Conductive solid heat storage material and preparation method thereof

Abstract

The invention discloses a conductive solid heat storage material and a preparation method thereof, and relates to the technical field of solid heat storage and energy storage. Mixing the pretreated steel slag with a conductive filler; and carrying out multi-particle-size grading on the mixed particles, uniformly mixing, sequentially carrying out compression molding and high-temperature sintering treatment on the compound steel slag, and cooling to obtain the steel slag-based solid heat storage material. A small amount of conductive filler is added into the steel slag, the conductivity of the steel slag is effectively improved, the steel slag serves as a resistance heating element and a heat storage medium at the same time, heating and heat storage functions are integrated, and therefore the heat storage system structure is simplified, the energy efficiency is improved, the cost is reduced, and high-value utilization of steel slag solid waste is achieved.

Description

Technical Field

[0001] This invention relates to the field of solid thermal energy storage technology, and more specifically, to a conductive solid thermal energy storage material and its preparation method. Background Technology

[0002] With the accelerated transformation of the global energy structure, the proportion of renewable energy power generation continues to rise, and its inherent intermittency and volatility pose a severe challenge to the grid's peak-shaving capacity. Solid thermal storage technology, with its advantages of high safety and large capacity, has become an important energy storage means to utilize off-peak electricity for "peak shaving and valley filling." Traditional solid thermal storage technology is represented by solid thermal storage electric boilers, which indirectly heat the heat storage body, such as magnesia bricks, through discrete heating elements such as resistance wires and heating tubes. Although this technology is mature and widely used, the separation of heating elements and heat storage bodies generally leads to problems such as system structural redundancy, low heat transfer efficiency, uneven temperature distribution, and poor modular integration, which seriously restricts its flexible deployment capability in diverse scenarios. To overcome these bottlenecks, recent research has focused on developing integrated thermal storage materials that can be directly energized and heated by adding highly conductive phases such as carbon fiber, graphite powder, or metal particles to refractory bricks and concrete matrices. However, this method usually faces the problem of excessively high conductive filler content (15-30 wt%), resulting in a significant increase in material costs and making it difficult to guarantee the economic viability of industrial applications.

[0003] Against this backdrop, steel slag, a major metallurgical solid waste with an annual output exceeding 120 million tons and a comprehensive utilization rate of less than 35%, shows potential to replace traditional heat storage media due to its rich content of various metal oxides, excellent intrinsic heat storage capacity, and good thermal conductivity. However, the conductive phase in primary steel slag is dispersed, and the contact resistance between particles is huge, resulting in a macroscopic resistivity as high as 10⁻⁶. 2 -10 4 The conductivity of steel slag is too low (Ω·m) to meet the conductivity threshold requirements for direct electric heating. Therefore, there is an urgent need to develop a precise conductivity enhancement strategy tailored to the properties of steel slag. By controlling its microstructure and conductive network, the strategy can achieve integrated heating and heat storage functions while maintaining low cost. Furthermore, by combining this with a modular design concept, the strategy can promote the high-value and engineering applications of steel slag-based functional materials in power grid peak-shaving scenarios.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a conductive solid thermal storage material and its preparation method. By adding a small amount of conductive filler to steel slag, the conductivity of the steel slag is effectively improved, enabling it to function as both a resistance heating element and a thermal storage medium, thus integrating heating and thermal storage functions. This simplifies the structure of the thermal storage system, improves energy efficiency, reduces costs, and achieves high-value utilization of steel slag solid waste.

[0006] This invention is implemented as follows: In a first aspect, the present invention provides a conductive solid thermal storage material comprising 90-99.5 wt% steel slag and 0.5-10 wt% conductive filler.

[0007] In an optional embodiment, the steel slag is selected from at least one of converter slag, electric furnace slag, or blast furnace slag, and the sulfur content in the steel slag is <0.5% and the phosphorus content is <0.8%.

[0008] In an optional embodiment, the conductive filler is selected from at least one of graphite powder, carbon black, carbon fiber, or metal powder.

[0009] In an optional embodiment, the solid heat storage material further includes a binder, wherein the binder is selected from at least one of water glass or phenolic resin, and the amount added is 3-8 wt%.

[0010] In an optional embodiment, the solid thermal storage material has a room temperature resistivity of 0.1-10 Ω·m and a density of 2.2-2.8 g / cm³. 3 Specific heat capacity 0.8-1 J / (g·K), heat storage density 280-450 kWh / m³ 3 Thermal conductivity 1.5-2.5 W / (m·K).

[0011] Secondly, the present invention provides a method for preparing a conductive solid thermal storage material, comprising the following steps: pretreating steel slag; mixing the pretreated steel slag with conductive filler; grading the mixed particles into multiple particle sizes and mixing them evenly; sequentially pressing and molding the compounded steel slag and performing high-temperature sintering treatment; and obtaining the steel slag-based solid thermal storage material after cooling.

[0012] In an optional embodiment, the pretreatment includes crushing, screening, and magnetic separation of the steel slag; the crushed steel slag particles include coarse particles of 300-750 μm, medium particles of 150-300 μm, and fine particles of 5-150 μm, wherein the coarse particles account for 50-55 vol%, the medium particles account for 25-35 vol%, and the fine particles account for 15-30 vol%.

[0013] In an optional embodiment, the mixing is selected from at least one of direct blending or binder-assisted blending; If direct blending is used, the high-temperature sintering is carried out in an air atmosphere or a reducing atmosphere, the sintering temperature is 1000-1250℃, the heating rate is 1-3℃ / min, and the holding time is 2-4h. If a binder is used to assist in blending, the high-temperature sintering is carried out in an air atmosphere or a reducing atmosphere, the sintering temperature is 250-800℃, the heating rate is 1-3℃ / min, and the holding time is 2-4h.

[0014] In an optional embodiment, the pressing pressure is 8-20 MPa and the holding time is 30-60 s.

[0015] In an optional embodiment, the cooling step includes: cooling the workpiece from the high-temperature sintering temperature to 600°C at a cooling rate of 1-2°C / min; and then allowing the workpiece to cool to room temperature in air from 600°C.

[0016] The present invention has the following beneficial effects: This invention utilizes low-value steel slag to enhance its conductivity and adds a small amount of conductive filler, enabling the steel slag to possess both excellent conductivity and heat storage properties. The integrated design, where heat is directly generated and stored within the heat storage material, eliminates the heat transfer issues from the heating element to the heat storage body inherent in traditional solid-state heat storage methods, avoiding energy efficiency losses caused by temperature gradients and interfacial thermal resistance. Furthermore, the integrated heating and heat storage module units can be flexibly combined in series and parallel to construct heat storage systems covering a full power range from 10 kW to 100 MW. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0018] The following provides a detailed description of a conductive solid thermal storage material and its preparation method proposed in this application.

[0019] Firstly, this invention provides a conductive solid thermal storage material comprising 90-99.5 wt% steel slag and 0.5-10 wt% conductive filler. The core principle of this method lies in introducing a small amount of highly conductive filler into the steel slag matrix, and using uniform dispersion technology and appropriate molding processes to achieve directional arrangement or overlap of the conductive filler at the gaps and interfaces between steel slag particles, thereby constructing a continuous and dense three-dimensional conductive network within the insulating or semi-conductive steel slag matrix. This network can serve as a preferential pathway for electron transport, significantly reducing the transition barrier of electrons at the particle interface and effectively bypassing the bottleneck of discontinuous distribution and high contact resistance of the original conductive phase of the steel slag.

[0020] This technological approach offers several significant advantages: First, it achieves a qualitative leap in conductivity through extremely low doping levels, drastically reducing the amount of high-cost conductive materials used. This effectively controls raw material costs while ensuring conductivity, significantly improving the economic feasibility of steel slag-based thermal storage materials. Second, the three-dimensional conductive network imparts a uniform Joule heating effect to the material, resulting in a more consistent temperature distribution within the heating element after energization. This avoids the localized overheating and thermal stress concentration problems associated with traditional resistance wire heating methods, improving the material's service stability and cycle life. Third, the conductive network and the steel slag thermal storage matrix are deeply integrated at the microscale. The system integrates the heating element and the heat storage unit, eliminating the complex heating element layout and thermal interface management required in traditional electric boilers. This significantly simplifies the system structure and enhances its integration and modularity. Fourth, the preparation process has good raw material adaptability and scalability potential. It allows for flexible control of the conductive phase type and blending process based on different steel slag phase compositions and particle size distributions. This facilitates continuous production from material preparation to component molding, providing reliable technical support for the standardized application of steel slag-based heat storage modules in scenarios such as grid peak shaving, industrial waste heat recovery, and clean heating.

[0021] In an optional embodiment, the steel slag is selected from at least one of converter slag, electric furnace slag, or blast furnace slag, avoiding steel slag with excessive sulfur and phosphorus content. The sulfur content in the steel slag is <0.5%, and the phosphorus content is <0.8%. Excessive sulfur and phosphorus content will hinder their return to the metallurgical process for closed-loop utilization—phosphorus will lead to a sharp increase in dephosphorization burden and make it impossible to smelt high-quality steel, while sulfur is likely to trigger environmental penalties and increase disposal costs. Secondly, phosphorus will degrade the crystallinity homogeneity of the thermal storage material, and sulfur will easily induce low-melting-point brittle phases. Both will significantly reduce the mechanical strength and service life of the thermal storage components during long-term thermal cycling.

[0022] In optional embodiments, the conductive filler includes, but is not limited to, graphite powder, carbon black, carbon fiber, or metal powder, and the conductive particles can be added individually or in combination.

[0023] In an optional embodiment, the solid thermal storage material further includes a binder, which includes, but is not limited to, water glass or phenolic resin, and the amount of binder added is 3-8 wt%.

[0024] In an optional embodiment, the solid thermal storage material has a room temperature resistivity of 0.1-10 Ω·m and a density of 2.2-2.8 g / cm³. 3 Specific heat capacity 0.8-1 J / (g·K), heat storage density 280-450 kWh / m³ 3 Thermal conductivity 1.5-2.5 W / (m·K).

[0025] Secondly, the present invention provides a method for preparing a conductive solid thermal storage material, comprising the following steps: S1. Pretreatment of steel slag.

[0026] Specifically, the pretreatment includes crushing, screening, magnetic separation, washing and drying of the steel slag; In an optional embodiment, the crushed steel slag particles include coarse particles of 300-750 μm, medium particles of 150-300 μm and fine particles of 5-150 μm, wherein coarse particles account for 50-55 vol%, medium particles account for 25-35 vol%, and fine particles account for 15-30 vol%.

[0027] Further magnetic separation is performed to remove large pieces of metallic iron, retaining dispersed fine metallic iron to avoid local short circuits and ensure uniform current distribution. The steel slag is then washed and dried to remove dust and soluble salts.

[0028] S2. Mix the pretreated steel slag and conductive filler.

[0029] In some preferred embodiments, the mixing step is selected from at least one of direct blending or binder-assisted blending.

[0030] Specifically, when directly mixing steel slag with conductive filler, a V-type mixer is used at a speed of 15-25 rpm for 20-30 minutes; when mixing steel slag with conductive filler and binder, a stirring mixer is used at a speed of 80-120 rpm for 10-15 minutes.

[0031] Furthermore, the resistivity of the composite steel slag was measured to ensure that the resistivity of the modified steel slag was 0.1-10 Ω·m.

[0032] S3. The mixed particles are graded into multiple sizes and mixed evenly. The compound steel slag is first pressed into shape, then subjected to high-temperature sintering treatment, and finally cooled to obtain steel slag-based solid heat storage material.

[0033] Specifically, the modified steel slag is graded into multiple particle sizes and then mixed evenly using a V-type mixer to ensure uniform distribution of particles of different sizes.

[0034] In some embodiments, the multi-particle size distribution is 45-55 vol% coarse particles, 15-25 vol% medium particles, and 15-25 vol% fine particles.

[0035] In some embodiments, the pressing pressure is 8-20 MPa and the holding time is 30-60 s.

[0036] In some embodiments, if direct blending is used, the high-temperature sintering is carried out in an air atmosphere or a reducing atmosphere, the sintering temperature is 1000-1250℃, the heating rate is 1-3℃ / min, and the holding time is 2-4h. If a binder is used to assist in blending, the high-temperature sintering is carried out in an air atmosphere or a reducing atmosphere, the sintering temperature is 250-800℃, the heating rate is 1-3℃ / min, and the holding time is 2-4h.

[0037] Furthermore, when water glass is used as a binder, the sintering temperature is 250-350℃; when phenolic resin is used as a binder, the sintering temperature is 600-800℃.

[0038] In some embodiments, the cooling step includes: cooling the workpiece from the high-temperature sintering temperature to 600°C at a cooling rate of 1-2°C / min; and then allowing the workpiece to cool to room temperature in air from 600°C.

[0039] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0040] Example 1 This embodiment provides a conductive solid thermal storage material comprising 90 wt% steel slag and 10 wt% conductive filler.

[0041] Its preparation method includes the following steps: Converter slag and steel slag are selected, and the steel slag particles are crushed, screened, magnetically separated, and washed. When directly mixing steel slag with conductive filler, use a V-type mixer at 20 rpm for 25 minutes; when mixing steel slag with conductive filler and binder, use a stirring mixer at 100 rpm for 15 minutes. The modified steel slag was graded into multiple particle sizes, with 50 vol% coarse particles, 25 vol% medium particles, and 25 vol% fine particles. The slag was mixed for a certain period of time using a V-type mixer to ensure that the particles of different sizes were evenly distributed.

[0042] The compound steel slag was subjected to a pressure of 10 MPa and held for 60 seconds. Sintering was carried out in a reducing atmosphere at a sintering temperature of 1100℃, a heating rate of 2℃ / min, and a holding time of 2 hours.

[0043] Finally, the workpiece is cooled from the high-temperature sintering temperature to 600 °C at a cooling rate of 2 °C / min; then the workpiece is allowed to cool to room temperature in air from 600 °C.

[0044] Example 2 This embodiment provides a conductive solid thermal storage material, the preparation method of which is the same as that of Example 1, the only difference being that the steel slag content is 95 wt% and the conductive filler content is 5 wt%.

[0045] Example 3 This embodiment provides a conductive solid thermal storage material, the preparation method of which is the same as that of Example 1, the only difference being that the steel slag content is 99.5 wt% and the conductive filler content is 0.5 wt%.

[0046] Example 4 This comparative example provides a conductive solid heat storage material, the preparation method of which is the same as that of Example 2, the only difference being: the steel slag content is 90 wt%, the conductive filler content is 5 wt%, the binder content is 5 wt%, and the binder is phenolic resin; The sintering temperature was 600 ℃, the sintering time was 2 h, and the sintering atmosphere was an inert atmosphere.

[0047] Experimental Example 1 The performance of the steel slag-based solid thermal storage materials prepared in Examples 1-4 was tested, and the test results are shown in Table 1.

[0048] Table 1. Performance Test Results

[0049] The experimental results show that different component ratios affect the performance of steel slag-based solid thermal storage materials. Regarding electrical conductivity, the room temperature resistivity gradually increases with decreasing conductive filler content. Example 1 (10 wt% conductive filler) exhibits the lowest resistivity at 2.4 Ω·m, demonstrating the best conductivity; while Example 3 (0.5 wt% conductive filler) shows the highest resistivity at 7.1 Ω·m, indicating the worst conductivity. This demonstrates that the addition of conductive filler significantly improves the material's conductivity. In terms of density, Example 3 has the highest density (2.63 g / cm³), while Example 1 has the lowest (2.12 g / cm³), suggesting that the addition of conductive filler may have introduced lighter components or increased porosity, thus reducing the overall density. Specific heat capacity and thermal storage density increase with increasing steel slag content. Example 3 exhibits the highest specific heat capacity (0.85 J·g·K) and thermal storage density (369 kWh / m³), highlighting the advantage of steel slag in thermal storage capacity. Regarding thermal conductivity, Example 1 showed the highest (1.82 W / (m·K)) and Example 3 showed the lowest (1.64 W / (m·K)), indicating that conductive fillers help improve thermal conductivity.

[0050] Although Example 4 added an additional 5 wt% binder compared to Example 2, its overall performance was still better. Compared to Example 2, Example 4 had a slightly higher room temperature resistivity (5.1 Ω·m vs. 4.5 Ω·m), but it remained within an acceptable range; its density was slightly lower (2.21 g / cm³ vs. 2.33 g / cm³), while its specific heat capacity was similar (0.81 vs. 0.82), its heat storage density was slightly lower (294 vs. 311 kWh / m³), and its thermal conductivity was slightly lower (1.71 vs. 1.79 W / (m·K)). However, overall, the introduction of the binder did not significantly deteriorate the material's heat storage or electrical conductivity, but improved its formability and structural stability. Therefore, it still exhibited a good balance in overall performance and has certain practical value.

[0051] In summary, this invention utilizes low-value steel slag for conductivity enhancement modification, requiring only a small amount of conductive filler (e.g., 5 wt%) to achieve excellent electrical conductivity (room temperature resistivity as low as 4.5 Ω·m) while maintaining high heat storage density (e.g., 311 kWh / m³) and specific heat capacity (0.82 J·g·K). This synergistic optimization of conductivity and heat storage lays the material foundation for an integrated design that allows heat to be generated and stored directly within the heat storage material. This design eliminates the heat transfer link between the heating element and the heat storage body in traditional solid heat storage methods, effectively avoiding energy efficiency losses caused by temperature gradients and interfacial thermal resistance. A comparison of Examples 2 and 4 shows that even with the introduction of a small amount of binder, the material maintains a relatively balanced heat storage and electrical conductivity (heat storage density 294 kWh / m³, resistivity 5.1 Ω·m), demonstrating good process adaptability and performance stability in practical applications. Based on this, the integrated heat generation and heat storage module unit can be flexibly combined in series and parallel to cover the full power range from 10 kW to 100 MW, and build heat storage systems that are suitable for different scales, providing an efficient and scalable technical path for fields such as industrial waste heat recovery and clean energy consumption.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A conductive solid heat storage material, characterized in that, It includes 90-99.5 wt% steel slag and 0.5-10 wt% conductive filler.

2. The conductive solid heat storage material according to claim 1, characterized in that, The steel slag is selected from at least one of converter slag, electric furnace slag, or blast furnace slag, and the sulfur content in the steel slag is <0.5% and the phosphorus content is <0.8%.

3. The conductive solid heat storage material according to claim 1, characterized in that, The conductive filler is selected from at least one of graphite powder, carbon black, carbon fiber, or metal powder.

4. The conductive solid heat storage material according to claim 1, characterized in that, The solid thermal storage material also includes a binder, which is selected from at least one of water glass or phenolic resin, and the amount added is 3-8 wt%.

5. A conductive solid heat storage material according to claim 1, characterized in that, The solid thermal storage material has a room temperature resistivity of 0.1-10 Ω·m and a density of 2.2-2.8 g / cm³. 3 Specific heat capacity 0.8-1 J / (g·K), heat storage density 280-450 kWh / m³ 3 Thermal conductivity 1.5-2.5 W / (m·K).

6. A method for preparing a conductive solid thermal storage material as described in any one of claims 1-5, characterized in that, Includes the following steps: Pretreatment of steel slag; Pretreated steel slag and conductive filler are mixed; the mixed particles are subjected to multi-size gradation and mixed evenly; the compounded steel slag is pressed and sintered at high temperature in sequence; after cooling, steel slag-based solid thermal storage material is obtained.

7. The method for preparing a conductive solid heat storage material according to claim 6, characterized in that, The pretreatment includes crushing, screening and magnetic separation of the steel slag; the crushed steel slag particles include coarse particles of 300-750 μm, medium particles of 150-300 μm and fine particles of 5-150 μm, wherein the coarse particles account for 50-55 vol%, the medium particles account for 25-35 vol%, and the fine particles account for 15-30 vol%.

8. The method for preparing a conductive solid heat storage material according to claim 6, characterized in that, The mixing is selected from at least one of direct blending or binder-assisted blending; If direct blending is used, the high-temperature sintering is carried out in an air atmosphere or a reducing atmosphere, the sintering temperature is 1000-1250℃, the heating rate is 1-3℃ / min, and the holding time is 2-4h. If a binder is used to assist in blending, the high-temperature sintering is carried out in an air atmosphere or a reducing atmosphere, the sintering temperature is 250-800℃, the heating rate is 1-3℃ / min, and the holding time is 2-4h.

9. The method for preparing a conductive solid thermal storage material according to claim 6, characterized in that, The pressing pressure is 8-20 MPa, and the holding time is 30-60 s.

10. The method for preparing a conductive solid heat storage material according to claim 6, characterized in that, The cooling step includes: cooling the workpiece from the high-temperature sintering temperature to 600°C at a cooling rate of 1-2°C / min; and then allowing the workpiece to cool to room temperature in air from 600°C.

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