Difunctional composite molten salt with heat storage and CO2 capture functions

Abstract

The invention provides a difunctional composite molten salt with both heat storage and CO2 trapping, which comprises a trapping agent and a basic chloride molten salt, in terms of molar mass, the content of the trapping agent is 5-15%, and the content of the basic chloride molten salt is 85-95%; the basic chloride molten salt comprises more than two of CaCl2, NaCl, KCl and LiCl, and the basic chloride molten salt has the melting point of less than or equal to 600 DEG C, the specific heat capacity of more than or equal to 1.0 J / g.K, the heat conductivity of more than or equal to 0.5 W / m.K and the heat stability of more than or equal to 800 DEG C; the trapping agent comprises more than one of CaO and Li2O. According to the invention, the dual effects of waste heat storage and CO2 capture in high-temperature flue gas can be synchronously realized, the specific heat capacity of the dual-function molten salt can reach 1.0 J / g.K or above, the utilization rate of the CO2 capture agent can reach 70-80%, and efficient heat storage and CO2 capture are facilitated.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature thermal storage and carbon capture materials, specifically relating to a dual-function composite molten salt that combines thermal storage and CO2 capture. Background Technology

[0002] The steel industry accounts for 16% of China's CO2 emissions, making CO2 capture and utilization extremely important. The flue gas emitted from various kilns in the steel industry not only contains high concentrations of CO2 but also a large amount of waste heat, making it a "carbon-heat" symbiotic waste gas that combines carbon resources and thermal energy. However, traditional carbon capture and utilization (CCUS) technologies typically suffer from high energy consumption, complex processes, and low efficiency. Especially in the resource utilization of high-temperature flue gas, it is difficult to achieve a synergistic effect between CO2 capture and waste heat recovery, leading to the dual pressures of energy waste and carbon emissions.

[0003] Molten salts, due to their excellent thermal stability, high heat capacity, and CO2 chemical absorption capacity, are a potential medium for waste heat storage and CO2 capture. Molten salts, represented by alkali metal and alkaline earth metal chlorides, can efficiently store waste heat from metallurgical furnace flue gas, capture CO2, and generate stable carbonates. Simultaneously, the heat storage molten salt system can also serve as a high-temperature electrolyte, further decomposing the captured carbonates into elemental carbon and oxygen through electrolysis, thus achieving CO2 resource immobilization and metallurgical recycling.

[0004] However, existing research focuses on single-function applications of molten salt thermal storage or CO2 capture, and lacks systematic research on the synergistic integration of thermal storage and CO2 capture technologies. It is unclear which molten salt system can simultaneously achieve efficient coupling and compatibility between waste heat storage and CO2 capture in metallurgical flue gas.

[0005] In summary, considering the coexistence of "waste heat and CO2" in typical high-temperature flue gas from converters, a molten salt system with both high-temperature heat storage and CO2 capture functions was designed and developed. This lays the foundation for further CO2 molten salt electrolysis of elemental carbon and is expected to simultaneously realize the integrated and synergistic utilization of waste heat and CO2 from high-temperature flue gas in the iron and steel metallurgy industry, providing a new solution for energy conservation and emission reduction in the metallurgical industry. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a dual-function composite molten salt that combines heat storage and CO2 capture. It aims to achieve a wide high-temperature operating range through reasonable selection of components and ratios, enabling stable operation at high temperatures and efficient CO2 capture and waste heat storage.

[0007] To achieve the above objectives, as one aspect of the present invention, a dual-functional composite molten salt combining heat storage and CO2 capture is provided, comprising a capture agent and a basic chloride molten salt, wherein the capture agent content is 5-15% and the basic chloride molten salt content is 85-95% by molar mass;

[0008] The basic chloride molten salt includes two or more of CaCl2, NaCl, KCl, and LiCl, and meets the following requirements: melting point ≤600℃, specific heat capacity ≥1.0J / g·K, thermal conductivity ≥0.5W / m·K, and thermal stability ≥800℃.

[0009] The trapping agent includes one or more of CaO and Li2O.

[0010] As a preferred embodiment of the present invention, a dual-function composite molten salt that combines heat storage and CO2 capture, the carbonate generated by the capture agent has a decomposition temperature ≥800 ℃.

[0011] As a preferred embodiment of the present invention, a dual-functional composite molten salt combining heat storage and CO2 capture, the basic chloride molten salt components and proportions, by molar mass, are selected from any of the following combinations:

[0012] 1) CaCl2:NaCl = 40~50:55~45,

[0013] 2) CaCl2:KCl = 20~30:75~65,

[0014] 4) CaCl2:LiCl = 35~45:60~50,

[0015] 5) LiCl:NaCl = 60~70:35~25,

[0016] 6) LiCl:KCl = 55~65:40~30.

[0017] As a preferred embodiment of the present invention, a dual-function composite molten salt that combines heat storage and CO2 capture, when the basic molten salt system contains CaCl2, the CO2 capture agent is CaO; when it contains LiCl, the CO2 capture agent is Li2O; and when it contains both CaCl2 and LiCl, the CO2 capture agent is CaO.

[0018] This invention creatively proposes that mixing molten salt with heat storage function with a CO2 capturing agent can effectively achieve a synergistic effect. This is because, on the one hand, when the composite molten salt containing the above components absorbs heat from the flue gas, the basic chloride molten salt melts, and the capturing agent dissolves in the basic chloride molten salt. In the subsequent CO2 capturing process, the capturing reaction changes from a gas-solid reaction to a gas-liquid reaction, which can significantly improve the capturing effect of the capturing agent. On the other hand, the addition of the capturing agent affects the density, temperature range, and specific heat capacity of the basic chloride molten salt, which can effectively improve the heat adsorption capacity.

[0019] In this invention, the melting point, specific heat capacity, thermal conductivity, and thermal stability parameters of the basic chloride molten salt have a significant impact on the heat absorption and CO2 capture effect. Specifically, regarding the melting point, a lower melting point results in a wider heat storage temperature range, which is more conducive to maximizing the absorption of waste heat from the flue gas. Regarding specific heat capacity, a higher specific heat capacity of the molten salt means that a unit mass of molten salt absorbs more heat per unit temperature increase. Regarding thermal conductivity, a higher thermal conductivity means a faster rate of heat absorption from the flue gas. Regarding thermal stability, higher thermal stability of the molten salt results in a higher upper limit for heat storage temperature and a wider heat storage temperature range, which is more conducive to maximizing the absorption of waste heat from the flue gas. Therefore, in the technical solution of this invention, the basic chloride molten salt needs to be formulated to meet the following requirements: melting point ≤ 600℃, specific heat capacity ≥ 1.0 J / g·K, thermal conductivity ≥ 0.5 W / m·K, and thermal stability ≥ 800℃.

[0020] In this invention, there are specific requirements for the content of the precipitant and the basic chloride molten salt. This is because when the content of the precipitant in the composite molten salt is too low, the CO2 capture amount is low, and the ideal capture effect cannot be achieved. When the content of the precipitant in the composite molten salt is too high, on the one hand, after the precipitant reaches saturation, its utilization rate begins to decrease; on the other hand, the molten salt system will change from a liquid state to a liquid-solid mixture state, thereby affecting the CO2 capture effect. Based on this, in the technical solution of this invention, it is preferable to control the proportion of the precipitant in the composite molten salt to be 5~15 mol%, and more preferably 8~12 mol%.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The composite molten salt of the present invention can simultaneously achieve the dual effects of waste heat storage and CO2 capture in high-temperature flue gas through a synergistic promotion method;

[0023] 2. The specific heat capacity of the bifunctional molten salt can reach over 1.0 J / g·K, and the utilization rate of the CO2 scavenger can reach 70%~80%, which is conducive to efficient heat storage and CO2 capture.

[0024] 3. After dual-function molten salt thermal storage and CO2 capture, high-temperature CO2-containing molten salt of 600-800℃ can be obtained, which lays the foundation for subsequent CO2 electrolysis utilization and molten salt-water steam heat exchange to obtain high-temperature and high-pressure superheated steam for efficient power generation. Detailed Implementation

[0025] The technical solutions described below in conjunction with the embodiments will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1

[0027] A dual-function composite molten salt combining heat storage and CO2 capture comprises a capture agent and a basic chloride molten salt, wherein the capture agent content is 10% and the basic chloride molten salt content is 90% by molar mass.

[0028] The basic chloride molten salt is CaCl2 and NaCl, and the ratio of CaCl2 to NaCl is 48:52 by molar mass. The resulting basic chloride molten salt has a melting point of 495℃, a specific heat capacity of 1.214 J / (g·K), and a thermal conductivity of 0.53 W / (m·K). The catching agent is CaO.

[0029] The composite molten salt was subjected to heat storage and capture experiments at 700℃ / 10vol%CO2. The results showed that the CO2 capture amount was 3.68 wt% (mainly CaCO3 was generated), the capture agent utilization rate was 72%, and the heat storage performance of the molten salt after CO2 capture was as follows: melting point was 475℃, specific heat capacity was 1.346 J / (g·K), and thermal conductivity was 0.57 W / (m·K), indicating that it has efficient heat storage and CO2 capture capabilities.

[0030] Example 2

[0031] A dual-function composite molten salt combining heat storage and CO2 capture comprises a capture agent and a basic chloride molten salt, wherein the capture agent content is 15% and the basic chloride molten salt content is 85% by molar mass.

[0032] The basic chloride molten salt is CaCl2 and KCl, and the ratio of CaCl2 to KCl is 29:71 by molar mass. The resulting basic chloride molten salt has a melting point of 587℃, a specific heat capacity of 1.194 J / (g·K), and a thermal conductivity of 0.55 W / (m·K). The catching agent is CaO.

[0033] The composite molten salt was subjected to heat storage and capture experiments under 700℃ / 10vol%CO2 conditions. The results showed that the CO2 capture amount was 2.83 wt% (mainly CaCO3 was generated), the capture agent utilization rate was 70%, and the heat storage performance of the molten salt after CO2 capture was as follows: melting point was 508℃, specific heat capacity was 1.371 J / (g·K), and thermal conductivity was 0.52 W / (m·K), indicating that it has efficient heat storage and CO2 capture capabilities.

[0034] Example 3

[0035] A dual-function composite molten salt combining heat storage and CO2 capture comprises a capture agent and a basic chloride molten salt, wherein the capture agent content is 10% and the basic chloride molten salt content is 90% by molar mass.

[0036] The basic chloride molten salt is CaCl2 and LiCl, and the ratio of CaCl2 to LiCl is 42:58 by molar mass. The resulting basic chloride molten salt has a melting point of 482℃, a specific heat capacity of 1.163 J / (g·K), and a thermal conductivity of 0.57 W / (m·K). The catching agent is CaO.

[0037] The composite molten salt was subjected to heat storage and capture experiments at 700℃ / 10 vol% CO2. The results showed that the CO2 capture amount was 3.64 wt% (mainly CaCO3), the capture agent utilization rate was 75%, and the heat storage performance of the molten salt after CO2 capture was as follows: melting point 455℃, specific heat capacity 1.211 J / (g·K), thermal conductivity 0.62 W / (m·K), indicating that it has efficient heat storage and CO2 capture capabilities.

[0038] Example 4

[0039] A dual-function composite molten salt combining heat storage and CO2 capture comprises a capture agent and a basic chloride molten salt, wherein the capture agent content is 10% and the basic chloride molten salt content is 90% by molar mass.

[0040] The basic chloride molten salt is LiCl and KCl, and the ratio of LiCl to KCl is 65:35 by molar mass. The resulting basic chloride molten salt has a melting point of 351℃, a specific heat capacity of 1.133 J / (g·K), and a thermal conductivity of 0.51 W / (m·K). The catching agent is Li2O.

[0041] The composite molten salt was subjected to heat storage and capture experiments at 700℃ / 10 vol% CO2. The results showed that the CO2 capture amount was 5.52 wt% (mainly generating Li2CO3), the capture agent utilization rate was 77%, and the heat storage performance of the molten salt after CO2 capture was as follows: melting point 333℃, specific heat capacity 1.192 J / (g·K), thermal conductivity 0.50 W / (m·K), indicating that it has efficient heat storage and CO2 capture capabilities.

[0042] Example 5

[0043] A dual-function composite molten salt combining heat storage and CO2 capture comprises a capture agent and a basic chloride molten salt, wherein the capture agent content is 15% and the basic chloride molten salt content is 85% by molar mass.

[0044] The basic chloride molten salt is LiCl and NaCl, and the ratio of LiCl to KCl is 65:35 by molar mass. The resulting basic chloride molten salt has a melting point of 552℃, a specific heat capacity of 1.213 J / (g·K), and a thermal conductivity of 0.59 W / (m·K). The catching agent is Li2O.

[0045] The composite molten salt was subjected to heat storage and capture experiments at 700℃ / 10 vol% CO2. The results showed that the CO2 capture amount was 2.82 wt% (mainly generating Li2CO3), the capture agent utilization rate was 71%, and the heat storage performance of the molten salt after CO2 capture was as follows: melting point 525℃, specific heat capacity 1.257 J / (g·K), thermal conductivity 0.62 W / (m·K), indicating that it has efficient heat storage and CO2 capture capabilities.

[0046] Comparative Example 1

[0047] A composite molten salt comprising a catching agent and a base chloride molten salt, wherein the catching agent comprises 10% by molar mass and the base chloride molten salt comprises 90% by molar mass;

[0048] The basic chloride molten salt is MgCl2 and NaCl, and the ratio of MgCl2 to NaCl is 48:52 by molar mass. The resulting basic chloride molten salt has a melting point of 461℃, a specific heat capacity of 1.183 J / (g·K), and a thermal conductivity of 0.51 W / (m·K). The catching agent is MgO.

[0049] The composite molten salt was subjected to heat storage and capture experiments at 700℃ / 10vol%CO2. The results showed that the CO2 capture amount was 0 wt% (no carbonate was produced), the capture agent utilization rate was 0%, and the heat storage performance of the molten salt after CO2 capture was: melting point 457℃, specific heat capacity 1.196 J / (g·K), and thermal conductivity 0.53 W / (m·K).

[0050] Compared with Example 1, this comparative example uses MgO as a trapping agent. The decomposition temperature of MgO to MgCO3, which reacts with CO2, is 300°C. Therefore, it is easily decomposed at a flue gas temperature of 700°C, ultimately resulting in the inability to trap CO2.

[0051] Comparative Example 2

[0052] A composite molten salt comprising a catching agent and a base chloride molten salt, wherein the catching agent content is 15% and the base chloride molten salt content is 85% by molar mass.

[0053] The basic chloride molten salt is NaCl and KCl, and the ratio of NaCl to KCl is 52:48 by molar mass. The resulting basic chloride molten salt has a melting point of 657℃, a specific heat capacity of 1.083 J / (g·K), and a thermal conductivity of 0.47 W / (m·K). The catching agent is CaO.

[0054] The composite molten salt was subjected to heat storage and capture experiments at 700℃ / 10vol%CO2. The results showed that the CO2 capture amount was 0.93wt% (mainly CaCO3 was generated), the capture agent utilization rate was 26.3%, and the heat storage performance of the molten salt after CO2 capture was as follows: melting point was 645℃, specific heat capacity was 1.106J / (g·K), and thermal conductivity was 0.48 W / (m·K).

[0055] Compared to Example 2, this comparative example did not use CaCl2 as the base molten salt, but instead used CaO as the trapping agent. Due to the high melting point of chloride molten salt, the solubility of CaO in the molten salt is very low, making it difficult to react with CO2 to form carbonates, ultimately resulting in the inability to achieve efficient CO2 capture. Simultaneously, the high melting point of chloride molten salt (657 °C) leads to a narrow thermal storage temperature range, failing to meet the thermal storage performance requirements.

[0056] Comparative Example 3

[0057] A composite molten salt comprising a catching agent and a base chloride molten salt, wherein the catching agent content is 15% and the base chloride molten salt content is 85% by molar mass.

[0058] The basic chloride molten salt is CaCl2 and LiCl, and the ratio of CaCl2 to LiCl is 63:37 by molar mass. The resulting basic chloride molten salt has a melting point of 642℃, a specific heat capacity of 1.091 J / (g·K), and a thermal conductivity of 0.58 W / (m·K). The catching agent is CaO.

[0059] The composite molten salt was subjected to heat storage and capture experiments at 700℃ / 10vol%CO2. The results showed that the CO2 capture amount was 0.33wt% (producing CaCO3 and Li2CO3), the capture agent utilization rate was 15.8%, and the heat storage performance of the molten salt after CO2 capture was as follows: melting point was 625℃, specific heat capacity was 1.115J / (g·K), and thermal conductivity was 0.58 W / (m·K).

[0060] Compared with Example 3, this comparative example used a CaCl2-LiCl ratio of 63 mol%:37 mol% as the base molten salt system, which had an excessively high melting point (642 °C). Under actual working conditions, the kinetic conditions were insufficient, making it difficult for CaO to react effectively with CO2 to form carbonates, ultimately resulting in low CO2 capture amount and low capture agent utilization.

[0061] Comparative Example 4

[0062] A composite molten salt comprising a catching agent and a base chloride molten salt, wherein the catching agent comprises 10% by molar mass and the base chloride molten salt comprises 90% by molar mass;

[0063] The basic chloride molten salt is LiCl and KCl, and the ratio of LiCl to KCl is 22:78 by molar mass. The resulting basic chloride molten salt has a melting point of 705℃, a specific heat capacity of 1.197 J / (g·K), and a thermal conductivity of 0.44 W / (m·K). The catching agent is Li2O.

[0064] The composite molten salt was subjected to heat storage and capture experiments at 700℃ / 10vol%CO2. The results showed that the CO2 capture amount was 0.12wt% (mainly generating Li2CO3), the capture agent utilization rate was 8.8%, and the heat storage performance of the molten salt after CO2 capture was: melting point 642℃, specific heat capacity 1.249J / (g·K), and thermal conductivity 0.44 W / (m·K).

[0065] Compared to Example 4, this comparative example uses a LiCl:KCl = 22 mol% : 78 mol% mol% molal salt system as the base, resulting in an excessively high melting point. Under actual operating conditions, the kinetics are insufficient, making it difficult for Li2O to react with CO2 to form carbonates, ultimately failing to achieve efficient CO2 capture. Furthermore, the excessively high melting point of this comparative example also fails to meet the thermal storage performance requirements.

[0066] Comparative Example 5

[0067] A composite molten salt comprising a catching agent and a base chloride molten salt, wherein the catching agent comprises 10% by molar mass and the base chloride molten salt comprises 90% by molar mass;

[0068] The basic chloride molten salt is LiCl and NaCl, and the ratio of LiCl to NaCl is 88:12 by molar mass. The resulting basic chloride molten salt has a melting point of 585℃, a specific heat capacity of 0.917 J / (g·K), and a thermal conductivity of 0.47 W / (m·K). The catching agent is CaO.

[0069] The composite molten salt was subjected to heat storage and capture experiments at 700℃ / 10vol%CO2. The results showed that the CO2 capture amount was 2.62wt% (with Li2CO3 as the main product), the capture agent utilization rate was 55.8%, and the heat storage performance of the molten salt after CO2 capture was as follows: melting point was 542℃, specific heat capacity was 0.979J / (g·K), and thermal conductivity was 0.48 W / (m·K).

[0070] Compared with Example 5, this comparative example used LiCl:NaCl = 88 mol% : 12 mol% as the base molten salt. Although it can achieve efficient CO2 capture, the specific heat capacity and thermal conductivity of the molten salt system are low, which means that it also cannot meet the requirements for thermal storage performance.

[0071] It should be noted that, based on the above embodiments of the present invention, those skilled in the art can fully realize the scope of the independent claims and dependent claims of the present invention, and the implementation process and methods are the same as those in the above embodiments; and the parts of the present invention not described in detail belong to the well-known technology in the art. However, the protection scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the protection scope of the present invention.

Claims

1. A dual-functional composite molten salt combining heat storage and CO2 capture, characterized in that, It includes a trapping agent and a basic chloride molten salt, wherein, by molar mass, the trapping agent content is 5-15% and the basic chloride molten salt content is 85-95%; The basic chloride molten salt includes two or more of CaCl2, NaCl, KCl, and LiCl, and meets the following requirements: melting point ≤600℃, specific heat capacity ≥1.0J / g·K, thermal conductivity ≥0.5W / m·K, and thermal stability ≥800℃. The trapping agent includes one or more of CaO and Li2O.

2. The bifunctional composite molten salt as described in claim 1, characterized in that, The carbonate generated by the trapping agent has a decomposition temperature ≥800 ℃.

3. The bifunctional composite molten salt as described in claim 1, characterized in that, The basic chloride molten salt composition and proportions, on a molar mass basis, are selected from any combination of the following: 1) CaCl2:NaCl = 40~50:55~45, 2) CaCl2:KCl = 20~30:75~65, 4) CaCl2:LiCl = 35~45:60~50, 5) LiCl:NaCl = 60~70:35~25, 6) LiCl:KCl = 55~65:40~30.

4. The bifunctional composite molten salt as described in claim 1, characterized in that, When the basic molten salt system contains CaCl2, the CO2 scavenger is CaO; when it contains LiCl, the CO2 scavenger is Li2O; when it contains both CaCl2 and LiCl, the CO2 scavenger is CaO.