Page 146 - Chemical engineering design

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CHEMICAL ENGINEERING
So at the pinch hot streams will be at:
Ž
90 C 10 D 100 C
and the cold at:
Ž
90 10 D 80 C
To design the network for maximum energy recovery: start at the pinch and match
streams following the rules on stream heat capacities for matches adjacent to the pinch.
Where a match is made: transfer the maximum amount of heat.
The proposed network is shown in Figure 3.31.

100°C 80°C
3200 kW 1800 kW 600 kW
180°C 40°C
1
1500 kW 1200 kW
150°C 60°C
2
1300 kW
180°C
30°C
3
160°C 80°C
4
1600 kW Pinch

Figure 3.31. Network, example 3.17

The methodology followed in devising this network was:

Above pinch

1. CP hot CP cold
2. Can match stream 1 and 2 with stream 3 but not with stream 4.
3. Check the heat available in bringing the hot streams to the pinch temperature.
stream 1 H D 40.0 180 100 D 3200 kW
stream 2 H D 30.0 150 100 D 1500 kW
4. Check the heat required to bring the cold streams from the pinch temperature to
their target temperatures.
stream 3 H D 60.0 180 80 D 6000 kW
stream 4 H D 20.0 160 80 D 1600 kW
5. Match stream 1 with 3 and transfer 3200 kW, that satisfies (ticks off) stream 1.
6. Match stream 2 with 3 and transfer 1500 kW, that ticks off stream 2.
7. Include a heater on stream 3 to provide the balance of the heat required:

H hot D 6000 4700 D 1300 kW
8. Include a heater on stream 4 to provide heat load required, 1600 kW.