Height of silo storage shall not be more than twice the diameter. Provide
a minimum of one meter 3 feet of freeboard above the ash level. Design of
support steel shall be approved by the ash system supplier. Design silo in
accordance with the Uniform Building Code. The design shall take into
account seismic load, wind load, snow load, equipment loads and an ash bulk
density of 1120 kg per cubic meter 70 pounds per cubic foot. Ash silo
support shall be free standing and shall be of sufficient height to allow
gravity discharge of ash through the rotary ash conditioner to a [truck]
[railroad car].
Provide access to the stair tower with intermediate
platforms at 3.66 meters 12 feet intervals which access the ash conditioner
level, silo floor level and silo roof level. Platforms from adjacent
structures with stair access may be provided in lieu of the stair tower,
but ladders with safety cages and access platforms must be additionally
provided. Provide ladder with stainless steel fall prevention device on
inside of silo from manhole in top of silo to bottom of silo. [Provide
silo roof enclosure and unloader room enclosure each with a single one by 2
meters 3 by 7 foot access door, [_____] by [_____] meter foot double door,
two windows, ventilator, [heater], insulated metal panel siding to match
boiler plant walls and electrical lighting and convenience receptacles.
Unloader room enclosure shall have reinforced concrete floor.]
2.11.5.1
Construction
Construct silo of steel with refractory lining or of concrete staves with
steel hoops and concrete roof. Roof accessories shall include manhole,
relief valve and vent filter. Bottom of silo shall be [conical, sloped a
minimum of 45 degrees.] [flat with a steel plate feeding hopper in bottom
of silo to funnel the ash into the inlet of the rotary vane feeder.]
Provide hopper with expansion joints and sufficient poke holes with cover
or cap.
2.11.5.2
Concrete Stave Silo
Construct concrete stave silo of either lightweight solid or hollow precast
concrete staves with post-tensioned steel reinforcing hoops around the
exterior. Mechanically measure and mix materials in concrete staves.
Vibrate and shape staves under pressure and steam or air cure.
a.
Wall Coating: Coat interior surface with a three-step process of
a brush coat, scratch coat, and finish trowel coat of a mixture of
fine sand and portland cement in accordance with silo
manufacturer's recommendations. Apply each coat successively to
produce a smooth interior surface. Work mixture into the formed
horizontal and vertical grooves to permanently interlock the
concrete staves. Brush coat the exterior surface with a double
application of waterproof mixture. Mixture shall include a
chemical agent for waterproofing and portland cement, sand, and
water. Work coating into joints and over the steel reinforcing
hoops to form a weatherproof protective coating.
b.
Steel Reinforcing Hoops: Galvanized steel rods not less than 14 mm
9/16 inch in diameter with not less than 16 mm 5/8 inch rolled
threads. Join hoop ends together with nuts and heavy malleable
galvanized iron lugs or heavy duty galvanized steel lugs to a
close tolerance for a tight fit. Electrogalvanize rods, nuts, and
lugs to ensure adequate protection against corrosion.
Rods shall
be high quality, metallurgically sound steel with tensile strength
not less than 448 MPa 65,000 pounds per square inch (psi), yield
point not less than 276 MPa 40,000 psi, and a minimum elongation
SECTION 15502N
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