Co-gasification of blended lignite and wood pellets in a 100 kW dual fluidised bed steam gasifier: The influence of lignite ratio on producer gas composition and tar content

Abstract

A study has been conducted on co-gasification of blended lignite and wood on the performance of a 100kW dual fluidised bed (DFB) steam gasifier. In the experiments, inert silica sand was used as the bed material and the operating temperature in the bubbling fluidised bed gasification reactor (BFB) was controlled at 800°C while that in the fast fluidised bed combustion reactor (FFB) was maintained at 850°C. Lignite was blended with radiata pine sawdust at mass ratios of lignite in the blend being 0% (or 100% wood), 40%, 70% and 80%, respectively. The blends were then pelletised for the tests. For the 100% lignite run, lignite particles supplied (without pelletising) were used. From the experimental results, it was found that the producer gas yield and producer gas compositions were non-linearly correlated to the lignite to wood ratio, which shows a synergy with the pelletising blending. The experimental results also show that with the lignite to wood ratio increasing from 0% to 100%, the H2/CO ratio increased asymptotically from 1.0 to 2.4 while the tar concentration and tar yield decreased from 9.0 to 2.7g/Nm3 and from 6.6 to 2.3g/kgdry fuel, respectively. The optimum H2/CO ratio of 2 for Fischer–Tropsch synthesis can be achieved by blending 40% lignite and 60% wood as feedstock, therefore, use of expensive catalytic bed material or increase of gasification temperature over 800°C to achieve this target H2/CO ratio may not be necessary.