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Coal Ash Landfills –A Case Study
Roger ClarkeManager, Waste & Remediation
MPCA Aug. 25, 2008
2
What is Coal Ash?
Unburned portion of fuelMostly comprised of minerals commonly found in soilHas trace elements such as arsenic, chromium, cadmium, lead & mercury
3
How Coal Ash Is Generated?
4
Types of Ash:
Fly AshBottom AshSlagScrubber Residues
Magnified view of Fly Ash Particles
5
0
200,000
400,000
600,000
800,000
1,000,000
1,200,000
1,400,000
Tons
Ash
Gen
erat
ed
NSP PSCO SPS
Xcel Energy Region
Tons DisposedTons Utilized
2007 Coal Ash Generation:
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What Factors Affecting Coal Ash Composition?
Fuel SourceCombustion Process
— Circulating Fluidized Bed — Pulverized Coal (example SHERCO)— Cyclone (example A.S. King)
Emission Control Devices— Sulfur Control — NOx Control— Particulate Control— Mercury Control
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Coal and Additives:Trace Metal Analysis
Rochelle Westmoreland Petcoke
Antimony mg/kg -1 1.029 4Arsenic mg/kg -1 1.263 -8Barium mg/kg 183 194.2 2.1Beryllium mg/kg -0.2 0.371 -0.2Boron mg/kg 24 77.3Bromine mg/kg -20Cadmium mg/kg -0.2 0.274 -0.4Chlorine mg/kg -50Chromium mg/kg 4 4.034 -0.8Cobalt mg/kg 2 2.579 -2Copper mg/kg 9 7.000 -2Fluorine mg/kg 68 -10Lead mg/kg 2 6.13 -2Lithium mg/kg 3 16.24Manganese mg/kg 9 78.89 1.1Mercury mg/kg 0.05 0.095 0.05Molybdenum mg/kg -2 3.395 8Nickel mg/kg 3 3.211 199Selenium mg/kg -1 1.158 -8Silver mg/kg -0.2 0.476 -0.4Strontium mg/kg 148 448.6 1Thallium mg/kg -1 -20Tin mg/kg -1 1.432 -8Vanadium mg/kg 9 10.053 1041Zinc mg/kg 6 5.211 2Zirconium mg/kg 8 15.778 -0.4
Current Blend
Coal Trace Element Summary:PPM – Dry Basis Cordero Rojo SoilArsenic (As) 1.4 1 to 50Barium (Ba) 373 100 to 3000Boron (B) 44 2 to 100Cadmium (Cd) 0.2 0.1 to 0.7Chromium (Cr) 6.1 1 to 100Copper (Cu) 14.5 2 to 100Lead (Pb) 3.1 2 to 200Mercury (Hg) 0.1 0.01 to 0.3Molybdenum (Mo) 2.1 0.2 to 5Nickel (Ni) 2.5 5 to 500Selenium (Se) 1.1 0.1 to 2Strontium (Sr) 254 50 to 1000Vanadium (Va) 21.7 20 to 500Zinc (Zn) 10.2 10 to 300
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Typical Chemical Composition of Fly Ash
Sulfur2.1% Moisture
0.1% Alkalines1.0%Magnesium Oxide
4.7%
Calcium Oxide28.3%
Iron Oxide6.3%
Aluminum Oxide19.9%
Unburned Carbon (LOI)0.4%
Silicon Dioxide37.3%
Major Constituents: Fly Ash
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Typical Chemical Composition of Cement
Sulfur0.00%
Moisture0.00%
Alkalines0.21%
Magnesium Oxide2.39%
Unburned Carbon (LOI)0.59%
Silicon Dioxide21.62%
Aluminum Oxide4.54%
Iron Oxide2.76%
Calcium Oxide67.89%
Major Constituents: Cement
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Typical Chemical Composition of Bottom Ash
Silicon Dioxide49.3%
Aluminum Oxide19.8%
Iron Oxide6.2%
Calcium Oxide18.8%
Magnesium Oxide4.2%
Potassium Oxide0.3%
Sodium Oxide1.4%
Major Constituents: Bottom Ash
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Relative Chemical Content:
Fly Ash Total Composition: (ppm, dry)
Black Dog 3&4 MN ChronicIndustrial SRVs
Arsenic (As) 13 25Barium (Ba) 5,260 12,500Boron (B) 582 23,000Cadmium (Cd) 2.7 250Chromium (Cr) 66 425 (as VI)Copper (Cu) 148 9,000Lead (Pb) 33 700Mercury (Hg) 0.10 2Molybdenum (Mo) 9.0 --Nickel (Ni) 30.2 3,000Selenium (Se) 10.4 1,250Sodium (Na) 10,483 --Sulfur (S) 30,136 --Zinc (Zn) 77 7,000
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What is Leachate?Leachate is defined as “liquid that has percolated through solid waste and has extracted, dissolved, or suspended materials from it”Leachate generation controlled by:
— Type of material and its porosity— Precipitation levels— Facility design— Operational controls such as size of working face
Leachate chemistry controlled by:— Characteristics of the waste material— Volume of contact water— Chemistry of the contact water
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Other2%
Potassium1%
Alkalinity1%
Calcium4%
Sodium36%Sulfate
56%
Leachate: Primary Constituents
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Leachate:Minor Constituents
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TCLP Test Results: 2008
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NSP Disposal Facility Design