area and shall extend not less than 70 percent up the hopper height.
Provide modular hopper heaters having a flexible heating face to conform to
the irregularities of the hopper surface to provide maximum heat transfer.
Where modular heaters do not fit, provide tape heaters or flexible blanket
heaters. Heaters shall be maximum 0.0046 W/mm2 3 W/in2 of resistance
element, with a minimum 6 parallel resistance path, rated at 2.7 kw/m2 250
W/ft2 but designed to operate at 2.2 kW/m2 200 W/ft2. Use Series 600
stainless steel alloy or nickel-chrome heating elements and encase in a
minimum 20 Gage aluminum or aluminized-steel mounting pan or casing.
Provide heaters with attached metal labels listing the heater's wattage and
voltage.
2.5.4.2
Throat Heaters
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NOTE: The hopper throats are normally part of the
ash evacuation valve connected to the hopper outlet
flange. This cast iron valve housing creates a
restrictive outlet, a common area for pluggage
unless the flyash is heated; thus the hopper throat
heaters are intended for the inlet of the ash
evacuation valve housing. Insulate the hopper
throats with a 50 mm 2 inch air gap with 80 mm 3
inches of insulation.
**************************************************************************
Provide tape heaters or flexible blanket heaters having a single Series 600
stainless steel alloy or nickel-chrome heating element, rated at 2.7 kW/m2
250 W/ft2. Design heaters to operate at 2.2 kW/m2 200 W/ft2 and to remain
on during startup, offline, and online operating conditions. Encase in a
minimum 20 Gage aluminum or aluminized-steel mounting pan or casing.
Provide attached metal labels listing the heater's wattage and voltage.
[2.6
WEATHER ENCLOSURES--REVERSE AIR CLEANING SYSTEM
**************************************************************************
NOTE: Select the applicable paragraph(s) from the
following:
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Provide a weather-tight enclosure, including lighting, to enclose the top
and the bottom of the baghouse. Enclose hoppers within the bottom weather
enclosure. Conform to SMACNA Arch. Manual. Seal joints by continuous
fillet or complete penetration groove welds.
Do not use caulking. Design
enclosures to withstand differential thermal expansion between housing and
weather enclosures. Design weather enclosure roof to support minimum 4.8
kPa 100 psf. Space roof purlins so that roof deck span will not exceed
2.12 m 7 feet. Provide additional support for equipment placed on the
roof. Slope and extend top surface and top surfaces of appurtenant
structures, but not less than 25 mm one inch beyond side insulation, to
allow water runoff and to prevent pooling. Provide a safety rail around
the top perimeter surface, a 80 mm 3 inch fascia rain barrier of 6 mm 1/4
inch ASTM A 242/A 242M steel plate, a 80 mm 3 inch kickplate of 6 mm 1/4
inch ASTM A 242/A 242M steel plate, and drain holes to permit water runoff.]
[WEATHER ENCLOSURE--PULSE JET CLEANING SYSTEM
Provide an insulated clean gas outlet plenum directly above the bags. Since
the outlet plenum shall enclose the entire top of the baghouse, do not
SECTION 15863N
Page 30
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