KR100993689B1 - Method for separating and recovering carbon dioxide - Google Patents

Abstract

The present invention relates to a method for recovering carbon dioxide emitted in the production process using a chemical absorption method.

The present invention separates and recovers carbon dioxide and oxygen separated in the preheating process before the carbon dioxide absorbed absorption solution is regenerated in a regeneration tower without mixing with a separator gas discharged at a high temperature from the upper part of the regeneration tower. While it is possible to reduce the deterioration of carbon dioxide absorption due to oxidative decomposition, by heat-exchanging the absorbed solution condensed in the cooling process for separate recovery and recovery with the absorbed solution regenerated at a high temperature in the regeneration tower, the temperature of the condensed absorbent solution is increased and regenerated. By reducing the temperature of the absorbent solution, energy efficiency can be improved by reducing the carbon dioxide absorption capacity of the carbon dioxide absorbent by oxygen, thereby reducing the total carbon dioxide absorbent consumption and reducing the cost of carbon dioxide in the exhaust gas. efficiently, In addition, it provides a separate recovery method of carbon dioxide that can be separated and recovered more environmentally friendly.

 Carbon dioxide, separation, recovery, amine absorbent, absorption tower, regeneration tower

Description

Method for separating and recovering carbon dioxide

The present invention relates to a method for separating and recovering carbon dioxide, and more particularly, to a method for recovering carbon dioxide when carbon dioxide and oxygen are present in exhaust gas by using a chemical absorption method.

With the recent recognition of the seriousness of global warming, countries around the world are struggling to come up with measures for greenhouse gases.

Particularly, since the contribution of carbon dioxide to global warming is 50%, which is greater than global warming gases, global society is showing specific movements to suppress carbon dioxide emissions through various international agreements.

Countries with high industrial dependence on fossil fuels such as Korea are urgently required to take countermeasures due to the severe economic impact expected by these international trends.

Absorption methods for removing or separating carbon dioxide are classified into physical absorption methods and chemical absorption methods according to the presence or absence of a chemical reaction between carbon dioxide and an absorbent, and both methods are commercially developed and applied to actual processes.

The technique of removing carbon dioxide by chemical absorption has long been developed. Processes using alkanol amines were patented in the United States in the 1930s and were initially industrialized as triethanolamine (TEA), but many amines have since Currently, mono ethanol amines (MEA, Monoethanolamine) and diethanolamine (DEA) are the most used.

In the chemical absorption system, an absorption method using chemically absorbing carbon dioxide in an absorption tower by selecting an amine solution having excellent absorbency to carbon dioxide as an absorbent to separate the carbon dioxide, and then changing the temperature and pressure to separate it.

The amine solution, a chemical absorbent with affinity for carbon dioxide, absorbs the carbon dioxide contained in the exhaust gas supplied into the absorption tower, and the absorbent containing a large amount of carbon dioxide is heated in the process to be separated into the original amine solution and carbon dioxide and thus high purity. CO2 is stored in another reservoir, and the regenerated amine solution is separated and recovered by repeating a series of cycles where the heat is removed from the heat exchanger and then circulated back to the absorption tower.

For example, as shown in FIG. 1, the exhaust gas containing carbon dioxide is supplied to the absorption tower 10 in which the packing material with a large surface area is filled so that gas-liquid contact may be performed smoothly, and the absorption tower 10 Contact with absorbent in the state of the solution sprayed at the top of the) under atmospheric pressure to absorb the carbon dioxide in the exhaust gas in the absorption solution in the temperature range around 40 ~ 50 ℃.

Heat-exchanging the absorbing solution emitted from the absorption tower 10, that is, the absorbing solution absorbed carbon dioxide and the regenerated column 11 after being heated and regenerated at a temperature range of about 120 ° C. and then released through the heat exchanger 12b. Heat is exchanged in the group 12a and preheated first.

As the temperature rises during the preheating process, the gas liberated in the carbon dioxide absorbing solution is separated from the separation drum 13a and then sent to the cooler 14a together with the separator gas discharged from the upper end of the regeneration tower 11.

The carbon dioxide absorbing solution separated from the separation drum 13a is heat-reduced in the heat exchanger 12b with the absorbing solution regenerated and discharged in the regeneration tower 11 and then preheated to a higher temperature at a higher temperature. Inflow.

In the regeneration tower 11, the carbon dioxide absorption solution is heated at a temperature range of about 120 ° C. to free carbon dioxide, and then discharged to the upper portion of the regeneration tower 11, where the absorption solution is regenerated and discharged together with the free carbon dioxide. The vaporized absorption solution is cooled and condensed in the cooler 14a. The vaporized absorption solution is then separated from the separation drum 13b and refluxed to the regeneration tower 11, and the free gaseous carbon dioxide is compressed and stored in a tank at high pressure. do.

The absorption liquid regenerated through the heat exchanger 12a is cooled in the cooler 14b, and then supplied to the absorption tower 10 to absorb carbon dioxide.

Here, reference numeral 15 denotes a novel absorbent liquid reservoir, and 16 denotes an absorbent liquid heater.

As an absorbent of the chemical absorption method, most of the amine-based absorbent solutions are widely used in the world at present, and the types of amines used in such absorbent solutions are monoethanolamine, diethanolamine, triethanolamine, methyl diethanolamine, Diisopropylamine, diglycolamine, piperazine, 2-piperadinethanol, hydroxyethylpiperazine, 2-amino-2methyl-1-propanol, 2-ethylamino-ethanol, 2-methylamino-ethanol, In addition to 2-diethylamino-ethanol, dozens are present and are usually used in a solvent such as water in a concentration range of 20 to 60 wt%.

This amine compound has a higher reactivity with carbon dioxide at room temperature and atmospheric pressure than other absorbents, and thus has high separation efficiency in separating carbon dioxide present at a low concentration in exhaust gas discharged at a large flow rate in a temperature range of 40 to 50 ° C. under atmospheric pressure. However, when oxygen is present, there is a problem in that carbon dioxide absorption is lowered by oxidative decomposition by reacting with oxygen.

Since oxygen is present in the exhaust gas containing most of the carbon dioxide, when the amine absorption solution is used as the carbon dioxide absorbent, the carbon dioxide absorption ability of the amine absorption solution is continuously lowered by oxidative decomposition by oxygen.

The higher the concentration of oxygen, the higher the temperature, the better the oxidative decomposition reaction occurs, so that the absorption of the carbon dioxide absorption of the absorbing solution occurs more severely in the process of recovering and regenerating carbon dioxide by heating the used absorbing solution to a high temperature.

In the conventional chemical absorption method, in order to solve this problem, the regenerated absorbent solution is continuously replenished with a new absorbent solution to maintain a constant carbon dioxide absorption capacity of the entire absorption system.

As an example of monoethanolamine, one of the amine compounds, which is currently used as a carbon dioxide absorbent, it is about 230 tons per year in the process of absorbing and separating 100,000 tons of carbon dioxide per year by using a 30 wt% monoethanolamine aqueous solution as an absorbent. The new absorbent solution is discarded after being used, and the cost of purchasing, using and discarding the new carbon dioxide absorbent accounts for more than 15% of the total cost of recovering and separating carbon dioxide.

Therefore, in order to lower the carbon dioxide recovery cost and increase the eco-friendliness of the carbon dioxide absorption technology according to the waste generation, it is required to develop a technology for reducing the carbon dioxide absorbent consumption.

Accordingly, the present invention is conceived to solve the problems described above, carbon dioxide (CO ₂₎ is the CO ₂ and oxygen (O ₂₎ is separated in the course of pre-heating prior to reproduction on the regeneration column to the absorption absorbent solution regeneration column upper end It is an object of the present invention to provide a method for separating and recovering CO ₂ that can reduce the CO ₂ absorption capacity decrease due to oxidative decomposition of the absorbent solution at high temperature by not separating and recovering the mixture separately from the separator gas discharged at a high temperature.

Further, to recover the present invention is not mixed with the separation being discharged at a high temperature for CO ₂ and O ₂ to be separated in the course of pre-heating prior to reproducing the absorption solution with a CO ₂ absorption in the regeneration column in the regeneration column the upper end gas, separately By heat-exchanging the absorbed solution condensed during the cooling process with the absorbed solution regenerated at a high temperature in the regeneration tower, the separation of CO ₂ can improve the energy efficiency by increasing the temperature of the condensed absorbent solution and lowering the temperature of the regenerated absorbent solution. Another purpose is to provide a recovery method.

Thus, the present invention by reducing the CO ₂ absorption capacity reduction in the CO ₂ absorbent by the O _2, to reduce the total CO ₂ absorbent consumption On the other hand, the CO ₂ in a cost savings enemy in the exhaust gas, energy-efficient, and more environmentally friendly It is an object of the present invention to provide a technique for separating and recovering water.

A first step of the separation method for recovering CO ₂ provided by the present invention in order to attain the object is to feed the exhaust gas containing CO ₂ in the absorber absorbs CO ₂ in the absorbent solution, which is discharged from the absorption tower In the _{second step} of preheating the CO ₂ absorption solution and the absorption solution emitted from the regeneration tower by first preheating, separating the gases (CO ₂ and O ₂ ) liberated from the CO ₂ absorption solution from the separation drum, the isolated CO ₂ absorbing solution in which to absorb the solution and the heat released from the regeneration column the second pre-heating, heating the third step with, CO ₂ absorbing solution from the regeneration column to flow into the upper end portion of the regeneration column in which glass the CO ₂ After that, the absorbent solution is regenerated, and the free CO ₂ and vaporized absorbent solution are cooled and condensed, separated from the separation drum, and some are refluxed to the regeneration tower, while the free gaseous CO ₂ is compressed and stored in the tank. 4th stage On the other hand, the CO ₂ and O ₂ liberated in the second step is recovered separately and cooled and condensed in a cooler, and then separated into the absorbed solution and free CO ₂ and O ₂ condensed in the separation drum, The separated CO ₂ is characterized in that it further comprises a fifth step of compression and storage with the CO ₂ separated in the regeneration tower.

Here, in the fifth step, the condensed absorbent solution separated from the separation drum is heat-exchanged with the absorbent solution regenerated at a high temperature in the regeneration tower to increase the temperature of the condensed absorbent solution, thereby preheating the primary with the absorbent solution emitted from the absorption tower. It is preferable to further include a sixth step of supplying to the absorption tower by lowering the temperature of the regenerated absorption solution.

The separation and recovery method of CO ₂ according to the present invention provides the following effects.

The CO ₂ in the exhaust gas containing the CO ₂ and O ₂ with a reduced cost, energy-efficient may also be separated and recovered in an environmentally.

Oxidative decomposition reaction of the amine-based compound according to the O ₂ is the higher the concentration of O _2, the higher the temperature it better occurs, the solubility of oxygen relative to the absorbent solution at a given temperature range is lowered the higher the temperature, the relatively low In the temperature range (e.g. around 50 ^o C to around 80 ^o C), do not mix the liberated O ₂ with the discharge gas at a relatively high temperature (e.g. around 100 ^o C) at the top of the regeneration tower. but, also the regeneration column that is driving the non-reacted residual o ₂ at a high temperature (for example, the upper end portion is 100 ^o C before and after the lower end 120 ^o C before and after) by not separating, cooling and recovering separately without entering, CO ₂ absorbing solution Consumption can be reduced, thereby reducing the cost of purchasing, using and discarding new absorbent solutions.

As such, by reducing the amount of chemicals used and the amount of waste, the effect of increasing the environmental friendliness of the CO ₂ absorption technology is also obtained.

In addition, by separately exchanging the cooled and condensed absorbent solution with the absorbent solution regenerated at a high temperature in the regeneration tower, the energy efficiency can be improved by increasing the temperature of the condensed absorbent solution and lowering the temperature of the regenerated absorbent solution. Therefore, additional energy costs can be saved.

For the above reason, the present invention enables to recover CO ₂ discharged to the atmosphere cost-effectively, energy-efficiently, environmentally friendly, and ultimately contribute to global warming prevention efforts.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

First, in order to effectively separate and recover CO ₂ from the exhaust gas containing CO ₂ and O ₂ , a brief look at the conventional chemical absorption method is as follows.

If the number of the CO ₂ by the conventional chemical absorption method separate group in the absorber - when the CO ₂ in the exhaust gas by the liquid contact and absorption in the absorption solution, the presence O ₂ is also dissolved in a small amount absorbing solution with the exhaust gas do.

At this time, the amount of O ₂ absorbed in the absorbent solution is less than 1% of the amount of CO ₂ absorbed, but since the new O ₂ is continuously dissolved in the absorbent solution during the repeated absorption-regeneration process, the CO ₂ absorption capacity of the absorbent solution continues to occur. This, in turn, has a significant impact on the performance degradation of the overall CO ₂ absorption system.

As shown in FIG. 1, the used absorbing solution discharged from the absorption tower 10 is preheated primarily in the heat exchanger 12a around 50 ° C., and thus absorbed as the temperature increases during the preheating process around 80 ° C. The dissolved CO ₂ in the solution begins to liberate, with O ₂ also liberated.

After the liberated gas is separated from the separation drum 13a, the gas is sent to the cooler 14a together with the separator gas discharged at a high temperature around 100 ° C at the upper end of the regeneration tower 11.

When the separator gas is cooled to about 50 ° C. through the cooler 14a, the vaporized absorption solution contained in the separator is condensed, and then separated from the separation drum 13b and returned to the regeneration tower.

At this time, O ₂ contained in the gas in the separation drum 13b is dissolved in the condensed absorption solution and flows into the high temperature regeneration tower (for example, the upper end is about 100 ° C. and the lower part is about 120 ° C.).

Oxidative decomposition reaction of the amine-based compound according to the O ₂ is the higher the concentration of O _2, takes place better the higher the temperature, the solubility of O ₂ for an absorbent solution at a given temperature range is lowered the higher the temperature, the conventional The compound absorption method separates the free O ₂ from the separation drum 13a while the temperature rises in the heat exchanger 12a (for example, from about 50 ° C to about 80 ° C), and then the high temperature in the regeneration tower 11. The amine system is brought into contact with the vaporized absorbent solution which has already reacted with the remaining O ₂ (for example, O _{2 which} is liberated while increasing the temperature between about 80 ° C. and about 120 ° C.) at a temperature of about 100 ° C. It can be seen that the oxidative degradation of the compounds occurs better.

In addition, the solubility of O ₂ in the absorbent solution in a given temperature range is increased as the temperature is lower, the conventional chemical absorption method is vaporized from the regeneration tower 11 of the O ₂ separated from the separation drum (13a) O ₂ unreacted with the absorbing solution is easily dissolved in the absorbing solution by contact with the relatively low temperature (eg, around 50 ° C) absorbing solution cooled and condensed in the cooler 14a, and the separation drum 13b. In the regeneration tower 11 and reacting with O ₂ and an amine compound at high temperature (for example, around 100 ° C. at the upper end and at about 120 ° C. at the lower end) to increase the CO ₂ absorption capacity of the absorption solution. Can be.

Based on the above matters can implement the carbon dioxide separation recovery method of the present invention.

The present invention provides the following two CO ₂ separation recovery method.

The first method of separating and recovering CO ₂ from the exhaust gas containing CO ₂ and O ₂ is to recover CO ₂ and O ₂ which are separated during the preheating process before the absorption solution absorbed by CO ₂ is regenerated in the regeneration tower. The present invention provides a method of reducing the CO ₂ absorption capacity due to oxidative decomposition of an absorbent solution at high temperature without mixing with the separator gas discharged at a high temperature from the upper end.

A method for separation and recovery of CO ₂ in the second CO ₂ and O ₂ is the exhaust gas included with, the CO ₂ and O ₂ to be separated in the course of pre-heating before the CO ₂ to regenerate the absorbed amine-based absorption solution from the regeneration column Instead of mixing with the separator gas discharged at high temperature from the upper part of the regeneration tower, the condensed absorbent solution is exchanged with the absorbed solution regenerated at high temperature in the regeneration tower to increase the temperature of the condensed absorbent solution. It provides a method of improving the energy efficiency by lowering the temperature of the absorbed solution.

Hereinafter, although the specific embodiment of this invention is described in FIG. 2, this invention is not limited to this embodiment, FIG. 2 has shown only main equipment, and attached equipment was abbreviate | omitted.

As shown in FIG. 2, the exhaust gas containing both CO ₂ and O ₂ is supplied to the absorption tower 10, and gas-liquid contact is performed to absorb CO ₂ in the exhaust gas into the absorption solution. O ₂ coexisted in the solution is also dissolved in a small amount of the absorbing solution.

At this time, the amount of O ₂ absorbed in the absorption solution is less than 1% of the CO ₂ absorption amount, and depends on conditions such as the concentration of O ₂ in the exhaust gas, the type and concentration of the absorption solution, and the reaction temperature of the absorption tower.

Absorption solution at about 50 ° C emitted from the absorption tower 10 is heated and regenerated at a temperature range of about 120 ° C in the regeneration tower 11 to be discharged, and is then absorbed through the heat exchanger 12b and the heat exchanger 12a. Preheated primarily by heat exchange at

As the temperature rises around 80 ° C. during the preheating process, CO ₂ dissolved in the absorbing solution is gradually released, and O ₂ is released together.

At this time, depending on conditions such as the concentration of O _{2 in the} exhaust gas, the type and concentration of the absorption solution, the reaction temperature of the absorption tower, and the like, 25 to 45% of the O ₂ dissolved in the absorption tower is liberated in the absorption solution.

The free CO ₂ and O ₂ are separated in the separation drum 13a, whereby the relatively high temperature (e.g. around 80 ° C) causes evaporation of the absorbent solution at the gas-liquid interface of the separation drum 13a. do.

In order to recover the evaporated absorption solution at this time, the separator gas is cooled and condensed in the cooler 14c connected to the upper side of the separating drum 13a, and then connected to the cooler 14c side. To a separate separation drum (13c).

Subsequently, the absorbing solution condensed in the separation drum 13c is separated and sent to the heat exchanger 12c, and the free CO ₂ and O ₂ are separated from the separation drum 13c, and CO ₂ at this time is the regeneration tower 11. Compress and store with CO ₂ separated from

Absorption solution condensed at a relatively low temperature (eg, about 40 ° C) in the heat exchanger 12c is relatively high temperature (eg, about 58 ° C) through the heat exchanger 12b and the heat exchanger 12a. Heat-exchanged with the regenerated absorption solution, and the temperature rises to around 51 ° C, and is then returned to the heat exchanger 12a together with the used absorption solution around 50 ° C discharged from the absorption tower 10.

Meanwhile, the regenerated absorption solution discharged from the regeneration tower 11 is cooled to about 45 ° C. while being heat-exchanged with the absorption liquid condensed in the heat exchanger 12c, and then recirculates 30 ° C. to be replenished to maintain a constant CO ₂ absorption capacity of the entire absorption system. It is supplied back to the absorption tower 10 with the new absorption solution of.

In addition, the CO ₂ absorbing solution (eg, CO ₂ absorbing solution from the condensed absorbing solution and the released absorbing solution) separated in the separating drum 13a may be regenerated and released from the regeneration tower 11. After the heat exchange in the heat exchanger (12b) to be secondarily preheated to a higher temperature, it is introduced into the upper end of the regeneration tower (11), in the regeneration tower (11) to heat the CO ₂ absorption solution at a temperature range around 120 ℃ ₂ is liberated and then discharged to the upper part of the regeneration tower 11, where the absorbent solution is regenerated and the vaporized absorbent solution discharged with the released CO ₂ is cooled and condensed in the cooler 14a, and subsequently separated. Separated from the drum (13b) and refluxed to the regeneration tower (11), the free gaseous CO ₂ is compressed and stored in the tank at high pressure.

The embodiment provided by the invention in the form of CO CO ₂ separated by a _second separation method for recovering chemical absorption method that can be applied to the recovery technique process principle in Fig. 2 not necessarily constrained to (device configuration), "CO ₂ and O ₂ is the higher the concentration of O ₂ in the exhaust gas are included with, and the higher the temperature may be any that meet only the requirements of absorption performance and separation and recovery of CO ₂ with absorbent to decrease the depth ", particularly It should not be limited to any process.

1 is a view showing the principle of a process for separating and recovering carbon dioxide in exhaust gas using a conventional chemical absorption method

2 is a view illustrating the principle of a process for separating and recovering carbon dioxide when carbon dioxide and oxygen are present together in exhaust gas according to the present invention.

<Description of the symbols for the main parts of the drawings>

10: absorption tower 11: regeneration tower

12a, 12b, 12c: heat exchanger 13a, 13b, 13c: separation drum

14a, 14b, 14c: Cooler 15: New absorbent liquid reservoir

16: absorber heater

Claims (2)

Supplying exhaust gas containing carbon dioxide to the absorption tower to absorb carbon dioxide into the absorption solution; A second step of preheating the carbon dioxide absorption solution emitted from the absorption tower and the absorption solution released from the regeneration tower by first preheating and separating the gases (carbon dioxide and oxygen) liberated from the carbon dioxide absorption solution in the separation drum; A third step of heat-exchanging the carbon dioxide absorbing solution separated from the separation drum with the absorbing solution discharged from the regeneration tower and preheating the secondary to the upper end of the regeneration tower; The carbon dioxide absorption solution is heated in the regeneration tower to liberate carbon dioxide. The absorption solution is regenerated, and the free carbon dioxide and vaporized absorption solution are cooled and condensed. A fourth step of compressing and storing the compressed gaseous carbon dioxide in a tank; In the separated recovery method of carbon dioxide comprising: After recovering the carbon dioxide and oxygen liberated in the second step separately and cooling and condensing in a cooler, and separated into the absorbing solution condensed in the separation drum and free carbon dioxide and oxygen, the separated carbon dioxide is separated from the regeneration tower Separation and recovery method of carbon dioxide characterized in that it further comprises a fifth step of compression storage with carbon dioxide. The method of claim 1, wherein the condensed absorbent solution separated from the separation drum is heat exchanged with the absorbent solution regenerated at a high temperature in the regeneration tower to increase the temperature of the condensed absorbent solution. Separation and recovery method of carbon dioxide characterized in that it further comprises a sixth step of supplying to the absorption tower by lowering the temperature of the pre-heated and regenerated absorption solution.

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