Materials Characterization Paper

In Support of the

Advanced Notice of Proposed Rulemaking –

Identification of Nonhazardous Materials That Are Solid Waste

Coal Combustion Products - Coal Fly Ash, Bottom Ash, and Boiler Slag

December 17, 2008

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1.	Definition of CCPs

Coal combustion products (CCPs) are formed during coal-burning processes
in power plants and industrial boilers.  Coal combustion produces
various forms of CCPs that are categorized by the process in which they
are generated. The CCPs that can be used as ingredients in the
manufacture of portland cement include:  

Fly ash: Exhaust gases leaving the combustion chamber of a power plant
entrain particles during the coal combustion process.  To prevent fly
ash from entering the atmosphere, power plants use various collection
devices to remove it from the gases that are leaving the stack. Fly ash
is the finest of coal ash particles.

Bottom ash:  With grain sizes ranging from fine sand to fine gravel,
bottom ash is coarser than fly ash.  Utilities collect bottom ash from
the floor of coal burning furnaces used in the generation of steam, the
production of electric power, or both. The physical characteristics of
the products generated depend on the characteristics of the furnace.

Boiler Slag:  Boiler slag consists of molten ash collected at the base
of cyclone and pulverized coal boilers.  Facilities cool boiler slag
with water, which then shatters into black, angular pieces that range in
size from course sand to fine gravel and have a smooth appearance.  

2.	Annual Quantities of CCPs Generated and Used

Sectors that generate CCPs: 

The coal-fired power industry, represented by NAICS sector 221112 –
Fossil Fuel Electric Power Generation, is the largest generator of CCPs.
Other industries, such as commercial boilers and mineral and grain
processors that use coal as a fuel source, also produce small quantities
of CCPs.  

Quantities and prices of CCPs generated:   

In 2007, the coal-fueled electric power industry generated approximately
71.7 million tons of fly ash, 18.1 million tons of bottom ash, and 2.1
million tons of boiler slag.

In 2003, the price per ton of concrete-quality fly ash, freight on board
(FOB) (i.e., costs net of shipping or transport costs), ranged from
$0-$45 (ACAAa).

In 2003, the price per ton of bottom ash ranged from $3-$8 FOB (ACAAa).

The price of boiler slag could not be determined at this time; as with
many small markets, it may be that most transactions involving boiler
slag are private.

Trends in generation of CCPs:  

The coal-fired power industry is the largest generator of CCPs in the
United States. Coal-generated electricity supplies approximately 50
percent of the electricity consumed in the United States (American Coal
Foundation). Since electricity demand is projected to increase in coming
years, and coal will continue to be an important fuel source, the
quantity of CCPs produced and available for beneficial reuse may also
increase (USDOE 2008, p.10). While other industries that use coal as a
fuel source in commercial or industrial boilers (e.g., mineral and grain
processors) also produce CCPs, these quantities tend to be small, and
increases or decreases in their production will not have a significant
impact on the overall trend in CCP production.

3.	Uses of CCPs

Ingredient and combustion uses of CCPs:  

Fly ash, bottom ash, and boiler slag can be added to the raw material
feed in clinker manufacturing to contribute specific required
constituents, such as silica, alumina, and calcium, in the final cement
composition.

Fly ash with high unburned carbon content can also be reburned in cement
kilns for energy recovery at the same time as it provides ingredient
value.

Non-combustion uses of CCPs:

Fly ash can be used in a number of non-combustion applications.  It’s
most common, and most high-value, use is as a supplementary cementitious
material in concrete (i.e., a substitute for, or amendment to, portland
cement in concrete mixes).  In this application, fly ash can provide
certain material advantages such as greater workability, higher
strength, and increased longevity in the finished concrete product.  Fly
ash is also used as a partial substitute for virgin dirt, sand, or
gravel in structural fill, or as a substitute for portland cement in
waste stabilization (ACAA 2006).

Bottom ash can be used to offset virgin sand and gravel in applications
such as structural fill, road base, and concrete (ACAA 2006).

Boiler slag can be used to offset virgin sand and gravel in applications
such as structural fill and blasting grit (ACAA 2006).

Quantities of CCPs landfilled: 

In 2007, 40 million tons fly ash, 9.2 million tons bottom ash, and 0.41
million tons boiler slag were landfilled, representing roughly 56
percent, 60 percent, and 20 percent of production, respectively.

Quantities of CCPs stockpiled/stored:

The American Coal Ash Association (ACAA) estimates that between 100
million and 500 million tons of fly ash have accumulated in U.S.
landfills since the 1920s, when the disposal of fly ash in landfills
began.  It is unclear, however, how much of this fly ash is available
for beneficial use.  

The recoverability of fly ash depends significantly on the manner in
which it is disposed.  Fly ash disposed of in a monofill or holding pond
likely would be suitable for beneficial use because it has generally not
been commingled with other materials.  Unfortunately, the ACAA is
unaware of data indicating how much of the 100-500 million tons of
stockpiled fly ash is deposited in monofills or holding ponds

The recovery of landfilled ash for beneficial reuse does not appear to
be widely practiced. Although a portion of the fly ash located in
stockpiles across the U.S. may be available for beneficial use, a recent
analysis of the market for fly ash found that approximately 49 percent
of the 72.4 million tons of fly ash generated in 2006 was beneficially
used (ACAA).  Therefore, even if large quantities from stockpiles were
made available, it is unlikely that the quantity re-used would increase
significantly. In other words, the demand for fly ash appears to be met
by existing production.

Certain electric utilities, however, have pursued programs to recover
ash for use of its residual unburned carbon in power plants.  Examples
include: 

Wisconsin Energy Corporation began reburning ash at its Pleasant Prairie
Power Plant in 2000 and expanded reburning to include ash recovered from
landfills in 2001 after receiving approval under Wisconsin’s first
Environmental Cooperative Agreement.  The patented process can use
either dry high-carbon fly ash directly from the company’s older power
plants, or use moist high-carbon ash from WEC’s power plants,
stockpiles, existing landfills, and remediation projects.  According to
its 2006 Performance Report, WEC reburned approximately 11,023 short
tons of recovered landfill ash in 2002 (WEC 2006a, p.69). 

In 2001, Western Kentucky Energy's Coleman station in Hawesville,
Kentucky, inaugurated an ash-recovery program developed by staff at the
University of Kentucky Center for Applied Energy Research (CAER). The
CAER researchers developed a system to remove fly ash from holding ponds
and extract carbon to create a reburning fuel or several other products
(BNET 2002, pp. 1-2).  

Wisconsin Energy Corporation also recovers landfilled ash for sale as a
construction material.  Under the Environmental Cooperative Agreement
and Wisconsin regulations for beneficial industrial byproduct use, the
company recovered 31,967 short tons (706.293 cubic feet) of coal ash
from its P4 landfill and sold it as a base material to replace stone or
gravel under roads, parking lots, and buildings.  Since 2002, more than
93,696 short tons have been recovered (WEC 2006a, p.70). 

 Exhibit 1:  Overview of Generation and Use of CCPs in 2007

Commodity	Annual Quantity Generated 	Annual Quantity Used as Ingredient
Annual Quantity Landfilled	Annual Quantity in Other Uses	Total Quantity
Stockpiled as of 2006



Fuel	Cement Ingredient in Kilns





-----------------------------Short Tons -------------------------

Coal fly ash	71.7 million	Undetermined	3.6 million	40.07 million	28.03
million	100 – 500 milliona

Bottom ash	18.1 million	0	0.61 million	10.80 million	6.69 million
Undetermined

Boiler slag	2.1 million	0	0.007 million	0.41 million	1.65 million
Undetermined



Sources:

Unless otherwise noted, data is from American Coal Ash Association.
(ACAA), 2006, Coal Combustion Product (CCP) Production and Use Survey,
accessed at: 

http://www.acaa-usa.org/associations/8003/files/2007_ACAA_CCP_Survey_Rep
ort_Form%2809-15-08%29.pdf. 

Notes:

a. Personal communication with Dave Goss, ACAA, November 27, 2006.



4.	Management and Combustion processes for CCPs

Types of units using CCPs:

When used in clinker manufacture, fly ash, boiler slag, and bottom ash
are fed into cement kilns with other raw material feed.

Sourcing of CCPs:

Although electric utility companies produce ash at their coal-fired
power plants, most utilities do not handle, dispose of, and/or sell the
ash that they produce. There are approximately 40 to 50 commercial ash
marketing firms operating throughout the United States, in all states
except Hawaii. In addition to commercial ash marketing organizations,
certain coal-burning electric utility companies have formal ash
marketing programs of their own. Most coal-burning electric utility
companies currently employ an ash marketing specialist whose
responsibility it is to monitor ash generation, quality, use or
disposal, and to interface with the ash marketers or brokers who are
under contract to the utility companies (Turner Fairbank Highway
Research Center).

Processing of CCPs:  

Use of CCPs as a raw feed in cement kilns does not require processing. 
However, kilns do require feed of consistent quality, quantity, and
composition in order to ensure that the feed mix in the kiln is
appropriate.  In particular, levels of key metals (e.g., iron and
alumina) in CCPs are carefully calibrated with other ingredients to
ensure that the final cement product has the correct mineral and metal
content.

Due to its pozzolanic properties, stockpiled class C fly ash may harden
over time if exposed to moisture. (Class F fly ash does not exhibit this
characteristic). Hardened class C fly ash must be crushed prior to
beneficial use but is typically limited to use as an aggregate in
concrete. Class F fly ash does not loose reactivity over time and can be
recovered from stockpiles for use in concrete, but it is unclear to what
extent stockpiled Class F fly ash can be used in cement kilns, or
whether it requires processing prior to use.  

Bottom ash may require stockpiling for a short period of time (at least
1 or 2 days) to allow excess water to drain prior to beneficial use.
Ponded bottom ash reclaimed from a lagoon should be stockpiled and
allowed to drain for a somewhat longer time period, perhaps up to 1 or 2
weeks, depending on the amount of rainfall. After size reduction, bottom
ash can be screened to produce different size ranges, if desired.
(Turner Fairbank Highway Research Center).

An example of the recovery process used by  Wisconsin Energy Corp.
includes:

Identifying a disposal site that contains the byproducts (typically fly
ash 

and bottom ash) and removing a portion of the byproduct;

The removed materials are crushed, screened, and periodically sampled in


accordance with ASTM D2234;

Analyzing a sample of the portion of the byproducts to determine the
loss on ignition of the portion of the byproducts;

Either fly ash or bottom ash or a mixture of both is added in a fine
particle condition to the furnace of a pulverized coal boiler in a small
proportion to the pulverized coal fed to the furnace.  The ash is burned
with the pulverized coal.  The proportion of coal ash is preferably in
the range of 1 percent to 3.5 percent, by weight, of the pulverized
coal.  

Introducing the portion of the byproducts along with pulverized coal
into a pulverized coal furnace if the portion of byproducts has a loss
on ignition greater than or equal to a predetermined loss on ignition
value (typically greater than or equal to 1 to 5 percent); and

Burning the portion of the byproducts in the furnace with the pulverized
coal to render the byproducts into a commercially valuable fly ash and
bottom ash having very low loss on ignition, typically lower than 3
percent (WEC 2003, p.7; WEC, p.1). 

State status of CCPs use as ingredient:  

In the state of Wisconsin, Wisconsin Energy Corporation has an agreement
with the state to burn recovered landfill ash at their power plants.

At this stage, we have not identified any other states that have
specifically given beneficial use designation to the use of CCPs in
clinker manufacture, or that prohibit fly ash use in clinker, but we
have not performed an exhaustive investigation of state activities and
regulations.

5.	CCP Composition and Impacts

Composition of CCPs:

The chemical properties of fly ash are influenced to a great extent by
those of the coal burned. There are basically four types, or ranks, of
coal, each of which varies in terms of its heating value, its chemical
composition, ash content, and geological origin: anthracite, bituminous,
subbituminous, and lignite. The principal components of bituminous coal
fly ash are silica, alumina, iron oxide, and calcium pxide, with varying
amounts of residual, unburned carbon, as measured by the loss on
ignition. Silica, alumina, and calcium are also the primary ingredients
in portland cement, along with iron oxide.  Lignite and subbituminous
coal fly ashes are characterized by higher concentrations of calcium and
magnesium oxide and reduced percentages of silica and iron oxide, as
well as a lower residual carbon content, compared with bituminous coal
fly ash. Very little anthracite coal is burned in utility boilers, so
there are only small amounts of anthracite coal fly ash. Fly ash
contains trace metals, such as vanadium, zinc, copper, chromium, nickel,
lead, arsenic, and mercury.

Bottom ash and boiler slag are composed principally of silica, alumina,
and iron oxide, with smaller percentages of calcium and magnesium
oxides, sulfates, and other compounds. The composition of the bottom ash
or boiler slag particles is controlled primarily by the source of the
coal and not by the type of furnace. Bottom ash or boiler slag derived
from lignite or sub-bituminous coals has a higher percentage of calcium
oxide than the bottom ash or boiler slag from anthracite or bituminous
coals. (Turner-Fairbank Highway Research Center).

All of these materials provide effective substitutes for most or all of
the raw materials in cement, but the relative levels of different oxides
must be carefully managed to ensure that the kiln product meets industry
specifications.

Impacts of CCPs use:

In clinker manufacture, CCPs partially offset the need for virgin
silica, iron, and alumina sources. Using CCPs in the cement kiln can
reduce the unit consumption of virgin feed stock materials, which may
reduce the overall emissions associated with materials extraction and
processing, since CCPs generally require less pre-processing than the
virgin materials they replace.  

With respect to emissions from the cement kiln itself, to the extent
CCPs have a lower emission profile than the virgin materials they
replace, overall emissions will be reduced. However, CCPs may have
higher emissions of pollutants such as mercury than virgin silica, iron
and alumina sources when burned in the kiln.

The specific lifecycle impacts of CCP use as a raw material in clinker
production are not evaluated here because of uncertainties in lifecycle
scenario development. For example, it is difficult to determine the
replacement ratio between CCPs and other raw feed materials in clinker
production. Thus, the correct quantity of material to be modeled is
unclear. In addition, CCPs may substitute for a combination of virgin
raw materials and other secondary materials (e.g., blast furnace slag,
foundry sand, cement kiln dust, etc.); the choice of material often
depends on location-specific factors such as the proximity of material
sources to the cement kiln and relative availability of different
materials. Avoided upstream impacts depend heavily on the specific
material being displaced in the lifecycle scenario.

When fly ash with a high unburned carbon content is introduced to the
cement kiln during clinker manufacture, fuel supply may be reduced to
accommodate the additional energy provided by the carbon in the fly ash
(Bhatty, Javed et al. 2001). 

One health risk issue is currently gaining attention in the use of fly
ash in high-heat applications such as cement manufacture.  When exposed
to elevated temperatures (approximately 2,750 degrees Farenheit) in a
cement kiln, laboratory experiments have found that mercury is readily
released from fly ash (Pflughoeft-Hasset et al. 2007). At this time, the
level of mercury in fly ash has not been considered significant enough
to create a health risk.  However, as coal utilities increasingly employ
mercury capture technologies, some facilities may implement technologies
that result in fly ash with much higher mercury content that is not
suitable for use in cement manufacture.  Other, more expensive
technologies would ensure that most or all fly ash is separate from
mercury capture; at this point it is not clear how much, if any, fly ash
would be affected by mercury capture technology.  

Combustion of stockpiled CCPs to produce a low loss on ignition (LOI)
coal ash  has several potential advantages: 

Removal, recovery, and characterization of landfilled CCPs so that
recovered CCPs may be put to beneficial use. Characterization includes
energy content, sulphur content, moisture, and trace metals content for
energy and air emissions analyses. 

Preservation of licensed landfill space. 

Preservation of coal reserves by recovering heat from reclaimed CCPs. 

Production of low LOI coal ash that may be substituted for portland
cement thereby reducing the need for portland cement and reducing air
emissions from its production process.

Reduced need for limestone quarries (due to the use of ash as a
substitute for portland cement) and landfill sites (WEC, p.2).

References

American Coal Ash Association (a), “Frequently Asked Questions,”
accessed at:     HYPERLINK "http://www.acaa"  www.acaa-usa.org . 

American Coal Ash Association. (ACAA), 2007, Coal Combustion Product
(CCP) Production and Use Survey, accessed at: 

http://www.acaa-usa.org/associations/8003/files/2007_ACAA_CCP_Survey_Rep
ort_Form%2809-15-08%29.pdf.

American Coal Foundation, “All About Coal: Fast Facts About Coal,”
accessed at:     HYPERLINK
"http://www.teachcoal.org/aboutcoal/articles/fastfacts.html" 
http://www.teachcoal.org/aboutcoal/articles/fastfacts.html .

American Coalition for Clean Coal Electricity (ACCCE), “America’s
Power: Factoids,” accessed at:   HYPERLINK
"http://www.americaspower.org/The-Facts/Factoids" 
http://www.americaspower.org/The-Facts/Factoids 

Bhatty, Javed et al., “Use of High-Carbon Fly Ash In Cement
Manufacture,” Cement Americas, May 1, 2001, accessed at:   HYPERLINK
"http://cementamericas.com/mag/cement_highcarbon_fly_ash/" 
http://cementamericas.com/mag/cement_highcarbon_fly_ash/ . 

BNET Business Network, “Disposal and Reuse of Coal Combustion
Byproducts; With Scores of New Coal-Fired Projects Now Being Considered
in the US, Coal Combustion Byproducts are Gaining the Attention of
Owners, Developers, Financial Backers, Governments, Environmental
Groups, and the General Public,” 2002, accessed on August 21, 2008,
at:  
http://findarticles.com/p/articles/mi_qa5392/is_200201/ai_n21309385.

Turner Fairbank Highway Research Center and the Federal Highway
Administration, User Guidelines for Waste and Byproduct Materials in
Pavement Construction, accessed at:   HYPERLINK
"http://www.tfhrc.gov/hnr20/recycle/waste/begin.htm" 
http://www.tfhrc.gov/hnr20/recycle/waste/begin.htm .

Pflughoeft-Hasset et al., 2007, Analysis of How Carbon-Based Sorbents
Will Impact Fly Ash Utilization and Disposal, Presented at 2007 World of
Coal Ash, May 7-10, 2007, Covington, Kentucky, accessed at:   HYPERLINK
"http://www.flyash.info/2007/151pflug.pdf" 
http://www.flyash.info/2007/151pflug.pdf . 

United States Census Bureau, 2002 Economic Census, Industry Snapshots
for Cement Manufacturing, accessed on August 18, 2008 at:   HYPERLINK
"http://quarterhorse.dsd.census.gov/TheDataWeb_HotReport/servlet/HotRepo
rtEngineServlet?emailname=bh@boc&filename=mfg1.hrml&20071204152004.Var.N
AICS2002=327310&forward=20071204152004.Var.NAICS2002" 
http://quarterhorse.dsd.census.gov/TheDataWeb_HotReport/servlet/HotRepor
tEngineServlet?emailname=bh@boc&filename=mfg1.hrml&20071204152004.Var.NA
ICS2002=327310&forward=20071204152004.Var.NAICS2002 . 

United States Department of Energy, Energy Information Administration
(EIA). 2008, “Annual Energy Outlook 2008 with Projections to 2030,”
Publication DOE/EIA-0383 (2008), June 2008.

United States Environmental Protection Agency (EPA). March 15, 1999,
Technical Background Document for the Report to Congress on Removing
Wastes from Fossil Fuel Combustion: Waste Characterization, accessed at:
http://www.epa.gov/epawaste/nonhaz/industrial/special/fossil//ffc2_399.p
df

United States Environmental Protection Agency (EPA). April 28, 2008,
Study on Increasing the Usage of Recovered Mineral Components in
Federally Funded Projects Involving Procurement of Cement or Concrete to
Address the Safe, Accountable, Flexible, Efficient Transportation Equity
Act: A Legacy for Users.

Wisconsin Energy Corporation (WEC). 2006 Performance Report,
Environmental Performance, 2006a accessed on August 21, 2008, at:  
HYPERLINK "http://www.wisconsinenergy.com/performrpt/index.htm" 
http://www.wisconsinenergy.com/performrpt/index.htm .

Wisconsin Energy Corporation (WEC). Annual Performance Report,
Environmental Cooperative Agreement, Pleasant Prairie Power Plant,
Pleasant Prairie, Wisconsin, June 2006b, accessed on August 25, 2008 at:
 http://dnr.wi.gov/org/caer/cea/ecpp/agreements/wepco/reports/2006report
.pdf

Wisconsin Energy Corporation (WEC). “Amendment and Extension of the
Environmental Cooperative Agreement between We Energies’ Pleasant
Prairie Power Plant and Wisconsin Department of Natural Resources,”
Fact Sheet, Pub #CO-312, February 2006c, accessed on August 25, 2008 at:
 http://dnr.wi.gov/org/caer/cea/ecpp/agreements/wepco/agreements/amended
/factsheet20060205.pdf

Wisconsin Energy Corporation (WEC). “Coal Combustion Products
Utilization Handbook,” first published in 2000, second edition 2004,
accessed on August 22, 2008 at: 
http://www.bloomconsultants.com/published-MT_Coal-Combustion.htm

 This paper focuses on CCPs used primarily as an ingredient in cement
manufacture; see the Materials Characterization Paper for Coal Refuse
for further information on mining rejects and combustion applications.

 The report indicates that between 2003 and 2006, the facility did not
reburn any recovered coal ash from its landfill.  During these years,
however, the facility continued to reburn coal ash generated by power
plants. 

 During a pilot project to reprocess landfilled combustion products that
was conducted by Wisconsin Energy Corporation in July and October 1998,
samples were collected every 30 minutes from the transfer point where
the ash fell onto the stacker conveyor during the entire operation per
the ASTM standard, and a composite sample was prepared for every 5,000
tons processed and tested.

 Landfill ash recovery operations at the Western Kentucky Energy
(Coleman Station) involves the following activities. Ash first must be
recovered from the pond or landfill and then separated into its
fundamental components:  carbon, silicates, and high-density, iron-rich
materials. A coarse carbon-fuel product is recovered by density
separation using concentrating spirals.  A fine carbon-fuel product is
recovered with flotation cells.

   Listed by relative frequency.  See USEPA, March 15, 1999.  

 Recovery of landfilled ash may require extra screening.  For example,
during the removal of ash from a landfill in Wisconsin in 2000, the
removed materials were crushed, screened and periodically sampled in
accordance with ASTM D2234.  It was found that over 99 percent of the
material removed consisted of coal combustion products, with foreign
materials consisting of lost items from landfill operators (e.g., soda
cans, safety ribbon, gloves, etc.) (WEC, 2006, p3).

		Coal Combustion Products

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