MgSO_(4)·7H_(2)O for thermochemical energy storage:Hydration/dehydration kinetics and cyclability

In recent decades,MgSO_(4)·7H_(2)O(epsomite)has attracted significant attention as a promising thermochemical-based thermal energy storage material due to its high theoretical energy density,wide availability,and affordability.Despite extensive research efforts,progress in achieving high-energy density has been limited,primarily due to inadequate understanding of its reaction mechanisms and unfavorable dehydration/hydration kinetics.This study systematically investigated the hydration/dehydration kinetics and cyclability of MgSO_(4)·7H_(2)O.The results reveal that the dehydration process is influenced by the heating rate,with an optimal rate of 5℃/min,resulting in a seven-step MgSO_(4)·7H_(2)O dehydration process with a dehydration heat close to the theoretical value.The reaction kinetic analysis indicated that the rate of hydration was approximately 50%lower than that of dehydration.In addition,thermal cycling tests of MgSO_(4)·7H_(2)O under the conditions of this study(small sample size)indicated good cyclability,with hydration rates increasing with increasing cycling numbers up to approximately 10 cycles where level-off occurs.These results are consistent with scanning electron microscopy analyses,which revealed the formation of cracks and channels in the salt hydrate particles,facilitating mass transfer and improved kinetics.

Carbon dioxide reforming of methane over bimetallic catalysts of Pt-Ru/γ-Al_2O_3 for thermochemical energy storage

The reaction of CO2 reforming of CH4 has been investigated with y-A1203-supported platinum and ruthenium bimetallic catalysts, with the specific purpose of thermochemical energy storage. The catalysts were prepared by using the wetness impregnation method. The prepared catalysts were characterized by a series of physico-chemical characterization techniques such as BET surface area, thermo-gravimetric （TG）, transmission electron microscope （TEM） and X-ray photoelectron spectroscopy （XPS）. In addition, the amount of carbon deposits on the surface of the catalysts and the type of the carbonaceous species were discussed by TG. It was found that the bimetallic Pt-Ru/7-A1203 catalysts exhibit both superior catalytic activity and remarkable stability by comparison of monometallic catalysts. During the 500 h stability test, the bimetallic catalyst showed a good performance at 800 ~C in CO2 reforming of CH4, exhibiting an excellent anti-carbon performance with the mass loss of less than 8.5%. The results also indicate that CO2 and CH4 have quite stable conversions of 96.0 % and 94.0 %, respectively. Also, the selectivity of the catalysts is excellent with the products ratio of CO/H2 maintaining at 1.02. Furthermore, it was found in TEM images that the active carbonaceous species were formed during the catalytic reaction, and well-distributed dot-shaped metallic particles with a relatively uniform size of about 3 nm as well as amorphous carbon structures were observed. Combined with BET, TG, TEM tests, it is concluded that the selected bimetallic catalysts can work continuously in a stable state at the high temperature, which has a potential to be utilized for the closed-loop cycle of the solar thermochemical energy storage in future industry applications.

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

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

Flow characteristics simulation of spiral coil reactor used in the thermochemical energy storage system

According to environmental and energy issues,renewable energy has been vigorously promoted.Now solar power is widely used in many areas but it is limited by the weather conditions and cannot work continuously.Heat storage is a considerable solution for this problem and thermochemical energy storage is the most promising way because of its great energy density and stability.However,this technology is not mature enough to be applied to the industry.The reactor is an important component in the thermochemical energy storage system where the charging and discharging process happens.In this paper,a spiral coil is proposed and used as a reactor in the thermochemical energy storage system.The advantages of the spiral coil include simple structure,small volume,and so on.To investigate the flow characteristics,the simulation was carried out based on energy-minimization multi-scale model(EMMS)and Eulerian two-phase model.CaCO_(3) particles were chosen as the reactants.Particle distribution was shown in the results.The gas initial velocity was set to 2 m·s^(-1),3 m·s^(-1),and 4 m·s^(-1).When the particles flowed in the coil,gravity,centrifugal force and drag force influenced their flow.With the Reynold numbers increasing,centrifugal and drag force got larger.Accumulation phenomenon existed in the coil and results showed with the gas velocity increasing,accumulation moved from the bottom to the outer wall of the coil.Besides,the accumulation phenomenon was stabilized whenφ>720°.Also due to the centrifugal force,a secondary flow formed,which means solid particles moved from the inside wall to the outside wall.This secondary flow could promote turbulence and mixing of particles and gas.In addition,when the particle volume fraction is reduced from 0.2 to 0.1,the accumulation at the bottom of the coil decreases,and the unevenness of the velocity distribution becomes larger.

Investigation of Particle Breakdown in the Production of Composite Magnesium Chloride and Zeolite Based Thermochemical Energy Storage Materials

Composite thermochemical energy storage(TCES)represents an exciting field of thermal energy storage which could address the issue of seasonal variance in renewable energy supply.However,there are open questions about their performance and the root cause of some observed phenomena.Some researchers have observed the breakdown of particles in their production phase,and in their use.This study seeks to investigate the underlying cause of this breakdown.SEM and EDX analysis have been conducted on MgCl2 impregnated 13X zeolite composites of differing diameters,as well as LiX zeolite.This was done in order to study the level of impregnation of salt into the zeolite matrix,as well as the effect this impregnation process has on the morphology of the zeolite.Analysis was conducted using ImageJ software to study the effect of the impregnation process on the diameter of the particles.It has been found that a by weight impregnation concentration of magnesium chloride of 11.90%for the LiX zeolite,and 7.59%and 5.26%for the large diameter 13X zeolite and the small diameter 13X zeolite respectively has been achieved.It has been found that the impregnation process significantly affects themorphology of 13X zeolite particles,causing large fissures to form,and eventually resulting in the previously found breakdown of these particles.It has been verified that a primary factor influencing the breakdown of the 13X zeolite particles is the efflorescence and sub-fluorescence phenomena,which leads to a build-up of crystals in the zeolite pores.It has also been found that prolonged impregnation times and the use of high concentration salt solutions in the soaking process can induce significant crystal growth which also leads to the breakdown of these particles.Results demonstrate that LiX zeolite is the optimum host matrix choice in these conditions.These results will allow for the design of more resilient composite TCES particles.

Ca-based materials derived from calcined cigarette butts for CO_(2)capture and thermochemical energy storage

Cigarette butts(CBs)are one of the most common types of litter in the world.Due to the toxic substances they contain,the waste generated poses a harmful risk to the environment,and therefore there is an urgent need for alternative solutions to landfill storage.Thus,this work presents a possible revalorization of this waste material,which implies interesting environmental benefits.CBs were used as sacrificial templates for the preparation of CaO-based materials by impregnation with calcium and magnesium nitrates followed by flaming combustion.These materials presented enhanced porosity for their use in the Calcium Looping process applied either to thermochemical energy storage or CO_(2)capture applications.The influence of the concentration of Ca and Mg in the impregnating solutions on the multicycle reactivity of the samples was studied.An improved multicycle performance was obtained in terms of conversion for both applications.

Fabrication of LiOH-metal organic framework derived hierarchical porous host carbon matrix composites for seasonal thermochemical energy storage

By virtue of its long lifespan and outstanding storage intensity with near-zero heat loss,salt hydrate thermochemical energy storage(TES)materials provide a feasible option for the effective use of renewable energy and overcoming its unsynchronized supply and demand.Here,an activated porous carbon originating from the zeolite imidazolate framework(ZHCM)is fabricated and served as the carbon matrix for the LiOH TES material.The as-synthesized Li/ZHCM2-40 not only has excellent storage intensity(maximum 2414.2 kJ·kg^(−1))with low charging temperature,but also shows great hydration properties stemming from the ultrahigh surface area and hierarchical porous structure of ZHCM2.Besides,this composite material exhibits superior thermal conductivity,while its storage intensity is only attenuated by 10.2%after 15 times of consecutive charge-discharge process,revealing its outstanding cycle stability.And the numerical simulation results also demonstrate its superior heat transfer performance.The developed LiOH TES composite may afford a new avenue for efficient low-grade thermochemical energy storage and liberate the possibility of further exploration of metal organic frameworks derived porous carbon matrix in the future.

Granular porous calcium carbonate particles for scalable and high-performance solar-driven thermochemical heat storage

Calcium carbonate is promising thermochemical heat storage material for next-generation solar power systems due to its high energy storage density,low cost,and high operation temperature.Researchers have tried to improve energy storage performances of calcium carbonate recently,but most researches focus on powders,which are not suitable for scalable applications.Here,novel granular porous calcium carbonate particles with very high solar absorptance,energy storage density,abrasive resistances,and energy storage rate are proposed for direct solar thermochemical heat storage.The average solar absorptance is improved by 234%compared with ordinary particles.Both cycle stability and abrasive resistances are excellent with almost no decay of energy storage density over 25 cycles nor apparent particle weight loss over 24 h of continuous operation insides a planetary ball mill.In addition,the decomposition temperature is reduced by 2.8%–5.6%while the reaction rate of heat storage is enhanced by 80%–205%depending on the CO_(2) partial pressure.The decomposition process of doped granular porous CaCO_(3) particles is found to involve three overlapping processes.This work provides new routes to achieve scalable direct solar thermochemical heat storage for next-generation high-temperature solar power systems.