US2278525A - Conveyer and coucher belt process and machine for thickening pulp - Google Patents

Description

April 7, 1942- J. P. RICH ETAI. 2,278,525

CONVEYER AND COUCHER BELT PROCESS AND MACHINE FOR THICKENING PULP Filed April 17, 19:59

Patented Apr. 7, 1942 CONVEYER AND COUCHER BELT PROCESS AND MACHINE FOR THICKENING PULP John P. Rich 'and Elmer R.' Burling, Nashua, N. H., assignors to Improved Paper Machinery Corporation, Nashua, N. H., a corporation of vMaille Application April 17, 1939, serial No. 268,354

8 Claims.

'This invention has to do with a machine and process for reducing the water content of pulp stocks and other similar materials. It deals with an improved 'method of collecting on the filter surface pulp materials, particularly with and during the vlatter stage, and o f expressing, by

, pressure, the water brother liquid from the freshly deposited materials so that they may be delivered from the machine as free from water or other liquid content as practicable.

This machine may employ the usual rotating cylinder or drum, the surface of which forms the filter, and which may be covered with fine wire cloth or any other suitable filtering material. This drum or cylinder may be immersed in a tank or vat to'which the liquid to be thickened is supplied, the water or other liquid of these materials being drawn through the filter surface by gravity, by suction, or by any other suitable or desired means, thereby separating the liquid from the solid constituents of the material to be thickened.

As the materials are deposited in increasing.

thickness on the fllter surface,the continued movement ef this surface through the tank or vat eventually brings the deposit out of the liquid in the vat. At this time, there is still a large amount of liquid in the deposited material, much of which can be removed by compressing the dev posit against the'lter surface, thereby squeezing out the water or other liquid into the interior of the filter drum, from which itis removed by any convenient means. It has heretofore been customary to use one or more rolls which are pressed against the deposit on the cylinder either by their weight or by'springs or by additional weights, so that pressure is placed on the partially solidified pulp layer, which pressure is used to force or express the liquid remaining 'in the deposit through the nlter surface. l

These rolls are sometimes made up in sections to take care of the unevenness of the pulp deposit in certain cases, and sometimes a belt or apron, en' which rollers or weights are placed, is'. wrapped over a considerable portion of the drum surface.

Such belts are permeable and are used where it is necessary or desirable to wash the solids deposited on the filter surface -by means of fresh water sprayed over the deposit', .the belts being of a waterand air Vpermeable belt through vwhich the wash liquid may pass or to permit airsto be drawn through 'both the belt and deposit. to as-4 sist in cleaning or removing the wash water previously sprayed on'the deposit, or on the belt.

It has for its object almost adlametrically opposite purpose, namely, to collect or assist in the collection on the lter surfaceofa deposit l of uniform thickness, and of greatly increased quantity, as is hereinafter described more'in detail, and further to provide means for expressing the liquid from such deposit progressively, so that the deposit Awill not be disrupted, and to giveA time for the liquid to pass through the deposit to the interior of the filter and thus be separated entirely from the deposit on the `filter surface. It is obvious that the foregoing desideratumcould not be attained by the use of a permeable belt, as pressure applied by the belt to the pulp deposit would force the liquid in the deposit into and through the belt from which it could readily pass back into the supply from whichithe defeating one object deposit is drawn,. thereby of our invention.

In contra-distinction to these 'methods we i employ a short section of an impervious flexible', material, in the form of a combined coucher and conveyer belt so mounted and arranged in're lation to the lter surface, and its deposit that it not only aids in the collection of materials on the filter surface, but also effects a gradually increasing pressure on' the deposit so that the liquid remaining therein is expressed through the deposit gradually, and no opportunity is presented for' the liquid in the deposit to be pushed along the surface of the deposit ahead of the point where pressure is applied, but rather this liquid is driven or forced directly through the deposit and through the lter surface, effecting its complete and final removal from the deposit.

In describing our invention, reference is made ,l

l to the following' figures: l l A Fig. 1 shows a conventionaltype of thickener or lter drum immersed in a tank or vat, with our deposit conveyer arranged to simply express liquid from the deposited material and 'to remove these materials from the filter surface.

Fig, 2 is a sectional view through theY conveyer and its guiding roll.

effective to retain the deposit on the filter sur- Fig. 3 shows the preferred form of our ldevice l in which the conveyer belt is immersed, at its lowest point, in the mixture in the tank. There is also shown a third or take-up roll, be used or not as desired.-

In Fig. l I'is a vat or tank of any suitable filewhich can sign to which the liquid materials P to be thickcned are supplied through pipe or opening 2 with the usual conventional baille board 3 to deflect and distribute these materials uniformly over the entire area of the tank I. Usually the liquids are' maintained at some fixed level W. L., this level varying somewhat without interfering with the operation of the machine. Rotating in the tank or vat I -is a lter drum 6 covered with some suitable lter material -1 such as wire cloth or screen. The liquid which passes through this screen may pass directly to the interior of the drum, or pass into segmental sections near the -exterior of the drum as at I from which the liquid is'removed by any suitable means commonly employed in machines of this type.

The filter drum 6 may be supportedv for rotation at its periphery, or it may rotate about a shaft 9 supported with suitable bearings in or on the end of the tank I. The character of the filter drum, its mounting, or the tank or vat used to supply the material to be thickened, forms no part of this invention and is illustrated herein simply to show a commonly accepted and conventional means for collecting the solids and of the pulp materials from the liquid in the vat,

with the removal from these deposited materials, after they leave the vat, of as much liquid as is possible. and with a clean and complete re moval of these materials from the lter surface, y

so that it may again be utilized to receive a fresh deposit or layer of the liquid-permeated pulp.

As the fiiter drum 6 rotates in the direction of the arrow, the liquid of the mixture of tank I ows thru the filter surface 'I leaving a deposit of solids in increasing thickness as indicated at Illa, |0b and' Ic and Iild. As the thickness of deposit increases,'the resistance to the flow of liquid through this deposit obviously increases, and if the lter drum 6 were turning slow enough,

these two forces would eventually tend to bal- .7:

ance themselves and deposition on the filter surface 1 would virtually cease. In order, however, that the capacity of the machine may be at its maximum, the cylinder 6 is rotated at a speed in direction of arrow which does not permit the end point of deposition to be reached, but utilizes a period of immersion and deposition time which will deposit the maximum amount of solids on the filter surface in a given time and not permit a portion of the filter surface travel to be wasted by having it moved so slowly that deposition has ceased or has become very slow.

However, one condition occurs which has heretofore been very troublesome, and has interfered with the proper operation of machines of this type, and one of the principle objects of our invention has been not only to obviate and remove entirely this difiiculty, but to provide a mechanism which will so operate as to convert this difficulty into an asset, thereby eliminating previous unsatisfactory operation, and at the same time greatly increasing lche capacity and usefulness of the machine.

'I'his is accomplished mainly by the arrangement shown in Fig. 3. We have already described However, :i

' retaining thereon a fairly solid and stable layer or mat of material, but it also draws liquid from the solid materials in the vat which materials are not actually deposited on the filter surface, so by the time that the filter surface passes point I 0a the liquid in the tank I at area Il has become very much thicker than at point Ilia and frequently so thick that the solids therein will not adhere to the other materials deposited on the filter surface. It may become so thick, and so dense, that it actually scrapes on' some of the materials already deposited, further aggravating the condition in area II and greatly reducing and interfering with the operation and capacity'of the machine.

In order to obviate this serious difllculty, we provide means for mechanically removing the thickened material from area II and depositing it on the layer [0c-d, smoothing out said layer and providing a mat of uniform thickness and quantity, consolidating these materials from area i I with mat luc-d, expressing the water or other liquid from both mats, and nally removing them cleanly from the filter surface at point I3.

The coucher and conveyer belt previously mentioned is indicated at Il, this conveyer belt either being carried by a main roll I5 and an idler roll I6 as shown in Fig. l or by a main roll I1, an idler and take-up roll I8, and a collecting roll I9. as shown 1in Fig. 3. It may be guided by flanges 20 on roll l5 or by flanges on other rolls or by any other suitable means.

It will be observed in Fig. 3 that the collecting roll I9 with its conveyer belt Ida is immersed somewhat below the level of the liquid pulp material.; P and into the area Il where the thickened materials accumulate for reasons heretofore described. The conveyer belt moving in the direction of arrow Y at a speed closely coinciding with surface speed of the pulp mat on the filter surface, tends to draw the thickened pulp materials from area Il toward the filter surface by mechanical means, through the motion of the conveyer belt Ma through thickened materials in area II in a direction towards the filter surface 1.

It will be observed that the collecting roll I9 is so mounted that a considerable space is provided between the conveyer belt Ma and the filter surface 'I as indicated at Z. This space at point Z provides room for the thickened materials to enter between the belt and the previously deposited materials Illa to Illd, this space being, in effect, wedge-shaped, tapering upward, and due to the combined motion of conveyer belt Ma and the filter surface 1, with the mat IOd thereon, the thickened materials from area Il are drawn from this area into space Z between the conveyer belt Ida and the mat Iild where they are consolidated with this mat. This enables added solids to be removed from the liquid in the vat I by the addition of materials at point Z, thereby greatly increasing the capacity of the machine.

Referring to Fig. 3, it will be noted that three areas or zones are indicated on the filter surface as A, B and C. Area or zone A indicates sirable to remove.

. desirable or'necessary.

that section .beyond point IUc-d, where normal depositions of solids on the iilter surface has practically ceased, and where, without our cievice, not onlyA would additional deposit orrcollection of materials be ineffective, but also where Y.

l able to collect on the filter surface still contains a considerable quantity of liquid which it is de- In order to retain the filter mat in a iirm, even layer to facilitate its removal from the filter surface, it is necessary to express the water from this mat, after leaving zone A, gradually, otherwise the layer will be disrupted and broken, particularly if any attempt is made to force the water from the mat too rapidly, in which case both solids and water will be forced back down through zone'A and into area II, defeating the very object sought and the result already attained, and greatly lmpairing the usefulness and capacity of the machine. Extra large couch rolls are sometimes used to increase the length of time of compression at any given speed, but it will be readily seen that we have provided a ldevice more effective than even a couch roll of infinite diameter.

By allowing a substantial interval of time during which the mat or cake is compressed with progressively increasing pressure, it is readily possible to extract a greater amount of liquid,

partially around roll I8 (Fig. 3) at which point the mat can be removed by any suitable means such as doctor plate 26. This doctor plate is preferably located at such a point 25 that the natural bending of the conveyer belt Ilia around roll- I8 tends to loosen the mat from the belt and facilitate its removal. The 'doctor plate 26 is also located so that any adjustment of belt tension by movement of roll I5 does not materially change the relation of the doctor plate and the belt; or affect the removal of the mat lfrom the belt. In Fig. l the doctor plate 26a may be located at any convenient point, but preferably somewhat below the center of main roll I5arid just after or about the time that the belt I4 is leaving the roll on its return to roll I6. y

In order to keep the inner surface of the conveyer belt clean and-free from pulp deposit, a shower pipe 21 may be located as `shown in Figs. 1 and 3 and a shower of water, as indicated, sprayed over the inside of the belt, which water will carry any fibres or other solids washed oi the surface of the belt out over the edges of the [belt -and out over the ends .of rolls I6 and I9.

thereby'keezping the interior of the belt clean. Where the collecting roll I9 is immersed below the surface W. L. of the liquid, the ends of said and thereforedeliver drier solids from the device.

This is particularly useful where the liquids 'contain ingredients which it is desired to separate from the solids and where the liquids have been added to the solids in the vat as in the case of multiple stage pulp washing.

As shown in Fig. 3. the conveyer belt Ila is stretched between the main roll I1 and the collecting roll I9 ina curve or arc tending to compress the pulp layers against the filter surface. with the degree of such compression in zone B being determined by the tightness of the conveyer belt 14a. which is regulated by the tightener roll I8. It wil be readily observed that gradually increasing pressure is imparted to the mat throughout zone B in the direction of the arrow. affording opportunity and time for the water still contained in themat after leaving area A to be expressed through the mat. and through the filter surface 1, instead of being forced back.

wardly or downwardly into area II.

After this compression period through zone B, the mat passes directly under the main roll I1 at which time additional pressure is'placed on the mat through zone C by either the weight of the roll I1 or such additional weight 2| as may be Underl certain conditions, it may be desirable to have less weight on zone C than the weight of the roll I1, which may `be accomplished bv a' counterbalancing weight 2Ia as shown. By suitable arrangement of roll mayrbe provided with anges, or the edges of the belt Ila may pass closely between cover plates'extending above the surface W. L. so that pulp or`otherI solids are excluded from the interior of the belt. The surplus water from shower pipe 21l running out over the roll anges or over the topof the cover plates, serves to keep the interiorbelt surface clean and to prevent pulp materials from enteringthis area.

It has alreadybeen 'pointed outthat the beltA Ila is impervious to either water or air, hence the water from shower pipe 21 canin no way find its way to the pulp mat and can in no way interfere or reduce the extraction of water from the mat in zonesgB and C.

Having thus described our invention, what we claim is: f 4

1. Apparatus of the class described, comprising a container for a mixture of solids and liquids. a filter drum therein adapted to collect a layer or mat of semi-solid vmaterial on its surface, a roll mounted above said vat, a sec'ondroll mounted somewhat below the level of mixture in,

' ture. and having its surface spaced further from weights 2l .and 2Ia. it is possible to impart any i' desired pressure throughout zone C. these weights .acting about fulcrum F. Afterthe final TII compression of the deposited mat in zone C, it will thedrum surface'than that of the iirst mentioned roll, and an impervious belt stretched between said rolls and adapted to contact the semisolid material on the surface of the lter drum with increasing vpressure as the material moves from the zone adjacent to the second roll to th zone adjacent to the first roll.

2.'Apparatusof -the class described, comprising a container for a mixturel of solids and liq- 'uids. a filter drum therein adapted to collect'and retain on its surface amat or layer of semi-solid material` an impervious conveyer belt, a plurality of rolls over which operates said belt, one of said rolls being immersed somewhat below the level of the liquid materials from which the mat on the filter drum is collected. and adjacent the drum surface in the zone in which the drum emerges from the mixture of materials. and having its surface spaced further from the drum surface than that of anotherv of said rolls, means to drive said conveyer or coucher belt at a speed substantiallythe same as the surface speed of the mat on said filter drum, and means to remove from said belt the mat which has collected thereon.

3. An apparatus for thickening pulp comprising a vat adapted to contain a liquid-pulp mixture, a filter drum arranged for submergence in said mixture, and having means operableA by dif- 'ferential pressure to collect on its surface a layer of semi-solid material from the mixture, means partially submerged in the liquid-pulp mixture, and independent of said differential pressure means to impose additional material upon said drum and upon the material collected thereon, including means to compress and consolidate the material collected by the two means, and to remove the combined, compressed and consolidated materials from the surface of the filter drum.

4. The method of thickening liquid pulp mixtures, which comprises the extraction of a certain portion of the liquid content from said mixture through a filter surface, leaving a layer of uncompressed semi-solid material deposited thereon, of initially pressing said semi-solid layer at substantially right angles to the filter surface. and while said surface is submerged below the liquid mixture level, of imposing additional and gradually increasing pressure on said semi-solid layer of material in the zone through which the layer of semi-solid material leaves the mixture for gradual extraction of additional liquid content from and through said layer, said liquid being expressed through said filter surface, and of applying further and additional pressure on said layer to effect added liquid extraction from said layer and its removal through said lter surface.

5. The method of thickening pulp mixtures which comprises the extraction of a certain portion of the liquid content from said mixture b y a differential head on a lter surface, leaving a layer of semi-solid material deposited on said .i

filter surface, of gathering additional material by means independent of that causing the first deposit, and of consolidating said additional materials with said initially deposited materials by pressure at substantially right angles to the filter surface, of imposing additional and gradually increasing pressure on said materials, said pressure compressing them against the filter surface and effecting gradual extraction of liquid content from and through said material, and through said filter surface, and of subsequently applying additional or greater pressure on said layer to effect further liquid extraction and its removal through said lter surface.

6. Apparatus of the class described comprising a vat containing a mixture to be filtered, a filter drum adapted for immersion and rotation in said vat, means to'rernove a portion of the liquid from said vat mixture through the filter drum surface, the remaining thickened material being partially retained on and moving with said drum surface with other thickened material being closely adjacent to said drum surface but not attached thereto. a pair of rolls adjacent said drum surface, and one of which is located adjacent the zone at which the filter drum emerges from the mixture, said roll being partially submerged, and having its surface spaced further from the drum surface than that of the other roll, an impervious belt carried by said rolls and so located by one of said rolls that it is in contact with the thickened vat material both on said filter drum surface and immediately adjacent thereto, and means to move said rolls and said belt in synchronism with the thickened materials collected by cooperative effort of said drum and said belt.

'7. Apparatus of the class described comprising a vat, a filter drum in said vat, means to collect on the surface of said drum and accumulate immediately adjacent said surface a mass of partially thickened material, and means adjacent and submerged with respect to the emerging zone of' the filter drum surface to collect, compress, and discharge said partially thickened material, said means having a surface adjacent and submerged with respect said drum surface and spaced further from the drum surface at points nearest the mass of material than at points above the material.

8. A pulp thickener comprising a vat contalning the mixture to be thickened, a filter drum partially immersed in the vat mixture and rotatable therein, means to collect on the surface of said rotating filter drum and immediately adjacent to said surface at the point where said drum emerges from the mixture a mass of partially thickened material, means comprising a moving belt partially immersed in said mixture adjacent to the zone where said drum emerges therefrom for collecting, compressing, and discharging said thickened material, said belt being so positioned adjacent the surface of the drum as to converge toward said surface in the direction of the movement of the drum and belt as the drum surface passes away from the mixture.

JOHN P. RICH. ELMER R. BURLING.

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