Numerical Simulation Of Combustion Process And NO_x Emission Of Semi-coke Pulverized Coal Combustion Of A 300MW Boiler

Semi-coke is a type of flammable solid product obtained by dry distillation of bituminous coal or lignite at medium or low temperatures.If a large blending proportion of semi-coke can be obtained in the combustion of mixed semi-coke and pulverized coal in the boiler,the mixing can not only expand the fuel range of coal-fired mixed combustion in the pulverized coal boiler of the power plant,but also facilitate the utilization of downstream products by coal quality,thereby increasing the utilization of coal powder.However,the semi-coke ignition temperature is high and it is a flame-retardant fuel.To ensure the burn-up rate of the semi-coke while large-scale blending is required,a higher combustion temperature is required,which is contrary to the requirement of reducing the NO_x emission in the furnace.Therefore,it is especially necessary to study the use of staged combustion technology to achieve low NO_x emissions from semi-coke pulverized coal combustion.In this paper,the CFD numerical simulation method is used to study the NO_x emission of the semi-coke pulverized coal blending combustion of a 300MW tangentially round boiler.Firstly,using the concentrated pulverized coal direct current experimental system,the combustion condition of the semi-coke blended pulverized coal was studied under the condition of 45%semi-coke blending,and the relevant combustion data obtained were obtained under the same working conditions using Fluent software.The analog data is compared to verify the reliability of the mathematical model used in this paper.Based on the verification of the model,this paper changes the different parameters and studies the NO_x of the 300MW boiler under the conditions of variable mixing ratio,variable particle size,variable combustion rate,variable refuel ratio and adjusted semi-coke pulverized coal fuel layer.Firstly,the numerical simulation of the boiler under different mixing ratios of semi-coke is carried out.The research shows that with the increase of the proportion of semi-coke mixing,the temperature of the center of the furnace increases,and the ignition distance of the pulverized coal fuel blended with the semi-coke is in the furnace.The distance from the primary air vent to the fuel reaching the specified ignition temperature is also increasing,while the NO_x emissions in the furnace increase and the burnout rate decreases.And when the semi-coke blending ratio reaches 60%,the excessively high blending ratio greatly increases the difficulty of the semi-coke ignition.In the case of a certain proportion of semi-coke blended coal powder,the numerical simulation of the blending combustion of different semi-coke particle sizes is carried out.The results show that with the semi-coke blending ratio,the particle size of the semi-coke particles Lowering,the CO concentration in the main combustion zone increases,and the ignition distance decreases.And as the particle size of the semi-coke particles decreases,the burnout rate of the furnace exit increases and eventually remains stable.In the case of a certain proportion of semi-coke blended pulverized coal,the numerical simulation of semi-coke pulverized coal combustion under different burnout rates of the furnace was carried out.The study shows that the temperature in the furnace also increases with the increase of the burnout rate.Constantly decreasing,the CO concentration in the main combustion zone is increased,and the NOx emissions in the furnace are also reduced.When the exhausted wind rate is 15%,the NOx emission of the furnace outlet is483.7mg/Nm~3 when the blending ratio of the semi-coke is 60%,and the burnout rate is 96.2%,which can meet the relatively high burnout rate of the fuel.It can also guarantee low NOx emissions from combustion.Under the condition of fuel classification,the effect of different reburning fuel ratios on NOx emissions was studied when semi-coke was used as reburning fuel and semi-coke pulverized coal mixed fuel was used as the main combustion zone fuel(60%of which was mixed with semi-coke).Studies have shown that as the reburning fuel ratio increases,the NO concentration growth rate in the reburning zone decreases,and the refueling fuel ratio has the lowest growth rate at 25%,which is not only due to the temperature drop in the furnace,but also because of the semi-coke coke pair.Reduction of NOx,thereby reducing NOx emissions.Under the condition of fuel grading,the semi-coke and pulverized coal were distributed in different fuel layers when the semi-coke occupied three layers of fuel and the remaining two layers were all bituminous fuel layers.Studies have shown that when the semi-coke fuel layer is distributed in the upper part of the main combustion zone,the pulverized coal fuel is distributed in the lower part of the main combustion zone,which can not only obtain a higher nitrogen oxide reduction rate,but also take into account the burnout and economy of the coal powder semi-coke..