Insight into the effects of hydrogen on inside-valve flow and Joule-Thomson characteristics of hydrogen-blended natural gas: A numerical study

Blending hydrogen into natural gas is a feasible way to transport hydrogen via natural gas pipelines. In hydrogen-blended natural gas (HBNG) pipelines, choking is an essential process that concerns safety issues like condensation and hydrate formation inside valves and the Joule-Thomson (J-T) characteristics like temperature drops, isenthalpic curve (IC), Joule-Thomson coefficient (JTC). However, these two aspects of HBNG differ from those of natural gas, and the differences in inside-valve flow remain unknown, and those in J-T characteristics remain less clear. Given the incapability of the isenthalpic model in obtaining inside-valve flow fields, we conduct a comprehensive study on the effects of hydrogen on inside-valve flow and J-T characteristics of HBNG by combining the computational fluid dynamics (CFD) model and the isenthalpic model. We develop a numerical model by coupling the isenthalpic equations, the conservation equations, the k-ω turbulence equations, and the species transport equations. For the first time, we discuss the effects of hydrogen on the temperature, pressure, and velocity fields of HBNG and evaluate the risks of p-T curves entering vapor-liquid equilibrium and hydrate formation regions. Then, we analyze the effects of hydrogen on ICs and JTCs. Results indicate that with increasing hydrogen mole fraction (HMF), the temperature along the center line rise, the minimum temperature increases roughly linearly, and the corresponding positions shift to the throat in a rough linear law. The JTCs of HBNG roughly linearly decrease with increasing HMF from 0% to 30%.