JPS58122018A - Treating method of methane fermentation gas - Google Patents

Abstract

PURPOSE:To recover carbon dioxide by applying a pressure swing method utilizing adsorbents. CONSTITUTION:Since the gases generated from a methane fermentation tank 1 contain usually impurities such as gaseous hydrogen sulfide, the gases are passed through a desulfurizing device 2 and are then increased in pressure to necessary pressure by a pressure increasing machine 3. Needless to say, in the case of fermentation gases contg. no hydrogen sulfide or the like, there is no need for any desulfurizing device and the pressure of said gases is increased as it is. The gases increased in pressure are cooled with a cooler 4 to reduce the moisture therein; thereafter, the gases are introduced into an adsorption tower 5 packed therein with adsorbents. The tower is constituted of at least two towers. If the number of the tower increases, the rate of recovery increases as well, but initial costs increase correspondingly; therefore, usually said tower is constituted of 2-6 units. With this pressure swing device, the carbon dioxide in the fermentation gases is adsorbed, and the concn. of methane in the gases is increased. Said gases are fed to the user side through a buffer tank 8. The adsorbed carbon dioxide is evacuated and desorbed by a vacuum pump 6.

Description

[Detailed description of the invention] The present invention relates to a method for treating methane fermentation gas.

More specifically, the present invention relates to a method for recovering carbon dioxide gas in gas generated by a methane fermentation method using a pressure swing method (alternate pressure fluctuation method).

Digested methane fermentation gas from sewage sludge, which is fermentation gas, usually contains 3
Contains 5 to 40 Vo1% carbon dioxide gas.

For this reason, its use was limited due to its low calorific value.

It is possible.

The present inventors focused on this point and, as a result of repeated studies, came up with the idea of using a pressure swing method to remove carbon dioxide gas, and arrived at the present invention.

Conventionally known methods for removing carbon dioxide gas from waste gas in one yield include the chemical absorption method, which involves absorbing with an alkali solution such as an amine aqueous solution or potassium carbonate aqueous solution and regenerating it by heating, and the water absorption method, which absorbs it with pressurized water and releases it under reduced pressure. It is being However, the former requires a large amount of thermal energy during regeneration, and the latter requires 30 kV/cjG due to physical absorption! i! It is not suitable for methane fermentation gas because it needs to be at a pressure of 30°C and the daily production cost is high. In addition, as a method for removing carbon dioxide from methane fermentation gas, JP-A-56-1187
Publication No. 91 describes a method in which methane fermentation gas is brought into contact with water in a tank, and the absorbed water is taken out of the tank and diffused into the atmosphere. They discovered a way to recover gas.

That is, the gist of the present invention is a method for recovering carbon dioxide gas in gas generated by a methane fermentation method using a pressure swing method. According to the method of the present invention, the adsorption pressure is low and the energy required is only the electric power required for pressurization, which is not necessary in the case of a pressurized fermenter, and carbon dioxide gas can be recovered extremely economically.

The methane fermentation gas from which carbon dioxide has been removed by the method of the invention is advantageous for use since it is delivered from the pressure swing device at increased pressure. For example, when it is used as a fuel for a heat III engine such as a gas engine or a gas turbine, it can be used in a heat engine in a pressurized state, so it can be used as it is in a supercharged engine.

The pressure of the pressure swing method of the present invention is 10 = t/
If it exceeds cdG, the equipment cost will increase, and various commercially available adsorbents such as doo-olide molecular sheep, silica gel, alumina gel, etc. can be used for this, but if carbon molecular sheep is used, the processing capacity per unit volume of adsorbent will be lower. It is advantageous compared to other adsorbents because it has a high resistance to residual moisture in the gas and has a long service life.

The concentration of gas generated in a methane fermentation tank is usually around 35°C or 55°C, both of which are saturated with water, so the concentration should be at least 40°C or lower, preferably 20°C.
CI! i! It is desirable to reduce moisture content by cooling to a certain degree. However, depending on the type of adsorbent, it may be necessary to dehydrate and dry it at a lower temperature, so in this respect as well, it is advantageous to use carbon molecular sheep as described above.

The present invention will be explained below according to the flow sheet shown in FIG.

The gas generated from the methane fermentation tank 1 usually contains impurities such as hydrogen sulfide gas, so after passing through the desulfurizer 2, the gas is boosted to a required pressure in a pressure booster 113.

Naturally, if the fermentation gas does not contain hydrogen sulfide or the like, a desulfurizer is not necessary and the pressure is increased as is.

The gas pressurized to 1 pressure is cooled by cooler 4 to lower the moisture content.
, is introduced into an adsorption tower 5 filled with an adsorbent.

The adsorption tower is composed of at least two towers, and although the recovery rate increases as the number of towers increases, the equipment cost also increases, so it is usually composed of two to six towers. This pressure swing device adsorbs carbon dioxide gas in the fermentation gas, increases the methane concentration in the gas, and sends it to the usage side 7 through the buffer tank 8. On the other hand, the carbon dioxide gas adsorbed in the adsorption tower 5 is desugarized under reduced pressure by the vacuum pump 6.

Naturally, in the case of atmospheric pressure, the vacuum pump 6 is not necessary. The desorbed carbon dioxide makes the storage tank 7 available for light use. Depending on the purpose, this carbon dioxide gas may be transported and used as is, or it may be introduced into conventional liquefied carbon dioxide production equipment to produce liquefied carbon dioxide gas.

Embodiments of the present invention will be specifically described below.

For the treatment of sewage sludge generated from sewage treatment plants, the gas generated by aqueous acid production (so-called methane fermentation) is composed of 30 to 35 volts of carbon dioxide, the remainder being methane, and a small amount of hydrogen, nitrogen, and acid. Gas removed, 5v0
Contains 1% carbon dioxide and is refined into calories. When this gas is used in conventional gas engines,
Compared to methane fermentation gas from which carbon dioxide gas has not been removed, the calories are 5,000 to 6,000 Kal/N- to 8,000 K.
cal/N♂, and its efficiency increased by about 25% when used as fuel for gas engines. On the other hand, carbon dioxide gas whose pressure was reduced to 70 torr using a vacuum pump was obtained with a purity of 99%. This is of sufficient purity as a conventional liquefied carbon dioxide raw material.

The electric power in this case is 0.15KW/Nf fermentation gas,
It is very economical compared to the conventional method, and only about 1/3 of the electricity generated due to the improved efficiency of the gas engine is sufficient, making it very economical in terms of energy balance.

The method of the present invention can be applied not only to methane fermentation gas from sewage treatment sludge, but also to the treatment of methane gas containing carbon dioxide gas in biomass systems and the like.

Applicant: Shintetsu Kagaku Kogyo Co., Ltd. Representative: Hiroshi Sasaki Procedural Amended Type February 1980 Zsu1, Indication of Patent Application: 1981 Patent Application No. 06 My
r No. 2, Title of the invention Method for treating methane fermentation gas a, Relationship to the case of the person making the amendment Patent applicant postal code @ 673-01 Address Hyogo prefecture txtfiii5MWa 4
First name of address e - Tetsu Kagaku Kogyo Co., Ltd. 4, Date of amendment order Voluntary 1 5,
Subject of amendment Application and Specification 6, contents of amendment The application and Memorandum S sent on January 12, 1980 are submitted as attached (there are no changes in the contents as they are engravings).
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Claims (1)

[Claims] (1) A method for recovering carbon dioxide gas in gas generated by a methane fermentation method using a pressure swing method. ;, (2> Claims in which the furrowing pressure of the pressure swing method is large; negative pressure or more and 10 Ka/jG or less (1)
) method described. (1) The method described. The method according to claim (1) using sheep. (6) The method according to claim (1), wherein the temperature of the generated gas is reduced to 40° C. or lower. (7) The method according to claim fl(1), which uses a pressure swing method equipped with a desulfurization mechanism.