Carbon sequestration steel slag-sodium nitrate composite phase change heat storage material and preparation method thereof

Abstract

The invention discloses a carbon sequestration steel slag-sodium nitrate composite phase change heat storage material and a preparation method thereof, and belongs to the field of heat storage phase change materials. The preparation method of the carbon sequestration steel slag-sodium nitrate composite phase change heat storage material comprises the following steps: mixing steel slag, water and a CO2-containing gas component, and carrying out mineralization reaction to obtain carbon sequestration steel slag; mixing the carbon sequestration steel slag with sodium nitrate to obtain a premix, and sintering to obtain the carbon sequestration steel slag-sodium nitrate composite phase change heat storage material. The carbon sequestration steel slag-sodium nitrate composite phase change heat storage material obtained according to the preparation process limited by the invention has excellent heat storage performance, complete appearance and low possibility of cracking, successfully completes coupling of a CO2 mineralization technology and a heat storage technology, and can enable the latent heat of the material to be 72-89 kJ / kg.

Description

Technical Field

[0001] The present invention relates to the field of heat storage phase change materials, and in particular to a carbon-fixed steel slag-sodium nitrate composite phase change heat storage material and a preparation method thereof. Background Art

[0002] The increase in carbon dioxide (CO2) emissions has led to the global greenhouse effect. In order to reduce its impact on the earth's ecological environment and the sustainable development of human society, how to reduce CO2 emissions has become a key issue that needs to be urgently addressed in today's society.

[0003] At present, the comprehensive utilization rate of steel slag, a by-product of steel production, is still relatively low, and its main application areas are still concentrated in building materials and road engineering. The accumulation of large amounts of steel slag not only occupies valuable land resources, but also may cause potential harm to the surrounding environment, such as soil pollution and water pollution. As an alkaline solid waste, steel slag contains 50-70% calcium oxide (CaO) and magnesium oxide (MgO), which gives it certain advantages in CO2 storage and utilization. It can replace traditional ores (such as olivine) for CO2 capture and fixation. In addition, steel slag is economical, cheap and easy to obtain, so it has also been tried as a skeleton material to load phase change materials to prepare composite phase change heat storage materials. However, most of the calcium ions in steel slag exist in the form of silicates. This structural characteristic results in the generally low thermal conductivity of the prepared composite phase change materials, limiting its application effect in the field of heat storage. If steel slag can be used simultaneously for CO2 storage and the preparation of composite phase change heat storage materials, it is expected to further enhance the comprehensive performance of the heat storage materials while reducing the accumulation of steel slag solid waste and the manufacturing cost of composite phase change heat storage materials.

[0004] In related research, scholars have explored the preparation of composite phase-change heat storage materials based on steel slag. However, existing steel slag-based composite phase-change materials still have some shortcomings in practical applications. For example, in the field of waste heat recovery (300-400°C) in selective catalytic reduction (SCR) denitrification systems, the main technologies currently used include waste heat boilers, direct heat exchanger supply, organic Rankine cycle, and phase-change heat storage systems. Among them, phase-change heat storage technology has been widely used in this field due to its ability to adapt to the intermittent and irregular nature of waste heat release. Currently, phase-change materials suitable for waste heat recovery in this temperature range mainly include metal alloys (such as aluminum-silicon alloys), carbonates (such as Li2CO3, Na2CO3), and nitrates (such as NaNO3, KNO3). However, these phase-change materials still have room for further improvement in terms of heat storage performance, economic efficiency, and corrosion resistance. Summary of the Invention

[0005] The present invention aims to provide a carbon-fixed steel slag-sodium nitrate composite phase-change thermal storage material and its preparation method to address the aforementioned problems in the background art. The carbon-fixed steel slag-sodium nitrate composite phase-change thermal storage material, obtained according to the preparation process defined in the present invention, exhibits excellent thermal storage performance, a complete appearance, and is resistant to cracking. It successfully couples CO2 mineralization technology with thermal storage technology, achieving a latent heat of 72-89 kJ / kg.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] One of the technical solutions of the present invention is to provide a method for preparing a carbon-fixing steel slag-sodium nitrate composite phase change heat storage material, comprising the following steps:

[0008] Mixing steel slag, water and CO2-containing gas components, and subjecting them to mineralization reaction to obtain carbon-fixed steel slag;

[0009] The carbon-fixed steel slag and sodium nitrate are mixed to obtain a premix, and the premix is ​​sintered to obtain the carbon-fixed steel slag-sodium nitrate composite phase change heat storage material.

[0010] Preferably, the temperature of the mineralization reaction is 45-75° C., the pressure is 0.75-1.05 MPa, and the time is 1-4 h, more preferably 1-3 h; the mineralization reaction is carried out under stirring conditions, and the stirring rate is 650-950 r / min.

[0011] Preferably, the mass ratio of water to steel slag is 15-45; the proportion of CO2 in the CO2-containing gas component is ≥99 vol%; and the particle size D50 of the steel slag is 45-65 μm.

[0012] If the particle size of the steel slag is too large, it will be difficult to fully contact and react with the CO2 introduced into the high-pressure reactor due to its small specific surface area; if the particle size of the steel slag is too small, on the one hand, it will lead to higher grinding costs, and on the other hand, it will cause the reaction layer to become thicker, hindering the reaction.

[0013] Under the conditions of the mineralization reaction defined in the present invention, it can be ensured that the calcium ions in the steel slag are more smoothly converted into calcium carbonate, thereby obtaining carbon-fixed steel slag.

[0014] Preferably, the mass ratio of the carbon-fixing steel slag to sodium nitrate is 5-6:4-5, more preferably 5:5.

[0015] Limiting the carbon-fixed steel slag and sodium nitrate to the above range is more conducive to improving the latent heat value of the prepared composite phase change heat storage material, so that the latent heat value can vary within the range of 72-89 kJ / kg.

[0016] Preferably, after the mineralization reaction, the step of crushing to a particle size D50 of 200-500 μm is further included, more preferably crushing to a particle size D50 of 300-400 μm; the particle size D50 of the sodium nitrate is 100-200 μm, more preferably 100-150 μm.

[0017] If the particle size of the solid carbon steel slag is too large, it will be unfavorable for the solid carbon steel slag to adsorb molten sodium nitrate; if the particles of the solid carbon steel slag are too small, the solid carbon steel slag will find it difficult to support the structural system of the phase change material, causing the skeleton to collapse and affecting the preparation process of the composite phase change heat storage material.

[0018] If the particle size of sodium nitrate is too large, it will be easy for sodium nitrate to fill unevenly in the voids of solid carbon steel slag during heating, reducing the heat storage density; if the particle size of sodium nitrate is too small, the grinding cost will be high, and agglomeration may occur before reaching the melting point, affecting the heat storage performance.

[0019] Preferably, before the sintering operation, the premix is ​​further subjected to a pressing step, wherein the pressing pressure is 3-11 MPa and the pressing time is 1-5 min, and the sample obtained after the pressing is cylindrical.

[0020] Preferably, within this range, the composite phase change heat storage material embryo can be completely formed and has a certain degree of compactness, while the tablet pressing mold can be kept intact and not deformed.

[0021] More preferably, the cylinder has a diameter of 5-20 mm, more preferably 10-15 mm, and a height of 2-4 mm, more preferably 2 mm.

[0022] Preferably, the sintering temperature is 330-360° C., the heating rate is 1-20° C. / min, and the holding time is 90 min.

[0023] Sodium nitrate can melt sufficiently and rapidly within this temperature range, penetrate into the pores of the carbon-fixed steel slag and form a tight composite structure.

[0024] Preferably, the preparation method comprises the following steps:

[0025] (a) drying the steel slag at 100-130° C. for 6-12 h, and then ball-milling the steel slag to a particle size D50 of 45-65 μm to obtain the treated steel slag for later use;

[0026] (b) placing the treated steel slag in an autoclave at a temperature of 75° C., a pressure of 0.85 MPa of a CO 2 -containing gas component (wherein CO 2 accounts for 99 vol%), a liquid-to-solid ratio of 35, a stirring rate of 650 rpm, and a reaction time of 1-3 h to prepare carbon-fixed steel slag;

[0027] (c) drying the carbon-fixed steel slag at 100-130° C. for 6-12 hours, and then ball-milling the slag to a particle size D50 of 300-400 μm to obtain treated carbon-fixed steel slag for later use;

[0028] The sodium nitrate is dried at 100-130° C. for 6-12 hours, and then ball-milled to a particle size D50 of 100-150 μm to obtain the treated sodium nitrate for later use;

[0029] (d) mixing the carbon-fixing steel slag treated in step (c) with sodium nitrate in a mass ratio of 5-6:4-5 to obtain a premix;

[0030] (e) pressing the premix at a pressure of 3-11 MPa for 1-5 minutes to obtain a cylindrical green embryo with a diameter of 5-15 mm and a height of 2-4 mm;

[0031] (f) placing the cylindrical green body in a sintering device, heating the temperature from 20°C to 200°C at a heating rate of 5-10°C / min, then heating the temperature to 330-360°C at a heating rate of 1-5°C / min, and maintaining the temperature for 90 minutes to obtain the solid carbon steel slag-sodium nitrate composite phase change heat storage material.

[0032] The second technical solution of the present invention is to provide a carbon-fixing steel slag-sodium nitrate composite phase change heat storage material obtained according to the above preparation method.

[0033] The third technical solution of the present invention is to provide an application of the above-mentioned carbon-fixing steel slag-sodium nitrate composite phase change heat storage material in the field of waste heat recovery in a selective catalytic reduction denitrification system.

[0034] The technical principles of the present invention are as follows:

[0035] When steel slag is directly used as the skeleton material of sodium nitrate to prepare a composite phase change heat storage material, the heat storage performance of the product is relatively poor. However, the present invention prepares carbon-fixed steel slag by first placing the steel slag in a high-pressure reactor to undergo a mineralization reaction with CO2, and then sintering it with sodium nitrate at high temperature, thereby obtaining a composite phase change heat storage material with good morphology, stable chemical properties, and high heat storage density. After the CO2 mineralization reaction, the calcium silicate in the steel slag is converted into calcium carbonate with a higher thermal conductivity, and some silicon dioxide is also generated, which improves the thermal conductivity and compressive strength of the product. After testing, the thermal conductivity and compressive strength of the carbon-fixed steel slag-sodium nitrate composite phase change heat storage material and the steel slag-sodium nitrate composite phase change heat storage material prepared by the present invention reached 1.1504W·m -1 ·K -1 , 53.2MPa and 0.9677W·m -1 ·K -1, 46.9MPa, proving that the introduction of mineralization technology promotes the thermal conductivity and compressive resistance of the material.

[0036] The beneficial technical effects of the present invention are as follows:

[0037] The carbon-fixed steel slag-sodium nitrate composite phase change heat storage material obtained according to the preparation process defined in the present invention has excellent heat storage performance, a complete appearance, and is not prone to cracking. It successfully couples CO2 mineralization technology with heat storage technology, and can make the latent heat of the material between 72-89 kJ / kg.

[0038] When the steel slag after the mineralization and carbon fixation treatment of the present invention is used as the skeleton of the composite phase change material, its thermal conductivity, compressive strength, etc. are significantly enhanced. It is more efficient in recycling the waste heat (300-400°C) of the selective catalytic reduction (SCR) denitrification system and has good application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0040] Figure 1 This is a flow chart for preparing the carbon-fixed steel slag-sodium nitrate shaped composite phase change heat storage material of Example 1;

[0041] Figure 2 The green embryo and the carbon-fixed steel slag-sodium nitrate shaped composite phase change heat storage material in Example 1 are real pictures; wherein (a) is the green embryo, and (b) is the carbon-fixed steel slag-sodium nitrate shaped composite phase change heat storage material;

[0042] Figure 3 This is a test diagram of the heat storage performance of the products of Examples 1-4 and Comparative Examples 1, 3, and 4. DETAILED DESCRIPTION

[0043] Various exemplary embodiments of the present invention are now described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the present invention.

[0044] In addition, for numerical ranges in the present invention, it is understood that each intervening value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any stated value or stated range, and any other stated value or intervening value in the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

[0045] Unless otherwise specified, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention pertains. Although preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention. It should be noted that any details not described herein are conventional procedures in the art and are not the focus of the present invention.

[0046] The terms “include,” “including,” “have,” “contain,” etc. used in the present invention are open-ended terms, meaning including but not limited to.

[0047] The raw materials used in the following examples and comparative examples of the present invention are all commercially available products.

[0048] Example 1

[0049] A method for preparing a carbon-fixing steel slag-sodium nitrate composite phase change heat storage material, comprising the following steps:

[0050] (a) drying the steel slag at 120° C. for 6 h, and then ball-milling the steel slag to a particle size D50 of 50 μm to obtain the treated steel slag for later use;

[0051] (b) placing the treated steel slag in an autoclave at a temperature of 75° C., a pressure of 0.85 MPa of a CO 2 -containing gas component (wherein CO 2 accounts for 99 vol%), a liquid-to-solid ratio of 35, a stirring rate of 650 rpm, and a reaction time of 2 h to prepare carbon-fixed steel slag;

[0052] (c) drying the carbon-fixed steel slag at 120° C. for 6 h, and then ball-milling the slag to a particle size D50 of 300 μm to obtain treated carbon-fixed steel slag for later use;

[0053] The sodium nitrate was dried at 120° C. for 6 h, and then ball-milled to a particle size D50 of 100 μm to obtain the treated sodium nitrate for later use;

[0054] (d) mixing the carbon-fixing steel slag treated in step (c) with sodium nitrate in a mass ratio of 5:5 to obtain a premix;

[0055] (e) pressing the premix under a pressure of 5 MPa for 3 minutes to obtain a cylindrical green embryo (carbon-fixed steel slag-sodium nitrate shaped composite phase change thermal storage material green embryo) with a diameter of 15 mm and a height of 2 mm;

[0056] (f) The cylindrical green body was placed in a sintering device and heated to 200°C at a heating rate of 5°C / min, then to 340°C at a heating rate of 1°C / min, and held at this temperature for 90 minutes to obtain the final product (carbon-solidified steel slag-sodium nitrate shaped composite phase change thermal storage material). The thermal properties and compressive tests of the carbon-solidified steel slag-sodium nitrate shaped composite phase change thermal storage material were conducted, and the latent heat value was 85 kJ / kg, the thermal conductivity coefficient, and the compressive strength were 1.1504 W·m, respectively. -1 ·K -1 , 53.2MPa.

[0057] Figure 1 This is a flow chart for preparing the carbon-fixed steel slag-sodium nitrate shaped composite phase change heat storage material of Example 1.

[0058] Figure 2 These are the actual images of the green embryo and the carbon-fixed steel slag-sodium nitrate shaped composite phase change heat storage material in Example 1. (a) is the green embryo, and (b) is the carbon-fixed steel slag-sodium nitrate shaped composite phase change heat storage material.

[0059] Depend on Figure 2 It can be seen that the appearance of the prepared carbon-fixed steel slag-sodium nitrate composite phase change heat storage material is intact and there is no cracking on the surface.

[0060] Figure 3 The thermal storage performance (DCS) test diagram of the products of Examples 1-4 and Comparative Examples 1, 3, and 4.

[0061] Depend on Figure 3 It can be seen that the latent heat value of the solid carbon steel slag-sodium nitrate shaped composite phase change heat storage material obtained in Example 1 is 89 kJ / kg.

[0062] Example 2

[0063] The only difference from Example 1 is that the mass ratio of carbon-fixing steel slag to sodium nitrate in step (d) is adjusted to 6:4.

[0064] The product of this embodiment has a good appearance and no cracks on the surface. Figure 3 It can be seen that the latent heat value of the solid carbon steel slag-sodium nitrate shaped composite phase change heat storage material obtained in Example 2 is 72 kJ / kg.

[0065] Example 3

[0066] The only difference from Example 1 is that the mass ratio of carbon-fixing steel slag to sodium nitrate in step (d) is adjusted to 5.5:4.5.

[0067] The product of this embodiment has a good appearance and no cracks on the surface. Figure 3 It can be seen that the latent heat value of the solid carbon steel slag-sodium nitrate shaped composite phase change heat storage material obtained in Example 3 is 79 kJ / kg.

[0068] Example 4

[0069] A method for preparing a carbon-fixing steel slag-sodium nitrate composite phase change heat storage material, comprising the following steps:

[0070] (a) drying the steel slag at 100° C. for 3 h, and then ball-milling the steel slag to a particle size D50 of 50 μm to obtain the treated steel slag for later use;

[0071] (b) placing the treated steel slag in an autoclave at a temperature of 75° C., a CO 2 -containing gas component (of which CO 2 accounts for 99 vol %), a pressure of 0.85 MPa, a liquid-to-solid ratio of 35, a stirring rate of 650 r / min, and a reaction time of 3 h to prepare carbon-fixed steel slag;

[0072] (c) drying the carbon-fixed steel slag at 100° C. for 3 h, and then ball-milling the slag to a particle size D50 of 300 μm to obtain treated carbon-fixed steel slag for later use;

[0073] The sodium nitrate was dried at 100° C. for 5 h, and then ball-milled to a particle size D50 of 100 μm to obtain the treated sodium nitrate for later use;

[0074] (d) mixing the carbon-fixing steel slag treated in step (c) with sodium nitrate in a mass ratio of 5:5 to obtain a premix;

[0075] (e) pressing the premix under a pressure of 7 MPa for 3 min to obtain a cylindrical green embryo (carbon-fixed steel slag-sodium nitrate shaped composite phase change thermal storage material green embryo) with a diameter of 15 mm and a height of 2 mm;

[0076] (f) The cylindrical green body was placed in a sintering device and heated to 200°C at a heating rate of 5°C / min, then heated to 330°C at a heating rate of 1°C / min, and kept at this temperature for 90 min to obtain the final product (carbon-solidified steel slag-sodium nitrate shaped composite phase change thermal storage material).

[0077] The product of this embodiment has a good appearance and no cracks on the surface. Figure 3 It can be seen that the latent heat value of the solid carbon steel slag-sodium nitrate shaped composite phase change heat storage material obtained in Example 4 is 89 kJ / kg.

[0078] Comparative Example 1

[0079] The only difference from Example 1 is that the mass ratio of carbon-fixing steel slag to sodium nitrate in step (d) is adjusted to 4:6.

[0080] The appearance of the product obtained in this comparative example is no longer intact, and some carbon-fixing slag supports have collapsed, and nitrate has leaked. Figure 3 It can be seen that the heat storage density of the composite phase change heat storage material of Comparative Example 1 is 113 kJ / kg.

[0081] Comparative Example 2

[0082] The only difference from Example 1 is that the mass ratio of carbon-fixing steel slag to sodium nitrate in step (d) is adjusted to 3:7.

[0083] The product obtained in this comparative example exhibited significant deformation and leakage, making it unusable. This was because the sodium nitrate content was too high, and the carbon-fixed steel slag could no longer support the infiltration of the molten sodium nitrate, causing the sodium nitrate to flow out and the carbon-fixed steel slag matrix to collapse.

[0084] Comparative Example 3

[0085] The only difference from Example 1 is that the mass ratio of carbon-fixing steel slag to sodium nitrate in step (d) is adjusted to 7:3.

[0086] The appearance of the product obtained in this comparative example is complete and there is no leakage on the surface. Figure 3 It can be seen that the heat storage density of the solid carbon steel slag-sodium nitrate shaped composite phase change heat storage material obtained in Comparative Example 3 is 58 kJ / kg, which is lower than that in Example 1. This shows that as the mass proportion of solid carbon steel slag increases, although the sample is still formed, its heat storage performance is greatly reduced.

[0087] Comparative Example 4

[0088] The only difference from Example 2 is that mineralization carbon fixation treatment is no longer performed, and the carbon-fixing steel slag in step (d) is directly replaced by the treated steel slag of step (a) of equal mass, which is mixed with sodium nitrate in a mass ratio of 6:4, and then subjected to subsequent treatment to finally obtain a steel slag-sodium nitrate shaped composite phase change heat storage material.

[0089] The product obtained in this comparative example has a complete appearance and no surface leakage; its thermal conductivity is 0.9677 W·m -1 ·K -1 , the compressive strength is 46.9MPa, which is relatively poor. Figure 3 It can be seen that the heat storage density of the steel slag-sodium nitrate shaped composite phase change heat storage material obtained in Comparative Example 4 is 74 kJ / kg, which is consistent with the heat storage intensity of the product of Example 2.

[0090] It can be seen from the products of Examples 1-4 that by adjusting the mass ratio of carbon-fixing steel slag to sodium nitrate, the latent heat of phase change can be fluctuated between 72-89 kJ / kg.

[0091] It can be seen from Examples 1-4 and Comparative Examples 1-2 that too high a sodium nitrate content will lead to deformation and leakage, making it impossible to use it in practice; it can be seen from the comparison between Examples 1-4 and Comparative Example 3 that too low a sodium nitrate content used in step (d) will lead to a significant decrease in heat storage density and low use value.

[0092] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a carbon-fixing steel slag-sodium nitrate composite phase change heat storage material, characterized in that: The following steps are involved: Mixing steel slag, water and CO2-containing gas components, and subjecting them to mineralization reaction to obtain carbon-fixed steel slag; The carbon-fixed steel slag and sodium nitrate are mixed to obtain a premix, and the premix is ​​sintered to obtain the carbon-fixed steel slag-sodium nitrate composite phase change heat storage material.

2. The preparation method according to claim 1, characterized in that The temperature of the mineralization reaction is 45-75° C., the pressure is 0.75-1.05 MPa, and the time is 1-4 hours. The mineralization reaction is carried out under stirring conditions, and the stirring rate is 650-950 r / min.

3. The preparation method according to claim 1, characterized in that The mass ratio of water to steel slag is 15-45; the proportion of CO2 in the CO2-containing gas component is ≥99 vol%; and the particle size D50 of the steel slag is 45-65 μm.

4. The preparation method according to claim 1, characterized in that The mass ratio of the carbon-fixing steel slag to sodium nitrate is 5-6:4-5.

5. The preparation method according to claim 1, characterized in that After the mineralization reaction, the method further comprises a step of crushing the sodium nitrate to a particle size D50 of 200-500 μm; the particle size D50 of the sodium nitrate is 100-200 μm.

6. The preparation method according to claim 1, characterized in that Before the sintering operation, the premix is ​​also subjected to a step of pressing and molding. The pressure of the pressing and molding is 3-11 MPa and the time is 1-5 minutes.

7. The preparation method according to claim 1, characterized in that The sintering temperature is 330-360° C., the heating rate is 1-20° C. / min, and the holding time is 90 min.

8. A carbon-fixing steel slag-sodium nitrate composite phase change heat storage material obtained according to the preparation method according to any one of claims 1 to 7.

9. Use of the carbon-fixing steel slag-sodium nitrate composite phase change heat storage material according to claim 8 in the field of waste heat recovery in a selective catalytic reduction denitration system.

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