CFD optimisation of hydrogen blending in high-pressure natural gas pipelines with T-junction configurations

• CFD study of H 2 injection in high-pressure natural gas pipelines with T-Junctions. • Effect of injector diameter, location, tilt angle, flow rate and H 2 volume fraction. • Results showed a high local H 2 concentration in the injection vicinity. • Analysis of a double injection T-Junction system with natural gas and H 2 premix. • Lateral double injection of the premixed enhances blending performance. In the short term, a viable pathway to achieving carbon neutrality is blending hydrogen with natural gas in existing pipelines. However, this approach presents significant engineering challenges, most notably hydrogen embrittlement (HE), which has the potential to compromise pipeline integrity. Given hydrogen’s lower density compared with natural gas, the likelihood of failure increases due to stratification and localised concentration. The present study employed computational fluid dynamics (CFD) to optimize the blending and injection of hydrogen through T-junctions in high-pressure natural gas pipelines. Blend quality was evaluated using the coefficient of variation (COV). A comprehensive analysis was conducted on single T-junction configurations, encompassing upper, lateral, and underside injections, with varying injection tilt angles ranging from 22.5° to 157.5°. The pipeline geometry and operational conditions were modelled based on the high-pressure Portuguese natural gas network. The findings demonstrated that underside injection was generally found to provide superior blending performance at low hydrogen blend ratios (HBR), although buoyancy effects remained a concern. To enhance blending and reduce local hydrogen concentration in the near-wall region, a double T-junction injection system was proposed. The approach proved effective at higher HBR, while for lower HBR (<20%), a dual horizontal injection of a hydrogen–natural gas premix emerged as the most versatile solution, ensuring homogeneous mixtures under a wide range of operating conditions.