Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Continuous chemical treatment or continuous charging or...
Patent
1997-12-04
2000-04-25
Nguyen, Dean T.
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Continuous chemical treatment or continuous charging or...
162 39, 162 45, 162 62, D21C 326
Patent
active
060540192
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method for continuous cooking of cellulose-containing fiber material which is impregnated, in a vessel, with liquid in a first cocurrent impregnation zone and a subsequent, second, cocurrent impregnation zone, the impregnation liquid, which consists of one or more of the following liquids--black liquor, white liquor, green liquor, another sulfide-containing solution and another sulfur-containing solution--being supplied, in a mixture with steamed fiber material, through a feeding system to the first cocurrent impregnation zone, and liquid for recovery being extracted at a first point situated at the end of the first cocurrent impregnation zone, and further impregnation liquid being supplied to the second cocurrent impregnation zone.
BACKGROUND AND SUMMARY OF THE INVENTION
Pre-impregnation of chips with sulfide-containing solutions accelerates the delignification and improves the selectivity in the subsequent sulfate cooking. The cooking can in this case be carried out at low kappa numbers without impairing the quality of the pulp. The strength characteristics, in particular the tearing strength, of pulp which has been cooked following such impregnation are substantially better. The improvement in the strength characteristics is retained or is even enhanced in the subsequent bleaching.
Pre-impregnation of chips is described extensively in the patent literature. Examples which may be mentioned here are EP-0 527 294, SE-359 331, SE-468 053 and SE-469 078.
However, the previously proposed methods for pre-impregnation of chips do not provide any possibility of controlling certain parameters during different parts of the impregnation, such as the HS.sup.- /OH.sup.- ratio, in order thereby to reduce the attack by the chemicals on the carbohydrates of the hemicellulose and of the cellulose and to reduce the shive content in the pulp, after the cooking, to an even lower level than has hitherto been possible, and such as the temperature, in order thereby to improve the heat economy.
The object of the present invention is to improve the impregnation by creating conditions which are such that certain parameters can be controlled to assume different values during different parts of the impregnation.
The method according to the invention is characterized in that liquid is extracted at a second point situated at the start of the second cocurrent impregnation zone and is made to circulate in an impregnation circulation which empties out at the center of the vessel at a point situated between said first and second points for extraction of liquid so that a free flow of liquid is established from the center of the vessel in a mainly radial direction, and in that said further impregnation liquid, which consists of one or more of the following liquids--black liquor, white liquor, green liquor, liquid from a transfer circulation between the impregnation vessel and a digester, and wash liquor--is supplied to said impregnation circulation for continued impregnation of the fiber material in the second cocurrent impregnation zone. The method according to the invention thus involves a continuous two-stage impregnation in one and the same vessel.
Black liquor which is supplied to said impregnation circulation expediently has a temperature of 120-170.degree. C.
In an expedient embodiment of the invention, in which black liquor is extracted from the digester and is transferred to a plurality of flash cyclones which are connected in series, the black liquor which is supplied through said feeding system is part of the black liquor which is extracted from the digester, or of the effluent from one of said flash cyclones, preferably the last flash cyclone but one. Under the same conditions, black liquor which is supplied to said impregnation circulation can, in the same way, expediently be part of the black liquor which is extracted from the digester, or of the effluent from one of said flash cyclones.
According to the invention, it is advantageous for the impregnation liquids to be cho
REFERENCES:
patent: 3802956 (1974-04-01), Backlund
patent: 5080755 (1992-01-01), Backlund
patent: 5660686 (1997-08-01), Henricson et al.
Engstrom Johan
Hoglund Olav
Fasth Rolf
Kvaerner Pulping AB
Nguyen Dean T.
LandOfFree
Impregnation of fiber material in two subsequent concurrent impr does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Impregnation of fiber material in two subsequent concurrent impr, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Impregnation of fiber material in two subsequent concurrent impr will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-990638