Stability and oxidative stabilisation of sulphided calcareous sorbents from entrained flow gasifiers

Abstract

The stability of different sulphided materials (pure CaS particles, sulphided calcium hydroxide, sulphided limestone, sulphided dolomite and sulphided calcium magnesium acetate) when exposed to a moistened stream of air at ambient conditions has been studied. For all the analysed sorbents, the release of H 2S during exposure to a moistened stream of air is a function of the calcium sulphide content of the sorbent. The ratio between the amount of released sulphur and the amount of sulphur stabilised as sulphate or elemental sulphur is also a function of the initial calcium sulphide content of the sorbent. Additionally, the performance of air oxidation at different temperatures (800–980°C) for stabilisation of the sulphided sorbents has been analysed. The final apparent conversion achieved during air oxidation of the sulphided sorbents, including particles of sulphided calcium acetate, in the temperature range 800–980°C shows an inverse dependence with the (calcium sulphide content)/(specific surface area) ratio of the sorbents. The total amount of SO 2 released during air oxidation at high temperature is a function of the initial calcium sulphide content of the samples. Conversion degrees up to 100% have been obtained. For all sorbents, the conditions for complete stabilisation and negligible SO 2 release during oxidation were established. The differences found in final oxidation conversions and stability of the oxidised sorbents for increasing oxidation temperatures can be explained in terms of the oxidation mechanisms for low (<890°C) and high temperatures.