Ultrasonic Processing of Coal, Lignite, & Oil Sand/Shale

Reviewed by

Robert Nelson

    The processing of coal can be greatly improved by the application of ultrasound at every stage from prospecting to cleanup. The enhancements in some cases are of such magnitude as to offer revolutionary possibilities and significant savings of time, money, and equipment that could revitalize the coal industry.

The use of ultrasound in prospecting (pulsed ultrasound seismoscope) is an established technology. The rate of penetration of ultrasound increases with the coal’s rank (elasticity). Coal has an acoustic anisotropy. Ultrasonic resonance can be used to locate and to emulsify wax appearances in oil wells.

Ultrasound has been applied to drilling (for small samples) by NASA researchers, but it is not yet practical on a large scale. Albert Bodine received USP # 3,163,240 for a "Sonic Earth-Boring Drill", but it has not yet been adopted by the industry.

The properties of drilling fluids and plugging materials can be modified by ultrasound. For example, clay consumption in the preparation of drilling fluid is reduced by 30% when ultrasonic treatment is used. The rheology of drilling fluids can be modified. Ultrasound can be used to pump wells ( US Patents  #1,730,336 ~ # 1,730,337 ~ # 1,941,593 ~ # 2,444,912 ~ # 2,553,541 ~ # 2,553,542 ~ # 2,553,543 ~ # 2,572,977 ~ # 2,702,559 ~ # 2,953,095 ~ # 4,280,558 ~ # 4,295,799 ~ # 4,341,505 ~ # 4,381,177 ~ #4,398,870 ~ # 4,460,320 ~ # 4,449,892 ).

Sherstenv, et al., found that "Clay consumption in preparation of drilling fluids is decreased 30 % when ultrasonic treatment is used. The rheology of drilling fluids can be modified by ultrasonic treatment. Treatment of water or reagents in a magnetic field prior to their use for drilling fluid preparation decreases clay swelling". (Chemical Abstracts [CA] 124:150195)

USP # 4,266,879 describes a fluid resonator tube that generates ultrasonic pressure waves, which emulsify oil-water-wax, etc., or enhance secondary recovery from oil formations, slurries, &c. Borehole wax plugs can be removed by disintegration with ultrasound.

USP #5,462,116 was granted for a "Method of Producing Methane Gas from a Coal Seam" by stimulation with ultrasound.

USP # 4,280,558 describes the "Ultrasonic Recovery of Oil from Sand", in which water is pumped into an oil-bearing formation and ultrasound is applied to drive out the oil. (CA 95:153539)

The ultrasonic extraction of tar sand can be accomplished by sonifying a solution of sodium silicate. Bitumen is produced with very low ash content and virtually free of metals and asphaltenes. The cumulative recovery (based on C content) is ~ 95 % in a continuous operation.

Similarly, USP # 4,054,506, granted for ultrasonic extraction of tar sand, claims that 78 % of the bitumen was removed in 60 seconds, and all of the bitumen was removed in 4 extractions with 60 KHz. (CA 88:25480)

Coal slurries can be treated with ultrasound to great advantage. The surface area and extractability of coal is thereby improved. Deashing and desulfurization are accomplished without undesirable chemical side-reactions, and in much less time. Flotation of fine particles can be significantly improved by microbubbles generated by a method of ultrasonic treatment developed at the Virginia Center for Coal & Minerals Processing (CA 121:13311).

Ultrasonic agitation is much more efficient than mechanical-rotational agitation with an impeller mixer in the selective agglomeration of coal slimes. (Powder Tech. 1984, 40(1-3):187-194 ~ CA 103:48468 )

Ultrasonic wet-grinding of coal can reduce the pyrite contamination from ~ 30 % to ~ 0.7 %, and clay similarly. Contaminants such as pyrites and clay are removed from the slurry by ultrasound at relatively low temperature and pressure and at increased throughput rates: "Ultrasonic treatment of coal suspensions increases the surface area and extractability of the coal, the amount of the increase depending on time, suspension liquidity, and coal type..." (USP # 4,156,593 ~ # 4,391,608 ~ British Patent # 2,139,245 ~ Japanese Patent # 82-128,791 ~ JP # 84-142,289 ~ S. African Patent # ZA 80-06,424 ~ CA 120:275037 ~ 121:259407 ~ 56:9911, &c).

According to the description in USP # 4,391,608, slurried coal is deashed and desulfurized by treatment with ultrasound (20 KHz, 0.7 W/cm2/30 minutes) flowed by separation and washing. Froth flotation alone resulted in coal containing 5 % ash and 1.22 % S. Ultrasonic treatment resulted in 4.07 % ash and 0.125 % S. (See also: USP # 4,537,599 ~ Japan Patent # 84-223,793 ~ Belgium Patent # 874,315 ~ CA 96:18067 ~ 99:90944 ~ 98:56945 ~ 102:206456 ~ 91:177966 )

According to Russian research, "Use of ultrasound-emulsified reagents gave up to 30% reduction in reagent consumption" in coal flotation. Numerous other studies confirm this and other improvements. (British Patent # 2,139,245 ~ Japan Patent # 84-233,793 ~ JP # 84-142,289 ~ CA 62:10254 ~ 97:75335 ~ 102:48468 ~ 121:13311 ~ 102:64815 )

Exposure of slurry containing both collector (kerosene) and frothing agent, however, "sharply decreased flotation efficiency", according to Soviet researchers. (CA 87:154619)

Deashing of coal can be improved by ultrasonic vibration of the filter, which eliminates clogging by preventing buildup of solids at the filter medium. (CA 121:259407 )

USP # 4,151,067 describes "Ultrasonic Production of Shale Oil" by treatment of a slurry of pulverized oil shale; the emulsion is separated by aeration; "The process has only moderate requirements for heat and energy."

Japan Patent # JP 97-40,980 describes a high-efficiency removal of sulfides and other impurities from coal by ultrasonic and electromagnetic treatment. (CA 126:253301)

South African Patent # ZA 80-06,424 claims that ultrasonic treatment of a coal slurry reduces particle size and detaches pyrites and ash from the coal. The impurities are removed from, the slurry according to density differences.

Corundum, silica, and other abrasives (such as are used in water-jets) can be removed and recycled from oil and other hydrocarbons by ultrasonic agitation of the slurry. (WO 93-09,859 ~ CA 119:273856 )

DOE Report 1981, DOE/PC/30143-T4 reports the effects of ultrasonic activation of several coal-cleaning processes: "In all cases, ultrasonic energy application demonstrated effects that would translate in production to processing efficiencies and/or capital equipment savings... Specifically, in the chlorinolysis reaction, pyritic S was removed 23 times faster with ultrasonics than without it... In NaOCl leaching, the total extraction rate was 3 times faster with ultrasonics. Two benefits were seen with oxydesulfurization: ultrasound doubled the reaction rate and allowed a pressure reduction from 960 psi to 500 psi. "

DOE Report 1991, DOE/PC/88883-T9 (CA 118:237345) describes the Electro-Acoustic Dewatering (EAD) process, which is expected to economically dewater filter cakes of ultrafine coal by a synergistic combination of electric and ultrasonic fields in conjunction with conventional mechanical processes.

Extractions such as dissolution of oil shale kerogen or removal of bitumen from coal can be performed in a small percentage of the time previously required for the same extractions without ultrasound. The extraction is much more complete, there is less disruption of chemical bonds, ash content is lower, the extract is virtually free of asphaltenes and metals. (USP # 4,151,067 ~ # 4,054,506 ~ Brazil Patent # 82-04,258 ~ CA 125:304721 ~ 87:154619 ~ 95:83380 ~ 81:124019, &c).

Ultrasonic extraction of coal (0.5-1.46 W/cm2) can extract at least 85 % of mobile organic matter without rupturing any chemical bonds. The average molecular weight of the extract is 340-1055. ( Fuel 1989, 68(10):1227-1233 ~ CA 99:142743 ~ 111:198237 )

According to USP #2,722,498, ultrasonic pressure waves (700 KHz) improve the extraction of shale; 1500 KHz / 0.6 kW, 5 minutes with carbon tetrachloride removes 50 % of organic material. The same extraction, for 15 hours without ultrasound, yields only 5 %. The amount of organic material extracted is tripled and the time required is reduced by 90 %. See also USP # 5,151,067.

Brazil Patent # BR 82-04,258 was granted for "Ultrasonic Extraction of Oil Shale". A mixture of pulverized oil shale and bitumen is heated to 300°-400° and treated with ultrasound: "The process produces a higher yield than previous techniques, produces relatively few and environmentally acceptable emissions, and uses a minimal amount of water". ( CA 99:161300 )

Similarly, Brazil Patent # 80-08,635 also utilizes ultrasonic extraction of oil shale by applying 20 KHz and 80 kg/cm2 to crushed oil shale for one minute to generate internal temperatures up to 315°, liberating petroleum extracts. ( CA 96:165417 )

Coal slurries can be liquified by ultrasound (with hydrogen & a catalyst), as described in Japan Patent # 81-127,684 and others. ( JP # 94-108,060 ~ JP # 94-108,062 ~ JP # 94-220,457 ~ Brazil Patent # 81-127,684 ~ BP # 80-08,634 ~ CA 105:211313 ~ 96:71736 )

As described in Russian Patent # 126,072, the concentration and dewatering of fine coal particles also can be improved in one stage by ultrasound. The process is "potentially more effective and economical than conventional thermal drying". Ultrasonic drying can be used to perform heatless drying of sensitive substances.

The liquefaction of coal can be accomplished by catalytic hydrogenation in the presence of ultrasound ( Japan Patent # 81-127,684 ~ JP # 94-220,457 ~ JP # 94-108,062 ~ JP # 94-108,061 ~ JP # 94-108,060 ~ CA 96:71736 ~ 121:13753 ~ 121:304495 )

Chemical reaction rates can be increased several hundred times by ultrasound. Thus, according to British Patent # 737,555, "Lignite dust having a calorific value of 5060 kcal/kg is gasified in air at 1200-1700° and at 0.8-1.5 atmosphere to give a gas having a calorific value of 745 kcal/cu m. by passing a shock wave of 126 MHz through the mixture. The shock wave is generated by the periodic compression obtained by the exothermic reaction of coal dust with air"" ( CA 50-6109 )

According to French Patent # 973,715, "Destructive hydrogenation [of shale, lignite, coal, peat, or petroleum residues] is conducted with the aid of high-frequency sound waves, i.e., 1-3 MHz. By establishing stationary waves, points of high pressure and temperature are set up every half wavelength, and conditions usually obtainable only in an autoclave can be obtained in contact with the atmosphere." ( CA 47:2461 )

Brazil Patent # 81-06,361 was granted for ultraviolet-ultrasonic gasification of oil shale, in which pulverized shale, catalysts, and wave are irradiated at 0.83 micron wavelength to give H and CO2. Ultrasound is used to maintain movement of the particles.

The US government is less enthusiastic. According to Gov. Rep. Announc. Index (US) 90(23), Abstr. # 060,438 (1990), the ultrasonic gasification of coal has been studied under numerous operating conditions, catalysts, and reactor configurations: "Overall, at the conditions and with the catalysts and slurry media tested, ultrasound was not effective in sustaining coal gasification reactions. The most favorable results were obtained with lignite-water slurry irradiated with high intensity ultrasound with KOH catalyst at 550° F and 1050 psig. After 1 hour sonification, the C conversion to gas was about 5 %". Ultrasound significantly increased the types and quantities of comments that were solubilized and reduced the particle size of lignite."

Japan Patent # 81,127,684, granted for ultrasonic hydrogenation of coal, describes the hydrogenation of powdered coal with copper chloride catalyst at 20 KHz for 1 hour to nearly double the yield of the same reaction without ultrasound. ( CA 96:71736 )

Waste gas containing NO2 or SO2 can be removed from waste gas by reaction with ammonia under the influence of ultrasound (13.56 MHz, ~ 500 W). "The SO2 reacts with part of the ammonia to form sulfuric acid and NO2, and the NO2 is reduced by the remainder of the ammonia to N..." ( CA 96:90996 ~ 95:155785 )

Coal treatment wastewater can be clarified by ultrasound, according to several patents (Romania Patent # 64,027 ~ Japan Patent # 76-138,055 ~ CA 87:28575 ~ 79:57346, &c )

Numerous patents have been granted for the emulsification of coal, oil and water by ultrasound Kurochkin, et al., used ultrasound for the improvement of petroleum processing by mixing of ~ 20 % gasoline into diesel for use in marine diesels, and removal of aromatic hydrocarbons from liquid paraffins. Fuel can be stabilized by sonification: "Ultrasound disperses asphaltenes and tars present in diesel fuels, thus improving their storage stability... Ultrasound (15 KHz) disperses all sedimenting impurities in a few minutes giving stable fuels". ( Japan Patent # 78-10,610 ~ JP # 82-81,820 ~ JP # 82-201,521 ~ JP # 82-91,729 ~ JP # 82-111,388 ~ JP # 81-52,613 ~ JP # 82-119,822 ~ CA 125:252368 ~ 96:38019 ~ 99:8017 ~ 98:218420 ~ 97:185215 ~ 97:219406 ~ 98:19110 ~ 98:201202 ~ 97:185222 ~ 97:219404 ).

Emulsions also can be demulcated by ultrasound: "Irradiation of unstabilized water-oil emulsions, e.g., petroleum-containing ship wastewaters, by an asymmetric sound field increases the rate of emulsion separation 15 times, as compared with untreated emulsions". ( CA 98:21738 )

USP # 4,126,547 was granted for a process of "Ultrasonic Oil Spill Remova".

The filtration of fine coal particulates from gas streams can be improved by ultrasonic excitation of the filter ( CA 95:48183 ).

Weiss, et al., received German Patent # 19-749,746 for their ultrasonic "Method and apparatus for chemical in situ cleanup of groundwater pipes", in which "Pollutants in groundwater and landfill leachate are decomposed by ultrasound in a frequency of 20-3000 KHz using ultrasound transmitters mounted on borehole pipes perpendicular to the direction of flow. The ultrasound-initiated decomposition converts the pollutants to volatile and less toxic or nontoxic compounds."

Ultrasound-enhanced soil washing has been investigated and the process optimized. Coal tar-contaminated soil was studied for the effects of factors such as ultrasonic power, dwell time, surfactant concentration, and solvent ratio: "Test results show that ultrasound energy... can enhance the soil washing process by more than 300%".

This informal review is not intended to be exhaustive, but merely to introduce the reader to the existence of these technologies, which obviously ought to be applied wherever it is practical, such as in the Karrick Process for low temperature carbonization of coal, or any other methods where it may improve production and reduce pollution.

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