Classifications

• • 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, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L5/00—Solid fuels
  • C10L5/02—Solid fuels such as briquettes consisting mainly of carbonaceous materials of mineral or non-mineral origin
  • C10L5/06—Methods of shaping, e.g. pelletizing or briquetting
  • C10L5/10—Methods of shaping, e.g. pelletizing or briquetting with the aid of binders, e.g. pretreated binders

Definitions

• the present invention concerns a briquetting process. More especially it concerns such a process which gives improved green strengths in "cold” briquetting, that is, briquetting at temperatures of up to 100°C.
• the present invention provides a process for the cold briquetting of fine coal, comprising mixing fine coal with a binder to produce a water-containing briquetting mix, and characterised by the presence in the briquetting mix of up to 2% by weight of the mix of a cement, and briquetting the mix, whereby the initial green strength of the resulting briquettes is improved.
• the process is nominally "cold", it is found that on the industrial scale the mix enters and leaves the briquette formation steps at a temperature above ambient, for example of the order of 60°C.
• a temperature above ambient for example of the order of 60°C.
• this mix retains sensible heat, or, depending upon the briquette formation step, friction and/­ or compression may give rise to heating of the briquette during formation.
• the present invention offers particular advantages as regards initial green strength if the briquetting step is carried out at temperatures above 50°C.
• the binder is a combination of molasses and an inorganic hardening agent, or a sugar or starch solution and an inorganic hardening agent, and we refer to our prior applications mentioned above for examples of such binders.
• Other binders may, however, be used if these are water-based and produce briquettes which have unsatisfactory green strength.
• the cement used is preferably OPC, which exhibits good results in tests and is readily available at low price, but other cements such as special portland cements, and high alumina cement may be used.
• Sorrel cement which is based on magnesium oxide and magnesium chloride
• the cement be pre-mixed with dry coal, either alone, or in combination with other hardening agents, prior to adding water-containing binders.
• the cement may be added to wet coal if it is combined with dry binders such as starch, either with or without hardening agents.
• Specific cements and coal/binder mixes should be routinely tested to ensure that they are satisfactory and yield briquettes of the desired appearance and properties.
• cement setting and hardening may be adjusted in known manner by mixing appropriate cements and/or by the incorporation of accelerators or retarders.
• the cement is used in an amount of up to 1%, more preferably, in an amount of up to 0.5%, by weight of the mix. Good results in preliminary tests have been achieved with amounts of cement of approximately 0.5% by weight.
• Preferred coals are high rank non-caking coals, especially those having low smoke emissions such as anthracite.
• the coal is of a particle size mainly below 3mm, and anthracite duff is especially suitable.
• the invention is also applicable to coals for power stations or steam raising and to coal blends containing caking coal components and/or treated coals, eg by mild oxidation or pyrolysis.
• the coal may be crushed or be the direct product of coal cutting.
• the briquetting step of the present invention includes all methods of forming agglomerates from fine coal, and these agglomerates may be of any size or shape according to market requirements. There may be mentioned forming agglomerates by extrusion, ringroll - or roll-pressing, die-pressing, rotary table pressing and pelletising, eg on a disc pelletiser.
• the process preferably includes a hardening stage to permit the green briquettes to gain additional strength, depending upon the binder used.
• a hardening stage to permit the green briquettes to gain additional strength, depending upon the binder used.
• the green briquettes harden over a period of 1 to 3 days at ambient temperature to give adequate crushing strengths, but the briquettes tend to have inadequate water resistance.
• the briquettes may be bagged in impervious sacks and allowed to further harden during storage.
• a hot curing step is included to speed up the hardening stage and to make the briquettes water resistant, and this may be carried out at temperatures of the order of 200 to 300°C for up to an hour.
• Hot curing may be conveniently carried out by passing the briquettes on a conveyor through an oven, in an atmosphere which may contain nitrogen, carbon dioxide, water vapour and/or oxygen. It is to be noted that the hot curing step does not correspond to a carbonisation step, and thus not only are there energy savings, but the solid yield on a dry basis is very high. Additionally, there is a reduced risk of pollution.
• the water resistance of the briquettes may be improved by an additional treatment with a spray or bath of a water proofing agent.
• a spray or bath of a water proofing agent Several agents are known to have been proposed including, for example, aluminium acetate.
• the present invention also provides briquettes formed using a process as described above.
• a fine anthracite from South Wales, was prepared by crushing and screening to minus 3mm.
• the anthracite was admixed with 8% of mollasses, 1% iron ore and 1% phosphoric acid, by weight of the final composition.
• the mixture was briquetted in a pilot plant roll press, for comparison with the same mixture together with additions of 0.25% and 0.5% of ordinary portland cement.
• a briquette manufacturing plant was continuously operated using anthracite which was crushed and screened to minus 3mm. It was then mixed with molasses, iron ore and phosphoric acid as in Example 1 and the mixture was further mixed with 1% by weight of Portland cement. The resulting mixture was briquetted in a roll press and hot cured. It was noted that there was a reduction in breakage of the briquettes through mechanical degradation, and this reduction resulted in an average increase in product yield of 13%.
• Example 1 was repeated except that 0.5% by weight of the final composition of xanthan gum was added.
• the addition of the gum had only a marginal effect upon the green crushing strength but produced a significant improvement on green shatter strength, thereby imparting improved mechanical handling characteristics.
• Example 3 was repeated except that 0.5% by weight of the final composition of guar gum was added. Again the addition of guar gum had only a marginal effect upon the green crushing strength but produced a significant improvement in green shatter strength, thereby imparting improved mechanical harding characteristics.

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• Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Environmental & Geological Engineering (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Geochemistry & Mineralogy (AREA)
• Geology (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Organic Chemistry (AREA)
• Solid Fuels And Fuel-Associated Substances (AREA)
• Curing Cements, Concrete, And Artificial Stone (AREA)

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Citations (6)

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• 1987
  • 1987-10-28 GB GB878725252A patent/GB8725252D0/en active Pending
• 1988
  • 1988-10-06 EP EP88309301A patent/EP0314322A3/fr not_active Withdrawn
  • 1988-10-06 GB GB8823443A patent/GB2211512A/en not_active Withdrawn
  • 1988-10-13 AU AU23707/88A patent/AU2370788A/en not_active Abandoned
  • 1988-10-17 ZA ZA887733A patent/ZA887733B/xx unknown
  • 1988-10-27 CN CN88107460A patent/CN1022845C/zh not_active Expired - Fee Related

Patent Citations (6)

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