Agglomeration and defluidization of silica sand and bentonite particles during empty fruit bunch (EFB) ash addition in bubbling fluidized bed (BFB) processes

Abstract

Interaction of silica sand or bentonite particles with alkaline components contained in ash of empty fruits bunches (EFB) was investigated by observation of agglomeration and defluidization behaviors in a bubbling fluidized bed process at conventional gasification temperatures. In this study, agglomeration and defluidization formation along with EFB ash addition were evaluated by differential pressure change of the fluidized bed, and sticky level of agglomerates estimated by elemental analysis of particles in bed residue and discharged line. Fluidization operation at 750°C showed that number of coarse agglomerates formed after at more than 0.12 wt% of EFB ash addition with high sticky level on silica sand particles while bentonite kept running in normal fluidization until 4.66 wt% addition. Bubbling fluidization at 800°C has a higher tendency to form bigger and stickier agglomeration on both particles. In the silica sand bed, hard and sticky agglomerates were built up to form extensive bulk agglomerates at more than 1.55 wt% ash addition. On the other hand, bentonite also produced huge agglomerates, but a part of the bed was still fluidized because of the formation of weak agglomerates. The difference was caused by the structure of the agglomerates. Application of bentonite in fluidized bed gasifiers is, therefore, more promising to maintain fluidization state than silica sand.