Heat exchanger network modifications

Linnhoff, B., and Parker, S. J., Heat Exchanger Network with Process Modifications, IChemE Annual Research Meeting, Bath, U.K., April 1984. 

If the capital cost of new heat transfer area is expressed in the form of Equation 18.6, then this will lead to poor retrofit projects. The problem with Equation 18.6 is that the optimization is likely to spread the new heat transfer area in the network in many locations, without incurring a cost penalty associated with the many modifications that would result. To ensure that new heat transfer area is not spread around throughout the existing heat exchanger network, a capital cost correlation should be used that is of the form ... 

Figure 18.39 The heat exchanger network can be optimized after each modification. (From Asante NDK and Zhu XX, 1997, Trans IChemE, 75A 349, reproduced by permission of the Institution of Chemical Engineers.)... 

This approach to heat exchanger network retrofit allows modifications to be introduced one at a time. In this way, the designer has control over the complexity of the network retrofit. At each stage, a suggested modification can be... 

Procedures for the actual synthesis of heat-exchanger networks are somewhat less well developed however, all of the standard process synthesis approaches— including systematic generation, evolutionary modification, and superstructure... 

The external modifications to retrofit the distillation system are considered as starting steps for the retrofit procedure. Simple modifications requiring little or no capital investment are implemented to improve the match between the heat exchanger networks (HEN) associated with the column and the available utilities. The external modifications do not change the column hardware and its internals [4]. 

Asante, N.D.K. and Zhu, X.X. (1996) An automated approach for heat exchanger network retrofit featuring minimal topology modifications. Computers and Chemical Engineering, 20 (Suppl. 1), S7-S12. 

Figure 20.1 Heat-exchanger network (a) Original configuration (b) modification with bypass.

Having identified the network pinch or the bottleneck, what can we do about it The answer is that only changes to the network stmcture can overcome the bottleneck. In the stage of selecting stmctural changes, the maximization of heat recovery is used as the selection criteria. Four types of modifications can be considered for the heat exchanger network, which are ... 

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