US2356285A - Apparatus for washing pulp - Google Patents

Description

E. T. STREET I APPARATUS Fofi WASHING; PULP Aug. 22, 1944;

Filed my 19, 1938 2 Sheets-Sheet 1 M AC Q QM, MM 9 n 0 M m E a 1 d y a E w w E him 06 o I "loll Miro wee 2 Sheets-Sheet 2 Tm mm STREET Filed May 19, 1938 APPARATUSHSR WASHING PULP Aug. 22, 1944.

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Edward T.'Street, Downingto'wn, 2a.,

Downingtown Manufacturing Company, ingtown, Pa., a corporation of Perms asslgnor to Downlvanla 1 Application May 19,1938, Serial No. 208,929

3 Claims.

In the art of manufacture of paper, cardboard, wallboard and the like from wood fiber it is customary to first reduce the wood which is used as raw material to chips by any one of several possible methods. These chips are then placed in a digester, together with a strong solution of chemicals in water, the digester being then sealed and its contents being cooked" for a substantial length of time under pressure. When the. process of digestion has advanced to the desired extent, the"digester, is unsealed and its pulp-like contents removed for further proc-' essing. 'The pulp stock delivered by the digester .includes all oi. the chemicals originally inserted into the digester for the purpose of breaking down the chips and it is then necessary to separate the pulp from such chemicals in order that the pulp itself may be substantially freed of the digesting chemicals before it is made into paper, fiber board or the like and also to recover the digesting chemicals for reuse. The chemicals used are costly and inasmuch 'as large quantities must necessarily be employed in large scale operations. it is essential, if the process is to be economically conducted, that a very large proportion of these chemicals be recovered. These facts have been long. appreciated by workers in the art and numerous suggestions have heretofore been made" looking toward the increased recovery of the chemicals made use of in order that the cost of. operation of the process a 'a-whole may be minimized. Where large quantities of water must necessarily be used to thoroughly wash the chemicals from the digested pulp the chemical solution becomes greately diluted and; before it can be reused; the large excess of water must be driven off. The cost of operation of the process as a whole bears a close relationship to the efllciency of the process used for the recovery of the digesting chemicals and in some cases it is actually found to be less costly to waste a substantial proportion of the chemicals used than it is to recover thesechemicals from a very dilute solution thereof. In other processes thechemicals are recovered in part and discarded in part. the object being in every' case to recover those chemicals which can be actuab" 1y recovered with economy and to discard those whichjmay not be economically recovered.

The present invention contemplates'the provision of "animproved apparatus for, and method of, washing theflbrous pulp delivered by a di-.v

gester so: that this pulp is substantially freed of all of the chemicals which were used in the digestingprocess, this washing operation being (Cl. 68-22) carried out in such gesting chemicals known processes.

of the chemical solution in the well-known recovery apparatus may a way that all portions of. the pulp delivered are subjected to the same washing action, a minimum quantity of water, however, being used so that the solution of didiluted only'to an extent heretofore realized with appreciably lessthan a result reconcentration be effected at small expense and the cost of minimized. I

Ihave discovered that it is possible to most economically and thoroughly wash freshly digested pulp if the pulp be reduced to the form of a'uni'form and homogeneous layer or, board and the washing operation be effected by pass ing the washing liquid through the board. Each fiber of which the board is composed, therefore, is subjected to the direct flow of the washing liquid and all fibers are washed to the same extent by such liquid. In other words, after the formation of a homogeneous'or uniform board of matted fiber, washingliquid may be passed therethrough in such manner that the rate of flow-through all portions of the board is the same, channeling, or more'rapid flow of wash liquid through one portion of the pulp mass than through another portion, bemg' avoided. All known processes heretofore or at present employed, involving the. passage of wash. liquid through a 'pulp body, have required the use of excessive quantities of the Washing liquid due to the tendency of such liquid to follow the line of least resistance through the pulp mass. This necessitates the use of excessive quantities 'of water if all parts ofthe pulp mass are to be adequately washed. 1 However, by reducing the pulp. mass to the form of a board which is uniform in character, and offers equal resistance to the passage of the'washmg liquid .over all areas thereof, this the use of, the smallest possible quantity oflwashing iliquid.

The impbved process also'includes as an important step-a fiber pressing operation interposed between the bo rd forming and washin operations. By causing the flber'to be depositedthe operation as. a whole I tendency to channel is wholly obviated and thorough washing is obtained by 2 a luted withwash liquid. Thus, by passing the freshly formed fibrous board between pressure rollers from 60% to 65%, or even more, of its contained liquid may be. mechanically removed, leaving in the boardonly a fraction of the chemical bearing liquid tobe removed by subsequentwashing operations. After the pressing step has been performed only about one and one half (1%) pounds of liquid per pound of fiber remains, whereas in prior processes seven or eight pounds of liquidv per pound of fiber or 85% to 90% of the chemical bearing liquid must be\re-,

moved by washing, and is thereby greatly di-v luted. -The great economy of the process is, in this respect, apparent.

While the improved method may be practiced with the aid of apparatus which may vary widely in design and construction, the freshly digested pulp may advantageously be introduced into the forming chamber of an apparatus of the type dis- .closedin my prior Patent 1,927,378 and that the assumes a causes the liquid to new through the abet-s iongitudinally of the board in a direction opposite to that in which the board is moving. This promotes thorough washing.

when the washing operation is accomplished in a series of stages the wash fluid which is used in the last stage may advantageously be fresh water and the board, after it passes this last wash- 1 ing station, is substantially tree of chemicals. The water which is passed through the board in the last washing station, which of course con that its thickness may be as' desired and removed from the chamber at the rate at whichitis-j -z formed,.to be subjected, after removal, to the stated pressing and washing operations. By preference, theprocess is practiced in an apparatus embodying endless upper and lower complementary foraminous "belts orforming wires, the board being formed by deposition of the fiber upon the upper reach of the lower belt and the lower reach of the upper belt resting 'upon the upper surface of the formed board and comprise ing-a confining means which prevents displacement of the fibers during the time that the board is undergoing pressure and washing l nuid isbeing passed through the same.

While I refer to a washingpperationperformed upon a "board" it will be understood that, while the pulp hasbeen reduced to board form, this does not mean thatflthe board has such strength that it may be used for any purpose. On the other hand the board" comprises interlaced fibers, includes no binding material and in reality is a flat, pulpy mass, and of uniform and homogeneous character throughout. In this state it offers no-great resistance to the. passage of liquid therethrough and washing operations may be easily and conveniently carried out by maintaining a body of washing fluid upon its upper rality of washing devices by which the board is successivelypassedsothat itmaybesaidtobe repeatedly washed. Advantageously also the board after each washing operation is subjected to the action of pressure rollers and by means of which fiuid contained therein is largely pressed .out. .The pressure applied to the board by the rollers likewise distributes the wash liquid through tains, after such passage, a quantity of chemicals in solution, is collected, elevated by means, of a pump, and used as the washing liquid at the preceding or next tolast washing station, and

where there are three 'or more washing stations a given quantity of wash liquid will be passed through the board three or more times, being advanced from station to station in a direction opposite to that in which the board is moving. Any

number of washing operations may be carried out in this way and the number of times that the board will be subjected to such washing operations will depend upon the chemicals used in the-di- 'gestive process, the thickness of the board, the

speed at which the board is moving, the character of the fibers, andlupon other factors. Where suction boxes are employed the rate of flow of wash liquid may be controlled by regulating carefully the degree of vacuum which exists in the suction boxes.

through the board, is'rich in the chemicals removed from the board and is passed on to any well-known recovery apparatus whereby excess water is driven oil. The invention contemplates a number of novel and improved features, both in the method and apparatus, not heretofore referred to, but which will be hereinafter described in detail and pointed "out in theappended claims. Two typical forms of apparatus by which the cal section, and partially in side elevation, one

form ofboard forming, and board washing apparatus, many of the conventional features of such apparatus-having been omitted in order that the more essential features may be more clearly perceived; Figure 2 is a vertical section, taken longitudinally of the machine, through a pair of pressure rollers and the adjacent means for passing wash liquid through the board;

Figure 3 is a section on line 3-3 of Figure 2; Figure 4 is a view, generally similar to Figure l,

"of a form of apparatus for use in the practice of the novel method, certain elements of this apparatus differing in form and ari'angement from the corresponding elements shown in the apparatus illustrated in Fiwe 1; and

FIgureSisa sectiononIineHoIFlgureL -transverse vertical section and generally tri-' thebodyof' the andjo a certain extent (6 angular in longitudinal vertical section, as shown.

- The bottom of the chamber comprises'the upper horizontal reach of a foraminous belt or wire indictated at II, this reach-of belt upon rollers II mounted in the frame,of the machine apdmoving, when-,the machine is in The liquid from the last washing'operation' which may have been passed several times aaaaaec operation, in the direction indicated by the arrow A. While any given areaof the forming wire'l2.

-is disposed beneath the stationary portion of the 21 being driven at the same speed as that at which the lower belt I 2 is driven, and in the direction forming chamber ID the pulp stock liquid passes downwardly through the same and the flbers dispersed in this liquid are deposited upon the upper surface of the belt, a board or mat being thus gradually built up on each. such section of the issues from the discharge end of the forming chamber is of the desired thickness. Novelty is Edge or in my prior Patent 1,927,378, elsewhere Y herein referred to.

There is diagrammatically illustrated at l4 a tank or receptacle for digested but unwashed pulp stock which has been refined or both refined and screened to render it suitable for introduction into the forming chamber. The discharge pipe I5 from tank l4 leads to the intake of a variable speed pump l6 which may be of theicentrifugal type, this pump discharging into conduit I l which in turn opens into a mixing. chamber Ill. at the extreme end of the forming chamber l0. By regulating the speed of pump ii the rate of delivery of unwashed pulp stock to the mixing chamber may 'be accurately controlled and the level of the upper surface of the pulp stock in the forming chamber kept at the desired height. Another adof the arrow B. Thereafter the board is retained between parallel -reaches of the upper and lower forming wires orbelts until it is discharged by the apparatus, the board at the discharge end of the machine being indicated at 2-8. Four pairs vantage of utilizing a pump of this type is that it will deliver the pulp stock into the forming chamber without the creation of foam. The

stream of unwashed pulp stock entering the extreme end of the mixing chamber encounters a. a series of baiiles l0 and it is while the pulp stock is passing through the tortuous passage thus defined that it is mixed with a diluting'liquid for the purpose of more widely dispersing the fibrous elements in-the body of liquid in order that the subsequent deposition of the fibers on the forming wire or belt may proceed uniformly over the entire area of that portion of the belt which coinprises the movable bottom of the forming chamber, and a uniform board be produced. Thus the v liquid which passes through the forming wire or belt l2 at the bottom of the formingchamber is collected in a pan 20, from which pan it flows downwardly through a short vertical conduit 2| into a liquid receiving tank 22. From this tank it is drawn by means of a variable speed centrifugal pump 23 and passed through a conduit 24 of large cross-section at a relatively low rate of speed to be eventually discharged upwardly through an aperture in the bottom of the mixing rolls.

of horizontally disposed mainpress rolls are shown, the rolls of the first pair being indicated 'at'29 and 30, and the rolls of theremaining pairs being indicated at 3| and 32, 33 and 34 and 35 and 36 respectively.- The. fibrous board and its associated confining wires pas successively between the pairs of rolls and at each roll pass are subjected to pressure, thedegree or extent of which may be varied as desired by means of weights or adjustable springs. In the case of the apparatus shown at least the upper rolls 29, 3|, 33 and 35 are vertically movable andv any conventional weighting or resilient means may be employed to thrust the rolls downwardly.

A plurality of wash liquid retaining boxes are shown, these boxes being indicated at 38, 39 and 40 respectively and being positioned intermediate the upper main press rolls, onebox between each two rolls. Vacuum chambers are indicated at 4|. 42 and 43, one such vacuum chamber underlying each wash liquid box, the board 26 and its confining wires, of course, passing between each wash liquid box and the vacuum chamber underlying the same. The several wash boxes38, 33 and 40 are supported upon the upper main press rolls so that these boxes will be raised and lowered simultaneously with the associated press rolls and boxes from the press rolls includes longitudinally extending supporting rods or bars 45 and 46 each such bar having upwardly curved portions or loops which overlie and rest upon the several roll necks so that the. supporting bars 45 and 46 are actually carried by the necks of the upper main press Each wash box is provided with two bracket members at each end, these brackets'being. indicated at 41 and 48 respectively and each bracket having an extension overlying the ad-' jacent longitudinally extending bar. 'Adjusting screws 49 and 50 extend downwardly through and have threaded engagement with the cylindrical threaded walls of apertures formed in the overhanging portions of brackets 41 and 48 the lower ends of. these screws resting upon the box supporting bars 45 and 46 respectively. By means lower edge of each wash box relatively to the supporting bars 45 and '46 may be determined and hence the positions of these lower edges accurately.

4 its lower edge with a sealing member 52 which streams are intimately intermingled in passing through the tortuous conduit defined by the bailies,

Ill and the walls of the chamber, and before entering the forming chamber.

.As the formed board leaves the fdrming cham .ber it passes beneath a series of primary press rolls indicated at 26 and at this point the upper forming wire or' belt, which is indicated at 21, comes into contact with its upper surface, the belt bears upon the upper forming wire 21 in order that'a body of wash liquid of substantial depth may be maintained in the box without causing excessive leakage between the lower edges of the box and the wire and board beneath the same. These sealing members may be formed in various ways and of various materials. The vacuum chamber associated with each' wash liquid box includes a foraminous top, one such top being indicated at 54 in Figures 2 and 3, the upper surface of the top member 54 being flat so that the upper reach of the lower forming wire may slide a freely thereacross. It will be perceived from Flgof these adjusting screws the exact position of the ures 2 and 3 that, while the suction box has substantially the same length as the superposed wash liquid box, measured transversely of the machine, it is substantially longer, measured longitudinally of the machine, its upper member 5| extending into close proximity to the adjacent roll pass. Hence .when a partial vacuum is created within the suction box suction is applied over a greater area of the fiber board than that which is covered by the associated wash liquid box and the suction "created will-not only draw wash liquid from the box, through the intermediate board, but will also draw directly through the board the body of liquid which is developed upon its upper surface by reason of the pressing action of the adjacent pair of main press rolls, such a. quantity of expressed liquid being indicated at 55 in Figure 2. This construction is such that foaming of the liquid, as it is drawn from and through the board, is minimized.

' Clean wash water is introduced into the last of the wash liquid boxes, i. e., into box 40, through a conduit 56 and if desired steam may be likewise introduced into the stream of wash water through a conduit 51 for the purpose of heating the water, water and steam valvesbeing indicated at 58 and 51' respectively. Water passing from wash liquid box 49 through the board 28 is collected in the vacuum chamber 43 and escapes from this chamber through a pipe 59 into a, downtake 60 leading to a separating chamber 6|. The downtake 60 has a portion extending upwardly above the conduit 59 and the upper end of this upward extension communicates with a horizontally disposed pipe or manifold 62 which is in constant communication with a vacuum pump or the like. A pressure gauge is indicated at 63, and a valve,at 64 by means of which the degree of vacuum existing in the pipe 60 below this valve, and hence in the separating chamber 6|, and in the vacuum box 43, may be controlled. By regulating the degree of vacuum in the vacuum box the rate of flow of wash liquid through the moving board at this point may be controlled. A liquid circulating pump is indicated at 6 6, this pump working against the vacuum existing in separating chamber GI and serving to withdraw liquid from this chamber. The outlet of pump 65 communicates with a vertically extending pipe or conduit 51 having a horizontal branch 58 terminating in a downwardly extending end portion 59 positioned directly above the next ad- Jacent wash liquid box 39. By similar means the wash liquid which is collected in the vacuum box 42 is delivered to the wash liquid box 38. The wash liquid collected in the vacuum chamber 4| is, however, pumped to the recovery system, the pipe leading to the recovery system which may be employed. A vacuum box 12, positioned anteriorly to the first pair of main press rolls 29 and 30, serves to draw liquid from the board, no wash water being'ap'plied to the upper surfaces of the board at this point, and as this liquid is very rich in chemicals, being undiluted with wash liquid, it is separately demeans for flowing a stream of pulp stock horizontally onto the forming wire and elements in the nature of side boards or deckels for laterally confining this stream on the wire until all of its free liquid has passed through the wire. Also, in this apparatus water columns are employed to create sub-atmospheric pressures in the suction boxes instead of vacuum pumps directly con-' nected to water and gas separating chambers, such as used in the apparatus first described.

Here unwashed pulp stock from tank 88 is forced by pump 8| into a mixing or dilution box 82 where it meets the stream of black liquor issuing from pipe 83 and the intermingled streams, after passing baflles 84 and 85, pass over the curved forewall 86 of the box 82 directly onto the forming wire 81. The liquid carrier for the fibers passes through the wire before the stream has travelled, on the wire, more than. a few feet, leaving a liquid-soaked fibrous mat or board on the upper surface of the wire. The fiber bearing liquid is thus under negligible static head when flowed onto the wire but by regulating the rate of flow of pulp stock and the speed of movement of the wire the rate of fiber deposition can be closely controlled and very satisfactory results obtained. The side boards or deckels 82 prevent the fiber carrying liquid from flowing laterally from the wire 81. Y

The board compressing and washing means are substantially as before except in that the conduits 88, 89 and 90 leading downwardly from the suction boxes 9|, 92 and 93 are relatively long livered to the recovery system by means of sepa- The apparatus illustrated in Figures 4 and 5 is,

in major respects, similar to that shown in Figure 1, but instead of a forming chamber of the type shown in that figure it includes a simple and are open at their lower ends to discharge into liquid collecting water seal boxes 94, 95 and 96. Pumps 91, 98 and 99 draw liquid from these boxes, respectively, but these pumps do not work against a vacuum nor draw from chambers containing both gas and liquid, so that danger of foamin'g is minimized. In operation the level of the water columns in pipes 88, 89 and 98 Will be at such height above the seal boxes 94, 95 and 96, respectively, that each water column .will

balance the vacuum and, as additional water collects in each pipe it will displace some of the water previously collected, which will then flow into the seal box and be eventually removed by the associated pump. The additional suction chamber I 80 is likewise provided with an extended downtake pipe IOI, water seal box I02, and pump I93.

In practicing the process upon either form of apparatus both pulp stock liquid and wash water are maintained at relatively high temperatures for best results. Thus I prefer to have the temperature of the fiber carrying liquid in the neighborhood of 190 F. when it is passed onto the forming wire and the wash liquid is preferably maintained at a temperature of between F. and 200 F.

These relatively high temperatures are maintained in order to keep the black liquor in freely flowing condition. The viscosity of this liquid increases as its temperature falls and even at room temperatures it may be too viscous. Also the wash water dilutes the black liquor more rapidly at high temperatures, which is helpful in washmg.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. Pulp washing apparatus comprising in combination, an elongated foraminous belt, stationary means above the belt for continuously depositing fiber thereon at a uniform rate, mechahorizontally spaced upper rollers for successively nism for advancing thebelt at uniform speed past said means so that'a continuous fibrous board, homogeneous and uniform in thickness, is in constant course of formation on said belt, a second foraminous belt positioned above the first, a connection between said mechanism and said second belt whereby said second belt is driven at the same linear velocity as the first belt, means constraining said belts to move along predetermined paths, causing them first to gradually approach each other to place the newly formed board under light but gradually increasing pressure and to thereafter closely confine the board during its travel to a point of discharge, where the belts again separate, said means including cooperating lower and upper pressure rollers engaging the respective belts and coacting to subject the previously lightly compacted board to heavy pressure as it advances to remove therefrom the greater portion of its contained liquid, and means to continuously wash the board after such compression, said last mentioned means including a box having an open bottom for maintaining a substantial body of wash water continuously in full contact with a large area of the upper foraminous belt.

2. Pulp washing apparatus comprising in combination, an elongated foraminous belt, stationary means above the belt for continuously depositing fiber thereon at a uniform rate, mechanism for advancing the belt at uniform speed past said means so that a continuous fibrous board, homogeneous and uniform in thickness, is in constant course of formation on said belt, a second foraminous belt positioned above the first, a connection between said mechanism and said second belt whereby said second belt is driven at the same linear velocity as the first belt, means constraining said belts to move along predetermined paths, causing them first to gradually approach each other to place the newly formed board under light but gradually increasing pressure and to thereafter closely confine the'board during its travel to a point of discharge, where the belts again separate, said means including engaging the upper foram nous belt and correspondingly spaced rollers for engaging the lower belt and coacting with said upper rollers, respectively, to successively subject all areas of the moving board to heavy pressure, and means intermediate, and supported by, said spaced upper rollers for maintaining a substantial body of wash water continuously in full contact with a larg area of the upper foraminous belt. 3. Pulp washing apparatus comprising in combination, an elongated foraminous belt, stationary means above the belt for continuously depositing fiber thereon at a uniform rate, mechanism for advancing the belt at uniform speed past said means so that a continuous fibrous board, homogeneous and uniform in thickness,

is in constant course of formation on said belt, a second foraminous belt positioned above the first, a connection between said mechanism and said second belt whereby said second belt is driven at the same linear velocity as the first belt, means constraining said belts to move along predetermined paths, causing them first to gradually approach each other to place the newly formed board under light but gradually increasing prescure and to thereafter closely confine the board during its travel to a point of discharge, where the belts again separate, said means including horizontally spaced upper rollers for successively engaging the upper foraminous belt and correspondingly spaced rollers for engaging the lower belt and coacting with said upper rollers, respectively, to successively subject all areas of the moving board to heavy pressure, means intermediate th upper rollers for maintaining a substantial body of wash water continuously in full contact with a large area of the upper foraminous belt, and means intermediate the lower rollers for applying suction to the lower foraminous belt, said last mentioned means underlying the first mentioned means and also an arear of the lower belt immediately preceding the pass between the 5 second pair of coacting pressure rollers.

EDWARD 12 STREET.

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