CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of application Ser. No. 12/579,800, filed Oct. 15, 2009, now abandoned, which is incorporated herein by reference. 
     This is a Continuation Application of PCT Application No. PCT/JP2008/072433, filed Dec. 10, 2008, which was published under PCT Article 21(2) in Japanese. 
     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2007-318632, filed Dec. 10, 2007, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a condenser condensing steam into condensate with cooling water. 
     2. Description of the Related Art 
     A condenser applied to, for example, a nuclear power plant or a thermal power plant, condenses turbine exhaust steam which has ended an expansion work by steam turbine, into condensate, with cooling water. The cooling water used in such a condenser is sea water or fresh water from a cooling tower. The cooling water is made to flow in a heat-transfer pipe arranged in the condenser to exchange heat with the exhaust steam introduced into the condenser and condense the turbine exhaust steam. 
     One of the types of condenser is a multistage pressure condenser which comprises a plurality of, i.e. two or three main body shells (i.e. a plurality of condensers) and in which pipes are serially arranged such that the cooling water pass through each of the main body shells at a plurality of times. In the main body shell of the multistage pressure condenser which is arranged on a slip stream side of the flow path of the cooling water, vacuum in the main body shell becomes lower due to rise of cooling water temperature. For this reason, the pressure of the turbine exhaust steam introduced into the main body shell arranged at the slip stream side of the flow path of the cooling water becomes higher. 
     Temperature of the condensate condensed in the condenser becomes a saturation temperature which substantially corresponds to the turbine exhaust pressure introduced into the main body shell of the condenser. Thus, in the multistage pressure condenser in which the main body shells are different in pressure, condensate temperatures of the multistage pressure condenser having, for example, three types of pressures in the main body shells are higher in order of a high pressure condenser, an intermediate pressure condenser and a low pressure condenser. 
     Since the condensate generated in the condenser is supplied again to the system as feed water, a higher temperature of the condensate is desirable in terms of heat efficiency. In the above-described three-shell multistage pressure condenser, it is preferable to make the condensate of a comparatively low temperature generated in the intermediate pressure condenser and the low pressure condenser close to the condensate temperature in the high pressure condenser. 
       FIG. 4A  is a front sectional view showing a structure of a conventional multistage condenser  100 .  FIG. 4B  is a side sectional view showing the structure of the conventional multistage condenser  100 . 
     The multistage condenser  100  is constituted by connecting a high pressure condenser  1 , an intermediate pressure condenser  2  and a low pressure condenser  3  which are different in inner pressure, serially in this order. 
     The high pressure condenser  1  has a high pressure turbine  81  mounted on a head side, and a high pressure cooling tube bank  8  constituted by a number of heat-transfer pipes is provided inside the condenser. At a bottom portion of the high pressure condenser  1 , a high pressure hot well  6  is provided and a condensate outlet box  7  is also provided at a lower side. 
     The high pressure hot well  6  consists of a liquid phase part  6   a  serving as the bottom portion where the condensate is stored, and a vapor phase part  6   b  provided between the liquid phase part  6   a  and the high pressure cooling tube bank  8 . In addition, a heater drain tube  13  is connected to the high pressure condenser  1  and a high pressure baffle  9  is provided at the connection part. 
     The intermediate pressure condenser  2  has a lower inner pressure than the high pressure condenser  1 , and has an intermediate pressure turbine  82  mounted on a head side. An intermediate pressure cooling tube bank  28  constituted by a number of heat-transfer pipes is provided inside the condenser, similarly to the high pressure condenser  1 . A reheat chamber  22  partitioned by a pressure shroud  4  is provided at a lower portion of the intermediate pressure cooling tube bank  28 . 
     In the reheat chamber  22 , a steam duct  10  serving as high pressure steam introducing means, connected to the high pressure condenser  1 , is provided. At a bottom portion of the intermediate pressure condenser  2 , an intermediate pressure hot well  26  is provided. The intermediate pressure hot well  26  consists of a liquid phase part  26   a  serving as a bottom portion where the condensate is stored, and a vapor phase part  26   b  provided above the liquid phase part  26   a . The vapor phase part  26   b  is the reheat chamber  22 . The liquid phase part  6   a  of the high pressure hot well  6  and the liquid phase part  26   a  of the intermediate pressure hot well  26  communicate with each other by a condensate tube  11 . 
     The low pressure condenser  3  has a lower inner pressure than the intermediate pressure condenser  2 , and has a low pressure turbine  83  mounted on a head side. A low pressure cooling tube bank  38  constituted by a number of heat-transfer pipes is provided inside the condenser, similarly to the high pressure condenser  1  and the intermediate pressure condenser  2 . A reheat chamber  23  partitioned by a pressure shroud  5  is provided at a lower portion of the low pressure cooling tube bank  38 . 
     In the reheat chamber  23 , a steam duct  30  serving as high pressure steam introducing means is provided and connected to the reheat chamber  22  of the intermediate pressure condenser  2 . At a bottom portion of the low pressure condenser  3 , a low pressure hot well  36  is provided. The low pressure hot well  36  consists of a liquid phase part  36   a  serving as a bottom portion where the condensate is stored, and a vapor phase part  36   b  provided above the liquid phase part  36   a . The vapor phase part  36   b  is the reheat chamber  23 . The liquid phase part  26   a  of the intermediate pressure hot well  26  and the liquid phase part  36   a  of the low pressure hot well  36  communicate with each other by a condensate tube  31 . Furthermore, the heater drain tube  13  is connected to the low pressure condenser  3 , and a low pressure baffle  39  is provided at the connection part. 
     As cooling water, for example, sea water is introduced into each of the high pressure cooling tube bank  8 , the intermediate pressure cooling tube bank  28  and the low pressure cooling tube bank  38 . In the multistage pressure condenser, the high pressure cooling tube bank  8 , the intermediate pressure cooling tube bank  28  and the low pressure cooling tube bank  38  are connected serially. The cooling water is first introduced into the low pressure cooling tube bank  38 , passes through the intermediate pressure cooling tube bank  28  after passing through the low pressure cooling tube bank  38 , and is finally introduced intro high pressure cooling tube bank  8  and discharged. 
     In the high pressure cooling tube bank  8 , the high pressure turbine exhaust which finishes the work at the high pressure turbine  81  and is supplied to the high pressure condenser  1  is condensed as a high pressure condensate by exchanging heat via the heat-transfer pipes with the cooling water of the highest temperature introduced into the high pressure cooling tube bank  8 , and is recovered in the liquid phase part  6   a  of the high pressure hot well  6  of the high pressure condenser  1 . 
     In the intermediate pressure cooling tube bank  28 , the intermediate pressure turbine exhaust which finishes the work at the intermediate pressure turbine  82  and is supplied to the intermediate pressure condenser  2  is condensed as an intermediate pressure condensate by exchanging heat via the heat-transfer pipes with the cooling water passing through the intermediate pressure cooling tube bank  28 . The intermediate pressure condensate is temporarily stored on the pressure shroud  4  of the intermediate pressure condenser  2  and then sprayed into the reheat chamber  22  through a number of circle holes formed on a perforated panel provided on the pressure shroud  4 . The high pressure steam is introduced into the reheat chamber  22  from the vapor phase part  6   b  of the high pressure hot well  6  provided in the high pressure condenser  1  via the steam duct  10 . The intermediate pressure condensate sprayed into the reheat chamber  22  by the high pressure steam is directly reheated by the heat exchange. The reheated intermediate condensate is finally stored in the liquid phase part  26   a  of the intermediate pressure hot well  26 , supplied to the liquid phase part  6   a  of the high pressure hot well  6  via the condensate tube  11 , and supplied to a feed water heater (not shown) through a condensate outlet box  7 . 
     In the low pressure cooling tube bank  38 , the low pressure turbine exhaust which finishes the work at the low pressure turbine  83  and is supplied to the low pressure condenser  3  is condensed as a low pressure condensate by exchanging heat via the heat-transfer pipes with the cooling water of the lowest temperature passing through the low pressure cooling tube bank  38 . The low pressure condensate is temporarily stored on the pressure shroud  5  of the low pressure condenser  3  and then sprayed into the reheat chamber  23  through a number of circle holes formed on a perforated panel provided on the pressure shroud  5 . The high pressure steam in the vapor phase part  6   b  of the high pressure hot well  6  is further introduced into the reheat chamber  23  from the reheat chamber  22  serving as the vapor phase part  26   b  of the intermediate pressure hot well  26  via the steam duct  30 . The low pressure condensate sprayed into the reheat chamber  23  by the high pressure steam is directly reheated by the heat exchange. The reheated low condensate is finally stored in the liquid phase part  36   a  of the low pressure hot well  36 , supplied to the liquid phase part  6   a  of the high pressure hot well  6  via the condensate tube  31 , the liquid phase part  26   a  of the intermediate pressure hot well  26  and the condensate tube  11 , and supplied to a feed water heater (not shown) through the condensate outlet box  7 . 
     A heater drain generated by condensing in the feed water heater bleed steam of the steam turbine for reheating the feed water flows into the heater drain tube  13 . The flowing heater drain, which is recovered in the high pressure condenser  1  or the low pressure condenser  3 , collides with the high pressure baffle  9  or the low pressure baffle  39 , reduces the flow force and falls into the liquid phase part  6   a  of the high pressure hot well  6  or the liquid phase part  36   a  of the low pressure hot well  36 . 
     As for a known condenser, for example, Jpn. Pat. Appln. KOKAI Publication No. 11-173768, Jpn. U.M. Appln. KOKOKU Publication No. 49-12482, Japanese Patent No. 3706571, Jpn. Pat. Appln. KOKAI Publication No. 49-032002 and the like should be referred to. 
     BRIEF SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     The temperature of the heater drain recovered in the condenser is higher than the saturation temperature in the condenser, and oxygen is often dissolved in the heater drain at a high concentration. In some cases, 40% or more of the entire fluid flowing in the condenser is the heater drain. For this reason, the temperature of the heater drain and oxygen dissolved in the heater drain give great influences to the performance and operation of the heater and plant. 
     When the heater drain collides with the baffle and falls similarly to the prior art, oxygen dissolved in the heater drain does not completely discharge but falls into the hot well, which results in increasing the concentration of oxygen dissolved in the condensate or greatly waving the liquid surface in accordance with the fall into the hot well. 
     If a large quantity of oxygen is dissolved in the condensate, the constituent elements of the power plant are corroded due to the chemical reaction and the like. The oxygen dissolved in the condensate therefore needs to be maintained at a low concentration at any time during the operation of the plant. 
     The present invention has been accomplished under those circumstances. The object of the present invention is to obtain a condenser capable of reducing oxygen dissolved in the heater drain recovered in the condenser. 
     Means for Solving the Problem 
     A condenser according to one aspect of the present invention comprises: a high pressure side condenser; a high pressure side cooling tube bank provided inside the high pressure side condenser, which has a high pressure side cooling water introduced therein and condenses a high pressure side turbine exhaust by heat exchange with the high pressure side cooling water to obtain a high pressure side condensate; a high pressure side hot well provided at a bottom portion of the high pressure side condenser; a low pressure side condenser which has an inner pressure lower than the high pressure side condenser; a low pressure side cooling tube bank provided inside the low pressure side condenser, which has a low pressure side cooling water introduced therein and condenses a low pressure side turbine exhaust by heat exchange with the low pressure side cooling water to obtain a low pressure side condensate; a pressure shroud provided at a lower part than the low pressure side cooling tube bank, inside the low pressure side condenser; a low pressure side hot well provided at a lower part of the pressure shroud, of the low pressure side condenser; high pressure steam introducing means provided at the low pressure side hot well, for communicating with an inner side of the high pressure side condenser and introducing high pressure steam; low pressure side condensate introducing means provided at the pressure shroud, for introducing a low pressure side condensate into the low pressure side hot well; a flash box which communicates with at least one of the high pressure side hot well and the low pressure side hot well, flashes a heater drain from a feed water heater, and urges at least one of the high pressure side hot well and the low pressure side hot well to recover the flashed heater drain; and a flash steam path which introduces flash steam generated inside the flash box into at least one of an interval between the high pressure side cooling tube bank and the high pressure side hot well and an interval between the low pressure side cooling tube bank and the low pressure side hot well. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1A  is a front sectional view showing a structure of a multistage condenser according to the first embodiment of the present invention. 
         FIG. 1B  is a side sectional view showing the structure of the multistage condenser according to the first embodiment of the present invention. 
         FIG. 2A  is a front sectional view showing a structure of a multistage condenser according to the second embodiment of the present invention. 
         FIG. 2B  is a side sectional view showing the structure of the multistage condenser according to the second embodiment of the present invention. 
         FIG. 3A  is a front sectional view showing a structure of a multistage condenser according to the third embodiment of the present invention. 
         FIG. 3B  is a side sectional view showing the structure of the multistage condenser according to the third embodiment of the present invention. 
         FIG. 4A  is a front sectional view showing a structure of a multistage condenser according to the prior art. 
         FIG. 4B  is a side sectional view showing the structure of the multistage condenser according to the prior art. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention are explained below with reference to the accompanying drawings. 
     1 st  Embodiment 
       FIG. 1A  is a front sectional view showing a structure of a multistage condenser  101  according to the first embodiment of the present invention.  FIG. 1B  is a side sectional view showing the structure of the multistage condenser  101  according to the first embodiment. 
     In  FIG. 1A  and  FIG. 1B , the same constituent elements as those of the prior art shown in  FIG. 4A  and  FIG. 4B  are denoted by the same reference numbers as those in  FIG. 4A  and  FIG. 4B  and their detailed explanations are omitted. 
     In the conventional multistage condenser shown in  FIG. 4A  and  FIG. 4B , the high pressure baffle  9  is provided at the connection part between the heater drain tube  13  and the high pressure condenser  1 , and the low pressure baffle  39  is provided at the connection part between the heater drain tube  13  and the low pressure condenser  3 . In the multistage condenser  101  according to the present embodiment, however, the high pressure baffle  9  or the low pressure baffle  39  is not provided, but a high pressure flash box  14  is provided on an outside surface of the high pressure condenser  1  and a low pressure flash box  24  is provided on an outside surface of the low pressure condenser  3 . 
     A heater drain path  15  formed in a reverse concave shape is provided in the high pressure flash box  14  provided on the outside surface of the high pressure condenser  1 . One of lower parts of the heater drain path  15  formed in the reverse concave shape is partitioned into a drain channel part  15   a  and a flash steam path  17  adjacent thereto by a partition plate  15   d . At a lower part of the drain channel part  15   a  partitioned by the partition plate  15   d , a connection port  13   a  urging the heater drain from the heater drain tube  13  to be introduced into the flash box  14  is provided. An upper part of the flash steam path  17  communicates with the drain channel part  15   a . At a lower part of the flash steam path  17 , an equalizing port  18  communicating with the vapor phase part  6   b  of the hot well  6  of the high pressure condenser  1  is provided. The partition plate  15   d  partitioning the drain channel part  15   a  and the flash steam path  17  is set to be high such that the heater drain supplied in the drain channel part  15   a  does not flow into the flash steam path  17  over the partition plate  15   d.    
     A lower end portion of the other lower part of the heater drain path  15  formed in a reverse concave shape is a drain fall part  15   c  which communicates with the liquid phase part  6   a  of the high pressure hot well  6 . The drain fall part  15   c  is adjacent to the drain channel part  15   a  and a partition plate  15   e  is provided therebetween. The partition plate  15   e  is set to be lower than the partition plate  15   d  such that the heater drain introduced from the connection port  13   a  into the drain channel part  15   a  flows from the drain channel part  15   a  into the drain fall part  15   c . Furthermore, porous plates  20  are provided at a plurality of steps inside the drain fall part  15   c . In addition, a horizontal portion is provided on the drain channel part  15   a  on the side of the partition plate  15   e , and this portion forms a free liquid level part  15   b.    
     In other words, in the present embodiment, the heater drain path  15  formed in the flash box  14  is constituted by three parts, i.e., the drain channel part  15   a , the drain fall part  15   c  and the flash steam path  17 . 
     The heater drain introduced into the high pressure flash box  14  flows into the drain channel part  15   a  and is boiled at, particularly, the free liquid level part  15   b  to release flash steam. After that, heater drain  16  flows down in the drain fall part  15   c  over the partition plate  15   e , becomes a liquid column at the porous plates  20  arranged at a plurality of steps in the drain fall part  15   c , and increases an area of contact with the steam. At this time, the heater drain  16  falls while releasing the non-flashed steam, releases uncondensed gas such as oxygen dissolved in the heater drain  16 , and deaerated. The deaerated heater drain  16  joins the condensate stored in the liquid phase part  6   a  of the high pressure hot well  6  from a bottom portion of the drain fall part  15   c . The flash steam and uncondensed gas generated from the heater drain  16  are introduced into the flash steam path  17  over the partition plate  15   d  from an upper part of the drain channel part  15   a  to flow into the vapor phase part  6   b  of the hot well  6  (between the high pressure cooling tube bank  8  and the high pressure hot well  6 ) from the equalizing port  18  provided at the lower end of the flash steam path  17 . 
     In the present embodiment, the low pressure flash box  24  is further provided on the side surface of the low pressure condenser  3 . The heater drain path  15  is constituted by the drain channel part  15   a , the drain fall part  15   c  and the flash steam path  17 , similarly to the high pressure flash box  14 , and the low pressure flash box  24  acts similarly. The steam and the uncondensed gas flowing through the flash steam path  17  of the low pressure flash box  24  are introduced into the vapor phase part  36   b  of the hot well  36  of the low pressure condenser  3  (between the low pressure cooling tube bank  38  and the low pressure hot well  36 ), i.e., into the reheat chamber  23  from the equalizing port  18 . In the multistage condenser, as described above, the high pressure hot well  6 , the intermediate pressure hot well  26  and the low pressure hot well  36  act similarly since they communicate with each other at the vapor phase part by the steam tubes  10  and  15  and at the liquid phase part by the condensate tubes  11  and  16 . 
     Thus, according to the present embodiment, the heater drain  16  can be recovered in the multistage condenser  101  after the uncondensed gas such as dissolved oxygen is reduced sufficiently. 
     In addition, since the flash steam generated in the high pressure flash box  14  and the low pressure flash box  24  according to the present embodiment is introduced into the multistage condenser  101  via the flash steam path  17 , the flash steam can be used to reheat the condensate flowing down from the pressure shroud  4  and the pressure shroud  5  and the heat efficiency can be thereby enhanced. 
     Furthermore, the high pressure flash box  14  and the low pressure flash box  24  according to the present embodiment maintain wide space for boiling the heater drain  16  by forming the free liquid level part  15   b  having a wide surface area at the drain path part  15   a  in the heater drain path  15 , and can efficiently perform flashing and promote deaeration. In addition, by forming the free liquid level part  15   b , the liquid level inside the drain tank connected to the heater drain system can also be controlled to be at a predetermined height. 
     2 nd  Embodiment 
       FIG. 2A  is a front sectional view showing a structure of a multistage condenser  102  according to the second embodiment of the present invention.  FIG. 2B  is a side sectional view showing the structure of the multistage condenser  102  according to the second embodiment. 
     The same constituent elements as those of the first embodiment shown in  FIG. 1A  and  FIG. 1B  are denoted by the same reference numbers as those in  FIG. 1A  and  FIG. 1B  and their detailed explanations are omitted. 
     The flash steam path  17  is provided adjacent to the drain channel part  15   a  of the heater drain path  15  via the partition plate  15   d  in  FIG. 1A  and  FIG. 1B . In a high pressure flash box  34  and a low pressure flash box  44  of the multistage condenser  102  according to the present embodiment, a flash steam path  47  is arranged adjacent to the drain fall part  15   c , at a lower part of the free liquid level part  15   b  of the drain channel part  15   a . Steam outlets  19  for supplying flash steam into the flash steam path  47  are provided on a wall surface of the drain fall part  15   c  which faces the flash steam path  47 . 
     In this structure, the flash steam generated from the drain fall part  15   c  passes through the steam outlets  19  and is supplied to the flash steam path  47  after contacting the heater drain  16  falling down from the porous plates  20 . 
     Since the falling heater drain  16  and the steam can thereby contact easily, deaeration of the uncondensed gas such as dissolved oxygen in the heater drain  16  can be promoted, the heater drain  16  can be recovered in the multistage condenser  102  after performing the deaeration sufficiently, and the same advantage as that of the first embodiment can be obtained. 
     In addition, the heater drain path  15  formed in each of the high pressure flash box  34  and the low pressure flash box  44  according to the present embodiment, is in an approximately rectangular shape, and can be downsized as compared with the high pressure flash box  14  and the low pressure flash box  24  according to the first embodiment. 
     3 rd  Embodiment 
       FIG. 3A  is a front sectional view showing a structure of a multistage condenser  103  according to the third embodiment of the present invention.  FIG. 3B  is a side sectional view showing the structure of the multistage condenser  103  according to the third embodiment. 
     The same constituent elements as those of the first embodiment shown in  FIG. 1A  and  FIG. 1B  are denoted by the same reference numbers as those in  FIG. 1A  and  FIG. 1B  and their detailed explanations are omitted. 
     The heater drain path  15  is formed in the reverse concave shape in  FIG. 1A  and  FIG. 1B . In a high pressure flash box  54  and a low pressure flash box  64  of the multistage condenser  103  according to the present embodiment, a heater drain path  55  is formed in a shape of approximately rectangular parallelepiped, and the heater drain path  55  shaped in an approximately rectangular parallelepiped is partitioned into a drain fall part  55   c  and the flash steam path  17  by a partition plate  55   d . The heater drain path  55  according to the present embodiment does not have a drain channel part or a free liquid level part, but is constituted by the only drain fall part  55   c  and flash steam path  17 . The connection port  13   a  for introducing the heater drain into the flash box  54  is provided at an upper end of the drain fall part  55   c  and, and a lower end of the drain fall part  55   c  communicates with the liquid phase part  6   a  of the high pressure hot well  6 . The porous plates  20  are provided at a plurality of steps in the drain fall part  55   c , similarly to the first and second embodiments. 
     The heater drain  16  becomes a liquid column at the porous plates  20  arranged at a plurality of steps in the drain fall part  55   c , increases an area of contact with the steam, falls down while releasing the flash steam, releases uncondensed gas such as oxygen dissolved in the heater drain  16 , and is thereby deaerated. 
     Thus, in the present embodiment, too, the heater drain  16  can be recovered in the multistage condenser  103  after sufficiently reducing the uncondensed gas such as dissolved oxygen and the like, similarly to the first and second embodiments. 
     In addition, since the flash steam generated in the high pressure flash box  54  and the low pressure flash box  64  is introduced into the multistage condenser  103  via the flash steam path  17 , the flash steam can be used to reheat the condensate flowing down from the pressure shroud  4  and the pressure shroud  5  and the heat efficiency can be thereby enhanced. 
     Moreover, in the present invention, since the heat drain path  55  is constituted by the only drain fall part  55   c  and the flash steam path  17 , the high pressure flash box  54  and the low pressure flash box  64  can be further downsized. 
     In the present embodiment, too, the steam outlets  19  may be provided on the drain fall part  55   c  to urge the falling heater drain  16  to contact a more quantity of the flash steam, similarly to the second embodiment shown in  FIG. 2A  and  FIG. 2B . 
     In the first to third embodiments, the multistage condenser having the high pressure condenser, the intermediate pressure condenser, and the low pressure condenser combined is described. However, the present invention can be applied to all of multistage condensers having a plurality of condensers of different pressures combined, such as a multistage condenser having a high pressure condenser and a low pressure condenser combined, and the like. 
     In those embodiments, the flash box is provided on each of the high pressure condenser and the low pressure condenser. However, the flash box may be provided on all or one of condensers, for example, of some of condensers such as a high pressure condenser, an intermediate pressure condenser and a low pressure condenser. In addition, one of the flash boxes according to the first to third embodiments can be arranged on the high pressure condenser and one of the others can be arranged on the low pressure condenser. The flash boxes can be applied in combination. 
     Furthermore, in those embodiments, the flash boxes are provided on the outside surfaces of the condensers, but may be provided on any parts of the entry side of the heater drain into the condensers, such as the inner side surfaces of the condensers, or separately from the condensers. 
     In addition, the multistage condenser is exemplified in the above-described embodiments, but the present invention is not limited to this, but can also be applied to a single-pressure condenser (condenser constituted by one shell). In a case where any one of the flash boxes described in the first to third embodiments is provided on a condenser of a single turbine, the heater drain introduced into the condenser can be separated into the vapor phase and the liquid phase and dissolved oxygen in the heater drain can be reduced. 
     The present invention can provide a condenser capable of separating a heater drain introduced therein into a vapor phase and a liquid phase and reducing oxygen dissolved in the heater drain.
A condenser includes a high pressure side condenser, a high pressure side cooling tube bank, a high pressure side hot well, a low pressure side condenser, a low pressure side cooling tube bank, a pressure shroud provided inside the low pressure side condenser, a low pressure side hot well, high pressure steam introducing portion, low pressure side condensate introducing portion, a flash box which communicates with at least one of the high pressure side hot well and the low pressure side hot well, flashes a heater drain from a feed water heater, and urges at least one of the high pressure side hot well and the low pressure side hot well to recover the flashed heater drain, and a flash steam path which introduces flash steam generated inside the flash box into at least one of the high pressure side hot well and the low pressure side hot well.