Method for continuous cooking of chemical pulp to improve heat economy
AssigneeKvaerner Pulping AB
InventorsVidar Snekkenes, Lennart Gustavsson
Life of this patent
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Abstract
A method for the continuous cooking of chemical pulp with the aim of achieving improved heat economy in a digester system having a vessel (1) for impregnation and a vessel (2) for cooking the impregnated cellulose chips. A part of the black liquor (14) withdrawn from the digester (2) is added at the beginning of a transfer system (4) to increase the temperature of the chips mixture in the transfer system (4). A fraction of the transport fluid (10) from the transfer system (4) that is continuously withdrawn from the impregnated chips fed into the top of the digester is returned to the impregnation vessel (1) at essentially the maintained transfer temperature.
Claims13
A method for the continuous cooking of chemical pulp to improve heat economy in the digester system, comprising:
- providing an impregnation vessel having an inlet defined therein, the impregnation vessel being in fluid communication with a digester via a transfer system, the digester having an outlet defined therein;
- feeding a mixture of cellulose chips and process fluid into the inlet of the impregnation vessel;
- impregnating the cellulose chips in the impregnation vessel at a predetermined impregnation temperature Timp;
- feeding the impregnated cellulose chips to the digester through the transfer system;
- cooking the impregnated cellulose chips at a predetermined temperature Tcook;
- feeding pulp dissolved in the digester out through the outlet of the digester:
- withdrawing black liquor from the digester via a cooking withdrawal after partial or complete cooking of the cellulose chips;
- leading the withdrawn black liquor to the transfer system at a bottom of the impregnation vessel;
- mixing the withdrawn black liquor with the impregnated cellulose chips in the transfer system for transport onwards to a top of the digester;
- adding a part of the black liquor from the black liquor withdrawal to an addition point of the impregnation vessel without cooling the withdrawn black liquor, the black liquor having a withdrawal temperature Tav, to a beginning of the transfer system, the black liquor having maintained essentially the temperature Tav, to raise a temperature of a chips mixture in the transfer system;
- a transport fluid being continuously withdrawn from the chips mixture at an end of the transfer system, the transport fluid maintaining a transport temperature Ttransp;
- and
- returning the transport fluid to the impregnation vessel without heating at a location that is upstream of the transfer system and the addition point of the black liquor wherein the black liquor from the black liquor withdrawal maintains a temperature of Tav that exceeds the temperature Ttransp of the transport fluid that is withdrawn from the top of the digester by at least 50°C., such that Tav−Ttransp≧5° C.
Dependencies are inferred from the claim text.