Thermochemical Storage Materials Research Articles

A two-stage sorption strategy to improve heat storage performance of salt/porous matrix composites

Composites combining salt hydrates and porous matrix like metal–organic frameworks (MOFs) are used to enhance the performance of thermochemical storage materials. However, the mechanism for the enhancement and the strategy for the selection of salt hydrates and porous matrix are not clear. The heat storage performance is determined by water adsorption dynamics, capacity and their sorption energy of the single components. The single components (salts or matrix) normally have either fast water adsorption dynamics or high-water uptake capacity, but not both of them. In this study, we investigate the enhancement of adsorption in composite materials, and a novel strategy is then proposed to combine the advantages from adsorbents with higher adsorption dynamics at low water partial pressure with those with a high capacity at high water partial pressure to promote the water adsorption capacity and kinetics, hence efficient energy storage. Two types of composites have been used to demonstrate the two-stage strategy developed in this study, in which SrCl2 and SrBr2 are incorporated into MOF MIL-101(Cr) to enhance adsorption and heat storage. In these composites, SrCl2 and SrBr2 can be regarded as the moisture pumps, capturing water vapour from air to improve the adsorption dynamics, while MIL-101(Cr) with high adsorption capacity functions as a water reservoir to take the water accumulated by the salts. Through this two-stage design, the water sorption capacity of the composites is 2–3 times higher than the water uptake of either salts or MOF within 120 min. As SrCl2 has a faster water adsorption kinetics than SrBr2, SrCl2/MIL-101(Cr) reaches an uptake of 0.73 g/g, however, the water sorption capacity of SrBr2/MIL-101(Cr) is 0.54 g/g. The composite samples also present good heat storage capacities of 1462 J/g for SrCl2/MIL-101(Cr) and 1526 J/g for SrBr2/MIL-101(Cr), and good cycling stability after 15 repeating adsorption/desorption cycles.

Cycling Stability of Calcium-Impregnated Vermiculite in Open Reactor Used as a Thermochemical Storage Material

Recent research into thermochemical storage (TCS) materials has highlighted their promising potential for seasonal building heating, through energy capture and release during dehydration and hydration cycling. A common TCS material used throughout this investigation was calcium chloride (CaCl2)-impregnated vermiculite-based salt in matrix (SIM). This material was assessed for its robustness during charging and discharging cycles to assess its behavior and in terms of energy stability and chemical stability; the results of which showed consistent volumetric energy density and maximum temperature changes over seven cycles. The calcium SIM did, however, show a decline in leachable Ca content, which was presumed to be a result of stabilization within the vermiculite, and chloride concentration showed little change over the course of the study. Real-time visualization using a high-resolution microscope of calcium SIM particles showed a salt phase change and migration of liquid salt into the valleys of the lamella. A novel cobalt chloride (CoCl2) SIM was used to visualize the hydration path across the particle, through distinct color changes depending on hydration state. The results indicated that the topography of the vermiculite played a significant role in the passive hydration modeling.

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 Multi-Criteria decision making (MCDM) methodology for high temperature thermochemical storage material selection using graph theory and matrix approach

Industrial waste heat is currently underutilized due to the techno-economic challenges, inherent variability and intermittency of this source. To overcome the existing barriers, reduce the emission of greenhouse gases and protect the global environmental conditions, energy recovery is one of the most effective strategies. In the design of heat storage systems, the material selection procedure plays an important role and requires complex interrelationships between the various factors and parameters to be elucidated toachieve the best candidate material for a given application. This paper presents a Multi-Criteria Decision Making (MCDM) methodology based on Graph Theory and Matrix approach for high temperature thermochemical storage (TCS) material selection. Furthermore, the presented approach has been used to select the suitable candidate material for recovering the high temperature waste heat (over 500 °C) in Port Talbot Steelworks.

Water sorption-based thermochemical storage materials: A review from material candidates to manufacturing routes

A comprehensive and updated review is provided in this article, with a focus on water sorption-based thermochemical storage (WSTCS) materials, covering materials and their manufacturing routes. The state of the art of 22 most relevant salt hydrates is classified into seven groups (bromides, sulphates, carbonates, chlorides, nitrates, hydroxides, and sulphides) and studied as candidates. This is followed by a discussion on TCS material manufacturing, covering both conventional (shaping, pelletizing, etc.) and more advanced routes (e.g., extrusion, 3D printing, encapsulation, etc.). Finally, concluding remarks are presented, including limitations and future potentials for TCS research.

Viability of waste heat capture, storage, and transportation for decentralized flowback and produced water treatment

The use of waste heat has been proposed to reduce the energy footprint of membrane distillation for flowback and produced water (FPW) treatment. However, its feasibility has not been fully understood for FPW treatment. Accordingly, this study performs systematic assessments through thermodynamic modelling of waste heat capture, storage, and transportation for decentralized FPW treatment at well pads located in the Denver-Julesburg Basin. A wide range of sensible, phase-change, and thermo-chemical storage materials were assessed for their effectiveness at the utilization of waste heat from on-site hydraulic fracturing engines and natural gas compressor stations, in order to overcome the temporal or spatial mismatch between waste heat availability and FPW generation. Our results show that the type of storage material being used can have a high impact on the efficiency of waste heat utilization and the treatment capacity of membrane distillation. Sensible storage materials only utilize sensible heat capacities, while phase-change materials have improved performance because they are able to additionally store latent heat. However, sensible and phase-change storage materials lose 11–83% of heat due to conversion inefficiencies caused by their changing temperatures. Thermo-chemical materials, on the other hand, have the highest potential for use because they collect and release heat at constant temperatures. We identified three thermo-chemical storage materials (magnesium sulfate, magnesium chloride, and calcium sulfate) with the best efficiencies due to their elevated discharge temperatures which reduce the energy consumption of membrane distillation. In addition, these materials have high volumetric energy storage density, which enables capture and transportation of waste heat from remote locations such as natural gas compressor stations to the well sites, yielding up to 70% reduction in transportation costs relative to moving FPW to centralized treatment facilities at natural gas compressor stations. Our study, for the first time, demonstrates the importance of selecting appropriate energy storage material for leveraging low-grade thermal energy such as waste heat to power membrane distillation for decentralized wastewater treatment.

Techno-Economic Analysis of Candidate Oxide Materials for Thermochemical Storage in Concentrating Solar Power Systems

The thermal storage capability is an important asset of state-of-the-art concentrating solar power plants. The use of thermochemical materials, such as redox oxides, for hybrid sensible/thermochemical storage in solar power plants offers the potential for higher specific volume and mass storage capacity and as a consequence reduced levelized cost of electricity making such plants more competitive. For the techno-economic system analysis, three candidate redox materials were analyzed for their cost reduction potential: cobalt-based, manganese–iron–based, and perovskite-based oxide materials. As a reference process the use of inert commercial bauxite particles (sensible-only storage) was considered. A solar thermal power plant with a nominal power of 125 MWe and a storage capacity of 12 h was assumed for the analysis. For each storage material a plant layout was made, taking the specific thermophysical properties of the material into account. Based on this layout a particle break-even cost for the specific material was determined, at which levelized cost of electricity parity is achieved with the reference system. Cost factors mainly influenced by the material selection are storage cost and steam generator cost. The particle transport system cost has only a minor impact. The results show differences in the characteristics of the materials, for example, regarding the impact on storage size and cost and the steam generator cost. Regarding the economic potential of the candidate redox materials, the perovskite-based particles promise to have advantages, as they might be produced from inexpensive raw materials.

Development of a reactive force field for [formula omitted]n[formula omitted], and the application to thermochemical energy storage

Calcium chloride salt hydrates (CaCl2·nH2O) have a high potential to be used as thermochemical storage material (TCM). However, specific material properties – e.g., slow diffusion, low thermal conductivity, melting temperature, and crystal stability – inhibits further implementation as robust TCM. Inherent bulk crystal defects like cracks, pores, and grain boundaries promoted during the (de) hydration cycle of the TCM, affect these material properties. Reactive force field molecular dynamics (ReaxFF-MD) is used to investigate CaCl2·nH2O (physical and chemical) properties, as well as the effect of crystal defects on them. In this sense, a new ReaxFF force field is developed, which can describe stable CaCl2·nH2O structures, accurate descriptions of crystal surface energies, and multiple material indicators like charges, reaction enthalpies, and radial distribution functions. The new force field is further used to investigate the thermal conductivity, dehydration echanisms/kinetics, and crack formation upon heating of the crystal. The thermal conductivity is found to be 1.1 and 0.5 W/mK for respectively CaCl2 and CaCl2·2H2O, which is in good agreement with experimental results. Additionally, we investigated the influence of grain boundaries and the salts’ anisotropic crystal morphology and found that both grain boundaries and the typical layered structure in z-direction lower the thermal conductivity. By investigating dehydration mechanisms, it is shown that initial dehydration is 1.9–2.5 times lower in the z-direction, also due to the typical layered morphology. For all directions, superficial dehydrated CaCl2 layers impede dehydration of core layers, but cracks and pores significantly promote it. These molecular-scale findings reveal nanoscale opportunities that could benefit the TCM.

Using Thermochemical Materials as a Heat Source for Poultry Egg Incubation

This study aims to use one thermochemical storage materials system as a heat source for poultry egg incubation. Three types of activated thermochemical storage materials (TCMs) were used as an energy storage medium. These materials are Silica gel self-indicating (blue/pink), commercial white Silica gel, and Natural Zeolite. An open thermochemical system was applied inside a poultry egg incubator. The TCMs were humidified by the vapor produced from the evaporation of the water by an ultra-sonic humidifier at atmospheric pressure. The thermal recovery process aims to release the stored energy in TCMs. Two types of poultry egg incubator used during this study. The first one was the traditional poultry incubator (electricity incubator). The traditional egg incubator dimensions were 57×66×59 cm with capacity of 125 hen egg- 76 hatching. The second one was the prototype of a thermochemical poultry egg incubator. The thermochemical poultry egg incubator contained sensors to control and measure the temperature and humidity inside the incubator. The designed incubator egg dimensions were 56x39x28.5 cm, with a capacity of 25 eggs. The total heat losses by the wall and ventilation were 9.8 and 1.5W, respectively. The heat production by 25 eggs due to metabolic activities was 3.65 W. The total energy needed for the incubation process was 36.09W. The container of storage material with dimensions of 35x35x5 cm with 3.5 kg capacity allocated inside the incubator. The container's surface is covered with aluminum sheet with 0.5 mm thickness supplied with fins. The egg tray is placed on the aluminum sheet, and the eggs were placed horizontally in the tray. The energy consumption for traditional and thermochemical incubators for 21 days was 19.25 kWh and 11.2 kWh, respectively. The energy saving by thermochemical prototype incubator was 41.8%. The percentage of hatchability for traditional and prototype incubator was 80.9% and 71.4%, respectively.

MgSO4-expanded graphite composites for mass and heat transfer enhancement of thermochemical energy storage

Sorption based thermochemical energy storage using salt hydrates offers several potential advantages if engineered properly, compared with sensible and latent heat storage technologies, including low heat loss, small volume change and high energy density. Two of key technological challenges are low mechanical structure stability, which determines the life-span; and slow charging and discharging kinetics, which depends largely on mass and heat transfer. As the heat and mass transfer relates to structure and composition of thermochemical storage materials, the two key challenging aspects are coupled and the use of engineered composite thermochemical materials provides an avenue to address the challenges. In this paper, we report a novel thermochemical storage composite material, consisting of magnesium sulfate (MgSO4, the thermochemical storage material) and expanded graphite (EG, heat transfer enhancer and structural stabiliser), prepared by impregnation of MgSO4 into EG. The composite has been characterized by various methods, including scanning electron microscopy (SEM), differential scanning calorimeter (DSC), thermogravimetry (TG), transient plane heat source method and dynamic vapor sorption (DVS). The results showed that the MgSO4-EG composite containing 60% MgSO4 displayed superior heat and mass transfer properties. The hydration time of MgSO4 was shorten to about 1/4 of its pure and original form and the thermal conductivity was increased by more than 84.8% through the MgSO4 impregnation into EG.

Performances Assessment of Tricalcium Aluminate as an Innovative Material for Thermal Energy Storage Applications

In this paper, tricalcium aluminate hexahydrate (Ca3Al2O6·6H2O), thanks to its appropriate features, was assessed as an innovative, low-cost and nontoxic material for thermochemical energy storage applications. The high dehydration heat and the occurring temperature (200–300 °C) suggest that this material could be more effective than conventional thermochemical storage materials operating at medium temperature. For these reasons, in the present paper, Ca3Al2O6·6H2O hydration/dehydration performances, at varying synthesis procedures, were assessed. Experimentally, a co-precipitation and a solid–solid synthesis were studied in order to develop a preparation method that better provides a performing material for this specific application field. Thermal analysis (TGA, DSC) and structural characterization (XRD) were performed to evaluate the thermochemical behavior at medium temperature of the prepared materials. Furthermore, reversibility of the dehydration process and chemical stability of the obtained materials were investigated through cycling dehydration/hydration tests. The promising results, in terms of de/hydration performance and storage density (≈200 MJ/m3), confirm the potential effectiveness of this material for thermochemical energy storage applications and encourage further developments on this topic.

K2CO3 in closed heat storage systems

Potassium carbonate, K2CO3, has been identified as one of the most promising thermochemical storage materials for the built environment. Where a lot of knowledge has been gained on hydration/dehydration behavior at atmospheric (open system) conditions, little is known of this process under pure water vapor conditions (closed vacuum system). In this paper, for the first time, the equilibrium behavior and reaction kinetics of a K2CO3 composite are investigated under pure water vapor conditions, as present in closed vacuum systems. In this work the metastable behavior of a K2CO3 composite is investigated under vacuum conditions and compared to its metastable behavior under atmospheric conditions. It is found that the metastable zone is also present in vacuum conditions, however induction times in the metastable zone are much shorter which indicates a faster nucleation rate in vacuum conditions.Moreover the effect of inert gasses in a closed system is studied and it is shown that it is critical to remove all sources of non-condensable gasses. Finally in cyclic measurements it is shown that K2CO3 is stable in multi cyclic experiments, concluding that it is a suitable material for a heat battery based on the concept of a closed reactor.

Double hydrates salt as sustainable thermochemical energy storage materials: Evaluation of dehydration behavior and structural phase transition reversibility

Currently, thermochemical energy storage (TCES) offers the opportunity to relieve the enormous gap of energy demand and supply in the solar energy field. This method has its specific requirements, such as high energy storage density, good thermal stability, high reaction enthalpy, high heat capacity and switched temperature range of thermochemical storage material (TCM) for low to medium temperature building applications. This paper reports the synthesis of blödite-type structure Na2M(SO4)2·4H2O (M = Zn, Mg) and copper kröhnkite phase Na2Cu(SO4)2·2H2O. Their structural and thermal behavior were also investigated to explore a new temperature range using incorporated salts. An evaluation of potential energy storage density, structural reversibility, thermal cycling stability and storage efficiency of double salts compared to pure hydrates salts as TCM was carried out. The preliminary results show a good structural matching of synthesized double salts confirmed by XRD, FTIR, and Raman spectroscopy, while the transition phase investigation since dehydration process was reported by XRD and Raman spectroscopy. Moreover, Na2Zn(SO4)2·4H2O exhibited a suitable charging range temperature (<105 °C), good cycling stability at the first ten hydration/dehydration cycles with an excellent energy storage density of 4.7 GJ m−3 and an interesting theoretical efficiency up to 77.4%.

Investigation of calcium hydroxide powder for thermochemical storage modified with nanostructured flow agents

Thermal energy storage is a key component for power supply based on concentrating solar power. A promising thermochemical storage material in terms of cost-efficiency, storage density and reaction temperatures is based on the chemical reaction of calcium oxide with water. Handling of the solid materials, however, has proven to be difficult due to their powdery state particularly in dynamic storage systems. It is therefore proposed in the presented work to modify calcium hydroxide powder with nanostructured flow agents to improve the powder's flowability. Therefore, five additives consisting of nanostructured silicon and/or aluminium oxide were mixed systematically with calcium hydroxide powder and the flowability of the mixtures was determined using a ring shear cell. Four additives caused an improved flowability of the powder with additive weight fractions of 6–12%. After thermochemical cycling of the mixtures, however, flowability of the mixtures was clearly decreased while that of the pure powder was increased. Analysis of the samples showed a correlation between growth in particle size and increased flowability. Additionally, formation of calcium silicate and/or aluminate phases led to a decrease in absolute heat release of up to 50% as measured by thermal flux calorimetry, although some of the side products seemingly add to the measured heat release by hydrating exothermally. Based on these results, stabilisation of a moderately increased particle size preferably without the addition of additives is recommended, as a sole prevention of agglomeration by means of flow agents does not result in a manageable storage material.

Adapting the MgO-CO2 Working Pair for Thermochemical Energy Storage by Doping with Salts: Effect of the (LiK)NO3 Content

The MgO-CO2 working pair has been regarded as prospective for thermochemical energy storage (TCES) due to its relatively high heat storage capacity, low cost, and wide availability. This study is aimed at the optimization of the molar salt content, α, for the MgO modified with the eutectic mixture of LiNO3 and KNO3 (Li0.42K0.58NO3) which was earlier shown to provide high conversion, Δx, in heat-storage/release processes at 300–400 °C. The composites that have different salt content were prepared and carbonation kinetics was investigated under various conditions (carbonation temperature, Tcarb., is 290–360 °C and CO2 pressure, P(CO2), is 50–101 kPa). Significant accelerating effect was revealed at α ≥ 0.05, and the Δx value was maximized at α = 0.10–0.20. The largest conversion of 0.70 was detected at α = 0.10 and Tcarb. = 350 °C that corresponds to the specific useful heat (Qcomp.) is 1.63 MJ/kg-composite. However, the salt content of 0.20 ensures the high conversion, Δx = 0.63–0.67 and Qcomp. = 1.18–1.25 MJ/kg-composite in the whole temperature range between 290 and 350 °C. The (LiK)NO3/MgO composite with an optimal salt content of 0.20 exhibits reasonable durability through cyclic experiment at 330 °C, namely, the stabilized reacted conversion Δx = 0.34 (Qcomp. = 0.64 MJ/kg-composite). The studied (Li0.42K0.58)NO3 promoted MgO-CO2 working pair has good potential as thermochemical storage material of middle temperature heat (300–400 °C).

Techno-economic assessment of seasonal heat storage in district heating with thermochemical materials

Thermochemical energy storage provides opportunities for pressure-less and low-loss seasonal storage at high energy densities. For that purpose, appropriate storage concepts are drafted and examined in technical, ecological and economic terms, considering suitable materials, energy sources, and charge and discharge reactor concepts. The results illustrate that the choice of the district heating grid to be supplied, the locations of the energy sources for charging, and the transfer distance have major influence on the potential use cases for thermochemical storage (TCS) materials. Grids with a high number of full load hours and low power demand (base load coverage) are much better suited to this type of heat storage compared to peak load applications, allowing the high fixed material costs and investment to be recouped. The use of hydration-based TCS materials (hydrates and hydroxides) is particularly suitable if costs for material transport and supply of the required water vapor can be avoided. Thus, with industrial waste heat as a low cost energy source, heat production costs around 100 €/MWh could be achieved. For larger spatial distances between the energy source and the grid, metallic TCS materials are favourable due to higher storage densities. Major costs in the heat recovery of redox materials are those for the electrical energy needed for reduction, resulting in total costs well above 120 €/MWh. In all cases investigated, the calculated heat production costs for thermochemical storage are significantly above those of conventional district heating applications. This paper supports a pre-selection of relevant TCS materials and applications in district heating for future detailed analysis.

Hydrated Salt/Graphite/Polyelectrolyte Organic-Inorganic Hybrids for Efficient Thermochemical Storage.

Hydrated salt thermochemical energy storage (TES) is a promising technology for high density energy storage, in principle opening the way for applications in seasonal storage. However, severe limitations are affecting large scale applications, related to their poor thermal and mechanical stability on hydration/dehydration cycling. In this paper, we report the preparation and characterization of composite materials manufactured with a wet impregnation method using strontium bromide hexahydrate (SBH) as a thermochemical storage material, combined with expanded natural graphite (G). In addition to these fully inorganic formulations, an organic polyelectrolyte (PDAC, polydiallyldimethylammonium chloride) was exploited in the structure, with the aim to stabilize the salt, while contributing to the sorption/desorption process. Different formulations were prepared with varying PDAC concentration to study its contribution to material morphology, by electron microscopy and X-ray diffraction, as well as water sorption/desorption properties, by thermogravimetry and differential calorimetry. Furthermore, the SBH/G/PDAC powder mixture was pressed to form tabs that were analyzed in a climatic chamber, which is evidence for an active role of PDAC in the improvement of water sorption, coupled with a significant enhancement of mechanical resistance upon hydration/dehydration cycling. Therefore, the addition of the polyelectrolyte is proposed as an innovative approach in the fabrication of efficient and durable TES devices.

A Critical Review of Solid Materials for Low-Temperature Thermochemical Storage of Solar Energy Based on Solid-Vapour Adsorption in View of Space Heating Uses.

The present report deals with low-temperature thermochemical storage for space heating, which is based on the principles of vapour adsorption onto solid adsorbents. With the aim of obtaining comprehensive information on the rationalized selection of adsorbents for heat storage in open sorption systems operating in the moist-air flow mode, various materials reported up to now in the literature are reviewed by referring strictly to the possible mechanisms of water vapour adsorption, as well as practical aspects of their preparation or their application under particular operating conditions. It seems reasonable to suggest that, on the basis of the current state-of-the-art, the adsorption phenomenon may be rather exploited in the auxiliary heating systems, which provide additional heat during winter’s coldest days.

Thermochemical behavior of perovskite oxides based on LaxSr1-x(Mn, Fe, Co)O3-δ and BaySr1-yCoO3-δ redox system for thermochemical energy storage at high temperatures

LaxSr1-x(Mn, Fe, Co)O3-δ, and BaySr1-yCoO3-δ perovskite oxide powders were investigated as potential thermochemical energy storage (TES) materials operated at high temperatures above 600 °C. The purpose of the research is to provide complete characterization of the impact of partial A- and B-site substitution on the reactivity, kinetics, redox reaction repeatability and charging/discharging storage capacity. The perovskite oxides were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) at temperatures of 500–1100 °C. Thermal energy storage was evaluated in terms of the enthalpy of the reversible reactions of oxygen release (reduction) and uptake (oxidation) upon heating the oxide materials in air stream. Among the perovskites tested, Ba0.3Sr0.7CoO3-δ and Ba0.7Sr0.3CoO3-δ powders were suitable thermochemical storage materials operating at above 600 °C in terms of chemical reactivity, charging/discharging temperatures and storage capacities, kinetics of oxygen uptake/release, and repeatability of thermochemical cycling. Further, charging/discharging capacity for both perovskites was comparable to that for Fe-doped manganese oxide.

Discharge performance of blended salt in matrix materials for low enthalpy thermochemical storage

A novel study is undertaken on low cost thermochemical storage which utilizes temperatures which are compatible with low grade renewable energy capture. The discharge performance of thermochemical storage matrix materials is assessed using a custom developed experimental apparatus which provides a means of comparing materials under scaled reactor conditions. The basic performance of three salts (CaCl2, LiNO3 and MgSO4) was investigated and their subsequent performance using layering and blending techniques established that the performance could be increased by up to 24% through the correct choice of mixing technique. Layering the CaCl2 on the LiNO3 provided the most efficient thermal release strategy and yielded a thermal storage density of 0.2 GJ/m3. The research also uniquely highlights the important finding that incorrect mixing of the materials can lead to a significant reduction in efficiency with freely mixed CaCl2 and LiNO3 possessing a storage capacity of less than 0.01 GJ/m3 as a result of chemical interactions between the deliquesced materials in close proximity. The paper has impact for the design and control of thermochemical storage systems as it clearly identifies how performance can be improved or degraded by the choice and the structuring of the materials.