Remove hydrogen sulphide (H2S) and hydrogen poly-sulphides (H2Sx) dissolved in liquid sulphur.
Hydrogen sulphide is a highly toxic and potentially explosive gas. A concentration of 600 ppmv is lethal and is explosive at approximately 3.5% vol. Dissolved H2Sx is decomposed and H2S is released in storage, during loading and unloading and also during transportation, thus leading to potentially dangerous conditions.
Liquid sulphur flowing from the Claus plant to the sulphur pit contains typically 250-350 ppmw of H2S + H2Sx. Sulphur is degassed using a contacting trayed section inside a concrete box or alternatively in a steel column. Sulphur from the pit is pumped into the degassing box where it is first sprayed and subsequently contacted with hot compressed air. Stripping air promotes the decomposition of polysulphides and releases the dissolved H2S. Degassed sulphur is returned to the product section of the sulphur pit with less than 10 ppmw of H2S. Addition of chemicals is not required.