Synthesizing Of Multi-stream Heat Exchanger Networks With Pseudo-temperature Of Stream

Multi-stream Heat Exchanger Network is a new type of heat exchanger networks.Compared with traditional two-stream heat exchangers, multi-stream heat exchangers possess many advantages such as high efficiency, compact structure and low cost.Although multi-stream heat exchangers are widely used in process industries such as gas processing and petrochemical industries, much work during the last two decades is focused on conventional two-stream heat exchanger networks.Few studies have been done on mathematical models and their solution techniques for heat exchanger network (HEN) synthesis with multi-stream heat exchangers.Based on the mathematical model of multi-stream heat exchanger networks, we adopt stream pseudo-temperature instead of stream actual-temperature to synthesize this networks.The work in this paper involves following subjects:1) Determining the relationship of temperature difference contribution value and equal exergy loss of heat transferThe determining of temperature difference contribution value has two methods at present.One is the same temperature difference contribution value to all process streams, the other bases the heat transfer coefficient and heat transfer area cost of the unit to determine temperature difference contribution value.Based on the two methods, we bring forward a new method which considering equal exergy loss into temperature difference contribution value.This method gives attention to thermodynamic and economic influence factors, and we use two actual process examples to explain the rationality of the new method.2) Using pseudo-temperature of stream to synthesize multi-stream heat exchanger networkThe method of stream pseudo-temperature can make the distribution of heat transfer temperature difference more reasonable, realize vertical match of the streams, and get reasonable initial population and reduce the total cost of network.We adopt the pseudo-temperature instead of actual temperature of stream for generating a reasonable initial population, then use GA/SA to synthesize multi-stream heat exchanger network and analyze the network economy to literature examples.We can prove that pseudo-temperature method is more efficient than actual temperature to synthesis of HEN, and economical advantage of multi-stream heat exchanger network over traditional two-stream heat exchanger network is illustrated through calculations.3) Comparing the three different temperature determining difference contribution value methodsWe synthesize multi-stream heat exchanger network using the three different determiningtemperature difference contribution value methods to three examples from literatures.And the results indicate that the method considering equal exergy loss is better than the other methods.But considering the randomicity of SA/GA algorithm, this work is only initial and not mature yet.