Thermochemical Storage System Research Articles

Quantifying the decarbonization potential of mobile heat battery in low-temperature district heating

This research assesses the potential of a mobile thermochemical storage system, the mobile heat battery (M-HB), for decarbonizing a low-temperature district heating (DH) system in the Netherlands. The assessment is built on a case study where the M-HB is used to transport waste heat from different sources to a neighborhood interface of a DH system. This case study utilizes a simulation-based methodology to calculate the emissions from grid electricity, DH, and M-HB transport and charging. Building performance simulation is used as the main experimental method in combination with both empirical data and theoretical assumptions. Various system operational strategies and uncertain factors are explored, and waste heat sources are screened by different decarbonization targets. Findings indicate that using the M-HB can reduce the operational carbon emissions by up to 80 %, from approximately 60–70 KgCO2/GJ of the system without M-HB to around 13 KgCO2/GJ in optimal scenarios. Emissions from M-HB transport and charging are identified as more influential to the decarbonization potential than other considered factors, which addresses the significance of choosing proper waste heat sources. Despite some limitations from data availability and assumptions, this work identifies both opportunities and challenges for using M-HB to decarbonize DH systems.

Design of reactive particle fluidized bed heat exchangers for gas–solid thermochemical energy storage

Concentrated solar power (CSP) systems integrated with a supercritical carbon dioxide (sCO2) Brayton power cycle are regarded as the primary future direction for CSP technologies. Calcium-based particles can be a suitable storage medium to achieve high temperatures exceeding 750 ℃. However, there have been few studies on reactive particle/sCO2 heat exchangers (HXs) to drive high-performance power cycles with high energy storage efficiencies. In this paper, the mechanisms by which chemically reactive particles release energy in a fluidized bed (FB) heat exchanger has been investigated to evaluate the performance of thermochemical storage systems. A 1-MWt thermal duty fluidized bed heat exchanger with sCO2 as the working fluid operating at 988 K was designed in different configurations, featuring single stage and multistage counter-flow HXs. A detailed shell and tube model combining the chemical reaction kinetics and the heat transfer between the fluidized particle and sCO2 FB HX design was developed. A comparison of sensible and chemical heat materials shows that thermochemical energy storage is advantageous due to the relatively short tube length and slow particle mass flow rate. The tube length and particle mass flow rate are reduced by 3.5 and 11.5 times, respectively. The average chemical conversion is 97.30 % for a one-stage heat exchanger, which is lower than the 99.95 % conversion achieved by the two-stage heat exchanger. Additionally, a sensitivity analysis was carried out to understand the impacts of key operating parameters on the process performance. These findings provide insights into the operational stability and efficiency of the system, contributing to the development of advanced heat exchangers for thermochemical energy storage applications.

Optimization of the Coating Process of a Ca(OH)2‐Based Thermochemical Energy Storage Material

AbstractA promising candidate for a thermochemical storage system implemented into district heating is a previously developed core‐shell material based on CaO/Ca(OH)2. Proceeding from the preliminary manufacturing process, this work aims to optimize relevant material properties as mechanical stability and shell uniformity, by varying defined parameters during a reproduceable coating procedure, ready for commercial upscaling.

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.

Annular vertical cylindrical thermochemical storage system with innovative flow arrangements for improved heat dispatch towards space heating requirements

Thermochemical energy storage is a potential solution for low-temperature seasonal energy storage systems and for improving renewable solar thermal energy share in the global energy mix. Such systems can help in meeting the heating requirements in the Indian Himalayan region in an environment-friendly manner. A few studies have attempted to understand the performance of strontium bromide hexahydrate-monohydrate-based storage as a thermochemical energy storage medium. The present study evaluates the performance of the vertical cylindrical annular reactor configuration, considering innovative radial airflow configurations. A two-dimensional axisymmetric model has been developed to study the effect of the various geometrical and operating parameters. During the charging (dehydration) process, the outward flow configuration exhibits substantially higher exergy efficiency as against the inward flow counterpart, with the difference being more pronounced (∼6–8%) at lower aspect ratios (0.5–1.0). The flow work requirement is higher for the outward flow during the hydration (discharging process), resulting in better performance for the inward flow counterpart. Upon increasing the volumetric air flow rate, the pressure drop across the reactive bed is found to increase substantially, leading to lower exergy efficiencies for higher flow rates. During the hydration process, the exergy efficiency for the inward flow becomes almost constant (∼15%) for a relative humidity level exceeding 60%, whereas that for the outward flow gradually increases to reach ∼ 5% for an 80% relative humidity. The ratio of thermal energy stored to the flow work required is higher for the outward flow. The energy output to flow work ratio is about 35% higher for the inward flow for the aspect ratio of 4.

Thermochemical heat storage through CaO-Mayenite/CaCO3 system: Thermal performances comparison for two synthesis methods

ThermoChemical Storage systems (TCS) are gaining attention for long term-thermal energy storage applications. Those systems can successfully increase the electricity generation flexibility in CSP (Concentrated Solar Power) plants or optimize the heat recovery and storage in energy-intensive industries (EII) as well. CaO/CaCO3 based systems are currently broadly investigated for thermochemical storage, either natural or synthetic materials. Among these, CaO/Mayenite (Ca12Al14O33) sorbents are considered very promising. CaO/Mayenite (Ca12Al14O33) based material was developed according to two different synthesis methods. The first one consisted in a one-step sol-gel method where aluminium precursor and pure CaO are weighted to obtain the exact weight ratio of 75/25 (CaO/Ca12Al14O33). In the second one, a two-step method was adopted: pure Mayenite was preliminarily synthetized by one step sol-gel method and CaO/Mayenite was obtained by direct wet mixing with pure CaO. Samples obtained were characterized by XRD, SEM, TGA, nitrogen physisorption, Raman spectroscopy and thermal stability was tested over 40 charging/discharging cycles in TGA. Raman spectra revealed free oxygen O2− presence in the structure of Mayenite and in CaO-Mayenite samples as well, lying at 1128 cm-1. Thermal properties such as thermal conductivity, heat capacity and volumetric energy density storage have been determined. The thermal conductivity found were 0.377 ± 0.004 (W/mK) for A; 0.101 ± 0.006 (W/mK) for B and for Mayenite 1.16 ± 2.7 10−4 (W/mK). It was found that two step method led to a better performing material in terms of carbonation reaction reactivity, and hence thermal storage. This material showed 50 % carbonation reaction conversion value at 40th cycle, corresponding to 0.250 g CO2/g dry sample, which is 4 times higher than CaO conversion. At 40th cycle, moderate sintering effect is remarked, with 2.3 % conversion drop, indicating that Mayenite insertion effectively acts as spacer. Volumetric storage energy density Sd has been determined for both samples and compared to CaO at increasing cycle number. Sample B storage density was effectively even at 40th cycle with 0.69 GJ/m3, thus about 3.5 times higher than CaO.

A design optimization method for solar-driven thermochemical storage systems based on building performance simulation

The challenge of the temporal mismatch between energy supply and demand in buildings is growing with the increasing share of renewable energy in total energy consumption. Among all the state-of-the-art energy storage solutions, thermochemical heat storage shows a unique potential thanks to its considerable energy density, acceptable cost, and negligible heat loss. For this reason, it becomes a promising alternative to common sensible heat storage solutions for building applications. The integration of such a novel technology in buildings necessitates a method for the assessment of its potential impact and benefit, the comparison to common alternatives, and the optimization of the system design. This work proposes a method based on modeling and simulation of the interaction between the thermochemical heat storage system and the building using a data-driven surrogate model of the storage system in combination with a building performance simulation engine. The data-driven model was developed and validated based on laboratory measurements of a novel closed-loop thermochemical heat storage system, the heat battery (HB). The method was demonstrated in a case study to identify the optimal size of the HB in a solar-driven configuration based on a residential building use case. The results show that the heat battery can digest the thermal energy transferred from the solar thermal collector to reduce the original electricity consumption for heating the detached house (0.7 MWh to 1.0 MWh in considered cases) without any obvious sacrifice in thermal comfort and that the small-scale HB (with a storage volume below 160 l) shows efficient usage of the designed storage capacity.

Performance evaluation of a solar thermal storage system proposed for concentrated solar power plants

This study aims to assess the performance of the Hybrid Solar Thermal Storage (HSTS) system, the storage system proposed for concentrated solar power (CSP) plants. The heat storage hybridisation concept is based on coupling latent phase change material (PCM) and thermochemical storage system containing paired metal hydride (MH) beds. One base design which uses only thermochemical heat storage mode and two designs of the HSTS system with two distinct PCM heat exchanger designs (i.e., shell-and-tube and cylinder with truncated hollow cones) are proposed and numerically investigated. To predict the dynamic behavior of the three storage systems, a bidimensional mathematical model is established and a numerical code written in Fortran-90 is developed. Key performance indicators used to evaluate the performance of the three storage systems include volumetric storage capacity, specific power, state of hydrogen charge, and energy storage efficiency. Comparing the performance of the three systems reveals that the HSTS system's energy storage efficiency increased by 36% due to the integration of a reaction heat recovery internal system based on Na3Al as PCM. The use of the PCM in truncated hollow cones resulted in a 36.4% reduction of the heat charging and discharging time, an 18.5% increase storage capacity, and a 54.1% increase in specific power. In addition, this study proves that the third design can be imlpemented as a HSTS system in a solar power plant with the following performance indexes: 128 W/kg- Mg2FeH6, 160 MJ/m3 and 88% for specific power, volumetric storage capacity and energy storage efficiency, respectively.

Comparative experiments on a new CaCl2-based composite material and zeolite 13X inside a thermochemical heat storage reactor

Thermal energy storage includes sensible, latent and thermochemical heat storage. The latter is particularly interesting because the heat is stored as a chemical potential, which reduces heat loss in long-term applications. The viability of thermochemical storage systems strongly depends on the energy density of the storage material. The development of high energy density materials is thus essential to achieve compact systems suitable for a wide range of applications. A new sol-gel composite material is investigated here: it is composed of CaCl2 dispersed within a matrix of silica and PEG-600 polymer. Composite materials containing CaCl2 have the highest storage capacities and seem to be the most promising candidates. The aim is to develop a composite that is both efficient and stable. The suitability of the material depends on the ability of the PEG to stabilise calcium chloride and prevent its deliquescence and leakage. The experimental results are compared to those obtained using zeolite 13X, which is a reference adsorbent material.

A review on high‐temperature thermochemical heat storage: Particle reactors and materials based on solid–gas reactions

AbstractIn order to produce electricity beyond insolation hours and supply to the electrical grid, thermal energy storage (TES) system plays a major role in CSP (concentrated solar power) plants. Current CSP plants use molten salts as both sensible heat storage media and heat transfer fluid, to operate up to 560°C. To meet the future high operating temperature and efficiency, thermochemical storage (TCS) emerged as an attractive alternatives for next generation CSP plants. In these systems, the solar thermal energy is stored by endothermic reaction and subsequently released when the energy is needed by exothermic reversible reaction. This review compares and summarizes different thermochemical storage systems that are currently being investigated, especially TCS based on metal oxides. Various experimental, numerical, and technological studies on the development of particle reactors and materials for high‐temperature TCS applications are presented. Advantages and disadvantages of different types heat storage systems (sensible, latent, and thermochemical), and particle receivers (stacked, fluidized, and entrained), have been discussed and reported.This article is categorized under: Sustainable Energy > Solar Energy Emerging Technologies > Energy Storage Emerging Technologies > Materials

Storing solar energy in continuously moving redox particles – Experimental analysis of charging and discharging reactors

The ability to store energy in the form of high-temperature heat is one of the key advantages of concentrated solar energy over other renewable sources. Higher energy densities compared to the state of the art can be achieved through a wider range of operating temperatures and by adding chemical energy storage. Thermochemical storage (TCS) systems can operate in almost any temperature range, depending on the material chosen, providing high energy densities through a reversible reaction and allow long-term storage.This work shows the development and experimental evaluation of a complete pilot-scale TCS system. The storage material is a metal oxide, namely manganese-iron oxide, which undergoes consecutive reduction (endothermic) and oxidation (exothermic) reaction cycles. The metal oxide is shaped into mm-size granules. The TCS cascade applies two reactors: one operating on-sun and used to store the solar energy and a separate one, operating off-sun, for the release of heat. The first reactor is a solar rotary kiln that transfers concentrated solar energy directly to the reactive particles, which are heated and reduced. The heat is released afterwards from the particles to the air flowing countercurrent, in a vertical moving bed reactor. Here, both sensible and chemical energy generated by the reverse chemical oxidation reaction is transferred. The continuously operated rotary kiln can heat up about 10 kg/h of particles to an outlet temperature of close to 1000 °C and achieve a maximum conversion of about 70 %. The moving bed, which can be operated continuously 24 h, has a similar particle mass flow and can heat 150 l/min from 300C to 880 °C. The reactors allowed the storage and release of up to 2.1 kW of thermal power.

Redox cycle of calcium manganite for high temperature solar thermochemical storage systems

Thermochemical energy storage via metal oxide redox cycling is a potential cost-effective approach to store solar energy both chemically and thermally at high temperatures, enabling efficient solar thermal power production round-the-clock and on-demand. Perovskite manganites are a low-cost redox material that undergoes reversible reaction without side reactions up to 1000 °C and offers high storage capacities, which makes them promising energy storage materials in next-generation solar thermal power plants. In this study, the thermal properties of a typical perovskite manganite, CaMnO3, has been studied. CaMnO3 shows 893.2 kJ/kg energy storage capacity from 200 °C to 1000 °C, and 0.133 non-stoichiometry in N2. The material exhibits excellent stability with 150 redox cycles between 500 °C and 1000 °C. The thermodynamic efficiencies of two solar-driven combined cycle power systems with CaMnO3 based thermochemical energy storage system are also investigated. 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. Preliminary results for a system with 120 MW nominal solar power input at a solar concentration ratio of 1000 are presented, designed for constant round-the-clock operation with 9 h of on-sun and 15 h of off-sun operation. The CaMnO3 particles store and release energy via the sensible heat and reaction heat, yield a net power block efficiency of approximately 60% and an overall energy conversion efficiency of up to 48.7%. Required storage tank sizes for the solids are estimated to be up to 2–3 smaller than those of state-of-the-art molten salt systems.

Review of Technologies and Recent Advances in Low-Temperature Sorption Thermal Storage Systems

Sorption thermochemical storage systems can store thermal energy for the long-term with minimum amount of losses. Their flexibility in working with sustainable energy sources further increases their importance vis-à-vis high levels of pollution from carbon-based energy forms. These storage systems can be utilized for cooling and heating purposes or shifting the peak load. This review provides a basic understanding of the technologies and critical factors involved in the performance of thermal energy storage (TES) systems. It is divided into four sections, namely materials for different sorption storage systems, recent advances in the absorption cycle, system configuration, and some prototypes and systems developed for sorption heat storage systems. Energy storage materials play a vital role in the system design, owing to their thermal and chemical properties. Materials for sorption storage systems are discussed in detail, with a new class of absorption materials, namely ionic liquids. It can be a potential candidate for thermal energy storage due to its substantial thermophysical properties which have not been utilized much. Recent developments in the absorption cycle and integration of the same within the storage systems are summarized. In addition, open and closed systems are discussed in the context of recent reactor designs and their critical issues. Finally, the last section summarizes some prototypes developed for sorption heat storage systems.

Experimental study on heat release characteristics of thermochemical heat storage considering various operating parameters

Thermochemical heat storage is a promising energy storage method and has received much attention in recent years. To improve the design and application of such systems, a better understanding of the characteristics of thermochemical heat storage is required. In this study, we analyze the heat release characteristics of thermochemical heat storage considering various operating parameters, such as charging temperature, humidity, and material. Three different thermochemical materials are considered herein, namely, zeolite 13X, zeolite 5A, and silica gel. The temperature profile at the inlet and outlet of the storage chamber, and that inside the chamber packed with thermochemical material, were measured. The pressure drop across the chamber was measured as well. The results indicate that the heat release characteristics change with position and time. Furthermore, the temporal curves of released heat are significantly affected by charging temperature and humidity. Zeolite 13X rapidly released a large amount of heat within a short period of time, whereas silica gel gradually released a small amount of heat, over a longer duration of time. The pressure drop across the chamber was found to vary with the bead size of the thermochemical material. Thus, the operating parameters including charging temperature, humidity, and material, have a significant effect on the characteristics of heat release. The data obtained herein can serve as a reference for the design of thermochemical storage systems.

4‐Temperatures Approach: Testing Thermochemical Heat Storage Materials Under Application Conditions

AbstractThermochemical heat storage offers the possibility to achieve high thermal energy storage capacities compared to sensible and latent heat storage. To quantify this advantage, thermochemical storage systems have to be evaluated under application conditions. The proposed 4‐temperatures approach delivers a first step toward a realistic testing of thermochemical working pairs. As an example, the approach is applied to testing the working pair zeolite/water under the conditions of the application of seasonal storage of solar thermal heat for domestic heating purposes.

A Discussion of Possible Approaches to the Integration of Thermochemical Storage Systems in Concentrating Solar Power Plants

One of the most interesting perspectives for the development of concentrated solar power (CSP) is the storage of solar energy on a seasonal basis, intending to exploit the summer solar radiation in excess and use it in the winter months, thus stabilizing the yearly production and increasing the capacity factor of the plant. By using materials subject to reversible chemical reactions, and thus storing the thermal energy in the form of chemical energy, thermochemical storage systems can potentially serve to this purpose. The present work focuses on the identification of possible integration solutions between CSP plants and thermochemical systems for long-term energy storage, particularly for high-temperature systems such as central receiver plants. The analysis is restricted to storage systems potentially compatible with temperatures ranging from 700 to 1000 °C and using gases as heat transfer fluids. On the basis of the solar plant specifications, suitable reactive systems are identified and the process interfaces for the integration of solar plant/storage system/power block are discussed. The main operating conditions of the storage unit are defined for each considered case through process simulation.

Ice-templated nanocellulose porous structure enhances thermochemical storage kinetics in hydrated salt/graphite composites

Abstract The freeze-drying technique is employed for the production of novel strontium bromide/graphite/nanocellulose composites for thermochemical heat storage application. The aim is to obtain a better control and stability of salt organization within the composite, while maximizing the air/salt and salt/graphite interfacial areas and enhancing mass and heat transfer associated to the salt hydration and dehydration. A comparison with a conventional wet impregnation method is also reported. The morphology was investigated by means of scanning electron microscopy. Differential scanning calorimetry was employed to evaluate the energy storage density, while hydration kinetics were evaluated at 23 °C and 50% RH. The wet impregnation approach delivered materials with a limited porosity while freeze-drying produced highly porous structures with oriented channels for moisture transport across the composite. The organic binder provided an active contribution to the energy storage process, producing energy storage densities up to 764 kJ/kg, 48% greater than the theoretical value. Freeze-dried nanocellulose composites evidenced a significant increase of 54% in the hydration kinetics, compared to the pristine salt. Based on these results, the freeze-drying of ternary composites based on salt hydrate, graphite and nanocellulose is envisaged as a promising route for the production of fast charge and discharge thermochemical storage systems.

Industrial carnallite-waste for thermochemical energy storage application

The key to successful development and implementation of thermochemical storage systems is the identification of high energy density and low-cost storage materials. In this work, an industrial waste based on a double salt hydrate, coming from non-metallic mining was studied for thermochemical storage applications. Initially, chemical characterization was performed and determined that carnallite-waste material consists of 73.54 wt% of KCl·MgCl2·6H2O and impurities such as NaCl (23.04 wt%), KCl (1.76 wt%) and CaSO4 (1.66 wt%). Using thermal analyses methods, the operating conditions such as temperatures and partial pressures, were optimized for seasonal thermochemical storage applications to PHy = 1.3 kPa and ϑHy = 40 °C, and to PDe = 4.0 kPa and ϑDe = 110 °C. Under these conditions, the reaction reversibility over 10 cycles (10 years) was significantly high, with only 8.5% decrease in chemical reversibility. Furthermore, the duration of dehydration and hydration isotherms was optimized to 15 and 360 min, respectively. Finally, 1.129 GJ/m3 energy storage density was calculated after the tenth cycle of hydration/dehydration for this material. Hence 7.1 m3 of carnallite was estimated to meet the demand of 8 GJ of energy for an average household during the six months of cold seasons. These results are comparable and competitive with an energy storage density of materials such as K2CO3 and MgCl2, reported as promising for seasonal thermochemical storage applications. It should be noted that carnallite-waste material has no commercial value so far and its use contributes to developing sustainable low-cost thermochemical energy storage systems.

Water heating by Parabolic Trough Collector with storage in the Ouargla region of Algerian Sahara

Abstract The PTC is one of the most important solar concentrating systems, the most effective in producing steam in thermal power plants. In order to increase the efficiency of PTC, we did an experimental study has been performed based on the design and completion of a 1.8 m × 1.6 m PTC solar collector, with the addition of a flat glass cover in order to maintain the optical properties of the reflector and the glass envelope of dust, and moisture due to wind and rain on the one hand, and to increase thermal insulation and increase the thermal efficiency on the other hand. According to the solar radiation, and climatic conditions of Ouargla, we recorded the temperature of the outlet water and then calculate the thermal efficiency during the day, for different water flows. Where the experimental results showed the effectiveness of the glass cover by increasing the thermal efficiency to 9% during the peak period of radiation solar system (Soudani et al., 2017). In order to extend the results to different dimensions of PTC length and larger mass flows, we prepared a numerical simulation of the PTC model. After verifying the reliability of this model by comparing the numerical simulation results with the experimental results, we record the effect of PTC length and mass flow of water on outlet water temperature. To store this heat for the absence of the sun, we used a heat pump which is a thermo-chemical storage system, consisting of water as sorbet and sodium chloride as the sorbent, and then study the effect of different parameters on the performance of the thermo chemical heat pump.

Experimental and numerical analysis of seasonal solar‐energy storage in buildings

This paper presents seasonal-energy storage of solar energy for the heating of buildings. We distinguish several types of seasonal storage, such as latent, sensible, and chemical storage, among which the thermochemical storage is used and analysed in this research. In the first part, a laboratory heat-storage tank, which was made in the laboratory for heating, sanitary, and solar technology and air conditioning from the Faculty of Mechanical Engineering, University of Ljubljana, Slovenia, was presented. The experimental model was tested for charging and discharging mode. Two types of numerical models for sorption thermal-energy storage exist, which are microscale and macroscale (integral). For microscale analysis, the analysis system (ANSYS) model can be used to simulate the behaviour in the adsorption reactor. On macroscale or integral scale, TRaNsient SYStem (TRNSYS) model was used to perform the operation of the storages on the yearly basis. In the second part the simulation of the underfloor heating system operation with a built-in storage tank was carried out for two locations, Ljubljana and Portorož. Furthermore, the comparison between a thermochemical and sensible-heat storage was performed with TRNSYS and Excel software. In this comparison, the focus was on the surface parameters of the SCs and volume of the thermal-storage tank for the coverage of the energy demand for selected building. With this analysis, we would like to show the advantage of the thermochemical storage system, to provide greater coverage of the energy demand for the operation of the building, compared with the seasonal sensible-heat storage (SSHS). Such a heat-storage technology could, in the future, be a key contributor to the more environmentally friendly and more sustainable way of delivering energy needs for buildings.