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Filtration Table of Contents
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Filter Supplier Directory
Many
industrial operations generate acid or caustic fumes that can
damage or destroy filters, system components,
and construction materials. The air cleaning system designer
must select components and materials of construction suitable
for the corrosive environment to ensure high levels of system
performance and reliability.
Acid resistant pre-filters and HEPA filters
are available. These filters utilize media constructed with
Nomex or Kevlar®
fibers mixed with glass fibers during manufacturing,
epoxy-coated separators to extend the life of the
aluminum separators, and stainless steel frames.
Metal filters with a demonstrated suitability
for a corrosive atmosphere, in accordance with the ASME AG-Code 4
,
are recommended for hydrogen fluoride or other highly acidic
applications. Hydrogen fluoride is a concern
because it will attack the glass media. Wood-case filters are
vulnerable to attack by nitric acid that will
form nitrocellulose.
Stainless steel is recommended for ductwork
and housings when corrosion can be expected. Even this material may be insufficient
in some cases, and coated (e.g., vinyl, epoxy) stainless
steel or fiber-reinforced plastics
may be necessary. The system designer can either:
(1) use existing databases containing information about the
performance of materials
(including the filter media) exposed to various
concentrations of corrosive contaminants, or (2)
perform actual testing to validate the air cleaning system
design.
Scrubbers or air washers may be employed to
pre-treat the air or gas before it enters the air cleaning
system or to scrub the air stream of caustic agents, but consideration must also be
given to moisture
carryover if the scrubbers or air washers are not designed
and operated properly. Stainless steel moisture
separators are recommended ahead of the filters. Corrosion is
always a danger, but is not always obvious.
Electrical and electronic components are
particularly susceptible to corrosive atmospheres. Plastics
become brittle over
time, contacts corrode, etc. For this reason, all electronic
components must be environmentally qualified
for the intended application.
Care must be exercised in selecting and using
gaskets, as some gasket material reacts with the moisture in
the airstream and
releases chlorides that can corrode steels (including
stainless steel). Gasket material selection should
also include consideration of the effects of the material’s
use in acidic, radioactive, or other harsh environments.
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