Comparative study of single and multi-layered packed-bed thermal energy storage systems for CSP plants
TL;DR: In this paper, the effect of phase change materials (PCM) on the discharge duration of a multi-layer thermal energy storage (TES) system was analyzed for a storage tank operating between 563 and 663 K with bed dimensions of 12 and 14.38 m using solar salt as Heat Transfer Fluid (HTF).
Abstract: The Multi-layered Thermal Energy Storage (TES) tank consists of three regions–top and bottom part is packed with suitable Phase Change Materials (PCM) and low-cost pebbles are placed in the middle region, whereas entire tank portion is filled by solid fillers in Single-layered tank system. For a storage tank operating between 563 and 663 K with bed dimensions of 12 and 14.38 m using Solar salt as Heat Transfer Fluid (HTF), it is observed that the duration of discharge for multi-layered tank is 5.32 h whereas it is 4.19 h for single-layered tank with a Reynolds number of 10. The effect of intermediate melting temperature range of PCMs are also analyzed by taking PCMs with sharp as well as intermediate melting ranges. Further, comparison of single and multi-layered systems is carried out by analyzing the temperature profiles and width of both PCM layers. The width of top and bottom PCM layers of tank is varied from 0 to 30% to analyze its effect on the discharging duration. It is observed that multi-layered system provides extra discharge of 1 h with introduction of PCM at top and bottom with a width of 10%. Discharge duration increases with increase in PCM width whereas the percentage increase in duration of discharge with increase in PCM width is comparatively less. It is also seen that PCMs with sharp melting point performs better compared to one having intermediate range of melting temperatures. Multi-layered configuration concept offers best possibilities as integration to CSP plants with desired efficiency.
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TL;DR: In this article , a solar integrated combined organic ranking cycle and multi-stage desalination with packed bed thermal energy storage is proposed, and thermo-economic-environmentally analyzed for residential areas to increase the self-sustainability.
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01 Jan 2022
TL;DR: An overview of thermocline packed-bed TES systems, covering storage mechanisms, packing configurations, and the application temperature ranges, is provided in this article , where the influencing factors, that is, operational, geometrical, and thermophysical parameters, on the thermal performance of storage system are also surveyed.
Abstract: Solar energy as a promising and renewable energy source has been applied in diverse filed for human activities. Thermal energy storage (TES) is applied to overcome the intrinsic deficiency of solar energy by migrating the dispatching between the energy supply and demand. The thermocline packed-bed TES system acted as dual-media is alternative to conventional two-tank system, exhibiting excellent cost and heat capacity advantages. It has been widely used, not only for high-temperature applications such as for the concentrated solar power, but also for industrial waste heat recovery at medium-temperature and for low temperature applications in built-environment. This book chapter provides an overview of thermocline packed-bed TES systems, covering the storage mechanisms, packing configurations, and the application temperature ranges. The influencing factors, that is, operational, geometrical, and thermophysical parameters, on the thermal performance of storage system are also surveyed. Some numerical simulation models are presented based on dimensional numbers, phase numbers, ignoring/nonignoring temperature gradient inside particles, etc. In all, the thermocline packed-bed tank with latent-sensible fillers is prospective to be promoted in future industries due to the advantages of low cost, stable performance, and high energy density. The existing challenges are also identified, including the thermocline stability, the packing topology, and the control strategy under variable operational parameters.
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TL;DR: In this paper, it is shown that in layered systems different convective flow patterns appear than in the single-layer case, where the number and constellation of convection cells characterize steady flow patterns.
Abstract: Convective motions are a multi-physics phenomenon, in which flow and transport processes interact in a two-way coupling. The density of the fluid depends on the value of transport variable and this back-coupling leads to non-linear behaviour. For the classical constellation of a closed fluid container heated from below convective motions appear, when a critical threshold for the Rayleigh number is exceeded. The heat transfer due to convection is much higher than in the case of pure conduction. Here systems of three layers are examined in detail. Using numerical CFD modelling it is shown that in layered systems different convective flow patterns appear than in the single layer case. The number and constellation of convection cells characterize steady flow patterns. Using a parametric sweep over the relevant parameter range of layer Rayleigh numbers and layer thicknesses we determine diagrams that show the excess heat or mass transfer of the dominant convection patterns, measured by the Nusselt- or Sherwood numbers.
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TL;DR: In this article, the different storage concepts are reviewed and classified, and modellization of such systems is reviewed, and all materials considered in literature or plants are listed. But only a few plants in the world have tested high temperature thermal energy storage systems.
Abstract: Concentrated solar thermal power generation is becoming a very attractive renewable energy production system among all the different renewable options, as it has have a better potential for dispatchability. This dispatchability is inevitably linked with an efficient and cost-effective thermal storage system. Thus, of all components, thermal storage is a key one. However, it is also one of the less developed. Only a few plants in the world have tested high temperature thermal energy storage systems. In this paper, the different storage concepts are reviewed and classified. All materials considered in literature or plants are listed. And finally, modellization of such systems is reviewed.
1,445 citations
TL;DR: In this article, the published heat transfer data obtained from steady and nonsteady measurements are corrected for the axial fluid thermal dispersion coefficient values proposed by Wakao and Funazkri.
993 citations
978 citations
TL;DR: In this paper, the development of a thermocline system that uses molten-nitrate salt as the heat transfer fluid is described and compared to a two-tank molten salt system.
Abstract: Thermal storage improves the dispatchability and marketability of parabolic trough power plants allowing them to produce electricity on demand independent of solar collection. One such thermal storage system, a thermocline, uses a single tank containing a fluid with a thermal gradient running vertically through the tank, where hotter fluid (lower density) is at the top of the tank and colder fluid is at the base of the tank. The thermal gradient separates the two temperature potentials. A low-cost filler material provides the bulk of the thermal capacitance of the thermal storage, prevents convective mixing, and reduces the amount of fluid required. In this paper, development of a thermocline system that uses molten-nitrate salt as the heat transfer fluid is described and compared to a two-tank molten salt system. Results of isothermal and thermal cycling tests on candidate materials and salt safety tests are presented as well as results from a small pilot-scale (2.3 MWh) thermocline.
519 citations
TL;DR: In this article, a literature review was carried out to evaluate the state of the art of thermal energy storage applied to parabolic trough power plants, where the heat transfer fluid (HTF) also serves as storage medium.
Abstract: A literature review was carried out to critically evaluate the state of the art of thermal energy storage applied to parabolic trough power plants. This survey briefly describes the work done before 1990 followed by a more detailed discussion of later efforts. The most advanced system is a 2-tank-storage system where the heat transfer fluid (HTF) also serves as storage medium. This concept was successfully demonstrated in a commercial trough plant (13.8 MW e SEGS I plant; 120 MWh t storage capacity) and a demonstration tower plant (10 MW e Solar Two; 105 MWh t storage capacity). However, the HTF used in state-of-the-art parabolic trough power plants (30-80 MW e ) is expensive, dramatically increasing the cost of larger HTF storage systems. Other promising storage concepts are under development, such as concrete storage, phase change material storage, and chemical storage. These concepts promise a considerable cost reduction compared to the direct 2-tank system, but some additional R&D is required before those systems can be used in commercial solar power plants. An interesting and likely cost-effective near-term option for thermal energy storage for parabolic trough power plants is the use of an indirect 2-tank-storage, where another (less expensive) liquid medium such as molten salt is utilized rather than the HTF itself.
380 citations