Method for removing nitrogen oxides

Abstract

The invention belongs to the technical field of air pollution prevention and control, and particularly relates to a method for removing nitrogen oxides. The coal ash is used for constructing a heterogeneous Fenton-like advanced oxidation system for wet denitration, the coal ash contains metal elements such as iron, aluminum and titanium, and metal or metal oxide in the coal ash is used as a catalyst for activating hydrogen peroxide to generate free radicals, so that the catalytic activity of hydrogen peroxide is improved. Hydroxyl free radicals, superoxide free radicals and other reactive oxygen substances generated by activating hydrogen peroxide through the synergistic effect of the metal elements have super-strong oxidation capacity, nitric oxide can be oxidized into water-soluble nitric oxide and converted into nitrate and nitrite ions, and therefore the removal efficiency of the nitric oxide is improved, the removal effect is good, and the method is suitable for industrial production. Secondary pollution is avoided, and the product is clean. And moreover, the fly ash can catalyze hydrogen peroxide to generate free radicals at room temperature, the reaction condition is mild, a good denitration effect is realized under a low-temperature condition, the cost is low, and the problem of reutilization of fly ash solid wastes is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of air pollution prevention and control, and particularly relates to a method for removing nitrogen oxides. Background Art

[0002] Nitrogen oxides (NO x ) as a main component in industrial flue gas, are one of the main causes of acid rain and photochemical smog, and are also important precursor substances for the formation of particulate matter in the air. In order to remove nitrogen oxides from flue gas, the current mainstream treatment technologies are mainly dry removal technologies (SCR and SNCR technologies).

[0003] Although the dry removal technology is widely used and solves the problem of nitrogen oxide removal to a certain extent, the mainstream dry technologies generally have the problem of low removal efficiency for nitrogen oxides in low-temperature flue gas (below 120°C), and the defect of poor removal timeliness can no longer meet the increasingly rich scenarios of nitrogen oxide removal. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for removing nitrogen oxides, and the method provided by the present invention can "treat waste with waste" and efficiently remove nitrogen oxides from low-temperature flue gas.

[0005] In order to achieve the above purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a method for removing nitrogen oxides, comprising the following steps:

[0007] Mix fly ash, water, hydrogen peroxide and NO x flue gas for the first time to carry out a denitrification reaction; the fly ash includes iron oxide, aluminum oxide and titanium oxide.

[0008] Preferably, the temperature of the denitrification reaction is 25-65°C, and the pH value is 9-12; the denitrification reaction is carried out under stirring conditions.

[0009] Preferably, the mass ratio of the fly ash to water is 1:100-200.

[0010] Preferably, the molar mass ratio of the hydrogen peroxide to water is (0.5-3) mol: 1 kg.

[0011] Preferably, the NO x concentration of the NO in the flue gas x is 300-400 ppm.

[0012] Preferably, the pressure of the NO x flue gas is atmospheric pressure; the flow rate of the NO x flue gas is 200-400 mL / min.

[0013] Preferably, the iron oxide content of the fly ash is 12-30 wt%, the aluminum oxide content is 25-40 wt%, and the titanium oxide content is 2-5 wt%.

[0014] Preferably, the particle size of the fly ash is below 150 μm.

[0015] Preferably, the first mixing is as follows: mixing the fly ash with water to obtain a denitrification slurry, mixing the desulfurization slurry with hydrogen peroxide to obtain a treatment liquid, and then introducing NO x flue gas.

[0016] Preferably, after the first mixing, adjusting the pH value of the obtained mixing system is further included.

[0017] The present invention provides a method for removing nitrogen oxides. The present invention uses fly ash to construct a heterogeneous Fenton-like advanced oxidation system for wet denitrification. The fly ash contains metal elements such as iron, aluminum, and titanium. The present invention uses the metals or metal oxides in the fly ash as catalysts for activating hydrogen peroxide to generate free radicals. The active oxygen substances such as hydroxyl radicals and superoxide radicals generated by activating hydrogen peroxide through the synergistic effect of these metal elements have super strong oxidation ability, can oxidize nitric oxide into nitrogen oxides that are easily soluble in water, and are converted into nitrate and nitrite ions, thereby improving the removal efficiency of nitrogen oxides in low-temperature flue gas, having good removal effect, no secondary pollution, and clean products.

[0018] The results of the examples show that after reacting for 300 min by the method of the present invention, the removal efficiency of nitrogen oxides in low-temperature flue gas is still above 49%, and even reaches 74.2%, reaching a relatively high treatment level, and achieving the goal of "treating waste with waste". Moreover, the generation of free radicals by fly ash catalyzing hydrogen peroxide can be carried out at room temperature, the reaction conditions are mild, good denitrification effect can be achieved under low-temperature conditions, the operation is simple, the catalyst is easily obtained, the cost is low, and the problem of reusing fly ash solid waste is solved. Description of the Drawings

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0020] Figure 1 It is a relationship diagram of denitrification efficiency and time for Examples 1-3;

[0021] Figure 2 It is a relationship diagram of denitrification efficiency and time for Examples 4-6;

[0022] Figure 3 XRD patterns of fly ash after pretreatment in Examples 1 - 6. Detailed implementation manners

[0023] The present invention provides a method for removing nitrogen oxides, comprising the following steps:

[0024] Mix fly ash, water, hydrogen peroxide and NO x in the first flue gas for denitrification reaction; the fly ash includes iron oxide, aluminum oxide and titanium oxide.

[0025] In the present invention, the iron oxide content of the fly ash can be 12 - 30 wt%, specifically 12.23 wt%, 15 wt%, 20 wt% or 25 wt%; the occurrence form of the iron oxide is Fe 2 O 3 .

[0026] In the present invention, the aluminum oxide content of the fly ash can be 25 - 40 wt%, specifically 25.53 wt%, 30 wt%, 35 wt% or 40 wt%; the occurrence form of the aluminum oxide is Al 2 O 3 .

[0027] In the present invention, the titanium oxide content of the fly ash can be 2 - 5 wt%, specifically 2 wt%, 2.5 wt%, 3.0 wt%, 3.5 wt%, 3.89 wt%, 4.5 wt% or 5.0 wt%; the occurrence form of the titanium oxide is TiO 2 .

[0028] In the present invention, the particle size of the fly ash can be below 150 μm, specifically 150 μm, 135 μm, 124 μm, 105 μm, 90 μm, 70 μm, 50 μm or 30 μm.

[0029] In the present invention, the fly ash is preferably pretreated before use; the pretreatment is preferably: crushing the fly ash and then sieving it. By pretreatment in the present invention, impurities in the fly ash are removed.

[0030] In the present invention, the water is preferably deionized water.

[0031] In the present invention, the mass ratio of the fly ash to the water can be 1:100 - 200, specifically 1:105, 1:120, 1:135, 1:150, 1:160, 1:180 or 1:195.

[0032] In the present invention, the concentration of the hydrogen peroxide can be 30 wt%.

[0033] In the present invention, the molar mass ratio of the hydrogen peroxide to water can be (0.5 - 3) mol: 1 kg, specifically, it can be 0.6 mol: 1 kg, 0.8 mol: 1 kg, 1 mol: 1 kg, 1.5 mol: 1 kg, 2 mol: 1 kg, 2.5 mol: 1 kg or 2.8 mol: 1 kg.

[0034] In the present invention, the NO x in the flue gas (flue gas containing nitrogen oxides) x concentration can be 300 - 400 ppm, specifically, it can be 310 ppm, 320 ppm, 340 ppm, 360 ppm, 380 ppm or 395 ppm.

[0035] In the present invention, the pressure of the NO x flue gas is preferably atmospheric pressure; the flow rate of the NO x flue gas can be 200 - 400 mL / min, specifically, it can be 210 mL / min, 230 mL / min, 260 mL / min, 280 mL / min, 300 mL / min, 330 mL / min, 350 mL / min, 375 mL / min or 395 mL / min.

[0036] In an embodiment of the present invention, the NO x flue gas is preferably a mixture of oxygen, nitric oxide and nitrogen; the content of the oxygen can be 9.5 - 10.5 vol%, the concentration of the nitric oxide can be 300 - 400 ppm, and the balance is nitrogen.

[0037] In the present invention, the first mixing preferably includes Method 1 and Method 2; Method 1 is preferably: mixing the fly ash with water to obtain a denitrification slurry, keeping it warm for standby, mixing the desulfurization slurry with hydrogen peroxide to obtain a treatment liquid, and then introducing NO x flue gas into the treatment liquid.

[0038] In the present invention, Method 2 is preferably: mixing the fly ash with water to obtain a denitrification slurry, keeping it warm for standby, introducing NO x flue gas into the desulfurization slurry, and then adding hydrogen peroxide to the desulfurization slurry for mixing.

[0039] In the present invention, the first mixing is preferably stirring mixing; the rotation speed of the stirring mixing can be 500 - 1500 r / min, specifically, it can be 700 r / min, 1000 r / min or 1300 r / min. By the above stirring mixing, the present invention prevents the catalyst from sinking to the bottom.

[0040] In the present invention, the heat preservation is preferably carried out under water bath conditions; the temperature of the heat preservation can be 45 °C, and the heat preservation time can be 10 min.

[0041] In the present invention, after the first mixing, it is preferably further included to adjust the pH value of the obtained mixed system; the target pH value for adjusting the pH value can be 9-12; the reagent used for adjusting the pH value preferably includes one or several of alkali and acid; the alkali preferably includes one or two of sodium hydroxide and potassium hydroxide; the acid is preferably hydrochloric acid. By adjusting the pH value to the target range in the present invention, the decomposition efficiency of hydrogen peroxide can be improved, thereby further improving the removal efficiency of nitrogen oxides.

[0042] In the present invention, the temperature of the denitrification reaction can be 25-65 °C, specifically 35 °C, 45 °C or 55 °C, the pH value can be 9-12, specifically 10.5 or 11.5; the denitrification reaction can be carried out under stirring conditions; the rotation speed of the stirring can be 1000 r / min.

[0043] In order to further illustrate the present invention, the solutions of the present invention will be described in detail below with reference to the drawings and embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0044] Example 1

[0045] The fly ash is crushed and screened through a 100-mesh sieve to remove the impurities therein, and the pretreated fly ash with a particle size less than 150 μm is obtained. The XRF and XRD test results are shown in Table 1 and Figure 3 as shown. Weigh 1.0 g of the pretreated fly ash and mix it with 170 mL of water under stirring conditions at 1000 r / min to obtain a denitrification slurry. Put the denitrification slurry into a denitrification reactor and keep it warm for 10 min under a stirring speed of 1000 r / min and a 45 °C water bath condition. Adjust the total gas flow rate of the N 2 , O 2 , NO mixed gas to 300 mL / min, the NO concentration is 300 ppm, and the O 2 concentration is 10 vol%. Pass the adjusted mixed gas into the denitrification reactor, add hydrogen peroxide with a concentration of 30% to the denitrification reactor so that the hydrogen peroxide concentration in the denitrification slurry is 1.5 mol / L, adjust the pH value to 10.5 with sodium hydroxide with a concentration of 10 mol / L, and then collect the tail gas of the denitrification reactor and use a flue gas analyzer to measure the NO x content, and calculate the removal efficiency of nitrogen oxides. The results are shown in Figure 1 as shown. It can be seen from Figure 1 that after 300 min of reaction, the denitrification efficiency is still 50.8%.

[0046] Example 2

[0047] The fly ash was crushed and passed through a 100-mesh sieve to remove impurities therein, obtaining pretreated fly ash with a particle size less than 150 μm. The XRF and XRD test results are shown in Table 1 and Figure 3 as follows. Weigh 1.0 g of the pretreated fly ash and mix it with 170 mL of water under stirring conditions at 1000 r / min to obtain a denitrification slurry. Put the denitrification slurry into a denitrification reactor and keep it warm for 10 min under stirring speed of 1000 r / min and 45 °C water bath conditions. Adjust the total gas flow rate of the N 2 , O 2 , NO mixed gas to 300 mL / min, the NO concentration to 300 ppm, and the O 2 concentration to 10 vol%. Pass the adjusted mixed gas into the denitrification reactor, add 30% hydrogen peroxide to the denitrification reactor to make the hydrogen peroxide concentration in the denitrification slurry 1.5 mol / L, adjust the pH value to 11.0 with 10 mol / L sodium hydroxide, then collect the tail gas of the denitrification reactor, and use a flue gas analyzer to measure the NO x content therein, and calculate the denitrification efficiency of nitrogen oxides. The results are shown in Figure 1 as follows. It can be seen from Figure 1 that after reacting for 300 min, the denitrification efficiency is still 55.1%.

[0048] Example 3

[0049] The fly ash was crushed and passed through a 100-mesh sieve to remove impurities therein, obtaining pretreated fly ash with a particle size less than 150 μm. The XRF and XRD test results are shown in Table 1 and Figure 3 as follows. Weigh 1.0 g of the pretreated fly ash and mix it with 170 mL of water under stirring conditions at 1000 r / min to obtain a denitrification slurry. Put the denitrification slurry into a denitrification reactor and keep it warm for 10 min under stirring speed of 1000 r / min and 45 °C water bath conditions. Adjust the total gas flow rate of the N 2 , O 2 , NO mixed gas to 300 mL / min, the NO concentration to 300 ppm, and the O 2 concentration to 10 vol%. Pass the adjusted mixed gas into the denitrification reactor, add 30% hydrogen peroxide to the denitrification reactor to make the hydrogen peroxide concentration in the denitrification slurry 1.5 mol / L, adjust the pH value to 11.5 with 10 mol / L sodium hydroxide, then collect the tail gas of the denitrification reactor, and use a flue gas analyzer to measure the NO x content therein, and calculate the denitrification efficiency of nitrogen oxides. The results are shown in Figure 1 as follows. It can be seen from Figure 1It can be seen that after 300 min of reaction, the denitrification efficiency is still 74.2%.

[0050] Example 4

[0051] The fly ash was crushed and screened through a 100-mesh sieve to remove impurities therein, and the pretreated fly ash with a particle size less than 150 μm was obtained. The XRF and XRD test results are shown in Table 1 and Figure 3 as follows. 1.0 g of the pretreated fly ash was weighed and mixed with 180 mL of water under stirring conditions of 1000 r / min to obtain a denitrification slurry. The denitrification slurry was put into a denitrification reactor and kept warm for 10 min under stirring speed of 1000 r / min and 45 °C water bath conditions. Adjust the total gas flow rate of N 2 , O 2 , NO mixed gas to 300 mL / min, the NO concentration to 300 ppm, and the O 2 concentration to 10 vol%. The adjusted mixed gas was introduced into the denitrification reactor, and 30% hydrogen peroxide was added to the denitrification reactor to make the hydrogen peroxide concentration in the denitrification slurry 1.0 mol / L. The pH value was adjusted to 11.5 with 10 mol / L sodium hydroxide. Subsequently, the tail gas of the denitrification reactor was collected, and the NO x content therein was measured using a flue gas analyzer, and the denitrification efficiency of nitrogen oxides was calculated. The results are shown in Figure 2 as follows. It can be seen from Figure 2 that after 300 min of reaction, the denitrification efficiency is still 49.2%.

[0052] Example 5

[0053] The fly ash was crushed and screened through a 100-mesh sieve to remove impurities therein, and the pretreated fly ash with a particle size less than 150 μm was obtained. The XRF and XRD test results are shown in Table 1 and Figure 3 as follows. 1.0 g of the pretreated fly ash was weighed and mixed with 170 mL of water under stirring conditions of 1000 r / min to obtain a denitrification slurry. The denitrification slurry was put into a denitrification reactor and kept warm for 10 min under stirring speed of 1000 r / min and 45 °C water bath conditions. Adjust the total gas flow rate of N 2 , O 2 , NO mixed gas to 300 mL / min, the NO concentration to 300 ppm, and the O 2 concentration to 10 vol%. The adjusted mixed gas was introduced into the denitrification reactor, and 30% hydrogen peroxide was added to the denitrification reactor to make the hydrogen peroxide concentration in the denitrification slurry 1.5 mol / L. The pH value was adjusted to 11.5 with 10 mol / L sodium hydroxide. Subsequently, the tail gas of the denitrification reactor was collected, and the NOx content, calculate the removal efficiency of nitrogen oxides, and the results are as Figure 2 shown. According to Figure 2 it can be seen that after 300 min of reaction, the denitrification efficiency is still 72.2%.

[0054] Example 6

[0055] Crush the fly ash, sieve it through a 100-mesh sieve, remove the impurities therein, and obtain pretreated fly ash with a particle size less than 150 μm. The XRF and XRD test results are shown in Table 1 and Figure 3 shown. Weigh 1.0 g of the pretreated fly ash and mix it with 160 mL of water under stirring conditions of 1000 r / min to obtain a denitrification slurry. Put the denitrification slurry into a denitrification reactor and keep it warm for 10 min under stirring speed of 1000 r / min and 45 °C water bath conditions. Adjust the total gas flow rate of N 2 , O 2 , NO mixed gas to 300 mL / min, the NO concentration is 300 ppm, and the O 2 concentration is 10 vol%. Pass the adjusted mixed gas into the denitrification reactor, add hydrogen peroxide with a concentration of 30% to the denitrification reactor so that the hydrogen peroxide concentration in the denitrification slurry is 2.0 mol / L, adjust the pH value to 11.5 with sodium hydroxide with a concentration of 10 mol / L, then collect the tail gas of the denitrification reactor, and use a flue gas analyzer to measure the NO x content, calculate the removal efficiency of nitrogen oxides, and the results are as Figure 2 shown. According to Figure 2 it can be seen that after 300 min of reaction, the denitrification efficiency is still 71.1%.

[0056] Table 1 XRF data of pretreated fly ash in Examples 1 - 6

[0057] Substance <![CDATA[Al 2 O 3 > <![CDATA[SiO 2 > <![CDATA[P 2 O 5 > <![CDATA[SO 3 > <![CDATA[K 2 O]]> CaO <![CDATA[TiO 2 > Content (wt%) 25.5278 46.2552 0.4566 2.0855 2.1082 3.9493 3.8881 Substance MnO <![CDATA[Fe 2 O 3 > NiO CuO ZnO <![CDATA[Ga 2 O 3 > <![CDATA[As 2 O 3 > Content (wt%) 0.1096 12.2316 0.0181 0.0386 0.0239 0.0082 0.0088 Substance <![CDATA[SeO 2 > <![CDATA[Rb 2 O]]> SrO <![CDATA[Y 2 O 3 > <![CDATA[ZrO 2 > <![CDATA[Nb 2 O 5 > BaO Content (wt%) 0.0043 0.0095 0.1864 0.0109 0.0824 0.0114 0.1574

[0058] According to Table 1 and Figure 3 it can be seen that the pretreated fly ash contains Fe 2 O 3 component, and its content is 12.23 wt%; Al 2 O 3 component, and its content is 25.53 wt%; TiO 2The component has a content of 3.89 wt%. In the present invention, these three components in fly ash are used as catalysts for activating hydrogen peroxide to generate free radicals. The reactive oxygen species such as hydroxyl radicals and superoxide radicals generated by activating hydrogen peroxide through the synergistic action of these metal elements have extremely strong oxidation ability, can oxidize nitric oxide into nitrogen oxides that are easily soluble in water, and convert them into nitrate and nitrite ions, thereby improving the removal efficiency of nitrogen oxides. The removal effect is good, there is no secondary pollution, and the product is clean.

[0059] As can be seen from the above embodiments, the method for removing nitrogen oxides provided by the present invention uses fly ash as a heterogeneous Fenton-like catalyst for wet denitrification, which not only realizes the reuse of solid waste fly ash, but also does not produce secondary pollution during the denitrification process, and can obtain good nitrogen oxide removal efficiency in a low-temperature environment.

[0060] Although the above embodiments have made a detailed description of the present invention, they are only a part of the embodiments of the present invention, not all of them. Other embodiments can also be obtained based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for removing nitrogen oxides, characterized in that: The following steps are involved: Fly ash, water, hydrogen peroxide and NO x The flue gas is first mixed to perform a denitration reaction; the fly ash includes iron oxide, aluminum oxide and titanium oxide.

2. The method according to claim 1, characterized in that The temperature of the denitration reaction is 25-65° C., and the pH value is 9-12; the denitration reaction is carried out under stirring conditions.

3. The method according to claim 1, characterized in that The mass ratio of the fly ash to water is 1:100-200.

4. The method according to claim 1 or 3, characterized in that: The molar mass ratio of the hydrogen peroxide to water is (0.5-3) mol:1kg.

5. The method according to claim 1, characterized in that The NO x NO in flue gas x The concentration is 300-400ppm.

6. The method according to claim 1 or 5, characterized in that: The NO x The pressure of flue gas is atmospheric pressure; the NO x The flow rate of flue gas is 200~400mL / min.

7. The method according to claim 1 or 3, characterized in that: The fly ash has an iron oxide content of 12-30 wt %, an aluminum oxide content of 25-40 wt %, and a titanium oxide content of 2-5 wt %.

8. The method according to claim 1, characterized in that The particle size of the fly ash is less than 150 μm.

9. The method according to claim 1, characterized in that: The first mixing step is: mixing the fly ash with water to obtain a denitrification slurry, mixing the desulfurization slurry with hydrogen peroxide to obtain a treatment liquid, and then introducing NO into the treatment liquid. x Smoke.

10. The method according to claim 1 or 9, characterized in that: After the first mixing, the method further comprises adjusting the pH value of the obtained mixed system.

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