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Publication numberUS3245535 A
Publication typeGrant
Publication dateApr 12, 1966
Filing dateMay 23, 1963
Priority dateMay 23, 1963
Publication numberUS 3245535 A, US 3245535A, US-A-3245535, US3245535 A, US3245535A
InventorsCowan Ben
Original AssigneeCowan Ben
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Vertical pressure type pulp screen
US 3245535 A
Abstract  available in
Images(3)
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Claims  available in
Description  (OCR text may contain errors)

April 12, 1966 cow 3,245,535

VERTICAL PRESSURE TYPE PULP SCREEN le May 2 3 3 Sheets-Sheet 1 illlllil W Mimi 'allmT' mm- INVENTOR BE Cow/w ATTORNEYS A ril 12, 1966 B. OWAN 3,245,535

VERTICAL PRESSURE TYPE PULP SCREEN Filed May 25, 1965 5 Sheets-Sheet 2 INVENTOR BEN COWAN ATTORNEYS April 1966 B. cowAN 3,245,535

VERTICAL PRESSURE TYPE PULP SCREEN Filed May 23, 1963 5 Sheets-Sheet 3 INVENTOR FYI-7.- El BEN Cow/m A TTORNE YS United States 3,245,535 VERTECAL PRESSURE TYPE PULP SiIREEN Ben Cowan, 5460 Patricia Ave., Montreal, Quebec, Canada Filed May 23, 1963, Ser. N 0. 2$2,666 4 Claims. (ill. 209240) This invention relates to rotary pulp screens of the vertical pressure type and particularly to a screen in which the rejects and that portion of acceptable fibres carried with the rejects are passed to a lower restricted annular area where the acceptable fibres and the rejects are separated from each other with the fibres being passed through the screen and the rejects are discharged through a reject discharge chamber and through a reject discharge opening.

The conventional pressure or drowned type screen has been used recently in applications where it is necessary to prevent the entry of air into the'pulp. In this case the screening operation is conducted under a slight pressure, in a completely closed system from feed'to discharge.

In the conventional pressure or drowned type of screen, the reject material remains in the inside of the screen plate and a current must be induced along the face of the plate to move the rejects positively to the discharge point. As the feed stock is the only fluid available to move the rejects in this manner, a large amount of good fibre must be rejected together with the true rejects, in order to discharge the rejects from the screen. The usual practice is to rescreen the rejects and their attached fibres over a coarse screen which accepts of the fibre back into the system. The net result is a screening whose cf".- ciency is determined by rejects screening and not the primary screening.

l in the present invention, in order to avoid the rejecting of a-fairly large quantity of fibre with the true rejects, the medium carrying the rejects, i.e., the mixture of pulp and liquor, is displaced at'the bottom area of the screen by a clear liquor which is maintained at a pressure in excess of that of the screen feed pressure. This clear liquor under pressure separates the pulp from the rejects and washes it through the screen and the rejects continue down, carried by the clear liquor, into a reject chamber and to the reject discharge outlet.

, The invention consists essentially in the provision of a vertically disposed rotary impeller which is provided with a core in the form of a hollow frustrurn of a cone whose apex is pointed in the direction of the stock inlet of the screen. The impeller is provided with a series of vertically disposed blade-s radiating outwards at right angles to the axis of the impeller and extending along the surface of the impeller core and projecting upwards to the top level of the screen. A stationary core formed from a frustrum of a cone, axially mounted about the drive shaft supporting the impeller, projects upwardly into the lower portion of the impeller core and is spaced radially inwards of the inner surface of the impeller core. A white water or clear liquor supply is connected to an opening in the side of stationary core to direct an annular jet downwards towards the annular reject chamber formed at the periphery of the large diameter end of the stationary core and also directs jets through the apertures in the adjacent wall of the impeller core and into the annular space between the lower end of the impeller core and the adjacent surface of the screen. It is in this annular space Where the rejects are washed to separate the Patent 'ice fibres which are passed radially outwards through the screen while the rejects are carried axially downwards by the liquor flow into the annular reject chamber.

The conical section of the impeller core with the large end of the cone located adjacent the reject discharge, provides a continually decreasing area of flow axially towards the reject end of the screen and maintains the axial velocity of flow of the rejects along the inside of the screen towards the reject discharge. The axial section of the stationary corerelative to the impeller core provides a continually decreasing area of flow axially of the white water and ensures passage of the white water, or liquor under centrifugal force, through the apertures in the impeller core to mix with and dilute the rejects in the constricted area between the impeller core and the inner surface of the screen and thus to separate the fibres still clinging to the rejects. Thus, in the area of the screen adjacent the annular reject compartment, the dilution liquor is used to wash away, through the screen, the acceptable fibres and the rejects are then discharged through the annular reject chamber.

The object of the invention is to provide a vertical type pulp screen operating under pressure in which approximately all of the pulp fibres are screened from the reject material.

A further object of the invention is to provide a vertical type pulp screen operating under pressure in which, in the final stage, the mixture of pulp fibres and reject material remaining Within the screen is washed and separated by liquor other than that carrying the pulp into the screen.

A further object of the invention is to provide a vertical type pulp screen operating under pressure in which the impeller includes a conical member eflecting a continually decreasing area of flow of pulp stock axially downwards towards the reject end of the machine.

A further object of the invention is to provide a vertical type pulp screen in which a conical member will maintain the axial velocity of flow of the rejects along the inside of the screen plate towards the reject end of the machine.

A further object of the invention is to provide a vertical type pulp screen in which the impeller includes a pair of conical members having concentric annular openings at their lower end aligned with an annular reject receiving chamber.

A further object of the invention is to provide a vertical type pulp screen in which an outer conical member is provided with jet apertures by means of which jets of white Water are directed on to the reject material to wash any fibres clinging to the rejects out through the screen.

These and other objects of the invention will be apparent from the following detailed description and the accompanying drawings showing a preferred embodiment of the invention, in which:

FIG. 1 is a vertical side elevation of the pulp screen looking on the inlet and discharge openings.

FIG. 2 is a horizontal section of the screen taken on the line 2-2 of FIG. 1.

FIG. 3 is an enlarged vertical section of the screen taken on the line 33 of FIG. 1.

FIG. 4 is a vertical elevation of the screen rotor partly in section.

FIG. 5 is a bottom plan view of the rotor shown in FIG. 4.

FIG. 6 is a vertical section of the fixed conical section of the machine showing the reject discharge from the screen.

Referring to the drawings, the pulp screen 5 is of the vertical type adapted to operate under pressure and consists of an outer circular casing 6 whose wall is slightly tapered to provide a larger diameter at its lower discharge end than at its upper inlet end.

The casing 6 is closed at its top end by the plate 7 and at its lower end by the annular plate 8 which supports on its under side the annular reject discharge chamber 9 to which the reject discharge outlet 10 is connected. The base 11 of which the end plate 8 forms a part, supports the casing 6. The base 11 is in turn supported in an elevated position by the foundation base 12.

The annular screen plate 13 has its lower end 14 secured to the plate 8 at the outer periphery of the annular reject chamber 9.

A stationary core member 15 in the form of a frustrum of a cone has its base secured to the plate 8 at the inner peripheral edge of the annular reject discharge chamber 9. The upper end of the core member 15 is closed 05 by a plate 16 having a centrally aligned seal ring 17, the purpose of which will be explained later.

The upper end of the annular screen plate 13 is secured to the annular plate 13 which is secured to. the inner surface of the casing 6 at a predetermined distance down from the top of the casing to define an inlet chamber 1?. The plate 18 is supported in place by a series of brackets 20. The annular space 21 between the screen plate 13 and the casing 6 defines a screened fibre chamber having a pulp fibre discharge opening 22. A pulp fibre inlet 23 leads to the inlet chamber 19 of the machine.

The impeller 24 of the machine has a core 25 in the form of a frustrum of a cone whose larger diameter is located in the horizontal plane of the bottom end 26 of the impeller. The peripheral edge 27 of the large end. of the cone 25 is such that when the impeller is axially aligned with the core member 15 the peripheral edge 27 of the core member 25 is located approximately midway of the radial width of the annular reject chamber 9 (FIG. 3) and approximately a similar distance from the adjacent edge of the stationary core, member 15. The core member 25 is closed off at the top by the plate 28. A plate 29 parallel with the plate 28 is located intermediate the height of the core 25. The plates 28 and 29 are provided with axial apertures 30 and 31 and an axial sleeve 32 is located between these two plates.

A series of vertically disposed blades 33 are secured along their inner vertical edges 34 to the outer surface of the core 25. The blades 33 radiate outwards from the axis of the impeller 24. and each project above the top of the core 25 and are secured at their topmost edges 35 to the annular ring 36. The top of the impeller, defined by the annular ring 36 is approximately level with the plate 18 securing the top end of the screen plate 12 in the casing 6.

A series of nozzle apertures 37 are located in the tapered wall of the impeller core 25 near its lower end and etween each of the impeller blades 33.

The impeller 2 is driven by means of the drive shaft 38 extending upwards into the sleeve 32 and secured thereto by the key 39. The shaft 33 is an extension of the drive sleeve 49 to which is secured the drive pulley 41 which, in turn, is driven by the motor 42 through the belt drive 43. A drive shaft bearing assembly .4 is mounted between the upper and lower horizontal plates 8 and 45 of the screen supporting base 11 to support the drive shaft 38-40, in its vertically aligned position. Suitable belt tensioning means 46 are provided for tensioning the belt 43.

The impeller 24 is secured against axial movement by the nut 47 threaded on the threaded extension 48 of the shaft 38.

A spring 4 located about the drive sleeve 4% and between the seal member 17 on the core member 15 and the plate 29 of the impeller core member 25 acts as a cushion between the stationary and moving elements of the machine. The seal member 17 provides a fluid seal between the stationary and moving members of the screen.

A separate source of white liquor is fed through the pipe 59 and through the wall of the stationary core member 15 into the space 51. between the core member 15 and the adjacent walls of the rotating core member 25 of the impeller 24.

An eyebolt S2 is provided for removal of the top cover plate 7, eyebolts 53 provide for removal of the impeller 24- while eyebolts 54 provide for removal of the stationary core 15.

In the operation of this invention the screen is designed to operate under pressure i.e. with the interior of the screen being completely filled with pulp stock. The pulp stock is delivered to the inlet chamber 19 at the top of the screen through the pulp inlet 23. From the chamber 19 the pulp stock is directed downwards between the blades 33 and over the surface of the conical core 25 in the direction of the arrows A, shown in FIG. 3, towards the interior surface of the screen plate 13. In the area between the impeller top ring 36 and the bottom of the screen plate 13, a large portion of the pulp fibres are washed through the screen plate 13 and are discharged from the screen through the discharge outlet 22.

Because of the conical core member 25 of the impeller there is provided a continually decreasing area of flow axially of the pulp fibres towards the annular opening 55 from the interior of the screen into the annular reject chamber 9, and therefore there is maintained an axial velocity of how of the reject material along the inside of the screen plate 13. At the restricted passage leading to the annular opening 55, indicated by the arrows B, the reject material is subjected to a separate washing by liquor fed through the pipe into the space 51. Here the liquor is projected through the nozzle apertures 37 against the reject material to thoroughly wash and sep arate only pulp fibres still clinging to the reject material, forcing the pulp fibres through the screen plate 13 and into the stream of pulp fibres being discharged through the pulp outlet 22.

The heavier reject material falls down through the annular opening into the reject chamber 9 and is dis-' charged through the discharge outlet 10.

Suitable valves at the inlet and outlets of the screen (not shown) ensure that the screen is kept filled at all times.

By the use of the above described invention the axial flow of the heavier reject material is maintained downwards along the interior of the screen and through the rericted annular opening 55 into the annular chamber 9, and by the use of a separate source of washing liquor and not pulp stock, the reject material is thoroughly washed to the extent that in actual operation less than 1% of the good fibre in the feed of the screen may be discharged with the rejects, whereas this may be as high as 20% with conventional pressure type screens hitherto in use. The basic principle behind the design of this screen is the use, in a screen under pressure, of an external liquid to displace the pulp medium used to carry the tailings through the screen, and thereby to carry the tailings from the screen in a medium free from acceptable material. This gives a complete separation of acceptable and unacceptable material in a single screen which is kept under pressure.

This result can be achieved presently in open type conventional screens, but cannot be achieved by any pressure type screen now in use.

The open type of screen cannot be used in certain applications where exposure to air will cause entrainment of air bubbles in the liquid medium with consequent production of foam and ill eifects on the pulp or paper making process. This screen combines all the advantages of conventional open screen with perfect separation and a closed screen with no air entrainment.

Under certain conditions it may be desirable to operate the screen without the addition of dilution wash water at the bottom of the screen. In such case the valve 56 in the feed water pipe 50 is closed oif and the unit operated as an ordinary pressure screen.

What I claim is:

1. A pulp screening machine of the vertical pressure operated type, the said machine including a base, a bearing vertically aligned in the said base, a drive shaft in said bearing and means to drive the said shaft, a casing axially mounted on said base with respect to the said drive shaft, a top closure plate for said casing, a pulp feed inlet to the said casing adjacent the top end thereof and a pulp discharge outlet adjacent the lower end of said casing, an annular perforated screen plate within said casing and supported on said base, means to support the top end of said screen plate to said casing at a point adjacent the lowermost edge of the said pulp feed inlet and defining with said casing a pulp feed chamber above said screen plate, a rotary impeller axially mounted on said drive shaft, the said impeller comprising a core member in the form of a frustrum of a cone whose larger diameter is located immediately above the said base and spaced inwardly of the said screen plate to define a restricted annular reject discharge opening whose smaller diameter is locate-d a distance downwards from the top end of the said screen plate, a series of blades secured to the said core member and radiating outwards therefrom, the said blades projecting upwards from said core member to the level of the top of said screen plate, an annular reject chamber in the said base whose outer periphery coincides with the inner peripheral surface of the said screen plate and in communication with the interior thereof through said annular reject discharge opening, a stationary core member in the form of a frustum of a core mounted on said base axially about said drive shaft and projecting into the lower end of the said impeller core member and spaced radially inwards of the surface thereof to define a restricted annular passage between the core stationary member and said impeller core member communicating with the said annular reject chamber, means to feed a supply of washing liquor to the space between said stationary core member and the impeller core member, and a series of apertures in said impeller core member directing streams of washing liquor from the space between the core members against the said screen plate adjacent the said annular reject chamber.

2. A pulp screening machine of the vertical pressure operated type, the said machine including a vertically disposed casing having top and bottom closure plates, a pulp feed inlet to the casing adjacent its top end and a pulp discharge outlet to the casing adjacent its lower end, an annular perforated screen plate within said casing supported on the said bottom closure plate, means to support the top end of the said screen plate at a point adjacent the lowermost edge of the said pulp feed inlet and defining a pulp feed chamber above said screen plate, a rotary impeller axially mounted within said screen plate, the said impeller comprising a core member whose lower end is located in the horizontal plane of the lower end of said screen plate, the said core member effecting a progressive reduction in area of the screening chamber in a downward direction and a series of vertically disposed blades secured to the surface of said core member and radiating outwards therefrom towards said screen plate, the lower ends of said core member and said screen plate defining a first annular reject discharge outlet, a stationary core member projecting upwardly from the said bottom closure plate within the said impeller core member and defining therewith a wash liquor pressure chamber, the lower ends of said impeller core member and stationary core member defining an annular wash liquor discharge outlet concentric with said first annular discharge outlet, and a reject receiving chamber in said bottom closure V 6 plate, the said reject receiving chamber communicating with the said screening chamber and wash liquor pressure chamber through the said concentric annular discharge outlets.

3. A pulp screening machine of the vertical pressure operated type, the said machine including a vertically disposed casing having top and bottom closure plates, a pulp feed inlet to the casing adjacent its top end and a pulp discharge outlet to the casing adjacent its lower end, an annular perforated screen plate within said casing supported on the said bottom closure plate, means to support the top end of the said screen plate at a point adjacent the lowermost edge of the said pulp feed inlet and defining a pulp feed chamber above said screen plate, a rotary impeller axially mounted within said screen plate, the said impeller comprising a core member whose lower end is located in the horizontal plane of the lower end of said screen plate, the said core member effecting a progressive reduction in area of the screening chamber in a downward direction and a series of vertically disposed blades secured to the surface of said core member and radiating outwards therefrom towards said screen plate, the lower ends of said core member and said screen plate defining a first annular reject discharge outlet, a stationary core member in the form of a frustum of a cone, projecting upwards from the said bottom closure and within the said impeller core member and defining therewith a wash liquor pressure chamber, the larger diameter of the said stationary core member being located in the plane of the lower end of the said impeller core member and defining therewith an annular outlet from the said wash liquor pressure chamber concentric with said first annular discharge outlet, and a reject receiving chamber in said bottom closure plate, the said reject receiving chamber communicating with the said screening chamber and wash liquor pressure chamber through the said concentric annular discharge outlets.

4. A pulp screening machine of the vertical pressure operated type, the said machine including a vertically disposed casing having top and bottom closure plates, a pulp feed inlet to the casing adjacent its top end and a pulp discharge outlet to the casing adjacent its lower end, an annular perforated screen plate within said casing supported on the said bottom closure plate, means to support the top end of the said screen plate at a point adjacent the lowermost edge of the said pulp feed inlet and defining a pulp feed chamber above said screen plate, a rotary impeller axially mounted within said screen plate, the said impeller comprising a core member whose lower end is located in the horizontal plane of the lower end of said screen plate, the said core member effecting aprogressive reduction in area of the screening chamber in a downward direction and a series of vertically disposed blades secured to the surface of said core member and radiating outwards therefrom towards said screen plate, the lower ends of said core member and said screen plate defining a first annular reject discharge outlet, a stationary core member projecting upwardly from the said bottom closure plate within the said impeller core member and defining therewith a wash liquor pressure chamber, a wash liquor feed pipe connected through said stationary core member, feeding wash liquor into said wash liquor pressure chamber, a series of apertures in the said impeller core member, the said apertures permitting the injection of wash liquor to between the said impeller and the screen plate adjacent the lower end thereof, the lower ends of the said impeller core member and stationary core member defining an annular wash liquor discharge outlet concentric with said first annular discharge outlet, and a reject receiving chamber in said bottom closure plate, the said reject receiving chamber communicating with the said screening chamber and wash liquor pressure chamber through the said concentric discharge outlets.

(References on following page) References c115 by the Examiner F OREIGN PATENTS UNITED STATES PATENTS 115,639 1/1946 Sweden.

5,25% 5 HARRY THORNTON, Primary Examiner. 1:856:176 5/1932 Tfrimbf 11:11:11: 209306 FRANK LUTTER, Examiner.

1,990,992 2/1935 Lang 210-415 R. HALF-ER, Assistant Examiner.

Patent Citations
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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3363759 *Apr 29, 1964Jan 16, 1968Bird Machine CoScreening apparatus with rotary pulsing member
US3420373 *Apr 1, 1966Jan 7, 1969Allen Bruce HunterPulp screens
US3508651 *Apr 19, 1968Apr 28, 1970Hooper & Co Ltd S WMethod and apparatus for screening pulp
US3898157 *Mar 19, 1974Aug 5, 1975Hooper & Co Ltd S WTwo stage pressure pulp screen device with stationary cylindrical screen
US3914172 *Aug 23, 1973Oct 21, 1975Highratio Screens LtdPulp stock pressure screen
US4000063 *Mar 28, 1975Dec 28, 1976Kamyr, Inc.Apparatus for separating knots from pulp
US4234417 *Mar 29, 1979Nov 18, 1980Gauld Equipment Manufacturing Co.Fibrous stock screen
US4267035 *Aug 27, 1979May 12, 1981The Black Clawson CompanyPressurized rotary screening apparatus
US4287055 *Jun 28, 1979Sep 1, 1981Firma Hermann Finckh Maschinenfabrik Gmbh & Co.Method of sorting fibre suspensions as well as a pressure sorter for performing the method
US4749474 *Aug 27, 1986Jun 7, 1988Ingersoll-Rand CompanyScreening apparatus
CN102666978A *Dec 13, 2010Sep 12, 2012美佐纸业股份有限公司Unit, arrangement and method for screening of cellulose pulp
CN102666978B *Dec 13, 2010Aug 3, 2016维美德技术有限公司用于筛选纤维素纸浆的单元、结构和方法
DE3015833A1 *Apr 24, 1980Nov 13, 1980Uniweld IncSiebvorrichtung fuer pulpe
DE3240487A1 *Nov 2, 1982May 3, 1984Ni I Pk I Celljuloznogo MasinoPressurised classifier for fibre suspensions
EP0025310A1 *Aug 26, 1980Mar 18, 1981The Black Clawson CompanyPressurized rotary screening apparatus
EP0404624A2 *Jun 5, 1990Dec 27, 1990Valmet Paper Machinery Inc.Method for controlling pressurized screening device and pressurized screening device
EP0404624A3 *Jun 5, 1990Jul 31, 1991Valmet Paper Machinery Inc.Method for controlling pressurized screening device and pressurized screening device
WO2011078764A1 *Dec 13, 2010Jun 30, 2011Metso Paper, Inc.Unit, arrangement and method for screening of cellulose pulp
Classifications
U.S. Classification209/240, 209/306, 209/255, 209/273
International ClassificationD21D5/06
Cooperative ClassificationD21D5/06
European ClassificationD21D5/06