JPH05237341A - Method for removing carbon dioxide in waste combustion gas - Google Patents

Abstract

PURPOSE:To remove CO2 included in waste combustion gas by bringing water solution of ethylene diamine and/or diethylene triamine into contact with waste combustion gas under atmospheric pressure. CONSTITUTION:As an absorbent, ethylene diamine and/or diethylene triamine are used. And after humidifying and cooling waste combustion gas, it is introduced into a CO2 removing tower 1, where the waste combustion gas comes into contact with a liq. absorbent of constant concentration fed from a nozzle 7 countercurrently in the lower packed part 2, causing CO2 in waste gas to be absorbed and removed, permitting CO2-free waste combustion gas to go towards an upper packed part 3. Since reaction heat is generated in this absorption, after the liq. absorbent which has absorbed CO2 is given heat exchange, it is introduced into an adsorbent regenerating tower 15. Here the liq. absorbent is heated and regenerated and CO2 is separated and recovered.

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, it relates to a method for removing CO _{2 in} combustion exhaust gas under atmospheric pressure using an aqueous solution of a specific amine.

[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 there is an urgent need to take countermeasures 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 for the demand for emission control to increase. 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 recovering CO ₂ in the combustion exhaust gas by contacting the combustion exhaust gas of the boiler with an alkanolamine aqueous solution and the like C
Methods for storing O ₂ without releasing it to the atmosphere have been 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 absorbent for absorbing and removing CO _{2 in} combustion exhaust gas, the absorption of CO ₂ per a predetermined amount of amine aqueous solution having a predetermined concentration is absorbed. It is not always satisfactory in view of the amount and absorption rate, and further the thermal energy required for the regeneration of the alkanolamine aqueous solution after absorption.

By the way, there are many known techniques for separating an acidic gas such as CO ₂ from various mixed gases using an amine compound other than the alkanolamine. Most of these techniques use hindered amines.

[0006]

As described above, there is a demand for a method of efficiently absorbing and removing CO ₂ from combustion exhaust gas. Especially when treating combustion exhaust gas with an aqueous solution containing a constant concentration of CO ₂ absorbent, C
A major problem for the time being is to select an absorbent having a large O ₂ 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.

[0007]

In view of the above-mentioned problems, the inventors of the present invention have diligently studied an absorbent used for removing CO _{2 in} combustion exhaust gas, and as a result, it is effective to use a specific amine. It was possible to complete the present invention by obtaining the knowledge that

That is, the present invention relates to ethylenediamine and / or
Alternatively, it is a method of contacting an aqueous solution of diethylenetriamine with combustion exhaust gas under atmospheric pressure to remove CO ₂ from the combustion exhaust gas.

[0009]

The absorbent used in the present invention is ethylenediamine (EDA) or diethylenetriamine (DETA). These may be used alone or in combination of both.

In the present invention, other amines may be mixed with EDA and / or DETA. Such amines include, in addition to the above-mentioned alkanolamines, ethyleneamines such as triethylenetetramine, tetraethylenepentamine and pentaethylenehexamine, and further 2-amino-2-methyl-1-propanol and 2-ethylamino. Ethanol, 2-piperidine ethanol, 2-amino-2-methyl-1,3-propanediol, t-butyldiethanolamine, 2-amino-
Examples thereof include 2-hydroxymethyl-1,3-propanediol, piperazine, piperidine, morpholine and glycine.

In the present invention, EDA and / or DETA are used in the form of an aqueous solution (hereinafter sometimes referred to as "absorption liquid"). The concentration of these amines in the aqueous solution is usually 25 to 65.
%, Preferably 30 to 60% by weight. The temperature of the aqueous solution at the time of contact with combustion exhaust gas is usually 30 to 70.
It is in the range of ° C.

If necessary, a corrosion inhibitor, an amine deterioration inhibitor, etc. may be added to the aqueous solution used in the present invention.

The term "atmospheric pressure" in the present invention includes a pressure range in the vicinity of atmospheric pressure at which 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 section, 3 is an upper packing section or a tray, 4 is a CO ₂ removal tower combustion exhaust gas supply port, 5 is a CO ₂ removal combustion exhaust gas discharge port, and 6
Is an absorption liquid supply port, 6'is a regeneration tower reflux water supply port, 7 is a 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 absorbing CO ₂ , 14 is a heat exchanger, and 15 is absorption liquid regeneration (hereinafter referred to as “regeneration”). Column), 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 a recovered CO ₂ discharge. Line, 23 is a regenerator reflux condenser, 24 is a nozzle, 25 is a regenerator reflux water supply line,
Reference numeral 26 is a combustion exhaust gas supply blower, and 27 is a cooler.

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 is brought into contact with the filling portion 10 to be humidified and cooled, and then 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 is collected 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.

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 by the absorption liquid. The removed and de-CO ₂ combustion exhaust gas goes to the upper filling part 3. The absorption liquid supplied to the CO ₂ removal tower 1 is CO ₂
Of the reaction gas due to the absorption of
The temperature becomes higher than the temperature in the above, and is sent to the heat exchanger 14 by the absorption liquid discharge pump 13 that has absorbed CO ₂ , is heated, and is guided to the absorption liquid regeneration tower 5. The temperature of the regenerated absorption liquid is adjusted by the heat exchanger 14 or the heat exchanger 1 as necessary.
4 and the absorption liquid supply port 6 can be performed by the cooler 27.

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,
CO is cooled by 14₂Returned to Tower 1. Absorption liquid re
CO separated from the absorption liquid in the upper part of the raw tower 15₂
Is the reflux water supplied from the nozzle 24 and the upper filling section 19.
Contacted, cooled by the regeneration tower reflux condenser 23, CO ₂
CO in the separator 21₂Reflux with condensed water vapor
CO separated from water and recovered CO₂CO from the discharge line 22₂Times
Guided to the collection process. Part of the reflux water is the reflux water pump 20
And is recycled to the regeneration tower 15, and part of it is recycled to the regeneration tower.
CO removal via in 25₂Regeneration tower reflux water supply port 6'of tower 1
Is supplied to. This regenerated reflux water contains a small amount of absorption liquid.
CO is removed₂With the exhaust gas in the upper packing part 3 of the tower 1.
Trace of CO contained in exhaust gas₂Contribute to the removal of
It

[0019]

EXAMPLES The present invention will be specifically described below with reference to examples. (Example 1, Comparative Example 1) EDA aqueous solution (absorption liquid) 20
CO ₂ absorption under the conditions was measured by supplying a mixed gas equivalent to LNG-burning combustion exhaust gas to a flask containing 0 ml and bubbling in liquid under atmospheric pressure and measuring the CO ₂ concentration in the liquid. Amount (CO ₂ mol / EDA mol,
Nm ³ CO ₂ / m ³ absorbing solution) was determined. For comparison, a 30% by weight aqueous solution of MEA was used and the amount of absorption was similarly determined.

Further, the tangent slope at the start of aeration was determined from the graph of the relationship between the CO ₂ concentration in the gas at the outlet of the flask and the aeration time, and the CO ₂ initial absorption rate of the absorbing liquid was set to 3 of MEA.
It was determined by the ratio with the case of a 0 wt% aqueous solution (40 ° C.). The processing conditions are as follows.

(1) Treatment conditions Absorption liquid temperature: 40, 60 ° C. Concentration of EDA or MEA in the absorption liquid: 30% by weight, 4
5% by weight Mixed gas composition: CO ₂ 10%, O ₂ 3%, N ₂ 87% Mixed gas supply rate: 1 liter / minute Outside air temperature: 20 ° C.

(2) Test results Table 1 shows the results of the absorption test. In addition, the CO ₂ absorption amount (Nm ³ CO ₂ / m ³ absorption liquid) at an absorption liquid concentration of 30% by weight
The relationship between temperature and temperature is shown in FIG. In Table 1, no value indicates that the measurement could not be performed because the evaporation of EDA was larger than that of the absorbing solution.

[0023]

[Table 1]

(Example 2) The absorption amount and CO ₂ initial absorption rate were measured in the same manner as in Example 1 using the DETA absorbing solution. The results are shown in Table 2 and FIG.

[0025]

[Table 2]

As is clear from Tables 1 and ₂ , the use of an aqueous solution of ethylenediamine or diethylenetriamine as the CO ₂ absorption liquid in the combustion exhaust gas according to the present invention achieves a significant improvement in the absorption amount as compared with the MEA.
As a result, the amount of the absorbing liquid used can be significantly reduced as compared with the case of using MEA, so that the energy and cost required for absorbing and removing CO ₂ from the combustion exhaust gas can be significantly reduced.

Further, from FIG. 2, as the absorbent, EDA or DE is used.
It can be seen that when TA is used, the amount of CO ₂ absorbed is greatly reduced due to the rise in the temperature of the absorbing solution, as compared with the case where MEA is used. This is due to M
It shows that heat energy can be saved more than when using EA.

[0028]

As described in detail above, by using the aqueous solution of EDA or DETA as the absorbing liquid in the combustion exhaust gas under atmospheric pressure by the method of the present invention, the absorption amount of CO ₂ can be reduced more than that in the case of using MEA. Significant improvement in terms is achieved. Further, CO ₂ can be removed more efficiently in terms of regeneration energy than in the case of using MEA.

[Brief description of drawings]

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

FIG. 2 shows the amount of absorption (Nm ³
A chart showing the relationship between CO ₂ / m ³ absorbent, vertical axis) and temperature (° C, horizontal axis).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shigeru Shimojo Inventor Shigeru Shimojo 3-3-22 Nakanoshima, Kita-ku, Osaka City, Osaka Prefecture Kansai Electric Power Co., Inc. (72) Mutsunori Karazaki 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Sanryo Heavy Industries Co., Ltd. Head Office (72) Inventor Masaki Iijima 2-5-1, Marunouchi, Chiyoda-ku, Tokyo Sanryo Heavy Industries Co., Ltd. Head Office (72) Toru Seto 4-6 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture 22 Mitsubishi Heavy Industries, Ltd. Hiroshima Research Institute (72) Inventor Kaoru Mitsuoka 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City Hiroshima Prefecture Mitsubishi Heavy Industries Ltd. Hiroshima Research Institute

Claims (1)

[Claims] 1. A method of removing CO ₂ in the combustion exhaust gas by bringing an aqueous solution of ethylenediamine and / or diethylenetriamine into contact with the combustion exhaust gas under atmospheric pressure.