Flue gas treatment method of alumina thermoelectric system

Abstract

The invention provides a flue gas treatment method for an aluminum oxide thermoelectric system, and aims to solve the technical problems that a cloth belt dust collector needs to be cleaned regularly, and the service life of the cloth belt dust collector is seriously influenced by high-temperature flue gas. The treatment method comprises the following steps: S10, waste heat recovery: enabling flue gas to flow through a heat exchange pipe; s20, pre-dedusting is carried out; s30, cooling, and spraying slurry into the flue gas; s40, performing desulfurization, and doping AlO into the slurry obtained in the step S30; s50, denitration is conducted, specifically, an SCR denitration catalyst is selected to conduct denitration treatment on the flue gas; s60, adsorbing and removing dust, namely weaving polyacrylonitrile-based activated carbon fibers into a three-dimensional net-shaped filter layer, and removing dust from the flue gas; and S70, performing feedback control. Firstly, flue gas is cooled through waste heat recovery, then primary dust removal is conducted on the flue gas in a multi-stage centrifugal mode, and then the purpose of dust removal is achieved in an adsorption mode after cooling, desulfurization and denitrification.

Description

Technical Field

[0001] The present invention relates to the technical field of flue gas treatment, and in particular to a flue gas treatment method for an alumina thermoelectric system. Background Art

[0002] The thermal power system (such as coal-fired or gas-fired boiler) in the alumina production process will produce a large amount of flue gas, and its treatment technology needs to comprehensively consider sulfur oxides (SO2) and nitrogen oxides (NO x ) Coordinated control of multiple pollutants such as particulate matter (PM), heavy metals (such as mercury) and carbon dioxide (CO2).

[0003] Currently, most methods of treating particulate matter in flue gas use cloth belt dust collectors, which filter the particulate matter in the flue gas through the air permeability and smaller pore size of the cloth belt.

[0004] As far as the current treatment method is concerned, the bag dust collector needs to be cleaned from time to time. At the same time, the high temperature flue gas will seriously affect the service life of the belt dust collector. Summary of the Invention

[0005] In view of the technical problems that the cloth belt dust collector is needed to be cleaned regularly and the high temperature of the flue gas seriously affects the service life of the cloth belt dust collector in the prior art for collecting particulate matter in the flue gas, the present invention provides a flue gas treatment method for an alumina thermoelectric system. First, the flue gas is cooled by recovering waste heat, and then the flue gas is preliminarily removed from the dust by multi-stage centrifugation. After cooling, desulfurization and denitrification, adsorption is used to achieve the purpose of dust removal.

[0006] The technical solution of the present invention is:

[0007] A flue gas treatment method for an alumina thermoelectric system comprises the following steps:

[0008] S10, waste heat recovery, allowing the flue gas to flow through the heat exchange tubes and exchange heat with the medium in the heat exchange tubes;

[0009] S20, pre-dust removal, preliminary dust removal of flue gas through multi-stage centrifugal method;

[0010] S30, cooling the flue gas by spraying Ca(OH)2 slurry into the flue gas, so that the flue gas forms a temperature gradient layer in the spraying area of ​​the Ca(OH)2 slurry;

[0011] S40, desulfurization, adding Al2O3 to the Ca(OH)2 slurry in step S30 as a catalyst for SO2 adsorption and oxidation reaction;

[0012] S50, denitrification, selecting an SCR denitrification catalyst mixed with CeO2-MnO2 to denitrify the flue gas;

[0013] S60, adsorption dust removal, uses polyacrylonitrile-based activated carbon fibers woven into a three-dimensional mesh filter layer to remove dust from flue gas;

[0014] S70, feedback control, deploys high-temperature infrared spectrometer and beta-ray dust meter to analyze the components in the flue gas and determine whether the flue gas meets the emission standards.

[0015] Optionally, in step S10, the heat exchange tube is a spiral structure, and the material of the heat exchange tube is silicon carbide;

[0016] The temperature of the flue gas passing through the heat exchange tube is measured to reduce the temperature to below 300°C.

[0017] Optionally, in step S20, the multi-stage centrifugation method includes:

[0018] S21, primary separation, the flue gas is fed into the cyclone at a speed of 35m / s along the tangential direction to separate particles with a size greater than 50μm;

[0019] S22, secondary separation, the guide vanes set in the middle of the cyclone accelerate the flow rate of the flue gas to 50m / s, and separate particles with a particle size of less than 50μm;

[0020] S23, dust collection, collects and processes the dust at the bottom of the cyclone.

[0021] Optionally, a nitrogen backflushing system is provided at the bottom of the cyclone, and the bottom of the cyclone is backflushed once at a pressure of 0.6 MPa at regular intervals.

[0022] Optionally, step S30 specifically includes:

[0023] S31, bringing the flue gas into contact with the atomized Ca(OH)2 slurry to reduce the flue gas temperature to 200°C;

[0024] S32. A layer of air wall is distributed around the atomization area of ​​the Ca(OH)2 slurry, and a temperature gradient layer is generated in the flue gas.

[0025] Optionally, in step S31, the concentration of the Ca(OH)2 slurry is 15%, and the particle size is less than or equal to 10 μm;

[0026] In step S32, compressed air at 0.4 MPa is used to form an air wall.

[0027] Optionally, in step S40, 5% γ-Al2O3 is added to the Ca(OH)2 slurry, with a specific surface area of ​​>200 m2 / g.

[0028] Optionally, in step S50, the SCR denitration catalyst uses TiO2 as a carrier, loads a VW-Ti oxide system, and is doped with 5% CeO2-MnO2, and reacts with the flue gas in a temperature range of 180°C-250°C.

[0029] Optionally, in step S60, the diameter of the polyacrylonitrile-based activated carbon fiber is less than or equal to 8 μm, and the specific surface area is 1,200 m² / g.

[0030] Optionally, in step S70, if the flue gas meets any of the following conditions, the process returns to step S20:

[0031] Condition 1: The concentration of particulate matter is greater than 5mg / Nm³;

[0032] Condition 2: Sulfur oxide concentration is greater than 30mg / Nm³;

[0033] Condition 3: Nitrogen oxide concentration is greater than 40mg / Nm³.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] First, the flue gas passes through heat exchange tubes to recover the heat in the flue gas. The medium in the heat exchange tubes is used to transport the heat to the heat demand location within the plant, achieving energy recovery. A multi-stage centrifugal method is then used to initially remove particulate matter from the flue gas. Further cooling is achieved by spraying Ca(OH)2 slurry, and by adding Al2O3 to the Ca(OH)2 slurry, sulfur oxides in the flue gas are catalyzed to form nitrogen. The flue gas is then denitrified using an SCR denitrification catalyst, and activated carbon is used to adsorb the remaining particulate matter in the flue gas. Finally, the flue gas is tested to ensure it meets emission standards before being discharged.

[0036] Through this technical solution, the flue gas can be effectively cooled, dusted, desulfurized and denitrified, so that the flue gas meets the emission requirements and avoids the use of a cloth belt dust collector. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0038] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0039] Hereinafter, only certain exemplary embodiments are briefly described. As will be appreciated by those skilled in the art, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and description are to be considered as illustrative in nature and not restrictive.

[0040] The disclosure below provides many different embodiments or examples for realizing different structures of the present invention. In order to simplify the disclosure of the present invention, the components and settings of specific examples are described below. Of course, they are merely examples and are not intended to limit the present invention. In addition, the present invention may repeat reference numbers and / or reference letters in different examples. Such repetition is for the purpose of simplicity and clarity and does not in itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides examples of various specific processes and materials, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0041] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0042] Example:

[0043] See also Figure 1 This embodiment discloses a flue gas treatment method for an alumina thermoelectric system, which specifically includes the following steps:

[0044] S10, waste heat recovery, allowing the flue gas to flow through the heat exchange tubes and exchange heat with the medium in the heat exchange tubes;

[0045] The heat exchange tube has a spiral structure and is arranged in a flue gas pipeline. The heat exchange tube is made of silicon carbide, which has the advantages of high temperature resistance (>600°C) and high thermal conductivity (>120 W / m·K).

[0046] In step S10, the temperature of the flue gas in contact with the heat exchange tube is controlled at 400°C ± 10°C, and the temperature of the flue gas passing through the heat exchange tube is measured to ensure that the temperature of the flue gas drops below 300°C (generally controlled at 280°C ± 10°C) after passing through the heat exchange tube.

[0047] In step S10, the heat recovered from the medium in the heat exchange tube can also be used for heating in the factory or driving an absorption refrigeration unit, thereby realizing energy recovery and utilization.

[0048] In addition, an ultrasonic vibrator can be installed on the outer wall of the heat exchange tube, working at a frequency of 20kHz and a power of 500W / m² to prevent dust accumulation on the heat exchange tube.

[0049] S20, pre-dust removal, involves preliminary dust removal from the flue gas through a multi-stage centrifugal process. The primary equipment used is a cyclone, which consists of a cylindrical outer tube, a central tube located in the middle of the outer tube's top, and spiral guide vanes within the central tube. The inner wall of the cyclone can also be coated with a silicon carbide composite material to enhance its high-temperature and corrosion resistance.

[0050] Specifically, in step S20, the multi-stage centrifugation method includes:

[0051] S21, primary separation, the flue gas is fed into the cyclone at a speed of 35m / s along the tangential direction to separate particles with a size greater than 50μm;

[0052] Among them, a cyclone with a diameter of 2.5 meters is used. The flue gas enters the cyclone along the horizontal tangent from the top of the side wall of the cyclone, forming a spiral downward external vortex. At this time, particles in the flue gas with a particle size greater than 50μm move toward the wall of the cyclone due to the density difference under the action of centrifugal force, and finally slide into the ash hopper at the bottom of the cyclone. The flue gas after preliminary dust removal forms an internal vortex in the opposite direction and is discharged from the top of the cyclone.

[0053] In step S21 , the removal rate of particles with a diameter greater than 50 μm can reach more than 85%.

[0054] S22, secondary separation, accelerates the flow rate of the flue gas through the guide vanes set in the middle of the cyclone, so that the flow rate of the flue gas reaches 50m / s, and particles with a particle size of less than 50μm are separated.

[0055] Since the flue gas after preliminary dust removal is discharged from the top of the cyclone, a spiral guide blade is set in the middle of the cyclone. The inclination angle of the spiral guide blade is 45°, which further accelerates the flue gas, enhances the centrifugal force of the flue gas, and separates the particles that are not separated in step S21.

[0056] In step S22, the removal rate of particles with a diameter greater than 50 μm can reach more than 94%, the removal rate of particles with a diameter between 10 μm and 50 μm can reach more than 65%, and the concentration of particles with a diameter less than 10 μm can be significantly reduced.

[0057] S23, dust collection, collects and processes the dust at the bottom of the cyclone.

[0058] A nitrogen backflush system is installed on the ash hopper at the bottom of the cyclone. The bottom of the cyclone is backflushed at a pressure of 0.6 MPa at regular intervals (e.g. 30 minutes) to avoid an increase in the pressure drop of the flue gas in the cyclone due to dust accumulation, thereby reducing energy consumption.

[0059] In addition, referring to step S10 , an ultrasonic vibrator may be provided on the inner wall of the cyclone to avoid dust accumulation on the inner wall of the cyclone.

[0060] S30: Cooling the flue gas by spraying Ca(OH)2 slurry into the flue gas, so that a temperature gradient layer is formed in the flue gas within the spraying area of ​​the Ca(OH)2 slurry. This step is performed in a reaction tower, the top of which is provided with a flue gas inlet, an atomizing nozzle, and an annular nozzle array, with the flue gas inlet located in the middle of the annular nozzle array.

[0061] Specifically, step S30 includes:

[0062] S31. Flue gas is introduced into the reaction tower through the flue gas inlet, and a mist of Ca(OH)2 slurry is sprayed into the reaction tower through an atomizing nozzle, so that the Ca(OH)2 slurry contacts the flue gas. The atomized Ca(OH)2 slurry droplets absorb heat during evaporation, thereby reducing the flue gas temperature to 200° C. The concentration of the Ca(OH)2 slurry is 15%, and the particle size is less than or equal to 10 μm.

[0063] In step S31, the Ca(OH)2 slurry is atomized and mixed with the high-temperature flue gas, and a chemical reaction occurs simultaneously:

[0064]

[0065] In step S31, preliminary desulfurization and cooling are performed, and the calcium-sulfur ratio is reduced to 1.05-1.1.

[0066] S32. Compressed air at 0.4 MPa is sprayed around the atomization area of ​​the Ca(OH)2 slurry through an annular nozzle array to form an air wall. Flue gas is sprayed into the flue gas at a speed of 50 m / s-60 m / s in the vertical direction, and a temperature gradient layer is generated in the flue gas (the inner high-temperature core area is 200°C and the outer low-temperature edge area is 180°C).

[0067] An annular nozzle array sprays air at a 45° angle toward the inner wall of the reactor, creating a counter-pressure gradient with the main flue gas stream and inducing vortex mixing. The kinetic energy of the compressed air is converted into thermal energy, which is then blocked by an air barrier to prevent the high-temperature flue gas from directly contacting the equipment wall, thereby preventing localized overheating and condensation.

[0068] In addition, controlling the temperature difference in the reaction tower within ±5°C can also avoid the formation of low-temperature by-products such as ammonium bisulfate.

[0069] S40, desulfurization, adding Al2O3 to the Ca(OH)2 slurry in step S30 as a catalyst for adsorption of SO2 and oxidation reaction.

[0070] In step S40, 5% γ-Al2O3 with a specific surface area of ​​>200 m2 / g is added to the Ca(OH)2 slurry. The reaction mechanism is:

[0071]

[0072] S50, denitrification, selecting an SCR denitrification catalyst mixed with CeO2-MnO2 to denitrify the flue gas;

[0073] In step S50, the SCR denitration catalyst uses TiO2 as a carrier, loads a VW-Ti oxide system, and is doped with 5% CeO2-MnO2, and reacts with the flue gas in a temperature range of 180°C-250°C.

[0074] The specific formula of the SCR denitrification catalyst is TiO2 (80-90 wt%), WO3 (5-10 wt%), V2O5 (1-3wt%), CeO2 (5-10wt%), and MnO2 (5-10wt%). The particle size of TiO2 is 50 nm-100 nm, and the specific surface area is ≥80 m² / g.

[0075] The specific preparation of the SCR denitration catalyst includes:

[0076] S51. Pretreatment: Titanite-type TiO2 is soaked in 5% nitric acid for 12 hours to remove surface impurities and enhance porosity; nitric acid pretreatment increases the surface acidity of TiO2 and enhances the adsorption capacity of active components.

[0077] S52, impregnation, immersing TiO2 in a solution containing ammonium metavanadate (NH4VO3) and ammonium metatungstate ((NH4)6W 12 O 39 ) mixed solution, with V2O5 and WO3 loadings controlled at 1.5wt% and 3.0wt%, respectively. Cerium nitrate (Ce(NO3)3·6H2O) and manganese nitrate (Mn(NO3)2·4H2O) solutions were added, adjusting the Ce / Mn molar ratio to 1:1 and the total doping amount to 5wt%. After this step (S52), a catalyst precursor is formed. The Ce-Mn co-doping optimizes the catalyst's redox performance. CeO2 provides oxygen storage capacity, while MnO2 promotes the oxidation of NO to NO2, accelerating the "fast SCR" reaction.

[0078] S53, drying: the impregnated catalyst precursor is dried at 120°C for 6 hours.

[0079] S54, calcination, the first stage is calcination at 350 ° C for 2 hours to decompose nitrate and form V2O5WO3 crystal phase, the second stage is calcination at 500 ° C for 5 hours to promote the formation of CeO2-MnO2 and TiO2 solid solution.

[0080] S55, hydrophobic modification treatment, the calcined catalyst is immersed in silica sol (SiO2 content 10%) for 30 minutes, and then heat-treated at 300°C for 2 hours to form a hydrophobic SiO2 coating.

[0081] Among them, the hydrophobic coating reduces the adhesion of dust and water vapor in the flue gas, which can extend the service life of the catalyst.

[0082] The typical denitration reaction formula in step S50 is:

[0083]

[0084] S60, adsorption dust removal, uses a three-dimensional mesh filter layer woven from polyacrylonitrile-based activated carbon fibers to remove dust from flue gas. The polyacrylonitrile-based activated carbon fibers have a diameter of 8μm or less and a specific surface area of ​​1,200 m² / g. This polyacrylonitrile-based activated carbon can also simultaneously adsorb heavy metals such as Hg and Pb, with an adsorption capacity exceeding 200 mg / g, as well as residual sulfur oxides and nitrogen oxides.

[0085] S70, feedback control, deploying a high-temperature infrared spectrometer and a beta-ray dust detector to analyze the components in the flue gas to determine whether the flue gas meets the emission standards. If the flue gas meets any of the following conditions, return to step S20:

[0086] Condition 1: The concentration of particulate matter is greater than 5mg / Nm³;

[0087] Condition 2: Sulfur oxide concentration is greater than 30mg / Nm³;

[0088] Condition 3: Nitrogen oxide concentration is greater than 40mg / Nm³.

[0089] In this embodiment, the flue gas is first passed through a heat exchange tube to recover the heat in the flue gas. The medium in the heat exchange tube is then used to transport the heat to the heat-demanding location within the plant, achieving energy recovery. A multi-stage centrifugal process is then used to initially remove particulate matter from the flue gas. Further cooling is achieved by spraying a Ca(OH)2 slurry, and Al2O3 is added to the Ca(OH)2 slurry to catalyze sulfur oxides in the flue gas to form nitrogen. The flue gas is then denitrated using an SCR denitration catalyst, and activated carbon is used to adsorb any remaining particulate matter in the flue gas. Finally, the flue gas is tested to ensure it meets emission standards before being discharged.

[0090] Through this technical solution, the flue gas can be effectively cooled, dusted, desulfurized and denitrified, so that the flue gas meets the emission requirements and avoids the use of a cloth belt dust collector.

[0091] The above-described embodiments merely represent specific implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A flue gas treatment method for an alumina thermoelectric system, characterized in that: The following steps are involved: S10, waste heat recovery, allowing the flue gas to flow through the heat exchange tubes and exchange heat with the medium in the heat exchange tubes; S20, pre-dust removal, preliminary dust removal of flue gas through multi-stage centrifugal method; S30, cooling the flue gas by spraying Ca(OH)2 slurry into the flue gas, so that the flue gas forms a temperature gradient layer in the spraying area of ​​the Ca(OH)2 slurry; S40, desulfurization, adding Al2O3 to the Ca(OH)2 slurry in step S30 as a catalyst for SO2 adsorption and oxidation reaction; S50, denitrification, selecting an SCR denitrification catalyst mixed with CeO2-MnO2 to denitrify the flue gas; S60, adsorption dust removal, uses polyacrylonitrile-based activated carbon fibers woven into a three-dimensional mesh filter layer to remove dust from flue gas; S70, feedback control, deploys high-temperature infrared spectrometer and beta-ray dust meter to analyze the components in the flue gas and determine whether the flue gas meets the emission standards.

2. The flue gas treatment method according to claim 1, characterized in that: In step S10, the heat exchange tube is a spiral structure, and the material of the heat exchange tube is silicon carbide; The temperature of the flue gas passing through the heat exchange tube is measured to reduce the temperature to below 300°C.

3. The flue gas treatment method according to claim 1, characterized in that: In step S20, the multi-stage centrifugation method includes: S21, primary separation, the flue gas is fed into the cyclone at a speed of 35m / s along the tangential direction to separate particles with a size greater than 50μm; S22, secondary separation, the guide vanes set in the middle of the cyclone accelerate the flow rate of the flue gas to 50m / s, and separate particles with a particle size of less than 50μm; S23, dust collection, collects and processes the dust at the bottom of the cyclone.

4. The flue gas treatment method according to claim 3, characterized in that: A nitrogen backflush system is set at the bottom of the cyclone, and the bottom of the cyclone is backflushed once at a pressure of 0.6 MPa at regular intervals.

5. The flue gas treatment method according to claim 1, characterized in that: The step S30 specifically includes: S31, bringing the flue gas into contact with the atomized Ca(OH)2 slurry to reduce the flue gas temperature to 200°C; S32. A layer of air wall is distributed around the atomization area of ​​the Ca(OH)2 slurry, and a temperature gradient layer is generated in the flue gas.

6. The flue gas treatment method according to claim 5, characterized in that: In step S31, the concentration of the Ca(OH)2 slurry is 15% and the particle size is less than or equal to 10 μm; In step S32, compressed air at 0.4 MPa is used to form an air wall.

7. The flue gas treatment method according to claim 1, characterized in that: In step S40, 5% γ-Al2O3 with a specific surface area greater than 200 m2 / g is added to the Ca(OH)2 slurry.

8. The flue gas treatment method according to claim 1, characterized in that: In step S50, the SCR denitration catalyst uses TiO2 as a carrier, loads a VW-Ti oxide system, and is doped with 5% CeO2-MnO2, and reacts with the flue gas in a temperature range of 180°C-250°C.

9. The flue gas treatment method according to claim 1, characterized in that: In step S60, the diameter of the polyacrylonitrile-based activated carbon fiber is less than or equal to 8 μm, and the specific surface area is 1,200 m² / g.

10. The flue gas treatment method according to claim 1, characterized in that: In step S70, if the flue gas meets any of the following conditions, the process returns to step S20: Condition 1: The concentration of particulate matter is greater than 5mg / Nm³; Condition 2: Sulfur oxide concentration is greater than 30mg / Nm³; Condition 3: Nitrogen oxide concentration is greater than 40mg / Nm³.

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