Heat exchanger network retrofit through heat transfer enhancement

摘要

Heat exchanger network retrofit plays an important role in energy saving in process industry. Many design methods for the retrofit of heat exchanger networks have been proposed during the last three decades. Conventional retrofit methods rely heavily on topology modifications which often results in a long retrofit duration and high initial costs. Moreover, the addition of extra surface area to the heat exchanger can prove difficult due to topology, safety and downtime constraints.;These problems can be avoided through the use of heat transfer enhancement in heat exchanger network retrofit. This thesis develops a heuristic methodology and an optimization methodology to consider heat transfer enhancement in heat exchanger network retrofit. The heuristic methodology is to identify the most appropriate heat exchangers requiring heat transfer enhancements in the heat exchanger network. From analysis in the heuristic roles, some great physical insights are presented.;The optimisation method is based on simulated annealing. It has been developed to find the appropriate heat exchangers to be enhanced and to calculate the level of enhancement required. The new methodology allows several possible retrofit strategies using different retrofit methods be determined. Comparison of these retrofit strategies demonstrates that retrofit modification duration and pay-back time are reduced significantly when only heat transfer enhancement is utilised.;Heat transfer enhancement may increase pressure drop in a heat exchanger. The fouling performance in a heat exchanger will also be affected when heat transfer enhancement is used. Therefore, the implications of pressure drop and fouling are assessed in the proposed methodology predicated on heat transfer enhancement. Methods to reduce pressure drop and mitigate fouling are developed to promote the application of heat transfer enhancement in heat exchanger network retrofit. In optimization methodology considering fouling, the dynamic nature of fouling is simulated by using temperature intervals. It can predict fouling performance when heat transfer enhancement is considered in the network.Some models for both heat exchanger and heat transfer enhancement are used to predict the pressure drop performance in heat exchanger network retrofit. Reducing pressure by modifying heat exchanger structure is proposed in this thesis. From case study, the pressure drop increased by heat transfer enhancement can be eliminated by modifying heat exchanger structure.