Thermodynamic and cost analysis of Organic Rankine Energy Storage (ORES) systems

• Ano de defesa: 2020
• Autor(a) principal: Maury Martins de Oliveira Junior
• Orientador(a): Matheus Pereira Porto
• Banca de defesa: Rafael Augusto Magalhães Ferreira, Thales Alexandre Carvalho Maia, Paulo Alexandre Costa Rocha, Jonathan Radcliffe
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Minas Gerais
• Programa de Pós-Graduação: Programa de Pós-Graduação em Engenharia Mecanica
• Departamento: ENG - DEPARTAMENTO DE ENGENHARIA MECÂNICA
• País: Brasil
• Palavras-chave em Português: Organic Rankine Cycle; Intermittent energy generation; Energy storage; Organic Ćuid
• Link de acesso: http://hdl.handle.net/1843/38138; https://orcid.org/0000-0001-9445-9696

CAES (Compressed Air Energy Storage) and LAES (Liquid Air Energy Storage) are two of the most promising long-term energy storage solutions. However, CAES requires robust equipments and components due to the higher working pressures involved and also lower energy density, while LAES requires air liquefaction cycles,which imposes a relevant restriction to efficiency and increase costs. This work evaluate the potential use of organic fluids as an energy storage medium and proposed an energy storage system, named ORES (Organic Rankine Energy Storage) as na alternative to LAES and CAES. The objective of the ORES system is to gather some of the qualities and mitigate some of the drawbacks of both CAES and LAES. This study first focused on the evaluation of the potential of organic fluids as na energy storage medium in terms of exergy density and cost of the storage system (tank and fluid). Before evaluating the storage system, a set of five organic fluids was selected based on technical maturity, safety and environmental factors, namely R-152a, R-134a, R-142b, R-365mfc and R-141b. The evaluation of the potential of organic fluids as an energy storage medium showed that all of the evaluated working fluids achieved an exergy density higher than that of compressed air. The maximum exergy density for the organic fluids ranged from 8 to 15 kWh −3 for pressures up to 4,200 kPa while the maximum exergy density for compressed air is 6.5 kWh −3 and 180 kWh −3 for liquid air. The cost of the storage system (tank and fluid) was found to be around 33% cheaper for the organic fluids close to their respective critical pressure when compared to the cost for compressed air at common CAES operational pressure (8,000 kPa). Then, the cost per unit exergy was calculated, R-152a, R-134a and R-142b had the lower cost per unit exergy. While the minimum cost per unit exergy for compressed air ranged from 3,000 to 5,000 $ kWh−1, the cost for R-152a, R-134a and R-142b ranged from 1,000 to 2,000 $ kWh−1 for storage volumes of 2 and 10 m3, respectively. In the second part of this study, a novel energy storage system based on the ORC (Organic Rankine Cycle) was proposed. The ORES system was evaluated under a quasi-steady state analysis and transiente analysis for the same fluids as for the organic fluid potential analysis. The quasisteady state analysis evaluated the effects of pressure at the HPT (High Pressure Tank) and the superheating degree on round-trip efficiency and the transient analysis evaluated the effects of high and low pressure tank volume on efficiency, energy density and CAPEX. The round-trip efficiency of the ORES system was relatively high for both the quasi-steady state and transient analysis, reaching up to 74% and 73%, respectively, similar to that of CAES and LAES. However, the energy density for all organic fluids was lower than that of CAES, reaching only up to 2.29 kWh m−3 for R-365mfc. This study showed that organic fluids have the potential to be an alternative to CAES and LAES for medium-scale, long-duration, energy storage systems, both in terms of efficiency and cost. It is believed that the proposed system can be further improved and, potentially, surpass the energy density of CAES while also reducing CAPEX, which was already cheaper than CAES.