GB2227303A - The formation of an ice sheet and the use thereof in sorting - Google Patents
The formation of an ice sheet and the use thereof in sorting Download PDFInfo
- Publication number
- GB2227303A GB2227303A GB9001252A GB9001252A GB2227303A GB 2227303 A GB2227303 A GB 2227303A GB 9001252 A GB9001252 A GB 9001252A GB 9001252 A GB9001252 A GB 9001252A GB 2227303 A GB2227303 A GB 2227303A
- Authority
- GB
- United Kingdom
- Prior art keywords
- sheet
- liquid
- particles
- frozen
- frozen material
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25C—PRODUCING, WORKING OR HANDLING ICE
- F25C5/00—Working or handling ice
- F25C5/14—Apparatus for shaping or finishing ice pieces, e.g. ice presses
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
- B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
- B07B13/00—Grading or sorting solid materials by dry methods, not otherwise provided for; Sorting articles otherwise than by indirectly controlled devices
- B07B13/003—Separation of articles by differences in their geometrical form or by difference in their physical properties, e.g. elasticity, compressibility, hardness
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25C—PRODUCING, WORKING OR HANDLING ICE
- F25C1/00—Producing ice
Landscapes
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Mechanical Engineering (AREA)
- Thermal Sciences (AREA)
- General Engineering & Computer Science (AREA)
Abstract
The invention provides a method and apparatus for forming a sheet of frozen material such as ice. A first liquid 16 is floated on a second liquid 10 having a higher specific gravity than the first liquid. The lighter liquid typically has a lower freezing point than the other liquid and is cooled by evaporator coils 20 to below the freezing point of the other liquid, so that a frozen layer 24 is formed at the interface between the liquids. The frozen layer 24 is withdrawn in the form of a continuous sheet and can be used in sorting heated particulate material 28 on the basis of the interaction between the particles and the frozen sheet. <IMAGE>
Description
THE FORMATION OF PN ICE SHEET PND THE USE THEREOF IN SORTING
BACKGROUND TO THE INVENTION
THIS invention relates to the formation of a sheet of frozen material and to the use of the sheet in a sorting system.
One, but not the only, application of the invention is in the formation of an ice sheet and the use of that sheet in sorting diamond particles from gangue particles.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided a method of forming a sheet of frozen material comprising floating a first liquid on a second liquid having a higher specific gravity than the first liquid, the liquids being immiscible, one of the liquids having a lower freezing point than the other liquid, cooling the former liquid to a temperature below the freezing point of the latter liquid so that a frozen layer of the latter liquid is formed at the interface between the liquids, and withdrawing the frozen layer in sheet form.
The first liquid may, for instance, be a saturated aliphatic hydrocarbon such as hexane, octane or paraffin, and the second liquid water. The floating liquid, typically hexane, may be cooled by evaporator coils conveying an evaporating refrigerant through the hexane.
Further according to the first aspect of the invention there is provided apparatus for forming a sheet of frozen material comprising:
a first, open-bottomed container;
a second, open-topped container, the first container
being disposed above the second container;
cooling means associated with one of the containers;
and
conveyor means;; the first and second containers holding respective first and second immiscible liquids in use, the second liquid having a higher specific gravity than the first liquid so that the first liquid floats on the second liquid thereby defining an interface between the liquids, one of the liquids having a lower freezing point than the other liquid, the cooling means operating to cool the former liquid. to below the freezing point of the latter liquid so that a frozen layer of the latter liquid is formed at the interface, the conveyor means operating to withdraw the frozen layer in sheet form.
The sheet of frozen material formed in the manner specified above may be used to sort particulate material on the basis of different thermal properties. One application would be in the sorting of diamond particles and diamondiferous particles having a high diamond content, say 50% or more, from gangue particles, the diamond and diamondiferous particles having a higher thermal conductivity and heat capacity than the gangue particles with which the diamond and diamondiferous particles are associated.
According to a second aspect of the invention, therefore, there is provided a method of sorting particulate material which includes particles having different thermal properties, the method comprising depositing the particles on a sheet of frozen material formed according to the method of the invention, the particles being at a higher temperature than the sheet of frozen material, and distinguishing particles having desired characteristics from gangue particles on the basis of their interaction with the sheet of frozen material.
Further according to the second aspect of the invention, there is provided sorting apparatus for sorting particulate material in which particles having desired characteristics have different thermal properties from gangue particles, the sorting apparatus comprising apparatus for forming a sheet of frozen material according to the invention and further comprising means for depositing the particulate -material on the sheet of frozen material and sorting means for recovering the particles having desired characteristics separately from the gangue particles.
The particles of the particulate material are preferably heated up and deposited onto the sheet of frozen material with the result that the diamond and diamondiferous particles either melt through the sheet more quickly than the other particles or adhere to the sheet by melting and refreezing of the frozen material in their immediate vicinities while the other particles do not so adhere.
BRIEF DESCRIPTION OF THE DRAWING
The invention will now be described in more detail, by way of example only, with reference to the accompanying drawing which illustrates the invention diagrammatically.
DESCRIPTION OF AN EMBODIMENT
In the drawing an open-topped water bath accommodating a volume of water 10 is indicated with the numeral 12.
Supported just above the water in the bath 12 is an open-ended container 14 accommodating a volume of a liquid 16 with a lower specific gravity than that of water. The liquid 16 is a straight-chain saturated aliphatic hydro carbon having a carbon number of six or greater, such as hexane, octane or paraffin. A prototype of the invention was tested with hexane. The hexane, having a lower specific gravity than the water, floats on top of the water with a clear hexane/water interface 18 between them.Evaporator coils 20 are arranged in the hexane 16 and are supplied with a suitable refrigerant which evaporates through the coils to cool the hexane to a temperature less than the freezing point of the water i.e. normally less than OOC. The hexane has a freezing point of about -800C so there is no danger of the hexane freezing if its temperature is reduced by the evaporator coils to about -500C. At this hexane temperature, however, the water freezes at the interface 18 and forms a layer of ice.
Crimp rollers 22 engage the layer of ice formed at the interface 18 and withdraw it continuously in the form of a sheet 24. The ice sheet is carried away from the water bath by a further set of conveyor rollers 23.
The ice sheet 24 can be used to sort particulate material on the basis of different thermal properties of the particles.
As illustrated, an endless conveyor belt 26 is arranged above the ice sheet 24 and is supplied with particulate material 28 to be sorted through a chute 29. In this embodiment, the particulate material is composed of diamond and diamondiferous particles 32 and gangue particles 34. The belt 26 is made of steel and its upper run is heated from below by means of radiant heaters 30. The heated particles 28 fall off the discharge end of the belt 26 onto the ice sheet.
The diamond and diamondiferous particles 32 have a higher thermal conductivity and heat capacity than the gangue particles 34. Thus they are heated up more quickly on the belt 26. Soon after they land on the ice sheet 24, the diamond and diamondiferous particles melt through the ice as shown at 36. Some time after, the gangue particles are able to melt through the ice sheet as shown at 38. Separate receptacles 40 and 42 are provided beneath the ice sheet to collect the diamond and gangue fractions.
Instead of allowing the particles to melt right through the ice sheet 24 as described above, it would also be possible to arrange the various parameters so that the diamonds and diamondiferous particles, upon landing on the the ice sheet, merely melt the ice immediately in their vicinities. The ice sheet is created and maintained at a low enough temperature for the "puddles" of melted ice around the diamonds and diamondiferous particles to refreeze so that the diamond particles are held captive by i.e. adhere to, the ice sheet. The gangue particles rest loosely upon the surface of the ice sheet. At a downstream position, the gangue particles may be removed from the ice sheet, for example by sweeping with a rotating brush. Subsequently the ice sheet is melted to release the diamonds which are therefore recovered separately from the gangue particles.
The melted ice is returned to the bath 12 for re-use.
Although reference has been made specifically to the sorting of diamond particles from gangue particles, it should be appreciated that an ice sheet formed in accordance with the invention can be used to sort other particles on the basis of their thermal properties.
It will also be realised that although the invention has been described with reference to the use of hexane and water, so that a sheet of ice is obtained, different liquids could be used, providing a sheet of frozen material other than ice.
Claims (26)
1.
A method of forming a sheet of frozen material comprising floating a first liquid on a second liquid having a higher specific gravity than the first liquid, the liquids being immiscible, one of the liquids having a lower freezing point than the other liquid, cooling the former liquid to a temperature below the freezing point of the latter liquid so that a frozen layer of the latter liquid is formed at the interface between the liquids, and withdrawing the frozen layer in sheet form.
2.
A method according to claim 1 wherein the first liquid is a saturated aliphatic hydrocarbon and the second is liquid is water, the frozen layer comprising ice.
3.
A method according to Claim 2 wherein the first liquid is a straight-chain saturated aliphatic hydrocarbon with a carbon number of six or greater.
4.
A method according to any one of Claims 1 to 3 wherein the first liquid is cooled by evaporator coils disposed in the first liquid and conveying a refrigerant therethrough.
5.
A method according to any one of claims 1 to 4 wherein the frozen layer is withdrawn by crimp rollers which engage the layer.
6.
Apparatus for forming a sheet of frozen material comprising:
a first, open-bottomed container;
a second, open-topped container, the first container
being disposed above the second container;
cooling means associated with one of the containers;
and
conveyor means; the first and second containers holding respective first and second immiscible liquids in use, the second liquid having a higher specific gravity than the first liquid so that the first liquid floats on the second liquid thereby defining an interface between the liquids, one of the liquids having a lower freezing point than the other liquid, the cooling means operating to cool the former liquid to below the freezing point of the latter liquid so that a frozen layer of the latter liquid is formed at the interface, the conveyor means operating to withdraw the frozen layer in sheet form.
7.
Apparatus according to claim 6 wherein the first liquid is a saturated aliphatic hydrocarbon and the second liquid is water, the cooling means being associated with the first container.
8.
Apparatus according to Claim 7 wherein the first liquid is a straight-chain saturated aliphatic hydrocarbon with a carbon number of six or greater.
9.
Apparatus according to any one of Claims 6 to 8 wherein the cooling means comprises at least one evaporator coil disposed within the first container.
10.
Apparatus according to any one of Claims 6 to 9 wherein the conveyor means comprises crimp rollers disposed about the interface between the first and second liquids, the rollers being adapted to engage and withdraw the layer of frozen material formed at the interface.
11.
A method of sorting particulate material which includes particles having different thermal properties, the method comprising depositing the particles on a sheet of frozen material formed according to the method of any one of Claims 1 to 5, the particles being at a higher temperature than the sheet of frozen material, and distinguishing particles having desired characteristics from gangue particles on the basis of their interaction with the sheet of frozen material.
12.
A method according to Claim 11 wherein diamond and diamondiferous particles are sorted from gangue particles.
13.
A method according to Claim 9 or Claim 12 wherein the particulate material is heated before being deposited on the sheet of frozen material.
14.
A method according to any one of Claims 11 to 13 wherein the particles having desired characteristics melt through the sheet of frozen material sooner or later than the gangue particles, the particles having desired characteristics being collected at a first location which is spaced from a second location at which the gangue particles melt through the sheet of frozen material.
15.
A method according to any one of Claims 11 to 13 wherein the particles having desired characteristics melt the frozen material in their immediate vicinities to a greater extent than the gangue particles, the melted frozen material being allowed to refreeze so that the particles having desired characteristics are trapped in the sheet of frozen material.
16.
A method according to claim 15 wherein the gangue particles are swept off the sheet of frozen material before the trapped particles are released by melting the sheet.
17.
Sorting apparatus for sorting particulate material in which particles having desired characteristics have different thermal properties from gangue particles, the sorting apparatus comprising apparatus for forming a sheet of frozen material according to any one of Claims 6 to 10 and further comprising means for depositing the particulate material on the sheet of frozen material and sorting means for recovering the particles having desired characteristics separately from the gangue particles.
18.
Sorting apparatus according to claim 17 including heater means for heating the particulate material before it is deposited on the sheet of frozen material.
19.
Sorting apparatus according to Claim 17 or Claim 18 wherein the means for depositing the particulate material on the sheet of frozen material comprises a conveyor belt having a discharge end disposed above the sheet.
20.
Sorting apparatus according to claim 19 wherein the conveyor belt is metallic, at least one heater being disposed adjacent to the belt to heat the belt in use, so that the belt imparts heat to the particulate material.
21.
Sorting apparatus according to any one of Claims 17 to 20 wherein the sorting means comprises first and second spaced apart receptacles, respectively located to collect the particles having desired charactertistics as they melt through the sheet of frozen material at a first location, and to collect the gangue particles as they melt through the sheet of frozen material at a second location.
22.
Sorting apparatus according to any one of Claims 17 to 20 wherein the sorting means comprises sweeping means for removing gangue particles which are loosely adhered to the sheet of frozen material, so that particles having desired characteristics which are trapped in the sheet can be recovered by melting the frozen material.
23.
A method of forming a sheet of ice as herein described with reference to the accompanying drawing.
24.
Apparatus for forming a sheet of ice as herein described with reference to the accompanying drawing.
25.
A method of sorting particulate material as herein described with reference to the accompanying drawing.
26.
Apparatus for sorting particulate material as herein described with reference to the accompanying drawing.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| ZA89437 | 1989-01-19 |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9001252D0 GB9001252D0 (en) | 1990-03-21 |
| GB2227303A true GB2227303A (en) | 1990-07-25 |
| GB2227303B GB2227303B (en) | 1992-07-29 |
Family
ID=25579563
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9001252A Expired - Lifetime GB2227303B (en) | 1989-01-19 | 1990-01-19 | The formation of an ice sheet and the use thereof in sorting |
Country Status (2)
| Country | Link |
|---|---|
| AU (1) | AU612535B2 (en) |
| GB (1) | GB2227303B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AU627542B2 (en) * | 1989-01-19 | 1992-08-27 | De Beers Industrial Diamond Division (Proprietary) Limited | Sorting method and apparatus |
| GB2229116B (en) * | 1989-02-20 | 1992-12-02 | De Beers Ind Diamond | Particle sorting method and apparatus |
-
1990
- 1990-01-19 AU AU48577/90A patent/AU612535B2/en not_active Ceased
- 1990-01-19 GB GB9001252A patent/GB2227303B/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| GB9001252D0 (en) | 1990-03-21 |
| AU612535B2 (en) | 1991-07-11 |
| GB2227303B (en) | 1992-07-29 |
| AU4857790A (en) | 1990-07-26 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19940119 |