JP2008075966A - Once-through exhaust heat recovery boiler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust heat recovery boiler capable of being started at a high speed by disposing a heating system in an evaporator circulation system of the once-through exhaust heat recovery boiler, and having high controllability and reliability. <P>SOLUTION: An economizer 1, an evaporator 2, and a superheater 4 are successively disposed from a downstream side to an upstream side in a combustion exhaust gas flow channel, fluid pipes are respectively disposed to allow the fluid to successively flow from the economizer 1 to the evaporator 2, a steam separator 3 and the superheater 4, and further a circulation pipe 15 is disposed to return the water separated by the steam separator 3 to the evaporator 2. The water inside of the evaporator 2 is warmed by the steam supplied from an auxiliary steam system 7 through a steam injection nozzle 12 in the circulation pipe 15 returning to an inlet of the evaporator 2 during a standby of an operation of a boiler, and circulated by using a circulation pump 6 to prevent the temperature decrease of the water in the evaporator 2 and its communication pipe 14 and to keep the water at a constant temperature, thus the temperature change in the system of the evaporator 2 is reduced in restarting the boiler, and the boiler can be started in a short time. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a combined power plant including a gas turbine, an exhaust heat recovery boiler, and a steam turbine, that is, an exhaust heat recovery boiler of a so-called combined plant, and more particularly to a system of a once-through exhaust heat recovery boiler.

The combined cycle plant is often required to be frequently started and stopped, and a system capable of shortening the start-up time is required for an exhaust heat recovery boiler that is one of the main machines.
FIG. 7 shows a schematic system diagram of a conventional natural circulation type exhaust heat recovery boiler in a combined cycle. A superheater 4, an evaporator 2, a economizer 1, and the like are arranged in order from a high temperature portion to a low temperature portion in an exhaust heat recovery boiler that is a flow path through which high-temperature exhaust gas from a gas turbine flows.

  The feed water is heated by the economizer 1 and then sent to the brackish water separation drum 24 disposed outside the high-temperature exhaust gas passage. The water separated from the steam by the brackish water separation drum 24 is sent to the evaporator 2, heated by the evaporator 2 to become steam, sent again into the brackish water separation drum 24, and steam separated in the brackish water separation drum 24 Is sent from the brackish water separation drum 24 to the superheater 4, superheated by the superheater 4, and supplied to the steam turbine.

  FIG. 8 shows a schematic system diagram of a conventional once-through exhaust heat recovery boiler in a combined cycle. Also in this case, the superheater 4, the evaporator 2, and the economizer 1 are arranged in order from the high temperature portion to the low temperature portion in the exhaust heat recovery boiler. The feed water heated in the economizer 1 is sent to the evaporator 2 and converted into steam, and then the steam is separated by the brackish water separator 3, and the separated steam is superheated by the superheater 4 and sent to the steam turbine. At that time, in the brackish water separator 3, saturated water is removed from the water whose state has been changed to steam in the evaporator 2, but since a relatively large amount of saturated water is generated when the boiler is started, the separated water is separated into brackish water. After being recovered in the water storage tank 5, the heat is recovered by recirculation to the inlet of the evaporator 2 (Japanese Patent Publication No. 2001-505645).

  Japanese Patent Application Laid-Open No. 2003-294201 provides a water supply circulation means for circulating water in the boiler system before starting the natural circulation type exhaust heat recovery boiler, and gradually raises the temperature of the entire water supply in the boiler system. A configuration is disclosed in which a steam hammer is not generated. In this invention, the feed water supplied to the feed water circulation means may be heated, but an example is disclosed in which steam in the boiler system is used as the heating means.

Japanese Patent Laid-Open No. 2000-46301 discloses an external steam in the can water in the evaporator installed upstream of the exhaust gas of the denitration device before the start-up ignition of the gas turbine in the natural circulation type exhaust heat recovery boiler of the combined cycle plant. Is introduced to increase the temperature at the inlet of the denitration device when the boiler is started to maintain the performance of the denitration catalyst, and at the same time, avoid the steam hammer in the heat exchange section of the evaporator.
Special table 2001-505645 gazette JP 2003-294201 A JP 2000-46301 A

In the natural circulation boiler, the evaporation pipe for evaporating the circulated water into steam is not capable of evaporating all of the water while flowing through the evaporation pipe, and the water that has not evaporated is sent to the brackish water separation drum. It is necessary to be sent and separated from the steam.
On the other hand, in the once-through boiler, the water in the evaporation pipe is not circulated, but is vaporized while flowing from the boiler inlet toward the boiler outlet so that the steam is sufficiently superheated at the boiler outlet.

  By the way, when the operation of the exhaust heat recovery boiler is stopped, the water temperature inside the pipe gradually decreases due to diffusion of normal heat. Therefore, when restarting the plant, it is necessary to suppress the startup speed of the gas turbine so that thermal fatigue does not occur in each part of the exhaust heat recovery boiler due to a rapid rise in temperature, which is particularly required in a combined cycle plant where an exhaust heat recovery boiler is installed. There was a problem that hindered startup at high speed.

  Since the natural circulation boiler uses a large-diameter, thick-walled high-pressure brackish water separation drum, it is necessary to suppress the startup speed of the gas turbine so as to suppress thermal fatigue, and the high speed of the plant after the operation of the exhaust heat recovery boiler is stopped. Cannot restart. For this reason, recently, once-through boilers suitable for high-speed startup have attracted attention.

  Therefore, the present invention can further shorten the start-up time of the once-through exhaust heat recovery boiler by installing a heating system in the evaporator circulation system of the once-through exhaust heat recovery boiler, and has excellent controllability and reliability. A high exhaust heat recovery boiler is provided.

In the present invention, the above problem is solved by the following means.
The invention according to claim 1 sequentially arranges a heat exchanger including a economizer (1), an evaporator (2), and a superheater (4) from the downstream side to the upstream side in the flue gas passage, Fluid pipes (14, etc.) that sequentially flow fluid from the economizer (1) to the evaporator (2), from the evaporator (2) to the brackish water separator (3), and from the brackish water separator (3) to the superheater (4) In a once-through exhaust heat recovery boiler provided with a circulation pipe (15) for returning the water separated from the brackish water mixed fluid by the brackish water separator (3) to the evaporator (2), pressure is applied to the circulation pipe (15). It is a once-through exhaust heat recovery boiler in which a pump (6) is installed and an auxiliary steam supply system (7) is installed downstream of the pressure pump (6).

  According to the second aspect of the present invention, a heat exchanger including a economizer (1), an evaporator (2), and a superheater (4) is sequentially arranged from the downstream side to the upstream side in the flue gas flow path. Fluid pipes (14, etc.) for sequentially flowing fluid from the evaporator (1) to the evaporator (2), from the evaporator (2) to the brackish water separator (3), and from the brackish water separator (3) to the superheater (4), respectively Furthermore, in the once-through exhaust heat recovery boiler provided with a circulation pipe (15) for returning water separated from the brackish water mixed fluid by the brackish water separator (3) to the evaporator (2), the water is separated at a parallel position of the circulation pipe (15). An auxiliary circulation pipe (17) provided with a pressure pump (16) for returning water separated from the brackish water mixed fluid to the evaporator (2) is provided, and an auxiliary steam supply system (7) is provided downstream of the pressure pump (16). This is an installed once-through exhaust heat recovery boiler.

  The invention according to claim 3 is a heat exchange system including a low pressure economizer (8), a economizer (1), an evaporator (2), and a superheater (4) from the downstream side to the upstream side in the flue gas passage. Fluid is arranged in order, and the fluid is flowed sequentially from the economizer (1) to the evaporator (2), from the evaporator (2) to the brackish water separator (3), and from the brackish water separator (3) to the superheater (4). In the once-through exhaust heat recovery boiler provided with a pipe (14) and a circulation pipe (15) for returning water separated from the brackish water mixed fluid by the brackish water separator (3) to the evaporator (2), the low pressure A low pressure economizer recirculation pipe (10) provided with a pressure pump (9) for flowing fluid from an outlet fluid pipe of the economizer (8) toward an inlet fluid pipe of the low pressure economizer (8) Connected and branched from the circulation pipe (15) for returning the water separated by the brackish water separator (3) to the evaporator (2), and the low-pressure charcoal saving A branch circulation pipe (18) for flowing a fluid is connected to the upstream side of the pressure pump (9) of the recirculation pipe (10), and from the downstream side of the pressure pump (9) of the low pressure economizer recirculation pipe (10). An evaporator circulation pipe (19) for flowing a fluid to an evaporator inlet of a circulation pipe (15) for returning water separated by the brackish water separator (3) to the evaporator (2) is connected to the evaporator circulation pipe ( 19) A once-through exhaust heat recovery boiler characterized in that an auxiliary steam supply system (7) is installed in 19).

  According to invention of Claim 1, an auxiliary steam supply system (7) is installed in the evaporator circulation piping (15) which returns the water isolate | separated from the brackish water mixed fluid with the brackish water separator (3) to the evaporator (2). By heating the fluid supplied to the evaporator (2), the startup time of the exhaust heat recovery boiler can be shortened.

  According to the invention described in claim 2, in the auxiliary circulation pipe (17) provided at the parallel position of the circulation pipe (15) for returning the water separated from the brackish water mixed fluid by the brackish water separator (3) to the evaporator (2). By installing the auxiliary steam supply system (7) and heating the fluid supplied to the evaporator (2), the startup time of the exhaust heat recovery boiler can be shortened.

  According to invention of Claim 3, the fluid in the branch circulation piping (18) branched from the circulation piping (15) which returns the water isolate | separated from the brackish water mixed fluid with the brackish water separator (3) to an evaporator (2) is used. It flows into the low pressure economizer recirculation pipe (10) on the upstream side of the pressure pump (9), and further from the downstream side of the pressure pump (9) via the evaporator circulation pipe (19) to the inlet of the evaporator (2). By flowing to the evaporator circulation pipe (15) connected to the unit, and installing the auxiliary steam supply system (7) in the evaporator circulation pipe (19) to heat the fluid supplied to the evaporator (2), The start-up time of the exhaust heat recovery boiler can be shortened.

The present invention will be described with reference to the drawings. In the description of the embodiments of the present invention, the following is assumed.
That is, the evaporator of a once-through boiler differs from the evaporator of a natural-circulation boiler, and the once-through boiler requires a circulation pipe that returns water to the evaporator. Does not return water. In the once-through boiler, the brackish water separator is installed to separate the brackish water only at start-up, but in the natural circulation boiler, the brackish water separator is used for brackish water separation in the entire operating range of the boiler. Thus, the once-through boiler and the natural circulation boiler cannot be viewed in the same row.

  FIG. 1 illustrates in detail the configuration of an embodiment of a once-through exhaust heat recovery boiler for a combined cycle according to the present invention. Also in this case, in the exhaust heat recovery boiler, the superheater 4, the evaporator 2 and the economizer 1, and in some cases the low-pressure economizer 8 and / or the reheater (not shown) from the high temperature portion to the low temperature portion. ) Is arranged. In addition, a circulation pipe 10 and a recirculation pump 9 are provided from the outlet pipe of the low pressure economizer 8 to the inlet pipe to prevent low-temperature corrosion, and a stop valve 13 is disposed in the circulation pipe 10 at the inlet / outlet of the recirculation pump 9. is doing. In addition, the fluid discharged from the low-pressure economizer 8 is sent to the economizer 1 by the pump 11, and the feed water heated by the economizer 1 is sent to the evaporator 2 to become steam, and then the brackish water separator The steam is separated by steam at 3, and the separated steam is superheated by the superheater 4 and sent to the steam turbine. At that time, in the brackish water separator 3, saturated water is removed from the water whose state has been changed to steam in the evaporator 2, but since a relatively large amount of saturated water is generated when the boiler is started, the separated water is braced. As described with reference to FIG. 8, the heat is collected in the water storage tank 5 and then recirculated to the inlet of the evaporator 2 to recover the heat.

  In the present embodiment, an auxiliary steam injection system 7 having a steam injection nozzle 12 is installed in the middle of a circulation pipe 15 returning from the brackish water separator water tank 5 to the evaporator 2 inlet, and the brackish water separator water tank 5 and the auxiliary steam. A circulation pump 6 is installed in the middle of the system 7.

When the exhaust heat recovery boiler is activated, the evaporator 2 is in a state of being filled with water, and the fluid inside the evaporator 2 is water. During the steady operation of the boiler, water is evaporated in the evaporator 2 and a two-phase flow of water and steam is generated. The two-phase flow is steam-separated by the steam separator 3, and the separated steam is superheated by the superheater 4 and sent to a steam turbine (not shown).
In the initial stage of shutdown of the exhaust heat recovery boiler, the evaporator 2 is evaporated due to residual heat, but is gradually cooled to stop the evaporation of water, and the two-phase flow of water and steam is water. Only phase.

Further, during operation of the boiler, the water in the evaporator 2 is heated by the steam supplied from the auxiliary steam system 7 via the steam injection nozzle 12 in the circulation pipe 15 returning to the inlet of the evaporator 2, and the circulation pump 6 is used to prevent the temperature of the water in the evaporator 2 and its connecting pipe 14 from being lowered and maintained at a constant temperature.
In this way, when the exhaust heat recovery boiler is restarted, the temperature change is mitigated by the system through which the evaporator 2 and the fluid flow, and the startup can be performed in a short time. Further, the steam supplied from the auxiliary steam system 7 is mixed with the water flowing through the circulation pipe 15 to the steam injection nozzle 12 provided in the circulation pipe 15 that returns to the inlet of the evaporator 2 at the time of restarting, thereby generating a water hammer. To prevent.

  FIG. 5 shows the temperature change of the water in the evaporator 2 when the exhaust heat recovery boiler is stopped and restarted. As shown in FIG. 5, the water in the evaporator 2 is lowered to 100 ° C. when the boiler is stopped, but it can be maintained at a constant temperature (200 ° C.) by supplying auxiliary steam. It is relaxed and can be started in a short time.

  FIG. 6 shows a comparison of the startup times of the conventional natural circulation type exhaust heat recovery boiler and the once-through type exhaust heat recovery boiler used in this embodiment. The start-up time of the conventional natural circulation type exhaust heat recovery boiler is about 60 minutes at the time of hot start, and the start-up time of the once-through type exhaust heat recovery boiler is about 40 minutes. Become. As described above, in this embodiment, the start-up time of the once-through exhaust heat recovery boiler is shorter than that of the conventional once-through exhaust heat recovery boiler.

  FIG. 2 details another embodiment of the present invention. In the present invention, a circulation pump 16 is provided in parallel with the circulation pipe 15 instead of providing the circulation pump 6 in the circulation pipe 15 returning to the evaporator 2 inlet from the brackish water separator storage tank 5 having the configuration of the first embodiment shown in FIG. A configuration in which the auxiliary circulation pipe 17 is provided and steam supplied from the auxiliary steam system 7 through the steam injection nozzle 12 to the auxiliary circulation pipe 17 is adopted.

In the configuration shown in FIG. 2, when the operation of the exhaust heat recovery boiler is stopped, the motor-operated valve 10 provided in the circulation pipe 15 is closed, and the feed water circulated to the evaporator 2 by the steam supplied from the auxiliary steam system 7 to the auxiliary circulation pipe 17 is heated. Thus, the temperature drop of the evaporator 2 and the communication pipe 14 is prevented. Since the steam injection nozzle 12 shown in FIG. 4 is installed in the auxiliary steam system 7, steam and water are smoothly mixed in the auxiliary circulation pipe 17, and generation of a water hammer can be prevented.
According to this embodiment, the feed water in the evaporator 2 is protected at a high temperature, and when the exhaust heat recovery boiler is restarted, the temperature change is mitigated in the evaporator system, and the start-up can be started in a short time.

Note that the circulation pump 6 shown in FIG. 1 is not installed in the circulation pipe 15 in order to use the circulation force of only the fluid head difference at the start of the exhaust heat recovery boiler. Therefore, there is a problem that the temperature of the fluid in the circulation pipe 15 is rapidly reduced when the boiler operation is stopped, as compared with the configuration in which the auxiliary steam system 7 is added to the circulation pipe 15 shown in FIG.
Table 1 summarizes the fluid flow paths used during start-up, normal operation, operation stop, and standby in the first and second embodiments in an easy-to-understand manner.

  The embodiment shown in FIG. 3 will be described in detail. In this embodiment, a branch circulation pipe 18 branched from the circulation pipe 15 returning to the evaporator 2 inlet from the brackish water separator water storage tank 5 having the configuration of Embodiment 1 shown in FIG. 1 and returning to the low pressure economizer 8 outlet is installed. The circulation pipe 15 returning to the evaporator 2 inlet is provided with a stop valve 20 without providing the circulation pump 6 shown in FIG. In addition, the low pressure economizer 8 has an inlet / outlet connected by a circulation pipe 10, a low pressure economizer recirculation pump 9 is provided in the circulation pipe 10, and a stop valve 13 is provided at the inlet / outlet of the low pressure economizer recirculation pump 9. , 13 are provided. In addition, a circulation pipe 19 is provided that is connected to a circulation pipe 15 that branches from the circulation pipe 10 that supplies fluid to the stop valve 13 on the inlet side of the low-pressure economizer 8 and returns to the evaporator 2 inlet. The circulation pipe 19 is provided with a steam injection nozzle 12, and the steam injection nozzle 12 has a configuration capable of supplying steam from the auxiliary steam system 7.

  In the above configuration, when the operation of the exhaust heat recovery boiler is stopped, the stop valve 13 in the circulation pipe 10 connecting the inlet / outlet of the low pressure economizer 8 is closed. With the stop valve 13 closed, the discharge pressure of the low pressure economizer recirculation pump 9 is used to reduce the fluid (water) at the outlet of the brackish water separator storage tank 5 from the circulation pipe 15 via the branch circulation pipe 18. The fluid (water) is mixed with the steam from the auxiliary steam system 7 and sent to the evaporator 2 at the steam injection nozzle 12 provided from the recirculation pipe 10 to the circulation pipe 19. Sent.

In this way, the circulating feed water is heated by the steam supplied from the auxiliary steam system 7, and the temperature of the evaporator 2 and its connecting pipe 14 can be prevented from lowering.
In addition, a steam injection nozzle 12 shown in FIG. 4 is installed in the auxiliary steam system 7 to perform mixing of steam and water to prevent generation of a water hammer.

さらに表３に実施例１、２、３を採用した場合の各々の利点を比較して示す。

According to this embodiment, the feed water in the evaporator 2 is protected at a high temperature, and when the exhaust heat recovery boiler is restarted, the temperature change is mitigated in the evaporator system, and the start-up can be started in a short time.
Table 2 summarizes the fluid flow paths used in Example 3 during start-up, normal operation, operation stop, and standby.

Further, Table 3 shows a comparison of the respective advantages when Examples 1, 2, and 3 are employed.

  According to the present invention, the start-up time of the exhaust heat recovery boiler combined plant can be expected to be shortened, and the superiority of the combined cycle plant can be further enhanced as a power generation facility with high start-up characteristics according to power demand.

It is a schematic systematic diagram of Example 1 of the present invention. It is a schematic systematic diagram of Example 2 of the present invention. It is a schematic systematic diagram of Example 3 of the present invention. It is the schematic of the steam injection nozzle to the fluid piping used in the Example of this invention. It is a figure which shows the temperature change of the water in the evaporator of the Example of this invention. It is a figure which shows the comparison of the starting time of the once-through-type waste heat recovery boiler of the Example of this invention, and the conventional natural circulation type waste heat recovery boiler. It is a schematic system diagram of the conventional natural circulation type exhaust heat recovery boiler. It is a schematic system diagram of the conventional once-through exhaust heat recovery boiler.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Economizer 2 Evaporator 3 Steam separator 4 Superheater 5 Steam separator water storage tank 6,16 Circulation pump 7 Auxiliary steam system 8 Low pressure economizer 9 Low pressure economizer recirculation pump 10 Motor operated valve 11 Feed water pump 12 Steam Injection nozzles 13 and 20 Stop valve 14 Connecting pipe 15 Evaporator circulation pipe 17 Auxiliary circulation pipe 18 Branch circulation pipe 19 Circulation pipe 24 Brackish water separation drum

Claims (3)

A heat exchanger including a economizer, an evaporator, and a superheater is sequentially arranged from the downstream side to the upstream side in the combustion exhaust gas flow path, and the economizer is connected to the evaporator, and the evaporator to the brackish water separator and the brackish water separator. In the once-through type exhaust heat recovery boiler provided with fluid piping that sequentially flows the fluid from the superheater to the superheater, and further provided with a circulation piping that returns the water separated from the brackish water mixed fluid by the brackish water separator to the evaporator,
A once-through exhaust heat recovery boiler, characterized in that a pressure pump is installed in the circulation pipe, and an auxiliary steam supply system is installed downstream of the pressure pump. Heat exchanger including economizer, evaporator and superheater are arranged sequentially from the downstream side to the upstream side in the flue gas flow path, and the superheater is fed from the economizer, from the evaporator to the brackish water separator, and from the brackish water separator. In the once-through exhaust heat recovery boiler provided with a fluid piping that sequentially flows the fluid to the evaporator, and further provided with a circulation piping that returns the water separated from the brackish water mixed fluid in the steam separator to the evaporator,
A once-through flow characterized in that an auxiliary circulation pipe having a pressure pump for returning water separated from the brackish water mixed fluid to the evaporator is provided at a parallel position of the circulation pipe, and an auxiliary steam supply system is installed downstream of the pressure pump. Type exhaust heat recovery boiler. A heat exchanger including a low pressure economizer, economizer, evaporator and superheater is sequentially arranged from the downstream side to the upstream side in the combustion exhaust gas flow path, from the economizer to the evaporator, from the evaporator to the brackish water separator, and In the once-through exhaust heat recovery boiler provided with fluid pipings that sequentially flow the fluid from the brackish water separator to the superheater, and further provided with circulation piping that returns the water separated from the brackish water mixed fluid by the brackish water separator to the evaporator,
A low pressure economizer recirculation pipe having a pressure pump for flowing fluid from an outlet fluid pipe of the low pressure economizer toward an inlet fluid pipe of the low pressure economizer is connected and separated by the brackish water separator A branch circulation pipe that branches from the circulation pipe for returning water to the evaporator and flows the fluid to the upstream side of the pressure pump of the low pressure economizer recirculation pipe is connected downstream of the pressure pump of the low pressure economizer recirculation pipe. An evaporator circulation pipe for flowing fluid is connected to an evaporator inlet of a circulation pipe for returning water separated by the brackish water separator from the side to the evaporator, and an auxiliary steam supply system is installed in the evaporator circulation pipe A once-through exhaust heat recovery boiler.

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