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Abstract
An important aspect of energy conservation is the establishment of an optional heat exchanger network (HEN) during the design of a plant. The problem of designing an optimal HEN synthesizing has received signification attention in chemical engineering. A very large number of analysis of HEN is well know which are now generally applied to the design of a chemical plant.
The impact of the variation of the minimum temperature approach (∆Tmin) on energy and capital targets is studied using recent development in the pinch technology. Optimal pinch approach temperature has been determined using the ’super targeting’ concept where proper trade-off between energy and capital targets is observed prior to design. A heuristic evolutionary approach has been used for the generation of the optimal HEN.
The worlds increasing energy prices and limited fossil fuel reserves push industries towards better utilization of energy and increased energy savings. Heat exchanger networks (HENs) form an important part in the overall chemical processes since the utilizes available heat from processes in the most economic way.
In industrial processes there are streams that need heating and streams that need cooling, usually achieved by using hot and cold utilities, respectively . HEN synthesis is a mean to obtain heating and cooling by process streams energetic integration, by using heat streams to heat cold streams and cold streams to cool hot streams . In this way it is possible to consumption energy, it is important to use a small number of heat transfer equipment, decreasing the fixed cost of the final network.
Numerous methods have been developed for the design HEN. These methods can be grouped into to different categories one relies on thermodynamic principles and few heuristic rules, where the designer manually synthesizes the network, whereas the other (algorithmic methods ) is based on mathematical programming . The first systematic methods in HEN were introduced Both recognized that it is possible to identify target that predict the maximum amount of energy that can be recovered, as wells the minimum number of units of the HEN. This method was named the pinch design and allows targets to be set which are in dependent of the structure of the network and are only based on stream data.
Pinch analysis is now globally known as a thermodynamic analysis tool which is based on the first and second law of thermodynamics. Pinch analysis sets design targets in terms of minimum utility consumption minimum number of units, and minimum area and cost for a given minimum temperature different (∆Tmin) using pinch analysis, the problem is reduced to two smaller regions, and HEN can be designed above the pinch and below the pinch separately by the following rules:
1)- No heat exchanger is allowed on exchange heat across the pinch.
2)- NO side of any heat exchanger can have a temperature difference below the minimum temperature difference.
3)- Cold utilities are only placed below the pinch, hot utilities above the pinch.