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The Challenge
Product sterilization companies are generally required to utilize a pollution control device, often referred to as an abator, for treatment of exhaust gases from their aeration rooms, sterilization chambers and vessels. 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.
The Solution
After examining various technology alternatives and multiple suppliers, the sterilization company chose Anguil Environmental Systems to provide a catalytic oxidizer that would result in NESHAP compliance and minimal downtime.
A back-vent and peak shaver 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.
The Result
Having experience with ethylene oxide emissions and sterilizer applications, Anguil recognized several unique challenges associated with this project. First, the catalytic oxidizer had 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. This buffer before the combustion device alleviates any concerns of property damage or personal 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 bypassing 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 comingling 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 fail-safe, 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 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.