Application And Research Of Low Temperature Waste Heat Recovery By Phase Change Heat Exchanger Technology

Phase change heat exchanger technology takes the lowest wall temperature of the the low-temperature heating surface of the boiler as a design parameter.Through the adjustment of the phase transition temperature of the heat exchanger,it can control the wall temperature of the low-temperature heating surface,effectively reduce the smoke exhaust temperature and fundamentally solve the acid corrosion problem at the same time.It is important for small and medium sized boilers to realize energy saving and emission reduction by applying phase change heat exchanger technology.?1?Summarizing the research progress and achievements of phase-change heat exchanger technology and analyzing the working principle and advantages of phase change heat exchanger technology.Comparing with the traditional heat exchange technology,Summarizing the technical characteristics of phase-change heat exchanger technology in reducing the temperature of exhaust gas and eliminating acid dew corrosion,and the significance of the application.?2?Based on the characteristics of low temperature corrosion,constant wall temperature,and controllable characteristics of phase change heat exchanger technology,researching on the apply of phase change heat exchanger for 10t/h coal-fired boiler.For the relevant parameters of boiler operation and energy saving requirements,thermal calculation and structural design of phase change heat exchanger system.With the phase-change heat exchanger technology apply,the temperature of boiler exhaust gas is reduced from 175?to 135?,which can save81.70 tons of standard coal consumption per year,reduce SO₂,CO₂ emissions by 8.93tons and 160.65 tons.The recovery of low-temperature waste heat has good economic and environmental benefits.?3?Numerical simulation on the flue gas side of phase-change heat exchangers to analyze the distribution of flow field,temperature field and pressure field on the flue gas side.Researching the influence of the inlet velocity of the flue gas,the distance between the fins and the distance between the finned tubes on the resistance of the flow and heat transfer.The results show that with the increase of the inlet velocity of the flue gas,the heat transfer performance is enhanced,the smoke pressure drop is increased,and the inlet velocity is appropriate from 6.5m/s to 8.5m/s.Increasing the fin spacing within a certain range can enhance heat transfer and reduce the smoke pressure drop.Considering the comprehensive performance,the fin spacing is 8mm¹0mm.The increase of the lateral spacing of the finned tubes can enhance the heat transfer and the increase of the longitudinal distance will weaken the heat transfer performance.The increase of the horizontal and vertical spacing of the fin tubes can reduce the pressure drop of the flue gas.?4?Aiming at the effects of heat flux,temperature of condensing wall surface,liquid filling rate,length of evaporative condensation section and other factors,simulated and analyzed the heat transfer performance of the internal working fluid in the phase change heat exchanger.The results show that the heat transfer coefficient increases with the increase of the heat flux,decreases with the increase of the temperature of the condensing wall surface,and decreases with the increase of the length ratio of the evaporating section and the condensing section.The actual operating conditions of 750W/m²,the evaporation section filling rate of 60%,the condensation wall surface temperature of 65?,the tube heat transfer effect is good,consistent with the theoretical design.Simulation shows that the applying of phase change heat exchanger can adjust the temperature of the condensing wall surface by adjusting the flow of cold source,affecting the flow and heat transfer in the tube,and realizing the regulation of the wall temperature of the heated surface.