Search Results (19)

The expected increase in energy production from VRE (Variable Renewable Energy) requires a significant increase in energy storage capacity, with thermal storage potentially offering a key contribution. However, heat transfer mechanisms can limit the maximum power instantaneously transferable to the storage medium, posing a significant operational challenge. An analysis is presented here of the power limitations that arise when molten salt thermal storage adopting Solar Salt (NaNO₃/KNO₃, 60/40%wt) is heated by electrical resistances (Joule heating), and a possible alternative—the volumetric heating of the salt mass by microwaves—is discussed. Results show that microwave heating is an interesting path to overcome the power limitations of Joule heating. A first, theoretical analysis indicates a potential increase of more than 10 times in the maximum power transferable per unit area. Thermal-fluid-dynamic and electromagnetic models have been developed to numerically test the performance of a one-tank thermocline system endowed with a microwave heater. The proposed heating system showed limitations in terms of the maximum power that can be transferred to the salt because of the high temperatures established in the boundary layer. Finally, it performs in a comparable way with respect to an (ideal) heating system based on the Joule effect. However, many design improvements can still be adopted to enhance the performance of the proposed technology, likely overcoming the performance reachable using Joule heating systems. Full article

The two-tank molten salt thermal storage system is the most common storage solution in concentrated solar power (CSP) plants. Solar salt (60% NaNO₃ + 40% KNO₃) is the most widely used energy storage material in solar thermal plants. In solar tower technology, where the molten salts must operate at temperatures ranging from 290 °C to 565 °C, several issues related to tank failures have emerged in recent years, with some of these failures attributed to the welding process. The welding process of joints in 316L stainless steel (ASS) probes exposed to a moving flow of a binary mixture containing 60% NaNO₃ and 40% KNO₃ (solar salt) is analysed. The results were evaluated using scanning electron microscopy (SEM) at 120, 500, 1000, 1500, and 2300 h of exposure. It was identified that arc mechanical oscillations significantly improve the microstructural properties and geometrical characteristics of welded joints, reducing structural defects and improving corrosion resistance. The technique promotes uniform thermal distribution, refined dendrite morphology, and homogeneous alloying element distribution, resulting in lower mass loss in high-temperature molten salt environments. Additionally, oscillation welding optimises the bead geometry, with reduced wetting angles and controlled penetration, making it ideal for high-precision industrial applications and extreme environments, such as molten salt thermal storage systems. Full article

Within the context of “peak carbon and carbon neutrality”, reducing carbon emissions from coal-fired power plants and increasing the proportion of renewable energy in electricity generation have become critical issues in the transition to renewable energy. Based on the principles of cascaded energy utilization, this paper improves the coupling methodology of an integrated solar thermal and coal-fired power generation system based on existing research. A parabolic trough collector field and a three-tank molten salt thermal energy storage system are connected in series and then in parallel with the outlet of the reheater. ASPEN PLUS V14 and MATLAB R2018b software were used to simulate a steady-state model and numerical model, respectively, so as to study the feasibility of the improved complementary framework in enhancing the peak load capacity of coal-fired units and reducing their carbon emissions. Actual solar radiation data from a specific location in Inner Mongolia were gathered to train a neural network predictive model. Then, the peak-shaving performance of the complementary system in matching load demands under varying hours of thermal energy storage was simulated. The findings demonstrate that, under constant boiler load conditions, optimizing the complementary system with a thermal energy storage duration of 5 h and 50 min results in an energy utilization efficiency of 88.82%, accompanied by a daily reduction in coal consumption by 36.49 tonnes. This indicates that when operated under the improved coupling framework with optimal parameters, the peak regulation capabilities of coal-fired power units can be improved and carbon emission can be reduced. Full article

Molten salt energy storage technology shows great potential in a sustainable energy integrated system for its excellent thermal energy storage efficiency and environmental adaptability, and it has received much attention from the academic community. To improve the efficiency of traditional dual-tank heat storage systems, a new distributed single tank thermal storage system with an internal heat source was proposed. The single tank was designed according to API 650 and EN 13445-3:2012 specifications, and the specific data of the storage tank was obtained by combining application examples. The results show the following: (1) the stress of the molten salt storage tank with internal electric heating increases during the heating process, and the peak stress appears at the connection position below the tank body and the electric heater sleeve. (2) The increasing electric heater sleeves lead to the increase in tank stress, and when the number of electric heater sleeves increases from four to eight, the tank stress increases by 24%. (3) The stress of the tank reduces with the increasing axial height of the electric heater sleeve. The stress of the tank is reduced by 8% when the position of the electric heater sleeve is increased from 400 mm to 800 mm. This study can provide some theoretical support for the design and optimization of a single-tank molten salt heat storage system and provide a reference for the design of such storage tanks with a built-in heat source. Full article

The degradation of complex geological structures due to thermo-mechanical cycling results in a reduction in bearing capacity, which can readily induce engineering issues such as uneven settlement, cracking, and even the destabilization of the foundations of molten salt storage tanks. This study establishes a foundational model for a molten salt storage tank through the use of COMSOL Multiphysics and conducts a numerical simulation analysis to evaluate the settlement deformation and temperature distribution of the foundation under the influence of thermo-mechanical coupling. Concurrently, the research proposes two distinct design approaches for the tank’s foundational structure. A comparative analysis of the results indicates that the use of a pile raft foundation in conjunction with a traditional foundation mode results in a reduction of settlement at the center of the foundation’s top surface by 380.1 mm, while also decreasing the maximum effective stress in the steel ring wall by 240.7 MPa. The thermal effects impact a depth of 10 m in the foundation soil and an influence radius of 20 m. Additionally, the foundation soil exhibits optimal thermal insulation properties, resulting in minimal energy loss. These findings indicate that the pile raft foundation in conjunction with a traditional foundation mode displays remarkable adaptability to complex geological conditions, with both settlement and temperature distribution of the foundation maintained within acceptable limits. Full article

Concentrating solar power plants use sensible thermal energy storage, a mature technology based on molten salts, due to the high storage efficiency (up to 99%). Both parabolic trough collectors and the central receiver system for concentrating solar power technologies use molten salts tanks, either in direct storage systems or in indirect ones. But even though this is a mature technology, it still shows challenges in its implementation and operation. This paper underscores the critical importance of stringent design criteria for molten salt tanks in thermal storage technology. Focusing on the potential ramifications of design failures, the study explores various dimensions where an inadequate design can lead to severe consequences, even jeopardizing the viability of the entire technology. Key areas discussed include structural integrity, corrosion, thermal shock, thermal expansions, and others. By elucidating the multifaceted risks associated with design shortcomings, this paper aims to emphasize the necessity of thorough reviews and adherence to robust design principles for ensuring the success, safety, and sustainability of thermal storage technology. Full article

The exploitation of solar irradiation is a critical weapon for facing the energy crisis and critical environmental problems. One of the most emerging solar technologies is the use of solar towers (or central receiver systems) coupled with high-performance thermodynamic cycles. In this direction, the present investigation examines a solar tower coupled to a closed-loop Brayton cycle which operates with supercritical CO₂ (sCO₂) as the working medium. The system also includes a storage system with two molten salt tanks for enabling proper thermal storage. The sCO₂ is an efficient fluid that presents significant advancements, mainly reduced compression work when it is compressed close to the critical point region. The novelty of the present work is based on the detailed dynamic investigation of the studied configuration for the year period using adjustable time step and its sizing for achieving a continuous operation, something that makes possible the establishment of this renewable technology as a reliable one. The analysis is conducted with a developed model in the Modelica programming language by also using the Dymola solver. According to the simulation results, the yearly solar thermal efficiency is 50.7%, the yearly thermodynamic cycle efficiency is 42.9% and the yearly total system efficiency is 18.0%. Full article

To address the growing problem of pollution and global warming, it is necessary to steer the development of innovative technologies towards systems with minimal carbon dioxide production. Thermal storage plays a crucial role in solar systems as it bridges the gap between resource availability and energy demand, thereby enhancing the economic viability of the system and ensuring energy continuity during periods of usage. Thermal energy storage methods consist of sensible heat storage, which involves storing energy using temperature differences; latent heat storage, which utilizes the latent heat of phase change materials; and thermochemical heat storage, which utilizes reversible chemical reactions through thermochemical materials. The objective of this review paper is to explore significant research contributions that focus on practical applications and scientific aspects of thermal energy storage materials and procedures. For each type of storage, different materials have been examined, taking into consideration the most recent studies, both for medium and long-term storage and, when possible, comparing methodologies for the same purpose. It has been observed that TCHS systems have the potential to reduce the volume of chemical storage tanks by 34 times using chemical reactions. Among the SHS materials, water, molten salts, and graphite exhibit the highest energy density, with graphite also possessing remarkable thermal conductivity. Nanoparticles can enhance the thermophysical properties of TES materials by increasing their thermal conductivity and wettability and improving intermolecular characteristics. The use of biobased PCMs for applications that do not require very high temperatures allows for maximizing the efficiency of such storage systems. Full article

Fluid-fueled molten-salt reactors (MSRs) are actively being developed by several companies, with plans to deploy them internationally. The current IAEA inspection tools are largely incompatible with the unique design features of liquid fuel MSRs (e.g., the complex fuel chemistry, circulating fuel inventory, bulk accountancy, and high radiation environment). For these reasons, safeguards for MSRs are seen as challenging and require the development of new techniques. This paper proposes one such technique through the observation of the reactor’s off-gas. Any reactor design using low-enriched uranium will build up plutonium as the fuel undergoes burnup. Plutonium has different fission product yields than uranium. Therefore, a shift in fission product production is expected with fuel evolution. The passive removal of certain gaseous fission products to the off-gas tank of an MSR provides a valuable opportunity for analysis without significant modifications to the design of the system. Uniquely, due to the gaseous nature of the isotopes, beta particle emissions are available for observation. The ratios of these fission product isotopes can, thus, be traced back to the relative amount and types of fissile isotopes in the core. This proposed technique represents an effective safeguards tool for bulk accountancy which, while avoiding being onerous, could be used in concert with other techniques to meet the IAEA’s timeliness goals for the detection of a diversion. Full article

Carnot batteries store surplus power as heat. They consist of a heat pump, which upgrades a low-temperature thermal energy storage, a high-temperature storage system for the upgraded thermal energy, and a heat engine that converts the stored high-temperature thermal energy into power. A Carnot battery is proposed based on supercritical CO₂ Brayton thermodynamic cycles. The low-temperature storage is a two-tank molten salt system at 380 °C/290 °C fed by a field of parabolic trough collectors. The high-temperature storage consists of another two-tank molten salt system at 589 °C/405 °C. Printed circuit heat exchangers would be required to withstand the high pressure of the cycles, but shell and tube heat exchangers are proposed instead to avoid clogging issues with molten salts. The conventional allocation of high-temperature molten salt heat exchangers is then modified. Using solar energy to enhance the low-temperature thermal source allowed a round-trip efficiency of 1.15 (COP of 2.46 and heat engine efficiency of 46.5%), thus increasing the stored power. The basic configuration has a levelised cost of storage of USD 376/MWh while replacing the shell and tube heat exchangers with hybrid printed circuit heat exchangers is expected to lower the cost to USD 188/MWh. Full article

The flow heat transfer and stress distribution of the shell and tube superheater of the steam generation system in a 50 MW molten salt tank solar thermal power station are studied by numerical simulation, and the influence of the flow pattern of molten salt and water vapor in the shell-and-tube superheater on the heat transfer efficiency and stress distribution under the heat–fluid–solid coupling condition is deeply studied. When the water vapor is located on the tube side of the superheater, the molten salt is located on the shell side, and the counterflow is used in the superheater, the water vapor outlet meets the inlet temperature of the steam turbine, and the heat exchange efficiency of the superheater can reach 94.2%. The optimum inlet temperatures of molten salt and steam in the superheater are 563 and 345 °C, respectively, and the optimum flow rate of molten salt at the inlet of the superheater is 2.5 m/s. Compared with the stable condition, the heat exchange efficiency can be increased by 2.9%, the equivalent stress value is reduced from 335.63 to 312.60 MPa, and the deformation is reduced by 0.48 mm. Full article

In this study, three slots containing an anode chamber, a cathode chamber, and a middle pole chamber were designed by applying the Hittorf method, and a two-way coupling model of the flow field and electric field was established using the COMSOL system. The electric field distribution in the constructed model was simulated, and the model reliability, boundary conditions, and related parameters were verified. A three-chamber tank was utilized to investigate the migration numbers change rule and migration mechanism of Y(III) ions in the AlF₃–(Li,Na)F system. The migration number of Y(III) ions in the AlF₃–(Li,Na)F–Y₂O₃ molten salt linearly increased from 0.70 to 0.80 with an increase in temperature from 900 to 1000 °C. When the (Li,Na)F/AlF₃ molar ratio was between 2.0 and 2.5, the migration number of Y(III) ions was relatively constant, and its average value was approximately 0.75. Meanwhile, at (Li,Na)F/AlF₃ molar ratios higher than 2.5, the migration number of Y(III) ions linearly decreased from 0.75 to 0.45. Finally, in the current density range of 1.0–2.0 A/cm², the migration number of Y(III) ions increased almost linearly from 0.65 to 0.85. Full article

In this work, the integration of a grid-scale ternary-Pumped Thermal Electricity Storage (t-PTES) with a nuclear power generation to enhance operation flexibility is assessed using physics-based models and digital real time simulation. A part of the electricity from the nuclear power generation is delivered to the grid, and the balance is used to power a heat pump that can be augmented by an auxiliary resistive load element to increase the charging rate of the thermal storage. This increases the thermal potential between hot and cold thermal stores (usually solid materials or molten salts inside large storage tanks). The thermal energy is transformed back into electricity by reversing the heat pump cycle. Different transient scenarios including startup, shutdown, and power change for grid-connected operation are simulated to determine the behavior of the hybrid nuclear-t-PTES system operating under variable loads that constitute a departure from conventional, baseload nuclear plant operation schemes. Ternary refers to the three modes operation: (i) heat pump (including heating coil), (ii) heat engine, and (iii) simultaneous operation of heat pump (including heating coil) and heat engine during changeover from pumping to generation or vice-versa. The controllability of t-PTES in the short timescales as a dynamic load is used to demonstrate operational flexibility of hybrid nuclear plants for flexible operation through advanced load management. The integration of t-PTES into nuclear power systems enhances the system flexibility and is an enabler for high penetration of renewable energy resources. Full article

In this study, two schemes of solar electrical power generation are designed and compared according to solar collection area minimization. The one comprises the parabolic trough collector, dual-tank of molten salt heat storage, and Organic Rankine cycle. The other consists of photovoltaic cell, polymer electrolyte membrane water electrolyzer, and polymer electrolyte membrane fuel cell. The effects of irradiation value, environmental temperature, and energy storage type on thermodynamic performance were investigated. The results indicated that the solar irradiation value had a more obvious effect on the PV (photovoltaic) cell performance than environmental temperature, and the PTC (parabolic trough concentrator) performance was improved with the increases of solar irradiation value and environmental temperature. The environmental temperature effect was negligible; however, the influence of irradiation value was obvious. Irradiation value had a positive effect on the former system, whereas it demonstrated the opposite for the latter. The latter system had much lower efficiency than the former, due to the low conversion efficiency between hydrogen energy and electrical energy in the polymer electrolyte membrane water electrolyzer and fuel cell. Stated thus, the latter system is appropriate for the power generation system with non-energy storage, and the former system is promising in the power generation system with energy storage. Full article

Thermal energy storage (TES) systems are key components for concentrated solar power plants to improve their dispatchability and for shifting the energy production efficiently to high revenue periods. The commercial state of the art is the molten salt two tank storage technology. However, this TES confronts some issues like freezing and decomposition, which require continued technical attention. Furthermore, the molten salt itself is very expensive compared to other storage materials. A TES option that possesses a high cost reduction potential and the ability to increase the whole power plant efficiency is the regenerator-type energy storage. Here, a packed bed inventory of waste metallurgical slag from electric arc furnace (EAF) can achieve further cost reduction. Despite previous studies regarding the use of steelmaking slag as an inventory material for thermal energy storages, there are still basic questions to be answered. This work presents experimental thermal performance and thermo-structural stability studies of slag-based TES, obtained during the European project REslag. The EAF slag and different insulation options were tested for their thermomechanical strength in a uniaxial compression test rig. The thermal cyclic behavior was investigated in a pilot TES plant with temperatures up to 700 °C. The experimental results confirm the suitability of steelmaking slag as thermal energy storage inventory material. Furthermore, a comparison of experimental and simulation model results shows an agreement of over 90%. Full article