Heat exchanger network retrofit considering pressure drop and heat-transfer enhancement

For the heat-exchanger-network (HEN) retrofit project to be successful it should satisfy not only a specified heat-recovery target but also pressure-drop constraints. The problem of dealing with the pressure-drop aspects is very complex, since there are many options that affect pressure drop. To integrate these options more systematically and solve this problem more effectively, a decomposition strategy is proposed. At the first stage the unit-based model is used to indicate which units require additional area. In the second stage, special attention is paid to these units, where area distribution, shell arrangements, the use of heat-transfer enhancement, and other options are optimized for these units. At the same time, the units without additional area requirement are modeled using simple models. Thus units with and without additional area requirements are treated differently during optimization, By doing this, the pressure drop can be calculated accurately while the overall model remains simple and easy to solve. Heat transfer enhancement is a very attractive option for HEN retrofit, since it call effectively eliminate or reduce the additional surface area space. This will eliminate additional piping, new shells or units, and their required space, which lead to much lower modification costs and less implementation time.