04/00618 Zinc ferrite and related sorbents for hot gas desulfurization process: Ishimori, M. et al. Preprints of Symposia — American Chemical Society, Division of Fuel Chemistry, 2003, 48, (1), 413–414

Abstract

In order to realize the highly effective coal gasification power plants, development of hot-gas cleanup system, especially highly efficient desulfurization technology for hot coal gas is required. We have studied zinc ferrite and related compounds as sorbents for hot reductive gas produced by an entrained-flow gasifier, with consideration of the results of desulfurization operations at Nakoso pilot plant. The characteristics of zinc ferrite and related systems were investigated in terms of sorbents for hot-gas desulfurization process using simple reductive gas involving reductive sulfur substance represented by H2S, as described hereafter. Experimental Sorbents. Zinc ferrite and related sorbents were prepared as follows. A mixed solution of zinc nitrate (1.5 mol/l, 50 ml) and iron nitrate (III) (1.5 mol/l, 100 ml) was stirred in a flask in the presence of colloidal silica. Then ammonia aqueous solution was added to this solution. The precipitates obtained from the solution (pH 7-8) were washed with water after filtration, dried at 120 °C and calcined at 800°C for 5h. ZnFe2O4-SiO2 sorbent thus obtained was confirmed by XRD analysis. ZnFe2O4-SiO2-ZrO2 or ZnFe2O4-SiO2-TiO2 sorbent was prepared by mixing ZnFe2O4-SiO2 sorbent with ZrO2 or with TiO2 (anatase), and calcined at 500 °C for 1h. The composition of the sorbents was determined by the atomic ratio of component oxides using XRF (X-ray fluorescence system) and ICP (Inductively coupled plasma) methods. Desulfurization. Sorbent performance test for desulfurizationregeneration (cycle of sulfidation and oxidation of sorbent) was carried out in a down flow fixed-bed reactor made of quartz under atmospheric pressure. The reductive gas for H2S absorption test is composed of 20% of H2, 1000 ppmv of H2S, and N2 (balance). The sorbent such as ZnFe2O4-SiO2-ZrO2 (or TiO2) system was prepared by composition of 200 mg of ZnFe2O4-SiO2 sorbent and 400 mg of ZrO2 (or TiO2). Analyses of the inlet gas and outlet gas from the reactor were carried out by gas chromatography using a thermal conductivity detector (TCD) and a flame photometric detector (FPD). The total gas flow rate was 100 ml/min (20°C, standard) by using mass flow controllers. Concentration of H2S at the outlet of the