GB1578126A

GB1578126A - Screw presses

Info

Publication number: GB1578126A
Application number: GB890476A
Authority: GB
Original assignee: GEC Diesels Ltd
Current assignee: MAN Energy Solutions UK Ltd
Priority date: 1977-05-13
Filing date: 1977-05-13
Publication date: 1980-11-05

Description

(54) IMPROVEMENTS IN OR RELATING TO SCREW PRESSES (71) We, GEC DIESELS LIMITED, of Vulcan Works, Newton-le-Willows, Lancashire WA12 8RU, a British Company, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to screw presses for expressing liquid from compressible material such as sludge and relates particularly though not exclusively to screw extrusion filter presses for the continuous extraction of liquid from sludge materials. References to sludge material are to be taken to include any combination of liquid and compressible solid material from which the liquid will not immediately drain off.

Screw extrusion filter presses are known in which a helical screw conveyor is arranged to convey material along a confined perforated conduit and to extrude it through a restricted discharge opening which exerts a back pressure on the material within the conduit. The material is thus compressed and liquid is expressed from it through the apertures in the conduit.

A problem with screw extrusion presses of this kind is that material often becomes plugged between the flights of the screw so that the screw then behaves as a solid shaft and is unable to move the material forward.

The press then has to be dismantled to remove the " plugging" material from between the flights of the screw.

It is an object of the present invention to provide a screw press filter in which the abovementioned disadvantage is overcome or at least substantially reduced.

According to the present invention, in a screw press filter for expressing liquid from sludge material, and comprising screw means arranged within a conduit to drive sludge through the conduit by a combination axial and rotary movement, the conduit providing egress for liquid through the conduit wall and having a discharge opening for sludge at the downstream end of the conduit, driving means is arranged to rotate the screw means in a direction against the hand of its thread and to reciprocate the screw means axially in synchronism with the rotation so that forward axial movement of the screw means combines with the rotational movement to drive sludge through the conduit, while reverse axial movement of the screw means substantially cancels the driving effect of the rotational movement, and wherein means downstream of the screw means provides resistance to the flow of the sludge material, to tend to compress it in the conduit.

Said means providing resistance to flow may comprise a reduction in the cross section of the conduit, or may be constituted by the discharge opening, or by both.

The discharge opening is preferably adjustable to control the back pressure and period of dwell of material in the conduit.

Where there is provided a section of reduced cross section this may be of uniform cross section and may be preceded by a tapered section providing a smooth transition between the cross sections.

Alternatively, the section of reduced cross section may be of tapered cross section, reducing in a downstream direction. Where there is a section of uniform reduced cross section this may be followed by a further tapered section and a further section of uniform cross section.

One embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings of which: Figure 1 is a sectional elevation of a screw extrusion press filter in accordance with the present invention; and Figure 2 is a sectional end view of the filter along the line II-II of Figure 1.

Referring to the drawings the press filter comprises a hollow cylindrical outer casing 1 formed in thiee separate axial sections 2, 3 and 4 clamped together around annular flanges 5, 6 by means of releasable fastenings (not shown) which permit rapid dismantling of the casing for maintenance purposes.

The outer casing 1 is internally lined with a perforated tubular conduit 8 supported at regular intervals along its length within the casing 1 by spacers 9 so as to define therebetween an annular gap 10. The conduit 8 comprises three axial sections 13, 14, 15 which correspond in shape to sections 2, 3, 4 of the outer casing 1, and as shown are integrally formed, although they may be separately formed and joined together by any suitable means.

The conduit 8 comprises an upstream section 13 of uniform diameter, an intermediate tapered section 14 whose diameter reduces in the down stream direction, and a downstream section of uniform diameter smaller than that of section 13. The reduction in diameter of the conduit thus provides a resistance to the flow of the material such as to produce a back pressure on the upstream material in the region of the screw thread. It will be clear that references to "upstream" and "downstream", "forward" and "reverse", relate to the direction of flow of the sludge as driven by the filter.

Attached to the downstream end of section 4 of the outer casing 1 is a frustoconical discharge nozzle 12 of resilient material, e.g. rubber, which provides a restricted opening for the discharge of compressed solid material from the filter press. A further resistance to flow and consequent back pressure is thus provided.

Enclosed within the upstream section 13 of the conduit is a single helix screw 16 supported for rotational and reciprocating motion in a bearing 11 at the upstream end of the filter press for forcing material along the conduit 8 towards the discharge nozzle 12 at the downstream end.

The outer casing 1 and conduit 8 are each provided with a respective inlet opening 17, 18, in register with one another through which material to be treated can be fed to the screw conveyor 16 by any suitable means. In the present arrangement material to be treated is fed at a controlled rate from a pressure vessel (not shown) by means of a pressure lock 19 (see Figure 2) comprising a paddle 21 rotatably supported within a cylindrical casing 22 on a drive shaft 23 extending transversely across the path of the material. A filtrate outlet 24 is provided on the underside of the section 2 of the outer casing for the discharge of filtrate collected therein in use of the filter press.

Independent drive means (not shown) are provided for driving the pressure lock Waddle 21, and for driving the screw 16 whereby to impart simultaneous reciprocating and rotary motion thereto. The rotary motion is, of course, against the hand of its thread, i.e. it is anti-clockwise looking towards the bearing end, so as to provide a forward driving action on the material. The drive means for effecting the reciprocation and rotation of the screw 16 is synchronised so that for each thread pitch of axial movement, the screw rotates through one revolution the material thus remains stationary during the return reciprocating stroke. As shown the screw is arranged to reciprocate in each direction through a distance of two pitches of the screw thread i.e. the screw will rotate through four revolutions during one complete reciprocation cycle.Other suitable ratios may be used.

In use of the filter press, moisture-laden material to be treated is fed at a controlled rate into the upstream end of the conduit 8 through the inlet openings 17, 18 by the pressure lock 19 driven through shaft 23.

The simultaneous reciprocation and rotation of the screw 16 within the conduit 8 will force the material forward along the conduit towards the discharge nozzle 12 by imparting to it a direct axial thrust component due to the reciprocating " plunger" action, together with a thrust component derived from the screwing action of the screw 16. Thus during the forward reciprocation stroke the two thrust components will combine to push the the material forward, while during the return reciprocation stroke they will cancel and the material will remain stationary with respect to the conduit 8.

Beyond the downstream end of the screw 16, the material is compressed into a reduced volume as it is forced through the tapered section 14 of the conduit, and into the downstream uniform section 15. This exerts a back-pressure on the material in the upstream section 13 which thus compacts material therein and expresses moisture from the material through the apertures in the conduit. Moisture is similarly expressed from the compacted material in the tapered and downstream sections 14, 15 of the conduit as it is forced forward to be extruded through the discharge nozzle 12 which also causes a back-pressure to be exerted on the material therein to further compact it. Filtrate forced from the compacted material within the conduit through the apertures thereof drains through the annular gap 10 between the outer casing 1 and the conduit towards the filtrate outlet 24.

In a modification of the embodiment illustrated the discharge nozzle 12 may be adjusted to vary the size of the discharge opening and thus the back pressure applied by it to the material within the conduit.

This may be effected by replacing the nozzle shown with similar nozzles of differing size.

Alternatively, adjustable spring-loaded closing devices or mechanical nip-valves may be used.

In further modifications of the present embodiment, the conduit section enclosing the screw may be tapered in one or more places, so as to progressively compact the material before it reaches the downstream end of the screw. In such a case the respective axial sections of the screw will be reduced in diameter to match the internal diameter of the surrounding conduit section.

Alternatively or additionally the end of the conduit 8 downstream of the screw may be tapered in one or more additional places so that its cross-sectional area reduces towards the discharge opening in a number of stages each comprising a tapered section followed by a section of uniform diameter. In some cases however the conduit may terminate substantially at the downstream end of the screw 16, the material then being fed by the reciprocating screw directly into a tapered discharge nozzle or other suitable throttling means for exerting a back pressure on the material in the conduit. Alternatively the conduit may extend downstream of the screw with the same diameter, terminating in a suitably restricted discharge opening.

It will be appreciated that the respective lengths and diameters of the conduit sections may be varied according to differing operating conditions.

The means for providing resistance to flow has been described, in the above embodiment, as restrictions of the diameter of the conduit and reducing or extruding discharge nozzles.

An alternative flow resistance may be provided by maintaining uniform conduit diameter and turning the discharge end upwards into a vertical or angled conduit to provide hydraulic pressure on the material emerging from the screw.

It is envisaged that the invention may also be applied to screw extrusion filter presses having more than one reciprocating single or multi-start helical screw with the conduit and outer casing suitably shaped to accommodate them.

The filter may be operated horizontally as illustrated, or tilted so that the discharge end is higher than the inlet end with the filtrate outlet, or outlets, suitably positioned to permit discharge of the filtrate from within the outer casing 1.

WHAT WE CLAIM IS: 1. A screw press filter for expressing liquid from sludge material, comprising screw means arranged within a conduit to drive sludge through the conduit by a combination of axial and rotary movement, tiie conduit providing egress for liquid through the conduit wall and having a discharge opening for sludge at the downstream end of the conduit, wherein driving means is arranged to rotate the screw means in a direction against the hand of its thread and to reciprocate the screw means axially in synchronism with the rotation so that forward axial movement of the screw means combines with the rotational movement to drive sludge through the conduit while reverse axial movement of the screw means substantially cancels the driving effect of the rotational movement, and including means downstream of the screw means providing resistance to the flow of the sludge material, to tend to compress it in the conduit.

2. A filter according to Claim 1, wherein said means providing resistance to flow comprises a reduction in the cross section of the conduit.

3. A filter according to Claim 1 or Claim 2, wherein said means providing resistance to flow comprises said discharge opening.

4. A filter according to Claim 3, wherein said discharge opening is adjustable to control the back pressure and period of dwell of material in the conduit.

5. A filter according to Claim 2, wherein the section of reduced cross section is of uniform cross section and is preceded by a tapered section providing a smooth transition between the cross sections.

6. A filter according to Claim 2, wherein the section of reduced cross section is of tapered cross section, reducing in a downstream direction.

7. A filter according to Claim 5, wherein said section of uniform cross section is followed by a further tapered section and a further section of uniform cross section.

8. A screw press filter substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. material before it reaches the downstream end of the screw. In such a case the respective axial sections of the screw will be reduced in diameter to match the internal diameter of the surrounding conduit section. Alternatively or additionally the end of the conduit 8 downstream of the screw may be tapered in one or more additional places so that its cross-sectional area reduces towards the discharge opening in a number of stages each comprising a tapered section followed by a section of uniform diameter. In some cases however the conduit may terminate substantially at the downstream end of the screw 16, the material then being fed by the reciprocating screw directly into a tapered discharge nozzle or other suitable throttling means for exerting a back pressure on the material in the conduit. Alternatively the conduit may extend downstream of the screw with the same diameter, terminating in a suitably restricted discharge opening. It will be appreciated that the respective lengths and diameters of the conduit sections may be varied according to differing operating conditions. The means for providing resistance to flow has been described, in the above embodiment, as restrictions of the diameter of the conduit and reducing or extruding discharge nozzles. An alternative flow resistance may be provided by maintaining uniform conduit diameter and turning the discharge end upwards into a vertical or angled conduit to provide hydraulic pressure on the material emerging from the screw. It is envisaged that the invention may also be applied to screw extrusion filter presses having more than one reciprocating single or multi-start helical screw with the conduit and outer casing suitably shaped to accommodate them. The filter may be operated horizontally as illustrated, or tilted so that the discharge end is higher than the inlet end with the filtrate outlet, or outlets, suitably positioned to permit discharge of the filtrate from within the outer casing 1. WHAT WE CLAIM IS:

1. A screw press filter for expressing liquid from sludge material, comprising screw means arranged within a conduit to drive sludge through the conduit by a combination of axial and rotary movement, tiie conduit providing egress for liquid through the conduit wall and having a discharge opening for sludge at the downstream end of the conduit, wherein driving means is arranged to rotate the screw means in a direction against the hand of its thread and to reciprocate the screw means axially in synchronism with the rotation so that forward axial movement of the screw means combines with the rotational movement to drive sludge through the conduit while reverse axial movement of the screw means substantially cancels the driving effect of the rotational movement, and including means downstream of the screw means providing resistance to the flow of the sludge material, to tend to compress it in the conduit.