Abstract
One of the most interesting perspectives for the development of concentrated solar power (CSP) is the storage of solar energy on a seasonal basis, intending to exploit the summer solar radiation in excess and use it in the winter months, thus stabilizing the yearly production and increasing the capacity factor of the plant. By using materials subject to reversible chemical reactions, and thus storing the thermal energy in the form of chemical energy, thermochemical storage systems can potentially serve to this purpose. The present work focuses on the identification of possible integration solutions between CSP plants and thermochemical systems for long-term energy storage, particularly for high-temperature systems such as central receiver plants. The analysis is restricted to storage systems potentially compatible with temperatures ranging from 700 to 1000 °C and using gases as heat transfer fluids. On the basis of the solar plant specifications, suitable reactive systems are identified and the process interfaces for the integration of solar plant/storage system/power block are discussed. The main operating conditions of the storage unit are defined for each considered case through process simulation.
Highlights
The authors developed detailed models of the reactors and made less severe assumptions on the variables characterizing the other elements of the thermal energy storage systems, including the assumption that the temperature of the fluid leaving the solar field equals that of the fluid fed to the thermochemical storage (TCS) unit, even in presence of an intermediate heat exchanger, and that the storage unit provides heat at temperatures that are sufficiently high to run the power block
The process interfaces for the integration of concentrated solar power (CSP) technologies with thermochemical storage systems can be numerous and depend on the specifications and operating conditions of the CSP plant
In the discharging phase the system is operated at a higher pressure level to increase the temperature at which the accumulated heat is released and to improve the kinetics of the carbonation reaction; the optimal operating pressure was identified through the process analysis of the entire flow sheet represented in Figure 16b, taking into account the upstream and downstream operations of the TCS unit
Summary
The possibility of providing 24-h continuous supply of solar energy is a key factor in the development of concentrated solar power (CSP) technologies [1]. Strohle et al [19] focused on the restrictions imposed by the choice of the reactor type, i.e., packed bed or fluidized bed reactor, on the CSP/TCS integration when employing the Mn2 O3 /Mn3 O4 system To this end, the authors developed detailed models of the reactors and made less severe assumptions on the variables characterizing the other elements of the thermal energy storage systems, including the assumption that the temperature of the fluid leaving the solar field equals that of the fluid fed to the TCS unit, even in presence of an intermediate heat exchanger, and that the storage unit provides heat at temperatures that are sufficiently high to run the power block. The analysis is aimed at understanding the feasibility of direct contact schemes, in which the same gas is used as heat transfer fluid in the solar receiver and TES unit and as working fluid in the power block This solution provides an advantage in terms of energy efficiency and plant simplicity, but it introduces several constraints regarding the operating pressures and temperatures. In the present analysis the attention is placed on the identification of possible integration schemes between the solar plant and thermochemical unit with the evaluation of the main process parameters ( temperature and pressure) of the reactor
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