In the last couple of posts we have been talking about protecting ozone generators from damage. Today we will cover preparing the feed gas for the generator. The most important parameter in gas preparation, whether it is an air fed or oxygen fed system, is moisture control. Virtually all ozone generator manufacturers insist on dry gas being fed to their units. Typical dew points are -100 degrees F.
For air fed systems, refrigeration units on the compressors and desiccant dryers were used in the past. More recently pressure swing absorption (PSA) systems have been adopted. the latter have fewer moving parts and are easier to maintain. They do require higher pressure compressed air, in range of 100 psi to work efficiently. In any event, the goal is to remove the water to the -100 degree F dew point level.
For oxygen systems, PSA systems can also be used. In this case, oxygen is concentrated from air to 90-93% in the system. Water is also captured in this process, so dry oxygen gas is prepared. Alternatively, liquid oxygen can be evaporated as the feed gas. This material is inherently dry.
To insure effective drying, moisture sensors should be employed, especially in larger system. These monitors can directly provide the dew point value. Alarms can alert operators, or computer systems, to take action before moisture levels reach values that can result in damage to the equipment. For smaller system, silica gel moisture indicators are a low cost option to follow moisture changes as a change in color of the gel.
PSA systems can be a source of particulate contamination in the gas stream due to the attrition of the molecular sieves used to absorb nitrogen or water. So the use of particulate filters is important. these filters should be in the range of 0.5 to 1.0 micron in size.
For PSA systems, oxygen sensors can provide the oxygen concentration in the gas feed. an alternative is to follow the pressure of the concentrator since a drop of pressure below the recommended level is also an indication the the output concentration has been compromised.
Both ozone generators and PSA systems can be adversely affected by oil and other hydrocarbons. This can be a severe problem with oil lubricated compressors, but hydrocarbons from the environment can also pass through oil free compressors. In the case of oil lubricated compressors, coalescing filters must be used. It is also recommended to use activated carbon filters to polish the gas stream to remove any remaining hydrocarbon. Such filters cna lower hydrocarbon levels to less than 3 ppm.
The cost of a good gas preparation system is well below the potential damage cost by contaminated gas reaching the generator or explain why the generator is not producing ozone at the design vale.