l) Hopper heaters or other supplemental heat should be considered
in colder climates or on systems that frequently cycle on-line and off-line.
Bag life is considerably reduced on systems that frequently pass through the
acid and/or moisture dew points. Heaters should maintain internal hopper skin
temperature at 200 degrees F (93.3 degrees C).
Adequate means of maintaining bag tension must be provided.
a minimum should provide for:
differential pressure indication across entire
baghouse and each individual
module, individual module isolation, automatic
and manual cleaning capability
based on pressure drop across the collector on
timed cycle, emergency bypass
capability for high pressure differential, low
and high temperature
conditions, low oxygen conditions.
o) Collector manufacturer should furnish his field representative
to assist the Contractor in the installation and startup of the collector and
to train the Government's operating personnel.
p) Proper startup and shutdown procedures must be specified and
followed. The shutdown procedure must provide for maximum removal of residual
ash and flue gas (by repetitive cleaning cycles and fresh air purging).
Residual ash and oxides of sulfur and nitrogen form acids which will cause
corrosion in an off-line unit, especially if the unit is unheated and subject
to temperature swings through the moisture dewpoint.
Performance. The reverse air collector is capable of meeting all
existing particulate emission standards.
A properly designed collector can meet the New Source Performance
Standard (NSPS) of 0.05 lb/million Btu input (0.021 kg/kJ). Some guarantees
are now being given of 0.03 lb/million Btu input (0.013 kg/kJ). However, the
design shall conform to requirements set out in the construction permit for
the particular site. Conduct source emissions tests at design conditions in
accordance with EPA 40 CFR Part 60, Appendix A.
The stack emission or efficiency requirement must comply with
weight emission standards, opacity regulations, or community standards for
visible emissions. Compliance with existing emission codes may not satisfy
the opacity regulation. Similarly, opacity regulations may not be as
demanding as community standards. A specific quantitative emission rate must
be selected on the basis of the goals established.
Stack opacity is influenced by particle size and quantity. For
example, with pulverized coal-fired boilers, about 45 percent of the ash
particles are below 10 microns in size; for a stoker-fired boiler, about 25
percent are below 10 microns. A visually acceptable stack for these two
options might require residuals of 0.02 grains per dry standard cubic feet
(gr/dscf) and 0.04 gr/dscf, respectively.