Overview
CEN ISO/TR 24094:2007 (adopted from ISO/TR 24094:2006) provides validation methods for gaseous reference materials used in natural gas analysis. The Technical Report defines how to validate calorific value and density values that are calculated from routine natural gas analyses by statistically comparing them with direct measurements made using a reference calorimeter and a density balance. The report documents the VAMGAS project approach and confirms that careful application of current ISO methods gives agreement between calculated and reference-measured physical properties.
Key Topics
- Scope and objective: Validation of calculated calorific value (superior calorific value) and density derived from natural gas composition.
- VAMGAS project structure:
- Part 1 - comparison of values calculated from primary reference gas mixtures (PRMs) (gravimetrically prepared) against reference measurements.
- Part 2 - gas chromatography (GC) intercomparison using PRMs as calibrants; calculated properties compared with reference instruments.
- Reference measurements: Use of a reference calorimeter (Ofgem/Ofgas, UK laboratory) and a precision density balance (Ruhrgas, Germany laboratory) to obtain benchmark values.
- Analytical chain covered:
- Gravimetric preparation of calibration gas mixtures (PRMs) per ISO 6142.
- Gas chromatographic analysis of natural gas (ISO 6974 series).
- Calculation of physical properties from composition per ISO 6976.
- Statistical comparison and validation methods: Robust statistics to assess agreement between calculated and measured values.
- Limitations noted: Physical property measurements (calorific value, density) cannot uniquely identify or validate full gas composition - a given CV or density can correspond to many different mixtures.
Applications
- Gas laboratories and metrology institutes validating calibration gases and measurement systems.
- Natural gas suppliers, transmission operators and distributors seeking confidence in billing/fiscal energy calculations and quality assurance.
- Accreditation bodies and test houses running interlaboratory comparisons or validating analytical methods.
- Producers of calibration gas mixtures (PRMs) for demonstrating traceability and conformity.
- Use cases include fiscal metering validation, QA/QC of gas composition analysis, and establishing measurement traceability for calorific value and density.
Related Standards
- ISO 6142 - Gravimetric preparation of calibration gas mixtures
- ISO 6974 (Parts 1–6) - Natural gas GC analysis with defined uncertainty
- ISO 6976 - Calculation of calorific values, density and Wobbe index from composition
- GUM - Guide to the expression of uncertainty in measurement
This Technical Report is essential reading for professionals involved in natural gas measurement, calibration gas production, and validation of analytical chains where accurate calorific value and density are critical. Keywords: CEN ISO/TR 24094:2007, ISO/TR 24094:2006, natural gas analysis, gaseous reference materials, validation methods, calorific value, density, VAMGAS.