Design and optimization of heat exchanger network in olefin unit of oil refinery

Abstract

The design of heat exchanger network (HEN) is an important part of the synthesis process. Optimum design of HEN can cause significant reduction in the total cost of the plant. In the mid 80’s, famous industrial companies started using a systematic approach to HEN design, called “PINCH METHOD”. This method, which is based on thermodynamic concept, is now the most applicable technique for HEN design. The superiority of this method over other techniques has encouraged industries to use it not only for grass root design, but also to retrofit their existing plants. This study investigates the systematic approach to retrofit an existing plant using the “Pinch Method”. The method was applied on the distillation unit of Isfahan refinery preheat train. Increasing crude oil of Isfahan refinery up to 50% has caused heat load increase at atmospheric furnace (H-101). This in fact, has created a serious operational problem. Retrofitting the preheat train network, however, makes the temperature of the crude oil entering the furnace to rise and, therefore reduces the heat load of the atmospheric furnace. Results show that it is possible to reduce the load of the atmospheric furnace up to 25% and restore the normal operational condition, only by USD 1 million investments. This implies a payback time of 9 months. On the other hand, applying the retrofitting technique to both nominal capacity (100,000 barrel) and increase capacity (150,000 barrel) show that despite significant increase, the key retrofitting variables remain almost unchanged. Therefore, the suggested retrofitting procedure for Isfahan refinery will be applicable to all capacities ranging from 100,000 barrel to 150,000 barrel. However, at a capacity higher than 150,000 barrel, the chance of inducing bottlenecks, for example at atmospheric tower hydraulic should be taken into consideration.