Applicability of equations of state across a range of pressure and temperature conditions for surface and underground hydrogen storage

Abstract The transition to renewable energy has spotlighted hydrogen as a versatile and sustainable energy carrier. Its storage, however, requires a comprehensive understanding of thermodynamic behaviour under diverse pressure and temperature conditions. This study evaluates the applicability of eleven equations of state (EoS), most of which are implemented in commercial reservoir and process engineering software, for predicting the gas deviation factor (Z) of hydrogen across a wide range of conditions. Using an extensive experimental dataset of pure hydrogen comprising pressures and temperatures from various hydrogen storage applications, including high-pressure tanks, salt caverns, and depleted reservoirs, the accuracy of these EoS was assessed using various error metrics. PTV was found to be more appropriate for steel pipe storage, while RKMC and PTV were suitable for plastic pipe storage. RKS was identified as the most appropriate EoS for vehicle storage tanks, Type I storage, and salt caverns. For Type II, Type III, Type IV, and Type V storage systems, both PRTCC and RKS were found to be appropriate, while depleted reservoirs were best represented by RKS and PRTCC. The findings highlight the varying suitability of EoS for specific storage applications. Statistical and machine learning regressive models and contour plots were also developed for estimating Z-factors, providing critical insights for the design and optimization of hydrogen storage systems. These results contribute to advancing hydrogen storage technologies, paving the way for its widespread adoption in sustainable energy systems.