(245g) A Thermodynamic, Technical, and Economic Evaluation of Hydrogen Blending in Natural Gas Pipelines

With the implementation of net zero CO₂ emission policies, hydrogen has become a promising alternative energy carrier, with its appeal originating from its wide abundance, high energy density per unit mass, clean combustion, and versatile production pathways and industrial applications [1]. Nonetheless, the realization of a hydrogen dependent economy is hindered by the current state of available and affordable technology for hydrogen production, storage, transportation and emerging applications.

Blending hydrogen with natural gas has been proposed as an interim solution for the gradual integration of hydrogen into the current energy mix. On one front, the combustion of H₂ + NG mixtures can enhance the carbon footprint associated with natural gas combustion, as water is the only byproduct from H₂ combustion [2]. On another front, H₂ can be transported to end-users without the incurred costs of building dedicated H₂ transmission networks, relying on the already existing natural gas transmission pipelines, with downstream H₂ separation units permitting end users to recover H₂ for intended industrial application [2]. However, much remains to be unknown regarding the impact of H₂ composition on the change in the thermodynamic properties and pipelines integrity of transported natural gas, mainly composed of methane, and hence the practicality of H₂ blending in natural gas pipelines. The required breadth of thermodynamic property data, at different operating conditions and H₂ content is very demanding in terms of resources and time from the experimental point of view. Thus, thermodynamic modeling tools are required to provide accurate, reliable, and rapid predictions of the effect of H₂ content on the thermophysical and transport properties of natural gas of interest for pipeline transmissions.

In this work, the polar soft-Statistical Associating Fluid Theory (soft-SAFT) equation of state (EoS) [3] have been employed to systematically investigate the effect of H₂ composition on the change in the thermodynamic properties of natural gas, at conditions relevant to pipeline transmission. The thermodynamic modeling of pure fluids within the framework of polar soft-SAFT is done in a coarse-grain manner by representing fluids by a set of molecular parameters characterizing key structural and energetic features spanning across non-association and non-polar fluids such as H₂, CH₄, C₂H₆, and n-C₃H₈, and quadrupolar fluids such as CO₂ and N₂. The evaluation of the accuracy and robustness of the thermodynamic model was performed in a systematic manner by examining a range of properties such as phase equilibria, critical loci, single-phase density, heat capacity, speed of sound, Joule-Thomson coefficient, compressibility factor, and viscosity, compared to available experimental data for binary mixtures containing H₂ and multicomponent systems with H₂ + CH₄ + other major NG components. Additionally, the accuracy of polar soft-SAFT was also benchmarked to widely used thermodynamic models in oil & gas industry, namely, Peng-Robinson EoS, and the multiparameter semiempirical GERG-2008 model. The results of the systematic validation established a higher overall predictive accuracy of the molecular theory compared to the other models, particularly for modeling phase equilibria, critical loci, compressibility factor, and viscosity [4]. Consequently, the polar soft-SAFT was used to quantify the change in H₂ + CH₄ properties as a function of H₂ content relative to CH₄, i.e., NG in this case, at conditions typical for pipeline transmission. The predictive analysis revealed major changes in density, and speed of sound associated with increasing H₂ content, while viscosity was the least affected property [4].

The thermodynamic model was subsequently integrated with techno-economic evaluation to assess the impact of H₂ content on key operational parameters for NG transmission inclusive of pressure drop, temperature profile, change in compression requirements, energy delivery rate, and their relation to changes in the operational cost of the pipeline transmissions.

This framework with a molecular-based EoS at its center permits the precise determination of allowable threshold for the addition of hydrogen into natural gas pipelines without jeopardizing the safety margin, and the operational integrity of existing pipeline transmissions grids, while permitting the gradual decarbonization of the current energy mix.

This work is funded by Khalifa University of Science and Technology (RC2-2019-007). Computational resources from the Research and Innovation Center on CO₂ and Hydrogen (RICH Center) are gratefully acknowledged.

References

[1] I. Staffell; D. Scamman, A. Velazquez Abad; P. Balcombe, Energy Environ. Sci., 12 (2019), 463–491

[2] I. Jain, Int. J. Hydrogen Energy, 34 (2009) 7368–7378.

[3] I. I. I. Alkhatib, L. M. C. Pereira, J. Torne, L. F. Vega, Phys. Chem. Chem. Phys., 22 (2020) 13171–13191.

[3] I. I. I. Alkhatib, A. AlHajaj, A. Almansoori, L. F. Vega, Ind. Eng. Chem. Res., (2022) DOI: 10.1021/acs.iecr.2c00363.