WHY IS PURITY OF OXYGEN IS SO IMPORTANT IN OZONE GENERATION?
The importance of oxygen feed quality to an Ozone generators performance and reliability cannot be understated. It has to have the required purity, the required pressure and the required dew point. All the three will affect the performance and the reliability of the system. Often the oxygen system in not given the requisite importance and resulting in frequent failures of system and the process.
PURITY: This has reference to the percentage of oxygen in the gas. Oxygen plants generally produce oxygen at around 93 % purity. Liquid Oxygen has about 99 % and above purity. This means that if we feed 93% oxygen, it means that the oxygen gas contains 93 % oxygen, and the rest inert gasses like Argon etc. To remove the more than 78 percent Nitrogen from the Air will require special media that is very expensive. The media should also be selected so that it consistently adsorbs the nitrogen required to produce over 93 percent oxygen gas. Ozone generators are calibrated to produce ozone at different concentrations depending on the volume and purity of the feed gas will affect ozone production, subsequently the process. Most of the time this factor is ignored. Cost of oxygen plants can be manipulated based on the quantity of molecular sieves used and the pre treatment of air.
The molecular sieve media is hygroscopic. That means it can absorb moisture if it is exposed and deteriorate in quality, affecting the purity of the oxygen. Small oxygen concentrators that are used take air from the plant room and hence water /moisture in the room, relative humidity can all interfere in the performance. To prevent accumulation of water vapor in the plant room, it is always suggested to have free recirculating air by way of an exhaust fan. The systems are to be installed in a dry place. In larger oxygen plants this issue is resolved since compressed dry air is used.
PRESSURE: Many ozone generators require high pressure (2-3 Bar) oxygen as feed gas. . By stipulation of high pressure they are ruling out high dew points (PDP) . This is because the higher the air is compressed the more water is removed and the performance of the molecular sieves are far better at higher pressures. Small Oxygen concentrators provide oxygen at very low concentrations (the medical oxygen generators). Small Oxygen concentrators at high pressure are manufactured by very few companies like Sequel, Airsep. They are classified for industrial use and are expensive. Customers often do not want to use them since they are averse to the high cost-plus service availability if required. Normally these units are very dependable.
DEW POINT (Pressure Dew point) Dew point suggests the quantity of moisture in the air. It is specifically important if air is used as feed gas. Using feed gas as air will generate up to 5 % ozone concentration (since air has only 19-21 % oxygen compared to 93 % and above in oxygen). However, in the manufacturing of an oxygen system the PDP of the air feed to the oxygen plant is important since excess moisture will affect the performance of the Molecular sieves. Hence air preparation becomes very important and design of the air preparation will have a bearing up to the ozone production.
Therefore, it is important that prospective users of ozone realize the importance of the oxygen system that is supplied with the ozone generator. In my 30 years of experience in ozone, 70% of the issues with ozone systems are due to the oxygen system. Oxygen plants meant for an ozone system have unique specifications and are quite different from oxygen systems supplied to other industries like steel plants etc.
