Application note

Oxygen content in blanket gas applications
Benefits:
Panametrics designed systems
maximize uptime:• Sample system design mitigatesliquid carry-over to the sensor• XMO2 thermoparamagnetic
sensor more immune to minor
liquid carry-over• XDP display/controller drives
solenoid valves in the sample
system for automatedcalibrations

Summary
Chemical, petrochemical, biochemical, and pharmaceutical companies, as well
as research institutions, may store liquids in large tanks, have mixing chambers, or
may have reaction processes where the presence of oxygen could lead to a fire oran explosion.

Application
Oxygen is measured in inert gases that blanket hydrocarbon and other organic
liquids during storage, mixing, or other processes.

Challenge
Air can leak into the vapor space above hydrocarbon liquids stored in tanks orprocess vessels. To remove the oxygen present due to the air leaking into thevessel, inert gases, such as nitrogen or carbon dioxide, are used to purge the vapor
space above the liquids. The oxygen level must be kept below the lower explosive
limit (LEL) of the hydrocarbon vapors present.
Prior to the use of thermoparamagnetic oxygen analyzers in this application,
electrochemical sensors were used, often without a proper sample system,
resulting in condensing hydrocarbons fouling/destroying the sensor. Frequent
manual calibration to ensure the sensor responds to changes in oxygen andreplacement due to liquid carry-over result in high maintenance andoperating costs.

Solution

Specifications

Continuous monitoring of the oxygen content using athermoparamagnetic oxygen analyzer with an analyzer
display package and a properly designed sample system(with solenoid valves for auto-calibration) provides
maintenance-free operation. The sample system canmitigate liquid condensation reaching the sensor. The sensor
design has no moving parts, thus any liquid carry-over canbe easily drained. The automatic calibration triggered by thecontroller minimizes manual calibration.

Application: 0 to 4% O2, (O2 below LEL)
Balance N2
Typical range is 0 to 21% O2

A typical installation includes a thermoparamagnetic oxygen
sensor mounted in a sample system like the one shown, witha display/controller that can actuate the solenoid valves forregular auto-calibration. In most applications, ambient air isthe span gas and the nitrogen from the purge system is thezero gas.
Galvanic fuel cell transmitters provide a lower up-front costalternative. They are more susceptible to liquid carry overand the sensors are a consumable spare part. The sample
system design shown above would remain the same, withthe galvanic transmitter replacing the thermoparamagnetictransmitter in the sample system shown.
In most applications, the appropriate location of the oxygen
measurement system is at or near the top of the vessel orstorage tank. The purge nitrogen source passes throughthe eductor in the sample system to draw the sample fromthe headspace. Liquids from the liquid dump, bypass filter
bottom flow, and the sample are returned with the nitrogenback to the headspace in a closed-loop system, thus venting
nothing to the atmosphere. Alternatively, during calibration,
the span gas may be vented to atmosphere so that thesystem does not introduce air into the headspace, even insmall amounts.

Temperature: Ambient
Pressure: Near 0 psigSample
inlet
CoolingcoilOxygen
analyzer

FilterPressure
gageLiquiddumpFlowmeter
Drain totank

Air inlet
Nitrogen inlet
EductorCalibration
gas outlet

Pressure
regulator

Flow diagram for typical low-pressure inerting sample system for percent
oxygen analysis

Panametrics, a Baker Hughes business, provides solutions in the toughest
applications and environments for moisture, oxygen, liquid and gas flow
measurement.
Experts in flare management, Panametrics technology also reduces flareemissions and optimizes performance.
With a reach that extends across the globe, Panametrics’ criticalmeasurement solutions and flare emissions management are enablingcustomers to drive efficiency and achieve carbon reduction targets acrosscritical industries including: Oil & Gas; Energy; Healthcare; Water andWastewater; Chemical Processing; Food & Beverage and many others.
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BHCS38774 (04/2023)

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