Browsing by Author "Pinheiro, Carla I.C."
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- Computational model of a Calcium-looping fluidized bed calcination reactor with imposed concentrated solar irradiancePublication . Rodrigues, Diogo; Rivero, Mayra Alvarez; Pinheiro, Carla I.C.; Cardoso, João P.; Mendes, Luís FilipeABSTRACT: The Calcium-looping process is a promising option for thermochemical energy storage in concentrating solar power plants. A crucial element of this process is the solar calcination reactor, where the endothermic reaction of CaCO3 calcination occurs with formation of CaO and CO2. The solar energy that is chemically stored in the reaction products can be retrieved by the exothermic reaction of CaO carbonation when needed. In this article, a new computational model is developed for the solar calcination reactor in this Calcium-looping process. The calcination reaction takes place in the riser of a continuous circulating fluidized bed that corresponds to an absorber tube exposed to concentrated solar radiation, which allows the reaction chamber to be indirectly heated. A core-annulus heat transfer model and a modified version of the Kunii-Levenspiel fluid dynamics model are used. In contrast to previous models found in the literature, the change in the mass flow rate of the species and in the density of the phases due to the reaction is considered. Simulation studies are performed with a fixed and imposed concentrated solar irradiance on the reactor wall, which varies in both the axial and angular directions. Wall conduction in the angular direction is also considered. The results show that nearly complete calcination can be achieved with a reactor of 4 m of height. A sensitivity analysis with respect to the model parameters and inlet conditions shows that the calcination conversion is mostly affected by the solids mass flow rate and the bed temperature at the inlet.
- Modelling a calcium-looping fluidised bed calcination reactor with solar-driven heat fluxPublication . Rivero, Mayra Alvarez; Rodrigues, Diogo; Pinheiro, Carla I.C.; Cardoso, João P.; Mendes, Luís FilipeABSTRACT: A new unidimensional computational model is developed to simulate a calcination reactor in a Calcium-looping process for thermochemical energy storage in concentrating solar power systems. The proposed reactor is an absorber tube exposed to concentrated solar radiation. This tube is also the riser of a circulating fluidised bed where the calcination reaction takes place. The proposed heat transfer process models are based on the core-annulus model and the hydrodynamic model is a modified version of the Kunii-Levenspiel model. The model considers the change in the mass flow rate of species and the density change of the phases in the axial direction of the reactor, usually considered constant in the models found in the literature. A higher calcination efficiency, up to 8 p.p., is obtained for the studied reference case when assuming constant density and mass flow rate. Simulations were performed by imposing a solar-driven non-uniform heat flux distribution on the reactor wall. The results show that a 6 m height reactor allows achieving a calcination efficiency of 66% for the reference conditions used. A sensitivity analysis shows that the solids mass flow rate and the inlet bed temperature are the parameters that most affect the calcination process efficiency.
- Solid-gas reactors driven by concentrated solar energy with potential application to calcium looping: A comparative reviewPublication . Rivero, Mayra Alvarez; Rodrigues, Diogo; Pinheiro, Carla I.C.; Cardoso, João P.; Mendes, Luís FilipeABSTRACT: The calcium looping process, based on the reversible calcination-carbonation reaction cycle of CaCO3-CaO, is an emerging and promising technology for thermochemical energy storage in concentrating solar power plants. In this process, concentrated solar energy is used to carry out the endothermic solar-driven calcination of CaCO3 with formation of CaO and CO2 as products in a solid-gas reactor. In this review, a number of experimental studies of solid-gas reactors driven by concentrated solar energy are discussed, with a particular focus on solar reactors for calcination of CaCO3 or with that potential application. The solid-gas reactors for solar-driven calcination of CaCO3 reported in the literature achieved a total efficiency of 16.6%-88% for a mass flow rate up to 25 kg h(-1) and a power up to 55 kW. Also, a detailed comparison of the different types of solid-gas reactors driven by concentrated solar energy is provided by outlining their advantages and disadvantages according to several relevant criteria. This review is intended to be a valuable tool for the selection of a reactor configuration for future studies related to solar-driven calcination of CaCO3.