Hydrogen Segregation Study for the Safe Transport and Use of Hydrogen-Natural Gas Blends

There are extensive existing natural gas delivery networks, and natural gas end-use equipment (boilers, gas turbines, furnaces...), that can be used safely without or with minor modifications for low concentration hydrogen blend with natural gas. Depending on the natural gas compositions and pipeline conditions, typical acceptable safe hydrogen concentration in the piping system may range from 5 to 30% for transportation, and 5 to 20% for end-use equipment without equipment modifications. But there are recent reports on hydrogen segregation issues in the delivery system, which raises concerns that hydrogen concentration spiking may occur locally inside the delivery pipeline, or inside the user fence after the local blending stations. The higher-than-expected hydrogen concentrations may adversely affect both the delivery pipeline material safety and the end-use equipment combustion safety. By using computational fluid dynamic (CFD) tools, this study has evaluated potential hydrogen segregation issues on both delivery pipeline and end-use piping, for different key piping components, for example pipe branching and turns, pressure reducing and regulating, and flow measurement components besides straight pipe sections. The modelling efforts have considered a full range of mechanisms that may cause hydrogen segregation, including turbulence, buoyancy, gravity, centrifugal force, and temperature effects applicable to each of the above components. Results show that segregation can happen under certain conditions, and worth our attention and further evaluation. This study provides real world insights towards hydrogen-safe operations.