JP2012117703A - Exhaust heat recovery boiler, and method for preventing corrosion during stopping of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent corrosion of a heat transfer tube by preventing corrosiveness caused by moisture absorption of ammonium sulfate or acid ammonium sulfate deposited on the heat transfer tube while a gas turbine functioning as a heat source with respect to an exhaust heat recovery boiler is stopped.SOLUTION: A feed-water system including a closed-loop is so configured that when the operation of the exhaust heat recovery boiler is stopped or started, the closed-loop is passed through a high/medium-pressure feed-water pump minimum flow system 43 branched before a high-pressure feed-water stop valve 41 from the outlet pipe 42 of a high/middle pressure feed-water pump 37 and is returned from a low-pressure economizer inlet feed-water pipe 46 to the pump 37 through a low-pressure economizer 1 and the outlet pipe 35 thereof. Feed-water temperature is raised by the pump 37 to maintain the heat transfer tube temperature of the whole low-pressure economizer 1 at a high temperature, for example, 100°C or higher. Thereby, the ammonium sulfate or acid ammonium sulfate deposited on the heat transfer tube is kept in a dry state not causing the corrosiveness. When the temperature of the closed-loop is excessively raised, a low-pressure economizer bypass valve 51 and a feed-water stop valve 34 are opened. Thereby, the feed-water temperature of the inlet of the pump 37 is set to temperature with flushing occurring or less by cold water from a condenser 28.

Description

  The present invention relates to an exhaust heat recovery boiler in a combined power plant and a method for preventing corrosion during stopping of the boiler.

  As a plant optimal for high-efficiency power generation and intermediate load operation, there is a combined power plant that uses LNG as fuel for a gas turbine. The combined power plant includes a waste heat recovery boiler that recovers heat of exhaust gas discharged from the gas turbine, and generates power by driving the steam turbine with steam generated in the exhaust heat recovery boiler. Is. The structure of the water supply system of such an exhaust heat recovery boiler will be described with reference to the drawings.

FIG. 3 is a system diagram of a conventional exhaust heat recovery boiler.
An exhaust heat recovery boiler is provided in an exhaust gas passage into which exhaust gas (shown as a gas flow in the figure) from a gas turbine (not shown) is introduced, and the exhaust gas after heat recovery by the exhaust heat recovery boiler is the exhaust gas at the outlet Is exhausted from the exhaust heat recovery boiler. In the present specification, the exhaust gas passage in the exhaust heat recovery boiler is described as an exhaust gas passage through which gas flows in the horizontal direction, but the exhaust gas passage may be oriented in the vertical direction.

  In the exhaust heat recovery boiler shown in FIG. 3, the low-pressure economizer 1, the low-pressure evaporator 2, the medium-pressure economizer 3, the medium-pressure evaporator 4, the low-pressure superheater sequentially from the most downstream side to the most upstream side of the exhaust gas passage. 5, high pressure economizer 6, medium pressure superheater 7, denitration device 8, high pressure evaporator 9, high pressure primary superheater 10, primary reheater 11, secondary reheater 12 and high pressure secondary superheater 13. Is arranged. Above the low-pressure evaporator 2, the intermediate-pressure evaporator 4 and the high-pressure evaporator 9, steam and water are separated from the brackish water mixture supplied from the low-pressure evaporator 2, the intermediate-pressure evaporator 4 and the high-pressure evaporator 9, respectively. A low-pressure brackish water separation drum 16, a medium-pressure brackish water separation drum 17, and a high-pressure brackish water separation drum 18 are disposed, and further, the low-pressure, medium-pressure, and high-pressure economizers 6, A low pressure having a low pressure feed water flow rate adjustment valve 21, an intermediate pressure feed water flow rate adjustment valve 22 and a high pressure feed water flow rate adjustment valve 23 for adjusting the flow rate when supplying the brackish water mixture to the high pressure brackish water separation drums 16, 17, 18; Medium pressure and high pressure brackish water separation drum water supply pipes 25, 26, 27 and the like are respectively arranged.

  Further, the steam used for power generation by a generator (not shown) by driving the steam turbine is supplied to the condenser 28. From the outlet of the condenser 28, a condensate pump 29 provided in the water supply system 32, a ground steam condenser (condenser for ground seal of the steam turbine) 30, and a flow meter 31, Water is introduced into the low-pressure economizer 1 from the low-pressure economizer inlet water supply system 46 via the low-pressure water pump 33 and the low-pressure water supply stop valve 34 provided in the latter half portion in sequence.

  During start-up and during operation, the low-pressure economizer 1 heats the feed water by the gas turbine exhaust gas, and a part of the feed water is supplied via the low-pressure bracking separation drum feed pipe 25 provided with the low-pressure feed water flow rate adjusting valve 21. To the low-pressure evaporator 2. The remaining feed water heated by the low-pressure economizer 1 is sent to the high / intermediate pressure feed water pump 37 in the high / intermediate pressure feed water communication pipe 42 and is boosted by the high / intermediate pressure feed water pump 37. The feed water extracted from the middle stage of the high / medium pressure feed water pump 37 is sent to the medium pressure economizer 3 through an intermediate pressure economizer inlet communication pipe 39 provided with an intermediate pressure feed water stop valve 38. Further, the feed water whose pressure has been increased to a high pressure by the high / medium pressure feed water pump 37 is supplied to the high pressure economizer 6 through a high / medium pressure feed water communication pipe 42 having a high pressure feed water stop valve 41. Furthermore, the start-up time of the exhaust heat recovery boiler can be shortened by performing a standby operation before the gas turbine is ignited at the time of starting the high / medium-pressure feed water pump 37. If the minimum flow system 43 branched from the high and medium pressure water supply communication pipe 42 between the installation part of the high and medium pressure water supply pump 37 is provided and the on-off valve 44 of the minimum flow system 43 is opened, the minimum flow system 43 The water supply can be returned to the condenser 28 via.

  In such a conventional system, when the boiler is started, first, the low pressure water supply stop valve 34 of the water supply system 32 supplied to the low pressure economizer 1 from the condenser 28 is closed, and the water supply from the condenser 28 is low pressure. From the front of the water supply stop valve 34, the low pressure water supply pump 33 returns to the condenser 28 via the low pressure water supply pump minimum flow system 45. After the discharge pressure from the low-pressure feed water pump 33 has risen to a predetermined pressure or higher, the minimum flow of the low-pressure feed water pump 37 can be secured. As a next step, the low-pressure feed water stop valve 34 is opened to reduce the feed water pressure. The high / intermediate pressure water supply communication pipe 42 is passed through the economizer 1 to secure the minimum flow of the high / intermediate water supply pump 37 using the high / intermediate water supply pump minimum flow system 43 upstream of the closed high pressure water supply stop valve 41. .

  A flow meter 31 and a check valve 35 are provided in the high / medium pressure feed water communication pipe 42 between the high / medium pressure feed water pump 37 and the high pressure feed water stop valve 41. The flow meter 31 is also provided in the low-pressure steam separation drum water supply pipe 25, the medium pressure economizer inlet communication pipe 39, the high and medium pressure water supply communication pipe 42, and the low pressure economizer inlet temperature adjustment system 47. The medium pressure economizer inlet communication pipe 39 and the high / medium pressure water supply communication pipe 42 are also provided.

  Further, the feed water heated by the low-pressure evaporator 2 is steam-separated by the low-pressure steam separation drum 16, the separated steam is sent to the low-pressure superheater 5, and the separated water is sent to the low-pressure evaporator 2 again. The steam superheated by the low pressure superheater 5 is supplied to the steam turbine.

The feed water heated by the intermediate pressure economizer 3 is supplied from the intermediate pressure steam separation drum 17 to the intermediate pressure evaporator 4 via the intermediate pressure steam separation drum feed pipe 26 provided with the intermediate pressure feed water flow rate adjustment valve 22. . Further, the feed water heated by the intermediate pressure evaporator 4 is subjected to steam separation by the intermediate pressure steam separation drum 17, the steam is sent to the intermediate pressure superheater 7, and the water is sent again to the intermediate pressure evaporator 4. The steam superheated by the medium pressure superheater 7 is sequentially sent to the primary reheater 11 and the secondary reheater 12, and then supplied to the steam turbine. The high-pressure feed water sent to the high-pressure economizer 6 is supplied from the high-pressure steam separation drum 18 to the high-pressure evaporator 9 via the high-pressure steam separation drum feed pipe 27 having the high-pressure feed water flow rate adjusting valve 23. Further, the feed water heated by the high-pressure evaporator 9 is steam-separated by the high-pressure steam separation drum 18, and the steam is sent to the high-pressure primary superheater 10 and the high-pressure secondary superheater 13 to be superheated and then supplied to the steam turbine. . The water separated by the high-pressure brackish water separation drum 18 is sent to the high-pressure evaporator 9 again.
Further, a denitration device 8 is disposed between the intermediate pressure superheater 7 and the high pressure evaporator 9. Ammonia is injected into the denitration device 8 from the upstream side during operation of the exhaust heat recovery boiler.

  In the exhaust heat recovery boiler, at the time of start-up, a part of the feed water is extracted from the intermediate portion of the heat transfer pipe of the high pressure economizer 6 and passes through the low pressure economizer inlet temperature adjustment system 47 and the low pressure economizer inlet water supply system 46. And supplied to the low pressure economizer 1. The temperature of the feed water supplied to the low pressure economizer 1 from the low pressure economizer inlet temperature adjustment system 47 and the low pressure economizer inlet water supply system 46 is the exhaust gas in the exhaust heat recovery boiler of a normal LNG-fired combined plant. The temperature is controlled to be 50 to 60 ° C. in order to make the dew point temperature of the water that is not condensed with water.

  In an exhaust heat recovery boiler of a combined power plant that uses LNG as a fuel for a gas turbine, sulfur is not contained in the exhaust gas of the gas turbine that is a heat source, so ammonium sulfate or acidic ammonium sulfate is usually used in the heat transfer tube of the exhaust heat recovery boiler. Does not adhere. Therefore, there is no problem that the ammonium sulfate or acidic ammonium sulfate adhering to the heat transfer tube absorbs moisture in the atmosphere after startup and the heat transfer tube corrodes significantly during the plant shutdown period (referred to as being stopped). There is no special consideration in terms of equipment or operation so that the deposits on these heat transfer tubes do not absorb moisture during or during a can stop.

  In the exhaust heat recovery boiler of a combined power plant using LNG as a gas turbine fuel as described above, the minimum flow system 43 of the high / medium pressure feed water pump 37 is usually configured to return the feed water to the condenser 28, and the exhaust heat Since the feed water from the condenser 28 is supplied to the minimum flow system 43 via the low pressure economizer 1 until the gas turbine is ignited at the time of starting the recovery boiler, the low pressure economizer 1 The temperature is controlled to about 29 ° C. by being controlled by the temperature of the water supplied from the condenser 28.

  When such a system configuration is applied, the heat transfer tubes are cooled during the initial start-up period or during the plant shutdown period, so that the exhaust gas with a denitration device is used in a combined power plant that uses fuel containing sulfur in the gas turbine. In a heat recovery boiler or the like, ammonium sulfate or acid ammonium sulfate adhering to the heat transfer tube due to ammonia injection during normal operation may absorb moisture in the atmosphere when the can stops, and the heat transfer tube may be significantly corroded.

  Further, in Patent Document 1 below, when a converter boiler used for waste heat recovery of smelting exhaust gas containing sulfurous acid gas is shut down, the temperature of the converter boiler water is maintained above the acid dew point to constitute the converter boiler. In order to prevent the acid dew point corrosion of the equipment to be generated, an invention is disclosed in which a part of the steam of another waste heat boiler is supplied to the converter boiler.

JP 2008-232546 A

  The invention described in Patent Document 1 is an invention related to a converter boiler for recovering waste heat of smelting exhaust gas, and is an independent steam generator for generating steam by recovering exhaust heat from a gas turbine of a power plant according to the present invention. It is not a heat utilization system in the exhaust heat recovery system.

  Conventionally, in a boiler for an independent exhaust heat recovery system for steam generation used in a combined power plant system as shown in FIG. 3, a water supply system is used so that the heat transfer tubes are not cooled during the initial start of the boiler or during the combined power plant stop period. No special consideration is given in terms of equipment or operation.

  However, in a combined power plant that uses fuel containing sulfur in the gas turbine, an exhaust heat recovery boiler with a denitration device is used. During normal operation of this exhaust heat recovery boiler, ammonia is injected to denitrate exhaust gas. However, with the conventional technology shown in FIG. 3, the heat transfer tube of the boiler is cooled during the initial startup of the exhaust heat recovery boiler or during the thermal power plant stop period. There has been a drawback that the ammonium sulfate or acidic ammonium sulfate adhering to the heat transfer tube absorbs moisture in the atmosphere, and the heat transfer tube may corrode significantly.

  It is an object of the present invention to prevent the corrosion of heat transfer tubes by preventing ammonium sulfate or acidic ammonium sulfate adhering to the heat transfer tubes from absorbing moisture in the atmosphere during the period when the gas turbine serving as a heat source is stopped. It is providing the waste heat recovery boiler which can prevent, and the corrosion prevention method in the can stop.

  The present invention employs the following water supply system configuration in order to solve the above problems.

  That is, the invention according to claim 1 is for generating steam by heating the feed water flowing in from the condenser storing water collected from the steam turbine using the heat of the combustion exhaust gas containing sulfur. A superheater, an evaporator, a reheater, a low-pressure side economizer, and at least one of a plurality of economizers having a pressure higher than that of the low-pressure side economizer, the superheater, the evaporator, and the economizer In an exhaust heat recovery boiler equipped with a denitration device and a denitration device, the outlet of the low pressure side economizer (1) having a heat transfer tube group to which ammonium sulfate or acidic ammonium sulfate is likely to adhere is higher than the low pressure side economizer (1). A first water supply pipe (42) having a first water supply pump (37) for sequentially supplying water to one or more economizers (3, 6), and a low-pressure economizer provided at the inlet of the low-pressure economizer (1) The inlet water supply pipe (46), one of the one or more economizers (3, 6) on the high pressure side, and the low A second water supply pipe (47) for adjusting the temperature of the low pressure economizer inlet connected to the water saver inlet water supply pipe (46), and a first water supply pipe (42 downstream of the first water supply pump (37) installation part (42) ) And a circulating water supply pipe (43) that circulates the water supply toward the inlet water supply pipe (46) of the low-pressure side economizer (1), and is lifted by the first water supply pump (37) when stopped. Constructs a feed water circulation system consisting of a closed loop that circulates the first feed water pipe (42), the circulating feed water pipe (43), the low pressure economizer inlet water feed pipe (46), and the low pressure economizer (1) using temperature. This prevents the corrosion of the waste heat recovery boiler from being stopped by maintaining the temperature at which ammonium sulfate or acidic ammonium sulfate adhering to the heat transfer tube group of the low-pressure economizer (1) is in a dry state.

  The invention described in claim 2 is the first water supply pipe (42) on the upstream side from the first water supply pump (37) installation part, and the low pressure side economizer (1) from the connection part of the circulation water supply pipe (43). A low pressure economizer bypass water supply pipe (50) with an open / close valve (51) for bypassing the low pressure economizer (1) is provided between the low pressure economizer inlet water supply pipe (46) close to the inlet of the A low-pressure economizer bypass feed water pipe (50) and a low-pressure economizer inlet water feed pipe (46) have a first feed stop valve (34) for supplying water from the condenser (28) (32) ) And a feed water temperature measuring device (53) is provided in the first feed water pipe (42) on the upstream side of the installation portion of the first feed water pump (37), and measured by the feed water temperature measuring device (53). The first feed water stop valve (34) and the on-off valve (51) are controlled to open and close according to the feed water temperature. Is a corrosion prevention method in Tomakan exhaust heat recovery boiler according.

  According to the third aspect of the present invention, the water supply corresponding to the amount of water supplied from the condenser (28) to the low pressure side economizer (1) via the low pressure economizer inlet water supply pipe (46) is supplied to the low pressure side economizer. The method for preventing corrosion during stopping of an exhaust heat recovery boiler according to claim 1, further comprising a feed water discharge system (25) for discharging from the outlet of the charcoal unit (1) toward the evaporator (2). is there.

  The invention according to claim 4 is a feed water recovery pipe having a second feed water stop valve (59) in the circulating feed pipe (43) on the upstream side from the connection part of the feed water system (32) from the condenser (28). One end of (58) is connected, the other end of the water supply recovery pipe (58) is connected to the condenser (28), the first water supply pipe (42), the circulating water supply pipe (43), and the low pressure economizer inlet water supply When not operating the feed water circulation system which consists of a closed loop which circulates piping (46) and a low voltage | pressure side economizer (1), the 1st water supply stop valve (34) provided in the water supply system (32) is opened, and circulation water supply piping 3. The method for preventing corrosion during stopping of an exhaust heat recovery boiler according to claim 2, wherein water supplied from (43) is allowed to flow into a condenser (28).

  The invention according to claim 5 is a superheater for generating steam by heating the feed water flowing in from the condenser storing water recovered from the steam, using the heat of the combustion exhaust gas containing sulfur. An evaporator, a reheater, a low-pressure side economizer, and at least one of a plurality of economizers having a pressure higher than that of the low-pressure side economizer, a superheater, an evaporator, and a economizer; In an exhaust heat recovery boiler equipped with a denitration device, one or more pressures higher than the low-pressure side economizer (1) from the outlet of the low-pressure side economizer (1) having a heat transfer tube group to which ammonium sulfate or acidic ammonium sulfate easily adheres A first water supply pipe (42) having a first water supply pump (37) for sequentially supplying water to the economizer (3, 6), and a low-pressure economizer inlet water supply provided at the low-pressure side economizer (1) inlet One of the pipe (46), the one or more economizers (3, 6) on the high-pressure side, and the low-pressure economizer inlet water supply pipe 46), the second water supply pipe (47) for adjusting the temperature of the low pressure economizer inlet and the first water supply pipe (42) downstream from the installation portion of the first water supply pump (37) are branched off. The first feed water using the circulating water supply pipe (43) circulated toward the low pressure economizer inlet water supply pipe (46) of the low pressure side economizer (1) and the temperature rise by the first water feed pump (37) A feed water circulation system capable of forming a closed loop that circulates the pipe (42), the circulation water supply pipe (43), the low pressure economizer inlet water feed pipe (46), and the low pressure side economizer (1) is provided. It is an exhaust heat recovery boiler.

  According to the sixth aspect of the present invention, there is provided a low-pressure side economizer between the first water supply pipe (42) and the low-pressure economizer inlet water supply pipe (46) on the upstream side of the first water supply pump (37) installation portion. 1) A low-pressure economizer bypass water supply pipe (50) with an on-off valve (51) that bypasses 1) is provided, and the low-pressure economizer bypass water supply pipe (50) is supplied with water from the condenser (28). A water supply system (32) having a first water supply stop valve (34) to be supplied is connected, and a water supply temperature measuring instrument (42) is connected to the first water supply pipe (42) upstream from the first water supply pump (37) installation part. 53) and a control device (60) for controlling the opening and closing of the first water stop valve (34) and the on-off valve (51) in accordance with the feed water temperature measured by the feed water temperature measuring device (53). The exhaust heat recovery boiler according to claim 5, wherein the boiler is a waste heat recovery boiler.

  According to the seventh aspect of the present invention, one end of the water supply recovery pipe (58) having the second water supply stop valve (59) is connected to the upstream side from the connection part with the circulating water supply pipe (43) of the water supply system (32). The exhaust heat recovery boiler according to claim 5, wherein the other end of the water supply recovery pipe (58) is connected to the condenser (28).

(Function)
When the gas turbine is stopped and the heat source to the exhaust heat recovery boiler is lost, the vacuum of the condenser 28 is not broken, and the upstream side of the exhaust heat recovery boiler from the condensate pump 29 to the low-pressure feed water pump 33 (hereinafter referred to as “the exhaust heat recovery boiler”). The water supply system 32 (which may be referred to as a pre-boiler) is in an operating state, and the high / medium pressure water supply pump 37 is in a minimum flow operation state, and a standby operation is performed in the period until the next gas turbine start-up.

  The minimum flow of water supply by the high and medium pressure water supply pump 37 flows through the high and medium pressure water supply communication pipe 42, branches before the high pressure water supply stop valve 41 provided in the high and medium pressure water supply communication pipe 42, and passes through the high and medium pressure water supply pump minimum flow system 43. Then, a closed loop system is constructed in which the low-pressure economizer inlet water supply system 46 returns to the high-medium-pressure water supply pump 37 again via the low-pressure economizer 1 and the high-medium-pressure water supply communication pipe 42.

  By performing the minimum flow operation of the high / medium pressure feed water pump 37 in this system configuration, the temperature of the feed water is raised every time the high / low pressure feed water pump 37 passes, so that the heat transfer tube temperature of the entire low pressure economizer 1 is, for example, 100 ° C. or more. The ammonium sulfate or acid ammonium sulfate adhering to the heat transfer tube can be maintained in a dry state that does not cause corrosion.

  On the other hand, if the minimum flow operation is continued in the closed loop system configuration for a long time, the temperature in the system will continue to rise, and there is a risk that flushing may occur at the inlet of the high and medium pressure feed water pump 37. Is provided with a low-pressure economizer bypass system 50 capable of supplying cold water from the condenser 28. The temperature is monitored by a low-pressure economizer outlet feed water thermometer 53 provided in the high / medium-pressure feed water communication pipe 42. When the temperature reaches a specified temperature, the low-pressure economizer bypass valve 51 is opened so that the cold water from the condenser 28 is The charcoal bypass system 50 is allowed to flow into the closed loop system configuration, and the inlet water supply temperature of the high and medium pressure water supply pump 37 is adjusted to the flushing generation temperature or lower.

  At this time, in order to discharge the chilled water flow that has just flowed in from the condenser 28 side to the outside of the closed loop system, the low pressure feed water flow rate adjustment valve 21 is slightly opened to a specified opening, and the system is connected to the low pressure brackish water separation drum 16. Miss the water supply inside. When this operation is repeated and the water level of the low-pressure bracking water separation drum 16 reaches a specified level, the water is discharged out of the system by the drum blow 54.

  According to the present invention, in a waste heat recovery boiler with a denitration device used in a combined power plant that uses a fuel containing sulfur content in a gas turbine, the high and medium pressure feed pump 37 has a minimum flow in the closed loop system configuration when stopped. By operating, the heat transfer tube temperature of the low-pressure economizer 1 as a whole is kept at a high temperature of, for example, 100 ° C. or higher, so that ammonium sulfate or acid ammonium sulfate can be prevented from absorbing corrosive moisture and causing corrosion. Can be maintained in a state.

  Further, by continuing the minimum flow operation in the closed loop system configuration over a long period of time, when the temperature in the system rises, the low pressure economizer bypass system 50 opens the low pressure economizer bypass valve 51 so that the condenser is opened. It is possible to adjust the feed water temperature at the inlet of the high / medium pressure feed water pump 37 to be equal to or lower than the flushing generation temperature by allowing cold water from 28 to flow in.

At this time, in order to discharge the flow rate of the cold water flowing from the condenser 28 side to the outside of the closed loop system, the low pressure feed water flow rate adjustment valve 21 is slightly opened to a specified opening, and the system is supplied to the low pressure brackish water separation drum 16. Miss the water supply inside. When this operation is repeated and the water level of the low-pressure bracking water separation drum 16 reaches a specified level, the water is discharged out of the system by the drum blow 54.
Further, in the exhaust heat recovery boiler to which the present invention is applied, if a damper is installed in the outlet duct or the outlet flue, the NOx emission amount at the time of starting the plant can be reduced.

It is a block diagram of the waste heat recovery boiler of one Example of this invention. It is a block diagram of the waste heat recovery boiler of one Example of this invention. It is a block diagram of the waste heat recovery boiler of a prior art.

The present invention will be described based on the following embodiments.
An exhaust heat recovery boiler system diagram of an embodiment of a combined power plant to which the present invention is applied is shown in FIG. The configuration of the water supply system shown in FIG. 1 will not be described for the same parts as those shown in FIG.

  That is, the minimum flow system 43 of the high and medium pressure water supply pump 37 branched from the outlet of the high and medium pressure water supply pump 37 in front of the high pressure water supply stop valve 41 provided in the intermediate and high pressure water supply communication pipe 42 is a low pressure economizer inlet water supply system. 46, a closed loop that returns from the low-pressure economizer inlet water supply system 46 via the low-pressure economizer 1 to the low-pressure economizer 1 through the medium-high pressure water supply connection pipe 42 and returns to the high-medium pressure water supply pump 37 again. This embodiment is characterized in that it can be configured.

  When the gas turbine stops and the heat source for the exhaust heat recovery boiler disappears, the vacuum of the condenser 28 is not broken, and the water supply system 32 of the pre-boiler from the condensate pump 29 to the low pressure feed pump 33 is put into operation. The high / intermediate pressure water supply pump 37 is set to the minimum flow operation state, and the standby operation is performed in the period until the next gas turbine activation.

By performing the minimum flow operation of the high and medium pressure feed water pump 37 in the closed loop system configuration, the temperature of the feed water is increased every time the high and medium pressure feed water pump 37 passes, so that the heat transfer tube temperature of the entire low pressure economizer 1 is, for example, 100 It can be kept at a high temperature of not lower than ° C., and ammonium sulfate or acidic ammonium sulfate adhering to the heat transfer tube can be maintained in a dry state that does not cause corrosiveness.
On the other hand, if the operation is continued in the closed-loop minimum flow system configuration for a long time, the temperature in the closed-loop system configuration continues to rise, and flushing may occur at the inlet of the high-medium pressure feed water pump 37. A low-pressure economizer bypass system between a low-pressure economizer inlet water supply system 46 closer to the inlet of the low-pressure economizer 1 than a connection with the system 43 and an intermediate-high pressure water supply communication pipe 42 near the outlet of the low-pressure economizer 1 50 is provided so that cold water from the condenser 28 can flow into the low-pressure economizer bypass system 50. That is, the low-pressure economizer bypass system 50 is connected to a water supply system 32 having a water supply stop valve 34 that supplies water from the condenser 28.
Further, a feed water thermometer 53 is provided in the intermediate / high pressure water supply communication pipe 42 on the upstream side from the installation portion of the high / medium pressure feed water pump 37.

  In the minimum flow operation of the high and medium pressure water supply pump 37, the high and medium pressure water supply water passes through the medium and high pressure water supply connecting pipe 42 on the outlet side of the high and medium pressure water supply pump 37, branches in front of the high pressure water supply stop valve 41, and the high and medium pressure water supply pump minimum. It is configured in a closed loop that passes through the flow system 43 and returns to the high / medium pressure feed water pump 37 again via the low pressure economizer inlet feed pipe 46, the low pressure economizer 1, and the intermediate / high pressure feed water connection pipe 42. By performing the minimum flow operation of the high / medium pressure feed water pump 37 in this system configuration, the temperature of the feed water is raised every time the high / low pressure feed water pump 37 passes, so that the heat transfer tube temperature of the entire low pressure economizer 1 is, for example, 100 ° C. or more. Therefore, it is possible to maintain ammonium sulfate or acidic ammonium sulfate adhering to the heat transfer tube in a dry state that does not cause corrosiveness.

  On the other hand, if the minimum flow operation is continued in the closed loop system configuration for a long time, the temperature in the system continues to rise, and there is a possibility that flushing may occur at the inlet of the pump 37. The low-pressure economizer outlet feed water thermometer 53 monitors the temperature, and when the specified temperature is reached, the low-pressure economizer bypass valve 51 and the low-pressure feed water stop valve 34 are opened to supply the cold water from the condenser 28 to the medium-high pressure water supply. The feed water temperature at the inlet of the high / medium pressure feed water pump 37 is adjusted to be equal to or lower than the flushing generation temperature by flowing into the communication pipe 42.

  At this time, in order to discharge the flow rate of the cold water flowing in from the condenser 28 side to the outside of the system, the low-pressure feed water flow rate adjustment valve 21 is slightly opened to the specified opening, and the closed-loop system is connected to the low-pressure brackish water separation drum 16. Miss the water supply inside. When this operation is repeated and the water level of the low-pressure bracking water separation drum 16 reaches a specified level, the drum blow 54 discharges water to the outside of the closed loop system.

  In addition, when the exhaust heat recovery boiler is activated, the pump group is activated by first starting the condensate pump 29, then starting the low-pressure feed water pump 33, and finally starting the high / medium pressure feed water pump 37. After the condensate pump 29 and the low-pressure feed pump 33 are activated, the minimum flow feed water of the feed water system 32 by the two pumps 29 and 33 from the front of the low-pressure feed stop valve 34 is closed with the low-pressure feed stop valve 34 closed. Return to condenser 28 via 45.

  At this time, if the low-pressure economizer bypass system 50 is taken out from the water supply system 32 on the upstream side of the low-pressure feedwater stop valve 34, the inlet of the high / medium-pressure feedwater pump 37 is not pressurized, so the low-pressure economizer The shut-off operation pressure of the low-pressure feed pump 33 applied to the low pressure feed water stop valve 34 is directly applied to the condenser bypass valve 51 as a differential pressure.

  It is desirable that the low pressure economizer bypass system 50 be taken out from the downstream of the low pressure water supply stop valve 34 because such an excessive differential pressure may be damaged when applied to the low pressure water supply stop valve 34. However, if the low-pressure feed water stop valve 34 is strong, the low-pressure economizer bypass system 50 may be disposed on the upstream side of the low-pressure feed water stop valve 34.

  With the water supply system configuration of the exhaust heat recovery boiler, the heat transfer pipe of the exhaust heat recovery boiler is cooled by being governed by the temperature of the water supplied from the condenser 28 even when the gas turbine is not ignited. There is nothing to do.

  In addition, even when the combined power plant is stopped and the heat source supplied to the exhaust heat recovery boiler disappears, the condensate pump does not break the vacuum of the condenser 28 until the next start-up of the plant. If the pre-boiler water supply system 32 from 29 to the low-pressure feed water pump 33 is operated and the high / medium pressure feed water pump 37 is put on standby in a minimum flow operation state, ammonium sulfate or acid attached to the heat transfer pipe of the exhaust heat recovery boiler Ammonium sulfate can be maintained in a dry state, and corrosion of the heat transfer tube can be prevented.

  In addition, if a damper is installed in the outlet duct and the subsequent outlet flue in the exhaust heat recovery boiler to which the present invention is applied, the temperature rise effect in the water supply system by the minimum flow operation of the above-described high / medium pressure water supply pump 37 is utilized. Since the ambient temperature in the exhaust heat recovery boiler can be maintained at a high temperature, it is possible to advance the timing of injecting ammonia into the denitration device 8 at the next startup of the plant. It can be reduced.

  Note that the high-pressure water supply stop valve 41 provided in the medium-high pressure water supply communication pipe 42 needs to be closed in order to “prevent water falling” when the can stops. Specifically, this is to prevent the following phenomenon from occurring. In other words, when the volume of the fluid in each heat exchanger decreases with heat dissipation when the can stops, the water supply system (high / intermediate pressure water supply communication pipe) 42 with the high / intermediate pressure water supply pump 37 is connected to the exhaust heat recovery boiler (HRSG) main body. Therefore, when the high-pressure water supply stop valve 41 is open, the flow of water supply from each heat exchanger of the exhaust heat recovery boiler to the high / medium-pressure water supply communication pipe 42 can be made through the high-pressure water supply stop valve 41. As a result, there is a place where there is no water supply at the top of the heat transfer unit. At first glance, “cold” steam is actually present in the portion of the heat transfer that appears to be a cavity. When the boiler is started in this state, the hollow portion disturbs and it takes time for water filling in the heat transfer device, and the steam in the hollow portion is steam even though it is “cold”. This may cause a phenomenon such as a water hammer to occur at startup.

  In addition, the high-pressure feed water flow control valve 23 in the high-pressure steam separation drum feed pipe 27 at the outlet of the high-pressure economizer 6 is closed without closing the high-pressure feedwater stop valve 41 when the can is stopped. Although it is conceivable to form a closed loop of the feed water system that returns from the high pressure economizer 6 to the low pressure economizer inlet temperature control system 47 via the high / medium pressure feed water connection pipe 42, the inside of the heat transfer pipe is warmed. The high-pressure feed water flow rate adjustment valve 23 in the high-pressure brackish water separation drum feed pipe 27 of the charcoal unit 6 originally has its role in feed water flow rate adjustment and is not adapted to a large differential pressure, and thus is easily damaged. Although the water supply flow rate control valve 23 capable of withstanding a large differential pressure can be manufactured, it is very expensive because it is very expensive.

  As another embodiment of the present invention, in addition to the configuration shown in FIG. 1, a condenser is provided on the upstream side of the connection portion of the minimum flow system 43 of the high-medium pressure feed water pump 37 shown in FIG. 2 to the water supply system 32. A configuration may be added in which a water supply recovery pipe 58 for recovering the water supply is provided to 28 and a water supply stop valve 59 is provided in the water supply recovery pipe 58. By providing the water supply stop valve 59 in the water supply recovery pipe 58, the water supply can be returned from the water supply recovery pipe 58 to the condenser 28 instead of the low pressure economizer 1.

DESCRIPTION OF SYMBOLS 1 Low pressure economizer 2 Low pressure evaporator 3 Medium pressure economizer 4 Medium pressure evaporator 5 Low pressure superheater 6 High pressure economizer 7 Medium pressure superheater 8 Denitration device 9 High pressure evaporator 10 High pressure primary superheater 11 Primary reheat 12 Secondary reheater 13 High pressure secondary superheater 16 Low pressure brackish water separation drum 17 Medium pressure brackish water separation drum 18 High pressure brackish water separation drum 21 Low pressure feed water flow rate adjustment valve 22 Medium pressure feed water flow rate adjustment valve 23 High pressure water flow rate adjustment valve 25 Low pressure Brackish water separation drum water supply pipe 26 Medium pressure brackish water separation drum water supply pipe 27 High pressure steam water separation drum water supply pipe 28 Condenser 29 Condensate pump 30 Ground steam condenser 31 Flow meter 32 Water supply system 33 Low pressure feed water pump 34 Low pressure feed water stop valve 35 Check valve 37 High and medium pressure water supply pump 38 Medium pressure water supply stop valve 39 Medium pressure economizer inlet communication pipe 41 High pressure water supply stop valve 42 High and medium pressure water supply communication pipe 43 High and medium pressure water supply pump minimum flow System 44 On-off valve 45 Low-pressure feed pump minimum flow system 46 Low-pressure economizer inlet system 47 Low-pressure economizer inlet temperature control system 50 Low-pressure economizer bypass system 51 Low-pressure economizer bypass valve 53 Water feed thermometer 54 Drum blow 58 Water supply Recovery piping 59 Water supply stop valve 60 Control device

Claims (7)

A superheater, an evaporator, a reheater, and a heater for generating steam by heating the feed water flowing in from a condenser storing water collected from the steam turbine by using the heat of combustion exhaust gas containing sulfur At least a superheater, an evaporator and a economizer among a plurality of economizers composed of a low-pressure economizer and one or more economizers higher in pressure than the low-pressure economizer, and exhaust heat provided with a denitration device In the recovery boiler,
Water is sequentially supplied from the outlet of the low-pressure side economizer (1) having a heat transfer tube group to which ammonium sulfate or acidic ammonium sulphate easily adheres to one or more high-pressure economizers (3, 6) from the low-pressure side economizer (1). A first water supply pipe (42) having a first water supply pump (37) to perform,
A low-pressure economizer inlet water supply pipe (46) provided at the low-pressure economizer (1) inlet;
One of the one or more economizers (3, 6) on the high pressure side, and a second water supply pipe (47) for adjusting the temperature of the low pressure economizer inlet connected to the low pressure economizer inlet water supply pipe (46), ,
Circulating water supply pipe for branching from the first water supply pipe (42) downstream from the first water supply pump (37) installation section and circulating the water supply toward the inlet water supply pipe (46) of the low-pressure side economizer (1) (43)
The first water supply pipe (42), the circulation water supply pipe (43), the low pressure economizer inlet water supply pipe (46), and the low pressure side economizer ( Waste heat recovery characterized by maintaining a temperature at which ammonium sulfate or acidic ammonium sulfate adhering to the heat transfer tube group of the low-pressure economizer (1) is kept in a dry state by configuring a feed water circulation system consisting of a closed loop circulating 1) Corrosion prevention during boiler can stop. The first water supply pipe (42) on the upstream side of the first water supply pump (37) installation part and the low pressure economizer near the inlet of the low pressure side economizer (1) from the connection part of the circulation water supply pipe (43) A low pressure economizer bypass water supply pipe (50) with an on-off valve (51) that bypasses the low pressure side economizer (1) is provided between the inlet water supply pipes (46),
A water supply system having a first water supply stop valve (34) for supplying water from the condenser (28) to the low pressure economizer bypass water supply pipe (50) and the low pressure economizer inlet water supply pipe (46) ( 32)
The first water supply pipe (42) on the upstream side of the first water supply pump (37) installation part is provided with a water supply temperature measuring device (53),
The exhaust heat recovery boiler according to claim 1, wherein the first feed water stop valve (34) and the on-off valve (51) are controlled to open and close according to the feed water temperature measured by the feed water temperature measuring device (53). Corrosion prevention method during stopping.   From the outlet of the low-pressure side economizer (1), feed water corresponding to the amount of water flowing into the low-pressure side economizer (1) from the condenser (28) via the low-pressure economizer inlet water supply pipe (46). 2. A method for preventing corrosion during stopping of an exhaust heat recovery boiler according to claim 1, further comprising a feed water discharge system (25) for discharging toward the evaporator (2). One end of a water supply recovery pipe (58) having a second water supply stop valve (59) is connected to the circulating water supply pipe (43) on the upstream side of the connection part of the water supply system (32) from the condenser (28). Connect the other end of the water supply recovery pipe (58) to the condenser (28),
When the feed water circulation system consisting of a closed loop that circulates through the first feed water pipe (42), the circulation feed water pipe (43), the low pressure economizer inlet feed pipe (46), and the low pressure side economizer (1) is not operated, The exhaust heat recovery boiler according to claim 2, characterized in that the first water supply stop valve (34) provided in the system (32) is opened and water supplied from the circulating water supply pipe (43) is caused to flow to the condenser (28). To prevent corrosion of steel cans. Superheaters, evaporators, reheaters and low pressures to generate steam by heating the feed water flowing from the condenser that stores the water recovered from the steam using the heat of the combustion exhaust gas containing sulfur At least a superheater, an evaporator, and a economizer among a plurality of economizers composed of a side economizer and one or more economizers higher in pressure than the low-pressure side economizer, and exhaust heat recovery provided with a denitration device In the boiler
Water is sequentially supplied from the outlet of the low-pressure side economizer (1) having a heat transfer tube group to which ammonium sulfate or acidic ammonium sulphate easily adheres to one or more high-pressure economizers (3, 6) from the low-pressure side economizer (1). A first water supply pipe (42) having a first water supply pump (37) to perform,
A low-pressure economizer inlet water supply pipe (46) provided at the low-pressure economizer (1) inlet;
One of the one or more economizers (3, 6) on the high pressure side, and a second water supply pipe (47) for adjusting the temperature of the low pressure economizer inlet connected to the low pressure economizer inlet water supply pipe (46), ,
Branches from the first water supply pipe (42) downstream from the first water supply pump (37) installation part and circulates the water supply toward the low-pressure economizer inlet water supply pipe (46) of the low-pressure economizer (1) A circulating water supply pipe (43),
The first water supply pipe (42), the circulation water supply pipe (43), the low-pressure economizer inlet water supply pipe (46), and the low-pressure side economizer (1) are utilized by using the temperature rise by the first water supply pump (37). An exhaust heat recovery boiler provided with a feed water circulation system capable of forming a closed closed loop. On-off valve for bypassing the low-pressure side economizer (1) between the first feed water pipe (42) and the low-pressure economizer inlet water supply pipe (46) on the upstream side of the first feed pump (37) installation part ( 51) with a low pressure economizer bypass water supply pipe (50),
A water supply system (32) having a first water supply stop valve (34) for supplying water from the condenser (28) is connected to the low pressure economizer bypass water supply pipe (50),
The first water supply pipe (42) on the upstream side of the first water supply pump (37) installation part is provided with a water supply temperature measuring device (53),
The control device (60) for opening and closing the first water supply stop valve (34) and the on-off valve (51) according to the water supply temperature measured by the water supply temperature measuring device (53) is provided. 5. An exhaust heat recovery boiler according to 5.   One end of the water supply recovery pipe (58) having the second water supply stop valve (59) is connected to the upstream side from the connection with the circulation water supply pipe (43) of the water supply system (32), and the water supply recovery pipe (58) 6. The exhaust heat recovery boiler according to claim 5, wherein the other end is connected to a condenser (28).

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