Oxidative filtration for flyash & tar removal from 1.0 MW_th fixed-bed biomass air gasification

Experimental campaigns were performed with the aim to study the hot gas filtration process during the pilot-scale biomass gasification at GIEC. This paper gives an overview of the continuous and steady filtration tests performed with stable pressure drop (ΔP) for over 200 h in 400–600 °C, using wood chip and charcoal as the feedstock. The ceramic candles show good long-term filtration performance with a permanent cake layer serving as an extra filtration medium. Tar content is found to be the controlling resistance for the biomass gasification-filtration process. A novel oxidative filtration is reported to lead to a simultaneous removal of carbonaceous flyash particles (CFPs) and tars as well as a dramatic ΔP decrease with no obvious degradation in the heating value of the producer gas, in which a tiny amount of additional air (≤5.5 vol%) is introduced into the producer gas. Under the optimum condition, the CFP removal efficiency is always >99.0% and the tar removal efficiency of 92.2% could be achieved, with ΔP kept within a range of 1000–2000 N m⁻² at the gas superficial velocity of 1.5–2.0 cm s⁻¹ and 0.5–1.5% oxygen content of the producer gas (O₂%). It is found that filter candles could act as a reactor without any catalyst to partially oxidize tars and CFPs with a little heat generation when hot gas filtration is operated in the presence of low oxygen concentration in 400–600 °C. The efficient CFP removal and tar reduction during the high-temperature oxidative filtration is beneficial for downstream units and their operability.