US3607618A - Wood-pulping process - Google Patents

Abstract

Woolly wood fibers having lengths in the range of one-sixteenth to one-quarter of an inch and cross-sectional dimensions within the range of 0.1 to 0.05 mm., obtained by grinding wood chips of the order of one inch in length in a ribbed plate grinder, are digested in a continuous type of digester by heating such fibers at a temperature in the range of 220* F. to 330* F. for a period of 1 to 20 minutes in acid bisulfite, bisulfite or neutral sulfite cooking liquor. The consistency of the mixture is controlled by regulating the amount of cooking liquor which is recirculated through the digester, and the consistency of the mixture governs the speed of its flow through the digester and consequently controls the cooking time.

Description

United States Patent [72] Inventors Curt Uschmann Lebanon; Erik Berglund, Oswego, both of Greg. [21] Appl. No. 680,731 [22] Filed Nov. 6, 1967 [45] Patented Sept. 21, 1971 [73] Assignee Process Development Corporation Portland, Oreg.

[54] WO0D-PULPING PROCESS 2 Claims, 1 Drawing Fig.

[52] US. Cl 162/17, 162/24, 162/41, 162/61 [51] Int. Cl D2lb1/04, D21c 3/24 [50] Field oiSeorch 162/17, 19, 24, 28,41,71,61,25

[56] References Cited UNITED STATES PATENTS 2,508,043 5/1950 Schaefer 162/96 X 2,789,051 4/1957 Obenshain... 162/17 3,192,102 6/1965 Nolan 162/24 DIGESTEI? 14s No. 28 pp. 38-41 Rydholm, Pulping Processes pp. 50- 52 lnterscience Publishers New York 1965 Primary Examiner-S. Leon Bashore Assistant Examiner-Thomas G. Scavone Attorney-Robert W. Beach ABSTRACT: Woolly wood fibers having lengths in the range of one-sixteenth to one-quarter of an inch and cross-sectional dimensions within the range of 0.1 to 0.05 mm., obtained by grinding wood chips of the orderof one inch in length in a ribbed plate grinder, are digested in a continuous type of digester by heating such fibers at a temperature in the range of 220 F. to 330 F. for a period of l to 20 minutes in acid bisulfite, bisulfite or neutral sulfite cooking liquor. The consistency of the mixture is controlled by regulating the amount of cooking liquor which is recirculated through the digester, and the consistency of the mixture governs the speed of its flow through the digester and consequently controls the cooking time.

DRAINER 1J Another object is to provide such a process which is economical because it requires a smaller quantity of chemicals than would be used in comparable processes and enables cooking of the pulp to be controlled more easily and accurate ly in a continuous process.

A further object is to digest woolly wood fibers in the production of pulp which are produced by a procedure which minimizes damage to and weakening of the fibers.

The drawing illustrates diagrammatically equipment which can be utilized in performing the process of the invention.

Wood chips utilized in the production of pulp according to the present invention are of the conventional type used in the production of pulp, being approximately 1 inch in length. Such chips are customarily, though not necessarily, coniferous and may be produced from logs or from wood waste. For the purpose of this invention, the chips can be produced from wood waste from lumber mills and other woodworking plants or from forest waste logs or pulp logs and debris. In the performance of the present process, it is necessary that such chips be treated specially before being defiben'zed, such as being dried, moistened, steamed, soaked or digested. On the contrary, such chips can be defiberized without increasing or decreasing their natural moisture content. 7

The pulp chips are mechanically defiberized in a ribbed rotary plate grinder. A grinder which is satisfactory for this purpose is shown in Uschmann US. Pat. No. 2,776,800. In such a plate grinder the chips are fed between relatively rotating ribbed plates. One plate may be rotated and the cooperating plate held stationary or two cooperating plates may be rotated respectively in opposite directions. Most of the fibers resulting from such grinding are one-quarter of an inch or less in length and have cross-sectional dimensions in the range of 0.1 to 0.05 mm. Such fibers have from 20 to 40 times more surface area than splinters or slivers. Such large surface area greatly increases the contact area between the cooking liquor and the wood during the subsequent cooking process and is very important in expediting cooking of the pulp and uniformity of the resulting product.

The defibration of the wood chips by use of a ribbed plate grinder is much more desirable than breaking up the chips by use of a hammer mill or rod mill because the pounding of such mills flattens and weakens the fibers instead of merely pulling them apart. Consequently, the resulting pulp, after being cooked, is weaker than that produced from woolly wood fiber discharged from a plate grinder.

From the defibrating chip grinder 1 shown in the drawing the resulting woolly wood fibers, having a length in the range of one-sixteenth of an inch to one-quarter of an inch and a maximum cross-sectional dimension in the range of 0.1 to 0.05 mm., are fed into the digester 2 through a suitable pressure-retaining feeder 3. This feeder can be of the compaction feed-screw type, or a dry blower, or rotary feeder, which is capable of feeding the wood fibers into the digester while it is maintained under pressure sufficient to keep the temperature of its contents above the boiling point of water. Alternatively, the wood fibers can be supplied to liquid being fed into the digester so as to form a slurry with such liquid.

Other ingredients fed into the digester 2 are steam through a steam supply line 4 in sufiicient quantity and at a temperature high enough to maintain the contents of the digester heated to the proper degree and, through a supply line 5, makeup chemicals to replace chemicals discarded from the digester. In addition, cooking liquor is recirculated continuously, being withdrawn through a line 6 from the drainer 7 by a pump 8. Such pump forces the recirculating liquor through a control valve 9 and a return line 10 into the upper portion of the digester. A slurry containing cooked pulp and a greater or lesser quantity of waste cooking liquor which has not passed through the drainer screen for recirculation to the digester is withdrawn from the drainer above its screen through the line 1 l.

The cooking liquor used in the digester is of conventional type depending upon the characteristics of the pulp desired and the purpose for which the pulp is to be used. Such cooking liquor can, for example, be of the acide bisulfite type, as described in US Pat. No. 3,192,102, at column 10, lines 45 to 65 or of the bisulfite type, such as described in that patent at column 12, lines 30 to 43, or of the neutral sulfite type, such as described in that patent at column 12, line 74, to column l3, line 2, and column 13, lines 18 to 21. If the temperature of the cooking liquor within the digester is maintained in the temperature range of 220 to 330 F. requiring a pressure within the range of 3 p.s.i.g., to p.s.i.g., sufiicient cooking of the wood fibers can be accomplished within a period of 1 minute to 20 minutes.

The effectiveness of the cooking liquor in the digester can be regulated by adjusting the proportion of the cooking liquor which is recirculated through the system 6, 8, 9 and 10, as compared to the amount which is discarded through line 11 with the cooked wood fibers. The more liquor recirculated, the more dilute will be the mixture in the digester and, consequently, the faster such mixture will flow through the digester. The speed of flow of the mixture through the digester can thus be regulated to provide the appropriate amount of time to afiord proper cooking of the wood fibers. The large surface area of the woolly fiber material provides a large surface area for contact of the cooking liquor and reduces the penetration required to cook the wood so that the effectiveness of the cooking operation is greatly increased over the conventional operation of cooking wood in the form of pulp chips or even slivers. Moreover, the uniformity of cooking effect on the wood fibers is greatly increased.

The amount of lignin extacted from the wood fibers depends, of course, on the type and concentration of cooking liquor used, the temperature of the cooking liquor and the cooking time. For some uses, it is desirable to wash the cooked wood fiber for the purpose of removing from it the waste cooking liquor carrying the lignin. On the other hand, if the resulting pulp is to be used in the manufacture of fiberboard, for example, it is not objectionable for the lignin content of the cooking liquor to remain mixed with, although extracted from, the cooked fiber. In such case, instead of washing the waste sulfite liquor from the pulp, the water content can simply be evaporated leaving the lignin behind deposited on the fiber so that its binding characteristics can be utilized in the production of fiberboard.

As in other types of pulp-making processes, the waste liquor should be burned or should be purified before being discarded to a natural water course to avoid water pollution.

I claim:

1. The process of making wood pulp which comprises grinding wood chips into woolly fibrous material in which the ground fibers have a length in the range of one-sixteenth of an inch to one-quarter on an inch and maximum cross-sectional dimensions in the range of 0.1 to 0.05 mm, and thereafter digesting the woolly wood fibrous material in a pulp-cooking liquor heated to a temperature in the range of 220 to 330 F. selected from the group consisting of acid bisulfite liquor, bisulfite liquor and neutral sulfite liquor for a period within the range-of l to 20 minutes in a continuous process by feeding the woolly fibrous material into a digester, withdrawing the digested pulp and cooking liquor from the digester without interruption of the digesting process, separating the digested pulp from the cooking liquor and returning the cooking liquor to the digester.

The whole was passed into an oven at 150 C., and kept there for 1-2 minutes. Thereafter, onto the previous layer a second layer (foamed) was spread. which consisted of:

PVC, paste making resin having a K-value of 72 dioctyl phthalate 100 parts (by weight) 80 parts (by weight) The initial thickness of this layer was 200 microns.

The whole was then passed into an oven at 200 C. and kept there for l-2 minutes. The release paper was then removed. The system was then subjected to a slight tension in order to facilitate the separation of those components that were incompatible with each other; then the system was coupled to a cotton jersey fabric (with the second layer adjacent to the fabric), after preliminarily having spread on the fabric some plastisol of the first layer which served as a binder. Said coupling occurred in about 1 minute in an oven heated to ISO-170 C.

The poromeric material thus obtained showed the following air transpiration rates:

Pressure (mm. Hg)

The release paper was then removed and the system was subjected to a slight tension and subsequently was coupled to a jersey fabric made of polyamide fibers, the second layer being adjacent to the fabric after preliminary having spread on the fabric some plastisol of the first layer which serves as a binder.

The poromeric material thus obtained shows the following air transpiration rates:

Pressure cm. of air (mm.Hg) hr. cm.

4U 80 60 121 I00 205 ISO 270 Example 3 100 parts (by weight) PVC, paste making resin with a

Claims (1)

1. 2. The process defined in claim 1, including controlling the amount of cooking liquor returned to the digester to regulate the amount of dilution of the mixture in the digester and consequently to control the time the mixture remains in the digester.

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