A steel slag-based solid thermal storage material and its preparation method

Abstract

This invention discloses a steel slag-based solid thermal energy storage material and its preparation method, relating to the field of solid thermal energy storage technology. The preparation method includes: pretreating steel slag; placing the pretreated steel slag in a reducing atmosphere; heating it to the reduction temperature and holding it at that temperature for a period of time; then naturally cooling it; mixing the modified steel slag with multiple particle sizes; sequentially pressing and molding the compounded steel slag; and finally, cooling it to obtain the steel slag-based solid thermal energy storage material. This integrated design, which allows the steel slag to possess both good electrical conductivity and thermal storage properties, and allows heat to be generated and stored directly within the thermal energy storage material, eliminates the heat transfer link from the heating element to the heat storage body in traditional solid thermal energy storage methods, avoiding energy efficiency losses caused by temperature gradients and interfacial thermal resistance. Furthermore, the integrated heating and thermal storage module units can be flexibly combined in series and parallel to construct thermal energy storage systems with a full power range of 10 kW to 100 MW.

Description

Technical Field

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

[0002] With the rapid increase in the proportion of renewable energy sources such as wind and solar power in the power grid, the intermittency and volatility of their power generation pose significant challenges to the stable operation of the power system. Developing cost-effective energy storage technologies, especially those capable of large-scale, long-term energy storage, is crucial for balancing grid load and improving the absorption capacity of renewable energy. Solid thermal storage technology, as an important physical energy storage method, converts electrical energy into heat energy during off-peak hours and releases it for utilization during peak hours, effectively achieving peak shaving and valley filling, and is one of the effective solutions to the grid peak-shaving problem. Currently, the most widely used solid thermal storage technology is the solid thermal storage electric boiler. This technology uses independent heating elements such as resistance wires or electric heating tubes to heat solid thermal storage materials such as magnesium bricks. Although the technology is relatively mature, its separation of "heat generation" and "heat storage" leads to problems such as system complexity, low heat transfer efficiency, and uneven temperature within the thermal storage body. Furthermore, the overall integration and modularity of the device are not high, limiting its flexible deployment and application in various scenarios.

[0003] On the other hand, my country's steel industry generates over 120 million tons of steel slag annually, but its comprehensive utilization rate is low, and large-scale stockpiling causes serious resource waste and environmental pressure. Steel slag is mainly composed of metal oxides and possesses good heat storage potential and a certain degree of thermal conductivity. However, the resistivity of natural steel slag is too high (10⁻⁶ Ω·cm). 2 -10 4 With a thermal density of Ω·m, it cannot be directly energized to generate heat, making it difficult to use as an integrated electrothermal energy storage material. Therefore, developing a new type of steel slag-based thermal storage material that integrates grid peak-shaving needs with solid waste resource utilization has become the key to solving this problem.

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

[0005] The purpose of this invention is to provide a steel slag-based solid thermal storage material and its preparation method. By reducing and modifying the iron oxide component in steel slag, the electrical 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 method for preparing a steel slag-based solid thermal storage material, comprising the following steps: pretreating the steel slag, placing the pretreated steel slag in a reducing atmosphere, heating it to the reduction temperature and holding it at that temperature for a period of time, and then cooling it naturally; distributing the modified steel slag into multiple particle size distributions and mixing them evenly, pressing and molding the compounded steel slag in sequence and sintering it at high temperature, and obtaining the steel slag-based solid thermal storage material after cooling.

[0007] In an optional embodiment, the steel slag is preferably 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 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%.

[0009] In an optional embodiment, the reducing atmosphere includes at least one of CO or H2; And / or, when the reducing atmosphere is CO, the concentration of CO is 10-50 vol%. And / or, when the reducing atmosphere is H2, the concentration of H2 is 10-30 vol%. And / or, when the reducing atmosphere is a mixture of CO and H2, the concentration of CO in the mixture is 20-35 vol%, and the concentration of H2 is 10-20 vol%. And / or, the flow rate of the reducing atmosphere gas is 0.5-1.5 L / (min·kg).

[0010] In an optional embodiment, the reduction temperature is 400-950℃, the heating rate is 1-5℃ / min, and the holding time is 0.5-4h.

[0011] In an optional embodiment, the multi-particle size distribution is 45-55 vol% coarse particles, 15-25 vol% medium particles, and 15-25 vol% fine particles.

[0012] In an optional embodiment, the pressing pressure is 8-20 MPa and the holding time is 30-60 s.

[0013] In an optional embodiment, 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.

[0014] 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.

[0015] Secondly, the present invention provides a steel slag-based solid thermal storage material, wherein the room temperature resistivity of the solid thermal storage material is 0.1-10 Ω·m and the density is 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).

[0016] The present invention has the following beneficial effects: This invention utilizes low-value steel slag to enhance its electrical conductivity and then modifies it with iron oxide reduction, giving the slag both excellent electrical conductivity and heat storage properties. The integrated design, where heat is directly generated and stored within the heat storage material, eliminates the heat transfer link from the heating element to the heat storage body 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 steel slag-based solid thermal storage material and its preparation method proposed in this application.

[0019] This invention proposes a method for preparing a steel slag-based solid thermal storage material. This method increases the conductive phase content by reducing hematite and part of the floating body in the steel slag to magnetite, thereby constructing a continuous conductive network. The method includes the following steps: S1. Pretreatment of steel slag.

[0020] The steel slag is preferably 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%, avoiding steel slag with excessive sulfur and phosphorus content.

[0021] In some embodiments, 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%.

[0022] 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.

[0023] S2. Place the pretreated steel slag in a reducing atmosphere, heat it to the reducing temperature and hold it thereafter, then let it cool naturally to room temperature.

[0024] Specifically, the pretreated steel slag particles are modified by reducing the iron oxide content: the steel slag is placed in a tubular furnace or rotary kiln, a reducing atmosphere is introduced at a certain flow rate, the temperature is raised to a certain temperature and held for a period of time, and then naturally cooled to room temperature.

[0025] In some embodiments, the reducing atmosphere includes at least one of CO or H2; And / or, when the reducing atmosphere is CO, the concentration of CO is 10-50 vol%. And / or, when the reducing atmosphere is H2, the concentration of H2 is 10-30 vol%. And / or, when the reducing atmosphere is a mixture of CO and H2, the concentration of CO in the mixture is 20-35 vol%, and the concentration of H2 is 10-20 vol%. And / or, the flow rate of the reducing atmosphere gas is 0.5-1.5 L / (min·kg).

[0026] It should be noted that "kg" in the reducing atmosphere flow rate refers to "per kilogram of steel slag".

[0027] In some embodiments, the reduction temperature is 400-950℃, the heating rate is 1-5℃ / min, and the holding time is 0.5-4h.

[0028] XRD analysis of the phase composition of the steel slag after reduction modification confirmed the formation of Fe3O4. Further resistivity measurement confirmed that the resistivity of the modified steel slag was 0.1-10 Ω·m.

[0029] S3. The modified steel slag is graded into multiple particle sizes and mixed evenly.

[0030] Specifically, the modified steel slag is graded into multiple particle sizes and mixed for a certain period of time using a V-type mixer to ensure that particles of different sizes are evenly distributed.

[0031] 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.

[0032] S4. The compounded steel slag is pressed and sintered at high temperature in sequence, and after cooling, the steel slag-based solid heat storage material is obtained.

[0033] In some embodiments, the pressing pressure is 8-20 MPa and the holding time is 30-60 s.

[0034] In some embodiments, 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.

[0035] 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.

[0036] It should be noted that "room temperature" in the preparation method of this application is 15-30℃.

[0037] Secondly, the present invention provides a steel slag-based solid thermal storage material, wherein the room temperature resistivity of the solid thermal storage material is 0.1-10 Ω·m and the density is 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).

[0038] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0039] Example 1 This embodiment provides a method for preparing a steel slag-based solid thermal storage material, which includes the following steps: Converter slag and steel slag are selected, and the steel slag particles are crushed, screened, magnetically separated, and washed. The pretreated steel slag was placed in a tubular furnace / rotary kiln, and a reducing atmosphere of CO was introduced at a flow rate of 1 L / (min·kg), with an atmosphere concentration of 20 vol%. The temperature was increased to 600℃ at a rate of 3℃ / min and held for 2 hours. The modified steel slag was subjected to multi-size gradation, with coarse particles of 45-55 vol%, medium particles of 15-25 vol%, and fine particles of 15-25 vol%, and was mixed in a V-type mixer for 30 min. The compound steel slag was subjected to a pressure of 15 MPa and held for 60 seconds. Sintering was carried out in an air atmosphere at a sintering temperature of 1100℃, a heating rate of 3℃ / min, and a holding time of 2 hours.

[0040] 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.

[0041] The solid thermal storage material described above has a room temperature resistivity of 7.2 Ω·m and a density of 2.7 g / cm³. 3 Specific heat capacity 0.82 J / (g·K), heat storage density 310 kWh / m³ 3 Thermal conductivity 1.52 W / (m·K).

[0042] Example 2 This embodiment provides a method for preparing a steel slag-based solid thermal storage material, the steps of which are the same as those in Example 1, the only difference being: The reducing atmosphere has a CO concentration of 30 vol% and a reduction temperature of 700℃. The above-mentioned solid thermal storage material has a room temperature resistivity of 5.3 Ω·m and a density of 2.5 g / cm³. 3 Specific heat capacity 0.85 J / (g·K), heat storage density 332 kWh / m³ 3 Thermal conductivity 1.61 W / (m·K).

[0043] Example 3 This embodiment provides a method for preparing a steel slag-based solid thermal storage material, the steps of which are the same as those in Example 1, the only difference being: The reducing atmosphere had a CO concentration of 40 vol% and a reduction temperature of 800℃. The room temperature resistivity of the above-mentioned solid thermal storage material was 4.9 Ω·m, and its density was 2.4 g / cm³. 3 Specific heat capacity 0.88 J / (g·K), heat storage density 350 kWh / m³ 3 Thermal conductivity 1.68 W / (m·K).

[0044] Analysis of the experimental results from Examples 1 to 3 shows that as the CO concentration in the reducing atmosphere increases from 20 vol% to 40 vol% and the reduction temperature rises from 600℃ to 800℃, the reduction degree of iron oxide in the steel slag gradually deepens, and the room temperature resistivity of the material decreases from 7.2 Ω·m to 4.9 Ω·m, significantly enhancing its conductivity. This change directly supports the integrated design goal of "the material itself possessing conductivity and being able to directly conduct electricity to generate heat," providing a physical basis for achieving in-situ heat generation within the heat storage body. Simultaneously, the specific heat capacity, heat storage density, and thermal conductivity of the material all increase synchronously. The heat storage density increases from 310 kWh / m³ to 350 kWh / m³, indicating that the modification treatment enhances conductivity without sacrificing heat storage performance; on the contrary, structural evolution and phase reconstruction improve thermal properties. The slight decrease in density helps reduce module weight, improving system economy and installation convenience.

[0045] In summary, this invention successfully optimizes the electrical conductivity and thermal storage performance of steel slag by controlling the degree of reduction modification, transforming low-value steel slag into an integrated thermal storage material with both heating and storage functions. This approach eliminates the interfacial thermal resistance and temperature gradient between the heating element and the heat storage body in traditional thermal storage systems at the material level, significantly reducing energy loss. Furthermore, based on modular series-parallel combinations, it allows for the flexible construction of thermal storage systems covering a wide power range from 10 kW to 100 MW, demonstrating promising prospects for large-scale application and significant value for technology promotion.

[0046] 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 method for preparing a steel slag-based solid thermal storage material, characterized in that, It includes the following steps: The steel slag is pretreated by placing it in a reducing atmosphere, heating it to the reduction temperature and holding it at that temperature for a period of time, and then cooling it naturally. The modified steel slag is graded into multiple particle sizes and mixed evenly. The compounded steel slag is then pressed and sintered at high temperature. After cooling, the steel slag-based solid thermal storage material is obtained.

2. The method for preparing a steel slag-based solid thermal 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 method for preparing a steel slag-based solid thermal storage material according to claim 1, 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%.

4. The method for preparing a steel slag-based solid thermal storage material according to claim 1, characterized in that, The reducing atmosphere includes at least one of CO or H2; And / or, when the reducing atmosphere is CO, the concentration of CO is 10-50 vol%. And / or, when the reducing atmosphere is H2, the concentration of H2 is 10-30 vol%. And / or, when the reducing atmosphere is a mixture of CO and H2, the concentration of CO in the mixture is 20-35 vol%, and the concentration of H2 is 10-20 vol%. And / or, the flow rate of the reducing atmosphere gas is 0.5-1.5 L / (min·kg).

5. The method for preparing a steel slag-based solid thermal storage material according to claim 1, characterized in that, The reduction temperature is 400-950℃, the heating rate is 1-5℃ / min, and the holding time is 0.5-4h.

6. The method for preparing a steel slag-based solid thermal storage material according to claim 1, characterized in that, The multi-particle size distribution is 45-55 vol% coarse particles, 15-25 vol% medium particles, and 15-25 vol% fine particles.

7. The method for preparing a steel slag-based solid thermal storage material according to claim 1, characterized in that, The pressing pressure is 8-20 MPa, and the holding time is 30-60 s.

8. The method for preparing a steel slag-based solid thermal storage material according to claim 1, characterized in that, The high-temperature sintering is carried out in an air atmosphere or a reducing atmosphere, with a sintering temperature of 1000-1250℃, a heating rate of 1-3℃ / min, and a holding time of 2-4h.

9. The method for preparing a steel slag-based solid thermal storage material according to claim 1, 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.

10. A steel slag-based solid thermal storage material prepared by the method according to any one of claims 1-9, 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).