Numerical Investigation on Cofiring Characteristics of Biomass Syngas and Coal in a 660-MW Tower Boiler

Cofiring biomass syngas (BS) with pulverized coal under the oxy-fuel condition is a promising technology, which could encourage the utilization of biomass energy and reduce the emission of greenhouse gases. To investigate cofiring characteristics of biomass syngas and coal, a numerical study was conducted. The influences of oxy-fuel condition, syngas quality, and injection position on temperature distributions and flue gas components in boiler furnace were analyzed. To predict cofiring characteristics accurately under oxy-fuel conditions, a new refined weighted-sum-of-gray-gases model, HCN oxidation model, and NO-char reaction model were used. The simulation results show that syngas reburning and oxy-fuel conditions could reduce NO emission. The NO emission in O2/CO2 conditions is higher than that in air. Biomass syngas with higher calorific values contributes to higher furnace temperatures. Besides, biomass syngas with higher hydrocarbon components is beneficial to lower NO emission. Compared to pure coal combustion, NO concentration at the furnace outlet reduces by 40.2%, 69.0%, and 35.2% in the cases of cofiring with Type A, B, and C biomass syngas at a cofiring ratio of 10%, respectively. The injection position of biomass syngas also has crucial impacts on cofiring characteristics and NO emissions. NO emission has the lowest value when the biomass syngas is injected at the bottom level of the reburn zone. This study could provide a reference for optimization of boiler design and operation when cofiring biomass syngas with pulverized coal under the oxy-fuel condition.