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

The safety of Hydrogen blended natural gas (HBNG) in confined space is an issue, especially for ventilation process. In this study, leakage and ventilation processes of low pressure HBNG with different hydrogen blended ratio(HBR) in confined space are simulated and validated by experiment based on similarity criteria. For leakage process, the leak direction and HBR does not significantly affect gas accumulation behavior. The required time for gas cloud to fill space decreases slightly with HBR rising and they generally show linear relationship. For 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 dissipate increases with total leakage mass and decreases with HBR. For different ventilation conditions, the ranking of required time to exhaust leaked gas is low > center > 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.

Methods
This study was done using CFD software called fluent. All data were obtained from post-processing of the CFD simulation results. The software chosen for post-processing in this study was Tecplot. The physical variables in the study, except for the hazardous gas cloud volume, can be easily obtained under conditions of some understanding of post-processing. The hazardous gas cloud volume is the sum of the approximate grid volumes, and the method of obtaining it is explained in detail in the manuscript.