METHOD FOR RECOVERING PULPING CHEMICALS AND REDUCING THE CONCENTRATION OF POTASSIUM AND CHLORIDE THEREIN

摘要

In a digester, wood chips and white liquor are combined and cooked under pressure to pulp the wood. This produces black liquor which is concentrated and burned in a recovery boiler. The recovery boiler produces ash that contains sodium, sulphur, potassium and chloride. The ash is dissolved and subjected to a process that recovers sodium sulfate and burkeite. The concentration of potassium and chloride is reduced, in part at least, by subjecting the ash to adiabatic cooling in a crystallizer which produces glaserite and a purge stream rich in chloride. By leaching the glaserite, sodium sulfate is removed from the glaserite, leaving potassium sulfate. The recovered sodium sulfate and burkeite can be recycled and used as pulping chemicals. The removed potassium and chloride can be further treated or appropriately discarded.