Method for producing superheavy oil emulsion fuel and fuel produced thereby

A method for producing a superheavy oil emulsion fuel comprising the steps of (i) preparing a liquid mixture comprising a superheavy oil, water, one or more nonionic surfactants having an HLB (hydrophilic-lipophilic balance) of 13 to 19, and optionally one or more stabilizers, and then agitating the resulting liquid mixture with a high shear rate of 1000/sec to 60000/sec, to give an oil-in-water (O/W) type emulsion fuel having a superheavy oil concentration of from 74 to 82% by weight; and (ii) adding at least one of ionic dispersants, and optionally water, to the emulsion fuel obtained in step (i), and then blending and agitating the resulting liquid mixture with a shear rate of 10/sec to 10000/sec, to give an oil-in-water (O/W) type emulsion fuel having a superheavy oil concentration of from 68 to 79% by weight. In step (i), the nonionic surfactants are contained in an amount of from 0.1 to 0.8% by weight of the emulsion fuel obtained in step (i), and the stabilizers are contained in an amount of from 0.001 to 0.5% by weight of the emulsion fuel obtained in step (i). In step (ii), the ionic dispersants are contained in an amount of from 0.01 to 0.5% by weight of the emulsion fuel obtained in step (ii).

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method for producing an oil-in-water 
type, superheavy oil emulsion fuel which is usable as fuels for 
thermoelectric power generation and an emulsion fuel produced by the above 
method. 
2. Discussion of the Related Art 
It has been well known that the superheavy oil emulsion fuels give stable 
emulsion fuels when used together with additives, such as emulsifiers and 
stabilizers, and various excellent emulsifiers to be used in emulsion fuel 
compositions have been developed (See Japanese Patent Laid-Open No. 
1-185394, U.S. Pat. No. 5,024,676, and Japanese Patent Laid-Open No. 
1-313595). However, insufficient long-term storage stability and the need 
for large amounts of emulsifiers are being problems in the conventional 
methods. There is a need for, the concentration of the superheavy oil to 
be made as high as possible. This is owing to the fact that the higher the 
concentration of the superheavy oil, or lower the concentration of water 
in the emulsion fuel, the smaller the heat loss during the combustion of 
the emulsion fuel resulting in a more valuable emulsion fuel. Therefore, 
an emulsion fuel having a high concentration of a superheavy oil and a 
small amount of coarse particles, with good flowability and easy handling 
is highly advantageous with respect to smaller heat loss and the ability 
to dilute the emulsion fuel. 
Accordingly, an object of the present invention is to provide a method for 
producing an easy-to-handle superheavy oil emulsion fuel having a high 
superheavy oil concentration, good flowability, and good long-term storage 
stability. 
Another object of the present invention is to provide a superheavy oil 
emulsion fuel obtainable by the above method. 
These and other objects of the present invention will be apparent from the 
following description. 
SUMMARY OF THE INVENTION 
As a result of intensive research in view of solving the above problems, 
the present inventors have found that a stable emulsion can be obtained by 
agitating particular amounts of a superheavy oil, water, and nonionic 
surfactants, and optionally stabilizers, first under a high shear rate, 
and then agitating, after adding ionic dispersants, under medium shear 
rate, to give an emulsion fuel at a desired concentration of the 
superheavy fuel. The present invention has been completed based upon these 
findings. Incidentally, in the second step, only at least one of 
surfactants and stabilizers may be added without adding water. 
Specifically, the present invention is concerned with the following: 
(1) A method for producing a superheavy oil emulsion fuel comprising the 
steps of: 
(i) preparing a liquid mixture comprising a superheavy oil, water, one or 
more nonionic surfactants having an HLB (hydrophilic-lipophilic balance) 
of 13 to 19, and optionally one or more stabilizers, and then agitating 
the resulting liquid mixture with a high shear rate of 1000/sec to 
60000/sec, to give an oil-in-water (O/W) type emulsion fuel having a 
superheavy oil concentration of from 74 to 82% by weight, wherein the 
nonionic surfactants are contained in an amount of from 0.1 to 0.8% by 
weight of the emulsion fuel obtained in step (i), and wherein the 
stabilizers, when added, are added in an amount of from 0.001 to 0.5% by 
weight of the emulsion fuel obtained in step (i); and 
(ii) adding at least one ionic dispersant, and optionally water, to the 
emulsion fuel obtained in step (i), and then blending and agitating the 
resulting liquid mixture with a shear rate of 10/sec to 10000/sec, to give 
an oil-in-water (O/W) type emulsion fuel having a superheavy oil 
concentration of from 68 to 79% by weight, wherein the ionic dispersants 
added in step (ii) are added in an amount of from 0.01 to 0.5% by weight 
of the emulsion fuel obtained in step (ii); 
(2) The method described in item (1), wherein at least one of anionic 
surfactants and cationic surfactants is further added in the preparation 
of the liquid mixture in step (i), the weight ratio of at least one of 
anionic surfactants and cationic surfactants to the nonionic surfactants 
being from 1/100 to 1/4; 
(3) The method described in item (1) or item (2), wherein the stabilizers 
are at least one member selected from polymeric compounds and 
water-swellable clay minerals; 
(4) The method described in any one of items (1) to (3), wherein the 
oil-in-water (O/W) type emulsion fuel in step (i) has a superheavy oil 
concentration of from 77 to 81% by weight; 
(5) The method described in any one of items (1) to (4), wherein in the 
preparation of the liquid mixture in step (i), the nonionic surfactants 
are added in an amount of from 0.2 to 0.4% by weight of the emulsion fuel 
obtained in step (i), and the stabilizers, when added, are added in an 
amount of from 0.005 to 0.1% by weight of the emulsion fuel obtained in 
step (i); and wherein in step (ii), the dispersants are contained in an 
amount of from 0.02 to 0.2% by weight of the emulsion fuel obtained in 
step (ii); 
(6) The method according to any one of items (1) to (5), wherein the weight 
ratio of the nonionic surfactants to the ionic dispersants, namely 
nonionic surfactants/ionic dispersants, is from 90/10 to 60/40 in the 
superheavy oil emulsion fuel obtained in step (ii); 
(7) The method described in any one of items (1) to (6), wherein the liquid 
mixture in step (i) is agitated with a shear rate of from 5000/sec to 
20000/sec, and wherein the liquid mixture in step (ii) is agitated with a 
shear rate of from 100/sec to 6000/sec; 
(8) The method described in any one of items (1) to (7), wherein the 
oil-in-water (O/W) type emulsion fuel obtained in step (i) comprises oil 
droplets having a particle size distribution of which a 50%-cumulative 
particle size is from 3 to 30 .mu.m, and coarse particles having particle 
sizes of 150 .mu.m or more occupy 3% by weight or less in the entire oil 
droplets; (9) The method described in any one of items (1) to (8), wherein 
the oil-in-water (O/W) type emulsion fuel obtained in step (i) has a 
viscosity at 25.degree. C. of from 400 to 3000 c.p.; 
(10) The method described in any one of items (1) to (9), wherein a 
homomixer equipped with a high-shear turbine mixer is used in step (i) as 
an agitator with a high shear rate; 
(11) The method described in any one of items (1) to (10), wherein the 
oil-in-water (O/W) type emulsion fuel obtained in step (i) comprises oil 
droplets of which coarse particles having particle sizes of 150 .mu.m or 
more occupy 2% by weight or less in the entire oil droplets; 
(12) The method described in any one of items (1) to (11), wherein in the 
preparation of the liquid mixture in step (i), at least one member 
selected from magnesium acetate, magnesium sulfate, magnesium nitrate, 
calcium acetate, calcium sulfate, calcium nitrate, iron acetate, iron 
sulfate, and iron nitrate is further added to the liquid mixture, in an 
amount of from 0.01 to 0.2% by weight of the emulsion fuel obtained in 
step (i); and 
(13) A superheavy oil emulsion fuel obtainable by the method described in 
any one of items (1) to (12). 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention will be explained in detail below. 
The method for producing superheavy oil emulsion fuel of the present 
invention comprises two steps, namely step (i) and step (ii). The method 
of the present invention will be described in detail for each step (i) and 
step (ii). 
1. Step (i) 
Step (i) comprises preparing a liquid mixture comprising a superheavy oil, 
water, one or more nonionic surfactants having an HLB 
(hydrophilic-lipophilic balance) of 13 to 19, and optionally one or more 
stabilizers, and then agitating the resulting liquid mixture with a high 
shear rate of 1000/sec to 60000/sec, to give an oil-in-water (O/W) type 
emulsion fuel having a superheavy oil concentration of from 74 to 82% by 
weight, wherein the nonionic surfactants are contained in an amount of 
from 0.1 to 0.8% by weight of the emulsion fuel obtained in step (i), and 
wherein the stabilizers, when added, are added in an amount of from 0.001 
to 0.5% by weight of the emulsion fuel obtained in step (i). 
The "superheavy oil" usable in the present invention refers to those in a 
solid or semi-fluid state at room temperature, which do not flow unless 
heated to a high temperature. Examples of the superheavy oils include the 
following: 
(1) Petroleum asphalts and mixtures thereof; 
(2) Various treated products of petroleum asphalts, intermediates, 
residues, and mixtures thereof. 
(3) High pour point-oils which do not even flow at high temperatures, or 
crude oils; 
(4) Petroleum tar pitches and mixtures thereof; and 
(5) Bitumens (Orinoco tar and athabasca bitumen). 
Examples of the nonionic surfactants usable in the present invention 
include the following ones: 
(i) Alkylene oxide adducts of compounds having phenolic hydroxyl groups, 
such as phenol, m-cresol, butylphenol, octylphenol, nonylphenol, 
dodecylphenol, p-cumylphenol, and bisphenol A. 
(ii) Alkylene oxide adducts of formalin (formaldehyde) condensates of 
compounds having phenolic hydroxyl groups, such as alkylphenols, phenol, 
m-cresol, styrenated phenol, and benzylated phenol, wherein the average 
degree of condensation is 1.2 to 100, preferably 2 to 20. 
(iii) Alkylene oxide adducts of aliphatic alcohols and/or aliphatic amines 
each having 2 to 50 carbon atoms. 
(iv) Block or random addition polymers of ethylene oxide/propylene oxide, 
ethylene oxide/butylene oxide, ethylene oxide/styrene oxide, ethylene 
oxide/propylene oxide/butylene oxide, ethylene oxide/propylene 
oxide/ethylene oxide, and ethylene oxide/propylene oxide/styrene oxide. 
(v) Alkylene oxide adducts of polyhydric alcohols, such as glycerol, 
trimethylolpropane, pentaerythritol, sorbitol, sucrose, polyglycerols, 
ethylene glycol, polyethylene glycols, propylene glycol, and polypropylene 
glycols, or those of esters formed between the above-described polyhydric 
alcohols and fatty acids having 8 to 18 carbon atoms. 
(vi) Alkylene oxide adducts of polyvalent amines having a plurality of 
active hydrogen atoms, such as ethylenediamine, tetraethylenediamine, and 
polyethyleneimine (weight-average molecular weight: 600 to 10,000). 
(vii) Products formed by addition reaction of alkylene oxides with a 
mixture comprising one mol of fats and oils comprising triglyceride and 
0.1 to 5 mol of one or more polyhydric alcohols and/or water, the 
polyhydric alcohol being at least one member selected from the group 
consisting of glycerol, trimethylolpropane, pentaerythritol, sorbitol, 
sucrose, ethylene glycol, polyethylene glycols having a weight-average 
molecular weight of 1000 or less, propylene glycol, and polypropylene 
glycols having a weight-average molecular weight of 1000 or less. 
In each of the nonionic surfactants (i) to (vii), the alkylene oxide means, 
for example, ethylene oxide, propylene oxide, butylene oxide, styrene 
oxide, and combinations thereof. 
In the present invention, the nonionic surfactants may be used alone or in 
combination of two or more kinds. Among the above nonionic surfactants, a 
preference is given those listed under item (i), specifically, alkylene 
oxide adducts of compounds having phenolic hydroxyl groups, such as 
octylphenol, nonylphenol, and dodecylphenol. 
The nonionic surfactants usable in the present invention have an HLB of 
usually from 13 to 19, preferably from 13.5 to 15.5. The HLB of the 
nonionic surfactants is from 13 to 19 in order to obtain stable emulsion. 
The "HLB"values in the present invention refer to an abbreviation of a 
hydrophilic-lipophilic balance calculated from the Griffin's equation. 
Specifically, the HLB is an index for surface activity by expressing 
intensity ratios between a hydrophilic property and a lipophilic property 
of amphiphilics. Here, the found values of Griffin et al. are employed (W. 
C. Griffin, "Kirk-Othmer Encyclopedia of Chemical Technology," 3rd Ed., 
Vol. 8, p.913-916, John-Wiley (1979)). 
The nonionic surfactant in the present invention used is added in an amount 
of from 0.1 to 0.8% by weight, preferably from 0.2 to 0.4% by weight, of 
the emulsion fuel obtained in step (i). The amount is preferably 0.8% by 
weight or less, from the aspect of maintaining good particle size of the 
oil particles in the resulting emulsion fuel without being too small, and 
the amount is preferably 0.1% by weight or more, from the aspect of 
maintaining good particle size of the oil particles without being too 
large as well as having good emulsion stability by the sufficient 
inclusion of the surfactants. 
In the preparation of the liquid mixture in step (i), in addition to the 
nonionic surfactants, commercially available anionic surfactants and 
cationic surfactants may be optionally added to the liquid mixture, a 
weight ratio of the optional surfactants to the nonionic surfactant being 
preferably from 1/100 to 1/4, more preferably from 1/20 to 1/5. 
Examples of the anionic surfactants usable in the present invention include 
the following ones. 
(i) Sulfonates of aromatic ring compounds, such as naphthalenesulfonates, 
alkylnaphthalenesulfonates, alkylphenolsulfonates, and 
alkylbenzenesulfonates, or formalin (formaldehyde) condensates of 
sulfonates of aromatic ring compounds, wherein the average degree of 
condensation of formalin is from 1.2 to 100, more preferably from 2 to 20, 
and wherein the sulfonates are exemplified by ammonium salts; lower amine 
salts, such as monoethanolamine salts, diethanolamine salts, 
triethanolamine salts, and triethylamine salts; and alkali metal salts or 
alkaline earth metal salts, such as sodium salts, potassium salts, 
magnesium salts, and calcium salts. 
(ii) Lignin sulfonic acid, salts thereof, or derivatives thereof, formalin 
(formaldehyde) condensates of lignin sulfonic acid and sulfonic acids of 
aromatic compounds, such as naphthalenesulfonic acid and 
alkylnaphthalenesulfonic acids, and salts thereof, wherein the salts for 
both the lignin sulfonates and the sulfonates of aromatic compounds are 
exemplified by ammonium salts; lower amine salts, such as monoethanolamine 
salts, diethanolamine salts, triethanolamine salts, and triethylamine 
salts; and alkali metal salts or alkaline earth metal salts, such as 
sodium salts, potassium salts, magnesium salts, and calcium salts, and 
wherein the average degree of condensation of formalin is from 1.2 to 50, 
preferably from 2 to 20. Among the lignins, excellent performance at high 
temperatures can be particularly achieved when a modified lignin, for 
instance, those substituted by one or more carboxyl groups, is used. 
(iii) Polystyrenesulfonic acids or salts thereof, copolymers of 
styrenesulfonic acid with other copolymerizable monomer(s), or salts 
thereof, wherein the weight-average molecular weight is from 500 to 
500,000, preferably from 2,000 to 100,000, and wherein the salts are 
exemplified by ammonium salts; lower amine salts, such as monoethanolamine 
salts, diethanolamine salts, triethanolamine salts, and triethylamine 
salts; and alkali metal salts or alkaline earth metal salts, such as 
sodium salts, potassium salts, magnesium salts, and calcium salts. Here, 
typical examples of the copolymerizable monomers include acrylic acid, 
methacrylic acid, vinyl acetate, acrylic ester, olefins, allyl alcohols 
and ethylene oxide adducts thereof, and acrylamide methylpropylsulfonic 
acid. 
(iv) Polymers of dicyclopentadienesulfonic acid or salts thereof, wherein 
the weight-average molecular weight of the polymers is from 500 to 
500,000, preferably from 2,000 to 100,000, and wherein the salts are 
exemplified by ammonium salts; lower amine salts, such as monoethanolamine 
salts, diethanolamine salts, triethanolamine salts, and triethylamine 
salts; and alkali metal salts or alkaline earth metal salts, such as 
sodium salts, potassium salts, magnesium salts, and calcium salts. 
(v) Copolymers of maleic anhydride and/or itaconic anhydride with other 
copolymerizable monomer(s), or salts thereof, wherein the weight-average 
molecular weight is from 500 to 500,000, preferably from 1,500 to 100,000, 
and wherein the salts are exemplified by ammonium salts; and alkali metal 
salts, such as sodium salts and potassium salts. Here, typical examples of 
the copolymerizable monomers include olefins, such as ethylene, propylene, 
butylene, pentene, hexene, heptene, octene, nonene, decene, undecene, 
dodecene, tridecene, tetradecene, pentadecene, and hexadecene, styrene, 
vinyl acetate, acrylic ester, acrylic acid, and methacrylic acid. 
(vi) Maleinized liquid polybutadienes or salts thereof, wherein the 
weight-average molecular weight of the liquid polybutadienes as the 
starting materials is from 500 to 200,000, preferably from 1,000 to 
50,000, and wherein the degree of maleinization is at a level necessary 
for dissolving the maleinized liquid polybutadiene in water, preferably 
from 40 to 70%, and wherein the salts are exemplified by ammonium salts, 
and alkali metal salts, such as sodium salts and potassium salts. 
(vii) Anionic surfactants having in the molecule one or two hydrophilic 
groups, selected from the following (a) to (h): 
(a) Sulfuric ester salts of alcohols having 4 to 18 carbon atoms, wherein 
the salts are exemplified by ammonium salts; lower amine salts, such as 
monoethanolamine salts, diethanolamine salts, triethanolamine salts, and 
triethylamine salts; and alkali metal salts or alkaline earth metal salts, 
such as sodium salts, potassium salts, magnesium salts, and calcium salts. 
Typical examples thereof include sodium dodecyl sulfate and sodium octyl 
sulfate. 
(b) Alkanesulfonic acids, alkenesulfonic acids, and/or alkylarylsulfonic 
acids, each having 4 to 18 carbon atoms, or salts thereof, wherein the 
salts are exemplified by ammonium salts; lower amine salts, such as 
monoethanolamine salts, diethanolamine salts, triethanolamine salts, and 
triethylamine salts; and alkali metal salts or alkaline earth metal salts, 
such as sodium salts, potassium salts, magnesium salts, and calcium salts. 
Typical examples thereof include sodium dodecylbenzene sulfonate, sodium 
butylnaphthalene sulfonate, and sodium dodecane sulfonate. 
(c) Sulfates or phosphates of alkylene oxide adducts of compounds having in 
the molecule one or more active hydrogen atoms, or salts thereof, wherein 
the salts are exemplified by ammonium salts, or alkali metal salts or 
alkaline earth metal salts, such as sodium salts, potassium salts, 
magnesium salts, and calcium salts. Typical examples thereof include 
sulfuric ester sodium salts of polyoxyethylene(3 mol) nonyl phenyl ether, 
and phosphoric ester sodium salts of polyoxyethylene(3 mol) dodecyl ether. 
(d) Sulfosuccinic ester salts of saturated or unsaturated fatty acids 
having 4 to 22 carbon atoms, wherein the salts are exemplified by ammonium 
salts, and alkali metal salts, such as sodium salts and potassium salts. 
Typical examples thereof include sodium dioctylsulfosuccinate, ammonium 
dioctylsulfosuccinate, and sodium dibutylsulfosuccinate. 
(e) Alkyldiphenylether disulfonic acids or salts thereof, of which the 
alkyl group has 8 to 18 carbon atoms, and wherein the salts are 
exemplified by ammonium salts, or alkali metal salts or alkaline earth 
metal salts, such as sodium salts, potassium salts, magnesium salts, and 
calcium salts. 
(f) Rosins or salts thereof, wherein the salts are exemplified by ammonium 
salts, and alkali metal salts, such as sodium salts and potassium salts. 
Examples thereof include mixed tall acids comprising a tall rosin and a 
higher fatty acid, and salts thereof. 
(g) Alkanefatty acids or alkenefatty acids each having 4 to 18 carbon 
atoms, or salts thereof, wherein the salts are exemplified by ammonium 
salts, and alkali metal salts, such as sodium salts and potassium salts. 
(h) .alpha.-Sulfofatty ester salts of which the alkyl group has 4 to 22 
carbon atoms and derivatives thereof, wherein the salts are exemplified by 
ammonium salts, or alkali metal salts or alkaline earth metal salts, such 
as sodium salts, potassium salts, and magnesium salts. 
Among the anionic surfactants listed above, a preference is given to the 
lignin sulfonates, the formalin condensates of lignin sulfonic acid and 
the formalin condensates of naphthalenesulfonic acid or salts thereof, and 
the formalin condensates of naphthalenesulfonates because they show 
overall superior performance in charging the particles. 
The cationic surfactants usable in the present invention are the following 
ones. 
(i) Alkylamine salts and/or alkenylamine salts obtainable by neutralizing 
an alkylamine or alkenylamine, each of alkyl or alkenyl group having 4 to 
18 carbon atoms, with an inorganic acid and/or an organic acid, such as 
hydrochloric acid and acetic acid. 
(ii) Quaternary ammonium salts represented by the following general 
formulae (A), (B), and (C): 
##STR1## 
wherein R.sub.1, R.sub.2, R.sub.3, and R.sub.4, which may be identical or 
different, independently stand for an alkyl group or alkenyl group, each 
having 1 to 18 carbon atoms; and X.sup.- stands for a counter anion, 
including chlorine ion or bromine ion; 
##STR2## 
wherein R.sub.1, R.sub.2, R.sub.3, and X.sup.- are as defined above; and 
##STR3## 
wherein R.sub.5 stands for an alkyl group or alkenyl group having 8 to 18 
carbon atoms; R.sub.6 stands for a hydrogen atom or a methyl group; and 
X.sup.- is as defined above. 
(iii) Alkylbetaines or alkenylbetaines represented by the following general 
formula: 
##STR4## 
wherein R stands for an alkyl group or alkenyl group, each having 8 to 18 
carbon atoms. 
(iv) Alkylamine oxides or alkenylamine oxides represented by the following 
general formula: 
##STR5## 
wherein R is as defined in item (iii). (v) Alkylalanines or 
alkenylalanines represented by the following general formula: 
##STR6## 
wherein R is as defined in item (iii). (vi) Alkylene oxide adduct 
polymers of diamine or triamine represented by the following general 
formula (D) or (E): 
##STR7## 
wherein R is as defined in item (iii); and Y and Y', which may be 
identical or different, each stands for an oxyethylene moiety represented 
by the general formula: 
##STR8## 
wherein m stands for a number of from 1 to 50. (vii)Polyamine salts 
represented by the following formula (F) or (G): 
EQU RNHC.sub.3 H.sub.6 NHX' (F) 
EQU RNH (C.sub.3 H.sub.6 NH).sub.2 X' (G) 
wherein R is as defined in item (iii); and X' stands for an inorganic acid 
or organic acid, such as hydrochloric acid and acetic acid. 
Examples of stabilizers which may be used in combination with the nonionic 
surfactants in step (i) include (1) polymeric compounds, including 
naturally occurring polymers and synthetic polymers, and (2) 
water-swellable clay minerals. In other words, the stabilizers usable in 
the present invention may be selected from items (1) and (2) listed below. 
(1) Polymeric Compounds 
Hydrophilic Naturally Occurring Polymers Derived from Naturally Occurring 
Substances 
Hydrophilic Polymers Derived from Microorganism (Polysaccharides) 
1) Xanthan gum 
2) Pullulan 
3) Dextran 
Hydrophilic Polymers Derived from Plants (Polysaccharides) 
1) Derived from marine algae: agar, carrageenan, furcellaran, alginic acid 
and salts (Na, K, NH.sub.4, Ca, or Mg) thereof 
2) Derived from seeds: locust bean gum, guar gum, tara gum 
3) Trees (exudates): gum arabic, gum karaya, gum tragacanth; and 
4) Derived from fruits: pectin 
Hydrophilic Polymers Derived from Animals (Proteins) 
1) Gelatin 
2) Casein 
Naturally Occurring Polymer Derivatives 
1) Cellulose derivatives, such as carboxymethylcellulose 
2) Chemically modified starch 
Water-Soluble Synthetic Polymers 
(a) Homopolymers or copolymers of acrylic acid or derivatives thereof 
represented by the following general formula: 
##STR9## 
wherein R' stands for a hydrogen atom, a methyl group, or an ethyl group; 
M.sub.1 stands for a hydrogen atom, a sodium ion, a potassium ion, a 
lithium ion, or an ammonium ion; Z.sub.1 stands for a divalent group which 
is derived from a monomer and salts thereof copolymerizable therewith, the 
divalent group being represented by the following general formula: 
##STR10## 
wherein R' and M.sub.1 are as defined above, wherein the salts of the 
copolymerizable monomers are exemplified by ammonium salts, sodium salts, 
potassium salts, and lithium salts; and n stands for a number of from 50 
to 100,000. Examples of the copolymerizable monomers include maleic acid 
(anhydride), itaconic acid (anhydride), .alpha.-olefins, acrylamide, 
vinylsulfonic acid, allylsulfonic acid, methallylsulfonic acid, and 
acrylamidomethylpropylsulfonic acid, and salts thereof, including ammonium 
salts, sodium salts, potassium salts, and lithium salts; dialkyl 
aminoethyl methacrylates, such as dimethyl aminoethyl methacrylate and 
diethyl aminoethyl methacrylate and salts thereof, including halogenides, 
such as chloride, diethyl sulfate, and dimethyl sulfate. 
(b) Homopolymers or copolymers of acrylamide or derivatives thereof 
represented by the following general formula: 
##STR11## 
wherein R" stands for a hydrogen atom or a C.sub.2 H.sub.4 OH group; 
Z.sub.2 stands for a divalent group which is derived from a monomer or 
salts thereof, the divalent group being represented by the following 
general formula: 
##STR12## 
wherein R" is as defined above, and wherein the salts of the 
copolymerizable monomers are exemplified by ammonium salts, sodium salts, 
potassium salts, and lithium salts; and n stands for a number of from 50 
to 100,000. Examples of the copolymerizable monomers include vinylsulfonic 
acid, allylsulfonic acid, methallylsulfonic acid, 
acrylamidomethylpropylsulfonic acid, and salts thereof, including ammonium 
salts, sodium salts, potassium salts, and lithium salts; dialkyl 
aminoethyl methacrylates, such as dimethyl aminoethyl methacrylate and 
dimethyl aminoethyl methacrylate and salts thereof, quaternary compounds 
thereof, including halogenides, such as chloride, diethyl sulfate, and 
dimethyl sulfate; styrene; .alpha.-olefins having 2 to 18 carbon atoms; 
and vinylallyl alcohols. 
(c) Homopolymers of maleic anhydride or itaconic anhydride, or copolymers 
thereof represented by the following general formula: 
##STR13## 
wherein M.sub.2 stands for a maleic anhydride unit or itaconic anhydride 
unit; Z.sub.3 stands for an .alpha.-olefin unit, the .alpha.-olefins 
including ethylene, propylene, butylene, isobutylene, octene, decene, and 
dodecene, or a styrene unit; and n stands for a number of from 50 to 
100,000. 
(d) Polyvinyl alcohols or copolymers thereof represented by the following 
general formula: 
##STR14## 
wherein Z.sub.4 stands for a vinyl acetate unit or styrene unit; and n' 
stands for a number of from 30 to 100,000. 
(e) Homopolymers of vinylpyrrolidone, or copolymers thereof represented by 
the following general formula: 
##STR15## 
wherein Z.sub.5 stands for a divalent group which is derived from a 
monomer copolymerizable with a vinylpyrrolidone monomer, wherein the salts 
of the monomers copolymerizable with vinylpyrrolidone monomers include 
ammonium salts, sodium salts, potassium salts, and lithium salts. Examples 
of the monomers copolymerizable with the vinylpyrrolidone monomer or salts 
thereof include acrylamide, vinylsulfonic acid, methallylsulfonic acid, 
maleic anhydride, itaconic anhydride, and salts thereof, such as ammonium 
salts, sodium salts, potassium salts, and lithium salts; styrene; 
.alpha.-olefins having 2 to 18 carbon atoms; and n stands for a number of 
from 50 to 100,000. 
(f) Polyalkylene oxides having a weight-average molecular weight of from 
10,000 to 5,000,000, wherein the ethylene oxide content is 95% by weight 
or more, which may include those containing in the molecule 5% by weight 
or less of various block polymers of propylene oxide, butylene oxide, and 
styrene oxide or alkylallyl groups or alkyl groups. 
Among these polymeric compounds, naturally occurring polymeric derivatives, 
including cellulose derivatives, such as carboxymethylcellulose, and 
hydrophilic polymers derived from microorganism, such as xanthan gum, are 
suitably used in the present invention. 
(2) Water-Swellable Clay Minerals 
The water-swellable clay minerals usable in the present invention include 
the following ones. 
The clay minerals usable in the present invention is a highly swellable 
fine clay mineral, wherein the term "highly swellable" clay minerals refer 
to those bound with a large amount of water molecules when the clay 
minerals are suspended in water, so as to have a relaxation time (T.sub.2) 
for water molecules of preferably from 900 msec or less, more preferably 
500 msec or less, the relaxation time for water molecules being measured 
by a nuclear magnetic resonance spectrometer when the clay minerals are 
suspended in water in an amount of 1% by weight on a dry basis. When the 
relaxation time for the water molecules is 900 msec or less, a good 
binding force of the clay minerals to the water molecules can be 
maintained, thereby making it possible to sufficiently attain the effects 
of the present invention. In addition, the term "fine clay mineral" refers 
to the clay minerals having an average particle size of preferably from 
100 .mu.m or less. The clay mineral has an average particle size of 
preferably 100 .mu.m or less, a good binding force of the clay minerals to 
the water molecules can be maintained, and at the same time sedimentation 
of the clay minerals is liable to be inhibited, thereby making it possible 
to sufficiently attain the effects of the present invention. 
Specifically, the fine clay minerals having a high swellability and a high 
binding force to the water molecules, including smectites, vermiculites, 
and chlorites, fall within the scope of the present invention. Among them, 
however, those having a T.sub.2 value exceeding 900 msec are outside the 
scope of the present invention. Further, since kaolin produced in Georgia, 
U.S.A., general kaolin and talc have weak binding forces to the water 
molecules, they are excluded from the scope of the present invention. 
The highly swellable fine clay minerals, such as smectites, vermiculites, 
and chlorites, usable in the present invention will be explained in detail 
below. 
(A) Smectite has a complicated chemical composition comprising two 
tetrahedral sheets and one octahedral sheet inserted therebetween (namely 
a 2:1 layer), because substitution takes place in a wide range and various 
ions accompanied by water molecules are intercalated. The smectite is 
represented by, for example, the following general formula: 
EQU X.sub.m (Y.sup.2+, Y.sup.3+).sub.2-3 Z.sub.4 O.sub.10 (OH).sub.2.nH.sub.2 O 
, 
wherein X stands for K, Na, 1/2 Ca, or 1/2 Mg; y.sup.2+ stands for 
Mg.sup.2+, Fe .sup.2+, Mn.sup.2+, Ni.sup.2+, Zn.sup.2+, or Li, Y.sup.3+ 
stands for Al.sup.3+, Fe.sup.3+, Mn.sup.3+, or Cr.sup.3+ ; and Z stands 
for Si and/or Al, with proviso that X, Y, and Z stand for an intercalated 
cation, an octahedral cation, and a tetrahedral cation, respectively. 
Typical examples of the smectites are the following ones: 
Dioctahedral (octahedral cations being mainly trivalent): 
Montmorillonites represented by, for example, the following formula: 
EQU X.sub.0.33 (Al.sub.1.67 Mg.sub.0.33)Si.sub.4 O.sub.10 (OH).sub.2.nH.sub.2 O 
; 
Beidellites represented by, for example, the following formula: 
EQU X.sub.0.33 (Al.sub.2)(Al.sub.0.33 Si.sub.3.67)O.sub.10 (OH).sub.2.nH.sub.2 
O; 
and 
Nontronites represented by, for example, the following formula: 
EQU X.sub.0.33 (Fe(III).sub.2)(Al.sub.0.33 
Si.sub.3.67)O.sub.10,(OH).sub.2.nH.sub.2 O. 
Trioctahedral (octahedral cations being mainly divalent): 
Saponites represented by, for example, the following formula: 
EQU X.sub.0.33 (Mg.sub.3)(Al.sub.0.33 Si.sub.3.67)O.sub.10 (OH).sub.2.nH.sub.2 
O; 
Iron saponites represented by, for example, the following formula: 
EQU X.sub.0.33 (Mg,Fe(II)).sub.3 (Al.sub.0.33 Si.sub.3.67)O.sub.10 
(OH).sub.2.nH.sub.2 O; 
Hectorites represented by, for example, the following formula: 
EQU X.sub.0.33 (Mg.sub.2.67 Li.sub.0.33 )Si.sub.4 O.sub.10 (OH).sub.2.nH.sub.2 
O; 
Sauconites represented by, for example, the following formula: 
EQU X.sub.0.33 (Mg,Zn).sub.3 (Si.sub.3.67 Al.sub.0.33)O.sub.10 
(OH).sub.2.nH.sub.2 O; 
and 
Stevensites represented by, for example, the following formula: 
X.sub.0.33/2 (Mg.sub.2.97)Si.sub.4 O.sub.10 (OH).sub.2.nH.sub.2 O. 
Among the smectites listed above, the montmorillonites, the beidellites, 
and the nontronites constitute a series which can be subjected to 
isomorphous substitution. The stevensites have layer charges of one-half 
of that of the other smectites, and thus having an intermediary property 
of the dioctahedral smectites and the trioctahedral smectites. 
(B) Vermiculites pertain to 2:1 layer silicates and are represented by, for 
example, the following formula: 
EQU (Mg,Fe(III),Al).sub.2-3 (Si.sub.4-x Al.sub.x)O.sub.10 (OH).sub.2 
(M.sup.+,M.sup.2+.sub.1/2).sub.x.nH.sub.2 O. 
In the above formula, M stands for an intercalated exchangeable cation, and 
when the vermiculite is in the form of coarse particles, M is mainly 
composed of Mg. "n" in the above formula stands for the amount of water, 
and when the intercalated cation is Mg, water forms a bimolecular layer 
over a wide temperature range and n is in the range of from about 3.5 to 
5. "x" in the above formula stands for layer charges which are in the 
range of from 0.6 to 0.9. 
In the above formula, it is assumed that all of the layer charges are 
generated by the substitution of tetrahedral cations. However, in certain 
cases, the octahedral sheet may actually carry a negative charge to which 
the layer charges are ascribed. The number of octahedral cations is 2 to 
3, and the vermiculites are classified into dioctahedral vermiculites and 
trioctahedral vermiculites. The vermiculites in the form of coarse 
particles obtainable by the weathering of biotite and phlogopite are 
trioctahedral vermiculites. 
(C) The structures of the chlorites are similar to those of the smectites 
and the vermiculites, and the base plane interval is 14 to 15 .ANG.. The 
chlorites are typically a 2:1 hydrated silicate which can be classified 
into trioctahedral chlorites and dioctahedral chlorites depending on the 
properties of the 2:1 layer. 
The trioctahedral chlorites are represented by, for example, the following 
formula: 
EQU (R.sub.6-x.sup.2+ R.sub.x.sup.3+)(Si.sub.4-x Al.sub.x)O.sub.10 (OH).sub.8. 
In the above formula, R.sup.2+ is mainly composed of Mg.sup.2+ and 
Fe.sup.2+, which may also include Mn.sup.2+ and Ni.sup.2+ ; and R.sup.3+, 
is mainly composed of Al, which may also include Fe.sup.3+ and Cr.sup.3+. 
"x" in the above formula is a value of from 0.8 to 1.6. 
A chlorite wherein R.sup.2+ is mainly composed of Mg.sup.2+ is so-called 
"clinochlore" e.g. (Mg.sub.5 Al)(SI.sub.3 Al)O.sub.10 (OH).sub.8 !; and a 
chlorite wherein R.sup.2+ is mainly composed of Fe(II) is so-called 
"chamosite" e.g. (Fe.sub.5 Al)(Si.sub.3 Al)O.sub.10 (OH).sub.8 !. 
Examples of other trioctahedral chlorites include "pennantite" wherein 
R.sup.2+ is mainly composed of Mn(II); and "nimite" wherein R.sup.2+ is 
mainly composed of Ni(II). 
The dioctahedral chlorites wherein the octahedral cation is mainly composed 
of Al are classified into the following three kinds. 
Sudoite e.g. (Mg,Al).sub.4.6-5 (Si,Al).sub.4 O.sub.10 (OH).sub.8 ; 
Cookeite e.g. (LiAl.sub.4)(Si.sub.3 Al)O.sub.10 (OH).sub.8 ; and 
Donbassite e.g. Al.sub.4-4.2 R.sub.0.2 (Si,Al).sub.4 O.sub.10 (OH).sub.8. 
The clay minerals comprising montmorillonite, the clay mineral pertaining 
to smectite, as the main component, and further containing as impurities, 
quartz, .alpha.-cristobalite, opal, feldspar, mica, zeolite, calcite, 
dolomite, gypsum, and iron oxide are so-called "bentonite." The bentonites 
include sodium bentonite rich in Na ions and calcium bentonite rich in Ca 
ions. Since sodium bentonite has high swellability, it falls within the 
scope of the clay minerals of the present invention, while calcium 
bentonite has notably low swellability that it is excluded from the scope 
of the present invention. 
These stabilizers are contained in an amount of from 0.001 to 0.5% by 
weight, preferably from 0.001 to 0.1% by weight, most preferably from 
0.005 to 0.1% by weight, of the emulsion fuel obtained in step (i). The 
addition of the stabilizers allows to suppress the mobility in the 
interface of the oil droplets, so that the resulting emulsion fuels may be 
stabilized. 
In addition, aside from the stabilizers mentioned above, at least one 
member selected from magnesium acetate, magnesium sulfate, magnesium 
nitrate, calcium acetate, calcium sulfate, calcium nitrate, iron acetate, 
iron sulfate, and iron nitrate is further added to the liquid mixture, may 
be added, to thereby give a good emulsion stability effect. In this case, 
these stabilizers are contained in an amount of from 0.01 to 0.2% by 
weight, preferably from 0.05 to 0.1% by weight, of the emulsion fuel 
obtained in step (i). 
In step (i), the agitators to be used when preparing a liquid mixture 
comprising a superheavy oil, water, a nonionic surfactant, and optional 
stabilizers are not particularly required to have high shear rates, and 
any one of general agitators, such as propeller agitators, will suffice. 
The agitation after the preparation of the liquid mixture needs to be 
carried out by agitators with high shear rates. Examples thereof include 
line mixers, arrow blade turbine blade mixers, full margin-type blade 
mixers, high-shear turbine mixers, and homogenizers. From the viewpoint of 
industrial efficiency, homomixers equipped with high-shear turbine mixers 
are preferably used. Here, the term "high shear rate" refers to a shear 
rate of from 1,000/sec to 60,000/sec, preferably from 5,000/sec to 
20,000/sec. By agitating with such a high shear rate, the oil-in-water 
(O/W) type emulsion fuel having a concentration of the superheavy oil of 
from 74 to 82% by weight, preferably from 77 to 81% by weight. By 
agitating the liquid mixture with such a high shear rate, the oil-in water 
(O/W) emulsion fuel having a superheavy oil concentration of from 74 to 
82% by weight, preferably from 77 to 81% by weight can be produced. The 
water is added in step (i) so as to make up 100% by weight with the entire 
emulsion fuel, namely, the amount of water is from 17 to 25% by weight. 
The kinds and the amounts of the nonionic surfactants, the shear rates, and 
time required for agitation of the liquid mixture, and viscosity during 
agitation have to suitably adjusted so that the oil-in-water (O/W) 
emulsion fuel obtained in step (i) has a particle size distribution 
wherein a 50%-cumulative particle size is preferably from 3 to 30 .mu.m, 
more preferably 8 to 20 .mu.m, and wherein coarse particles having 
particle sizes of 150 .mu.m or more occupy preferably 3% by weight or 
less, more preferably 2% by weight or less, still more preferably 1% by 
weight or less, in the entire emulsion fuel. The viscosity of the 
resulting oil-in-water emulsion fuel is preferably 400 c.p. or more (at 
250.degree. C.), more preferably from 400 to 3000 c.p. (at 25.degree. C.). 
Incidentally, the term "particle size" used herein refers to particle 
diameter. The "particle size" and "amount of coarse particles" are 
evaluated by methods described in Examples which are set forth 
hereinbelow. 
2. Step (ii) 
Step (ii) comprises adding at least one of water and ionic dispersants to 
the emulsion fuel obtained in step (i), and then blending and agitating 
the resulting liquid mixture with a shear rate of 10/sec to 10000/sec, to 
give an oil-in-water (O/W) type emulsion fuel having a superheavy oil 
concentration of from 68 to 79% by weight, wherein the ionic dispersants, 
when added, are contained in an amount of from 0.01 to 0.5% by weight of 
the emulsion fuel obtained in step (ii). 
The ionic dispersants usable in step (ii) include the following anionic 
surfactants. 
(i) Sulfonates of aromatic ring compounds, such as naphthalenesulfonates, 
alkylnaphthalenesulfonates, alkylphenolsulfonates, and 
alkylbenzenesulfonates, or formalin (formaldehyde) condensates of 
sulfonates of aromatic ring compounds, wherein the average degree of 
condensation of formalin is from 1.2 to 100, more preferably from 2 to 20, 
and wherein the sulfonates are exemplified by ammonium salts; lower amine 
salts, such as monoethanolamine salts, diethanolamine salts, 
triethanolamine salts, and triethylamine salts; and alkali metal salts or 
alkaline earth metal salts, such as sodium salts, potassium salts, 
magnesium salts, and calcium salts. 
(ii) Lignin sulfonic acid, salts thereof, or derivatives thereof, formalin 
(formaldehyde) condensates of lignin sulfonic acid and sulfonic acids of 
aromatic compounds, such as naphthalenesulfonic acid and 
alkylnaphthalenesulfonic acids, and salts thereof, wherein the salts for 
both the lignin sulfonates and the sulfonates of aromatic compounds are 
exemplified by ammonium salts; lower amine salts, such as monoethanolamine 
salts, diethanolamine salts, triethanolamine salts, and triethylamine 
salts; and alkali metal salts or alkaline earth metal salts, such as 
sodium salts, potassium salts, magnesium salts, and calcium salts, and 
wherein the average degree of condensation of formalin is from 1.2 to 50, 
preferably from 2 to 20. Among the lignins, excellent performance at high 
temperatures can be particularly achieved when a modified lignin, for 
instance, those substituted by one or more carboxyl groups, is used. 
(iii) Polystyrenesulfonic acids or salts thereof, copolymers of 
styrenesulfonic acid with other copolymerizable monomer(s), or salts 
thereof, wherein the weight-average molecular weight is from 500 to 
500,000, preferably from 2,000 to 100,000, and wherein the salts are 
exemplified by ammonium salts; lower amine salts, such as monoethanolamine 
salts, diethanolamine salts, triethanolamine salts, and triethylamine 
salts; and alkali metal salts or alkaline earth metal salts, such as 
sodium salts, potassium salts, magnesium salts, and calcium salts. Here, 
typical examples of the copolymerizable monomers include acrylic acid, 
methacrylic acid, vinyl acetate, acrylic ester, olefins, allyl alcohols 
and ethylene oxide adducts thereof, and acrylamide methylpropylsulfonic 
acid. 
(iv) Polymers of dicyclopentadienesulfonic acid or salts thereof, wherein 
the weight-average molecular weight of the polymers is from 500 to 
500,000, preferably from 2,000 to 100,000, and wherein the salts are 
exemplified by ammonium salts; lower amine salts, such as monoethanolamine 
salts, diethanolamine salts, triethanolamine salts, and triethylamine 
salts; and alkali metal salts or alkaline earth metal salts, such as 
sodium salts, potassium salts, magnesium salts, and calcium salts. 
(v) Copolymers of maleic anhydride and/or itaconic anhydride with other 
copolymerizable monomer(s), or salts thereof, wherein the weight-average 
molecular weight is from 500 to 500,000, preferably from 1,500 to 100,000, 
and wherein the salts are exemplified by ammonium salts; and alkali metal 
salts, such as sodium salts and potassium salts. Here, typical examples of 
the copolymerizable monomers include olefins, such as ethylene, propylene, 
butylene, pentene, hexene, heptene, octene, nonene, decene, undecene, 
dodecene, tridecene, tetradecene, pentadecene, and hexadecene, styrene, 
vinyl acetate, acrylic ester, acrylic acid, and methacrylic acid. 
(vi) Maleinized liquid polybutadienes or salts thereof, wherein the 
weight-average molecular weight of the liquid polybutadienes as the 
starting materials is from 500 to 200,000, preferably from 1,000 to 
50,000, and wherein the degree of maleinization is at a level necessary 
for dissolving the maleinized liquid polybutadiene in water, preferably 
from 40 to 70%, and wherein the salts are exemplified by ammonium salts, 
and alkali metal salts, such as sodium salts and potassium salts. 
(vii) Anionic surfactants having in the molecule one or two hydrophilic 
groups, selected from the following (a) to (h): 
(a) Sulfuric ester salts of alcohols having 4 to 18 carbon atoms, wherein 
the salts are exemplified by ammonium salts; lower amine salts, such as 
monoethanolamine salts, diethanolamine salts, triethanolamine salts, and 
triethylamine salts; and alkali metal salts or alkaline earth metal salts, 
such as sodium salts, potassium salts, magnesium salts, and calcium salts. 
Typical examples thereof include sodium dodecyl sulfate and sodium octyl 
sulfate. 
(b) Alkanesulfonic acids, alkenesulfonic acids, and/or alkylarylsulfonic 
acids, each having 4 to 18 carbon atoms, or salts thereof, wherein the 
salts are exemplified by ammonium salts; lower amine salts, such as 
monoethanolamine salts, diethanolamine salts, triethanolamine salts, and 
triethylamine salts; and alkali metal salts or alkaline earth metal salts, 
such as sodium salts, potassium salts, magnesium salts, and calcium salts. 
Typical examples thereof include sodium dodecylbenzene sulfonate, sodium 
butylnaphthalene sulfonate, and sodium dodecane sulfonate. 
(c) Sulfates or phosphates of alkylene oxide adducts of compounds having in 
the molecule one or more active hydrogen atoms, or salts thereof, wherein 
the salts are exemplified by ammonium salts, or alkali metal salts or 
alkaline earth metal salts, such as sodium salts, potassium salts, 
magnesium salts, and calcium salts. Typical examples thereof include 
sulfuric ester sodium salts of polyoxyethylene(3 mol) nonyl phenyl ether, 
and phosphoric ester sodium salts of polyoxyethylene(3 mol) dodecyl ether. 
(d) Sulfosuccinic ester salts of saturated or unsaturated fatty acids 
having 4 to 22 carbon atoms, wherein the salts are exemplified by ammonium 
salts, and alkali metal salts, such as sodium salts and potassium salts. 
Typical examples thereof include sodium dioctylsulfosuccinate, ammonium 
dioctylsulfosuccinate, and sodium dibutylsulfosuccinate. 
(e) Alkyldiphenylether disulfonic acids or salts thereof, of which the 
alkyl group has 8 to 18 carbon atoms, and wherein the salts are 
exemplified by ammonium salts, or alkali metal salts or alkaline earth 
metal salts, such as sodium salts, potassium salts, magnesium salts, and 
calcium salts. 
(f) Rosins or salts thereof, wherein the salts are exemplified by ammonium 
salts, and alkali metal salts, such as sodium salts and potassium salts. 
Examples thereof include mixed tall acids comprising a tall rosin and a 
higher fatty acid, and salts thereof. 
(g) Alkanefatty acids or alkenefatty acids each having 4 to 18 carbon 
atoms, or salts thereof, wherein the salts are exemplified by ammonium 
salts, and alkali metal salts, such as sodium salts and potassium salts. 
(h) .alpha.-Sulfofatty ester salts of which the alkyl group has 4 to 22 
carbon atoms and derivatives thereof, wherein the salts are exemplified by 
ammonium salts, or alkali metal salts or alkaline earth metal salts, such 
as sodium salts, potassium salts, and magnesium salts. 
Among the anionic surfactants listed above, a preference is given to the 
lignin sulfonates, the formalin condensates of lignin sulfonic acid and 
the formalin condensates of naphthalenesulfonic acid or salts thereof, and 
the formalin condensates of naphthalenesulfonates because they show 
overall superior performance in charging the particles. 
The weight ratio of the ionic dispersants to the nonionic surfactants used 
in step (i) is preferably from 10/90 to 40/60 in the superheavy oil 
emulsion fuel obtained in step (ii). 
The amount of the ionic dispersants in the present invention are so 
adjusted that the amount thereof makes up from 0.01 to 0.5% by weight, 
preferably 0.02 to 0.2% by weight of the emulsion fuel obtained in step 
(ii). The ionic dispersant may be added as it is, or as an aqueous 
solution. 
In addition, cationic surfactants, nonionic surfactants, thickening agents, 
and the stabilizers, namely polymeric compounds or water-swellable clay 
minerals usable in step (i), may be added as long as added in an amount 
expressed by weight ratio to the anionic dispersants, is preferably within 
the range of from 1/100 to 1/5. 
In step (ii), the agitation while adding to and blending at least one of 
water and ionic dispersants with the emulsion fuel obtained in step (i) is 
carried out with a generally employed agitator, such as propeller 
agitators. In step (ii), subsequent to the preparation of the liquid 
mixture, the resulting liquid mixture is agitated with a sheer rate of 
from 10/sec to 10000/sec, preferably from 100/sec to 6000/sec. The shear 
rate is preferably 10000/sec or less from the viewpoint of significantly 
reducing the effects to the oil droplet particles of the emulsion fuel 
obtained in step (ii), thereby making it possible to maintain good 
long-term storage stability of the resulting emulsion fuel. 
The resulting emulsion fuel obtained in step (ii) comprising the 
oil-in-water (O/W) droplets has a superheavy oil concentration of from 68 
to 79% by weight, preferably from 75 to 79% by weight, and a viscosity at 
25.degree. C. is preferably from 200 to 1500 c.p., more preferably from 
300 to 600 c.p. When optionally using water, the concentration of the 
superheavy oil in the emulsion fuel obtainable in step (ii) is lowered 
from that in the emulsion fuel obtainable in step (i) preferably by 1 to 
6% by weight. Also, the emulsion fuel obtained in step (ii) comprises the 
oil-in-water (O/W) droplets having a particle size distribution of which a 
50%-cumulative particle size is preferably from 8 to 30 .mu.m, more 
preferably from 10 to 20 .mu.m, still more preferably from 12 to 16 .mu.m, 
and coarse particles having particle sizes of 150 .mu.m or more occupy 
preferably 3% by weight or less, more preferably 2% by weight or less, 
still more preferably 1% by weight or less, in the entire oil droplets, 
which is usable as fuels for thermoelectric power generation. 
The superheavy oil emulsion fuel obtainable by the method of the present 
invention having a high superheavy oil concentration has a small amount of 
coarse particles and good flowability, and also has good long-term storage 
stability, so that its handling is made easy, thereby making it highly 
valuable when used as fuels.