3 - Investigation of cushion gas/working gas ratios of underground salt caverns for hydrogen storage

Abstract

In this study, an investigation is made on the ratio of cushion gas to working gas in the storage of hydrogen gas at different depths in underground salt caverns. For this purpose, hydrogen storage parameters are determined for six salt caverns of the same size and characteristics but different depths in the same salt dome area. A minimum gas pressure inside the caverns is required to avoid some adverse effects such as collapse and cracking due to the pressure drop that occurs during the withdrawal of the stored hydrogen gas. Since this pressure required for cavern safety is provided by the cushion gas left in the cavern, determining the cushion gas/working gas ratio has a key role in preserving the structure of the caverns and balancing the storage cost. Therefore, in addition to calculating the energy value of the hydrogen stored in the caverns, the optimum cushion gas/working gas ratios are determined by using some mathematical equations for six salt caverns with different vertical depths. According to the calculations, while the total volume of the stored hydrogen gas at a depth of 1000m is approximately 76×106Nm3, 33.46% of it cannot be used as cushion gas. Likewise, while the total volume of the stored hydrogen gas at a depth of 1500m is approximately 106.55×106Nm3, 34.29% of it cannot be used as cushion gas.