WO2007093015A1

WO2007093015A1 - Clarifier

Info

Publication number: WO2007093015A1
Application number: PCT/AU2007/000180
Authority: WO
Inventors: Alan Lewis Fitzmaurice
Original assignee: Alan Lewis Fitzmaurice
Priority date: 2006-02-17
Filing date: 2007-02-19
Publication date: 2007-08-23

Abstract

A clarifier (10) where flocculated relatively unclarified juice enters the clarifier at (11) and clarified juice is drawn off through an outlet pipe (12). The juice flow is controlled by having an intake edge a depth so there is a annular downward plug flow before cross flow commences. A rotary shaft (13) is located in the centre of the clarifier and drives a bottom scraper assembly 14 for removal of mud sediment from the clarifier and a scraper (15) used to remove floating particles which accumulate at the sides of the clarifier shaft (13) rotates at approximately (3) revolutions per hour. Relatively clarified juice passes through a perforated take off cone or cylinder (25) and the distance between an intake edge (26) and the perforated take off (25) is so chosen so that the mud is removed by sedimentation and the floating particles removed by flotation, mud is depicted by the closely spaced lines at (34). The velocity in region (36) is about 5mm/sec and the highest velocity is about 10mm/sec in the region (37). Velocity in the region (30) is down to zero. Velocities are shown across the drawing.

Description

CLARIFIER

FIELD OF THE INVENTION

THIS INVENTION relates to clarifers and in particular but not limited to a clarifier for sugar cane juice. BACKGROUND OF THE INVENTION

Sugar cane juice is usually passed through a clarifier in an effort to remove "mud" and so called "floaters" from the juice.

Juice extracted from sugar cane contains impurities including mud and fine fibre particles which should be removed to produce a high quality sugar for human consumption.

In a sugar cane factory "juice clarifers" are used to remove most of these impurities. This separation is achieved with the aid of a flocculent which ties the minute impurities into bundles called flocks which, because of their increased mass, sink to the bottom of the clarifier onto trays or tray type units where they are removed by scrapers.

Some particles retain air and rather than sink float these are known as floaters which are fine cane fibre particles called "bagacillo" and these along with small mud particles may remain entrained in the clarified juice and flow to the take off troughs therefore reducing the quality of the clarified juice. Examples of sugar cane juice clarifers are disclosed in US Patents

4,279,747; 3,140,200; 4,603,000; 7,160,394; and 4,192,752. The disclosure of these patents is incorporated herein by reference but the disclosure herein should not be considered an admission that any of the information in these documents is common general knowledge. OBJECT OF THE INVENTION

The object of the present invention is to provide a clarifier which forces the unclarified juice to flow substantially horizontally in a maximum depth column to slow its horizontal flow and allow flocculated mud particles to drop out of this column early, to the bottom of the clarifier for removal and the floaters and gas particles with adhering mud and bagacillo particles to rise out of this column to the surface of the juice for removal as well. Both impurities are separated from the clarified juice. The clarified juice flows through a perforated, partitioned or slotted central cone to forcefully spread out the vertical depth of the juice flow by restricting the flow to decrease its horizontal flow rate to allow maximum time for the mud particles and floaters to separate from this flowing body of juice and therefore increase the capacity of the clarifier.

In the present specification and claims the flow of juice depends on the configuration of the inlet and outlets, so the invention may be put into practice with outward flow or inward flow so wherever inward flow from the periphery is described or claimed it should be understood that the inlet and outlets may be reversed.

OUTLINE OF THE INVENTION

In one broad aspect the invention resides in a clarifier where flocculated relatively unclarified liquid enters the clarifier at and clarified liquid is drawn off through an outlet pipe the flow being controlled by having an intake edge at depth so there is a annular downward plug flow before cross flow commences.

In one aspect therefore the present invention resides in a juice clarifier including a generally horizontal juice flow passage at depth across the clarifier from a entry to an exit, the exit having slow flow means to limit the flow of unclarified juice from the entry along the horizontal flow passage way, the entry juice having relatively heavy flocculated mud particles entrained therein and relatively light floaters entrained therein, the horizontal flow path is sufficiently slow as to enable floaters to move to the surface and flocculated mud particles to sink to the bottom to provide a relatively pure clarified juice at a take off.

In another preferred embodiment there is provided a rotary shaft clarifier driving a bottom scraper assembly for removal of mud sediment from the clarifier and a scraper used to remove floating particles which accumulate at the sides of the clarifier, the clarifier having a sedimentation tank, which has a conical base section and a mud outlet section for discharge of mud settling on the insides of the conical base, the insides of the conical base being progressively scraped by scraper blades of the scraper assembly as it moves around the bottom of the tank , relatively clarified juice passes through a perforated take off at a distance between a vertical intake having a lower intake edge defining a depth of commencement of cross flow and the take off, the distance between the intake edge and the take off being so chosen and arranged along the accompanying flow rate so that the mud being removed by sedimentation and the floating particles removed by flotation is optimised, the distance between an intake edge and the take off and the depth of the intake are selected so that the flow rate optimises the clarification.

Preferably, juice is caused to flow across the bottom of the intake edge generally horizontally at depth showing a generally horizontal flow albeit slightly upward toward the take off, the flow overall being designed to cause circulation at adjacent and above the intake edge to promote movement of floaters to a region adjacent the periphery of the clarifier.

Preferably, as the juice enters below the intake edge larger mud particles are already sinking toward the bottom such that a higher proportion of mud is being deposited adjacent the outside of the clarifier while at the same time floating particles amass as a annular ring.

Preferably, flow from the intake edge is uniform at about 5 mm/sec due to a feed launder at the entry to the clarifier. The launder includes a perforated plate with holes to allow passage of larger mud particles and to provide uniform or "plug" flow within the inlet down to the intake edge.

Typically, the entry juice follows an initial substantially vertical plug flow downward into the clarifier.

Preferably, the relatively unclarified juice enters either from a centre feed cylinder/cone, or preferably, an outside feed ring (both of which may be perforated, partitioned or slotted to increase the depth of the horizontally flowing juice column).

Preferably clarified juice, to exit, preferably, though a perforated, partitioned or slotted central take off cylinder/cone or through a perforated, partitioned outer ring. Thus in relation to the above the flow maybe inward or outward.

Preferably, controlled flow of juice from a lower entry point to a perforated, partitioned or slotted take off cylinder, preferably an inverted truncated cone, if in the centre or alternatively a perforated partitioned or slotted take off ring on the outer circumference. Typically a juice flow is forced to spread up and/or down as it travels from a horizontal entry point at depth to an exit cylinder/inverted cone or outer ring, to decrease its horizontal speed and so increase the time required for separation of flocculated mud particles and floaters. Typically the choice of the perforated, partitioned or slotted entry and/or perforated partitioned or slotted exit cylinder/cone or outer ring is dimensioned and chosen so as to spread out the vertical depth of the horizontal juice flow to forcefully slow its cross flow rate.

Preferably, the entry should be an outer feed ring to minimise the downward flow rate of an initial vertical flow of incoming flocculated juice, to allow maximum separation of mud particles prior to the horizontal flow.

Typically, the outward flow rate of "floaters" is very slow and therefore time is required to allow these particles to separate from the horizontal flow of juice. For this reason either a central perforated, partitioned or slotted take off cylinder/cone or a perforated, partitioned or slotted outer take off ring is required to increase the depth of the horizontally flowing juice column to reduce its flow rate across the given maximum time for this separation process.

Preferably, clarifier has a base, the base of the clarifier should be a cone with an angle downward towards the centre of at least 20 degrees to the horizontal to improve mud removal and increase mud compaction, (heavy muds) for minimum juice content in the mud being separated from the juice. In order to remove floaters it is typically preferable to have a skimmer type or other type floater removal system. Preferably, flow across the clarifier promotes circulation adjacent the inlet to cause a low or zero flow region for collection of floaters. This circulation also preferably, provides an upflow to aid movement of floaters to the region for collection of floaters. Downward flow through the inlet is purposely set low, at about 5mm/sec to promote uniform slow velocity flow across the clarifier and thereby promote separation of floaters and mud.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the present invention may be more readily understood and put into practical effect reference will now be made to the accompany drawings which illustrate a preferred embodiment of the invention and wherein:-

Figure 1 is a schematic sectional drawing through a clarifier according to the present invention;

Figure 2 is drawing similar to Figure 1 but illustrated the flow process of juice through the clarifier.

Figure 3 is a computational fluid dynamics (CFD) model of a typical clarifier operation.

DETAILED DESCRIPTION OF THE DRAWINGS Referring to the drawings and initially to Figure 1 there is illustrated a clarifier 10 where flocculated relatively unclarified juice enters the clarifier at 11 and clarified juice is drawn off through an outlet pipe 12.

A rotary shaft 13 is located in the centre of the clarifier and drives a bottom scraper assembly 14 for removal of mud sediment from the clarifier and a scraper 15 used to remove floating particles which accumulate at the sides of the clarifier as will be described below.

The shaft 13 rotates at approximately 3 revolutions per hour. The clarifier includes a sedimentation tank shown generally at 16 which has a conical base section 17 and a mud outlet section at 18 mud settling on the insides of the conical surface 17 are progressively scraped from that surface by scraper blades 19, 20, 21 , 22, 23 and 24 as the scraper assembly 14 moves around the bottom of the tank 16. Relatively clarified juice passes through a perforated take off cone or cylinder 25 and the distance between an intake edge 26 and the perforated take off 25 is so chosen and arranged along with the dimensions of the perforations and the accompanying slow rate so that the mud is removed by sedimentation and the floating particles removed by flotation is optimised.

Thus the distance the relative dimensions and the depth of the intake 25 are selected so that the flow rate optimises the clarification. As illustrated in Figure 2 juice is caused to flow across the bottom of the intake edge 26 generally horizontally at depth as indicated by the solid lines 27 showing a generally horizontal flow albeit slightly upward toward the perforated cone or cylinder 25. This flow overall is designed to cause circulation at 29 which also promotes movement of floaters to the region 30. As the juice enters belowthe edge 26 larger mud particles will already be sinking toward the bottom and the arrows 28 indicate that a higher proportion of mud is being deposited adjacent the outside of the clarifier. Likewise the broken lines illustrate the flow of floating particles at 29 and these particles will tend to amass as a annular ring as indicated at 30 which is swept off into skimmer box 31 which is periodically washed to remove the particles entrained therein from the clarifier.

The flow from feed launder 32 is uniform at about 5 mm/sec due to the constructions of the feed launder shown in inset Figure 2B. The launder 32 induces a perforated plate 33 with holes of about 10 mm or so to allow passage of larger mud particles. This arrangement provides uniform or "plug" flow within the inlet down to edge 26.

Referring now to Figure 3 there is illustrated a CFD model of a 9750mm diameter clarifier with a flow rate of about 11 ,000 tonnes of juice per day. The mud is depicted by the closely spaced lines at 34. The velocity in region 36 is about 5mm/sec and the highest velocity is about 10mm/sec in the region 37. Velocity in the region 30 is down to zero. Velocities are shown across the drawing.

Whilst the above has been given by way of illustrative example of the present invention many variations and modifications thereto will be apparent to those skilled in the art without departing from the broad ambit and scope of the invention as set out in the appended claims.

Claims

1. A juice clarifier including a generally horizontal juice flow passage at depth across the clarifier from a entry to an exit, the exit having slow flow means to limit the flow of unclarified juice from the entry along the horizontal flow passage way, the entry juice having relatively heavy flocculated mud particles entrained therein and relatively light floaters entrained therein, the horizontal flow path is sufficiently slow as to enable floaters to move to the surface and flocculated mud particles to sink to the bottom to provide a relatively pure clarified juice at a take off.

2. A juice clarifier according to claim 1 wherein the entry juice follows an initial substantially vertical plug flow downward into the clarifier.

3. A juice clarifier according to claim 1 wherein the relatively unclarified juice enters either from a centre feed cylinder/cone, or preferably, an outside feed ring (both of which may be perforated, partitioned or slotted to increase the depth of the horizontally flowing juice column).

4. A juice clarifier according to claim 1 wherein clarified juice exit though a perforated, partitioned or slotted central take off cylinder/cone or through a perforated, partitioned outer ring.

5. A juice clarifier according to claim 1 wherein flow maybe inward or outward depending on where the juice entry and exit is located.

6. A juice clarifier according to claim 1 wherein controlled flow of juice is from a lower entry point to a perforated, partitioned or slotted take off cylinder, which comprises an inverted truncated cone, if in the centre or alternatively a perforated partitioned or slotted take off ring on an outer periphery of the clarifier.

7. A juice clarifier according to claim 1 wherein a juice flow is forced to spread up and/or down as it travels from a horizontal entry point at depth to an exit cylinder/inverted cone or outer ring, to decrease its horizontal speed and so increase the time available for separation of flocculated mud particles and floaters.

8. A juice clarifier according to claim 1 wherein the choice of the perforated, partitioned or slotted entry and/or perforated partitioned or slotted exit cylinder/cone or outer ring is dimensioned and chosen so as to spread out the vertical depth of the horizontal juice flow to forcefully slow its cross flow rate.

9. A juice clarifier according to claim 1 wherein the entry is be an outer feed ring adapted to minimise the downward flow rate of an initial vertical flow of incoming flocculated juice, to allow maximum separation of mud particles prior to the horizontal flow.

10. A juice clarifier according to claim 1 wherein the clarifier has a base, the base of the clarifier being a cone with an angle downward towards the centre of at least 20 degrees to the horizontal to improve mud removal and increase mud compaction, (heavy muds) for minimum juice content in the mud being separated from the juice.

11. A juice clarifier according to claim 1 wherein in order to remove floaters the clarifier includes a floater removal system.

12. A juice clarifier according to claim 1 wherein flow across the clarifier promotes circulation adjacent the inlet to cause a low or zero flow region for collection of floaters.

13. A juice clarifier according to claim 1 wherein flow across the clahfier promotes circulation adjacent the inlet to cause a low or zero flow region for collection of floaters, this circulation also providing an upflow to aid movement of floaters to the region for collection of floaters.

14. A juice clarifier according to claim 1 wherein downward flow through the inlet is purposely set low, at about 5mm/sec to promote uniform slow velocity flow across the clarifier and thereby promote separation of floaters and mud. a clarifier 10 where flocculated relatively unclarified juice enters the clarifier at 11 and clarified juice is drawn off through an outlet pipe 12.

15. A clarifier where flocculated relatively unclarified liquid enters the clarifier at and clarified liquid is drawn off through an outlet pipe the flow being controlled by having an intake edge at depth so there is a annular downward plug flow before cross flow commences.

16. A rotary shaft clarifier driving a bottom scraper assembly for removal of mud sediment from the clarifier and a scraper used to remove floating particles which accumulate at the sides of the clarifier, the clarifier having a sedimentation tank, which has a conical base section and a mud outlet section for discharge of mud settling on the insides of the conical base, the insides of the conical base being progressively scraped by scraper blades of the scraper assembly as it moves around the bottom of the tank , relatively clarified juice passes through a perforated take off at a distance between a vertical intake having a lower intake edge defining a depth of commencement of cross flow and the take off, the distance between the intake edge and the take off being so chosen and arranged along the accompanying flow rate so that the mud being removed by sedimentation and the floating particles removed by flotation is optimised, the distance between an intake edge and the take off and the depth of the intake are selected so that the flow rate optimises the clarification.

17. A clarifier according to any one of the preceding claims wherein juice is caused to flow across the bottom of the intake edge generally horizontally at depth showing a generally horizontal flow albeit slightly upward toward the take off, the flow overall being designed to cause circulation at adjacent and above the intake edge to promote movement of floaters to a region adjacent the periphery of the clarifier.

18. A clarifier according to any one of the preceding claims wherein as the juice enters below the intake edge larger mud particles are already sinking toward the bottom such that a higher proportion of mud is being deposited adjacent the outside of the clarifier while at the same time floating particles amass as a annular ring.

19. A clarifier according to any one of the preceding claims wherein flowfrom the intake edge is uniform at about 5 mm/sec due to a feed launder at the entry to the clarifier.

20. A clarifier according to any one of the preceding claims wherein flowfrom the intake edge is uniform at about 5 mm/sec due to a feed launder at the entry to the clarifier, the launder including a perforated plate with holes to allow passage of larger mud particles and to provide uniform or "plug" flow within the inlet down to the intake edge.

21. A sugar cane juice clarifier according to claim 15.