Overview: Air Dispersion Modeling
iFluids Engineering & Consultancy WLL conducted an Air Dispersion Analysis for multiple relief case scenarios to assess the impact of H2S and CO2 pollutants released during cold venting in pressure relief operations at Qatar Gas. The study compares pollutant concentrations with Qatar Ambient Air Quality Standards beyond the project boundary and evaluates exposure limits per OSHA’s 8-hour TWA standard.
Key Findings:

- H2S Concentrations: Highest near the vent stack but within the project boundary.
- CO2 Emissions: Rapid dilution leads to negligible environmental impact.
- H2S Ground-Level Concentrations (GLC): Align closely with Qatar Ambient Air Quality Guidelines for emergency relief scenarios.
- Safety Recommendations: Toxic gas detectors advised at air inlet ducts within 30m of the vent stack.
- Vent Stack Suitability: A 35m height and 1m diameter vent stack ensures safe dispersion, meeting workplace and environmental standards.
CO2 Export Facilities Project – Qatar Gas
Qatar Gas is developing a CO2 Export Facility to process CO2-rich off-gas from AGE absorbers at its South Plant, involving:
- Dehydration of CO2-rich gas using TEG (Triethylene Glycol).
- Compression of CO2-rich streams via three existing Acid Gas Compressors.
- Dense phase CO2 export via centrifugal pumps to QP Station A6.
Integration of relief and vent systems into a new Vent Stack System to prevent flare flame-out.
Scope of Work: Vent Dispersion Study
The Vent Dispersion Study evaluates the vent stack design to ensure safe pollutant dispersion. Key aspects:
- Covers a 25km x 25km project area.
- Uses AERMOD modeling with NOAA meteorological datasets (2010-2020).
- Compares emission scenarios with Qatar Ambient Air Quality Limits and OSHA’s Permissible Exposure Limits.
Dispersion Modeling Approach
- Flat terrain and rural dispersion settings selected.
- Meteorological data analysis over a 10-year period (2010-2020).
- Receptors incorporated for accurate ground-level concentration (GLC) assessments.
- Hourly meteorology data applied for worst-case scenario predictions.
- Vent stack modeled as a continuous emission source, ensuring regulatory compliance.
Results and Compliance
- Maximum pollutant concentrations remain within project boundaries.
- Workplace exposure limits for H2S (70 mg/m³) and CO2 (900 mg/m³) as per OSHA are not exceeded.
- Primary & Secondary Relief Case Scenarios confirm safe dispersion with a 35m vent stack height and 1m diameter.
- Toxic gas detectors recommended at strategic locations for rapid detection and mitigation of H2S releases.
Conclusion
The Air Dispersion Analysis confirms that the vent stack does not pose environmental or workplace hazards. With appropriate safety measures, including toxic gas detectors, the current configuration meets Qatar Gas Loss Prevention Philosophy requirements. Further vent gas dispersion studies can refine H2S gas detector placements to enhance workplace safety.