Chemical Engineering Plant Design

Lek WanthaLecture 01

What is Chemical Process?

A chemical process is a process which raw material are transformed or converted into desired product.

Strategies for Chemical Product Design

• Need• Ideas• Selection•Manufacture

Need for Process Design

• To produce desired product• To convert a purchased raw material• To convert a waste by-product to a valuable product• To find a new way of producing an existing product• To exploit a new technology

What is a process design?

• Process design establishes the sequence of chemical and physical operations; operating conditions; the duties; major specifications and materials of construction of all process equipment; the general arrangement of equipment needed to ensure proper functioning of plant; line sizes; and principal instrument.

Plant & Process

General Structure of Plant

Process ProductStorage

Raw MaterialStorage

Utilities

• It is important to keep in mind that design problems are open ended and may have many solutions that are attractive and near optimal.

• No two designers design a complex process

following exactly the same steps.

Process Design Constraints

• When considering possible ways of achieving the objective, the designer will be constrained by many factors which will narrow down the number of possible designs; but, there will rarely be just one possible solution to the problem, just one design.

Process Design Constraints

• Several alternative ways of meeting the objective will normally be possible, even several best designs, depending on the nature of the constraints.

Constraints

• External constraints - the constraints that are outside the designer’s influence.

- Physical laws- Resources- Safety regulations- Economics- Standard & Codes- Government controls

Constraints

• Internal constraints - the constraints that are capable of relaxation by the designer as part of his general strategy in seeking the best design.

- Choice of process/unit operations/process conditions/nature of construction/etc.

Steps in Designing Chemical Processes

• Assess Primitive Problem• Survey Literature• Process Creation• Development of Base Case• Detailed Process Synthesis Using Algorithmic Method• Plantwide Controllability Assessment• Detailed Design, Equipment Sizing and Cost Estimation, Profitability Analysis, and Optimization.

Steps in Designing Chemical Processes

• Written Process Design Report and Oral Presentation• Final Design, Construction, Start-up, and Operation

The “Process” of Design

• Conception and Definition• Flow Sheet Development• Design of Equipment• Economic Analysis• Optimization• Reporting

Unit Operations for Chemical Process

• Chemical reaction• Separation of chemicals• Phase separation• Change of temperature• Change of pressure• Change of phase• Mixing and splitting of streams or branches

Chemical Reactors

• Stirred Tank• Tubular Flow Reactors• Gas-Liquid Reactions• Fixed Bed Reactors• Moving Bed Reactors• Fluidized Bed Reactors• Kiln and Hearth Furnaces

Solid-Solid Separations

• Screening (sieving)• Liquid-solid cyclones• Hydroseparators and sizers (classifier)• Tables• Classifying centrifuges• Flotation separators• Magnetic separator• Electrostatic separators

Liquid-Solid Separations

• Thickeners and Clarifiers• Filtrations• Centrifuges• Hydrocyclones (liquid-cyclone)• Pressing (expression)• Solid drying

Gas-Solid Separations

• Gravity settle• Impingment separators• Centrifugal separators (cyclones)• Filters• Wet scrubbers• Electrostatic precipitators

Gas-Solid Separations

• Gravity settle• Impingment separators• Centrifugal separators (cyclones)• Filters• Wet scrubbers• Electrostatic precipitators• Phase separator (Flash Drum)

Liquid-Liquid Separations

• Decanters (settlers)• Plate separators• Coalesces• Centrifugal separators

Separation of Dissolved Solids

• Evaporators• Crystallization

Separation of Dissolved Liquids

• Distillation• Solvent extraction (liquid-liquid extraction)• Crystallization• Adsorption• Membrane Separation

Heat Transfer Equipment

• Double-pipe Heat Exchangers• Shell-Tube Heat Exchangers• Plate Heat Exchangers• Direct-contact Heat Exchangers• Air-cooled Exchangers• Fired Heaters (Furnaces and Boilers)• Condensers• Reboilers and Vaporisers

Change of Pressure

• Increase of Pressure- Pump- Compressor

• Decrease of Pressure- Vale- Expander

Mixing and Agitation

• Stirred Tank• Suspension of Solids• Gas Dispersion• In-Line-Blenders and Mixers

Transfer of Solids

• Equipment for Gas Transport- Fans- Compressors

• Equipment for Liquid Transport- Pump

Fluid Transport Equipment

• Slurry Transport• Pneumatic Conveying• Mechanical Conveyors and Elevators

- Screw Conveyors- Belt Conveyors- Bucket Elevators and Carriers

• Solids Feeders

Utilities

• Steam• Heat Transfer Fluids• Refrigerants• Cooling Water• Cooling Air• Fuel• Compressed Air• Instrument Air• Electricity