Because there has been no economically viable way to remove water from ultrafine coal slurries, the ultrafine particles that are the residue of the coal-cleaning process have traditionally been discarded.
Now, Peter Bethell, director of coal preparation at Arch Coal, claims that a hyperbaric centrifuge developed at Virginia Tech has reduced the moisture content of ultrafine coal to less than 20 per cent, transforming it to a saleable product.
Bethell said: ‘The results were very favourable. This is material we would have had to discard; therefore, such success would mean reduced refuse in the environment and improved economic returns for the company.’
Decanter Machine of Johnson City, Tennessee, built the prototype unit that was used at Mingo Logan Coal Company’s Cardinal Preparation Plant, a subsidiary of Arch Coal.
Roe-Hoan Yoon, a professor of mining and mineral engineering at Virginia Tech, who developed the centrifuge along with his colleagues, said: ‘This technology can be used to remove ash, to re-mine the fine coal discarded to impoundments and to help companies minimise waste generation.
Wally Schultz, executive vice-president of Decanter Machine, added: ‘The prototype unit was trailer-mounted and capable of processing approximately 30 gallons per minute of feed slurry.’
However, plans to install the new technology in the US may be delayed. During the recent economic downturn, the price of coal dropped steeply, which may be a barrier for immediate installation of commercial-scale units at plants.
But Bethall added: ‘When the market improves, we will probably be able to justify spending the capital to install full-scale units.’