WO1996013375A1

WO1996013375A1 - Device for adjusting counterpressure in a screw press

Info

Publication number: WO1996013375A1
Application number: PCT/NO1995/000189
Authority: WO
Inventors: Ingvar IDSØ
Original assignee: Reime A/S
Priority date: 1994-10-26
Filing date: 1995-10-17
Publication date: 1996-05-09
Also published as: AU3817795A; NO300533B1; NO944062D0; NO944062L

Abstract

A device for adjusting counterpressure within a screw press comprising an inlet for mass (4a) to be separated into a liquid phase (4b) having an insignificant content of dry substance and a phase (4c, 4d) having a substantially higher dry substance content; a rotary feed screw (2) assigned to a strainer pipe (7) surrounding the feed screw (2) and being self surrounded by a jacket (8) having a discharge (9) for said liquid phase (4b); an axially directed outlet (11) for separated mass (4d, 4e); means (12) for throttling the outlet (11), establishing a counterpressure within the screw press; an axially displaceable liquid barrier breaker (16) for adjusting said counterpressure and adapted, being able to break down, a liquid barrier formed by separated mass (4d). In activated positions, the liquid barrier breaker (16) breaks down the liquid barrier to a varying degree, and the counterpressure is varied correspondingly.

Description

DEVICE FOR ADJUSTING COUNTERPRESSURE IN A SCREW PRESS

The present invention relates to a device for adjusting counterpressure in a screw press, wherein the screw press comprises an inlet for untreated or partly pretreated mass to be dewatered respectively separated into a liquid phase and a phase having a considerable larger content of dry substance than the liquid phase; at least one feed screw in the form of a rotatable screw conveyor and which, along a longitudinal section thereof, is assigned a strainer pipe which, in its turn, is surrounded by a jacket having an outlet for the liquid phase, said strainer pipe - possibly through an annular or tubular transition member - being assigned a preferably axially directed outlet for the dewatered, dried mass, and wherein means are disposed, in order to throttle the outlet for dewatered mass and to establish a counterpressure within the screw press, and where a device is disposed for adjusting the counter pressure within the screw press and has the form of a "liquid barrier breaker", i.e. a device adapted to break down a liquid barrier in the form of a counter pressure forming layer of dewatered mass.

Such a screw press can be used for dewatering/separation of a great number of untreated masses. An example of such a use is disclosed in NO laying-out publication No. 168,401, where a screw press of the introductorily defined kind is used for separating manure from domestic animals into liquid manure and more or less solid manure mass. Another example of use or application consists in the recovery of fruit juice from a fruit mass, wherein the "dewatered" fruit mass is almost worthless for human comsumption, the juice being the separated phase to take care of.

However, the present invention is not restricted to dewatering/separating of certain untreated/partly pretreated masses, but is generally useful for treating any masses whatsoever, provided that they contain liquid which, wholly or in part, is desired to be separated from the material phase which eventually has the largest content of dry substance.

Thus, a screw press of the kind concerned consists of one or more feed screws rotating within a strainer pipe, i.e. a pipe having a number of through-going perforations which may be positioned evenly distributed across the entire pipe jacket or which may be concentrated to certain portions thereof. Such strainer pipes are well known and do not as such constitute subject matter of the present invention. The feed screw or the feed screws are formed such that it/they carry the mass forwardly within the strainer pipe, simultaneously as it/they establish a pressure within the strainer pipe and, thus, press liquid and/or small particles out through the perforations of the strainer pipe, larger particles being fed forwardly in the direction of the feed screw axis and out through the outlet. In order to achieve the desired dewatering, the screw press must be shaped and designed such that a counter pressure is built up within the strainer pipe.

Therefore, the screw press has a device throttling the flow of dewatered mass in the outlet thereof and/or a screw and/or a strainer member which is shaped and designed such that the pressure is caused to increase as a result of a gradually reduced flow area in the downstream direction. The counterpressure will be dependent on the dimensions of the screw press and on the mass supplied thereto as well as the consistence of said mass. If the screw press is not designed for one mass only having identical properties from time to time, it is necessary to be capable of adjusting the pressure within the screw press dependent on the kind of mass dewatered and on the consistence exhibited by the mass at any time. Moreover, it will also be possible to adjust the degree of dewatering by means of the same adjustment. If a possibility of adjusting lacks, this may cause the following disadvantages dependent on the mass and the consistence thereof: (a) too high pressure may overload the screw press; (b) and/or may result in too much dry substance in the reject water; (c) and/or too high content of dry substance in the dewatered mass constituent; (d) too low pressure, so that the dewatering becomes unsufficiently; (e) and/or that the screw press will get erratic running; and/or (f) occurence of a blow-out.

Among known devices for adjusting counterpressure in a screw presses, the following could be mentioned:

The liquid barrier in the form of said counterpressure- for ing layer of dewatered mass, said layer extending laterally to the direction of the feed screw axis, may - in accordance with NO laying-out publication No. 168,401 - be scraped off from the downstream side by means of a piece of a screw conveyor or a similar scraping means which, preferably, is formed such that it contributes to the conveying of the dewatered mass towards an outlet. This known scraping means is disposed on the shaft of the main screw conveyor and is, consequently, rotated therefrom. This scraping means serves exclusively to maintaining the thickness of the liquid barrier of equal size, the liquid barrier being supplied to make it thicker from the upstream side approximately i. the same pace as it is scraped off at the downstream side.

Likewise, a telescopic outlet is known which can be varied in length and made longer or shorter and thereby adjust the counterpressure by means of altering the thickness of the liquid barrier.

Further, it is known to use weights which can be adjusted, possibly replaced by heavier/lighter weights, in order to change the press from a closure device disposed at the outlet for dewatered mass. Also, it is known to use springs attacking on said outlet-closure device, and which are tensioned/slackened for changing the press of a closure device at said outlet for dewatered mass.

The object of the present invention has been to provide a liquid barrier breaker for adjusting counterpressure in a screw press, said liquid barrier breaker is deactivateable and activateable by covering the same from time to time and uncovering the same gradually from a deactivated position. Such a novel liquid barrier breaker does not break down the liquid barrier when it is deactivated, but when activated it will break down a smaller or larger portion of the liquid barrier, thus reducing the counterpressure.

Said objects are realized through the features as defined in the following claims.

The liquid barrier breaker may - as known per se - be formed as a screw conveyor piece. The liquid barrier breaker is disposed such that it can be covered and deactivated, e.g. by being pushed more or less into a downstreamly open, hollow shaft forming part of the main feed screw, the activation being realized by pulling the liquid barrier breaker out from the cavity of the shaft by means of a motion screw engaging into a nut and being operated through an external hexagonal head on the motion screw. The liquid barrier breaker may - as known per se - be operated by means of the main feed screw, and is connected thereto through a means displaceable longitudinally. The mode of operation for an examplary embodiment of a screw press comprising one feed screw, a cylindrically shaped strainer member as well as a one-piece disc driven by the feed screw, a constricted outlet upstream the outlet opening, provided with preferably longitudinal fins, as well as an adjustable liquid barrier breaker driven by the feed screw, is, in principle, the same as when the screw press has more than one feed screw, a differently shaped strainer member and/or lacks said constriction, lacks fins at said constriction, as well as lacks said disc or possible wings thereon.

An examplary embodiment is further explained in the following with reference to the attached drawings, wherein:

Figures 1 - 3 show a side elevational view of a screw press where important members such as inlet, outlet, strainer pipe and surrounding jacket as well as a longitudinal portion of the hollow shaft of the screw conveyor are shown in axial sectional view,

Figure 1 showing the screw press during the starting up step;

Figure 2 showing the screw press during operation;

Figure 3 showing the screw press in adjusted condition.

During the starting up of the screw press, a motor 1 sets a feed screw 2 in the form of a screw conveyor in rotation through a gear 3.

The untreated or partly pretreated mass 4a to be dewatered, is conducted into a feed housing 5 through an inlet 6. The feed screw 2 feeds the mass in the longitudinal direction thereof from the feed housing 5 and into a strainer pipe 7, which may have any suitable shape besides a tubular shape, a curved, perforated plate surrounding the feed screw 2 radially from below and laterally will be useful for the purpose.

The strainer pipe 7 or another strainer member is surrounded radially by a jacket 8 provided with one or more downwardly directed discharges 9. The liquid or reject water 4b of the mass 4a is pressed through the strainer and caught by the jacket 8, from where the liquid is fed out through the discharge 9. The mass becomes dewatered more and more as it is fed forwardly by the feed screw 2 within the strainer pipe 7, simultaneously as the feed screw 2 exerts a constantly increasing radial pressure on the mass 4c in a direction towards the strainer pipe 7, so that more and more liquid 4b is pressed through the strainer pipe 7 and out into the annulus 10 between the strainer pipe 7 and the surrounding jacket 8. At the outlet 11 for dewatered mass 4c, a one-piece, driven, rotary disc 12 has been disposed downstream relative to the outlet opening. The disc 12 is adapted to be pressed resiliently/yieldingly in a direction towards the opening of the outlet 11,in order to cover and seal the opening or - when the disc 12 occupies a position at a certain distance from the outlet opening, downstream relative to the same - throttle the opening in a varying degree, dependent on the axial distance from the disc to the outlet opening. Typically, the disc will seal the opening of the outlet 11 partly.

When the screw press has built up a sufficient amount of dewatered mass 4c, the dewatered mass seals against the outlet 11 and forms a mass plug/liquid barrier 4d.

During operation, this liquid barrier 4d will fill the entire space from the end of the feed screw 2 and forwardly to the outlet 11/the disc 12. The liquid barrier 4d forms by itself a counterpressure, but it becomes pushed axially forwards by means of the pressure from the feed screw 2, so that the pressure from the liquid barrier 4d will result in that the disc 12 is pressed away from the outlet, figure 2, so that the dewatered mass may leave the outlet 11. Upstream relative to the opening of the outlet 11 for dewatered mass, the strainer pipe end 7 respectively an annular end piece 13 is tapering conically in a direction towards said outlet opening, in order to form a constriction, for the purpose of increasing the counterpressure. The effect from this constricted portion 13 can be increased through the provision of longitudinal fins 14. Both these measures contribute to prevent that the liquid barrier 4d rotates with the feed screw 2 and/or with the disc 12. Thus, a continuous process is achieved, new mass 4a being constantly supplied and fed into the strainer pipe 7 by means of the feed screw 2, which also presses the mass 4c radially towards the strainer pipe 7, so that liquid 4b is pressed through the perforations of the strainer pipe 7 and out into the space 10 between strainer pipe 7 and surrounding jacket 8, from where liquid flows out from the discharge 9. Simultaneously, dewatered mass 4c is fed towards the liquid barrier 4d and out from the outlet 11 for dewatered mass. If new mass 4a is not supplied through the inlet 6, the forwardly directed feeding stops, but because the one-piece rotary disc 12 which is pressed against the opening of the outlet 11, the machine will not be discharged.

If the consistence of mass 4a supplied is changed, through becoming e.g. substantially softer/more moist or drier or the structure is changed due to more or less mucic substance or larger or smaller particles, the one-piece, rotary disc 12 will control the pressure such that no blow-out or no overload of the screw press takes place, and the content of dry substance in dewatered mass 4e becomes approximately the same as before. If the liquid barrier 4d and possibly mass 4c around the feed screw 2 rotates together with the latter, the feed screw 2 will not feed the mass forwardly, and the entire process stops. If the liquid barrier 4d rotates together with the one-piece, rotary disc 12, the latter will not carry the mass away from itself, and the mass 4d will, thus, also easily start to rotate with the feed screw 2. Both these disadvantageous conditions are warded off by means of the conical constricting member 13 and the fins 14 on the internal side of the same.

In a preferred embodiment of the invention, the undivided, rotary disc 12, forming the subject matter for a separate patent application, is formed with one or more wings 15 contributing to carry dewatered mass 4e away. But also without wings, the undivided disc will act as a feed-out means for dewatered mass because of the rotation thereof; this contrary to known crescent-shaped covers disposed at the opening of the outlet 11 and adapted to establish a counterpressure within a screw press.

In order to adjust the counterpressure within the screw press, figure 3, there has been disposed a so-called liquid barrier breaker 16 formed as a feed out screw-piece, contributing to feeding dewatered mass 4e out from the screw press. The liquid barrier breaker 16 is disposed axially displaceable in relation to the stationary outlet 11 for dewatered mass 4e. It is noted that a similar feed out screw-piece serving as a liquid barrier breaker in the screw press according to NO laying-out publication No. 168,401, indeed is rotary, but certainly not adapted to be covered and deactivated.

The liquid barrier breaker 16 is disposed such that it can be deactivated by being pushed into the hollow shaft 2 ' of the main feed screw 2, and activated by being pulled out from the same by means of an adjusting screw/motion screw 17 connected to a hexagonal head 18 at the end of the screw press. The motion screw 17 is screwed by means of a hexagonal head 18 in and out of a stationary nut 19 within the hollow shaft 2' of the feed screw 2. The liquid barrier breaker 16 is driven rotationally by means of the feed screw 2, a thin bar 20 welded firmly to the inner end of a cylindrical portion 21 on the liquid barrier breaker 16 passing through an axially directed hole in the nut 19.

A liquid barrier 4d filling the entire outlet 11 from the end of the feed screw 2 and completely up to the rotary disc 12, will form a high counterpressure within the screw press, while a liquid barrier 4d broken down by the liquid barrier breaker 16 and fed out by means of the same, will form a lower counterpressure within the screw press. Thus, the counterpressure is adjusted by means of the liquid barrier breaker's 16 position of displacement in relation to the downstream end of the feed screw 2.

Through a bearing housing 22, the disc 12 is displaceably disposed on a pipe 23 surrounding the motion screw 17 and is assigned a spring-loaded linkarm system, represented at 25, seeking to keep the disc 12 elastically resiliently pressed against the outlet 11 for dewatered mass. This spring-loaded linkarm system is partly hidden by adjacent portions of the screw press, but it is mainly based on the effect of the springs 24 and consititutes, in other respects, neither directly nor indirectly, any part of the subject matter of the present invention which relates to the liquid barrier breaker 16 and components cooperating therewith, in combination with the components of the screw press necessary for the implementation of the intentional technical effect of the invention.

Claims

10C l a i m s

1. A device for adjusting counterpressure within a screw press comprising an inlet for untreated or partly pre¬ treated mass (4a) to be dewatered respectively separated into a liquid phase (4b) having an insignificant content of dry substance and a phase (4c, 4d) having a substantially higher dry substance content, said screw press, moreover, comprising at least one feed screw (2) in the form of a rotary screw conveyor which, along a longitudinal section, is assigned a strainer member, e.g. in the form of a concentric strainer pipe (7) surrounding the feed screw (2) , said strainer pipe (7) being surrounded more or less by a jacket 3 with discharge (9) for said liquid phase (4b) , the downstream end of said strainer member/pipe (7) - possibly through a pipe/tubular transition/completion member (13) joined thereto - being assigned a preferably axially directed outlet (11) for dewatered mass (4d, 4e) , said outlet (11) being assigned means (12) for throttling the same, in order to establish a counterpressure within the screw press, and wherein a device (16) is disposed for adjusting said counterpressure and adapted to break down, wholly or partly, a liquid barrier formed by dewatered mass (4d) upstream relative to said outlet (11) , c h a r a c t e r i z e d i n that said device (16) is adapted to be displaced between an activated position wherein it influences and breaks down the liquid barrier (4d) and a deactivated, more or less covered position wherein it does not - or only to a insignificant degree - influences said liquid barrier (4d) .

2. A device as set forth in claim 1, c h r a c t e r i z e d i n that the shaft (2*) of the feed screw (2), at least along a downstream longitudinal section, is formed hollow and exhibits an open downstream end, and that said liquid barrier breaker/device (16) is wholly or partly insertable into the cavity of the feed screw shaft (2'), in order to be deactivated to a larger or smaller degree in this position of insertion.

3. A device as set forth in claim 1 or 2, c h a r a c t e r i z e d i n that said liquid barrier breaker/device (16) is connected to an axially directed motion screw (17) having an external control means, e.g. a polygonal head (18) , and which engages into an internally threaded, axial hole in a nut body (19) which is placed within the interior of the hollow feed screw shaft (2'), so that rotation of said head (18) causes axially directed displacement of the motion screw (17) and, thus, of said liquid barrier breaker/device (16) in relation to the hollow feed screw shaft's (2') downstream end respectively in relation to the outlet (11) for dewatered mass (4d, 4e) .

4. A device as set forth in any one of the preceding claims, c h a r a c t e r i z e d i n that said liquid barrier breaker/device (16) has a rectilinear member (20) extending parallel to the axis of the feed screw (2) , and which engages displaceably into a hole coaxial therewith and formed into said nut body (19) , such that the liquid barrier breaker/ device (16) is driven by the feed screw (2) when the latter is rotated.

5. A device as set forth in any one of the preceding claims, c h a r a c t e r i z e d i n that said liquid barrier breaker/device (16) - as known per se - has the form of a screw conveyor piece shaped and designed to break down said liquid barrier (4d) , simultaneously as it contributes to feeding dewatered, loosened mass (4d) towards said outlet (11) , and that the screw conveyor piece (16) has a maximum diameter which is substantially smaller than the maximum diameter of the main feed screw (2) .

6. A device as set forth in claim 1, c h a r a c t e r i s e d i n that the downstream end portion of the strainer member

(7) respectively a ring/tubular portion (13) joined thereto, tapers conically in a direction towards the outlet (11) for dewatered mass (4d, 4e) .

7. A device as set forth in claim 6, c h a r a c t e r i z e d i n that said conically tapering portion (13) is provided with one or more fins (14) extending in the longitudinal direction of the feed screw (2) .