Pollution controlled polysulfide recovery process

Abstract

Abstract A chemical recovery process for a polysulfide paper pulping system is described. After the polysulfide digestion, the pulp washing is carried 3. in an essentially oxygen-free environment to minimize the oxidation of NaSH. about spent liquor is then pre-evaporated, makeup with a recycle stream of liquor containing Na2CO3 and NaHCO3 and subjected to a soap skimming operation. The mixture is next carbonated to convert Na2CO3 conventional to NaHCO3 and stripped to release H2S. The stripping and carbonation are accomplished by passing flue gas through the stripping tower and the carbonating tower. The H2S is converted to sulfur by the use of a liquid catalyst and the formed sulfur is then 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. The desulfurized liquor from the stripping operation is subjected to an oxidizing-decomposing operation to oxidize residual sulfides and decompose residual NaHCO3. The pH of the so treated liquor is then increased to baout 12.5 by the addition of makeup NaOH and recycled and separately oxidized white liquor. The resulting mixture is then evaporated to about 50 percent dry solids concentration. Finally, direct contact evaporation and combustion of the spent liquor occur as in convention kraft chemical recovery systems. Means for recovering all sulfur compounds in vent gases and condensates from all mill process units are included to reduce air and water pollution.

Inventors

• 👤 Carl Bertil Fogman
• 👤 Hugh Wharton Nelson
• 👤 Utah Tsao

Bibliographic Details