PROBLEM
Product sterilization companies are generally required to
utilize a pollution control device for treatment of exhaust gases
from their aeration room and sterilization chambers. In the
United States, they need to be in compliance with NESHAP (National
Emission Standards for Hazardous Air Pollutants) regulations that
dictate a 99% destruction efficiency of EtO (Ethylene Oxide), or
concentration levels below one part-per-million by
volume.
One contract sterilization company was using a wet scrubbing
system that was no longer a viable means of EtO removal. To
further complicate the situation, their high production levels
meant they could not afford a factory shutdown in excess of
eighteen hours. This time limitation made the procurement of
a pre-tested, pre-assembled pollution control system a
necessity.
ACTION
After examining various technology alternatives and multiple
suppliers, the sterilization company chose Anguil Environmental
Systems, Inc. to provide a catalytic oxidizer that would result in
NESHAP compliance and minimal downtime.
A peak shaver and wet scrubber were also considered
upstream of the oxidizer to prevent emission spikes from
causing an upset condition, however a detailed application analysis
showed it was not necessary on this particular
application.
SOLUTION
Having experience with ethylene oxide emissions and sterilizer
applications, Anguil recognized several unique challenges
associated with this project. First, the catalytic oxidizer
had to be able to control both the high concentration, low air
volume exhaust from the sterilization chamber's vacuum pump, as
well as the low concentration, high volume exhaust from the
aeration room. The high concentration from the vacuum pumps
of nearly 300,000 parts per million by volume caused a sharp
temperature increase, and demanded that the catalyst have a large
operational temperature window. At the same time, the
catalyst needed a low operational temperature when treating the low
concentration exhaust (10 parts per million by volume) from the
aeration chamber.
To satisfy both these needs, Anguil, in conjunction with their
catalyst supplier, performed extensive research and was able to
supply a base metal type catalyst with an operational temperature
of 275°F and an operational temperature window of over 500°F.
On some sterilizer installations, the highly concentrated
chamber emissions present another set of challenges. Because
they generally come in spikes when the chamber is evacuated, Anguil
often recommends and installs a peak shaver or wet-scrubber,
upstream of the oxidizer, as a safety precaution. Safety is
always a priority on Anguil oxidizers, having this buffer before
the combustion device alleviates any concerns of property damage or
personnel injury.
The next challenge Anguil faced for this application was
designing and building a system that not only met NESHAP
regulations but would also operate cost-efficiently. Due to
stringent ethylene oxide regulations, catalyst bed by-passing had
to be completely avoided. To facilitate this, Anguil altered
their traditional design and placed the base metal catalyst in
horizontal tray configurations. This minimized the bypassing
concerns associated with air passing around the catalyst media or
bed.
To keep operating costs down and prevent leakage that could
result in a co-mingling of the clean and dirty air streams, a 65%
effective 304L stainless steel leak-and-dye tested shell and tube
heat exchanger was used in the oxidizer. Unlike other
manufacturers who recommended a plate type heat exchanger, Anguil
was able to guarantee 0% leakage of VOC-laden air into the clean
air stream. As a failsafe, Anguil installed an induced draft
fan on the catalytic oxidation system. By placing the fan on
the discharge side of the oxidizer rather than placing it on the
inlet side, the system was under a continuous negative
pressure. This meant that any leakage associated with the
oxidation system would be released back into the system, rather
than out into the work environment.
The entire interior reactor of the oxidizer was constructed of
304L stainless steel, surrounded by mineral wool insulation and an
outer aluminized steel frame. This unique design offers
multiple benefits, including increased equipment life, as compared
to the industry-standard aluminized steel reactor interior.
Another accommodation Anguil had to consider was the customer's
time restrictions due to high production levels. Anguil's
solution was to completely pre-assemble, pre-wire and pre-test the
system prior to shipment. The customer's 18-hour time
restriction was met with time to spare.