Investigation of simultaneous removal of ammonia and hydrogen sulphide from producer gas in biomass gasification by titanomagnetite

A novel hot gas cleaning process using titanomagnetite for the simultaneous removal of ammonia (NH3) and hydrogen sulphide (H2S) from a producer gas in biomass gasification has been developed. In a hot reactor operated at 500-800 °C and under atmospheric pressure, NH3 is removed by a decomposition reaction to N2 and H2, whereas H2S is removed by an adsorption reaction. Titanomagnetite was tested using three different gas streams, namely 2000 ppmv NH3 in Ar, 2000 ppmv NH3 and 230 ppmv H2S in Ar, and 2000 ppmv NH3 and 230 ppmv H2S in a simulated biomass producer gas. From the experimental results, it was discovered that ferrite (α-Fe) was readily formed by the H2 reduction of titanomagnetite and that almost complete decomposition of NH3 (100%) was achieved in Ar gas at 700 and 800 °C. The presence of H2S in a gas mixture of NH3 and Ar slightly reduced the catalytic activity for NH3 decomposition at 700 and 800 °C (>96%), and H2S adsorption of greater than 98% could be achieved in the same temperature range. Under the coexistence of a simulated biomass producer gas, the NH3 decomposition rate and H2S adsorption rate were decreased at 800 °C, which could be due to the high content of H2 (45 vol%) in the feed gas that favours the reverse reaction of NH3 decomposition and H2S adsorption, the increased surface coverage of the active α-Fe phase by adsorbed hydrogen, and the competition of α-Fe for the reverse water-gas shift reaction. Moreover, it was discovered that temperature significantly affected the removal of NH3 and H2S in the simulated biomass producer gas and thus the operation temperature needs to be optimised.