Page 140 - Academic Press Encyclopedia of Physical Science and Technology 3rd Chemical Engineering

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Encyclopedia of Physical Science and Technology EN002G-100 May 19, 2001 18:49

762 Chemical Process Design, Simulation, Optimization, and Operation

FIGURE 7 Total design project. (Adapted from Westerberg et al., 1979.)

operability and controllability improvements come at the design is iterative in nature, such that considerations of
cost of additional equipment and modifications to existing operability and dynamic controllability (through numeri-
process designs. Capital costs are weighed against oper- cal simulation studies) may cause the process designer to
ating costs and other losses that result from nonflexible modify the design. This in turn leads to processes that are
process designs. capable of lower variability and hence improved product
A primary focus in process design is to produce de- quality as measured by process capability indices. Pro-
signs that have good overall operability characteristics, as cess variability is minimized/distributed among all the
determined by safety and environmental considerations, unit operations (not just in the “end of the process”),
low product variability, low operating costs, and ease of and the resulting design is robust to deficiencies that may
startup/shutdown. The process design and control system occur (heat-exchanger fouling, loss of equipment, etc.).