Patent Description:
Flue gas, which is generated through the combustion of fossil fuel in a boiler of a thermoelectric power plant or the like using a large amount of fossil fuel, contains CO<NUM>. A method of removing and recovering CO<NUM>, which is contained in flue gas, by bringing flue gas, which contains CO<NUM>, into gas-liquid contact with an amine-based CO<NUM> absorbent in a CO<NUM> absorber so that CO<NUM> is absorbed in the CO<NUM> absorbent, and a method of storing the recovered CO<NUM> without releasing the recovered CO<NUM> into the atmosphere have been energetically studied.

For example, there is used a method of making the CO<NUM> absorbent absorb CO<NUM>, which is contained in the flue gas, in the CO<NUM> absorber to remove CO<NUM> from the flue gas, regenerating the CO<NUM> absorbent by releasing CO<NUM>, which is absorbed in the CO<NUM> absorbent, in a regenerator, and reusing the CO<NUM> absorbent to remove CO<NUM> from flue gas by circulating the CO<NUM> absorbent in the CO<NUM> absorber again (for example, see Patent Literature <NUM>). In this case, the CO<NUM> absorbent absorbing CO<NUM> releases CO<NUM> by being heated with steam in the regenerator. As a result, highly-pure CO<NUM> is recovered.

Since a CO2 recovery device, which uses a method of absorbing, removing, and recovering CO<NUM> from gas, which contains CO<NUM>, such as flue gas, by using a CO<NUM> absorbent, is additionally installed on a combustion facility, the operating cost of the CO<NUM> recovery device should be reduced as much as possible. In particular, much thermal energy is consumed for the release of CO<NUM> in a regenerator of the CO<NUM> recovery device. Further, if the consumption of the CO<NUM> absorbent is large, the amount of a CO<NUM> absorbent to be additionally supplied is increased. Accordingly, the increase of operating cost is caused.

For this reason, there is demanded a CO<NUM> recovery device that improves CO<NUM> recovery efficiency, reduces the consumption of the CO<NUM> absorbent, and reduces operating cost when recovering CO<NUM> from the flue gas.

The invention has been made in consideration of the above-mentioned circumstances, and an object of the invention is to provide a CO<NUM> recovery device that efficiently recovers CO<NUM>, reduces the consumption of a CO<NUM> absorbent, and reduces operating cost.

According to a first aspect of the present invention in order to solve the above mentioned problems, there is provided a CO<NUM> recovery device according to claim <NUM>.

According to a second aspect of the present invention, there is provided the CO<NUM> recovery device according to claim <NUM>.

Further embodiments are provided in the dependent claims.

According to the CO<NUM> recovery device of the invention, it is possible to efficiently recover CO<NUM>, to reduce the consumption of a CO<NUM> absorbent, and to reduce operating cost.

The invention will be described in detail below with reference to the drawings. Meanwhile, the invention is not limited by the following forms that embody the invention (hereinafter, referred to as embodiments). Further, components of the following embodiments include components that can be easily supposed by those skilled in the art and substantially the same components, that is, components corresponding to a so-called equivalent range. Furthermore, components disclosed in the following embodiments may be appropriately combined with each other.

A CO<NUM> recovery device according to a first embodiment of the invention will be described with reference to the drawings. <FIG> is a diagram simply illustrating the structure of a CO<NUM> recovery device according to the first embodiment of the invention. As illustrated in <FIG>, the CO<NUM> recovery device <NUM> according to this embodiment includes a cooling unit <NUM>, a CO<NUM>-absorbing unit <NUM>, and an absorbent regenerating unit <NUM>. The cooling unit <NUM> cools flue gas 14A by bringing the flue gas 14A containing CO<NUM> into contact with water <NUM>, and is provided in a cooling tower <NUM>. Further, the CO<NUM>-absorbing unit <NUM> removes CO<NUM> from flue gas 14B by bringing the flue gas 14B into contact with a CO<NUM> absorbent (lean solution) <NUM> which absorbs CO<NUM>. In this embodiment, the CO<NUM>-absorbing unit <NUM> includes a cocurrent flow CO<NUM>-absorbing unit <NUM> that removes CO<NUM> from the flue gas 14B by bringing the flue gas 14B into contact with a CO<NUM> absorbent (semi-rich solution) <NUM>, which has absorbed CO<NUM>, in a cocurrent flow, and a countercurrent CO<NUM>-absorbing unit <NUM> that removes CO<NUM> from flue gas 14C by bringing the flue gas 14C into contact with the CO<NUM> absorbent <NUM> in a countercurrent flow. Furthermore, the absorbent regenerating unit <NUM> regenerates the CO<NUM> absorbent <NUM> by releasing CO<NUM> from a rich solution <NUM>, and is provided in an absorbent regenerator (hereinafter, referred to as a regenerator) <NUM>.

In this embodiment, the cocurrent flow CO<NUM>-absorbing unit <NUM> is provided in a cocurrent flow CO<NUM> absorber <NUM> and the countercurrent CO<NUM>-absorbing unit <NUM> is provided in a CO<NUM> absorber <NUM>.

In this embodiment, the CO<NUM>-absorbing unit <NUM> includes one cocurrent flow CO<NUM>-absorbing unit <NUM> and one countercurrent CO<NUM>-absorbing unit <NUM>. However, the CO<NUM>-absorbing unit <NUM> may include a plurality of cocurrent flow CO<NUM>-absorbing units <NUM> and one countercurrent CO<NUM>-absorbing unit <NUM>, may include one cocurrent flow CO<NUM>-absorbing unit <NUM> and a plurality of countercurrent CO<NUM>-absorbing units <NUM>, or may include a plurality of cocurrent flow CO<NUM>-absorbing units <NUM> and a plurality of countercurrent CO<NUM>-absorbing units <NUM>.

In the CO<NUM> recovery device <NUM>, the CO<NUM> absorbent <NUM>, which absorbs CO<NUM> contained in the flue gas 14A, circulates among the cocurrent flow CO<NUM> absorber <NUM>, the CO<NUM> absorber <NUM>, and the regenerator <NUM> (hereinafter, referred to as "in a system"). In this embodiment, the rich solution <NUM>, which has absorbed CO<NUM> contained in the flue gas 14B, is fed to the regenerator <NUM> from the cocurrent flow CO<NUM> absorber <NUM>. The CO<NUM> absorbent (lean solution) <NUM>, which is regenerated by removing almost all of CO<NUM> from the rich solution <NUM> in the regenerator <NUM>, is fed to the CO<NUM> absorber <NUM> from the regenerator <NUM>. The CO<NUM> absorbent (semi-rich solution) <NUM>, which has absorbed CO<NUM> remaining in the flue gas 14C, is fed to the cocurrent flow CO<NUM> absorber <NUM> from the CO<NUM> absorber <NUM>.

The flue gas 14A is gas that contains CO<NUM> discharged from industrial equipment, such as a boiler or a gas turbine. After the pressure of the flue gas 14A is increased by a flue gas blower or the like, the flue gas 14A is sent to the cooling tower <NUM>.

The cooling tower <NUM> is a tower that cools the flue gas 14A by water <NUM>. The cooling tower <NUM> includes spray nozzles <NUM> that spray the water <NUM> into the tower, and a cooling unit <NUM>. The flue gas 14A is cooled by coming into counterflow contact with the water <NUM> sprayed from the spray nozzles <NUM> in the cooling unit <NUM> of the cooling tower <NUM>.

The water <NUM> of which the temperature has become high by the heat exchange between the water <NUM> and the flue gas 14A is stored in the bottom of the cooling tower <NUM>. The water <NUM> stored in the bottom of the cooling tower <NUM> is extracted from the bottom of the cooling tower <NUM>, and is cooled by exchanging heat with cooling water <NUM> in a cooler <NUM>. Then, the water <NUM> is fed to the cooling tower <NUM>. Accordingly, the water <NUM> is circulated and used to cool the flue gas 14A.

The cooled flue gas 14B is discharged from the cooling tower <NUM> through a flue gas duct <NUM> that connects the cooling tower <NUM> to the CO<NUM> absorber <NUM>, and is fed to the CO<NUM>-absorbing unit <NUM>.

As described above, the CO<NUM>-absorbing unit <NUM> includes the cocurrent flow CO<NUM>-absorbing unit <NUM> and the countercurrent CO<NUM>-absorbing unit <NUM>. The flue gas 14B is fed to the cocurrent flow CO<NUM> absorber <NUM> including the cocurrent flow CO<NUM>-absorbing unit <NUM> and the CO<NUM> absorber <NUM> including the countercurrent CO<NUM>-absorbing unit <NUM> in this order.

The cocurrent flow CO<NUM> absorber <NUM> is provided between the cooling tower <NUM> including the cooling unit <NUM> and the CO<NUM> absorber <NUM>. In this embodiment, the cocurrent flow CO<NUM> absorber <NUM> including the cocurrent flow CO<NUM>-absorbing unit <NUM> is provided on the most upstream side in the flow direction of the flue gas 14B flowing in the CO<NUM>-absorbing unit <NUM>. The flue gas 14B discharged from the cooling tower <NUM> is fed to the cocurrent flow CO<NUM> absorber <NUM> through the flue gas duct <NUM>.

The cocurrent flow CO<NUM> absorber <NUM> is a tower that removes CO<NUM> from the flue gas 14B by bringing the flue gas 14B into contact with the semi-rich solution <NUM>, which is discharged from the CO<NUM> absorber <NUM>, in a cocurrent flow. The cocurrent flow CO<NUM> absorber <NUM> includes spray nozzles <NUM> and the cocurrent flow CO<NUM>-absorbing unit <NUM> that are provided in the tower. The spray nozzles <NUM> spray the semi-rich solution <NUM> downward. After the semi-rich solution <NUM> is discharged from the CO<NUM> absorber <NUM> through a semi-rich solution extraction line <NUM> and is cooled by exchanging heat with cooling water <NUM> in a cooler <NUM>, the semi-rich solution <NUM> is fed to the cocurrent flow CO<NUM> absorber <NUM>. Further, the flue gas 14B is supplied from the top of the cocurrent flow CO<NUM> absorber <NUM>, and flows in the tower toward the bottom of the tower.

Accordingly, since the semi-rich solution <NUM> is cooled before being supplied into the cocurrent flow CO<NUM> absorber <NUM>, the semi-rich solution <NUM> can further absorb CO<NUM>, which is contained in the flue gas 14B, in the cocurrent flow CO<NUM> absorber <NUM>. Therefore, it is possible to increase the concentration of CO<NUM> contained in the rich solution <NUM> that is stored in the bottom of the cocurrent flow CO<NUM> absorber <NUM>.

Further, since the semi-rich solution <NUM> is cooled before being supplied into the cocurrent flow CO<NUM> absorber <NUM>, the semi-rich solution <NUM> can lower the temperature of the flue gas 14C fed to the CO<NUM> absorber <NUM> by coming into contact with the flue gas 14B. For this reason, as described below, it is possible to increase the absorption amount of CO<NUM>, which is contained in the flue gas 14C, even in the CO<NUM> absorber <NUM>. Accordingly, it is possible to improve the absorption efficiency of CO<NUM>. Furthermore, since the temperature of the flue gas 14C fed to the CO<NUM> absorber <NUM> is lowered, the steam pressure of the absorbent of the lean solution <NUM> is reduced. Accordingly, it is possible to reduce the consumption of the absorbent. Moreover, the temperature of the absorbent rises due to the heat of reaction that is generated at the time of absorption of CO<NUM>, but the flue gas 14C is cooled on the upstream side of the CO<NUM> absorber <NUM>. Accordingly, the rise of the temperature of the absorbent is also suppressed, so that it is possible to suppress the degradation of the absorbent.

Further, in a CO<NUM> recovery device in the related art, a cooling tower <NUM> and a CO<NUM> absorber <NUM> have been connected to each other by a flue gas duct <NUM>. In contrast, the CO<NUM> recovery device <NUM> according to this embodiment is provided with the cocurrent flow CO<NUM> absorber <NUM> on the flue gas duct <NUM>. Accordingly, according to the CO<NUM> recovery device <NUM> of this embodiment, it is possible to effectively use an installation area since the cocurrent flow CO<NUM> absorber <NUM> is provided on the flue gas duct <NUM> of the CO<NUM> recovery device that has been already provided in the related art.

When the cross-sectional area of the cocurrent flow CO<NUM>-absorbing unit <NUM> is denoted by S1 and the cross-sectional area of the countercurrent CO<NUM>-absorbing unit <NUM> is denoted by S2, the cross-section ratio (S1/S2) of the cocurrent flow CO<NUM>-absorbing unit <NUM> is preferably <NUM> or less, more preferably <NUM> or less, and still more preferably <NUM> or less. Accordingly, since it is possible to suitably maintain a contact rate between the semi-rich solution <NUM> and the flue gas 14B in the cocurrent flow CO<NUM> absorber <NUM>, it is possible to maintain the absorption efficiency of CO<NUM> that is contained in the flue gas 14B. As a result, it is possible to reduce the amount of steam that is consumed by a regenerating superheater (reboiler) <NUM> of the regenerator <NUM>. Moreover, even though the cross-section ratio (S1/S2) of the cocurrent flow CO<NUM>-absorbing unit <NUM> is small, it is possible to suitably maintain the contact rate between the semi-rich solution <NUM> and the flue gas 14B in the cocurrent flow CO<NUM> absorber <NUM> by increasing the filling height of the cocurrent flow CO<NUM>-absorbing unit <NUM> as much as that. Therefore, it is possible to maintain the absorption efficiency of CO<NUM> that is contained in the flue gas 14B.

Further, the semi-rich solution <NUM> is previously cooled in the cooler <NUM> before being supplied to the cocurrent flow CO<NUM> absorber <NUM>. However, when the semi-rich solution <NUM> does not need to be cooled, the semi-rich solution <NUM> may not be cooled in the cooler <NUM>.

The flue gas 14C, which has come into gas-liquid contact with the semi-rich solution <NUM> in the cocurrent flow CO<NUM> absorber <NUM>, is sent to the CO<NUM> absorber <NUM> from the side wall of the bottom of the CO<NUM> absorber <NUM>.

Furthermore, the rich solution <NUM>, which has absorbed CO<NUM> contained in the flue gas 14B in the cocurrent flow CO<NUM>-absorbing unit <NUM>, is stored in the bottom of the cocurrent flow CO<NUM> absorber <NUM>. The rich solution <NUM> stored in the bottom of the cocurrent flow CO<NUM> absorber <NUM> is extracted from a rich solution feed line <NUM>; is pumped from the bottom of the cocurrent flow CO<NUM> absorber <NUM> by a rich solvent pump <NUM> that is provided outside; exchanges heat with the CO<NUM> absorbent <NUM>, which is regenerated in the regenerator <NUM>, in a rich/lean solution heat exchanger <NUM>; and is then supplied into the regenerator <NUM> from the side surface of the regenerator.

A part of the rich solution <NUM>, which is stored in the bottom of the cocurrent flow CO<NUM> absorber <NUM>, may be extracted from a rich solution extraction-branch line <NUM>, may be mixed to the semi-rich solution <NUM>, and may circulate in the cocurrent flow CO<NUM> absorber <NUM> so as to be used. Accordingly, since the rich solution <NUM> can remove CO<NUM> from the flue gas 14B by further absorbing CO<NUM>, which is contained in the flue gas 14B, in the cocurrent flow CO<NUM> absorber <NUM>, it is possible to further increase the concentration of CO<NUM> contained in the rich solution <NUM>. As a result, it is possible to reduce the amount of steam that is consumed by the reboiler <NUM>.

Further, when the flow rate of the semi-rich solution <NUM>, which is supplied to the cocurrent flow CO<NUM> absorber <NUM> from the CO<NUM> absorber <NUM>, is denoted by A1 and the flow rate of the rich solution <NUM>, where the rich solution <NUM> stored in the cocurrent flow CO<NUM> absorber <NUM> is supplied to the cocurrent flow CO<NUM> absorber <NUM> through the rich solution extraction-branch line <NUM>, is denoted by A2, a reflux ratio (A2/A1) of the rich solution <NUM> is in a range of <NUM> to <NUM>. Accordingly, it is possible to efficiently absorb CO<NUM>, which is contained in the flue gas 14B, while suitably maintaining the rich solution <NUM> that is fed to the regenerator <NUM> and regenerated.

The CO<NUM> absorber <NUM> is a tower that removes CO<NUM> from the flue gas 14C by bringing the flue gas 14C into contact with the CO<NUM> absorbent <NUM>. The CO<NUM> absorber <NUM> includes the countercurrent CO<NUM>-absorbing unit <NUM>, spray nozzles <NUM>, a water washing unit <NUM>, and a demister <NUM>. The flue gas 14C, which is fed into the CO<NUM> absorber <NUM>, flows in the tower toward the top of the tower from the bottom of the tower. The spray nozzle <NUM> is a nozzle that sprays the CO<NUM> absorbent <NUM> downward. In this embodiment, the countercurrent CO<NUM>-absorbing unit <NUM> is provided at the lower portion of the CO<NUM> absorber <NUM>.

The flue gas 14C, which rises in the tower, comes into contact with the CO<NUM> absorbent <NUM>, which contains, for example, a basic amine compound as a base, in a countercurrent flow in the countercurrent CO<NUM>-absorbing unit <NUM>. Accordingly, CO<NUM> contained in the flue gas 14C is absorbed in the CO<NUM> absorbent <NUM>.

The semi-rich solution <NUM>, which has absorbed CO<NUM> contained in the flue gas 14C in the countercurrent CO<NUM>-absorbing unit <NUM>, is stored in the bottom of the CO<NUM> absorber <NUM>. As described above, the semi-rich solution <NUM>, which is stored in the bottom of the CO<NUM> absorber <NUM>, is extracted from the semi-rich solution extraction line <NUM>, is fed to the cocurrent flow CO<NUM> absorber <NUM>, and absorbs CO<NUM>, which is contained in the flue gas 14B, by coming into contact with the flue gas 14B in a cocurrent flow.

Furthermore, the water washing unit <NUM> and the demister <NUM> are provided on the downstream side in the CO<NUM> absorber <NUM> in the flow direction of the flue gas 14C. In this embodiment, the water washing unit <NUM> and the demister <NUM> are provided above the countercurrent CO<NUM>-absorbing unit <NUM> in the tower. After the CO<NUM> absorbent <NUM> contained in CO<NUM>-removed flue gas <NUM>, from which CO<NUM> has been removed in the countercurrent CO<NUM>-absorbing unit <NUM>, is removed from the CO<NUM>-removed flue gas <NUM> in the water washing unit <NUM> and the demister <NUM>, the CO<NUM>-removed flue gas <NUM> is released to the outside of the system from the top of the CO<NUM> absorber <NUM>.

Water <NUM>, which is supplied from the outside, is sprayed in the water washing unit <NUM> from spray nozzles <NUM>, so that impurities contained in the CO<NUM>-removed flue gas <NUM> are removed in the water washing unit <NUM>. After the water <NUM>, which is sprayed from the spray nozzles <NUM>, is recovered by a receiving unit <NUM>, is fed to the outside of the tower by a pump <NUM>, and is cooled in a cooler <NUM> by cooling water <NUM>, the water <NUM> is fed to the spray nozzles <NUM> so as to be used while circulating.

In this embodiment, the CO<NUM>-absorbing unit <NUM> includes one cocurrent flow CO<NUM>-absorbing unit <NUM> and one countercurrent CO<NUM>-absorbing unit <NUM>. However, this embodiment is not limited thereto, and the CO<NUM>-absorbing unit <NUM> may include a plurality of cocurrent flow CO<NUM>-absorbing units <NUM> and one countercurrent CO<NUM>-absorbing unit <NUM>, may include one cocurrent flow CO<NUM>-absorbing unit <NUM> and a plurality of countercurrent CO<NUM>-absorbing units <NUM>, or may include a plurality of cocurrent flow CO<NUM>-absorbing units <NUM> and a plurality of countercurrent CO<NUM>-absorbing units <NUM>.

In this embodiment, the CO<NUM> absorber <NUM> includes one countercurrent CO<NUM>-absorbing unit <NUM> that is provided therein. However, the CO<NUM> absorber <NUM> may include a plurality of cocurrent flow CO<NUM>-absorbing units <NUM> and one countercurrent CO<NUM>-absorbing unit <NUM> that are provided therein, may include one cocurrent flow CO<NUM>-absorbing unit <NUM> and a plurality of countercurrent CO<NUM>-absorbing units <NUM> that are provided therein, or may include a plurality of cocurrent flow CO<NUM>-absorbing units <NUM> and a plurality of countercurrent CO<NUM>-absorbing units <NUM> that are provided therein.

<FIG> is a diagram simply illustrating another structure of the CO<NUM> recovery device according to this embodiment. The CO<NUM> absorber <NUM> may have two stages of countercurrent CO<NUM>-absorbing units <NUM>-<NUM> and <NUM>-<NUM> as illustrated in <FIG>, or may have three or more stages. If the CO<NUM> absorber <NUM> is provided with the countercurrent CO<NUM>-absorbing units <NUM>-<NUM> and <NUM>-<NUM>, a semi-rich solution 24B, which has absorbed CO<NUM> remaining in the flue gas 14C after the lean solution <NUM> is sprayed from spray nozzles <NUM>-<NUM> and passes through the countercurrent CO<NUM>-absorbing unit <NUM>-<NUM>, is stored in a receiving unit <NUM>. Subsequently, after the semi-rich solution 24B, which is stored in the receiving unit <NUM>, is cooled in a cooler <NUM> by cooling water <NUM>, the semi-rich solution 24B is sprayed from spray nozzles <NUM>-<NUM> and passes through the countercurrent CO<NUM>-absorbing unit <NUM>-<NUM>, so that the semi-rich solution 24B is changed into a semi-rich solution 24A. The semi-rich solution 24A is stored in the bottom of the CO<NUM> absorber <NUM>.

In this case, this embodiment is not limited to a case where the semi-rich solution 24B, which has absorbed CO<NUM> in the countercurrent CO<NUM>-absorbing unit <NUM>-<NUM>, is supplied to the countercurrent CO<NUM>-absorbing unit <NUM>-<NUM> and the semi-rich solution 24A, which has absorbed CO<NUM> in the countercurrent CO<NUM>-absorbing unit <NUM>-<NUM>, is supplied to the cocurrent flow CO<NUM>-absorbing unit <NUM>. The rich solution <NUM> that has absorbed CO<NUM> in the cocurrent flow CO<NUM>-absorbing unit <NUM>, and the semi-rich solutions 24A and 24B that have absorbed CO<NUM> in the countercurrent CO<NUM>-absorbing units <NUM>-<NUM> and <NUM>-<NUM>, respectively, may be supplied to the cocurrent flow CO<NUM>-absorbing unit <NUM> and any one or both of the countercurrent CO<NUM>-absorbing units <NUM>-<NUM> and <NUM>-<NUM> again after being cooled.

Further, the rich solution <NUM>, which is stored in the bottom of the cocurrent flow CO<NUM> absorber <NUM> as illustrated in <FIG>, is supplied to the regenerator <NUM> as described above. The regenerator <NUM> is a tower that includes the absorbent regenerating unit <NUM> and regenerates the rich solution <NUM> as the lean solution <NUM> by releasing CO<NUM> from the rich solution <NUM>. The rich solution <NUM>, which is released into the regenerator <NUM> from the top of the regenerator <NUM>, is heated by steam <NUM> that is supplied from the bottom of the regenerator <NUM>. The steam <NUM> is generated by the heat exchange between the lean solution <NUM> and saturated steam <NUM> in the regenerating superheater (reboiler) <NUM>. The rich solution <NUM> absorbs heat by being heated by the steam <NUM>, so that most of CO<NUM> contained in the rich solution <NUM> is released. When reaching the bottom of the regenerator <NUM>, the rich solution <NUM> is changed into the CO<NUM> absorbent (lean solution) <NUM> from which almost all CO<NUM> has been removed.

After the lean solution <NUM>, which is stored in the bottom of the regenerator <NUM>, is fed as a CO<NUM> absorbent by a lean solvent pump <NUM> and is cooled in a lean solvent cooler <NUM> by the heat exchange with cooling water <NUM>, the lean solution <NUM> is fed to the CO<NUM> absorber <NUM>.

Meanwhile, CO<NUM> gas <NUM> containing vapor is released from the top of the regenerator <NUM>. After the CO<NUM> gas <NUM> containing vapor is discharged from the top of the regenerator <NUM>, vapor contained in the CO<NUM> gas <NUM> is condensed in a condenser <NUM> by cooling water <NUM>, and water <NUM> is separated by a separation drum <NUM>. After that, CO<NUM> gas <NUM> is released to the outside of the system and is recovered. Further, the water <NUM>, which is separated by the separation drum <NUM>, is supplied to the upper portion of the regenerator <NUM> by a condensed water circulating pump <NUM>.

As described above, the CO<NUM> recovery device <NUM> according to this embodiment includes the cocurrent flow CO<NUM> absorber <NUM> that includes the cocurrent flow CO<NUM>-absorbing unit <NUM> and is provided between the cooling tower <NUM> and the CO<NUM> absorber <NUM>, and uses the semi-rich solution <NUM>, which has absorbed CO<NUM> contained in the flue gas 14C in the CO<NUM> absorber <NUM>, as an absorbent that further absorbs CO<NUM> contained in the flue gas 14B in the cocurrent flow CO<NUM> absorber <NUM>. Accordingly, it is possible to increase the concentration of CO<NUM> contained in the rich solution <NUM> that is stored in the bottom of the cocurrent flow CO<NUM> absorber <NUM>. Moreover, since the semi-rich solution <NUM> is previously cooled before being supplied into the cocurrent flow CO<NUM> absorber <NUM>, it is possible to lower the temperature of the flue gas 14C that is fed to the CO<NUM> absorber <NUM>. For this reason, it is also possible to increase the absorption amount of CO<NUM>, which is contained in the flue gas 14C, in the CO<NUM> absorber <NUM> and to reduce the consumption of the absorbent. In addition, since it is possible to provide the cocurrent flow CO<NUM> absorber <NUM> on the flue gas duct <NUM> of the CO<NUM> recovery device that has been already provided, it is possible to effectively use an installation area.

Accordingly, since it is possible to efficiently use steam required for releasing CO<NUM>, which is contained in the CO<NUM> absorbent <NUM>, in the regenerator <NUM> without the waste of steam, it is possible to increase the operating efficiency of the CO<NUM> recovery device <NUM>.

Meanwhile, the CO<NUM> recovery device <NUM> according to this embodiment is adapted so that the countercurrent CO<NUM>-absorbing unit <NUM> is provided in the CO<NUM> absorber <NUM>.

A CO<NUM> recovery device according to a second embodiment of the invention will be described with reference to the drawings. Since the structure of the CO<NUM> recovery device according to this embodiment is the same as the structure of the above-mentioned CO<NUM> recovery device illustrated in <FIG>, a diagram illustrating the structure of the CO<NUM> recovery device will not be provided and description will be made using only drawings illustrating the structure of a cooling tower and a CO<NUM> absorber. Meanwhile, the same members as the members of the CO<NUM> recovery device illustrated in <FIG> and <FIG> are denoted by the same reference numerals and the description thereof will not be made. Further, a case where two countercurrent CO<NUM>-absorbing units <NUM> are provided as illustrated in <FIG> will be described in this embodiment.

<FIG> is a diagram simply illustrating a part of the structure of the CO<NUM> recovery device according to the second embodiment of the invention. As illustrated in <FIG>, the CO<NUM> recovery device according to this embodiment has a structure where the CO<NUM> recovery device according to the first embodiment illustrated in <FIG> further includes a countercurrent CO<NUM>-absorbing unit <NUM> provided on the most upstream side in the flow direction of the flue gas 14B. That is, the CO<NUM> recovery device according to the embodiment includes countercurrent CO<NUM>-absorbing units <NUM>-<NUM> and <NUM>-<NUM> that are provided in the CO<NUM> absorber <NUM>, the cocurrent flow CO<NUM> absorber <NUM> that is provided between the cooling tower <NUM> and the CO<NUM> absorber <NUM>, and the countercurrent CO<NUM>-absorbing unit <NUM> that is provided on the downstream side of the cooling unit <NUM>, which is provided in the cooling tower <NUM>, in the gas flow direction (in an upper portion of the tower).

The cooling tower <NUM> includes spray nozzles <NUM> and the countercurrent CO<NUM>-absorbing unit <NUM> that are provided therein. The countercurrent CO<NUM>-absorbing unit <NUM> removes CO<NUM> from the flue gas 14B by bringing the cooled flue gas 14B into contact with a rich solution 18A, which is discharged from the cocurrent flow CO<NUM> absorber <NUM>, in a countercurrent flow.

The spray nozzles <NUM> spray the rich solution 18A downward. After the rich solution 18A is discharged from the cocurrent flow CO<NUM> absorber <NUM> through a rich solution extraction line <NUM> and is cooled in a cooler <NUM> by the heat exchange with cooling water <NUM>, the rich solution 18A is fed to the countercurrent CO<NUM>-absorbing unit <NUM>.

The countercurrent CO<NUM>-absorbing unit <NUM> is provided on the downstream side of the cooling unit <NUM> in the gas flow direction. In this embodiment, the countercurrent CO<NUM>-absorbing unit <NUM> is provided above the cooling unit <NUM> of the cooling tower <NUM>. For this reason, the flue gas 14B, which is cooled in the cooling unit <NUM> of the cooling tower <NUM>, flows to the countercurrent CO<NUM>-absorbing unit <NUM>.

After coming into contact with the cooled flue gas 14B in the countercurrent CO<NUM>-absorbing unit <NUM>, the rich solution 18B is stored in a receiving unit <NUM>.

The flue gas 14B, which is supplied to the countercurrent CO<NUM>-absorbing unit <NUM>, comes into counterflow contact with the rich solution 18A in the countercurrent CO<NUM>-absorbing unit <NUM>. The rich solution 18A absorbs CO<NUM>, which is contained in the flue gas 14B, by coming into counterflow contact with the flue gas 14B in the cocurrent flow CO<NUM> absorber <NUM>. Accordingly, it is possible to remove CO<NUM> from the flue gas 14B.

The rich solution 18B is stored in the receiving unit <NUM> after coming into contact with the cooled flue gas 14B in the countercurrent CO<NUM>-absorbing unit <NUM>. However, the rich solution 18B, which is stored in the receiving unit <NUM>, is extracted from a rich solution feed line <NUM>, and is supplied to the regenerator <NUM>.

The CO<NUM> recovery device according to this embodiment uses the semi-rich solution 24A, which is discharged from the CO<NUM> absorber <NUM>, as an absorbent that absorbs CO<NUM> contained in flue gas 14C-<NUM> in the cocurrent flow CO<NUM> absorber <NUM>. Further, the CO<NUM> recovery device uses the rich solution 18A, which is discharged from the cocurrent flow CO<NUM> absorber <NUM>, as an absorbent that further absorbs CO<NUM> contained in the flue gas 14B in the cooling tower <NUM>. That is, the rich solution 18A is an absorbent that has absorbed CO<NUM> contained in the flue gas 14C-<NUM> in the cocurrent flow CO<NUM> absorber <NUM> and has absorbed CO<NUM> contained in flue gas 14C-<NUM> in the CO<NUM> absorber <NUM>. For this reason, it is possible to further increase the concentration of CO<NUM> contained in the rich solution 18B, which is stored in the receiving unit <NUM> of the cooling tower <NUM>, by using the rich solution 18A as an absorbent that further absorbs CO<NUM> contained in the flue gas 14B in the countercurrent CO<NUM>-absorbing unit <NUM>.

A part of the rich solution 18B, which is stored in the receiving unit <NUM>, may be extracted from a rich solution extraction-branch line <NUM>, may be mixed to the rich solution 18A, and may circulate in the countercurrent CO<NUM>-absorbing unit <NUM> so as to be used. Accordingly, since the rich solution 18A can remove CO<NUM> from the flue gas 14B by further absorbing CO<NUM>, which is contained in the flue gas 14B, in the countercurrent CO<NUM>-absorbing unit <NUM>, it is possible to further increase the concentration of CO<NUM> contained in the rich solution 18B.

Moreover, as for the flow rate A3 of the rich solution 18A that is supplied to the cooling tower <NUM> from the cocurrent flow CO<NUM> absorber <NUM> and the flow rate A4 of the rich solution 18B, where the rich solution 18B stored in the cooling tower <NUM> is supplied to the cooling tower <NUM> through the rich solution extraction-branch line <NUM>, a reflux ratio (A4/A3) of the rich solution 18B is preferably in a range of <NUM> to <NUM> and more preferably in a range of <NUM> to <NUM>. Accordingly, it is possible to absorb CO<NUM>, which is contained in the flue gas 14B, while suitably maintaining the rich solution 18B that is fed to the regenerator <NUM> and regenerated.

Further, since the rich solution 18A is cooled before being supplied into the cooling tower <NUM>, the rich solution 18A can lower the temperature of the flue gas 14C-<NUM> fed to the CO<NUM> absorber <NUM> by coming into contact with the flue gas 14B. Furthermore, since the semi-rich solution 24A is also cooled before being supplied into the cocurrent flow CO<NUM> absorber <NUM>, the semi-rich solution 24A also can lower the temperature of the flue gas 14C-<NUM> that is fed to the CO<NUM> absorber <NUM>. For this reason, it is possible to increase the absorption amount of CO<NUM>, which is contained in the flue gas 14C, in the CO<NUM> absorber <NUM>. Accordingly, it is possible to improve the absorption efficiency of CO<NUM> and to reduce the consumption of the absorbent.

In addition, since the CO<NUM> recovery device according to this embodiment is provided with the cocurrent flow CO<NUM> absorber <NUM> on the flue gas duct <NUM> of the CO<NUM> recovery device having been already provided and is provided with the countercurrent CO<NUM>-absorbing unit <NUM> on the downstream side in the cooling tower <NUM> in the gas flow direction (in an upper portion of the tower), it is possible to effectively use an installation area.

As described above, according to the CO<NUM> recovery device of this embodiment, since it is possible to improve the absorption efficiency of CO<NUM>, which is contained in the flue gas 14A, into a CO<NUM> absorbent <NUM> and to reduce the consumption of the absorbent contained in the CO<NUM> absorbent <NUM>, it is possible to efficiently use the CO<NUM> absorbent <NUM>. Accordingly, since it is possible to efficiently use steam required for releasing CO<NUM>, which is contained in the CO<NUM> absorbent <NUM>, in the regenerator <NUM> without the waste of steam, it is possible to further increase the operating efficiency of the CO<NUM> recovery device. Further, it is also possible to more effectively apply this embodiment to the device that has been already provided.

Next, the test results of the reduction rate of the amount of steam, which is consumed by the reboiler when the CO<NUM> recovery device according to this embodiment is used, will be described.

When the cocurrent flow CO<NUM> absorber <NUM> was provided between the cooling tower <NUM> and the CO<NUM> absorber <NUM> as in the CO<NUM> recovery device <NUM> according to the first embodiment of the invention illustrated in <FIG>, the reduction rate of the amount of steam consumed by the reboiler <NUM> was examined in each of a case where the height of the cocurrent flow CO<NUM>-absorbing unit <NUM> of the cocurrent flow CO<NUM> absorber <NUM> was changed, a case where the reflux ratio (A2/A1) of the semi-rich solution <NUM> circulating in the cocurrent flow CO<NUM> absorber <NUM> was changed, and a case where the cross-section ratio (S1/S2) between the cocurrent flow CO<NUM> absorber <NUM> and the CO<NUM> absorber <NUM> was changed. Hereinafter, description will be made with reference to the CO<NUM> recovery device <NUM> according to the first embodiment of the invention illustrated in <FIG>.

<FIG> is a diagram illustrating a relation between the filling height of the cocurrent flow CO<NUM>-absorbing unit <NUM> of the cocurrent flow CO<NUM> absorber <NUM> and the reduction rate of the amount of steam that is consumed by the reboiler <NUM>. Meanwhile, Comparative Example <NUM> is a test example where the filling height of the countercurrent CO<NUM>-absorbing unit <NUM> of the CO<NUM> absorber <NUM> is <NUM>% in a CO<NUM> recovery device in the related art without the cocurrent flow CO<NUM> absorber <NUM>. In Comparative Example <NUM>, the amount of steam consumed by the reboiler <NUM> was a reference value (<NUM>%). Example <NUM>-<NUM> is a test example where the filling height of the cocurrent flow CO<NUM>-absorbing unit <NUM> of the cocurrent flow CO<NUM> absorber <NUM> is <NUM>% when the filling height of the countercurrent CO<NUM>-absorbing unit <NUM> of the CO<NUM> absorber <NUM> is <NUM>%. Example <NUM>-<NUM> is a test example where the height of the cocurrent flow CO<NUM>-absorbing unit <NUM> of the cocurrent flow CO<NUM> absorber <NUM> is <NUM>% when the height of the countercurrent CO<NUM>-absorbing unit <NUM> of the CO<NUM> absorber <NUM> is <NUM>%. Example <NUM>-<NUM> is a test example where the height of the cocurrent flow CO<NUM>-absorbing unit <NUM> of the cocurrent flow CO<NUM> absorber is <NUM>% when the height of the countercurrent CO<NUM>-absorbing unit <NUM> of the CO<NUM> absorber <NUM> is <NUM>%. In all of Examples <NUM>-<NUM> to <NUM>-<NUM>, the reflux ratio (A2/A1) of the rich solution <NUM> between the flow rate A1 of the semi-rich solution <NUM>, which is supplied to the cocurrent flow CO<NUM> absorber <NUM> from the CO<NUM> absorber <NUM>, and the flow rate A2 of the rich solution <NUM>, where the rich solution <NUM> stored in the cocurrent flow CO<NUM> absorber <NUM> is supplied to the cocurrent flow CO<NUM> absorber <NUM> through the rich solution extraction-branch line <NUM>, was <NUM> and the cross-section ratio (S1/S2) of the cocurrent flow CO<NUM>-absorbing unit <NUM> between the cross-sectional area S1 of the cocurrent flow CO<NUM>-absorbing unit <NUM> and the cross-sectional area S2 of the countercurrent CO<NUM>-absorbing unit <NUM> was <NUM>.

As illustrated in <FIG>, the reduction rate of the amount of steam consumed by the reboiler <NUM> was increased as the filling height of the cocurrent flow CO<NUM>-absorbing unit <NUM> of the cocurrent flow CO<NUM> absorber <NUM> was increased. Accordingly, when the cocurrent flow CO<NUM> absorber <NUM> is provided on the flue gas duct <NUM>, it is possible to increase the reduction rate of the amount of steam consumed by the reboiler <NUM> as the filling height of the cocurrent flow CO<NUM>-absorbing unit <NUM> of the cocurrent flow CO<NUM> absorber <NUM> is increased.

<FIG> is a diagram illustrating a relation between the reflux ratio (A2/A1) of the semi-rich solution <NUM> where the semi-rich solution <NUM> is circulated again in the cocurrent flow CO<NUM> absorber <NUM> and the reduction rate of the amount of steam that is consumed by the reboiler <NUM>. Meanwhile, Comparative Example <NUM> is a test example where the filling height of the countercurrent CO<NUM>-absorbing unit <NUM> of the CO<NUM> absorber <NUM> is <NUM>% in the CO<NUM> recovery device in the related art without the cocurrent flow CO<NUM> absorber <NUM> as in Comparative Example <NUM>. In Comparative Example <NUM>, the amount of steam consumed by the reboiler <NUM> was a reference value (<NUM>%). Each of Examples <NUM>-<NUM> to <NUM>-<NUM> is a test example where the height of the cocurrent flow CO<NUM>-absorbing unit <NUM> of the cocurrent flow CO<NUM> absorber <NUM>, when the height of the countercurrent CO<NUM>-absorbing unit <NUM> of the CO<NUM> absorber <NUM> is <NUM>%, is <NUM>% so that the cross-section ratio (S1/S2) is <NUM>. In Example <NUM>-<NUM>, the reflux ratio of the semi-rich solution <NUM> was <NUM>. In Example <NUM>-<NUM>, the reflux ratio of the semi-rich solution <NUM> was <NUM>. In Example <NUM>-<NUM>, the reflux ratio of the semi-rich solution <NUM> was <NUM>.

As illustrated in <FIG>, the reduction rate of the amount of steam consumed by the reboiler <NUM> was increased as the reflux ratio (A2/A1) of the rich solution <NUM> circulated in the cocurrent flow CO<NUM> absorber <NUM> was increased. Accordingly, when the cocurrent flow CO<NUM> absorber <NUM> is provided on the flue gas duct <NUM>, it is possible to increase the reduction rate of the amount of steam consumed by the reboiler <NUM> as the reflux ratio of the rich solution <NUM> circulated in the cocurrent flow CO<NUM> absorber <NUM> is increased.

<FIG> is a diagram illustrating a relation between the cross-section ratio of the cocurrent flow CO<NUM> absorber <NUM> and the reduction rate of the amount of steam that is consumed by the reboiler <NUM>. Meanwhile, Comparative Example <NUM> is a test example where the filling height of the countercurrent CO<NUM>-absorbing unit <NUM> of the CO<NUM> absorber <NUM> is <NUM>% in the CO<NUM> recovery device in the related art without the cocurrent flow CO<NUM> absorber <NUM> as in Comparative Examples <NUM> and <NUM>. Each of Examples <NUM>-<NUM> to <NUM>-<NUM> is a test example where the height of the cocurrent flow CO<NUM>-absorbing unit <NUM> of the cocurrent flow CO<NUM> absorber <NUM>, when the filling height of the countercurrent CO<NUM>-absorbing unit <NUM> of the CO<NUM> absorber <NUM> is <NUM>%, is <NUM>% so that the reflux ratio (A2/A1) of the rich solution <NUM> is <NUM>. In Example <NUM>-<NUM>, the cross-section ratio (S1/S2) of the cocurrent flow CO<NUM>-absorbing unit <NUM> was <NUM>. In Example <NUM>-<NUM>, the cross-section ratio (S1/S2) of the cocurrent flow CO<NUM>-absorbing unit <NUM> was <NUM>. In example <NUM>-<NUM>, the cross-section ratio (S1/S2) of the cocurrent flow CO<NUM>-absorbing unit <NUM> was <NUM>.

As illustrated in <FIG>, when the cross-section ratio (S1/S2) of the cocurrent flow CO<NUM>-absorbing unit <NUM> was <NUM> or <NUM>, the reduction rate of the amount of steam consumed by the reboiler <NUM> was large as compared to when the cross-section ratio (S1/S2) of the cocurrent flow CO<NUM>-absorbing unit <NUM> is <NUM>. The reduction rate of the amount of steam consumed by the reboiler <NUM> when the cross-section ratio (S1/S2) of the cocurrent flow CO<NUM>-absorbing unit <NUM> was <NUM> was substantially the same as that when the cross-section ratio (S1/S2) of the cocurrent flow CO<NUM>-absorbing unit <NUM> was <NUM>. Accordingly, when the cocurrent flow CO<NUM> absorber <NUM> is provided on the flue gas duct <NUM>, it is possible to increase the reduction rate of the amount of steam, which is consumed by the reboiler <NUM>, by making the cross-section ratio (S1/S2) of the cocurrent flow CO<NUM>-absorbing unit <NUM> larger than <NUM>.

<FIG> is a diagram illustrating a relation between a case where the cross-section ratio (S1/S2) of the cocurrent flow CO<NUM>-absorbing unit <NUM> and the filling height of the cocurrent flow CO<NUM>-absorbing unit <NUM> are changed, and the reduction rate of the amount of steam that is consumed by the reboiler <NUM>. Example <NUM>-<NUM> is a test example where the height of the cocurrent flow CO<NUM>-absorbing unit <NUM> of the cocurrent flow CO<NUM> absorber <NUM> is <NUM>%, the reflux ratio (A2/A1) of the rich solution <NUM> is <NUM>, and the cross-section ratio (S1/S2) of the cocurrent flow CO<NUM>-absorbing unit <NUM> is <NUM> when the height of the countercurrent CO<NUM>-absorbing unit <NUM> of the CO<NUM> absorber <NUM> is <NUM>%.

As illustrated in <FIG>, when the cross-section ratio (S1/S2) of the cocurrent flow CO<NUM>-absorbing unit <NUM> was <NUM>, the reduction rate of the amount of steam consumed by the reboiler <NUM> was small as compared to when the cross-section ratio (S1/S2) of the cocurrent flow CO<NUM>-absorbing unit <NUM> is <NUM>. However, when the filling height of the cocurrent flow CO<NUM>-absorbing unit <NUM> was increased, the reduction rate of the amount of steam consumed by the reboiler <NUM> was increased as compared to when the cross-section ratio (S1/S2) of the cocurrent flow CO<NUM>-absorbing unit <NUM> was <NUM>. Accordingly, when the cocurrent flow CO<NUM> absorber <NUM> is provided on the flue gas duct <NUM> and the cross-section ratio (S1/S2) of the cocurrent flow CO<NUM>-absorbing unit <NUM> is small, it is possible to increase the reduction rate of the amount of steam, which is consumed by the reboiler <NUM>, by making the filling height of the cocurrent flow CO<NUM>-absorbing unit <NUM> high.

<FIG> is a diagram illustrating a relation between the filling height of the cocurrent flow CO<NUM>-absorbing unit <NUM> of the cocurrent flow CO<NUM> absorber <NUM> and the reduction rate of the amount of steam that is consumed by the reboiler <NUM>. Meanwhile, Comparative Example <NUM>-<NUM> is a test example where the filling height of the countercurrent CO<NUM>-absorbing unit <NUM> of the CO<NUM> absorber <NUM> is <NUM>% in the CO<NUM> recovery device in the related art without the cocurrent flow CO<NUM> absorber <NUM> as in Comparative Example <NUM>. In Comparative Example <NUM>-<NUM>, the amount of steam consumed by the reboiler <NUM> was a reference value (<NUM>%). Comparative Example <NUM>-<NUM> is a test example where the countercurrent CO<NUM>-absorbing unit <NUM> of the CO<NUM> absorber <NUM> is formed in two stages and the sum of the filling heights of the countercurrent CO<NUM>-absorbing units <NUM>-<NUM> and <NUM>-<NUM> is <NUM>% in the CO<NUM> recovery device in the related art without the cocurrent flow CO<NUM> absorber <NUM>. Example <NUM>-<NUM> is a test example where the filling height of the cocurrent flow CO<NUM>-absorbing unit <NUM> is <NUM>% when the sum of the filling heights of the countercurrent CO<NUM>-absorbing units <NUM>-<NUM> and <NUM>-<NUM> of the CO<NUM> absorber <NUM> is <NUM>%. Example <NUM>-<NUM> is a test example where the filling height of the cocurrent flow CO<NUM>-absorbing unit <NUM> is <NUM>% when the sum of the filling heights of the countercurrent CO<NUM>-absorbing units <NUM>-<NUM> and <NUM>-<NUM> of the CO<NUM> absorber <NUM> is <NUM>%. Example <NUM>-<NUM> is a test example where the filling height of the cocurrent flow CO<NUM>-absorbing unit <NUM> is <NUM>% when the sum of the filling heights of the countercurrent CO<NUM>-absorbing units <NUM>-<NUM> and <NUM>-<NUM> of the CO<NUM> absorber <NUM> is <NUM>%. Further, in all of Examples <NUM>-<NUM> to <NUM>-<NUM> and Comparative Example <NUM>-<NUM>, the filling height of the countercurrent CO<NUM>-absorbing unit <NUM>-<NUM> was <NUM>% and the filling height of the countercurrent CO<NUM>-absorbing unit <NUM>-<NUM> was <NUM>%. Furthermore, in all of Examples <NUM>-<NUM> to <NUM>-<NUM> and Comparative Examples <NUM>-<NUM> and <NUM>-<NUM>, the reflux ratio (A2/A1) of the rich solution <NUM> was <NUM> and the cross-section ratio (S1/S2) of the cocurrent flow CO<NUM>-absorbing unit <NUM> was <NUM>.

As illustrated in <FIG>, when the CO<NUM> absorber <NUM> included the countercurrent CO<NUM>-absorbing units <NUM>-<NUM> and <NUM>-<NUM> so that the countercurrent CO<NUM>-absorbing unit <NUM> of the CO<NUM> absorber <NUM> was formed in two stages, the reduction rate of the amount of steam consumed by the reboiler <NUM> was increased as compared to when the CO<NUM> absorber <NUM> included the countercurrent CO<NUM>-absorbing unit <NUM> so that the countercurrent CO<NUM>-absorbing unit <NUM> of the CO<NUM> absorber <NUM> was formed in one stage (see Comparative Examples <NUM>-<NUM> and <NUM>-<NUM>). Moreover, when the countercurrent CO<NUM>-absorbing unit <NUM> of the CO<NUM> absorber <NUM> was formed in two stages and the cocurrent flow CO<NUM> absorber <NUM> was provided on the flue gas duct <NUM> as in Example <NUM>-<NUM>, the reduction rate of the amount of steam consumed by the reboiler <NUM> was further increased. Further, as in Examples <NUM>-<NUM> to <NUM>-<NUM>, the reduction rate of the amount of steam consumed by the reboiler <NUM> was increased as the filling height of the cocurrent flow CO<NUM>-absorbing unit <NUM> of the cocurrent flow CO<NUM> absorber <NUM> was increased. Accordingly, when the countercurrent CO<NUM>-absorbing unit <NUM> of the CO<NUM> absorber <NUM> is formed in a plurality of stages and the cocurrent flow CO<NUM> absorber <NUM> is provided on the flue gas duct <NUM>, it is possible to further increase the reduction rate of the amount of steam that is consumed by the reboiler <NUM>. Furthermore, it is possible to increase the reduction rate of the amount of steam, which is consumed by the reboiler <NUM>, as the height of the cocurrent flow CO<NUM>-absorbing unit <NUM> of the cocurrent flow CO<NUM> absorber <NUM> is increased.

<FIG> is a diagram illustrating a relation between the filling height of the countercurrent CO<NUM>-absorbing unit <NUM> and the reduction rate of the amount of steam that is consumed by the reboiler <NUM>. Meanwhile, Comparative Example <NUM>-<NUM> is a test example where the filling height of the countercurrent CO<NUM>-absorbing unit <NUM> of the CO<NUM> absorber <NUM> is <NUM>% in the CO<NUM> recovery device in the related art without the cocurrent flow CO<NUM> absorber <NUM> as in Comparative Example <NUM>-<NUM>. In Comparative Example <NUM>-<NUM>, the amount of steam consumed by the reboiler <NUM> was a reference value (<NUM>%). Comparative Example <NUM>-<NUM> is a test example where the countercurrent CO<NUM>-absorbing unit <NUM> of the CO<NUM> absorber <NUM> is formed in two stages and the sum of the filling heights of the countercurrent CO<NUM>-absorbing units <NUM>-<NUM> and <NUM>-<NUM> is <NUM>% in the CO<NUM> recovery device in the related art without the cocurrent flow CO<NUM> absorber <NUM> as in Comparative Example <NUM>-<NUM>. Comparative Example <NUM>-<NUM> is a test example where the sum of the filling heights of the cocurrent flow CO<NUM>-absorbing unit <NUM> is <NUM>%, the countercurrent CO<NUM>-absorbing unit <NUM> of the CO<NUM> absorber <NUM> is formed in two stages, and the sum of the filling heights of the countercurrent CO<NUM>-absorbing units <NUM>-<NUM> and <NUM>-<NUM> is <NUM>% in the CO<NUM> recovery device including the cocurrent flow CO<NUM> absorber <NUM>. Example <NUM>-<NUM> is a test example where the filling height of the countercurrent CO<NUM>-absorbing unit <NUM> is <NUM>% when the sum of the filling heights of the countercurrent CO<NUM>-absorbing units <NUM>-<NUM> and <NUM>-<NUM> of the CO<NUM> absorber <NUM> is <NUM>%. Example <NUM>-<NUM> is a test example where the filling height of the countercurrent CO<NUM>-absorbing unit <NUM> is <NUM>% when the sum of the filling heights of the countercurrent CO<NUM>-absorbing units <NUM>-<NUM> and <NUM>-<NUM> of the CO<NUM> absorber <NUM> is <NUM>%. Example <NUM>-<NUM> is a test example where the filling height of the countercurrent CO<NUM>-absorbing unit <NUM> is <NUM>% when the sum of the filling heights of the countercurrent CO<NUM>-absorbing units <NUM>-<NUM> and <NUM>-<NUM> of the CO<NUM> absorber <NUM> is <NUM>%. Further, in all of Examples <NUM>-<NUM> to <NUM>-<NUM> and Comparative Example <NUM>-<NUM>, the filling height of the countercurrent CO<NUM>-absorbing unit <NUM>-<NUM> was <NUM>% and the filling height of the countercurrent CO<NUM>-absorbing unit <NUM>-<NUM> was <NUM>%. Furthermore, in all of Examples <NUM>-<NUM> to <NUM>-<NUM> and Comparative Example <NUM>-<NUM>, the filling height of the cocurrent flow CO<NUM>-absorbing unit <NUM> of the cocurrent flow CO<NUM> absorber <NUM> was <NUM>%. Moreover, in all of Examples <NUM>-<NUM> to <NUM>-<NUM> and Comparative Example <NUM>-<NUM>, the reflux ratio (A2/A1) of the rich solution 18A was <NUM> and the cross-section ratio (S1/S2) of the cocurrent flow CO<NUM>-absorbing unit <NUM> was <NUM>. Further, in each of Examples <NUM>-<NUM> to <NUM>-<NUM>, the reflux ratio (A4/A3) of the rich solution 18B between the flow rate A3 of the rich solution 18A, which is supplied to the cooling tower <NUM> from the cocurrent flow CO<NUM> absorber <NUM>, and the flow rate A4 of the rich solution <NUM>, where the rich solution 18B stored in the cooling tower <NUM> was supplied to the cocurrent flow CO<NUM> absorber <NUM> through a rich solution extraction-branch line <NUM>, was <NUM>.

Claim 1:
A CO<NUM> recovery device (<NUM>) comprising:
a cooling tower (<NUM>) including a cooling unit (<NUM>) for bringing the flue gas, which contains CO<NUM>, into contact with water so as to cool flue gas;
a CO<NUM>-absorbing unit (<NUM>) including:
at least one countercurrent CO<NUM>-absorbing unit (<NUM>, <NUM>-<NUM>, <NUM>-<NUM>), located in a CO<NUM> absorber (<NUM>), for bringing the flue gas into contact with the CO<NUM> absorbent in a countercurrent flow so as to remove CO<NUM> from the flue gas, the at least one countercurrent CO<NUM>-absorbing unit (<NUM>, <NUM>-<NUM>, <NUM>-<NUM>) being provided in the CO<NUM> absorber (<NUM>); and
at least one cocurrent flow CO<NUM>-absorbing unit (<NUM>), located in a cocurrent flow CO<NUM> absorber (<NUM>), for bringing the flue gas into contact with the CO<NUM> absorbent in a cocurrent flow so as to remove CO<NUM> from the flue gas, wherein the cocurrent flow CO<NUM> absorber (<NUM>) being provided upstream of the CO<NUM> absorber (<NUM>);
a regenerator (<NUM>) including an absorbent regenerating unit (<NUM>) for releasing CO<NUM> from a rich solution (<NUM>) so as to regenerate the CO<NUM> absorbent as a lean solution (<NUM>), the rich solution (<NUM>) being the CO<NUM> absorbent having absorbed CO<NUM> and the lean solution (<NUM>) being reused in the CO<NUM>-absorbing unit (<NUM>); wherein
the CO<NUM> recovery device (<NUM>) further comprising:
a semi-rich solution extraction line (<NUM>) for supplying a semi-rich solution (<NUM>) from a flue gas introduction side of the at least one cocurrent flow CO<NUM>-absorbing unit (<NUM>), the semi-rich solution (<NUM>) being a solution that has absorbed CO<NUM> and is stored in a bottom of at least one countercurrent CO<NUM>-absorbing unit (<NUM>, <NUM>-<NUM>, <NUM>-<NUM>); and
a rich solution feed line (<NUM>) for supplying a rich solution (<NUM>) to the regenerator (<NUM>), the rich solution (<NUM>) being stored in a bottom of the cocurrent flow CO<NUM> absorber (<NUM>)
characterized in that the CO<NUM> recovery device (<NUM>), further comprising:
a rich solution extraction-branch line (<NUM>) for extracting the rich solution (<NUM>) stored in the cocurrent flow CO<NUM> absorber (<NUM>), mixing it to the semi-rich solution (<NUM>) and circulating it in the cocurrent flow absorber (<NUM>), wherein
a reflux ratio (A2/A1) between a flow rate (A1) of the semi-rich solution (<NUM>) and a flow rate (A2) of the rich solution (<NUM>) is in a range of <NUM> to <NUM>.