GB2390986A

GB2390986A - Liquid extracting apparatus

Info

Publication number: GB2390986A
Application number: GB0214490A
Authority: GB
Inventors: Tom Craggs
Original assignee: C D BISSELL ENGINEERING Ltd
Current assignee: C D BISSELL ENGINEERING Ltd
Priority date: 2002-06-24
Filing date: 2002-06-24
Publication date: 2004-01-28
Anticipated expiration: 2022-06-24
Also published as: GB2390986B; GB0214490D0

Abstract

Apparatus for extracting liquid from a sludge comprises a first zone 2 having a portion of decreasing cross sectional area, a second zone 4 downstream of the first zone where the sludge is exposed to a reduced pressure to enhance drying of the sludge and means 28 for propelling the sludge trough the zones. In use, sludge is introduced trough inlet 11 into the first zone which may be a drum 2 having a cylindrical 12 and a frustoconical 14 portion. Preferably a filter 20 of wire, plastic, ceramic or other conventional material lines an inner surface of the drum 2 and as the sludge passes through, by rotation of the means 28 which may be a spiral or screw-shaped blade, water contained within the sludge passes through the filter 20 and then to drains 26. Sludge passed to the second zone 4 is exposed to a reduced pressure preferably by means of a vacuum pump and may be heated by steam or radiated heat. Preferably thickened sludge forms a cake and is extruded from an opening 40.

Description

' D5S,TION

SLUDGE TRE8TMF.NT

The present invention relates to a method and apparatus for extracting liquid from a sludge.

5 By-products and waste products from many industrial processes, including water treatment and particularly sewage treatment, commonly take the form of sludges or slurries containing solid and liquid components. It is generally desirable to separate 10 solids from liquids in order to reuse or dispose of the components safely and efficiently. In doing so, various factors need to be considered. The process must in many cases be carried out on a large scale, and may involve hazardous gases and/or solvents, to which 15 exposure must be avoided. For example, sewage may generate gases such as hydrogen sulphide and methane.

Methods currently used for dewatering sewage sludge include centrifuging, filtering using a filter press or sand filter and belt pressing. However, all 20 of these processes suffer drawbacks, particularly in failing to extract a sufficient amount of liquid from the solid component. A less than satisfactory level of extraction results in large amounts of semisolid waste, which is costly to handle and to transport for 25 recycling or disposal. In cases where the liquid is a toxic or flammable solvent, this poses safety and environmental concerns.

in It is an object of the present invention to provide an apparatus and method of separating a liquid from a solid, which addresses one or more of the abovementioned problems.

5 For the purpose of this specification, the term

"sludge" is to be understood to mean a mixture of liquid and solid in any proportion. It may also refer to a combination of immiscible liquids, for example oil and water, such as is encountered in an oil slick.

10 According to a first aspect of the invention there is provided an apparatus for extracting liquid from a sludge, comprising: a plurality of communicating zones for receiving the sludge; 15 means for propelling the sludge though the zones successively; wherein the zones are of decreasing cross sectional area, and wherein there is provided a filter means for extracting liquid from the sludge as it is 20 propelled through the zones.

Preferably each zone is defined as an enclosed chamber in communication with at least one other zone.

Preferably, one or more of the zones is frustoconical. Also preferably, the filter means are 25 located along a wall of at least one of the enclosed zones. More preferably, the filter means are located along a frustoconical wall.

Y Preferably, the means for propelling the sludge comprises at least one rotatably mounted blade. More preferably, the blade or blades are screwshaped.

Preferably, the blade is mounted on a rotatable shaft 5 which is axially disposed within one or more of the zones. More preferably the shaft passes axially through the successive zones.

Preferably, the apparatus includes a first zone having a frustoconical portion, and a screw-shaped lo blade disposed about an axial rotatable shaft, for propelling the sludge through the zone. Yet more preferably, the frustoconical portion is provided with walls of filter membrane for allowing emergent liquid to drain therethrough. More preferably still, the 15 apparatus includes pumping means for enhancing drainage of the liquid. Alternatively, the liquid may be allowed to drain freely under gravity. The filter membrane wall may be axially rotatable to allow the area used for filtering to be renewed periodically, 20 thus prolonging the life of the membrane and avoiding the need for frequent replacement.

Preferably, the screw-shaped blade is provided with brushes along its edge. Alternatively it may be provided with squeegees.

25 Downstream of the first zone there is preferably a hot-box zone wherein the sludge is exposed to increased temperature and/or reduced pressure to enhance drying

/ of the sludge. Preferably there is located a baffle plate having perforations via which the sludge is extruded to enter the hot-box. Also preferably, the hot box includes means for slicing the emergent sludge, 5 preferably perpendicularly to the direction of movement of the sludge, to produce pellets.

Preferably, there is a peripheral porous gasket at the interface between each successive zone for allowing drainage of emergent liquid as the sludge is propelled lo through the zones.

According to a second aspect of the invention there is provided a method of extracting liquid from a sludge, comprising the steps of: introducing the sludge into a first zone of 15 gradually decreasing cross-sectional area; propelling the sludge in a forwards direction through the zone to force liquid to emerge from the sludge, and draining the excess liquid via a permeable 20 membrane. Preferably the method includes the further step of propelling the resultant sludge through a second zone of reduced cross-sectional area to force further liquid from the sludge.

25 Preferably the method includes the further step of exposing the resultant sludge to heat and/or a reduced pressure environment to enhance removal of liquid and

the release of vapours. Further preferably, the sludge is extruded to increase its surface area prior to exposure to heat and/or reduced pressure. The extrusion of the sludge can assist in creating a closed 5 chamber to allow pressure reduction therein, despite flow of sludge through the chamber. Preferably, the sludge is extruded via a baffle plate having a plurality of extrusion apertures. Preferably, the extruded sludge is then chopped into pellets to 10 maximize its surface area during its exposure to heat and/or reduced pressure.

According to a third aspect of the invention, there is provided the use of the above described apparatus for the extraction of a liquid from a liquid 15 solid mixture.

The apparatus and method of the invention offers several advantages over known sludge treatment systems.

The present method is able to achieve a treated product a high proportion of solids, depending on the type of 20 sludge. This value is significantly higher than that of known methods. The volume and weight of end-product cake is thus reduced, which in turn reduces the cost of transporting and disposal. Also, a greater proportion of the liquid is recovered for reuse or disposal.

25 Unlike existing sludge treatment systems, the present apparatus and method may also be used to separate immiscible liquids. For example, the present

N invention is useful in the clean up of oil-spills. An oil-water mixture can be introduced into the first zone and propelled through the successive zones. The water component will form a distinct lower layer and will 5 drain off through the filter means under gravity or due to suction, while the upper oil layer will be propelled through the successive zones at a speed sufficient to prevent drainage. Additionally/alternatively the filter means in such an embodiment may be such as to 0 pass one liquid and not the other - e.g. to be permeable to water but not oil.

A further advantage of the present invention is that the sludge may be entirely contained during and after processing, thus preventing release of toxic or 15 hazardous materials into the surroundings, and preventing exposure of an operator to the sludge, the filtrate or any vapours released.

The present invention has applications in a wide range of fields, which include but are not limited to

20 the treatment of sewage sludge, by-products and waste from industrial processes, and the cleaning up of oil spillages. According to a fourth aspect of the present invention there is an apparatus for extracting liquid 25 from a sludge, comprising at least one chamber having an inlet, an outlet and means for propelling the sludge along a travel direction from the inlet to the outlet,

wherein cross-sectional area of the chamber diminishes progressively along the travel direction and filter means are provided for releasing fluid from the sludge as it is propelled through the chamber.

5 The invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a view along a radial direction of an apparatus for treating a sludge according to a specific 10 embodiment of the invention, some parts of the apparatus being cut-away to show interior components.

Figure 2 is a cross section along the line A-A in Fig. 1 of a baffle plate of the apparatus shown in Fig. 1. 15 Figure 3 is a schematic diagram of an operating system for use in accordance with the apparatus of Fig. Figure 4 is an enlarged section through a wall of a wet box drum of the same apparatus.

20 Referring firstly to Fig. 1, a sludge-separating apparatus 1 comprises a wet box drum 2 and a series of further zones 3, 4, 5, 6 and 7 of decreasing cross sectional area, through which the sludge is conveyed successively. An inlet port 11 allows sludge to be 25 introduced into the wet box drum. A rotatable shaft 10 is axially disposed through the wet box drum 2 and the zones 3, 4, 5, 6 and 7. The wet box drum 2 comprises a

cylindrical portion 12 and a frustoconically shaped cone portion 14 which are defined by outer circumferential walls 16 and a back plate 18 both comprising three layers as seen in Fig. 4.

5 The inner surface layer of the walls 16 and back plate 18 consists of a filter membrane 20 which may be of any conventional material, e.g. wire, cloth, porous plastic or ceramic. Adjacent the filter membrane 20 is a membrane backing layer 22, which is in this 10 embodiment shaped to provide a plurality of channels 21. The membrane backing layer serves to promote and speed filtrate away to drain. Thirdly, an impermeable outer casing 24, typically of stainless steel, protects the filter membrane 20 and backing layer 22 and retains 15 filtered liquid, guiding it to drains 26. The drains 26 are located at intervals so as to couple with the threelayer walls 16 and back plate 18 providing an outlet through the outer casing 24 and thus allowing the filtrate to drain away. The drains 26 may be 20 provided with a pump or may be free-draining. Although much of the extracted fluid drains downwards through the lower region of the walls 16, the entire circumference of the walls are of filter membrane material. The wet box drum is rotatable so that the 25 region of membrane on the underside can be replaced simply by rotating the drum. This helps to prevent blockages and to prolong the life of the filter.

The portion of the axial shaft 10 within the wet box drum 2 carries a spiral or screw-shaped blade 28 which acts as an auger and propels sludge through the drum 2 upon rotation of the shaft 10. The outer edge 5 of the blade 28 is provided with brushes 30 which sweep across the surface of the walls 16. In alternative embodiments, the brushes may be replaced by squeegees.

Alternatively, brushes or squeegees need not be present. 10 As an alternative to the illustrated embodiment, the blade 28 may in some cases be fixed relative to the wet box drum 2 with the drum itself being rotatably mounted. Drive to the drum in such an embodiment could conveniently be provided by means of a large cog around 15 the drum's circumference, driven through a smaller pinion upon an engine or motor.

The second zone 3 is in communication with the wet box drum 2 so that the processed sludge emerging from the drum 2 is forced into the zone 3. The interface 20 between zones 2 and 3 is defined by a further section of spiral blade 32 which propels the sludge further in a forward direction and into the zone 4. At the interface, the zones 2 and 3 are connected by a body joint ring 38, this joint having a porous gasket 34 via 25 which any emergent liquid may drain to the drain 26.

Zones 3 and 4 are separated by a baffle plate 32 containing apertures 33 allowing passage of sludge

between the two zones by extrusion, as shown in Fig. 2.

The size and number of apertures 33 in the baffle plate 32 will depend directly on the nature of the sludge being processed. At the periphery of the baffle plate 5 32 is provided a porous gasket 34 which allows extracted liquid to escape to drain via drain 26.

Similarly, porous gaskets are located at the other main flanges in the apparatus.

Zone is a "hot box", wherein heat energy is lo generated by a heater (not shown in Fig. 1). The heater may provide heat in the form of steam, electrical resistance heat or radiated heat. The currently preferred arrangement uses infra red lamps arranged in an upper region of the hot box to radiate 15 directly onto the material being processed.

Additionally, the pressure in the hot box 4 is reduced by means of a vacuum pump (not shown in Fig. 1) connected to the hot box 4 via an outlet duct 34. In this way vapour pressure in the hot box is reduced and 20 evaporation of liquid from the sludge is promoted. In tests it has been observed that sludge extruded through the baffle plate may rupture on entry to the hot box due to rapid decompression. Closure of the hot box, needed to sustain a partial vacuum therein, is provided 25 simply by virtue of the sludge at its inlet and outlet.

Nonetheless in tests a vacuum of -0.7 bar has been created. The baffle plate 32 assists in providing the

^ required meal.

The axial shaft 10 bears a pair of spaced-apart blades 36 for slicing the emergent sludge into pellets as it progresses through the hot box.

5 The subsequent zones 5, 6 and 7 are frustoconical, each having a successively decreasing cross-sectional area. As with zones 3 and 4, at the beginning of each zone, there is located a body joint ring 38 having a porous gasket 34. A segment of spiral blade 32 is 10 disposed on the shaft 10 just upstream of each of the body joint rings 38 to force liquid from the sludge, which can then be drained via the porous gasket 32 at each stage.

Note that in each of the zones 2, 3, 4, 5, 6 and 7 15 a blade 28, 32 is arranged on short distance upstream of each of the porous gaskets 34. The repeated pressure and subsequent relaxation created by passage of the blades assists in de-watering in these regions and the liquid thereby released is provided with a 20 short route to drain through the gaskets.

The final zone 7 terminates in an opening 40 from which the thickened sludge, now in the form of a cake, is discharged for disposal or reuse.

A method of processing a sludge using the above 25 described apparatus will now be described in detail, with reference to Figs. 1 and 2.

A pre-conditioned sludge in the form of a

liquid/solid mix is fed into the wet box drum 2 via the inlet port 11. Generally, preconditioning is carried out by any known process, e.g. by adding a flocculating agent. Within the wet box drum 2 the liquid phase of 5 the mixture percolates through the filter membrane 20 . and is channeled to the drain 26 by gravity. If desired, a suction pump may be used to enhance draining of the liquid at each of the stages described. The thickened sludge is propelled axially forwards over the 10 filter membrane 20, always having liquid drawn from it, by the outer edge of the rotating spiral blade 28. The brushes 30 help to sweep the solid over the surface of the membrane 20, thus preventing the solids from being driven into the membrane. This helps to prolong the 5 life of the filter membrane. Upon reaching the end of the blade 28, the sludge becomes stationary and is only advanced by further thick sludge displacing it.

As the sludge is moved forwards, it is propelled into the cone portion 14 of the wet box drum 2. The 20 sludge in contact with a lower portion of the wall 16 is forced upwards along the rising gradient of the wall 16, allowing further liquid to be removed via the filter membrane 20. The angle between the axial shaft 10 and the frustoconical wall 16 dictates the release 25 rate of the liquid from the sludge. The angle of incline of the wall 16 must thus be selected carefully when constructing the plant. If the angle is too

steep, the sludge will be driven into the membrane, whilst an angle which is too shallow will not promote an adequate rate of liquid release. The angle must therefore be matched against empirical sludge data for 5 the type of sludge to be processed.

The progressively diminishing cross-sectional area of the wet box drum 2, and of subsequent zones, not only applies pressure to the sludge but also matches its diminishing volume as liquid is extracted.

10 Near the truncated end of the cone portion 14 there is a break in the spiral blade 28. This allows the sludge, which by now has a thick, claylike consistency, to rest and for any residual emergent liquid to drain as previously described.

15 The sludge increases in density and is pushed from the cone portion 14 and into the adjacent medium pressure zone 3. In this zone the thickened sludge is propelled axially forwards by the blade 32. The gradually decreasing cross-section of zone 3, together 20 with the movement of the blade 32 squeezes the sludge and forces more liquid out. The liquid drains near to the body joint ring 38, where it escapes through the porous gasket 34.

At the end of the medium pressure zone 3, the 25 sludge, now thickened to the form of a cake, is pressed against the baffle plate 32. This plate provides back pressure to ensure effective liquid release in the

J medium pressure zone 3, and to form a continually replacing seal to the hot box 4. The cake is extruded through the apertures 33 of the baffle plate, thus increasing in surface area upon entry into the hot box 5 4. The aforementioned rupturing of the extruded cake due to reduced pressure and/or increased heat in the hot box 4 also increases cake surface area.

Rotation of the blades 36 slices the extruded cake into smaller pellets, thus further increasing the 10 surface area. The cake pellets are heated under reduced pressure as they progress through the hot box.

This has the effect of rupturing the pellets due to the expansion of vapours within the cake. At this stage, the vapours are released and are drawn away by vacuum 15 via outlet duct 34 and are then introduced into the liquid removal system so that all of the liquid removed is consolidated for processing or disposal. Thus all vapours and odours are contained and are not discharged into the environment. A further effect of heating the 20 pellets is that they may be pasteurized.

The rotating blade 32 forces the cake into the next zone 5, which decreases in cross-sectional area.

The cake is thus forced together and reconstituted under pressure. In subsequent zones 6 and 7, the 25 pressure is further increased as a result of the decrease in cross-section, and any additional excess fluid squeezed from the cake is forced to drain via the

jr porous gaskets 34 located at the body joint rings 38.

The resultant cake is extruded from the end of the apparatus via opening 40 into a skip or conveyor for removal. At the opening 40 a passive infrared sensor 5 (PIR) is positioned (not shown in Fig. I) so that it sees the expelled cake and triggers a wire cutter to chop the cake into bricks or pellets of predetermined size to facilitate convenient further processing or disposal. 10 Fig. 3 shows schematically an operating system for carrying out the sludge treatment process. A typical sequence of operations in the method is described as follows: (1) Start-up sequence 15 Firstly, the main drive motor M.1 is activated and valves V9 and V10 are opened. Motor M.1 controls rotation of the axial shaft 10. After a delay of some 10 seconds, the sludge feed pump motor M.2 is started to deliver conditioned sludge to the first stage of the 20 machine. After a further delay of 5 seconds, the vacuum filtrate pump motor M.3 is started to commence suction. After a further 20 seconds the vacuum pump motor M.4 starts, and 30 seconds later the heaters are switched on. This completes the plant start-up 25 sequence.

- VAhYE POSIZIQ_0N START Ep COME VALVE_MBE OPUS CLoE Set on Commissioning V.1. + V.2. +

5 V.3. +

V.4. +

V.5. +

V.6. +

V.7. +

10 V.8. +

V.9. +

V.10. +

The valve positions shown are the normal running 15 positions of the valves during operation of the equipment. (2) Normal operation Prior to entering the wet box drum 2, the sludge 20 passes via a flowmeter 106 and an inline mixer 107.

Passage of the sludge through the apparatus is described above with reference to Fig. 1.

(3) Backwashing 25 During normal running, the liquid level within the wet box drum 2 rises as the membrane starts to blind.

This problem is overcome by backwashing the filter.

The internal level of liquid is monitored by a level indicator 101, which is programmed to signal when a 30 pre-set maximum level is reached. The signal sets in operation the backwash sequence.

The initiating signal from the level indicator 10

J stops the sludge feed pump motor M.2. The filtrate drain pump motor M.3 and the main drive motor M.1 continue running for a further 20 seconds before they are also stopped. After a further 5 seconds the valves 5 change over to their backwash positions and the vacuum pump motor M.4 stops. In Fig. 3 backwash flow is shown by arrows in broken lines whereas flow during normal operation is shown by the solid arrows.

10 z _ COMMENTS Vet OpEN CLQS Set on Commissioning V.1. + V.2. +

15 V.3 +

V.4. +

V.5. +

V.6. +

V.7. +

20 V.8. +

V.9. +

V.lO. + _ 25 A 5 second dwell is allowed to ensure that the valves have completed their changeover, then the vacuum pump motor M.4 is started. After a 2 second delay the filtrate drain pump motor M. 3 starts. The motors M.3 and M. 4 run for at least 2 minutes to effect 30 backwashing, after which period the motor M. 3 shuts down, followed 5 seconds later by the vacuum pump motor M. 4. The valves are then reset to their normal operating positions and start-up of the system as previously described is automatically initiated.

age-/' (4) cake discharge port At the cake discharge port a PIR (passive infra red sensor) is positioned so that it sees the cake and triggers the solenoid operated cutter 102 to chop the 5 cake into pellets or bricks of predetermined size which are then discharged into skip 103. The pellets are in fact toroidal due to the shape ofthe nozzle through which they are extruded. Any convenient cutting device could of course be used in place of the wire cutter.

(5) flocculation / coagulation The level indicator 101 is pre-programmed to respond to a predetermined low level as well as a maximum upper level. The level indicator must indicate 15 above the low-level in order for the system to function. In the event that the indicator 101 shows a level at or below the low level, the valves V.9 and V.lo will close and the filter plant will shut down until the level is replenished.

While the above described apparatus and method illustrate preferred features of the invention, variations and modifications are envisaged without departing from the scope of the invention as claimed.

25 For example the various zones illustrated need not be co-axial. The wet box drum 2 could be arranged with its axis vertical on its inlet of an upper region, subsequent zones being oriented as shown in Fig. 1 30 G:\CBIENT\4o5-4o9\CAFl\4o764S\GB\MASTER.

Claims

y ChAIMS 1. An apparatus for extracting liquid from a sludge, comprising:

a plurality of communicating zones for receiving 5 the sludge, including a first zone having a portion of decreasing cross-sectional area, and a second zone downstream of the first zone wherein the sludge is exposed to reduced pressure to enhance drying of the sludge; and 10 means for propelling the sludge though the zones successively. 2. An apparatus according to claim l further comprising a filter means for extracting liquid from the sludge as it is propelled through the zones.

15 3. An apparatus according to claim 1 or 2 wherein one or more of the zones has a frustoconical portion.

4. An apparatus according to claim 2 or 3 wherein the filter means are located along a wall of at least one of the zones.

20 5. An apparatus according to claim wherein the filter means are located along a frustoconical wall.

6. An apparatus according to any one of the preceding claims wherein the means for propelling the sludge comprises at least one rotatably mounted blade.

25 7. An apparatus according to claim 6 wherein the

blade is screw-shaped.

8. An apparatus according to claim 6 or 7 wherein the blade is mounted on a rotatable shaft which is axially disposed within one or more of the zones.

5 9. An apparatus according to claim 8 wherein the shaft passes axially through the successive zones.

10. An apparatus according to any one of the preceding claims including pumping means for enhancing drainage of the liquid.

10 11. An apparatus according to any one of the preceding claims comprising a filter membrane wall which is axially rotatable to prolong the life of the membrane and to avoid the need for frequent replacement.

12. An apparatus according to claim 6 wherein the 15 screw-shaped blade is provided with brushes along its edge. 13. An apparatus according to any one of the preceding claims including means for providing a reduction in pressure in the second zone.

20 14. An apparatus according to claim 13 further including means for increasing temperature in the second zone.

15. An apparatus according to any one of the preceding claims comprising a baffle plate having perforations 25 via which the sludge is extruded to enter the second

zone. 16. An apparatus according to any one of the preceding claims wherein the second zone includes means for slicing the emergent sludge to produce pellets.

5 17. An apparatus according to any one of the preceding claims comprising a peripheral porous gasket at the interface between each successive zone for allowing drainage of emergent liquid as the sludge is propelled through the zones.

10 18. A method of extracting liquid from a sludge, comprising the steps of: introducing the sludge into a first zone having a portion of gradually decreasing cross-sectional area; propelling the sludge in a forwards direction 15 through the zone to force liquid to emerge from the sludge; draining the excess liquid via a permeable membrane; further propelling the resultant sludge through a 20 second zone in which the resultant sludge is exposed to a reduced pressure environment to enhance removal of liquid and release of vapours.

19. A method according to claim 18 wherein the resultant sludge is additionally exposed to heat within 25 the second zone.

20. A method according to any one of the preceding claims including the further step of extruding the sludge to increase its surface area upon entry into the second zone.

5 21. A method according to claim 20 wherein the sludge is extruded via a baffle plate having a plurality of extrusion apertures.

22. A method according to claim 20 or 21 including the further step of chopping the extruded sludge into 10 pellets to maximise its surface area.

23. Use of an apparatus according to any one of claims g61 to 17 for extracting a liquid from a liquid-solid mixture. 24. A method of extracting liquid from a sludge 15 substantially as hereinbefore described with reference to the accompanying drawings.

25. An apparatus for extracting liquid from a sludge substantially as hereinbefore described with reference to the accompanying drawings.