JPH06218396A - Anaerobic digesting device and sludge feed method - Google Patents

Abstract

PURPOSE:To reduce equipment cost, decrease the amount of space required for installing equipment, and obviate clogging and increase in pressure due to sludge by heating feed sludge by causing the feed sludge to be heat exchanged with digested sludge drawn out of a digester and circulating the digested sludge from a drawing-out passage to a sludge feed passage. CONSTITUTION:Feed sludge transferred by a sludge transfer pump 6 is heat exchanged with digested sludge at a sludge/sludge heat exchanger 2 so as to be heated by the heat held in the digested sludge and distributed to digesters 1a-1d at predetermined time intervals by a distributor 3. After completion of distribution, the digested sludge of nearly the same amount as the fed sludge is drawn out for the same time period, and such operation is repeated in each of the digesters 1a-1d successively. When the amount of liquid of a sludge feed tank falls to a certain amount, the pump 6 is stopped to stop the feed of sludge and at the same time a circulation valve 12 of the digested sludge is opened and the degested sludge is circulated via a sludge feed passage 14 before the exchanger 2 and a circulation passage 17, so that the sludge is always sent without being disturbed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anaerobic digestion apparatus for biologically anaerobic digesting organic sludge such as sewage sludge and a sludge supply method in this apparatus.

[0002]

2. Description of the Related Art In order to efficiently treat organic sludge by an anaerobic digester, it is necessary to control the temperature of sludge in a digestion tank to a predetermined temperature at which biological activity is effectively maintained. Incidentally, in the medium temperature fermentation treatment, 30 to 40 ° C, preferably 35 to 38 ° C, and the high temperature fermentation treatment, 45 to 55 ° C,
Preferably, the treatment is controlled at 47 to 50 ° C.

In order to maintain the treatment temperature without being affected by the fluctuation of the outside air temperature depending on the season, the digestion tank is equipped with a heating pipe, or the outside of the digestion tank is provided with a hot water / sludge heat exchanger. The sludge in the tank is circulated and heated to heat it by exchanging heat with hot water, or steam is blown directly into the sludge in the digestion tank to heat it.

[0004] Conventionally, hot water or steam which is a heating source of sludge is generally hot water or steam recovered from an attached digestion gas power generation facility. Etc., the amount of heat is insufficient with only the heating source, so a hot water boiler is usually installed separately, and the temperature is maintained by a plurality of hot water / sludge heat exchangers.

[0005]

Conventionally, as described above, a hot water boiler is separately installed and a part of the digested gas generated by the anaerobic digestion process is consumed to cope with the problem. Therefore, the fuel gas for power generation is used. As a result, it has not been used effectively enough, and the equipment cost and equipment installation area are too large.

[0006] As a heating source, a method of exchanging heat between the digested sludge extracted from the digestion tank and the supplied sludge supplied to the digestion tank to recover and utilize the amount of heat held by the digested sludge has been considered. In the conventional device and operation control method, sludge retention in the used sludge / sludge heat exchanger cannot be prevented and is easily clogged, and there is a problem in selecting a sludge supply pump due to increased pressure loss. Had not been implemented.

Accordingly, the present invention is a sludge / sludge heat exchanger capable of sufficiently effectively utilizing the digestive gas produced by the anaerobic digestion process, reducing the facility cost and reducing the facility installation area. Retaining heat recovery of digested sludge using
It is made for the purpose of providing an anaerobic digester and a sludge supply method which do not cause clogging and increase in pressure loss due to sludge as in the conventional case.

[0008]

The gist of the present invention for achieving the above object is to raise the supply sludge by exchanging heat between the supply sludge supplied to the digestion tank and the digestion sludge extracted from the digestion tank. A sludge / sludge heat exchanger for heating is provided, and a digestion sludge is provided with a circulation channel for circulating from the extraction channel to the sludge supply channel upstream of the sludge / sludge heat exchanger. Anaerobic digester.

Further, in the method of anaerobic digestion of organic sludge by the anaerobic digestion apparatus having a plurality of digestion tanks, in the same digestion tank, sludge distribution / supply operation and digestion sludge withdrawal are performed. In order not to overlap with the operation, and to control the opening and closing of the input valve and the withdrawal valve provided in each flow path so that each of the operations sequentially moves to each digestion tank at a predetermined time interval, and the sludge supplied from the sludge supply tank At the stop of
The sludge supply method is characterized in that the circulation valve is controlled to be opened so that the digested sludge is supplied to the sludge supply flow path upstream of the sludge / sludge heat exchanger through the circulation flow path.

[0010]

[Operation] The supplied sludge transferred by the sludge transfer pump is
Heat is exchanged with digested sludge in the sludge / sludge heat exchanger and heated by the amount of heat retained by the digested sludge. The supply sludge whose temperature has been raised is distributed and supplied to each digestion tank by a distributor at predetermined time intervals.

After the sludge is sequentially supplied to each digestion tank for one cycle, the sludge is again supplied to the first digestion tank. Immediately before that, the operation for extracting the digested sludge in substantially the same amount and for the same time as the supplied sludge is performed. This is performed and this operation is sequentially repeated in each digester.

As a result, the sludge is supplied and the sludge is withdrawn in the same amount in the entire digester at the same time, and pressure fluctuations on the digested gas side that are generated are not caused, so that the digested gas is used. The operation in is extremely easy.

When the amount of liquid in the sludge supply tank drops to a certain amount, the sludge transfer pump is stopped and the sludge supply is stopped, but at the same time, the digestive sludge circulation valve is controlled to open, and the digested sludge becomes sludge / sludge heat. Since the sludge is circulated in the sludge supply passage in the preceding stage of the exchanger, the sludge always flows without staying, and there is no risk of clogging the heat exchanger and increasing pressure loss.

In the above description, it is not possible to raise the temperature to the temperature for maintaining the biological activity in the digestion tank only by recovering the calorific value of the digested sludge by the sludge / sludge heat exchanger, so that steam is usually blown directly into the sludge. Or, it is necessary to attach a hot water / sludge heat exchanger to further heat the sludge.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system diagram related to the main part of one embodiment of the present invention. Reference numeral 1 is a digestion tank, which is provided with an arbitrary number of bases depending on the amount of organic sludge to be treated, but it is preferable to provide two or more tanks,
In this embodiment, four tanks 1a to 1d are provided.

2 is a sludge for exchanging heat between the supplied sludge and the digested sludge to raise the temperature of the supplied sludge by the amount of heat retained by the digested sludge /
The sludge heat exchanger is preferably a spiral heat exchanger, but any heat exchanger having a shape that does not form a sludge stagnant area can be used.

Reference numeral 3 denotes a distributor for distributing and supplying sludge to a plurality of digestion tanks 1a to 1d, and a sludge distribution / supply flow passage 15 provided with an injection valve 10 for controlling the injection into each digestion tank 1 is branched. It is connected to the digestion tanks 1a to 1d.

Reference numeral 4 is a sludge supply tank for storing the treated organic sludge, and 5 is a digestion sludge storage tank for storing the digested digested sludge. A liquid level gauge 20 is attached to the sludge supply tank 4, Further, based on the output signal from the liquid level gauge 20, the sludge transfer pump 6 is started and stopped, and the circulation valve 12 and the transfer valve 1 are operated.
A control device 21 for controlling the opening and closing of 3 is provided.

Reference numeral 6 is a transfer pump for transferring the sludge from the sludge supply tank 4 to the digestion tank 1, and reference numeral 7 is a digestion sludge pump for extracting the digested sludge from the digestion tank 1 and transferring it to the digestion sludge storage tank 5.

Reference numeral 14 is a sludge supply passage connected from the sludge supply tank 4 to the distributor 3 via the sludge / sludge heat exchanger 2, and 15 is branched from the distributor 3 and provided with inlet valves 10a to 10d. Sludge distribution and supply channels connected to tanks 1a to 1d, 1
6 is an extraction valve 1 for extracting digested sludge from the digestion tanks 1a to 1d
It is an extraction flow path of digested sludge which comprises 1a to 11d and is connected to the digested sludge storage tank 5.

Reference numeral 17 is a circulation flow path which is provided with a circulation valve 12 and is connected from the digestion sludge withdrawal flow path 16 to the sludge supply flow path 14 in the preceding stage of the sludge / sludge heat exchanger 2, and when sludge supply is stopped, The digested sludge is circulated to the sludge / sludge heat exchanger 2 to prevent sludge retention.

The circulation passage 17 is preferably provided so as to be branched from the withdrawal passage 16 at the latter stage of the sludge / sludge heat exchanger 2, but may be provided so as to be branched from the withdrawal passage 16 at the former stage. . Reference numeral 18 denotes a digestion gas flow path for transferring the digestion gas generated by the digestion process to the gas holder.

Although not shown, since it is impossible to maintain the temperature of the sludge in the digestion tank only with the sludge / sludge heat exchanger 2, a hot water / sludge heat exchanger is used in this embodiment. Although attached, a process of heating steam by blowing steam directly into the sludge may be used.

Further, the warm water for heating is preferably recovered from a digestion gas power generation facility which is generally installed conventionally, but the hot water or steam may be manufactured by installing a hot water boiler or the like. .

Next, the action of digesting organic sludge such as sewage sludge by the anaerobic digester having the above-mentioned structure will be described. The organic sludge to be treated is temporarily stored in the sludge supply tank 4 until a constant liquid amount is reached.

After the amount of sludge in the sludge supply tank 4 reaches a certain amount, the sludge is extracted by the transfer pump 6, and the supply passage 1
4 is supplied to the sludge / sludge heat exchanger 2, and heat is exchanged with the digested sludge while flowing through the heat exchanger 2, and is heated by the amount of heat held by the digested sludge.

The sludge whose temperature has been raised is further controlled via the distributor 3 by the injection valves 10a, 10b, 10c and 10d so that the digestion tanks 1a and 1b are discharged from the respective distribution supply flow paths 15 at predetermined time intervals. 1c and 1d are sequentially distributed and supplied.

The sludge supplied to the digestion tank 1 is uniformly mixed with the sludge accumulated in the tank and is anaerobically treated. However, the above-mentioned heating alone is influenced by the fluctuation of the outside temperature depending on the season and the biological activity is always maintained. Since it cannot be maintained at a certain temperature, it can be circulated to the attached hot water / sludge heat exchanger,
Further heated.

The temperature at which the biological activity is maintained is 30 to 40 ° C., preferably 35 to 38 in the medium temperature fermentation treatment.
℃, 45-55 ℃ in high temperature fermentation treatment, preferably 47-
It is 50 ° C.

After the sludge is sequentially supplied to the digestion tanks 1a to 1d for one cycle, the sludge is again supplied to the first digestion tank 1a. Immediately before that, the extraction valve 11a is opened and the digestion sludge pump 7 operates. The extraction operation of digested sludge is performed in the same amount and for the same time as the supplied sludge.

The digested sludge extracted by the digested sludge pump 7 flows through the outflow passage 16, and the sludge / sludge heat exchanger 2
After being subjected to heat exchange with the supplied sludge, further sent to the digested sludge storage tank 5 and stored therein, it is treated by a sludge treatment device such as a solid-liquid separation device (not shown) in the subsequent stage.

By sequentially repeating the above-mentioned operations in the digestion tanks 1a to 1d, the digestion apparatus as a whole can supply sludge and withdraw the digested sludge at the same time and in the same amount. Since the pressure fluctuation on the gas side is not caused, the operation in utilizing digestion gas becomes extremely easy.

When the amount of liquid in the sludge supply tank 4 decreases to a certain amount, the sludge transfer pump is stopped and the sludge supply is stopped. At the same time, the digestive sludge circulation valve 12 is controlled to open, and the digested sludge is converted into sludge. / Sludge heat exchanger 2 Since it is circulated in the sludge supply flow path 14 in the previous stage, sludge is sludge / sludge heat exchanger 2
There is no risk of blockage of the heat exchanger and increase of pressure loss, because it constantly flows without staying inside.

The operation and stop of the sludge transfer pump 6 and the control of the opening / closing valve of the circulation valve 12 and the transfer valve 13 are performed by the sludge supply tank 4
It is performed by the control device 21 based on the output signal of the liquid level gauge 20 attached to the.

The on-off valve control of the supply sludge supply valve 10 and the digested sludge withdrawal valve 11 is usually performed by a timer control based on a preset time interval.

[0036]

The following effects can be obtained by the anaerobic digester and the sludge supply method of the present invention. B) The amount of heat retained by the digested sludge is recovered and used to raise the temperature of the sludge supplied to the digestion tank. Therefore, the temperature of the sludge in the digestion tank is maintained by the hot water recovered from the attached digestion gas power generation facility. It is possible to use only the gas, and the digestive gas can be effectively used, and it is not necessary to separately install a hot water boiler, so that the equipment cost can be reduced and the equipment installation area can be reduced.

(B) Since a sludge accumulation area does not occur in the sludge flow passage of the sludge / sludge heat exchanger, there is no risk of clogging by the sludge and increase in pressure loss.

C) Since the supply of sludge and the extraction of digested sludge do not overlap with each other in the same digestion tank, the untreated sludge does not short-pass, and the supply and the extraction are the same in the entire digester. Moreover, since the same amount is used, there is no risk of pressure fluctuations on the digestive gas side, and the operation in utilizing digestive gas becomes easy.

[Brief description of drawings]

FIG. 1 is a system diagram related to a main part of an embodiment of the present invention.

[Explanation of symbols]

 1: Digestion tank 2: Sludge / sludge heat exchanger 3: Distributor 4: Sludge supply tank 5: Digestion sludge storage tank 6: Sludge transfer pump 7: Digestion sludge pump 10: Input valve 11: Extraction valve 12: Circulation valve 13 : Transfer valve 14: Supply flow path 15: Distribution supply flow path 16: Extraction flow path 17: Circulation flow path 20: Liquid level gauge 21: Control device

Claims (2)

[Claims] 1. In an anaerobic digester for anaerobic digesting organic sludge, the supply sludge is heated by exchanging heat between the supply sludge supplied to the digestion tank and the digestion sludge extracted from the digestion tank. Anaerobic property of organic sludge, which is equipped with a sludge / sludge heat exchanger and a circulation channel that circulates digested sludge from the extraction channel to the sludge supply channel before the sludge / sludge heat exchanger. Digestive equipment. 2. The anaerobic digester according to claim 1, wherein
In a method for anaerobic digestion of organic sludge with a device provided with a plurality of digestion tanks, the sludge distribution / supply operation and the digestion sludge extraction operation in the same digestion tank do not overlap, and the respective operations are performed. While controlling the opening and closing of the input valve and the withdrawal valve equipped in each flow path so that it sequentially moves to each digestion tank at a predetermined time interval, when the sludge supply from the sludge supply tank is stopped, the digested sludge passes through the circulation flow path / A sludge supply method characterized in that a circulation valve is controlled to be opened so that the circulation valve is supplied to the sludge supply passage in the preceding stage of the sludge heat exchanger.