A method for denitrifying flue gas

Abstract

The present invention relates to a method for denitrifying flue gas, which method comprises: S1, bringing a catalyst into contact with flue gas containing O2 and NO x at 100-280°C to conduct an oxidation reaction, oxidizing NO in the flue gas into NO2 to obtain oxidized flue gas; S2, bringing the oxidized flue gas into contact with an absorption liquid for oxidation absorption, the absorption liquid containing hydrogen peroxide and nitric acid; wherein, the catalyst contains nano-composite material particles with a core-shell structure, the nano-composite material particles comprise a nickel oxide core and a graphitized carbon shell coated on the outer surface of the nickel oxide core, and based on the total weight of the nano-composite material particles, the carbon content of the nano-composite material particles is not more than 5% by weight. The method of the present invention can effectively reduce the temperature of denitrification treatment on the premise of ensuring the denitrification effect.

Description

Technical Field

[0001] The invention relates to a flue gas denitrification method. Background Art

[0002] The reduction method is mainly used as the industrial flue gas denitrification technology in China, and almost all of them use SCR, SNCR and SCR-SNCR combined technology. This technology uses catalysis or high temperature to reduce NO in flue gas. x Reducing nitrogen to non-toxic and harmless nitrogen and emitting it into the atmosphere is currently the most widely studied commercial denitrification technology with the most mature catalysts. Theoretically, this technology does not produce other by-products, is environmentally friendly, and is suitable for large-scale flue gas emission treatment.

[0003] The existing technology has the following problems: high initial investment and maintenance costs, flue gas volume, NO x Factors such as concentration changes can easily lead to excessive ammonia injection, causing ammonia escape and secondary pollution. x The nitrogen in the flue gas is a potential important resource, which cannot be recycled in the denitrification process of this technology. Faced with the worsening environmental problems and increasingly stringent environmental protection standards, a future-oriented resource recovery and efficient flue gas denitrification industrial technology is needed, and researchers are gradually shifting their attention to the oxidation absorption denitrification method. Summary of the invention

[0004] The object of the present invention is to provide a method for flue gas denitration, which has low denitration temperature and high denitration efficiency.

[0005] In order to achieve the above object, the present invention provides a method for flue gas denitrification, the method comprising:

[0006] S1, make the catalyst contain O2 and NO x The flue gas is contacted with the flue gas at 100-280° C. to carry out a catalytic oxidation reaction, oxidizing NO in the flue gas into NO2, thereby obtaining oxidized flue gas;

[0007] S2, contacting the oxidized flue gas with an absorption liquid for oxidation absorption, wherein the absorption liquid contains hydrogen peroxide and nitric acid;

[0008] The catalyst contains nanocomposite particles with a core-shell structure, wherein the nanocomposite particles include a nickel oxide core and a graphitized carbon shell coated on the outer surface of the nickel oxide core. The carbon content of the nanocomposite particles is not more than 5% by weight based on the total weight of the nanocomposite particles.

[0009] Optionally, the volume space velocity is 1000-5000h -1 , the temperature of the catalytic oxidation reaction is 150-280°C.

[0010] Optionally, the content of O2 in the flue gas is 5-20% by volume, and the content of NO in the NO x is greater than 80% by volume.

[0011] Optionally, the absorption liquid is an aqueous solution containing nitric acid and hydrogen peroxide. The concentration of nitric acid is 5-20% by volume, and the concentration of hydrogen peroxide is 0.5-5% by volume.

[0012] Optionally, the oxidation degree of NO in the oxidized flue gas x is 45-65%.

[0013] Optionally, the liquid-gas volume ratio of the absorption liquid to the oxidized flue gas is (0.02-1):1.

[0014] Optionally, based on the total weight of the nanocomposite particles, the carbon content of the nanocomposite particles is 0.5-2% by weight.

[0015] Optionally, the weight ratio of the carbon element content determined by X-ray photoelectron spectroscopy to the carbon element content determined by elemental analysis in the nanocomposite particles is 10 or more;

[0016] In the Raman spectrum of the nanocomposite particles, the peak intensity of the G peak near 1580 cm -1 is greater than the peak intensity of the D peak near 1320 cm -1 by a ratio greater than 2;

[0017] The average particle size of the nanocomposite particles is 1-100 nm.

[0018] Optionally, in step S1, the catalytic oxidation reaction is carried out in a catalytic oxidation reactor, and the catalytic oxidation reactor is selected from a radial adiabatic fixed-bed reactor, an axial adiabatic fixed-bed reactor, or a shell-and-tube fixed-bed reactor.

[0019] Optionally, in step S2, the oxidized flue gas and the absorption liquid are brought into countercurrent contact in an oxidation absorption tower for the oxidation absorption;

[0020] Preferably, the oxidized flue gas is introduced from the bottom of the oxidation absorption tower, and the absorption liquid is introduced from the top of the oxidation absorption tower.

[0021] Through the above technical solution, the method of the present invention uses a catalyst containing nanocomposite particles to carry out denitrification treatment on the flue gas, which can effectively reduce the temperature of the denitrification treatment, and has a high denitrification efficiency. An absorption liquid is used to carry out oxidation absorption treatment on the oxidized flue gas obtained by denitrification, avoiding environmental pollution.

[0022] Other features and advantages of the present invention will be described in detail in the subsequent specific implementation part. Brief Description of the Drawings

[0023] The drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention, but do not limit the present invention. In the drawings:

[0024] Figure 1 It is a schematic structural diagram of a specific embodiment of the system adopted by the flue gas denitrification method of the present invention.

[0025] Description of Reference Numerals

[0026] 1. First pipeline; 2. Catalytic oxidation reactor; 3. Second pipeline

[0027] 4. Oxidation absorption tower; 5. Spraying device; 6. Liquid storage tank

[0028] 7. Centrifugal pump; 8. Third pipeline Specific Embodiments

[0029] The following detailed description of the specific embodiments of the present invention is provided with reference to the drawings. It should be understood that the specific embodiments described herein are only for explaining and illustrating the present invention and are not used to limit the present invention.

[0030] In the first aspect of the present invention, a method for denitrifying flue gas is provided. The method includes: S1. Contacting a catalyst with flue gas containing O2 and NO x at 100 - 280°C for a catalytic oxidation reaction to oxidize NO in the flue gas to NO2, obtaining oxidized flue gas; S2. Contacting the oxidized flue gas with an absorption liquid for oxidation absorption, the absorption liquid containing hydrogen peroxide and nitric acid; wherein, the catalyst contains nano-composite material particles with a core-shell structure, the nano-composite material particles include a nickel oxide core and a graphitized carbon shell coated on the outer surface of the nickel oxide core, and based on the total weight of the nano-composite material particles, the carbon content of the nano-composite material particles is not more than 5% by weight.

[0031] The method of the present invention can perform denitrification treatment on any flue gas containing nitrogen oxides, such as industrial flue gas, automobile exhaust gas, etc. Compared with the single denitrification means using gas-phase selective reduction technology or wet denitrification technology, in the method of the present invention, a catalyst containing nano-composite particles with a core-shell structure is brought into contact with the flue gas for oxidative denitrification reaction, and absorption is combined with an absorption liquid containing hydrogen peroxide and nitric acid. It can effectively reduce the temperature of the denitrification reaction and further reduce the energy consumption of the system on the premise of ensuring the denitrification effect (the denitrification efficiency can reach more than 90%). Moreover, it avoids the problems of high equipment cost, complex structure, secondary pollution, and difficult product recovery in gas-phase selective reduction technology or wet denitrification technology, and is an efficient and environmentally friendly technology for controlling air pollutants.

[0032] In a specific embodiment of the present invention, the catalyst is nano-composite particles with a core-shell structure.

[0033] In a specific embodiment of the present invention, the space velocity can vary within a relatively large range, for example, it can be 1000 - 5000 h -1 , preferably 3000 - 4000 h -1 , and the temperature of the catalytic oxidation reaction is 150 - 280 °C. Among them, the space velocity refers to the ratio of the volume of the raw material entering the reactor per hour to the volume of the catalyst in the reactor.

[0034] In the method of the present invention, the catalytic oxidation reaction is carried out by utilizing the residual oxygen in the flue gas without additional oxygen supplementation. In one embodiment, the content of O2 in the flue gas can be 5 - 20 vol%, and the content of NO in the NO x is greater than 80 vol%.

[0035] In a preferred embodiment of the present invention, the absorption liquid is an aqueous solution containing nitric acid and hydrogen peroxide. The concentration of nitric acid in the aqueous solution can vary within a relatively large range, for example, it can be 5 - 20 vol%, preferably 10 - 15 vol%, and the concentration of hydrogen peroxide is 0.5 - 5 vol%, preferably 1 - 2 vol%. Among them, nitric acid plays a role in increasing the solubility of NO, improving the gas-liquid mass transfer efficiency, and at the same time as a product is generated, the concentration of nitric acid continuously rises; hydrogen peroxide is continuously consumed as an oxidant and the concentration decreases. By detecting the concentration of the aqueous solution containing nitric acid and hydrogen peroxide, when the concentration of hydrogen peroxide is low and the concentration of nitric acid is high, for example, the concentration of hydrogen peroxide is 0.02 - 0.1 vol% and the concentration of nitric acid is 15 - 25 vol%, by discharging the absorption liquid and supplementing H2O2 and H2O, the recovery of HNO3 is achieved and the above aqueous solution can be continuously used for denitrification operation. When the above aqueous solution containing nitric acid and hydrogen peroxide is used to oxidatively absorb the oxidized flue gas, nitrogen oxides can be further converted to obtain nitric acid that can be reused, realizing the recovery of nitrogen elements.

[0036] In one embodiment of the present invention, NO in the oxidized flue gas x has an oxidation degree of 45-65%, preferably 50-55%. When the oxidation degree of NO in the oxidation oxygen x is within the above range, it is beneficial to promote more sufficient contact between NO and NO2 therein with the absorption liquid for the oxidation absorption process and generate nitric acid without generating other by-products. The oxidation degree refers to the molar ratio of NO2 in the main components NO and NO2 of NO in the oxidized flue gas. The higher the proportion of NO2, the x higher the oxidation degree of NO. x

[0037] According to the present invention, the liquid-gas volume ratio of the absorption liquid to the oxidized flue gas can be (0.02-1):1, preferably (0.05-0.1):1.

[0038] According to the present invention, based on the total weight of the nanocomposite particles, the carbon content of the nanocomposite particles is 0.5-2% by weight, preferably 0.5-1% by weight. The carbon content of the nanocomposite particles in this application is measured by elemental quantitative analysis using an elemental analyzer.

[0039] In a specific embodiment of this application, the weight ratio of the carbon element content determined by X-ray photoelectron spectroscopy to the carbon element content determined by elemental analysis in the nanocomposite particles is 10 or more, preferably 20-50, more preferably 30-50. The carbon element content determined by X-ray photoelectron spectroscopy refers to the relative content of carbon element on the material surface measured by elemental quantitative analysis using an X-ray photoelectron spectrometer as an analysis tool. The carbon element content determined by elemental analysis refers to the relative content of the total carbon element of the material measured by elemental quantitative analysis using an elemental analyzer as an analysis tool. When the ratio of the carbon element determined by X-ray photoelectron spectroscopy to the carbon element content determined by elemental analysis is larger, it indicates that most of the carbon in the entire nanocomposite particles is concentrated on the material surface, forming a carbon shell, and thus forming the aforementioned core-shell structure.

[0040] In one embodiment of the present invention, in the Raman spectrum of the nanocomposite particles used in the present invention, the ratio of the intensity of the G peak near 1580 cm -1 to the intensity of the D peak near 1320 cm -1 is greater than 2. Those skilled in the art know that both the D peak and the G peak are Raman characteristic peaks of the C atom crystal. The D peak represents the defect of the C atom lattice, and the G peak represents the C atom Sp 2Hybrid in-plane stretching vibration. It can be understood that the larger the ratio of the intensity of the G peak to the intensity of the D peak, the more graphitic carbon exists in the nanoparticles of the nanocomposite compared to amorphous carbon. That is to say, the carbon element in the nanoparticles of the nanocomposite of the present invention mainly exists in the form of graphitic carbon. This graphitic carbon has better antioxidant properties and can synergistically increase the catalytic activity with the nickel oxide nanoparticles in the core, thereby improving the performance of the entire composite material.

[0041] In a specific embodiment of the present invention, the nanoparticles of the nanocomposite are spherical or quasi-spherical, and the average particle size of the nanoparticles of the nanocomposite can be 1-100 nm, preferably 2-40 nm.

[0042] In a specific embodiment of the present invention, in step S1, the catalytic oxidation reaction is carried out in a catalytic oxidation reactor. The present invention does not limit the specific type of the catalytic oxidation reactor. For example, the catalytic oxidation reactor can be a fixed bed reactor, such as a radial adiabatic fixed bed reactor, an axial adiabatic fixed bed reactor or a shell and tube fixed bed reactor, preferably an axial adiabatic fixed bed reactor.

[0043] In a specific embodiment of the present invention, in step S2, the oxidized flue gas and the absorption liquid are brought into countercurrent contact in an oxidation absorption tower for the oxidation absorption; preferably, the oxidized flue gas is introduced from the bottom of the oxidation absorption tower, and the absorption liquid is introduced from the top of the oxidation absorption tower. More preferably, in order to make the absorption liquid and the oxidized flue gas fully contact, a spraying device for spraying the absorption liquid is further provided at the top of the oxidation absorption tower. The oxidation absorption tower is well-known to those skilled in the art, and the present invention does not make specific limitations thereto. For example, it can be a spray tower, a packed tower, a bubble column or a plate tower. As Figure 1 shown, in a preferred specific embodiment of the present invention, the method for denitrifying flue gas includes: sending the flue gas through a first pipeline 1 into a catalytic oxidation reactor 2 to contact with a catalyst at 150-250 °C for a catalytic oxidation reaction to oxidize NO in the flue gas into NO2, sending the oxidized flue gas obtained from the catalytic oxidation reaction through a second pipeline 3 into the oxidation absorption tower 4 from the bottom air inlet, spraying the absorption liquid downward from the spraying device 5 at the top of the oxidation absorption tower 4 to contact with the oxidized flue gas for oxidation absorption to remove nitrogen oxides in the flue gas, discharging the tail gas from the top air outlet through a third pipeline 8, returning the absorption liquid after oxidation absorption to the storage tank 6, and at least part of the absorption liquid after oxidation absorption is transported to the top of the tower for circulating spraying by a centrifugal pump 7. Among them, the absorption liquid after oxidation absorption can be separated and recovered according to the concentration change. The catalyst contains nanoparticles of a core-shell structure nanocomposite, and the nanoparticles of the nanocomposite include a nickel oxide core and a graphitized carbon shell coated on the outer surface of the nickel oxide core. Based on the total weight of the nanoparticles of the nanocomposite, the carbon content of the nanoparticles of the nanocomposite is not more than 5% by weight.

[0044] The present invention will be further described below through embodiments, but the present invention is not limited thereby.

[0045] The flue gas is simulated industrial flue gas, in which the content of NO is 0.08% by volume, the content of O2 is 5% by volume, the content of NO2 is 0.004% by volume, and the balance is N2.

[0046] The denitrification rate in the flue gas is calculated by the following formula:

[0047] In the following embodiments, the following nano-composite particles are used as catalysts respectively. The composition and parameter characteristics of the nano-catalytic particles used in each embodiment are shown in Table 1.

[0048] Among them, the elements on the surface of the nano-composite particles are detected by an X-ray photoelectron spectroscopy analyzer (XPS). The X-ray photoelectron spectroscopy analyzer used is an ESCALab220i-XL type ray electron energy spectrometer produced by VG Scientifc company and equipped with Avantage V5.926 software. The X-ray photoelectron spectroscopy analysis test conditions are: the excitation source is monochromatic A1Ka X-ray, the power is 330W, and the base vacuum during the analysis test is 3×10 -9 mbar.

[0049] The analysis of carbon (C) element is carried out on an Elementar Micro Cube element analyzer, which is mainly used for the analysis of four elements: carbon (C), hydrogen (H), oxygen (O), and nitrogen (N). The specific operation methods and conditions are as follows: The sample is weighed 1mg - 2mg in a tin cup, put into the automatic sampler, and enters the combustion tube through a ball valve for combustion. The combustion temperature is 1000°C (in order to remove the atmospheric interference during sampling, nitrogen purge is used). Then, the gas after combustion is reduced by reducing copper to form nitrogen, carbon dioxide and water. The mixed gas is separated by three desorption columns and detected by a TCD detector in turn. The analysis of oxygen element is carried out by high-temperature decomposition. Under the action of a carbon catalyst, the oxygen in the sample is converted into CO, and then CO is detected by TCD. Since the nano-composite particles used in the present invention only contain carbon and metal oxides, the total content of metal oxides can be known from the content of carbon element.

[0050] The Raman detection of the present invention uses a LabRAM HR UV-NIR type laser confocal Raman spectrometer produced by HORIBA company of Japan, and the laser wavelength is 325nm.

[0051] Table 1

[0052]

[0053] Example 1

[0054] In this embodiment, the nano-composite particle A1 is used as the catalyst.

[0055] S1. Place 10 g of the catalyst in a continuous flow fixed-bed reactor, and feed the flue gas into the fixed-bed reactor at 280 °C to contact with the catalyst for catalytic oxidation reaction to obtain oxidized flue gas; wherein, the space velocity is 2000 h -1 , and the oxidation degree of NO x in the oxidized flue gas is 55%.

[0056] S2. Feed the oxidized flue gas into the oxidation absorption tower from the bottom air inlet, and make it contact countercurrently with the absorption liquid fed from the top of the tower for oxidation absorption; the liquid-gas volume ratio of the absorption liquid to the oxidized flue gas is 0.1:1, and the absorption liquid is an aqueous solution containing nitric acid and hydrogen peroxide, wherein the content of nitric acid is 12 vol% and the content of hydrogen peroxide is 1 vol%. The denitrification rate of the flue gas is 90%.

[0057] Example 2

[0058] The same method as in Example 1 is used for denitrification of flue gas, except that in step S1, the flue gas is contacted with the catalyst for catalytic oxidation reaction at 100 °C, and the oxidation degree of NO x in the oxidized flue gas is 45%. The denitrification rate of the flue gas is 85%.

[0059] Example 3

[0060] The same method as in Example 1 is used for denitrification of flue gas, except that in step S1, the space velocity is 6000 h -1 , and the oxidation degree of NO x in the oxidized flue gas is 40%. The denitrification rate of the flue gas is 80%.

[0061] Example 4

[0062] The same method as in Example 1 is used for denitrification of flue gas, except that in step S2, the liquid-gas volume ratio of the absorption liquid to the oxidized flue gas is 0.02:1. The denitrification rate of the flue gas is 78%.

[0063] Example 5

[0064] The same method as in Example 1 is used for denitrification of flue gas, except that the nano-composite particle A2 is used as the catalyst. The denitrification rate of the flue gas is 80%.

[0065] Example 6

[0066] The same method as in Example 1 is used for denitrification of flue gas, except that the nano-composite particle A3 is used as the catalyst. The denitrification rate of the flue gas is 75%.

[0067] Comparative Example 1

[0068] 10 g of NiO / Al2O3 catalyst was placed in a continuous flow fixed-bed reactor. The flue gas was sent into the fixed-bed reactor at 300 °C to contact with the catalyst for catalytic oxidation reaction to obtain oxidized flue gas. Among them, the volume space velocity was 2000 h -1 , NO x The oxidation degree was 20%. The oxidized flue gas was sent into the oxidation absorption tower from the bottom inlet, and made to contact countercurrently with the absorption liquid sent from the top of the tower for oxidation absorption. The liquid-gas volume ratio of the absorption liquid to the oxidized flue gas was 0.1:1; the absorption liquid was 10 wt% NaOH aqueous solution, and the denitration rate of the flue gas was 80%.

[0069] Comparative Example 2

[0070] 10 g of NiO / Al2O3 catalyst was placed in a continuous flow fixed-bed reactor. The flue gas was sent into the fixed-bed reactor at 300 °C to contact with the catalyst for catalytic oxidation reaction to obtain oxidized flue gas. Among them, the volume space velocity was 2000 h -1 , NO x The oxidation degree was 20%. The oxidized flue gas was sent into the oxidation absorption tower from the bottom inlet, and made to contact countercurrently with the absorption liquid sent from the top of the tower for oxidation absorption. The liquid-gas volume ratio of the absorption liquid to the oxidized flue gas was 0.1:1. The absorption liquid was an aqueous solution containing nitric acid and hydrogen peroxide, where the content of nitric acid was 12 vol% and the content of hydrogen peroxide was 1 vol%. The denitration rate of the flue gas was 85%.

[0071] As can be seen from the above, the method of the present invention can effectively reduce the reaction temperature of flue gas denitration, and has a high denitration efficiency, and the denitration process is environmentally friendly and pollution-free.

[0072] The preferred embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0073] In addition, it should be noted that, among the various specific technical features described in the above specific embodiments, they can be combined in any appropriate manner without conflict. To avoid unnecessary repetition, the present invention will not describe various possible combination methods separately.

[0074] In addition, any combination can be made between various different embodiments of the present invention, as long as it does not violate the idea of the present invention, it should also be regarded as the content disclosed by the present invention.

Claims

1. A method for denitrifying flue gas, the method comprising: S1. Contact the catalyst with the flue gas containing O2 and NO x at 150 - 280 °C to carry out a catalytic oxidation reaction, oxidize NO in the flue gas to NO2, and obtain oxidized flue gas; The volumetric space velocity of the catalytic oxidation reaction is 1000 - 5000 h -1 ; The oxidation degree of NO x in the oxidation flue gas is 50 - 55%; S2. Making the oxidized flue gas contact with an absorption liquid for oxidative absorption; the liquid-gas volume ratio of the absorption liquid to the oxidized flue gas is (0.02 - 1):1; the absorption liquid is an aqueous solution containing nitric acid and hydrogen peroxide, the concentration of the nitric acid is 5 - 20% by volume, and the concentration of the hydrogen peroxide is 0.5 - 5% by volume; Wherein, the catalyst contains nano-composite material particles with a core-shell structure, the nano-composite material particles include a nickel oxide core and a graphitized carbon shell coated on the outer surface of the nickel oxide core. Based on the total weight of the nano-composite material particles, the carbon content of the nano-composite material particles is not more than 5% by weight; detecting the concentration of the aqueous solution containing nitric acid and hydrogen peroxide, when the concentration of hydrogen peroxide is 0.02 - 0.1% by volume and the concentration of nitric acid is 15 - 25% by volume, discharging the absorption liquid and supplementing H2O2 and H2O.

2. The method according to claim 1, wherein The content of O2 in the flue gas is 5 - 20% by volume, and the NO x content of NO in it is greater than 80% by volume.

3. The method according to claim 1, wherein Based on the total weight of the nano-composite material particles, the carbon content of the nano-composite material particles is 0.5 - 2% by weight.

4. The method according to claim 1, wherein The weight ratio of the carbon element content determined by X-ray photoelectron spectroscopy to the carbon element content determined by elemental analysis in the nano-composite material particles is 10 or more; In the Raman spectrum of the nanocomposite particles, the peak intensity ratio of the G peak near 1580 cm -1 to the peak intensity of the D peak near 1320 cm -1 is greater than 2; The average particle size of the nano-composite material particles is 1 - 100 nm.

5. The method according to claim 1, wherein In step S1, the catalytic oxidation reaction is carried out in a catalytic oxidation reactor, and the catalytic oxidation reactor is selected from a radial adiabatic fixed bed reactor, an axial adiabatic fixed bed reactor or a shell-and-tube fixed bed reactor.

6. The method according to claim 1, wherein In step S2, making the oxidized flue gas and the absorption liquid contact countercurrently in an oxidation absorption tower for the oxidative absorption.

7. The method according to claim 6, wherein, In step S2, introducing the oxidized flue gas from the bottom of the oxidation absorption tower and introducing the absorption liquid from the top of the oxidation absorption tower.

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