Method for removing nitrogen oxide, method for recovering carbon dioxide, and gas treatment apparatus

Abstract

To provide a novel method for efficiently removing nitrogen oxides from a gas mixture containing nitrogen oxides containing NO.SOLUTION: Disclosed is a method for removing nitrogen oxides comprising, in the following order: increasing a concentration of NO2 in a gas mixture containing nitrogen oxides containing NO; and bringing the gas mixture into contact with a treatment liquid containing water, thereby reducing a concentration of nitrogen oxides in the gas mixture. A method for recovering carbon dioxide from the gas mixture from which nitrogen oxides have been removed is also disclosed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for removing nitrogen oxides, a method for capturing carbon dioxide, and a gas treatment device. [Background technology]

[0002] In a process for recovering carbon dioxide from flue gas, the flue gas may be pretreated using a desulfurization device and a denitration device in order to remove acidic gases in advance (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-244454 Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure relates to a novel method for efficiently removing nitrogen oxides, including NO (nitric oxide), from a gas mixture containing nitrogen oxides. [Means for solving the problem]

[0005] The present disclosure includes the following: [1] Increasing the concentration of NO2 in a gas mixture containing nitrogen oxides including NO; contacting the gas mixture with a treatment liquid comprising water, thereby reducing the concentration of nitrogen oxides in the gas mixture; in this order, Methods for removing nitrogen oxides. [2] The method according to [1], wherein the concentration of NO2 in the mixed gas is increased by controlling the time from when the mixed gas is generated until when the mixed gas comes into contact with the treatment liquid. [3] The method according to [1], wherein the mixed gas is an exhaust gas discharged from a calcination furnace, and the concentration of NO2 in the mixed gas is increased by controlling the time from when the mixed gas is discharged from the calcination furnace to when the mixed gas comes into contact with the treatment liquid. [4] The method according to [3], wherein the concentration of NO2 in the mixed gas is increased by controlling the time from when the mixed gas is discharged from the calcination furnace until when the mixed gas comes into contact with the treatment liquid to 10 minutes or more. [5] The method according to [2], further comprising contacting a part or all of the mixed gas after contact with the treatment liquid with the treatment liquid again. [6] The method according to any one of [1] to [5], wherein the treatment liquid is water. [7] The method according to any one of [1] to [6], wherein the mixed gas further contains oxygen. [8] The method according to any one of [1] to [7], wherein the concentration of nitrogen oxides in the mixed gas is 10 ppm by volume or more and 500 ppm by volume or less, based on the volume of the mixed gas. [9] The method according to any one of [1] to [8], wherein the concentration of NO2 in the mixed gas is increased until the ratio of the concentration of NO2 to the concentration of nitrogen oxides becomes 0.3 or more.

[10] Reducing the concentration of nitrogen oxides in a mixed gas containing carbon dioxide and nitrogen oxides including NO by the method described in [1] to [9]; recovering carbon dioxide from the mixed gas; in this order, How to capture carbon dioxide.

[11] a gas flow path through which a mixed gas containing nitrogen oxides including NO flows; a gas-liquid contact section that brings a water-containing treatment liquid into contact with the mixed gas; Equipped with The gas processing device, wherein the gas flow path is configured to increase the concentration of NO2 in the mixed gas.

[12] the mixed gas further comprises carbon dioxide; The gas treatment device further includes a carbon dioxide recovery unit that recovers carbon dioxide from the mixed gas after contact with the treatment liquid.

[11] The gas treatment device according to

[11] . [Effects of the Invention]

[0006] Nitrogen oxides including NO can be efficiently removed from a mixed gas containing nitrogen oxides. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic diagram showing an example of a gas treatment device and a calcination device. [Figure 2] 1 is a schematic diagram showing an example of a gas treatment device and a calcination device. [Figure 3] FIG. 1 is a schematic diagram showing an apparatus for testing removal of nitrogen oxides from a mixed gas. DETAILED DESCRIPTION OF THE INVENTION

[0008] The present invention is not limited to the following examples.

[0009] FIG. 1 is a schematic diagram showing an example of a gas treatment device for recovering carbon dioxide and a calcination device connected to the gas treatment device. The calcination device 100 shown in FIG. 1 is an example of an apparatus for producing cement clinker by calcining cement raw materials. The calcination device 100 includes a calcination section 30 for calcining the cement raw materials, a rotary kiln 40 for calcining the cement raw materials, a cooling section 45 for cooling the cement clinker formed in the rotary kiln 40, and a raw material mill 50 for accommodating the cement raw materials. The rotary kiln 40 includes a cylindrical calcination furnace 41 having a calcination chamber 41A and a burner 42 disposed at one end of the calcination furnace 41. The calcination section 30 is connected to the end of the calcination furnace 41 opposite the burner 42. The cement clinker formed in the calcination chamber 41A is discharged as a product via a cooling section 45 connected to the end of the calcination furnace 41 on the burner 42 side.

[0010] The calcination section 30 includes four cyclones C1, C2, C3, and C4, a calciner 32, a rising duct 34, a raw material charging chute 36, a charging section 37, and a discharge section 38. The cyclones C1, C2, C3, and C4, and the calciner 12 are arranged vertically in a staggered order from top to bottom. The rising duct 34 is connected to the bottom of the calciner 32 and is connected to the bottom of the firing furnace 41. The raw material charging chute 36 extends from the lowest cyclone C4 to the inside of the bottom of the firing furnace 41. The charging section 37 is located between the topmost cyclone C1 and the cyclone C2 below it. The discharge section 38 is located above the topmost cyclone C1.

[0011] The charging section 37 is connected to the raw material mill 50 by piping 61. The discharge section 38 is connected to the raw material mill 50 by piping 62. A silo 51 may be provided between the charging section 37 and the raw material mill 50. The cement raw material in the raw material mill 50 is introduced into the calcination section 30 from the charging section 37 via the piping 61 and the silo 51. The silo 51 is configured to temporarily store the granular cement raw material from the raw material mill 50. The silo 51 is configured to timely supply the granular cement raw material to the charging section 37. The introduced cement raw material flows through the calcination section 30 generally in the order of cyclone C1, cyclone C2, cyclone C3, calciner 32, and cyclone C4, and then is introduced into the firing chamber 41A through the raw material charging chute 36.

[0012] The cement raw materials are burned in the burning chamber 41A to form cement clinker. The exhaust gas generated during the burning process is usually composed of carbon dioxide and nitrogen oxides (NO X ) and oxygen. Nitrogen oxides may further include NO2 and the like. The exhaust gas is discharged from the calciner mainly toward the rising duct 34 of the calciner section 30. The exhaust gas that flows into the rising duct 34 flows through the calciner section 30, generally via the calciner 32, cyclone C4, cyclone C3, cyclone C2, and cyclone C1, in that order, and is then discharged from the discharge section 38. The exhaust gas discharged from the discharge section 38 flows through piping 62 to the raw material mill 50. Carbon dioxide is recovered by the gas treatment device 200 from some or all of the mixed gas, which is the exhaust gas discharged from the raw material mill 50 toward piping 63 connected to the raw material mill 50. A dust collector 52 may be provided between the raw material mill 50 and the gas treatment device 200. The dust collector 52 is configured to separate powder or granular materials (powders or particles) contained in the mixed gas (exhaust gas) from the gas. The dust collector 52 may be, for example, an electrostatic precipitator or a bag filter.

[0013] The gas treatment device 200 is mainly composed of a pipe 64 constituting a gas flow path 70 through which the mixed gas flows, a gas-liquid contact unit 1, a carbon dioxide capture unit 2, and a pipe 66 connecting the gas-liquid contact unit 1 and the carbon dioxide capture unit 2. The gas-liquid contact unit 1 is a device for bringing a treatment liquid containing water into contact with the mixed gas. After contacting the treatment liquid, the mixed gas is introduced through the pipe 66 into the carbon dioxide capture unit 2, where the carbon dioxide is captured.

[0014] In the gas treatment device 200, the gas flow path 70 upstream of the gas-liquid contactor 1 is configured to increase the concentration of NO2 in the mixed gas. The concentration of NO2 in a mixed gas containing carbon dioxide and NO tends to increase over time as NO2 is generated by oxidation of NO. NO is poorly soluble in water, whereas NO2 is soluble in water. Therefore, when the proportion of NO2 in nitrogen oxides is high, the nitrogen oxides are more likely to be efficiently removed by a treatment liquid containing water. When the mixed gas contains oxygen, NO is more likely to be oxidized, and the concentration of NO2 is more likely to increase over time.

[0015] In order to increase the concentration of NO2 in the mixed gas, for example, the time from when the mixed gas is generated in the calciner 41 until when it comes into contact with the treatment liquid in the gas-liquid contact section 1 (hereinafter sometimes referred to as "residence time") can be controlled. Typically, the NO2 concentration can be increased by extending the residence time. A long residence time for increasing the NO2 concentration can be ensured, for example, by controlling the length of the gas flow path 70, the gas flow rate in the gas flow path 70, or a combination of these. The long gas flow path 70 can be formed, for example, by a long pipe. A gas flow path in which the mixed gas circulates through part of the pipe multiple times may be formed.

[0016] The residence time for increasing the NO concentration may be, for example, 5 minutes or more, 10 minutes or more, 15 minutes or more, 20 minutes or more, 25 minutes or more, or 30 minutes or more. The residence time for increasing the NO concentration may be, for example, 90 minutes or less, or 60 minutes or less. The residence time here refers to the time required for the mixed gas (exhaust gas) to flow from the time the mixed gas (exhaust gas) is discharged to the outside of the calciner 41 until it first comes into contact with the treatment liquid in the gas-liquid contact section 1. In the example of FIG. 1, the residence time refers to the time required for the mixed gas (exhaust gas) to flow from the time the mixed gas (exhaust gas) flows into the rising duct 34 until it first comes into contact with the treatment liquid in the gas-liquid contact section 1. The residence time may be calculated based on the gas flow rate, the volume of the flow path through which the mixed gas flows, and the like. In the case of exhaust gas generated in equipment other than a kiln for burning cement clinker as shown in Figure 1, the residence time can also be considered to be the time from when the exhaust gas (mixed gas) is discharged outside the equipment until the mixed gas first comes into contact with the treatment liquid.

[0017] FIG. 2 is a schematic diagram showing another example of a gas treatment device for recovering carbon dioxide and a calcination device connected to the gas treatment device. The gas treatment device 200 shown in FIG. 2 differs from the gas treatment device of FIG. 1 in that it includes a circulation pipe 65 connecting the gas-liquid contact section 1 with a pipe 63 located upstream of the gas-liquid contact section 1. A gas flow path 70 through which the mixed gas circulates is formed by the pipes 64 and 65 and a portion of the pipe 63 connected to the raw material mill 50 or the dust collector 52. By allowing some or all of the mixed gas after contact with the treatment liquid in the gas-liquid contact section 1 to flow into the pipe 65, the mixed gas after contact with the treatment liquid can be contacted again with the treatment liquid. As a result, a substantially long residence time that leads to an increase in the NO2 concentration can be ensured.

[0018] The treatment liquid provided in the gas-liquid contact section 1 can be water or an aqueous solution. Because CO2 is difficult to dissolve in water, using a treatment liquid containing water can efficiently remove nitrogen oxides while maintaining a high concentration of carbon dioxide in the mixed gas. In this disclosure, the term "water" is used to include not only pure water but also ordinary water (e.g., tap water or industrial water) containing unavoidable trace amounts of impurities. The proportion of water in the treatment liquid may be, for example, 95% by mass or more, 96% by mass or more, 97% by mass or more, 98% by mass or more, 99% by mass or more, 99.9% by mass or more, or 99.99% by mass or more, based on the mass of the treatment liquid, or 100% by mass or less. The treatment liquid may also be an alkaline aqueous solution containing a base. Examples of bases that can be contained in the treatment liquid include sodium carbonate, sodium bicarbonate, and sodium hydroxide.

[0019] The concentration of nitrogen oxides in the mixed gas decreases upon contact with the treatment liquid. However, it is not necessary to remove all of the nitrogen oxides in the mixed gas. The nitrogen oxide removal rate, which is the proportion of nitrogen oxides removed in the gas-liquid contact section 1 to the nitrogen oxides in the mixed gas at the time of generation or discharge from the calciner, may be, for example, 5.0% by volume or more, 10% by volume or more, or 100% by volume or less, 90% by volume or less, 80% by volume or less, 70% by volume or less, 60% by volume or less, or 50% by volume or less.

[0020] The temperature of the treatment liquid that comes into contact with the mixed gas in the gas-liquid contact section 1 may be, for example, 10°C or higher and 60°C or lower. The temperature of the mixed gas introduced into the gas-liquid contact section 1 may be, for example, 20°C or higher and 50°C or lower.

[0021] The gas-liquid contact section 1 can be any treatment device capable of contacting a gas with a liquid. For example, the gas-liquid contact section 1 can be a wet scrubber comprising a treatment tower provided with a gas inlet and a gas outlet, and a treatment liquid disposed in the treatment tower.

[0022] The ratio (space velocity) of the flow rate (mL / h) of the mixed gas introduced into the gas-liquid contact section 1 to the volume (mL) of the treatment liquid is, for example, 50 h -1 More than 250h -1 It may be the following:

[0023] The nitrogen oxide concentration in the mixed gas may be 10 ppm by volume or more, 50 ppm by volume or more, 100 ppm by volume or more, 150 ppm by volume or more, or 200 ppm by volume or more, or 500 ppm by volume or less, based on the volume of the mixed gas. The nitrogen oxide concentration in the mixed gas at the time of being discharged from the calcination furnace may be within these ranges. However, the nitrogen oxide concentration is the concentration of the total amount of nitrogen oxides including NO and NO2, and often does not substantially change with an increase in the NO2 concentration.

[0024] The NO2 concentration in the mixed gas (initial mixed gas) when discharged from the calcination furnace may be 0 ppm by volume or more and 50 ppm by volume or less, based on the volume of the mixed gas. The NO2 concentration in the mixed gas when first contacted with the treatment liquid may be higher than the NO2 concentration in the initial mixed gas and may be 0 ppm by volume or more and 150 ppm by volume or less, based on the volume of the mixed gas. In the mixed gas (initial mixed gas) when discharged from the calcination furnace, X The ratio of the concentration of NO2 to the concentration of NO2 (NO2 / NO X ) may be 0 or more and 0.2 or less. In the mixed gas at the time of first contact with the treatment liquid, NO X The ratio of the concentration of NO2 to the concentration of NO2 (NO2 / NO X ) may be 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, or may be 1.0 or less.

[0025] According to the method of the present disclosure, a relatively high carbon dioxide concentration can be maintained in the intermediate mixed gas that is contacted with the treatment liquid and then introduced into the carbon dioxide capture unit 2. For example, the carbon dioxide concentration in the mixed gas that is contacted with the treatment liquid and before being introduced into the carbon dioxide capture unit 2 can be 8.0 vol% or more, 9.0 vol% or more, 10 vol% or more, 11 vol% or more, 12 vol% or more, 13 vol% or more, 14 vol% or more, or 15 vol% or more, based on the volume of the mixed gas. There is no particular upper limit to the carbon dioxide concentration in the mixed gas, but it is, for example, about 25 vol%.

[0026] The carbon dioxide capture unit 2 is not particularly limited and can be a normal device capable of capturing carbon dioxide from a mixed gas. For example, the carbon dioxide capture unit 2 may be a device provided with an absorption liquid that absorbs carbon dioxide. In the carbon dioxide capture unit 2, carbon dioxide can be efficiently obtained by capturing carbon dioxide from a mixed gas containing carbon dioxide at a relatively high concentration. Removal of nitrogen oxides in advance can suppress deterioration of the carbon dioxide capture unit 2 and contribute to stable carbon dioxide capture.

[0027] (Verification test 1) Exhaust gas (NO) emitted from a rotary kiln in a cement factory X A mixture of nitrogen oxides (NOx, NO ... X The ratio of the NO2 concentration to the NO2 concentration (volume ratio, NO2 / NO X ) is also shown.

[0028] [Table 1]

[0029] (Verification test 2) Using the test apparatus shown in Fig. 3, a test for removing nitrogen oxides from a mixed gas G0 containing carbon dioxide and nitrogen oxides was conducted in an environment of approximately 25°C. The test apparatus shown in Fig. 3 has a gas-liquid contact section 1 containing a treatment liquid 10, and traps 21A and 21B provided upstream and downstream of the gas-liquid contact section 1, respectively. Trap 21A is provided mainly to prevent backflow. Trap 21B is provided mainly to dehumidify the mixed gas G1 after contact with the treatment liquid 10. A pump 22 and a flow meter 23 are provided downstream of trap 21B.

[0030] In the gas-liquid contact section 1, 200 mL of water was placed in a container 15 as the treatment liquid 10. As the mixed gas G0, flue gas 1 or flue gas 2 discharged from a rotary kiln in a cement factory and further dehumidified was introduced into the treatment liquid 10 via a trap 21A. The nitrogen oxide concentrations were 180.0 ppm by volume in flue gas 1 and 215.6 ppm by volume in flue gas 2. The mixed gas G0 was passed through a flow rate of 0.5 L / min and a space velocity of 150 h -1 The mixed gas G1 was introduced into the treatment liquid 10 for 20 minutes under the above conditions. The total amount of the introduced mixed gas G0 was 10 L. After contact with the treatment liquid 10, the mixed gas G1 was collected in the gas pack 24A. Furthermore, the mixed gas G0 was collected directly into the gas pack 24B via the flow meter 23 without contacting with the treatment liquid 10.

[0031] After being collected in gas pack 24B, mixed gas G0 was collected for exhaust gas 1 after 10 minutes, 30 minutes, 60 minutes, 120 minutes, or 240 minutes, and mixed gas G0 was collected for exhaust gas 2 after 10 minutes, 30 minutes, 60 minutes, or 90 minutes, and was introduced into treatment liquid 10 under the same conditions as the factory exhaust gas before being collected in gas pack 24B for the first time. Each mixed gas G1 after contact with treatment liquid 10 was collected in gas pack 24A.

[0032] Nitrogen oxides (NO) in the mixed gas collected in Gas Pack 24A or 24B XThe concentration of NO in the mixed gas after treatment collected in Gas Pack 24A was measured. X and NO concentration in the untreated mixed gas immediately after collection in Gas Pack 24B. X The NO concentration is the percentage of nitrogen oxides removed from the untreated gas mixture. X The removal rate was calculated, and the results are shown in Table 2. When exhaust gas discharged from a rotary kiln in a cement factory and further dehumidified was brought into contact with treatment liquid 10 under the same conditions as above, the NOx removal rate was essentially 0%.

[0033] [Table 2]

[0034] The results of Verification Test 1 and Verification Test 2 confirmed that the NO2 concentration increases by increasing the residence time of the mixed gas (exhaust gas), and that nitrogen oxides can be efficiently removed by contacting the mixed gas with an increased NO2 concentration with the treatment liquid. [Explanation of symbols]

[0035] 1...gas-liquid contact section, 2...carbon dioxide recovery section, 10...treated liquid, 15...container, 21A, 21B...trap, 22...pump, 23...flow meter, 24A, 24B...gas pack, 30...calcination section, 32...calciner furnace, 34...rising duct, 36...raw material charging chute, 37...charging section, 38...discharge section, 40...rotary kiln, 41...firing furnace, 41A...firing chamber, 42...burner, 45...cooling section, 50...raw material mill, 61, 62, 63, 64, 65, 66...piping, C1, C2, C3, C4...cyclone, G0...mixed gas (untreated), G1...mixed gas (after contact with treated liquid), 100...firing device, 200...gas treatment device.

Claims

1. NO in a mixed gas containing nitrogen oxides including NO ２ Increasing the concentration of contacting the gas mixture with a treatment liquid comprising water, thereby reducing the concentration of nitrogen oxides in the gas mixture; in this order, Methods for removing nitrogen oxides.

2. By controlling the time from when the mixed gas is generated until when it comes into contact with the treatment liquid, the NO in the mixed gas can be reduced. ２ The method of claim 1 , wherein the concentration of

3. The mixed gas is an exhaust gas discharged from a calcination furnace, and by controlling the time from when the mixed gas is discharged from the calcination furnace to when the mixed gas comes into contact with the treatment liquid, NO in the mixed gas is ２ The method of claim 1 , wherein the concentration of

4. By controlling the time from when the mixed gas is discharged from the calcination furnace until when it comes into contact with the treatment liquid to 10 minutes or more, the NOx content in the mixed gas is reduced. ２ The method of claim 3, wherein the concentration of

5. The method of claim 2 , further comprising contacting a part or all of the mixed gas with the processing liquid again after contacting the mixed gas with the processing liquid.

6. The method of claim 1 wherein the treatment liquid is water.

7. The method of claim 1 , wherein the gas mixture further comprises oxygen.

8. 2. The method of claim 1, wherein the concentration of nitrogen oxides in the mixed gas is 10 ppm by volume or more and 500 ppm by volume or less, based on the volume of the mixed gas.

9. NOx relative to nitrogen oxide concentration ２ The NO concentration in the mixed gas is 0.3 or more. ２ The method of claim 1 , wherein the concentration of

10. 10. The method of claim 1, comprising: reducing a concentration of nitrogen oxides in a gas mixture containing carbon dioxide and nitrogen oxides including NO; recovering carbon dioxide from the mixed gas; in this order, How to capture carbon dioxide.

11. a gas flow path through which a mixed gas containing nitrogen oxides including NO flows; a gas-liquid contact section that brings a water-containing treatment liquid into contact with the mixed gas; Equipped with The gas flow path is configured to ２ wherein the gas treatment device is configured to increase the concentration of

12. the mixed gas further comprises carbon dioxide; The gas treatment device further includes a carbon dioxide recovery unit that recovers carbon dioxide from the mixed gas after contact with the treatment liquid. The gas treatment device of claim 11 .

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