CA1181590A - Coal slurry composition - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A coal-water slurry of a coal concentration of 50 to 80 percent by weight having excellent fluidity, dis-persion stability, and stability when left standing comprises: (a) a coal powder of which 71 to 85 percent by weight are coal particles of particle sizes of 74µ
or smaller, and which, moreover, has a particle size distribution such that, when said distribution is re-presented on a Rosin-Rammler chart, the gradient (in terms of the value of tan .alpha.) of the straight line join-ing two points respectively corresponding to the quanti-ty (percent by weight) of particles of particle sizes less than 44µ and to the quantity (percent by weight) of particles of particle sizes less than 74µ is 0.4 to 0.9;
(b) at least one species of a specific surfactant; and (c) water.

Description

~ ~1 8 ~

COAL SLURRY COMPOSII'ION

BACK~ROUND OF THE INVENTION
This inven-tion relates generally to aqueous slurry compositions of coal. More specifically, the invention relates to a coal slurry composition which is an aqueous slurry composition of coal powder having a specific particle size distribution, possesses excel]ent disper-sion stability, and, moreover, does not form a hard cake by consolidation of sediments tending to occur when left standing for a long period, that is, has excellent stability when left to lie still.
In recent years, diversification of energy sources and ensuring of stable supplies of energy have become important problems because of reasons such as limits to the reserves of petroleum, which has heretofore been used in greatest quantity as an energy source and the consequent rise in prices of petroleum products. In viewof these circumstances, the effective utilization of coal, which is still available in great reserves and is not maldistributed but exists throughout the world, is being reconsidered.
In the case o coal, however, since it is a solid, differing from petroleum, transporta-tion thereof through pipelines is not readily possible, whereby coal is markedly disadvan-tageous in handling. Further, since coal, in general, contains a great ash content in . . . _ g ~

comparison with petroleum, there arise problems such as lower calorific value and the need -to dispose of fly ash. Accordingly, with the object of overcoming these difficulties in handling coal, various studies are being made on methods of pulverizing coal, dis-persing it in water to render it into slurry form, and using the slurry.
However, a slurry of this character is accompanied by the problems of a great increase in viscosity when the coal concentration is increased, which results in a loss in fluidity, a drop in transfer efficiency when, conversely, the coal concentration is decreased, and, further, high cost also in the water removal step, and it is difficult to discover a suitable coal concentra-tion. This is attributable to agglomeration in thewater of the coal particles in the coal-water slurry, which causes an increase in the slurry viscosity and a reduction in its fluidity. In a coal-water slurry, the smaller the coal particles are, the better is the dis-persion stability, but the cost of fine pulverizationincreases with increase in the degree of fineness of pulverization.
When a surface-active agent (hereinafter referred to as a surfactant), which is a dispersant, is added to a coal-water slurry, the surfactant is adsorbed on the interfaces of the coal particles and the water and gives rise to such effects as separation of the coal particles away from each other and prevention of the coal particles from mutually agglomerating, whereby the surfactant can be expected to create a good dispersion state~ As dis-persants of this character, alkyl (phenyl) ether sulfate (Japanese Patent Laid Open Publication No. 20090/1981), sulfonated products of polycyclic aromatic compounds having in some cases a hydrocarbon group as a substituent and salts thereof (Japanese Laid Open PubLication No.
21636/1981) and others have been proposed.
However, in the case where these dispersants are used, while the fluidity is improved, sediments which set-tle when the slurry is left standing for a long period con-solidate and form a hard cake, which has been a great problem in actual practice.
SU~ARY OF THE INVENTION
Accordingly, we have carried out a research direct-ed toward obtaining a coal-water slurry in which the above described problems have been solved, and which has excellent fluidity and has no tendency to form a hard cake, that is, has excellent stability when left standing (hereinafter referred to as "static stability"). As a result, we have arrived at and developed this invention.
According to this invention, briefly summarized, there is provided a coal slurry composition comprising, essentially:
(a) a coal powder of which 71 to 85 percent by weight are coal particles of particle sizes of 74~ or smaller, 1 ~ 8 ~
and which, moreover, has a particle size distribution such that, when said distribution is represented on a Rosin-Ra~nler chart, the gradient (in terms of the value of tan ~) of the straight line joining two points respectively corresponding to the quantity (percent by weight) of particles of particle sizes less than 44~
and to the quantity (percent by weight) of particles of particle sizes less than 74~ is 0.4 to 0.9;
(b) at least one species of surfactant selected from the group consisting of sulfonated products of naphthalene and creosote oils, salts thereof and addi-tion condensation products thereof with an aliphatic aldehyde, and addition condensation products of amino-triazines containing a sulfonic acid group with an aliphatic aldehyde, and salts thereof; and (c) water.
The precise reasons why the coal-water slurry of this invention has excellent fluidity and static stability are not entirely clear but are thought to be as follows. In a coal powder wherein the coal particle si~e distribution has been specially adjusted as in the above mentioned component (a), the fine coal particles are adsorbed around the coarse coal particles to form a loose network structure. As a result, the separation by settling of the coarse coal particles is suppressed, and the standing stability becomes good. Furthermore, the fine coal particles enter into the gaps between the coarse coal particles, whereby a state close to that of maximum-density filling is attained, and for this reason the slurry has fluidi-ty even with a high coal concentration. The surfactant which is the component Ib) is an anionic surfactant and, being adsorbed in great quantity on the coal ma-terial within the coal particles in the coal-water slurry, imparts an electric charge, thereby improving the dispersibility of the coal particles in the slurry and thus increasing the fluidity.
The coal-water slurry of this invention, because of the above described constitution, has good fluidity and excellent static stability. The phrase "good static stability" as used herein includes the case wherein the sediments are soft and are easily re-dispersed. Particularly, in contrast to a coal-water slurry of the prior art obtained by using only a dis-persant, in which, when left standing, sediments form a consolidated hard cake, in the coal-water slurry of this invention, a hard cake of this nature is not formed.
For this and other reasons, the industrial worth of this invention may be said to be very high.
The nature, utility, and fur~her features of this invention will be more clearly apparent from the follow-ing detailed description commencing with a considerationof general aspects of the invention and concJuding with a presentation of preferred embodiments thereof including cj ~

synthesis examples and examples cf practice when read in conjunction with the accompanying drawings, briefly described below.
~RIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is an example of a Rosin-Rammler chart indicating the particle size distribution of coal powder used in the preparation of a coal slurry composition, the nlimbers (No.) in this chart correspondiny to the numbers of the coal powder components la) usecl in Example 1 set forth hereinafter; and FIG. 2 is a simplified elevation showing a rod penetration testing apparatus for use in evaluating the static stability of coal slurry compositions.
DETAILED DESCRIPTION OF THE INVENTION
Composition The coal slurry composition of this invention com-prises com~onents (a), (b) and (c) stated hereinabove.
The preferable proportions of the components in the co~l slurry composition of this invention are as follows.
Throughout the following description and in the accompany-ing drawings, quantities expressed in percent (%) and parts are by weight. The preferable proportion of the component (a), coal powder, is 50 to 80%; that of the component (b~, surfactant, is 0.01 to 5%; and that of the component (c), water is 15 to 45%. Particularly, 60 to 75% of the component (a), 0.03 to 2.0% of the t ~

component (b), and 25 to 35% of the ccmponent (c) are more preferable.
Coal owder Particles of the coal powder used in this inven-tion of particle sizes of 74 microns (~) or smallerare in a proportion of 71 to 85 percent. When direct combustion of the slurry is considered, it is preferable that particles of particle sizes of 74~ and smaller be in a proportion of 75 to 80 percent. Furthermore, it is necessary that this coal powder have a particle dis-tribution such that the value of -tan ~. (alpha) is 0.4 to 0.9, preferably 0.5 to 0.8, where tan ~ is the slope or gradient of the straight line joining the point indieating -the quantity (percent) of partieles of partiele sizes smaller than 44~ and the point indieating the quantity (percent) of particles of partiele sizes smaller than 74~ when plotted on a Rosin-Rammler ehart.
As long as these eonditions are satisfied, the line indieating the partiele size distribution obtained by ~0 plotting on this ehart may be straight line, a eurved line, or a eombination of a straigh-t line and a eurved line. Furthermore, it may be a line having a point of infleetion. In addition, the eoal powder used may laek a partiele size fraetion which has been separated through elassification processing.
As shown in FIG. 1, in a Rosin-Rammler chart, the abscissa represents particle size (diameter) on a s ~ ~

logarithmic scale, and the ordinate represents quan-tity passing through (percent) on a special scale.
This kind of chart is being widely distributed by Nippon Funtai Kogyo Kyokai (Japan Powder Industries Association) and other organizations.
In general, in the case where a coal is pulverized simply in a ball mill or the like, the coal powder obtained will not satisfy the particle size distribu-tion conditions as described above and has a relatively narrow particle size distribution of a value of tan ~
of the order of l.0 to 1.2. With a coal powder having a particle size distribution of this character, an aqueous slurry having excellent dispersion stability coupled with excellent standing stability, which is the object of this invention, will not be obtained.
In order to obtain coal powder having a par-ticle size distribution as described above which can be used in this invention, it is necessary to resort to a specially devised powder preparation method and not to use a simple pulverizing method. For example, a method such as that wherein a plurality of pulverizing machines are used in parallel to produce a suitable particle size distribution or that wherein, after pulverization with a pulverizing machine, classification with sieves is carried out can be adopted. The pulverizing machine may be of any suitable form such as a ball mill, COlloid mill, or attritor. The pulverizing method may be dry-type pulveriza-tion or wet-type pulverization in water.
We have found tha-t a coal concentration in the coal slurry composition of 50 to 80 percent, parti~
cularly 60 to 75 percent, is desirable. If this con-centration is too low, the calorific value of theslurry will drop, and, at the same time, direct com-bustion will become difficult. On the other hand, if the concentration is excessively high, the slurry viscosity wi]1 become excessively high, and the slurry fluidity will kecome poor. Although the optimum con-centration differs with the specie of coal and its particle size, a concentration within the above stated ranges will be found to be suitable in almost all cases.
~his invention is applicable to coals such as anthracite, bituminous coal, sub-bituminous coal, brown coal and the like.
Dispersion aid-Surfactants As mentioned hereinabove, an aqueous slurry of coal powder of a specified particle size distribution is stabilized, when the slurry comprises an anionic surfact-ant (Component b) of a restricted group as set forth below, to have dispersion stability, static stability and fluidity which are remarkably higher than those obtain-able when the dispersion is stabilized with a surfactant of another grOup.
As to such surfactants, mention is made to sulfonated products of naphthalene or creosote oils, salts thereof and addition condensation products thereof with an aliphatic aldehyde; and addition condensation products of an aminotriazine with an aliphatic aldehyde contain-ing the sulfonic acid group and salts thereof. Examples of the salts of the sulfonated products include alkali metal salts such as sodium or potassium salt, alkaline earth metal salts such as calcium or magnesium salt, and ammonium and amine salts. In production of these sur-factants, the sulfonation step, the step of condensation with an aliphatic aldehyde and the step for convertion into a salt can be conducted in any sequencial order.
Among these surfactants, those which have formaldehyde addition-condensed therewith are especially effective, wherein the degree of addition-condensation of formalde-hyde is preferably 1.2 to 30, more preferably 1.2 to lO.
When the degree of addition-condensation of formaldehyde is lower than 1.2, the benefit afforded by the conden-sation is not very high, and when the degree of addition-condensation is higher than 30, on the other hand, the product is not very practicable due to poor solubility.
The term "degree of addition-condensation" or simply "degree of condensation" means the number of aryl rings such as naphthalene rings in the condensate produced.

The term "creosote oils" used in the present inven-tion means neutral oils having a boiling point of 200C

or higher derived from the tar produced from dry distil-lation of coal or an alkylated product thereof. Creosote oi.ls have heretofore been defined in several ways, but JIS (Japanese Industrial Standards) K 2439 (1978) tells that a creosote oil is a mixture of fractions not lower than middle oil region derived from distillation of coal tar, and is a product produced by blending fractions of middle oil, heavy oil, anthracene oil,etc., from which crystallizable ingredients such as naphthalene and anthracene and some other ingredients such as phenols and pyridines have been removed. Creosote oils available on the market in Japan are classified into types No.l, No.2 and No.3, creosote oil type No.l, for example, being a mixture of various compounds which meets such a specifi-cation that specific gravity is 1.03 or higher, moisture content is 3% or lower, and comprises 25% or lower of a fraction having a boiling point of 235C or lower, and 40% or higher of a fraction having a boiling point of 235 to 315C, the content of a fraction which is distilled off at 315C or lower being 50% or higher.
In the practice of the present invention, any of the creosote oils specified under JIS K 2439 (1978) and fractions obtained by distillation of the creosote oil such as those having a boiling point of 200 to 250C, of 240 to 260C, of 250 to 270C, or of 270 to 300C are usable. The alkylated products of the creosote oils or the fractions obtained therefrom are also usable and are included in the term 'icreosote oils". In production of the alkylated products, any suitable alkylation process can be resorted to. Sulfonation by means of fuming or conc. sulfuric acid in the presence of an alcohol results in concomitant alkylation. Examples of alcohols for alkylation includes monohydric alcohols of from 3 to 8 carbon atoms.
The addition-condensation products of aminotri-azines with an aliphatic aldehyde which have a sulfonate group are addition-condensation products of amino-S-triazines. Examples of the products include -those produced by a process taught in Japanese Patent Publica-tion No.21659/1968. The addition-condensation products are obtained by addition-condensing an amino-S-triazine such as melamine, hexamethylol melamine, acetoguanamine or benzoguanamine with an aliphatic aldehyde, preferably formaldehyde, and sulfonating the condensate obtained with a sulfonating a~ent such as sulfurous acid, sulfuric acid, sulfonic acid, hydrogen sulfurous acid, or a salt thereof, disulfite, dithionite, or pyrosulfite salt, or by addi-tion-condensing an amino-S-triazine sulfonic acid with an aldehyde, preferably formaldehyde. In one preferable embodiment of the present invention, the amino-S-triazine addition-condensation product is a sulfonated melamine resin which is produced from melamine-formaldehyde condensate sulfonated by Na2S2O3 or NaHSO3 to introduce a sulfonate group thereinto.

Production of the slurries-water content The coal-water slurry of coal ~owder in accordance with the present invention can be produced by any suit-able process or method. The process or method may, in general, comprise providing coal powder of a specified particle size distribution and processing the coal powder to form an aqueous slurry which contains the specified surfactant.
The content of water (Component(c)) in the slurry in accordance with the present invention is signifi.cant. If the water content is low, the dispersion stability will not be improved even if a surfactant, which is the Component (b), is added, and only a slurry of inferior fluidity can be obtained. On the other hand, when water is used in a proportion of 15 percent or more, preferably 25 percent or more, the dispersion stability is remark-ably improved, and the fluidity also becomes excellent.
However, when water is used in a great quantity, the calorific value decreases, and direct combustion also becomes difficult, and for this reason, a large content of water should be avoided. Accordingly, it is desirable that the water content be 15 to 45 percent, particularly 25 to 35 percent.
PREFERRED EMBODI~ENTS OF THE INVENTION
In order to indicate more fully the nature and utility of this invention, the following examples o~
synthesis of some surfactants (Component (b)) and a f. ~

specific example of practice of the coal-water slurry of this invention are set forth, it being understood that these exa~ples are presented as illustrative and are not intended to limit the scope of the invention.
Synthesis Example 1 567 parts o-f 37% formalin is adjusted to have pH
4.5 with caustic soda, and 294 parts of melamine is then added thereto. The mixture is heated to 75C into a clear solution. The solution is cooled to 45C, and 222 parts of Na2S2O3 is then added there-to. To the product is then added 332 parts of water and the product produced is adjusted to have pH 10.5 with caustic soda.
The solution is then heated at 80C for 2 hours. The solution is cooled to 50C, and is admixed with 2116 parts of water and 70 parts of conc. sulfuric acid.
The mixture is heated at 50C for 5 hours, and is adjust-ed to have pH 8.7 with caustic soda.
The solution thus obtained has a solid content of ca. 20%, a viscosity of 37 cp at 25C, and is miscible with water in various proportions.
Synthesis Example 2 567 parts of 37~ formalin is adjusted to have pH 4.5 with caustic soda, and 294 parts of melamine is then added thereto. The mixture is heated to 75C into a clear solution. The solution is cooled, and 222 parts of Na2S2O3 is then added thereto. To the solution is added 332 parts of water, and the solution is then adjusted to have pH 9.0 with caustic soda. The solution is heated at 80C for 2 hours. ~he solution is diluted with 2000 parts of water and is then cooled. The solution has a viscosity of 26.2 cp. and a solid content of ca.
20~.
Synthesis Example 3 Acetone guanine sulfonic acid is admixed with 30%
formalin in a mole ratio of 1:4.0, the mixture produced is heated to 70C, is adjusted to have pH 4.0 with caustic soda, and is then heated at 90C for 2 hours.
The solution thus obtained, which is miscible with water in various proportions, has a viscosity of 346 cp. at 20C and a solid content of ca. 50%.
Synthesis Example 4 Benzoguanamine sulfonic acid is admixed with 30~
formalin at a mole ratio of 1:4Ø The admixture is then heated to 70C, adjusted to have pH 4.0, and is then heated at 90C for Z hours. The solution thus produced, which is miscible with water in various proportions, has a viscosity of 2330 cp. at 2nC and a solid content of ca. 50%, Example 1 1) Preparation of coal powder A ball mill of 30-cm diameter was charged with magnetic balls (comprised of a mix-ture in a ratio of 1:1 of l-cm diameter balls and 0.5-cm diameter balls) in a quantity corresponding to approximately 1/2 of the ~ ~s :~ s ~

interior volume of the ball mill and 2 kg oE Tatung coal in one instance and Miike coal in another instance.
The compositions of these coals are shown in Table 1.
Pulverization was then carried out by rotating the ball mill at 50 rpm for 1 hour in each instance. The coal powder thus obtained was classified with sieves of 45-, 100-, 200-, and 350-mesh sizes, whereupon it was found to have a particle size distribution as shown in Table 2.
With Tatung coal and Miike coal and by a similar method, pulverization and classification by sieving of a great quantity of coal were carried out, and five lots of coal powder divided respectively into particles remaining on a 48-mesh sieve, those of 48- to 100-mesh size, those of 100- to 200-mesh size, those of 200-to 325-mesh size, and those passing through a 325-mesh sieve were obtained. These five lots of powder were blended in the proportions set forth in Table 3 thereby to prepare a plurality of coal powder samples respective-ly of specific particle size distributions. The pro-perties of these coal powder samples are shown in Table 4, and a Rosin-Rammler chart for some of these coal powder samples is shown in FIG. 1. The sieve used for classifi-cation is the Tyler Sieve shown in, for example, PERRY:
CHEMICAL ENGINEERS HANDBOOK.

Table 1. Coa.1 composition Elementary analysis Coal mine Country _ _ (dr 7 basis) Coal C _ H _ N S

Coal Tatung Chl~.a 4 5 7 00.9 . sample Mlike Jap 4.8 6 70.9 25.9 Table 2 Particle size distribution (wt.%) Remaining¦ Passing on a 48- ¦48 - 100 100 - 200 200 - 325 through a mesh ¦ mesh mesh mesh 325-mesh sieve* ¦ sieve Component 39 23 18 8 12 _ No.9 6 ~ 19 25 18 32 * Tyler sieve ~ ~8~

Ta~le_ __ _ Blending proportion (wt.~) Component Remaining _ _ _ Passing (a), No. on a 48-48 - 100 100 - 200 200 - 325 through mesh mesh mesh mesh 325-mesh sieve _ _ sieve

2 18 22 25 12 23 __ l

3 6 ]9 1 25 118 32 ___ I

4 0.5 6.5 1 18 20 55 _ . _ _ 27 11 ]2 8 42 7 - 6 7 1 12 8 6' l .

, I
0.5 6.5 1 18 1 20 55 I

-18~

4. ~

Tab e 4 _ ._ Gradient, tan ~,of Component Coal 74-~ particles line joining points (a), No. sample and smaller of wt.~ passing No.(wt.%) through 44~ and of wt % passing throuch 1* 1 20 1.0 2* " 35 3* ll 50 0 4* ll 75 ~ ~ u.

8 " ll 0.7 9* 2 50 1.0 ~ 75 5 * Comparison product 3, ~

2) Production of coal slurry Aqueous solutions of the surfactant components indicated in Tab]es 5 and 6 and various surfactant components prepared in the aforedescribed synthesis examples were prepared by adding specific quantities of the surfactants to water. To each of these aqueous solutions, specific quantities of the coal powders, which are the components (a), prepared in section 1) set forth above. Each mixture thus obtained was agitat~
ed for 5 minutes in a mixer "Homomixer" (mfd. by Tokushu Kikako, Japan) operated at 5,000 rpm to prepare a coal slurry composition of a specific concentration. The blending proportions of the components are set forth in Table 6.

Table 5. (1) Components Ib), surfactants Component _ (b), No. Compound b-1-(lj naphthalenesulfonic acid Na salt " " (2) formalin condensate of b-1-(1) (degree of condensation 2) " " (3) (ditto) (degree of condensation 4) . ' " (4~ (ditto) (degree of condensation 8) " " (5) naphthalenesulfonic acid " " (6) formalin condensate of b-1-(5) (degree of condensation 2) " " (7) (ditto) (degree of condensation 4) " " (8) (ditto) (degree of condensation 8) 3 ~

Table 5 (2) Component ¦ Compound No. I
b-3-(1) sulfonation product (Na salt) of creosote ( 1) oil " " (2) formalin condensate of b-3-(l)(degree of con-densation 2) " " (3) (ditto) ( " " 4 ) " " (4) (ditto) ( " " 6) " " (5) sulfonation product (Na sa]t) of butylated creosote oil " " (6) formalin condensate of b-3-(5) (degree of condensation 2) " " (7) sulfonation product (Na salt) of hexylated creosote oil " " (8) formalin condensate of b-3-(7) (degree of condensation 4) (9) sulfonation product (Na salt) of creosote oil formalin condensate (degree of condensation 3) " " (10~ sulfonation product (Na salt) of creosote oil-naphthalene mixture (1:1 by wt.) " " (11) formalin condensate (Na salt) (degree of con-densation 4) of sulfonation product (Na salt) of creosote oil - butylnaphthalene mixture (1:1) " " (12) formaline condensate of b-3-(10) (degree of condensation 4) c-l sodium lignosulfonate c-2 polyoxyethylenenonylphenylester (EO: 7 mol) c-3 sodium alkylbenzenesulfonate (alkyl group C = 12) * creosote oil type 1.

s3 3) Evaluation of fluidity and static _tability The viscositi.es at 25 C of the coal slurry com-positions prepared in section 2) were measured, and the respective fluidities were evaluated. A lower viscosity of slurry has better fluidity.
Next, the static stabillties of the coal slurry compositions were evaluated by using a glass rod inter-penetration testing apparatus of the construction and size shown in FIG. 2. In FIG. 2, the unit of height dimensions is millimeter (mm). Each of the coal-water slurries 2 prepared as described hereinbefore in section 2) was left standing in a 500-cc measuring (graduated) cylinder 3 for one day. Thereafter, the time for inter-penetration of a vertical glass rod 1 of 50-g weight through each slurry composition was measured and taken as the measure of its static stability. That is, if the sedimentary substances in the slurry form a hard cake and consolidate, the interpenetration time will be long, and, in an extreme case, the glass rod will stop at an intermediate point. On the other hand, when the slurry has good static stability and does not separate, or, even if it separates somewhat, the sediments are soft, the interpenetration time will be short. The results of this test are shown in Table 6.

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Claims (4)

WHAT WE CLAIM IS:

1. A coal slurry composition comprising, as essential components: (a) a coal powder of which 71 to 85 percent by weight are coal particles of particle sizes of 74µ or smaller, and which, moreover, has a particle size dis-tribution such that, when said distribution is represented on a Rosin-Rammler chart, the gradient in terms of the value of tan .alpha. of the straight line joining two points respectively corresponding to the quantity in percent by weight of particles of particle sizes less than 44µ and to the quantity in percent by weight of particles of particle sizes less than 74µ is 0.4 to 0.9; (b) at least one species of surfactant selected from the group consist-ing of sulfonated products of naphthalene and creosote oils, salts thereof and addition-condensation products thereof with an aliphatic aldehyde, and addition-condensation products of aminotriazines containing a sulfonic acid group with an aliphatic aldehyde, and salts thereof; and (c) water.

2. A coal slurry composition according to claim 1 in which: the quantity of the coal powder of component (a) is 50 to 80 percent; the quantity of the surfactant of component (b) is 0.01 to 5 percent; and the quantity of the water of component (c) is 15 to 45 percent, all percentages being by weight and based on the total weight of the components (a), (b) and (c).

3. A coal slurry composition according to claim 1 in which the coal powder of component (a) has a particle size distribution such that said gradient in terms of tan .alpha. of said Rosin-Rammler chart is 0.5 to 0.8.

4. A coal slurry composition according to claim 2 in which the coal powder of component (a) has a particle size distribution such that said gradient in terms of tan .alpha. of said Rosin-Rammler chart is 0.5 to 0.8.