CA1197984A

CA1197984A - Dispersions of coal in water useful as a fuel

Info

Publication number: CA1197984A
Application number: CA000438012A
Authority: CA
Inventors: Richard G. Donnelly
Original assignee: Occidental Research Corp
Current assignee: Occidental Research Corp
Priority date: 1982-09-30
Filing date: 1983-09-29
Publication date: 1985-12-17
Also published as: DE3364982D1; JPS5998193A; WO1984001387A1; EP0120946A4; KR840006188A; EP0120946A1; EP0120946B1; ZA837229B; PH17144A; US4722740A

Abstract

DISPERSIONS OF COAL IN WATER USEFUL AS A FUEL

ABSTRACT
A dispersion of coal in water includes particulate coal dispersed in an aqueous solution including a multi-component additive. The multi-component additive includes a water-soluble, nonionic wetting agent, a water-soluble, low molecular weight polymer, and a water-soluble, medium-to-high molecular weight polymer. The particulate coal has a particle size distribution with a major portion of particulate coal having an average particle size of from about 75 µm to about 35 µm and a minor portion of particulate coal having an average particle size of about 6 µm to about 15 µm.

Description

57-o-~
DISPERSIONS OF COAL IN WATER USEFUL AS A FUEL

FIELD OF THE INVENTION
The instant invention relates to a dispersion of coal in water which comprises particulate coal disp~rsed in an aqueous solution, which solution comprises a multi-component additive.
The multi-component additive comprises (a) a water-soluble, nonionic wetting agent, ~b) a water~soluble, low molecular weight polymer, and ~c) a water-soluble, m~dium-to-high molecular weight .
polymer O
The above dispersion is useful as a fuel, e.g. as a substitute for residual oil or coal. The instant dispersion baing fluid combines the econom~ of coal as a boiler fuel with the ease of transportation and combustion of residual oil.

s~79~

BACKGROUND OF THE PRIOR ART
l The use of dispersions of coal in water or oil as a fuel in ¦
¦ place of residual oil is well known. The objective in using l such dispersions is to take advantage of the economy and 5 ¦ availability of coal in a fluid fuel which can be easily ¦ transported and atomized for combustion. Of course, since the ¦ objective is to replace fuel oil, the dispersions of coal in ¦ water are of especial interest, provided that such dispersions ¦ c~n be loaded with sufficient coal to avoid a ~ignificant fuel 10 ¦ value debit.
¦ Dispersions of coal tend to sediment while quiescent.
¦ ~That is, the particulate coal settles to the bottom of a ¦ storage tank, resulting in a non-homogeneous dispersion.3 Such ¦ non-homogeneous dispersions are difficult to burn efficiently as 15 ¦ the fuel val~e will vary with amount of particulate coal that is ¦ found in the dispersion. Dispersions of coal may therefore be ¦ agitated continuously or made up just privr to use to avoid ¦ sedimentation prob~ems. Both approache~ are not completely ¦ ~atisfactory, and in fact at times it is impossible to 20 ¦ ~edisp~se sedimented co~l without heroic efforts.
Various methods have been utilized to stabilize dispersio~s l of coal and to allow redispersion of the coal without expending ¦ large amounts of mechanical energy. For example, it is known l that more finely ~round coal is easier to disperse ~nd also once 251 such fin~ly ground coal is disp~rsed, it exhibits tendency to avoid s~dimentation. Therefore, one approach to stabilizing di~persion~ of coal has b~en to grind the coal to a very fine average particle si2e.

I

1~ 1 1 ~ 3~3~ 1 Intensive grinding requires very large amounts of mechani- ¦
cal energy, and therefore to some extent defeats the economical advantage of usin~ coal dispersions in place of residual or fuel oil. That is, the major reason that it is desirable to substitute disp~rsions of coal for fuel oil in boilers and other combus~ion means is that coal is more economical and more highly available energy source than fuel oil. Thus, a process requiring the input of energy to more finely grind the coal is somewhat counterproductive.
It is also known that increasing viscosity of the coal dis-persions provides resistance to sedimentation. However! the higher viscosity dispersions are difficult to handle and burn.
That is, it is well known that above a certain viscosity it is difficult to ~ransport coal-dispersions between storage vessels - and combustion facilities. Moreover, e~ficient burning requires complete atomization in the com~ustion zone of the boilerD ~igh viscosity hinders such complete atomization. Therefore, al~hough high viscosity coal dispersions are resistant ~o ~edimentation, the problems caused by such high viscosity may outweigh the benefits.
Various investigators have utilized additive~ to overcome the above problem~. For example, Krause et al, in U.S. Patent No. 4,101~293 teach that dispersions of coal in fuel oil may be ~ade stable ~o storage by incorporating a stabilizer prepared by reacting blends of unsaturated aliphatic and cycloaliphatic carboxylic acids with alkali metal hydroxides or amines~ The di~persions taught in such patent are limited to oil continuous dispersions unlike the di~persion~ of the present invention and I

!
are loaded with no more than 50%, by weight, coal. Moreover, it is clear (as discussed below) that the incorporation of alkali metal or nitrogen moieties (from the alkali metal hydroxide and the amine, respectively) is undesirable from the standpoint of 5 ¦ ash handling and pollution.
Meyer, in U.S. Patent 4,130,400, avoids the use of an addi-tive which causes pollution and ash handling problems, by means of an additive comprising a copolymer of alkylstyrene. Such l addi ive would not be effective in stabilizing dispersions of 10 ¦ coal in water since it is insoluble in water. In fact, the patentee notes that one of the objects of his invention is to ¦ avoid the incorporation of water in the disclosed dispersions.
Yamamura et al, n U.S. Patent 4,330,301, discloses that a l sulfonated polynuclear dispersant is useful in dispersing coal 15 ¦ in w~ter. Again, the utilization of sulfur moieties and the ¦ sodium, calcium, ammonium ~alt neutralizing agents, as taught by ¦ the patentees is undesirable from a pollution and ash handling ¦ ~tandpoint.
¦ Braun et al, in UOS. Patent 4,242~098, teaches that the 20 ¦ addition of small amou~t~ of water-soluble polymers to aqueous ¦ coal slurries p~rmit formulation of a mobile slurry containing up to 78% co~l. The water-soluble polymers which can be used ¦ include poly(ethylene oxide), par ially hydrolyzed polytacryl-¦ amide~, hydroYyethyl cellulose, ~uaternary nitrogen-substituted 25 I c@llulose ethers~ xanthan gum, hydroxypropyl guar gum~ and ¦ carboxymethyl hydroxypropyl guar gum. The patentee is only ¦ concerned with tran~porting coal wherein the dispersion is ~ ~3~9 798 ~ I
continuously agitated and does not consider the use of multi-component additive systems to provide a dispersion of coal in water which is stable to storage, and easy to burn, as well as l easy to transport.
S¦ Finally~ Burgess, in U.S. Patent 4,304, 573, indicates that the prior art worker will go to an extreme to prepare disper-sions of coal. The indicated approach requires the graft poly-merization of monomers on the coal surface o render such surface hydrophobic and oleophilic. No such extreme is contem-plated in the process of the instant invention.

9~

SUMMARY OF THE INVENTION
The instant invention relates to a dispersion of coal in water comprising particula-te coal dispersed in an aqueous solution with a multi-component addi-tive, said dis-persion comprising from about 60 to about 80 percent by weight of coal, wherein the multi-component additive com-prises:
(a) a water-soluble nonoinic wetting agent selected from the group consisting of reaction products of alkyl radi-cal substituted phenol and an epoxide, said alkyl radical having from about 8 to about 12 carbon atoms and said epoxide selected from the group consisting of ethylene oxide, propy-lene oxide ancl mix-tures -thereof, said reaction products hav-ing an HLB of from about 10 to about 19, (b) a water~soluble, low molecular weigh-t polymer selected from the group consisting of polyols represen-ted by the general formula HO-CH-CH2-0- (CH2-CE[-O) xH, R R

wherein R is selected independently from each other from the group consisting of methyl and hydrogen and x is an integer selected to provide a polymer having a molecular weight of from about 400 to about 1200, and (c) a water-soluble, medium-to-high molecular weigh-t polymer selected from the group consisting of ethoxylated cellulose, propoxylated cellulose, polyacrylic acid, starch, xanthan gum/ guar gum, polyvinyl alcohol and m:ixtures thereof.
A preferred amount of the water-soluble nonionic wetting agent is from about 0.1 to about 2.5%, by weight:

' r a preferred amount of the water~soluble low molecular weight polymer ls from about Q.01 to about 0,3%, by weighti and a preferred amount of the water-soluble medium~to-high molecular weight polymer is from about 0.01 to about 0.4% by welght.
The above dlspersion of coal in water is prepared by a novel method which comprises:
(aj com~ining (i) an a~ueous solutlon comprising a water-soluble, nonionic wettlng agent and a low molecular weight polymer; (li) a first dispersion of coal in water, said first disperslon comprising a first portion of parti-culate coal having a weight average particle size of from about 6 to 15 ~m; and (iii) a second portion of particulate coal having a welght average particle size of from about 35 to about 75 ~m to ~rovide a second disperslon of caal in water, said second dispersion comprising from about 10 to about 33%, by weight coal, of said first porti.on of parti-culate coal, and (b) combining an aqueous solution comprising a water-soluble, medium-to-high molecular weight polymer with said second dispersion to provide a third dispersion of coal in water, said third dispersion being characterized as having a viscosity suitable fo.r pumping and atomization in a burner nozzle and as resistant to sedimentation and hard packing for extended periods of time.

~9~7~

More preferably, said second dispersion of coal in water is divided into two portions, the first portion, comprising from about 10 to about 33% by weight coal of said second dispersion is milled to comminute the particulate coal dispersed therein to a weight average particle size of from about 6 to about 15,um and said milled dispersion is recycled to the above process as said first dispersion of coal in water. The remainder of said second dispersion of coal in water, after combining with the aqueous solution of a water-soluble medium-to-high molecular weight polymer, may be recovered as product.
Figure 1 is a diagrammatic view showing the various steps of an embodiment of the method for preparing a dispersion of coal in water according to the present invention; and Figure 2 is also a diagrammatic view showing a part different from Figure 1 of an alternative embodiment of the method.

7 ~
Il I
D~,TAILED DESCRIPTION OF THE INVENTION
_ ._ The instant invention may be conveniently understood by reference to the ollowing figure. Prepared coal (11~ having particles generally smaller than 3 inches in diameter is transferred by means (12) for example a truck to a feed hopper ~13~. Feed hopper (13) is utilized to pass the coal to a conveyer belt (14) which delivers the coal ~o crusher (15). The coal is crushed in crusher (15) to a particle size generally smaller than 3/8 inch diameter. The crushed coal is passed from crusher ~15) to conveying means e.g., conveyer belt (16) where it is passed into contact with the magnetic field of a magnetic separator (17) which is utilized to removed any tramp iron.
~dditional magnetic 9eparator ~18) may be utilized at conveyer (14) to as5i9t in the removal of iron prior to crushing.) The crushed coal (depleted in particulate iron) is me~ered to mill (19)o In mill ~19), which may be a ball ~ill or a bowl mill or any of a num~er of well-known mills, the coal is crushed to a weight average particle size of about 75 ~m to 35 ~m. Such crushing in mill (19) i5 carried out in the pre~ence of an inert ga~. For example, air and fuel is passed into an inert gas g~neratOr (21) wherein fuel is combusted to a gaseous product comprisin~ carbon dioxide and water. Such gaseous product carrie~ with it the excess oxygen fed to the combuster and the unburned nitrogen. Th~ gaseous product is combined with air fed with the coal and from other sources to insure that the o~ygen concentration is such that rapid or explosive oxidation of the fre hly ground coal does not occur.

_ g _ 'I i 9~7y~

Such inert gas atmosphere is then passed in admixture with air through compressor (20) into mill (19). The crushed coal from mill (19) is then passed into cyclone (22~ wherein fines are passed therefrom as overhead into a fine particulate collection device, su~h as a bag house (23). The underflow from the bag house ~23) is passed to disposal. The overflow from the bag house (23), which in a substantially particulate-free gas stream containing air and the inert gas which is utilized to convey the coal from mill (19) to cyclone (22), is passed through compressor (24) and i9 recylced to the coal mill (19). The underflow from cyclone (22) is passed to coal bin (25) for storage. The coal from coal bin (25) which will have a weight average particle siz~
of about 75 ~m to about 35 ~m is passed into a weighing zone, i.e. r weigh feeder (26) wherein a suitable amount of coal for preparing the ~lurry o the instant invention is metered into th primary mixer (27). Primary mixer (27) is fitted with mixing means (28) and heating/cooling means (28a). Water is passed intc primary mixer (27) throu~h line (27 B). In addition, there is a~
array of additive tanks (39 A, and B) which are in fluid communi-cation with primary mixer (27). In additive tank (30 A) the wetting agent noted above is eombined with wa~er to provide a solution which is passed into primary mixer ( 27) by means of pumE
~30~ At, For example, an aqueous solution of 70% of the pre-ferred ethoxylated alkylphenol may be made up in additive tank (30 A3 and passed into mixer (27) for preparation of coal slurry.
Similarly, in additive tank (30 B3 a low molecular weight water soluble polymer solution is mad~ up by mixing polypropylene gylcol with water to provide a solution comprising 10% by weight of the low molecular weight polymer. This solution is passed into mixer (27) by means of pump (30' B). Also added to primary mixer (27~ is an aqueou~ slurry of finely ground coal returning from fi~P grinder (31), as described urther below. The input to 5 ¦ mixer tank (27) including the weighed coal from weigh feeder ¦ (~6), water through line (27 B), additives from additives tanks (30 A) and (B) and a slurry of the finely ground coal from fine grinder (31) are combined to form a solution comprising approxi-l mately 70% by weight coal. The materials are retained in mixer 10¦ (27) for a ~ufficient time to obtain a homogeneous dispersion.
The dispersion from primary mixer (27) is passed through line (27 A) and pump (39) and is divided into two streams by flow splitter (40) and passed through lines (27' A) and (27a A). Mixer tank Il t27) is in fluid communication with fine grinder ~31) through lines (27 a) and ~27' a). Water and additional additives such as additional wetting agent and low molecular weight water soluble polymer may be provided as a so.lution through line ~31 a).
Preferably the split made at flow splitter (403 will provide 10 to 33% by weight of the dispersion of coal in water flowing thru line (27a) to fine grinder ~31) and the remainder to conditioning mixer (32~ described below, In fine grinder (31) the particulate size.of the coal is reduced further to an average particle size of within the range .6 ~m to lS ~m~ The dispersion or effluent from ~he fine grinder 25¦ (31) which may compri~e about 50% by weight of finely ground coal i~ returned to the primar~ mixer ~27) by means of line (31b) where it is combined with.the slurry formed within mixing ~ank (27). The purpose of combining the effluent from fine grinder ~/

¦l (31j with the slurry in primary mixer (31) is to provide a fraction of particles having a very small particle size in combination with the larger particles of coal found in the dispersion that is prepared in the mixing tank (27). In general, the metering is carried out so that the effluent from the primary mixer (27) which passes through line ~27~ A) into conditioning mixer 132) will comprise a slurry wherein the coal portion of which has about 25% by weight of coal that has passed through the fine grinder (31). Thus, a slurry having about 17.5 by weight of a weight average particle SiZP 6 ~m to 15 ~m coal and 52 . 5% by weight of a weight average particle size 35 l~m to 75 ~m coal is pass~d to the conditioning mixer (32) which is fitted with mixing means (33) and heating/cooling means (33a).
Condltioning mixer (32) is in fluid communication with additive tank (~0 C) through pump means 130' C) and line (30~ C).
Alternatively, the aqueous ~olution of additive C may be combined with the coal dispersion passing thru line ~27~ a~ in in-line mixer t38) prior to passage to mixex (32). It is important to note that the medium-to-high molecular weight makes it dificult to fully disperse additive C within the coal di~persion.
Therefore the alternative of passing the solution from additive (30 C) through in-line mixer (38~ rather than dire~tly into mixer (32) is preferred. Also the same medium-to high molecular weight requires th~t additive C not be sent through the fine grinder ~31) wherein the conditions of shear necessar~ for fi~e grinding would degrade ~he mol~cular weight of additive C.
In additive tanX (30 C) an a~ueous solution o~ a water soluble me~ium-to~high molecular weight polymer such as li .

~. ~ 9~
i , ¦! hydroxyethyl cellulose is prepared. The solution comprises about 1 weight percent of said high molecular weight polymer.
Mixing is continued in conditioning mixer ~32~ until a slurry having a 25C viscosity of about 1000 ~o 6000 centipoise, ~as measured using, for example, a Brookfield viscometer or a ~aake viscometer at typical pipe flow shear rates), a 25C specific gravity of 1.20 to 1.28, and stability against sedimentation of 30 days or more is prepared. The preferred slurry is shear-thinning, i.e., pseudoplastic and/or thixotropic as contrasted with dilatant slurries.
This slurry is passed via fluid communication means (32' A) to storage tank (34). Such storage tanks may be fitted with mixing means (35) to maintain the slurry in dispersion. The ~lurries of the instant inven~ion however do not necessarily lS require such mixing means since they are stable against sedimentation. The dispersion of coal in water which is stored in tank (34) may be passed through outlet means (36) and utilized for fuel.
Alternatively, as shown in Figure 2 the di~per~ion from primary mixer tank (27) may be ~plit by flow splitter (40') (in the proportions preferred above) and the stream passing to mixer (32) combined with the solution of additive C in in-line mixer /
39' prior to passing to said mixer 32. The alternate of Figure 2 is also preferred method of insuring dispersion of additive C in the coal dispersion without degradation of molecular weight.
~ ach of the above mixers and tank~ are known in the art devices, for example, turbine mixers, e cD may be utilized. The methods and materials o fabrication of suitable fluid communication mean~ D tanks, mixers, etc. are well known in the art and need not be discussed further.

The resulting dispersion of coal in water will have a vis-Il cosity of less than 6000 centipoise and be pseudoplastic and/or ¦¦ thixotropic which makes it amenable to pumping and atomization in burner nozzl~s. Such dispersion is also resistant toward sedimentation and hard packing for extended periods, for example, over thirty days~ when stored at temperatures of 30C or less.
The instant invention utilizes a novel non-ionic three com-¦ ponent additive system which insures the absence of sodium,potassium, calcium and ammonium ions which potentially interfere in a deleterious matter with the ash properties of coal during combustion by rendering the ash combustîon products more slag-ging, more fouling and/or more corrosive in nature. Further-more, the ,absence of nitrogen moieties enables preparation of coal,slurries having less environmental impact. The above salt moieties provide more ash since such salts usually wind up as a ~omponent of the ash.
The three component additive system allows for independent ad~ustment of the performance properties o~ the final dispersion of coal in water. The wetting agent, i.e., the non-ionic ~uractant, primarily affects pumpability at all rates of shear and at intermediate and long durations of shear. The low molecular weight water-soluble polymer contributes to easy redispersability upon eventual sedimentation and resi,st~
dsgradatio~ of rheology properties durin~ long term pumping.
The ~edium-to-high molecular weight water soluble polymer causes the particulate coal to interlock in a network which ensures stability at low rates of shear, but has relatively minor affect on pu~pability at medium and high rates of shear and at intermediate and long durations of shear. In addition, the '7~

wetting agent in combination w.ith the low molecular weight water !
soluble polymer is resistant to shear degradation and therefore may be utilized in the primary mixer (273 and/or the fine grinder (31). In contradistinction the medium-to-high molecular weight water soluble polymer is less resistant to shear;
therefore it is added in conditioning mixer (32) wherein the rate and duration of shear is insufficient to degrade molecular weight of said high molecular weight polymer.
The controlled distribution of particulate coal generated - by mixing fine and coarse grinds of various sizes in various ratios provides additional stability and loading of the above dispersions~ The fine particulate coal orients in the space between the coarse partlculate coal and therefore increases the loading. Moreover the fine particulate coal may increase the lS - mobility of the large particulate coal by lubricating the passage of large coal particles over each other.

~I I

The following examples are preferred embodiments of the instant lnvention.

Example 1 A dispersion of coal and water having 68% by weight coal is prepared by means of th~ above process. The weight ratio of the coarse to fine particulate coal is three to one. The weight average par~icle size of the coarse coal is 45 ~m and the weight av~rage particle size of tha fine coal is 8 ~m. Dry coarse coal in 51 parts is mixed with: i) 50~ slurry of fine coal in 34 parts; ii~ 1 part of an aqueous solution comprising 70 weight % of nonylphenolethoxylate having 4~ moles ethylene oxide; iii) 1 part of an aqueous solution of 10 weight ~ of polypropyleneglycol having molecular weight of about 400; and lv3 8 parts of additional water~, The resulting slurry is mixed in a mixing tank or other ~ixer such as primary mixer (27) and then passed into a mixing tank cr other mixer such as co~ditioning mixer (32), wherein S parts of an aqueous solution of 2 weight ~ hydroxy ethylcellulose having viscosity of a~out 5000 cp at ~5C is added to the slurry with agitation.
~0 defoamer or antifoamer such as a polysiloxane, for example polydimethylsiloxane, i~ al~o addPd to said primary mixer.
biocide ~uch as 1,2 benzisothiazolin-3-one may be added to such dî~p~rsion at a level of about 0.1% by weight~ The resulting dispersion of coal in water has the following characteristics:

2 The vi~cosity of the dispersion as mea~ured u~ing a Brookfiel~ or ~aake viscometer is 1200 to 1800 centipoise at 25C and at a shear rate of 100 ~econds)~l. The dipersion r~duces in visGosity with increasing rate of shear and with Il I

increasin~ d~ration of shear. That is, the dispersion is ¦ psuedoplastic and thixotropic as contrasted with the more common ¦ dilatant dispersions which thicken as shear rate increases. The ¦ viscosity increases at temperatures well below and well above 5 1 25C, but the dispersion remains pumpable at 1C and at 60C.
The specific gravity of the dispersion is 1.25 at 25C. The dispersion remains stable against sedimentation for a minimum of 90 days when stored in the laboratory in a non-agitated state at 25C. Any sediment which forms over this period and up to at least 120 days under these conditions is readily redispersible.
The dispersion remains fluid and non-sedimenting after long durations (in excess of two hours~ of high speed shearing. The dispersion has nearly identical rheological properties after multiple cycles of freezing and thawing. The dispersion resulting from this formulation will adequately atomize and will burn in test furnaces operated according to accepted practice.
This dispersion exhibits high combustion efficiency (99+% carbon burnout~ and acceptable flame stability under reasonable combustion conditio~s in such te!~t furnaces.
In comparison~ another coal dispersion in water is made up in a manner similar to he previous dispersion except that the loading is 65% by weight of a 5ingle size ~rind coal having a weight average particles size of 45 ~m. The antifoam is added at a weight of OqOS% based on the dispersion. The viscosity is lB00 to 2100 centipoi~es at a shear rate of 100 seconds -1.
Rowever, without the fines the stability to storage at room temperature is only about 60 days. The stability for both samples is measured by observing the tendency for coal to accumulate on the bottom in non-agita~ed samples held in bottles 30l of diameter at least 10 cm, ~he duration of stability is that ¦ t1se by which 2~ by weight of the cosl has settled.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS.

1. A dispersion of coal in water comprising parti-culate coal dispersed in an aqueous solution with a multi-component additive, said dispersion comprising from about 60 to about 80 percent by weight of coal, wherein the multi-component additive comprises:
(a) a water-soluble nonionic wetting agent selected from the group consisting of reaction products of alkyl radi-cal substituted phenyl and an epoxide, said alkyl radical having from about 8 to about 12 carbon atoms and said epoxide selected from the group consisting of ethylene oxide, propy-lene oxide and mixtures thereof, said reaction products having an HLB of from about 10 to about 19, (b) a water-soluble, low molecular weight polymer selected from the group consisting of polyols represented by the general formula wherein R is selected independently from each other from the group consisting of methyl and hydrogen and x is an integer selected to provide a polymer having a molecular weight of from about 400 to about 1200, and (c) a water-soluble, medium-to-high molecular weight polymer selected from the group consisting of ethoxylated cellulose, propoxylated cellulose, polyacrylic acid, starch, xanthan gum, guar gum, polyvinyl alcohol and mixtures thereof.

2. The dispersion of claim 1 wherein said coal com-prises a controlled particle size distribution wherein a major portion of said particulate coal has an average parti-cle size of from about 75 µm to about 35 µm and a minor portion of said particulate coal has an average particle size of from about 6 µm to about 15 µm.

3. The dispersion of claim 2 wherein the ratio of said major to said minor portion varies from about 2 to 1 to about 10 to 1, by weight.

4. The dispersion of claim 1 wherein in the formula of the water-soluble low molecular weight polymer (b) R is a methyl radical.

5. The dispersion of claim l wherein said water-soluble, medium-to-high molecular weight polymer (c) is hydroxyethyl cellulose.

6. The dispersion of claim 2, 4 or 5 wherein said water-soluble, nonionic wetting agent is selected from the group consisting of an ethylene oxide adduct of nonyl phenol comprising about 40 moles of ethylene oxide per mole of nonyl phenol and an ethylene oxide adduct of octyl phenol comprising about 9 moles of ethylene oxide per mole of nonyl phenol.

7. A dispersion of coal in water which comprises from about 60 to about 80%, by weight, particulate coal dis-persed in an aqueous solution, said aqueous solution com-prising a multi-component additive, soluble therein, wherein said multi-component additive comprises (a) from about 0.1 to about 2.5% by weight, of a water-soluble nonionic wetting agent selected from the group con-sisting of reaction products of alkyl radical substituted phenol and an epoxide, said alkyl radical having from about 8 to about 12 carbon atoms and said epoxide selected from the group consisting of ethylene oxide, propylene oxide and mixtures thereof, said reaction products having an HLB of from about 10 to about 19, (b) from about 0.01 to about 0.3%, by weight, of a water-soluble, low molecular weight polymer selected from the group consisting of polyols selected from the group represented by the general formula wherein R is independently selected from the group consisting of methyl, and hydrogen radicals and x is an integer selected to provide a polymer having a molecular weight of from about 400 to about 1200; and, (c) from about 0.01 to about 0.4%, by weight, of a water-soluble, high molecular weight polymer selected from the group consisting of ethoxylated cellulose, propoxylated cellulose, acrylic acid, starch, xanthan gum, guar gum, polyvinyl alcohol, and mixtures thereof.

8. A method for preparing a dispersion of coal in water which comprises the steps of:
(a) combining (i) an aqueous solution comprising a water-soluble, non-ionic wetting agent and a low molecular weight polymer; (ii) a first dispersion of coal in water, said first dispersion comprising a first portion of parti-culate coal having a weight average particle size of from about 6 to 15 µm; and (iii) a second portion of particulate coal having a weight average particle size of from about 35 to about 75 µm to provide a second dispersion of coal in water, said second dispersion comprising from about 10 to about 33%, by weight coal, of said first portion of parti-culate coal, and (b) combining an aqueous solution comprising a water-soluble, high molecular weight polymer with said second dispersion to provide a third dispersion of coal in water, said third dispersion being characterized as having a vis-cosity suitable for pumping and atomization in a burner nozzle and resistant to sedimentation and hard packing for extended periods of time.

9. The method of claim 8, further comprising dividing said second dispersion into two portions, a first portion comprising from about 10 to about 33%, by weight coal of said second dispersion, milling said first portion to comminute the particulate coal dispersed therein to a weight average particle size of from about 6 to about 15 µm and recycling said milled dispersion to step (a) as said first dispersion.

10. A dispersion of coal in water which comprises from about 60 to about 80%, by weight, particulate coal dispersed in an aqueous solution, said coal having a con-trolled particle size distribution wherein a major portion of said particulate coal has an average particle size of from about 75 µm to about 35 µm and a minor portion of said particulate coal has an average particle size of from about 6 µm to about 15 µm, and said aqueous solution com-prises a multi-component additive r soluble therein, wherein said multi-component additive comprises (a) from about 0.1 to about 2.5%, by weight, of a water-soluble non-ionic wetting agent selected from the group con-sisting of reaction products of alkyl radical substituted phenol and an epoxide, said alkyl radical having from about 8 to about 12 carbon atoms and said epoxide selected from the group consisting of ethylene oxide, propylene oxide and mixtures thereof, said reaction products having an HLB of from about 10 to about 19, (b) from about 0.01 to about 0.3%, by weight, of a water-soluble, low molecular weight polymer selected from the group consisting of polyols selected from the group rep-resented by the general formula wherein R is independently selected from the group consisting of methyl, and hydrogen radicals and x is an integer selected to provide a polymer having a molecular weight of from about 400 to about 1200; and, (c) from about 0.01 to about 0.4%, by weight, of a water-soluble, high molecular weight polymer selected from the group consisting of ethoxylated cellulose, propoxylated cellulose, acrylic acid, starch, xanthan gum, guar gum, poly-vinyl alcohol, and mixtures thereof.

11. The dispersion of claim 10, wherein R is methyl and said water-soluble, high molecular weight polymer is hydroxyethyl cellulose.

12. The dispersion of claim 1, 2 or 3, wherein said water-soluble, nonionic wetting agent is selected from the group consisting of nonionic surfactants having an HLB of from about 10 to 17.8.

13. The dispersion of claim 4, 5 or 7, wherein said water-soluble, nonionic wetting agent is selected from the group consisting of nonionic surfactants having an HLB of from about 10 to 17.8.

14. The dispersion of claim 10 or 11, wherein said water-soluble, nonionic wetting agent is selected from the group consisting of nonionic surfactants having an HLB of from about 10 to 17.8.

15. The method of claim 8, wherein said water-soluble, nonionic wetting agent is selected from the group consisting of nonionic surfactants having an HLB of from about 10 to 17.8.

16. The method of claim 9, wherein said water-soluble, nonionic wetting agent is selected from the group consisting of nonionic surfactants having an HLB of from about 10 to 17.8.

17. The method of claim 15, wherein said water-soluble, nonionic wetting agent is selected from the group consisting of reaction products of alkyl radical substituted phenol and an epoxide, said alkyl radical having from about 8 to about 12 carbon atoms and said epoxide selected from the group con-sisting of ethylene oxide, propylene oxide and mixtures thereof.

18. The method of claim 16, wherein said water-soluble, nonionic wetting agent is selected from the group consisting of reaction products of alkyl radical substituted phenol and an epoxide, said alkyl radical having from about 8 to about 12 carbon atoms and said epoxide selected from the group con-sisting of ethylene oxide, propylene oxide and mixtures thereof.