A modeling approach to co-firing biomass/coal blends in pulverized coal utility boilers: Synergistic effects and emissions profiles

Pulverized coal power plants in Chile are evaluating to reduce CO2 emissions by co-firing coal with biomass, which is CO2-neutral. A computational fluid dynamics model was used in this study to predict the performance of a 150 MW commercial boiler co-firing pulverized coal with pine sawdust. Synergistic effects were identified by burnout, thermal and hydrodynamic profiles. Co-firing was simulated with 5% of biomass substitution, and feeding in the first level of burners. The model was validated using data from the power plant. The results show an expected decrease in SO2 emissions and a negligible reduction in heat transferred to the water tubes (0.6%). Biomass presence increased the burning rate of fuel particles, as shown by higher CO2 emissions and a lower CO concentration, per unit of thermal power. The model reveals synergistic effects, proved by an increase in temperature, due to an early combustion of biomass particles, increase in the coal combustion rate, and a better temperature distribution in the boiler. These synergistic effects were compared with results obtained at bench scale reported in the literature. Thus, it was concluded that a relatively small replacement of coal by biomass could significantly improve the fuel combustion process and the boiler performance.