Pulp mill recovery system

Claim 1

A method of increasing recovery capacity of a kraft pulp mill without substantially increasing the emissions from a smelting kraft recovery furnace having a boiler section, comprising, cooking cellulosic material thereby to produce a kraft pulp, separating spent black liquor from said pulp, concentrating said black liquor, injecting a portion of said concentrated black liquor to an oxidation zone in said kraft recovery furnace whereby a char is formed and collected as a char bed on a hearth at the bottom of said kraft recovery furnace, maintaining a reducing atmosphere in said char bed, thereby to transform sodium sulfate contained in said spent black liquor to sodium sulfide, injecting a further portion of said spent black liquor to an oxidation zone external of said Kraft recovery furnace thereby to form pellets containing sodium carbonate and sodium sulfate from said further portion of said black liquor, injecting said pellets free from entraining liquid into said kraft recovery furnace and onto said char bed, said pellets being substantially spherical and sufficiently large so that there is no significant entrainment of the pellets by the furnace gases and yet small enough so that operation of the furnace is not disrupted to render the process inoperative, and maintaining a temperature and reducing conditions in said bed thereby to convert sodium sulfate in said pellets to sodium sulfide, and withdrawing a smelt of sodium sulfide and sodium carbonate from said kraft furnace.

Claim 2

A method of increasing recovery capacity of a kraft pulp mill without substantially increasing the emissions from a smelting kraft recovery furnace having a boiler section, comprising, cooking cellulosic material thereby to produce a kraft pulp, separating spent black liquor from said pulp, concentrating said black liquor, injecting a portion of said concentrated black liquor to an oxidation zone in said kraft recovery furnace whereby a char is formed and collected as a char bed on a hearth at the bottom of said kraft recovery furnace, maintaining a reducing atmosphere in said char bed, thereby to transform sodium sulfate contained in said spent black liquor to sodium sulfide, injecting a further portion of said spent black liquor to an oxidation zone external of said Kraft recovery furnace thereby to form pellets containing sodium carbonate and sodium sulfate from said further portion of said black liquor, injecting said pellets free from entraining liquid into said kraft recovery furnace and onto said char bed, said pellets being substantially spherical and sufficiently large so that there is no significant entrainment of the pellets by the furnace gases and yet small enough so that operation of the furnace is not disrupted to render the process inoperative, and maintaining a temperature and reducing conditions in said bed thereby to convert sodium sulfate in said pellets to sodium sulfide, and withdrawing a smelt of sodium sulfide and sodium carbonate from said kraft furnace.