Page 152 - Process Equipment and Plant Design Principles and Practices by Subhabrata Ray Gargi Das

5.10 Design illustration 149

Problem 5.2. Thermal design of a petrochemical process with 2 cold and 3 hot streams and no phase
change needs to be optimised for minimum utility consumption. The starting and target temperatures
of the streams as well as the product of their specific heat and flow rate (CP) are shown in Table P5.2A.
Referring to Table 5.2, we consider DT min ¼10 C.

Solution

Table P5.2A Stream specification table.
TS [ TT [

TSLðDT min =2Þ TTLðDT min =2Þ
for hot stream for hot stream
TS [ TT [

TSDðDT min =2Þ TTDðDT min =2Þ
Stream TS TT CP (kW/ DH for cold stream for cold stream
no. Type ( C) ( C) C) (kW) ( C) ( C)

1 Cold 140 230 0.2 18 145 235
2 Cold 20 180 0.8 128 25 185
4 Hot 300 230 0.2 14 295 225
5 Hot 300 40 0.3 78 295 35
6 Hot 200 30 0.1 17 195 25
Hot and cold utilities are available at temperatures above the highest and the lowest temperatures in the process.

Hot and cold utilities are available at temperatures above the highest and the lowest temperatures in
the process.

DT min ¼ 10 C

Temperature interval heat balance and problem table cascade is shown for this case in Table P5.2B.
The pinch temperature based on the cascade is at the lowest temperature (25 C) of the cascade,

indicative of a threshold problem requiring only a hot section design.