Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03B—SEPARATING SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS
  • B03B9/00—General arrangement of separating plant, e.g. flow sheets
  • B03B9/005—General arrangement of separating plant, e.g. flow sheets specially adapted for coal
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03B—SEPARATING SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS
  • B03B1/00—Conditioning for facilitating separation by altering physical properties of the matter to be treated
  • B03B1/04—Conditioning for facilitating separation by altering physical properties of the matter to be treated by additives
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G OR C10K; LIQUIFIED PETROLEUM GAS; USE OF ADDITIVES TO FUELS OR FIRES; FIRE-LIGHTERS
  • C10L5/00—Solid fuels
  • C10L5/02—Solid fuels such as briquettes consisting mainly of carbonaceous materials of mineral or non-mineral origin
  • C10L5/34—Other details of the shaped fuels, e.g. briquettes
  • C10L5/36—Shape
  • C10L5/366—Powders
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G OR C10K; LIQUIFIED PETROLEUM GAS; USE OF ADDITIVES TO FUELS OR FIRES; FIRE-LIGHTERS
  • C10L9/00—Treating solid fuels to improve their combustion
  • C10L9/10—Treating solid fuels to improve their combustion by using additives

Definitions

• the instant invention pertains to methods of cleaning fine coal of its impurities in aqueous media and removing the process water from both the clean coal and refuse products to the levels that can usually be achieved by thermal drying.
• Coal is an organic material that is burned to produce heat for power generation and for industrial and domestic applications. It has inclusions of mineral matter and may contain undesirable elements such as sulfur and mercury. Coal combustion produces large amounts of ash and fugitive dusts that need to be handled properly. Therefore, run-of-the mine coal is cleaned of the mineral matter before utilization, which also helps increase combustion efficiencies and thereby reduces CO 2 emissions. In general, coarse coal (50 x 0.15 mm) can be cleaned efficiently by exploiting the specific gravity differences between the coal and mineral matter, while fine coal (approximately 0.15 mm and smaller) is cleaned by froth flotation.
• the agglomerates formed by these processes are usually large enough to be separated from the mineral matter dispersed in water by simple screening. Further, selective agglomeration gives lower-moisture products and higher coal recoveries than froth flotation. On the other hand, it suffers from high dosages of oil.
• the amounts of oil used in the selective agglomeration process are typically in the range of 5 to 30% by weight of feed coal (S,C. Tsai, in Fundamentals of Coal Beneficiation and Utilization, Elsevier, 2982, p. 335).
• agglomerates have void spaces in between the particles constituting agglomerates that are filled-up with water, in which fine mineral matter, e.g., clay, is dispersed, which in turn makes it difficult to obtain low moisture- and low-ash products.
• Attempts were made to overcome this problem by using sufficiently large amounts of oil so that the void spaces are filled-up with oil and thereby minimize the entrapment of fine mineral matter.
• Capes et al. Pander Technology, vol. 40, 1 84, pp. 43-52 found indeed that the moisture contents were in excess of 50% by weight when the amount of oil used was less than 5%. By increasing the oil dosage to 35%, the moisture contents were substantially reduced to the range of 17-18%.
• Chang et al. U.S. Patent No. 4,613,429 disclosed a method of cleaning fine coal of mineral matter by selective transport of particles across the water/liquid carbon dioxide interface.
• the liquid CO2 can be recycled.
• a report shows that the clean coal products obtained using this liquid carbon dioxide (LICADO) process contained 5-15% moisture after filtration (Cooper et al., Proceedings of the 25th Intersociety Energy Conversion Engineering Conference, 1990, August 12-17, 1990, pp. 137-142).
• Yoon et al. U.S. Patent No. 5,459,786
• the dewatering is achieved by allowing the liquids to displace surface moisture.
• fine coal refers to coal containing particles mostly smaller than 1 mm in diameter, but the most significant benefits of this invention can be realized with fine coal containing particles less than 0.25 mm.
• a hydrophobic liquid is added to an aqueous medium, in which fine coal is dispersed, and the suspension (or slurry) is agitated. Addition of the hydrophobic liquid can take place when the suspension (or slurry) is being agitated.
• the hydrophobic liquid is chosen so that its contact angle on the coal surface, as measured through the aqueous phase, is larger than 90°. Use of such a liquid allows coal particles to be engulfed (or transported) into the hydrophobic liquid phase, leaving hydrophilic mineral matter in the aqueous phase.
• the amount of the hydrophobic liquid to be added should be large enough so that all of the recoverable coal particles can be engulfed (or immersed) into the hydrophobic liquid phase.
• the coal particles engulfed into the hydrophobic liquid phase are essentially dry because the water in contact with the hydrophobic surface is displaced spontaneously by the hydrophobic liquid during the process of engulfment
• the dewatering by displacement (DBD) process has a problem in that significant amounts of the process water can be entrained into the organic phase in the form of water drops stabilized by hydrophobic coal particles. It is well known that particles with contact angles larger than 90° stabilize water drops in oil phase forming a water-in-oil emulsion (Binks, Current Opinion in Colloid and Interface Science, vol 7, 2002, pp. 21-41). It has been found that much of the water entrained into the hydrophobic liquid phase is present as large globules.
• the hydrophobic liquid containing dry coal particles and entrained water as water-in-oil emulsion is phase-separated from the aqueous phase containing hydrophilic mineral matter.
• the hydrophobic liquid is transferred to a size-size separator, such as screen, classifier, and/or cyclone, to remove the globules of water from the dry coal particles.
• the smaller size fraction e.g., screen underflow
• the larger size fraction e.g., screen overflow
• the larger size fraction can be re-dispersed in water and subjected to another set of agitation and screening to recover additional coal.
• the larger size fraction may be returned to the feed stream to allow the misplaced coal particles to have another opportunity to be recovered.
• the larger globules of water can be readily removed. It would be difficult, however, to remove the smaller droplets stabilized by finer coal particles using the currently available size-size separation technologies, making it difficult to obtain effectively dry coal particles containing less than 1% moisture.
• the cut size of the size-size separation step e.g., by increasing the screen aperture, to obtain higher moistures, e.g., 5 to 10% by weight.
• the clean coal product which is now substantially free of mineral matter and surface moisture may then be subjected to aprocess, in which a small amount of residual hydrophobic liquid is recovered and recycled.
• the water droplets (or globules) are broken up using an appropriate mechanical means such as ultrasonic vibration so that the hydrophobic coal particles are detached from the water droplets (or globules) and dispersed in the hydrophobic liquid.
• the organic liquid phase in which the coal particles are dispersed is separated from the aqueous phase in which hydrophilic mineral matter is dispersed, and then subjected to appropriate solid- liquid separation means such as settling, filtration and/or centrifugation.
• the recovered hydrophobic liquid is recycled.
• the small amount of the hydrophobic liquid that may be adhering onto the surface of the hydrophobic particles (or solids) obtained from the solid-liquid separation step is also recovered and recycled using processes that may involve vaporization and condensation.
• the hydrophobic liquid in which dry coal and water globules are dispersed, is subjected to a solid-liquid separation using a centrifuge, filter, roller press, or other suitable separator.
• the water-in-oil emulsions become smaller in size by expression and drainage, leaving only very small droplets of water trapped in between particles.
• the entrapped interstitial water is released by disturbing the cake structure, in which the small droplets are entrapped, by high-shear agitation.
• a combination of the solid-liquid separation involving expression and drainage and the additional step involving high-shear agitation allows the moisture contents to be reduced to less than 8% by weight, the levels that can usually be achieved by thermal drying.
• the extent of the moisture reduction can be achieved by controlling the process of high-shear agitation in terms of agitation intensity, duration, and devices employed.
• the hydrophobic liquids used in most of the embodiments of the instant invention are recovered and recycled. Bulk of the liquid is recovered without involving phase changes, while only the small amount of the residual hydrophobic liquid adhering onto the surface of hydrophobic particles (e.g., coal) is recovered by vaporization and condensation. If the liquid has a boiling point below the ambient, much of the processing steps described above are carried out in pressurized reactors. In this case, the small amount of the residual hydrophobic liquid can be recovered in gaseous form by pressure release, which is subsequently converted back to liquid before returning to the circuit. If the boiling point is above the ambient, the hydrophobic liquid is recovered by evaporation. Thermodynamically, the energy required to vaporize and condense the recyclable hydrophobic liquids disclosed in the instant invention is substantially less than that required to vaporize water from the surface of coal particles,
• the high-shear dewatering (HSD) process can also be used for the clean coal product obtained by a process not involving the DBD or oil agglomeration process described in the instant invention, e.g., flotation. It is necessary, however, that the clean coal product be dcwatered by filtration, centrifugation or any other method to produce a cake in which small droplets of water are trapped in between the coal particles.
• the HSD process can also be used to remove the water from a filter cake formed by hydrophilic particles such as silica and clay.
• the invention may be practiced with different types of coal including without limitation bituminous coal, anthracite, and subbituminous coal.
• Figures la and lb illustrate the concept of dewatering by displacement for coal.
• Figure 2 is a graph showing the contact angles of n-alkane hydrophobic liquids on the surface of a hydrophobic coal immersed in water.
• Figure 3 is a schematic representation of one embodiment for the present invention.
• Figure 4 is a schematic representation of another embodiment of the present invention.
• Figure 5 is a schematic representation of still another embodiment of the present invention.
• dG/dA must be less than zero.
• Figure lb shows the contact angle ( ⁇ ) measured through the aqueous phase of a hydrophobic liquid placed on a coal surface in water. At the three-phase contact, one can apply the Young's equation:
• the clean coal products obtained in conventional oil agglomeration processes exhibit high moisture contents, typically in the range of 30-55% by weight.
• methods of removing the entrained water have been developed so that the moisture can be readily reduced to substantially lower levels.
• the globules of water are removed using a size-size separation method selected from those including but not limited to screens, classifiers, and cyclones. These methods can remove the globules of water that are considerably larger than coal particles.
• the water drops stabilized by hydrophobic coal particles are broken up by appropriate mechanical means such as ultrasonic vibrator, magnetic vibrator, grid vibrator, etc., so that the coal particles are dispersed in the hydrophobic liquid, while the water drops free of coal particles drain into the aqueous phase.
• the organic phase in which coal particles are dispersed are then phase separated from the aqueous phase In which mineral matter is dispersed.
• the former is subjected to appropriate solid-liquid separation, while the latter is drained off.
• the hydrophobic liquid recovered from the solid-liquid separation step is recycled.
• the clean coal particles obtained from the solid/liquid separation step are substantially free of surface moisture.
• the coal particles may be subjected to a negative pressure or gentle heating to recover the residual hydrophobic liquid as vapor, which is subsequently condensed back to a liquid phase and recycled.
• the drops (or globules) of water are removed using a solid- liquid separation method selected from those including but not limited to filters, centrifuges, and presses. It is believed that much of the entrained water globules are expressed and/or drained during the solid-liquid separation process, leaving behind only the interstitial water droplets entrapped in between the particles constituting a filter cake.
• the filter cake is then subjected to a high-shear agitation to dislodge the entrapped water droplets from surrounding coal particles and release them to the vapor phase in which they can readily vaporize due to the large surface-to- volume ratio and higher vapor pressure due to large radius of curvature. Some of the released water droplets may exit the system into the atmosphere.
• FIG. 3 shows an example of the first embodiment of the instant invention.
• Coal slurry 301 is fed to a mixing tank 302, along with a hydrophobic liquid 303 recovered downstream and a small amount of make-up hydrophobic liquid 304.
• the hydrophobic liquid is broken to small droplets, which in rum undergo hydrophobic interactions with coal particles.
• the mixed slurry is transferred to a phase separator 305, in which hydrophobic liquid and water are phase-separated.
• the coal particles are engulfed into the liquid phase, while mineral matter is left behind in the aqueous phase.
• the latter 306 containing mineral matter is removed as reject, and the former 307 containing both the coal particles free of surface moisture and the globules of water stabilized by coal particles overflows onto a size-size separator (e.g., screen) 308.
• the hydrophobic liquid and the coal particles dispersed in it report to the smaller size fraction 309, i.e., underflow.
• the coal particles dispersed in the hydrophobic liquid is practically free of surface moisture due to the dewatering (or drying) by displacement (DBD) mechanism depicted in Figure 1.
• DBD displacement
• the globules of water formed and entrained into the hydrophobic liquid phase during mixing 302 and phase separation 305 report to the larger size fraction 310, i.e., overflow.
• the overflow stream 310 is returned to the mixing tank 302 to give the misplaced coal particles another opportunity to be recovered to the underflow stream 309 of the size-size separator 308.
• the underflow stream 309 consists of clean coal particles and the spent hydrophobic liquid. If the amount of hydrophobic liquid 303, 304 used in this embodiment is small relative to the amount of the coal in the feed stream 301, as in oil agglomeration, the underflow 309 would consist mainly of coal particles and a relatively small amount spent hydrophobic liquid adhering to the coal surface. In this case, the underflow 309.
• the solid 313 leaving the hydrophobic liquid recovery system 31 1 represents the clean coal product with low moisture.
• the coal recovery and the moisture content of the product coal would vary depending on the efficiency of the size-size separator 308 and the size distribution of the water droplets stabilized by coal particles. For the case of using screen for size-size separation, the use of multiple-deck screens may be useful to control coal recovery and product moisture.
• the recovery system 31 1, 312. When using a large amount of a hydrophobic liquid, it may be separated from the coal present in the underflow stream 309 by solid-liquid separation before feeding the underflow stream 309 to the recovery system 310, 311.
• FIG 4 shows another embodiment of the present invention, in which the amount of the hydrophobic liquid used is large,
• the front end is the same as in Figure 3 in that coal slurry 401 is mixed 402 with the hydrophobic liquid recovered downstream 403 and added as a make-up source 404.
• a novel feature of this embodiment is that the water droplets (or globules) stabilized by coal particles are broken up in the phase separator 405 by means of an appropriate mechanical means 406 (e.g. sonic or magnetic vibrator), so that the coal particles are more fully dispersed in the hydrophobic liquid phase.
• the aqueous phase containing mineral matter is removed as reject 407.
• the overflow 408 from the phase separator 405 is directed to a settler (e.g., thickener) 409, in which coal particles settle to the bottom and the hydrophobic liquid is recovered as overflow 410 and returned to the mixer 402,
• the settled material 411 is then subjected to another type of solid-liquid separation (e.g., filtration) 412. with the separated liquid (or filtrate) 413 being returned to the mixer 402.
• the dry coal product 414 is then subjected to the hydrophobic liquid recovery system 415, 416 to recover the small amount of the residual hydrophobic liquid adhering to the surface of coal in the same manner as in Figure 3.
• the exit stream 417 from the recovery system 415 represents a low-ash and low-moisture clean coal product.
• FIG. 5 represents still another embodiment of the instant invention.
• the front end of the process is the same as the first and second embodiments shown in Figure 3 and 4, where coal slurry 501 is fed to a mixing tank 502 which receives hydrophobic liquid recovered downstream 503 and added as a make-up source 504.
• the mixture is fed to a phase separator 505, in which the hydrophobic liquid containing coal and the aqueous phase containing mineral matter are phase separated.
• the latter is removed as reject 506, while the former 507 is fed to a solid-liquid separator 508 (e.g., centrifuge), where much of the spent hydrophobic liquid recovered as underflow 509 is returned to the mixer 502.
• a solid-liquid separator 508 e.g., centrifuge
• the overflow 510 containing coal particles, a small amount of residual hydrophobic liquid adhering to the coal surface, and the tiny droplets of water trapped in between coal particles is then fed to the hydrophobic liquid recovery system 511, 512 to recover the spent hydrophobic liquid 503 for recycle.
• the discharge 513 from the recovery system 511 may have a desirable amount of moisture for downstream processing such as briquetting. If not, it may be subjected to a high-shear dewatering (HSD) device 514, in which the tiny droplets of water are dislodged from coal or vaporized quickly due to the large surface area-to-volume ratio.
• HSD high-shear dewatering
• the exit from the HSD device 514 is fed to a dry coal collection device 515 such as bag house or cyclone, where coal particles are collected as underflow 516 and the liberated water droplets and/or water vapor 517 exit(s) the collection device.
• the HSD device 513 may be selected from but not limited to dynamic or static mixer, rotating fan, fluidized-bed, vibrating screen, and air jet.
• the HSD process can reduce the moisture of coal to less than 8%, a level that can usually be achieved by thermal drying.
• the moisture level can be controlled by adjusting the rate and duration of high-shear agitation.
• the HSD process works well without an external heat source, the use of heated air may facilitate the process or reduce moisture to a lower level.
• the HSD process can be used not only for drying hydrophobic coal fines but also for drying hydrophilic mineral fines (e.g., minerals in reject 306, 407, and 506 in Figures 3-5).
• hydrophilic mineral fines e.g., minerals in reject 306, 407, and 506 in Figures 3-5.
• an aqueous suspension of mineral matter or any other hydrophilic particulate materials is dewatered first by using a conventional process, such as centrifuge, filter, or roller press, to form a filter cake, in which a small amount of water is entrapped at the void spaces formed in between the fine particles.
• the filter cake is then subjected to the HSD method described above.
• hydrocarbon oils which include aliphatic and aromatic hydrocarbons whose carbon numbers are less than 18.
• DBD dewatering by displacement
• shorter- chain n-alkanes and alkenes, both unbranched and branched, and cycloalkanes and cycloalkenes, with carbon numbers of less than eight may be used so that the spent hydrocarbon oils can be readily recovered and recycled.
• Liquid carbon dioxide is another hydrophobic liquid that can be used for the DBD process.
• reagents When using longer-chain alkanes and alkenes, recycling may be difficult. Therefore, in these instances only small amounts of the reagents are preferably used as agglomerants.
• the reagent costs can be reduced by using the hydrophobic liquids from unrefined petroleum sources.
• ligroin light naphtha
• naphtha and petroleum naphtha diesel fuel, and mixtures thereof may be used.
• small amounts of kerosene and heating oils whose carbon numbers are in the range of 12-18 may be used.
• the DBD and selective agglomeration processes are ideally suited for separating hydrophobic particulate materials (e.g., high-rank coals) from hydrophilic materials (e.g., silica and clay), with the resulting hydrophobic materials having very low surface moistures.
• the processes as described in the instant invention can also be used for separating one-type of hydrophilic materials from another by selectively hydrophobizing one but not the other(s).
• the processes can be used to separate copper sulfide minerals from siliceous gangue minerals by using an alkyl xanthate or a thionocarbaraate as hydrophobizing agents for the sulfide minerals.
• the DBD concept can be used for non-thermal drying of fine coal or any other particulate materials after appropriate hydrophobization.
• a volume of pentane was added as a hydrophobic liquid to the coal slurry placed in a 350 ml glass separatory funnel.
• the coal slurry was received from the Moss 3 coal preparation plant, Virginia, at 15% solids by weight.
• the material in the funnel was agitated vigorously by handshaking for 4 minutes and let to stand for phase separation.
• Coal particles agglomerated (or were engulfed into the hydrophobic liquid) and formed a layer on top of the aqueous phase.
• the stopcock By opening the stopcock at the bottom, the aqueous phase was removed along with the mineral matter dispersed in it.
• the hydrophobic liquid remaining in the funnel was agitated again for a short period of time and let to stand.
• Example 2 Another test was conducted in the same manner as described in Example 1 on a fine coal sample (100 mesh x 0) from the Cardinal coal preparation plant, West Virginia. This sample was much finer than the one used in Example 1, with 80% of the material finer than 44 ⁇ m.
• 800 ml of the slurry at 4.3% solids was placed in a 1 liter separatory funnel along with 200 lb/ton of pentane as a hydrophobic liquid. After agitation and settling, the aqueous phase containing mineral matter was drained off, and the pentane mixed with coal particles was left behind in the funnel. The excess pentane was allowed to evaporate, and the clean coal product analyzed for ash and moisture.
• the ash content was reduced from 35.6% in the feed to 3.7% with a combustible recovery of 83.7%, but the moisture was as high as 48.7%.
• the high moisture content was again due to the entrainment of the water droplets stabilized by coal particles.
• Example 2 The same coal sample used in Example 2 was subjected to another test under identical conditions, except that an additional step was taken to remove the entrained globules of water and obtain low moisture products.
• the additional step involved the use of a screen to separate the water droplets from the dry fine coal particles obtained by the DBD process depicted in Figure 1.
• the clean coal product obtained using the procedure described in Example 2 was screened to obtain dry coal particles as screen underflow and water droplets as screen overflow. Initially, a 140-mesh screen was used for the separation, in which case the amount of dry coal obtained was only about 25% by weigh of the feed. Therefore, the screen overflow was subjected to another stage of the DBD process, and the product was screened again to obtain additional recovery of dry coal.
• the moisture content remained as high as 52,2%, as shown in Table 4, mostly due to the entrained water globules stabilized by hydrophobic coal particles.
• the clean coal product was dewatered by a horizontal basket centrifuge to reduce the moisture content to 18,2%.
• the centrifuge product was then fed to a squirrel-cage fan by means of a vibratory feeder.
• the exit stream from the fan was collected in a small home-made bag house.
• the collected coal sample assayed 1% moisture, as shown in the table.
• the method disclosed in this example produced a dry coal with 1% moisture with the ash content reduced from 36.7 to 8.6% with a 90% combustible recovery.
• the ash content could have been reduced further, if the clean coal product was re-pulped and cleaned again before the centrifugation and high-shear dewatering (HSD) steps commenced.
• HSD high-shear dewatering
• the water droplets were reduced in size but still filled the void spaces in between the coal particles.
• the tiny droplets of entrapped water were then separated from the coal particles by the high-shear agitation in air.
• the tiny water droplets exited the system and/or evaporated quickly without applying heat due to the high curvature and/or the large surface area-to-volume ratio of the water droplets.
• the Cardinal coal sample was treated with 200 lb/ton of pentane in the same manner as described in Examples 2 and 3.
• the clean coal product was dewatered by means of a vacuum filter rather than a centrifuge as in Example 4, The filter cake was then fed to a squirrel-cage fan to further reduce the moisture to 1.7%, as shown in Table 5.
• the ash content of the product coal was relatively high due to the entrainment of mineral matter. In a continuous process, this problem can be readily addressed by installing an appropriate agitator or implementing a two- step process.
• the fine coal sample from the Cardinal plant was subjected to two stages of agglomeration using a total of 360 lb/ton of pentane.
• the clean coal product was dewatered using a vacuum filter, and the filter cake dried using a squirrel-cage fan in one test and an air jet in another to obtain 1.4 and 2.1% moistures, respectively.
• Both of these devices were designed to provide high-shear agitation in air to dislodge the small droplets of water from the fine coal particles that had been dried by the displacement mechanism depicted in Figure 1. Both of these mechanical devices seemed to be equally efficient in drying fine coal without using an external heat source.
• Table 6 show that the ash contents were substantially lower than obtained in Example 5, which can be attributed to the two stages of cleaning operations employed,
• the clean coal product was dewatered using a laboratory-scale horizontal basket centrifuge to reduce the moisture to 21.4%. The centrifuge product was then subjected to a high-shear agitation provided by a squirrel-cage fan to obtain 0.9% moisture. The recoveries for the centrifugation and high-shear agitation were not determined.
• a nominally 100 mesh x 0 coal sample assaying 36.8% ash was obtained from the Litwar coal preparation plant, West Virginia. A size analysis of the sample showed that 7.8% of the material was coarser than 150 ⁇ and 80.1% was finer that 44 ⁇ . It was cleaned of its ash- forming mineral matter by froth flotation rather than using the DBD or the selective agglomeration processes described in the foregoing examples.
• a Denver laboratory flotation machine with a 4-liter stainless steel cell was used. The flotation test was conducted with 3 lb/ton diesel oil as collector and 1.2 lb/ton MIBC as frother at 2.6% solids.
• the froth product was subjected to another stage of flotation test without using additional reagent to obtain a clean coal product with 4.2% ash and 8.3% solids.
• the product was vacuum- filtered using 5 lb/ton of sorbitan monooleate as a dewatering aid.
• the filter cake containing 19.6% moisture was then subjected to a high-shear agitation provided by a squirrel-cage fan to further reduce the moisture to 0.9% by weight,
• a copper ore sample was ground in a ball mill for 8 to 20 minutes and the mill products were subjected to a series of flotation tests.
• a composite of the reject materials at 10% solids was dewatered to 15,6% by means of an air pressure filter at 20 psi.
• the filter cake was then subjected to a high-shear agitation in a squirrel-cage fan to further reduce the moisture to 0.7% as shown in Table 9.
• the composite reject material was conditioned with 5 lb/ton
• the coal sample was a cyclone overflow from a pond recovery plant containing mostly -44 ⁇ materials, which assayed 38% ash by weight. In the plant, the ultrafine coal was not being processed due the difficulties in both recovery, and dewatering.
• a volume of the coal slurry was added to a kitchen blender and diluted to approximately 3% solids with tap water. The amount of coal in the mixer was approximately 20 g. After adding 20 ml of pentane to the mixer, the slurry was agitated at a
• the coal sample used in this example was the same as in Example 10.
• a volume (1 liter) of coal slurry containing approximately 40 g of coal was added to a kitchen blender (mixer). After adding 0.5 liter of pentane to the mixer, the mixture was agitated at a low r.p.m.
• the agitated slurry was slowly transferred to a 1-inch diameter phase separator, which was made of a 3/4-inch diameter glass column with a 9-inch height.
• an ultrasonic probe was installed at the base of the column to provide a mechanical energy to dislodge the coal particles from the surfaces of the water drops, which tended to congregate at the phase boundary between water and oil due to gravity.
• the column was also equipped with an overflow launder at the top to collect the clean coal product semi-continuously. With the application of the ultrasonic energy, it was possible to dislodge the coal particles from the water droplets and allow them to be more fully dispersed in the oil phase. Water was then introduced to the base of the settling column to flood the organic phase into the launder, while the aqueous phase was removed from the bottom. The collected coal and ash products were weighed and analyzed for ash and moisture to obtain

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