Managing Coal Combustion Residues in Mines (2006) / Chapter Skim
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2 Coal Combustion Residues
2 Coal Combustion Residues
Pages 27-58
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From page 27... ...
A variety of solid materials may be generated from the combustion of coal, including fly ash, bottom ash, boiler slag, and residues from air pollution control technologies, such as flue gas desulfurization (FGD) materials (Figure 2.1)
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From page 28... ...
28 mine abandoned = via site of ) and AML x surrounding O, 2 (H NO, material with pollutants function 2 Stack and/or of a Gas CO is refuse technique, Gas disposal)
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From page 29... ...
For example, mercury tends to adsorb to fly ash unless another material, such as activated carbon, is added to the flue gas to capture the mercury preferentially. Bottom Ash and Boiler Slag Bottom ash typically consists of large ash particles that accumulate at the bottom of the boiler.
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From page 30... ...
Boiler slag is a CCR that is expected to be produced in diminished quantities in the future because of the retirement of the older boilers that produce liquid slag in significant quantities. Residues from Air Pollution Control Technologies Several air pollution control regulations have been enacted to improve air quality in the United States.
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From page 31... ...
The Clean Air Interstate Rule incorporates and goes beyond the existing Clean Air Act Acid Rain Program and may lead to more FGD materials being produced or to a new material produced by the introduction of new technologies. Nitrogen Oxide Emissions Control Technology There are several types of NOx emissions control technologies.
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From page 32... ...
. NOTE: This figure does not include the approximately 5 million short tons of CCR produced by independent power producers firing coal refuse.
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From page 33... ...
This section describes the factors influencing the characteristics of CCRs and presents information on the physical and chemical characteristics of various CCRs. Factors Influencing the Characteristics of Coal Combustion Residues There are several factors that influence the physical and chemical characteristics of the CCRs produced, including 1.
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From page 34... ...
boilers and co-fire coal refuse with limestone, resulting in a highly alkaline CCR. Combustion Technology The effects of combustion technology on the characteristics of CCRs vary based on the source coal and the operating conditions.
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From page 35... ...
Mineralogy The mineralogical characteristics of CCRs reflect the source coal, the combustion process itself, and any pollution control technologies used. Pulverized coal combustion occurs at high temperature (typically above 1400ºC)
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From page 36... ...
. Pulverized coal fly ash particles tend to melt at high combustion temperatures and condense as spheres, resulting in relatively low surface area for this small grain size (0.7 to 37 m2/g)
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From page 37... ...
The acidic fly ashes generally came from power plants burning bituminous coal extracted from southeastern or mid-Atlantic states. Trace Element Content The trace elements contained in CCRs are derived from naturally occurring minerals present in the source coal.
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From page 38... ...
For example, with an ash content of 12.5 percent, nonvolatile metals should be found at eightfold higher concentrations in bulk CCRs than in the source coal. The trace element content of coal varies across coal types (Figure 2.4)
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From page 39... ...
. Radioactive Content A few trace elements found in source coal are inherently radioactive; therefore, concern has been raised that CCRs may also be radioactive.
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From page 40... ...
AnthraciteBituminous Bed Boiler Coal: Bottom (see FBC FBC FBC Coal: Subbituminous Coal: Soils Coal: Types of Soils, Source Coal and CCRs FIGURE 2.4 Bulk selected trace metal constituent concentrations in soils, source coal, and CCRs. For comparison with a familiar natural material, trace metal concentrations in soil are also presented.
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From page 41... ...
AnthraciteBituminous Bed Boiler Coal: Bottom (see FBC FBC FBC Coal: Subbituminous Coal: Soils Coal: Types of Soils, Source Coal and CCRs between graphs. Soil data reflect a median value from the USGS soils database of the following states: Texas, New Mexico, Pennsylvania, Louisiana, Oklahoma, West Virginia, Maryland, Michigan, Arizona, Kentucky, New Jersey, Illinois, Indiana, New York, Tennessee.
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From page 42... ...
Boiler Slag (ppm) Constituent Median Range Median Range Median Range Aluminuma -- -- -- -- -- -Antimonyb 4.6 0.2-205 4.0 0.18-8.4 0.8 0.25-1.0 Arsenicb 43.4 0.0003-391.0 4.7 0.80-36.5 4.5 0.01-254 Bariumb 806.5 0.02-10,850 633 24-9,630 413 6.19-1,720 Berylliumb 5.0 0.200-2,105 2.2 1.4-2.9 7.0 7.0-7.0 Boronb 311 2.98-2,050 90.0 1.79-390 49.5 0.10-55.0 Cadmiumb 3.4 0.01-76.0 003.1 0.050-5.5 40.5 0.01-40.5 Chromiumc 136 3.6-437 120 3.4-350 -- -ChromiumVIb 90 0.19-651 121.0 3.41-4,710 158 1.43-5,981 Cobaltc 35.9 4.90-79.0 24 7.1-60.4 -- -Copperc 112 0.20-655 61.1 2.39-146.3 32.0 1.37-156 Fluorinec 29.0 0.40-320 50.0 2.5-104 -- -Irona -- -- -- -- -- -Leadb 56.8 0.02-273 13.2 0.86-843.0 8.0 0.40-120 Manganesec 250 24.5-750 297 56.7-769 -- -Mercuryb 0.1 0.013-49.5 0.009 0003-0.040 9.5 0.016-9.5 Molybdenuma -- -- -- -- -- -Nickelb 77.6 0.1-1,270 79.6 1.9-1,267 83.0 3.3-177 Potassiuma -- -- -- -- -- -Seleniumb 7.7 0.0003-49.5 0.8 0.007-9.0 4.5 0.10-14.0 Silverb 3.2 0.01-49.5 3.0 0.06-7.1 37.0 0.01-74.0 Strontiumc 775 30.0-3,855 800 170-1,800 -- -Thalliumb 9.0 0.15-85.0 na 2.0 38.5 33.5-40.0 Vanadiumb 252 43.5-5,015 141 24.0-264 75.0 75.0-320.0 Zincb 148 0.28-2,200 52.6 3.80-717 35.8 4.43-530 NOTE: FGD = flue gas desulfurization; ppm = parts per million.
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From page 43... ...
The committee recommends that existing data-gathering mechanisms be expanded to include comprehensive reporting of CCR generation quantities and classifications, and clarified to allow for a clear determination as to its disposal or use.
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From page 44... ...
For example, the committee received information from the State of Penn sylvania on the annual quantity of CCRs generated from coal refuse-fired facilities. Because of the large volumes of CCRs generated at Pennsylvania's coal refuse fired facilities that are subsequently used in mine reclamation, those numbers were included in this report.
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From page 45... ...
Of the reported 126 million short tons of CCRs produced in 2003 by utilities and independent power producers, approximately 44 million short tons were used outside of mine settings for a variety of alternative applications such as concrete, structural fill projects, or waste stabilization (ACAA, 2005a)
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From page 46... ...
. Engineered Fill Fly ash and bottom ash can be used to produce road base materials, manufactured aggregates, flowable fills, structural fills, and embankments.
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From page 47... ...
. Soil Amendments Coal combustion residues can also be used to modify soils chemically or physically.
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From page 48... ...
Although the recycling of various CCRs into engineered products is the preferred alternative, conditions do not always lend themselves to such a solution. In these cases, CCR disposal alternatives are usually limited to surface impoundments, landfills, or placement in coal mines where the CCRs are utilized in mine reclamation.
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From page 49... ...
The FBC CCRs generated by coal refuse fired facilities are highly alkaline and have been used in mine reclamation and for treatment of acid mine drainage in areas near the plant. For example, the Mount Carmel co-generation plant consumed a total of 8 million short tons of coal refuse from 1990 through 2002 and produced 5 million short tons of CCR for mine recla mation neighboring the plant during that period, reclaiming 209 acres.
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From page 50... ...
.2 The data currently available on CCR use and disposal do not differentiate between the amount of CCRs being used in engineered products outside of coal mines, the amount being used in coal mines as minefill, and the amount being used in smaller engineering applications (e.g., road aggregate) within the mine area.
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From page 51... ...
The placement of CCRs generated by coal refuse-fired facilities in Pennsylvania for mine reclamation rose steadily from 89,000 short tons in 1988 to the almost 5 million short tons in 2002 and is expected to continue to increase as more facilities are developed (PADEP, 2004)
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From page 52... ...
In surface mines, minefilling generally involves the placement of CCRs as a monofill, a layered fill, or a blended mixture of coal refuse and CCR (Figure 2.9)
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From page 53... ...
(B) Aerial shot of the filled Big Gorilla pit.
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From page 54... ...
Mine sealing generally involves injecting a fly ash grout mixture into boreholes in the underground mines to seal off problem areas. Certain CCRs may also be used to treat pyritic spoils that result in acid mine drainage.
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From page 55... ...
Sparking would be hazardous in both working and abandoned underground coal mines that may have accumulations of methane gas.
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From page 56... ...
The committee recommends expanding existing data gathering mechanisms to include comprehensive reporting of CCR generation quantities and classifications, and clarifying those mechanisms to allow for a clear determination as to disposal or use. This chapter outlines the many alternatives available for CCR disposal and use, including applications in surface and underground coal mines.
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From page 57... ...
The characteristics of a particular CCR stream, coupled with the aforementioned considerations, are key to determining the best options for disposal and use of CCRs. Therefore, the committee concludes that understanding both the characteristics of CCRs and the options available for their disposal and use are critical to sound CCR management and that such characteristics and options are highly site specific.
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