Flue gas treatment system and flue gas treatment method for low-temperature desulfurization and denitrification by using red mud as catalyst
By using red mud as a catalyst, the dry flue gas treatment system solves the problems of high operating costs and low efficiency of integrated desulfurization and denitrification equipment, achieves low-temperature and high-efficiency desulfurization and denitrification, reduces costs, and promotes the reuse of solid waste resources.
Patent Information
- Application Number
- CN202511139448.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-14
- Publication Date
- 2025-12-19
AI Technical Summary
In existing technologies, integrated desulfurization and denitrification equipment has high operating costs and low efficiency. Traditional methods are also energy-intensive and costly, making it difficult to widely apply in industrial flue gas treatment, especially in my country's power industry where its application is relatively limited.
Using red mud as a catalyst, a dry flue gas treatment system is used to oxidize sulfur dioxide to sulfur trioxide and nitric oxide to nitrogen dioxide by utilizing the red mud's redox properties. The generated sulfates and nitrates can be utilized as resources, reducing ammonia usage and lowering energy consumption.
It achieves efficient desulfurization and denitrification at low temperatures, reduces investment and operating costs, simplifies the process, promotes the reuse of solid waste resources, and the generated by-products can be recycled.
Smart Images
Figure CN121155342A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of flue gas purification technology, specifically relating to an integrated flue gas treatment system and method that utilizes a catalyst for desulfurization and denitrification. 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 substances is a pressing issue for my country, and the implementation of ultra-low emission standards for pollutants is also a problem that existing production enterprises must address.
[0003] 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
[0004] The purpose of this invention is to provide a flue gas treatment system that utilizes red mud as a catalyst for low-temperature desulfurization and denitrification. This system is simple in structure, easy to manufacture, safe and reliable in use, and convenient for implementation and widespread application. It can shorten the process, reduce investment costs, and has promising practical application prospects.
[0005] According to three main aspects of the present invention, a dry flue gas treatment system for desulfurization and denitrification is provided:
[0006] 1. The flue gas denitrification and desulfurization reaction unit mainly includes a red mud drying and grinding kiln and a bag filter reactor. The red mud drying and grinding kiln adopts a drum form, with its inlet and outlet connected to the flue. It utilizes the heat of the flue gas to dry the red mud, while simultaneously pulverizing the red mud inside the kiln. When the raw flue gas enters the drying and grinding kiln, the red mud dust formed during the drying process mixes with the flue gas. The sulfur dioxide and nitrogen oxides in the red mud are simultaneously adsorbed by the red mud, and under the catalytic action of the red mud dust, an oxidation-reduction reaction occurs, generating nitrogen dioxide and sulfur trioxide. At the same time, it reacts with the water adsorbed by the red mud dust to generate sulfites, sulfates, and nitrates. Meanwhile, the remaining sulfur dioxide in the flue gas is also absorbed by the catalyst to generate sulfites. The flue gas containing red mud dust enters the bag filter reactor through the outlet of the drying and grinding kiln, where it is adsorbed on the surface of the filter bags and continues to react with sulfur dioxide and nitrogen monoxide in the flue gas. After the surface of the red mud dust is saturated with adsorbed sulfates, sulfites, and nitrates, it is discharged into the washing tank through the dust collector.
[0007] 2. Sulfate Removal System: Sulfates, sulfites, and nitrates generated by red mud dust absorption are introduced into the washing tank along with the red mud. After thorough stirring, a red mud slurry is formed. Then, calcium sulfate is precipitated using quicklime slurry. Because the solution contains a certain amount of sulfite, oxygen is introduced to completely oxidize the sulfite. The mixture is then filtered. After liquid-solid separation, a solid red mud containing calcium sulfate and a solution mainly composed of sodium nitrate are generated. The red mud is returned to the drying and grinding 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.
[0008] 3. Calcium salt softening evaporation system: The solution is mainly composed of sodium nitrate, but contains a certain amount of calcium ions and the solution is highly alkaline, making it difficult to evaporate and crystallize. Carbon dioxide gas is introduced to react with the calcium ions in the solution, thereby removing the calcium ions, reducing the alkalinity of the solution, and increasing the solution temperature, ultimately generating a high-purity sodium nitrate solution for evaporation and crystallization.
[0009] Furthermore, the dust collector outlet is connected to the drying and grinding kiln inlet, the drying and grinding kiln outlet is connected to the bag filter reactor inlet, the bag filter reactor outlet is connected to the induced draft fan inlet, and the induced draft fan outlet is connected to the flue. The softening tower inlet is connected to the main flue gas duct via a carbon dioxide induced draft fan, and the softening tower flue gas outlet is connected to the main flue gas duct. Sulfur dioxide and nitrogen oxide analyzers, as well as temperature, pressure, and airflow meters, are installed on the inlet and outlet flues of the desulfurization and denitrification reaction unit.
[0010] Furthermore, the bottom outlet of the bag filter reactor is connected to the washing tower, the liquid outlet pump of the washing tower is connected to the inlet of the plate and frame filter, the outlet of the plate and frame filter is connected to the liquid inlet of the softening tower, and the discharge port of the plate and frame filter is connected to the feed port of the drying and grinding kiln.
[0011] Furthermore, the outlet of the softening tower's liquid outlet pump is connected to a filter, and the filter outlet is connected to an evaporation crystallization device.
[0012] As can be seen from the above technical solution, the catalyst used in this invention is red mud, which is a solid waste residue produced during the production of alumina from bauxite.
[0013] 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.
[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0015] After the raw flue gas passes through a dust collector to remove dust, it enters a drying and grinding kiln. Inside the kiln, the flue gas comes into full contact with the red mud, which has a high moisture content, drying the red mud. Then, it enters the grinding stage. The red mud dust reacts with nitric oxide and sulfur dioxide in the flue gas under the action of oxygen. Excess sulfur dioxide is also absorbed by the red mud, reacting with alkaline components such as sodium and calcium in the red mud to form corresponding sulfates, nitrates, and sulfites. The red mud dust, having adsorbed sulfates, nitrates, and sulfites, enters a bag filter reactor and is trapped on the surface of the filter bags, forming a reaction layer of red mud dust. This layer reacts with nitric oxide and sulfur dioxide in the flue gas. When the red mud adsorption reaction approaches saturation, the red mud powder is discharged into a washing tower 5 and thoroughly stirred. The washed slurry, after filtration, undergoes another desulfurization and denitrification reaction. The solution is then treated with oxidation, desalination, softening, and evaporation before being reused as a resource. This method mainly utilizes the characteristics of red mud to stimulate the reducing properties of sulfur dioxide and nitric oxide, oxidizing sulfur dioxide to sulfur trioxide and nitric oxide to nitrogen dioxide, thereby converting the difficult-to-remove nitric oxide in flue gas into nitrogen dioxide, which is then adsorbed by the catalyst and removed by desorption.
[0016] This invention primarily utilizes the characteristics of red mud to activate the reducing properties of sulfur dioxide and nitric oxide, oxidizing sulfur dioxide to sulfur trioxide and nitric oxide to nitrogen dioxide. This converts the difficult-to-remove nitric oxide in flue gas into nitrogen dioxide, which is then adsorbed by a catalyst and subsequently removed by desorption. Compared to traditional NH3-SCR ammonia injection denitrification, this denitrification reaction does not require ammonia as a reducing agent, uses red mud as a low-cost catalyst, significantly reducing costs. Furthermore, the reaction temperature is lower, and the denitrification reaction occurs after flue gas dust removal, minimizing the impact of dust on the reaction. The generated sulfates and nitrates can be recovered. Compared to traditional wet limestone desulfurization, it has lower energy consumption, a simpler structure, and enables the reuse of solid waste resources. Attached Figure Description
[0017] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.
[0018] Figure 1 This is a schematic diagram of a flue gas treatment system that uses red mud as a catalyst for low-temperature desulfurization and denitrification according to the present invention.
[0019] Figure 2 This is a schematic diagram of the structure of a drying and grinding kiln.
[0020] In the picture:
[0021] 1-Dust collector; 2-Drying and grinding kiln; 21-Drying section; 22-Grinding section; 23-Tilting plate; 3-Bag reactor; 4-Induced draft fan; 5-Scrubbing tower; 6-First plate and frame filter; 7-Softening tower; 8-Second plate and frame filter; 9-Nitrate evaporator. Detailed Implementation
[0022] 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.
[0023] 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.
[0024] 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."
[0025] The present invention will now be described in further detail with reference to the accompanying drawings:
[0026] The present invention discloses a flue gas treatment system for low-temperature desulfurization and denitrification using red mud as a catalyst, comprising a red mud drying and grinding kiln 2, a bag filter reactor 3, a scrubbing tower 5, a softening tower 7, a dust collector 1, a filter, an evaporator, etc.
[0027] The main process is as follows: After the raw flue gas passes through the dust collector 1 to remove dust, it enters the drying and grinding kiln 2. Inside the drying and grinding kiln 2, the flue gas comes into full contact with the red mud, which has a high moisture content. The red mud is dried and then enters the grinding stage. The red mud dust reacts with nitric oxide and sulfur dioxide in the flue gas under the action of oxygen. Excess sulfur dioxide is also absorbed by the red mud and reacts with alkaline components such as sodium and calcium in the red mud to form corresponding sulfates, nitrates, and sulfites. The red mud dust that has adsorbed sulfates, nitrates, and sulfites enters the bag filter reactor 3 and is trapped on the surface of the filter bag, forming a reaction layer of red mud dust. The red mud reacts with nitric oxide and sulfur dioxide in the flue gas. When the red mud adsorption reaction is close to saturation, the red mud powder is unloaded into the washing tower 5 and thoroughly stirred. The washed slurry, after being filtered, undergoes a desulfurization and denitrification reaction again. The solution is then treated by oxidation, desalination, softening, and evaporation before being reused as a resource. This method mainly utilizes the characteristics of red mud to stimulate the reducing properties of sulfur dioxide and nitric oxide, oxidizing sulfur dioxide to sulfur trioxide and nitric oxide to nitrogen dioxide, thereby converting the difficult-to-remove nitric oxide in flue gas into nitrogen dioxide, which is then adsorbed by the catalyst and removed by desorption.
[0028] Compared with traditional NH3-SCR ammonia injection denitrification, this invention's denitrification reaction does not require ammonia as a reducing agent, and uses red mud as a catalyst, which is less expensive, resulting in significant cost savings. Furthermore, the reaction temperature is lower, and the denitrification reaction is carried out after flue gas dust removal, reducing the impact of dust on the denitrification reaction. The generated sulfates and nitrates can be recycled. Compared with traditional wet limestone desulfurization, it has lower energy consumption, a simpler structure, and enables the reuse of solid waste resources.
[0029] The main reaction equation in the drying and grinding kiln 2, inside the bag filter, is as follows:
[0030] NO + SO₂ + O₂ → NO₂ + SO₃
[0031] 2SO2 + 2H2O + O2 → 2H2SO4
[0032] 4NO + 3O₂ + 2H₂O → 4HNO₃
[0033] The main reaction equations within scrubbing tower 5 are as follows:
[0034] Ca(OH)₂ + Na₂SO₃ → CaSO₃ + 2NaOH
[0035] Ca(OH)₂ + Na₂SO₄ → CaSO₄ + 2NaOH
[0036] The main reaction equations in softening tower 7
[0037] Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
[0038] To better illustrate the technical effects of the present invention, the present invention provides the following specific embodiments to illustrate the above technical process:
[0039] Example 1: A flue gas treatment system using red mud as a catalyst for low-temperature desulfurization and denitrification, which mainly includes:
[0040] Red mud drying and grinding kiln 2: It adopts a drum form and puts red mud inside as raw material. After the raw flue gas enters the drying kiln, the red mud dust formed during the drying process mixes with the flue gas. The sulfur dioxide and nitrogen oxides in the flue gas are simultaneously adsorbed by the red mud. Under the catalytic action of the red mud dust, an oxidation-reduction reaction occurs to generate nitrogen dioxide and sulfur trioxide. At the same time, it reacts with the water adsorbed by the red mud dust to generate sulfite, sulfate and nitrate. Meanwhile, the remaining sulfur dioxide in the flue gas is also absorbed by the catalyst to generate sulfite.
[0041] Baghouse dust collector reactor: A baghouse reactor 3 is used. Red mud dust enters the baghouse reactor 3 from the drying kiln with the flue gas and is adsorbed on the surface of the bag. It continues to react with sulfur dioxide and nitric oxide in the flue gas. After the surface of the red mud dust is saturated with sulfate, sulfite and nitrate, it is discharged to the washing tower 5 through the dust collector.
[0042] The sulfate removal system employs washing tower 5. Sulfates, sulfites, and nitrates generated from red mud dust absorption enter washing tower 5 along with the red mud. After thorough stirring, a red mud slurry is formed. This slurry then undergoes a calcium sulfate precipitation reaction with quicklime. Since the solution contains a certain amount of sulfite, oxygen is introduced to completely oxidize the sulfite. The solution is then filtered. After liquid-solid separation, a solid red mud containing calcium sulfate and a solution primarily composed of sodium nitrate are produced. Sodium nitrate has high utilization value and can be reused.
[0043] Calcium salt softening evaporation system: Softening tower 7 is used. The solution, which is mainly composed of sodium nitrate, contains a certain amount of calcium ions and is highly alkaline, making it difficult to evaporate and crystallize. Carbon dioxide gas is introduced to react with the calcium ions in the solution, thereby removing the calcium ions, reducing the alkalinity of the solution, and increasing the solution temperature. Finally, a high-purity sodium nitrate solution is generated for evaporation and crystallization.
[0044] Dust collector 1: Removes the vast majority of dust from the flue gas, reducing the amount of dust entering the drying kiln, thus not affecting the desulfurization and denitrification efficiency of the red mud.
[0045] The red mud drying and grinding kiln 2 is filled with sufficient red mud as a catalyst, and red mud is the core working medium of this flue gas treatment system. Red mud is a strongly alkaline solid waste emitted during the alumina industrial production process. It is a solid waste with fine particle size and complex mineral composition, and its chemical composition is closely related to the alumina production process and the source of bauxite. Structurally, red mud has the characteristics of high water content and high porosity. The red mud particles are small and have a rich pore structure, which gives red mud a large specific surface area. In terms of composition, red mud contains a large number of active ingredients. Bayer process red mud has a high Fe2O3 content, and Fe2O3 is an iron-based material with good denitrification performance.
[0046] Red mud has a particle size between 1 and 100 micrometers, a specific surface area of 20 to 50 m² / g, and a moisture content between 20 and 50%. The applicable temperature for desulfurization and denitrification of red mud is between 80 and 150℃. After desulfurization and denitrification, the generated sulfates and nitrates adhere to the particle surface, clogging the pores, covering the active ingredients in the red mud, and reducing its utilization rate. When the desulfurization and denitrification utilization rate decreases, the red mud particles are unloaded into a cloth bag 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 proven that after red mud was reused more than ten times, its 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.
[0047] The red mud used in the denitrification reactor is a special catalyst that can promote the denitrification reaction and participate in the desulfurization reaction. Oxygen is required in both the desulfurization and denitrification processes. 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 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 desulfurization; higher moisture content decreases denitrification efficiency while increasing desulfurization efficiency. When the moisture content in the flue gas exceeds 10%, it has a significant impact on denitrification.
[0048] Drying and grinding kiln 2 adopts a drum form, such as Figure 2As shown, the kiln is divided into a drying section 21 and a grinding section 22. The flue gas and red mud move in opposite directions. The red mud enters the drying section 21 from the kiln tail via a spiral. In the drying section 21, the red mud rotates with the kiln body and is continuously stirred and tumbled by the turning plates 23 on the kiln wall. The red mud is continuously broken into powder, fully reacting with the flue gas and being carried out of the kiln. Some lumpy red mud enters the grinding section 22 through the intermediate partition. Grinding is done using a ball mill, and the partition is porous, allowing the lumpy red mud to enter the grinding section 22. In the grinding section 22, the red mud is completely pulverized, fully contacting the high-temperature flue gas and being carried out of the grinding section 22. Some hard impurities in the red mud are discharged from the kiln through the porous partition at the kiln head. The kiln should meet the following basic requirements: the flue gas velocity inside the kiln should be high enough to ensure that larger dust particles can be carried out of the kiln, generally controlled between 15 and 20 m / s, while the flue gas temperature at the kiln tail should be between 100 and 120℃.
[0049] The bag filter reactor 3, used for desulfurization and denitrification, consists of several units. To minimize the impact of bag backflushing on the desulfurization and denitrification process, the number of units is greater than 10. Each unit contains several filter bags, and the inlet and outlet of each unit can be isolated for mutual isolation during filter bag maintenance. The bag filter reactor 3 is equipped with a large bypass, which is opened during system startup and closed when the system temperature rises.
[0050] The filter bags are made of polyester or polypropylene fibers, resistant to acid and alkali corrosion, and heat-resistant up to 130℃. They also possess low water absorption and high air permeability. Long filter bags with a diameter of 200–300 mm and a length of 5–8 m are used to reduce the volume of the bag filter reactor 3, while ensuring a filter air velocity of 0.5–1 m / min to ensure that the red mud particles on the filter bag surface fully react with nitrogen monoxide and sulfur dioxide in the flue gas. The reactor consists of several units, each with a pneumatic valve installed at the inlet and outlet to control the pressure difference between each unit between 2–3 kPa. When the pressure difference between the filter bags is high, the filter bag blowing pressure and frequency are increased.
[0051] The washing and desalination unit mainly includes a washing tower 5, a dewatering machine, a circulating pump, an outlet pump, a water seal tank, and a mixer. The red mud catalyst, which has been repeatedly recycled and is nearing its exhaustion in the reaction tower, is conveyed to the washing tower 5. The washing tower 5 is filled with industrial water. Under the action of the mixer in the washing tank, the red mud particles are thoroughly stirred to become a red mud slurry. Simultaneously, sulfates, sulfites, nitrates, and other products generated within the red mud particles are dissolved in the washing liquid. Then, the red mud is separated from the solution by the dewatering machine. The separated red mud is then dried again, granulated, and reused for desulfurization and denitrification.
[0052] The solution in scrubbing tower 5 is oxidized, converting some sulfites into sulfates. To improve oxidation efficiency and reduce tower size, oxygen is introduced into scrubbing tower 5 and maintained at a high pressure to enhance oxidation efficiency. The oxygen concentration inside the tower is kept above 50%, which also promotes the oxidation of sulfites. Simultaneously, a water seal is used to control the pressure inside the tower between 3-5 kPa, further facilitating the oxidation reaction. Scrubbing tower 5 employs a gas-liquid countercurrent contact method, ensuring sufficient contact and reaction between the introduced oxygen and the sprayed slurry to oxidize all sulfites into sulfates. Simultaneously, quicklime slurry is introduced to fully react with sulfate and magnesium ions in the solution, generating solid precipitates such as gypsum and magnesium hydroxide. The pH of the solution in scrubbing tower 5 is controlled between 9-10. The solution is then filtered to remove the gypsum and magnesium hydroxide precipitates, thereby removing sulfates and magnesium and aluminum compounds, leaving sodium, calcium, and nitrates as the main components.
[0053] The calcium salt softening evaporation system includes the softening tower 7, a spray layer, a demister layer, a carbon dioxide induced draft fan 4, a dust collector, a circulating pump, a discharge pump, a filter, and an evaporator. The slurry in the washing tower 5 passes through the filter and then enters the softening tower 7. The carbon dioxide induced draft fan 4 introduces clean flue gas into the tower, allowing the calcium in the solution to fully react with the carbon dioxide in the clean flue gas. After the reaction is complete, the clean flue gas returns to the main flue and is discharged. The pH of the solution in the softening tower 7 is controlled between 8 and 9 to ensure that all calcium ions in the solution are converted into calcium carbonate precipitate, which is then removed from the solution through the filter. After softening, the solution mainly contains sodium nitrate and a small amount of potassium nitrate. Simultaneously, as the clean flue gas passes through the softening tower 7, the temperature of the solution inside the tower 7 is raised to 80-90℃, causing a large amount of water to evaporate. When the sodium nitrate concentration in the solution reaches 10%, it enters the evaporator for evaporation and crystallization, ultimately extracting the sodium nitrate for resource recovery and utilization.
[0054] The dust concentration at the outlet of the electrostatic precipitator is 20 mg / m³. 3 The following steps ensure that a large amount of dust does not adhere to the catalyst surface, thus affecting the normal use of the catalyst.
[0055] 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.
[0056] Figure 1 The diagram schematically illustrates a flue gas treatment system according to an embodiment of the present invention. In this embodiment, the process of using a flue gas treatment system employing red mud as a catalyst for low-temperature desulfurization and denitrification includes the following steps:
[0057] 1. Before the system is ready to start, a certain amount of red mud catalyst is delivered to the drying and grinding kiln 2, and water of appropriate level is injected into the washing tower 5. The circulation pump is then started to circulate.
[0058] 2. After starting the induced draft fan 4, the flue gas is discharged through the bypass of the bag filter reactor 3. When the flue gas temperature is normal and the electrostatic precipitator is put into normal operation, the flue gas is introduced into the bag filter reactor 3. After the bag filter temperature rises to normal, the drying and grinding kiln 2 is started. According to the concentration of sulfur dioxide and nitrogen oxides at the outlet, the amount of red mud catalyst entering the drying and grinding kiln 2 is adjusted to keep a certain filling amount in the drying and grinding kiln 2 constant.
[0059] 3. The bag filter reactor 3 removes the degraded red mud dust from the filter bag through a pulse jet, and then the dust enters the scrubbing tower 5 through a star valve.
[0060] 4. Red mud particles are fed into washing tower 5 and thoroughly stirred into red mud slurry by a mixer. Sulfates, sulfites, nitrates and other products in the red mud dissolve in the slurry. Quicklime water is introduced to control the pH of the solution in washing tower 5 between 9 and 10. When the solid content of the slurry is high, the effluent pump is started to send the slurry to the first plate and frame filter 6. The filtrate is returned to washing tower 5. When the solid alkalinity is high and the calcium sulfate content is low, it is recycled for regranulation.
[0061] 5. When the nitrate concentration in the solution in the washing tower 5 is high, reaching 1-5%, it is sent to the softening tower 7 through the outlet pump. The circulation pump of the softening tower 7 is started for circulation. Then, the carbon dioxide induced draft fan 4 is started to deliver carbon dioxide into the softening tower 7, controlling the pH of the slurry at 8-9 to ensure that the calcium ions in the solution react fully with the carbon dioxide. When there is solid content in the solution, the discharge pump is started to send the slurry to the first plate and frame filter 6 for liquid-solid separation. The filtrate is returned to the softening tower 7, and the calcium carbonate solid is sent to the granulation area for recycling.
[0062] 6. When the nitrate concentration in the slurry is high (30%), the filtrate from the second plate and frame filter 8 is fed into the nitrate evaporator 9 for crystallization and evaporation. The main component after evaporation is sodium nitrate, which can be used as fertilizer. The water is returned to the washing tower 5 for reuse.
[0063] 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 flue gas treatment system using red mud as a catalyst for low-temperature desulfurization and denitrification, characterized in that: It includes a dust collector (1), a drying and grinding kiln (2), a bag filter reactor (3), an induced draft fan (4), a scrubbing tower (5), a first plate and frame filter (6), and a softening tower (7); The outlet of the dust collector (1) is connected to the flue gas inlet of the drying and grinding kiln (2); The drying and grinding kiln (2) is equipped with a red mud catalyst. The dust outlet of the drying and grinding kiln (2) is connected to the air inlet of the bag filter reactor (3); The outlet of the baghouse reactor (3) is connected to the inlet of the softening tower (7) via an induced draft fan (4); The outlet at the bottom of the bag filter reactor (3) is connected to the inlet of the washing tower (5); The discharge port of the washing tower (5) is connected to the inlet of the first plate and frame filter (6); The filtrate outlet of the first plate and frame filter (6) is connected to the liquid inlet of the softening tower (7); The discharge port of the first plate and frame filter (6) is connected to the red mud inlet of the drying and grinding kiln (2).
2. The flue gas treatment system using red mud as a catalyst for low-temperature desulfurization and denitrification according to claim 1, characterized in that: It also includes a second plate and frame filter (8) and a nitrate evaporator (9); The outlet of the softening tower (7) is connected to the inlet of the second plate and frame filter (8); The filtrate outlet of the second plate and frame filter (8) is connected to the nitrate evaporator (9).
3. The flue gas treatment system using red mud as a catalyst for low-temperature desulfurization and denitrification according to claim 2, characterized in that: The drying and grinding kiln (2) is in the form of a drum; The red mud catalyst in the drying and grinding kiln (2) has a red mud particle size between 1 and 100 micrometers, a specific surface area of 20 to 50 m² / g, and a water content between 20 and 50%.
4. The flue gas treatment system for low-temperature desulfurization and denitrification using red mud as a catalyst according to claim 3, characterized in that: The drying and grinding kiln (2) includes a drying section (21) and a grinding section (22); A porous partition is provided between the drying section (21) and the grinding section (22); A ball mill is installed in the grinding section (22).
5. The flue gas treatment system using red mud as a catalyst for low-temperature desulfurization and denitrification according to claim 4, characterized in that: The inner wall of the drying and grinding kiln (2) is equipped with a material-turning plate (23).
6. The flue gas treatment system for low-temperature desulfurization and denitrification using red mud as a catalyst according to claim 5, characterized in that: The outlet of the baghouse reactor (3) is connected to the chimney via the main flue gas duct through the induced draft fan (4); The flue gas outlet of the softening tower (7) is connected to the main flue gas duct; The main flue gas duct at the outlet of the baghouse reactor (3) is equipped with a sulfur dioxide analyzer and a nitrogen oxide analyzer, as well as a thermometer, a pressure gauge and an air volume meter.
7. The flue gas treatment system for low-temperature desulfurization and denitrification using red mud as a catalyst according to claim 6, characterized in that: The bag reactor (3) consists of several units, each of which contains several bags, and the inlet and outlet of each unit are isolated separately. The bag reactor (3) is made of polyester or polypropylene fiber bag; The diameter of the bag reactor (3) is 200-300 mm and the length is 5-8 m.
8. A flue gas treatment method for a flue gas treatment system using red mud as a catalyst for low-temperature desulfurization and denitrification, wherein the flue gas treatment system is the flue gas treatment system for low-temperature desulfurization and denitrification using red mud as a catalyst as described in any one of claims 1-7, characterized in that... Includes the following steps: After the flue gas passes through the dust collector (1) to remove the dust, it enters the drying and grinding kiln (2). The flue gas in the drying and grinding kiln (2) undergoes denitrification and desulfurization under the action of red mud, while the red mud is ground into red mud dust. Red mud dust in the drying and grinding kiln (2) and flue gas after denitrification and desulfurization enter the bag filter reactor (3) together. The red mud dust is trapped on the surface of the bag to form a reaction layer of red mud dust, which continues to react with the flue gas after denitrification and desulfurization. When the reaction layer of red mud dust is saturated, the red mud dust is sent into the washing tower (5) and mixed with quicklime water to form red mud slurry; When the nitrate in the red mud slurry in the washing tower (5) reaches the first threshold, the red mud slurry is filtered through the first plate and frame filter (6), the filtrate is sent to the softening tower (7) to react with carbon dioxide, and the filter residue is sent to the drying and grinding kiln (2) for granulation. The slurry after reaction in the softening tower (7) is sent to the second plate and frame filter (8) for liquid-solid separation. The filtrate is returned to the softening tower (7), and the filter residue is recycled for granulation. When the nitrate in the slurry after reaction in the softening tower (7) reaches the second threshold, the filtrate from the second plate and frame filter (8) is sent to the nitrate evaporator (9) for crystallization evaporation.
9. The flue gas treatment method of the flue gas treatment system using red mud as a catalyst for low-temperature desulfurization and denitrification according to claim 8, characterized in that: The first threshold is a nitrate concentration of 1-5%; The second threshold is a nitrate concentration greater than 30%.
10. The flue gas treatment method of the flue gas treatment system using red mud as a catalyst for low-temperature desulfurization and denitrification according to claim 9, characterized in that: After the reaction in the baghouse reactor (3), part of the flue gas is discharged from the chimney, and the other part is transported to the softening tower (8) as carbon dioxide.