EP0106130B1

EP0106130B1 - Coal-aqueous mixtures and process for preparing same

Info

Publication number: EP0106130B1
Application number: EP83108876A
Authority: EP
Inventors: Mark Seymour
Original assignee: Standard Oil Co
Current assignee: Standard Oil Co
Priority date: 1982-09-10
Filing date: 1983-09-08
Publication date: 1988-04-06
Also published as: ATE33397T1; EP0106130A3; CA1200697A; DK409683D0; ES525431A0; ES8502470A1; EP0106130A2; JPS5964696A; PT77319B; DK162654B; DK162654C; GR79060B; ZA836671B; JPH0316997B2; DK409683A; PT77319A; DE3376219D1

Abstract

Coal-aqueous mixture having high solids content and excellent stability are provided by an improved process involving selective mixing and other conditions.

Description

The present invention relates to a method for forming coal-aqueous mixtures.
Coal as an energy source is in abundant supply. It is estimated that in the United States there is more energy available in coal than in petroleum, natural gas, oil shale and tar sands combined. The substitution of coal for natural gas and oil on a large scale would therefore seem a ready-made solution to our energy problems. Unfortunately, however, unlike oil and gas consumption, coal use is limited not by reserves or production capacity but rather by the extraordinary industrial and regulatory difficulties of burning it in a convenient, efficient and environmentally acceptable manner.
A number of techniques are being explored to provide coal as a more useful energy source. One such technique employs gasification methods such as destructive distillation, to effect the conversion of coal to a gas of low or medium calorific value. In another approach, high pressure hydrogenation is utilized to liquefy coal to make it more suited for transport, burning and the like.
Another technique suggested, and the one to which the present invention relates, is the technique whereby solid coal particles are dispersed in a fluid carrier medium, such as fuel oil or water to form coal-aqueous or coal-oil mixtures.
Coal-oil and coal-aqueous mixtures, however, are distinct systems, each having its own difficulties of formulation. For example, while coal and oil are relatively compatible, coal and water are not. Thus, unlike in the formulation of coal-oil admixtures, in the formulation of coal-aqueous admixtures, the initial dispersing of the coal in the continuous water phase, especially large amounts of coal, represents a challenging obstacle. Moreover, after dispersion, stabilizing, i.e. keeping the coal from settling out of the water phase, must be also achieved.
Such coal mixtures offer considerable advantages. They are more readily transported than dry solid coal, are more easily stored and are less subject to the risks of explosion by spontaneous ignition, the latter being a significanat factor in handling coal. In addition, providing coal in a fluid form can permit its burning in apparatus normally used for buring fuel oil. This can greatly facilitate the transition from fuel oil to coal as a primary energy source, another highly desirable result.
Various coal-oil and coal-aqueous mixtures have been described in the literature. For example, British Patent No. 1,523,193 discloses a mixture comprised of fuel oil and from 15 to 55% by weight of finely ground coal particles reduced in particle size to 10 microns or finer. The effort required to grind coal to such fine sizes, however, makes the process less economically attractive. Moreover, the-use of fuel oil as a carrier medium negates the requirement of lessening our dependence upon fuel oil.
U.S. Patent No. 4,251,229 is an example of coal-oil mixtures stabilized with high molecular weight adducts of alkylene oxide and an alcohol, an amine, a carboxylic acid or phenol having at least three active hydrogens. In this patent, oil is the continuous carrier phase and accordingly, the stabilization of the coal, as emphasized repeatedly therein, in the continuous oil phase, is essentially the only concern.
U.S. Patent No. 4,242,098 discloses aqueous coal slurry compositions containing water soluble polymers, which are thickeners, such as xanthan gum, hydroxypropyl guar gum or poly(ethylene oxide) having a molecular weight over 100,000.
In United States Patent No. 3,762,887, there is disclosed a dispersion of coal in an aqueous medium wherein the coal is ground to a defined array of particle sizes, a substantial portion of which being about 325 mesh Tyler Standard screen or even finer. Here again, substantial and selective grinding of the coal is required.
United States Patent No. 4,217,109, discloses a technique for cleaning and dispersing coal in water utilizing dispersing agents which by selective adsorption impart different electrical charges to the carbon particles and the impurities. The dispersing agents taught are polyelectrolytes, such as alkali metal and ammonium salts of polycarboxylic acids and polyphosphates.
The article titled "Development and Evaluation of Highly-Loaded Coal Slurries" published in the 2nd International Symposium on Coal-Oil Mixture Combustion, November 27-29, 1979, teaches coal-aqueous mixtures using coal of bimodal particle size distributions and containing modified starches, biocides and a wetting agent such as TRITON X, an octylphenoxy (ethyleneoxy) ethanol surfactant of low molecular weight.
And according to United States Patent No. 3,617,095 a still further method is mentioned in the literature for forming emulsions of bulk solids by admixing the solid, such as coal, with water and oil in the presence of an oxyalkylated octyl phenol emulsifying agent.
Finally, a number of further patents disclose mechanical treatments and dispersants for providing coal in a carrier medium. See e.g., United States Patents Nos. 4,088,453; 4,104,035; 3,620,698; 3,764,547; 3,996,026; 3,210,168; 3,524,682; 4,330,301; 4,305,729; European Patent No. 0 050 412 and PCT International Application No. WO 81-01152.
While the art has attempted to provide coal in dispersed fluid form, as evidenced by the above- described procedures, there still remains the need for improving these methods in order to provide coal mixtures without undue mechanical or chemical treatment. It would be highly desirable to provide coal in aqueous mixture form wherein only minor amounts of additive materials are needed to disperse the coal to high solids concentrations of 70% by weight, or higher. It would be further desirable to provide coal-aqueous mixtures wherein the coal is pre-cleaned of impurities so that the resultant mixtures are clean burning or relatively clean burning and thus more environmentally acceptable.
U.S. Patent No. 4,358,293 dated November 9, 1982, discloses the surprising discovery that certain polyalkyleneoxide nonionic surfactants are excellent additives for forming coal-aqueous mixtures having high coal solids concentrations. It is also disclosed therein that polyalkyleneoxide nonionic surfactants of high molecular weight having a hydrophobic portion, and a hydrophilic portion, the hydrophilic portion being comprised of at least about 100 ethylene oxide repeating units, provide coal-water dispersions having very high coal solids concentrations of about 70% by weight coal, or higher, when the surfactant is present in an amount sufficient to disperse the particulate coal in water. The resultant mixtures are free- flowing and are adapted to provide coal in a form ready for transport, storage and clean-burning. Surprisingly, the surfactants employed can differ in chemical structure so long as they are of the selected type, are of sufficient molecular weight and are comprised of at least about 100 units of ethylene oxide.
It has now been further surprisingly discovered that by employing certain processing conditions, hereinafter described in detail, in the preparation of the coal-aqueous slurries disclosed in the aforementioned U.S. Patent No. 4,358,293, even more improved coal-aqueous slurries are provided. For example, the coal slurries prepared in accordance with the present invention are characterized by high solids content, excellent long term storage stability and other advantages which will become apparent hereinafter.
The present invention relates to a method for forming a coal-aqueous mixture in which a polyalkylene oxide non-ionic surfactant having a hydrophobic portion and hydrophilic portion, said hydrophilic portion being comprised of at least 100 units of ethylene oxide is admixed under stirring with water and particulate coal is admixed thereto under further agitating, characterized in that (i) the admixing of the surfactant with water is effected under low speed agitation conditions (500 to 1500 rpm), (ii) the admixing of the particulate coal to the admixture resulting from step (i) is effected under medium speed agitation conditions (1000 to 3000 rpm), and (iii) the resultant coal containing the mixture of step (ii) is agitated under high speed conditions (3000 to 6000 rpm).
The coal-aqueous slurries obtained by the present invention are comprised of coal or other carbonaceous material as the dispersed solid; water as the carrier medium; and a polyalkyleneoxide nonionic surfactant, as further described herein.
As used herein "polyalkyleneoxide nonionic surfactant" connotes all compositions, compounds, mixtures, polymers, etc. having in whole or in part an alkylene oxide repeating unit of the structure:
and having a hydrophobic portion and a hydrophilic portion and which does not dissociate or ionize in solution. These surfactants have a polymeric portion comprised of repeating units of ethylene oxide of the general formula:
Moreover, the polyalkyleneoxidè nonionic surfactant compositions employed in this invention are of high molecular weight, i.e., 4,000 or higher, depending on the particular surfactant employed, are hydrophilic and are comprised of at least 100 repeating units of the ethylene oxide monomer. In addition, the surfactants utilized have a hydrophobic portion and a hydrophilic portion and are nonionic. Being nonionic, these compositions are generally not subject to ionization in aqueous solutions of acid or alkali.
Suitable hydrophilic polyalkyleneoxide nonionic surfactants for use in this invention are the commercially available glycol ethers of alkyl phenols of the following general formula I:
wherein R is substituted or unsubstituted alkyl of from 1 to 18 carbon atoms, preferably 9 carbon atoms; substituted or unsubstituted aryl, or an amino group and n is an integer of at least 100.
These nonionic surfactants are available in a wide array of molecular weights depending primarily on the value of "n", i.e., the number of ethylene oxide repeating units. Surprisingly, it has been found that these surfactants of a high molecular weight of 4,000 or higher wherein "n" is at least 100, or higher are particularly effective as dispersants for forming coal-aqueous mixtures to high coal solids concentration requiring little if any further additives, to form highly flowable liquids.
Procedures for the preparation of the glycol ethers of formula I are well known and are described, for example, in United States Patents Nos. 2,213,477 and 2,496,582. Generally, the production of these compositions involves the condensation of substituted phenols with molar proportions of ethylene oxide monomer.
Thus, polyalkyleneoxide nonionic surfactants suitable for use in the invention include the glycol ethers of alkylated phenols having a molecular weight of at least 4,000 of the general formula:
wherein R is substituted or unsubstituted alkyl of from 1 to 18 carbon atoms, preferably 9 carbon atoms; substituted or unsubstituted aryl, or an amino group, and n is an integer of at least 100. The substituents of the alkyl and aryl radicals can include halogen, hydroxy, and the like.
Other suitable nonionic surfactants are the poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) or, as otherwise described, propoxylated, ethoxylated propylene glycol nonionic surfactant block polymers having a molecular weight of at least 6,000 of the general formula:
wherein a, b and c are whole integers and wherein a and c total at least 100.
Still other polyalkyleneoxide nonionic surfactants suitable for use in the invention are the block polymers of ethylene and propylene oxide derived from nitrogen-containing compositions such as ethylene diamine and having a molecular weight of at least 14,000 of the general formula:
wherein Ri is an alkylene radical having 2 to 5 carbon atoms, preferably 2; R₂ is alkylene radical having 3 to 5 carbon atoms, preferably 3; a, b, c, d, e, f, g and h are whole integers; and e, f, g and h total at least 100.
The coal-aqueous mixture compositions of the invention herein are characterized by having a high coal solids content and a relatively low viscosity of 2,000 to 6,000 mPa-S (2,000 to 6,000 centipoise) or lower as measured, e.g., in a Brookfield viscometer, model #RVT, fitted with a number 3 spindle, at 100 r.p.m. even at solids level of 70% by weight, or higher, based oon the total weight of the mixture. These compositions can also include amounts of conventional flow modifying materials, such as thickeners, glues, defoaming agents, salts, etc., depending upon the use intended.
The products of the invention contain only minor amounts of surfactant additives in the order of 0.1 to 3.0 percent by weight. They further contain particulate coal as the dispersed solid in an amount from 45 to 80 percent; water as the carrier medium in an amount of from 19.9 to 52 percent and, if desired, from 0.1 to 2 percent of a thickener or thickeners; 0.01 to 2 percent of a defoaming agent and 0.1 to 2 percent of salts, anti-bacterial agents, caustic or other additive flow control agents, all of the percentages given being based on the total weight of the mixture.
The most preferred glycol ethers of the type generally described in formula I are the nonylphenoxy(polyethyleneoxy)ethanol compositions of the formula:
wherein n is 100 or higher.
Commercially available surfactants of this type are supplied by the GAF Corporation under the designations IGEPAL^O CO-990 and IGEPAL^O CO-997. Other commercially available surfactants of this type are supplied by the Thompson-Hayward Chemical Co. under the designation T-Det^@ N-1 00, and Whitestone Chemical Co. under the designation ICONOL^O NP-100.
As stated hereinbefore, another group of polyalkyleneoxide nonionic surfactants useful in the invention are the well known poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) nonionic surfactant block polymers. These surfactants comprise the block polymers of ethylene oxide and propylene oxide with the repeating units of propylene oxide constituting the hydrophobic portion of the surfactant, and the repeating units of ethylene oxide constituting the hydrophilic portion of the surfactant. These block polymer compositions are of the general formula II:
wherein a, b and c are whole integers and wherein a and c total at least 100.
These compositions can be prepared, and are commercially available, in a variety of molecular weights, depending primarily on the number of repeating units of propylene and ethylene oxide. It has been found that these block polymers having a molecular weight of at least 6,000 and comprising at least 100 repeating units of ethylene oxide are excellent additives for dispersing coal in a water carrier to the desired high coal solids concentrations of 45 to 80 percent, preferably about 70 percent coal particles, based on the weight of the total mixture. Thus, with reference to the above formula II, the poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) nonionic surfactants suitable for use in the invention are those wherein a, b and c are integers and a and c total 100 or higher.
Suitable procedures for the production of the block polymers of Formula II are described in the patent literature in, for example, United States Patents Nos. 2,674,619; 2,677,700 and 3,101,374.
Generally, these block polymers are prepared by a controlled addition of propylene oxide to the two hydroxyl groups of propylene glycol to form the hydrophobe, followed by the controlled addition of ethylene oxide to "sandwich" in the hydrophobe between the two hydrophilic polyethyleneoxide groups.
The nonionic surfactants of this type (Formula II having the requisite number of at least 100 units of ethylene oxide are available from the BASF-Wyandotte Corporation under the PLURONIC^* designation, Series Nos. F-77, F-87, F-68, F-88, F-127, F-98, and F-108. These compositions have at least 100 ethylene oxide units, as per the following table of these PLURONIC surfactants:
As also described hereinbefore, a further group of polyalkyleneoxide nonionic surfactants suitable as coal dispersants herein are the nitrogen containing block polymers of the general formula III:
wherein R₁ is an alkylene radical having 2 to 5 carbon atoms, preferably 2; R₂ is alkylene radical having 3 to 5 carbon atoms, preferably 3; a, b, c, d, e, f, g and h are whole integers; and e, f, g and h total at least 100.
These materials are prepared by the addition of a C₃ to C_s alkylene oxide to an alkylene diamine under conditions to add two polyoxyalkylene groups to each of the nitrogen groups in the presence of a catalyst so as to polymerize the oxyalkylene groups into the desired long-chained polyoxyalkylene radicals. After the desired addition and polymerization of the C₃ to C_s alkylene oxide group has been completed, ethylene oxide is introduced and is added to the polyoxyalkylene groups to impart the desired hydrophilic characteristics to the compound. The preparation of these materials from commercially available alkylene diamines and alkylene oxides is known in the art.
In general, the agents are prepared by mixing the C₃ to C₅ alkylene oxide with the alkylene diamine at atmospheric or elevated pressures, at temperatures between about 50 to 150° centigrade and in the presence of an alkaline catalyst such as an alkali metal hydroxide or alcoholate. The degree of polymerization or the size of the hydrophobic group is controlled by the relative proportions of C₃ to C_s alkylene oxide and alkylene diamine, the alkylene oxide being introduced in a sufficient quantity to obtain a hydrophobic base weight of 2000 to 3600 units although other weights can be provided.
These surfactants (Formula III) having the requisite number of at least 100 ethylene oxide repeating units are available from the BASF Wyandotte Chemicals Corporation under the TETRONIC@ designations Series Nos. 1107; 1307; 908 and 1508. These compositions have at least 100 ethylene oxide units, as per the following table of these TETRONIC surfactants.
Any of a wide array of coals can be used to form the coal-aqueous mixtures of the invention, including anthracite, bituminous, sub-bituminous, mine tailings, fines, lignite and the like. Other finely divided solid carbonaceous materials may also be used, e.g., coke, prepared either from coal or from petroleum.
To form the coal-aqueous mixtures, coal is pulverized to approximately 90% finer than 0.044 mm (200 mech Tyler Standard screen size), although courser or finer particle sizes can be employed, if desired.
Advantageously, according to the invention, the untreated pulverized raw coal, is beneficiated, i.e., cleaned of amounts of ash and sulfur. The art will appreciate that mixtures formed of beneficiated coal offer considerable advantage. They are clean burning or relatively clean burning, and are more suited for burning in apparatus for powering utilities, home burners and the like without undue burdensome and expensive cleaning apparatus.
Any of a wide array of beneficiating treatments can be employed in preparing the particulate coals, including conventional heavy-media separations, magnetic seperation and the like. The preferred method for providing the beneficiated coal particles is by a chemical treatment process such as described in U.S. Patent No. 4,304,573.
Generally, according to the preferred chemical beneficiation treatment method, raw as-mined coal is ground in the presence of water to a particle size of about 200 mesh. The ground coal is treated in an aqueous medium with a monomeric compound, generally an unsaturated polymerizable composition such as readily available tall oil fatty acids in the presence of a metal initiator such as cupric nitrate; and minor amounts of fuel oil, all in an aqueous phase are also present. The ground coal so treated is made hydrophobic and oleophilic and is separated from the unwanted ash and sulfur by a froth flotation technique.
The cleaned coal recovered from the preferred chemical treatment process, now in the form of beneficiated coal particles, is suited for the coal-aqueous mixtures of the invention. These coal particles are characterized by having an ash content reduced to levels of 0.5 to 6.0% and a sulfur content reduced to levels of 0.5 to 2.0%.
As in said U.S. Patent No. 4,358,293 it is preferred herein to form the coal-aqueous mixture by first adding the surfactant to water together with other additives such as conventional defoaming agents, if desired. This admixing can be done with stirring at conditions of atmospheric or nearly atmospheric temperature and pressure. Thereafter, the particulate coal, preferably beneficiated coal particles, is added to the mixture to produce a coal-aqueous mixture of high coal solids content of 45 to 80% by weight coal, based on the total weight of the mixture at atmospheric or nearly atmospheric temperatures and pressures. If desired, thickeners can then be added to further stabilize the mixture to assist in preventing the coal particles from settling when the mixture is to be stored for extended periods. Caustic soda or other bases can also be added at this point. As will be apparent, adding thickeners in or near the final stage is preferred so that the stirring requirements are kept at a minimum. The coal-aqueous mixtures can be prepared in a batch operation or in the continuous mode. In continuous production, the coal can be admixed with water in a first stage along with other flow control agents such as the surfactant. The compositions of the first stage can then be transferred continuously to a second stage wherein the thickener is added. Again, adding the thickener at the later stage results in reduced stirring requirements.
In accordance with the discovery of the present invention, it has now been found that further specific processing conditions provide for a more improved coal-aqueous product, as well as, avoiding certain problems, such as deleterious foaming and flocculation during processing. More particularly, in preparing the coal-aqueous compositions of the present invention, the surfactant and other additives, such as conventional defoaming agents, if desired, are first added to water and mixed, under low speed agitation conditions (500 rpm to 1500 rpm, preferably 1000 rpm) for a time of from 30 seconds to 3 minutes, preferably about 1 minute. Thereafter, the particulate coal, preferably beneficiated coal particles, is added to the mixture and admixed therein under moderate or medium agitation conditions (1000 rpm to 3000 rpm, preferably about 2000 rpm) for a time sufficient to provide a wetted out admixture. Usually this time is in the range of from 5 minutes to 20 minutes. At this time, the agitation of the admixture is increased to a high speed (3000 rpm to 6000 rpm, preferably about 4000 rpm) for a time sufficient to disperse the coal, usually from 5 minutes to 15 minutes, preferably about 10 minutes. If desired, thickeners are then added to the slurry under the afore-described high speed agitation conditions, e.g. 4000 rpm, for a further time of from 1 minute to 3 minutes, preferably about 2 minutes. In the preparation of a most preferred formulation, other ingredients, such as viscosity stabilizers and antibacterial agents are then added to the formulation at said high speed agitation for a further time of from 1 minute to 3 minutes, preferably about 2 minutes. By wetted out or wet as used herein, it is meant that the surface of each coal particle is covered with water.
Typical mixing or dispersiong apparatus employed herein include for example Premier Mill Co.'s Hi-Vispersator^O High-Speed Disperser.
It is to be understood that the above indicated residence times, temperatures, mixing speeds, etc. may vary within the defined limits according to specific process requirements such as the volume of ingredients, size of apparatus, mixing efficiency, etc. Thus, for example, depending on the scale of the operation, e.g. pilot plant, plant, etc., these process conditions of the present invention may be adjusted accordingly.
It has been found that by employing these aforedescribed specific conditions of the present invention, the coal is allowed to be dispersed in a surfactant/antifoam solution at relatively low viscosity, while the surfactant is orienting at the coal-water interface. The anti-foam agent controls the level of foam caused by the surfactant being agitated in solution. The thickeners are added after the coal is adequately dispersed to impart the desired rheological and suspension properties from flocculating by forming a protective colloid.
As indicated above, additives that can be added to the coal-aqueous mixture include defoaming agents, thickeners, salts, bases, other flow modifying agents and combinations of these materials.
Generally, the defoaming agents that can be used are conventional and include both silicon and non- silicon containing compositions. A commercially available defoaming agent suitable for use in the mixtures is COLLOID 691, supplied by Colloids, Inc. This composition generally comprises a mixture containing mineral oil, amide and an ester.
Thickeners can also be added to the mixture. They are added to increase the non-settling characteristics of the composition. Suitable thickeners include, for example, xanthum gum, guar gum, glue and the like. Other thickeners include, for example, alkali soluble acrylic polymers (e.g. ACRYSOL@ ICS-1 sold by the Rohm and Haas Company). Combinations of these thickeners are also contemplated herein. For the purposes herein, the thickeners are generally used in amounts ranging from 0.01 to 3.0% by weight, based on the total weight of the mixture.
In preparing the compositions containing the preferred 70% by weight coal, based on the weight of the total mixture, the polyalkyleneoxide nonionic surfactants are preferably mixed with water in a proportion of about 0.3 part by weight surfactant to 29.3, parts by weight, water at atmospheric or nearly atmospheric temperatures and pressures. A defoaming agent is also added to the water in an amount of about 0.03, part by weight, to assist in processing. The pulverized coal is then mixed with the water in a proportion of 70 parts by weight coal to 29.3 parts by weight of water to obtain a flowable liquid. If desired, to the mixture can then be added 0.12 to 0.15, part by weight, of thickener or thickeners to provide protection against settling. Other additives such as salts or bases, antibacterial agents such as formaldehyde, and the like, viscosity stabilizers, such as ammonia, can also be added in 0.2 to 0.3, part by weight, of the total mixture to further assist in dispersing the coal and providing the other obvious advantages.
The following examples will further illustrate the invention:

Example 1

The following formulation is used to prepare an aqueous coal slurry in accordance with the improvement of the present invention.
Footnote to Table

1. Industrial Water
2. Surfactant - BASF Wyandotte Corp.
3. Anti-foam Agent - Colloids, Inc.
4. Pocahontas Clean Coal
5. Xanthan Gum - Kelco Division, Merck & Co., Inc.
6. Guar Gum - Hercules, Inc.
7. Formaldehyde Solution - Borden Chemicals
8. Ammonium Hydroxide - Fischer Scientific

The ingredients are added in the order listed. A high-speed disperser, namely a High-Vispersator is used to stir, mix and disperse the materials into a stable homogeneous slurry. Ingredients 1, 2 and 3 are stirred together for one minute at low speed (1,000 rpm). The coal is added to this solution at medium speed (2000 rpm) for a sufficient time to wet the coal particles and disperse the coal in ingredients 1, 2 and 3. Then the speed of the disperser is increased to high speed (4000 rpm) for 10 minutes to further disperse the coal particles. Ingredients 5 and 6 are then added with the disperser at high speed. After two minutes ingredients 7 and 8 are added and the batch is considered complete after an additional two minutes of mixing at high speed. All mixing is carried out at atmospheric temperatures and pressures.

Example 2

The following formulation is used to prepare an aqueous coal slurry in accordance with the improvement of the present invention.
The ingredients are added in the order listed. A high-speed disperser, namely a High-Vispersator is used to stir, mix and disperse the materials into a stable homogeneous slurry. Ingredients 1, 2 and 3 are stirred together for one minute at low speed (1,000 rpm). The coal is added to this solution at medium speed (2,000 rpm) for a sufficient time to wet the coal particles and disperse the coal in ingredients 1, 2 and 3. Then the speed of the disperser is increased to high speed (4,000 rpm) for 10 minutes to further disperse the coal particles. Ingredients 5 and 6 are then added with the disperser at high speed. After two minutes ingredients 7 and 8 are added and the batch is considered complete after an additional two minutes of mixing at high speed. All mixing is carried out at atmospheric temperatures and pressures.

Example 3

Example 4

Example 5

The following formulation is used to prepare an aqueous coal slurry in accordance with the improvement of the present invention.
The ingredients are added in the order listed. A high-speed disperser, namely a High-Vispersator is used to stir, mix and disperse the materials into a stable homogeneous slurry. Ingredients 1, 2 and 3 are stirred together for one minute at low speed (1,000 rpm). The coal is added to this solution at medium speed (2,000 rpm) for a sufficient time to wet the coal particles and disperse the coal in ingredients 1, and 3. Then the speed of the disperser is increased to high speed (4,000 rpm) for 10 minutes to further disperse the coal particles. Ingredients 5 and 6 are then added with the disperser at high speed. After two minutes ingredients 7 and 8 are added and the batch is considered complete after an additional two minutes of mixing at high speed. All mixing is carried out at atmospheric temperatures and pressures.

Example 6

Example 7

Example 8

Example 9

Example 10

The following formulation is used to prepare an aqueous coal slurry in accordance with the improvement of the present invention.
The ingredients are added in the order listed. A high-speed disperser, namely a High-Vispersator is used to stir, mix and disperse the materials into a stable homogeneous slurry. Ingredients 1, 2 and 3 are stirred together for one minute at low speed (1,000 rpm). The coal is added to this solution at medium speed (2,000 rpm) for a sufficient time to wet the coal particles and disperse the coal in ingredients 1, 2 and 3. Then the speed of the disperser is increased to high speed (4,000 rpm) for 10 minutes to further disperse the coal particles. Ingredients 5 and 6 are then added with the disperser at high speed. After two minutes ingredients 7 and 8 are added and the batch is considered complete after an additional two minutes of mixing at high speed. All mixing is carried out at atmospheric temperatures and pressures.
From the foregoing it will be seen that coal-aqueous mixtures are readily provided having significantly high solid concentrations. The mixtures can be provided in a clean form ready for burning in utility burners, home burners and the like with little if any need for additional cleaning to remove ash and sulfur.

Claims

1. A method for forming a coal-aqueous mixture in which a polyalkylene oxide non -ionic surfactant having a hydrophobic portion and hydrophilic portion, said hydrophilic portion being comprised of at least 100 units of ethylene oxide is admixed under stirring with water and particulate coal is admixed thereto under further agitating, characterized in

(i) that the admixing of the surfactant with water is effected under low speed agitation conditions at from 500 to 1500 rpm,

(ii) that the admixing of the particulate coal to the admixture resulting from step (i) is effected under medium speed agitation conditions at from 1000 to 3000 rpm, and

(iii) that the resultant coal containing the mixture of step (ii) is agitated under high speed conditions at from 3000 to 6000 rpm.

2. The method of Claim 1 wherein said medium speed agitation in step (ii) is carried out for a time sufficient to wet the coal particles and said high speed agitation is carried out for a time sufficient to disperse the coal.

3. The method of Claim 1 or 2 wherein an antifoam agent is added to the mixture during step (i).

4. The method of Claim 3 wherein said antifoam agent is comprised of a mixture of mineral oil, amide and polyethylene glycol oleate ester.

5. The method of any of Claims 1 to 4 wherein the particulate coal is added in an amount from 45 to 80 percent; the water is added in an amount from 19.9 to 52 percent; and the polyalkyleneoxide nonionic surfactant is added in an amount from 0.1 to 3.0 percent based on the total weight of the mixture.

6. The method of any of Claims 1 to 5 wherein the polyalkyleneoxide nonionic surfactant comprises a composition of the formula

wherein R is substituted or unsubstituted alkyl of from 1 to 18 carbon atoms; substituted or unsubstituted aryl or an amino group, and n is an integer of at least 100 or a composition of the formula

wherein

R₁ is an alkylene radical having 2 to 5 carbon atoms;

R₂ is an alkylene radical having 3 to 5 carbon atoms;

a, b, c, d, e, f, g, and h are whole integers and

e, f, g, and h total at least 100 or a composition of the formula

wherein a, b and c are whole integers and a and c total at least 100.

7. The method of Claim 6 wherein R₁ is an alkylene radical having 2 carbon atoms and R₂ is an alkylene radical having 3 carbon atoms and R is nonyl.

8. The method of any of Claims 1 to 7 including the further step of: (iv) admixing a thickening agent under high speed agitation conditions at from 3000 to 6000 rpm, to the admixture resulting from step (iii).

9. The method of Claim 8, wherein said thickening agent is xanthan gum, guar gum, cellulose gum, glue or alkali soluble acrylic polymer.

10. The method of Claims 8 or 9 including the further step of:

(v) admixing an additive selected from an antibacterial agent, salts, bases or ammonia or mixtures thereof to the mixture resulting from step (iv), under high speed agitation at from 3000 to 6000 rpm.