Alternatives for Future Coal Waste Disposal - Coal Waste Impoundments: Risks, Responses, and Alternatives - page 120

SIDEBAR 7.2 LEVELS OF COAL PREPARATION
There are five levels of coal preparation.
Level 0 —The coal is not cleaned, and run-of-mine coal is shipped
directly to the customer.
Level 1 —The run-of-mine coal is crushed to below a maximum size,
and undesirable constituents are removed. The product of Level 1
preparation is commonly termed “raw coal.”
Level 2— The product from Level 1 is sized as coarse and fine coal.
The coarse coal is cleaned to remove impurities; the fine material is
added to the cleaned coarse coal or marketed as a separate product.
Level 3— The fine product from Level 2 is sized into two products:
intermediate and fine. The intermediate product is cleaned to remove
impurities. The fine material is added to the cleaned product or marketed
separately.
Level 4— Cleaning is extended to the fine material from Level 3.
SOURCE: BTU Magazine, 1982.
size and amount of fine particles produced), and the local geology (e.g.,
abundant clay in adjacent strata can produce a refuse stream that is more
difficult to dewater).
It has been nearly 20 years since dry coal preparation methods were used
in the U.S. coal industry. According to Couch (1991), in the early 1960s, dry
coal cleaning accounted for about 10 percent of all coal that was cleaned, but
since then it has dropped to less than 1 percent. Dry cleaning is usually
accomplished with “air jigs” or “air tables” using oscillating and fluidized bed
principles. Most of the dry methods require closely sized and moisture-free
feed. A combination of factors associated with the dry methods—particle size,
dust, transport, health and safety, noise, and the better performance of wet
processes—have contributed to the near abandonment of dry coal cleaning
processes in recent years. The increased use of water for dust control in
underground mines, and the increased efficiency of wet cleaning methods have
continued the sharp decline in the use of dry cleaning methods at the mines.
However, dry coal preparation methods, which do not create the same disposal
challenges as slurry waste, can be effective in areas where the water supply is
restricted.
Currently, most coal preparation plants recover fine coal only from the size
fraction greater than 100 mesh (150 micrometer). Typically, this is done with
water-only cyclones, spirals, or both for 16 × 100 mesh (1.0 × 150 micrometer)
material. Particles smaller than 100 mesh (150 micrometer)