TM 5-810-15
reuse. The ash ponds which act as a solid liquid
6-3. Bottom ash hydraulic conveying systems.
separator must have a considerable area since
a. General. Hydraulic conveying systems are
retention time is the only means to allow ash to
generally used for only bottom ash handling sys-
settle and separate from the conveying water. If fly
tems. Bottom ash is collected in a water impounded
ash is conveyed to the ash pond, the pond must be
refractory lined steel hopper, which will be sized to
greatly enlarged because of the extremely slow
store a minimum of twelve hours production of ash
settling rate.
under the worst coal conditions at maximum
c. Dewatering bins. Dewatering bins receive the
continuous boiler steam output rating. The water
ash water slurry and drain the water from the
impounded bottom ash hopper allows ash to fall
accumulated ash. Dewatering bins, like the ash
through a clinker grinder or crusher where the ash
ponds, can work in a closed system or an open
is ground to a predetermined size prior to entry
system where water is allowed to drain to waste. In
into a hydraulic ejector or in some instances to
most cases the discharge of water is not allowed by
material handling pumps. The ash is sluiced from
regulation, so a closed recycling dewatering system
the plant to ash ponds or to dewatering bins. Figure
will be discussed. After passing through the bottom
6-2 shows a typical sluice conveyor arrangement.
ash hopper the ash is pumped to two dewatering
The ash slurry is conveyed by a system of ash sluice
bins. While one bit receives ash slurry the other bin
centrifugal pumps. Ash handling pumps are
is draining or decanting to separate the solids and
discussed in paragraph 7-13. Most hydraulic
liquids. The dewatered bottom ash is discharged
ejectors are jet pumps requiring high pressure ash
from the bin to trucks or railcars as shown in figure
sluice centrifugal pumps to supply the water that is
6-4. Each dewatering bin will be sized for at least
used to convey the ash to the storage area. This
36 hour storage for a total of 72 hours storage for
arrangement eliminates the need for a downstream
long weekends when trucks or rail service is not
transfer tank and the use of pumps to convey the
available. The dewatering bins will be designed
abrasive ash slurry as shown in figure 6-3. The high
with a 30-degree angle of repose for the ash at the
pressure ash sluice pumps are also used for hopper
top of the bins. The dewatering bins will be
washdown nozzles. Low pressure ash sluice
designed to hold the determined ash capacity at an
centrifugal pumps supply water for bottom ash
ash/water density of 62.4 pounds per cubic foot
hopper furnace sealing and for coaling the refrac-
(pcf) and be designed structurally for an ash/water
tory lined hoppers, and inspection windows.
density of 110 pcf. From the dewatering bins which
b. Ash ponds. The ash ponds receive the ash
act as the solid/liquid separator, the decanted water
slurry from the bottom ash hopper. Ash ponds must
with some entrained ash fines flows by gravity into
be sealed to prevent seepage into ground water.
a settling tank for the second stage of separating
Ash ponds can be constructed in a manner to allow
the ash from the sluicing water. The settling tank
the water to be stored and returned to the plant for
6-2
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