JP2890043B1 - Anaerobic digestion method and apparatus for organic sludge - Google Patents

Abstract

A method for anaerobic digestion of organic sludge is provided.
The high-temperature heating air obtained by using the combustion heat of the digestion gas is brought into direct contact with the sludge to efficiently heat the sludge without causing a scaling trouble. SOLUTION: The concentrated sludge is heated and then subjected to anaerobic digestion, wherein (a) heat is recovered as heating air from the combustion heat of digested gas through a gas heat exchanger 14;
(B) The heated air is brought into direct contact with the digested sludge and the concentrated sludge in the heating tower 16 to heat the sludge. (C) The heated sludge is supplied to the high-temperature digestion tank 10 for anaerobic digestion. ,
The heating tower exhaust air is supplied to the gas heat exchanger 14 and the digestion gas combustion furnace 1
2 at least.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for anaerobic digestion of organic sludge such as sewage sludge. The present invention relates to a method and apparatus for performing anaerobic digestion after heating with heated air obtained by heat exchange.

[0002]

2. Description of the Related Art As a method for reducing the amount of organic sludge, an anaerobic digestion method is conventionally known (for example, see Japanese Patent Publication No. 7-108399). In the conventional anaerobic digestion method, a two-phase digestion method (a method in which two stages of acid fermentation and anaerobic digestion are provided) and a high-temperature digestion method are known as methods for increasing the digestion rate and digestion efficiency. And in the sludge heating step before the digestion step, steam or hot water is used.

[0003]

The conventional sludge heating apparatus using steam requires a qualification for operation because it uses a boiler, and it is difficult to save labor because the operator cannot leave the site. In the case of the hot water heating method, unmanned operation is possible. However, since an indirect heat transfer type heat exchanger is required, scale grows on the heat transfer surface (the cause of scaling is sludge in sludge. As the temperature of Ca increases, the solubility decreases and crystals are precipitated as crystals), and the thermal efficiency deteriorates. In addition, as long as hot water is used, the temperature on the high temperature side is 100 ° C. or less, so that high temperature digestion (55 ° C.
For this reason, heat exchange with a high-temperature heat medium is efficient, but in hot water, the temperature difference is small and the efficiency is poor.

The present invention has been made in view of the above points, and an object of the present invention is to concentrate organic sludge using heated air obtained by exchanging heat with the flue gas of a digestion gas generated in an anaerobic digestion step. An object of the present invention is to provide a method and an apparatus for anaerobically digesting sludge after efficiently heating the sludge. It is another object of the present invention to provide a two-phase high-temperature anaerobic digestion method and apparatus capable of effectively heating sludge.
It is a further object of the present invention to provide a method and an apparatus for anaerobic digestion of organic sludge which can reduce the ammonia concentration in digested sludge.

[0005]

In order to achieve the above object, the method for anaerobic digestion of organic sludge of the present invention is a method of anaerobically digesting concentrated sludge after heating it.
(A) from the heat of digestion gas combustion through the gas heat exchanger,
Heat is recovered as heated air, and (b) the heated air is brought into direct contact with digested sludge and concentrated sludge in a heating tower to heat the sludge; (c) The heated sludge is supplied to a high-temperature digester To perform anaerobic digestion and supply the heated tower exhaust air to at least one of a gas heat exchanger and a digestive gas combustion furnace (see FIGS. 1 to 3).

In the method of the present invention, the concentrated sludge is heated in a medium-temperature heating tower (first heating tower), then acid-fermented, and then the acid-fermented sludge is further heated to a high-temperature heating tower (second heating tower). Anaerobic digestion after heating in a heating tower).
Heat is recovered as heated air from the combustion heat of the digested gas via a gas heat exchanger, and (b) the heated air and acid fermentation (3)
(0-40 ° C.) and the sludge is brought into direct contact with a high-temperature heating tower (second heating tower) to heat the sludge to 50-60 ° C., and (c)
The sludge heated in the high-temperature heating tower is converted into a high-temperature digestion tank (50-55).
° C) to perform anaerobic digestion, and supply high-temperature heating tower exhaust air to a medium-temperature heating tower (first heating tower). (D) Medium-temperature heating of concentrated sludge and high-temperature heating tower exhaust air Direct contact with the tower, the heated sludge is supplied to the medium-temperature acid fermentation tank and acid fermented,
(E) introducing the exhaust air from the intermediate-temperature heating tower into the gas heat exchanger and recovering heat as heated air by indirectly contacting with the exhaust gas from the digestion gas; and introducing the heated air into the high-temperature heating tower. It is characterized by comprising a step of heating sludge and supplying it to a high-temperature digestion tank (see FIG. 4).

Further, the method of the present invention comprises heating a concentrated sludge with a digested sludge desorbent, acid-fermenting, heating the acid-fermented sludge with heated air, and then performing anaerobic digestion. (A) heat is recovered as heating air from the combustion heat of the digested gas through a gas heat exchanger, and (b) the heated air and sludge after acid fermentation (30 to 40 ° C.) are heated to a high temperature. (C) supplying the heated sludge to a high-temperature digestion tank (50 to 55 ° C.) to perform anaerobic digestion, and (D) Dewater the high-temperature (50-55 ° C) digested sludge as it is, and indirectly contact the high-temperature desorbed liquid and the concentrated sludge with the sludge heat exchanger to heat the concentrated sludge. Then, the heated concentrated sludge is supplied to a medium-temperature acid fermentation tank to perform acid fermentation, and then supplied to a high-temperature heating tower to be heated air. Sludge by direct contact with 50
It is characterized by comprising a step of heating to ６０60 ° C. and supplying it to a high-temperature digestion tank (see FIG. 5).

Further, in the method of the present invention, the concentrated sludge is heated with a digested sludge desorbing solution, and then subjected to acid fermentation. A method in which part of digested sludge from a tank is supplied to a high-temperature heating tower and heated with heated air, and then the heated sludge is supplied to a high-temperature digester, wherein (a) combustion of digested gas Heat is recovered from the heat as heated air through a gas heat exchanger,
(B) The heated air is brought into direct contact with a part of the digested sludge from the high-temperature digester in a high-temperature heating tower to bring the sludge to 50 ° C. or more,
Desirably, it is heated to 55 ° C. or more, (c) The heated sludge is supplied to a high-temperature digestion tank (50 to 55 ° C.), and the high-temperature heating tower exhaust air is supplied to the gas heat exchanger and the digestion gas combustion furnace. (D) high temperature (50-55 ° C)
Of the digested sludge is directly dewatered, the concentrated sludge is heated by indirectly contacting the high-temperature desorbed liquid and the concentrated sludge with a sludge heat exchanger, and then the heated concentrated sludge is heated in a medium-temperature acid fermenter (30). ~
(40 ° C.) for acid fermentation and then to a high-temperature digestion tank for anaerobic digestion (see FIG. 6).

In this method, an alkali agent is added to the digested sludge supplied to the high-temperature heating tower, and at least a part of the exhaust air containing ammonia exhausted from the high-temperature heating tower is used as combustion air for digestion gas. Then, it is preferable to reduce the ammonia concentration in the digested sludge by burning and decomposing the ammonia. As the alkaline agent, an aqueous solution of NaOH, an aqueous solution of Ca (OH) _{2, an} aqueous solution of CaO, an aqueous solution of Mg (OH) _{2, an} aqueous solution of MgO and the like are used.

The anaerobic digester for organic sludge of the present invention comprises:
A heating tower for heating at least one of the concentrated sludge and digested sludge with heated air, a high-temperature digestion tank for anaerobic digestion of the sludge heated by the heating tower, and Digestion gas combustion furnace for burning the digestion gas, a gas heat exchanger for heating the air with the combustion exhaust gas from the digestion gas combustion furnace, and a gas heat exchanger and digestion for the exhaust air from the heating tower And a discharge air conduit for introduction into at least one of the gas combustion furnaces (see FIGS. 1 to 6).

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments and can be implemented with appropriate modifications. is there. FIG. 1 shows an apparatus for performing an anaerobic digestion method of organic sludge according to a first embodiment of the present invention. Part or all of the digestion gas (CH ₄ , CO _2, etc.) from the high temperature digestion tank 10 maintained at 50 to 55 ° C. is supplied to the digestion gas combustion furnace 12 and burns. Digestion gas combustion furnace 1
2 is introduced into the gas heat exchanger 14, where a part of the exhaust air from the heating tower 16 is indirectly heated to 6
Use heated air at around 00 ° C. The heated air is supplied to the heating tower 1
6 and supplied to the heating tower 16
To heat the digested sludge and the concentrated sludge. Reference numeral 18 is a sludge spraying device. The heated sludge heated to 50 to 60 ° C. in the heating tower 16 is sent to the high-temperature digestion tank 10 to be anaerobically digested. Part of the exhaust air from the heating tower 16 is supplied to the gas heat exchanger 14.
And the remainder of the exhaust air from the heating tower 16 is used as combustion air for the digestion gas combustion furnace 12. 20 is an exhaust air conduit to the gas heat exchanger, 22 is an exhaust air conduit to the digestion gas combustion furnace, and 24 is a combustion air supply pipe.

In the apparatus shown in FIG. 1, a part of the exhaust air from the heating tower 16 is supplied to the gas heat exchanger 14, and the remaining part of the exhaust air is supplied to the digestion gas combustion furnace 12 to be included in the exhaust air. The ammonia gas is burned and decomposed in the digestion gas combustion furnace 12. As shown in FIG. 2, all of the exhaust air from the heating tower 16 is supplied to the digestion gas combustion furnace 12 for combustion air. And the gas heat exchanger may be configured to supply fresh air. When the concentration of ammonia in the exhaust air from the heating tower 16 is low, the entire amount of the exhaust air from the heating tower 16 is introduced into the gas heat exchanger 14 as shown in FIG. You can also.

FIG. 4 shows an apparatus for performing an anaerobic digestion method of organic sludge according to a second embodiment of the present invention. Part or all of the digestion gas (CH ₄ , CO _2, etc.) from the high temperature digestion tank 10 maintained at 50 to 55 ° C. is supplied to the digestion gas combustion furnace 12 and burns. The flue gas from the digestion gas combustion furnace 12 is introduced into the gas heat exchanger 14, where it is heated from a medium-temperature heating tower (first heating tower) 26 for heating the concentrated sludge to a medium temperature of 30 to 40 ° C. Is heated indirectly to about 600 ° C. This heated air is supplied to a high-temperature heating tower (second heating tower) 30 to be brought into direct contact with sludge (30 to 40 ° C.) after acid fermentation and heated to a high temperature of 50 to 60 ° C. The sludge heated in the high-temperature heating tower 30 is supplied to the high-temperature digestion tank 10 and is subjected to anaerobic digestion. In addition, the temperature in the high-temperature digestion tank 10 is 50 to 55 ° C. The exhaust air from the high-temperature heating tower 30 is supplied to the intermediate-temperature heating tower 26 and is brought into direct contact with the concentrated sludge to heat the concentrated sludge to 30 to 40 ° C. The heated sludge is supplied to a medium-temperature fermenter 28 for acid fermentation. The temperature in the medium-temperature acid fermentation tank 28 is 30 to
40 ° C. The acid-fermented sludge is supplied to the high-temperature heating tower 30. Reference numerals 32 and 34 denote sludge dispersing devices, and reference numeral 36 denotes a stirrer. In the present embodiment, the exhaust air from the high-temperature heating tower 30 is
Since heat exchange is performed with the raw sludge (condensed sludge) in the intermediate temperature heating tower 26, heat recovery can be performed twice, and there is an advantage that the heat efficiency is increased.

FIG. 5 shows an apparatus for performing an anaerobic digestion method of organic sludge according to a third embodiment of the present invention. Part or all of the digestion gas (CH ₄ , CO _2, etc.) from the high temperature digestion tank 10 maintained at 50 to 55 ° C. is supplied to the digestion gas combustion furnace 12 and burns. The flue gas from the digestion gas combustion furnace 12 is introduced into the gas heat exchanger 14, where the exhaust air from the high temperature heating tower 30 is indirectly heated to 600
Use heated air around ° C. The heated air is supplied to the high-temperature heating tower 3
And heated directly to a high temperature of 50 to 60 ° C. by directly contacting the sludge after acid fermentation (30 to 40 ° C.). The sludge heated in the high-temperature heating tower 30 is supplied to the high-temperature digestion tank 10 and is subjected to anaerobic digestion. The temperature in the high-temperature digester 10 is 50
５５55 ° C. Digested sludge from the high temperature digester 10 (50
(−55 ° C.) is introduced into the dehydrator 38 and dehydrated at a high temperature to form a dehydrated cake. The high-temperature (50-55 ° C.) desorbed liquid is sent to the sludge heat exchanger 40, where it is indirectly contacted with the concentrated sludge to heat the sludge to 30-40 ° C. The heated sludge is introduced into the medium-temperature acid fermentation tank 28 to perform acid fermentation. The acid fermentation sludge at 30 to 40 ° C. is supplied to the high-temperature heating tower 30, heated to 50 to 60 ° C., and then sent to the high-temperature digestion tank 10. 34 is a sludge spraying device, and 36 is a stirrer.

Conventionally, high-temperature digested sludge and raw sludge (concentrated sludge)
And a method of indirectly contacting with a heat exchanger to recover heat has been proposed, but there is a problem in the structure of the heat exchanger for sludge containing a large amount of foreign matter. That is, it is necessary to have a structure that can easily clean both heat transfer surfaces and a structure of a heat exchanger having high heat transfer efficiency. In the case of the hot water heating method, a structure that can inspect and clean only the sludge side should have been used. In the present embodiment, since the high-temperature desorbed liquid and the raw sludge (condensed sludge) that can be handled in the same manner as hot water without containing foreign matter are heat-exchanged, the heat exchanger conventionally used for hot water heating is directly used. It has the advantage that it can be used for heat recovery.

FIG. 6 shows an apparatus for performing an anaerobic digestion method of organic sludge according to a fourth embodiment of the present invention. Part or all of the digestion gas (CH ₄ , CO _2, etc.) from the high-temperature digestion tank 10 maintained at 50 to 55 ° C. is supplied to a digestion gas combustion furnace and burns. The flue gas from the digestion gas combustion furnace 12 is introduced into a gas heat exchanger 14, where a part of the exhaust air at 60 to 70 ° C. from the high-temperature heating tower 30 is indirectly heated and heated air at about 600 ° C. And The heated air is brought into direct contact with a part of the digested sludge from the high-temperature digester 10 in the high-temperature heating tower 30 to bring the digested sludge to 50 ° C. or higher, for example, 5 ° C.
0-60 ° C, desirably 55 ° C or higher, for example 55-60
After heating to ° C., it is supplied to the high-temperature digestion tank 10. Part of the exhaust air from the high-temperature heating tower 30 is sent to the gas heat exchanger 14 as described above, and the remainder of the exhaust air from the high-temperature heating tower 30 is supplied to the digestion gas combustion furnace 12 as combustion air. Is done.

The remainder of the digested sludge from the high-temperature digester 10 is dehydrated by the dehydrator 38 while maintaining the high temperature (50-55 ° C.), and separated into a high-temperature (50-55 ° C.) desorbed liquid and a dewatered cake. The hot desorbed liquid is sent to the sludge heat exchanger 40, where:
The sludge is heated to 30 to 40 ° C by indirect contact with the concentrated sludge. The heated sludge is introduced into the medium-temperature acid fermentation tank 28 to perform acid fermentation. The acid fermented sludge at 30 to 40 ° C. is sent to the high-temperature digester 10 and mixed with the heated sludge of 50 ° C. or higher, for example, 55 ° C. or higher, from the high-temperature heating tower 30 and heated to 50 to 55 ° C. Sexually digested. 34 is a sludge spraying device, and 36 is a stirrer.

An alkaline agent such as an aqueous NaOH solution, an aqueous Ca (OH) ₂ solution, or an aqueous CaO solution is added to the digested sludge supplied to the high-temperature heating tower 30 so that the exhaust air containing ammonia exhausted from the high-temperature heating tower is discharged. A part is used as combustion air of the digestion gas combustion furnace 12 to decompose ammonia into nitrogen, thereby lowering the ammonia concentration in the digested sludge. In this case, the digestion gas combustion furnace 1
2 also functions as a deodorizing furnace. The alkali agent is added so that the pH of the digested sludge becomes a high pH of 9 or more. When the digested sludge is set at a high pH of 9 or more, the equilibrium solubility of alkaline ammonia in the digested sludge is reduced, so that the ammonia is stripped, and the efficiency of high-temperature digestion can be increased by self-digestion. In the conventional method,
Heat treatment and the addition of an alkaline agent were performed only for ammonia stripping, which was uneconomical. However, in this embodiment, heat is digested at a high temperature to supply the sludge after treatment to the anaerobic digestion tank. Another advantage is that the alkaline agent can be used for improving the efficiency of high-temperature digestion.

[0019]

EXAMPLES Examples are shown below to further clarify the features of the present invention. Example 1 A concentrated sludge (water content: 97 wt%) obtained by concentrating sewage sludge in a gravity sedimentation type thickening tank was treated as raw sludge according to the flow shown in FIG. 4 to perform anaerobic digestion. 1 in FIG.
Table 1 and Table 2 show the properties of each fluid indicated by line numbers
As shown in FIG.

[0020]

[Table 1]

[0021]

[Table 2]

Example 2 The same sludge as the concentrated sludge used in Example 1 was used as raw sludge.
Processing was performed according to the flow shown in FIG. 5 to perform anaerobic digestion.
The properties of each fluid indicated by line numbers 1 to 14 in FIG. 5 are as shown in Tables 3 and 4.

[0023]

[Table 3]

[0024]

[Table 4]

[0025]

As described above, the present invention has the following effects. (1) Heat is recovered as heated air from the combustion heat of the digestion gas, and the heated air is brought into direct contact with the sludge to heat the sludge, thereby eliminating scaling problems. (2) High-temperature heated air of about 600 ° C. is obtained by using the heat of digestion gas combustion, and the high-temperature heated air is brought into direct contact with sludge for efficient heat exchange, thus reducing the capacity of the equipment. be able to. (3) In the process of heating sludge, it has been conventionally known that a method of performing high-temperature treatment under as aerobic (air) conditions as possible promotes the digestion reaction (digestion rate and digestibility by aerobic heat treatment). Conventionally, this treatment had to be performed in a pressure vessel such as an autoclave.
With the method and the apparatus of the present invention, the effect can be performed under normal pressure without using a special pressure reactor. (4) In the case of exchanging heat between the high-temperature desorbed liquid and the raw sludge, the desorbed liquid does not contain foreign matter and can be handled in the same manner as hot water, so the heat used in the conventional hot water heating method is used. Heat can be recovered in the exchanger. (5) When the raw sludge is introduced and treated in the order of a medium-temperature heating tower, a medium-temperature acid fermentation tank, and a high-temperature heating tower, the exhaust air from the high-temperature heating tower outlet is supplied to the medium-temperature heating tower to generate the raw sludge and heat. Since the heat exchange can be performed, heat recovery can be performed twice, and the heat efficiency can be increased. (6) When ammonia stripping is performed by adding an alkali agent to a part of digested sludge, heat can be used for high-temperature digestion, and the alkali agent can be used for high-temperature digestion efficiency.

[Brief description of the drawings]

FIG. 1 is a flow sheet showing an example of an apparatus for performing an anaerobic digestion method of organic sludge according to a first embodiment of the present invention.

FIG. 2 is a flow sheet showing another example of an apparatus for performing the anaerobic digestion method of organic sludge according to the first embodiment of the present invention.

FIG. 3 is a flow sheet showing still another example of the apparatus for performing the anaerobic digestion method of organic sludge according to the first embodiment of the present invention.

FIG. 4 is a flow sheet showing an apparatus for carrying out an anaerobic digestion method of organic sludge according to a second embodiment of the present invention.

FIG. 5 is a flow sheet showing an apparatus for performing an anaerobic digestion method of organic sludge according to a third embodiment of the present invention.

FIG. 6 is a flow sheet showing an apparatus for performing an anaerobic digestion method of organic sludge according to a fourth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 High temperature digestion tank 12 Digestion gas combustion furnace 14 Gas heat exchanger 16 Heating tower 18, 32, 34 Sludge spraying apparatus 20, 22 Discharge air conduit 24 Combustion air supply pipe 26 Medium temperature heating tower 28 Medium temperature acid fermentation tank 30 High temperature heating Hot tower 36 Stirrer 38 Dehydrator 40 Sludge heat exchanger

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C02F 11/00-11/20 B09B 3/00

Claims (6)

(57) [Claims] 1. A method for anaerobically digesting concentrated sludge after heating it, comprising: (a) recovering heat as combustion air from a combustion heat of digested gas through a gas heat exchanger;
The heated air is brought into direct contact with the digested sludge and the concentrated sludge in a heating tower to heat the sludge. (C) The heated sludge is supplied to a high-temperature digestion tank for anaerobic digestion, and the heated tower is discharged. An anaerobic digestion method for organic sludge, comprising a step of supplying air to at least one of a gas heat exchanger and a digestion gas combustion furnace. 2. A method in which concentrated sludge is heated in a medium-temperature heating tower, is subjected to acid fermentation, and then the acid-fermented sludge is further heated in a high-temperature heating tower and is subjected to anaerobic digestion. a)
Heat is recovered as heated air from the heat of digestion gas combustion via a gas heat exchanger, and (b) the heated air is brought into direct contact with the sludge after acid fermentation in a high-temperature heating tower to heat the sludge. ,
(C) The sludge heated in the high-temperature heating tower is supplied to the high-temperature digestion tank for anaerobic digestion, and the high-temperature heating tower exhaust air is supplied to the medium-temperature heating tower. (D) Condensed sludge and high-temperature heating The exhaust air from the tower is brought into direct contact with the intermediate-temperature heating tower, and the heated sludge is supplied to the intermediate-temperature acid fermentation tank for acid fermentation. (E) The exhaust air from the intermediate-temperature heating tower is introduced into the gas heat exchanger. Heat recovery as heated air by indirectly contacting with the digestion gas combustion exhaust gas, introducing this heated air into a high-temperature heating tower, heating the sludge and supplying it to the high-temperature digestion tank An anaerobic digestion method of organic sludge characterized by the following. 3. A method in which concentrated sludge is heated with a digested sludge desorbent, acid-fermented, and acid-fermented sludge is heated with heated air, followed by anaerobic digestion, wherein (a) )
Heat is recovered as heated air from the heat of digestion gas combustion via a gas heat exchanger, and (b) the heated air is brought into direct contact with the sludge after acid fermentation in a high-temperature heating tower to heat the sludge. ,
(C) The heated sludge is supplied to the high-temperature digestion tank for anaerobic digestion, and the high-temperature heating tower exhaust air is supplied to the gas heat exchanger. (D) The digested sludge is dewatered as it is, and the desorbed liquid is removed. The concentrated sludge is heated by indirectly contacting the concentrated sludge with a sludge heat exchanger, and then the heated concentrated sludge is supplied to a medium-temperature acid fermentation tank for acid fermentation, and then supplied to a high-temperature heating tower. To heat the sludge by direct contact with heated air and supply it to the high-temperature digester,
An anaerobic digestion method for organic sludge, comprising the steps of: 4. The concentrated sludge is heated with a digested sludge desorbing solution, and then subjected to acid fermentation. The acid-fermented sludge is supplied to a high-temperature digestion tank for anaerobic digestion. A method in which a part is supplied to a high-temperature heating tower and heated with heated air, and then the heated sludge is supplied to a high-temperature digester,
(A) from the heat of digestion gas combustion through the gas heat exchanger,
(B) heating the sludge by bringing the heated air into direct contact with a part of the digested sludge from the high-temperature digester in a high-temperature heating tower, and (c) heating the sludge; Is supplied to the high-temperature digestion tank, and the high-temperature heating tower exhaust air is supplied to at least one of the gas heat exchanger and the digestion gas combustion furnace,
(D) The remaining part of the digested sludge is dewatered as it is, the desorbed liquid and the concentrated sludge are brought into indirect contact with a sludge heat exchanger to heat the concentrated sludge, and then the heated concentrated sludge is transferred to a medium-temperature acid fermentation tank. A method for anaerobic digestion of organic sludge, comprising the steps of: feeding and acid fermenting and then feeding to a high-temperature digestion tank for anaerobic digestion. 5. An alkali agent is added to digested sludge supplied to a high-temperature heating tower, and at least a part of exhaust air containing ammonia exhausted from the high-temperature heating tower is used as digestion gas combustion air. The method for anaerobic digestion of organic sludge according to claim 4, wherein the ammonia concentration in digested sludge is reduced by decomposing ammonia. 6. A heating tower for heating at least one of the concentrated sludge and digested sludge with heated air, a high-temperature digester for anaerobically digesting the sludge heated by the heating tower, A digestion gas combustion furnace for burning digestion gas from the high-temperature digestion tank, a gas heat exchanger for heating air with flue gas from the digestion gas combustion furnace, and gas exhausted from the heating tower An anaerobic digester for organic sludge, comprising: a heat exchanger and an exhaust air conduit for introduction into at least one of a digestion gas combustion furnace.