JP3482688B2 - Method of treating exhaust gas from anaerobic treatment equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating exhaust gas from an anaerobic treatment apparatus, and more particularly to a method for industrially treating exhaust gas containing methane gas discharged from an anaerobic treatment apparatus by catalytic combustion. .

[0002]

2. Description of the Related Art Conventionally, exhaust gas containing methane gas generated from a high load anaerobic wastewater treatment equipment such as a UASB (fluidized bed type) or a fixed bed type has been mainly used as a fuel for a boiler. When not using,
Excess gas combustion towers may be installed side by side with the anaerobic treatment device for the disposal of exhaust gas discharged during inspection.

This is because it is judged that it is not preferable in terms of the global environment to release a large amount of methane gas even temporarily, in addition to the prevention of danger such as explosion (by the way, methane gas is 20 times as much as carbon dioxide gas). It is expected that these movements will spread not only to large-scale treatment facilities but also to small-scale treatment facilities that mainly perform atmospheric emission disposal. .

By the way, there are types of surplus gas combustion towers such as an internal combustion type and an external combustion type, both of which are considerably expensive as a single piece of equipment to be purchased and are comparable in price to a boiler. Further, even if the gas is disposed of by combustion without being effectively used because it is a small-scale device, not only the combustion tower but also a functional gas holder is required. That is, combustion refers to a chemical change in which a substance is oxidized in the air to form a flame, and it is important to set conditions that satisfy the combustion concentration range specific to the fuel and the combustion start temperature. Since all of the current combustion towers use the flame combustion method and it is necessary to maintain the air-fuel ratio within a certain range, the gas holder is used for adjustment.

[0005]

As described above, the provision of the combustion tower and the surplus gas combustion tower, which essentially requires the gas holder, causes the cost for that purpose to be considerably large in the installation cost of the entire equipment. Therefore, it is not industrially advantageous.

In addition, in the flame combustion by the surplus gas combustion tower, LPG for ignition is required, and the cost for that is also increased. Moreover, in flame combustion, unreacted products remain in the low temperature region and N _{2 in the} air in the high temperature region.
However, there is a problem that the combustion temperature is not easily controlled due to the problem that the NOx is oxidized to generate thermal NO _x .

Furthermore, since flame combustion produces a flame, a worker for monitoring is required to ensure safety,
In addition to being difficult to unmanned, maintenance of the combustion tower is not easy and its life is short. Incidentally, in flame combustion, the life of the combustion tower body is 2-3 years.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a method for treating methane gas-containing exhaust gas discharged from an anaerobic treatment apparatus in a stable and efficient manner, safely and at low cost. And

[0009]

A method for treating exhaust gas from an anaerobic treatment apparatus according to claim 1 , wherein the exhaust gas from the anaerobic treatment apparatus is an oxygen-containing gas in the raw water of the anaerobic treatment apparatus.
The odorous substance-containing exhaust gas generated from the above is mixed and then brought into contact with a catalyst carrying a metal under heating conditions.
A method for treating exhaust gas from the anaerobic treatment apparatus according to claim 2.
Mixes the oxygen-containing gas with the exhaust gas from the anaerobic treatment device.
After the methane gas concentration was adjusted to 0.08-0.8%, 2
Contact with a metal-supported catalyst under heating conditions of 50-600 ° C.
Characterized by being touched.

[0010]

In the present invention, the exhaust gas from the anaerobic treatment device is treated by catalytic combustion. Catalytic combustion is a process in which a combustible gas is brought into contact with air on a solid catalyst to cause an oxidation reaction, and there is no limitation on the air-fuel ratio, and combustion can be performed in a wide fuel concentration range. With such catalytic combustion,
The following operational effects can be obtained.

Even if the amount of gas generation changes, combustion can be performed by sending constant air and controlling the temperature without adjusting the air-fuel ratio. For this reason, a gas holder for making the combustion concentration uniform becomes unnecessary, and it is possible to reduce the electricity or instrumentation costs associated therewith.

[0012] The heater is preheated and can stand on its own after ignition. Therefore, the LPG for ignition is unnecessary.

Compared with flame combustion, the safety is high and unmanned is easy.

Maintenance is easy and the life of the device is long.

By the way, since methane gas has a higher combustion start temperature than propane or butane, it is considered to be a relatively difficult fuel to be catalytically burned, but by using a catalyst carrying a metal such as Pt, Pd or Rh as a catalyst. Therefore, catalytic combustion can be easily performed.

[0016]

Embodiments of the method for treating exhaust gas from an anaerobic treatment apparatus according to the present invention will be specifically described below with reference to the drawings.

FIG. 1 is a system diagram showing a method according to an embodiment of the present invention.

In the method shown in FIG. 1, the drainage is pipe 1
1 is introduced into the high load anaerobic treatment apparatus 1 and is anaerobically treated, and the contained organic matter is converted to methane gas. Treated water whose organic matter concentration has been reduced by anaerobic treatment is pipe 1
2 is discharged from the system. In this anaerobic treatment, since the exhaust gas generated from the anaerobic treatment apparatus 1 contains sulfides such as hydrogen sulfide, in order to prevent sulfur oxides from being generated during catalytic combustion, first, Desulfurize exhaust gas discharged. That is, the exhaust gas is introduced into the desulfurization tower 2 through the pipe 13 for desulfurization treatment. Then, the desulfurization treatment gas is directly supplied to the pipe 15 without adjusting the gas flow rate.
It is introduced into the catalytic combustion tower 3 through the pipe 14 together with the air supplied at a constant flow rate from. That is, as described above, in this catalytic combustion, since there is no limitation on the air-fuel ratio, it is not necessary to adjust the gas flow rate. The amount of air supplied to the catalytic combustion tower 3 may be the minimum amount necessary to burn the maximum amount of exhaust gas generated from the anaerobic treatment device 1, and the amount of air supply may be changed according to the scale and conditions of the anaerobic treatment device. Once set, stable treatment can be performed regardless of fluctuations in the amount of exhaust gas generated from the anaerobic treatment device.

In this catalytic combustion tower 3, the methane gas in the exhaust gas is efficiently catalytically oxidized. In the catalytic combustion tower 3, the processing gas having a significantly reduced methane gas concentration is discharged from the system through the pipe 16.

Next, an example of the anaerobic treatment apparatus to which the present invention is applied will be described with reference to FIG.

FIG. 2 shows an anaerobic treatment apparatus suitable for anaerobic treatment of high-concentration organic wastewater such as beer wastewater, in which the organic wastewater introduced from the pipe 31 as raw water is stored and preconditioned. As a raw water adjusting tank 21 that also serves as an acid production tank for heating and adjusting pH, the effluent discharged from the raw water adjusting tank 21 through the pipe 32 is diluted by adding warm dilution water supplied from the pipe 33. An organism that deodorizes exhaust gas sent from a UASB-type methane fermentation tank (anaerobic treatment device) 22 that decomposes organic matter contained in the warmed liquid by anaerobic treatment to methane and a raw water adjusting tank 21 through a pipe 34 The deodorizing device 23 and the biological deodorizing device 24 for deodorizing the exhaust gas sent from the methane fermentation tank 22 through the pipe 35 are mainly configured.

In order to apply the method of the present invention to such an anaerobic treatment apparatus, a methane fermentation tank 22 is shown in FIG.
From the desulfurization tower 25 for treating the exhaust gas (methane gas) discharged from the pipe 36 (36a, 36b) from the desulfurization tower 25 and the desulfurization treatment gas discharged from the desulfurization tower 25 via the pipe 37 together with the air from the pipe 38 to perform catalytic combustion. A catalytic combustion tower 26 that discharges gas from the system through a pipe 39 is provided. In addition,
In the figure, a pipe 40 is a pH adjusting agent supply pipe such as NaOH, a pipe 41 is a pipe for circulating treated water of a methane fermentation tank extracted from an extraction pipe 42, and a dilution outflow from the raw water adjusting tank 21 described above. The liquid supply pipe 32 is connected to the circulation pipe 41. Further, this circulation pipe 41 has a plurality of sides (7 in the figure) connected to the bottom of the methane fermentation tank 22.
It is branched into a branch pipe of (main), and the inflow liquid to the methane fermentation tank 22 is uniformly fed. Four
Reference numeral 3 is a pipe for discharging treated water of the methane fermentation tank 22. Further, P ₁ and P ₂ are pumps.

In this embodiment, the methane fermentation tank 2
In the upper part of the inside of 2, the oblique partition plates 27A and 27B are installed with their upper ends connected to the tank top plate and their lower ends as free sides. This partition plate 27A, 27
Of the B, the lower end side of one partition plate 27B is provided below the lower end side of the other partition plate 27A, and the lower end side of the partition plate 27B is provided below the partition plate 27A. The extraction pipe 42 is provided so as to be inserted into a region partitioned by the partition plates 27A and 27B.

For treating beer effluent with such a treatment facility, for example, the beer effluent is first introduced into the raw water adjusting tank 21 through the pipe 31 and stored therein to absorb fluctuations in the raw water flow rate. In the meantime, the liquid in the tank 21 is heated and the pH is adjusted by adding a pH adjusting agent such as NaOH through the pipe 40. The liquid in the raw water adjusting tank 21 is preferably heated to 30 to 40 ° C. and adjusted to pH 5.0 to 6.0 by pH adjustment.

As described above, by heating and adjusting the pH, organic substances such as sugars and proteins in the stored liquid in the raw water adjusting tank 21 are decomposed into lower fatty acids such as acetic acid and propionic acid by the action of the spoilage bacteria. To be done. With the progress of the production of this organic acid, butyric acid, propionic acid, hydrogen sulfide and other malodorous substances are generated. To do.

In this biological deodorization, the exhaust gas in the raw water conditioning tank 21 contains a high concentration of malodorous substances. Therefore, if this is directly sent to the biological deodorization device 23, the packing material in the device 23 will be significantly blocked. . Therefore, this exhaust gas is sent to a water washing tower (not shown) for washing with water to remove components such as an organic acid and hydrogen sulfide, which are easily dissolved in water, into water in advance, and then to the biological deodorizer 23. To pay. The exhaust gas may be sent to the catalytic combustion tower as air for the catalytic combustion tower instead of being treated by the biological deodorizer.

The liquid in which the organic acid is stored and stored in the raw water adjusting tank 21 is taken out from the pipe 32 equipped with the pump P ₁ and mixed with warmed dilution water of about 37 to 47 ° C. from the pipe 33. , To the methane fermentation tank 22.

By mixing the warmed diluted water, the COD _cr concentration in the mixed liquid of the outflow liquid of the raw water adjusting tank 21 and the diluted water (hereinafter sometimes referred to as “diluted raw water”) is 30,000 m.
It is preferably adjusted to g / l or less. The temperature of the diluted raw water is preferably adjusted so that the liquid temperature in the methane fermentation tank 22 is about 30 to 35 ° C. CO of this diluted raw water
When the D _cr concentration exceeds 30,000 mg / l, the load on the methane fermentation tank 22 becomes too large, and good treated water cannot be obtained. The liquid temperature in the methane fermentation tank 22 is 30
Optimum methane fermentation conditions are ~ 35 ° C.

The methane fermentation tank 22 is loaded with granulated anaerobic sludge (granule sludge / microorganisms),
As a result, the organic substances in the diluted raw water introduced into the tank 22 are efficiently converted to methane. The efficiency of the methane fermenter according to this example is very high, for example, 15 to 30 kg-
High processing is possible even under high load conditions of COD _cr / m ³ / day. The size of the methane fermentation tank 22 is 3.3 m (width) x 3.3 m (length) x 6.0 m.
It is preferable that the height is within (height) and the volume can be carried by a truck or the like.

The treated water in the methane fermentation tank 22 is extracted from the extraction pipe 42.
The water is extracted from the tank, a part of the water is circulated to the bottom of the tank 22 through the circulation pipe 41, and the rest is treated water, which is fed from the pipe 43 to the secondary treatment step or the like. The treated water in the methane fermentation tank is generally one in which 90% or more of the organic matter in the diluted raw water has been decomposed and removed, and can be easily treated in the secondary treatment step without increasing the load. In the usual case, the treated water is sent to a raw water tank for brewing wastewater, treated with activated sludge, and finally discharged into sewer.

On the other hand, the exhaust gas produced in the methane fermentation tank 22 contains hydrogen sulfide and the like together with methane gas.
This exhaust gas is sent from the pipes 36a, 36b and 36 to the desulfurization tower 25.
To remove the sulfides such as hydrogen sulfide, and then pipe 37
Is sent to the catalytic combustion tower 26 together with the air from the pipe 38 for catalytic combustion treatment, and the treated gas is discharged to the outside of the system through the pipe 39.

The partition plate 2 above the methane fermentation tank 22
Exhaust gas containing a small amount of hydrogen sulfide generated from the treated water side partitioned by 7A and 27B is sent to the biological deodorizing device 24 through the pipe 35 for deodorizing treatment to prevent secondary pollution due to bad odor. The biological deodorizer 24 may not be separately provided, and the exhaust gas from the methane fermentation tank 22 may be fed to the biological deodorizer 23 to perform the deodorizing process.

In the present invention, the catalytically active component is a noble metal such as platinum (Pt), palladium (Pd), rhodium (Rh), or an oxide of a base metal such as cobalt (Co) and chromium (Cr) (Co ₃ O _4). , Cr ₂ O ₃ etc.) supported on a carrier such as alumina, silica-alumina, silica or titania in an amount of 0.05 to 10% by weight, preferably 0.1 to 5% by weight.

The catalytic combustion with such a catalyst is 250
It is preferably carried out under heating conditions of about 600 ° C. This temperature can be easily realized by heating with an electric heater or the like, and after combustion is started and stabilized, external heating is not necessary.

When the exhaust gas is desulfurized in advance during catalytic combustion, an adsorbent such as iron sulfide or activated carbon can be used for desulfurization treatment.

The present invention will be described in more detail with reference to specific examples.

Example 1 According to the method shown in FIG. 1, the exhaust gas generated from the high load anaerobic treatment apparatus (UASB) shown in FIG. 2, which processes beer wastewater, is desulfurized in a desulfurization tower filled with an iron oxide adsorbent. After that (hereinafter, the obtained desulfurized gas is referred to as “raw gas”. The composition of this raw gas was as shown in Table 1.)
The mixture was mixed with air in an amount of about 100 to 1000 times the volume of the raw gas, and the mixture was ventilated through a catalytic combustion tower for catalytic combustion.

As the catalytic combustion tower, a column having a diameter of 2.5 cm was filled with a catalyst (Pd loading amount 0.5% by weight) in which Pd was supported on alumina pellets (average particle diameter 2 mm) so that the height was 5 cm. And packed in a packed bed capacity of 24.5 cm ³
Was used. The inlet temperature of the catalytic combustion tower was adjusted to 350 ° C by a heater.

The air flow rate to the catalytic combustion tower is 4 liters / m.
in (SV = 9800 hr ⁻¹ ) and the raw gas flow rate is 4 to
The composition of the processing gas was examined by changing it in the range of 40 ml / min. As a result, the processing gas shown in Table 1 could be stably obtained.

From this, according to the treatment method by catalytic combustion of the present invention, even if the flow rate of the raw gas is changed and the methane gas concentration at the inlet of the catalytic combustion tower is changed within the range of 0.08 to 0.8%. The methane gas concentration at the outlet is stable at 0.01% or less, and it is clear that stable processing can be performed regardless of the air-fuel ratio.

[0041]

[Table 1]

[0042]

As described in detail above, according to the method for treating exhaust gas from the anaerobic treatment apparatus of the present invention, the methane gas-containing exhaust gas discharged from the anaerobic treatment apparatus can be stably and efficiently and safely. It can be processed at low cost.

The method for treating exhaust gas from an anaerobic treatment apparatus of the present invention aims to reduce exhaust gas treatment cost as an alternative means of the surplus gas combustion tower provided in the conventional high load anaerobic treatment apparatus, and Its industrial utility is extremely large, such as introducing flue gas into a facility that emits air to prevent the explosion of methane gas and to protect the environment.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of a method for treating exhaust gas from an anaerobic treatment apparatus of the present invention.

FIG. 2 is a system diagram showing details of an anaerobic treatment apparatus.

[Explanation of symbols]

1 High load anaerobic treatment equipment 2 desulfurization tower 3 catalytic combustion tower 21 Raw water adjusting tank 22 Methane fermenter 23,24 Biological deodorizer 25 Desulfurization tower 26 Catalytic combustion tower 27A, 27B partition plate 28 Granule sludge

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Claims (2)

(57) [Claims] 1. A malodor produced from raw water of the anaerobic treatment device as an oxygen-containing gas in the exhaust gas from the anaerobic treatment device.
A method for treating exhaust gas from an anaerobic treatment apparatus, which comprises mixing a substance-containing exhaust gas and then bringing the mixture into contact with a catalyst carrying a metal under heating conditions. 2. The exhaust gas from the anaerobic treatment device contains oxygen.
Mixing the gas with the methane gas concentration of 0.08-0.8%
Then, the metal is supported under the heating condition of 250 to 600 ° C.
Anaerobic treatment device characterized by contacting with a catalyst
The method of treating these exhaust gases.