Spartan Environmental Technologies provides ozone water treatment systems for a variety of applications. As we have mentioned in previous posts, one of the key elements of such systems is gas preparation. Oxygen or dried air can be used to make ozone. In this post we are going to discuss oxygen preparation systems for ozone generation.
The use of oxygen for the production of ozone permits higher rates of production for a given machine (80% more production) with higher ozone concentration (2-3% versus 6-10%). Higher concentration ozone is beneficial since it allows for easier dissolution into water. On the other hand, producing oxygen is more difficult than simply drying air. This means that much more air has to be processes to make oxygen than to dry air. The more compressed air required the larger the compressor and the more energy required. These costs offset to some extent the benefits of oxygen inside the ozone generator.
Spartan ozone water treatment systems employ oxygen concentrators using pressure swing absorption (PSA). This process employs two columns filled with molecular sieves, porous ceramic materials that reversibly absorb nitrogen and water from air on the surfaces.
Compressed air (90 psi pressure and filtered to remove hydrocarbons and particulates) is fed to one of the two columns. Under pressure nitrogen and water is absorbed on the surfaces of the molecular sieves. As the nitrogen and water are removed, the concentration of the oxygen is increased to the 90-95% level. This is enough to significantly increase the efficiency of an ozone generator versus the use of dried air.
Once the column has been filled with nitrogen and water, it needs to be unloaded. This is done by purging the column at atmospheric pressure (0 psig) with product gas from the other column that is operating. This dry oxygen laden gas caries away the nitrogen and water captured on the molecular sieves, making them ready to repeat the process. So while one column is producing oxygen the second column is being regenerated.
The ratio of air fed into the sieves to the amount of oxygen produced is about 11:1. So, if we wanted to produce 260 SCFH (4 SCFM) of oxygen, we would need 45 SCFM of air. The reason for the discrepancy with the natural ratio of oxygen to nitrogen in air (~1:5) is the amount of product gas (two thirds of total oxygen flow from the operating column) used to purge the column being regenerated. This means that the usable product is only one third of the total flow of oxygen from the operating column. The schematic above illustrates the process.
The only moving parts in the PSA process are the solenoid valves used to switch the flow of gas through the columns. Thus the process is highly reliable. Pressure switches and oxygen analyzers can follow the process and insure proper operation.
Contact Spartan if you are considering an ozone water treatment system. Spartan supplies complete system including gas preparation, ozone generation and down stream processes.