Red mud-based oxygen carrier preparation system and method

Abstract

The application provides a preparation system and method of a red mud-based oxygen carrier. The preparation system comprises a reduction reactor and a combustion activator. The reduction reactor is used for reducing treatment of red mud to obtain red mud reduction products. The combustion activator is used for combustion activation treatment of the red mud reduction products, so that Fe elements in the red mud reduction products are oxidized into Fe2O3 to obtain red mud combustion activation products. The red mud combustion activation products are continuously circulated into the reduction reactor for reduction treatment and combustion activation treatment until the metallization rate of the red mud reduction products is greater than or equal to 80%, and the circulation is ended to obtain the red mud-based oxygen carrier. Through the multiple reduction-combustion circulation treatment, the iron elements in the red mud are gathered, and the reduction difficulty is reduced. Not only the energy consumption and equipment operation cost can be reduced, but also the red mud can be directly converted into the oxygen carrier which can be applied to the chemical looping combustion fuel without additional magnetic separation equipment.

Description

Technical Field

[0001] This application relates to the fields of chemical engineering, non-ferrous metallurgy, and environmental protection. Specifically, it relates to a system and method for preparing a red mud-based oxygen carrier. Background Technology

[0002] Red mud is an industrial solid waste generated during the production of alumina from bauxite. The Bayer process, due to its low energy consumption and simple process, accounts for over 90% of global alumina production, resulting in a massive amount of Bayer process red mud emissions. Bayer process red mud is not only highly alkaline, and long-term storage can easily lead to serious ecological and environmental problems such as soil alkalization and water pollution, but it also occupies a large amount of land resources. However, at the same time, Bayer process red mud generally has an iron content of over 30%, is rich in iron-bearing minerals such as hematite, and possesses extremely high resource recovery value, making it a potential low-cost iron-containing raw material. Therefore, developing high-value-added resource utilization technologies for Bayer process red mud, especially for the efficient recovery and utilization of its iron content, has become one of the core research directions in the field of sustainable development of the aluminum industry and solid waste pollution control.

[0003] Chemical Looping Combustion (CLC), a novel and highly efficient clean combustion technology, achieves indirect combustion of fuel and air through a cyclic redox reaction of an oxygen carrier between a fuel reactor and an air reactor. This directly yields high-purity CO2, significantly reducing carbon capture costs and demonstrating broad application prospects in energy utilization and environmental protection. The oxygen carrier is the core material of CLC technology, and its performance directly determines combustion efficiency, system stability, and operating costs. Traditional oxygen carriers often use transition metal oxides such as NiO, CuO, and Fe2O3, but these raw materials are expensive, and some metals are toxic, limiting their large-scale industrial application. Against this backdrop, the preparation of low-cost oxygen carriers from industrial solid waste has become a research hotspot. Bayer red mud, rich in Fe2O3 and containing high iron content, is one of the ideal raw materials for preparing oxygen carriers for CLC.

[0004] Currently, research on the application of red mud in chemical looping combustion has made some progress both domestically and internationally, mainly focusing on the preparation and performance optimization of red mud-based composite oxygen carriers, and the recovery of iron from red mud using chemical looping processes. For example, some studies have used an impregnation method to impregnate the surface of red mud with copper to prepare composite oxygen carriers, utilizing the synergistic effect of copper and Fe2O3 in red mud to enhance the reactivity of the oxygen carrier; other studies have combined red mud with copper ore, accelerating coal coke gasification and improving chemical looping combustion efficiency through the synergistic effect between the components. In the reduction treatment of red mud, existing technologies mostly employ high-temperature reduction processes, such as using H2 or CO-H2 mixed gas to reduce red mud at 700~1000℃ to improve the reduction degree of iron. Some studies have achieved a reduction degree of over 99% by optimizing process parameters, but it is necessary to strictly control the red mud particle size to below the micrometer level, and the reduction time is as long as 4 hours, resulting in high energy consumption and equipment costs. Another technology uses the high-temperature reducing atmosphere of the fuel reactor in the chemical looping gasification process to reduce hematite in Bayer process red mud in situ, and then recover iron elements through magnetic separation. Although this technology can reduce costs by utilizing the reducing atmosphere of the process itself, the reduction process depends on the high-temperature environment of the fuel reactor (usually 850~950℃), and the core objective is the recovery of iron elements, without focusing on optimizing the circulation activity of red mud in the chemical looping combustion process.

[0005] In view of the above, this application is hereby submitted. Summary of the Invention

[0006] The main objective of this application is to provide a red mud-based oxygen carrier and its preparation system and method, in order to solve the problem of high energy consumption and equipment operating costs caused by long-term reduction of red mud at high temperatures of 700℃~1000℃ or higher in the prior art.

[0007] To achieve the above objectives, according to one aspect of this application, a preparation system for a red mud-based oxygen carrier is provided, the preparation system comprising:

[0008] A reduction reactor is used to reduce red mud to obtain reduced red mud products.

[0009] The combustion activator is connected to the outlet of the reduction reactor. The combustion activator is used to activate the red mud reducing agent by combustion, so that the Fe element in the red mud reducing agent is oxidized to Fe2O3, and the red mud combustion activated product is obtained.

[0010] The outlet of the combustion activator is connected to the inlet of the reduction reactor to allow the red mud combustion activator to be fed into the reduction reactor for continued reduction and combustion activation treatment until the metallization rate of the red mud reduced product is ≥80%. The reduction and combustion activation treatments are then terminated, and the red mud reduced product is discharged from the outlet of the reduction reactor to obtain red mud-based oxygen carrier.

[0011] Furthermore, the preparation system also includes a reducing gas supply device, and the reducing reactor is provided with a reducing gas inlet. The reducing gas supply device is connected to the reducing reactor through the reducing gas inlet.

[0012] Furthermore, the preparation system also includes a combustion-supporting gas supply device, and the combustion activator is provided with a combustion-supporting gas inlet. The combustion-supporting gas supply device is connected to the combustion activator through the combustion-supporting gas inlet.

[0013] Furthermore, the preparation system also includes a gas-solid separator, which is installed on the pipeline between the outlet of the reduction reactor and the inlet of the combustion activator. The gas-solid separator is used to separate the reducing gas entrained in the red mud reducing agent.

[0014] Furthermore, the preparation system also includes a reducing gas preheating device, which is installed on the pipeline between the reducing gas supply device and the reducing gas inlet.

[0015] Furthermore, the preparation system also includes a combustion-supporting gas preheating device, which is installed on the pipeline between the combustion-supporting gas supply device and the combustion-supporting gas inlet.

[0016] Furthermore, the reduction reactor is selected from bubbling fluidized bed, circulating fluidized bed, or tunnel kiln.

[0017] Furthermore, the combustion activator is selected from swirl burners, jet bed burners, or circulating fluidized bed burners.

[0018] To achieve the above objectives, according to a second aspect of this application, a method for preparing a red mud-based oxygen carrier is provided, the method comprising:

[0019] Step S1: The red mud is passed into a reduction reactor for reduction treatment to obtain red mud reduced product;

[0020] Step S2: The red mud reducing agent is passed into a combustion activator for combustion activation treatment, so that the Fe element in the red mud reducing agent is oxidized to Fe2O3, and red mud combustion activated agent is obtained.

[0021] Step S3: Return the red mud combustion activator to step S1 for reduction and combustion activation treatment until the metallization rate of the red mud reduction product is ≥80%, then end the cycle to obtain red mud-based oxygen carrier.

[0022] Furthermore, in step S1, the red mud undergoes reduction treatment under the action of reducing gas at a temperature of 500~650℃.

[0023] Furthermore, the reduction treatment temperature is 550~650℃.

[0024] Furthermore, the reduction treatment time is 1~3 hours, and the reduction treatment pressure is 0.1~0.5 MPa.

[0025] Furthermore, the reducing gas is selected from at least one of hydrogen, a mixture of carbon monoxide and hydrogen, and purified industrial gas.

[0026] Furthermore, in the mixture of carbon monoxide and hydrogen, the volume ratio of carbon monoxide to hydrogen is 1:1 to 2:1.

[0027] Furthermore, the theoretical mass ratio of reducing gas to hydrogen required for deoxygenation of red mud is 3:1 to 5:1.

[0028] Furthermore, the red mud reducing agent is mixed with combustion-supporting gas for combustion activation treatment at a temperature of 800~950℃ for a time of 20~70min.

[0029] Furthermore, the combustion-supporting gas is an oxygen-containing gas.

[0030] Furthermore, the combustion-supporting gas is air.

[0031] Furthermore, the oxygen-to-material ratio of the combustion-supporting gas to the red mud reducing agent is 1.2:1 to 1.5:1.

[0032] Furthermore, in step S1, the red mud is first crushed to form red mud powder, and then the red mud powder is fed into a reduction reactor for reduction treatment.

[0033] Furthermore, the red mud powder has a particle size of 100μm~250μm and a moisture content of ≤2wt%.

[0034] Furthermore, the feed rate of red mud powder into the reduction reactor is 50~100 kg / h.

[0035] Furthermore, based on Fe2O3, the iron content of the red mud is ≥30%, and the water content is ≤15wt%.

[0036] Applying the technical solution of this application, red mud is reduced in a reduction reactor to obtain a reduced red mud product. This product is then activated by combustion in a combustion activator, oxidizing the Fe element in the reduced red mud to Fe₂O₃, resulting in a combustion-activated red mud product. This combustion-activated product is returned to the reduction reactor for further reduction and combustion activation treatments until the metallization rate of the reduced red mud is ≥80%. The cycle then ends, yielding a red mud-based oxygen carrier. This application employs multiple reduction-combustion cycles to aggregate iron elements in the red mud, reducing the difficulty of reduction. This not only reduces energy consumption and equipment operating costs but also eliminates the need for additional magnetic separation equipment, directly converting red mud into an oxygen carrier suitable for chemical looping combustion fuels.

[0037] Furthermore, the preparation method of the red mud-based oxygen carrier provided in this application has a simple process flow, which can not only solve the environmental problems of red mud accumulation, but also further promote the large-scale and industrial application of chemical looping combustion technology, thereby achieving the dual goals of "treating waste with waste and efficient utilization of resources". Attached Figure Description

[0038] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0039] Figure 1 A schematic diagram of a red mud-based oxygen carrier preparation system provided in some embodiments of this application is shown;

[0040] Figure 2 The diagram shows the metallization rate of the red mud reduced product obtained according to Examples 2 and 16 of this application under different combustion activation times.

[0041] The above figures include the following reference numerals:

[0042] 100. Reduction reactor; 110. Reduction gas preheating device; 120. Reduction gas supply device; 200. Combustion activator; 210. Gas-solid separator; 220. Combustion gas preheating device; 230. Combustion gas supply device. Detailed Implementation

[0043] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the embodiments.

[0044] As described in the background section of this application, existing technologies use red mud to undergo long-term reduction at temperatures above 700℃~1000℃, resulting in high energy consumption and equipment operating costs. To address these issues, this application provides a system and method for preparing a red mud-based oxygen carrier.

[0045] In a first typical embodiment of this application, a system for preparing a red mud-based oxygen carrier is provided, comprising: a reduction reactor 100 and a combustion activator 200, wherein the reduction reactor 100 is used to reduce red mud to obtain a red mud reduced product; the inlet of the combustion activator 200 is connected to the outlet of the reduction reactor 100, and the combustion activator 200 is used to perform combustion activation treatment on the red mud reduced product, so that the Fe element in the red mud reduced product is oxidized to Fe2O3, to obtain a red mud combustion activated product; the outlet of the combustion activator 200 is connected to the inlet of the reduction reactor 100, so that the red mud combustion activated product is fed into the reduction reactor 100 for continued circulation for reduction treatment and combustion activation treatment until the metallization rate of the red mud reduced product is ≥80%, the reduction treatment and combustion activation treatment are ended, and the red mud reduced product is discharged from the outlet of the reduction reactor 100 to obtain a red mud-based oxygen carrier.

[0046] It should be noted that, in this application, the red mud reducing agent with a metallization rate ≥80% is the red mud-based oxygen carrier. To increase the metal activation rate of the red mud-based oxygen carrier, the number of cycles of reduction treatment and combustion activation treatment can be increased.

[0047] In this application, red mud refers to industrial solid waste generated during the production of alumina from bauxite.

[0048] In this application, to ensure that the red mud has sufficient oxygen-carrying potential, Bayer process red mud was selected as the core raw material, and its iron content is ≥30% (calculated as Fe2O3). In addition, to avoid increased energy consumption and particle agglomeration due to water evaporation during the reduction process, the water content of the red mud is ≤15wt%.

[0049] The red mud-based oxygen carrier preparation system provided in this application involves reducing red mud in a reduction reactor 100 to obtain a red mud reduced product, and then activating the red mud reduced product through a combustion activator 200 to oxidize the Fe element in the red mud reduced product to Fe2O3, thereby obtaining a red mud combustion activated product. The red mud combustion activated product is then returned to the reduction reactor 100 for further reduction and combustion activation treatment until the metallization rate of the red mud reduced product is ≥80%, at which point the cycle ends and the red mud-based oxygen carrier is obtained.

[0050] The red mud-based oxygen carrier preparation system provided in this application uses a reduction reactor 100 connected to a combustion activator 200. Without the need for additional magnetic separation equipment, red mud can be directly converted into an oxygen carrier that can be used in chemical looping combustion fuels. The process is relatively simple, which can not only solve the environmental problems of red mud accumulation, but also further promote the large-scale and industrial application of chemical looping combustion technology, thereby achieving the dual goals of "treating waste with waste and efficient utilization of resources".

[0051] In some embodiments, the preparation system of red mud-based oxygen carrier further includes a reducing gas supply device 120. The reduction reactor 100 is provided with a reducing gas inlet. The reducing gas supply device 120 is connected to the reduction reactor 100 through the reducing gas inlet to introduce reducing gas into the reduction reactor 100, so that the red mud is reduced under the action of the reducing gas, and the Fe2O3 in the red mud is reduced to elemental iron and low-valence iron oxides such as Fe3O4.

[0052] In some embodiments, the preparation system of red mud-based oxygen carrier further includes a reducing gas preheating device 110, which is disposed on the pipeline between the reducing gas supply device 120 and the reducing gas inlet, so as to preheat the reducing gas and then introduce it into the reduction reactor 100, thereby further improving the stability of the internal temperature of the reduction reactor 100, and further improving the efficiency of the reduction process and reducing the cost.

[0053] In some embodiments, a gas distributor is also provided inside the reduction reactor 100 to make the reducing gas more evenly distributed inside the reduction reactor 100, so that the red mud is in a fluidized state in the reducing gas atmosphere, thereby making the reducing gas and red mud more fully contacted and further improving the reduction efficiency.

[0054] In some embodiments, the red mud-based oxygen carrier preparation system is further provided with a first temperature monitoring device, which is used to monitor the real-time temperature of the reduction process inside the reduction reactor 100 in order to maintain the temperature stability inside the reduction reactor 100.

[0055] In some embodiments, the preparation system of red mud-based oxygen carrier further includes a combustion-supporting gas supply device 230, and the combustion activator 200 is provided with a combustion-supporting gas inlet. The combustion-supporting gas supply device 230 is connected to the combustion activator 200 through the combustion-supporting gas inlet so that the combustion-supporting gas is introduced into the combustion activator 200 so that the red mud reducing agent is subjected to combustion activation treatment under the action of the combustion-supporting gas.

[0056] In some embodiments, the preparation system of red mud-based oxygen carrier further includes a combustion gas preheating device 220, which is disposed on the pipeline between the combustion gas supply device 230 and the combustion gas inlet, so as to facilitate the preheating of the combustion gas by the combustion gas preheating device 220 before it is introduced into the combustion activator 200, thereby further improving the temperature stability inside the combustion activator 200.

[0057] In some embodiments, the preparation system for red mud-based oxygen carriers further includes a second temperature monitoring device for monitoring the real-time temperature of the combustion activation process inside the combustion activator 200, so as to maintain the temperature stability inside the combustion activator 200.

[0058] In some embodiments, the preparation system of red mud-based oxygen carrier further includes a flue gas treatment device. The combustion activator 200 is provided with a flue gas outlet. The flue gas treatment device is connected to the flue gas outlet of the combustion activator 200 to purify the flue gas discharged from the combustion activator 200 before discharge, thereby improving environmental safety.

[0059] In some embodiments, the preparation system for the red mud-based carrier further includes a gas-solid separator 210, which is disposed on a pipeline between the outlet of the reduction reactor 100 and the inlet of the combustion activator 200. The gas-solid separator 210 is used to separate the reducing gas entrained in the red mud reducer.

[0060] In some specific embodiments, the gas-solid separator 210 is provided with a gas outlet, which is connected to the inlet of the reducing gas preheating device 110, so as to recycle the reducing gas separated by the gas-solid separator 210 and reduce the energy consumption of raw materials. The gas-solid separator 210 is also provided with a solid outlet, which is connected to the inlet of the combustion activator 200, so as to pass the red mud reduced material after removing the entrained reducing gas into the combustion activator 200 for combustion activation treatment.

[0061] To further improve the purity of the reducing gas discharged from the gas-solid separator 210, it is preferable that a tail gas treatment device is also installed on the pipeline between the gas-solid separator 210 and the reducing gas preheating device 110, so that the gas discharged from the gas-solid separator 210 is purified by the tail gas treatment device and then fed into the gas preheating device for recycling.

[0062] In some specific embodiments, the reduction reactor 100 is selected from at least one of a bubbling fluidized bed, a circulating fluidized bed, or a tunnel kiln. Using a bubbling fluidized bed or a circulating fluidized bed as the reduction reactor 100, with a preferred option being a circulating fluidized bed (suitable for large-scale production), the circulating fluidized bed offers advantages such as sufficient gas-solid contact, uniform temperature distribution, and controllable material residence time, ensuring efficient reaction between red mud and reducing gas. If fluidized bed equipment is lacking under current conditions, a tunnel kiln or other reactor can be used as an alternative. By optimizing the gas distributor structure and adding a material stirring device, sufficient contact between the reducing gas and red mud can be ensured. Simultaneously, the reduction time can be appropriately extended to compensate for the slightly lower gas-solid contact efficiency of a fixed bed. The reduction temperature remains within the medium-low temperature range of 500-650℃, and the specific process parameters for the reduction treatment remain unchanged. The reduction process is achieved by leveraging the advantages of a fixed bed device's simple structure and convenient operation and maintenance.

[0063] In some specific embodiments, the combustion activator 200 is selected from a swirl burner, a jet-driven bed burner, or a circulating fluidized bed burner, preferably a swirl burner, to further improve the efficiency of the combustion activation treatment. Jet-driven bed burners have the characteristics of high material circulation intensity and good combustion temperature uniformity. When replacing a swirl burner with a jet-driven bed burner, the combustion activation treatment temperature can be appropriately increased and the combustion activation treatment time shortened to achieve sufficient oxidation of low-valent red mud reducing agents. Circulating fluidized bed burners are suitable for large-scale continuous production and have the advantages of high combustion efficiency and a wide load adjustment range. When replacing a swirl burner with a circulating fluidized bed burner, the combustion activation temperature can be appropriately increased and the combustion activation time extended. Sufficient oxidation can be ensured by optimizing the secondary air ratio.

[0064] In a second typical embodiment of this application, a method for preparing a red mud-based oxygen carrier is provided, comprising:

[0065] Step S1: The red mud is passed into the reduction reactor 100 for reduction treatment to obtain red mud reduced product;

[0066] Step S2: The red mud reducing agent is passed into the combustion activator 200 for combustion activation treatment, so that the Fe element in the red mud reducing agent is oxidized to Fe2O3, and red mud combustion activated agent is obtained.

[0067] Step S3: Return the red mud combustion activator to step S1 for reduction and combustion activation treatment until the metallization rate of the red mud reduction product is ≥80%, then end the cycle to obtain red mud-based oxygen carrier.

[0068] As mentioned earlier, in this application, the red mud reducer with a metallization rate ≥80% is the red mud-based oxygen carrier. To improve the metal activation rate of the red mud-based oxygen carrier, the number of cycles of reduction treatment and combustion activation treatment can be increased.

[0069] In this application, red mud refers to industrial solid waste generated during the production of alumina from bauxite. Specifically, to ensure that the red mud has sufficient oxygen-carrying potential, Bayer process red mud is selected as the core raw material, and its iron content is ≥30% (calculated as Fe2O3). In addition, to avoid increased energy consumption and particle agglomeration due to water evaporation during the reduction process, the water content of the red mud is ≤15wt%.

[0070] The specific equipment selection for the reduction reactor 100 and the combustion activator 200 is as described in the first typical embodiment above, and will not be repeated here.

[0071] In this application, red mud is reduced and activated by combustion in a fluidized bed reactor to obtain red mud combustion activated material. This activated material is then cyclically reduced and activated again until the metallization rate of the reduced red mud reaches ≥80%, at which point the cycle ends, yielding a red mud oxygen carrier. This application not only utilizes multiple reduction-combustion cycles to aggregate iron in red mud, reducing reduction difficulty and increasing metallization rate, but also eliminates the need for additional magnetic separation steps, directly converting red mud into an oxygen carrier suitable for chemical looping combustion fuels. The preparation method is relatively simple, while simultaneously addressing the environmental problems associated with red mud accumulation. This can further promote the large-scale, industrial application of chemical looping combustion technology, thereby achieving the dual goals of "waste treatment and efficient resource utilization."

[0072] In some embodiments, in step S1, the red mud undergoes reduction treatment under the action of the reducing gas at a temperature of 500~650℃. In some preferred embodiments, the reduction treatment temperature is 550~650℃, and the reduction treatment time is 1~3 hours. The reduction treatment pressure is 0.1~0.5MPa. This application overcomes the limitations of traditional red mud reduction, which relies on high temperatures or low metallization rates, by employing a medium-low temperature reduction of 500~650℃. Combined with the efficient gas-solid contact characteristics of a fluidized bed reactor, this avoids red mud particle adhesion while achieving a full reaction between hydrogen and red mud powder, significantly reducing energy consumption (30%~50% lower than existing high-temperature reduction processes). Specifically, the reduction treatment temperature is any value or a range between any two of the following: 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, 600℃, 610℃, 620℃, 630℃, 640℃, and 650℃; the reduction treatment time is any value or a range between any two of the following: 1h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, 2h, 2.2h, 2.5h, 2.8h, and 3h; and the reduction treatment pressure is any value or a range between any two of the following: 0.1MPa, 0.2MPa, 0.3MPa, 0.4MPa, and 0.5MPa.

[0073] When a circulating fluidized bed is used as the reduction reactor 100 for reduction treatment, the preferred reduction treatment time is 1-2 hours. When a tunnel kiln is used as the reduction reactor 100 for reduction treatment, the preferred reduction time is adjusted to 2-3 hours to better achieve the reduction process.

[0074] In some specific embodiments, the reducing gas is selected from at least one of hydrogen, a mixture of carbon monoxide and hydrogen, and purified industrial coal gas. To further improve the efficiency of the reduction process, the purity of the reducing gas is preferably ≥99%.

[0075] The main components of the purified industrial gas are CO and H2, and the total volume fraction of the two is ≥90%. Using purified industrial gas as a reducing gas can reduce the cost of reducing agent and realize the resource utilization of industrial by-products.

[0076] In some specific embodiments, the volume ratio of carbon monoxide to hydrogen in the carbon monoxide and hydrogen mixture is 1:1 to 2:1. By mixing carbon monoxide and hydrogen, costs can be reduced, and the synergistic reduction effect of CO and H2 can be utilized to ensure the reduction effect. Specifically, the volume ratio of carbon monoxide to hydrogen in the carbon monoxide and hydrogen mixture is any value or a range between any two of the following: 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, and 2:1.

[0077] To further improve the mixing of reducing gas and red mud for reduction treatment, in some embodiments, the mass ratio of reducing gas to hydrogen theoretically required for deoxygenation of red mud is 3:1 to 5:1. Specifically, the mass ratio of reducing gas to red mud is any value from 3:1, 3.5:1, 4:1, 4.5:1, 5:1, or any range between two of these values.

[0078] In this application, the mass of hydrogen theoretically required for deoxygenation of red mud is the same as the mass of hydrogen theoretically required for deoxygenation treatment of all components in the red mud.

[0079] To further enhance the combustion of red mud reducing agents and combustion-supporting gases in the combustion activator 200, the temperature and time of the combustion activation treatment are controlled. In some embodiments, in step S2, the red mud reducing agents and combustion-supporting gases are mixed for combustion activation treatment. The temperature of the combustion activation treatment is 800~950℃, and the time is 20~70min. Specifically, the combustion activation treatment temperature is any value or a range between any two of 800℃, 810℃, 820℃, 830℃, 840℃, 850℃, 860℃, 870℃, 880℃, 890℃, 900℃, 910℃, 920℃, 930℃, 940℃, and 950℃; the combustion activation treatment time is any value or a range between any two of 20min, 30min, 40min, 50min, 60min, and 70min.

[0080] When the combustion activator 200 is a swirl burner, the preferred combustion activation temperature is 800~900℃ and the combustion activation time is 30~60min, so as to improve the efficiency of the combustion activation process.

[0081] When a jet-driven bed burner is used as the combustion activator 200, the preferred combustion activation temperature is 850~950℃ and the combustion time is 20~40min, which is more conducive to improving the efficiency of combustion activation while ensuring the full oxidation of red mud reducing materials.

[0082] When a circulating fluidized bed burner is used as the combustion activator 200, the preferred combustion activation temperature is 850~950℃ and the combustion time is 40~70min, which is more conducive to improving the efficiency of combustion activation while ensuring the complete combustion of red mud reducing materials.

[0083] In some specific embodiments, the combustion-supporting gas is an oxygen-containing gas, preferably air, to further reduce costs.

[0084] To improve the combustion efficiency of the combustion-supporting gas and the red mud reducer, in some embodiments, the oxygen-to-material ratio of the combustion-supporting gas to the red mud reducer is 1.2:1 to 1.5:1. Specifically, the oxygen-to-material ratio of the combustion-supporting gas to the red mud reducer is any value among 1.2:1, 1.3:1, 1.4:1, and 1.5:1, or any range between two of these.

[0085] In this application, the oxygen-to-material ratio refers to the ratio of the total mass of oxygen in the combustion-supporting gas to the theoretical mass of oxygen required to oxidize Fe in red mud powder to Fe2O3.

[0086] In some embodiments, in step S1, in order to facilitate full contact between the red mud and the reducing gas and improve the efficiency of the reduction treatment, it is preferable to first crush the red mud to form red mud powder, and then pass the red mud powder into the reduction reactor 100 for reduction treatment.

[0087] In some specific embodiments, the preferred particle size of the red mud powder is 100μm~250μm and the moisture content is ≤2wt%, so as to promote sufficient contact between the red mud powder and the reducing gas while avoiding the impact of excessive moisture content in the red mud powder on the stability of the reducing atmosphere and the reduction efficiency.

[0088] In some specific embodiments, after the red mud is initially crushed by a jaw crusher, it is further refined by an air jet mill and then screened by a grading sieve to obtain red mud powder with a particle size of 100μm~250μm. The red mud powder is then fed into a dryer and dried at 100~110℃ for 2~3 hours to remove adsorbed water, ensuring that the moisture content of the dried red mud powder is ≤2wt%. This prevents moisture from affecting the stability of the reducing atmosphere and the reduction efficiency during the fluidized bed reduction process. A suitable particle size range for the red mud powder further facilitates the reduction reaction during the reduction treatment, and controlling the moisture content further prevents the red mud particles from agglomerating during the reduction process. Specifically, the particle size of the red mud powder is any value or a range between any two of the following: 100μm, 11μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm, 190μm, 200μm, 210μm, 220μm, 230μm, 240μm, and 250μm; and the moisture content of the dried red mud powder is any value or a range between any two of the following: 2wt%, 1.5wt%, 1wt%, 0.5wt%, and 0wt%.

[0089] To further improve the efficiency of the reduction process, in some embodiments, the feed rate of red mud powder into the reduction reactor 100 is 50~100 kg / h. Specifically, the feed rate of red mud powder is any value or a range between 50 kg / h, 60 kg / h, 70 kg / h, 80 kg / h, 90 kg / h, and 100 kg / h.

[0090] In some preferred embodiments, in step S1, to avoid impurities in the air affecting the stability of the reduction process, a protective gas is preferably introduced into the reduction reactor 100 during the heating stage when the reduction reactor 100 is heated to the reduction treatment temperature, and the reducing gas is introduced during the heat preservation stage when the reduction treatment temperature is reached. When the heat preservation stage ends, a protective gas is also introduced into the reduction reactor 100 during the cooling stage when the reduction treatment temperature is cooled to room temperature. The protective gas preferably includes any one or a mixture of nitrogen, argon, or helium. Introducing a protective gas during the heating and cooling stages can remove air from the reactor, which can further prevent the iron oxides in the red mud from being re-oxidized before the reduction treatment, thereby ensuring the purity of the reduced product during the reduction treatment and promoting a stable reduction reaction.

[0091] In some preferred embodiments, in step S3, the red mud combustion activator is returned to step S1 for reduction and combustion activation treatment. Generally, 3 to 5 cycles are sufficient to obtain red mud reducer with a metallization rate of ≥80%, and the metallization rate of the red mud reducer can even be increased to over 90%, resulting in a red mud-based oxygen carrier with higher combustion efficiency.

[0092] To further improve the metallization rate in the red mud-based oxygen carrier, the number of cycles can be increased appropriately.

[0093] The beneficial effects of this application will be further illustrated below with reference to embodiments and comparative examples.

[0094] Example 1

[0095] like Figure 1 As shown, this embodiment provides a system for preparing a red mud-based oxygen carrier.

[0096] The preparation system of the red mud-based oxygen carrier includes a reduction reactor 100 and a combustion activator 200. The reduction reactor 100 is used to reduce red mud to obtain red mud reduced product. The inlet of the combustion activator 200 is connected to the outlet of the reduction reactor 100. The combustion activator 200 is used to perform combustion activation treatment on the red mud reduced product to obtain red mud combustion activated product.

[0097] The outlet of the combustion activator 200 is connected to the inlet of the reduction reactor 100, which is used to pass the red mud combustion activator into the reduction reactor 100 for continued circulation to carry out reduction treatment and combustion activation treatment until the metallization rate of the red mud reduced product is ≥80%. The reduction treatment and combustion activation treatment are then ended, and the red mud reduced product is discharged from the outlet of the reduction reactor 100 to obtain red mud-based oxygen carrier.

[0098] In some preferred embodiments, the preparation system of red mud-based oxygen carrier further includes a reducing gas supply device 120. The reduction reactor 100 is provided with a reducing gas inlet. The reducing gas supply device 120 is connected to the reduction reactor 100 through the reducing gas inlet to introduce reducing gas into the reduction reactor 100, so that the red mud is reduced under the action of the reducing gas, and the Fe2O3 in the red mud is reduced to elemental iron and low-valence iron oxides such as Fe3O4.

[0099] In some preferred embodiments, the preparation system of red mud-based oxygen carrier further includes a reducing gas preheating device 110, which is installed on the pipeline between the reducing gas supply device 120 and the reducing gas inlet to preheat the reducing gas before it is introduced into the reduction reactor 100, thereby further improving the stability of the internal temperature of the reduction reactor 100, and thus further improving the efficiency of the reduction process and reducing the cost.

[0100] In some preferred embodiments, a gas distributor is also provided inside the reduction reactor 100 to make the reducing gas more evenly distributed inside the reduction reactor 100, so that the red mud is in a fluidized state in the reducing gas atmosphere, thereby making the reducing gas and red mud more fully contacted and further improving the reduction efficiency.

[0101] In some preferred embodiments, the red mud-based oxygen carrier preparation system is further provided with a first temperature monitoring device, which is used to monitor the real-time temperature of the reduction process inside the reduction reactor 100 in order to maintain the temperature stability inside the reduction reactor 100.

[0102] In some preferred embodiments, the red mud-based oxygen carrier preparation system further includes a combustion-supporting gas supply device 230. The combustion activator 200 is provided with a combustion-supporting gas inlet, and the combustion-supporting gas supply device 230 is connected to the combustion activator 200 through the combustion-supporting gas inlet to introduce combustion-supporting gas into the combustion activator 200 so that the red mud reducing agent undergoes combustion activation treatment under the action of the combustion-supporting gas. In some embodiments, the red mud-based oxygen carrier preparation system further includes a combustion-supporting gas preheating device 220, which is disposed on the pipeline between the reducing gas supply device 120 and the reducing gas inlet, so as to facilitate the preheating of the combustion-supporting gas by the combustion-supporting gas preheating device 220 before introducing it into the combustion activator 200, thereby further improving the temperature stability inside the combustion activator 200.

[0103] In some preferred embodiments, the preparation system of red mud-based oxygen carrier further includes a second temperature monitoring device for monitoring the real-time temperature of the combustion activation process inside the combustion activator 200, so as to maintain the temperature stability inside the combustion activator 200.

[0104] In some preferred embodiments, the preparation system of red mud-based oxygen carrier further includes a flue gas treatment device. The combustion activator 200 is provided with a flue gas outlet. The flue gas treatment device is connected to the flue gas outlet of the combustion activator 200 to purify the flue gas discharged from the combustion activator 200 before discharge, thereby improving environmental safety.

[0105] In some preferred embodiments, the preparation system for the red mud-based carrier further includes a gas-solid separator 210, which is disposed on a pipeline between the outlet of the reduction reactor 100 and the inlet of the combustion activator 200. The gas-solid separator 210 is used to separate the reducing gas entrained in the red mud reducer.

[0106] In some specific embodiments, the gas-solid separator 210 is provided with a gas outlet, which is connected to the inlet of the reducing gas preheating device 110, so as to recycle the reducing gas separated by the gas-solid separator 210 and reduce the energy consumption of raw materials. The gas-solid separator 210 is also provided with a solid outlet, which is connected to the inlet of the combustion activator 200, so as to pass the red mud reduced material after removing the entrained reducing gas into the combustion activator 200 for combustion activation treatment.

[0107] To further improve the purity of the reducing gas discharged from the gas-solid separator 210, it is preferable that a tail gas treatment device is also installed on the pipeline between the gas-solid separator 210 and the reducing gas preheating device 110, so that the gas discharged from the gas-solid separator 210 is purified by the tail gas treatment device and then fed into the gas preheating device for recycling.

[0108] Among them, the combustion activator 200 is a swirl burner, and the reduction reactor 100 is a bubbling fluidized bed reactor.

[0109] The following examples and comparative examples use red mud A or red mud B as raw materials, and the specific compositions of red mud A and red mud B are shown in Table 1 below.

[0110] Table 1

[0111]

[0112] Example 2

[0113] This embodiment provides a method for preparing a red mud-based oxygen carrier, the method comprising the following steps:

[0114] (1) Red mud A is crushed by a crusher and then passed through a 60-150 mesh sieve to screen out red mud powder with a particle size of 100-250μm. It is dried at 105℃ for 2.5h to make the moisture content of the dried red mud powder ≤2wt%. The dried red mud powder is fed into a bubbling fluidized bed reactor and heated to 600℃. It is then reduced at 0.1MPa and the temperature is maintained for 1.5h to obtain red mud reduced product. Nitrogen gas is introduced throughout the heating and cooling process of the bubbling fluidized bed reactor. When the temperature inside the bubbling bed reactor reaches 600℃, it enters the heat preservation period. During the heat preservation period, hydrogen gas is introduced. The mass ratio of hydrogen gas introduced into the bubbling fluidized bed reactor to the hydrogen gas theoretically required for deoxygenation of red mud powder is controlled to be 4:1.

[0115] (2) Air and red mud reducing agent are mixed at an oxygen-to-material ratio of 1.3:1 and passed into a cyclone activator for combustion activation treatment to obtain red mud combustion activated agent. The combustion activation treatment temperature is 850℃ and the combustion treatment time is 45min.

[0116] (3) Return the red mud combustion activated material to the bubbling fluidized bed reactor and repeat steps (1) and (2) to perform reduction treatment and combustion activation treatment. After the first reduction treatment (0 combustion activation treatments), the second reduction treatment (1 combustion activation treatment), the third reduction treatment (2 combustion activation treatments), the fourth reduction treatment (3 combustion activation treatments), and the fifth reduction treatment (4 combustion activation treatments), the red mud reduced material is taken for metallization rate detection.

[0117] Example 3

[0118] The difference between this embodiment and embodiment 2 is that in step (1), the temperature of the reduction treatment is 500°C and the time of the reduction treatment is 2 hours.

[0119] Example 4

[0120] The difference between this embodiment and embodiment 2 is that in step (1), the temperature of the reduction treatment is 550°C and the time of the reduction treatment is 1.8h.

[0121] Example 5

[0122] The difference between this embodiment and embodiment 2 is that in step (1), the temperature of the reduction treatment is 650°C and the time of the reduction treatment is 1 hour.

[0123] Example 6

[0124] The difference between this embodiment and embodiment 2 is that, in step (1), a tunnel kiln is used as the reduction reactor and the reduction treatment time is adjusted to 3 hours.

[0125] Example 7

[0126] The difference between this embodiment and embodiment 2 is that in step (1), the temperature of the reduction treatment is 490°C and the time of the reduction treatment is 2 hours.

[0127] Example 8

[0128] Compared with Example 2, the difference in this embodiment is that in the adjustment step (1), the mass ratio of hydrogen gas introduced into the bubbling fluidized bed reactor to the hydrogen gas theoretically required for deoxygenation of red mud powder is 3:1.

[0129] Example 9

[0130] The difference between this embodiment and embodiment 2 is that, in step (1), the mass ratio of hydrogen gas introduced into the bubbling fluidized bed reactor to the hydrogen gas theoretically required for deoxygenation of red mud powder is 5:1.

[0131] Example 10

[0132] The difference between this embodiment and embodiment 2 is that the temperature of the combustion activation treatment in step (2) is adjusted to 800°C and the combustion activation treatment time is adjusted to 60 min.

[0133] Example 11

[0134] The difference between this embodiment and embodiment 2 is that the temperature of the combustion activation treatment in step (2) is adjusted to 900°C and the combustion activation treatment time is adjusted to 30 min.

[0135] Example 12

[0136] The difference between this embodiment and embodiment 2 is that the adjustment step (2) is a jet bed burner, the temperature of the combustion activation treatment is adjusted to 950°C, and the combustion activation treatment time is 20 min.

[0137] Example 13

[0138] The difference between this embodiment and embodiment 2 is that the adjustment step (2) uses a circulating fluidized bed burner, the temperature of the combustion activation treatment is adjusted to 900℃, and the combustion activation treatment time is 70min.

[0139] Example 14

[0140] Compared with Example 2, the difference in this embodiment is that in the adjustment step (1), the mass ratio of hydrogen gas introduced into the bubbling fluidized bed reactor to the hydrogen gas theoretically required for deoxygenation of red mud powder is 1:1.

[0141] Example 15

[0142] The difference between this embodiment and embodiment 2 is that the temperature of the combustion activation treatment in step (2) is adjusted to 750°C and the combustion activation treatment time is adjusted to 60 min.

[0143] Example 16

[0144] The difference between this embodiment and embodiment 2 is that the raw material in step (1) is red mud B.

[0145] Experimental Example 1

[0146] The metallization rate of the red mud reduced products prepared in Examples 2-16 was tested. The specific test method was as follows: chemical analysis was performed according to the national standard GB / T 24235-2009.

[0147] The test results are shown in Table 2.

[0148] Table 2

[0149]

[0150] Figure 2 The metallization rate diagrams of red mud reduced products under different combustion activation cycles are obtained for Examples 2 and 16. Figure 2 It can be seen that the metallization rates of the red mud reduced products obtained in Examples 2 and 16 without combustion activation treatment were 41.2% and 42.2%, respectively. The metallization rate of the red mud reduced product obtained in Example 2 after two combustion activation treatments was 85.9%, and the metallization rate of the red mud reduced product obtained in Example 16 after three combustion activation treatments was 83.5%. It can be concluded that multiple reduction-combustion cycle treatments can cause iron elements in red mud to accumulate, increase the metallization rate in the red mud reduced product, reduce the reduction difficulty, and further reduce energy consumption and equipment operating costs without the need for additional magnetic separation equipment.

[0151] Comparing Examples 2 and 6, it can be seen that the metallization rate of the red mud reduced product obtained by using a bubbling fluidized bed reactor in step (1) is higher. This demonstrates the high efficiency of the gas-solid contact characteristics of the fluidized bed reactor, which avoids the adhesion of red mud particles while achieving a full reaction between hydrogen and red mud powder.

[0152] Compared with Example 7, Examples 2-5 show that when the reduction treatment temperature is in the range of 550~650℃, the sintering of red mud powder can be avoided. At the same time, hydrogen has sufficient reducing activity, which can further increase the metallization rate of the red mud reduced product obtained by the reduction treatment and reduce energy consumption.

[0153] Compared with Example 14, Examples 2 and 8-9 show that when the mass ratio of reducing gas to red mud is in the range of 3:1 to 5:1, the metallization rate of the red mud reduced product prepared by multiple reduction-combustion treatments is higher, and red mud oxygen carrier can be obtained after two combustion activation treatments.

[0154] By comparing Example 2 with Examples 11-13 and Example 15, it was found that when the combustion activation treatment temperature is between 800 and 950°C, the metallization rate of the red mud reduced product is higher. The appropriate temperature can more efficiently oxidize the elemental iron, Fe3O4 and other substances in the red mud reduced product to Fe2O3, thereby making the metallization rate of the red mud reduced product after cyclic reduction treatment higher.

[0155] As can be seen from the above description, the embodiments of this application achieve the following technical effects:

[0156] This application uses a reduction reactor to reduce red mud, obtaining a reduced red mud product. This product is then activated by combustion in a combustion activator, oxidizing the Fe element to Fe₂O₃, resulting in an activated red mud product. This activated red mud product is returned to the reduction reactor for further reduction and combustion activation treatments until the metallization rate of the reduced red mud product is ≥80%. The cycle then ends, yielding a red mud-based oxygen carrier. This application employs multiple reduction-combustion cycles to aggregate iron in the red mud, reducing the difficulty of reduction. This not only lowers energy consumption and equipment operating costs but also eliminates the need for additional magnetic separation equipment, directly converting red mud into an oxygen carrier suitable for chemical looping combustion fuels.

[0157] Furthermore, the preparation method of the red mud-based oxygen carrier provided in this application has a simple process flow, which can not only solve the environmental problems of red mud accumulation, but also further promote the large-scale and industrial application of chemical looping combustion technology, thereby achieving the dual goals of "treating waste with waste and efficient utilization of resources".

[0158] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a red mud-based oxygen carrier, characterized in that, The preparation method includes: Step S1: The red mud is passed into the reduction reactor (100) for reduction treatment to obtain red mud reduced product; Step S2: The red mud reduced product is passed into a combustion activator (200) for combustion activation treatment, so that the Fe element in the red mud reduced product is oxidized to Fe2O3, and red mud combustion activated product is obtained. Step S3: Return the red mud combustion activator to step S1 for the reduction treatment and combustion activation treatment until the metallization rate of the red mud reduced product is ≥80%, then end the cycle to obtain the red mud-based oxygen carrier. In step S1, the red mud undergoes reduction treatment under the action of reducing gas at a temperature of 500-650℃.

2. The preparation method according to claim 1, characterized in that, In step S1, the reduction treatment time is 1~3 hours, and the reduction treatment pressure is 0.1~0.5 MPa.

3. The preparation method according to claim 1, characterized in that, In step S2, the red mud reducing agent is mixed with the combustion-supporting gas to carry out the combustion activation treatment. The temperature of the combustion activation treatment is 800~950℃ and the time of the combustion activation treatment is 20~70min.

4. The preparation method according to any one of claims 1 to 3, characterized in that, In step S1, the red mud is first crushed to form red mud powder, and then the red mud powder is passed into the reduction reactor (100) for the reduction treatment.

5. The preparation method according to any one of claims 1 to 3, characterized in that, The red mud has an iron content of ≥30% and a water content of ≤15wt% based on Fe2O3.

6. The preparation method according to any one of claims 1 to 3, characterized in that, The preparation method is carried out in a red mud-based oxygen carrier preparation system, the preparation system comprising: A reduction reactor (100) is used to reduce red mud to obtain a reduced red mud product; Combustion activator (200), the inlet of which is connected to the outlet of the reduction reactor (100), the combustion activator (200) is used to perform combustion activation treatment on the red mud reducing material, so that the Fe element in the red mud reducing material is oxidized to Fe2O3, and red mud combustion activated material is obtained; The outlet of the combustion activator (200) is connected to the inlet of the reduction reactor (100) to allow the red mud combustion activator to be fed into the reduction reactor (100) for continued circulation of the reduction treatment and the combustion activation treatment until the metallization rate of the red mud reduced product is ≥80%. The reduction treatment and the combustion activation treatment are then terminated, and the red mud reduced product is discharged from the outlet of the reduction reactor (100) to obtain the red mud-based oxygen carrier.

7. The preparation method according to claim 6, characterized in that, The preparation system further includes a reducing gas supply device (120), the reducing reactor (100) is provided with a reducing gas inlet, and the reducing gas supply device (120) is connected to the reducing reactor (100) through the reducing gas inlet; The preparation system also includes a combustion-supporting gas supply device (230), and the combustion activator (200) is provided with a combustion-supporting gas inlet. The combustion-supporting gas supply device (230) is connected to the combustion activator (200) through the combustion-supporting gas inlet.

8. The preparation method according to claim 6, characterized in that, The preparation system also includes a gas-solid separator (210), which is located on the pipeline between the outlet of the reduction reactor (100) and the inlet of the combustion activator (200). The gas-solid separator (210) is used to separate the reducing gas entrained in the red mud reducing agent.

9. The preparation method according to claim 7, characterized in that, The preparation system further includes a reducing gas preheating device (110), which is disposed on the pipeline between the reducing gas supply device (120) and the reducing gas inlet; The preparation system also includes a combustion-supporting gas preheating device (220), which is installed on the pipeline between the combustion-supporting gas supply device (230) and the combustion-supporting gas inlet.

10. The preparation method according to claim 6, characterized in that, The reduction reactor (100) is selected from a bubbling fluidized bed, a circulating fluidized bed, or a tunnel kiln; And / or, the combustion activator (200) is selected from a swirl burner, a jet bed burner, or a circulating fluidized bed burner.

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