FREQUENTLY ASKED QUESTIONS about Ozone Destruct Units
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What is an ozone
destruct unit?
An ozone destruct unit
catalytically destroys excess ozone gas produced in an ozonation process. These
processes include:
1. Off-gas from an ozone
contacting tank
2. Excess ozone produced in a corona discharge process
3. Exhaust from an ozone analyzer
4. Corona Treating
(used to apply adhesives to tapes & films)
Although ozone gas is
unstable and will thermally decompose on its own, it is often advantageous to
destroy it more rapidly.
Why do we want to
destroy ozone?
Ozone is a very corrosive
gas, causing damage to many materials, including non-stainless metals and most
plastics and rubber. In addition, personnel exposure limits set by OSHA are 0.10
ppm over an eight hour period and 0.30 pm for 15 minutes. The IDLH for ozone is 5
ppm. Please see the Ozone MSDS sheet for more information on the toxicity of
ozone.
Depending on local
regulations it may also be illegal to discharge ozone gas into the atmosphere.
How does it work?
The ozone gas is passed
through a bed of manganese dioxide which catalytically converts the ozone back
to oxygen gas. This process is exothermic and often produces enough heat to make
the reaction go very quickly. This type of process is often referred to as a
Thermal-catalytic destruct unit.
This process is a true
catalytic process and the catalyst bed is not consumed. A catalyst bed should
last 1-5 years depending on usage and the carrier gas of the ozone. If the ozone
is produced in air, the life of the catalyst bed will be shorter than if the
ozone is produced in oxygen gas.
Why do some ozone
destruct units have heaters?
Ozone gas applications can
be either wet or dry. If the ozone is first contacted with water, such as in a
contact tank for treating water, the ozone off-gas is saturated. Even though the
conversion of ozone to oxygen is exothermic, a heater is required to keep the
catalyst material above the dewpoint. This is especially true on start-up of the
destruct unit before it reaches a higher temperature. This is also true if the exotherm
is not enough to keep the catalyst dry. The catalyst will lose its reactivity if
it becomes wet and must be either replaced or baked in an oven at 500 F until it
is dry.
Examples of dry
applications are those in which the ozone gas does not come into contact with
water, such as in a CVD process, downstream of a gas phase process ozone
analyzer, or in a process where excess ozone from a generator must be
eliminated.
How quickly does
the reaction take place?
The reaction is almost
instantaneous. The ozone will only be destroyed once it makes contact with the
catalyst. Proper destruct unit design ensures that the ozone is thoroughly
mixed as it passes through the catalyst. The
Ozone Interceptor
has been specially designed to destroy ozone concentrations & high flowrates.
