Combustion Performance and Ash Compositions during Biomass/Semi-Coke Blended Fuel Oxy-Fuel Circulating Fluidized Bed Combustion

Co-combustion biomass with semi-coke under oxy-fuel combustion is a promising way to reduce CO2 emission and achieve the integrated utilization of biomass and semi-coke. To provide hints on the further industrial utilization, cornstalk was co-combusted with Shenmu semi-coke under oxy-fuel combustion atmospheres in a 50 kW circulating fluidized bed (CFB) test rig, of which the operating parameters can be well controlled. Results showed that semi-coke can achieve stable combustion under an oxy-fuel combustion atmosphere with 30% inlet oxygen concentration. Although inferior to that of cornstalk/coal blended fuel, the combustion performance (ignition and pollutants emission) of cornstalk/semi-coke blended fuel was superior to that of unblended semi-coke. In addition, the increase in the blending ratio of cornstalk or inlet oxygen concentration under the oxy-fuel combustion atmosphere was conducive to reduce the emission concentrations of CO, N2O, and NO. K tended to release into the gas phase during co-combustion with the semi-coke process, especially under a high blending ratio. High CaO content in semi-coke or coal would result in enrichment of S in bottom ash and circulating ash, which, in turn, inhibited the reaction between S-containing species and KCl, while Cl would accomplish almost total release from fuel, and then it would be enriched in deposits.