Abstract:
A method for flue gas treatment includes branching part of a flue gas stream emitted from a gas turbine from an upstream side or a downstream side of an exhaust heat recovery boiler and subjecting the branched part to combustion with a fuel in an auxiliary boiler so as to increase carbon dioxide concentration in the branched part prior to recombining the flue gas stream from the auxiliary boiler with the remaining part of the flue gas stream from the gas turbine to form a combined flue gas stream having a carbon dioxide concentration for efficient recovery in a carbon dioxide recovery apparatus.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and an apparatus for flue gas treatment that improve efficiency of treatment of carbon dioxide contained in a flue gas emitted from, for example, a gas turbine. 
     2. Description of the Related Art 
     Various techniques have been proposed to separate carbon dioxide from a flue gas generated in power plants thereby to tackle the global warming. Proposed techniques include, for example, Pressure Swing Adsorption (PSA), membrane separation, and chemical absorption. Currently, carbon dioxide separators are rarely used in gas turbine combined plants which are high-efficiency power plants. When the carbon dioxide separators are employed, however, efficiency of net power generation deteriorates significantly because carbon dioxide concentration in a flue gas emitted from such plants is relatively low and a large amount of power is required for separation (see Japanese Patent Application Laid-Open No. 2000-337108, for example). 
     Further, the carbon dioxide concentration in a flue gas emitted from a gas turbine is as low as 3.93%. In order to recover carbon dioxide from such facility, a large volume of flue gas must be treated, and hence a large carbon dioxide recovery apparatus must be employed. 
     When the flue gas emitted from the gas turbine is recycled and reused in the same gas turbine for several times, the carbon dioxide concentration can be increased. However, modification of piping systems of existing facilities is difficult. Specifically, such modification of specification is difficult to realize in the gas turbine. Thus, such techniques are not actually adopted. 
     As an alternative, plural gas turbines can be installed in series so that the flue gas of an upstream gas turbine is sequentially used in a downstream gas turbine. However, the specification of the gas turbine is determined scrupulously in a design phase, and there is little possibility of actual application of a simple serial installation and sequential use of plural gas turbines for the increase in carbon dioxide concentration. 
     As another alternative, it is possible to add a fuel to a flue gas emitted from an existing gas turbine and to re-burn in an exhaust heat recovery boiler. As shown in  FIG. 12 , in this case, while the carbon dioxide concentration in a flue gas  12  emitted from a gas turbine (G/T)  11  is 3.92 volume percent [vol %], the carbon dioxide concentration in a flue gas  14  from an exhaust heat recovery boiler (such as a heat recovery steam generator: HRSG)  13  can be as high as 4.6 vol %. However, it is difficult to add a large amount of fuel and re-burn. In addition, the increase is merely approximately 15%, which is insignificant. Thus, conventionally proposed techniques cannot achieve significant improvements in recovery efficiency of the carbon dioxide recovery apparatus. 
     In view of the foregoing, it is desirable to increase the carbon dioxide concentration in a flue gas emitted from a gas turbine in an existing gas turbine facility by a simple modification so as to improve the efficiency of carbon dioxide recovery. 
     SUMMARY OF THE INVENTION 
     In view of the above, an object of the present invention is to provide a method and an apparatus for flue gas treatment that improve efficiency of treatment of carbon dioxide contained in a flue gas emitted from, for example, a gas turbine. 
     As a result of strenuous efforts to solve the problems as described above, the inventors of the present invention have found that, in the recovery of carbon dioxide, it is necessary to generate a high-pressure, high-temperature steam for the recovery and compression of carbon dioxide, and that a boiler which usually uses air for steam generation can use a flue gas from a gas turbine instead of the air for combustion so that the carbon dioxide concentration in the flue gas is increased. 
     A method according to the first aspect of the present invention for flue gas treatment includes causing a combustion in a boiler using at least a part of a flue gas emitted from a gas turbine and introduced from at least one of an upstream side and a downstream side of an exhaust heat recovery boiler that recovers a high-temperature heat of the flue gas so as to increase a concentration of carbon dioxide in the flue gas, and recovering carbon dioxide in a carbon dioxide recovery apparatus. 
     According to the second aspect of the present invention, in the method of the first aspect, the boiler generates a high-pressure steam required for recovery and compression of carbon dioxide. 
     An apparatus according to the third aspect of the present invention for flue gas treatment includes a gas turbine, a boiler that causes a combustion of a flue gas emitted from the gas turbine, and a carbon dioxide recovery apparatus that recovers carbon dioxide after an increase of carbon dioxide concentration in a flue gas emitted from the boiler. 
     According to the fourth aspect of the present invention, the apparatus of the third aspect further includes an exhaust heat recovery boiler arranged at a downstream side of the gas turbine, wherein a flue gas emitted from the exhaust heat recovery boiler is burnt in the boiler so that the carbon dioxide concentration in the flue gas emitted from the boiler is increased, and the carbon dioxide recovery apparatus recovers carbon dioxide after the increase of the carbon dioxide concentration. 
     According to the fifth aspect of the present invention, the apparatus of the third aspect further includes an exhaust heat recovery boiler arranged at a downstream side of the gas turbine, wherein a part of a flue gas emitted from the exhaust heat recovery boiler is burnt in the boiler, a flue gas emitted from the boiler is combined with the flue gas emitted from the exhaust heat recovery boiler so that carbon dioxide concentration in a combined flue gas is increased, and the carbon dioxide recovery apparatus recovers carbon dioxide after the increase of the carbon dioxide concentration. 
     According to the sixth aspect of the present invention, the apparatus of the third aspect further includes an exhaust heat recovery boiler arranged at a downstream side of the gas turbine, wherein a part of a flue gas emitted from the gas turbine is burnt in the boiler, a flue gas emitted from the boiler is combined with a flue gas emitted from the exhaust heat recovery boiler so that carbon dioxide concentration of a combined flue gas is increased, and the carbon dioxide recovery apparatus recovers carbon dioxide after the increase of the carbon dioxide concentration. 
     According to the seventh aspect of the present invention, the apparatus of the third aspect further includes plurality of the gas turbines, and plural exhaust heat recovery boilers arranged respectively at downstream sides of the gas turbines except for one gas turbine, wherein the boiler causes a combustion of a total amount of a flue gas emitted from the one gas turbine, a flue gas emitted from the boiler is combined with flue gases emitted respectively from the exhaust heat recovery boilers so that carbon dioxide concentration of a combined flue gas is increased, and the carbon dioxide recovery apparatus recovers carbon dioxide after the increase of the carbon dioxide concentration. 
     According to the eighth aspect of the present invention, in the apparatus according to the third aspect, the boiler generates a high pressure steam required for recovery and compression of carbon dioxide. 
     According to the ninth aspect of the present invention, in the apparatus according to the fourth aspect, the boiler generates a high pressure steam required for recovery and compression of carbon dioxide. 
     According to the tenth aspect of the present invention, in the apparatus according to the fifth aspect, the boiler generates a high pressure steam required for recovery and compression of carbon dioxide. 
     According to the eleventh aspect of the present invention, in the apparatus according to the sixth aspect, the boiler generates a high pressure steam required for recovery and compression of carbon dioxide. 
     According to the twelfth aspect of the present invention, in the apparatus according to the seventh aspect, the boiler generates a high pressure steam required for recovery and compression of carbon dioxide. 
     According to the thirteenth aspect of the present invention, in the apparatus according to the eighth aspect, the boiler generates a high pressure steam required for recovery and compression of carbon dioxide. 
     The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a flue gas treatment apparatus according to a first embodiment; 
         FIG. 2  is a schematic diagram of a flue gas treatment apparatus according to a second embodiment; 
         FIG. 3  is a schematic diagram of a flue gas treatment apparatus according to a third embodiment; 
         FIG. 4  is a schematic diagram of a flue gas treatment apparatus according to a fourth embodiment; 
         FIG. 5  is a schematic diagram of a flue gas treatment apparatus according to a fifth embodiment; 
         FIG. 6  is a schematic diagram of a flue gas treatment apparatus according to a test example 1; 
         FIG. 7  is a schematic diagram of a flue gas treatment apparatus according to a comparative example 1; 
         FIG. 8  is a schematic diagram of a flue gas treatment apparatus according to a test example 2; 
         FIG. 9  is a schematic diagram of a flue gas treatment apparatus according to a test example 3; 
         FIG. 10  is a schematic diagram of a flue gas treatment apparatus according to a test example 4; 
         FIG. 11  is a schematic diagram of a flue gas treatment apparatus according to a test example 5; and 
         FIG. 12  is a schematic diagram of a conventional flue gas treatment apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Exemplary embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the present invention is not limited by the following embodiments. Further, elements of the following embodiments may include those easily conceivable by those skilled in the art or those substantially the same therewith. 
     First Embodiment 
     A flue gas treatment apparatus according to a first embodiment of the present invention will be described with reference to the accompanying drawings. 
       FIG. 1  is a schematic diagram of the flue gas treatment apparatus according to the first embodiment. 
     As shown in  FIG. 1 , a flue gas treatment apparatus  10 - 1  of the first embodiment includes a gas turbine (G/T)  11  that is a combustion apparatus causing combustion using, for example, natural gas fuel and air, an exhaust heat recovery boiler (such as HRSG)  13  that recovers high-temperature heat (of approximately 580° C.) of a flue gas  12  emitted from the gas turbine  11 , an auxiliary boiler  15  that causes combustion of a branched part  14   a  (of 10% to 30%) of a flue gas  14  emitted from the exhaust heat recovery boiler  13 , and a carbon dioxide recovery apparatus  18  that recovers carbon dioxide in a combined flue gas  17  which includes the flue gas  14  from the exhaust heat recovery boiler  13  and a flue gas  16  from the auxiliary boiler  15 . 
     In  FIG. 1 , reference character  20  indicates carbon dioxide separated by the carbon dioxide recovery apparatus  18 ,  21  indicates a carbon dioxide compression apparatus,  22  indicates carbon dioxide compressed in the carbon dioxide compression apparatus  21 ,  23  indicates a steam turbine (S/T),  25  and  26  indicate chimneys, and B 1  to B 3  indicate blowers. 
     In the first embodiment, at a downstream side of the exhaust heat recovery boiler (HRSG)  13  which recovers high-temperature heat (of approximately 580° C.) of the flue gas  12  emitted from the gas turbine  11 , the part  14   a  of the flue gas  14  is branched and supplied to the auxiliary boiler  15  and used in place of air for combustion, so that the carbon dioxide concentration in the flue gas  16  emitted from the auxiliary boiler  15  increases. 
     Here, the rate of the branched part of the flue gas  14  can be changed appropriately according to boiler plants, and preferably is 10 to 30%. 
     The carbon dioxide contained in the flue gas at an increased concentration is recovered by the carbon dioxide recovery apparatus  18 , and recovered carbon dioxide  20  is compressed in the carbon dioxide compression apparatus  21 . Compressed carbon dioxide  22  is transported to an outside system, for example, to a urea plant, methanol plant, dimethyl ether plant, plant (such as GTL plant) for synthesizing heating oil and light oil, and to the earth, or introduced into an underground oil mine in a compressed state for an improvement of a recovery rate of crude oil, whereby carbon dioxide emission into an atmosphere can be made substantially zero or zero. 
     As can be seen from the above, the flue gas treatment apparatus according to the first embodiment of the present invention includes the gas turbine  11  and the auxiliary boiler  15  that causes combustion of the flue gas  12  emitted from the gas turbine  11 , and the exhaust heat recovery boiler  13  is arranged at the downstream side of the gas turbine  11  in such a manner that the flue gas  14  emitted from the exhaust heat recovery boiler  13  is combined with the flue gas  16  emitted from the auxiliary boiler  15 , which causes combustion of the part  14   a  of the flue gas  14  emitted from the exhaust heat recovery boiler  13 , whereby the carbon dioxide concentration in the flue gas  16  emitted from the auxiliary boiler  15  can be increased and the recovery efficiency of the carbon dioxide recovery apparatus  18  can be improved. 
     As the carbon dioxide recovery apparatus, a known apparatus which uses a carbon dioxide absorbent (such as amine solution) and includes a carbon dioxide absorption tower for absorbing carbon dioxide and a recovery tower for separating carbon dioxide from the carbon dioxide absorbent to reuse the carbon dioxide absorbent can be used. 
     Further, since the auxiliary boiler  15  can generate a high-pressure steam required for the recovery of carbon dioxide by the carbon dioxide recovery apparatus  18  and the compression of carbon dioxide by the carbon dioxide compression apparatus  21 , steam generated in the exhaust heat recovery boiler  13  is not used in the recovery of carbon dioxide. After being used in the carbon dioxide compression apparatus  21 , the high-pressure steam is employed for separating carbon dioxide in the carbon dioxide recovery apparatus  18 . Thereafter, condensate is returned to the auxiliary boiler  15 . 
     According to the first embodiment of the present invention, the concentration of carbon dioxide coming into the carbon dioxide recovery apparatus can be increased. Further, the fuel consumption of the auxiliary boiler can be reduced through the use of exhaust heat coming out from the exhaust heat recovery boiler. 
     Second Embodiment 
     A flue gas treatment apparatus according to a second embodiment of the present invention will be described with reference to the accompanying drawings. 
       FIG. 2  is a schematic diagram of the flue gas treatment apparatus according to the second embodiment. 
     As shown in  FIG. 2 , a flue gas treatment apparatus  10 - 2  of the second embodiment includes a gas turbine (G/T)  11  that is a combustion apparatus causing combustion using, for example, natural gas fuel and air, an exhaust heat recovery boiler (such as HRSG)  13  that recovers high-temperature heat (of approximately 580° C.) of a flue gas  12  emitted from the gas turbine  11 , an auxiliary boiler  15  that causes combustion of a branched part  12   a  of the flue gas  12  emitted from the gas turbine  11 , and a carbon dioxide recovery apparatus  18  that recovers carbon dioxide in a combined flue gas  17  which includes a flue gas  16  emitted from the auxiliary boiler  15  and a flue gas  14  emitted from the exhaust heat recovery boiler  13 . 
     In the first embodiment, the branch is formed at the downstream side of the exhaust heat recovery boiler  13 . In the second embodiment, a branch is formed at the upstream side of the exhaust heat recovery boiler  13  so that a part of the high-temperature flue gas  12  (of approximately 580° C.) is introduced into the auxiliary boiler  15 , whereby a fuel supplied to the auxiliary boiler  15  can be reduced significantly. 
     The rate of the branched part of the flue gas  12  can be changed appropriately according to boiler plants, and preferably is 8 to 30%. 
     As can be seen from the above, the flue gas treatment apparatus according to the second embodiment of the present invention includes the gas turbine  11  and the auxiliary boiler  15  that causes combustion of the flue gas  12  emitted from the gas turbine  11 , and the exhaust heat recovery boiler  13  is arranged at the downstream side of the gas turbine  11  in such a manner that the flue gas  14  emitted from the exhaust heat recovery boiler  13  is combined with the flue gas  16  emitted from the auxiliary boiler  15 , which causes combustion of the part  12   a  of the flue gas  12  emitted from the gas turbine  11 , whereby the carbon dioxide concentration in the flue gas  16  emitted from the auxiliary boiler  15  can be increased and the recovery efficiency of the carbon dioxide recovery apparatus  18  can be improved. 
     Third Embodiment 
     A flue gas treatment apparatus according to a third embodiment of the present invention will be described with reference to the accompanying drawings. 
       FIG. 3  is a schematic diagram of the flue gas treatment apparatus according to the third embodiment. 
     As shown in  FIG. 3 , a flue gas treatment apparatus  10 - 3  of the third embodiment includes gas turbines (G/T)  11  arranged in parallel as combustion apparatuses causing combustion using, for example, natural gas fuel and air, exhaust heat recovery boilers (such as HRSG)  13  arranged in parallel to recover high-temperature heat (of approximately 580° C.) of flue gases  12  emitted from the gas turbines  11 , a carbon dioxide recovery apparatus  18  that recovers carbon dioxide in a flue gas which includes flue gases  14 - 1  to  14 - 4  from the plural exhaust heat recovery boilers  13 - 1  to  13 - 4 , and a boiler  19  that causes combustion of a total amount of the flue gas  12  emitted from at least one gas turbine  11 - 5  among the plural gas turbines, and the carbon dioxide recovery apparatus  18  recovers carbon dioxide in a combined flue gas  17  which includes a flue gas  16  emitted from the boiler  19  and the flue gases  14 - 1  to  14 - 4 . 
     Some large-scale plants have plural gas turbine facilities. For the treatment of flue gas emitted from boilers of such plant, flue gas from one gas turbine facility among plural gas turbine facilities is directly introduced into the boiler  19  so as to increase carbon dioxide concentration in the flue gas  16 . Then, the flue gas with an increased carbon dioxide concentration is combined with the flue gases  14 - 1  to  14 - 4  emitted respectively from the exhaust heat recovery boilers  13 - 1  to  13 - 4  connected respectively to the gas turbines (gas turbine facilities)  11 - 1  to  11 - 4 , so that the carbon dioxide concentration in the combined flue gas  17  is increased. 
     As can be seen from the above, the third embodiment of the present invention deals with a facility where plural gas turbine facilities are installed, by introducing a total amount of a flue gas  12 - 5  emitted from at least one gas turbine  11 - 5  among the plural gas turbines into the boiler  19  to cause combustion so as to increase the carbon dioxide concentration in the flue gas  16  emitted from the boiler  19 , and further combining the flue gases  14 - 1  to  14 - 4  from the exhaust heat recovery boilers  13 - 1  to  13 - 4  of the rest of the gas turbine facilities with the flue gas  16  to supply the combined flue gas to the carbon dioxide recovery apparatus  18 , whereby the efficiency of the recovery of carbon dioxide can be improved. 
     Fourth Embodiment 
     A flue gas treatment apparatus according to a fourth embodiment of the present invention will be described with reference to the accompanying drawings. 
       FIG. 4  is a schematic diagram of the flue gas treatment apparatus according to the fourth embodiment. 
     As shown in  FIG. 4 , a flue gas treatment apparatus  10 - 4  of the fourth embodiment includes a gas turbine (G/T)  11  that is a combustion apparatus causing combustion using, for example, natural gas fuel and air, a boiler  19  that causes combustion of a total amount of a flue gas  12  emitted from the gas turbine  11 , and a carbon dioxide recovery apparatus  18  that recovers carbon dioxide in a flue gas  16  emitted from the boiler  19 . 
     In the first and the second embodiments described above, a branch is formed at the downstream side or the upstream side of the exhaust heat recovery boiler. In the fourth embodiment, a total amount of the high-temperature flue gas  12  (of 580° C.) emitted from the gas turbine  11  is directly introduced into the boiler  19  without any branches, whereby the carbon dioxide concentration in the flue gas  16  emitted from the boiler  19  is increased. Further, an excess of generated steam can be supplied to a steam turbine (S/T)  24  for power generation. 
     As can be seen from the above, according to the fourth embodiment of the present invention, the total amount of the flue gas  12  from the gas turbine  11  is introduced into the boiler  19  and burnt so as to increase the carbon dioxide concentration in the flue gas  16  emitted from the boiler  19 , whereby the recovery efficiency of the carbon dioxide recovery apparatus  18  can be improved. 
     Fifth Embodiment 
     A flue gas treatment apparatus according to a fifth embodiment of the present invention will be described with reference to the accompanying drawings. 
       FIG. 5  is a schematic diagram of the flue gas treatment apparatus according to the fifth embodiment. 
     As shown in  FIG. 5 , a flue gas treatment apparatus  10 - 5  of the fifth embodiment includes a gas turbine (G/T)  11  that is a combustion apparatus causing combustion using, for example, natural gas fuel and air, an exhaust heat recovery boiler (such as HRSG)  13  that recovers high-temperature heat (of approximately 580° C.) of a flue gas  12  emitted from the gas turbine  11 , an auxiliary boiler  15  that causes combustion of a total amount of a flue gas  14  emitted from the exhaust heat recovery boiler  13 , and a carbon dioxide recovery apparatus  18  that recovers carbon dioxide in a combined flue gas  17  which includes a flue gas  16  from the auxiliary boiler  15 . 
     In the first and the second embodiments described above, the branch is formed at the downstream side or the upstream side of the exhaust heat recovery boiler  13 . In the fourth embodiment, a total amount of the flue gas  14  emitted from the exhaust heat recovery boiler  13  is directly introduced into the auxiliary boiler  15  without any branches, whereby the carbon dioxide concentration in the flue gas  16  emitted from the auxiliary boiler  15  is increased. Further, an excess of generated steam can be supplied to a steam turbine (S/T)  24  for power generation. 
     Test examples exemplifying an effect of the present invention will be described below, though the present invention is not limited thereby. 
     Test Example 1 
       FIG. 6  is a schematic diagram of an apparatus similar to the flue gas treatment apparatus according to the first embodiment shown in  FIG. 1 . In the apparatus of  FIG. 6 , the flue gas  12  of 580° C. emitted from the gas turbine  11  was introduced into the exhaust heat recovery boiler  13 , and the part  14   a  (branched rate: 14.2%, flow rate: 182,100 Nm 3 /H) of the flue gas (flow rate: 1,282,400 Nm 3 /H, CO 2  concentration: 3.93 vol %, O 2  concentration: 11.43 vol %) 14 emitted from the exhaust heat recovery boiler  13  was introduced into the auxiliary boiler  15 . 
     In the test example 1, an employed gas turbine was PG724 (FA type) of General Electric Company. The flue gas  14  emitted from the exhaust heat recovery boiler included 70.25 vol % of nitrogen, 11.43 vol % of oxygen, 3.93 vol % of carbon dioxide, and 13.55 vol % of water, and the temperature was 88.4° C. 
     The flow rate and the thermal capacity of fuel supplied to the auxiliary boiler  15  were 8,560 Nm 3 /H and 80.5×106 Kcal/H, respectively, and the CO 2  concentration in the flue gas  16  was 8.2 vol % (the flow rate and the O 2  concentration in the flue gas  16  were 190,660 Nm 3 /H and 2.0 vol %, respectively). The CO 2  concentration in the combined flue gas  17  which included the flue gas  14  (flow rate: 1,100,300 Nm 3 /H, branched rate: 85.8%) and the flue gas  16  was 4.6 vol % (the flow rate of the combined flue gas  17  was 1,290,960 Nm 3 /H). 
     Comparative Example 1 
       FIG. 7  is a schematic diagram of an apparatus similar to the flue gas treatment apparatus of the test example 1 shown in  FIG. 6 . In the apparatus of  FIG. 7 , however, the flue gas  14  (flow rate: 1,282,400 Nm 3 /H, CO 2  concentration: 3.93 vol %, and O 2  concentration; 11.43 vol %) from the exhaust heat recovery boiler  13  was not introduced into the auxiliary boiler  15 , and instead, an air (flow rate: 93.660 Nm 3 /H) was introduced into the auxiliary boiler  15 . 
     In the comparative example 1, since the introduced air was of a low temperature, the flow rate of the fuel supplied to the auxiliary boiler  15  was 8,851 Nm 3 /H (and the thermal capacity was 83.2×106 Kcal/H), and the CO 2  concentration of the flue gas  16  was 8.6 vol % (flow rate: 102,510 Nm 3 /H, and O 2  concentration: 2.0 vol %). The CO 2  concentration of the combined flue gas  17  which included the flue gas  14  and the flue gas  16  was 4.3 vol % (and the flow rate was 1,384,900 Nm 3 /H). 
     Thus, it is found that test example 1 can realize higher increase in the carbon dioxide concentration than the comparative example 1. 
     Test Example 2 
       FIG. 8  is a schematic diagram of an apparatus similar to the flue gas treatment apparatus according to the second embodiment shown in  FIG. 2 . In the apparatus of  FIG. 8 , a part (branched rate: 9.5%, flow rate: 120,890 Nm 3 /H) of the flue gas  12  (flow rate: 1,282,400 Nm 3 /H, CO 2  concentration: 3.93 vol %, and O 2  concentration; 11.43 vol %) emitted from the gas turbine  11  was introduced into the auxiliary boiler  15 . 
     In this example, since the introduced flue gas  12  was of a high temperature (of 580° C.), the fuel supplied to the auxiliary boiler  15  could be reduced to 5,700 Nm 3 /H, which was a significant reduction from the amount used in the test example 1. 
     The CO 2  concentration in the combined flue gas  17  which included the flue gas  14  (branched rate: 90.5%, flow rate: 1,161,510 Nm 3 /H) and the flue gas  16  (flow rate: 126,590 Nm 3 /H, CO 2  concentration: 8.2 vol %, and O 2  concentration; 2.0 vol %) was 4.35 vol % (and the flow rate was 1,288,100 Nm 3 /H). 
     Test Example 3 
       FIG. 9  is a schematic diagram of an apparatus similar to the flue gas treatment apparatus according to the third embodiment shown in  FIG. 3 . In the apparatus of  FIG. 9 , among the plural (five in the test example 3) gas turbines respectively indicated as first to fifth gas turbines  11 - 1  to  11 - 5 , the first to the fourth gas turbines  11 - 1  to  11 - 4  were connected respectively to the exhaust heat recovery boilers  13 - 1  to  13 - 4  for the exhaust heat recovery, so that flue gases  12 - 1  to  12 - 4  (for each, flow rate: 1,282,400 Nm 3 /H, CO 2  concentration: 3.93 vol %, O 2  concentration: 11.43 vol %) therefrom were introduced into the exhaust heat recovery boilers  13 - 1  to  13 - 4 , respectively, while the total amount of the flue gas  12 - 5  from the fifth gas turbine  11 - 5  was introduced into the boiler  19 . The flow rate of the fuel supplied to the boiler  19  was 28,530 Nm 3 /H. 
     In this example, since the total amount of the flue gas  12 - 5  from the fifth gas turbine  11 - 5  was introduced into the boiler  19 , the CO 2  concentration in the combined flue gas  17  which included the flue gases  14 - 1  to  14 - 4  and the flue gas  16  (flow rate: 1,310,930 Nm 3 /H, CO 2  concentration: 6.2 vol %) could be increased to 4.4 vol % (and the flow rate was 6,440,530 Nm 3 /H). 
     Test Example 4 
       FIG. 10  is a schematic diagram of an apparatus similar to the flue gas treatment apparatus according to the fourth embodiment shown in  FIG. 4 . In the apparatus of  FIG. 10 , the total amount of the flue gas  12  (flow rate: 1,282,400 Nm 3 /H, CO 2  concentration: 3.92 vol %, and O 2  concentration: 11.43 vol %) emitted from the gas turbine  11  was introduced into the boiler  19 . The flow rate of the fuel supplied to the boiler  19  was 60,500 Nm 3 /H. 
     In this example, since the total amount of the flue gas  12  from the gas turbine  11  was introduced into the boiler  19 , the CO 2  concentration in the flue gas  16  (flow rate: 1,342,900 Nm 3 /H, O 2  concentration: 2.0 vol %) could be increased to 8.87 vol %. 
     Test Example 5 
       FIG. 11  is a schematic diagram of an apparatus similar to the flue gas treatment apparatus according to the fifth embodiment shown in  FIG. 5 . In the apparatus of  FIG. 11 , the exhaust heat of the flue gas  12  (of 580° C.) from the gas turbine  11  was recovered in the exhaust heat recovery boiler  13 , and the total amount of the flue gas  14  (flow rate: 1,282,400 Nm 3 /H, CO 2  concentration: 3.92 vol %, O 2  concentration: 11.43 vol %) from the exhaust heat recovery boiler  13  was introduced into the auxiliary boiler  15 . The flow rate of the fuel supplied to the auxiliary boiler  15  was 60,280 Nm 3 /H. 
     In this example, the CO 2  concentration in the flue gas  16  emitted from the auxiliary boiler  15  was 8.7 vol % (and the flow rate was 1,342,680 Nm 3 /H). 
     As can be seen from the test examples 1 to 5, when a part or a whole of the flue gas at the upstream side or the downstream side of the exhaust heat recovery boiler (HRSG), which recovers a heat of a high-temperature flue gas emitted from the gas turbine, is introduced and burnt in the auxiliary boiler and the boiler as in the embodiments of the present invention, the carbon dioxide concentration in the flue gas can be increased. Therefore, the efficiency of the subsequent recovery of the carbon dioxide in the carbon dioxide recovery apparatus can be increased. 
     According to the embodiments of the present invention, a part or a whole of the flue gas is introduced into the auxiliary boiler and the boiler and burnt so that the carbon dioxide concentration in the flue gas is increased, whereby the recovery efficiency of the carbon dioxide recovery apparatus can be improved. In addition, since the auxiliary boiler and the boiler can generate a high-pressure steam required for the recovery and the compression of carbon dioxide, the steam generated in the exhaust heat recovery boiler is not used in the recovery of carbon dioxide. 
     INDUSTRIAL APPLICABILITY 
     As can be seen from the foregoing, according to the method and the apparatus for flue gas treatment according to the present invention, a part or a whole of the flue gas at the upstream side or the downstream side of the exhaust heat recovery boiler (HRSG), which recovers a heat of the high-temperature flue gas, is introduced and burnt in one of the auxiliary boiler and the boiler so that the carbon dioxide concentration in the flue gas is increased, and subsequently the carbon dioxide recovery apparatus recovers carbon dioxide. Therefore, the method and the apparatus for flue gas treatment according to the present invention are suitable for recovery of carbon dioxide in gas turbine plants. 
     Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.