RESEARCH REPORT
RESIDUAL FUEL OIL-WATER EMULSIONS
Contract No. PH 86-68-84
Task Order No. 16
to
NATIONAL AIR POLLUTION CONTROL
ADMINISTRATION
Division of Process Control Engineering
January 12, 1970
BATTELLE MEMORIAL INSTITUTE
COLUMBUS LABORATORIES
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SUMMARY REPORT
on
RESIDUAL FUEL OIL-WATER EMULSIONS
Contract No. PH 86-68-84
Task Order No. 16
to
NATIONAL AIR POLLUTION CONTROL
ADMINISTRATION
Division of Process Control Engineering
January 12, 1970
by
R. E. Barrett, J. W. Moody, H. R. Hazard,
A. A. Putnam, and D. W. Locklin
BATTELLE MEMORIAL INSTITUTE
Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
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A B STRACT
This task report describes the development of
techniques for the preparation of emulsions of No. 6 residual
fuel oil and water. It also includes the preliminary design
of a combustion test rig for studying the combustion of heavy
oils and emulsions and pollutant emission produced by burning
these fuels.
Stable emulsions containing up to 30 percent water;
by weight, were prepared from 9 samples of residual fuel oils.
No emulsifying agents were required as the oils apparently
contained natural emulsifiers. Emulsions containing basic
additives were also prepared. The emulsions did not appear
to break during atomization.
The preliminary design of the combustion test rig
showed that a rig could be constructed to operate with either
combustion intensity or pressure drop comparable to that of
a full-scale unit. This can be accomplished by varying the
firing rate from 1.5 gph for constant combustion intensity
firing to about 8.0 gph for constant pressure drop firing.
A variable swirl-type burner was designed to provide the
flexibility needed for this range of combustion conditions.
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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> Memorial Institute • COLUMBUS LABORATORIES
505 KING AVENUE COLUMBUS, OHIO 43201 • AREA CODE 614, TELEPHONE 299-3151 • CABLE ADDRESS: BATMIN
January 12, 1970
National Air Pollution Control Administration
3914 Virginia Avenue
Cincinnati, Ohio 45226
Attention Mr. John H. Wasser, Project Officer
Division of Process Control Engineering
Contract No. PH 86-68-84
Task Order No. 16
Gentlemen:
We have completed our assignment under the subject
task order and hereby enclose 20 copies of our summary report,
"Residual Fuel Oil-Water Emulsions".
The report outlines the procedure developed for
preparation of residual fuel oil-water emulsions and contains
data on certain important properties (particularly viscosity)
of the emulsions. Modeling criteria for simulating industrial
combustion systems on a laboratory scale are discussed, and a
preliminary design of a residual fuel-oil combustion test rig
is presented.
If you have any questions, we would be pleased to
discuss any of the points in greater detail.
Sincerely,
D. W. Locklin
Associate Chief
Thermal Systems Division
DWL:jc
Enc. (20)
cc: Mr. R. P. Hangebrauck
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TABLE OF CONTENTS
Page
INTRODUCTION 1
TASK OBJECTIVE 1
SUMMARY AND CONCLUSIONS 2
BACKGROUND 3
CHARACTERISTICS OF RESIDUAL FUEL OILS 4
Bureau of Mines Survey of Burner Fuel Oils, 1968 10
Residual Fuel Samples Obtained For This Study 17
EXPERIMENTAL PROCEDURES AND RESULTS 17
. Preparation of Water-in-Oil Emulsions 17
Identification of Emulsion Type 22
Incorporation of Basic Additives in
Water-in-Residual Oil Emulsions 22
Properties of Water-in-Residual Fuel Oil Emulsions 24
Static Viscosity Measurements 24
Dynamic Viscosity Measurement 26
Viscosities of Emulsions Compared to Base Fuels 30
Flow Instabilities Observed in Emulsions 30
Thermal Stability Tests 37
Atomization Trials 37
PRACTICAL CONSIDERATIONS IN UTILIZING EMULSIFIED FUELS 39
Pumping and Atomization 39
Effect on Corrosion and Deposits of Basic
Materials in Fuel Oil-Water Emulsions 43
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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TABLE OF CONTENTS (Continued)
Page
PRELIMINARY DESIGN OF A COMBUSTION TEST RIG 47
Characteristics of Industrial Boilers 48
Time-Temperature Relationships 49
Scaling and Modeling Considerations 51
Constant Combustion Intensity 'Model 54
Constant-Pressure-Drop Model 57
Quasi-Constant-Combustion-Intensity Model .......... 59
Comparison of Models With the Full-Scale Unit 59
Other Scaling Phenomena 62
Design of Combustion Test Rig 63
Furnace Design 63
Burner Design 66
Auxiliary Equipment 68
Estimated Construction Cost 68
ACKNOWLEDGMENTS 70
REFERENCES 71
APPENDIX A-l
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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SUMMARY REPORT
on
RESIDUAL FUEL OIL-WATER EMULSIONS
Contract No. PH 86-68-84
Task Order No. 16
by
R. E. Barrett, J. W. Moody, H. R. Hazard, A. A. Putnam, and D. W. Locklin
INTRODUCTION
The Division of Process Control Engineering of the National Air
Pollution Control Administration is presently evaluating methods of reducing
air-pollutant emissions from combustion devices including oil burners for
space heating.
For the domestic oil burner part of this program, NAPCA is conducting
tests in a furnace which utilizes a 1-gph high-pressure atomizing burner firing
(1 2)
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. Battelle provided support for the NAPCA program in an
(3)
earlier task that resulted in development of preparation techniques for
water-in-distillate fuel-oil emulsions and preliminary firing of these emulsions,
Subsequent studies by NAPCA burning emulsified distillate fuel oil produced
evidence that some pollutant emissions (specifically NO ) were reduced.
In view of these results, NAPCA extended its interest in emulsified
fuels to include residual fuel oil. Because of the greater difficulty in
obtaining good atomization of heavy fuel oils, secondary atomization due to
emulsification may produce greater benefits (such as reduction of hycrocarbon,
carbon monoxide, and/or particulate emissions) when used with these fuels.
TASK OBJECTIVE
Battelle's assignment under this task order was to develop techniques
for preparing emulsions of water in typical residual fuel oils, to describe the
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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relative merits and problems encountered in the practical application of residual
fuel oil emulsions, and to prepare a preliminary design and cost estimate for
construction of a laboratory-scale residual-oil-fired combustion test rig.
SUMMARY AND CONCLUSIONS
Relatively stable water-in-residual fuel oil emulsions have been pre-
pared from 9 residual oil samples. Preparation of these emulsions did not
require the addition of an emulsifying agent because the oils apparently con-
tained sufficient natural emulsifiers. Several chemically basic materials, which
might react with sulfur or sulfur compounds in a furnace environment, were also
incorporated into the emulsions.
Experimental results indicate that the emulsions remain stable when
stored at temperatures of 6 F for 2 hours and 160 F for 3 days. Results of a
brief atomization trial of a single emulsion suggested that the emulsion was not
broken during atomization.
Viscosity of the residual fuel oils and the emulsions was measured at
temperatures of 100, 122, and 160 F and at three shear rates. Each of the oils
and most emulsions exhibited near-Neutonian properties. The emulsions were con-
sistently more viscous than the residual oils from which they were made.
Approximately 20 F additional preheat will be necessary when firing emulsions
to obtain viscosities equal to the viscosities at which residual oils are
typically atomized.
No inherent property of the emulsions would rule out their use as
fuels. The potential benefits of improved combustion through better atomization,
possibly resulting in lower pollutant emissions, seems to warrant further investi-
gation of the use of emulsified residual fuel oils. Specifically, the program
should be extended to combustion trials and emission measurements.
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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The preliminary design of a combustion test rig in which to conduct
this investigation is described in this report. It appears that a practical
laboratory rig can be constructed to fire about 1.5 gph, but that a special
burner will be required to provide the needed flexibility. The estimated cost
to construct and instrument this rig is about $48,000. This cost estimate
does not include costs associated with further burner development or gas analysis
and emission measurement.
BACKGROUND
NAPCA became interested in evaluating emulsified oil-water fuels as a
result of improved combustion (evidenced by shorter combustion times) reported
by other investigators. The concept of firing fuel oil-water emulsions to
obtain secondary atomization and, therefore, improve combustion was advanced by
Ivanov and others in 1957, and further discussed by Ivanov and Nefedov
in 1962. In the desired type of oil-water emulsion., each fuel oil droplet
contained one or more small droplets of water. As the emulsion was sprayed
into a hot chamber, they found that the water within the fuel droplet vaporized
before the fuel was consumed. The pressure generated within the fuel drpplet
by the vaporizing water was sufficient to rupture the fuel droplet in a miniature
explosion. This shattering or secondary atomization of the fuel droplet produces
further reduction in the effective droplet size and exposes a greater surface area
of fuel for vaporization, mixing, and burning, thus providing more rapid and
improved combustion.
In a previous program , a method for preparing stable water-in-dis-
tillate fuel oil emulsions was developed and these emulsions were fired in a
burner similar to that used by NAPCA. In subsequent work at the NAPCA Division
of Process Control Engineering, measurements showed evidence that emulsi-
fication of water in No. 2 fuel oil could reduce NO emissions. The work
x
described here is an extension of that previous program to include the study of
emulsions of water-in-residual fuel oils.
Most of the literature on water-petroleum emulsions deals with methods
of breaking oil-field emulsions or with the commercially important oil-in-water
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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bituminous emulsions used in road work. However, emulsified fuels have been the
subject of a number of patents and papers over the years. Of prime pertinence
(4-7)
to this program is the aforementioned work of Ivanov et al who suggested
the concept of improving combustion processes by emulsifying water in fuel oils.
/Q \ /Q\
Also of interest is the work of Cornet and Nero and Maillard who
demonstrated that emulsification of water in diesel fuels increased the
efficiency of an engine under certain conditions and reduced the amount of smoke
in the exhaust and the amount of carbon deposit in the engine. The preparation
of water-in-fuel oil emulsion has been described in a number of patents and,
recently, water-in-oil emulsions have been developed as fire-resistant hydraulic
are cui
(13-26)
fluids . Oil-in-water emulsions are currently being investigated for use
as a fire resistant fuels for aircraft
CHARACTERISTICS OF RESIDUAL FUEL OILS
Properties of residual fuel oils vary widely depending on crude source,
refinery processing, and blending. Specifications for residual oils are
established in ASTM Standard D-396 for grades as follows:
Viscosity Range .
Grade SSU @ 100 F . Preheating
No. 5 (light) 150-300 requires little or no
preheating for firing
No. 5 (heavy) 350-750 generally requires pre-
heating for firing and
often for handling
No. 6 900-9000 requires preheating for
both firing and handling
Fuels within these grades require different equipment and different levels of
preheating to reduce the viscosity necessary for handling and firing.
BATTELL.E MEMORIAL. INSTITUTE - COLUMBUS LABORATORIES
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Table 1 shows the complete ASTM specifications for all grades. It
should be noted that the range of properties permitted by the ASTM standard is
much greater for No. 6 grade than the No. 5 grades. (No. 4 oil is sometimes
considered as a residual fuel oil, but is not included in the scope of this
s tudy.)
An example of the variation in properties that are introduced by crude
(27)
source is shown in Table 2 from data presented by Siegmund . Besides the
differences in listed properties of the crudes, there are also variations in
basic crude composition; for example, the Tia Juano medium crude is a low wax
crude and the Libyan crude is a paraffin or high-wax crude. Processing
variations, such as the several desulfurization processes, can also introduce
considerable variation into properties of residual fuel oils.
Important properties of finished fuels can be controlled by blending
of residual from different crudes and/or by blending with distillate stocks to
reduce viscosity, pour point, or sulfur. The varying degree of distillate
blending adds to the wide variations in properties of No. 6 oil observed in
the marketplace.
Fuel properties are likely to change somewhat in the next few years.
Air pollution regulations are already limiting suflur content of fuel oils in
many areas and this trend will most certainly increase. For fuels used in
New York City, sulfur content is now limited to 1.0 percent and in a few years
the limit is scheduled to drop to 0.3 to 0.4 percent. To meet such require-
ments, refiners can control sulfur content to some extent by a combination of
crude selection, processing, and blending.
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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TABLE 1. ASTM D-396 SPECIFICATIONS FOR FUEL OILS
Grade of Fuel OH a
izins pat-type barnera u>d other)
burners requiring thu rrade of foci)
No. 2 jdomestic heating for use in burner*}
loot requiring No. 1 fuel oil )
11 . JPrthratinis Dot usually required forl
Ibaodlioc or burning /
[Preheating may be required]
N». i jdeprndinc on climate and}
(LJcbt) (equipment J
No. 5 fPrrheatioK may be required for]
(Heavy) (burning and, in cold climate*.)
( may be required lor handling |
M_ . /Prebeatinr required (or burning)
""- " land handling /
Flaab
Paint,
degP
(de(C)
Min
100 or
lenl
(38)
100 or
lenl
(3»)
130 or
lecal
wcr cradc.
fcoU|vit|f USA Ihc sulfur limit for No. 2 shall be 1.0 percent.
' Ix-pnl rci|uirrmcnls to be met.
r or liiirhcr iwur point* may be specified whenever renuircd by conditionsol storage or use. When pour point less than 0 F U specified, the minimum viscosity 'Sail be 1-SeSt (J2.0
MC. Siiyboll Univcrul) and the minimum 90 per cent |X>int shmll be waived^
'The I't i>cr cent di^iilbtion temiierature |K>int may be specified at 44
/»•• ;......!.. • _. _.t r__-_» .• • i
. , _.. . _, , i 440 F (W6C) maximum for use in other than atomizing burners.
Viscosity values in parentheses are for informitton only and not pccessariry limiting.
* The amount of water by distillation plus the sediment by extraction shall not exceed 2.00 per cent. The amount of sediment by extractkn shall not exceed 0JO per cent. A deduction
in quantity nhall be made for all water and sediment io excess of IX) per cent.
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TABLE 2. CHARACTERISTICS OF MIDDLE EAST AND VENEZUELAN CRUDES AND FUEL OILS<>27)
2 Light Arabian Kuwait _ Tia Juana Med _ Libyan
m
2
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>
r API Gravity
z
l! Sulfur, Wt Z
c
fi Pour Point, °F
i
n
£ Viscosity SSU @ 100'F
i SSF <§ 122°F
Vanadium PPM
r
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§ Nickel PPM
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Crude
34.7
1.7
-15
44
—
13
4
Fuel Oil
15.5
3.0
+55
—
175
37
11
Crude
31.4
2.5
-20
56
—
31
7
Fuel Oil
15.5
4.0
+55
—
175
61
14
Crude
26.5
1.5
-40
116
—
156
20
Fuel Oil
16.3
2.0
+20
—
170
240
31
Crude
39.2
0.2
+40
40.5 •
—
3
^^^
Fuel Oil
22.2
0.4
+105
—
65
10
^^
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TABLE 3. SUMMARY OF GRADE 5 (light) FUELS
DMrlcti «***»* fo.b
T«rt
Vbcolry
BnMaricet 100* T. t^tfUtdkjM
AJTWW
M^iocj
D445
» w«*l
Mlit.
32
Max.
AS
BMnnchn
A,»,C
D,E,F,O,J
7
MlriMi A~rag> Mkntmm
13.4 1«.B B.»
170 - 208
».a 47.3 W
-40 - 13
0.4* 1.01 1.4
3.3 71 10 3
0.006 0.042 0 16
O.O5 O.I 0.3
South*!* nglon
D
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16 4
37J
^
1 J6
6 3
0 023
0 1
COTMlra^oi
e.r.o
1,0,0, 1.J.K.L
10
Mlnlmm Atmmgt Hciimum
92 16 7 • 20 7
13.6 48.0 <9
18 (4) 21
•13 - 33
0 64 1 33 34
31 60 92
0 006 0 017 0 025
Uek, MMtoln raglv
H.I.J.K
8 D C F C I
4
Maliui A»rag> M»l«u>
S7J 54.0 68.7
W40.M M«l«.
l>4,N,0,r
e F o i K
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60
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TABLE 4. SUMMARY OF GRADE 5 (heavy) FUELS
oo
GMpophic rflttrtbuHcn of tumr fcwl «lb y
Dtitricb within im^ion
Addliioml dlitricH y
rtmbn of fawb
T8».
Fbsk point, femkr-AtortmcloMd row— * F.
W.U. — J l«1]«llll !• (HI
ASTM EK
Atathnrf
on
96 nojwl
fcUn.
130
r»BMfHi
Mn.
Eostwnf^eD
A,I,C
t,F,C
4
MInhM AMIDO* Mud«*
161 20>
.200 - 7D
0 55 \J3 J JO
Souttwn raplon
D
C
3
MlnlMB ^••tvi fMbxlwMi
17* - >200
-30 - B
1.44 2 11 JJ5
40 77 I2J)
0 01 0 017 0 03
Central ragl«n
I,F,O
C,D,J
7
MIMfmM A««ooa Mudw«
4 4 15 J It J
lot . >200
-20 - 65
0 55 1 73 J J3
4 0 4 J t 0
0 001 0 015 0.03
0.00 01 01
RocVy Mou««lr> myton
H.I,JrK
UM
6
Minim* A~m«» Mixlwm
14 10 I 17 •
194 - 240
-15 - 95
1-45 2 11 2 9t
UM.N,O,r
H,K
13
MInjflM Awog* f%ri-if-
162 -240
-25 - 95
Data From Bureau of Mines Survey, 1968
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TABLE 5. SUMMARY OF GRADE 6 FUELS(28)
G~V««MC «u.U
tM
<-— i-r * **
Fb* point. Pinkr-Mnoni cloul MM * F.
V.n»l>r
•». _l- •».
tlll^lllMIIM OV^on r«uoW
A* *.
T^llmirY by •«*™gri^. M« pprcont
ASTM a
M«hd
oar
on
068
077
DI24
D4C
095
M7]
M M0>lr
Ml».
—
ISO
45
•HRh
Atex.
.
HO
OJO
BM«ni Mttat
»,»,c
O.t.F.O.J
' Ja'
UM_ A~R>g» *tai~.
7U 1J.1 llj
1*9 -MO
67 1B.I 110
10 - 100
1 11.4 1IJ
OJO O.OU 0.1B3
0.0 0.01 OJ5
.0 .07 0.4
VartWil ngl«n
D
A,»,C,0,E,G,J
10
Minimal *-~=W« M»l«u>
3.9 10.4 14.6
170 236
IIS 179 1 200
10-90
JJ 14.1 ll.l
0.01 0.0*6 0.189
0.0 O.O7 0.1
0.02 .06 J
C«Hlgl raglo*
t,F,O
A,l,C,D,M,l,J,K,l.
»
Mal«ra A»n>o> »%«lm«.
-4.7 10.1 1B.1
165 315
55 169 9 310
10-90
0.6 10.6 18.3
0.003 0.030 0.10
0.0 0.07 .29
.0 .OB 0.4
lack? UtouMoln mlo»
M,I,J,K
ft.D.C.f G L,M N
Mlnl»un A^rao* Haiimi*
-1.5 e.O 15 J
198 - 340
43 5 164 1 295
10 - 100
6.3 11 0 16
•C0.01 0.090 0.12
0.0 0.05 OJ
.0 .12 J
UM.N.O.F
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21
Mlnlu. A.OT>B> "n-*-i^
2.9 77 11 J
170 - 339
15 - 100
59 12 3 17 4
O.OB 0.0*9 0.12
0.0 0.09 OJ
0.02 .11 J
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Data From Bureau of Mines Survey, 1968
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10
Bureau of Mines Survey of
Burner Fuel Oils, 1968
The most comprehensive information on properties of fuels sold in
the U.S. is provided by the Bureau of Mines annual survey of burner fuel oils
This provides data on samples as marketed in different geographic regions.
(29)
Tables 3, 4, and 5 summarize data on No. 5 and No. 6 oils by marketing
regions, showing minimum, arithmetic average, and maximum values of significant
/ o o \
properties . These cover 15 samples of No. 5 (light), 24 samples of No. 5
(heavy), and 81 samples of No. 6 oil. It is noted that there is a significant
variation in average values of some properties from region to region and, also,
that there is a wide range in the property values within any region.
The data are summarized on a national basis in Tables 6, 7, and 8.
The median value of properties is defined as that value where one half the
samples were above and one half were below for the property of interest.
Figure 1 shows the effect of temperature on viscosity for the ranges
of No. 5 and No. 6 oils reported in the survey. Median values are also shown.
TABLE 6. NATIONAL SUMMARY OF PROPERTIES FOR
NO. 5 (LIGHT) BURNER FUEL OIL (1968)
Fuel
Minimum
Median
Maximum
Gravity, API
Flash point, F
Viscosity, kinematic at 100 F, cs
Pour point, F
Sulfur content, wt. percent
Carbon residue, percent
Ash, wt. percent
Water and sediment, vol. percent
5.5
170
s 34
-40
0.64
3.1
.006
.0
17.9
200
47
0
1.25
6.4
.016
.1
20.9
230
69
75
3.4
10.5
.18
.3
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TABLE 7. NATIONAL SUMMARY OF PROPERTIES FOR
NO. 5 (HEAVY) BURNER FUEL OIL (1968)
Fuel
Minimum
Median
Maximum
o
Gravity, API
Flash point, F
Viscosity, kinematic at 100 F
Viscosity, Furol at 122 F.sec
Pour point, F
Sulfur content, wt. percent
Carbon residue, percent
Ash, wt. percent
Water and sediment, vol. percent
4.6
162
69
21
-30
.55
3.8
.008
.05
13.8
198
105
27
0
1.52
7.5
0.02
0.1
18.3
240
154
37.5
95
3.25
10.8
.08
.3
TABLE 8. NATIONAL SUMMARY OF PROPERTIES FOR
NO. 6 BURNER FUEL OIL (1968)
Fuel Minimum
Gravity, API
Flash point, F
Viscosity, Furol at 122 F.sec
Pour point , F
Sulfur content, wt . percent
Carbon residue, percent
Ash, wt. percent
Water by distillation, vol. percent
Sediment by extraction, wt. percent
-4.7
165
43.5
10
.18
.6
.003
.0
.0
Median
10.5
209
178
35
1.33
11.6
.03
.05
.05
Maximum
22.5
395
310
100
3.25
18
.35
.35
.5
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Recommended atomizing
viscosity ranges for boilers;
Natural draft
Forced draft
100-150 SSU
150-200 SSU
in
s «.
in V
> |
o u»
O C
E °
I °
I5OO
IOOO
5OO-
Forced draft
1_
Natural draft
100
80
60
40
30
No. 5 heavy
60
-4O
6-
4-
80 90 TOO HO 120 130 I4O I&O ISO 170 180 190 2OO 210 22O 230 240 250 260 270 280
ii liiiiliiiilriiiliiilliiiiliiiiliiiilniilii.il.iiiliiiil.iiiliiiilimliillliillliiiiliililiilllllliliiiilllllliililiillllll llllllllllilliiiliilililMliiiiliiiillillllllllillllliiiliiiiliiiiliinl
Temperature, F
FIGURE I. VISCOSITY-TEMPERATURE RELATION FOR RESIDUAL FUEL OILS IN 1968 BUREAU OF MINES SURVEY
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In an attempt to define "typical" oils within the No. 6 grade, several
plots were made of important properties for fuels reported in the Bureau of
Mines Survey. These plots included:
sulfur content vs viscosity (Figure 2)
sulfur content vs gravity (Figure 3)
gravity vs viscosity (Figure 4) .
The only plot which may be interpreted as showing groupings of residual oils is
sulfur content vs viscosity. Figure 2 shows this plot with the major oil
grouping shown by dotted lines. Four groups of oils may be identified as follows
e low viscosity, low sulfur (9 oils)
• medium viscosity, low to medium sulfur (34 oils)
• medium viscosity, high sulfur (9 oils)
• high viscosity, low to medium sulfur (10 oils).
Table 9 gives the median viscosity and sulfur content for each of these four
groups of residual oils.
TABLE 9. MEDIAN PROPERTIES OF FOUR GROUPS OF RESIDUAL OILS
Fuel
Viscosity, Saybolt
Furol at 122 F, sec
Sulfur content,
wt. percent
Low vise.,
low suflur
106
0.81
Med . vise,,
low to med.
sulfur
175
1.27
High vise.,
Medium vise., low to med.
high sulfur sulfur
180
2.64
261
0.90
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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Letters refer to fuel samples obtained for
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s
40
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120 160 200 240
Viscosity, seconds, Saybolt Furol at 122 F
280
320
360
FIGURE 2. SULFUR CONTENT VERSUS VISCOSITY FOR NO. 6
RESIDUAL FUEL OILS
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FIGURE 3. SULFUR CONTENT VERSUS GRAVITY FOR NO. 6
RESIDUAL FUEL OILS
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17
Residual Fuel Samples Obtained For This Study
As part of this study, five refiners were contacted and asked to
supply sample quantities (5 gallons) of typical No. 6 residual fuel oils for
the emulsification trials. Nine samples were supplied by the refiners.
Table 10 lists the properties of the nine oils as supplied by the
refiners. Figures 2, 3, and 4 show how these oils compare to all No. 6 residual
fuel oils marketed during 1968. It can be seen from these plots that at least
seven of the oils obtained for this program were generally characteristic of
"average" No. 6 fuel oils.
EXPERIMENTAL PROCEDURES AND RESULTS
The experimental portion of this study consisted of preparing water-
in-oil emulsions, determining basic properties of the emulsions, and conducting
"cold" atomization trials (without flame) to determine if the emulsions break
during atomization.
Preparation of Water-in-Oil Emulsions
(3)
In the previous work on water-in-distillate fuel oil emulsions it
was found that a surfactant was required to produce stable emulsions. Early in
this study it became apparent that very stable water-in-residual fuel oil
emulsions could be prepared by simply mixing water and No. 6 grade fuel oils
with sufficient agitation. This is not surprising when it is recalled that a
large percentage of crude oils are obtained from the wells as water-in-oil
emulsions.
Crude oil contains a number of constituents which tend to promote
the formation of emulsions when the oil and water are mixed. Among the most
common substances are naphthenic acids and their salts, asphalt particles,
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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TABLE 10. PROPERTIES OF RESIDUAL-OIL SAMPLES USED IN EMULSION EXPERIMENTS
(a)
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3)
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Oil Sample
Crude source
Properties
o
Gravity, API
Flash point, F
Viscosity, Saybolt
sec.Furol at 122 F
Pour point , F
Sulfur content ,wt. pet.
Carbon residue ,wt .pet .
Ash, wt.pct.
Water & sediment,
vol .pet.
Vanadium, ppm
Sodium, ppm
Lead , ppm
Manganese, ppm
Magnesium, ppm
Calcium, ppm
Nickel , ppm
Iron, ppm
fs\ Pi-r»rvo i- f- i o c ciinnl i f* H }
A
Mid-Cont .
9.3
315
188(C)
30-40
1.45
0.22
0.04
117.5
18.0
<1.0
<1.0
6.2
34.4
26.9
ITT T*o-p-inoT*c
B C
W. Coast
8.3 14.6
173 151.
15
1.3 2.14
0.09
0.3
208
41
12
21
81
<6
D E
Africa Mid-Cont.
22.3 10.9
260 225
56.3 196.3
95 25
0.59 0.96
6.65 8.9
0.004 0.05
0.10 0.20
F G H J
Venezuela Gulf Coast Venezuela W. Coast
/•L. \
14.1 12.0 15.5 6.8V ;
206 155 265
195.4 165 170(b) 120(b)
20 35 5
2.37 2.1 1.5 i-S,,,
9.6 12.6Cb)
0.05 0.02 0.06
0.10 0.2
236 79
86 78
m
in
(b) Converted from other units
(c) From Battelle data
-------
19
microscopic paraffin flakes, certain heavy hydrocarbons and clay or earthy
matter. Many of these constituents, particularly the naphthenic acids and heavy
hydrocarbons, are also found in residual fuel oils. The presence of these
materials accounts for the ease with which water-in-oil emulsions can be formed
with these oils.
However, the composition of crude oils and, hence of residual fuel
oils vary considerably according to their geographic source. The method of
refining also affects the composition of residual fuel oils. It is not to be
expected, then, that the same type and concentration of naturally occurring
emulsifiers will be found in all residual fuel oils. Therefore, it was important
in this work to examine fuel oils from a number of sources to determine how
common is the emulsification behavior of residual fuel oils.
It was found that each of the No. 6 grade fuel oils formed water-in-
oil emulsions without the use of added emulsifying agents. The concentration
range of stable emulsions was found to depend strongly on the method and
temperature of mixing. Figure 5 illustrates the effects of these variables on
the stable concentration range of emulsions formed with Oil A. Unstable
emulsions immediately broke into two layers: (1) a relatively dilute oil-in-
water emulsion which, in most cases, settled to the bottom of the container,
and (2) a water-in-oil emulsion.
In Figure 5, the percent of the total volume occupied by the water-in-
oil layer is plotted as a function of the concentration (weight percent) of
water in the total system. The only stable emulsions are those which remained
100 percent water-in-oil emulsions. Curve 1 of the figure was generated by
adding all the water in one step to the oil and mixing in a Waring Blendor.
The mixture was stirred, at room temperature for 2 to 3 minutes. Under these
conditions, stable emulsions containing up to about 35 weight percent water in
the internal phase could be prepared. The stable concentration range extends
to at least 50 weight percent if the water is added dropwise at room temperature
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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100
Curve 3
20 40 60 80 100
Water in Emulsion, weight percent
FIGURE 5. EFFECT OF MIXING VARIABLES ON STABLE
CONCENTRATION RANGE OF OIL A EMULSIONS
o Curve I. Water added in one step, room temperature
A Curve 2. Water added dropwise, room temperature
a Curve 3. Water added in one step, oil 150-200 F,
water boiling
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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21
as shown by the one point plotted for Curve 2. (Curve 2 is really an extension
of Curve 1.) At this point the emulsion became so viscous that stirring on the
Blenclor became difficult. Emulsions containing up to about 60 weight percent
water were prepared when the components were heated,as shown by Curve 3. In
these experiments, boiling water was added, in one step, to Oil A which was pre-
heated to 150 F to 200 F. The mixtures were then stirred 2 to 3 minutes on the
Blendor.
The stable concentration range which might be obtained with all the
oils is indicated by the data of Table 11. These data were obtained by adding
the water in one step at room temperature (except where noted) to the oil on
the Waring Blendor and mixing for 2 to 3 minutes. Although some difference in
the behavior of the various oils is noted, the data indicate that emulsions
containing up to about 30 weight percent water in the internal phase can be
prepared easily with all the oils. The concentration range of stable emulsions
could probably be extended in every case by modifying the mixing conditions.
Sufficient oils were included in these experiments that it is felt that these
conclusions can be extended to all common residual fuel oils.
TABLE 11. STABILITY CONCENTRATION RANGE OF
WATER-IN-OIL EMULSIONS*
Water
Weight
Percent
20
40
60
Volume appearing as W/0 Emulsion, Percent of total
Oil A
100
97
45
Oil B
100
99
60
Oil C
100
93
53
Oil D**
100
100
100
Oil E
100
100
50
Oil F
100
99
54
Oil G
100
92
50
Oil H
100
90
67
Oil J
100
100
81
* Emulsions prepared at room temperature (except for Oil D) by adding water in
one step to oil on Waring Blendor and mixing 2 to 3 minutes.
** Emulsions with Oil D mixed at 150 F to 200 F.
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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22
Identification of Emulsion Type
Identifying the type of emulsion (water-in-oil or oil-in-water)
obtained when the components were mixed was difficult. The dye tests which were
(3\
so valuable with the water-distillate fuel oil studies were useless in this
work because of the dark color of the residual oils. Nor could definite con-
clusions be obtained from microscopic examination because of the rapid changes
which occurred when the emulsions were spread on a microscope slide. In
addition, the Waring Blendor whipped air into the emulsions and it was difficult
to distinguish an air bubble from a water droplet in the internal phase.
Therefore, a number of other tests were applied to establish the
emulsion type. These tests included:
(1) Color: Water-in-oil emulsions were black or dark brown while oil-in-
water emulsions were a lighter brown.
(2) Phase Dilution: A drop of oil or water was floated on a few cc of the
emulsion. If oil were the continuous phase, the oil drop would disperse
but not the water drop. If water were the continuous phase, only the
water drop would disperse. Since sometimes the water droplet would sink
through the emulsion, great care had to be taken in interpreting this test.
(3) Filter Paper Wetting: A drop of emulsion was placed on a piece of filter
paper. Oil-in-water emulsions spread rapidly, often leaving a dark spot
of oil near the center of the area.
In combination, and with experience, these tests were sufficient to distinguish
the emulsion type.
Incorporation of Basic Additives in
Water-in-Residual Oil Emulsions
NAPCA suggested that basic additives might be included in the emulsions,
These additives might react during combustion with sulfur from the fuel to reduce
sulfur oxide emissions. The additives of interest to NAPCA were NaOH, NH.OH,
Ca(OH)9 and Mg(OH)9« The sulfur compounds that formed could be removed from the
gas stream by conventional techniques.
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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Methods of incorporating each of these basic additives in the
emulsions were developed. Reagent grade compounds were used in all cases.
The water-soluble additives (NaOH and NH.OH) were first dissolved in
water before emulsification with the oil.
For the water-insoluble additives (Ca(OH) and Mg(OH) ), initial
attempts to produce stable emulsions were made by mixing the additive with
either water or oil. In the case of Ca(OH)_ it made no difference if the
compound was mixed first with water or oil; stable water-in-oil emulsions
resulted in either case. Conversely, it was discovered that Mg(OH)9 had to be
mixed with the oil first. If Mg(OH)9 were wet with water first, stable emulsions
could not be obtained. The emulsions were prepared by adding the aqueous phase
to the oil phase in one step at room temperature and mixing for 2 to 3 minutes
on the Waring Blendor.
About 10 weight percent of each additive was incorporated in emulsions
containing 20 weight percent water. (Concentrated NH.OH was used to yield
emulsions containing about 7 weight percent NH., and 23 weight percent water.)
In each case, the amount of additive was more than sufficient to react with all
the sulfur present in any of the oils.
With the exception of NH OH, the additives were compatible with all
the oils tested. Table 12 summarizes the data. It should be noted that NH.OH
4
formed stable emulsions with only the Mid-Continent and Gulf Coast oils.
Additional experiments with NaOH suggested that the compatible
additives and water could be incorporated in the emulsions in a wide range of
concentration ratios.
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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24
TABLE 12. COMPATIBILITY OF BASIC ADDITIVES AND EMULSIONS
Oil
Geographic
Source of Crude
Additive
A
B
C
D
E
F
G
H
J
Mid-Continent
West Coast
--
Africa
Mid -Continent
Venezuela
Gulf Coast
Venezuela
West Coast
NaOH
S
S
S
S
S
S
S
S
S
NH.OH
S*
U
U
- _**
S
U
S
U
U
Ca(OH)n
L
S
S
S
S
S
S
S
S
S
Mg(OH)2
S
S
S
S
S
S
S
S
S
S = Stable
U = Unstable
* Emulsion broke after several weeks.
** Since Oil D had to be heated for processing NH.OH was not added.
Properties of Water-in-Residual Fuel Oil Emulsions
Emulsification of residual fuel oil has a pronounced effect on some
fuel properties important to combustion. Viscosity is of prime importance in
its effect on atomization and on preheat required for pumping and atomization.
Therefore, rather extensive measurements were made of viscosity of both the
base oils and the emulsions.
Static Viscosity Measurements
The kinematic viscosity of emulsions prepared with Oil A was measured
at 122 F using a Saybolt viscometer equipped with a Universal orifice. Table
13 lists the results of these measurements.
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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25
It was observed that the viscosity of the emulsions increased with
water content. The presence of the water-soluble additive NaOH had little or
no effect on the viscosity of the emulsion; however, the insoluble additives,
Ca(OH)9 and Mg(OH)9, increased the viscosity of the emulsions. Air which was
whipped into the emulsions during mixing, interfered with viscosity measure-
ments, causing high values in some cases.
TABLE 13. VISCOSITY OF EMULSIONS WITH OIL A
Composition,
weight percent
Oil A
Oil A
Water
Oil A
Water
Oil A
Water
Oil A
Water
Oil A
Water
NaOH
Oil A
Water
Ca(OH)2
Oil A
Water
Mg(OH).
100
95
5
90
10
80
20
70
30
70
20
10
70
20
10
70
20
10
Viscosity at 122 F
seconds, Saybolt
Furol
262
267
360
385
760
442
916
1100
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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Dynamic Viscosity Measurement
Viscosity measurements were also made using a Ferranti-Shirley cone-
plate viscometer. This instrument is useful for determining viscosity as a
function of both temperature and of shear rate. For non-Newtonian materials,
such as emulsions, the viscosity may vary with time as well as with shear rate
due to structural changes. Because the cone-plate viscometer shears the
sample continuously, time-dependent variations can be studied easily.
For these measurements, the Ferranti viscometer was programmed to
shear a sample of emulsion at shear rates from zero to over 15,000 reciprocal
seconds. This range should cover all of the conditions encountered in an
emulsion in pipe flow. Shear rates in a burner nozzle might be momentarily
higher. Measurements were made at 100 F, 122 F, and 160 F.
Viscosity-temperature data was obtained on 22 samples which included:
9 residual oils, as received
9 emulsions, one of each oil with 20-percent water
2 additional emulsions of Oil A containing
10 and 30-percent water, respectively
2 emulsions of Oil A containing 20-percent water
and 10-percent Ca(OH). and Mg(OH)., respectively.
Data were recorded continuously on a X-Y recorder, with shear rate
(a function of cone speed) on the Y axis and shear stress on the X-axis. Thus,
a continuous curve of shear stress versus shear rate was obtained for each
sample.) Viscosity is defined as the ratio of shear stress to shear rate at
any point on the curve. Three shear rates were selected for data tabulation:
about 1700, 8400, and 15,000 sec" . (Actual shear rate differed slightly for
specific runs because two different cones with slightly different constants
were used. The variation is not significant for data interpretation.)
The viscosity calculated from the basic data is in absolute units,
namely centipoises. These units may be converted to kinematic viscosity
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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27
(centistokes) by dividing the absolute viscosity by the sample density at the
temperature of measurement. Kinematic viscosity may be further converted to
seconds Saybolt Universal or seconds Saybolt Furol through use of ASTM
tables. Since one of the objectives of this study was to observe the effects
of temperature on the residual fuels and their emulsions, most of the data have
been expressed in seconds Saybolt Universal, (SSUj and plotted on ASTM D341-43
graph paper. The Saybolt Furol scale applies only to measurements at 122 F and
hence cannot be used for showing viscosity-temperature relationships. However,
Saybolt Furol values were calculated for all emulsions at 122 F and are also
reported. The Furol values obtained were in reasonable agreement with the
values available from suppliers of the fuels.
The absolute accuracy of these data are affected by a number of possible
errors, as will be discussed. Overall, the cumulative, errors are not highly
significant, in most cases being less than 10 percent. Thus, the data as given
are quite adequate for both a general impression of emulsion behavior and for
engineering calculations of pipe flow.
One source of error is shear heating. At the viscosity level of these
fuels and their emulsions, even the excellent temperature control features of
the Ferranti viscometer cannot prevent shear heating at the higher shear rates.
The amount of shear heating for each determination was registered by a thermo-
couple in the plate of the viscometer. At the highest viscosities and shear
rates (at 100 F), this rise was typically four or five degrees F. At the lowest
viscosity tabulated at a shear rate of 1700 sec , the rise was negligible. The
rate of change of viscosity with temperature is about 4 percent per degree at
100 F for these fuels. Therefore, a five degree rise in temperature is signifi-
cant. This rise was taken into account in interpretation of the flow curves
for non-Newtonian character. All of them display what could be interpreted as
reversible shear-thinning, but calculation showed that most of that could be
accounted for by shear heating. It is for this reason that the decision was
made to ignore non-Newtonian shear thinning in plotting the results.
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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TABLE 14. VISCOSITIES OF RESIDUAL OILS AND EMULSIONS
(At Shear Rate of 1700 sec'1)
Residual Oil Sample
Viscosity, seconds
Saybolt Universal, at 122 F
Viscosity, seconds
Saybolt Furol, at 122 F
Oil A
Oil B
Oil C
Oil D
Oil E
Oil F
Oil G
Oil H
Oil J
Base Oil
1850
1950
2240
487
1980
2100
1730
1790
1330
20- percent
water emulsion
3020
1850
3600
779
2240
2920
2760
2760
3330
Base Oil
188
198
228
51
202
214
177
182
135
20-percent
water emulsion
307
188
367
80
228
297
281
281
339
Emulsion
Oil A+10-percent
water emulsion
Viscosity, seconds
Saybolt Universal, at 122 F
2340
Viscosity, seconds
Saybolt Furol, at 122 F
238
Oil A+30-percent
water emulsion
4570
470
Oil A+20-percent
water +10-percent
Ca(OH) emulsion
Oil A+20-percent
water +10-percent
Mg(OH)2 emulsion
3600
2730
367
277
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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A second source of errors in the data is the decision to ignore
density in converting centipoises to Saybolt units. Enough data were available
for the samples to show that their specific gravity were mostly in the range
from 0.95 to 1.0 at 75 F. The decrease in density for hydrocarbons of this
type between 75 F and 160 F is only about 4 percent. Therefore, because labora-
tory determination of actual densities at elevated temperatures for the samples
would have required extensive effort, it seemed reasonable to ignore the small
error involved.
A third source of error in the viscosity values is the small error
caused by time-dependent viscosity changes in the emulsion samples. Most of
the emulsions experienced a small change of viscosity due to shear during the
measurement procedure. However, this viscosity change was usually only a few
percent. The few cases of gross change are noted in the graphs or the dis-
cussion of results given later.
Measurements showed that the residual fuels themselves seem to be
slightly shear-thinning at high shear rates (10,000 sec or more). Addition
of emulsified water increases this tendency for some of the oils. However,
the maximum temporary viscosity loss is on the order of 20 percent. Therefore,
this amount of non-Newtonian behavior does not seem highly significant in terms
of pipe flow or atomization.
Finally, there may have been some slight error in the determinations
made at 160 F because of evaporation of part of the emulsion. Nearly all the
samples, including the fuels themselves, showed a tendency to increase in
viscosity with time. The most probable explanation for this is evaporation of
a small amount of light hydrocarbon.
Overall, despite the errors noted, the results are believed to be
reasonably accurate for the purpose intended.
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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Viscosities of Emulsions Compared to Base Fuels
Figures 6 to 15 present results of the viscosity measurements. These
plots of viscosity in seconds, Saybolt Universal, versus temperature have been
arranged to provide a comparison between the particular residual fuel sample
and its emulsion. Saybolt Universal values are approximately ten times as large
as Saybolt Furol values. Table 14 summarizes the viscosity data in both units.
The data show that in all cases, with the possible exception of Oil B,
the emulsion is more viscous than the base fuel by amounts ranging from 50 to
100 percent. The difference is relatively small for Oils B and E and peaches.
a maximum with Oil J. The viscosity-temperature dependence of the emulsions
is little different from that of the fuels.
Figure 6 shows the viscosities of emulsions of Oil A with 10, 20, and
30 percent water. The data show that the viscosity of the emulsion increased
with increasing water content.
The special emulsions of Oil A were examined in which solid material
had been dispersed. One contained calcium hydroxide, and the other contained
magnesium hydroxide. The calcium hydroxide emulsion was considerably higher
in viscosity than the magnesium hydroxide one (Fig. 15^ and it was unstable at the
highest shear rates at 100 and 122 F. The magnesium hydroxide emulsion showed
evidence in the storage bottle of having some free water or at least an oil-in-
water exterior phase. The bottle surface appeared to be water-wet rather than
oil-wet as for all the other emulsions.
Flow Instabilities Observed in Emulsions
Three types of instability were observed during the viscosity measure-
ments. One was a time-dependent shear-thickening. That is, the viscosity
increased slightly due to the shearing action generated during the viscosity
determination itself. This was observed for nearly all of the emulsions at all
temperatures. A likely explanation is that the emulsions had begun to grow
coarser in texture due to long standing. Thus the shearing had the effect of
homogenizing or redispersing the emulsion to a finer texture.
BATTEULE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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20.000
10,000
5000
2000
^ 1000
JS 750
o
tn
> 500
300
200
150
100
Oil A
10 percent water
emulsion
20 percent water emulsion
30 percent water emulsion
100
120
140
160
Temperature, F
180
200
220
240
FIGURE 6. VISCOSITIES OF OIL A AND WATER-IN-OIL A EMULSIONS
100
100
140 160 ISO
Temperature, F
200
220
240
FIGURE 7 VISCOSITIES OF OIL 8 AND WATER-IN-OIL B EMULSION
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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3
(/>
VI
in
o
o
V)
20000,
10,000
5000
2000
1000
750
500
300
200
150
100
1 I.I I
100 120 140 160 ISO
Temperoture, F
1 1 L.
' 200
J 1 L
220
240
FIGURE 8. VISCOSITIES OF OIL C AND WATER-IN-OIL C EMULSIONS
100
100
120 140 160 180
Temperoture, F
200
220
240
FIGURE 9. VISCOSITIES OF OIL D AND WATER-IN-OIL D EMULSIONS
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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ioou
120
140 160
Temperature, F
220
240
FIGURE 10. VISCOSITIES OF OIL E AND WATER-IN-OlL E EMULSION
100
100
00 160 ISO
Temperature, F
200
220
240
FIGURE II. VISCOSITIES OF OIL F AND WATER-IN-OlL F EMULSIONS
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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100
100
140 160 180
Temperature, F
200
220
240
FIGURE 12. VISCOSITIES OF OIL G AND WATER-IN-OIL G EMULSIONS
100
100 120 140 160 ISO
Temperature, F
200
220
240
FIGURE 13. VISCOSITIES OF OIL H AND WATER-IN-OIL H EMULSIONS
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in
V)
O
u
20.000
10,000
5000
2000
1000
750
500
300
200
150
100
-Emulsion
100 120 140 160 160 200 220 240
Temperature, F
FIGURE 14. VISCOSITIES OF OIL J AND WATER-IN-OIL J EMULSIONS
20.000
10.000
5000
2000
D
>: 1000
8 75°
> 500
300
200
150
100
Emulsions:
70 wt percent, Oil A
20 wl percent, water
10 wt percent, basic additive
J l 1 1_
100 120 140 160 180
Temperature, F
200
220
240
FIGURE 15. VISCOSITIES OF WATER-IN-OIL A EMULSIONS CON-
TAINING BASIC ADDITIVES
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The second type of flow instability observed is known to rheologists
(29 30)
as the "Weissenberg Effect ' . In the cone-plate viscometer, the phenomenon
appears as an escape of the sample from the shear zone between the cone and
plate. Some of the fluid actually flows out of the shear zone and climbs up on
the revolving cone. The effect may be seen visually before an actual loss of
fluid from the shear zone occurs because the meniscus around the edge of the
shear zone becomes doughnut shaped. When fluid actually leaves the shear zone,
the torque (shear stress) on the cone drops suddently and erratically. If the
shear rate is lowered, the fluid will usually relax and refill the shear zone.
At present there is no satisfactory explanation of why and how this phenomenon
occurs in emulsions, it occurred only with the Oil A emulsion containing 30 per-
cent water at 100 and 122 F, and with the Oil B emulsion at 122 F. The Oil B
emulsion also showed signs of such behavior at 160 F, but with other complications.
The structure which gives rise to the Weissenberg effect probably would
not significantly alter flow of the emulsion in pipes. However, it might
possibly alter the spray pattern generated from a nozzle.
The third type of flow instability was a partial separation or breaking
of the emultion to release free water. This phenomenon was observed with the
following:
Oil B emulsion at 122 F
Oil D emulsion at 160 F
Oil C emulsion at 160 F
Oil H emulsion at 160 F.
Free water could be seen on the surface of these samples after shearing when
the cone and plate were separated.
It is not clear what effect these instabilities might have on the
behavior of these emulsions in handling in a burner system. Actual pumping and
burning tests would be necessary to determine what effects, if any, occur.
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Thermal Stability Tests
The thermal stability of the emulsions were investigated at both high
and low temperatures. At elevated temperatures, NH OH is readily lost from the
emulsion due to evaporation. However, all the other emulsions were found to be
stable for at least three days at 160 F. In addition, all emulsions (except
that containing NH.OH) were placed in a boiling water bath (212 F) for one hour,
Except for a slight loss of water by evaporation, no changes were apparent.
Finally, no changes were apparent when the emulsions were stored at 6 F for 2
hours. Thus, each of the emulsions except those containing NH.OH appear to be
stable over a wide temperature range.
Atomization Trials
Atomization trials were conducted without combustion to determine if
the water-residual fuel oil emulsion remained emulsified or broke due to shear
stresses during the atomization process. The atomization trials were conducted
using a 20 percent water emulsion of Oil A. A quantity of base Oil A was also
atomized to provide a reference for comparison purposes.
To lower the viscosity for pumping, a double-boiler arrangement was
used to preheat the oil to a temperature of 130 F to 165 F. A steam jacket was
used over the fuel line to heat the fuel to the desired temperature for atomiza-
tion. Due to the fact that the water in the emulsion would readily evaporate
or boil at high temperatures (200 F to 250 F), the steam jacket was located
downstream of the pump; the pressure in this section of the fuel/line would
prevent boiling. The emulsion was atomized at temperatures of 175 to 250 F.
Base oil was atomized at 115 to 200 F.
A Delavan"Industrial Aero" air-atomizing nozzle was used for these
trials. Both the atomizing air pressure and the fuel line pressure were main-
tained at about 20 psig. The fuel flow rate was about 1.1 to 1.3 gph.
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Samples of spray drops were collected during atomization of both the
water-residual oil emulsion and the residual oil. Drops were collected on clean
glass microscope slides by manually passing the slides through the spray.
Individual drops were examined under 200X magnification.
Examination of emulsion drops showed a multitude of small (several
micron) circles within the drops which were interpreted to be water droplets
within the emulsion drop. However, a smaller number of similar circles were
also observed near the surface of drops of the residual oil. Existence of these
circles in the residual oil caused some uncertainty in identifying the circles
as water droplets. This prevents a positive statement that water droplets were
contained in the emulsion drops on the slides. However, no separate water and
oil phases were observed on the slides, suggesting that the emulsion had not
broken.
For the emulsion only, an estimate was made of droplet sizes from the
droplets collected on the slides. These estimates are:
Emulsion temperature Estimated droplet Estimated number-
at nozzle, F diameter range, ^ average droplet diameter, y.
175 4-250 100
200 4-200 100
250 4-100 60
From observations of the sprays it appeared that atomization of the emulsion at
250 F produced a spray fineness that approached the fineness of a distillate oil
spray at room temperature. Atomization of emulsion at 175 F and 200 F produced
coarser sprays. It was not possible to determine if "secondary atomization" of
the emulsion droplets might have been occuring at 250 F although this may have
been happening as the fuel temperature was above the boiling point of water.
Results of these "cold" atomization trials were interpreted to show
that residual oil-water emulsion can be atomized in conventional fuel systems
without the emulsion breaking. The higher fuel viscosity will probably require
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higher preheat temperatures. It was decided that the only real measure of the
atomization quality of the emulsion will be results obtained in a combustion rig.
PRACTICAL CONSIDERATIONS IN UTILIZING EMULSIFIED FUELS
A number of practical problems must be evaluated when considering the
ji
including:
use of emulsified fuels. The previous report mentioned some of these problems,
(1) Logistics (Either stable emulsions or on-site preparation
are required and,for premixed emulsions, the
water adds to the total weight to be transported)
(2) Corrosion (The presence of water in the fuel system is
likely to aggrevate corrosion problems)
(3) Stability (Long-term storage stability, is needed at a
range of temperatures.)
Two additional problems come to mind when considering the use of emulsified
residual fuels, including emulsions containing basic additives. These two
problems are:
(4) Pumpability and atomization problems
(5) Corrosion and deposits on the boiler fire-side
surfaces due to the presence of basic additives.
Each of these problems will be discussed in the following report sections.
Other factors to be recognized in the use of emulsified fuels include
a slight reduction in theoretical flame temperature and a slight increase in
heat loss. Both of these effects are caused by the heat absorbed by the water
in the emulsion and were explored in the previous report.
Pumping and Atomization
Data in the technical literature and results of Battelle's experi-
mental studies both indicate that the viscosity of water-in-oil emulsions is
greater than the viscosity of the base oil. Because the viscosity of residual
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oils is already high, preheating is required for pumping and atomization. Thus,
an increase in viscosity presents a practical problem which must be evaluated.
In fact, the detailed viscosity measurements reported earlier were designed to
provide the input for this evaluation.
(27)
Figure 16, from Siegmund , shows the limits of easy pumpability and
the absolute limit of pumpability. He states that, "above 1000 cp (about
4600 SSU) pumping difficulty can be expected and above 2500 cp (£bout 11,000 SSU)
a major loss in pump capacity is normally encountered". This indicates the
level of preheat required for handling of No. 6 oils.
For atomization, No. 6 fuel oils are usually preheated to the temper-
(27 31 32)
ature required to reduce viscosity to 100 to 150 SSU ' ' . Oils in this
viscosity range can be atomized in pressure or two-fluid atomizers conventionally
used.
Figure 17 shows the approximate temperature required to reduce the
viscosity of No. 6 oils to 150 SSU. Because most No. 6 oils are in the 130 to
210 seconds, Saybolt Furol, viscosity range at 122 F (1300 to 2000 seconds,
Saybolt Universal, at 122 F) the normal fuel temperature for atomization is 204 F
to 218 F.
However, the viscosity increase of 20 percent water emulsions for the
nine oils utilized in this study would require an average of about 20 F additional
preheating to produce the same viscosity for atomization. (The better atomization
expected of emulsions due to "secondary atomization" may reduce the required
fuel temperature slightly, but this defeats one purpose of firing the emulsion.)
Heating of emulsions to temperatures above 160 F for long periods of
time may tend to evaporate the water and destroy the emulsion. Therefore, for
firing of emulsions it appears that the final heating of the oil must occur
between the fuel pump and the nozzle. At this location,the fuel is under pres-
sure and evaporation and/or boiling will be reduced.
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m
r
r
m
2
m
2
O
5
>
r
z
H
C
-I
m
i
n
o
r
c
z
09
C
CD
O
J)
O
2500
UJ
t/2
o
Q.
0
tn
o
o
to
1000
POUR
POINT
ABSOLUTE LIMIT
OF PUMPABILITY
\
LIMIT OF
EASY PUMPABILITY
\
\
VISCOSITY
DEVIATION
TEMPERATURE
FIGURE 16. DEVIATION OF VISCOSITY FROM GRADE LINE
ABOVE POUR POINT (27)
-------
400
C\J
CO
8
O
xa
>«
o
•o
c
o
o
0)
o
o
o
CO
300
200
100
50
160
Majority of No. 6 fuel
oils marketed in U.S.
4000
CM
00
O
3000 e
0)
2000 $
c
o
o
a>
in
1000 2*
200 220
Atomizing Temperature, F
240
260
500
FIGURE 17. PREHEAT NEEDED FOR RESIDUAL OILS HAVING
DIFFERENT BASE VISCOSITIES TO REDUCE THE
ATOMIZING VISCOSITY TO 150 SSU
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Therefore, if heating of the fuel is required for pumping, also likely
due to increased viscosity, two separate heating systems will be required.
This may present an unacceptable burden to the operator.
(33)
However, Ludera claims that water-in-oil emulsions can be produced
that have lower viscosities than the base oils. This reference should receive
further attention.
Effect on Corrosion and Deposits of
Basic Materials in Fuel Oil-Water Emulsions
Alkaline materials may be added to residual fuel oil-water emulsions
to capture SO- resulting from combustion of sulfur-bearing fuels. If the
resulting change in pH of the water phase does not affect the characteristics
of the emulsifying surfactant, the S0--capturing additive can be any of several
different substances. Practically, if any appreciable amount of SO- were to be
removed, the additive must be inexpensive, which practically limits it to slaked
lime or to calcined dolomite or magnesite. Other factors aside, NaOH or Na CO-
might be considered as alkaline additives but their cost would be excessive in
the amounts required. For example, if the residual fuel contained 4 percent
sulfur, or roughly 13.5 pounds of sulfur per barrel of fuel oil, then 27 pounds
of S09 would be formed and approximately 24 pounds of CaO or 17 pounds of MgO
would be necessary on a stoichiometric basis to convert the SO- from one barrel
of fuel oil into CaSO. or MgSO. . If NaOH were added in sufficient amounts to
4 4
convert all the S09 in the flue gas to Na SO., about 34 pounds would be required
per barrel of fuel oil. The question then arises, what effect will these large
amounts of additive have on corrosion and deposits in the boiler?
Residual fuel oil seldom contains more than 0.1 percent ash, with the
value usually about 0.05 percent. Even for the higher level, the ash in a
barrel of fuel oil would weigh only 3.4 pounds, so that the amount of CaO to be
added to capture all the SO- from that barrel of oil would be 7 times greater
than the ash in the fuel. With MgO, the weight of additive would be 5 times
greater than the ash, and with NaOH, 10 times greater. Therefore, it is evident
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that the solids in the flue gas would be predominantly from the additive, and
that the ash in the fuel would be an insignificant part of any deposits that
formed on heat-receiving surfaces.
Corrosion of superheaters and reheaters in oil-fired steam generators
invariably can be attributed to the formation of a liquid phase on the metal
surface at temperatures in the range of 1100 F to 1300 F. These highly cor-
rosive liquid films are of two types, (1) alkali iron trisulfates such as
Na.Fe (SO,)„, and (2) vanadium compounds, typically sodium vanadyl vanadate,
•J *T J
5Na O'V *11V 0 (melting point of 1071 F), and vanadium pentoxide, V_0 (melting
point of 1243 F). The corrosion mechanisms here are not important, but it has
been thoroughly established that corrosion will not take place unless a liquid
phase is present; gas-phase oxidation is no worse in flue-gas atmospheres than
in air so that it can be essentially ignored for alloys normally suitable for
high-temperature operation. Liquid films, however, are highly objectionable
and must be prevented.
Two methods exist for controlling such liquid films: (1) establish
conditions that prevent the series of chemical reactions that lead to the
formation of these low-melting compounds, or (2) provide sufficient nonreactive
material to absorb the molten compound physically so that it has no access to
the metal surface below the deposit. The large amounts of CaO or MgO necessary
to capture SO- would function by both of these methods to prevent metal wastage.
Lime and magnesia are highly reactive with SO.,, and in their presence the SO., in
flue gas will be vanishingly small, certainly less than 5 ppm. Under such
conditions, the complex trisulfates cannot form and external corrosion would
not occur by reaction between the alkalies in the oil ash and the metal surface.
These reactions can only take place at superheater metal temperatures when the
SO., exceeds about 250 ppm. Sulfur trioxide plays no part in the formation of
vanadium compounds, but here the physical adsorptive nature of the lime and
magnesia would prevent the presence of a continuous liquid film.
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Added sodium salts would behave oppositely. The compound that would
form eventually is Na SO,. Its melting point is 1625 F, so that the direct
reaction product, by itself, would not be molten at superheater metal tempera-
ture. However, the tendency to form the molten complex trisulfates at the
expense of the oxides on the hot metal surfaces would be greatly enhances with
large amounts of Na SO, present. Also, the formation of low-melting sodium
vanadates could be expected. Hence, increasing the sodium content of deposits
would add greatly to the likelihood of serious metal wastage. Therefore, no
sodium compounds should be added to fuel oil-water emulsions if metal wastage
is to be prevented.
It can be concluded, then, that enough lime and magnesia added to a
fuel oil-water emulsion to capture the SO. in flue gas would provide conditions
on superheater and reheater surfaces such that no metal wastage should occur.
Low-temperature corrosion of air heaters similarly would be unlikely because
no S0_ would be present in the flue gas and hence the dewpoint would be low.
Formation of deposits could be troublesome with additives. Coals
containing large amounts of CaO in their ash, for example Australian brown
coals, frequently cause trouble by forming massive deposits of CaSO on heat-
receiving surfaces. This effect usually is attributed to the nature of the
CaSO, crystallites, which develop an interlocking structure that is extremely
difficult to disrupt with soot blowers. Magnesia may behave similarly, but its
role is less clear. Experience thus far with limestone injection systems for
capturing S0? when burning pulverized coal has not shown similar problems with
deposits, but operating periods have been short and this point has not yet been
proved. Sodium compounds invariably lead to objectionable deposits, and it has
been shown repeatedly with coal ash that the amount of deposit formed is directly
related to the sodium content of the deposit.
Other alkaline additives than NaOH, CaO, or MgO, for example ammonia
or methyl amine, or any other additive not containing a metal salt or compound,
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will have no effect on corrosion and deposits. Additives have not been shown to
affect the combustion process enough to influence formation of S0~ in flames.
Similarly, no additives free of metal ions have been shown to have any effect,
either positive or negative, on corrosion or deposits.
Results of trials of steam injection into the combustion region of a
laboratory combustion apparatus have shown that the presence of the increased
moisture tended to reduce the rate of deposit form.
in the form of an emulsion might behave similarly.
(34)
moisture tended to reduce the rate of deposit formation . Water in the fuel
In summary, additives containing sodium should be avoided as they are
likely to create corrosion and deposit problems. Other additives should not
present these problems.
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PRELIMINARY DESIGN OF A COMBUSTION TEST RIG
The final aspect of this study consisted of the design of a laboratory-
scale combustion unit for simulation of industrial combustion processes. This
small burner-furnace rig suitable for burning residual fuel, emulsified fuel,
and other liquid fuels at about 2 gph, is intended to simulate combustion
conditions comparable to those in industrial boilers. This rig may be used for
studies of factors affecting combustion quality and pollutant emissions such as:
additives, emulsions, and various combustion parameters including recirculation
and two-stage burning.
Special consideration in the design of the combustion rig was given
to aspects which result from the large scaling factor (about 600 to 1). When
scaling combustion processes over this range, it is impossible to simultaneously
maintain both combustion-zone residence time and turbulence in the model equal
to those of the full-scale unit. However, to reduce combustion volume and
conserve space, industrial units are designed for higher turbulence levels than
are necessary for satisfactory combustion. Therefore, it appears possible to
achieve the desired residence times while maintaining satisfactory combustion,
although the turbulence level would be below that of industrial units.
A combustion rig designed to duplicate the residence times of a full-
scale industrial unit can also be operated at high turbulence levels by restrict-
ing the inlet air passage to increase the pressure drop.
Therefore, a combustion rig was designed for maximum flexibility of
operation, so as to permit conducting experiments at both high turbulence and
at long residence times. Flexibility can be provided by the use of variable
geometry air registers, variable swirl, variable air and fuel pressures at
atomizers, variable firing rate and air-fuel ratio, and by controlling wall
temperatures with insulation and/or auxiliary heating.
Design of the unit also included simulation of the time-temperature
profile of industrial units in the post-combustion region.
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Characteristics of Industrial Boilers
The objective of the preliminary design of the combustion test rig
is to simulate as nearly as possible the furnace conditions existing in full-
scale industrial boilers generating about 100,000 Ib/hr of steam.
Because a boiler is designed to generate steam, the important design
criteria must include providing sufficient heat transfer surface to generate
the required quantity of steam. A portion of the needed heat-transfer surface
is located on the furnace walls in the form of water tubes. The remaining heat
transfer surface is located in the path of the flue gas leaving the furnace and
takes the form of superheaters, reheaters, and economizers. The heat.-transfer
surface on the furnace walls must be sufficient to lower exit gas temperatures
to the point where superheat temperature can be held to an acceptable level.
Factors which affect the heat-transfer rate to the walls and, therefore, surface
area requirements include gas temperatures and velocities, flame dimensions
which influence radiation, and ash deposits on the wall tubes.
Providing a geometric arrangement of the furnace which includes the
required heat-transfer surface results in a furnace volume which serves as the
combustion space. The combustion intensity (in terms of heat-release rate per
unit volume of furnace) for a given heat-transfer rate, is dependent upon
furnace shape and size. For example, for a cubical furnace with each dimension
2 3
equal to L1, the wall surface area is 6(L') and the furnace volume is (L1) .
Therefore, the surface-to-volume ratio reduces to 6/L1. (For furnaces of other
shapes, the constant would be some value other than 6.) If heat-transfer rates
are constant, the combustion intensity is a constant divided by L1, and decreases
as boiler size increases. Thus, for furnaces of similar shape for a given heat-
transfer rate, the combustion intensity is inversely proportional to boiler size.
Residence time for combustion for these similar units is inversely proportional
to combustion intensity and, therefore, is directly proportional to furnace
size.
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In practice, an effort is made to minimize the volume of large
furnaces by adding heat-transfer surface in the form of curtain walls or plat-
tens of tubes, or by use of multiple furnaces of smaller size. Using these
techniques, and by taking advantage of the higher radiation flux in larger
furnaces, it has proven possible to operate with combustion intensities of
3
20,000 to 30,000 Btu/ft -hr in the largest furnaces. Although ingenuity is
required to add heat-transfer capability to large furnaces, the design of small
furnaces may require less than full water cooling to keep gas temperatures in
the furnace high because the surface-to-volume ratio for a small furnace may be
as much as 10 times that in a large furnace. Techniques for maintaining high
gas temperatures include use of tube-and-tile walls (water tubes fairly widely
spaced in front of a refractory wall), or by use of refractory sections in the
furnace.
For the purpose of modeling a typical industrial furnace, a value of
3
30,000 Btu/ft -hr has been selected as a suitable combustion intensity. A
furnace for generating steam at a rate of 100,000 Ib/hr would have a firing rate
of about 140,000,000 Btu/hr. Therefore, the volume of the furnace would be
3
4650 ft or about a 17-foot cube. The unit will burn about 940 gph of No. 6
2 2
fuel oil. Surface area of this furnace would be 5 (L1) = 1650 ft . The
average rate of wall heat transfer to provide a 2200 F furnace exit gas temper-
2
ature would be about 23,000 Btu/ft -hr.
Time-Temperature Relationships
Little data giving gas residence time-temperature relationships in
industrial boilers appears to have been published. However, residence time can
be estimated by a dimensional analysis of a boiler furnace. Roughly, 10 Ib/hr
of air is required for combustion to generate 10,000 Btu/hr. Therefore,
3
30»v Ib/hr air is required to support combustion at intensity 30,000 Btu/ft -hr
3
in a furnace volume of V ft . The specific volume of combustion products, v ,
O 3
at an average furnace temperature of 2500 F is:
RT
_ 53.35 x 2960 _ 3
- 14.7 x 144 ' 75 ft
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Therefore, the volume of gas passing through the furnace,Q, is
Q = 75 x 30-V ft3/hr = .625 V ft3/sec.
o o
Residence time in the furnace will be
Vo ft3 Vo
T = ^ = =1.6 seconds.
Q ft /sec .625 VQ
Likewise, residence times for other combustion intensities are:
Combustion intensity, Residence times,
3
Btu/ft -hr sec
50,000 1.0
20,000 2.4
15,000 3.2
Figure 18 shows time-temperature plots for 3 oil-fired central-station
utility boilers . These units are designed for firing rates of 3 to 20 times
that of a 100,000 Ib/hr industrial boiler. Gas temperatures at the inlet to the
superheater would be 2000 F to 2300 F. Therefore, most of the residence time
shown on Figure 18 occurs in the heat-transfer region and only 1.5 to 3 seconds
of this time occurs in the combustion region.
Although it would be desirable to determine the absolute values for
each of the various parameters for industrial furnaces, as mentioned earlier,
there is little data available in the literature. However, it will be shown in
the next section of this report that the scaling can be done on a comparative
basis and absolute magnitudes are not needed for design purposes.
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3000
51
Pittsburgh No. I, 165 mw
Approx
furnace
region
j
Lending No. I, 55 mw
Pittsburgh No. 5, 335 mw
5 10 15
Time, seconds
20
FIGURE 18. TIME-TEMPERATURE DATA FOR THREE
UTILITY BOILER FURNACES
Scaling and Modeling Considerations
It is not possible to make a small-scale model that simultaneously
simulates turbulence and mixing conditions and residence times. Instead, it is
necessary to limit the modeling to simulate either turbulence and mixing or
residence time. Both can be achieved in the same combustion rig for different
runs by choice of the particular operating conditions.
Where flame geometry, flame temperature, completeness of combustion,
and effects of turbulence and mixing on completeness of combustion are the vari-
ables of primary interest, it appears desirable to model with velocity and pres-
sure drop at about the same levels as in the prototype. However, where a
phenomenon controlled by chemical kinetics is of primary interest, it appears
necessary to model to provide suitable time-temperature profiles rather than
maintaining velocity and turbulence levels. Phenomena in combustion of heavy
oil in industrial furnaces that are controlled by reaction kinetics include the
formation of nitrogen oxides and the oxidation of S0~ to SO-. If reaction
kinetics phenomena are to be the subject of research, then it appears necessary
that the model closely simulate prototype profiles of temperature and residence
time. In such a model the velocities and turbulence will be lower than in proto-
type units. However, prototype units are usually designed for higher turbulence
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than required for satisfactory combustion so as to minimize furnace size. It
is likely that the reduced turbulence of the model will still be adequate to
provide satisfactory combustion.
Basically, two scaling criteria are available for consideration in
planning the design of the combustion test rig to model full-scale units. These
two criteria are:
(1) constant combustion intensity
(2) constant inlet pressure drop or air velocity.
The first of these criteria provides a model having residence times similar to
those in the full-scale unit. Turbulence in this model is less than in the full-
scale unit. The second criteria provides a model having turbulence comparable
to the full-scale unit. However, this high turbulence for the model results in
combustion being completed rapdily in a small volume so that residence times are
much shorter than in full-scale units.
Illustration of each criteria by the use of an example will aid in
evaluating the merits of each model. Consider a full-scale axial flow furnace
of firing rateF1 , length L1, square in cross-section having width W", and M
2
burners per row. This furnace can be divided in M sub-furnaces with two types
of walls, conducting and perfectly insulated. Each sub-furnace would have a
F'
firing rate F, where F = —r ; length L, where L = L'; and width and height W,
W' M
where W = — . This sub-rurnace will have 0 to 4 conducting walls and the
M
remainder perfectly insulated walls.
For example in Figure 19, consider a furnace of dimensions of 14.4 ft x
2
14.4 ft x 22.4 ft (W1 x W x L1) with four burners (M ) and firing at a rate of
140,000,000 Btu/hr (F') or 940 gph oil. The combustion intensity is 30,000
3
Btu/ft -hr.
F1
Now for the sub-furnace: F = —-r = 235 gph oil
L = L1 = 22.4 ft.
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The flow pattern in the furnace might be considered to consist of a
highly turbulent recirculation region followed by a plug flow region.« It will
also be considered that the flow in each sub-furnace is identical and independent
and also consists of a turbulent recirculation zone and a plug flow zone. The
modeling problem can now be simplified to modeling the one burner sub-furnace
rather than the multiple-burner unit. To avoid confusion of the model or test
rig with the sub-furnace in the following discussions of modeling and combustion
test rig design, the sub-furnace will henceforth be spoken of as the "full-
scale unit" or "prototype".
W' = 14.4'
FIGURE 19. FULL-SCALE FURNACE (4 BURNERS) DIVIDED INTO
4 SUB-FURNACES FOR MODELING PURPOSES
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Consideration can now be given to the two scaling criteria mentioned
previously :
(1) constant combustion intensity
(2) constant pressure drop.
Constant Combustion Intensity Model.
A constant combustion intensity model would be designed for a volume
3
firing rate of 30,000 Btu/ft -hr, identical with the combustion intensity of the
full-scale unit.
To preserve the flow pattern of the furnace, the geometric proportions
of the model and the full-scale unit should be identical. To maintain constant
geometric proportions, each dimension of the sub-furnace should be reduced by a
scale factor n. Therefore, the volume of the model will be related to the
3
volume of the full-scale unit (or sub-furnace) by n . Maintaining combustion
intensity, the ratio of fuel flow rates will be proportional to volume ratio
and thus to n . The minimum firing rate for which satisfactory nozzle per-
formance can be achieved is about 1.5 gph, so this rate is chosen for the model.
mu •* W L
Therefore, if n = — = —
w I
n3= W!L = 235 =
w£ 1.5
n = (157)1/3 = 5.4
then
w = — = •^-. - = 1.33 ft = 16 inches
n 5.4
A = t = 22^ £t = 4.17 ft = 50 inches.
Gas velocity (U for the full-scale unit and u for the model) is pro-
portional to volumetric throughput of gas (Q for the full-scale unit and q for
the model) and inversely proportional to cross -section area. Therefore, for
the full-scale unit (K is a constant):
»-*
W
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and for the model
w
Additionally, the volumetric throughput of gas is proportional to the
firing rate. Because the combustion intensity is held constant, the volumetric
throughput of gas is also proportional to furnace volume (V for the full-scale
unit and v for the model). Then,
3. - 2.
v ~ V
and
V vn n
It follows that,
„ 22
Kq q UW „ q (w n ) u U
u = 2 2 = U 3" ' 2~^ = ~ =
w w Q (qn ) w n 5.4
Combustion intensities (C. for the full-scale unit and C for the
fs m
model) were set equal. Therefore,
where
C = C,
m fs
C = H*
m v
and
Cfs = H V
and H is a constant.
Reynolds numbers (R.. for the full-scale unit and R for the model)
are related by
Rfs = P'WU
R = P'wu
m
where P1is a fluid property factor.
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S° that P'WKC L
R, = — rr~ = WC£ LK1
fs H fs
and P'WKC
R = H = wC £K' = C K'
m H m m 2
n
n2 ~29
The Reynolds number for the model is only 1/29 that of the full-scale unit.
Considering residence time (T for the full-scale unit and t for the
model):
U
and t = -
u
but
Therefore, residence times are equal in both furnaces.
A final useful factor in evaluating modeling methods is the location
of the flame with respect to the furnace length. Flame location will be related
quite closely to other variables such as the location at which the air jet fills
the furnace. It may be assumed that the angle of expansion of the air jet
(assuming a point source) is independent of Reynolds number. Although it might
appear at first glance that the air jet expansion angle would also be dependent
on axial velocity, this is not what occurs. The assumption of air-jet expansion
angle being independent of Reynolds number implies that the increased axial
velocity (which would tend to reduce the expansion angle) is offset by increased
turbulence intensity present with the higher velocities.
Hence, the distance from inlet to the location at which the jet fills
the furnace (X for the full-scale unit and x for the model) is directly pro-
portional to width and height of the furnace. Therefore, for the full-scale
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unit:
For the mode 1:
57
X = BW and — = — (B is a constant)
Li J-i
_, x Bw
x = Bw and — = — .
i, i
Continuing,
/" W
x _ By n
= = JJW = X .
' = -
Therefore, the flame shape is identical in the model and full-scale unit.
Constant-Pressure-Drop Model. A constant-pressure-drop model would
be designed for the same air velocity through the inlet wall in both the model
and the full-scale unit. Using symbols as previously defined, but realizing
that numerical values for the model variables will be different than for the
constant combustion intensity model, the following analysis can be made.
Constant pressure drop requires that U = u.
Volume throughput of gas is proportional to gas velocity and cross-
section area,
- K
and
uw2 = U W 2 = I f UW2 = £
K K ( n; 2 ' K 2
n n
and
2 _ 0
n ^
q
but
Q 235
= T~T = 157
q 1.5
therefore
n2 = 157
and
n = J 157 = 12.5
consequently
w = - = 7.2 ft = 0<58 ft = 6.9 inches.
n 12.5
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To maintain identical flow patterns in the model and full-scale unit,
dimensions must be proportional. Therefore,
= 1.8 ft = 21.5 inches.
Combustion intensity for the full-scale unit is
( VTL )
and for the model
/'uw
c =HWV = = ---n=nCf -12.5C.
m v -r— K.jfc ,L. KL fs fs
(w£) K(n}
Therefore, the combustion intensity for the model is 12.5 times the combustion
intensity of the full-scale unit.
Reynolds numbers are related by
and
Rfs = P'WU
R =P'wu=P' ( )U -.O-
m n n n 12.5
Therefore, the Reynolds number of the model is roughly one-twelfth that of the
full-scale unit.
Finally, considering residence times
T = —
U
and
JL _ f L \ -L -^ L *- -*- m
C -u - ^ n ;'U ' n * U n1 ' 12^ X '
Therefore, the residence time in this model is about one-twelfth of that of the
full-scale unit.
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Considering flame shape
W
x = Bw _ B n BW = X
it, Si L. L ~ L
n
and the flame shape is accurately modeled.
Quasi-Constant-Combustion-Intensity Model
A third model (referred to as the quasi-constant-combustion-intensity
model) can be constructed by using the same velocity and cross-section area as
the constant pressure drop model but increasing the length £, to equal L. Then
2
uw
c =H*= ^ = ™=C
m V W2L KL fs
L L
and t = - = - = T
u U
with apparent combustion intensity and residence time in the model and full-scale
units being equal.
However, for this model
B.£
* = Mii = • n = I • BW _ I £ _ I £. •
i SL ~ L ~n L~nL~ 12.5 L
The flame is quite distorted in the model and, in fact, combustion is limited
to the space near the inlet wall. Added length, which appears to reduce com-
bustion intensity, in reality only serves as a post-combustion space.
Comparison of Models With the Full-Scale Unit
The following table summarizes the relationship of important variables
for the modeling criteria discussed above. It is obvious that each model has
its advantages and shortcomings.
The constant combustion intensity model provides the desired residence
times and flame shape, but at a lower turbulence level (Reynolds number).
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Width = Height
Length
Velocity
Residence Time
Combustion Intensity
Reynolds Number
Flame Shape
Full-Scale Unit
W
L
U
Constant
Combustion
Intensity
W
5.4
L
5.4
U
5.4
Constant
Pressure
Drop
W
12.5
_L
12.5
U
Quasi-
Constant
Intensity
Model
W
12.5
L
U
'fs
fs
'fs
12.5 C
fs
fs
29
X
L
X
L
12.5
X
L
fs
R,
fs
12.5
1 X
12.5 L
Although the turbulence level is reduced for this model, most practical furnaces
are designed for turbulence levels far in excess of the turbulence necessary
for combustion. This is done to reduce flame length and allow construction of
small, space-efficient units. The turbulence level designed for..our model
should be adequate for the purposes of this study.
The constant-pressure-drop model maintains flame shape but both
residence time and turbulence level are reduced. An order of magnitude reduction
in residence time would severely affect the validity of pollutant reaction data.
Finally, the quasi-constant combustion intensity model apparently
preserves the residence time of the full-scale unit but at a loss in turbulence
and with a distorted flame shape. Although the residence time is apparently
preserved, the change of flame shape results in most of this residence time
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61
being in the post-combustion region and not the combustion region as desired.
The combustion region residence time would be essentially identical to that of
the constant-pressure-drop model.
y"3 f \
Brown and Thring considered two types of modeling in connection
with the use of pressure-jet burners in marine boilers. They list the variation
of several parameters with scale for the two cases of constant velocity (constant
pressure drop) and constant residence time (constant combustion intensity).
Agreement between parameters for their hot model and for the full-scale unit
appears slightly better for the constant-residence-time model, but agreement is
satisfactory in both cases.
It is possible to provide a reasonable simulation of the constant
combustion intensity and the constant pressure drop models in a single model
combustion chamber by using two levels of firing rate. A low rate, such as
1.5 gph, would provide full-scale unit residence times, while a higher firing
rate, such as 8 gph, would simulate velocities and mixing effects comparable to
the full-scale units. Because of the relatively large size of the combustion
space for the residence-time simulation, the heat loss to the chamber walls will
be a critical factor in simulating flame temperature. In order to avoid ex-
cessive chilling of the flame by wall radiation it will be necessary to provide
effective insulation or, perhaps, auxiliary heating in the walls to limit heat
2
loss to about 4500 Btu/ft -hr. However, for proper temperature conditions when
firing at the higher rate simulating constant-velocity conditions, wall heat loss
2
should be about 22,000 Btu/ft -hr.
The foregoing discussion is based upon the premise that velocities in
the combustion space are determined by size of the space. Actually, they are
controlled by burner design, and it is possible to use a turbulent burner of
small size to form a small flame in a large combustion space. Accordingly, it
appears quite feasible to simulate both residence time and turbulence levels in
the same furnace model at about the same firing rates by using two different
burners having widely different velocities. A large, low-velocity burner would
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form a large flame that fills the combustion space, and a small, high-velocity
burner would form a small, highly-turbulent flame that occupies about 1/5 of the
available furnace volume. Using this expedient, it is probable that either
residence time or velocity can be simulated at about the same firing rate in
the same model furnace.
Other Scaling Phenomena
Several other scaling phenomena (nozzle scaling, heat flux, and
buoyancy) are discussed in the Appendix. Summarizing these discussions:
1. Nozzle scaling: To obtain the same droplet size as in a full-
scale unit would require reducing air pressure (assuming two
fluid atomizers) and/or reducing fuel viscosity for the model.
2. Heat flux: The insulating value of all furnace walls of the
model will have to be increased relative to the full-scale unit.
3. Buoyancy: Buoyancy effects in the model will be greater than
in the full-scale unit but should not be a problem.
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Design o£ Combustion Test Rig
Figure 20 summarizes the modeling considerations discussed in the fore-
going sections. The approach starts with the full-scale industrial boiler and
moves step-by-step through a sub-section of the full-scale furnace to a square-
sectioned model and, finally, to a circular equivalent model for the proposed
combustion test rig.
Furnace Design
Figure 21 is a section view of the furnace for the proposed combustion
test rig. It consists of a cylindrical cavity 18 inches in diameter and 50
inches long. Dimensionally, this furnace is similar to the furnace with 16 inch x
16 inch cross section. However, the cylindrical shape provides a more symmetrical
model which eliminates corner effects. The outer shell of the rig is 10-gage
steel and is airtight; the furnace is lined with insulating firebrick 4.5 inches
thick, with block-type insulation between the brick and the shell. Several
sampling ports in one side will provide for traversing across the flame at
various distances from the burners. An axial port, at the outlet, will permit
axial traversing should this prove desirable.
The outlet diameter for the model furnace would be reduced to six
inches to enclose the flame and provide for normal recirculation and normal
radiation losses.
The space within this furnace is designed for a combustion intensity
•j
of 30,000 Btu/ft -hr when firing at a rate of 222,000 Btu/hr or about 1.5 gph of
No. 6 fuel oil. Residence time in the furnace will be about 1.7 sec, comparable
to residence times in the full-scale units mentioned earlier. For time-tempera-
ture relations in the model comparable to that of the prototype, the heat-trans-
2
fer rate to the walls should be about 4500 Btu/ft -hr when firing to simulate
2
residence time, and about 22,000 Btu/ft -hr when firing to simulate furnace
velocity.
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Furnace
Operational Parameters
Firing rate: 140,000,000 Btu/hr
Combustion intensity: 30,000 Btu/ft3-hr
Firing rate
Cross section
675,000 Btu/ft2-hr
Full-scale industrial furnace
Firing rate:
35.000.00.0 Btu/hr
Combustion intensity- 30.000 Btu/ft -hr
Firing rote
Cross section
675.000 Btu/ft2-hr
Constant combustion
intensity model
Constant
Combustion
Intensity
Constant
Pressure
Drop
Firing rate: 222.000 Btu/hr 1.200,000 Btu/hr
Combustion intensity: 30.000 Btu/ft3-hr 162,000 Btu/ft3-hr
F'rmg r°te : 125.000 Btu/ft2-hr 675.000 Btu/ft2-hr
Cross section
Cylindrical equivalent of
constant combustion
intensity model
Firing rate: 222.000 Btu/hr 1,200,000 Btu/hr
Combustion intensity 30,000 Btu/ft3-hr 162,000 Btu/ft3-hr
Firing rote
Cross section
125.000 Btu/fr-hr 675.000 Btu/ft-hr
FIGURE 20. MODELING PROCEDURE TABULATING OPERATIONAL PARAMETERS
FOR FULL-SCALE FURNACES AND MODELS
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>
H
H
m
r
r
m
2
m
2
o
z
01
H
-I
C
H
m
i
n
o
r
c
2
ID
C
l/i
CD
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Air inlets
Sampling
and observation
ports
Shell-10 gage black sheet steel, 33 x 60
Block-type thermal insulation
Insulating firebrick, 4.5" thick
dTb
Burner assembly
Section A-A
Probe on
centeriine
O
5
m
FIGURE 21. FURNACE SECTION OF COMBUSTION RIG
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66
To simulate time-temperature gradients to lower temperatures, as for
the passes through the boiler heat-transfer surfaces, the furnace length would
be extended and/or cooling surface added to obtain gas cooling at the desired
rate.
Burner Design
Figure 22 is a cross-section of the model burner. The burner
incorporates considerable flexibility to permit operation over a range of
conditions. It is possible to vary the firing rate, the flame velocity, the
swirl angle, and the type of fuel fired. When all air is admitted through the
axial holes in the plate to the left of the burner throat in Figure 22, all flow
will be axial. The turbulence level in this axial stream will be relatively
high because air is admitted at a velocity of about 50 fps or more through 24
holes; the jets from these holes will merge in the burner throat to provide a
highly turbulent stream at low axial velocity. By adjustment of the proportion
of air flow to the swirl vanes and to the axial holes, the percentage of swirl
in the burner throat can be adjusted at will. Because of the high turbulence
from the axial-flow holes, the overall turbulence level will remain about the
same as the tangential velocity is reduced.
The burner throat of 3.5-inches diameter is designed for an axial
velocity of 15 fps, to produce a large flame that will fill the furnace. In
order to simulate velocities in a full-scale boiler burner, two alternatives are
available. First, the firing rate can be increased by a factor of five (to 8 gph)
with no other changes. The flame size and shape will be about the same as with
the low firing rate, but the residence time will be reduced by a factor of five.
Alternatively, an insert can be placed in the burner throat (see Figure 22),
reducing its diameter from 3.5 inches to 2.875 inches. (This insert can be a
metal ring held in place by set screws.) The throat velocity, with this change,
will increase by the required factor of about 5 so that full prototype velocity
will be obtained at the 1.6 gph firing rate. With this change, the flame should
become much smaller and will not fill the combustion space.
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Swirl air
H
m
r
r
m
2
m
2
O
2
en
H
H
C
H
m
n
o
r
c
2
0)
C
-I
o
5
m
tn
Mounting plate
Throat insert, 2-7/8" ID
-Air atomizing nozzle
-(24) holes, 1/4" diam
Axial stream
air
Cast refractory , V/
\\ nozzle is
adjustable
axially
12 vanes,
2-1/4 x 3/4",
opening 0.5" or less
Detail of swirl vanes
FIGURE 22. DETAIL OF BURNER FOR COMBUSTION RIG
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68
The fuel nozzle shown is a Delavan "Industrial Aero" air-atomizing
nozzle which was used for the "cold" atomization trials of No. 6 emulsions
reported earlier.
A combustion rig of the type discussed above is sufficiently versatile
to have a wide variety of uses. Other possible uses of this rig include studies
of the effect of combustion variables such as droplet size, air-fuel ratio, and
external recirculation of flue gas on pollutant emissions. With the addition
of controlled-temperature heat-transfer tubes, the rig would also be useful for
studying the effects of additives on superheater tube corrosion and deposits.
It is possible to fire natural gas in this burner by replacing the
fuel nozzle with a gas injector. Pulverized coal can also be fired by sub-
stituting a coal nozzle for the oil atomizer. The coal nozzle would require a
central cone to form a conical coal dispersion much like an oil spray. In a
previous furnace of this size at Battelle, coal was fired at rates from 50 to
100 Ib/hr.
Auxiliary Equipment
Figure 23 shows a schematic layout of the laboratory setup required
to support the rig. Included are a source of burner air, two parallel air flow-
meters and control valves for the two burner air inlets,and a fuel pump and
preheater to heat the oil to the required atomizing temperature of about 250 F.
Instrumentation is also required for sampling and analysis of furnace and exhaust
gas and for temperature measurement. Fuel rate would be controlled by operation
of a variable-displacement pump and measured by weighing.
Estimated Construction Cost
The estimated cost for constructing and checking out an oil-fired com-
bustion test rig as described above and placing it in operation is approximately
$48,000.. This estimate is based on costs at Battelle-Columbus including shop,
technician, technical supervision and overhead.
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m
>
H
H
m
r
r
m
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2
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en
H
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H
m
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c
5
ID
C
in
m
o
H
O
Flowmeters
Control for swirl
and axial stream air
Blower
Preheater
element
Cooling water
Supply and return
To gas analysis
equipment
Gas-sampling probe
Sampling and
observation ports
Final
oil heater
Oil pump
Heated oil tank
on scales
FIGURE 23. LABORATORY SETUP FOR COMBUSTION RIG
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70
It assumes that the burner design has been established through preliminary trials
and is not included in the cost estimate. Costs associated with gas analysis
and emission measurements are not included.
The total cost estimate consists of the following items:
1. Final detailed design of the burner, furnace,
heat exchanger, and instrumentation
2. Construction of burner
3. Construction of furnace
4. Construction of heat exchanger
5. Assemble rig with oil preheat system,
controls and instrumentation
6. Sufficient firing and checkout to select
operational parameters at various firing
rates.
ACKNOWLEDGMENTS
Contributions of the following Battelle staff members are acknowledged
Dr. David B. Cox in determining viscosity and rheological properties,
Robert D. Giammar and James J. Tavor in performing the "cold" atomization
trials, Dr. James A. Gieseke in examining atomized droplets, and William T.
Reid in evaluating the corrosion and deposits tendencies.
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REFERENCES
1. Wasser, J. H., Hangebrauck, R. P., and Schwartz, A. J., "Effects of Air-
Fuel Stoichiometry on Air Pollutant Emissions from an Oil-Fired Test
Furnace", Jour. Air Pollution Control Assoc., Vol. 18 (5), May, 1968,
pp 332-337.
2. 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., September 17 & 18, 1968,
19 pp.
3. Barrett, R. E., Moody, J. W., and Locklin, D. W., "Preparation and Firing
of Emulsions of No. 2 Fuel Oil and Water", NAPCA Contract No. PH 86-68-84,
Task Order No. 8, November 1, 1968, 36 pp.
4. Ivanov, V. M., Kantorovich, B. V., Rapiovets, L. S., and Khotuntsev, L. L.,
"Fuel Emulsions for Combustion and Gasification", Vestn. Akad. Nauk SSSR
(5) May, 1957, pp 56-59.
5. Ivanov, V. M., and Nefedov, P. I., "Experimental Investigation of the
Combustion Process on Natural and Emulsified Fuels", NASA Tech. Transl.
TT F-258, Jan. 1965, 23 pp.
6. Ivanov, V. M., Kantorovich, B. V., Rapiovets, L. S., and Khotuntsev, L. L.,
"Treating Viscous Crude Fuel Oil Containing Water", USSR Patent No.
117106, Jan. 1959; (Chem. Abstracts, Vol. 53, p. 20786 e) .
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"Use of Heavy Petroleum Residues and Tars as Emulsified Fuels for Combustion
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1959, 156 pp.
8. Cornet, I., and Nero, W. E., "Emulsified Fuels in Compression Ignition
Engines", Ind. Eng. Chem.,Vol. 47, (10), Oct. 1955, pp 2133-2141.
9. Maillard, A., "The Combustion of Aqueous Emulsions of Mineral Oils in
Diesel Motors", Comptes Rendus, Vol. 231, 1950, pp. 363-364.
10. Sumner, C. G., "Clayton's Emulsions and Their Technical Treatment", Fifth
Ed., J. and A. Churchill, Ltd., (London) 1954, p 409.
11. Coleman, L. E., "Development of a Fire-Resistant Emulsion Hydraulic Fluid",
Jour. Inst. Petroleum, Vol. 50 (492), Dec. 1964, pp 334-344.
12. Coker, G. T., Jr., and Francis, C. E., "The Place for Emulsions as Fire
Resistant Power Transmission Fluids", Lubrication Engineering, Vol. 12
(5), Sept-Oct. 1956, pp 323-326.
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REFERENCES (Continued)
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 Con-
ference, Washington, B.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,
B.C., March 17-21, 1968, 5 pp.
15. McCourt, E. P., "Developments in the U.S. Army Emulsified Fuels Program",
AIAA Paper 68-558, Prese ted at AIM 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". USAAVIABS Tech-
nical Report 67-62, Nov., 1967, 134 pp.
17. Stockton, W. W., and Olsen, C. L., "Feasibility of Burning Emulsified Fuel
in a 71M100 Engine", USAAVIABS Technical Report 67-74, Feb. 1968, 60 pp.
18. Custard, G. H., "Vulnerability Evaluation of Emulsified Fuels for Use in
Army Aircraft", USAAVIABS Technical Report 68-20, April, 1968, 151 pp.
19. Harris, J. C., and Steinmetz, E. A., "Investigation and Analysis of Air-
craft Fuel Emulsions", USAAVIABS Technical Report 67-70, Dec., 1967, 180 pp.
20. "Investigation of a Feasibility of Burning Emulsified Fuel in Gas-Turbine
Engines", USAAVIABS 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
Aeronautic Meeting, New York, April 24-27, 1967, 9 pp.
23. Koblish, T. R., Roberts, R. A., Schwartz, H. R., Gordon, R. D., and Ault,
E. A., "Emulsified Fuels Combustion Study", USAAVIABS Technical Report
69-4, Feb., 1969, 121 pp.
24. Atkinson, A. J., "Evaluation of Experimental Safety Fuels in a Conventional
Gas Turbine Combustion System", Naval Air Propulsion Test Center, Report
No. NA-69-1, April, 1969, 25 pp.
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REFERENCES (Continued)
25. Harvey, T., and Monarch, J., "Environmental Testing of a Gas Turbine Engine
Utilizing EF4-101 Emulsified JP-4 Fuel", USAAV1ABS Technical Report 68-55,
August, 1968, 45 pp.
26. Urban, C. M., Bowden, J. N., and Gray, J. T., "Emulsified Fuels Character-
istics and Requirements", USAAVLABS Technical Report 69-24, March, 1969,
90 pp.
27. Siegmund, C. W., "Low Sulfur Fuel Oil Characteristics", Paper No. 69-195,
Presented at 62nd Annual Meeting of Air Pollution Control Assoc., June
22-26, 1969, New York, N.Y., 28 pp.
28. Blade, 0. C., "Burner Fuel Oils, 1968", U.S. Dept. of Interior, Bureau of
Mines, Petroleum Products Survey No. 56, Sept., 1968, 34 pp.
29. Jobling, A., and Roberts, J. E., "Goniometry of Flow and Rupture",
Rheology, Vol. 2, Chapt. 13, Academic Press, 1956.
30. Weissenberg, K., "A Continuum Theory of Rheological Phenomena", Nature
Vol. 159 (4035), March 1, 1947, pp 310-311.
31. "Viscosity-Temperature Relation for Fuel Oils", Chart published by Esso
Research and Engineering Co., 1959, 1 p.
32. Safford, D., "Fuel Oil Burner Equipment Modifications and Adjustments
Versus Changes in Residual Oil Characteristics", Paper No. 69-197, Pre-
sented at 62nd Annual Meeting of Air Pollution Control Assoc, June 22-26,
1969, N.Y., N.Y., 10 pp.
33. Ludera, L., "Water Emulsions at Boiler Fuel Oils and Possibilities of
Using them as Liquid Fuels", Gospodarka Paliwami i Energia, Vol. 1, 1965,
PP 5-9.
34. Gearing, W. A., How, M. E., Kear, R. W., and Whittingham, G., "The Effect
of Combustion-Air Humidification on the Formation of Deposits in Pulverized-
Coal Firing", Jour. Inst. Fuel, Vol. 28 (178), Nov. 1955, p. 549.
35. Salo, E. A., "Visible Emissions from the Combustion of Fuel Oil", Paper
No. 69-194, Presented at 62nd Annual Meeting of Air Pollution Control
Assoc., June 22-26, 1969, N.Y., N .Y., 19 pp.
36. Brown, A. M., and Thring, M. W., "The Application of Pressure-Jet Burners
to Marine Boilers", Tenth Symposium (International) on Combustion, The
Combustion Institute, Pittsburgh, Pa., 1965, pp 1203-1218.
37. Wigg, "Drop-Size Prediction for Twin-Fluid Atomizers", Jour. Inst. Fuel,
Vol. 37 (286), Nov. 1964, pp 500-505.
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APPENDIX
BATTELLE MEMORIAL INSTITUTE - COLUMBUS LABORATORIES
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APPENDIX
A. INCORPORATION OF BASIC ADDITIVES IN
WATER-IN-DISTILIATE FUEL OIL EMULSIONS
One aspect of this task order was to determine if basic additives
could be incorporated into water-in-distillate fuel oil emulsions such as pre-
(3)
pared under the previous task order .
In the earlier work, a surfactant which promoted stable water-in-
distillate oil emulsion was identified. The surfactant consisted of 4 parts
(by weight) of sorbitan sesquioleate and 1 part polyoxyethylene (20) sorbitan
monopalmitate.
In this task, relatively stable water-in-distillate oil emulsions con-
taining 20 weight percent water and 10 weight percent NH.OH, Ca(OH)~ or Mg(OH)?
were prepared using this surfactant and the procedures described in the report
(3)
on Task Order No. 8 . However, the surfactant is not compatible with NaOH.
A suitable emulsion containing NaOH was prepared using about 5 weight percent
naphthenic acid as an emulsifying agent. (Naphthenic acids are constituents of
crude and distillate oils.)
None of these water-in-distillate fuel oil emulsions containing basic
additives exhibited long-term stability. However, they appeared to be suitable
for preliminary burner tests.
B. OTHER SCALING CONSIDERATIONS
Three other factors which must be considered in modeling and choice
of conditions are (1) nozzle scaling, (2) wall heat flux and (3) buoyancy of
hot gases. These additional considerations are discussed in this Appendix.
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A-2
Nozzle Scaling
In choosing a two-fluid nozzle for the combustion rig, the question
occurs as to what is the relationship between the atomization in the full-scale
boiler and that in the combustion rig. It is assumed that the flow rate of
atomizing air for the model nozzle and the full-scale or prototype nozzle do not
have to be in the same ratio as the firing rates, as each is only a small
fraction of the total air flow in the corresponding combustion chamber.
Momentum Flux. To obtain the same momentum flux ratio (atomizing air
to total combustion air) in the model and the prototype, and assuming that the
fuel adds no momentum when it is injected or aspirated by the air flow in the
nozzle ,
(£4^>(!£0
where d = characteristic nozzle dimension for a series of geometrically
similar nozzles (d for model nozzle, D for full-scale unit nozzle)
q and Q = volumetric air flow rates through nozzles
of the model and prototype
p = density of atomizing air
Si
p = density of combustion air.
For the constant-combustion-intensity model, this reduces to,
2
n =
As n is fixed, it is seen that this equation expresses a relationship between
the atomizing air-flow rate and the characteristic dimension of the nozzle. The
exact range of dimensions and flow rates to be considered would result from
comparison with various prototype designs.
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A-3
Further, the nozzle for the model is expected to be fired at only
1/m of the design maximum firing rate of the nozzle. Thus, q = _!_ q ,. If the
design firing rate for a series of nozzles is proportional to d , and assuming
the prototype is fired at the design firing rate for the nozzle, then
and
n'
Therefore,
Q 7/2/ 1/2 .
_a _ n /m
qa =
However, by direct scaling of the nozzle dimensions and for constant
atomizing air pressure,
a 2
= n
qa,d
and thus,
qa,d 3/2/ 1/2
qa
3/2/ 1/2
= n / m
Therefore, the atomizing air pressure for nozzle of the combustion rig would have
to be reduced by a factor
. 3/2/ 1/2. 1/2 f 3 Nl/^
(n /m ) or ( n )
m
Obviously, if the nozzle for the model is fired at its design maximum
firing rate, then m reduces to 1.0 in all above equations.
Droplet Size. FromWigg's study of drop size from several two-fluid
(37)
atomizing nozzles , it is found that drop size is a function of
(Y'V2) (Pfqf)a (Paqa + Pfq£rV1/ui
Paqa
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A-4
where
•y and Y = viscosity of oil in model and prototype
u and
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A-5
Heat Flux
The heat flux to the walls should also be considered. For the constant
combustion intensity model, the firing rate, and thus heat input, scales
3
according to n . The heat loss varies with area. Thus, to maintain the ratio
of heat loss to heat input,
n 2 f U2T
c w a Cf0w L
m rs
where y and Y are the wall thickness is of the model and full-scale unit and
AT and ATf are temperature drops through the furnace wall for the model and
full-scale unit. If AT = AT, , this leads to
m f s
y kfs
n = £ .
m
With typical values, a magnesia wall in the model could replace a steel wall of
the same thickness in the full-scale unit. Considering the case of an insulating
wall in the prototype, the problem becomes more severe. First, it is noted
that the thickness, y, now becomes a matter of inches rather than fractions of
an inch. Furthermore, easily available materials with much lower k values are
not available.
However, if AT < AT.. , then
m is
k AT
y fs A fs
n =Y -k— • AT~ ' '
m " m
Hence, reasonable values of y and k could be obtained by decreasing AT con-
siderably. This could be accomplished by heating the outside walls of the model
There is another aspect to the heat conduction that must be considered
That is the transfer of heat to the wall from the gas: Roughly speaking, if the
gas temperature profile is the same, the ratio of heat transfer to the walls to
the heat input varies with Reynolds number to the minus 0.2 power. Thus, the
loss on this basis would be 0.4 or about 2.0 times as much for the model as for
the full-scale unit. Assuming the insulation for the model has been selected
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A-6
to maintain the ratio of heat loss to heat input, the higher heat flux on the
inner wall will force the inner surface temperature of the wall up in the model
and partly correct the problem. However, to compensate as nearly as possible,
the insulating value of the wall should be improved, by relaxing the require-
ment on the matching of wall surface temperature on the inside. For the final
design, sample computations could be made using reasonable values for both metal
and ceramic full-scale unit walls.
Buoyancy Effects
The Froude number (Fr for the full-scale unit and Fr for the model)
fs m
is the pertinent expression for considering the effect of buoyancy on the flow
pattern. It is noted that
•fs gL
-, .,2 Fr,
T^ — ~~ \ "" } — ~ *r IB
m g£ n n gL n
g(n)
for the constant combustion intensity case. Thus, the Froude number cannot be
held constant (unless g varies which is impracticable). A little consideration
shows that the ratio of the buoyancy-induced deflection to horizontal distance,
or fractional deflection, increases with n. Thus, a fractional deflection from
buoyancy effects in the prototype of 2 percent would be about 12 percent in the
model. The deflection would probably not be a problem in the model.
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A-7
C. NOMENCLATURE
d - characteristic nozzle dimension, nozzle for model
g - gravitational constant
k - thermal conductivity of wall, full-scale unit
k - thermal conductivity of wall, model
m
H - length of furnace cavity, model
n - scaling factor, subfurnace to model
q - gas throughput, model
q - atomizing air, volumetric flow rate, model
a
q ,d - design atomizing air volumetric flow rate, nozzle for model
3
q - gas throughput of model for design firing rate of model nozzle
q - oil volumetric flow rate, model
t - residence time, model
u - gas velocity, model
v - volume of furnace cavity.model
v - specific volume of combustion products, average
3
w - width of furnace cavity, model
x - distance for jet to fill furnace, model
y - wall thickness, model
B - constant
D - characteristic nozzle dimension, nozzle for full-scale unit
F - firing rate, subfurnace
F' - firing rate, full-scale unit
Fr, - Froude number, full-scale unit
f s
Fr - Froude number, model
m
H - constant
K - constant
K1 - constant
L - length of furnace cavity, subfurnace
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NOMENCLATURE (Continued)
L1 - length of furnace cavity, full-scale unit
2
M - number of burners, full-scale unit
P - pressure
P1 - fluid property factor
Q - gas throughput, full-scale unit
Q - atomizing air, volumetric flow rate, full-scale unit
3
Q, - oil volumetric flow rate, full-scale unit
R - gas constant
T - residence time, full-scale unit
T - absolute temperature of flue gas, average
a
T - residence time in furnace of volume V
o o
U - gas velocity, full-scale unit
U. - characteristic nozzle internal air velocity
V -volume of furnace cavity, full-scale unit
V - volume of a furnace
o
W -width of furnace cavity, subfurnace
W1 - width of furnace cavity, full-scale unit
X - distance for jet to fill furnace, full-scale unit
Y - wall thickness, full-scale unit
p - combustion intensity, full-scale unit
i S
C - combustion intensity, model
m
RP - Reynolds number, full-scale unit
L S
R - Reynolds number, model
m
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NOMENCLATURE (Continued)
A.T.. - temperature difference across wall, full-scale unit
.L S
AT - temperature difference across wall, mocel
m
v - viscosity of oil, model
Tm
Y - viscosity of oil, prototype
p - density of atomizing air
p - density of combustion air
p - density of fuel oil
a - surface tension of oil, model
m
a - surface tension of oil, prototype
P
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