JPH08103629A - Method for removing carbon dioxide in combustion exhaust gas - Google Patents

Abstract

PURPOSE: To provide a method for removing CO2 contained in combustion exhaust gas. CONSTITUTION: The method for removing CO2 in combustion exhaust gas is constituted so that the combustion gas under the atmospheric pressure is brought into contact with a mixed aq. solution containing 100 pts.wt. amino acid metallic salt (X) expressed by general formula, CH3 NR<1> CHR<2> COOM (Each of R<1> and R<2> represents hydrogen or a lower alkyl group and when R<1> is hydrogen, R<2> is the lower alkyl group, when R<1> is the lower alkyl group, R<2> is hydrogen and M represents an alkali metal), 1-25 pts.wt. pyperazine (Y) and 10-10000ppm copper compound (the content per the mixed aq. solution) expressed in terms of bivalent Copper ion.

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 combustion exhaust gas, more specifically, a specific amino acid metal salt, a specific amine compound,
Further, it relates to a method for removing CO _{2 in} combustion exhaust gas by 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 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, the combustion exhaust gas of the boiler is brought into contact with an alkanolamine aqueous solution or the like to remove and recover CO ₂ in the combustion exhaust gas, and a recovery method. C
Methods for storing O ₂ without releasing it to the atmosphere have been vigorously studied.

Examples of the alkanolamine include monoethanolamine (MEA), diethanolamine, triethanolamine, methyldiethanolamine, diisopropanolamine and diglycolamine (DGA), but MEA is usually preferred.
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 such as thermal energy required for the regeneration of the alkanolamine solution after the absorption, be said to be necessarily be satisfactory Absent.

Further, by using an MEA aqueous solution, oxygen and C
CO from the high temperature combustion exhaust gas containing O ₂ by gas-liquid contact
_{When 2} is continuously absorbed and removed, a CO ₂ absorption tower in contact with the combustion exhaust gas containing CO ₂ and oxygen and an absorption solution, a regeneration tower for heating the absorption solution to release CO ₂ and regenerate the absorption solution, and further Corrosion of pipes, heat exchangers, pumps, and other equipment that uses metal. Therefore, the service life of the device design using the materials used in a normal chemical plant becomes extremely short, and even if it can be carried out in a laboratory, it cannot be established as an industrial process.

Such oxygen and CO₂Combustion exhaust gas containing
From an aqueous solution of MEA or a similar compound.
CO₂CO using an absorbing solution₂Of equipment that absorbs
US Pat. No. 4,440,731 is a method for improving
No. specification. According to this proposal,
At least 50ppm or more of divalent copper in the absorption solution
Ions, and also dihydroxyethylglycine,
Alkali metal carbonate, alkali metal or ammonium
Um permanganate, alkali metal carbonate or
Ammonium thiocyanate, nickel or bismuth
Oxides and the like are also added. By this method
For example, when processing combustion gas with high oxygen concentration,
It is described that decomposition of MEA and the like can be suppressed. this
In the examples of the US patent, water of MEA is used as the amine compound.
Only test examples using solutions are described.
30 lbs of C in Luxe 30% MEA solution
O₂And 15 lbs of oxygen and seeded at a temperature of 130 ° C.
Various mild steel specimens in the presence of various corrosion inhibitors (MILD STEEL COU
PONS) is being tested for accelerated corrosion. as a result,
Corrosion degree of about 40-52 mi when no corrosion inhibitor is added
200ppm of copper carbonate [Cu] for 1 / y (mpy)
CO₃・ Cu (OH)₂・ H ₂O, CuCO₃The amount is 56
Wt%] to 0.9 to 1.2 mpy
It is stated that corrosion can be suppressed. Also different from these
In addition, the formula represented by the general formula [1] used in the present invention described later is
One of the metal salts of mino acids is an aqueous solution of C in combustion exhaust gas.
O₂Used for recovery, or another as an aqueous solution
CO₂And H₂H from synthetic gas containing S₂Only S
The technique used for selective recovery is already known.

[0006]

As described above, a method for efficiently removing CO ₂ from combustion exhaust gas is desired. In particular, when treating a combustion exhaust gas with an aqueous solution containing a constant concentration of CO ₂ absorbent, CO ₂ per unit mole of the absorbent is
It is an important task to select an absorbent having a large absorption amount, a CO ₂ absorption amount per unit volume of the aqueous solution, and a large absorption rate. Furthermore, after absorbing CO _2, an absorbent that separates CO ₂ and regenerates the absorbing liquid requires less heat energy is desired. Above all, 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 device 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. Being a liquid is very important.

[0007]

In view of the above-mentioned problems, the inventors of the present invention have made earnest studies on an absorbent used for removing CO _{2 in} combustion exhaust gas, and as a result, have found that a relatively small amount of a specific amine acid metal salt is contained. Is particularly effective in improving the absorption rate of the amino acid metal salt, and further containing a predetermined amount of a divalent copper compound in the mixed aqueous solution markedly improves the carbon steel. Based on the finding that the corrosiveness can be suppressed, the present invention has been completed.

That is, according to the present invention, 100 parts by weight of the amino acid metal salt (X) represented by the following general formula [1], 1 to 25 parts by weight of piperazine (Y), and further converted into divalent copper ions. A mixed aqueous solution containing a copper compound in the range of 10 to 1000 ppm (content with respect to the mixed aqueous solution) is brought into contact with combustion exhaust gas under atmospheric pressure to produce CO in the combustion exhaust gas.
It is a method of removing ₂ .

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

[0009]

The lower alkyl group represented by R ¹ and R ² of the amino acid metal salt (X) represented by the general formula [1] used in the present invention is exemplified by methyl group, ethyl group, propyl group and the like. However, a methyl group is particularly preferable. Examples of the alkali metal represented by M include sodium and potassium, but potassium is preferable. Examples of the amino acid metal salt (X) represented by the general formula [1] include potassium dimethylaminoacetate and potassium α-methylaminopropionate, among which potassium dimethylaminoacetate is preferable.

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

In a mixed aqueous solution (hereinafter also referred to as "absorption liquid") containing an amino acid metal salt (X) and piperazine (Y) used as an absorption liquid for CO _{2 in} combustion exhaust gas, and a divalent copper compound described below. 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. The copper compound is not limited, but preferably, for example, copper carbonate [CuC
O ₃ · Cu (OH) ₂ · H ₂ O]. Copper carbonate is also called as basic copper carbonate, and its addition amount is 10 to 1000 ppm in terms of divalent copper ion,
Preferably 100 to 800 ppm, more preferably 2
The range is from 00 to 600 ppm.

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

The process that can be employed in the method for 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 performed.
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.

[0018]

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

(Reference Examples 1 to 4 and Comparative Reference Examples 1 to 4) Potassium dimethylaminoacetate or potassium α-methylaminopropionate as the amino acid metal salt (X) and piperazine were placed in a glass reaction container installed in a constant temperature bath. 50 ml of an aqueous solution prepared by mixing at a concentration shown in Table 1 was added, and the temperature was adjusted to 4
The test gas was passed under atmospheric pressure with stirring at 0 ° C. at a flow rate of 1 liter / min. The test gas is CO ₂ : 10 mol%, O ₂ : 3
A model combustion exhaust gas (corresponding to LNG burning) at 40 ° C. having a composition of mol% and N ₂ : 87 mol% was used.

Continuing to pass the test gas, CO ₂
When the concentrations became equal, the CO ₂ contained in the absorbing solution was measured using a CO ₂ analyzer (total organic carbon meter), and CO ₂
Saturated absorption (Nm ³ CO ₂ / m ³ aqueous solution, mol CO ₂ /
Molar amino acid metal salt) was determined. Further, the composition of the gas discharged from the glass reactor was continuously measured by a gas analyzer, and the first CO ₂ concentration (initial exit gas C
The O ₂ concentration) and the CO ₂ absorption rate (initial absorption rate) were determined.

As is clear from the results shown in Table 1, when the amino acid metal salt (X) is mixed with a relatively small amount of piperazine (Y), the initial outlet is more than that when the amino acid metal salt (X) is used alone. It can be seen that the gas CO ₂ concentration is remarkably low and that the absorption rate is significantly improved. This is particularly remarkable when a small amount of piperazine is used in potassium dimethylaminoacetate. Similarly, when using a small amount of piperazine in potassium dimethylaminoacetate,
It also shows that the time required for 90% saturation is considerably shortened. For comparison, Table 1 shows the results when piperazine and MEA were used alone.

[0022]

[Table 1]

Reference Example 5 and Comparative Reference Example 5 Reference Example 1 was used to examine the thermal energy required to regenerate the absorbing liquid.
Also, the heat of reaction (absorption calorific value) between the absorbing liquid used in Comparative Reference Example 4 and CO ₂ was measured. 200 g of the absorbing solution was put into an adiabatic tester, stirred with a magnetic stirrer, and left until the temperature of the aqueous solution became stable. Next, add pure CO ₂ to about 200
It was blown into the tester at a rate of cc / min, and the CO ₂ flow rate at the tester inlet and outlet 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), 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 mol section. The heat capacity of the tester is 30.0 V when 200 g of water is put in the tester.
The heater was energized for a predetermined time at 0.3 A, 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. Table 2 shows the results.

[0024]

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

(Examples 1 and 2, Comparative Examples 1 and 2) Test pieces of carbon steel (SS41) (surface area of about 1.9 inch ² and weight of about 8.2 g) were designated as JIS R6252.
120, No. 240, No. Polishing was carried out in order of 400 pieces of abrasive paper, followed by washing with acetone, vacuum drying, and weighing. Then, the test piece was transferred to a glass tester filled with 700 ml of an absorption solution saturated with CO ₂ in advance, placed in a 2 liter pressure vessel made of stainless steel in the atmosphere, and sealed. This stainless steel pressure vessel was allowed to stand in a high temperature dryer at a temperature of 130 ° C. for 48 hours, 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 so that the absorbing solution contained the indicated amount of copper ion converted into divalent copper ion.

[0026]

[Table 3] *: The value in () indicates the converted value of mpy.

[0027]

As described in detail above, 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) with respect to combustion exhaust gas under atmospheric pressure. By containing it and using it as a CO ₂ absorbing solution, the CO ₂ absorption rate can be improved more than that in the case of using the amino acid metal salt (X) alone, and it is corrosive, particularly to carbon steel. Was significantly improved. In addition, CO ₂ can be removed more efficiently from the viewpoint of regeneration energy than when MEA is used.

[Brief description of drawings]

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

Front page continuation (72) Inventor Masaki Iijima 2-5-1, Marunouchi Chiyoda-ku, Tokyo Sanryo Heavy Industries Co., Ltd. (72) Inventor Kaoru Mitsuoka 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries Ltd. Hiroshima Research Center

Claims (1)

[Claims] 1. Amino acid gold represented by the following general formula [1]:
Genus salt (X) 100 parts by weight, piperazine (Y) 1 to 25 parts by weight
The range of parts, further 10 to 1 converted to divalent copper ions
Copperation in the range of 000 ppm (content in mixed aqueous solution)
The mixed aqueous solution containing the compound and the combustion exhaust gas under atmospheric pressure
Contact with CO in the combustion exhaust gas ₂Who remove
Law. [Chemical formula 1] CH₃NR¹CHR²COOM [1] (R¹And R²Represents hydrogen or a lower alkyl group, or
Tsu R¹R is hydrogen²Is a lower alkyl group
R¹When is a lower alkyl group, R²Is hydrogen
And M represents an alkali metal. )