抄録
Low temperature gasification technologies for biomass are required to achieve a higher efficiency. However, large amount of tar, which causes many troubles in down stream, is produced in low temperature conditions. Tar reduction is needed to develop a low temperature gasification technology. It is well known that porous catalyst particles absorb tar and carbon is deposited on the surface of particles in a packed bed reactor at 1000K. Confirmation of this effect in more dilute conditions such as fluidized bed or circulating fluidized bed is needed when this effect is applied to actual processes. Therefore, gasification experiments of biomass by a circulating fluidized bed gasifier were carried out. Alumina-base porous particles were used as a bed material. Wood chip less than 2mm was fed continuously into the bottom of riser and temperature in the riser was set in the range of 873 - 973K. Nitrogen was used as a fluidizing gas and steam or air was added in some experiments. Porous particles were regenerated by a fluidized bed combustor, in which deposited carbon on the surface of particles was burned, and recycled into the bottom of the riser. Experimental results showed that porous particles successfully absorb tar in the riser. Typical tar concentration in the produced gas was about 20 - 30 g/m3N at 940K. H2, CO and CH4 were main component in the produced gas. Especially, H2 concentration exceeded more than 60% due to decomposition of tar by the porous particles when regeneration was omitted. These results suggest that using porous particles as a bed material can be applicable to actual low temperature biomass gasification processes.
