2025 Spring Meeting and 21st Global Congress on Process Safety

(142c) Experimental Study of Combustion Characteristic of Methane and Hydrogen Under O2/CO2 Atmosphere

Authors

Yi Liu - Presenter, SINOPEC Research Institute of Safety Engineering Co. Ltd.
Yujie Lin, State Key Laboratory of Chemical Safety
Chang Qi, State Key Laboratory of Chemical Safety
Guanlin Peng, SINOPEC Research Institute of Safety Engineering Co. Ltd.
Anfeng Yu, SINOPEC Research Institute of Safety Engineering Co. Ltd.
Oxygen-rich combustion has been increasingly applied in industry as an effective means of enhancing combustion and improving carbon capture. However, while higher oxygen concentrations increase both combustion temperature and NOx emissions, O2/CO2 atmospheres have been introduced in oxy-fuel combustion to help control NOx emissions. Despite these benefits, oxy-fuel combustion poses challenges: It raises the risk of unexpected fires and increases explosion overpressure, limiting its industrial application. To assess these risks, especially under O2/CO2 conditions, it is essential to understand key combustion characteristics, such as flammability limits, explosion overpressure, and maximum pressure rise rate across various oxygen volume concentrations and equivalence ratios. While studies have explored these characteristics under O2/N2 atmospheres, limited research exists on combustible gases under O2/CO2 conditions. The differences in specific heat capacity between CO2 and N2, and the active role CO2 plays in competing with fuel gases for free radicals, make combustion behaviors in O2/CO2 and O2/N2 atmospheres fundamentally distinct. Therefore, further research into combustion characteristics in O2/CO2 atmospheres is crucial for industrial safety and design.

In this study, methane and hydrogen, typical combustible gases in the petrochemical industry, were selected for examination. A 20 L vertical cylindrical vessel, made of 316 stainless steel to withstand high explosion pressures in an oxy-fuel environment, was used to measure flammability limits, explosion overpressure, and maximum pressure rise rate across oxygen concentrations ranging from 21% to 80% and equivalence ratios from 0.6 to 1.2. The fuel mixture was ignited by a ~4.0 J high-voltage spark, with a pressure transducer (AE-H, Nanjing Aire Sensing Technology Co., Ltd.) recording the pressure-time signal at a sampling rate of 250 kHz. After each ignition, the vessel was flushed with dry air to prevent residual exhaust from affecting subsequent tests. Temperature was maintained within 24.5–25.5°C.

Alongside existing data from previous studies, this work provides insights into the combustion characteristics of methane and hydrogen in O2/CO2 atmospheres with oxygen concentrations from 21% to 100%. The thermal theory commonly used to calculate flammability limits in O2/N2 atmospheres was validated using experimental flammability data under O2/CO2 conditions. Results reveal that as oxygen concentration increases, the upper flammability limits of both methane and hydrogen expand, while the lower flammability limits remain relatively unchanged. Explosion overpressure and the maximum pressure rise rate also increase with higher oxygen concentrations for both gases. The equivalence ratio significantly affects explosion overpressure and pressure rise rates, with the highest values observed when the equivalence ratio exceeds 1. Additionally, hydrogen exhibits higher explosion overpressure and pressure rise rates than methane under similar conditions. These trends are consistent with those observed in O2/N2 atmospheres, though flammability limits are narrower, and explosion overpressure is lower in O2/N2 environments. For instance, methane’s flammability limit in an O2/CO2 ratio of 8:2 is 50.8%, compared to 94.5% in an O2/N2 ratio of 8:2. Similarly, the upper flammability limit of hydrogen is 87.35% in an O2/CO2 ratio of 1:1, compared to 93% in an O2/N2 ratio of 1:1. In O2/N2=21:79, hydrogen’s explosion overpressure at the lower upper flammability limit reaches approximately 0.8 MPa, which is significantly higher than in other scenarios.

This study contributes valuable experimental data on flammability limits, explosion overpressure, and maximum pressure rise rates for methane and hydrogen in O2/CO2 atmospheres. These findings are instrumental in determining safe operational conditions and informing risk assessments for industrial applications. Further research will expand upon this data to refine safety guidelines.