Method for preparing fly ash-based thermal storage material

Abstract

The application provides a method for preparing a fly ash-based heat storage material, comprising the following steps: S1, performing plasma pretreatment on fly ash; S2, mixing, ball milling and pressing the pretreated fly ash and a composite reducing agent into a green body, wherein the composite reducing agent comprises a preset percentage of graphite, biomass charcoal and polycarbosilane, and the carbon content is in a predetermined proportion; S3, placing the green body in a multi-mode microwave reactor to perform a microwave reduction reaction and simultaneously build a multi-level pore structure; and S4, synchronously applying pulse plasma in the microwave reduction process to generate active oxygen species and oxidize calcium-magnesium oxides into a loose porous layer, so as to prepare the fly ash-based heat storage material. The application can significantly improve the heat storage performance of the fly ash-based material.

Description

Technical Field

[0001] This invention relates to the fields of industrial solid waste resource utilization and clean energy production technology, and more specifically, to a method for preparing fly ash-based thermal storage materials. Background Technology

[0002] In existing technologies, the preparation and application of fly ash-based materials have received widespread attention, especially in the fields of high-performance concrete and zeolite synthesis.

[0003] The invention patent CN119954450A, entitled "A Preparation Method of High-Performance Self-Compacting Concrete," solves the problems of interfacial compatibility and mass transfer pathways by adding graphene oxide and nano-silica aerogel, but it does not address the improvement of the thermal storage performance of fly ash-based materials or the design of multi-level porous structures. The invention patent CN115784254A, entitled "A Preparation Method of Fly Ash-Based MFI Structured Nanozeolite," effectively improves the mass transfer efficiency and specific surface area of ​​the material by introducing mesopores, but this method mainly focuses on catalytic, adsorption, and separation applications, and does not address the preparation and performance optimization of thermal storage materials.

[0004] The aforementioned existing technologies have made some progress in improving the performance and expanding the application fields of fly ash-based materials, but there are still shortcomings in the preparation of thermal storage materials, especially in improving the thermal storage performance of materials through hierarchical pore structure design and plasma-assisted microwave reduction technology.

[0005] In particular, how to effectively utilize plasma technology for pretreatment, and how to design composite reducing agents and control the pore structure during microwave reduction to achieve the preparation of high-performance thermal storage materials with high conversion rate and low energy consumption, are key issues that have not yet been solved in the existing technology. Summary of the Invention

[0006] In view of the above problems, the purpose of this invention is to provide a method for preparing fly ash-based thermal storage materials. Specifically addressing the aforementioned technological gaps, this invention proposes an innovative method for preparing high-performance fly ash-based thermal storage materials using plasma-assisted microwave reduction coupled with multi-level pore structure design. The aim is to significantly improve the thermal storage performance of fly ash-based materials through plasma pretreatment, composite reducing agent design, pore structure control during microwave reduction, and plasma-assisted in-situ strengthening techniques.

[0007] The present invention provides a method for preparing fly ash-based thermal storage materials, comprising the following steps: S1: performing plasma pretreatment on fly ash; S2: The pretreated fly ash is mixed with the composite reducing agent, ball-milled, and pressed into a blank. The composite reducing agent consists of graphite, biochar, and polycarbosilane in a predetermined percentage, with the carbon content in a predetermined ratio. S3: The preform is placed in a multi-mode microwave reactor to carry out a microwave reduction reaction and simultaneously construct a multi-level porous structure. S4: During the microwave reduction process, pulsed plasma is applied simultaneously to generate active oxygen species, which oxidize calcium and magnesium oxides into a loose porous layer to produce fly ash-based thermal storage materials.

[0008] In step S1, plasma pretreatment of fly ash is performed, including: treating fly ash with a dielectric barrier discharge reactor, introducing a mixture of H2 and Ar, dissociating H2 to generate active hydrogen atoms through non-thermal plasma, selectively reducing iron oxides to convert them into elemental iron, and simultaneously vaporizing alkali metal oxides, thereby avoiding the occurrence of melting and pore blockage.

[0009] 3. The method for preparing fly ash-based thermal storage material according to claim 2, wherein the volume ratio of H2 to Ar is ≥20%.

[0010] The mass percentages of graphite, biochar, and polycarbosilane in the composite reducing agent are designed based on the chemical composition and content of the fly ash-based raw material, and the predetermined ratio of carbon content is designed according to the composition of the composite reducing agent and the chemical composition of the fly ash-based raw material.

[0011] In step S2, when the pretreated fly ash is mixed with the composite reducing agent, 5 wt% ammonium carbonate pore-forming agent is added so that CO2 and NH3 are generated during microwave heating decomposition in step S3, forming a macroporous-mesoporous hierarchical structure.

[0012] In step S3, microwave selective heating of the carbon source creates localized ultra-high temperatures around the carbon particles. These localized ultra-high temperatures promote the vaporization of SiO2 into SiO, and SiO and CO are deposited on the inner wall of the mesopores to form nano-SiC, thus preventing the decomposition of mullite.

[0013] In step S3, the temperature of the microwave reduction reaction is 1460±50°C.

[0014] In S4, the frequency of the pulsed plasma is 1 kHz and the power is 2 kW.

[0015] A neural network model is established, with input parameters including the reaction conditions for preparing the fly ash-based thermal storage material and output as the SiC conversion rate; it is trained based on at least 200 sets of historical experimental data, and the reaction conditions for preparing the fly ash-based thermal storage material are iteratively optimized and controlled in real time.

[0016] The reaction conditions include fly ash composition, plasma power, microwave temperature, and holding time.

[0017] As can be seen from the above description, the beneficial effects of the method for preparing fly ash-based thermal storage materials provided by the present invention are: (1) Through plasma pretreatment, composite reducing agent design, pore structure control during microwave reduction, and plasma-assisted in-situ strengthening, the thermal storage performance of fly ash-based materials is significantly improved. (2) The macro-mesoporous hierarchical structure has a higher specific surface area, stronger adsorption capacity, and larger micropore volume. (3) High-purity nano-SiC can be prepared on a large scale without the need for a harsh sintering process, saving energy costs. (4) Real-time control of process parameters based on machine learning can effectively improve SiC yield and reduce energy consumption. Attached Figure Description

[0018] Other objects and results of the invention will become more apparent and readily understood by referring to the following description taken in conjunction with the accompanying drawings, and with a more complete understanding of the invention. In the drawings: Figure 1 A flowchart illustrating a method for preparing fly ash-based thermal storage materials according to an embodiment of the present invention; In all the accompanying drawings, the same reference numerals indicate similar or corresponding features or functions. Detailed Implementation

[0019] In the following description, numerous specific details are set forth for illustrative purposes and to provide a thorough understanding of one or more embodiments. However, it will be apparent that these embodiments may also be implemented without these specific details. In other instances, well-known structures and devices are shown in block diagram form for ease of description of one or more embodiments.

[0020] This invention can be modified and has various embodiments, with specific embodiments illustrated in the accompanying drawings. However, this invention is not limited to this particular implementation and all modifications, equivalents, and substitutions falling within the spirit and technical scope of this invention are to be understood as included.

[0021] Ordinal terms such as "first," "second," etc., may be used to describe various constituent elements, but the constituent elements are not limited to these terms. These terms are used only to distinguish one constituent element from another. For example, without departing from the scope of the claims of this invention, a second constituent element may be named a first constituent element, and similarly, a first constituent element may be named a second constituent element. The term "and / or" includes a combination of multiple associated described items or one of multiple associated described items.

[0022] It should be understood that when referring to a constituent element being "connected" or "in contact" with other constituent elements, this includes not only cases where it is directly connected or in contact with other constituent elements, but also cases where other constituent elements exist between them. Conversely, when referring to a constituent element being "directly connected" or "directly in contact" with other constituent elements, it should be understood that no other constituent elements exist between them.

[0023] In the description of the embodiments, when it is stated that a certain component is formed "on or under" other components, "on or under" includes both two components that are in direct contact with each other and at least one other component that is configured to be formed between the two components. Furthermore, when expressed as "on" or "under", based on a certain component, it refers not only to the upper direction but may also include the lower direction.

[0024] The terminology used in this application is for illustrative purposes only and is not intended to limit the invention. Unless the context clearly specifies otherwise, singular expressions include plural expressions. In this application, it should be understood that terms such as "comprising" or "having" are used to specify the presence of features, numbers, steps, operations, constituent elements, components, or combinations thereof described in the specification, and do not preclude the presence or additional possibilities of one or more other features, numbers, steps, operations, constituent elements, components, or combinations thereof.

[0025] Unless otherwise defined, including technical or scientific terms, all terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Terms as defined in commonly used dictionaries should be interpreted in a meaning consistent with their meaning in the context of the relevant art, and should not be construed as having an ideal or overly formal meaning unless explicitly defined in this application.

[0026] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0027] like Figure 1 As shown, the method for preparing fly ash-based thermal storage materials proposed in this embodiment is a method for preparing high-performance fly ash-based thermal storage materials by plasma-assisted microwave reduction coupled multi-level porous structure design.

[0028] The method for preparing fly ash-based thermal storage materials in this embodiment includes the following steps: S1: Plasma pretreatment is performed on fly ash.

[0029] This step is the activation and purification stage of fly ash, which uses low-temperature plasma technology to remove impurities in fly ash that are harmful to the subsequent microwave reduction process.

[0030] Plasma pretreatment of fly ash includes: treating fly ash using a dielectric barrier discharge (DBD) reactor, introducing a mixture of H2 and Ar, and using non-thermal plasma to dissociate H2 into active hydrogen atoms (H), selectively reducing iron oxides such as FeO to elemental iron, while simultaneously vaporizing alkali metal oxides (KO / NaO), thereby preventing melting and pore blockage. The volume ratio of H2 to Ar is ≥20%.

[0031] S2: The pretreated fly ash is mixed with the composite reducing agent, ball-milled, and pressed into a blank. The composite reducing agent consists of graphite, biochar, and polycarbosilane in a predetermined percentage, with the carbon content in a predetermined ratio.

[0032] The mass percentages of graphite, biochar, and polycarbosilane in the composite reducing agent are designed based on the chemical composition and content of the fly ash-based raw materials, and the predetermined proportion of carbon content is designed according to the composition of the composite reducing agent to ensure its reducing capacity.

[0033] In this embodiment, the composite reducing agent comprises 50% graphite, 30% biochar (coconut shell derived), and 20% polycarbosilane (PCS), with a predetermined carbon content ratio of C / Si = 3.5. The composite reducing agent should be designed and prepared before step S1. Biochar can increase the specific surface area, which is beneficial for mass transfer; PCS pyrolysis generates nano-SiC seeds, which lowers the nucleation energy barrier; the carbon content of C / Si = 3.5 (molar ratio) can effectively reduce the amount of free carbon residue.

[0034] This step involves mixing the pretreated fly ash, composite reducing agent, and ammonium carbonate pore-forming agent. When mixing the pretreated fly ash with the composite reducing agent, 5 wt% ammonium carbonate pore-forming agent is added. This allows for the generation of CO2 and NH3 during microwave heating and decomposition in S3, forming a macroporous-mesoporous hierarchical structure to achieve pore structure control. The addition of 5 wt% ammonium carbonate is an optimized result, ensuring improved mass transfer and green body strength.

[0035] S3: The preform is placed in a multi-mode microwave reactor for microwave reduction reaction, simultaneously constructing a multi-level porous structure. The temperature of the microwave reduction reaction can be 1460±50°C.

[0036] This step is the microwave reduction-coupled hierarchical pore construction stage. The reaction mechanism is as follows: microwave selective heating of the carbon source creates localized ultra-high temperatures (>1600°C) around the carbon particles. These localized ultra-high temperatures promote the vaporization of SiO2 into SiO. SiO and CO are then deposited on the inner walls of the mesopores as nano-SiC, preventing mullite decomposition and enhancing the material's mechanical properties. A small amount of nano-SiC is deposited in the macropores.

[0037] S4: During the microwave reduction process, pulsed plasma is applied simultaneously to generate active oxygen species (O*), which oxidize calcium and magnesium oxides (CaO / MgO) into a loose porous layer, preventing the formation of a dense passivation film, thus producing fly ash-based thermal storage materials. The frequency of the pulsed plasma can be 1 kHz and the power can be 2 kW.

[0038] This step is plasma-assisted in-situ enhancement, which can achieve surface modification of calcium and magnesium oxides without destroying the constructed hierarchical porous structure.

[0039] Process parameters can also be optimized through machine learning, establishing a neural network model. Input parameters include the reaction conditions for preparing fly ash-based thermal storage materials, with SiC conversion rate as the output. Data training is conducted based on at least 200 sets of historical experimental data, iteratively optimizing and controlling the reaction conditions for preparing fly ash-based thermal storage materials in real time. Reaction conditions may include fly ash composition, plasma power, microwave temperature, and holding time.

[0040] Taking magnesium cement clinker as a fly ash-based raw material as an example, the specific operation steps are as follows: The fly ash was pretreated with plasma using a dielectric barrier discharge (DBD) plasma generator, with argon and hydrogen as carrier gases, of which hydrogen accounted for 20% by volume. The mechanism of action was as follows: the non-thermal plasma dissociated hydrogen to generate active hydrogen atoms, selectively reducing iron(III) oxide to elemental iron, while simultaneously vaporizing potassium oxide and sodium oxide into high-temperature water vapor, preventing melting and blockage.

[0041] Composite reducing agent design and reducing capacity analysis: The main chemical composition and content of magnesium cement clinker are: calcium oxide (CaO) 76.9%, silicon dioxide (SiO2) 18.8%, aluminum oxide (Al2O3) 11.2%, and chromium trioxide (Cr2O3) 0.05%. Since the raw materials in this embodiment contain almost no iron oxides, the composite reducing agent focuses on the carbothermic reduction of SiO2 and the partial reduction conversion of Al2O3. The selected biochar has a high specific surface area, which is beneficial to SiO gas phase mass transfer deposition; polycarbosilane (PCS) serves as a SiC seed precursor; and graphite provides long-range reducing capacity as the main carbon source. Reducing capacity matching: The main chemical composition of magnesium cement clinker matches the reducing capacity of biochar. Excellent composite reducing capacity: By mass percentage, the composite reducing agent composition is 50% graphite, 30% biochar, and 20% polycarbosilane, corresponding to a C / Si molar ratio of 3.5. The reducing power of the composite reducing agent is significantly improved, with a reduction rate of more than 80% for both iron oxide and aluminum oxide.

[0042] Microwave reduction coupled multi-level pore construction: Pretreated fly ash was mixed with a designed composite reducing agent and 5wt% ammonium carbonate pore-forming agent and pressed into lumps, which were then placed in a multi-mode microwave reactor (MMR) to form a macro-mesoporous hierarchical structure. During the plasma-assisted in-situ enhanced microwave process, pulsed plasma (frequency 1kHz, power 2kW) was applied simultaneously to generate active oxygen species (O*). Magnesium olivine oxide (CaMg(OH)2) formed a loose porous layer, preventing the formation of a dense passivation film.

[0043] Machine learning was used to optimize process parameters and establish a neural network model: input parameters (fly ash composition, plasma power, microwave temperature, holding time, etc.) output predicted SiC conversion rate; data training: based on 200 sets of historical experimental data (moisture content 13%, carbonization rate 70%), iterative optimization was performed, and reaction conditions were adjusted in real time. The optimal process parameters for SiC synthesis were determined using the machine learning model: plasma power 2kW, microwave temperature 800°C, and holding time 20min.

[0044] A high-performance thermal storage material based on fly ash was prepared using an optimized plasma-assisted microwave heating integrated device, comprising: S1: pretreating fly ash using a plasma pretreatment method; S2: mixing the pretreated fly ash with a composite reducing agent and pressing it into briquettes; S3: placing the briquettes in a multi-mode microwave reactor and holding them at 1473K for 20 minutes; S4: simultaneously applying pulsed plasma (frequency 1kHz, power 2kW) in the multi-mode microwave reactor. The heating and pulsed plasma effects generated in S3 and S4 can achieve in-situ enhancement of microwave deoxidation under mmWave (millimeter wave) conditions.

[0045] The method for preparing fly ash-based thermal storage materials according to the present invention has been described above by way of example with reference to the accompanying drawings. However, those skilled in the art should understand that various modifications can be made to the method for preparing fly ash-based thermal storage materials according to the present invention without departing from the scope of the invention. Therefore, the scope of protection of the present invention should be determined by the contents of the appended claims.

Claims

1. A method for preparing fly ash-based thermal storage materials, characterized in that, Includes the following steps: S1: Plasma pretreatment of fly ash; S2: The pretreated fly ash is mixed with the composite reducing agent, ball-milled, and pressed into a blank. The composite reducing agent consists of graphite, biochar, and polycarbosilane in a predetermined percentage, with the carbon content in a predetermined ratio. S3: The preform is placed in a multi-mode microwave reactor to carry out a microwave reduction reaction and simultaneously construct a multi-level porous structure. S4: During the microwave reduction process, pulsed plasma is applied simultaneously to generate active oxygen species, which oxidize calcium and magnesium oxides into a loose porous layer to produce fly ash-based thermal storage materials.

2. The method for preparing fly ash-based thermal storage materials according to claim 1, characterized in that, In step S1, plasma pretreatment of fly ash is performed, including: treating fly ash with a dielectric barrier discharge reactor, introducing a mixture of H2 and Ar, dissociating H2 to generate active hydrogen atoms through non-thermal plasma, selectively reducing iron oxides to convert them into elemental iron, and simultaneously vaporizing alkali metal oxides, thereby avoiding the occurrence of melting and pore blockage.

3. The method for preparing fly ash-based thermal storage materials according to claim 2, characterized in that, The volume ratio of H2 to Ar is ≥20%.

4. The method for preparing fly ash-based thermal storage materials according to claim 1, characterized in that, The mass percentages of graphite, biochar, and polycarbosilane in the composite reducing agent are designed based on the chemical composition and content of the fly ash-based raw material, and the predetermined ratio of carbon content is designed according to the composition of the composite reducing agent and the chemical composition of the fly ash-based raw material.

5. The method for preparing fly ash-based thermal storage materials according to claim 1, characterized in that, In step S2, when the pretreated fly ash is mixed with the composite reducing agent, 5 wt% ammonium carbonate pore-forming agent is added so that CO2 and NH3 are generated during microwave heating decomposition in step S3, forming a macroporous-mesoporous hierarchical structure.

6. The method for preparing fly ash-based thermal storage materials according to claim 1, characterized in that, In step S3, microwave selective heating of the carbon source creates localized ultra-high temperatures around the carbon particles. These localized ultra-high temperatures promote the vaporization of SiO2 into SiO, and SiO and CO are deposited on the inner wall of the mesopores to form nano-SiC, thus preventing the decomposition of mullite.

7. The method for preparing fly ash-based thermal storage materials according to claim 1, characterized in that, In step S3, the temperature of the microwave reduction reaction is 1460±50°C.

8. The method for preparing fly ash-based thermal storage materials according to claim 1, characterized in that, In S4, the frequency of the pulsed plasma is 1 kHz and the power is 2 kW.

9. The method for preparing fly ash-based thermal storage materials according to claim 1, characterized in that, A neural network model is established, with input parameters including the reaction conditions for preparing the fly ash-based thermal storage material and output as the SiC conversion rate; it is trained based on at least 200 sets of historical experimental data, and the reaction conditions for preparing the fly ash-based thermal storage material are iteratively optimized and controlled in real time.

10. The method for preparing fly ash-based thermal storage materials according to claim 9, characterized in that, The reaction conditions include fly ash composition, plasma power, microwave temperature, and holding time.

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