Composite calcium-based heat storage material with stepped hole structure as well as preparation method and application of composite calcium-based heat storage material

Abstract

The invention discloses a composite calcium-based heat storage material with a stepped hole structure as well as a preparation method and application of the composite calcium-based heat storage material, and belongs to the technical field of energy storage materials. The particle is prepared from a precursor containing calcium hydroxide, a micron-sized microcrystalline cellulose pore-forming agent and an Al, Fe, Mn, Ce and Zr multi-element doping agent through hydrothermal pretreatment, extrusion-rolling forming, microwave-assisted calcination, high-temperature calcination and carbonation treatment. The particle has a nano-micron stepped hole structure, and through the synergistic effect of multi-element doping and the hole structure, the solar spectrum absorptivity (gt; 85%), cycling stability (25 times of cycling conversion rate attenuation lt; 2%), reaction rate and mechanical strength, is suitable for an 800 DEG C high-temperature solar energy direct-driven heat storage system, and has the advantages of cheap raw materials, greenness and environmental protection, and good application prospect.

Description

Technical Field

[0001] This invention relates to the field of energy storage materials technology, specifically to a composite calcium-based thermal storage material with a stepped pore structure, its preparation method, and its application. Background Technology

[0002] Solar energy, due to its cleanliness and renewability, is an ideal choice for addressing the energy crisis and climate change. However, the inherent intermittency and instability of solar radiation severely restrict its large-scale application. Therefore, developing efficient and low-cost thermal energy storage technologies to convert unstable solar energy into a stable and adjustable form of energy is crucial. In applications such as concentrated solar power (CSP), storing captured solar thermal energy is an ideal way to achieve this goal.

[0003] Currently, molten salt sensible heat storage technology has become the most commercially viable and widely used thermal storage solution due to its simple principles, mature processes, and readily available materials. However, a core limitation of this technology is that the maximum applicable temperature of commonly used molten salts is approximately 550℃. Exceeding this limit can easily lead to thermal decomposition and corrosion, posing safety risks. The peak efficiency record of existing butterfly-Stirling solar thermal power generation demonstration systems is 30%. This relatively low photothermal conversion efficiency is one of the key factors hindering the large-scale promotion of solar thermal power generation globally. Currently, the working fluid inlet temperature range of the thermodynamic cycle system is 500℃ to 540℃. Research shows that raising this temperature to 600 to 700℃ would significantly optimize the thermodynamic cycle process and improve the overall efficiency of the entire solar thermal power generation system. This places new demands on the thermal storage system to operate stably at high temperatures of 600℃ to 700℃. Simultaneously, to achieve high-efficiency power generation, the thermal storage system must also possess characteristics of low heat loss and high thermal storage efficiency. Among numerous thermal energy storage solutions, calcium-based materials have demonstrated great potential in the field of thermochemical thermal energy storage due to their advantages such as high thermal energy density, high operating temperature, and readily available and inexpensive raw materials. However, pure calcium carbonate materials suffer from drawbacks such as weak spectral absorption capacity, low mechanical strength and fragility, and insufficient cycle stability, making it difficult to meet the stringent requirements of efficient solar direct-drive thermochemical thermal energy storage systems. Therefore, there is an urgent need in this field for a new technical solution that can improve the solar spectral absorption capacity, cycle stability, and mechanical strength of calcium-based thermal energy storage materials, thereby promoting the practical application of solar direct-drive thermochemical thermal energy storage technology. Summary of the Invention

[0004] The purpose of this invention is to provide a composite calcium-based thermal storage material with a tiered pore structure, its preparation method, and its application. By doping to construct a stable framework, creating pores to optimize the transport path, and shaping to enhance mechanical properties, a thermal storage material with high cycle stability, high photothermal conversion efficiency, high reaction rate, and high mechanical strength is obtained. This solves the problems existing in calcium-based thermal storage materials in the above-mentioned technical background and improves the comprehensive performance of composite calcium-based materials.

[0005] To achieve the above objectives, the present invention provides a method for preparing a composite calcium-based thermal storage material with a tiered pore structure, wherein the composite calcium-based thermal storage material is prepared by calcination and carbonation of precursor particles containing Ca(OH)2, a pore-forming agent and a multi-element dopant.

[0006] The multi-element dopants are compounds each containing Al, Fe, Mn, Ce, and Zr elements; the heat storage particles have a nano-micron ladder-pore structure.

[0007] Preferably, the metal cations in the multi-component dopant react with Ca. 2+ The molar ratio is: Ca 2+ :Al 3+ :Fe 3+ :Mn 2+ :Ce 3+ :Zr 4+ =100:(8-12):(6-10):(4-6):(2-4):(1-3).

[0008] Preferably, the mass ratio of pore-forming agent to calcium hydroxide is (30-50):100, wherein the pore-forming agent is micron-sized microcrystalline cellulose.

[0009] Preferably, it includes the following steps:

[0010] Step S1: Mix Ca(OH)2, pore-forming agent and multi-element dopant, and add deionized water to make a mixed slurry;

[0011] Step S2: Perform hydrothermal pretreatment on the mixed slurry obtained in step S1;

[0012] Step S3: Adjust the moisture content of the product obtained in step S2 to 10wt%-60wt%, and obtain spherical precursor particles by extrusion-spheronization.

[0013] Step S4: The precursor particles obtained in step S3 are first subjected to microwave-assisted calcination, and then subjected to high-temperature calcination.

[0014] Step S5: The calcined product obtained in step S4 is subjected to carbonation treatment under a CO2 atmosphere to obtain the composite calcium-based thermal storage material.

[0015] Preferably, in step S2, the hydrothermal pretreatment temperature is 100-150℃ and the time is 1-4h.

[0016] Preferably, in step S4, the microwave-assisted calcination temperature is 400-600℃ and the time is 20-40 min; the high-temperature calcination temperature is 800-1000℃ and the time is 1-3 h.

[0017] Preferably, in step S5, the carbonation treatment temperature is 600-800℃ and the time is 0.5-2h.

[0018] The present invention also provides a composite calcium-based thermal storage material with a stepped pore structure prepared by the above preparation method.

[0019] This invention also provides the application of the above-mentioned composite calcium-based thermal storage material with a stepped pore structure in solar thermal storage.

[0020] This invention is based on calcium carbonate / calcium oxide cyclic thermochemical heat storage. Solar irradiation decomposes calcium carbonate into calcium oxide and carbon dioxide, converting light into chemical energy for storage. When energy needs to be released, calcium oxide reacts with carbon dioxide to form calcium carbonate, releasing heat. The basic calcium-based heat storage material is modified through the synergistic effect of multi-element doping, hierarchical porous structure design, and optimized preparation process.

[0021] Firstly, at the chemical composition level, multi-metal doping is key to improving the intrinsic properties of materials. Introduced elements such as aluminum and zirconium react with some calcium during high-temperature calcination to form high-melting-point inert ceramic phases (such as calcium aluminate and calcium zirconate). These ceramic phases act like tiny skeletons embedded in the calcium matrix, physically preventing the migration and merging of CaO grains at high temperatures. This significantly inhibits structural collapse and activity decay during repeated thermal cycling, thereby improving the material's thermal stability and cycle durability. Simultaneously, oxides of transition metals such as iron and manganese are excellent photothermal materials. Their introduction transforms the originally highly reflective white calcium carbonate into a dark composite material capable of efficiently absorbing a broad spectrum of sunlight. This significantly enhances the absorption capacity of the originally white, highly reflective calcium carbonate across the entire solar spectrum (especially the visible-near-infrared band), allowing the material to more efficiently convert focused solar energy into heat, directly driving the decomposition reaction of calcium carbonate. Furthermore, cerium, due to its unique oxygen storage and release capabilities, may help regulate the local chemical environment during the reaction process, further enhancing reaction kinetics and anti-aging properties.

[0022] Secondly, at the microstructural level, this invention ingeniously combines two pore-forming technologies: the decomposition of a pore-forming agent (microcrystalline cellulose) and microwave-assisted calcination. The micron-sized pore-forming agent, after combustion, leaves micron-sized macropores penetrating the particles. These channels act as diffusion pathways for carbon dioxide gas to enter and exit the particles, solving the problem of slow gas diffusion caused by product layer blockage. Microwave calcination promotes rapid evaporation of internal moisture and instantaneous crystal nucleation, resulting in abundant nanoscale pores. This provides a large specific surface area and numerous active sites for the decomposition / regeneration reaction of calcium carbonate. This nano-micron ladder-like pore structure synergistically optimizes mass and heat transfer efficiency during the reaction process and, by buffering the volume change stress during the reaction, simultaneously enhances the material's reactivity and mechanical strength.

[0023] Finally, at the manufacturing process level, this invention ensures that the material ultimately possesses excellent mechanical strength and performance through hydrothermal pretreatment and extrusion-spheronization granulation. The hydrothermal process promotes uniform mixing and pre-reaction of the components at the molecular level, laying the foundation for the formation of a uniform and stable composite structure. Furthermore, preparing the mixture into uniformly sized spherical particles facilitates the formation of regular packing in the actual thermal storage reactor, reduces airflow resistance, and provides sufficient mechanical strength to withstand bed pressure and wear, preventing pulverization and ensuring the long-term stable operation of the system.

[0024] Therefore, this invention provides a composite calcium-based thermal storage material with a stepped pore structure, its preparation method, and its application, which has the following beneficial effects:

[0025] (1) Improve cycle stability: The stable framework formed by multi-element doping can effectively prevent the migration and growth of CaO grains at high temperature, so that the material can still maintain high porosity and reactivity after multiple heat storage-heat release cycles.

[0026] (2) Enhanced solar spectrum absorption capacity: Fe, Mn and other dopants turn the originally white calcium-based material into a dark color, which greatly improves its absorption rate of sunlight, enabling efficient direct solar energy drive without the need for intermediate heat exchange fluid, reducing heat loss links, lowering costs, and improving the overall conversion efficiency of light-heat-chemical energy.

[0027] (2) Excellent reaction kinetics and heat storage density: The large nanoscale specific surface area provides abundant reaction sites; the ladder-pore structure ensures rapid CO2 transport. At the same time, by controlling the amount of dopant, the volume occupied by the inert framework is limited, and the volumetric heat storage density of the material is still much higher than that of sensible heat storage of molten salt.

[0028] (4) High mechanical strength: The stable ceramic composite structure formed by spherical granulation and high-temperature calcination gives the particles sufficient mechanical strength to resist wear and pressure drop in the reaction bed and prevent them from pulverizing. This ensures long-term stable operation in reactors such as fixed beds or moving beds and avoids powder clogging the system.

[0029] (5) High temperature heat storage: The high temperature stability of the calcium-based composite material after composite doping is further enhanced, and the working temperature can easily reach 800℃ or even higher.

[0030] (6) The raw materials are cheap and environmentally friendly: the main materials Ca(OH)2 (derived from limestone) and the pore-forming agent microcrystalline cellulose (derived from plants) are inexpensive and widely available, and the whole process does not involve toxic substances, which meets the core requirements of low cost and environmental friendliness for large-scale energy storage technology.

[0031] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0032] Figure 1 The images shown are SEM images of the composite calcium-based heat removal material prepared in Example 1 of this invention; (a) is a low-magnification SEM image with a scale bar of 20 μm; and (b) is a high-magnification SEM image with a scale bar of 2 μm. Detailed Implementation

[0033] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the invention should be considered equivalent substitutions and are included within the scope of protection of the invention. Furthermore, it should be understood that after reading the contents of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims and are all within the scope of protection of the invention.

[0034] In this document, references to embodiments mean that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0035] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0036] Unless otherwise specified, the reagents, instruments, and equipment used in this invention are all commonly used by those skilled in the art.

[0037] Example 1

[0038] This embodiment provides a method for preparing a composite calcium-based thermal storage material with a tiered porous structure, specifically including the following steps:

[0039] Step S1: Weigh 100g of Ca(OH)2, then proceed according to Ca... 2+ :Al 3+ :Fe 3+ :Mn 2+ :Ce 3+ :Zr 4+The molar ratio of Al(NO3)3·9H2O, Fe(NO3)3·9H2O, Mn(NO3)2·4H2O, Ce(NO3)3·6H2O and ZrO(NO3)2·xH2O are weighed out. Then, 40% of the mass of Ca(OH)2 microcrystalline cellulose is weighed out. The above raw materials are mixed and 150 mL of deionized water is added to make a mixed slurry.

[0040] Step S2: Transfer the mixed slurry obtained in step S1 to a high-pressure reactor and perform hydrothermal pretreatment at 120°C for 2 hours.

[0041] Step S3: Adjust the moisture content of the product obtained in step S2 to 35 wt%, and use an extrusion-spheronization machine to form spherical precursor particles with a diameter of about 1.5 mm.

[0042] Step S4: Place the precursor particles obtained in step S3 in a microwave oven and calcine them at 500°C for 30 minutes. Then transfer the particles to a muffle furnace and calcine them at 900°C for 2 hours.

[0043] Step S5: The calcined product obtained in step S4 is carbonated at 650°C for 1 hour in a furnace filled with CO2 (flow rate of 100 mL / min) to finally obtain the target product A1, the SEM image of which is shown below. Figure 1 As shown, by Figure 1 As shown in Figure (a), the prepared material contains a pore structure formed by microcrystalline cellulose, which constitutes a macroscopic channel for rapid gas transport, thus helping to improve the material's reactivity and mass transfer efficiency. As shown in Figure (b), there are a large number of nanoscale pore structures inside the micron-sized pores, which can further increase the material's specific surface area.

[0044] Example 2

[0045] This embodiment provides a method for preparing a composite calcium-based thermal storage material with a tiered porous structure. The only difference from Embodiment 1 is that this embodiment follows the Ca... 2+ :Al 3+ :Fe 3+ :Mn 2+ :Ce 3+ :Zr 4+ The molar ratio of Ca(OH)2, Al(NO3)3·9H2O, Fe(NO3)3·9H2O, Mn(NO3)2·4H2O, Ce(NO3)3·6H2O and ZrO(NO3)2·xH2O were weighed out, and the rest were the same as in Example 1, which will not be repeated here. Finally, the target product A2 was obtained.

[0046] Example 3

[0047] This embodiment provides a method for preparing a composite calcium-based thermal storage material with a tiered porous structure. The only difference from Embodiment 1 is that this embodiment follows the Ca... 2+ :Al 3+ :Fe 3+ :Mn 2+ :Ce 3+ :Zr 4+ The molar ratio of Ca(OH)2, Al(NO3)3·9H2O, Fe(NO3)3·9H2O, Mn(NO3)2·4H2O, Ce(NO3)3·6H2O and ZrO(NO3)2·xH2O were weighed out, and the rest were the same as in Example 1, which will not be repeated here. Finally, the target product A3 was obtained.

[0048] Example 4

[0049] This embodiment provides a method for preparing a composite calcium-based thermal storage material with a tiered pore structure. The only difference from Embodiment 1 is that in this embodiment, 30% of the mass of Ca(OH)2 microcrystalline cellulose is weighed. The rest is the same as in Embodiment 1 and will not be repeated here. The final product A4 is obtained.

[0050] Comparative Example 1 (lacking multi-component dopants)

[0051] This comparative example provides a method for preparing calcium-based thermal storage particles. The only difference between this comparative example and Example 1 is that 100g of Ca(OH)2 and 40g of microcrystalline cellulose (MCC) are weighed in this comparative example, and no multi-element dopants are added. The rest of the preparation method and process parameters are exactly the same as those in Example 1, and will not be repeated here. The final product B1 is obtained.

[0052] Comparative Example 2 (partial element doping)

[0053] This comparative example provides a method for preparing calcium-based thermal storage particles. The only difference between this comparative example and Example 1 is that 100g of Ca(OH)2 is weighed in this comparative example and prepared according to Ca... 2+ :Al 3+ :Fe 3+ :Mn 2 The molar ratio of Al(NO3)3·9H2O, Fe(NO3)3·9H2O and Mn(NO3)2·4H2O were weighed out with no Ce and Zr elements. The rest of the preparation method and process parameters were exactly the same as in Example 1, and will not be repeated here. Finally, the target product B2 was obtained.

[0054] Comparative Example 2 (Design without stepped holes)

[0055] This comparative example provides a method for preparing calcium-based thermal storage particles. The only difference between this comparative example and Example 1 is that no pore-forming agent is added in this comparative example, and the microwave-assisted calcination step in the preparation method is omitted, and the particles are directly calcined in a muffle furnace. All other steps are the same as in Example 1, and will not be repeated here. The final product B3 is obtained.

[0056] The products obtained in Examples 1-4 and Comparative Examples 1-3 were subjected to the following performance tests. The test methods are as follows, and the test results are shown in Table 1.

[0057] Solar spectral absorptivity: The particles were compacted, and the reflectance spectrum in the wavelength range of 300-2000 nm was measured using a UV-Vis spectrophotometer. The average absorptivity under the AM1.5 standard solar spectrum was calculated.

[0058] Cyclic stability: Tested using a simultaneous thermal analyzer, the temperature was raised to 800°C in a N2 atmosphere and held for 15 minutes (thermal storage decomposition), then switched to a 50% CO2 / N2 atmosphere and held for 20 minutes (exothermic carbonation). This cycle was repeated 25 times. The carbonation conversion rate (X) of the 25th cycle was recorded. 25 ), and calculate the rate of decrease in conversion rate relative to the first cycle.

[0059] Reaction kinetics: Tests were conducted using a simultaneous thermal analyzer under a pure N2 atmosphere. A small amount of carbonized particles were subjected to calcination decomposition tests at a heating rate of 10 °C / min. The peak decomposition temperature (Tpeak) and peak decomposition rate (Vpeak, mass loss rate) were recorded.

[0060] Mechanical abrasion resistance: Take 10g of particles with a diameter of 600-710μm and put them into a ball mill for 24 hours. After ball milling, measure the mass fraction of particles that still remain in the particle size range of 600-710μm (retention rate) and the mass fraction of particles that become powder (particle size <100μm) (powdering rate).

[0061] Table 1 Performance Test Data

[0062]

[0063]

[0064] As can be seen from the data in Table 1, Examples 1-4 of the present invention achieve synergistic optimization of various properties by combining multi-element doping (Al, Fe, Mn, Ce, Zr) with nano-micron ladder pore structure, and the overall performance is significantly better than all comparative examples.

[0065] The doping of Ce and Zr is crucial for achieving ultra-high cycling stability and reactivity. The performance of Comparative Example 2 is inferior to that of Example 1 in all aspects, especially in cycling stability (conversion rate decrease of 15.2% vs. 1.5%) and reaction kinetics (decomposition temperature of 815℃ vs. 785℃). This proves that Ce and Zr are not dispensable. They play a key synergistic role in suppressing deep sintering and reducing the reaction energy barrier.

[0066] The stepped pore structure is key to ensuring high heat storage density and long-term stability. The cycling stability of Comparative Example 3 is far worse than that of Example 1, and its absolute conversion rate (68.5%) in the 25th cycle is also extremely low. This indicates that even with complete elemental doping, without the micron-scale gas diffusion channels constructed by the pore-forming agent and microwave calcination, CO2 cannot effectively diffuse into the particle interior, causing the internal material to be unable to participate in the reaction, and the heat storage density and long-term stability will deteriorate sharply.

[0067] Al and Fe / Mn respectively establish the basic framework stability and basic light absorption capacity, while Ce / Zr further enhances cycle stability and reaction kinetics. The tiered porous structure is the channel that ensures the transport of reactant gases and achieves high conversion rate and high volumetric heat storage density; the absence of any part will lead to significant performance shortcomings in the material. Based on this, the present invention successfully prepared a composite calcium-based heat removal material with excellent properties, including high light absorption (>85%), ultra-high cycle stability (attenuation <2%), high reactivity (rapid decomposition at low temperature), and high mechanical strength (wear resistance >95%).

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. 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 still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a composite calcium-based thermal storage material with a stepped porous structure, characterized in that: The composite calcium-based thermal storage material is prepared by calcination and carbonation of precursor particles containing Ca(OH)2, pore-forming agent and multi-component dopants. The multi-element dopants are compounds that each contain Al, Fe, Mn, Ce, and Zr elements; the composite calcium-based thermal storage material has a nano-micro stepped pore structure.

2. The method for preparing a composite calcium-based thermal storage material with a stepped porous structure according to claim 1, characterized in that: The metal cations in the multi-component dopant and Ca 2+ The molar ratio is: Ca 2+ :Al 3+ :Fe 3+ :Mn 2+ :Ce 3+ :Zr 4+ =100:(8-12):(6-10):(4-6):(2-4):(1-3).

3. The method for preparing a composite calcium-based thermal storage material with a stepped pore structure according to claim 1, characterized in that: The mass ratio of pore-forming agent to calcium hydroxide is (30-50):100, wherein the pore-forming agent is micron-sized microcrystalline cellulose.

4. The method for preparing a composite calcium-based thermal storage material with a stepped porous structure according to claim 1, characterized in that, Specifically, the following steps are included: Step S1: Mix Ca(OH)2, pore-forming agent and multi-element dopant, and add deionized water to make a mixed slurry; Step S2: Perform hydrothermal pretreatment on the mixed slurry obtained in step S1; Step S3: Adjust the moisture content of the product obtained in step S2 to 10wt%-60wt%, and obtain spherical precursor particles by extrusion-spheronization. Step S4: The precursor particles obtained in step S3 are first subjected to microwave-assisted calcination, and then subjected to high-temperature calcination. Step S5: The calcined product obtained in step S4 is subjected to carbonation treatment under a CO2 atmosphere to obtain the composite calcium-based thermal storage material.

5. The method for preparing a composite calcium-based thermal storage material with a stepped porous structure according to claim 4, characterized in that: In step S2, the hydrothermal pretreatment temperature is 100-150℃ and the time is 1-4h.

6. The method for preparing a composite calcium-based thermal storage material with a stepped pore structure according to claim 4, characterized in that: In step S4, the microwave-assisted calcination temperature is 400-600℃ and the time is 20-40 min; the high-temperature calcination temperature is 800-1000℃ and the time is 1-3 h.

7. The method for preparing a composite calcium-based thermal storage material with a stepped pore structure according to claim 4, characterized in that: In step S5, the carbonation treatment is carried out at a temperature of 600-800℃ for 0.5-2 hours.

8. A composite calcium-based thermal storage material with a stepped porous structure, characterized in that: The composite calcium-based thermal storage material with a stepped pore structure is prepared by the preparation method described in any one of claims 1-7.

9. The application of the composite calcium-based thermal storage material with a stepped pore structure as described in claim 8, characterized in that: The composite calcium-based thermal storage material with a stepped pore structure is used in solar thermal storage.

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