Method for polysulfide production in a kraft pulp mill

A method for producing an oxidized white liquor, for use in a kraft pulp mill which comprises the steps of:

• (a) feeding green liquor to a slaker, adding burnt lime to the green liquor, and passing the liquor from the slaker to a series of causticizing vessels;
• (b) withdrawing causticized liquor containing calcium carbonate from the series of causticizing vessels and passing the causticized liquor to a first filtering process to obtain an accept flow of white liquor with a first order of suspended solids measured in ppm and a reject flow of lime mud
• (c) passing the accept flow of white liquor through a second filtering process to obtain a filtered white liquor with a second order of suspended solids measured in ppm, said second order of suspended solids being at least half the order as of the first order of suspended solids and below 5 ppm, said second filtering process comprising an essentially continuously operating cross flow filter, whereby a permeate passing through cross flow filter elements in the cross flow filter forms the filtered white liquor and the discharged flow of retentate (V1) is bled off and sent back to the causticizing vessels, and
• (d) passing the filtered white liquor through a polysulfide reactor with addition of an oxygen containing gas for promoting conversion of sulfides to polysulfide.