Development and Assessment of a Novel Hydrogen Storage Unit Combined with Compressed Air Energy Storage

The present study concerns the development andperformance assessment of a novel hydrogen storage system which is operated ata constant pressure where it is also integrated with a compressed air storagesystem to supply the necessary pressure needs. The uniqueness of the system isthat there is a two-chamber storage system where the air is stored in onechamber while hydrogen is stored in the other one. These two chambers work in asynchronized manner where one is compressed while the other one is expanded.For example, the air is compressed in the air chamber to expand hydrogen forreleasing to the fuel cell and vice versa. Integration of the compressed airstorage into the present system helps keep the hydrogen storage chamber at thedesired storage pressure. For this purpose, the air is compressed into thechamber during the hydrogen discharging period, while air is released from thechamber during the hydrogen charging period. In order to exploit the additionalbenefit of the compressed air, an ammonia-fueled Brayton cycle is incorporatedinto the current system. Furthermore, this newly developed system is firstanalyzed thermodynamically by using both energy and exergy approaches toconfirm its conceptually correct functionality and write the balance equationsfor system analysis and secondly assessed for its performance through energyand exergy efficiencies. Moreover, the results indicate that the compressed airas a part of the Brayton cycle covers the total energy demands of hydrogencompression and cooling. In terms of storage efficiencies, the energy andexergy efficiencies for the charging period are found to be 72.65% and 71.52%,while they become 35.3% and 35.24% for discharging period, respectively. Theoverall system energy and exergy efficiencies are calculated to be 35.00% and34.38% for a period of 12 hour charging and a period of 6 hour discharging.