GB2077632A - Separation of mixtures of solids and liquids - Google Patents

Abstract

Oil palm sludge effluent is fed into a drum (6) which is continuously rotated about its horizontal axis. Solids collect on the imperforate cylindrical drum wall and liquids escape through screened apertures (26, 32) in the drum end walls, one (10) of which is centrally apertured for introduction of the effluent and removal of the solids, the other (8) being connected to a shaft (12) by which the drum is rotated. When liquid in the vessel in which the drum is contained reaches a predetermined level, electric control equipment effects movement of a scraper blade (58) towards the cylindrical wall to scoop the solids into a hopper which guides them out of the drum, and the effluent supply is stopped. When the blade reaches an end position, close to the drum wall, it is returned and the effluent supply is resumed. <IMAGE>

Description

SPECIFICATION Separation of mixtures of solids and liquids The invention relates to the separation of mixtures of liquids and solids.

The invention is applicable in particular to the separation of wet solid waste from colloidal oil palm sludge effluent, although it can be applied generally to the separation of solids/liquid mixtures. After the treatment of fresh dil palm fruit bunches by steaming to above 100"C, they are crushed to extract oil palm and a sludge effluent remains which contains solid waste coated with a film of palm oil, water, and plam oil itself. The effluent is thus starchy and is colloidal in nature. Disposal of this sludge effluent, of which an oil palm mill of 20 tons capacity will produce about 100 tons in working day, persents serious problems, in particular because of its high Biochemical Oxygen Demand (BOD) which averages 20,000 parts per million (ppm). Legislative standards in some countries require a BOD of less than 50 ppm.In order to reduce pollution it is therefore desirable to separate the effluent into the solid wastes, which can be dried and converted into animal feed, from the liquid. This can be further treated to recover residual crude oil palm and dissolved solid waste, and can then be readily further treated for reduction of its BOD content to an acceptable level.

The invention is thus concerned with the provision of a method of and an apparatus for the convenient separation of liquid/solids mixtures, particuiarly, but not exclusively, the separation of oil palm sludge effluent.

The invention accordingly provides an apparatus for the separation of a mixture of solids and liquids, the apparatus comprising a drum having the axis thereof extending substantially horizontally, drive means for rotating the drum about the axis thereof, inlet means for the introduction of a liquid/solid mixture into the drum whereby the mixture is subjected to centrifugal force by the rotation of the drum, the drum having a side wall arranged for collection thereon of the solids of the mixture and at least one end wall perforated for the escape of the liquid of the mixture, and discharge means for removing the solids from the side wall and conveying them outwardly of the drum.

The invention also provides a method of separating a solid/liquid mixture, the method comprising the steps of rotating about the axis thereof a drum containing the mixture, the drum axis being substantially horizontal, to cause the solids to collect on the drum side wall and the liquid to escape from the drum axially thereof, and removing the collected solids from the side wall for discharge from the drum.

The drum side wall is preferably an imperforate circular cylindrical wall, with both end walls provided with apertures arranged to permit escape of liquids but to retain solids of a desired particle size. The apertures are conveniently relatively large apertures covered by a gauze of suitable mesh size. To prevent obstruction of the apertures by the solids, steam under pressure can be directed against the apertures continuously during operation. One drum end wall can be annular, to permit introduction of the mixture and discharge of the solids, and the drum can be rotatably supported by the other end wall.

According to a further feature of the invention the solids collected on the cylindrical drum wall are removed therefrom by a scraper blade positioned adjacent the wall and associated with discharge guide means for conveying the solids outwardly of the drum. The discharge guide means can comprise a hopper having a floor inclined to the horizontal to promote discharge of the solids, the blade cooperating with one wall of the hopper.

According to a further feature of the invention, the scraper blade is arranged to be movable between positions respectively spaced from and in operative relation to the drum side wall. Whilst in the former position, a layer of solids is built up on the side wall, to be removed when the blade moves to its operative position. This blade movement can be effected in a predetermined cycle or in response to a sensed condition, for example the thickness of the layer of solids or of a liquid layer carried thereon. The blade movement to the operative position can be coordinated with-an interruption of the supply to the drum interior of the mixture to be separated. After a predetermined time interval, which can correspond to the time taken by the knive to return to the inoperative position, the supply of the mixture can be resumed and the cycle repeated.The drum rotation can be continuous through this cyclic operation.

The invention is further described below, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic side view of a separator apparatus embodying the invention; Figure 2 is a front view of the apparatus; Figures 3 and 4 are respectively front and rear view of end plates of a drum included in the apparatus, with associated parts; Figure 5 is a perspective view of a holder for the drum; Figure 6 is a perspective view of a scraper blade received in the drum; Figure 7 is a schematic perspective view into the interior of the drum, and of associated parts in exploded relationship; Figure 8 is a perspective view of the scraper blade and an associated hopper; and Figure 9 is an electric circuit diagram of control equipment associated with the apparatus.

The illustrated separator apparatus is intended for the separation of oil palm sludge effluent. It comprises a support frame 2 of metal girders supporting a two part drum 4 at one end and a support table 5 at the other. A circular cylindrical separator drum 6 is mounted within the drum cover with appropriate spacing from the drum cover wall, and with its axis extending generally horizontally.

The drum 6, which may be of polished mild steel, has an imperforate side wall and is closed at one end by an apertured plate 8 of similar material, whilst the other end is partidily closed by an apertured annular end plate 10. The drum 6 is supported for rotation about its axis on a drive shaft 12 connected to the end closure plate 8 by means of a drum holder 14 splined to the shaft, and bolted to the plate by bolts 1 6. The drum cover 4 has a base formed as a flat hopper, from which a liquid discharge conduit 7 extends to a suitable receptacle.

The drive shaft 1 2 extends through a seal 1 8 in a rear wall of the drum cover and is received in spaced ball bearings 20 mounted on the support table 5. The shaft 12 rotated by a three-phase electric motor 22 which is also mounted on the support table 5 and which drives the shaft by a belt and pulley system of which pulleys 24 are shown in Fig.

2.

Both of the drum end plates 8, 10 are provided with a series of equi-angularly spaced circular apertures. As shown, the end plate 8 has ten of these apertures 26. In an apparatus suitable for treating about 5 tons of sludge effluent per hour, the drum will have an external diameter of about 110 cm, and the apertures 26 can be about 1 5 cm in diameter; they may be spaced from the inner wall of the drum by about 13 mm. The cylindrical wall of the drum is about 1 3 mm.

and thicknesses of the walls 8, 10 are respectively about 20 mm. and 13 mm. Over the apertures 26, stainless steel gauzes 28 of 40 mesh are secured by rings 30.

The annular end plate 10 of the drum likewise has ten circular holes 32 equi-angularly spaced around it; these holes may be about 10 cm. in diameter. A stainless steel gauze 34 of 40 mesh is secured by a ring 36 over each of these apertures, which are again positioned about 1 3 mm, from the inner surface of the drum. In addition, overflow holes 38 of small diameter are provided in the annular end plate 10. As shown, there are thirty of these holes 38, each of which is about 25 mm, in diameter, and they are grouped into clusters of three equi-angularly spaced around the end plate between the apertures 32.

Projecting into the drum through the central aperture of the end plate 10 is an inlet pipe 40 for the colloidal oil palm sludge effluent.

This pipe 40 is sealed through the front wall 42 of the drum cover 4 at 44 and extends into the drum 6 in the axial direction, at a position towards the base of the drum and adjacent to the inner edge of the drum end plate 10. The pipe 40 has a closed end and a longitudinal slit 46 in its wall through which the incoming sludge effluent passes from the pipe into the drum interior. Outwardly of the apparatus, the pipe 40 is connected to a source of the sludge effluent through an elec- trically driven pump 41.

A steam supply pipe 48 extends downwardly at the top of the apparatus, from a source of steam under pressure and has a generally horizontal portion extending through the front cover wall 42 into the upper part of the drum interior. This portion joins a downwardly extending portion which leads into a generally horizontally extending manifold 50 providing a nozzle 52 at each end through which a steam jet is applied to the two drum end plates 8, 10 at the vicinity of the screened apertures therein. Steam can escape from the top of the cover 4 through an outlet 51.

Also extending through the cover front wall 42 into the drum interior is a horizontal shaft 54 having secured thereto by means of transverse arms 56 a a rigid scraper blade 58 of rectangular shape. The blade 58 can turn with the shaft 54 about the shaft axis between two end positions, in one of which the blade free edge is spaced by some 25 cm. from the cylindrical wall of the drum. In the other end position, the free edge of the blade 58 is spaced from the cylindrical wall by only about 1.5 mm. The blade 58 extends axially so as to be similarly spaced from the end plates 8, 10.

Fixedly received within the drum 6 for cooperation with the blade 58 is a hopper. The hopper comprises walls 60 and 62 extending upwardly from a trough-shaped curved floor 64. The wall 60 is generally vertical and is positioned about centrally of the drum, the other wall 62 being inclined towards the cylindrical wall to underlie the shaft 54 and thereby from a continuation of the blade 58.

A segmental end wall 66 provided with a slot for reception of the shaft 54 joins the walls 60, 62 at the front end of the drum, and at the upper end of the wall 60, a lip 68 projects generally horizontally forwardly. The floor 64 of the hopper is inclined from the drum end plate 8 downwardly to the cover front wall 42 on which the hopper is supported by means of a pipe 70 which generally continues the shape of the curved floor 64.

The pipe 70 extends through the cover wall 42 and then extends downwardly to a discharge outlet for solids scraped by the blade 50 from the drum wall and collected in the hopper.

To enable the blade shaft 54 to rotate between its end positions, the shaft projects outwardly through a seal in the cover end wall 42 and is then received through bearings 72 carried by a pillar 74 extending upwardly from the support frame 2 of the apparatus.

Below the bearings 72, the pillar 74 supports an electric motor 76, which drives a reduction gear device 78 through a belt and pulley drive 79. The gear device 78 has a vertically extending output shaft which drives through a further belt and pulley drive 81 a tapped collar 80, restrained against axial movement, through which extends a threaded spindle 82.

The spindle 82 is held against rotation by means of a linkage 84 connected between the upper end of the shaft and the free end of a control arm 86 projecting laterally from the end of the blade shaft 54. Depending on the direction of rotation of the motor 76, the threaded spindle 82 will be raised or lowered by rotation of the tapped collar 80 and the shaft 54 will be rotated accordingly. Limit switches 88, 90 are positioned so as to be actuated by the control arm 86 in positions thereof corresponding to the end positions of the blade 58. The electric motor 76 is controlled by these switches by the circuitry shown in Fig. 9.

Also received within the drum is a liquid level sensor 92 which is carried by a bracket 94 projecting from the cover front wall 42.

The water level sensor 92 is arranged to provide an electric signal when contacted by the liquid layer carried on the layer of solids deposited on the drum cylindrical wall.

The operation of the apparatus is electrically controlled by the circuitry shown in Fig. 9 and is as follows.

To commence operation, a control switch 100 is closed so as to cause the three-phase electric motor 22 to rotate the drum 6, for example at 660 revolution per minute. This motor 22 operates continuously during operation of the apparatus. At this time, a water level relay 105 and a time delay relay 106 are turned on, and the latter activates the pump motor 41 after an adjustable preset time delay to allow the drum 6 to reach running conditions. The sludge effluent is then pumped into the drum through the inlet pipe 40. At this time, the scraper blade control arm 86 is in engagement with the upper limit switch 90, the blade 58 being spaced away from the cylindrical drum wall. Steam is supplied to the drum interior through the steam pipe 48.

During this initial part ot the operating cycle, the rotation of the drum 6 causes the solid contents of the sludge effluent to be deposited on the inner surface of the cylindrical wall by the centrifugal forces generated by the drum rotation. Liquid including crude oil and very tiny solid particles which have passed through the gauzes 28, 34 is impelled through the screened apertures 26, 32 at the drum end plates 8, 10, and this liquid falls to the base of the drum cover 4 and flows out through the conduit 7. As the wet solid waste accumulates in thickness in the drum, the thickness of the liquid layer carried on the solid waste layer within the drum increases radially until the level sensor 92 is actuated.

When this occurs, the current to the pump motor 41 is cut off and the flow of sludge effluent into the drum 6 ceases. At this time also a time delay relay 102 is switched on to allow a selectively adjustable peribd of a few seconds during which nothing further happens, escept that the drum rotation squeezes out further liquid from the wet solid waste. At the end of this time delay, the relay 102 passes current to a contactor 104 which in turn passes current to the upper limit switch 90. Switch 90 passes current to a contactor 108 to activate the motor 76 to move the blade 58 progressively to its operative position. The accumulated wet solid waste deposited on the cylindrical drum wall is thereby scraped off into the hopper and discharges through the outlet pipe 70.

After removal of the wet solid waste, the control arm 86 comes into contact with the lower limit switch 88, which passes current to a contactor to cause the motor 76 to turn in the opposite direction so as to bring the blade 50 back to its inoperative position. In this position, the arm 86 engages the upper limit switch 90 to cut off the current to the motor 76 to end movement of the blade. The contactor 104 passes current in one direction only, that is, to the upper limit switch 90 which passes current to the contactor 108, but current cannot travel from the contactor 108 back to the contactor 104, as is necessary to prevent constant motion of the blade 58. As soon as the blade 58 is brought back to its inoperative position, the relays 105 and 106 are switched on again. The whole cycle of operation, which commences with the introduction of sludge into the drum, is then repeated.

It will be appreciated that the separator apparatus specifically described can be modified in various ways, for example as regards its size and shape, to better suit the treatment of different mixtures, and to have a different throughput, without thereby departing from -the scope of the invention.

Claims (1)

1. An apparatus for the separation of a mixture of solids and liquids, the apparatus comprising a drum having the axis thereof extending substantially horizontally, drive means for rotating the drum about the axis, inlet means for the introduction of a liquid/solid mixture into the drum whereby the mixture is subjected to centrifugal force by the rotation of the drum, the drum having a side wall arranged for collection thereon of the solids of the mixture and at least one end wall perfo rated for the escape of the liquid of the mixture, and discharge means for removing the solids from the side wall and conveying them outwardly of the drum.

2. An apparatus as claimed in claim 1 wherein the side wall is an imperforate circular cylindrical wall.

3. An apparatus as claimed in claim 1 or 2 wherein the drum has an end wall with a central aperture for introduction of a liquid/ sowed mixture to be separated and for removal of separated solids, and a drive shaft extending coaxially from the other end wall.

4. An apparatus as claimed in claim 1, 2 or 3 having a steam supply system applying a steam jet to the perforations in the or each end wall from within the drum.

5. An apparatus as claimed in claim 1, 2, 3 or 4 wherein the discharge means comprises a scraper blade movable between an operative position in adjacency to the drum side wall for removing solids deposited thereon and an inoperative position spaced from the drum side wall.

6. An apparatus as claimed in claim 5 having means for moving the scraper blade to the operative position in response to a predetermined condition.

7. An apparatus as claimed in claim 6 wherein the predetermined condition comprises the sensing by a level sensor of the thickness of a liquid layer overlaying the solids deposited on the drum side wall.

8. An apparatus as claimed in claim 6 or 7 having means for moving the scraper blade back to the inoperative position after a predetermined delay.

9. An apparatus as claimed in claim 6, 7 or 8 having means for interrupting the introduction of the mixture into the drum as long as the scraper blade is out of the inoperative position.

10. An apparatus as claimed in any one of claims 5 to 10 wherein the discharge means comprises a guide device for receiving solids scraped from the drum side wall by the scraper blade and for guiding the solids outwardly from the drum.

11. An apparatus as claimed in claim 10 wherein the guide device comprises a hopper having floor inclined downwardly and outwardly of the drum.

t2. An apparatus substantially as herein described with reference to the accompanying drawings.

1 3. A method of separating a solid/liquid mixture, the method comprising the steps of rotating about the axis thereof a drum containing the mixture, the drum axis being substantially horizontal, to cause the solids to collect on the drum side wall and the liquid to escape from the drum axially thereof, and removing the collected solids from the side wall for discharge from the drum.

14 A method as claimed in claim 13 wherein the collected solids removed from the drum side wall intermittently.

15. A method as claimed in claim 14 wherein the supply of the mixture to the drum is interrupted during the removal of the solids.

16. A method as claimed in claim 1 5 wherein the removal of the solids is commenced with a predetermined delay after interruption of the supply of the mixture to the drum, to allow further liquid to be withdrawn from the collected solids.

17. A method as claimed in claim 14, 15; or 16 wherein the removal of the solids from the cylindrical wall is commenced when a liquid layer carried on the collected solids on the drum side wall reaches a predetermined depth.

18. A method as claimed in claim 14, 15, 16 or 17 wherein the removal of the solids is effected by moving a scraper towards the drum side wall from an inoperative position.

19. A method as claimed in claim 1 8 wherein the supply of the mixture to the drum is resumed in response to the movement of the scraper to the inoperative position.

20. A method as claimed in any one of claims 1 3 to 18 wherein the mixture is a colloidal mixture.

21. A method as claimed in claim 20 wherein the mixture is a starchy oily colloidal mixture.

22. A method as claimed in claim 21 wherein the mixture comprises oil palm sludge effluent.

23. A method of separating a mixture of solids and liquid substantially as herein described.