Packed Column Refinery Gas Analysis System Based on the Agilent 7890B GC System and G3507A Large Valve Oven

Importance of the Topic

Refinery gas analysis is a fundamental practice in petrochemical processing, providing critical information on hydrocarbon composition, permanent gases, and sulfur compounds. Accurate quantification of light hydrocarbons up to C6+, hydrogen, oxygen, and trace sulfur species informs operational safety, process optimization, and product specification compliance.

Objectives and Study Overview

This work details the development and evaluation of a three‐channel Refinery Gas Analyzer (RGA) based on the Agilent 7890B gas chromatograph and the G3507A Large Valve Oven (LVO). The primary goals were to achieve reliable separation of hydrocarbons (methane through C6+), stable measurement of permanent gases including O₂, N₂, CO, CO₂, precise hydrogen quantification over a broad concentration range, and optional detection of H₂S and COS.

Methodology and Instrumentation

The RGA system employs seven columns and three detectors:

• Channel 1: Flame Ionization Detector (FID) with an alumina PLOT column for hydrocarbons (C1–C6+), temperature‐programmed in the main oven.
• Channel 2: Thermal Conductivity Detector (TCD) in the G3507A LVO, isothermal at 65 °C or 70 °C, separating permanent gases (O₂, N₂, CO, CO₂) and H₂S/COS when corrosion‐resistant hardware is used.
• Channel 3: Side-mounted TCD for hydrogen analysis using N₂ carrier, temperature‐programmed in the main oven.

Column configuration:

• Columns 1–3: 1/8″ packed columns coiled on 1″ or 1 5/8″ mandrels inside the LVO for temperature stability.
• Columns 4–5: Additional packed columns in the main oven for extended hydrocarbon range up to C9 (not recommended for samples above C9).
• Columns 6–7: Capillary columns in the main oven to improve resolution for lighter components.

Key operational parameters include a split/splitless inlet at 120 °C with helium carrier (100:1 split), FID at 250 °C, TCD1 at 260 °C (He carrier), TCD2 at 250 °C (N₂ carrier), and main oven programming from 60 °C to 190 °C. The LVO remains isothermal and decoupled from the main oven, enabling consistent permanent gas analysis.

Main Results and Discussion

Repeatability studies using custom gas blends demonstrated excellent precision:

• Retention time RSD < 0.13% and area RSD < 0.35% for hydrocarbon and permanent gas peaks at LVO temperatures of 65 °C and 70 °C.
• Detection limits in the low ppm to 0.01 mol% range for key analytes (hydrocarbons, H₂, O₂, CO, CO₂) and 300–500 ppm for H₂S and COS.

Long‐term oxygen stability testing over 60+ runs at 65 °C revealed minimal drift after initial conditioning, confirming the benefit of isothermal operation to avoid chemisorption losses. A typical full‐scale analysis of a refinery gas checkout sample completed in under 18 minutes, achieving baseline separation of 20+ hydrocarbon isomers and clear resolution of permanent gases and hydrogen.

Benefits and Practical Applications

The integration of the G3507A LVO with the 7890B GC offers:

• Stable and reproducible permanent gas measurements by maintaining columns isothermally.
• Flexible valve configurations supporting up to six heated ports for complex sample routing.
• Rapid multi‐component analysis within a sub‐20 minute cycle time for routine process monitoring.
• Optional corrosion‐resistant flow paths for sulfur species quantification in quality control workflows.

Future Trends and Potential Applications

Emerging directions for refinery gas analysis include:

• Integration of mass spectrometric or micro-GC detectors for extended compound identification.
• Automated valve switching and AI‐driven data interpretation to enhance method robustness.
• Miniaturized, field-deployable GC systems for on-stream analysis and real-time process feedback.
• Advanced materials for column and valve components to extend lifetime under aggressive sample matrices.

Conclusion

The three‐channel RGA system utilizing the Agilent 7890B GC and G3507A LVO achieves precise, repeatable analysis of hydrocarbons, permanent gases, hydrogen, and sulfur compounds within a single instrument. The thermally independent LVO ensures stable oxygen response and flexible method optimization, making this approach well suited for routine refinery QA/QC and process monitoring.

References

No specific literature references were provided in the original text.