Oxygen Recycle Systems
As noted in other sections of this website, typical ozone generators produce anywhere from 6-15% ozone from oxygen
feed. This means that 85-94% of the oxygen is wasted if not recovered. Since oxygen generation or purchase is a major
expense for making ozone, recycling of oxygen after the water treatment process has been considered over the years. It
is also important to note that producing more concentrated ozone increases both the capital and operating cost of an
ozone water treatment system. This further makes recycling of interest since producing ozone at lower concentration
might be more economical if the oxygen can be recovered.
Three concepts have been considered for oxygen recovery in ozone water treatment applications:
In the first case, oxygen from the contact vessel which is saturated with water and at atmospheric pressure can be used
in some other process at the facility. In a wastewater treatment plant for example, the oxygen could be fed to a blower for
an activated sludge process. Oxygen is more effective than air in these situations and since the oxygen would otherwise
be wasted, this is a very cost effective application for the spent oxygen. This type of oxygen recovery application is
practiced in some facilities. Other applications exist in the pulp and paper industry. Unfortunately, in many water
treatment applications effective use of the ozone in other processes is not possible.
The second option is to take the oxygen from the ozone contact vessel and use it to feed the ozone generator. This is
difficult to do since the oxygen is full saturated with water, may contain hydrocarbons stripped from the water and is at
atmospheric pressure. Ozone generators require extremely dry gas, -70 degrees F or better, low impurity levels and
pressures from 10-20 psi. The cost for drying, cleaning and increasing the pressure of this off gas has not been found to
be economical.
Recently, Air Products and ITT WEDECO have disclosed a process call "Short Loop Recycle". In this process, shown
below, oxygen is fed to an ozone generator. The oxygen ozone gas mixture is then fed to an adsorption bed where the
ozone is adsorbed and the oxygen passes through. This oxygen is recycled back to the ozone generator. Adsorption
bed is cycled to strip the ozone from the by a carrier gas, dried air. The air ozone mixture is then fed to the contact
vessel where the air, after removal of any remaining ozone, is vented to atmosphere. The developers claim that ozone
concentrations of 1-12% can be achieved with this process. It is not economical possible to exceed about 3% ozone in
air directly.
The claimed advantages of the process include:
As noted in other sections of this website, typical ozone generators produce anywhere from 6-15% ozone from oxygen
feed. This means that 85-94% of the oxygen is wasted if not recovered. Since oxygen generation or purchase is a major
expense for making ozone, recycling of oxygen after the water treatment process has been considered over the years. It
is also important to note that producing more concentrated ozone increases both the capital and operating cost of an
ozone water treatment system. This further makes recycling of interest since producing ozone at lower concentration
might be more economical if the oxygen can be recovered.
Three concepts have been considered for oxygen recovery in ozone water treatment applications:
- Oxygen recovery downstream of the ozone contact vessel not for use in the ozone system
- Oxygen recovery downstream of the ozone contact vessel for recycle to the ozone system
- Oxygen recovery downstream of the ozone generator, but upstream of the ozone contact vessel for recycle to the
ozone generator
In the first case, oxygen from the contact vessel which is saturated with water and at atmospheric pressure can be used
in some other process at the facility. In a wastewater treatment plant for example, the oxygen could be fed to a blower for
an activated sludge process. Oxygen is more effective than air in these situations and since the oxygen would otherwise
be wasted, this is a very cost effective application for the spent oxygen. This type of oxygen recovery application is
practiced in some facilities. Other applications exist in the pulp and paper industry. Unfortunately, in many water
treatment applications effective use of the ozone in other processes is not possible.
The second option is to take the oxygen from the ozone contact vessel and use it to feed the ozone generator. This is
difficult to do since the oxygen is full saturated with water, may contain hydrocarbons stripped from the water and is at
atmospheric pressure. Ozone generators require extremely dry gas, -70 degrees F or better, low impurity levels and
pressures from 10-20 psi. The cost for drying, cleaning and increasing the pressure of this off gas has not been found to
be economical.
Recently, Air Products and ITT WEDECO have disclosed a process call "Short Loop Recycle". In this process, shown
below, oxygen is fed to an ozone generator. The oxygen ozone gas mixture is then fed to an adsorption bed where the
ozone is adsorbed and the oxygen passes through. This oxygen is recycled back to the ozone generator. Adsorption
bed is cycled to strip the ozone from the by a carrier gas, dried air. The air ozone mixture is then fed to the contact
vessel where the air, after removal of any remaining ozone, is vented to atmosphere. The developers claim that ozone
concentrations of 1-12% can be achieved with this process. It is not economical possible to exceed about 3% ozone in
air directly.
The claimed advantages of the process include:
- Reduction in operating costs, approximately 70% of the oxygen can be recovered.
- Reduction of dissolved oxygen (DO) levels in water, in some applications like drinking water DO can cause
corrosion issues - Increased ozone concentration from lower concentration feed, some application require high ozone concentration
- Increase in ozone pressure, as noted above most ozone generators operate at 10-20 psi, this process can boost
pressure of the gas which can be helpful in some applications
Spartan Environmental Technologies
Air and Water Treatment
Air and Water Treatment
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Phone: 800-492-1252
Fax: 440-368-3569
E-mail: info@
spartanwatertreatment.com
Ozone Oxygen Recycling Systems
