Mixing mechanisms of hydrogen-blended natural gas in subsea pipelines: Effects of injection angles

Abstract

The global transition toward renewable energy has made hydrogen blending in natural gas pipelines a promising approach for reducing carbon emissions. Nevertheless, the considerable dissimilarities in the gaseous characteristics of hydrogen and methane present considerable challenges for the efficient mixing and transportation of these substances, particularly in the context of submarine pipeline systems. This study investigates the impact of varying hydrogen injection angles (45°, 90°, and 135°) on mixing efficiency and pressure loss in hydrogen-natural gas pipelines. Using numerical simulations, we analyzed the coefficient of variation (COV) to quantify mixing uniformity and calculated the pressure drops associated with each configuration. Results indicate that a 135° injection angle significantly enhances mixing at higher flow velocities, creating counter-vortices that improve hydrogen dispersion within the methane stream. Conversely, vertical injection (90°) is most effective under low-speed conditions due to favorable flow dynamics that promote thorough mixing with minimal stratification. Mixing intensity improves as the flow rate increases, although stratification becomes more pronounced, especially at lower angles. The study concludes that injection angle and flow rate are critical factors in achieving optimal hydrogen blending within natural gas pipelines. Findings provide valuable insights into subsea pipeline design and operational strategies for hydrogen blending, supporting the broader goal of integrating hydrogen into existing gas infrastructure as part of the global carbon reduction initiative.