Extraction of elemental sulphur from sulphur compound gases

A process for the extraction of sulphur compound gases from a supply gas in the form of elemental sulphur, the process comprising forming a downwardly moving bed of catalyst in a container, introducing catalyst into the container at the top of the bed at a temperature less than the dew point of sulphur, withdrawing catalyst from the bottom of the bed, injecting the supply gas into the container at the bottom of the bed at a temperature higher than the boiling point of sulphur such that the gases at the top of the bed react on the catalyst to form elemental sulphur which condenses on the catalyst and such that the gases at the bottom of the bed vaporize and strip the condensed elemental sulphur from the catalyst, withdrawing from the container at a first withdrawal position and a second withdrawal position spaced along the height of the bed gases comprising less than the total flow of gases in the container, condensing and extracting elemental sulphur from said withdrawn gases and returning said gases to the bed at a first return position and a second return position, the container providing a path for flow of the bed of catalyst, which path is substantially free from valving arrangements restricting the flow of catalyst, wherein the first return position is downstream of the second withdrawal position and wherein the second withdrawal position is arranged relative to the first withdrawal position and first return position such that substantially the whole of the remainder of the gases not withdrawn at the first withdrawal position is withdrawn together with a proportion of the gases returned at said first return position.