Modified calcium-based thermochemical heat storage material and preparation and performance regeneration method thereof

Abstract

This invention discloses a method for modifying and regenerating the performance of a calcium-based thermochemical thermal storage material. The modified calcium-based material obtained exhibits high cycle stability and energy storage density even at high temperatures, especially after long periods of heat storage and release cycles. The regeneration method of this invention uses citric acid to dissolve the microscopic sintering morphology of the calcium-based thermal storage material, restoring its porous structure and achieving material morphology reconstruction. Furthermore, the regenerated thermal storage material has a small grain size and improved specific surface area and pore volume. Since the modified calcium-based thermal storage material prepared by this invention inherently possesses high cycle stability, maintaining high heat storage and release performance even after 100 cycles, combined with the performance regeneration method of this invention, it is expected to achieve thousands of stable cycles for the calcium-based thermochemical thermal storage material, thereby promoting the practical application of thermochemical thermal storage.

Description

Technical Field

[0001] This invention belongs to the field of thermochemical energy storage materials technology, specifically relating to a method for modifying and regenerating the performance of a calcium-based thermochemical heat storage material. Background Technology

[0002] High-temperature heat collected using solar thermal technology holds promise for replacing traditional fossil fuels and meeting the demand for high-grade heat sources in industrial production and the power industry. However, solar thermal utilization suffers from drawbacks such as volatility, intermittency, and instability, necessitating the integration of efficient thermal storage technologies to achieve continuous and stable energy output.

[0003] Compared to sensible heat storage and phase change heat storage, thermochemical heat storage has advantages such as a wide temperature range, storage across time and space, and low heat loss. Furthermore, the heat storage density of most thermochemical heat storage systems is far higher than that of sensible heat storage and phase change heat storage. It is one of the most promising high-temperature heat storage methods for concentrated solar power.

[0004] Among numerous thermochemical energy storage systems, the CaCO3 / CaO system possesses the advantages of high temperature range, high energy density, low cost, and safety without pollution, with a theoretical energy density as high as 1780 kJ / kg. However, with the increase in the number of heat storage and release cycles, particle sintering leads to a rapid decline in the energy storage performance of calcium-based materials, resulting in poor cycle stability. This severely restricts the practical application of calcium-based thermochemical heat storage materials. Although many studies have improved the cycle stability of CaCO3 / CaO, its performance still declines in the later stages of cycling. Considering the inherent property of high-temperature sintering of calcium-based materials, it is difficult to maintain high heat storage and release performance through modification. Therefore, it is urgent to activate the sintered material after cycling to meet the needs of large-scale industrial application of the CaCO3 / CaO thermochemical heat storage system. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0006] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0007] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a modified calcium-based thermochemical heat storage material.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: including a calcium-based material with calcium nitrate tetrahydrate as a precursor, and a modifier Al2O3 with aluminum nitrate nonahydrate as a precursor and a modifier MgO with anhydrous magnesium chloride as a precursor;

[0009] The modified calcium-based thermochemical heat storage material comprises, by molar percentage, 70-95 parts of calcium-based material and 5-30 parts of modifier.

[0010] Another objective of this invention is to overcome the shortcomings of the prior art and provide a method for preparing modified calcium-based thermochemical thermal storage materials.

[0011] To solve the above-mentioned technical problems, the present invention provides the following technical solution: including,

[0012] As a preferred embodiment of the preparation method of the calcium-based thermochemical heat storage material of the present invention, wherein: the precursor of the calcium-based material and the organic acid are dissolved in anhydrous ethanol and stirred to obtain solution A;

[0013] The precursors of modifier Al2O3 and MgO are dissolved in anhydrous ethanol and stirred to obtain solution B;

[0014] Solution A and solution B are mixed and heated with stirring until the solution becomes gel-like;

[0015] The gel-like product was vacuum dried and then ground into powder. It was then pyrolyzed at high temperature and cooled to obtain a modified calcium-based thermochemical heat storage material.

[0016] The precursor of the calcium-based material is calcium nitrate tetrahydrate, the precursor of the modifier Al2O3 is aluminum nitrate nonahydrate, and the precursor of the modifier MgO is anhydrous magnesium chloride.

[0017] In a preferred embodiment of the preparation method of the modified calcium-based thermochemical heat storage material of the present invention, the organic acid includes one or more of citric acid, gluconic acid, and glacial acetic acid, and the molar ratio of the precursor of the calcium-based thermochemical heat storage sintering material to the organic acid is 1:0.5-2.

[0018] In a preferred embodiment of the preparation method of the modified calcium-based thermochemical heat storage material of the present invention, the heating and stirring are carried out at a stirring speed of 300-400 rpm and a stirring temperature of 100-200℃.

[0019] In a preferred embodiment of the preparation method of the modified calcium-based thermochemical heat storage material of the present invention, the vacuum drying is carried out at a temperature of 120–240°C for a time of 180–300 min.

[0020] In a preferred embodiment of the preparation method of the modified calcium-based thermochemical thermal storage material of the present invention, the high-temperature pyrolysis is to raise the temperature to 700-900°C at a rate of 1-10°C / min and hold it at that temperature for 0.5-2 hours.

[0021] Another objective of this invention is to overcome the shortcomings of the prior art and provide a method for regenerating modified calcium-based thermochemical thermal storage materials.

[0022] To solve the above-mentioned technical problems, the present invention provides the following technical solution: including,

[0023] The modified calcium-based thermochemical thermal storage material that needs to be regenerated is mixed with organic acid, and then subjected to magnetic stirring, vacuum drying, and high-temperature calcination to achieve the performance regeneration of the modified calcium-based thermochemical thermal storage material.

[0024] The calcium-based chemical thermal storage material that needs to be regenerated includes modified calcium-based thermochemical thermal storage material that has been sintered after thermal storage and release cycles.

[0025] As a preferred embodiment of the performance regeneration method for the modified calcium-based thermochemical thermal storage material of the present invention, the organic acid includes one or more of citric acid, gluconic acid, and glacial acetic acid.

[0026] The molar ratio of the modified calcium-based thermochemical heat storage material to the organic acid is 1:0.5-2.

[0027] As a preferred embodiment of the performance regeneration method for the modified calcium-based thermochemical thermal storage material of the present invention, the stirring speed of the magnetic stirring is 300-400 rpm and the stirring temperature is 100-200℃.

[0028] The vacuum drying temperature is 120–240°C, and the drying time is 180–300 min.

[0029] As a preferred embodiment of the performance regeneration method for the modified calcium-based thermochemical thermal storage material described in this invention, the high-temperature calcination involves heating to 700-900°C at a rate of 1-10°C / min and holding at that temperature for 0.5-2 hours.

[0030] Beneficial effects of this invention:

[0031] (1) The modified calcium-based material provided by the present invention still has high cycle stability and energy storage density after long-term heat storage and release cycles under high temperature conditions. The energy storage density after 100 heat storage and release cycles is 2.8 times that of the unmodified material.

[0032] (2) The present invention improves the energy storage density of sintered modified calcium-based materials from 574.9 kJ / kg to 1136.7 kJ / kg through the performance regeneration method. That is, the energy storage density after performance regeneration is 1.98 times that of the original. Moreover, the sintered modified calcium-based materials still have high cycle stability in 100 heat storage and release cycles after regeneration.

[0033] (3) The regeneration method of the present invention uses citric acid to dissolve the microscopic sintering morphology of calcium-based thermal storage material, thereby restoring the porous structure of the calcium-based material and realizing the reconstruction of the material morphology. Moreover, the thermal storage material after performance regeneration has a small grain size and improved specific surface area and pore volume.

[0034] (4) Since the modified calcium-based thermal storage material prepared by the present invention has high cycling stability and still maintains high thermal storage and release performance after 100 cycles, and with the performance regeneration method of the present invention, it is expected to achieve thousands of stable cycles of calcium-based thermochemical thermal storage material, thereby promoting the practical application of thermochemical thermal storage. Attached Figure Description

[0035] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0036] Figure 1 This is a comparison chart of the cycling performance of the two materials under mild heat storage and release conditions in Example 7 of the present invention.

[0037] Figure 2 This is a comparison chart of the cycling performance of the two materials under harsh heat storage and release conditions in Example 7 of the present invention.

[0038] Figure 3 This is a diagram showing the improvement in the effective conversion rate of the two materials after performance regeneration in Example 8 of the present invention.

[0039] Figure 4 This is a comparison chart of the instantaneous conversion rates of the carbonation reaction of the two materials after performance regeneration in Example 8 of the present invention.

[0040] Figure 5 This is a diagram showing the evolution of the microstructure of the two materials before and after performance regeneration in Example 8 of the present invention.

[0041] Figure 6 This is a performance comparison diagram of the present invention before and after performance regeneration and in subsequent cycles in Embodiment 8.

[0042] Figure 7 This is a comparison diagram of the performance of the material in Comparative Example 2 of the present invention before and after steam regeneration and subsequent cycles. Detailed Implementation

[0043] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0044] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0045] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0046] The energy storage density described in this embodiment of the invention is calculated based on the theoretical maximum energy storage density of pure CaCO3 material (1780 kJ / kg). The formulas for calculating the effective conversion rate and energy storage density are as follows:

[0047]

[0048]

[0049] Among them, X ef，N E represents the effective conversion rate of the material after the Nth cycle. g，N The energy density of the material after the Nth cycle is represented by m. car，N With m cal，N Let represent the sample mass after the Nth carbonation and the sample mass after the Nth calcination, respectively. Let ΔH represent the molar masses of CaO, CO2, and CaCO3, respectively. r This represents the standard decomposition enthalpy of CaCO3 (1780 kJ / kg).

[0050] In this embodiment of the invention, a surface area and porosity analyzer (Autosorb-IQ3) was used to test the particle size distribution of the corresponding materials at the micron level. A Da Vinci XRD apparatus was used to analyze the phase composition of the corresponding materials using X-ray diffraction (XRD) at room temperature. A Gemini300 instrument was used for scanning electron microscopy (SEM) to observe the changes in the microstructure of the corresponding materials before and after cycling.

[0051] In this invention, a calcination / carbonation cycle test is conducted on the material using a simultaneous thermal analyzer (STA8000, PerkinElmer). This test method can also be used to rapidly sinter calcium-based thermochemical heat storage materials, wherein:

[0052] The mild heat storage and release cycle conditions are: calcination at 800℃ in N2 atmosphere for 5 min, and carbonation at 750℃ in CO2 atmosphere for 10 min;

[0053] The stringent heat storage and release cycle conditions are: calcination at 950℃ in a CO2 atmosphere for 10 minutes, and carbonation at 750℃ in a CO2 atmosphere for 10 minutes.

[0054] The commercial calcium carbonate used in the embodiments of this invention was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; anhydrous citric acid, anhydrous ethanol, calcium nitrate tetrahydrate, and aluminum nitrate nonahydrate were purchased from Sinopharm Chemical Reagent Co., Ltd.; anhydrous magnesium chloride was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; and deionized water was purchased from Beijing Innocare Technology Co., Ltd. Unless otherwise specified, all raw materials used were of analytical grade.

[0055] Example 1

[0056] Weigh 1000 mg of calcium nitrate tetrahydrate and 813.6 mg of anhydrous citric acid, dissolve them in an appropriate amount of anhydrous ethanol, and stir with a glass rod to prepare solution 1.

[0057] Weigh 198.6 mg of aluminum nitrate nonahydrate and 50.4 mg of anhydrous magnesium chloride, dissolve them in an appropriate amount of anhydrous ethanol, and stir with a glass rod to prepare solution 2.

[0058] Mix solutions 1 and 2 in a beaker, add a small amount of deionized water, place the beaker on a magnetic stirrer and heat it at 400 rpm at 100°C until the solution becomes gel-like.

[0059] The gel was placed in a vacuum drying oven and dried at 180°C for 240 minutes.

[0060] The dried sample was thoroughly ground into powder using a mortar and pestle and placed in a muffle furnace. The temperature was increased from 30°C to 800°C at a rate of 2°C / min and maintained at 800°C for 60 min, followed by natural cooling to room temperature.

[0061] An AlMg-modified calcium-based material was prepared and named CaNCA-AlMg.

[0062] Example 2

[0063] This embodiment is based on Example 1, except that the modifier precursor aluminum nitrate nonahydrate is changed to tetrabutyl titanate, and other process conditions are the same as in Example 1.

[0064] TiMg-modified calcium-based material was prepared and named CaNCA-TiMg.

[0065] Example 3

[0066] This embodiment is based on Example 1, except that the modifier precursor anhydrous magnesium chloride is changed to tetrabutyl titanate, and other process conditions are the same as in Example 1.

[0067] TiAl-modified calcium-based material was prepared and named CaNCA-TiAl.

[0068] Example 4

[0069] This comparative example is based on Example 1, except that the precursor material of the modifier is only aluminum nitrate nonahydrate, and other process conditions are the same as in Example 1.

[0070] An Al-modified calcium-based material was prepared and named CaNCA-Al.

[0071] Example 5

[0072] This comparative example is based on Example 1, except that the precursor material of the modifier is only tetrabutyl titanate, and other process conditions are the same as in Example 1.

[0073] A Ti-modified calcium-based material was prepared and named CaNCA-Ti.

[0074] Example 6

[0075] This comparative example is based on Example 1, except that the precursor material for the modifier is only anhydrous magnesium chloride, and the other process conditions are the same as in Example 1.

[0076] Ti-modified calcium-based material was prepared and named CaNCA-Mg.

[0077] The calcium-based materials prepared in Examples 1 to 6 were subjected to 100 cycles of mild heat storage and release cycling. The results are shown in Table 1.

[0078] Table 1. Different calcium-based modified materials ratios and their corresponding energy storage performance

[0079]

[0080]

[0081] The above results indicate that the CaNCA-AlMg material prepared from calcium nitrate tetrahydrate, aluminum nitrate nonahydrate, and anhydrous magnesium chloride, i.e., the material described in Example 1, has a maximum conversion rate X. ef,max The CaNCA-AlMg material exhibits the highest conversion rate and stability after 100 cycles, and the best energy storage effect. Therefore, the following study uses CaNCA-AlMg material as the regeneration target.

[0082] Example 7

[0083] In this embodiment, the CaNCA-AlMg material prepared in Example 1 was subjected to high-temperature cycling to test its heat storage and release performance under different conditions, with commercial calcium carbonate CaCO3 as a control.

[0084] The materials were subjected to 100 calcination / carbonation cycles in a synchronous thermal analyzer under mild heat storage and release conditions. A comparison of the cycle performance of the two materials is attached. Figure 1 As shown, the effective conversion rate of CaCO3 in the first cycle was 69.7%, corresponding to an energy storage density of 1240.7 kJ / kg. However, with the increase of the number of cycles, the effective conversion rate decreased rapidly, dropping to 23.5% after 100 cycles, corresponding to an energy storage density of 418.3 kJ / kg. The effective conversion rate of CaNCA-AlMg in the first cycle was 64.7%, corresponding to an energy storage density of 1153.4 kJ / kg. However, it had high cycle stability throughout the cycle process, with an effective conversion rate of 61.5% after 100 cycles, corresponding to an energy storage density of 1094.7 kJ / kg.

[0085] Since harsh heat storage and release conditions are more likely to cause material sintering, in order to further compare the performance differences between the two materials, the unmodified material CaCO3 and the modified material CaNCA-AlMg described in Example 1 were subjected to 50 calcination / carbonation cycles in a simultaneous thermal analyzer. The cycle conditions were set to harsh heat storage and release conditions. The comparison of the cycle performance of the two materials is attached. Figure 2 As shown, the effective conversion rate of CaCO3 in the first cycle was 68.2%, corresponding to an energy storage density of 1214.0 kJ / kg. Under harsh cycling, the effective conversion rate dropped sharply, decreasing to 14.0% after 50 cycles, corresponding to an energy storage density of 249.2 kJ / kg. The effective conversion rate of CaNCA-AlMg in the first cycle was 67.1%, corresponding to an energy storage density of 1194.4 kJ / kg. However, the effective conversion rate also decreased under harsh cycling, reaching 54.6% after 50 cycles, corresponding to an energy storage density of 971.9 kJ / kg.

[0086] The results above show that although the heat storage and release performance of both materials decreased, the performance of commercial calcium carbonate (CaCO3) material showed a more significant decline.

[0087] Example 8

[0088] This embodiment describes the performance regeneration of thermochemical thermal storage materials that require regeneration.

[0089] Weigh out 500 mg each of commercial calcium carbonate (CaCO3) and modified material (CaNCA-AlMg), and prepare sintered CaCO3 and modified material (CaNCA-AlMg) by 50 cycles of calcination / carbonation in a tubular furnace under harsh heat storage and release conditions. These are named CaCO3-S and CaNCA-AlMg-S, respectively, and are the thermochemical heat storage materials that need to be regenerated.

[0090] 400 mg of CaCO3-S was mixed with 768.4 mg of anhydrous citric acid, dissolved in deionized water, and stirred thoroughly. The mixture was then placed on a magnetic stirrer and heated at 400 rpm at 100 °C until it evaporated to dryness. The dried sample was placed in a vacuum drying oven at 180 °C for 240 min. The dried sample was then thoroughly ground into powder using a mortar and pestle and placed in a muffle furnace. The temperature was increased from 30 °C to 800 °C at a rate of 2 °C / min and maintained at 800 °C for 60 min, followed by natural cooling to room temperature. The resulting sintered unmodified material after performance regeneration was named CaCO3-SR.

[0091] 400 mg of the sintered modified material CaNCA-AlMg-S was mixed with 768.4 mg of anhydrous citric acid, dissolved in deionized water, and stirred thoroughly. The mixture was then placed on a magnetic stirrer and heated at 400 rpm at 100 °C until it evaporated to dryness. The dried sample was placed in a vacuum drying oven at 180 °C for 240 min. The dried sample was then thoroughly ground into powder using a mortar and pestle and placed in a muffle furnace. The temperature was increased from 30 °C to 800 °C at a rate of 2 °C / min and maintained at 800 °C for 60 min, followed by natural cooling to room temperature. The sintered modified material with regenerated properties was obtained and named CaNCA-AlMg-SR.

[0092] The sintered unmodified material CaCO3-S and modified material CaNCA-AlMg-S underwent a single calcination / carbonation test in a simultaneous thermal analyzer, with mild heat storage and release conditions set to determine their effective conversion rate and energy storage density. Simultaneously, the regenerated CaCO3-SR and CaNCA-AlMg-SR under the same conditions were subjected to another calcination / carbonation test to determine their effective conversion rate and energy storage density. Comparative analysis reflects the performance activation effect of this invention.

[0093] The improved conversion efficiency of the two materials after performance regeneration is shown in the attached figure. Figure 3 As shown, the instantaneous conversion rate of its carbonation reaction is compared with that in the attached figure. Figure 4As shown, after sintering the materials through 50 rigorous thermal cycles, the effective conversion rate of the prepared CaCO3-S was only 20.1%, corresponding to a storage energy density of 357.8 kJ / kg; the effective conversion rate of CaNCA-AlMg-S was 32.3%, corresponding to a storage energy density of 574 kJ / kg; after performance regeneration, the effective conversion rate of the unmodified material CaCO3-SR was 84.7%, corresponding to a storage energy density of 1508.1 kJ / kg, an increase of 422% compared to before performance regeneration; the effective conversion rate of the modified material CaNCA-AlMg-S was 63.9%, corresponding to a storage energy density of 1136.7 kJ / kg, an increase of 198% compared to before performance regeneration.

[0094] according to Figure 4 The carbonation reaction curves show that the conversion rate of the two materials before performance regeneration hardly increased in the slow reaction stage, indicating that pore blockage was caused by sintering. After performance regeneration, the conversion rate of both materials not only increased significantly in the fast reaction stage, but also showed a significant upward trend in the slow reaction stage. This indirectly reflects that both materials have a complex porous structure after performance regeneration, which promotes the heat storage and release reaction. In summary, the performance regeneration method adopted in this invention can effectively improve the performance of sintered materials.

[0095] Phase analysis, microstructure analysis and pore structure analysis were performed on calcium-based materials CaCO3-S and CaCO3-SR after performance regeneration to reveal their performance regeneration mechanism.

[0096] Based on the phase analysis results, the grain size was determined by the full width at half maximum (FWHM) of the X-ray diffraction peaks. The results showed that the grain size of CaCO3-S was 92.8 nm, while the grain size of CaCO3-SR after performance regeneration decreased to 56.9 nm, indicating that the performance regeneration process significantly reduced the grain size. The smaller grain size has a certain inhibitory effect on the sintering of the material, thereby improving its heat storage and release performance.

[0097] Based on the pore structure analysis results, the specific surface area, specific pore volume, and pore size of CaCO3-S are 0.807 m² / s. 2 / g, 0.008cm 3 / g and 1.934nm; while the specific surface area, specific pore volume, and pore size of the regenerated CaCO3-SR increased to 3.382m. 2 / g, 0.039cm 3 / g and 3.828nm. This indicates that the performance regeneration process restores the material's porous structure, allowing the gas-solid reaction to proceed more fully, thereby improving the material's heat storage and release performance.

[0098] The microstructure evolution of CaCO3-S and CaNCA-AlMg-S before and after performance regeneration was further analyzed, as shown in the attached figure. Figure 5 As shown. Figure 5 (a) shows CaCO3-S before performance regeneration. It can be seen that the sintered CaCO3-S is blocky with almost no pores, indicating that the particles are severely agglomerated and the pores are blocked. Figure 5 (b) indicates that after performance regeneration, CaCO3-SR forms a porous structure with abundant pores, providing sufficient contact area and mass transfer channels for gas-solid reactions, thereby improving the effective conversion rate of the material; Figure 5 (c) represents CaNCA-AlMg-S before performance regeneration. Although the material also has a certain degree of sintering, it still has some pore structure, indicating that AlMg modification has an anti-sintering effect, so that the material still maintains a certain pore structure and slows down the degree of performance degradation. Figure 5 (d) shows the regenerated CaNCA-AlMg-SR, demonstrating the formation of a complex hierarchical porous structure that enhances its thermal storage and release performance. Furthermore, AlMg modification enables the material to maintain its porous structure during subsequent thermal storage and release cycles, thus ensuring high cycling stability. Therefore, the performance regeneration method employed in this invention can reconstruct the microstructure of both unmodified and modified materials, restoring their porous structure and thereby improving their thermal storage and release performance.

[0099] Example 9

[0100] Subsequent cycle tests were conducted on the CaCO3-SR and CaNCA-AlMg-SR regenerated in Example 8 of the present invention to measure the subsequent cycle stability of the regenerated materials.

[0101] One hundred calcination / carbonation cycles were performed in a synchronous thermal analyzer under mild heat storage and release conditions. The performance comparison of the two materials before and after performance regeneration and in subsequent cycles is attached. Figure 6 As shown in the figure, cycle 0 represents the heat storage and release performance data of CaCO3-S and CaNCA-AlMg-S before performance regeneration. Although CaCO3-S achieved an effective conversion rate as high as 84.7% in the first cycle, the material struggled to maintain its pore structure due to the lack of a modifier. With increasing cycle count, sintering intensified, and the effective conversion rate rapidly decreased, dropping to 25.6% after 100 cycles. CaNCA-AlMg achieved an effective conversion rate of 63.9% in the first cycle and 50.7% after 100 cycles. AlMg modification ensured a strong interaction between the calcium-based material and the inert material in the modifier, inhibiting grain growth and pore blockage, thus maintaining a certain level of cycle stability after performance regeneration.

[0102] Example 10

[0103] In this embodiment, different types and concentrations of organic acids were used to treat sintered modified calcium-based materials to investigate the effect of regeneration conditions on regeneration effect. The variables are set as shown in Table 2.

[0104] Table 2 Different regeneration conditions settings

[0105]

[0106] The regenerated materials CaNCA-AlMg-SR-C1, CaNCA-AlMg-SR-A1, and CaNCA-AlMg-SR-G1 were subjected to one heat storage and release cycle to test their regeneration effect. The results showed that, compared to citric acid, using glacial acetic acid or gluconic acid as the organic acid for performance regeneration resulted in a decrease in the effective conversion rate of the regenerated materials. This mainly depends on the degree to which the organic acid dissolves the calcium-based sintered material and the sufficiency of the high-temperature pyrolysis process. According to the chemical formula, calcium gluconate has the highest O2 requirement for combustion, while calcium citrate has the lowest. Therefore, at the same temperature and combustion time, calcium citrate burns more completely, forming the most developed pore structure, while calcium gluconate or calcium acetate, due to their difficulty in complete combustion, have underdeveloped pore structures and poorer energy storage performance after regeneration.

[0107] The above comparative experiments show that citric acid is suitable as a performance regenerator for calcium-based sintered materials, but the content of citric acid needs further optimization. The CaNCA-AlMg-SR-C1, CaNCA-AlMg-SR-C0.5, and CaNCA-AlMg-SR-C2 described in Table 2 were subjected to one heat storage and release cycle to test their regeneration effect. The results show that CaNCA-AlMg-SR-C1 has the highest effective conversion rate, i.e., Ca... 2+ The optimal molar mixing ratio with citric acid is 1:1. When the citric acid content is too low, the calcium-based sintered material does not dissolve sufficiently in citric acid, resulting in insufficient pore structure formation during morphology reconstruction and thus a decrease in effective conversion rate. When the citric acid content is too high, the excess citric acid will release a large amount of heat through pyrolysis at high temperatures. The resulting high temperature accelerates the growth of CaO grains, causing the pores formed by gas escape during morphology reconstruction to be re-blocked, thereby reducing its effective conversion rate.

[0108] Comparative Example 1

[0109] This invention provides another recycling method to demonstrate the superiority of the recycled materials and recycling method of this invention.

[0110] Weigh 240 mg of nano-sized CaCO3 and 460.8 mg of anhydrous citric acid, dissolve them in a beaker containing 20 mL of anhydrous ethanol, and stir with a glass rod to obtain the first solution.

[0111] Weigh 12.7 mg of anhydrous MgCl2 and measure 1.3 mL of tetrabutyl titanate solution. Mix the two and dissolve them in a beaker containing 10 mL of anhydrous ethanol. Stir with a glass rod to prepare a second solution.

[0112] The first and second solutions were placed in an ultrasonic dispersion cleaner and ultrasonically treated for 30 minutes each at an ultrasonic frequency of 40 kHz. The two ultrasonically dispersed solutions were then mixed, and deionized water was added dropwise to the mixed solution while stirring with a glass rod.

[0113] The beaker containing the mixed solution was placed on a magnetic stirrer and heated at 400 rpm. The mixture was stirred at 80°C for 100 min to ensure thorough mixing and evaporation. The sample was then thoroughly ground into powder using a mortar and pestle and placed in a muffle furnace for constant calcination at 700°C in an air atmosphere for 1 h. The resulting material was named nanoCaCA-TiMg.

[0114] NanoCaCA-TiMg was weighed and subjected to 50 calcination / carbonation cycles in a tube furnace under harsh heat storage and release conditions to prepare sintered nanoCaCA-TiMg, which was named nanoCaCA-TiMg-S. Its performance was then regenerated using a steam regeneration method.

[0115] The nanoCaCA-TiMg-S sample was placed in a vacuum drying oven and heated for 240 min at 180°C under a steam atmosphere, followed by a further 240 min under a vacuum atmosphere to ensure thorough drying. The dried sample was then thoroughly ground into powder using a mortar and pestle and placed in a muffle furnace. The temperature was increased from 30°C to 800°C at a rate of 2°C / min and maintained at 800°C for 60 min. It was then allowed to cool naturally to room temperature, yielding the steam-regenerated material, named nanoCaCA-TiMg-SR.

[0116] One hundred calcination / carbonation cycles were performed in a synchronous thermal analyzer under mild heat storage and release conditions. The performance comparison of the material before and after steam regeneration and in subsequent cycles is attached. Figure 7 As shown.

[0117] It can be seen that the effective conversion rate increased from 53.4% ​​to 63.9% after steam regeneration, but the stability was poor in subsequent cycles, dropping to 33.1% after 100 cycles. This indicates that the performance of nanoCaCA-TiMg is worse than that of the CaNCA-AlMg material described in Example 1, and also that the steam regeneration method has limited regeneration effect on the material, lower than the citric acid regeneration method described in Example 3.

[0118] In summary, the performance regeneration method of this invention is simple to operate and low in cost. Combined with AlMg modification to improve the energy storage density and stability of the material in 100 cycles, it is expected to achieve thousands of stable cycles for calcium-based thermochemical thermal storage materials, thereby promoting the practical application of thermochemical thermal storage.

[0119] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a modified calcium-based thermochemical heat storage material, characterized in that: include, The precursor of the calcium-based material and an organic acid were dissolved in anhydrous ethanol and stirred to obtain solution A; The precursors of modifier Al2O3 and MgO are dissolved in anhydrous ethanol and stirred to obtain solution B; Solution A and solution B are mixed and heated with stirring until the solution becomes gel-like; The gel-like product was vacuum dried and then ground into powder. It was then pyrolyzed at high temperature and cooled to obtain a modified calcium-based thermochemical heat storage material. The precursor of the calcium-based material is calcium nitrate tetrahydrate, the precursor of the modifier Al2O3 is aluminum nitrate nonahydrate, and the precursor of the modifier MgO is anhydrous magnesium chloride. Based on the molar percentages of the modified calcium-based thermochemical heat storage material, the calcium-based material comprises 70-95 parts, and the modifier comprises 5-30 parts; The modified calcium-based thermochemical thermal storage material is sintered after thermal storage and release cycles. It is then mixed with citric acid at a molar ratio of 1:1, followed by magnetic stirring, vacuum drying, and high-temperature calcination to achieve performance regeneration. The high-temperature calcination involves heating to 700-900°C at a rate of 1-10°C / min and holding at that temperature for 0.5-2 hours.

2. The preparation method of the modified calcium-based thermochemical heat storage material as described in claim 1, characterized in that: The molar ratio of the precursor to the organic acid in the calcium-based chemical thermal storage sintering material is 1:0.5~2.

3. The preparation method of the modified calcium-based thermochemical heat storage material as described in claim 1, characterized in that: The heating and stirring process involves a stirring speed of 300-400 rpm and a stirring temperature of 100-200℃.

4. The preparation method of the modified calcium-based thermochemical heat storage material as described in claim 1, characterized in that: The gel-like product is vacuum dried and then ground into powder, wherein the drying temperature is 120~240℃ and the drying time is 180~300min.

5. The preparation method of the modified calcium-based thermochemical heat storage material as described in claim 1, characterized in that: The high-temperature pyrolysis involves heating to 700-900℃ at a rate of 1-10℃ / min and holding at that temperature for 0.5-2 hours.

6. The preparation method of the modified calcium-based thermochemical heat storage material as described in claim 1, characterized in that: The magnetic stirring speed of the modified calcium-based thermochemical heat storage material after sintering and mixing with citric acid after heat storage and release cycle is 300~400 rpm and the stirring temperature is 100~200℃. The drying temperature for vacuum drying is 120~240℃, and the drying time is 180~300min.

7. The modified calcium-based thermochemical thermal storage material prepared by the preparation method according to any one of claims 1 to 6.

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