JP6733928B1 - Digestive tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digestion tank capable of improving the uniformity of mixing of digested substances in the entire inner space of the digestion tank. SOLUTION: The digestion tank is provided with an inner side surface 6s that defines an inner space 2 for accommodating a substance to be digested and converges toward the upper end 2u and the lower end 2b of the inner space 2 toward the center side of the inner space 2. In 1A, the digestion target W stored in the internal space 2 is stirred by the stirring mechanism 10 around an axis parallel to the vertical direction, and the digestion target is generated by the baffle plate 20A protruding upward from the lower end portion 2b of the internal space 2. An upward flow is formed in W from the lower end portion 2b of the internal space 2 upward, and a poor flow portion is unlikely to occur. Therefore, to improve the uniformity of mixing of the digested material W in the entire internal space 2 of the digestion tank 1A. You can [Selection diagram] Figure 1

Description

The present invention relates to a digestion tank.

A digestion tank has been proposed for digesting digestible substances while accommodating digestible substances such as sludge. For example, Patent Document 1 discloses a digestion tank in which a draft tube is installed parallel to the vertical direction in the center of the inside of the digestion tank. The substance to be digested contained in the digestion tank is sucked from the upper end of the draft tube and discharged from the lower end of the draft tube. As a result, the substance to be digested contained in the digestion tank is agitated.

Japanese Patent Laid-Open No. 11-90492

By the way, although the above technique has excellent performance for digesting the digested material, it consumes a large amount of energy for stirring the digested material by the draft tube. Therefore, for example, there is also proposed a digestion tank in which an impeller that rotates around a rotation axis parallel to the vertical direction is arranged inside the digestion tank, and by rotating the impeller, the substance to be digested contained in the digestion tank is stirred. ing. However, with this technology, although the energy required to stir the digested material is reduced, there is also a portion where the flow velocity of the stirred digested material is low, which results in uniform mixing of the digested material in the entire internal space of the digestion tank. There is room for improvement.

Therefore, an object of the present invention is to provide a digestion tank capable of improving the uniformity of mixing of digested substances in the entire internal space of the digestion tank.

The present invention provides a side wall having an inner side surface that converges toward the center side of the internal space as it reaches the upper end and the lower end of the internal space while defining the internal space that houses the digested material, and the internal space housed in the internal space. The digestion tank is provided with a stirring mechanism for stirring the digested product around an axis parallel to the vertical direction, and a baffle plate protruding upward from the lower end of the internal space.

According to this configuration, a side wall having an inner side surface that converges toward the center side of the inner space as it reaches the upper end and the lower end of the inner space while defining the inner space that houses the digested material, and is housed in the inner space. In a digestion tank equipped with a stirring mechanism for stirring the digested substance around an axis parallel to the vertical direction, the digestible substance stored in the internal space is stirred around the axis parallel to the vertical direction by the stirring mechanism, The baffle plate that protrudes upward from the lower end of the space forms an upward flow upward from the lower end of the internal space in the digested material, and it is difficult for a poor flow to occur, so digestion in the entire internal space of the digestion tank It is possible to improve the uniformity of mixing of the substances.

Also, the present invention defines a bottom wall having an inner bottom surface that defines a lower end portion of the internal space that houses the digested material, defines the internal space, and extends from a peripheral edge portion of the inner bottom surface, and an upper end portion of the internal space and A side wall having an inner side surface that converges toward the center of the inner space as it reaches the lower end, a stirring mechanism that stirs the digested material contained in the inner space around axes parallel to the up-down direction, and upward from the inner bottom surface. And an inner bottom surface having a wider flat surface than the upper surface portion defined by the upper edge portion of the side wall at the upper end portion of the internal space, and the baffle plate protruding upward from the flat surface. It is a digestive tank.

According to this configuration, the bottom wall having the inner bottom surface that defines the lower end portion of the internal space that houses the digested material, and the inner space that extends from the peripheral edge portion of the inner bottom surface, and the upper end portion of the internal space and In a digestion tank having a side wall having an inner side surface that converges toward the center side of the internal space as it reaches the lower end, the digestion target contained in the internal space is agitated around an axis parallel to the vertical direction by the agitation mechanism. The baffle protruding upward from the inner bottom surface forms an upward flow upward from the lower end of the internal space in the digested material, and the inner bottom surface is the upper edge of the side wall at the upper end of the internal space. Since the baffle plate has a flat surface wider than the upper surface defined by the section, the baffle projects upward from the flat surface, a faster upward flow is formed, and a poor flow part is less likely to occur. It is possible to further improve the uniformity of mixing of the digested material in the whole.

In the digestive tank of the present invention, it is preferable that the baffle plate is radially arranged at the central portion of the lower end portion of the internal space in a plan view.

According to this configuration, the baffle plate is radially arranged in the central portion of the lower end portion of the internal space in a plan view, a faster upward flow is formed, and a poor flow portion is less likely to occur. It is possible to further improve the uniformity of the mixture of the digested material in the entire space.

Further, it is preferable that the stirring mechanism has a paddle that is parallel to the vertical direction and a rotation shaft that rotates the paddle about an axis that is parallel to the vertical direction.

According to this configuration, the stirring mechanism has a paddle that is parallel to the vertical direction and a rotating shaft that rotates the paddle about an axis that is parallel to the vertical direction, and that stirs the digested material with less energy than the impeller. You can

Further, it is preferable that the inner side surface includes a curved line in a cross-sectional view taken along a cross section parallel to the vertical direction, but the present invention is not limited thereto.

According to this configuration, since the inner surface includes a curved line in a cross-sectional view that is parallel to the vertical direction, a dead water area is unlikely to occur, good stirring is performed, the quality and temperature of the digested material are made uniform, and the digestion gas is digested. It is effective for promoting gas separation and preventing scum generation.

Further, the inner side surface is a middle part where the vertical distance between the upper end portion and the lower end portion of the internal space is the same in a cross-sectional view taken along a cross section parallel to the vertical direction, and the inner surface becomes the inner portion as it reaches the upper end portion and the lower end portion of the internal space. It is preferred to include a converging curve on the side of the center of the space.

According to this configuration, the inner side surface is an intermediate portion where the vertical distance between the upper end portion and the lower end portion of the internal space is equal to each other in a cross-sectional view taken along a cross section parallel to the vertical direction. Since it includes a curve that converges toward the center of the internal space as it reaches, the dead water area is unlikely to occur in the middle part of the internal space that houses the digested material, good stirring is performed, and the quality and temperature of the digested material It is effective for homogenization, promotion of gas separation of digestion gas, and prevention of scum generation.

According to the digester tank of the present invention, it is possible to improve the uniformity of mixing of the digested material in the entire inner space of the digester tank.

(A) is a vertical cross-sectional view showing the digestion tank according to the first embodiment, and (B) is a horizontal cross-sectional view taken along the line α of (A). It is a figure which shows the flow of the to-be-digested substance in the internal space of the conventional digestion tank. It is a figure which shows the flow of the to-be-digested substance in the internal space of the conventional digestion tank. It is a figure which shows the flow of the to-be-digested substance in the internal space of the digestion tank which concerns on 1st Embodiment. (A) is a vertical cross-sectional view showing a digestive tank according to the second embodiment, and (B) is a horizontal cross-sectional view taken along the β line of (A). It is a figure which shows the flow of the to-be-digested substance in the internal space of the digestion tank which concerns on 2nd Embodiment. It is a graph which shows the average flow velocity of the to-be-digested substance of the internal space with respect to the power of a paddle or an impeller in an experiment example. It is a graph which shows the circulation amount of the digested material in the internal space with respect to the peripheral velocity of the tip of the paddle in the experimental example. It is a graph which shows the circulation amount of the digested material in the internal space with respect to the power of the stirring mechanism in the experimental example.

Hereinafter, the digestion tank according to the present invention will be described in detail with reference to the drawings. As shown in FIG. 1(A) and FIG. 1(B), the digestion tank 1A according to the first embodiment of the present invention has an internal space 2 for accommodating an object to be digested W such as sludge and an external space for covering the internal space 2. It is composed of a shell 3. The digestive tank 1A has an oval shape as a whole. 1 A of digestive tanks are equipped with the pedestal part 4 in the lower part. In order for the digestion tank 1A to be stably installed, the pedestal portion 4 is embedded in the ground E and placed on a bottom plate (not shown). The digestion tank 1A has, for example, a total height of 20 to 30 m, a total width of 10 to 20 m, and a capacity of 2000 to 4000 m ³ .

The digestion tank 1A includes a bottom wall 5A having an inner bottom surface 5b that defines a lower end portion 2b of the internal space 2 that stores the digested material W. The digestion tank 1A extends obliquely upward from the peripheral edge portion 5p of the inner bottom surface 5b toward the outside of the inner space 2 while defining the inner space 2, and reaches the upper end portion 2u and the lower end portion 2b of the inner space 2. A side wall 6 having an inner side surface 6s that focuses on the center side of the internal space 2 is provided. In the present embodiment, the inner bottom surface 5b is narrower than the upper surface portion 7 defined by the upper edge portion 6u of the side wall 6 at the upper end portion 2u of the internal space 2. The diameter of the inner bottom surface 5b is, for example, 0.5 to 1.5 m. In the present embodiment, the inner bottom surface 5b may be omitted and the inner space 2 may be defined only by the inner side surface 6s. The inner surface 6s includes a curve 6c between the lower portion and the upper portion in a cross-sectional view taken along a cross section parallel to the vertical direction. More specifically, the inner side surface 6s is an intermediate portion 2m in which the vertical distance between the upper end portion 2u and the lower end portion 2b of the internal space 2 is the same in a cross-sectional view taken along a cross section parallel to the vertical direction. It includes a curve 6C that converges toward the center of the internal space 2 as it reaches the upper end 2u and the lower end 2b. The inner side surface 6s includes straight lines in the lower and upper portions excluding the curves 6c and 6C in a cross-sectional view taken along a cross section parallel to the vertical direction.

In the digestion tank 1A of this embodiment, the ratio of the total width to the total height of the internal space 2 is, for example, 0.62 to 0.72. The ratio of the diameter of the inner bottom surface 5b to the total width of the internal space 2 is, for example, 0.03 to 0.09. The ratio of the diameter of the upper surface portion 7 to the entire width of the internal space 2 is, for example, 0.12 to 0.36. The ratio of the curvature radius of the curve 6C of the intermediate portion 2m of the inner side surface 6s to the total width of the inner space 2 is, for example, 0.62 to 0.74. The curve 6C of the middle portion 2m of the inner surface 6s is, for example, an arc of about 90°. In a cross-sectional view taken along a plane parallel to the vertical direction, the angle from the horizontal of the lower and upper straight lines excluding the curve 6c of the inner side surface 6s and the curve 6C of the middle portion 2m of the inner side surface 6s is, for example, 40° to 50°. Is.

1 A of digestive tanks are equipped with the stirring mechanism 10 which stirs the to-be-digested object W accommodated in the internal space 2 around the axis|shaft parallel to an up-down direction. The stirring mechanism 10 includes a paddle 11 that is parallel to the vertical direction, a rotating shaft 12 that rotates the paddle 11 around an axis that is parallel to the vertical direction, and a drive unit 13 that is a power source that rotates the rotating shaft 12. The drive unit 13 is an electric motor arranged on the upper surface portion 7. A paddle 11 is suspended from a drive unit 13 via a rotary shaft 12 parallel to the vertical direction. The term “around an axis parallel to the vertical direction” means that the axis of stirring is substantially vertical, for example. Further, the paddle 11 which is parallel to the vertical direction means that the paddle is substantially vertical, for example. Further, the rotating shaft 12 that rotates the paddle 11 around an axis parallel to the vertical direction means that the rotating shaft 12 is substantially vertical, for example. With respect to the tank diameter Dh which is the diameter of the internal space 2 at the height of the upper end of the paddle 11, the blade diameter d which is the diameter of the paddle is in the range of blade diameter d/tank diameter Dh=0.1 to 0.95. Is preferable, and the range of blade diameter d/tank diameter Dh=0.25 to 0.8 is more preferable.

As shown in FIGS. 1(A) and 1(B), the digestion tank 1A includes a baffle plate 20A protruding upward from a lower end portion 2b of the internal space 2. In the present embodiment, the baffle plate 20A projects upward from the lower portions of the inner bottom surface 5b and the inner side surface 6s. As shown in FIG. 1(B), the baffle plate 20A is radially arranged in the central portion 2c of the lower end portion 2b of the internal space 2 in a plan view. In the present embodiment, about four baffle plates 20A are radially arranged in a cross shape while being spaced from each other so as to surround the center 5c of the inner bottom surface 5b. With respect to the tank diameter Dh of the internal space 2, the baffle plate diameter dRAD, which is the diameter of the range in which the baffle plate 20A projects upward from the lower portions of the inner bottom surface 5b and the inner side surface 6s, is the baffle plate diameter dRAD/tank diameter Dh= The range of 0.05 to 1.0 is preferable, and the range of baffle plate diameter dRAD/tank diameter Dh=0.25 to 0.8 is more preferable. With respect to the blade diameter d of the paddle 11, the baffle plate protrusion length L, which is the protrusion length from the inner bottom surface 5b of the baffle plate 20A, is in the range of baffle plate protrusion length L/blade diameter d=0.05 to 0.8. The range of baffle plate protrusion length L/blade diameter d=0.1 to 0.6 is more preferable.

The baffle plate 20A protruding upward from the lower end portion 2b of the inner space 2 does not necessarily mean that the baffle plate 20A is in contact with the lower end portion 2b and the inner bottom surface 5b of the inner space 2. For example, the baffle plate 20A projecting upward from the lower end portion 2b of the internal space 2 means that between the lower end of the baffle plate 20A and the inner bottom surface 5b, 1/10 to 10% of the projecting length from the inner bottom surface 5b of the baffle plate 20A. It also includes the case where there is a gap of about 1/5. The baffle plate 20A projecting upward from the lower end portion 2b of the internal space 2 may project upward only from the inner bottom surface 5b, or may project upward only from the lower part of the inner side surface 6s.

In addition, the center portion 2c of the lower end portion 2b of the internal space 2 does not necessarily have to be exactly the center of the lower end portion 2b of the internal space 2 in plan view. The center portion 2c of the lower end portion 2b of the internal space 2 is preferably the center of the lower end portion 2b of the internal space 2 in a plan view, but is not limited thereto.

Further, the baffle plate 20A being arranged radially in the central portion 2c of the lower end portion 2b of the internal space 2 in the plan view means that the baffle plate 20A is necessarily present above the center 5c of the inner bottom surface 5b and the center 5c. You don't need to be. For example, as in the present embodiment, the plurality of baffles 20A may extend to the outside of the internal space 2 while being spaced apart from each other so as to surround the center 5c of the inner bottom surface 5b. Further, the fact that the baffle plate 20A is radially arranged in the central portion 2c of the lower end portion 2b of the inner space 2 in a plan view means that the baffle plate 20A does not necessarily mean a straight line passing through the center 5c of the inner bottom surface 5b and the center of the inner bottom surface 5b. It does not need to exist above the straight line passing through 5c. For example, the baffle plate 20A may be arranged at a position separated from above a straight line passing through the center 5c of the inner bottom surface 5b and a straight line passing through the center 5c of the inner bottom surface 5b, and may extend outside the inner space 2. Further, the radial arrangement means that the baffle plate 20A may have a curved line in a plan view instead of a straight line.

According to this embodiment, the inner side surface 6s that defines the inner space 2 for accommodating the digested substance W and converges toward the center side of the inner space 2 toward the upper end 2u and the lower end 2b of the inner space 2 is provided. In the digestion tank 1A, the digestion target W stored in the internal space 2 is stirred by the stirring mechanism 10 around an axis parallel to the vertical direction, and the baffle plate 20A protruding upward from the lower end portion 2b of the internal space 2 causes An upward flow is formed in the digested material W from the lower end portion 2b of the internal space 2 upward, and a poor flow portion is unlikely to occur. Therefore, the uniformity of the digested material W in the entire internal space 2 of the digestion tank 1A is made uniform. Can be improved.

For example, as shown in FIG. 2, in the digestion tank 100, a draft tube 31 is installed in the center of the internal space 2 of the digestion tank 100 in parallel with the vertical direction. The digested material W stored in the digestion tank 100 is sucked from the upper end of the draft tube 31 and discharged from the lower end of the draft tube 31. As a result, the digested material W stored in the digestion tank 100 is agitated. In FIGS. 2, 3, 4, and 6 below, the flow indicated by the arrow in the internal space 2 indicates that the flow velocity is low in the order of the solid line, the broken line, and the dotted line.

In such a digestion tank 100, a strong discharge flow is generated from the draft tube 31 to the inner bottom surface 5b, but is greatly attenuated at the inner bottom surface 5b, resulting in a very gentle stirring as a whole. In addition, as shown by the broken line arrow and the dotted line arrow in the internal space 2, when the flow velocity is low in many areas and the digested material W is sludge, the mixture of the concentrated sludge and the digested sludge is not sufficient. .. In addition, the flow is biased, and a local circulation flow due to a short path occurs in the lower portion of the internal space 2.

In addition, as shown in FIG. 3, in the digestion tank 200, an impeller 41 that rotates around a rotation axis 42 that is parallel to the vertical direction is arranged in the internal space 2, and the impeller 41 rotates to accommodate the impeller 41 in the digestion tank 100. The digested product W thus prepared is stirred. In such a digestion tank 200, as shown by a solid arrow in the internal space 2, the flow is short-passed in the lower part of the internal space 2, and a flow pattern divided into the upper part and the lower part of the internal space 2 is formed.

Further, in the digestion tank 200, as shown by a dotted arrow in the internal space 2, in the central portion 2c of the lower end portion 2b of the internal space 2, the stagnation region expands, so that the specific gravity in the digested material W such as sludge is large. Solid substances are likely to accumulate. Further, in the digestion tank 200, a region having a low flow velocity can be seen near the central portion 2c of the lower end portion 2b in the internal space 2 and near the inner side surface 6s. Further, in the digestion tank 100, the action of mixing the digested material W such as sludge is not sufficient, temperature unevenness is likely to occur, and scum may be generated.

On the other hand, in the digestion tank 1A of the present embodiment, an upward flow is formed from the central portion 2c of the lower end portion 2b of the internal space 2 as indicated by the solid arrow in the internal space 2 of FIG. No defective parts are seen and good fluidity is obtained. Further, in the digestion tank 1A of the present embodiment, the large circulation flow of the digested material W is formed in the internal space 2, and the entire digested material W in the internal space 2 can be uniformly stirred. In addition, in the digestion tank 1A of the present embodiment, a sufficient flow velocity can be secured in almost all areas of the internal space 2, and there is little concern about accumulation or scum generation.

Further, in the present embodiment, the baffle plate 20A is radially arranged in the central portion 2c of the lower end portion 2b of the internal space 2 in a plan view, a faster upward flow is formed, and a poor flow portion is less likely to occur. It is possible to further improve the uniformity of mixing of the digested material W in the entire inner space 2 of the digestion tank 1A.

In addition, in the present embodiment, the stirring mechanism 10 has a paddle 11 that is parallel to the vertical direction and a rotary shaft 12 that rotates the paddle 11 around an axis that is parallel to the vertical direction. The digested material W can be stirred with less energy than the impeller 41.

In addition, in the present embodiment, since the inner surface 6s includes the curve 6c in a cross-sectional view in a cross section parallel to the vertical direction, a dead water area is unlikely to occur, good stirring is performed, and the quality and temperature of the digested material W are uniform. It is effective in promoting gasification, promoting gas separation of digestion gas, and preventing scum generation.

Further, in the present embodiment, the inner surface 6s is an intermediate portion 2m in which the vertical distance between the upper end portion 2u and the lower end portion 2b of the internal space 2 is equal to the internal space 2m in a cross-sectional view taken along a cross section parallel to the vertical direction. 2 includes a curved line 2C that converges toward the center side of the internal space 2 as it reaches the upper end 2u and the lower end 2b of the internal space 2, so that a dead water area is unlikely to occur in the intermediate portion 2m of the internal space 2 that stores the digested material W, which is good. It is effective in that the quality and temperature of the digested material are made uniform, the gas separation of the digested gas is promoted, and the generation of scum is prevented.

The second embodiment of the present invention will be described below. As shown in FIG. 5(A) and FIG. 5(B), in the present embodiment, the digestion tank 1B has a bottom wall having an inner bottom surface 5b that defines a lower end portion 2b of the internal space 2 that stores the digested material W. With 5B. In this embodiment, the inner bottom surface 5b is an essential component. On the other hand, similarly to the first embodiment, the inner side surface 6s of the side wall 6 defines the inner space 2 and extends obliquely upward from the peripheral portion 5p of the inner bottom surface 5b toward the outer side of the inner space 2, As it reaches the upper end 2u and the lower end 2b of the internal space 2, the light is focused toward the center of the internal space 2. The inner side surface 6s includes a curve 6c in a cross-sectional view taken along a cross section parallel to the vertical direction. The inner side surface 6s is a middle portion 2m in which the vertical distance between the upper end portion 2u and the lower end portion 2b of the internal space 2 is equal to the upper end portion 2u and the lower end portion of the internal space 2 in a cross-sectional view in a cross section parallel to the vertical direction. It includes a curve 6C that converges toward the center of the internal space 2 as it reaches the portion 2b. The inner side surface 6s includes a straight line in the upper part except the lower part including the curve 6c in a cross-sectional view taken along a cross section parallel to the vertical direction.

The inner bottom surface 5b has a flat surface 5s wider than the upper surface portion 7 defined by the upper edge portion 6u of the side wall 6 at the upper end portion 2u of the internal space 2. Having the flat surface 5s includes, for example, a case where the flat surface 5s has any of undulations and inclinations of 3% or less with respect to the diameter of the flat surface 5s. In the present embodiment, the flat surface 5s is a plane substantially parallel to the horizontal direction. In this embodiment, the inner bottom surface 5b is a flat surface 5s. The inner bottom surface 5b has a diameter that is, for example, 2 to 4 times that of the upper surface portion 7. The diameter of the inner bottom surface 5b is, for example, 5 to 15 m. The total height, width and capacity of the digestion tank 1B are the same as those of the digestion tank 1A of the first embodiment. The stirring mechanism 10 is also the same as that of the digestion tank 1A of the first embodiment. The preferable range of blade diameter d/tank diameter Dh is also the same as in the digestion tank 1A of the first embodiment.

In the digestion tank 1B of this embodiment, the ratio of the total width to the total height of the internal space 2 is, for example, 0.82 to 0.92. The ratio of the diameter of the inner bottom surface 5b to the total width of the internal space 2 is, for example, 0.54 to 0.64. The ratio of the diameter of the upper surface portion 7 to the entire width of the internal space 2 is, for example, 0.12 to 0.36. The ratio of the radius of curvature of the curves 6c and 6C of the inner surface 6s to the total width of the internal space 2 is, for example, 0.62 to 0.74. The curve 6C of the middle portion 2m of the inner surface 6s is, for example, an arc of about 90°. An angle from the horizontal of the upper straight line excluding the curve 6c of the inner side surface 6s and the curve 6C of the intermediate portion 2m of the inner side surface 6s is, for example, 40° to 50° in a cross-sectional view taken along a cross section parallel to the vertical direction. ..

The digestion tank 1B includes a baffle plate 20B that projects upward from the inner bottom surface 5b. The baffle plate 20B projects upward from the flat surface 5s of the inner bottom surface 5b. As shown in FIG. 5(B), the baffle plate 20B is radially arranged in the central portion 2c of the lower end portion 2b of the internal space 2 in a plan view. In the present embodiment, about four baffle plates 20B are radially arranged in a cross shape while being spaced from each other so as to surround the center 5c of the inner bottom surface 5b. Other matters such as the preferable range of the baffle plate diameter dRAD/tank diameter Dh and the baffle plate protruding length L/blade diameter d are the same as those of the digestion tank 1A of the first embodiment.

According to the present embodiment, the bottom wall 5B having the inner bottom surface 5b that defines the lower end portion 2b of the inner space 2 that houses the digested material W, and the peripheral portion 5p of the inner bottom surface 5b that defines the inner space 2 are provided. In the digestion tank 1B provided with the side wall 6 that extends and reaches the upper end 2u and the lower end 2b of the internal space 2 and converges toward the center side of the internal space 2, the internal space by the stirring mechanism 10 The digested substance W housed in 2 is agitated around an axis parallel to the vertical direction, and the digested substance W is directed upward from the lower end portion 2b of the internal space 2 by the baffle plate 20B protruding upward from the inner bottom surface 5b. In addition to forming the upward flow, the inner bottom surface 5b has a flat surface 5s wider than the upper surface portion 7 defined by the upper edge portion 6u of the side wall 6 at the upper end portion 2u of the inner space 2, and the baffle plate 20B. Is projected upward from the flat surface 5s, a faster upward flow is formed, and a poor flow portion is less likely to occur, so that the uniformity of the mixture of the digested material W in the entire inner space 2 of the digestion tank 1B is further improved. Can be made.

That is, as shown by the solid arrow in the internal space 2 of FIG. 6, in the digestion tank 1B of the present embodiment, the central portion 2c of the lower end portion 2b of the internal space 2 is the same as in the digestion tank 1A of the first embodiment. As a result, an upward flow is formed, a flow failure portion in the internal space 2 is not seen, and good mixing uniformity is obtained. Further, in the digestion tank 1B of the present embodiment, the large circulation flow of the digested substance W is formed in the internal space 2, and the entire digested substance W in the internal space 2 can be uniformly stirred. In addition, in the digestion tank 1B of the present embodiment, a sufficient flow velocity can be secured in most regions of the internal space 2, and there is little concern about accumulation or scum generation.

Furthermore, in the digestion tank 1B of the present embodiment, a higher flow velocity can be obtained in the peripheral portion 5p of the inner bottom surface 5b than in the digestion tank 1A of the first embodiment, and the digested material W such as sludge It is possible to further prevent the accumulation of solid substances having a large specific gravity. In addition, in the digestion tank 1B of the present embodiment, a larger circulation amount of the digested material W can be obtained as compared with the digestion tank 1A of the first embodiment.

(Experimental example)
Hereinafter, experimental examples of the present invention will be described. As Experimental Example 1, the digestive tank 1A of the first embodiment, as Experimental Example 2 the digestive tank 1B of the second embodiment, as Comparative Example 1 the digestive tank 100 shown in FIG. 2 and as Comparative Example 2 shown in FIG. A fluid analysis by CFD (Computational Fluid Dynamics) was performed on the digestion tank 200. The fluid analysis by CFD was performed by "ANSYS Fluent 19.0" (trade name) of ANSYS. The capacities of the digestion tank 1A, the digestion tank 1B, the digestion tank 100 and the digestion tank 200 are all 3000 m ³ . The diameter of the digestion tank 1A is 16.7 m, the diameter of the digestion tank 1B is 17.0 m, and the diameter of the digestion tank 100 is 16.7 m. The depth of the digested material W in the digestion tank 1A is 23.95 m, the depth of the digested material W in the digestion tank 1B is 19.85 m, and the depth of the digested material W in the digestion tank 100 is 23. It is 9 m, and the depth of the digested material W in the digestion tank 200 is 23.95 m.

The average flow velocity when the digested material W was stirred was measured by the digestion tanks 1A, 1B, 100 and 200. For the digestion tank 1A and the digestion tank 1B, the flow rate of the ascending flow immediately above the baffles 20A and 20B was measured as the circulation amount. In the horizontal cross section of the internal space 2 at a height of 0.4 times the diameter of the baffles 20A and 20B from the inner bottom surface 5b, the area of the region where the upward flow is generated was obtained. The circulation amount was calculated from the product of the average flow velocity of the ascending flow in the region and the area of the region. In the digestion tank 100, the circulation amount was the same as the input set value of the discharge flow rate of the draft tube 31. In addition, the digestion tank 200 was excluded from the measurement of the circulation amount because it is difficult to evaluate the circulation flow in the entire inner space 2.

The fluid analysis result by CFD shows that when the rotation speed of the paddle 11 of the digestion tank 1A is 4.20 min ^-1 , the average flow velocity of the digested substance W in the internal space 2 is 0.282 m/s, and the maximum flow velocity is 1. It was 0.39 m/s, the circulation rate was 4032 m ³ /hr, the power was 2.418 kW, and the power density was 0.806 W/m ³ .

The fluid analysis result by CFD shows that when the rotation speed of the paddle 11 of the digestion tank 1B is 4.12 min ⁻¹ , the average flow velocity of the digested substance W in the internal space 2 is 0.287 m/s, and the maximum flow velocity is 1. The power was 0.41 m/s, the circulation rate was 5364 m ³ /hr, the power was 2.473 kW, and the power density was 0.824 W/m ³ .

The fluid analysis result by CFD shows that when the discharge flow rate of the draft tube 31 of the digestion tank 100 is 1500 m ³ /hr, the average flow velocity of the digested substance W in the internal space 2 is 0.03 m/s, and the maximum flow velocity is 3 The circulation rate was 1500 m ³ /hr, which was the same as the discharge flow rate of the draft tube 31 as described above, the power was 11.0 kW, and the power density was 3.667 W/m ³ .

The fluid analysis result by CFD shows that when the rotation speed of the impeller 41 of the digestion tank 200 is 9.60 min ⁻¹ , the average flow velocity of the digested substance W in the internal space 2 is 0.171 m/s, and the maximum flow velocity is 3 The power density was 0.04 m/s, the power was 2.704 kW, and the power density was 0.901 W/m ³ .

From the fluid analysis results by these CFD, although the maximum flow velocity of the digestion tanks 1A and 1B is slower than that of the digestion tanks 100 and 200, the average flow velocity is 9 times or more faster than that of the digestion tank 100 and 60% of that of the digestion tank 200. It was faster than that. This means that the digestion tanks 1A and 1B have a higher flow velocity than the digestion tanks 100 and 200 in the entire inner space 2. In addition, the digestion tank 1A and the digestion tank 1B have power consumption that is ¼ or less that of the digestion tank 100, and the power consumption has been reduced by 8% or more compared to the digestion tank 200. The average flow velocities of the digestion tank 1A and the digestion tank 1B were about the same. However, the digestive tank 1B had a circulation amount increased by 30% or more as compared with the digestive tank 1A.

Further, as shown in FIG. 7, in the fluid analysis result by CFD, the average flow velocity of the digested material W in the internal space 2 with respect to the power of the paddle 11 of the digestion tank 1A of Experimental Example 1 and the digestion tank 1B of Experimental Example 2 is: Average velocity of the digested material W in the internal space 2 with respect to the power of the draft tube 31 of the digestion tank 100 of Comparative Example 1 and average velocity of the digested material W in the internal space 2 with respect to the power of the impeller 41 of the digestive tank 200 of Comparative Example 2. Was faster than. The average flow velocity of the digested material W in the internal space 2 with respect to the power of the paddle 11 in the digestion tank 1A and the digestion tank 1B was about the same.

As shown in FIG. 8, in the fluid analysis result by CFD, the circulation amount of the digested substance W in the internal space 2 with respect to the peripheral velocity of the tip of the paddle 11 is such that the digestion tank 1B of Experimental Example 2 has a digestion tank 1A of Experimental Example 1. Was over. As shown in FIG. 9, the circulation amount of the digested material W in the internal space 2 with respect to the power of the paddle 11 of the digestion tank 1A of Experimental Example 1 and the digestion tank 1B of Experimental Example 2 is the draft of the digestion tank 100 of Comparative Example 1. It was larger than the circulation amount of the digested material W in the internal space 2 with respect to the power of the tube 31. Regarding the circulation amount of the digested material W in the internal space 2 with respect to the power of the paddle 11, the digestion tank 1B of Experimental Example 2 exceeded the digestion tank 1A of Experimental Example 1.

The present invention can be implemented in various forms including various modifications and improvements based on the knowledge of those skilled in the art, including the above-described embodiments. Further, it is also possible to configure the modified example by utilizing the technical matters described in the above-mentioned embodiment. For example, in the digestion tanks 1A and 1B, the digestive tanks 1A and 1B have an oval shape, and the inner surface 6s includes a curve 6c in a cross-sectional view in a cross section parallel to the vertical direction. However, the inner surface 6s may be composed of only straight lines in a sectional view in a cross section parallel to the vertical direction, and the digestion tanks 1A and 1B are parallel to the vertical direction in a sectional view parallel to the vertical direction. It may have a hexagonal inner side surface 6s having opposite sides.

1A, 1B... Digestion tank, 2... Internal space, 2u... Upper end part, 2b... Lower end part, 2c... Central part, 2m... Intermediate part, 3... Outer shell, 4... Pedestal part, 5A, 5B... Bottom wall, 5b ... inner bottom surface, 5p... peripheral portion, 5s... flat surface, 5c... center, 6... side wall, 6s... inner side surface, 6u... upper edge portion, 6c... curved line, 6C... curved line, 7... upper surface portion, 10... stirring mechanism , 11... Paddle, 12... Rotating shaft, 13... Drive part, 20A, 20B... Baffle plate, 31... Draft tube, 41... Impeller, 42... Rotating shaft, 100, 200... Digestion tank, E... Underground, W... Digested material, Dh... tank diameter, d... blade diameter, dRAD... baffle plate diameter, L... baffle plate protruding length.

Claims (5)

A bottom wall having an inner bottom surface that defines the lower end of the internal space that houses the substance to be digested;
A sidewall having an inner side surface that defines the inner space, extends from the peripheral edge of the inner bottom surface, and converges toward the center of the inner space as it reaches the upper end and the lower end of the inner space,
A stirring mechanism for stirring the digested material contained in the internal space around an axis parallel to the vertical direction,
A baffle protruding upward from the inner bottom surface,
Equipped with
The inner bottom surface has a flat surface wider than an upper surface portion defined by an upper edge portion of the side wall at an upper end portion of the internal space,
The baffle plate is a digestive tank that protrudes upward from the flat surface. The digestive tank according to claim 1 , wherein the baffle plate is radially arranged in a central portion of a lower end portion of the internal space in a plan view. The digestion tank according to claim 1 or 2 , wherein the stirring mechanism has a paddle that is parallel to the vertical direction and a rotation shaft that rotates the paddle about an axis that is parallel to the vertical direction. The inner surface comprises a curved when viewed in section according to a cross section parallel to the vertical direction, digester according to any one of claims 1-3. The inner surface is an intermediate portion where the vertical distance between the upper end and the lower end of the internal space is the same in a cross-sectional view taken along a cross section parallel to the vertical direction, and as the upper end and the lower end of the internal space are reached. The digestive tank according to any one of claims 1 to 5 , comprising a curve that converges toward the center side of the internal space.

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