|
The Washplant Feed Conveyor discharges to a surge bin, with water added at the transfer point. Feeders draw from
<br />the surge bin to feed the coal to a series of screens, heavy-media cyclones (using a slurry of magnetite and water to
<br />separate the coal from the heavier refuse material), classifying cyclones, wash screens, and centrifuges, producing both
<br />a coarse and fine coal product, which are combined and discharge to the Overland Conveyor. Coal refuse is separated
<br />from the coal stream in the cyclones, with the coarse refuse passing over screens to drain and then to the Coal Refuse
<br />Conveyor, and the fine refuse being transferred to the Thickener to reduce water content. The Washplant will require
<br />approximately 600 gpm of make-up water, to address losses to the coal product, coarse refuse, and fine refuse streams
<br />(note that most of the water from the fine refuse stream is recovered and recycled to the Mine water supply system,
<br />which include the Washplant feed water). The coal preparation circuit also includes the magnetite recovery and
<br />recycling system, and a water filtration and recycle system, to minimize water use requirements. The coal preparation
<br />equipment, along with associated chute-work, and control and monitoring systems, are housed in the Washplant
<br />Building, a steel frame building with steel siding and roof (55 x 125 x 80 feet high), which sets directly over the
<br />Overland Conveyor. The building sets on a reinforced concrete slab (58 x 128 x 1 foot thick).
<br />The Coal Refuse Conveyor (48-inch belt w/500 tph capacity), transfers coarse coal refuse from the Washplant to a
<br />Refuse Bin. The Refuse Bin is used to load trucks, which haul the coal refuse material to the existing permitted Coal
<br />Refuse Disposal area. The Coal Refuse Conveyor is designed to handle current requirements of 500 tph, as well as
<br />possible future system expansion. The Refuse Conveyor is supported by two steel support bents, and utilizes the
<br />typical conveyor construction. The conveyor bents set on reinforced concrete caissons, as previously described. The
<br />Refuse Bin is a steel frame building (30 x 30 x 50 feet high) with steel siding and roof which supports a 200-ton pre-
<br />fabricated steel surge bin and contains minor chute-work and a dust collection system. The Refuse Bin sets on a
<br />reinforced concrete slab floor.
<br />The Washplant II Thickener, which is used to partially dewater the fine coal refuse, is a reinforced concrete tank
<br />approximately 50 feet in diameter, and 12 feet high. A flocculating agent is introduced into the tank, and ahigh-
<br />efficiency underflow system mixes the flocculant with the fine refuse stream, causing the refuse particles to
<br />agglomerate and settle from suspension. The decant water discharges through a filter and is recycled to the Washplant.
<br />The fine refuse slurry normally discharges through an 1,800-foot, 6-inch diameter discharge line connecting to an 8-
<br />inch drop-borehole and underground piping system, which carries the slurry to an area of sealed underground mine
<br />workings. Underground, water decants from the fine refuse slurry and flows downgradient to a sump where a pumping
<br />system is used to recover and recycle the water. In order to address emergency mine dewatering requirements, slurry
<br />may be temporarily diverted to an incised basin within the Area 1 Pit permitted mine refuse disposal area, with decant
<br />of clarified water to the Area 1 Pit Mine Water Storage Reservoir. Coal fines that accumulate in this temporary basin
<br />will be allowed to dry-out and will then be transferred to the permanent Coal Refuse Disposal area.
<br />When the new Washplant and Thickener were installed, a new Thickener Overflow Sump was constructed to contain
<br />minor amounts of washdown water and to serve as a temporary catch basin for the contents of the Thickener, if
<br />required for maintenance or under upset conditions. The Thickener Overflow Sump is located between the Refuse
<br />Conveyor and Sedimentation Pond D. The Thickener Sump is partially incised, incorporates a compacted clay liner to
<br />minimize seepage, and is sized to fully contain the contents of the Washplant II Thickener (150,000 gallons) plus
<br />minor amounts of washdown water and incident precipitation for the design event. Impoundment design, operation,
<br />and maintenance information for the Thickener is provided in Exhibit 8X. Given that the potential for both the
<br />Washplant I and Washplant II Thickeners to experience an upset or require maintenance at the same time is negligible,
<br />with completion of the Washplant II Thickener Overflow Sump, the Washplant I Thickener Overflow Sump was
<br />decommissioned, filled-in and replaced by a discharge pipe from the Washplant I Thickener to the new Washplant II
<br />Thickener Overflow Sump. As an incised and closed basin (ie: no outlet) the only potential inputs to the Sump are
<br />thickener overflow, washdown water, or minor incident precipitation, which are subsequently pumped back into the
<br />system by a portable floating pump installation. The 4-inch thickener overflow line has been extended to the new
<br />Thickener Overflow Sump (4,800 feet), allowing overflow from either thickener to be controlled by valves and routed
<br />to the Sump. Water level in the Sump is monitored and managed as part of the ongoing Washplant operations.
<br />Given the power and system control requirements for the Washplant, an associated Motor Control Center
<br />• (MCC)/Office Building was constructed immediately adjacent to the Washplant. The MCC/Office Building houses
<br />electrical, control, and monitoring equipment for the Washplant and includes office space.
<br />MR08-230 2.05-32.3 11/20/08
<br />
|