Study On Application Of Shell And Tube Heat Exchanger In Waste Heat Recovery Of Multicomponent Gas

With the development of our country's industrialization process,energy crisis is getting worse.It's urgent to research and exploit the renewable clean energy.The future energy system should develop towards strong coupling and renewable,which requires the adjustment of current energy structure.Solar energy,abundant resources and strong renewability,is great energy source.However,there are still some problems in the application,such as discontinuity,unevenness and largely influenced by the climate and regions.So the large-scale use of solar energy needs to be converted into other form of energy to storage and deployment.There are many ways to store solar energy,especially the chemical way has significant advantage.Recombination reaction of methanol vapor with the use of solar to produce hydrogen is a promising way.It has high export product temperature,which can be used for waste heat recovery to save energy.At present,it's the main way to exchange heat that using the tube and shell heat exchanger at home and abroad.In the process of waste heat recovery using the tubular heat exchanger,the type and initial working conditions of cold and hot fluid will have an impact on the heat transfer performance of the heat exchanger and the energy use ratio of the waste heat recovery system.This paper has studied from these aspects.The export product of recombination reaction to produce hydrogen is mainly composed of hydrogen,water steam and carbon dioxide in a certain proportion.In the process of heat exchange,there are many factors affecting the heat transfer effect of cold and hot fluid,especially the flow diffusion of each component during the synthesis gas in the tube heat exchanger will has a great influence on heat transfer.In order to study the heat transfer process of high temperature multicomponent gas in tube and shell heat exchanger,a three-dimensional steady state numerical model was established based on fluid flow model,heat transfer theory and mass transfer model,and the accuracy of the model was verified by Kern criterion method.The effect of substance diffusion on the temperature field of the heat exchanger and the concentration field distribution of each components of the heat flow was analyzed.The results show that the substance diffusion changes the original distribution of the components in the heat flow mixed gas and the hydrogen which is dominant in the heat transfer diffuses reversely,exchanges heat with the higher temperature heat flow near the inlet,consumes the heat of high temperature fluid by it own,thus reducing the performance of heat exchanger.When substance diffusion is taken into account,the equivalent heat transfer coefficient reduces from 16.564W/(m~2·K)to 15.955W/(m~2·K),indicating that substance diffusion has a great impact on the working performance of tube and shell heat exchanger.Therefore,it is necessary to consider the substance diffusion of fluid when studying the performance of tube and shell heat exchanger.The inlet parameters of the heat exchanger was optimized and analyzed with taking into account the substance diffusion factors between multi-component gases and the exergy efficiency is used as an evaluation index for the heat transfer effect of the heat exchanger.The exergy efficiency of heat exchanger was calculated in four aspects respectively included the inlet velocity and temperature of the cold fluid,the inlet velocity of hot flow mixed gas and the mixing ratio of each components.The calculated results show that,within an interval of working condition parameters,due to the large temperature difference between the hot and cold flows,the irreversible loss of the heat exchange process is large,and the exergy efficiency of the heat exchanger is about 36%.Considering the actual situation and heat transfer performance comprehensively,when the inlet velocity of cold flow is 0.1m/s,the inlet temperature is 298.15K,the inlet velocity of hot synthesis gas is 1.5m/s,the inlet temperature is 523.15K,and the inlet mixing ratio of hydrogen,carbon dioxide and water vapor is 3:1:1,the heat transfer effect is the best.The results provide a reference for the precise design of tube and shell heat exchangers with mixed gas media and the engineering application of tube and shell heat exchangers in waste heat recovery systems.According to the characteristics of the coupling and multi-stage use of the energy system,the author constructed a solar methanol steam reforming hydrogen-cogeneration system.The tube and shell heat exchanger is used in the waste heat recovery of the system.Taking the climate samples of Chongqing from July to September as reference,the solar radiation variation of typical days in summer was tested and calculated.The energy efficiency of the system changed with time in typical days was analyzed,and the optimization measures were put forward for more efficient operation of the system.