Hydrogen blending in gas pipelines: Fluid-dynamic insights, risks, and recommendations

Massive theoretical and applied research is underway worldwide to assess the viability of transporting natural gas-hydrogen blends in pipelines. For the first time, this work derives simplified but closed-form equations that describe how changes in gas properties due to hydrogen blending at different volumes map to specific changes in pressure drop, compressor power, and linepack. These first-of-their-kind equations, which are extensively validated against transient gas flow models, enabled three unprecedented and unique findings. The first finding, which quantifies how a change in demand maps to a change in delay and swing on the supply side, reveals that pressure swings increase monotonically with an increase in hydrogen blending volume, translating into an increase in pipeline fatigue and risk of failure. The second finding crucially shows that pressure drop does not monotonically increase with an increase in hydrogen blending volume; in fact, it is highest at around 85 % hydrogen volume, not at 100 %. The third finding shows that the decrease in linepack, as a result of an increase in hydrogen volume, is not only related to the gross calorific value of the gas mixture, but also to the pressure-to-compressibility factor ratio, suggesting that smaller parallel pipelines can offset this linepack reduction compared to a single larger pipeline.