Page 247 - Sustainability in the process industry

224 Cha p te r T e n

Exchanger Hot side violation Cold side violation
E1 No Yes
E2 Yes Yes
E4 No No
E5 Yes Yes
E7 Yes No

TABLE 10.2 Exchangers That Violate the Pinch (Problem 1)

Stream T [°C] T [°C] CP [kW/°C]
in out
1 Cold 38 205 11
2 Cold 66 182 13
3 Cold 93 205 13
4 Hot 249 121 17
5 Hot 305 66 13

TABLE 10.3 Process Stream Data for Problem 2

10.1.2 Heat Pinch Technology: Second Problem

Problem 2: Task Assignment
The stream data for a process are as listed in Table 10.3. The hot utility
is steam at 200°C, the cold utility is water at 38°C, and ΔT = 24°C.
min
(a) Plot the Composite Curves (CCs) for this process.
(b) Determine Q , Q , and the Pinch temperatures.
H,min C,min
(c) Assuming that the cost of cooling water and steam is 18.13
−1
−1
and 37.78 $ kW y , plot the minimum annual cost for the
utilities as a function of ΔT in the range 51–54°C (in 1°
min
increments).
(d) Design a network that features a minimum number of units
and maximum energy recovery for ΔT = 24°C.
min
Problem 2: Solutions
Answer to (a). The Composite Curves for the process stream data are shown in
Figure 10.5.
Answer to (b). The position of the CCs in Figure 10.5 indicates that, for
ΔT = 24°C, this is a threshold problem at the cold end: Q = 0 kW. On the
min H,min
cold end there is excess of hot streams, which means that some cold utility is
required: Q = 482 kW.
C,min