Gas analyzers for oxygen, nitrogen and argon production on air separation units

Working for you to enhance operational safety, maximize process efficiency and optimize product yield

Paying for its self with better profits – a case study in argon recovery

Argon is often a highly valuable by-product from ASU operations. Maximizing the argon yield from an ASU can often make or break the process economics. Optimization of the LP distillation column and the argon column operation requires measurement of oxygen in the argon column feed. A process value of 8 to 10% is common. Getting this process parameter right is one of the best ways to ensure that the maximum amount of argon is recovered for sale and to avoid it flowing out with the pure oxygen. Percentage level oxygen measurement is where the Magnos28 excels. 

And with our patented Microwing technology, measurement accuracy is high and drift is low. This means that you can rely on your instrument to support your process all of the time whilst instrumentation calibration costs can be reduced.

Measurement of the final product oxygen purity is also essential for contractual product quality assurance. And it is a tell tale sign of argon slippage from the ASU also. With a measured value typically at 99.6% and a range between 98 and 100% the suppressed zero capability of the Magnos28 comes to the fore in this application. Considering the improved argon recovery from precise oxygen purity measurement, the one time investment to replace an existing oxygen analyzer with a new Magnos28 can pay back within a year on larger ASUs and with a couple of years on smaller ones. For new projects, we believe that specification of the Magnos28 from the start will quickly become the new industry standard.

While the Magnos28 is the perfect sensor for the complete Vol % Range like the lowest 0-0.5 vol% to up to the highest suppressed 99.5-100 vol% range, the ZO23 O2 trace analyzer is the perfect choice for proofing the absence respectively the smallest ppm concentrations between 0 and 1 ppm of oxygen in inert gases e.g. such as nitrogen, carbon dioxide or noble gases like argon.


Process safety – where reliability matters most

The principal precautions against hydrocarbon contaminant build up in the cryogenic liquid in the ASU are well established and focus on carbon dioxide analysis at the warm end of the ASU and hydrocarbons analysis in the cryogenic liquid oxygen sump. Analysis of carbon dioxide after the pre-purification unit (PPU) using a gas analyzer such as the Uras26 is important to ensure that this gas does not enter the ASU because it solidifies and causes blockages. Furthermore, detection of carbon dioxide break-through from the PPU is used to warn about the possibility that hydrocarbons such as methane or ethane are not being removed by the PPU and are also entering the ASU. This serves as an early warning system.

Analysis of hydrocarbons in the cryogenic liquid where there is the highest potential concentration of hydrocarbon contaminants (generally by extraction of liquid oxygen from the main reboiler sump) is the second line of defence. For the THC measurement, many instrument engineers and plant operators will be familiar with flame-ionisation-detector (FID) gas analyzers such as the Fidas24. This technology has an established history in this application and can be operated either with, or without a methane cutter to provide THC and non-methane HC (NMHC) readings. Whilst the technique is robust, it does require specialty gases grades of high purity hydrogen and instrument air for its operation to create the flame. Cylinder change overs of these consumable gases are required in addition to occasional calibration using a certified specialty gas mixture.

For additional speciation within the hydrocarbons our Uras26 NDIR instrument is suitable. It can be configured to measure up to four separate IR-active species, for example: methane, ethane, ethylene and propane. These are some of the main hydrocarbon contaminants that have the potential to accumulate in the liquid oxygen in the ASU main reboiler sump.

Regular acetylene analysis can be performed by taking liquid oxygen samples and sending them to a specialised accredited offsite contract laboratory. Most operators are looking to detect acetylene at less than 0.5 VPM and reliable and precise continuous gas analysis techniques for acetylene measurement in the sub-VPM level are not common. But, we believe that our LGR-ICOS analyzer is up to the task. This enhanced laser technique is capable of accurate trace hydrocarbon measurements in a complex background gas matrix.

As a bonus, the Uras26 and LGR-ICOS instrumentation above require no consumable gases and have minimal calibration gas mixture requirements. This simplifies gas analyzer maintenance and reduces their cost of ownership.  It all adds up to safe and productive ASU operations.

Continuous gas analyzers for ASU risk managment, process control, yield optimsiation and quality control

Flexibility to customize your instrument from these continuous gas analyzer modules

Magnos28 – paramagnetic analyzer for percentage level oxygen analysis. Typical applications include ASU oxygen purity control, ASU waste nitrogen purity control and ASU argon column feed oxygen purity control.
 – NDIR (non-dispersive infrared) analyzer capable of measuring various gases including carbon monoxide, carbon dioxide, methane and other light hydrocarbons. Core application is ASU PPU carbon dioxide breakthrough detection. Also suitable for detection of various light hydrocarbons in the reboiler sump liquid oxygen for process safety.
Fidas24 – FID (flame ionisation detector) analyzer for hydrocarbon detection. This instrument is also available with a cutter to measure non-methane hydrocarbons in addition to THC. Frequently specificied for hydrocarbon measurement in reboiler sump liquid oxygen, which is critical for ASU process safety.
LGR-ICOS – laser process analyzers for online VPM level acetylene analysis. An innovative, automated and cost effective approach to ASU reboiler cryogenic safety.
ZO23 – zirconium oxide trace oxygen in nitrogen analyzer. Ideal for confirmation of pure nitrogen product quality control with trace oxygen measurement.


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