Experimental study and empirical modeling of CO and NO behaviors in a fluidized-bed combustor firing pelletized biomass fuels

The combustion and emission characteristics were studied in a fluidized-bed combustor burning pellets of five biomass feedstocks: cassava rhizome, eucalyptus bark, rubberwood sawdust, rice husk, and teak sawdust. During combustion tests with an individual pelletized fuel, the heat input to the combustor was ~ 200 kW th , with excess air varied from 20 to 80%. Temperature and gas concentrations were monitored along the combustor height and also at stack to quantify the major gaseous emissions and combustion efficiency of the reactor for the selected fuels and operating conditions. Experimental data revealed a good/fair similarity of the relative axial profiles of temperature, CO, and NO inside the combustor for different fuels fired at variable excess air. Empirical models for predicting the relative axial profiles of the temperature and major gaseous pollutants were derived via regression analysis of experimental data. Using the models, these variables can be predicted at any level in the combustor with an acceptable uncertainty for specified operating parameters. To meet the domestic emission standards for CO and NO, the selected biomass fuels should be fired at excess air of ~ 40%. Under these operating conditions, high (99.2–99.8%) combustion efficiency can be achieved during fluidized-bed combustion of the selected fuels.