Project Demonstrates Removal of Water from Ultrafine Coal Waste
A novel technology that could help release some currently unusable energy in an estimated 2 billion tons of coal waste in the U.S. has been demonstrated by a Department of Energy–supported project, the federal body said on Tuesday.
The DOE said that a full-scale test of the so-called “advanced hyperbaric centrifuge technology” at a Jim Walter Resources Inc. coal-cleaning plant in Alabama resulted in the “successful reduction of moisture from ultrafine coal waste.” The test conducted by the DOE’s National Energy Technology Laboratory (NETL), the Virginia Polytechnic Institute, and the State University (Virginia Tech) reportedly used the patented process to effectively remove water from very fine coal “slurries,” or a mixture of waste coal “fines” and water.
According to the DOE, U.S. coal producers each year discard large amounts of moisture-laden fines (small, coarse coal particles) that are typically deposited in containment ponds or impoundments as a slurry. “In some cases the water is evaporated to stabilize the deposits before they are recovered in surface reclamation; in others, the waste coal—which represents a potentially useful energy resource—is not recovered for a variety of technological, operational, market, or other reasons,” the DOE said.
The technology is aimed at separating the fine coal particles from water, allowing their recovery for energy while simultaneously cleaning up the environment and providing jobs in the coal-cleaning industry. “The technology represents a major step forward in clean coal separation and could pave the way not only for the use of billions of tons of waste, but also the 70 million to 90 million tons of fine coal refuse added to slurry impoundments by the U.S. coal industry each year,” the DOE said.
Developed and patented by researchers at Virginia Tech, the hyperbaric centrifuge technology was subsequently sublicensed to Decanter Machine Inc., of Johnson City, Tenn., which built the initial prototype unit that successfully dewatered fine coal to a level of 13% to 19% moisture at a rate of 30 gallons per minute. Coal recovery from the sludge was reportedly greater than 97%.
Decanter Machine then constructed a full-scale commercial unit capable of handling 600 gallons of slurry per minute. Jim Walter Resources successfully tested the full-scale commercial unit at the greater rate, again dewatering the ultrafine coal to less than 20% moisture by applying a combination of air pressure and centrifugal force to significantly reduce moisture.
“The success of the hyperbaric centrifuge has addressed a variety of issues associated with the coal-cleaning process,” the DOE said. “In the past, removing moisture from very fine coal particles had been difficult. Methods typically used, such as thermal dryers or mechanical dewatering, had either proven too costly or had been unable to dewater ultrafine coal particles of 0.1 millimeters or less.”