From aromatic tars to light hydrocarbon gas species during biomass steam gasification in a 100kW dual fluidised bed gasifier

In biomass gasification, gas cleaning to remove and convert tar compounds is one of the main challenges for the successful commercialisation of biomass gasification. In order to understand tar formation mechanism during the gasification process, and estimate the tar yield under different operating conditions, this study has investigated tar yield and composition both from initial devolatilization stage and final the subsequent gasification stage. Experiments were conducted on a 100kW dual fluidised bed (DFB) gasifier over the temperature range of 700-800degreesC with a residence time of 1.9 -2.5 s. Tar components were quantified by gas chromatography with a flame ionisation detector (GC-FID) analysis. The experimental results showed that a close correlation between the aromatic tar components formed in the initial devolatilization stage and the concentration changes in light hydrocarbon gases (CH4, C2H4 and C2H6) in the producer gas. The forms of these relations vary with the gas species and are affected by operating conditions of gasification, types of gasifier and biomass composition. These results will help understand the tar conversion and transformation process during the biomass steam gasification and optimise the gasification process for low tar concentration in the producer gas.