University of Khartoum

Heat Exchanger Networks Retrofit Using Problem Decomposition

Heat Exchanger Networks Retrofit Using Problem Decomposition

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Title: Heat Exchanger Networks Retrofit Using Problem Decomposition
Author: M. Adam, Abdel Samed
Abstract: Energy conservation is currently one of the greatest challenges for chemical process industries world wide and especially in oil refineries and chemical industries. Reducing energy consumption and using energy more efficiently is becoming increasingly important, as the impact of energy use on the environment, and the need for reduced cost of production becomes vital. Utilizing Process Integration (PI) techniques for both new and retrofit plant designs enables the process engineer to create efficient energy recovery systems with lower production cost and improved environmental performance. Among the energy recovery systems, heat exchanger networks are of great importance. In process integration, heat exchanger networks are synthesized and retrofitted using two methods which are the Pinch Technology method and the Mathematical Programming method. Despite its success, conventional Pinch Technology methods face serious criticisms. Much of these criticisms related to the complexities in the resultant structure of the heat exchanger networks. The complexity in the network is brought about by the fast development in Pinch technology without taking into consideration the ease of plant operation. These complex HENs make the plant operators face difficulties in understanding where individual streams were going. The criticisms can be removed by decomposing the overall problem into a number of sub-problems associated with specific parts of the process under consideration. Decomposing the problem has major benefits; o It will allow the designer to produce energy-efficient network structures that are simple. o It will control piping costs and avoid the hazards associated with over-integration. o It will simplify the network design and retrofit processes. o It will avoid the need for sophisticated network-optimization procedures o It can be employed using any process-integration targeting software. This has implications for software vendors and purchasers In this study, the “Problem Decomposition” method (also called “Structural Targeting” method) based on Pinch Technology was applied to retrofit existing heat exchanger networks which were retrofitted using the traditional Pinch Technology retrofit method. The example networks were selected from published scientific papers. At the end of the study a comparison between the results of the two retrofit methods was made. Three case studies were selected for this purpose; a Crude Distillation Unit and two Pulp & Paper plants. The heat exchanger networks of these plants were originally retrofitted using the traditional retrofit method. The results obtained after the application of the Problem Decomposition retrofit method to these case studies, showed much better results in the final retrofitted heat exchanger networks compared to the results that obtained by using the traditional method. The criteria on which the comparison was based are : • The amount of savings in hot utility consumption • The payback period on the capital investment due to the addition of new heat transfer area to the existing heat exchanger networks or due to the installation of new heat exchangers • The structure of the final retrofitted heat exchanger networks • The simplicity of the design phase and the ability of the designer to interact with the analysis and design phases during the retrofit design work.
URI: http://khartoumspace.uofk.edu/handle/123456789/9866
Date: 2015-04-28


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