JPH05269496A - Method for digesting cake-like sludge - Google Patents

Abstract

PURPOSE:To efficiently digest cake-like sludge within a short time by sufficiently heating and stirring dehydrated cake-like sludge in a digestion tank to promote the discharge digestion gas. CONSTITUTION:Dehydrated cake-like sludge A is supplied to a digestion tank 1 to be digested and a part of the digested cake-like sludge is circulated by the circulating pipe 12 provided to the outside of the digestion tank 1. A part of the digestion gas generated from the digestion tank 1 is compressed by a gas compressor 19 to be raised in temp. and the high temp. digestion gas is blown into the cake-like sludge in the digestion tank 1 through a gas blow pipe 18 and the cake-like sludge in the digestion tank 1 is heated and mixed by the blown-in high temp. digestion gas to be promoted in its digestion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently digesting cake-like sludge obtained by dehydrating organic sludge such as sewage.

[0002]

2. Description of the Related Art Sewage such as sewage is conventionally treated by the following method. That is, sewage is guided to a settling basin, and sludge such as sediment in the sewage is settled in the settling basin for primary separation. Then, the wastewater from which the sludge is primarily separated is guided to the aeration tank, and the wastewater is aerated in the aeration tank. In this way, the aeration-treated wastewater is guided to the final settling basin, and in the final settling basin, the sludge remaining in the wastewater is precipitated and separated. Next, the slurry-like sludge taken out from the final settling tank is concentrated in a concentration facility. Next, the concentrated slurry sludge is supplied to the digestion tank, and the digestion treatment is performed in the digestion tank. The sludge thus digested is discarded or incinerated.

FIG. 2 is a schematic vertical sectional view showing a conventional digester. As shown in FIG. 2, in the conventional digester, one end of the digester 1 and the supply port provided on the top wall of the digester 1 are connected to the concentrated slurry sludge in the digester 1. And a gas discharge pipe 3 for discharging the digested gas generated in the digestion tank 1, one end of which is connected to a gas supply port provided on the top wall of the digestion tank 1. And a steam blowing pipe 4 for blowing the heating steam into the digestion tank 1, and a discharge pipe 5 provided in the lower portion of the digestion tank 1 for discharging the digested cake-like sludge.

The concentrated slurry-like sludge passes through the supply pipe 2 and is supplied from the supply port provided on the top wall of the digestion tank 1. The slurry sludge thus supplied is retained in the digestion tank 1 in an anaerobic state for a certain period of time. High-temperature steam is blown into the slurry-like sludge in the digestion tank 1 through the blowing pipe 4, and the slurry-like sludge is heated by the injected steam. As a result, the slurry-like sludge is fermented with methane, and the organic matter in the sludge is decomposed and digested. The digested sludge reaches the lower part of the digestion tank 1 due to the difference in liquid level, and is discharged through the discharge pipe 5. The digestion gas generated by fermentation passes through the gas discharge pipe 3 and the digestion tank 1
Discharged from. The discharged digestion gas is collected and used as fuel for boilers and the like.

FIG. 3 is a schematic vertical sectional view showing another example of the conventional digester. In this example, the above-mentioned high-temperature steam is not blown into the digestion tank 1, but instead, digested slurry sludge in the lower part of the digestion tank 1 is provided with a circulation pump 6 and a heat exchanger 7 in the middle thereof. By the circulation pipe 8 thus provided, the digestion tank 1 is circulated back through the supply port on the top wall thereof. The heat exchanger 7 heats the slurry sludge passing through the high temperature medium from the heating source 9 through the same. Therefore, the slurry sludge exiting the heat exchanger 7 becomes high in temperature,
By returning such a high temperature slurry-like sludge into the digestion tank 1, the slurry-like sludge in the digestion tank 1 is heated,
Accelerate its digestion.

[0006]

The above-mentioned conventional method has the following problems. Recently, the slurry sludge taken out from the final settling tank was concentrated in a concentrating facility,
Next, the concentrated slurry sludge is dehydrated in a dehydration facility to form a cake, and the dehydrated cake sludge is supplied to a digestion tank and digested in the digestion tank. Since the water content of the dehydrated cake-like sludge is about 75 to 80%, the volume of the digestion tank 1 to which such dehydrated cake-like sludge is supplied can be made smaller than before. Therefore, the cost of the digestion equipment can be reduced.

However, since the dehydrated cake-like sludge has a low water content of about 75 to 80% as described above, its fluidity is far worse than that of the non-dehydrated slurry-like sludge. As a result, the conventional digester shown in FIGS. 2 and 3 cannot stir the cake-like sludge supplied in the digester tank, and cannot uniformly heat the cake-like sludge in the digester tank. ..

In the method of heating the cake-like sludge in the digestion tank 1 by blowing high-temperature steam into the digestion tank 1 as shown in FIG. 2, the water content of the cake-like sludge is changed by the injected steam. Raises the problem of high. Further, depending on the method of heating the sludge by the heat exchanger as shown in FIG. 3, there is a problem that the heat exchanger is blocked by the cake-like sludge passing therethrough. Therefore, depending on the conventional digestion method, it takes a long time to digest the cake-like sludge, and the digestion becomes insufficient.

Therefore, the object of the present invention is to solve the above-mentioned problems and to allow dehydrated cake-like sludge to be uniformly heated and stirred in the digestion tank without increasing its water content. Accordingly, it is an object of the present invention to provide a method for digesting cake-like sludge that can efficiently digest the cake-like sludge in a short time.

[0010]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to solve the above-mentioned problems. As a result, a part of the cake-like sludge digested in the digestion tank is circulated in the digestion tank by the circulation mechanism provided outside the digestion tank, and a part of the digestion gas discharged from the digestion tank, The digested gas, which has been compressed by a gas compressor and whose temperature has risen by being compressed in this way, is blown into the cake-like sludge in the digestion tank, and the cake-like sludge is heated and agitated. It was found that the cake-like sludge can be efficiently digested in a short period of time by uniformly heating and stirring.

The present invention has been made based on the above findings, and the method of the present invention supplies dehydrated cake-like sludge into a digestion tank, and the dehydrated cake-like sludge is supplied into the digestion tank. Digested, part of the digested cake-like sludge, by a circulation mechanism provided outside the digestion tank,
A portion of the digestion gas that was forcedly circulated in the digester tank, generated in the digester tank and discharged from the digester tank was compressed by a gas compressor, and thus compressed to raise the temperature. Digestion gas is blown into the cake-like sludge in the digestion tank to heat and agitate the cake-like sludge, thus efficiently digesting the cake-like sludge in the digestion tank. Is.

Next, the method of the present invention will be described with reference to the drawings. FIG. 1 is a schematic vertical sectional view showing an example of an apparatus for carrying out the method of the present invention. As shown in FIG. 1, the apparatus for carrying out the method of the present invention comprises a digestion tank 1, a supply tank 10 provided in the vicinity of the digestion tank 1, and a circulation pump provided at the bottom of the digestion tank 1. 11 and circulation pump 11
A circulation pipe 12 whose one end is connected to the other end and the other end is connected to a supply port provided in the top wall 1a of the digestion tank 1,
, A discharge pipe 14 branched from a position close to the circulation pump 11 and having a first switching valve 13 in the middle thereof, a supply pump 15 provided at the bottom of the supply tank 10, and one end of which is connected to the pump 15. And a second switching valve provided between the supply pipe 16 having the other end connected in the middle of the circulation pipe 12 and the connection portion of the circulation pipe 12 with the discharge pipe 14 and the connection portion with the supply pipe 16. 17, a gas discharge pipe 3 for discharging a digested gas generated in the digestive tank 1, one end of which is connected to a gas outlet provided on the top wall of the digestive tank 1, , A gas blow-in pipe 18 vertically inserted through the top wall, and one end of the gas blow-out pipe 3 is connected in the middle, and the other end is connected to the gas blow-in pipe 18, and a gas compressor 19 is in the middle thereof.
Is provided with a branch pipe 20.

The cross-sectional shape of the digestion tank 1 is circular or square so that sludge digested in the digestion tank 1 can be efficiently supplied to the circulation pump 11 provided in the lower portion of the digestion tank 1. The lower part 1b of the digestion tank 1 has a hopper shape. A screw conveyor for scraping the digested cake may be provided at the lower end discharge port of the digestion tank 1.

[0014]

[Function] The second switching valve 17 is opened and the circulation pump 11 is driven to forcibly discharge the digested cake-like sludge in the lower portion 1b of the digestion tank 1 from the digestion tank 1 and pass through the circulation pipe 12 again. It is supplied into the upper part of the digestion tank 1 from the supply port of its top wall. In this way, the digested cake-like sludge circulates in the digestion tank 1 and the circulation pipe 12. On the other hand, the cake-like sludge A, which has been concentrated in a not-illustrated concentrator and then dehydrated in the not-illustrated dehydrator, is supplied into the supply tank 10 from above.

The cake-like sludge A in the supply tank 10 is
Is supplied to the digested cake-like sludge as seed sludge, which circulates in the circulation pipe 12 through the supply pipe 16 by the supply pump 15 provided at the lower part of the circulation pipe 12, and is sufficiently mixed in the circulation pipe 12. Then, it is supplied into the digestion tank 1. Therefore,
The cake-like sludge having poor fluidity is mixed with the seed sludge in the circulation pipe 12 and sufficiently stirred while circulating in the circulation pipe 12 and the digestion tank 1.

The cake-like sludge thus supplied to the digestion tank 1 is allowed to stay in the digestion tank 1 in an anaerobic state for a certain period of time to ferment methane. As a result, the cake-like sludge in the digestion tank 1 is decomposed and its organic components are digested.

The digestion gas generated in the digestion tank 1 is
The gas is discharged from the digestion tank 1 through the gas discharge pipe 3, and is collected and used as fuel for a boiler or the like. A part of the digested gas is guided to the branch pipe 20 and compressed by a gas compressor 19 provided in the middle of the branch pipe 20. When the digestion gas is compressed by the gas compressor 19, the temperature of the gas increases by about 10 ° C. per 0.1 Kg / cm ² . The high-temperature digestion gas whose temperature has risen in this way is blown into the digestion tank 1 through the gas blowing pipe 18.

The high-temperature digestion gas blown into the digestion tank 1 causes the cake-like sludge in the digestion tank 1 to be heated and agitated without increasing the water content thereof, and the compaction is prevented, and the cake-like sludge is generated. It promotes the release of digestive gas. Therefore, the cake-like sludge in the digestion tank 1 can be efficiently digested in a short time.

Excess digested cake-like sludge in the digestion tank 1 is forcibly discharged by the circulation pump 11 through the discharge pipe 14 by closing the second switching valve 17 and opening the first switching valve 13. ..

[0020]

As described above, according to the method of the present invention, dehydrated cake-like sludge can be stored in a digester tank as follows.
It can be uniformly heated and stirred without increasing its water content, which has an industrially useful effect of efficiently digesting cake-like sludge in a short time.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view showing an example of an apparatus for carrying out the method of the present invention.

FIG. 2 is a schematic vertical sectional view showing an example of a conventional device.

FIG. 3 is a schematic vertical sectional view showing another example of a conventional device.

[Explanation of symbols]

 1 digestion tank 2 supply pipe 3 discharge pipe 4 steam injection pipe 5 discharge pipe 6 circulation pump 7 heat exchanger 8 circulation pipe 9 heating source 10 supply tank 11 circulation pump 12 circulation pipe 13 first switching valve 14 discharge pipe 15 pump 16 Supply pipe 17 Second switching valve 18 Gas blowing pipe 19 Gas compressor 20 Branch pipe A Cake sludge

Claims (1)

[Claims] 1. A dehydrated cake-like sludge is supplied into a digestion tank, the dehydrated cake-like sludge is digested in the digestion tank, and a part of the digested cake-like sludge is removed from the digester tank. By a circulation mechanism provided outside, the digestion tank is forcibly circulated, a part of the digestion gas generated in the digestion tank and discharged from the digestion tank is compressed by a gas compressor, Then, the digested gas whose temperature has been increased by being compressed is blown into the cake-like sludge in the digestion tank to heat and agitate the cake-like sludge, and thus the cake-like sludge in the digestion tank is efficiently produced. A method for digesting cake-like sludge, which comprises digesting into cake.