Overview
ISO 23874:2006 - Natural gas - Gas chromatographic requirements for hydrocarbon dewpoint calculation - defines gas‑chromatography performance and procedures required to determine the hydrocarbon dewpoint of treated natural gas (transmission/pipeline quality). The standard specifies analysis depth and uncertainty control so that an appropriate equation of state can be used to calculate the hydrocarbon dewpoint (including cricondentherm) for gases with maximum dewpoints between 0 °C and −50 °C at pressures of 2 MPa (20 bar) to 5 MPa (50 bar).
Key features:
- Focus on hydrocarbons from C5 to C12 (higher hydrocarbons handled as fractions).
- n‑Pentane is used as a bridge/reference component; C6+ hydrocarbons measured relative to n‑pentane.
- Major components (N2, CO2, C1–C5 range) measured using ISO 6974 methods.
Key Topics and Requirements
- Measurement scope: Comprehensive analysis for inert gases and hydrocarbons up to C12; helium, hydrogen, water and sulfur not required unless >0.01 mole fraction.
- Measurement systems: Separate systems for major components (per ISO 6974) and for higher hydrocarbons (Annex A gives typical conditions). Detection typically expects a predictable mass/carbon‑based response (commonly an FID).
- Performance limits: Capability to detect individual alkanes up to n‑dodecane and down to ~1×10‑7 mole fraction (0.1 ppm).
- Identification & quantification: Unidentified C7+ components are allocated by carbon number or molar mass; alkanes C7+ are summed by carbon number and treated as fractions for dewpoint input. Boiling points for fractions are interpolated between n‑alkanes.
- Calibration & reference gases: Use of CRM mixtures - CRM1 for major components (ISO 6974) and CRM2 containing at least n‑pentane, n‑hexane, benzene, cyclohexane, n‑heptane, toluene, methylcyclohexane and n‑octane.
- Analytical procedures: Validation steps include precision evaluation (area ratios vs. n‑pentane), determination of relative response factors (multiple repeat analyses of CRM2), and validation of fraction data.
- Uncertainty: The standard addresses compositional uncertainty and the analytical contribution to hydrocarbon‑dewpoint uncertainty.
Applications and Users
ISO 23874:2006 is intended for practical use by:
- Gas chromatography laboratories performing natural gas composition analysis.
- Transmission and pipeline operators ensuring gas quality and compliance with dewpoint specifications.
- Custody transfer, metering and contractual verification where hydrocarbon dewpoint and phase behavior are critical.
- Gas processing engineers and safety teams avoiding liquid dropout/condensation in high‑pressure systems.
Keywords: ISO 23874:2006, hydrocarbon dewpoint, natural gas, gas chromatography, C5 to C12, n‑pentane, cricondentherm, FID, equation of state.
Related Standards
- ISO 6974 (all parts) - Determination of composition by gas chromatography
- ISO 6975 - Extended analysis - Gas‑chromatographic method
- ISO 10715 - Natural gas sampling guidelines