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
  • B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
  • B03D3/00—Differential sedimentation
  • B03D3/06—Flocculation
• • 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
  • B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
  • B03D1/00—Flotation
  • B03D1/001—Flotation agents
  • B03D1/004—Organic compounds
  • B03D1/006—Hydrocarbons
• • 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
  • B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
  • B03D1/00—Flotation
  • B03D1/001—Flotation agents
  • B03D1/004—Organic compounds
  • B03D1/016—Macromolecular compounds
• • 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
  • B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
  • B03D1/00—Flotation
  • B03D1/02—Froth-flotation processes
• • 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
  • B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
  • B03D2201/00—Specified effects produced by the flotation agents
  • B03D2201/04—Frothers
• • 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
  • B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
  • B03D2203/00—Specified materials treated by the flotation agents; specified applications
  • B03D2203/02—Ores
  • B03D2203/04—Non-sulfide ores
  • B03D2203/08—Coal ores, fly ash or soot
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
  • F02B3/00—Engines characterised by air compression and subsequent fuel addition
  • F02B3/06—Engines characterised by air compression and subsequent fuel addition with compression ignition

Definitions

• This invention concerns recovering coal from aqueous slurries of coal fines also contain­ing associated impurities as suspended fine solids and compositions of use in the recovery process.
• Coal as mined con­tains a proportion of impurities (hereinafter called 'shale') and, in the case of the fine particles present, separation of the coal from the shale presents considerable problems.
• 'shale' impurities
• This fine 'coal' typically has a substantial coal content but also a substantial shale content so it is important to make use of the coal content but also to remove shale from it.
• Modern coal prep­aration processes result in the fines (separated from coarser material) being in the form of aqueous slurries.
• the usual separation technique applied to the aqueous slurry of fines is to pass the slurry through a hydrocyclone and then feed the hydrocyclone underflow to a screen having apertures of about 0.25 mm.
• the 'product' i.e. coal fines with a reduced proportion of shale fines is the matter retained by the screen whilst the hydrocyclone overflow and the matter passing through the screen are discarded.
• a consequent disadvantage is that the significant proportion of the coal having particle sizes below 0.25 mm is lost.
• coal fines are selectively agglomerated, with respect to shale fines, by use of an oil 'binder' and the coal agglomerates are then sep­arated from the shale fines by a screening or classification process.
• oil agglomeration Another technique that has been proposed for separating coal fines from shale fines in aqueous slurries is oil agglomeration.
• coal fines are selectively agglomerated, with respect to shale fines, by use of an oil 'binder' and the coal agglomerates are then sep­arated from the shale fines by a screening or classification process.
• the process has the disadvantage of requiring a substantial pro­portion of oil in relation to the solids in the slurry being treated.
• a method of recovering coal fines from an aqueous slurry also containing shale as suspen­ded fine solids comprises adding to the slurry a hydrophobic polymer in a liquid, organic carrier, agitating the mixture, introducing gas into the mixture to form bubbles whereby flocs of coal fines formed are caused to float and discarding the underlying slurry containing shale.
• coal fines can be flocculated efficiently by use of hydrophobic polymers and that the flocculation is highly selective for coal fines in preference to shale fines.
• flocs of coal fines are formed selectively in preference to flocs of shale fines and a high degree of selectivity can be achieved.
• the agglomeration of the coal fines into flocs reduces the exposed surface area of the coal and thereby reduces entrainment of shale fines with the coal.
• the coal fines can be formed into flocs of sufficient strength to survive vig­orous agitation of the slurry and by agitation of the slurry the flocs of coal fines can be caused to 'extrude' shale fines and water that may initially have been entrained within the flocs.
• the method of the invention should be performed as a froth flotation in a froth flotation cell, using, in addition to polymer and carrier, a frother, as used in conventional froth flotation processes.
• the organic liquid not only acts as a carrier for the polymer but it also acts as a so-called collector in the conventional froth flotation sense.
• the polymer dosage may be as low as say 0.5 kg/tonne of slurry solids.
• high yields are obtainable i.e. not only is the method highly selective as between coal fines and shale fines but also a high proportion of the coal fines, particularly those of very low particle sizes (less than about 50 microns) can be recovered.
• hydrophobic polymers may be used but polybutadienes and polyvinylethers have been found to be particularly satisfactory in the case of the more aliphatic coals e.g. steam coals.
• polymers having aliphatic units are preferred in the case of the more ali­phatic coals whilst for the more aromatic coals e.g. anthracite polymers having aromatic units are preferred as aliphatic polymers are less effective with such coals than they are with the more aliphatic coals.
• the polymer should be hydrophobic rather than merely contain a proportion of hydrophobic units.
• polymers containing ether linkages as in polyvinylethers are suitably hydrophobic, such polymers as polyacrylamides are hydrophilic and are of low selectivity for the flocculation of coal in preference to shale and such polymers as polyacrylic esters are also too hydrophilic.
• Gas oil has been found to be a particu­larly satisfactory carrier for suitable polymers having aliphatic units.
• carriers that may be used include diesel oil, and kerosene and other petroleum and coal-based distillates.
• a co-solvent compatible with the carrier may be used.
• co-solvents that may be used include toluene, xylenes and other aromatic sol­vents and hexane and other paraffinic solvents. Co-solvents may be particularly useful if the polymer is of high molecular weight and/or if the polymer comprises aromatic units and the carrier is of mainly aliphatic character.
• the efficiency of the method is depen­dent on the dosage rate of the polymer in relation to the solids in the slurry.
• some recovery of the coal fines may be achieved with a dosage rate as low as for example, 2.45 kg. poly­mer/tonne of slurry solids but under the same conditions an almost doubled dosage rate of 4.71 gave far superior results.
• the optimum dosage rate in any particular case is that just suffi­cient to cause effective flocculation of substan­tially all the coal fines. Whilst high selectivity may be retained with lesser rates, only partial recovery of the coal fines is then achievable. Rates higher than the optimum are simply wasteful of the polymer.
• an additive composition for use in the froth flotation method of the invention comprises a hydrophobic polymer and a frother in a liquid, organic carrier.
• the composition com­prises 5 - 25% of the polymer, 5 - 25% of frother and 50 - 90% of carrier, all by weight.
• the frother may be as in the known froth flotation process, and may be for example methyl isobutyl carbinol or a mixture of polypropylene glycol ethers available under the tradename TEEFROTH G.
• the com­position is preferably used in an amount not greater than 10 kg per tonne of slurry solids, especially 0.5 - 5 kg per tonne.
• the method of the invention gives rise to a secondary advantage in that the coal flocs formed are more readily filtered than coal fines which have not been flocculated. Moreover, not only can the filtration be carried out more quickly but also it gives rise to a coal residue having the advantage of a lower water content.
• the method of the invention is applic­able to coal/shale slurries of the types that in the past have been subjected to conventional froth flotation processes.
• the size of the coal and shale particles is usually less than 500 microns and commonly up to 50% by weight of the particles can have sizes less than 50 microns.
• Process I Three different treatment processes were applied to the slurry.
• Process I the chosen additive was added to a sample of the slurry in a separating funnel and the mixture stirred at a low speed such that thorough mixing occurred but there was substantially no creation of air bubbles in the slurry.
• the stirring was then dis­continued, solids allowed to sediment out, the sediment separated from the slurry above and both the sediment and the overlying slurry collected, the sediment returned to the funnel, water added and the resultant mixture again stirred slowly, the stirring again discontinued and solids again allowed to sediment out and the sediment separated from the overlying slurry and both collected.
• the sediment was filtered, dried and weighed (to determine the product yield of the process) and then burnt and reweighed (to determine the ash content of the product).
• the two portions of collected separated slurry were separately fil­tered and the residues dried, weighed and burnt (to determine their ash contents).
• Process II the above process was generally repeated but using high speed stirring such that numerous air bubbles were created in the slurry and caused solids to float rather than sediment out. Accordingly in this process on each of the two occasions the underlying slurry was separated from the floated-out solids rather than the sediment being separated from the over­lying slurry.
• Process III the chosen additive was added to a sample of the slurry and the mixture then subjected to froth flotation using froth flotation apparatus of the Leeds cell design.
• the floated-out matter was separated from the underlying slurry and the latter collected and the former returned with added water to the Leeds cell which was then operated again.
• the floated­-out matter was again separated from the under­lying slurry and both collected.
• the floated-out matter was filtered, dried and weighed (to deter­mine the product yield) and burnt and re-weighed (to determine the ash content of the product).
• the two portions of collected separated slurry were separately filtered and the residues dried, weighed and burnt.
• Example 1.6 in the Table is shown as being conducted according to Process II. However, although high speed stirring was used such that numerous air bubbles were created in the slurry, the solids sedimented out rather than floated and thus the separation steps were conducted in accor­dance with Process I rather than Process I.
• Examples 1.1 and 1.2 which use Process I, are included only for comparison purposes.
• the product ash contents are high, signifying a sub­stantial proportion of shale in the product.
• Example 1.3 which uses Process II, gives a much lower ash content but the yield is low.
• Example 1.4 where the additive application rate is approx­imately doubled, gives a much higher yield but the ash content is still low.
• Examples 1.5 again using Process II, gives a good yield of low ash content and the high ash contents of the tailings signify that little coal is lost in the tailings. The contrast with Example 1.2 using Process I but otherwise generally similar is very marked.
• Example 1.6 is included only for com­parison purposes and shows that Process II is not effective in the absence of the polymer: whilst the product yield is high, the product has a high ash i.e. shale content.
• Example 1.9 included only for compari­son purposes, shows that if gas oil and frother are used in Process III without the polymer a greatly reduced yield results.
• Process IV which was the same as Process III described in Example 1 except that froth flotation was done once instead of twice, was carried out on an aqueous coal/shale slurry from a coal preparation plant using in one series of experiments an additive composition according to the invention and in another series of experi­ments the froth flotation oil in current use on the plant at the time.
• the ash content of the solids in the slurry was 36.5% by weight, and of the solids 69% by weight were of particle size less than 53 microns.
• composition of the additive was, by weight: 60% gas oil 20% mixture of polypropylene glycol ethers (TEEFROTH G) 20% polyvinyl ethyl ether (LUTONAL A25)
• the results obtained using the additive composition are, over the range of dosages invest strictlyigated, superior to those obtained using the conventional froth flotation oil, and particularly at high dosages are characterised by higher weight yields and lower product ash contents. For example at a dosage of 1.21 kg ash is reduced by 5.6% by weight and the yield increased by 2.8% by weight.
• Process IV as described in Example 2 was carried out on a sample of particle size less than 105 microns screened from a run-of-mine coal/­shale slurry in which the particle size of the solids was less than 500 microns.
• the ash content of the solids in the sample was 45% by weight. 86% by weight of the solids in the sample had a particle size of less than 20 microns and an ash content of 46.4% by weight, and the remaining 14% by weight contained 30% by weight ash.
• Example 2 The additive composition described in Example 2 was compared with a proprietary froth flotation oil used in a conventional froth flota­tion process.
• a bulk feed sample of a coal/shale slurry was screened at 500 microns. Part of the sample 30 was retained for normal froth flotation for comparison purposes and the remainder was classi­fied in a 5 cm hydrocyclone.
• the underflow was diluted with water to approximately 6% solids by weight and similar froth flotation treatments were carried out on portions of the diluted material to those carried out on the overflow material.
• Froth flotation was also carried out on the retained screened feed sample using the froth flotation oil normally used to treat the particular coal/shale slurry in practice.
• results demonstrate the benefits to be obtained by using a hydrocyclone to split the feed for a conventional froth flotation into one fraction containing fine particles of a size pre­dominantly less than 50 microns (overflow) and another fraction containing relatively coarse particles of a size predominantly in the range of 50 - 500 microns (underflow) and then treating the fraction containing the fines by the method of the invention and the other fraction by a con­ventional froth flotation process.

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• 1986
  • 1986-05-14 GB GB868611747A patent/GB8611747D0/en active Pending
• 1987
  • 1987-05-14 EP EP87304307A patent/EP0246105B1/fr not_active Expired - Lifetime
  • 1987-05-14 ES ES198787304307T patent/ES2040251T3/es not_active Expired - Lifetime
  • 1987-05-14 DE DE8787304307T patent/DE3777448D1/de not_active Expired - Fee Related
  • 1987-05-14 GB GB8711401A patent/GB2190310B/en not_active Expired - Fee Related
• 1989
  • 1989-10-25 GB GB8924001A patent/GB2225260B/en not_active Expired - Fee Related
• 1992
  • 1992-03-27 ZM ZM15/92A patent/ZM1592A1/xx unknown

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