Preliminary Characterization Study

Traditional Fuels and Key Derivatives 

Prepared in Support of the

Advanced Notice of Proposed Rulemaking –

Identification of Nonhazardous Materials That Are Solid Waste

	

December 11, 2008

                              

Introduction

	This document summarizes the features, composition, and characteristics
of both traditional fuels used in stationary combustion sources and
their key derivatives.  Traditional fuels include fossil fuels (coal,
fuel oil and natural gas) and wood.  Derivatives include:

Coal-based derivatives: bituminous coke, coal tar oil, blast furnace
gas, and coke oven gas, and 

Petroleum-based derivatives: petroleum coke, refinery gas, and asphalts.

	For each fuel, this memorandum presents the following information to
the extent readily available:

										     

Chemical Composition. Fuels are often described by an ultimate and/or
proximate analysis. An ultimate analysis is an elemental analysis of
major components, typically carbon, hydrogen, oxygen, nitrogen and
sulfur as well as ash. Meanwhile a proximate analysis determines the
moisture, volatile matter, fixed carbon and ash content of the fuel. 
Gaseous fuels and some liquid fuels can also be described by their
constituent compounds.  In general, the compositional analysis is
presented on a weight basis for liquid and solid fuels and on a
volumetric basis for gaseous fuels.

Heating Value (Calorific Value).  The heating value of a fuel is its
energy value or its heat of combustion (i.e., the energy released when a
unit mass (or volume) of the fuel is burned).  The heating value of a
fuel may be measured according to its higher heating value (HHV) or its
lower heating value (LHV). The HHV, or the gross heat of combustion, is
the energy released when the products of combustion are brought to a
standard temperature and any water produced from the process is
condensed.  The LHV, also referred to as the net heat of combustion,
treats the moisture produced from combustion as vapor. Unless specified
otherwise, all heating values presented in this document are HHVs and
will be presented on an as-received basis (i.e., with moisture and ash
included).

Composition of Non-Fuel Constituents and Impurities.  Non- fuel
constituents include gases with no fuel value such as nitrogen, carbon
dioxide and inert gases as well as moisture and ash. Impurities (i.e.,
contaminants) may include sulfur compounds and trace metals such as
mercury, vanadium, cadmium, chromium and lead. Impurity levels are
typically presented as parts per million by weight (ppm) or parts per
million by volume (ppmv)

We present this information by the major fuel groupings outlined above. 
Section 2 describes coal and its derivatives. Petroleum-derived fuels
are detailed in Section 3, while Section 4 presents information on
natural gas.  Section 5 provides the composition and other
characteristics of wood.

Limitations of this Analysis:

	

This document presents information that is readily available from
engineering reference publications and reputable online sources. A
search of scientific, peer-reviewed journals was not performed due to
time and budget constraints.

When possible, we present composition and heating values that are
representative of the values associated with a given fuel.  However, for
some fuels where the available data were limited, we present data from
specific samples that were readily available.  These sample data may or
may not be representative.

Coal & Derivatives

       Coal

The ASTM (Method D-388) classification for coal ranks coal into four
primary classes based on its volatile matter and fixed carbon content as
well as its heating value.  The four categories (highest to lowest rank)
are: 

Anthracite

Bituminous

Sub-bituminous

Lignite

Each of these classes is further divided into subclasses by the ASTM
classification. In general the higher rank coals have higher carbon
content and lower hydrogen and oxygen content in comparison to the lower
ranked coals. Most coals burned in combustion units are either
sub-bituminous or bituminous.

 

Anthracite: Anthracite coal is glossy black, hard, and by definition has
a fixed carbon content of more than 86% (dry, ash free basis) and a
volatile content of less than 14% (dry, ash free basis). Heating values
typically are on the order of 13,000 Btu/lb. Anthracite coal is
primarily found in northeastern Pennsylvania, and represents less than
2% of the US coal demonstrated reserve base. 

Bituminous:  Bituminous coal in general has lower fixed carbon (<86%,
dry, ash free) and higher volatiles than anthracite.  This coal has
banded layers that alternate between glossy black and dull black.
Heating values for bituminous coal range from 10,500 to 14,000 Btu/lb.  
Bituminous coals are the most abundant class of coal in the US and make
up 53% of the demonstrated US coal reserve.  Bituminous coal is found in
many states east of the Mississippi River, including Illinois, Kentucky,
West Virginia, and Pennsylvania.

Sub-bituminous: These coals are also black in color but with less
banding and a higher moisture content than bituminous coals.  Heating
values range from 8,500 to 11,000 Btu/lb. Although heating values are
lower than for bituminous coal, sub-bituminous varieties in the US tend
to have a relatively lower sulfur content than bituminous coals. 
Sub-bituminous coal represents approximately 37% of US coal reserves;
sub-bituminous reserves are highest in the states of Montana and
Wyoming.

Lignite: This is the lowest ranked coal. Lignite has a brown-black color
and is soft relative to the other types of coal. Heating values may
range from 4000-8000 Btu/lb.  Lignite is found in North Dakota, Montana
and Texas and accounts for about 9% of US coal reserves.

    

	Table 2-1 presents composition and heating value data from Avallone &
Baumeister for select US Coals for each of the classes described above.,
 Note that the data in Table 2-1 are sample values; properties may vary
widely within each rank.  

Chemical Composition. As indicated in Table 2-1, most ranks of coal
consist primarily of carbon.  

Non- Fuel Constituents. Moisture and ash represent the non-combustible
constituents in coal. The primary components of ash are silicon dioxide,
aluminum oxide, ferric oxide, and calcium oxide. (See Table 2-1)

Contaminants. One trace constituent of particular concern in coal is
mercury.  The mercury content of coal ranges from less than 0.1 ppm to
1.8 ppm with a median value of 0.11 ppm.  Approximately 80% of samples
tested below 0.25 ppm. Coal may also contain several other metals such
as arsenic, chromium and manganese as shown in Table 2-1. 

Trace Organics: Data on trace organics in U.S. coal are not readily
available. One study from Spain, however, analyzed five Spanish and
South African coal samples for volatile organics. Of the several
organics detected, only two were 40 CFR 261 Appendix VIII hazardous
constituents. Results for these two organics are shown in Table 2-1. 

Additional information on the characteristics of coal is available in
the US Geological Survey coal quality database, which has information on
over 7,000 Coal samples.



     Fuels Derived from Coal     

                                 

Bituminous Coke – Bituminous coke is derived from the destructive
distillation or pyrolysis of bituminous coal.  This involves heating
coal to very high temperatures (over 1000 °C) in the absence of air in
a furnace.  Much of the moisture and volatile components are driven off
leaving behind a product high in carbon. While coke is the desired end
product of the distillation/pyrolysis process, fuel gases, tar and oil
with fuel value are also typically produced.  A large fraction of
bituminous coke (approximately 90%) is burned in blast furnaces for
steelmaking. The remainder is largely used in foundries and for space
heating.

Table 2-2 shows the typical chemical composition and heating value of
bituminous coke.  Unsurprisingly, the fixed carbon and ash content are
much higher than the corresponding values for coal. The heating value of
bituminous coke is comparable to coal.  Table 2-2 also presents
composition and heating value estimates for coke breeze, an undersized
coke (particle size < 15 mm), comprising  about 5% of the total
bituminous coke production.  Coke breeze is not suitable for firing in a
blast furnace but is typically used for steam generation.  Information
on the impurities contained in blast furnace coke is not readily
available, but such information is available for coke breeze, as shown
in Table 2-2.

Coal Tar Oil: Coal tars are liquid products of the carbonization
process to produce coke. They may range from free-flowing, low viscosity
liquids to highly viscous coal tar pitch.

Table 2-3 shows an ultimate analysis of coal tar fuels CTF 50 and CTF
400.,   The table also presents estimates of the heating value for CTF
50 and CTF 400, as well as information on the non-fuel constituents and
trace metals in these fuels.    

Table 2-3 also presents viscosity values for CTF 50 and CTF 40,
expressed in centistokes (cSt). For comparison, water has a viscosity of
about 1 cSt at 20°C and a liquid with a viscosity of 2 cSt at 20°
would have twice the viscosity of water.

Because coal tar oil is made up of a complex mixture of more than a
thousand individual compounds, fractional distillation of coal tar oil
can yield a spectrum of compounds for use in resins, polymers, motor
fuel, wax and electrode compounds.

Coke Oven Gas: Coke oven gas is the gaseous non-condensable fraction
generated from the coke production process.  As the analysis (by
component) in Table 2-4 shows, coke oven gas is primarily composed of
hydrogen and methane. The heating value is approximately 600 Btu/ft3 and
is about 55-60% that for natural gas (on a volume basis). 

Impurities in coke oven gas may include hydrogen sulfide, ammonia, and
hydrogen cyanide.,  Table 2-4 also shows the specific gravity of coke
oven gas.

Blast Furnace Gas:  Blast furnace gas is a low quality gas that is a
by-product of the blast furnace reduction process. Table 2-4 presents
volumetric composition and heating value estimates for this fuel.
Although the heating value is low, the amount of gas generated by blast
furnaces makes it economically feasible to recover the energy.  The
energy value is low because approximately 70% of the volume of this fuel
is made up of nitrogen and carbon dioxide.  Blast furnace gas may
include small quantities of impurities including hydrogen cyanide. 
Table 2-4 also shows the specific gravity of blast furnace gas. Blast
furnace gas is either burnt as fuel or flared.

Petroleum Fuels

This section presents characterization data for fuels produced by
petroleum refineries as well as their derivatives.  Although
transportation fuels (e.g., gasoline and diesel) make up most of the
petroleum-based fuel sold in the U.S., this section focuses on petroleum
fuels utilized by stationary combustion sources.

Fuel Oil

The term fuel oil may refer to any product derived from petroleum that
has volatility lower than that of gasoline. The ASTM D396-2(a)
specification divides fuel oil into several classes, from fuel oil No.1
to fuel oil No. 6, based on boiling range, composition, and other
physical properties.  Fuel oils are generally classified as either
distillate or residual based on whether they are vaporized in normal
refining operations. Usually, fuel oils No. 1 and 2 are distillate
fuels; No. 5 and No. 6 fuel oils are residual fuels, and No.4 is a blend
of distillate and residual fuels.  Note that diesel has similar but not
identical properties and specifications to fuel oil No.2.

Table 3-1 provides the chemical composition, heating values, and typical
physical properties of various classes of fuel oil such as flash point,
specific gravity, API gravity, and viscosity.  The flash point is the
temperature to which the liquid must be heated to produce vapors that
flash but do not burn continuously.  API gravity is calculated by:

 

Composition: Fuel oils are primarily composed of hydrocarbons,
specifically paraffins, isoparafins, napthenes and aromatics. Table 3-1
shows an ultimate analysis for different types of fuel oil from Perry et
al. 

Heating Values. Fuel oil heating values range from 18,000 to 20,000
Btu/lb or 130,000 to 150,000 Btu/gallon. As indicated in the table,
residual fuel oils are extremely viscous and must be heated in order to
be transported and atomized in a burner.  

Moving along the scale from No. 1 fuel oil to No. 6 fuel oil, the
characteristics of fuel oil changes as follows: 

The boiling point increases. For No. 1 oil, the boiling points of the
different constituents range from 150-300 °C, while for No. 6 oil this
range is 200-550 °C. 

The density increases (i.e., API gravity decreases)

Viscosity increases from an average of about 1.8 centistokes (cSt) for
No. 1 Oil to 90-400 cSt for No. 6 oil.

Heating values decrease slightly.

Impurities: As indicated in Table 3-1, the heavier fuel oils have higher
levels of sulfur than the lighter fuel oils.  The trace metal levels
shown in the table are from testing performed in 1998 for the
development of the comparable fuels specification, which was published
in 1999.  This testing involved eleven samples for No. 2 fuel oil, one
sample of #1 fuel oil, and seven samples of #6 fuel oil.  Note that
Perry et al. indicate that the nickel content of No. 6 Fuel Oil ranges
from 10-500 ppm and that vanadium concentrations in No. 6 Fuel Oil range
from 10-500 ppm.

Trace Organics: In developing the specifications for comparable fuels,
EPA tested samples of fuel oil for most of the hazardous organics listed
in Appendix VIII of 40 CFR Part 261.  Specifications were developed for
almost 200 individual volatile and semi-volatile toxic organic compounds
(including hydrocarbons, oxygenates, nitrogenated organics, sulfonated
organics, halogenated organics, and PCBs). Table 3-1 includes the
concentrations for the Appendix VIII organics that were detected.

Other Petroleum Derivatives

Petroleum Coke – Petroleum coke is produced when vacuum distillation
residues from the petroleum refining process are sent through a coker
where most of the volatiles are burned off.  Petroleum coke may be
called delayed coke or fluid coke, depending on the type of
process/reactor used.  Table 3-2 provides an ultimate and proximate
analysis for petroleum coke based on data from Avallone & Baumeister and
Stultz & Kitto. 

Petroleum coke is used as the primary fuel or as supplementary fuel in
fluidized bed boilers as well as a supplementary fuel in pulverized coal
boilers and cyclone boilers. 

Table 3-2 also provides a detailed ash analysis for petroleum coke.  As
indicated in the table, nickel and  vanadium levels are high similar to
the residual fuel oils because heavy metals tend to concentrate in the
heavier fraction of crude oil from which petroleum coke is produced. 

 

Refinery Gas – Refinery gas is a general term describing the
non-condensable fractions from various refinery processes, including
atmospheric distillation, coking, reforming and cracking.  These gases
are sometimes blended together and are typically used by refineries for
their energy value. 

The composition of refinery gas is highly variable, although the primary
constituents are C1-C4 hydrocarbons (methane, ethane and propane in
particular).  Table 3-3- presents composition information for two
blended refinery gas samples and composition data from a 2003 lifecycle
emissions study.,  

Estimated heating values for refinery gas are on the order of 1300-1500
Btu/scf.   On a volume basis this is a little higher than natural gas
because refinery gas contains a greater fraction of heavier gases.

Asphalts – Asphalt is made from the residue that remains after the
vacuum distillation process at petroleum refineries.  It has a
consistency ranging from a viscous liquid to a glassy solid.  Table 3-4
presents an ultimate analysis range for four asphalt samples. 
Impurities include sulfur, vanadium and nickel and their reported
concentrations are highly dependent on the source crude.  Heating values
for asphalt are on the order of 17,000-18,000 Btu/lb.

Asphalt is primarily used as a paving and roofing material.  Asphalt is
also used in asphalt-based paints, in lining irrigation canals and water
reservoirs, and in adhesives in electrical laminates. Although the use
of asphalt as a fuel is not common, boilers have been designed to burn
asphalt.



Natural Gas

Natural gas is widely used by boilers due to its low content of ash,
ease of handling, and ease of combustion.  In addition, natural gas is a
cleaner burning fuel than other fossil fuels.  The primary constituent
of natural gas is methane.  Other paraffinic hydrocarbons such as
ethane, propane, and butane, as well as other diluents gases (e.g.,
nitrogen), may be also present.  The composition of natural gas field
samples as well as pipeline gas is shown in Table 4-1.

Heating Value: The heating value of natural gas, like its composition,
varies by region but usually is in the range from 950-1150 Btu per cubic
feet.  Diluents include carbon dioxide and nitrogen.

Impurities: Trace contaminants found in natural gas include hydrogen
sulfide and other sulfur compounds. If naturally occurring levels are
high, these compounds are removed using various processes because most
pipeline specifications limit the level of sulfur compounds that may be
contained in pipeline gas.   Other impurities may include mercury in
very low levels. As Table 4-1 indicates, mercury levels are well below
one part per billion (ppbv).  Trace levels of odorants (eg. mercaptans)
are often added to pipeline gas, which allows natural gas leaks to be
easily detected.  

Trace organics:  Only limited information on the organics content of
natural gas was readily available.  The one organics analysis identified
examined volatile organics concentrations in natural gas samples from
three California utility plants. Only two 40 CFR 261 Appendix VIII
hazardous organics were detected. (See Table 4-1). 



Wood

Wood is burned primarily in industries where wood residues are obtained
as a by-product.  

Table 5-1 shows the properties of wood on a dry basis and an ash
analysis based on data from Stultz & Kitto.  Wood has a lower carbon
content and a much higher oxygen content compared to coal. 

Heating values for wood (on a dry basis) are in the range 8000-9000
Btu/lb.  Wet wood can have a significantly lower heating value.  As
indicated in Table 5-1, the sulfur content of wood is relatively low.
Trace metals in wood may include lead and cadmium.

References

Avallone, E.A., & Baumeister, T.(eds), “Mark’s Standard Handbook for
Mechanical Engineers,” 9th Edition, 1987, p 7-19.

Baukal & Schwartz, 2001, “The John Zink Combustion Handbook” CRC
Press.

Bragg, L., et al, USGS Coal Quality (COALQUAL) Database: Version 2.0,  
HYPERLINK
"http://energy.er.usgs.gov/products/databases/CoalQual/index.htm" 
http://energy.er.usgs.gov/products/databases/CoalQual/index.htm ,
accessed Nov 2008.

Chevron Products Company, 2007, “Diesel Fuels Technical Review.”

Chow, W., & Conner, K.K., 1993, “Managing Hazardous Air Pollutants:
State of the Art, CRC Press.

Cross, R., 1919, “A Handbook of Petroleum, Asphalt, and Natural Gas”
Kansas City Testing Laboratory.

Culp, A.W., 1979, “Principles of Energy Conversion,” McGraw Hill.

Davidson, R. A., “Trace Elements in Coal” 1996, Energeia, v.7, No.3,
University of Kentucky, Center for Applied Research.

Delucchi, M., 2003 “A Lifecycle Emissions Model: LifeCycle Emissions
from Transportation Fuels, Motor Vehicles, Transportation Modes,
Electricity Use, Heating and Cooking Fuels, and Materials.,
UCD-ITS-RR-03-17, available from   HYPERLINK
"http://www.repositories.cdlib.org/itsdavis" 
http://www.repositories.cdlib.org/itsdavis .

Fernandez-Martinez , G., et al, 2000, “Determination of Volatile
Organic Compounds in Coal, Fly Ash, and Slag Samples by Direct Thermal
Desorption/GC/MS, Analusis, v 28, pp 953-959.

Gupta, C.K., 2006, Chemical Metallurgy: Principles and
Practice,Wiley-VCH.

Hunt, P.J., et al, 1999, “Boiler Designs for Asphalt Fuels,”
POWER-GEN ‘99 International New Orleans, Louisiana, November, 1999.

Kidnay, A.J., et al, 2006 “Fundamentals of Natural Gas Processing”
CRC Press.

Kohl, A., et al, 1997 “Gas Purification,” Gulf Professional
Publications. 

Ocean Surveys Etc., 2005, Site Demonstration of the AQUABLOK™ Sediment
Capping Technology,   HYPERLINK "http://www.hsrc-ssw.org/6MonthAppH.pdf"
 http://www.hsrc-ssw.org/6MonthAppH.pdf , accessed November 2008.

Perry, R.H., Green, D.W., Mahoney, J.O., “Perry’s Chemical
Engineers’ Handbook, 1997, 7th Edition, McGraw Hill.

Skov, E.R., et al, “Coal Tar Chemicals and Syncrude Oil Production
from Low-Rank Coals using Mild-Temperature Pyrolysis,” Proc of AICHE
Spring National Meeting, Houston, TX, April 2007. AICHE Session 16002.

Speight, J.G. 2006, “The Chemistry and Technology of Petroleum,” CRC
Press.

Stultz & Kitto, eds, 1992 “Steam: It’s Generation and Use,” 40th
Edition.

Tilman, D.A., et al, 2004, “Fuels of Opportunity, Elsevier.

US DOE, EIA,   HYPERLINK
"http://www.eia.doe.gov/cneaf/coal/reserves/reserves.html" 
http://www.eia.doe.gov/cneaf/coal/reserves/reserves.html , Accessed Nov
2008.

USDOE, EIA,   HYPERLINK
"http://tonto.eia.doe.gov/dnav/ng/hist/n9190us3m.htm" 
http://tonto.eia.doe.gov/dnav/ng/hist/n9190us3m.htm , accessed November
2008.

USEPA, 2003, AP-42, Ch.1.6, “Wood Residue Combustion in Boilers”,  
HYPERLINK "http://www.epa.gov/ttn/chief/ap42/ch01/final/c01s06.pdf" 
http://www.epa.gov/ttn/chief/ap42/ch01/final/c01s06.pdf , accessed Nov
2008.

USEPA, “AP 42: Compilation of Air Pollution Emissions Factors, Vol  I:
Stationary Point and Area Sources,” 5th Edition, 1995, Ch.1.3 Fuel Oil
Combustion.

USEPA, 1999 “Final Technical Support Document for Hazardous MACT
Standards,” Vol. IV: Compliance with the HWC MACT Standards” Ch.17. 

US Geological Survey, 2001 “Mercury in Coal- Abundance, Distribution,
and Modes of Occurrence, USGS Fact Sheet FS-095-01.

Wess, J., et al,  2004, “Asphalt (Bitumen), Concise International
Assessment Document 59, World Health Organization.”

 For example a typical ultimate analysis might be: 60% carbon, 15%
hydrogen, 10% oxygen, 3% nitrogen, 2% sulfur, and 10% ash. Ash, while
part of the ultimate analysis, is shown separately because it represents
a fraction of the fuel that does not burn.

   HYPERLINK "http://www.eia.doe.gov/cneaf/coal/reserves/reserves.html" 
http://www.eia.doe.gov/cneaf/coal/reserves/reserves.html , Accessed Nov
2008

 Coal’s color is indicative of its age.  As coal ages in the ground,
its color changes from brown to dull black to glossy black.

 Avallone, E.A., & Baumeister, T.(eds), “Mark’s Standard Handbook
for Mechanical Engineers,” 9th Edition, 1987, p 7-19

 The values shown in the table only describe the specific samples shown
although they were selected to be representative of the rank in general.

 US Geological Survey, 2001 “Mercury in Coal- Abundance, Distribution,
and Modes of Occurrence, USGS Fact Sheet FS-095-01

 Davidson, R. A., “Trace Elements in Coal” 1996, Energeia, v.7,
No.3, University of Kentucky, Center for Applied Research.

 Fernandez-Martinez , G., et al, 2000, “Determination of Volatile
Organic Compounds in Coal, Fly Ash, and Slag Samples by Direct Thermal
Desorption/GC/MS, Analusis, v 28, pp 953-959

 Bragg,L., et al, USGS Coal Quality (COALQUAL) Database: Version 2.0,  
HYPERLINK
"http://energy.er.usgs.gov/products/databases/CoalQual/index.htm" 
http://energy.er.usgs.gov/products/databases/CoalQual/index.htm ,
accessed Nov 2008.

 Ocean Surveys Inc., 2005, Site Demonstration of the AQUABLOK™
Sediment Capping Technology,   HYPERLINK
"http://www.hsrc-ssw.org/6MonthAppH.pdf" 
http://www.hsrc-ssw.org/6MonthAppH.pdf , accessed November 2008

 Perry, R.H., Green, D.W., Mahoney, J.O., “Perry’s Chemical
Engineers’ Handbook, 1997, 7th Edition, McGraw Hill..

 CTF stands for coal tar fuel. The designation CTF 50 and CTF 400
indicate the temperature to which the oil must be pre-heated (50 °F and
400°F, respectively) in order to be atomized in a burner.

 Viscosity values shown is for kinematic viscosity = dynamic
viscosity/density.  Note viscosity decreases with temperature for
liquids.

 Skov, E.R., et al, “Coal Tar Chemicals and Syncrude Oil Production
from Low-Rank Coals using Mild-Temperature Pyrolysis,” Proc of AICHE
Spring National Meeting, Houston, TX, April 2007. AICHE Session 16002.

 Kohl, A., et al, 1997 “Gas Purification,” Gulf Professional
Publications. 

 Note that for many gaseous fuels, impurities such as ammonia, and
hydrogen cyanide are mostly removed prior to being used as a fuel in a
boiler

 Specific gravity is the ratio of the density of the substance to a
reference substance. The reference substance is air for a gas and water
for a liquid.

 Culp, A.W., 1979, “Principles of Energy Conversion,” McGraw Hill.

 Gupta, C.K., 2006, Chemical Metallurgy: Principles and
Practice,Wiley-VCH

 USEPA, “AP 42: Compilation of Air Pollution Emissions Factors, Vol 
I: Stationary Point and Area Sources,” 5th Edition, 1995, Ch.1.3 Fuel
Oil Combustion.  Distillate fuels are lighter, less viscous, and have a
lower boiling range when compared with residual fuels.

 Property values from, Stultz & Kitto, eds, “Steam: It’s Generation
and Use,” 40th Edition, 1992, p 8-14.

 See USEPA, 1999 “Final Technical Support Document for Hazardous MACT
Standards,” Vol. IV: Compliance with the HWC MACT Standards” Ch.17 

Table 3-1 shows the highest level detected.  Most of the compounds that
EPA tested for were not detected.  Comparable fuel specifications are
based on either the highest detected value or the highest detection
limit among all samples. See USEPA (1999) op cit.

 Tilman, D.A., et al, 2004, “Fuels of Opportunity, Elsevier.

 Ibid.

 Hydrocarbons with one to four carbon atoms.

 Baukal & Schwartz, 2001, “The John Zink Combustion Handbook” CRC
Press

 Delucchi, M., 2003 “A Lifecycle Emissions Model: LifeCycle Emissions
from Transportation Fuels, Motor Vehicles, Transportation Modes,
Electricity Use, Heating and Cooking Fuels, and Materials.,
UCD-ITS-RR-03-17, available from   HYPERLINK
"http://www.repositories.cdlib.org/itsdavis" 
http://www.repositories.cdlib.org/itsdavis 

 Speight, J.G. 2006, “The Chemistry and Technology of Petroleum,”
CRC Press.

 Wess, J., et al,  2004, “Asphalt (Bitumen), Concise International
Assessment Document 59, World Health Organization”

 Cross, R., 1919, “A Handbook of Petroleum, Asphalt, and Natural
Gas” Kansas City Testing Laboratory.

 Wess, op cit.

 Hunt, P.J., et al, 1999, “Boiler Designs for Asphalt Fuels,”
POWER-GEN ‘99 International, New Orleans, Louisiana, November, 1999.

 Natural gas with a high level of hydrogen sulfide is called sour gas.

 Kidnay, A.J., et al, 2006 “Fundamentals of Natural Gas Processing”
CRC Press.

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 USEPA, 2003, AP-42, Ch.1.6, “Wood Residue Combustion in Boilers”,  
HYPERLINK "http://www.epa.gov/ttn/chief/ap42/ch01/final/c01s06.pdf" 
http://www.epa.gov/ttn/chief/ap42/ch01/final/c01s06.pdf , accessed Nov
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