Thermodynamic analysis of a novel trigeneration process of hydrogen, electricity and desalinated water: the case of Na-O-H cycle, GEN-IV nuclear reactors and MED installation

• Autor(a) principal: João Gabriel de Oliveira Marques
• Data de Publicação: 2021
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Repositório Institucional da UFMG
• Texto Completo: http://hdl.handle.net/1843/37960; https://orcid.org/0000-0001-7516-610X
• topic: Trigeneration of H2, electricity and desalinated water; Na-O-H thermochemical cycle; GEN-IV nuclear reactors; MED desalination; Thermal performance; EES software; Engenharia nuclear; Reatores nucleares; Dessalinização da água; Eletricidade

Hydrogen (H2) is a substance with a wide range of important applications like NH3 production. H2 can be obtained according to different processes, including the Na-O-H (sodium-oxygen-hydrogen) thermochemical cycle that breaks water through cyclic chemical reactions sustained by a heat source at specified temperature levels. In this context, GEN-IV (Generation IV) nuclear reactors are suitable energy options for these kind of processes because they are designed to provide electricity together with high temperature applications. At the same time, water could be get by means of MED (Multi-Effect Distillation), a desalination method that harvest waste heat from thermal systems to get fresh water from saline one. Then, H2 production from Na-O-H cycle through the heat supplied by GEN-IV reactors coupled to a MED unit enables the trigeneration of electricity, H2 and H2O, three important goods for society. Therefore, the first main aim of this thesis is to evaluate the thermal performance of this trigeneration process, a new one, considering three 1000 MWth GEN-IV technologies as the heat sources for both Na-O-H cycle plus a MED installation. This goal is developed by implementing mass, energy, entropy and exergy balances in the Engineering Equation Solver (EES) software to determine the amount of H2, electricity and desalinated H2O acquired. Consonant with preliminary results, this trigeneration process has potential to produce around 5 kg/s of H2, 400 MWe and 800 kg/s of H2O. These are theoretical and maximized values in function of all simplifications considered in the research. In the second main aim is investigated if there are other variations (b, c, d and e) of the Na-O-H cycle that have higher thermal performance when compared to its classic form, variation (a), evaluated in the first maim objective. According to the results, variation (e) has energy efficiency around 77% while variation (a) has energy efficiency near 52%. In the third main aim is established the thermodynamic limits (the minimum requirements of enthalpy change and other thermodynamic parameters) for thermochemical water splitting cycles starting from systems similar to the Na-O-H cycle. The results showed that all thermochemical cycles must have enthalpy change superior to 283.83 kJ to produce 1 mol of H2 gas. As it is being demonstrated in this study, it is possible to conclude that the trigeneration process of H2, water and electricity has potential to attempt the demand for such goods through more research and development of the systems analyzed.