US2901039A - Apparatus for preconditioning chips in a digester - Google Patents

Description

Aug. 25, 1959 S. A. SALMONSON APPARATUS FOR PRECONDITIONING CHIPS IN A DIGESTER Filed vDec. 20, 1954 2 Sheets-Sheet 1 v l o. 3% A g 109$ AD 5% AD QQM PRiOR ART //\/z/-/\ TUE SVEN A. SALMQNSON ,4 TTUFF/VE V5 S. A. SALMONSON Aug. 25, 1959 APPARATUS FOR PRECONDITIONING CHIPS IN A DIGESTER 2 Sheets-Sheet 2 Filed Dec. 20, 1954 //\/Z/E/\/ TE/FF 'SVEN A.SALMON5ON United States Patent APPARATUS FOR PRECDNDTTIONING CHIPS [N A DIGESTER Sven A. Salmonson, Portland, Oreg. Application December 20, 1954, Serial No. 476,480

3 Claims. (Cl. 162-246) This invention relates to an improved apparatus for preconditioning chips in a digester, and the present application is a continuation-in-part of my co-pending application, Serial No. 291,626, filed June 4, 1952, for Method of and Apparatus for Packing Chips in a Digester, now abandoned.

In the art of pulp making, utilizing a chemical reduction of wood chips in a digester, it is desirable that the chips be evenly distributed in the digester, or, in other words, that the density of the mass of chips in the digester be uniform throughout the digester. Uniform distribution density makes it possible for the cooking liquor to circulate evenly within the digester to cause the liquor penetration of the chips to be uniform, resulting in a high quality pulp. It has been endeavored to obtain such uniform mass density by the use of auxiliary equipment comprising steam injection means which pre-steams and distributes the chips as they are fed to the digester. Previous pre-steam means have not been entirely successful because the auxiliary equipment used therefor impedes and retards the flow of chips into the digester and also retards the outward flow of air within the digester, it being desirable to facilitate the escape of air from the digester when the digester is being charged, not only for the purpose of completing the charging operation more quickly, but also to exclude air from the chips as they pack in the digester for avoiding dilution of the steam atmosphere and for permitting free circulation and uniform penetration of the cooking liquor. Portable apparatus heretofore proposed for pre-steaming treatment is further objectionable because of the delay and manual labor involved in manipulating the apparatus in each charging phase of the digester cycle, both of which factors increase operating costs.

It is, therefore, an important object of the present invention to provide an improved chip digester having steam injection means which pre-steams wood chips and distributes them in a uniform mass density in the digester, and, more importantly, which permits free discharge of trapped air in the digester to avoid the formation of air pockets in the chip mass; to provide a chip distributor having improved steam injection means which permits the free flow of chips into said digester whereby the loading of the digester can be accomplished with facility; and to provide an improved chip distributor having automatic control means whereby steam injection nozzles therein are operative only when chips are being fed to said digester.

The invention, in brief, resides in a novel chip distributor utilizing steam injection means for pre-steaming wood chips as they are loaded into the digester. The nozzles are mounted in the walls of the digester and are directed radially inwardly for projecting steam into engagement with chips being loaded into the digester. In an alternative embodiment of the invention, steam control means, actuated by moving wood chips, is provided for automatically projecting steam only during the time that the digester is being charged. Air outlet or discharge means are provided to prevent air from becoming trapped in the digester as it is being charged.

While the present apparatus is especially designed for the reduction of wood chips in the production of paper pulp by the sulphite process, it is to be understood that fibrous material of other character may be likewise treated in the preparation of pulp for this and other purposes as the manufacture of nitrocellulose, cellulose acetate, pyroxylin, rayon and other analogous materials; likewise, the invention is not limited to the sulphite method of reduction but may be applied to soda, sulphate, semi-chemical, and modified ground wood pulp treatment.

The invention will be better understood] and additional objects and advantages will become apparent from the following description taken in connection with the accompanying drawings which illustrate preferred forms of the invention. It is to be understood, however, that the invention may take still other forms, and that all such modifications and variations within the scope of the appended claims which will occur to persons skilled in the art are included in the invention.

In the drawings:

Figure 1 is a fragmentary sectional view through the top portion of the present digester, showing the air discharge means and one form of steam nozzle mounting arrangement;

Figure 2 is a sectional view taken on the line 2-2 of Figure 1;

Figure 3 is an elevational view of a prior art digester with a portion of said digester broken away;

Figure 4 is a fragmentary sectional view through the top portion of a digester showing an alternative form of nozzle mounting, and also showing automatic steam control means for the nozzles; and

Figure 5 is a diagrammatic view of the steam control means.

Referring to Figures 1 and 2, 10 designates a chemical pulp digester adapted to be charged with Wood chips 11 and adapted to subject the chips to a cooking liquor at elevated temperature and pressure for reducing the chips to pulp. Digester '10 has a charging inlet or filler opening passageway 12 in communication with a hopper v13, or other feed means, for feeding chips to the digester.

The digester is provided with a plurality of bores 18 adjacent the top for receiving nozzles 20. Bores 18 open through bosses 21 on the outer surface of the digester 10, and apertured plates 22 are secured on the bosses by means of screws 23. The outer ends of nozzles. 20 are each provided with a check valve 25 and a control or throttle valve 26, and are connected to a manifold pipe 27 by T connections 28. Pipe 27 and nozzles 20 receive steam under pressure from a lead-in pipe 29 having shut-off valve 30 therein.

As best seen in Figure 2, the bores 18 extend radially so that the nozzles 20 are directed toward the axis of the digester. The tips of the nozzles, however, are located back from the axis so that chips which fall into the digester are in the path of steam being projected from the nozzles. With this nozzle mounting arrangement the inlet to the digester is entirely open and free to receive the stream of chips and permit the escape of air from the digester whereby the digester can be rapidly charged to reduce the batch time, and, in general, to increase the yield of the digester.

With the arrangement above described, the chips fall freely into the digester and are uniformly pre-steamed by jets of steam. The chips are distributed evenly as the digester fills, and, with the absence of air pockets in the mass, the cooking liquor is permitted uniformly to circulate in the mass, with the result that the temperature and liquor concentration throughout the digester are uniform, resulting in a high quality pulp. The absence of air pockets furthermore permits tighter packing of the chips and the digester is adapted to contain a larger chip charge. Figure 3 shows one type of prior art digester 10a wherein the chips 11a fall by gravity in a conical pile. In this type of structure, air pockets will form in the mass of chips to cause a poor quality pulp to be produced. There is no steam pre-treatment.

Figures 4 and show a modified form of the invention. A digester 35 having a charging inlet or filler opening 36 is adapted to be charged with wood chips 37 received from a hopper or other feed means 38. Digester 35 is provided with inclined bores 40 adjacent the top for receiving nozzles 41. Bores 40 open through bosses 42 on the outer surface of the digester, and apertured plates 43 are secured on the bosses by screws 44. Nozzles 41 are each provided with a check valve 45 and a control or throttle valve 46 at their outer ends and are connected to a manifold pipe 48 by T connections 49. Steam is supplied to the manifold pipe 48 and the nozzles 41 through a lead-in pipe 50 having a shut-off valve 51 therein.

Bores 40 are in inclined positions so that the nozzles 41 are directed toward the axis of the digester and are adapted to project steam on chips being fed through the filler opening 36. The steam projected from the nozzles pre-steams the chips and the angular position of the nozzles forcefully drives the chips downwardly into the digester so that said chips are firmly packed therein without air pockets formed in the chip mass.

This embodiment employs automatic steam control means actuated by the stream of chips falling through the filler opening, the automatic control means being illustrated diagrammatically in Figure 5. The control means comprises a switch housing 55 having a lever arm 56 pivotally mounted through an opening 57 in one end thereof and extending into the path of moving chips being discharged by the hopper or other feed means 38. The switch housing 55 could be mounted at any place in the filler opening 36, but, preferably, as shown, it is carried in a spacer block 58 between the hopper and the top of the digester filler opening.

Switch lever arm 56 has an enlarged chip engaging plate 60 on its outer end and is pivotally mounted in a boss 61 formed as a part of a flexible diaphragm 62 which prevents chips and dust from entering the switch housing 55. The inner end of arm 56 is urged downwardly by a compression spring 64 and engages a switch arm 65 which is biased upwardly by spring 66. Switch arm 65, which comprises one contact of a switch, is electrically connected to a lead wire 67 by means of a connector 68 mounted in the Wall of the switch housing, and the arm 65 is adapted to engage a contact 69 connected to a wire 70 by means of a connector 71. The contacts are closed when the outer end of switch lever arm 56 is pivoted downwardly due to the falling chips in engagement therewith but in the rest position of the parts, arm 56 is pivoted upwardly to break contacts 65 and 69 as shown in Figure 5.

The closing of switch contacts 65 and 69 energizes a solenoid 75 electrically connected to the wire 70 and a lead Wire 7012:. Solenoid 75 has a plunger 76 connected to a lever 77 which operates a bypass valve 78 enclosed in a housing 79. Valve housing 79 is connected to a fluid pressure line 80 and is provided with a relief port 81. Spring 82 normally holds the valve closed against pressure line 80, as shown, when solenoid 75 is de-energized.

Pressure line 80 has a shut-off valve 85 on the outlet side of valve housing 79 and terminates in a valve housing 86 connected into the steam lead-in pipe 50. Housing 86 has a cylinder 87 at its upper end, a pair of chambers 89 at its lower end and a central bore 90 extending between the cylinder 87 and one of the chambers 89. A valve stem 91 is .slidable in bore 90 and has a piston 92 on its upper end for movement in cylinder 87, and a valve 93 on its lower end. Chambers 89 communicate by means of an aperture 95, and aperture 95 is engaged by valve 93 to provide a seat therefor for controlling the flow of steam between the two chambers 89. Valve 93 is biased upwardly into engagement with its seat by spring 96 carried on the valve stem between piston 92 and the bottom of cylinder 87.

The operation of the control system is as follows. When no chips are passing through the filler opening 36 of the digester, spring 64 holds the inner end of the arm 56 in a lowered position whereby switch cont-acts 65 and 69 are open. Fluid pressure is constantly maintained in the pipe 80, and when the valve 78 is held by spring 82 in the position shown in Figure 5, no fluid pressure is admitted to cylinder 87 of valve housing 86 whereby the piston 92 and stem 90 are biased upwardly and the valve 93 seats in the aperture 95. When the lever arm 56 is pivoted by means of a chip load thereon, the contacts 65 and 69 are closed and solenoid 75 is energized to rotate the valve 78 to a position whereby the inlet opening from pipe 80 into the housing 79 is opened and the relief port 81 is closed. Fluid pressure is thereby admitted to the cylinder 87 in valve housing 86 and the piston 92 is forced downwardly to unseat the valve 93. Steam will thus flow through pipe 50 and will continue to flow until solenoid 75 is de-energized by reason of the contacts 65 and 69 being opened when the arm 56 is permitted to move upwardly to its rest position. In the de-energized position of the solenoid 75, relief port 81 is opened, whereby fluid pressure which is present in the cylinder 87 can be relieved. Spring 96 then re-closes the valve 93.

This embodiment also has air discharge means for facilitating the free escape of air which may become trapped in the digester while the digester is being charged. A vertical discharge pipe 100 is mounted in the top wall of the digester and has a nozzle 101 and shut-ofi valve 102. A portion of pipe 100 projects interiorly of the digester, and this projecting portion has a plurality of small vent holes 103 of a size to permit air to enter the pipe 100 but to prevent chips from passing therethrough. The bottom end of the pipe may have vent holes or perforations therein similar to the lower portions of the side walls to assist in permitting air to escape through the discharge pipe. Thus with the air escaping freely through pipe 100 there is no back pressure in the digester to retard the entrance of chips in a substantially solid stream through the inlet opening 36 and the charging time is reduced to a minimum. The rate of steam injection is controlled so that substantially all the steam is condensed on the old chips and no steam pressure is produced to retard the free fall of the chips through inlet opening 36. After charging, the vent valve 102 is closed.

The present arrangement of nozzles is designed to deliver steam at an unusually fast rate in order to enhance the effectiveness of the pre-steaming treatment. The best results have been otbained with a steam flow at the rate of twenty thousand to twenty-five thousand pounds per hour at a steam pressure of to pounds per square inch. With this character and intensity of treatment, the chips are well distributed and pre-steamed, causing the digester to be uniformly packed and causing substantially all the air to be excluded and driven out through the vent pipe. In the use of prior portable devices for this purpose insertable through the charging opening, it is found that a steam flow at as high a rate as only eight thousand pounds per hour in a digester of the same size causes objectionable air lock which interferes with the free flowing of the chips into the digester. Such a low rate of steam introduction has been found insuflicient properly to pre-steam the chips and accomplish the improved results of the present invention.

Having now described my invention and in what manner the same may be used, what I claim as new and desire to protect by Letters Patent is:

1. A digester for the chemical reduction of fibrous material, such as wood chips, to pulp comprising, a digester wall having a top portion with a vertical central charging inlet passageway which is adapted to be closed during a cooking operation, a plurality of steam nozzles mounted in and projecting through a portion of said wall around said passageway of greater diameter than said passageway and directed approximately horizontally and radially inwardly immediately below said top wall portion and the lower end of said passageway, said nozzles being spaced from the center of the projected area of said passageway and projecting only slightly into said projected area to discharge jets of steam radially into the center of a falling stream of said material introduced through said passageway, said inlet passageway being unencumbered and unobstructed for the substantially unimpeded rapid admission of said material.

2. A digester as defined in claim 1 including an air vent pipe for the digester projecting through said top wall portion, and a valve in said pipe.

3. A digester as defined in claim 1 including steam supply means connected to said nozzles, valve means in said steam supply means, a control element having an actuating member projecting into the path of said stream of material, and means operated by actuation of said control element to open said valve when said actuating member is deflected by said material.

References Cited in the file of this patent UNITED STATES PATENTS 1,813,205 Scholz et a1. July 7, 1931 1,998,875 Koda Apr. 23, 1935 2,029,086 Svensson Jan. 28, 1936 2,451,073 Cowherd Oct. 12, 1948 2,475,850 Moore et a1 July 12, 1949 2,483,426 Moore Oct. 4, 1949 2,614,923 Tarkkonen Oct. 21, 1952 FOREIGN PATENTS 537,749 Germany Nov. 6, 1931 59,371 Norway May 16, 1938

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