Process Gas Composition Analysis: GC, MS and Photometer
Multi-component analysis of process gases: process gas chromatographs, mass spectrometers, process photometers and portable IR analyzers.
Measurement methods: Gas Chromatography, Process Mass Spectrometry, IR / FTIR Spectroscopy, Process Photometry
Why is gas composition measured?
In refineries, petrochemical, fertilizer and gas processing plants, the composition of process gases determines product quality, safety and efficiency. An impurity in feed gas can poison a catalyst, the composition of fuel gas changes combustion tuning, and the component ratio in product gas determines the sales specification. Multi-component analysis systems, which monitor several or even dozens of components simultaneously, are therefore used rather than measuring a single gas.
Where is gas composition measured?
- Refinery and petrochemical units: In feed, intermediate and product streams.
- Gas processing and filling: In quality control and at transfer points.
- Biogas and CO₂ production: In purity and impurity monitoring.
- Site and occupational hygiene: In confined space and leak surveys with portable instruments.
Methods for measuring gas composition
- Gas chromatography: The sample is injected into columns through a rotary valve, components are separated and measured by detectors such as TCD, FID or FPD; results are sent to the DCS.
- Process mass spectrometry: The sample is ionized and separated according to mass-to-charge ratio; many components can be measured simultaneously and very quickly. With a multi-stream sample selector, dozens of measurement points can be monitored by one instrument.
- Process photometry: Light absorption at selected wavelengths is measured; a fiber optic connection allows the electronics to be kept outside the hazardous area.
- IR / FTIR spectroscopy: Many gas and vapor components are measured on one instrument by infrared absorption.
Choosing a process gas analyzer
- Number of components, concentration range and required response time
- Sample preparation and sample line design
- Hazardous area classification and cabinet requirement
- Calibration gas and data integration (Modbus, OPC)
Gas composition analysis with Tetra
Tetra supplies Yokogawa GC8000, Thermo Scientific Prima PRO, Galvanic FPA4100 and MIRAN SapphIRe instruments. It integrates ATEX cabinets and sample preparation systems at its own facility, and provides installation, commissioning, calibration and service in Türkiye.
Frequently asked questions
Should you choose a process gas chromatograph or a mass spectrometer?
A gas chromatograph separates components as it measures, which makes it strong for complex mixtures and separating isomers, but its analysis cycle is on the order of minutes. A process mass spectrometer measures many components within seconds and has an advantage in multi-point monitoring, but it cannot always distinguish components of the same mass. The choice depends on the component list, required response time and number of measurement points.
What is the difference between TCD and FID detectors?
A TCD (thermal conductivity detector) senses the difference in thermal conductivity relative to the carrier gas; it responds to almost any component, including permanent gases such as hydrogen, nitrogen and CO₂. An FID (flame ionization detector) is very sensitive to hydrocarbons but does not see permanent gases. An FPD is used for selective measurement of sulfur components.
How are process gas analyzers calibrated?
Calibration is performed with certified calibration gases containing the measured components in the expected concentration range. On process GCs, automatic calibration can be programmed at set intervals; the composition of the calibration gas should be as close as possible to the process gas. After calibration, drift in response factors and retention times is monitored to track column and detector condition.
Why does the sample preparation system matter in gas analysis?
An analyzer's accuracy depends on the sample reaching it being representative of the process. Condensation, adsorption, long line lag or liquid carryover compromise the measurement, so the sample line is designed with pressure reduction, heating, filtering and a fast return (bypass) loop. Because a large share of analyzer faults originate in the sample system, it should be addressed separately in the maintenance plan.
Products measuring this parameter
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