The report gives results of a study of carbide lime--a by-product of acetylene manufacture, primarily calcium hydroxide--used in a flue gas desulfurization (FGD) system at Louisville Gas and Electric (LGE). The study was undertaken to: identify sulfite ion oxidation inhibitors in carbide lime, and develop an analytical method for sulfite that avoids the interferences observed in analyzing scrubber liquors from LGE's FGD system. Thiosulfate was identified as the oxidation inhibitor in carbide lime; it was also identified (along with other reduced sulfur species) as a source of interference in the iodine titration method used at LGE for sulfite analysis. Bench-scale tests verified the presence of thiosulfate as a major inhibition to sulfite oxidation in simulated scrubber liquors. This means that the low oxidation rate (e.g., that reported at LGE with carbide lime) results in a greatly reduced tendency to calcium sulfate (gypsum) scaling, therefore a greatly improved FGD system reliability. The amount of thiosulfate required for scale-free scrubber operation is unknown. However, to bring the thiosulfate level of commercial lime up to that found in carbide lime would cost $1.50 per ton of lime (using sodium thiosulfate pentahydrate at $12 per 100 pounds). The ion chromatograph was found to be the best analytical tool for determining sulfite concentrations in carbide lime liquors.

Contract no. 68-02-2608, task no. 21, program element no EHE624A. Issued Sept. 1978. Includes bibliographical references.