Numerical investigation for hazardous gas cloud form and dissipation behaviour of hydrogen-blended natural gas in a confined space

The safety of hydrogen-blended natural gas (HBNG) in a confined space is an issue, especially for ventilation processes. In this study, leakage and ventilation processes of low-pressure HBNG with different hydrogen-blended ratio (HBR) in a confined space are simulated and validated by experiment based on similarity criteria. For the leakage process, the leak direction and HBR do not significantly affect gas accumulation behaviour. The required time for a gas cloud to fill space decreases slightly with HBR rising and they generally show a linear relationship. For the ventilation process, the main influences on the leakage process are the total leakage mass and the ventilation conditions. The required time for hazardous gas cloud dissipation increases with total leakage mass and decreases with HBR. For different ventilation conditions, the ranking of required time to exhaust leaked gas is low > centre > high > mix. Through the analysis of pressure distribution, it is found time difference is produced by different airflow patterns. With the asymmetric layout, outside air rushes into the confined space from the high side and then flows out from the low side carrying the leaked HBNG. These findings inform the design of ventilation for HBNG utilization scenarios like restaurant facing the street.