Page 68 - Sustainability in the Process Industry Integration and Optimization

CHAPTER 4

Process Integration

for Improving

Energy Efficiency

eat recovery is widely applied in industrial processes and
has an extensive historical record. However, systematic
Hmethods for performing heat recovery are relatively new
when compared with the age of modern industry.

4.1 Introduction to Heat Exchange and Heat Recovery

In industry, large amounts of thermal energy are used to perform
heating. Examples of this can be found in crude oil preheating before
distillation, preheating of feed flows to chemical reactors, and heat
addition to carry out endothermic chemical reactions. Similarly,
some processes—such as condensation, exothermal chemical
reactions, and product finalization—require that heat be extracted,
which results in process cooling. There are several options for utility
heating; these include steam, hot mineral oils, and direct fired
heating. Steam is the most prevalent option because of its high
specific heating value in the form of latent heat. Utility cooling
options include water (used for moderate-temperature cooling when
water is available), air (used when water is scarce or not economical
to use), and refrigeration (when subambient cooling is needed). Heat
recovery can be used to provide either heating or cooling to processes.
Heat recovery may take various forms: transferring heat between
process streams, generating steam from higher-temperature process
waste heat, and preheating (e.g., air for a furnace, air or feed water for
a boiler using waste heat).
Heat transfer takes place in heat exchangers, which can employ
either direct mixing or indirect heat transfer via a wall. Direct heat
exchange is also referred to as nonisothermal mixing because the
temperatures of the mixed streams are different. Mixing heat
exchangers are efficient at transferring heat and usually have low
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