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

摘要

A novel hot gas cleaning process using titanomagnetite for the simultaneous removal of ammonia (NH_3) and hydrogen sulphide (H_2S) from a producer gas in biomass gasification has been developed. In a hot reactor operated at 500-800 ℃ and under atmospheric pressure, NH_3 is removed by a decomposition reaction to N_2 and H_2, whereas H_2S is removed by an adsorption reaction. Titanomagnetite was tested using three different gas streams, namely 2000 ppmv NH_3 in Ar, 2000 ppmv NH_3 and 230 ppmv H_2S in Ar, and 2000 ppmv NH_3 and 230 ppmv H_2S in a simulated biomass producer gas. From the experimental results, it was discovered that ferrite (α-Fe) was readily formed by the H_2 reduction of titanomagnetite and that almost complete decomposition of NH_3 (100%) was achieved in Ar gas at 700 and 800 ℃. The presence of H_2S in a gas mixture of NH_3 and Ar slightly reduced the catalytic activity for NH_3 decomposition at 700 and 800 ℃ (＞96%), and H_2S adsorption of greater than 98% could be achieved in the same temperature range. Under the coexistence of a simulated biomass producer gas, the NH_3 decomposition rate and H_2S adsorption rate were decreased at 800 ℃, which could be due to the high content of H_2 (45 vol%) in the feed gas that favours the reverse reaction of NH_3 decomposition and H_2S 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 NH_3 and H_2S in the simulated biomass producer gas and thus the operation temperature needs to be optimised.