CA1080157A - Process for separating mixtures of particles - Google Patents
Process for separating mixtures of particlesInfo
- Publication number
- CA1080157A CA1080157A CA268,991A CA268991A CA1080157A CA 1080157 A CA1080157 A CA 1080157A CA 268991 A CA268991 A CA 268991A CA 1080157 A CA1080157 A CA 1080157A
- Authority
- CA
- Canada
- Prior art keywords
- magnetic
- fraction
- particles
- feeding
- heavy
- 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.)
- Expired
Links
Landscapes
- Separation Of Solids By Using Liquids Or Pneumatic Power (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The disclosure embraces a process for separating mixtures of particles such as fine coal and shale and includes the steps of mixing the raw coal and shale with a heavy media suspension of magnetizable particles and separating the mixture into heavy and light fractions, feeding the heavy and light fractions to separate screens on which the light and heavy fractions are drained and washed to recover coarse clean coal and coarse washed refuse as well as undiluted and dilute suspensions of these particles; the undiluted suspensions are combined and, at a secondary separating stage, the derived undiluted secondary mixture is separated into heavy and light fractions with the heavy and light fractions being diluted by the dilute suspensions from the respective heavy and light fractions obtained at the first separation stage and screens;
the light and heavy fractions from the secondary separation stage are then fed through recovering apparatus to recover a fine coal fraction, a fine refuse fraction and the magnetizable particles which are thereafter mixed with the raw coal at the initial stage of the process.
The disclosure embraces a process for separating mixtures of particles such as fine coal and shale and includes the steps of mixing the raw coal and shale with a heavy media suspension of magnetizable particles and separating the mixture into heavy and light fractions, feeding the heavy and light fractions to separate screens on which the light and heavy fractions are drained and washed to recover coarse clean coal and coarse washed refuse as well as undiluted and dilute suspensions of these particles; the undiluted suspensions are combined and, at a secondary separating stage, the derived undiluted secondary mixture is separated into heavy and light fractions with the heavy and light fractions being diluted by the dilute suspensions from the respective heavy and light fractions obtained at the first separation stage and screens;
the light and heavy fractions from the secondary separation stage are then fed through recovering apparatus to recover a fine coal fraction, a fine refuse fraction and the magnetizable particles which are thereafter mixed with the raw coal at the initial stage of the process.
Description
2 894 CA
The present invention relates to the field of particle separation and, more specifically, to recovery of a fine grade coal by means of heavy media suspens ions .
As a result of the increasing scarcity of raw materials and fuels, S It Is desirable to recover as much uS~ble coal as is economically and physlcally posslble.
As is well known, one of the chief diffLculties in using coal as a fuel is the pollution that results as a consequence of the high sulfur content in the coal. It has been found, however, that very fine coal is relatively free of sulfur thus rendering the recovery of fine coal fractions hlghly deslrable.
A number of processes have been developed for recoverlng flne coal in the order of 0. 5 mm or smaller. A suchllke process Is froth flotatlon, whlch Is, however, not or less sultable for some types of coal.
For Instance, oxldlzed coal cannot efflclently be recovered by froth flotatlon. A more sultable process Is then a separatlon accordlng to speclflc gravlty uslng llquld separatlng medla.
Apart from the Inltlal capital investment in constructlng a separatlng process plant, one of the major cost factors in running such plants resides In the consumptlon of fresh water needed to efficiently carry out the process. Accordingly, the prlor art has endeavored to reduce the consumption of fresh water required to successfully effect coal washing and particle .' 10~30157 separation. However, such processes have, in general, resulted in an increase in equipment cost per unit quantity of coal pro- -cessed per unit of time as a consequence of the necessity of clarifying or purifying the water used in the process.
Disclosures representative of the prior art in this field are Canadian Patents Nos. 506,145 of September 28, 1954 (Fontein), 551,737 of ~anuary 1, 1958 (Marot), 606,220 of October 4, 1960 (Leeman) and 652,359 of November 13, 1962 (Leeman).
It is an object of the present invention to provide a coal cleaning and recovery process which effects a substantial saving in the quantity of water required in the process. Further, it is an object of the present invention to provide a separating process capable of recovering extremely fine particles of coal ;
as well as for providing a process that has an inherent flexibil-ity in selecting the level of discrimination among the particles of coal and refuse to be recovered.
In the following "raw fine coal" denotes raw coal having a particle size of no more than about 12.5 mm. Raw coal is a mixture of clean coal and refuse (shale). Raw fine coal usually is a minus 12.5 mm size fraction obtained by screening from raw run-of-mine-coal. This raw fine coal and the remaining coarser raw coal are usually cleaned separately to obtain coal of higher purity.
In summary, the invention provides a continuous process for recovering clean coal from raw fine coal having a particle size of no more than about 12.5 mm and comprising moderately fine -coal particles having a particle size between about 0.5 mm and about 12.5 mm, moderately fine refuse particles having a particle size between about 0.5 mm and about 12.5 mm, finer coal particles having a particle size between about 0.1 mm and about 0.5 mm, finer refuse particles having a particle size between about
The present invention relates to the field of particle separation and, more specifically, to recovery of a fine grade coal by means of heavy media suspens ions .
As a result of the increasing scarcity of raw materials and fuels, S It Is desirable to recover as much uS~ble coal as is economically and physlcally posslble.
As is well known, one of the chief diffLculties in using coal as a fuel is the pollution that results as a consequence of the high sulfur content in the coal. It has been found, however, that very fine coal is relatively free of sulfur thus rendering the recovery of fine coal fractions hlghly deslrable.
A number of processes have been developed for recoverlng flne coal in the order of 0. 5 mm or smaller. A suchllke process Is froth flotatlon, whlch Is, however, not or less sultable for some types of coal.
For Instance, oxldlzed coal cannot efflclently be recovered by froth flotatlon. A more sultable process Is then a separatlon accordlng to speclflc gravlty uslng llquld separatlng medla.
Apart from the Inltlal capital investment in constructlng a separatlng process plant, one of the major cost factors in running such plants resides In the consumptlon of fresh water needed to efficiently carry out the process. Accordingly, the prlor art has endeavored to reduce the consumption of fresh water required to successfully effect coal washing and particle .' 10~30157 separation. However, such processes have, in general, resulted in an increase in equipment cost per unit quantity of coal pro- -cessed per unit of time as a consequence of the necessity of clarifying or purifying the water used in the process.
Disclosures representative of the prior art in this field are Canadian Patents Nos. 506,145 of September 28, 1954 (Fontein), 551,737 of ~anuary 1, 1958 (Marot), 606,220 of October 4, 1960 (Leeman) and 652,359 of November 13, 1962 (Leeman).
It is an object of the present invention to provide a coal cleaning and recovery process which effects a substantial saving in the quantity of water required in the process. Further, it is an object of the present invention to provide a separating process capable of recovering extremely fine particles of coal ;
as well as for providing a process that has an inherent flexibil-ity in selecting the level of discrimination among the particles of coal and refuse to be recovered.
In the following "raw fine coal" denotes raw coal having a particle size of no more than about 12.5 mm. Raw coal is a mixture of clean coal and refuse (shale). Raw fine coal usually is a minus 12.5 mm size fraction obtained by screening from raw run-of-mine-coal. This raw fine coal and the remaining coarser raw coal are usually cleaned separately to obtain coal of higher purity.
In summary, the invention provides a continuous process for recovering clean coal from raw fine coal having a particle size of no more than about 12.5 mm and comprising moderately fine -coal particles having a particle size between about 0.5 mm and about 12.5 mm, moderately fine refuse particles having a particle size between about 0.5 mm and about 12.5 mm, finer coal particles having a particle size between about 0.1 mm and about 0.5 mm, finer refuse particles having a particle size between about
- 3 -:: `
~)81)~S~
0.1 mm and about 0.5 mm and finest particles having particle size beIow about 0.1 mm with the aid of a heavy medium comprising magnetizable particles as weighting material comprising the steps of (a) mixing in a mixing tank said raw fine coal with said heavy medium and feeding the resulting mixture to a first hydrocyclone separator means to divide said mixture into a speci-fically heavy fraction containing the bulk of the said moderately fine refuse particles and a specifically light fraction contain-ing the bulk of the said moderately fine coal particles, (b) feeding said specifically light fraction over a first draining screen means and a first washing screen means and said specifi-cally heavy fraction over a second draining screen means and a second washing screen means while spraying rinsing water onto said fractions on each said washing screen means and recovering a washed moderately fine coal fraction from said specifically light fraction and a washed moderately fine refuse fraction from said specifically heavy fraction and undiluted suspensions con-taining finer and finest particles from said first and second draining screen means, and dilute suspensions containing finer and finest particles from said first and second washing screen means, (c) feeding said undiluted suspensions and heavy medium to a first collecting tank, splitting the mixture collected in said collecting tank into two streams, recycling one of said streams to said mixing tank and feeding the other stream to a secondary hydrocyclone separator means to separate said other stream into a secondary specifically heavy fraction containing the bulk of the said finer refuse particles and a secondary speci-fically light fraction containing the bulk of the said finer coal particles, (d) diluting said secondary specifically light fraction with said fine dilute suspension derived from said first washing screen means and diluting said secondary specifically heavy fraction with said dilute suspension derived from said second washing screen means, (e~ recovering said magnetic particles from said diluted secondary specifically light fraction in first recovering means and recovering said magnetic particles from said diluted secondary specifically heavy fraction in second recovering means.
For better recovering of the magnetic material, in the process according to the invention said recovering of said magnetic particles from said diluted secondary specifically light fraction in first recovering means is preferably carried out by separating said fraction into a tertiary relatively coarse and a tertiary relatively fine light fraction and feeding said tertiary relatively coarse and relatively fine light fractions to first and second magnetic separators respectively, and said recovering of said magnetic particles from said diluted secondary specifically heavy fraction in second recovering means is carried out by separating said fraction into a tertiary relative-ly coarse and a tertiary relatively fine heavy fraction and feeding said tertiary relatively coarse and relatively fine heavy fractions to third and fourth magnetic separators respect-ively, and a further step is included comprising feeding atleast a portion of said diluted tertiary relatively fine light fraction from which said magnetic particles have been substan-tially recovered to a second collecting tank for further use in the process. Preferably liquid suspension collected in this second collecting tank is fed upstream of said second recovering means to further dilute said diluted secondary heavy fraction.
With this arrangement, the necessity of using large quantities of either clarified or fresh water in the recovery of the magnetic particles at this stage of the process can be entirely eliminated without any significant reduction in the proportion of magnetic particles recovered.
Advantages of the invention will become apparent as ~ - 5 consideration is given to the following detailed description of an embodiment of the invention and accompanying drawing in `~
which:
Figure lA and B is a schematic illustration of the various stages of a process according to the present invention wherein the lines represent conduits and the arrows the direction of flow in each conduit.
- 5a -, - -Referrir.g to Figure lA, raw coal which is a mixture of coal, shale and various refuse particles which has first been screened to remove all particles larger than e.g. approximately a half inch in size is introduced into a mixing tank 10 together with a suspension of magnetizable particles which may include recycled coal and refuse elemer.ts at 12. The mixing tank 10 is provided with an overflow 14 to provide a constant head of pressure of e.g. 4.5 m of liquid column, but that can be selected in the rar,ge from 3 m to 6 m of liquid column.
From the outlet of the mixing tank 10, the mixture which is called a heavy media mixture is fed to a first separating stage 16 which may consist of a hydrocyclone or a plurality of hydro-cyclones in parallel which function to separate the mixture according to the density of the particles. Thus, a relatively ls light fraction will be introduced into the collecting tank 13, whereas a relatively heavy fraction will be introduced into the collecting tank 20.
The relatively heavy and light fractions are then passed tangentially to sieve bends 22 and 24 which, preferably, -;
have a fairly large radius of curvature of e.g. about 1000 mm and slot widths o~ approximately 1 mm so that only particles smaller than approximately O.S mm will pass therethrough.
At this jur,cture, it should be noted that since for practical purposes the input to the first separating stage is ' 10~0~7 ,, ~.
conventionally large in volume, the hydrocyclones used in the first separating stage should all be of the low pressure heavy media type which are unable to discriminate between particles of less than about 0.5 mm in size. ~he particles that do not pass : 5 through the slots of the sieve bends 22 and 24 are passed to drair,ir,g screens 23 and 25 and rinsing screens 26 and 28 respectively where the fractions are first drained and then ; rinsed off with clarified water from nozzles 30 and by fresh water from the nozzles 32. Thus, clean coarse coal is recovered at 34 and clean coarse refuse is recovered at 36. ;
The drainings from sieve bends 22 and 24 and the draining `-screens 23 and 25 which comprise the major portion of the heavy medium and unseparated fine particles are collected and fed to a tank 38 via a specific gravity controller 40 which also receives lS the suspension overflowing at 14 from the mixing tank 10 and recovered heavy media from a subsequent stage of the process.
From tar.k 38, a portion of the heavy media containing magnetite ar.d unseparated fine particles is fed back through pump 42 to a collecting tank 44 whère the medium is re-introduced for mixture with the incoming raw coal.
The remaining portion of the heavy medium from tank 38 is fed via pump 46 to a secondary separating stage which may comprise a plurality of hydrocyclones in parallel as at 48 which should be of the high pressure type so as to be able to separate particles smaller thar. about 0.5 mm. The operating pressure of these hydrocyclones is preferably selected in the range from 8 to ~()801S~7 ~
15 m of liquid column. The hydrocyclone 48 will separate the incoming suspension of particles ir. heavy media into a relatively light fraction which is collected in tank 50 and which consists -~' mainly of coal and heavy media and a relatively heavy fractior, which is collected in tank 52 which consists primarily of refuse and heavy media.
According to the present invention, the fractions from the secondary separating stage 48 are then diluted with the dilute suspensionsderived at 27 and 29 from the rinsing screens 26 and 28. Thus, the dilute suspension from the coarse light fraction is introduced at 54 and the dilute suspension from the coarse heavy fractionlis introduced at 56. Additionally, the light f'raction is '~
further diluted with clarified water as at 58, whereas, according to a preferred embodiment of the present invention the heavy fraction is further diluted by liquid as at 60 which originates on the light fraction side of the secondary separating stage, as will be ex-plained hereinafter.
Ir order to recover the magnetic particles and separate them from the fine coal and refuse fractions, the suspensions in collecting tanks 50 and 52 are I'ed tan~entially throu~h one or more rapped sieve bends 62 and 64 for -the ]ight fractions composed of coal and magnetic particles and 66 and 68 for the heavy fraction composed of refuse and magnetic particles. 'I`he drainings from the sieve bends 62 and 64 are fed to a first series of magnetic separators 72 ar,d 74 while the relatively coarser particles are fed to a second series of magnetic separators 76 and 78. The magnetic particles are collected at 80 and 82 and fed by l~Olg7 suitable conduits back to the tank 38 via the specific gravity controller 40 either directly or through a splitter box 84. The splitter box 84 is lir,ked by conduits to acorltinuous cycling storage facility consisting of a tank 86 and conduits 88 and 90 so that a sufficient quantity of magnetic particles in suspension will be available for maintaining the specific gravity of the heavy media at the required value. The operation of such storage facilities is well understood in the art and will therefore not be further described.
Returning now to the ref`use side of the secondary separating stage 48, as previoUsly noted, the heavy fraction from the apex outlet of the hydrocyclone 48 is collected in tank 52 where it is mixed with the dilute suspension as at 56 derived at 29 from the rinsing screen 28. I`he contents of the collecting tank 52 are contir,uously fed to the series of rapped sieve bends 66 and 68 with the drainings from the sieve bends 66 and 68 being fed to a third series of magnetic separators 92 and 94 while the coarser particles are mixed ~ith clarified li4uid as clt 91 and 93 and are then fed to a fourth series of magne-tic separators 96 and 98.
In an alternative embodiment of the present invention the plurality of magnetic separators on the coal and refuse sides, may each be a common magnetic separator having different sections for the different f`ractions. For example, the magnetic separators at 72 and 76 may be replaced by a common magnetic separator having two separating sections.
~ ~o80~7 Just as with the light fraction magnetic separators 72 through 78, the magnetic particles are recovered from the magnetic separators 92 through 98 for the re-use in the process by being combined with the magnetic particles recovered from the magnetic separators 72 through 78.
Preferably according to the present invention, the suspensions recovered from the magnetic separators 72 and 74 which includes the Elnest coal and shale fractlons below e.g. 0.1 mm is fed vLa conduit 100 directly to a collectlng tank 102. Whereas the clean coal recovered from the magnetic separators 76 and 78 is fed first to a centrifuge 104 (Flgure lB) via conduit 106. The centrifuge 104 recovers clean coal at 108 which w ill be in the order of 0.5-0.1 mm in size . The liquLd recovered from the centrlfuge 104 is fed back through conduit 110 to the tank 102.
From tank 102, the relatively clean liquLd which is commonly water is pumped vla pump 112 back to collecting tank 52 to be used as a dllutlon medlum to facllltate separatLon of the magnetlc partlcles from the refuse coming from the apex of the hydrocyclone stage 48. Thus, the necessity for employing eLther clarified or fresh water at this stage is ellmlnated whlch wlll result in a large conservation of water. For example, where the process Is designed ts accomodate approximately 300 tons per hour of raw coal, a saving of approximately 1,300 gallons per minute can be effected. This is achievable by virtue of the feature of the present inventlon that the liquid collected In tank 102 will have an essentially negligible portion of clean coal therein as a result of the preceding steps of the process. As Indicated in broken lines, from the tank 102 the liquid can also be pumped via pump 112 and a conduit 136 to a thickener 124 to separate~y recover a finestfraction relatLvely rich in coal at 134; the conservation of water is then, however, much less.
Returning now to the refuse side of the secondary separating stage ~Q~0157 48, the suspensions recovered from the drainings of Lhe sieve bends 66 and 68 after removal of the magnetic particles in magnetic separators 92 and 94, may be fed directly to a pump tank 114 whereas the coarse particles from the sieve bends 66 and 68 after removal of the magnetic particles in magnetic separators 96 and 98 are fed to a centrifuge 116 which produces clean refuse at 118 and water containing only the fines particles at 120. If it is desired to remove such particles, this suspension may be combined with the suspension derived from the magnetic separators 92 and 94 and then fed to a thickener 122.
As is conventLonal, the thickener 122 is employed to remove the flnes partLcles Ln the order of 0.1 mm or less .
Other types of apparatus may, of course, be employed such as flotation tanks or filters. Water is recovered at tank 126 from the thickener 122, and then pumped via pump 128 to a tank 130 where the water is stored for use in the process previously described. The bottom product of the thickener is discharged vLa conduit 132.
From the foregolng, it will be seen, that the process of the present Lnvention will enable the recovery of the finest of coal partLcles whLch, as prevLously noted, are substantLally free of sulphur thus renderLng such a product desLrable for use in many industrial applications. Further, thc opcration of tlte process can be adjusted very simply to vary the separation dis-crimination of the process while maintaining a substantial saving in water consumption.
It will be obvious to those skilled in the art that various modifications may be made in the process of the present ;:
invention without departing from the spirit and scope thereof as defined in the appended claims.
"
'
~)81)~S~
0.1 mm and about 0.5 mm and finest particles having particle size beIow about 0.1 mm with the aid of a heavy medium comprising magnetizable particles as weighting material comprising the steps of (a) mixing in a mixing tank said raw fine coal with said heavy medium and feeding the resulting mixture to a first hydrocyclone separator means to divide said mixture into a speci-fically heavy fraction containing the bulk of the said moderately fine refuse particles and a specifically light fraction contain-ing the bulk of the said moderately fine coal particles, (b) feeding said specifically light fraction over a first draining screen means and a first washing screen means and said specifi-cally heavy fraction over a second draining screen means and a second washing screen means while spraying rinsing water onto said fractions on each said washing screen means and recovering a washed moderately fine coal fraction from said specifically light fraction and a washed moderately fine refuse fraction from said specifically heavy fraction and undiluted suspensions con-taining finer and finest particles from said first and second draining screen means, and dilute suspensions containing finer and finest particles from said first and second washing screen means, (c) feeding said undiluted suspensions and heavy medium to a first collecting tank, splitting the mixture collected in said collecting tank into two streams, recycling one of said streams to said mixing tank and feeding the other stream to a secondary hydrocyclone separator means to separate said other stream into a secondary specifically heavy fraction containing the bulk of the said finer refuse particles and a secondary speci-fically light fraction containing the bulk of the said finer coal particles, (d) diluting said secondary specifically light fraction with said fine dilute suspension derived from said first washing screen means and diluting said secondary specifically heavy fraction with said dilute suspension derived from said second washing screen means, (e~ recovering said magnetic particles from said diluted secondary specifically light fraction in first recovering means and recovering said magnetic particles from said diluted secondary specifically heavy fraction in second recovering means.
For better recovering of the magnetic material, in the process according to the invention said recovering of said magnetic particles from said diluted secondary specifically light fraction in first recovering means is preferably carried out by separating said fraction into a tertiary relatively coarse and a tertiary relatively fine light fraction and feeding said tertiary relatively coarse and relatively fine light fractions to first and second magnetic separators respectively, and said recovering of said magnetic particles from said diluted secondary specifically heavy fraction in second recovering means is carried out by separating said fraction into a tertiary relative-ly coarse and a tertiary relatively fine heavy fraction and feeding said tertiary relatively coarse and relatively fine heavy fractions to third and fourth magnetic separators respect-ively, and a further step is included comprising feeding atleast a portion of said diluted tertiary relatively fine light fraction from which said magnetic particles have been substan-tially recovered to a second collecting tank for further use in the process. Preferably liquid suspension collected in this second collecting tank is fed upstream of said second recovering means to further dilute said diluted secondary heavy fraction.
With this arrangement, the necessity of using large quantities of either clarified or fresh water in the recovery of the magnetic particles at this stage of the process can be entirely eliminated without any significant reduction in the proportion of magnetic particles recovered.
Advantages of the invention will become apparent as ~ - 5 consideration is given to the following detailed description of an embodiment of the invention and accompanying drawing in `~
which:
Figure lA and B is a schematic illustration of the various stages of a process according to the present invention wherein the lines represent conduits and the arrows the direction of flow in each conduit.
- 5a -, - -Referrir.g to Figure lA, raw coal which is a mixture of coal, shale and various refuse particles which has first been screened to remove all particles larger than e.g. approximately a half inch in size is introduced into a mixing tank 10 together with a suspension of magnetizable particles which may include recycled coal and refuse elemer.ts at 12. The mixing tank 10 is provided with an overflow 14 to provide a constant head of pressure of e.g. 4.5 m of liquid column, but that can be selected in the rar,ge from 3 m to 6 m of liquid column.
From the outlet of the mixing tank 10, the mixture which is called a heavy media mixture is fed to a first separating stage 16 which may consist of a hydrocyclone or a plurality of hydro-cyclones in parallel which function to separate the mixture according to the density of the particles. Thus, a relatively ls light fraction will be introduced into the collecting tank 13, whereas a relatively heavy fraction will be introduced into the collecting tank 20.
The relatively heavy and light fractions are then passed tangentially to sieve bends 22 and 24 which, preferably, -;
have a fairly large radius of curvature of e.g. about 1000 mm and slot widths o~ approximately 1 mm so that only particles smaller than approximately O.S mm will pass therethrough.
At this jur,cture, it should be noted that since for practical purposes the input to the first separating stage is ' 10~0~7 ,, ~.
conventionally large in volume, the hydrocyclones used in the first separating stage should all be of the low pressure heavy media type which are unable to discriminate between particles of less than about 0.5 mm in size. ~he particles that do not pass : 5 through the slots of the sieve bends 22 and 24 are passed to drair,ir,g screens 23 and 25 and rinsing screens 26 and 28 respectively where the fractions are first drained and then ; rinsed off with clarified water from nozzles 30 and by fresh water from the nozzles 32. Thus, clean coarse coal is recovered at 34 and clean coarse refuse is recovered at 36. ;
The drainings from sieve bends 22 and 24 and the draining `-screens 23 and 25 which comprise the major portion of the heavy medium and unseparated fine particles are collected and fed to a tank 38 via a specific gravity controller 40 which also receives lS the suspension overflowing at 14 from the mixing tank 10 and recovered heavy media from a subsequent stage of the process.
From tar.k 38, a portion of the heavy media containing magnetite ar.d unseparated fine particles is fed back through pump 42 to a collecting tank 44 whère the medium is re-introduced for mixture with the incoming raw coal.
The remaining portion of the heavy medium from tank 38 is fed via pump 46 to a secondary separating stage which may comprise a plurality of hydrocyclones in parallel as at 48 which should be of the high pressure type so as to be able to separate particles smaller thar. about 0.5 mm. The operating pressure of these hydrocyclones is preferably selected in the range from 8 to ~()801S~7 ~
15 m of liquid column. The hydrocyclone 48 will separate the incoming suspension of particles ir. heavy media into a relatively light fraction which is collected in tank 50 and which consists -~' mainly of coal and heavy media and a relatively heavy fractior, which is collected in tank 52 which consists primarily of refuse and heavy media.
According to the present invention, the fractions from the secondary separating stage 48 are then diluted with the dilute suspensionsderived at 27 and 29 from the rinsing screens 26 and 28. Thus, the dilute suspension from the coarse light fraction is introduced at 54 and the dilute suspension from the coarse heavy fractionlis introduced at 56. Additionally, the light f'raction is '~
further diluted with clarified water as at 58, whereas, according to a preferred embodiment of the present invention the heavy fraction is further diluted by liquid as at 60 which originates on the light fraction side of the secondary separating stage, as will be ex-plained hereinafter.
Ir order to recover the magnetic particles and separate them from the fine coal and refuse fractions, the suspensions in collecting tanks 50 and 52 are I'ed tan~entially throu~h one or more rapped sieve bends 62 and 64 for -the ]ight fractions composed of coal and magnetic particles and 66 and 68 for the heavy fraction composed of refuse and magnetic particles. 'I`he drainings from the sieve bends 62 and 64 are fed to a first series of magnetic separators 72 ar,d 74 while the relatively coarser particles are fed to a second series of magnetic separators 76 and 78. The magnetic particles are collected at 80 and 82 and fed by l~Olg7 suitable conduits back to the tank 38 via the specific gravity controller 40 either directly or through a splitter box 84. The splitter box 84 is lir,ked by conduits to acorltinuous cycling storage facility consisting of a tank 86 and conduits 88 and 90 so that a sufficient quantity of magnetic particles in suspension will be available for maintaining the specific gravity of the heavy media at the required value. The operation of such storage facilities is well understood in the art and will therefore not be further described.
Returning now to the ref`use side of the secondary separating stage 48, as previoUsly noted, the heavy fraction from the apex outlet of the hydrocyclone 48 is collected in tank 52 where it is mixed with the dilute suspension as at 56 derived at 29 from the rinsing screen 28. I`he contents of the collecting tank 52 are contir,uously fed to the series of rapped sieve bends 66 and 68 with the drainings from the sieve bends 66 and 68 being fed to a third series of magnetic separators 92 and 94 while the coarser particles are mixed ~ith clarified li4uid as clt 91 and 93 and are then fed to a fourth series of magne-tic separators 96 and 98.
In an alternative embodiment of the present invention the plurality of magnetic separators on the coal and refuse sides, may each be a common magnetic separator having different sections for the different f`ractions. For example, the magnetic separators at 72 and 76 may be replaced by a common magnetic separator having two separating sections.
~ ~o80~7 Just as with the light fraction magnetic separators 72 through 78, the magnetic particles are recovered from the magnetic separators 92 through 98 for the re-use in the process by being combined with the magnetic particles recovered from the magnetic separators 72 through 78.
Preferably according to the present invention, the suspensions recovered from the magnetic separators 72 and 74 which includes the Elnest coal and shale fractlons below e.g. 0.1 mm is fed vLa conduit 100 directly to a collectlng tank 102. Whereas the clean coal recovered from the magnetic separators 76 and 78 is fed first to a centrifuge 104 (Flgure lB) via conduit 106. The centrifuge 104 recovers clean coal at 108 which w ill be in the order of 0.5-0.1 mm in size . The liquLd recovered from the centrlfuge 104 is fed back through conduit 110 to the tank 102.
From tank 102, the relatively clean liquLd which is commonly water is pumped vla pump 112 back to collecting tank 52 to be used as a dllutlon medlum to facllltate separatLon of the magnetlc partlcles from the refuse coming from the apex of the hydrocyclone stage 48. Thus, the necessity for employing eLther clarified or fresh water at this stage is ellmlnated whlch wlll result in a large conservation of water. For example, where the process Is designed ts accomodate approximately 300 tons per hour of raw coal, a saving of approximately 1,300 gallons per minute can be effected. This is achievable by virtue of the feature of the present inventlon that the liquid collected In tank 102 will have an essentially negligible portion of clean coal therein as a result of the preceding steps of the process. As Indicated in broken lines, from the tank 102 the liquid can also be pumped via pump 112 and a conduit 136 to a thickener 124 to separate~y recover a finestfraction relatLvely rich in coal at 134; the conservation of water is then, however, much less.
Returning now to the refuse side of the secondary separating stage ~Q~0157 48, the suspensions recovered from the drainings of Lhe sieve bends 66 and 68 after removal of the magnetic particles in magnetic separators 92 and 94, may be fed directly to a pump tank 114 whereas the coarse particles from the sieve bends 66 and 68 after removal of the magnetic particles in magnetic separators 96 and 98 are fed to a centrifuge 116 which produces clean refuse at 118 and water containing only the fines particles at 120. If it is desired to remove such particles, this suspension may be combined with the suspension derived from the magnetic separators 92 and 94 and then fed to a thickener 122.
As is conventLonal, the thickener 122 is employed to remove the flnes partLcles Ln the order of 0.1 mm or less .
Other types of apparatus may, of course, be employed such as flotation tanks or filters. Water is recovered at tank 126 from the thickener 122, and then pumped via pump 128 to a tank 130 where the water is stored for use in the process previously described. The bottom product of the thickener is discharged vLa conduit 132.
From the foregolng, it will be seen, that the process of the present Lnvention will enable the recovery of the finest of coal partLcles whLch, as prevLously noted, are substantLally free of sulphur thus renderLng such a product desLrable for use in many industrial applications. Further, thc opcration of tlte process can be adjusted very simply to vary the separation dis-crimination of the process while maintaining a substantial saving in water consumption.
It will be obvious to those skilled in the art that various modifications may be made in the process of the present ;:
invention without departing from the spirit and scope thereof as defined in the appended claims.
"
'
Claims (11)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A continuous process for recovering clean coal from raw fine coal having a particle size of no more than about 12.5 mm and comprising moderately fine coal particles having a particle size between about 0.5 mm and about 12.5 mm, moderately fine refuse particles having a particle size between about 0.5 mm and about 12.5 mm, finer coal particles having a particle size between about 0.1 mm and about 0.5 mm, finer refuse parti-cles having a particle size between about 0.1 mm and about 0.5 mm and the finest particles having a particle size below about 0.1 mm with the aid of a heavy medium comprising magnetizable particles as weighting material comprising the steps of (a) mixing in a mixing tank said raw fine coal with said heavy medium and feeding the resulting mixture to a first hydrocyclone separator means to divide said mixture into a speci-fically heavy fraction containing the bulk of the said moderately fine refuse particles and a specifically light fraction contain-ing the bulk of the said moderately fine coal particles, (b) feeding said specifically light fraction over a first draining screen means and a first washing screen means and said specifically heavy fraction over a second draining screen means and a second washing screen means while spraying rinsing water onto said fractions on each said washing screen means and recovering a washed moderately fine coal fraction from said specifically light fraction and a washed moderately fine refuse fraction from said specifically heavy fraction and un-diluted suspensions containing finer and finest particles from said first and second draining screen means, and dilute sus-pensions containing finer and finest particles from said first and second washing screen means, (c) feeding said undiluted suspensions and heavy medium to a first collecting tank, splitting the mixture collected in said collecting tank into two streams, recycling one of said streams to said mixing tank and feeding the other stream to a secondary hydrocyclone separator means to separate said other stream into a secondary specifically heavy fraction containing the bulk of the said finer refuse particles and a secondary specifically light fraction containing the bulk of the said finer coal particles, (d) diluting said secondary specifically light fraction with said fine dilute suspension derived from said first washing screen means and diluting said secondary specifically heavy fraction with said dilute suspension derived from said second washing screen means, (e) recovering said magnetic particles from said diluted secondary specifically light fraction in first recovering means and recovering said magnetic particles from said diluted secondary specifically heavy fraction in second recovering means.
2. The process as claimed in claim 1 wherein said recover-ing of said magnetic particles from said diluted secondary specifically light fraction in first recovering means is carried out by separating said fraction into a tertiary relatively coarse and a tertiary relatively fine light fraction and feeding said tertiary relatively coarse and relatively fine light frac-tions to first and second magnetic separators respectively, and said recovering of said magnetic particles from said diluted secondary specifically heavy fraction in second recovering means is carried out by separating said fraction into a tertiary relatively coarse and a tertiary relatively fine heavy fraction and feeding said tertiary relatively coarse and relatively fine heavy fraction to third and fourth magnetic separators res-pectively, and comprising the further step of feeding at least a portion of said diluted tertiary relatively fine light fraction from which said magnetic particles have been substantially recovered to a second collecting tank for further use in the process.
3. The process as claimed in claim 2 comprising the further step of feeding liquid suspension collected in said second collecting tank upstream of said second recovering means to further dilute said diluted secondary heavy fraction.
4. The process as claimed in claim 2 wherein said separa-ting of said diluted secondary specifically light and heavy fractions into tertiary relatively coarse and relatively fine fractions is carried out by means of screens having a curved slotted surface by separately feeding said diluted secondary fractions generally tangentially to such curved slotted sur-faces.
5. The process as claimed in claim 2 including the steps of feeding the non-magnetic fraction derived from said first magnetic separator to a fifth magnetic separator and feeding the non-magnetic fraction derived from said second magnetic separator to a sixth magnetic separator.
6. The process as claimed in claim 5 wherein the magnetic particles recovered from said first, second, fifth and sixth magnetic separators are fed to a mixing tank and including the step of feeding raw coal into said mixing tank to form a mixture of said solid particles to be separated and heavy medium.
7. The process as claimed in claim 5 including the step of feeding the non-magnetic fraction recovered from said fifth magnetic separator to a dewatering means and feeding the liquid recovered from said dewatering means to said collecting tank.
8. The process as claimed in claim 5 or 6 or 7 including the steps of dewatering the non-magnetic fraction recovered from said fifth magnetic separator and thickening the liquid removed in said dewatering step and the liquid collected in said collecting tank.
9. The process as claimed in claim 5 including the steps of feeding the non-magnetic fraction derived from said fourth magnetic separator to a seventh magnetic separator of said second recovering means and feeding the non-magnetic fraction derived from said third magnetic separator to an eighth magnetic separator of said second recovering means and combining the magnetic particles recovered from third, fourth, seventh and eighth magnetic separators of said second recovering means with the magnetic particles recovered from said first recovering means for re-use in said process.
10. The process as claimed in claim 2 including the steps of feeding the non-magnetic fractions recovered from said magnetic separators of said second recovering means to dewatering means.
11. The process as claimed in claim 9 or 10 including the steps of feeding the non-magnetic fraction from said seventh magnetic separator of said second recovering means directly to a thickener feeding a non-magnetic fraction from said eighth magnetic separator of said second recovering means to a dewatering means and feeding the liquid removed in said dewatering means to said thickener.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US64633976A | 1976-01-02 | 1976-01-02 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1080157A true CA1080157A (en) | 1980-06-24 |
Family
ID=24592665
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA268,991A Expired CA1080157A (en) | 1976-01-02 | 1976-12-31 | Process for separating mixtures of particles |
Country Status (3)
| Country | Link |
|---|---|
| AU (1) | AU503005B2 (en) |
| CA (1) | CA1080157A (en) |
| ZA (1) | ZA76930B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103964145A (en) * | 2014-05-07 | 2014-08-06 | 中石化宁波工程有限公司 | Accurate coal blending process |
| CN113731620A (en) * | 2021-08-10 | 2021-12-03 | 新疆宝明矿业有限公司 | Medium recovery method and medium recovery system |
-
1976
- 1976-02-17 ZA ZA930A patent/ZA76930B/en unknown
- 1976-12-24 AU AU20922/76A patent/AU503005B2/en not_active Expired
- 1976-12-31 CA CA268,991A patent/CA1080157A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103964145A (en) * | 2014-05-07 | 2014-08-06 | 中石化宁波工程有限公司 | Accurate coal blending process |
| CN113731620A (en) * | 2021-08-10 | 2021-12-03 | 新疆宝明矿业有限公司 | Medium recovery method and medium recovery system |
Also Published As
| Publication number | Publication date |
|---|---|
| ZA76930B (en) | 1977-01-26 |
| AU2092276A (en) | 1978-06-29 |
| AU503005B2 (en) | 1979-08-16 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4802976A (en) | Method for recovering fine clean coal | |
| US2932395A (en) | Process of separating mixtures of particles | |
| US10799880B2 (en) | Method and apparatus for washing and grading silica sand for glass production | |
| CA1118723A (en) | Heavy magnetic media hydrocyclonic separation process with screening, magnetic separation and recycling of liquids | |
| GB1526591A (en) | Process for recovering usable materials from waste material containing metals and non-metals | |
| US4140628A (en) | Dense medium separation | |
| CN110523524A (en) | A kind of full grade of anthracite is selected to simplify sorting process | |
| JP2019103989A (en) | Cleaning classification processing method of contaminated soil | |
| CN111515018B (en) | Coal slime grading and sorting process in coking coal separation plant | |
| US3794162A (en) | Heavy medium beneficiating process | |
| US2690261A (en) | Concentration of minerals | |
| US2387866A (en) | Heavy media separation process | |
| US2429436A (en) | Combined gravity classification and screening of ore | |
| US2781906A (en) | Process and apparatus for the separation of mixtures of solid particles | |
| US2654479A (en) | Separation of suspensions of solid matter in liquids | |
| CN214021353U (en) | Gravity-flotation combined separation system for refractory fluorite ores | |
| CA1080157A (en) | Process for separating mixtures of particles | |
| CN113631739B (en) | Recovery of chromite fines | |
| US3638791A (en) | Method for treatment of heavy media | |
| US3687284A (en) | Reconditioning of suspensions used in the separation of minerals | |
| US2860782A (en) | Process for separating a mixture of solid particles | |
| CN113210125B (en) | Method and system for re-washing heavy medium of partial middlings | |
| US3023893A (en) | Process for separating particles of solid x | |
| US2949190A (en) | Separation of fine sized solids | |
| US3064813A (en) | Method and means for filtration of slurries |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |