Natural Gas and hydrogen blending: a perspective on numerical modeling and CFD analysis for transient and steady-state scenarios

Abstract The integration of hydrogen as an energy carrier into an existing natural gas pipeline infrastructure presents a promising option for the decarbonization of the energy sector. However, using hydrogen in natural gas pipelines requires overcoming engineering challenges attributed to physical property and design considerations for both natural gas and hydrogen which may result in pipeline failures. To this end, this study employs a multi-software engineering approach to model both steady-state and transient behaviors of natural gas pipelines blended with hydrogen under cyclic variations. For transient state modeling, the Crank-Nicolson implicit scheme is applied to a 100 km pipeline with 200 nodes, using a time interval of 20 s in MATLAB. The one dimensional flow modeling aspects are analyzed in more detail with the finite element method in COMSOL. The study also highlights the importance of pipeline inventory analysis, focusing on the trade-off between gas transport capacity and flexibility; particularly with respect to packing and drafting operations. The intrinsic properties of hydrogen blends (0–20 %) are analyzed using the GERG Equation of State (EoS) in ASPEN. Results indicate that the COMSOL model shows less stability than the Crank-Nicolson method for abrupt demand changes, with a percentage error of ±11 % compared to the benchmark study. Additionally, inventory analysis suggests that to prevent pipeline failure, the pipeline can only be drafted for 3.6 h. Steady-state analysis reveals that blending hydrogen into natural gas significantly impacts pipeline design, with changes in specific gravity, compressibility factor, and speed of sound. The study also finds that higher hydrogen blending reduces the pressure drop under isothermal conditions, resulting in lower compressor power requirements. This modeling approach provides a foundation for strategies aimed at adapting natural gas infrastructure for hydrogen use.