Research On Characteristic Of NO_x Emission During Shenfu Semicoke Air-staged Combustion

semi-coke is abtained though low-rank coal pyrolysis in medium and low temperature.The industrial pulverized coal boiler system which was developed by China Coal Research Institute Company of Energy Conservation has the characteristic of high efficiency and energy saving.If semi-coke is used as fuel of industrial pulverized coal boiler,the fuel of industrial pulverized coal boiler can be broaden,and it has a positive effect on coal staged utilization.semi-coke has a bad ignition properties.Combustion temperature must be increased if semi-coke is used as fuel of industrial pulverized coal boiler.But it is on the opposite side of NO_x decrease.Besides,semi-coke has a low volatile,in which active group used for NO_x decrease is lower.Thus,we need a better combustion organization to insure a high burnout rate and low NO_x emission.Air-staged combustion,which has been proved to be effective for industrial pulverized coal boiler,need a further research on semi-coke to explore its NO_x emission principle.A two-stage drop-tube furnace system was usd to simplify the combustion of boiler in a tube.In consideration of the low volatile,we set all the temperature of fuel-rich zone above 1000? to get a higher heating rate and a faster volatile yielding.First,non-staged combustion and air-staged combustion was studied to investigate properties of NO_x emission and find a best ratio of secondary air.In order to have a further research on the mechanism of NO_x emission and Shenfu semi-coke combustion properties,micro-pole and microstructure was observed.Finally,Shenfu bituminous coal air-staged combustion experiment was conducted in comparison with Shenfu semi-coke to get the adaptive properties.In this paper,we came to conclusions as below:1.We can draw the conclusions through the comparison of Shenfu semi-coke and Shenfu bituminous coal that Shenfu semi-coke has a bad properties in ignition and combustion,and in order to have a high combustion efficiency,the combustion temperature must be increased.Through the non-staged combustion of Shenfu semi-coke,we studied the impact of the temperature of the fuel-rich zone and the stoichiometric ratio on NO_x emission and found that NO_x emission increases with the emperature of the fuel-rich zone and the stoichiometric ratio.Thus increasing the temperature of the fuel-rich zone can intensify combustion.In contrast experiment with Shenfu bituminous coal,we can obtain from the difference caused by volatile that increasing the temperature of the fuel-rich can accelerate the fuel N yielding and semi-coke combustion.2.The impact of the temperature of the fuel-rich zone and ratio of secondary air on NO_x emission,burnout rate and NO_x removal rate was investigated in Shenfu semi-coke air-staged combustion.A few conclusions were drawn:When a proper ratio of secondary air is chosen,increasing the temperature of fuel rich zone can decrease NO_x emission and abtain a high brun-out rate;The best ratio of the secondary air is 0.56(The stoichiometric ratio of fuel rich zone is 0.73;The ratio of over fire air is 0.39),at which the NO_x emission is below 120 mg/m3,and the burnout rate NO_x decrease rate are all at a optimal value;Through the analysis of pole and microstructure properties,we proved again the increasing temperature of the fuel-rich zone accelerates the semi-coke combustion and 0.56(The stoichiometric ratio of fuel rich zone is 0.73;The ratio of over fire air is 0.39)is the best secondary ratio.3.By comparing with Shenfu bituminous coal air-staged combustion,we found that Shenfu semi-coke has a good adaptive properties in air-staged combustion.And,as bituminous coal has high volatile,we can see clearly that the increasing of the temperature of the fuel-rich zone is good for low NO_x emission and combustion,when a proper ratio of the secondary air is chosen.The decrease rate of semi-coke is above 90%and higher than bituminous coal.But,The burn-out rate of bituminous coal is5%higher than that of semi-coke.Above all,we can conclude that semi-coke combustion can get low NO_x emission through air-staged combustion,but its burnout rate is lower and we can solve through properly designing burner,increase residence time of fuel-rich zone,and mixed combustion with bituminous coal.