Carbon dioxide trapping method

Abstract

The invention provides a carbon dioxide trapping method which comprises the following steps: carrying out gas-liquid contact on an ammonia water solution and gas containing carbon dioxide to form saturated carbon-rich ammonia water; the method comprises the following steps: contacting and reacting saturated carbon-rich ammonia water with steel slag powder, controlling the temperature in the reaction process to be 30-70 DEG C, and carrying out solid-liquid separation on a reaction product after the reaction is finished to obtain a liquid product and a solid product. The carbon dioxide trapping method provided by the invention not only can realize efficient trapping of carbon dioxide, but also remarkably reduces the energy consumption in the absorbent regeneration process and even the overall energy consumption of the system.

Description

Technical Field

[0001] The invention relates to a method for capturing carbon dioxide, and belongs to the technical field of carbon dioxide capture. Background Art

[0002] In the context of the urgent need to solve the current carbon emission problems at home and abroad, developing a CO2 capture technology with high absorption efficiency, low regeneration energy consumption, and green environmental protection is the current development direction of CO2 capture technology.

[0003] Chemical absorption is currently one of the mainstream technologies for capturing carbon dioxide (CO2). The most typical of these are the ammonia and alcoholamine processes, both of which share nearly identical CO2 absorption principles. However, compared to the commonly used ethanolamine (MEA) process, the ammonia process offers higher CO2 removal efficiency, lower costs, less corrosion to equipment, and no issues with absorbent degradation. During ammonia absorption, absorbent regeneration is crucial for the operation of an integrated absorption-desorption cycle. Research has shown that absorbent regeneration typically requires high temperature and high pressure to ensure the decomposition of carbonate and bicarbonate ions. Therefore, energy consumption during absorbent regeneration can account for 50% to 80% of the total energy consumption of CCUS (carbon capture, utilization, and storage).

[0004] Therefore, how to reduce the energy consumption of the absorbent regeneration process and even the overall energy consumption of the system while achieving effective carbon dioxide capture is a problem that needs to be solved. Summary of the Invention

[0005] In view of the above problems, the present invention provides a method for capturing carbon dioxide, which can achieve effective capture of carbon dioxide and low-energy regeneration of the absorbent.

[0006] To achieve the above-mentioned purpose, the present invention provides a method for collecting carbon dioxide, comprising the following steps: S1, bringing an ammonia solution into gas-liquid contact with a gas containing carbon dioxide to form a saturated carbon-rich ammonia solution; S2, bringing the saturated carbon-rich ammonia solution into contact with steel slag powder and reacting the saturated carbon-rich ammonia solution, controlling the temperature during the reaction to be 30-70°C, and after the reaction is completed, performing solid-liquid separation on the reaction product to obtain a liquid product and a solid product.

[0007] In step S1, the concentration of the ammonia solution used can be 1 mol / L or higher. While increasing the concentration of the ammonia solution can improve carbon dioxide absorption, the volatilization problem caused by excessively high concentrations cannot be ignored. Therefore, the concentration of the ammonia solution is generally controlled between 1 and 4 mol / L. This concentration is obtained by diluting 28 to 30 wt% concentrated ammonia solution, for example, by mixing concentrated ammonia solution with deionized water. Therefore, the replenishment method of the present invention further includes the step of preparing the ammonia solution.

[0008] In the present invention, the gas containing carbon dioxide, although called "gas," may contain small amounts of solids and liquids. For example, it may be flue gas. Flue gas is a complex mixture of gases and dust. Gases include water vapor, sulfur dioxide, nitrogen, oxygen, carbon monoxide, carbon dioxide, hydrocarbons, and nitrogen oxides; dust includes fuel ash, coal particles, oil droplets, and high-temperature cracking products. The present invention does not specifically limit the specific source of the carbon dioxide-containing gas, but includes gases produced as by-products from industrial furnaces (such as blast furnaces, lime calciners, coke ovens, etc.), sintering or hot rolling processes, power generation, waste heat boilers, and the like.

[0009] By fully contacting the ammonia solution with the carbon dioxide-containing gas, the ammonia solution and the carbon dioxide can fully react to produce saturated carbon-rich ammonia solution containing ammonium bicarbonate. The present invention does not particularly limit how to achieve gas-liquid contact. The gas containing carbon dioxide can be bubbled into the ammonia solution or performed in an absorption tower, such as a packed tower or a spray tower. The specific method of gas-liquid contact can be determined based on factors such as the actual industrial scale.

[0010] Theoretically, since what is obtained in step S1 is saturated carbon-rich ammonia water, the carbon dioxide content in the gas containing carbon dioxide has little effect on the amount of carbon dioxide that can be absorbed by the ammonia solution; the amount of carbon dioxide absorbed should depend on the concentration of the ammonia solution. However, the experimental results show that this is not strictly true, and the reason is currently unknown. Generally speaking, the capture scheme of the present invention is relatively more suitable for treating gases containing carbon dioxide, such as flue gas with a carbon dioxide content of 10 to 30 v%. In practice, if the carbon dioxide content is not within the above range, the gas containing carbon dioxide can also be treated first so that the volume concentration of carbon dioxide therein is as close to the above range as possible, or as close to the above volume concentration range.

[0011] The steel slag used in step S2 can be, for example, the steel slag produced in the converter steelmaking process, which contains a large amount of metal oxides such as calcium oxide and magnesium oxide, and is therefore alkaline, and is therefore also called alkaline steel slag. Of course, it can also be alkaline steel slag from other sources. At present, the resource recycling rate of steel slag is low, and the characteristics of steel slag itself also determine that its recycling ratio within steel enterprises or its resource utilization ratio in other industries such as building materials is limited. Therefore, the present invention uses steel slag as a mineralizer, which not only has important theoretical and practical significance for CO2 emission reduction and atmospheric protection, but also the waste utilization of steel slag is of great significance to green chemical industry.

[0012] The reaction between the steel slag powder and the saturated carbon-rich ammonia water is that the active components CaO and MgO in the steel slag react with the carbon-containing ions in the carbon-rich ammonia water to form solid phase CaCO3 and MgCO3 precipitation, thus achieving the mineralization and fixation of CO2; on the other hand, the alkaline steel slag dissolves in water and ionizes OH - , and NH4 in carbon-rich ammonia water + The reaction generates NH3, thereby achieving the regeneration of carbon-rich ammonia water.

[0013] It's easy to understand that relatively small-particle steel slag powder is more conducive to a thorough and rapid reaction with saturated carbon-rich ammonia. In practice, the mesh size of the steel slag powder is typically controlled to no more than 200 mesh, meaning the particle size is approximately 74 microns or less. This allows for a thorough and rapid reaction between the steel slag powder and the carbon-rich ammonia. To this end, the replenishment method of the present invention may further include crushing or grinding the steel slag into steel slag powder.

[0014] The experimental results show that reasonable control of the solid-liquid ratio between steel slag and saturated carbon-rich ammonia water can ensure the efficient and sufficient progress of the reaction. Among them, if the solid-liquid ratio is too low, the reaction rate is slow and it is difficult to proceed in the positive reaction direction of generating solid products; conversely, if the solid-liquid ratio is too high, the reaction rate will also be reduced, resulting in insufficient reaction. For this reason, in the specific implementation process, the solid-liquid ratio is usually controlled at 0.1-0.6 g / mL, which is equivalent to every 100 mL of saturated carbon-rich ammonia water reacting with 10-60g of steel slag. In a further scheme, the solid-liquid ratio can be controlled at 0.2-0.6 g / mL, in particular 0.4-0.6 g / mL, and further 0.5-0.6 g / mL. In practice, the solid-liquid ratio can be determined according to the specific composition of the steel slag to achieve the best reaction effect.

[0015] Reasonable control of the reaction time also facilitates the full reaction between the steel slag powder and the saturated carbon-rich ammonia solution. In practice, the reaction time is typically controlled to be no less than 30 minutes. As the reaction time increases, the amount of CaCO3 and MgCO3 precipitates generated also increases. However, when the reaction time exceeds a critical value, further extension of the reaction time does not significantly increase the amount of precipitate generated. Therefore, considering the overall reaction effect and time cost, the reaction time can generally be controlled to 30 to 70 minutes, particularly 45 to 70 minutes, and even more preferably 50 to 70 minutes.

[0016] The present invention does not particularly limit the equipment for the solid-liquid contact and reaction between the saturated carbon-rich ammonia water and the steel slag powder. For example, it can be a solid-liquid phase reaction tower. The appropriate equipment can be selected according to factors such as the actual industrial scale.

[0017] As mentioned above, during the reaction between the steel slag powder and the saturated carbon-rich ammonia solution, the carbon-rich ammonia solution is also regenerated. That is, after the reaction is completed, the liquid product obtained by solid-liquid separation of the reaction product can also be called a regeneration liquid. It contains NH3 and water. Therefore, this liquid product can be recycled, that is, returned to step S1. Of course, considering the loss during the regeneration process, it is best to supplement the liquid product, i.e., the regeneration liquid, with fresh ammonia solution. The supplementation amount can be based on reaching the initial amount of ammonia solution in step S1.

[0018] The present invention does not impose any particular limitation on how to achieve solid-liquid separation of the reaction product, and commonly used solid-liquid separation methods in industry, such as vacuum filtration, can be used.

[0019] The present invention provides a method for capturing carbon dioxide, which uses steel slag as a regeneration agent for carbon-rich ammonia water. While effectively mineralizing and fixing CO2, it also realizes low-energy chemical regeneration of the carbon-rich ammonia absorbent, thereby exploring a low-energy, low-cost CO2 capture and mineralization process route. In particular, by optimizing the process conditions in the mineralization and fixing carbon dioxide process, the regenerated liquid can still maintain a high absorption and capture efficiency after four absorption-regeneration cycles, which is significantly higher than the absorption efficiency of the traditional thermal regeneration process. At the same time, the energy consumption in the regeneration process and the overall energy consumption of the system are significantly reduced. In addition, compared with the prior art in which alkaline steel slag is first leached and then mineralized, on the one hand, the absorption and capture efficiency of carbon dioxide can be improved and the mineralization amount can be increased by optimizing the process parameters in the mineralization reaction process. On the other hand, a large amount of leaching agent can be saved, and the subsequent waste liquid treatment problem is avoided, thereby significantly reducing the cost of carbon dioxide capture, shortening the capture cycle, and also benefiting environmental protection, thereby being more conducive to promotion and application in practice. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A comparison chart of the mineralization amounts of the capture methods provided in Examples 1-3 of the present invention;

[0021] Figure 2 A comparison chart of the mineralization amounts of the capture methods provided in Examples 1, 4-5 of the present invention;

[0022] Figure 3 A comparison chart of the mineralization amounts of the capture methods provided in Examples 1, 6-7 of the present invention;

[0023] Figure 4 This is a performance comparison chart of the capture method of Example 8 of the present invention (30 min, 70° C., 0.6 g / mL) and the traditional thermal regeneration method of Comparative Example 1 (30 min, 115° C.). DETAILED DESCRIPTION

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are not all embodiments of the present invention. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0025] Example 1

[0026] This embodiment provides a method for capturing carbon dioxide, which specifically includes the following steps:

[0027] S1. Dilute 28 wt% concentrated ammonia water with deionized water to an ammonia solution with a molar concentration of 2 mol / L;

[0028] S2. Bubble simulated flue gas containing 10% CO2 into the ammonia solution until saturated carbon-rich ammonia water is formed at room temperature, and then stop bubbling the simulated flue gas.

[0029] S3. Take 100 mL of saturated carbon-rich ammonia water and add 60 g of steel slag powder (equivalent to a solid-liquid ratio of 0.6 g / mL). The steel slag powder is below 200 mesh and has a pH value of 11. During the mineralization process, the temperature is maintained at 70°C. After the reaction time reaches 70 minutes, the reaction product is collected and vacuum filtered to obtain a filtrate (regenerated liquid) and a solid portion.

[0030] S4. Add a small amount of fresh ammonia solution to the filtrate, the added amount being sufficient to reach the volume of the ammonia solution when step S2 is first performed, and then continue to circulate steps S2-S4 for 4 times.

[0031] The mineralization capacity is the difference between the absorption load and the regeneration load: mineralization capacity = absorption load - regeneration load. The absorption load refers to the amount of CO2 in the saturated ammonia water formed after complete CO2 absorption. Considering that in reality, it is impossible for all CO2 absorbed in the saturated carbon-rich ammonia water to react with the steel slag, and some will remain. Therefore, the regeneration load refers to the amount of CO2 remaining in the regeneration liquid formed after the saturated carbon-rich ammonia water reacts with the steel slag. Therefore, the difference between the amount of CO2 in the saturated carbon-rich ammonia water and the amount of CO2 in the regeneration liquid is the amount of CO2 that is mineralized and fixed by the steel slag into solid precipitates such as CaCO3.

[0032] According to calculation, the mineralization amount using the method of this embodiment is 0.342 molCO2 / molNH3.

[0033] Example 2-3

[0034] Examples 2-3 respectively provide a method for capturing carbon dioxide, and the specific steps and process conditions thereof are substantially the same as those of Example 1, with the only difference being that in step S3, the reaction temperature of Example 2 is maintained at 50°C, and the reaction temperature of Example 3 is maintained at 30°C.

[0035] Calculations show that the mineralization amount using the method of Example 2 is 0.325 molCO2 / molNH3; and the mineralization amount using the method of Example 3 is 0.112 molCO2 / molNH3.

[0036] like Figure 1 As shown in the data from Examples 1-3, the capture method of the present invention can achieve sufficient carbon dioxide capture and low-energy regeneration of carbon-rich ammonia from steel slag at relatively low mineralization temperatures (30-70°C). Furthermore, a further comparison of the data from Examples 1-3 shows that, under otherwise identical conditions, the higher the mineralization temperature, the better the mineralization efficiency (regeneration efficiency). Increasing the temperature from 30°C to 50°C significantly increases the mineralization yield, while increasing the temperature from 50°C to 70°C only modestly increases the yield. Further testing indicates that further increases in the mineralization efficiency (regeneration efficiency) after the mineralization temperature exceeds 70°C do not significantly increase the mineralization efficiency (regeneration efficiency). Therefore, in practice, the mineralization temperature can be controlled within the range of 30°C to 70°C, particularly within the range of 45°C to 70°C, and even more particularly within the range of 50°C to 70°C.

[0037] Examples 4-5

[0038] Examples 4-5 respectively provide a method for capturing carbon dioxide, and their specific steps and process conditions are basically the same as those of Example 1, with the only difference being that in step S3, the amount of steel slag powder added in Example 4 is 20 g (equivalent to a solid-liquid ratio of 0.2 g / mL), and the amount of steel slag powder added in Example 5 is 40 g (equivalent to a solid-liquid ratio of 0.4 g / mL).

[0039] Calculations show that the mineralization amount using the method of Example 4 is 0.245 molCO2 / molNH3; and the mineralization amount using the method of Example 5 is 0.251 molCO2 / molNH3.

[0040] like Figure 2As shown, from the data of Examples 1, 4-5, it can be seen that the more steel slag is added, that is, the higher the solid-liquid ratio, the better the mineralization efficiency (regeneration efficiency). When the solid-liquid ratio is between 0.2 g / mL and 0.4 g / mL, the mineralization amount is around 0.250 molCO2 / molNH3, and the increase is limited; and when the solid-liquid ratio is further increased, the increase in the mineralization amount is obvious. When the solid-liquid ratio is 0.6 g / mL, the mineralization amount reaches 0.342 molCO2 / molNH3. After further testing, the results show that when the solid-liquid ratio exceeds 0.6 g / mL, the increase in mineralization efficiency is not obvious if the solid-liquid ratio is further increased, and may even decrease slightly. The inventors speculate that this may be because a too low solid-liquid ratio will limit the forward reaction in step S3. However, an excessively high solid-liquid ratio will also increase the viscosity of the slurry, making it difficult for the steel slag as a solid phase in the reaction system to be effectively decomposed in the liquid phase; in addition, after the formation of calcium carbonate and magnesium carbonate precipitates, the Ca 2+ / Mg 2+ Therefore, the appropriate solid-liquid ratio provides sufficient space and active sites for the mineralization reaction, increasing the CO2 and Ca 2+ / Mg 2+ Therefore, in practice, the solid-liquid ratio can be controlled in the range of 0.2 g / mL to 0.6 g / mL, especially in the range of 0.5 g / mL to 0.6 g / mL.

[0041] Examples 6-7

[0042] Examples 6-7 respectively provide a method for capturing carbon dioxide, and the specific steps and process conditions thereof are substantially the same as those of Example 1, with the only difference being that in step S3, the reaction time (mineralization time) of Example 6 is 30 minutes, and the reaction time of Example 7 is 50 minutes.

[0043] Calculations show that the mineralization amount using the method of Example 6 is 0.135 molCO2 / molNH3; and the mineralization amount using the method of Example 7 is 0.174 molCO2 / molNH3.

[0044] like Figure 3 As shown in the data from Examples 1, 6, and 7, the longer the mineralization time, the better the mineralization efficiency (regeneration efficiency). In particular, the increase from 50 to 70 minutes significantly increased the amount of mineralization. However, further testing showed that when the mineralization time exceeds 70 minutes, further extension of the reaction time did not significantly increase the amount of precipitate generated. The inventors speculate that this may be because the mineralization reaction has essentially reached equilibrium by the time the mineralization time reaches 70 minutes, so further extension of the reaction time results in essentially no change in the amount of mineralization.

[0045] Example 8

[0046] S1. Dilute 28 wt% concentrated ammonia water with deionized water to an ammonia solution with a molar concentration of 2 mol / L;

[0047] S2. Bubble simulated flue gas containing 30% v% CO2 into the ammonia solution until saturated carbon-rich ammonia water is formed at room temperature, and then stop bubbling the simulated flue gas.

[0048] S3. Take 100 mL of saturated carbon-rich ammonia water, add 60 g of steel slag powder (equivalent to a solid-liquid ratio of 0.6 g / mL), the steel slag powder is below 200 mesh, the pH value is 11, the temperature is maintained at 70°C during the mineralization process, and the reaction time reaches 30 minutes. Collect the reaction product and perform vacuum filtration to obtain a filtrate and a solid portion;

[0049] S4. Add a small amount of fresh ammonia solution to the filtrate, the added amount being sufficient to reach the volume of the ammonia solution when step S2 is first performed, and then continue to circulate steps S2-S4 for 4 cycles.

[0050] Comparative Example 1

[0051] This comparative example adopts a traditional carbon dioxide capture method, which specifically includes the following steps:

[0052] S10, using deionized water, diluting 28 wt% concentrated ammonia water to an ammonia solution with a molar concentration of 2 mol / L;

[0053] S20, bubbling simulated flue gas containing 30% v% CO2 into the ammonia solution until saturated carbon-rich ammonia water is formed at room temperature, and then stopping the introduction of the simulated flue gas;

[0054] S30. Take 100 mL of saturated carbon-rich ammonia water and keep it at 115°C for 30 minutes to achieve thermal regeneration of the absorption liquid. The CO2 in it is collected and purified, and then compressed and liquefied into liquid CO2 and injected into the underground for storage.

[0055] S40, adding a small amount of fresh ammonia solution to the regeneration liquid, and cyclically executing steps S20 to S40, with a total of 4 cycles.

[0056] The mineralization amount of 4 cycles in Example 8 and Comparative Example 1 were compared respectively. The results are as follows Figure 4 As shown. Figure 4It can be seen that the capture method of Example 8 (marked as 60g steel slag mineralization regeneration in the figure) removes carbon dioxide from flue gas at a rate comparable to that of the conventional carbon dioxide capture method (Comparative Example 1, marked as conventional thermal regeneration in the figure) over four cycles. In particular, after four cycles, the mineralization rate in Example 8 is significantly higher than that in Comparative Example 1. Furthermore, it is noted that conventional carbon dioxide capture methods require the regeneration solution to be regenerated at high temperatures. This demonstrates that the capture method of the present invention not only increases carbon dioxide removal but also significantly reduces energy consumption during the regeneration process and overall.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for capturing carbon dioxide, characterized in that: The steps include: The ammonia solution is brought into gas-liquid contact with a gas containing carbon dioxide to form saturated carbon-rich ammonia water; The saturated carbon-rich ammonia water is brought into contact with the steel slag powder and reacted, and the temperature during the reaction process is controlled to be 30-70°C. After the reaction is completed, the reaction product is subjected to solid-liquid separation to obtain a liquid product and a solid product.

2. The capture method according to claim 1, characterized in that: The concentration of the ammonia solution is 1-4 mol / L; and the volume content of the carbon dioxide in the gas containing carbon dioxide is 10-30%.

3. The capture method according to claim 1 or 2, characterized in that: The temperature during the reaction is controlled to be 50-70°C.

4. The capture method according to any one of claims 1 to 3, characterized in that: The solid-to-liquid ratio of the steel slag to the saturated carbon-rich ammonia water is 0.1-0.6 g / mL.

5. The capture method according to claim 4, characterized in that: The solid-to-liquid ratio of the steel slag to the saturated carbon-rich ammonia water is 0.5-0.6 g / mL.

6. The capture method according to any one of claims 1 to 5, characterized in that: The time during the reaction is controlled to be no less than 30 minutes.

7. The capture method according to claim 6, characterized in that: The reaction time is controlled to be 30 to 70 minutes.

8. The capture method according to claim 7, characterized in that: The reaction time is controlled to be 45 to 70 minutes.

9. The capture method according to any one of claims 1 to 8, characterized in that: The mesh number of the steel slag powder does not exceed 200 meshes.

10. The capture method according to any one of claims 1 to 9, characterized in that: Also includes: The liquid product is supplemented with an aqueous ammonia solution and circulated for the gas-liquid contact.

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