Application of passive autocatalytic recombiners for hydrogen mitigation: 2D numerical modeling and experimental validation

Abstract

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, a H2 leak creates potential for accumulation of flammable gases. A Passive Autocatalytic Recombiner (PAR) is a safety device for preventing H2 accumulation. PAR is equipped with catalyst plates that assist the activation of the H2 recombination with oxygen (O2) at low concentrations. The heat released from the reaction decreases the gas density, creating a self-sustained natural convective flow, continuously supplying the catalyst surface with H2 present in the air surrounding the PAR. In this study, a 2D numerical model is developed to simulate PAR operation. The model is used to analyze surface reactions, forced versus natural convective flow, plate spacing, heat losses, hydrogen recombination rates, carbon monoxide (CO) poisoning and their influence on the catalyst performance. Experimental data are used for model calibration and validation, showing good agreement for different conditions. The model shows that H2 is almost entirely recombined whereas CO is only partially recombined. Natural and forced convection flows result in similar velocity profiles and large plate spacing produces higher temperatures, higher velocities but lower H2 conversion. Moreover, the model shows a new feature for simulating CO poisoning via surface reactions. Overall, the model provided novel insights into PAR operation, showing the importance of surface reactions and it will be useful to assess design aspects and the effectiveness of PARs for H2 mitigation.