JPH0970521A - Method for removing carbon dioxide in waste combustion gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately remove CO2 from combustion gas from a power plant effectively utilizing LNG in LNG fired power plants by membrane separating CO2 in waste combustion gas using differential pressure between pressure of waste combustion gas and pressure inside hollow fiber as driving force. SOLUTION: Waste gas 1 is led to a hollow fiber membrane type gas separation membrane 17 having separating power of CO2 and others such as N2 and O2 . Since the hollow fiber membrane is evacuated to a saturation pressure in a solidifying column 20 cooled by cryogenic LNG 19, CO2 and a small quantity of N2 , O2 and the like 18 preferentially permeates through the membrane according to the partial pressure thereof. Gas that has permeated through the hollow yarn membrane is cooled by the cryogenic LNG 19 and is separated into solidified CO2 21 and a small quantity of impure gas 22 composed of N2 , O2 and the like. The solidified CO2 21 is taken out outside the system, and the impurity gas 22 is sucked by a vacuum pump 23 and is merged with gas that has not permeated through the hollow fiber membrane in the hollow fiber type gas separation membrane 17 and is released in the air as treated gas 2.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for removing CO _{2 in} combustion exhaust gas from a thermal power plant.

[0002]

2. Description of the Related Art The treatment of CO _{2 in} flue gas is carried out using CO ₂
Is generally used for absorbing CO ₂ and then CO ₂ is diffused from the absorbing solution. That is, in this method, as shown in FIG.
The CO ₂ is absorbed by contacting the absorption liquid 4 therewith, and the exhaust gas 1 becomes the processing gas 2 and is released to the atmosphere.
The used absorption liquid 5 is withdrawn from the bottom of the absorption tower 3, heated by the used absorption liquid transfer pump 6 in the heat exchanger 7, and then sent to the regeneration tower 8. In the regeneration tower 8, the steam generated in the reboiler 9 is brought into contact with the used absorption liquid 5 to generate CO ₂
Is emitted from the used absorption liquid and sent to the condenser 10, where it is separated into CO ₂ gas 11 and water 12 (liquid), and CO ₂
The gas 11 is further cooled in the liquefaction tower 13 and liquefied CO
₂ (reference numeral 14) is liquefied and taken out of the system. On the other hand, the absorption liquid regenerated in the regeneration tower 8 (regenerated absorption liquid 15) is withdrawn from the bottom of the regeneration tower 8, cooled by the regenerated absorption liquid feed pump 16 in the heat exchanger 7, and then stored in the absorption tower 3. It is fed to the top and reused.

[0003]

CO _{2 in} flue gas
The most important factor in the practical application of the treatment is the reduction of the energy required for the CO ₂ treatment and the downsizing of the apparatus therefor. Since the conventional method of contacting the absorption liquid with a large amount of exhaust gas, for dissipating CO ₂ by heat or increased absorption tower, the spent absorbent that has absorbed CO ₂ in the regeneration tower,
There was a problem that the amount of heat required for this was high.

In the LNG-fired thermal power plant, when LNG stored at about atmospheric pressure and -162 ° C. is used as a fuel, the pressure is increased by a pump and heat (for example, seawater holding heat) is added from the outside. It vaporizes and heats to about room temperature, but most of the cold heat generated at this time was not used effectively and was discarded.

In view of the above-mentioned state of the art, the present invention solves the problems of increasing the size of equipment and increasing the required energy associated with CO ₂ gas absorption and removal in the conventional method, and at the same time, makes effective use of LNG in an LNG-fired power plant. An object of the present invention is to provide a method for purposefully removing CO ₂ from combustion exhaust gas from a thermal power plant.

[0006]

Means for problem is solved of the present invention the CO ₂ in the exhaust gas combustion exhaust gas flue gas or denitration process was denitration and desulfurization process of thermal power plants by CO ₂ selectively permeable hollow fiber membrane type gas separation membrane At the time of separation, CO ₂ which is a permeating gas from the gas separation device is cooled by using cold heat of liquefied natural gas, solidified to reduce the volume, and the inside of the hollow fiber membrane of the gas separation device is decompressed and burned. C in the combustion exhaust gas using the pressure difference between the exhaust gas pressure and the internal pressure of the hollow fiber as the driving force.
CO in flue gas characterized by membrane separation of O ₂
Method ₂ of removal.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION First, the present invention employs a hollow fiber membrane-type gas separation membrane capable of taking a large contact area with a gas per unit volume as means for separating CO ₂ from exhaust gas in order to make the apparatus compact. , Expand this part of the flue and install it in this. The hollow fiber membrane type gas separation membrane has a functional group,
There are many types depending on the molecular weight, but generally the inner diameter is several hundred μ
m, wall thickness: a polyimide film of several tens of μm is used.

Next, in order to reduce energy, the hollow fiber membrane type gas separation membrane is usually used by pressurizing or depressurizing the inside of the hollow fiber membrane with a vacuum pump. The permeated gas of the hollow fiber membrane type gas separation membrane is LNG. The inside of the hollow fiber membrane is decompressed by liquefying and reducing the volume by cold heat, and CO ₂ in the exhaust gas is permeated through the membrane using the pressure difference from the atmospheric pressure as a driving force to decompose. This is CO
_{2 has} a boiling point of −78.48 ° C. (1 atm = 1.03 kg /
cm ² ), the saturation pressure at −100 ° C. is 0.12 kg / c
Since it is m ^2, it is possible in principle by using LNG cold heat of about -162 ° C.

C passed through the hollow fiber membrane type gas separation membrane
Although O during ₂ small N _2, impurities such as O ₂ is contained, they are decomposed as a residual gas during the solidification of the CO ₂ gas by LNG cold, it is removed by a vacuum pump.

The present invention is applied to denitration of LNG-fired thermal power plants, etc.
When applied as CO ₂ treatment in flue gas of desulfurized combustion exhaust gas or denitration-treated combustion exhaust gas, the device becomes more compact and energy consumption can be reduced as compared with the conventional device. It also enables effective use of LNG cold heat.

[0011]

EXAMPLES The effects of the present invention will be clarified by giving concrete examples of the present invention.

(Example 1) (Structure of Example 1) An example in which the present invention is applied to CO ₂ treatment in flue gas of a LNG-fired thermal power plant,
Hereinafter, description will be given with reference to FIG. The exhaust gas 1 is guided to the hollow fiber membrane type gas separation membrane 17 having the ability to separate CO ₂ and other N ₂ , O _{2 and the} like. Since the inside of the hollow fiber membrane is depressurized to the saturation pressure in the solidification tower 20 cooled by the LNG cold heat 19, CO ₂ and a small amount of N ₂ , O _2, etc. 18 preferentially permeate the membrane according to the partial pressure. . The gas that has passed through the hollow fiber membrane is cooled by the LNG cold heat 19 in the solidification tower 20 and solidified CO
Is separated into _two 21 and N _2, a small amount of impure gas consisting O ₂ or the like 22. The solidified CO ₂ 21 is taken out of the system, the impure gas 22 is sucked by the vacuum pump 23, merges with the gas that has not permeated the hollow fiber membrane in the hollow fiber membrane-type gas separation membrane 17, and is used as a treatment gas 2 in the atmosphere. Is released to.

(Experimental Example 1) Pressure: atmospheric pressure (1.
03ata), temperature: CO _{2 at} 100 ° C .: 8.55 vo
1%, O ₂ : 2.41 vol%, N ₂ : 71.77vo
1%, H ₂ O: 17.27vol% exhaust gas,
When a gas having CO ₂ as a main component which permeates the hollow fiber membrane is cooled by cold heat of −160 ° C., it is brought into contact with a hollow fiber membrane of a polyimide membrane having a diameter of about 300 μm and a film thickness of about 40 μm.
The inside of the hollow fiber membrane is depressurized to about 0.8 to 0.9 ata, and the differential pressure acts as a driving force, and 0 to 40% of CO _{2 in} the exhaust gas is reduced.
% Is separated and collected.

(Embodiment 2) FIG. 2 shows CO _{2 in} flue gas.
An example of a CO ₂ gas separation unit of the processing apparatus is shown. The hollow fiber membrane type separation membrane 1 is placed in the CO ₂ separation section 24 in which a part of the flue is enlarged.
7 is installed. The exhaust gas 1 is guided to the CO ₂ separation unit 24, and CO ₂ (a small amount of N ₂ ,
18 (including O ₂ etc.) and the processing gas 2.

[0015]

【The invention's effect】

(1) By using a hollow fiber membrane type gas separation membrane that allows a large contact area with gas per unit area and installing a part of the flue gas in an enlarged manner, it can be made more compact than the conventional device. (2) The permeated gas of the hollow fiber membrane-type gas separation membrane is liquefied and reduced by LNG cold heat to reduce the pressure inside the hollow fiber and use atmospheric pressure to permeate CO ₂ and also to permeate a small amount of N ₂ in CO _2. Impurities such as ₂ , O _{2 and the} like are separated when the CO ₂ is solidified by LNG cold heat and removed by a vacuum pump, so that the energy consumption can be reduced as compared with the conventional device. (3) Furthermore, most of the LNG that has been discarded so far
Effective use of cold heat becomes possible.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is an explanatory view of another embodiment of the present invention.

FIG. 3 is an explanatory view of a conventional method for removing CO ₂ in exhaust gas.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuo Akutsu 4-1 Egasaki-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Toki Electric Power Co., Inc. Energy and Environmental Laboratory (72) Inventor, Hikaru Kitamura Wadazaki, Hyogo-ku, Kobe-shi, Hyogo Prefecture 1-1-1 Machi Mitsubishi Heavy Industries, Ltd. Kobe Shipyard (72) Inventor Yoshimasa Ando 1-1-1, Wadasakicho, Hyogo-ku, Kobe, Hyogo Prefecture Mitsubishi Heavy Industries Ltd. Kobe Shipyard (72) Inventor Matsumoto Hikiyo 2-1-1 Niihama, Arai-cho, Takasago, Hyogo Mitsubishi Heavy Industries Ltd. Takasago Research Laboratory (72) Inventor Yasuo Kageyama 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Sanryo Heavy Industries Co., Ltd.

Claims (1)

[Claims] 1. A combustion exhaust gas subjected to denitration / desulfurization treatment of a thermal power plant.
CO or flue gas that has undergone denitration treatment₂Selective transparency
Of CO in the exhaust gas by a gas-permeable hollow fiber membrane type gas separation membrane₂To
When separating, it is the permeated gas from the gas separation device.
CO₂Is cooled and solidified by using the cold heat of liquefied natural gas.
Volume inside the hollow fiber membrane of the gas separator
The pressure difference between the combustion exhaust gas pressure and the hollow fiber pressure.
CO in combustion exhaust gas as driving force₂The membrane separation
Characteristic CO in combustion exhaust gas ₂Removal method.