JP2016112497A - Carbon dioxide collection device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon dioxide collection device and method suppressing low the discharge amount of low-boiling point compounds such as ammonia, ethyl amine or the like generated by decomposition of amines used for absorption of carbon dioxide.SOLUTION: In an absorption tower 1 of a carbon dioxide (CO) collection device, an absorption part 11 and a cleaning part are installed. The absorption part 11 comprises a filling layer and a shelf stage, and the cleaning part comprises a lower-stage cleaning part 24a and an upper stage cleaning part 24b. A COcollection method includes: feeding to the cleaning part, the aqueous solution of mineral acid or its salt prepared in a cleaning tank 40; cleaning by a cleaning liquid, a COabsorption-treated exhaust from the absorption part 11 to remove alkanolamine and/or alkanolamine decomposition products accompanying the gas; absorbing a greater part of alkanolamine having high solubility in water at the lower stage cleaning part 24a and further cleaning the exhaust again at the upper stage cleaning part 24b; and transferring the CO-rich absorption liquid obtained in the absorption tower 1 to a desorption tower 2 to desorb and collect CO.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a carbon dioxide recovery apparatus and recovery method. More specifically, the present invention relates to a carbon dioxide recovery apparatus and recovery capable of keeping low emissions of low-boiling compounds such as ammonia and ethylamine generated by decomposition of alkanolamine used for carbon dioxide absorption to the atmosphere. Regarding the method.

A boiler used in a thermal power plant or the like is one of devices that emit a large amount of carbon dioxide. Carbon dioxide is considered to be one of the causative substances of global warming. Therefore, various studies for reducing carbon dioxide emissions have been conducted.
There is known an apparatus for recovering carbon dioxide by absorbing carbon dioxide in combustion exhaust gas with an absorbing solution. As an absorbent used in such a device, an aqueous solution containing amines (hereinafter sometimes referred to as an amine absorbent) is usually used.
Combustion exhaust gas contains oxygen, nitrogen and the like in addition to carbon dioxide. The amines in the amine absorbing solution may be decomposed by the oxygen and converted into a low molecular weight and low boiling point compound. Low boiling point compounds produced by decomposition of such amines include ammonia (boiling point -33 ° C), methylamine (boiling point -6 ° C), dimethylamine (boiling point 6.9 ° C), trimethylamine (boiling point 2.87 ° C), ethylamine (boiling point 16.6 ° C). ), N-ethylmethylamine (CAS number: 624-78-2, boiling point 35 ° C) N, N-dimethylethylamine (CAS number: 598-56-1, boiling point 37 ° C), diethylamine (CAS number 109-89-) 7, boiling point 55.5 ° C).

  The exhaust gas from which carbon dioxide has been removed by the amine absorbing liquid is often accompanied by amines derived from the amine absorbing liquid in the form of mist or vapor. For this reason, it is common practice to wash away the accompanying amines by washing the exhaust gas from which carbon dioxide has been removed with water or a low-concentration amine compound aqueous solution. The temperature at the time of washing varies depending on the specifications of the carbon dioxide absorption tower. In the carbon dioxide absorption tower having a structure in which the amine absorption liquid and the combustion exhaust gas are brought into countercurrent contact, it is often designed at about 20 to 60 ° C. Washing at this temperature is effective for recovering ethanolamine having a boiling point of 170 ° C., which is often used in amine absorbing liquids, but is not so effective for recovering low-boiling compounds produced by decomposition of amines.

  In order to prevent evaporation and scattering of amines and low-boiling compounds accompanying the exhaust gas from which carbon dioxide has been removed, Patent Document 1 proposes a method of adding an acid such as sulfuric acid or boric acid to cleaning water. Patent Document 2 proposes a method in which exhaust gas from which carbon dioxide has been removed is first washed with an acidic washing liquid having a pH of 6 or less and then washed with water. Sulfuric acid and boric acid are expected to improve the removal efficiency of low-boiling compounds because they convert low-boiling compounds produced by the decomposition of amines into high-boiling sulfates and borates.

JP 2013-107069 A Special table 2012-520167 gazette

  However, the acid is consumed not only by the low-boiling compounds produced by the decomposition of the amines but also by the amines themselves, so that the removal efficiency of the low-boiling compounds is as high as expected without adding a large amount of acid. Does not improve. If the two-stage cleaning with the acidic aqueous solution and the water cleaning is performed, the amount of water in the system is excessively increased, and the mass balance of the water in the entire recovery device may be lost. Furthermore, it is necessary to perform distillation, electrodialysis, ion exchange, and the like for the regeneration treatment of an acidic aqueous solution containing an acid such as sulfuric acid or boric acid, and there is a concern about an increase in carbon dioxide recovery cost.

  The problem of the present invention is that carbon dioxide that does not cause the above problems and that can suppress the emission of low-boiling compounds such as ammonia and ethylamine generated by the decomposition of amines used for carbon dioxide absorption can be kept low. It is to provide a recovery device and a recovery method.

As a result of studies to solve the above problems, the present invention including the following embodiments has been completed.
[1] obtaining a carbon dioxide by absorbing the CO ₂ lean absorbing solution CO ₂ absorption treated exhaust gas and CO ₂ rich absorbent liquid in the treated gas (I), 2 to CO ₂ absorption treated flue gas by the washing liquid A step (II) of removing alkanolamine and alkanolamine decomposition products accompanying the CO ₂ absorption-treated exhaust gas by washing more than once, heating the CO ₂ rich absorption liquid to desorb carbon dioxide, and CO ₂ lean Heat exchange is performed between the CO ₂ rich absorbent obtained in step (III) and step (I) to obtain the absorbent and the CO ₂ lean absorbent obtained in step (III), and obtained in step (I). A step (IV) of heating the obtained CO ₂ rich absorbent and cooling the CO ₂ lean absorbent obtained in the step (III), and the CO ₂ lean absorbent and the CO ₂ rich absorbent are aqueous solutions containing alkanolamines. Each time in step (II) Cleaning liquid used for washing is an aqueous solution containing a mineral acid or a mineral acid salt, and a method for recovering carbon dioxide comprising the step (V) for adjusting the pH of the cleaning solution to be used for the final wash in 5 below.

[2] Step (VI) of adding a part or all of the cleaning liquid used for each cleaning other than the first to the cleaning liquid used for the previous cleaning, and the cleaning liquid used for the first cleaning The method for recovering carbon dioxide according to [1], further comprising a step (VII) of adding a part or all of the above to a CO ₂ lean absorbent or a CO ₂ rich absorbent.
[3] The carbon dioxide recovery method according to [1] or [2], further including a step of cooling the cleaning liquid used for each cleaning and reusing it for the same cleaning.
[4] The carbon dioxide recovery according to any one of [1] to [3], wherein the cleaning liquid used for the first cleaning is maintained at a temperature not higher than the highest boiling point of the alkanolamine decomposition products. Method.

[5] An absorption part capable of obtaining a CO ₂ -absorbed exhaust gas and a CO ₂ -rich absorbent by bringing the gas to be treated and the downstream CO ₂ -lean absorbent into countercurrent contact with each other, and ascending CO ₂ Two or more stages of cleaning units capable of bringing the absorption-treated exhaust gas and the down-flow cleaning liquid into countercurrent contact with each other, heating the CO ₂ rich absorption liquid to desorb carbon dioxide and regenerating it as a CO ₂ lean absorption liquid Detachable part, heat exchange part capable of heat exchange between the CO ₂ lean absorbent regenerated in the detachment part and the CO ₂ rich absorbent obtained in the absorbent part, and a CO ₂ lean absorbent and The CO ₂ rich absorption liquid is an aqueous solution containing alkanolamine, the cleaning liquid used in each stage cleaning section is an aqueous solution containing a mineral acid or a mineral salt, and the pH of the cleaning liquid used in the uppermost cleaning section is 5 Have the following adjustments Carbon dioxide recovery unit.

[6] Piping for adding a part or all of the cleaning liquid used in the cleaning section of each stage other than the lowermost stage to the cleaning liquid used in the cleaning section of the lower stage, and the lowermost cleaning section [5], further comprising a pipe for adding a part or all of the cleaning liquid used in the above to the CO ₂ lean absorbing liquid used in the absorbing part or the CO ₂ rich absorbing liquid obtained in the absorbing part. Carbon dioxide recovery equipment.
[7] A cooling unit for lowering the temperature of the cleaning liquid used in the cleaning unit, and a pipe for circulating the cleaning liquid between the cleaning unit and the cooling unit are further provided in each stage, [5] or [6 ] The carbon dioxide recovery apparatus described in the above.
[8] The carbon dioxide recovery apparatus according to [7], wherein the temperature of the cleaning liquid used in the lowermost cleaning unit is maintained at a temperature equal to or lower than the highest boiling point of the alkanolamine decomposition products.

  According to the carbon dioxide recovery apparatus and recovery method of the present invention, the amount of low boiling point compounds such as ammonia and ethylamine generated by the decomposition of amines used for carbon dioxide absorption can be reduced to the atmosphere. . Moreover, since the carbon dioxide recovery apparatus and recovery method of the present invention do not supply excess water for cleaning, the amount of water in the system does not become excessive, and the mass balance of water is maintained. Furthermore, since the amount of HSS produced is small, the burden of reclaimer processing is low.

It is a figure which shows one Embodiment of the carbon dioxide collection apparatus of this invention. FIG. 3 is a diagram illustrating a cleaning unit of Example 1. 6 is a view showing a cleaning unit of Comparative Example 1. FIG. It is a figure which shows the washing | cleaning part of the comparative example 2. FIG. 6 is a diagram illustrating a cleaning unit of Example 2. It is a figure which shows the relationship between ammonia concentration in the gaseous phase of ammonia water, and pH.

In the carbon dioxide recovery method according to one embodiment of the present invention, the carbon dioxide contained in the gas to be treated is absorbed into the CO ₂ lean absorbent to obtain the CO ₂ absorption treated exhaust gas and the CO ₂ rich absorbent (I). the CO ₂ absorption treated flue gas and washed 2 more times with washing solution, removing the alkanolamines and alkanolamine degradation products accompanying the CO ₂ absorption treated flue gas (II), heating the CO ₂ rich absorbent solution carbon dioxide is desorbed Te, between the CO ₂ lean absorbing liquid to obtain a (III), CO ₂ rich absorbent solution obtained in step (I) and step (III) obtained in CO ₂ lean absorbing solution Heat exchange in step (IV) to warm the CO ₂ rich absorbent obtained in step (I) and cool the CO ₂ lean absorbent obtained in step (III), and the CO ₂ lean absorbent and CO ₂ Rich absorbent is alkanol Adjusting the pH of the cleaning liquid used for the final cleaning to 5 or less, and the cleaning liquid used for each cleaning in step (II) is an aqueous solution containing a mineral acid or a mineral salt. (V) is included.

  Combustion exhaust gas generated by burning coal, petroleum, biomass fuel, and shale gas contains carbon dioxide, sulfur oxide, nitrogen oxide, oxygen, nitrogen, and the like. The to-be-treated gas used in the present invention may be the combustion exhaust gas itself, but the combustion exhaust gas is denitrated by an ammonium catalytic reduction method, a wet lime gypsum method, an alkaline solution absorption method, a lime slurry absorption method, A gas that is substantially free of sulfur oxides and nitrogen oxides, which is subjected to a desulfurization process by a spray drying method, an activated carbon adsorption method, or the like, is preferable. A trace amount of sulfur oxide or nitrogen oxide is combined with alkanolamine in the absorption liquid circulating in the carbon dioxide recovery device to form a heat stable salt (HSS). The HSS is processed in a reclaimer installed as an accessory device of a carbon dioxide recovery device. The HSS can be regenerated into alkanolamine by treatment with a reclaimer.

The CO ₂ rich absorbent and the CO ₂ lean absorbent are aqueous solutions containing alkanolamine. CO ₂ rich absorbent solution is obtained by absorbing carbon dioxide in the CO ₂ lean absorbing solution. Moreover, it can be regenerated into a CO ₂ lean absorbing solution by heating the CO ₂ rich absorbing solution to desorb carbon dioxide. Examples of the alkanolamine that can be used in the present invention include alcoholic hydroxyl group-containing primary amines such as monoethanolamine and 2-amino-2-methyl-1-propanol, and alcoholic hydroxyl groups such as diethanolamine and 2-methylaminoethanol. Examples thereof include secondary amines containing alcohol, tertiary amines containing alcoholic hydroxyl groups such as triethanolamine and N-methyldiethanolamine. Further, the absorption liquid may contain a carbon dioxide absorption accelerator or a corrosion inhibitor, and further methanol, polyethylene glycol, sulfolane and the like as other media.

By absorbing carbon dioxide contained in the gas to be treated into the CO ₂ lean absorbent, the CO ₂ -absorbed exhaust gas can be obtained. The exhaust gas that has undergone the CO ₂ absorption treatment is washed twice or more with a washing liquid. By this cleaning, alkanolamine and alkanolamine decomposition products accompanying the CO ₂ absorption-treated exhaust gas are removed.

Since the alkanolamine in the CO ₂ absorption-treated exhaust gas has a low vapor pressure with respect to water, the alkanolamine is largely distributed to water or the low-concentration aqueous solution by washing with water or the low-concentration aqueous solution of alkanolamine. On the other hand, the alkanolamine decomposition product in the exhaust gas that has been subjected to the CO ₂ absorption treatment has a high vapor pressure with respect to water, so that even if it is washed with water or a low-concentration aqueous solution of alkanolamine, it is largely distributed in the gas phase.
As shown in FIG. 7, alkanolamine decomposition products, such as ammonia, have a low vapor pressure for aqueous solutions containing mineral acids or mineral salts, preferably aqueous solutions containing mineral acids or mineral salts adjusted to pH 5 or lower. Therefore, by the washing | cleaning by the aqueous solution containing a mineral acid or a mineral acid salt, many are distributed to the aqueous solution containing a mineral acid or a mineral acid salt. Therefore, in the present invention, an aqueous solution containing a mineral acid or a mineral acid salt is used as a cleaning liquid in each washing, and an aqueous solution containing a mineral acid or a mineral acid salt adjusted to pH 5 or less is adopted as a washing liquid in the final washing. To do. The pH is adjusted at least for the cleaning liquid used for the final cleaning. Although pH may be adjusted with respect to the washing | cleaning liquid used for washing | cleaning other than the last round, the necessity is low. The pH can be adjusted by adding a mineral acid or a mineral acid salt to water or a low-concentration aqueous solution of alkanolamine.

Examples of the mineral acid used in the present invention include sulfuric acid, hydrochloric acid, nitric acid, boric acid and the like. As mineral salts, sulfate amine salts, nitrate nitrate salts, specifically sulfate alkanolamine salts such as aminoethanol sulfate and methyldiethanolamine sulfate, nitrate alkanolamine salts such as aminoethanol nitrate and methyldiethanolamine nitrate, etc. Is mentioned. When the mineral acid or mineral acid salt added to the cleaning liquid is excessively accumulated as HSS or the like in the system, it can be treated in the reclaimer as described above. And it can use as a mineral salt for adding the sulfate sulfate salt, the nitrate nitrate salt, etc. which are collect | recovered with a reclaimer to a washing | cleaning liquid. The lower limit of the addition amount of the mineral acid or the mineral acid salt is such an amount that the pH of the final cleaning solution is 5 or less. The upper limit of the addition amount of the mineral acid or mineral acid salt is not particularly limited, but it is preferable from the viewpoint of cost to make the amount equal to the number of moles of the alkanolamine decomposition product contained in the exhaust gas subjected to the CO ₂ absorption treatment. In addition, mineral acids form salts with amines, but mineral salts do not form new amine salts, so mineral salts can be preferably used for pH adjustment.

  A part or all of the cleaning solution used for each cleaning other than the first time can be added to the cleaning solution used for the previous cleaning of the previous time as it is or after adjusting the pH if necessary. The alkanolamine concentration of the cleaning liquid used for each cleaning is lower than the alkanolamine concentration of the cleaning liquid used for the previous cleaning. On the other hand, the alkanolamine concentration in the gas phase at each cleaning is lower than the alkanolamine concentration in the gas phase at the previous cleaning. By adding the cleaning liquid used for each cleaning to the cleaning liquid used for the previous cleaning, the cleaning effect of the previous cleaning can be improved.

Furthermore, a part or all of the cleaning liquid used for the first cleaning is replenished with alkanolamine as it is or as necessary to make a CO ₂ lean absorbing liquid or a CO ₂ rich absorbing liquid, preferably a CO ₂ rich absorbing liquid. Can be added. The alkanolamine concentration in the cleaning solution used for the first cleaning is lower than the alkanolamine concentration in the CO ₂ lean absorbing solution, but the alkanolamine recovered in the two or more cleanings accumulates in the cleaning solution used in the first cleaning. Thus, the consumption of alkanolamines can be saved by adding it to the CO ₂ lean absorbent or CO ₂ rich absorbent.

Since the cleaning liquid used for each cleaning rises in temperature by contact with the exhaust gas that has been subjected to the CO ₂ absorption treatment, it can be cooled and reused for the same cleaning. The temperature of the cleaning liquid is not particularly limited as long as alkanolamine or alkanolamine decomposition products can be removed. Is preferably maintained. Moreover, it is preferable to set the cleaning liquid so that the temperature decreases as the process proceeds from the first time to the last time.
Since the cleaning liquid used for the cleaning can finally be used as the absorbing liquid, it is not necessary to install a cleaning liquid disposal apparatus.

The carbon dioxide recovery apparatus according to an embodiment of the present invention makes the CO ₂ absorption treated exhaust gas and the CO ₂ rich absorbent liquid in countercurrent contact with the upstream gas to be treated and the downstream CO ₂ lean absorbent. Absorbing part that can be obtained, two or more stages of cleaning part that can make countercurrent contact between the exhaust gas that has been treated with the up-flowing CO ₂ absorption and the down-flowing cleaning liquid, and the CO ₂ rich absorbing liquid is heated to desorb carbon dioxide desorption unit capable of reproducing the separated so CO ₂ lean absorbing solution, be heat exchange between the desorption part CO ₂ rich absorbent liquid obtained in the absorption unit and the regenerated CO ₂ lean absorbing solution in A heat exchanging section that can be used, and the CO ₂ lean absorbing liquid and the CO ₂ rich absorbing liquid are aqueous solutions containing alkanolamines, and the cleaning liquid used in each stage of the cleaning section is an aqueous solution containing a mineral acid or a mineral salt, and Used for the upper cleaning section And it has a means for adjusting the pH of the cleaning solution to 5 or less.

  FIG. 1 is a diagram showing an embodiment of the carbon dioxide recovery apparatus of the present invention. The apparatus has an absorption tower 1 and a desorption tower 2 as main equipment. In the apparatus shown in FIG. 1, an absorption unit 11 and a cleaning unit 24 are installed in an absorption tower 1. The absorption part 11 has the same structure as the equipment used for a known gas absorption operation. For example, a packed bed and a shelf are mentioned. The packed bed is filled with fillers such as Raschig rings, mesh rings, pole rings, coil packs, helipacks, Dixon packings, McMahon packings, and eyeballs, and is designed to increase the contact area of gas and liquid.

The gas 3 to be treated is supplied below the absorption section 11 of the absorption tower 1. The CO ₂ lean absorbent 4 is fed through the nozzle onto the absorber 11 of the absorption tower. In the absorption unit 11, the gas to be treated 3 is caused to flow upward and the CO ₂ lean absorbent 4 is caused to flow downward to bring the gas to be treated 3 and the CO ₂ lean absorbent 4 into countercurrent contact. Carbon dioxide in the gas to be treated is absorbed by the CO ₂ lean absorbent, and the exhaust gas that has undergone the CO ₂ absorption treatment is discharged from above the absorber, and the CO ₂ rich absorbent is discharged from below the absorber. The CO ₂ rich absorbent is stored in the bottom 10.

In the apparatus shown in FIG. 1, the cleaning unit is provided with a lower cleaning unit 24a and an upper cleaning unit 24b. An aqueous solution of mineral acid or mineral acid salt is prepared in the cleaning liquid tank 40.
In the lower-stage washing unit 24a, the CO ₂ absorption-treated exhaust gas from the absorption unit 11 is washed with the lower-stage washing liquid poured from the nozzle 9a to remove alkanolamine and / or alkanolamine decomposition products accompanying the gas. Since alkanolamine has a high solubility in water, most of the alkanolamine is absorbed by the lower cleaning liquid in the lower cleaning section 24a. The lower cleaning liquid poured from the nozzle 9a is extracted from the tray at the lower part of the lower cleaning section 24a, adjusted in temperature by the cooler 8a, and poured again from the nozzle 9a.

In the apparatus shown in FIG. 1, an aqueous solution of a mineral acid or a mineral salt is supplied through a pipe 41, and the pH of the upper cleaning liquid is adjusted to 5 or less. In the upper cleaning section 24b, the CO ₂ absorption-treated exhaust gas cleaned by the lower cleaning section 24a is cleaned again with the upper cleaning liquid poured from the nozzle 9b to remove alkanolamine and / or alkanolamine decomposition products accompanying the gas. Most of the alkanolamine and / or alkanolamine decomposition products are absorbed by the upper cleaning liquid. The CO ₂ -absorbed exhaust gas 3 ′ cleaned with the upper cleaning liquid is discharged from the top 5. A demister may be installed at the outlet of the upper cleaning section in order to recover the cleaning liquid mist accompanying the released gas. Thereby, the loss of the cleaning liquid can be reduced. The upper cleaning liquid poured from the nozzle 9b is extracted from the tray at the lower part of the upper cleaning section 24b, adjusted in temperature by the cooler, and poured again from the nozzle 9b. The lower-stage cleaning unit 24a and the upper-stage cleaning unit 24b have the same structure as the equipment used for a known gas absorption operation. For example, a packed bed and a shelf are mentioned.

In the apparatus shown in FIG. 1, piping is performed so that a part of the upper cleaning liquid extracted from the tray of the upper cleaning section 24 b can be transferred to the nozzle 9 a of the lower cleaning section 24 a one stage before. In addition, a pipe for transferring the lower cleaning liquid extracted from the tray of the lower cleaning section 24a branches in the middle, and a pipe 20 is provided to join the bottom 10 of the absorption tower where the CO ₂ rich absorbing liquid is stored.

  In the apparatus shown in FIG. 1, two lower cleaning units and an upper cleaning unit are provided. However, if necessary, one or more additional cleaning units may be further provided between the lower and upper cleaning units. The structure and piping of the additional cleaning unit may be the same structure and piping as the lower cleaning unit or the upper cleaning unit. The temperature of the cleaning liquid is highest in the lowermost cleaning section, and becomes lower as the upper cleaning section becomes.

The CO ₂ rich absorption liquid accumulated in the bottom 10 of the absorption tower is extracted from the bottom, heated by the heat exchanger 22, and then poured from the nozzle 14 onto the top of the desorption section 15 of the desorption tower 2. The poured liquid descends the desorption part 15 and accumulates at the bottom 13 of the desorption tower 2. The liquid collected at the bottom of the desorption tower is a CO ₂ lean absorbent having a low carbon dioxide content. A reboiler 23 is attached to the bottom of the desorption tower. The vapor obtained by heating and vaporizing the CO ₂ lean absorbent in the reboiler 23 raises the desorption part 15 and heats the CO ₂ rich absorption liquid descending the desorption part 15 to a temperature of about 100 to 125 ° C. Is removed. In the desorption section 15 of the desorption tower 13, the temperature at the bottom is usually higher than the temperature at the top. The structure of the detachment part 15 is not particularly limited, and may be, for example, a packed bed filled with a packing such as Raschig ring or a shelf.

The CO ₂ lean absorption liquid accumulated at the bottom of the desorption tower is extracted, cooled by the heat exchanger 22, and then returned to the absorption tower 1. In the heat exchanger 22, the CO ₂ lean absorbing liquid (about 110 to 120 ° C.) extracted from the bottom 13 of the desorption tower and the CO ₂ rich absorbing liquid (50 to 60) extracted from the bottom 10 of the absorbing tower. Heat exchange is performed between the temperature and the temperature. As the heat exchanger, an existing heat exchanger such as a spiral heat exchanger, a plate heat exchanger, or a multi-tubular heat exchanger can be used.

The carbon dioxide desorbed in the desorbing unit 15 is accompanied by CO ₂ absorbent mist and vapor. Therefore, the desorbed carbon dioxide is washed with washing water in the water washing unit 25. And the carbon dioxide which passed through the water washing | cleaning part 25 is cooled with the cooler 19, and the vapor | steam which accompanies carbon dioxide is condensed, and condensed water is obtained. Carbon dioxide and condensed water are separated by the CO ₂ separator 17. The condensed water is poured from the nozzle 20 and used as cleaning water in the water cleaning unit 25. In the present invention, a part of the obtained condensed water can be mixed with the cleaning liquid.

  The present invention will be described more specifically with reference to the following examples. In addition, this invention is not limited by these Examples.

Example 1
Carbon dioxide was recovered under the following operating conditions using the carbon dioxide recovery apparatus shown in FIG. FIG. 2 is an enlarged view of the cleaning unit 24.
[Operating conditions]
Gas to be treated supplied from under the absorption section: temperature 40 ° C., supply amount 500 Nm ³ / h (wet), carbon dioxide concentration in dry gas 12%
CO ₂ -lean absorbent supplied from above the absorber: monoethanolamine aqueous solution having a temperature of 40 ° C. and a concentration of 30% CO ₂ rich absorbent supplied from above the desorber: temperature 100 ° C.
Desorption tower pressure 160 kPa (gauge)
Absorption liquid temperature in reboiler 23: 120 ° C
Cooler 19 temperature: 30 ° C
Liquid gas ratio in the absorption part: 3.0 (L / Nm ³ )
Absorption liquid circulation rate: 1500L

Liquid gas ratio in the cleaning section: 2.0 (L / Nm ³ )
Cleaning liquid in the cleaning liquid tank 40 installed in the upper cleaning section: 1.2% concentration sulfuric acid aqueous solution Supply of cleaning liquid from the cleaning liquid tank 40 installed in the upper cleaning section: 10 kg / h
Cleaning liquid in the cleaning liquid circulation line of the upper cleaning section: control to pH 4.5 to 5 and temperature 50 ° C
Part of the upper cleaning liquid is added to the lower cleaning liquid. Cleaning liquid in the cleaning liquid circulation line of the lower cleaning section: No pH control

(Operation result)
Carbon dioxide recovery: 90%
CO ₂ absorption treated exhaust gas discharged from above the upper cleaning section 24b: temperature 50 ° C.
Exhaust gas after CO ₂ absorption treatment under the lower cleaning section 24a: temperature 60 ° C., monoethanolamine concentration in the gas of 1000 ppmv (ppmv is a volume fraction of 1 million), ammonia concentration in the gas of 30 ppmv
Exhaust gas after CO ₂ absorption treatment under the upper cleaning section 24b: monoethanolamine concentration in the gas of 100 ppmv, ammonia concentration in the gas of 30 ppmv, containing low-boiling amine decomposition products other than ammonia CO ₂ absorption on the upper cleaning section 24b Treated exhaust gas: Monoethanolamine concentration in gas less than 1 ppmv, ammonia concentration in gas less than 1 ppmv, low-boiling amine decomposition product concentration other than ammonia less than 1 ppmv Absorbed solution in cleaning liquid recovery line 20 of lower cleaning section 24a: 0.11 kg / h (= 1.2 mol / h) of monoethanolamine sulfate and ammonium sulfate

Comparative Example 1
The same apparatus as in Example 1 was used except that the cleaning unit 24 was changed to the cleaning unit 124 shown in FIG. Then, carbon dioxide was recovered under the following operating conditions.
(Operating conditions)
Cleaning liquid in the cleaning liquid tank 42 installed in the upper cleaning section 24b: Water Cleaning liquid supply amount from the cleaning liquid tank 42 installed in the upper cleaning section 24b: 5 kg / h
Cleaning liquid in cleaning liquid circulation line of upper cleaning section 24b: No pH control Cleaning liquid in cleaning liquid tank 44 installed in lower cleaning section 24a: 18.4% sulfuric acid aqueous solution Cleaning liquid from cleaning liquid tank 44 installed in lower cleaning section 24a Supply amount: 5kg / h
Cleaning liquid in the cleaning liquid circulation line of the lower cleaning section 24a: control to pH 5.5 The cleaning liquid recovery lines 30 and 31 are independently installed in the upper cleaning section 24b and the lower cleaning section 24a, respectively, and the upper cleaning liquid is not added to the lower cleaning liquid. .
Except these, the same as Example 1.

(Operation result)
Exhaust gas after CO ₂ absorption treatment under the upper cleaning section 24b: monoethanolamine concentration in the gas of 20ppmv, ammonia concentration in the gas of 5ppmv, containing low-boiling amine decomposition products other than ammonia CO ₂ absorption on the upper cleaning section 24b Treated exhaust gas: Monoethanolamine concentration in gas of less than 1 ppmv, ammonia concentration in gas of 5 ppmv, containing low-boiling amine decomposition products other than ammonia Absorbing liquid in cleaning liquid recovery line 31 of lower cleaning section 24a: 0.92 kg / h (= 9.6 mol / h) of monoethanolamine sulfate and ammonium sulfate

Comparative Example 2
The same apparatus as in Example 1 was used except that the cleaning unit was changed to the cleaning unit 224 shown in FIG. Then, carbon dioxide was recovered under the following operating conditions.
[Operating conditions]
Cleaning liquid in the cleaning liquid tank 44 installed in the upper cleaning section 24b: sulfuric acid aqueous solution having a concentration of 18.4% Cleaning liquid supply amount from the cleaning liquid tank 44 installed in the upper cleaning section 24b: 5 kg / h
Cleaning liquid in the cleaning liquid circulation line of the upper cleaning section 24b: Control to pH 5.5 Cleaning liquid in the cleaning liquid tank 42 installed in the lower cleaning section 24a: Water Cleaning liquid supply amount from the cleaning liquid tank 42 installed in the lower cleaning section 24a: 5 kg / h
Cleaning liquid in the cleaning liquid circulation line of the lower cleaning section 24a: No pH control The cleaning liquid recovery lines 31 and 32 are independently installed in the upper cleaning section 24b and the lower cleaning section 24a, respectively, and the upper cleaning liquid is not added to the lower cleaning liquid.
Except these, the same as Example 1.

(Operation result)
Exhaust gas after CO ₂ absorption treatment under the upper cleaning section 24b: monoethanolamine concentration in the gas of 150 ppmv, ammonia concentration in the gas of 30 ppmv, containing low-boiling amine decomposition products other than ammonia CO ₂ absorption on the upper cleaning section 24b Treated exhaust gas: monoethanolamine concentration in gas 2ppmv, ammonia concentration in gas less than 1ppmv, low boiling point amine decomposition product concentration other than ammonia less than 1ppmv Absorbed solution in cleaning liquid recovery line 31 of upper cleaning section 24b: 0.14kg / h (= 1.5 mol / h) of monoethanolamine sulfate and ammonium sulfate

Example 2
The same apparatus as in Example 1 was used except that the cleaning unit 24 was changed to the cleaning unit 324 shown in FIG. Then, carbon dioxide was recovered under the following operating conditions.
[Operating conditions]
Middle cleaning section 24c installed Cleaning fluid in cleaning liquid circulation line of middle cleaning section 24c: No pH control Same as Example 1 except for these.

(Operation result)
Exhaust gas after CO ₂ absorption treatment under the upper cleaning section 24b: monoethanolamine concentration in the gas of 30 ppmv, ammonia concentration in the gas of 30 ppmv, containing low-boiling amine decomposition products other than ammonia CO ₂ absorption on the upper cleaning section 24b Treated exhaust gas: Monoethanolamine concentration in gas less than ppmv, ammonia concentration in gas less than 1 ppmv, low-boiling amine decomposition product concentration other than ammonia less than 1 ppmv Absorbed solution in cleaning liquid recovery line 20 of lower cleaning section 24a: 0.05 kg / h (= 0.5 mol / h) of monoethanolamine sulfate and ammonium sulfate

The above results are summarized in Table 1. The recovery apparatus (Examples 1 and 2) of the present invention has a smaller sulfuric acid supply amount than the recovery apparatus of the comparative example, and the concentration of monoethanolamine (MEA) and ammonia (NH ₃ ) in the exhaust gas from the top of the absorption tower. The concentration can be lowered. Moreover, the production amount of monoethanolamine sulfate and ammonium sulfate (HSS) is small.

Claims (8)

To obtain a CO ₂ absorption treated exhaust gas and CO ₂ rich absorbent solution to absorb carbon dioxide in the treated gas to CO ₂ lean absorbing solution (I),
The CO ₂ absorption treated flue gas and washed 2 more times with washing solution, removing the alkanolamines and alkanolamine degradation products accompanying the CO ₂ absorption treated flue gas (II),
A step (III) of heating the CO ₂ rich absorbing liquid to desorb carbon dioxide to obtain a CO ₂ lean absorbing liquid;
Step by heat exchange with the CO ₂ lean absorbent liquid obtained in CO ₂ rich absorbent solution and process obtained in (I) (III), warmed the resulting CO ₂ rich absorbent solution in step (I) And the step (IV) for cooling the CO ₂ lean absorbent obtained in the step (III), and the CO ₂ lean absorbent and the CO ₂ rich absorbent are aqueous solutions containing alkanolamine, and each washing in the step (II) (V) adjusting the pH of the cleaning liquid used for the final cleaning to 5 or less, wherein the cleaning liquid used for the cleaning is an aqueous solution containing a mineral acid or a mineral acid salt
Of carbon dioxide containing Step (VI) of adding a part or all of the cleaning solution used for each cleaning other than the first to the cleaning solution used for the previous cleaning, and a part of the cleaning solution used for the first cleaning Or step (VII) of adding the whole to the CO ₂ lean absorbent or CO ₂ rich absorbent
The method for recovering carbon dioxide according to claim 1, further comprising:   The method for recovering carbon dioxide according to claim 1 or 2, further comprising a step of cooling the cleaning liquid used for each cleaning and reusing it for the same cleaning.   The method for recovering carbon dioxide according to any one of claims 1 to 3, wherein the cleaning liquid used for the first cleaning is maintained at a temperature not higher than the highest boiling point among the boiling points of the alkanolamine decomposition products. An absorption part capable of obtaining a CO ₂ absorption-treated exhaust gas and a CO ₂ rich absorption liquid by counter-current contact between the gas to be treated in the upward flow and the CO ₂ lean absorption liquid in the downward flow;
Two or more stages of cleaning units capable of bringing the upflow CO ₂ absorption treated exhaust gas and the downflow cleaning liquid into countercurrent contact,
A desorption part capable of heating the CO ₂ rich absorption liquid to desorb carbon dioxide and regenerating it into a CO ₂ lean absorption liquid;
A heat exchanging unit capable of exchanging heat between the CO ₂ lean absorbent regenerated in the desorption part and the CO ₂ rich absorbent obtained in the absorber, and the CO ₂ lean absorbent and the CO ₂ rich absorbent Is an aqueous solution containing alkanolamine, the cleaning liquid used in each stage cleaning section is an aqueous solution containing a mineral acid or a mineral salt, and means for adjusting the pH of the cleaning liquid used in the uppermost cleaning section to 5 or less A carbon dioxide recovery device. Used to add a part or all of the cleaning solution used in the cleaning section of each stage other than the bottom stage to the cleaning liquid used in the cleaning section of the lower stage, and to the cleaning section in the bottom stage. The carbon dioxide according to claim 5, further comprising a pipe for adding a part or all of the washed liquid to the CO ₂ lean absorbent used in the absorber or the CO ₂ rich absorbent obtained in the absorber. Recovery equipment. The carbon dioxide according to claim 5 or 6, further comprising a cooling part for lowering the temperature of the cleaning liquid used in the cleaning part, and a pipe for circulating the cleaning liquid between the cleaning part and the cooling part in each stage. Recovery equipment.   The carbon dioxide recovery apparatus according to claim 7, wherein the temperature of the cleaning liquid used in the lowermost cleaning section is maintained at a temperature not higher than the highest boiling point of the alkanolamine decomposition products.

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