NO854325L - ENRICHED COAL PRODUCTS AND MANUFACTURING COAL OIL MIXTURES. - Google Patents

Description

The invention relates to the enrichment of coal, and more particularly to an improved method for the enrichment of coal and the separation of contaminants from the coal and the formation of stable, enriched coal mixtures, such as coal-oil mixtures.

Known reserves of coal and other solid, carbon-containing fuel materials in the world are far greater than the known reserves of petroleum and natural gas combined. Despite this enormous prevalence of coal and related solid carbonaceous materials, reliance on these reserves, especially coal, as primary energy sources has not been encouraged for the most part. The availability of cheaper, cleaner-burning, more easily extractable and transportable fuels, such as petroleum and natural gas, has previously meant that coal has largely been limited to playing only a supporting role in the energy sector.

However, current world events have forced a new focus on global energy needs and on the availability of those reserves that will fully satisfy those needs. The realization that reserves of petroleum and natural gas are rapidly being depleted in connection with sky-high petroleum and natural gas prices, and the unrest that prevails in the areas of the world that have the largest amounts of these reserves, has ignited new interest in utilizing solid, carbon-containing materials, especially coal, as primary energy sources.

As a result, enormous efforts have been made to make coal and related solid carbonaceous materials equivalent or better energy sources than petroleum or natural gas. In connection with e.g.

coal, a large part of these efforts have been directed towards overcoming the environmental problems associated with the production, transport and combustion of coal. For example, the health and safety risks associated with the operation of coal mines have been significantly reduced with the introduction of new legislation that applies to coal mine operations. In addition, a large number of methods have been tried and developed to make coal burn cleaner, be more suitable for combustion and be easier to transport.

Gasification and liquefaction of coal are two such known methods. Detailed descriptions of various coal gasification and liquefaction processes can be found, e.g. in Encyclopedia of Chemical Technology, Kirk-Othmer, Third Edition (1980), Volume 11, pp. 410 - 422 and 449 - 473. However, these methods typically require a high energy input and also the use of high temperature and high pressure equipment, whereby an extensive application and the value of these has been reduced.

Methods to facilitate the transfer of coal to liquid have also been developed. Such a process is described in US patent 4,033,852. In this process, part of the coal's surface is chemically modified in a solvent, and the effect of this means that the coal can be more easily transferred to liquid in a solvent than natural forms of coal, whereby a preliquefied, viscous product can be recovered by extraction.

Besides gasification and liquefaction, other methods for converting coal into more convenient forms for combustion and transport are also known. For example, the production of coal-oil and coal-water mixtures is described in the litte-tour. Such coal mixtures offer considerable advantages. Besides the fact that they can be transported more easily than dry, solid coal, they can be stored more easily and are less exposed to the risk of explosion in the event of spontaneous ignition. Conversion of coal to a fluid state also makes it possible to carry out combustion in ordinary devices for burning fuel oil. Such an opportunity could greatly contribute to the transition from fuel oil to coal as the primary energy source. Typical coal-oil and coal-water mixtures and their preparation are described in US patents 3,762,887, 3,617,095, 4,217,109 and

4,101,293 and in British patent specification 1,523,193.

Regardless of the form in which the coal is finally used, however, the coal or the coal combustion products must be cleaned because they contain significant amounts of sulphur, nitrogen compounds and minerals, including significant amounts of metal contaminants. When these materials are burned, they are transferred to the environment in the form of sulfur dioxides, nitrogen oxides and compounds of metallic pollutants. If coal is to be accepted as a primary energy source, it must be cleaned to prevent pollution of the environment either by cleaning the combustion products from coal or by cleaning the coal itself before it is burned.

Both physical and chemical coal cleaning (enrichment) processes have therefore been investigated. In general, physical coal cleaning processes involve pulverizing the coal to release the impurities, the fineness of the coal generally determining the degree of release of the impurities.

Due to the fact that the costs of preparing the coal rise exponentially with the quantity of fines to be processed, there is, however, an upward economic limit in terms of size reduction. Moreover, grinding down coal even to an extremely finely divided form need not effectively remove all contaminants. Based on the physical properties that affect the separation of coal from the contaminants, physical coal cleaning methods are generally divided into four categories: gravity-based, flotation-based, magnetic and electrical methods. In contrast to physical coal cleaning, chemical cleaning methods for coal are at a very early stage of development. Known chemical coal cleaning methods include e.g. oxidative desulphurisation of coal (sulfur converted into a water-soluble form by oxidation with air), leaching with trivalent iron salt (oxidation of pyritic sulfur with trivalent iron sulphate) and leaching with hydrogen peroxide-sulphuric acid. Other methods are also described in the above-mentioned book Encyclopedia of Chemical Technology, Vol.. 6, pp. 314 - 322.

Although it is clear from the above that enormous efforts have been made to make coal a more usable energy source, further work and improvements are still necessary and desirable before coal, coal mixtures and other solid carbonaceous fuel reserves can be widely accepted as primary energy sources.

The present invention thus relates to a method which comprises contacting coal in an aqueous medium with a surface treatment mixture comprising a polymerizable monomer, a polymerization catalyst and a liquid, organic carrier, whereby a hydrophobic and oleophilic coal product is obtained which is suitable for treatment to remove further ash and sulfur using water separation methods. The product obtained is very suitable for the production of enriched coal slurries and/or purified particulate coal.

According to a further embodiment of the present invention, this also relates to an improved method for the enrichment of coal, where coal is surface-treated chemically with an aqueous medium to make the coal hydrophobic and oleophilic, after which the hydrophobic and oleophilic coal phase is separated from the ash-containing water phase and the hydrophobic and oleophilic coal phase is extracted, and the method is characterized by the fact that the chemically surface-treated, hydrophobic and oleophilic coal is subjected to high shear mixing with an aqueous washing medium, whereby additional ash and other hydrophilic contaminants are released in the aqueous medium and a hydrophobic coal phase floats on and is separated from a water phase.

From the drawings show

fig. 1 a flowchart for the method according to the present invention, where solid, carbonaceous material, such as coal, is enriched,

fig. 2 a flow chart of a preferred method by which solid, carbonaceous materials, such as coal, are beneficiated in accordance with the present invention,

fig. 3 a further flow chart for another preferred embodiment of the present method and

fig. 4 a typical container that can be used in carrying out the present method.

In the present method, a highly enriched coal product is produced by surface-treating coal particles in an aqueous medium with a surface treatment mixture comprising a polymerizable monomer, a polymerization catalyst and a liquid, organic carrier, whereby the coal particles are made hydrophobic and oleophilic. The present method thus produces a highly enriched coal product with a relatively low water content which can be dewatered

(dried) further to a remarkable extent without the use of heat energy. The ash content of the coal produced by the present process is reduced to low concentrations, and mineral sulfur compounds present are also removed. The final coal product also has improved heat content and can be burned as a solid fuel or combined with fuel oil or water to form highly desirable enriched coal mixtures or slurries that can be easily transported and burned cleanly.

As used herein, the term "concentration" shall include methods for cleaning or otherwise removing contaminants from a substrate, such as coal, and for extracting coal from coal streams, such as extraction of coal from waste streams by coal treatment processes and concentration or dewatering of coal streams or slurries, such as e.g. by removing water in e.g. pipelines for coal slurries.

According to one embodiment of the present method where raw coal from coal mines is used as raw material, it is preferred to initially reduce the raw coal or other solid, carbonaceous material to particles of liter diameter and to remove unwanted rocks, heavy ash and similar materials which are have been collected during the mining operation. The coal is thus pulverized and initially cleaned, usually in the presence of water in which the coal is suspended and/or sufficiently moistened so that it will become flowable. The coal is pulverized using common equipment, such as ball or rod mills, crushers or similar equipment.

It is generally desirable although not necessary for the present method to use certain water conditioning additives (treatment agents) in the pulverization step. Such additives make it easier to make the ash more hydrophilic, and this facilitates the separation of the ash in a way that will be discussed in more detail below. Typical additives that can be used according to the invention include common inorganic and organic dispersants and surfactants and/or wetting agents. Preferred rates for this purpose include sodium carbonate or sodium pyrophosphate etc.

The aqueous coal slurry formed in the pulverization step is typically a slurry with a ratio between coal and water of 0.5:1 - 1:5, preferably approx. 1:3, based on"" the weight. If the water treatment additives are used as described above, these are used in small quantities, as a rule e.g. in an amount of 0.25 - 5%, based on the weight of dry coal. Although it is generally recognized that more pollutants are released with decreasing coal size, the law of diminishing returns applies in that there is an economic optimum that determines the degree of pulverization. According to the invention, however, in any case it is generally desirable to crush the coal to a particle size of from 48 to less than 325 mesh, preferably approx. 80% of the particles must have a size of approx. 200 mesh (Tyler sieves).

Any coal can be used in the present process. These typically include e.g. bituminous coal, sub-bituminous coal, anthracite or brown coal etc. Other solid, carbonaceous fuel materials,

such as oil shale, tar sands, coke, graphite, mine tailings,

coal from scrap heaps, coal processing fines, coal fines from mine ponds or tailings, or carbon-containing excrement etc., can also be treated with the present method. The term "coal" shall therefore include these types of other solid, carbon-containing fuel materials or streams.

When the present enrichment process is carried out,

the aqueous slurry of coal containing the pulverized coal is contacted and mixed with a surface treatment mixture consisting of a polymerizable monomer, a polymerization catalyst, and a small amount of a liquid organic carrier, such as fuel oil.

Any polymerizable monomer can be used in the surface-treated polymerization reaction medium. Although it is more convenient to use monomers which are liquid at ambient temperature and pressure, gaseous monomers containing olefinic unsaturation which enable polymerization with the same or different molecules can also be used. Monomers that can be used in carrying out the present method can thus be characterized by means of the formula XHC=CHX' where X and X' can both be hydrogen or any of a wide range of different organic radicals or inorganic substituents enter. As examples, it can be mentioned that such monomers can include ethylene, propylene, butylene, tetrapropylene, isoprene, butadiene such as 1,4-butadiene, pentadiene, dicyclopentadiene, octadiene, olefinic petroleum fractions, styrene, vinyl-toluene, vinyl chloride, acrylonitrile, methacrylonitrile, acryl- amide, methacrylamide, N-methylolacrylamide, acrolein, maleic acid, maleic anhydride, fumaric acid or abietic acid etc.

A preferred group of monomers for use in carrying out the present method are unsaturated carboxylic acids, esters, anhydrides or salts thereof, especially those comprised by the formula ri where R is

RC-OR'

an olefinic unsaturated organic radical preferably containing 2-30 carbon atoms, and where R' is hydrogen, a salt-forming cation such as an alkali metal, alkaline earth metal or ammonium cation, or a saturated or ethylenically unsaturated hydrocarbon radical preferably containing 1-30 carbon atoms and is unsubstituted or substituted with one or more halogen atoms, carboxylic acid groups and/or hydroxyl groups in which the hydroxyl hydrogen atoms may be replaced by saturated and/or unsaturated acyl groups which preferably contain 8-30 carbon atoms. Particular monomers covered by the above structural formula include unsaturated fatty acids such as oleic acid, linoleic acid, linolenic acid or ricin-oleic acid, mono-, di- or tri-glycerides or other esters of unsaturated fatty acids, acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, ethylhexyl acrylate , tart. butyl acrylate, oleyl acrylate, methyl methacrylate, oleyl methacrylate, stearyl acrylate, stearyl methacrylate, lauryl methacrylate, vinyl acetate, vinyl stearate, vinyl myristate, vinyl laurate, unsaturated vegetable seed oil, soybean oil, collophonium acids, dehydrated castor oil, linseed oil, olive oil, peanut oil, tall oil

or crude oil etc. Tall oil and corn oil have been shown to

give particularly advantageous results when used in the practice of the present method. Corn oil is particularly preferred. It should also be clearly understood that materials containing compounds covered by the above formula and which also contain e.g. saturated fatty acids, such as palmitic acid or stearic acids etc,

can also be used in the execution of the present method. This also applies to monomers consisting of aliphatic and/or polymeric petroleum materials.

The amount of polymerizable monomer will vary depending on the desired degree of surface treatment. However, in general, monomer amounts of 0.005 -

0.1%, based on the weight of dry coal, is used.

The catalysts used in the enriching surface treatment reaction for the coal in carrying out the present process are any such catalysts that are commonly used in polymerization reactions. These include e.g. anion-active, cation-active or free-radical catalysts. Free radical catalysts or catalyst systems (also referred to as addition polymerization catalysts, vinyl polymerization catalysts, or polymerization initiators) are preferred. Examples can thus be mentioned of free radical catalysts such as inorganic or organic peroxides, such as benzoyl peroxide, methyl ethyl ketone peroxide, tert. butyl hydroperoxide, hydrogen peroxide, ammonium persulfate, di-tert. butyl peroxide, tert. butyl perbenzoate, peracetic acid or such non-peroxy free radical initiators as the diazo compounds, such as 1,1<1->bisazoisobutyronitrile etc.

Any catalytic amount (e.g. 0.45 kg per ton of added dry coal) of the catalysts described above can typically be used.

Moreover, for free-radical polymerization systems free-radical initiators are usually used which act to assist the initiation of the free-radical reaction. Any free radical initiators described in the prior art can be used here, such as those described e.g. in US patent 4 033 852. In particular, it can be mentioned that initiators include e.g. water-soluble salts, such as sodium perchlorate or perborate, sodium persulfate, potassium persulfate, ammonium persulfate, silver nitrate, water-soluble salts of precious metals such as platinum or gold, sulfites, nitrites and other compounds containing the similar oxidizing anions, or water-soluble salts of iron, nickel, chromium , copper, mercury, aluminium, cobalt, manganese, zinc, arsenic, antimony, tin or cadmium etc.

Particularly preferred initiators are the water-soluble copper salts, i.e. the monovalent or divalent copper salts, such as copper acetate, copper sulphate and copper nitrate. The most advantageous results have been obtained using divalent copper nitrate, CuCNO-^^- Additional initiators which may be used in carrying out the present process are described in co-pending US patent application 230,063, filed January 29, 1981. Among others these initiators include metal salts of organic groups, typical metal salts of organic acids or materials containing organic acids, such as naphthenates, tallates or octanoates etc, or other organic soluble metal salts, the metals comprising copper, chromium, mercury, aluminium, antimony, arsenic, cobalt , manganese, nickel, tin, lead, zinc, rare earth metals, mixed rare earth metals or mixtures thereof or double salts of such metals. The combination of copper and cobalt salts, especially of divalent copper nitrate and cobalt naphthenate, has been shown to give particularly good and synergistic results.

The amount of free-radical initiators which it is intended to use in carrying out the present method can be any catalytic amount and is generally within the range of 10-1000 parts per million (ppm) of the metal part of the initiator, preferably 10 - 200 ppm, based on the amount of dry coal.

The surface treatment reaction mixture used according to the present invention also comprises a liquid organic carrier. This is used to promote contact between the surface of the coal particles and the polymerization reaction medium. Liquid organic carriers that can be used according to the invention thus include e.g. fuel oil, such as fuel oil No. 2 or No. 6, liquid organic carriers that are not fuel oil, such as hydrocarbons comprising e.g. benzene, toluene, xylene, hydrocarbon fractions, such as naphtha or petroleum fractions with a medium boiling point (boiling point '100 - 180° C), dimethylformamide, tetrahydrofuran, tetrahydro-furfuryl alcohol, dimethylsulfoxide, methanol, ethanol, iso-propyl alcohol, acetone, methyl ethyl ketone, ethyl acetate or the like compounds or mixtures thereof.

The amount of liquid organic carrier, such as fuel oil, which is used in the surface treatment reaction according to the invention, is generally within the range of 0.25 - 5% by weight, based on the weight of dry coal.

The surface treatment reaction included in the present method can be carried out in an aqueous medium. The amount of water used for this purpose is generally 65 - 95% by weight, based on the weight of the coal slurry.

The conditions of the surface treatment reaction will of course vary depending on the particular reactants used and on the desired results. However, in general, any polymerization reactions which lead to a hydrophobic or oleophilic surface being formed on the coal can be used. More particularly, typical reaction conditions include e.g. temperatures within the range 10 - 90° C, the pressure from atmospheric pressure to near atmospheric pressure and a contact time, i.e. reaction time, from 1 second to 30 minutes, preferably from 1 second to 3 minutes. The surface treatment reaction is preferably carried out at a temperature of 15 - 80° C and at atmospheric pressure for approx. 2 minutes. The longer the reaction time, the better the results will generally be.

When carrying out the present method, the coal can be brought into contact with the surface treatment constituents using different methods. For example, one method consists in supplying the aqueous slurry of pulverized coal through a spray device, e.g. a nozzle, and adding the surface treatment ingredients, i.e., the polymerizable monomer, polymerization catalyst, initiator, and liquid organic carrier, to the aqueous charcoal shower. The overall spray mixture obtained is then introduced into an aqueous medium in an enrichment container. According to a preferred embodiment of this method, when this method is used, the surface-treated, aqueous coal mixture" which is now in the container is recycled to the same container by re-feeding the mixture into the container through at least one of the aforementioned spray devices.

In another method, the aqueous coal slurry and surface treatment ingredients, i.e. polymerizable monomer, polymerization catalyst, initiator and liquid organic carrier, are mixed in a premix tank and the resulting mixture is sprayed, e.g. through a nozzle, into an aqueous medium in an enrichment vessel. In a further and third method, the obtained surface-treated, aqueous coal mixture which has been formed in the enrichment vessel, in accordance with the above-described second method, is recycled to the same vessel by re-feeding the mixture into the vessel through at least one of the aforementioned spraying devices.

As the surface treatment reaction is completed, the hydrophobic and oleophilic enriched carbon particles float to the surface of the liquid mass. The ash, which still remains hydrophilic, tends to settle to the bottom and transfer to the water phase. The coal obtained from the reaction with the polymerizable surface treatment mixture described above is thus strongly hydrophobic and oleophilic and therefore floats easily on and can be easily separated from the aqueous phase so that a finished washing water and high coal yields are obtained. The liquid and hydrophobic coal can thus be easily separated from the aqueous phase (e.g. a skimming sieve can be used for the separation) which contains ash, sulfur and other contaminants that have been removed from the coal.

While not fully understood and while not wishing to be bound by any theory, it is believed that the surface treatment polymerization reaction leads to the formation of a polymeric, organic coating on the surface of the coal by molecular grafting of polymeric side chains onto the coal molecules.

When carrying out the present method, the surface-treated coal is preferably subjected to at least one further washing step in which the coal phase or phases are redispersed, with good stirring, e.g. when using rapid mixers, in the form of a slurry in fresh wash water. The initially surface-treated coal is preferably added to the washing water under atomizing pressure via a spray nozzle and thus forms small droplets in air which are forcefully directed towards and into the surface of the fresh water mass. In this way, complete air is incorporated into the system.

When the spraying is performed, the wash water and the treated coal phase are intimately mixed with each other under high-speed agitation and/or shear generated due to the nozzle under superatmospheric pressure. In this way, jets of coal particles are brought into intimate contact with the wash water via one or more openings in the spray nozzle, thereby causing air to be captured, both when passing through the nozzle and when impacting against and into the air-water interface in the wash water bath.

In US Patent Applications 230,058 and 230,059 both filed on January 29, 1981, a particularly effective method and apparatus for separating the treated coal particles from unwanted ash and sulfur in the water phase using an air entrainment spray technique is described,

where a coal-foam phase is formed by the treated aqueous coal slurry being sprayed or injected into the surface of the cleaning water. Briefly, with the method and apparatus described in the above-mentioned US patent applications, the coal slurry is injected through at least one selected spray nozzle, preferably of the type with a hollow cone, by pressure of e.g. 1.05 - 1.41 kg/cm 2 at a distance above the surface of the water and into the surface of the water so that aeration and foaming of the coal particles is achieved, whereby these particles will float on the surface of the water and can be skimmed off.

The above-described washings can be carried out on the treated coal slurry simply in the presence of water at a temperature of e.g. 10 - 90° C, preferably approx. 30° C, using 99 - 65% by weight of water, based on the weight of the added dry coal. Alternatively, further amounts of any or all of the surface treatment ingredients described above, i.e. polymerizable monomer, catalyst, initiator, liquid organic carriers, can also be added to the wash water. Furthermore, the washing conditions, e.g. temperature, contact time, etc., used when these ingredients are used, be the same as if only water is present, or the washing conditions may be the same as those described above in the case of surface treatment of the coal with a surface treatment mixture. Of course, if desired, water conditioning additives can also be used during the washing steps.

After washing and/or further surface treatment, the enriched coal can be dried to low water concentrations simply by means of mechanical devices, such as in centrifuges or pressure or vacuum filters, etc., thereby avoiding the need for expensive heat energy to remove residual water. The enriched coal produced by the present process, as described above, generally contains 0.5 - 10.0% by weight of ash, based on the weight of dry coal. Also, the sulfur content is from 0.1 to 4.0% by weight, preferably 0.3-2.0% by weight, based on the weight of dry coal, and the water content is 2-25, preferably 2-15% by weight, based on on the weight of dry coal.

At this stage the enriched coal can be used

as a fuel product with a high energy content and with a reduced content of ash and sulphur. This enriched fuel product can be used in a directly fired combustion device. The enriched particulate coal can alternatively be mixed with a carrier, such as oil, so that a very stable and highly enriched coal slurry is obtained, such as a coal-oil mixture (COB). Oil, preferably fuel oil, such as No. 2 or No. 6 fuel oil, is mixed with the enriched coal in any desired ratio. These ratios typically include 0.5 - 1.5 parts by weight of coal per 1 part oil by weight. A weight ratio of 1:1 is preferably used.

It will also be understood that the solid, enriched coal product according to the invention can also be redispersed in aqueous systems to be pumped through pipelines. In order to achieve improved stability, if desired, selected metal ions, in the form of their hydroxide or oxide, can be added to the aqueous dispersion to preferably regulate the pH of the slurry to above 7. Thus, for this purpose, alkali and/or 'alkaline earth metal', such as sodium -, potassium, calcium or magnesium etc, hydroxides or oxides are used. Sodium hydroxide is preferred.

It has also been shown according to the invention that a stabilized coal-oil mixture can be obtained when an alkali or alkaline earth metal, e.g. sodium, potassium or magnesium etc, -salt of a fatty acid with

fi

the formula R"C-OH where R" is a saturated or an olefinically unsaturated organic radical. The above described unsaturated

fatty acids, i.e. with the formula rEor', where R' denotes hydrogen or R is as defined above, can also be used here. The presence of these fatty acid salts in the enriched coal-oil mixtures according to the invention makes it possible to easily disperse the coal in the fuel oil to produce a gel or another material which delays bottom deposition for an almost unlimited time. Other metal ions besides alkali or alkaline earth metal ions can also be used to form stabilizing fatty acid salts. These other metals include e.g. iron, zinc or aluminum etc.

The amount of fatty acid used to form the stable coal-oil mixture will generally be 3.0 - 0.5% by weight, based on the total weight of the mixture. The amount of alkali or alkaline earth metal-containing compound used to form the gel will be sufficient to neutralize a substantial part of the fatty acid and thus generally varies from 0.1 to 1.0, usually from 0.1 to 0, 6, wt%, based on the total weight of the coal-oil mixture. Preferably, 1.5% by weight of acid and 0.3% by weight of neutralizing compound are added to a 50:50 coal-oil mixture.

As an alternative method of forming stable coal-oil mixtures, the coal-oil mixture can be subjected to a further surface treatment reaction, where additional amounts of polymerizable monomer and polymerization catalyst are added to a mixture of the enriched coal in oil. In this case, the polymerizable monomer is in an unsaturated carboxylic acid as described above, preferably tallow oil, used in an amount of 3.0 - 0.5% by weight, preferably 1.5% by weight, based on the weight of the mixture. The polymerization catalyst can be any of those described above and is preferably divalent copper nitrate, used in an amount of 2 - 10 ppm, preferably 5 ppm, based on the total weight of the mixture. The polymerizable monomer and polymerization catalyst are added to the coal-oil mixture while stirring. Next, an alkali or alkaline earth metal compound, such as sodium hydroxide, is added to the mixture in an amount of 0.6 - 0.1% by weight, preferably 0.3% by weight, based on the total weight of the mixture. The product obtained is a preferred stabilized coal-oil mixture.

Other methods that can be used here to produce stable enriched coal-oil mixtures are described in US patent applications 230 055 and 230 064 filed on January 29, 1981. More specifically, in US patent application 230 055 a method for the formation of stable coal-oil mixtures is described, where enriched coal is mixed with a fatty acid ester, such as triglyceride, preferably tallow, and a base, such as sodium hydroxide. Briefly explained, in US patent application 230 06 4 a method for the formation of stabilized coal-oil mixtures is described, where coal, oil, polymerizable monomer and polymerization catalyst are mixed with each other under low shear conditions and at elevated temperature, and immediately thereafter the mixture is subjected to stirring with high shear force at the same elevated temperature. The resulting coal-oil mixture is then treated with a gelling agent, such as a hydroxide, e.g. sodium hydroxide, to form a stable enriched coal-oil mixture in the form of a gel or thixotropic mixture.

The coal-fuel oil products, i.e. the coal-oil mixtures, according to the present invention, have distinctive properties. The present coal-oil mixtures are, for example, thixotropic, have increased energy content and can utilize coal with low ash, low sulfur and low moisture content and a number of different coal qualities, and they can imply a potentially greatly expanded market for coal as a fuel-fluid, whereby the saving of petroleum will be facilitated.

As an example of an embodiment of the present method, reference can be made to fig. 1 where raw coal extracted by mining is pulverized in a pulverization zone 10 in the presence of water and, if desired, in the presence of water conditioning additives while forming an aqueous coal slurry, This aqueous coal slurry is mixed in a line 6 with surface treatment reagents and/or additives introduced into the line 6 from tanks 1, 2, 3 and 4 via a line 5, and the coal slurry treated in this way is introduced as shown in an enrichment zone 12. Tanks 1, 2, 3 and 4 contain e.g. respectively polymerizable monomer, free-radical catalyst, free-radical initiator and liquid organic carrier. Raw coal from mining is introduced into the zone 10 via a line 23, water is introduced via a line 21 and water conditioning additives can be introduced via a line 25. Unwanted materials, such as rocks, are removed via a line 27.

Water is generally the main component in the enrichment zone 12. The treated coal slurry which is introduced via the line 6 into the zone 12 is now thus hydrophobic and oleophilic, and after it has been mixed with the washing water in the zone 12, e.g. by means of a rapid mixing device or by means of a spray atomizer, it will easily float on the surface of the water, whereby a carbon foam phase and an aqueous phase are formed in the zone 12. The carbon foam phase in the zone 12 can be easily removed from the zone 12 (e.g. by skimming) via a line 47, so that an enriched, i.e. clean, coal product according to the invention with reduced ash, sulfur and water content is obtained. If desired, the clean coal from line 4 7 can be further dried to remove additional water. The aqueous phase remaining in zone 12 contains ash, sulfur and other hydrophilic impurities and can be removed from this via a line 11.

When the present method is carried out in accordance with fig. 1, alternatively the surface treatment reagents and/or additives can be mixed with the aqueous coal slurry directly in the enrichment zone 12. These reagents and/or additives can be introduced into the zone 12 via a line 31 (monomer), a line 33 (free-radical catalyst), one wire 35 (free-radical initiator), one wire 37 (water)

and a line 39 (liquid organic carrier). The coal slurry is introduced via line 6 into zone 12 and is thus mixed with the reagents in zone 12. As described above, the surface treatment additives can be introduced in another way into the coal shower coming from line 6.

As shown in fig. 2, the present method can be carried out continuously with raw coal from mining as starting material and with a coal-oil mixture as end product, although other raw materials and products, such as enriched particulate coal and coal-water mixtures, can also be used and produced. According to fig. 2, raw coal is thus first pulverized in a pulverization zone 10A in the presence of water and, if desired, water conditioning additives while forming an aqueous coal slurry. This aqueous coal slurry is introduced via a line 9 into a mixing zone 11 and mixed in this with surface treatment reagents/additives supplied from reagent and/or additive tanks IA, 2A and 3A and 4A via a line 8. The tanks IA, 2A, 3A and 4A contains e.g. respectively polymerizable monomer, free-radical catalyst, free-radical initiator and liquid organic carrier. Raw coal from mining is introduced into zone 10A via a line 2 3A, water is introduced via a line 21A, and water conditioning additives can be introduced into zone 10A via a line 25A. The mixture obtained in the mixing zone 11, which contains the initially chemically treated hydrophobic and oleophilic coal, is then introduced into a first enrichment zone 12A via a line 29.

Alternatively, surface treatment additives (or additional surface treatment additives), i.e. polymerizable monomer, polymerization catalyst and liquid organic carrier as described above, may be added directly to zone 12A (or to zones 14 and 16) e.g. via a line 31A (monomer), a line 33A (free-radical catalyst), a line 35A (free-radical initiator), a line 37A (water) and a line 39A (liquid organic carrier) or they can be premixed with the slurry of pulverized coal in lines leading to the enrichment zones or containers in the zones. When the surface treatment reagents/additives are added directly to zone 12A, the coal slurry from zone 10A can be added directly to zone 12A

via line 9A and line 29. Also, the coal slurry in the enrichment vessel as described above can be recirculated within each particular vessel to achieve better mixing and separation.

The coal in zone 12A is very strongly hydrophobic and oleophilic, and after good stirring with e.g. a rapid mixing device or a spray atomiser, a coal foam phase is obtained which is recovered. A sieve can advantageously be used to separate and extract the flocculated coal. If desired, the mined coal via lines 47 and 49 can be introduced into a further series of washing steps (e.g. zones 14 and 16) in which further ash is released into the water phase by further stirring the mined hydrophobic coal foam from zone 12A using rapid mixers or other devices, such as a syringe atomizer.

The suspension phase with water-moistened ash, which is also formed in zone 12A, can be extracted and transferred for scrapping and extraction of water, after which the water can be recycled to be used again in the process, as shown in fig. 2.

Further ash and sulfur can also, as indicated above, be removed from the enriched coal foam phase by means of a series of water washing steps in countercurrent, i.e. that the water phase in the washing zones 14 and 16 can be recycled to a preceding washing zone, as also shown in fig. 2. In addition to water, as indicated above, zones 12A, 14 and 16 may also contain any or all of the above chemical surface treatment additives. The finished washed and surface-treated coal that leaves the zone 16 via a line 57 can be dried to a very low water concentration, e.g.

by centrifugation. The water removed in the centrifuge can also be recycled in the process, as shown. The mined, dry, enriched coal product can be used directly as such

as a solid fuel or it can be mixed with a carrier to form a highly desirable enriched coal slurry, as a coal-oil liquid fuel mixture.

In the production of the coal-oil mixture, it is shown in fig. 2 that the dry-enriched, surface-treated coal is introduced into a coal-oil dispersion mixing apparatus in which

preferably an acid R"S-OH as described above, such as tall oil or naphthenic acid, can be added together with alkali metal hydroxide, such as sodium or calcium hydroxide, forming a stable dispersion. If desired, further surface treatment of the coal can be carried out in coal-oil dispersion - the mixing apparatus by adding a polymerizable monomer and polymerization catalyst to the mixture, as described above, with or without the subsequent addition of alkali or alkaline earth hydroxide. The production of the coal-fuel dispersion can be carried out continuously or in batches, e.g.

in common paint making mill equipment in which tongue,

small grinding pieces are used to subject the dispersion to shear so that a non-sedimenting, flowable coal-fuel product is formed which is thixotropic.

It will be understood that although coal which has been enriched as described here is used for the coal-oil mixing process as described here, any coal, e.g. raw coal or coal that has been enriched by processes that are not described here, etc., are also used for the production of stable coal-oil mixtures in accordance with the present method.

In fig. 3 shows a further preferred embodiment of the present method. Raw coal from mining is introduced into a pulverizing zone 70 via a line 10 3 and is pulverized in the zone 70 in the presence of water which is added via a line 101. The water preferably contains a conditioning or treatment additive, such as an inorganic or organic surfactant, wetting agent or dispersant etc, which improves the effect of the water. Typical organic surfactants, such as Triton® X-100, include anionic, cationic, and nonionic materials. Sodium pyrophosphate is a preferred additive for use according to the invention. Conditioning ingredients can be introduced in zone 70, e.g. via a line 105. The aqueous coal slurry in the zone 70 is transferred to a mixing zone 82 via a line 81 and mixed in this with reagents/additives from tanks IB, 2B, 3B and 4B such as e.g. contains respectively polymerizable monomer, free-radical catalyst, free-radical initiator and liquid organic carrier.

The aqueous, chemically treated hydrophobic and oleophilic coal slurry mixture formed in zone 82 is transferred to a first water wash zone 72 via line 107 and through a high shear nozzle D, whereby the flow velocity and shear forces are believed to break down the coal phase flow to very small droplets which, in turn, can pass through an air interface in the washing zone 72 and collide downwards with force and are forced as jets into the mass of the water in e.g. a tank or tanks. If desired, additional surface treatment reagents and/or additives, as described above, can be added to zone 72 (and/or zones 74

and 76) e.g. via a line 109 (polymerizable monomer),

a line 111 (free-radical catalyst), a line 113 (free-radical initiator), a line 115 (water) and a line 117 (liquid organic carrier). The hydrophobic and oleophilic carbon phase formed in zone 72 is then preferably, as shown, introduced into a further series of wash zones via conduit 47.

Without it being intended here to be limited to any theory or reaction mechanism, it is believed that it will be useful to discuss the phenomena which are believed to give some of the advantageous results obtained by the present method. It is thus assumed that the high shear forces that arise from the mixture, e.g. in the nozzle D, facilitates the breakdown of the coal-oil-water flocculator as the dispersed particles forcefully enter the surface of the water in the tank, whereby ash and other contaminants are wetted with water and released from the spaces between the coal flocculants. These are thereby broken down so that the captured ash and other contaminants are freed and transferred to the aqueous phase and thus separated from the coal particles. The finely divided coal particles whose surfaces are now assumed to be surrounded by polymer and liquid organic carrier, such as fuel oil, now also contain (trapped) air which has been sorbed into the atomized particles as a result of the shearing action of the nozzle. The combination of surface treatment and sorbed air means that the flocculated coal has a reduced apparent density and will float on the surface of the water in the form of a separated coal foam phase. The coal particles thus have a density that is less than that of the water, repel water due to their increased hydrophobicity and quickly float to the surface of the water.

By means of the above-mentioned method, not only is ash essentially completely removed from the treated coal product, but the captured air and the more hydrophobic and oleophilic coal surfaces give a noticeable increase in the yield of total enriched, treated coal which is finally extracted.

The still hydrophilic ash remains in the bulk of the aqueous phase and tends to settle to the bottom of the tank under the influence of gravity and is removed from the zone 72 in the form of an ash-water stream 119 from the bottom of the container. A small amount of pulverized coal which may be incompletely separated can be transferred with the aqueous phase (removed ash-water stream) to a pulverized coal extraction zone 121, as shown in FIG. 3. Extracted coal fines can be recycled to the aqueous coal slurry in zone 70 via a line 123.

The washing process which is carried out in the zone 72 can be repeated using a counter-current washing system, whereby the coal becomes constantly cleaner by being successively introduced into the enrichment zones 74 and 76 via lines 47 and 49, as shown in fig. 3. At the same time, the clean wash water becomes increasingly loaded with water-soluble and water-moistened solid contaminants that are removed by the wash water.

As mentioned above, the intimately mixed ash-water slurry emerging from zone 72 and containing certain small amounts of particulate coal is transferred to a pulverized coal recovery zone 121 in which high ash, low water solids are recovered and ejected to is removed from the process, while the finely divided coal is recycled, as shown. The wash water can be further treated at 125 to regulate the condition of the wash water before it is recycled. The purified water is recycled to the original aqueous coal slurry or for such other refreshment as the overall process may require to balance the material flow.

As shown in fig. 3, the coal foam basins obtained in zones 72 and 74 can be introduced for further washing via nozzles or E and F. In this way, the coal particles are again atomized. The speed and high shearing force obtained by using the nozzles E and F again make it possible to bring washing water into contact with any ash that is still in the spaces in the coal floccules, whereby the release of ash into the aqueous phase is facilitated in each washing step. The aqueous phases in zones 72, 74 and 76 cause the flocculated mass of coal-oil-air to float up to the top of the respective tanks.

The final coal foam phase in zone 76 is transferred via a line 5 7 to a centrifuge to be dried. The enriched, clean coal phase is thereby strongly dried without the need for heat energy, and this is believed to be because the flocculated, dry coal that is extracted from the mechanical drying step has a reduced attraction for: water between the large coal ol jeoverf leter and the water that is physically enclosed between these.

The dry, hydrophobic, cleaned coal can advantageously be used at this stage as a solid fuel with a higher energy content and with a reduced ash and sulfur content, and this fuel is designated as Product I. The solid fuel can be used for direct firing or for to form enriched coal slurries as described above.

Another embodiment of the present method is, as indicated above, that a liquid fuel mixture is provided which is easily pumped in the form of a liquid, but which has such a biological quality that it is a thixotropic liquid. A thixotropic liquid is a liquid that has a "structure" or tendency to become viscous and gel-like at rest, but which loses its viscosity,

and the "structure" or gel is noticeably and quickly broken down when the thixotropic liquid is exposed to shear stresses, such as during stirring in mixing and pumping processes or during heating.

When carrying out the present method, as shown in fig. 3, the dry, enriched coal product I mixed with a certain amount of fuel oil (e.g. in a weight ratio of 1:1 and preferably heated to reduce the viscosity, especially if the fuel oil is of a high viscosity grade) in a mixing tank such that a pumpable fluid mixture is obtained.

The fuel oil-coal mixture in the mixing zone can alternatively be subjected to a further surface treatment step, in line with the general reaction method used for the first surface treatment enrichment as described above. For this purpose, any of the polymerizable monomers specified above, such as tall oil or corn oil, etc., can be used and added to the mixing zone together with any of the polymerization catalysts and/or initiators specified above. In addition, the saturated carboxylic acids described above can be used alone or optionally together with the unsaturated acids. If the saturated acids are used alone, initiators and catalysts do not need to be used. Naphthenic acids are examples of saturated acids that can be used.

The mixture of surface-treated coal, fuel oil and carboxylic acid can then be substantially neutralized with a water-soluble alkali metal compound, such as a hydroxide, e.g. sodium hydroxide, calcium hydroxide or mixtures thereof, as indicated above, to form a stable coal-oil mixture. A liquid, pure coal-oil fuel mixture (Product II) that does not show a tendency to settle, is recovered, storable, and is a liquid high-energy source for a variety of different end-uses.

The enriched coal product I can alternatively be slurried with water to form aqueous coal slurries or mixtures.

In fig. 4 shows a unit 55 which is suitable as a foam flotation container which can be used in any of the washing and/or enrichment zones for carrying out the present method. In this unit, the aqueous coal slurry, i.e. mixture of coal, water and preferably surface treatment reagents/additives, is injected into the container via line 29 and spray nozzles 61. Additional surface treatment reagents/additives or possibly other desired components can also be supplied via lines 31, 33, 35, 37 and 39. In this container, the coal foam is skimmed off from the main part of the container and into a collection section and can be introduced into the next zone, e.g. via a line 14 7. The aqueous ash phase in the main part of the container is removed, e.g. via a wire 41.

It will be understood that any of the zones shown in fig. 1-3, can be constituted by a single container or zone or by any number of containers or zones which are arranged in a manner suitable for carrying out the present method.

Example 1

200 g of Pittsburgh coal with an initial ash content of 6.2% and an initial sulfur content of 1.5% is pulverized in the presence of 400 g of water to a size of 200 mesh using a coal mill unit. The coal is transferred to a mixing container. In the container containing the charcoal, 0.05 g of corn oil, 2.0 g of fuel oil No. 2, 1.0 cm^ of a 5% solution of hydrogen peroxide in water and 2.0 cm<3>of a solution of divalent copper nitrate in water. The mixture is stirred and heated for approx. 2 minutes to approx. 30° C. The resulting mixture is injected into a container containing pure water, and foaming occurs. The coal in the coal foam phase is skimmed away from the surface of the water. The water phase, which contains large amounts of hydrophilic ash and sulphur, is discarded.

The cleaning method is repeated two more times using clean water, and the foamed coal is skimmed from the surface of the water. The particulate coal was then dried to a water content of 15%, based on the weight of dry coal, using a Buchner laboratory funnel. The ash content of the finished particulate product is reduced to 1.5% and the sulfur content to 0.8%.

Example 2

The method according to Example 1 is repeated using equivalent amounts of (a) petrol from coking oven, (b) oleic acid and (c) tallow oil, all of which are used as a substitute for the corn oil. A cleaned particulate coal product is obtained with an ash content of approx. 3% and a moisture content of approx. 15%, based on the weight of the dry coal.

Example 3

The procedure of Example 1 is repeated using (a) Kittanning coal, (b) Illinois No. 6 coal, and (c) lower Freeport coal instead of the Pittsburg coal.

A cleaned coal product with an ash content of approx. 3% and a moisture content of 15%, based on the weight of the dry coal, is obtained.

Example 4

200 g of Illinois coal No. 6 which had been size-reduced into lumps with a size of approx. 6.4 mm and has an ash content of 19.9%, crushed to a particle size of approx. 28 mesh and then pulverized to a particle size of 200 mesh in a laboratory ball mill in the presence of water to form a liquid aqueous coal slurry. The slurry's liquid phase contains approx. 65% water, based on the total weight of the slurry.

50 mg of tallow oil, 10 g of fuel oil, 250 mg of sodium pyrophosphate, 100 mg of divalent copper nitrate and 1.0 g of H202 (5% solution in water) are added to the above aqueous

coal slurry at a temperature of 30 - 40° C. The hydrophobic, surface-treated coal phase that is obtained is recovered by removing it from the surface of the aqueous phase on which it floats. The aqueous phase contains the hydrophilic ash and wreckage.

After several repeated dispersions in clean, soft water containing sodium pyrophosphate, at approx. 30° C is extracted

the surface treated coal. The coal's water content is approx.

5% after the coal has been filtered through a Buchner funnel (ordinary processing coal, i.e. without chemical surface treatment, usually retains 20 - 50% water when ground down to the same size).

The mined, mechanically dried, treated, enriched coal is mixed with 160 g of fuel oil, and a further 5 g of tall oil is added. After careful mixing at 85° C, sodium hydroxide, equivalent to the mixture's acid number, is added to the mixture and mixed into it.

After a delay of several months, no bottom deposit in the mixture of coal-liquid fuel can be observed.

Example 5

The procedure according to Example 4 is repeated, except that gram-equivalent amounts of the following polymerizable monomers are used instead of the tall oil used in Example 4:

(a) gasoline from coking oven and (b) oleic acid.

The surface of the pulverized coal is changed in a similar way so that highly hydrophobic coal particles are obtained which are treated in a similar way as described in Example 4.

In each case, the same amount of tall oil is mixed with the extracted enriched coal after drying. The acidity is neutralized with sodium hydroxide, and similar liquid coal-oil suspensions are prepared, all of which are thixotropic due to the selected metal ion displacing the sodium ion in the sodium hydroxide that was originally added. No bottom deposition can be observed during several weeks regardless of the monomer used for the surface treatment reaction.

Example 6

The procedure according to Example 4 is repeated, but with the change that 2 g of benzoyl peroxide is used instead of hydrogen peroxide. In addition, 2 g of Triton (9)-X-100 as a surfactant and 25 g of sodium pyrophosphate are present in the original aqueous slurry. The ash in the obtained aqueous phase is filtered out after treatment with lime. The treated coal's ash content is reduced from approx. 19.9% to approx. 4.7% after five separate washings where the water also contains Triton - X-100 and sodium pyrophosphate. The tall oil used for the surface treatment reaction and the tall oil used for the formation of the stable coal-oil mixture were first neutralized with sodium hydroxide and then treated with an equivalent amount of calcium hydroxide. The coal-oil mixture is thixotropic and gel-like, this suggests that no bottom deposition is expected with prolonged standstill.

Example 7

235 g of enriched coal with a moisture content of 15% and prepared as described in Example 1, is filled into a container in which a stabilized coal-fuel oil mixture is formed by adding to the coal 200 g of fuel oil No. 2, 6.0 g of tall oil, 1, 0 g of a 0.1% solution of f^C^ (or benzoyl peroxide) in water (toluene) and 2.0 g of a 0.1% aqueous solution of divalent copper nitrate. The mixture is stirred for approx. 1.0 minute at a temperature of approx. 85° C. 1.5 g of sodium hydroxide is added to the mixture, and stirring is continued for 5.0 minutes at a temperature of approx. 25° C. The coal-oil mixture obtained is a stabilized gel and stays that way for an unlimited time.

Claims (4)

1. Enriched coal product, characterized in that it includes surface-treated, hydrophobic and oleophilic coal with a reduced ash content of 0.5-10% by weight, based on the weight of dry coal, and a) in intimate mixture with fuel oil, b) in the form of a slurry mixed with a carrier or c) in intimate mixture with water and a sufficient quantity of an alkali or alkaline earth metal hydroxide or -oxide until the aqueous coal mixture has a pH above 7. 2. Procedure for the production of coal-oil mixtures, characterized in that powdered coal is mixed with a polymerizable monomer, a saturated fatty acid or mixtures thereof in the presence of fuel oil and with a) an alkali or alkaline earth hydroxide or b) a polymerization catalyst via the use of a polymerizable monomer. 3. Method according to claim 2, characterized in that powdered coal is mixed with a polymerizable monomer and a polymerization catalyst in the presence of fuel oil, after which a hydroxide is introduced into the obtained coal-oil mixture to form a stabilized coal-oil mixture. 4. Method according to claim 3, characterized in that tall oil is used as polymerizable monomer, as polymerization catalyst a mixture of a free-radical catalyst and free-radical initiator and as hydroxide sodium hydroxide.