Chapter 5

 PLANT DESIGN

CONTENTS:

• Chemical Engineering Plant Design

• Sequence of Steps in Developing a Project

• Plant Location

• Plant Layout

• Storage of materials

• Materials Handling

• Utilities

The general term plant designplant design includes all engineering aspects involved in the development of either a new, modified, or expanded industrial plant. In this development, the chemical engineer will be making economic evaluations of new processes, designing individual pieces of equipment, or developing a plant layout. Because of these many design duties, the chemical engineer is many times referred to as a design engineerdesign engineer.

Chemical Engineering Plant Design

On the other hand, a chemical engineer specializing in the economic aspects of the design is often referred to as a cost engineercost engineer. The term process engineeringprocess engineering is used in connection with economic evaluation and general economic analyses of industrial processes, while process designprocess design refers to the actual design of the equipment and facilities necessary for carrying out the process. Similarly, the meaning of plant designplant design is limited by some engineers to items related directly to the complete plant, such as plant layout, general service facilities, and plant location.

Chemical Engineering Plant Design Cont’d

Sequence of steps in developing a project

Time sequence

Project Steps

Process identification

Laboratory scale process research

Bench scale investigations

Preliminary economic evaluation

Process development

Mass and energy balance

Detailed process design

Site selection

Refined economic evaluation

Design Fixed

Detailed economic evaluation

Engineering flow scheme

Basic design

Detailed construction plan

Detail design

Procurement

Construction

Startup

Plant Location

The geographical location of any industrial plant has strong influence on the success of the project. Considerable care must be exercised in selecting the plant site, and many different factors must be considered. Primarily, the plant should be located where the minimum cost of production and distribution can be obtained, but other factors, such as room for expansion and safe living conditions for plant operators as well as the surrounding community, are also important.

Plant Location Factors

1. Raw materials availability

2. Markets

3. Energy availability

4. Climate conditions

5. Transportation facilities

6. Water supply

7. Waste disposal

8. Labor supply

9. Taxation and legal restrictions

10. Site Characteristics

11. Flood and fire protection

12. Community factors

Individual risk: --- Risk ContoursPLANT LOCATION AND RISK:ISO-risk contours represent the geographical variation of the risk for a hypothetical individual who is positioned at a pacticular location for 24 hrs/day, 365 days / year

LSIR: Location specific individual risk

Plant Layout

After the process flow diagrams are completed and before detailed piping, structural, and electrical design can begin, the layout of process units in a plant and the equipment within these process units must be planned. This layout can play an important part in determining construction and manufacturing costs, and thus must be planned carefully with attention being given to future problems that may arise. Since each plant differs in many ways and no two plant sites are exactly alike, there is no one ideal plant layout. However, proper layout in each case will include arrangement of processing areas, storage areas, and handling areas in efficient coordination and with regard to such factors as:

Plant Layout Cont’d

1. New site development or addition to previously developed site

2. Type and quantity of products to be produced

3. Type of process and product control

4. Operational convenience and accessibility

5. Economic distribution of utilities and services

6. Type of buildings and building-code requirements

7. Health and safety considerations

8. Waste-disposal requirements

9. Auxiliary equipment

10. Space available and space required

11. Roads and railroads

12. Possible future expansion

Typical Master Plot Plan

ISCO Chemical Company Ferrous Sulfate Recovery Plant Master Plot Plan: Scale ½”=10 ft

Picking-plant area (extend lot 200 ft east )

Future Process Area

x x x x x x x x x x x x x x x x x x x x x

x x x x x x x x x x x x x x x x x x x x x x x x x

N

Landscaped Area

Parking Area

Railroad siding

Future Storage

AreaPower-point

Area

Loading

Packing and

shipping area

ReservoirNeutralizing tanks

Chem

ical

pro

cess

ing

Are

a

Roadw

ay

office

shop

toilets

x

x

x

x

x

x

x

x

x x x

x

x

x

x

List of plant units in a typical layout

. Process units·     Tank farms·     Loading and unloading facilities·     Flares·     Power, boilers and incinerators·     Cooling towers·     Substations, large electrical switch yards·     Central control houses·     Warehouses·     Analytical laboratories·     Incoming utility metering and block systems·     Fire hoses, fixed monitors, reservoirs and emergency fire pumps·     Waste treatment areas·     Maintenance buildings and areas·     Administrative buildings

Storage

Adequate storage facilities for raw materials, intermediate products, final products, recycle materials, off-grade materials, and fuels are essential to the operation of a process plant. A supply of raw materials permits operation of the process plant regardless of temporary procurement or delivery difficulties. Storage of intermediate products may be necessary during plant shutdown for emergency repairs while storage of final products makes it possible to supply the customer even during a plant difficulty or unforeseen shutdown. An additional need for adequate storage is often encountered when it is necessary to meet seasonal demands from steady production.

Storage Cont’d

Bulk storage of liquids is generally handled by closed spherical or cylindrical tanks to prevent the escape of volatiles and minimize contamination. Liquids with vapor pressures above atmospheric must be stored in vapor-tight tanks capable of withstanding internal pressure. If flammable liquids are stored in vented tanks, flame arresters must be installed in all openings except connections made below the liquid level.

Storage Cont’d

Gases are stored at atmospheric pressure in wet- or dry-seal gas holders. The wet-gas holder maintains a liquid seal of water or oil between the top movable inside tank and the stationary outside tank. In the dry-seal holder the seal between the two tanks is made by means of a flexible rubber or plastic curtain.

 

Solid products and raw materials are either stored in weather-tight tanks with sloping floors or in outdoor bins and mounds. Solid products are often packed directly in bags, sacks, or drums.

Vertical tank installation

Materials Handling

Materials-handling equipment is logically divided into continuous and batch types, and into classes for the handling of liquids, solids, and gases. Liquids and gases are handled by means of pumps and blowers; in pipes, flumes, and ducts; and in containers such as drums, cylinders, and tank cars. Solids may be handled by conveyors, bucket elevators, chutes, lift trucks, and pneumatic systems. The selection of materials-handling equipment depends upon the cost and the work to be done. Factors that must be considered in selecting such equipment include:

Materials Handling Cont’d

1. Chemical and physical nature of material being handled

2. Type and distance of movement of material

3. Quantity of material to be moved per unit time

4. Nature of feed and discharge from materials-handling equipment

5. Continuous or intermittent nature of materials handling

Perry

pumping

Rotary blower

Vacuum pump selection

Perry

Belt conveyors

Bucket elevator

Utilities

1. In the chemical industries, power is supplied primarily in the form of electrical energy. Agitators, pumps, blowers, compressors, and similar equipment are usually operated by electric motors.

2. When a design engineer is setting up the specifications for a new plant, a decision must be made on whether to use purchased power or have the plant set up its own power unit. It may be possible to obtain steam for processing and heating as a by-product from the self-generation of electricity, and this factor may influence the final decision.

3. Power can be transmitted in various forms, such as mechanical energy, electrical energy, heat energy, and pressure energy. The engineer should recognize the different methods for transmitting power and must choose the ones best suited to the particular process under development.

Utilities Cont’d

4. Steam is generated from whatever fuel is the cheapest, usually at pressures of 450 psig (3100 kPa) ore more, expanded through turbines or other prime movers to generate the necessary plant power, and the exhaust steam is used in the process as heat. The quantity of steam used in a process depends upon the thermal requirements, plus the mechanical power needs, if such a power is generated in the plant.

5. Water for industrial purposes can be obtained from one of two general sources: the plant’s own source or a municipal supply. If the demands for water are large, it is more economical for the plant to provide its own water source. Such a supply may be obtained from ground water or surface water sources. Before a company agrees to go ahead with any new project, it must ensure itself of a sufficient supply of water for all industrial, sanitary, and safety demands, both present and future.

List of utilities

• Compressed Air: Plant and Instrument • Natural Gas • Fire Protection • City and Process Water • Chilled Water • Wastewater • Welder Water • Hot Water Heating • Steam and Condensate • Fuel Handling: Gasoline, Diesel, … • Cooling and Tower Water • Motor/Hydraulic/Cutting Oil • Process Gases: N, H2 and CO2

Tube boiler