Special Report No. 71-01: Suggested Procedures for the Conduct of Lime Kiln Studies to Define Minimum Emissions of Reduced Sulfur Through Control of Kiln and Scrubber Operating Var

Recent technical advances in the control of the emission of gaseous odorous sulfur compounds from the Kraft pulping process have established the lime kiln to be a major point source contribution of hydrogen sulfide amounting to as much as 1 pound reduced sulfur per ton air dried pulp. New generation Kraft recovery boilers which eliminate the use of the direct contact evaporator have demonstrated their emission of hydrogen sulfide can be maintained at levels of less than 0.1 pounds per ton of air dried pulp. Indications are that direct contact evaporator type systems can approach similar stack emission rates with the practice of complete black liquor oxidation and maintenance of a suitably high pH in the liquor feed. Non-condensables from the multiple-effect evaporators and digesters can be virtually completely destroyed by thermal oxidation in the lime kiln or by equivalent treatment. It is therefore desirable that kiln and scrubber operating variables which control the emission of hydrogen sulfide and other reduced sulfur be identified to determine what level of minimum reduced sulfur emission can be achieved through control of operating variables.