Numerical Simulation Of Sodium Concentration Distribution In The Furnace Considering Homogeneous Condensation And Heterogeneous Reaction

To address the serious staining problem of high alkali coal in the boiler combustion process in East China,an alkali metal sodium migration model including homogeneous condensation and heterogeneous reaction of gas-phase sodium was developed based on the EDC pulverized coal combustion model.On the one hand,the EDC pulverized coal combustion model was used to investigate the combustion reaction and gas-phase sodium alkali metal distribution in the furnace,and on the other hand,the gas-phase sodium concentration distribution in the furnace was analyzed using the established alkali metal sodium migration model with homogeneous condensation and heterogeneous reaction of gas-phase sodium,in order to predict the migration and transformation of gas-phase sodium-containing compounds in the furnace more comprehensively.In addition,the distribution of aerosol particles formed by gas-phase alkali metal homogeneous condensation in the furnace was also analyzed,and these studies can provide reference for the search of economic and efficient alkali metal control methods.Firstly,a model of sodium alkali metal migration in the pulverized coal furnace was established.The model is based on the EDC pulverized coal combustion model and the computational models of gas-solid flow field,turbulence model and gas-phase chemical reaction,including the sub-models of alkali metal vapor homogeneous condensation and heterogeneous reaction.In addition,the derivation of mathematical equations of the gas-phase sodium alkali metal homogeneous condensation model and the implementation of UDF and UDS in Fluent prepared in this paper are analyzed in detail.Secondly,the combustion characteristics of the furnace and the migration and transformation law of gas-phase sodium alkali metal in a four-corner cut circle boiler are simulated numerically using the EDC pulverized coal combustion model.The simulation results show that the sodium in the quadrangular coal precipitates as NaCl and Na and then participates in the gas phase reaction in the furnace,mainly NaCl（49%）,Na（40%）and NaOH（9%）in the main burner area.At the bottom of the cold ash hopper,NaCl accounts for about 24%,Na₂SO₄ and Na₂Cl₂ for about 36%and 24%,respectively.The gasphase sodium compounds at the exit of the furnace are mainly NaCl and Na₂SO₄,accounting for 67%and 26.5%,respectively,with small amounts of NaHSO₄（1.5%）and Na₂Cl₂（5%）also present.Finally,based on the EDC pulverized coal combustion model,the homogeneous condensation and heterogeneous reaction models of gas-phase alkali metal sodium were added to simulate the sodium concentration distribution in the furnace,and in addition,the distribution of aerosol particles formed by homogeneous condensation in the furnace and the effect of different furnace temperatures on the formation of aerosol particles were investigated.The results showed that the gas-phase sodium sulfate concentration at the furnace exit was reduced by about 22.9%after the addition of homogeneous condensation and heterogeneous reaction.As for the aerosol particles formed by homogeneous condensation,they are mainly distributed in the cold ash hopper and the near-wall area of the furnace exit.And the reduction of furnace temperature will intensify the formation of aerosol particles in the furnace.