GB1444127A - Process for the desulphurization of sulphur dioxide-containing off-gases using a solid sulphur dioxide acceptor - Google Patents

Abstract

1444127 Desulphurization of sulphur dioxidecontaining gas SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ BV 26 Sept 1973 [28 Sept 1972] 45026/73 Heading C1A In a process for the desulphurization of sulphur dioxide-containing off-gases, using a solid sulphur-dioxide acceptor which is regenerated with a reducing gas as and when it has become loaded, and the sulphur-dioxide-rich regeneration off-gas obtained processed to elemental sulphur, at least three zones with solid sulphur dioxide acceptors are used in desulphurization of the off-gas, which zones are successively put into operation for the acceptance with subsequent regeneration in such a manner that as and when the solid acceptor in one zone has become loaded, the solid acceptor in another zone has become regenerated, a substantially constant stream of sulphur-dioxiderich off-gas being obtained, which off-gas is subsequently subjected to a reducing treatment in such a manner that two-thirds of the sulphur dioxide product is reduced to hydrogen sulphide, whereafter in a liquid medium elemental sulphur is formed from the hydrogen sulphide and the remaining portion of the sulphur dioxide. Preferred acceptors comprise a metal and/or metal compound on a suitable carrier, especially copper and/or copper oxide on alumina, and specified liquid media include aqueous solution, organic liquids and molten sulphur. Preferably five or more zones are used, at least three being in the acceptance stage and at least two in the regeneration stage, the number of zones in the acceptance stage always being greater than the number of zones in the regeneration stage, where more than five zones are used. After regeneration a zone may be purged with an inert gas before being used for acceptance, and after acceptance purging with an inert gas is effected before the said zone is used for regeneration. Suitably the pre-regeneration purge commences in one zone, which is to be regenerated at the moment that the after-regeneration purge in the other zone, which is to be used for acceptance, is completed, and the total time of pre-purging, regenerating and after-purging for each zone is always shorter than the total acceptance time for each zone. Regeneration may be effected using a hydrogen-containing gas diluted with steam, the off-gas after the reducing treatment being cooled before introduction into the liquid medium. One-third of the sulphur dioxide-rich waste gas may be by-passed around the reducing treatment and the remaining two-thirds of the gas reduced and cooled before entering the liquid medium. Reduction may be effected catalytically at 200‹ to 650‹ C., or thermally at 600‹ to 1400‹ C. Preferred catalysts are Group VI and/or Group VIII metal-containing catalysts on an inorganic oxide carrier, e.g. Mo, W and/or Cr, Fe, Co, or Ni on alumina, silica, magnesia, boria, zirconia or thoria, and Ni/Mo/ Al 2 O 3 and Co/Mo/Al 2 O 3 catalysts are preferred. Thermal reduction may be effected by supplying the sulphur dioxide-rich off gas together with light hydrocarbons and a deficiency of oxygen or of oxygen containing gas to a combustion zone. Formation of elemental sulphur in the liquid medium may take place at a temperature above the dewpoint of water. After the off-gas has passed the liquid medium it may be recycled to the zones with solid sulphur-dioxide acceptors after having passed or without having passed a combustion zone.