Ozone gas can be dissolved into pressurized, flowing water via a simplestatic mixer. Pressurized Ozone gas can flow into a water stream using a TEE provided the ozone gas pressure is greater than the water pressure. A downstream static mixer can then be used to thoroughly mix the ozone gas into the water.
Water should be pressurized when using a static mixer to aid solubility of ozone gas into water. Therefore, the ozone gas must be under pressure to force into the water flows. We have found that water pressure around 30 PSI is ideal for mass transfer, however higher or lower pressures can also be used.
- Simple, effective system design with no moving parts
- Great option for pressurized water
- More energy efficient than a venturi as a pressure differential across the mixer is not requied
- Easier to contain ozone gas and maintain a safe environment due to ozone off-gassing
- Can work with water that may plug or obstruct a venturi injector
- Higher risk of water back-flow into ozone generator due to pressurized water
- Requires flowing, pressurized water
- Greater risk of water backing up into the ozone generator as the water is pressurized
Ozone gas is partially soluble into liquid. However, using proper methods and equipment high mass transfer efficiencies can be realized with any method of dissolving ozone into water. Review the tips below to help design a proper system using a static mixer in your ozone application.
Fundamentals of Ozone Solubility:
-Lower temperatures increase the solubility rate of ozone gas into liquid
-Higher pressures increase the solubility rate of ozone gas into liquid
-Higher ozone gas concentrations increase the solubility rate of ozone gas into liquid
Design considerations for your ozone system using a venturi injector:
Static mixer installation tips:
- Install static mixer shortly after the ozone injection point, within 12-inches if possible. Typically ozone bubbles will shear as they enter the water but combine again into a large air-pocket in the top of the pipe. Take advantage of the smaller bubbles as soon as possible.
- If flowing water into a tank, install the static mixer within 12” from the tank
- If flowing water into an un-pressurized tank, consider using an orifice to create back-pressure on the static mixer to improve solubility
- Ensure proper flow-rate of water to achieve optimum water velocity for the mixer in use
Water flow rate:
Water must be flowing at a specific flow-rate for the static mixer to function properly. While water flows can vary slightly, there is an optimum range of flow rates for each static mixer. The veloxity of water through the venturi is important for proper mixing. Low water velocity will not properly mix the ozone gas due to poor bubble shearing. High water velocity will create a high pressure drop across the mixer. Optimum water flow-rates for the PVC static mixer can be calculated using the information below:
Target water velocity = 5-10 ft/second
V = Velocity
D = Diameter in inches
Q = flow-rate in GPM (gallons per minute)
V=(Q x 0.402)/D2
(10 GPM x 0.402) / 0.75-inch2 = 7.15 ft/second
For a 10 GPM water flow a ¾” static mixer would be suggested
Pressure - More is better:
Ozone solubility is the rate at which ozone can be dissolved into liquid. Think of it as a theoretical maximum. The solubility of ozone gas into liquid us affected greatly by the pressure of the water, among other factors.
The chart and table below illustrate the solubility of ozone gas into water as it relates to the pressure of that water.
The static mixer does not create or require a pressure differential across the unit to dissolve ozone into water. Therefore, the ideal installation of the static mixer is in a flowing, pressurized water line prior to a contact or holding tank.
Gas to Liquid Ratio:
Gas to liquid ratio refers to the volume of gas added to the volume of liquid. The less gas dissolved into liquid will inherently increase your solubility rate of that gas into liquid.
For example, consider the following examples, using LPM (liters per minute) for simplicity:
- 1 LPM of gas dissolving into 100 LPM of liquid. This volume of gas would easily dissolve into the liquid
- 50 LPM of gas dissolving into 100 LPM of liquid. While possible, it would be more challenging to dissolve this amount of gas into liquid.
Certainly the lowest gas:liquid ratio is ideal. We suggest maintaining a gas:liquid ratio of 0.5 or 1:2 meaning 50 LPM of gas dissolving into 100 LPM of liquid is the greatest amount of gas one should dissolve into that liquid flow.
Use with venturi injector:
There has been a theory that suggests using a static mixer with a venturi injector is helpful in mass transfer. However, with a properly sized and functioning venturi the use of a static mixer after the venturi is more of a hindrance to mass transfer of ozone into water than an aide. A properly sized and functioning venturi injector will dissolve ozone gas into water very quickly. This ozone that is dissolved into the water can be flashed off the water with force. A static mixer after a venturi has the tendency to flash-off the dissolved ozone and force the ozone back into the gaseous state.
In low-pressure pipeline applications where pressure is not available on the pipeline to aide in ozone solubility a static mixer could be used after the venturi. If water is flowing to an un-pressurized tank that is a great distance from the venturi injector a static mixer could be used directly before the tank to break up large gas bubbles before the tank. This will allow smaller bubbles to enter the tank and rise slowly in the tank.
Water back-flow prevention:
The static mixer is typically used in a pressurized water line with flowing water. In this application, ozone gas pressure must be higher than the water pressure to force the ozone gas into the water. However, when the ozone generator/oxygen concentrator is turned OFF there is a chance for pressurized water to flow toward the ozone generator in the ozone gas line. Proper back-flow devices will be required to prevent water from damaging the ozone generator and other sensitive equipment.
Check valves can be used, electric ball valves, or water trapping devices that will trap and drain water from the water line. Whatever you choose, test and/or replace it frequently to ensure there is no chance that water can enter your ozone generator cell.
Also, all check valves fail. One check valve is never sufficient, and check valves alone are typically not sufficient.