Overview
ISO 2615:2024 - Analysis of natural gas - Biomethane - Determination of the content of compressor oil - provides standardized guidance for sampling and gas‑chromatographic analysis of compressor oil in biomethane and compressed natural gas (CNG). The method defines sampling on high‑efficiency coalescing filters (including collection of the first two cubic metres of gas at standard conditions at a refuelling station), recovery of oil from filters and buffer tanks, and quantification by GC/MS or GC/FID. It applies only to compressed gases at pressures > 18 MPa and covers compressor oil mass fractions from 3 mg/kg to 30 mg/kg, expressed as mass fraction.
Key topics and technical requirements
- Sampling principle: Rapid pressure drop through a nozzle spray to condense oil droplets onto coalescing filters; two filters in series (main + backup) and a buffer tank collect condensate.
- Sampling volume: Typical arrangement targets the first two m3 (standard conditions) delivered at refuelling stations.
- Analytical methods: Gas chromatography with either mass spectrometer (GC/MS, EI mode) or flame ionization detector (GC/FID).
- Calibration: Use compressor oil samples from the same station or equivalent oils; calibration standards prepared by diluting oil to 1–10 mg/ml in an analytical solvent.
- Extraction procedures: Two validated options - ultrasonic extraction with nitrogen flush, and pressurised fluid extraction (cells up to 150 °C, static pressures to 10 MPa).
- Materials & purity:
- Sampling filters: borosilicate microfiber coalescing filters (>99.99% efficiency at 0.01 µm).
- Solvents: analysis grade dichloromethane, pentane, hexane (same solvent for extraction and calibration).
- Gases: nitrogen (≥99.999% purity; THC < 0.5 µmol/mol) and compressed liquid propane (≥99.999%).
- Scope limits: Applicable only to compressed gas at p > 18 MPa; measurement range 3–30 mg/kg.
- Quality & traceability: Methods reference ISO/IEC Guide 98‑3 (uncertainty), ISO/IEC 17025 (laboratory competence) and ISO 6974 series for GC composition analysis.
Practical applications and users
- Biomethane and CNG refuelling station operators (monitor oil carryover).
- Gas laboratories performing composition and contaminant analysis (GC/MS, GC/FID).
- Compressor and lubricant manufacturers (performance and compatibility checks).
- Regulators and certification bodies ensuring fuel quality for grid injection or transport use.
- Operators implementing biomethane specifications (supports ISO 15403‑1, EN 16723 series).
Related standards
Keywords: ISO 2615:2024, biomethane, compressor oil, sampling, coalescing filters, gas chromatography, GC/MS, GC/FID, CNG, refuelling station, oil mass fraction.
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