Hydrogen Sulfide Retention on Limestone at High Temperature and High Pressure

Abstract

The suitability of limestone as a sorbent for hydrogen sulfide was tested at coal gasification conditions. Experiments were carried out in a fixed bed reactor at pressures and temperatures up to 10 bars and 1223 K respectively. The influence of pressure, temperature, particle size and gas composition was tested. Especially the partial pressure of CO₂ relative to the calcination pressure is important for the sulfur capacity of the limestone. This partial pressure is in practical systems determined by the gasification process employed. At low partial pressure of CO₂ the limestone calcines and CaCO₃ is converted into CaO. At these conditions an almost quantitative conversion of CaO to CaS was observed. The rate of reaction between CaO and H₂S increased with decreasing particle diameter. At high partial pressure of CO₂, CaCO₃ is stable and the limestone remains uncalcined. In this case the ultimate degree of conversion into CaS was below 0.25 even for very porous limestones. The conclusion is that for gasification processes with a partial pressure of CO₂ below the equilibrium pressure over CaCO₃, e.g. 0.2 bar at 1073 K and 2.0 bar at 1173 K, limestone is a suitable sorbent for hydrogen sulfide.