Process for removing sulfur moieties from claus tail-gas

Abstract

Claus tail-gas containing H.sub.2 S and SO.sub.2 in a mol ratio of 2:1 is passed in contact with a catalyst-adsorbent bed (19A) at a temperature of 135.degree. to 150.degree. C. and a space velocity of 50 to 1500 h.sup.-1 whereby elemental sulfur produced by the reaction of H.sub.2 S and SO.sub.2 is deposited upon and/or adsorbed on said bed. The resulting sulfurous gas mixture is cooled by indirect heat exchange (26) to a temperature of 120.degree. to 135.degree. C. and liquid elemental sulfur is recovered (27,54,55,101) the sulfurous gas (28) thereafter being cooled and diluted by adding cool inert gas (34) thereto to maintain the water partial pressure below the saturation vapor pressure, and the cooled diluted gas mixture is contacted with a bed of catalyst-adsorbent (32A) at a temperature of 90.degree. to 125.degree. C. whereby further elemental sulfur is produced by the reaction of SO.sub.2 and H.sub.2 S. The elemental sulfur deposits upon and/or is adsorbed on the catalyst-adsorbent and the resulting purified gas (34) is incinerated (37) and discharged (38) to the atmosphere. In one embodiment, the gas from the indirect heat exchange step (26) is contacted with catalyst-adsorbent (30A) at 120.degree. to 135.degree. C. before cool inert gas (34) is mixed therewith, elemental sulfur being deposited upon and/or adsorbed on the catalyst-adsorbent. Elemental sulfur is removed from the catalyst-adsorbent beds by a hot, inert purge gas (44,46) which is cooled (19B,52) for sulfur recovery. The purge gas is cooled (52) at the end of the sulfur-recovery step to cool the catalyst-adsorbent beds for a further cycle of sulfur recovery from Claus tail-gas.