Numerical Simulation Of Low NO_x Combustion In A 300MW Coal-fired Boiler Under Deep Peaking

With the large-scale connection of renewable energy to the grid,the deep peakin g of thermal power units is becoming more and more frequent.At present,research w ork on the impact of NOx emission concentration is mainly focused on the high load c onditions of boilers,and it is urgent to reduce NOx emission and maintain safe and sta ble operation of the units during deep peaking.Therefore,it is important to study the c ombustion conditions and NOx emission characteristics of boilers during deep peakin g operations.In this paper,according to the actual situation of the boiler,the GAMBIT softwar e is used to analyse the overall structure and carry out mesh division for a 300 MW fou r-angle cut circle coal-fired boiler,select a reasonable calculation model,carry out nu merical simulation for different working conditions and analyse the simulation results.Under BMCR conditions,the combustion characteristics of the furnace were analyse d and the reasonableness of the model was verified by combining the data obtained in the field.In the case of deep peaking,the flow combustion and NOx generation chara cteristics of the furnace were analysed by changing the parameters of excess air coeffi cient,SOFA air rate and burner concentration ratio of the boiler unit,and the optimal values of the above parameters under different loads were explored to optimise the op erating conditions of the unit.The following conclusions were drawn from the full res earch work.(1)The velocity,temperature,and component distribution laws obtained from the numerical simulations under BMCR conditions of the boiler are consistent with the hi gh-temperature combustion characteristics of the boiler,and the deviations are within tolerable limits when the calculated results are compared with the field values,indicat ing that the model calculations are accurate.(2)When changing the excess air coefficient α of the boiler unit,the best excess air coefficient is 1.25 for deep peaking,and when changing the SOFA air rate of the b oiler unit,the best SOFA air rate is 28% at 30% load,26% at 40% load and 26% at 50% load.The optimum SOFA air rate at 30% load is 28%,at 40% load is 26%,at 50%load is 24%,and as the load increases the SOFA air rate decreases.When changing th e boiler unit’s burner concentration ratio μ,the optimum burner concentration ratio is2.4 at 30% load,2.6 at 40% load,and 2.8 at 50% load,which increases as the load inc reases.