Abstract
Thermal-energy storage systems consisting of multiple tanks allow the implementation of thermocline-control methods, which can reduce the drop in the outflow temperature during discharging and increase the volumetric storage density and utilization factor. Multi-tank systems based on the extraction and mixing thermocline-control methods were assessed using simulations assuming fluvial rocks as storage material and compressed air as heat-transfer fluid. For adiabatic conditions, the simulations showed improved performance for all multi-tank systems, with diminishing improvements as the number of tanks increases. The mixing method performed better than the extraction method. The mixing method delivered an outflow temperature drop of 5.1% using two tanks whose total volume was 2.15 times smaller than that of the single-tank system. For diabatic conditions, more than three tanks were not beneficial. With two tanks, the mixing method attained a temperature drop of 5.8% with a volume that is 2.5 times smaller than that of the single-tank system. The exergy efficiency of the two-tank system was 91.3% compared to 98.1% of the single-tank system. The specific material costs of the two-tank system were 1.5 times lower than those of the single-tank system.
Highlights
Thermal-energy storage (TES) is a key component of advanced adiabatic compressed air energy storage (AA-CAES) and concentrated solar power (CSP) plants
The design of TES systems for CSP plants has received a lot of attention, see, e.g., the overviews of Kuravi et al [2] and Pelay et al [3], while by comparison the design of TES systems for AA-CAES plants has received less attention
The operation of a CSP plant is largely dictated by local insolation conditions that can be forecast with good accuracy, as described by Schroedter-Homscheidt and Wilbert [6]
Summary
Thermal-energy storage (TES) is a key component of advanced adiabatic compressed air energy storage (AA-CAES) and concentrated solar power (CSP) plants. Thermal total quantity charge discharge fluid solid rate non-dimensional example, the diameters of existing tunnel boring machines are typically less than about 18 m [13,14] This places a premium on TES designs that minimize the volume required to store a specified amount of thermal energy. TCC methods can deliver relative increases in the utilization factor of 38.8% and 73.4% at quasi-steady conditions for a stand-alone TES operating with air or molten salt as heat-transfer fluids (HTF), respectively, at the expense of small decreases in the cycle exergy efficiency. Cárdenas and Garvey [21] studied two-tank TES systems that are subjected to a perturbed sinusoidal energy flow during charging and discharging Using simulations, they designed a two-tank system whose large and small tanks were supplied with the low- and high-frequency energy flows, respectively. In contrast to the work of Cárdenas and Garvey [21], we do not neglect the heat losses to the ambient
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