Ozone installations are very important for water treatment. The efficiency of the entire installation is critical for treatment performance. Using Primozone ozone technology along with a suitably designed ozone solution will translate into reduced running costs and lower investment costs.
High ozone concentration and high gas pressure are revolutionizing the way ozone installations are designed as they enable improvement of performance at different points in the system.
Two possible reactions can take place during the course of ozone production. Based on the design of an ozone generator, the probability of the required reaction, that is ozone production can be increased significantly.
Since oxygen will always be present, the outgoing gas will continue to be a mixture. In fact, the ratio between the oxygen and the outgoing ozone is what constitutes the concentration of ozone concentration. Such ozone concentrations are often expressed by utilizing g/Nm3 or wt %. Figure 1 shows the savings in oxygen at high ozone concentrations.
- g/Nm3: This refers to ozone weight in comparison to the remaining volume of the gas, at a specified pressure and temperature.
- wt %: This is usually around 10wt % , which means that the ozone gas is 10% of the overall weight of the gas mixture
Figure 1. The graph shows savings in oxygen at high ozone concentrations. From 10 to 20 wt%, the oxygen need is halved.
The amount of ozone, determined in g/h, is the overall amount of ozone created each hour. Based on the concentration of the gas mixture, the entire amount of oxygen required to generate ozone will differ considerably. For instance, if the concentration of ozone is doubled, the quantity of oxygen feed to the system is decreased to 50%, as shown in Figure 1.
Basics - Ozone Production
Commercial or industrial ozone generators are fed with a minimum of 95% oxygen from LOX or PSA. The ozone generator introduces energy to the diatomic oxygen molecules through electrical discharges, thus breaking up the covalent bond that exists between the oxygen atoms, which in turn forms the molecule.
The outcome is O2= 2xO1. The O1, which is often known as oxygen radicals, attempts to locate a lower energy state and based on the availability of other molecules, they form one or two possible reactions with other oxygen molecules or atoms, that is, oxygen (O1+O1=O2) or ozone (O1+O2=O3). These reactions will take place within an ozone generator. This converts the outgoing gas from an ozone generator into a gas mixture between ozone and oxygen.
The surface area between the water and the gas is increased to optimize the process of dissolving ozone in water. This can be carried out using static mixers, bubble diffusers, or venturi injectors.
Given a specified gas volume, small gas bubbles tend to exhibit a bigger surface than a large, single bubble. This means that gas bubbles which are very small are dissolved in a better way.
After the ozone has been generated, it must be dispersed in the water that needs to be treated. Once the ozone is suitably dissolved, it will locate pollutants to react with. The ozone oxidation or ozone reaction takes place when the ozone is converted into oxygen radical (O1) and oxygen (O2).
This oxygen radical reacts with the pollutant present in the water. As soon as the radical has reacted with the pollutant, only oxygen alone remains. Upon increasing the surface, only ozone will be dissolved until the saturation limit has been reached.
In order to dissolve more ozone, the saturation limit can be further increased by raising the pressure. When ozone is being dissolved in water, the major challenge would be to dissolve sufficient ozone to reach the PPM demand of the customer.
Methods of Increasing Ozone Dissolution in Water
Two options are available to increase ozone dissolution in water: increase the pressure of the dissolution system, or reduce the amount of oxygen that has to be dissolved, for instance having higher ozone concentration.
It all comes down to the physical law devised by William Henry in back in 1803, also called Henry's law. This is defined as “at a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid”.
Figure 2 shows how the amount of dissolved ozone is directly proportional to the gas pressure at a specified temperature, and Figure 3 shows how the amount of dissolved ozone is directly proportional to the ozone concentration at a specified temperature.
Figure 2. Amount of dissolved ozone is directly proportional to the gas pressure at any given temperature (here 10° C)
Figure 3. Amount of dissolved ozone is directly proportional to the ozone concentration at any given temperature (here 10° C)
In order to allow gas flow from the generators to the dissolution system, the dissolution system must exhibit a lower pressure than the ozone generators.
However, the saturation limit for the water depends on the true pressure at the dissolution. As a result, the discharge pressure of the ozone generator becomes very important.
Primozone Ozone Technology
The high ozone concentration of up to 20wt% and the high pressure of up to 4bar/58psi facilitated by the Primozone ozone technology will enhance the performance of ozone installation by:
- Allowing up to 95% more dissolved ozone in the water
- Reducing the amount of oxygen required to 50%
- Producing 50% less off-gas
Figure 4. Diagram of Primozone ozone technology
All the above factors translate into reduced running costs and lower investment costs. Figure 4 shows a layout of Primozone ozone technology.
This information has been sourced, reviewed and adapted from materials provided by Primozone.
For more information on this source, please visit Primozone.