Thermochemical Energy Storage Research Articles

Thermochemical battery prototypes with conductive heat extraction

Thermochemical energy storage is a viable option for large-scale storage of renewable energy. Functional storage systems require a high cycling capacity and an efficient heat extraction unit to guarantee reliable energy storage and subsequent power production. This article investigates the performance of thermochemical battery prototypes that use conductive heat extraction via metallic rods. The thermodynamics and kinetics of the storage material, CaCO3-Al2O3 (20 wt%), used in the prototypes, were studied along with the cyclic carbon dioxide sorption capacity, which was retained at 60 %. The reaction thermodynamics and kinetics of this doped CaCO3 compound are similar to those reported for pure calcium carbonate (ΔHdes = 173 ± 10 kJ.mol−1 CO2 and ΔSdes = 147 ± 9 J.mol−1 CO2·K−1). The two prototypes were constructed using either a stainless-steel rod or a stainless-steel tube with a copper core as conductive heat exchanger. The thermochemical battery prototypes (∼1 kg) cycled >30 times, with thermal charging (calcination) and discharging (carbonation) at ∼900 °C. The storage material is sensitive to the operating conditions of pressure and temperature, which influence the formation of various calcium aluminium oxide compounds that either catalyse or inhibit the cyclic capacity. The carbon dioxide sorption capacity in the prototypes was found to be limited (20 %) and capacity loss was correlated to the temperature distribution through the storage material and limited by the heat transfer rate of the heat extraction system. The heat transfer performance of the stainless-steel rod was inadequate, while the copper core allowed for better system performance.

Li4SiO4-Based Heat Carrier Derived from Different Silica Sources for Thermochemical Energy Storage

Thermochemical energy storage (TCES) is one of the key technologies facilitating the integration of renewable energy sources and mitigating the climate crisis. Recently, Li4SiO4 has been reported to be a promising heat carrier material for TCES applications, owing to its moderate operation temperature and stability. During the synthetic processes, the properties of the Si source used directly influence the performance of derived Li4SiO4 materials; however, the internal relations and effects are not yet clear. Hence, in this work, six kinds of SiO2 sources with different phases, morphology, particle size, and surface area were selected to synthesize a Li4SiO4-based TCES heat carrier. The physicochemical properties of the SiO2 and the corresponding derived Li4SiO4 were characterized, and the comprehensive performance (e.g., heat storage/releasing capacity, rate, and cyclic stability) of the Li4SiO4 samples was systematically tested. It was found that the silica microspheres (SPs), which possess an amorphous phase, uniform micro-scale structure, and small particle size, could generate Li4SiO4 TCES materials with a highest initial capacity of 777.7 kJ/kg at 720 °C/900 °C under pure CO2. As a result, the SP-L showed an excellent cumulative heat storage amount of 5.84 MJ/kg within 10 heat-releasing/storage cycles, which was nearly 1.5 times greater than the value of Li4SiO4 derived from commonly used silicon dioxide. Furthermore, the effects of the utilized Si source on the performance of as-prepared Li4SiO4 and corresponding mechanisms were discussed, which offers guidance for the future selection of Si sources to produce high-performance Li4SiO4-based TCES heat carriers.

Investigation on YSZ- and SiO2-Doped Mn-Fe Oxide Granules Based on Drop Technique for Thermochemical Energy Storage.

The Mn-Fe oxide material possesses the advantages of abundant availability, low cost, and non-toxicity as an energy storage material, particularly addressing the limitation of sluggish reoxidation kinetics observed in pure manganese oxide. However, scaling up the thermal energy storage (TCES) system poses challenges to the stability of the reactivities and mechanical strength of materials over long-term cycles, necessitating their resolution. In this study, Mn-Fe granules were fabricated with a diameter of approximately 2 mm using the feasible and scalable drop technique, and the effects of Y2O3-stabilized ZrO2 (YSZ) and SiO2 doping, at various doping ratios ranging from 1-20 wt%, were investigated on both the anti-sintering behavior and mechanical strength. In a thermal gravimetric analyzer, the redox reaction tests showed that both the dopants led to an enhancement in the reoxidation rates when the doping ratios were in an appropriate range, while they also brought about a decrease in the reduction rate and energy storage density. In a packed-bed reactor, the results of five consecutive redox tests showed a similar pattern to that in a thermal gravimetric analyzer. Additionally, the doping led to the stable reduction/oxidation reaction rates during the cyclic tests. In the subsequent 120 cyclic tests, the Si-doped granules exhibited volume expansion with a decreased crushing strength, whereas the YSZ-doped granules experienced drastic shrinkage with an increase in the crushing strength. The 1 wt% Si and 2 wt% Si presented the best synthetic performance, which resulted from the milder sintering effects during the long-term cyclic tests.

Fungible, Multiyear Solar Thermochemical Energy Storage Demonstrated via the Cobalt Oxide Cycle

Abstract We present a proof of concept demonstration of solar thermochemical energy storage on a multiple year time scale. The storage is fungible and can take the form of process heat or hydrogen. We designed and fabricated a 4-kW solar rotary drum reactor to carry out the solar-driven charging step of solar thermochemical storage via metal oxide reduction–oxidation cycles. During the summer of 2019, the solar reactor was operated in the Valparaiso University solar furnace to effect the reduction of submillimeter cobalt oxide particles in air at approximately 1000∘C. A particle collection system cooled the reduced particles rapidly enough to maintain conversions of 84–94% for feed rates of 2.9−60.8gmin−1. The solar-to-chemical storage efficiency, defined as the enthalpy of the reduction reaction at 1000∘C divided by the solar energy input, reached 20%. Samples of the reduced cobalt oxide particles were stored in vials in air at room temperature for more than 3 years. The stored solar energy was released by reoxidizing samples in air in a benchtop reactor and by electrochemically reoxidizing samples to produce H2. Measurements of the oxygen uptake by the reduced metal oxide confirm its promise as a medium to store and dispatch solar energy over long durations. Linear sweep voltammetry and bulk electrolysis demonstrate the promise of H2 production at 0.55 V relative to the normal hydrogen electrode, 0.68 V below the 1.23 V potential required for conventional electrolysis.

Two-Stage Solar–NaOH Thermochemical Heat Pump Heating System for Building Heating: Operations Strategies and Theoretical Performance

Heating buildings with solar energy is challenged by the seasonal mismatch between solar availability and heating demand. Thermochemical energy storage is a promising technology to overcome this challenge because of its high energy density. In building applications, space requirement is also an important consideration. Therefore, both the storage space and collector areas are important considerations, with only the latter often being neglected in previous studies. This paper proposes a novel two-stage thermochemical heat pump heating system based on the working pair of NaOH/H2O. We demonstrate that this system can work with a concentration difference (70% wt–30% wt) for the climate in hot summer and cold winter regions in China. The energy storage density based on the discharged solution is 363 kWh/m3. With this solar-driven thermochemical heat pump heating system, 35.13 m2 of collectors and 10.48 tons of 70% wt NaOH solution are sufficient to complete a full charge–discharge cycle and meet the heating demand of a single-family house (winter space heating + DHW: 9370 kWh, summer DHW: 2280 kWh). The theoretical maximum storage for solution (discharged + water tank) is 32.47 m3. Compared with the sensible seasonal storage alternative, the collector area is reduced by 12.5% and the storage space is reduced by 59%, with a possible further reduction through optimization. With the potential to be further optimized for space saving, the two-stage solar–NaOH heat pump heating system is an energy-efficient and space-efficient heating system for buildings in the hot summer and cold winter regions of China.

Enhancement effects of hydrolysable/soluble Al-type dopants on the efficiency of CaO/CaCO3 thermochemical energy storage

Modification of CaO-based materials using Al-type dopants has been considered a promising method to enhance energy storage performance. The synergistic multi-doping effects of different Al-type dopants (soluble, hydrolysable and insoluble) on the energy storage performances, thermophysical and mechanical properties of CaO-based materials have never been reported. The hydrolysable/soluble Al-type supports co-doped CaO-based pellets were prepared, which exhibited superior energy storage density, multi-cycle stability, reaction rate, thermal conductivity and crushing strength compared to undoped CaO pellets. The regulation mechanisms of hydrolysable/soluble Al-type dopants (AlN/Al(NO3)3) on the reaction kinetics, multi-cycle stability, thermophysical properties and mechanical properties of CaO-based pellets were revealed. The addition of different Al-type dopants results in different dispersions of the formed Ca12Al14O33, which leads to different micro-morphologies and pore structures of CaO-based pellets. Hydrolysable Al-type dopants exhibit a more concentrated distribution in CaO-based pellets and the pellets have smaller crystallite sizes of CaO and predominantly microporous pores, which results in the high CO2 reactivity. Soluble Al-type dopants exhibit a more uniform dispersion in CaO-based pellets and the pellets have larger crystallite sizes of CaO and obvious pore channels, which results in the improved cyclic stability and decomposition kinetics. The optimized CaO-based pellets combine the advantages of the two Al-type dopants and present an increasing trend of energy storage density during the cyclic process. Its energy storage density remains 1571 kJ/kg after 50 cycles, and the value for CaO is only 569 kJ/kg. In addition, the optimal synthesized material has excellent thermal conductivity and crushing strength, which are 1.36 and 9.75 times those of CaO, respectively.

Methanol-based thermochemical energy storage (TCES) for district heating networks

With increasing volatility in natural gas markets and the need for residential heat, research for alternative thermal systems based on green hydrogen-based fuels is necessary. Massive implementation of hydrogen in the current fleet presents a challenge for the decarbonisation of conventional thermal processes. This paper presents the integration of green methanol from a seasonal thermochemical energy storage system (TCES) coupled with district heating networks (DHN). It allows for a solar-based storage and low-temperature heat generation from the exothermic discharge reaction. The system uses concentrated solar thermal energy to decompose methanol into syngas at moderate temperatures (<315 °C), reducing GHG emissions from combustion to meet residential heat. Its potential is assessed through an analysis of 458 rural municipalities in Spain, achieving a substitution of 3.1 % of the natural gas demand. The system allows the production of green fuels from syngas using an open-loop approach, offering new market pathways in primary sector. In a closed-loop configuration, roundtrip efficiencies exceeding 60 % and chemical conversion efficiencies exceeding 70 % are reached, resulting in a global efficiency of 12 % for the DHN and methanol-TCES. The results show a levelized cost of stored energy highly competitive with other storage systems (<200€/MWh), given its simplicity.

Effect of hydrogen permeation and operating parameters on thermochemical performance of solar-driven steam methane reforming membrane reactor

When the steam methane reforming membrane reactor is coupled with trough solar collector to achieve solar thermochemical energy storage, the dimension of the membrane reactor is enlarged and the catalyst filling amount increases dramatically. As a results, the hydrogen permeation property should be well addressed to match the permeation and the reaction characteristics for a better energy storage performance. In the present paper, the effect of hydrogen permeation, including the effective permeation area and the membrane permeance was investigated by numerical simulations. Results show that the sensitivity factors of the membrane surface area on CH4 conversion, H2 yield and H2 recovery are 0.379, 0.325 and 2.196 respectively while that of membrane permeance are 0.007, 0.009 and 0.488 respectively. This indicates that influence of membrane surface area is more remarkable and H2 recovery is the most sensitive to the hydrogen permeation. The reactor with a membrane tube diameter of 50 mm and a permeance of 1.07 × 10−2 mol/(m2·s·Pa0.62) can achieve best reaction performance. Besides the reaction performance, a solar thermochemical system is proposed and a solar-to-fuel efficiency is defined to evaluate the thermochemical performance. Again the aforementioned reactor has the highest solar-to-fuel efficiency which can exceed 70 %. Furthermore, for a better thermochemical performance, lower inlet mass flow rate and higher inlet temperature are recommended, but too small or too high values should be avoided to maintain the operating temperature of the membrane. A suitable combination of pressures in the reaction side and the permeating side is also suggested. The results of the present paper reveal the role of hydrogen permeation and helps the reactor design.

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.

Pilot-scale investigation of high-temperature thermochemical energy storage based on the material system CaO/Ca(OH)2 in a bubbling fluidized bed

Utilizing fluidized bed technology for thermochemical energy storage with CaO/Ca(OH)2 is promising for temperatures from 400 °C to 600 °C in industrial-scale applications. Much progress has been made on laboratory scale to develop this technology in recent years. Continuously changing material properties throughout storage cycles, mainly due to particle breakage, are identified to be challenging for scale-up. Transferability to large-scale systems needs to be examined.Investigations on a pilot scale (di = 257 mm, h = 600 mm, steam for fluidization, 700 °C, 6 barg) are done. A temperature-induced (456 °C discharging and 586 °C charging) and a pressure-induced (1.5 barg discharging and 3.5 barg charging) cyclization is performed. The applicability of standard scaling rules (scaling factor of 17) is possible. Fluidization regimes and breakage rates are transferrable. A detailed experimental characterization of the storage materials fluidization properties that are crucial for scale-up is done using a fluidization test rig (di = 140 mm, h = 658 mm, nitrogen for fluidization, ambient temperature and pressure).

Modeling CO2 Adsorption in a Thin Discrete Packing.

Local dynamics of CO2 adsorption in a discrete packing contained in a thin tube was assessed by 3D modeling. Thin tube packed bed adsorbers are currently used over tube structures in thermochemical energy storage systems and atmospheric revitalization of confined spaces. Driven by the interplay between key factors such as the exothermicity and the fluid flow, the advective transport was found less effective than the diffusive one on the breakthrough trends of CO2 which displayed significant concentration gradients at both inter- and intraparticle scales. The lack of angular symmetry inside the particles by the reduction in resistance to mass transfer in the area of solid particles exposed to high velocities led to greater convective transports from the bulk of the gaseous phase to the pores. The result of the modeling agreed with the experimental data obtained at the exit of the adsorber, helping reduction in reliance on the empirical dispersion models used in the one-dimensional modeling.

Study on heat transport analysis and improvement method in a single CaCO3 pellet for thermochemical energy storage

CaCO3/CaO thermochemical energy storage (TCES) pellets have significant advantages in bulk energy storage density, transport, and utilization. However, severe heat transport limitations within the milli-sized CaCO3 significantly affect the TCES efficiency and economy. Currently, investigations on the effect of initial porosity, bulk gas flow velocity, and reaction rate on heat transport and methods of enhancing the heat transport inside the pellet are lacking. In this paper, we developed a mathematical model coupling calcination reaction, mass transfer, and heat transfer to reveal the effects of pellet parameters and operating conditions on heat transport and reaction conversion rate within a CaCO3 pellet. The results show that the size of the CaCO3 pellet, bulk gas temperature, and reaction rate generate the most pronounced impacts on heat transport in a single CaCO3 particle during the TCES process. Furthermore, the heat transport inside the CaCO3 pellet can be improved by appropriately increasing the bulk gas flow velocity. Finally, this paper first numerically investigates the addition of SiC as a thermal conductivity enhancer to improve the heat transport performance inside a CaCO3 pellet. This study can guide the design of high-performance CaCO3 composite pellets and inform the selection of operating conditions for subsequent reactor applications.

Doping effects on magnesium hydroxide: Enhancing dehydration and hydration performance for thermochemical energy storage applications

Thermochemical energy storage (TCES) holds significant promise owing to its remarkable energy storage density and extended storage capabilities. One of the most extensively studied systems in TCES involves the reversible hydration/dehydration reaction of magnesium hydroxide (Mg(OH)2) to magnesium oxide (MgO). This system suffers from several challenges such as the dehydration temperature of 360 °C, which is considered higher for some applications, low kinetics, and conversion fraction, in addition to the conversion decay after cycles. Nonetheless, it is essential to recognize that each material within thermochemical systems has distinct operational requirements, including temperature and pressure conditions, making them suitable for specific applications. Consequently, the development of materials is a pivotal factor in expanding the effectiveness of sustainable technologies. This research addresses challenges associated with the reversible reaction by partially substituting Mg with transition metal elements like Zn, Ni, Mn, Co, and Cu, leading to the development of new materials Mg1-xMx(OH)2 with x = 0.05. The results indicate successful synthesis of hydroxide systems through coprecipitation. Morphological analysis reveals that material morphology plays a significant role in the performance of thermochemical systems. Additionally, the developed materials demonstrate a reduction in dehydration temperature, reaching 295 °C with cobalt doping. There is also an increase in the conversion reaction, with a 10 % improvement in energy density recorded for the material doped with 5 % Zn. Lastly, the developed materials exhibit good cyclability performance for up to 6 cycles.

Review on thermal properties and reaction kinetics of Ca(OH)2/CaO thermochemical energy storage materials

AbstractThermochemical energy storage technology is one of the most promising thermal storage technologies, which exhibits high energy storage capacity and long‐term energy storage potentials. The low‐cost, safe, and reliable calcium oxide/calcium hydroxide (CaO/Ca(OH)2) system has become the preferred thermochemical energy storage material system to solve the problem of renewable energy consumption. This study reviews the structural, thermodynamic, and kinetic properties influencing the absorption and desorption reactions of calcium oxide (CaO) and calcium hydroxide (Ca(OH)2) in thermal energy storage applications. It is found that the transformation of crystal structure from cubic to hexagonal upon hydration is attributed to volume expansion and crack formation facilitating diffusion. The specific heat capacities of CaO and Ca(OH)2, as well as reaction enthalpies, are studied across temperature ranges. Most studies on reaction kinetics are focused on the effect of factors such as temperature, particle size, and material content. Strategies to mitigate issues such as particle agglomeration and enhance reaction efficiency are discussed, including the incorporation of enhancing materials such as γ‐Al2O3. This study underscores the importance of the core reaction material content and the enhancing materials that are used to optimise energy density in thermal chemical water‐absorption and ‐desorption reactions.

Heat storage and release characteristics of a prototype CaCO3/CaO thermochemical energy storage system based on a novel fluidized bed solar reactor

CaCO3/CaO thermochemical energy storage (TCES) system has a high heat storage density (1780 kJ/kg) along with high heat storage and release temperature (650–850 °C), which can be applied to concentrated solar power (CSP) technology utilizing CO2 Brayton cycles to improve power generation efficiency. There are several problems to be urgently resolved in current CaCO3/CaO solar calciners, such as poor heat and mass transfer and low thermochemical efficiency. This paper proposed a prototype CaCO3/CaO TCES system based on a novel fluidized bed solar reactor, which has a serrated arc surface in alignment with the direction of the incident solar rays to receive concentrated solar energy. The natural limestone particles were used as the reactive particles. The effects of operating modes (intermittent/continuous), initial mass of reactive particles, and initial carbonation temperature Tcar,initial on the heat storage and release characteristics of the TCES system were experimentally explored. During the carbonation reaction stage, the effective carbonation degrees in the continuous mode were generally higher than in the intermittent mode under the experimental conditions and declined at a slower rate. The reactive particles were recovered from the reactor for microstructural characterization after completing the experiments, high-temperature particle agglomeration and pore structure clogging were directly responsible for the decrease of the effective carbonation degree. In the continuous mode, the average thermochemical and total thermal efficiencies of 24.7 % and 53.5 % were obtained in the 1st calcination reaction, respectively, which represents significant advantages over other CaCO3/CaO solar calciners. The novel fluidized bed reactor demonstrated excellent fluidization in the experiments and did not exhibit mechanical deformation after multiple experiments under non-uniform concentrated radiation provided by an 84 kWe high-flux solar simulator. Overall, this paper provides a successful gas-solid reactor design to be coupled with CSP technology.

A scaling rule for power output of salt hydrate tablets for thermochemical energy storage

Salt hydrates are thermochemical materials capable of storing and releasing heat through reversible reaction with water vapor. In a heat battery, salt hydrate tablets of millimeter size are necessary to ensure a sufficient permeability of the packed bed. A profound understanding of the hydration process of these tablets is required to improve their kinetic performance. In this study we show that the hydration timescale of salt tablets is transport limited and that it depends primarily on the porosity and on the driving force (Δp). From gravimetric measurements done on SrBr2·6H2O and CaC2O4 we derived the intrinsic reaction and effective diffusion coefficients (k and Deff) and found that they validate a front-diffusion limited hydration hypothesis. In particular, the obtained Deff values (0.8–4.5 mm2 s−1) only depend on the tablets' porosities. Based on these parameters, we calculated the second Damköhler number (DaII) and proved that many other hydration reactions are diffusion limited. In the case of identical structures, the power output is therefore controlled only by the driving force. Its variation could be predicted by calculation of a so-called power scaling factor (Λ) for a selection of salts. This power scaling factor depends on the enthalpy (ΔH) and entropy (ΔS) of the reaction. For a temperature output of 40 °C and at 12 mbar most hydration reactions fall in the interval 0<Λ<30 and Λ exceeds 30 only in very few cases. This parameter establishes therefore another important constraint to the selection of the most ideal salt. Suitable strategies to circumvent the diffusion limitation will lead to the development of next generation salt hydrate tablets for thermochemical energy storage.

Experimental study of the new composite materials for thermochemical energy storage

Thermochemical energy storage (TCES) is a promising technology to support the world's initiatives to reduce CO2 emissions and limit global warming. In this paper, we have synthesized and characterized a new three-component composite materials consisting of a mixture of calcium chloride and iron powder confined inside the expanded vermiculite. The new approaches of studying composite sorbents of ammonia using a gas flow-through microcalorimetry proposed in this work. The energetics of adsorption as a function of ammonia uptake was measured at room temperature (RT), 106 and 150 °C. The enthalpy of NH3 sorption in eight cycles tested ranged from 12.2 to 39.1 kJ mol−1. The strength of ammonia sorption on composite surface was characterized by TPD (Temperature Programmed Desorption). Based on the NH3-TPD profiles of composites it was found that the high-temperature desorption peaks of vermiculite sample shifted to lower temperature after the deposition of salt. The characterization of the composites was complemented by the laboratory analyses using XRD, WD-XRF, FTIR, TG/DTG, SEM-EDS and nitrogen sorption isotherms at −196 °C (BET method). The composite impregnated with 37 wt% of salt has the highest enthalpy and sorption capacity, thus seems to be the most promising candidates for the heat storage systems.

Study on the Catalytic Effect of Converter Dust on In Situ Online Reforming of Metallurgical By‐Product Gas and Thermochemical Energy Storage Analysis

In situ online reforming of converter gas and coke oven gas is realized by injecting coke oven gas into converter flue. This process utilizes methane dry reforming reaction to achieve heat energy recovery and CO2 capture and utilization. Moreover, the converter flue provides an excellent thermodynamic, kinetic, and catalytic environment. Experiments show that converter dust greatly improves the conversion rate of CH4 and CO2, and increases with the increase of the addition of converter dust. The conversion of CH4 reaches above 80% at 1150 °C, which is about 40% higher than that without catalyst. The CO2 conversion is more than 85% at 1150 °C, while it is only about 50% without catalysis. In addition, through the study of the main components of converter dust, the order of promoting CH4 decomposition is: Fe &gt; Fe3O4≈CaO &gt; FeO; the order of promoting effect on C–CO2 reaction is: Fe3O4 &gt; CaO &gt; FeO &gt; Fe. Finally, the reforming energy storage is calculated by thermodynamic calculation and experimental data. The reforming energy storage of tonne crude steel is about 159.589 MJ, accounting for 44.5% of the total physical heat energy of converter flue gas, and CO2 emission reduction in converter flue gas is more than 50%.

Establishment of light‐dependent photo‐thermal kinetic model for methane dry reforming and performance optimization in a cavity reactor

AbstractSolar methane dry reforming (MDR) reaction is a highly promising technology for long‐term energy storage due to its eco‐friendly nature and high‐value‐added product. Numerous present works mainly focused on the photo‐thermal catalysts, few of them discussed photo‐thermal coupled kinetics. Therefore, this article proposed a light‐dependent kinetic model for MDR. In the model, not only the effect of temperature and species concentration were included, but also the radiation was considered, which is different from the conventional kinetic model. Solar radiation is divided into thermal‐effect and light‐promoted‐effect part and coupled with the heat and mass transportation and chemical reaction. The average relative error of established model is only 0.97% under dark condition, and 13.2% under light condition. Then, the impacts of operating condition in a cavity reactor were investigated by established coupled optical‐photo‐thermal dynamics–computational fluid dynamic model to improve the efficiency of chemical conversion. The results show that when GHSV is 48.21 h−1, light increased the reaction rate by 1.59 times and thermochemical energy storage efficiency by 18.5%. When CH4/CO2 = 1, the formation rates of syngas and thermochemical energy storage efficiency are the highest. This work provides a highly coupled photo‐thermal kinetic model and a method for modeling and condition optimization.

A multi-scale experimental study on calcium-looping for thermochemical energy storage using the CO2 captured from power generation systems

The reversible carbonation/calcination reaction of calcium-rich particles (i.e., so-called calcium-looping), whether in an open loop configuration or in a closed cycle, has attracted significant attention in recent years for utility-scale thermochemical energy storage. The calcium-looping process and its variants can be used in conjunction with solid fuel-based conversion systems (e.g., combustors, gasifiers, pyrolysers, etc.) to store thermal energy in chemical form using the CO2 captured from the flue gas streams of these systems with CO2 concentrations typically ranging between 5 and 20 vol%. The calcium-looping-based processes, however, are very much scale dependant. What we know today about the application of the calcium-looping-based processes for thermochemical energy storage is largely based on small-scale experiments reported in the open literature. A multi-scale study was therefore conducted over that past four years to address this shortcoming by conducting a series of complementary experiments at instrument-scale (e.g., thermogravimetric analysers “TGA”), bench-scale, laboratory-scale, and pilot-scale.It was found that the results at different scales were not linearly correlated. For instance, while the calcination and carbonation temperatures had an impact on the reactivities of the calcium-rich particles, the extent of the impact was different at the instrument-scale (e.g., TGA), bench-scale, laboratory-scale, and pilot-scale. The differences between instrument-scale results and those of other scales are largely assigned to the absence of diffusional limitations for the transport of heat and mass at instrument-scale. Diffusional limitations, however, depend on the size and volume of a given system and as such underpin the discrepancies that we have seen among the experimental data collected at the bench, laboratory, and pilot-scales. For example, in our study the low calcination and carbonation temperatures typically resulted in higher reactivities at bench and laboratory-scales while the reactivity of calcium-rich particles at the pilot-scale remained largely unaffected by the calcination and carbonation temperature. Also, the extent of the deactivation of calcium-rich particles over the first few calcium-looping cycles differed at bench, laboratory, and pilot-scales. Hence, any industrial scale use of calcium-looping-based processes for thermochemical energy storage must be backed up by multi-scale studies like that reported here so that the scaling effects are well understood, and proper mitigation measures are implemented.