Abstract: To clarify the thermodynamic behavior of underground tunnel-type hydrogen storage during injection and production, a thermodynamic model of hydrogen nonisothermal flow is established, and its reliability is verified. The thermodynamic evolution and local high-temperature phenomenon during the operation of hydrogen storage caverns are analyzed, and the temperature nonuniformity coefficient (K_T) is introduced to quantitatively evaluate the degree of temperature localization. The effects of the number of injection-production holes and the hydrogen injection time and temperature on the uniformity of the hydrogen temperature field in the cavern are discussed. Moreover, corresponding optimization measures are proposed. The results demonstrate that under a fixed maximum operating pressure, increasing the number of injection-production holes in the cavern reduces K_T. The K_T of a cavern with four injection-production holes is 0.10, which is 70% lower than that of a cavern with a single hole. Furthermore, prolonging the hydrogen injection time reduces K_T in the cavern. Shorter hydrogen injection times correspond to faster injection rates, resulting in enhanced eddy-current phenomenon after hydrogen injection, which increases the nonuniformity of the temperature distribution. Reducing the hydrogen injection temperature decreases the maximum temperature of the cavern, but aggravates the degree of temperature localization. For a hydrogen injection temperature of 20 °C, the average storage temperature is 111.8 ℃, which is slightly higher than the temperature of 100.9 ℃ obtained for a hydrogen injection temperature of 0 ℃, although K_T is 26% lower than that obtained at 0 ℃. Finally, the engineering risk of temperature monuniformity is analyzed. Through process optimization, K_T is reduced to <0.10, the cavern temperature is near the safety threshold, and the engineering risk is greatly reduced.

Key words: underground hydrogen storage, tunnel-type hydrogen storage cavern, spatial temperature distribution, number of injection-production holes, optimization measures