Engineering Clean Air - Purafil

Engineering Clean Air
E-Newsletter Brought to You by Purafil Technical Services
Sincerely,
Technical Services Department
Purafil, Inc.
Purafil's scientists and researchers publish this e-newsletter
specifically for the engineering community. This exclusive
newsletter will include information and explanations on the
latest technology changes, regulations, standards, solutions,
research findings and other information of value to consulting
and specifying engineers.
Please feel free to forward to your engineering colleagues
and have them join the Engineering Clean Air e-newsletter
community by clicking the link to the right.
About Purafil, Inc.
For more than 40 years, Purafil has been a world leader in the development of gas-phase air filtration
media and systems designed to eliminate and control gaseous contaminants. We were the first to
propose standards for industrial facilities using electronic process controls. Today, these standards
are used worldwide.
Purafil offers the widest variety of gas-phase air filtration media and award-winning systems for the
control of any Indoor Air Quality (IAQ) challenge. Purafil provides engineered, clean air solutions in an
array of markets including commercial, industrial, water wastewater, museums and cleanrooms.
Purafil's dry-chemical air cleaning media removes specific gases and contaminants from high-volume
facilities in order to control corrosion, improve process reliability and IAQ, as well as save money.
Purafil's state-of-the-art laboratory and research facility offers valuable customer services, such as
media life analysis, air quality assessment, and circuit board failure evaluation. In addition to those
valued process, Purafil also offers a variety of technical services to ensure clean air and customer
satisfaction. Purafil's ongoing commitment to quality, customer satisfaction and safety are exemplified
by earning the latest ISO 9001:2008 quality management system certification, numerous industry
awards and an obligation to the research and development of new clean air technologies.
Purafil,Inc.
2654 Weaver Way
Doraville, Georgia 30340
Phone: 800-222-6367 or 770-662-8545
www.purafil.com
October 2012
In This Issue
Fiberglass versus Stainless
Steel for Use in Tub Scrubbers
Related Links/ Information/
Events
Contaminant of the Month:
Hydrogen Chloride
Purafil Solutions: Tub
Scrubber System (TSS)
Companion Paper: Are Ill
Winds Blowing at Your
Refinery?
JOIN the Engineering Clean
Air Community E-mail List!

Fiberglass versus Stainless Steel for Use in Tub Scrubbers
Many corrosion and odor control applications require the
use of large amounts of dry-scrubbing media for optimum
control of chemical contaminants. These systems provide
extremely high contaminant removal efficiency and media
service life insuring optimum system performance.
These filtration systems can be made from a number of
different materials depending on the application and
customer requirements. Most common are aluminum,
stainless steel and fiberglass. Fiberglass (or fiber)
reinforced plastics (FRP) are composite structural materials
containing high strength fibrous embedded reinforcements
that develop mechanical properties greatly superior to the
base resin. There are many plastic materials that can be
used in FRP, and Purafil uses polyester due to its superior
properties.
Tub scrubbers made from fiberglass reinforced polyester
can offer significant benefits over metal vessels
manufactured from materials such as aluminum and
stainless steel. There are generally three ways in which FRP
has an advantage over metals:
1. Weight: generally a substantial reduction weight in can be achieved due to the lower density of
FRP versus stainless steel or aluminum. When compared to a stainless steel system, one made
from FRP would have less than one-quarter the weight. This equates to lower shipping and
handling costs - especially for transcontinental or transoceanic shipments. Most Purafil FRP air
filtration systems can be moved with forklifts and would not require hiring a crane to do the lifting
and placement.
2. Fewer Parts: Consolidating many parts of an assembly into one part is a major benefit gained by
using FRP. Part consolidation reduces part count, fasteners and assembly time. This in turn
significantly reduces maintenance requirements.
3. Customization: The fiber/resin mix and stacking sequence can be adjusted to meet specific
stiffness/strength/manufacturing requirements. Purafil has use FRP in the construction of air
filtration systems containing as much as 25,000 pounds of media.
Weight savings is often mentioned as the single most important advantage of FRP but the reduction in the
number of parts and the cost savings associated with it is often a more significant factor. FRP vessels can
be fabricated as a single unit whereas metal vessels often consist of multiple parts that have to be welded
and inspected. If done improperly, welding stainless steel can produce weak points in the systems which
are oftentimes where corrosive attack can begin.
In addition to the advantages highlighted above, FRP is comparable or superior to metals in several others
ways.
FRP provides excellent corrosion and chemical resistance compared to metals such as aluminum
and painted or galvanized steel and is very comparable to that of stainless steel. With FRP
construction, system maintenance is virtually eliminated.
FRP provides optimal dielectric strength as an electrical insulator versus the electrical conductivity
of steel. FRP systems do not require grounding to ensure safety against direct or indirect contact.
FRP is significantly more cost effective than stainless steel and is very competitive with other
metals.

FRP is extremely easy to drill, cut, and punch compared to all metals. Retrofitting is essentially
eliminated because of the ability to modify FRP vessels using knock-out panels. If modifications
are required, FRP components generally do not require special tools or fixtures and work can be
performed on site with minimum downtime.
FRP systems are lightweight and easy to handle compared to metal systems.
Our comparison of FRP to stainless steel and aluminum is summarized in Table 1 below.
Table 1. Comparison of FRP to Metals Commonly Used in Industrial Applications
Fiberglass reinforced
polyester (FRP) Stainless Steel
Physical strength
Strong
High strength
Acids: recommended Acids: recommended
in most applications in most applications
Bases: recommended Bases: recommended
in most applications in most applications
Solvents:
Solvents:
recommended
recommended
Corrosion resistance
in most applications in most applications
Chemical resistance
Excellent
Excellent
Relative cost
Low
High
Impact resistance
Moderate
High
Tensile strength
Moderate
High
Ease of drilling, punching, and cutting
Very Easy
Extremely hard
Dielectric strength
Electrical insulator Electrical conductor
Thermal conductivity
Thermal insulator Thermal conductor
Weight, lb/ft 3
111
489
Aluminum
Strong
Acids: limited use
in most applications
Bases: very limited use
in most applications
Solvents: recommended
in most applications
Good
Moderate
Moderate to high
High
Hard
Electrical conductor
Thermal conductor
169
FRP and stainless steel are given an "Excellent" for chemical resistance. This is an important factor to
consider when deciding on choice of materials for an air filtration system that is to be used in a corrosive
(aggressive) environment. Although generally considered to be a corrosion-resistant material, stainless
steel can experience corrosion that can be described in a variety of technical terms that include: galvanic
corrosion, pitting, intergranular corrosion, stress corrosion, cracking, erosion corrosion, fretting,
concentrated cell or crevice corrosion, and selective leaching. Additional general information on the
corrosion of stainless steel is shown on the following page.
In summary, Purafil air filtration systems made from FRP are:
Equal to stainless steel in corrosion and chemical resistance, and far better than carbon steel
Strong enough to hold up under extreme conditions
Lighter and easier to transport and handle
Less expensive to ship
Much easier to punch, drill or saw
Non conductive – an electrical insulator rather than electrical conductor
Purafil FRP systems also outperform other non metallic alternatives in areas such as:
Chemical resistance
Protection against degradation due to UV exposure
Resistance to extreme temperatures
Flame retardant properties
Because of its physical, chemical, and mechanical properties, there are many application where fiberglass
reinforced polyester is an acceptable, and often preferred, alternative to stainless steel. Purafil has been
manufacturing systems with FRP for more than 25 years in a wide range of industrial corrosion control
applications. Purafil currently has more than 5,000 FRP air filtration systems in use around the world,
with a majority of these being used for corrosion control in the pulp and paper industry. Other industry
applications include refining, petrochemicals, chemical processing, and wastewater.
For more information on Purafil’s selection of corrosion control solutions as well as all of our dry-scrubbing
media products and air filtrations systems contact us at 1-800-222-6367 (U.S.), 1-770-662-8545 (Canada
and International), or submit an e-mail to technicalservices@purafil.com, or visit www.purafil.com.

Related Links/Information/Events
SMTA China North Conference – November, 2012, Wuhan, China: Controlling Creep Corrosion in
Datacom / IT Equipment. (http://www.smta.org/china/wuhan.cfm).
Winter ITRS ITWG/IRC Workshop – December 3-4, 2012, The Ambassador Hotel, Hsinchu, Taiwan
(http://www.google.com/url?sa=t&rct=j&q=winter%20itrs%20itwg%2Firc%20workshop%20&source=we
b&cd=1&cad=rja&ved=0CCEQFjAA&url=http%3A%2F%2Fwww.itrs.net%2FLinks%2F2012Summer%2F20
12%2520ITRS%2520WINTER%2520INFO.ppt&ei=Vk-FUK_VAYn-
8ASNl4GYDQ&usg=AFQjCNEGjIma6ALY1JRtPgb6Vr9LRUW2IA).
ASHRAE 2013 Winter Conference – January 27-30, 2013, Dallas, Texas: Purafil is moderating and
presenting a paper for a seminar titled ―Reliability Concerns for Data Center IT Equipment: Contamination
Issues, Standards Actions, and Case Studies.‖
(http://ashrae.org/File%20Library/docLib/Dallas/TechProgram_Dallas13.pdf).

Contaminant of the Month
Hydrogen Chloride (HCl, molecular weight 36.46), is a colorless gas at room temperature which forms
white fumes of hydrochloric acid upon contact with atmospheric humidity. Hydrogen chloride gas and
hydrochloric acid are important in industry. Hydrochloric acid, the aqueous solution of hydrogen chloride,
is also commonly given the formula HCl.
Hydrogen chloride is a diatomic molecule, consisting of a hydrogen atom and a chlorine atom connected
by a covalent single bond. Since the chlorine atom is much more electronegative than the hydrogen atom,
the covalent bond between the two atoms is quite polar. Consequently, the molecule has a large dipole
moment with a negative partial charge at the chlorine atom and a positive partial charge at the hydrogen
atom. In part because of its high polarity, HCl is very soluble in water (and in other polar solvents).
Upon contact, water (H2O) and HCl combine to form hydronium cations H3O + and chloride anions Cl –
through a reversible chemical reaction:
HCl + H2O → H3O + + Cl -
The resulting solution is called hydrochloric acid, a very strong acid. The acid dissociation or ionization
constant is large, which means HCl dissociates or essentially ionizes in water completely. Even in the
absence of water, hydrogen chloride can still act as an acid. For example, hydrogen chloride can dissolve
in certain other solvents such as methanol, protonate molecules or ions, and serve as an acid-catalyst for
chemical reactions where anhydrous (water-free) conditions are desired.
HCl + CH3OH → CH3O+H2 + Cl –
Because of its acidic nature, hydrogen chloride is corrosive, particularly in the presence of moisture.
Most hydrogen chloride is used in the production of hydrochloric acid. It is also an important reagent in
other industrial chemical transformations, e.g.:
Hydrochlorination of rubber
Production of vinyl and alkyl chlorides
In the semiconductor industry, it is used to both etch semiconductor crystals and to purify silicon via
trichlorosilane (SiHCl3).
It may also be used to treat cotton for delinting, and to separate it from wool.
In the laboratory, anhydrous forms of the gas are particularly useful for generating chloride-based Lewis
acids, which must be absolutely dry for their Lewis sites to function.
Hydrogen chloride forms corrosive hydrochloric acid on contact with water found in body tissue. Inhalation
of the fumes can cause coughing, choking, inflammation of the nose, throat, and upper respiratory tract,
and in severe cases, pulmonary edema, circulatory system failure, and death. Skin contact can cause
redness, pain, and severe skin burns. Hydrogen chloride may cause severe burns to the eye and
permanent eye damage.
The gas, being strongly hydrophilic, can be easily scrubbed from the exhaust gases of a reaction by
bubbling it through water, producing useful hydrochloric acid as a byproduct.
Any equipment handling or exposed to hydrogen chloride gas must be checked on a routine basis;
particularly valve stems and regulators. The gas requires the use of specialized materials on all wetted
parts of the flow path, as it will interact with or corrode numerous materials hydrochloric acid alone will
not; such as stainless and regular polymers.
The control of HCl and other acid gases can be achieved using Purafil’s dry-scrubbing chemical filters. For
best results against HCl, the use of Puracarb media is recommended. For applications involving high
concentrations of HCl deep-bed systems such as Purafil’s Deep Bed Scrubber or Tub Scrubber are
advisable. Visit the Purafil website for more information on the control of corrosive chemical contaminants.

Purafil Solutions – The Purafil Tub Scrubber System (TSS)
The Purafil Tub Scrubber System (TSS) provides clean
air—free of corrosive gases and particulates—into
environments housing sensitive electronics and
electrical equipment. The TSS is a cost-effective means
of preventing damage caused by corrosive gases
typically found in industrial settings. A three foot deep
media bed makes the TSS particularly effective in high
contaminant areas. Pulp and paper mills, refineries,
steel mills, smelters, chemical and petrochemical plants
worldwide use this single-bed system to solve corrosion
problems.
The TSS has recently undergone its first major design
update in more than 10 years. The media vessel (or
―tub‖) has been changed from the original rectangular
shape in favor of a round FRP vessel. This design
change presents immediate advantages to the customer
including:
Manufacturing flexibility – allows the use of standard FRP vessels that can be locally sourced by our
licensed equipment fabricators.
Greater structural integrity- the FRP tubs are filament wound designed to meet or exceed industry
accepted standards.
Smaller footprint – less space required.
Less ductwork / few joints – reduces the time and cost of installation and setup.
Cost competitiveness – the new TSS design is more economical.
Provides Corrosion-Free Air: The Tub Scrubber’s fundamental design provides three feet of media
depth in a single media bed to scrub high levels of gaseous contaminants from the air stream. In
accordance with industry standards for controlled environments set by the
International Society of Automation (ISAS71.04-1985), the Tub Scrubber provides ―G1‖ class air to
pressurize control rooms and motor control centers. This conforms to the warranty requirements of most
computer and instrument manufacturers.
Low Maintenance: The Tub Scrubber is designed for years of low-maintenance service.
The Scrubber’s three foot media bed is designed for long service (typically one year or longer), and media
change-out is simple and fast. The TSS is constructed of non-corrosive fiberglass. The filters, blower
section, and media bed are designed to be easily accessible.
System Flexibility: Systems are available from 500 up to 6000 CFM, offering equipment flexibility to
meet specific design requirements.
Local Service: Purafil’s network of local representatives offers convenient and timely service. Purafil’s
representatives are professionals who can provide in-depth technical assistance and a comprehensive
service program. Additionally, each Tub Scrubber System is fully supported by Purafil’s laboratory services
which include media life analysis and corrosion classification coupon testing – all aimed at insuring
ongoing system integrity.
Companion Paper
―Are Ill Winds Blowing at Your Refinery?‖