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Clamp-on Ultrasonic Technology for Non-Invasive Standard Volume Gas Flow Measurement

9 Dec 2021  |
As a leader in the field of non-invasive flow measurement with ultrasonic technology, FLEXIM has long-term experience in measuring hydrogen.

With a new and sophisticated feature ‒ the Natural Gas Engine ‒ FLEXIM’s gas flowmeters FLUXUS G are now able to determine the standard volume flow rate of gases even with varying compositions.

Content matters. This is particularly true for natural gas. The calorific value of natural gas primarily depends on its composition. Changes in supply and demand as well as the target to reduce significantly the carbon foodprint have led to changing transport routes and therefore to changing gas compositions. Hydrogen will play a crucial role in the energy transition. Network operators are aware of the challenges this poses.

Normal practice for flow measurement in transport processes of gaseous hydrocarbons is the calculation of standard volumes. For this purpose, an actual volume flow, temperature and pressure are measured. In addition, the agreed-upon standard pressure and the standard temperature are specified. In addition, the gas composition is known, e.g. using a gas chromatograph. Then a standard volume flow can be calculated from the operating volume flow using a flow computer. This approach is relatively expensive and time-consuming and may be delayed.

Flow computers work with thermodynamic equations which calculate all important state variables of gas mixtures at specified pressure and temperature. Especially important for flow applications are compressibility, molecular weight, density and calorific value.

Acoustic analytics

FLEXIM’s new approach is based on the measurement of the sonic velocity. Typcial gas compositions have their characteristic sonic fingerprint. With a database of thousands of gas flow measuring points, FLEXIM developed a new functionality for its gas flowmeters FLUXUS G: The Natural Gas Engine, NGE.

Supported by the same thermodynamic equations as a flow computer, the Natural Gas Engine, also calculates compressibility, molecular weight, and density. However, the difference is that the gas composition does not have to be known, only the class of natural gases needs to be selected by the user. Then, the exact calculation of compressibility, molecular weight and density is done with the NGE from the measurement of pressure, temperature, and sound velocity.

Proven performance

As the only manufacturer of clamp-on ultrasonic measuring technology, FLEXIM has been invited to participate in the Joint Industry Project (JIP) on “Suitability of natural gas flow meters for renewable gases”. The test facility was the multiphase flow lab at DNV in Groningen. The user group was formed by all major pipeline operators in the EU. The manufacturer group was formed by all well-known custody transfer gas flowmeters in the majority with USM, but also some turbine flowmeters.

The results of the studies are outstanding for FLEXIM: The flow meters’ capabilities to handle natural gas mixtures with up to 30% Hydrogen and up to 20% CO2 were tested during the project. Here is a summary of FLEXIM’s test results with the FLUXUS G721 that was installed in dual channel arrangement:

  • Over the entire test program, the FLUXUS G721 performed within its specified measurement uncertainty (±1…2%) and repeatability (0.15%).
  • The average repeatability overall flow points was 0.11% for the FLUXUS G721. The inline ultrasonic meters had values between 0.055% and 0.136% for average repeatability.
  • The FLUXUS G721 performed better than some of the custody transfer inline meters tested.

“We live in interesting times“, states Eike Schwede, FLEXIM’s sales director for the Middle East: “The oil & gas industry will have to reinvent itself, it has to become more efficient and more flexible at the same time. As flexibility is our cardinal virtue, we feel ideally prepared for transformation processes, both by our mind-set as by our technology. And with almost twenty years of experience in non-invasive gas measurement, we are ready for the era of hydrogen.“

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As the technological leader in the field of non-invasive ultrasonic flow measurement with ultrasound, FLEXIM continuously sets standards. Our clamp-on ultrasonic measurement systems FLUXUS measure virtually anything that flows, liquids as well as gases. Today,...

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