Geology Reference
In-Depth Information
feasibility is assessed for the project, and the marketability of the fine coal
product (i.e., potential buyers, final destination for the fine coal product, means
of transport) is investigated.
The excavation of the slurry material from the impoundment and delivery
to the fine coal recovery plant is the most critical consideration in the
development of a fine coal recovery project. Regardless of the simplicity or
sophistication in the design of the fine coal recovery plant, the slurry delivered
to the system requires a consistent feed rate (tons per hour) and percentage of
solids concentration (weight of slurry and water) to maintain efficiency.
Three methods for coal slurry removal and delivery systems are used:
conventional excavation methods; stationary pump and wash-down systems;
and dredge operations. Conventional excavation and earth-moving equipment
includes earth-mover pans, excavators, backhoes, drag-lines, front-end loaders,
dump trucks, and farm tractors equipped with discs or harrows. The stationary
pump and wash-down system agitates, washes, and keeps in suspension the
slurry material within the area around and directed to the suction of the floating
agitator-feed pump. Dredging uses a floating pump with a movable suction
device. It excavates along a side-to-side arcing or slewing motion with a
positive forward movement, cutting materials from beneath the surface of the
water and creating a slurry to be delivered to the pump suction. During removal
of the fine coal, the site is vulnerable to storm water runoff and to slumping of
surrounding slopes, and adequate diversion structures must be used to route
excess water from the facility.
The design of a fine coal recovery plant is the same as that in conventional
coal preparation plants and typically processes the slurry material that is smaller
than 3/8 inch. The recovery plant includes sumps, pumps, vibrating screens,
sieve bends, cyclones, spirals, flotation cells or columns, centrifuges,
conveyors, and thickeners—each unit system being of sufficient size and
capacity to handle a specific feed rate and the size characteristics of the slurry
material. The refuse from a remining operation can be handled with a variety of
methods that are site specific because each impoundment has its own design,
site conditions, and slurry materials. Methods include those outlined in this
chapter such as underground injection, thickening of slurry, multiple cell
construction deposition within the same impounding structure, a combination of
these listed, or simply disposing of the refuse in a separate part of the
impoundment being remined.
Recovery of fine coal from slurry impoundments is an established practice.
The committee concludes that as advances are made in the use of low value
coal or coal water slurry, remining of slurry impoundments can be an attractive
source for fuel supply.
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