Thermochemical Energy Storage System Research Articles

Exploring a novel tubular-type modular reactor for solar-driven thermochemical energy storage

Thermochemical energy storage (TCES) has gained extensive attention as a potential solution to address the mismatch between solar thermal energy production and demand. In this study, a novel tubular-type modular TCES reactor is introduced. COMSOL modelling of the system is developed and experimentally validated using a laboratory-scale TCES system. Both types of reactors show similar temperature increases, intensifying with higher inlet relative humidity. Their maximum temperature lifts exceeding 26 °C at 90 % RH. Tubular designs offer better axial flexural strength and dispersion of TCES composite materials compared to plate structures. This property of tubular structures beneficial reducing bed thickness and pressure drop and enhancing equivalent thermal efficiency. Simulations show tubular-type modular reactors reduce pressure drop by 4–5 times compared to plate-type modular reactors, increasing equivalent thermal efficiency by nearly 7% points. Increasing the number of reactor beds and inner tube radius improves equivalent thermal efficiency due to reduced bed thickness and pressure drop. As the number of matrix rows and columns in the reactor bed increases from 2 to 10, bed thickness decreases from 0.058 m to 0.012 m, reducing pressure drop from 845.53 Pa to 38 Pa and increasing equivalent thermal efficiency from 78.82 % to 96.61 %.

Experimental investigation on thermochemical heat storage using CaO/CaCO3 in a cyclone reactor

In this study, a cyclone reactor with a secondary flow effect was applied to the CaCO3/CaO thermochemical energy storage system. An experimental platform for thermochemical energy storage with a cyclone reactor was built. A cold-state experiment was performed to study the feeding and conveying performance of CaCO3 and CaO particles. The experimental results reveal that the average feeding speeds of CaCO3 and CaO were 25.7–29.6 g/min and 3.5–11.0 g/min, respectively. The effects of different heating temperatures (750–950 °C) and inlet air velocities (4–14 m/s) on the reaction performance were studied. The results indicate that CaCO3 decomposes above 750 °C. The reaction degree increased with increased reaction temperature, and the peak value of the outlet CO2 concentration peaked (4.72 %) when the heating temperature was 950 °C, where the reaction degrees under different air velocities were similar. In addition, the inlet air velocity and the outlet relative humidity decreased owing to the formation of CO2 and CaO. In the energy release experiment, it was difficult to smoothly feed CaO into the cyclone reactor for synthesis owing to its characteristics, and no obvious change in the CO2 concentration was observed at the outlet. The energy storage reaction and flow characteristics were experimentally studied to provide a reference for the design of thermochemical energy storage reactors.

A cascaded thermochemical energy storage system enabling performance enhancement of concentrated solar power plants

Calcium looping (CaL) thermochemical energy storage (TCES) exhibits promising potential for application in concentrated solar power (CSP) plants. However, the CSP-CaL integrating system encounters challenges related to elevated heat loss and diminished power generation efficiency. Herein, for the sake of a more rational heat management and enhanced energy utilization, we propose a cascaded energy storage and utilization strategy. Accordingly, a cascaded TCES system model consisting of Calcium looping and Magnesium looping (MgL)-MgCO3/MgO thermochemical cycle subsystem is developed. The energy analysis and exergy analysis results show that the solar power efficiency and exergy efficiency of the considered system are 41.7% of 44.7%, which are 2.6% and 2.8% higher than the single CaL energy storage CSP system, respectively, demonstrating the superiority of the proposed strategy and system for CSP application. Furthermore, the operation strategy of the system under off-design conditions is proposed by considering the real solar irradiation, and the yearly overall solar power efficiency is 39.2%. The economic analysis of the proposed system indicates that the levelized cost of electricity ranges from 179–156 $/MWh for different plant sizes and is superior in large-scale CSP plants. The cascaded energy storage and utilization strategy of thermochemical cycles with different working temperatures provides better dispatchability to meet the different thermal energy demands.

Experimental investigation of CaCO3/CaO reaction pair in a fixed bed reactor for CSP application

CaCO3/CaO thermochemical energy storage (TCES) system has been widely studied on laboratory scale for its potential in concentrated solar power (CSP) plants. However, there is still need for the large-scale experiments based on which a detailed analysis can be obtained to improve this system for real-time applications. In this study, we developed a packed bed reactor capable of operating at high temperature and pressure providing the carbonation and decarbonation reactions of CaCO3/CaO reaction pair. The heat storage process is studied with the aspect of different decarbonation temperatures and different sample sizes (amount of sample in grams) placed in the reactor. Furthermore, we compared the heat storage performance of pure and composite samples. The heat release process is performed by varying the concentration of CO2 and the sample size of the loaded material. The results showed that the heat storage rate and efficiency improve by increasing the temperature of the decarbonation, implying that this reaction must be carried out above 925 °C for better performance. The heat is released smoothly and at a good rate when the concentration of CO2 is high in the reactor. Also, carbonation reaction (heat release process) depicts that CaCO3/CaO TCES system has a great potential to be used as a heat pump and is capable of upgrading the temperature of the released heat from lower to higher value.

A scaling procedure for designing thermochemical energy storage system

Thermochemical energy storage (TCES) technology offers a promising avenue for achieving prolonged thermal energy storage through reversible gas-solid reactions. In the present work, a scaling analysis approach is presented to derive the relevant length and time scales for heat charging and discharging processes occurring inside a porous reactor bed of a TCES system. The processes involved are vapour flow through the porous bed, coupled heat and mass transfer, and heat and mass absorption/release in conjunction with reaction kinetics, for the case of water vapour and potassium carbonate as the gas-solid pair. This analysis employs an order-of-magnitude approach on mass, momentum, and energy conservation equations. The scaling analysis of continuity and momentum equations derives the scale for critical vapour penetration depth. It signifies the length scale beyond which pressure drop becomes significant, leading to a significant reduction in the reaction rate. Similarly, a critical thermal diffusion length scale is derived from the scaling analysis of the energy equation. This scale signifies the length beyond which the reaction rate drops significantly due to limited thermal diffusion. The derived scales characterize the performance of the energy storage bed and help in determining bed dimensions for an effective flow of heat and water vapour through the bed.

Energetic and exergetic performance analyses of mobile thermochemical energy storage system employing industrial waste heat

With an expanding urban population and increasing energy consumption, the demand for air conditioning is projected to reach 45 % of total energy demand by 2050. Based on projections, there will be a massive demand for air conditioning purposes, and energy consumption for air conditioning will also increase. Mobile thermo-chemical energy storage (MTES) offers an alternative by utilizing waste heat from power plants for heating and cooling via sorption heat storage. MTES proves advantageous due to its portability and phase change material transport capability. This study focuses on an MTES system applied in District Energy Networks (DEN) for cooling application. An analytical model has been developed to evaluate the system performance by considering energy efficiency ratio, round-trip efficiency, coefficient of performance, energetic efficiency, exergy destruction rate, and exergetic coefficient of performance as the performance parameters. Results show that an average round-trip efficiency of 53 %, maximum COP of 1.74, and exergy efficiency of 46.7 % is obtained for the year 2022. Notably, the MTES truck achieves a 50 % exergy efficiency. This study contributes insights into efficient waste heat utilization for sustainable cooling solutions.

A perspective on high‐temperature heat storage using liquid metal as heat transfer fluid

AbstractEnergy storage systems are essential to secure a reliable electricity and heat supply in an energy system with high shares of fluctuating renewable energy sources. Thermal energy storage systems offer the possibility to store energy in the form of heat relatively simply and at low cost. In concentrating solar power systems, for instance, molten salt‐based thermal storage systems already enable a 24/7 electricity generation. The use of liquid metals as heat transfer fluids in thermal energy storage systems enables high heat transfer rates and a large operating temperature range (100°C to >700°C, depending on the liquid metal). Hence, different heat storage solutions have been proposed in the literature, which are summarized in this perspective. Based on these, future technical advances are suggested such as reducing the liquid metal share in the heat storage, using waste material as storage medium or using liquid metal as heat transfer fluids not only in sensible, but in latent or thermochemical energy storage systems. The use of waste material in a packed bed configuration with 5% porosity, for example, can bring down the storage material costs to 2%–3% of the costs of a liquid metal‐only storage system. Furthermore, future application fields beyond concentrating solar power are proposed: supply of industrial process heat, waste heat integration and power‐to‐heat‐to‐power processes.

Experimental investigations to measure thermodynamic properties of MWCNT/MnCl2 composite material for thermochemical energy storage system

Experimental investigations to measure thermodynamic properties of MWCNT/MnCl2 composite material for thermochemical energy storage system

Influence of Long-Term CaO Storage Conditions on the Calcium Looping Thermochemical Reactivity.

Long-term storage capability is often claimed as one of the distinct advantages of the calcium looping process as a potential thermochemical energy storage system for integration into solar power plants. However, the influence of storage conditions on the looping performance has seldom been evaluated experimentally. The storage conditions must be carefully considered as any potential carbonation at the CaO storage tank would reduce the energy released during the subsequent carbonation, thereby penalizing the round-trip efficiency. From lab-scale to conceptual process engineering, this work considers the effects of storing solids at low temperatures (50-200 °C) in a CO2 atmosphere or at high temperatures (800 °C) in N2. Experimental results show that carbonation at temperatures below 200 °C is limited; thus, the solids could be stored during long times even in CO2. It is also demonstrated at the lab scale that the multicycle performance is not substantially altered by storing the solids at low temperatures (under CO2) or high temperatures (N2 atmosphere). From an overall process perspective, keeping solids at high temperatures leads to easier heat integration, a better plant efficiency (+2-4%), and a significantly higher energy density (+40-62%) than considering low-temperature storage. The smooth difference in the overall plant efficiency with the temperature suggests a proper long-term energy storage performance if adequate energy integration is carried out.

Energy Efficiency and Techno-Economic Analysis of a Thermochemical Energy Storage System by Using a Fluidized Bed Reactor Integrated with a Steam Rankine Cycle of a Biomass Power Plant

Energy Efficiency and Techno-Economic Analysis of a Thermochemical Energy Storage System by Using a Fluidized Bed Reactor Integrated with a Steam Rankine Cycle of a Biomass Power Plant

Method for screening paired metal hydrides with appropriate phase change material for a thermochemical energy storage system

Thermochemical energy storage (TES) systems using coupled metal hydrides (MHs) have long been recognized as an option for sustainable energy systems such as solar power plants. The MHs-TES system consists of two linked MH beds (energy storage bed and hydrogen storage bed) that exchange hydrogen during the heat storage/release cycles. The heat reaction of the hydrogen storage bed is stored in a PCM as latent heat, which is recovered during the heat release step. One of the main issues of the MHs-TES system is selecting the best-suited combination of MHs and compatible PCM to satisfy application requirements. Herein, an approach is proposed for screening the right pairs of hydrides and the suitable PCM. To assess this procedure's effectiveness, a 2D-mathematical model is developed, and a computer code is established. In addition, using this code, the dynamic behavior of the MHs-TES system and the effect of the hydrogen storage bed temperature on the system's performance are examined. The Mg2Fe alloy as HTMH bed, and two LTMH beds as LTMH (LaNi4.25Al0.75 at medium temperature and LaNi5 at low temperature) are used. With an efficiency of 86.5%, the results show that Mg2Fe/LaNi5 is a viable MHs combination for a thermal storage system.

Performance assessment and optimization of concentrated solar power plants with paired metal hydride-based thermochemical energy storage

The main objective of this study is to evaluate the innovative future concept of a concentrated solar power (CSP) plant, specifically focusing on a CSP-driven Rankine cycle. Additionally, a suggested energy storage solution for the analyzed CSP plant is the thermochemical energy storage (TCES) approach. The TCES system used paired metal hydrides integrated with phase change material (PCM). A comprehensive mathematical model has been developed to enable performance predictions for the entire CSP plant as well as each of its components. This model considers the thermal coupling between the solar field, the thermochemical storage system, and the power block in order to assess the overall performance of the CSP plant. Utilizing this successfully verified model with reference data, a parametric study is conducted on various operating parameters to identify optimal operating points for the storage system in relation to the overall efficiency of the CSP plant. Furthermore, the critical issue of appropriate and novel concepts for MHs-based TCES integration in CSP plants is discussed in detail. The CSP plant's performance was examined as a function of storage cycle duration, charging and discharging temperatures, melting PCM temperature, and thermal efficiency. Based on the findings, it has been observed that higher charging temperature and integration of PCM into the thermochemical energy storage (TCES) system can lead to a significant reduction of 13-fold in the required solar collector area and a notable increase of 77 % in the efficiency of the CSP plant. Thus, the proposed TCES system appears to be the most promising future heat storage system for CSP plants.

Indirect power cycles integration in concentrated solar power plants with thermochemical energy storage based on calcium hydroxide technology

Thermochemical energy storage is attracting interest as a relevant alternative energy storage system in concentrating solar power plants. Efficient, low-cost, and environmentally friendly thermal energy storage is one of the main challenges for the large-scale deployment of solar energy. The reversible hydration/dehydration process of calcium oxide is one of the most promising concepts for energy storage integration at intermediate temperatures in solar plants. The efficient integration of concentrated solar power with a thermochemical energy storage system based on the calcium hydroxide concept, individually or integrated into a hybrid system with sensible heat storage, can be a feasible solution for long-term energy storage. Efficient energy recovery and subsequent power production are crucial. This work presents a novel analysis of the indirect integration of different power cycle configurations to optimise the roundtrip efficiency of the system. Steam Rankine, closed CO2 Brayton, and organic Rankine cycles are considered. The analyses show power block efficiencies in the range of 38–50%, with a global roundtrip efficiency of 37.1% in the case of the CO2 supercritical cycle.

Fluidisation of Thermochemical Energy Storage Materials: Degradation Assessment

ABSTRACT Composite zeolites impregnated with anhydrous salt particles are promising materials for use in domestic thermochemical energy storage (TCES), however they have limited power output. Fluidization has the potential to increase the mass and heat transfer of TCES systems. In this study, a composite TCES material of LiX zeolite impregnated with MgCl2 salt is produced. This material and a LiX zeolite batch are then fluidized at different gas velocities to study whether degradation of these particles occurs when fluidizing. Images of the particles after fluidizing are analyzed using a validated method utilizing microscope images and specialized software used to study whether fragmentation or abrasion have been induced by fluidization. Composite particles were found to have increased average diameter by 7%−8%, which could be due to imperfect dehydration of these particles after the impregnation process, but also due to observed salt conglomerates present on the surface of some particles. Overall, excess degradation was not found due to fluidization at any gas velocity. No mass loss was measured in any sample after fluidization, and no appreciable fragmentation was observed. The LiX zeolite and composite particles measured 0.6192 mm and 0.6799 mm prior to fluidization and measured 0.6405 mm and 0.7088 mm after fluidization. However, this change is not statistically significant, and it is shown that a change in diameter is unlikely. Despite this, some fines have been produced which were found to have an average diameter of 3.60 μm (σ = 1, ±2.34 μm), and as such present a hazard if inhaled.

Al- and Cr-doped Co3O4/CoO redox materials for thermochemical energy storage in concentrated solar power plants

The redox system of Co3O4/CoO is very promising for the thermochemical energy storage systems coupled to concentrated solar power plants because of its high energy storage density and reversibility. Nevertheless, the practical application of Co3O4/CoO system is limited by thermal hysteresis of the redox reaction and material sintering. Here, we synthesized Co-based metal oxides doped with Al and Cr, and studied the influence of the doping of these two metal elements on the thermochemical properties and sintering resistance of the pure Co3O4/CoO system. Both Al and Cr doping narrows the thermal hysteresis of the Co3O4/CoO system. In particular, when the molar doping rate of Al is 10%, the thermal hysteresis of Co–Al oxides is only 4.02 °C, which is much narrower than that of pure Co3O4, and the increase of its oxidation temperature also means that a higher level of thermal energy can be released during oxidation. In the redox cycle, the addition of Al inhibits material sintering and the formation of a loose porous structure facilitates the oxidation, ensuring the reversibility of the redox reaction. The 10% Al–Co honeycomb shows stable conversion behavior with an average conversion of 77.75% in 15 redox cycles. Co–Al oxides exhibit excellent oxidative exothermic characteristics and long-term cycle stability, making them suitable for efficient thermochemical energy-storage processes.

Organolithium-derived alkali-doped highly durable Li4SiO4 heat carrier for solar thermochemical energy storage

Thermochemical energy storage (TCES) technology plays a vital role in utilizing solar energy to produce electricity. However, traditional TCES technologies such as calcium looping route suffer from unsatisfactory long-term durability. Lithium looping has demonstrated excellent cyclic stability, but it has been rarely employed for energy storage. In this work, organolithium-derived Li4SiO4 heat carrier was synthesized and further decorated with alkali doping. The porous microstructures and wrinkled surfaces of organolithium-derived Li4SiO4 were demonstrated, with alkali doping facilitating the formation of low-temperature eutectic materials and reducing CO2 diffusion resistance, thereby enhancing its cyclic energy storage performance. Li4SiO4 doped with 3 wt% K2CO3 shows energy storage density of as high as 638.23 kJ/kg, equal to a high conversion of 81.41% over long storage/release tests of 15 cycles. The high energy density and excellent cyclic durability of Li4SiO4 were attributed to its porous microstructures and formed eutectic melts. Furthermore, for practical application, the carbonation (or heat release) temperature for Li4SiO4 looping TCES system was optimized. To sum up, Li4SiO4 exhibits great potential as a candidate for thermochemical energy storage in solar energy utilization due to its excellent long-term cyclic durability.

Integration of a novel Chemical Looping Combustion reactor into a thermochemical energy storage system

This study analyses the performance of a back-up power process that uses a novel chemical looping packed bed air reactor to oxidize a batch of reduced solids while heating high pressure flowing air. In this arrangement, the solids are slowly oxidized by a diffusionally-controlled flow of oxygen perpendicular to the main air flow, thus imposing very long oxidation times for all reacting particles. A decay in the thermal power output of the reactor can be expected with time due to the increasing resistance to O2 diffusion towards the unreacted oxygen carrier particles as the reaction progresses. In this work, integration of the dynamic system formed by the reactor and the power plant used to produce power from the exploitation of the variable thermal output of the reactor is investigated. Different case studies are assessed for decarbonization of energy production and storage of renewable energy. The reactor is rated at a maximum 50 MWth power output in all cases, employing iron- or nickel-based particles as oxygen carrier. A simplified model for mass and heat transfer in the proximity of the wall orifices allows the definition of operating windows and reactor dimensions. In the chosen case examples, each single reactor operates in discharge mode for around 4–5 h (depending on plant configuration) as a back-up power generator, heating up a compressed air stream up to ∼ 1000 °C and achieving an energy density between 816 and 2214 kWhth/m3. Gas turbines in recuperative, steam injected and combined cycle power plant architectures integrated in the novel chemical looping combustion (CLC) reactor are investigated. Cycle efficiencies up to 49% are calculated for systems that make use of a single reactor configuration and exploit the residual heat for power production through a organic Rankine cycle (ORC) bottomed system. A more flexible multi-reactor configuration is also investigated to address the unavoidable decay in power output during discharge and provide power output controllability. The levelized cost of electricity (LCOE) is estimated be comparable to system elements from the literature when H2 is used as reducing gas. The use of biogas to reduce the solids during the energy charge stage is found to be particularly advantageous, leading to LCOE values between ∼ 120 and 175 €/MWh for the reference reactor system using iron-based solids. This also allows achieving negative CO2 emissions if the captured CO2 generated during the reduction stage is stored.

Integration of calcium looping and calcium hydroxide thermochemical systems for energy storage and power production in concentrating solar power plants

Energy storage is a key factor in the development of renewables-based electrical power systems. In recent years, the thermochemical energy storage system based on calcium-looping has emerged as an alternative to molten salts for energy storage in high-temperature concentrated solar power plants. This technology still presents some challenges that could be solved by integrating the thermochemical energy storage system based on calcium hydroxide. This work studies a novel concentrated solar power system integrating calcium-looping and calcium hydroxide thermochemical energy storage systems. The results show that the combined use of hydration-dehydration cycles in the calcination-carbonation processes of the calcium looping for energy storage could partially solve the issue related to the multicyclic deactivation of calcium oxide. The improvement in the conversion of calcium oxide during carbonation is demonstrated experimentally when hydration-dehydration cycles are combined. Numerical simulations demonstrate the technical feasibility of the integrated process, with efficiencies ranging between 38-46%, improved with the increase in calcium oxide conversion in the carbonator, showing the potential of the proposed integration.

Fabrication of structure-improved, sintering-resistant Li4SiO4 materials for stabilized thermochemical energy storage in concentrated solar power plants

Thermochemical energy storage has been considered as a promising technology for the future high-temperature solar thermal conversion and utilization in concentrated solar power plants. In this work, Li4SiO4/CO2 thermochemical energy storage system was designed based on the reversible reaction Li4SiO4 + CO2↔Li2SiO3 + Li2CO3. The proposed Li4SiO4-based system, which possesses a heat releasing temperature of ∼700 °C, fills in the gaps of medium temperature TCES materials. Furthermore, structure-improved, sintering-resistant Li4SiO4 materials with stabilized performance were fabricated by using organic lithium precursor and cerium addition, and corresponding enhancement mechanisms were systematically studied. It is concluded that the utilization of lithium salicylate could effectively improve the surface morphology as well as the specific surface area of Li4SiO4 particles. And the Ce addition could enhance the cyclic stability of Li4SiO4 by forming anti-sintering CeO2 fine particles inside. As a result, the obtained L-S-Ce2.5 exhibits an average capacity of 671.3 kJ/kg with the capacity decay as low as 13 kJ/kg per cycle, which is of great significance for the practical long-term heat storage/releasing applications at medium temperature.

Experimental and numerical studies of Ca(OH)2/CaO dehydration process in a fixed-bed reactor for thermochemical energy storage

The Ca(OH)2/CaO thermochemical energy storage (TCES) system based on calcium looping has received extensive attention owing to its high energy storage density, prolonged energy storage time, and environmental friendliness. The heat storage process of the Ca(OH)2/CaO TCES system in a mixed heating reactor was evaluated in this study, by employing a combination of direct and indirect heating modes. The dehydration process was studied experimentally, and a numerical model was established and verified based on the experimental results. The dehydration behavior of 500 g of Ca(OH)2 powder was investigated in a fixed-bed reactor with mixed heating. The experimental and simulation results indicated that mixed heating causes combined centripetal and horizontal propulsion. Heat input is the main limiting factor in the heat storage process, because the radial advance of the reaction is hindered by the low thermal conductivity of the solid reactant particles. Heat transmission partitions were added to enhance the performance of the reactor. The performance of the modified reactor was compared with that of a conventional reactor. The radial heat transmission partitions in the modified reactor effectively enhance the energy storage rate and reduce the reaction time by 59.5% compared with the reactor without partitions.