Page 107 - Sustainability in the Process Industry Integration and Optimization

84 Cha p te r F o u r

2. Identification of the heat recovery targets and the heat
recovery Pinch, as explained in Section 4.3.
3. Synthesis
4. Evolution of the HEN topology

The first two steps were discussed in previous sections. The synthesis
step begins by dividing the problem at the Pinch and then positioning
the process streams as shown in Figure 4.49.
The engineering practice suggests starting the network design
from the Pinch (the most restricted part of the design owing to
temperature differences approaching ΔT ) and then to place
min
heat exchanger matches while moving away from the Pinch
(Figure 4.50). When placing matches, several rules have to be followed
in order to obtain a network that minimizes utility use: (1) no
exchanger may have a temperature difference smaller than ΔT ;
min

No cross-Pinch heat transfer A cross-Pinch heat transfer match

C

C

H

H
FIGURE 4.48 The grid diagram and implications of the Pinch.

CP
[kW/°C]
PINCH
40°C 150°C 250°C
2 15
80°C 150°C 200°C
4 25

20°C 140°C 180°C
1 20
140°C 230°C
3 30

Q Hmin = 750 kW Q Cmin = 1000 kW
FIGURE 4.49 Dividing at the Pinch for the streams in Table 4.2.