Page 109 - Sustainability in the Process Industry Integration and Optimization

86 Cha p te r F o u r

CP
PINCH [kW/°C] T
CP HOT > CP COLD
150°C 250°C
2 15
PINCH 4
150°C 200°C
4 25
HEAT
EXCHANGER ΔT min
MATCH 1
140°C 180°C
1 20
ΔH
Temperature difference smaller
140°C 230°C
3 30 than ΔT min
INFEASIBLE!
FIGURE 4.51 An infeasible heat exchanger match above the Pinch.

PINCH CP
[kW/ºC]
T
150ºC 250ºC
2 15
PINCH
4
150ºC 200ºC
4 25
HEAT
EXCHANGER 3
MATCH
140ºC 180ºC ΔT min ΔH
1 20 The match is feasible
140ºC 230ºC
3 30

FIGURE 4.52 A feasible heat exchanger match above the Pinch.

temperature profiles in the direction away from the Pinch. Thus, the
rule above the Pinch may be expressed as follows:

CP hot stream d CP cold stream (4.9)

The logic below the Pinch is symmetric. This part of the design is
a net heat source, which means that the heating requirements of the
cold streams have to be satisfied by matching up with hot streams.
The same type of reasoning as before yields the following requirement:
the CP value of a cold stream must not be greater than the CP value