Reduction of Odorous Reduced Sulfur Emissions from Kraft Pulp Mills Using Green Liquor Dregs, 2005 Engineering, Pulping & Environmental Conference

This study has investigated the use of mill-generated green liquor dregs to reduce TRS emissions in mill waste gas streams to concentrations below the odor threshold. To be able to implement a process technology that employs a sorbent (i.e., dregs) that is self-generated, readily available, and does not produce a secondary waste stream that requires additional treatment should be an attractive low-cost alternative. Laboratory experiments have shown that a packed bed of dregs can lower total reduced sulfur concentrations to nondetectability continuously for extended periods. Based upon results from individual metal sulfide/oxide trials, it is believed that two different catalytic oxidation mechanisms are responsible for the removal of TRS gases by green liquor dregs. Iron and manganese oxides and sulfides showed an ability to oxidize H2S and methyl mercaptan to SO2 and elemental sulfur, which in turn reacted with methyl mercaptan and/or DMS and DMDS to form dimethyl polysulfides. CaCO3 showed an ability to oxidize all four TRS gases directly to SO2; the lack of polysulfide formation in this case suggests that either elemental sulfur is not an intermediate in the oxidation of the TRS gases, or that elemental sulfur may form, but does not react with the TRS gases to form polysulfides. A mill trial has verified results, and a mechanism for the reduced sulfur gas removal is proposed.