JPH05184866A - Equipment for removing carbon dioxide in combustion exhaust gas and method therefor - Google Patents

Abstract

PURPOSE:To maintain water balance in the whole equipment in a system as well as in a CO2 removing tower by regulating the temp. of alkanolamine aqueous solution fed to the CO2 removing tower so that inlet and outlet temp. of combustion exhaust gas of the CO2 removing tower may mutually be the same. CONSTITUTION:In CO2 removing apparatus where combustion exhaust gas and alkanolamine aqueous solution are made to be in contact to remove CO2 incorporated in the combustion exhaust gas, on the combustion exhaust gas downstream side of a contact part 2 where alkanolamine aqueous solution and combustion exhaust gas are in countercurrent contact, is provided a contact part 3 where reflux water of an alkanolamine aqueous solution regenerating tower 18 and combustion exhaust gas from which CO2 is removed are in countercurrent contact. The temp. of alkanolamine aqueous solution fed to the CO2 removing tower 1 is regulated so that inlet and outlet temp. of combustion exhaust gas of the CO2 removing tower 1 may be the same.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for removing CO ₂ (carbon dioxide) contained in flue gas, and more specifically to removing CO _{2 from} flue gas using an alkanolamine aqueous solution as an absorbent. Apparatus and method.

[0002]

2. Description of the Related Art In recent years, the greenhouse effect of CO ₂ has been pointed out as one of the causes of the global warming phenomenon, and there is an urgent need to take countermeasures internationally in order to protect the global environment. CO ₂
The emission sources of carbon dioxide are all human activity fields that burn fossil fuels, and their emission regulations are likely to be tightened in the future. Along with this, for a power generation facility such as a thermal power plant that uses a large amount of fossil fuel, a method of recovering CO ₂ in the combustion exhaust gas by bringing the combustion exhaust gas of the boiler into contact with an alkanolamine aqueous solution or the like, and the recovered CO _The method of storing ₂ without releasing it to the atmosphere is being actively studied.

Examples of the alkanolamine that absorbs CO ₂ include aqueous solutions of monoethanolamine, diethanolamine, triethanolamine, methyldiethanolamine, diisopropanolamine, diglycolamine and the like, or mixed aqueous solutions thereof. Usually, an aqueous solution of monoethanolamine (MEA) is preferably used.

The process of removing CO ₂ contained in the combustion exhaust gas by using an alkanolamine aqueous solution, particularly an MEA aqueous solution, will be described with reference to FIG. In FIG. 2, only the main equipment is shown and the auxiliary equipment is omitted.

In FIG. 2, 01 is a CO ₂ removal tower, 02 is a lower filling section, 03 is an upper filling section, 04 is a CO ₂ removal combustion gas supply section, 05 is a CO ₂ removal exhaust gas discharge section, 06
Is a MEA aqueous solution supply port, 07 is a nozzle, 08 is a liquid holding unit, 09 is a water circulation pump, 010 is a cooler, 011 is a nozzle, 012 is a CO ₂ absorbing MEA aqueous solution discharge port, 013.
Is a push blower. Further, 014 is a combustion exhaust gas supply port, 015 is a combustion exhaust gas cooler, 016 is a circulation pump,
Reference numeral 017 is a cooler, 018 is a nozzle, and 019 is a condensed water discharge line.

[0006] The combustion exhaust gas generated by a boiler or the like and to be discharged from the chimney has a normal temperature of 100 to 150 ° C.
After being cooled in the flue gas cooling tower 015 and discharging a part of the condensed water to the outside of the system through a condensed water discharge line 019, CO ₂ removal
It is supplied to the CO ₂ removal tower 01 from the tower combustion exhaust gas supply port 04. The combustion exhaust gas is brought into countercurrent contact with the MEA aqueous solution having a constant concentration and temperature supplied from the MEA aqueous solution supply port 06 through the nozzle 07 in the lower filling section 02, and C in the combustion exhaust gas is discharged.
O ₂ is absorbed and removed by the MEA aqueous solution. MEA aqueous solution that has absorbed CO ₂ is discharged by the CO ₂ absorbing aqueous MEA solution outlet 012, is sent to the MEA aqueous solution regeneration tower (not shown), it is recycled to the aqueous MEA solution supply port 06 of the.

On the other hand, the combustion exhaust gas de-CO ₂ in the lower filling section 02 goes to the upper filling section 03 through the liquid retaining section 08. The exhaust gas heats up due to the reaction between the exhaust gas temperature (CO ₂ in the combustion exhaust gas and MEA, and the temperature of the de-CO ₂ combustion exhaust gas after gas-liquid separation is the combustion exhaust gas temperature supplied from the de-CO ₂ tower combustion exhaust gas supply port 04. It becomes higher.) Saturated water vapor that meets the conditions. Further, since this CO ₂ -exhausted exhaust gas contains MEA corresponding to the MEA vapor pressure of the MEA aqueous solution at that temperature, the CO ₂ -exhaust gas is directly removed from the CO ₂ removal column 01.
₂ MEA when discharged outside the system through the combustion exhaust gas outlet 05
And the pollution of the surrounding atmosphere. The water balance in the system is also lost. Therefore, an appropriate amount of condensed water after gas-liquid separation is guided to the cooler 010 by the water circulation pump 09, where the circulating water is cooled and the circulating water is supplied to the nozzle 011.
The CO ₂ combustion exhaust gas that is more dispersed and released, and is rising is brought into countercurrent contact with the upper filling portion 03 to lower the temperature of the CO ₂ combustion exhaust gas and to condense water and the vapor of MEA to remove the MEA. I try not to diffuse it into the atmosphere.

Although the combustion exhaust gas cooling system illustrated in FIG. 2 is not limited, it is mainly used for a fuel containing a relatively large amount of hydrogen such as LNG, and is contained in the combustion exhaust gas as described above. When the steam derived from the fuel is cooled, it becomes condensed water and accumulates. Therefore, it is always discharged from the condensed water discharge line 019 as excess water. The cooling system for the combustion exhaust gas is not limited to this, but there is a humidification cooling method mainly applied to a boiler that burns a fuel containing a relatively large amount of carbon such as coal and heavy oil. For this purpose, it is not necessary to install the heat exchanger 017 as described later, but the circulating water and the combustion exhaust gas are simply brought into contact with each other to cool them by evaporation of water, and the circulating water is gradually lost by evaporation. Therefore, it will be supplied from the outside.

[0009]

Although the conventional method and apparatus for removing CO ₂ described with reference to FIG. 2 is useful as such, alkanol which is an absorbent that is taken out of the CO ₂ column outside the system is still used. There is a problem that the amount of amine is large and therefore the loss of the valuable absorbent is large, and the accompanying air pollution occurs.

In the above CO ₂ removal method and apparatus, ammonia is detected in the CO ₂ removal exhaust gas exhausted from the CO ₂ removal exhaust gas outlet 05 though it is a trace amount. It is speculated that the origin of this ammonia is that part of the alkanolamine decomposes in the process system. When ammonia is added to the fuel for the purpose of reducing NOx in the combustion exhaust gas, another cause of the detection of ammonia may be residual ammonia. In any case, even if the amount of ammonia is small, if ammonia is directly discharged to the atmosphere together with the CO ₂ -exhausted exhaust gas, it can cause a new environmental problem as a bad odor and must be removed. However, the amount of ammonia contained in the treated exhaust gas is very small, and how to remove this efficiently has been a problem.

[0011]

Means for Solving the Problems The inventors of the present invention have earnestly studied the above-mentioned problems of the process for removing CO ₂ in the combustion exhaust gas by using alkanolamine as shown in FIG. Remove the reflux water from C
It has been found that it is effective to contact the exhaust gas without CO ₂ in the O ₂ column, and the present invention has been completed.

Namely, first the of the present invention, by contacting the flue gas with an aqueous alkanolamine solution, in the de CO ₂ device for removing CO ₂ contained in the combustion exhaust gas, the combustion exhaust gas with an alkanolamine solution to countercurrent contact Combustion exhaust gas, characterized in that it is provided on the downstream side of the combustion exhaust gas of the contact portion, in which the reflux water of the alkanolamine aqueous solution regeneration tower and the CO ₂ -depleted CO ₂ -exhausted exhaust gas come into countercurrent contact. This is a CO ₂ removal device.

[0013] The second invention is provided in the de CO ₂ device of the flue gas, the removal CO ₂ device to a flue gas temperature of the inlet and outlet of the flue gas removing CO ₂ device in the same The method for removing CO _{2 from} combustion exhaust gas is characterized by controlling the temperature of the alkanolamine aqueous solution. Hereinafter, the present invention will be described in detail.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the apparatus and method for removing CO _{2 from} combustion exhaust gas according to the present invention will be described with reference to FIG. In FIG. 1, only the main equipment is shown and the auxiliary equipment is omitted.

With reference to FIG. 1, 1 is a CO ₂ removal tower, 2 is a lower packing part, 3 is an upper packing part or tray, 4 is a CO ₂ removal tower combustion exhaust gas supply port, 5 is a CO ₂ removal combustion exhaust gas discharge port, and 6
Is an MEA aqueous solution supply port, 7 is a nozzle, 8 is a regeneration liquid recirculation liquid supply port, 9 is a nozzle, 10 is a combustion exhaust gas cooler, 11 is a nozzle, 12 is a filling section, 13 is a humidification cooling water circulation pump,
Reference numeral 14 is a makeup water supply line, 15 is a CO ₂ absorption MEA aqueous solution discharge pump, 16 is a heat exchanger, 17 is a cooler, 18 is an MEA aqueous solution regeneration (hereinafter also referred to as “regeneration”) tower, 19
Is a nozzle, 20 is a lower filling part, 21 is a regenerative heater (reboiler), 22 is an upper filling part, 23 is a reflux water pump, 2
4 is a CO ₂ separator, 25 is a recovered CO ₂ discharge line, 26
Is a regeneration tower reflux condenser, 27 is a nozzle, 28 is a regeneration tower reflux water supply line, and 29 is a combustion gas supply blower.

In FIG. 1, the combustion exhaust gas is pushed into the combustion exhaust gas cooler 10 by the combustion exhaust gas supply blower 29, and is brought into contact with the humidified cooling water from the nozzle 11 at the filling section 12 to be humidified and cooled to remove CO ₂ tower combustion. It is led to the CO ₂ removal tower 1 through the exhaust gas supply port 4. Depending on the type of fuel and cooling conditions, the temperature of the flue gas at the inlet to the CO ₂ removal column 1 is usually 50 to 80 ° C., but the apparatus and method of the present invention do not necessarily require further cooling. Therefore, the cooler 017 shown in FIG. 2 is unnecessary. The humidified cooling water that has come into contact with the combustion exhaust gas collects in the lower portion of the combustion exhaust gas cooler 10 and is circulated to the nozzle 11 by the pump 13. Since the humidified cooling water is gradually lost by humidifying and cooling the combustion exhaust gas, it is replenished by the makeup water supply line 14.

The combustion exhaust gas forced into de CO ₂ column 1 is countercurrent contacted with a filler portion 2 and the MEA aqueous solution of a predetermined concentration is supplied from the nozzle 7 as described in Figure 2, the flue gas CO ₂ Is absorbed and removed by the MEA aqueous solution,
The de-CO ₂ combustion exhaust gas goes to the upper filling part 3. CO ₂ removal
The MEA aqueous solution supplied to the tower 1 absorbs CO _2, and due to the reaction heat due to the absorption, the temperature becomes higher than the temperature at the supply port 6 and is sent to the heat exchanger 16 by the CO ₂ absorbing MEA aqueous solution discharge pump 15. It is heated and guided to the regeneration tower 18. In the method of the present invention, by adjusting the temperature of the MEA aqueous solution supplied to the CO ₂ removal column 1, C
Most of the heat of reaction due to the absorption of O ₂ is carried away to the outside of the CO ₂ removal column 1 by the MEA aqueous solution returning to the regeneration tower 18. The temperature of the MEA aqueous solution is controlled by the heat exchanger 16 or, if necessary, the heat exchanger 16 and the MEA aqueous solution supply port 6.
It can be performed by the cooler 17 provided between the two.
After the inside of the system reaches a steady state, the temperature of the MEA aqueous solution normally supplied to the CO ₂ removal column 1 also becomes constant. As a result, the temperature of the combustion exhaust gas hardly rises due to the reaction heat, and the CO ₂ removal tower 1 is raised and discharged at a temperature substantially the same as the supply temperature of the combustion exhaust gas supply port 4. It should be noted that the term “identical” here does not mean a strict meaning and is included in the same range in a state where the water balance of the CO ₂ removal column 1 described later is maintained even if a slight temperature difference occurs.

By adjusting the temperature of the MEA aqueous solution supplied from the MEA aqueous solution supply port 6 so that the combustion exhaust gas temperature is the same at the inlet and the outlet of the CO ₂ removal tower 1,
_{2 The} tower 1 and the water balance of the whole system of Fig. 1 will be maintained. Therefore, even if the temperature of the combustion exhaust gas supplied to the CO ₂ removal tower 1 is as high as 50 to 80 ° C., the cooler 010 installed in the process of FIG. 2 is unnecessary. Even if the temperature of the combustion exhaust gas discharged from the CO ₂ removal column 1 is high, the apparatus and method of the present invention that uses the reflux water from the regeneration tower 18 for the CO ₂ removal column 1 as described below is used outside the MEA system. Is effectively prevented.

In the regeneration tower 18, the MEA aqueous solution is regenerated by heating by the regeneration heater 21, cooled by the heat exchanger 16 and returned to the CO ₂ removal tower 1. In the upper part of the regeneration tower 18, the CO ₂ separated from the MEA aqueous solution comes into contact with the reflux water supplied from the nozzle 27, is cooled by the regeneration tower reflux condenser 26, and is entrained in CO ₂ by the CO ₂ separator 24. The steam is separated from the condensed reflux water, and is introduced from 25 to the CO ₂ recovery step. A part of the reflux water is recycled to the regeneration tower 18 by the reflux water pump 23.

The apparatus and method of the present invention are characterized in that a part of this reflux water is supplied to the CO ₂ removal column 1 through the regeneration tower reflux water supply line 28 through the regeneration tower reflux liquid supply port 8 and the nozzle 9. Is. By making countercurrent contact between the combustion exhaust gas containing the degassed CO ₂ MEA vapor and this reflux water at the filling portion or the portion constituted by the tray 3, the MEA vapor in the combustion exhaust gas is reduced to almost zero. Since more reflux water is one which is separated from the CO ₂ in the CO ₂ separator 24, CO ₂ is contained at a concentration near saturation or to that at the temperature in the water. For example CO ₂
When the temperature of the reflux water separated by the separator 24 is around 40 ° C., the reflux water contains approximately 400 ppm of CO ₂ .

The de-CO ₂ combustion exhaust gas lower filling portion 2 of the de-CO ₂ column 1 is as high as 50 to 80 ° C., the vapor partial pressure equivalent relatively large amount of MEA vapor at that temperature, the ammonia and water vapor traces It flows upwards, and comes into contact with the above-mentioned reflux water supplied from the regeneration tower 18 through the regeneration tower reflux water supply line 28. However, since ammonia and MEA are weak bases, the reflux water containing weakly acidic CO ₂ in a substantially saturated state and the de-CO ₂ combustion exhaust gas are brought into contact with each other at the upper contact portion 3, so that the upper filling portion of FIG. Compared with the case of the prior art shown in FIG. 2 which uses water, these can be effectively prevented from being taken into the reflux water and released into the atmosphere. The reflux water supplied to the CO ₂ removal tower 1 comes into contact with the CO ₂ removed exhaust gas to absorb MEA and ammonia, then descends the CO ₂ removal tower 1, mixes with the MEA aqueous solution, and is returned to the regeneration tower 18. It will be. The reflux water supplied to the CO ₂ removal tower 1 is a part of the total reflux water, and is eventually returned to the regeneration tower 18, so there is no problem in terms of water balance in the system.

It should be noted that the MEA contained in the CO ₂ -exhausted exhaust gas reacts with the CO ₂ contained in the reflux water, which is the same as the reaction occurring in the lower filling section 2. Further, ammonia in the CO ₂ -exhausted exhaust gas reacts with CO ₂ in the reflux water to cause any of the reactions represented by the following formulas, and is absorbed by water as ammonium carbonate salts. NH ₃ + CO ₂ + H ₂ O → NH ₄ HCO ₃ ... Formula (1) 2 NH ₃ + CO ₂ + H ₂ O → (NH ₄ ) ₂ CO ₃ ... Formula (2)

Ammonium carbonate salts produced by the above reaction formula, particularly NH ₄ HCO ₃ , are relatively stable in an aqueous solution, and ammonia is removed from the CO ₂ -exhausted exhaust gas as ammoniacal salts into the atmosphere. The release of is suppressed to some extent. If the flue gas treatment is continued as it is, these ammonium salts will be accumulated in the system and decomposed in the regeneration process to return to ammonia, so it is difficult to completely suppress the release of ammonia.

In FIG. 1, the combustion exhaust gas is cooled by the humidification cooling method, but it is not always necessary and the process using the cooler shown in FIG. 2 may be used. However, according to the present invention, even if the temperature of the CO ₂ -exhausted exhaust gas is high and a large amount of MEA vapor corresponding to the temperature is contained, the CO ₂ -containing regeneration tower reflux water is used to effectively discharge the exhaust gas. Can be prevented. Therefore, by adopting the process of FIG. 1 as described above, the cooler 017 of FIG. 2 becomes unnecessary, which is advantageous in terms of cost.

[0025]

EXAMPLES The embodiments of FIG. 1 of the present invention and the embodiments of FIG. 2 showing the conventional apparatus and method are shown in Table 1 and Table 2, respectively, to prove the effect of the present invention.

[Table 1]

[Table 2]

[0026]

As described in detail above, according to the present invention in which a part of the reflux water of the regeneration tower is used in the CO ₂ removal tower, the remaining CO ₂ absorbed CO _{2 in the} combustion exhaust gas is removed. It has become possible to effectively suppress the alkanolamine that is brought out of the system. Similarly, the amount of ammonia contained in the combustion exhaust gas in a trace amount can be suppressed to some extent. Then, the circulating water at the top of the CO ₂ removal towers and the cooling device therefor which were conventionally required are no longer required. Further, according to the present invention, the temperature of the combustion exhaust gas supplied to the CO ₂ removal tower and the CO ₂ removal
Since the temperature of the MEA aqueous solution supplied to the tower is adjusted so that the exhaust temperature of the combustion exhaust gas becomes the same, the water balance of the tower and the entire internal system can be maintained.

[Brief description of drawings]

FIG. 1 is an example of a process employed in the CO ₂ removal apparatus and method of the present invention.

FIG. 2 is an example showing a part of a conventional CO ₂ removal device.

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

Claims (2)

[Claims] 1. A contacting the flue gas with an aqueous alkanolamine solution, in the de CO ₂ device for removing CO ₂ contained in the combustion exhaust gas, after flue gas with an aqueous alkanolamine solution is of the combustion exhaust gas contact portion for countercurrent contact On the flow side, reflux water of the alkanolamine aqueous solution regeneration tower and CO
De CO ₂ of the combustion exhaust gas leaving CO ₂ combustion _exhaust gas ₂ has been removed, characterized by comprising providing a contact portion for countercurrent contact
apparatus. 2. A de-CO ₂ system of the combustion exhaust gas according to claim 1, the flue gas leaving CO ₂ column inlet and aqueous alkanolamine solution to be supplied to the de-CO ₂ column to the same flue gas temperature at the outlet A method for removing CO _{2 from} combustion exhaust gas, which comprises controlling the temperature.