What began as a small in-house laboratory experiment to find a way to use discarded coal products called "fines" has now led to a full-scale demonstration that can boost coal operator profits, reduce waste at their plants, and recover valuable energy sources.
In full-scale tests conducted by CQ of Homer City, Pennsylvania, the GranuFlow process - which was developed and patented by scientists at the Office of Fossil Energy's National Energy Technology Laboratory (NETL) - has been shown to recover and clean a significant portion of coal fines.
Although other methods are available to capture coal fines, these processes become less efficient as particle sizes decrease. The fines captured through these processes also have a high moisture content, which can reduce their heating value and cause materials handling problems, such as sticking in bins and freezing in winter.
The captured fines can be thermally dried, but the process is expensive and energy intensive; moreover, a significant proportion of thermally dried fines can literally blow away with the wind.
In the GranuFlow process, a binder is added to fine-sized coal slurries to make the coal particles stick together or "agglomerate." The agglomerated fines are more efficiently captured during subsequent cleaning and dewatering, which reduces the size and number of impoundments.
The binder is applied in such a way that cake moisture decreases, possibly eliminating the need for thermal dryers, and the smallest particles are agglomerated, making the filter cake virtually dust-free.
NETL received patents for the process in 1990 and 1995.
Early research and scale-up demonstrations were funded by the US Energy Department's Office of Fossil Energy, while the most recent, full-scale demonstrations were conducted under the so-called Mining Industries of the Future Program within the DOE's Office of Energy Efficiency and Renewable Energy.