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54 Cha p te r F o u r
The appropriate value for ΔT is determined by economic trade-
min
offs. Increasing ΔT results in larger minimum utility demands and
min
increased energy costs; choosing a higher value reflects the need to
reduce heat transfer area and its corresponding investment cost.
Conversely, if ΔT is reduced then utility costs go down but
min
investment costs go up. This trade-off is illustrated in Figure 4.9.
4.3.2 The Heat Recovery Pinch
The heat recovery Pinch has important implications for the HEN
being designed. As illustrated in Figure 4.10, the Pinch sets the
absolute limits for heat recovery within the process.
COST
Total
Energy
Capital
1 2
Optimum ΔT
MIN
FIGURE 4.9 Trade-off between investment and energy costs as a function of
ΔT .
min
T Q H,min
PINCH
Q
c,min
ΔH
FIGURE 4.10 Limits for process heat recovery set by the Pinch.
