Mitigation strategies for hydrogen safety in the confined environment : CFD modelling and validation

Abstract

This research is based on experimental evaluation and computational fluid dynamics (CFD) modelling validation. Full-scale tests to investigate unintended hydrogen release were conducted at the HySA Mining Platform Test Facility for Green Mining. A PAR (passive autocatalytic recombiner) cylindrical-type catalyst unit has been tested in an in-house developed recombiner section testing station. Hydrogen concentrations were measured by means of high-precision H2 sensors, while the temperature of PAR catalyst has been evaluated utilizing a high-resolution infrared camera. Detailed three-dimensional calculations have been performed utilizing the STAR-CCM+ software package to simulate each experiment. Over the last twenty years, the importance of hydrogen as a prospective energy source has significantly increased. Utilizing hydrogen offers advantages in reducing carbon emissions generated by transportation systems. The current hydrogen economy growth is owed to the rapid development and employment of hydrogen fuel cell technology. Moreover, in efforts to achieve zero-carbon emission in the mining industry, they are looking for more perspective technologies in terms of clean and environmentally friendly energy carriers. Hydrogen fuel cell technology can make zero-carbon emissions a reality. However, due to specific combustion properties, the usage of hydrogen energy is accompanied by a risk of unintended leakage, dispersion, ignition, and deflagration inside a confined space. In this regard, mitigation strategies for hydrogen safety need to be investigated. The emergency hydrogen removal systems must be deployed to guarantee that the H2 concentration is diluted below the minimum flammability limit, even under severe accidents. One of the widely applied hydrogen safety technologies is utilizing a ventilation system. Forced ventilation can promote the removal of hydrogen from a confined space by means of mixing and diluting a flammable gas below the ignition limit. Another important approach that goes toward mitigation strategies for hydrogen safety is PAR. The spontaneous exothermic chemical reaction between hydrogen and oxygen leads to the heating of the catalyst surface and then activates natural convection inside the PAR. Eventually, by means of autocatalytic recombination reaction, the concentration of hydrogen reduces to lower than the flammable limit. Related to this, the CFD simulations method can be very helpful in terms of hydrogen safety research. However, there is an urgent need to develop and validate numerical models of hydrogen distribution processes in confined environments. Hydrogen release and subsequent dispersion, as well as a multi-step reaction of hydrogen autocatalytic recombination, can be investigated using commercially available CFD software.