JP2871334B2 - Method of removing carbon dioxide from flue gas - Google Patents

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 flue gas. More specifically, using an aqueous solution of a specific hindered amine,
The present invention relates to a method for removing CO ₂ in flue gas at atmospheric pressure.

[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. Along with this, a method and method for contacting boiler flue gas with an alkanolamine aqueous solution and removing and recovering CO ₂ in flue gas for power generation facilities such as thermal power plants that use large amounts of fossil fuels Methods for storing the released CO ₂ without releasing it to the atmosphere are being vigorously studied.

Examples of the alkanolamine include monoethanolamine, diethanolamine, triethanolamine, methyldiethanolamine, diisopropanolamine, and diglycolamine.
Usually, monoethanolamine (MEA) is preferably used.

However, even if the above-mentioned alkanolamine aqueous solution represented by MEA is used as an absorbing solution for absorbing and removing CO _{2 in} combustion exhaust gas, the absorption of CO ₂ per a predetermined amount of the aqueous amine 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 regeneration of the aqueous alkanolamine solution after absorption, which is not always satisfactory. is not.

There are many known techniques for separating an acidic gas from various mixed gases using an amine compound. JP-A-53-100180 discloses that (1) at least one secondary amino group or tertiary carbon atom which is 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 a sterically hindered amine containing a primary amino group bound to a tertiary amino alcohol and at least about 10 mol%, and (2) said amine mixture which is a physical absorbent for acidic gases A method for removing acidic gases, which comprises contacting a gaseous mixture with an amine-solvent liquid absorbent comprising a solvent for use, is described. Sterically hindered amines include 2-piperidineethanol [2- (2-hydroxyethyl) -piperidine] and 3-amino-3-methyl-
1-butanol and the like, a solvent such as a sulfoxide compound which may contain up to 25% by weight of water and the like. 35% CO ₂ and 10
Typical gaseous mixtures having 〜12% H ₂ S ”, and the examples use CO ₂ itself.

Japanese Patent Application Laid-Open No. 61-71819 discloses a composition for scraping an acidic gas containing a non-aqueous solvent such as a sterically hindered amine and sulfolane. As the sterically hindered primary monoamino alcohol, 2-amino-2-methyl-1-propanol (AMP) and the like are exemplified and used. In the embodiment, the gas to be treated is C
O ₂ and nitrogen, CO ₂ and helium are used. Further, an aqueous solution of an amine and potassium carbonate or the like is also used as the absorbent. It also describes the use of water. Further, the publication describes the advantage of the sterically hindered amine with respect to the absorption of CO ₂ using a reaction formula.

Chemical Engineering Science (C)
chemical Engineering Science), Vol. 41, No. 4, 99
Pages 7 to 1003 disclose the carbon dioxide absorption behavior of an aqueous solution of hindered amine 2-amino-2-methyl-1-propanol (AMP). As the gas to be absorbed, atmospheric pressure CO ₂ and a mixture of CO ₂ and nitrogen are used.

Chemical Engineering Science (C)
chemical Engineering Science), Vol. 41, No. 2, 40
On pages 5 to 408, the absorption rates of hindered amines such as AMP and linear amines such as MEA for CO ₂ and H ₂ S are reported at around normal temperature. According to this, when the partial pressure of CO ₂ is 1 atm, there is no significant difference between the two at an aqueous solution concentration of 0.1 to 0.3M. But,
Using an aqueous solution having a concentration of 0.1 M, the partial pressure of CO ₂ was adjusted to 1.0.
5. If the pressure is reduced to 0.05 atm,
MP has a much lower absorption rate than MEA.

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. 40
A technique for purifying synthesis gas containing 30% CO _{2 at} atmospheric pressure is disclosed.

[0010] German Patent Publication No. 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 washing liquid for refining natural gas, synthesis gas and gasified coal gas, and that piperazine is methyldiethanolamine. There is disclosed a technique used as a washing solution in an aqueous solution together with a solvent such as triethanolamine, diethanolamine, and monomethylethanolamine.

Similarly, Japanese Patent Application Laid-Open No. Sho 52-63171 discloses a CO containing a tertiary alkanolamine, a monoalkylalkanolamine or the like, and a piperazine derivative such as piperazine or hydroxyethylpiperazine added as an accelerator.
_Two absorbents are disclosed.

[0013]

As described above, there is a need for a method for efficiently removing CO ₂ from combustion exhaust gas.
In particular, when the flue gas is treated with an aqueous solution containing a certain concentration of a CO ₂ absorbent (amine compound), the CO ₂ absorption amount per unit mole of the absorbent at a predetermined concentration, and the CO ₂ absorption amount per unit volume of the aqueous solution at a predetermined concentration of the absorbent. CO ₂ absorption,
A major problem for the moment is to select an absorbent having a high absorption rate. Furthermore after absorption of CO _2, separating the 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, it is particularly effective to use a specific hindered amine. With the knowledge that there was, the present invention could be completed.

That is, the present invention relates to (1) alcoholic hydroxyl
And a secondary amino group, wherein the secondary amino group is
Attached to a group having a chain of 2 or more carbon atoms including atoms
Hindered amine having an N atom (A) (however, two or more
With an amino group) and under atmospheric pressure
Combustion exhaust gas characterized by contacting with combustion exhaust gas
A method for removing carbon dioxide from the inside, (2) the hindered ami
(A) is 2-methylamino-ethanol or 2-E
The above, wherein the amino acid is tylaminoethanol.
(1) Method for removing carbon dioxide in combustion exhaust gas, (3)
Di-unsubstituted alkylaminopropanol and di-unsubstituted
Hinnes selected from the group consisting of alkylaminobutanols
Aqueous solution of dadoamine (B) and flue gas under atmospheric pressure
Carbon dioxide in flue gas characterized by contacting
Method for removing element, and (4) the hindered amine (B)
Is 3-diethylamino-1-propanol.
Removal of carbon dioxide in combustion exhaust gas according to the above (3)
It is a method of leaving.

[0016]

The hindered amine used in the present invention has an alcoholic hydroxyl group in the molecule. The alcoholic hydroxyl group preferably has one in the molecule. Further, the molecular weight of the hindered amine is preferably 150 or less from the viewpoint of the ability to absorb CO ₂ per unit solution having a predetermined concentration.

Among the hindered amines used in the present invention,
(A) having an alcoholic hydroxyl group and a secondary amino group,
Secondary amino groups are those having 2 or more carbon atoms, including the bonding carbon atom.
A compound having an N atom bonded to a group having a chain.
In this compound, the number of carbon atoms is 2 or more including the bonding carbon atom.
Examples of the above group having a chain include, for example, those having usually 2 to 5 carbon atoms.
A hydroxyl-substituted alkyl group, preferably a hydroxyl group having 2 to 3 carbon atoms
It is an alkyl group which may be substituted.

[0018] Examples of the compounds belonging to (A) of this, 2 -
Et Chiruami Noe pentanol, 2 - main Chiruami Noe Tano <br/> le, 2 - flop Ropiruami Noe pentanol, 2 - b an isopropyl <br/> Ami Noe pentanol, 1 - d Chiruami Noe pentanol, 1 -
Main Chiruami Noe pentanol, 1 - flop Ropiruami Noe Tano <br/> le, 1 - Lee Sopuropiruami Noe ethanol or the like can be exemplified, among others 2 - d Chiruami Noe ethanol [EAE
Abbreviated], 2 - is preferably used main Chiruami Noe methanol [MAE abbreviated].

Among the hindered amines used in the present invention,
(B) is di-unsubstituted alkylaminopropanol or
Di-unsubstituted alkylaminobutanol. In these compounds, the two unsubstituted alkyl groups may be the same or different from each other and include a methyl group, an ethyl group, a propyl group, an isopropyl group and the like.

Such compounds include 1-diethyl
Amino-2-propanol, 3-diethylamino-1-
Propanol and the like can be exemplified.

The hindered amines selected from the above-mentioned groups used in the present invention can be used alone or in combination. The concentration of the hindered amine aqueous solution used as the absorbing solution is usually 25 to 65% by weight, though it depends on the kind of the hindered amine. The temperature of the hindered amine aqueous solution at the time of contact with the combustion exhaust gas is usually in the range of 30 to 70 ° C.

Further, a corrosion inhibitor, a hindered amine deterioration inhibitor and the like are added to the hindered amine aqueous solution as required.

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, reference numeral 1 denotes CO2 removal._TwoTower, 2 at the bottom
Filling unit, 3 is the above filling unit or tray, 4 is CO 2 removal_TwoTower
Combustion exhaust gas supply port, 5 de-CO_TwoFlue gas outlet, 6
Is an absorption liquid supply port, 7 is a nozzle, and 8 is provided as necessary.
9 is a nozzle, 10 is a filling part, 1
1 is a humidification cooling water circulation pump, 12 is a makeup water supply line,
13 is CO_TwoPump for absorbing liquid absorbed
Exchanger 15 is an absorbent regeneration (hereinafter also abbreviated as "regeneration")
Tower, 16 is a nozzle, 17 is a lower filling section, 18 is regeneration heating
Vessel (reboiler), 19 is the upper filling part, 20 is the reflux water port
Pump, 21 is CO _TwoSeparator, 22 is recovered CO_TwoDischarge line
, 23 is a regenerator cooling condenser, 24 is a nozzle, and 25 is a regenerator.
Live tower reflux water supply line, 26 is a combustion exhaust gas supply blower,
27 is a cooler, and 28 is a recycle 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 and comes into contact with the humidified cooling water from the nozzle 9 at the filling section 10.
Is fogging, is directed through a de-CO ₂ tower combustion exhaust gas feed port 4 to the de-CO ₂ column 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. To further cool the combustion exhaust gas from the humidified cooling state, a heat exchanger is placed between the humidified cooling water circulation pump 11 and the nozzle 9 to cool the humidified cooling water and supply it to the combustion exhaust gas cooler 8. It becomes possible.

The combustion exhaust gas pushed into the CO ₂ removal tower 1 is brought into countercurrent contact with the absorption liquid of a predetermined 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 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 absorbs, because of the heat of reaction due to the absorption becomes a temperature higher than the temperature in the normal supply port 6, it is fed to the heat exchanger 14 by absorbing solution discharge pump 13 that has absorbed CO _2, heated, absorbent regenerator It is led to 15. The temperature of the regenerated absorbent can be adjusted by the heat exchanger 14 or, if necessary, by the cooler 27 provided between the heat exchanger 14 and the absorbent supply port 6.

In the absorption liquid regeneration tower 15, the absorption liquid is regenerated in the lower filling section 17 by heating by the regeneration heater 18, cooled by the heat exchanger 14 and returned to the CO ₂ removal tower 1. In the upper part of the absorption liquid regeneration tower 15, the CO ₂ separated from the absorption liquid comes into contact with the reflux water supplied from the nozzle 24 at the upper filling section 19, and is cooled by the regeneration tower reflux cooler 23,
In the CO ₂ separator 21, water vapor accompanying the CO ₂ is separated from the condensed reflux water, and the recovered CO _{2 is} discharged from the CO ₂ discharge line 22.
It is led to the O ₂ recovery step. A part of the reflux water is refluxed by the reflux water pump 20 and most of the reflux water is returned to the absorbent regeneration tower 15, and a part of the reflux water is supplied to the regeneration tower reflux water supply port 28 of the CO ₂ removal tower 1 through the regeneration tower reflux water supply line 25. Supplied. Since the regenerated tower reflux water contains a trace amount of the absorbing solution, it comes into contact with the exhaust gas at the upper filling section 3 of the CO ₂ removal tower 1 and contributes to the removal of the trace amount of CO ₂ contained in the exhaust gas.

[0029]

The present invention will be described below in detail with reference to examples. (Examples and Comparative Examples) A glass reaction vessel (flask) placed in a thermostat was charged with 50 ml of an absorbing solution comprising a 30% by weight aqueous solution of hindered amine, and stirred at a temperature of 40 ° C.
A mixed gas (test gas) was passed through the flask at a flow rate of 1 liter / min under atmospheric pressure. Test gas CO ₂ 10 mol%, O ₂ 3 mol%, 40 having a composition of N ₂ 87 mole%
C. model combustion exhaust gas (equivalent to LNG-fired combustion exhaust gas) was used. The test gas was continuously passed, and when the CO ₂ concentration of the incoming and outgoing gas became equal, the CO ₂ contained in the absorbing solution was changed to CO _2
The measurement was performed using _two analyzers (total organic carbon meter) to determine the CO ₂ saturated absorption amount. Similar tests were conducted at temperatures of 60 ° C and 80 ° C. As a comparison, a 30% by weight aqueous solution of MEA was used in the same manner.

The results obtained are shown in Table 1 (results at 40 ° C.) and FIG. The unit of the vertical axis in FIG. 2 is Nm ³ CO ₂
/ M ³ aqueous solution, and the horizontal axis indicates temperature (° C.).

From the graph of the relationship between the CO ₂ concentration in the gas at the outlet of the flask and the aeration time, the tangent slope at the start of the aeration is determined, and the initial absorption rate of the CO _{2 of} the absorbing solution is adjusted to the same concentration of M
It was determined by the ratio to the EA aqueous solution.

[0032]

[Table 1]

[0033] As apparent from Table 1, the initial absorption rate of the aqueous hindered amine solution is the absorption solution of the present invention is not lower the extent that synchronized pre, equivalent or degree slightly smaller and MEA. The absorption rate may be improved by the addition of an absorption enhancer. On the other hand, the amount of CO ₂ absorbed per unit mole of hindered amine is larger than that of MEA. In addition,
Absorption per unit absorbent liquid volume depends on the kind of hindered amine is the degree slightly smaller than M EA.

FIG. 2 shows that when the hindered amine of the present invention is used, the decrease in the amount of CO ₂ absorbed by the increase in the temperature of the absorbing solution is larger than that in the case of MEA. This indicates that thermal energy can be saved in the regeneration of the absorbing solution as compared with the case where the MEA is used.

[0035]

As described in detail above, the use of a specific hindered amine aqueous solution as an absorbent in flue gas under atmospheric pressure by the method of the present invention makes it possible to reduce the CO ₂ absorption rate to the same or slightly lower than MEA. In this way, CO ₂ can be efficiently removed from the viewpoint of the absorption capacity and the regeneration energy of the absorbing solution.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a process that can be employed in the present invention.

FIG. 2 Amount of absorption at an absorption liquid concentration of 30% by weight (vertical axis)
4 is a table showing the relationship between temperature and the temperature (horizontal axis).

[Description of sign]

1 CO ₂ removal tower 15 Absorbent regeneration tower 18 Regeneration heater

Continued on the front page (72) Inventor Shigeru Shimojo 3-3-22 Nakanoshima, Kita-ku, Osaka City, Osaka Prefecture Inside Kansai Electric Power Co., Inc. (72) Inventor Mutsunori Karasaki 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Heavy Industries, Ltd. Company headquarters (72) Inventor Masaki Iijima 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Heavy Industries, Ltd.Headquarters (72) Inventor Toru Seto 4-622 Kanonshinmachi, Nishi-ku, Hiroshima-shi, Hiroshima Mitsubishi Heavy Industries, Ltd. Company Hiroshima Research Laboratory (72) Inventor Kaoru Mitsuoka 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries, Ltd. Hiroshima Research Laboratory (56) References JP-A-1-231921 (JP, A) JP-A-53-100171 (JP, A) JP-A-52-63171 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B01D 53/62

Claims (4)

(57) [Claims] 1. A have A alcohol hydroxyl group and a secondary amino group, carbon atoms said second amino groups, including the binding carbon atom 2
More having a N atom bound to a group having a chain Ruhi Sunda <br/> Doamin (A) (excluding those having two or more amino groups) and a combustion exhaust gas under aqueous and atmospheric pressure A method for removing carbon dioxide from combustion exhaust gas, which comprises bringing the carbon dioxide into contact. 2. The method according to claim 1, wherein the hindered amine (A) is 2-methyl
Ruamino-ethanol or 2-ethylaminoethanol
The method for removing carbon dioxide in combustion exhaust gas according to claim 1, wherein 3. A di-unsubstituted alkylaminopropanol.
And di-unsubstituted alkylaminobutanols?
Aqueous solution of hindered amine (B) selected under atmospheric pressure
Combustion exhaust gas, which is brought into contact with the combustion exhaust gas
How to remove carbon dioxide in wastewater. 4. The method according to claim 1, wherein the hindered amine (B) is 3-die.
Characterized by being tylamino-1-propanol
The method for removing carbon dioxide from combustion exhaust gas according to claim 3.