Operating Characteristics Of Thermoelectric Generator For Waste Heat Recovery Of Wet Flue Gas

At present,the share of natural gas in the total primary energy consumption of the world has risen to 24.7%.As the main component of natural gas is methane,the volume fraction of water vapor in the flue gas during the combustion of natural gas can reach 20%,and the latent heat of the vaporization is about 3700 k J/Nm³,which accounting for more than 11%of the high calorific value of natural gas.It is very important to fully recover and utilize the waste heat of wet flue gas,especially the condensing latent heat of water vapor,for improving the energy utilization rate of natural gas.Semiconductor thermoelectric generation technology is a new power generation technology that can directly convert heat energy into electric energy.It has been widely used in industrial waste heat recovery because of its advantages of noise-free,small volume and no working medium.The thermoelectric conversion law of thermoelectric generator based on the characteristics of wet flue gas is the main content in this paper.In this paper,wet air is used to simulate the wet flue gas during natural gas combustion,and thermoelectric generation experimental system of wet air is designed and built.According to the actual working conditions of wet flue gas,a rectangular section with length of 260 mm,width of 20 mm and height of 70 mm.The wet air temperature of 80～120℃,flow rate of 5～20g/s,and mass fraction of humidified water vapor of 5～20%were selected as experimental conditions.Firstly,in order to analyze the improvement effect of air humidification on the power generation parameters of thermoelectric generator,a comparative experiment of thermoelectric generatior of dry and wet air was carried out under the same conditions.The maximum output power of the wet air thermoelectric generator with water vapor mass fraction of 20%is obviously higher than that of the dry air thermoelectric generator,and the maximum thermoelectric conversion efficiency reaches0.897%,which is 2.18 times that of the dry air thermoelectric generator.Air humidification can significantly improve the power generation parameters of the thermoelectric generator.Secondly,the influence of wet air parameters on power output characteristics of thermoelectric generator is further studied.The results show that there is a critical mass fraction of water vaporω_v,cr,and the maximum output power can be effectively increased only when the mass fraction of water vapor is lower thanω_v,cr.The method of increasing the maximum output power by increasing the air flow rate is more significant in the low air flow range.Finally,the influence of wet air parameters on condensation heat transfer characteristics of thermoelectric generator is discussed.The condensate flow decreases rapidly with the increase of temperature and flow of wet air.When the mass fraction of water vapor reaches 20%,the heat transfer coefficient of convective condensation is 653 W/（m²·K）,which is 4.28 times that of 5%water vapor.However,increasing the mass fraction of water vapor enhances the heat transfer but also increases the flow loss,and the maximum pressure drop reaches 6 k Pa under the condition of 20%mass fraction of water vapor.