Experimental Study and SEM-EDS Analyses of Agglomerates from Gasification of Biomass in Fluidized Beds

Abstract

Fluidized bed gasification is an attractive conversion technology for production of sustainable energy from biomass. The advantages of excellent fluid mixing, high heat and mass transfer and uniform temperatures allow the fluidized beds to process biomass materials with different qualities under controlled operating conditions. However, processing biomass-derived fuels in fluidized bed can suffer from ash related problems. Bed agglomeration has been reported as one of the problematic issues prohibiting an economical and trouble-free operation. In this work, bed agglomeration of two different types of biomass, grass pellets and wood pellets, in a 20 kW laboratory scale bubbling fluidized bed gasifier was studied. The present study compares the agglomeration tendency of wood and grass pellets, focusing on the de-fluidization temperatures and the variation in microstructure and composition of agglomerates.  After each of the different tests, residual sand and agglomerates were discharged. A scanning electron microscope with energy dispersive X-ray spectroscopy was used for characterizing the morphology and the elemental composition of the collected agglomerates. The findings show that the surface of agglomerates formed during gasification of grass pellets were dominated by Si, Ca and K, while the surface of agglomerates from wood pellets mainly were dominated by Si and K.

Keywords: Biomass gasification, Biomass, fluidized bed, biomass characteristics, bed agglomeration, SEM-EDS analyses