Tar abatement in a fixed bed catalytic filter candle during biomass gasification in a dual fluidized bed

• A hot catalytic filter for tar abatement was tested at 800 °C.
• The tests were carried out with biomass tar produced in situ.
• Tar conversion reached 75% regardless the tar content at the catalytic filter inlet.
• For the tar produced at 850 °C, only naphthalene was detected at the filter outlet.
• High face velocities in the catalytic filter decreased tar conversion.

Catalytic filters are a novel technology for tar conversion in biomass gasification processes. Both particle elimination and tar abatement can be achieved in a single step at high temperatures minimizing energy efficiency penalties. This paper analyses the performance of a fixed bed catalytic filter candle in the reduction of biomass tar generated in situ in a dual fluidized bed gasifier (DFBG). In this study, the temperature of the filter was limited to 800 °C. Several variables affecting the performance of the filter were tested. Experiments at different gasification temperatures in the range 750–850 °C were performed so that the amount of tar reaching the catalytic filter was varied. The amount of tar at the catalytic filter inlet did not affect the tar conversion achieved which was around 75%. The major tar compound in the gasification gas at the outlet of the catalytic filter was naphthalene. At the highest temperature tested (850 °C), the tar content in the clean gas was 0.65 g/Nm3. The effect of the face velocity in the filter on the tar conversion reached was evaluated. Tar conversion decreased when the face velocity increased from 40 to 90 m/h as the residence time of the gas in the catalytic filter was lower. The ratio H2O to dry biomass was also varied (0.5–0.9) in order to produce tars of different nature. Higher conversions were achieved for higher values of this ratio.

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