skid-mounted. Vacuum/pressure pump shall be mounted separately.
The control cabinet may be mounted separately or skid-mounted on
the vacuum/pressure vessel skid. Capacity of the unit shall be
approximately [_____] metric tons/hour tons/hour of ash weighing
approximately [_____] kg/cubic meter pcf. Piping sizes for ash
collection system shall be designed to fit the unit supplied. The
vacuum/pressure system shall be used where storage silo is more
than 150 m 500 feet from the boiler plant. A vacuum system should
be used for capacities of less than 45 metric tons/hour 50
tons/hour per system.
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NOTE: Where characteristics of the fly ash require
additional treatment, a water spray shall be
incorporated in the filtering unit. If not
required, the portion included in the brackets shall
be deleted. Air discharged to the atmosphere must
meet the local air pollution standards.
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c.
Pump Unit: Vacuum or vacuum/pressure pump unit shall be sized to
match system design requirements. Pump unit shall be liquid-ring
type having round rotor with curved blades rotating in an
elliptical casing. Water alternately entering and leaving the
chambers within the rotor vanes shall provide the required pumping
action. Water within the casing shall act as an air cleansing
agent and the operation and maintenance of the unit shall not be
affected by dust-laden air. Unit shall be base-mounted with
electric motor drive and all required heat exchangers, separators,
and control valves. The vacuum pump inlet piping shall be
provided with a vacuum filter unit to remove the fly ash obtained
from the economizer ash hopper. The filter unit shall include a
metal housing containing filter bags and an automatic air purge
back-washing system. [A water spray shall be incorporated into
the filtering unit.] The filtering unit shall remove all fly ash
before discharge to the atmosphere.
d.
Control Cabinet: Control cabinet for the complete operation of
the system shall be supplied and shall include all running
indicating lights as required. A push-button switch shall be
conveniently located in the boiler house to start and stop the
system. A vacuum breaker, operating automatically from a timer,
shall be provided in the bottom ash conveyor line to break the
system vacuum.
e.
Controls: Controls for a combination vacuum/pressure system shall
have a selector switch set to automatic position to start the unit
in the vacuum cycle. High-level indicator in vacuum/pressure
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
SECTION 15555A
Page 80
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