FREQUENTLY
ASKED QUESTIONS
What
is an ozone destruct unit?
An ozone destruct unit is used to catalytically destroy excess ozone
gas produced in an ozonation process. These processes include:
1. Offgas from an ozone contacting tank
2. Excess ozone produced in a CVD process
3. Exhaust from an ozone analyzer
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 0.1 ppm over
an eight hour period and 0.3 pm for 15 minutes. The IDLH for ozone
is 5 ppm. Please see the MSDS sheet for ozone 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. See the section on Bed Fouling
for more information.
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 offgas 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 comes to 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 500F 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.
What is the catalyst
used in the ozone destruct unit?
The catalyst is known as a hopcalite-type of catalyst whose primary
constituents are manganese dioxide and copper oxide. The material
is not toxic or dangerous and can be disposed of in a Class 1 landfill.
Please see the MSDS sheet for the catalyst material.
Can I buy replacement
catalyst?
Replacement catalyst is available in 1,5 and 45 pound containers. |
