Combustion of some Thai agricultural and wood residues in a pilot swirling fluidized-bed combustor

This paper reports a comparative study of burning Thai rice husk, sunflower shells and fine rubberwood sawdust as well as co-firing of the sawdust and shredded eucalyptus bark in the swirling fluidizedbed combustor (SFBC). All experiments for firing individual fuels were performed for the combustor heat input of ∼300 kWth. However, in the co-firing tests, the fuel mixture was delivered at a fixed feedrate, while ranging mass fraction of the blended fuels. For each fuel option, excess air was varied from 20% to 80%, while a flowrate of secondary air was constant. Temperature and gas concentrations (O2, CO and NO) were measured in axial directions in the reactor, as well as at stack. Axial profiles of these variables were compared between the fuel options for selected operating conditions. The axial temperature profiles were weakly dependent on operating conditions, whereas the axial gas concentration profiles were apparently affected by fuel properties, excess air and secondary air injection. The behavior of CO and NO indicated the occurrence of three (or four) specific regions along the combustor height. As revealed by the experimental results, CO and NO emissions from the combustor can be controlled meeting the national emission standard, via maintaining excess air at ∼55%, for all the fuel options. At this excess air, high, 99.1–99.9%, combustion efficiency is achievable when burning these fuels in the SFBC. However, the best combustion and emission performance for the co-firing of rubberwood sawdust and eucalyptus bark can be ensured at 85% sawdust contribution to the combustor heat input.