Page 139 - Chemical engineering design

FUNDAMENTALS OF ENERGY BALANCES
Matching streams 1 and 4 and transferring the full amount of heat required to bring
stream 1 to the pinch temperature gives: 119
H ex D CP T s T pinch
H ex D 3.0 180 90 D 270 kW
This will also satisfy the heat load required to bring stream 4 to its target temperature:
H ex D 4.5 140 80 D 270 kW
2. Stream 2 can be matched with stream 3, whilst satisfying the heat capacity restriction.
Transferring the full amount to bring stream 3 to the pinch temperature:
H ex D 1.0 150 90 D 60 kW

3. The heat required to bring stream 3 to its target temperature, from the pinch temper-
ature, is:
H D 2.0 135 80 D 110 kW
So a heater will have to be included to provide the remaining heat load:
H hot D 110 60 D 50 kW

This checks with the value given by the problem table, Figure 3.23b.
The proposed network design above the pinch is shown in Figure 3.26.

CP
kW/°C
90°C 80°C
180°C 60°C 3.0
1
150°C 30°C
1.0
2

135°C 20°C
2.0
3
140°C 50 kW 60 kW 80°C
4.5
4
270 kW Pinch
Figure 3.26. Network design above pinch

Network design below the pinch
CP hot ½ CP cold
Ž
4. Stream 4 is at the pinch temperature, T s D 80 C.
5. A match between stream 1 and 3 adjacent to the pinch will satisfy the heat capacity
restriction but not one between streams 2 and 3. So 1 is matched with 3 transferring the
full amount to bring stream 1 to its target temperature; transferring:
H ex D 3.0 90 60 D 90 kW