Ozone Vent Gas Treatment
Ozone transfer efficiency, by whatever method of ozone contacting will never be 100% unless the water is treated with a
volume of ozone substantially below the demand. This can not be done an achieve treatment objectives, so due to
limitations in dissolving and the need to be sure treatment objectives are met, their will always be some ozone in the vent
gas from a ozone water treatment system.
In most cases this excess ozone needs to be reduced from typical values of 0.3% to 0.6% to less than 0.1%. This
decomposition can be achieved thermally or thermocatalytically. Before discussing the specific types of ozone destruct
units, it is important to understand the nature of the vent gas stream. Ozone emissions are covered by the Clean Air Act
and subsequent regulations associated with that act (see EPA Ozone Emission Fact Sheet). In some cases low
concentration ozone monitors are employed.
The ozone vent gas will likely come from either a contact/reactor vessel or from a degas tank. In both cases the gas will be
fully saturated with water at the temperature of the water in the vessel. In all ozone destruct systems the gas is heated, so
the water will remain in the gas phase past the heater and catalyst bed. As it cools down however, the water will begin to
condense. Provisions have to be made to drain this water out of the ozone destruct unit to prevent damage from the
catalyst bed and/or the heater element.
If the contact/reactor vessel is not pressurized as is the cases for most bubble diffuser system, a blower will need to be
fitted onto the ozone destroyer to pull a slight vacuum( -2 to -4 inches of water) to draw the vent gas into the destroyer. If
a degas tank is being employed, as in a side stream injection system, these tanks normally operate under pressure and
there should be sufficient pressure to push the vent gas through the ozone destroyer/destruct system.
There are three basic types of ozone destroyer (ozone destruct) system. Spartan provides all three types of ozone
destroyers (see our data sheet on ozone destroyers).
Thermal
Ozone decomposes spontaneously at elevated temperature to oxygen. Thermal ozone destroyers simply heat the vent
gas to the necessary temperature. The systems are the simplest and least expensive on a capital cost basis. They do
use more energy than other systems so they are usually only applied to relatively small ozone water treatment systems.
Essentially all of the gas that passes through the contact/reaction vessel must be heated to the decomposition
temperature (gas from the ozone generator, water vapor from the reactor vessel and any air that leaks into the contact
tank).
Thermal Catalytic
In the presence of a catalyst the temperature needed to decompose ozone is greatly reduced. This reduces the energy
required to for the ozone destruct system. However, the capital cost for the catalyst based system is higher than for a pure
thermal system. The additional capital cost is easily paid for as the size of the system increases. The catalyst is almost
always manganese dioxide. Activated carbon can decompose ozone, but it also burns, so it is not used for this purpose.
Heat Recovery Systems
Another way to reduce energy cost in a thermal based ozone destroyer is to heat the incoming vent gas with the treated
vent gas. This recaptures a portion of the energy used to heat the vent gas and reduces overall energy consumption.
These systems are only employed on the largest ozone water treatment systems.
Ozone transfer efficiency, by whatever method of ozone contacting will never be 100% unless the water is treated with a
volume of ozone substantially below the demand. This can not be done an achieve treatment objectives, so due to
limitations in dissolving and the need to be sure treatment objectives are met, their will always be some ozone in the vent
gas from a ozone water treatment system.
In most cases this excess ozone needs to be reduced from typical values of 0.3% to 0.6% to less than 0.1%. This
decomposition can be achieved thermally or thermocatalytically. Before discussing the specific types of ozone destruct
units, it is important to understand the nature of the vent gas stream. Ozone emissions are covered by the Clean Air Act
and subsequent regulations associated with that act (see EPA Ozone Emission Fact Sheet). In some cases low
concentration ozone monitors are employed.
The ozone vent gas will likely come from either a contact/reactor vessel or from a degas tank. In both cases the gas will be
fully saturated with water at the temperature of the water in the vessel. In all ozone destruct systems the gas is heated, so
the water will remain in the gas phase past the heater and catalyst bed. As it cools down however, the water will begin to
condense. Provisions have to be made to drain this water out of the ozone destruct unit to prevent damage from the
catalyst bed and/or the heater element.
If the contact/reactor vessel is not pressurized as is the cases for most bubble diffuser system, a blower will need to be
fitted onto the ozone destroyer to pull a slight vacuum( -2 to -4 inches of water) to draw the vent gas into the destroyer. If
a degas tank is being employed, as in a side stream injection system, these tanks normally operate under pressure and
there should be sufficient pressure to push the vent gas through the ozone destroyer/destruct system.
There are three basic types of ozone destroyer (ozone destruct) system. Spartan provides all three types of ozone
destroyers (see our data sheet on ozone destroyers).
Thermal
Ozone decomposes spontaneously at elevated temperature to oxygen. Thermal ozone destroyers simply heat the vent
gas to the necessary temperature. The systems are the simplest and least expensive on a capital cost basis. They do
use more energy than other systems so they are usually only applied to relatively small ozone water treatment systems.
Essentially all of the gas that passes through the contact/reaction vessel must be heated to the decomposition
temperature (gas from the ozone generator, water vapor from the reactor vessel and any air that leaks into the contact
tank).
Thermal Catalytic
In the presence of a catalyst the temperature needed to decompose ozone is greatly reduced. This reduces the energy
required to for the ozone destruct system. However, the capital cost for the catalyst based system is higher than for a pure
thermal system. The additional capital cost is easily paid for as the size of the system increases. The catalyst is almost
always manganese dioxide. Activated carbon can decompose ozone, but it also burns, so it is not used for this purpose.
Heat Recovery Systems
Another way to reduce energy cost in a thermal based ozone destroyer is to heat the incoming vent gas with the treated
vent gas. This recaptures a portion of the energy used to heat the vent gas and reduces overall energy consumption.
These systems are only employed on the largest ozone water treatment systems.
Spartan Environmental Technologies
Air and Water Treatment
Air and Water Treatment
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Spartan Environmental
Technologies, L.L.C.
7383 Lauren J Dr
Mentor, OH 44060
USA
Phone: 800-492-1252
Fax: 440-368-3569
E-mail: info@
spartanwatertreatment.com
Technologies, L.L.C.
7383 Lauren J Dr
Mentor, OH 44060
USA
Phone: 800-492-1252
Fax: 440-368-3569
E-mail: info@
spartanwatertreatment.com