RESEARCH REPORT
PREPARATION AND FIRING OF EMULSIONS OF
NO. 2 FUEL OIL AND WATER
Contract No. 86-68-84
Task Order No. 8
to
NATIONAL AIR POLLUTION CONTROL
ADMINISTRATION
Process Control Engineering Program
November 1, 1968
BATTELLE MEMORIAL INSTITUTE
COLUMBUS LABORATORIES
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SUMMARY REPORT
on
PREPARATION AND FIRING OF EMULSIONS OF
NO. 2 FUEL OIL AND WATER
Contract No. 86-68-84
Task Order No. 8
to
NATIONAL AIR POLLUTION CONTROL
ADMINISTRATION
Process Control Engineering Program
November 1, 1968
by
R. E. Barrett, J. W. Moody, and D. W. Locklin
I Property Of
i EPA Library
(HTTP WC 277111!
BATTELLE MEMORIAL INSTITUTE
Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
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ABSTRACT
This task report describes the development of techniques
for the preparation of emulsions of No. 2 fuel oil and water. The
resulting emulsions are suitable for firing in the experimental rig
being used by NAPCA to investigate factors influencing emissions
from domestic oil-heating equipment.
The wide range of available emulsifying agents was screened
to a workable number by using the HLB concept. A blend of two
commercially available emulsifying agents was identified as satis-
factory for preparing water-in-oil emulsions that contained up to
53 percent water and were stable over a 10-week period.
Atomization of the emulsions by a high-pressure nozzle
produced sprays having droplet size distributions similar to those
for No. 2 fuel oil. Emulsions containing 5, 10, 19, 29, and 53 per-
cent water were fired successfully in a conventional gun-type
burner without modification.
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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Memorial Institute - COLUMBUS LABORATORIES
505 KING AVENUE COLUMBUS, OHIO 432OI • AREA CODE 614, TELEPHONE 299-3151 • CABLE ADDRESS: BATMIN
National Air Pollution Control Administration
3914 Virginia Avenue
Cincinnati, Ohio 45226
Attention Mr. John H. Wasser, Project Officer
Process Control Engineering Program
November 1, 1968
Gentlemen:
Contract PH 86-68-84
Task Order No. 8
We have completed our assignment under the subject task order
and hereby enclose our summary report "Preparation and Firing of Emulsions
of No. 2 Fuel Oil and Water".
The report outlines the procedure developed for preparation of
fuel oil-water emulsions containing up to 50 percent water. Combustion
trials confirmed that these emulsions can be successfully fired with the
conventional gun-type oil burner now used in your NAPCA test rig.
If you have any questions, we would be pleased to discuss any
of the points in greater detail.
Sincerely,
David W. Locklin
Associate Chief
Thermal Systems Division
DWL:j c
Enc. 20
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TABLE OF CONTENTS
INTRODUCTION 1
TASK OBJECTIVE 2
SUMMARY AND CONCLUSIONS 2
HISTORICAL BACKGROUND 3
Preparation of Emulsified Fuels 3
Burning of Emulsified Fuels 4
EXPERIMENTAL PROCEDURES AND RESULTS 6
Preparation of Emulsified Fuels 6
Determination of Required HLB 6
Screening of Emulsifiers ..... 9
Preparation of Stable w/o Emulsions
for Combustion Trials 12
Burning of Emulsified Fuels 13
Description of Burner 13
Effect of the Emulsion on Atomization 14
Combustion Trials. . 20
COMMENTS 25
Practical Considerations in Utilizing Emulsified Fuels. ... 26
Logistics 26
Potential Problems 27
Other Considerations 27
Thermal Effects of Emulsions 28
Flame Temperature 28
NO Formation 30
X
Flue Gas Loss 30
ACKNOWLEDGMENTS 32
REFERENCES 33
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PREPARATION AND FIRING OF EMULSIONS OF
NO- 2 FUEL OIL AND WATER
by
R. E. Barrett, J. W. Moody, and D. W. Locklln
The Process Control Engineering Program of the National Air
Pollution Control Administration is presently evaluating methods of
reducing air-pollutant emissions from combustion devices, including
domestic oil burners for space heating. As a part of this program, NAPCA
is conducting tests in a furnace which utilizes a 1-gph high-pressure
(7 8^
atomizing burner firing commercial No. 2 fuel oil. ' These tests will
determine the extent to which air pollutants can be reduced by using
various fuel additives in domestic-size oil-heating units.
NAPCA became interested in evaluating emulsified oil-water
fuels as a result of reported improved combustion (evidenced by shorter
combustion times) by others using these fuels. The concept of firing fuel
oil-water emulsions to obtain secondary atomization and, therefore, improve
(9)
combustion was advanced by Ivanov, and others , in 1957, and further
discussed by Ivanov and Nefedov in a 1962 paper. In the desired type
of oil-water emulsion, each fuel oil droplet contains one or more small
droplets of water. As the emulsion is sprayed into the combustion chamber,
the water within the fuel droplet vaporizes before the fuel is consumed.
The pressure generated within the fuel droplet by the vaporizing water
is sufficient to rupture the fuel droplet in a miniature explosion. This
shattering or secondary atomization of the fuel droplet causes further
reduction in the fuel droplet size and exposes a greater surface area of
fuel for vaporization, mixing, and burning, thus providing more rapid and
improved combustion.
TASK OBJECTIVE
Battelle's assignment under this task order was to develop
techniques for preparing emulsions containing up to 50 percent water in
distillate fuel oil, and to develop a technique for firing the emulsions
in the NAPCA experimental rig.
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SUMMARY AND CONCLUSIONS
The objective of this task was accomplished. Relatively stable
emulsions containing 5 to 53 percent water were produced in quantities of
1/2 to 2 gallons from commercial No. 2 fuel oil, distilled water, and
commercial emulsifying agents. Satisfactory firing of these emulsions
was accomplished in a laboratory combustion chamber with a burner identical
to the burner used in NAPCA tests.
Stable water-in-oil emulsions were prepared by using a blend of
4 parts sorbitan sesquioleate and 1 part polyoxyethylene (20) sorbitan
monopalmitate. The emulsions were prepared by dissolving the surfactant
in commercial No. 2 fuel oil. Deionized water was added in one step and
the mixture was stirred for two minutes in a Waring blender. At higher
water contents, the procedures produced oil-in-water emulsions.
It should be pointed out that this task was not intended to
produce the "optimum" oil-water emulsion. It is likely that a more stable
emulsion and better control of particle size could be achieved by modifi-
cation of the surfactant blend and further development of the mixing
I
procedures.
Droplet size measurements were made on sprays of water-in-oil
emulsions containing up to 53 percent water by weight. The amount of
water added had little effect on droplet size.
Emulsions containing up to 53 percent water were fired in a
furnace similar to the NAPCA furnace. Combustion appeared generally as
good as when firing commercial fuel oil, although a perceptable change
in the flame was observed when switching from firing emulsions on to
firing fuel oil.
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Combustion measurements were made on emulsions containing up to
29 percent water. The relationship of smoke and 0 in the flue gas did
not show any significant difference when firing fuel oil and emulsions
at 1.0 gph. When firing at 1.25 gph, emulsified fuels required greater
excess air to reduce smoke to acceptable values.
HISTORICAL BACKGROUND
The background in the literature will be discussed in two parts,
pertaining (1) to the preparation of emulsified fuel, and (2) to their
combustion.
Preparation of Emulsified Fuels
The formulation of a stable emulsion is as much an art as it
is a science. Each system presents its own unique problem. The solution
involves the selection of a surfactant and the proper means of mixing the
components. Historically, the problem was solved empirically through
trial and error. At present, however, there are available thousands of
surfactants which can be used as emulsifying agents, and some means of
simplifying the selection is required.
A review of the literature was of but little help in the present
(a)
case. Recently, oil-in-water emulsions (o/w) of JP-4 fuel and water
have been developed to minimize the fire hazard, associated with jet air-
craft fuel . However, there has been little published on emulsions
of water as the internal phase in hydrocarbon fuels. The most pertinent
references are the studies of Ford and Furmidge on the stabilization
(a) o/w: an emulsion of discrete oil droplets in a continuous phase
of water
w/o: an emulsion of discrete water droplets in a continuous
phase of oil
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of water-in-oil emulsions using oil-soluble emulsifiers. These authors
conclude that such emulsifiers must be hydrophobic
must possess the correct hydrophilic-fipophilic
particular oil concerned.
in character and
balance (HLB) for the
The hydrophilic-lipophilic balance (HLB) is a concept introduced
(2)
by Griffin as a means of characterizing emulsifiers. The HLB expresses,
numerically, the balance between the lipophilic and hydrophilic portion
of a surfactant molecule. The HLB is a measure of the relative solubility
of the surfactant in oil and water.
The HLB concept was developed into a systematic scheme for
(3)
emulsifier selection by Atlas Chemical Industries, Inc. The scheme
involves, first, finding the required HLB for the desired emulsion then,
second, screening only those surfactants having the required HLB. This
is the technique used in this study to select an emulsifier to produce
stable w/o distillate fuel oilrwater emulsions.
Burning of JSmulsified Fuels
The literature search relative to producing and burning emulsions
consisted of:
1. Discussions with Battelle staff members having
experience relating to the subject.
2. A survey of FACTS ("Fuel Abstracts and Current
Titles") for the years 1955 to 1968.
3. A machine search of Defense Department AD
reports by the Defense Documentation Center.
4. A machine search of NASA literature.
(b) hydrophobic: tendency not to be soluble in water
(c) hydrophilic: high tendency to be soluble in water
(d) lipophilic: high tendency to be soluble in oil.
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In addition, the Air Pollution Technical Information Center was contacted,
but no specific references were identified by the Center.
The machine literature searches revealed few references con-
sidered pertinent. In fact, most references uncovered in the search of
Defense Department literature pertained to separation of water from fuel.
A search of recent issues of FACTS also produced references primarily
related to removing water from oil.
Discussions with Battelle staff members resulted in the identi-
fication of a number of references relating to producing and burning o/w
emulsified fuels. These emulsions are intended as safer fuels for air-
craft, especially helicopters. Although this literature was not especially
pertinent or helpful for the present study, some of the material relating
to corrosion problems may be useful if emulsified fuels become widely
used. Therefore, references are given in the bibliography for some of
(13-28)
these reports and papers
Three papers appeared to be especially pertinent to the subject
of burning water in oil emulsions:
(9)
j.. The primary interest of the paper by Ivanov, et al., is
preparation and burning of heavy or residual oils. They prepared w/o
emulsions from several heavy oils and tars. Water droplet size was 2 to
8 microns. Experimental results include a description of the process
occurring when a droplet of fuel or emulsion was injected into stationary
air within a heated, closed-end tube. When a droplet of kerosine was
injected into the heated air at 1300 F, there appeared to be evaporation
of the liquid fuel followed by ignition and combustion of the vapors.
However, when a droplet of water-in-oil emulsion (3 percent water in
kerosine) was injected into heated air at 1150 F, the drop appeared to
boil and break into fine particles before vaporizing and burning. Experi-
ments with residual oil-water and tar-water emulsions produced similar
results.
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2. The paper by Ivanov and Nefedov discusses combustion of
individual 800 to 3000 micron drops of water-in-kerosine and water-in
residual oil emulsions containing 20-40 percent water. Diameters of the
water droplets were 10-50 microns. The authors reported boiling of the emul-
sion droplet followed by a "microexplosion" of the drop due to.pressure from
the boiling water. This microexplosion, or secondary atomization, appeared
to reduce combustion times for the fuel droplets by 20 to 40 percent.
The authors also reported that the emulsified fuels appeared to exhibit
the same combustion improvements in practical furnaces as in the laboratory.
_3. A paper, by Ludera , deals primarily with the viscosity
reduction of water-in-oil emulsions when compared to the straight fuels.
Reduction in viscosity appeared significant.
EXPERIMENTAL PROCEDURES AND RESULTS
The experimental portion of this study consisted of two parts:
(1) determining procedures for making emulsified fuels and making suf-
ficient quantities for combustion trials, and (2) firing the emulsions in
a combustion chamber similar to that employed by NAPCA.
Although the scope of the task order for this project included
both distillate and residual fuels, experimental trials were limited to
distillate fuel emulsions.
Preparation of Emulsified Fuels
Determination of Required HLB
A kit* of surfactants of known HLB values ranging from 2 to 20
was used to determine the required HLB for the w/o emulsion desired.
* Atlas Chemical Industries, Inc.
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One cc of the surfactant was dissolved in 200 cc of No. 2 fuel oil. Ten cc
of deionized water was added in one step. The materials were then stirred
for one minute on the Waring blender. The emulsions were then poured
into 8 oz. narrow-mouth bottles and were allowed to stand.
Table 1 is a summary of the results obtained. The most stable
emulsions were obtained with surfactants of HLB values of 4 and 6. In
this series of tests the surfactants were used in concentrations of less
than 1 weight percent.
TABLE 1. DETERMINATION OF REQUIRED HLB
Test HLB
Number Value Results and Observations
1 2 Emulsion milky and opaque-
immediate separation
2 4 Emulsion milky and opaque-
separation within 1/2 hour
3 6 Emulsion milky and opaque-
partial separation within 1 hour
4 8 Emulsion milky and opaque-
immediate separation
5 10 Emulsion milky and opaque-
immediate separation
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Table 2 summarizes the results of another series of tests using
increased amounts of the surfactants. As before, the surfactants were
dissolved in 200 cc of No. 2 fuel oil; 10 cc of deionized water was added
and the mixture was stirred for one minute in the Waring blender. Again,
the most stable emulsions were obtained with a surfactant of HLB 6.
The results indicate that, for the particular surfactants and
fuel oil used, the optimum surfactant concentration was 2-3 weight percent.
For other surfactants and fuel oils, the optimum concentration would
probably vary.
The HLB value and surfactant concentrations determined in these
(4 5)
tests are consistent with the behavior reported for other w/o emulsions ' .
TABLE 2. EFFECT OF SURFACTANT CONCENTRATION ON
STABILITY OF EMULSION
Test
Number
1A
2A
3A
HLB
Value
2
4
6
Volume of
Surfactant
(cc)
5
5
5
Results and Observations
Emulsion separates immediately
Emulsion separates overnight
Stable emulsion but tends to
3C
4C
separate in time
Stable emulsion - tends to cream
in time - does not break
Emulsion separates immediately
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Screening of Emulsiflers
Having determined the required HLB, a number of commercially
available surfactants were screened. Those surfactants having HLB values
of about 4-6 were selected for these tests. However, in many cases the
HLB value of the candidate surfactants were not known. To calculate or
measure the HLB value of these surfactants was beyond the scope of this
program. Therefore, when the HLB value of a surfactant was not readily
available, McCuteheon's description of the surfactant and its uses
served as a basis for inclusion in the screening test. The HLB factor of
a surfactant blend is equal to the weighted average HLB of the ingredients.
Therefore, any desired HLB may be obtained by blending compatible sur-
factants in the proper ratio.
Because the emulsions were to be used as fuel, prime consideration
was given to those surfactants which would yield no residue or undesirable
product when burnt. Thus, surfactants such as the metallic soaps and
sulfur-containing compounds were not used in these tests.
The emulsions were prepared by dissolving the candidate sur-
factant in No. 2 fuel oil. Deionized water was added in one step and the
mixture was stirred for 2 minutes on the Waring blender. About 200 cc
of emulsion was prepared. The emulsions were stored in 8 oz narrow-mouth
bottles.
Table 3 is a summary of the surfactants tested and the results
obtained. The emulsions rated moderately stable tended to break or
separate after several days standing. The stable emulsions did not break
during a 10-week period. However, these emulsions did tend to "cream";
that is, the dense phase tended to settle to the bottom of the container.
These emulsions could be re-homogenized readily by shaking.
Moderately stable emulsions were obtained by use of sorbitan
sesquioleate (Arlacel C) and a modified phthalic glycerol alky.1 resin
(Triton B-1956).
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TABLE 3. SCREENING OF COMMERCIAL SURFACTANTS
Formula
Number
6
7
TA
8
&
9
Surfactant
Trade Name
Span 60
Arlacel C
Arlacel C
Triton B-1956
Triton B-1956
Dispersant NI-0
Chemical Name
Sorbitan monostearate
Sorbitan sesquioleate
Sorbitan sesquloleate
Modified phthalic
glycerol alkyl resin
Modified phthalic
glycerol alkyl realn
Condensation product of
Evulsion Formula
Concentration, Weight Percent
HLB No. 2
Value Manufacturer Oil Water Surfactant
<».T (1)
3-5 (1)
3.5 (1)
<2)
(2)
(3)
93-2
93.2
92.3
93-2
91.8
93-2
5-6
5-6
5-5
5.6
5-5
5.6
1.2
1.2
2.2
1.2
2-7
1.2
Results
Breaks Immediately
Moderately stable
Moderately stable
Moderately stable
Moderately stable
Breaks iranediately
Wspersant NI-0
ethylene oxide and an
alkyl phenol
Condensation product of
ethylene oxide and an
alkyl phenol
(3)
91.8 5-5
2-7
Breaks Immediately
10
11 .
12
13*
13A*
Igepal CO-530
Mulsor Ho. 8
Igepal CO-1+30
k Arlacel C
1 Tweeu kO
k Arleeel C
1 Tween UO
Honylphenoxypoly
(ethyleneoxy) ethanol
Long chain fatty acid
eater of glycols
Nonylphenoxypoly
(ethyleneoxy) ethanol
Sorbitan sesquloleate ^'^Ifi
Polyoxyethylene (20) 15. 7j
sorbltan nonopalmitate
Sorbitsm sesquioleate ^'^Ifi
Polyoxyethylene (20) 15-7)
sorbltan monopalmicatc
w
(5)
CO
(1)
(1)
93-2 5-6
93-2 5-6
93-2 5-5
93-2 5-5
87.0 10. k
1.2 Breaks immediately
1.2 Breaks immediately
1.2 Breaks Immediately
1.2 Stable emulsion
2.6 Stable emulsion
* Note: The surfactants used in Formulas 13 and ISA consisted of a blend of 1* parts (by weight) Arlacel C and 1
part Tween kQ. The VI£ at the blend was 6.
List of Manufacturers
TilAtlas Chemical Industries, Inc.
(2) Kohra and Haas Co.
3) Oronite Division, California Cheadcal Co.
General Aniline and Film Corp.
Synthetic Chemicals, Inc.
\ j/
81
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The most stable emulsions were obtained by use of a blend of
sorbitan sesquioleate and polyoxyethylene (20) sorbitan monopalmitate
(Tween 40). In this case, 4 parts of sorbitan sesquioleate (HLB 3.5
molecular weight 560) was blended with 1 part polyoxyethylene (20)
sorbitan monopalmitate (HLB 15.7 molecular weight 1290) to give a sur-
factant blend of HLB about 6 -- the required HLB of the desired emulsion.
The molecular weight of the blend can be taken as 706 for the purposes of
calculation.
Three qualitative tests were used to determine the type of
emulsion (w/o or o/w) obtained.
First, the emulsions were examined under an ultra-violet lamp.
If oil was the continuous phase, the emulsion would fluoresce uniformly.
If water were the continuous phase, the fluorescence would be spotty.
Second, a small amount of a solid, oil-soluble dye was added to
a few cc of the emulsion. If oil were the continuous phase, the dye would
dissolve and the emulsion would be colored. These tests were checked by
adding a water-soluble dye to a second portion of the emulsion. If oil
were the continuous phase,the dye would not dissolve; however, if water
were the continuous phase, the dye would dissolve and the emulsion would
be colored.
Finally, the type emulsion was tested by carefully floating a
drop of oil or water on a few cc of the emulsion. If oil were the con-
tinuous phase, the oil drop would disperse but not the water drop. If
water were the continuous phase, only the water drop would disperse.
In every case these tests proved both the moderately stable and
stable emulsions included in Table 3 were water-in-oil (w/o) emulsions.
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Attempts were made to measure the droplet size of the internal
phase of the stable emulsions by optical microscopy. However, because of
rapid Brownian movement and the coalescence of droplets when the emulsion
was placed on the microscope slide, it was not possible to measure the
droplet size accurately. From the observations it is estimated that the
average water droplet size was about 1 micron in diameter.
Preparation of Stable w/o Emulsions
for Combustion Trials
A series of stable emulsions containing various amounts of water
was prepared for the combustion trials by using the surfactant blend
described in the previous section (4 parts Arlacel C to 1 part Tween 40).
As before, the emulsions were prepared by dissolving the surfactant in
No. 2 fuel oil. Deionized water was added in one step and the mixture
was stirred two minutes on the Waring blender. Samples for combustion
trials (1/2 to 2 gallon) were prepared in batches of 200-250 cc.
Table 4 summarizes the formulas of the stable emulsions. Stable
w/o emulsions containing up to 53 weight percent water in the internal
phase were prepared using the surfactant blend. The emulsion containing
about 68 weight percent water (Formula 13F) proved to be an o/w type
emulsion. (Samples of this emulsion were not prepared for combustion or
burner trials.) Thus, the distillate fuel oil-water emulsions prepared
by these procedures invert at water concentrates between 53 and 68 weight
percent.
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TABLE 4. FORMULAS FOR STABLE EMULSIONS
Concentration, Weight Percent
Formula
Number
13
13A
13B
13C
13D
13E
13F
No. 2
Fuel Oil**
93.2
87.0
78.9
72.1
69.0
44.5
28.7
Water
5.5
10.4
18.8
25.8
28.8
52.8
- 67.9
Surfactant*
1.2
2.6
2.3
2.1
2.2
2.7
3.4
Emulsion
Type
w/o
w/o
w/o
w/o
w/o
w/o
o/w
* Note: Surfactant consisted of 4 parts (by weight)of
sorbitan sesquioleate and 1 part polyoxyethylene
(20) sorbitan monopaImitate--average molecular
weight of 706.
** 36° API Gravity @ 60 F.
Burning of Emulsified Fuelg
Description of Burner
To test fire the emulsions and assure that satisfactory com-
bustion was attainable, a burner and combustion chamber rig was con-
structed as similar as practical to the NAPCA rig. Details of the NAPCA
rig were obtained from the description in the 1966 paper by Wasser,
Hangebrauck, and Schwartz and from discussions and observations during
a visit to the NAPCA lab by project personnel.
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(8)
Figure 1 shows the current version of the experimental
furnace used for the NAPCA trials. The combustion chamber of the NAPCA
furnace shown is 12 inches higher than described in the 1966 paper .
Figure 2 shows the combustion chamber constructed at Battelle
using K.-30 firebrick lined with Fiberfrax. It is identical in con-
figuration to the NAPCA furnace. -The heat-exchanger section of the
apparatus constructed at Battelle is somewhat simpler in design than
that of the NAPCA furnace. For conditions where relatively good combustion
is obtained, the design of the heat-exchanger section should not signifi-
cantly affect the flame.
The gun burners used in both furnaces are identical. These
burners were manufactured by the Automatic Burner Corporation and are
designated as ABC Model 55J1 oil burners having No. 8269, 2-1/4-inch
diameter chokes; No. 7397, 3-1/2-inch diameter solid B-type static-pres-
sure disks; 7-3/4 inch long air tubes; and R-818481188 primary air cans.
Delavan 1.00 and 1.25 GPH, 80-degree Type A pressure-atomizing nozzles
were used at a pressure of 100 psi. While this burner is not the most
recent ABC design available, it is essentially identical to the one
operated by NAPCA.
Effect of the Emulsion on Atomization
One of the most significant factors affecting the combustion of
any liquid fuel is the droplet size of the atomized fuel spray. Converting
commercial fuel oil into a w/o emulsion could be expected to alter the
fuel properties which affect droplet size, namely viscosity, density, and
surface tension. Therefore, it was considered important to measure the
droplet size of unburned sprays of the w/o emulsions. Examination of
these sprays could also show if the emulsion was breaking up during the
atomization process, a phenomena which occurs for many o/w emulsion fuels
considered for aircraft application.
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Exhaust
Sampling area
Cooling air
Heat exchanger
Combustion
chamber
Air
Fuel oil
FIGURE 1. NAPCA EXPERIMENTAL FURNACE*8)
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Exhaust
Cooling
water
cTl
60"
Cooled
stack
Combustion
" chamber
Refractory ,
2i", 3000F
painted with
fiberfrax
slurry
Sampling point
centerline
FIGURE 2. BATTELLE EXPERIMENTAL APPARATUS
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Cold-spray atomization studies were made by pumping the fuel
through the gun-burner nozzle and passing a magnesium-oxide-covered slide
through the spray. The burner ignition and control circuits were dis-
connected for these experiments. The slides were examined under a micro-
scope with a Filar micrometer eyepiece and the diameters of 200 craters
were measured. Droplet diameter was determined from the slide craters by
(4)
the following correlation : (droplet diameter) = 0.82 x (crater diameter).
Figures 3 and 4 show the results of these droplet-size measure-
ments for commercial No. 2 fuel oil and for oil-water emulsions containing
5, 10, 19, 29, and 53 percent water.
Table 5 lists number-mean diameters and calculated mass-mean
diameters (using an assumed normal distribution of particle sizes) for
each fuel. These droplet sizes are in general agreement with those reported
(12)
by Tate and Olson : 83 micron mass-mean diameter for 1-gph hollow cone
nozzles of typical commercial design and atomizing No. 2 fuel oil.
TABLE 5. DROPLET SPRAY SIZES
Test Run
A-l
A-2
A- 3
A-4
B-l
B-2
B-3
Fuel
No. 2 fueloil
Emulsion - 5% water
Emulsion - 10% water
Emulsion - 19% water
No. 2 fueloil
Emulsion - 29% water
Emulsion - 53% water
Number mean
diam. , microns
30
32
37.5
34
31
32
33
Mass mean
diam. , microns
58
.60
76
70
77
79
81
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18
.O
E
0)
<
19% w/o emulsion
10% w/o emulsion
20 40 60 80 100
Particle Diameter , microns
150 200
FIGURE 3. DROPLET SIZE DISTRIBUTIONS FOR FUEL OIL AND EMULSIONS
CONTAINING 5, 10, AND 19 PERCENT WATER-TEST, SERIES A
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29 % w/o emulsion
53% w/o emulsion
0.5
10
20 40 60 80 100
Particle Diameter, microns
150 200
FIGURE 4. DROPLET SIZE DISTRIBUTIONS FOR FUEL OIL AND EMULSIONS
CONTAINING 29 AND 53 PERCENT WATER, TEST SERIES B
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Examination of droplets collected on glass slides while spraying
a 10 percent water emulsion showed that the emulsion did not break up
during the spraying process and that each droplet of oil contained drop-
lets of water estimated to be about 2 microns in diameter.
Combustion Trials
Each emulsion was fired in the combustion chamber to determine
general combustion characteristics of these fuels. Observations were of
two types: (1) qualitative observations of the flames were made to
determine if combustion appeared to be satisfactory on a gross scale (for
emulsions up to 53 percent water) ; (2) quantitative measurements were made
of oxygen, combustibles, and smoke in the flue gas (for emulsions up to
29 percent water) .
0 and percent combustibles in the flue gas were measured with
a Bailey Heat Prover and smoke measurements were made with the motorized
Bacharach smoke meter Model No. RDC (see Figure 2 for location). Measure-
ments for all data points indicated that combustibles were below 1000 ppm,
the threshold of sensitivity for the Heat Prover.
Each oil-water emulsion appeared to burn with about the same
flame volume and color as No. 2 fuel oil. Although there was a perceptible
change in flame appearance when switching from commercial fuel oil to
emulsions and back to fuel oil, no gross change in flame volume or length
or flame characteristic was observed.
Table 6 and Figures 5, 6, and 7 summarize the combustion data.
Considerable scatter of data is noted. Individual points within a given
trial were fairly consistent; however, reproducibility between apparently
similar trials was lacking.
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TABLE 6. RESULTS OF
^
-i
PI
r
r
m
z
i
o
x
r
z
H
H
C
PI
1
O
O
r
c
x
o
c
M
r
0
o
a
o
5
m
Water in fuel,
Test
1
2
3
4
5
6
7
8
9
10
11
12
13
volume
percent
0
5
9
17
0
0
0
17
0
26
0
0
17
weight
percent
0
6
10
19
0
0
0
19
0
29
0
0
19
COMBUSTION TESTS FOR COMMERCIAL NO. 2
IN QZ Z -L£ JN £/SZr A ^
capacity,
gph
1
1
1
1
1
1
1
1
1
1
1
1
1
.00
.00
.00
.00
.00
.00
.25
.25
.25
.25
.00
.00
.00
pressure,
psi
100
100
100
100
100
100
100
103
102
102
100
100
100
FUEL OIL AND w/o EMULSIONS
Oxygen in flue gas
at No. 2 smoke,
percent
2
2
2
2
3
3
0
2
0
3
2
3
2
.3
.1
.1
.9
.8
.0
.9
.5
.9
.4
.4
.0
.4
Fuel temperature,
F
76-86
-
82-96
86-97
77-89
76-85
83-92
81-91
74-87
78-88
76-82
74-84
79-89
Firing rate.
Btu/hr
127
99
84
112
no
129
110
130
103
114
109
95
,000
-
,000
,000
,000
,000
,000
,000
,000
,000
,000
,000
,000
1-0
-------
22
10
8
o
CO
Range of Trials 1,6,11, and 12
X Trial I
O Trial 6
A Trial I I
D Trial 12
\
\
\
\
NAPCA
(8)
\
\
\
\
\
234
Oxygen in Flue Gas, percent
FIGURE 5. SMOKE FROM BURNING COMMERCIAL, NO. 2 FUEL OIL
AT 1. 00 GPH
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10
8
$ 6
10% w/o emulsion ,
Trial 3
19% w/o emulsion,
Trials 4 and 13
5 % w/o emulsion ,
Trial 2
0
1234
Oxygen in Flue Gas, percent
FIGURE 6. SMOKE FROM BURNING FUEL OIL EMULSIONS AT 1. 00 GPH
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8
No.2 fuel oil,
/Trials 7and 9
19% w/o emulsion,
Trial 8
29% w/o emulsion,
. Trial 10
2 3
Oxygen in Flue Gas , percent
4
FIGURE 7, SMOKE FROM BURNING NO. 2 FUEL OIL AND TWO
W/O EMULSIONS AT 1. 25 GPH
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For the 1-gph nozzle (Figures 5 and 6), the addition of water
up to 29 percent did not have a consistent effect on the smoke vs 0_
relationship, within the reproducibility of the data. For the 1.25 gph
nozzle, higher percentages of water required consistently higher excess
air for the same smoke level.
The performance characteristic reported for the NAPCA test
(8)
rig , also shown in Figure 5, suggests a significant difference in
combustion conditions for that rig. Residence time and air patterns in
the two rigs should be similar by design, so it is possible that the
different characteristic is due to differences in atomization, fuel
characteristics, or combustion-2one temperature.
COMMENTS
The incentive for investigating the firing of emulsified fuels
lies in the potential benefits of reducing emissions of gaseous pollutants.
It was recognized at the outset that the emulsified No. 2 oil might not show
any substantial improvement in smoke performance. Because commercial
No. 2 fuel oil readily atomizes into fine droplets, secondary atomization
is not essential to clean combustion when firing this fuel with a proper
burner, The concept may be more effective in reducing both smoke and
gaseous emissions when applied to residual fuels, where atomization and
burning is more difficult.
Practical Considerations in Utilizing Emulsified Fuels
A few of the practical considerations of using fuel oil-water
emulsions are discussed below.
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3800
3600
3400
3200
3OOO
o
IL.
_ 2800
o
s
2600
24OO
2200
2000
Excess air
0%
25%
50%
75%
100%
10 20 30 40
Water in Fuel Emulsion , weight percent
50
FIGURE 8. THEORETICAL FLAME TEMPERATURES
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Logistics
Several logistic schemes might be considered for producing
emulsified fuels for commercial use.
Fuel emulsions could be generated at the refinery as a final
step in producing the marketable fuel. The fuel would then be distributed,
stored, and fired as an emulsion. This would require stable emulsions and
would result in an increased transportation cost per Btu delivered, as
the water in the emulsion would be shipped with the fuel.
A reduction in the long-distance transportation cost could be
achieved by preparing the emulsions just prior to local delivery of the
fueli This would require each fuel distributor be equipped for producing
emulsions.
Another method of preparing emulsions would be to generate the
emulsion at the point of consumption, just prior to firing the fuel. If
the emulsifying agent were already in the fuel as an additive, only water
would need to be added at the furnace. This might require a special mixing
device, or the fuel pump might be used for the mixing. It is possible
that the emulsion might even be produced at the nozzle. Generating
emulsions at the burner was not attempted in this study as the object
was not to develop a practical commercial scheme but, rather, to accomplish
firing of emulsified fuels for experimental purposes.
Potential Problems
Several problems may be encountered if emulsified fuels are
introduced as commercial fuels. Potential problems due to the presence
of water in the fuel include corrosion of the fuel tank and parts of the
oil handling system and gum formation in the fuel during storage and
handling. It has been a practice to reduce the water content of fuels
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to the lowest reasonable level to prevent corrosion and sediment or gum
formation. Although water within an emulsified fuel may behave differently
than water contained in conventional fuels, there is no reason to believe
that these problems will not exist. In fact, some of the major problems
encountered in tests with fuel-in-water emulsion fuels for aircraft have
been corrosion and filter blockage.
Another problem in storing and transporting emulsified fuels
might be freezing of the water droplet in cold weather. Freezing may
cause breaking of the emulsion, blockage of fuel lines and filters, and
excessive wear on pumps and valves during handling.
Proper maintenance of blending equipment would be required to
prevent difficulties from scaling and corrosion of the metering system
for water and the emulsifying agent.
The addition of water would increase the dew point of the flue
gas, so that greater consideration should be given to condensation problems,
Other Considerations
If the use of emulsified fuels becomes commercially feasible,
several details would need to be examined more thoroughly. These include:
(1) Is water quality critical? For example, is
distilled water required to prevent corrosion
and deposits in the nozzle and/or heat exchanger?
(2) Will the emulsifying agents cause corrosion
and/or deposits within the fuel handling or
firing system?
(3) Which of the many emulsifying agents available
should be used to produce emulsions with the
necessary long-term stability?
?
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(4) Will emulsifying of fuels add significantly
to total cost of operation?
Thermal Effects of Emulsions
Flame Temperature
Adding any material that is not a fuel to a combustion process
will lower the theoretical flame temperature due to the expenditure of
energy to heat the extra material up to the flame temperature. Therefore,
adding water to a combustion process by firing a fuel oil-water emulsion
suppresses peak flame temperatures. Because the mass of water added to
the fuel is small compared to the mass of the air required to burn the
fuel, the effect of the water in suppressing flame temperatures is less
than might be anticipated.
Figure 8 shows calculated theoretical flame temperatures for
combustion, in an adiabatic system, of fuel oil and fuel oil-water emulsions
containing up to 50 percent water. The range of the fuel-air ratio in
Figure 8 is zero to 100 percent excess air. Actual peak flame temperatures
in a real combustion device would be lower due to heat transfer from the
gas to the walls of the device during the combustion process.
•
Adding 50 percent water to the fuel reduces theoretical flame
temperatures by 260 F at zero excess air, 245 F at 25 percent excess air,
190 F at 50 percent excess air, 150 F at 75 percent excess air, and
120 F at 100 percent excess air. It can be seen from Figure 8 that in-
creasing excess air by about 15 percent reduces flame temperatures more
than adding sufficient water to the fuel to produce an emulsion containing
50 percent water.
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NO Formation
x
One potential benefit of any reduction in flame temperature is
a reduction in NO emissions. There is evidence that NO formation
x x
within combustion systems is more closely related to peak flame temperatures
than any other single variable.
Figure 9 shows the theoretically predicted nitrogen oxides
concentration at the peak flame temperature for combustion of fuel oil and
fuel oil-water emulsions. The model used for these calculations assumes
chemical equilibrium concentrations of all species included in the analysis
at the peak flame temperature. Reaction kinetics, or the time required
to achieve equilibrium conditions are ignored and, therefore, these results
can only serve as a guideline as to the general effect of water in the
fuel on nitrogen oxide emissions. Actual nitrogen oxide emissions would
be significantly below these calculated values.
FlueGas Loss
Assuming that the flue-gas temperature remains constant, the
addition of inert material, such as water, to fuel will tend to lower
the thermal efficiency of a combustion system. This occurs as a result
of the energy carried out in the flue gas by the additional inert
material. Moreover, the water will reduce the heating value of the fuel
by the amount of energy necessary to vaporize the water.
Although the addition of large quantities of water to the fuel
(up to 50 percent water) would be expected to significantly increase
flue-gas loss, the effect is not marked. This occurs because, even at
stoichiometric conditions, at least 14 times as much mass enters the
combustion system as air than as fuel. Adding 50 percent water to the
fuel only increases the total mass by 1 part in 30 or about 3 percent.
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4400
4000
3600
E
o.
a.
3200
2800
o
£ 2400
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32
Figure 10 shows calculated flue-gas loss as a percent of heating
value for fuel oil and fuel oil-water emulsions containing up to 50 per-
cent water at flue gas temperatures of 200 F, 500 F, and 800 F. It can
be seen that adding 50 percent water to the fuel increases the flue-gas
loss by less than 4 percent at flue-gas temperatures of 800 F, by about
2 percent at 500 F, and by less than 1 percent at 200 F.
Since the sacrifice in overall efficiency is relatively minor
it appears that, if firing fuel oil-water emulsions will significantly
reduce air pollutant emissions, the loss in efficiency would not be a
deterrent to the use of this technique.
ACKNOWLEDGMENTS
Contributions of the following Battelle staff members are
acknowledged: John F. Foster in formulating emulsions, Dr. James A. Gieseke
in measuring droplet sizes, Dr. William E. Wilson in calculating flame
temperatures and NO concentrations, and James J. Tabor in conducting the
X
laboratory trials.
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40
32
28
c 24
CL
Cft
(A
3
20
16
12
8
Excess air Exhaust temperature
100%
50%
0%
100 %
800 F
800 F
500 F
10 20 30 40 50
Water in Fuel Emulsion, weight percent
FIGURE 10. FLUE GAS LOSSES FOR COMBUSTION OF FUEL OIL AND FUEL
OIL-WATER EMULSIONS AT 0, 50, AND 100 PERCENT
EXCESS AIR
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REFERENCES
Preparation of (w/o) Emulsified Fuels
1. Ford, R. E., and Furmidge, C.G.L ./'Studies at Phase Interfaces, II.
The Stabilization of Water-in-Oil Emulsions Using Oil Soluble
Emulsifiers", J. Colloid and Interface Science, Vol. 22, 1966, p 331.
2. Gr.iff,in, W. C. /'Classification of Surface-Active Agents by HLB",
J. Soc. Cosmetic Chemists, Vol. 1, 1949, p. 311.
3. Atlas Chemical Industries, "The Atlas HLB System", 2nd Ed,, Wilmington,
Del., 1963.
4. Bennett, H., Bishop, J.L., and Wulfinghoff, ML. «, Practical Emulsions,
Vol. 1, Chemical Publishing Co., Inc., New \ork,1968.
5. Becker, P., Emulsions, Theory and Practice, 2nd Ed., Reinhold
Publishing Corp., New York, 1965.
6. McCuteheon, J.tW.., Detergents and Emulsif iers, 1964 Annual,
J. W. McCuteheon, Inc., Morristown, N.H., 1964.
Burning of (w/o) Emulsified Fuels
7. Wasser, J. H., Hangebrauck, R. P., and Schwartz, A. J., "Effects of
Air-Fuel Stoichiotnetry on Air Pollutant Emissions from an Oil-Fired
Test Furnace", Jour. Air Pollution Control Assoc., Vol. 18, No. 5,
May 1968, pp. 332-337.
8. Wasser, J. H., Martin, G. B., and Hangebrauck, R. P., "Effects of
Combustion Gas Residence Time on Air Pollutant Emissions From an
Oil-Fired Test Furnace," presented at NOFI Workshop, Linden, N.J.,
Sept. 17 & 18, 1968, 19 pp.
9. Ivanov, V. M., Kantorovich, B. V., Rapiovets, L. S., and Khotuntsev,
L. L. , "Fuel Emulsions for Combustion and Gasification", Jour. Acad.
Sci. U.S.S.R., May 1957, pp. 56-59.
10. Ivanov, V. M., and Nefedov, P. I., "Experimental Investigation of the
Combustion Process on Natural and Emulsified Fuels", NASA Tech.
Transl. TT F-258, January 1965, 23 pp.
11. Ludera, L.., "Water Emulsions of Boiler Fuel Oils and Possibilities
of Using Them as Liquid Fuels", Gospodarka Paliwami i Energia,
Vol. 1, 1965, pp. 5-9.
12. Tate, R. W., and Olson, E. 0., "Spray Droplet Size of Pressure-
Atomizing Burner Nozzles", ASHRAE Journal, Vol. 4, No. 3, March 1962,
pp. 39-43.
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REFERENCES (Continued)
Preparation and Burning of (o/w) Emulsified Fuels
13. Nixon, J., Wallace, T. J., and Beerbower, A., "Emulsified Fuel for
Military Aircraft", ASME Paper No. 68-GT-24, Presented at ASME Gas
Turbine Conference, Washington, D.C., March 17-21, 1968, 13 pp.
14. Harris, J. C., and Steinmetz, E. A., "Emulsified Gas Turbine Fuel",
ASME Paper No. 68-GT-17, Presented at ASME Gas Turbine Conference,
Washington, D.C., March 17-21, 1968, 5 pp.
15. McCourt, E. P., "Developments in the U.S. Army Emulsified Fuels
Program", AIAA Paper 68-558, Presented at AIAA Fourth Propulsion
Joint Specialist Conference, Cleveland, Ohio, June 10-14, 1968,
6 pp.
16. Nixon, J., Beerbower, A., Philippoff, W., Lorenz, P. A., and
Wallace, T. J., "Investigation and Analysis of Aircraft Fuel
Emulsions", USAAVLABS Technical Report 67-62, Nov., 1967, 134 pp.
17. Stockton, W. W., and Olsen, C. L., "Feasibility of Burning Emulsified
Fuel in a 71M100 Engine", USAAVLABS Technical Report 67-74, Feb.,
1968, 60 pp.
18. Custard, G. H., "Vulnerability Evaluation of Emulsified Fuels for
Use in Army Aircraft", USAAVLABS Technical Report 68-20, April,
1968, 151 pp.
19. Harris, J. C., and Steinmetz, E. A., "Investigation and Analysis of
Aircraft Fuel Emulsions", USAAVLABS Technical Report 67-70, Dec.,
1967, 180 pp.
20. "Investigation of a Feasibility of Burning Emulsified Fuel in Gas-
Turbine Engines", USAAVLABS Technical Report 67-24, March, 1967,
196 pp.
21. Roberts, R. A., "Evaluation of EF4-104 Emulsified Fuel in a Pratt
and Whitney Aircraft JT12 Engine", Presented at ASME Gas Turbine
Conference, Washington, D.C., March 17-21, 1968, 26 pp.
22. Beerbower, A., Nixon, J., Philippoff, W., and Wallace, T. J.,
"Thickened Fuels for Aircraft Safety", SAE Paper No. 670364,
Presented at National Aeronatuic Meeting, New York, April 24-27,
1967, 9 pp.
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REFERENCES (Continued)
23. Crawford, W. J. , III, "Operation of the GE T64 on Emulsified Fuel",
SAE Paper No. 670369, Presented at National Aeronautic Meeting,
New York, April 24-27, 1967, 14 pp.
25. Lucas, J, R., "A Preliminary Evaluation of an Emulsified Fuel Mixture
in the Model T63 Turbine Engine", SAE Paper No. 670368, Presented at
National Aeronautic Meeting, New York, April 24-27, 1967, 12 pp.
26. Opdyke, G., Jr., "Initial Experience with Emulsified Fuels at AVCO
Lycoming", SAE Paper No. 270366, Presented at National Aeronautic
Meeting, New York, April 24-27, 1967, 9 pp.
27. Harris, J. C., and Steinmetz, E. A., "Emulsified Jet Engine Fuel",
SAE Paper No. 270365, Presented at National Aeronautic Meeting,
New York, April 24-27, 1967, 8 pp.
28. Lissant, K. J.5 Hopper, L. R., and Harris, J. L., "HIPR Fuel Emulsion-
Preliminary Pumping Studies," source unknown, 16 pp.
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