Ozone Gas Mixing
Ozone is an unstable gas that is soluble in pure water in water at 0.64 on a vol/vol basis at 0 degrees C, which is greater than oxygen, but less than chlorine.
Ozonation is an absorption process hence mass transfer rate depends on Physical properties of phases, concentrations at the interface and Degree of turbulence.
Ozone decomposes and at 20 Centigrade its half life is approximately 20 minutes in Liquid. The ozone Gas must be mixed with water, dissolve into the water and have time to react with micro organisms or chemical compounds.
Ozone Concentration + Contact Time = CT Value
For example, a CT value 1.6. This means the dosage rate is 1.6 mg/l minutes. The operator has a choice of ozonation at 0.2 PPM for 8 minutes or 0.4 PPM for 6 minutes.
0.1 PPM of dissolved ozone for 10 minutes
0.2 PPM of dissolved ozone for 5 minutes
Once ozone gas is transferred into water, the dissolved ozone reacts with the organic and inorganics
Ozone Transfer Efficiency (TE) =(Ozone Feed) - (Ozone Out) / (Ozone Feed)
The amount of ozone created is dependent on several factors:
-
Influencing the solubility.
- Increasing the ozone concentration in the air (oxygen)
- Increasing air pressure (oxygen)
- Decreasing the water temperature
- Decreasing the amount of solutes
- Decreasing the pH
- Excess of UV-light + Hydrogen peroxide (AOP)
Bubble diffuser contactors
Bubble diffuser contactors use ceramic or stainless steel diffusers that are either rod-type or disc-type
to generate bubbles. In this case the flow pattern through the contact vessel and the depth of the diffusers are critical to the Transfer Efficiency. Off-gas is routed to an ozone destruct unit, usually
catalysts, thermal, or thermal/catalysts.
Venturi Injectors
Venturi Injectors work when pressurized water enters the injector inlet which Forces water through a conical body it changes into a high-velocity jet stream. This initiates a pressure differential between the inlet and outlet ports,which results in a decrease in absolute pressure, creating a vacuum, thereby enabling Ozone gas to be drawn through the suction port and Mixed into the water Line. Venturi Moc is in Stainless Steel 316 or Ozone Compatable Material which has a Non return Valve.
Static Mixers
A static mixer is a precision engineered device for the continuous mixing of fluid materials. Normally the fluids to be mixed are liquid, but static mixers can also be used to mix gas streams, disperse gas into liquid .The mixing elements provide a full radial, wall to wall distribution of the micron size ozone bubbles. Increase your Ozone bubble surface area by splitting them up into smaller bubbles.
Turbine Mixers
Turbine mixers are used to feed ozone gas into a contactor and mix the ozone with the water in the Contactor which uses a motor located outside the basin or a submerged turbine.
Ozone transfer efficiency for turbine mixers is high but the power required to achieve this efficiency is high and uses 6 to 15 ft Water Depth.
Sufficient contact time may not be available in the turbine basin to meet disinfection CT requirements; consequently additional contact volume may be required.
| Advantages | Disadvantages |
|---|---|
| High Ozone Transfer | High Energy |
| Contactor depth lesser than bubble diffusion | High Maintenance |
| Aspirating turbines Can draw off-gas from other chambers for reuse | Constant gas flow rate should be maintained, reducing ozone transfer efficiency |
| Eliminates diffuser clogging concerns | High Cost |