New Process of Highly Concentrated Polysulfide Liquor by Electrolysis of White Liquor (III), 2001 Pulping Conference Proceedings

M. Shimizu, K. Wantanabe, K. Kurosu, Y. Nanri, T. Andoh, J. Tanaka--The electrolytic polysulfide generation system can efficiently produce highly concentrated PS liquor from white liquor compared to the air-oxidation method. Simultaneously, caustic soda and hydrogen gas are generated. By applying this system to modified cooking method the pulp yield can be significantly increased. The economics of actual installation depend on the electrolyzer size and the electric power consumption. We should determine the suitable amount of PS generation optimizing the size and consumption requirement in each mill. We looked through the partial white liquor treatment in the electrolyzer as the efficient utilization of this system to control the amount of PS generation. In the combination of the partial white liquor treatment and modified cooking method, a significant increase of the pulp yield and the reduction of active alkali requirement were obtained at relatively low PS concentration, not necessarily the maximum PS concentration. Therefore, it is expected that the electrolyzer size and the electric power consumption can be optimized and the economics can be minimized. Moreover, we tested mechanical life of every component and long-term performance of the pilot plant electrolyzer by using mill white liquor. The long-run operation of 6 months was successfully achieved without any overhaul maintenance.