Daily Operation Toolkit
GAS QUALITY & WOBBE
GPA 2172 / ISO 6976 heating value and combustion metrics.
- ISO 6976:2016
- GPA 2172 (reference-condition convention)
- AS 4564 (default interchangeability band only)
Gas Quality & Wobbe calculates heating value, Wobbe Index and relative density for a natural gas stream to ISO 6976:2016, on a wet or dry basis, and tests the Wobbe Index against an interchangeability band.
Capabilities
- Gross (HHV) and net (LHV) heating value.
- Wobbe Index, tested against a user-set band (AS 4564 by default).
- Real specific gravity, total inerts and compressibility at standard conditions.
- Wet or dry basis: an entered water-vapour content re-normalises the composition before calculation.
- Selectable reference conditions: three ISO combustion/metering temperature pairs, or the GPA 2172 60°F/60°F convention.
- Exportable PDF report.
Why the results hold up
ALKANE calculates heating value, relative density and Wobbe Index by the ISO 6976:2016 summation method, the current international basis for natural gas calorific value. The standard’s summation-factor correction from ideal to real-gas conditions is applied at the selected combustion and metering reference conditions.
Verification
ALKANE’s V&V Diagnostics includes a gas quality suite, which checks the engine against published reference data. Details are on Validation & Verification.
Scope
Summation factors for undecanes, dodecanes, helium and the two heavy pseudo-cuts (C13–C15 and C16–C20) are estimated, because ISO 6976 has no table entry for them. The method is best suited to pipeline-quality sales gas. A composition that condenses at the selected reference conditions has no defined heating value or Wobbe Index, and none is reported. Wobbe Index is one interchangeability measure; the applicable tariff specification governs.