WO1982001376A1

WO1982001376A1 - A dispersion fuel and a method for its manufacture

Info

Publication number: WO1982001376A1
Application number: PCT/SE1981/000298
Authority: WO
Inventors: Ab Boliden
Original assignee: Fahlstroem Per A
Priority date: 1980-10-17
Filing date: 1981-10-13
Publication date: 1982-04-29
Also published as: SE443797B; DK247882A; ZA816900B; SE8007305L; NO821998L; JPS57501632A; EP0051053A1; CA1185792A

Abstract

A dispersion liquid fuel comprising solid fine-grain carbonaceous particles dispersed in an oil-in-water, micro-emulsion with surfactants stabilizing the emulsion. The oil-in-water emulsion comprises more than 5% by weight water, 5-30% by weight mineral oil, 5-30% by weight of lower alkanols and up to 5% by weight emulsifier. The oil may comprise a mineral oil having a higher viscosity than 5 cSt, preferably higher than 10 cSt, for example firing oil 3. The invention also relates to a method for manufacturing the dispersion fuel.

Description

A DISPERSION FUEL AND A METHOD FOR ITS MANUFACTURE

Description

Technical field

The present invention relates to a new type of liquid fuel, comprising a dispersion of solid particles in liquid phase, and to a method for manufacturing such a fuel.

Background of the Invention

Because of the rising prices of oil, progressively increasing interest is turned towards alternative energy sources which can be transformed into fuels replacing oil. Among those fuels conceivable as alternative energy sources are the solid fuels, and not least fossil-type fuels such as shistous, peat, pitch coal and mineral coal. Even carbonaceous, renewable energy sources from plants are considered such as wood, timer offal!, algaes and seeweed, as well as cultivated biomass as straw, alder and sallow. The renewable energy sources are as a rule more rich in water and thus more difficult to disintegrate than the fossile ones. Thus, large power (thermal) plants have been developed, and combustion furnaces and gas purification plants have been adapted to this new fuel.

The problem of replacing oil, however, is of great significance also in conjunction with smaller plants for energy production, where costs and environmental problems related to the handling of shale, peat, wood,and coal when firing with solid fuel are difficult to overcome. It is therefore necessary to be able to use solid fuel, in the same manner, as oil-type liquid fuels. Many proposals have been put forward concerning so-called liquid fuels, comprising a particulate. fuel in a suspension or a dispersion and these proposals can be placed in three main groups; water-carried systems, oil-carried systems and methanol-carried systems. Coal-oil mixtures are those which are most obvious,- and the usefulness of such mixtures will be readily realised by those skilled in this particular art, in which the oil is extended by admixing finely divided wood, peat or coal therewith. One problem with such mixtures, however, is that the solid material must be ground and substantially all water removed, and that the dry particles must then be wetted with oil and a homogenous dispersion of the coal in the oil produced. A further problem exists when using a highly pure coal raw material which cannot be purified while producing the oil suspension.

Certain of these problems can be solved by using methanol instead of oil. Methanol, however, raises the price of the end product, since at least 30% by weight comprises methanol, and particularly because methanol is normally produced from coal or oil, with a thermal efficiency of about 50%.

Consequently water-carried liquid-coal fuels have also been developed. One such fuel is based on finely ground mineral coal, water and surfactants. One advantage afforded by this system is that there is obtained when grinding and purifying the coal, by flotation, an aqueous coal product which can be utilized without it being necessary to remove all the water. One problem, however, is that of producing stable suspensions which enable the liquid fuel to be used without requiring excessive measures to prevent the phases separating during storage and transportation of the suspension using a more natural aqueous, renewable energy source the suspension in water to a liquid or pumpable fuel means an unsuitably high percentage of water present which decreases the efficiency in thermal energy transformation.

Description of the present Invention

It has now been found that a particularly stable and easily combustible dispersion fuel. can be produced by suspending aqueous finely-divided carbon-containing particles in a liquid of particular composition. This liquid may suitably be present in the state of a so-called micro-emulsion. Preferably, the fuel comprises more than 50% by weight solid finely-ground carbon-containing particles, and the liquid phase of the suspension shall comprise more than 50% by weight water, 5-30% by weight of oil and up to 5% by weight emulsifier. The content of finely-ground carbon-containing particles shall be as high as possible, and the lower limit of 50% by weight is not critical. These fuels can be prepared from a number of fossile and renewable energy sources by suitable development of the process, which will be more closely described in the following.

An emulsion comprises two liquids which are only slightly soluble one within the other, in which one liquid is finely dispersed in the other. When the finely dispersed liquid comprises extremely small droplets in the order of 3-100 nm in the other liquid, the emulsion is normally referred to as a micro-emulsion. Micro-emulsions are stable at defined physical conditions and, if the liquids are trans parent, are completely clear liquids. Normally micro-emulsions contain surfactants to enable sufficiently small, stable liquid particles to be formed. A micro-emulsion exists within certain temperature ranges and is sometimes dependent on the pH of the phases. If the amount of finely-divided phase is increased the emulsion will be converted, via an intermediate stage in which the two phases comprise emulsified material and emulsifying agent, to a system in which the previously finely-divided phase will be the phase in which the other phase is emulsified.

A micro-emulsion may suitably be stabilized with fatty acid salts in combination with alcohols or amines. An optimal combination of surfactant as fatty acid salts and co-acting surfactant enables stable micro-emulsions having a high water content to be formed (Gillberg and Friberg ACS-Symposium and Evaporation-Combustion of Fuel droplets, San Francisco, August 1976). The alcohols may be monovalent or divalent and representative examples of such alcohols are pentanol, hexanol and heptanol, and also divalent alcohols such as hexandiol. Amines and aminor alcohols can also be used. Micro-emulsions are produced by, for example, dispersing oil spontaneously in water with the aid of mechanical forces and conventional surfactants. At given concentrations there are spontaneously formed clear transparent solutions with the addition of an alcohol or an amine having 5-7 carbon atoms, with emulsified droplets in the order of 8-80 nm. In technical processes no particular agitation is necessary to reach an emulsion. However, agitation to a certain extent may be necessary to bring large flows of different components together into intimate contact.

It has now been found possible to produce particularly advantageous dispersion fuels in which coal has been dispersed in a micro-emulsion, comprising more than 50% by weight water as the coherent phase and 5-30% by weight thick mineral oil and 5-30% by weight alcohol having one or two carbon atoms, and up to 5% by weight emulsifier.

By using methanol, ethanol or other lower alkanols such as isopropanol and any butanol or mixtures thereof in conjunction with mineral oil it is possible to produce dispersion fuels in micro-emulsion form, in which the oil phase comprises thick firing-oil. The amount of alcohol admixed is greater the higher the viscosity of the oil. By thick firing-oil is meant thick, sluggish firing-oil with a viscosity from 5 cSt, preferably higher than about 10 cSt at 50°C and higher, such as firing-oil grade 3, 4, 5, and 6. An emulsifier is a compound of the group fatty acid soaps, carboxylic acids having 4-8 carbon atoms, carboxylic acid esters having 4-8 carbon atoms in the carboxylic acid part, alcohols having 4-8 carbon atoms, and carboxy amines having 4-8 carbon atoms. Nonionic emulsifiers can also be used, such as harmonic mixtures of hydrocarbons having a boiling point of 150-275°C.

The new dispersion fuel constitutes a high-grade liquid fuel produced with a lower oil content and with a heavier firing oil than was previously possible. The novel fuel can be burned in small as well as large furnaces and plants and requires only the temperature to be maintained within the temperature range at which the micro-emulsion exists. By adding alcohol the lower temperature limit at which the micro-emulsion can no longer exist is decreased, which is an important advantage, and the risk of the fuel freezing when being stored and transported reduced. A secondary effect is that the alcohol can be used as a fuel component. Finally, the presence of a lower alcohol means a drying of the solid fuel when preparing the same to a dispersion.

The novel dispersion fuel is suitably produced by integrating the manufacture of the fuel with the purifying processes normally required when mining and grinding the intended carbonaceous materials. Thereby the fuel can be prepared particularly economical and the raw material and other process resources be utilized optimally. Dispersion fuels on a micro-emulsion base provides for a completely new group of fuels to be prepared, which are all pumpable and mixable with oil, carbon-oil-suspensions, carbon-methanol-suspensions and carbon-water -suspensions.

Dispersion fuels based on different carbon containing, combustible solid raw materials and their preparation will be more closely described in the following with reference tc a number of Examples in order to clarify the general intentions set forth above and to further demonstrate the scope of the invention.

Example 1

An oil containing shale material from the Mahogany-Zone, Colorado, USA was treated by wet grinding and enrichment of kerogene in accordance with the Swedish Patent S/N 7603646-6 (= US-B- 4.176.042). The kerogene concentrate thus obtained, by flotation and a following spherical oil agglomeration was thickened and filtered on a filter. In a following filtration system a micro-emulsion consisting of 30% by weight of water, 15% by weight of heavy shale oil, obtained in the shale oil refinery, 48% by weight of a mixture of lower alkanols, and 4% by weight of an emulsifying agent consisting of nonionic hydrocarbons and fatty acid amines were added to the filter cake. The addition of replacing micro-emulsion was interrupted when the kerogene-micro-emulsion dispersion had obtained a composition comprising 60% by weight of solid kerogene in a liquid phase and 40% by weight of a micro-emulsion consisting of 55% by weight of water, 20% by weight of heavy mineral oil, 5% by weight of an emulsifier and 20% by weight of a lower alkanol, (methanol). The kerogene dispersion thus obtained was intended to be fed to a plant for pyrolyzis according to SE,A,7903283-5, from which plant shale oil and shale gas are produced.

Example 2

Lignite from Powder River Basin, Wyoming, USA having a moisture content of 30% by weight of water was subjected to a wet grinding in a rod mill and a ball mill in a liquid consisting of a micro-emulsion of water, heavy oil, a lower alkanol, (ethanol), and an emulsifier. The grinding was finished when a particle size less of 100 microns had been obtained. By further addition of oil, alkanol and emulsifier in adjustable proportions the final contents of the dispersion was adjusted to 65% by weight of lignite, 22% by weight of water, 5% by weight of heavy oil, 6% by weight of ethanol, and 2% by weight of an emulsifier. (All calculations made on the total weight of the dispersion). The dispersion had a viscosity of 470 cP and was pumped to a power-heat plant where it replaced commonly used heavy oil No. 6.

Example 3

Petrocoke obtained at the final refinery of crude oil was subjected to wet grinding in a ball mill in a micro-emulsion consisting of 50% by weight of water, 12% by weight of so called slop oil, 26% by weight of a mixture of lower alkanols (C₁ - C₄), and 4% by weight of an emulsifier until the particles of the petrocoke passed a mesh size of 90 microns. The dispersion obtained was used in a steamship engine.

Example 4

Crude peat was prepressed and dewatered using oil in accordance with SE,A,8101623-0. The peat-oil-mixture thus obtained was provided with a mixture of water, a lower alkanol, (methanol) and an emulsifier of supplementing composition to give a liquid phase in the form of micro-emulsion consisting of 51% by weight of water, 29% by weight of heavy oil, 16% by weight of methanol, and 4% by weight of an emulsifier. The micro-emulsion comprised 45% by weight of the dis persion fuel, which could be used for direct combustion in a heat plant for oil combustion or in a gasification reactor for oil.

Example 5

Crude peat was prepressed in an angle press to a moisture content of 70% by weight of water. The peat mass was then added to a filter press together with a micro-emulsion consisting of water, oil, alkanol, and emulsifier in which press the water content of the peat was separated off and replaced by the micro-emulsion. The filter cake thus obtained was provided with further micro-emulsion so as to ob tain a composition in accordance with that of Example 4 above. The filtrate obtained was allowed to pass a bed of peat coke on which remaining organic compounds were absorbed, whereupon the peat coke after wet grinding to a small particle size was mixed with said dispersion fuel which had been adjusted to a power-heat-station orig inally constructed for oil.

Example 6

Charcoal prepared by dry distillation of sugar cane wood on a plantage in Mindanau, Philippines, was subject to dry grinding to a small particle size in a Raymond mill. After fine sieving the coal powder obtained was dispersed in a micro-emulsion consisting of 60% by weight of water, 12% by weight of heavy firing oil No. 4, 24% by weight of a mixture of lower alkanols (C₁ - C₄) comprising 75% by weight of methanol, and 4% by weight of an emulsifier i.a. consisting of an ammonia neutralized pine fatty acid. The charcoal particles were 63% by weight of the dispersion and had a particle size of less than 0.125 mm. The fuel was used to produce carbon oxide in a mobile apparatus. Exampl e 7

A mixture of wood of grown alder and grown sallow, as well as birch wood and pine forest waste was disintegrated and dried to a moisture content of 50% by weight of water. The wood mass was fed together with methanol-ethanol chilled to -90°C to a ball mill comprising ceramic balls. After the first milling step the mass as well as the liquid was fed to a second milling step in which the grinding bodies consisted of coal pieces having a piece size of 20 to 70 mm. The total mass was ground to a particle size of below 0.5 nm. After heat exchange to a temperature of +5°C using fresh methanol-ethanol and after separation off of the main part of the methanol-ethanol on a filter, the filter mass was provided with a micro-emulsion consisting of water, heavy oil No. 3, lower alkanols, and an emulsifier to form a stable dispersion in a micro-emulsion. The ready-to-use fuel contained 55% by weight of solid substance, 27% by weight of water, 6% by weight of heavy oil No. 3, 9% by weight of alkanols, and 3% by weight of an emulsifier and was used to heat tap water in a separate apparatus in a district heating plant.

Example 8

For the production of a dispersion fuel on basis of biomass according to Example 7 brown algae, straw were brought in, which components were fed into the second grinding step of Example 7. The feeding of algae and straw comprised 25% by weight of the wooden mass. The addition of micro-emulsion was similar to the one of Example 7 but the proportions of the ingredients were varied with regard to the water contents of the algae and the straw respectively so that the composition of the liquid phase was the same as in Example 7 above. The final dispersion was used in a district heating plant for production of hot tap water.

Example 9

Coal from a pit was pulverized by wet grinding and the thus formed coal suspension was separated by density separation, suitably in washing cyclons in a lighter fraction, which after dewatering and optional further grinding is used for the preparation of a disper sion fuel, and a heavier fraction which is further ground and flo tated.

In addition to subjecting the coal to conventional wet-grinding pro cesses, the coal may also be subjected to steam-splitting processes and leaching processes as a preparatory treatment prior to crushing the coal for further treatment. This method is described in SE,A, 7603646-6. When steam-splitting the coal, the coal is treated with a liquid under pressure and having an elevated temperature, whereafter the pressure is rapidly equalized to atmospheric pressure, whereupon liquid which has penetrated the coal is rapidly vapourized and splits the particles at the grain boundaries. The liquid used may, for example, be water. If sulphur dioxide is available, this can be uset to advantage in liquid form or dissolved in water, and subsequent to being used may be re-condensed and optionally re-cycled. Subsequent to steam-splitting the material, the material may be subjected to a leaching process such as to further loosen the grain boundaries and to facilitate further diminuation of the material, for example with a highly acid leaching liquid. Subsequent to subjecting the material to a flotation process or to a magnetic-separation process, for removing the pyrite present, the finely-divided mineral coal, which is free from sulphur, is passed to the dispersion-fuel manufacturing plant. A preceding, additonal purifying process may be carried out, by dividing the material into mutually different degrees of purity, by flotation or classification screening, where in the latter case coarse material is passed to a flotation plant prior to manufacturing the dispersion fuel.

For the purpose of recovering finely-divided material entering cyclones and filters, the material can be returned to a coal-agglomerating stage in which it is agglomerated with oil, whereafter the agglomerate is de-watered and passed to a mixer in which water, methanol and emulsifier are added and a micro-emulsion base is formed. This micro-emulsion base is mixed with the finely-divided coal phase in suitable proportions, i.e., so that the coal phase is more than 50% by weight of the dispersion fuel. In the aforegoing the coal phase has been described with reference to mineral coal, although it will be understood that other types of coal can be used, such as pitch coal, peat, asphalt and soot and coke products. Even biological products such as charcoal and biomass as well as shale material comprising kerogeπes can be used as the solid fine grain fuel. The impurity content of the solid fuel, in the form of inorganic salts and the like, will naturally be present in the ultimate dispersion fuel and, as will be understood, the presence of certain impurities must be taken into account when using the fuel.

The invention will now be described with reference to an example relating to the treatment of a bituminous mineral coal (steam coal) of conventional composition. One such steam coal has been obtained by treating so-called mining coal in a washing plant and is found available as bulk goods with a particle size beneath 40-50 mm. Manufacture of the fuel, described hereinafter, may either-be effected in direct connection with the primary production of steam coal, or at some location in the transport chain up to the final consumer station.

In accordance with a preferred embodiment of the invention, the coal required for the fuel mixture is supplied continuously to a wet grinding plant, comprising a rod mill, in which the coal is ground down to a particle size of at most 3-5 mm. The particles in the pulverized coal smaller than about 100 μm are separated off and the pulverized coal is de-watered in a centrifuge and then subjected to a density-separation process in a cyclone having heavy medium, in a known manner. In this separation process, the coal is divided into a light fraction having a separation limit of 1.3 g/cm³. The light fraction having a high carbon content and lower ash content is treated by itself, while the heavier fraction, in excess of 1.3 g/cm³ and having a low carbon content and a higher ash content, is also treated on its own, as hereinafter described. The light fraction is of such purity that subsequent to being filtered and further ground may be charged directly to the plant for the manufacture of dispersion fuel.

The heavier fraction, having the higher ash content and lower carbon content, is subjected to a further grinding process, in which it is ground to a particle size smaller than 0.1 mm in a closed circuit which incorporates a cyclone. The circuit also incorporates a classifier, from which the coal-water suspension is passed to a flotation purifying stage, where ash and pyrite are separated from the suspension to obtain a purified coal, which is admixed with the finely- ground coal obtained from the lighter fraction.

The coal-water suspension is passed to a thickener, where the major part of the water is removed from the suspension and returned to the process line.

The thickened product is passed to a further de-watering stage on a filter which operates under pressure and which is heated in order to remove as much water as possible. Water remaining in the filter cake is then displaced therefrom with the selected micro-emulsion base in a further filtering or de-watering stage, wherein water present in the pores of the filter cake is replaced with micro-emulsion base.

After said change of the liquid phase, the solid substance content of the coal-liquid mixture and liquid contained therein are adapted by further adjustment to the composition of the mixture, with the aid of dry coal or more micro-emulsion base.

When displacing the water with micro-emulsion base there is obtained a liquid mixture of water and emulsion base, which is passed to the fine-grain slurry separated from the primary slurry, and by suitable agitation the coal content is caused to agglomerate, to form a coal agglomerate, while simultaneously separating undesirable ash material and pyrite therefrom. The coal and oil agglomerate is agitated with a liquid containing an excess of the remaining components in the micro- emulsion system, for dispersion of the aggregate, whereafter the product is combined with a final micro-emulsion base. The above description of the process merely sets forth the main features of a method according to the invention. It will be understood by those skilled in the art that the density separation process described in the introduction can be omitted in certain cases, the coal in its entirety being ground to a size smaller than 100μm in a closed circuit which incorporates a classification apparatus. In certain cases it may be particularly suitable to incorporate a sulphur-flotation stage in the grinding circuit, so that as much pyrite as possible is separated at the earliest possible point of time in the treatment process, as previously mentioned. Subsequent to completion of the grinding process, the suspension of finely ground coal and water may be passed to a hydrocyclone and de-slurried. The coarser fraction, i.e. the fraction containing particles preferably greater than 20 μm, is subjected to coal flotation, thickening, filtering and displacement of the water phase with micro-emulsion, as described above, while the finer fraction, comprising particles smaller than 20 μm, is agglomerated with micro-emulsion in an excess quantity, from displacement of the liquid phase of the coarser fraction, and micro- emulsion comprising lighter oil components. The resultant fuels are particularly suited for diesel engines and more advanced combustion purposes. In addition to promoting the dispersion properties of the fuel, the surfactants can be selected so as to reduce the viscosity of the mixture, by selective adsorption on the mineral surfaces of further ionic substances, e.g., soap and fatty acids.

Example 10

At the preparation of a dispersion fuel based on coal in accordance with Example 9 a coal residue comprising 47% by weight of combustible material and 53% by weight of mineral was obtained. This residue was thickened and dewatered on a filter to a moisture content of 34% by weight based on the total. In a further filtration step the water was removed using a micro-emulsion consisting of water, heavy oil No. 5 also containing residues of organic solvents, and a mixture of lower alkanols, and an emulsifier. The coal residue thus treated thereby obtained a final moisture content of 32% by weight. The liquid consisted of a micro-emulsion of 51% by weight of water, 16% by weight of heavy oil, 21.9% by weight of alkanols, and 4.1% by weight of an emulsifier. The filtrate was recirculated and was used for flotation purposes in the preparation of the coal men tioned in Example 9 above. The dispersion of the coal residue was pumped to a gasification reactor for the preparation of a medium calorific, (about 300 B.T.U./c.ft.), synthetized gas whereby its energy content was well utilized.

Example 11

In the treatment of a coal residue as described in Example 10 above an equal amount of peat transferred into a dispersion fuel in accordance with Example 5 above was added to the coal residue after thick ening thereof. The additions of a micro-emulsion to the water removal step and the relations therebetween were varied with regard to the new blending relationship, whereby a dispersion fuel having a composition of the liquid as in Example 10 was obtained comprising 50% by weight of coal residue and 50% by weight of peat as solid phase. As well as in Example 10 the fuel was fed by pumping to a gasification reactor for the preparation of medium synthetized gas.

Example 12

Bituminous mineral coal having a high gas content was flotated free from mineral ingredients and pyrite in accordance with Example 9. The purified coal was dewatered on a filter and a subsequent removal of water with a micro-emulsion. Between the steps of thickening and filtration 5 kg of magnesium powder to which 2.5 kg of aluminium powder had been added, and which had been finely ground in a mixture of methanol and heavy oil No. 3, were added. The thus prepared dispersion fuel consisting of 67% by weight of coal including metal powder, 3% by weight of heavy oil No. 3, 9% by weight of a mixture of methanol, ethanol, and isopropanol in equal parts, and 4% by weight of an emulsifier as well as 17% by weight of water was stable. 20 kg of ammonium nitrate were dissolved per each 100 kg of dispersion fuel and the resulting dispersion thus obtained was used as jet fuel in air craft.

The described fuel mixture and its method of manufacture provide a pumpable, highly pure oil-like replacement fuel for oil, said fuel mixture having properties which lie close to those of oil. The fuel mixture provides a fuel which has substantially all the good properties of a coal-water mixture and which can be produced with a relatively limited amount of relatively low-grade oil and preferably from the alcohols methanol or ethanol, which in turn can be produced relatively simply. The risk of the fuel freezing, which is a serious risk in other water-based systems, is substantially reduced. Thus, there is produced a fuel whose manufacture is only dependent on oil to a very slight degree.

The combustibility of the fuel, expressed as the cεtane rating, is greater than that of other water-based coal fuels. The flammability of the fuel can be further increased by adding aluminium or magnesium powder.

Claims

1. A dispersion fuel comprising solid fine grain carbonaceous particles dispersed in a liquid medium with surfactants stabilizing the dispersion, characterized in that the liquid medium is a micro- emulsion of an oil-in-water type dispersing the carbonaceous particles, and whereby at least one lower alkanol having 1-4 carbon atoms is present as a transphase bridging agent.

2. A dispersion fuel according to Claim 1, characterized in that the carbonaceous particles comprise preferably more than 50% by weight of the fuel, and that the oil-in-water emulsion comprises more than 50% by weight water, 5-30% by weight mineral oil, 5-30% by weight methanol and up to 5% by weight emulsifier.

3. A dispersion fuel according to Claim 2, characterized in that the mineral oil used is an oil having a higher viscosity than 5 cSt at 50°C, preferably higher than 10 cSt.

4. A dispersion fuel according to Claim 3, characterized in that the mineral oil is firing oil No. 3.

5. A dispersion fuel according to Claim 2, characterized in that the emulsifier consists of one or more substances selected from the group fatty-acid soaps, carboxylic acids having 4-8 carbon atoms, carboxylic acid esters having 4-8 carbon atoms in the carboxyl chain, alcohols having 4-8 carbon atoms and carboxy amines having 4-8 carbon atoms.

6. A method for producing a dispersion fuel according to Claims 1-5, characterized by applying to moist fine-grain carbonaceous particles an emulsion of oil in water, in which the water is present in such an amount that together with the water present in the coal particles it comprises more than 50% by weight of the liquid in the dispersion fuel formed.

7. A method according to Claim 6, characterized in that the fine-grain carbonaceous particles comprise finely ground mineral coal.

8. A method according to Claim 6 and Claim 7, characterized in that the mineral coal is wet ground, density separated, subjected to flotation and dewatered, whereafter the dewatered mass of mineral coal is admixed with an oil-in-water emulsion which together with the water remaining in the mass of mineral coal forms a stable micro-emulsion containing more than 50% by weight water, 5-30% by weight mineral oil, 5-30% by weight ethanol or methanol and up to 5% by weight emulsifier.

9. A method according to Claim 8, characterized in that the oil-in-water emulsion is applied to the mass of mineral coal on a filter bed.