Ozone – The Science & Technology Part 2 ---Carona Discharge

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Created on Thursday, 02 June 2005 17:07

Written by Jack J. Reiff, President WET-TECH, The Ozone People

Science tries to duplicate and improve what Mother Nature performs. Ozone is no exception. Last month we looked at the UV Light (photo chemical) process of creating ozone. This month we’ll examine the carona discharge process.

Remember, when stimulated (agitated) by either an electric charge or Ultra Violet light (specific wavelength) the oxygen molecule (O2) breaks up and temporarily joins other oxygen molecules forming O3 (ozone) or other levels of ozone depending on the charge and feed source. These outside valences or oxygen molecules are not happy in this new arrangement and seek to disengage themselves creating oxidizing power – or ozone. Unlike most other chemicals, ozone has no natural resource or method of storage. It is generated on-site and due to its rapid decomposition; cannot be stored for extended periods of time.

Carona discharge requires the energetic excitement of molecular oxygen to redistribute itself into atomic oxygen in the form of O3. The “Silent Arc Discharge” known also as Carona Discharge or Brush Discharge has become the preferred method of ozone generation when outputs above 1 gram/hour are required. (See exhibit 1)

Carona discharge generators take on many forms, shapes, sizes and ozone outputs. What are the required components of a basic “Silent Arc” carona discharge ozone generator?

1. Two electrodes separated by a gap
2. A dielectric material inserted in to the gap
3. A feed gas flow containing oxygen inserted in to the gap
4. Sufficient voltage potential between the two electrodes to cause a current flow through the gas. Electrodes must provide a parallel position for energizing.

The reliability, performance and efficiency of the ozone generator depends on several factors. Since more than 80% of the applied electrical energy is converted to heat, the materials used in constructing the generator must be heat resistant. The heat generated must also be quickly and efficiently removed from the area or the heat will accelerate the decomposition of the ozone generated. Ozone generators are cooled by either air flow, refrigeration or water. Many manufacturers use heat sink devices in their design around the ozone components to direct heat away from the unit.

PROPER OZONE GENERATION
Feed gas decontamination is critical for good ozone generation. Heat, particulate matter, moisture, feed gas flow (volume,) pressure, vacuum, water conditions and other variables will affect the ozone quality and percentage of concentration. This is one reason that clean dry air or oxygen should be used in the generation of ozone. The EPA suggests that minimum moisture content below – 60 dew point (frost point) should be maintained with the feed source.

Clean air, free of particulate matter provides for maximum oxygen content in the volume of air being supplied as a feed gas. Dry air maximizes volume flow and eliminates the potential for nitrous oxide development when the Carona Arc energizes the feed gas. Nitrogen oxide, converted to nitric acid, is detrimental to the operating equipment and catalytically destroys the ozone.

The selection of the dielectric material is critical in the performance, output and life of the generator. When considering the dielectric it should be rated based on the continuous electron bombardment necessary to generate the desired ozone output. This same concern must be applied when selecting the electrodes.

To provide a sufficient voltage potential between the electrodes to generate the ozone, a transformer is incorporated in to the system to step up the voltage and operate between 10,000 and 25,000 volts at low amperage. Voltage varies based on ozone application design. Some transformers are dry and others are encased in oil, filled with silicone or other heat control material to maintain low operating temperatures. The line voltage to the transformers can be 120 VAC, 230 VAC or 440 VAC in single phase or 3 phase at 50 to 60 hz.

Ozone attacks and decomposes organic and inorganic materials. It attacks molecules that bond many soils to the fabrics we wash, enhancing removal of these soils from the fabric. The oxidation of inorganic material helps in the process of treating soluble soil, making it insoluble so that it can be precipitated out of solution. This attribute is the basis for wastewater treatment.

HARNESSING OZONE
So how can we harness ozone and apply it for practical benefits? One way is that of a venturi injector. This device, set in to the stream of the water that is in use and to be infused with the ozone, creates a pressure differential from the inlet to the outlet side of the device. This pressure differential creates a low pressure (vacuum) in the outlet flow of the water. This low pressure or vacuum is the suction for the ozone feed line in to the water flow. This type of application should be designed properly so that the loss of ozone in the vacuum does not inhibit the designed function of the ozone. The venturi system requires a water flow under pressure.

Another method is the use of a sparger which allows the ozone bubble into the water, under pressure, for dispersion in the water. This method provides for large and small bubbles of ozone to be applied and allows for off gassing unless destroyed. Specifically designed diffusers are also an effective and efficient method of applying ozone in to the wash liquor since ozone bubble size is controlled and will minimize off gassing. But remember, one size does not fit all applications.

When used properly, ozone can greatly enhance washroom technology both environmentally and economically.

The first installement of this two part series (OZONE – The Science & Technology with no myths) appeared in our May 2005 edition l