Mixing device

Abstract

To provide a stirring device and the like that can perform fluid stirring and fluid discharging in a balanced manner.SOLUTION: A stirring device 1 comprises a stirring tank 2 that stores fluid and can discharge the fluid through a discharging port 221 provided in a bottom part 22 thereof and a stirring blade 3 that rotates to stir the fluid in the stirring tank 2, in which a distance from a lower part 32 thereof to the bottom part 22 of the stirring tank 2 becomes larger as going from the discharging port 221 toward a side wall of the stirring tank 2. It is preferable that a maximum diameter d3 of the lower part 32 of the stirring blade 3 be 0.3 times or more and 0.7 times or less a diameter D of the stirring tank 2, and it is further preferable that the maximum diameter be 0.35 times or more and 0.5 times or less the diameter D of the stirring tank 2. In the stirring blade 3, a small-diameter part 332 having a diameter d2 smaller than the maximum diameter d3 of the lower part 32 is provided above the lower part 32.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a stirring device and the like. [Background technology]

[0002] Patent Document 1 discloses an agitation device that includes an agitation tank that contains a fluid to be agitated and that can discharge the agitated fluid from an outlet provided at the bottom of the tank. The agitation device is provided with agitating blades that agitate the fluid in the agitation tank by rotation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-83157 Summary of the Invention [Problem to be solved by the invention]

[0004] In the mixing device of Patent Document 1, the bottom of the mixing vessel is formed in a funnel or inverted cone shape with the outlet at the bottom, and the lower part of the mixing blade is positioned along this. When such a mixing blade is rotated, an outward fluid flow can occur from the outlet of the mixing vessel toward the side wall. If this flow discharges only liquid without discharging solids, the density of the fluid may increase. It is also possible to reduce the apex angle of the conical shape of the bottom to promote fluid discharge, but this may result in the fluid being discharged without being sufficiently agitated by the mixing blade.

[0005] The present invention has been made in view of the above circumstances, and its object is to provide an agitation device or the like that can perform a good balance between agitation and discharge of a fluid. [Means for solving the problem]

[0006] In order to solve the above problems, one embodiment of the stirring device of the present invention comprises a stirring tank that contains a fluid and can discharge the fluid from an outlet provided at the bottom of the stirring tank, and a stirring blade that stirs the fluid in the stirring tank by rotating, the distance between the bottom of the stirring blade and the bottom of the stirring tank increasing as the blade moves from the outlet toward the side wall of the stirring tank.

[0007] In this embodiment, when the stirring blade rotates, a downward flow occurs along the bottom of the stirring vessel from the outlet toward the side wall of the stirring vessel, and an upward flow occurs along the lower part of the stirring blade that gradually moves away from the bottom. These flows collide near the side wall of the stirring vessel, causing the outward velocity to be lost, so the stirred fluid gradually moves toward the inner outlet and is properly discharged.

[0008] Another aspect of the present invention is an agitating impeller that rotates to agitate a fluid in a stirred tank having a discharge port at its bottom, and the distance between the bottom of the impeller and the bottom of the stirred tank increases from the discharge port toward the side wall of the stirred tank. [Effects of the Invention]

[0009] According to the present invention, agitation and discharge of a fluid can be performed in a well-balanced manner. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. [Figure 2] The graph shows the results of measuring the concentration of the slurry fluid discharged when the liquid level reached each upper and lower position when the fluid was stirred and discharged in the discharge phase using multiple agitating blades with different maximum diameters at the bottom. [Figure 3] The graph shows the results of measuring the concentration of the slurry fluid discharged when the liquid level reached each upper and lower position when the fluid was stirred and discharged in the discharge phase using multiple agitating blades with different maximum diameters at the bottom. [Figure 4]The graph shows the results of measuring the concentration of the slurry fluid discharged when the liquid level reached each upper and lower position when the fluid was stirred and discharged in the discharge phase using multiple agitating blades with different maximum diameters at the bottom. [Figure 5] This shows the results of measuring the concentration of the slurry fluid discharged when the liquid level reaches each upper and lower position when a fluid is stirred and discharged in the discharge phase using a general stirring impeller. [Figure 6] This shows the results of measuring the concentration of the slurry fluid discharged when the liquid level reaches each upper and lower position when a fluid is stirred and discharged in the discharge phase using a general stirring impeller. [Figure 7] FIG. 10 is a vertical cross-sectional view of a modified example of the stirring device. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the description and drawings, identical or equivalent components, parts, and processes are designated by the same reference numerals, and redundant explanations will be omitted. The scale and shape of each part shown in the drawings are set for convenience to facilitate explanation, and should not be interpreted as limiting unless otherwise specified. The embodiments are merely examples and do not limit the scope of the present invention in any way. All features and combinations thereof described in the embodiments are not necessarily essential to the invention.

[0012] FIG. 1 is a longitudinal cross-sectional view of an agitator 1 according to an embodiment of the present invention. In this embodiment, the agitator 1 is installed vertically, i.e., the vertical or longitudinal direction in FIG. 1. The terms "vertical," "vertical," and "vertical" are used interchangeably, as are the terms "left-right," "lateral," and "horizontal." The present invention is also applicable to agitators 1 that are not installed vertically. In such cases, the terms "vertical," "vertical," and "vertical" are different from the vertical direction, and the terms "left-right," "lateral," and "horizontal" are different from the horizontal direction. As described below, the rotation axis 31 of the agitator blade 3 is provided in the vertical, vertical, and vertical directions, and therefore the vertical, vertical, and vertical directions are also referred to as axial directions. Furthermore, the left-right, horizontal, and horizontal directions are also referred to as radial directions because the left-right, horizontal, and horizontal directions determine the diameter of the agitator vessel 2 and the agitator blade 3.

[0013] The stirring device 1 includes a stirring tank 2 that contains the fluid to be stirred, and a stirring impeller 3 that stirs the fluid in the stirring tank 2. The stirring tank 2 includes a cylindrical straight body section 21 that is provided at the top and extends in the axial direction, and a bottom section 22 that is provided at the bottom so as to be continuous with the straight body section 21. The inner peripheral wall of the straight body section 21 has a circular cross section when viewed from above, and its diameter D is hereinafter also referred to as the diameter D of the stirring tank 2. At least a portion of the upper part of the straight body section 21 is open so that the fluid to be stirred can be introduced, and can be closed with a lid (not shown) or the like while the fluid is being stirred or discharged by the stirring impeller 3.

[0014] The bottom 22 of the stirring tank 2 is formed in a curved shape that bulges downward from the lower end of the straight body portion 21. The bulging end of the curved shape forms the lowest part of the stirring tank 2 in the center of the bottom 22, and a discharge port 221 is provided that can discharge the fluid in the stirring tank 2 to the outside of the stirring device 1. The discharge port 221 is configured to be openable and closable by a discharge port opening / closing device such as a valve (not shown). A valve or the like controlled to a closed state closes the discharge port 221 when the fluid to be stirred is introduced into the stirring tank 2 and held therein, or when the fluid before discharge is stirred with the stirring blades 3 to homogenize its concentration. A valve or the like controlled to an open state opens the discharge port 221 when the fluid to be discharged after its concentration has been homogenized is stirred with the stirring blades 3 and discharged.

[0015] The vertical distance T between the tangent line TL, which is the horizontal boundary line between the cylindrical body portion 21 and the curved bottom portion 22, and the surface or liquid level LL of the fluid in the stirring tank 2 before discharge through the discharge port 221 begins, is hereinafter also referred to as the reference height T.

[0016] The flat agitator blades 3, whose normal direction is perpendicular to the paper surface of FIG. 1, are provided rotatably around a vertical rotation axis 31 that is approximately aligned with the vertical central axis of the agitator tank 2. Above the rotation axis 31 (not shown), there are provided a rotation drive unit such as a motor that generates rotational power, and a rotational power conversion unit such as a transmission that converts the rotational power into a desired number of rotations (or rotational speed) or torque. Note that multiple agitator blades 3 may be provided on the rotation axis 31 as needed. The agitator blades 3 are mainly used to generate agitation power per unit volume Pv [kW / m] that is significantly different in two phases. 3 ] are rotated in different ways by a motor and / or a transmission connected to the rotating shaft 31.

[0017] The first phase is a stirring phase in which the outlet 221 is closed, and is, for example, 0.08 [kW / m 3 ] and 0.10 [kW / m 3 In this stirring phase, the concentration of the fluid in the stirring tank 2, which has been effectively stirred, pulverized, micronized, and mixed by the relatively large stirring power, is homogenized before the subsequent discharge phase. The second phase is a discharge phase in which the discharge port 221 is opened, and the pressure is, for example, 0.005 [kW / m 3 ] and 0.03 [kW / m 3 The agitator blades 3 are driven to rotate at a relatively slow speed so as to generate a relatively small Pv between

[0045] and

[0046] . In this discharge phase, the fluid of the desired concentration is discharged through the discharge port 221 while effectively maintaining the concentration homogenized in the previous agitation phase with a relatively small agitation power.

[0018] According to the stirring device 1 described above, any fluid (liquid) can be stirred in the stirring tank 2 and discharged out of the stirring tank 2 through two consecutive phases, a stirring phase and a discharge phase. However, the stirring blades 3 having the shape specifically described below are preferably applied to high-density slurry-like fluids (for example, particulate slurries containing particulate solids or film-like slurries containing film-like solids), and are particularly preferably applied to fibrous slurries containing fibrous solids with a fiber length between 0.5 mm and 20 mm (preferably about 10 mm) and a fiber diameter between 5 μm and 1000 μm (preferably about 200 μm).

[0019] The agitator 3 is formed with a lower portion 32, a constricted portion 33, and an upper end portion 34, in that order from bottom to top. As described below, the presence of the lower portion 32 of the agitator 3 allows the fluid agitated by the agitator 3 to be discharged from the outlet 221 while maintaining the desired concentration. This effect is enhanced by the constricted portion 33, but providing the constricted portion 33 on the agitator 3 is not essential to achieving the minimum effect of the present invention. The lower portion 32 is formed in a tapered or tapered shape from top to bottom. The upper end 321 of the lower portion 32 is positioned so that it approximately coincides with the tangent line TL, and the lower end 322 of the lower portion 32, which is also the lower end of the entire agitator 3, faces the outlet 221 across a distance b. It is preferable to reduce the distance b to promote the agitation and discharge effects of the agitator 3, as described below. However, if the distance b is too small, for example, a highly viscous fluid may not be discharged and may become clogged. Therefore, an optimal distance b is set depending on the characteristics of the fluid to be stirred and discharged, and the size and shape of the outlet 221 and / or the lower end 322. As shown in the figure, the lower end 322 of the agitator 3 and the outlet 221 at the bottom 22 of the agitator tank 2 are aligned on an extension of the rotation axis 31 of the agitator 3.

[0020] The axial distance between the lower portion 32 of the impeller 3 and the bottom 22 of the stirring vessel 2 increases from the central outlet 221 toward the straight body portion 21 that constitutes the sidewall of the stirring vessel 2. Specifically, the axial distance between the lower portion 32 of the impeller 3 and the bottom 22 of the stirring vessel 2 reaches a minimum value b at the center where the outlet 221 is located, and increases approximately linearly or linearly in proportion to the radial distance from the outlet 221. Note that the upper end 321 and the lower end 322 of the lower portion 32 of the impeller 3 are connected by a linear tapered portion 323, while the shape of the bottom 22 of the stirring vessel 2 is a gentle downward convex curve. Therefore, the axial distance between them does not strictly increase linearly, but at least increases monotonically. Note that the tapered portion 323 of the lower portion 32 of the impeller 3 is not limited to a linear shape; it may be a curved or polygonal line that is convex upward or downward. The bottom 22 of the stirring vessel 2 may also be a curved or horizontal line that is different from that shown in FIG. 1.

[0021] Furthermore, the diameter (horizontal dimension) of the lower portion 32 of the agitating impeller 3 increases linearly or linearly from the lower end 322 facing the discharge port 221 toward the upper end 321. Therefore, the diameter of the lower portion 32 of the agitating impeller 3 is greatest at the upper end 321. As will be described later, the maximum diameter d3 of the lower portion 32 of the agitating impeller 3 is preferably 0.3 to 0.7 times the diameter D of the agitating tank 2 (0.3D≦d3≦0.7D), and more preferably 0.35 to 0.5 times the diameter D of the agitating tank 2 (0.35D≦d3≦0.5D).

[0022] The constricted portion 33 provided above the lower portion 32 of the stirring blade 3 includes a lower tapered portion 331 whose diameter gradually decreases upward from the upper end portion 321 of the lower portion 32, an upper tapered portion 333 whose diameter gradually increases upward from above the lower tapered portion 331, and a small-diameter portion 332 connecting the lower tapered portion 331 and the upper tapered portion 333. The height t from the tangent line TL at the axial center of the small-diameter portion 332 is preferably 0 or more and 0.5 times or less of the reference height T (0 ≦ t ≦ 0.5T). Also, the diameter of the constricted portion 33 is minimized at the small-diameter portion 332. The diameter d2 of this small-diameter portion 332 (the minimum diameter of the constricted portion 33) is preferably 0.1 times or more and 0.3 times or less of the diameter D of the stirring tank 2 (0.1D ≦ d2 ≦ 0.3D), and more preferably 0.2 times or more and 0.3 times or less of the diameter D of the stirring tank 2 (0.2D ≦ d2 ≦ 0.3D). Also, the diameter d2 of the small-diameter portion 332 (the minimum diameter of the constricted portion 33) is smaller than the maximum diameter d3 of the lower portion 32 (d2 < d3). In the illustrated example, both the lower tapered portion 331 and the upper tapered portion 333 are linear, but one or both of them may be curved or polygonal lines convex upward or downward.

[0023] Before starting the discharge of fluid by the discharge port 221, the liquid level LL in the stirring phase or the like is between the small-diameter portion 332 and the upper end portion 34, specifically in the upper tapered portion 333. The diameter d1 of the stirring blade 3 (upper tapered portion 333) at the liquid level LL is preferably 0.4 times or more and 0.6 times or less of the diameter D of the stirring tank 2 (0.4D ≦ d1 ≦ 0.6D), and more preferably 0.45 times or more and 0.5 times or less of the diameter D of the stirring tank 2 (0.45D ≦ d1 ≦ 0.5D). Also, the diameter d1 of the stirring blade 3 at the liquid level LL is larger than the diameter d2 of the small-diameter portion 332 (d1 > d2). Also, the diameter d1 of the stirring blade 3 at the liquid level LL may be larger than the maximum diameter d3 of the lower portion 32 (d1 > d3). The upper end portion 34 of the upper tapered portion 333 extending above the liquid level LL may constitute the horizontal upper end of the stirring blade 3.

[0024] The diameter of the upper end 34 of the impeller 3 is larger than the diameter d1 of the impeller 3 at the liquid level LL, the diameter d2 of the small diameter portion 332, and the maximum diameter d3 of the lower portion 32 of the impeller 3. The diameter of the impeller 3 increases from the small diameter portion 332 toward the upper end 34 via the upper tapered portion 333. The apex angle r1 of an inverted truncated cone having the rotation surface of the upper tapered portion 333 as its side surface, or the rotation surface of the upper end 34 as its bottom surface and the rotation surface of the small diameter portion 332 as its top surface, or the angle formed by the two upper tapered portions 333, is preferably 40 degrees or more and 65 degrees or less (45°≦r1≦65°), more preferably 50 degrees or more and 55 degrees or less (50°≦r1≦55°). In addition, the apex angle r1 is preferably smaller than the apex angle r2 of the truncated cone having the rotation surface of the upper end portion 321 of the lower portion 32 as the bottom surface and the rotation surface of the small diameter portion 332 as the top surface, or the angle formed by the two downward tapered portions 331 (r1 <r2)。

[0025] When the lower part 32 of the agitator impeller 3 having the above-described configuration or shape rotates at a relatively low speed during the discharge phase, a downward flow F1L is generated along the bottom part 22 of the agitator vessel 2 from the discharge port 221 toward the side wall side (the side of the straight body part 21) of the agitator vessel 2, and an upward flow F1H is generated along the lower part 32 of the agitator impeller 3 that gradually moves away from the bottom 22. These flows F1L and F1H collide near the side wall of the agitator vessel 2, causing a loss of outward velocity, and the agitated fluid gradually moves toward the inner discharge port 221 while maintaining the desired concentration, and is appropriately discharged.

[0026] This effect occurs precisely because the lower part 32 (tapered part 323) of the agitating impeller 3 has a different shape from the bottom 22 of the agitating tank 2. In other words, in this embodiment, it is not necessary to make the shape of the lower part of the agitating impeller and the shape of the bottom of the agitating tank the same, as in Patent Document 1. Therefore, according to this embodiment, it is not necessary to adjust the shape of the lower part 32 of the agitating impeller 3 to match the shape of the bottom 22 of the agitating tank 2, and it is possible to provide a general-purpose agitating impeller 3 that can be applied to various agitating tanks 2 having different shapes of the bottom 22.

[0027] As with the lower part 32 of the impeller 3, when the constricted portion 33 rotates at a relatively low speed in a state in which the liquid level LL is relatively high during the discharge phase, for example, when the liquid level LL is located at the upper tapered portion 333, a downward flow F2L is generated along the downward tapered portion 331 from the small diameter portion 332 toward the side wall of the stirring tank 2 (toward the straight body portion 21), and an upward flow F2H is generated along the upper tapered portion 333 that gradually moves away from the downward tapered portion 331. These flows F2L and F2H collide near the side wall of the stirring tank 2, causing a loss of outward velocity, and the stirred fluid gradually moves downward while maintaining the desired concentration and is appropriately discharged from the discharge port 221.

[0028] As a result of the inventor's investigation, it was found that, among the various parameters of the agitator blade 3 having the above-mentioned configuration or shape, the maximum diameter d3 of the lower part 32 of the agitator blade 3 is the most important in achieving a good balance between agitation (or maintaining a uniform concentration) and discharge of the fluid when the liquid level LL is relatively low in the discharge phase, for example, when the liquid level LL is located at the tapered part 323 (no significant change in the action was observed as long as the other parameters were within the above-mentioned ranges). Figures 2 to 4 show the results of the discharge phase (agitation power Pv=0.01 [kW / m 3 The figures show the results of measuring the concentration (slurry concentration) of the slurry fluid discharged when the liquid level LL reached each vertical position (No. 1-10) during agitation and discharge of the fluid in the tank 2. In Figure 2, the maximum diameter d3 of the lower part 32 is 0.42D, in Figure 3, the maximum diameter d3 of the lower part 32 is 0.25D, and in Figure 4, the maximum diameter d3 of the lower part 32 is 0.74D. The liquid level LL is highest at the vertical position "No. 1" in the agitation tank 2, and "No. 10" is closest to the discharge port 221 of the bottom 22. Furthermore, the vertical position "No. 6" coincides with the tangent line TL.

[0029] In Figure 2 (d3 = 0.42D), the slurry concentration is nearly constant when the liquid level LL reaches each position from "No. 1" to "No. 10," demonstrating an excellent balance between the mixing of the fluid by the impeller 3 (or maintaining a uniform concentration) and the discharge. In Figure 3 (d3 = 0.25D), a large fluctuation is observed in the slurry concentration, where it rises below the tangent line TL and then gradually decreases. This is thought to be because when the liquid level LL falls below the upper end 321 of the lower part 32, the lower part 32 is no longer sufficiently mixing the fluid, and solids in the fluid are preferentially discharged, resulting in a subsequent decrease in the slurry concentration. In Figure 4 (d3 = 0.74D), the slurry concentration increases dramatically below the tangent line TL, and fibrous slurry is observed to have accumulated at the bottom 22 of the mixing vessel 2. This is thought to be because when the liquid level LL becomes lower than the upper end 321 of the lower part 32, the stirring of the fluid by the lower part 32 becomes too strong, preventing the solids in the fluid from being discharged and causing the liquid to be preferentially discharged, resulting in an increase in the subsequent slurry concentration. As a result of the above considerations, it was concluded that the maximum diameter d3 of the lower part 32 of the stirring blade 3 is preferably 0.3 to 0.7 times the diameter D of the stirring tank 2 (0.3D≦d3≦0.7D), and more preferably 0.35 to 0.5 times the diameter D of the stirring tank 2 (0.35D≦d3≦0.5D).

[0030] Figures 5 and 6 show the results of the discharge phase (agitation power Pv = 0.08, 0.10 kW / m) using a two-stage paddle impeller and a BB (Bull Blend) impeller, which are common agitation impellers. 3]) and the results of measuring the concentration of the slurry fluid (slurry concentration) discharged when the liquid level LL reached each upper and lower position (No. 1-10) during agitation and discharge of the fluid are shown as comparative examples. In Figure 5 (two-stage paddle impeller), the concentration of the discharged slurry drops significantly when the liquid level LL reaches the "No. 10" position closest to the discharge port 221, indicating that the fluid concentration is not maintained uniformly or that the fluid is not properly discharged from the discharge port 221. In Figure 6 (BB impeller), the concentration of the discharged slurry rises significantly when the liquid level LL reaches the "No. 10" position closest to the discharge port 221, indicating that the high-concentration fluid is not discharged from the discharge port 221 and is instead accumulating.

[0031] FIG. 7 is a longitudinal cross-sectional view of a modified example of the stirring device 1 of FIG. 1. Components similar to those in FIG. 1 are assigned the same reference numerals, and redundant explanations will be omitted. The stirring impeller 3 of this modified example is suitable when the reference height T is large, for example, when the reference height T exceeds 0.4D, and is provided with multiple constricted portions 33, 33' on the top and bottom. The upper end 334 of the first constricted portion 33 (and the lower end of the second constricted portion 33') has the above-mentioned diameter d1 corresponding to the liquid level LL in FIG. 1. The second constricted portion 33', which is provided above the lower first constricted portion 33, has the same configuration and shape as the first constricted portion 33.

[0032] Specifically, the second constricted portion 33′ includes a second downward tapered portion 331′ whose diameter gradually decreases upward from the upper end 334 of the first constricted portion 33; a second small-diameter portion 332′ extending upward to be continuous with the second downward tapered portion 331′; and a second upper tapered portion 333′ whose diameter gradually increases upward from the second small-diameter portion 332′. The diameter d2′ of the second small-diameter portion 332′ (the smallest diameter of the second constricted portion 33′) is equal to the diameter d2 of the first small-diameter portion 332 (the smallest diameter of the first constricted portion 33). Thus, for the pair of vertically adjacent small-diameter portions 332, 332′, the diameter of the stirring impeller 3 increases through the first upper tapered portion 333 and then decreases through the second downward tapered portion 331′ as it moves from the lower first small-diameter portion 332 to the upper second small-diameter portion 332′.

[0033] The liquid level LL during the agitation phase before the discharge of the fluid through the outlet 221 begins is located between the second small-diameter portion 332′ and the upper end 34, specifically, at the second upper tapered portion 333′. The diameter d1′ of the agitating impeller 3 (second upper tapered portion 333′) at the liquid level LL may be equal to the diameter d1 of the upper end 334 of the first constricted portion 33. The apex angle r1′ of an inverted truncated cone having the surface of rotation of the second upper tapered portion 333′ as its side face and the surface of rotation of the second small-diameter portion 332′ as its apex face, or the angle formed by the two second upper tapered portions 333′, may be equal to the apex angle r1 of an inverted truncated cone having the surface of rotation of the upper end 334 of the first constricted portion 33 as its bottom face and the surface of rotation of the first small-diameter portion 332 as its apex face, or the angle formed by the two first upper tapered portions 333.

[0034] When the agitator impeller 3 having the above-described configuration or shape rotates at a relatively low speed during the discharge phase, vertical flows F1L, F1H, F2L, and F2H as shown in Figure 1 are generated in the lower portion 32 and the first constricted portion 33, and at the same time, vertical flows similar to those in the first constricted portion 33 are also generated in the second constricted portion 33'. These vertical flows collide near the side wall of the agitator tank 2, causing a loss of outward velocity, so the agitated fluid gradually moves downward while maintaining the desired concentration and is appropriately discharged from the discharge port 221. Although two constricted portions 33 are provided in Figure 7, three or more constricted portions 33 may be provided if the reference height T is greater.

[0035] The present invention has been described above based on the embodiments. The embodiments are merely examples, and it will be understood by those skilled in the art that various modifications are possible in the combination of the respective components and treatment processes, and that such modifications are also within the scope of the present invention. [Explanation of symbols]

[0036] 1 Stirring device, 2 stirring vessel, 3 stirring blade, 21 straight body portion, 22 bottom portion, 31 rotating shaft, 32 lower portion, 33 constricted portion, 221 discharge port, 323 tapered portion, 331 lower tapered portion, 332 small diameter portion, 333 upper tapered portion.

Claims

1. a stirring tank that contains a fluid and is capable of discharging the fluid from a discharge port provided at a bottom portion that is formed in a curved shape that bulges downward; a flat-plate-shaped agitating impeller that agitates the fluid in the agitation tank by rotation, the agitating impeller having a distance between a lower portion including a lower end thereof and a bottom of the agitation tank increasing from the outlet toward a side wall of the agitation tank; Equipped with The discharge port is provided at the lowest part of the stirring tank in the center of the bottom. The lower end of the stirring blade faces the discharge port.

2. The stirring device according to claim 1 , wherein the diameter of the lower end of the stirring blade increases upward from the outlet.

3. 3. The stirring device according to claim 1, wherein the maximum diameter of the lower end of the stirring blade is 0.3 to 0.7 times the diameter of the stirring vessel.

4. 4. The stirring device according to claim 3, wherein the maximum diameter of the lower end of the stirring blade is 0.35 to 0.5 times the diameter of the stirring vessel.

5. The stirring tank includes a cylindrical straight body portion provided above the bottom portion and extending in the up-down direction, The bottom portion is provided downward so as to be continuous with the straight body portion, The stirring blade has the following configuration from bottom to top: The lower end portion is formed in a tapered shape or a tapered shape from above to below; a constricted portion provided above the lower end portion and including a small diameter portion having a diameter smaller than the maximum diameter of the lower end portion; an upper end portion provided above the constricted portion and having a diameter larger than the diameter of the small diameter portion; are formed in order, The small diameter portion is provided above a tangent line that is a horizontal boundary line between the body portion and the bottom portion. The stirring device according to any one of claims 1 to 4.

6. The stirring device according to claim 5 , wherein the diameter of the stirring blade decreases from the upper end of the lower end portion toward the small diameter portion.

7. 7. The stirring device according to claim 5, wherein the diameter of the small diameter portion is 0.1 to 0.3 times the diameter of the stirring tank.

8. The stirring device according to claim 5 , wherein a plurality of the small diameter portions are provided above the lower end of the stirring blade.

9. 9. The stirring device according to claim 8, wherein the diameter of the stirring blade increases and then decreases from the lower small diameter portion to the upper small diameter portion for each pair of adjacent small diameter portions.

10. 10. The stirring device according to claim 5, wherein the stirring blade has an upward tapered portion whose diameter increases upward from the small diameter portion.

11. 11. The stirring device according to claim 10, wherein the apex angle of the truncated cone, with the rotational surface of the upper tapered portion as a side surface and the rotational surface of the small diameter portion as a top surface, is between 40 degrees and 65 degrees.

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