05-06M
8.2 Feedwater Deaerators: Because of enhanced turndown capabilities, tray and
packed column types shall be used if there is sufficient building height
available for the deaerating section which is mounted on the deaerated water
storage tank. Where height is limited, spray-type units may be used. The
deaerated water storage tank shall be sized for 20 minutes storage from
overflow level at peak plant output requirements. Consideration should be
given to sizing the feedwater deaerator for future loads. Packaged boiler feed
pump/deaerator units should not be applied except where there are space
limitations. This is because packaged units often have pumps and piping packed
into a small space resulting in difficult access.
8.3 Boiler Feed Pump System: For most plants, the preferred arrangement is one
pump dedicated to each boiler, with cross connections allowing each pump to
provide emergency service to one other boiler. In the largest plants it may be
advantageous to provide a boiler feed header system with all pumps supplying
the common header. High efficiency multi-stage centrifugal ring section
diffuser pumps are preferred. Two-stage horizontal split case centrifugal
pumps may be applied on larger plants if the life cycle cost is less than for
multi-stage.
8.4 Pumps-General: Provide one standby pump for each service except boiler
feed systems where one pump is dedicated to each boiler. On boiler feed
service allow space for a future pump. Pumps shall operate continuously rather
than on-off. Motor kw (hp) shall be selected to be non-overloading at any
point on the pump performance (head - capacity) curve. Variable frequency
drives controlling discharge pressure may be applied on larger pumps, such as
over 7.5 hp.
8.5 Condensate Storage Tank: Shall be sized to accommodate surges without
overflow. Normally, a tank sized for 20 minutes minimum storage to overflow
at peak plant output requirements is satisfactory. The A/E must review the
condensate handling systems in all buildings to determine if any unusual
situations will require a larger condensate storage tank in the boiler plant.
Consideration should be given to sizing the tank for future loads.
8.6 Boiler Blow-off Tank:
8.6.1 The boiler blowoff tank shall be located within the boiler plant
building. Where possible, the blowoff inlet in the tank shall be at an
elevation below the elevation of the blowoff header to prevent sludge from
accumulating in the blowoff header. Where blowoff tanks cannot be installed
below the header, provide water flushing system to clean trapped horizontal
blowdown lines and provide a valved drain on the blowdown line to allow
draining the boilers.
8.6.2 The boiler blowoff tank size, connections, design and construction
requirements shall be in accordance with the recommendations contained in the
Rules and Recommendations for the Design and Construction of Boiler Blowoff
Systems, published by the National Board of Boiler and Pressure Vessel
Inspectors, Columbus, Ohio.
8.6.3 Blowoff tank volume shall be twice the volume of water contained in a
four inch blowdown of the largest boiler.
8.6.4 Provide automatic temperature control system which mixes city water with
the blowoff tank discharge water to limit the temperature of the water going
to the sewer to 60C (140F).
roller and spring-type hangers, anchors, trapezes, seismic bracing and special
supports. Detail the anchor designs and seismic bracing designs. Detail the
connections to the building structure when standard pipe hanger components
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