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What GC setup do I need for natural gas composition analysis?

 

Natural gas composition analysis requires a 200 Series GC configured with both a Thermal Conductivity Detector (TCD) and a Flame Ionisation Detector (FID). The TCD measures permanent gases (nitrogen, carbon dioxide, oxygen) and the FID measures hydrocarbons (methane through to hexanes and beyond). Both detectors run from a single sample injection.

Sample introduction

Natural gas is introduced to the GC as a gas phase sample through a gas sampling valve. The valve captures a fixed volume of gas and injects it onto the column at the start of the analytical run. This gives consistent, repeatable injection volumes without manual syringe handling.

What the analysis measures

A single run separates and quantifies the individual components present in the gas. Typical measured compounds include methane, ethane, propane, iso-butane, n-butane, iso-pentane, n-pentane, hexanes plus, nitrogen, carbon dioxide, and oxygen.

Calculated properties

The measured composition is used to calculate the physical and commercial properties of the gas. These calculations are performed automatically by the Clarity data station software and include calorific value (both superior/gross and inferior/net), Wobbe Index, specific gravity, real density, and compressibility factor.

These calculated values are what determine the commercial worth of the gas and whether it meets pipeline or grid injection specifications.

Standards compliance

The 200 Series GC natural gas configuration produces results in compliance with ASTM D1945 (standard test method for analysis of natural gas by GC), ISO 6974 (determination of composition with defined uncertainty), ISO 6976 (calculation of calorific values, density, and Wobbe Index), ASTM D3588 (calculation of heating value, compressibility, and specific gravity), and GPA 2172 (calculation of gross heating value, relative density, and compressibility).

Where this is used

Natural gas analysis by GC is standard practice at gas processing facilities, LNG import and regasification terminals, custody transfer and fiscal metering points, pipeline quality monitoring stations, and quality control laboratories supporting gas distribution networks.

Want to discuss natural gas analysis for your facility? Get in touch with the team.