Study On Recovery Of Flue Gas Waste Heat From Gas Boiler By Water Falling Film Spray

Flue gas waste heat recovery methods usually include heat exchanger and heat pump technology recovery.For flue gas waste heat,realizing heat and mass transfer between flue gas and spray liquid by using spray tower,the system thermal efficiency increases by more than 10%,getting better flue gas spray heat exchange effect.In the heating field of gas boiler or gas thermal power plant,spray heat exchange has broad application prospects.In the process of direct contact between high temperature flue gas and heat transfer medium,the problems is that the cooling water spray is not easy to uniform and impact the overall heat transfer effect.While falling film flow can increase the contact time between cold and hot fluid in spray process,therefore,the vertical plate structure are installed in spray tower,through the process of falling film spray to guarantee flue gas with enough contact time to enhance gas-liquid spray heat exchange effect.The study of flue gas and spray liquid on falling film spray heat exchange in vertical falling film plate structure is mainly about flue gas temperature,spray water temperature and the influence of the geometric structure parameters on spray heat exchange effect.Meanwhile the flue gas waste recovery of the spray heat exchange is used to analyze for district heating.It has important research significance to realize the deep recovery of gas waste heat.The main research contents of this paper are as follows:(1)Firstly,the physical and mathematical model in the flue gas spray heat exchange process is established.The existing relevant flue gas spray heat exchange numerical simulation technology is introduced.Through reasonable assumptions to simplify the process of flue gas spray heat exchange analysis,model theory includes continuity equation,momentum equation and energy equation of flow problem,as well as K-εturbulence model of the basic control equation theory and so on,building geometric structure model of flue gas spray tower.Related spray tower internal parameter given,the analysis of flue gas spray heat exchange effect considers heat exchange efficiencyη,based on inlet and outlet temperature of flue gas and spray liquid.It is used as an index to evaluate the heat exchange process of flue gas spray.(2)Secondly,under directly spray heat exchange and setting up the vertical plate structure spray heat exchange two ways,CFD numerical simulation research was carried out,analyzing flue gas temperature field,velocity field and spray droplet residence time,exploring the influence of vertical plate spacing D,vertical plate height H and vertical plate number n and other structural parameters on flue gas spray heat exchange performance.Under the same working conditions,compared with flue gas directly spray heat exchange,setting up the vertical plate structure in the spray tower can decrease the flue gas outlet temperature by 6K,increase the spray water temperature by 1.4K and rise flue gas spray heat exchange efficiency by 10.9%.Setting up vertical plate structure under the spray heat exchange,with the vertical plate spacing increasing from 0.075 m to 0.200 m,the flue gas outlet temperature is firstly down then up,and the spray water outlet temperature is firstly increase and then decrease.correspondingly,spray heat exchange efficiency increased from 51%to 76%and then dropped to 68%As the height of the vertical plate increased from 1.0m to 1.5m,the temperature at the flue gas outlet decreased,while the temperature at the spray water outlet increased,and the corresponding spray heat exchange efficiency increased from 70%to 83%.With vertical plate number increased from 0 to 12,the flue gas outlet temperature decreased,while the spray water outlet temperature rose.With the increase of vertical plate number.the change is more and more obvious,the corresponding spray heat exchange efficiency increased from 69%to 87%.Then,the spray heat exchange efficiency under direct spray and setting up vertical plate structure was compared and analyzed.When the spray heat exchange carried out under spray tower with vertical plate structure,the multi-factor analysis was researched about the heat exchange efficiency under the influence of some parameters,including the interaction relationship among the flue gas velocity,vertical plate spacing,vertical plate height and the number of vertical plates(3)Finally,waste heat recovery system for flue gas spray heat exchange was established,expounding flue gas spray waste heat utilization theory of heat pump type In the 10000m2 office building heating target,the flow of heating water is 51.7t/h,which can meet the heating demand of 55℃.On the 120day heating cycle every year,the required number of years for recovering the initial investment cost is 1.85 years.With the improvement of spray tower internal structure settings,it can effectively enhance heat exchange effect between flue gas and spray water.Spray water temperature after spray heat exchange rose to 50.6℃ and the highest recovery of waste heat can reach 5227 MJ.Compared with the original direct spray heat exchange mode,the waste heat recovery increased by 80%.Different spray water temperature leads to different power consumption of the heat pump.The spray water temperature of 38℃,the highest heat pump power consumption is 103.9 kW.The heat pump power consumption decreases with the increase of spray water temperature.At 51℃ spray water temperature,heat pump power consumption is 53.7 kW and reaches only 51.7%of the original power,compared to the initial temperature 38℃.Therefore,improving the spray water temperature can effectively reduce the power consumption of the waste heat recovery process.After obtaining higher spray water temperature,more waste heat utilization can be obtained,so as to achieve higher heating water temperature target.