2.5.4
In-Bed Tube Surface (AFB Designs)
In-bed tube surface shall be provided as required to achieve steam
generation or superheat temperature as defined in the data sheets. The
in-bed tubes shall be completely clear of bed material when the fluid bed
(at the bed weight specified by the manufacturer at boiler MCR) is slumped.
Alternatively, the manufacturer shall ensure that the tubes are protected
from overheating due to contact with a slumped bed and/or maintenance
problems due to moisture in a slumped bed.
2.5.5
Coal and Sorbent Feed Systems
All equipment required to provide a boiler feed system to convey coal and
sorbent to the boiler injection inlets shall be furnished. All components
of these systems shall be sized to provide flow of fuel and sorbent based
on MCR condition in the boiler and the design coal and sorbent specified.
The system shall be designed to minimize the segregation or generation of
fines.
2.5.5.1
AFB Coal Feed System
Coal feed systems for AFB may be either pneumatic under bed or spreader
stoker over-bed. For pneumatic under-bed feed systems, a feed point every
1.7 to 2.3 square meters 18 to 24 square feet shall be provided. The
system shall consist of a complete integrated system including weigh belt
feeder, lock hoppers, and/or other components necessary for the pneumatic
fuel injection system. Rotary type feeders shall not be used as the
primary pressure sealing device. The conveying air shall be considered
part of the combustion air. Coal feed shall be crushed to approximately
6.4 mm 1/4 inch and shall be capable of being used with fluidizing
velocities ranging from 1.2 to 3.7 m/second 4 to 12 fps. For these
systems, sorbent may be mixed with the coal in the appropriate proportion
and fed with the fuel. However, a separate sorbent feed system is
acceptable. Over-bed feed systems shall be designed to provide even
distribution over the entire bed. Heavy duty standard production
spreader/injector/feeders shall be provided for dispersing the specified
fuels into the boiler. The spreader/feeders shall be the chain type or
equal, as approved by the Contracting Officer. The feeder portion shall be
of the chain type with infinitely adjustable feed rate from 0 to 100
percent of rated capacity. The spreaders shall consist of adjustable
rotating paddles on a shaft designed to disperse the specified coals into
the boiler at the required locations and to minimize side throw into
adjacent bed compartments which may not be in operation. The spreaders
shall be capable of rotating at variable rates of speed. The
spreader/feeders shall have overfire capability to the extent required by
the design for use in compensating for a spreader/feeder out of service.
For spreader stoker coal feed systems, sorbent feed shall be by separate
systems. These systems shall consist of a method to feed the correct
proportion of sorbent over the load range to keep the sulfur oxides
emission in compliance. These systems shall feed over-bed or in-bed and
may be gravity, pneumatic, or a combination. Under-bed coal feed systems
shall be provided with coal dryers unless approved.
2.5.5.2
CFB Coal Feed Systems
For CFB systems, feed systems capable of providing the appropriate coal
feed over the load range shall be provided. These systems shall include
weigh belt feeders, rotary feeders, screw conveyors or air swept feeders,
or gravity-feed metered by weigh belt. Rotary type feeders shall not be
SECTION 15559A
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