Collaborative Optimization Of Heat Exchanger Network And Fractionation System

The distillation process is the most widely used unit operation in petroleum refining,petrochemical and other chemical processes, and it is also one of the highest energyconsumption unit in petrochemical industry. Meanwhile the heat exchanger network (HEN) isthe most important energy recovery system. As a result, the operation of HEN and distillationsystem largely influences the quality of products and the energy consumption. The twosub-systems are closely related to each other and restraint with each other. However, they arerarely considered together, people often deal with them separately in research: either thefractionation system is in a good condition, but the HEN can’t adapt with, or HEN is MERone, but with a poor operation flexibility fractionation system. Therefore, collaborativeoptimization of heat exchanger network and fractionation system is very necessary.A combination of process simulation and mechanism modeling is introduced in thispaper, supplemented by appropriate optimization algorithm to achieve the collaborativeoptimization of HEN and fractionation system. The main idea of this article is as follows:1) amathematical mechanism model of HEN is built in this paper; however, for the case ofdistillation tower, it is difficult to establish the mathematical model because of its complexmechanism theory. Fortunately, the simulation software (e.g. PRO/II, Aspen Plus) are widelyused nowadays, with the help of them, the simulation model of distillation tower can be built.2) In this paper, the exact performance of mutual restraint between HEN and fractionationsystem and the corresponding optimization measures have been proposed.3) This paperimproves the Dhulesia’s interpolation mathematical model to calculate different productsEngler distillation temperature with different pumparound flowrate.4) Establishing the objectfunction, with two weighting factors being added, which are used to represent the difficulty ofHEN retrofit and the level of fractionation system optimization respectively.5) Using geneticalgorithms combined with user interaction to achieve the collaborative optimization of HENand the fractionation system. Finally, the article summarizes the research above, and proposesa general method of collaborative optimization of HEN and the fractionation system and ablock diagram is attached. This method is applied in crude oil distillation unit of a domestic oil refinery. Asimulation model of pre-distillation tower, atmospheric tower and vacuum tower has beenbuilt. The HEN mathematical mechanism model was established. Objective function and themethod that using GA to solve this model under the constraints of all process requirementswere built. The case study shows very good results.