JPH05123534A - Recovery of carbon dioxide in combustion exhaust gas - Google Patents

Abstract

PURPOSE:To efficiently recover carbon dioxide contained in combustion exhaust gas by adjusting the temp. of exhaust gas in a specific temp. range before bringing the exhaust gas into contact with a monoethanolamine aqueous solution. CONSTITUTION:Carbon dioxide contained in combustion exhaust gas is absorbed and recovered using a monoethanolamine aqueous solution as an absorbing solution. At this time, the temp. of the exhaust gas is adjusted to the temp. range of 50-80 deg.C in a cooling tower 1 to bring the exhaust gas into contact with the monoethanolamine aqueous solution in an absorbing tower 2. By this method, carbon dioxide can efficiently be absorbed and recovered. The high temp. exhaust gas can be cooled by humidifying cooling merely using water and it is unnecessary to use a heat exchanger for accelerating the cooling of cooling water required heretofore.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering carbon dioxide contained in combustion exhaust gas. More specifically, the temperature of exhaust gas is cooled to a predetermined range by a humidification cooling method or the like, and an aqueous monoethanolamine solution is used as an absorption liquid. The present invention relates to a method for absorbing carbon dioxide contained in combustion gas and recovering carbon dioxide from an aqueous monoethanolamine solution.

[0002]

2. Description of the Related Art In recent years, the greenhouse effect of carbon dioxide has been pointed out as one of the causes of the global warming phenomenon, and countermeasures against it have become urgent internationally in order to protect the global environment. Sources of carbon dioxide gas cover all human activity fields that burn fossil fuels, and their emission regulations are likely to be tightened in the future. Therefore, for power generation facilities such as thermal power plants that use large amounts of fossil fuels, the method of recovering carbon dioxide in the combustion exhaust gas of the boiler and the method of storing the recovered carbon dioxide without releasing it to the atmosphere are vigorous. Is being researched by.

[0003]

By the way, a saturation curve under atmospheric pressure of 8 vol% carbon dioxide partial pressure when about 30 wt% monoethanolamine aqueous solution is used for absorbing carbon dioxide contained in combustion exhaust gas is shown in FIG. As shown.
In FIG. 3, the horizontal axis represents temperature (° C.) and the vertical axis represents the number of moles of carbon dioxide gas absorbed per unit mole of monoethanolamine. As is easily understood from FIG. 3, the lower the temperature of the carbon dioxide gas to be contacted, the larger the amount of carbon dioxide gas absorbed in the aqueous monoethanolamine solution. Furthermore, the absorption of carbon dioxide gas by the monoethanolamine aqueous solution is accompanied by heat generation,
From this point as well, it is said that the temperature of the exhaust gas to be contact-treated with the monoethanolamine aqueous solution is lower, and the cooling of the exhaust gas must be strengthened to, for example, about 30 to 50 ° C. For this reason, as a carbon dioxide gas recovery device for the exhaust gas, the cooling device for the exhaust gas is expensive, and even when the recovery device is in operation, the cooling water used for the exhaust gas cooling device is cooled. It cost a lot of money. In particular, when treating exhaust gas from a boiler that uses natural gas as a fuel, unlike the exhaust gas that uses coal or heavy oil as a fuel, the temperature does not easily drop only by the humidification treatment that makes contact with cooling water, and the heat exchanger cools it. There was a problem such as the need for contact with water fortified.

[0004]

Under the above circumstances regarding the exhaust gas temperature when absorbing and recovering the carbon dioxide gas contained in the combustion exhaust gas, the present inventors have considered the exhaust gas temperature and the carbon dioxide gas in the monoethanolamine aqueous solution. As a result of diligent examination of the relationship with the absorption amount of the exhaust gas, the temperature of the exhaust gas was surprisingly 30 to 50.
It was found that the absorption amount was higher at a temperature higher than 0 ° C, and the present invention was completed.

That is, the first aspect of the present invention is a method for absorbing and recovering carbon dioxide gas contained in combustion exhaust gas by using an aqueous monoethanolamine solution as an absorption liquid, and the exhaust gas temperature is higher than 50 ° C. and lower than 80 ° C. After adjusting to the range,
It is a method for recovering carbon dioxide gas, which is characterized in that it is brought into contact with an aqueous monoethanolamine solution.

A second aspect of the present invention is to carry out the first aspect of the present invention by a humidification cooling method.

Further, the third aspect of the present invention is to cool the combustion exhaust gas of high temperature by humidification cooling by a cooling water supply means having no heat exchanger, the carbon dioxide gas contained in the humidified and cooled exhaust gas is a monoethanolamine aqueous solution. A method for recovering carbon dioxide gas in a combustion exhaust gas, comprising: an absorption step for absorbing carbon dioxide gas by using the above method and a step for recovering carbon dioxide gas from an aqueous monoethanolamine solution. Hereinafter, the present invention will be described in detail.

[0008]

As the equipment for absorbing and recovering carbon dioxide gas contained in the combustion gas used in the method of the present invention, the equipment as shown in FIG. 1 can be exemplified. In FIG. 1, only the main equipment is shown and the auxiliary equipment is omitted.

In the carbon dioxide recovery method of the present invention, it is necessary to adjust the exhaust gas temperature to a range of more than 50 ° C. and 80 ° C. or less, particularly preferably 55 to 80 ° C., and then contacting it with an aqueous monoethanolamine solution. is there. As a method for adjusting the temperature in the range of more than 50 ° C. and 80 ° C. or less, it is preferable to use humidification cooling with equipment such as the cooling tower 1 in FIG.
It is not particularly limited to this. The combustion exhaust gas generated by the boiler or the like and discharged from the chimney is usually 100 to 15
It is introduced into the combustion gas cooling tower 1 through a line 5 at 0 ° C., and is subjected to countercurrent contact with water circulating in a line 13 by a pump 12 to be humidified and cooled.

In the present invention, unlike the prior art, it is not necessary to cool the exhaust gas to 30 to 50 ° C. by the cooling tower 1, and
It suffices to cool it in the range above 0 ° C and below 80 ° C.
The heat exchanger, which is conventionally required and installed in the line 13, is not particularly required, and water in liquid form may simply be circulated. The water may be not only river water but also seawater. Water lost by the humidification cooling is replenished in the line 13 by the line 15 from a supply source (not shown). The cooling tower 1 only needs to bring water and exhaust gas into contact with each other, and there is no particular need for a filler or the like in the tower. The temperature of the exhaust gas at the outlet of the cooling tower 1 can be adjusted by the amount of circulating water by the pump 12.

The exhaust gas cooled by humidification to a temperature above 50 ° C. and below 80 ° C. is introduced into absorption tower 2 via line 6. At the upper part of the absorption tower 2, the concentration of 20
About 30% by weight of monoethanolamine aqueous solution is supplied. The monoethanolamine aqueous solution is brought into countercurrent contact with the combustion gas and is sent from the lower part of the tower to the monoethanolamine aqueous solution regeneration tower 3 as a monoethanolamine aqueous solution absorbing carbon dioxide by a line 7. From the upper part of the absorption tower 2, the remaining combustion gas, which has absorbed carbon dioxide gas, is released to the atmosphere through the line 8.

In the monoethanolamine aqueous solution regeneration tower 3, the monoethanolamine aqueous solution is regenerated by heating with steam through the reboiler 14, and the absorption tower 2 is regenerated by the line 9.
Returned to. The carbon dioxide gas is guided to the recovery process by the line 10.

During operation of this carbon dioxide absorption / recovery system, monoethanolamine is accompanied by exhaust gas or becomes a deteriorated product and gradually lost to the outside of the system. Therefore, in order to replenish this, for example, a stock solution of monoethanolamine is supplied from the tank 4 in the middle of the line 7, and similarly, the tank 11
The dilution water is supplied into the system by.

As described above, in the cooling tower 1, the hot exhaust gas and water are simply brought into contact with each other to be humidified and cooled to 50 ° C.
The exhaust gas is cooled to a temperature range exceeding 80 ° C and below 80 ° C. Even though the carbon dioxide saturation curve of the monoethanolamine aqueous solution shows the tendency as shown in FIG. 3, even if such a relatively high temperature exhaust gas is contacted with the monoethanolamine aqueous solution, it is more than the case where the low temperature exhaust gas is contacted. It is presumed that the rate of absorption of carbon dioxide into the monoethanolamine aqueous solution is largely responsible for the increase in carbon dioxide absorption capacity.

Since the exhaust gas can be contacted with the monoethanolamine aqueous solution at a relatively high temperature simply by humidifying and cooling the exhaust gas, a heat exchanger for cooling the circulating water is not required in the line 13, and the equipment cost and operating cost thereof are reduced. You will be able to save a lot. The method of the present invention can be applied to, for example, exhaust gas using natural gas, heavy oil, coal or the like as a fuel. Hereinafter, the present invention will be specifically described with reference to examples.

[0016]

EXAMPLE FIG. 2 shows the results of investigating the relationship between the combustion exhaust gas temperature cooled by humidification cooling and the carbon dioxide absorption amount by the monoethanolamine aqueous solution using the apparatus of FIG. The units of the horizontal axis and the vertical axis in FIG. 2 are the same as those in FIG.
The cooling temperature of the exhaust gas by humidification cooling was adjusted by the amount of circulating water.

The experimental conditions are as follows. (1) Exhaust gas composition (vol%) Carbon dioxide 8.55 Oxygen 2.41 Nitrogen 71.77 Steam 17.27 (2) Exhaust gas temperature in line 5: 100 ° C (3) Concentration of monoethanolamine aqueous solution in line 9 : 3
0% by weight

It can be seen from FIG. 2 that the absorption amount of carbon dioxide gas increases with temperature and reaches a maximum value at about 70 ° C. From this, it is understood that it is not necessary to cool to the cooling temperature which was conventionally set to 30 to 50 ° C.

[0019]

As described above in detail, according to the present invention, the combustion exhaust gas is cooled to a range of more than 50 ° C. and 80 ° C. or less and brought into contact with an aqueous monoethanolamine solution to efficiently absorb carbon dioxide gas. Is now possible. Further, the high-temperature exhaust gas can be cooled simply by humidification with water, and it is no longer necessary to use a heat exchanger or the like which has been conventionally required for strengthening cooling of cooling water.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of a recovery facility used in the carbon dioxide recovery method of the present invention.

FIG. 2 is an exhaust gas contact temperature (horizontal axis) obtained by using the apparatus of FIG. 1 in Example and an absorption amount in an aqueous monoethanolamine solution (vertical axis: unit per 1 mol of monoethanolamine in the solution). Chart showing the relationship with the number of moles of carbon dioxide).

FIG. 3 is a chart showing a carbon dioxide saturation curve of a monoethanolamine aqueous solution.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Zenji Hotta 3-3-22 Nakanoshima, Kita-ku, Osaka City Kansai Electric Power Co., Inc. (72) Kenji Kobayashi 3-22-3 Nakanoshima, Kita-ku, Osaka Kansai Denryoku Co., Ltd. (72) Inventor Kunihiko Yoshida 3-11-20 Wakaoji, Amagasaki City Kansai Electric Power Co., Inc. Research Institute of Technology (72) Inventor Shigeru Shimojo 3-11-20 Wakaoji, Amagasaki Kansai Electric Power Co., Inc. (72) Inventor Mutsunori Karazaki 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Sanryo Heavy Industries Co., Ltd. (72) Inventor Masaki Iijima 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Hishi Heavy Industries Ltd. (72) Inventor Toru Seto 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City Mitsubishi Heavy Industries Ltd. Hiroshima Research Institute (72) Inventor Hikari KaoruAkira Hiroshima Nishi-ku Kan'onshin-cho, chome No. 6 No. 22 Mitsubishi Heavy Industries, Ltd. Hiroshima within the Institute

Claims (3)

[Claims] 1. A method for absorbing and recovering carbon dioxide gas contained in a combustion exhaust gas by using an aqueous monoethanolamine solution as an absorption liquid, wherein the exhaust gas temperature exceeds 50 ° C.
A method for recovering carbon dioxide, which comprises contacting with an aqueous monoethanolamine solution after adjusting the temperature to 0 ° C. or less. 2. The method for recovering carbon dioxide according to claim 1, wherein the temperature of the combustion exhaust gas at a high temperature is adjusted to a range higher than 50 ° C. and lower than 80 ° C. by a humidification cooling method. 3. A step of cooling high temperature combustion exhaust gas by humidification cooling by a cooling water supply means having no heat exchanger,
Carbon dioxide gas in combustion exhaust gas, comprising an absorption step of absorbing carbon dioxide gas contained in the humidified and cooled exhaust gas using an aqueous monoethanolamine solution and a step of recovering carbon dioxide gas from the aqueous monoethanolamine solution. Recovery method.