A study on sulphidation and regeneration of Z-Sorb III sorbent for H2S removal from simulated ELCOGAS IGCC syngas

The sulphidation and regeneration of the sorbent Z-Sorb III has been investigated at bench scale in a high-temperature, high-pressure fixed-bed unit, over a range of conditions relevant to the Puertollano IGCC plant (Spain). The effect of gas hourly space velocity (1000-5000h-1), temperature (673-773 K) and pressure (1-2 MPa) on sulphidation is studied. As predicted by thermodynamics, the sorbent is capable of reducing the H2S concentration from 10,000 ppmv to near 0 ppmv. The analysis of the experimental results shows that gas residence time has a strong effect on sorbent utilization. Below 2000h-1, the sorbent seems to promote the Boudouard reaction. As a result of this, CO content in the gas stream increases with simultaneous carbon formation in the solid phase. At higher gas velocities (3500h-1), CO disproportionation does not occur and the sulphidation reaction proceeds isothermally to complete conversion of ZnO. Further increase in space velocity to 5000h-1 leads to lower sorbent utilization, which is typical of diffusion-limited gas-solid heterogeneous reactions. On the other hand, sulphidation temperature has very little effect on sulphur loading uptake which is slightly higher at 773 K than at 673 K. Regarding the effect of pressure, the sorbent is most effective at 2 MPa, almost reaching the theoretical saturation capacity. The study of the durability of the sorbent is investigated through multiple sulphidation-regeneration cycles. Oxidative dry mild regeneration using an oxygen concentration of 2% v/v results in complete regeneration of the sulphided sorbent without severe structural property changes or activity loss. The primary reaction during regeneration of the sulphided sorbent is direct oxidation of the metal sulphide with SO2 release.