Thermodynamic and economic analysis of geothermal energy use in hydrogen production and liquefaction

Hydrogen, an alternative energy source, is subject of a lot of research work and some consider it as the energy of the future. If hydrogen is to become the energy of the future, it must be produced using renewable energy sources and the technical and economic problems on its production, storage, transportation, and use should be solved. There are various methods used in hydrogen production. These methods may require both electricity and heat inputs and renewable energies such as solar, wind, hydro and nuclear energy use are being investigated. Hydrogen can be stored and transported either as compressed gas or as a liquid occupying a small volume after being liquefied. Hydrogen liquefaction requires considerable energy consumption and involves advanced refrigeration techniques.The subject of this thesis is the thermodynamic and economic investigation of geothermal energy use in hydrogen production and liquefaction. For this aim, various methods used in hydrogen production and liquefaction are examined, the methods most suitable for geothermal energy use are identified, and appropriate models for using geothermal energy are structured. These models are simulated in computer environment, thermodynamic and economic analyses are done, and these models are compared using thermodynamic and economic performance criteria. When structuring the models, alternatives such as direct use of geothermal heat and/or the use of produced electricity are considered. A binary geothermal cycle is selected for power production. Electrolysis and high-temperature electrolysis are used for hydrogen production and a precooled Linde-Hampson cycle is used for hydrogen liquefaction. Also, an absorption refrigeration system is incorporated into the models for precooling of hydrogen before liquefaction.Seven models are developed and their thermodynamic and economic analyses are performed. The amount of hydrogen production and liquefaction per unit mass of geothermal water and the cost of producing and liquefying a unit mass of hydrogen are calculated for each model. The effects of geothermal water temperature on these performance parameters are studied. It appears that the amount of hydrogen production per unit mass of geothermal water increases and the cost of hydrogen production decreases as the geothermal temperature increases. An economic analysis indicates that the initial costs of the models involving hydrogen liquefaction are higher compared to the models not including liquefaction. The results of this thesis are compared to those involving wind, solar, and nuclear-based hydrogen production. The models developed in this study are applied to the geothermal resources in Turkey, and the potential amounts of hydrogen production are estimated.The results of this thesis indicate that geothermal-based hydrogen production and liquefaction may take an important place in a future renewable-based hydrogen economy as it can be accomplished with the current systems and technology.Keywords: Hydrogen, geothermal energy, hydrogen production, hydrogen liquefaction, hydrogen economy, hydrogen cost.