Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – With regeneration – reclamation – reuse – recycling or...
Patent
1995-12-01
1997-09-16
Czaja, Donald E.
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
With regeneration, reclamation, reuse, recycling or...
162 301, 162 35, 423183, D21C 1104
Patent
active
056676336
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the production of white liquor in the recovery of chemicals in a sulphate pulp process. More precisely, the invention relates to the production of white liquor having enhanced and/or reduced sulphidity starting from a calcium sulphide rich smelt of inorganic chemicals, which has been obtained by simultaneous combustion of black liquor and processing of lime sludge.
The production of a calcium sulphide rich smelt of inorganic chemicals in connection with simultaneous combustion of black liquor and processing of lime sludge has been described in the simultaneously filed patent application having the title "Combustion of black liquor".
BACKGROUND
In the production of pulp according to the sulphate pulp method wood, in the form of chips, is delignified in an alkaline solution, which mainly consists of NaOH and NaHS, in a pressurized cooking process, which in the final stage normally has a temperature in the range of 150.degree.-175.degree. C. The ratio of hydroxide ions [OH.sup.- ] to [HS.sup.- ] is normally within the range of 25-40% sulphide [2HS.sup.- ], calculated on the sum of the contents of sulphide ions and hydroxide ions.
An increased content of sulphide ions in relation to hydroxide ions in the cooking liquor increases the yield of pulp and, normally, improves the important properties of the final product. In the beginning of the cooking process, the so called impregnation stage, an increased proportion of sulphide ions forms the bases of a more efficient release of lignin during the actual cooking process. A simultaneous reduction of the contents of hydroxide ions decreases the degradation of cellulose, which results in an increased yield and higher quality of the final product.
The present invention provides a white liquor having enhanced sulphidity, which can be utilized in the above mentioned cooking process.
Further, the invention provides white liquor having reduced sulphidity. White liquor having reduced sulphidity may e.g. be used as a chemical in the production of bleached wood pulp.
DESCRIPTION OF THE INVENTION
The present invention provides a method of producing white liquor having enhanced and/or reduced sulphidity in the recovery of chemicals in a sulphate pulp process. The method implies that a calcium sulphide rich smelt of inorganic chemicals, which has been obtained by simultaneous combustion of black liquor and processing of lime sludge, is treated with an aqueous solution, whereupon the calcium sulphide in the smelt is present in solid form and the rest of the chemicals are present in solution, after which the solid calcium sulphide is separated, and manner to a white liquor having reduced sulphidity, whereupon optionally amount of white liquor, the [OH.sup.- ] of the white liquor reacting with CaS according to the reaction formula ]+[OH.sup.- ] is separated.
As initially indicated a calcium sulphide rich smelt of inorganic chemicals may be obtained when combustion of black liquor and processing of lime sludge are performed simultaneously, which is described in a patent application having the title "Combustion of black liquor" which is filed simultaneously with the present application.
The combustion may have taken place in a liquor combustion plant, which can be a conventional recovery boiler, but can also be a liquor gasification plant.
By the expression "the obtained solution is processed as a green liquor in per se known manner to a white liquor having reduced sulphidity" is meant in the specification and the appended claims that the obtained solution is processed in the same way as is known for processing of green liquor to white liquor. By "enhanced sulphidity" and "reduced sulphidity" is intended a comparison with the sulphidity of white liquor that has been previously produced in a conventional manner.
In one embodiment of the method according to the invention the solid Ca(OH).sub.2 separated in the method is further processed by addition thereof, after separation of the solid sulphide, to the obtained solution, and this is processed b
REFERENCES:
patent: 1560900 (1925-11-01), Drewsen
patent: 1743080 (1930-03-01), Bradley et al.
patent: 3336535 (1967-08-01), Cann
patent: 4941945 (1990-07-01), Pettersson
K. Salmenoja, "Development of Black Liquor Gasification", 1993 Engineering Conference, pp. 969-975.
Eriksson Ingemar
Granqvist Bertil
Pettersson Bertil
Czaja Donald E.
Korsnas AB
Nguyen Dean T.
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