Introduction to Ozone Generation Techniques – Corona, UV and Electrochemistry

Introduction to Ozone Generation Techniques – Corona, UV and Electrochemistry

Siemens developed the first ozone generator, which was based on corona discharges in 1957.   Today ozone is produced by several different methods both commercially and in the laboratory.

The generation of ozone involves the intermediate formation of atomic oxygen radicals which can react with molecular oxygen. All processes that can dissociate molecular oxygen into oxygen radicals have the possible for ozone generation. Energy supplies that make this action possible are electrons or photon energy. Electrons can be used from high-voltage supplies in the corona release, from nuclear supplies, and from electrolytic processes. appropriate photon quantum energy includes UV light of wavelengths lower than 200 nm and γ-rays.

In character, ozone generation occurs when oxygen molecules reacts in the presence of electrical discharges, e.g., lightning, and by action of high energy electromagnetic radiation. Some electrical equipment inadvertently generates levels of ozone that can be easily smelled; this is especially true if there is a spark or a very high voltage.

Ozone Generation by Corona release

Corona release in a dry course of action gas containing oxygen is presently the most widely used method of ozone generation for water treatment. The corona or plasma is produced in an ozone generator by applying a high voltage between two electrodes. Ozone is formed by the following responses:

A             1/2 O2 = O                   Heat of Reaction A= +59.1 Kcal

B             O + O2 = O3                Heat of Reaction B = -24.6 Kcal

AB          3/2 O2 = O3                  Heat of Reaction AB= +34.5 Kcal

The overall reaction (AB) that produces ozone requires energy and is an endothermic reaction that obtains energy from the electric release. A basic ozone generation system is composed of the following: gas source (compressed air or oxygen), gas dryers, and ozone generators.

It is of utmost importance that a dry course of action gas is applied to the corona release. Limiting nitric acid formation is also important in order to protect the generators and to increase the efficiency of the generation course of action. In normal operation of properly designed systems, a maximum of 3 to 5 g nitric acid is obtained per kilogram ozone produced with air. If increased amounts of water vapor are present, larger quantities of nitrogen oxides are formed when spark discharges occur. Also, hydroxyl radicals are formed that combine with oxygen radicals and also ozone. Both responses reduce the ozone generation efficiency. consequently, the dryness of the time of action gas is important in order to acquire a good provide of ozone. additionally, with air, nitrogen oxides can form nitric acid, which can cause corrosion.

The formation of ozone by electrical release in a course of action gas is based on the corona release in air or oxygen. In an ozone generator here are numerous distributed micro electrical discharges (arc or plasma) by which the ozone is effectively generated. It appears that each individual micro release lasts only several nanoseconds. The current density ranges between 100 and 1000 Amps/cm2. By using oxygen or enriching the time of action air in oxygen, the generating capacity of a given ozone generator can be increased by a factor ranging from 1.7 to 2.5 versus air alone. Whether using air or oxygen satisfy energy is lost in the form of heat, cooling of the time of action gas is very important. In smaller systems this is often down by using ambient air to cool one or both of the electrodes. In larger systems the cooling is typically done with water usually on the ground electrode.

Other methods of ozone generation include:

Photochemical Ozone Generation

The formation of ozone from oxygen exposed to UV light at 140-190 nm was first reported by Lenard in 1900 and fully assessed by Goldstein in 1903. It was soon recognized that the active wavelengths for technical generation are below 200 nm. In view of present technologies with mercury-based UV-emission lamps, the 254-nm wavelength is transmitted along with the 185-nm wavelength, so destruction of ozone occurs at the same time with its generation. additionally, the relative emission intensity is 5 to 10 times higher at 254 nm compared to the 185-nm wavelength. consequently only small amount of ozone can be produced.

Attempts to reach a appropriate photo stationary state of ozone formation with mercury lamps have failed. The main reason for this failure is that thermal decomposition is concomitant with ozone formation. Except for small-extent uses or synergistic effects, the UV-photochemical generation of ozone has not found extensive use.

Electrolytic Ozone Generation

Electrolytic generation of ozone has historical importance because synthetic ozone was first discovered by Schönbein in 1840 by the electrolysis of sulfuric acid. The simplicity of the equipment can make this course of action attractive for small-extent users or users in far away areas.

Many possible advantages are associated with electrolytic generation, including the use of low-voltage DC current, no satisfy gas preparation, reduced equipment size, possible generation of ozone at high concentrations, and generation in the water, eliminating the ozone-to-water contacting processes. Problems and drawbacks of the method include: corrosion and erosion of the electrodes, thermal overloading due to anodic over-voltage and high current densities, need for special electrolytes or water with low conductivity, and with the in-site generation course of action, incrustations and deposits are formed on the electrodes, and production of free chlorine is inherent to the time of action when chloride ions are present in the water or the electrolyte used.

Radiochemical Ozone Generation

High-energy irradiation of oxygen by radioactive rays can promote the formation of ozone. already with the popular thermodynamic provide of the time of action and the interesting use of waste fission isotopes, the cheminuclear ozone generation course of action has not however become a meaningful application in water or waste water treatment due to its complicated course of action requirements.

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