Page 43 - Sustainability in the process industry

20 Cha p te r T w o

2.9 The Role of PI in Making Industry Sustainable
Sustainability in the design and operation of industrial processes is
becoming a key issue of process systems engineering. There are MPR
tools for designing chemical processes that minimize costs (and thus
maximize profits). These MPR formulations typically are highly
complex; therefore, in practical applications, the original problem is
usually decomposed into smaller problems that are solved
sequentially.
There are several definitions of sustainability. It can be defined as
the capacity to sustain the viability of a given system. In this context,
sustainable development implies that current actions should not harm
future generations and that measurable indicators are needed to
ensure compliance. For industrial processes, the relevant indicators
are the rates of resource intake and effluent emissions. These factors
are usually expressed in terms of “footprints” (De Benedetto and
Klemeš, 2009)—for example, the carbon footprint (CFP) and/or water
footprint (WFP) of a process. The sustainability of an industrial process
depends on minimizing these footprints. For synthesis and design
problems, the measured indicators should apply to the proposed
system’s complete life cycle as part of a life-cycle assessment (LCA).
In short, PI has a direct impact on improving the sustainability
of a given industrial process. All PI techniques are geared toward
reducing the intake of resources and minimizing the release of
harmful effluents, goals that are directly related to the corresponding
footprints. Hence, employing PI and approaching the targeted
values will help minimize those footprints.
Footprint considerations, however, are only part of an industry’s
ultimate indicator—that is, its economic performance. This metric
takes the form of either cost or profit, depending on the selected system
boundaries. Thus, no matter how environmentally attractive a given
project may be, it will probably not be implemented unless doing so is
economically feasible. There are several ways to merge the objectives
of sustainability and profitability. The two most popular are
(1) expressing footprints in strictly economic terms and then folding
them into the cost or profit objective function; and (2) employing
multiobjective optimization, whereby footprint and economic
indicators are evaluated in parallel as objectives to be achieved.

2.10 Examples of Applied Process Integration
In this section, four examples illustrate the potential of PI to reduce
not only resource demand but also operational and capital costs.
The problem areas vary widely, yet in each case the application of
the PI techniques yields significant benefits. Only the main problem
points and outcomes are described here; see Chapter 11 for more
details.