JP7702792B2 - Stirring device and stirring method - Google Patents

Description

The present invention relates to an agitation device and an agitation method, and more specifically, to an agitation device and an agitation method that can be used to agitate and mix raw materials for methane fermentation with water, etc., for example, in a wet methane fermentation process.

Traditionally, methane fermentation is carried out by decomposing organic matter contained in livestock manure, sludge, food waste, etc. into methane gas and carbon dioxide gas, and is carried out by utilizing the metabolic action of methane fermentation microorganisms (e.g., acid-producing bacteria, acetogenic bacteria, methanogens, etc.) under anaerobic conditions without oxygen. Methane fermentation is classified into wet methane fermentation and dry methane fermentation depending on the solid concentration of the raw material to be fermented. Generally, wet methane fermentation targets raw materials with a solid concentration in the range of 4% to 12% by mass relative to the total mass, while dry methane fermentation targets raw materials with a solid concentration in the range of 20% to 40% by mass relative to the total mass. However, in dry methane fermentation, there are many equipment problems such as breakdowns of the stirring device due to the high solid concentration. Therefore, wet methane fermentation is more popular than dry methane fermentation.

The wet methane fermentation process generally consists of pretreatment in a raw material receiving tank, fermentation in a fermentation tank, desulfurization, and gas storage. The raw materials for methane fermentation often have a high moisture content, for example, around 80% by mass, relative to the total mass. For this reason, in wet methane fermentation, it is essential to adjust the moisture content (pretreatment) by adding water to solids such as livestock manure, sludge, and food waste. Methods for mixing the raw materials and water in pretreatment include, for example, methods using a vertical shaft agitator (Patent Document 1) or a submersible mixer.

The vertical shaft agitator described in Patent Document 1 has a rotating shaft that can be rotated from outside the tank, located at the center of a vertical cylindrical agitation tank, a flat bottom paddle attached to the lower part of the rotating shaft with a small gap between it and the bottom wall of the agitation tank, and a lattice blade consisting of vertical and horizontal members attached to the upper side of the bottom paddle. However, with this type of vertical shaft agitator, although it can mix solids that have settled in the liquid with the liquid, it is difficult to submerge solids floating on the liquid surface in the liquid and mix them. Therefore, it is difficult to achieve sufficient mixing with the vertical shaft agitator described in Patent Document 1.

An example of an underwater mixer is one that is equipped with a motor that can rotate at a constant speed, an agitator blade attached to the rotating shaft of the motor, and a guide ring that is provided to surround the outer periphery of the agitator blade. However, as with a vertical shaft agitator, such a underwater mixer can mix solids that have settled in the water with the water, but it is difficult to submerge solids floating on the surface of the water in the water and mix them. In addition, the agitator blades may wear out due to contact with solids in the raw materials, resulting in a decrease in mixing performance. Furthermore, when mixing raw materials with a high viscosity range, for example, tens of thousands of cP or more, the area that can be mixed remains around the underwater mixer where it is installed, making sufficient mixing difficult.

One method for solving these problems is, for example, a method using a horizontal shaft agitator (Patent Document 2). The horizontal shaft agitator described in Patent Document 2 is equipped with a cylindrical agitation tank having an inlet for materials and an outlet for sludge slurry, a number of protrusions that form an uneven surface on the inner wall surface of the agitation tank, and a number of agitation blade members that are rotatably attached inside the agitation tank. The agitation blade member also has a support that is implanted in the rotating shaft and an agitation blade that is attached to the tip of the support, and the tip of the agitation blade is configured as a sludge scraping surface that slides against the tip of the protrusion, and the side of the agitation blade is configured as a sludge agitation surface. However, since the agitation surface of the agitation blade is inclined with respect to the center line of the rotating shaft, even if the agitation blade tries to hook a solid floating on the liquid surface and sink it into the liquid, the solid may come off the agitation blade, and the solid may not be able to sink sufficiently into the liquid to be agitated and mixed.

Japanese Patent Application Publication No. 9-108557 JP 2003-47992 A Japanese Patent Application Publication No. 10-15372

The present invention has been made in consideration of the above problems, and its purpose is to provide a stirring device and a stirring method that can sufficiently stir and mix a stirring object that has high viscosity or contains solids floating on the liquid surface.

The above-mentioned problems in the conventional art can be solved by the invention described below.
That is, in order to solve the above-mentioned problems, the stirring device of the present invention comprises an agitation tank having an overall shape that is approximately cylindrical, which is placed horizontally on its side and into which solid and liquid objects to be stirred are added, a rotating shaft that extends in the direction of the central axis of the longitudinal direction inside the agitation tank and is rotatably supported, and at least one stirring member that is supported by the rotating shaft and rotates around the axis of the rotating shaft, wherein the agitation member has a support pillar having one end connected to the rotating shaft and the other end extending in a direction away from the rotating shaft, and a stirring paddle that is provided at the other end of the support pillar and is capable of scooping up the solid objects to be stirred, wherein the agitation paddle has a stirring surface that is parallel to the extension direction of the rotating shaft, and the area of the stirring surface is in the range of 4% to 45% of the maximum cross-sectional area of a cross section passing through the central axis of the longitudinal direction of the agitation tank.

According to the above configuration, a stirring member that can rotate around the axis of the rotating shaft is provided to stir the solid and liquid stirring objects. The stirring member has a support pole with one end connected to the rotating shaft and the other end extending in a direction away from the rotating shaft, and a stirring paddle provided at the other end of the support pole, and the stirring paddle is capable of scooping up the solid stirring objects. Furthermore, since the stirring paddle has a stirring surface that is parallel to the extending direction of the rotating shaft, for example, even if the solid stirring object floats on the liquid surface, the stirring paddle can hook the solid stirring object, sink it in the liquid, and stir and mix it. In addition, by setting the area of the stirring surface of the stirring paddle to a range of 4% to 45% of the maximum cross-sectional area of the cross section passing through the central axis in the longitudinal direction of the stirring tank, excessive stirring power for rotating the stirring member is suppressed, and even when the viscosity of the stirring object is high, stirring is prevented from remaining locally in the stirring tank, making it possible to stir over a wider range. As a result, the stirring efficiency is improved.

In the above configuration, it is preferable that the maximum distance from the rotating shaft to the tip of the stirring paddle of the stirring member is in the range of 90% to 99.5% of the minimum distance from the rotating shaft to the inner wall surface of the stirring tank.

By setting the gap between the tip of the stirring paddle of the stirring member and the inner wall surface of the stirring tank within the above numerical range, it is possible to reduce the possibility of the solid object to be stirred becoming caught between the stirring paddle and the inner wall surface of the stirring tank, and to reduce or suppress wear on the stirring paddle and the inner wall surface of the stirring tank. It is also possible to prevent the stirring from remaining localized within the stirring tank, enabling stirring over a wider area and improving the stirring efficiency.

In the above configuration, the stirring members are provided at multiple positions on the rotating shaft, spaced apart from each other, and the length of the support rod of each stirring member and the direction in which it extends from the rotating shaft are the same or different from each other, and it is preferable that the area and shape of the stirring surface of the stirring paddle of each stirring member are the same or different from each other.

In the above configuration, the stirring members are provided in multiple positions on the rotating shaft with their respective supports extending in different directions, and it is preferable that the lengths of the supports of each stirring member are the same or different, and that the areas and shapes of the stirring surfaces of the stirring paddles of each stirring member are the same or different.

In the above configuration, it is preferable that the shape of the stirring surface of the stirring paddle is flat or annular frame-like.

By making the shape of the stirring paddle's stirring surface flat, for example, when the stirring member is rotated to stir, the stirring paddle can reliably capture the solid stirring object floating on the liquid surface, improving the stirring efficiency. In addition, by making the shape of the stirring paddle's stirring surface annular frame, stirring can be performed while preventing excessive stirring power even when the stirring object has a high viscosity.

Furthermore, in the above configuration, it is preferable that the inner wall surface of the mixing vessel is a smooth surface.

For example, as in the above-mentioned Patent Document 2, if the tip of the stirring blade is provided as a sludge scraping surface that slides against the tip of the protrusion on the inner wall of the stirring tank, the solid stirring object will accumulate on the protrusion, making it difficult to mix the solid stirring object uniformly with the liquid stirring object. In addition, if the solid stirring object is something like a hard sludge lump with high mechanical strength, the tip of the stirring blade will be severely worn at the protrusion on the inner wall of the stirring tank, which will lead to a decrease in stirring performance. However, by making the inner wall surface of the stirring tank smooth as in the above-mentioned configuration, it is possible to prevent the solid stirring object from accumulating on the inner wall surface, and to further improve the stirring and mixing of the solid stirring object and the liquid stirring object. In addition, even if the solid stirring object is hard and has high mechanical strength, it is possible to suppress or reduce wear on the tip of the stirring paddle and prevent a decrease in stirring performance.

The stirring method according to the present invention is a stirring method using the stirring device to solve the above problems, characterized in that the liquid surface height of the liquid object to be stirred when the solid and liquid objects to be stirred are placed in the stirring tank is in the range of 30% to 90% of the height from the bottom to the top inside the stirring tank, and the stirring member is rotated around the axis of the rotation shaft so that at least a part of the stirring paddle of the at least one stirring member is exposed above the liquid surface of the liquid object to be stirred, thereby stirring and mixing the solid object to be stirred and the liquid object to be stirred.

In the above configuration, the liquid surface height of the liquid object to be stirred when the solid and liquid objects to be stirred are placed in the stirring tank is set to a range of 30% to 90% of the height from the bottom surface to the top surface inside the stirring tank. In addition, at least one of the stirring members is rotated around the axis of the rotation shaft so that at least a part of the stirring paddle is exposed above the liquid surface of the liquid object to be stirred. Furthermore, the stirring surface of the stirring paddle is parallel to the extension direction of the rotation shaft. As a result, in the above configuration, for example, even if the solid object to be stirred floats on the liquid surface, when the stirring paddle emerges from the liquid surface, the solid object to be stirred can be scraped up and then dropped to the liquid surface. In addition, when the stirring paddle sinks into the liquid, the solid object to be stirred can be hooked and submerged in the liquid for stirring.

In addition, in the above configuration, the area of the stirring surface of the stirring paddle is set in the range of 4% to 45% of the maximum cross-sectional area of the cross section passing through the central axis of the longitudinal direction of the stirring vessel, so that the stirring power required to rotate the stirring member is prevented from becoming excessive, and even when the viscosity of the material to be stirred is high, the stirring can be prevented from remaining localized within the stirring vessel, allowing mixing to be performed.

In the above-mentioned configuration, it is preferable that the rotation speed of the stirring member is in the range of 1 min ^-1 to 30 min ^-1 .

By setting the rotation speed of the stirring member to 1 min ^- 1 or more, good stirring by the stirring member can be maintained even when the viscosity of the material to be stirred is high (for example, when the viscosity is tens of thousands of cP or more). On the other hand, by setting the rotation speed of the stirring member to 30 min ^-1 or less, it is possible to prevent the stirring power for rotating the stirring member from becoming excessive. In addition, it is possible to reduce or prevent wear of the stirring paddle, etc. due to contact with the solid material to be stirred.

The present invention provides the following effects by the above-described means.
That is, according to the present invention, for example, even if the solid object to be stirred floats on the liquid surface, the stirring paddle of the stirring member can hook the solid object to be stirred and mixed by submerging it in the liquid. Also, even if the object to be stirred has a high viscosity, stirring is prevented from being limited to a local area in the stirring tank, and stirring over a wider area is possible, improving the stirring efficiency.

1 is a cross-sectional side view showing a stirring device according to a first embodiment of the present invention. This is a cross-sectional view taken along line A-A' in Figure 1. FIG. 6 is a cross-sectional side view showing a stirring device according to a second embodiment of the present invention. FIG. 11 is a partially enlarged plan view showing a modified example of the stirring member in the stirring device according to another embodiment of the present invention. FIG. 11 is a cross-sectional view showing a stirring device according to another embodiment of the present invention. FIG. 11 is a cross-sectional view showing a stirring device according to another embodiment of the present invention.

(Embodiment 1)
[Mixing device]
The stirring device according to the first embodiment will be described below with reference to Figures 1 and 2. Figure 1 is a cross-sectional side view showing the stirring device according to the first embodiment. Figure 2 is a cross-sectional view taken along line AA' in Figure 1. Note that parts that are not necessary for the description are omitted, and some parts are illustrated enlarged or reduced in size to facilitate the description.

As shown in FIG. 1, the mixing device 1 of this embodiment is a so-called horizontal type mixing device, and includes at least a mixing tank 11, a rotating shaft 12, a mixing member 13, a solid inlet 16, a liquid inlet 17, and an outlet 18. The mixing device 1 of this embodiment can be suitably used for pre-treatment, for example, in wet methane fermentation, in which solid objects to be mixed, such as livestock manure, sludge, and food waste, are mixed with liquid objects to be mixed, such as water.

As shown in Figs. 1 and 2, the stirring tank 11 has an overall cylindrical shape and is placed with its side horizontal. The inner wall surface of the stirring tank 11 is preferably smooth. This prevents the solid objects to be stirred from piling up, as occurs when protrusions or the like are provided on the inner wall surface, and improves the stirring and mixing of the solid objects to be stirred and the liquid objects to be stirred. It also reduces the chance of the solid objects to be stirred being pinched between the inner wall surface of the stirring tank 11 and the stirring member 13. As a result, even when the solid objects to be stirred are hard and have high mechanical strength, it is possible to suppress or reduce wear on the inner wall surface of the stirring tank 11 and the tip of the stirring member 13.

The rotating shaft 12 extends in the direction of the central axis in the longitudinal direction inside the stirring tank 11. The rotating shaft 12 penetrates the stirring tank 11 and is horizontally supported between a pair of bearings 14a, 14b provided outside the stirring tank. A motor 15 is connected to one end of the rotating shaft 12. The rotating shaft 12 can be rotated at any rotation speed by driving the motor 15. This allows the stirring member 13 to rotate in the direction indicated by the arrow in FIG. 2. The rotating shaft 12 may be provided at a position deviated from the central axis in the longitudinal direction inside the stirring tank 11 as long as the stirring member 13 does not come into contact with the inner wall surface.

The cross-sectional shape perpendicular to the extension direction (axial direction) of the rotating shaft 12 is approximately circular. In this case, the diameter of the cross-sectional shape is not particularly limited and can be set appropriately as needed.

The stirring members 13 have the function of stirring solid and liquid objects, and four of them are provided on the rotating shaft 12. Each stirring member 13 consists of a support 13a and one stirring paddle 13b.

The support 13a is rod-shaped, one end of which is connected to the rotating shaft 12, and the other end of which extends in a direction away from the rotating shaft 12. A stirring paddle 13b is provided at the other end. This allows each stirring member 13 to rotate around the axis of the rotating shaft 12 as the rotating shaft 12 rotates. In addition, each support 13a is connected to the rotating shaft 12 at positions spaced apart from each other at equal intervals so as to be perpendicular to the rotating shaft 12. Furthermore, each support 13a extends so that the direction away from the rotating shaft 12 differs by 180° from each other when viewed from the axial direction of the rotating shaft 12. The cross-sectional shape of the support 13a (cross-sectional shape in a direction perpendicular to the axial direction of the support 13a) is approximately circular. However, the present invention is not limited to this cross-sectional shape. The cross-sectional shape of the support 13a may be, for example, rectangular, etc.

The stirring paddle 13b is a flat plate with an overall rectangular shape, and is connected to the support 13a at the center of the stirring paddle 13b. Since the stirring paddle 13b is a flat plate with a rectangular shape, the stirring surface of the stirring paddle 13b is also rectangular. The stirring paddle 13b is provided at the other end of the support 13a so that the stirring surface is parallel to the axial direction (extension direction) of the rotating shaft 12 (see FIG. 2). By making the stirring surface parallel to the axial direction of the rotating shaft 12, for example, even if the solid stirring object floats on the liquid surface, the stirring paddle 13b can reliably capture the solid stirring object and sink it in the liquid to effectively stir and mix it.

The area of the stirring surface is preferably 4% to 45% of the maximum cross-sectional area of the cross section passing through the central axis in the longitudinal direction of the stirring tank 11, more preferably 6% to 30%, and particularly preferably 12% to 15%. By making the area of the stirring surface 4% or more, it is possible to prevent the stirring from remaining localized within the stirring tank 11, and to maintain good stirring. On the other hand, by making the area of the stirring surface 45% or less, it is possible to prevent the stirring power for rotating the stirring member 13 from becoming excessive. In other words, by keeping the area of the stirring surface within the above numerical range, it is possible to improve the stirring efficiency.

The thickness of the stirring paddle 13b depends on the material of the stirring paddle 13b, but is not particularly limited as long as the mechanical strength is sufficient to prevent the stirring paddle 13b from deforming during stirring. It is usually in the range of 3 mm to 20 mm, preferably 6 mm to 16 mm, and more preferably 9 mm to 12 mm.

The maximum distance from the rotating shaft 12 to the tip of the stirring paddle 13b is preferably 90% to 99.5% of the minimum distance from the rotating shaft 12 to the inner wall surface of the stirring tank 11, more preferably 92.5% to 98%, and particularly preferably 95% to 96%. By making the maximum distance from the rotating shaft 12 to the tip of the stirring paddle 13b 99.5% or less of the minimum distance from the rotating shaft 12 to the inner wall surface of the stirring tank 11, it is possible to reduce the possibility of the solid object being caught between the stirring paddle 13b and the inner wall surface of the stirring tank 11. As a result, for example, even if the solid object being stirred is mechanically strong and hard, it can be stirred while suppressing wear on the stirring paddle 13b and the inner wall surface of the stirring tank 11. On the other hand, by making the maximum distance from the rotating shaft 12 to the tip of the mixing paddle 13b 90% or more of the minimum distance from the rotating shaft 12 to the inner wall surface of the mixing tank 11, mixing is prevented from remaining localized within the mixing tank 11, enabling mixing over a wider area. As a result, mixing efficiency is improved.

The solid inlet 16 is for introducing solid materials to be stirred into the mixing tank 11, and is located at any position on the top surface of the mixing tank 11.

The liquid inlet 17 is for introducing the liquid to be stirred into the mixing tank 11, and is provided at any position on the top surface of the mixing tank 11.

The outlet 18 is for removing the mixture of solid and liquid objects to be stirred, and is provided at any position on the bottom of the mixing tank 11.

In the present embodiment, an example in which four stirring members 13 are provided has been described, but the present invention is not limited to this embodiment. For example, the number of stirring members 13 may be one or more, as necessary.

In addition, in this embodiment, an example has been described in which the inlets for feeding the solid and liquid objects to be stirred are separate, but the present invention is not limited to this. For example, the inlet may be provided at one location on the top surface so that the solid and liquid objects to be stirred can be fed at the same time.

[Stirring method]
Next, a method for stirring an object to be stirred using the stirring device 1 according to the present embodiment will be described below with reference to FIG.

First, the motor 15 is driven to rotate the rotating shaft 12, thereby rotating the stirring member 13 around the axis of the rotating shaft 12. Next, the liquid to be stirred is introduced into the stirring tank 11 through the liquid inlet 17. Furthermore, the solid to be stirred is also introduced through the solid inlet 16, and the liquid and solid to be stirred are stirred. The solid to be stirred may be introduced all at once, or may be introduced sequentially multiple times.

After the liquid and solid objects to be stirred are poured in, the liquid surface height of the liquid object to be stirred in the stirring tank 11 (i.e., the height from the bottom of the inside of the stirring tank 11 to the liquid surface of the liquid object to be stirred) is adjusted to be in the range of 30% to 90%, preferably 45% to 80%, and more preferably 60% to 75%, when the inner diameter of the stirring tank 11 is taken as 100%. By setting the liquid surface height of the liquid object to be stirred within the above numerical range, when the stirring paddle 13b of the stirring member rotating around the axis of the rotating shaft 12 reaches the top, at least a part of the stirring paddle 13b can be made to emerge from the liquid surface of the liquid object to be stirred. As a result, for example, when the stirring paddle 13b emerges from the liquid surface, the stirring paddle 13b can scoop up solids floating on the liquid surface and then drop them. In addition, when the stirring paddle 13b sinks into the liquid, the stirring paddle 13b can catch and sink solids floating on the liquid surface. As a result, it becomes possible to effectively stir solid objects floating on the liquid surface.

The inner diameter of the mixing tank 11 refers to the dimensions of the mixing tank 11 only, and does not include the dimensions of the solid inlet 16, liquid inlet 17, and outlet 18.

In addition, the rotation speed of the stirring member 13 is preferably 1 min ^-1 to 30 min ^-1 , more preferably 1 min ^-1 to 20 min ^-1 , and particularly preferably 1 min ^-1 to 10 min ^-1 . By setting the rotation speed of the stirring member 13 to 1 min ^-1 or more, good stirring by the stirring member 13 can be maintained even when the viscosity of the stirring object is high (for example, when the viscosity is tens of thousands of cP or more). On the other hand, by setting the rotation speed of the stirring member 13 to 30 min ^-1 or less, it is possible to suppress excessive load on the motor 15 that rotates the stirring member 13. In addition, it is possible to reduce or prevent wear of the stirring paddle 13b, etc. due to contact with the solid stirring object.

The stirring surface of the stirring paddle 13b is parallel to the extension direction of the rotation shaft. Therefore, the stirring member 13 stirs so that the stirring surface is perpendicular to the liquid surface of the object to be stirred. As a result, compared to when the stirring surface is not parallel to the extension direction of the rotation shaft, when the stirring paddle 13 emerges from the liquid surface, it is possible to reliably scrape up the floating solid object to be stirred, and when the stirring paddle 13 sinks into the liquid, it is possible to catch the solid object to be stirred and sink it into the liquid. As a result, the stirring efficiency is further improved.

In addition, by extending the four stirring members 13 alternately at 180° angles when viewed from the axial direction of the rotating shaft 12, it becomes possible to stir the solid stirring objects floating on the liquid surface with the stirring paddle 13b every time the rotating shaft 12 rotates 180°. This improves the stirring efficiency.

The mixing time (the mixing time after the liquid and solid objects to be mixed are added) is not particularly limited and can be set appropriately depending on the type of liquid and solid objects to be mixed, etc.

In this embodiment, a case has been described in which the liquid and solid objects to be stirred are sequentially added to the stirring tank 11 while the stirring member 13 is rotating. However, the present invention is not limited to this. For example, the liquid and solid objects to be stirred may be added in advance, and then the stirring member 13 may be rotated to perform stirring.

(Embodiment 2)
A second embodiment of the present invention will be described below with reference to Fig. 3. Fig. 3 is a cross-sectional side view showing a stirring device according to the second embodiment. Note that components having the same functions as those of the stirring device 1 according to the first embodiment are given the same reference numerals and detailed description thereof will be omitted.

[Mixing device]
The stirring device 2 according to the second embodiment differs from the stirring device 1 according to the first embodiment in that, in addition to the stirring member 13, four other stirring members 19 are further provided.

The stirring member 19 consists of a support 19a and a stirring paddle 19b. The support 19a is rod-shaped, and one end of the support 19a is connected to the rotating shaft 12 at the position where the stirring member 13 is connected. The other end of the support 19a extends in a direction opposite to the direction in which the support 13a moves away from the rotating shaft 12, that is, in a direction 180° different from the axial direction of the rotating shaft 12.

The cross-sectional shape of the support 19a (the cross-sectional shape in a direction perpendicular to the extension direction of the support 19a) is approximately circular. However, the present invention is not limited to this cross-sectional shape. For example, it may be rectangular, etc.

The overall shape of the stirring paddle 19b is rectangular, and is connected to the support 19a at the center of the stirring paddle 19b. Since the overall shape of the stirring paddle 19b is a rectangular flat plate, the stirring surface of the stirring paddle 19b is also rectangular. The stirring paddle 19b is provided at the other end of the support 19a so that the stirring surface is parallel to the axial direction (extension direction) of the rotating shaft 12. By making the stirring surface parallel to the axial direction of the rotating shaft 12, for example, even if the solid stirring object floats on the liquid surface, the stirring paddle 19b can reliably capture the solid stirring object and sink it in the liquid to effectively stir and mix it.

The length of the support 19a of the stirring member 19 is configured to be shorter than the support 13a of the stirring member 13. In addition, the area of the stirring paddle 19b of the stirring member 19 is configured to be smaller than the stirring paddle 13b of the stirring member 13. This makes it possible to avoid the stirring paddle 19b of the stirring member 19 coming into contact with the stirring paddle 13b of the stirring member 13. In this embodiment, by adopting such a configuration, the stirring member 13 with the relatively long support 13a can stir the stirring object in a range farther from the rotating shaft 12, while the stirring member 19 with the relatively short support 19a can stir the stirring object in the vicinity of the rotating shaft 12. This enables more efficient and uniform stirring throughout the stirring tank 11.

As in the first embodiment, the area of the stirring surface is preferably 4% to 45% of the maximum cross-sectional area of the cross section passing through the central axis in the longitudinal direction of the stirring tank 11, more preferably 6% to 30%, and even more preferably 12% to 15%. By making the area of the stirring surface 4% or more, the stirring is prevented from remaining locally in the stirring tank 11, and stirring over a wider area is possible. On the other hand, by making the area of the stirring surface 45% or less, the stirring power for rotating the stirring members 13 and 19 can be prevented from becoming excessive. In other words, by making the area of the stirring surface within the above numerical range, the stirring efficiency can be improved. In this embodiment, the area of the stirring surface means the sum of the area of the stirring surface of the stirring paddle 13b and the area of the stirring surface of the stirring paddle 19b.

The gap between the tip of the stirring paddle 19b and the inner wall surface of the stirring tank 11, i.e., the maximum distance from the rotating shaft 12 to the tip of the stirring paddle 19b, is not particularly limited as long as the stirring paddle 19b does not come into contact with the stirring paddle 13b of the stirring member 13.

In the present embodiment, an example has been described in which four stirring members 13 and four stirring members 19 are provided, but the present invention is not limited to this. There may be, for example, one stirring member 13 or multiple stirring members 19, as necessary.

[Stirring method]
The method for stirring an object to be stirred using the stirring device 2 according to the present embodiment can be performed in the same manner as the method for stirring an object to be stirred according to the above-described embodiment 1. Therefore, detailed description thereof will be omitted.

(Other matters)
In the above-mentioned first and second embodiments, the present invention has been described using representative examples of the position where the stirring member is provided on the rotating shaft, the length of the support, the extension direction of the support, the area of the stirring surface of the stirring paddle, and the shape of the stirring surface. However, the present invention is not limited to these embodiments. For example, when a plurality of stirring members are provided at any position on the rotating shaft in a state spaced apart from each other, the length of the support of each stirring member and the direction of extension from the rotating shaft may be the same or different from each other. Furthermore, the area of the stirring surface of the stirring paddle of each stirring member and the shape of the stirring paddle (stirring surface) may also be the same or different from each other.

For example, if multiple stirring members are provided at the same position on the rotation shaft with their respective supports extending in different directions, the lengths of the supports of each stirring member may be the same or different. Furthermore, the area of the stirring surface of the stirring paddle of each stirring member and the shape of the stirring paddle (stirring surface) may also be the same or different.

When the supports of each stirring member extend in different directions from the rotating shaft, it is preferable that the angle between the supports when viewed from the axial direction of the rotating shaft is in the range of 30° to 180°. By making the angle 30° or more, it is possible to reduce localized stirring by each stirring member in the stirring tank. As a result, the stirring efficiency is improved.

In addition, in regard to the shape of the stirring paddle, in the above-mentioned first and second embodiments, a rectangular flat plate has been described as an example. However, the present invention is not limited to this form. For example, the stirring paddle may be a flat plate-shaped one as shown in Fig. 4(a) to Fig. 4(f), or an annular frame-shaped one as shown in Fig. 4(g). Fig. 4(a) to Fig. 4(g) are partially enlarged plan views showing modified examples of the stirring member.

The stirring member 21 shown in FIG. 4(a) comprises a support 21a and a plate-shaped stirring paddle 21b that is approximately rectangular in plan view. The stirring paddle 21b is connected to the support 21a at its center. In addition, all corners of the stirring paddle 21b are rounded, which reduces or prevents wear due to contact with the solid object to be stirred.

The stirring member 22 shown in FIG. 4(b) comprises a support 22a and a plate-shaped stirring paddle 22b, the planar shape of which is approximately rectangular with notches at some of the corners. The stirring paddle 22b is connected to the support 22a at its center. The notch is structured such that a notch portion 22c is provided at the corner of the end opposite the end to which the support 22a is connected. By providing the notch portion 22c at the corner, it is possible to reduce or prevent wear due to contact with the solid object to be stirred. It is also possible to reduce the stirring power required to rotate the stirring member 22.

The stirring member 23 shown in FIG. 4(c) includes a support 23a and a plate-shaped stirring paddle 23b that is approximately circular in plan view. The stirring member 24 shown in FIG. 4(d) includes a support 24a and a plate-shaped stirring paddle 24b that is approximately elliptical in plan view. Even if the planar shape is approximately circular or approximately elliptical like these stirring paddles 23b and 24b, it is possible to reduce or prevent wear due to contact with the solid object to be stirred. It is also possible to reduce the stirring power required to rotate the stirring members 23 and 24.

The stirring member 25 shown in FIG. 4(e) includes a support 25a, and a first stirring paddle 25b and a second stirring paddle 25c, which are rectangular in plan view and plate-shaped. The first stirring paddle 25b is longer than the second stirring paddle 25c. The first stirring paddle 25b and the second stirring paddle 25c are each connected to the support 25a at the center. The first stirring paddle 25b and the second stirring paddle 25c are spaced apart from each other at an arbitrary distance. With the stirring member 25 having such a structure, even if the viscosity of the liquid to be stirred is high, it is possible to prevent the stirring power for rotating the stirring member 25 from becoming excessive. In addition, the solid stirring object floating on the liquid surface can be easily hooked, improving the stirring efficiency.

The stirring member 26 shown in FIG. 4(f) includes a support 26a and two plate-shaped stirring paddles 26b that are rectangular in plan view. Both of the two stirring paddles 26b are connected to the support 26a at the center. The two stirring paddles 26b are spaced apart from each other at an arbitrary distance. Even with the stirring member 26 having such a structure, as with the stirring member 25, the stirring power required to rotate the stirring member 26 is prevented from becoming excessive, and the stirring efficiency is improved by easily hooking the solid stirring object floating on the liquid surface.

The stirring member 27 shown in FIG. 4(g) includes a support 27a and a stirring paddle 27b in the shape of a rectangular ring frame in plan view. The stirring paddle 27b is connected to the support 27a at its center. By providing an opening 27c at the center of the stirring paddle 27b, the resistance that the stirring paddle 27b receives during stirring can be reduced. This makes it possible to prevent the stirring power required to rotate the stirring member 27 from becoming excessive, even when the viscosity of the liquid to be stirred is high. In addition, solid stirring objects floating on the liquid surface can be easily hooked, improving the stirring efficiency.

The area and thickness of the stirring surfaces of the stirring paddles 21 to 27 are as described in detail in the first embodiment.

In the above-mentioned first and second embodiments, the stirring tank is cylindrical in shape. However, the stirring tank of the present invention is not particularly limited as long as it is cylindrical. For example, the present invention may include a stirring tank 31 as shown in FIG. 5. FIG. 5 is a cross-sectional view showing a stirring device according to another embodiment. The cross section of the stirring tank 31 perpendicular to the longitudinal central axis has a semicircular shape below the rotating shaft 12 and a rectangular shape above the rotating shaft 12.

The present invention may also include a mixing vessel 32 and a solid inlet 33 as shown in FIG. 6. FIG. 6 is a cross-sectional view showing a mixing device according to another embodiment. The mixing vessel 32 has a cross section perpendicular to the central axis direction in the longitudinal direction, which is generally arc-shaped except for the top surface. The solid inlet 33 is for introducing solid objects to be mixed into the mixing vessel 32, and is provided on the top surface of the mixing vessel 32.

When the stirring tank 31 or 32 is used to stir solid and liquid objects, the liquid level of the liquid objects in the stirring tank 31 or 32 (the liquid level when the solid and liquid objects are put into the stirring tank 31 or 32) is in the range of 30% to 90%, preferably 45% to 80%, and more preferably 60% to 75% of the height from the bottom to the top inside the stirring tank 31 or 32, as in the case of embodiment 1. Here, the height from the bottom to the top in the case of the stirring tank 32 means the height to the inner wall surface of the stirring tank 32, not including the solid inlet 33.

The present invention can also be applied to a mixing vessel having a prismatic shape. Specific examples of a mixing vessel having a prismatic shape include a square prism, a pentagonal prism, and a hexagonal prism. However, a triangular prism shape is not preferable because the solid material to be mixed may become clogged at the corners formed by the bottom and side of the mixing vessel.

Example 1
In this example, coffee grounds, tea grounds, and water as objects to be stirred were stirred using the stirring device 1 shown in Figures 1 and 2. The specifications of the stirring device 1 were as follows.
Diameter of stirring tank 11: 600 mm
Capacity of mixing tank 11: 200 L
Size of the stirring paddle 13: length 65 mm, width 300 mm, thickness 9 mm
Total area of the stirring surface of the stirring paddle 13b: 78,000 ^mm2
The ratio of the area of the stirring surface of the stirring paddle 13b to the maximum cross-sectional area of the cross section passing through the central axis in the longitudinal direction of the stirring tank 11: 15%
The ratio of the maximum distance from the rotating shaft 12 to the tip of the stirring paddle 13b to the minimum distance from the rotating shaft 12 to the inner wall surface of the stirring tank 11: 95%
Gap between the stirring paddle 13b and the inner wall surface of the stirring tank 11: 15 mm

First, the motor 15 of the stirring device 1 was driven to rotate the rotating shaft 12, thereby rotating the stirring member 13 around the axis of the rotating shaft 12. Next, water was poured into the stirring tank 11 from the liquid inlet 17. After the water was poured, coffee grounds (moisture content 66% by mass, solid content 34% by mass) and tea grounds (moisture content 76% by mass, solid content 24% by mass) were poured into the stirring tank 11 all at once from the solid inlet 16.

The rotation speed of the stirring member 13 was set to 5 min ^-1 after the coffee grounds, tea grounds and water were added. The amounts of coffee grounds added were 29.4 kg, tea grounds added 41.7 kg and water added 128.9 kg. The liquid level of the stirring objects after the coffee grounds, tea grounds and water were added was 72% of the diameter of the stirring tank 11 (the height from the bottom to the top inside the stirring tank 11). The mass proportion of the solid stirring objects consisting of the solid contents of the coffee grounds and tea grounds was 10 mass% of the total mass of the stirring objects.

The coffee grounds and tea grounds were added, and after 30 minutes of stirring, the degree of stirring of the coffee grounds, tea grounds, and water was visually checked. As a result, the stirring state after 30 minutes was good, and the coffee grounds, tea grounds, and water were uniformly mixed.

The viscosity of the object to be stirred was also measured after 30 minutes had passed. The viscosity of the object to be stirred was measured using a Brookfield digital viscometer LVDV-I+ (model number, manufactured by Eiko Seiki Co., Ltd.). As a result, the viscosity of the object to be stirred was 105,000 cP. This confirmed that the stirring device 1 could be used to stir the object well even when the object to be stirred had a high viscosity.

Example 2
In this example, the amount of coffee grounds (moisture content 66% by mass, solid content 34% by mass) added was 38.2 kg, the amount of tea grounds (moisture content 76% by mass, solid content 24% by mass) added was 54.2 kg, the amount of water added was 107.6 kg, and the mass ratio of the solid stirring objects consisting of the coffee grounds and tea grounds solid content was changed to 13 mass% relative to the total mass of the stirring objects.Other than that, the coffee grounds, tea grounds and water were stirred in the same manner as in Example 1.

As a result, after the coffee grounds and tea grounds were added and stirring continued for 30 minutes, it was confirmed by visual inspection that the state of stirring of the coffee grounds, tea grounds and water was good, and that these stirring objects were mixed uniformly. In addition, the viscosity of the stirring object after 30 minutes was 235,000 cP, and it was confirmed that stirring could be performed well with the stirring device 1 even when the stirring object became extremely viscous.

Example 3
In this example, the amount of coffee grounds (moisture content 66% by mass, solid content 34% by mass) added was 88.2 kg, the amount of water added was 111.8 kg, and the mass ratio of the solid stirring object consisting of the solid content of the coffee grounds was changed to 15% by mass relative to the total mass of the stirring object. Otherwise, the coffee grounds and water were stirred in the same manner as in Example 1.

As a result, after the coffee grounds were added and stirring continued for 30 minutes, the state of stirring of the coffee grounds and water was good, and it was visually confirmed that these stirring objects were mixed uniformly. In addition, the viscosity of the stirring object after 30 minutes was 1,776 cP, confirming that stirring was performed well by the stirring device 1.

Example 4
In this example, the amount of coffee grounds (moisture content 66% by mass, solid content 34% by mass) added was 117.6 kg, the amount of water added was 82.4 kg, and the mass ratio of the solid stirring object consisting of the solid content of the coffee grounds was changed to 20% by mass relative to the total mass of the stirring object. Otherwise, the coffee grounds and water were stirred in the same manner as in Example 1.

As a result, after 30 minutes of stirring after adding the coffee grounds, the state of stirring of the coffee grounds and water was good, and it was visually confirmed that these objects were mixed uniformly. In addition, the viscosity of the object to be stirred after 30 minutes was 82,000 cP , and it was confirmed that stirring by the stirring device 1 could be performed well even if the object to be stirred became highly viscous.

Reference Signs List 1, 2 Stirring device 11, 31, 32 Stirring tank 12 Rotating shaft 13, 19, 21 to 27 Stirring member 13a, 19a, 21a to 27a Support 13b, 19b, 21b to 24b, 26b, 27b Stirring paddle 25b First stirring paddle 25c Second stirring paddle 15 Motor 16 Solid inlet 17 Liquid inlet 18 Extraction port 22c Notch 27c Opening 33 Solid inlet

Claims (8)

A mixing device used for mixing solids and liquids in a pretreatment process for fermentation in a wet methane fermentation process,
a mixing tank having an approximately cylindrical overall shape, the mixing tank being placed horizontally on a side surface thereof and into which the solid and liquid objects to be mixed are introduced;
a rotating shaft extending in a central axis direction of a longitudinal direction inside the mixing tank and rotatably supported;
At least one stirring member supported by the rotating shaft and rotating around an axis of the rotating shaft,
The stirring member has a support having one end connected to the rotating shaft and the other end extending in a direction away from the rotating shaft, and a stirring paddle provided at the other end of the support and capable of stirring up the solid stirring object,
The stirring paddle has a stirring surface that is parallel to the extension direction of the rotation shaft, and a perpendicular line of the stirring surface is perpendicular to the support of the stirring member ,
An agitation device in which the area of the agitation surface is in the range of 4% to 45% of the maximum cross-sectional area of a cross section passing through the central axis in the longitudinal direction of the agitation tank. The mixing device according to claim 1, wherein the maximum distance from the rotating shaft to the tip of the mixing paddle of the mixing member is in the range of 90% to 99.5% of the minimum distance from the rotating shaft to the inner wall surface of the mixing vessel. The stirring member is provided in a plurality of positions on the rotating shaft so as to be spaced apart from each other,
The length of the support rod of each stirring member and the direction in which the support rod extends from the rotation shaft are the same or different from each other,
3. The stirring device according to claim 1, wherein the areas and shapes of the stirring surfaces of the stirring paddles of the stirring members are the same or different from each other. The stirring member is provided in a plurality of positions on the rotation shaft, with each support extending in a different direction;
The lengths of the supports of the stirring members are the same or different from each other,
4. The stirring device according to claim 1, wherein the areas and shapes of the stirring surfaces of the stirring paddles of each stirring member are the same or different from each other. The stirring device according to any one of claims 1 to 4, wherein the shape of the stirring surface of the stirring paddle is flat or annular frame-like. The stirring device according to any one of claims 1 to 5, wherein the inner wall surface of the stirring tank is a smooth surface. A stirring method using the stirring device according to any one of claims 1 to 6,
The liquid level of the liquid object to be stirred when the solid and liquid objects to be stirred are charged into the stirring tank is set to a range of 30% to 90% of the height from the bottom surface to the top surface inside the stirring tank,
Rotating the stirring member about the axis of the rotation shaft so that at least a portion of a stirring paddle of the at least one stirring member is exposed above the liquid surface of the liquid to be stirred;
A stirring method for stirring and mixing the solid object to be stirred and the liquid object to be stirred. The stirring method according to claim 7, wherein the rotation speed of the stirring member is in the range of 1 min ⁻¹ to 30 min ⁻¹ .

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