Natural gas heating value measurement | Industrial, Medical And Specialty Gases | Coregas Australia

Natural gas heating value measurement

Measurement of the natural gas heating value is essential to fair billing. The GC-TCD instrument used for this requires high precision calibration gas mixtures to ensure precise analysis.

The natural gas distribution grid in Australia has multiple inlet points and take-off points. At these points where gas enters and exits the pipeline, it often changes ownership and is either sold or bought. These events are referred to as custody transfer. When a change of ownership of the gas takes place, there needs to be an accurate measurement of the gas flow rate.

Flow rate measurement takes place at natural gas metering stations for custody transfer

In addition to the flow rate, the billing of the natural gas will be based on its heating value, or Wobbe index, which is measured using a GC-TCD setup. The heating value of the natural gas is calculated by measuring the exact composition of the various hydrocarbons in the gas stream and the use of formulae and tables in ISO 6976:2016.

The GC-TCD analyser must be calibrated using high-precision synthetic natural gas calibration gas mixtures. For custody transfer measurements, it is general practice to use certified, traceable reference materials which are accredited to ISO/IEC 17025 or ISO 17034.

The exact composition of synthetic natural gas calibration mixtures for heating value and Wobbe index measurement varies depending on the chemicals present in the natural gas at that point in the gas distribution network. An example mixture might be something like this:

  • Nitrogen 2%
  • Carbon dioxide 3%
  • Ethane 8%
  • Propane 2%
  • Isobutane 0.5%
  • n-Butane 1%
  • Isopentane 0.3%
  • n-Pentane 0.2%
  • Methane 83% (balance)

At Coregas we have a broad NATA accreditation scope for the production of synthetic natural gas standards. We are able to produce multi-component ISO 17034 or ISO/IEC 17025-accredited reference materials with hydrocarbons from C1 to C10. In addition to the production of high-quality calibration gases we provide a speedy and reliable delivery service. We understand the pressures that exist in this business and the importance of maintaining the natural analysers in a good state of readiness and will always be willing to go the extra mile to get these gas mixtures to you as quickly as possible.

Accurate flow measurement using ultrasonic technology combined with accurate gas composition measurement using GC TCD techniques results in accurate billing of energy values

Gas control equipment selection

two-stage regulator should be specified for the carrier gas because this is a continuous flow application. Chrome-plated brass is suitable as a body material for these high purity gases. A single-stage regulator may be used for the calibration gas mixture because this is not a continuous flow application.

If the calibration gas has been ordered to contain traces of mercaptans or low levels of hydrogen sulphide, it is essential to specify a stainless steel regulator for this application. This will ensure the calibration gas purity is retained and to avoid any potential reactions with a brass body regulator.

Coregas is the exclusive distributor of the Spectron gas control equipment range, which includes the Spectrolab range of high purity specialty gases equipment range of regulators, in Australia. Both the single-stage and two-stage models required are available from our specialty gases customer service team.

In a class of our own

Cylinder gases ready for export
Cylinder gases ready for export

Coregas is a world class supplier of ISO 17034-certified reference materials for natural gas measurement calibration. Our NATA accreditation for multiple component natural gas standards, including reactive mercaptan components, has put our products on the map in Australia and overseas. We are proud to export our accredited calibration gas mixtures to locations as far away as South America.

Coregas natural gas standards with ISO 17034 accreditation are valued by our overseas customers