Optimization of Operating Conditions for the Catalytic Reduction of SO 2 Produced from Regeneration Process in Hot Gas Desulphurization

Abstract

In order to remove hydrogen sulphide from a synthetic gas produced in a gasifier, a hot gas desulphurization (HGD) system was set up in this study. HGD process in the IGCC consisted of sulphidation process, regeneration process and direct sulphur recovery process. The fluidized-bed reactor system for coal gas desulphurization and the fixed-bed reactor system for catalytic SO2 reduction were integrated and the optimum operating conditions for the direct sulphur recovery process were investigated in this study. Zinc-based sorbents (ZZF) were used for the hydrogen sulphide removal. The sulphur content of the gasified coal gas was reduced from 10000 parts per million to several ppmv in a fluidized-bed reactor. The concentration of SO2 in the exiting gas from the reactor during regeneration process was about 3 vol%. The produced SO2 in regeneration process was converted to elemental sulphur in the direct sulphur recovery process (DSRP). The catalytic reduction of SO2 was carried out on the Sn–Zr based catalysts with the simulated coal gas containing H2 and CO as reducing agents. The test for DSRP was performed in the temperature range of 300–550°C. Space velocity (GHSV) was 10000 cm3 g-cat h−1 and the mole ratio of reductants (H2 + CO) to SO2 was 2.5. All three unit processes in HGD, sulphidation, regeneration and DSRP, were integrated in this study. In the integrated tests, it was confirmed that the unreacted oxygen in the regeneration process caused a secondary reaction in DSRP. In order to prevent the secondary reaction, the unreacted oxygen was minimized during the regeneration process. Its amount was maintained less than 0.1 vol% at conditions of the 3 vol% concentration of oxygen in the entering gas to the reactor at 6508C. Around 92% conversion and 75% elemental sulphur yield were obtained in the DSRP test integrated with the desulphurization in a lab-scale fluidized-bed unit.