JP3233809B2 - Method for removing carbon dioxide in flue gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a relates to a method of removing CO ₂ (carbon dioxide) contained in combustion exhaust gas, more particularly, by using a mixed aqueous solution of secondary amine and tertiary amine, atmospheric pressure The present invention relates to a method for efficiently removing CO ₂ in the lower combustion exhaust gas.

[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 have been urgently required internationally to protect the global environment. CO ₂
As a source of the occurrence, all human activity fields burning fossil fuels tend to be increasingly demanded for emission control. To the target power generation facilities such as thermal power plants using large amounts of fossil fuels with this, a method of flue gas of a boiler into contact with an aqueous alkanolamine solution or the like to remove the CO ₂ in the combustion exhaust gas is recovered and, Methods for storing the recovered CO ₂ without releasing it to the atmosphere are being vigorously studied.

Examples of the alkanolamine include monoethanolamine, triethanolamine, N-methyldiethanolamine (MDEA), diisopropanolamine, and diglycolamine.
Usually, monoethanolamine (MEA) is preferably used. The use of other secondary and tertiary hindered amine aqueous solutions is also being studied.

However, even if the alkanolamine aqueous solution represented by MEA as described above is used as an absorbent for absorbing and storing CO _{2 in} combustion exhaust gas, the absorption of CO ₂ per a predetermined amount of the amine aqueous solution having a predetermined concentration can be achieved. The amount of CO ₂ absorbed per unit amine mole of the aqueous amine solution of the predetermined concentration, the absorption rate of CO _{2 at} the predetermined concentration, and the heat energy required for the regeneration of the aqueous alkanolamine solution after absorption. is not.

There are many known techniques for separating an acidic gas from various mixed gases using an amine compound. Japanese Patent Application Laid-Open No. 53-100180 discloses that (1) at least one secondary amino group or tertiary carbon atom which is a part of a ring and bonded to either a secondary carbon atom or a tertiary carbon atom; An amine mixture consisting of at least 50 mol% of sterically hindered amines containing bound primary amino groups and at least about 10 mol% of tertiary amino alcohols, and (2) said amines being physical absorbers for acidic gases A method for removing acidic gases comprising contacting a gaseous mixture with an amine-solvent liquid absorbent comprising a solvent for the mixture is described. Sterically hindered amines include 2-piperidineethanol [2- (2-hydroxyethyl) -piperidine] and 3-amino-3-methyl-1-butanol, and the solvent may contain up to 25% by weight of water. Examples of the processing gas include a sulfoxide compound and the like, as described in the upper left column of page 11 of the same publication, as “normal gaseous state having a high concentration of carbon dioxide and hydrogen sulfide, for example, 35% CO ₂ and 10 to 12% H ₂ S. mixture "is illustrated, also in the embodiment CO ₂ itself is used for.

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

[0007] Chemical Engineering Science (C
chemical Engineering Science
ce), Vol. 41, No. 4, pp. 997 to 1003 discloses carbon dioxide absorption behavior of an aqueous solution of a hindered amine, 2-amino-2-methyl-1-propanol (AMP). As the gas to be absorbed, CO _{2 at} atmospheric pressure and a mixture of CO ₂ and N ₂ are used.

[0008] Chemical Engineering Science (C
chemical Engineering science
ce), Vol. 41, No. 2, pp. 405-408, shows that hindered amines such as AMP and MEA
The absorption rates of aqueous solutions of such linear amines for CO ₂ and H ₂ S have been reported.

US Pat. No. 3,622,267 uses an aqueous mixture containing methyldiethanolamine and monoethylmonoethanolamine, and uses a high partial pressure of CO ₂ contained in a synthesis gas such as a partially oxidized gas such as crude oil. For example, a technique for purifying a synthesis gas containing 30% CO _{2 at} 40 atm is disclosed.

[0010] German Offenlegungsschrift 1,542,415 discloses a technique of 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. . Similarly, German Offenlegungsschrift 1,904,428 discloses a technique in which monomethylethanolamine is added for the purpose of improving the absorption rate of methyldiethanolamine.

US Pat. No. 4,336,233 discloses that a 0.81-1.3 mol / l aqueous solution of piperazine is used as a cleaning liquid for the purification of natural gas, synthesis gas and gasified coal gas, and that piperazine is methyl. A technique is disclosed which is used as a washing solution in an aqueous solution together with a solvent such as diethanolamine, triethanolamine, diethanolamine, and monomethylethanolamine.

Similarly, Japanese Patent Application Laid-Open No. 52-63171 suggests a CO ₂ absorbent obtained by adding a piperazine derivative such as piperazine or hydroxyethylpiperazine as an accelerator to a tertiary alkanolamine, a monoalkylalkanolamine or the like. However, in practice, the combination of monomethylaminoethanolamine and piperazine has not been tested as a monoalkyl alkanolamine, and it is also intended for synthesis gas,
There is no description of the removal of CO _{2 from} flue gas at atmospheric pressure.

[0013]

As described above, there is a need for a method for efficiently removing CO ₂ from flue gas. In particular, a certain concentration of CO ₂ absorbent (amine compound)
When processing flue gas with an aqueous solution containing a large problem of CO ₂ absorption, absorption of CO ₂ per unit volume of the aqueous solution, and to select a larger absorbent absorption rate of the immediate per absorbent unit mole It is. Further separating the CO ₂ after absorption of CO _2, heat energy less absorbent necessary for regenerating the absorbing solution is desired.

[0014]

Means for Solving the Problems In view of the above problems, the present inventors have conducted intensive studies on an absorbent used for removing CO ₂ in flue gas, and as a result, have found that a specific amine compound and a piperazine-based compound can be separated. The inventors have found that it is particularly effective to use an aqueous solution containing both of them, and have completed the present invention. That is, according to the present invention, an amine compound [1] represented by the following general formula and piperazine, 2-amine
Methylpiperazine, 2,3-dimethylpiperazine, 2,
An aqueous solution containing a piperazine compound [2] selected from the group of 5-dimethylpiperazine ,
The concentration of the product [1] is in the range of 15 to 65% by weight,
When the concentration of the azine compound [2] is 1.5 to 65% by weight
Soluble in an aqueous solution of the amine compound [1] at 30 ° C.
Within the range, and the total concentration of [1] and [2] is 70 times
A method is provided for removing CO ₂ in flue gas, which comprises contacting an aqueous solution of not more than 5% by volume with flue gas at atmospheric pressure.

Embedded image R ¹ CHR ² NHCH ₂ CH ₂ OH [1] (In the formula, R ¹ represents a hydrogen atom or a lower alkyl group having 1 to 4 carbon atoms, and R ² represents a hydrogen atom or a methyl group.) According to the present invention, the piperazine compound [2] is 2-methylpiperazine, and the amine compound [1] is 2-methylpiperazine.
- (n-butylamino) method for removing CO ₂ in the combustion exhaust gas is ethanol is provided.

[0015]

The present invention relates to a specific amine compound [1] and pipera
This is a method of removing CO _{2 in} combustion exhaust gas with an aqueous solution containing a gin-based compound [2]. By using an aqueous solution containing both compounds as an absorbing solution, an excellent solution not obtained by using each single compound can be obtained. Absorption performance is demonstrated. In the amine compound [1] represented by the above general formula used in the present invention, the lower alkyl group having 1 to 4 carbon atoms represented by R ¹ may be a methyl group, an ethyl group, an n-propyl group.
Group , isopropyl group, n-butyl group, isobutyl group, s
Examples thereof include an ec-butyl group and a tert-butyl group, preferably a methyl group, an ethyl group, an n-propyl group, and an n-butyl group, and particularly preferably an n-propyl group. R ² is hydrogen or a methyl group, preferably hydrogen.

Accordingly, the amine compound [1] represented by the above general formula includes 2- (methylaminoethanol,
-(Ethylamino) ethanol [EAE], 2- (n-
Propylamino) ethanol, 2- (n-butylamino) ethanol [n-BAE], 2- (n-pentylamino) ethanol, 2- (isopropylamino) ethanol, 2- (sec-butylamino) ethanol, 2- (sec-butylamino) ethanol
An example is (isobutylamino) ethanol, and particularly preferred is 2- (n-butylamino) ethanol [n-BAE]. In addition, you may use these amine compounds [1] in mixture of 2 or more types.

The concentration of the aqueous solution of the amine compound [1] and the piperazine compound [2] (hereinafter also referred to as absorption liquid) used for contact with the combustion exhaust gas of the present invention is usually 15 to 15%. 65% by weight, preferably 3%
It is in the range of 0 to 50% by weight.

On the other hand, the concentration of the piperazine compound [2] is usually in the range of 1.5 to 65% by weight. The concentration of the piperazine compound [2] in the absorbing solution is preferably as high as possible, as long as there is no hindrance. However, there is a compound having a low solubility depending on the type of the piperazine compound, such as piperazine. Therefore, in consideration of the lower limit temperature of the absorbing solution in the entire absorption step, within the above concentration range,
And it is used within a range that is soluble in an aqueous solution of the amine compound [1] at 30 ° C. From this viewpoint, the range of 1.5 to 15% by weight is preferable for the piperazine having relatively low solubility in water, and the range of 10 to 40% by weight, particularly 20 to 35% by weight for other piperazine-based compounds. Preferably, it is used. However, when the total concentration of both the amine compound [1] and the piperazine-based compound [2] is increased, the viscosity is increased.
It is preferred to use it in an amount of not more than weight%.

In the present invention, the temperature of the absorbent at the time of contact with the combustion exhaust gas is usually in the range of 30 to 70 ° C. In addition, the absorbing solution used in the present invention may optionally include a corrosion inhibitor,
A deterioration inhibitor and the like are added.

Further, the term "atmospheric pressure" in the present invention includes a pressure range near atmospheric pressure at which a blower or the like acts to supply combustion exhaust gas.

The process that can be employed in the method of the present invention for removing CO ₂ from flue gas is not particularly limited, but one 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 filling section, 3 is an upper filling section or tray, 4 is a CO ₂ removal tower exhaust gas inlet, and 5 is a CO ₂ removal section.
Combustion exhaust gas outlet, 6 is an absorbent supply port, 7 is a nozzle, 8
Is a flue gas cooler provided as required, 9 is a nozzle, 10 is a filling section, 11 is a humidification cooling water circulation pump, 12
Is a make-up water supply line, 13 is an absorption liquid discharge pump that has absorbed CO ₂ , 14 is a heat exchanger, 15 is an absorption liquid regeneration (hereinafter, referred to as
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, and 22 is recovered CO. ₂ discharge line, 23 is a regeneration tower reflux condenser, 24
Is a nozzle, 25 is a regeneration tower reflux water supply line, 26 is a combustion exhaust gas supply blower, 27 is a cooler, and 28 is a regeneration tower reflux water supply port.

In FIG. 1, the flue gas is pushed into the flue gas cooler 8 by the flue gas supply blower 26,
Contact with humidifying cooling water and the filling section 10 from the nozzle 9, is fogging, de-C through the de-CO ₂ tower combustion exhaust gas feed port 4
It is led to the O ₂ tower 1. The humidified cooling water in contact with the combustion exhaust gas accumulates 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 through 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 humidification cooling water and supply it to the combustion exhaust gas cooler 8. It becomes possible.

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

In the regeneration tower 15, the heating by the regeneration heater 18 is performed.
The absorption liquid is regenerated in the lower filling section 17 by heat, and the heat exchanger
14 and, if necessary, cooled by a cooler 27 to remove C
O_TwoReturned to Tower 1. Above the absorption liquid regeneration tower 15
And the CO separated from the absorbing solution _TwoIs supplied from nozzle 24
And is cooled by the regenerative tower reflux cooler 23.
Rejected, CO_TwoCO in the separator 21_TwoWater vapor associated with
Is separated from the condensed reflux water, and the recovered CO_TwoDischarge line 2
CO from 2_TwoGuided to the recovery process. Part of the reflux water is refluxed
The water is returned to the regeneration tower 15 by the water pump 20, and a part is regenerated.
CO 2 removal through the reflux water supply line 25_TwoRegeneration tower reflux of tower 1
The water is supplied to the water supply port 28. A trace amount of this recycle tower reflux water
Desorbed CO._TwoTop filling of tower 1
Contact with the exhaust gas in the part 3 and trace amount of CO contained in the exhaust gas
_TwoContributes to the removal of.

[0025]

【Example】

(Examples 1 to 3, Comparative Examples 1 to 4) In order to confirm the effect of the method for removing CO ₂ in flue gas according to the present invention, a small test apparatus schematically shown in FIG. 2 was used. In FIG.
The test gas 201 is introduced at a flow rate of 0.98 Nm ³ / h into a lower part of a stainless steel absorption tower 202 having a height of 1500 mm, an inner diameter of 50 mm and a filling height of 1000 mm. The composition of the test gas _{CO 2 10%, N 2 87} %, in which has been adjusted to O ₂ 3%. A nozzle 203 is provided above the absorption tower 202, and the regenerated and circulated absorption liquid is sprayed. A filling section 204 provided at the center of the absorption tower is filled with a 6 mm-length Dickson packing, and a hot water jacket 205 is provided therearound. A hot water circulating pump 206 for keeping the absorption temperature at 60 ° C. A tank 207 is provided. Above the absorption tower 202 is an absorption tower condenser 20.
8 is installed, the absorption processing gas is cooled here, and then analyzed by the absorption processing gas analyzer 209 and discharged. An absorption liquid extraction pump 210 is provided below the absorption tower, and the absorption liquid is preheated by a preheater 211 and controlled at a temperature of 110 ° C., and then guided to an upper part of the regeneration tower 212. Regeneration tower 212
Is made of stainless steel, has a height of 1500 mm, an inner diameter of 25 mm, and a filling height of 160 mm at the center, and is filled with the same packing as the absorption tower. The filling section is provided with a warm water jacket 213 for keeping the temperature constant, similarly to the absorption tower. The CO ₂ -rich absorbent flowing down from the upper part of the packed portion of the regeneration tower 212 is heated by the lower reboiler heater (electric heating) 214 (the temperature of the reboiler is controlled to 110 ° C.), and stripped by the generated steam to obtain a lean absorbent. 2.8 liters / h at the upper part of the absorption tower via the regeneration absorbent cooler 215, the regeneration absorbent extraction pump 216, the regeneration absorbent tank 217, the regeneration absorbent circulation pump 218, and the regeneration absorbent preheater 219. Circulated at a flow rate. Note that a part of the lean absorbent is supplied to the regeneration absorbent circulation pump 220.
At the inlet of the regeneration tower. A regeneration tower condenser 221 is provided at the upper part of the regeneration tower, and CO ₂ released from the absorbing solution is condensed and separated from water vapor by the condenser 221, and then an infrared CO ₂ gas meter (not shown, VIA51 manufactured by Horiba, Ltd.)
0) and is discharged via the regeneration tower gas scrubber 222.

An absorption / regeneration test was conducted using the above-mentioned small test apparatus and an absorption solution containing the compound shown in Table 1 under the absorption / regeneration conditions, and the inlet gas (test gas) of the absorption tower shown in Table 1 was used. CO ₂ concentration in the outlet gas (absorption processing gas), heat input of the reboiler (expressed in kW), CO ₂ concentration in the rich absorbing solution and the lean absorbing solution (according to TOC-5000 “Total Organic Carbon Analyzer” manufactured by Shimadzu Corporation) ) And the heat of regeneration. Table 1 shows the results. In addition, tests were performed by changing the heat input of the reboiler, and both the heat input of the reboiler and the amount of CO ₂ recovered per unit time when the inside of the system was stabilized were determined. The results are shown in Table 2. In addition, while the regenerated heat amount in Table 1 includes the heat radiation of the device, in Table 2, the value does not include the heat radiation of the device.

[0027]

[Table 1]

[0028]

[Table 2]

As can be seen from Tables 1 and 2, the mixed absorption solution of the amine compound [1] and the piperazine compound [2] according to the present invention can be used to prepare a conventional MEA aqueous solution or the amine compound [1]. As compared with the case where the piperazine compound [2] is used alone, the absorption capacity and the regenerative energy are greatly improved, which is extremely advantageous.

[0030]

As described above in detail, the treatment of the combustion exhaust gas under the atmospheric pressure by the method of the present invention makes it possible to comprehensively absorb CO ₂ more than in the case of using the conventional amine absorbing liquid. Improved performance is achieved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a process for removing CO _{2 in} combustion exhaust gas that can be employed in the present invention.

FIG. 2 is a schematic explanatory view of a small-sized test apparatus used in an embodiment of the present invention.

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masaki Iijima 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Heavy Industries, Ltd. Headquarters (72) Inventor Kaoru Mitsuoka 4-6-1 Kanon Shinmachi, Nishi-ku, Hiroshima, Hiroshima Prefecture 22 Hiroshima Research Laboratory, Mitsubishi Heavy Industries, Ltd. (56) References JP-A-52-63171 (JP, A) JP-A-54-40284 (JP, A) JP-A-6-198120 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B01D 53/62

Claims (2)

(57) [Claims] 1. An amine compound [1] represented by the following general formula, and piperazine, 2-methylpiperazine, 2,3
Aqueous solution containing a piperazine compound [2] selected from the group consisting of -dimethylpiperazine and 2,5-dimethylpiperazine, wherein the concentration of the amine compound [1] is 15 to 6;
5% by weight, and the concentration of the piperazine compound [2]
Amination at 1.5-65% by weight and 30 ° C
Within a range soluble in an aqueous solution of the compound [1], and [1]
A method for removing CO ₂ from flue gas, which comprises contacting an aqueous solution having a total concentration of 70% by weight or less with flue gas at atmospheric pressure. Embedded image R ¹ CHR ² NHCH ₂ CH ₂ OH [1] (In the formula, R ¹ represents a hydrogen atom or a lower alkyl group having 1 to 4 carbon atoms, and R ² represents a hydrogen atom or a methyl group.) 2. The piperazine compound [2] is 2-methylpiperazine, and the amine compound [1] is 2- (n
_{2. The} method for removing CO2 from flue gas according to claim 1, wherein the method is (butylamino) ethanol.