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P r o c e s s I n t e g r a t i o n f o r I m p r ov i n g E n e r g y E f f i c i e n c y 81

T T

ΔH ΔH
Hot streams Cold streams
(a) (b)

FIGURE 4.44 (a) Keep hot streams hot; (b) keep cold streams cold.

modification allows for more overlap of the curves and results in
improved heat recovery. In particular, energy targets improve if the
heating and cooling demands can be shifted across the Pinch. The
principle suggests (1) shifting hot streams (cooling demands) from
below to above the Pinch and/or (2) shifting cold streams (heating
demands) from above to below the Pinch. See Chapter 12 (and
Figure 12.7) for more details.

4.5 HEN Synthesis

Most industrial-scale methods synthesize heat recovery networks
under the assumption of a steady state.
4.5.1 The Pinch Design Method

The Pinch Design Method (Linnhoff and Hindmarsh, 1983) became
popular owing to its simplicity and efficient management of
complexity. The method has evolved into a complete suite of tools for
heat recovery and design techniques for energy efficiency, including
guidelines for changing and integrating a number of energy-intensive
processes.
HEN Representation
The representation of HENs by a general process flowsheet, as in
Figure 4.45, is not always convenient. The reason is that this
representation makes it difficult to answer a number of important
questions: “Where is the Pinch?” “What is the degree of heat recovery?”
“How much cooling and heating from utilities is needed?”
The so-called conventional HEN flowsheet (Figure 4.46) offers a
small improvement. It shows only heat transfer operations and is
based on a simple convention: cold streams run horizontally and hot