US1905161A - Method of and apparatus for hydrating cellulose pulp - Google Patents

Description

April 25, 1933. v w. T. DOYLE I 1,905,161

METHOD OF AND APPARATUS FOR HYDRATING CELLULOSE PULP f Filed April 26, 1932 2 Sheets-Sheet 1 April 25, 1933. w. T. DOYLE 1,905,161

METHOD OF AND APPARATUS FOR HYDRATING CELLULOSE PULP Filed April 26, 1932 2 Sheets-Sheet 2 5 1| 4/ A Z/Z'WZ/a k: 1 j 6M,

Patented Apr. 25 1933 UN TED STATES PATENT OFFICE WILLIAI '1. 0] DORCHESTE B, IASSAOHUSETTS, ASSIGNOB TO STUBTEVANT KILL COMPANY, 01 BOSTON, MASSACHUSETTS, A CORPORATION OF MASSACHU- SETTS- IE'I'EOD 0! AND APPARATUS FOR HYDBATING GEIIIIULOSE PULP Application filed April 28,

. means that the paper or other fibrous product made therefrom will have the proper density and closed in structure and that the gelatinized cellulose will bond the fibers together soas to lend the requisite mechanical properties to the paper or other fibrous product,

The degree to which beating is effected depends upon the kind of cellulose stock serving as raw material as well as upon the qualities desired in the finished manufacture and can be controlled by determining from time to time during the beating operation the socalled slowness value. which is considered to be a measure of the degree of hydration orgelatinization.

Heretofore the beating of cellulosIeIpulp has been generally accomplished in a ollander orbeater engine having a roll equipped with knives passing over a so-called bed plate at such a narrow clearance as to brush the fibers circulating past the clearance space. As hydration progressed, the beating was made harder by bringing the knives closer to the bed plate with the result that besides hydration a marked cutting of the fibers ensued. The cutting of the fibers is reflected in a dereciation of such qualities as tear resistance and fold endurance, which are tied up with fiber length, in the finished paper. The fore going trouble is accentuated when the beaten pulp is put through a J ordan'engine which 1s sometimes employed to complete the hydration of the fibers and which operates on the same principle as a Hollander.

In accordance with the present inventioncellulose pulp stock undergoes hydration as a thick aqueous suspension being re- 1982. Serial No. 807,528.

peatedly subjected to the action of a so-called ammermill which is designed to individualize the pulp fibers and to hydrate them efliciently and with much less cutting action than that encountered in an engine of the type previously described. In accomplishing this result, it is necessary to maintain a supply or batch of the stock as a thick aqueous sus ension, to remove the stock progressively rom the supply and to feed it through the hammermill, to return the stock to the supply, and to repeat the cycle until the degree of hydration desired for papermaking has been attained in the stock. More than this, however, in order to realize an efficient hydrating action, it is necessary to feed the stock into a hammermill'having the hammermill undergoing hydrating ac-v tion so that the mill operates constantl under load and hence efliciently. It is pre .erable that the rate of feeding of the stock into the mill be substantially equal to the rate of stock being discharged therefrom so that the mill may operate under a substan tially steady load and with no backflow of stock in the system.

In practising the foregoing method, I employ a circulatory channel for keeping a supply or batch of the stock undergoing treatment, e. g., an oval-shaped tub such as forms part of the usual Hollander. Included as part of the circulatory system is the ham mermill casing, which has an intake communicating with the supply in the channel and whose outletdelivers the discharged material, including water and stock, back to the channel. The hammermill itself may afford all the circulating action, although, if desired, a pump or other suitable means may be used to promote circulation. From Q e lpermitthe accumulation of. stock The mill is operated to deliver.

standpoint of efiiciency, it is desirable that the hammermill rate upon stock of high consistency or thic ess. In order to secure good circulation in the system and at the same time to deliver thick stock to the hammermill, provision may be made to thicken the stock near the intake of the hammermill and to dilute the stock at a point remote from the intake so as to avoid sluggishness in the movement of the stock to the intake.

With the foregoing and other features and objects in view, the present invention will now be described in greater detail in conjunction with the accompanying drawings, wherein Figure 1 represents a plan view of an apparatus embodying the present invention.

Figure 2 is a vertical, transverse section through the hammermill on the line 22 of Figure 1.

Figure 3 is an end elevation of an ad ustable bearing for the shaft of the hammermill.

Figure 4 constitutes a section on the line 4.4 of Figure 2.

Figure 5 illustratesanother form of apparatus embodying the present invention.

Figure 6 is a composite view made up of a fragmentary section on the line 6-6 of Figure 5 and a side elevation of one end of the apparatus.

Referring in detail first to Figure 1 of the drawings, the apparatus shown comprises an oval-shaped tub 1, such as forms part of the ordinary beating engine. Into this tub may be put raw material of any suitable character, e. g., sulphite, kraft, or ground-wood pulp,

- rag or rope stock, or the like. The pulp may be furnished to the tub as in the form of laps or sheets, together with sufiicient water to produce, say, a 5% aqueous pulp suspension. The supply thus furnished makes what may be termed a main circuit around the tub and through the casing of a hammermill shown installed centrally on one side of the tub. The casing, as can be best seen from Figures 2 and 4, is of generally cylindrical shape, and

. includes an intake openin directly into the main stream of pulp stoc and of sufiicient size to permit sheets of pulp to pass therethrough into the casing. The casing is made up of an external shell 3, which is lined at spaced zones a, b, and c with curved plates 4, suitably secured to the shell and presenting a series of spaced bars or ribs extending longitudinally of the shell. Between the plates at b and 0 are a series of longitudinal slots or openings through the shell, defined by spaced bars 6 anchored at their ends to the end walls 7 of the shell. These openings are shown through an upper side of the shell opposite to the intake opening and serve to permit discharge of the water and stock from the casing. over an incline sloping into the main channel of the .tub. A cover or shield 8 shown above'the tub and near the discharge openings serves to direct the discharged material into the main channel. The cover may overlap the shell 3 sufliciently to permit bolts 9'to be threaded therethrough and to clam a curved discharge gate 10 against the shelll By loosening the bolts 9, the gate 10 may be moved to close more or less of'the opemngs and thereby to regulate the volume of material being discharged from the casing. At the intake opening, there is shown a flat plate 11, which is pivoted at its rear end 12 so as to permit its forward end to be adjusted to clear the hammers to the desired extent and hence to regulate the disintegrating or breaking action on sheet pulp or other stock used as a raw material. The desired adjustment of the plate 11 may be made by turning a bolt 13 threaded through the bottom of the tub and engaging under the plate. As shown, the casing further includes a curved plate 14 located between the curved lates at a and b. The plate 14 can also be ad usted toward. and away from the hammers so as to control their breaking action on the stock by turning bolts 15 passing through suitable openings in the shell 3 and in threaded engagement with the proceeds is to some extent determined by the gate opening.

The stock introduced into the hammermill undergoes a succession of hammering impacts delivered by successive rows of hammers 17 pivotally mounted in spaced relationship on a suitable rotor. 'The rotor is made up of a series of annular plates 18, which are assembled alternately with a series of washers 19 on rods 20, which pass therethrough and whose ends are provided as with heads riveted onto the end plates so as to prevent lateral movement of the plates and washers. The plates and washers may be keyed to a shaft 21 passing therethrough and through the end walls 7 of the shell. The inner end of each hammer may be of a'thickness corresponding substantially to that of each washer 19, so that they may be fit in between successive plates and their inner ends be engaged by a rod 22 passed alternately therethrough and through the plates. The en ing the end plates. Each end of the sha t 21 Flo is shown journaled for rotation in suitable bearings in a block24 maintained on suitable su ports. Each block is preferably adjustab e both sidewise and vertically, so as to permit the free ends of the hammers to strike any locality inside the casing-or to move past with a particular clearance. As shown, each block rests on a pair of superposed plates 25 having inclined contacting faces and capable of being made to slide relative to each other so as to raise or lower the block. Extending from opposite ends of each .plate are bolts 26 which pass through brackets 27 and which are engaged at their ends by nuts 28. These nuts can be turned to effect the desired vertical adjustment of the block. A pair of bolts 29 threaded through the'brackets 27 so that their ends engage opposite sides of the block can serve as the means for effecting 3 sidewise movement of the block. The shaft 21 may be driven by any suitable means, as by a pulley 30 aflixed to one end and deriving its motive power through a belt 31 from any suitable source of power (not shown).

As already stated, the conditions under which the hammermill is operated should-be such that stock is always present therein, as this makes for higher eificiency The stock in the hammermill is of higher consistency than the main body of stock in the tub by virtue of the fact that there is a much greater tendency for the free water to pass through the discharge openings than for the stock. The increased concentration realized .in the hammermill will vary, depending upon such factors as the size and number of discharge orifices and the speed at which the mill is run, but in any event, a lower consumption of power for a given amount of hydration is realized as a result of the increased concentration. v

The pulp suspension may to advantage undergo a thickening immediately before it enters the hammermill. To this end, a hollow drum 32 whose periphery is covered with wire cloth may be caused to rotate partially submerged in the pulp suspension near the intake of the mill. The shaft 320 of the drum may be journalled for rotation in the walls of the tub and be driven by suitable means (not shown). The drum may, as illustrated, be constructed like the usual washer drum,- and permit water to pass into its interior and to flow by gravity through an open side, while the thickened pulp picked up on the peripher falls immediately outside the intake of t e mill. Inasmuch as the water removed from the stock contains gelatinized cellulose, fiber fragments, and the like, which are valuable paper-making ingredients, this. water is preferably used for diluting the stock and increasing its mobility.

As illustrated, the water flows-into a tank 33 from which it is withdrawn by a pump 34 and passed through a pipe 35 terminating as a pair of valved outlets 36.. These outlets are shown arranged to return thewater under pressure. at spaced points near that end of the vat opposite to where the drum is located.

By directing the water at two or more points 1n the vat, the stock becomes dilued quickly and uniformly and is impelled as a mass toward the thickening drum. Of course, the

diluting water-may be-returned to the stock in the vat in any'other suitable way.

Rather than thickening the stock before it goes intothe hammermill, the stock may be pumped into 'a mill so constructed and arranged 'as topermit a thickening effect by free drainage of the water through the discharge openings. An apparatus designed according to this principle is depicted in Figure 5 wherein the tub 37 is U-shaped and s equlpped with an outlet 38 at one end leadmg to a centrifugal pump 39. shown operated by a pulley-driven shaft 40. The pump removes the stock from one end of the tub and forces it upwardly through a pipe 41 leading to the intake end of a hammermill 42 which is arranged above the other end of the tub. This hammermill may be of a construction substantially like that previously described excepting that the discharge openings 43 extend longitudinally through the bottom of the casing. It is thus seen that gravitation of the water through the discharge openings as well as forcible flow induced by centrifugal action is had, with the result that immediately upon entering the mill, the stock undergoes dewatering and the m ll operates upon a thicknened stock. At thls point, it may be mentioned that in the case of both the apparatus shown in Figures 1 and 2 and that shown in Figures 5 and 6, the stock constantly present in the hammermill, whether or not it undergoes previous thickening as described, is at a higher consistency than the main supply of stock in the vat. This is, of course,'on account of the free flow of water takingplace through the outlet of the hammermill and, accordingly, the dewatering action thereby realized on the stock remaining in the mill. But, as already indicated, this dewatering action is had to a greater degree with the apparatus shown in Figures 5 and 6.

After the apparatus has operated on the stock for awhile, the temperature of the stock rises and this rise in temperature continues so that, depending upon revailing atmospheric temperature, the stoc may become quite warm or even hot. The developthe apparatus of the present invention under fibered raw material, the discharge openings the eflicient operating conditions described. Inasmuch as heated stock does not undergo hydration as readily as cool stock and may, lead to papers of poorer chemical and physical characteristics, it is preferable to cool the stockas it is undergoing hydration; Cooling may be performed in any suitable way, but as shown in Figures 2 and 6, a portion 44 of the outer shell 3 of the hammermill may be made hollow so as to permit cold water or other cooling medium to be circulated therethrough and thereby to carry away the heat generated by the operation of the hammermill on the-stock. More or less of the shell may be jacketed with water or other cooling medium as desired. A cooling effect may also be had by 1n ect1ng cool, compressed air into the pipe 35, the air further functioning to assist the dilutmgwater in impelling the stock toward the thlckening drum.

One of the factors in the design of the hammermill to be given consideration is the size of the discharge openings. As already stated, this size must be correlated w1th a total number of openings comporting' w th the maintenance of stock in the hammermlll during the operation of the apparatus. If the raw material is of a kind apt to clog the openings, the desired rate of discharge of stock from the hammermill is preferably secured through the use of few, say one comparatively large opening. whereas 1f the raw material can pass through the openlngs freely, it is preferable to use a larger numberof smaller openings to realize the desired rate of discharge. For example, in the case of sulphite pulp, which is a comparatively finemay be of a width of, say, to but in the case of rope stock or other coarse-fibered pulp, wider openings of a width of, say, to are preferably used. In both cases, however, the number of openings or overall opening must be coordinated with a size of opening conducive to the proper rate of discharge of stock from the mill. It might be mentioned that hammermills such as I employ are operated at such high speeds that considerable centrifugal force is developed tending to discharge forcibly the stock through the exit openings. Thus the ends of the hammers may move at a speed of about 7500 feet or more per minute. At such high speed, there is also a tendency for the pulp to be deposited as a layer on the bars constituting the inner face of the mill; and the action of the rapidly moving hammer ends against this relatively stationary pulp layer is evidently to broom and fray the pulp fibers so as to cause their hydration. The mill may be run with the free ends of the hammers clearing the lining of the casing, in which case the friction of the hammers on the fibers induces hydration while preserving largely fiber length. It

is, however, possible .to adjust the blades so that they actually strike or contact with the bars of the lining and thereby cut or shorten the fibers much in the same way that this is done in the usual beating or Jordan engine. In most instances, however, it 1s deslred to keep the average length of the fibers used possible to preserve substantially the fiber length of the pulp used as a raw material and at the same time to attain a degree of slowness in the beaten pulp consonant with optimum paper manufacture. The preservation of fiber len th is, as already stated, of importance in tllat long fiber length is accompanied by high tear resistance and folding endurance in the paper, but the hydra-i tion of pulp is also essenial to the realization of papers possessin the uniformity of texture and 0 high ullen' or bursting strength. The process and apparatus of the present invention makes for a realization of all these various desiderata.

I claim:

1. A cyclic method of hydrating cellu I lose pulp stock for papermaking or the like,

which comprises preparing and maintaining a supply of such stock as a. thick aqueous suspension, progressively removing stock from said supply and feeding it into a casing having an outlet through which the water of said suspension may freely flow but designed to permit the accumulation of stock in said casing, subjecting the stock in said" casing to a swift succession of hammering lmpacts under condltlons to discharge forcefully only a portion of said stock through said openlngs, returning the discharged stock ing a plurality of openings through which the Water of said suspension may freely flow .to said supply, and repeating the cycle until but designed to permit the accumulation of stock in said casing, subjecting the stock in said casing to a swift succession of hammering impacts under conditions to discharge forcefully only a portion of said stock through said openings, returning the discharged stock to said supply, and repeating I the step of feeding stock from said supply into said casing at a rate substantially equal to the rate of stock being discharged from said casing until the degree of hydration desired for papermaking has been produced in the stock.

3. A cyclic method of hydrating pulp stock for papermaking or the like, which comprises preparing and maintaining a supply of such stock as a thick, aqueous suspension, progressively removing stock from said supply and feeding it into a casing having an outlet through which the water of said suspension may freely flow but designed to permit the accumulation of stock in said casing, subjecting the stock while in said casing ata consistency higher than that of said supply to a swift succession of hammering impacts under conditions to discharge forcefully only a portion of said stock through said opening, returning the discharged stock to said supply, and repeating the cycle until the degree of hydration desired for papermaking has been produced in the stock.

4. A cyclic method of hydrating pulp stock for papermaking or the like, which comprises preparing and maintaining a supply of such stock as a thick, aqueous suspension; progressively removing stock from said supply, thickening it, and feeding it into a casing having an outlet through which the water of said suspension may freely flow but designed to permit the accumulation of stock in said casing; subjecting the thickened stock in said casing to a swift succession of hammering impacts under conditions to discharge forcefully only a portion of said stockthrough said opening; returning the discharged stock to said supply; and repeating the cycle until the degree of hydration desired for papermaking has been produced in the stock.

5. Apparatus of the class described comprising in combination, a vat for maintaining a supply of cellulose pulp stock as an aqueous suspension, a casing having an intake communicating with the supply in said vat and a plurality of openings of comparatively small width discharging into said vat, a hammermill arranged within said casing to deliver a swift succession of hammering impacts to stock within said casing and to discharge forcefully only a portion of said stock through said openings into said vat, and means for progressively feeding the stock from said vat into said casing at a rate ensuring the operation of said hammermill under load at all times.

6. Apparatus of the class described comprising in combination, a circulatory channel for maintaining a supply of cellulose pulp stock as an aqueous suspension, a generally cylindrical casing in said channel having an intake communicating with the supply in said channel and a plurality of openings of comparatively small width discharging into said channel, a rotary hammermill arranged within said casing to deliver a swift succession of hammering impacts to stock within said casing and to discharge forcefully only a portion of said stock through said openings into said channel, and means for progressively feeding the stock from said channel into said casing at a rate substantially equal to the rate of stock being discharged from said casing.

7. Apparatus of the class described comprising in combination, a circulatory channel for maintaining a supply of cellulose pulp stock as an aqueous suspension, a generally cylindrical casing in said channel having an intake communicating with the supply in said channel and a. plurality of comparatively small openings discharging into said channel, means for thickening said stock adjacent to said intake, a rotary hammermill arranged within saidcasing to deliver a swift succession of hammering impacts tostock within said casing and to discharge forcefully only a portion of said stock through saidopenings into said channel, and means for progressively feeding the stock from said channel into said casing at a rate substantially equal to the rate of stock being discharged from said casing.

8. Apparatus of the class described comprising in combination, a circulatory channel for maintaining a supply of cellulose stock as an aqueous, suspension, a generally cylindrical casing in said channel having an intake communicating with the supply in said channel and a plurality of comparativel small openings discharging into said channe a rotary hammermill arranged within said v casing to deliver a swift succession of hammering impacts to stock within said casing and to discharge forcefully only a portion of said stock through said openings into said channel, means for progressively removing water from said stock at a point in said channel adjacent to the intake to said casing, means for returning said water at a point in said channel remote from said intake, and means for progressively feeding the stock from said channel into said casing at a rate substantially equal to the rate of stock being discharged from said casing.

In testimony whereofI have aflixed my

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