Numerical simulation on fuel nitrogen conversion in flameless oxy-fuel combustion of biomass-pulverized coal blends
Flameless oxy-fuel combustion significantly reduces NOx emissions and captures high concentrations of CO2,positioning it as a leading technology in clean and low-carbon combustion.Biomass,a widely available renewable energy source,can effectively reduce CO2 emissions when co-fired with pulverized coal.This study investigates the nitrogen conversion characteristics of biomass-coal blends under flameless oxy-fuel combustion through simulations conducted on a 0.58 MW combustion furnace.The simulations incorporate a reaction mechanism and radiation model suitable for oxy-fuel combustion.After verifying the model and algorithms,the study examines the fuel nitrogen conversion mechanism.The results indicate that as the biomass blending ratio increases from 0 to 100%,the low-oxygen zone in the furnace expands,and the distribution of CO widens.Additionally,the peak temperature inside the furnace rises.Specifically,when the blending ratio is 50%,the temperature increase compared to pure pulverized coal combustion is 47℃,and at a blending ratio of 70%,the increase is 55℃.For pure biomass combustion,the peak temperature reaches 1 850 K,which is 71℃higher than that of pure pulverized coal combustion.When the biomass blending ratio increases from 0 to 50%,NO reburning decreases significantly by more than 61%compared to pure coal combustion and remains relatively unchanged with further increases in the blend ratio.Despite the higher volatile content of biomass compared to coal,the total NO from volatiles remains almost constant after blending.The fixed carbon nitrogen decreases significantly after blending due to the lower fixed carbon content in biomass,leading to a reduction in NO emissions.When the blending ratio increases from 0%to 100%,NO emissions decrease by 51%.
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