Abstract
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 °C, followed by air combustion of the char). The cold gas efficiency (77–81%), gas composition and tar content (0.9–2.3 g/kgdaf) 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/kgdaf. 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.
Highlights
Fluidised-bed gasification is one of the major process to reach a high gas product yield from a large panel of carbonaceous resources
We aim at investigating the fluidised bed gasification of two oak bark/wheat straw blends, of the same oak bark alone, and of an atypical biomass industry coproduct: lignin residue remaining from bioethanol production
A focus is made on temperature measurement in the bubbling fluidised bed, both during biomass gasification and char combustion tests
Summary
Fluidised-bed gasification is one of the major process to reach a high gas product yield from a large panel of carbonaceous resources (biomass, wastes). Autothermal gasification with O2 , or so-called ‘allothermal’ gasification in a dual fluidised bed, generally performed with steam, can allow producing an almost inert gas free synthesis gas, well-adapted for further biofuel or chemical product synthesis [1]. Tar species present in the synthesis gas should always be removed to reach very low content values, in order to avoid catalyst poisoning in the synthesis process. The gas composition should be adapted to reach the synthesis process specifications (target H2 /CO ratio usually). This can be performed by adapting the gasification conditions and the type of bed material [2], or by using catalysts in fixed beds after the gasification step [3]
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