Case Study

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• Quality Considerations
  
• Equipment Corrosion Prevention
  
• Maximizing Ozone Transfer Efficiency for Higher Ozone Concentration
  
• Drinking Water Applications
  
• Wastewater Applications
  
• Recreational Water Applications: Performance Advantages
  
• Recreational Water Applications: A Marketing Advantage
  
• Price Considerations

Called the Pressure Swing Adsorption (PSA) oxygen generator and manufactured by AirSep Corporation of Buffalo, NY, is designed as an alternative to conventional air dryers for all ozone applications by providing a continuous, on-site supply of oxygen-enriched air in a range of flow rates.

Quality Considerations
David Capehart, EDC Ozone Systems applications specialist, says the primary reason for the company's selection of the oxygen generator over a conventional air dryer is "manufacturing" quality.

"We think of our ozone generators as ‘manufacturing facilities' for ozone," he explained. "In any manufacturing process, raw material quality and quantity is critical to the quality and quantity of the final product. Our final product is ozone (O₃), which is made from oxygen(O₂). But the ambient air we breathe is typically said to be comprised of only about 21% oxygen, with the rest being 78% nitrogen and 1% assorted other gases. The AirSep oxygen generator's synthetic zeolite molecular sieve adsorbs the nitrogen, while allowing the oxygen component of the air to proceed into our ozone generator reaction chamber, where the ozone is ‘manufactured'."

Continuing with the manufacturing model, Capehart noted it was easy to understand that starting with a "pure" oxygen (O₂) stream gives a better quality final product, O₃.

"We must consider the fact that the ozone we ‘manufacture' often is used as a component of water that must be of the highest quality," said Capehart. "The use of even the highest quality dried air, but still containing nitrogen, would be considered contamination in many water treatment applications. One example is disinfection of stored ultrapure water, which must be done with oxygen as the feed gas to our ozone generators."

Equipment Corrosion Prevention

Capehart added that this technology also offered protection against the formation of corrosive nitric acid, but with a major difference when compared to air dryers.

"We know that EDC ozone generators must be supplied feed gas from some form of air preparation device," he explained. "Moisture must be removed from the ambient air, or nitric acid will be formed in the ozone reaction chamber, causing rapid and catastrophic damage to the ozone generator and associated equipment. Typical desiccant air dryers will prevent the formation of nitric acid and other nitrogenous substances in the ozone generator reaction chamber, with the air preparation device typically fed by a source of compressed air. The PSA technology, which must employ an air compressor, dries the air as well as any desiccant air dryer does. But the big difference is AirSep's ability to remove the nitrogen, which is the key for making it ideal for most applications we encounter."

Maximizing Ozone Transfer Efficiency for Higher Ozone Concentration

In addition, Capehart said his company had found that mass transfer of ozone into the water being treated was much more efficient when they utilized a smaller gas stream with a higher concentration of ozone.

"Driving a gas into a liquid is a challenge, no matter how small the volume of gas," said Capehart. "It is much more efficient to mix a pound of ozone into a body of water if the ozone is contained in a gas stream that is not burdened with a large quantity of useless ‘baggage' such as nitrogen. And the resultant higher concentration of ozone provides advantages that are especially significant in recreational water and wastewater applications. We call it introducing high concentration ozone (HCO)."

Drinking Water Applications

Capehart stated that EDC had found most applications of ozone for drinking water to be best served by the use of oxygen rather than dried ambient air for ozone generator feed gas.

"The use of oxygen prevents the unintentional mass transfer of nitrogen during the introduction of ozone into the water," said Capehart. "Some waters are poised on the brink of exceeding allowable nitrite/nitrate levels. These waters might not be considered as candidates for ozone treatment if the only feed gas available to us was dried ambient air still burdened with nitrogen."

Wastewater Applications

Capehart said that EDC's enhanced ability to oxidize, through deployment of HCO, had proven to be a valuable asset for many waste treatment applications.

"The applications range from treating water that has been used for cleaning golf course maintenance equipment to water that has been used for in-place washing of military aircraft engines," he said, "with the treatment to a level of quality that is suitable for re-use. Closed loop recycling eliminates the need to pay for more water, or to prove compliance with discharge requirements; water re-use is even more desirable than water conservation. These applications typically range from 10 to 100 gallons per minute."

Capehart said that desired results for wastewater applications often simply could not be obtained without the increased ozone concentration in the output stream that is a direct result of increased oxygen in the feed gas.

"It's like having three times as many soldiers available at a critical point in a battle," he said. "The high concentration ozone can set off chain reactions that might not be initiated when dried ambient air is used for feed gas."

Recreational Water Applications: Performance Advantages

Capehart noted that recreational waters were very well served by using ozone as an adjunct to the ever-present halogen disinfection agents that must be employed in pools, spas, wave pools, and other recreational or decorative water features. But high concentration ozone, with oxygen as the feed gas, was especially beneficial.

"Ozone serves to reduce loading on the designated disinfection agent—chlorine, bromine, etc.—and thereby reduces the consumption—and cost—of the chemical," he said. "However, once again, quality is the deciding factor when selecting HCO with oxygen as the feed gas, to assist chlorine or bromine in keeping these waters safe from microbiological contamination. This is because HCO is able to kill or inactivate many deadly organisms within seconds. These same deadly organisms would be able to withstand an assault by lesser chemicals for several minutes."

He elaborated that in addition to disinfection, high concentration ozone often is able to oxidize some elusive contaminants to a more filterable form, a capability sometimes called micro-flocculation.

"Water being treated with HCO, assisted by adequate filtration and chemical treatment technology, is almost always measurably clearer than similar waters that have identical filtration and chemical treatment, but do not have the benefit of HCO," he concluded. "This is because the increased ozone concentration, made possible as a result of the increased oxygen concentration in the feed gas, can accomplish more powerful chemical reactions. It is capable of initiating reactions that are much more powerful than can be initiated by low concentration ozone from ozone generators using dried ambient air as feed gas."

Recreational Water Applications: A Marketing Advantage

Capehart described his company's recreational water applications as ranging from 200,000 gallon school swimming pools to 1,500,000 gallon waterpark wave pools, with the availability of a smaller oxygen generator providing a key advantage.

"We've used many different AirSep oxygen generators to provide oxygen as the feed gas for these applications," said Capehart. "But the availability of smaller units helped us penetrate the swimming pool market, where the appearance of larger units sometimes caused concern among maintenance workers about their capability for any necessary troubleshooting. One engineer convinced me that it was simpler to address the customers' concern by using the smaller unit, which could be easily shipped for service if needed, than to ‘sell' the customers on the reliability and simplicity of the technology."

Capehart said EDC began several years ago to use the smaller units in multiple, totally self-contained arrays, instead of larger units. Four, six, or 10 of them feed into a single manifold, which in turn leads into the ozone generator. Each unit, which can provide 12 cfh at 94% purity, weighs only 48 lbs., which maintenance people know can be easily shipped back and forth by standard courier if there's any problem.

"With this deployment," he noted, "the ozone treatment system remains on line even if one of the units is in the shop. And we've noticed these smaller units are quite durable, with more sent back to Buffalo because of equipment room flooding than from unit failure."

Price Considerations

Capehart said that price, while not the primary reason for selecting the PSA oxygen generation technology, was nevertheless a favorable aspect.

"For example," he explained, "two of their smaller units are equivalent in price to a desiccant dryer and associated air compressor, receiver tank, auto condensate purge, etc., that would be required to feed a typical application for us. But the dollars-per-gram-per-hour of ozone generation is less than one-half as much with oxygen as the feed gas. Furthermore, electrical consumption also is more affordable when using oxygen in the same scenario. Oxygen feed electrical consumption is 72% of the desiccant feed electrical consumption, based on kw hours used per pound per day of ozone produced."

EDC Ozone Systems offers units ranging in ozone output from 28 gram/hr to 2700 gram/hr, with larger units designed to be serviceable while on-line if necessary, and all units featuring state-of-the-art control options. For further information, contact EDC Ozone Systems Division, 3110 W. Story Road, Irving, Texas 75038; phone 972-257-0322; fax 972-257-9769.

AirSep Pressure Swing Adsorption (PSA) oxygen generators provide a continuous, on-site supply of oxygen-enriched air with a -100ºF(-73ºC) dew point at purities ranging from 70% to 95%. For further information, contact AirSep Corporation, 290 Creekside Drive, Buffalo, NY 14228-2070; phone 716-691-0202; fax 716-691-8304.