Page 84 - Sustainability in the Process Industry Integration and Optimization

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 61

utility type (hot or cold) are identified over the variation range; in
contrast, pinched problems require both hot and cold utilities over
this range. When synthesizing HENs for threshold problems, one
can distinguish between two subtypes (see Figure 4.16):

1. Low-threshold ΔT : Problems of this type should be treated
min
exactly as Pinch-type problems.
2. High-threshold ΔT : For these problems, it is first necessary
min
to satisfy the required temperature for the no-utility end
before proceeding with the remaining design (using the tick-
off heuristic; see Figure 4.53).

4.3.5 Multiple Utilities Targeting

Utility Placement: Grand Composite Curve
In many cases, more than one hot and one cold utility are available
for providing the external heating and cooling requirements after
energy recovery and it is necessary to find and evaluate the

(a) T ST
Utilities
[MW]

CW
ST
ΔT min = 10°C

10°C ΔT min CW
ΔH [MW]
Low Threshold ΔT min
(b) T
ST
Utilities
[MW]

ST

CW
ΔT min = 10°C

10°C ΔT min ΔH [MW]
High Threshold ΔT min

FIGURE 4.16 Threshold problems.