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Alternatives to Coal Waste Sludge
Companies can process coal without risking community health and safety
“Dry cleaning methods should generate fewer environmental problems and require less energy than wet washing methods.”
University of Arkansas, Published by US Department of Energy
www.netl.doe.gov/publications/proceedings/99/99ucr/mazumder.pdf
Alternatives to coal sludge/ slurry impoundments are available at every step of the coal mining and burning process. Different situations will call for different technologies, and there are a variety of options available:
- Eliminate Pre-washing; ship coal directly to Power Plants for more efficient separation
- Dry Cleaning Process
- Dry Press, Dewatering Process
- Process Coal Slurry for Energy
Storing dangerous chemicals in huge ponds of water simply does not make sense as it drastically increases the volume of the dangerous material. Alternatives reduce the amount of toxic material, making it easier to store it more responsibly.
Eliminate Pre-washing
MagMill: Installed at the front end of power plants to dry-clean the coal, the MagMill lowers overall emissions while eliminating the need for pre-washing. It can be retro-fitted onto existing power plants and actually lowers the overall cost because the coal is cheaper without the expense of pre-washing.***call 412-573-0191 / FAX 412-573-0196. Ask about “non-hazardous waste stream that can be impounded” and whether/where it is being used. http://www.magneticseparation.com/sitehtml/magmill.php
It is often easier for power plants to utilize dry waste because of the high heat involved in the coal burning process, and it is even easier for new plants to separate contaminants. Power plants already need to capture contaminants and reduce emissions, so they are equipped to process the waste.
Filters in plants capture dangerous contaminants before they are released into the air, and without the use of water, so the volume of waste remains low.
Dry Cleaning Methods
Coal can be cleaned with any of several dry processes, which separate dirt and contaminants from the coal without the use of water.
Electrostatic separation: Mineral matter is relatively conducting, does not retain an electric charge, and is thrown from the drum. Coal is relatively non-conducting and does retain a charge, and it adheres to the drum until being swept off with a brush. Research is being conducted to refine the process and make it more cost-effective. http://www.australiancoal.csiro.au/pdfs/Donnelly.pdf
Magnetic Separators: The process is somewhat similar to electrostatic separation, using magnets rather than electrical charge. Research suggests that some versions of magnetic separators will reduce costs significantly—the Rare Earth Magnetic Separator (REM) can handle 4-5 tons/hour, offers 13% lower capital cost, and 50% of the operating costs compared to wet system for production of a fine coal product of equivalent energy level. http://www.australiancoal.csiro.au/pdfs/Donnelly.pdf
Dry Press Filter, Dewatering
Even if coal is washed using a wet process, which creates the coal slurry, the slurry does not need to be disposed of immediately into impoundments or injected into abandoned mines. Dewatering processes press or filter the water from the waste.
Wet processes are used, they can be “closed-circuit” so that the waste is de-watered and the water reused. De-watered waste can be disposed of more safely than the huge volume of liquid coal slurry currently produced.
Several methods are available and fairly widely used. The most appropriate method depends on the slurry composition and planned disposal method. Gravity, pressure, vacuum, and centrifugal methods are all in use currently. Flocculants can be added to further lower the moisture. Hot air systems may be included for additional drying. Optimization of the Dewatering Performance of a Steel Belt Filter. By: Mohanty, M. K.; Wang, Z.; Huang, Z.; Hirschi, J.. Coal Preparation, Jan-Apr2004, Vol. 24 Issue 1/2, p53-68, 16p; (AN 14117371)
After the slurry is dewatered, it can be mixed with ash or course refuse, or other dry materials. The cakes that are formed can be stacked above ground and a contained facility.
Using Coal Slurry for its Energy
PepTec: This process converts the slurry to a usable fuel by capturing the coal particles and converting tailings into usable land. It is a subsidiary of DTE energy, and has been used at several locations while in the research and development stage, including at the Kanawha Eagle plant in Comfort, WV. A commercial application has begun in Ohio that is expected to produce up to 500,000 tons of fine coal fuel annually. Call John Austerberry, (313) 235-8859 or Lorie N. Kessler, (313) 235-8807 http://dteenergy.com/news/releases/dtePeptec.html?searchType=byBusiness&searchValue=Investors
Modern Power Plants: These plants can burn slurry. They often convert the cleaned coal into slurry to feed into the gasifier. Some designs can directly use the “dirty” slurry from impoundments as well, and most can handle a dirtier coal product. http://www.discover.com/issues/dec-06/features/clean-coal-technology/?page=1; http://books.nap.edu/openbook.php?record_id=10212&page=131; DOE
| The Sludge Safety Project cannot endorse any of these methods, as we do not know the effects on communities. We are simply providing a brief summary of alternatives to coal waste sludge that exist to date. |
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