Temperature Profile Mapping over a Catalytic Unit of a Hydrogen Passive Autocatalytic Recombiner: An Experimental and Computational Fluid Dynamics Study

Passive autocatalytic recombiners (PARs) are used for the removal of accidentally released hydrogen inside confined spaces. The high catalyst surface temperature is an important safety issue to be considered in the use of a PAR. The ability to predict the catalyst surface temperature could be very useful in preventing the self-ignition and explosion of hydrogen inside the PAR. This study seeks to investigate the changes in temperature profiles of the PAR catalytic section upon variation of the inlet hydrogen concentration. Experiments were conducted on a small-scale test setup. The catalytic section comprised cylindrical ceramic elements arranged in parallel and held upright by a stainless-steel frame. The temperature profiles were measured with a high-resolution infrared camera. The commercial computational fluid dynamics (CFD) code STAR-CCM+ was used as a numerical tool for modeling the gas mixture flow inside the experimental setup and the chemical reaction kinetics. The results of numerical studies are presented and compared with experimental results. The presented CFD-based approach and software offer an appropriate numerical tool for the investigation of hydrogen safety issues. Finally, the catalyst was subjected to a prolonged high-temperature combustion fatigue procedure to determine its stability. The surface of the fatigued catalyst was evaluated by scanning electron microscopy and energy-dispersive X-ray spectroscopy. It was found that decomposition of the protective surface layer occurred at elevated temperatures; the catalytic activity was unaffected by this. In addition, a relatively uniform reactive metal particle size was maintained over the entire temperature range, suggesting that no aggregation occurred.