Fast on-line monitoring of fuel gases

Significance of the topic

Process control in furnaces and power generation depends critically on accurate, timely knowledge of fuel gas properties. Variable composition fuels change calorific value, density and stoichiometric air demand, which directly affect combustion efficiency, product quality and equipment lifetime. Fast, comprehensive on-line analysis enables feed-forward control strategies that reduce waste, prevent burner damage and improve thermal consistency across petrochemical complexes and integrated steel works.

Objectives and study overview

The application note describes the capabilities and industrial performance of the Thermo Scientific Prima PRO Process Mass Spectrometer (MS) for rapid on-line measurement of fuel gas composition and derived energy parameters. The goals are to demonstrate: rapid multi-component analysis, derivation of calorific value, Wobbe Index, stoichiometric air requirement and CARI, multi-stream sampling capability, analytical precision/stability and suitability for continuous process control environments.

Used instrumentation

• Prima PRO Process Mass Spectrometer with a laminated scanning magnetic sector analyzer — chosen for high precision, stability and contamination resistance.
• Rapid Multistream Sampler (RMS) — 32- or 64-port heated (up to ~120°C) stream selector with optical encoding and digital flow monitoring.
• Thermo Scientific GasWorks software — supports unlimited analysis methods and per-stream optimization of speed versus precision.
• Outputs and integration interfaces — analog (4–20 mA, 0–10 V), Modbus, Profibus and OPC for plant host connectivity.

Methodology

• Principle: Ionization of sample gas followed by mass separation using magnetic/electric fields and detection of ion currents; the magnetic sector provides flat-topped peaks and high linearity.
• Quantification: Mole-fraction based composition enables calculation of lower/higher calorific values, mixture density, specific gravity, Wobbe indices, stoichiometric air requirement (SAR) and Combustion Air Requirement Index (CARI) using standard formulae (ISO 6976:2016).
• Sampling: RMS allows rapid automated switching between many process streams with user-configurable settling times; stream flow is recorded and can trigger alarms on flow loss.
• Performance evaluation: Independent testing by EffecTech (ISO/IEC 17025) using nine gravimetrically prepared reference gases across wide concentration ranges; linearity and precision assessed with 10 s cycle times and multi‑day stability tests.

Main results and discussion

• Speed: Full compositional analyses typically completed in ≤30 s, including stream switching.
• Precision and linearity: Typical compositional precision better than 0.1% relative (≈0.01 mol% absolute); magnetic sector analyzer yielded significantly better linearity than a thermal conductivity detector (TCD) gas chromatograph in independent tests.
• Stability: Characteristic flat-topped peaks produce stable concentration readouts; typical calibration interval is about one month with automatic calibration support.
• Long-term performance: Demonstrated 24-hour and 30-day runs on calibration cylinders showed low standard deviations and relative standard deviations (RSD) often well below 1% for major components; minor components showed slightly higher RSDs but remained within acceptable process-control tolerances.
• Derived properties: Calculated calorific values, Wobbe indices, density and CARI were reproducible and suitable for feed-forward combustion control; higher calorific value accounts for latent heat of vaporization of combustion water when required.
• Multistream capability: RMS design minimized dead volume and improved reliability over solenoid manifolds or rotary valves, enabling practical on-line monitoring across up to 64 streams with digital flow supervision.

Benefits and practical applications

• Enables feed-forward control: Real-time compositional data supports proactive adjustments of fuel and combustion air flows for stable furnace temperatures.
• Improved combustion efficiency: Accurate Wobbe and SAR/CARI calculations reduce fuel waste from over- or under‑airing and extend burner life.
• Process flexibility: Single analyzer can replace multiple calorimeters, density meters and discrete oxygen analyzers, reducing cost and maintenance complexity.
• Environmental and safety monitoring: Quantification of species such as H2S, NH3 and light aromatics informs emissions control and safety management.
• Integration: Standard industrial outputs and software allow direct interfacing with plant DCS/PLC systems for automated control and alarms.

Future trends and potential uses

• Adoption with hydrogen-rich and variable renewable gas blends: As fuel mixes evolve, fast multi‑component MS will be critical for safe and efficient combustion of new fuels.
• Tighter integration with advanced process control and machine learning: Predictive models can use high-frequency compositional data for optimized combustion setpoints and predictive maintenance.
• Enhanced remote diagnostics and cloud data services: Remote performance monitoring and centralized calibration analytics will reduce on-site interventions.
• Expanded analyte libraries and customized methods: Flexible software allows rapid method updates to include emerging contaminants or heavier hydrocarbons as needed.
• Hardware developments: Improvements in sampler reliability, reduced footprint and lower power consumption to support wider industrial deployment.

Conclusion

The Prima PRO Process MS combined with a Rapid Multistream Sampler provides fast, accurate, stable and flexible on-line analysis of complex fuel gases. Its high precision, excellent linearity and multi-stream capability make it well suited for feed-forward combustion control across petrochemical and metallurgical plants. By replacing multiple specialized analyzers, the system simplifies instrumentation, lowers operational cost and improves process efficiency and safety.

References

1. ISO 6976:2016 Calculation of calorific values, density, relative density and Wobbe indices from composition.
2. ISO 10723:2012 Natural gas — Performance evaluation for analytical systems.
3. R. Wright, 2004, Mass spectrometry: gas analysis, In: Encyclopaedia of Analytical Science, 2nd ed., Volume 5, pp. 493–501, Elsevier.