Application of Passive Autocatalytic Recombiners for Hydrogen Mitigation: 2D Numerical Modeling and Experimental Validation

The widespread production and use of hydrogen (H2) requires safe handling due to its wide range of flammability and low ignition energy. In confined and semi-confined areas, such as garages and tunnels, a hydrogen leak will create a potential accumulation of flammable gases. Hence, forced ventilation is required in such confined spaces to prevent hydrogen hazards. However, this practice may incur higher operating costs and could become ineffective during a power outage. Passive Autocatalytic Recombiners (PARs) are defined as safety devices for preventing hydrogen accumulation in confined spaces. PARs have been widely adopted for hydrogen mitigation in nuclear containment buildings in worst case accident scenarios, where forced ventilation is not feasible. PARs are equipped with catalyst plates that self-start due to hydrogen reacting with oxygen at relatively low concentrations (<2 vol. % H2 in air). The heat generated from the reaction creates a self-sustained flow, continuously supplying the catalyst surface with fresh hydrogen and oxygen. In this study, a 2D transient numerical model has been developed in COMSOL Multiphysics to simulate the operation of PARs. The model was used to analyze the effect of surface reactions on the catalyst temperature, flow dynamics, self-start behaviour, forced versus natural convective flow, and steady-state hydrogen recombination rates. The model was also used to simulate carbon monoxide poisoning and its influence on the catalyst performance. Experimental data were used for model calibration and validation, showing good agreement for different conditions. Overall, the model provides novel insights into PARs operation, such as radiation and poisoning effects on the catalyst plate. As a next step, assessment of the effectiveness of PARs is underway, to mitigate hydrogen hazards in selected confined and semi-confined areas including nuclear and non-nuclear applications.