Patent Publication Number: US-2022228515-A1

Title: Gas turbine plant

Description:
TECHNICAL FIELD 
     The present disclosure relates to a gas turbine plant. 
     Priority is claimed on Japanese Patent Application No. 2019-136180, filed Jul. 24, 2019, the content of which is incorporated herein by reference. 
     BACKGROUND ART 
     In a power plant using fossil fuel, for example, in a plant equipped with a gas turbine, high-temperature exhaust gas is generated in accordance with operation of the gas turbine. Regarding a technology for effectively utilizing heat of this exhaust gas, an exhaust heat recovery boiler has been put into practical use (Patent Document 1 below). An exhaust heat recovery boiler is a device generating high-temperature/high-pressure steam due to heat of exhaust gas. Specifically, an exhaust heat recovery boiler has a flue through which exhaust gas of a gas turbine circulates, and a coal economizer, a vaporizer, and a superheater which are arranged in order from a downstream side toward an upstream side inside this flue. 
     Incidentally, exhaust gas of a gas turbine contains a large amount of carbon dioxide. From a viewpoint of environmental conservation, a technology of removing as much carbon dioxide from exhaust gas as possible is required. Regarding such a technology, for example, the plant described in Patent Document 2 below is known. The plant described in Patent Document 2 is equipped with a gas turbine, an exhaust heat recovery boiler provided along a flue gas path in which exhaust gas of the gas turbine circulates, and a carbon dioxide recovery device. Carbon dioxide contained in the exhaust gas is absorbed and removed by an absorption liquid inside the carbon dioxide recovery device. 
     CITATION LIST 
     Patent Literature 
     
         
         [Patent Document 1] 
         Japanese Patent No. 4690885 [Patent Document 2] 
         Published Japanese Translation No. 2015-519499 of the PCT International Publication 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In the carbon dioxide recovery device described above, a chemical agent having amine as a main component is used as an absorption liquid. This absorption liquid has an appropriate temperature range for efficiently absorbing carbon dioxide. 
     Namely, when the temperature of exhaust gas is excessively high or excessively low, efficiency of absorption of carbon dioxide deteriorates. Therefore, as in the plant described in Patent Document 2 above, when exhaust gas is directly circulated from an exhaust heat recovery boiler to a carbon dioxide recovery device, due to the excessively high temperature of exhaust gas, there is a likelihood that the efficiency of recovery of carbon dioxide will deteriorate. 
     The present disclosure has been made in order to resolve the foregoing problems, and an object thereof is to provide a gas turbine plant in which carbon dioxide can be recovered with higher efficiency. 
     Solution to Problem 
     In order to resolve the foregoing problems, a gas turbine plant according to the present disclosure includes a gas turbine that is configured to be driven by means of combustion gas generated due to combustion of fuel; an exhaust line that is configured to guide exhaust gas discharged from the gas turbine to the outside; an exhaust heat recovery boiler that is provided in the exhaust line, is configured to generate steam due to heat of the exhaust gas discharged from the gas turbine, and guide the exhaust gas which has passed through the inside of the exhaust heat recovery boiler to the exhaust line; a carbon dioxide recovery device that is provided on a downstream side of the exhaust heat recovery boiler in the exhaust line and is configured to recover carbon dioxide contained in the exhaust gas flowing in the exhaust line; a heat exchanger that is provided between the exhaust heat recovery boiler and the carbon dioxide recovery device in the exhaust line and is configured to cool the exhaust gas to a temperature set in advance; and a circulation line that branches from a position between the carbon dioxide recovery device and the heat exchanger in the exhaust line and is connected to an inlet of the gas turbine. The carbon dioxide recovery device has an absorption tower which is configured to absorb carbon dioxide contained in the exhaust gas by causing the exhaust gas at the temperature set in advance and an absorption liquid to come into contact with each other. The heat exchanger is formed of a material having a higher corrosion resistance than a material forming the exhaust heat recovery boiler. 
     Advantageous Effects of Invention 
     According to the gas turbine plant of the present disclosure, carbon dioxide can be recovered with higher efficiency. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view illustrating a constitution of a gas turbine plant according to an embodiment of the present disclosure. 
         FIG. 2  is a schematic view illustrating a constitution of an exhaust heat recovery boiler according to the embodiment of the present disclosure. 
         FIG. 3  is a schematic view illustrating a constitution of a carbon dioxide recovery device according to the embodiment of the present disclosure. 
         FIG. 4  is a schematic view illustrating a modification example of the gas turbine plant according to the embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     (Constitution of Gas Turbine Plant) 
     Hereinafter, a gas turbine plant  100  according to an embodiment of the present disclosure will be described with reference to  FIGS. 1 to 3 . As illustrated in  FIG. 1 , the gas turbine plant  100  according to the present embodiment includes a gas turbine  1 , an exhaust heat recovery boiler  2 , a carbon dioxide recovery device  3 , a heat exchanger  4 , a smokestack  5 , a moisture separation device  6 A, an intake filter  6 B, a carbon dioxide compression apparatus  7 , an exhaust line L 1 , a circulation line L 2 , a steam supply line L 4 , a steam recovery line L 5 , a supplementary combustion burner B, and a control device  90 . 
     (Constitution of Gas Turbine) 
     The gas turbine  1  has a compressor  11 , a combustor  12 , and a turbine  13 . The compressor  11  generates high-pressure compressed air by compressing air taken in from outside. The combustor  12  generates high-temperature/high-pressure combustion gas through combustion of a mixture of this compressed air and fuel. The turbine  13  is rotatively driven by means of combustion gas. For example, a rotation force of the turbine  13  is utilized for driving of a generator G connected to the same shaft as the turbine  13 . High-temperature exhaust gas is discharged from the turbine  13 . This exhaust gas is sent through the exhaust line L 1  connected to a downstream side of the turbine  13  to the exhaust heat recovery boiler  2  provided on the exhaust line L 1 . 
     (Overview of Exhaust Heat Recovery Boiler) 
     The exhaust heat recovery boiler  2  generates high-temperature/high-pressure steam by performing heat exchange between exhaust gas of the gas turbine  1  and water. A constitution of the exhaust heat recovery boiler will be described below. The carbon dioxide recovery device  3  is provided on the downstream side of the exhaust heat recovery boiler  2  on the exhaust line L 1 . Low-temperature exhaust gas which has been subjected to heat exchange with water by the exhaust heat recovery boiler  2  is sent to this carbon dioxide recovery device  3  through the exhaust line L 1 . 
     (Overview of Carbon Dioxide Recovery Device) 
     In the carbon dioxide recovery device  3 , when an absorption liquid having amine as a main component is brought into gas-liquid contact with exhaust gas, carbon dioxide contained in the exhaust gas becomes chemically bonded to the absorption liquid. (An absorption liquid may be a chemical absorbent having components other than amine.) Accordingly, a great part or all of the carbon dioxide in the exhaust gas is removed. A constitution of the carbon dioxide recovery device  3  will be described below. Exhaust gas after carbon dioxide is removed therefrom is sent to the smokestack  5  through the exhaust line L 1  and diffuses into the atmosphere. 
     On the other hand, carbon dioxide separated from exhaust gas is sent to the carbon dioxide compression apparatus  7  through a recovery line L 6 . The carbon dioxide compression apparatus  7  has a compressor main body  71 , a drive unit  72 , and a storage unit  73 . The compressor main body  71  is driven by the drive unit  72  so as to compress carbon dioxide. Compressed carbon dioxide is liquefied and is then transported to the storage unit  73 . 
     (Constitution of Circulation Line) 
     On the foregoing exhaust line L 1 , one end of the circulation line L 2  branching from the exhaust line L 1  is connected to a part at a position between the exhaust heat recovery boiler  2  and the carbon dioxide recovery device  3 . 
     The other end of the circulation line L 2  is connected to the compressor  11  of the gas turbine  1 . Namely, a part of exhaust gas flowing in the exhaust line L 1  can be caused to flow back to the gas turbine  1  (compressor  11 ) through this circulation line L 2 . In addition, a temperature sensor T serving as a measurement part of outlet temperature, the moisture separation device  6 A, and the intake filter  6 B are provided on the circulation line L 2 . 
     The temperature sensor T measures the temperature of exhaust gas. The value of the temperature measured by the temperature sensor T is sent to the control device  90  as an electrical signal. The moisture separation device  6 A removes moisture contained in the exhaust gas circulating in the circulation line L 2 . The intake filter  6 B removes air taken in from the atmosphere and soot and dust contained in the exhaust gas circulating in the circulation line L 2 . A constitution in which no moisture separation device  6 A and no intake filter  6 B is provided can also be employed. 
     (Overview of Heat Exchanger) 
     On the exhaust line L 1 , the heat exchanger  4  is provided at a position on an upstream side of a branch point of the circulation line L 2  and the exhaust line L 1  described above, and on the downstream side of the exhaust heat recovery boiler  2 . The heat exchanger  4  cools exhaust gas circulating in the exhaust line L 1  to a temperature set in advance. Exhaust gas cooled by the heat exchanger  4  is sent to the carbon dioxide recovery device  3  on the downstream side through the exhaust line L 1 . A constitution of the heat exchanger  4  will be described below. 
     (Piping System of Steam) 
     Next, a piping system for steam in the gas turbine plant  100  will be described. The exhaust heat recovery boiler  2  is connected to the carbon dioxide recovery device  3  through the steam supply line L 4 . Steam generated in the exhaust heat recovery boiler  2  is supplied to the carbon dioxide recovery device  3  through this steam supply line L 4 . Details will be described below. In the carbon dioxide recovery device  3 , carbon dioxide is separated from an absorption liquid in a state in which carbon dioxide has been bonded thereto, due to heat of steam supplied through the steam supply line L 4 . Steam (or water) which is at a low temperature after being utilized in the carbon dioxide recovery device  3  is sent to the exhaust heat recovery boiler  2  again through the steam recovery line L 5 . A condenser  61  for returning low-temperature steam which has been recovered from the carbon dioxide recovery device  3  to water, and a water feeding pump  62  for pressure-feeding this water are provided on the steam recovery line L 5  (refer to  FIG. 2 ). 
     (Constitutions of Exhaust Heat Recovery Boiler and Heat Exchanger) 
     Next, with reference to  FIG. 2 , constitutions of the exhaust heat recovery boiler  2  and the heat exchanger  4  will be described. As illustrated in the same diagram, the exhaust heat recovery boiler  2  has a flue  21 ; a coal economizer  22 , a vaporizer  23 , and a superheater  24  which are disposed inside this flue  21 ; a steam turbine ST; the condenser  61 ; and the water feeding pump  62 . Inside the flue  21 , the coal economizer  22 , the vaporizer  23 , and the superheater  24  are arranged in this order from the downstream side toward the upstream side in a direction in which exhaust gas flows. The heat exchanger  4  is provided on the upstream side of the coal economizer  22  in a water-feeding direction. 
     The heat exchanger  4  is connected to the downstream side of the steam recovery line L 5 . The heat exchanger  4  has a cylinder  41  communicating with the flue  21 , and a heat exchanger main body  42  provided inside this cylinder  41 . 
     When the carbon dioxide recovery device  3  is not connected to a latter stage of this heat exchanger  4 , a recirculation system having a piping L 200 , a circulation pump  200 , and a piping L 201  in  FIG. 2  can be provided. When the exit temperature of the heat exchanger  4  is heated to 80° C. or higher by adjusting the circulation flow rate in the recirculation system, water condensation in the exhaust gas inside the heat exchanger  4  can be curbed. Accordingly, corrosion of a piping  42  is avoided and a high exit temperature of the smokestack  5  is maintained so that corrosion or generation of white smoke at the exit are curbed. On the other hand, in the present embodiment, the temperature of exhaust gas at the exit of the heat exchanger  4  can be reduced and costs can be reduced by eliminating this circulation system. In each of the parts constituting the heat exchanger  4 , piping in which steam or water circulates (heat exchanger main body  42 ) is formed of a material having a higher corrosion resistance than piping of the exhaust heat recovery boiler  2 . Regarding such a material, specifically, SUS or Inconel is favorably used (the piping of the exhaust heat recovery boiler  2  is generally formed of a carbon steel as an example). 
     The coal economizer  22  performs heat exchange between water sent through the heat exchanger  4  and exhaust gas, thereby heating the water. The vaporizer  23  performs heat exchange between high-temperature water which has been heated by the coal economizer  22  and exhaust gas, thereby further heating the water and generating steam. This steam is sent to the superheater  24 . The superheater  24  generates superheated steam by superheating steam through heat exchange with exhaust gas. 
     Superheated steam generated by the superheater  24  is sent to the steam turbine ST. The steam turbine ST is rotatively driven by steam so as to supply power to a generator or the like (not illustrated) connected to the same shaft. In addition, at least a part of steam generated by the vaporizer  23  is sent to the carbon dioxide recovery device  3  through the steam supply line L 4  described above and is utilized as a heat source. In addition, exhaust air of the steam turbine ST is sent to the condenser  61  through a turbine exhaust line L 4   b . A constitution in which no steam turbine ST is provided can also be employed. 
     Moreover, the supplementary combustion burner B for supplementary heating of exhaust gas is provided at an end portion of the entrance side of the flue  21  (namely, a side on which exhaust gas flows in). Regarding the supplementary combustion burner B, specifically, a burner or a torch forming a combustion flame using fuel shared with the combustor  12  described above is favorably used. An output of the supplementary combustion burner B can be changed by the control device  90  on the basis of a measurement value of the temperature sensor T. 
     (Constitution of Carbon Dioxide Recovery Device) 
     Subsequently, with reference to  FIG. 3 , a constitution of the carbon dioxide recovery device  3  will be described. As illustrated in the same diagram, the carbon dioxide recovery device  3  has an absorption tower  31 , a regeneration tower  32 , a heat exchanger  33 , a reboiler  34 , a cooler  36 , a first pump P 1 , and a second pump P 2 . 
     The absorption tower  31  has a tubular shape extending in an upward-downward direction, and the exhaust line L 1  is connected to a lower portion thereof. Inside the absorption tower  31 , an absorption liquid which can be chemically bonded to carbon dioxide flows downward from above. Regarding such an absorption liquid, specifically, an aqueous solution of amine including monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), diisopropanolamine (DIPA), and methyldiethanolamine (MDEA), an organic solvent containing no water, a mixture thereof, or an amino acid-based aqueous solution is favorably used. In addition, an absorption liquid other than amine may be used. 
     Exhaust gas which has flowed into the lower portion inside the absorption tower  31  rises inside the absorption tower  31  while coming into contact with an absorption liquid flowing from above. At this time, carbon dioxide contained in the exhaust gas is chemically absorbed into the absorption liquid. The remaining exhaust gas from which carbon dioxide has been removed flows into the exhaust line L 1  again from an upper portion of the absorption tower  31 . 
     The absorption liquid that has absorbed carbon dioxide is sent to the heat exchanger  33  through an absorption liquid recovery line L 31  connected to the lower portion of the absorption tower  31 . The first pump P 1  for pressure-feeding an absorption liquid is provided on the absorption liquid recovery line L 31 . Details will be described below. In the heat exchanger  33 , heat exchange is performed between an absorption liquid which has been regenerated by being heated in the regeneration tower  32  and an absorption liquid before regeneration. Accordingly, the absorption liquid before regeneration is in a state in which the temperature thereof has risen to a certain degree. After passing through the heat exchanger  33 , the absorption liquid before regeneration is sent to the upper portion of the regeneration tower  32  through the absorption liquid recovery line L 31 . 
     The regeneration tower  32  is a device for regenerating an absorption liquid in a state in which carbon dioxide has been absorbed (carbon dioxide has been separated out). A part of an absorption liquid heating line L 33  is inserted into the regeneration tower  32 . The reboiler  34  is provided on the absorption liquid heating line L 33 . High-temperature steam is supplied to the reboiler  34  through the steam supply line L 4  described above. In the reboiler  34 , due to heat exchange with this steam, a part of water contained in the absorption liquid is heated and becomes stripping steam. Inside the regeneration tower  32 , stripping steam comes into contact with the absorption liquid before regeneration supplied through the absorption liquid heating line L 33 . Accordingly, carbon dioxide diffuses from the absorption liquid before regeneration, and the absorption liquid is regenerated (is brought into a state containing no carbon dioxide). Carbon dioxide which has diffused from the absorption liquid before regeneration is sent to the carbon dioxide compression apparatus  7  described above through the recovery line L 6  connected to the upper portion of the regeneration tower  32 . 
     A part of the absorption liquid after regeneration (that is, a component which has not become stripping steam) is sent to an extraction line L 32  connected to a lower portion of the regeneration tower  32 . The heat exchanger  33 , the cooler  36 , and the second pump P 2  are provided in this order on the extraction line L 32 . When the second pump P 2  is driven, the absorption liquid after regeneration is supplied from the regeneration tower  32  to the heat exchanger  33 . 
     The second pump P 2  may be provided between the heat exchanger  33  and the regeneration tower  32  or between the cooler  36  and the heat exchanger  33 . In the heat exchanger  33 , as described above, heat exchange is performed between the absorption liquid before regeneration and the absorption liquid after regeneration. The temperature of the absorption liquid after regeneration falls while passing through the heat exchanger  33  and the cooler  36 . The low-temperature absorption liquid after regeneration is supplied to the upper portion of the absorption tower  31 . 
     (Constitution of Control Device) 
     Subsequently, the control device  90  will be described. As illustrated in  FIG. 1 , this control device  90  has an input unit  91 , a determination unit  92 , and a burner adjustment unit  93 . The temperature of exhaust gas in the circulation line L 2  measured by the temperature sensor T is input as an electrical signal to the input unit  91 . The determination unit  92  determines whether or not the temperature of exhaust gas measured by the temperature sensor T is within a range set in advance. The burner adjustment unit  93  sends out a signal for adjusting an output of the supplementary combustion burner B (that is, an amount of fuel supply) on the basis of a signal sent from the determination unit  92 . 
     Here, inside the exhaust heat recovery boiler  2 , a temperature and a pressure of generated steam are set in accordance with performance requirements of the vaporizer  23 . Therefore, for example, when the temperature of exhaust gas flowing into the exhaust heat recovery boiler  2  is changed in an increasing direction, the temperature of exhaust gas at the exit of the heat exchanger  4  changes in a decreasing direction to maintain the temperature and the pressure. On the other hand, when the temperature of exhaust gas flowing into the exhaust heat recovery boiler  2  is changed in the decreasing direction, the temperature of exhaust gas at the exit of the heat exchanger changes in the increasing direction to maintain the temperature and the pressure described above. Here, in the present embodiment, the control device  90  changes the output of the supplementary combustion burner B on the basis of the temperature of exhaust gas measured by the temperature sensor T serving as a measurement part of outlet temperature. 
     Specifically, when the determination unit  92  determines that the temperature measured by the temperature sensor T is higher than the temperature set in advance, the burner adjustment unit  93  changes the output of the supplementary combustion burner B in the increasing direction. As a result, the temperature of exhaust gas at the entrance of the flue  21  rises, whereas the exit temperature of the heat exchanger  4  (temperature of exhaust gas) changes in the decreasing direction. When the determination unit  92  determines that the temperature measured by the temperature sensor T is lower than the temperature set in advance, the burner adjustment unit  93  changes the output of the supplementary combustion burner B in the decreasing direction. 
     As a result, the temperature of exhaust gas at the entrance of the flue  21  falls, whereas the exit temperature of the heat exchanger  4  (temperature of exhaust gas) changes in the increasing direction. The aforementioned “temperature set in advance” indicates a temperature range in which an absorbent circulating in the absorption tower  31  of the carbon dioxide recovery device  3  can exhibit maximum absorption performance. Regarding such a temperature, specifically, it is desirable to be within a range of 30° C. to 50° C. More desirably, this temperature range is 35° C. to 45° C. 
     Most desirably, this temperature is set to 40° C. 
     (Operational Effects) 
     Next, operation of the gas turbine plant  100  according to the present embodiment will be described. When the gas turbine  1  is driven, exhaust gas is generated from the turbine  13 . The temperature of this exhaust gas falls while passing through the exhaust heat recovery boiler  2 , and then the exhaust gas flows into the carbon dioxide recovery device  3 . 
     In the carbon dioxide recovery device  3 , carbon dioxide is removed from exhaust gas as described above. Thereafter, the exhaust gas diffuses into the atmosphere from the smokestack  5 . Carbon dioxide removed from exhaust gas is liquefied and stored by the carbon dioxide compression apparatus  7 . 
     Here, in the carbon dioxide recovery device  3  described above, a chemical agent having amine as a main component is used as an absorption liquid. This absorption liquid has an appropriate temperature range for efficiently absorbing carbon dioxide. Namely, when the temperature of exhaust gas is excessively high or excessively low, there is concern that the efficiency of absorption of carbon dioxide may deteriorate. 
     Here, in the gas turbine plant  100  according to the present embodiment, the heat exchanger  4  is provided on the downstream side of the exhaust heat recovery boiler  2  on the exhaust line L 1 . According to this constitution, exhaust gas discharged from the exhaust heat recovery boiler  2  passes through the heat exchanger  4  so as to be cooled to the temperature set in advance described above and is then sent to the carbon dioxide recovery device  3 . Namely, the temperature of exhaust gas can be reduced to a favorable reaction temperature region of the absorption liquid. Therefore, carbon dioxide in the exhaust gas can be more efficiently absorbed by the absorption liquid. 
     In the heat exchanger  4 , when exhaust gas is cooled, there is a likelihood that moisture contained in the exhaust gas will be condensed and dewing will occur. Due to such dewing, there is also concern that corrosion may occur in the piping inside the heat exchanger  4 . However, in the foregoing constitution, the piping (heat exchanger main body  42 ) of the heat exchanger  4  is formed of a material having a higher corrosion resistance than a material forming the exhaust heat recovery boiler  2 . Therefore, even when the dewing has occurred, a likelihood of occurrence of corrosion inside the heat exchanger  4  can be reduced. 
     Here, inside the exhaust heat recovery boiler  2 , the temperature and the pressure of generated steam are set on the basis of performance requirements of the vaporizer  23 . Therefore, for example, when the temperature of exhaust gas flowing into the exhaust heat recovery boiler  2  is changed in the increasing direction, the temperature of exhaust gas at the exit of the heat exchanger  4  changes in the decreasing direction to maintain the temperature and the pressure. On the other hand, when the temperature of exhaust gas flowing into the exhaust heat recovery boiler  2  is changed in the decreasing direction, the temperature of exhaust gas at the exit of the heat exchanger  4  changes in the increasing direction to maintain the temperature and the pressure described above. Namely, according to the foregoing constitution, when the control device  90  changes the output of the supplementary combustion burner B on the basis of the temperature measured by the temperature sensor T serving as a measurement part of outlet temperature, the exit temperature of the heat exchanger  4  can be freely adjusted. As a result, the temperature of exhaust gas flowing into the carbon dioxide recovery device  3  can be more minutely controlled. 
     Specifically, according to the foregoing constitution, when the temperature measured by the temperature sensor T is higher than the temperature set in advance, the control device  90  changes the output of the supplementary combustion burner B in the increasing direction. Accordingly, the exit temperature of the heat exchanger  4  can be reduced. As a result, the temperature of exhaust gas flowing into the carbon dioxide recovery device  3  can be more minutely controlled. 
     In addition, according to the foregoing constitution, when the temperature measured by the temperature sensor T is lower than the temperature set in advance, the control device  90  changes the output of the supplementary combustion burner B in the decreasing direction. Accordingly, the exit temperature of the heat exchanger  4  can be increased. As a result, the temperature of exhaust gas flowing into the carbon dioxide recovery device  3  can be more minutely controlled. 
     Furthermore, according to the foregoing constitution, in the heat exchanger  4 , exhaust gas is cooled such that the temperature thereof is within a range of 30° C. to 50° C. Accordingly, carbon dioxide can be more efficiently absorbed and removed from exhaust gas in the carbon dioxide recovery device  3  connected to the downstream side of the heat exchanger  4 . 
     Moreover, according to the foregoing constitution, the carbon dioxide recovery device  3  can be attached to an existing gas turbine plant afterward by only providing the heat exchanger  4 . Namely, the carbon dioxide recovery device  3  can be attached to an existing gas turbine plant without performing large-scale repair. Accordingly, environmental performance of an existing gas turbine plant can be improved at lower costs. Moreover, due to the foregoing supplementary combustion burner B, the amount of steam generated in the exhaust heat recovery boiler  2  can be increased, and a decrease in output of the steam turbine in  FIG. 2  caused by steam to be supplied to the reboiler  34  in  FIG. 3  can be restored. 
     Generally, when the carbon dioxide recovery device  3  is installed in a coal-fired boiler, an oil-fired boiler, or a GTCC exhaust gas system, since the temperature of exhaust gas described above is higher than an operation temperature of the absorption tower  31 , a constitution in which a quencher disposed in a former stage of the absorption tower  31  is conceivable for the purpose of reducing the temperature or removing impurities in the exhaust gas. In the present embodiment, the temperature of exhaust gas can be reduced to the operation temperature of the absorption tower  31 . Therefore, a quencher can be unequipped or miniaturized. 
     OTHER EMBODIMENTS 
     Hereinabove, the embodiment of the present disclosure has been described in detail with reference to the drawings. However, the specific constitution is not limited to this embodiment and also includes design change and the like within a range not departing from the gist of the present disclosure. 
     For example, in addition to the constitutions of the foregoing embodiment, as illustrated in  FIG. 4 , a constitution further including a quencher  40  and an exhaust gas cooler  50  can also be employed. The quencher  40  is provided between the heat exchanger  4  and the carbon dioxide recovery device  3  in the exhaust line L 1 . The quencher  40  is a cooling device for further reducing the temperature of exhaust gas discharged from the heat exchanger  4 . When the quencher  40  is provided, the temperature of exhaust gas can be further reduced (cooled) before the exhaust gas flows into the carbon dioxide recovery device  3 . Therefore, for example, even when exhaust gas in the heat exchanger  4  is insufficiently cooled, a cooling effect can be supplemented by the quencher  40 . In the foregoing embodiment, since the temperature of exhaust gas has become low in advance by the heat exchanger  4 , even when the quencher  40  is provided, for instance, a capacity of the quencher  40  can be curbed to a very small level. Accordingly, a further reduction of manufacturing costs can be achieved. 
     The exhaust gas cooler  50  is provided on the upstream side of the compressor  11  in the circulation line L 2 . The exhaust gas cooler  50  is a device for reducing the temperature of exhaust gas flowing into the compressor  11 . When the exhaust gas cooler  50  is provided, efficiency of compressing the compressor  11  can be further improved. In the foregoing embodiment, since the temperature of exhaust gas has become low in advance by the heat exchanger  4 , even when the exhaust gas cooler  50  is provided, for instance, the capacity of the exhaust gas cooler  50  can be curbed to a very small level. Accordingly, further reduction of manufacturing costs can be achieved. 
     &lt;Appendix&gt; 
     The gas turbine plant described in each embodiment is ascertained as follows, for example. 
     (1) A gas turbine plant ( 100 ) according to a first aspect includes a gas turbine ( 1 ) that is configured to be driven by means of combustion gas generated due to combustion of fuel; an exhaust line (L 1 ) that is configured to guide exhaust gas discharged from the gas turbine ( 1 ) to the outside; an exhaust heat recovery boiler ( 2 ) that is provided in the exhaust line (L 1 ), is configured to generate steam due to heat of the exhaust gas discharged from the gas turbine ( 1 ), and guide the exhaust gas which has passed through the inside of the exhaust heat recovery boiler ( 2 ) to the exhaust line (L 1 ); a carbon dioxide recovery device ( 3 ) that is provided on a downstream side of the exhaust heat recovery boiler ( 2 ) in the exhaust line (L 1 ) and is configured to recover carbon dioxide contained in the exhaust gas flowing in the exhaust line (L 1 ); a heat exchanger ( 4 ) that is provided between the exhaust heat recovery boiler ( 2 ) and the carbon dioxide recovery device ( 3 ) in the exhaust line (L 1 ) and is configured to cool the exhaust gas to a temperature set in advance; and a circulation line (L 2 ) that branches from a position between the carbon dioxide recovery device ( 3 ) and the heat exchanger ( 4 ) in the exhaust line (L 1 ) and is connected to an inlet of the gas turbine ( 1 ). The carbon dioxide recovery device ( 3 ) has an absorption tower ( 31 ) which is configured to absorb carbon dioxide contained in the exhaust gas by causing the exhaust gas at the temperature set in advance and an absorption liquid to come into contact with each other. The heat exchanger ( 4 ) is formed of a material having a higher corrosion resistance than a material forming the exhaust heat recovery boiler ( 2 ). 
     Here, in the carbon dioxide recovery device ( 3 ), a chemical agent having amine as a main component is used as an example of an absorption liquid. This absorption liquid has an appropriate temperature range set in advance for efficiently absorbing carbon dioxide. Namely, when the temperature of exhaust gas is excessively high or excessively low, efficiency of absorption of carbon dioxide deteriorates. According to the foregoing constitution, exhaust gas discharged from the exhaust heat recovery boiler ( 2 ) passes through the heat exchanger ( 4 ) so as to be cooled to the temperature set in advance and is then sent to the carbon dioxide recovery device ( 3 ). Therefore, carbon dioxide in the exhaust gas can be more efficiently absorbed by the absorption liquid. 
     (2) The gas turbine plant ( 100 ) according to a second aspect further includes a measurement part of outlet temperature (T) that is configured to measure an exit temperature of the heat exchanger ( 4 ), a supplementary combustion burner (B) that is configured to heat the exhaust gas flowing into the exhaust heat recovery boiler ( 2 ), and a control device ( 90 ) that is configured to change an output of the supplementary combustion burner (B) on the basis of the exit temperature. 
     Here, inside the exhaust heat recovery boiler ( 2 ), the temperature and the pressure of generated steam are set. Therefore, for example, when the temperature of exhaust gas flowing into the exhaust heat recovery boiler ( 2 ) is changed in an increasing direction, the temperature of exhaust gas at the exit of the heat exchanger ( 4 ) changes in a decreasing direction to maintain the temperature and the pressure. On the other hand, when the temperature of exhaust gas flowing into the exhaust heat recovery boiler ( 2 ) is changed in the decreasing direction, the temperature of exhaust gas at the exit of the heat exchanger ( 4 ) changes in the increasing direction to maintain the temperature and the pressure described above. Namely, according to the foregoing constitution, the control device ( 90 ) changes the output of the supplementary combustion burner (B) on the basis of the temperature measured by the measurement part of outlet temperature (T). Accordingly, the exit temperature of the heat exchanger ( 4 ) can be freely adjusted. As a result, the temperature of exhaust gas flowing into the carbon dioxide recovery device ( 3 ) can be more minutely controlled. 
     (3) In the gas turbine plant ( 100 ) according to a third aspect, the control device ( 90 ) changes an output of the supplementary combustion burner (B) in an increasing direction when the exit temperature is higher than the temperature set in advance. 
     Here, inside the exhaust heat recovery boiler ( 2 ), the temperature and the pressure of generated steam are set. Therefore, for example, when the temperature of exhaust gas flowing into the exhaust heat recovery boiler ( 2 ) is changed in the increasing direction, the temperature of exhaust gas at the exit of the heat exchanger ( 4 ) changes in the decreasing direction to maintain the temperature and the pressure. Namely, according to the foregoing constitution, when the temperature measured by the measurement part of outlet temperature (T) is higher than the temperature set in advance, the control device ( 90 ) changes the output of the supplementary combustion burner (B) in the increasing direction so that the exit temperature of the heat exchanger ( 4 ) can be reduced. As a result, the temperature of exhaust gas flowing into the carbon dioxide recovery device ( 3 ) can be more minutely controlled. 
     (4) In the gas turbine plant ( 100 ) according to a fourth aspect, the control device ( 90 ) changes an output of the supplementary combustion burner (B) in a decreasing direction when the exit temperature is lower than the temperature set in advance. 
     Here, inside the exhaust heat recovery boiler ( 2 ), the temperature and the pressure of generated steam are set. Therefore, for example, when the temperature of exhaust gas flowing into the exhaust heat recovery boiler ( 2 ) is changed in the decreasing direction, the temperature of exhaust gas at the exit of the heat exchanger ( 4 ) changes in the increasing direction to maintain the temperature and the pressure described above. Namely, according to the foregoing constitution, when the temperature measured by the measurement part of outlet temperature (T) is lower than the temperature set in advance, the control device ( 90 ) changes the output of the supplementary combustion burner (B) in the decreasing direction. Accordingly, the exit temperature of the heat exchanger ( 4 ) can be increased. As a result, the temperature of exhaust gas flowing into the carbon dioxide recovery device ( 3 ) can be more minutely controlled. 
     (5) In the gas turbine plant ( 100 ) according to a fifth aspect, the temperature set in advance is within a range of 30° C. to 50° C. 
     According to the foregoing constitution, in the heat exchanger ( 4 ), exhaust gas is cooled such that the temperature thereof is within a range of 30° C. to 50° C. Accordingly, in the carbon dioxide recovery device ( 3 ) connected to the downstream side of the heat exchanger ( 4 ), carbon dioxide can be more efficiently absorbed and removed from exhaust gas. 
     (6) In the gas turbine plant ( 100 ) according to a sixth aspect, the carbon dioxide recovery device ( 3 ) further has a quencher ( 40 ) for cooling the exhaust gas flowing into the absorption tower ( 31 ). 
     According to the foregoing constitution, the temperature of exhaust gas can be further reduced (cooled) by the quencher ( 40 ) before the exhaust gas flows into the absorption tower ( 31 ). Therefore, for example, even when exhaust gas in the heat exchanger ( 4 ) is insufficiently cooled, a cooling effect can be supplemented by the quencher ( 40 ). 
     INDUSTRIAL APPLICABILITY 
     According to an aspect of the present invention, carbon dioxide can be recovered with higher efficiency. 
     REFERENCE SIGNS LIST 
     
         
         
           
               100  Gas turbine plant 
               1  Gas turbine 
               2  Exhaust heat recovery boiler 
               3  Carbon dioxide recovery device 
               4  Heat exchanger 
               5  Smokestack 
               6 A Moisture separation device 
               6 B Intake filter 
               7  Carbon dioxide compression apparatus 
               11  Compressor 
               12  Combustor 
               13  Turbine 
               21  Flue 
               22  Coal economizer 
               23  Vaporizer 
               24  Superheater 
               31  Absorption tower 
               32  Regeneration tower 
               33  Heat exchanger 
               34  Reboiler 
               36  Cooler 
               40  Quencher 
               41  Cylinder 
               42  Heat exchanger main body 
               50  Exhaust gas cooler 
               61  Condenser 
               62  Water feeding pump 
               90  Control device 
               91  Input unit 
               92  Determination unit 
               93  Burner adjustment unit 
               200  Circulation pump 
             B Burner 
             G Generator 
             T Temperature sensor 
             L 1  Exhaust line 
             L 2  Circulation line 
             L 4  Steam supply line 
             L 4   b  Turbine exhaust line 
             L 5  Steam recovery line 
             L 6  Recovery line 
             L 31  Absorbent recovery line 
             L 32  Extraction line 
             L 33  Absorbent heating line 
             L 200 , L 201  Piping 
             P 1  First pump 
             P 2  Second pump 
             ST Steam turbine