Numerical Simulation Of Combustion In A680MW Supercritical Wall-tangentially Fired Boiler

Wall-Tangentially combustion is to dispose the burner near the center of wall of thefurnace, so the pulverized coal can be entrainment of the high temperature flue gas heatand radiant heat of the furnace, the high degree of turbulence and burn rate, furtherbroaden the coal adaptability, and the flame is not easy to shift to ensure the long-termsafe and efficient boiler operation. So there will be good application prospect. But theresearch is mostly in the pilot phase, so it is very necessary to fully understand thecharacteristics and performance of the wall tangentially fired way. This paper carried outcoal blended combustion numerical simulation researches on a680MW supercriticalpulverized-coal wall-tangential combustion utility boiler. This work has significance ofengineering applications，in order to be applied to the guidance boiler optimization run.Firstly, the basic situation of the wall tangentially fired boiler which was modeledand meshed according to the actual size was introduced, then the reasonablemathematical model chosen for calculation. The gas flow, pulverized coal combustionand NO_Xformation characteristics of rated operating condition were simulated.Simulation results show that the tangential in the furnace formed well, and difficult toshift, and filled with high rigidity of the flame jet; thermal load distribution was uniformand the temperature dead band was not exist, a high temperature region is mainly close tobut not brush the wall; residual rotation smaller, furnace exit flue gas temperaturedifference was small for20K. Pulverized coal burn rate was high, the furnace exit to flyback to low carbon content was low, and the NO_Xemissions only was262mg/m~3(6%O2).Finally, on the basis of the rated operating condition, by changing the amount ofoxygen in the furnace, variable the mill combination and variable overfire air rate,variable load, etc., the gas flow, combustion and NO_Xformation characteristics of thefurnace were examined. With the increase of oxygen, coal burnout rate increase, the thecarbon content of fly ash decrease, but little change in NO_Xemissions; overfire air rate increases, strengthen in the effect of air classifier, make the NO_Xdecreased, but if thewind rate was too large, the NO_Xemissions will be increase, when the ratio is35%, theNO_X emission being lower, combustion efficiency being high but carbon content of flyash lower; when the upper burner is turned off, combustion efficiency is high, strengthenthe effect of the air classifier, the NO_Xemissions are greatly reduced; With the reductionof the boiler load, boiler combustion efficiency decrease, but greatly reduce NO_Xcontentof the export.