Removal of sulphur from coal by air oxidation at 350–450 °C

Abstract

Abstract The extent of sulphur removal from seven U.S. coals has been studied by low-temperature oxidation. The total sulphur in these coals varied between 3 and 7% by weight. The pyritic sulphur constituted approximately 50% of the total sulphur. A major part of the study has been carried out at oxidation temperatures of 350, 400 and 450 °C. Temperature, up to 450 °C, is a prime factor determining the extent of desulphurization. The efficiency of removal is controlled by the diffusion of oxygen into coal and its pyrite. More than 90% of the pyritic sulphur can be removed at 450 °C in 10 min in some cases. The rate of removal is unaffected by the build-up of sulphur dioxide concentration in the air stream to at least 10%. That is, the level of sulphur dioxide concentration in the effluent gases can be increased for sulphuric acid manufacture by successive recycling of the effluent gases over fresh charges of coal. The calorific value and the VM decrease during this desulphurization treatment. The importance of the loss can be minimized if the desulphurized coal is fed directly to the boiler while at about 450 °C. The process can be made self-sustaining by proper control of the coal/air ratio.