Patent Application
20120325089
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2011-137716, filed on Jun. 21, 2011, the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to a carbon dioxide capturing device and a carbon dioxide capturing method.
Recently, in connection with the capture of carbon dioxide, a carbon dioxide capture and storage (CCS) technique has been drawing attention as an effective measure against the problem of global warming causing anxiety on a global scale. In particular, methods of capturing carbon dioxide by a water solution have been studied for process exhaust gases generated in thermal power plants, iron works and so on.
However, according to conventional carbon dioxide capturing techniques, a carbon dioxide containing exhaust gas and an absorbing liquid supplied to an absorption tower and the inside of the absorption tower need to be cooled to keep a low temperature in the absorption tower so that high carbon dioxide capturing performance is maintained. In order to inhibit the discharge of absorbing liquid components within the exhaust gases in the absorption tower and a regeneration tower to the outside of a carbon dioxide capturing system (hereinafter simply referred to as a “system”), it is necessary to decrease the temperature of a gas condenser for cooling the exhaust gases from the absorption tower and the regeneration tower. Another problem is that the concentration of the absorbing liquid drops if a large amount of water included in a carbon dioxide containing gas is introduced into a carbon dioxide capturing device without being cooled. This leads to high cooling power energy on the one hand and low carbon dioxide separating/capturing performance on the other.
In the accompanying drawings:
a) is a diagram showing the overall configuration of a carbon dioxide capturing device according to Embodiment 1;
b) is a diagram illustrating a cooler provided in the carbon dioxide capturing device shown in
In accordance with an embodiment, a carbon dioxide capturing device includes an absorption tower, a regeneration tower, and a cooling unit. A gas containing carbon dioxide and a lean liquid which absorbs carbon dioxide from the gas is introduced to the absorption tower. The absorption tower brings the gas and the lean liquid into contact with each other to generate a rich liquid in which carbon dioxide is absorbed and then discharges the rich liquid. The regeneration tower is configured to generate a lean liquid in which carbon dioxide is separated from the rich liquid by heating the rich liquid from the absorption tower and diffusing vapor containing carbon dioxide from the rich liquid, and then return the lean liquid to the absorption tower. The cooling unit is configured to cool at least one of the gas, the lean liquid, and the rich liquid. The cooling unit comprises first and second coolers which are connected in series to each other and to which first and second cooling mediums are introduced, respectively. The first cooling medium is generated outside the carbon dioxide capturing device without using power for cooling in the carbon dioxide capturing device. The second cooling medium is generated by using power for cooling in the carbon dioxide capturing device. The first cooler is located upstream of the second cooler.
Embodiments will now be explained with reference to the accompanying drawings. Like components are given like reference numbers throughout the drawings and repeated descriptions thereof are approximately omitted.
a) is a diagram showing the overall configuration of a carbon dioxide capturing device according to Embodiment 1.
The absorption tower 20 is constituted by, for example, a counter-flow gas-liquid contactor. A carbon dioxide containing exhaust gas G1 is supplied to the absorption tower 20 from its bottom, and an absorbing liquid for absorbing carbon dioxide (hereinafter referred to as a “lean liquid LL”) is introduced to the absorption tower from its top. The absorption tower 20 brings the carbon dioxide containing exhaust gas G1 into gas-liquid contact with the lean liquid LL so that the carbon dioxide containing exhaust gas G1 is absorbed by the lean liquid LL. The absorption tower 20 thereby generates a rich liquid RL in which carbon dioxide is absorbed, and then discharges the rich liquid RL from its bottom. The absorption tower 20 is structured to have a filler or a tray disposed therein for efficient gas-liquid contact. A carbon dioxide containing gas G3 supplied to the absorption tower 20 may be, but not exclusively, for example, a combustion exhaust gas or a process exhaust gas. As the lean liquid LL, it is possible to use, but not exclusively, for example, an amine solution such as monoethanolamine or diethanolamine, and an alkaline solution, as well as an ionic liquid and its solution. A decarbonated gas G4 after the removal of carbon dioxide in the absorption tower 20 is discharged from the top of the absorption tower 20.
The rich liquid RL discharged from the bottom of the absorption tower 20 is introduced into the regenerated heat exchanger 40 through the pump P1. The regenerated heat exchanger 40 heats the introduced lean liquid LL, and supplies the heated lean liquid LL to the regeneration tower 30. In the present specification, the lean liquid LL is defined as an absorbing liquid containing a smaller amount of carbon dioxide than the rich liquid RL.
The regeneration tower 30 heats the introduced lean liquid LL, and thereby diffuses and releases most of carbon dioxide from the lean liquid LL together with vapor, and then discharges a carbon dioxide containing vapor GS from its top. The regeneration tower 30 is also structured to have a filler or a tray disposed therein for efficient gas-liquid contact. The lean liquid LL after the removal of most of carbon dioxide is returned to the absorption tower 20 through the regenerated heat exchanger 40.
In the present embodiment, the carbon dioxide containing exhaust gas G1 is brought in from an inlet 10, and supplied to the absorption tower 20 via the desulfurizer 60, the cooler CH31, and the gas-liquid separator 501. The desulfurizer 60 will be described later.
Each of the coolers CH31, CH32, CH11, CH12, and CH33 includes a first cooler CL1 and a second cooler CL2 connected in series to the first cooler CL1 as comprehensively indicated by a sign CH in
As shown in
A second cooling medium CM2 is supplied to the second cooler CL2. In contrast to the first cooling medium CM1, the second cooling medium CM2 is a cooling medium generated by using power, and includes cool water or a cooling medium cooled by, for example, a refrigerator such as a chiller, a heat pump outside the carbon dioxide capturing device 1 according to the present embodiment, and a cryogenic cooling medium such as cool water or a cooling medium cooled by liquid nitrogen, dry ice, or liquid helium. In the present embodiment, the second cooling medium CM2 corresponds to, for example, a second cooling medium.
The gas-liquid separator 501 discharges condensed water generated in the cooler CH31 to the outside of the carbon dioxide capturing device 1, and thereby prevents a large amount of water from being brought into the carbon dioxide capturing device 1. This makes it possible to prevent the drop of the concentration of the lean liquid LL and the resulting deterioration of carbon dioxide capturing performance and to maintain the capturing performance while minimizing the operation for managing the concentration of the lean liquid LL. The carbon dioxide containing exhaust gas G1 which has passed through the gas-liquid separator 501 is supplied to the absorption tower 20 as the carbon dioxide containing exhaust gas G3. In the present embodiment, the gas-liquid separator 501 and the later-described gas-liquid separators 502 and 503 correspond to, for example, water removers.
The desulfurizer 60 is disposed between the inlet 10 and the cooler CH31, and removes an acidic component such as a sulfur oxide component SOx included in the carbon dioxide containing exhaust gas G1. The desulfurizer 60 is provided with the cooler CH32, so that the carbon dioxide containing exhaust gas G1 is also cooled when the acidic component is removed.
The decarbonated gas G4 discharged from the absorption tower 20 is supplied to the cooler CH11, and is cooled to a temperature at which condensed water is generated, in the same manner as the cooling method described above in connection with the cooler CH31. The gas containing the cooled condensed water is separated into a gas and a liquid by the gas-liquid separator 502, and the condensed water is partly or entirely supplied again to, for example, the absorption tower 20 through the pump P2 in the carbon dioxide capturing device 1. This prevents water vapor in the decarbonated gas G4 from being discharged to the outside of the carbon dioxide capturing device 1. The cooler CH11 is provided prior to the gas-liquid separator 502 in the present embodiment, but is not exclusively provided in this form, and may be, for example, incorporated in the gas-liquid separator 502.
The regeneration tower 30 is constituted by, for example, a counter-flow gas-liquid contactor, and a liquid retained therein is heated in the reboiler 70 by heat exchange with high-temperature steam which is heat supplied from outside. The carbon dioxide containing vapor GS is supplied to the cooler CH33, and is cooled to a temperature at which condensed water is generated, in the same manner as the cooling method described above in connection with the cooler CH31. This prevents water vapor in the carbon dioxide containing vapor GS from being discharged to the outside of the carbon dioxide capturing device 1. The condensed water generated in the cooler CH33 passes through the gas-liquid separator 503, and a gas component mainly including carbon dioxide and a liquid component mainly including water in the carbon dioxide containing vapor GS are partly or entirely supplied again to the system, for example, the regeneration tower 30 by the pump P3.
The gas-liquid separator 502 has a water washing unit 110 therein, and thereby prevents the dispersion of the lean liquid. The dispersion amount of the absorbing liquid is determined by the vapor pressure at the temperature of the exhaust gas. Therefore, the water washing unit 110 needs to be sufficiently cooled, so that the cooler CH12 is provided in the present embodiment, and the decarbonated gas G4 in the gas-liquid separator 502 is cooled. In the present embodiment, the water washing unit 110 corresponds to, for example, a dispersion prevention unit. The water washing unit 110 does not need to be incorporated in the gas-liquid separator 502, and may be disposed prior to or subsequently to the gas-liquid separator 502 before the introduction of a gas to be treated or after the discharge of the gas. The water washing unit 110 is not exclusively disposed prior to or subsequently to the gas-liquid separator 502 and in the gas-liquid separator 502, and is also preferably disposed in the gas-liquid separator 503 or disposed prior to or subsequently to the gas-liquid separator 503. An example of the relation between the temperature of the exhaust gas in the dispersion prevention facility and the amount of a dispersed absorbing liquid is shown in a graph of
Along the passage where the lean liquid LL is supplied to the absorption tower 20 from the regeneration tower 30, a cooler CH22 is further provided between the regenerated heat exchanger 40 and the absorption tower 20. In the same manner as the above-described method of cooling by the cooler CH31, the lean liquid LL is cooled by a first cooling medium and a second cooling medium that are supplied from the outside, and then returned to the absorption tower 20.
Now, a carbon dioxide capturing method using the carbon dioxide capturing device 1 according to the present embodiment is described as a carbon dioxide capturing method according to Embodiment 1.
Initially, as a first process, the carbon dioxide containing exhaust gas G1 and the lean liquid LL are introduced into the absorption tower 20 where the carbon dioxide containing exhaust gas G1 and the lean liquid LL come into contact with each other and the carbon dioxide containing exhaust gas G1 is absorbed in the lean liquid LL to generate the rich liquid RL. In this first process, the step of absorption is preferably carried out at a low temperature to improve carbon dioxide absorbing performance. Thus, regarding the carbon dioxide containing gas G3 introduced into the absorption tower 20, the carbon dioxide containing exhaust gas G1 is cooled to a low temperature within the room temperature, preferably to 35° C. to 40° C. or less by a cooling process that uses the cooler CH31, and then supplied to the absorption tower 20 as the carbon dioxide containing gas G3. The lean liquid LL introduced into the absorption tower 20 from the regenerated heat exchanger 40 is also cooled to a low temperature within the room temperature, preferably to 35° C. to 40° C. or less by a cooling process that uses the cooler CH22, and then supplied to the absorption tower 20.
In order to control the discharge amount of water vapor from the system, the water vapor contained in the decarbonated gas G4 discharged from the absorption tower 20 is cooled by a cooling process that uses the cooler CH11, and condensed water is generated. The generated condensed water is partly or entirely returned to the absorption tower 20 via the gas-liquid separator 502 by the pump P2.
The rich liquid RL generated by the first process is supplied to the regeneration tower 30 by the pump P2, and heated by the reboiler 70 in a second process. As a result, the carbon dioxide containing vapor GS is discharged from the top of the regeneration tower 30, and the lean liquid LL in which carbon dioxide is separated from the rich liquid RL is generated and returned to the absorption tower 20 via the regenerated heat exchanger 40 for reuse in the first process. In this way, the rich liquid RL which has captured carbon dioxide is regenerated as the lean liquid LL.
In order to control the discharge amount of water vapor from the system, the water vapor in the carbon dioxide containing vapor GS discharged from the regeneration tower 30 is also cooled by a cooling process, and condensed water is thereby generated and separated by the gas-liquid separator 503. The condensed water is partly or entirely returned to the regeneration tower 30 from the gas-liquid separator 503 by the pump P3, and thereby returned to the system.
In the series of processes described above, the carbon dioxide containing exhaust gas G1, the lean liquid LL supplied to the absorption tower 20, the decarbonated gas G4, the carbon dioxide containing vapor GS, and the desulfurizer 60 are cooled through the first cooler CL1 by the first cooling medium including, for example, seawater generated substantially without using power, and further introduced into the second cooler and then cooled by, for example, cool water which is generated by cooling to a low temperature by use of a power-driven device such as a chiller. Thus, power cooling energy can be reduced as compared with the case where a cooling target is cooled solely by the second cooling medium which is generated by cooling to a low temperature by use of a power-driven device such as a chiller.
In order to ascertain the power energy reducing effect according to the present embodiment, Reference example 1 that only uses the second cooling medium generated by using power is compared with the present embodiment by use of a process simulator. In the comparison, the same conditions are provided regarding the carbon dioxide capture amount and capture rate. In the present embodiment, the amount of vapor introduced into the regeneration tower 30 is reduced to provide the same performance condition as Reference example 1. An example of simulative comparison results is shown in a table of
As shown in
Thus, according to the present embodiment, the cooling power energy can be reduced to 41% as compared with Reference example 1, as shown in
Reference example 1 is based on the assumption that the chiller is used for cooling. Otherwise, the same advantageous effects are also provided when equipment such as a refrigerator is used for cooling or when a cryogenic cooling medium such as liquid nitrogen, dry ice, or liquid helium is used. When the cryogenic cooling medium is used, the power necessary to cool the cryogenic cooling medium can be reduced.
Now, a carbon dioxide capturing device according to Embodiment 2 is described with reference to
As has been previously described, the lean liquid LL introduced to the absorption tower and a carbon dioxide containing exhaust gas G1 come into contact with each other in the absorption tower, and carbon dioxide is absorbed in the lean liquid LL by the first process. As the absorption reaction in this case is an exoergic reaction, the temperature in the absorption tower rises. The rise of the temperature in the absorption tower decreases absorbing performance.
Thus, in the present embodiment, the lean liquid LL in the absorption tower 22 is extracted during the first process, and introduced to and cooled by the cooler CH34 disposed outside the absorption tower 22. Further, the lean liquid LL cooled by the cooler CH34 is again supplied to the absorption tower 22 through a pump P4. The lean liquid LL reduced in temperature by this cooling process is introduced into the absorption tower 22, so that a lower temperature can be kept in the absorption tower 22 and carbon dioxide absorbing efficiency is improved as compared with the case where the lean liquid LL is not cooled. The temperature of the lean liquid LL after cooling is preferably 35° C. or less. Therefore, the lean liquid LL is preferably also cooled through the second cooler CL2 by using not only the first cooling medium generated substantially without using power but also the second cooling medium cooled by use of power such as a chiller.
In the present embodiment, its advantageous effects remain the same even when extractors and suppliers are disposed in a plurality of parts of the absorption tower 22 that need to be cooled. Moreover, the effect of reducing the cooling power energy remains unchanged even when the lean liquid LL to be extracted is all or part of the lean liquid LL running through the tower.
In the example described according to the present embodiment, the cooler CH34 for cooling the lean liquid LL in the absorption tower 22 is disposed outside the absorption tower 22, but this is not a restriction. For example, any device that can cool the lean liquid LL, such as an absorption tower built-in cooler, may be disposed inside the absorption tower 22.
According to the carbon dioxide capturing devices in the two embodiments described above, the carbon dioxide containing exhaust gas G1, the decarbonated gas G4, the carbon dioxide containing vapor GS, and the lean liquid LL are cooled through the first cooler CL1 by the first cooling medium generated substantially without using power before cooled by passing, through the second cooler CL2, the second cooling medium which is generated by cooling to a low temperature by use of power. Thus, power cooling energy can be reduced, and electric energy can be reduced accordingly.
According to the carbon dioxide capturing method in at least one of the embodiments described above, the gases, the vapor, and the lean liquid LL are cooled by the first cooling medium generated substantially without using power before cooled by the second cooling medium which is generated by cooling to a low temperature by use of power. Thus, the cooling power energy can be reduced, and electric energy can be reduced accordingly.
Although the condensed water separated by the gas-liquid separator 503 is configured to be returned to the regeneration tower 30 in the embodiments described above, the condensed water can be returned to the absorption tower 20 or can be mixed with the lean liquid LL which has passed through the regenerated heat exchanger 40. Alternatively, the condensed water may be used for other purposes.
Furthermore, although the carbon dioxide capturing device includes the pumps P1 to P4 in the embodiments described above, not all of these pumps do not need to be provided as shown in
The coolers CH11, CH12, CH22, and CH31 to CH34 are configured to be arranged outside the absorption tower 20 or the regeneration tower 30 in
Although the first cooler CL1 and the second cooler CL2 are used in the embodiments described above, the coolers are not limited thereto. Three or more coolers including, for example, a third cooler and a fourth cooler may be used for cooling. Moreover, although the two-step coolers CH are used in every cooler in the embodiments described above, the two-step coolers may be only applied to some of the coolers, for example, to the coolers for the lean liquid LL.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-137716 | Jun 2011 | JP | national |
