Thermochemical composite heat storage material and preparation method thereof

Abstract

The invention provides application of a calcium oxide composite material in a thermochemical heat storage material. The calcium oxide composite material comprises nano calcium oxide particles and micron calcium oxide blocks; in the microstructure of the calcium oxide composite material, nano calcium oxide particles form a nano calcium oxide aggregate with a porous structure; the micron calcium oxide block body is a micron calcium oxide block body with a plurality of gaps formed by layering and cracking; nano calcium oxide particles and nano calcium oxide aggregates are compounded on the micron calcium oxide blocks. The invention also provides a thermochemical composite heat storage material and a preparation method thereof, the material has abundant gradient mass transfer channels and volume expansion buffer spaces on the basis of realizing high filling density of heat storage components, and high energy density, high activity and high conversion rate are jointly realized; the structural stability is high, the blocking effect of a mass transfer channel can be inhibited, and the conversion rate of 95% or above can still be kept after 300 times of heat charging and discharging circulation; and the preparation process is simple and low in cost.

Description

Technical Field

[0001] The present invention relates to the technical field of Ca(OH)2 / CaO / H2O thermochemical energy storage materials, and relates to a thermochemical composite energy storage material and a preparation method thereof. In particular, it relates to the application of calcium oxide composite materials in thermochemical energy storage materials, a thermochemical composite energy storage material and a preparation method thereof. Background Art

[0002] Energy storage technologies are classified into three types according to the heat storage principle: sensible heat energy storage, latent heat energy storage and thermochemical energy storage. Compared with sensible heat and latent heat energy storage, thermochemical energy storage shows obvious advantages: high mass energy storage density, wide heat storage temperature range, long storage cycle, small heat loss, and ability to transport over long distances. In the existing thermochemical storage system, Ca(OH)2 / CaO / H2O is a typical heat storage system in the medium and high temperature range, and has important application value in solar thermal utilization and industrial waste heat recovery.

[0003] At present, the Ca(OH)2 / CaO / H2O energy storage material is still in the laboratory research and development stage, mainly because the energy storage density and efficiency of this system still cannot meet the requirements of industrial applications. The core performance of thermochemical energy storage materials is energy storage density, reaction activity, stability and heat and mass transfer ability. However, the existing optimization technologies are difficult to balance the performance requirements in multiple aspects.

[0004] Some research solutions have also been disclosed in existing literature. For example, in "Synthesis and performances evaluation of the spindle-shaped calcium hydroxide nanomaterials for thermochemical energy storage" in Journal of Nanoparticle Research (2019) 21:262, the spindle-shaped calcium hydroxide nanomaterials are disclosed for application in Ca(OH)2 / CaO / H2O thermochemical energy storage. By reducing the particle size and increasing the specific surface area, the reaction rate and conversion rate are improved. However, the resulting high porosity leads to a decrease in the packing density and energy density. And in "Investigation on the calcium hydroxide / calcium oxide thermochemical energy storage system with potassium nitrate addition" in Solar Energy Materials & Solar Cells (2020) 215:110646, potassium nitrate composite calcium hydroxide is disclosed for application in Ca(OH)2 / CaO / H2O thermochemical energy storage. By doping / composite with heat storage inert components, the reaction activation energy is reduced. In addition, "Reaction Performance of Calcium Hydroxide and Expanded Graphite Composites for Chemical Heat Storage Applications" in ISIJ International (2015) 55:457 reports the enhancement of heat transfer in the Ca(OH)2 / CaO / H2O thermochemical energy storage process through the composite of graphite and calcium hydroxide. However, the doping modification strategy sacrifices the proportion of the main heat storage material and the volumetric energy density of the heat storage system.

[0005] Therefore, how to find a more suitable thermochemical energy storage material for the Ca(OH)2 / CaO / H2O energy storage system to solve the above problems existing in the prior art has become one of the focuses widely concerned by many forward-looking front-line researchers in the industry. Summary of the Invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide an application of calcium oxide composite material in thermochemical energy storage materials, a thermochemical composite energy storage material and a preparation method thereof, in particular a thermochemical composite energy storage material and a preparation method thereof. The thermochemical composite energy storage material provided by the present invention has rich gradient mass transfer channels and volume expansion buffer spaces on the basis of realizing a high filling density of energy storage components, jointly realizing high energy density, high activity and high conversion rate. Moreover, the preparation process is simple, the cost is low, it can meet the needs of large-scale production, and it is more suitable for industrial application and development.

[0007] The present invention provides an application of calcium oxide composite material in thermochemical energy storage materials;

[0008] The calcium oxide composite material includes nano calcium oxide particles and micro calcium oxide blocks;

[0009] In the microscopic morphology of the calcium oxide composite material, the nano calcium oxide particles form nano calcium oxide aggregates with a porous structure;

[0010] The micro calcium oxide block is a micro calcium oxide block with multiple cracks formed by delamination;

[0011] The micro calcium oxide block is compounded with nano calcium oxide particles and nano calcium oxide aggregates.

[0012] Preferably, the particle size of the nano calcium oxide particles is 10-100 nm;

[0013] The formation specifically means that the nano calcium oxide particles connect and grow to form aggregates with a porous structure and / or the aggregates stack to form aggregates with a porous structure;

[0014] The pore diameter of the porous structure is 1-200 nm.

[0015] Preferably, the nano calcium oxide particles and / or nano calcium oxide aggregates are compounded on the surface of the micro calcium oxide block and / or in the gaps of the micro calcium oxide block;

[0016] The application is specifically an application in the Ca(OH)2 / CaO / H2O thermochemical energy storage system.

[0017] Preferably, the size of the micro calcium oxide block is 1-10 μm;

[0018] The length of the gap is 1-10 μm;

[0019] The width of the gap is 1-200 nm.

[0020] The present invention provides a thermochemical composite energy storage material, including nano calcium oxide particles and micro calcium oxide blocks;

[0021] In the microscopic morphology of the calcium oxide composite material, nano-calcium oxide particles form nano-calcium oxide aggregates with a porous structure;

[0022] The micron calcium oxide block is a micron calcium oxide block with multiple cracks formed by delamination cracking;

[0023] The micron calcium oxide block is compounded with nano-calcium oxide particles and nano-calcium oxide aggregates.

[0024] Preferably, the pores formed by the connection and growth of the nano-calcium oxide particles, the pores formed by the stacking between the aggregates, the cracking gaps of the micron calcium oxide block, and the voids between the micron calcium oxide block / nano-calcium oxide aggregate together constitute a gradient mass transfer channel;

[0025] The size of the voids ≥ 500 nm;

[0026] In the thermochemical composite heat storage material, the percentage of the calcium molar number of micron calcium oxide in the total calcium content is 30% - 80%.

[0027] Preferably, the specific surface area of the thermochemical composite heat storage material is 1 - 50 m 2 / g;

[0028] The average pore size of the thermochemical composite heat storage material is 1 - 10 nm;

[0029] The pore volume of the thermochemical composite heat storage material is 0.05 - 0.2 cm 3 / g;

[0030] The apparent density of the thermochemical composite heat storage material is 0.5 - 2.0 g / cm 3 .

[0031] The present invention also provides a preparation method of a thermochemical composite heat storage material, comprising the following steps:

[0032] 1) Mix micron calcium oxide powder with nano-calcium-based thermal decomposition material to obtain a mixed powder;

[0033] 2) Heat-treat the mixed powder obtained in the above step to obtain a thermochemical composite heat storage material.

[0034] Preferably, the particle size of the micron calcium oxide powder is 1 - 10 μm;

[0035] The particle size of the nano-calcium-based thermal decomposition material is 10 - 200 nm;

[0036] The nano-calcium-based thermal decomposition material is a material whose thermal decomposition product is nano-calcium oxide and gas.

[0037] Preferably, the nano calcium-based thermal decomposition material includes, but is not limited to, one or more of calcium carbonate, calcium acetate, calcium hydroxide, calcium lactate, and calcium gluconate;

[0038] The mixing method includes, but is not limited to, one or more of stirring, grinding, ball milling, and alternating layer-by-layer mixing;

[0039] The temperature of the heat treatment is 200-1000 °C;

[0040] The time of the heat treatment is 0.5-48 h.

[0041] The present invention provides an application of a calcium oxide composite material in a thermochemical energy storage material; the calcium oxide composite material includes nano calcium oxide particles and micron calcium oxide blocks; in the microscopic morphology of the calcium oxide composite material, the nano calcium oxide particles form nano calcium oxide aggregates with a porous structure; the micron calcium oxide blocks are compounded with nano calcium oxide particles and nano calcium oxide aggregates. Compared with the prior art, the present invention believes that in the paper "Journal of Nanoparticle Research (2019) 21:262", although the morphology of calcium hydroxide is designed as a spindle-shaped nanostructure, which further improves the specific surface area and reactivity of the material, the energy storage material is a single-component calcium hydroxide nanomaterial. Due to the small size and high porosity of the nanoparticles, the packing density of the energy storage active component will decrease, thereby limiting the improvement of the energy storage density; moreover, as a single energy storage active component, since the calcium content ratio and true density of calcium hydroxide are both lower than those of calcium oxide, a high packing density of the energy storage active component cannot be achieved, thereby reducing the energy storage density. In the technical solution of "Solar Energy Materials & Solar Cells (2020) 215:110646", potassium nitrate is used as an energy storage inert substance, and an addition amount of 10 wt% is required to play an activation role. The addition of a certain proportion of energy storage inert components will lead to a decrease in the packing density of the energy storage active component, thereby limiting the improvement of the energy storage density. At the same time, as a single energy storage active component, calcium hydroxide is filled into the energy storage reactor. Since the calcium content ratio and true density of calcium hydroxide are both lower than those of calcium oxide, a high packing density of the energy storage active component cannot be achieved, thereby reducing the energy storage density.

[0042] There are also technical solutions for studying hollow nanostructured calcium oxide (Fuel Processing Technology (2021) 217: 106834). However, the research of the present invention believes that when hollow nanostructured calcium oxide is used as a single heat storage component to fill the heat storage reactor, the high porosity reduces the filling density of the heat storage active component, thereby reducing the heat storage energy density. Moreover, carbonaceous nanospheres are used as hard templates to construct the hollow nanostructure. Not only is it necessary to first synthesize the template agent, but also to remove the template agent. The synthesis process flow is complex and the operation is cumbersome, and the conversion rate of calcium element to the product is very low. Therefore, the present invention believes that during the thermochemical reaction cycle, if there is not enough space between locally over-dense calcium oxide particles, adjacent particles are likely to grow together during the hydration reaction, blocking the mass transfer channel and leading to the attenuation of the reaction rate and conversion rate, that is, the "blocking effect"; at the same time, when calcium oxide reacts with water to form calcium hydroxide, a significant volume expansion will occur. The higher the filling density, the higher the volume expansion rate, and the highest expansion rate can reach 0.95. Under the condition of a fixed volume, the space limitation will inhibit the conversion rate and reaction rate of the exothermic hydration reaction process. Therefore, to achieve the goal of commercial application of the Ca(OH)2 / CaO / H2O thermochemical heat storage system, it is necessary to improve the reaction rate and conversion rate on the basis of ensuring a high filling density of the heat storage active component.

[0043] Based on this, the present invention creatively designs a calcium oxide composite material with a specific microscopic morphology and structure and uses it in thermochemical heat storage materials, which can greatly improve the reaction rate and conversion rate on the basis of ensuring a high filling density of the heat storage active component. The present invention also provides a thermochemical composite heat storage material and a preparation method thereof. The thermochemical composite heat storage material is a composite material composed of nano-calcium oxide particles and micron-sized calcium oxide blocks. The nano-calcium oxide is in the form of nanoparticles that connect and grow to form aggregates with a porous structure, which are scattered or adhered to the surface of the micron-sized calcium oxide blocks; the small nano-pores formed by the connection and growth of the nano-calcium oxide particles and the larger nano-pores formed by the stacking of the aggregates; the size of the micron-sized calcium oxide blocks is in the micron level, and the blocks are stratified and cracked to form a large number of micro-nano scale gaps. The pores of these nano-calcium oxides, the gaps of the micron-sized calcium oxides, and the spaces around the micron-sized calcium oxide blocks / nano-calcium oxide aggregates together constitute a gradient mass transfer channel.

[0044] The thermochemical composite heat storage material provided by the present invention has rich gradient mass transfer channels and volume expansion buffer spaces on the basis of achieving a high filling density of heat storage components, jointly realizing high energy density, high activity and high conversion rate; the porous structure formed by the connection and growth of nanoparticles not only has high structural stability, but also can inhibit the blocking effect of the mass transfer channels, and can still maintain a conversion rate of more than 95% after 300 charge-discharge cycles. Moreover, the preparation process is simple, with good controllability, high stability, mild conditions and low cost, which can meet the needs of large-scale production and is more suitable for industrial application and development. Description of the Drawings

[0045] Figure 1 It is a photograph of the appearance of the thermochemical composite heat storage material provided by the present invention;

[0046] Figure 2 It is the XRD curve of the thermochemical composite heat storage material provided by the present invention;

[0047] Figure 3 It is the SEM photograph of the thermochemical composite heat storage material provided by the present invention;

[0048] Figure 4 It is the high-magnification SEM photograph of nano-calcium oxide in the thermochemical composite heat storage material provided by the present invention;

[0049] Figure 5 It is the high-magnification SEM photograph of micro-calcium oxide in the thermochemical composite heat storage material provided by the present invention;

[0050] Figure 6 It is the pore size distribution diagram (BJH-adsorption) of the thermochemical composite heat storage material provided by the present invention;

[0051] Figure 7 It is a schematic flow chart of the preparation method of the thermochemical composite heat storage material provided by the present invention. Detailed Embodiments

[0052] In order to further understand the present invention, the preferred embodiments of the present invention will be described below in conjunction with examples. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention rather than limiting the claims of the present invention.

[0053] For all raw materials of the present invention, there is no particular limitation on their sources, and they can be purchased on the market or prepared by conventional methods well-known to those skilled in the art.

[0054] For all raw materials of the present invention, there is no particular limitation on their purity. The present invention preferably uses analytical pure or conventional purity used in the field of thermochemical heat storage material preparation.

[0055] Thermochemical heat storage: Based on the reaction heat (endothermic / exothermic) of a reversible chemical reaction process, heat is stored and released to achieve the heat storage function. For example, the decomposition of calcium hydroxide into calcium oxide and water is an endothermic reaction process for storing heat; its reverse reaction, the reaction of calcium oxide with water to form calcium hydroxide, is an exothermic reaction for releasing heat.

[0056] Reaction equation: ΔH = 104.4 kJ / mol.

[0057] The present invention provides an application of a calcium oxide composite material in a thermochemical heat storage material;

[0058] The calcium oxide composite material includes nano-calcium oxide particles and micro-calcium oxide bulk;

[0059] In the microscopic morphology of the calcium oxide composite material, the nano-calcium oxide particles form nano-calcium oxide aggregates with a porous structure;

[0060] The micro-calcium oxide bulk is a micro-calcium oxide bulk with layered cracking to form multiple gaps;

[0061] The micro-calcium oxide bulk is compounded with nano-calcium oxide particles and nano-calcium oxide aggregates.

[0062] In the present invention, the particle size of the nano-calcium oxide particles is preferably 10 - 100 nm, more preferably 30 - 80 nm, and even more preferably 50 - 60 nm.

[0063] In the present invention, the formation is specifically preferably that the nano-calcium oxide particles connect and grow to form aggregates with a porous structure and / or the aggregates stack to form aggregates with a porous structure, and more preferably that the nano-calcium oxide particles connect and grow to form aggregates with a porous structure or the aggregates stack to form aggregates with a porous structure.

[0064] In the present invention, the pore diameter of the porous structure is preferably 1 - 200 nm, more preferably 10 - 150 nm, and even more preferably 50 - 100 nm.

[0065] In the present invention, the nano-calcium oxide particles and / or nano-calcium oxide aggregates are preferably compounded on the surface and / or in the gaps of the micro-calcium oxide bulk, and more preferably compounded on the surface or in the gaps of the micro-calcium oxide bulk.

[0066] In the present invention, the application is specifically preferably an application in a Ca(OH)2 / CaO / H2O thermochemical heat storage system.

[0067] In the present invention, the size of the micro-calcium oxide bulk is preferably 1 - 10 μm, more preferably 3 - 8 μm, and even more preferably 5 - 6 μm.

[0068] In the present invention, the length of the slit is preferably 1 to 10 μm, more preferably 3 to 8 μm, and still more preferably 5 to 6 μm.

[0069] In the present invention, the width of the slit is preferably 1 to 200 nm, more preferably 10 to 150 nm, and still more preferably 50 to 100 nm.

[0070] The thermochemical composite heat storage material provided by the present invention is a composite material composed of nano-calcium oxide particles and micro-calcium oxide blocks. Among them, the nano-calcium oxide is particles with a size of 10 to 100 nm, which are connected and grown to form an aggregate with a porous structure, and are scattered or adhered on the surface of the micro-calcium oxide blocks; the pores formed by the connection and growth of the nano-calcium oxide particles and the pores formed by the stacking of the aggregates have a diameter of about 1 to 200 nm; the size of the micro-calcium oxide blocks is about 1 to 10 μm, and the blocks are stratified and cracked to form a large number of slits (with a length of about 1 to 10 μm and a width of about 1 to 200 nm); the specific surface area of the thermochemical composite heat storage material measured by nitrogen adsorption and desorption characterization is about 1 to 50 m 2 / g, the average pore size is about 1 to 10 nm, and the pore volume is about 0.05 to 0.2 cm 3 / g. The pores of the nano-calcium oxide, the slits of the micro-calcium oxide, and the voids around the micro-calcium oxide blocks / nano-calcium oxide aggregates (void size ≥ 500 nm) together constitute a gradient mass transfer channel.

[0071] The present invention provides a thermochemical composite heat storage material, including nano-calcium oxide particles and micro-calcium oxide blocks;

[0072] In the microscopic morphology of the calcium oxide composite material, the nano-calcium oxide particles form nano-calcium oxide aggregates with a porous structure;

[0073] The micro-calcium oxide blocks are micro-calcium oxide blocks with layered cracks forming multiple slits;

[0074] The micro-calcium oxide blocks are compounded with nano-calcium oxide particles and nano-calcium oxide aggregates.

[0075] In the present invention, in the thermochemical composite heat storage material, part of the nano-calcium oxide particles are scattered, and part are compounded on the micro-calcium oxide blocks. Similarly, some of the nano-calcium oxide aggregates are scattered, and some are compounded on the micro-calcium oxide blocks. Specifically, the nano-calcium oxide aggregates adhere to the micro-calcium oxide blocks and also coat the micro-calcium oxide blocks.

[0076] In the present invention, the pores formed by the connection and growth of the nano-calcium oxide particles preferably, the pores formed by the stacking of the aggregates, the cracked slits of the micro-calcium oxide blocks, and the voids between the micro-calcium oxide blocks / nano-calcium oxide aggregates together constitute a gradient mass transfer channel.

[0077] In the present invention, the size of the voids is preferably ≥500 nm, more preferably ≥600 nm, and even more preferably ≥800 nm.

[0078] In the present invention, in the thermochemical composite heat storage material, the percentage of the calcium molar number of micron calcium oxide in the total calcium content is preferably 30% - 80%, more preferably 40% - 70%, and even more preferably 50% - 60%.

[0079] In the present invention, the specific surface area of the thermochemical composite heat storage material is preferably 1 - 50 m 2 / g, more preferably 5 - 50 m 2 / g, and even more preferably 15 - 45 m 2 / g.

[0080] In the present invention, the average pore size of the thermochemical composite heat storage material is preferably 1 - 10 nm, more preferably 3 - 8 nm, and even more preferably 5 - 6 nm.

[0081] In the present invention, the pore volume of the thermochemical composite heat storage material is preferably 0.05 - 0.2 cm 3 / g, more preferably 0.08 - 0.17 cm 3 / g, and even more preferably 0.11 - 0.14 cm 3 / g.

[0082] In the present invention, the apparent density of the thermochemical composite heat storage material is preferably 0.5 - 2.0 g / cm 3 , more preferably 0.8 - 1.8 g / cm 3 , and even more preferably 1.0 - 1.5 g / cm 3 .

[0083] In the present invention, the thermochemical composite heat storage material further includes calcium hydroxide impurities and calcium carbonate impurities. Among them, the impurities in the thermochemical composite heat storage material are mainly formed by calcium oxide contacting water and carbon dioxide in the air, and have no direct relation with the selection of the calcium-based thermal decomposition material. However, in practical applications, different raw material sources may also have other impurities. Therefore, the present invention is not limited to the above two kinds of impurities.

[0084] In the present invention, the mass fraction of the calcium hydroxide impurities can be <5%, or ≤4%, or ≤3%. The mass fraction of the calcium carbonate impurities can be <5%, or ≤4%, or ≤3%.

[0085] The present invention is to complete and refine the overall technical solution, better ensure the composition of the thermochemical composite heat storage material, the specific gradient mass transfer channel structure and the volume expansion buffer space, and further improve its energy density, activity and conversion rate. The above thermochemical composite heat storage material may specifically include the following content:

[0086] The characteristics of the thermochemical composite heat storage material specifically include that the thermochemical composite heat storage material is a composite material composed of nano calcium oxide particles and micron calcium oxide blocks.

[0087] Among them, the nano calcium oxide is nano particles with a size of 10-100 nm, which are connected and grown to form an aggregate with a porous structure, and are scattered or adhered on the surface of the micron calcium oxide block. The pores formed by the connection and growth of the nano calcium oxide particles and the pores formed by the stacking of the aggregates have a diameter of about 1-200 nm. The size of the micron calcium oxide block is about 1-10 μm, and the block is stratified and cracked to form a large number of gaps (with a length of about 1-10 μm and a width of about 1-200 nm).

[0088] Specifically, the specific surface area of the thermochemical composite heat storage material measured by nitrogen adsorption and desorption is about 1-50 m 2 / g, the average pore size is about 1-10 nm, and the pore volume is about 0.05-0.2 cm 3 / g.

[0089] Specifically, the pore channels of the nano calcium oxide, the gaps of the micron calcium oxide, and the voids (with a size ≥ 500 nm) around the micron calcium oxide block / nano calcium oxide aggregate together constitute the gradient mass transfer channel.

[0090] The thermochemical composite heat storage material provided by the present invention has high energy density, high activity and high stability. The calcium-containing ratio of calcium oxide is high (mass fraction 71%) and the true density is high (3.35 g / cm 3 ), the porosity of the micron calcium oxide is low, which can significantly improve the filling density of the heat storage active component; moreover, the particle size of the nano-porous calcium oxide is small and has a porous structure, so that the thermochemical composite heat storage material has a large specific surface area (1-50 m 2 / g) to achieve high reaction activity. At the same time, the pore channels of the nano calcium oxide, the gaps of the micron calcium oxide, and the voids (with a void size ≥ 500 nm) around the micron calcium oxide block / nano calcium oxide aggregate together constitute the gradient mass transfer channel. The present invention strengthens the mass transfer channel and can also buffer the volume expansion of the hydration reaction, thereby achieving high reaction activity and high conversion rate. Moreover, the nano calcium oxide particles in the thermochemical composite heat storage material are connected and grown into a porous structure, and this pore structure is stable, avoiding the "blocking effect" between particles, thereby achieving high cycle stability of the heat storage performance.

[0091] See Figure 1 , Figure 1Appearance photo of the thermochemical composite heat storage material provided by the present invention.

[0092] See Figure 2 , Figure 2 XRD curve of the thermochemical composite heat storage material provided by the present invention.

[0093] It can be proved by Figure 2 that the main component of the powder in the thermochemical composite heat storage material is calcium oxide containing a small amount of calcium hydroxide (●) and calcium carbonate (■) impurities.

[0094] See Figure 3 , Figure 3 SEM photo of the thermochemical composite heat storage material provided by the present invention.

[0095] See Figure 4 , Figure 4 High-magnification SEM photo of nano-calcium oxide in the thermochemical composite heat storage material provided by the present invention.

[0096] See Figure 5 , Figure 5 High-magnification SEM photo of micro-calcium oxide in the thermochemical composite heat storage material provided by the present invention.

[0097] See Figure 6 , Figure 6 Pore size distribution diagram (BJH-adsorption) of the thermochemical composite heat storage material provided by the present invention.

[0098] The pore distribution of the thermochemical composite heat storage material provided by the present invention mainly comes from the connection and growth of nano-calcium oxide particles, the accumulation of nano-calcium oxide aggregates, and the cracking gaps of micro-calcium oxide blocks.

[0099] The present invention provides a preparation method of a thermochemical composite heat storage material, comprising the following steps:

[0100] 1) Mix the micro-calcium oxide powder with the nano-calcium-based thermal decomposition material to obtain a mixed powder;

[0101] 2) Heat-treat the mixed powder obtained in the above step to obtain the thermochemical composite heat storage material.

[0102] The present invention first mixes the micro-calcium oxide powder with the nano-calcium-based thermal decomposition material to obtain a mixed powder.

[0103] In the present invention, the particle size of the micro-calcium oxide powder is preferably 1-10 μm, more preferably 3-8 μm, and even more preferably 5-6 μm.

[0104] In the present invention, the particle size of the nano calcium-based thermal decomposition material is preferably 10-200 nm, more preferably 50-160 nm, and even more preferably 90-120 nm.

[0105] In the present invention, the nano calcium-based thermal decomposition material is preferably a material whose thermal decomposition products are nano calcium oxide and gas.

[0106] In the present invention, the nano calcium-based thermal decomposition material preferably comprises one or more of calcium carbonate, calcium acetate, calcium hydroxide, calcium lactate, and calcium gluconate, and more preferably is calcium carbonate, calcium acetate, calcium hydroxide, calcium lactate, or calcium gluconate.

[0107] In the present invention, the mixing method preferably comprises one or more of stirring, grinding, ball milling, and alternating layer-by-layer mixing, and more preferably is a plurality of stirring, grinding, ball milling, and alternating layer-by-layer mixing.

[0108] Finally, in the present invention, the mixed powder obtained in the above steps is heat-treated to obtain a thermochemical composite heat storage material.

[0109] In the present invention, the temperature of the heat treatment is preferably 200-1000 °C, more preferably 400-900 °C, and even more preferably 600-800 °C.

[0110] In the present invention, the time of the heat treatment is preferably 0.5-48 h, more preferably 10-40 h, and even more preferably 20-30 h.

[0111] In order to complete and refine the overall technical solution of the present invention, better ensure the composition of the thermochemical composite heat storage material and the specific gradient mass transfer channel structure and volume expansion buffer space, and further improve its energy density, activity, and conversion rate, the above thermochemical composite heat storage material may specifically include the following:

[0112] See Figure 7 , Figure 7 is a schematic process flow diagram of the preparation method of the thermochemical composite heat storage material provided by the present invention. Among them, 1-reactor; 2-uniform mixing; 3-thermal decomposition gas product; 4-thermochemical composite heat storage material.

[0113] The present invention provides a preparation method of a thermochemical composite heat storage material (such as Figure 7 ):

[0114] The powdery micron calcium oxide is fully mixed with the nano calcium-based thermal decomposition material, and the calcium-based thermal decomposition material therein is fully decomposed through one-step heat treatment to generate nano calcium oxide particles and discharge gas products; the nano calcium oxide particles are connected and grown into a porous structure, and a composite system formed with micron calcium oxide is the target thermochemical composite heat storage material. The preparation process is simple, the cost is low, and it can meet the needs of large-scale production.

[0115] Specifically, micron calcium oxide in powder form and nano calcium-based thermal decomposition materials are uniformly mixed in a certain proportion, where the percentage of the calcium molar content of the micron calcium oxide in the total calcium content is 30% to 80%.

[0116] Specifically, the particle size of the micron calcium oxide is 1 to 10 μm.

[0117] Specifically, the particle size of the nano calcium-based thermal decomposition materials is 10 to 200 nm.

[0118] Specifically, the calcium-based thermal decomposition materials are characterized in that they are thermally decomposed at a certain temperature, and the decomposition products are nano calcium oxide and gas. The calcium-based thermal decomposition materials include, but are not limited to, any one or a mixture of more than one of the following: calcium carbonate, calcium acetate, calcium hydroxide, calcium lactate, and calcium gluconate.

[0119] Specifically, the mixing methods include, but are not limited to, any one or a combination of more than one of the following methods: stirring, grinding, ball milling, alternating layer-by-layer mixing, etc.

[0120] Specifically, the above-mentioned mixed powder is heat-treated at a certain temperature (200 - 1000) for a certain period of time (0.5 - 48 h) until the calcium-based thermal decomposition materials are completely decomposed, generating nano calcium oxide particles and discharging gas products; the composite system formed by the nano calcium oxide and the micron calcium oxide is the target thermochemical composite heat storage material.

[0121] The thermochemical composite heat storage material developed by the present invention, on the basis of realizing a high filling density of the heat storage components, has rich gradient mass transfer channels and volume expansion buffer spaces, jointly realizing high energy density, high activity and high conversion rate; the porous structure formed by the connection and growth of nano particles not only has high structural stability, but also can inhibit the blocking effect of the mass transfer channels, and can still maintain a conversion rate of more than 95% after 300 charge-discharge cycles.

[0122] The above content of the present invention provides the application of calcium oxide composite materials in thermochemical energy storage materials, a thermochemical composite energy storage material and a preparation method thereof. The calcium oxide composite material designed by the present invention has a specific microscopic morphology and composite structure, and is used in thermochemical energy storage materials, which can greatly improve the reaction rate and conversion rate on the basis of ensuring a high filling density of heat storage active components. The present invention also provides a thermochemical composite energy storage material and a preparation method thereof. The thermochemical composite energy storage material is a composite material composed of nano calcium oxide particles and micron calcium oxide blocks. The nano calcium oxide is nano particles, which are connected and grown to form an aggregate with a porous structure, and are scattered or adhered on the surface of the micron calcium oxide blocks; the small nano pores formed by the connection and growth of nano calcium oxide particles and the larger nano pores formed by the stacking of aggregates; the micron calcium oxide blocks are micron-sized, and the blocks are layered and cracked to form a large number of micro-nano gaps. The pores of these nano calcium oxides, the gaps of micron calcium oxides and the voids around the micron calcium oxide blocks / nano calcium oxide aggregates together constitute a gradient mass transfer channel.

[0123] The thermochemical composite energy storage material provided by the present invention has rich gradient mass transfer channels and volume expansion buffer spaces on the basis of realizing a high filling density of heat storage components, and jointly realizes high energy density, high activity and high conversion rate; the porous structure formed by the connection and growth of nano particles not only has high structural stability, but also can inhibit the blocking effect of the mass transfer channel, and can still maintain a conversion rate of more than 95% after 300 charge-discharge cycles. Moreover, the preparation process is simple, has good controllability, high stability, mild conditions and low cost, can meet the needs of large-scale production, and is more suitable for industrial application and development.

[0124] In order to further illustrate the present invention, the following examples are used to describe in detail the application of the calcium oxide composite material provided by the present invention in thermochemical energy storage materials, a thermochemical composite energy storage material and a preparation method thereof. However, it should be understood that these examples are implemented on the premise of the technical solution of the present invention, and the detailed implementation manners and specific operation processes are given, only to further illustrate the features and advantages of the present invention, rather than a limitation on the claims of the present invention. The protection scope of the present invention is not limited to the following examples.

[0125] Example 1

[0126] The powdery micron calcium oxide and nano calcium acetate are fully mixed to obtain a mixed powder material. The mixed powder material is heat-treated at 800 °C for 4 h. The nano calcium acetate therein is completely decomposed to generate nano calcium oxide particles and discharge gas products. The nano calcium oxide particles are connected and grown into a porous structure and form a composite system with micron calcium oxide to obtain a thermochemical composite energy storage material.

[0127] Among them, the particle size of micron calcium oxide is 1-10 μm, the particle size of nano calcium acetate is 10-100 nm, and the micron calcium oxide and nano calcium acetate in powder form are ball-milled and mixed according to the proportion that the calcium molar content of micron calcium oxide accounts for 30% of the total calcium content.

[0128] Characterize the thermochemical composite heat storage material prepared in Example 1 of the present invention.

[0129] The characterization results are as Figures 2 to 6 shown.

[0130] Perform performance tests on the thermochemical composite heat storage material prepared in Example 1 of the present invention.

[0131] The charge and discharge performance test of the thermochemical composite heat storage material is as follows:

[0132] Weigh 15 g of the thermochemical composite heat storage material prepared in Example 1, and complete the cyclic thermal decomposition reaction (heat charging process) and hydration reaction (heat discharging process) in a vacuum-sealed tubular reactor. The heat charging temperature is 550 °C, the water vapor pressure during heat discharging is 60 kPa, and the difference between the weight after heat discharging and the weight after heat charging is the actual hydration / dehydration amount. By comparing with the theoretical hydration / dehydration amount, the hydration (heat discharging) / decomposition (heat charging) conversion rate is calculated. After 300 charge and discharge cycles, there is no obvious attenuation, and the heat discharging / heat charging conversion rates are both maintained above 95%.

[0133] Example 2

[0134] Fully mix the micron calcium oxide and nano calcium hydroxide in powder form to obtain a mixed powder. Heat-treat the mixed powder at 700 °C for 5 h. The nano calcium hydroxide therein completely decomposes to generate nano calcium oxide particles and discharge gas products. The nano calcium oxide particles connect and grow into a porous structure, and form a composite system with the micron calcium oxide to obtain a thermochemical composite heat storage material.

[0135] Among them, the particle size of micron calcium oxide is 1-10 μm, the particle size of nano calcium hydroxide is 10-100 nm, and the micron calcium oxide and nano calcium hydroxide in powder form are ball-milled and mixed according to the proportion that the calcium molar content of micron calcium oxide accounts for 60% of the total calcium content.

[0136] Characterize the thermochemical composite heat storage material prepared in Example 2 of the present invention.

[0137] The microscopic morphology is basically the same as that of Example 1.

[0138] Perform performance tests on the thermochemical composite heat storage material prepared in Example 2 of the present invention.

[0139] The charge and discharge performance test of the thermochemical composite heat storage material is as follows:

[0140] Weigh 15 g of the thermochemical composite heat storage material prepared in Example 2, and complete the cyclic thermal decomposition reaction (heat charging process) and hydration reaction (heat release process) in a vacuum-sealed tubular reactor. The heat charging temperature is 550 °C, the water vapor pressure during heat release is 60 kPa. The difference between the weight after heat release and the weight after heat charging is the actual hydration / dehydration amount. By comparing with the theoretical hydration / dehydration amount, the hydration (heat release) / decomposition (heat charging) conversion rate is calculated. After 300 cycles of heat charging and heat release, there is no obvious attenuation, and the heat release / heat charging conversion rates are both maintained above 96%.

[0141] Example 3

[0142] Fully mix powdery micron calcium oxide and nano calcium carbonate to obtain a mixed powder. Heat-treat the mixed powder at 1000 °C for 8 h. The nano calcium carbonate therein completely decomposes to generate nano calcium oxide particles and expel gas products. The nano calcium oxide particles connect and grow into a porous structure, forming a composite system with micron calcium oxide to obtain a thermochemical composite heat storage material.

[0143] Among them, the particle size of micron calcium oxide is 1 - 10 μm, the particle size of nano calcium carbonate is 50 - 200 nm. The powdery micron calcium oxide and nano calcium carbonate are ball-milled and mixed according to the proportion that the percentage of calcium molar content of micron calcium oxide in the total calcium content is 40%.

[0144] Characterize the thermochemical composite heat storage material prepared in Example 3 of the present invention.

[0145] The microscopic morphology is basically the same as that of Example 1.

[0146] Conduct performance tests on the thermochemical composite heat storage material prepared in Example 3 of the present invention.

[0147] The heat charging and heat release performance test of the thermochemical composite heat storage material is as follows:

[0148] Weigh 15 g of the thermochemical composite heat storage material prepared in Example 3, and complete the cyclic thermal decomposition reaction (heat charging process) and hydration reaction (heat release process) in a vacuum-sealed tubular reactor. The heat charging temperature is 550 °C, the water vapor pressure during heat release is 60 kPa. The difference between the weight after heat release and the weight after heat charging is the actual hydration / dehydration amount. By comparing with the theoretical hydration / dehydration amount, the hydration (heat release) / decomposition (heat charging) conversion rate is calculated. After 300 cycles of heat charging and heat release, there is no obvious attenuation, and the heat release / heat charging conversion rates are both maintained above 97%.

[0149] The above has introduced in detail the application of the calcium oxide composite material provided by the present invention in thermochemical energy storage materials, a thermochemical composite energy storage material and its preparation method. In this article, specific examples are used to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention, including the best mode, and also enables any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention. The protection scope of the present invention patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements that are not different from the literal expression of the claims, or if they include equivalent structural elements that have no substantial difference from the literal expression of the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. Application of calcium oxide composite materials in thermochemical energy storage materials; The calcium oxide composite material includes nano calcium oxide particles and micron calcium oxide bulk; In the microscopic morphology of the calcium oxide composite material, the nano calcium oxide particles form nano calcium oxide aggregates with a porous structure; The micron calcium oxide bulk is a micron calcium oxide bulk with layered cracking to form multiple gaps; The micron calcium oxide bulk is compounded with nano calcium oxide particles and nano calcium oxide aggregates.

2. The application according to claim 1, characterized in that, The particle size of the nano-calcium oxide particles is 10-100 nm; The formation specifically means that the nano-calcium oxide particles connect and grow to form aggregates with a porous structure and / or the aggregates stack to form aggregates with a porous structure; The pore diameter of the porous structure is 1-200 nm.

3. The application according to claim 1, characterized in that, The nano-calcium oxide particles and / or nano-calcium oxide aggregates are compounded on the surface and / or in the gaps of the micron-calcium oxide bulk; The application specifically refers to the application in the Ca(OH)2 / CaO / H2O thermochemical energy storage system.

4. The application according to claim 3, characterized in that, The size of the micron-calcium oxide bulk is 1-10 μm; The length of the gap is 1-10 μm; The width of the gap is 1-200 nm.

5. A thermochemical composite energy storage material, characterized in that, It includes nano-calcium oxide particles and micron-calcium oxide bulk; In the microscopic morphology of the calcium oxide composite material, the nano-calcium oxide particles form nano-calcium oxide aggregates with a porous structure; The micron-calcium oxide bulk is a micron-calcium oxide bulk with layered cracking to form multiple gaps; The micron-calcium oxide bulk is compounded with nano-calcium oxide particles and nano-calcium oxide aggregates.

6. The thermochemical composite energy storage material according to claim 5, characterized in that, The pores formed by the connection and growth of the nano-calcium oxide particles, the pores formed by the stacking of the aggregates, the cracking gaps of the micron-calcium oxide bulk, and the voids between the micron-calcium oxide bulk / nano-calcium oxide aggregates together constitute a gradient mass transfer channel; The size of the voids ≥500 nm; In the thermochemical composite energy storage material, the percentage of the calcium-containing mole number of micron-calcium oxide in the total calcium content is 30%-80%.

7. The thermochemical composite energy storage material according to claim 5, characterized in that, The specific surface area of the thermochemical composite heat storage material is 1 to 50 m 2 / g; The average pore size of the thermochemical composite energy storage material is 1-10 nm; The pore volume of the thermochemical composite heat storage material is 0.05 to 0.2 cm 3 / g; The apparent density of the thermochemical composite heat storage material is 0.5 to 2.0 g / cm 3 .

8. A preparation method of a thermochemical composite energy storage material, characterized in that, It includes the following steps: 1) Mix the micron-calcium oxide powder with the nano-calcium-based thermal decomposition material to obtain a mixed powder; 2) Heat-treat the mixed powder obtained in the above step to obtain a thermochemical composite energy storage material.

9. The preparation method according to claim 8, characterized in that, The particle size of the micron-calcium oxide powder is 1-10 μm; The particle size of the nano-calcium-based thermal decomposition material is 10-200 nm; The nano-calcium-based thermal decomposition material is a material whose thermal decomposition product is nano-calcium oxide and gas; 10. According to the preparation method described in claim 8, characterized in that, The nano-calcium-based thermal decomposition material includes one or more of calcium carbonate, calcium acetate, calcium hydroxide, calcium lactate, and calcium gluconate; The mixing method includes one or more of stirring, grinding, ball milling, and alternating layer-by-layer mixing; The temperature of the heat treatment is 200-1000 °C; The time of the heat treatment is 0.5-48 h.

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