When ozone is produced from oxygen by corona discharge, the oxygen source must be extremely dry (dew point less
than -100 degree F) in order to maintain good efficiency in the ozone generation process and to prevent damage to the
ozone generator and its components. The three principal feed gases are dried air, oxygen concentrated from air on site
using pressure swing adsorption (PSA) and liquid oxygen (LOX)
The selection of feed gas is primarily an economic decision. Pure oxygen allows for the most efficient operation of the ozone generator and down stream processes, but these benefits are off set by the cost of the oxygen (either made on site or purchased).
In some cases, for the purpose of chemical reaction, high concentrations of ozone are required. Air fed ozone generators can only make up to 4 wt.% ozone and more typically 2-3 wt.% ozone. Oxygen fed systems can produce 6-15 wt.% ozone and more typically 6-10 wt.% ozone.
For the most part, smaller systems use air feed or oxygen from PSA. Larger systems typically use LOX. As noted above the final decision is often dictated by the site specific economics which take into account the local cost of LOX, power costs, capital costs, method of mixing ozone with water, reliability of LOX supply, predicted cost increases in LOX and various other factors.
To achieve maximum efficiency, some ozone generators running on oxygen have a small amount of nitrogen added to the gas feed. The addition of nitrogen, typically 1-4% of the total feed gas, allows the generators to prodcue the highest ozone concentrations at the best efficiency. In PSA gas feed systems, the nitrogen is a naturally a part of the gas mix along with argon. For LOX systems, nitrogen is added, often by adding a stream of dried air to the LOX feed. It should be noted that certain types of ozone generators are not helped by the addition of nitrogen. So, the advice of the specific ozone generator manufacturer should be sought in this regard.
It is worth noting that one of the benefits of using oxygen is that the ozone generator is typically smaller than for a system using dry air. While this is an advantage in terms of capital cost, it also means that a switch back to air would create a significant reduction in capacity.
A detail discussion on each type of gas feed system and gas feed economics can be found by following the links below