JPH08257353A - Process for removing carbon dioxide in combustion exhaust gas - Google Patents

Abstract

PURPOSE: To remove efficiently CO2 in combustion exhaust gas by bringing aqueous solution containing a diamine compound represented by specified formula into contact with combustion exhaust gas under atmospheric pressure. CONSTITUTION: In the case of removing CO2 in combustion exhaust gas in a boiler of a power generator in a terminal power station using a large amount of fossil fuel, water solution containing a diamine compound represented by formula (wherein, R<1> -R<4> represent respective lower 1-3C alkyl) is brought into contact with combustion gas under atmospheric pressure. As the diamine compound, bis(2-dimethylaminoethyl) ether may be mentioned, and the concentration of its water solution is set in the range of 15-65wt.%. Also for the purpose of increasing the CO2 absorption capability of absorbing solution, some other amine compound can be mixed in, and as the another compound to be used, 2-methylaminoethanol, 2-ethylaminoethanol or the like can be mentioned.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing CO ₂ (carbon dioxide) contained in a combustion exhaust gas, and more specifically, a combustion exhaust gas under atmospheric pressure using an aqueous solution containing a specific diamine compound. The present invention relates to a method for efficiently removing CO ₂ from the inside.

[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 countermeasures against it have become urgent internationally in order to protect the global environment. CO ₂
As the source of the emission of carbon dioxide, it extends to all human activity fields that burn fossil fuels, and there is a tendency that the demand for emission control thereof becomes even stronger. 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 contacting the combustion exhaust gas of a boiler with an alkanolamine aqueous solution or the like to remove CO ₂ from the combustion exhaust gas, and collecting A method of storing recovered CO ₂ without releasing it to the atmosphere has been vigorously studied.

Examples of the alkanolamine include monoethanolamine, triethanolamine, N-methyldiethanolamine (MDEA), diisopropanolamine and diglycolamine.
Usually monoethanolamine (MEA) is preferably used. However, even with the aqueous alkanolamine solution, such as described above typified by MEA as an absorbent for absorbing and removing CO ₂ in the combustion exhaust gas, the absorption of CO ₂ per predetermined amount of the aqueous amine solution having a predetermined concentration, predetermined CO ₂ absorption quantity per unit amine molar concentration of the amine aqueous solution, the absorption rate of CO ₂ at a given concentration, more in light like the heat energy required for the regeneration of the alkanolamine solution after the absorption, not always be satisfactory.

By the way, there are many known techniques for separating an acidic gas from various mixed gases using an amine compound. JP-A-53-100180 discloses (1) at least one secondary amino group which is part of a ring and is bonded to either a secondary carbon atom or a tertiary carbon atom, or An amine mixture comprising at least 50 mol% of a sterically hindered amine containing a primary amino group bonded to three carbon atoms and at least about 10 mol% of a tertiary amino alcohol, and (2) a physical absorbent for acidic gases. A process for the removal of acid gases is described which comprises contacting an amine-solvent liquid absorbent consisting of a solvent for an amine mixture, usually with a gaseous mixture. As the sterically hindered amine, 2-piperidine ethanol [2- (2-
Hydroxyethyl) -piperidine] and 3-amino-3
-Methyl-1-butanol and the like, and as a solvent, 2
Further examples of process gases such as sulfoxide compounds, which may contain up to 5% by weight of water, are listed in the upper left column of page 11 of the publication, "High concentrations of carbon dioxide and hydrogen sulphide, eg 35
% CO ₂ and 10-12% H ₂ S in a normally gaseous mixture ”, and CO ₂ itself is used in the examples.

JP-A-61-71819 describes a composition for acidic gas scraping containing a sterically hindered amine and a non-aqueous solvent such as sulfolane. Further, this publication describes the advantage of sterically hindered amines with respect to CO ₂ absorption by using a reaction formula.

Chemical Engineering Science (C
chemical engineering science
ce), Vol. 41, No. 4, pp. 997-1003, the carbon dioxide absorption behavior of an aqueous solution of 2-amino-2-methyl-1-propanol (AMP) which is a hindered amine is disclosed. As the gas to be absorbed, CO _{2 at} atmospheric pressure and a mixture of CO ₂ and N ₂ are used.

Chemical Engineering Science (C
chemical engineering sien
ce), Vol. 41, No. 2, p. 405-408, hindered amines such as AMP and MEA at around room temperature.
Absorption rates of CO ₂ and H ₂ S from various aqueous solutions of such linear amines have been reported.

US Pat. No. 3,622,267
Is methyldiethanolamine and monoethylmonoethano
Of the crude oil etc.
CO with high partial pressure contained in synthesis gas such as partial oxidation gas₂,
For example, 30% CO at 40 atmospheres ₂Purify contained syngas
The technology is disclosed.

German Laid-Open Patent No. 1,542,415 discloses a technique for adding a monoalkylalkanolamine or the like to a physical or chemical absorbent in order to improve the absorption rate of CO ₂ , H ₂ S and COS. There is. Similarly, German Published Patent 1,904,428 discloses a technique in which monomethylethanolamine is added for the purpose of improving the absorption rate of methyldiethanolamine.

In US Pat. No. 4,336,233, 0.81 to 1.3 mol / liter aqueous solution of piperazine is used as a cleaning liquid for the purification of natural gas, synthetic gas and gasified coal gas, and piperazine is used. A technique is disclosed in which an aqueous solution is used as a cleaning liquid together with a solvent such as methyldiethanolamine, triethanolamine, diethanolamine, and monomethylethanolamine.

Similarly, JP-A-52-63171 discloses a CO ₂ absorbent obtained by adding a piperazine derivative such as a tertiary alkanolamine or a monoalkylalkanolamine to a piperazine or a hydroxyethylpiperazine derivative as a promoter. Has been done.

[0012]

As described above, there is a demand for a method of efficiently removing CO ₂ from combustion exhaust gas. In particular, when treating combustion exhaust gas with an aqueous solution containing a constant concentration of CO ₂ absorbent (amine compound), selecting an absorbent having a large CO ₂ absorption amount per unit mol of the absorbent and a large absorption rate should be solved. It is an issue. Further separating the CO ₂ after absorption of CO _2, less absorbent of the heat energy required in regenerating the absorption liquid is desired.
Although it is difficult to meet all of these desirable requirements with the use of one kind of amine compound, if a compound satisfying some requirements is found, a more preferable requirement by a mixing column with another amine compound is found. There is a possibility of approaching to.

[0013]

In view of the above problems, the inventors of the present invention have diligently studied an absorbing solution used for removing CO _{2 in} combustion exhaust gas, and as a result, it is particularly effective to use a specific diamine compound. It was possible to complete the present invention by obtaining the knowledge that That is, according to the present invention, there is provided a method for removing CO _{2 in} combustion exhaust gas, which comprises contacting an aqueous solution containing a diamine compound represented by the following general formula [1] with combustion exhaust gas under atmospheric pressure. To be done.

Embedded image R ¹ R ² NCH ₂ CH ₂ OCH ₂ CH ₂ NR ³ R ⁴ [1] (wherein R ¹ , R ² , R ³ and R ⁴ each have 1 carbon atom)
~ 3 represents a lower alkyl group. Further, according to the present invention, there is provided a method for removing CO ₂ in the combustion exhaust gas, wherein the diamine compound is bis (2-dimethylaminoethyl) ether. Further, according to the present invention, there is provided a method for removing CO ₂ in the combustion exhaust gas in which the concentration of the aqueous solution is in the range of 15 to 65% by weight.

[0014]

In the diamine compound represented by the general formula [1] used in the present invention, the lower alkyl group having 1 to 3 carbon atoms represented by R ¹ , R ² , R ³ and R ⁴ is a methyl group or an ethyl group. Examples thereof include a group, a propyl group, and an isopropyl group, and a methyl group is particularly preferable. That is, as specific compounds, bis (2-dimethylaminoethyl) ether, bis (2-diethylaminoethyl) ether, bis (2-dipropylaminoethyl) ether and the like can be mentioned, with bis (2 being particularly preferred). -Dimethylaminoethyl) ether. The diamine compounds represented by the general formula [1] can be used alone or in a mixture of two or more kinds.

The concentration of the aqueous solution of the diamine compound (hereinafter, also referred to as absorbing solution) used for contact with the combustion exhaust gas of the present invention is usually 15 to 65% by weight, preferably 30 to 50% by weight. The temperature of the absorbing liquid at the time of contact with combustion exhaust gas is
It is usually in the range of 30 to 70 ° C.

If necessary, a corrosion inhibitor, a deterioration inhibitor, etc. are added to the absorbent used in the present invention.

Further, in order to increase the CO ₂ absorption capacity of the absorbing solution, one or more other amine compounds may be mixed. As other amine compounds, for example, 2-methylaminoethanol, 2-ethylaminoethanol, 2-
Isopropylaminoethanol, 2-n-butylaminoethanol, piperazine, 2-methylpiperazine, 2,
Examples thereof include 5-dimethylpiperazine, piperidine, 2-piperidinoethanol and the like. When these other amine compounds are used, as long as they are soluble in water together with the diamine compound of the general formula [1], the concentration of these other amine compounds alone is usually 1.5 to 50% by weight.
In the range of, preferably 5 to 40% by weight.

The term "atmospheric pressure" in the present invention includes a pressure range in the vicinity of atmospheric pressure to the extent that a blower or the like acts to supply combustion exhaust gas.

The process that can be used in the method of removing CO ₂ in the combustion exhaust gas of the present invention is not particularly limited, but an example thereof will be described with reference to FIG. In FIG. 1, only the main equipment is shown and the auxiliary equipment is omitted. In 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 CO ₂ removal
Combustion exhaust gas discharge port, 6 absorption liquid supply port, 7 nozzle, 8
Is a combustion exhaust gas cooler provided as necessary, 9 is a nozzle, 10 is a filling part, 11 is a humidification cooling water circulation pump, 12
Is a makeup water supply line, 13 is an absorption liquid discharge pump that has absorbed CO ₂ , 14 is a heat exchanger, and 15 is absorption liquid regeneration (hereinafter,
"Regeneration" is also abbreviated) tower, 16 is a nozzle, 17 is a lower filling section, 18 is a regenerative heater (reboiler), 19 is an upper filling section, 20 is a reflux water pump, 21 is a CO ₂ separator, 22 is CO recovery. ₂ discharge lines, 23 is a regenerator reflux condenser, 24
Is a nozzle, 25 is a regeneration tower recirculation water supply line, 26 is a combustion exhaust gas supply blower, 27 is a cooler, and 28 is a regeneration tower recirculation water supply port.

In FIG. 1, the combustion exhaust gas is pushed into the combustion exhaust gas cooler 8 by the combustion exhaust gas supply blower 26,
The humidified cooling water from the nozzle 9 comes into contact with the filling section 10, is humidified and cooled, and is decarbonized through the CO ₂ tower combustion exhaust gas supply port 4.
It is led to the O ₂ tower 1. The humidified cooling water that has come into contact with the combustion exhaust gas collects in the lower part of the combustion exhaust gas cooler 8 and is circulated to the nozzle 9 by the pump 11. 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 12. When the combustion exhaust gas is further cooled from the humidified cooling state, a heat exchanger is placed between the humidification cooling circulation pump 11 and the nozzle 9 to cool the humidified cooling water and supply it to the combustion exhaust gas cooler 8. It will be possible.

The combustion exhaust gas pushed into the CO ₂ removal tower 1 is brought into countercurrent contact with the absorption liquid having a constant concentration supplied from the nozzle 7 in the lower filling section 2, and CO ₂ in the combustion exhaust gas is absorbed and removed by the absorption liquid. Then, the de-CO ₂ combustion exhaust gas goes to the upper filling section 3. The absorption liquid supplied to the CO ₂ removal tower 1 is CO
₂ is absorbed, and due to the heat of reaction due to the absorption, the temperature is usually higher than the temperature at the absorption liquid supply port 6, and is sent to the heat exchanger 14 by the absorption liquid discharge pump 13 that has absorbed CO ₂ and is heated. Guided to the regeneration tower 5. The temperature of the regenerated absorption liquid is adjusted by the heat exchanger 14 or, if necessary, the cooler 2 provided between the heat exchanger 14 and the absorption liquid supply port 6.
7 can be performed.

In the regeneration tower 15, heating by the regeneration heater 18 is applied.
The absorption liquid is regenerated in the lower filling part 17 by heat,
14 and optionally C by being cooled by the cooler 27.
O₂Returned to Tower 1. Smell above the absorption liquid regeneration tower 15
CO separated from the absorption liquid ₂Is supplied from the nozzle 24
It comes into contact with the reflux water that is generated and is cooled by the regeneration tower reflux condenser 23.
Rejected, CO₂CO in the separator 21₂Water vapor
Is separated from the condensed reflux water, and the recovered CO₂Discharge line 2
CO from 2₂Guided to the recovery process. Part of reflux water is reflux
The water pump 20 recirculates to the regeneration tower 15, part of which is the regeneration tower.
CO removal via the reflux water supply line 25₂Recycle tower recycle tower 1
It is supplied to the water supply port 28. This regeneration tower reflux water has a trace amount
Since it contains the absorption liquid of₂Top filling of tower 1
Trace amount of CO contained in the exhaust gas coming into contact with the exhaust gas in Part 3
₂Contribute to the removal of.

[0023]

EXAMPLES C of the diamine compound used in the present invention is described below.
According to the example in which the O ₂ absorption capacity was examined by the small-scale absorption test,
The present invention will be specifically described. (Example 1, Comparative Example 1) 50 ml of a 30% by weight aqueous solution of bis (2-dimethylaminoethyl) ether was placed in a glass reaction container placed in a constant temperature bath. While stirring at a temperature of 40 ° C., the test gas was passed under atmospheric pressure at a flow rate of 1 liter / min through the absorbing liquid through a filter so as to easily generate bubbles. As a test gas, CO ₂ 10 mol%, O ₂
A model combustion exhaust gas at 40 ° C. having a composition of 3 mol% and N ₂ 87 mol% was used. Continued throughout the test gas, at the time when the concentration of CO ₂ out gas become equal, the CO ₂ contained in the absorbing solution was measured using a CO ₂ analyzer (total organic carbon meter), 90% saturated and the CO ₂ Saturated absorption (Nm ³ CO ₂
/ M ³ absorption liquid, mol CO ₂ / mol absorbent) was determined. As Comparative Example 1, an absorption test using an MEA aqueous solution was conducted.
Table 1 shows the results. It was confirmed that the absorbing solution can be regenerated without any trouble by heating the mixed solution after absorption.

[0024]

[Table 1]

As is clear from the results shown in Table 1, by using an aqueous solution of bis (2-dimethylethylaminoethyl) ether, which is one of the diamine compounds used in the present invention, as a combustion exhaust gas absorbing solution, an MEA aqueous solution is obtained. It can be seen that the saturated absorption amount per mol is superior to the case of using.

(Example 2, Comparative Example 1) In order to investigate the thermal energy required for regenerating the absorbing liquid, the absorbing liquid (concentration 30% by weight) used in Example 1 and Comparative Example 1 and CO ₂ were used. The reaction heat (absorption calorific value) was measured. 200 g of the absorbing solution was put in an adiabatic tester, stirred with a magnetic stirrer, and left until the temperature of the absorbing solution became stable. Next, add pure CO ₂ to about 2
Blowing into the tester at a rate of 00 cc / min, the CO ₂ flow rate at the inlet and outlet of the tester and the temperature of the absorbing liquid were continuously recorded. The test was terminated when the CO ₂ flow rate at the outlet of the tester increased rapidly. Absorbing liquid moles of absorbed CO ₂ to (moles load), reaction heat (kcal when absorbing liquid from a raised temperature from blowing initiation of CO ₂ is 1 mol absorb CO ₂
/ Mol) was determined. The heat capacity of the tester is 200 g of water.
Was put in a tester, and the heater was energized at 30.0 V and 0.3 A for a predetermined time, and the temperature was calculated from the temperature rise. The temperature range of the test was 20 to 80 ° C, and the room temperature at the time of measurement was 20 to 25 ° C. As a result, it was 15.2 kcal / mol CO ₂ in the bis (2-dimethylaminoethyl) ether, whereas it was 19.4 kcal / mol CO ₂ in the MEA aqueous solution. As can be seen from this, the absorption liquid of bis (2-dimethylaminoethyl) ether according to the present invention and CO
The heat of reaction of ₂ is on average smaller than in the case of the MEA absorbing liquid, and the energy required for regeneration is smaller than in the case of MEA, which is advantageous.

[0027]

As described in detail above, according to the method of the present invention, the aqueous solution of the diamine compound represented by the general formula [1] is used as the absorbing solution in the combustion exhaust gas under atmospheric pressure. As compared with the case of using an aqueous solution, a process in which the recovery energy of CO ₂ is generally small becomes possible.

[Brief description of drawings]

FIG. 1 is an explanatory view of a process of removing CO _{2 in} combustion exhaust gas that can be adopted in the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaki Iijima 2-5-1, Marunouchi, Chiyoda-ku, Tokyo Sanryo Heavy Industries Co., Ltd. (72) Inventor Kaoru Mitsuoka 4-6 Kannon Shinmachi, Nishi-ku, Hiroshima-shi, Hiroshima No.22 inside Hiroshima Research Laboratory, Mitsubishi Heavy Industries, Ltd.

Claims (3)

[Claims] 1. A diamine represented by the following general formula [1]:
Contact of aqueous solution containing compound with combustion exhaust gas under atmospheric pressure
CO in combustion exhaust gas characterized by ₂Remove
How to do. [Chemical formula 1] R¹R²NCH₂CH₂OCH₂CH₂NR³R^Four [1] (In the formula, R¹, R², R³And R^FourEach has 1 carbon
~ 3 represents a lower alkyl group. ) 2. The method for removing CO _{2 in} combustion exhaust gas according to claim 1, wherein the diamine compound is bis (2-dimethylaminoethyl) ether. 3. The C in the combustion exhaust gas according to claim 1 or 2, wherein the concentration of the aqueous solution is in the range of 15 to 65% by weight.
A method of removing O ₂ .