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The procedures to follow in the design of threshold problems are discussed by Smith
(1995) and IChemE (1994). CHEMICAL ENGINEERING
3.17.6. Multiple pinches and multiple utilities
The use of multiple utilities can lead to more than one pinch in a problem. In intro-
ducing multiple utilities the best strategy is to generate at the highest level and use at the
lowest level. For a detailed discussion of this type of problem refer to Smith (1995) and
IChemE (1994).

3.17.7. Process integration: integration of other process operations
The use of the pinch technology method in the design of heat exchanger networks has been
outlined in Sections 3.17.1 to 3.17.6. The method can also be applied to the integration
of other process units; such as, separation column, reactors, compressors and expanders,
boilers and heat pumps. The wider applications of pinch technology are discussed in the
Institution of Chemical Engineers Guide, IChemE (1994) and by Linnhoff et al. (1983),
and Townsend and Linnhoff (1982), (1983), (1993).
Some guide rules for process integration:
1. Install combined heat and power (co-generation) systems across the pinch; see
Chapter 14.
2. Install heat engines either above or below the pinch.
3. Install distillation columns above or below the pinch.
4. Install heat pumps across the pinch; see Section 3.16.7.
The techniques of process integration have been expanded for use in optimising mass
transfer operations, and have been applied in waste reduction, water conservation, and
pollution control, see Dunn and El-Halwagi (2003).

Example 3.18
Determine the pinch temperatures and the minimum utility requirements for the streams
set out in the table below, for a minimum temperature difference between the streams of
Ž
20 C. Devise a heat exchanger network to achieve the maximum energy recovery.
Stream Heat capacity Source Target Heat
Ž
Ž
Ž
number Type kW/ C temp. C temp. C load kW
1 hot 40.0 180 40 5600
2 hot 30.0 150 60 2700
3 cold 60.0 30 180 9000
4 cold 20.0 80 160 1600

Solution
The construction of the problem table to find the minimum utility requirement and the
pinch temperature is facilitated by using a spreadsheet. The calculations in each cell are
repetitive and the formula can be copied from cell to cell using the cell copy commands.