The mixing characteristics of natural gas and hydrogen based on the Soave–Redlich–Kwong equation of state

This study investigates the blending characteristics of natural gas (NG) and hydrogen in a Kenics static mixer using computational fluid dynamics. The effectiveness of the adopted numerical model is experimentally validated. The scenario of high-pressure, long-distance NG pipelines is considered, and the Soave–Redlich–Kwong equation of state is applied. The mixing uniformity and pressure loss are adopted as evaluation criteria to analyze the impact of factors such as the deflection angle of spiral blades, the number of blades, the length-to-diameter ratio, the hydrogen blending ratio (HBR), the pipeline pressure, and the temperature on mixer performance, followed by structural optimization of the mixer. It is found that a Kenics static mixer with two spiral blades, a length-to-diameter ratio of 2, and a deflection angle of 135° can achieve a mixing uniformity of 95% at the blade outlet while minimizing pressure loss. Increasing the HBR helps improve the mixing uniformity but also increases the pressure loss of the mixer. Increasing the pipeline pressure while keeping the hydrogen mole fraction constant enhances the mixing uniformity but also increases the pressure loss. Increasing the gas temperature reduces the mixing uniformity and the pressure loss. Overall, pipeline pressure and temperature changes have a minimal impact on the mixing characteristics. Under high-pressure conditions, the use of a real gas model is essential. This study provides theoretical guidance for the design of static mixers for hydrogen blending in high-pressure NG pipelines.