EPA-600/2-77-008b
January 1977
Environmental Protection Technology Series
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into five series. These five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed to develop and
demonstrate instrumentation, equipment, and methodology to repair or prevent
environmental degradation from point and non-point sources of pollution. This
work provides the new or improved technology required for the control and
treatment of pollution sources to meet environmental quality standards.
EPA REVIEW NOTICE
This report has been reviewed by the U.S. Environmental
Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the
views and policy of the Agency, nor does mention of trade
names or commercial products constitute endorsement or
recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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E PA-600/2-77-00 8b
January 1977
EXPERIMENTAL EVALUATION
OF FUEL OIL ADDITIVES
FOR REDUCING EMISSIONS AND
INCREASING EFFICIENCY OF BOILERS
by
RobertD. Giammar, Albert E. Weller,
David W. Locklin, and Horatio H. Krause
Battelle-Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
Contract No. 68-02-0262
ROAPNo. 21ADG-020
Program Element No. 1AB014
Project Officers:
W. Steven Lanier W. R. Minning
Industrial Environmental Research Lab Office of Energy Conservation
Office of Energy, Minerals, and Industry and Environment
Research Triangle Park, NC 27711 Washington, DC 20461
Prepared for
U.S. Environmental Protection Agency U.S. Federal Energy Administration
Office of Research and Development Office of Energy Conservation
Washington, DC 20460 and Environment
Washington, DC 20461
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ABSTRACT
In this research program, the effectiveness of combustion-type fuel-
oil additives to reduce emissions and increase efficiency was evaluated
in a 50-bhp (500 kW) commercial oil-fired packaged boiler. Most additive
evaluation runs were made during continuous firing, constant-load
operation of the boiler.
Additives, both proprietary and pure compounds, containing certain
alkaline-earth and transition metals in concentration in the range of 20
ppm to 50 ppm were effective in reducing carbon particulate emissions by
as much as 100 percent when firing residual oil. These additives also
were effective in reducing emissions of smoke and polycyclic organic
matter. No additive was found to be effective in reducing either nitrogen
oxides or sulfur oxides.
Certain of these additives used in residual oil permitted an increase
in overall boiler efficiency by reducing stack gas loss, without increasing
particulate emissions. This efficiency gain, approximately 2 percent, was
achieved through (1) appropriate readjustment to permit boiler operation
at lower excess air levels and (2) reducing the fouling of boiler heat-
transfer surfaces.
Both proprietary and pure compounds were found to be equally effective.
Thus, if additives are used, cost savings can be maximized by using pure
compounds which are less expensive.
iii
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CONTENTS
Abstract iii
Figures v
Tables vii
Acknowledgment viii
1. Introduction 1
2. Objective and Scope 3
3. Summary of Results 4
4. Significance and Limitations of the Results 6
5. Background 8
Additive types 8
Review of literature regarding experimental
additive investigations 10
Basis for efficiency gain by additive utilization. . . 12
Factors affecting boiler efficiency 14
6. Plan of Experimental Investigation 19
Experimental facility 19
Fuels 24
Experimental procedure 25
Analytical procedures 30
7. Experimental Results 31
8. Interpretation of Results 37
Residual oil evaluation runs 39
9. Economics of Additive Utilization 68
10. Possible Mechanisms by Which Additives Affect
Particulate emissions 71
11. Perspective on Fuel Additives 73
Possible limitations to the use of additives 73
Appendices
A. Excerpts from "Combustion Additives for Pollution
Control: (4) State-of-the-Art Review 79
B. Appraisal of fuel-handling additives 86
References 106
IV
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FIGURES
Number Page
1 Approximate stack gas loss as a function of stack-gas
temperature 15
2 Bacharach smoke versus excess air level indicating boiler
operating points of maximum particulate reduction or
minimum incremental gain in efficiency 18
3 Experimental 50-bhp research boiler facility 20
4 Schematic of experimental facility 21
5 Smoke emission as a function of C02 for 50-bhp research
boiler and the average of several commercial boilers. . . 26
6 Particulate loading versus C02 for the 50-bhp boiler
fired with residual oil 27
7 Smoke emissions as function of C02 for the 50-bhp boiler
prior to and after cleaning burner nozzle 29
8 Summary of the additive evaluation runs with distillate
oil at 80 percent load and 14.0 percent CC>2 38
9 Smoke versus CC>2 level for reference distillate oil ... 38
10 Summary of the additive evaluation runs with the one percent
sulfur residual oil at 80 percent load and 12.8
percent C02 40
11 Summary of the additive evaluation runs with the two percent
sulfur residual oil at 80 percent load and 12.8
percent CO 42
12 The effectiveness of barium naphthenate in reducing
particulate at variable boiler load for constant air/
fuel ratio with residual oil 45
13 Smoke versus C02 level for the residual oil and selected
additives 46
14 POM and particulate loading as a function of C02 for the
1 percent sulfur residual oil 59
v
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FIGURES (continued)
Numb er Page
15 POM loading versus particulate loading for residual oil
at 12.8 percent CC>2 and 80 percent load 60
16 Particle-size distribution for runs with and without
additives 62
17 Medial test applied to plot of carbon content of filter
as a function of sulfate level of filter 63
18 Stack-gas temperature as a function of time firing two-
percent sulfur oil at 80 Ib/hr 66
19 Fuel savings achieved by the utilization of additives. . 70
VI
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TABLES
Number Page
1 Classes of Additives by Function in Oil and Coal
Combustion Systems 8
2 Combustion Additives Selected for Experimental Study. . 23
3 C-H-N-S and Ash Content in Weight Percent of the
Fuels Used in this Program 24
4 Summary of Evaluation Runs With Distillate Oil 32
5 Summary of Evaluation Runs With One Percent
Sulfur Residual Oil 33
6 Summary of Evaluation Runs With Two Percent
Sulfur Residual Oil 35
7 Analysis of Filter Catches for Selected Additives
at Boiler Operating Condition of 12.8 Percent C02
and 14.2 Percent C02 48
8 POM Quantification 51
9 Comparison of POM Loading With Particulate Loading
and Smoke Level 57
10 Cost of Treating 10,000 Gallons of Fuel Oil Based
Upon Dosage of 27 ppm Metal /Gallong of Fuel Oil. . . 69
11 Effect of Phenol Additive on Acid and Sludge Formation
in Light Oil 91
12 Types of Corrosion Inhibitors 94
13 Comparison of Dispersant Effect of Salts of Isocetyl
Benzene Sulfonic Acid 96
14 Pour-Point Depressants Developed in Recent Years. . . 99
15 Efficiency of Metal Deactivators 103
VII
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ACKNOWLEDGMENT
The research covered in this report was performed pursuant to
Contract No. 68-02-1262 with the U.S. Environmental Protection Agency,
Combustion Research Section. The authors acknowledge the assistance
of EPA Project Officers W. S. Lanier and G. B. Martin who participated
in planning this program and have provided helpful comments. The
authors also thank other members of the Battelle-Columbus staff who have
contributed to this study — R. E. Barrett, R. Coleman, H. R. Hazard,
L. J. Hillenbrand, A. Levy, T. C. Lyons, and H. G. Leonard, for their
advice and assistance in carrying out the research.
viii
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SECTION 1
INTRODUCTION
For over 125 years, manufacturers of additives have claimed that
improved performance of combustion equipment can be achieved by adding
various proprietary materials to the fuel or the flame. The aim of additive
utilization has varied through these years depending largely on the problem
area of interest at that time. Earlier interest was focused on additives
to minimize corrosion and deposits on heat transfer surfaces. The current
concern in limiting air pollution has stimulated an interest in additives
as a low-cost technique for reducing emissions. Now, with possible fuel
shortages and increasing fuel costs, additives are being considered as a
means to improve boiler efficiency.
While qualitative observations and commercial claims for the
effectiveness of fuel additives in reducing emissions and increasing boiler
efficiency are numerous, the effectiveness of some of these additives has
been questioned because of the lack of consistent results in actual commer-
cial usage. This inconsistency, in part, could be attributed to the methods
utilized in field evaluation and, perhaps, to differences in combustion
equipment, operation, and maintenance. Also, relatively few quantitative
data are available from experimental investigations in which conditions are
well defined and in which pertinent measurements have been made.
In an effort to establish the effectiveness of additives, the U.S.
Environmental Protection Agency (EPA) conducted an in-house research program
to evaluate about 300 fuel additives as to their potential for reducing
various emissions from distillate-fuel fired residential furnaces (1). The
results were variable, but a number of additives were found to reduce parti-
culate emissions and smoke. A second EPA program examined the effectiveness
1
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of several fuel additives in reducing S0? when firing residual oil, but none
were found to be effective for SO. control (2).
This investigation extends those programs to larger combustion
systems, with emphasis on the evaluation of combustion additives used for
residual fuel oil. of particular interest was the determination of additive
effectiveness in reducing smoke and particulate emissions, including poly-
cyclic organic matter (POM). The Federal Energy Administration, by funding
through this EPA contract, has extended the study to include evaluation of
additives as a means of increasing overall boiler efficiency, and, thus,
conserving fuel.
Other aspects of this program, reported elsewhere, include:
• State-of-the-art review of combustion additives for
pollution control (3). Appendix A contains the
summary and conclusions from this report.
• Experimental studies to investigate NO formation
in CO flames (4). X
This report combines both the EPA and FEA aspects of the study and
includes pertinent information from the reports mentioned above.
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SECTION 2
OBJECTIVE AND SCOPE
The objective of this experimental research program was to provide
a controlled and documented evaluation of the effectiveness of proprietary
combustion-type fuel-oil additives and pure compounds for reducing air pol-
lutant emissions and for increasing boiler efficiency. This research
investigation focused on those combustion additives intended to improve
combustion and reduce smoke and particulate emissions by their action in the
combustion or flame zone. Although it is recognized that fuel-handling
additives (intended to improve the handling or storage characteristics of
the fuel) and post-flame treatment additives (intended to control corrosion
and deposits on boiler surfaces) can be effective in maintaining burner
performance and boiler efficiency, these types of additives were not
systematically studied in this program. An exception to the above statement
are the organo-metallic compounds which are used as both combustion-improver
and post-flame-treatment additives.
The experimental program was conducted in a commercial fire-tube
packaged-boiler of 50 boiler horsepower capacity (500 kW) firing both
distillate and residual oils. The boiler was tuned to operate at a base-
line condition, such that smoke emission levels were representative of
similar boilers observed during a field investigation of boiler emissions (5).
At the baseline condition, the boiler was probably tuned to a better condition
than most operating units in which combustion additives are tried (typically
additives are not used unless the boiler operator is grasping for some means
to meet emission or other criteria).
A total of 24 fuel additives of representative fuels were evaluated
when firing residual oils at a continuous rate (thus producing constant-load
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operation). Eleven of the additive types were also evaluated when firing
distillate oil. In addition, some additives were evaluated under cyclic
operation, variable load, and with a detuned burner so that the effective-
ness of additives could be assessed as a function of these operating
parameters. The majority of the evaluation runs were "short-term" in that
emission data were obtained over a 2-hour period. Also, several "long-
term" runs were conducted in that data were obtained over a 60 to 80 hour
period to assess possible improvements in boiler efficiency.
Gaseous and particulate emissions were measured for baseline and
additive runs. For many runs, sampling and analysis for POM emissions were
conducted, and for a few runs, the particle size of particulate emissions
was determined.
SECTION 3
SUMMARY OF RESULTS
The principal results of this experimental research investigation
can be summarized as follows:
• Alkaline-earth and transition metal additives used
in concentrations of 20 ppm to 50 ppm of metal in
residual oil were effective in reducing carbon
particulate emissions by as much as 100 percent.
However, data suggest that, for burners having
higher emissions in the baseline condition, higher
additive concentration would be required to
achieve the same level of effectiveness.
• Additives, both proprietary and pure compounds,
containing certain alkaline-earth and transition
metals were effective in increasing the efficiency
of a boiler fired with residual oil (without
increasing emissions) by reducing stack loss
through (1) permitting boiler operation at lower
burner excess-air levels and (2) reducing the
fouling of boiler heat-transfer surfaces. For
the 50-bhp (500 kW) boiler during 80-hour runs, a
gain in efficiency of 2 percent was achieved,
approximately half from reduction in excess air
levels and half from reduction of fouling. This
does not imply that such an increase could be
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realized under all field conditions and definitely
would not be achieved without appropriate boiler
adjustment.
• Optimum savings in fuel costs could be realized by
utilizing pure compound combustion additives in
this boiler. Proprietary additives, used at effec-
tive concentrations, cost at least twice that of
the most effective pure compound additives and,
thus, tend to reduce the savings realized from
burning less fuel. With a typical current market
price of oil ($.30/gal), utilization of pure
compounds would be cost effective when an incre-
mental gain in boiler efficiency of at least 0.6
percent is realized. For the least expensive
proprietary additive, an incremental gain in
boiler efficiency of at least 1.5 to 2 percent
would have to be realized before they could
economically be justified.
• The alkaline-earth and transition metal additives
were also observed to be effective in reducing
emissions of smoke and polycyclic organic
matter.
• These additives appeared to be equally effective
in reducing particulate emission levels from a
tuned and detuned burner. However, they appeared
to be less effective for reducing smoke from
detuned burners.
• In cyclic operation where particulate and POM
emissions were higher than steady-state operation,
additives were more effective in reducing POM
than particulates.
• The use of metal-containing additives in
combustion systems that generate little or no
carbon particulate, such as well-designed and
maintained boilers firing distillate oil,
could result in higher particulate emissions
due to the added metallic components.
• Additives effective in reducing carbon parti-
culate emissions were observed to reduce the
equivalent aerodynamic mass mean diameter of
particles. Overall, the mass of particulate
emission in the respirable range was reduced
by these additives.
• No additive was found to be effective in reducing
either nitrogen oxides or sulfur oxides emissions.
• CO emission levels (<15 ppm) and gaseous hydro-
carbon emission levels (<10 ppm) for the baseline
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condition were almost negligible so that there
was no potential for additives to be effective
in reducing these emissions.
Although additives were effective in reducing particulate emissions,
alternate means for control of particulate emissions and boiler efficiency
must be recognized. Utilizing existing burner technology to achieve improved
air-fuel mixing and careful attention to boiler maintenance may be more cost
effective than the use of fuel additives.
SECTION 4
SIGNIFICANCE AND LIMITATIONS OF THE RESULTS
The results of this study indicate that additives can be effective
in promoting carbon burnout, providing the combustion conditions are not
otherwise conducive to complete carbon burnout. The extent of carbon
particulate reduction for any specific boiler would be dependent upon the
interrelation among the specific boiler and burner design features, fuel,
and the additive type and additive dosage.
Although criteria identifying the specific additive and concen-
tration for all types of oil-fired boilers were not developed, it is
reasonable to assume that the results of this study can be applied to most
systems, as the mechanistic effects of additives are not restricted to a
specific type of combustion system. However, for additives to be effective
in increasing efficiency, the potential must exist to decrease stack loss
by a reduction in excess air level and/or a reduction in the fouling
of heat transfer surfaces.
With technological advances and modern equipment designs, it is
possible to achieve relatively low carbon particulate emissions and boiler
efficiencies near 85 percent without the use of additives. This performance
is realized by the use of: state-of-the-art burners, most of which are
capable of satisfactorily operating at excess air levels less than 15
percent [and some utility boilers even as low as 1 percent (6) ] , while
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generating little or no smoke or carbon particulate; economizers and air
preheaters that lower stack gas exit temperatures below 350 F (177 C); and
soot blowers to remove deposits from heat transfer surfaces. It is unlikely
that additives would be effective in improving efficiency or reducing
emissions from such systems. However, in terms of the overall economics,
these optimum efficiency designs cannot be justified for every boiler
installation. In addition, there are many existing boilers that were mar-
ginally designed or are poorly maintained and, thus, generate relatively
high levels of particulate and which operate at relatively low efficiencies.
It is in these systems that the results of this study indicate that
consideration could be given to the use of additives. However, before
additives are used, it is recommended that the burners be tuned to achieve
optimum performance which may alleviate any need for an additive.
The results of these studies indicate that additives can be effec-
tive in promoting carbon burnout and, thus, permit operation at increased
efficiency. The exact incremental gains in efficiency for any specific
boiler would be dependent upon the interrelation among such factors as the
specific boiler design, fuel used, and the additive type and additive dosage.
For the boiler system, the controlling factor for additive effectiveness is
not the type of boiler system itself (whether it is fire-tube or water tube).
Rather the important factors are the conditions in the preflame, flame, and
immediate postflame regimes as governed by the design and operation of the
burner. The physical and chemical properties of the oil have an effect on
the character of the particulate. Also, certain impurities and trace elements
in the oil may affect the mechanistic action of the additive. Thus, if
additives are to be used, the type and concentration will be dependent
upon the design and operation of the burner and by the fuel used.
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SECTION 5
BACKGROUND
ADDITIVE TYPES
In the course of the development of oil-firing technology, additives
have been developed for a variety of purposes. As shown in Table 1, these
additives can be divided into three general classes, according to their
function:
Class I. Fuel-handling additives
Class II. Combustion additives
Class III. Postflame treatment additives.
TABLE 1. CLASSES OF ADDITIVES BY FUNCTION IN OIL AND COAL COMBUSTION SYSTEMS
CLASS I.
FUEL-HANDLING ADDITIVES
For Improved Storage
and Handling
CLASS II.
COMBUSTION ADDITIVES
For Improved Combustion and
Pollutant Reduction
CLASS III.
POST-FLAME TREATMENT ADDITIVES
For Post-Flame Treatment
Fuel stability additives
- Sludge and gum inhibitors
- Detergents
- Metal deactivators
- Color stabilizers
Flow improvers
- Pour-point depressants
Demulsifying agents
Anti-static additives
Anti-icing compounds
Corrosion inhibitors
(for tank protection)
Combustion improvers
- To reduce smoke or
particulates
- To reduce CO, hydrocarbons,
or polycyclic organic
matter
Additives to alter particulate
size or character
Additives to reduce formation of
pollutant gases
- Nitrogen oxides, NO
- Sulfur trioxide, SO,
Soot removers (from heat-transfer
surfaces)
Additives to control fireside
corrosion or slag deposits
Additives to enhance particulate
collection in electrostatic
precipitators
SO scavengers
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Class I Additives—
The fuel-handling additives may be considered those whose purpose is
to insure the quality of the oil in storage and handling — up to the time
it is delivered to the burner. Consequently, this class of additives
includes: (1) antioxidants, which prevent deterioration of the oil by
reaction with oxygen during storage, (2) pour-point depressants, which reduce
oil viscosity for ease of handling, (3) corrosion inhibitors, which prevent
contamination of the oil by rust from the storage tanks, (4) metal deactiva-
tors, which tie up trace metals that catalyze oil deterioration, and
(5) miscellaneous additives for such functions as sludge dispersant or
water emulsification. These additives are usually mixtures of complex
organic compounds in a suitable solvent for introduction into the oil. A
review of these additives is contained in Appendix B.
Class II Additives—
Combustion additives are intended to reduce the amounts of pollutants
formed during combustion, or to convert the pollutants into easily removable
solids. A variety of organic, organometallic, and inorganic compounds have
been tried for this purpose and it has been found that the organometallies
are most effective, particularly in view of the relative ease of introduction
into the fuel. These compounds introduce a metal which either acts as a
catalyst for the combustion reaction, or promotes free radical formation
that inhibits pollutant-developing reactions. The organic portion of the
additive molecule provides the needed solubility in the oil and also
influences the stability and volatility of the additive. Such additives are
effective in reducing the unburned carbon in the particulate emissions.
Since they affect the carbon combustion, they may also be capable of
reducing the amount of polycyclic organic matter formed during combustion.
Little effect of combustion additives has been found on gaseous
pollutants such as nitrogen oxides or sulfur oxides. A summary of techni-
cal literature relating to Class II additives is contained in a separate
report — "Combustion Additives for Pollution Control - A State of the Art
Review" (3).
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Class III Additives—
Post-flame treatment additives include various scavenging agents,
pollutant property modifiers, and agents that modify the catalytic proper-
ties of exposed heat exchanger and breeching surfaces. However, the
development of additives to reduce corrosion has received the most atten-
tion. These corrosion additives are aimed at reducing the corrosive attack
of combustion gases and fly ash on the heat transfer surfaces of the boiler.
[A summary of corrosion additives intended for fireside corrosion control is
contained in Reid's Monograph on external corrosion and deposits (7).]
Class III additives are primarily alkaline materials either formed by
oxidation of a metal in the flame or added at some point after the combustion
zone. Their action is to neutralize the sulfur oxides in the flue gases and
any sulfuric acid which might be condensed from the gas stream in regions
of the boiler where the temperature falls below the acid dewpoint. Compounds
of magnesium, calcium, and zinc have proven most useful for this purpose.
In the case of magnesium, it also serves to reduce corrosion from vanadium
by forming vanadates with high melting points. As in the case of the
combustion additives, the most effective corrosion additives are the organo-
metallic compounds which can be readily dissolved in the fuel. (Additional-
ly, certain of these organometallic compounds can be considered as both
Class II and Class III type additives.)
REVIEW OF LITERATURE REGARDING EXPERIMENTAL
ADDITIVE INVESTIGATIONS
To guide the selection of additives for this program, the literature
pertaining to experimental studies of combustion additives was reviewed (3).
Previous investigators have used a wide variety of organic, organometallic,
and inorganic compounds in efforts to reduce the amounts of pollutants
formed during combustion, or to convert the pollutants into easily remov-
able solids.
The greatest amount of effort in additive development has been devoted
to particulate emissions. This emphasis has been the result of the almost
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universal recognition of smoke as an undesirable emission over a period of
many years. For obtaining reduction in particulate formation in fuel-oil
combustion processes, experimental evidence indicated that compounds of
the transition metals, manganese, iron, nickel, and cobalt, could be
effective (8). The alkaline earth metals, barium and calcium, also gave
evidence of useful activity (9,10). The best results were obtained with
organometallic derivatives of these metals. The organic portion of the
molecule provides the needed solubility in oil and also influenced the
stability and volatility of the additive molecule.
Only a few investigations have examined the effect of additives on
potential carcinogenic materials in the particulate emissions, but this
aspect is presently receiving a significant amount of attention. Such
potential carcinogenic agents are found, primarily, in the POM that forms
during the combustion of the fuel (11,12). Most of the early research
was done with gas flames or light fuel such as distillate oil. The
additives which were reported as effective in reducing the POM emissions
included organic compounds such as nitroparaffins and peroxides (13), as
well as organometallic compounds of manganese and iron (14). Although
the physical state of POM and the carbonaceous portion of the particulate
is different, their probable common origin and chemical reactivity suggest
that an additive effective for one would have some effect on the other.
This result was generally observed in earlier diesel engine studies, and
where both types of emissions were measured, the POM usually was reduced
to a greater extent than was the particulate (13). [It should be noted
that the techniques used in the collection and analysis of POM compounds
have undergone extensive development since these early studies. These
early POM determinations usually were reported as only one or two species,
such as benz(a) pyrene, while current techniques scan for approximately 18
species during analysis. In addition, some of the POM emissions that have
been reported in the literature use the BaP emission as the key to which
a constant factor is applied to predict total POM levels. The data con-
tained in this report and another EPA program (EPA Contract No. 68-02-1848)
indicate this method of predicting total POM is somewhat questionable, as
the ratio of the BaP emission to the total POM emissions varies considerably.]
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A previous EPA program involved tests of numerous commercial additives
used with distillate heating oil in a residential oil burner (1). In
general, the additives were found to have a minor effect compared to the
opportunity for emission control by proper adjustment and operation of the
burner. However, the additives containing manganese, iron, or cobalt did
reduce the particulate emissions. A few organic formulations containing
no metals gave moderate reductions in particulates, but the concentrations
of the additives required were too high to be practical. No changes were
observed in the amounts of nitrogen oxides or sulfur oxide emissions with
any of the additives.
Another EPA program was an investigation of the effectiveness of
several proprietary fuel-oil additives in reducing sulfur oxide emissions
when firing residual oil in a commercial boiler (2). No effects of the
additives were found for sulfur oxide emissions or for nitrogen oxides.
The experience of the EPA investigators with the inefficacy of additives
for reducing the nitrogen oxides or sulfur dioxide in the emissions, veri-
fired the generally negative results reported in earlier literature (3).
Only in the case of sulfur trioxide, which is present to the extent of 25
to 30 ppm in the flue gases, has an additive effectiveness been demonstrated
at reasonable additive concentrations. Chemicals which form basic oxides
such as magnesium, calcium, and zinc have reduced sulfur trioxide levels
substantially (15). One area of particular concern was whether the various
additives which did result in reduced SO- did so by oxidizing the pollutant
into metallic sulfate.
BASIS FOR EFFICIENCY GAIN BY
ADDITIVE UTILIZATION
The efficiency of a boiler can be expressed as:
Boiler Efficiency = 1 - (Combustion Loss) - (Miscellaneous Loss) - (Stack Loss),
Oil-fired boilers operating at any acceptable condition have low concentrations
of CO, unburned carbon, and unburned hydrocarbons in their stack gases and
consequently have negligible combustion losses. The miscellaneous loss,
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insofar as it is real rather than the accumulation of errors in the boiler
heat balance, represents the heat loss from the external boiler surface or
jacket. Typically, miscellaneous losses are a few percent. Clearly,
additives have no effect on combustion losses or miscellaneous losses.
The stack loss represents the heat carried away in the stack gases,
the largest loss in heat (and thus efficiency) for the boiler. Stack losses
are typically between 15 and 30 percent of the heating value of the fuel.
Stack loss is numerically equal to
(mass of stack gas) x (specific heat of stack gas) x (stack
temperature - ambient temperature) + (latent heat of the
moisture formed from the hydrogen in the fuel).
The mass of stack gas is equal to the mass of the products of stoichiometric
combustion plus the mass of excess air. The stack temperature is deter-
mined by the amount of heat transfer surface in the boiler and the effective-
ness of this surface, the effectiveness being decreased by fouling with
soot and particulates, and reduced residence time accompanying higher
excess air levels.
Combustion additives that effectively control smoke and particulate
can influence the stack loss both directly and indirectly. The direct
effect results from the reduced fouling of heat exchanger surfaces conse-
quent to the reduced smoke and particulate levels, and possibly through
some change in the characteristics of the particles which reduces their
fouling tendency. The indirect effect is a result of the fact that the
minimum acceptable excess air level, at least in commercial and small
industrial oil-fired boilers, is controlled by the maximum acceptable smoke
density, typically a Bacharach Smoke Number of 4 (16). Thus, a combustion
additive that reduces the smoke density will permit operation at lower
excess air levels without exceeding the maximum acceptable smoke density.
The efficiency gain that can be obtained through these mechanisms
cannot exceed the stack loss (about 20 percent in typical operation) and,
in fact, is limited to a fraction of this loss. Thus, a well designed and
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and maintained commercial boiler firing residual oil may operate at an
excess air level of 20 percent. If such a boiler could be fired at the
stoichiometric fuel-air ratio, the incremental gain in efficiency (reduc-
tion in stack loss) could be due to the reduced mass of stack gas would
be about 2 percent. (Obviously the gain would be higher for a poorly
maintained unit operating at a high excess air level.) The accompanying
reduction in stack loss due to the reduced gas velocity and increased
residence time in the boiler cannot be conveniently calculated but is rela-
tively smaller. The gain in boiler efficiency that can be achieved by
reduced fouling of the heat transfer surfaces is dependent on the boiler
maintenance (frequency of cleaning) but may represent about 1 percent
under reasonably typical conditions.
The results of the study conducted for FEA show that combustion addi-
tives that reduce stack-gas particulate loadings are generally effective
in reducing the smoke density and visa versa. Thus, those combustion
additives found effective as pollution controls may also be expected to be
effective in promoting the achievement of higher boiler efficiency.
FACTORS AFFECTING BOILER EFFICIENCY
For a given boiler, additional heat transfer surface (such as
economizers and air heaters) can be added to increase efficiency. However,
the only operating variables that can be controlled by the boiler operator
or serviceman are mass of excess air and heat exchanger cleanliness.
Excess Air
Figure 1 indicates an approximate relation between stack gas loss
(or incremental gain in boiler efficiency) and stack gas temperature for
several excess air levels. Excess air levels of less than 15 percent can
be achieved with modern burner design (17), although there are a signifi-
cant number of boilers operating at substantially higher excess air levels.
Typical excess air levels vary with the size of the unit, with the smaller
units having less sophisticated controls or operator attention and, thus,
operating at higher excess air levels than the larger units. It is
14
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estimated that typical excess air levels in the field run approximately as
follows (18).
Capacity Percent Excess Air
Less than 100 bhp (1 MW)* 50
*#
100 bhp (1 MW) to 60,000 pph (17 MW) 35
Greater than 60,000 pph 15
- pph = pounds per hour of steam generated.
** MW refers to thermal rather than electrical.
Accordingly, the greatest potential for increasing boiler efficiency by
reducing excess air would be for those boilers having capacity of less than
60,000 pph. Many of these boilers could be "tuned" to operate at lower
excess air levels, but the actual level would be dependent on the specific
boiler installation and its operational and maintenance procedures.
jleat Transfer Surface
From Figure 1 (at 20 percent excess air), the incremental gain in
boiler efficiency is about 2-1/2 percent for each 100 F reduction in stack
gas temperature. The temperature of the stack gas leaving the boiler (not
including heat recovery equipment such as economizers and air preheatrrs)
is partially determined by the saturated water temperature corresponding to
the boiler operating pressure. Typically, for low-pressure boilers, the
stack gas temperature is about 500 F (260 C) and would be proportionally
higher as the boiler operating pressure increases. The removal of heat
from products of combustion becomes expensive after the stack gas tempera-
ture drops below 500 F (260 C)(19).
The use of additional boiler convection surface to recover (19) heat
from flue gases at temperatures below 500 F (260 C) is usually impractical.
However, economizers and air heaters can be included in designs or added
on to systems that can economically justify heat recovery. The use of
this equipment can lower stack gas temperatures below 250 F (177 C), and
thus, achieve gains in efficiency of at least 3 to 5 percent for low-
pressure boilers and 6 to 10 percent for high-pressure boilers (17).
Historically, these types of heat recovery devices have been applied
only to units with high load factors with capacities over 100,000 pph
16
-------
steam. However, the economizer has been found economically feasible in
certain (high load factor) units with capacity as low as 30,000 pph (17),
while the air heater becomes economical for some boilers with capacities
as low as 50,000 pph (19).
EFFECT OF ADDITIVES: INCREASED EFFICIENCY
VERSUS REDUCED EMISSIONS
The improved combustion achieved by using additives can be translated
into the following results:
(1) Reduced emissions of smoke and particulate and reduced
fouling of heat transfer surfaces resulting in increased
boiler efficiency
(2) Increased boiler efficiency by operation at lower excess
air.
The benefits are somewhat competing and maximizing one reduces the other.
Figure 2 illustrates the effectiveness of additives on emissions and
excess air. Assume Curve A is the smoke versus excess air curve of the
boiler firing without additives and that Point X is the condition at
which the boiler is operating. Also, assume that the use of an effective
additive alters the smoke versus excess air relationship to that of Curve
B. Now the boiler can be operated at Point Y with the same excess air as
Point X, but with a reduction in smoke emissions and some small incre-
mental gain in boiler efficiency because of reduced fouling. Also,
the boiler can be operated at Point Z with the same smoke emission as
Point X, but with a reduction in excess air and some reduction in
fouling so that the incremental gain in boiler efficiency is greater
than that achieved at Point Y. The boiler can be operated at some point
between Point Y and Point Z, with some reduction in both smoke and excess
air. However, the maximum reduction in emissions and the maximum reduc-
tion in excess air cannot be realized simultaneously.
17
-------
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40 35 30 25 20 15
Excess Air, percent
10
FIGURE 2. BACHARACH SMOKE VERSUS EXCESS AIR LEVEL
INDICATING BOILER-OPERATING POINTS OF
MAXIMUM SMOKE REDUCTION OR MAXIMUM
INCREMENTAL GAIN IN EFFICIENCY
18
-------
SECTION 6
PLAN OF EXPERIMENTAL INVESTIGATION
Proprietary and pure compound additives were evaluated in a modified
commercial packaged boiler with both distillate and residual oil.
EXPERIMENTAL FACILITY
Figures 3 and 4 show the overall experimental facility. The basic
element of this facility is a 50-bhp (500 kW) commercial fire-tube boiler
capable of firing natural gas, distillate oil, and residual oil at rates up
to 2 million Btu/hr (0.59 MW) and generating up to 1500 Ib/hr (680 kg/hr)
2
of steam at 15 psig (103 kN/m ). A special sampling platform was erected
over the boiler to permit sampling in a straight section of stack and
facilitate overall sampling procedures.
Fire-Tube Packaged Boiler
Although fire-tube packaged boilers of the type used in this program
are fully automated, some modifications in the 50-bhp (500 kW) boiler were
made to provide greater flexibility and more accurate control in the
operation of the boiler. The air and oil control linkages of the burner
were disconnected so that combustion air-flow rates and fuel-flow rates
could be controlled independently. Combustion air was metered through a
thin-plate orifice and distillate oil flow rate with a rotameter. When
firing residual oil, oil firing rate was determined from beam-scale
readings.
Because a continuous fuel flow rate could not be maintained within a
2 percent range with the oil pump and preheater system supplied with the
boiler, this assembly was replaced by a variable speed, positive-displacement
gear pump and temperature controllers that could provide a constant fuel
19
-------
FIGURE 3. EXPERIMENTAL 50-BHP RESEARCH BOILER FACILITY
20
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21
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temperature and delivery rate to the burner nozzle. With this system, air/
fuel ratios and firing rates remained constant within 2 percent throughout
the duration of an experimental run.
Sampling Platform
A sampling platform was erected above the boiler outlet to permit
sampling in a straight section of the 12-inch (0.30 m) diameter insulated
stack, 15 pipe diameters downstream of the boiler outlet. At this loca-
tion, velocity and temperature profiles (measured with a hot-wire anemo-
meter and thermocouple) were flat so that traversing was not necessary
during particulate sampling.
SELECTION OF ADDITIVES
This investigation, as indicated previously, was confined to fuel
additives that were intended to improve combustion. Pure compounds as
well as proprietary additives were considered so that a broad range of
materials could be evaluated. However, the selection of additives was
restricted to materials that when burned would not generate new toxic
pollutants or increase the levels of those already present. Accordingly,
compounds containing nitrogen, sulfur, or metals known to be toxic were
not considered. Likewise, compounds required to be used at impractical
concentrations (over 1 percent by weight) were rejected.
Additive Types
Combustion additives can be categorized as
• Organometallic
• Organic
• Inorganic.
Table 2 categorizes the additives used in this study according to defined
types and subtypes. Inorganic additives were not evaluated because of their
insolubility in oil. The additives listed in Table 2 were selected on the
basis of the results of an earlier EPA study (1) and a state-of-the-art
review of additive technology that included theoretical considerations of
the mechanism of pollutant formation and possible modes of additive
action (3).
22
-------
TABLE 2. COMBUSTION ADDITIVES SELECTED FOR
EXPERIMENTAL STUDY
ORGANOMETALLIC
ORGANIC
KaphtVienates
Cobalt
Iron
Manganese
Barium
Iron + barium
Zinc
Calcium
Cyclopentadlenes
Manganese - CI-2 (24 % Mn)
Iron - Pd 1654 (1% Fe)
Sulfonates
Barium
Ethyl Hexoate
Barium
Carbonyls
Iron
Other
MC-7 soluble fs.flj; M 3% B }
Rolf it e 404 (27, Mn) '
Hydrocarbon
LSD (C_H0, trace metals)
/ o
Improsoot (C7Hg, trace metals)
Triple E
Toluene (CyH_, pure hydrocarbon)
Vatcon 130 (trace metals)
Ether
Diglyme
Alcohol
Ethyl
Hexyl
Acid
Napthenic
Ethyl hexoic
23
-------
Additive Concentrations
Initially, additive concentrations were based on those reported in
the literature (3); for proprietary additives, the concentrations were
those recommended by the additive manufacturer. The results of the
earlier additive evaluation runs then became the basis for selection of
additive concentrations for later runs. For pure compounds, additive
concentrations were based on introducing sufficient amounts of the additive
to obtain 27 ppm of metal in the oil (0.1 g metal/gal of fuel oil). For
a limited number of these compounds, concentrations were varied from 5 ppm
of metal up to 100 ppm metal in the oil to determine the relation between
concentration and the effectiveness of an additive. In addition to the
manufacturer's recommendation several proprietary additives were evaluated
at concentrations corresponding to about 20 to 50 ppm of metal in the oil.
FUELS
Additives were evaluated with both distillate and residual fuel oils.
The major effort of research, however, was conducted with residual oils
and included both a 1 percent sulfur and a 2 percent sulfur oil. To provide
a relatively consistent fuel oil supply, each of these oils was procured
3 3
in 5000 (18.9 m ) to 6000 gallon (22.7 m ) lots and stored in 55 gallon
3
(0.21 m ) drums. A second shipment of the 2 percent sulfur oil was
required to complete the long term evaluation runs. Table 3 lists some
of the properties of these fuels.
TABLE 3. C-H-N-S AND ASH CONTENT IN WEIGHT PERCENT
OF THE FUELS USED IN THIS PROGRAM
API
Gravity,
Fuel
Distillate oil
Residual oil
Residual oil
Residual oil
e
35.
15.
13.
13.
4
1
2
2
Viscosity
@ 122 F,
ssf
—
80
100
100
Nominal
Sulfur
Content, I
—
1
2
2
C
86
87
88
87
.4
.5
.4
.9
H
13.
11.
10.
10.
N
6
1 0.31
4 0.5
9 0.5
S Ash
<0 . 1 <0 .
0.95 <0.
1.75 0.
1.40 0.
01
04
020
018
(a) Second load.
24
-------
EXPERIMENTAL PROCEDURE
To provide a controlled and valid evaluation of each additive, specific
experimental procedures were developed to minimize operational variations
over the entire period of experimentation.
Basis for the Selection of
Baseline Condition
To provide a realistic condition to evaluate additives, the boiler was
tuned to produce a characteristic smoke curve representative of those
generated from other commercial boilers (5). The tuning consisted of
altering the mixing pattern of the burner by removing one of the diffuser
rings.
Figure 5 shows the characteristic smoke curves of the 50-bhp test
boiler and the average of several commercial boilers firing a residual
oil. [This residual oil was not the same oil used in this program
but was the reference fuel used in obtaining the boiler smoke data on EPA
Contract No. 68-02-0251 (5)]. Figure 6 is a curve of particulate loading
as a function of CO (air/fuel ratio) for a constant firing rate. From
earlier investigations (3), it was determined that additive action was
only effective on carbon particulate only. Accordingly, additives were
evaluated at a combustion condition that generated carbon particulate.
The air/fuel ratio corresponding to 12.8 percent CO- was selected as one
that generated a sufficient level of carbon particulate yet was insensi-
tive enough so that small changes in air/fuel ratio did not produce a
significant change in particulate emission level.
Particulate consists of two basic components: (1) an ash component
originating with the fuel and (2) a carbon component resulting from
incomplete combustion. When additives containing an ash (i.e., metal
containing additives) are used, this ash becomes a third source of
particulate in the stack gases. For combustion at a constant air/fuel
ratio, the ash loading in the products of combustion (due to fuel ash)
should be constant, assuming no accumulation on the boiler surfaces; the
carbon loading could vary depending upon the completeness of combustion.
25
-------
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50-hp research
boiler
Average of other
commercial boilers
8
10
12
13
14
15
C02, percent
FIGURE 5. SMOKE EMISSION AS A FUNCTION OF C02 FOR 50-BHP
RESEARCH BOILER AND THE AVERAGE OF SEVERAL
COMMERCIAL BOILERS(5)
26
-------
180
160
140
*> 120
Z
100
TJ
o
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80
60
40
20
9 10 II 12 13 14
C02, percent
15
16
FIGURE 6. PARTICULATE LOADING VERSUS C02 FOR THE 50-BHP
BOILER FIRED WITH RESIDUAL OIL
27
-------
To minimize the variation in ash loading, all particulate measurements were
made at the same air/fuel ratio corresponding to 12.8 percent C0? (about
20 percent excess air). A baseline firing rate of 80 Ib/hr (36 kg/hr) was
selected to correspond to a boiler load of 80 percent, identified by ABMA
as being typical of field operation of commercial boilers (5).
Baseline and Additive Evaluation Runs
In general, each additive was evaluated from runs made on one day as
follows:
(1) The reference fuel oil was fired at a constant rate in
the boiler facility, and gaseous and smoke emission
data were obtained over a range of air/fuel ratios.
(2) Filterable particulate emission (probe and filter catch
only) was determined at one selected air/fuel ratio.
(3) The additive-containing fuel was then fired at the
same firing rate over the same range of air/fuel ratios
to generate a boiler performance curve with the addi-
tive corresponding to (1).
(4) A particulate sample was obtained with the additive-
containing fuel ratio as for (2) above. Thus, the
effectiveness of each additive could be determined by
comparing the smoke and gaseous characteristic curves
and the particulate loadings with and without additive
for runs made on the same day. (Except as noted, all
data reported in this report were obtained at steady
state operation of the burner.)
The baseline run consisted of (1) and (2), and the evaluation run consisted
of (3) and (4).
Burner Maintenance
At the completion of each day's experimentation, the entire fuel
system was cleaned. The fuel nozzle was removed and cleaned in kerosine
while the pump and fuel oil lines were purged with No. 2 oil. It was
observed that if these maintenance procedures were not followed, over a
period of several weeks the fuel nozzle would become fouled and burner
performance would degenerate as indicated by the characteristic smoke
curves of Figure 7. As a consequence, the baseline condition could
have changed each day and all the additives could not have been evaluated
under identical operating conditions. The gradual degeneration in boiler
performance was attributed to plugging of the fuel lines by the residual
28
-------
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a) 6
.0
E
5 5
o
to
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o 4
o
jr
o
o
CO
x Prior to cleaning nozzle
o After cleaning nozzle
2 week
interval
10
12
13
14
15
C02, percent
FIGURE 7. SMOKE EMISSIONS AS FUNCTION OF C02 FOR THE 50-BHP
BOILER PRIOR TO AND AFTER CLEANING BURNER NOZZLE
29
-------
oil remaining in the lines when the boiler was not to be used. No degener-
ation was observed during continuous operation of the boiler as the
characteristic smoke curves were nearly identical at the beginning and the
end of each baseline run including the long-term baseline run.
ANALYTICAL PROCEDURES
Particulate and POM samples were collected by a modified EPA Method
5 procedure with the probe wash and filter catch being used to determine
the filterable particulate loadings and an adsorbent column being used
to determine POM loadings (20). (The filter temperatures were 350 F rather
than 250 F as in Method 5 to be compatible with POM sampling system.)
Flue gas constituents were determined by: paramagnetic analysis
for oxygen; flame ionization detection for unburned hydrocarbons; nondis-
persive infrared for carbon monoxide, carbon dioxide, and nitric oxide;
and a dry electrochemical analyzer for sulfur dioxide. Smoke emissions
were determined with a Bacharach smoke tester according to the ASTM filter-
paper method (D2156-65) for smoke measurements.
30
-------
SECTION 7
EXPERIMENTAL RESULTS
The results of the additive evaluation runs in terms of the additive's
ability to reduce particulate loadings and smoke levels in the stack are listed
by fuel type in the following tables:
Table 4. Evaluation Runs With Distillate Oil
Table 5. Evaluation Runs With 1 Percent Sulfur Residual Oil
Table 6. Evaluation Runs With 2 Percent Sulfur Residual Oil.
2
Particulate emissions are listed in milligrams per cubic meter (mg/Nm ) of flue
gas at standard conditions. Smoke levels listed are for the additive evalua-
tion run.
For the distillate oil runs, the boiler was fired continuously at
approximately 80 Ib/hr (36 kg/hr) at 14.0 percent CO . Likewise for most of
the residual oil runs, the boiler was fired continuously at approximately
80 Ib/hr (36 kg/hr) at 12.8 percent CO . However, as indicated in Tables 5
and 6 some runs were conducted at different conditions so the effects of
additives at other modes of boiler operation could be examined.
The run numbers do not represent the chronological order in which the
additives were run, but are presented in groupings of specific additive types
or a specific set of boiler operating conditions. The additive concentra-
tions or dosages are either designated as ppm metal in the fuel oil for the
metal-containing additives, or by volume percent for the pure organic
compounds. For organic compounds containing trace metals, both the weight
percent of metal and volume percent of the additive are given.
31
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SECTION 8
INTERPRETATION OF RESULTS
Tables 4, 5, and 6 include the particulate loadings for both the daily
baseline run and the additive run made that same day. The data were statis-
tically treated to determine what level of variation in the particulate load-
ing by additive utilization was statistically meaningful. The arithmetic
mean of the particulate loading of the daily baseline runs was used as the
standard for evaluating the effectiveness of additives in reducing particulate
emissions. For the same oil, as discussed earlier, the ash loading for every
baseline run should be nearly the same and, accordingly, any deviation in the
baseline particulate loadings from day-to-day would have to be attributed to the
deviations in the carbon portion of the particulate loading. Assuming that the
variations in the particulate loadings for the daily baseline runs were the
result of random instrument or measurement errors, the use of the arithmetic
mean of the particulate loadings of all daily baseline runs minimizes the effect
of these random variations on the additive evaluation. However, it may bias
the results somewhat in that additives with high (or low) daily baseline partic-
ulate loadings (assuming these observed loadings are "real") appear less (or
more effective than if the particulate loading of the additive run had been
compared with the specific daily baseline loading. Regardless of which method
of comparison is used, the overall conclusions would be similar.
DISTILLATE OIL EVALUATION RUNS
Figure 8 graphically shows that the use of additives can be detrimental
in those systems that generate no appreciable quantities of carbon particulate.
When firing distillate oil without an additive, analysis of the particulate
catch indicated less than 1 percent carbon present for boiler operation
with less than 8 percent excess air (14 percent CO ). Accordingly, the
addition into the oil of the metallic inert contained in the additive
37
-------
ro
40
Arithmetic mean-
of baseline runs
Particulate Load
ro
0 O
^H^M
\
1 23 4 567 8 9 10 II 12
Run No.
FIfiURE 8. SUMMARY OF THE ADDITIVE EVALUATION RUNS WITH DISTILLATE
OIL AT 80 PERCENT LOAD AND 14.0 PERCENT C00
a>
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12 13 14
C02, percent
15
16
FIGURE 9. SMOKE VERSUS C02 LEVEL FOR
REFERENCE DISTILLATE OIL
38
-------
could only increase the participate loading. Evaluation runs were not con-
ducted at higher particulate loadings because the air/fuel ratio could not
be controlled with sufficient accuracy to obtain reproducible particulate
emission data. As shown in Figure 9, for CO levels above 14 percent, a
slight change in the air/fuel ratio would produce a significant change in
particulate emission level.
It can be conjectured that the use of additives with distillate oil firing
would allow boilers to be operated at lower excess levels (where appreciable
carbon particulate would be generated without additives) and, thereby,
increase efficiency. If it were possible to operate at these low excess air
levels, sophisticated controls or manual attention would be required to con-
trol the air/fuel ratio precisely, as any slight change in boiler operation
(e.g., fuel temperature, air temperature, etc.) could cause a drastic change
in the excess air level and the emission of particulates, CO, and unburned
hydrocarbons. Figure 9 illustrates this point for smoke. Only in the largest
boilers would these controls be economically feasible, and the larger oil-fired
boilers generally are fired with residual fuel oil.
RESIDUAL OIL EVALUATION RUNS
Additives were evaluated with two different residual oils, a 1-percent
sulfur oil and a 2-percent sulfur oil. In general, the results of the
evaluation runs with the two oils were similar. The difference in the base-
3
line particulate loadings for the two oils (88.6 mg/Nm ) for the 1-percent
3
sulfur oil and 72.1 mg/Nm for the 2-percent sulfur oil) is attributed to
differences in physical and chemical properties of the fuels.
Statistical Significance
Figure 10 shows graphically the effectiveness of the proprietary
additives and the organo-metallic and organic pure compound additives in
reducing filterable particulate emissions from the combustion of the 1-
percent sulfur residual oil fired continuously at 80 percent load and 12.8
percent CO . The arithmetic mean particulate emissions for the baseline
3
runs, 89 mg/Nm , and the estimated ash component of the particulate loading
are shown.
39
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40
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Also shown in Figure 11 is a line located at two standard deviations
3
(2 a = 18 mg/Nm ) below the baseline average. This standard deviation is
based on the individual baseline measurements and is regarded as equally
valid for the particulate measurements with additives. Although the use
of two standard deviations strictly requires the assumption of normality
to correspond to a 95 percent confidence level, it is used here in a broad
sense to indicate a reasonably high, but unknown, confidence level. Addi-
tives producing particulate emission levels falling below this line (at 71
3
mg/Nm ) are concluded to have been effective in reducing particulate
emissions with a statistical significance (not due to chance) at this
reasonably high confidence level. Additives producing particulate
3 3
emission levels above 71 mg/Nm but below 86 mg/Nm (determined from the
standard error of the mean of the baseline runs) suggest that these addi-
tives are effective, but that more experimental data are required to
establish the level of statistical significance.
In addition, the measurements indicate that some additives are more
effective in reducing particulate than others. However, by assuming that
3
a standard deviation of 9 ing/Nm also applies to the additive runs, a
statistical treatment of the data would indicate that improvement with the
•
various effective additives was not statistically different.
Likewise, Figure 11 graphically shows the effectiveness of proprietary,
organo-metallic, and organic metallics in reducing particulate from the com-
bustion of the 2-percent sulfur residual oil fired continuously at 80 percent
load and 12.8 percent CO .
3
The arithmetic mean of these runs is 72 mg/Nm while the standard deviation
3
is only 5 mg/Nm . Again, the same statistical reasoning discussed previously
applies to these runs.
Effect of Additive Type and Concentration
The data presented in Tables 5 and 6 and Figures 8 and 9 show that some
additives containing metals substantially reduced particulate emissions. The
additives that were effective contained certain alkaline-earth or transition
41
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metals and were used in concentrations corresponding to the addition of between
20 ppm and 50 ppm of metal to the fuel oil. Proprietary additives of the
organic type with some trace metals also were shown to be effective at concen-
trations that corresponded to the addition of at least 15 ppm of metal to the
fuel oil. As in the case of the additive "Formula LSD", these concentrations
were significantly higher than those recommended by the manufacturer.
In general, the organo-metallic compounds listed in Tables 5 and 6 were
effective in reducing particulate except for an additive in the subclass cyclo-
pentadienes (CI-2) and zinc naphthenate. The proprietary additive CI-2
(represented by Runs 17, 18, 51, and 53), although observed to be effective
in reducing particulate from a residential oil burner firing distillate oil
(1), proved only marginally effective in the 50-bhp (500 kW boiler firing
residual oil; its ineffectiveness might be attributed to the type of bonding
structure of this compound, although Ferrocene (Run 54), another type of
metallic cyclopentadiene, proved effective in reducing carbon particulate.
The data indicate that the most effective additive constituents are compounds
of the alkaline-earth metals (barium and calcium) and the transition metals
(manganese, iron, and cobalt). Zinc, an element just beyond the above tran-
sition metals, was found to be an ineffective additive.
The use and effectiveness of the "effective" additives at higher concen-
trations might be expected to produce a greater reduction in emissions. How-
ever, it was observed that, even though carbon burnout can be further promoted-
at higher concentrations, the net reduction in particulate is not substantial
because of the additional particulate generated by the metallic inert contained
in the additive.
Some of the pure organic additives appeared effective in reducing partic-
ulate emissions. However, these additives had to be used at impractically high
concentrations to be marginally effective and, therefore, could not be considered
as a viable method of controlling particulate emissions.
The organic acids, naphthenic and hexoic (Runs 82 and 83) were only
evaluated to determine if the organic carrier of the metal in the
43
-------
organo-metallic additives had any effect on particulate reduction. Obviously
they did not.
Effect of Additives on Carbon Particulate
For the baseline operating condition of 80 percent load at 12.8 percent
CO , the carbon content of the filterable particulate from the majority of runs
with both residual oils was measured as between 40 and 50 percent (with the
remaining portion being the ash component associated with the inerts of the
fuel oil). Accordingly, because combustion additives are intended to promote
more complete burnout of carbon, they can only reduce particulate loadings by
up to 50 percent—unless the use of additives caused a larger portion of the
particulate to remain within the combustion system. This would probably be
undesirable, as it would cause fouling of heat transfer surfaces.
From Figures 10 and 11, it can be seen that the most effective additives
reduced particulate loading levels to values comparable with particulate
generated by the ash in the fuel. This reduction represents about a 50 per-
cent reduction in particulate emissions and the nearly total elimination of
carbon particulate emissions.
Variable Load Runs. This observation that particulate loading can be
reduced by about 50 percent is further verified by the results of Runs 25, 26,
46, 47, 48, and 49 in which the boiler was fired at five boiler loads.
Figure 12 shows the particulate loading generated by the boiler operated at
each of five loads with and without barium naphthenate as the additive. For
the baseline runs, particulate loadings were higher at the extremes of the
load range. However, with the use of barium naphthenate, particulate loadings
were reduced to approximately the same level, regardless of load. The average
particulate loading for these additive runs was about 10 percent higher than
the anticipated ash level from firing the referenced fuel alone—this can be
attributed to the increase in metallic inert of the oil by addition of the
barium naphthenate. Analysis of the particulate catch obtained from these addi-
tive runs showed that over 80 percent of the particulate was ash (or less than
20 percent of the particulate was carbon).
44
-------
140
120
100
ro
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60
40
20
0
Baseline
100 %
load
80%
load
I | Barium
(IJIJj Naphthenate
35%
load
80%
load
65%
load
55%
load
46 26 25 47
Run Number
48
49
FIGURE 12. THE EFFECTIVENESS OF BARIUM NAPHTHENATE IN
REDUCING PARTICIPATE AT VARIABLE BOILER
LOAD FOR CONSTANT AIR/FUEL RATIO WITH
RESIDUAL OIL
45
-------
8
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o Baseline
+ Run No. 31 cobalt naphthenate
x Run No. 26 barium naphthenate
Particulate
ratio (carbon
particulate
ratio)
22% ./I0% 75%
Excess air
level
10
12 13 14
C02, percent
15
16
FIGURE 13. SMOKE VERSUS C02 LEVEL FOR THE RESIDUAL
OIL AND SELECTED ADDITIVES. The numbers
apply to the intersection of the curves
with the coordinate lines.
46
-------
Effect of Additives on Smoke
As a measure of the effectiveness of additives in reducing particulate
emissions over a range of air/fuel ratios, Bacharach smoke measurements were
made at about 6 excess air levels for every daily baseline run and every addi-
tive run to enable plots as in Figure 13. This figure shows the effect of
cobalt naphthenate (Run 31) and barium naphthenate (Run 26) on smoke emissions.
In general, the relation between Bacharach smoke and C09 for the daily base-
line runs (as shown by the curve in Figure 13) remained constant from day-
to-day—as would be expected from the small variations in particulate loadings
of these runs. Accordingly, the effectiveness of the additive could be
evaluated semiquantitatively by comparing the smoke characteristic curves with
and without the additive. The differences in smoke levels of these curves
could be related to the differences in both total and carbon particulate load-
ings at some C0~ level. For example, at 12.8 percent CO-, examination of the
data from Figure 13, Table 5, and the analyses of the filter catches of Runs
26 and 31 for carbon, indicates the following
Reduction in Particulate Loading Ratio
Bacharach Smoke Total Carbon
No. from 4 to Particulate Particulate
Run 26, Barium naphthenate 1.0 0.55 0.17
Run 31, Cobalt naphthenate 2.5 0.68 0.35 .
Thus, these additives were effective in reducing both smoke and carbon parti-
culate, and the additive (barium naphthenate) that was most effective in re-
ducing smoke emissions also was most effective in reducing particulate emissions-
Effect of Additives on Carbon
Particulate at Higher Loadings
In Runs 84, 85, and 86, additives were evaluated at a boiler operating
condition of 14.2 percent CO , an operating point at which approximately three
times the carbon particulate is generated as at 12.8 percent CO . (This factor
of three was determined by carbon analysis of the filter catches for the baseline
runs at 14.2 percent CO and 12.8 percent CO..) A comparison of the carbon
analysis of the filter catches of these runs with those for the same additives
and additive concentrations (Runs 64, 73, and 74) indicates that, at the higher
47
-------
particulate loading (presumably due to increased carbon emission), additives
removed a lower percentage of the carbon particulate but a larger total amount,
Table 7 summarizes these results.
TABLE 7. ANALYSIS OF FILTER CATCHES FOR SELECTED
ADDITIVES AT BOILER OPERATING CONDITION
OF 12.8 PERCENT C02 AND 14.2 PERCENT CO .
Carbon, mg
Carbon for Baseline Run
Minus Carbon for
Additive Run, mg
Carbon Reduction
With Additive,
percent
Run C02, %
Baseline
64, 85 (barium hexoate)
73, 86 (barium
naphthenate)
74, 84 (calcium
naphthenate)
12.8
45
6
7
3
14.2
125
35
35
21
12.8
—
39
38
42
14.2
—
90
90
104
12.8
—
87
85
93
14.2
—
72
72
83
These results are consistent with the model that proposes that the in-
creased carbon particulate loading at 14.2 percent CO. is due to an increase
in particle size (rather than an increase in number of particles), and that
the action of the additive in destroying the carbon particles is surface
limited. Accordingly, as the carbon particles increase in size there is
more surface to react with the additive and thus, a larger amount of carbon
can be destroyed. However, as the particle size increases, the surface-to-
mass ratio decreases restricting the reaction of the additive on the total
mass of carbon.
Effect of Additives With a Detuned Boiler
The boiler was "detuned" following the above reported additive runs to
simulate a boiler in poor operating condition by (1) replacing the standard
20 gal/hr (76 £/hr) nozzle with a 10 gal/hr (38 £/hr) nozzle, while maintain-
ing firing rate, (2) decreasing oil preheat temperature from 170 F to 135 F
(77 C to 57 C), and (3) bleeding off a portion of the atomizing air. This
third change had the most dramatic effect in that the fuel spray would impinge
48
-------
on the wall and produce a locally smoky fuel-rich flame. Although the overall
air/fuel ratio could be controlled to maintain a constant CO level of 12.8
percent, smoke levels for the baseline runs at this air/fuel ratio would vary
from Bacharach smoke of 3 to 7. In addition, the smoke characteristic curves
could not be reproduced with any high degree of accuracy.
The use of the additives in the "detuned" boiler (Runs 87, 88, 89, and 90)
did not improve the reproducibility of the smoke data over the range of air/
fuel ratios of interest (9 to 14 percent CO ), although the additives decreased
the smoke levels somewhat. These additives appeared to be more effective in
reducing smoke from a "tuned" boiler than a "detuned" boiler. However, the
relative reduction in relative particulate emission levels was about the same
for either a tuned or detuned boiler. Apparently, the additives were not
effective in destroying or inhibiting the formation of soot or smoke produced
from the fuel distilled off the combustion chamber walls.
Effect of Additives in Cyclic Operation
To obtain a measure of the effectiveness of additives in a more normal
operating mode for small boilers, an evaluation run (Run 50) was conducted
while the boiler was operated on a cycle of 15 minutes on and 5 minutes off
at 80 percent load and 12.8 percent CO . (This would not be a typical opera-
ting cycle for most larger commercial boilers and nearly all industrial boilers.
To meet a varying load, the firing rate for these boilers is modulated so that
there is continuous combustion.) If the assumption is made that the ash
component of the particulate emission is the same for cyclic operation as it
is for steady-state operation, the additive reduced carbon particulate by only
50 percent in cyclic operation in comparison to over 80 percent for steady-state
operation. During this mode of operation, the character of the particulate
(such as unburned vaporized fuel oil or larger particle size) could be different
than during steady-state combustion. The additive may not be as effective in
reducing the quantity of this altered particulate.
While these results are illustrative, additional information is needed
on the effect of additives under different conditions of cyclic operation for
small commercial boilers.
49
-------
Effect of Additives on POM
Table 8 summarizes the polycyclic organic matter (POM) data that includes
both the steady-state and cyclic runs. Sampling and analysis for POM were
conducted during a limited number of additive runs that are indicated by the
suffix "a" in Table 8. The data in Table 8 include both the total POM and
species quantification for over 15 compounds, the majority of which are listed
as potentially carcinogenic by the National Academy of Science (12) . The
"stars" indicate the relative levels of potential carcinogenicity, with no
stars being noncarcinogenic while the 4 stars indicate the highest level.
Steady-State Runs. Table 9 includes a comparison of the total POM loadings
with carbon particulate loadings and Bacharach smoke levels for the runs listed.
From Table 9, and as discussed previously, certain additives are effective in
reducing carbon particulate for the residual oil runs; however, the effect of
additives on POM emission levels is somewhat inconclusive because of the large
amount of scatter in the data points and the limited number of POM baseline
data. From Figure 14, a plot of particulate and POM loadings as a function
of CO (and, thus, excess air) generated during the residual oil checkout
runs, the scatter of data in Table 9 is not unexpected when considering that
a small decrease in excess air can drastically increase the POM emission level
due to the sharp change in the slope of the POM curve at 12.8 percent—where
the additive evaluation runs were made. In addition, because the concentration
of POM in the liquid fuel is 20,000 to 100,000 times greater than the concen-
tration measured in the stack gas, any emission of unburned fuel can have a
great effect on the POM levels measured in the stack. Thus, it is possible
that subtle changes in the combustion process (that cannot be detected by
gross analysis of stack gas composition) may have a significant effect on
POM emissions. Such factors would tend to mask an additive effect, especially
considering that for most runs POM loadings were observed to be less than
3
10 yg/Nm for continuous steady-stati
the threshhold level of measurement.
3
10 yg/Nm for continuous steady-state operation and that these levels approach
50
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However, from Figure 14 there appears to be a direct relation between
particulate and POM emission levels suggesting that additives effective in
reducing particulate emissions may also be effective in reducing POM emissions.
Figure 15, a plot of POM loading versus particulate loading for Runs 13, 14,
15, 16, 17, 19, and 20 tend to further support this relation. Additional data,
however, are required to determine the statistical significance of the effect
of additives on POM.
Cyclic Runs. POM measurements were also made during the cyclic operation
of the boiler in Run 50. Although this size boiler would not be operated in
an on-off cycle, but rather modulated to meet load, it was felt that some use-
ful data could be obtained by operating the boiler over a cycle of 15 minutes
on and 5 minutes off. As noted in Table 5 for Run 50, particulate loadings
increased by a factor of about two for both the baseline and the barium
naphthenate additive runs. However, POM levels for the baseline run in-
3
creased by over two orders of magnitude (924 ug/Nm ), although the POM
emissions still were much higher than for steady-state runs. The high levels
of POM emissions observed during cyclic operation of the boiler could be
attributed to several factors associated with the generation and formation
of POM, including transients in atomization and ignition. It is believed that
POM is generated in the 1000 F (540 C) to 1500 F (810 C) temperature range and
that this temperature range occurs more frequently, or for a longer duration,
in transient combustion than in continuous steady-state combustion. In addi-
tion because the POM concentration is higher in the fuel than in the stack
gases, any unburned or partially burned fuel which enters the exhaust during
startup and shutdown would increase POM emissions.
Effect of Additives on Particle Size
Particle-size measurements of particulate emissions were made using an
Andersen cascade impactor for the baseline condition (no additive) and for two
additives. These runs were conducted in the "tuned" boiler firing the 2
percent sulfur residual oil at the reference condition of 12.8 percent CO
at an 80 percent boiler load.
58
-------
160
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140
120
100
80
60
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• POM
10
II 12 13
C02, percent
14
32
28
24
1=
16 .E
•o
o
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12 2
8
15
FIGURE 14. POM AND PARTICULATE LOADING AS A FUNCTION OF
C02 FOR THE 1 PERCENT SULFUR RESIDUAL OIL
59
-------
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Figure 16 shows the particle-size distribution of these runs plotted
on log probability paper. For the conditions examined, both the barium
naphthenate (51 ppm) and the Ethyl CI-2 (27 ppm) that were effective in
reducing the particulate loading caused a decrease in particle size over the
entire range of measurement (0.5 micron to 14 micron). Figure 16 indicates
that these additives reduced the equivalent aerodynamic mass mean diameter
from approximately 2 microns (with no additive) to less than 0.5 micron.
However, these additives reduced the total amount of respirable particulate
emission (fine particles smaller than 3 microns).
Effect of Additives on Sulfates,
Nitrates, and Trace Metals
Particulate samples were analyzed for sulfates, nitrates, and trace
metals for about 30 runs with and without additives. The sulfate and nitrate
analyses indicate that there was no significant difference between the sulfate
and nitrate levels found in the particulate catch for additive and nonadditive
runs.
Sulfates. If additive action can be attributed to a catalytic reaction,
it may be hypothesized that additives effective in reducing carbon particulate
also may increase sulfate level. It was conjectured that these additives not
only promoted the catalytic reaction of carbon burnout, but also promoted the
reaction of sulfur dioxide to sulfur trioxide and, consequently, to a sulfate.
However, the data did not confirm this hypothesis as indicated in Figure 17,
a plot of carbon content as a function of sulfate content from the analysis of
the filter catch for evaluation runs with and without additives. Examination
of the data utilizing the Medial Test (21) indicates no significant relation
between carbon and sulfate levels. In addition, Figure 17 indicates that the
additives had no significant effect on sulfate levels but had a significant
effect in reducing carbon levels.
Nitrates. Analysis of the particulate filter catch indicates that less
than 0.1 percent of the filter catch was measured as a nitrate. Additives had
no measurable effect on this level.
Trace Metals. Trace metal content of the particulate samples were
determined by a semiquantitative emission spectrographic analysis. Because
the trace metal analysis was semiquantitative and the level of metal addition
61
-------
>>
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1
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99.9
99
98
95
90
80
70
60
50
40
30
20
T
T
T i r
Particulate Loading
• No additive 83.6mg/Nm3
• Barium Naphthenate (51 ppm) 57.7mg/Nm3
A Ethyl CI-2 (27 ppm) 66.3mg/Nm3
I
I
I
1.2 0.3 0.5 1.0 24 10
Equivalent Particle Diameter, microns
20
FIGURE 16. PARTICLE-SIZE DISTRIBUTION FOR RUNS
WITH AND WITHOUT ADDITIVES
62
-------
bU
40
01
E
o
_a
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O
20
Q
i | i | i
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+ Additive o
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Average filter weight for
baseline run = 100 mg +
_ Volume of gas sampled °
= 1.7 Nm3
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II
i 1 i
0 10 20
S04 , mg
1 '
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0 °
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0 +
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1 +
1 1
30 40
FIGURE 17. MEDIAL TEST APPLIED TO PLOT OF CARBON CONTENT OF
FILTER AS A FUNCTION OF SULFATE LEVEL OF FILTER
63
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into the oil was about 10 percent of the inerts contained in the oil, a mass
balance for a given metal could not be conducted. However, the analyses
indicated the expected result that the use of metal-containing additive in-
creased the corresponding metal content of the particulate catch.
Effect of Additives on
Gaseous Emissions
Gaseous emission (NO, SO , CO, and HC) were measured over a range of
air/fuel ratios for each additive run and the corresponding baseline run.
Additives were observed not to significantly effect the emission levels
of nitrogen oxide, sulfur dioxide, carbon monoxide, and gaseous hydrocarbons.
Although it appears possible that additives may be effective in reducing carbon
monoxide and gaseous hydrocarbon emission levels, these levels (CO < 15 ppm
and HC < 10 ppm) were almost negligible for the baseline condition, so that
there was no potential for additives to be effective in reducing these
emissions. Nitrogen oxide and sulfur dioxide emission levels were measured
as approximately 250 ppm and 950 ppm, respectively, firing the 2 percent sulfur
residual oil at 12.8 percent CO with and without an additive.
Effect of Additives on Boiler Efficiency
Incremental gains in efficiency by utilization of certain additives can
be achieved through a reduction in excess air levels and/or a reduction in
fouling of heat transfer surfaces. These incremental gains can be assessed
by comparison of (1) the excess-air levels of boiler operation at a constant
smoke or particulate level, and (2) the rate of fouling of heat-transfer
surfaces (the time-rate of change of stack-gas temperature) with and without
the additives. The incremental gains observed in this experimental program
were based upon relative differences (in excess air and stack temperature)
rather than measurement of absolute overall efficiency as determined by the
ASME Power Test Codes.
The incremental change in boiler efficiency for each additive run is
not given, as this determination is not a direct measurement; however, the
particulate loading ratios, determined by a direct measurement technique,
listed in Tables 5 and 6 give an indication of the potential for efficiency
improvement. Those additives (certain formulations contain alkaline-earth
64
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and/or transition metals) that are the most effective in reducing particulate
levels were also observed to be the most effective in increasing boiler
efficiency.
Two types of evaluation runs, (1) short term, and (2) long term, were used
to determine the incremental gain in efficiency by additive utilization for
steady-state operation. The short-term runs were about two hours in duration,
in which the effect of additive to reduce excess air levels for a given smoke
or a particulate level was determined. The effect of the additive on heating-
surface fouling was determined in the long-term runs which were up to 80 hours
in duration.
Short-Term Runs. The effect of an additive on boiler efficiency can be
estimated from the smoke characteristic curves that are generated during each
evaluation run. Figure 13 shows that the use of certain types of additives
can shift this characteristic smoke curve to the right (to lower excess air
levels for the same smoke number). As indicated for a Bacharach smoke number
of 4, the use of cobalt naphthenate (Run 31) and barium naphthenate (Run 26)
can decrease the excess air levels from the baseline condition of 22 percent
to 10 and 5 percent, respectively. This decrease in excess air corresponds
to an incremental gain in efficiency of approximately 0.9 percent for Run 31
and approximately 1.3 percent for Run 26, assuming a stack-gas temperature
of 450 F (230 C). (A decrease in excess air level also causes a slight decrease
in stack-gas temperature, resulting in a slight additional increase in effi-
ciency. This factor was not included in estimating the efficiency gain.)
Long-Term Runs. Figure 18 is a plot of the stack-gas temperature as a
function of time for the five long-term runs with the 2 percent sulfur residual
oil. The two dashed curves (Run 93 and 94) denote runs conducted firing
the second load of this oil. The boiler operating conditions for these runs
are sumarized in Table 5. Barium naphthenate was used at two boiler operating
conditions; one condition (Run 92) at the same excess air level as the baseline
run and the other condition (Run 91) at approximately the same smoke density
and the same particulate loading as the baseline run.
65
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490
480
470
460
Q.
E
£
u> 440
o
(254)
(249)
(243)
(238)
(232)
Baseline, 12.8% C02
o
o
430
420
410
400
(2271
Ethyl CI-2.12.8%C02
(30 ppm Mn) Run 94
- Calcium naph-
thenate,l2.8%C02
— (27ppm Ca)Run93
Barium naphthenate
I2.8%C02
(51 ppm Ba) Run 91
Barium naphthenate I4.2%C02
(51 ppm Ba) Run 92
(210)
(204)
10 20 30 40
Time, hours
50
60
70
80
FIGURE 18. STACK-GAS TEMPERATURE AS A FUNCTION OF TIME
FIRING TWO-PERCENT SULFUR OIL AT 80 LB/HR
66
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The objective of these long-term runs was to obtain a measure of the
fouling of the boiler heat-transfer surfaces with and without additives.
From comparison of the stack-gas temperature profiles of the additive Runs
92, 93, and 94 with that of the baseline, it is apparent that these additives
are effective in reducing fouling of the heat transfer surfaces during the
first 60 hours. It is difficult to extrapolate these curves to obtain a
measure of the fouling over an extended period of time, particularly in
the case of the baseline run where an apparent decrease in slope occurred
after 50 to 60 hours of operation. However, if it is assumed that the
time-rate-of-change of the stack-gas temperature (the slope of the curves)
is approximately the same after 60 hours, it can then be determined that an
incremental increase in efficiency of about 1 percent can be achieved by a
reduction in fouling (lower stack temperature) by the use of additives.
In additive Run 91, the excess-air level was reduced to generate the
same particulate and smoke levels as the baseline run. As previously dis-
cussed, a reduction in excess-air level increases efficiency by reducing the
mass of the flue gas and lowering stack-gas temperature. This decrease in
stack temperature is in addition to that realized by a reduction in fouling.
Although the particulate loadings of Run 91 and the baseline are approximately
equal, it is apparent from the stack-gas temperature profiles of these runs
that the rates of fouling for the additive run is lower than for the baseline
runs. This difference may be due to a difference in the character, and
possibly the size, of the particulate generated with and without the additive.
The combination of the reduction in fouling and the reduction in excess-air
level accounts for an overall incremental gain in efficiency of about 2 percent
over that of the baseline run. This incremental gain in efficiency of 2 percent
was the maximum gain achieved (for the 50-bhp boiler) for the most effective
additive, and would be less for the other additives.
The gain in efficiency of about 2 percent achieved in the laboratory
boiler does not imply that the same incremental gain can be realized under
all field conditions. Additionally, the maximum gain in any boiler would
only be achieved with appropriate burner adjustment to allow operation at
lower excess air.
67
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SECTION 9
ECONOMICS OF ADDITIVE UTILIZATION
The economics of additive utilization depend upon a number of factors,
some of which are definitive such as the cost of the fuel and the additive;
others are less definitive, such as the potential for increased boiler
efficiency achieved by using additives or the equivalent cost of alternative
emission controls. The following discussion provides some guidelines which
can be useful in assessing the economics of additive usage for a given boiler
installation. To assess efficiency aspects on a national basis would require
engineering data on fuel consumption, excess air levels, stack-gas tempera-
tures, smoke density and carbon particulate levels in a variety of typical
and well-tuned and maintained boiler systems.
Additive Cost
3
Table 10 gives the cost of treating 10,000 gallons (37.8 m ) of fuel,
based upon a dosage of 27 ppm metal per gallon of fuel, for the pure and
proprietary compounds that were found effective in reducing smoke and carbon
particulate (and thus increase efficiency). It should be noted that dosages
of greater than 27 ppm metal per gallon of fuel would be required for some
of the proprietary additives to be effective in reducing carbon particulate
and smoke (and thus increase efficiency). Clearly, the most cost-effective
additives were the pure compounds such as calcium naphthenate at a treatment
of $18/10,000 gallons, while the treatment cost of the least expensive
proprietary additive was $35/10,000 gallons. Use of many of the proprietary
additives would be considerably higher than $35/10,000 gal. In addition to
the cost of the additive, other costs associated with the handling of the
additive must also be considered to determine the actual fuel savings from
additive utilization.
68
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TABLE 10. COST OF TREATING 10,000 GALLONS OF FUEL OIL
BASED UPON DOSAGE OF 27 PPM METAL/GALLON
OF FUEL OIL(a)
Cost of Treatment
Additive ($/10,000 gal)
Calcium naphthenate 18
Barium naphthenate 20
Cobalt naphthenate 70
Iron naphthenate 22
Barium ethyl hexoate 60
Iron pentacarbonyl 120
MC-7 soluble (Apollo chemical) 35
Improsoot (commercial chemical) 200
Formula LSD (commercial chemical) 230
Rolfite 404 (Andrew Rolfe chemical) 200
Watcon 130 (industrial chemical) 270
Ferrocene (arapahoe) 50
(a) Cost figures were based upon drum quantities or bulk
lots, f.o.b., the point of supply as of October 1, 1975.
Fuel Savings
In addition to the costs associated with the additive, the fuel savings
realized from additive use are dependent upon the fuel cost and efficiency
as indicated in Figure 19. Thus, for the least expensive pure compounds,
incremental gains in efficiency of 0.6 percent would have to be realized to
economically justify additive utilization, while they would have to be at
least 1.5 percent for the least expensive proprietary. From Figure 19 it
can be observed that as the price of fuel increases (assuming the cost of
the additive does not), the incremental gain in efficiency need not be as
great to justify the use of the additives.
69
-------
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70
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In terms of generating steam, the use of least expensive pure compounds
in an appropriately adjusted boiler to achieve a 2 percent incremental gain
in efficiency results in a fuel savings of $50 per million pounds of steam
generated. This calculation was based on a fuel cost of $0.30 gallon, a
boiler efficiency of approximately 80 percent, and additive treatment cost
of $20/10,000 gallons. For a 50-hp boiler and using an annual load factor
of 0.25 for this type of boiler (22) a net savings of about $150/yr would
be achieved by the use of pure compounds, not considering additional equip-
ment costs. Including the capital costs (pump, mixing section, etc.) and
maintenance of an additive handling system, this fuel saving would be reduced;
it is questionable whether the use of even the least expensive pure compounds
can be economically justified in this size of equipment. However, the in-
crease in boiler efficiency does extend allotment or supply of fuel oil which
may be a more important consideration under some circumstances than the fuel
cost savings.
SECTION 10
POSSIBLE MECHANISMS BY WHICH
ADDITIVES AFFECT PARTICULATE EMISSIONS
To explain the difference in performance by the various metals which
achieved some reduction in the particulate emissions, it is necessary to
hypothesize as to the mechanism by which they act. The transition metals,
iron, manganese, and cobalt, are known to be oxidation catalysts in a variety
of chemical systems. Consequently, their activity could be attributed to
catalytic enhancement of the carbon burnout in the fly ash. Differences
among these metals could result from the degree of catalysis displayed by
the particular metal. However, in these experiments, no statistically
significant difference was found between the performance of these three
metals.
The alkaline-earth metals, barium and calcium, are not noted for
catalytic activity, so the mechanism by which they reduce particulates is
likely very different from that of the transition metals. It has been
71
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suggested by Friswell (23) that alkaline-earth metals may function by pro-
moting the dissociation of water to H atoms and OH radicals, a process
occurring only at high temperature. The OH radicals are involved in the
combustion of carbon:
C + OH -v CO + H
CO + OH -> CO + H
The H atoms, in turn, react with oxygen in the combustion air to form addi-
tional OH radicals and 0 atoms, namely, 0 + OH -> H + 0.
For differences between various compounds of the same metal, the bond
strength between the metal and the remainder of the molecule may be the con-
trolling factor. This aspect was explored most completely for barium. The
number of available materials was limited by the necessity that they be
soluble in the oil. In this investigation, the naphthenate, hexoate, and
the sulfonate were used, all of which are barium salts of organic acids.
Although some differences in performance of these barium derivatives can be
noted from the data presented in Tables 5 and 6, additional data are needed
to make a statistically valid evaluation. In the cases of iron and manganese,
the situation is similar, although the compounds used for this study cannot
be as readily compared. These mechanistic considerations can be used to
explain differences, but the possibility should not be eliminated that other
properties, such as volatility of the additive and the nature of the oil, may
influence the effectiveness of the additive in reducing particulate emissions.
The possible mechanisms of additive actions are discussed in greater
detail in the state-of-the-art report (3); excerpts of that summary are
reproduced in Appendix A of this report.
72
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SECTION 11
PERSPECTIVE ON FUEL ADDITIVES
In this study, additives containing certain metals used at concentrations
of approximately 20 ppm to 50 ppm of metal in the fuel oil were found effec-
tive in reducing carbon particulate emissions and, therefore, total particulate
emissions.Although the scope of this program considered other pollutants
besides carbonaceous particulate, additives were not found effective in re-
ducing other pollutants.
The results of this study, for the most part, have confirmed the observa-
tions of other researchers and have extended the range of investigation of
proprietary additives and pure compounds to include well-controlled tests in
commercial-size combustion equipment firing residual fuel oil. It should be
re-emphasized that the mechanisms involved in additive action are not fully
understood and there is evidence to indicate that additives effective in one
system firing one type of fuel may not be equally effective in another system
or when firing a different fuel.
Although the mechanistic actions were not directly investigated experi-
mentally, theoretical considerations and limited data suggest that a better
understanding of these mechanisms can ultimately lead to additive utilization
criteria for many types of combustion systems (3). Mechanisms of nucleation
and catalysis should be considered further in light of the interrelation of the
combustion system, fuel properties, and additive type and concentration.
POSSIBLE LIMITATIONS TO THE USE OF ADDITIVES
Before any general or widespread use of fuel-oil additives can be
recommended, a perspective should be developed for each type of boiler in-
stallation, to include these additional considerations:
73
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• Combined emission impact, including effects of the
additive on various pollutants
• Possible toxic effects of trace pollutant emissions
resulting from materials introduced with the additives
• Effects of equipment characteristics on fuel additive
effectiveness
• Practical considerations of additive use, other than
simply the reduction of one or more pollutants
• Comparison of the effectiveness of additives with
alternative control means.
Because of the wide variability of boiler/burner designs and operating conditons
expected in commercial and industrial use, a field test program would be an
essential part of any general assessment of additive effectiveness. However,
the incentives for such a program may be low in view of the relatively low
benefits gained by additive utilization in comparison with other alternatives.
Additional comments on each of these possible limitations are presented below.
Overall Emission Impact
The overall or net impact of a fuel additive on a number of different
pollutants must be considered in combination so that means for solving one
pollutant problem do not create another problem by bringing about an in-
crease in another pollutant. For example, some additives may affect reduc-
tions in one pollutant but increase the emission of another pollutant.
Toxic Effects
Included in the overall consideration of additive usage is the possi-
bility that materials present in additives may produce pollutants which are
toxic. For example, metal-containing additives will result in emissions of
the metal or metals, the possible adverse health effects of which must be
balanced against the reduced emissions of the target pollutant. In many
cases, the potential adverse effects of such emissions are not adequately
understood.
74
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The Effect of Equipment Characteristics
on Fuel Additive Effectiveness
In the case of fuel impurities (such as sulfur and heavy metals) and
the nitrogen oxides, the evidence for additive effectiveness is too uncertain
and the possible modes of action too obscure to permit any rational discussion
of how their effectiveness may be influenced by equipment characteristics.
In some case of products of incomplete combustion, especially carbon
particulates and soot or smoke, there is both experimental evidence of addi-
tive effectiveness in continuous combustion systems and reasonable conjecture
as to how the additives function. Consequently, for additives effective in
reducing smoke and carbon particulate, some consideration of the influence of
equipment characteristics, or combustion conditions, is possible. Such
influences may explain the varying degrees of effectiveness found for the
same or similar additive by different investigators. Following are some
examples of equipment characteristics that may influence additive effectiveness,
Effects of Fuel-Air Ratio. It is easy to conceive that fuel-air ratio
may affect the performance of additives intended to control emissions of
products of incomplete combustion, since, in the extreme case of substoichio-
metric air, combustion must be incomplete regardless of additive effectiveness.
The suggestion that barium functions as a free radical promoter and is thus
active in the high-temperature region of active combustion, while the trans-
ition metals accelerate the oxidation of solid carbon in the post-flame region,
has been proposed as an explanation for an observed difference in the effective-
ness of these additives at differing fuel-air ratios. Thus, the effectiveness
of barium in suppressing smoke was little affected by the overall fuel-air
ratio, while the effectiveness of the transition metal manganese was observed
to decline with excess air.
Effects of Time-Temperature Relationships. The belief that the transition
metals are active in the postflame region also suggests that their effective-
ness may be influenced by the rate of heat extraction from the combustion
products. If the combustion space is small and the products cooled rapidly,
the catalyzed oxidation of the carbon particles may be quenched and the
transition-metal additives would be relatively ineffective. Such rapid
75
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postflame cooling would have a lesser effect on the action of barium or,
assuming a similar basis of action, the other alkaline earth metals
because this type of additive is thought to be active at high temperatures.
In contrast, low combustion temperature, such as accompanying two-stage or
distributed combustion, might reduce the effectiveness of the alkaline earth
metals without greatly affecting the activity of the transition metals.
Effects of Fuel Vaporization and Fuel-Air Mixing. The possibility
exists for the fuel additive to be separated from the region where its
activity is needed. Thus, an additive retained in a coke or ash particle
would be ineffective in reducing smoke emissions. Likewise, smoke formed
during the initial burning of the fuel might be little affected by an addi-
tive released from the liquid fuel at a latter stage of the combustion
process. Separations such as these, or their reverse, will be influenced by
the volatility and thermal stability of the additive, the character of the
fuel, and the thermal regime characterizing the vaporization zone of the
equipment.
At the moment, the above descriptions of possible influences of equipment
types on additive effectiveness must be regarded as providing a basis for
anticipating such influences rather than being definitive examples. Experi-
mental investigations under controlled conditions will be required to
identify the parameters of importance for various equipment and additive types.
Other Practical Considerations
Practical considerations that may limit the feasibility of additives
include possible effects on (1) storage stability and handling characteristics
of specific fuels, or (2) deposits in burner parts of flue passes. (Storage
stability includes such aspects as sediment, gum formation, and especially
moisture sensitivity. A review of Class I fuel-handling additives is con-
tained in Appendix B of this report.) Such effects may not be easily
predictable without investigation of additives under specific field condi-
tions to be encountered.
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Alternative Approaches
Other alternative means of emission control and increasing efficiency
may be more effective than the use of additives in many applications. Because
particulate emission control and increased efficiency are somewhat competing
and maximizing one may reduce the other, alternative concepts to additive use
may be more attractive. Both practical effectiveness and cost effectiveness
should be considered.
Emission Control—
The most viable approach to control of particulate emissions from oil-
fired equipment is to insure proper burner design, correct burner adjustment
to obtain good fuel-air mixing, the desired thermal environment and adequate
controls to automatically maintain these conditions. Utilization of existing
combustion technology generally can reduce emissions resulting from incomplete
combustion. Fuel switching from residual oil to distillate oil is an alter-
native that can reduce emissions but this control strategy must be evaluated
in terms of both the availability of distillate oil and the price differential
with residual oil.
Another situation where additives may prove useful is in conjunction with
combustion modification (such as staged combustion) intended to control nitrogen
oxides. If it should develop that such modifications lead to excessive emissions
of products of incomplete combustion, especially soot, fuel additives may offer
a route to overall emission control. At present, this possibility has not been
sufficiently investigated to permit drawing definite conclusions.
Efficiency Gain—
It appears that additive utilization for improved efficiency has its
greatest potential in low-pressure boilers with capacities of less than about
30,000 pounds steam per hour. For larger boilers the economics suggest the
consideration of heat recovery equipment that can achieve incremental gains
in efficiencies of as much as 10 percent, whereas additives may increase
efficiencies by only a few percent. Also, in these larger units, boilers
are equipped with more sensitive controls than the smaller units and,
thereby, are capable of operating with minimal amounts of excess air.
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From an economic standpoint, additive utilization at best would be cost
effective only if boiler efficiency can be increased by at least 1 percent
or at 500 F, an incremental reduction in excess air of about 10 percent.
Accordingly, assuming 15 percent excess air as a minimum level for satis-
factory boiler operation, the potential exists for additive utilization to
be cost effective for those boilers that cannot be "tuned" and operated for
extended periods of time at less than 25 percent excess air. It is likely
that additive utilization also would reduce fouling so that the incremental
reduction in excess air need not be as great as 10 percent for additives to be
cost effective. However, it is difficult to characterize every boiler with
only one or two parameters. Thus, before any generalized recommendations
regarding additive utilization in a specific boiler can be made, the
economic aspects of the boiler installation must be assessed.
In short, the needed perspective must include consideration of the full
spectrum of pollutants, emission control alternatives and economic aspects of
increased efficiency applicable to each type of boiler installation.
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APPENDIX A
EXCERPTS FROM
COMBUSTION ADDITIVES FOR POLLUTION CONTROL:
STATE-OF-THE-ART REVIEW *
ABSTRACT
Fuel additives have been used, or proposed for use, to serve a variety
of functions in combustion systems. This report covers a state-of-the-art
review of combustion-type fuel additives as to their potential in reducing
air-pollutant emissions for oil and coal firing. The report contains two
complementary parts: (1) a review of combustion mechanisms as they relate to
ae'-.itive action in controlling emissions, and (2) a review of experimental
investigations of combustion-type fuel additives.
The review of technical literature revealed relatively limited quantita-
tive data from experimental investigations on combustion additives in which
conditions are well defined. However, there is evidence for some measure of
control of emissions by fuel additives.
The evidence for control by fuel additives of visible smoke and carbon
particulate is relatively strong, and the evidence for control of polycyclic
organic matter (POM) j_s somewhat weaker. The evidence for control of NO
x
is quite weak. Significant control of S0_ or total sulfur emissions by fuel
additives does not appear to be possible, although emissions of SO can be
reduced. Possibilities for the control of emissions of ash, or specific
ash constituents by fuel additives, is restricted to enhancing the collect-
ability of ash particles. Little experimental evidence is available for
control of hydrocarbons or CO emissions by fuel additives, although
theoretical considerations suggest that some degree of control might be
possible. Practical considerations and other possible limitations to the
use of additives are also reviewed.
Reference (4) 7Q
-------
OVERVIEW AND CONCLUSIONS
The conclusions reached by this overall review are discussed below by the
category of pollutants, followed by general comments on the use of fuel addi-
tives; then, recommendations are presented relating to further R&D needed
to fill gaps in information. Although a number of possibilities for ad-
vancing the state-of-the-art are suggested, with few exceptions, the pro-
bability of a successful and practically useful outcome for emission control
is relatively low, compared to opportunities for improvements by good com-
bustion design and practice.
The following overview summarizes principal conclusions on combustion-
type fuel additive effects as related to:
1. Products of incomplete combustion
2. Emissions resulting from fuel impurities
3. Emissions of nitrogen oxides
4. Boiler efficiency
ADDITIVE EFFECTS ON PRODUCTS OF INCOMPLETE COMBUSTION
Products of incomplete combustion include CO, hydrocarbon, POM, smoke or
soot, and coke particles. This class of pollutants offers perhaps the most
fertile field for additive application. Recorded research is limited to
"particulates" (i.e., smoke or soot and coke particles, and POM), although
one might expect additives affecting any of the products of incomplete combus-
tion would have detectable effects on the others. Obviously, the ash portion
of the particulate emission (or fly ash) cannot be reduced by an additive;
however, the combustible or carbon portion can be reduced.
Effects on Combustible Particulates
The greatest effort in fuel additive studies has been devoted to
particulate and smoke emissions. For minimizing particulate formation in
fuel-oil combustion processes, experimental evidence shows that the most
effective agents are compounds of some transition metals (manganese, iron,
nickel, and cobalt) and some alkaline-earth metals (barium and calcium).
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Organometallic derivatives of these metals have given the best results. The
organic portion of the molecule provides the needed solubility in the oil,
while also influencing the stability and volatility of the additive molecule.
It is generally proposed that the transition metals catalyze the oxida-
tion of soot in the hot combustion gases. Of the alkaline-earth metals,
barium has been suggested to act as a catalyst for the decomposition of
hydrogen and water, promoting the destruction of soot by the free radicals
thus generated.
No research clearly pertaining to coke-particle emissions was found.
While it may reasonably be assumed that the same type of additives effective
in reducing smoke or soot emissions will be effective in reducing coke
particle emissions, the optimum additive volatility or thermal stability may
differ. A possibility exists for the application of selected cracking catalysts
to inhibit coke formation from heavy oils.
Finally, questions concerning electrical effects in smoke formation and
their relation to the effectiveness of some types of additives have not been
resolved. Systematic research with additives selected or designed to produce
specific flame ionization levels would be needed to explore this point.
Effects on Polycyclic Organic Matter (POM)
Polycyclic organic matter (POM) comprises a class of potentially
hazardous pollutants generally resulting from incomplete combustion (13).
This class includes (1) polynuclear aromatic hydrocarbons, commonly identified
in the literature as PNA or PAH, and (2) nitrogen-containing heterocyclic
compounds.
Only a few investigations have reported the effects of additives on POM
emissions, and much of this research has been directed toward diesel engines
rather than boiler applications. Thus, the reported effects of such additives
as nitroparaffin, nitrate esters, organic peroxides, etc., may have limited
meaning in boiler combustion. Also, it should be recognized that most of the
investigations reporting on POM were published 5 or 10 years ago; the techniques
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of collecting and analyzing POM have advanced considerably during that time
and are still being developed.
Although the physical state of POM and soot are different, their probable
common ancestry and chemical reactivity suggest that an additive effective for
one would be at least somewhat effective for the other. This conjecture is
generally supported by the experimental evidence, but with one interesting
exception: an "oil-soluble barium compound", moderately effective in reducing
diesel smoke, was reported as having no effect on POM. If, in fact, barium
functions as a free-radical promoter, one would expect it to be particularly
effective in reducing POM as compared to the postflame oxidation catalysts,
such as the transition metals are believed to be. However, if one accepts the
conjecture that an oxidation catalyst-type additive that is effective in re-
ducing soot would also be effective in reducing POM, there still is no reason
to assume that the optimum additive stability and volatility would be the same
for both pollutants.
While an additive that reduces particulate may affect some reduction in
POM emissions, there is a need for additive investigations specifically
directed to POM control.
Effects on Carbon Monoxide and Hydrocarbons
CO and hydrocarbons are significant pollutants, but their emission levels
are usually relatively low from continuous combustion systems like boilers;
consequently, few investigations have been reported on the effects of additives
on these pollutants from boilers. Generally, the oxidation-catalysts effective
in reducing soot or, especially POM, might be expected to have some effect
on CO and hydrocarbon emissions. In view of the relative unimportance of these
emissions from boilers, investigation of this aspect does not appear to be
justified.
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ADDITIVE EFFECTS ON EMISSIONS
RESULTING FROM FUEL IMPURITIES
The fuel impurities considered here are sulfur and ash. These impurities
are considered pollutants regardless of the form in which they are emitted.
Effects on Sulfur Compounds
Mechanistically, no fuel additive can be expected to have a direct effect
on the emission of sulfur present in the fuel. Most of the sulfur in the fuel
leaves the system as SO (assuming that the combustion is not unusually fuel
rich). Typically, only 1 to 3 percent of the sulfur leaves the system as SO ,
depending on combustion conditions. In addition, emissions can include partic-
ulate sulfates. (It may be noted that some additives may change the chemical
or physical form of the sulfur emissions to one that is not detected by the
sampling and analytical techniques commonly used to determine SO or SO
emissions.)
Various fuel additives, mostly basic in character, have been used to
scavenge SO or, used in much larger amounts in downstream addition, to
scavenge SO . (This reaction with SO is typically incomplete, and the addi-
tive must be used in quantities substantially greater than the stoichiometric
amount to achieve high reductions.) It is possible that an additive could be
found that would promote the reaction of SO with basic materials; the reported
ability of sodium chloride to enhance the absorption of sulfur oxides by the
limestone in fluidized-bed coal combustors suggests that such effects exist.
However, the large quantity of basic material required, even if used stoichio-
metrically, still may limit any practical application in ordinary combustion
systems.
Effects on Ash
Additives may change the physical properties of ash, but no additive
can be expected to reduce the combustion generation of ash constituents
contained in the fuel. However, ash collectability may be influenced. SO
and other conditioners are sometimes added in the postcombustion zone to
reduce the resistivity of fly ash, and thus promote its collection in electro-
static precipitators. There may also be an opportunity of accomplishing this
conditioning through the use of compounds (other than sulfur) added to the fuel.
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ADDITIVE EFFECTS ON NITROGEN OXIDES
Nitrogen oxide emissions are attributed to two sources: thermal fixation
of nitrogen and the oxidation of organically bound-nitrogen compounds in the
fuel. The reported examples of additives causing significant (though not major)
reductions in NO emissions seem more puzzling than illuminating. The mechanisms
X
by which the observed effects could have been produced are obscure.
Effects on Thermal-Fixation Processes
The importance of 0- and N-atom levels in the mechanism for the fixation
of nitrogen suggests that additives which might reduce, principally, the con-
centration of 0-atoms could be effective in reducing NO . In practice, addi-
X
tives have not been especially effective in this regard. One of the problems
is that hypothetical additives which might reduce the 0-atom level by promoting
atom recombination reactions, or by retarding the combustion reactions leading
to 0-atom formation, could be too detrimental to the overall combustion process.
Effects on Fuel-Nitrogen Conversion
NO is formed more readily from chemically bound-nitrogen species than
X
from the fixation process. To reduce NO from fuel-N species requires that the
decomposition of the fuel-N be diverted to N or NO, rather than active CN
or NH species. No additives have been found which accomplish this. Interest-
ingly, however, there is evidence that NH species can limit, and perhaps reduce,
the conversion efficiency of fuel-N compounds to NO.
On the basis of the information available, it is possible that some minor
degree of NO control may be obtained with fuel additives; the probability of
X
practical success, however, still appears questionable.
ADDITIVE EFFECTS ON BOILER EFFICIENCY
Two routes are open to influence boiler efficiency by fuel or combustion
additives: (1) through cleaning or maintaining the cleanliness of heat ex-
changer surfaces, or (2) by controlling pollutants, particularly visible
smoke, thus permitting operation at reduced excess air levels. Additives
intended to remove or modify soot and other surface deposits have a signifi-
cant history but are outside the scope of this report. However, additives which
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suppress smoke (soot) and other carbon particulate may both reduce the rate
of fouling of the heat exchange surface and permit operation at lower excess
air levels. The possible efficiency gain depends on the smoke-limited excess-
air level of the specific burner-boiler combination, its normal rate of foul-
ing, and the frequency of cleaning. Efficiency gains of a few percent may
be possible in small boilers which are reasonably maintained and adjusted.
In larger boilers, with well-designed fuel-air mixing, equipped with soot
blowers and possibly heat-recovery equipment, and subject to skilled
maintenance and adjustment, additives offer little promise of efficiency
gains.
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APPENDIX B
APPRAISAL OF FUEL-HANDLING ADDITIVES*
SUMMARY AND CONCLUSIONS
Additives which fulfill their function prior to the combustion
of a fuel oil (Class I additives) are discussed in this appendix. The
efficiency of boiler operation sometimes may be enhanced by these fuel-
handling additives, because they prevent formation of materials that may
clog burner components and possibly reduce efficiency by impairing burner
performance.
Fuel-handling additives have been developed to be effective in
performing functions as
o Oxidation inhibitors
o Corrosion inhibitors
o Dispersants
o Pour-point depressants
o Metal deactivators
o Antistatic additives
o Biocides.
Additives performing the first three functions are routinely added by most
U.S. refineries to No. 2 distillate heating oils as part of the normal
"additive package" because nozzle ports for oil burners used in residential
and commercial combustion equipment are especially sensitive to clogging.
Fuel-handling equipment systems and atomizers designed for heavier fuels
are more tolerant to deposits, and these additives are less frequently added
by the refiner as a normal procedure. Additives serving the other functions
are added as dictated by the nature of the fuel or circumstances of use.
Study was conducted as part of the FEA-supported portion of the program.
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Inhibiting oxidation of the fuel oil is the most important of the
functions of fuel-handling additives. Oxidation results in sludge formation,
which causes clogging problems, particularly with distillate oils. Effec-
tive antioxidant additives based on amines and phenols have been produced
in the past and new types are being developed as fuels with different pro-
perties appear on the market. In spite of the antioxidants, some sludge
still forms; thus, dispersant additives are used to put the sludge into
collodial suspension. The most effective dispersants are metal salts of
sulfonic acids and phenols. For many years, ashless additives based on
amines have been used and recently amine derivatives of organic phosphates
have been developed.
Water in fuel oils will separate and corrode the tanks and lines,
so corrosion inhibitors are required. The most successful additives of this
type have been high-molecular-weight carboxylic, sulfonic, or phosphoric
acids and their neutralization products with organic bases. These compounds
displace the water from contact with the metal. Water-soluble inhibitors
such as sodium nitrite are often used in residential applications.
To maintain fuel flow, particularly in cold weather, pourpoint
depressants are used. These materials are semiresinous polymers of high
molecular weight which modify the crystals of waxy substances in the oils.
Naphthalene-wax and phenol-wax condensation products have been used for
this purpose, but ethylene-vinyl acetate copolymers are in greatest use as
pourpoint depressants.
Other types of fuel-handling additives which are used include
(1) metal deactivators, which are needed where small amounts of transition
metals in the oil catalyze its oxidation, (2) antistatic additives, which
prevent the accumulation of electrical charges that can cause fires and
explosions, and (3) biocides, which inhibit microbiological deterioration
of the oil.
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The need for additives to perform the above functions varies with
the nature of the application and the optimum choice of additives varies
with the nature of the base fuel, its compatability with other fuels, the
conditions of its storage, handling, and use. In view of the many
variables involved and the lack of "universal additives" that can assure
good overall fuel-handling performance on a cost-effective basis with
all fuels, the recommendation of the oil refiner should be followed for
a particular installation. Many refiners maintain a marketing/technical
service staff to evaluate special needs encountered in the field and to
make such recommendations. In most cases, an effective "additive
package" will already be supplied with the fuel. This treatment, when
combined with proper storage tank maintenance, will control most fuel
oil problems.
Efficient operation of oil-burning equipment thus can be main-
tained over a period of service by the use of fuel-handling additives that
prevent deterioration of the fuel and clogging of fuel lines, filters,
or burner nozzles. However, little information is available in the
technical or noncommercial literature that documents quantitative gains
in efficiency of equipment operating in the field.
Unlike the case of combustion-type additives, where improper
use can increase air pollutant emissions, the misapplication or over-
dosage of fuel-handling additives is unlikely to result in increased air
pollutants. For unusual applications of storage or use, the oil refiner
should be consulted. Indiscriminate use of additives could cause in-
compatability problems that will deteriorate fuel quality.
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INTRODUCTION
The objective of this appendix is to review the state-of-the-art of fuel
additives which are designed to improve the handling of the fuel oil prior to
combustion. These additives contribute to the overall efficiency of the boiler
operation by maintaining the handling quality of the fuel prior to intro-
duction into the burner and by affording protection to the burner components.
Additives to fuel oils are needed for several purposes, the most impor-
tant of which is oxidation inhibition. Both distillate and residual fuel
oils are subject to sludge formation as a result of the oxidation of some
of the hydrocarbon components of the fuel oil. Sludge can plug oil lines,
strainers, and burner nozzles. Additives are also needed to prevent
corrosion in the fuel-oil-handling system, to provide detergent and dis-
persant action, and to emulsify the water that finds its way into the oil.
As more low sulfur oils are put into use, additives to depress the pour-
point of the oil have become more important. There are also other functions
of additives, such as metal deactivators, antistatic agents and biocides.
The importance of fuel-handling additives for the efficiency of boiler
operation has been described in general terms by several authors in recent
years (24-26). More detailed discussions of the types of additives and
their functions were presented by Guthrie in 1960 (27) and by Lodwick in
1964 (28). Symposia papers on additives have been published by the ASTM
(29) and the American Chemical Society (30). Much of the information in
these earlier articles was directed to additives for gasoline and kerosines.
However, some of the data are appropriate for fuel oils, and this appendix
includes the pertinent information from these publications and provides
recent data to establish the current status of fuel-handling additives.
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OXIDATION INHIBITORS
Fuel oils are essentially mixtures of hydrocarbons, which are subject
to oxidation to some extent. Oxidation forms gums which become colloidal,
then agglomerate and precipitate. The rate at which the oxidation occurs
depends on the molecular structure of the hydrocarbon, which in turn will be
affected by the treatment the oil has received. Thus, cracked distilates
usually deteriorate faster than straight-run distillates. These oils con-
tain unsaturates which are susceptible to oxidation. Experiments performed
in an oxygen atmosphere have shown that sludge formation can occur in as
little as 2 to 4 days (31) under such accelerated conditions. The oxidation
of the oil resulted in the formation of acids, ketones, aldehydes, and esters
from the hydrocarbons.
Scientists are in general agreement that the oxidative deterioration
of the fuel oils proceeds by a series of free radical reactions involving
the hydrocarbons. Oxygen molecules first react with the hydrocarbon to
form the free radicals.
RH + 0 -> R- + HOO- .
The hydrocarbon free radical then reacts further to form a peroxy radical:
R- + 02 -> ROD- .
This in turn reacts with more of the hydrocarbon to generate more R- radicals
which continue the chain reaction:
ROD- + RH -> ROOH + R- .
The hydroperoxides so formed may add to double bonds in unsaturated molecules
to continue the free radical reactions, or they may convert into alcohols,
ketones, and acids.
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Oxidation inhibitors function by removing the peroxy radicals, thus
breaking the chain. The best known and most widely used chain-breaking
antioxidants are aromatic amines and alkyl phenols . These function by
readily furnishing a hydrogen atom to the peroxy radical:
ROD- + InH -»- ROOH + In'
The inhibitor free radical which is formed (In-) then disappears by reacting
with another such radical, resulting in an inactive product.
The most commonly used phenol-type oxidation inhibitors are 2,4-
dimethyl-6-tert-butyl phenol and 2,6-di-tert-butyl-4-methyl phenol. The
first named is a liquid and often is preferred over the second one for this
reason, even though the latter is more efficient as an antioxidant. Some
typical laboratory results in reducing acid formation and sludge with the
second compound are shown in Table 11, where 1.5 percent of the additive
completely prevented sludge formation at 175 C in a light oil (32). This
dosage is much greater than would be used in practice, and phenol-type
additives are normally used at concentrations of a few hundred ppm by weight.
Recent work by British investigators claimed that 2-tert-butyl-4-ethyl phenol
also is an effective antioxidant (33) .
TABLE 11. EFFECT OF PHENOL ADDITIVE
ON ACID AND SLUDGE FORMATION
IN LIGHT OIL
Additive
Concentration, Acid No.,
Wt Percent
0.0
0.5
1.0
1.5
2.0
mg KOH/g
1.92
1.62
1.08
0.50
0.21
Sludge,
Wt Percent
1.64
1.24
0.44
None
None
(a) 2,6-di-tert-butyl 4-methyl phenol (Ref. 32)
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A number of amines have been employed as antioxidants and the most
popular one has been N,N'-di-sec-butyl p-phenylene diamine. This compound
can release two hydrogen atoms readily and hence stop two oxidation chains
per molecule of the amine. Although the amine-type inhibitor is more effec-
tive than the phenols on a weight basis, there is little to choose between
them on a cost effectiveness basis. A recent development in the amine-type
inhibitors has been the use of amino-guanidine derivatives (34). They have
been recommended for use in fuel oils at concentrations from I to 10 pounds
per 1000 barrels of oil (approximately 3-30 ppm by weight). In oxidation
stability tests these derivatives lengthened the induction period by a
factor of 2 to 2.4, depending on the derivative used. Amine borates also
have been introduced for use as antioxidants (35). These compounds are
cyclic borates of polymeric alkanol-amines and were claimed to be effective
at a concentration of only 0.001 weight percent (10 ppm).
Compounds containing both phosphorus and sulfur in the form of esters
of dithiophosphoric acid have been utilized as fuel oil additives because
they function both as antioxidants and corrosion inhibitors. Recently barium
and zinc salts of the above esters with cycloalklyphenols have been syn-
thesized (36). It was found that the barium compounds were more effective
than the zinc compounds for both purposes. Research into the mechanism by
which dithiophosphoric acid esters function has revealed that they react with
hydroperoxides formed in the oil to give disulfides and stop the oxidation
chain reaction (37). Other multifunctional additives of this type have been
made by reacting dithiophosphoric acid with amides of polyisobutenyl
carboxylic acid (38). They were demonstrated to function as dispersants for
sludge as well as corrosion and oxidation inhibitors.
Another recent development has been the use of glycerol esters con-
taining metal oxides as oxidation inhibitors (39). For this purpose, a
mixture containing a glyceryl stearate, a naphthenic oil, a surfactant, and
both aluminum and magnesium oxide was recommended for use at a concentration
of 0.2 gallon per 1000 gallons of fuel oil (in the order of 200 ppm by
weight).
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CORROSION INHIBITORS
Fuel oils can become contaminated with rust when water enters the storage
or distribution system either by condensation or accidentally. Residual oils
in particular are subject to contamination with salt water as a result of
being transported in tankers. Because hydrocarbon fuels are essentially
nonpolar, they can be easily displaced by water from contact with the metal
surface of the storage tanks or transfer lines. As a result a water-sludge
blanket will be formed at the metal surface. In the case of residual oils,
the potential for corrosion is enhanced by the presence of organic sulfur
compounds which are acidic. These acids dissolve in the water-sludge layer
and attack the steel containers. The corrosion products in turn increase the
sludge formation. The corrosion-inhibiting additives can be used most
effectively by adding them to the storage tank. Distillate oils contain
even fewer compounds which can reduce corrosion, so these additives are
useful in the light fuels as well, particularly to prevent surface roughness
in pipelines, which would increase pressure drop.
The most successful materials which have been used as additives against
corrosion are high molecular weight carboxylic, sulfonic, or phosphoric acids,
salts of these acids, and products of neutralization of the acids with organic
bases such as amines. When dissolved in the hydrocarbons, these materials have
the property of forming an adsorbed film on the metal in contact with the liquid.
This film is hydrophobic and displaces the water from the metal surface. The
polar end of the inhibitor molecule becomes attached to the metal surface while
the other end of the molecule is dissolved in the fuels. If sufficient inhibitor
is present, a compact barrier layer of its molecules on the metal prevents
penetration by water. Corrosion is then prevented by this impermeable mono-
molecular film.
Although amine derivatives of phosphates and sulfonates have been used
predominantly as corrosion inhibitors in past years, new formulations continue
to appear. Typical materials in use are shown in Table 12. A new approach
to napthalene sulfonates has recently been developed in France, in which a
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long-chain unsaturated hydrocarbon containing 15 to 20 carbon atoms is
condensed with the naphthalene before sulfonation (40).
(a)
TABLE 12. TYPES OF CORROSION INHIBITORS'
(b)
Recommended Concentration,
Material lb/1000 barrels oil
Alkyl amino phosphate 5.5 - 20
Ethylene diamine dinonyl
naphthalene sulfonate 17 - 20
Octyl phosphate ester +
octylamines + octyl alcohols 7-20
Dimerized linoleic acid 4-16
(a) Ref. 28.
(b) 1 lb/1000 barrels is approximately 3 ppm by weight.
Succinic acid derivatives also are being introduced as corrosion in-
hibitors. One such additive contains a substituted succinic acid and an
aliphatic tertiary amine (41). Another formulation consists of the magnesium
salt of a substituted succinic acid (42). Several new anticorrosion agents
for fuel oils incorporate amines into the mixture in some fashion. These
include amine dicarboxylic acids (43) , alkyl aminopropanol (44), a poly-
alkylene amine mixed with a nitrated oil and a polybasic organic acid (45),
and reaction products of amines with phenols and aldehydes (46).
Synergistic mixtures of diamides are formed by condensing dicarboxylic
acids with diamines. Steel samples were exposed to distillate oils with and
without the additives, at a temperature of 100 F. Sixty-five percent of the
steel surface was rusted in 4 hours without the additive, while in the
presence of the diamides, at concentrations of 1 and 2 pounds per 1000
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barrels (approximately 3-6 ppm), only 20 percent of the steel was rusted.
However, the best additives will keep rusting below 5 percent in such circum-
stances.
Magnesium compounds also have been developed for anticorrosion purposes.
One such formulation includes magnesium hydroxy carboxylic acid in an organic
solvent (48). Another consists of magnesium hydroxide and sodium stearate
mixed in a water suspension, then dried and milled to a particle size of 0.05
micrometer. This additive is designed to be introduced into the oil as a
powder, and good dispersability is claimed (49).
DISPERSANTS
Even though antioxidants are added to fuel oils, some sludge may still
be formed, particularly if the storage period is lengthy. Carryover of
sludge particles can plug fuel filters and severely reduce oil preheater
efficiency. In distillates, dispersants combat filter plugging caused
by bacteria and dirt as well. Particularly in the case of residual oils,
efficient combustion requires optimum atomization, which in turn depends on
a uniform supply of oil having a controlled viscosity. The presence of sludge
adversely affects these parameters, and can also foul or plug burner tips,
thereby making it difficult to maintain stable burner conditions. All of
these problems can be alleviated by a sludge-dispersant additive, used at
concentrations up to 150 ppm by weight in distillates and up to 500 ppm in
residual oils. A dispersant additive should be used cautiously if sludge has
accumulated in the storage tank. Otherwise the surfactant property of the
additive may bring enough of the sludge into suspension to cause clogging
problems.
A dispersant functions by absorbing on the surfaces of materials which
are insoluble in the oil and converting them into stable colloidal sus-
pensions. Various petroleum and metal sulfonates, metal phenolates, dialkyl
dithiophosphates of metals, and metal phenol sulfides possess these dispersing
properties and have been used in the past years as dispersant additives.
Electron microscope examination of the action of calcium sulfonate and barium
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dialkyl dithiophosphate additives on asphaltene sludges has shown that
particles originally 2 to 4 micrometers in diameter are reduced to less than
0.1 micrometer by the dispersing action (50). In general, barium salts are
better dispersants than calcium salts of the same organic compound. Many
factors have been shown to be important in determining the effectiveness of
a dispersant. Thus, for example, the activity of a sulfonate salt depends
on the molecular weight of the sulfonic acid, the solubility of the sulfonate
in the oil, the nature of the metal forming the salt, and the catalytic
effect of the salt on the oil oxidation (32). The difference in dispersing
ability of various metal sulfonates is shown in Table 13, in terms of the
length of time required to centrifuge a carbon black suspension out of the
treated oil. Although the cobalt and lead derivatives showed a slightly
greater dispersant efficiency than barium, the latter is usually used because
it is more cost effective.
TABLE 13. COMPARISON OF DISPERSANT EFFECT
OF SALTS OF ISOCETYL BENZENE
SULFONIC
Oil Treatment
No additive
Calcium salt
Barium
Strontium
Lead
Cobalt
Copper
Centrifuging Time,
minutes
70
90
105
90
110
140
80
96
-------
The development of improved dispersant formulations is required from
time to time as new oil sources are found, because different properties are
encountered in these oils. For example, the action of a calcium petroleum
sulfonate has been shown to be improved by synthesizing a mixture which also
contains calcium formate (51) . Aluminum sulfonate likewise has been re-
commended as a dispersant (52) . Although barium sulfonate compounds have
been used extensively in the past, a barium sulfanilate derivative recently
has been recommended for improved performance (53).
Another type of compound which has been developed for sludge dispersancy
in recent years is the completely organic structure which has the advantage
of being ash free. The monoethanolamine salts of alkyl phosphates are repre-
sentative of this class of materials (54). Amine salts of phosphate esters
derived from polyalcohols also have been synthesized for dispersant purposes
(55). An amine phosphate product obtained by reaction with sorbitol dioleate
gave a 98 percent flow in a pumping test when added to fuel oil at a concen-
tration of 0.013 g per 100 ml (about 140 ppm). The flow with untreated oil
was only 14 percent (56).
Various other mixtures synthesized recently have proved to be successful
sludge dispersants. A magnesium derivative of an amine oleate is claimed to
combine the ability to disperse sludge with the ability to reduce sulfur
dioxide emission, the latter through the action of the magnesium (57). An
ethylene oxide-aniline-formaldehyde polymer esterified with oleic acid
also has been used (58). Other ashless polymers prepared from maleic,
fumaric, vinyl, and methacrylic esters combine the sludge dispersant
properties with those of pour-point depressants (59).
POUR-POINT DEPRESSANTS
While pour-point depressants are used in many types of oils, this type
of additive is especially useful in residual oils. The residual oils require
heated storage tanks and transfer lines to handle them properly. Hence,
pour-point depressants can be particularly effective for this type of fuel
oil when it is subject to congealing by precipitated wax.
97
-------
The use of pour-point depressants in distillates is governed by economic
considerations, as the additives are an alternate to kerosene dilution or
lower distillation endpoint to achieve the desired properties.
Pour-point depressants are made up, in general, of semiresinous high
molecular weight polymers. The most important types used in past years have
been (1) wax-naphthalene condensation products, (2) phenol-wax condensation
products, and (3) methacrylate polymers. These polymers function by modifying
the crystals of the waxy substances in the oils, thus reducing formation of
immobilizing aggregates (60). Pour-point depressants are effective at con-
centrations ranging from 0.02 to 0.2 percent by weight (200 to 2000 ppm)
depending on the oil and the pour point desired.
There has been a flurry of activity in the development of new formula-
tions for pour-point depressants in recent years. This effort may be the
result of greater use of waxy, low-sulfur fuels to meet emission regulations
for sulfur oxides. These fuels have higher pour points than were previously
encountered. The increased interest may also be the result of oil property
variation because new sources are being tapped and new blends are being made.
Over 30 patents for new pour-point additives granted in the last few years
attest to the significant interest in this field. The types of materials
covered by these patents can be classed in seven groups:
1. Ethylene-vinyl ester copolymers, which constitutes the largest number
2. Fatty acid esters of polyhydric alcohols
3. Esters of dicarboxylic acids and polyalcohols
4. Derivatives of amines
5. Mixtures of organic acid chlorides and polymers
6. Derivatives of polymerized olefins
7. Organics mixed with distillate oil fractions.
A list of the materials covered by these patents is presented in Table 14, which
includes the pour-point data where available (61-91). The data show that in
these cases, a concentration of about 0.1 weight percent (100 ppm) in the fuel
oil resulted in a pour-point lowering of 20 to 40 F.
98
-------
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100
-------
MISCELLANEOUS ADDITIVE TYPES
Other types of additives are used for fuel oils to a lesser degree than
those previously discussed. The source of the oil and its treatment prior
to use will determine whether or not a metal deactivator additive is needed.
The conditions of pumping and spark-generating hazards may dictate the need
for an antistatic additive. The susceptibility of some oils to microbial
growth may require the addition of a biocide. Additives have been developed
to fulfill each of these purposes.
Metal Deactivators
The metal content of a fuel oil can catalyze the oxidation of the oil
and result in more rapid sludge formation than would otherwise be the case.
In addition, mercaptide gels can form on copper and brass parts of the fuel
system. Although metals are more concentrated in residual oils than in the
original crude, they are tied up in porphyrin-type complexes and are
relatively inactive. However, even distillate fuel may contain several parts
per million of copper, iron, manganese, zinc, lead, nickel, calcium barium,
sodium, potassium, and lithium (92). Of these, the transition metals, copper,
iron, manganese, and nickel are the most potent catalysts, and metal de-
activators are designed to affect them especially. These metals are powerful
hydroperoxide decomposers and act as a catalytic means of providing a con-
stant source of free radicals for oxidation chain initiation. However, by
complexing the metal with an organic molecule, it can be prevented from
participating in such catalytic activity. Large molecules which can
"surround" the metal atom to form a chelate compound are used as deactiva-
tors. The compound N,N'-disalicylidene 1,2-propylene diamine is very effec-
tive in some cases:
CH = N - CH. - CH - N = CH
101
-------
In this formula M represents a bivalent metal which has covalent bonds to the
oxygen atoms and coordination bonds with unshared electron pairs on the nitro-
gen atoms. Copper can be effectively prevented from further reaction by
formation of such a compound.
In addition to the diamine shown above, other organic compounds containing
nitrogen and oxygen in suitable positions to chelate the metal atom have proven
to be useful deactivators. However, formation of the chelate does not always
assure deactivation, and some combinations of metal and organic compound
actually are activators, because of increased electron transfer capabilities.
This effect is illustrated in Table 15 which shows both deactivation and activa-
tion by some organic compounds. Copper is completely deactivated by all of
them, but only one of these compounds works successfully with manganese. Con-
sequently, it is important to know which of the metals predominate in the oil
in order to select the proper additive. In general, copper is the commonest
contaminant, probably because copper chloride is sometimes used to convert
mercaptans into disulfides during refining. There can also be copper pickup
from valves and pumps in the distribution system. Fortunately, copper is
relatively easy to deactivate, but nickel and manganese would present problems.
The obvious solution would be to use an additive which deactivates all four
metals, such as the tetrasalicylidene derivative in Table 15, but such materials
are more expensive. Thus, additive cost may be a consideration, although de-
activators are used at a concentration of only 5 to 10 ppm by weight.
A recent development in this field is the use of amido triazoles as
chelating compounds (93). The simplest of these compounds involves bonding
with oxygen and nitrogen as illustrated above. However, some compounds of
this type can be made with a sulfur atom in the molecule. The bonding to the
metal can then be accomplished via sulfur and nitrogen, thus providing a
stronger chelation effect.
102
-------
TABLE 15. EFFICIENCY OF METAL DEACTIVATORS
(a)
Deactivation (-) or Activation (+),
percentage for metal at indicated
concentration, pom
Compound
Cu
1.0
Fe
0.87
Ni
0.92
Mn
0.86
N,N'-Disalicylidene
1,2-propylene diaraine -100
Salicylaldoxime -100
N-Salicylidene-o-
aminophenol -100
2,2', 4'-Trihydroxyazo-
benzene -100
N,Nl,N",N"'-Tetrasalicyl-
idene tetra(aminomethyl)
methane -100
+43
0 -100
-100
-100
-100
nd(b) +103
+55
+124
-100
nd
+84
+73
-100
(a) Reference 28.
(b) nd = not determined.
ANTISTATIC ADDITIVES
Explosions and fires caused by static electrical discharges can occur in
fuel storage tanks and lines both during storage and handling. Although this
problem is most important for aviation fuels, antistatic additives have been
developed for use in other distillate fuels. When a fuel oil of low electrical
conductivity flows through a pipe, a separation of electrical charges can
occur and a static charge is built up in the liquid. This charge separation
can lead to high voltages with the possibility of spark discharges which may
ignite the fuel vapors. Charge generation is increased by high pumping rates
or by contact with equipment having a high surface area such as water separators
or fuel filters. However, if the fuel conductivity is increased by an additive,
the charge built up in the liquid can leak back to the container wall.
103
-------
The antistatic additives used in the past have been three-component
systems consisting of (1) the chromium salt of an alkylated salicylic acid,
(2) calcium di(2-ethylhexyl) sulfo-succinate, and (3) an organic polymer,
which functions as the additive stabilizing agent. Such an additive when used
at a concentration of about 1 ppm will raise the conductivity of a jet fuel to
what is considered a safe level (50 picomho/meter).
A recently developed antistatic additive is the reaction product of an
amine with a copolymer of methyl vinyl ether and maleic anhydride (94). The
conductivity of a fuel (boiling range 320 to 720) was increased from 9 to
551 picomho/meter by the addition of 5 Ib of the product to 1000 barrels of
the fuel (about 15 ppm). Another amine-type additive increased the con-
ductivity of a distillate oil by a factor of 100 when 50 ppm of a 1 percent
solution in xylene was used (95).
The effectiveness of chromium compounds as additives was demonstrated by
the chromium tris (acylanthranilate) class of compounds. When the acyl part
of the molecule was from oleic acid, the conductivity of a distillate oil was
4
increased by a factor of 10 with the additive at a concentration of
5 g/metric ton (5 ppm) (96). Simple chromium salts of oleic or naphthenic
acids also have been recommended as antistatic additives (97). Mixtures of
these acids with ferrocene derivatives and cyclopentadienyl manganese tri-
carbonyl also are claimed to be effective.
Synergistic effects also have been observed in antistatic additives for
distillate fuels (98). The antistatic activity of barium and zinc naphthenates
and octoates was enhanced by mixing them with another additive composition
based on tallow diamine and alkyl phosphates.
104
-------
BIOCIDES
Although some light oils can be used to control biocidal attack on
selected crops, the fuel oils themselves can be subject to attack by
bacteria and fungi. These organisms can grow at an oil-water interface in
storage tanks in all climates, and it can be particularly serious in tropical
climates where both the temperature and the humidity are high. This attack
generates materials in the oils which can clog the fuel filters.
Trialkyl benzylammonium salts have been recommended as fungicides for
fuel oils (99). Derivatives made with long-chain alkyl groups ranging from
C to C were used. In addition, cetyl pyridinium sulfates also were
8 22
found effective. Boron compounds are widely used as oil-soluble bactericides.
Compounds containing two nitrogen atoms in a five-membered ring structure
(pyrazolidones) with three alkyl or aryl sidechains likewise have been
developed as additives to inhibit the microbiological contamination of
petroleum products (100).
105
-------
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107
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113
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TECHNICAL REPORT DATA
(Please read I unmet ions on //,. ret ersc hcjorc coniplcnnsl
1. REPORT NO.
EPA-600/2-77-008b
3. RfcCIPIfcNT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Experimental Evaluation of Fuel Oil Additives for
Reducing Emissions and Increasing Efficiency of
Boilers
5. REPORT DATE
January 1977
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Robert D. Giammar, Albert E. Weller,
David W. Locklin, and Horatio H. Krause
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Battelle-Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
10. PROGRAM ELEMENT NO.
1AB014;'ROAP 21ADG-020
11. CONTRACT/GRANT NO.
68-02-0262
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development*
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Task Final; 5/72-12/75
14. SPONSORING AGENCY CODE
EPA-ORD
15. SUPPLEMENTARY NOTES (*) Cosponsor of this report is FEA, Office of Energy Conservation
and Environment, Washington, DC 20461. EPA project officer is W.S. Lanier; FEA
project officer is W. R. Minning.
16. ABSTRACT rpne repOrt gives results of an evaluation of the effectiveness of combustion-
type fuel oil additives to reduce emissions and increase efficiency in a 50-bhp (500 kw'
commercial oil-fired packaged boiler. Most additive evaluation runs were made
during continuous firing, constant-load operation of the boiler. Additives, both pro-
prietary and pure compounds, containing alkaline-earth and transition metals in
concentrations between 20 and 50 ppm were effective in reducing carbon particulate
emissions by as much as 100 percent when firing residual oil. They also were effec-
tive in reducing emissions of smoke and polycyclic organic matter. No additive was
found to be effective in reducing either NOx or SOx. Certain of these additives used
in residual oil permitted an increase in overall boiler efficiency by reducing stack
gas loss, without increasing particulate emissions. This efficiency gain, about 2%,
was achieved by: appropriate readjustment to permit boiler operation at lower excess
air levels; and reducing the fouling of boiler heat-transfer surfaces. Both proprie-
tary and pure compounds .were found to be equally effective. Thus, if additives are
used, cost savings can be maximized by using the less expensive pure compounds.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI field/Group
Air Pollution; Combustion; Fuel Additives* Air
Organometallic Compounds; Organic Com
pounds; Inorganic Compounds; Residual
Oils*; Boilers; Burners; Efficiency*;
Flue Gases; Heat Loss; Nitrogen Oxidas;
Carbon Monoxide; Hydrocarbons; Polycy-
clic Compounds; Fouling; Heat Transfer
Pollution Control;
Stationary Sources*;
Combustion Additives*;
Fuel Handling Additives*
Distillate Oils; Excess
Air; Particulates*; Poly
cyclic Organic Matter*
13B; 2IB; 2ID
07C
13A;
20M;
13. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (Tins Report)
Unclassified
21. NO. OF PAGES
122
20. SECURITY CLASS (Tilts page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
114
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