Ozone is a powerful oxidant used in air and water disinfection because it can destroy a wide variety of compounds, especially organic ones such as bacteria and fungi that come into contact with ozone molecules. (Ozone is commonly known for being a chemically unstable compound that spontaneously breaks down into oxygen after the treatment process). The reason ozone cannot be stored in a cylinder is that high pressures are needed to store it. Therefore, ozone must be produced on site.
Professional ozone production has three requirements. These include:
- High ozone output
- Low concentration of nitrogen oxides
- High ozone concentration
Oxygen Concentration & Ozone Output
Oxygen concentration has a significant impact on ozone output.
The output of an ozone generator (or the production power of ozone ) P (g/hour) and the concentration of ozone C (g/m3) characterizes the quality of ozone generator.
Both of them are important for the effectiveness. It is important to be aware of the generator’s power for different applications. It is well known that greater ozone concentrations are more soluble in water. According to figure 1 given below, ozone output has increased from 3 g/hr to 24 g/hr, while oxygen concentration has increased from 21 percent to 98 percent.
An oxygen generator usually produces twice as much ozone as one using dry air (2X). Here the ratio is nearly 8 (8X), (24.5 grams per hour vs. 2.85 grams per hour). Because the ambient air was humid (air humidity > 80 %, at 24 ℃), low oxygen output can be achieved because of the very high productivity of oxygen.
In comparison with humid ambient air, feed gas with 35 percent oxygen doubles ozone production (5.94 g/hr vs 2.85 g/hr). By using oxygen as a feed gas (98 percent) with a high oxygen concentration, the production of ozone is improved since radicals ( ions and electrons) generated by corona discharge are more likely to bombard oxygen molecules.
Concentration of ozone versus oxygen concentration shows a similar pattern: the greater the oxygen concentration in feed gas, the greater the concentration of ozone (21% oxygen produced ~9 g/m3 ozone, 98% oxygen provides 80 g/m3 ozone).
Figure 1: Ozone output (g/hr) & ozone concentration (g/cubic meter) vs. oxygen concentration (%) of inlet gas (ambient temperature » 24 oC, flow rate » 5 L/min, electric current of the ozone generator ~AC 2.5 A, 220 V
In industries that produce hundreds of kilograms of ozone per hour, oxygen is usually supplied from pressure cylinders or liquid oxygen. A small-scale ozone generator (50-200g per hour) uses zeolites as an adsorbent and feeds its gases with oxygen produced by PSA generators. Utilizing the oxygen, the output of ozone is equal to that of fractional distilling liquefied air, which produces 24 grams of ozone per hour.
In addition, concentrating oxygen does not result in nitric acid formation in the ozone generator, so it prevents the formation of metallic details being damaged by nitric acid.
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