Page 465 - Advanced thermodynamics for engineers

456 CHAPTER 19 PINCH TECHNOLOGY

mC Q
Hot stream
310 302 300
3 4.28 40.7 MJ/h
210.8 MJ/h
205 132 34 MJ/h 120
H 1 2.88 244.8 MJ/h
220 6.7 MJ/h 218
2 2.88 6.7 MJ/h
Cold streams
FIGURE 19.11
Completing the heat transfer network.

mC Q

205
310 3 4.28 449.4 MJ/h
Hot streams 245 5 95 2.84 426.0 MJ/h

65
280 7
34.0 72.0 2.38 511.7 MJ/h
MJ/h MJ/h
205
H 1 95 2.88 316.8 MJ/h
6.7 511.7
210.8 MJ/h MJ/h
220 MJ/h 408.7 2 40 2.88 518.4 MJ/h
Cold streams 205 MJ/h 354.0 4 150 7.43 408.7 MJ/h

MJ/h
140
6 65 4.72 354.0 MJ/h
FIGURE 19.12
Composite diagram for heat exchange network.

The previous analysis has considered the problem in discrete parts, but it is now possible to
combine all these subsections into a composite diagram, and this is shown in Fig. 19.12.
The diagram given in Fig. 19.12 suggests that seven heat exchangers are required, but the diagram
is not the most succinct representation of the network problem, which is better displayed as shown in
Fig. 19.13, which grows directly out of the original arrangement shown in Fig. 19.4.
This case was a relatively straightforward example of a heat exchanger network in which it was
always relatively easy to match the streams, because there was always sufficient temperature differ-
ence to drive the heat transfer processes. The next example shows what happens when there is not
sufficient temperature difference to drive the heat transfer processes.