JPH08173992A - Agitator for sludge digestion tank - Google Patents

Abstract

PURPOSE: To provide an agitator which can make a good agitating state of a digestion tank irrespective of the form of the main body of the tank and can be installed even in an existing cylindrical digestion tank in which the strength of the main body is low. CONSTITUTION: An apparatus has an upper sludge passage pipe 4 with an opening 6 formed at a position close to the level of a liquid surface 51 in a digestion tank main body 1 and a lower sludge passage pipe 5 with an opening 7 formed at a position close to the bottom surface 3 of the main body 1. The other ends of the two sludge passage pipes penetrate the outer wall of the main body 1 and are connected through a sludge circulating pump 8 arranged outside the side wall of the main body 1. Since the pump 8 is located outside the main body 1, a pump with larger volume can be installed, Consequently, an intensive circulating current can be formed in the main body 1 to eliminate a dead space in terms of agitation. Scum and deposit on the bottom of the tank can be mixed with sludge, preventing the accumulation of scum and deposit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sludge digestion tank stirring device for anaerobic fermentation of organic sludge such as sewage sludge.

[0002]

2. Description of the Related Art As an agitator for a sludge digestion tank, a gas agitation type agitator installed in a so-called cylindrical digestion tank whose body is a cylindrical digestion tank, and a vertical section of the digestion tank main body There is an agitator with an egg-shaped surface, a draft tube type agitator installed in a so-called egg-type digester.

FIG. 2 is a vertical sectional view showing a conventional cylindrical digestion tank. The stirrer in this cylindrical digestion tank pressurizes a part of the digestion gas extracted from the gas extraction pipe 23 by a blower (not shown), and introduces this gas into the digestion tank main body 1 from the gas blowing pipe 24 immersed in sludge. It is designed to be blown in. By this gas injection, a vertical circulation flow is formed in the digestion tank main body 1, and the sludge in the tank is agitated. In the figure, 21 is a sludge input pipe, and 22 is a sludge extraction pipe. Further, 50 indicates sludge, and 51 indicates the liquid level of sludge.

FIG. 3 is a vertical sectional view showing a conventional egg-type digestion tank. The stirrer in this type of digestion tank is a stirrer 3 provided vertically with a screw 34 at the top of the digestion tank body 30.
1 and a straight tubular draft tube 32 that is erected in a state of being connected to the stirrer 31. The upper end of the draft tube 32 is located near the liquid surface above the digester tank body 30,
The lower end is located near the bottom of the tank, and the screw 34 of the stirrer is inserted into the opening at the upper end. For this reason, the combination of the screw 34 and the draft tube 32 has the same configuration as that of the vertical axial flow pump. Therefore, by rotating the screw 34, sludge in the tank is removed from the draft tube 32.
Is sucked in at one end and discharged from the other end. Then, by rotating the screw 34 in the normal direction or in the reverse direction, the discharge (suction) points of the sludge are exchanged, and a circulation flow as shown by the solid line or the broken line in the figure is formed in the digestion tank body 30. The circulation flow agitates the sludge in the entire tank. In the figure, 33 is a shaft of a screw, and 35 is a motor. 50 is sludge, 5
1 shows the liquid level of sludge.

As shown in FIG. 4, the stirrer 31 is installed with a concrete slab 38 penetrating the top of the digestion tank body 30 located directly above the draft tube 32. In this case, the bearing box 40 is embedded with the mortar 39, and the output shaft of the motor 35 and the shaft 33 of the screw are inserted through the bearing box 40.
Are connected.

[0006]

Among the agitators installed in the two types of digestion tanks, the gas agitation type agitator installed in the cylindrical digestion tank shown in FIG. 2 blows gas. Circulating flow is caused by the upward flow generated at that time. However, the range in which the circulating flow is generated is limited only to the periphery of the gas blowing pipe 24, so that a dead space that is not stirred can be formed in the tank. For this reason, sludge is not sufficiently stirred in a cylindrical digestion tank equipped with a gas stirring type stirring device.

[0007] Since the stirring is not sufficiently performed,
In a cylindrical digestion tank with a gentle slope at the bottom, there arises a problem that sand easily accumulates at the bottom. In addition, since the cylindrical digestion tank has a wide cross-section and the portion where the liquid surface of sludge is formed is wide, scum generated on the liquid surface is less likely to be crushed at the location away from the gas blowing part, There is also the problem of accumulating without mixing in. Therefore, when a gas-stirring type cylindrical digestion tank is used, it is often necessary to clean the inside of the tank, which causes a problem that continuous operation for a long period of time is difficult. Further, in the gas stirring type stirrer, the pressure of the gas supplied to the gas blowing pipe 24 must be increased to a pressure equal to or higher than the liquid pressure of the gas jetting portion, so that there is a drawback that the power required for this is large. .

On the other hand, the draft tube type stirrer installed in the egg digester shown in FIG. 3 forms a smooth circulating flow throughout the vessel when the digester body is oval in shape. However, even if this stirring device is installed in a cylindrical digestion tank, it is difficult to form a smooth circulating flow as in the case of an egg digestion tank. That is, when the draft tube type stirring device is installed in the cylindrical digester, the tank body of the cylindrical digester is not vertically long but rather flat, so that there is no dead space in the tank that is not stirred. It is desirable that the agitator 31 has a larger capacity than that of the egg digester so that more sludge can be sucked and discharged. Then, in order to float the sediment such as sand accumulated on the bottom or to suck the scum on the liquid surface and mix it into the sludge, the agitator 31 of the stirrer 31 is allowed to suck more sludge. You must improve your ability.

However, the draft tube type agitator is
As shown in FIG. 4, since the shaft 33 is hung vertically on the top of the digester tank body and is suspended like a shaft 33 having a length reaching below the liquid surface, consideration is given to the steady rest of the shaft 33. ing. Therefore, in order to increase the capacity of the stirrer 31, its structure must be made stronger, and when a draft tube type stirrer is installed in a cylindrical digestion tank, the equipment cost is high. There is a problem to say.

Further, when considering installing a draft tube type stirring device in a cylindrical digestion tank, in the present situation that many gas stirring type cylindrical digestion tanks have already been constructed, this existing cylindrical digestion tank is installed. It is also desirable to consider the case where the tank is modified and a new stirrer is installed.
However, the existing cylindrical digester is not based on the assumption that a mechanical stirrer is installed on the top of the digester.Since the slab thickness at the top is thin and its strength is small, it is not possible to stir like a draft tube. The device cannot be installed.

The present invention has been made in order to solve the above problems, and can maintain a good stirring state in the digestive tank body regardless of the shape of the digestive tank body. It is an object of the present invention to provide a stirring device for a sludge digestion tank which can be installed in an existing cylindrical digestion tank having a low strength.

[0012]

In order to achieve the above-mentioned object, in the invention of claim 1, an opening is provided in a portion of the digestive tank main body located near the level where the liquid surface is formed. It has an upper sludge flow pipe and a lower sludge flow pipe provided with an opening at a position located near the bottom surface, and the other ends of the upper sludge flow pipe and the lower sludge flow pipe respectively penetrate the outer wall of the digester tank body. Is located outside the digestion tank body, and the other ends of the upper sludge flow pipe and the lower sludge flow pipe are connected via a sludge circulation pump arranged outside the digestion tank body.

According to the second aspect of the invention, the sludge circulation pump is configured such that the rotation direction thereof can be forward and reverse, and the rotation speed thereof is variable.

[0014]

In the present invention, the sludge circulation pump extracts sludge from the digester tank body, and the sludge is returned to the digester tank body to form a circulation flow in the tank. To stir. In this case, since the sludge circulation pump is arranged outside the digestion tank main body, an ordinary pump such as an axial flow pump or a mixed flow pump capable of handling sludge can be used. In this way, the sludge circulation pump is not a special one and is placed outside the digestion tank body, so there are no restrictions on its installation location, etc.
It can be installed at an appropriate place such as on a pedestal provided on the ground. Therefore, there is no restriction on the capacity of the sludge circulation pump to be installed, and a large capacity sludge can be installed as needed. If a sludge circulation pump with a large capacity is installed, more sludge can be extracted and sent into the tank to form a strong circulation flow, so that the circulation flow spreads over a wide range.

Further, in the present invention, two sludge flow pipes (upper sludge flow pipe and lower sludge flow pipe) which serve as a suction pipe or a discharge pipe for sludge are arranged in the digester tank body,
These two sludge flow pipes are connected via a sludge circulation pump, and the upper sludge flow pipe is provided with an opening near the level where the liquid level is formed during operation, and the lower sludge flow pipe is connected. Since an opening is provided in a part located near the bottom surface of the digester, any of the above two sludge flow pipes sucks the sludge near the liquid surface of the digestion tank body or near the tank bottom, and removes this sludge from the tank. It is designed to discharge near the bottom or near the liquid surface.

As described above, the stirring device of the present invention comprising the above two sludge flow pipes and the sludge circulation pump serves as a sludge transportation means, and when the sludge circulation pump is started, the stirring device is placed in the tank. A circulating flow can be created with a space between them. Therefore, the openings of the two sludge flow pipes existing near the liquid surface or near the bottom of the tank serve as the starting point or the ending point of the circulation flow, and the circulation flow in the vertical direction is easily formed.

If the sludge flow pipe as described above is not provided in the digestion tank body, the start point and the end point of the circulation flow will be around the wall surface of the digestion tank body, so that the circulation flow is formed. In order to expand the area, the sludge discharge flow rate and the sludge flow rate must be increased to send the sludge to a distant place, which requires a large amount of energy. Moreover, it is easy to create a dead space that is not stirred.

As long as stirring is carried out to smoothly ferment the sludge, it is sufficient that a circulation flow is formed to such an extent that the entire tank can flow. Sediments such as generated scum and sand settling at the bottom of the tank must be mixed into sludge to prevent their accumulation. However, in the case of a cylindrical digestion tank, if a circulating flow is formed only for flowing sludge, only a part of the scum on the liquid surface is sucked and mixed into the sludge, In addition, only a part of the bottom sediment is blown up and is mixed into the sludge. This is due to the shape of the cylindrical digestion tank. In the cylindrical digestion tank, the area where the liquid surface is formed is relatively large, and the tank bottom has a large area and its slope is large. This is because the suctioned scum and the blown-up deposits are limited to those existing around the mud flow pipe.

With respect to this problem, according to the present invention, the sludge circulation pump has a variable rotation speed, and a larger amount of sludge is temporarily sucked and discharged to form a stronger circulation flow in the entire tank. Is able to. For this reason, it is possible to appropriately attract the scum from the distance and mix it in the sludge, or blow up the distant sediment and mix it in the sludge as appropriate. If there is, scum and sand will not accumulate.

[0020]

EXAMPLE FIG. 1 is a vertical cross-sectional view showing a state in which an example of the present invention is installed in a cylindrical digestion tank. Reference numeral 1 denotes a main body of a digestion tank, the body 2 of which has a cylindrical shape, and a bottom 3 of which has a mortar shape. One end of the digestion tank body 1 is inside the digestion tank body 1.
Sludge located near the level where the liquid level is formed in the center of the upper part (below the level where the liquid level is formed during operation), and the other end penetrates the outer wall of the digestion tank body 1 and is located outside thereof. A distribution pipe 4 and a lower sludge distribution pipe 5 having one end located near the bottom of the digester tank body 1 near the bottom and the other end penetrating the outer wall of the digester tank body 1 and located outside thereof are provided. There is. An opening 6 and an opening 7 are provided at the ends of the upper sludge flow pipe 4 and the lower sludge flow pipe 5 inside the digestion tank body 1, respectively. A sludge circulation pump 8 is arranged outside the side wall of the digestion tank body 1 so that the rotation direction can be forward and reverse, and the rotation speed thereof is variable. Is connected to the other ends of the upper sludge flow pipe 4 and the lower sludge flow pipe 5. The upper part of the upper sludge flow pipe 4 in the digestion tank body 1 is fixed by a tie rod 11 stretched on the inner wall. Further, the lower sludge flow pipe 5 is attached at its lower portion to a plurality of legs 12 provided at the bottom of the tank. Reference numerals 9 and 10 denote valves installed to open and close when the sludge circulation pump 8 is inspected or repaired. The type of the sludge circulation pump 8 is not particularly limited as long as it can appropriately change the suction direction and the discharge direction to opposite directions, such as an axial flow pump and a mixed flow pump. . In the figure, 13 is a sludge input pipe, and 14 is a sludge extraction pipe. Further, 50 indicates sludge, and 51 indicates the liquid level of sludge.

As described above, since the circulation pump 8 is arranged outside the side wall of the digestion tank main body 1, the load of the circulation pump 8 is not applied to the digestion tank main body 1, and its vibration causes the vibration of the digestion tank main body 1. It is difficult to reach the body 1. Therefore, the circulation pump 8 can be installed even in the existing digestive tank main body 1 having a small strength.

The digestion tank, which is continuously operated and in which flammable gas is generated, cannot be opened except in special cases, but the circulation pump 8 having a drive unit may be in a state requiring inspection or repair. is there. However, since the circulation pump 8 is arranged outside the digestion tank body 1, it is not necessary to open the digestion tank body 1 at the time of inspection or repair, and the pump 8 is stopped and the valves 9 and 10 are closed. Since it is only necessary to perform the operation described above, the inspection and repair can be performed very easily and quickly. Further, when a problem occurs in the circulation pump 8, the inspection / repair can be immediately carried out.

Both ends of the upper sludge flow pipe 4 and the lower sludge flow pipe 5 inside the digestion tank body 1 are located in the liquid, and the sludge circulation pump 8 sucks the sludge.
Since the actual head of discharge is zero, the required power of the circulation pump 8 is very small even if more sludge is pumped.

Next, the stirring of sludge by the stirring apparatus of this embodiment will be described. The agitation device of this embodiment includes an upper sludge flow pipe 4, a lower sludge flow pipe 5, and a sludge circulation pump 8.
Since the three members are arranged and connected as described above, the three members transport sludge in the digestion tank body 1 near the liquid surface or near the tank bottom to near the tank bottom or near the liquid surface. Has become a means to do. That is, when the sludge circulation pump 8 is operated, for example, the sludge sucked from the opening 6 of the upper sludge flow pipe is once drawn out of the digestion tank body 1 and then fed into the digestion tank body 1 again, Discharge from the opening 7 of the lower sludge flow pipe. Therefore, a vertical circulation flow is formed in the tank as shown by the solid arrow in the figure. Further, when the rotation direction of the sludge circulation pump 8 is reversed, the suction point and the discharge point of the sludge are opposite to those described above, and a circulation flow as indicated by a dashed arrow in the figure is formed. Such a circulation flow agitates the sludge in the tank.

At this time, the flow of sludge in the tank changes depending on the amount of sludge sucked (discharged) by the sludge circulation pump 8, and the flow rate and flow velocity of the circulation flow increase as the amount increases. Therefore, as the sludge suction amount increases, the sludge flow also spreads laterally, and the entire tank is in a good stirring state. Then, when the flow rate and the flow velocity of the circulation flow in the tank further increase, the scum existing on the liquid surface around the digestion tank main body 1 is attracted to the opening 6 of the upper sludge flow pipe, and then the opening 6
Is drawn into and mixed in sludge. Also, the digestion tank body 1
The sediment existing on the bottom of the surrounding area is also blown up by the flow of sludge discharged from the opening 7 of the lower sludge flow pipe and mixed into the sludge.

Therefore, in the operation of the cylindrical digester equipped with the stirring device of this embodiment, the load of the sludge circulation pump 8 is appropriately changed depending on the situation inside the digester main body 1. When stirring the inside of the tank to the extent that a dead space cannot be created, the amount of sludge suctioned by the sludge circulation pump 8 is set to an extent that a circulating flow is formed to the extent that the sludge in the entire tank flows. Also,
When the amount of scum accumulated on the liquid surface increases and the amount of deposits on the bottom of the tank increases, the rotation speed of the sludge circulation pump 8 is temporarily increased to increase the sludge suction amount. .

In the above description, only the case where the digestion tank equipped with the stirring device of the present invention is of a cylindrical type has been described, but in the stirring device of the present invention, the digestion tank to be installed has a cylindrical shape. The present invention is not limited to the above, but can be applied to an egg digester. Also in this case, the same effect as in the above embodiment can be obtained.

[0028]

According to the present invention, since the sludge circulation pump is arranged outside the digestion tank main body, there is no restriction on the installation place, and a pump having a large capacity can be installed if necessary. Therefore, a strong circulating flow can be formed in the digester tank body, and the entire tank can be in a good stirring state with no dead space.

Further, the sludge circulation pump of the present invention is not restricted by the installation place unlike the conventional draft tube type agitator in which the installation place is limited to only the top of the digestion tank body. It can also be installed in an existing cylindrical sludge digestion tank where the strength of the digestion tank body is low.

Further, in the present invention, since the sludge circulation pump has a variable rotation speed, if necessary,
More sludge can be sucked and discharged to form a stronger circulation flow in the entire tank, and scum existing on the liquid surface around the digester tank body and sediment on the tank bottom can be mixed into the sludge. Therefore, accumulation of scum and deposits can be prevented.
Therefore, it is not necessary to clean the inside of the digestion tank body for a long period of time, and continuous operation can be performed.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a state in which an embodiment of the present invention is installed in a cylindrical digestion tank.

FIG. 2 is a vertical cross-sectional view showing a conventional cylindrical digestion tank.

FIG. 3 is a vertical cross-sectional view showing a conventional egg-type digestion tank.

FIG. 4 is a vertical cross-sectional view showing a conventional draft tube stirrer in an egg-type digestion tank.

[Explanation of symbols]

 1 Cylindrical digester main body 2 Body of cylindrical digester main body 3 Bottom of cylindrical digester main body 4 Upper sludge distribution pipe 5 Lower sludge distribution pipe 6 Opening upper sludge distribution pipe 7 Opening lower sludge distribution pipe 8 Sludge circulation Pump 9, 10 Valve 11 Tie rod 12 Leg 13 Sludge input pipe 14 Sludge extraction pipe 50 Sludge 51 Liquid level of sludge

Claims (2)

[Claims] 1. An upper sludge flow pipe having an opening in a portion located near a level where a liquid level is formed in a digester tank body, and a lower sludge flow pipe having an opening provided in a portion located near a bottom surface. And a pipe, and the other ends of the upper sludge flow pipe and the lower sludge flow pipe penetrate the outer wall of the digestion tank body and are located outside the digestion tank body, respectively. An agitator for a sludge digestion tank, the other end of which is connected via a sludge circulation pump arranged outside the digestion tank body. 2. The agitator for a sludge digestion tank according to claim 1, wherein the sludge circulation pump is configured such that the rotation direction thereof can be rotated normally and reversely, and the rotation speed thereof is variable.