Reduction of odorous reduced sulfur emissions from kraft pulp mills using green liquor dregs

摘要

This study investigated the use of mill-generated green liquor dregs to reduce total reduced sulfur (TRS) emissions in mill waste gas streams to concentrations people would not smell.We also propose a mechanism for reduced sulfur gas removal.Laboratory experiments have shown that a packed bed of dregs can continuously lowerTRS concentrations to nondetectability for extended periods.Results from individual metal sulfide and oxide trials suggest that two different catalytic oxidation mechanisms are responsible for the removal ofTRS gases by green liquor dregs.Iron and manganese oxides and sulfides showed an ability to oxidize hydrogen sulfide and methyl mercaptan to sulfur dioxide and elemental sulfur.Those,in turn,reacted with methyl mercaptan or dimethyl sulfide and dimethyl disulfide to form gaseous dimethyl polysutfides.Calcium carbonate was able to oxidize all fourTRS gases directly to sulfur dioxide.The lack of polysulfide formation in this case suggests that either elemental sulfur is not an intermediate in the oxidation of theTRS gases or that elemental sulfur may form,but does not react with,theTRS gases to form polysulfides.A mill trial has verified the laboratory results.