US 4,988,441 AGrant
Clarification Apparatus
Issue Date:1991-01-29
•24 Claims
•5 Drawing Sheets
Abstract
Liquor-clarifying apparatus comprises a tank 1, inlets 2 for suspension to be clarified, outlet 3 for clarified water, outlet 4 for sedimented solids, and a plurality of settling assemblies each comprising a stack 6 of downwardly inclined plates 7 mounted around a vertical collection duct 39. This duct generally comprises a downwardly extending duct 18 that leads directly into an upwardly extending duct 27. The plates 6 are preferably conical or pyramidal and are preferably self-spacing and capable of being clipped together by a push fit. A downwardly extending skirt 40 may be provided. Orifices 25 allow clarified liquid to pass from between the plates into the collection duct and preferably these orifices are elongated.
Metadata
Inventor
- John Moir
Application Information
Application Number:US 3911330
Filing Date:1989-08-08
Priority Date:1988-08-09
Art Unit:136
Classifications
IPC:
B01D 2102
Field of Search:
210521;522;802;541;532.1
Patent Drawings (5 sheets)
Description
The invention is illustrated in the accompanying drawings in which
FIG. 1 shows a perspective view, part broken away, of an apparatus according to the invention;
FIG. 2 shows, in enlarged perspective, part of a stack of pyramids of the type shown in FIG. 1;
FIG. 3 shows a modified forms of pyramid;
FIGS. 4a and 4b show, in exploded view, a composite collection duct of the type used in FIG. 1;
FIG. 5 shows, in diagrammatic vertical cross-section, the assembled composite collection duct of FIGS. 4a and 4b;
FIGS. 6 and 7 are sections similar to FIG. 5 but of different composite collection ducts.
The apparatus comprises a tank 1, inlets 2 for suspension to be clarified, outlets 3 for clarified water and outlet 4 for sedimented solids from a sedimentation conical zone 5 positioned beneath the rectangular tank 1. Within the tank 1 there are a plurality of stacks 6 of pyramids 7 mounted around a central composite duct 39. Each stack is positioned such that clarified liquid flowing up through the duct through the center of the stack emerges through the corresponding outlet 3.
The inlets 2 are elongate slots in the bases of troughs 9 in upper raised surfaces 10 of the tank. The troughs 9 open into a launder 12 and suspension to be clarified is pumped into this launder through pipe 8. It overflows from this launder along the troughs 9 and down through the inlets 2, into the chamber.
Liquid that has been clarified and is passing up through the stack 6 emerges from the outlets 3 in launders 13 between the raised parts 10 and that are blanked off at 14 but that open into a launder 15 provided with an outlet pipe 16. A vertically adjustable weir 17 is positioned at the ends of the launders 13 so as to control the depth of clarified liquid held in the launders Generally the weir 17 is adjusted to be, for instance, 0.5 to 5 cm above the base of the launder 13 so as to hold clarified water to this depth in the launder, as this helps maintain uniform flow of clarified water up through the stacks 6.
Each stack 6 consists of a plurality of setting plates 7. As shown in the drawings, these plates have the shape of pyramids but they could be, for instance, cones. Each pyramid may consist solely of outwardly inclined surfaces in which event each is preferably a tight sliding fit over a composite duct 39 that can be a downwardly extending duct 18 that is closed at the end 19, as shown in FIG. 4. However the pyramids or cones can have vertically extending necks 20 at their uppermost edges and these necks can slide over the duct 18 or they can inter-engage with each other so as to define the duct 18. The inter-engagement may be by means of, for instance, ribs 21 that clip over one another to hold the pyramids rigidly with respect to one another.
Suspension flows down through the tank between the adjacent stacks and enters at the slot 22 between the lowermost edges of the lower part 23 of an adjacent pair of plates. The suspension flows upwardly between the inclined plates towards the upper part 24 and as it flows up between the plates solids tend to sediment on to the lower plate 7L while clarified liquor tends to rise up against the upper plate 7U. The cell between these plates is closed at its upper part 24 by a neck 20 or the pipe 18 but orifices 25 are provided in this upper part to allow the clarified water to escape from the cell into the central duct defined by the neck 20 or the pipe 18.
FIG. 3 shows a pyramidal duct of the same general construction as the ducts illustrated in FIG. 2 except that a skirt 40 extends vertically downwards from the lowermost edge 41 of each of the pyramids The vertical spacing between adjacent pyramids is defined by the vertical height of the neck 20 and the skirt 40 has a vertical dimension less than about 3/4 of the vertical spacing between the pyramids so as to ensure that the slot 23 that is defined between the lowermost edge 42 of the skirt and the lowermost edge of the next adjacent pyramid is at least about 1/4 of the vertical spacing between the pyramids If the slot is too narrow then excessive mixing of the solids and the incoming suspension may occur. Preferably the vertical dimension of the skirt 40 is about half the vertical length of the neck 20.
The top of the outer duct 18, or the duct defined by the necks 20 of the pyramids, is blanked off (for instance as at 19 in FIG. 5) so that the flow through this duct has to be downwardly. If the duct is defined by pipe 18 then this is provided with orifices 26 in positions to match those of orifices 25.
The area of the orifices can decrease downwardly, for instance the orifices at the top of FIG. 4a are very much larger than the orifices at the bottom.
As shown in FIG. 5, the composite duct 39 is formed of a downflow collection pipe 18 or the vertical necks 20 and a co-axial, smaller, upflow duct 27 fitted in it. This duct is open at its lower end 28 so that the clarified water that flows downwardly along the annulus around duct 27 reverses its flow at the bottom 28 and flows upwardly through the duct 27 to the outlet 3, which is surrounded by a plate 19 that blanks off the top of the outer duct 18.
As shown in FIG. 2 to 4, the orifices are elongated slots extending over at least three quarters of the horizontal length of the plates at the position of the orfices, i.e. at top part 24, thus promoting uniformity of flow.
In FIG. 6, the composite duct 39 comprises a short downflow duct 31, leading at 32 into an inner coaxial upflow duct that has a narrow portion 33 and that leads into an upflow collection portion 34.
In FIG. 7, the composite duct 39 has two short downflow ducts 35 and 36. The upflow duct consists of a narrow portion 37 leading into a wider portion 38 leading into a collection portion 34 This provides a particularly convenient way of obtaining different flow rates through different orifices even though the orifices are all of the same dimensions. Also, replacement of downflow ducts 31, or 35 and 36, by different ducts having different lengths or radii permits further variation in flow rates. Three or more short downflow ducts may be used if required.
To install apparatus according to the invention it is preferred to provide in the desired place of use (for instance in a mine) the tank 1 provided with the necessary inlets and outlets 2 to 5, and subsequently to install in the tank a plurality of settling assemblies, each consisting of a stack 6 of the settling plates mounted around a vertical collection duct. The vertical collection duct may be fitted previously in the chamber, in which event the plates are merely fitted over it, but it is often preferred that an assembly comprising part or all of the vertical collection duct and the stack should be preassembled and inserted into the chamber.
In each of the examples the clarification -apparatus used was substantially as shown in FIG. 1, comprising a vertical rectangular tank having a height 2.13 meters and cross sectional area 0.21 m.sup.2 with a sedimentation conical zone positioned beneath the rectangular tank for collection and removal of settled solids. Feed and overflow launders were also fitted at the top of the tank and stacks of pyramids were arranged inside the tank.
The central duct formed by each stack of pyramids had square cross sectional area, with the sides of the square base of the pyramids having length 15 cm. The slope of the pyramids was 53.degree. to the horizontal. The central collection duct was provided with slots, through which clarified water could escape.
Example 1
Four stacks of pyramids each comprising 30 pyramids spaced 2.5 cm apart, were arranged in the tank, in two pairs, each pair discharging into one of two launders.
Two of the stacks were according to the prior art and were operated with the central duct being a simple, single pipe so that clarified liquid could flow through the slots and into the duct and escaped upwards out of the apparatus (up flow only).
The remaining two stacks were operated in accordance with the invention (FIG. 6) with the top 50% of the pyramids delivering clarified liquids upwards, in the same way but with the bottom 50% of the pyramids delivering clarified water into the central duct consisting of a downwardly extending duct placed inside and coaxial with the upwardly extending collection duct so that clarified liquid flowed into the central duct and downwards through an outer sleeve, between the two ducts and then into the inner downwardly extending duct to flow upwards out of the apparatus, i.e., the initial removal of clarified water was downflow followed by upflow out of the apparatus, according to the invention (bottom 50% initial downflow).
The apparatus was operated for a substantial period of time with a feed rate of 15 m/hour (i.e., the volume of suspension for clarification entering the tank measured in m.sup.3 per hour per m.sup.2 of tank area).
The suspension used for clarification was an aqueous solution of china clay particles with a solids content 580 mg per liter.
The rate of delivery of clarified water from both pairs of stacks was about 15 m/hour and the solids content of the clarified water was found to be 35 mg per liter for both pairs of stacks.
It was found that over the period of operation solid particles accumulated at the base of the upflow only stacks, to a level of about 8 cm whilst the stacks according to the invention in which the bottom 50% of pyramids delivered into a downflow collection duct did not accumulate any significant amount of solids.
Example 2
Two stacks of pyramids having downflow collection of clarified water, according to the invention, each comprising 30 pyramids spaced 2.5 cm apart, were arranged in the tank. Aqueous suspension of china clay particles, having a solids content of 490 mg per liter was fed to the tank at a rate of 20 m per hour. The overflow of the clarified water was also at a rate of approximately 20 m per hour. The resultant clarified liquid contained a solids content of 51 mg per liter.
This process was repeated using pyramids having skirts as illustrated in FIG. 3. Due to the extra height of the skirts, only 15 pyramids could be arranged in a stack, with spacing of 5 cm (2 inches). In addition, the area of the orifices, per pyramid was twice the area for the apparatus having 30 pyramids, in order to provide a total equal area of the orifices per stack. The same aqueous china clay suspension having solids content of 490 mg per liter was supplied to the clarification apparatus at a rate of 20 m per hour, again the overflow rate of clarified liquid was approximately 20 m per hour. The solids content of the clarified liquid was even more significantly reduced to 31 mg per liter. Thus, even though the number of pyramids (i.e. the settlement area) was reduced, an even more efficient clarification was achieved.
In each of these examples the plant was operated at a flow rate for the suspension approximately 4 or 5 times a suitable flow rate in the absence of a stack, thus illustrating the benefit of the inclusion of the stack. In other processes the flow rates can be up to 10 or more times a suitable flow rate for an apparats in which there are no stacks.
Claims
I claim:
1. Liquor clarifying apparatus comprising: a tank having a top; at least one inlet into the tank; at least one launder in the top of the tank and from which liquid can be discharged; a plurality of first outlets for clarified liquor and that open into the at least one launder; at least one second outlet from the base of the tank for separated solids, and a plurality of settling assemblies wherein each settling assembly comprises a substantially vertical collection duct that leads up into one of the said first outlets for discharging clarified liquor into one said launder a stack of substantially pyramidal settling plates each of which comprises a neck portion and a downwardly inclined pyramidal portion, each adjacent pair of pyramidal plates being spaced apart by spacing means consisting essentially of a substantially vertical neck to define a pyramidal cell that leads from the neck downwardly through an inclined length of 5 to 30 cm to a parallel sided outlet slot that extends around the pyramidal cell and that has a vertical depth of at least 1 cm, and in which each neck has a length of 1-10 cm and is either a separate spacer neck or is integral with one of the said pyramidal plates, the collection duct either comprises the said integral necks or pipe over which the necks are slidably fitted, and there are orifices extending from each cell through each neck and into the duct for passage of clarified liquor from each cell into the duct and up into the launder.
2. Apparatus according to claim 1 in which the necks are integral, the collection duct is defined by the said integral necks and the necks are provided with inter-engaging fit means for securing the plates one above the other by push interengagement of the fit means.
3. Apparatus according to claim 1 in which the collection duct comprises an outer, downwardly extending, duct that is either defined by the said integral necks or is a pipe over which the necks are slidably fitted, and an inner substantially co-axial upwardly extending duct is so arranged within the downwardly extending duct that clarified liquor that enters the orifices extending into said downwardly extending duct first flows down the the downwardly extending duct and then flows up the upwardly extending duct to one of the said first outlets.
4. Apparatus according to claim 3 in which the downwardly extending duct collects from at least the lowermost 25% of the plates and the upwardly extending duct has orifices extending through the wall of the upwardly extending duct above the downwardly extending duct and collects from uppermost plates in the stack.
5. Apparatus according to claim 3 in which the upwardly extending duct extends along substantially the entire length of the downwardly extending duct.
6. Apparatus according to claim 1 including means for keeping the stack under axial compression.
7. Apparatus according to claim 1 in which the plates are formed of a plastics material having density below 1.
8. Apparatus according to claim 1 in which the orifices have a horizontal length greater than half the horizontal length of the uppermost edges of the plates at the neck portion.
9. Apparatus according to claim 1 in which the pair of adjacent settling plates defines a downwardly inclined substantially parallel-sided cell having an open slot defined b the lowermost edges of the pair.
10. Apparatus according to claim 1 in which each plate has a skirt extending downwardly from its lowermost edge to define a slot with the lowermost edge of the adjacent lower plate, the vertical dimension of the slot being less than 3/4 of the vertical distance between the plates in the cell.
11. Apparatus according to claim 1 in which there are at least 30 of the said plates in each said stack having a vertical separation of 1 to 5 cm.
12. Apparatus according to claim 1 in which there are at least 30 of the said plates in each stack, with a gap of 2 to 10 cm between each pair of plates, and in which the said inclined length of each pyramidal cell is from 5 to 20 cm and the said cell and the said parallel sided outlet slots each have a vertical depth of from 1 to 5 cm.
13. A settling assembly constructed and arranged to be fitted within a liquid clarifying apparatus comprising a tank having a top, a first inlet into the tank, at least one launder in the top of the tank from which liquid can be discharged, a plurality of first outlets for clarifying liquor and that open into the at least one launder, and at least one second outlet from the base of the tank for separated solids, wherein the settling assembly comprises a substantially vertical collection duct that can lead up into one of the said first outlets for discharging clarified liquor into one said launder a stack of substantially pyramidal settling plates each of which comprises a neck portion and a downwardly inclined pyramidal portion, each adjacent pair of pyramidal plates being spaced apart by spacing means consisting essentially of a substantially vertical neck to define a pyramidal cell that leads from the neck downwardly through an inclined length of 5 to 30 cm to a parallel sided outlet slot that extends around the pyramidal cell and that has a vertical depth of at least 1 cm, and in which each neck has a length of 1-10 cm and is either a separate spacer neck or that is integral with one of the said pyramidal plates, the collection duct either comprises the said integral necks or a pipe over which the necks are slidably fitted, and there are orifices extending from each cell through each neck and into the duct for passage of clarified liquor from each cell into the duct and up into the launder.
14. An assembly according to claim 13 in which the necks are integral, the collection duct is defined by the said integral necks and the necks are provided with interengaging fit means for securing the plates one above the other by push interengagement of the fit means.
15. An assembly according to claim 13 in which the collection duct comprises an outer, downwardly extending, duct that is either defined by the said integral necks or is a pipe over which the necks are slidably fitted, and an inner substantially co-axial upwardly extending duct is so arranged within the downwardly extending duct that clarified liquor that enters the orifices extending into said downwardly extending duct first flows down the the downwardly extending duct and then flows up the upwardly extending duct to one of the said first outlets.
16. An assembly according to claim 15 in which the downwardly extending duct collects from at least the lowermost 25% of the plates and the upwardly extending duct has orifices extending through the wall of the upwardly extending duct above the downwardly extending duct and collects from uppermost plates in the stack.
17. An assembly according to claim 15 in which the upwardly extending duct extends along substantially the entire length of the downwardly extending duct.
18. An assembly according to claim 13 including means for keeping the slack under axial compression.
19. An assembly according to claim 13 in which the plates are formed of a plastics material having density below 1.
20. An assembly according to claim 13 in which the orifices have a horizontal length greater than half the horizontal length of the uppermost edges of the plates at the neck portion.
21. An assembly according to claim 13 in which the pair of adjacent settling plates defies a downwardly inclined substantially parallel-sided cell having an open slot defined b the lowermost edges of the pair.
22. An assembly according to claim 13 in which each plate has a skirt extending downwardly from its lowermost edge to define a slot with the lowermost edge of the adjacent lower plate, the vertical dimension of the slot being less than 3/4 of the vertical distance between the plates in the cell.
23. An assembly according to claim 13 in which there are at least 30 of the said plates in said stack having a vertical separation of 1 to 5 cm.
24. An assembly according to claim 13 in which there are at least 30 of the said plates in said stack and in which the said inclined length of each pyramidal cell is from 5 to 20 cm and the said cell and the said parallel sided outlet slots each have a vertical depth of 1 to 5 cm.
Patent Citations (7)
| Patent | Date | Inventor | Cited By |
|---|---|---|---|
| US2314977 | 1943-03-01 | Green | |
| US2570304 | 1951-10-01 | Bach | |
| US2793186 | 1957-05-01 | Dunell et al. | |
| US3306456 | 1967-02-01 | Fromson et al. | |
| US3718257 | 1973-02-01 | Bach | |
| ATX240827 | 1965-06-01 | ||
| GBX5340 | 1891-01-01 |