Fine Particle Emissions from Residual Fuel Oil Combustion:
Characterization and Mechanisms of Formation
William P. Linak*, C. Andrew Miller
Air Pollution Prevention and Control Division, MD-65
National Risk Management Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711 USA
Jost O.L. Wendt
Department of Chemical and Environmental Engineering
University of Arizona
Tucson, AZ 85721 USA
Prepared for presentation at
28"1 International Symposium on Combustion
University of Edinburgh
Edinburgh, Scotland
July 30 - August 4, 2000
Oral Presentation Preference
Soot, PAH and Air Toxics Colloquium
Word Count:
submitted: December 9, 1999
~corresponding author
tel: (919) 541-5792
fax: (919) 541-0554
e-mail: linak.bill@epa.gov
Text:
References: 64 lines x7
Tables: 1x200
Figures: 1x200.4x400
2986
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Total:
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ABSTRACT
The characteristics of particulate matter (PM) emitted from residual fuel oil combustion
in two types of combustion equipment were compared. A small commercial 732kW fire-tube
boiler yielded a weakly bimodal particulate size distribution (PSD) with over 99% of the mass
contained in a broad coarse mode, and only a small fraction of the mass in an accumulation mode
consistent with ash vaporization. Bulk samples collected and classified by a cyclone indicate
that 30 to 40% of the total paniculate emissions were less than approximately 2.5/xm
aerodynamic diameter (PM2,). The coarse mode PM was rich in char, indicating relatively poor
carbon burnout, although calculated combustion efficiencies exceeded 99%. This characteristic
behavior is typical of this type of small boiler. Larger scale, utility units firing residual oil were
simulated using an 82kW laboratory-scale refractory-lined combustor. PM emissions from this
unit were in good agreement with published data including published emission factors. These
data indicated that the refractory-lined combustor produced lower total but greater fine
particulate emissions, as evident from a single unimodal PSD centered at approximately 0.1/xm
diameter. Bulk cyclone segregated samples indicated that all the PM were smaller than 2.5/im
aerodynamic diameter, and loss on ignition (LOI) measurements suggested almost complete char
burnout. These findings are interpreted in the light of possible mechanisms governing the
release of organically bound refractory metals, and may have particular significance in
considering the effects of fuel oil combustion equipment type on the characteristic attributes of
the fine PM emitted into the atmosphere, and their ensuing health effects.
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INTRODUCTION
Recently, airborne fine particulate matter (PM) has become the subject of considerable
environmental interest due to the results of a number of studies correlating short term exposures
of ambient levels of fine PM with acute adverse health effects[l-4]. Consequently, ambient
concentrations and source emissions of fine PM, defined as less lhan 2.5^m in diameter (PM25),
• face the possibility of increased regulation[5]. Numerous causative theories exist; however,
health effect researchers have identified at least two properties of ambient particle composition
that appear to exacerbate health damage. These are the presence of transition metals (e.g., Cu,
Fe, V, Ni, and Zn)[6-8] and aerosol acidity. In addition to particle composition, another apparent
factor influencing health impact is the presence of ultrafine particles (<0.1^ni in diameter)[2].
All three characteristics, transition metals, acidity, and ultrafine size, are exhibited by the PM
generated from the combustion of residual fuel oils. Hence, one might hypothesize residual fuel
oil combustion to be suspect, as far as emission of toxic fine particles are concerned. Therefore,
while previous work[9] examined the effects of fuel oil compositions on the physical and
chemical characteristics of fine PM, this paper describes the effects of different combustion
equipment types. The results of both studies can be used as the basis for ultimately linking
measures of acute pulmonary damage to combustion engineering variables.
EXPERIMENTAL
Particle characteristics and emissions are compared from two types of combustion
systems. These can be considered to represent extremes of a range of practical conditions under
which fuel oil is bumed. Although they may not represent specific boilers in all respects, they
are investigated here with a view to determining how this range of combustion conditions
influence the characteristics of fine particles, and the mechanisms which form them. The first
system is a small fire-tube boiler, in which combustion occurs in tubes surrounded by water or
steam. These types of small boilers have large heat transfer surfaces, small volumes, relatively
short residence times, cold walls, and high gas quenching rates, and often produce emissions
with relatively high carbon contents due to unburned carbonaceous char. The second system is a
laboratory-scale refractory-lined combustor designed to simulate the time/temperature
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environments of larger utility boilers and incinerators. In large utility boilers the water or steam,
rather than the combustion gases, is contained in tubes. These systems, including the refractory-
lined combustor, operate at higher temperatures with lower quenching rates. As will be
discussed later, particle emissions from this system contain very little unbumed carbon and better
approximate emissions from large oil-fired utility boilers as reported in the literature.
Fire-tube Boiler
Experiments were performed using the commercially available, North American, three-
pass, fire-tube package boiler shown in Fig. 1. This unit is equipped with a 732kW North
American burner with an air-atomizing oil nozzle. Oil temperature and oil and atomizing air
pressures are independently controlled to ensure proper oil atomization. Figure 1 indicates the
locations of several sampling ports. Temperatures at these locations ranged from 450 to 550K.
Additional system details are presented elsewhere[9].
Refractorv-lined Combustor
Experiments were also performed using the 59kW laboratory-scale refractory-lined
combustor also shown in Fig. 1. This research unit was designed to simulate the
time/temperature and mixing characteristics of practical gas- and oil-fired combustion systems.
This unit is equipped with an International Flame Research Foundation (IFRF) moveablc-block
variable-air swirl burner which incorporates an air-atomizing oil nozzle positioned along its
center axis and swirling air which passes through the annulus around the fuel injector to promote
flame stability. The burner was configured for a high swirl flame (IFRF Type 2, swirl
No.= 1.48) with internal recirculation. Gas and aerosol samples were taken from stack locations
at temperatures of approximately 670K. All experiments (fire-tube boiler and refractory-lined
combustor) were performed at a stoichiometric ratio (SR) of 1.2 without secondary air preheat.
Particulate Sampling and Analysis
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PM measurements were performed using several methods. Standard EPA Methods 5 and
60 sampling and analytical procedures were used to determine total particulate and metal
concentrations! 10-12] using inductively coupled plasma (ICP) mass spectrometry. Other metal
analyses were determined by x-ray florescence (XRF) spectroscopy. Additional samples were
analyzed by x-ray absorption fine structure (XAFS) spectroscopy, an element-specific structural
analysis that is useful for determining trace element speciation and forms of occurrence in
chemically and structurally complex materials like combustion ash[ 13,14].
PSDs were determined by three techniques: electrical mobility and inertial impaction for
sampled aerosols; and light scattering for in-situ in-stack analyses. Extractive samples were
taken for inertial impaction and electrical mobility analyses using an isokinetic aerosol sampling
system described elsewhere[15,16]. These diluted samples were directed to a Thermo-Systems
Inc. scanning mobility particle sizer (SMPS) configured to yield 54 channels evenly spaced
(logarithmically) over a 0.01 to l.O^tm diameter range. Extracted samples during the fire-tube
boiler experiments were directed to an Andersen Inc. eight-stage, 25L/min, atmospheric pressure
in-stack cascade impactor. An MSP Inc. ten-stage, 30L/min Micro-Orifice Uniform Deposit
Impactor (MOUDI) was used during the refractory-lined combustor experiments. In-situ light
scattering PSDs were obtained using an Insitec Inc. particle counter sizer velocimeter with a
working range of approximately 0,3 to 100/im diameter which slightly overlapped and extended
the PSD data collected by the SMPS, Scanning electron microscope (SEM) samples were
collected on silver membrane filters to minimize particle charging effects.
In order to collect larger quantities of size-segregated PM for parallel toxicological
studies and XAFS analyses, a large dilution sampler capable of sampling 0.28m3/min of flue gas
was used[17]. The extracted sample passed through a cyclone (50 and 90% collection
efficiencies for 1.8 and 2.5p.m diameter PM, respectively) and was then diluted with clean
filtered ambient air (2.8m3/min) to approximately ambient temperature (3s residence time). The
resulting PM was collected on 64.8cm diameter Teflon-coated glass fiber filters, transferred to
sampling jars, and made available for subsequent chemical, physical, or biological analysis.
-------
The No. 6 oil used in both experimental systems contained 2.33% sulfur and 0,1% ash.
Operational characteristics for both systems included similar oil temperatures (380-400K),
atomizing air pressures (200-240kPa), and stoichiometrics (SR=1.2). The droplet PSD produced
using the Delavan Airo Combustion air-atomizing oil nozzle (model 30615-84) in the fire-tube
boiler was relatively narrow with a mean diameter between 30 and 40/xm. The refractory-lined
combustor experiments used a similar Spraying Systems Co. (model Air Atom 1/4-JSS) an-
atomizing oil nozzle and produced PSDs believed to be similar to those for the boiler studies.
Therefore, any differences in carbon burnout may be attributed to differences in temperature
history rather than in droplet size.
RESULTS AND DISCUSSION
Equilibrium Predictions
Although numerous previous studies report on equilibrium predictions in combustion
environments, there are relatively few results for the inorganic ash species and concentrations
pertinent to residual oil combustion. Thermochemical predictions were determined using the
Chemical Equilibrium Analysis (CEA) computer code for calculating complex chemical
equilibrium compositions! 18] with thermochemical data taken from the literaturef 18-26]. Of
interest is the thermodynamic partitioning between vapor and condensed phases, as well as the
partitioning between various species. The fuel ultimate analysis and trace element
concentrations were taken from Miller et al.[9]. However, only trace elements with
concentrations greater than Ifig/g of oil were considered in the calculations.
Figure 2 presents the results for seven trace elements. Mass fractions of the elements (as
indicated species) are plotted against temperature. The elemental dew points are calculated to
range from 1800K for V to 900K for Cr. These predictions indicate that, at the concentrations
present in fuel oil, all seven elements might vaporize within the combustion environment. The
dew points are lower than those calculated for pulverized coal and incineration applications,
because of the low ash and metal concentrations[27]. These calculations indicate possible
vaporization of Cr, for example, which is usually considered to be nonvolatile. In fact, in
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contrast to calculations performed for higher Cr concentrations (100 vs. 0,03ppm)[28], Fig. 2
indicates that Cr203(s) is not a predicted condensed species at intermediate temperatures. All
seven elements are predicted to form sulfates at lower temperatures (700-1100K) and this may
well affect the solubility and perhaps the bio-availability and toxicity associated with these trace
elements.
Particle Size Distributions
Figure 3 presents representative particle volume distributions for the fire-tube boiler
(open symbols) and refractory-lined combustor (shaded symbols) experiments. With extra detail
shown in the inset, these electrical mobility and light scattering measurements span four decades
of particle diameter (O.Ol-lOO^m). The fire-tube boiler PSDs indicate that most of the particle
volume is associated with large (coarse mode) particles greater than 10/an diameter. However,
the inset shows that even the fire-tube boiler (open symbols) produces a small accumulation
mode with a mean diameter between 0.07 and 0.08^m, which is notably smaller than that for the
refractory-lined combustor (shaded symbols). Thus, both configurations produced an ultrafine
mode, but only the fire-tube boiler produced a bimodal PSD with a very large and dominant
coarse mode.
This type of bimodal PSD is consistent with a mechanism of metal
vaporization/nucleation/coagulation/condensation and incomplete burnout of residual fuel
cenospheres[9]. SEM images of oil char collected from the fire-tube boiler showed a sponge-
like morphology that clearly suggests swelling and extensive pore formation. In general, the
extent of ash (metal) vaporization is dependent on carbon burnout. For incomplete combustion,
a substantial fraction of the trace metals remain trapped in the unbumed char particles, and never
escape into the vapor phase. However, as the combustion gases cool, those metals which have
vaporized will condense on existing surfaces or, if supersaturation partial pressures are large
enough, will nucleate to form new particles. The distinctive submicron peak (between 0.07 and
0.08/xm diameter) is clearly indicative of particles formed by nucleation, coagulation, and
condensation of materials that have vaporized. Thus, when large portions of the metal
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constituents fail to vaporize (open symbols), the accumulation mode will be very much smaller
than when they do vaporize (shaded symbols).
The refractory-lined combustor volume PSD (shaded symbols) consists exclusively of a
narrow submicron accumulation mode with a mean diameter of approximately 0,1 nm, and both
light scattering measurements and the lack of any cyclone catch containing gray or black
¦ particles with measurable LOI support this. Clearly, as the oil char is consumed, the metals have
vaporized almost completely and subsequently nucleated and grown to form the distinctive
accumulation mode shown in Fig. 3. Comparison between the areas under the submicron
volume PSD for the two types of equipment suggests that, while only a very small fraction
(<1%) of the metal trace elements are vaporized in the fire-tube boiler, well over 99% of these
constituents vaporize in the refractory-lined combustor.
Comparison of Calculated and Measured Mass Concentrations
Total mass concentrations were calculated by integrating measured volume PSDs and
applying assumptions on appropriate densities, and compared to mass concentrations measured
independently (Table 1). Particle densities of 3.5 and i.85g/cm3 were chosen for the
accumulation (SMPS) and coarse (INSITEC) modes, respectively, based on average densities of
trace element sulfates and oxides and activated carbons and oil chars taken from the literature.
The calculated mass concentrations of 180 and 93mg/m3 for the boiler and combustor,
respectively, agree remarkably well with the independently measured mass concentrations of 184
and 93mg/m3 for the boiler and combustor experiments, respectively.
Elemental Composition and Particle Size
As expected, trace element measurements showed similar mass emissions for both the
fire-tube boiler and refractory-lined combustor experiments (data not reported here). However,
PM from the fire-tube boiler had high values for LOI ranging from 60 to 85%, while the
refractory-lined combustor samples did not. For the latter, the sum of V, Ni, Zn, Fe, Cu, Pb, and
S, as elements, account for 21.6mg/m3 or 23% of the total mass emissions; whereas, when
-------
counted as sulfates, they account for 67,lmg/m3 or approximately 72% of the total mass
emissions, XAFS spectroscopy indicated that, while a large portion (40-60%) of the sulfur
measured in the fire-tube boiler PM existed as unoxidized organic sulfur (predominantly
thiophenic sulfur), essentially all (99%) of the particulate bound sulfur in the refractory-lined
combustor samples was in the form of sulfates.
Figure 4 presents elemental mass fractions vs. particle diameter for six metals and sulfur
from the refractory-lined combustor tests, Metals were analyzed by XRF and ICP spectroscopy
while sulfur and sulfate were determined by XRF and ion chromatography (IC) analysis,
respectively. In general, XRF and ICP analyses produce similar results, and the emissions of
these elements are concentrated in particles between approximately 0.08 and 0.2/xm diameter
(i.e., the accumulation mode shown on Fig. 3), Sulfur and sulfates are present within particles of
the same size. Note that Fig. 4 also indicates the presence of a distinct mode at approximately
1/xm diameter for the "less-volatile" metals (V, Ni, Zn, and possibly Cu), but not for the semi-
volatile metal Pb. These data are consistent with the conjecture that less-volatile metals are
released very late during the final stages of heterogeneous char combustion, while more volatile
metals may vaporize more easily from interior surfaces and diffuse away from the char particle
earlier in the process. The "less-volatile" metals are vaporized primarily as a consequence of the
oxidation of neighboring carbon structures to which they are inherently bound.
Model Predictions
Experimental results were compared to model predictions using a multi-component
aerosol simulation code (MAEROS)[29]. The puipose of these calculations was to illustrate that
the resulting PSDs for both systems could be predicted using the same modeling approach
involving char particle burnout (or premature quenching) followed by homogeneous nucleation
and coagulation of a portion of the PM mass, A secondary objective was to determine the extent
to which differences in coagulation rates caused by large differences in vaporized mass and
resulting number densities might account for the differences in the measured PSDs. Details
regarding the application of MAEROS to combustion environments can be found elsewhere[30].
-------
Figure 5 illustrates the predicted PSD evolution for both the fire-tube boiler and refractory-lined
combustor. Coagulation was the only mechanism considered.
To examine particle evolution within the fire-tube boiler, 99.8% of the 180mg/mJ PM
mass was distributed among 13 sections (within MAEROS) so as to simulate the coarse mode
mass PSD illustrated in Fig. 3. The remaining 0.2% of this mass was assigned to section 2
(0.0021-0.0046/an diameter) to simulate the nucleation of a vapor fume (see Table 1). The
initial number concentration was 1.5xl016/m\ with the nucleating vapor accounting for well over
99.99% of these particles. System pressure and temperature were maintained at 1.01xl05Pa and
810K, respectively, to simulate post-flame conditions. Following this initial distribution, Fig. 5
presents calculated mass PSDs at 0.1, 1.0, and 10s. While these three PSDs also represent
180mg/m3, number concentrations decline as coagulation proceeds. At 1.0 and 10.0s the
coagulating nuclei have grown into the 0.01 to 0.1/xm diameter range. These times represent a
range of typical residence times within combustion systems. At 10s, number concentrations
have fallen to 1.2xlOl4/m\ and the coagulating nuclei are accumulating in a mode with a mean
diameter of approximately 0,02/im (see Fig. 5 insets). The distribution of the coarse mode PM is
relatively unaffected by these processes.
In contrast to the boiler simulation, 100% of the 90mg/m3 PM mass measured in the
refractory-lined combustor was assigned to section 2. Again, this initial distribution corresponds
to the partitioning seen in Table 1, and indicates complete oxidation of the oil char and
vaporization of the inorganic elements followed by homogeneous nucleation. The initial number
concentration is 2.7xl018/m3. In comparison to the boiler simulation, Fig. 5 indicates that these
nuclei tend to coagulate much more quickly, due to the much larger number concentration. At 1
and 10s, as number concentrations fall to 8.2xl014 and 7.6xl013/'m\ respectively, coagulation
slows considerably causing the aerosol to accumulate into a mode between approximately 0.07
and 0.2/xm diameter. Coagulation processes predict that the accumulation mode produced from
the refractory-lined combustor would have a larger mean diameter compared to the accumulation
mode produced from the fire-tube boiler. This prediction is reflected in the measurements. The
accumulation mode measured from the refractory-lined combustor matches the predicted PSD,
while the predicted accumulation mode for the fire-tube boiler (0.02/im diameter) slightly under-
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predicts the measured value (~0.07/irn diameter). Heterogeneous condensation of a portion of
the vapor on existing nuclei is a competing process and has been shown to increase particle
growth rates[31]. Additionally, the coagulation mechanism does not include the effect of
differing fractal properties of any agglomerates that may be formed. It has been assumed here
that only spheres result from the coagulation process.
CONCLUSIONS
The effects of combustion configuration on fine particle emissions from residual fuel oil
combustion were examined. A laboratory-scale refractory-lined combustor, which was shown to
simulate combustion conditions of a large utility residual oil fired boiler (as far as particulate
emission factors were concerned), produced fly ash particles with an essentially unimodal PSD
with a mean diameter of approximately O.l/zm. Conversely, a pilot-scale fire-tube package
boiler produced particles with a weak bimodal size distribution, which included a small fraction
(~0.2%) of the mass with particle diameters below 0,1/i.m and a large fraction (-99.8%) of the
mass with particle diameters between 0.5 and 100/xm. Here the large particles were shown to
consist of large porous carbonaceous cenospheres resulting from poor carbon burnout, and this
characteristic is not uncommon for that class of equipment. Although the total particulate mass
concentrations in the flue gas of the refractory-lined combustor were less than half of those of the
fire-tube boiler, ultrafine particle concentrations of the refractory-lined combustor were notably
larger than those measured for the fire-tube boiler. Volume PSDs obtained from two
independent particle sizing instruments were, with only a few very reasonable assumptions,
consistent with independently measured total mass emission rates, for both equipment types.
ACKNOWLEDGMENTS/DISCLAIMER
Portions of this work were conducted under EPA P.O. 8CR244NASX with I.O.L. Wendt
and EPA Contract 68-C-99-201 with ARCADIS Geraghty & Miller. The research described in
this article has been reviewed by the Air Pollution Prevention and Control Division, U.S. EPA,
and approved for publication. The contents of this article should not be construed to represent
Agency policy nor does mention of trade names or commercial products constitute endorsement
or recommendation for use.
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REFERENCES
1. Wilson, R., and Spengler. J.D., eds., Particles in Our Air: Concentrations and Health Effects,
Harvard Univ. Press, Cambridge, MA (1996).
2. U.S. Environmental Protection Agency, National Ambient Air Quality Standards for
Particulate Matter; proposed decision, 40 CFR, Part 50 (1996).
3: Bachmann, J.D., Damberg, R.J., Caldwell, J.C., Edwards, C., and Koman, P.D., "Review of
the National Ambient Air Quality Standards for Particulate Matter: Policy Assessment of
Scientific and Technical Information," EPA-452/R-96-013 (NTIS PB97-115406), Office of Air
Quality Planning and Standards, Research Triangle Park, NC (1996).
4. Wolff, G.T., Closure by the Clean Air Scientific Advisory Committee (CASAC) on the staff
paper for particulate matter. EPA-SAB-CASAC-LTR-96-008, U.S. Environmental Protection
Agency, Washington, DC, June 13, 1996.
5. Federal Register, 62 FR 38652, July 18, 1997.
6. Dreher, K., Costa, D., Hoffman, A., Bonner, J., and Osornio-Vargas, A., "Pulmonary Toxicity
of Uban Air Particulate Matter (PM), Air & Waste Management Association Meeting on
Measurement of Toxic and Related Air Pollutants, Research Triangle Park, NC, 1996.
7. Dreher, K., Jaskot, R., Richards, J.H., Lehmann, J.R., Winsett, D., Hoffman, A., and Costa,
D., Amer. J. Respir, Crit. Care Med., 153(4:A15) (1996).
8. Dreher, K., Jaskot, R., Lehmann, J.R., Richards, J.H., McGee, J.K., Ghio, A.J., and Costa,
D.L., J. Toxicol. Environ. Health, 50:285-305 (1997).
9. Miller, C.A., Linak, W.P., King, C., and Wendt, J.O.L., Combust. Sci, Technoi, 134:477-502
(1998).
10. Garg, S., EPA Method 0060 - Methodology for the Determination of Metals Emissions in
Exhaust Gases from Hazardous Waste Incineration and Similar Combustion Processes, in
Methods Manual for Compliance with the BEF Regulations: Burning Hazardous Waste in Boilers
and Industrial Furnaces, EPA/530-SW-91-010 (NTIS PB91-120006), pp.3-1 through 3-48,
Office of Solid Waste and Emergency Response, Washington, DC, 1990.
11. EPA Test Method lA-Sample and Velocity Traverses for Stationary Sources with Small
Stacks or Ducts, in 40 CFR Part 60 Appendix A, Government Institutes Inc., Rockville, MD,
1994.
12. EPA Test Method 5 - Determination of Particulate Emissions from Stationary Sources, in 40
CFR Part 60 Appendix A, Government Institutes Inc., Rockville, MD, 1994.
-------
13. Galbreath, K.C., Zygarlicke, C.J., Huggins, F.E., Huffman, G.P., and Wong, J.L., Energy
&Fuels, 12:818-822(1998).
14. Huggins, F.E., and Huffman, G.P., J. Hazardous Materials, in press (1999).
15. Scotto, M.A., Peterson, T.W., and Wendt, J.O.L., Twenty-fourth Symposium (International)
on Combustion, The Combustion Institute, Pittsburgh, PA, pp.1109-1118, 1992.
16. Linak, W.P., Srivastava, R.K., and Wendt, J.O.L., Combust. Sci. Technol., 101(l-6):7-27
(1994).
17. Steele, W.J., Williamson, A.D., and McCain, J.D., "Construction and Operation of a 10 cfm
Sampling System with a 10:1 Dilution Ratio for Measuring Condensable Emissions," EPA/600-
8-88-069 (NTIS PB88-198551), Air and Energy Engineering Research Laboratory, Research
Triangle Park, NC, 1988.
18. McBride, B.J., Gordon, S., and Reno, M.A., "Coefficients for Calculating Thermodynamic
and Transport Properties of Individual Species," NASA Technical Memorandum 4513 (1993).
19. Chase, M.W. Jr., JANAF Thermochemical Tables, 3rd ed., parts 1&2. American Institute of
Physics, New York, NY, 1986.
20. Barin, I,, Knacke, O., and Kubaschewski, O., Thermochemical Properties of Inorganic
Substances, Springer-Verlag, New York, NY, 1973.
21. Barin, I., Knacke, O., and Kubaschewski, O., Thermochemical Properties of Inorganic
Substances, supplement, Springer-Verlag, New York, NY, 1977.
22. Barin, I., Thermochemical Data of Pure Substances, VCH Verlagsgesellschaft, New York,
NY, 1989.
23. Barin, I., Thermochemical Data of Pure Substances, VCH Verlagsgesellschaft, New York,
NY, 1993.
24. TAPP - Thermodynamic Properties Software, V2.2, ES Microware Inc., Hamilton, OH
(1995).
25. Ebbinghaus, B.B., Combust. Flame, 101:119-137 (1993).
26. Ebbinghaus, B.B., Combust. Flame, 93:311-338 (1995).
27. Linak, W.P., and Wendt, J.O.L., Fuel Process. Technol., 39:173-198 (1994).
28. Linak, W.P., Ryan, J.V., and Wendt, J.O.L., Combust. Sci. Techno!., 116-117:479-498
(1996).
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29. Gelbard, F. and Seinfeld, J.H., J. Colloid Interface Sci., 78(2):485-501 (1980).
30. Linak. W.P., and Wendt, J.O.L.. Prog. Energy Combust. Sci,, 19:145-185 (1993).
31. Davis, S.B., Gale, T.K., Wendt, J.O.L., and Linak, W.P., Twenty-seventh Symposium
(International) on Combustion, The Combustion Institute, Pittsburgh, PA, pp.1785-1791, 1998.
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Tabic 1. Comparison of calculated mass concentrations determined from measured volume PSDs with measured mass
concentrations determined by EPA Method 5[ 12].
VOLUME
CONCENTRATIONS
(MEASURED)
(^m'/cm3)
MASS
CONCENTRATIONS
(CALCULATED)
(mg/nv,)!
MASS
CONCENTRATIONS
(MEASURED)
(mg/m:r
BOILER
COMBUSTOR
BOILER
COMBUSTOR
BOILER
COMBUSTOR
SMPS
8.8e+l
2.7e+4
0.31
93
-
-
INSITEC
9.8e+4
1.9e+2
180
0.36
-
-
TOTAL
9.Se+4
2.7e+4
180
93
184 (6.2)3
93
'Assumed fine mode particle density = 3,5g/cm3 based on typical densities for vanadium species. Assumed coarse mode
panicle density = 1.85g/cm}.
"Measured mass concentrations determined using EPA Method 5.
'Number in parentheses indicated standard deviation based on multiple measurements.
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Fire-tube boiler
To air pollution control system
Electrical mobility
inertial impactors
Dilution sampler —
in-situ light scattering
Gas sample port
Fuel oil
Steam out-*
Oil heater
Air blower
Natural gas
Water in
Fig. 1 - Two EPA combustion systems.
Refractory-lined combustor
To air pollution control system
Gas sample port
In-situ light scattering
Dilution sampler, electrical mobility, inertia! impactors
Refractory
sections
-Cooling water
Moveable-
block burner
Fuel oil
Atomizing air
Combustion air
-------
CQ
ro
¦
J3
CO
w
CL
c
p
c
CD
CD
X3
C
c
3
ID
—*
©
9-
o"
o"
3
£/5
Mass fraction of element as indicated speciess
3
"D
ro
—%
03_
C
CD
W O
—t I «MI, 1
N
3
C/5
O
k
3
o
j
N /
\
3 /
\ N
°/
\
/
-------
I I » II
electncai mobility
H
3 5e+4
ight scattering
<««««(
0e+0+~®
0.01
0.1 1 10
Diameter, Dp (//m)
o Fire-tube boiler
• Refractory-lined combustor
100
Fig. 3 - Measured volume PSDs.
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Vanadium
o XRF
• ICP
Nickel
O XRF
• ICP
O XRF
ICP
O XRF
• ICP
Copper
O XRF
Lead
O XRF
Sulfur
O XRF (S)
• IC (SO4-2)
0.01 0.1 1 10 100
Aerodynamic diameter, Dp (//m)
Fig. 4 - Elemental PSDs from the refractory-lined combustor.
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TECHNICAL REPORT DATA
N RM RL~ RT P~ P~ 468 (Please read Inunuctions on the reverse before completing)
1. REPORT NO. 2.
EPA/600/A-00/06 9
3, RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Fine Particle Emissions from Residual Fuel Oil Com-
bustion; Characterization and Mechanisms of For-
mation
S. REPORT DATE
6. PERFORMING ORGANIZATION CODE
7. AUTHORIS)
W. P. Linak and C. A. Miller (EPA), and J. C. L. Wendt
University of Arizona)
8. PERFORMING ORGANIZATION REPORT NO,
9. PERFORMING ORGANIZATION NAME AND ADDRESS
University of Arizona
Department of Chemical and Environmental
Engineering
Tucson. Arizona 85721
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
EPA P.O. 8CR244NASX
(Univ. of AZ)
12. SPONSORING AGENCY NAME AND AOORESS
EPA, Office of Research and Development
Air Pollution Prevention and Control Division
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Published paper; 1/98-6/99
14. SPONSORING AGENCY CODE
EPA/600/13
15.supplementary notes project officer is W. P. Linak, Mail Drop 65, 919/541-
5792. Presented at 28th Int. Symp. on Combustion, Edinburgh, Scotland, 7/30-
8/4/00.
is. abstract The paper gives results of a comparison of the characteristics of particu-
late matter (PM) emitted from residual fuel oil combustion in two types of combus-
tion equipment. A small commercial 732-kW fire-tube boiler yielded a weakly bi~
modal particulate size distribution (PSD) with >99% of the mass contained in a broad
coarse mode, and only a small fraction of the mass in an accumulation mode consis-
tent with ash vaporization. Bulk samples collected and classified by a cyclone indi-
cate that 30-40% of the total PM emissions were < about 2.5 micrometers aerody-
namic diameter (PM2.5). The coarse mode PM was rich in char, indicating rela-
tively poor carbon burnout, although calculated combustion efficiencies were >99%.
This characteristic behavior is typical of this type of small boiler. Larger scale,
utility units firing residual oil were simulated using an 82-kW laboratory-scale re-
factory-lined combustor. PM emissions from this unit were in good agreement
with published data, including published emission factors. These data indicate that
the refractory-lined combustor produced lower total but greater fine particulate
emissions, as evident from a single unimodal PSD centered at about 0.1 micro-
meter diameter. Bulk cyclone-segregated samples indicated that all the PM were
smaller than 2. 5 micrometers aerodynamic diameter.
17. KEY WORDS AND DOCUMENT ANALYSIS
». DESCRIPTORS
b» IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution
Particles
Emission
Residual Oils
Combustion
Measurement
Pollution Control
Stationary Sources
Particulate
13B
14G
11H, 2 ID
2 IB
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (S-73J
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10Oi—1 -0"
0.5H
Fire-tube boiler
180 mg/m3
50-
co
O)
C
.2
2
4—•
c
©
o
c
o
o
(C
1" i rump i " i I IHn| T r r i II11
t = 0.1 s
0.001 0.01 0.1 1
1 I I I 11III 1 1 I11 H'l'T'l 1 I I I 111 r | Till llll| 1—I I I llll
t= 1.0 s
r"» TTimj—i "i i »in»| "t it inn
0.001 0.01 0.1 1
i ill Wl| t "i 11 mi| "T™TTTHfjj ¦ ¦ "i1 i m in?| j i i i nil
nifij i i 11 m
0.001 0.01 0.1
llll nil) 1 111 IIN| 1 I I I IIII I"
0.001 0.01 0.1 1
Refractory-lined combustor
90 mg/m3
T—I' I I llll
10 100 0.001
I - 0.1 s
t= 1.0 s
[—i uii
t= 10s
i i i m 11
Diameter, Dp (jjm)
0.01 0.1 1 10
Diameter, Dp (jjm)
100
Fig. 5 - Predicted evolution of PSDs by coagulation.
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