vessel shall actuate necessary controls to cut off the vacuum
gathering system and pressurize the vessel for pressure discharge
of collected material. A low-pressure switch in the control panel
shall sense the pressure drop in conveying pressure and shall
return the unit to vacuum operation. The unit shall operate
continuously in this manner until manually shut down. Setting
selector switch in manual position shall shut the unit down after
filling. Discharge shall then be accomplished by pressing the
manual discharge button. A high vacuum switch with time delay
shall be provided to shut the system down automatically in the
event none of the inlet valves are actuated. Switches and
controls shall be heavy-duty type in accordance with NEMA ICS 1.
f.
Automatic Air Valve: Automatic air valve shall be provided at
economizer or air preheater ash inlet hopper discharge slide gate
to allow air into system without causing a vacuum within the
boiler ash hopper. Slide gate shall be provided as part of the
ash system and shall be manually-operated and interlocked to
actuate the automatic air inlet valve.
2.30.1.5
Ash Silo
The ash storage silo shall have a capacity of not less than [_____] metric
tons tons of ash and fly ash considered to have an average weight of
[_____] kg/cubic meter pcf. This capacity shall be based on a minimum of
24 hours [60 hours if ash cannot be removed on weekends]. The silo shall
be made of welded steel with a cone bottom for truck filling and shall be
supported on a structural steel tower. All elements exposed to the
exterior shall be designed for wind loads of [_____] kg/square meter psf.
A 4.3 m 14 foot clearance shall be provided under the hopper outlet fitting
or appurtenance. Silo shall be provided with steel ladder and safety cage
from the ground level to roof, steel ladder inside storage bin, and an
angle railing around the roof perimeter. Minimum plate thickness shall be
6.4 mm 1/4 inch. Silo shall be complete with all accessories required for
an operable installation including, but not limited to, high ash level
detector, roof manhole, pressure and relief valve, and other roof openings,
as necessary. Interior coating shall be coal-tar epoxy conforming to SSPC
Paint 16.
a.
Ash storage silo for vacuum system shall be provided with two
stage separators [and a tertiary bag filter]. The primary
receiver shall be cylindrical and shall be constructed entirely of
sectional steel or cast plates suitable for this special service.
The receiver shall be not less than 900 mm 3 feet in diameter.
Flanges and bolts shall be on the outside, and the impact of ash
shall be directed against heavy iron wear plates of
abrasive-resistant alloy. The receiver shall be provided with an
air-tight discharge passage not less than 450 mm 18 inches in
diameter for free flow of clinkers. The receiver shall have means
for positive, periodic, and automatic operation in dumping its
entire contents into the silo; in addition, the system shall be so
designed that all suction is positively shut off from the receiver
during its dumping period so that no dust can be sucked out
through the exhaust while the discharge of the receiver is open or
opening. The air from the primary receiver shall enter an
external secondary separator which shall remove 90 percent of the
dust not collected by the primary receiver. The combined
efficiency of the primary and external secondary separators [and
tertiary bag filter] shall be not less than 98 percent. The
SECTION 15559A
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