US2771361A

US2771361A - Defibration processes

Info

Publication number: US2771361A
Application number: US260352A
Authority: US
Inventors: Birdseye Clarence; Harold D Stuck
Original assignee: Process Evaluation and Development Corp
Current assignee: Process Evaluation and Development Corp
Priority date: 1951-12-07
Filing date: 1951-12-07
Publication date: 1956-11-20
Anticipated expiration: 1973-11-20

Description

.Nov. 20, 1956 c. BIRDSEYE ET AL 2,771,361

DEFIBRATION PROCESSES Filed Dec. 7, 1951- V 2 Sheets-Sheet l INVEN TOR.

MWr ZjZ? Nov. 20, 1956 c. BIRDSEYE ETAL 2,771,361

DEFIBRATION PROCESSES Filed Dec. 7, '1951 2 Sheets-Sheet 2 IN VEN TOR.

United States Patent DEFIBRATION PROCESSES Clarence Birdseye, Gloucester, and Harold D. Stuck, Andover, Mass, assignors, by mesne assignments, to Process Evaluation and Development Corporation, New

This invention comprises a new, improved and continuous process of defibrating vegetable matter. It has an important field of use in the defibration of Wood chips for making wood pulp in the manufacture of paper, and will be described in its application to that industry.

The process of our invention is characterized by the steps of first contacting dry chips of wood or other vegetableflmatter with, or immersing them in, a solvent solution effective to dissolve the intercellular binding components of the wood and to renderit plastic in consistency, then removing a considerable part of the solution and effecting practically complete separation of the chips into individual cells or fibres without detrimental chemical change or appreciable physical damage. The latter step may be carried out mechanically or by explosive expansion and in some cases additional steps,

such as bleaching, may be includedias integral parts of our process. 4

Heretofore defibration of wood chips has most commonly been effected by processes in which large charges of batches of chips have been subjected to digestant solutions maintained at high temperature and steam pressure for relatively long periods (e. g., 100 p. s. i. and 338 F. for 4 to 6 hours), reduced non-explosively to atmospheric pressure, and then subjected to mechanical abrasion to complete defibration. The fibers of pulp so produced are straight, smooth, and nearly round in cross-section,

and to impart to the fibers the roughness, curliness and flatness needed for the manufacture of strong paper, such pulp must be first passed through a beater to roughen the cells (fibers) and to increase the rate at which the fibers free themselves of water on the papermaking machine. Subsequently they must be frayed and cut in a Jordan to increase still further their felting qualities, Both the beating and the Jordaning are time-consuming and very costly and impart undesirable as Well as desirable qualities to the pulp fibers. Moreover, the very slowness of present batch cooking methods damages the ultimate product by over-digestion of those individual outer cells freed from the chips early in the digestion period.

-The novel process of our present invention obviates the undesirable features of these prior batch processes and possesses certain characteristic advantages of its own. It is carried out continuously and thus requires considerably less expensive apparatus to produce the same amount of finished product in twenty-four hours as compared to the present conventional batch equipment. It may be carried out at substantially higher temperatures and pressures applied for only brief periods, thus facilitating procedure and avoiding the damage to peripheral cells that results from slower processes, and it lends itself to heat interchange and other economies not heretofore practical in conventional processes.

.tory results are insured.

" ice Going more into detail, we prefer first to mix the dry chips at atmospheric pressure with a digestant solution efiective to dissolve the intercellular lignin, resin and binding components of the chips and render them nonbrittle or plastic in consistency. The mixture is then both heated and pressurized, and may then be circulated at a constant rate thnough a digesting zone conveniently supplied by pipe coils of substantial length. The temperature and pressure of the mixture may be adjusted and controlled during every phase of the process.

It is advantageous in most cases to. add a wetting agent to the digestant solution and thus to increase the rapidity of its penetrating and solvent action. A bleaching agent may also be added to the solvent solution and bleaching of the fibers thus carried out to a greater or'lesser extent simultaneously with the digestion of the chips. It follows, of course, that the solution may simultaneously contain both a wetting agent and a bleaching agent. 7 Or, in some instances, we prefer to bleach the digested material while under substantial pressure and at a temperature above 212 F., between the time excess black liquor has been removed from thematerial and the time the latter is completely clefibrated by explosion It has been found desirable to insure complete immersion of the dry chips in the solvent solution in. order to insure prompt and uniform penetration of all the chips by the solution. As herein shown, this is brought about by passing the mixture of chips and solution through pipe coils which are completely filled with the mixture. Or, when it is wished to utilize existing equipment, vertical batch digesters may be used and their contents fed direct to a screwpress for the purposes hereinafter mentioned.

When the wood has been brought to the required con.- dition the major part of the spent solvent solution (known in the industry as black liquor) is separated from the partially digested mass 'of treated wood. This step is of especial importance because it separates from the mass of treated wood a" large volume of hot solution and so makes available its energy for utilization by heat exchange in the process or elsewhere, and it also presents the digested or partially digested wood mass in the best condition for further treatment, For example, the moist wood mass may be mechanically disintegrated in pressing or 'it may be extruded as a compact plug of fiber under such substantial internal pressure that it may be disintegrated by the explosive expansion of contained gas generated by sudden pressure reduction when it is discharged to the atmosphere.

In general it has been found that if from one-quarter to three-quarters of the spent solution is removed from in and around the wood before the explosion, satisfac- If the chips themselves are thoroughly saturated no excess free liquid need be present. If desired, an ingredient such as liquid carbon dioxide, compressed air, hydrogen peroxide or sodium carbonate may be added at any stage of the process for the purpose of increasing the fluid pressure about or within the mass without appreciably increasing its temperature.

An advantage of the process herein disclosed is that it produces individual fibers which are frayed, flattened or curled so that they will, with little or no beating, felt together tightly and produce tough paper with exceptionally great tear resistance. This is efiected without breaking or otherwise materially reducing the tensile strength of the fibers; and it is believed that this fraying,

mined point within the tank.

3 flattening and curling of the fibers is due in part to abrasion in a screw-press under great pressure and high temperature, and in part to the explosive-expansion of gas both between and even within the individual fibers or cells. The fibers thus produced by our novel process are preferable to the straight and smooth surface fibers heretofore produced, both in point of tensile strength and in capacity for rapid felting action.

For purposes of illustration, the invention will now be described in connection with apparatus diagrammatically shown in the accompanying drawings in which:

Figs. 1 and 2 are separated views, partly in section and partly in elevation, showing the connected parts of the same apparatus, and

Fig. 3 is a view in longitudinal section showing a portion of the apparatus of modified design.

Th apparatus as illustrated includes a vertical mixing tank 10 shown herein as having in its upper head an inlet chute 11 for the solid raw material to be treated; for example, wood reduced to chips of convenient size. supply pipe 13 is shown as also entering the top of the tank and through this a solvent solution may be supplied for mixing with the wood chips. This may be a hot caustic solution or any other standard or special solution at any desired temperature, and may be selected in accordance with the material to be treated and the end product desired. It may contain a wetting agent such as Tergitol 08, which is the sodium salt of a sulfate of a higher synthetic alcohol, or any equivalent wetting agent.

1.5% hydrogen peroxide or'sodium peroxide as a bleaching agent.

The mixing tank is provided with a motor-driven stirrer 12 and this is designed to agitate thoroughly the mixture of chips and hot solvent solution at any desired temperature so as to assure fixed proportions of chips and solution at the exit from the mixing tank. The process is designed for continuous operation and accordingly chips and solution will be fed to the tank 10.at a regulated uniform rate to maintain the liquid level at a predeter- The mixing tank 10 is herein shown as equipped at its lower end with an outlet duct or pipe 14 through which the mixture ofchips and solution passes from the tank to a power-driven pump 15 .by which they are advanced under any desired pressure and maintained under said pressure as they pass through the digesting zone of the apparatus.

The digesting zone is composed by the discharge pipe 16 from the pump 15, a heating unit 17, and pipe coils 18 of sufiicient length and diameter to give the digesting system the desired capacity and the digesting phase of the process the desired interval of time. The mixture reaching the pump 15 may be at any desired temperature and pressure, but in passing the pump its pressure is substantially increased and is maintained during its passage through the pipe coils 18. The discharge pipe 16 carries the mixture to the heater 17, herein shown as being gas .or oil fired. In passing through the heater and throughout the pipe 18 the mixture will'be undenapproximately the same pressure as when itleaves the pump l5-except for negligible losses due to -f1'ictionandimay be -:main- .tained at any desired temperature up :to that-of esteam under corresponding pressure. i In.shortgthe temperature .of the solutiomandac'hips can beeitheri held :constant, "increased or lowered as it passes through pipe 18. Air

purge outlet valve 19 aids in keeping the pipe '18 completely full of liquid and the fibrous material in the pipe submerged. The pipe and other heated parts of the apparatus will be insulated, as at 20; and a reheater 21 may be provided at any desired location in the pipe line.

The digested mixture passes from the pipe coil 18 through an outlet pipe 22 to the head of an insulated conical screwpress 23, of any suitable commercial type. The press is herein shown as having an inner perforated wall 24 and a power driven spiral screw 25. The inner wall of the press is provided with an insulated concentric jacket 26 in which the hot solution is received under pressure as the chips, which are now partly disintegrated or at least reduced to a plastic consistency, are gradually compressed and reduced to a dense fibrous plug which is forced downwardly and out through the nozzle 27 at the lower or smaller end of the press. This plug, of course, is subjected to an ejecting pressure equal to or exceeding that maintained in the whole system beyond the pump 15. In addition to its compressing effect upon the digested chips, the screwpress has a pronounced disintegrating or fractionating effect in working the chips upon each other and against the metal of the press. Thus at a single step black liquor is removed from the mass of fibrous material and simultaneously the pieces thereof are fractionated as just explained.

The fibrous plug emerging from the nozzle 27 enters a reservoir chamber 28 into which the nozzle empties, and this reservoir is provided with an expansible bladder diaphragm 29 which serves to maintain an even pressure within the reservoir even though the contents therein may vary considerably in volume from time to time. The chamber 28 is provided also with an outlet duct 30 having a pair of spaced quick-opening valves 31. The construction is such that the upper of these valves is opened when the lower valve is closed and vice versa. In practice the fiber charge is confined under any desired pressure and mixed with any desired quantity and kind of liquid in the reservoir or expansion chamber 28 and is discharged in measured charges through outlet duct 30 with explosive violence; that is to say, when the uppermost valve is opened the duct between the two valves is immediately filled with the charge still under pressure; and then, when the upper valve is closed and the lower valve opened, the charge is explosively ejected and subjected to a practically instantaneous reduction of pressure, thus completing the separation of the fibrous material into individual cells or fibers.

In case it is desired to increase the moisture content of the fibrous mass above that of the plug passing through the nozzle 27, a by-pass pipe line 32 is provided which leads from the jacket of the press to the expansion chamber 28. A power-driven pump 33 is provided in this line by which a measured amount of the spent caustic solution, or any other desired liquid, may be delivered under pressure to the chamber 28.

.A'discharge pipe 34 leads from the jacket of the screw press through a pump 35 to a heat exchanger 36 and thence to a pipe 37 through which the'liquid passes for further processing. The heat exchanger 36 may be utilized to pre-heat the fresh hot digestant solution (white liquor) supplied through a pipe 38 emerging after it leaves the heater into a pipe 13 already mentioned in connection with the. mixing tank.

The pressure chamber 28 is herein shown as provided with a valved supply pipe 39 .by which a pressureincreasing ingredient such as compressed air or sodium carbonate may be admitted to thepressure chamber 28 for the purpose of increasing the pressure of the fibrous mass without substantially increasing its temperature. This increased pressure in the product mass serves to increae the speed with which the mass is ejected .tothe atmosphere and thereby increases the violence of the explosion of the material.

Process Example I.Raw material: dry commercial chips of New England white spruce 7 Feed into a large open digestion (soaking) tank containing agitating and mixing means (this open tank, not shown in drawings, may be of any desired shape and construction) dry chips and digestant solution #1 in the ratio of 1 pound ofchips for each 8 pounds of digestant solution. The chips may be supposed to contain from about 10% to about 50% of water, by weight, when fed into the soaking tank, and the chip-solution ratio may be .varied to meet processing requirements. Preferably, the chips and solution should be heated to, and maintained at, approximately 100 C. during the soaking period, during whichif containing about 10% moisture when fed to the soaking tank--they will absorb solution equivalent to approximately 140% of their original weight, and will then have a greater specific gravity than the solution and so will sink to the bottom of the tank, from which they may be withdrawn by any desired meanse. g. a bottom rake.

After being sutficiently soaked, as above, the chips are removed from the open soaking tank, drained, and mixed in the tank 10 with approximately four times their weight of solution #2 fed to tank 10 through pipe 13. Through pipe 14 the mixture of soaked chips and digestant solution, preferably having a temperature of about 190 F., is fed to the pump 15 which passes them into the pipe 16 with little change in temperature but under a pressure of about 105 p. s. i. The rate of feed from tank 10 should be such that about 60 minutes will be required for chips to pass through pipe 18.

From pipe 16 the chips and solution pass through the heater 17, where their temperature is raised to approximately 340 F. After leaving the heater 17 the mixture is forced into and through digester coil 18 and thence, still under approximately 100 p. s. i. and at 338 E, into the continuous screwpress 23.

In the press 23 all free solution (by now become black liquor) is removed from around the chips and passed through the perforated area of the press walls 24 into the jacket area whence it flows through the pipe 34, through the pump 35 and the heat-exchanger 36 and thence through the pipe 37 to strainers, concentrators and/ or any other desired equipment for regenerating or reconditioning the solution. By the time the chips enter the press 23 they are preferably so nearly digested that many single cells and small bundles of cells (shives) have already been separated from the :chips and have become suspended in the solution. Some of these free cells pass through the strainer'wall 24 of the press and are carried out of the press jacket 26 into the pipe 34, and thence through the system, to be finally recovered from the black liquor by means of any desired commercial equipment.

In the meantime fibrous material, too coarse to pass through the perforated press walls 24, is forced toward the narrow end of the press 23, being progressively compacted, dewatered and fractionated by abrasion until it finally emerges from the press discharge nozzle 27 as a press cake having a moisture content of preferably, between 40 and 60 percent. Just before emerging from the press at 23 the fibrous material will have a temperature of not less than about 338 F., and will be under a screw-generated pressure of 500 p. s. i. or more. This highly-compacted fibrous plug serves to prevent 'blowbacks from the chamber 28 into the press, even when pressures in the former are made higher than in the latter.

After leaving discharge nozzle 27 of the press the presscake enters the chamber 28, where it is met by about 4 times its own volume of water heated to 338 -F. A stirring device 40 will break up the presscake and mix it with the hot water to form a soupy mass of such consistency that it will pass freely through the explosion chamber 30. Meanwhile compressed air, also heated to about 338 F., will be injected into chamber 28 at 250 p. s. i. to raise the pressure within the chamber to that pressure.

By means of the pair of alternately opening valves 31 the coarse pulp and hot water mixture will alternately enter, and be explosively expelled from the chamber 28.

Process Example 1I.Dry commercial oak chips In this case dry (moisture content about 10% to 50%) oak chips (e. g. northern red oak) are continuously fed through hopper 11 into tank 10 at the rate of 2000 pounds per hour. Simultaneously, digestant solution (white liquor) warmed to about F. is fed into the tank 10 through pipe 13 at the rate of approximately 10,000

pounds per hour. Chips, which would otherwise float in the upper part of tank 10, are kept evenly mixed through the white liquor by propeller 12, and the mixture is continuously withdrawn at the rate of about 12,000 p. p. h. through the pipe 14 and fed to the pump 15 which ejects the mixture into pipe 16 at a pressure of about 205 p. s. i. The digestant used in this case is Solution No. 2 above identified. In the heater 17 chips and liquor are heated to about 389 F, and then the mixture passes into conduit 18, through which it passes in about 10 minutes.

From the time the mixture enters the press 23 to the moment of explosion from chamber 28 procedure is as set forth in Solution No. 1, above.

The by-pass pipe line 32 is shown as provided with a valved supply pipe 41 for hot water which may be sup plied when desired as explained under the heading Process Example I. The by-pass line is also provided with a second valved supply pipe 42 by which any other agent such as bleaching liquid may be delivered to the chamber 28 while the fiber is still maintained under substantial pressure.

Fig. 3 illustrates how the apparatus may be modified in order that the compressed fibrous plug may be disintegrated by being exploded directly into the atmosphere. In this instance the plug will be ejected from the nozzle 42 of the screw press into the open end of a funnel-like member 43 in which the separated fibers are collected. Previously the major part of the black liquor will have been squeezed out of the fiber plug in concentrated form and when the plug reaches atmospheric pressure it will be exploded by the steam of its residual moisture.

The nozzle 42 of the screw press is shown as surrounded by an insulated induction coil of heavy wire 44 through which a high frequency electric current may be passed in order to supply additional heat at this point in the process if that is found to be desirable.

While the invention has been described specifically as a new and improved process, it includes also within its scope novel features of apparatus, and also as a new article of commerce an unbeaten and unjordaned wood pulp of which the majority of its fibers are flattened, curled and roughened and thus adapted for immediate transformation into paper.

Having thus disclosed our invention and described in detail an illustrative manner of putting it into elfect, we claim as new and desire to secure by Letters Patent:

1. In a continuous defibrating process, the steps of freeing a mass of digested vegetable fibre by compression from excess digestant solution and introducing the mass as press cake into a confined space containing hot water,

breaking up the press cake by stirring and meanwhile subjecting the aqueous mixture-to superatmospheric pressure.

2. The process defined in claim 1 in which the press cake is introduced into a confined space containing approximately four times its own volume of water heated to about 340 F. and therein subjected to fluid pressure of about 250 p. s. i.

3. The process defined in claim 1 in which the excess digestant solution is removed from the mass of digested vegetable fibre as the mass is formed into press cake, and

then a part of the removed solution is delivered under pressure to the confined space in which the press cake is subsequently broken up under superatrnospheric pressure.

5 References Cited in the file of this patent UNITED STATES PATENTS Re. 19,288 Bacchus Aug. 28, 1934 70,474 Russell Nov. 5, 1867 10 131,465 Russell Sept. 17, 1872 369,836 Blackman Sept. 13, 1887 530,635 Blackman Dec. 11, 1894 1,236,072 Ellis Aug. 7, 1917 1,505,934 Olier .Aug. 19, 1924 15 8 Mason V Mar. 30, 1926 Mitscherling Feb. 24, 1931 Wollenberg June 27, 1933 Mason Aug. 15, 1933 De La Roza May 23, 1939 Dreyfus Feb. 19,1946 Heritage Aug. 6, 1946 Deuchler Sept. 16, 1947 Zeehuisen Jan. 4, 1949 Jensen Nov. 14, 1950 Ernst Oct. 30, 1951 Kehoe Nov. 4, 1952 FOREIGN PATENTS France May 13, 1922

Claims

1. IN A CONTINUOUS DEFIBRATING PROCESS, THE STEPS OF FREEING A MASS OF DIGESTED VEGETABLE FIBRE BY COMPRESSION FROM EXCESS DIGESTANT SOLUTION INTRODUCING THE MASS AS PRESS CAKE INTO A CONFINED SPACE CONTAINING HOT WATER, BREAKING UP THE PROCESS CAKE BY STIRRING AND MEANWHILE