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Process design in the field of chemical engineering is the design of industrial processes to produce desired physical and/or chemical transformation of substance. Process design is central to chemical engineering and it integrates most of the basic components of that field. The design starts at a conceptual level and ends in the form of fabrication and construction specifications and plans.

Process design can be the design of new facilities or it can be the modification or expansion of existing facilities.

Although chemical engineering is involved in the design of many equipment items used in industrial chemical processes, equipment design is not usually included in process design.

Documentation

Process design documents serve to define the design and they ensure that the design components fit together. They are useful in communicating ideas and plans to other engineers involved with the design, to external regulatory agencies, to equipment vendors and to construction contractors.

In order of increasing detail, process design documents include:

• Block Flow Diagrams (BFD): Very simple diagrams composed of rectangles and lines indicating major material or energy flows.

• Process Flow Diagrams (PFD's): Typically more complex diagrams of major unit operations as well as flow lines. They usually include a material balance, and sometimes an energy balance, showing typical or design flow rates, key stream compositions, and the pressures and temperatures of the key stream and equipment items.

• Piping and Instrumentation Diagrams (P&ID's): Diagrams showing each and every pipeline with piping class (carbon steel or stainless steel) and pipe size (diameter). They also show valving along with instrument locations and process control schemes.

• Specifications: Written design requirements of all major equipment items.

Process designers also typically write operating manuals on how to start-up, operate and shut-down the process.

After construction and initial start-up operation of the process facility, the process design documents are retained by the facility management and operating personnel for future reference as may be needed. The documents are also useful when facility modifications or expansions are planned.

Design Considerations

Designs have objectives and constraints, and even a simple process requires a trade-off among such factors.

Objectives that a design may strive to include:

• Throughput rate
• Process yield
• Product purity

Constraints include:

• Capital cost
• Available space
• Safety concerns
• Environmental impact and projected effluents and emissions
• Waste production
• Operating and maintenance costs

Other factors that designers may include are:

• Reliability
• Redundancy
• Flexibility
• Anticipated variability in feedstock and allowable variability in product.

Sources of Design Information

Designers usually do not start from scratch, especially for complex projects. Often the engineers have pilot plant data available or data from full-scale operating facilities. Other sources of information include proprietary design criteria provided by process licensors, published scientific data, laboratory experiments, and input.

Computer Help

The advent of low cost powerful computers has aided complex mathematical simulation of processes, and simulation software is often used by design engineers. Simulations can identify weaknesses in designs and allow engineers to choose better alternatives.

However, engineers still rely on experience, logic and intuition when designing a process. Human creativity is still an important element in complex designs.

References

+++++++++++++++++++++++++++++++++++++++++++++++++ Related Articles subpage

• Chemical engineering
• Chemical plant
• Process simulation
• Environmental engineering
• List of Chemical Process Simulators
• List of Dynamic Process Simulators
• Process engineering
• Process safety
• Unit operation
• Unit process

Bibliography subpage

• Kister, Henry Z. (1992). Distillation Design, 1st Edition. McGraw-Hill. ISBN 0-07-034909-6. 
• Perry, Robert H. and Green, Don W. (1984). Perry's Chemical Engineers' Handbook, 6th Edition. McGraw-Hill. ISBN 0-07-049479-7. 
• Bird, R.B., Stewart, W.E. and Lightfoot, E.N. (August 2001). Transport Phenomena, Second Edition. John Wiley & Sons. ISBN 0-471-41077-2. 
• McCabe, W., Smith, J. and Harriott, P. (2004). Unit Operations of Chemical Engineering, 7th Edition. McGraw Hill. ISBN 0-07-284823-5. 
• Seader, J. D., and Henley, Ernest J. (1998). Separation Process Principles. New York: Wiley. ISBN 0-471-58626-9. 
• Chopey, Nicholas P. (2004). Handbook of Chemical Engineering Calculations, 3rdEdition. McGraw-Hill. ISBN 0071362622. 
• Himmelbau, David M. (1996). Basic Principles and Calculations in Chemical Engineering, 6th Edition. Prentice-Hall. ISBN 0133057984. 
• Editors: Jacqueline I. Kroschwitz and Arza Seidel (2004). Kirk-Othmer Encyclopedia of Chemical Technology, 5th Edition. Hoboken, NJ: Wiley-Interscience. ISBN 0-471-48810-0. 
• King, C.J. (1980). Separation Processes, 2nd. McGraw Hill. ISBN 0-07-034612-7. 
• Peters, M. S., and Timmerhaus K. D. (1991). Plant Design and Economics for Chemical Engineers, 4th edition. McGraw Hill. ISBN 0-07-100871-3. 
• J. M. Smith, H. C. Van Ness and M. M. Abott (2001). Introduction to Chemical Engineering Thermodynamics, 6th edition. McGraw Hill. ISBN 0-07-240296-2. 

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