LOW TEMPERATURE RECOVERY OF KRAFT BLACK LIQUOR

摘要

A kraft black liquor recovery system utilizing three separate reactors for liquor pyrolysis, sulfate reduction and carbon plus organics combustion, respectively. Oxidized black liquor is pyrolyzed in a fluid bed reactor. The temperature in the fluid bed reactor is 600.degree.C or lower.The resulting char, containing Na2CO3 and Na2SO4 and a significant amount of carbon, is separated from the pyrolysis gases and introduced in an indirect heated reactor where reduction of Na2SO4 to Na2S takes place in the solid state under an atmosphere generated by the reduction. The reduced char is cooled and leached to produce green liquor. The leached char and gases from the pyrolysis and reduction reactors are burned in a fluid bed combustion unit operating below the melting point of mixtures of Na2CO3 and Na2SO4. The fluid bed particles, consisting mainly of Na2CO3 and Na2SO4, serve to remove the volatile oxidized sulfur species formed by combustion of the pyrolysis gas. The overflow of pellets are ground and dissolved in the incoming heavy black liquor feed.