TM 5-810-15
of the vanes, fan discharge volume and pressure are
required to make available adequate NPSH for an
changed to give new system operating points. With
effective pump.
fixed speed motors, power usage only slightly
(3) Construction. The pumps will be con-
diminishes as air volume is reduced; this system will
structed in a horizontal split case configuration
operate economically if air volume is 75 percent or
with a heavy duty slurry type enclosed impeller.
above the design volume. Movement of vanes is
Replaceable shaft sleeves, suction sideplates and
non linear so they have to move more at low loads.
rear sideplates will be provided. The pump will
(3) Two speed motors, generally of speed
include oil lubricated bearings and a stuffing box
ratios of 4:3 or 3:2 with variable inlet vanes will
packing for external clean water injection.
provide economical operation down to 40 percent
(4) Pump materials. Ash sluice pumps will
of the design volume.
be designed of abrasion resistant alloys to provide
(4) Variable speed drive on ID fan, two
an acceptable life.
speed or variable speed motor on FD fan, with
c. Bottom ash pump.
variable inlet vanes on boiler outlet damper, are
(1) Application. The bottom ash pump
generally required for most efficient operation of
transfers the slurry from the bottom ash hopper dis-
heating plant boiler systems with power drive
charge to a disposal area, either dewatering bins or
requirements in excess of 10 hp. The benefits of a
ash handling ponds. The bottom ash pump is not
variable speed drive are greater when the boiler is
needed if the ash sluice pumps are designed to
operated at lower loads. A life cycle cost analysis
pump the water through the hopper discharge to
(LCCA) should be performed based on the number
the disposal system.
of hours at each load to justify the use of a variable
(2) Sizing. The bottom ash pump is most
speed drive. The variable speed gives an infinite
generally used with a surge tank downstream of the
series of fan curves from which the points of
ash hopper offering a controlled NPSH. Two 100
highest system efficiency can be chosen. Fans with
percent capacity pumps will be used to provide full
both adjustable speed capability and control inlet
backup. The capacity of the bottom ash pumps
vanes provide the most energy efficient operation.
depend on the hydraulic ash handling system
Control dampers may be provided for multiple coal
demands. The capacity must be greater than the ash
fired units with auxiliary oil firing for startup of
sluice pump capacity. The discharge head of the
boiler and adjustment of air flow. If oil is fired in a
bottom ash pump will be designed to overcome the
boiler designed for coal firing, excessive dampering
piping losses and static head to a dewatering bin.
may set up objectionable vortexing of the air
(3) Construction. The pumps will be con-
currents in the breeching and ductwork unless
structed in a horizontal, vertical split case, end
variable speed drives are used in the system.
suction back pullout configuration with a heavy
e. Fan motors. Motors will be selected for the
duty, slurry type enclosed impeller. Replaceable
maximum duty required by the fan under most
shaft sleeves, suction sideplates and rear side-plates
severe anticipated operating conditions. Motor se-
will be provided. The pump will include oil
lection is discussed in chapter 10.
lubricated bearings and a stuffing box packing for
external clear water injection.
7-13.
Hydraulic ash handling pumps.
(4) Pump materials. Bottom ash pumps will
be designed of abrasion resistant alloys to provide
a. Application. Bottom ash can be conveyed
an acceptable life.
hydraulically from a bottom ash hopper by means
d. Ash sluice water recirculation pumps.
of mechanical pumps. Hydraulic ash handling
(1) Application.
Ash
sluice
water
systems are discussed in chapter 6.
recirculation pumps are used for returning ash pond
b. Ash sluice pump.
water to a surge tank for the ash sluice pump
(1) Application. The ash sluice pump pumps
suction.
recycle sluice water through the bottom ash hopper
(2) Sizing. Two 100 percent capacity pumps
outlet to be disposed.
will be used to provide full backup. The capacity of
(2) Sizing. Two 100 percent capacity pumps
the recirculation pumps must exceed the ash sluice
will be used to provide full backup. The capacity of
pump capacities. The NPSH available will be the
the ash sluice pumps will depend on the hydraulic
atmospheric pressure of the ash pond plus the
ash handling system demands. The discharge head
depth of the impeller minus the resistance of the
of the ash sluice pump will be designed to over-
suction bell piping. The discharge head of the
come the piping losses and static head to a
recirculation pumps must overcome piping losses
dewatering bin or surge tank. A jet pump hydraulic
and the surge tank static head.
system will demand higher pressure pumps to allow
the jet pump to function properly. A surge tank is
7-13
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