A study on combustion of oil palm empty fruit bunch in a fluidized bed using alternative bed materials: Performance, emissions, and time-domain changes in the bed condition

High-alkali empty fruit bunch (EFB), a biomass residue from the Thai palm oil industry, was burned in a fluidized-bed combustor using alumina sand, limestone, and dolomite as the bed material to prevent bed agglomeration. During the experiments, EFB was fired as pre-dried fuel at fixed (40 kg/h) fuel feeding, whilst excess air varied from about 20% to 80%. Temperature, O2, CO, CxHy (as CH4), and NO were recorded along the combustor height and at stack, to investigate the combustion and emission performance of the reactor. Physical and chemical conditions of the bed materials and those of particulate matter emitted from the combustor were examined at different operating times using SEM−EDS and XRF techniques, and a particle size analyzer. To achieve high (98.4-99.1%) combustion efficiency of the combustor, meeting the national CO and NO emission limits, excess air of about 40% is required when burning pre-dried EFB in a fluidized bed of alumina sand, whereas 60% excess air is suitable with limestone and dolomite. By using the selected bed materials, bed agglomeration can be prevented, thus ensuring safe and high-efficient combustion of this biomass for a relatively long time. However, the bed materials are subject to substantial time-domain changes in their physical and chemical properties.