Extended kraft cooking with white liquor added to wash circulation

(19)

(11)

EP 0 476 230 A3

(12)	EUROPEAN PATENT APPLICATION

(88)	Date of publication A3:
	09.06.1993 Bulletin 1993/23

(43)	Date of publication A2:
	25.03.1992 Bulletin 1992/13

(21)	Application number: 91108241.0

(22)	Date of filing: 22.05.1991

(51)	International Patent Classification (IPC)⁵: D21C 3/02, D21C 7/00

(84)	Designated Contracting States:
	AT DE FR GB IT SE

(30)

Priority:

17.09.1990 US 583043

(71)	Applicant: Kamyr, Inc.
	Glens Falls, New York 12801-3686 (US)

(72)	Inventors:
	Stromberg, Bertil Kamyr Inc. New York 12801-3686 (US) Jiang, Jian Kamyr Inc. New York 12801-3686 (US) Laakso, Richard Kamyr, Inc. New York 12801-3686 (US) Phillips, Joseph Kamyr Center New York 12801-3686 (US) Greenwood, Brian Kamyr Center New York 12801-3686 (US) Prough, James Kamyr Inc. New York 12801-3686 (US)

(74)	Representative: UEXKÜLL & STOLBERG
	Patentanwälte Beselerstrasse 4 22607 Hamburg 22607 Hamburg (DE)

(56)

References cited: :

(54)	Extended kraft cooking with white liquor added to wash circulation

(57) In the continuous kraft pulping of comminuted cellulosic fibrous material (e.g. wood chips) to produce paper pulp, viscosity for a given Kappa Number is significantly increased (e.g. at least about 20%) by adding kraft white liquor to the wash recirculation loop (38-40) in a continuous digester (19). Optimum results are obtained when kraft white liquor is also added to a recirculation loop (28-30) at a central portion of the digester, so that the majority of the digester has countercurrent flow between white liquor and cellulosic material. About 5-20% of the total white liquor necessary to effect kraft cooking is introduced in the wash circulation, and about 10-20% is introduced into the central portion recirculation. The temperature in the wash zone is maintained at about 140-175°C.

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