Liquid Oxygen Systems (LOX) for Ozone Generators

Liquid Oxygen (LOX) Systems for Ozone Generation

Liquid oxygen systems are typically used to provide feed gas for larger ozone generator systems. Most new drinking water plants employ LOX feed gas systems. The choice of LOX as the feed gas for an ozone generator is primarily an economic decision in most other ozone water treatment applications. The principal components of a LOX system are the cryogenic storage tank, ambient vaporizer, pressure relief and control valves, and a nitrogen injection system.

Supplemental nitrogen injection is used to increase ozone generator efficiency. A 10-20% increase in ozone generator efficiency can be obtained with a 1-3% nitrogen concentration in the feed gas. The nitrogen injection system is essentially an air compressor with an air drier (air is 78% nitrogen and 21 % oxygen).

The most expensive component of the LOX system is the cryogenic tank. It is heavily insulated to minimize boil off of the LOX. Despite this precaution, LOX will boil off at a rate of 0.3-0.5% of tank volume per day. Pressure relief valves are used to prevent tank damage from pressure rise and to capture some of the boil off for use in the system. A reasonable size for the LOX tank is 15 days at maximum LOX requirement. Consideration should be given to emergency situations that might cut off the supply of LOX to the facility, floods, snow storms, etc. This might suggest a larger storage volume.

At least two vaporizers are used in a LOX system. One is operating while the other is on standby or defrosting. Defrosting is necessary to due to ice build-up. In Northern climates heaters to increase gaseous oxygen temperature may be used.

The LOX system can be purchased or it can be provided as part of the contract for the supply of oxygen. Int he latter case the oxygen supplier rents the equipment or includes the cost as part of the cost of the oxygen. In either case, the oxygen supplier should monitor and maintain the LOX system since they have the special skills required for this kind of work.