IN-SITU PRODUCTION OF POLYSULFIDE LIQUOR IN A KRAFT MILLS CAUSTICIZERS .2. PROCESS SCALE-UP AND ECONOMICS

Batch and continuous pilot plant trials at two kraft mills, summarized in Part I, confirmed the technical feasibility of partial and selecti ve oxidation of a portion of the sulphide in white liquor to polysulph ide, using lime mud as the primary oxidation catalyst. Full-scale syst ems for a 1000-t/d kraft mill were designed using engineering data fro m the plot plant trials. Capital costs for a system utilizing oxygen w ere found to be significantly lower than for a system utilizing air or for commercial systems utilizing activated carbon catalysts. Assuming a 2%, increase in pulp yield in comparison to conventional kraft pulp ing, payback periods of 1.2 to 5.8 months were estimated.