US2425024A - Apparatus for producing pulp from cellulosic material - Google Patents

Description

1947- J. B. Bsvsmnes ETAL 2,425,024

APPARATUS FOR PRODUCING PULP FROM CELLULOSIC MATERIAL Filed Nov. 21, 1942 5 Sheets-Sheet 1 +5 5 i INVENTORS JAMES BRQOKES BEVERlDE RICHARD DUNLAP KEHOE ALPHONSE SURWQ BY WWW.

ATTORNEY g- 1947' J. B. BEVERIDGE ETAL 2,425,024

APPARATUS FOR PRODUCING PULP FROM CELLULOSIC MATERIAL Filed Nov. 21, 1942 5 Sheets-Sheet 2 I f 3 25 24 \i I I14 27 as as as 26 i INVENTOR' JAMES BROOKES BEVERIDGE RICHARD DUNLAP KEHOE ALPHONSE SURINO BY W m ATTORNEY 1947' J. B. BEVERIDGE HAL 2,425,024

APPARATUS FOR PRODUCING PULP FROM CELLULOSIC MATERIAL 5 Sheets-Sheet 3 Filed Nov. 21, 1942 FIG. 4. 53 45 I \39 t I i 2| M 69 h I 76 I e7 65 I M 10 s INVENTORS ALPHONSE SURINO ATTORNEY Aug. 5, 1947. J. B. BEVERIDGE arm. 2,425,024

APPARATUS FOR PRODUCISG PULP FROM CELLULOSIC MATERIAL Filed Nov. 21, 1942 5 Sheets-Sheet 4 INVENTORS JAMES BROOKESBEVERIDGE RICHARD DUNLAP KEl-IOE ALPHONSE SURINO ATTORNEY g- 1947- 4 .s. B. BEVERIDGE ETAL 2,425,024

APPARATUS FOR rnonucme PULP mom canumosxc MATERIAL Filed Nov. 21, 1942 5 Sheets-Sheet 5 FIG. 7.

INVENTORS JARQES BRO RES BEVERIDGE IGHARO NLAP KEHOE ALPHONSE SURINO ATTORNEY Patented Aug. 5, 1947 APPARATUS FOR PRODUCING PULP FROM CELLULOSIC MATERIAL James Brookes Beverldge, Westmount, Quebec, Canada, Richard Dunlap Kehoe, Hadlyme, Conn., and Alphonse Surino, Bronxville, N. Y., asslgnors to Paper and Industrial Appliances,

. Inc., New York, N. Y., a corporation of New York Application November 21, 1942, Serial No. 466,410

1 Claim. 1

This invention relates to therecovery of individualized fibers in a pulp mass, such as are useful in the making of paper, wall board, dry felts, and the like. In the recovery of such fibers it is important not only that they be individualized without harmful loss of natural fiber length, but that the fibers be substantially dellgnified, that is freed of the layer of lignin and other binding material that surrounds the fiber proper, since the removal of that layer renders the fibers capable of fibrillation, that is of being bewhiskered by the formation on them of branch fibrillae. The branch'fibrillae cause a stronger interlocking of the fibers into a web, and thus make a denser and stronger end product.

Consequently, this invention may be said to relate to the kind of production of fibrous pulp from cellulosic material, whereby the pulp is treated by attrition effects as it passes between the abrading faces of a pair of companion discs in a rotary refiner to effect de-fibration of the pulp following a conditioning or retreatment performed upon the raw or starting material, for instance ligneous material such as wood chips or wood waste or a mixture of both, or a mixture containing sawdust, or other fibrous materials such as fiax, wheat and other straws, grasses, bagasse, or linters, i

As one step in the attainment of these objectives, it has been proposed to make use of the apparatus of the patent to Asplund No. 2,145,851 which practices the process of the Asplund Patent No. 2,008,892. The inventions of these two patents are characterized by maintaining in a pressure chamber certain temperature and pressure conditions. The raw cellulosic material is pressure-fed to the chamber to be de-fibrated in an attrition mill, while still subject to such temperature and pressure conditions. After passing through the de-fibering mill, the resulting socalled Asplund pulp is released from the pressure environment by using the pressure to blow pulp into a trap chamber having alternatingly operated valves, from which it passes into an outside space that is exposed to atmospheric pressure.

A further step towards attaining the objective of improved fiber characteristics, such as flexibility, pliability, toughness and strength, as well as full fiber length, was made by way of improving the Asplund apparatus, and treatment method in the manner disclosed in the copending patent application of Beveridge and Kehoe, Serial No. 351,670, now Patent No. 2,323,194, and Serial No. 484,444, new Patent No. 2,422,522. These improvements cover apparatus and process characterized by changing the temperature-pressure treatment chamber to include a chemical-bearing saturated steam atmosphere with positive means for impelling the cellulosic material therethrough at a controlled rate while in non-flooded condition, wherein the chemical has lignin solvent action so that the lignin content of the material is substantially lessened, as the individualized fibers are thus more eifectively freed of it. The fibers are thus rendered susceptible to fibrillation. The fibers obtained by these improvements upon the Asplund method and apparatus will herein for convenience be termed improved Asplund fibers or as a fibrous pulp they may be termed improved Asplund pulp.

Preceding the present invention we have observed and found that in addition to its outstanding fiber characteristics the improved Asplund fiber pulp acquires a sleekness, slipperiness, or soapiness, perhaps due to the chemical treatment that accompanies the temperature-pressure treatment, and consequently the pretreated pulp develops a tendency to pass or slip past the attrition faces in the rotary refiner without receiving its full. or adequate share of the refining or defibration treatment. We have also observed that the pressure under which the pulp is discharged from the refiner and from the system appears to encourage, at least momentarily, this phenomenon. In other words, certain otherwise desirable characteristics of the improved Asplund fiber'are attained at the price of a somewhat lowered effectiveness in the operation of the refiner.

Therefore, this invention revolves about the defibering attrition mill through which pulp passes that has the aforementioned characteristics. Such a mill comprises a casing which houses two dics having abutting abrading faces, and of which one is stationary and the other is adapted to rotate. Material from the heat and pressure en-' tions are in turn based upon the apparatus and procedure laid down in the aforementioned patents'to Asplund, the corresponding apparatus and process are herein represented by Way of illustration, to have the invention appear in a proper environment. It is the best and most effective practical application of this refiner improvement that we are aware of at present, but it is not to be considered as a limitation to the broader aspects of this invention.

For the purpose of dealing with this invention and for convenient identification, this improved de-fibrating mill will herein be termed as a stock retarding or self choking de-fibrating mill or refiner.

The original Asplund process may benefit from the operation of a de-fibrating mill that is improved in accordance with. this invention which compensates for the tendency of pulp passing through the mill too fast during periods of pulp discharge, when steam from the pressure system momentarily expands through the de-fibratlng mill and blows out the pulp;

In distinction from conventional cellulose digesting or cooking process in which the material is submerged or flooded with a liquor that has the property of loosening those substances in the wood that tend to bind the fibers together, the Asplund process and apparatus provide for a conditioning treatment, that is preliminary softening or partial dissolving or disintegration of the lignin or binding matter in the wood chips or ligno-cellulose material, and a subsequent mechanical de-fibration or refiner treatment to take place in a steam atmosphere, that is under certain temperature and pressure conditions.

It has operated successfully in a temperature range from 212 F. to 350 F. at a. superatmospheric pressure corresponding to saturated steam of those temperatures, and pressures of 150 lbs. to 160 lbs. have been found acceptable.

Steam treatment under such conditions is said by Asplund to require a period of something less than 60 seconds and on the average of 40 to 50 seconds, to cause softening of the middle lamella of the ligneous' material, (that is in effect the binder constituent for holding the fibers together in bundles) so that it can be separated into fibers when subjected to the action of the de-fibratingmill.

Under such process conditions the Asplund apparatus is adapted to absorb material or material mixtures of a grade, type or fineness, for instance sawdust or the like, that are not ordinarily acceptable for use in the conventional cellulose, digesting and cooking steps.

The Asplund apparatus is capable of continuous operation, since the ligno-cellulose material or wood chips are pressure fed against and into the steam pressure atmosphere mentioned in the interior of the Asplund treatment system. In order to introduce the wood chips into the pressure system, a plunger feeding device may be used whereby the wood chips are compressed or briquetted, so to speak, or a. continuous screw feeding device is employed whereby a continuous strand or plug of the compressed material is.

forced directly into the pressure treatment system. The feed pressure exerted upon the material by the feed devices forming the plug is sufllcient to seal off the steam at the feed end of the system. Once inside the pressure treatment system the wood chips are first subjected to direct contact with the steam and then fed within the pressure system to a rotary refiner or de-fibrater. The finished or de-fibrated stock leaves the steam pressure system by way of a trap space having an inlet and an outlet valve that are operated in opens to discharge the contents of the trap space into the atmosphere. After the outlet valve closes on the thus emptied trap space, the inlet valve opens again, allowing the steam in the system to expand through the refiner into the trap space as the latter refillswith finished defibrated pulp from the refiner.

The Asplund system of treatment is improved in accordance with the disclosures of the aforementioned copending applications by modifying or elaborating upon the pretreatment or conditioning phase in the temperature-pressure system, whereby delignification of, or removal of binding matter from the fibrous material is carried to a point unattainable with the Asplund process, so that not only will the fibers thereafter be effectively individualized without substantial loss of length, but also be rendered susceptible to becoming fibrillated. This will herein be designated as the improved Asplund process.

The modified or improved Asplund conditioning treatment just referred to comprises passing the wood chips under mild stirring at a controlled rate along a substantially horizontal path through a special detention or reaction treatment space or chamber in which a steam atmosphere of suitable temperature-pressure conditions is maintained while imposing upon'the material thus being detained a supporting delignifying chemical treatment. While the length of the period of treatment allowed for by Asplund is dependent upon the construction and capacity of the apparatus and under the conditions variable only within relatively narrow limits, with the improved Asplund process the factors of pressure, temperature, detention time, rate of stirring and the degree and timing of the chemical treatment become variables controllable relative to one another, and in such a manner that the operation is more flexible, and conductable within wider limits, and so that optimum results may be obtained with respect to the quality of the end product as well as with respect to the conduct of the process itself. A chemical or chemicals introduced or atomized into the detention zone, have a supporting or intensifying solvent action upon or are capable of rendering soluble the resins, lignin, and other binding matter contained in the cellulosio material being thus treated, but especially the lignin.

The chemical may be organic or inorganic, or may be acid or alkaline. It may be sodium hydrate or other sodium compound, or a mixture thereof. It may be a sodium acid sulphate, a free acid, an oxidizing or wetting agent. The chemical may be supplied to the chips or starting material in any desirable phase, namely solid, liquid or gaseous or in the form of vapors, either directly into the system or the chips may be presaturated or pretreated before being fed into the system.

In view of the foregoing, it is a more specific object of this invention to design a. rotary refiner or de-fibrating mill in such a manner that it will retard the passage of a sleek pulp through the refiner sufiiciently for controlling or at least retarding the rate at which pulp is passed through the disc-bearing de-fibrating mill, to avoid a premature release of pulp from the system before it is thoroughly de-fibrated.

Another object is to avoid inadequate detention of the material in the de-fibration treatment phase, when that inadequacy is due to the pressure discharge of the material from the refiner, that is when the material is blown through the refiner because of the pressure in the system.

In setting up this problem and contemplating its solution, we have visualized that the very rotation of the refiner should dynamically set up counter-acting or self-choking reactive forces effective upon the pulp in such a manner that its passage through the refiner, that is, its passage between the attrition discs and past the attrition faces, will be sufilciently retarded.

Features of this invention find embodiment in the design and arrangement of the grinding faces of the de-fibrating discs, and especially in the manner in which they are grooved. That is to say, the grooves are directionally disposed in such a manner that there is effected a relative retardation of the pulp passing outwardly between the discs. -Specific features therefore are found in the layout and configuration of the grooves and lands of the attrition discs or bodies. According to one feature the grooves or lands have a generally curved configuration with the convexity of the curves facing opposite to the direction of rotation of the refiner disc. The curvature thus is opposite to what it would be in the vanes of a centrifugal pump. In this way there is set up a self-choking effect or reactive force upon the pump passing over the attrition faces and through the narrow clearance between the refiner discs and through the grooves, and this effect or reactive force intensifies with the speed of rotation.

We have furthermore observed that incident to the opening of the inlet valve leading to the discharge trap space, the steam in the pressure system tends to expand at least momentarily through the clearance between the refiner discs into the trap space, as the trap space at the and through the grooves into the trap space, en-

hances the tendency of sleek pulp to pass through the de-fibrating zone of the refiner without receiving its potential full share of de-fibrating treatment. Consequently another problem is to reduce or compensate for the efiects upon the pulp movement of such steam expansion. A feature therefore resides in correlating the characteristics of the de-fibrating discs with the pressure of their environment that blows material through and from the discs when the pulp is discharged or released from the pressure system.

Another feature lies in the provision of means for equalizing at least to some extent the pressure diiferential that is momentarily set up between the inlet and the exit of the refiner due to the fiow restriction or obstruction represented by the pulp filled clearance between the refiner discs.

pressure differential between the inlet and the eidt side of the refiner.

The invention possesses other objects and features of advantages, some of which with the foregoing will be set forth in the following description. In the following description and in the claims, parts will be identified by specific names for convenience, but they are intended to be as generic in their application to similar parts as the art will permit. In the accompanying drawings there has been illustrated the best embodiment ofthe invention known to me, but such embodiment is to be regarded as typical only of many possible embodiments, and the invention is not to be limited thereto.

For example, while the novel groove pattern on the de-fibrating discs, that constitutes a part of this invention, is herein shown to comprise curved groove portions disposed in the outer zone of the disc, it should be understood that the invention is not limited to this specific embodiment as to shape. That is to say, the characteristic feature of the groove pattern may be more broadly defined as comprising groove portions located in the outer zone of the discs, and disposed at an angle with respect to further inwardly located adjacent groo've portions, the relative angularity being such as to set up a scooping or self-choking or retarding effect with respect to the passage of thepulp between the de-fibrating discs.

The novel features considered characteristic of our invention are set forth with particularity in the appended claim. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment when read in connection with the accompanying drawings in which Fig. 1 is a side view of an apparatus for treating fibrous raw material according to the improved Asplund process, by pre-treatlng and then de-fibrating the material in a steam atmosphere of certain temperature pressure conditions while superimposing thereon chemical treatment effects, the apparatus comprising the improvements in the de-fibrating mill whereby pulp thus preconditioned is more efi'ectively de-fibrated with the mill housing partly broken away to show the novel groove pattern on the attrition discs.

Fig, 2 is a front view of the apparatus of Fig. 1, with parts broken away.

Fig. 3 is a top view upon the apparatus of Fig. 1

along the line 3-3, with one end portion of the Fig. 6 is a greatlyenlarged part-sectional side;

view of the de-fibration mill showing a section through the de-fibratingdiscs and segments, and

provided with a novel pressure equalizing connection on the housing.

Fig. 7 shows the improved pattern comprising novel curved grooves in the abrading face of a defibrating attrition disc,

'In the drawings, the numeral ill represents a chip bin or hopper to which the chips of wood of the raw cellulosie starting material are supplied, from which the chips pass to a horizontal cylindrical casing l I in which operates a screw or other conveyer or pusher i2 operated 'by a suitably driven reduction gearing i3. This arrangement is mounted upon a base l4 supported from a floor i5. The chips are expelled from the casing past a weighted valve "5 into a steam chamber H to which steam is supplied through the medium of a. valved steam line i8. To the steam line l8, there may be supplied, if desired, one or more chemicals through the medium of a valved chemical line i8 connected to some high, pressure line.

From the steam chamber H, the chip stock or fiber stock is passed into a reaction chamber or pressure-temperature treatment .zone, indicated generally by C. Such a chamber comprises a vertically disposed entrance or neck section 28 for receiving the chips or stock from the steam chamher. The neck or pipe 28 is connected to a substantially horizontally disposed top or primary chamber portion or pipe 2| that forms with the neck 20 an inverted T; This top chamber 2| has a closure plate 22 at its right hand end (Fig. 2) and a somewhat similar closure plate 23 at its opposite end. Adjacent each end of the chamber 2|, there are provided vertically disposed pipes 24 and 25 respectively. These pipes are connected to similar pipes 28 and 21 respectively that are upstanding from a secondary or lower, horizontally disposed chamber portion or pipe 28 in a manner that aligned pipes 24 and 26, and 25' and 21 comprise passageways for stock to pass from the primary horizontal chamber 2| to the secondary chamber 28.

Secondary chamber 28 has its ends closed by plates 29 and 38 respectively. At the central portlon of chamber 28 there is a vertically disposed outlet pipe 3|. In the primary chamber 2| there is provided a screw or ribbon conveyer 32 whose flights or ribbons are so arranged that stock entering the chamber from neck 28 is split or spread, with some being impelled toward each end of the chamber, as shown by the arrows in Fig. 2; Since the cross-sectional areas of the chambers 2| and 28 are not less than that'of neck pipe 28, the stock spreads out in the chambers and its level rarely extends above the axis line of the chambers.

' 33 and 34 represent suitable drive means for operating and conveyers 32 in the primary chamber 28 and a ribbon conveyer 35 in thesecondary chamber. Ribbon conveyer 35 is arranged to convey stock from the ends of secondary chamber 28 toward its center outlet 3 i The ribbons are interrupted at 38 in order to facilitate the passage of the stock into the outlet pipe 3|. Aligned with vertical pipes 24 and 25 of the primary chamber are inspection or hand- hole cleanoutpipes 31 and 38 respectively.

The stock or chips passing through reaction chamber C via outlet pipe 3| may go to further treatment. or it may be passed through a further reaction chamber that is a duplication of the reaction chamber C and therefore herein not shown but broken away except for its inlet connection 3| and its outlet connection 3|, while the location of that additional chamber asa whole within the system isrindicated by the letter C. A pressure-equalizing pipe 85 extends from the inlet end of the reaction chamber C to the outlet end 0! reaction chamber 0'.

From outlet pipe 3| the pre-treated material or stock falls into a compartment 38 in which operates a discharging screw or ribbon conveyer or expeller 48 that extends into a pipe section 4|, and is suitably driven as by gearing 42 and a motor 43 mounted on a base 43 The pipe 4| connects centrally or axially with the casing of a de-fibrating mill or refiner 44 of the rotary disc type, that embodies special improvements pertaining to the de-fibrating step in the apparatus arrangement of this invention. A greatly enlarged part-sectional detailed view of the de-fibrating mill 44 is shown in Fig. 6, and a face view of improved abrading surfaces on the attrition segments of the mill is shown in Fig. 7. The housing of the mill ha an inlet portion or flange 45 that connects with the pipe 4|.

Opposite therefrom and coaxial therewith the housing has mounted therein a horizontal i1npeller shaft 48 provided with a tapered end portion 48 extending inside the housing, upon which is keyed a rotary disc 41 from the circumference of which extend radial vanes 41; the disc 41 in turn carries an annular attrition plate 48 held in place upon the disc 41 by means of a cap nut 49 screwed upon the reduced and threaded extremeend portion 50 of the shaft 48, which cap nut is provided with lugs 5| or the like for tightening it This cap nut has an outer cone shaped configuration 52 to help streamline the course of the pulp flowing through the inlet portion 45 into the mill. The rotary attrition plate 48 has an inner zone P that is provided with ribs 53 for guidance and preliminary attrition, and an outer zone Q being shaped to have mounted therein abrading segments 54 which in turn are provided with a novel pattern of grooves extending outwardly in the general direction of the ribs or grooves 53.

place upon the attrition plate 48 in a known manner by means of bolt and nuts 55. The rotary abrading segments 54 cooperate face to face with stationary abrading segments 58 that are substantially similar to the rotary abrading seg-.

ments 54. A more detailed description of the novel groove pattern in both these segment that constitute a part of this invention, will be more specifically described below. The stationary segments 58 are held in place by means of bolts 51 upon a stationary attrition plate 58 that is fixed to the housing of the mill by means of bolts 59, and it has auxiliary ribs or grooves 59 for preliminary attrition that are somewhat shorter than the corresponding grooves in the rotary attrition plate 48, since the stationary attrition plate 58 ha a. central opening to match the pulp inlet that is larger than the central opening of the rotary attrition plate 48. 'The housing of the mill is split along a plane extending transversely of the axis of rotation of the shaft 48, and accordingly it comprises a housing portion 8| that is shown to be integral with the inlet flange 45,

The segments 54 are shown to be secured in inlet portion 45 and being passed outwardly between the opposed or abutting abrading segments 54 and 56 whereby it is de-iibrated, leaves the mill housing through a lateral outlet connection 61 that is provided upon and shown to be integral with the portion 62 of the mill housing.

From there the de-fibrated pulp passes through a sequence of elbows 68, 69 and in to a trap space H represented by an S-shaped pipe portion 12, and from there through a bent outlet discharge portion or pipe 13. At each end of the trap space or S-shaped pipe there is provided an inlet valve V1 and an outlet V2 respectively.

The inlet valve V1 is shown to comprise a seat member 14 interposed between the flanges of the elbow portion '!0 and of the S-shaped. pipe portion 12, and an associated valve member 15 having a valve stem I6 extending through the wall of the S-shaped pipe or trap space. The outlet valve V2 is substantially identical to the inlet valve V1 in that it comprises a seat member 11,

a valve member 18, and a valve stem 19 that extends through the wall of the bent discharge pipe 13. A mechanism comprising the valves V1 and V2 is known of itself and described in the patent to Asplund (No. 2,145,851), and therefore a mechanism for automatically actuating these valves in alternation is not herein shown except diagrammatically as indicated by the letter M.

The function of that valve mechanism is such that the valves V1 and V: operate in alternation,

that is to say the valve V1 opens while the the discharge.

Wth the refining mill subjected to the pressure environment that is maintained in the pretreatment phase of this apparatus embodiment, it will be understood that there is a tendency of the pressure from the mill to momentarily blow de-fibrated pulp into the trap space H, since at the moment that the inlet valve V1 opens,

. the back pressure in the trap space H is substantially equal to the lower pressure of the outside atmosphere due to the outlet valve V2 having previously been opened and closed during the discharge of a preceding batch of trapped pulp.

Referring to Fig. 7 there will now be described the layout of a novelgrooved pattern on the abrading faces of the improved abrading segments.

One such segment designated in Fig. 7 by the letter Z, has an outer zone S that is occupied by grooves 80 having a substantially straight inner end portion and a curved outer end portion, and also occupied by somewhat shorter or medium long curved grooves BI, and by still shorter or short curved grooves 82. In distinction from the short grooves 82 and the medium long grooves 8!, the first mentioned grooves 80 will herein be termed the long curved grooves. This segment Z further has an inner zone R occupied by substantially straight although slightly tapered outwardly extending long grooves 83 alternating with similar although somewhat shortor straight grooves 84 herein called the short straight grooves.

It will be seen that the long curved grooves 1 80 of the outer zone S are staggered with respect to the straight-long and medium- long grooves 83 and 84 respectively of the inner zone It, and that both the curved grooves 80 and the straight grooves 83 and 84 extend relative to each other in such'a manner that the inner endportion of the curved grooves 80 and the outer end portions of the straight grooves 83 and 84 occupy an intermediate zone T represented by the overlap between the outer zone S and the inner zone R.

It will be seen that in this arrangement or pattern the straight long grooves 83 register with the curved short grooves 82, while the straight short grooves 84 register with the curved medium long grooves 8|. The curved long grooves 80 are out of registry with the straight grooves 83 and 84 and are consequently disposed so as to extend into the respective spaces therebetween.

Operation The effect of the practice of this invention in comparison with either the original Asplund method or the improved Asplund method, may

be expressed in the following tabulation:

Undue acceleration of passage of the pulp past the abrading faces of the de-flbrating discs (as is responsible for inadequate de-fibration) may be caused by any one or any combination of the following factors:

(a) The centrifugal force exerted upon the pulp passing through the mill by the rotation of the disc,

(b) The pressure or steam atmosphere under which the de-fibrating in the mill may be allowed to take place,- and which pressure blows the pulp out of the mill when discharging,

(c) The slipperiness, soapiness or sleekness which the pulp acquires due to pretreatment ina chemical-bearing steam atmosphere in the defibrating mill.

Therefore, according to this invention, a retardation of the rate of pulp passage past the abrading faces is desirable (1) In the original Asplund method and apparatus (according to the aforementioned patents) because of the presence of the above factors (a) and (b),

(2) In the Asplund method as improved by Beveridge and Kehoe (according to their aforementioned copending patent applications) due to the presence of factors (a), (b) and (c).

It has been stated that according to the afore mentioned Asplund patents, unsubmerged lignocellulose materials such as wood, straw, flax and the like have been subjected to steam heat, moisture and superatmospheric pressure for softening the middle lamella, and the material was then put through a grinding or de-fibrating refiner while still subject to the temperature-pressure conditions. This produces an improved fiber product, but as the fibers when subjected to grinding still contained their lignin sheath, layer or armor, the grinding seemed tobreak or shorten the fibers as it had little or no effect on removing the lignin sheath from the fibers. Still, when practicing this Asplund method in conjunction with the improved de-fibration step according to this invention, the benefit thereby obtainable is due to the fact that the improved de-fibration operation tends to compensate for the above identified factors of (a) centrifugal forces in the grinding mill, and (b) the steam or blowout pressure, both of which otherwise would tend to reduce the effectiveness of the de-iibration step.

The fibers exhibit the particularly desirable characaaoas acteristics of natural strength, toughness and flexibility, without substantial impairment of the natural fiber length which it is highly desirable to preserve as far as possible-through the operation.

What seems to happen in the treatment method according to that embodiment is that the middle lamella, that is in effect the binder constituent for holding the fibers together in bundles. is softened or otherwise made amenable to the subsequent refining or grinding or de-fibrating operation whereby the bundles of fibers are pulled apart or individualized. Moreover, this treatment appears to overcome an ever present difficulty, namely the breakage and shortening of the fibers, sothat they retain substantially their full length. Also it appears that this treatment not only affects the natural binder substance or middle lamella, but in distinction from the original Asplund process that involves no chemical along with the steam, it furthermore cleans the individual fibers of the lignin and any other gums or waxes as well that surround them like a sheath or armor. Yet, the slipperlness of the pulp due to this treatment and whereby the relative efiectiveness of the cle-fibrating operation is liable to be reduced, is at least partially compensated for in the practice of this invention.

This treatment further involves the use of appropriate chemicals to establish and maintain certain pH conditions in the material being treated, as well as appropriate dilution conditions and concentrations of the chemicals. For producing individualized fibers having the aforementioned desirable characteristics from lignoceilulose material, the treatment further involves the special correlation with each other of such operating factors as moisture, temperature, pressure, amount of chemicals used, their character and their concentration. It also involves as another factor to be correlated, the time element, so that the material is passed through the pre treatment section at a controlled rate while being continually redistributed whereby there is discouraged localized overheating, localized degrading of the fibers and discoloration.

For its particular results as to fiber characteristics this treatment also involves maintaining in the pretreatment zone a steamand chemicalcontaining atmosphere at super-atmospheric pressure and an atmosphere such that moisture and soluble chemicals therein are maintained atomized. At the same time it provides for an enlarged conduit section or extended path of treatment along which the material being treated in that atmosphere can be spread out to overcome compacting tendency, and it provides means for positively impelling the material through the conduit in a manner whereby the material is continually turned or rolled over so that fresh surfaces of the material are continually exposed to the treatment atmosphere. In view of the importance of the factor of detention time in conjunction with all the other factors, the rate of passage of the material through the treatment conduit according to this embodiment, is controllable by adjusting the rate by which the im pelling means are operated.

The environment of the material or chips inthe treatment zone iskept so that there is a. minimum of liquid therein and a maximum of vapor. The steam used may be supplemented with one or morechemicals that aid in the d-lignification of, and other treatment effects upon the wood chips or other starting material, orthe material 12 can be supplied with the chemicals priorto its introduction into the reaction chamber.

After grinding, the de-fibrated mass is subjected to washing as soon as possible so that excess chemicals, middle lamella, lignin solutes, color and other impurities are removed from the mass :before they are reabsorbed by the fibers. Such reabsorption does not appear to take place in the mill itself while a suitable temperaturepresure atmosphere is maintained therein. But after the stock is released from the pressure and temperature of the mill, it should be quenched and agitated rapidly with wash water so that the solutes and other impurities arewashed free of the fibers before they can congeal on or around the fibers, for these impurities seem to be thermoplastic.

According to this embodiment, the cellulose starting material is pressure fed in the form of substantially dry chips of wood that are compressed into plugs as they are pressure fed into a reaction chamber that has an atmosphere of steam ranging from 212 F. to 390 F. at pressures corresponding to saturated steam of the temperature used. After the chips, flax, straw or other starting materials have been introduced into this environment, they are passed to a reaction chamber thatis substantially horizontal and has a cross-sectional area that is largerthan the preceding zone, and is provided with mechanical means, such as a screw for impelling the chips therethrough whereby the plugs of introduced chips disintegrate into individual chips, and the chips are spread out so that a maximum of their surface is exposed and continually reexposed to the environment of steam, temperature and pressure, and of chemical. Indeed, in the embodiment shown the chips are raked or impelled first in one direction and then in another, in an enlarged conduit that is only partially filled with chips. i

In making use of the apparatus thus described, the ligno-cellulosic material to be treated, such as chips of wood from deciduous and coniferous trees, or cut straw, flax, bagasse and the like, is supplied to the hopper i0 whence it is compressed and compacted in casing H by means of screw conveyer l2 into plugs that are pressurefed past weighted valve i5 into the steam chamber ii that is in the nature of a pre-heater, under conditions that the feeding does not prevent the maintaining of the heat, steam and pressure conditions in the treatment chamber shown generaliy at C (and additionally if desired C). Steam for providing the heat and moisture and pressure conditions in the chamber is pumped thereto through pipe i 8. If chemicals are to be introduced directly, they are pumped through pipe i9. Since it is desirable that they be atomized, an atomizing device A is made use of where the chemical conducting pipe i9 joins the steam pipe i8.

The chips or other material is forced against the high pressure in the chamber, by the pressure feeding device or screw 12 along the steam chamber or conduit i1 until it falls down neck 2!! into enlarged chamber 2|. The pressure compresses the wood to substantially twice its normal density. In this chamber, the material spreads out since it does not nearly fill the cross sectional area thereof, and is impelled by screw conveyer 32, under conditions that tend to uncompact or decompress the material and also to roll the material over and over upon itself for continually exposing fresh surfaces thereof to the atmosphere of the chamber- The material then falls to the lower chamber or conduit-28 where another screw or ribbon conveyer 35 continues the continual exposing of fresh surfaces and impels the material to fall through neck 3|, either to a further reaction chamber C or directly to compartment 39, depending upon whether or not a second reaction chamber C be used. The speed of impelling of the material, and thus its time of transit through the reaction chamber C is controlled by the pitch of the rate of rotation of the screw conveyers 3-2 and 85.

By the treatment of the material or stock in the reaction chamber C that has an atmosphere of high temperature, high pressure, steam and chemicals wherein the stock'is agitated in nonsubmergence at intensity less than that for causing de-fibration, what happens is that the heat and moisture softens the middle lamella or binder of the fiber bundles and there is sufficient agitation of the stock in the chamber to permit the bundles of fibers to be exposed to the action of the atomized chemical, since the atmosphere of the chamber is like a mist or fog of steam and chemical. Each fiber has a sheath, layer or armor of lignin that nature seems to have provided to protect the more soluble lignin-complex that exists between the cellulose core of the fiber and the lignin sheath. This complex contains a heterogeneous mixture of lignin, hemicellulose, and carbohydrates such as sugars, or more particularly pentosanes and polysaccharides. The lignin of this complex seems to be more soluble than the lignin of the fiber enveloping sheath. Therefore, the lignin sheath must be made pervious to the steam present for dissolving the solu-ble constituents of the internal complex. This is accomplished by making use of chemicals that render that lignin in its different I forms soluble under the conditions of heat, pressure and moisture prevailing in the reaction chamber. soluble involves a time factor and this is provided for by the effective length of the reaction chamber, the rate of passage through which is controlled by the screw conveyers. Since the stock is not submerged in liquid, the chemical reaction between the chemical and the 'lignin takes place between a solid and a wet gas or vapor. Therefore, fresh surfaces of the solid must be continually brought into contact with the gas, and the distributing action of the screw conveyer accomplishes this result.

As the stock leaves the reaction chamber, it comprises a mixture of bundles of fibers, lamella, and chemicals, lignin and some other impurities including color constituents, in solution phase. By lessening the lignincontent of the fibers, it has been found that they are amenable to the defibering action of the grinding station with little or no tendency to become shortened or otherwise degraded, for it is their content of lignin sheathing that heretofore has caused such unsatisfactory results from the refining or de-fibering station. I I

In the reaction chamber, there is maintained a super-atmospheric pressure of from 100 to 150 pounds per square inch, although the yardstick to be used is to maintain a pressure that yields acondition in which the wood of the chips is thoroughly impregnated. The temperature However, this rendering of the lignin maintained varies with (1) whether or not chemicals are used, and (2) the degree of cleanliness required of the fibers. If no chemicals are employed, the temperature used is usually be- 14 tween 365 and 390 F., whereas, if chemicals are employed, good results have been attained with a temperature as low as 270 F.

With respect to the chemicals that can be used, they divide themselves generally into two groups, those that are acidic in character, and those that are alkaline. Certain factors must be borne in mind, in determining which to use. The hemicellulosic constituents of the wood are subject to hydrolysis and this is accomplished in either acid or alkaline medium. Also, the removal of incrustants varies with the kind and concentration of chemicals employed. For example, soda and sulphate liquors have been found to be much more reactive to hemicellulosic material during the early stages of cooking than they were to lignin. Also, soda and sulphate liquors remove the intercellular substance, between the primary walls, very rapidly, but do not attack the cell wall lignin to any great extent until the former is 7 nearly completely removed. Sulphite liquor does not have this selective action, but removes both intercellular and cell wall lignin, at about the same rate, though more slowly than the rate at which alkaline liquors dissolve lignin.

Chemicals that can be used comprise:

The concentration of 'the chemicals used ranges from 0.5 pound to 4 pounds per gallon. The usual concentration used is 2 pounds per gallon or approximately 20% concentration by weight of chemical. The usual concentration by weight of chemical in the reaction chamber is 5%. These figures are based on a feed rate of 1000 pounds of chips per hour on the bone dry basis, a steam consumption of 700 pounds per hour with approximately 500 pounds per hour condensed in the chamber, and a chemical feed of 10 per cent based on the bone dry chips fed.

The dilution in the reaction chamber including condensed steam and moisture in fibrous material is 50-95%.

The dissolving action of the chemicals is greater for increased acidity or alkalinity. The pH values of the eiliuent from the de-flbered material may betaken as a measure of the extent to which the chemicals employed are consumed or absorbed. This represents an important control method for the amount of chemicals to be added to the raw material in the apparatus. Conductance measurements may also be used for quick control. i I

It can be said that our prevailing pH range when acidic chemicals are used is from l to 6 and when alkaline chemicals are used, from 7 to 12. But normally, our rangeis between 3 and 9. When acids are used, the cooking starts very acid but during the reaction time, the acidity is absorbed by combining with the lignin present so that the actual pH of the discharging. fiber increases. a y

In the same .way, if an alkali is used, whatever pH is started with the pH of the finished fiber is less.

The time of passage or transit of the stock through the chemical atmosphere of the reaction chamber can be used somewhat as a micrometer adjustment to supplement the quantity of chemicals added. 011 the whole, the time of transit should be at least one minute and can be as long as sixty minutes. The reason for this is that the chemical reaction is a surface contact phenomenon and therefore the greater the surface contact, the greater the efiiciency of the reaction. This is where the distributing and stock turning-over action of the screws of the reaction chamber are effective.

The stock in the reaction chamber must be protected from localized overtreatment or excessive breaking down or degrading of .the fiber structure, so the chemical present must not be too strong or too highly concentrated. It may be said that by practicing the Asplund process without chemicals, a recovery of 93% of the wood input is recovered in fibers, whereas by the practice of this invention the yield of recovered fiber can be from 50% to 90%. The diflerence is accounted for mainly by the lessened lignin content of the fibers as yielded by the practice of this invention. The concentration of the chemical used is controlled by the amount of water or moisture added. The chips normally contain from 30-50% moisture, or for each part of dry material, they have from one-third to one-half part of moisture. With that as a starting point, steam and chemical solution is added to maintain in the atmosphere of the reaction chamber, a moisture content of between 50 to 95% of the material on a dry basis.

From the reaction chambers C and C the stock passes into the outlet receiver or chamber 39 whence the screw feeder ll feeds it to the defibrating mill M. While the general structure and de-fibrating function of such a mill is substantially well known, its de-fibratory effect is improved or modified in the practice of the present invention because of the effect of the improved type or shape of the groove pattern provided on the grinding or abrading segments 54 16 tween the opposed segments, that is sufiicient at least to partially compensate for those factors that tend to speed the fibers past the attrition zone in a manner whereby they are inadequately de-flbrated. Those factors are (a) The centrifugal force due to the rotation of the rotary segments, 7

(b) The steam pressure from the preceding reaction chamber that tends to blow pulp through the mill periodically as the discharge mechanism M operates, and

(c) The slipperiness or soaplness or sleekness acquired by the stock because of the preceding chemical treatment in the reaction chamber.

Thus because of this invention there are combined all of the advantagesof the improved fiber characteristics due to the improved Asplund treatment (whereby the reaction chamber as well as the subsequent mill operation take place under elevated temperatures and pressures of a steamchemical atmosphere) with the effects of high grade de-fibration or individualization of the n ers.

The finished fibers leave the mill '44 by way of the outlet connection 81, and passing on through the elbows 68, 59 and I1, enter the trap space ii, and from there pass out of the pressure atmosphere to be washed and further treated. Due to the quickly alternating operation of the valves V1 and V2, the operation of the trap space ll is such that the material discharges from the pressure system in intermittent although near-continuous flow. As the trap valve V1 opens (the trap outlet valve V: being closed), the steam atmosphere expanding from the mill into the trap space blows a charge of the finished material into the trap space. The valve Vi then closes. and

' when thereupon the trap outlet valve Vz opens,

the pulp they might be compared to the effect of rotary scoops, that is contrary to the eilect of the blades or vanes of a centrifugal pump.

Thi invention is not limited to fashioning both the rotary as well as the stationary segments in the same manner, and for instance, the one may have curved, and the opposite segments may have straight grooves. As one of a number of possible embodiments it is herein contemplated to have the curves of the stationary segments curved in a direction opposite to the curvature of the grooves on the rotary segments, the sense of both curves, of course, being that of having a relative scooping or self-choking effect upon the pulp passing through the attrition zone.

The effect of the curvature of the grooves is to set up a reactive or choking force relative to the pulp passing through the attrition zone bethe trapped material is discharged, the discharge being helped by the expansion of that portion of the steam atmosphere that has been trapped along with the material in the trap space I I. Due to the special drive mechanism M there is a rapid succession of such valve operating cycles.

The equalizing connection 84 between the inlet and theoutlet end of the housing of the mill 44 may be employed for the purpose of reducing or compensating, at least partially, for the effect of the aforementioned factor (b) ;'that is, the blowing-through effect of the steam pressure.

Thisspecific compensatory eflect may be adjusted or eliminated as the case may be, by means 2: a control valve (not shown) in the connection We claim:

Apparatus for the preparation of defibrated cellulosic fibers which comprises aclosed treatment chamber, means for continually feeding cellulosic material thereinto, means for continually supplying steam to the chamber for maintaining therein an ever-changing vapor body comprising steam having a temperature above 212 F. and super-atmospheric pressure adapted for conditioning said material in said vapor body for deflbration, a refiner having a casing provided with an inlet for passing the so-conditioned material from said chamber to the refiner and whereby the casing communicates with the chamber while being subject to such temperature and pressure, refiner discs face to face in said casing and rotatable with respect to one another with a clearance between'the faces through which such material is impelled by the vapor escaping therethrough from the chamber, outlet means associated with the casing through which defibrated material is sub- 17 stentially continually emitted in suspension in 1 the escaping vapor, conveyor means for mechanicelly controlling the rate of feed of the material from the chamber to the refiner discs,-and retarding means substantially independent of the clearance setting of the discs providing grooves alternoting with that lands in the face of at least one disc and having a. bend in the direction of the rotation of the disc for retarding the transit of the material relative to the flow rate 01 the escaping vapor so that a sumcient quantity of such me.- teriel is detained sufiiciently between the discs to have a, deflbreting action on itself within said clearance while minimizing the deterioration of fiber length.

JS BROOKES RICHARD D i r ALPHONSE SURINO.

REFERENCES CE'KED I M STATES 5'3" Number ame to Re. 1,380 Kingsiand Jan. 6,1863 Re. 1,381 Kingsland Jan. 6, 1863 29%,911 11, 1994 Prior Q. in :1.

Number 1 1 Name Date Bernard Oct. 14, 1884 li-I'ussey Mar. 10, 1931 Oflermanns June 2'7, 1939 Easier Dec. 9, 1941 u 1. l Apr. 27, 1943 Coleman June 12, 1860 Fairclough Nov. 30, 1869 Gould Jan. 20, 1885 Bryant Oct. 20, 1914 Asplund Feb. 7, 1939 Sutherland May 2, 1939 Beveridge June 29, 19 13 Mnrkley Sept. 10, 1910 FOREIGN PA 1' Country Date Germany June 10, 1886 Australia. Apr. 10, 1933 Sweden .1 June 11, 1940 Great Britain 1911 DTHER REFERENCES Technical Association Papers, Series 20 (1937) imges 192 and 195.

Chemicol Engineers Handbook, by Perry, pub-

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