JP5448883B2 - Once-through exhaust heat recovery boiler - Google Patents

Description

  The present invention relates to an exhaust heat recovery boiler suitable for high-capacity and high-efficiency in a combined cycle power generation facility, and in particular, has a technology for reducing specifications of a start blow water system and preventing condensation at the entrance of a economizer when the boiler is started. It relates to a waste heat recovery boiler.

  FIG. 6 which shows a prior art is a block diagram which shows the plant structure of a general combined cycle power generation facility. According to FIG. 6, natural gas or the like is burned in the gas turbine 1 to generate power, and the high-temperature gas turbine exhaust gas is sent to the exhaust heat recovery boiler 2. In the exhaust heat recovery boiler 2, the feed water sent from the condenser 5 by heat recovery from the exhaust gas is converted into steam, and the generated steam is sent to the steam turbine 3 to generate power by the generator 4. The steam that has worked in the steam turbine 3 is converted into feed water by the condenser 5 and sent to the exhaust heat recovery boiler 2 again.

  FIG. 7 is a diagram illustrating an example of a system configuration of a conventional once-through exhaust heat recovery boiler. The exhaust gas from the gas turbine is sent from the high-pressure superheater 23 which is the first heat exchanging part to the low-pressure economizer 9 installed in the gas last flow part, and heat recovery is performed. According to FIG. 7, the feed water sent to the exhaust heat recovery boiler by the condensate pump 6, the condensate demineralizer 7, and the low pressure feed water pump 8 is heated by the low pressure economizer 9 and passed through the high and medium pressure feed water pump 13. It is supplied to the economizer 15 and the high-pressure economizer 19. The high-pressure feed water heated by the high-pressure economizer 19 is converted into steam by the high-pressure evaporator 21, further superheated, and then supplied to the high-pressure superheater 23 via the high-pressure steam separator 22.

  In addition, an activation blow line 25 connected to the condenser 5 is installed from the lower part of the high-pressure steam separator 22, and when the water level of the steam separator 22 rises from a specified value at the time of activation, the activation blow valve 26 is turned on. Open and drain the saturated water in the brackish water separator 22 to the condenser 5. Further, a system that recirculates the feed water from the intermediate stage of the high and medium pressure feed water pump 13 to the inlet of the low pressure economizer 9 by the economizer recirculation line 14 and raises the feed water from the outlet of the low pressure feed pump 8 to the dew point temperature or higher. It is said.

  Further, for example, FIG. 4 of Patent Document 1 discloses a system path through which low-pressure steam from the boiler flows into the condenser through a bypass valve in the initial stage of startup of the exhaust heat recovery boiler. Furthermore, a conventional technique for providing a heat exchanger in the path of high-temperature blow water and passing low-temperature feed water through the heat exchanger to cool the blow water by heat exchange of the low-temperature feed water to prevent the occurrence of flushing is, for example, This is proposed in Patent Document 2. According to this patent document 2, while providing a blow valve in the blow path which takes out the can water in a boiler main body as blow water, the heat exchanger which passes boiler feed water is provided in the downstream of the blow valve.

JP-A-4-347306 JP 2002-22106 A

  In the system configuration of the conventional once-through type exhaust heat recovery boiler shown in FIG. 7, the fluid whose flow volume is increased due to the flushing of the start blow water, which is saturated water, due to the pressure loss in the piping and the pressure reduction in the control valve. Needs to be sent to the condenser 5. In addition, the startup blow water is drained by the differential pressure between the brackish water separator 22 and the condenser 5, but the differential pressure is small particularly when starting from a state where the pressure in the evaporator is low. Furthermore, in the once-through type, since there is no large-capacity water holding facility such as a drum, when a large amount of saturated water flows from the evaporator 21 into the brackish water separator 22 at the initial stage of startup, the startup blow line 25 immediately goes out of the system. It is necessary to drain.

  Therefore, it is necessary to increase the size of the piping of the start blow line 25 and the start blow valve 26 so that a large amount of water can be discharged with a small differential pressure. The distance to the condenser 5 is relatively long and flushing is considered. Costs increased due to the need to select valves and piping specifications. In addition, the allowable differential pressure of the start blow valve 26 cannot be secured sufficiently, and it may be difficult to select the valve.

  Further, in the system configuration of the once-through exhaust heat recovery boiler shown in FIG. 7, the feed water from the intermediate stage of the high and medium pressure feed water pump 13 is recirculated to the inlet of the low pressure economizer 9 by the economizer recirculation line 14. Although it is set as the system which raises the feed water from the low-pressure feed pump 8 exit more than dew point temperature, since the low-pressure economizer 9 is installed in the gas most downstream part, a delay arises until the exhaust gas temperature from a gas turbine rises. For this reason, since it takes time to increase the feed water temperature at the outlet of the low pressure economizer outlet 9 that is sent to the low pressure economizer 9 inlet via the economizer recirculation line 14, the low pressure economizer at the initial start-up time Condensation at the 9 entrance is unavoidable, which causes a problem of corrosion accompanying long-time operation.

  Further, in Patent Document 1, it is disclosed to provide a path for sending low-pressure steam from the boiler to the condenser when the exhaust heat recovery boiler is started. However, no consideration is given to prevention of the occurrence of flushing with respect to the low-pressure steam. Not. Furthermore, in the above-mentioned Patent Document 2, it is disclosed that when the blow water is discharged from the boiler, the blow water is prevented from being flushed, but there is a lack of consideration for reusing the blow water. In addition, there remains a problem in the efficiency of heat exchange of blown water.

  The object of the present invention is to reduce the specifications of the start blow water piping and valves necessary for draining the start blow water at the start of the exhaust heat recovery boiler, and to reliably drain the start blow water, It is intended to provide an exhaust heat recovery boiler that prevents condensation on the floor and improves economy and reliability.

In order to solve the above problems, the present invention mainly adopts the following configuration.
A superheater that generates steam at a temperature and pressure according to the pressure required by the steam turbine, from the upstream side to the downstream side of the exhaust gas passage through which the exhaust gas from the gas turbine flows, by the internal fluid absorbing the heat of the exhaust gas. A through flow in which an evaporator and a economizer are provided, and the internal fluid from the condenser installed at the outlet of the steam turbine is supplied to the economizer, evaporator and superheater via a low-pressure feed pump In the type exhaust heat recovery boiler, a heat exchanger is provided in the middle of the start blow water pipe for circulating the internal fluid extracted from the lower part of the brackish water separator provided at the inlet of the superheater to the condenser, and the heat exchanger Is provided with a cooling water pipe for extracting and supplying a part of the internal fluid from the downstream side of the low-pressure feed water pump, and further, the internal heated by heat exchange with the start blow water in the heat exchanger Fluid cooling water And it is provided with a return pipe for recirculating back to the upstream side position from the withdrawn position of the tube.

  In addition, from the upstream side to the downstream side of the exhaust gas flow path through which the exhaust gas from the gas turbine flows, the internal fluid absorbs the heat of the exhaust gas and generates steam at a temperature and pressure corresponding to the pressure required by the steam turbine. A superheater, an evaporator and a economizer are provided, and the internal fluid from the condenser installed at the outlet of the steam turbine is supplied to the economizer, the evaporator and the superheater via a low-pressure feed water pump. In the once-through exhaust heat recovery boiler, the internal fluid from the condenser is supplied from the low pressure economizer to the low pressure evaporator and the low pressure superheater via the low pressure feed water pump, and from the outlet of the low pressure economizer. A high-pressure economizer and a high-pressure superheater are branched and supplied from the high-pressure economizer to the high-pressure evaporator and high-pressure superheater, and a water supply line is provided from the intermediate stage of the high-medium-pressure feedwater pump to the medium-pressure economizer Of the high pressure superheater A heat exchanger is provided in the middle of the start blow water pipe for circulating the internal fluid extracted from the lower part of the brackish water separator provided in the mouth to the condenser, and the heat exchanger has an intermediate stage of the high and medium pressure feed water pump. A cooling water pipe is provided for extracting and supplying a part of the water supply from the outlet of the water supply, and the water supply heated by heat exchange with the start blow water in the heat exchanger is returned to the outlet of the low pressure water supply pump The return pipe is provided.

  In addition, from the upstream side to the downstream side of the exhaust gas flow path through which the exhaust gas from the gas turbine flows, the internal fluid absorbs the heat of the exhaust gas and generates steam at a temperature and pressure corresponding to the pressure required by the steam turbine. A superheater, an evaporator and a economizer are provided, and the internal fluid from the condenser installed at the outlet of the steam turbine is supplied to the economizer, the evaporator and the superheater via a low-pressure feed water pump. In the once-through exhaust heat recovery boiler, the internal fluid from the condenser is supplied from the low pressure economizer to the low pressure evaporator and the low pressure superheater via the low pressure feed water pump, and from the outlet of the low pressure economizer. A high-pressure economizer and a high-pressure superheater are branched and supplied from the high-pressure economizer to the high-pressure evaporator and high-pressure superheater, and a water supply line is provided from the intermediate stage of the high-medium-pressure feedwater pump to the medium-pressure economizer Of the high pressure superheater A heat exchanger is provided in the middle of the start blow water pipe for circulating the internal fluid extracted from the lower part of the brackish water separator provided in the mouth to the condenser, and the heat exchanger has an intermediate stage of the high and medium pressure feed water pump. A cooling water pipe is provided for extracting and supplying a part of the water supply from the outlet of the water supply, and the water supply heated by heat exchange with the start blow water in the heat exchanger is returned to the outlet of the low pressure water supply pump A return pipe is provided, and a economizer recirculation line that diverges from the outlet of the intermediate stage of the high-medium pressure feed water pump and circulates to the inlet of the low-pressure economizer is provided.

  According to the present invention, by installing a heat exchanger in the start blow line and reducing the temperature of the start blow water, the flushing in the start blow pipe is suppressed, and the pressure in the start blow pipe and the start blow valve is increased. It is possible to reduce the loss, reduce the specifications of the start blow pipe and start blow valve, and provide a highly reliable once-through exhaust heat recovery boiler that is excellent in economy.

  Furthermore, since the inlet water supply temperature of the exhaust heat recovery boiler rises early, corrosion due to condensation at the entrance of the economizer can be suppressed, and a highly reliable once-through exhaust heat recovery boiler can be provided. It becomes.

It is a block diagram which shows the 1st Example of the waste heat recovery boiler which concerns on embodiment of this invention. It is explanatory drawing which shows the pressure distribution of the starting blow line in the exhaust heat recovery boiler which concerns on this embodiment by comparison with a prior art. It is explanatory drawing which shows the characteristic of the inlet water supply temperature of the economizer in the waste heat recovery boiler which concerns on this embodiment in comparison with a prior art. It is a block diagram which shows the 2nd Example of the waste heat recovery boiler which concerns on embodiment of this invention. It is a block diagram which shows the 3rd Example of the waste heat recovery boiler which concerns on embodiment of this invention. It is a block diagram which shows the plant structure of a general combined cycle power generation equipment. It is a figure which shows the example of the system | strain structure of the conventional once-through-type waste heat recovery boiler.

A once-through exhaust heat recovery boiler according to an embodiment of the present invention will be described in detail below with reference to FIGS. First, a technical flow leading to an embodiment of the present invention will be described. As a measure to improve power generation efficiency by increasing the temperature and pressure of steam generated by exchanging heat with exhaust gas from a gas turbine, at least the main high-pressure system employs a once-through exhaust heat recovery boiler that does not have a steam drum installed. The In large-capacity combined cycle power generation facilities, the steam system of the exhaust heat recovery boiler is composed of three systems: a high-pressure system, an intermediate-pressure reheat system, and a low-pressure system to improve the efficiency of exhaust heat recovery. When the once-through type is configured by such a reheat triple pressure method, during normal operation, all the fluid from the outlet of the evaporator becomes a once-through flow that is sent to the superheater via the brackish water separator.

  On the other hand, at start-up, a two-phase flow of saturated water and saturated steam flows from the outlet of the evaporator into the brackish water separator, the saturated steam is sent to the superheater, and the saturated water is kept at a level below the predetermined water level of the brackish water separator. Control operation is performed (see FIG. 7). If the specified water level of the brackish water separator is exceeded during this operation, the start blow valve installed in the start blow line (the line from the brackish water separator to the condenser) is controlled to open so that the saturated water in the brackish water separator However, the once-through type does not have a large-capacity water storage facility like a drum. Therefore, the start blow line needs to have a sufficient capacity according to the fluctuation of the amount of saturated water flowing into the brackish water separator.

  In addition, since the exhaust heat recovery boiler receives a rapid heat input from the gas turbine at the beginning of startup, it is necessary to discharge a large amount of saturated water from the startup blow line from the evaporator to the brackish water separator particularly at the beginning of startup. In this case, discharge is performed due to a pressure difference and a head difference. Furthermore, when sending the start blow water to the condenser, it is necessary to connect with a long horizontal pipe from the brackish water separator to the condenser, but because the saturated water flows, the pre-flow pipe of the start blow valve In this case, flushing occurs due to a drop in fluid pressure due to pressure loss in the tube, and the specific volume of the fluid in the tube increases. As the specific volume increases, the flow velocity in the pipe increases and the pressure loss increases.

  In addition, it is necessary to consider a large increase in the size of the downstream piping of the start blow valve in consideration of pressure reduction flushing at the start blow valve. In order to drain the start blow water under such conditions, it is necessary to increase the size of the start blow pipe and the start blow valve to reduce the resistance in the pipe, resulting in an increase in cost. In addition, when the start blow piping and the start blow valve size sufficient to drain the start blow water are not selected, the water level of the brackish water separator is greatly increased, which may lead to a trip or the like.

  In order to prevent corrosion due to condensation in the exhaust heat recovery boiler, a recirculation system that recirculates the feed water at the low pressure economizer outlet or the middle pressure economizer to the economizer inlet side and raises it above the dew point temperature. Although it is installed (see Fig. 7), since the water supply in the economizer is not sufficiently heated at the beginning of startup, it takes time until the water supply temperature at the economizer inlet reaches the dew point or higher. Temporary condensation was inevitable, and the problem of corrosion associated with long-term operation occurred.

  Therefore, in the embodiment of the present invention, generally speaking, a heat exchanger is installed in the startup blow system, and the feed water from the low-pressure feed pump outlet is used as cooling water at the start of startup when a large amount of startup blow occurs. When the temperature of the blow water is lowered by the heat exchanger, it is possible to prevent flushing in the upstream piping of the start blow valve and reduce the occurrence of flushing in the downstream piping of the start blow valve. Therefore, it is possible to reduce the size of the start blow water piping and the start blow valve, thereby reducing the cost. In addition, by using the cooling water and recirculating the heated water supply to the economizer inlet, the water supply temperature at the beginning of the startup rises early, so that corrosion due to condensation can be suppressed, and exhaust heat recovery It becomes possible to increase the reliability of the boiler.

  Next, a first example of the exhaust heat recovery boiler according to the embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a configuration diagram illustrating a first example of an exhaust heat recovery boiler according to an embodiment of the present invention. FIG. 2 is an explanatory view showing the pressure distribution of the startup blow line in the exhaust heat recovery boiler according to the present embodiment in comparison with the prior art. FIG. 3 is an explanatory diagram showing the characteristics of the inlet water supply temperature of the economizer in the exhaust heat recovery boiler according to this embodiment in comparison with the prior art.

  The first embodiment shown in FIG. 1 is the same as the configuration shown in FIG. 7 except for the heat exchanger 27, the cooling water line 28, and the cooling water valve 29. A heat exchanger 27 is installed on the inlet side of the start blow line 25 (the upstream side of the start blow valve 26 in FIG. 1), and the coolant line branched from the outlet of the low-pressure feed pump 8 as the coolant sent to the heat exchanger 27 28 and the cooling water valve 29 are installed, and the water supply after the heat exchange is returned to the inlet side of the low-pressure water supply pump 8. In an operation region where a large amount of startup blow occurs at the initial stage of startup, the cooling water valve 29 is opened and feed water having a low temperature is sent to the heat exchanger 27 through the cooling water line 28.

  The starting blow water in the saturated water state drained from the brackish water separator 23 passes through the heat exchanger 27 to be in a subcooled state, and the occurrence of flanking due to pipe pressure loss in the upstream pipe of the start blow valve 26 can be prevented. Further, flushing after the pressure is reduced by the start blow valve 26 is reduced. On the other hand, the cooling water rises in temperature by passing through the heat exchanger 27 and is recirculated to the inlet of the low-pressure feed water pump 8. Here, the part of the water supply that has been warmed through the cooling water line 28 and the heat exchanger 27 may be basically any part after the condensate demineralizer 7, but in the configuration example shown in FIG. In order to prevent empty suction of the low-pressure feed water pump 8, the suction side of the pump 8 is provided. That is, the water supply whose temperature has been increased by heat exchange is returned to the upstream side from the cooling water extraction position. As a result, the temperature of the feed water sent to the low pressure economizer 9 rises early.

  The effect of this invention is demonstrated using FIG.2 and FIG.3. As shown in FIG. 2, for the startup blow system, the piping size before and after the startup blow valve 26 becomes very large in the conventional system, and the allowable differential pressure of the startup blow valve 26 cannot be sufficiently secured and cannot be selected. there were. That is, the allowable pressure loss of the start blow line is an added value obtained by adding the upstream flow pipe pressure loss, the back flow pipe pressure loss of the start blow valve, and the allowable differential pressure of the start blow valve.

  Here, by cooling the start blow water according to the configuration of the present embodiment shown in FIG. 1, the pressure loss in the pipe can be greatly reduced, and the tolerance of the start blow valve as shown in the case (1) in which the pipe diameter is not changed. The pressure increases greatly, and it becomes possible to employ a small-sized valve. Moreover, as shown in the case (2), by allocating a part of the increase in the allowable differential pressure to the allowable pressure loss on the piping side, the size of the start blow piping can be reduced (for example, before the valve The pipe diameter of the flow is reduced to 150A, and the pipe diameter on the downstream side of the valve is reduced to 200A). At that time, since flushing is suppressed, it is possible to relax the selection conditions for the materials of the start blow valve 26 and the start blow pipe 25. Furthermore, since the instability factor which influences pressure loss is suppressed and flushing is removed, anxiety, such as being unable to discharge start blow water, is eliminated.

  Further, as shown in FIG. 3, for the inlet water supply temperature of the low-pressure economizer 9, there is a time zone in which the water supply temperature is lower than the dew point temperature at the start of startup after gas turbine ignition (GT ignition) in the conventional system. Therefore, a dew condensation state is temporarily generated, and corrosion progresses gradually by a long time operation. On the other hand, by adopting the configuration shown in the present embodiment shown in FIG. 1, it is possible to increase the feed water temperature early, and to suppress the occurrence of corrosion due to condensation.

  As described above, the feature of the first embodiment is that a heat exchanger is installed in the startup blow line, and the temperature of the startup blow water is reduced by heat exchange with the feed water from the outlet of the low-pressure feed water pump. In addition to suppressing the occurrence of flushing in the piping and downstream of the start-up blow valve, the heated cooling water is recirculated to the low-pressure feed pump inlet to quickly raise the feed water temperature, and condensation at the inlet of the economizer It is what suppresses. Thus, since the increase in the specific volume of the fluid in the startup blow water piping and the startup blow valve wake is suppressed, the resistance in the pipe is reduced. As a result, it is possible to reduce the size and specifications of the start blow water piping and the start blow valve. In addition, since an unstable element called flushing is suppressed, it is possible to reliably drain the start blow water. Furthermore, corrosion at the entrance of the economizer associated with condensation is suppressed, and reliability is improved.

  Next, a second example of the exhaust heat recovery boiler according to the embodiment of the present invention will be described below with reference to FIG. FIG. 4 is a block diagram showing a second example of the exhaust heat recovery boiler according to the embodiment of the present invention. In the second embodiment, the economizer recirculation line 14 from the intermediate stage of the high and medium pressure feed water pump 13 is used for the heat exchanger 27. Here, the economizer recirculation line 14 returns to the outlet of the low-pressure feed pump after passing through the heat exchanger 27. In this embodiment, the economizer recirculation line 14 including the existing valve shown in FIG. 7 is used for heat exchange of the heat exchanger 27 without installing the cooling water line 28 and the cooling water valve 29 shown in FIG. It is used for. The same effect as in the first embodiment can be obtained without newly installing the cooling water line 28 and the cooling water valve 29 shown in FIG.

  Next, a third example of the exhaust heat recovery boiler according to the embodiment of the present invention will be described below with reference to FIG. FIG. 5 is a block diagram showing a third example of the exhaust heat recovery boiler according to the embodiment of the present invention. In the third embodiment, the cooling water take-out position used for heat exchange of the heat exchanger 27 is an intermediate stage of the high-medium pressure feed water pump 13. Here, the economizer recirculation line 14 returns to the outlet of the low-pressure feed pump after passing through the heat exchanger 27.

  In this embodiment, the economizer recirculation line 14 shown in FIG. 1 is used as it is. The reason why the line 14 coexists is that hot water returning to the low-pressure water supply line through the heat exchanger 27 due to the occurrence of flushing may change in temperature over time, and the temperature change of the return hot water The water supply temperature of the low-pressure water supply line may fluctuate unstable near the dew point temperature. Therefore, this economizer recirculation line 14 is provided, and the function of raising the feed water temperature below the dew point temperature with the feed water from this line 14 is achieved to prevent dew condensation at the economizer entrance. In the third embodiment, the same effect as that of the first embodiment of FIG. 1 can be obtained.

DESCRIPTION OF SYMBOLS 1 ... Gas turbine, 2 ... Waste heat recovery boiler, 3 ... Steam turbine, 4 ... Generator, 5 ... Condenser, 6 ... Condensate pump, 7 ... Condensate demineralizer, 8 ... Low-pressure feed pump, 9 ... Low pressure economizer, 10 ... low pressure drum, 11 ... low pressure evaporator, 12 ... low pressure superheater, 13 ... high medium pressure feed water pump, 14 ... economizer recirculation line, 15 ... medium pressure economizer, 16 ... medium pressure Drum, 17 ... medium pressure evaporator, 18 ... medium pressure superheater, 19 ... high pressure economizer,
DESCRIPTION OF SYMBOLS 20 ... High pressure feed water control valve, 21 ... High pressure secondary evaporator, 22 ... High pressure steam separator, 23 ... High pressure superheater, 25 ... Startup blow line, 26 ... Startup blow valve, 27 ... Heat exchanger, 28 ... Cooling water Line, 29 ... Cooling water valve

Claims (5)

A superheater that generates steam at a temperature and pressure according to the pressure required by the steam turbine, from the upstream side to the downstream side of the exhaust gas passage through which the exhaust gas from the gas turbine flows, by the internal fluid absorbing the heat of the exhaust gas. A through flow in which an evaporator and a economizer are provided, and the internal fluid from the condenser installed at the outlet of the steam turbine is supplied to the economizer, evaporator and superheater via a low-pressure feed pump In the type exhaust heat recovery boiler,
A heat exchanger is provided in the middle of the startup blow water piping that circulates the internal fluid extracted from the lower part of the brackish water separator provided at the inlet of the superheater,
The heat exchanger is provided with a cooling water pipe for extracting and supplying a part of the internal fluid from the downstream side of the low-pressure feed water pump, and further heated by heat exchange with the start blow water in the heat exchanger. A once-through exhaust heat recovery boiler is provided, wherein a return pipe is provided for returning the internal fluid returned to a position upstream from the extraction position of the cooling water pipe for recirculation. In claim 1,
A once-through exhaust heat recovery boiler, wherein an extraction position of the cooling water pipe is an outlet of the low-pressure feed pump, and a return position of the return pipe is an inlet of the low-pressure feed pump. In claim 1 or 2,
The internal fluid from the condenser is supplied from the low-pressure economizer to the low-pressure evaporator and the low-pressure superheater via the low-pressure feedwater pump, branches from the outlet of the low-pressure economizer, and passes through the high-medium pressure feedwater pump. While being supplied to the high pressure economizer, a water supply line is provided to be supplied to the intermediate pressure economizer from an intermediate stage of the high and medium pressure feedwater pump,
A once-through exhaust heat recovery boiler, characterized in that a economizer recirculation line is provided that branches from an outlet of an intermediate stage of the high-medium pressure feed water pump and circulates to an inlet of the low-pressure economizer. A superheater that generates steam at a temperature and pressure according to the pressure required by the steam turbine, from the upstream side to the downstream side of the exhaust gas passage through which the exhaust gas from the gas turbine flows, by the internal fluid absorbing the heat of the exhaust gas. A through flow in which an evaporator and a economizer are provided, and the internal fluid from the condenser installed at the outlet of the steam turbine is supplied to the economizer, evaporator and superheater via a low-pressure feed pump In the type exhaust heat recovery boiler,
The internal fluid from the condenser is supplied from the low-pressure economizer to the low-pressure evaporator and the low-pressure superheater via the low-pressure feedwater pump, branches from the outlet of the low-pressure economizer, and passes through the high-medium pressure feedwater pump. The high-pressure economizer is supplied to the high-pressure evaporator and the high-pressure superheater, and a water supply line is provided to the medium-pressure economizer from the intermediate stage of the high-medium-pressure feedwater pump,
A heat exchanger is provided in the middle of the startup blow water piping that circulates the internal fluid extracted from the lower part of the brackish water separator provided at the inlet of the high pressure superheater,
The heat exchanger is provided with a cooling water pipe for extracting and supplying a part of the feed water from an outlet of an intermediate stage of the high / medium pressure feed water pump, and further by heat exchange with the start blow water in the heat exchanger. A once-through exhaust heat recovery boiler, characterized in that a return pipe is provided for returning the heated feed water to the outlet of the low-pressure feed pump. A superheater that generates steam at a temperature and pressure corresponding to the pressure required by the steam turbine, from the upstream side to the downstream side of the exhaust gas flow path through which the exhaust gas from the gas turbine flows, by the internal fluid absorbing the heat of the exhaust gas. A through flow in which an evaporator and a economizer are provided, and the internal fluid from the condenser installed at the outlet of the steam turbine is supplied to the economizer, evaporator and superheater via a low-pressure feed pump In the type exhaust heat recovery boiler,
The internal fluid from the condenser is supplied from the low-pressure economizer to the low-pressure evaporator and the low-pressure superheater via the low-pressure feedwater pump, branches from the outlet of the low-pressure economizer, and passes through the high-medium pressure feedwater pump. The high-pressure economizer is supplied to the high-pressure evaporator and the high-pressure superheater, and a water supply line is provided to the medium-pressure economizer from the intermediate stage of the high-medium-pressure feedwater pump,
A heat exchanger is provided in the middle of the startup blow water piping that circulates the internal fluid extracted from the lower part of the brackish water separator provided at the inlet of the high pressure superheater,
The heat exchanger is provided with a cooling water pipe for extracting and supplying a part of the feed water from an outlet of an intermediate stage of the high / medium pressure feed water pump, and further by heat exchange with the start blow water in the heat exchanger. A return pipe for returning the heated feed water to the outlet of the low-pressure feed pump;
A once-through exhaust heat recovery boiler, characterized in that a economizer recirculation line is provided that branches from an outlet of an intermediate stage of the high-medium pressure feed water pump and circulates to an inlet of the low-pressure economizer.

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