Ceramic fiber tube and preparation method thereof

Abstract

The invention provides a ceramic fiber tube and a preparation method thereof, the ceramic fiber tube is provided with a tube body, the tube body is provided with multiple fiber filter paper layers formed by overlapping fiber cotton layers, and the tube body comprises a denitration area and a CO removal area which are arranged along the wall thickness direction; the denitration area comprises a fiber filter paper layers, the CO removal area comprises b fiber filter paper layers, and a + b is greater than or equal to 100; the pipe body is overlapped between the adjacent fiber filter paper layers to form nanoscale pores, and the pore diameter of the nanoscale pores is 10-50nm; and the CO removal area at least further comprises a CO catalyst which is loaded in the pores and on the surface of the fiber cotton in a nano-scale manner. Different active components are loaded on the carrier structure according to functional areas, and the number of layers of the fiber filter paper layers and nanoscale pores are configured, so that the three-in-one design of partition loading, gradient pores and collaborative catalysis is realized, the technical bottleneck of collaborative purification of multiple pollutants in complex flue gas is overcome, and the application prospect is wide. And high efficiency, economical efficiency and long service life are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial waste gas treatment, and in particular to a ceramic fiber tube and a preparation method thereof. Background Art

[0002] Ceramic fiber filter tubes are commonly used to filter solid particulate matter. In certain industrial waste gas treatment applications, such as those in glass melting furnaces, coking plants, waste incineration, and the steel and coal industries, they are primarily used for dust removal in high-temperature environments. However, their direct use in treating CO (carbon monoxide) waste gas is less common. CO is a colorless, odorless, and highly toxic gas that binds to hemoglobin 200-300 times more strongly than oxygen. This gas can cause hypoxia in human tissue, leading to headaches, coma, and even death. CO leaks or excessive emissions in industrial environments pose a direct threat to the lives of workers and nearby residents. The explosive limit of CO in air is 12.5% ​​to 74%. Uncontrolled CO concentrations in industrial waste gas can cause explosions (e.g., in coking plant gas purification systems). While not a directly potent greenhouse gas, CO indirectly exacerbates the greenhouse effect by participating in atmospheric photochemical reactions to produce ozone (O3). CO reacts with nitrogen oxides (NOx) and volatile organic compounds (VOCs) to form photochemical smog, contributing to smog and acid rain (e.g., the impact of untreated waste incineration waste gas on regional air quality).

[0003] Traditional methods for treating CO mainly include catalytic combustion, thermal oxidation, adsorption, and membrane separation. Catalytic combustion uses a catalyst to lower the combustion temperature of carbon monoxide, allowing it to react with oxygen at a lower temperature to produce carbon dioxide. This method effectively removes CO from exhaust gases with low energy consumption. However, the catalyst has a limited service life and requires regular replacement or maintenance. The temperature and composition of the exhaust gas must be controlled, and the catalyst is susceptible to poisoning or failure, especially in the presence of high humidity or toxic gases. Furthermore, the treatment effect on high-concentration CO is poor. Thermal oxidation heats the exhaust gas to a high temperature, causing the CO to react with oxygen to produce CO2. This method consumes a lot of energy and requires a high-temperature environment, resulting in high operating costs. Treatment capacity is affected by the exhaust gas temperature and gas composition, and some CO may not be fully converted. Adsorption uses solid adsorbents (such as activated carbon and molecular sieves) to absorb CO, reducing the CO concentration in the exhaust gas. However, the adsorbent's adsorption capacity is limited and requires regular replacement or regeneration. Membrane separation separates CO from other gases through a selectively permeable membrane. Membrane separation equipment for this method is relatively expensive, requiring a high initial investment. Differences in membrane selectivity are affected by changes in gas composition, and long-term use can lead to membrane clogging or aging. It is not effective for treating waste gas with high CO concentrations. It also has low treatment capacity for industrial waste gas with complex components, making it unsuitable for treating large-scale waste gas.

[0004] If ceramic fiber filter tubes are loaded with catalysts for catalytic combustion (such as RCO), elements such as sulfur (S), chlorine (Cl), and phosphorus (P) in the exhaust gas will react with the active sites of the catalyst, causing the catalyst to become poisoned and ineffective. Summary of the Invention

[0005] In view of this, an embodiment of the present invention provides a ceramic fiber tube and a preparation method thereof to eliminate or improve one or more defects existing in the prior art.

[0006] In a first aspect, the present invention provides a ceramic fiber tube, comprising a tube body having multiple fiber filter paper layers formed by stacking fiber cotton layers with cloth, the tube body comprising a denitration zone and a CO removal zone arranged along the wall thickness direction; the denitration zone comprising a layer a of stacked fiber filter paper layers, and the CO removal zone comprising a layer b of stacked fiber filter paper layers, wherein a+b≥100; the tube body comprises nanoscale pores stacked between adjacent fiber filter paper layers, the pore size of the nanoscale pores being between 10 and 50 nm; the denitration zone further comprising at least a denitration catalyst loaded in the pores and on the surface of the fiber filter paper layers, and the CO removal zone further comprising at least a nanoscale CO catalyst loaded in the pores and on the surface of the fiber cotton layers.

[0007] In some embodiments, the denitrification zone is located in the outer layer of the tube body, and the CO removal zone is located in the inner layer of the tube body; or, the CO removal zone is located in the outer layer of the tube body, and the denitrification zone is located in the inner layer of the tube body.

[0008] In some embodiments, the denitration zone and the CO removal zone are configured to at least partially overlap, and the denitration catalyst and the CO catalyst are both loaded in the fiber filter paper layer in the overlapping area.

[0009] In some embodiments, the total wall thickness of the tube body is 18-21 mm, the thickness of the denitrification zone is configured to be no less than 2 / 3 of the total wall thickness, and the thickness of the CO removal zone is configured to be no less than 1 / 3 of the total wall thickness; alternatively, the number of fiber filter paper layers in the denitrification zone is configured to be no less than 2 / 3 of the total number of fiber filter paper layers of the tube body, and the number of fiber filter paper layers in the CO removal zone is configured to be no less than 1 / 3 of the total number of fiber filter paper layers of the tube body.

[0010] In some embodiments, the nanoscale pores of the tube body are asymmetric gradient pores, the pore size of the nanoscale pores changes gradiently in the direction of the wall thickness, and gradually increases from the outside to the inside, so that the resistance of the flue gas flowing from the outside to the inside is gradually reduced; the porosity of the tube body is ≥80%, the porosity changes gradiently in the direction of the wall thickness, and gradually increases from the outside to the inside.

[0011] In some embodiments, the tube body is a multi-layer fiber filter paper structure with nano-scale pores formed by centrifuging a slurry composed of Al2O3 / SiO2 ceramic fibers and auxiliary materials, and the diameter of the Al2O3 / SiO2 ceramic fibers is 3~5μm.

[0012] In some embodiments, the CO catalyst includes at least one of a Pd-based catalyst, a Pt-based catalyst, a copper-based catalyst, a cobalt-molybdenum-based catalyst, an iron-based catalyst, and a nitrogen-doped graphene catalyst.

[0013] In some embodiments, the denitration catalyst includes at least V2O5, TiO2 and CeO2.

[0014] In some embodiments, the CO catalyst includes Pt, the denitration catalyst includes V2O5, TiO2 and CeO2, and the mass proportions of Pt, V2O5, TiO2 and CeO2 are 0.1-0.5wt%, 22.4-23.7 wt%, 67.1-71.2 wt% and 5-10 wt%, respectively; alternatively, the CO catalyst includes Pt, the denitration catalyst includes V2O5, TiO2 and CeO2, and the tube body is further loaded with WO3 and MnO2; the mass proportions of Pt, V2O5, TiO2, CeO2, WO3 and MnO2 are 0.1-0.5wt%, 22.4-23.7 wt%, 67.1-71.2 wt%, 5-10 wt%, 1.5-2.5 wt% and 1.5-2.5 wt%, respectively.

[0015] In a second aspect, the present invention further provides a method for preparing the above-mentioned ceramic fiber tube, wherein the thickness of the denitrification zone is configured to be equal to the total wall thickness of the tube body; the CO removal zone is located in the inner layer of the tube body, and its thickness is configured to be equal to 1 / 3 of the total wall thickness of the tube body, and the method comprises the following steps: After the ceramic fiber tube body is prepared, a nano-impregnation liquid containing a denitration catalyst is used, and a directional impregnation process is adopted from the inside out to achieve a gradient concentration loading of the denitration catalyst throughout the thickness of the tube body wall. During the denitration catalyst impregnation process, the drying temperature of the outer layer of the tube body is controlled to be higher than the temperature of the inner layer, so that the evaporation of the nano-impregnation liquid in the outer layer is large, resulting in the migration and loading of the denitration catalyst, so that the concentration of the denitration catalyst gradually decreases from the outside to the inside. After the denitration catalyst is loaded, a nano-impregnation solution containing a CO catalyst is used to achieve a gradient concentration loading of the CO catalyst on the inner 1 / 3 of the tube wall by a directional impregnation process from the inside to the outside.

[0016] In a third aspect, the present invention further provides a method for preparing the above-mentioned ceramic fiber tube, wherein the denitrification zone is located in the outer layer of the tube body, and its thickness is equal to 2 / 3 of the total wall thickness of the tube body; the CO removal zone is located in the inner layer of the tube body, and its thickness is equal to 1 / 3 of the total wall thickness of the tube body, and the method comprises the following steps: After the ceramic fiber tube body is prepared, a nano-impregnation solution containing a denitration catalyst is used, and a directional impregnation process from the outside to the inside is adopted to achieve a gradient concentration loading of the denitration catalyst on the outer layer of the tube at 2 / 3 of the total wall thickness; Using a nano-impregnation solution containing CO catalyst, a directional impregnation process from the inside to the outside is adopted to achieve a gradient concentration loading of CO catalyst in the inner 1 / 3 of the tube wall.

[0017] In some embodiments, the directional impregnation process from outside to inside or the directional impregnation process from inside to outside uses negative pressure outside the tube body or positive pressure inside the tube body to assist infiltration, so that the pressure difference between the inside and outside is 0.05-0.1 MP; The specific surface area of ​​the nano impregnation solution is greater than 60m 2 / g, laser particle detection data Dv (50) is between 0.075-0.1μm, Dv (99) <1.0μm; After the denitration catalyst and CO catalyst are fully loaded, the tube body is subjected to a gradient drying treatment at 60~100℃.

[0018] In a fourth aspect, the present invention further provides an application of the above-mentioned ceramic fiber tube in the coordinated purification of CO, HC, VOCs and NOx in industrial waste gas, with an operating temperature of 180°C to 320°C.

[0019] The ceramic fiber tube of the present invention achieves strong oxidative degradation of CO, HC, and VOCs and efficient reduction of NOx in a high-temperature environment by distinguishing functional areas, configuring different catalysts and active components in different functional areas, and precisely controlling the number of layers and pore configuration of the fiber filter paper layer. Its excellent conversion rate and removal rate make it an ideal choice for waste gas treatment in industrial fields such as steel and coking. It can effectively cope with complex pollutant combinations and achieve efficient and continuous waste gas purification.

[0020] Additional advantages, objects, and features of the present invention will be set forth in part in the following description and will become apparent to those skilled in the art upon examination of the following or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained by the structures particularly pointed out in the description and drawings.

[0021] Those skilled in the art will understand that the purposes and advantages that can be achieved by the present invention are not limited to the above specific descriptions, and the above and other purposes that can be achieved by the present invention will be more clearly understood based on the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings described herein are intended to provide a further understanding of the present invention, constitute a part of this application, and are not intended to limit the present invention. The components in the drawings are not drawn to scale but are intended solely to illustrate the principles of the present invention. To facilitate illustration and description of certain aspects of the present invention, corresponding portions in the drawings may be exaggerated, i.e., may appear larger than other components in an exemplary device actually fabricated according to the present invention.

[0023] Figure 1 Schematic diagram of the overall structure of a ceramic fiber tube in one embodiment of the present invention.

[0024] Figure 2 Schematic diagram of the layered structure of the ceramic fiber tube in Example 1 of the present invention.

[0025] Figure 3 Schematic diagram of the layered structure of the ceramic fiber tube in Example 2 of the present invention.

[0026] Figure 4 Schematic diagram of the layered structure of the ceramic fiber tube in Example 3 of the present invention.

[0027] Figure 5 This is a cross-sectional photograph of a ceramic fiber tube in one embodiment of the present invention.

[0028] Figure 6 This is an electron microscope image of the fiber cotton mesh structure inside the ceramic fiber tube in one embodiment of the present invention.

[0029] Figure 7 This is a micrograph showing the distribution of the catalyst on the surface of fiber cotton in one embodiment of the present invention.

[0030] Figure 8 1 is an experimental data curve of the removal efficiency of the ceramic fiber tube in one embodiment of the present invention at different high concentrations of pollutants and different temperatures.

[0031] Reference numerals: 11, denitrification zone; 12, CO removal zone. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and the accompanying drawings. Here, the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0033] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, the accompanying drawings only show structures and / or processing steps closely related to the solutions according to the present invention, while other details that are not closely related to the present invention are omitted.

[0034] It should be emphasized that the term "include / comprises" when used herein refers to the existence of features, elements, steps or components, but does not exclude the existence or addition of one or more other features, elements, steps or components.

[0035] It should also be noted that, unless otherwise specified, the term "connection" herein may refer not only to a direct connection but also to an indirect connection involving an intermediate.

[0036] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the accompanying drawings, the same reference numerals represent the same or similar components, or the same or similar steps.

[0037] In order to solve the various problems of industrial waste gas CO treatment in the existing technology and to realize the CO treatment function of ceramic fiber tubes, the present invention creatively proposes a ceramic fiber tube and a preparation method thereof. The ceramic fiber tube has its functional areas differentiated, which can at least greatly improve the CO treatment capacity of industrial waste gas.

[0038] In a first aspect, the present invention provides a ceramic fiber tube, such as Figure 1 As shown, the ceramic fiber tube includes a flange and a tube body. The tube body is open at the flange end for outputting clean flue gas after pollutants are filtered and catalytically treated by the tube body, and the other end of the tube body is closed. The tube body has a multi-layer fiber filter paper layer formed by stacking fiber cotton layers on top of cloth. It can be understood that the fiber cotton is ceramic fiber. The slurry is centrifuged and layered on top of the cloth to form a tube body with a certain strength. The layered structure of the tube body can be referred to Figure 5 The product cross-sectional photo of the ceramic fiber tube shown can demonstrate that the tube body of the ceramic fiber tube has a structure of stacked fiber filter paper layers.

[0039] Further, if Figure 2 or Figure 3 As shown, the tube body includes a denitration zone 11 and a CO removal zone 12 arranged along the wall thickness direction; further, the denitration zone 11 includes a stacked fiber filter paper layer, and the CO removal zone 12 includes b stacked fiber filter paper layers, wherein a+b≥100. In the embodiment of the present invention, each fiber filter paper layer of the tube body can provide a huge specific surface area for loading various catalysts, such as denitration catalysts, CO oxidation catalysts, etc. The stacking of hundreds of layers increases the total effective catalytic / adsorption area by several orders of magnitude. Figure 6 When the flue gas flows through this complex nano-fiber network with hundreds of layers, the path becomes extremely tortuous, which greatly prolongs the contact time between the flue gas and the catalytic active sites / adsorption sites; this design significantly improves the reaction efficiency and conversion rate of denitrification (NOx reduction) and CO oxidation.

[0040] In the above embodiment, the denitrification zone 11 and the CO removal zone 12 are zoned, allowing for independent optimization of each region. For example, the fibers in the denitrification zone 11 can be loaded with a denitrification catalyst optimally suited for the SCR reaction, while the fibers in the CO removal zone 12 can be loaded with a highly active CO catalyst, thereby avoiding interference or deactivation between the different catalysts. Furthermore, the fiber density, porosity, and layer thickness of each zone can be adjusted based on reaction requirements. For example, if the denitrification reaction requires a longer contact time, a thicker or more porous denitrification zone 11 can be designed. If the CO oxidation reaction is faster, a relatively thinner or slightly more porous CO removal zone 12 can be designed to reduce pressure drop. Optionally, a physical or chemical property gradient (such as decreasing porosity or catalyst concentration gradient) can be implemented from the inlet to the outlet within the denitrification zone 11 or the CO removal zone 12 to match the changing pollutant concentrations and reaction kinetics during the reaction, achieving the most efficient resource utilization and purification results.

[0041] Furthermore, the tube body is stacked between adjacent layers of fiber filter paper to form nano-scale pores, and the pore size of the nano-scale pores is between 10 and 50 nm. More specifically, referring to Figure 6 Hundreds of fiber layers form an extremely complex three-dimensional pore structure, ensuring pore diameters within the aforementioned range. These nanoscale pores allow particulate matter (especially submicron-sized PM2.5 / PM1) to be efficiently captured through a variety of mechanisms, including inertial collision, interception, diffusion, and electrostatic attraction, as it flows through the fiber layers. This results in filtration efficiency far exceeding that of the simpler structures of existing ceramic tubes. The multi-layered structure effectively disperses airflow, reduces channeling, and ensures a more even flow of smoke throughout the filtration / catalytic zone, fully utilizing all active surface areas.

[0042] Conventional fiber filter tubes in the existing art primarily rely on micron-sized pores (>1μm) to intercept larger particles, but have limited capture efficiency for PM1 (<1μm) and even nano-sized particles (such as soot, metal aerosols, and carbon black). Compared to conventional fiber filter tubes, the 10-50nm interlayer pores in the embodiments of the present invention precisely cover the "most penetrating particle size range" for the most challenging ultrafine particles, PM0.1-PM0.5 (100-500nm). When pollutant nanoparticles move within the narrow 10-50nm pores, they are struck by gas molecules and produce intense Brownian motion, exponentially increasing the probability of collision with the fiber surface. If the fibers or loaded catalysts are charged, the electrostatic field is stronger within the narrow nano-scale space, effectively attracting charged ultrafine particles. The ceramic fiber tubes in the embodiments of the present invention can achieve a capture efficiency of over 99.9% for particles larger than PM0.1, achieving near-zero emissions or theoretically zero emissions.

[0043] Furthermore, the denitration zone 11 at least includes a denitration catalyst loaded in the pores and on the surface of the fiber filter paper layer, and the CO removal zone 12 at least includes a CO catalyst loaded in the pores and on the surface of the fiber cotton at the nanoscale. Figure 6 and Figure 7 (The raised parts marked 1-8 are the catalysts / catalytic active sites attached to the surface of the fiber cotton). The micron-level fiber spacing and huge surface area greatly promote the diffusion and mass transfer rate of pollutant molecules from the gas phase to the catalytic active sites on the fiber surface, greatly improving the efficiency of the catalytic reaction.

[0044] In the above embodiment, the ceramic fiber tube structure formed by stacking more than 100 layers of fiber filter paper significantly improves the overall mechanical strength, rigidity and thermal shock resistance of the tube body, and can withstand pressure difference fluctuations, airflow scouring and temperature changes during the operation of the flue gas system and the start-up and shutdown process, reducing the risk of cracking, deformation or collapse and extending the service life.

[0045] In the aforementioned embodiment, the ceramic fiber tube, with its 100-layer fiber filter paper structure and 10-50 nm interlayer nanopores, achieves a quantum leap in CO removal capabilities by nanoscale loading of CO catalysts (such as Pt / Pd nanoclusters and CuO-MnO2 composite oxides) on the fiber surface and within the pores. This three-dimensional loading of catalysts on the fiber cotton surface and within the pores significantly increases the density of active sites. Platinum nanoparticles with a diameter of 2-5 nm can be embedded into the pore walls to prevent self-clogging. The 10-50 nm pores force pollutant-laden flue gas to diffuse along the inner walls, significantly increasing the collision frequency between pollutant molecules and the catalyst.

[0046] To further explain the reaction rate doubling mechanism, taking the chemical reaction process of CO as an example, when CO and O2 are confined in pores of 10~50nm, the molecular mean free path is compressed from micron level to nanometer level, and the collision frequency of CO molecules in the pores increases from 10 9 The number of times per second jumped to 10 12 times per second; nanopores have a higher adsorption selectivity for O2 than CO, creating an oxygen-rich microenvironment on the catalyst surface and achieving localized oxygen concentration polarization; confined space enhances the vibrational energy of the Pt-CO bond, reducing the activation energy from 80 kJ / mol to 50 kJ / m, thereby lowering the apparent activation energy. This embodiment also reduces the CO ignition temperature, enabling a low-temperature process. This ceramic fiber filter tube is suitable for treating flue gas with high CO concentrations (e.g., 10,000 mg / Nm³) during sintering operations in the steel industry.

[0047] In the above embodiments, the present invention can achieve the coordinated treatment of multiple pollutants (such as dust, SO2, CO, NOx, HCl, HC, dioxins and VOCs, etc.) by the layered layout of the CO removal zone 12 and the denitrification zone 11 on the pipe body, and by utilizing the filtering effect of the outer wall of the pipe body on dust and desulfurizer or adsorbent, and can also avoid mutual interference caused by functional mixing.

[0048] The present invention fully utilizes the high specific surface area, high temperature resistance and ability to be processed into complex shapes of ceramic fiber materials. It is particularly suitable for high-end flue gas treatment application scenarios that require deep purification, high removal efficiency, treatment of complex pollutants and harsh working conditions (such as high temperature, high dust, and corrosive atmosphere).

[0049] It is understood that the above-mentioned desulfurizer or adsorbent can be lime or bicarbonate, and the desulfurizer or adsorbent that reacts with SO2 is filtered through the outer wall of the tube body, that is, the outer wall of the tube body realizes the desulfurization bed or dust collection effect. The reaction process of the pollutants that can be treated by the desulfurizer or adsorbent is as follows: SO2+Ca(OH)2=CaSO3+H2O CaSO3+½O2=CaSO4 SO3+Ca(OH)2=CaSO4+H2O 2HCl+Ca(OH)2=CaCl2+H2O 2HF+Ca(OH)2=CaF2+2H2O NH3 or urea is used as a reducing agent to achieve denitration when passing through the denitration zone 11 of the pipe body. When the flue gas passes through the denitration zone 11, a denitration reaction is carried out under the action of the denitration catalyst, with a high removal rate and low NH3 escape efficiency. The denitration reaction principle is as follows: 4NO+4NH3+O2=4N2+6H2O 2NO2+4NH3+O2=3N2+6H2O According to actual conditions, the distribution order and position of the denitrification zone 11 and the CO removal zone 12 of the ceramic fiber tube in the embodiment of the present invention can have various embodiments to suit different application scenarios.

[0050] Example 1 like Figure 2As shown, the denitrification zone 11 is located on the outer layer of the tube, while the CO removal zone 12 is located on the inner layer. In this embodiment, the present invention enhances sulfur protection and heat utilization through the zonal reconstruction of "desulfurization-denitrification-CO removal." The adsorbent dust collection effect achieved by the outer tube wall prioritizes SO2 removal, preventing sulfate from entering the denitrification zone 11 and poisoning the denitrification catalyst (e.g., V2O5-WO3 / TiO2) or the CO catalyst (e.g., Pt / Al2O3), thereby extending the overall filter life. High-temperature exhaust gas (e.g., steel sintering flue gas temperatures of 300-400°C) enters the outer denitrification zone 11, where the required denitrification reaction temperature (180-400°C) is reached. The inner CO catalytic combustion temperature (e.g., 250-350°C) is naturally maintained by waste heat, reducing external heating energy consumption. The N2 and H2O generated in the denitrification zone 11 dilute the CO concentration, reducing the explosion risk of the inner CO catalytic combustion. NH3 not fully consumed in the denitrification reaction can participate in the catalytic oxidation of CO (e.g., 4CO + 2NO + 4NH3 → 4CO2 + 3N2 + 6H2O), improving the synergistic removal rate of nitrogen oxides and CO. The layered tube arrangement of this embodiment is applicable to the treatment of high-dust, high-sulfur, and high-temperature flue gases from coal-fired power plants, as well as flue gases containing heavy metal dust and dioxin precursors from waste incinerators.

[0051] Example 2 like Figure 3 As shown, the CO removal zone 12 is located in the outer layer of the tube body, and the denitrification zone 11 is located in the inner layer of the tube body. In this embodiment, the Pt-based CO catalyst in the CO removal zone 12 can initiate CO oxidation at a relatively low temperature at the flue gas inlet, solving the problem of low denitrification efficiency under low-temperature conditions. The heat released during the CO oxidation and combustion removal process can heat the flue gas, thereby preheating the flue gas and activating the catalytic effect of the inner denitrification zone 11. For example, after sulfides react with the desulfurizer or adsorbent, dust can be filtered and adsorbed on the outer wall of the tube body, protecting the subsequent CO catalyst from poisoning. By removing CO first, CO can be prevented from competing with NH3 (the denitrification reductant) for adsorption on the catalyst in the denitrification zone 11, thereby improving denitrification efficiency. The layered tube arrangement of this embodiment is suitable for treating low-temperature, high-CO-concentration flue gas in the steel sintering industry, as well as for treating flue gas containing large molecules such as tar in coking plant exhaust.

[0052] Example 3 like Figure 4As shown, the denitrification zone 11 and the CO removal zone 12 are all arranged in an overlapping manner. Optionally, more than 100 layers of fiber filter paper are all loaded with denitrification catalysts and CO catalysts. Each layer of fiber filter paper provides denitrification and CO catalytic sites, which can significantly shorten the reaction path and realize the "NOx reduction-CO oxidation" 100-layer relay reaction in the nano-scale pores, greatly improving the treatment effect. Optionally, the active component CeO2 carrier not only provides oxygen vacancies for the SCR, but also protects the CO catalyst from sulfur poisoning. This arrangement can reduce the resistance at the interface of the functional partitions and reduce the pressure drop. The pipe structure of this embodiment is applicable to compact flue gas treatment systems such as clean flue gas treatment of natural gas boilers and ship exhaust treatment.

[0053] Optionally, the denitrification zone 11 and the CO removal zone 12 are configured to at least partially overlap, with both the denitrification catalyst and the CO catalyst loaded within the fiber filter paper layer in the overlapping region. This design, by partially or completely overlapping the denitrification zone 11 and the CO removal zone 12, explores a new approach for the coordinated treatment of multiple pollutants. The partial overlap between the denitrification zone 11 (SCR) and the CO removal zone 12 utilizes the oxidizing properties of the denitrification catalyst (such as V2O5-WO3 / TiO2) to promote the coordinated removal of CO and NOx (e.g., 4CO + 2NO2 → 4CO2 + N2), improving theoretical conversion efficiency by 10% to 20%. The heat released by the catalytic combustion of CO (250-350°C) provides temperature compensation for the denitrification reaction in the overlapping region, making it particularly suitable for low-temperature exhaust gas scenarios and reducing external heating energy consumption.

[0054] In some embodiments, the tube body of the present invention can have a wall thickness of approximately 20 mm, such as ±2 mm. The thickness of each fiber filter paper layer is approximately 0.1-0.3 mm. The centrifugal fabrication process allows for precise control of the porosity of each stacked fiber filter paper layer, achieving a balance between high throughput and high capture efficiency.

[0055] Optionally, the total wall thickness of the tube body is 18-21 mm, the thickness of the denitrification zone 11 is configured to be no less than 2 / 3 of the total wall thickness, and the thickness of the CO removal zone 12 is configured to be no less than 1 / 3 of the total wall thickness. Alternatively, the design may be such that the number of fiber filter paper layers in the denitrification zone 11 is configured to be no less than 2 / 3 of the total number of fiber filter paper layers in the tube body, and the number of fiber filter paper layers in the CO removal zone 12 is configured to be no less than 1 / 3 of the total number of fiber filter paper layers in the tube body. This design allows the ceramic fiber filter tube to leverage the thickness or number of layers of the denitrification zone 11 to ensure high treatment efficiency even if the denitrification reaction is slow. The efficient catalytic effect of the CO removal zone 12, which has a smaller thickness or number of layers, can achieve low-temperature instantaneous purification of CO.

[0056] Furthermore, the nanopores in the ceramic fiber tubes of this invention create a honeycomb network that increases the specific surface area of ​​the ceramic fibers to 300–500 m² / g (compared to 50–100 m² / g for conventional micron-sized pores). This significantly increases the loading density of the CO catalyst and boosts the CO oxidation reaction rate several times higher than that of conventional filter tubes. The three-dimensional interconnected network of nanopores anchors the CO catalyst, inhibiting migration and aggregation at high temperatures. The capillary action of the nanopores promotes rapid desorption of reaction products (such as CO2) and reduces carbon clogging.

[0057] In some embodiments, the pores in the tube body of the ceramic fiber tube are asymmetric gradient pores, and the pore size of the nanoscale pores changes gradiently in the wall thickness direction and gradually increases from the outside to the inside, so that the resistance of the flue gas flowing from the outside to the inside is gradually reduced; this design is also different from existing ceramic tubes, and overcomes the problem of excessive pressure drop caused by deep filtration of ceramic tubes with larger wall thickness.

[0058] Optionally, the porosity of the tube body is ≥80%, and the porosity varies gradiently in the wall thickness direction and gradually increases from the outside to the inside. The high-porosity design can provide growth space for the CO catalyst, significantly increasing the number of catalytic active sites. In this embodiment, the dual-gradient change design of pore size and porosity can reduce pressure drop and is suitable for high-flow flue gas treatment; the life of the ceramic fiber tube is greatly improved; and this design can also realize a low-temperature purification route.

[0059] In some embodiments, the tube body is a multi-layer fiber filter paper layer structure with nano-scale pores formed by centrifugal distribution of a slurry composed of Al2O3 / SiO2 ceramic fibers and auxiliary materials, and the diameter of the Al2O3 / SiO2 ceramic fibers is 3~5μm. Al2O3 / SiO2 ceramic fibers can withstand high temperatures above 1200°C (softening point > 1600°C) and are suitable for high-heat exhaust gas scenarios such as glass melting furnaces and steel sintering. The ceramic fiber tube made of Al2O3 / SiO2 ceramic fibers has excellent corrosion resistance in the pH range of 3~11, and is resistant to acidic (such as SO2, HCl) and alkaline (such as NH3) gas erosion. Its service life is more than 50% longer than that of ordinary aluminum silicate fibers. Using fibers with a diameter of 3~5μm, such as 4μm fibers, the specific surface area can reach 357m 2 / g, significantly increasing the specific surface area and achieving highly efficient capture of nanoparticles. SiO2 provides Brønsted acid sites, while Al2O3 provides Lewis acid sites, synergistically promoting the SCR denitrification reaction. The ratio of Al2O3 to SiO2 ceramic fibers can be adjusted based on actual needs.

[0060] In some embodiments, the CO catalyst includes at least one of a Pd-based catalyst, a Pt-based catalyst, a copper-based catalyst, a cobalt-molybdenum-based catalyst, an iron-based catalyst, and a nitrogen-doped graphene catalyst. Pd-based catalysts may include Pd-Cu / hydroxyapatite (HAP) catalysts and palladium-gold catalysts. Pt-based catalysts may include Pt / Al2O3. Copper-based catalysts may include Cu-Zn catalysts, Fe-Cr catalysts, and conventional copper oxide-manganese dioxide catalysts.

[0061] In some embodiments, the denitration catalyst comprises at least V2O5, TiO2 and CeO2. Among them, the V-Ti system is the main catalyst for SCR denitration, and TiO2 can provide a high specific surface area (>80 m 2 / g) and sulfur resistance. CeO2 regulates the redox cycle through its oxygen storage capacity (OSC), promoting the conversion of SO2→SO3 and inhibiting sulfate deposition, thus solving the problem of sulfur poisoning.

[0062] In some embodiments, the CO catalyst includes Pt, and the denitration zone 11 also includes at least V2O5, TiO2, and CeO2 impregnated within its pores. The mass proportions of Pt, V2O5, TiO2, and CeO2 are 0.1-0.5 wt%, 22.4-23.7 wt%, 67.1-71.2 wt%, and 5-10 wt%, respectively. In this formulation, Pt catalyzes CO at low temperatures, the V-Ti system denitrates, and CeO2 resists sulfur. The gradient distribution of the three complements each other's functions, enabling efficient combination and use of multi-effect catalysts.

[0063] In some embodiments, the CO catalyst includes Pt, the denitration catalyst includes V2O5, TiO2, and CeO2, and the tube is further loaded with WO3 and MnO2. The mass proportions of Pt, Pt, V2O5, TiO2, CeO2, WO3, and MnO2 are 0.1-0.5 wt%, 22.4-23.7 wt%, 67.1-71.2 wt%, 5-10 wt%, 1.5-2.5 wt%, and 1.5-2.5 wt%, respectively. In this formulation, Pt catalyzes CO at low temperatures, the V-Ti system denitrates, CeO2 resists sulfur, WO3 significantly increases the SCR reaction rate, and reduces the ignition temperature. MnO2 enables low-temperature oxidation of CO and protects Pt from sulfide poisoning.

[0064] In a second aspect, the present invention further provides a method for preparing the above-mentioned ceramic fiber tube, wherein the thickness of the denitrification zone 11 is configured to be equal to the total wall thickness of the tube body; the CO removal zone 12 is located in the inner layer of the tube body, and its thickness is equal to 1 / 3 of the total wall thickness of the tube body, and the method comprises the following steps: After the ceramic fiber tube body is prepared, a nano-impregnation liquid containing a denitration catalyst is used, and a directional impregnation process from the inside to the outside is adopted to achieve a gradient concentration loading of the denitration catalyst in the entire thickness direction of the tube wall; during the denitration catalyst impregnation process, the drying temperature of the outer layer of the tube body is controlled to be higher than the temperature of the inner layer, so that the evaporation amount of the nano-impregnation liquid in the outer layer is large, resulting in the migration and loading of the denitration catalyst, so that the concentration of the denitration catalyst gradually decreases from the outside to the inside.

[0065] After the denitration catalyst is loaded, a nano-impregnation solution containing a CO catalyst is used to achieve a gradient concentration loading of the CO catalyst on the inner 1 / 3 of the tube wall by a directional impregnation process from the inside to the outside.

[0066] In this embodiment, the preparation method of the ceramic fiber tube achieves precise spatial gradient distribution of the catalyst while maintaining the simplicity of the process through the innovative design of "full-wall denitrification gradient + local enrichment of CO"; the denitrification catalyst has the maximum concentration in the outer layer of the tube body, which greatly improves the active points in the flue gas inlet area and reduces the amount of catalyst used. The CO catalyst generally uses precious metals and is confined to the inner layer of the tube body, which is economical and can also avoid high-temperature sintering of the outer layer or poisoning and deactivation due to sulfides. This method achieves a full-wall denitrification gradient and an inner-layer CO catalyst gradient through double impregnation and temperature field control without the need for complex masks.

[0067] In a third aspect, the present invention further provides a method for preparing the above-mentioned ceramic fiber tube, wherein the denitrification zone 11 is located in the outer layer of the tube body, and its thickness is equal to 2 / 3 of the total wall thickness of the tube body; the CO removal zone 12 is located in the inner layer of the tube body, and its thickness is equal to 1 / 3 of the total wall thickness of the tube body, and the method comprises the following steps: After the ceramic fiber tube body is prepared, a nano-impregnation solution containing a denitration catalyst is used, and a directional impregnation process from the outside to the inside is adopted to achieve a gradient concentration loading of the denitration catalyst on the outer layer of the tube, which is 2 / 3 of the total wall thickness. The denitration catalyst is impregnated from the outside to the inside, which can achieve the effect of the denitration catalyst being concentrated outside and diluted inside to match the NOx concentration attenuation in the flue gas. Using a nano-impregnation solution containing CO catalyst, a directional impregnation process from the inside out is used to achieve a gradient concentration of CO catalyst in the inner 1 / 3 of the tube wall. The impregnation of CO catalyst from the inside out can be distinguished from the impregnation process of denitrification catalyst.

[0068] In this embodiment, the method achieves precise spatial distribution of catalysts in the denitration zone 11 and the CO zone through a process design involving bidirectional countercurrent gradient impregnation of the denitration catalyst and the CO catalyst. The denitration catalyst concentration is configured to be high on the outside and low on the inside to match the NOx decay dynamics, while the CO catalyst concentration is configured to be high on the inside and low on the outside to adapt to the exothermic reaction temperature field and improve the CO oxidation removal efficiency. This method can solve the problems of catalyst waste, cross-contamination, and pore clogging in traditional processes. It is particularly suitable for complex flue gas scenarios with high dust, high sulfur, and high CO content, providing a high-performance and low-cost manufacturing paradigm for near-zero emissions.

[0069] In the above two preparation methods, after the ceramic fiber tube body is prepared, a specific surface area of ​​60m 2 / g, laser particle detection data Dv (50) between 0.075-0.1μm, Dv (99) <1.0μm, the nano-impregnation solution containing chloroplatinic acid, ammonium metavanadate, titanium dioxide and cerium dioxide adopts a directional impregnation process to achieve uniform loading of active components, and uses negative pressure outside the filter tube or positive pressure inside the filter tube to assist penetration, so that the internal and external pressure difference is 0.05~0.1MP; after sufficient impregnation, it is dried at a gradient of 60~100℃.

[0070] Alternatively, the ceramic fiber tube body can be prepared using a silica sol-ceramic fiber slurry. The silica sol acts as a binder, creating nanoscale pores during the centrifugal spreading process, avoiding the closed-pore issues associated with traditional extrusion molding and ensuring uniform pore distribution. In the nano-impregnation solution, the catalyst precursor is loaded onto a nano-TiO2 carrier, forming a mesoporous network structure through a sol-gel method, with pore sizes ranging from 2 to 8 nm.

[0071] Alternatively, chloroplatinic acid (HPtCl) can be used as a Pt precursor, providing Pt active sites for catalyzing low-temperature CO oxidation. H2PtCl·6H2O is dissolved in dilute hydrochloric acid (pH 2-3) at a concentration of 0.01-0.05 mol / L. Chloroplatinic acid (HPtCl) is highly dispersed and provides an ultra-active surface.

[0072] Alternatively, ammonium metavanadate (NH4VO3) is a precursor to V2O5, the primary active phase in the denitrification (SCR) process. It synergizes with TiO2 and is then evenly dispersed on the TiO2 surface. Dissolve NH4VO3 in aqueous ammonia (pH 8-9) and heat to 60°C to promote dissolution and avoid precipitation.

[0073] Optionally, titanium dioxide (TiO2) provides high surface area (>80m 2 / g), used to support the active layer; high specific surface area anatase phase TiO2 (such as specific surface area>80m 2 / g, pore size 5-10 nm).

[0074] Alternatively, cerium dioxide (CeO2) is an oxygen storage agent that resists sulfur poisoning and is used to regulate the redox cycle. CeO2 nanoparticles (30-50 nm in diameter) can be synthesized by precipitation-calcination and ultrasonically dispersed in deionized water.

[0075] Alternatively, mix the four components in a ratio of Pt:V:Ti:Ce (Pt:V:Ti:Ce = 0.1-0.5:22.4-23.7:67.1-71.2:5-10), add a dispersant (e.g., polyethylene glycol PEG-4000), and magnetically stir for 2 hours. Furthermore, to prevent agglomeration, use an ultrasonic disruptor (500 W, 20 kHz) for 30 minutes to break up particle aggregates. Adjust the pH of the mixture to 4-5 (using acetic acid) to enhance the surface zeta potential of the nanoparticles (absolute value >30 mV) and prevent sedimentation.

[0076] Optionally, the particle size distribution in the nano-impregnation solution is configured to be Dv(50)=0.075-0.1μm and Dv(99)<1.0μm. High-pressure homogenization combined with ultrasonic cavitation can be used to control the particle distribution. Dv(50) is configured to be 75-100nm to match the 10-50nm gap between ceramic fibers; Dv(99) is configured to be less than 1000nm to prevent clogging of capillary channels or nano-scale pores.

[0077] Alternatively, negative pressure suction is used to cause the impregnation liquid to permeate from the inner wall of the ceramic fiber tube outward, or from the outer wall inward. The active components (Pt and V2O5) are preferentially concentrated in the inner layer, while CeO2 is gradiently dispersed outward, forming an "inner catalyst-outer protection" structure. The carrier pore size matches the impregnation liquid particle size, ensuring that the active components are anchored to the pore surface and preventing clogging.

[0078] Alternatively, a gradient drying process can be configured as follows: 60°C for 2 hours → 80°C for 2 hours → 100°C for 1 hour, gradually removing moisture and preventing capillary forces from destroying the pore structure. After gradient drying, the tube can also be activated by calcination, such as calcining at 350°C for 2 hours in an air atmosphere, to decompose NH₄VO₃ into V₂O₅ and reduce H₂PtCl₆ into Pt nanoparticles with a particle size of 2-5 nm.

[0079] The preparation method in the embodiment of the present invention can match the nanopores with the particles to maximize the exposure of active sites; the use of directional impregnation and gradient drying processes can avoid structural collapse and ensure the long-term stability of the structure.

[0080] In the present invention, the ceramic fiber tube prepared by the above preparation method was experimentally verified under different temperatures and different CO and NOx concentration conditions. The experimental scenario focused on the flue gas in the sintering process of the steel industry. For example, the original CO concentration in the exhaust gas from the sintering machine head is usually 5000-10000 mg / m³, and the original NOx concentration in the sintering flue gas is generally 200-600 mg / m³. In this experiment, the original CO concentration was controlled at 6050-8295 mg / m³. 3 , increase the original NOx concentration and control it at 1413-1821 mg / m 3 , which is a flue gas with high concentration of pollutants.

[0081] Combine Figure 8 As shown in the table below, CO removal efficiency reaches a high starting point of 75.0% at 200°C, then steadily increases, reaching a high-efficiency plateau (removal efficiency >85%) at around 240°C, nearing saturation at around 280°C, and achieving high-temperature stability at around 300°C. NOx removal efficiency is generally superior to CO, maintaining high efficiency throughout the temperature range of 180°C-320°C, reaching a removal rate of 97.1% at 295°C. Data demonstrates that this ceramic fiber tube can also be used in the low-temperature range (180°C-240°C), achieving CO removal rates ≥60.3% and NOx removal rates ≥75.2% for flue gas with high pollutant concentrations. This temperature range is fully suitable for treating flue gas with medium and low pollutant concentrations. The ceramic fiber tube exhibits excellent performance in the medium-temperature range (240°C-320°C), with CO removal rates ≥85.1% and NOx removal rates ≥92.3%.

[0082] Fourthly, the present invention also provides a use of the aforementioned ceramic fiber tube for the coordinated purification of CO, HC, VOCs, and NOx from industrial waste gas, operating at a temperature of 180°C to 320°C. This ceramic fiber tube not only efficiently removes CO from waste gas, but also simultaneously treats harmful substances such as HC, VOCs, NOx, and dioxins. This coordinated purification feature gives the filter tube broad potential for application in industrial waste gas treatment, particularly in complex waste gas sources where multiple pollutants need to be removed simultaneously.

[0083] The ceramic fiber tube of the present invention uses a catalyst in the CO removal zone 12 to promote the oxidation of CO, converting it to carbon dioxide (CO2), achieving efficient CO removal. VOCs (volatile organic compounds) are another important pollutant in industrial waste gas. The catalytic material in the ceramic fiber tube promotes the oxidation of VOCs, converting them into harmless substances (such as water and carbon dioxide). The denitrification catalyst in the filter tube removes NOx through a selective catalytic reduction reaction, converting it to nitrogen and water vapor. Due to the filter tube's high-temperature stability, it can operate for long periods in high-temperature industrial environments while maintaining its filtration and catalytic performance. High temperatures help maintain catalyst activity and accelerate the oxidation of CO and VOCs, thereby improving purification efficiency. Experimental verification has shown that the ceramic fiber tube achieves strong oxidative degradation of CO, HC, and VOCs, as well as efficient NOx reduction, within a temperature range of 240°C to 320°C, with CO removal rates ≥85% and NOx removal rates ≥92%. It is suitable for the coordinated purification of multiple pollutants in complex flue gases from industries such as steel and coking.

[0084] It should be understood that the present invention is not limited to the specific configurations and processes described above and illustrated in the figures. For the sake of brevity, a detailed description of known methods is omitted. In the above embodiments, several specific steps are described and illustrated as examples. However, the method of the present invention is not limited to the specific steps described and illustrated. Those skilled in the art may make various changes, modifications, and additions, or change the order of the steps after understanding the spirit of the present invention.

[0085] In the present invention, features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, and / or combined with or replace features of other embodiments.

[0086] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations to the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A ceramic fiber tube, characterized in that: The ceramic fiber tube has a tube body, which has multiple fiber filter paper layers formed by stacking fiber cotton layers with cloth, and the tube body includes a denitrification zone and a CO removal zone arranged along the wall thickness direction; The denitrification zone includes a layer of fiber filter paper stacked together, and the CO removal zone includes a layer of fiber filter paper stacked together, wherein a+b≥100; The tube body is stacked between adjacent fiber filter paper layers to form nano-scale pores, and the pore diameter of the nano-scale pores is between 10 and 50 nm; The denitration zone at least includes a denitration catalyst loaded in the pores and on the surface of the fiber filter paper layer, and the CO removal zone at least includes a nano-scale CO catalyst loaded in the pores and on the surface of the fiber cotton.

2. The ceramic fiber tube according to claim 1, characterized in that The denitrification zone is located in the outer layer of the tube body, and the CO removal zone is located in the inner layer of the tube body; or The CO removal zone is located in the outer layer of the tube body, and the denitrification zone is located in the inner layer of the tube body.

3. The ceramic fiber tube according to claim 1 or 2, characterized in that: The denitration zone and the CO removal zone are configured to at least partially overlap, and the denitration catalyst and the CO catalyst are both loaded in the fiber filter paper layer in the overlapping area.

4. The ceramic fiber tube according to claim 3, characterized in that The total wall thickness of the tube body is 18-21 mm, the thickness of the denitrification zone is configured to be no less than 2 / 3 of the total wall thickness, and the thickness of the CO removal zone is configured to be no less than 1 / 3 of the total wall thickness; or The number of fiber filter paper layers in the denitrification zone is configured to be no less than 2 / 3 of the total number of fiber filter paper layers in the tube body, and the number of fiber filter paper layers in the CO removal zone is configured to be no less than 1 / 3 of the total number of fiber filter paper layers in the tube body.

5. The ceramic fiber tube according to claim 3, characterized in that: The nano-scale pores of the tube body are asymmetric gradient pores, the pore diameter of which changes gradually in the wall thickness direction and gradually increases from the outside to the inside, so that the resistance of the smoke flowing from the outside to the inside is gradually reduced; The porosity of the tube body is ≥80%, the porosity changes gradually in the wall thickness direction, and gradually increases from the outside to the inside.

6. The ceramic fiber tube according to claim 1, characterized in that The tube body is a multi-layer fiber filter paper structure with nano-scale pores formed by centrifuging a slurry composed of Al2O3 / SiO2 ceramic fibers and auxiliary materials. The diameter of the Al2O3 / SiO2 ceramic fibers is 3-5 μm.

7. The ceramic fiber tube according to claim 1, characterized in that The CO catalyst includes at least one of a Pd-based catalyst, a Pt-based catalyst, a copper-based catalyst, a cobalt-molybdenum-based catalyst, an iron-based catalyst, and a nitrogen-doped graphene catalyst.

8. The ceramic fiber tube according to claim 1, characterized in that The denitration catalyst includes at least V2O5, TiO2 and CeO2.

9. The ceramic fiber tube according to claim 1, characterized in that The CO catalyst includes Pt, the denitration catalyst includes V2O5, TiO2 and CeO2, and the mass proportions of Pt, V2O5, TiO2 and CeO2 are 0.1-0.5 wt%, 22.4-23.7 wt%, 67.1-71.2 wt% and 5-10 wt% respectively; or, The CO catalyst includes Pt, the denitration catalyst includes V2O5, TiO2 and CeO2, and the tube body is further loaded with WO3 and MnO2; the mass proportions of Pt, V2O5, TiO2, CeO2, WO3 and MnO2 are 0.1-0.5 wt%, 22.4-23.7 wt%, 67.1-71.2 wt%, 5-10 wt%, 1.5-2.5 wt% and 1.5-2.5 wt%, respectively.

10. A method for preparing a ceramic fiber tube according to any one of claims 1 to 9, characterized in that: The thickness of the denitrification zone is equal to the total wall thickness of the pipe body; the CO removal zone is located in the inner layer of the pipe body, and its thickness is equal to 1 / 3 of the total wall thickness of the pipe body. The method comprises the following steps: After the ceramic fiber tube body is prepared, a nano-impregnation liquid containing a denitration catalyst is used, and a directional impregnation process is adopted from the inside out to achieve a gradient concentration loading of the denitration catalyst throughout the thickness of the tube body wall. During the denitration catalyst impregnation process, the drying temperature of the outer layer of the tube body is controlled to be higher than the temperature of the inner layer, so that the evaporation of the nano-impregnation liquid in the outer layer is large, resulting in the migration and loading of the denitration catalyst, so that the concentration of the denitration catalyst gradually decreases from the outside to the inside. After the denitration catalyst is loaded, a nano-impregnation solution containing a CO catalyst is used to achieve a gradient concentration loading of the CO catalyst on the inner 1 / 3 of the tube wall by a directional impregnation process from the inside to the outside.

11. A method for preparing a ceramic fiber tube according to any one of claims 1 to 9, characterized in that: The denitrification zone is located in the outer layer of the pipe body, and its thickness is equal to 2 / 3 of the total wall thickness of the pipe body; the CO removal zone is located in the inner layer of the pipe body, and its thickness is equal to 1 / 3 of the total wall thickness of the pipe body. The method comprises the following steps: After the ceramic fiber tube body is prepared, a nano-impregnation solution containing a denitration catalyst is used, and a directional impregnation process from the outside to the inside is adopted to achieve a gradient concentration loading of the denitration catalyst on the outer layer of the tube at 2 / 3 of the total wall thickness; Using a nano-impregnation solution containing CO catalyst, a directional impregnation process from the inside to the outside is adopted to achieve a gradient concentration loading of CO catalyst in the inner 1 / 3 of the tube wall.

12. The preparation method according to claim 10 or 11, characterized in that: The directional impregnation process from outside to inside or the directional impregnation process from inside to outside adopts negative pressure outside the tube body or positive pressure inside the tube body to assist infiltration, so that the pressure difference between the inside and outside is 0.05~0.1MP; The specific surface area of ​​the nano impregnation solution is greater than 60m 2 / g, laser particle detection data Dv (50) is between 0.075-0.1μm, Dv (99) <1.0μm; After the denitration catalyst and CO catalyst are fully loaded, the tube body is subjected to a gradient drying treatment at 60~100℃.

13. Use of the ceramic fiber tube according to any one of claims 1 to 9 in the coordinated purification of CO, HC, VOCs and NOx in industrial waste gas, wherein the operating temperature is 180°C to 320°C.

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