A dewatering technology developed at Virginia Tech has succeeded in reducing the moisture content of ultrafine coal to less than 20%, transforming it to a salable product. The demonstration was the result of a seven-year, $13-million cooperative effort supported by the Department of Energy Office of Fossil Energy’s National Energy Technology Laboratory (NETL).
Roe-Hoan Yoon, the Nicholas T. Camicia Professor of Mining and Mineral Engineering in Virginia Tech’s College of Engineering, and his colleagues developed a hyperbaric centrifuge that can efficiently dewater coal as fine as talcum powder. Such coal fines presently must be discarded by even the most advanced coal cleaning plants because its moisture content in conventional dewatering systems make it unmarketable.
During recent prototype tests at Arch Coal Company’s Cardinal plant in Logan County, W.Va., the technology reduced the moisture to a level that the waste coal can now be marketed commercially. The result is significant to the energy consumer in that US coal producers each year discard large amounts of moisture-laden coal fines that can potentially be salvaged for energy use while simultaneously cleaning up the environment.
The hyperbaric centrifuge is like the spin cycle on a washing machine, with the addition of compressed air. Combining increased spinning and compressed air has a synergistic effect and cuts the moisture in half compared to conventional technology.—Roe-Hoan Yoon
Waste coal slurry went through the centrifuge at a rate of 30 gallons per minute and was dewatered to 13-19% moisture with coal recovery greater than 97%. The prototype unit tested at the Cardinal plant was constructed by Decanter Machine Company, Johnson City, Tenn., as part of a license agreement with Virginia Tech. Based on the successful test result, the company is currently building a full-size commercial unit with a capacity of 600 gallons per minute. Virginia Tech holds a US patent on the technology, as well as international patents in seven countries.
There has been no technology to economically dewater coal fines below 44 microns. Now this technology can be used in conjunction with the Microcel technology developed many years ago to remove ash, to re-mine the fine coal discarded to impoundments and to help companies minimize waste generation. People living in coal mining districts will see fewer and smaller slurry ponds.—Roe-Hoan Yoon
The success of the hyperbaric centrifuge is significant in that the high moisture content of fine coal waste forces coal producers to discard the waste in storage areas called waste impoundments. Estimates indicate that these impoundments nationwide hold about 2 billion tons of fine coal in abandoned ponds and an additional 500 million to 800 million tons in active ponds.
Removing moisture from very fine coal particles left over from the coal preparation process has been difficult in the past. Conventional methods such as thermal dryers or mechanical dewatering have either been too costly or have been unable to dewater ultrafine coal particles (0.1 millimeters or less). The hyperbaric centrifuge addresses those issues.
Yoon and Luttrell have also received $1 million in funding from the US Department of State to also help the Indian coal industry produce a cleaner product. And the Virginia Tech researchers anticipate another project to be funded by Coal India Limited (CIL), the largest coal company in India, with the same a similar objective. The US Department of Energy has been negotiating with CIL for this project on behalf of Virginia Tech.
However, plans to install the new technology in the United States may be stalled. During the recent economic downturn, the price of coal dropped precipitously, which may be a barrier for immediate installation of commercial-scale units at plants.
Yoon is the founding director of the Center for Advanced Separation Technology (CAST), a consortium of seven universities including Virginia Tech, West Virginia University, University of Kentucky, Montana Tech, University of Nevada at Reno, New Mexico Tech, and the University of Utah. Its goal is to develop advanced separation technologies as applied to energy resources and environmental control.
In October 2008, Yoon was elected to the National Academy of Engineering.