JP3197172B2 - Method for removing carbon dioxide in 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, and more particularly, to a specific amino acid metal salt, a specific amine compound,
Furthermore, the present invention relates to a method for removing CO _{2 in} combustion exhaust gas using a mixed aqueous solution containing a specific metal compound.

[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, the combustion exhaust gas of boilers into contact with an aqueous alkanolamine solution or the like, is a method and recovered to the recovered CO ₂ removal in the combustion exhaust gas C
Methods for storing O ₂ without releasing it to the atmosphere are being vigorously studied.

Examples of the alkanolamine include monoethanolamine (MEA), diethanolamine, triethanolamine, methyldiethanolamine, diisopropanolamine, diglycolamine (DGA), and the like, and MEA is preferably used.
However, even if the alkanolamine aqueous solution represented by MEA as described above is used as an absorbent for absorbing and removing CO ₂ in the combustion exhaust gas, the absorption amount of CO ₂ per a predetermined amount of the aqueous amine solution having a predetermined concentration, a predetermined amount, In terms of the amount of CO ₂ absorbed per unit amine mole of the aqueous amine solution of a given concentration, the absorption rate of CO _{2 at} a given concentration, and the thermal energy required for regeneration of the aqueous alkanolamine solution after absorption, it is not necessarily satisfactory. Absent.

In addition, oxygen and C are dissolved by using an MEA aqueous solution.
CO by gas-liquid contact from the hot combustion exhaust gas containing O ₂
Continuing with the absorption and removal of the _2, the CO ₂ and absorption tower of the CO ₂ oxygen contact with the flue gas and absorption solution containing, regeneration tower to absorb the solution was heated to liberate the CO ₂ to regenerate the absorbent solution, and further Corrosion occurs in piping, heat exchangers, pumps, and other equipment that uses metal. For this reason, in the design of an apparatus using materials used in a normal chemical plant, the service life is significantly shortened, and even if it can be performed in a laboratory, it cannot be realized as an industrial process at all.

[0005] Such oxygen and CO_TwoIncluding combustion exhaust gas
From aqueous solutions of MEA or similar compounds.
CO_TwoCO using absorption solution_TwoCorrosion of equipment to absorb
As a method of improving the above, US Pat. No. 4,440,731
It is proposed in the specification. According to this proposal,
At least 50 ppm or more of divalent copper in such an absorbing solution
Ions, and also dihydroxyethyl glycine,
Alkali metal carbonate, alkali metal or ammonium
Permanganate, alkali metal carbonate or aluminum
Ammonium thiocyanate, nickel or bismuth
Oxide and the like are also added. This way
For example, when processing combustion gas with high oxygen concentration,
It is described that decomposition of MEA and the like is suppressed. this
In the examples of the US patent, MEA water is used as the amine compound.
Only test examples using solutions are described.
30 lbs of C in a 30% aqueous MEA solution
O_TwoAnd 15 lbs of oxygen, seed at 130 ° C
Mild steel specimens (MILD STEEL COU) in the presence of various corrosion inhibitors
PONS). as a result,
Corrosion degree about 40-52mi when no corrosion inhibitor is added
200 ppm of copper carbonate [Cu
CO_Three・ Cu (OH)_Two・ H _TwoO, CuCO_ThreeThe quantity is 56
Wt%] to 0.9 to 1.2 mpy
It is stated that corrosion is suppressed. Also separate from these
In the following, there will be described an atom represented by the general formula [1] used in the present invention described later.
One of the metal salts of amino acid is C
O_TwoUsed for recovery, or another as an aqueous solution
CO_TwoAnd H_TwoH from synthetic gas containing S_TwoOnly S
Techniques used for selective recovery are already known.

[0006]

As described above, there is a need for a method for efficiently removing CO ₂ from flue gas. In particular, when treating flue gas with an aqueous solution containing a certain concentration of CO ₂ absorbent, CO ₂ per unit mole of absorbent is used.
It is important to select an absorbent having a large absorption amount, an absorption amount of CO ₂ per unit volume of the aqueous solution, and an absorption rate. Furthermore after absorption of CO _2, separating the CO _2, the heat energy required in regenerating the absorbing solution - less absorbent is desired. In particular, it is desired to improve the absorption rate of an absorbent having a small absorption rate despite its large CO ₂ absorption capacity. In addition, the removal equipment used to remove CO ₂ from the combustion exhaust gas is usually made of metal, especially carbon steel, which is cheaper than stainless steel, in most cases. It is very important that it is a liquid.

[0007]

Means for Solving the Problems In view of the above problems, the present inventors have conducted intensive studies on absorbents used for removing CO ₂ in flue gas, and found that a relatively small amount of a specific metal salt of aminic acid is contained in the absorbent. A mixed aqueous solution in which a specific amine compound is mixed is particularly effective in improving the absorption rate of the amino acid metal salt, and the mixed aqueous solution contains a predetermined amount of a divalent copper compound. The knowledge that corrosiveness is suppressed was obtained, and the present invention was completed.

That is, the present invention relates to an amino acid metal salt (X) represented by the following general formula (1): 100 parts by weight, piperazine (Y): 1 to 25 parts by weight, and further converted to divalent copper ions. A mixed aqueous solution containing a copper compound in a range of 10 to 1000 ppm (content based on the mixed aqueous solution) is brought into contact with flue gas at atmospheric pressure to reduce CO2 in the flue gas.
_This is a method for removing ₂ .

## STR2 ## CH ₃ NR ¹ CHR ² COOM (1) (R ¹ and R ² represent hydrogen or a lower alkyl group, and R ² when R ¹ is hydrogen a lower alkyl group, R ¹ is When it is a lower alkyl group, R ² is hydrogen and M represents an alkali metal.)

[0009]

The lower alkyl group represented by R ¹ and R ² in the amino acid metal salt (X) represented by the general formula [1] used in the present invention is exemplified by a methyl group, an ethyl group and a propyl group. Although it is possible, a methyl group is particularly preferable. Examples of the alkali metal represented by M include sodium and potassium, and potassium is preferable. Examples of the amino acid metal salt (X) represented by the general formula [1] include potassium dimethylaminoacetate and potassium α-methylaminopropionate, with potassium dimethylaminoacetate being preferred.

In the present invention, piperazine (Y) is used together with the amino acid metal salt (X). The mixing ratio of the amino acid metal salt (X) and the piperazine (Y) was such that piperazine (Y) was 1 to 2 with respect to 100 parts by weight of the amino acid metal salt (X).
It is in the range of 5 parts by weight, more preferably in the range of 1 to 10 parts by weight.

In a mixed aqueous solution (hereinafter also referred to as "absorbent solution") to which an amino acid metal salt (X) and piperazine (Y) used as an absorbing solution of CO ₂ in flue gas and a divalent copper compound described later are added. The concentration of the amino acid metal salt (X) is usually 15 to 65% by weight.

A divalent copper compound is added to the mixed aqueous solution used in the present invention. Although such a copper compound is not limited, preferably, for example, copper carbonate [CuC
O ₃ .Cu (OH) ₂ .H ₂ O]. Copper carbonate is also known as basic copper carbonate, its addition amount is 10 to 1000 ppm in terms of divalent copper ions,
Preferably 100 to 800 ppm, more preferably 2
The range is from 00 to 600 ppm.

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 temperature of the mixed aqueous solution at the time of contact with the combustion exhaust gas is usually 30 to 70 ° C.
Range.

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, flue gas is pushed into a flue gas cooler 8 by a 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 absorbing solution of 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 absorbing solution. 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.

[0018]

The present invention will be described below in detail with reference to examples. Since the absorption performance of the mixed aqueous solution of the present invention for CO ₂ hardly changes depending on the presence or absence of the divalent copper compound,
Regarding the absorption performance, the results of the mixed aqueous solution to which the divalent copper compound was not added are shown as Reference Examples and Comparative Reference Examples.

(Reference Examples 1 to 4, Comparative Reference Examples 1 to 4) Potassium dimethylaminoacetate or potassium α-methylaminopropionate, and piperazine as amino acid metal salts (X) were placed in a glass reaction vessel installed in a thermostat. Was mixed at the concentration shown in Table 1 and the temperature was 4
Under stirring at 0 ° C., the test gas was passed at atmospheric pressure at a flow rate of 1 liter / min. Test gas: CO ₂ : 10 mol%, O ₂ : 3
A model combustion exhaust gas (equivalent to LNG firing) at 40 ° C. having a composition of mol% and N ₂ : 87 mol% was used.

The test gas continues to pass through, and the CO ₂
When the concentrations become equal, CO ₂ contained in the absorbing solution was measured using a CO ₂ analyzer (total organic carbon meter), and CO _{2 was} measured.
Saturated absorption (Nm ³ CO ₂ / m ³ aqueous solution, molar CO ₂ /
Molar amino acid metal salt). The composition of the gas discharged from the glass reactor is continuously measured by a gas analyzer, and the initial CO ₂ concentration (initial outlet gas C) contained therein is measured.
O ₂ concentration) and the absorption rate of CO ₂ (initial absorption rate) were determined.

As is clear from the results in Table 1, by using a relatively small amount of piperazine (Y) mixed with the amino acid metal salt (X), the initial outlet can be reduced as compared with the case where the amino acid metal salt (X) is used alone. It can be seen that the gas CO ₂ concentration is significantly lower, and that the absorption rate has been greatly improved. This is particularly noticeable when a small amount of piperazine is used for potassium dimethylaminoacetate. Similarly, when a small amount of piperazine is used for potassium dimethylaminoacetate,
It also shows that the time required for 90% saturation is significantly reduced. For comparison, Table 1 shows the results when piperazine and MEA were used alone.

[0022]

[Table 1]

(Reference Example 5, Comparative Reference Example 5) In order to examine the heat energy required for regenerating the absorbent, Reference Example 1 was used.
The heat of reaction (absorption heat value) between the absorbing solution used in Comparative Reference Example 4 and CO ₂ was measured. 200 g of the absorbing solution was placed in an adiabatic tester, stirred with a magnetic stirrer, and allowed to stand until the temperature of the aqueous solution was stabilized. Then pure CO ₂ from about 200
cc / min at blowing the the tester, CO ₂ flow rate of the inlet and outlet of the tester and the temperature of the absorbing solution continuously recorded.
The test was terminated when the CO ₂ flow rate at the outlet of the tester sharply increased. Absorbing liquid moles of absorbed CO ₂ to (moles load), absorbs reaction heat (Kcal / mol) when absorbing liquid from a raised temperature from blowing initiation of CO ₂ is 1 mol absorb CO ₂ CO ₂ Was calculated for each mole interval. In addition, the heat capacity of the tester was as follows.
The heater was energized at 0.3 A for a predetermined time, and the temperature was determined 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. Table 2 shows the results.

[0024]

[Table 2] * Piperazine: 3 wt% addition As can be seen from Table 2, the heat of reaction between the mixed aqueous solution of amino acid metal salt and piperazine and CO ₂ is smaller than in the case of MEA, and the energy required for regeneration will be greater than in the case of MEA. It is found to be significantly smaller and advantageous.

(Examples 1 and 2 and Comparative Examples 1 and 2) A test piece (surface area: about 1.9 inch ² , weight: about 8.2 g) of carbon steel (SS41) was prepared according to JIS R6252.
120, no. 240, no. It was polished using 400 abrasive papers in that order, then washed with acetone, vacuum dried and weighed. Next, the test piece was transferred to a glass tester filled with 700 ml of an absorbing solution saturated with CO ₂ in advance, and placed in a 2 liter stainless steel pressurized container in the atmosphere and sealed. The stainless steel pressurized container was allowed to stand at a temperature of 130 ° C. for 48 hours in a high-temperature dryer, and then the test piece was taken out, washed, vacuum-dried, and weighed. The test was repeated twice for the same absorbent. Table 3 shows the results. In the table, “copper ion” means that carbon copper was added to the absorption solution so as to include the indicated amount of copper ion in terms of divalent copper ion.

[0026]

[Table 3] *: () Shows the converted value of mpy.

[0027]

As described above in detail, according to the method of the present invention, a divalent copper compound is further added to a mixed aqueous solution of a specific amino acid metal salt (X) and piperazine (Y) against flue gas at atmospheric pressure. By containing it and using it as a CO ₂ absorbing solution, an improvement in the CO ₂ absorption rate is achieved as compared with the case where the amino acid metal salt (X) is used alone, and the corrosiveness, particularly the corrosiveness to carbon steel. Has been significantly improved. Further, as compared with the case of using the MEA, from the viewpoint of regeneration energy, it became to the CO ₂ can be efficiently removed.

[Brief description of the drawings]

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

Continued on the front page (72) Inventor Masaki Iijima 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Heavy Industries, Ltd. Headquarters (72) Inventor Kaoru Mitsuoka 4-2-2 Kanon Shinmachi, Nishi-ku, Hiroshima-shi, Hiroshima Mitsubishi (56) References JP-A-52-63171 (JP, A) JP-A-52-154991 (JP, A) JP-A-6-91135 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B01D 53/62

Claims (1)

(57) [Claims] An amino acid gold represented by the following general formula [1]:
100 parts by weight of genus salt (X), 1 to 25 piperazine (Y)
Parts by weight, and further 10 to 1 in terms of divalent copper ions.
Copper in the range of 000 ppm (content based on mixed aqueous solution)
The mixed aqueous solution containing the compound and the flue gas at atmospheric pressure.
The CO in the flue gas is brought into contact _TwoWho remove
Law. Embedded image CH_ThreeNR¹CHR^TwoCOOM [1] (R¹And R^TwoRepresents hydrogen or a lower alkyl group;
One R¹When R is hydrogen^TwoIs a lower alkyl group
R¹Is a lower alkyl group;^TwoIs hydrogen
And M represents an alkali metal. )