Fluidised Bed Gasification of Diverse Biomass Feedstocks and Blends-An Overall Performance Study

The aim of this work is to investigate the fluidised bed gasification of several pure and blended feedstock prepared in the form of pellets: oak bark, two bark/wheat straw blends (85/15 and 50/50 wt%) and lignin residue remaining from bioethanol production. Gasification conditions were defined to be representative of dual fluidised bed ones (steam gasification at 850 degrees C, followed by air combustion of the char). The cold gas efficiency (77-81%), gas composition and tar content (0.9-2.3 g/kg(daf)) are close for the gasification of bark and the two bark/wheat straw blends. For lignin residue, the cold gas efficiency is lower (71%), and the tar content is 9.1 g/kg(daf). The agglomeration propensity is much higher for lignin residue than for the other feedstock. This was put into evidence with in-bed temperature measurements at different levels, and confirmed with post-test size screening of the bed material particles. The 50/50 wt% bark/wheat straw blend seems to undergo defluidisation in combustion, however followed by refluidisation of the bed. These findings were also well correlated with a predictive model for defluidisation.