Ultraviolet lamps have been used for decades to generate ozone. This lamp
emits UV light at 185 nanometers (nm). Light is measured on a scale called an
electromagnetic spectrum and its increments are referred to as nanometers.
Figure 1 represents an electromagnetic scale; note the location of
higher-frequency ultraviolet light relative to visible light (the range of light
perceptible by the human eye).
Wavelengths in nm
Air (usually ambient) is
passed over an ultraviolet lamp, which splits oxygen (O2) molecules
in the gas. The resulting oxygen atoms (O-), seeking stability,
attach to other oxygen molecules (O2), forming ozone (O3).
The ozone is injected into the water, or air stream, where it inactivates
contaminants by actually rupturing
the organisms’ cell wall.
Corona Discharge (CD)
The technologies involved in corona discharge ozone generation are varied, but
all operate fundamentally by passing dried, oxygen-containing gas through an
electrical field. The electrical current causes the “split” in the oxygen
molecules as described in the section on ultraviolet ozone generation. Past this
common feature the variations are many, but the generally accepted technologies
can be divided into three types - low frequency (50 to 100 Hz), medium frequency
(100 to 1,000 Hz), and high frequency (1,000 + Hz). Since 85% to 95% of the
electrical energy supplied to a corona discharge ozone generator produces heat,
some method for heat removal is required. Also, proper cooling significantly
affects the energy efficiency of the ozone generator, so most corona discharge
systems utilize one or more of the following cooling methods: Air or water.
Ozone Being created via Corona Discharge.
At the heart of a corona
discharge ozone system is the dielectric. The electrical charge is diffused over
this dielectric surface, creating an electrical field, or “corona”.
Critical to CD ozone systems
is proper air preparation. The gas feeding the ozone generator must be very dry
(minimum -80 degrees F), because the presence of moisture affects ozone
production and leads to the formation of nitric acid. Nitric acid is very
corrosive to critical internal parts of a CD ozone generator, which can cause
premature failure and will significantly increase the frequency of maintenance.
The chart below shows that relative ozone output decreases as moisture content
Of the ozone technologies
mentioned above, none has a clear advantage. However, to help narrow the field
for a particular application, consider the amount of ozone required. You may
find that low and medium frequency ozone systems will have prohibitively high
initial costs for applications requiring less than ten lbs./day. However, they
have a proven history of durability and reliability. High frequency ozone
generators seem to have the best combination of cost efficiency and reliability
for applications requiring less than ten lbs/day of ozone output.
of Corona Discharge ozone generation