JPS5825520B2 - Method for removing carbon dioxide gas from gas generated by methane fermentation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing carbon dioxide from gas generated in a methane fermentation method, and particularly to the above-mentioned method with extremely low construction and operating costs.

Conventionally, carbon dioxide gas in gas produced by methane fermentation has been removed by the methods shown in FIGS. 1A and 1B.

In FIG. 1A, gas 2 generated from a liquid mixture 1 of methane bacteria and raw organic matter in a methane fermentation tank I is introduced into a floating roof type gas tank 2 through a line 3.

In the gas tank (2), numeral 5 is a floating roof that moves up and down depending on how much gas 6 remains therein, and 7 is a liquid such as water.

Gas 6 in the gas tank ■ is transferred to line 8 depending on usage conditions.
It is extracted from the tank and led to the deoxidizing tower (■).

In the deoxidizing tower (2), a deoxidizing agent such as fresh water or alkali is supplied from line 9 (recycled liquid discharged from line 17, which will be described later, is often used, and expensive amines are added thereto) 10 is circulated through the pump 13, line 15, and spray nozzle 16, and when the deoxidizer 10 flows down from the spray nozzle 16 into the filler 11, it comes into gas-liquid contact with the above gas, and the Absorbs carbon dioxide gas.

The liquid that has absorbed this carbon dioxide gas is processed by a valve (electric valve, solenoid valve, etc.) or pump 14 that is operated by an electric signal from equipment 12 that controls the water level of the deoxidizer 10 to prevent it from losing its deoxidizing effect. The amount is discharged from line 1T in proportion to the amount replenished from line 9.

On the other hand, the gas from which carbon dioxide has been removed and whose methane concentration has increased is sent from line 18 to the gas utilization system.

Of course, the line from line 8 to line 18 is filler material 1.
If passing 1 once does not show sufficient effect,
Part or most of the gas in the line 18 may be returned to the drain in the line 8 using a blower or the like, and the gas may be passed through the filler 11 several times.

FIG. 1B shows a case where a pressure vessel type gas tank (2) is used, and the manner in which carbon dioxide is removed in the deoxidizing column (2) is the same as in FIG. 1A above.

In addition, in FIG. 1B, 4 is a compressor, 22 is a solenoid valve or an electric valve, 22 is a pressure reducing valve, 19, 20.

21 is equipment for controlling pressure, such as compressor 4 and electromagnetic (
This is to give a signal to the valve 22 to stop its operation.

However, the methods shown in FIGS. 1A and 1B have the following drawbacks.

(1) Deoxidizing tower■ Because the main body handles flammable gas, it requires an expensive structure similar to the methane fermentation tank I and gas tanks n and n' for seals and frames, which not only increases construction costs but also reduces operational costs. Also requires caution.

(2) It is necessary to constantly inject the deoxidizing agent from the line 9, resulting in high operating costs.

(3) In the method shown in Figure 1B, pressure control equipment 19°2
A complicated control system such as 0.21, electromagnetic (operated) valve 22, and pressure reducing valve 22 is required, and the control system for combustible gas not only requires a very high number of equipment, but also has complicated operation.

(4) The gas generated in the methane fermentation tank I contains 40 to 50 carbon dioxide gas, and in the system to remove carbon dioxide gas from it, it is first transferred to the gas tank ■.

Storing the gas in ■' itself requires an enormous amount of gas tanks n and n', which is wasteful.

The present invention has the following features: (1) When removing carbon dioxide gas, no special chemicals such as alkalis or amines are used, and almost no new supply of fresh water is required (resource saving and low operating costs) (11) The purpose is to simplify the handling line for combustible gas (avoid danger, reduce costs), (iii) to reduce the size of the gas tank, and to manufacture the deoxidizing tower at low cost.

The above purpose is to bring the gas generated by methane fermentation into contact with water in a gas tank to absorb and remove carbon dioxide from the gas,
The carbon dioxide absorbing liquid is taken out of the gas tank, brought into contact with the atmosphere to release the carbon dioxide in the liquid to the atmosphere, and the carbon dioxide releasing liquid is circulated back into the gas tank. This can be achieved by the carbon dioxide removal method.

Hereinafter, the method of the present invention will be explained in detail with reference to the accompanying drawings.

FIG. 2 is an explanatory diagram showing one embodiment of the method of the present invention.

In FIG. 2, ■ is a methane fermentation tank, 1 is a liquid undergoing methane fermentation, a group of methane bacteria acts on the raw organic material, and gas 2 is generated by the next reaction.

Raw material organic matter + (in some cases H20) → CH4↑+CO2↑+ (in some cases H20) The ratio of CH4 to CO2 is CH4 is 50-60%, C02
is 50-40%.

The above gas 2 is introduced from line 3 into floating roof type gas tank 1.

5 of the gas tank 1 is a floating roof, 6 is gas, 7 is water with specifications similar to fresh water, 28 is a spray nozzle for liquid (water) supplied from line 27, which will be described later, and 29 is a filling for gas-liquid contact. It is a material.

In this gas tank (1), the gas 6 comes into gas-liquid contact with the liquid (water) from the line 27, and the following reaction occurs.

■ CO2+H20=H++HCO3−ヰ2H”+C0
−−・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・(1)
■ Dissolves in water as CO2.

・・・・・・・・・・・・・・・・・・(2) By the way, the gas sent from line 3 contains a large amount of CO2, ranging from 50 to 40, as mentioned above, so it contains a large amount of CO2. is dissolved, and the reaction of ■ naturally shifts to the one marked with ■, and some of it is HCO3.
It dissolves in large quantities as - and as CO3-.

This liquid is drawn out from the gas tank (1) by the pump 26, and part or most of it is circulated and supplied into the gas tank (1) through the above-mentioned line 27.

On the other hand, the gas from which CO□ has been removed is sent from line 18 to the utilization system.

The gas in the line 18 is CH480-90, and the rest is mainly CO2 at 10-20%.

In addition, the above liquid is introduced from line 30 to deoxidizing tower ■1,
It is stored in the liquid reservoir 31 at the bottom.

The liquid in the liquid reservoir 31 is extracted by a pump 32 and sent to a line 33.
The water is circulated and used as the specified water 7 in the gas tank, and is also circulated from the line 34 to the deoxidizing tower (2) and sprayed from the spray nozzle 35 to the gas-liquid contact filler 11.

In this deoxidizing tower (1), outside air is introduced through line 38 by fan 36 and released through line 37. When this outside air passes through packing material 11, it comes into contact with the above liquid and is used for the next reaction. occurs, and CO2, HCO3-2C in the liquid
O3-1 is removed to the outside air.

2H++C03-=H++HC03-jC02↑+HO
・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
・(3) In other words, 002 in the atmosphere is generally 0.03%
Therefore, the reaction naturally moves in the direction of the arrow, and even the dissolved CO2 is released into the outside air as CO2, and the liquid is deoxidized.

Note that 12 in the figure is equipment for controlling the water level of the liquid distillate 31, and operates the above-mentioned pump 26 by an electric signal.

As mentioned above, the CO2 contained in the gas generated in the methane fermentation tank (2) is absorbed in the floating roof gas tank (1) by the liquid 7 used for sealing the tank (2). The CO□ absorbed in the liquid is released to the outside of the atmosphere in the deoxidizing tower ■1, while the liquid that has released CO2 returns to the gas tank ■1 and is used as a liquid for absorbing the CO2 in the gas. It is.

The liquid circulates within the system, but the gas remains in the tank (2) and is eventually sent to the utilization system through the line 18.

The C04 degree of the gas in the line 18 has generally decreased to 10 to 20 degrees, but in order to further reduce this, the design and specifications of the system from the filler 29 or pump 26 to the line 33 must be changed. The storage time in the gas tank 1 may be increased.

The longer this storage time, the less CO2 is produced.

Note that the amount of CO□ dissolved in fresh water at room temperature is approximately the same volume under 1 atm, while the amount of CH4 contained in the same gas dissolved in water is at most 0.05 volume. The amount of methane lost is negligible.

In addition, the removal of CO2 in the present invention is performed using 1 for gas tank.
If the water volume in 7 and the maximum volume in 6 are the same, the ratio of the gas residence time in 6 to the liquid transfer time for 7 and the deoxidizing bath is equal or greater, and during that liquid transfer time, the gas tank It is only necessary that (1) and the deoxidizing group (1) fully exhibit their functions, and the embodiment shown in FIG. 2 and the embodiment shown in FIG. 3, which will be described later, are well established.

FIG. 3 shows another embodiment of the method of the present invention, in which CO
#The action is the same as in the case of Fig. 2 described above, but differs from the case of Fig. 2 in the following points.

In FIG. 3, the gas 6 in the gas tank 2 is circulated through the line 23, the pump 24, and the gas diffuser 25 to bring it into sufficient contact with the liquid 7, and CO2 is absorbed and removed by the liquid 7 through the reactions 1 and 2 above.

The liquid that has absorbed this CO2 is introduced into the deoxidizing group (this is a water tank) I2 via a line 39 and a pump 40.

The introduced liquid 41 is brought into contact with the outside air guided from a line 44 by a compressor or blower 43 and discharged from a diffuser 45, and the filler 11 is used to sufficiently effect this contact.
While passing through the liquid, CO2 moves from the liquid to the outside air side due to the reaction described in 3 above, and is released into the atmosphere from the line 46 along with the outside air.

The liquid from which C02 has been removed in this way is circulated through the line 42 to the gas tank (2).

In addition, in FIG. 3, in order to reduce the CO2 concentration of the gas sent from the line 18 to the utilization system to 10 to 20% or less,
As in the case of Fig. 2, either increase the storage time of the gas in the gas tank 2, or
The design and specifications of the system can be changed to provide greater capacity.

The effects of the method of the present invention explained above are summarized as follows.

(a) Conventional deoxidizing groups were used for combustible gas handling equipment, which required airtightness and the electrical equipment used had to meet explosion-proof standards; however, the deoxidizing group of the present invention Since the target is processed, it does not need to be made in a sloppy manner, resulting in a significant cost reduction.

(b) Conventional gas tanks also store CO2 to be removed, and this CO2 accounts for nearly half of the gas generated by methane fermentation, so they have a large capacity, but the gas tank of the present invention has a large capacity. Since CO□ is rapidly absorbed and removed within the tank, the capacity is only about 4 liters compared to conventional tanks.
This results in a significant cost reduction.

(c) There is no expensive electrical control system.

(d) There is no need for a deoxidizing agent or a large amount of fresh water, which were required with conventional deoxidizing groups.

(e) The combustible gas handling system is extremely simple, with only a gas tank.

Cf) “It is possible to increase the calories of gas obtained by methane fermentation by about twice while exhibiting the above effects.

[Brief explanation of the drawing]

FIGS. 1A and 1B are explanatory diagrams showing a method for removing carbon dioxide gas from gas generated by the conventional methane fermentation method. FIGS. FIG.

Claims (1)

[Claims] 1. Gas generated by methane fermentation is brought into contact with water in a gas tank to absorb and remove carbon dioxide from the gas, and the carbon dioxide absorption liquid is taken out of the gas tank and brought into contact with the atmosphere to remove carbon dioxide from the liquid. A method for removing carbon dioxide from the gas, characterized in that the carbon dioxide gas is released into the atmosphere, and the carbon dioxide releasing liquid is circulated back into the gas tank.