Ozone is a natural gas which forms in the atmosphere when an oxygen atom (O) joins with an oxygen molecule (O2) to form ozone (O3). This reaction requires the input of energy (such as a lightning strike), to join the oxygen atom with the oxygen molecule. As soon as the energy source is removed, the ozone immediately decomposes. Ozone is a colorless gas but has a very pungent odor. Although ozone has an extremely short life-span, it is one of the most powerful oxidizing agents produced and effectively neutralizing endo-toxins, viruses, bacteria, fungi and organic material extremely rapidly. Usually a ship-board Ozone generator takes ambient air and strips away the nitrogen, concentrating the oxygen content – which is then passed through a high voltage or high frequency electrical field to produce ozone. The ozone is then injected into the incoming ballast water to oxidize and neutralize any harmful aquatic species. A percentage of the aquatic species, especially any bacteria and viruses in the ballast water, are killed by direct contact with the ozone. The remainder are killed or neutralized when the ozone reacts with other chemicals that occur naturally in seawater, to form hypobromous acid, a highly effective disinfectant in its own right. Both ozone and hypobromous acid disintegrate extremely rapidly – ensuring that there is no damage to the receiving waters into which the treated ballast water is discharged. Air contains 21% oxygen, 78% nitrogen, 0.9% argon, and 0.1% other gases.
These system usually consists of an Air compressor that produces between 5 and 8 bar of compressed air by inhaling the air of the atmosphere and provides compressed air to oxygen generator through air receiver; as raw material for oxygen generator.
In the NK -O3 type Ozone system the Oxygen generators separate oxygen from compressed air through a unique Pressure Swing Adsorption (PSA) process. The PSA process uses two vessels filled with molecular sieve (a synthetic zeolite)
As compressed feed air flows through one of the vessels, the molecular sieve adsorbs nitrogen. The remaining oxygen passes through the vessel and exits as the product gas. Before the absorber becomes saturated with nitrogen, the feed air is diverted to the second vessel. At that point, the sieve in the first vessel regenerates by desorbing the nitrogen through depressurization and purging it with oxygen from the second vessel. This process is then repeated in the second vessel to complete a cycle that allows the oxygen generator to deliver a constant flow of product oxygen at 90% minimum purity. Under normal operating conditions, the molecular sieve is completely regenerative and will last indefinitely.
Air and oxygen receiver provide stabilized flow and pressure to the oxygen and ozone generator by reducing the pulsation respectively.
Air receiver stores compressed air for peak demand in excess of compressor flow rate. Air receiver increases the cooling of the compressed air and collects possible residual condensate and oil droplets. The pressure variations in the air net will be equalized and short cycle loading and unloading of the compressor minimized. Ozone is generated by converting part of the oxygen gas molecules O2 within a gap formed between two electrodes. When applying an alternating high voltage to the high voltage electrode, micro-discharges will take place in the discharge gap which will dissociate the oxygen molecules. Some of the freed oxygen atoms O will recombine with the remaining oxygen molecules O2 to form ozone O3. This principle is usually called "Silent Electrical Discharge".
O + O2 = O3
The ozone concentration of the gas at the outlet of the generator is expressed by the ratio of the ozone mass produced divided by the total outlet gas mass (% by weight) or the mass of ozone produced per volume of outlet gas (g/Nm3 ).
The ozone generation modules are cooled with water to efficiently remove all the heat generated by the generated by the process. Ozone generation is very sensible to the cooling water temperature and the gas quality. The lower the temperature, the higher the ozone efficiency will be.
An Ozone destructor is used to converts any unused ozone back to oxygen before release to the atmosphere. The ozone destructor is used to run the ozone system without injecting the ozone in the ballast water. It will help to evaluate the good operation of the ozone system.
Due to the hazardous and corrosive nature of ozone even in low concentrations, no ozone containing gas should be released into the atmosphere. The residual ozone concentration according to the safety requirements of lower than 0.2 ppmv will be observed. The unit comprises welded stainless steel housing and the catalyst. The destructor works according to the principle of catalytic ozone destroying. The gas flow to be treated will be passed through the catalyst. The residual ozone in the off-gas will be converted into oxygen on the surface of the composition metal catalyst. The off-gas flow has to be vented into open air. During this process, heat of reaction is released.
Ozone injector is very important equipment for ballast water treatment system using ozone as disinfection material. To increase disinfection effect and reduce toxic by-products, ozone should be introduced very quickly and uniformly to ballast water.
The Neutralizer is designed to remove Total Residual Oxidants (TRO) from ships’ ballast water that has been treated by the Ozone System. The Neutralizer makes the TRO concentration below 0.4mg/L by dosing neutralizer automatically, prior to discharge of the treated ballast water. Thiosulfate is usually used in the TRO neutralizer
Ambient ozone monitors can be tripped by the ozone leak in the ozone system. When an ozone alarm has been given the ozone production must be interrupted. All personnel must be evacuated from the contaminated area. The room containing ozone should only be entered when wearing a suitable breathing apparatus.
The TRO analyzer uses colorimetric DPD chemistry or an electrical TRO sensor to continuously monitor water for TRO.
