Combustion of an oil palm residue with elevated potassium content in a fluidized-bed combustor using alternative bed materials for preventing bed agglomeration

•We examine biomass combustion in a fluidized bed of alumina, dolomite and limestone.•No features of bed agglomeration have been observed during the combustion tests.•A coating consisting of ash-related elements is formed on alumina grain surfaces.•A carryover of Al2O3 from the alumina bed increases a risk of bed agglomeration.•Substitution of entrained bed particles is required when using dolomite/limestone.

Palm kernel shell (PKS) was burned at 45 kg/s and excess air of 20–80% in a fluidized-bed combustor using alumina, dolomite, and limestone as the bed material. Temperature and gas concentrations were recorded along the reactor centerline as well as at stack. A SEM–EDS analysis was performed to investigate morphology and elemental composition of bed particles. An X-ray fluorescence method was used to determine the composition of used/reused bed materials and PM emitted from the combustor at different operating times. Excess air of 40% seems to be most appropriate for burning PKS in this combustor with an alumina bed, whereas 60% excess air is more suitable when using dolomite and limestone, as ensuring high (98.6–98.9%) combustion efficiency and acceptable CO and NO emissions. By using the selected bed materials, bed agglomeration can be prevented in this combustor. However, the bed materials exhibit substantial time-domain changes in physical and chemical properties.