Process for simultaneously removing nitrogen oxides, sulfur oxides, and particulates

Claim 1

A gas purification process, comprising the steps of: cracking a hydrocarbon feedstock in a reactor of a catalytic cracking unit in the presence of a cracking catalyst under catalytic cracking conditions to produce an upgraded cracked product leaving spent cracking catalyst; regenerating said spent cracking catalyst in a regenerator; emitting particulate-laden regenerator off-gases comprising nitrogen oxides, suflur oxides, and cracking catalyst particulates from said regenerator; passing said regenerator off-gases and a nitrogen oxide-capturing reducing agent generally downwardly together through a substantially vertical conduit of a granular bed filter and scrubber, and thereafter, through at least a portion of a downwardly moving bed of sulfur oxide-capturing and pariticulate-removing material to remove a substantial portion of said cracking catalyst particulates, nitrogen oxides, and sulfur oxides from said regenerator off-gases so as to produce molecular nitrogen and substantially purified gases having a substantially lower concentration of nitrogen oxides, sulfur oxides, and cracking catalyst particulates than said regenerator off-gases and leaving spent sulfur oxide-capturing and particulate-removing material with said cracking catalyst particulates and sulfur-containing deposits thereon selected from the group consisting of sulfur oxides, sulfates, and combinations thereof; removing said spent material from said granular bed filter and scrubber and feeding said removed material to a generally upright lift pipe riser having an overhead collection vessel; regenerating said spent sulfur oxide-capturing and particulate-removing material in said lift pipe riser while simultaneously moving said spent sulfur oxide-capturing and particulate-removing material substantially upwardly through said lift pipe riser to substantially remove said cracking catalyst particules and said sulfur-containing deposits from said spent sulfur oxide-capturing and particulare-removing material while emitting effluent gases containing said removed particulates and sulfur-containing gases selected from the group consisting of hydrogen sulfide, sulfur oxides, and combinations thereof, liberated from said sulfur-containing deposits; feeding said regenerated sulfur oxide-capturing and particulate-removing material directly to said granular bed filter and scrubber from said lift pipe riser for use as part of said downwardly moving bed; removing a substantial portion of said particulates from said effluent gases in at least one cyclone; recovering elemental sulfur from said sulfur-containing gases in said effluent gases from said lift pipe riser in a sulfur recovery unit; said sulfur oxide-capturing and particulate-removing material being selected from the group consisting essentially of absorbers and adsorbers with at least one promoter thereon, said adsorbers comprising an oxide of at least one metal selected from the group consisting of aluminum, bismuth, manganese, yttrium, antimony, copper, tin, rare earth metals, Group 1a metals, and Group 2a metals, and said promoter comprising at least one member, in a free or combined form, selected from the group consisting of rare earth metals, Group 8 nobel metals, chromium, vanadium, rhenium, antimony, silver, and combinations thereof; and at least 90% by weight of said sulfur oxides in said regenerator off-gases are removed by said bed.