Design Guide for Community Water Systems - The Water, Sanitation ...

and fire codes. Emergency exhaust fans must be provided in the roomscontaining the ozone generators to remove ozone gas if leakage occurs. Aportable purge air blower that will remove residual ozone in the contactorsprior to entry for repair or maintenance should be provided.5.5.9. Construction Considerations.Prior to connecting the piping from the desiccant dryers to the ozonegenerators the air compressors should be used to blow the dust out of thedesiccant. The contactors should be tested for leakage after sealing theexterior. This can be done by pressurizing the contactors and checking forpressure losses. Connections on the ozone service line should be tested forleakage using the soap-test method.5.6. Ozone Feed Gas PreparationFeed gas can be air, high purity oxygen, or oxygen enriched air. Air handlingequipment on conventional low pressure air feed systems shall consist of an aircompressor, water/air separator, refrigerant dryer, heat reactivated desiccant dryer,and particulate filters. Some “package” ozonation systems for small systems maywork effectively operating at high pressure without the refrigerant dryer and with a“heat-less” desiccant dryer. In all cases the design engineer must ensure that themaximum dew point of -60°C (-76° F) will not be exceeded at any time. For oxygenfeedsystems, dryers typically are not required.5.6.1. Air Compression.a. Air compressors shall be of the liquid-ring or rotary lobe, oil-lesspositive displacement type for smaller systems or dry rotary screwcompressors for larger systems.b. The air compressors shall have the capacity to simultaneously providefor maximum ozone demand, provide the airflow required for purgingthe desiccant dryers (where required) and allow for standby capacity.c. Air feed for the compressors shall be drawn from a point protected fromrain, condensation, mist, fog, and contaminated air sources to minimizemoisture and hydrocarbon content of the air supply.d. A compressed air after-cooler and/or entrainment separator withautomatic drain shall be provided prior to the dryers to reduce the watervapor.e. A back-up air compressor must be provided so that ozone generation isnot interrupted in the event of a break-down.5.6.2. Air Drying.a. Dry, dust free and oil- free feed gas must be provided to the ozonegenerator. Dry gas is essential to prevent formation of nitric acid, toincrease the efficiency of ozone generation, and to prevent damage toAug. 29, 2003Page 121