Experimental Investigation And Numerical Simulation Of Co-combustion Of Coal And Biomass In Fluidized Bed

Coal and biomass mixed combustion technology effectively reduces the consumption rate of coal and pollutant emissions.The mixed combustion of coal and biomass in fluidized bed was carried out in this paper.The mixed combustion process of coal and biomass was simulated,and the combustion characteristics,pollutant emission characteristics and mutual influence were studied during the mixed combustion of coal and biomass,providing the basic data for industrial application.The effects of combustion temperature,mass mixing ratio,excess air coefficient,fluidization velocity and secondary air rates on combustion characteristics were studied.The combustion characteristics of coal are improved after burning biomass.With the increase of combustion temperature,the temperature of dilute phase region increases,and the CO emission concentration and the carbon content of fly ash decrease with the increase of combustion temperature.When the mixing ratio increased from 0% to 30%,850 ℃,the CO emission concentration decreased from 119.3ppm to 75.1ppm(wood chips)and 86ppm(rice straw),and the carbon content of fly ash decreased from 6.2% to 4%(wood chips)and 3.1%(rice straw).With the excess air coefficient increased,dilute phase temperature and CO emission concentration increased first and then decreased,and the carbon content of fly ash gradually decreased.With the increase of fluidization velocity,the concentration of CO emission increases,and the carbon content of fly ash decreases first and then increases.Compared with pure coal combustion,CO combustion with biomass has greater influence on fluidization velocity.With the increase of the secondary air rate,the CO emission concentration decreased first and then increased,and the carbon content of fly ash decreased.The effect of the secondary air rate on the temperature of the dilute phase region is not significant.The effects of combustion temperature,mass mixing ratio,excess air coefficient,fluidization velocity,secondary air rate and calcium sulfur molar ratio on pollutant emission were studied.Compared with coal combustion alone,the mixture of biomass can effectively improve the emission of NO and SO2,and its emission reduction effect is closely related to the species of biomass,the content of volatiles and alkali metals.When the mixing ratio increased from 0% to 30%,850 ℃,the NO emission concentration was reduced from 378 ppm to 291.2ppm(wood chips)and 301.9ppm(rice straw),and the SO2 emission concentration was reduced from 267 ppm to 147.2ppm(wood chips)and 183ppm(rice straw).With the increase of combustion temperature,NO emission concentration and SO2 emission concentration increase.The emission reduction of biomass decreases with the increase of mass mixing ratio.With the increase of excess air coefficient,the NO emission concentration increases rapidly,and the SO2 emission concentration increases first and then decreases.With the increase of fluidization velocity,NO emission concentration and SO2 emission concentration increase gradually,and the trend of increase is slower.With the increase of the secondary air rate,the NO emission concentration first decreased and then increased,and the SO2 emission concentration gradually decreased.The best secondary air rate was about 20%.The addition of desulfurizer can effectively control the emission of SO2.The greater the Ca/S ratio,the better desulfurization effect and the best calcium and sulfur ratio is 2.5~3.The 2D integrated CFD models including coupled flow,heat and mass transfer and chemical reaction were established.The numerical simulation results are in good agreement with the experimental results,which verifies the accuracy of the calculation model.The flow field,temperature field and combustion characteristics are analyzed.The fluidized bed is in a stable fluidized state,and the volatile fraction is mainly in the dilute phase.When the coal is mixed with sawdust,the highest temperature in the fluidized bed is higher than that in the pure coal.The distribution of component concentration field in fluidized bed is reasonable.O2 concentration decreases with the increase of fluidized bed height,and CO2 concentration reaches the maximum near the inlet.Due to the oxidation of nitrogen and sulfur in coke combustion and volatilization,the concentrations of NO and SO2 are higher near the inlet.With the increase of excess air coefficient,the concentration of NO increased,and the SO2 emission concentration did not change significantly.