Study on burning oil palm kernel shell in a conical fluidized-bed combustor using alumina as the bed material

Fluidized-bed combustion of high-alkali biomass fuels is associated with a high risk for bed agglomeration when using conventional bed material (silica sand). In this work, oil palm kernel shell was burned in the conical fluidized-bed combustor (FBC) using alumina sand as the bed material to avoid this operational problem. Thermogravimetric characteristics of the selected biomass were investigated prior to combustion experiments to assess its thermal and combustion reactivity. The combustion tests were performed at rated (45 kg/h) and reduced (30 kg/h) fuel feed rates with excess air within 20-100% for each combustor load. SEM/EDS analysis of the original/reused bed material was performed for different operating times when running the combustor at the rated load. For the ranges of operating conditions, combustion efficiency of the conical FBC was basically high, about 99%, whereas the major gaseous (CO and NO) emissions from the combustor were at levels meeting the national emission limits. No evidence of bed agglomeration was observed during the entire test period of about 45 h. A thin coating (rich with Al, Si, Ca, Mg, and Fe) was observed on external and internal surfaces of the bed material particles at all the operating times. However, the chemical composition of the bed material exhibited substantial time-domain changes indicating a gradual reduction in the bed capability to withstand bed agglomeration during the combustion of oil palm kernel shell.