The Blending of Hydrogen and Natural Gas by Direct Injection Into High-Pressure Large-Diameter Gas Transmission Pipelines

Abstract For many countries, blending hydrogen with natural gas into the existing gas transmission network is one of the critical steps towards energy transition. Blending allows relatively direct access to a market for hydrogen. It targets CO2 emissions associated with domestic and industrial consumption via existing connections. This is evidenced by the fact that in the EU 40% of households are connected to the gas network [1]. Blending has been trialled with medium-pressure, small-diameter public networks at relatively low volume flow rates for consumers, equivalent to a village. These first trials have proven hydrogen blending using a blending skid [2]; however, scaling a skid concept up from medium-pressure distribution diameters to transmission diameters and high pressures (32-inch and 85 barg, respectively) would require significant investment with sizeable equipment and a potentially disruptive intervention. Considerable economies can be obtained by injecting the hydrogen directly into the pipeline and using the pipeline itself as a mixer component. The challenges associated with this are achieving adequate mixing within a reasonable number of diameters downstream from the injection point, not exposing the inside surface of the pipeline to unacceptable percentages of hydrogen with the risk of embrittlement, and designing a nozzle or nozzles that are practical from a manufacturing perspective, allow inline inspection, don’t introduce a structural weakness, or have demanding construction or operational implications. This paper proposes various solutions with results backed by analytical modelling using Computational Fluid Dynamics (CFD).