The concepts of heat-exchanger networks and pinch technology are discussed. When designing these networks to recover process heat, it is often necessary to have a close temperature approach between process streams, which leads to large heat exchangers with multiple shells. Multiple-shell heat exchangers are often constructed from sets of 1−2 shell-and-tube exchangers stacked together. For costing considerations, the cost of the multiple-shell heat exchanger is best estimated as a number of smaller 1−2 exchangers. Consider a heat exchanger constructed of carbon steel and designed to withstand a pressure of 20 barg in both the shell and tube sides. This equipment has a heat exchange area of 400 m². 

Do the following:

• Determine the bare module cost of this 4-shell and 8-tube pass heat exchanger as four, 1−2 exchangers, each with a heatexchange area of 100 m².
• Determine the bare module cost of the same exchanger as if it had a single shell.
• What is the name of the principle given in this chapter that explains the difference between the two answers in (a) and (b)?