Experimental Study On The Load Response Rate Under The Dynamic Combined Combustion Of PC Coal And CFB Coal In CFB Boiler

For the low load response rate of circulating fluidized bed(CFB)unit,the experiments of dynamic combined combustion of low calorific coal and high calorific pulverized coal were carried out based on a 240t/h CFB boiler.The influences of the single CFB coal step,the coal feeding position(secondary air pipes,coal feeding pipes),the calorific values of pulverized coal(19.30 MJ/kg,27.17 MJ/kg)and the feeding amount of pulverized coal on CFB heat load response rates were studied.The characteristics of heat transfer coefficients during the dynamic combined combustion experiments were analyzed,and the combustion performance and pollutant emission characteristics of the circulating fluidized bed boiler under combined combustion were also given.The test results showed that the load response rates of combined combustion that the pulverized coal was added through secondary air ducts was 6.03MW/min(3.57%ECR/min),and the load response rate was 2.69MW/min with a single coal step.Dynamic combined combustion can improve the natural thermal inertia of circulating fluidized bed boiler and enhance its ability to participate in peak regulation of power grid.Based on cluster renewal model,the heat transfer coefficients of the membrane wall in the dilute phase zone in CFB boiler were calculated,and the heat transfer coefficients characteristics of dynamic combined combustion were studied.come to the following conclusions:(1)During the dynamic combined combustion experiments,the extra pulverized coal didn't have much influence on the concentration and didn't change convective heat transfer coefficient of dilute phase zone in CFB boiler,because the convective heat transfer coefficient in CFB boiler mainly depends on material concentration.(2)Compared with the cases of single CFB coal step combustion,due to the intense combustion of pulverized coal in dynamic combined combustion,the temperature rapidly increased in a short time,and strengthened the coke burning in furnace,so the radiant heat transfer was enhanced and the thermal flux of furnace surface was improved.The temperature should increase during dynamic combined combustion,and the nitrogen oxides could rise a little.But adding pulverized coal was not the direct reason of the increases of NO_X emission concentration.By controlling the combustion atmosphere in the furnace,the formation of nitrogen oxides should be controlled effectively under the combined combustion mode.