An NH3-SCR denitration system and method for synergistically purifying CO

Abstract

The present invention belongs to the technical field of industrial flue gas purification, and more specifically, relates to an NH3-SCR denitration system and method for co-purifying CO. Based on the differences in the oxidation reaction mechanisms of NH3 and CO, the present invention designs a core-shell catalyst and uses it in the denitration system to achieve the co-oxidation of NH3 and CO. At the same time, the heat released by the co-oxidation of NH3 / CO is utilized to increase the inlet flue gas temperature of NH3-SCR and improve the denitration efficiency. The present invention utilizes the differences in the reaction mechanisms of NH3-SCR denitration, NH3 oxidation, and CO oxidation to achieve the efficient co-purification of multi-components such as industrial flue gas NO x , escaped NH3, and CO. Through functional integration, the system energy consumption is significantly reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of industrial flue gas purification, and more specifically relates to an NH3-SCR denitration system and method for co-purifying CO. Background Art

[0002] Industries using fossil energy as fuel usually generate a large amount of flue gas containing NO x and CO, such as the sintering process in the steel industry, etc. The direct emission of these waste gases will pose a serious threat to the ecological environment and human health. The selective catalytic reduction method using NH3 as a reducing agent is the mainstream technology for industrial source flue gas denitration at present. In order to meet the increasingly stringent ultra-low emission requirements of NO x the amount of ammonia injection is usually greater than the theoretical reaction stoichiometric ratio (NH3 / NO = 1), resulting in serious secondary pollution of NH3 escape.

[0003] CN112892547A discloses a catalyst and preparation method for simultaneously removing nitrogen oxides and carbon monoxide. The catalyst is a supported catalyst, using γ-Al2O3 as a carrier and oxides of Mn, Cu, and Ce as active components. The metal salts of Mn, Cu, and Ce are made into a mixed salt solution according to a certain ratio, and the metal precursors are uniformly loaded on the surface of the γ-Al2O3 carrier under ultrasonic assistance, and then dried and calcined to obtain the supported catalyst. The catalyst has excellent NH3-SCR and CO oxidation performance under medium and low temperature conditions, and can simultaneously achieve the efficient removal of NO x and CO. This invention only realizes the co-removal of NO x and CO, and does not consider the secondary pollution caused by excessive injection of NH3.

[0004] CN117654543A discloses a preparation method for a catalyst for low-temperature selective catalytic oxidation of escaped ammonia. The catalyst contains noble metal elements and transition metal oxides, where the noble metal elements include but are not limited to one or two or more of gold, silver, platinum, palladium, etc., and their loading amount is 0.1%-10%. The transition metals include copper and iron, and their mass ratio is 1:5-5:1. This invention only solves the problem of low-concentration NH3 escape during the NH3-SCR denitration process, and does not achieve the co-removal of CO.

[0005] In view of the deficiencies of the prior art, there is an urgent need to provide a method for co-purifying various pollutants such as industrial flue gas NO x NH3, and CO. Summary of the Invention

[0006] The object of the present invention is to provide an NH3-SCR denitration system and method for co-purifying CO. Based on the difference in the oxidation reaction mechanisms of NH3 and CO, a core-shell catalyst is designed to achieve the co-oxidation of NH3 and CO, and the heat released by the co-oxidation of NH3 / CO is used to increase the temperature of the flue gas at the inlet of NH3-SCR, thereby improving the denitration efficiency. Through functional integration, the present invention significantly reduces the energy consumption of the denitration system and realizes the co-purification of multiple pollutants such as NO x , NH3, and CO in industrial flue gas to solve the problems existing in the above-mentioned prior art.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] One of the technical solutions of the present invention: Provide an NH3 / CO co-oxidation catalyst, and the NH3 / CO co-oxidation catalyst is a core-shell catalyst;

[0009] The core-shell catalyst has an NH3 oxidation catalyst as the core layer structure and a CO oxidation catalyst as the shell layer structure.

[0010] Further, the core layer structure includes redox sites and acidic sites; the shell layer structure includes redox sites.

[0011] Optionally, the redox sites in the core layer structure include Pt δ+ ions and / or Ag δ+ ions, and the acidic sites include at least one of W δ+ ions, Mo δ+ ions, and Nb δ+ ions; the redox sites in the shell layer structure include at least one of Cu δ+ ions, Co δ+ ions, Mn δ+ ions, and Fe δ+ ions.

[0012] Optionally, the core layer is Pt / WO3, Pt / MoO3, Pt / Nb2O5, Ag / WO3, Ag / MoO3, or Ag / Nb2O5, and the shell layer is CuO x (x = 1, 1 / 2), CoO x (x = 1, 3 / 2, 4 / 3), MnO x (x = 3 / 2, 4 / 3, 2), or FeO x (x = 1, 3 / 2, 4 / 3).

[0013] In some specific embodiments, the diameter of the core-shell catalyst is 10-30 nm, the specific surface area is 200-400 m 2 / g, and the thickness of the shell layer structure is 2-5 nm.

[0014] The second technical solution of the present invention: Provide an NH3-SCR denitration system for co-purifying CO, and the NH3-SCR denitration system includes: a flue gas heat exchanger and a denitration reactor;

[0015] Among them, the denitration reactor includes an intake pipe arranged at the top, an outlet pipe arranged at the bottom, and sequentially arranged from top to bottom: an ammonia injection grid, an NH3-SCR catalyst fixed bed layer, and a fixed bed layer containing the above-mentioned NH3 / CO co-oxidation catalyst;

[0016] The flue gas heat exchanger is fixedly arranged around the intake pipe and the outlet pipe of the denitration reactor, and is used to collect the heat released by the reaction of the fixed bed layer of the NH3 / CO co-oxidation catalyst and transfer it to the intake pipe of the denitration reactor to increase the temperature of the flue gas;

[0017] The number of layers of the NH3-SCR catalyst fixed bed layer is two layers.

[0018] The third technical solution of the present invention: Provide an NH3-SCR denitration method for co-purifying CO, use the above-mentioned denitration system for denitration, and the steps include:

[0019] Industrial flue gas flows in from the intake pipe, mixes with NH3 supplied by the ammonia injection grid, and then flows through the NH3-SCR catalyst fixed bed layer, and NO x Selective catalytic reduction reaction occurs under the action of the NH3-SCR catalyst to obtain intermediate flue gas;

[0020] The intermediate flue gas flows through the fixed bed layer of the NH3 / CO co-oxidation catalyst, and CO oxidation reaction and NH3 oxidation reaction occur under the action of the NH3 / CO co-oxidation catalyst to obtain the discharged flue gas;

[0021] The discharged flue gas is discharged through the exhaust pipe, and the heat of the CO oxidation reaction and the NH3 oxidation reaction is collected by the flue gas heat exchanger and used to increase the temperature of the industrial flue gas flowing in from the intake pipe.

[0022] Further, the industrial flue gas includes NO x and CO.

[0023] Preferably, the concentration of NO x in the industrial flue gas is 200mg / Nm 3 ~500mg / Nm 3 , and the concentration of CO is 5000mg / Nm 3 ~15000mg / Nm 3 .

[0024] Further, the temperature of the industrial flue gas is 120~200°C.

[0025] Further, the space velocity of the industrial flue gas flowing through the fixed bed layer of the NH3-SCR catalyst is 3000 h -1 ~60000 h -1 .

[0026] Further, the NH3-SCR catalyst is a V-W / TiO2 catalyst.

[0027] Preferably, in the V-W / TiO2 catalyst, the V content is 0.3 wt.% to 0.5 wt.%, the W content is 1 wt.% to 5 wt.%, and the specific surface area of TiO2 is 150 - 250 m 2 / g.

[0028] Further, the ammonia injection amount of the ammonia injection grid is greater than the theoretical ammonia-nitrogen ratio of the NH3-SCR reaction, and preferably the ammonia-nitrogen ratio is 1 to 1.5.

[0029] Further, the transition flue gas includes CO and NH3.

[0030] Preferably, the concentration of CO in the transition flue gas is 5000 mg / Nm 3 ~15000 mg / Nm 3 , and the concentration of NH3 is 2.5 mg / Nm 3 ~50 mg / Nm 3 .

[0031] Further, the space velocity of the transition flue gas flowing through the fixed bed layer of the NH3 / CO co-oxidation catalyst is 50000 h -1 ~150000 h -1 .

[0032] In the present invention, the temperature of the discharged flue gas obtained after the CO oxidation reaction and the NH3 oxidation reaction of the transition flue gas can be increased by 30 - 70 °C compared with the temperature of the transition flue gas.

[0033] Technical solution four of the present invention: Provide an application of the above-mentioned NH3 / CO co-oxidation catalyst or the above-mentioned denitration system or the above-mentioned method in synergistically purifying NH3 and CO pollutants in industrial flue gas.

[0034] Further, the application of the above-mentioned NH3 / CO co-oxidation catalyst in synergistically purifying NH3 pollutants and CO pollutants in industrial flue gas specifically includes passing the transition flue gas containing NH3 pollutants and CO pollutants treated by the NH3-SCR catalyst through the NH3 / CO co-oxidation catalyst to carry out the CO oxidation reaction and the NH3 oxidation reaction, so as to achieve the efficient synergistic purification of multi-components such as industrial flue gas NO x , escaped NH3, and CO.

[0035] The present invention discloses the following technical effects:

[0036] Based on the difference in the reaction mechanisms of NH3 and CO oxidation, the present invention designs a core-shell catalyst. According to the objective fact that the Gibbs free energy of the CO oxidation reaction is lower than that of the NH3 oxidation reaction, the NH3 oxidation catalyst is placed in the core layer of the core-shell material, and the CO oxidation catalyst is placed in the shell layer of the core-shell material. By the exothermic oxidation of high-concentration CO, the flue gas temperature is increased to promote the occurrence of the NH3 oxidation reaction. At the same time, acidic sites are added to the core layer to promote the adsorption of NH3 on the catalyst surface. Making full use of the heat released by the co-oxidation reaction of NH3 / CO, the heat is transferred to the inlet flue gas of NH3-SCR through a flue gas heat exchanger, significantly reducing the energy consumption of the denitration system (the denitration system in the prior art needs to be supplemented with heat treatment, and the heat treatment will increase the carbon dioxide emissions) and the V content in the catalyst, while improving the denitration efficiency of NH3-SCR. The efficient removal of multiple pollutants is achieved, and the economic benefits are remarkable. Brief Description of the Drawings

[0037] The drawings forming a part of this application are used to provide a further understanding of this application. The schematic embodiments of this application and their descriptions are used to explain this application and do not constitute an improper limitation of this application. In the drawings:

[0038] Figure 1 It is a schematic diagram of the denitration system device of the present invention; wherein, 1 is a flue gas heat exchanger, 2 is an ammonia injection grid, 3 is a fixed bed layer of NH3-SCR catalyst, 4 is a fixed bed layer of NH3 / CO co-oxidation catalyst, 5 is a CO oxidation catalyst, 6 is an NH3 oxidation catalyst, 7 is an intake pipe, and 8 is an outlet pipe. Detailed Description of the Invention

[0039] The various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation embodiments of the present invention.

[0040] It should be understood that the terms used in the present invention are only for describing specific embodiments and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0041] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although this invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of this invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the said documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0042] Without departing from the scope or spirit of this invention, various improvements and changes can be made to the specific embodiments of the specification of this invention, which are obvious to those skilled in the art. Other embodiments obtained from the specification of this invention are obvious to those skilled in the art. The specification and examples of this invention are merely exemplary.

[0043] Regarding the use of "comprising", "including", "having", "containing", etc. in this article, they are all open-ended terms, meaning including but not limited to.

[0044] Figure 1 It is a schematic structural diagram of the denitration system of this invention; wherein, 1 is a flue gas heat exchanger, 2 is an ammonia injection grid, 3 is a fixed bed layer of NH3-SCR catalyst, 4 is a fixed bed layer of NH3 / CO co-oxidation catalyst, 5 is a CO oxidation catalyst, 6 is an NH3 oxidation catalyst, 7 is an intake pipe, and 8 is an outlet pipe.

[0045] The NO in the industrial flue gas used in the specific embodiment of this invention x has a concentration of 400 mg / Nm 3 , and the CO has a concentration of 10000 mg / Nm 3 .

[0046] The NH3 / CO co-oxidation catalyst used in the specific embodiment of this invention has a diameter of 20 nm, a specific surface area of 320 m 2 / g, and the shell structure thickness is controlled at about 4 nm.

[0047] Example 1

[0048] Using Figure 1 the denitration method of NH3-SCR for co-purifying NH3 and CO using the denitration system shown, the steps include:

[0049] Industrial flue gas (180 °C) flows through the fixed bed layer of NH3-SCR catalyst (20000 h -1 ) from the intake pipe, and NO occurs under the action of NH3 supplied by the ammonia injection grid (ammonia-nitrogen ratio is 1.5) xThe selective catalytic reduction reaction is carried out to obtain the transition flue gas (180 °C); the transition flue gas flows through the fixed bed layer of the NH3 / CO co-oxidation catalyst (60000 h -1 ), and the CO oxidation reaction occurs under the action of the shell structure of the NH3 / CO co-oxidation catalyst, and the NH3 oxidation reaction occurs under the action of the core structure to obtain the discharged flue gas (230 °C); the discharged flue gas passes through the flue gas heat exchanger to transfer the heat to the industrial flue gas in the NH3-SCR intake pipeline.

[0050] Among them, the number of layers of the NH3-SCR catalyst fixed bed is two; 0.5 wt.% V-1 wt.% W / TiO2 catalyst (other existing NH3-SCR catalysts can also achieve the technical purpose of the present invention) is used as the NH3-SCR catalyst, and the specific surface area of TiO2 is between 150 and 250 m 2 / g; Ag / WO3@CuO x (x = 1 and / or 1 / 2) catalyst is used as the NH3 / CO co-oxidation catalyst.

[0051] It should be particularly noted that when x is 1 or 1 / 2 or the two forms coexist, the technical effects are basically the same (the same applies to the following x values).

[0052] In this example, the preparation method or commercial purchase route of the 0.5 wt.% V-1 wt.% W / TiO2 catalyst is not limited and does not affect the realization of the technical effect. The following is one of the conventional preparation methods. The steps are as follows: Preparation of 0.5 wt.% V-1 wt.% W / TiO2 catalyst by impregnation method: Stir in an aqueous solution at room temperature for more than 1 h, after rotary evaporation and drying, place it in a muffle furnace and calcine at 400 °C for 4 h to obtain the 0.5 wt.% V-1 wt.% W / TiO2 catalyst. Among them, TiO2 is P25, purchased from Sigma; the WO3 precursor is ammonium metatungstate; the V2O5 precursor is ammonium metavanadate; the raw material ratio is formulated according to the loading amount.

[0053] The Ag / WO3@CuO x (x = 1 and / or 1 / 2) catalyst (wherein, Ag is 1 wt%, WO3 is 3 wt%) in this example has the following preparation steps:

[0054] S1. Using carbon spheres (CSs) as a template, Ag / WO3 is loaded on the surface of nano-CSs by impregnation method. Among them, the Ag precursor is silver nitrate, and the WO3 precursor is ammonium metatungstate. At room temperature, stir CSs in an aqueous solution of silver nitrate and ammonium metatungstate (the molar ratio of silver nitrate to ammonium metatungstate is 1:16.75) for more than 1 h. After rotary evaporation and drying, place it in a muffle furnace and calcine at 500 °C for 4 h to remove the CSs template to obtain Ag / WO3;

[0055] CSs were obtained by hydrothermal method: Dissolve sucrose (0.06 mol, 20 g) in distilled water (400 mL), stir evenly, then transfer the sucrose solution to a 500 mL capacity sealed polytetrafluoroethylene-lined autoclave (maintain at 200 °C for 5 h). After the reaction, naturally cool to room temperature, centrifuge to collect the brown product, wash it several times with ethanol and distilled water, and dry it at 60 °C for 12 h to obtain CSs;

[0056] S2. CuO was supported on the surface of Ag / WO3 by impregnation method x (x = 1 and / or 1 / 2), where the precursor of CuO x (x = 1 and / or 1 / 2) is copper nitrate. Stir Ag / WO3 in an aqueous solution of copper nitrate at room temperature for more than 1 h. After rotary evaporation and drying, place it in a muffle furnace and calcine at 400 °C for 4 h to obtain Ag / WO3@CuO x (x = 1 and / or 1 / 2) catalyst.

[0057] In the flue gas discharged, NO x emission concentration ≈ 40 mg / Nm 3 , CO emission concentration ≈ 2500 mg / Nm 3 , NH3 emission concentration ≈ 2 mg / Nm 3 .

[0058] Example 2

[0059] Compared with Example 1, the only difference is that Ag / WO3@CuO x (x = 1, 1 / 2) catalyst was adjusted to Pt / WO3@CuO x (x = 1 and / or 1 / 2) catalyst.

[0060] Pt / WO3@CuO in this example x (x = 1 and / or 1 / 2) The preparation steps are as follows:

[0061] Compared with the preparation method of Ag / WO3@CuO x (x = 1 and / or 1 / 2) in Example 1, the only difference is that silver nitrate was replaced with chloroplatinic acid.

[0062] In the flue gas discharged, NO x emission concentration ≈ 50 mg / Nm 3 , CO emission concentration ≈ 2000 mg / Nm 3 , NH3 emission concentration ≈ 1.5 mg / Nm 3 .

[0063] Example 3

[0064] Compared with Example 1, the only difference is that Ag / WO3@CuOx (x = 1 and / or 1 / 2) The catalyst was adjusted to Ag / WO3@CoO x (x = 1, and / or 3 / 2, and / or 4 / 3) The catalyst (in the preparation method, copper nitrate was replaced with cobalt nitrate).

[0065] In the flue gas discharged, NO x Emission concentration ≈ 40 mg / Nm 3 , CO emission concentration ≈ 3500 mg / Nm 3 , NH3 emission concentration ≈ 2 mg / Nm 3 .

[0066] Comparative Example 1

[0067] Compared with Example 1, the difference is only that the fixed bed layer of the NH3 / CO co-oxidation catalyst was replaced with the fixed bed layer of the NH3-SCR catalyst.

[0068] In the flue gas discharged, NO x Emission concentration ≈ 50 mg / Nm 3 , CO emission concentration ≈ 10000 mg / Nm 3 , NH3 emission concentration ≈ 20 mg / Nm 3 .

[0069] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. For the same or similar parts among the embodiments, reference can be made to each other.

[0070] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An NH3-SCR denitration method for synergistically purifying CO, characterized in that the steps Comprising: Industrial flue gas flows in from the intake pipe, mixes with NH3 supplied by the ammonia injection grid, and then flows through the fixed bed layer of the NH3-SCR catalyst. Under the action of the NH3-SCR catalyst, the NO x selective catalytic reduction reaction occurs to obtain the transition flue gas; The transitional flue gas flows through the fixed bed layer of the NH3 / CO co-oxidation catalyst, and the CO oxidation reaction and the NH3 oxidation reaction occur under the action of the NH3 / CO co-oxidation catalyst to obtain the discharged flue gas; The discharged flue gas is discharged through the exhaust pipe, and the heat exchanger for flue gas is used to collect the heat of the CO oxidation reaction and the NH3 oxidation reaction and is used to increase the temperature of the industrial flue gas flowing in from the intake pipe; The NH3 / CO co-oxidation catalyst is a core-shell catalyst, with the NH3 oxidation catalyst as the core layer structure and the CO oxidation catalyst as the shell layer structure; the diameter of the core-shell catalyst is 10-30 nm, the specific surface area is 200-400 m 2 / g, and the thickness of the shell layer structure is 2-5 nm; The redox sites of the core layer structure include Pt δ+ ions and / or Ag δ+ ions, and the acidic sites include at least one of W δ+ ions, Mo δ+ ions, and Nb δ+ ions; the redox sites of the shell layer structure include at least one of Cu δ+ ions, Co δ+ ions, Mn δ+ ions, and Fe δ+ ions.

2. The method according to claim 1, characterized in that, The industrial flue gas includes NO x and CO, with a temperature of 120 to 200 °C; and / or The space velocity of the industrial flue gas flowing through the fixed bed of the NH3-SCR catalyst is 3000 h -1 ~60000 h -1 ; and / or The ammonia injection amount of the ammonia injection grid is greater than the theoretical ammonia-nitrogen ratio of the NH3-SCR reaction.

3. The method according to claim 1, characterized in that The transitional flue gas comprises CO and NH3; and / or The space velocity of the described transitional flue gas flowing through the fixed bed layer of the NH3 / CO co-oxidation catalyst is 50,000 h -1 ~150,000 h -1 .

4. The method according to claim 1, wherein The NH3-SCR catalyst is a V-W / TiO2 catalyst; and / or The V content in the V-W / TiO2 catalyst is 0.3 wt.% to 0.5 wt.%, the W content is 1 wt.% to 5 wt.%, and the specific surface area of TiO2 is 150 to 250 m 2 / g.

5. An NH3-SCR denitration system for synergistically purifying CO for the method according to any one of claims 1-4, characterized in that, The NH3-SCR denitration system comprises: a flue gas heat exchanger and a denitration reactor; Wherein, the denitration reactor comprises an intake pipe arranged at the top, an outlet pipe arranged at the bottom, and successively arranged from top to bottom: an ammonia injection grid, a fixed bed layer of the NH3-SCR catalyst, and a fixed bed layer of the NH3 / CO co-oxidation catalyst; The flue gas heat exchanger is fixedly arranged around the intake pipe and the outlet pipe of the denitration reactor, and is used to collect the heat released by the reaction of the fixed bed layer of the NH3 / CO co-oxidation catalyst and transfer it to the intake pipe of the denitration reactor to increase the flue gas temperature; The number of layers of the fixed bed layer of the NH3-SCR catalyst is two.

6. Application of the NH3-SCR denitration system according to claim 5 or the NH3-SCR denitration method according to any one of claims 1 to 4 in co-purifying NH3 pollutants and CO pollutants in industrial flue gas.

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