System and method for capturing CO2 in alumina roasting flue gas and utilizing waste heat

Abstract

The invention provides a system and method for capturing CO2 in alumina roasting flue gas and utilizing waste heat, and belongs to the field of CO2 capturing. The system comprises a second-stage flue gas cooler, a gas inlet of the second-stage flue gas cooler is communicated with a high-temperature flue gas outlet, industrial water is introduced into a liquid inlet of the second-stage flue gas cooler, and the second-stage flue gas cooler is used for carrying out heat exchange on high-temperature flue gas and the industrial water to recover heat so as to obtain cooled gas and hot water; an inlet of the cooling and dehumidifying tower is communicated with a gas outlet of the two-stage two-stage flue gas cooler, and the cooling and dehumidifying tower is used for cooling the cooling gas again to obtain saturated feed gas; an inlet of the compressor is communicated with an outlet of the cooling and dehumidifying tower, and the compressor is used for increasing the pressure of the saturated feed gas to a set pressure; an inlet of the PSA device is communicated with an outlet of the compressor, and the PSA device is used for capturing CO2 in the saturated feed gas with the set pressure to obtain a CO2 product. Therefore, the capture efficiency of CO2 in the alumina roasting flue gas and the utilization efficiency of waste heat are improved at the same time.

Description

Technical Field

[0001] This application relates to the technical field of CO2 capture, and particularly to a system and method for CO2 capture and waste heat utilization in alumina calcination flue gas. Background Art

[0002] Currently, for every ton of primary aluminum produced globally on average, approximately 15.6 tons of carbon dioxide are emitted. Among them, the alumina production stage emits about 3.1 tons, accounting for 19.6%. During the alumina calcination process, a large amount of calcination flue gas is discharged into the air, which not only causes the greenhouse effect, but also leads to energy loss due to the lack of an effective waste heat utilization system for the flue gas, resulting in the flue gas being emptied. Capturing and recycling CO2 from the flue gas of alumina calciners is an important measure for the aluminum industry to reduce carbon emissions. Currently, there is no technology for capturing, recycling, and utilizing CO2 in the flue gas during the alumina calcination process in the alumina production field.

[0003] Generally speaking, according to the different sources of carbon dioxide and the different requirements of users for carbon dioxide, the main separation methods include two categories: physical absorption and chemical absorption. Among them, the more common carbon dioxide capture processes are as follows: propylene carbonate method (PC method), polyamine method (MDEA method), low-temperature methanol method, polyethylene glycol dimethyl ether method (NHD method), pressure swing adsorption method (PSA method). The pressure swing adsorption method is a relatively economical gas separation technology at present. The purification of CO2 using the pressure swing adsorption technology is mainly applied to the CO2 capture of flue gas in industries such as pressure swing boilers. Currently, it is not used for the CO2 capture of the flue gas generated during the alumina calcination process. However, the temperature and pressure of the flue gas generated during the alumina calcination process may fluctuate greatly. The pressure swing adsorption process requires stable temperature and pressure conditions to ensure efficient CO2 capture. The fluctuations in temperature and pressure may cause the performance of the adsorbent to decline, thereby affecting the CO2 capture efficiency. At the same time, the temperature of the alumina calcination flue gas is relatively high. In order to deal with the high-temperature flue gas, it may be necessary to complicate the PSA process flow design, such as adding cooling devices, adjusting the pressure change range, etc. This will increase the equipment investment and operating costs. Therefore, how to simultaneously improve the CO2 capture efficiency and waste heat utilization efficiency of alumina calcination flue gas is a technical problem that urgently needs to be solved at present. Summary of the Invention

[0004] This application provides a system and method for CO2 capture and waste heat utilization in alumina calcination flue gas to solve the following technical problem: how to simultaneously improve the CO2 capture efficiency and waste heat utilization efficiency of alumina calcination flue gas.

[0005] In the first aspect, this application provides a system for CO2 capture and waste heat utilization in alumina calcination flue gas, and the system includes:

[0006] Secondary flue gas cooler, the gas inlet of the secondary flue gas cooler is connected to the high-temperature flue gas outlet of the alumina calcination furnace, and industrial water is introduced into the liquid inlet of the secondary flue gas cooler to exchange heat between the high-temperature flue gas of the alumina calcination furnace and the industrial water to recover heat, obtaining cooled gas and hot water;

[0007] Cooling and dehumidifying tower, the inlet of the cooling and dehumidifying tower is connected to the gas outlet of the two-stage secondary flue gas cooler to further cool the cooled gas to obtain saturated raw material gas;

[0008] Compressor, the inlet of the compressor is connected to the outlet of the cooling and dehumidifying tower to increase the pressure of the saturated raw material gas to a set pressure; and

[0009] PSA device, the inlet of the PSA device is connected to the outlet of the compressor to capture CO2 in the saturated raw material gas with a set pressure to obtain CO2 product.

[0010] Optionally, the secondary flue gas cooler includes:

[0011] Primary cooling component, industrial water is introduced into the liquid inlet of the primary cooling component;

[0012] Secondary cooling component, the gas inlet of the secondary cooling component is connected to the high-temperature flue gas outlet of the alumina calcination furnace, the liquid inlet of the secondary cooling component is connected to the liquid outlet of the primary cooling component, and the gas outlet of the secondary cooling component is connected to the gas inlet of the primary cooling component.

[0013] Optionally, the PSA device includes:

[0014] PSA adsorption tower, the inlet of the PSA adsorption tower is connected to the outlet of the compressor;

[0015] PSA vacuum pump, the PSA vacuum pump is connected to the PSA adsorption tower;

[0016] Crude carbon dioxide gas buffer tank, the crude carbon dioxide gas buffer tank is connected to the PSA adsorption tower.

[0017] Optionally, the system further includes:

[0018] Gas-water separator, the inlet of the gas-water separator is connected to the compressor, and the outlet of the gas-water separator is connected to the PSA device.

[0019] Optionally, the system further includes:

[0020] Product compressor, the product compressor is connected to the PSA device.

[0021] Second aspect, the present application provides a method for CO2 capture and waste heat utilization in alumina calcination flue gas, the method comprising:

[0022] Performing heat exchange between the high-temperature flue gas of the alumina calcination furnace and industrial water to recover heat, obtaining a cooled gas and hot water;

[0023] Cooling the cooled gas again to obtain a saturated raw material gas;

[0024] Increasing the pressure of the saturated raw material gas to a set pressure; and

[0025] Capturing CO2 in the saturated raw material gas having the set pressure to obtain a CO2 product.

[0026] Optionally, the temperature of the saturated raw material gas ≤ 40 °C.

[0027] Optionally, the set pressure is 0.18 MPa to 0.22 MPa.

[0028] Optionally, the volume concentration of CO2 in the CO2 product ≥ 40%.

[0029] Optionally, the temperature of the high-temperature flue gas ≥ 180 °C; and / or,

[0030] The temperature of the hot water ≥ 80 °C; and / or,

[0031] The temperature of the industrial water ≤ 55 °C.

[0032] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0033] The present application provides a system for CO2 capture and waste heat utilization in alumina calcination flue gas. The system includes: a secondary flue gas cooler, the gas inlet of the secondary flue gas cooler is connected to the high-temperature flue gas outlet of the alumina calciner, and industrial water is introduced into the liquid inlet of the secondary flue gas cooler to exchange heat between the high-temperature flue gas of the alumina calciner and the industrial water to recover heat, obtaining cooled gas and hot water; a cooling and dehumidifying tower, the inlet of the cooling and dehumidifying tower is connected to the gas outlet of the two-stage secondary flue gas cooler to further cool the cooled gas to obtain saturated raw material gas; a compressor, the inlet of the compressor is connected to the outlet of the cooling and dehumidifying tower to increase the pressure of the saturated raw material gas to a set pressure; and a PSA device, the inlet of the PSA device is connected to the outlet of the compressor to capture CO2 in the saturated raw material gas with a set pressure to obtain CO2 products. This system integrates a secondary flue gas cooler, a cooling and dehumidifying tower, a compressor, and a PSA (pressure swing adsorption) device to form a complete CO2 capture and waste heat utilization process. Through the heat exchange process of the secondary flue gas cooler, the heat in the high-temperature flue gas is transferred to the industrial water, cooling the flue gas and obtaining hot water. Not only the waste heat in the flue gas is recovered, but also suitable temperature conditions are provided for subsequent CO2 capture; the temperature and humidity of the flue gas are further reduced through the cooling and dehumidifying tower to obtain saturated raw material gas. The cooling and dehumidifying process helps to reduce the moisture in the flue gas and improve the efficiency of subsequent CO2 capture; the pressure of the saturated raw material gas is increased to a set value through the compressor to meet the requirements of the PSA device for the pressure of the raw material gas. Using the principle of pressure swing adsorption of the PSA device, CO2 is captured from the saturated raw material gas to obtain CO2 products. Thereby, the CO2 capture efficiency and waste heat utilization efficiency in alumina calcination flue gas are improved simultaneously. Brief Description of the Drawings

[0034] The accompanying drawings herein are incorporated into the specification and form a part of this specification, showing embodiments consistent with the present application and, together with the specification, are used to explain the principles of the present application.

[0035] To more clearly illustrate the technical solutions in the embodiments of the present application or in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0036] Figure 1 It is a schematic diagram of a system for CO2 capture and waste heat utilization in alumina calcination flue gas provided by an embodiment of the present application;

[0037] Figure 2 It is a flowchart of a method for CO2 capture and waste heat utilization in alumina calcination flue gas provided by an embodiment of the present application;

[0038] Figure 3 Schematic diagram of a method for CO2 capture and waste heat utilization in alumina calcination flue gas provided by an embodiment of the present application;

[0039] Reference numerals:

[0040] 1 - Secondary flue gas cooler, 11 - Primary cooling component, 12 - Secondary cooling component, 2 - Cooling and dehumidifying tower, 3 - Compressor, 4 - PSA device, 41 - PSA adsorption tower, 42 - PSA vacuum pump, 43 - Crude carbon dioxide gas buffer tank, 5 - Gas - liquid separator, 6 - Product compressor. Detailed implementation manners

[0041] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the protection scope of the present application.

[0042] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the described range description has specifically disclosed all possible sub - ranges and single values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub - ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0043] In addition, in the description of the specification of this application, terms such as "including" and "comprising" mean "including but not limited to". In this text, relative terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this text, "and / or" describes the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Where A and B can be singular or plural. In this text, "at least one" means one or more, and "a plurality" means two or more. "At least one kind", "at least one of the following items (pieces)" or similar expressions refer to any combination of these items, including any combination of single item (piece) or plural items (pieces). For example, "at least one of a, b, or c", or "at least one of a, b, and c" can both represent: a, b, c, a - b (that is, a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively. The "parts representation method" such as weight parts and mass parts represents the proportional relationship between each component. In the proportional relationships involved in this text, the parameters that need to be described by the ratio should be understood as the antecedents of the ratio formula in the order of description, and the ratio numbers should be understood as the consequents of the ratio formula. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one by one with the ratio numbers in the ratio formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0044] Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment, etc. used in this application can be obtained through market purchase or can be prepared by existing methods.

[0045] Figure 1 It is a schematic diagram of a system for CO₂ capture and waste heat utilization in alumina calcination flue gas provided for the embodiments of this application.

[0046] Please refer to Figure 1 This application provides a system for CO₂ capture and waste heat utilization in alumina calcination flue gas. The system includes:

[0047] A secondary flue gas cooler 1, the gas inlet of the secondary flue gas cooler 1 is communicated with the high-temperature flue gas outlet of the alumina calcination furnace, and industrial water is introduced into the liquid inlet of the secondary flue gas cooler 1 to exchange heat between the high-temperature flue gas of the alumina calcination furnace and the industrial water to recover heat, obtaining cooled gas and hot water;

[0048] Cooling and dehumidifying tower 2, the inlet of the cooling and dehumidifying tower 2 is communicated with the gas outlet of the two-stage secondary flue gas cooler 1, so as to cool the cooling gas again to obtain saturated raw gas;

[0049] Compressor 3, the inlet of the compressor 3 is communicated with the outlet of the cooling and dehumidifying tower 2, so as to increase the pressure of the saturated raw gas to a set pressure; and

[0050] PSA device 4, the inlet of the PSA device 4 is communicated with the outlet of the compressor 3, so as to capture CO2 in the saturated raw gas with a set pressure to obtain a CO2 product.

[0051] It should be noted that the working principle of the secondary flue gas cooler 1 is mainly based on the heat exchange principle. It transfers the heat energy in the flue gas to the cooling medium through the heat exchange between the high-temperature flue gas and the cooling medium, thereby reducing the temperature of the flue gas.

[0052] The working principle of the PSA device 4 is mainly based on the selective adsorption and pressure swing desorption characteristics of the adsorbent. When the mixed gas passes through the adsorbent bed, due to the different adsorption capacities of the adsorbent for different gases, the separation of gases can be achieved. Specifically, when the pressure increases, the adsorbent selectively adsorbs certain gases (usually impurity gases or unwanted gases), while allowing other gases (usually the target gas) to pass through; when the pressure decreases, the adsorbed gas is desorbed from the adsorbent, thereby realizing the separation and purification of the gas.

[0053] In this application, through the heat exchange process of the secondary flue gas cooler 1, the heat in the high-temperature flue gas is transferred to industrial water, cooling the flue gas and obtaining hot water. Not only the waste heat in the flue gas is recovered, but also suitable temperature conditions are provided for the subsequent CO2 capture; through the cooling and dehumidifying tower 2, the temperature and humidity of the flue gas are further reduced to obtain saturated raw gas. The cooling and dehumidifying process helps to reduce the moisture in the flue gas and improve the efficiency of subsequent CO2 capture; through the compressor 3, the pressure of the saturated raw gas is increased to a set value to meet the requirement of the PSA device 4 for the raw gas pressure. The compressor 3 is a key device connecting the cooling and dehumidifying tower 2 and the PSA device 4, and its performance directly affects the CO2 capture efficiency. Using the pressure swing adsorption principle of the PSA device 4, CO2 is captured from the saturated raw gas to obtain a CO2 product. The PSA device 4 is the core device for realizing CO2 capture in the system.

[0054] In this application, the high-temperature flue gas of the alumina calcination furnace is heat-exchanged with industrial water, reducing the temperature of the flue gas entering the PSA device 4 and reducing the problems of adsorbent performance degradation and increased energy consumption caused by high temperature. By further reducing the temperature and humidity of the flue gas, a saturated raw material gas is obtained, avoiding the problems of adsorbent blockage and performance degradation caused by excessive moisture and impurities. By increasing the pressure of the saturated raw material gas to the set pressure, the adsorption efficiency and selectivity of CO2 on the adsorbent are improved, thereby increasing the CO2 capture amount. This system adopts advanced PSA technology and realizes efficient capture of CO2 by optimizing the selection of adsorbent, the design of adsorption towers, and the operation process, etc. It overcomes the problems of low efficiency and high energy consumption of traditional PSA devices 4 when capturing low-concentration CO2.

[0055] In some embodiments, the secondary flue gas cooler 1 includes:

[0056] A primary cooling assembly 11, with industrial water introduced into the liquid inlet of the primary cooling assembly 11;

[0057] A secondary cooling assembly 12, with the gas inlet of the secondary cooling assembly 12 connected to the high-temperature flue gas outlet of the alumina calcination furnace, the liquid inlet of the secondary cooling assembly 12 connected to the liquid outlet of the primary cooling assembly 11, and the gas outlet of the secondary cooling assembly 12 connected to the gas inlet of the primary cooling assembly 11.

[0058] In some embodiments, the PSA device 4 includes:

[0059] A PSA adsorption tower 41, with the inlet of the PSA adsorption tower 41 connected to the outlet of the compressor 3;

[0060] A PSA vacuum pump 42, with the PSA vacuum pump 42 connected to the PSA adsorption tower 41;

[0061] A crude carbon dioxide gas buffer tank 43, with the crude carbon dioxide gas buffer tank 43 connected to the PSA adsorption tower 41.

[0062] In some embodiments, the system further includes:

[0063] A gas-liquid separator 5, with the inlet of the gas-liquid separator 5 connected to the compressor 3 and the outlet of the gas-liquid separator 5 connected to the PSA device 4.

[0064] In some embodiments, the system further includes:

[0065] A product compressor 6, with the product compressor 6 connected to the PSA device 4.

[0066] Figure 2It is a flowchart of a method for CO2 capture and waste heat utilization in the flue gas of alumina calcination provided by an embodiment of the present application.

[0067] Please refer to Figure 2 , the present application provides a method for CO2 capture and waste heat utilization in the flue gas of alumina calcination, and the method includes:

[0068] S1. Conduct heat exchange between the high-temperature flue gas of the alumina calcination furnace and industrial water to recover heat, obtaining a cooled gas and hot water;

[0069] S2. Further cool the cooled gas to obtain a saturated raw material gas;

[0070] S3. Increase the pressure of the saturated raw material gas to a set pressure; and

[0071] S4. Capture CO2 in the saturated raw material gas with the set pressure to obtain a CO2 product.

[0072] In some embodiments, the temperature of the saturated raw material gas ≤ 40 °C.

[0073] In some embodiments, the set pressure is 0.18 MPa to 0.22 MPa.

[0074] In some embodiments, the volume concentration of CO2 in the CO2 product ≥ 40%.

[0075] In some embodiments, the temperature of the high-temperature flue gas ≥ 180 °C; and / or,

[0076] the temperature of the hot water ≥ 80 °C; and / or,

[0077] the temperature of the industrial water ≤ 55 °C.

[0078] After the cooled gas is further cooled to obtain a saturated raw material gas, its temperature ≤ 40 °C, which is beneficial to subsequent CO2 capture. By increasing the pressure of the saturated raw material gas to the set pressure (0.18 MPa to 0.22 MPa), the working conditions of the PSA device are optimized, and the CO2 capture efficiency is improved. The volume concentration of CO2 in the captured CO2 product ≥ 40%, indicating good capture effect and high application value. By conducting heat exchange between the high-temperature flue gas of the alumina calcination furnace and industrial water, the waste heat in the flue gas is recovered and hot water is generated. These hot waters can be used in processes such as red mud washing, thus reducing heat energy waste and directly saving steam. Exemplarily, the set pressure can be 0.18 MPa, 0.19 MPa, 0.20 MPa, 0.21 MPa, 0.22 MPa, etc., and the volume concentration of CO2 in the CO2 product can be 40%, 40.1%, 40.2%, 40.5%, 40.8%, 41%, 42%, etc.

[0079] This application integrates two technologies of waste heat recovery and CO2 capture, and has significant advantages in the alumina production industry. Specifically as follows:

[0080] (1) Efficient waste heat recovery: By exchanging heat between high-temperature flue gas and industrial water, this technology effectively recovers the waste heat in the flue gas and generates high-temperature hot water. This hot water can be used in processes such as red mud washing, reducing heat energy waste and directly saving steam resources.

[0081] (2) Automated CO2 capture: The CO2 capture technology adopted by this technology has a high degree of automation, is easy to operate, and does not require a large amount of manual intervention. No waste liquid, waste residue, etc. are generated during the capture process, meeting environmental protection requirements and achieving green production.

[0082] (3) Long-life adsorbent: The adsorbent used has the characteristics of simple regeneration and long service life, reducing operating costs and maintenance costs.

[0083] (4) High-concentration CO2 product: The volume concentration of the captured CO2 product is as high as 40%, which has high application value. It can be used in multiple fields such as chemical industry, food, and medical treatment, increasing the source of income.

[0084] (5) Remarkable energy conservation and emission reduction effects: Each ton of alumina reduces carbon by 100 kg, significantly reducing CO2 emissions and contributing to alleviating the global warming problem. It meets the national carbon reduction requirements and sets a benchmark for energy conservation and emission reduction in the alumina industry.

[0085] (6) Innovation and demonstration effect: This technology is the first to achieve CO2 capture in the roasting furnace system in the alumina production industry, with innovation. The alumina produced by applying this technology has become the first "zero-carbon" alumina in China, with good demonstration effect and promotion value. Through waste heat recovery and CO2 capture, production costs are reduced and economic benefits are improved. It meets the requirements of national environmental protection policies and sustainable development strategies, enhancing the corporate image and brand value.

[0086] In summary, this technology integrates two technologies of waste heat recovery and CO2 capture, and has significant advantages in the alumina production industry. It not only realizes the effective utilization of waste heat in high-temperature flue gas, but also successfully captures CO2 in the flue gas, reducing carbon emissions. At the same time, the characteristics of this technology such as high degree of automation, easy operation, no generation of waste liquid and waste residue, and long service life of the adsorbent make it perform well in both economic and social benefits. In the future, with the continuous improvement and popularization of the technology, this technology is expected to make greater contributions to energy conservation, emission reduction and sustainable development in the alumina industry.

[0087] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. For the experimental methods without specific conditions indicated in the following embodiments, they are generally determined according to industry standards. If there is no corresponding industry standard, they are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0088] Figure 3 It is a schematic diagram of a method for CO2 capture and waste heat utilization in the flue gas of alumina calcination provided by an embodiment of the present application.

[0089] Please refer to Figure 3 , a method for CO2 capture and waste heat utilization in the flue gas of alumina calcination provided by the embodiment, may specifically include the following steps:

[0090] 1. The 180°C flue gas from the alumina calcination furnace first passes through two-stage flue gas coolers to exchange heat with the 55°C industrial water in the alumina plant to recover heat, generating 80°C industrial hot water for heat use in red mud washing in the alumina plant. The flue gas is cooled to 72°C and then enters the cooling and dehumidification tower to further reduce the flue gas temperature, ensuring that the raw material gas entering the PSA section is 40°C saturated gas. After water separation, the raw material gas enters the pressure swing adsorption section.

[0091] 2. The raw material gas with a temperature ≤ 40°C first enters the raw material gas compressor to increase the pressure to 0.2 MPa, and then enters the gas-liquid separator to remove the liquid water. The raw material gas after water removal enters the PSA device, where carbon dioxide in the gas is absorbed, and the components that are not easily adsorbed flow out of the tower top and are discharged. When the adsorption front of the easily adsorbed components is about to reach the tower top, the gas supply is stopped, and the carbon dioxide in the adsorption tower is enriched through equal pressure reduction. After the equal pressure reduction ends, the carbon dioxide gas in the adsorption tower is put into the crude carbon dioxide gas buffer tank by vacuum pumping. After the vacuum pumping ends, it enters the next adsorption cycle again. In the whole operation process, each adsorption tower successively experiences steps such as adsorption, equal pressure reduction, and vacuum pumping to enter the next cycle.

[0092] (1) Adsorption process: The raw material gas from the waste heat recovery section, about 10 kPa and with a temperature less than 40°C, first enters the raw material gas booster fan to increase the pressure to about 0.2 Mpa. The raw material gas after being pressurized by the flue gas compressor enters the tower from the lower end of the adsorption tower. When flowing through the adsorption bed from bottom to top under the adsorption working pressure, carbon dioxide and a small amount of water vapor in the gas stream are selectively adsorbed by the adsorbent, and the unadsorbed nitrogen, oxygen, etc. pass through the process control valve and are discharged from the tower top after being stabilized by the pressure regulating system. Finally, the obtained product CO2 gas purity is greater than 40% (vol%), and it is then pumped out by a vacuum pump and sent to the carbon dioxide gas buffer tank.

[0093] (2) Equal pressure reduction process:

[0094] After the adsorption process ends, pressure equalization is carried out with the tower that needs first-stage pressure boosting through the programmed control valve, that is, the tower to be regenerated is connected to the outlet of other towers for pressure equalization. When the pressures of the two towers for pressure equalization are basically balanced, the pressure reduction of the regenerated tower stops.

[0095] (3) Vacuum pumping process

[0096] After the entire co-current pressure reduction process ends, a vacuum pump is used to pump the adsorption bed layer against the adsorption direction to thoroughly regenerate the adsorbent.

[0097] (4) Pressure equalization and boosting process

[0098] After the vacuum pumping process is completed, the corresponding programmed control valve is opened to equalize the pressure with other towers that need pressure reduction, and the adsorption tower is boosted in turn with the higher-pressure gas from other adsorption towers. Three consecutive pressure equalization and boosting processes need to be implemented.

[0099] (5) Final pressure boosting process

[0100] After the pressure equalization and boosting process is completed, the pressure of the adsorption tower is raised to the adsorption pressure by slowly and smoothly releasing air through the pressure boosting regulating valve. A complete "adsorption-regeneration" cycle is completed. The above adsorption and regeneration operations are alternately carried out for each adsorption tower to achieve continuous separation and purification of the gas.

[0101] This embodiment realizes the CO2 capture in the roasting furnace system. 2捕 collection, and the volume concentration of CO2 after capture is 40.21%. It not only effectively utilizes the heat in the production process, but also reduces the CO2 emissions. The carbon reduction per ton of alumina is 100 kg, meeting the national carbon reduction requirements. At the same time, the industrial hot water at 80°C generated is used for the heat required for red mud washing in the alumina plant.

[0102] In addition, one or more technical solutions in the embodiments of the present application at least have the following technical effects or advantages:

[0103] In the embodiments of the present application, two technologies of integrated waste heat recovery and CO2 capture are integrated. The process flow is simple. First, waste heat recovery is carried out on the high-temperature flue gas, and the heat-exchanged medium industrial hot water is used for red mud washing, reducing heat energy waste and directly saving steam; the CO2 capture technology has a high degree of automation, is easy to operate, does not generate waste liquid, waste residue, etc., and is economical and environmentally friendly; the regeneration of the adsorbent is simple and has a long service life.

[0104] In the embodiments of the present application, for the first time in the alumina production industry, CO2 capture in the roasting furnace system is realized. The alumina produced by applying this technology has become the first "zero-carbon" alumina in the country, having good economic and social benefits.

[0105] The above description is only a specific implementation manner of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but rather will conform to the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A system for capturing CO2 and utilizing waste heat from alumina roasting flue gas, the system comprising: A secondary flue gas cooler (1), wherein the gas inlet of the secondary flue gas cooler (1) is connected to the high-temperature flue gas outlet of the alumina roasting furnace, and industrial water is introduced into the liquid inlet of the secondary flue gas cooler (1), so as to perform heat exchange between the high-temperature flue gas of the alumina roasting furnace and the industrial water to recover heat, thereby obtaining cooling gas and hot water; A cooling and dehumidifying tower (2), the inlet of which is connected to the gas outlet of the two-stage secondary flue gas cooler (1), for cooling the cooled gas again to obtain saturated raw gas; A compressor (3), the inlet of the compressor (3) being connected to the outlet of the cooling and dehumidifying tower (2), for increasing the pressure of the saturated raw gas to a set pressure; as well as A PSA device (4), wherein the inlet of the PSA device (4) is connected to the outlet of the compressor (3) to capture CO2 in the saturated raw gas with a set pressure to obtain a CO2 product.

2. The system according to claim 1, characterized in that The secondary flue gas cooler (1) comprises: A primary cooling component (11), wherein industrial water is introduced into a liquid inlet of the primary cooling component (11); A secondary cooling component (12), wherein the gas inlet of the secondary cooling component (12) is connected to the high-temperature flue gas outlet of the alumina roasting furnace, the liquid inlet of the secondary cooling component (12) is connected to the liquid outlet of the primary cooling component (11), and the gas outlet of the secondary cooling component (12) is connected to the gas inlet of the primary cooling component (11).

3. The system according to claim 1, characterized in that The PSA device (4) comprises: A PSA adsorption tower (41), wherein the inlet of the PSA adsorption tower (41) is connected to the outlet of the compressor (3); A PSA vacuum pump (42), wherein the PSA vacuum pump (42) is in communication with the PSA adsorption tower (41); A crude carbon dioxide gas buffer tank (43), wherein the crude carbon dioxide gas buffer tank (43) is in communication with the PSA adsorption tower (41).

4. The system according to claim 1, characterized in that The system further comprises: An air-water separator (5), wherein the inlet of the air-water separator (5) is connected to the compressor (3), and the outlet of the air-water separator (5) is connected to the PSA device (4).

5. The system according to claim 1, characterized in that The system further comprises: A product compressor (6), the product compressor (6) is connected to the PSA device (4).

6. A method for capturing CO2 in alumina roasting flue gas and utilizing waste heat, the method comprising: The high-temperature flue gas of the alumina roasting furnace is heat-exchanged with industrial water to recover heat and obtain cooling gas and hot water; The cooled gas is cooled again to obtain saturated raw gas; Increasing the pressure of the saturated raw gas to a set pressure; and The CO2 in the saturated raw gas with a set pressure is captured to obtain a CO2 product.

7. The method according to claim 1, characterized in that The temperature of the saturated raw gas is ≤40°C.

8. The method according to claim 1, characterized in that The set pressure is 0.18MPa to 0.22MPa.

9. The method according to claim 1, characterized in that: The volume concentration of CO2 in the CO2 product is ≥40%.

10. The method according to claim 1, characterized in that The temperature of the high-temperature flue gas is ≥ 180°C; and / or, The temperature of the hot water is ≥80°C; and / or, The temperature of the industrial water is ≤55°C.

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