regulations, as specified. The bed temperature shall be controlled within
the appropriate range, normally 815 to 900 degrees C 1500 to 1650 degrees F
to enhance sulfur capture, inhibit the formation of nitrogen oxides,
enhance combustion efficiency, and limit carbon monoxide formation. In
AFBs, generally all the air required for combustion shall be introduced
through the nozzles in the distribution plate in order to reduce the
potential of forming reducing conditions within the bed that could cause
severe corrosion of in-bed surfaces. The use of over-fire air in
applications where it is needed to complete the burnout of carbon monoxide
and the combustion of fines in the freeboard shall require the approval of
the Contracting Officer who shall be satisfied that reducing conditions
will not exist. CFB boilers may introduce as much as 40 to 50 percent of
the combustion air as secondary air in one or more stages at various
locations above the distribution plate. The boiler and boiler accessories
shall be specifically designed to operate with the specified fuel and
sorbent. The boilers shall be complete with the required crushers, dryers,
coal and sorbent handling systems, burners, ignitors, air preheater,
economizer, soot blowers, boiler controls and instrumentation, furnace ash
handling system, draft systems, and superheater, where required.
2.5.1
General
The design, materials, and construction of equipment furnished shall
conform to the applicable requirements of ASME BPVC SEC I and NFPA 8501.
The Contractor shall furnish the Manufacturer's Data Report required by
ASME BPVC SEC I certified by the Authorized Inspector located in the
manufacturer's shop. Full provision shall be made so that each component
can expand and contract under the operating cycle of temperatures without
damage to itself or to any adjoining component, and without the leakage of
any contained fluid outwards, or of air either inwards or outwards. The
design of the unit shall accommodate thermal movement without side effects
such as tearing, buckling, distortion, or vibration. The design of the
unit shall prevent destructive vibration during normal operation. The
furnace shall be of the balanced draft type. The ducts and equipment from
the forced draft fan, including the fluidized bed plenums, shall be
designed for pressures in accordance with NFPA 8501. Access and
observation doors shall be provided to permit access to compartments and
the observation of critical portions of the furnace and fluid bed. Door
frames shall be securely anchored. Doors shall have a suitable durable
gasket, a device which when closed will force the door to an air-or
gas-tight seal, and an interior design which will minimize erosion or
deterioration of the inner surface from exposure to the internal conditions
at that point. Refractory shall be an integral part of the door. Access
doors shall be the manufacturer's standard that approaches in size 450 mm
18 inch wide by 400 mm 16 inch high. All observation ports and lance doors
shall be provided with sealing and aspirating air facilities. The
convection pass velocity shall not be greater than 15.2 m/second 50 fps.
The convection pass velocity shall be based on maximum guaranteed excess
air at Maximum Continuous Rating (MCR) plus five percentage points (i.e.,
if excess air is 20 percent, the convection pass velocity shall be based on
25 percent excess air). In CFB designs where convection surface exists in
the high solids circulation passes, a velocity not greater than 4.6
m/second 15 fps is permitted between the tubes, based on 25 percent excess
air. The design of the equipment shall be such that the interior surfaces
of all water-filled pressure parts and superheater sections shall be
capable of being chemically cleaned. Fill and drain connections shall be
furnished as required. Each header shall be drainable. The secondary air
and flue gas system resistance curves shall be provided by the Contractor.
SECTION 15559A
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