Unit 3 Typical Activities of Chemical Engineers-3

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2. Design
Based on the experience and data obtained in the laboratory and the pilot plant, a team of engineers is assembled to design the commercial plant. The chemical engineer’s job is to specify all process flow rates and conditions, equipment types and sizes, materials of construction, process configurations, control systems, safety systems, environmental protection systems, and other relevant specifications. It is an enormous responsibility.

The design stage is really where the big bucks are spent. One typical chemical process might require a capital investment of $50 to $100 million. That’s a lot of bread! And the chemical engineer is the one who has to make many of the decisions. When you find yourself in that position, you will be glad that you studied as hard as you did (we hope) so that you can bring the best possible tools and minds to bear on the problems.

The product of the design stage is a lot of paper:
(1) Flow sheets are diagrams showing all the equipment schematically, with all streams labeled and their conditions specified (flow rate, temperature, pressure, composition, viscosity, density, etc.)

(2) P and I (Piping and Instrumentation) Drawings are drawings showing all pieces of equipment (including sizes, nozzle locations, and materials), all piping (including sizes, materials, and valves), all instrumentation (including locations and types of sensors, control valves, and controllers), and all safety systems (including safety valve and rupture disk locations and sizes, flare lines, and safe operating conditions).

(3) Equipment specification Sheets are sheets of detailed information on all the equipment precise dimensions, performance criteria, materials of construction, corrosion allowances, operating temperatures, and pressures, maximum and minimum flow rates, and the like. These “spec sheets” are sent to the equipment manufacturers for price bids and then for building the equipment.