Pressure part flange faces should be raised face with 125- 250 AARH concenic or spiral serrated finish suitable for metal gaskets. p. Pressure part gaskets should be spiral wound metal gaskets with retaining rings.

5.5 REACTANT INJECTION SYSTEM

The RIS design should be in accordance with the following:

5.5.1 Piping design, fabrication, inspection, and testing should be in accordance with the RCDS piping requirements, as noted in 5.4.6, above.

5.5.2 RIS piping connections, inside the flue gas path, (Le., internal elements) should be socket or butt-welded.

5.5.3 Internal elements should be fed from a common external header.

5.5.4 Each spray nozzle assembly should be removable for maintenance. It is desirable to have the capability to remove individual spray nozzles while system is operating.

5.5.5 Spray nozzles and other internal elements should be 300 series stainless steel material.

5.5.6 Internal supports and guides of the injection grid components should be provided as required to prevent defor- mation of the components.

5.5.7 Reactant Injection Grid design should accommodate the entire range of possible operating temperatures. RIS design should be based on "no flow" conditions.

5.6 C ATALY ST/R EACTOR

5.6.1 Catalyst

a. The catalyst should be suitable for treating the flue gases specified on the data sheets. b. Au catalyst modules in a reactor should be identical in size and interchangeable. This concept should not prevent the use of test modules with coupons, or other form of monitoring device. c. It is recommended that IGCI standard catalyst module sizes be used whenever practical.

5.6.2 Reactor Housing

a. internal supports, bafes and other flue gas wetted components should be in accordance with the applicable design criteria of APT Standard 560. b. The reactor housing should be designed to accommodate the appropriate number of catalyst modules, plus space for one additional layer of catalyst modules. c. Sufficient maintenance access should be provided for both the initial and future catalyst layers, and associated equipment. d Provisions for thermal expansion should take into consid- eration the operating conditions specified on the data sheets.



STD.API/PETRO RP 53b-ENGL 1998 = 0732290 Ob08529 270


e. Placement of access lanes and cleaning facilities should 5.8 REFRACTORIES AND INSULATION anticipate future catalyst installation. f. A catalyst module support structure should be provided in the reactor housing. It should be designed to support and retain both initial and future catalyst modules. g. Internal seals should be provided to prevent bypass of flue gas around the catalyst modules. h. Provisions for catalyst module removal should be included in the reactor housing design.

a. Refractories and insulation should be designed in accordance with API Standard 560. b. ceramic and castable c. For floor coverings, the design should enable the floor to be walked on without damage. d. Ceramic fiber systems should be designed in accordance with API Publication 534.

are prefesred,

i. The catalyst reactor housing should have a bolted access

SYSTEMS door sized to allow catalyst removal.

5.7 STRUCTURES AND APPURTENANCES 5.9.1 General

5.7.1 General

5.9 INSTRUMENTATION AND ELECTRICAL

a. The equipment supplier should provide a P&ID, with

a. Structural steel, reactor casing, and ducting should be designed in accordance with API Standard 560. b. All loads from the catalyst modules and connecting ducting should be supported by the structural steel and should not be t ransmit ted by the insulation system. External steel frames should carry the structural loading. c. Metal casing may be used to provide lateral bracing between the structural columns and to support the insulation system. d. Structural steel should be designed to permit lateral and vertical expansion of all SCR parts. e. Structural supports should be designed to support ladders, stairs and platforms in existing and future locations.

5.7.2 Ladders, Platforms, and Stairways

a. Platforms, with handrails and ladders, should provide access to catalyst removal doors. Such platforms should not inhibit the removal of catalyst. b. Platforms and/or ladders should provide access to all instrumentation and controls, valves, dampers, operators, and access doors not accessible from grade. c. Catalyst access platform should be of sufficient size and strength to accommodate at least one module.

5.7.3 Casing and Ducts

a. Ducts and reactor casing should be designed in accordance with API Standard 560, Appendix E b. Casing plate should be seal-welded to prevent air and water infiltration. c. Lifting lugs should be provided on all ducting and reactor housing components. d. Bolt spacing on all duct flanges should be 150 mm (6") maximum. e. The transition angle from the upstream ducting to the SCR reactor housing should not be greater than a 30" included angle, unless flow distribution devices are provided. f. Expansion joints should be provided as required to accommodate system and/or component expansion and contraction.

instrument symbols and identification in accordance with ISA 55.1. b. The equipment supplier should provide all instrumentation and controls shown on the job P&D.

Wiring, calibration, and installation data should be provided by the equipment supplier for each instrument and/or panel.

5.9.2 Control and Dilution System

a. On skid-mounted systems, instrumentation and control wiring should be terminated in junction boxes. b. Available instrument power levels, and instrument air pressures should be specified on the data sheets. c. The RCDS will have a local control panel for the local start-up, shutdown, and annunciation of the system.

5.9.3 Control and Instrumentation Components

a. Each instrument should be documented on an ISA data sheet. b. The reactant flow control valve should have ANSI RF flanges, an integral UP convertor with filtedregulator, and gauges (to indicate instrument air supply and outlet pressures). c. The reactant shut-off valve should be rated ANSI Class V, with RF flanges, and a filter/regulator with pressure indicator. d. Pressure, differential pressure, and temperature transmitters should provide a 4-20 mA output. e. Thermocouples should be either Type J or K, with thermowell.

5.9.4 Electrical Components

a. Electrical enclosures in outdoor installations should be weatherproof. b. Motors, electrical components, and electrical installations should be suitable for the available utilities and area classification specified by the purchaser. c. Components with exposed copper part(s) should be avoided.



STD*API/PETRO RP 53b-ENGL 1798 0 7 3 2 2 9 0 Ob08530 T92


5.1 O INDUCED DRAFT FAN (IDF)

a. The KIF should be designed and manufactured in accordance with API Standard 560, Appendix E. The IDF should be sizdrated in accordance with API Standard 560, Appendix F. b. The iDF should be capable, as purchased or- when retrofit- ted, of passing the Test Block flow rate at the higher head value resulting from the installation of a "future layer of catalyst."

5.1 1 INSTRUMENT AND AUXILIARY CONNECTIONS

a. Nozzles and connections should be designed in accordance with API Standard 560. b. Sufficient connections should be provided to permit traverses of velocity, NO, concentration, ammonia concentration, and temperature upstream and downstream of the reactor.

5.12 SHOP FABRICATION AND FIELD ERECTION

a. Shop fabrication and field erection should be executed in accordance with API Standard 560. b. Suitable lifting lugs should be provided on all modules.

5.1 3 INSPECTION, EXAMINATION AND TESTING

a. inspection and testing of all mechanical components should be in accordance with API Standard 560. b. Performance testing is not included in this section, and should be performed in accordance with Section 6 and/or the purchaser's specifications.

6 Operations Description 6.1 SELECTIVE NON-CATALYTIC REDUCTION

6.1.1 General

The use of Selective Non-Catalytic Reduction (SNCR) units to reduce NO, emissions was pioneered in the early 1970s. This process does not require a catalyst. Flue gas temperatures should be in the range of 87O0-120O0C ( 1 6 W 22"F), with the optimum usually being 925"-1040"C (1700"-1900"F) depending on the reactant. Both aqueous and anhydrous ammonia, and urea, have been used as the reactant. NO, reduction is typically 40-75 '% with SNCR. The efficiency of the process decreases with low inlet NO, concentrations (below about 100 ppmvd) making high NO, reductions more difficult to achieve. The reactant to NO, operating ratio is 1-1.5 mole ammonia to 1 mole NO, for ammonia-based systems, and 0.5-0.75 mole urea to 1 mole NO, for urea-based systems. The injection rate is usually controlled based on ring rate and NO, emission. The ammonia slip is normally 5-20 ppmvd.

If urea is supplied in a concentrated liquid form (above 50% urea), then it must be kept above 20C (65F) to avoid

6.1.2 Flue Gas Temperature

The NO, reducing reaction is temperature sensitive. Con- trol over a range of operating conditions is difficult. Changes to the firing rate affect the flue gas temperature and velocity profile. If the temperature falls below or rises above the window, NO, emissions and/or ammonia slip will increase. Sometimes injectors are placed at different locations to reach the optimum temperature window over the operating range.

6.1.3 Reactant Injection

Ammonia injection uses a carrier such as steam or compressed air. Hydrogen injection or enhancer may also be required for low temperature applications. Urea-based systems do not require a carrier but use pressure atomizing to ensure aequate reactant mixing with the flue gas. Urea injection is pressure or air atomized. Off-line injectors are purged to keep them from plugging and overheating. Plugged injectors can cause erratic spray and tube impingement, leading to tube failure.

6.1.4 Excess Reactant

As previously discussed, ammonia slip can combine with sulfur tri-oxide and water vapor to form ammonium suifate ("4)zS0, and ammonium bisulfate (NI&)HSO,, which can result in convection coil surface fouling and visible stack plume.

Please refer to Figure 6 for formation of ammonium sulfate and ammonium bi-sulfate for various concentrations of NH3 and SO3. The area between the two lines indicate possible formation of both ammonium suifate ("&30, and ammonium bisulfate (NHJHSO,.

Ammonium sulfates can deposit on surfaces below 235C (450"F), or increase particulate emissions. Ammonium sulfate is a dry particulate that may contribute to plume formation. Ammonium bisulfate is highly acidic and sticky substance which can deposit on downstream equipment such as convection coils and air heaters causing pluggage and dete- riorating equipment performance. Deposits can be minimized by keeping ammonia slip low and monitoring downstream flue gas temperature. Deposits can be water washed on-line if the provision exists.

6.1.5 Reactant Handling

Aqueous ammonia will typically be a mixture of approximately 2630% ammonia and water, and is more commonly used. Demineralized water should be used in aqueous ammonia solutions to minimize fouling in the ammonia vaporizer. An alternative approach is utilization of anhydrous ammonia Anhydrous ammonia is toxic. It has a high vapor pressure at ambient temperature, and thus requires pressurized storage. crystallization.



STD-API/PETRO RP 53b-ENGL 1994 0732270 Ob06531 927 D


P a Q

O E

2 .- I

I c a, o c

O" r" z

100

10

1

o. 1 1 10 100 so, Concentration, pprnvd

lo00

Figure 6-Formation Temperature of Ammonium Sulfate and Ammonium Bisulfate for Various Concentrations of NH, and SO,

6.1.6 Energy Use

Operating costs and reliability will depend on the utilities required for reactant handling. SNCR systems employ pumps and heaters to feed the reactant. Steam or compressed air is used as a carrier for the ammonia-based system. For urea- based systems, plant water is required as an in-line diluent for distribution purposes.

6.1.7 Test Procedures

Emissions testing should follow EPA 40 CFR 60 subpart Db, unless otherwise dictated by local regulations. NO, analyzers will be required. Ammonia analyzers may be required as well to detect NH, slip.

6.2 SELECTIVE CATALYTIC NO, REDUCTION

6.2.1 General

The use of SCR systems to reduce NO, emissions was pioneered in the early 1970s. This process requires the use of a catalyst. Flue gas could be in the range of 165"-OO"C (325"- 1 100F) depending on the type of catalyst used.

Presently three types of catalysts are in use. They are low, medium, and high temperature. Both aqueous and anhydrous ammonia have been used as a reactant. NO, reduction can exceed 90% with SCR. NO, levels below 10 ppmvd can be achieved. In general, the ammonia-to-NO, ratio is 1.0 for

SCR. The injection rate is usually controlled based on the firing rate and NO, emissions. Ammonia slip is usually less than 5-10 ppmvd.

6.2.2 Catalyst Performance Versus Operating Hours

The performance of catalyst tends to deteriorate with time. The initial rate of catalyst deterioration is high but slows and becomes fairly steady as the catalyst ages. After the initial start up, the performance of catalyst is stabilized. Figure 7 shows a typical catalyst activity profile over a range of time. Main causes of deterioration are the catalyst poisons, chemical reactions with aikali metals and halogens, and sintering at very high gas temperatures, above 450C (840F) for vanadium catalyst.

6.2.3 Flue Gas Temperature

Flue gas temperature is the most important operating parameter that influences selection of the catalyst. Figure 8 shows a typical qualitative effect of gas temperature on the NO, reduction efficiency. The choice of the catalyst must consider the range of operating temperatures in the system. The flue gas temperature entering the catalyst bed should be uniform, preferably within i l0"C (20F).

a. Effect of Low Flue Gas Temperature: Lower flue gas temperatures reduce catalyst activity which may result in high



S T D * A P I / P E T R O RP 5 3 b - E N G L 1798 H 0732270 O b 0 8 5 3 2 Ab5


O 1 2 3 4 5 6

Operating Time, Years

Figure 74ata lyst Activity Profile versus Time-An Example for a Particular Situation

catalyst volume requirements. High efficiency, high surface area, low temperature catalyst systems are available which will perform down to 165C (325F). depending on the sulfur content in the fuel. b. Effect of Medium Flue Gas Temperahire: Medium range catalysts operate in the range of 29O040O0C (55O0-87O0F). At temperature above 80O"F, the metal coating migrates and localizes in spots, leaving the surface less reactive. Thermal shock can also lead to flaking of the catalyst coating. It is caused by rapid temperature changes, by excessive reaction temperature or from normal operation over an extended period. Metal coating and catalyst expand and contract at different rates due to their different thermal coefficients. c. Effect of High Flue Gas Temperature: Zeolite based catalysts can operate at a temperature range of 360-6000C (700-1100"F).

6.2.4 Flue Gas Flow Rates

NO, reduction catalysts are designed for certain flue gas temperature ranges and flows. Lower firing rates can reduce NO, reduction efficiency if flue gas temperature falls below design parameters. The NO, reduction efficiency of the catalyst is inversely proportional to space velocity. At flue gas flow rates greater than design, NO, reduction efficiency will be reduced. Figure 9 shows effect of space velocity on the performance of a typical catalyst.

6.2.5 Flue Gas Composition

Oxygen is needed in the flue gas to complete the reaction. The effect is significant only when the oxygen content in the flue gas is less than 2%.

If the flue gas temperature is allowed to drift too low the system tends to form suifates of ammonia which will deposit on the catalyst bed and inhibit the catalytic action.

Water vapor has the effect of shifting the equilibrium of the reaction so that with increasing water vapor, the catalyst per- fonnance is decreased.

6.2.6 AmmoniaNO, Ratio

The NO, removal efficiency increases with an increasing ammonia slip and reaches an asymptotic value after a certain quantity of ammonia slip as indicated in Figure 10. This means that there is a limit for the effect of excess ammonia in removing NO,. There is also a limit on ammonia slip usually set by local pollution authorities.

Failure to properly distribute NH, and NO, will result in selected areas of the catalyst bed not having sufficient ammonia to reduce NO, level of desired amount. In other areas, the ammonia will totally reduce the NO, and the excess ammonia will pass out the back of the catalyst as ammonia slip. Thus, NO, will not be sufficiently reduced and the ammonia slip will be higher than predicted

6.2.7 Ammonia Injection

The ammonia should be vaporized and mixed with air in the proper proportion prior to entry to the ammonia injection system. The mixture should contain less than 8% by volume to avoid lower explosive limit of 15.7% in the air. If the flue gas is used as the carrier, the SCR vendor should be referenced.

The ammonia injection should be uniform throughout the cross section of flue gas flow to insure uniform mixing of ammonia Typically, a mixing time of 0.5 to 1.0 second is provided. Alternately, mixing bafes are installed to insure uniform mixing. The concentration of ammonia at the catalyst face should not vary more than f10% RMS.




I I

I

I

I f (= LowTemperature Medium Temperature

O 100 200 300 400 Temperature (C)

Notes: T = 360C ",/NOx= 1.0

Figure &NO, Reduction versus Temperature for Different SCR Catalysts-Typical Example

O loo00 15ooo 20000

sv value (lh)

Figure +NO, Reduction Efficiency versus Catalyst Space Velocity-An Example Situation



~

STD-APIIPETRO RP 53b-ENGL L998 = 0732270 0b0853' i b38 D


a9 % U c P) U

w

.- E

.- 8

2 c U 3 U

s)"

98

96

94

92

90

88

86 O 10 20 30 60

NH, Slip(ppmvd)

Figure 1 &Typical NO, Reduction Efficiency and Ammonia Slip

6.2.8 Start-up

The manufacturer of the catalyst should supply start-up, normal operating and normal and emergency shut-down inshuc- tion and these instructions should be foilowed closely. The temperature of the catalyst bed should be raised at a predes- tined rate according to the manufacturer's recommendations.

6.2.9 Catalyst Replacement

'Ifipicaily catalyst will have 3-5 years guaranteed life. However catalyst life may be longer and is dependent on a number of parameters. It could be shorter due to any number of abnormal operating conditions. The manufacturer will dic- tate limits on operating temperature and pressure, as well as potential catalyst poisons. When the catalyst activity is depleted, another module could be added if room was left in the original design, or the existing modules could be replaced. Catalyst disposal should be in accordance with local regulations and manufacturer recommendations.

6.2.10 Catalyst Poisoning

Poisoning of catalyst leads to irreversible degradation of NO, reduction activity. Poisoning element (F', S , Pb, Zn, C1,

As, Hg) reacts with the metal catalyst surface, producing a non-reactive catalyst surface. It is mostly caused by dirty fuels. SCR specifications should contain fuel analysis, which includes trace elements.

6.2.1 1 Cataiyst Fouling

Catalyst bed pressure drop should be monitored to detect any signs of fouling. Catalyst fouling increases back pressure and reduces activity. Fouling can occur h m the following maioperation of the catalyst:

a. Burningdirty fuel. b. Sulfae deposition. c. Excessive fuel rich operation.

Operation with extremely bad combustion or smoking for long periods of time should be avoided. During such conditions unburnt hydrocarbons could deposit on the catalyst and cause performance degradation and require cleaning. Certain catalysts could oxidize the unbumt hydrocarbon, causing catalyst damage from localized hot spots. Vacuum cleaning of catalyst is recommended if fouling is

caused by surface dirt.



STD*API/PETRO RP 53b-ENGL 1778 0732270 Ob06535 5 7 9

APPENDIX A-POST-COMBUSTION NOx CONTROL DATA SHEETS



_

STD.API/PETRO R P S3b-ENGL 1778 W 0 7 3 2 2 7 0 Clb0853b 400

American Petroleum Institute JOB NO. ITEMNO. ___ PURCHASE ORDER NO.

SPECIFICATION NO. __ ~-

__ ~~

- 1

'2 '3 *4

*5 6 7 8 9

10 11 1: 1: 11

1:

1f l i 11 15 2( 21 2: 2. 24 2: 2f 27

2f 2E

3c 31 32 33 34 35 3c 37 38

3s 10

Il 12 13 44 15 16 17 48 49

50

51 52

53 54 55 56

-

_ _ ~

POST-COMBUSTION NOx CONTROL (API-RP536) SELECTIVE CATALYTIC NO. REDUCTION

DATA SHEET-CUSTOMARY UNITS

DATE ___ ~ ____ REVISION NO PAGE 1 OF 4 ~ ~ BY _ _ ~ _ ___~___.~

PROCESS DESIGN CONDITIONS

OPERATING CONDITIONS : EQUIPMENT FIRING RATE, mm Btulhr (LHV) (HHV) FLUE GAS FLOW TO BE TREATED, WET BASIS, Ibhr FLUE GAS TEMPERATURE ENTERING AIG, "F FLUE GAS TEMPERATURE ENTERING REACTOR, "F

FUEL DESCRIPTION FLUE GAS COMPOSITION:

OXYGEN (O,) (%volume, wet) NITROGEN (N,) (%volume. wet) WATER (H,O) (36 volume, wet)

CARBON DIOXIDE (CO,) (%volume, wet) ARGON (Ar) (?? volume, wet) PARTICULATES, Ibhr INLET NO,, (ppmvd) (Ib/hr) CORRECTED INLET NO, AT % O, (ppmvd) (Ibhr) INLETCO (ppmvd) (ibhr) INLET SO,, (ppmvd) (Ibhr) TRACE ELEMENTS, (ppmvd) (Ibhr):

FLUE GAS FLOW (veiticakipkiown) (horizontal) TO SCR AMMONINNO, MOLE RATIO (NHJNOJ TYPE OF AMMONIA (ANHYDROUS) (AQUEOUS) AMMONIA CONCENTRATION IN AQUEOUS SOLUTION, wt % DILUTION MEDIUM (AIR) (STEAM)

FLOW RATE, Ibhr TOTAL DILUTED AMMONIA FLOW RATE TO SCR, IWhr REQUIRED NO, REDUCTION EFFICIENCY, % SCR PERFORMANCE: POLLUTANT CONCENTRATION AT REACTOR EXIT:

CORRECTED NO. AT % O2 (ppmvd) (Ibhr) NO, I (ppmd) (ibnir)

SO, I (ppmvd) ( IbW CO, (ppmd (Imr)

SO, TO SO, OXIDATION RATE, % CALCULATED NO, REDUCTION EFFICIENCY, 36 GUARANTEED NO, REDUCTION EFFICIENCY, %

MINIMUM NORMAL MAXIMUM DESIGN

* DATA TO BE PROVIDED BY BUYER

REV

03/96

27



STD*API/PETRO RP 53b-ENGL L97d 0732290 Ob08537 347

POST-COMBUSTION NO, CONTROL (API-RP536) SELECTIVE CATALYTIC NO, REDUCTION

DATA SHEET4USTOMARY UNITS

I JOB NO. ITEM NO.

_ - ~ _~ SPECIFICATION NO

REVISION NO _ -_- DATE ~ PAGE - 2- OF 4 BY - _

~~~


1

2

3 4

5

6 7 8

9 10

11 12

13 14 15 16

17 18 19 20

21 22 23

PROCESS DESIGN CONDITIONS (CONTINUED) REV

SCR PERFORMANCE (CONTINUED) : MINIMUM NORMAL MAXIMUM DESIGN PREDICTED AMMONIA SLIP, ppmvd _ GUARANTEED AMMONIA SLIP, ppmvd PREDICTED REACTANT CONSUMPTION , Ib/hr GUARANTEED REACTANT CONSUMPTION, Ibihr CATALYST SPACE VELOCITY. l h r CATALYST AREA VELOCITY, nBr

FLUE GAS PRESSURE DROP ACROSS AIG, in H,O FLUE GAS PRESSURE DROP ACROSS REACTOR, in H,O CATALYST CATALYST TYPE

CATALYST COMPOSITION

DESIGN TEMPERATURE LIMIT, MIN /MAX, "F _ ~ INSTALLED CATALYST VOLUME, cubc feet EXPECTED CATALYST LIFE, years GUARANTEED CATALYST LIFE, years CATALYST POISONS (LIST ELEMENTS /COMPOUNDS) METHOD OF DISPOSALOF SPENTCATALYST ENVIRONMENTAL IMPACT OF SPENT CATALYST

-

_ ____- __ - _ _ ~_ ~~

~ ~ ~ - -

~ _ - _ -~~

~ _~ _ ~ __

_ - _ _ _ - _ - _ _ - __ __ _~ _ _

___ _ ~ ~~

_ _ _ _ _

_ _ _ _ _ _ _ - __ - - _ _ _~ _ _ -

_ _ _ _ _ _ _~ ~_ _. - _- ~

_ _-_ _

_ _ _~ ~~

MECHANICAL DESIGN CONDITIONS REACTOR HOUSING AND CATALYST

24

25 26

27

28 29 30 31 32

33 34

35

36 37 38

39

40 41

42 43 44

45 46 47

CATALYST

MANUFACTURERIIYPE CONFIGURATION (PLATE. HONEYCOMB. ETC)

MODULE SIZE, L x W (cmss section) x H (flow direetion), ft MODULE FRAME MATERIAL MODULE WEIGHT, Ib QUANTITY OF CATALYST MODULES NUMBER OF MODULE LAYERS/MODULES PER LAYER PROVISION FOR FUTURE LAYER OF CATALYST (YES) (NO)

REACTOR ORIENTATION (vertica!-up/down) (horizontal) SIZE (L x W x H). ft CASING MATERIALfHICKNESS, in. REFRACTORY LINING : SIDWEND WALLS

ROOF FLOOR

REACTOR HOUSING

DESIGN HOT FACE TEMPERATURE, (OF) DESIGN COLD FACE TEMPERATURE, (OF)

CATALYST LOADINWNLOADING FACILITIES REMOVABLE PANELS , NOILOCATIONSISIZES *. ACCESS EOORS, NOJLOCATIONSISIZES ** INSTRUMENT CONNECTIONS :

FLUE GAS PRESSURE-NOJLOCATION/SlZE

FLUE GAS TEMPERATURE-NO./LOCATION/SIZE

03/96

48 49 50 51 52

28

_ _ _ - -_____ _ _ _ _ SAMPLING PORTS-NO./LOCATION/SIZE REACTOR WEIGHT (WITHOUT MODULESMIITH MODULES), Ib ___ _ ~ _ _ _ _ ____ ~ -

NOTES **VENDOR TO FILLOUT DETAIL INFORMATION UNDER 'MISCELLANE0US'~PAGE 4-OF 4- _ _ __ _ _ -_ _




STD-API/PETRO RP 53b-ENGL 1958 B 0732270 0b08538 283 D

American Petroleum Institute _~ ITEMNO _ _ JOB NO

PURCHASE ORDER NO _~ ~ ~_

SPECIFICATION NO -

-

1

2

3 4 5 6

7 8 9

10 11 12 13 14 15 16 17 1s 19 20 21 22 23 24 25 26 27 2a 29 30 31

32 33 34 35 36 37 38 39 4c 41 4:

43 44 45 4e 47 4E 4s

5c 51 5: 52 54 5E

-

DATE ..______~__. ._ ~ POST-COMBUSTION NO, CONTROL (API-RP536) REVISION NO. SELECTIVE CATALYTIC NO. REDUCTION PAGE --3-. OF >-BY _ _ _ _ _ ~ _ ~

DATA SHEET-CUSTOMARY UNITS MECHANICAL DESIGN CONDITIONS (CONTINUED)

AMMONIA INJECTION SYSTEM MANIFOLD

SIZE, OD x THICKNESS, inches MATERIAL (ASTM SPECIFICATIONS AND GRADE) PIPING DESIGN CODES DESIGN TEMPERATURE (F) AND PRESSURE (pig) CORROSION ALLOWANCE, inches HYDROTEST PRESSURE, p i g TERMINAL CONNECTION, (FLANGED) (WELDED)

NO. OF BRANCHED PIPE PIPE SIZE, OD x THICKNESS, inches MATERIAL (ASTM SPECIFICATIONS AND GRADE) TOTAL NO. OF ORIFICES, ORIFICE SIZE PIPING DESIGN CODES DESIGN TEMPERATURE (F) AND PRESSURE (pig) CORROSION ALLOWANCE, inches HYDROTEST PRESSURE, pSig CONNECTION TO MANIFOLD, (FLANGED) (WELDED)

INJECTION GRID

AMMONIA CONTROL AND DILUTION SYSTEM EQUIPMEM INCLUDED ON SKID

O DILUTION AIR BLOWERS O AIRHEATER O AMMONIA VAPORIZER O MIXING VESSEUDEVICE O FILTERSSTRAINERS

INSTRUMENTATION INCLUDED: PRESSURE INDICATORS PRESSURE TRANSMITTERS PRESSURE SWITCHES FLOW INDICATORS TEMPERATURE INDICATORS TEMPERATURE TRANSMITTERS FLOW CONTROL VALVES PRESSURE REGULATORS ANALYZERS

PIPING PIPING CODE MATERIAL (ASTM SPECIFICATIONS AND GRADE) CORROSION ALLOWANCE, in

DILTION AIR BLWERS: QUANTITY MANUFACTURER AND TYPE FLOW RATE, scfh, DESIGNNORMAL STATIC PRESSURE, inches wc MOTOR MANUFACTURER HORSEPOWER

O LOCAL CONTROL PANEL O LOCAL STOP/EMERGENCY STOP SWITCHES O INTERCONNECTING PIPING & DUCTING O ELECTRICAL & INSTRUMENT WIRING O FLANGED CONNECTIONS SKID EDGE O DRAIN


03/98

29



- ~ _-

STD*API/PETRO RP 53b-ENGL 199d 111 0732270 Ob08537 LIT m

American Petroleum Institute SPECIFICATION NO -.

REVISION NO DATE -- POST-COMBUSTION NO. CONTROL (API-RP536)

- 1

2 3 4

5 6 7 8

9 IC Il

1;

I: I 4

I:

If l i I f I' !C !1 !Z

!$

!4

!e !f !i ?f !S c

1

1; E M 1: If 17

19 S It Il li I: 14 4!

If I 7 II I S 5l 5 5: 5: i s! 5(

-

SELECTIVE CATALYTIC NO. REDUCTION PAGE DATA SHEET-CUSTOMARY UNITS

MECHANICAL DESIGN CONDITIONS (CONTINUED) REV

DILLITION AIR BLOWERS (CONTINUED) POWER: VOLTAGUHERTUPHASE ISOLATION AND CHECK VALVES INCLUDED (YES) (NO) INLET AIR FILTEWSILENCER TYPE SPECIAL REQUIREMENTS

&MMONIA TANK MANUFACTURER CONFIGURATION (VERTICAUHORIZONTAL) DESIGN CODE ASME CODE STAMP (YES) (NO) DESIGN TEMPERATURE, "FAIESIGN PRESSURE, psig MATERIAL (ASTM SPECIFICATION AND GRADE) CAPACITY, gal SIZE (OD/ID x LENGTH Trr) in CORROSION ALLOWANCE, inches

MANUFACTUREFKWPE CONFIGURATION (VERTICAUHORIZONTAL) HEAT INPUT, (mmthr) (kW)/HEATING MEDIUM POWER : VOLTAGEIHERTUPHASE DESIGN CODE DESIGN TEMPERATURE, "FAIESIGN PRESSURE, psig MATERIAL (ASTM SPECIFICATION AND GRADE) CORROSION ALLOWANCE, inches VAPORIZER SIZE

AMMONIA VAPORIZER

AIR HEATER MANUFACTURER AND TYPE DESIGN HEAT INPUT, (mmthr) ( kW )/HEATING MEDIUM POWER: VOLTAGWERNPHASE SIZE

MISCELLANEOUS : PUTFORIS:

LOCATIONINO. WIDTH LENGTH/ARC

PIPE OF FLOORING, ETC.

DOORS NUMBER RCCESS DBSERVATION CATALYST REMOVAL INSPECTION - PAINTING AND GALVANIZING REQUIREMENTS

-_

ACCESS BY FROM

STAIRCRADDER GRADEIPLATFORMROCATION

LOCATION SIZE HINGED OR BOLTED

UTILTTY DATA

POWER VOLTAGEWERNPHASE INSTRUMENT POWER VOLTAGEIHERTUPHASE u n u n AIR PRESSURE NORMALIDESIGN. pslg INSTRUMENT AIR PRESSURE NORMAUDESIGN, psig STEAM PRESSURE NORMAUDESIGN, psig _ REACTANT PRESSURE NORMAUDESIGN, psig ELECTRICAL AREA CLASSIFICATION ' DATATO BE PROVIDED BY BUYER

_

- - TEMPERATURE NORMAUDESIGN, 'F - - TEMPERATURE NORMAVDESIGN, OF __._ -

__ .

03/90

30



~

STD.API/PETRO RP 53b-ENGL. 1998 W 0732270 O b 0 8 5 ~ O 931 =


POST-COMBUSTION NO, CONTROL (API-RP536) SELECTIVE CATALYTIC NO, REDUCTION

DATA SHEET-SI UNITS

ITEM NO - ~ JOBNO ~~

PURCHASE ORDER NO

SPECIFICATION NO

REVISION NO

PAGE 1 OF -4-- BY

~-

~- _ - ___ ____ - DATE . ~ _ _ _

~ _ _ _ _ _ _ ~ - 1 '2 '3 '4

'5 6 7

8 9

10

'1 1 '1 2 '1 3 '1 4

'1 5 '1 E '1 7 '1 a '1 9 '20 '21 '22 '23 '24 '25

'27 '28 '29

'30 '31

33 34 35

37

40

41

42 43 44

46 47

49

51 52 53 54 55 56

-

OPERATING CONDITIONS: EQUIPMENT FIRING RATE, MW (LHV) (HHV) FLUE GAS FLOW TO BE TREATED, WET BASIS, kg/s FLUE GAS TEMPERATURE ENTERING AIG, "C FLUE GAS TEMPERATURE ENTERING REACTOR, "C

FUEL DESCRIPTION FLUE GAS COMPOSITION:

OXYGEN (03 (%volume, wet) NITROGEN (N,) (%volume, wet) WATER (H,O) (%volume, wet) CARBON DIOXIDE (COJ (%volume, wet) ARGON (Ad (%volume, wet) PARTICULATES, kg/s INLET NO,, (ppmvd) (kgs)

INLETCO (ppmvd) (kgis) INLET SO,, (ppmvd) (kgis) TRACE ELEMENTS, (ppmvd) (kg/s):

CORRECTED INLET NO, AT% 0, (ppmvd) (kg/s)

FLUE GAS FLOW (vertical-upidown) (horizontal) TO SCR AMMONINNO, MO

api rec 536, post-combustion nox control for fired equipment

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