Abstract
We explore the thermodynamic efficiency of a solar-driven combined cycle power system with manganese oxide-based thermochemical energy storage system. Manganese oxide particles are reduced during the day in an oxygen-lean atmosphere obtained with a fluidized-bed reactor at temperatures in the range of 750–1600°C using concentrated solar energy. Reduced hot particles are stored and re-oxidized during night-time to achieve continuous power plant operation. The steady-state mass and energy conservation equations are solved for all system components to calculate the thermodynamic properties and mass flow rates at all state points in the system, taking into account component irreversibilities. The net power block and overall solar-to-electric energy conversion efficiencies, and the required storage volumes for solids and gases in the storage system are predicted. Preliminary results for a system with 100 MW nominal solar power input at a solar concentration ratio of 3000, designed for constant round-the-clock operation with 8 hours of on-sun and 16 hours of off-sun operation and with manganese oxide particles cycled between 750 and 1600°C yield a net power block efficiency of 60.0% and an overall energy conversion efficiency of 41.3%. Required storage tank sizes for the solids are estimated to be approx. 5–6 times smaller than those of state-of-the-art molten salt systems.
Highlights
Concentrating solar power (CSP) technologies offer the major benefit of enabling inexpensive thermal energy storage, which allows CSP plants to operate round-the-clock as well as on-demand
We explore the theoretical efficiencies achievable with a solar-driven combined cycle power plant, including a topping Brayton and a bottoming Rankine power cycle, with high-temperature thermochemical energy storage
More N2 means more solar energy is used directly for on-sun operation, while more Mn2O3 means more energy is stored for off-sun operation
Summary
Concentrating solar power (CSP) technologies offer the major benefit of enabling inexpensive thermal energy storage, which allows CSP plants to operate round-the-clock as well as on-demand. We explore the theoretical efficiencies achievable with a solar-driven combined cycle power plant, including a topping Brayton and a bottoming Rankine power cycle, with high-temperature thermochemical energy storage. In combined Brayton-Rankine power cycles, the benefit of high turbine entrance temperatures of gas turbines (> 1000°C [2]) is combined with the. Reduction in N2 gives access to the Mn3O4/MnO transition below the slagging temperature. This transition involves a high enthalpy of reaction, and strongly increases the mass-specific storage capacity of the solids. With the redox pair Mn2O3/MnO, operated over the temperature range 750–1600°C, the thermochemical storage process is described by: Reduction: Mn2O3 (750 C) 2MnO(1600 C) 1/2O2 (1600 C); h 304.7 kJ mol 1 (2)
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