POLLUTION CONTROLLED POLYSULFIDE RECOVERY PROCESS

摘要

A chemical recovery process for a polysulfide paper pulping system is described. After the polysulfide digestion, the pulp washing is carried out in an essentially oxygen-free environment to minimize the oxidation of NaSH. The spent liquor is pre-evaporated and mixed with a recycle stream of liquor containing Na2CO3 and NaHCO3. The mixture is next carbonated with a gas stream rich in CO2 which has been generated from lime kiln flue gas. The carbonated spent liquor is then vacuum stripped to release H2S which is converted to sulfur. The sulfur is mixed and reacted with Na2S in at least part of the white liquor to form sodium polysulfide. The polysulfide liquor and any remaining white liquor are returned to the digester.