US 5,174,860 A · Low temperature recovery of kraft black liquor

Abstract

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 Na.sub.2 CO.sub.3 and Na.sub.2 SO.sub.4 and a significant amount of carbon, is separated from the pyrolysis gases and introduced in an indirect heated reactor where reduction of Na.sub.2 SO.sub.4 to Na.sub.2 S 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 Na.sub.2 CO.sub.3 and Na.sub.2 SO.sub.4. The fluid bed particles, consisting mainly of Na.sub.2 CO.sub.3 and Na.sub.2 SO.sub.4, 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.

Claims20

Dependent claims

A process for the treatment of kraft black liquor comprising:

i) pyrolyzing kraft black liquor containing inorganic salts, said salts including an oxysulphur component and a carbonate component, at a temperature of not more than 600.degree. C. to produce a char containing carbon and said inorganic salts with minimal conversion of the oxysulphur component to sulphide,
ii) reducing said oxysulphur component of said char to a sulphide salt component with said carbon of said char inside the char, in an atmosphere generated by the reduction, at a temperature above 600.degree. C. and below the melting temperature of said salts in said char, said atmosphere favoring conversion to a sulphide with minimum production of hydrogen sulphide of other sulphur containing gases in said char at said temperature above 600.degree. C. and below the melting temperature of said salts in said char,
iii) cooling the char from ii),
iv) leaching the cooled char from iii) with an aqueous leaching liquid to leach inorganic salts comprising carbonates and sulphides therefrom, and
v) recovering the aqueous liquid bearing said salts from iv) as a green liquor.

2 more elements

Dependencies are inferred from the claim text.

Low temperature recovery of kraft black liquor

Life of this patent

Low temperature recovery of kraft black liquor

Life of this patent

Abstract

Claims20