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

5.5.1. Ozone Generatora. Capacity.1. The production rating of the ozone generators shall be stated inpounds per day and kw-hr per pound at a maximum cooling watertemperature and maximum ozone concentration.2. The design shall ensure that the minimum concentration of ozone inthe generator exit gas will not be less one percent, by weight.3. Generators shall be sized to have sufficient reserve capacity so thatthe system does not operate at peak capacity for extended periods oftime, which can result in premature breakdown of the dielectrics.4. The production rate of ozone generators will decrease with avariation in the supply temperature of the coolant throughout theyear. Curves or other data shall be used to determine productionchanges due to the temperature change of the supplied coolant. Thedesign shall ensure that the generators can produce the requiredozone at maximum temperature.5. Appropriate ozone generator backup equipment must be provided.b. Electrical.The generators can be low, medium or high frequency type.Specifications shall require that the transformers, electronic circuitry andother electrical hardware be proven, high quality components designedfor ozone service.c. Cooling. The required water flow to an ozone generator varies with theozone production. Normally unit design provides a maximum coolingwater temperature rise of 2.8°C (5°F). The cooling water must beproperly treated to minimize corrosion, scaling and microbiologicalfouling of the water side of the tubes. A closed loop cooling watersystem is often used to ensure proper water conditions are maintained.Where cooling water is treated cross connection control shall beprovided to prevent contamination of the potable water supply.d. Materials. To prevent corrosion, the ozone generator shell and tubesshall be constructed of Type 316L stainless steel.5.5.2. Ozone Contactors.The selection or design of the contactors and method of ozone applicationdepends on the purpose for which the ozone is being used.a. Bubble Diffusers. Where disinfection is the primary application, aminimum of two contact chambers, each equipped with baffles toprevent short-circuiting and induce countercurrent flow, shall beprovided. Ozone shall be applied using porous-tube or dome diffusers.b. The minimum contact time shall be ten minutes. A shorter contact timemay be approved if justified by appropriate design and CTconsiderations.c. For ozone applications in which precipitates are formed , such as withiron and manganese removal, porous diffusers should be used withAug. 29, 2003Page 117