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 OR C10K; LIQUIFIED PETROLEUM GAS; USE OF ADDITIVES TO FUELS OR FIRES; FIRE-LIGHTERS
  • C10L1/00—Liquid carbonaceous fuels
  • C10L1/32—Liquid carbonaceous fuels consisting of coal-oil suspensions or aqueous emulsions or oil emulsions
  • C10L1/326—Coal-water suspensions

Definitions

• This invention relates to the production of fuel slurries of coal in water which can be injected directly into a furnace as a combustible fuel.
• a high fuel value coal slurry can supplant large quantities of increasingly expensive fuel oil presently being used by utilities, ,factories, ships and other commercial enterprises. Since the inert water vehicle reduces fuel value in terms of BTU/lb (J/kg) it is desirable to minimise its concentration and maximise coal concentration for efficient use of the slurry as a fuel.
• a high coal content also improves the combustion characteristics of the slurry.
• the slurry be loadable with finely-divided coal in amounts as high, for example, as about 50% to 70% of the slurry.
• the slurry must be sufficiently fluid to be pumped and sprayed into the furnace.
• the coal particles must also be uniformly dispersed. The fluidity and dispersion must be stabley maintained during storage.
• An object of this invention is to provide an improved process for producing a slurry suitable for this purpose.
• This invention further provides a coal-water slurry which comprises:
• fluid, pourable slurries comprising up to about 70% or higher of coal stabley dispersed in water are produced by admixing finely-divided coal having a critical distribution of particle sizes, water, and an organic dispersant in a high shear rate mixer.
• An inorganic buffer salt may also be added.
• fluid as used in this specification and claims means a slurry which is fluid and pourable both at rest and in motion or a slurry which gels or flocculates into. a substantially non-pourable composition at rest and becomes pourably fluid with stirring or other application of relatively low shear stress.
• the partial size mixture necessary for fluidity of the highly loaded slurry, comprises ultrafine (UF) particles having a maximum size of up to about 10 ⁇ m MMD (mass mean diameter), preferably about l ⁇ m to 8gm MMD and larger particles (F/C) having a size range of about 20gm to 200ym MMD, preferably about 20gm to 150 ⁇ m MMD.
• UF particles should comprise about 10 to 30% by weight of the slurry, preferably about 15 to 25%.
• the actual degree of coal loading is not critical and will vary with the given use and operating equipment.
• concentration of coal successfully incorporated into a given slurry varies with such factors as the relative amounts of UF and F/C particles, size of the F/C particles used within the effective range, and the like. In general, percentage loading increases with increasing F/C size.
• An organic dispersant is essential to maintain the coal particles in stable dispersion. It has been found that the highly-loaded slurries are very sensitive to the particular type of surfactant used, especially with respect to fluidity and storageability.
• the dispersants which have proven to be effective in producing stable fluid mixes are high molecular weight alkaline earth metal (e.g. Ca, Mg) organosulfonates in which the organic moiety is poly-functional. Molecular weight of the organosulfonate is desirably about 1,000 to 25,000.
• the surfactant is used in minor amount, e.g. about 0.5 to 5 pph of coal, preferably about 1 to 2
• an inorganic, alkali metal (e.g. Na, K) buffer salt to stabilize pH of the slurry in the range of from pH 5 to 8, preferably from pH 6 to 7.5.
• the salt improves aging stability, pourability and handling characteristics of the slurry. It may be that the buffer counteracts potentially adverse effects of acid leachates from the coal.
• the salt such as sodium or potassium phosphate or carbonate, including their acid salts is used in minor amounts sufficient to provide the desired pH, e.g. about 0.1 to 2% based on the water.
• the inorganic salts also serve to reduce gaseous sulfur pollutants by forming non-gaseous sulfur compounds.
• the ultrafine and larger F/C coal particles, water, dispersant, and inorganic salt components are mixed in a blender or other mixing device which can deliver high shear rates.
• High shear mixing e.g. at shear rates of at least about 100 sec 1 , preferably at least about 500 sec -1 , is essential for producing a stable slurry free from substantial sedimentation.
• the use of high shear mixing and the dispersant appears to have a synergistic effect.
• Dispersant with low shear mixing results in an extremely viscous, non-pourable slurry, while high shear mixing without dispersant produces a slurry which is unstable towards settling. With both dispersant and high shear mixing a fluid, pourable, stable slurry can be obtained.
• the slurries are viscous, fluid dispersions which can generally be characterized as thixotropic or Bingham fluids having a yield point.
• the slurries may gel or flocculate when at rest into a substantially non-pourable composition but are easily rendered fluid by stirring or other application of relatively low shear stress. They can be stored for considerable periods of time without excessive settling or sedimentation.
• the slurries can be employed as fuels by injection directly into a furnace previously brought up to ignition temperature of the slurry. The finely divided state of the coal particles improves combustion efficiency. Since the dispersants are organic compounds, they may be biodegraded with time. This can readily be prevented by addition of a small amount of biocides.
• the ultrafine coal particles can be made in any suitable device, such as a ball mill or attritor, which is capable of very fine comminution.
• the coal is milled with water so that the UF particles are in water slurry when introduced into the mixer.
• Some of the dispersant can be included, if desired, in the UF milling operation to improve flow and dispersion characteristics of the UF slurry.
• the required larger size coal particles (20 ⁇ m to 200 ⁇ m) can be made from crushed coal in a comminuting device such as a hammermill equipped with a grate having appropriately sized openings. Excessively sized coal residue can be used for making the UF particles.
• coal concentrations as used in the specification and in the following examples is on a dried coal basis which normally equals 98.5% by weight of bone-dried coal.
• the 3.6 ⁇ m MMD UF particles employed in Examples 3 - 8 were prepared in accordance with Example 1 and the UF particles were introduced in the form of the Example 1 aqueous slurry containing a portion of the dispersant.
• the total amount of dispersant given in the Examples includes the portion introduced in this way.
• A. 65% by wt. of coal comprising 55% 110 ⁇ m MMD coal and 45% 3.6 ⁇ m MMD coal, 1,3% Marasperse C-21 (calcium ligning sulfonate) and 33.7% water were mixed in a blender at 6,000 RPM at a shear rate of 1,000 sec -1 .
• the resulting slurry was a paint-like gel that set into a soft gel which was easily stirred to a liquid. After 23 days, it exhibited no sedimentation and was easily restirrable to a uniform dispersion having relatively low viscosity - 6.7p.
• a mix was made identical to A except that 34gm MMD particles were substituted for the UF particles.
• the mix though initially fluid was unstable. Within 3 days it separated, forming a large supernatant and a highly packed subsidence. It could not be remixed into a uniform, pourable dispersion.
• A 65% coal slurry comprising 15% 3.6gm MMD and 50% 34gm MMD particles by wt. of the slurry, 1.3% Marasperse C-21 and 33.7% water were mixed in a blender at 6000 RPM.
• the resulting product was an uniformly dispersed gel which after 12 days in storage exhibited no supernatant, subsidence or sedimentation. The gel was non-pourable at rest and became a pourable fluid with stirring.
• a mix was made identical to A except that the blender was run at a low shear rate of 60 RPM (10 sec -1 ). The resulting slurry was unstable. Within 4 days it had separated into liquid and aggregated sediment.
• A 65% coal slurry comprising 26% 3.6 ⁇ m MMD particles and 39% 110 ⁇ m MMD particles, 13% Marasperse C-21 and 33.7% water were mixed in a blender at 6,000 RPM.
• the resulting product was a uniformly dispersed slurry which was fluid and pourable and after 10 days was still pourable and substantially free from subsidence or sedimentation.
• a mix was made identical to A except that the blender was run at a low shear rate of 10 sec -1 .
• the resulting slurry was unstable. Within 3 days, it had separated into supernatant and aggregated sediment.
• Example 3A A 65% coal slurry was made identical to Example 3A except that no dispersant was added. The resulting product had the consistency of a stiff grease.
• a 70% coal slurry comprising 45.5% 110 ⁇ m MMD particles and 24.5% 3.6 ⁇ m MMD particles, 1.4% Marasperse C-21, and 28.6% water solution buffered to pH 7 by 0,15% Na 2 HPO 4 added in the blender was mixed at 6,000 RPM.
• the resulting slurry has an EOM viscosity of 1.48 Kp, is fluid and pourable. After 7 days in storage it exhibited no supernatant liquid, settling or aggregation.
• Example 4A A mix was made identical to Example 4A except that Na 2 HP0 4 in amount providing buffered pH 7 was added in the blender. The resulting slurry was fluid and pourable. ' Its viscosity was EOM-T-bar 0.92 Kp. It retained its stability and pourability during storage and after 12 days was free from separation.
• a 65 wt. % coal slurry comprising 50 wt.% 34 ⁇ m MMD coal particles, 15 wt.%, 3.88 ⁇ m MMD (using 50 wt.% of slurry from 9A supra), 2 pph on coal of Marasperse C-21, and the remainder water, was mixed in a blender at a shear rate of 6,000 RPM (1000 see -1 ).
• the product was a uniformly-dispersed, pourable slurry. After 56 days the slurry was a stable, soft, non-pourable gel free from settling or sedimentation. There was a very slight supernatant. Probably caused by water evaporation and condensation on the surface. The thixotropic gel became easily pourable with slight stirring. At rest it returned to a stable non-pourable state within a short time. After 61 days it retained its stable characteristics after several stirrings to pourability.
• a slurry similar to 9B was prepared except that the mix was buffered to pH 7 by the addition of Na2HP04, The product was a uniformly-dispersed fluid slurry of relatively low viscosity. After 55 days the slurry was a weak, non-pourable gel free from settling or sedimentation. As in 9B there was a very slight supernatant. With slight stirring, it became very fluid and pourable.It was still stable and pourable after 24 hours and, although somewhat more viscous, retained its stability and pourabilty 5 days after the initial stirring.
• Example 3 demonstrates the need for the UF particles in controlled size distribution to impart stability.
• Examples 4 and 5 show the need for high shear rate mixing.
• Example 6 shows the importance of the dispersant.
• Example 7 illustrates the improvement made in a highly-loaded 70% slurry by use of an inorganic buffer salt and the adverse effect of low shear mixing.
• Example 8 shows that the use of the pH buffer salt maintained the slurry in a stable fluid condition.
• Example 9 shows that the buffer salt improved aging and its user and handling characteristics.

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• Chemical & Material Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Liquid Carbonaceous Fuels (AREA)
• Solid Fuels And Fuel-Associated Substances (AREA)
• Emulsifying, Dispersing, Foam-Producing Or Wetting Agents (AREA)
• Colloid Chemistry (AREA)

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• 1981
  • 1981-09-04 ZA ZA816150A patent/ZA816150B/xx unknown
  • 1981-09-14 AT AT81304187T patent/ATE11927T1/de not_active IP Right Cessation
  • 1981-09-14 DE DE8181304187T patent/DE3169061D1/de not_active Expired
  • 1981-09-14 EP EP81304187A patent/EP0050412B1/de not_active Expired
  • 1981-09-17 IL IL63866A patent/IL63866A/xx unknown
  • 1981-09-17 AU AU75439/81A patent/AU554293B2/en not_active Ceased
  • 1981-10-06 CA CA000387401A patent/CA1178441A/en not_active Expired
  • 1981-10-17 JP JP56164956A patent/JPS5796090A/ja active Pending

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