Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Continuous chemical treatment or continuous charging or...
Reexamination Certificate
1998-07-29
2001-01-30
Silverman, Stanley S. (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Continuous chemical treatment or continuous charging or...
C162S015000, C162S016000, C162S017000, C162S019000, C162S047000
Reexamination Certificate
active
06179958
ABSTRACT:
The present invention relates to a method for continuous cooking of cellulose-containing fibre material, the said method involving steaming the fibre material, impregnating the fibre material with impregnating liquid in an impregnation vessel, which impregnating liquid comprises fresh cooking liquid and spent liquor, extracting spent liquor from the impregnation vessel, cooking the impregnated fibre material in a digester at a predetermined cooking temperature in a plurality of cooking zones including an introductory co-current cooking zone and a concluding counter-current cooking zone, extracting spent liquor from the digester at a position between the said co-current and counter-current cooking zones, transferring at least the greater part of the said spent liquor from the digester to at least one position upstream of the digester, circulating the cooking liquid in a bottom circulation within the said counter-current cooking zone, heating the circulating cooking liquid by means of at least one heat exchange, and supplying wash liquid to the bottom of the digester.
In a cooking process, large amounts of energy are consumed in the form of steam. Of the many measures which are taken in order to achieve more economic operation, an important one is that of reducing the energy consumption.
The object of the present invention is to minimize the energy supplied from external sources under the specified process conditions.
The method according to the invention is characterized in that at least some of the said greater part of the digester extract, before being transferred to the said position upstream of the digester, undergoes heat exchange with at least some of the cooking liquid in the said bottom circulation.
The cooking temperature in the cooking zones of the digester is typically around 160° C., and the spent liquor extracted from the digester is therefore at this cooking temperature. According to the present invention, the energy which is released when the temperature is lowered to typically around 90° C. is utilized in such a way that it can be recirculated into the process, without cooling, for the purpose of generating warm water, since each joule of energy expended in this way requires a corresponding joule of energy supplied on the steam side.
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Lys{acute over (e)}n Claes Göran
Olsson Torbjörn Ulf
Wernqvist Gunnar Carl
Fasth Rolf
Fasth Law Offices
Halpern Mark
Kvaerner Pulping AB
Silverman Stanley S.
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