Millimeter-scale heat storage particles with multi-stage stepped hole structure and preparation method and application thereof

Abstract

The application discloses a kind of millimeter heat storage particles with multi-stage stepped hole structure and preparation method thereof, the particle is millimeter size, it has core-shell gradual change pore structure macroscopically, it has micron-nanometer stepped hole microscopically, so compared with the millimeter uniform structure particle prepared by traditional extrusion-rounding method has better mass transfer capacity, and its reaction rate is obviously improved.The millimeter core-shell structure heat storage particle with loose core and dense shell is obtained by new type centrifugal granulation-calcination process.

Description

Technical Field

[0001] This invention relates to a millimeter-sized thermal storage particle with a multi-level stepped pore structure, its preparation method and application, belonging to the field of solar thermochemical storage technology. Background Technology

[0002] The extensive use of fossil fuels has led to a continuous rise in atmospheric carbon dioxide concentration, exacerbating the greenhouse effect and causing sea-level rise. Vigorously developing renewable energy sources such as solar and wind power can effectively reduce the proportion of fossil fuels and is considered an effective means of achieving carbon neutrality. However, solar energy has inherent drawbacks such as instability and discontinuity. Therefore, in solar energy utilization fields such as concentrated solar thermal power generation, thermal storage systems are usually used. These systems convert solar energy into heat energy and store it when solar irradiance is sufficient, and release the heat for utilization when solar irradiance is insufficient, such as on cloudy days or at night. Among various thermal storage technologies, new thermal storage technologies, represented by calcium carbonate thermochemical thermal storage technology, have advantages such as high thermal density, high operating temperature, low heat loss during long-term energy storage, and large material reserves. They are considered to be a highly promising thermal storage method for next-generation solar thermal power generation technology.

[0003] In recent years, researchers have conducted numerous studies on calcium carbonate-based thermochemical thermal storage. In terms of materials development, research has mainly focused on improving the solar spectral absorption capacity and thermal storage / release cycle stability of calcium carbonate materials through methods such as elemental doping. However, the chemical reaction rate in the thermal storage / release process of calcium carbonate materials is slow, which leads to low efficiency of the thermal storage system. Therefore, it is urgent to achieve a synergistic improvement in the thermal storage density, solar spectral absorption rate, thermal storage / release cycle stability, and fast reaction rate of calcium carbonate thermochemical thermal storage materials. Summary of the Invention

[0004] Objectives of this invention: One objective is to provide a millimeter-scale thermal storage particle with a multi-level pore structure. By coupling the macroscopic core-shell structure with the microscopic micro-nano pore structure, carbon dioxide mass transfer within the particle is promoted, resulting in a significant decrease in reaction temperature and a significant increase in reaction rate. This avoids the problems of decreased thermal storage density and decreased mechanical stability caused by traditional doping modification methods. Another objective is to provide a method for preparing this millimeter-scale thermal storage particle. This method can realize the construction of the aforementioned novel structure and is expected to achieve large-scale production. The final objective is to provide the application of this millimeter-scale thermal storage particle in solar chemical thermal storage.

[0005] Technical solution: The millimeter-sized thermal storage particles with a multi-level stepped pore structure described in this invention are composite calcium carbonate particles. Macroscopically, they have a core-shell structure, and microscopically, they have a micron-nano stepped pore structure. The core-shell structure means that the core and outer layer of the millimeter-sized thermal storage particles have different porosities, that is, the inner core has multiple larger pores, and the outer shell has a relatively dense pore core.

[0006] Furthermore, the particle size of the composite calcium carbonate particles is 600~700 μm.

[0007] The method for preparing millimeter-scale thermal storage particles with a multi-level stepped pore structure according to the present invention includes the following steps: preparing composite calcium hydroxide precursor powder, preparing inner layer calcium hydroxide core, centrifugal growth to prepare precursor particles, calcination, and acidification.

[0008] (1) Preparation of composite calcium hydroxide precursor powder;

[0009] (2) Spray a binder solution onto the composite calcium hydroxide precursor powder. Under the action of the binder, the calcium hydroxide powder will grow together until the particle size reaches the target core diameter, thus obtaining the calcium hydroxide core.

[0010] (3) Spray binder and calcium hydroxide powder onto the calcium hydroxide core to grow a shell on the outer layer of the calcium hydroxide core to obtain precursor particles;

[0011] (4) The precursor particles are calcined in air and carbonized in a CO2 atmosphere.

[0012] Further, in step (1), the preparation of composite calcium hydroxide precursor powder includes the following steps: first, mixing micron-sized pore-forming agent with calcium hydroxide powder, adding transition metal element dopant solution and stirring evenly, drying, and ball milling.

[0013] Furthermore, the micron-sized pore-forming agent is microcrystalline cellulose, foxtail grass fibers, straw powder, or charcoal powder, and the transition metal element dopant is a transition metal salt or transition metal oxide. The transition metal element dopant is selected to improve the solar spectral absorption capacity and heat storage / release cycle stability of the calcium carbonate thermochemical thermal storage material. The transition metal element dopant, whether a transition metal salt or transition metal oxide, can be a nitrate or organic acid salt of a transition metal. The transition metal element is one or more of Al, Zr, Mn, Fe, Co, and Cu. The molar ratio of the transition metal dopant to calcium hydroxide is 100:5 to 100:35, and the mass-volume ratio of calcium hydroxide powder to the micron-sized pore-forming agent is 100:10 to 100:60. When using the transition metal element dopant, it must first be prepared into a solution with a molar concentration of 2 to 6 mol / L, uniformly mixed with calcium hydroxide powder, dried, and then crushed to obtain calcium hydroxide precursor powder.

[0014] Further, in steps (2) and (3), the binder is polyvinylpyrrolidone, the mass concentration of the binder solution is 1%, the blowing temperature during spraying is set to 30°C~80°C, and the pump speed is 1~10 mL / min. In step (2), the diameter of the calcium hydroxide core is 400~450 μm, and in step (3), the diameter of the precursor particles is 700~800 μm, and the Ca in the precursor particles... 2+ Al 3 + Fe 3+ Mn 2+ The molar ratio is 100:15:10:5. In step (4), the calcination conditions in air atmosphere are calcination at 600°C ~ 1000°C for more than 2 hours, and the carbonation conditions in CO2 atmosphere are calcination at 600°C ~ 800°C for more than 1 hour.

[0015] The present invention relates to the application of millimeter-sized thermal storage particles with a multi-level stepped pore structure in solar chemical thermal storage.

[0016] The millimeter-scale thermal storage particles with a multi-level stepped pore structure described in this invention employ a core-shell structure design coupled with pore-forming agent doping, solar spectrum absorption-enhancing element doping, and thermal storage / release cycle stability element doping modification. Compared to traditional simple doping modification methods, this achieves a synergistic improvement in thermal storage density, solar spectrum absorptivity, thermal storage / release cycle stability, mechanical wear resistance, and fast reaction rate. The millimeter-scale thermal storage particles of this invention have a macroscopic core-shell structure (the core and outer layer of the particle have different macroscopic porosities) and a micro- to nano-stepped pore structure, achieving chemical reaction rate optimization through multi-level structural optimization. Precursor particles consisting of an inner core and a growing outer layer are obtained through calcination and carbonation. The core in the core-shell structure particles is a composite calcium hydroxide particle with a certain porosity. The growing outer layer is formed by growing and coating the core with a composite calcium hydroxide material made of calcium hydroxide, a micron-scale pore-forming agent, and a transition metal element dopant.

[0017] The core-shell structure of this invention refers to the process optimization and control to achieve different porosities in the core and outer layers of the particles. By adding micron-sized pore-forming agents (such as microcrystalline cellulose), micron-sized pores can be generated during calcination. Components such as calcium hydroxide and nitrates in the heat storage particle precursor will generate nano-sized pores during calcination decomposition, thus constructing a micron-nano ladder-like pore structure. This structure can also effectively promote carbon dioxide mass transfer. The macroscopic variable porosity structure and the micron-nano ladder-like pore structure together constitute the core-shell structure, synergistically promoting the mass transfer process and accelerating the chemical reaction rate. This structure can promote the carbon dioxide mass transfer and diffusion in the heat storage and release chemical reaction, thereby lowering the reaction temperature and accelerating the reaction rate.

[0018] The preparation process of the millimeter-scale thermal storage particles of this invention mainly includes precursor powder preparation, core preparation, centrifugal granulation, calcination-acidification, and other processes. Specifically, the precursor powder preparation process involves first adding a micron-sized pore-forming agent and a transition metal element dopant solution to calcium hydroxide powder and stirring until homogeneous. Microcrystalline cellulose is used as the micron-sized pore-forming agent, and the transition metal element dopant is selected to improve the solar spectrum absorption capacity and thermal storage / release cycle stability of the calcium carbonate thermochemical thermal storage material. Subsequently, the precursor mixture is dried; finally, it is crushed into fine powder using a pulverizer and a planetary ball mill. In preparing the core-shell structure, the core is obtained through centrifugal granulation. Specifically, the composite calcium hydroxide precursor powder is fluidized under centrifugal force, and a viscous binder solution such as polyvinylpyrrolidone is sprayed onto the powder. Under the action of the binder, the calcium hydroxide powder undergoes agglomeration and growth, and the particle size gradually increases to the target core size. In the preparation of core-shell structures, the centrifugal granulation process involves fluidizing the parent core microspheres under centrifugal force. A viscous binder solution, such as polyvinylpyrrolidone, is sprayed onto the parent core, and composite calcium hydroxide powder is continuously added. Under the action of the binder, the calcium hydroxide powder adheres to the outer layer of the parent core and grows thicker, gradually increasing in particle size, resulting in precursor particles consisting of an inner parent core and a growing outer layer. By changing the centrifugal speed, powder application rate, and spraying rate, the macroscopic porosity of the parent core and the growing layer can be controlled. For example, a loose and porous core structure can be obtained first, and then the parameters can be changed to make the outer layer more dense. The calcination process is carried out in air, primarily to remove micron-sized pore-forming agents (such as microcrystalline cellulose), moisture, and nitrate ions from dopants, thereby obtaining composite calcium oxide particles with the corresponding target structure. These are then calcined in a carbon dioxide atmosphere to obtain composite calcium cuprate particles with the corresponding target structure.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: The millimeter-scale thermal storage particles of the present invention can reduce the thermal storage decomposition temperature and increase the thermal storage and release chemical reaction rate through the layered porosity structure and the stepped pore structure. Compared with the traditional method of accelerating the reaction rate by doping with inert materials, the problem of decreased thermal storage density and deterioration of particle strength of composite materials caused by doping can be avoided. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the process flow for preparing core-shell structured millimeter-scale thermal storage particles according to the present invention, wherein (a) is a flowchart for preparing composite calcium hydroxide precursor powder, (b) is a flowchart for making composite calcium hydroxide precursor particles, and (c) is a flowchart for particle calcination and molding.

[0021] Figure 2Here are SEM images of the composite calcium carbonate particles obtained in Comparative Example 1 and Example 1, where (a) is a macroscopic SEM image of the particles in Comparative Example 1, (b) is a cross-sectional view of the particles in Comparative Example 1, (c) is a microscopic SEM image of the particles in Comparative Example 1, (d) is a nanostructure SEM image of the particles in Comparative Example 1, (e) is a macroscopic SEM image of the particles in Example 1, (f) is a cross-sectional view of the particles in Example 1, (g) is a microscopic SEM image of the particles in Example 1, and (h) is a nanostructure SEM image of the particles in Example 1.

[0022] Figure 3 Figure 1 shows the CT morphology of the composite calcium carbonate particles obtained in Comparative Example 1 and Example 1. In Figure 1, (a) shows the macroscopic morphology of the particles in Comparative Example 1, (b) shows the cross-sectional morphology of the macroscopic morphology of the particles in Comparative Example 1, (c) shows the slice morphology of the macroscopic morphology of the particles in Comparative Example 1, (d) shows the top view of the slice morphology of the macroscopic morphology of the particles in Comparative Example 1, (e) shows the macroscopic morphology of the particles in Example 1, (f) shows the cross-sectional morphology of the particles in Example 1, (c) shows the slice morphology of the particles in Example 1, and (h) shows the top view of the slice morphology of the particles in Example 1.

[0023] Figure 4 The graphs show the thermogravimetric test results of calcium carbonate particles obtained in Example 1 and Comparative Example 1, where (a) represents the particle dispersion state and (b) represents the particle packing state.

[0024] Figure 5 It is 800 of the calcium carbonate particles obtained in Example 1 and Comparative Example 1. o Figure showing the results of the C isothermal decomposition test;

[0025] Figure 6 It is 800 of the calcium carbonate particles obtained in Example 1 and Comparative Example 1. o Figure 1; Results of isothermal carbonation kinetics test at C;

[0026] Figure 7 This is a comparison diagram of the specific surface area of ​​calcium carbonate particles obtained in Example 1 and Comparative Example 1.

[0027] Figure 8 The graph shows the test results of solar spectral absorption capacity, cycle stability and mechanical wear resistance of calcium carbonate particles obtained in Example 1 and Comparative Example 1. In this graph, (a) is the solar spectral absorption law of the obtained calcium carbonate particles, (b) is the average solar spectral absorption law of the obtained calcium carbonate particles, and (c) is the change of energy storage density of the obtained calcium carbonate particles over 25 cycles. Detailed Implementation

[0028] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0029] Example 1

[0030] Taking the preparation process of multi-level tiered porous particles as an example, the specific steps are as follows:

[0031] (1) Preparation of composite calcium hydroxide powder

[0032] Calcium hydroxide and microcrystalline cellulose were thoroughly mixed at a mass ratio of 100:20 to obtain a composite powder. Subsequently, a nitrate solution was prepared by adding aluminum nitrate nonahydrate, ferric nitrate nonahydrate, and a 50 wt% manganese nitrate aqueous solution to deionized water. The solution was then processed according to the Ca... 2+ Al 3+ Fe 3+ With Mn 2+ The molar ratio of each element is 100:15:10:5. A 2 mol / L aqueous solution of the nitrate is added to the composite powder of calcium hydroxide and microcrystalline cellulose and stirred thoroughly until the color is uniform. The moist mixture is then placed in a drying oven and dried at 80°C for 4-6 hours to completely remove moisture. Due to the high hardness of the dried material, the large, bonded particles need to be pre-crushed using a crusher to reduce their particle size, facilitating ball milling with a planetary ball mill to completely reduce it to a powder <50 μm, i.e., composite calcium hydroxide powder. During the preparation process... Figure 1 As shown in (a).

[0033] (2) After preparing the composite calcium hydroxide powder, centrifugal granulation and coating machine is used to prepare the composite calcium hydroxide core. The concentration of the polyvinylpyrrolidone aqueous solution as a binder is 1 wt%. Take 200 g of the composite calcium hydroxide powder prepared in step (1) and put it into the centrifugal chamber of the centrifugal granulation and coating machine. The centrifugal disc speed is set to 300 rpm and the blower temperature is set to 30°C. The polyvinylpyrrolidone aqueous solution is sprayed into the centrifugal chamber at a flow rate of 5 mL / min to obtain the composite calcium hydroxide core. During the preparation process, if Figure 1 As shown in (b).

[0034] (3) Weigh 200 g of the composite calcium hydroxide core microspheres obtained in step (2) and place them into the centrifuge chamber of the centrifuge granulation and coating machine. Set the centrifuge turntable speed to 300 rpm and the blower temperature to 30°C. After the composite calcium hydroxide core flows under the drive of the centrifuge turntable, sprinkle in 1 wt% of composite calcium hydroxide powder. After they are mixed evenly, turn on the spray system and spray the aforementioned 1 wt% concentration of polyvinylpyrrolidone solution onto the composite calcium hydroxide core in the chamber. The flow rate of the spray system is 5 mL / min. After the composite calcium hydroxide core microspheres are slightly moistened, continue to sprinkle composite calcium hydroxide powder into the chamber so that it coats the surface of the composite calcium hydroxide core microspheres. At this time, under the synergistic effect of powdering and spraying, the calcium hydroxide layer continuously thickens and the particle size increases accordingly. The particle size is continuously observed. After the particles grow to a certain size, they are removed and sieved through a standard sieve to retain the particles that reach the target size (700~800 μm). Particles that are too large are removed, and smaller particles are put back into the granulator to continue to grow larger, thus obtaining precursor particles.

[0035] (4) The precursor particles obtained by centrifugal granulation were placed in a muffle furnace and calcined at 900°C for 2 hours in air to obtain composite CaO particles. These particles were then acidified and calcined in a tube furnace under CO2 atmosphere for 1 hour to obtain composite CaCO3 products. The acidification and calcination temperature was 700°C. Sieving using a standard sieve revealed that the 700-800 μm precursor particles transformed into 600-700 μm composite calcium carbonate particles after calcination. The preparation process is as follows: Figure 1 As shown in (c);

[0036] Comparative Example 1

[0037] The control group used a more traditional extrusion-spheronization method to prepare composite calcium carbonate particles with a uniform structure. The specific steps are as follows:

[0038] (1) The preparation of composite calcium hydroxide powder is the same as in Example 1.

[0039] (2) Add water to the composite calcium hydroxide powder, adjust the composite calcium hydroxide powder to a suitable humidity (the water content is 10 wt% of the composite calcium hydroxide powder), and make the precursor mixture into composite calcium hydroxide granules by extrusion-spheronization granulator;

[0040] (3) The composite calcium hydroxide particles were calcined in air at 900°C for 2 hours to remove nitrate ions, moisture, microcrystalline cellulose, etc., to obtain composite calcium oxide particles with micron-nano ladder pore structure (the ladder pore structure is uniformly distributed and there is no core-shell structure).

[0041] (4) The above-mentioned composite calcium oxide particles were placed in a tube furnace and carbonated and calcined in a pure CO2 atmosphere for 1 hour. The carbonation and calcination temperature was set to 700°C to obtain composite calcium carbonate particles with a uniform stepped pore structure.

[0042] CT and SEM characterization were performed on the calcium carbonate particles obtained in Example 1 and Comparative Example 1, demonstrating their superior performance. The results are as follows: Figure 2 and 3 As shown. (Through) Figure 2 and 3 The SEM and CT morphology characterizations shown reveal that both types of particles exhibit a micron-nano tiered pore structure due to the use of transition metal doping and microcrystalline cellulose pore-forming agents. Compared to the uniformly distributed micron-nano pores in the particles prepared by the extrusion-spheronization method in Reference Document 1, the particles prepared in Example 1 based on this invention exhibit a distinct tiered pore structure, meaning that the inner core region has more and larger pores, while the outer layer is relatively dense. This invention refers to this structure, where the macroscopic tiered structure in the core-shell structure is coupled with the microscopic nano-micron tiered structure, as a multi-level tiered pore structure.

[0043] Thermogravimetric analysis (TGA) was performed on the calcium carbonate particles obtained in Example 1 and Comparative Example 1. Tests were conducted using small amounts of dispersed particles in both dispersed and packed states. The results are as follows: Figure 4 As shown.

[0044] like Figure 4 As shown, the decomposition temperature of the stepped porous structure particles in Example 1, whether in a dispersed or packed state, is 9 K and 17 K lower than that of the solid uniform particles prepared by the extrusion rounding method in Comparative Example 1.

[0045] The isothermal decomposition test of the calcium carbonate particles obtained in Example 1 and Comparative Example 1 at 800°C yielded the following results: Figure 5 As shown. By Figure 5 As can be seen, compared with the uniform particles in Comparative Example 1, the decomposition rate of the tiered porous particles in Example 1 is significantly faster. The peak reaction rate of the tiered porous particles in Example 1 reaches 1.504 K. -1 This represents an 8.62% increase compared to control 1.

[0046] The isothermal carbonation kinetics of the calcium carbonate particles obtained in Example 1 and Comparative Example 1 were tested at 800°C, and the results are as follows: Figure 6 As shown. By Figure 6 It can be seen that the reaction time of the stepped porous particles in Example 1 is significantly shorter than that of the uniform particles in Comparative Example 1, and the conversion rate of the stepped porous particles in Example 1 reaches 0.70 28.32% earlier.

[0047] The above results demonstrate that multi-level porous particles have significant kinetic advantages in thermal decomposition heat storage and carbonation heat release reactions.

[0048] The specific surface area of ​​the calcium carbonate particles obtained in Example 1 and Comparative Example 1 was measured, and the results are shown in Figure 7. The results indicate that the particles and powder prepared by the extrusion spheroidization method in Comparative Example 1 have a larger specific surface area. Furthermore, considering that both types of particles have the same proportion of transition metal doping and microcrystalline cellulose pore-forming agent, the specific surface area results demonstrate that it is indeed the multi-level ladder-like pore structure that causes the faster decomposition rate, rather than transition metal doping or micropores, thus proving the effectiveness of the novel structure proposed in this invention.

[0049] The calcium carbonate particles obtained in Example 1 and Comparative Example 1 were tested for key properties such as solar spectral absorptivity, heat storage and release cycle stability, and mechanical wear resistance. The results are as follows: Figure 8 As shown. By Figure 8 As shown in (a) to (b), due to the use of the same transition metal doping ratio, the particles of the two structures have similarly high solar spectral absorbance. Figure 8 As shown in (c), both types of particles also exhibit excellent heat storage and release cycle stability, with the heat storage density remaining essentially unchanged during 25 cycles.

[0050] In summary, based on the improvement of solar spectrum absorption capacity and heat storage and release cycle stability by transition metal element doping, and the construction of micron-nano ladder pores by pore-forming agent doping, the multi-level ladder pore structure particles and their preparation method proposed in this invention achieve a synergistic improvement of fast reaction rate, high heat storage density and the aforementioned performance.

Claims

1. A millimeter-sized thermal storage particle with a multi-level stepped pore structure, characterized in that, The millimeter-scale thermal storage particles are composite calcium carbonate particles, which have a core-shell structure on a macroscopic scale and a micron-nano tiered pore structure on a microscopic scale. The core-shell structure means that the core and outer layer of the millimeter-scale thermal storage particles have different porosities, that is, the inner core has multiple larger pores, and the outer shell has a relatively dense pore core with smaller pores.

2. The millimeter-sized thermal storage particles with a multi-level stepped pore structure according to claim 1, characterized in that, The particle size of the composite calcium carbonate particles is 600~700 μm.

3. The method for preparing millimeter-sized thermal storage particles with a multi-level stepped pore structure as described in claim 1 or 2, characterized in that, Includes the following steps: (1) Preparation of composite calcium hydroxide precursor powder; (2) Spray a binder solution onto the composite calcium hydroxide precursor powder. Under the action of the binder, the calcium hydroxide powder will grow together until the particle size reaches the target core diameter, thus obtaining the calcium hydroxide core. (3) Spray binder and calcium hydroxide powder onto the calcium hydroxide core to grow a shell on the outer layer of the calcium hydroxide core to obtain precursor particles; (4) The precursor particles are calcined in air and carbonized in a CO2 atmosphere.

4. The preparation method according to claim 3, characterized in that, In step (1), the preparation of the composite calcium hydroxide precursor powder includes the following steps: First, mix the micron-sized pore-forming agent with calcium hydroxide powder, add the transition metal element dopant solution, stir evenly, dry, and ball mill.

5. The preparation method according to claim 4, characterized in that, The micron-sized pore-forming agent is microcrystalline cellulose, foxtail grass, straw powder or charcoal powder, and the transition metal element dopant is a transition metal salt or transition metal oxide, wherein the transition metal element is one or more of Al, Zr, Mn, Fe, Co and Cu.

6. The preparation method according to claim 4, characterized in that, The mass-volume ratio of calcium hydroxide powder to micron-sized pore-forming agent is 100:10~100:60, and the molar ratio of transition metal dopant to calcium hydroxide is 100:5~100:

35. When using transition metal dopant, it is necessary to first prepare a solution with a molar concentration of 2~6 mol / L and mix it evenly with calcium hydroxide powder. After drying and crushing, it is prepared into composite calcium hydroxide precursor powder.

7. The preparation method according to claim 3, characterized in that, In steps (2) and (3), the adhesive is polyvinylpyrrolidone, the mass concentration of the adhesive solution is 1~5wt%, and the blowing temperature is set to 30°C~80°C.

8. The preparation method according to claim 3, characterized in that, In step (2), the diameter of the calcium hydroxide core is 400~450 μm. In step (3), the diameter of the precursor particles is 700~800 μm. The precursor particles mainly contain Al, which is used to improve stability. 3+ Zr 4 Mn 2+ Total concentration and Ca 2+ A concentration molar ratio of not less than 8:100 is used to improve the solar absorbance of Fe. 3+ Co 2+ and Cu 2+ Total concentration and Ca 2+ The molar ratio of concentrations shall not exceed 5:

100.

9. The preparation method according to claim 3, characterized in that, In step (4), the calcination conditions in air atmosphere are calcination at 600°C ~ 1000°C for more than 2 hours, and the carbonation conditions in CO2 atmosphere are calcination at 600°C ~ 800°C for more than 1 hour.

10. The application of millimeter-sized thermal storage particles with a multi-level stepped pore structure as described in claim 1 or 2 in solar chemical thermal storage.

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