JPH1033938A - Recovery method of basic amine compound in waste gas from decarboxylation tower - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently recover a basic amine compound by spraying sulfuric acid to a remaining gas after absorption of carbon dioxide and collecting the produced sulfuric acid salts as mist in a demister at the time when a basic amine compound is recovered from a waste gas from a decarboxylation tower. SOLUTION: A combustion gas 1 containing carbon dioxide is supplied to a carbon dioxide absorptive part 3 installed in a lower part of a decarboxylation tower 2 and an amine absorptive liquid is supplied from the tip part of an absorptive part 3 to absorb carbon dioxide. The remaining gas rises in the amine recovering part 4 and is brought into gas-liquid contact with water supplied from the tip part at 20-60 deg.C and recovered in water phase. The waste gas from a decarboxylation tower is led to a demister 5 after diluted sulfuric acid is sprayed by a sulfuric acid spraying apparatus 5 installed in the rear flow of the decarboxylation tower 2 and the mist containing amine sulfate salt is captured and supplied to an auxiliary reproducing apparatus 13 and the remaining gas 7 is released to air. Meanwhile, the amine absorptive liquid is heated by a heat-exchanger 8 and after that, carbon dioxide is released in a reproducing tower 9 and the amine absorptive liquid is reproduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering a basic amine compound in a decarbonation tower exhaust gas in a decarboxylation process in which carbon dioxide in a gas containing carbon dioxide is absorbed by a basic amine compound.

[0002]

2. Description of the Related Art In recent years, thermal power generation equipment and boiler equipment use a large amount of coal, heavy oil or super heavy oil as fuel.
From the viewpoint of preventing air pollution and purifying the global environment, there has been a problem of quantitatively and quantitatively controlling the emission of sulfur oxides, nitrogen oxides, carbon dioxide, etc., mainly sulfur dioxide.
In particular, sulfur oxides become sulfuric acid mist or acid rain due to atmospheric moisture, and may damage human bodies, crops, forests, and the like. For this reason, various exhaust gas treatment methods, such as a dry method and a wet method, have conventionally been proposed and implemented for equipment that discharges a large amount of exhaust gas. For example, for desulfurization, a gypsum production method using lime as an absorbent has become mainstream from the viewpoint of economy.

[0003] In addition, recently, with respect to carbon dioxide and methane gas, reduction of carbon dioxide emission has been studied from the viewpoint of global warming. Therefore, for example, PSA
(Pressure swing) method, membrane separation and concentration method, immobilization by reaction with basic compounds, immobilization by assimilation of plants, liquefaction or solidification after separation and purification, refueling by hydrogenation, etc. Have been.

For this reason, the following technology is known as a conventional technology. For example, JP-A-6-86911 proposes a method of simultaneously performing desulfurization and decarboxylation. In this method, since the reaction between the amine and carbon dioxide is an exothermic reaction, the temperature of the absorbing solution increases and the vapor pressure of the amine increases. Therefore, since the amount of amine entrained in the gas increases, an amine recovery section is provided to bring the amine into gas-liquid contact and recover a part of the entrained amine in the aqueous phase. However, since the temperature of the water to be brought into gas-liquid contact in the recovery section is high, the amine is released out of the system along with the exhaust gas, which increases the operating cost and the released amine may cause air pollution problems. was there.

[0005]

DISCLOSURE OF THE INVENTION In view of the above-mentioned state of the art, the present invention relates to a method for removing carbon dioxide-containing gas from a decarbonation tower exhaust gas discharged when the gas is brought into contact with a basic amine compound absorbing solution to absorb and remove carbon dioxide. Another object of the present invention is to provide a method capable of efficiently recovering a basic amine compound entrained in the gas.

[0006]

Means for Solving the Problems As a result of intensive studies on the above problems, the present inventors spray sulfuric acid on the remaining gas that has absorbed carbon dioxide, and collect the generated sulfate as a mist with a demister. As a result, the present inventors have found that amines can be efficiently collected, thereby completing the present invention. That is, the present invention has the following configurations (1) to (3).

(1) A carbon dioxide-containing exhaust gas is brought into contact with a basic amine compound-containing absorbing solution in a decarbonation tower to absorb and remove carbon dioxide from the exhaust gas. The method is characterized in that the basic amine compound accompanying the exhaust gas is sprayed to form a basic amine compound sulfate, and the basic amine compound sulfate-containing gas is passed through a demister to collect the basic amine compound sulfate. A method for recovering a basic amine compound in a decarbonation tower exhaust gas.

(2) The basic amine compound-absorbed liquid from which carbon dioxide has been absorbed and removed by the decarbonation tower is heated by a regenerator provided downstream of the bottom of the decarbonation tower to release carbon dioxide and regenerate. A part of the basic amine compound absorbing solution is cooled and recycled to the decarbonation tower, and the remaining regenerated basic amine compound is sent to the auxiliary regenerating device together with the basic amine compound sulfate collected by the demister, and is sent to the device. Basic calcium or basic sodium is added to separate the basic amine compound absorbing solution and calcium sulfate or sodium sulfate, the basic amine compound absorbing solution is recycled to the decarbonation tower, and the calcium sulfate or sodium sulfate is The method for recovering a basic amine compound in a decarbonation tower exhaust gas according to the above (1), wherein the basic amine compound is taken out.

(3) The decarbonation tower is divided into a lower carbon dioxide absorption section and an upper amine recovery section, supplies exhaust gas containing carbon dioxide to the carbon dioxide absorption section, and absorbs carbon dioxide by the absorbing solution. The above (1) or (2), wherein the remaining gas absorbed is brought into gas-liquid contact with the washing water at 20 to 60 ° C. in the amine recovery section to recover a part of the accompanying basic amine compound in the aqueous phase. )).

In the present invention, the gas containing carbon dioxide to be treated may be a gas for fuel, a combustion exhaust gas of fuel, or various other gases. The gas of interest may include moisture, sulfur oxides, nitrogen oxides, oxygen or other acidic gases. The pressure of the gas may be in a pressurized state or a depressurized state, and the temperature may be low or high and is not particularly limited. Preference is given to combustion exhaust gas at normal pressure.

Examples of the basic amine compound (abbreviated as amine) used in the present invention include hydroxyamines such as monoethanolamine, diethanolamine and butylethanolamine, and tertiary amines such as dimethylaminoethanol and methylpyrrolidone. Examples include amines, hindered amines such as 2-amino-2-methyl-1-propanol, amino acids such as methylaminocarboxylic acid, and mixtures thereof. These amines are used in a solution state, and as a medium, methanol, polyethylene glycol, sulfolane, water and the like can be used, but water is preferably used.

[0012] The decarbonation tower is for dropping an amine absorbing liquid from the top of the tower and bringing it into gas-liquid contact with a carbon dioxide-containing gas supplied from the bottom to absorb and remove carbon dioxide. It may be. The decarbonation tower may be divided into a lower carbon dioxide absorption section and an upper amine recovery section, and the aqueous amine solution recovered in the amine recovery section is supplied to the top of the carbon dioxide absorption section together with the supplied amine absorption liquid. You may add it. In this case, water separated from carbon dioxide in a downstream side of the regeneration tower described later may be added to the top of the amine recovery unit.

The amine-containing absorbing solution reacts with carbon dioxide to form an amine carbonate complex, which is decomposed by heating to release carbon dioxide to regenerate the amine. The regenerated absorbent can be recycled and used in the decarboxylation step as it is. Since the carbon dioxide discharged from the upper part of the regeneration tower accompanies moisture, it is cooled by a condenser provided downstream of the regeneration tower and separated into carbon dioxide and water, and the water is used for water in the amine recovery part of the decarbonation tower. Is done.

On the other hand, in the decarboxylation step, heat is generated by the reaction between the amine compound and carbon dioxide (for example, when the gas temperature at the inlet of the carbon dioxide absorption section is about 60 ° C., the gas temperature at the absorption section outlet is about 80 ° C.). ), The vapor pressure of the amine in the absorbent increases, and the amount of amine entrained in the gas increases. For this reason, in the amine recovery section of the decarbonation tower, the amine is brought into gas-liquid contact with the washing water and a part of the accompanying amine is recovered in the aqueous phase. If it is too high, the amine is not sufficiently collected by the demister and about 70 ppm or more of the amine is entrained in the gas and released out of the system.

[0015] However, the remaining gas is sprayed with sulfuric acid by a sulfuric acid spraying device provided downstream of the decarbonation tower, and the sulfate of the basic amine compound produced by the reaction with the amine entrained in the exhaust gas passes through the demister. By collecting the mist as mist, the amount of amine entrained in the gas after passing through the demister is significantly reduced. The concentration of the sulfuric acid used in the present invention is not particularly limited, but dilute sulfuric acid is used in view of mist formation, ease of handling, cost, and the like. The amount of sulfuric acid is about a fraction to several times the amount of the amine entrained in the gas, and is preferably equimolar.

Further, the temperature of the washing water supplied to the amine recovery section is lowered, and the gas-liquid contact temperature of the amine recovery section is reduced to 20 to 60.
° C, preferably 20 to 50 ° C, the amount of amine entrained in the gas after passing through the demister is reduced, and the remaining gas is sprayed with sulfuric acid by a sulfuric acid spraying device provided downstream of the decarbonation tower. By passing the generated basic amine compound sulfate through a demister and collecting it as a mist, the amount of amine entrained in the gas after passing through the demister is further reduced.

As described above, by spraying sulfuric acid downstream of the decarbonation tower and passing the sulfuric acid through a demister, the amount of the entrained amine is reduced to 2 to 3 ppm or less. Cooling the temperature to a specific temperature will reduce it to 1 ppm or less. This is because the amine in the exhaust gas from the decarbonation tower becomes sulfate and the vapor pressure is reduced, and mist is easily formed. Also, the gas-liquid contact temperature of the amine recovery section is set to 20 to 60 ° C. It is considered that the collection efficiency was improved as a whole because the particle size was appropriately increased within a range where re-dispersion did not occur, and the viscosity of the mist was increased.

As the demister (also referred to as a mist separator), an ordinary two-stage inclined plate type, corrugated type, teardrop type or wire mesh type can be used, but preferably a wire mesh type. Further, the wire mesh type is preferably a thin fiber layered type. The demister may also be of a structure that can be cooled. The collected mist is collected at the bottom of the demister and is supplied as it is or dissolved in water or the like to the sub-regeneration device, and the amine is regenerated by adding a basic calcium substance or a basic sodium substance together with the regeneration absorption liquid. When adding a basic calcium substance, a solid-liquid separator is installed downstream of the secondary regenerator to separate the amine absorbent and the solid containing calcium sulfate by the solid-liquid separator, and the absorbent is decarbonated. The solid containing calcium sulfate is recycled to the column and discharged out of the system as gypsum, or when the solid contains calcium carbonate, it can be used as a basic calcium substance used in the desulfurization step. When adding a basic sodium substance, the amine can be distilled and recovered by supplying steam to the auxiliary regenerator.

Even when the gas is combustion exhaust gas and a desulfurization step is provided in advance, the amine compound sulfate may be generated and accumulated in the amine. However, the auxiliary regeneration step is provided as described above. There is no problem because the addition of the basic calcium substance regenerates the amine absorbing solution. As a result, the amount of amine discharged out of the system along with the exhaust gas is reduced to 1/30 or less of the conventional amount, and further 1/100.
It became possible to decrease to the following.

Hereinafter, the present invention will be described with reference to the drawings. FIG. 1 is an example of a process flow diagram of the present invention. The combustion exhaust gas 1 containing carbon dioxide is supplied to a carbon dioxide absorption section 3 provided at the lower part of the decarbonation tower 2, and the amine absorption liquid is supplied from the top of the carbon dioxide absorption section 3. Absorbs carbon dioxide. The remaining gas rises in the amine recovery section 4, and water supplied from the top thereof and 20 to
The amine is recovered in the aqueous phase by gas-liquid contact at 60 ° C.

The exhaust gas of the decarbonation tower 2 is sprayed with dilute sulfuric acid by a sulfuric acid spraying device 5 provided downstream of the decarbonation tower 2.
Furthermore, the mist containing the amine sulfate is guided to the demister 6 provided in the subsequent flow, and the residual gas 7 is released to the atmosphere. The collected amine sulfate mist is dissolved in water and supplied to the secondary regeneration device 13. On the other hand, the amine absorbing solution that has absorbed carbon dioxide is heated in the heat exchanger 8 by a part of the regenerated absorbing solution, and is supplied to the regeneration tower 9. The amine absorbing solution is heated to 80 to 150 ° C. to release carbon dioxide, regenerated, cooled by the heat exchanger 8, and partially supplied to the top of the carbon dioxide absorbing unit 3.

The remaining part of the regenerated absorbent together with the mist of the amine sulfate collected by the demister 6 together with the sub-regeneration device 13
And then regenerated to an amine absorbing solution by addition of a basic calcium substance 14, for example, and then separated into a regenerated amine absorbing solution and a solid 16 containing calcium sulfate by a solid-liquid separator 15, and the amine absorbing solution is The solid 16 containing calcium sulfate which is recycled to the decarbonation tower 2 is discharged out of the system as gypsum, or a desulfurization provided before the decarbonation tower 2 as a basic calcium substance when the solid contains calcium carbonate. It is supplied to a process (not shown).

The carbon dioxide released from the top of the regeneration tower 9 is saturated with moisture, cooled by the condenser 10 and separated by the separator 11. A part of the separated water is returned to the regeneration tower 9, and the rest is cooled to a predetermined temperature by the cooler 12 and supplied to the top of the amine recovery unit 4.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto.

(Example 1) 500 Nm ³ / Hr of desulfurized combustion exhaust gas containing 10% of carbon dioxide was supplied to a decarbonation tower, and a 30% by weight aqueous solution of monoethanolamine and gas /
Contact was made at a liquid ratio of 2.0 to absorb carbon dioxide. The amine concentration in the exhaust gas at the outlet of the decarbonation tower was 300 ppm.

The exhaust gas from the decarbonation tower is sprayed with a 1% aqueous sulfuric acid solution at a ratio of equimolar to the amount of the amine passing therethrough when passing through a sulfuric acid spraying device installed in the horizontal part downstream of the decarbonation tower. After passing through a demister (high-grade stainless steel glass wool layer wire mesh type, layer thickness: 200 mm), mist containing amine sulfate was collected and released to the atmosphere. The amine concentration in the exhaust gas at the outlet of the demister was constant at 3 ppm.

(Comparative Example 1) The same operation as in Example 1 was carried out except that sulfuric acid was not sprayed on the exhaust gas at the outlet of the carbon dioxide tower. The amine concentration in the exhaust gas at the outlet of the demister was as high as 70 ppm.

Example 2 500 Nm ³ / Hr of desulfurized combustion exhaust gas containing 10% of carbon dioxide was supplied to a carbon dioxide absorption section below a decarbonation tower, and monoethanolamine 3
The solution was brought into contact with a 0% by weight aqueous solution at a gas / liquid ratio of 2.0 at 60 ° C. to absorb carbon dioxide. The remaining exhaust gas was brought into gas-liquid contact with the washing water at 45 ° C. in the amine recovery section at the top of the decarbonation tower, and part of the amine was recovered in the aqueous phase. The amine concentration in the exhaust gas at the outlet of the decarbonation tower was 100 ppm.

When the exhaust gas from the decarbonation tower passes through a sulfuric acid spraying device installed in the horizontal part of the wake of the decarbonation tower, 1%
After the sulfuric acid aqueous solution is sprayed at a ratio equal to the amount of the amine passing through, the mist containing the amine sulfate is collected after passing through a demister (high-grade stainless steel glass wool layer wire mesh type, layer thickness 200 mm), Released to the atmosphere. The amine concentration in the exhaust gas at the outlet of the demister was 1 ppm or less.

(Example 3) A mist containing amine sulfate captured by the demister of Example 1 is dissolved in water, mixed with a part of the regenerated absorbent regenerated in the regenerator, and supplied to the sub regenerator. Then, lime milk was added and stirred. The resulting amine absorbent and the solid containing calcium sulfate and calcium carbonate are separated into solid and liquid by a centrifugal separator, and the amine absorbent is recycled to the carbon dioxide absorbing part, and the solid containing calcium sulfate and calcium carbonate is used in the desulfurization step. Supplied as a basic calcium substance.

Although the present invention has been described with reference to the embodiments, the present invention is not limited to a continuous method or a batch method.
It can also be performed by a semi-batch method.

[0032]

According to the present invention, the concentration of amine in the exhaust gas discharged from the decarbonation tower to the atmosphere can be greatly reduced, and the operating cost and air pollution can be improved.

[Brief description of the drawings]

FIG. 1 is a process flow diagram of the present invention.

Claims (3)

[Claims] 1. A carbon dioxide-containing exhaust gas is brought into contact with a basic amine compound-containing absorbent in a decarbonation tower to absorb and remove carbon dioxide from the exhaust gas, and sulfuric acid is sprayed on the decarbonation tower exhaust gas from a sulfuric acid spraying device. Making the basic amine compound entrained in the exhaust gas into a basic amine compound sulfate, and passing the basic amine compound sulfate-containing gas through a demister to collect the basic amine compound sulfate. For recovering a basic amine compound in a decarbonation tower exhaust gas. 2. A regenerating apparatus in which a basic amine compound-absorbed solution from which carbon dioxide has been absorbed and removed by a decarbonation tower is heated by a regenerating device provided downstream of the decarbonation tower at a liquid side to release carbon dioxide, and regenerated.
A part of the regenerated basic amine compound absorbing solution is cooled and recycled to the decarbonation tower, and the remaining regenerated basic amine compound is sent to the auxiliary regenerating device together with the basic amine compound sulfate collected by the demister. Basic calcium or basic sodium is added to the device to separate the basic amine compound absorbing solution and calcium sulfate or sodium sulfate, and the basic amine compound absorbing solution is recycled to the decarboxylation tower, and calcium sulfate or sodium sulfate is used. 2. The method for recovering a basic amine compound in exhaust gas from a decarbonation tower according to claim 1, wherein the acid is taken out of the system. 3. The decarbonation tower is divided into a lower carbon dioxide absorption section and an upper amine recovery section, supplies exhaust gas containing carbon dioxide to the carbon dioxide absorption section, absorbs carbon dioxide with the absorbing liquid, 3. A method according to claim 1, wherein the remaining gas absorbed is brought into gas-liquid contact with the washing water at 20 to 60 [deg.] C. in an amine recovery section, and a part of the accompanying basic amine compound is recovered in an aqueous phase. The method for recovering a basic amine compound described above.