ing was committed prior to 1991; funding since that time has declined to about $5 million annually (OFE, 2001a). DOE’s program in coal preparation devoted a major effort to the deep-cleaning process through the early 1980s, but the focus on postcombustion technologies for pollution control and the shifts in the coal market toward low-cost modest-quality fuel supplies shifted DOE’s emphasis in the late 1980s to recovery efficiency objectives. DOE’s program has contributed to the development of advanced cleaning processes for demineralization, including flotation, recovery of the fine particle fraction of pulverized coal, coal dewatering, and coal processing system simulation. At one point, interest developed in the cleaned, ultrafine fraction of pulverized coal that, if suspended in air or other fluids, could be used directly—for instance, for injection into turbines. This application has not been pursued, because natural gas (or coal gas) is now the preferred fuel.
DOE’s current program has declined to a relatively low priority “maintenance” level, with interest and support from the coal industry in continuing studies of cleaning and material-handling technologies as a means of training and educating qualified technical people to support the industry.
DOE’s program has contributed substantially since the 1970s to improving knowledge about advanced preparative treatment of coal. The accompanying process development is estimated to add substantially, however, to the cost of untreated coal.
The work also resulted in the commercialization of an advanced (Microcel1) flotation column and the precommercial testing of an air-sparged hydrocyclone for flotation separation. A continuous separation technology involving a packed separation column system has also been tested.
To improve the separation and capture of pulverized coal fines, the Granuflow process has been developed and licensed for commercialization. More exotic methods for beneficiation have reached development and testing, including the tribo-electric separation process, which was tested at (formerly) New England Electric’s Salem Harbor and Brayton Point plants, and micronized-magnetite cyclone cleaning for fine pulverized coal. In the current market, however, large-volume sales are directed toward low-cost coals; the added costs of cleaning are not justified. The existing technology for coal cleaning is sufficient to supply requirements for certain Eastern coals to users without additional costs of deep cleaning.
Advanced dewatering technologies for the fine particle fraction are being investigated as part of the Solid Fuels and Feedstocks Grand Challenge Program, with a target cost of $1 per ton of coal treated to improve the marketability of the fine fraction.
While the advanced technologies have reached at least pilot scale development, they have proven to be expensive alternatives to conventional practice. Discussions with two major coal suppliers and FE representatives suggest that the FE program has had only a marginal influence on coal cleaning technology as practiced today.
Coal cleaning generally is not applied to Western low-sulfur coal but remains an element in some Eastern coal processing. Perhaps equally important is DOE’s role in supporting coal preparation technology development in academia, which helps to train technical people for the industry.
Since coal cleaning and beneficiation add to the costs of pulverized coal supplies, there evidently is no current economic benefit for the application of the advanced technologies developed by DOE. However, as natural gas and oil prices increase, greater demand for deep-cleaned coal supplies may increase, and the use of DOE’s technology options may expand. However, the present high-volume market for coal focuses mainly on a low-cost supply. The market for high-quality or washed coal fills niches in the marketplace but does not represent a large segment by volume (mass).
The benefits matrix for coal preparation (Table F-1) indicates that economic benefits exist in the options and knowledge categories, but in the near term, the application of available optional technologies is not anticipated. The benefits in the knowledge category have led to spin-off applications of the Microcel flotation column for mineral recovery operations—for example, applications to copper, kaolin, and graphite processing. The Microcel column technology has been installed in about 70 plants worldwide for processing coal and other mineral resources. Other spin-off s of the DOE technology include mineral processing, application of the air-sparged hydrocyclone to fiber de-inking, and copper ore processing using the continuous packed column separator. The tribo-electric separator has been applied to unburned coal separation from fly ash used in cement production, as well as waste plastic recycling.
With increased environmental concerns about the collection and sequestration of ash, minerals, and sulfur from coal, deep coal cleaning may one day be used to separate waste material prior to combustion. This may become particularly important for removal and sequestration of heavy metals, including mercury. To account for this contingency, industry continues to support at least a minimal academic-style program in the coal preparation area.
Microcel is a novel froth flotation column cell for cleaning finely ground coal. The Microcel process uses microbubbles in a water-filled flotation column to separate mineral impurities from coal. It is particularly effective in cleaning very fine coal particles, typically smaller than grains of sand, that are often discarded in coal waste ponds. The University Coal Research Grant to Virginia Polytechnic Institute licensed it to Mineral Technologies International, Inc. There are 70 to 80 units installed worldwide.