Experimental Study On Preheating Characteristics And Pollutant Contral Of Ultra-low Volatile Carbon-based Fuel

Semi-coke and residual carbon,the by-products of pyrolysis or gasification of low-rank coal,belong to ultra-low volatile carbon-based fuels.The volatile content is usually less than 8%,far low than conventional coal.When burning these fuels with traditional technologies,problems such as high ignition point,difficult burnout and high NOx emission will be encoutered.In this paper,Shenmu semi-coke and gasification residual carbon were taken as the mian research objects,and high-temperature fuel nozzles with different types and different operating parameters were used in the 30 kW circulating fluidized bed preheating combustion test bench,in order to explore the preheating combustion characteristics of ultra-low volatile carbon-based fuel and the emission control characteristics of pollutant.The characteristics of ultra-low volatile carbon-based fuel preheated at high temperature and the effect of limestone on SO2 emission were studied in this paper.And meanwhile,the influence of operation factors such as air distribution modes,secondary air jet modes and NOx emission characteristics of ultra-low volatile carbon-based fuel was analyzed.The volatiles conversion rates of gasification residual carbon and Shenmu semi-coke were 63.4%and 78.4%respectively.The conversion rates of fixed carbon were 40.3%and 47.7%respectively.Studies on coaxial jet nozzles show that changing the ratio of internal and external secondary air,the combustor’s temperature variation trend is basically the same,and the influence law on NOx emission is also basically the same.Total secondary air volume can be used as the reference factor in the test.When the equivalent ratio of total secondary air volume is about 0.5,NOx emission can be effectively reduced.The change of temperature on the top of combustor is related to the change of secondary air flow area.Too short a reduction zone will cause a sharp drop in temperature at the top of the combustor.When the reduction zone length is 500 mm,NOx emission is the lowest,reaching 110 mg/m3(6%O2).At the same time,fractional combustion technology can effectively reduce NOx emissions,the reduction rate is more than 57%.Stxdy of extended type nozzle show that using the direct flow can get less NOx emission than using 30° angle of oblique flow.The final NOx emission are 99.7 mg/m3(6%O2)and 152.3 mg/m3(6%O2).When going the test high temperature fuel nozzle with a bluff body,the temperature at the top of the combustor is higher than the test without a bluff body about 200℃.With the addition of bluff body,the heating rate at the top of the combustor increased by about 43%.Obviously bluff body is help for burning,but do little use to reduce pollution.For gasification residual carbon preheating process adding limestone desulfurization experiment research,the experiment shows that when the Ca/S molar ratio of 0,1 and 2 respectively,the SO2 emission is respectively 1428,1167 and 676 mg/m3,shows that by adding limestone in the preheating burner can effectively reduce the SO2 emission,and with the increase of Ca/S molar ratio,the desulfurization efficiency increased.