System and method for manufacturing dry desulfurization and denitrification catalyst particles by using red mud

Abstract

The invention discloses a system and a method for manufacturing dry desulfurization and denitrification catalyst particles by using red mud, and belongs to the technical field of flue gas purification. The device is characterized in that desulfurized and denitrated red mud particles are discharged from a reaction tower, then enter a crusher to be crushed, then enter a stirrer to be mixed, humidified and prepared, then enter a granulation device 4 to be granulated, the granulated particles are dried and sieved, qualified particles return to the reaction tower to be continuously subjected to desulfurization and denitration reaction, and the desulfurized and denitrated red mud particles are obtained. And returning unqualified particles to the granulation device for re-granulation. The red mud is used as the catalyst, the price is low, the cost is saved, the reaction temperature is low, the denitration reaction can be carried out after flue gas dust removal, the influence of dust on the denitration reaction is reduced, generated sulfate and nitrate can be subjected to resource recycling, the energy consumption is lower, the structure is simpler, and solid waste resource recycling is achieved.

Description

Technical Field

[0001] This invention relates to the field of flue gas purification technology, specifically to a system and method for manufacturing catalyst particles for dry desulfurization and denitrification using red mud. Background Technology

[0002] With rapid industrialization, air pollution from coal-fired power generation has become increasingly prominent. For example, the flue gas produced in furnaces in thermal power plants, steel mills, cement plants, building materials factories, and metallurgical plants contains large amounts of pollutants such as sulfur dioxide, nitrogen oxides, and particulate matter, posing a significant threat to human health and the ecological environment. Excessive emissions of nitrogen oxides and sulfur dioxide not only severely damage the human respiratory system but also cause a series of irreversible environmental problems such as acid rain, photochemical pollution, and ozone layer depletion. Therefore, controlling the emissions of nitrogen oxides and sulfur dioxide is of paramount importance. How to economically and effectively remove and reduce these harmful pollutants is a crucial issue.

[0003] Material pollution is an urgent problem that my country needs to solve, and the implementation of ultra-low emissions of pollutants is also a problem that existing production enterprises need to solve.

[0004] Currently, the most mature and efficient denitrification process in China is selective catalytic reduction (SCR) denitrification. However, due to the difficulty in controlling catalyst activity and the large-scale use of ammonia during production, its application cost is high. Desulfurization mostly employs wet desulfurization technology, typically using limestone slurry as the desulfurizing agent. While achieving high desulfurization efficiency, it consumes a large amount of energy and water, and the desulfurization products are difficult to process. Denitrification and desulfurization of flue gas are two crucial control indicators. Currently, there is no mature integrated desulfurization and denitrification equipment applied in production. From practical application, integrated technology can complete the treatment of sulfur dioxide and nitrogen oxides within the same system, significantly improving desulfurization and denitrification efficiency. Due to technological limitations, the application of this technology in my country's power industry is limited, and many details still need improvement. Integrated desulfurization and denitrification processes have become a research hotspot for flue gas pollution control in various countries. Currently, the solid-phase absorption / regeneration integrated desulfurization and denitrification process remains in the research and development stage. Although a few demonstration projects have been implemented, high operating costs have hindered its large-scale promotion and application. Developing integrated desulfurization and denitrification technologies that are suitable for my country's national conditions, require less investment, have lower operating costs, are more efficient, and utilize by-products as resources will be a key focus for future development. Summary of the Invention

[0005] The purpose of this invention is to provide a dry treatment system that uses red mud as a catalyst to remove sulfur dioxide and nitrogen oxides together. This system mainly provides a granulation device to match the integrated desulfurization and denitrification system.

[0006] According to two main aspects of the present invention, a dry flue gas treatment system for desulfurization and denitrification is provided:

[0007] 1. The flue gas denitrification and desulfurization reaction unit mainly includes a convection reaction tower feed and discharge device. After the reaction tower is filled with red mud catalyst particles, the raw flue gas enters the reaction tower. Sulfur dioxide and nitrogen oxides in the flue gas are simultaneously adsorbed by the red mud particles, and under the catalytic action of the red mud, an oxidation-reduction reaction occurs to produce sulfates and nitrates. The exhausted red mud particles are discharged from the bottom of reaction tower 1 and regenerated by granulation. The top of the reaction tower is continuously replenished with regenerated red mud particles.

[0008] 2. Red Mud Granulation Unit: Red mud particles absorb sulfur dioxide and nitrogen oxides from flue gas to form sulfates, sulfites, and nitrates. After being discharged from the reaction tower, they enter the crushing unit to pulverize the red mud particles. Because the red mud particles discharged from the reaction tower have a low moisture content (less than 2%), a significant amount of dust is generated during the pulverization process. Therefore, the equipment must have good sealing properties, and comprehensive sealing or dust removal measures are essential. After several cycles, when the salt content in the red mud particles reaches 15%, 5-10% of the discharged amount is taken out for water washing to remove soluble salts produced during red mud desulfurization and denitrification, restoring the desulfurization and denitrification performance of the red mud. When the desulfurization and denitrification performance of the red mud is low, this portion of red mud is removed from the system and replenished with new red mud. The red mud after water washing and filtration has a high moisture content of approximately 40-60%, and needs to be dried and crushed before being pulverized together with other red mud. The pulverized new and old materials are then mixed again in a mixing device, while simultaneously increasing the moisture content of the red mud to between 15-20%. Based on the analysis of the desulfurization effect of the red mud, when the desulfurization effect is poor, quicklime can be added appropriately and thoroughly mixed with the red mud in the mixing device. The mixed red mud powder then enters a rotary drum granulator for granulation.

[0009] Some of the red mud enters the washing unit, where it is thoroughly stirred to form a red mud slurry. This slurry then undergoes a calcium sulfate precipitation reaction with quicklime. After liquid-solid separation, a solid red mud containing calcium sulfate and a solution primarily composed of sodium nitrate are generated. The red mud is then returned to the drying kiln for desulfurization and denitrification reactions. When the calcium sulfate content in the red mud is high, affecting the efficiency of the desulfurization and denitrification reactions, it is discharged from the system and replenished with new red mud. Because the sodium nitrate in the solution has high utilization value, it can be reused.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0011] After being discharged from the reaction tower, the desulfurized and denitrified red mud particles are crushed in a pulverizer, then mixed, humidified, and batched in a mixer. They are then granulated in a granulation unit. The granules are dried and sieved. Qualified particles are returned to the reaction tower for further desulfurization and denitrification, while unqualified particles are returned to the granulation unit for re-granulation. During the desulfurization and denitrification reaction, sulfur dioxide and nitrogen oxides in the flue gas react with alkaline components such as sodium and calcium in the red mud to form sulfates, sulfites, and nitrates. These sulfates, nitrates, and sulfites adhere to the surface of the red mud particles, clogging the micropores and preventing contact between sulfur dioxide and nitrogen oxides in the flue gas and the effective components in the red mud. This hinders the continued desulfurization and denitrification reaction, reducing the sulfur and nitrate capacities of the red mud. By crushing and re-granulating the particles, the un-sulfurized red mud is coated onto the particle surface, restoring the microporous environment of the red mud particles and allowing the red mud to be reused, thus increasing the sulfur and nitrate capacities per unit unit of red mud. Meanwhile, during the recycling of red mud, it is necessary to continuously replenish new red mud and remove some red mud with poor desulfurization and denitrification performance. Using red mud as a catalyst is inexpensive and cost-effective, and the reaction temperature is relatively low. The denitrification reaction can be carried out after flue gas dust removal, reducing the impact of dust on the denitrification reaction. The generated sulfates and nitrates can be recycled, resulting in lower energy consumption, a simpler structure, and the realization of solid waste resource reuse. Attached Figure Description

[0012] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0013] Figure 1 This is a schematic diagram of a system for manufacturing catalyst particles for dry desulfurization and denitrification using red mud.

[0014] In the picture:

[0015] 1-Reaction tower; 2-Pulverizing device; 3-Mixing device; 4-Granulation device; 5-Particle drying device; 6-Particle sieving device; 7-Washing device; 8-Filtration device. Detailed Implementation

[0016] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0017] The terminology used in one or more embodiments of this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the one or more embodiments of this specification. The singular forms “a,” “described,” and “the” as used in one or more embodiments of this specification and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used in one or more embodiments of this specification refers to and includes any or all possible combinations of one or more associated listed items.

[0018] It should be understood that although the terms first, second, etc., may be used to describe various information in one or more embodiments of this specification, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, first may also be referred to as second without departing from the scope of one or more embodiments of this specification, and similarly, second may also be referred to as first. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to a determination."

[0019] The present invention will now be described in further detail with reference to the accompanying drawings:

[0020] This invention relates to a granulation process for a red mud catalyst, which mainly includes processes such as crushing, mixing and humidifying, granulation, drying, and sieving of red mud raw materials. The red mud catalyst is mainly used in a dry desulfurization and denitrification integrated system for low-temperature flue gas.

[0021] Main process: After the desulfurized and denitrified red mud particles are discharged from reaction tower 1, they enter a pulverizer to crush the particles, then enter a mixer for mixing, humidification, and batching, and then enter granulation device 4 for granulation. The granulated particles are dried and sieved. Qualified particles are returned to reaction tower 1 to continue the desulfurization and denitrification reaction, while unqualified particles are returned to granulation device 4 for regranulation. During the desulfurization and denitrification reaction, sulfur dioxide and nitrogen oxides in the flue gas react with alkaline components such as sodium and calcium in the red mud to form corresponding sulfates, sulfites, and nitrates. Sulfates, nitrates, and sulfites adhere to the surface of the red mud particles, blocking the micropores of the red mud and preventing the contact between sulfur dioxide and nitrogen oxides in the flue gas and the effective components in the red mud, thus hindering the desulfurization and denitrification reaction and reducing the sulfur and nitrate capacities of the red mud. By crushing and regranulating the particles, the red mud without sulfate adhesion is coated on the particle surface, restoring the microporous environment of the red mud particle surface, allowing the red mud to be reused and increasing the sulfur and nitrate capacities per unit of red mud. Meanwhile, during the recycling of red mud, it is necessary to continuously replenish new red mud and remove some red mud with poor desulfurization and denitrification performance. Using red mud as a catalyst is inexpensive and cost-effective, and the reaction temperature is relatively low. The denitrification reaction can be carried out after flue gas dust removal, reducing the impact of dust on the denitrification reaction. The generated sulfates and nitrates can be recycled, resulting in lower energy consumption, a simpler structure, and the realization of solid waste resource reuse.

[0022] To better illustrate the technical effects of the present invention, the present invention provides the following specific embodiments to illustrate the above technical process:

[0023] Example 1: A method for manufacturing particles using red mud as a catalyst, which mainly includes:

[0024] Granular Crushing Unit 2: The desulfurization and denitrification saturated material discharged from reaction tower 1 is fed into crushing unit 2 via a feeding device. The particles are crushed to a size of less than 0.5 mm. After exiting crushing unit 2, the crushed material is sieved, and particles larger than 0.5 mm are returned to crushing unit 2. When replenishing new material, the new material is mixed with the old material, and the feed moisture content is controlled between 5-15%. Some of the washed material needs to be filtered. The red mud moisture content is between 40-60%, and it needs to be dried to reduce the moisture content to 30%. Then it is crushed into particles smaller than 5 cm and then fed into the crusher to be mixed and crushed with the raw materials.

[0025] Mixing and humidifying: The moisture content of the crushed red mud is too low and it is not suitable for drum granulation. The mixing device 3 sprays water to humidify it to 15-20%. At the same time, alkaline substances can be added in proportion to increase the sulfur capacity, such as adding 2-5% calcium hydroxide.

[0026] Rotary drum granulation: By adjusting the drum speed, feed rate, and water spray rate through the granulation device 4, the moisture content of the particles is controlled at 20-25%, the particle size is between 3-5mm, the pelleting rate is above 80%, and the compressive strength is above 10N.

[0027] Screening: Particles smaller than 3mm and larger than 5mm are returned to the inlet of the granulation device 4 for regranulation via the particle screening device 6.

[0028] Particle drying: The moisture content of the catalyst particles is reduced to 5-10% in the particle drying device 5 (drying kiln) using a hot air furnace. After drying, the catalyst particles are stored in the silo for later use.

[0029] Red mud serves as a catalyst for desulfurization and denitrification, and is the core working medium of this system. Red mud is a highly alkaline solid waste discharged during the alumina industrial production process. It is a fine-particle-size solid waste with a complex mineral composition, and its chemical composition is closely related to the alumina production process and the source of bauxite. Structurally, red mud is characterized by high water content and high porosity. Its small particle size and abundant pore structure result in a large specific surface area. Compositionally, red mud contains a large amount of active ingredients. Bayer process red mud has a high Fe2O3 content, and Fe2O3 is an iron-based material with excellent denitrification performance.

[0030] The red mud particles have a particle size of 3–5 mm, a specific surface area of ​​20–50 m² / g, and a moisture content of 5–10%. The applicable temperature for desulfurization and denitrification of red mud is between 80–150℃. After desulfurization and denitrification, the generated sulfates and nitrates adhere to the particle surface, clogging the micropores, covering the active ingredients, and reducing the utilization rate of the red mud. When the utilization rate decreases, the red mud particles are unloaded from reaction tower 1, crushed, and regranulated for reuse. This improves the pore blockage on the surface of the red mud particles and restores their desulfurization and denitrification performance. After multiple experiments, it was found that after more than ten reuses, the desulfurization and denitrification performance decreased significantly. However, after washing with water and drying and granulating, the desulfurization and denitrification performance of the red mud could be restored. Therefore, red mud can be reused multiple times for desulfurization and denitrification.

[0031] The red mud used in the desulfurization and denitrification reactor is a special catalyst that can promote the denitrification reaction and participate in the desulfurization reaction, achieving an ideal integrated desulfurization and denitrification mode. However, oxygen is required in the desulfurization and denitrification process. A higher sulfur-to-nitrate ratio in the flue gas results in better denitrification, but desulfurization performance declines more rapidly. Multiple experiments have shown that controlling the sulfur-to-nitrate molar ratio between 5 and 10 yields better desulfurization and denitrification efficiency. Furthermore, the moisture content in the flue gas has a significant impact on denitrification and denitrification; higher moisture content reduces denitrification efficiency while increasing desulfurization efficiency. When the moisture content in the flue gas exceeds 10%, it has a significant impact on denitrification.

[0032] Granulation device 4 adopts a rotary drum granulator, which has a wide applicable humidity range, high output, low energy consumption, and is easy to clean for sticky mineral materials.

[0033] The catalyst used in this invention is red mud particles. Red mud is a solid waste produced during the production of alumina from bauxite. Since 2017, my country has discharged as much as 100 million tons of red mud annually, with a total stockpile of more than 1.1 billion tons nationwide. Because it contains a lot of free alkali and heavy metals, it seeps into the ground through rainwater and pollutes water sources. Therefore, the high alkalinity and large output of red mud have caused serious land and environmental problems.

[0034] Red mud is named for its reddish-brown color due to the large amount of α-Fe2O3 it contains. However, the α-Fe2O3 content varies depending on the composition of bauxite in different regions of my country and the different processes used to produce alumina. As a result, the appearance color also varies. The α-Fe2O3 content of red mud in different regions of my country ranges from 7% to 40%. α-Fe2O3 has good denitrification activity, and the Al2O3 and TiO2 contained in red mud are common catalyst carrier materials. Therefore, red mud is highly alkaline, has a fine particle size, and a large specific surface area. It also contains valuable metal elements such as rare earth elements, so it has a good removal effect on acidic gases such as sulfur dioxide and nitrogen oxides in flue gas.

[0035] The flue gas treatment system in this embodiment has a simple structure, is easy to manufacture, is safe and reliable to use, and is easy to implement and promote. It can shorten the process and reduce investment costs, and has certain practical application prospects.

[0036] Figure 1 The diagram schematically illustrates a granulation system for flue gas treatment according to an embodiment of the present invention. In this embodiment, the flue gas treatment system mainly includes: a reaction tower 1, a crushing device 2, a mixing device 3, a granulation device 4, a particle drying device 5, a particle screening device 6, and a red mud washing device 7.

[0037] 1. Before the system is ready to start, a certain amount of red mud catalyst is delivered into reaction tower 1.

[0038] 2. After the induced draft fan is started, the flue gas enters the reaction tower 1 and is heated. At the same time, the desulfurization reaction begins. When the temperature reaches 80℃, the denitrification efficiency of the reactor increases. According to the concentration of sulfur dioxide and nitrogen oxides at the outlet, the amount of red mud catalyst entering and exiting the reaction tower 1 is adjusted to keep a certain amount of red mud filling in the reaction tower 1 constant.

[0039] 3. The failed red mud particles discharged from reaction tower 1 enter the crushing device 2 for crushing.

[0040] 4. The crushed red mud powder enters the mixing device 3, and water is added at the same time to moisten it to 15-20%.

[0041] 5. The moistened red mud powder enters the granulation device 4 for granulation.

[0042] 6. The prepared red mud granules are fed into the granule drying device 5 for drying, reducing the moisture content to 5-10%.

[0043] 7. After drying, the red mud particles are fed into the particle screening device 6 for screening. The qualified particles of 3-5mm are set aside for use, and the unqualified particles are crushed and re-granulated.

[0044] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions within the technical scope disclosed in the present invention should be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A manufacturing system of particles of a red mud dry desulfurization and denitrification catalyst, characterized by: It comprises a reaction tower (1), a crushing device (2), a mixing device (3), a granulating device (4), a granule drying device (5), a granule screening device (6), a water washing device (7) and a filtering device (8); The gas inlet of the reaction tower (1) is connected with the flue gas inlet; The reaction tower (1) is internally provided with red mud catalyst; The discharge outlet of the reaction tower (1) is divided into two routes, one of which is connected with the feeding inlet of the reaction tower (1) after passing through the crushing device (2), the mixing device (3), the granulating device (4), the granule drying device (5) and the granule screening device (6), and the other is connected with the feeding inlet of the water washing device (7); The discharge outlet of the water washing device (7) is connected with the crushing device (2) through the filtering device (8).

2. The red mud dry desulfurization and denitrification catalyst particle manufacturing system according to claim 1, characterized in that: The red mud catalyst in the reaction tower (1) has a particle size of 3-5 mm, a specific surface area of 20-50 m2 / g and a water content of 5-10%.

3. The red mud dry desulfurization and denitrification catalyst particle manufacturing system according to claim 2, characterized in that: The granule screening device (6) has a first discharge outlet and a second discharge outlet; The first and second screens are installed in the granule screening device (6) from top to bottom; The first discharge outlet is located between the first and second screens, and the second discharge outlet is located above the first screen and below the second screen; The first discharge outlet is connected with the feeding inlet of the reaction tower (1); The second discharge outlet is connected with the feeding inlet of the granulating device (4).

4. The red mud dry desulfurization and denitrification catalyst particle manufacturing system according to claim 3, characterized in that: The first screen of the granule screening device (6) has a screen hole diameter of 5 mm; The second screen of the granule screening device (6) has a screen hole diameter of 3 mm.

5. The red mud dry desulfurization and denitrification catalyst particle manufacturing system according to claim 4, characterized in that: The discharge outlet of the granule screening device (6) is connected with the feeding inlet of the reaction tower (1) through a bin.

6. A catalyst particle production method using the red mud dry desulfurization and denitrification catalyst particle production system according to any one of claims 1 to 5, characterized by, It comprises the following steps: The flue gas enters the reaction tower (1) and is subjected to denitrification and desulfurization under the action of the red mud particles; The failed red mud particles in the reaction tower (1) are sent to the crushing device (2) for crushing to obtain red mud powder; The red mud powder is sent to the mixing device (3) to be mixed and humidified with water to obtain humidified red mud powder; The humidified red mud powder is sent to the granulating device (4) for granulation to obtain prepared red mud particles; The prepared red mud particles are sent to the granule drying device (5) for drying to obtain dried red mud particles; The dried red mud particles are sent to the granule screening device (6) for screening, and the screened qualified red mud particles are sent to the reaction tower (1), and the screened unqualified red mud particles are sent to the crushing device (2) again.

7. The catalyst particle manufacturing method of the red mud dry desulfurization and denitrification catalyst particle manufacturing system according to claim 6, characterized in that: The red mud powder in the mixing device (3) is mixed and humidified with water to a humidity of 15-20%; The mixing device (3) further adds 2-5% of calcium hydroxide.

8. The catalyst particle manufacturing method of claim 7, wherein the particle drying device (5) reduces the moisture content to 5-10%.

9. The catalyst particle manufacturing method of claim 8, wherein the particle screening device (6) screens the qualified red mud particles to have a particle size of 3-5 mm. Further comprising the following steps: When the desulfurization and denitrification performance of the red mud particles in the reaction tower (1) decreases, 5-10% of the red mud particles discharged from the reaction tower (1) are sent to the water washing device (7) for water washing to obtain water-washed and filtered red mud particles; when the desulfurization and denitrification performance of the red mud is insufficient, the part of the red mud is excluded and new red mud is supplemented; 10. The catalyst particle manufacturing method according to claim 9, characterized by: The water-washed and filtered red mud particles are sent to the crushing device (2) for crushing together with the failed red mud particles. ​ ​

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