Alternatives for Future Coal Waste Disposal - Coal Waste Impoundments: Risks, Responses, and Alternatives - page 144

SIDEBAR 7.6 POND RECOVERY FACILITY
Ginger Hill is a coal slurry recovery facility in western Pennsylvania
that produces approximately 300,000 tons per year of synthetic fuel
(Akers et al., 2001). A dredge is used to extract the fines from the
impoundment. The slurry is pumped to a surge tank and then into the
cleaning plant. The coal is classified at 150 mesh (106 micrometer) using
15-inch classifying cyclones. Particles larger than 150 mesh (106
micrometer) are cleaned using water-only cyclones and spirals, with an
additional classification of the fine coal product by a two-stage Vari sieve.
Material smaller than 150 mesh (106 micrometer) material is classified
using a 6-inch classifying cyclone at 270 mesh (53 micrometers). The 150
x 270 mesh (106 x 53 micrometer) fraction is cleaned by column flotation.
After cleaning, all clean coal size fractions are mixed and dewatered by
two 40-inch decanter screen-bowl centrifuges. The clean fines are
pelletized using COVOL binder.
amounts of coal refuse larger than 28 mesh (600 micrometer) with
recoverable energy value. As processing technologies and the capacity of
dewatering equipment have improved, the proportion of particles smaller than
100 mesh (150 micrometer) in slurry refuse in impoundments has increased. In
many instances, the finer slurry materials being disposed of today with less
recoverable and marketable coal can close off access to the more amenable,
profitable, and recoverable slurry ( Sidebar 7.1 ).
If an impoundment contains at least 1 million tons of in-situ slurry, a
recovery rate of at least 30 percent of a marketable fine coal product (300,000
tons) from the slurry could prove to be a profitable venture. Fine coal from is
recovered from an impoundment through several stages: investigation
(preliminary site investigation, sampling and analysis of the slurry and
embankment materials, and engineering design and economic evaluation),
excavation and transport, and fine coal recovery.
The preliminary site investigation involves inspecting the impoundment
and reviewing maps and any other available information. The sampling and
analysis of slurry and embankment materials are the most critical and most
expensive phase of investigation. The preliminary sampling program requires
approximately three samples from each embankment and a detailed core
sampling plan throughout the basin. Samples are analyzed for size distribution,
float and sink characteristics, froth flotation, and percentage of moisture, ash,
sulfur, and energy value per pound. In addition to these standard analyses, it
may be advantageous to determine whether other materials, such as magnetite,
may be recovered from the slurry. During engineering design and economic
evaluation—the final phase of investigation—the economic