Flue gas analysis for biomass and coal co-firing in fluidized bed: process simulation and validation

Coal-conversion technologies, although used ubiquitously, are often discredited due to high pollutant emissions, thereby emphasizing a dire need to optimize the combustion process. The co-firing of coal/biomass in a fluidized bed reactor has been an efficient way to optimize the pollutants emission. Herein, a new model has been designed in Aspen Plus (R) to simultaneously include detailed reaction kinetics, volatile compositions, tar combustion, and hydrodynamics of the reactor. Validation of the process model was done with variations in the fuel including high-sulfur Spanish lignite, high-ash Ekibastuz coal, wood pellets, and locally collected municipal solid waste (MSW) and the temperature ranging from 1073 to 1223 K. The composition of the exhaust gases, namely, CO/CO2/NO/SO2 were determined from the model to be within 2% of the experimental observations. Co-combustion of local MSW with Ekibastuz coal had flue gas composition ranging from 1000 to 5000 ppm of CO, 16.2%-17.2% of CO2, 200-550 ppm of NO, and 130-210 ppm of SO2. A sensitivity analysis on co-firing of local biomass and Ekibastuz coal demonstrated the optimal operating temperature for fluidized bed reactor at 1148 K with the recommended biomass-to-coal ratio is 1/4, leading to minimum emissions of CO, NO, and SO2.

Automated summary

Coal-conversion technologies are often criticized for high pollutant emissions, highlighting the importance of optimizing the combustion process. Co-firing coal/biomass in a fluidized bed reactor has been shown to be an efficient way to achieve this. A new model designed in Aspen Plus was validated and found to accurately predict exhaust gas compositions. Sensitivity analysis on co-firing different fuels demonstrated optimal operating conditions for the fluidized bed reactor.