Oxygen analyzers, which can measure the oxygen level in enclosed spaces, are an essential piece of equipment for inert gas systems onboard vessels.
Regardless of the type of inert gas system – flue gas system, inert gas generator, nitrogen generator, etc – the data from oxygen analyzers ensures that the oxygen level of the product gas fulfils the required setting (typically 5% or less), which is the safety requirement to prevent cargo explosions. It also monitors the fuel to air ratio during combustion, which can be used to attain combustion and boiler efficiency.
There are three main types of marine oxygen analyzers available:
Zirconia Oxygen Analyzers
The main components of zirconia oxygen analyzers are a zirconia tube, porous platinum electrodes, and a DC voltmeter.
The platinum electrodes are both on the inner and outer side of the zirconia tube. One – either the inner or outer – side of the tube is in contact with the process/sample gas while the other is exposed to the surrounding air for reference. Because of the difference in concentrations of both gases, oxygen makes its way through the electrodes and tube from the more concentrated side to the less concentrated. During this process, the platinum acts as a catalyst by helping oxygen molecules to split into ions, allowing them to pass through the zirconia.
The DC voltmeter is then attached to the inner and outer electrodes for a potential difference reading. This measurement lets the analyzer accurately display the oxygen concentration in the gas being tested.
One of the main benefits of the zirconia oxygen analyzer is that it doesn’t require a sealed reference gas, which means that it can be utilized in any environment, even those with high temperatures and pressures. This is because instead of directly measuring the concentration of gas, it measures the partial pressure of the oxygen in a sample.
However, one major disadvantage of the system is that the temperature within the analyzer needs to be high for the oxidation process to occur. This causes changes in the sample gas temperature and high power consumption.
Galvanic Oxygen Analyzers
Galvanic oxygen analyzers are fuel cell based and thus involve an anode, often lead (Pb), and a cathode, often silver (Ag), reaction, similar to a battery. Both the anode and cathode are in an electrolyte solution. The cell contains a membrane that allows the oxygen to penetrate and gain the electrons emitted by the anode at the cathode, proportional to the rate of oxygen pressure.
The flow of electrons from this process creates a current that is proportional to the oxygen concentration, resulting in an oxygen measurement.
This type of oxygen analyzer is low cost and accurate within 0.1% of its oxygen percentage display, detecting any oxygen level from 0% to 100%. It is also very compact and doesn’t require any external power as the reaction it uses naturally occurs.
Paramagnetic Oxygen Analyzers
These types of oxygen analyzers make use of magnetic fields to measure oxygen levels. Because oxygen molecules are attracted by magnetic fields, as the gas being tested passes through this field, its rate of flow is impacted in proportion to the level of oxygen in the gas. This rate is then used to calculate the amount of oxygen present.
The device can detect oxygen levels from 0.5% to 100%.
Though these analyzers are relatively uncommon, they are very stable and aren’t impacted by mechanical shock.
Still, an issue with paramagnetic analyzers is that their readings can be affected by other gases that may mix with the test sample.
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About the author
GIANTECH specialises in the life cycle management of marine equipment. It is a leading marine engineering company with an experienced international service team specialising in inert gas systems, inert gas generators, nitrogen systems, boilers and burners, pressure-vacuum valves, incinerators and compressors on-board vessels.
For more information, please visit https://www.igiantech.com/services/inert-gas-system-servicing/
Note: This article provides general information only and does not represent formal advice or the positions of any equipment maker.