Page 448 - Design and Operation of Heat Exchangers and their Networks

CHAPTER 9

Optimal control process of heat

exchanger networks

a
b
Wilfried Roetzel , Xing Luo , Dezhen Chen c
a
Institute of Thermodynamics, Helmut Schmidt University/University of the Federal Armed Forces Hamburg,
Hamburg, Germany
b
Institute of Thermodynamics, Gottfried Wilhelm Leibniz University Hannover, Hannover, Germany
c
Institute of Thermal Energy and Environmental Engineering, Tongji University, Shanghai, China

The design of heat exchanger networks (HEN) has been discussed in
Chapter 6. Here, we will discuss the topic of the automatic control problem
for the operation of HEN. Compared with synthesis of nominal and flexible
HENs, less effort has been dedicated to find methods for the operation of a
HEN and its control. The concern on operation and control arises when they
have to deal with significant changes in the operating conditions such as dis-
turbances of inlet parameters and operation state changeover. A HEN is flex-
ible when it is capable of absorbing long-term variations on inlet stream
conditions or having the capability of changing stream temperature targets
significantly. This concept has been discussed by Floudas and Grossmann
(1986), Calandranis and Stephanopoulos (1986), Kotjabasakis and Linnhoff
(1986),and Galli and Cerda (1991). On the other hand, controllability is asso-
ciated with short-term perturbations, stability, and safe transitions from one
operating point to another. Morari (1983) used a term “resilience” to
describe the ability of a system to move fast or smoothly from one operating
condition to another, including start-up and shutdown, and to deal effec-
tively with disturbances. He also divided the problems of process systems into
two topics: static resilience and dynamic resilience. The static resilience refers
to the ability of a system to handle different feedstocks, product specifications,
operating conditions, etc. in the steady state, while the dynamic resilience is
concerned with the transient behavior in the event of a changeover or when
the disturbances enter the plant. Therefore, according to Morari’s definition,
resilience involves all the meaning of flexibility, operability, and controllabil-
ity. Therefore, a resilient synthesis means that the flexibility, operability, and
controllability of a HEN will be considered simultaneously.

Design and Operation of Heat Exchangers and their Networks © 2020 Elsevier Inc.
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