The present invention relates to a system for recovering carbon dioxide from flue gas, in which a reboiler in a regenerator can be compactly installed, and to a method therefor.
Greenhouse effect due to CO2 has been pointed out as a cause of global warming in recent years, and a measure against it has become an urgent issue internationally for protecting the global environment. Generation sources of CO2 include all sorts of human activity areas that burn fossil fuel, and demands for the reduction of discharge thereof are further increasing. Accompanying this trend, a method of removing and recovering CO2 in combustion flue gas by bringing combustion flue gas in a boiler into contact with amine CO2 absorbent, and a method of storing recovered CO2 without discharging it to the air have been strenuously researched, with regard to power generation facilities such as a thermal power plant that uses a large amount of fossil fuel.
As a process of eliminating and recovering CO2 in combustion flue gas by using the amine system CO2 absorbent, a process in which combustion flue gas is brought into contact with the CO2 absorbent in an absorber, and a process in which the absorbent having absorbed CO2 is heated in a regenerator to release CO2 and regenerate the absorbent so that the absorbent is circulated and reused in the absorber have been adopted (see, for example, Patent Documents 1 and 2).
In
The carbon dioxide (CO2) recovered is compressed by a CO2 compressor 1022, thereby acquiring high-pressure CO2 1023 of 10.0 to 15.0 megapascals (G). The CO2 recovering system can be provided afterwards for recovering CO2 from an existing flue gas source, or can be provided at the same time of newly installing a flue gas source.
A reboiler for evaporating a part of the extracted amine solution is installed at the bottom area of the regenerator 1008. The evaporated equilibrium vapor becomes stripping vapor for giving energy for amine-CO2 dissociation. Because the amine solution for absorbing CO2 is not tolerant to heat and is decomposed at a high temperature, although a high temperature is desired in view of stripping performance. Therefore, the regenerator 1008 operated at a temperature as low as possible, taking thermal decomposition into consideration. A reboiler heat source is also limited up to 150C. In view of avoiding decomposition, it is preferred that a contact time of the amine solution with the heat source is as short as possible.
As a type of the reboiler, a horizontal thermo-siphon reboiler and a kettle-type reboiler have been conventionally used.
In
The thermo-siphon reboiler 1030 is normally used as a reboiler of a distillation column. However, evaporated steam and liquid become the gas-liquid two phase flow 1034 in a mixed phase, which passes in the heat exchanger and through an outlet piping.
As an effective use of carbon dioxide in flue gas, conventionally, apart of carbon dioxide in the flue gas is only recovered to produce carbon dioxide for carbonated drink and dry ice. Recently, however, a greenhouse effect due to carbon dioxide has been pointed out as a cause of global warming, and a measure against it becomes imperative internationally for protecting global environment, and generation sources of carbon dioxide include all sorts of human activity areas that burn fossil fuel, and demands for reduction of discharge thereof are further increasing. Accompanying this trend, a method of removing and recovering the entire amount of CO2 in combustion flue gas by bringing combustion flue gas in industrial facilities such as a boiler and a gas turbine into contact with CO2 absorbent, and a method of compressing and storing recovered CO2 without discharging it to the air have been tested, with regard to power generation facilities such as a thermal power plant that uses a large amount of fossil fuel, and a technique for recovering carbon dioxide having high energy efficiency of the entire system has been eagerly desired.
Further, conventionally, use of carbon dioxide means production of dry ice and the like, and the production thereof can be realized sufficiently by using the horizontal thermo-siphon reboiler and the kettle-type reboiler. However, there are following problems when a large amount of carbon dioxide in large facilities is recovered, compressed, and stored.
For example, in a system in which 110-MW power generation facilities are used, when exhausted carbon dioxide is to be recovered, plural (at least four) reboilers need to be appropriately arranged around the regenerator 1008, to maintain reboiler performance. However, if the CO2 recovering system becomes larger, the size of the reboilers also become larger, and thus a very large installation area (250 m2) is required.
Further, at the time of maintenance of the horizontal thermo-siphon reboiler 1030, at the time of inspection, and at the time of cleaning when outside of the heat-transfer tube 1032 adhere scale, as shown in
That is, for example, in the case of a CO2 recovering apparatus in 110-MWe power generating facilities, for example, 1800 tubes per one regenerator are required, and in a maintenance operation, extraction work becomes difficult due to the heavy weight. Further, deflection at the time of extracting a tube bundle of, for example, about 12 meters becomes a problem.
Further, at the time of pulling out the tube bundle, a maintenance site for a pulling-out operation (more than double the installation area) is required. That is, a total area S3 (500 m2) of a site area S1 (250 m2) for installation and a maintenance site area S2 (250 m2) is required, and when there is no large spare space in the site, installation of a CO2 recovering system becomes difficult in existing large boiler facilities.
The present invention has been achieved in view of the above problems, and an object of the present invention is to provide a system for recovering carbon dioxide from flue gas, in which a reboiler in a regenerator can be compactly installed, and a method therefor, in facilities where CO2 or the like contained in flue gas is recovered.
According to an aspect of the present invention, a system for recovering carbon dioxide from flue gas includes: an absorber that brings CO2 absorbent that absorbs CO2 contained in flue gas discharged from a boiler plant into contact with the flue gas to remove CO2 from the flue gas; a regenerator that strips CO2 from CO2 absorbent that is fed from the absorber and has absorbed the CO2 to regenerate the CO2 absorbent; a plurality of internal shells provided at a bottom of the regenerator with a predetermined interval therebetween, into which regenerated CO2 absorbent is introduced by a feeding unit from a bottom side thereof so that the CO2 absorbent overflows from an upper opening thereof toward the bottom of the regenerator; and a reboiler that is inserted into the internal shell in a direction orthogonal to a vertical axis and includes a heat-transfer tube that reboils CO2 absorbent. The system transfers steam separated from CO2 absorbent reboiled by the heat-transfer tube to an upper part of a regenerator, and the system causes condensed CO2 absorbent to overflow from an upper end of the internal shell and to be discharged from a bottom side of a regenerator, and feeds the CO2 absorbent to an absorber side as regenerated CO2 absorbent.
Advantageously, in the system for recovering carbon dioxide from flue gas, two or more of the reboilers are inserted alternatively from right and left.
Advantageously, in the system for recovering carbon dioxide from flue gas, the heat-transfer tube bundle is provided with a reinforcement member.
Advantageously, in the system for recovering carbon dioxide from flue gas, the heat-transfer tube is constituted by a tube bundle having a rectangular shape in cross section.
According to another aspect of the present invention, a method for recovering carbon dioxide from flue gas for a system including an absorber that brings CO2 absorbent that absorbs CO2 contained in flue gas discharged from a boiler plant or the like into contact with the flue gas to remove CO2 from the flue gas, and a regenerator that strips CO2 from CO2 absorbent that is fed from the absorber and has absorbed the CO2 to regenerate the CO2 absorbent, includes: introducing regenerated CO2 absorbent into a plurality of internal shells at a bottom of the regenerator; reboiling the accumulated CO2 absorbent by a heat-transfer tube; generating steam by heating and boiling regenerated CO2 absorbent; striping CO2 having remained slightly; and temporarily accumulating CO2 absorbent condensed by stripping steam and residual CO2 and by overflowing from an upper end of the internal shell and falling down toward a bottom side of a regenerator; reusing the accumulated CO2 absorbent for absorption of CO2 by extracting from a bottom outlet and feeding to an absorber side.
According to the present invention, internal shells are provided at the bottom of a regenerator, and a reboiler including a heat-transfer tube that reboils CO2 absorbent is inserted into the internal shell. Therefore, a simplified reboiling system incorporated in a regenerator constituting a series of reboiling cycles, which can transfer steam separated from the CO2 absorbent reboiled by the heat-transfer tube to an upper part of the regenerator, cause the condensed CO2 absorbent to overflow from an upper end of the internal shell and be discharged from the bottom of the regenerator, and feed the CO2 absorbent to the absorber as regenerated CO2 absorbent (lean solution), can be established.
The present invention is explained below in detail with reference to the accompanying drawings. The present invention is not limited to the embodiments. In addition, constituent elements in the following embodiments include those that can be easily assumed by persons skilled in the art or that are substantially equivalent.
A system for recovering carbon dioxide from flue gas according to an embodiment of the present invention is explained with reference to the drawings.
In the present invention, the heat-transfer tube (a tube bundle that bundles a plurality of U-shaped heat-transfer tubes is not shown) 103 constituting a reboiler system is directly inserted into the internal shell 101 provided in the regenerator 1008, thereby considerably simplifying a feed piping of the absorbent and omitting a piping on a steam generator side. The U-shaped heat-transfer tubes 103 are bundled to form a tube bundle. In
In the present embodiment, as shown in
Specifically, the reboiler 100B is on the upper stage and is inserted from the right in
In the present embodiment, the internal shell 101 is provided inside the regenerator 1008, and the heat-transfer tube 103 constituting the rectangular tube bundle is inserted into the internal shell 101 in the regenerator 1008 to be soaked in the CO2 absorbent filled in the internal shell 101. As shown in
Regeneration of the rich solution 1007 by using the regenerator 1008 including the internal shells 101 is performed in the following manner. Hereinafter, the reboilers 100A to 100F are referred to as a reboiler 100, the heat-transfer tubes 103A to 103F are referred to as a heat-transfer tube 103, and the channels 120A to 120F are referred to as a channel 120. First, the rich solution 1007 in which CO2 has been absorbed by the absorber 1006 is introduced from the top of the regenerator 1008, comes in contact with steam at the time of falling down in the regenerator 1008 so that CO2 is separated and discharged from the top of the regenerator 1008 to regenerate the CO2 absorbent. The CO2 absorbent regenerated during falling down in the regenerator 1008 is then collected, as shown in
Meanwhile, in the respective channels 120 of the respective reboilers 100, the low-pressure steam 1031 enters into the upper part of the channel from a steam inlet nozzle 121, passes through the plurality of U-shaped heat-transfer tubes, applies heat to the CO2 absorbent that comes in contact with a tube barrel to condense the CO2 absorbent, and returns to a lower side of a partition plate 122. The condensed water 1035 is discharged to outside through a condensed-water outlet nozzle 123.
The CO2 absorbent introduced into the internal shell 101 is heat-exchanged with steam flowing in the respective U-shaped heat-transfer tubes of the heat-transfer tube 103, starts to boil while moving upward outside the respective U-shaped tubes, and moves upward at an accelerated pace to generate steam S. The CO2 absorbent condensed due to generation of the steam S overflows from an upper end of the internal shell 101 and flows down in a passage 132 toward the bottom of the regenerator 1008 and is accumulated therein. The condensed and regenerated CO2 absorbent is extracted from a bottom outlet 1008b, and is fed to the absorber 1006 as the lean solution 1009 via the line L2. On the other hand, the generated steam S passes through the chimney tray 110 and moves upward in the regenerator 1008. Reference numeral 133 denotes a liquid level of the CO2 absorbent. The liquid level 133 is controlled by a liquid-level meter (not shown).
As described above, according to the present invention, the internal shell 101 is provided in the regenerator 1008, and the reboiler 100 including the heat-transfer tube 103 is inserted therein so that the heat-transfer tube 103 is soaked in the CO2 absorbent in the internal shell 101. The heat-transfer tube 103 is efficiently arranged in the horizontal direction, so that a channel for covering the heat-transfer tube required in a conventional reboiler can be eliminated.
Further, in the regenerator 1008 according to the present invention, the regenerated CO2 absorbent to be fed to the internal shell 101 is fed to the absorbent feed headers 114 in the lower part of the internal shell 101 from the seal pan 111 in the upper part via the line L4. The regenerated CO2 absorbent is boiled due to heating of the heat-transfer tube 103, generates the steam S while moving upward in the reboiler 100, and is condensed. The condensed CO2 absorbent is caused to overflow, and passes through the passage 132 formed between a wall surface 1008a of the regenerator 1008 and a wall surface 101a of the internal shell 101 to return to the bottom of the regenerator, thereby establishing a simplified reboiling system.
That is, in the conventional system shown in
Further, scales adhering to outside of the heat-transfer tube need to be removed regularly. However, a maintenance worker can enter into the regenerator to clean the heat-transfer tube, without extracting the large heat-transfer tube to outside of the shell for cleaning as in the conventional reboiler, thereby enabling to perform the cleaning operation in a short period of time and with less cost.
The reboiler 100 in the regenerator 1008 according to the present invention is cleaned according to the following manner. First, at the time of periodical plant shut down (or periodical check), absorbent on the bottom of the regenerator 1008 and inside the internal shell 101 is discharged from a drain 101b and a bottom outlet 1008b provided at the bottom to the outside. Next, a maintenance worker enters into the regenerator 1008 from a manhole 130 provided on the side of the body of the regenerator 1008 with a cleaning hose, and passes through a baffle plate (works as a platform) 131 to perform cleaning of the U-shaped heat-transfer tubes (tube bundle). As a result, cleaning can be performed without extracting the heat-transfer tube to outside as in the conventional technique. As a result, only the maintenance worker is engaged with the cleaning operation, and a long (for example, about 10 to 15 meters) and heavy (for example, about 30 to 80 tons/tube) tube bundle does not need to be extracted by using a large heavy machine as in the conventional technique, thereby considerably improving working processing and workability at the time of cleaning. In the present embodiment, two manholes 130 are provided on the wall surface of the regenerator 1008 in the upper part of the internal shell 101 to facilitate an access to the heat-transfer tube 13. However, the number of manholes is not limited thereto.
That is, at the time of periodical plant shut down (or periodical check), a worker enters into the regenerator 1008 from the manhole 130 with a cleaning hose, and passes through the baffle plate 131, which also works as a platform, to remove scales adhering to the outer surface of the U-shaped tubes constituting the heat-transfer tube. A ladder (not shown) is provided inside the regenerator 1008, so that the worker can go around and clean all the heat-transfer tubes. Because the size of the heat-transfer tubes 103 arranged vertically is made the same, the workability of maintenance workers is improved.
At the time of extracting the CO2 absorbent from the drain 101b provided at the bottom of the internal shell 101, at least one safety valve is provided near the bottom of the internal shell 101, so that the absorbent left in the internal shell can be promptly discharged, in order to prevent that the inside of the bottom of the regenerator becomes empty and the absorbent is left in the internal shell 101. At the time of emergency, the absorbent having remained therein is quickly discharged.
As described above, according to the present invention, in the reboiling system that generates steam required for performing a regeneration process of CO2 absorbent having absorbed carbon dioxide, for example, of a carbon dioxide capture plant, the internal shell 101 is provided in the regenerator 1008, the reboiler 100 is installed in the internal shell 101, the low-pressure steam 1031 is introduced into the heat-transfer tube 103 of the reboiler 100, the steam S is generated by heating and boiling the regenerated CO2 absorbent, and CO2 having remained slightly in the internal shell 101 is discharged together with the steam S. On the other hand, the CO2 absorbent condensed by releasing steam and remained CO2 overflows from the upper end of the internal shell 101 toward the wall surface of the regenerator 1008, flows downward in the regenerator 1008 through the passage 132, and is temporarily accumulated therein. Thereafter, the CO2 absorbent is extracted from the bottom outlet 1008b, and is fed to the absorber 1006 as the lean solution 1009 via the line L2. As described above, according to the present invention, in the regenerator 1008, a simplified reboiling system incorporated in a regenerator, which constitutes a series of reboiling cycles, can be established in the regenerator 1008.
In the present embodiment, an example in which a plurality of (six in the present embodiment) reboilers 100A to 100F respectively including heat-transfer tubes 103A to 103F are installed in the internal shell 101 is explained. However, the present invention is not limited thereto, and one reboiler including a heat-transfer tube can be inserted and installed in the internal shell according to the size of the recovering apparatus to reboil the CO2 absorbent.
As described above, according to the system and method for recovering carbon dioxide from flue gas of present invention, internal shells are provided inside a regenerator, and a reboiler including a heat-transfer tube is installed in the internal shells, thereby enabling to constitute a simplified reboiling system incorporated in a regenerator, which establishes a series of reboiling cycles.
Number | Date | Country | Kind |
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2010-089636 | Apr 2010 | JP | national |