Page 76 - 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 53

allowed temperature difference is changed for the same set of hot
and cold streams. The larger is the value of ΔT , the smaller is the
min
possible maximum heat recovery. Specifying the minimum utility
heating, the minimum utility cooling, or the minimum temperature
difference fixes the relative position of the two Composite Curves
and hence the maximum possible amount of heat recovery. The
identified heat recovery targets are not absolute—they are relative
to the specified value of ΔT . If that value is increased, then the
min
minimum utility requirements also increase and the potential for
maximum recovery drops; see Figure 4.8.

T [°C]

200

150

100 Pinch

50
ΔT min = 10°C

0
ΔH [kW]
Q c,min = 328 Q rec = 5912 Q h,min = 1168
FIGURE 4.7 The HCC and CCC at ΔT = 10°C.
min

T [°C]

200

150
Pinch
100 ΔT min = 10°C

50
ΔT min = 20°C

0
ΔH [kW]
Q c,min = 328 Q rec = 5912 Q h,min = 1168
Q c,min = 728 Q rec = 5512 Q h,min = 1568
FIGURE 4.8 Variation of heat recovery targets with ΔT .
min