Device for reacting gas in liquid and method for processing nitrogen oxide

Abstract

To provide a processing method capable of efficiently processing NOx gas at low cost and recovering it as nitric acid, and a device suitably usable for gas reactions, including such a process.SOLUTION: Provided are a device for reacting a gas in a liquid, the device comprising a reaction vessel for containing the liquid, a stirring blade inserted into the reaction vessel, and a frame member provided substantially horizontally along the inner circumference of the side wall of the reaction vessel; and a method for processing nitrogen oxides using the device, the method producing nitric acid from nitrogen oxides and an oxidizing gas.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an apparatus for reacting a gas in a liquid and a method for treating nitrogen oxides. [Background technology]

[0002] Nitrogen oxides (NOx), such as nitric oxide and nitrogen dioxide, are produced, for example, by the combustion of petroleum fuels, and are also emitted from nitric acid wastewater discharged from various industries. NOx is harmful to living organisms, so it is necessary to remove it somehow. In addition, NOx (the nitric oxide in it) is oxidized, the nitrogen dioxide is dissolved in water, and recycled as nitric acid.

[0003] NOx produces nitrates when reacted with, for example, an aqueous solution of an alkali metal hydroxide. Therefore, by introducing the NOx into a gas scrubbing tower and spraying an aqueous solution of an alkali metal hydroxide inside the tower, the NOx can be recovered in water as nitrates.

[0004] For example, Patent Document 1 describes an exhaust purification device that suppresses the emission of unburned ammonia and nitrogen oxides generated when an internal combustion engine that uses ammonia as fuel is started, and proposes a catalyst that oxidizes and reduces the unburned ammonia and nitrogen oxides, and controlling the equivalence ratio of a mixture containing fuel and oxygen that is supplied to the internal combustion engine until the catalyst reaches a predetermined temperature.

[0005] Patent Document 2 describes a method for oxidizing waste materials such as biological materials by electrochemical treatment, and an apparatus and an electrochemical treatment system used therein. Claim 53 describes that in the apparatus, in order to vigorously stir the catholyte solution so as to oxidize nitrous acid and nitrogen oxides NOx, formation and bursting of microscopic bubbles induced by mechanical mixing or the like is provided, and air is introduced into the catholyte portion to promote the oxidation of nitrous acid and NOx.

[0006] And in Patent Document 3, NO XAs a method for denitrifying a gas to be treated that contains NO X is oxidized by ozone, and the remaining NO X It is also disclosed that ozone is added to an absorption liquid that absorbs and removes components. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2021-116802 A [Patent Document 2] Special Publication No. 2005-505398 [Patent Document 3] Patent No. 5963405 Summary of the Invention [Problem to be solved by the invention]

[0008] Since NOx is an acidic gas, it can be easily treated and recovered by using a basic solution such as an aqueous solution of an alkali metal hydroxide as the absorbing solution. However, the recovered material is in the form of a salt, and cannot be reused as nitric acid as it is. On the other hand, if pure water is used as the absorbing solution to treat NOx, the recovered material itself becomes nitric acid. However, NOx generally has low solubility in water. Therefore, when treating NOx in a scrubbing tower using water, a method of installing multiple scrubbing towers and spraying water multiple times can be considered. However, this method leads to increased equipment and operating costs.

[0009] The present invention has been made under the above circumstances, and aims to provide a processing method capable of processing NOx gas efficiently at low cost and recovering it as nitric acid, and an apparatus that can be suitably used for such processing and other gas reactions. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to solve the above problems. The inventors then conceived of an apparatus for reacting a gas in a liquid, comprising a reaction tank for containing a liquid, an agitator blade inserted into the reaction tank, and a frame member arranged in an approximately horizontal direction so as to follow the inner circumference of the side wall of the reaction tank, and thus completed the present invention.

[0011] That is, the present invention is as follows. The first invention is A reaction vessel for containing a liquid; A stirring blade inserted into the reaction vessel; A frame member provided in a substantially horizontal direction along the inner periphery of the side wall of the reaction vessel; a gas reacting device for reacting a gas in a liquid, comprising:

[0012] The second invention is The frame members are provided in a plurality at predetermined intervals in a substantially vertical direction, The stirring blade has a shaft portion that is inserted into the reaction vessel and extends in a substantially vertical direction, and a blade portion that extends in a substantially horizontal direction from the shaft portion toward an inner periphery of a side wall of the reaction vessel, This is the device described in the first invention, wherein the wing portion is disposed in a portion between any two adjacent frame members in a substantially vertical direction.

[0013] The third invention is The device according to the first or second aspect of the present invention, wherein the number of the frame members is 2 to 10.

[0014] The fourth invention is The apparatus according to any one of the first to third aspects of the present invention further comprises a plate member extending in a substantially vertical direction and disposed along the inner periphery of the side wall of the reaction tank.

[0015] The fifth invention is The apparatus according to any one of the first to fourth aspects of the present invention further comprises a gas inlet pipe opening in the reaction vessel.

[0016] The sixth invention is The reaction vessel has a substantially circular cross-sectional shape in a horizontal direction, In the device according to any one of the first to fifth aspects of the present invention, the frame member has a substantially horizontal cross-sectional shape that is annular along the inside of the circular outline.

[0017] The seventh invention is The device according to any one of the first to sixth aspects of the present invention is used for producing nitric acid from nitrogen oxides and an oxidizing gas in water.

[0018] The eighth invention is A method for treating nitrogen oxides, comprising the steps of: introducing nitrogen oxides and an oxidizing gas into the reaction tank of the apparatus according to the seventh invention, the reaction tank containing water as a liquid, while stirring the water with the stirring blade, to produce nitric acid.

[0019] The ninth invention is The apparatus according to the second or third aspect of the present invention is used, in which the reaction tank contains water as a liquid, This is a method for treating nitrogen oxides, in which nitric acid is produced by agitating the water in the reaction tank with the agitating blade while supplying nitrogen oxides and an oxidizing gas into the water.

[0020] The tenth invention is A ninth aspect of the present invention is a method for treating nitrogen oxides, wherein the water circulates within the region between two adjacent frame members by spreading from an approximately central portion in the approximately vertical and horizontal directions in the approximately vertical up-down directions and in the approximately horizontal directions, and then converging toward the approximately central portion.

[0021] The eleventh invention is The stirring power required by the stirring blade is 1500W / m 3 The above is the method for treating nitrogen oxides according to any one of the eighth to tenth aspects of the present invention. Effect of the Invention

[0022] According to the present invention, there is provided a processing method capable of processing NOx gas efficiently at low cost and recovering it as nitric acid, and an apparatus that can be suitably used for such processing and other gas reactions. [Brief description of the drawings]

[0023] [Figure 1] FIG. 2 is a schematic cross-sectional view of the inside of the device for reacting gases according to the present invention during operation. [Diagram 2] FIG. 2 is a plan view of an example of a wing portion used in the gas reaction device according to the present invention, the left side being a plan view and the right side being a side view. [Diagram 3] FIG. 2 is a perspective view of a multi-stage retention layer forming device used in Example 1 and Comparative Examples 1 to 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The configuration of the present invention will be described below in the following order: 1. An apparatus for reacting gases, 2. The operation of the apparatus for reacting gases, and 3. A method for treating nitrogen oxides (NOx).

[0025] 1. Apparatus for reacting gases An apparatus for reacting gases according to the present invention (hereinafter, may be referred to as "the apparatus of the present invention") will be described with reference to the drawings.

[0026] FIG. 1 is a schematic cross-sectional view of the inside of the apparatus 1 of the present invention when it is in operation, FIG. 2 is an example of a blade portion used in the apparatus for reacting gases according to the present invention, the left side being a plan view and the right side being a side view, and FIG. 3 is a perspective view of a multi-stage retention layer forming device used in the examples.

[0027] A multistage retention layer forming device shown in FIG. 3 is inserted into a reaction vessel 2, which is a cylindrical portion of the apparatus 1 of the present invention shown in FIG. 1. The reaction vessel 2 contains a liquid, and various reactions involving gas, which will be described later, are carried out inside the reaction vessel. The multistage retention layer forming device is equipped with a frame member 12, and when the multistage retention layer forming device is inserted into the reaction vessel 2, the frame member 12 fits exactly along the inner circumference of the side wall of the reaction vessel 2. The frame member 12 is formed in an approximately horizontal direction. The multistage "retention layer" will be described later.

[0028] The frame member 12 is typically a plate member having an opening in the center, through which liquid can be introduced into the reaction vessel 2 or an agitating blade can be inserted. The frame member 12 is provided in a substantially horizontal direction as described above. This "substantially horizontal direction" means that when the reaction vessel 2 is installed horizontally, if the opening of the frame member 12 is closed to form a single plate, the angle that the plate makes with the vertical direction is, for example, 85 to 95°.

[0029] From the viewpoint of uniformity and efficiency of the reaction carried out in the apparatus 1 of the present invention, the reaction tank 2 is preferably cylindrical, in which case the cross-sectional shape in the approximately horizontal direction of the reaction tank 2 is circular. In this case, the cross-sectional shape of the frame member 12 in the approximately horizontal direction is annular (donut-shaped) that fits within the circular outline of the cross-sectional shape of the reaction tank 2.

[0030] Moreover, a plurality of frame members 12 are typically provided at predetermined intervals in the substantially vertical direction. The size of the predetermined intervals is arbitrary and may be different from each other, but it is preferable that the intervals are substantially equal from the viewpoint of uniformity and efficiency of the reaction carried out in the apparatus 1 of the present invention. It is considered that the presence of the frame members 12 effectively forms a retention layer by reflux, which will be described later, and the time that gas remains in one retention layer is extended. The above-mentioned "substantially equal intervals" means that the coefficient of variation of the distance between adjacent frame members 12 is, for example, 0.2 or less.

[0031] The number of frame members 12 is not particularly limited, but is preferably 2 to 10, and more preferably 3 to 8, from the viewpoint of ensuring sufficient progress of the gas reaction in the device 1 and from the viewpoint of equipment costs.

[0032] From the viewpoint of effectively forming a retention layer, the width of the frame member 12 in the approximately horizontal direction is preferably 10% or more of the radius of the circle drawn by the inner circumference of the side wall of the reaction vessel 2 when the reaction vessel 2 is cylindrical. On the other hand, the diameter of the hole provided in the center of the frame member 12 may be large enough so that the shaft portion 16 and the stirring blade 11 described below can be easily inserted into and removed from the reaction vessel 2. Specifically, for example, the width of the frame member 12 in the approximately horizontal direction is 70% or less of the radius of the circle drawn by the inner circumference of the side wall of the (cylindrical) reaction vessel 2.

[0033] As shown in FIG. 1, an agitator blade 11 is inserted into the reaction vessel 2. More specifically, the agitator blade 11 is composed of a shaft portion 16 and a blade portion 13 extending from the shaft portion 16 at a substantially right angle (for example, the angle between the shaft portion 16 and the blade portion 13 is 85 to 95°). The shaft portion 16 is inserted in a substantially vertical direction along the central axis of the reaction vessel 2, which preferably has a cylindrical shape. As described above, the blade portion 13 extends from the shaft portion 16 at a substantially right angle, so that the blade portion 13 extends in a substantially horizontal direction. The shaft portion 16 is connected to an appropriate rotation mechanism, and the agitator blade 11 can be rotated by rotating the shaft portion 16 at a desired rotation speed.

[0034] Here, the shaft portion, blade portion, disk portion, and standing plate that constitute the agitating blade 11 will be described with reference to FIG. 2. The structure of the blade portion 13 that constitutes the agitating blade 11 and extends from the shaft portion 16 at a substantially right angle is not particularly specified, but for example, the blade portion 13 is provided with a disk portion 14 that extends from the shaft portion 16 toward the inner circumference of the side wall of the reaction tank 2. The disk portion 14 is provided with a standing plate 15 that is preferably erected substantially perpendicularly (the angle with the disk portion 14 is, for example, 85 to 95°) at that position. That is, the so-called disk turbine blade is preferable as the agitating blade 11. This is because the wall surface (standing plate 15) that is attached substantially perpendicular to the disk portion 14 has a shape that can efficiently cut off air bubbles.

[0035] The blade portion 13 extending toward the inner circumference of the side wall of the reaction vessel 2 is provided in a portion between any two adjacent frame members 12 in the approximately vertical direction. This allows the stirring blade 11 to stir the liquid in the reaction vessel 2, thereby favorably generating a gas-liquid two-phase reflux flow, which will be described later. From the viewpoint of favorably generating the reflux flow, it is preferable that the blade portion 13 is located approximately in the vertical center position of the two adjacent frame members 12 (for example, at a height of 40 to 60, when the height of the lower of the two frame members 12 is 0 and the height of the upper one is 100).

[0036] If the stirring power required by the rotating mechanism of the stirring blade 11 is strong, the bubbles can be cut into smaller pieces. 3 It is preferable that the device is configured to be capable of stirring at 1000 W / m or more. 3 More preferably, the device is configured to be capable of stirring at 1500 W / m or more. 3 It is particularly preferable that the stirring power required is 8000 W / m or more. There is no upper limit to the stirring power required, but the power is usually 8000 W / m 3 The following is the result.

[0037] Furthermore, although not shown in FIG. 1, it is also preferable to dispose a plate member extending in a substantially vertical direction as a so-called baffle member on the inner periphery of the side wall of the reaction tank 2 sandwiched between the adjacent frame members 12. FIG. 3 shows the multi-stage retention layer forming device 3 used in the embodiment, and a member with a plate thickness of 5 mm and a plate width of 15 mm connecting the frame members 12 also functions as a baffle member 26. By providing this plate member, the circulation can be more suitably generated, and the efficiency of the gas reaction can be improved. In the cross section of the reaction tank 2 in the substantially horizontal direction, the angle formed by the plate member (baffle member 26) and the inner periphery of the side wall of the reaction tank 2 is preferably 80 to 100°. When the reaction tank 2 is cylindrical, it is preferable that the angle formed by the tangent of the circle drawn by the inner periphery of the side wall at the point of contact between the circle and the plate member and the plate member is within the above range.

[0038] As shown in FIG. 3, the multi-stage retention layer forming device 3 is provided with a gas introduction pipe 21, which is connected by being inserted into the reaction vessel 2, and opens at any position in the reaction vessel 2, usually at the lower part, so that a gas can be introduced into the reaction vessel 2. Typically, the gas introduction pipe 21 is located below the lowest frame member 12 and opens near the approximate central axis of the reaction vessel 2 to form a gas introduction port 22. Meanwhile, the reaction vessel 2 is filled with a liquid solvent, which is a desired liquid such as water. With this configuration, a desired amount of a desired gas species can be introduced into the lowest part of the approximate central axis of the liquid solvent filled in the cylindrical reaction vessel 2.

[0039] By using the above-described apparatus 1 of the present invention, various gas-gas reactions and gas-liquid reactions can be efficiently carried out as described below. In particular, as shown in the examples described below, the apparatus 1 of the present invention can be suitably used for a reaction in which nitric acid is produced from nitrogen oxides (typically a mixture of nitric oxide and nitrogen dioxide) and an oxidizing gas in water. Other reactions that can be carried out using the apparatus 1 of the present invention include a reaction in which lithium carbonate is obtained by reacting an aqueous solution of lithium hydroxide with carbon dioxide.

[0040] 2. Operation of the device for reacting gases Next, the operation of the device 1 of the present invention will be specifically described with reference to FIG. 1. The reaction vessel 2 is filled with a liquid solvent, which is a desired liquid, and the stirring blade 11 is rotated by the above-mentioned rotation mechanism to flow the liquid solvent. Meanwhile, a desired gas species is introduced through the gas introduction tube 21 to the approximate center axis of the liquid solvent filled in the reaction vessel 2, preferably to the lowest point. Since the gas rises and exits above the liquid, the reaction time of the gas can be extended by introducing it to the lowest point. Then, the liquid solvent and the desired gas species are stirred by the stirring blade 11 to generate a gas-liquid two-phase flow, which is a gas-liquid mixture, and flowing in a turbulent state, so that a large number of fine bubbles containing the desired gas species are generated, moved, deformed, and burst in the liquid repeatedly an infinite number of times.

[0041] As a result, when the gas is a mixture of multiple gases and these gases react with each other, the inside of each bubble that is formed becomes a reaction field, increasing the opportunities for contact between the gases, and it is believed that the reaction is significantly promoted. When the gas in the gas reacts with the liquid (the substance inside), the interface between each bubble and the liquid becomes a reaction field, which also increases the contact area between the gas and the liquid, and it is believed that the reaction is significantly promoted. Similarly, when a gas dissolves into a liquid, the increase in the interface area is also believed to significantly promote dissolution.

[0042] In addition, due to the stirring by the stirring blade 11, a gas-liquid two-phase flow, which is a mixture of the liquid solvent and the desired gas species, circulates in the region in the reaction vessel 2 formed between two frame members 12 adjacent in the approximately vertical direction. It is considered that this gas-liquid two-phase flow spreads in the approximately vertical up-down direction and approximately horizontal direction from the approximately vertical and approximately horizontal center part of the region (the intersection position of the blade part 13 and the shaft part 16 of the stirring blade 11 in the region) due to the force of stirring. And since gas generally has a smaller specific gravity than the liquid solvent, it rises in the liquid in the reaction vessel 2. This rise is considered to occur mainly near the side wall of the reaction vessel 2, and the frame member 12 is at the end of the rising part, where the gas (gas-liquid two-phase flow) is repelled and returns (converges) to the approximately vertical and approximately horizontal center part of the region.

[0043] In this way, the gas-liquid two-phase flow circulates within the region sandwiched between two adjacent frame members 12, which prevents the gas from escaping from the region within the reaction vessel 2 and from the liquid within the reaction vessel 2, and is believed to increase the time (reaction time) that the gas remains in (the liquid within) the reaction vessel 2. The region formed by being sandwiched between two adjacent frame members 12 and through which the gas-liquid two-phase flow, which is a mixture of the liquid solvent and the desired gas species, circulates may be referred to as a "retention layer" in this specification.

[0044] Furthermore, a desired number of retention layers 24 can be provided in the reaction tank 2 by adjusting the number of frame members 12 and stirring blades 11 installed in the reaction tank 2. From the viewpoints of ensuring reaction time of the gas and equipment costs, the number of retention layers is preferably 1 to 10, and more preferably 2 to 8.

[0045] A plurality of retention layers 24 are provided, and while the gas-liquid two-phase flow flows and circulates in each retention layer, a portion of the gas-liquid two-phase flow in the lower retention layer 24 passes through the openings (holes) of the frame member 12 and moves to the upper retention layer 24, where the generation, movement, deformation, and bursting of bubbles are repeated. In this way, by providing a plurality of retention layers 24, it is believed that the retention time of the gas in the liquid can be extended and the dissolution of the gas into the liquid can be promoted.

[0046] It is considered that if the stirring power required by the above-mentioned rotating mechanism of the stirring blade 11 is strong, the bubbles are broken down finer, a stronger retention layer 24 is formed, and the retention time of the gas is extended. In order to form a good retention layer, a certain required power (150 W / m 3 More than 1000W / m 3 More preferably, 1500W / m 3 That's all. Normally 8000W / m 3 (which is less than or equal to) is required.

[0047] As explained above, in the present invention, the gas reaction is promoted through the generation of many fine bubbles by stirring with the stirring blades and the formation of a retention layer in the area between adjacent frame members by installing the frame members. For example, the reaction can be promoted by pressurizing the gas, but adopting such a method increases the equipment cost. In the present invention, the promotion of the gas reaction has been achieved with simple equipment consisting of a normal reaction tank, stirring blades, and frame members.

[0048] 3. Treatment method for nitrogen oxides (NOx) Using the device 1 of the present invention, the inside of bubbles generated in water is used as a reaction field to carry out an oxidation reaction of NOx (nitric oxide in NOx), and the product of the oxidation reaction (nitric oxide) and the nitrogen dioxide contained in NOx from the beginning can be absorbed into the water through the walls of the bubbles. This produces nitric acid, which can be reused for various purposes.

[0049] Specifically, water is introduced as a liquid solvent into the reaction tank 2 of the apparatus 1 of the present invention. Nitrogen oxides (NOx gas, which is a gas) and an oxidizing gas are introduced into this water through the gas inlet pipe 21. Examples of the oxidizing gas include oxygen, air, and ozone.

[0050] According to the above-mentioned configuration of the device 1 of the present invention, stirring is performed by the stirring blades 11, and a gas-liquid two-phase flow containing the introduced NOx gas and an oxidizing gas such as oxygen is circulated. A large amount of bubbles are generated in this circulating flow, and each of these bubbles becomes a reaction site for the oxidation of NOx (nitric oxide in the NOx). A retention layer 24 is formed in the area sandwiched between the adjacent frame members 12 in the reaction vessel 2, and the bubbles are retained therein for a long time while colliding with the frame members 12 and the side walls of the reaction vessel 2, thereby sufficiently oxidizing the NOx gas. The oxidized NOx gas, i.e., nitrogen dioxide and the nitrogen dioxide that was originally present in the NOx gas, are easily absorbed (dissolved) into the water phase from the outer walls of the bubbles. In other words, nitric acid is produced.

[0051] The ratio of NOx gas and oxidizing gas introduced into the device 1 of the present invention is preferably such that the oxidizing gas is in excess in terms of reaction efficiency. Specifically, for example, when the oxidizing gas is oxygen or air, it is preferable to introduce NOx gas and oxidizing gas at a volume ratio of NOx gas:oxygen (oxygen in air) of 1:30 to 1:1000. In this way, the production of nitric acid progresses, and when the desired nitric acid concentration is reached, the reaction (introduction of gas) can be stopped and the nitric acid aqueous solution can be recovered. When the focus is on the ability to remove NOx, the reaction can be stopped when the NOx concentration coming out directly above the reaction tank 2 reaches a predetermined value or more, and the water in the reaction tank 2 can be replaced. EXAMPLES

[0052] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to these examples.

[0053] <Example 1 and Comparative Examples 1 to 3> In Example 1 and Comparative Examples 1 to 3, the influence of the presence or absence of stirring and the presence or absence of a frame member on the denitrification rate shown in (Formula 1) described later was investigated.

[0054] The device used in Example 1 and Comparative Examples 1 to 3 is a multistage retention layer forming device shown in Fig. 3 inserted into a cylindrical reaction vessel. A gap of about several mm is provided between the multistage retention layer forming device and the inner circumference of the side wall of the reaction vessel. On the other hand, the device used in Comparative Examples 1 and 2 described below is a multistage retention layer forming device shown in Fig. 3 without the frame member 12 (donut-shaped ring) inserted into a reaction vessel.

[0055] The reaction vessel (a cylindrical reaction vessel into which the multi-stage retention layer forming device shown in Figure 3 is inserted) was fabricated using PVC piping (VP200A, length 650 mm), a PVC piping reducer (VP100A x VP200A), PVC piping (VP100A, length 200 mm), a flange (VP100A), and a blind flange (VP100A, 10K).

[0056] The multi-stage retention layer forming device was fabricated with the dimensions shown in Fig. 3. The material of each plate was PVC, and stainless steel (SUS304 series) was used for the gas inlet pipe 21 and the gas inlet 22. That is, in the device of the present invention used in this example, the frame members were installed horizontally along the inner circumference of the side wall of the reaction vessel, the number of frame members was 6, and the width of the frame members was 20% of the radius of the circle drawn by the inner circumference of the side wall of the reaction vessel. The gas inlet was opened 3 to 4 cm below the lowest frame member.

[0057] The following rotating mechanism and shaft were used: Equipment used: Three-one motor mixer (BLW1200, manufactured by Shinto Chemical Co., Ltd.)

[0058] The stirring blade used was a disk turbine blade equipped with five blades as shown in the schematic diagram of Figure 2. This was inserted vertically from the top of the device of the present invention so that its axis coincided with the center of the cylindrical circle of the reaction tank.

[0059] The test conditions carried out in Example 1 and Comparative Examples 1 to 3 will be described. The raw gas (NOx gas) used in the test was supplied from a commercially available NO gas cylinder. 2 A mixed gas was obtained by mixing oxygen gas and air as oxidizing gases at a predetermined flow rate ratio, and this mixed gas was introduced into the gas inlet 22 of the above-mentioned device.

[0060] At the gas inlet 22, the NOx gas concentration in the mixed gas was measured. Specifically, a NOx gas detector tube (Gas detector tube No. 11HA nitrogen oxides manufactured by GASTEC) and a gas aspirator (Gas detector tube type gas measuring device GV-100S manufactured by GASTEC) were used to aspirate 100 mL of the mixed gas and measure the NOx gas concentration.

[0061] In Example 1 and Comparative Examples 1 to 3, the stirring speed of the stirrer, the required stirring power, the presence or absence of a frame member, the NOx concentration in the mixed gas at the gas inlet position, and O 2 The concentrations, gas flow rates from the NO gas cylinder, air flow rates, and oxygen gas flow rates are shown in Table 1.

[0062] [Table 1]

[0063] Under the mixing conditions shown in Table 1, the above mixed gas was introduced into the device, and the NOx gas was oxidized and absorbed into pure water (NO was converted to NO 2 The NO is oxidized to 2 and NOx gas 2 The test was carried out to determine whether nitric acid was dissolved in pure water. In Example 1, the occurrence of a stagnant layer and fine bubbles between adjacent frame members was observed with the naked eye. In Comparative Examples 1 and 3, no stagnation layer was formed, and no generation of fine bubbles was observed. In Comparative Example 2, no stagnation layer was generated, and a vortex was generated by stirring. Furthermore, the generation of fine bubbles was observed with the naked eye.

[0064] Five minutes after the start of the introduction of the mixed gas into the device, the NOx gas concentration in the upper space of the reaction vessel was measured. The upper space of the reaction vessel, where the NOx gas concentration was measured, was the area directly above the uppermost liquid surface in the multi-stage retention layer forming device shown in Figure 3. The measurement results are shown in Table 2. From the above results, the denitrification rate was calculated. The denitrification rate was calculated from the following formula (1). Denitrification rate=(1-upper space NOx concentration / inlet position NOx concentration)×100(%)...(Formula 1) The results are shown in Table 2.

[0065] [Table 2]

[0066] From the results shown in Table 2, it can be seen that the denitrification rate is greatly increased by stirring the liquid, based on the comparison of Example 1 and Comparative Example 3 with Comparative Examples 1 and 2. This is because stirring generates fine bubbles in the liquid, which oxidize NO and reduce NO 2 This is believed to be due to the improved gas-liquid contact efficiency that allows the dissolution of ZnO in pure water.

[0067] Regarding the presence or absence of a frame member, it can be seen from the comparison results of Comparative Examples 1 and 3 that when stirring is not performed, there is essentially no effect on the denitrification rate. On the other hand, when stirring is performed, a comparison of Example 1 and Comparative Example 2 shows that by attaching a frame member to the device, the denitrification rate improves by about 10%.

[0068] Next, NO is oxidized to NO 2 And the NO 2In the denitration process, NO in the NOx gas at the outlet is dissolved in pure water and becomes nitric acid. 2 In terms of percentage, Example 1 has a percentage of 25%, whereas Comparative Example 2 has a percentage of 58%. This is because in Comparative Example 2, the oxidation reaction occurred frequently due to the improvement in the gas-liquid contact efficiency described above by stirring, and the amount of NO in the outlet gas was 500 ppm, but the amount of NO generated was 100 ppm. 2 This is probably because NO was not sufficiently dissolved in water. 2 The time it takes for the air bubbles containing NO to reach the top of the liquid in the device increases. 2 This is believed to be because the dissolution of

[0069] <Example 2> In Example 2, the influence of the stirring power requirement and the number of blades on the denitrification rate was investigated. The equipment used was the same as that used in Example 1, except that the multi-stage retention layer forming device shown in Figure 3 had one less frame member 12.

[0070] The test conditions carried out in Example 2 will be described. The raw gas (NOx gas) used in Example 2 was produced by adding zinc powder to nitric acid to produce nitrous acid gas (NO 2 The chemical reaction is as shown in (Equation 2). 2 and NO are in equilibrium. Zn+2HNO 3 →2NO 2 +Zn(OH) 2 ...(Formula 2)

[0071] Oxygen was added to the raw gas to produce mixed gas 1. Specifically, this gas was produced by pushing out the generated nitrous gas with oxygen. This mixed gas 1 was mixed with a mixed gas 2 of air and ozone, and introduced into the gas inlet of the above-mentioned device. Note that the ozone in the mixed gas 2 was generated by performing silent discharge in air for the purpose of gas-phase oxidation of NOx, and the O 2 It is produced by oxidizing part of the atmosphere (O 3 (It is a mixture of gases). The flow rates and other conditions of each of the above gases and the names of the samples are shown in Table 3 below.

[0072] [Table 3] However, *1: Condition 1 was performed without the blades of the top three mixing blades shown in Figure 1. *2: Condition 2 was performed without the blades of the top two agitator blades shown in Figure 1. *3: Condition 3 was performed without the blade portion of the top mixing impeller shown in Figure 1.

[0073] Under the stirring conditions shown in Table 3, mixed gas 1 (raw gas + oxygen) and mixed gas 2 (air + ozone gas) were mixed under each condition and introduced into the gas inlet of the device. Then, oxidation of NOx gas and absorption into pure water were carried out. Note that most of the NOx gas in this example was NO 2 It is believed that the main reaction was the absorption of the NOx gas into pure water.

[0074] As in Example 1, the NOx gas concentration at the gas inlet and the NOx gas concentration in the space above the water were measured to determine the denitrification rate in each sample. The above measurement results, together with the required mixing power, mixing speed, number of mixing blades, number of retention layers, and denitrification rate, are shown in Table 4. In Table 4, the samples are listed in order of the smallest required mixing power, for ease of data comparison.

[0075] [Table 4]

[0076] In addition, since the flow rate and composition of NOx gas in this Example 2 are different from those in Example 1, it is not possible to directly compare the magnitude of the denitrification rates. From the results of samples 2 and 3, it was found that when the number of blades of the impeller (number of stages of the retention layer) was the same, the denitrification rate improved with an increase in the stirring speed and the accompanying increase in the required stirring power. Also, from the results of samples 1 and 3 to 5, it was found that when the stirring speed was the same, the denitrification rate improved with an increase in the number of blades of the impeller (number of stages of the retention layer). [Explanation of symbols]

[0077] 1: Equipment 2: Reactor 3: Multi-stage retention layer forming equipment 11: Stirring blade 12: Frame material 13: Wings 14: Disk section 15: Standing board 16: Shaft 21: Gas inlet tube 22: Gas inlet 24: Retention layer 26: Baffle material

Claims

1. A reaction vessel for containing a liquid; A stirring blade inserted into the reaction vessel; A frame member provided in a substantially horizontal direction along the inner periphery of the side wall of the reaction vessel; An apparatus for reacting a gas in a liquid comprising:

2. The frame members are provided in a plurality at predetermined intervals in a substantially vertical direction, The stirring blade has a shaft portion that is inserted into the reaction vessel and extends in a substantially vertical direction, and a blade portion that extends in a substantially horizontal direction from the shaft portion toward an inner periphery of a side wall of the reaction vessel, The apparatus according to claim 1 , wherein the wing portion is disposed in a portion substantially vertically between any two adjacent frame members.

3. The apparatus of claim 2, wherein the number of frame members is between 2 and 10.

4. The apparatus according to claim 1 , further comprising a plate member extending in a substantially vertical direction and disposed along an inner periphery of a side wall of the reaction vessel.

5. 10. The apparatus of claim 1, further comprising a gas inlet tube opening into the reaction vessel.

6. The reaction vessel has a substantially circular cross-sectional shape in a horizontal direction, The apparatus according to claim 1 , wherein the frame member has a substantially horizontal cross-sectional shape that is annular along the inside of the circular contour.

7. 7. The apparatus according to claim 1, which is used to produce nitric acid from nitrogen oxides and an oxidizing gas in water.

8. 8. A method for treating nitrogen oxides, comprising the steps of: introducing nitrogen oxides and an oxidizing gas into a reaction tank of the apparatus according to claim 7, the reaction tank containing water as a liquid, while stirring the water with the stirring blades, to produce nitric acid.

9. 4. The apparatus according to claim 2 or 3, wherein the reaction tank contains water as a liquid, The method for treating nitrogen oxides comprises supplying nitrogen oxides and an oxidizing gas into the water in the reaction tank while stirring the water with the stirring blade, thereby generating nitric acid.

10. 10. The method for treating nitrogen oxides according to claim 9, wherein the water circulates within the region between two adjacent frame members by spreading from an approximately central portion in the approximately vertical and horizontal directions in the approximately vertical up-down directions and in the approximately horizontal directions, and then converging toward the approximately central portion.

11. The stirring power required by the stirring blade is 1500 W / m ３ The method for treating nitrogen oxides according to claim 8 .

Images