Biomass & Bioenergy, Vol.122, 145-155, 2019
Oxidative filtration for flyash & tar removal from 1.0 MWth fixed-bed biomass air gasification
Experimental campaigns were performed with the aim to study the hot gas filtration process during the pilotscale biomass gasification at GIEC. This paper gives an overview of the continuous and steady filtration tests performed with stable pressure drop (Delta P) for over 200 h in 400-600 degrees 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 Delta P 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 Delta P kept within a range of 1000-2000 N m(-2) M the gas superficial velocity of 1.5-2.0 cm s(-1) and 0.5-1.5% oxygen content of the producer gas (O-2%). 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 degrees C. The efficient CFP removal and tar reduction during the high-temperature oxidative filtration is beneficial for downstream units and their operability.