Page 188 - Sustainability in the Process Industry Integration and Optimization

CHAPTER 8

Combined

Process Integration

and Optimization

8.1 The Role of Optimization in Process Synthesis

Process Integration (PI), as defined in Chapter 2, is a family of
optimization methodologies for reducing resource or emissions
intensity of the analyzed processes and Total Sites. As such, it is
tightly related to optimization. In fact, PI and optimization
complement each other by their functionality. First, PI sets out the
strategy for designing and/or operating industrial processes. This
gives engineers some direction regarding how processes can be
designed or changed, answering the questions of “where we can go?”
and “what is to be done?” in order to achieve the business goals at
hand. In addition, PI provides quantitative targets for designers and
engineers; it does this by exploiting the physical (in the case of Heat
Integration, thermodynamical) background to answer the question
“how much is it possible to improve or achieve?” The targets in most
cases are upper bounds on the process performance or lower bounds
on the extent of resource use or emissions. In many cases the targets
are practically achievable, as in the case of designing Heat Exchanger
Networks (HENs) or water networks. The most obvious example is
heat recovery targets established by the Pinch point when analyzing
HEN problems. Since they are based on the Second Law of
Thermodynamics, it is proven that better heat recovery cannot be
achieved by any feasible system. If a realistic value for ΔT is
min
specified for their evaluation, the targets will be also practically
achievable. Of course, the additional factor of the capital costs for
implementing the heat exchangers generally tends to shift the
economic optimum of the designed HEN away from the maximum
recovery network.

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