Gradient heat preservation layer capable of being used for fused salt pipeline and preparation method and application of gradient heat preservation layer

Abstract

The invention provides a gradient heat preservation layer capable of being used for a molten salt pipeline and a preparation method and application of the gradient heat preservation layer. The preparation method of the gradient heat preservation layer comprises the following steps that S1, inner-layer rubber compound is prepared; s2, preparing an outer layer rubber compound; s3, superposing the inner-layer rubber compound on the outer-layer rubber compound to form composite boron-silicon rubber; lamination gaps of the composite boron-silicon rubber are eliminated by utilizing the solvation effect and the molecular diffusion effect of supercritical gas, and gradient pre-curing is performed under the directional induction of a gradient temperature field, so that the internal pre-curing degree of the composite boron-silicon rubber presents continuous gradient change along the thickness direction; a continuous gradient porous structure is constructed in the subsequent physical foaming process, and the gradient heat preservation layer is obtained; the gradient thermal insulation layer is prepared by the preparation method of the gradient thermal insulation layer, and is applied to the fields of photo-thermal power stations, petrochemical engineering or central heating. The scheme effectively reduces the heat conduction efficiency, reduces the heat loss of the fused salt pipeline, and improves the heat exchange efficiency of the fused salt energy storage system.

Description

Technical Field

[0001] The present invention relates to the field of pipeline insulation technology, and in particular to a gradient insulation layer that can be used for molten salt pipelines, a preparation method thereof, and applications thereof. Background Art

[0002] Molten salt, as an ideal heat transfer medium for solar thermal energy storage, offers advantages such as a high heat transfer coefficient, high specific heat, good fluidity, and resistance to scaling. Furthermore, in a nitrogen-sealed environment, it exhibits high thermal stability within the operating temperature range. For example, ternary salt has a safe operating range of 180°C to 450°C. During system operation, improving the thermal insulation of molten salt pipelines and preventing heat loss can effectively enhance the heat exchange efficiency of molten salt energy storage, which has significant practical significance and economic value. The design of the insulation layer must not only consider thermal insulation properties to reduce heat loss, but also possess flame retardancy, wear resistance, and long-term thermal stability to ensure its long-term safety.

[0003] Currently, the main materials used for molten salt pipeline insulation are rock wool felt and aluminum silicate wool. However, rock wool generates significant dust during handling and installation, which can impact human health and the station environment. During installation and maintenance, both rock wool felt and aluminum silicate wool have relatively low mechanical strength, making them susceptible to damage and increasing installation difficulties. Rock wool felt fibers can abrade the protective coating on the pipeline surface, especially in environments where pipelines undergo frequent maintenance or vibration. Aluminum silicate wool can become brittle and easily break after long-term use, reducing the integrity of the insulation layer and compromising the pipeline's thermal protection. The thermal expansion coefficients of rock wool felt and aluminum silicate wool do not match those of molten salt pipelines. Long-term temperature fluctuations can create gaps between the insulation layer and the pipeline, compromising insulation effectiveness and potentially causing uneven stress on the pipeline surface. Furthermore, in practical applications, molten salt pipeline insulation requires a metal outer sheath to protect the inner insulation layer from physical damage and chemical corrosion. However, this design not only increases material and installation costs but also can affect the pipeline's thermal expansion, requiring additional thermal compensation measures. Summary of the Invention

[0004] In response to the defects in the prior art, the purpose of the present invention is to provide a gradient insulation layer that can be used for molten salt pipelines, as well as its preparation method and application. Through the strategy of inducing in-situ curing of rubber by temperature field orientation, a rubber with a gradient curing degree is constructed. The thermal insulation rubber layer with a gradient porous structure is prepared by supercritical gas foaming technology, which effectively reduces the heat conduction efficiency, reduces the heat loss of the molten salt pipeline, and improves the heat exchange efficiency of the molten salt energy storage system.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions: According to a first aspect of an embodiment of the present invention, there is provided a method for preparing a gradient insulation layer that can be used for a molten salt pipeline, comprising the following steps: Step S1: preparing an inner layer rubber mix; Step S2: preparing an outer layer of rubber compound; Step S3: superimposing the inner layer of rubber mix on the outer layer of rubber mix to form a composite borosilicate rubber; the composite borosilicate rubber utilizes the solvation effect and molecular diffusion effect of supercritical gas to eliminate the lamination gaps, and performs gradient pre-curing under the directional induction of the gradient temperature field, so that the internal pre-curing degree of the composite borosilicate rubber presents a continuous gradient change along the thickness direction, thereby constructing a continuous gradient porous structure in the subsequent physical foaming process, that is, obtaining the gradient thermal insulation layer.

[0006] In a further preferred embodiment, step S3 specifically includes the following steps: Step S301: superimposing the inner rubber mix on the outer rubber mix to form the composite borosilicate rubber, and transferring the composite borosilicate rubber to a hot plate in a high-pressure reactor; then introducing the gas into the high-pressure reactor and stabilizing it within a preset pressure range; maintaining the gas under supercritical conditions for a first preset time to allow the gas to rapidly diffuse and dissolve in the composite borosilicate rubber, promote mutual diffusion between the inner rubber mix and the outer rubber mix, eliminate lamination gaps, and form a homogeneous system of the composite borosilicate rubber and gas; Step S302: Raising the temperature of the hot stage to a pre-curing temperature and maintaining it at a constant pressure and temperature for a second preset time, so that the composite borosilicate rubber is gradient pre-cured under the directional induction of the gradient temperature field, thereby causing the pre-curing degree inside the composite borosilicate rubber to present a continuous gradient change along the thickness direction, thereby obtaining a gradient pre-cured sample; wherein the pre-curing degree of the gradient pre-cured sample decreases from high to low along the thickness direction; Step S303: adjusting the temperature of the hot stage to a specified foaming temperature and maintaining it for a third preset time; rapidly releasing the pressure to a preset gauge pressure within a fourth preset time, causing the composite borosilicate rubber and gas homogeneous system to enter a thermodynamically unstable state; and inducing the gas to form pore nuclei within the gradient pre-cured sample under the action of the gas concentration gradient inside and outside the gradient pre-cured sample, which grows into a porous structure, thereby obtaining a gradient porous structure sample; wherein the average pore size of the gradient porous structure sample obtained by foaming presents a continuous gradient change from small to large along the thickness direction; Step S304: placing the gradient porous structure sample on a heating platform, solidifying the gradient porous structure sample and removing small molecules under a third preset condition, thereby obtaining the gradient thermal insulation layer.

[0007] In a further preferred embodiment, step S1 specifically includes the following steps: Step S101: adding borosilicate rubber, a reinforcing agent, and a structural regulator into a rubber internal mixer in order according to a proportion, and mixing under a first preset condition to obtain a first mixed rubber; Step S102: taking out the first rubber mix and re-mixing it to uniformly disperse the filler, thereby obtaining a first composite sample; Step S103: adding a curing agent to the first composite sample, mixing, and cold pressing to shape, thereby obtaining the inner layer rubber mixture.

[0008] In a further preferred embodiment, step S2 specifically includes the following steps: Step S201: adding borosilicate rubber, reinforcing agent, structural regulator, flame retardant, and boron-formaldehyde resin into a rubber internal mixer in order according to a proportion, and mixing under a second preset condition to obtain a second mixed rubber; Step S202: taking out the second rubber mix and re-mixing it to uniformly disperse the filler, thereby obtaining a second composite sample; Step S203: adding a curing agent to the second composite sample, mixing, and cold pressing to shape, thereby obtaining the outer layer rubber mixture.

[0009] In a further preferred embodiment, in step S301: the gas is carbon dioxide, the preset gas pressure range is 8 to 25 MPa, and the first preset time is 0.5 to 3 hours; In the step S302: the pre-curing temperature is 140-190° C., and the second preset time is 10-50 minutes; In step S303: the designated foaming temperature is 40-100° C., the third preset time is 0.5-2 hours, the fourth preset time is 1-5 seconds, and the preset pressure is 0 MPa; In the step S304: the third preset condition is curing at 160-220° C. for 0.1-3 hours.

[0010] In a further preferred embodiment, in step S101, the reinforcing agent is one of silicon dioxide, talc, glass fiber, carbon black, titanium dioxide, silver nanosheets, glass microbeads, montmorillonite, calcium carbonate, or mica; the structural regulator is one of hydroxy silicone oil, epoxy soybean oil, methyl silicone oil, vinyl silicone oil, polyether-modified silicone oil, or fluorosilicone oil; the first preset conditions are 80-130° C. and 40-90 r / min, and the mixing time under the first preset conditions is 10-30 min; In the step S102: the first rubber mix is ​​re-milled for 10 to 30 minutes; In the step S103: the curing agent is any one of dicumyl peroxide, dibenzoyl peroxide, and 2,4-dichlorobenzoyl peroxide.

[0011] In a further preferred embodiment, in step S201, the reinforcing agent is one of silicon dioxide, talc, glass fiber, carbon black, titanium dioxide, silver nanosheets, glass microbeads, montmorillonite, or calcium carbonate; the structural regulator is one of hydroxy silicone oil, epoxy soybean oil, methyl silicone oil, vinyl silicone oil, polyether-modified silicone oil, or fluorosilicone oil; the second preset conditions are 80-130° C. and 40-90 r / min, and the mixing time under the second preset conditions is 10-30 min; In the step S202: the second rubber mix is ​​re-mixed for 10 to 30 minutes; In the step S203: the curing agent is any one of dicumyl peroxide, dibenzoyl peroxide, and 2,4-dichlorobenzoyl peroxide.

[0012] According to a second aspect of an embodiment of the present invention, there is provided a gradient thermal insulation layer that can be used for a molten salt pipeline, which is prepared using any of the above-mentioned methods for preparing a gradient thermal insulation layer that can be used for a molten salt pipeline.

[0013] In a further preferred embodiment, the gradient insulation layer comprises a macroporous layer, a mesoporous layer, a microporous layer and a solid layer sequentially arranged along the thickness direction, and the macroporous layer is in contact with a molten salt pipe containing molten salt.

[0014] According to a third aspect of an embodiment of the present invention, an application of a gradient thermal insulation layer that can be used for a molten salt pipeline is provided. The gradient thermal insulation layer that can be used for a molten salt pipeline prepared by any of the above-mentioned preparation methods for a gradient thermal insulation layer that can be used for a molten salt pipeline is applied to solar thermal power stations, petrochemical industry or centralized heating fields.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. Based on the principle of heat conduction, this invention uses a temperature field to induce gradient curing of borosilicate rubber under high pressure. This achieves a gradient curing degree from the bottom heat source side to the top of the composite borosilicate rubber material, forming a gradient porous structure with gradually changing pore size. This gradient porous structure not only improves the thermal insulation effect of the thermal insulation layer, but also significantly reduces the overall heat loss of the molten salt pipeline by reducing the vertical transfer of heat, thereby improving the heat exchange efficiency of the molten salt energy storage system. This is of great significance for improving the energy utilization and economic efficiency of the entire energy system.

[0016] 2. This invention utilizes an innovative composite insulation layer design. By placing a flame-retardant and wear-resistant solid layer on the outermost edge of the gradient insulation layer, the design not only enhances the insulation layer's physical protection but also strengthens its stability under extreme temperatures and abrasion conditions. This significantly extends the insulation layer's service life and reduces material consumption and maintenance costs. Furthermore, the inclusion of the flame-retardant solid layer significantly improves the insulation layer's fire resistance, which is crucial for preventing fire accidents and protecting personnel, especially in high-temperature CSP plants.

[0017] 3. The present invention utilizes the solvation and molecular diffusion of supercritical carbon dioxide to eliminate gaps in the laminate. This process differs from traditional lamination processes in that it utilizes the pressure and plasticization of supercritical gas to eliminate gaps in the laminate. Supercritical carbon dioxide acts as an ideal solvent, significantly reducing the viscosity and mass transfer resistance of the composite borosilicate rubber. Furthermore, the solvation effect of supercritical carbon dioxide enhances the chain mobility of the composite borosilicate rubber, thereby accelerating molecular diffusion between the two layers of borosilicate rubber. This eliminates gaps between the laminated layers, enhancing the integrity and sealing of the insulation layer, and further improving the insulation effect and service life.

[0018] 4. The insulation layer design of this invention simplifies installation and maintenance processes, reduces construction difficulty and maintenance costs, and makes replacement and repair of the insulation layer more efficient. The gradient insulation layer design takes into account various environmental factors such as temperature fluctuations and chemical corrosion, ensuring excellent insulation performance in different environments.

[0019] 5. The present invention adopts supercritical carbon dioxide foaming technology, which is a clean preparation method that reduces the emission of chemical waste and meets the current requirements for environmental protection and sustainable development.

[0020] 6. The gradient insulation layer design of the present invention is not only suitable for solar thermal power stations, but can also be applied to other industrial fields that require efficient insulation, such as petrochemicals, centralized heating, etc., and has broad market application potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings: Figure 1 A schematic diagram of an application of a gradient insulation layer that can be used in a molten salt pipeline according to an embodiment of the present invention; Figure 2 A schematic structural diagram of a gradient insulation layer that can be used in a molten salt pipeline according to an embodiment of the present invention; Figure 3 A scanning electron microscope image of a gradient insulation layer that can be used in a molten salt pipeline, provided in an embodiment of the present invention.

[0022] In the picture: 1. Molten salt; 2. Molten salt pipeline; 3. Gradient insulation layer; 301. Macroporous layer; 302. Medium-porous layer; 303. Microporous layer; 304. Solid layer. DETAILED DESCRIPTION

[0023] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, without departing from the scope of the present invention, a number of variations and improvements may be made by those skilled in the art. These all fall within the scope of protection of the present invention.

[0024] First embodiment: This embodiment provides a method for preparing a gradient insulation layer that can be used for a molten salt pipeline, comprising the following steps: The first step is to prepare the inner layer rubber compound: (1) Add the borosilicate rubber raw rubber, reinforcing agent and structural regulator into a rubber internal mixer in order according to the proportion, and mix them at 80-130°C and 40-90 r / min for 10-30 minutes to obtain the first mixed rubber; (2) Take out the first mixed rubber and remix it for 10 to 30 minutes to evenly disperse the filler, thereby obtaining the first composite sample; (3) Adding a curing agent to the first composite sample and mixing thoroughly to obtain a first cured rubber mix, and cold pressing the first cured rubber mix to obtain an inner layer rubber mix.

[0025] The reinforcing agent is one of silicon dioxide, talc, glass fiber, carbon black, titanium dioxide, silver nanosheets, glass microbeads, montmorillonite, calcium carbonate, and mica; The structure regulator is one of hydroxy silicone oil, epoxy soybean oil, methyl silicone oil, vinyl silicone oil, polyether modified silicone oil, and fluorosilicone oil; The curing agent is any one of dicumyl peroxide, dibenzoyl peroxide, and 2,4-dichlorobenzoyl peroxide.

[0026] The second step is to prepare the outer layer of rubber compound: (1) Add borosilicate rubber, reinforcing agent, structural regulator, flame retardant and boron aldehyde resin into a rubber internal mixer in order according to the proportion, and mix them at 80-130°C and 40-90 r / min for 10-30 minutes to obtain the second mixed rubber; (2) Take out the second mixed rubber and remix it for 10 to 30 minutes to evenly disperse the filler, thus obtaining the second composite sample; (3) Adding a curing agent to the second composite sample and mixing thoroughly, a second cured rubber mix is ​​obtained after thorough mixing, and the second cured rubber mix is ​​cold pressed to form an outer layer rubber mix.

[0027] The reinforcing agent is one of silicon dioxide, talc, glass fiber, carbon black, titanium dioxide, silver nanosheets, glass microbeads, montmorillonite and calcium carbonate.

[0028] The structure regulator is one of hydroxy silicone oil, epoxy soybean oil, methyl silicone oil, vinyl silicone oil, polyether modified silicone oil and fluorosilicone oil.

[0029] The curing agent is any one of dicumyl peroxide, dibenzoyl peroxide, and 2,4-dichlorobenzoyl peroxide.

[0030] The third step is to prepare the gradient insulation layer: (1) The inner layer of rubber compound is superimposed on the outer layer of rubber compound to form a composite borosilicate rubber, and the composite borosilicate rubber is transferred to a hot plate in a high-pressure reactor; then, gas is introduced into the high-pressure reactor and stabilized to 8-25 MPa; under the supercritical condition of the gas, the pressure is maintained for 0.5-3 hours to allow the gas to quickly diffuse and dissolve in the composite borosilicate rubber matrix; the solvation effect of the gas is used to promote the mutual diffusion of the inner layer of rubber compound and the outer layer of rubber compound, eliminate the gap between the layers, and form a homogeneous system of composite borosilicate rubber and gas; (2) Slowly raising the temperature of the hot plate to 140-190°C and maintaining it at constant pressure and temperature for 10-50 minutes; so that the composite borosilicate rubber is gradient pre-cured under the directional induction of the gradient temperature field, and the degree of pre-curing inside the composite borosilicate rubber presents a continuous gradient change along the thickness direction, that is, a gradient pre-cured sample is obtained, so that a continuous gradient porous structure can be constructed in the subsequent physical foaming process; wherein the degree of pre-curing of the gradient pre-cured sample is from high to low along the thickness direction; (3) Adjust the temperature of the hot plate to the specified foaming temperature of 40-100°C and maintain it for 0.5-2 hours; quickly release the pressure to 0 MPa within 1-5 seconds, so that the composite borosilicate rubber and gas homogeneous system enters a thermodynamically unstable state. Under the action of the gas concentration gradient inside and outside the gradient pre-cured sample, the gas is induced to form pore nuclei in the gradient pre-cured sample and grow into a porous structure, thus obtaining a gradient porous structure sample; wherein, the average pore size of the gradient porous structure sample obtained by foaming shows a continuous gradient change from small to large along the thickness direction; (4) The gradient porous structure sample having a gradient porous structure is placed on a heating table and cured at 160-220°C for 0.1-3h to completely cure the gradient porous structure sample and remove small molecules, thereby obtaining a gradient thermal insulation layer having a gradient porous structure.

[0031] Among them, carbon dioxide is used as the gas.

[0032] In a specific embodiment, the method for preparing the gradient insulation layer that can be used for a molten salt pipeline comprises the following steps: Step 1: Prepare the inner layer compound 100 g of borosilicate rubber, 50 g of fumed silica, and 10 g of hydroxy silicone oil were sequentially added to a rubber internal mixer and mixed at 120° C. and 50 r / min for 20 min to obtain a first rubber mix; the first rubber mix was taken out and remixed for 10 min to uniformly disperse the filler to obtain a first composite sample; 0.2 g of dicumyl peroxide was added to the first composite sample and mixed thoroughly to obtain a first cured rubber mix; the mixture was passed through a mold and cold pressed to obtain an inner layer rubber mix.

[0033] Step 2: Prepare the outer compound 100 g of borosilicate rubber, 50 g of fumed silica, 10 g of hydroxy silicone oil, 25 g of zinc borate, and 40 g of boron aldehyde resin were sequentially added into a rubber internal mixer and mixed at 130° C. and 60 r / min for 20 min to obtain a second rubber mix; the second rubber mix was taken out and remixed for 20 min to uniformly disperse the filler to obtain a second composite sample; 0.2 g of diisopropylbenzene peroxide was added to the second composite sample and mixed thoroughly to obtain a second cured rubber mix; the rubber mix was passed through a mold and cold pressed to obtain an outer layer rubber mix.

[0034] Step 3: Prepare the gradient insulation layer An inner rubber mix is ​​superimposed on an outer rubber mix to form a composite borosilicate rubber, and the composite borosilicate rubber is transferred to a hot plate in an autoclave. Carbon dioxide is then introduced into the autoclave and stabilized at 18 MPa. The pressure is maintained under supercritical carbon dioxide for 2 hours to allow the supercritical carbon dioxide to rapidly diffuse and dissolve in the composite borosilicate rubber matrix. The solvation effect of the supercritical carbon dioxide is utilized to promote mutual diffusion between the two layers of rubber mixes, eliminate lamination gaps, and form a homogeneous system of the composite borosilicate rubber and supercritical carbon dioxide. The temperature of the hot plate is slowly raised to 150°C, and the pressure is maintained constant by a pressure regulator; curing is performed at constant pressure and temperature for 15 minutes, so that the composite borosilicate rubber undergoes gradient pre-curing under the directional induction of the gradient temperature field, thereby causing the pre-curing degree inside the composite borosilicate rubber to exhibit a continuous gradient change along the thickness direction, thereby obtaining a gradient pre-cured sample; wherein the pre-curing degree of the gradient pre-cured sample decreases from high to low along the thickness direction; The temperature of the hot stage was adjusted to a designated foaming temperature of 60°C and maintained for 0.5 hours. The pressure was rapidly released to a gauge pressure of 0 MPa within 1 to 5 seconds, causing the homogeneous system of the composite borosilicate rubber and supercritical carbon dioxide to enter a thermodynamically unstable state. Under the action of the gas concentration gradient inside and outside the gradient pre-cured sample, the supercritical carbon dioxide was induced to form pore nuclei within the gradient pre-cured sample, which then grew into a porous structure, thereby obtaining a gradient porous structure sample. The average pore size of the gradient porous structure sample obtained by foaming exhibited a continuous gradient change from small to large along the thickness direction. Finally, the gradient porous structure sample with a gradient porous structure was placed on a heating platform and cured at 210°C for 0.5h to completely cure the gradient porous structure sample and remove small molecules to obtain a gradient thermal insulation layer with a gradient porous structure.

[0035] The experimental results show that the microscopic morphology of the pore size in this example presents a significant gradient change. The pore size of the gradient insulation layer sample increases gradually from 30.2 μm to 472.5 μm from the small pore layer to the large pore layer, and the pore density increases from 5.9×10 5 pieces / cm 3 Gradually reduced to 7.0×10 3 pieces / cm 3 In addition, from Figure 3 (SEM image) It can be seen that there is no obvious gap between the solid layer and the porous layer, and the healing is good. The calculation results of the curing degree show that the curing degree of the sample after directional induced curing gradually decreases from the solid layer to the macroporous layer, from 82.1% to 13.8%. The specific data are shown in Table 1: Table 1 Average cell size (μm) Average cell density (cells / cm3) Degree of curing (%) Macroporous layer 472.5±9.3 <![CDATA[(7.0±0.3)×10 3 ]]> 13.8±2.0 Mesoporous layer 207.9±8.8 <![CDATA[(1.7±0.3)×10 5 ]]> 24.1±2.2 Small hole layer 30.2±2.1 <![CDATA[(5.9±0.2)×10 5 ]]> 48.3±2.6 Solid layer / / 82.1±4.7 The data in Table 1 were obtained according to the analytical test method, as follows: Scanning electron microscopy analysis: Field emission scanning electron microscopy (SEM) was used to analyze cross-sections of composite borosilicate rubber foam to investigate the average pore size and average cell density of samples with gradient pore structures. The analysis instrument was a SU8010 SEM from HITACHI, Japan. Figure 3 The figure below shows a scanning electron micrograph of a cross-section of a silicone rubber foam sample. The average pore size and average cell density were calculated from the SEM images using Image Pro Plus 6.0 software (IPP). The cell density was calculated according to the method proposed by Kumar et al., where n (>100) is the number of cells in the SEM micrograph and A is the area of ​​the SEM micrograph (in cm). 2 ), the basic idea is to convert the two-dimensional area density into three-dimensional volume density. The pore density per unit volume is: .

[0036] Differential Scanning Calorimetry Analysis: Thermal analysis experiments were conducted on gradient pre-cured samples using differential scanning calorimetry (DSC) to investigate the changes in the curing degree along the thickness direction of the in-situ pre-cured composite borosilicate rubber samples induced by the temperature field. The analytical instrument was a DSC 214 differential scanning calorimeter from Netzsch, Germany. t is the exothermic enthalpy of the curing reaction, and ∆Htotal is the exothermic enthalpy of the complete curing reaction of the uncured sample. The degree of curing (α) is: .

[0037] This embodiment provides a method for preparing a gradient insulation layer that can be used for a molten salt pipeline. By using a strategy of inducing the in-situ curing of rubber in a temperature field-oriented manner, a rubber with a gradient curing degree is constructed. Then, a thermal insulation rubber layer with a gradient porous structure is prepared by supercritical carbon dioxide foaming technology. Its core feature is that the pore size of the porous structure of the rubber gradually changes along the thickness direction, that is, from the pipeline side to the outside, the pore size changes from large to small. This effectively reduces the heat conduction efficiency, reduces the heat loss of the molten salt pipeline, and improves the heat exchange efficiency of the molten salt energy storage system. In addition, considering the actual application environment of the insulation layer, the present invention introduces a flame-retardant and wear-resistant solid layer in the outermost layer through a lamination method. During the in-situ curing process, the solvation effect and molecular diffusion effect of supercritical carbon dioxide are used to eliminate the lamination gaps. This innovative composite insulation layer not only improves the overall efficiency of the system, but also provides a more reliable guarantee for the safe operation of the solar thermal power station, and has good application prospects.

[0038] Second embodiment: like Figure 1-Figure 2 ( Figure 2 for Figure 1 As shown in the enlarged cross-sectional view of the structure corresponding to the position shown in A in the figure, this embodiment provides a gradient thermal insulation layer that can be used for a molten salt pipeline, which is prepared using the preparation method of the gradient thermal insulation layer for a molten salt pipeline provided by the first embodiment. The gradient thermal insulation layer 3 includes a large pore layer 301, a medium pore layer 302, a small pore layer 303 and a solid layer 304 arranged in sequence along the thickness direction. The large pore layer 301 is in contact with the molten salt pipeline 2 with molten salt 1 therein; wherein the pore diameters of the large pore layer 301, the medium pore layer 302 and the small pore layer 303 decrease in sequence.

[0039] Third embodiment: This embodiment provides an application of a gradient insulation layer that can be used for a molten salt pipeline. The gradient insulation layer that can be used for a molten salt pipeline prepared by the preparation method of the gradient insulation layer for a molten salt pipeline provided in the first embodiment is not only suitable for solar thermal power stations, but can also be used in other industrial fields that require efficient insulation, such as petrochemical industry, centralized heating, etc.

[0040] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and that persons skilled in the art may make various changes or modifications within the scope of the claims without affecting the essence of the present invention. The embodiments of the present invention and the features of the embodiments may be combined in any manner unless there is a conflict.

Claims

1. A method for preparing a gradient insulation layer that can be used for a molten salt pipeline, characterized in that: The following steps are involved: Step S1: preparing an inner layer rubber mix; Step S2: preparing an outer layer of rubber compound; Step S3: superimposing the inner layer of rubber mix on the outer layer of rubber mix to form a composite borosilicate rubber; the composite borosilicate rubber utilizes the solvation effect and molecular diffusion effect of supercritical gas to eliminate the lamination gaps, and performs gradient pre-curing under the directional induction of the gradient temperature field, so that the internal pre-curing degree of the composite borosilicate rubber presents a continuous gradient change along the thickness direction, thereby constructing a continuous gradient porous structure in the subsequent physical foaming process, that is, obtaining the gradient thermal insulation layer.

2. The method for preparing a gradient insulation layer for a molten salt pipeline according to claim 1, characterized in that: The step S3 specifically includes the following steps: Step S301: superimposing the inner rubber mix on the outer rubber mix to form the composite borosilicate rubber, and transferring the composite borosilicate rubber to a hot plate in a high-pressure reactor; then introducing the gas into the high-pressure reactor and stabilizing it within a preset pressure range; maintaining the gas under supercritical conditions for a first preset time to allow the gas to rapidly diffuse and dissolve in the composite borosilicate rubber, promote mutual diffusion between the inner rubber mix and the outer rubber mix, eliminate lamination gaps, and form a homogeneous system of the composite borosilicate rubber and gas; Step S302: Raising the temperature of the hot stage to a pre-curing temperature and maintaining it at a constant pressure and temperature for a second preset time, so that the composite borosilicate rubber is gradient pre-cured under the directional induction of the gradient temperature field, thereby causing the pre-curing degree inside the composite borosilicate rubber to present a continuous gradient change along the thickness direction, thereby obtaining a gradient pre-cured sample; wherein the pre-curing degree of the gradient pre-cured sample decreases from high to low along the thickness direction; Step S303: adjusting the temperature of the hot stage to a specified foaming temperature and maintaining it for a third preset time; rapidly releasing the pressure to a preset gauge pressure within a fourth preset time, causing the composite borosilicate rubber and gas homogeneous system to enter a thermodynamically unstable state; and inducing the gas to form pore nuclei within the gradient pre-cured sample under the action of the gas concentration gradient inside and outside the gradient pre-cured sample, which grows into a porous structure, thereby obtaining a gradient porous structure sample; wherein the average pore size of the gradient porous structure sample obtained by foaming presents a continuous gradient change from small to large along the thickness direction; Step S304: placing the gradient porous structure sample on a heating platform, solidifying the gradient porous structure sample and removing small molecules under a third preset condition, thereby obtaining the gradient thermal insulation layer.

3. The method for preparing a gradient insulation layer for a molten salt pipeline according to claim 1, characterized in that: The step S1 specifically includes the following steps: Step S101: adding borosilicate rubber, a reinforcing agent, and a structural regulator into a rubber internal mixer in order according to a proportion, and mixing under a first preset condition to obtain a first mixed rubber; Step S102: taking out the first rubber mix and re-mixing it to uniformly disperse the filler, thereby obtaining a first composite sample; Step S103: adding a curing agent to the first composite sample, mixing, and cold pressing to shape, thereby obtaining the inner layer rubber mixture.

4. The method for preparing a gradient insulation layer for a molten salt pipeline according to claim 1, wherein: The step S2 specifically includes the following steps: Step S201: adding borosilicate rubber, reinforcing agent, structural regulator, flame retardant, and boron-formaldehyde resin into a rubber internal mixer in order according to a proportion, and mixing under a second preset condition to obtain a second mixed rubber; Step S202: taking out the second rubber mix and re-mixing it to uniformly disperse the filler, thereby obtaining a second composite sample; Step S203: adding a curing agent to the second composite sample, mixing, and cold pressing to shape, thereby obtaining the outer layer rubber mixture.

5. The method for preparing a gradient insulation layer that can be used for a molten salt pipeline according to claim 2, characterized in that: In the step S301: the gas is carbon dioxide, the preset gas pressure range is 8 to 25 MPa, and the first preset time is 0.5 to 3 hours; In the step S302: the pre-curing temperature is 140-190° C., and the second preset time is 10-50 minutes; In step S303: the designated foaming temperature is 40-100° C., the third preset time is 0.5-2 hours, the fourth preset time is 1-5 seconds, and the preset pressure is 0 MPa; In the step S304: the third preset condition is curing at 160-220° C. for 0.1-3 hours.

6. The method for preparing a gradient insulation layer for a molten salt pipeline according to claim 3, characterized in that: In step S101, the reinforcing agent is one of silicon dioxide, talc, glass fiber, carbon black, titanium dioxide, silver nanosheets, glass microbeads, montmorillonite, calcium carbonate, or mica; the structural regulator is one of hydroxy silicone oil, epoxy soybean oil, methyl silicone oil, vinyl silicone oil, polyether-modified silicone oil, or fluorosilicone oil; the first preset conditions are 80-130° C. and 40-90 r / min, and the mixing time under the first preset conditions is 10-30 min; In the step S102: the first rubber mix is ​​re-milled for 10 to 30 minutes; In the step S103: the curing agent is any one of dicumyl peroxide, dibenzoyl peroxide, and 2,4-dichlorobenzoyl peroxide.

7. The method for preparing a gradient insulation layer for a molten salt pipeline according to claim 4, characterized in that: In step S201, the reinforcing agent is one of silicon dioxide, talc, glass fiber, carbon black, titanium dioxide, silver nanosheets, glass microbeads, montmorillonite, or calcium carbonate; the structural regulator is one of hydroxy silicone oil, epoxy soybean oil, methyl silicone oil, vinyl silicone oil, polyether-modified silicone oil, or fluorosilicone oil; the second preset conditions are 80-130° C. and 40-90 r / min, and the mixing time under the second preset conditions is 10-30 min; In the step S202: the second rubber mix is ​​re-mixed for 10 to 30 minutes; In the step S203: the curing agent is any one of dicumyl peroxide, dibenzoyl peroxide, and 2,4-dichlorobenzoyl peroxide.

8. A gradient insulation layer that can be used for molten salt pipelines, characterized in that: The thermal insulation layer is prepared by the method for preparing a gradient thermal insulation layer that can be used for a molten salt pipeline according to any one of claims 1 to 7.

9. The gradient insulation layer for molten salt pipeline according to claim 8, characterized in that: The gradient thermal insulation layer comprises a macroporous layer, a medium-porous layer, a microporous layer and a solid layer which are sequentially arranged along the thickness direction. The macroporous layer is in contact with a molten salt pipeline in which molten salt is arranged.

10. An application of a gradient insulation layer for a molten salt pipeline, characterized in that: The gradient insulation layer for molten salt pipelines prepared by the preparation method of the gradient insulation layer for molten salt pipelines as described in any one of claims 1 to 7 is used in the fields of solar thermal power stations, petrochemical industry or centralized heating.

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