Numerical Simulation Of The Combustion Characteristic In A300mw Down-fired Boiler With Swirl Or Single-injection Burner

Nowadays so many boilers have the problem of high NOxemissions, as theenvironmental protection policy increasingly strict, it is urgent to reduce pollutantemission. In this paper, the numerical simulation is used to study a B&W300MWdown-fired boiler, and get the following results:The correctness of the model selections is verified by comparing the simulationresults (temperature、atmosphere) of a original burner with EI-XCL burners with theindustrial data.Changing the on-arch burners to single-injection burners, the study results showthat:(1) As the staged air decline angle increases, the inject depth of the mixing flowand the width of the high temperature flame in the furnace both increase, while the NOxemission decrease. But too big angle tend to cause the scour of the furnace hopper;(2)As the staged air ratio increases, the on-arch-secondary air ratio decreases, and airflowrigidity tended to tail off, the depth that reach to the furnace hopper decreases, coalignition early; when the staged air ratio reach to35%,skew combustion appear in thefurnace; the staged air ratio increase from20%to30%, the NOxemission reduce from700mg/m3to683mg/m3;(3) As the vent air decline angle increases, the dead stagnationzone in the lower furnace reduced, the location of the high temperature flame get down,the NOxemission reduce in turn, skew combustion appear in the furnace when the ventair decline angle is38°.Taking the combustion、furnace hopper slagging risk、and NOxemission into consideration,it is advice that staged air decline angle is30°, staged airratio is30%and vent air decline angle is33°.Appling the central-fuel-rich burner (CFR) on the down-fired boiler, the effect ofthe concentration rate on the combustion characteristic was studied. and then study theeffect of the concentration rate, then both the over-fired air (OFA) and CFR technologywere used in down-fired boiler, and get following conclusions: the flow field is moreand more symmetrical as the concentration rate increases, the NOxemission reduce, andthe NOxemission decreases after using OFA technology.Compared to two kinds of schemes, the parameters of the furnace outlet ofsingle-injection technology is better than that of the CFR technology, but CFRtechnology is much simpler in modification, so combine site condition and economyanalysis of the two kinds of schemes to evaluate and select.