JPH1047606A - Feed water temperature control method and apparatus in exhaust reheating type combined cycle plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate dew concentration of SO3 on the water feed inlet side of a gas low pressure feed water heater. SOLUTION: When the temperature of feed water W fed from a gas low pressure feed water heater 17 is lower than a specified value, the opening of a flow rate control valve 29 provided on a feed water circulation pipe 26 is adjusted so that the flow rate of circulation water WC circulating through the gas low pressure feed water heater 17 reaches a specified value predetermined. When the temperature on the inlet side of the gas low pressure feed water heater 17 of the feed water W circulated to be introduced into the gas low pressure feed water heater 17 reaches a specified value, the opening of the flow rate control valve 29 is adjusted on the basis of the temperature of the feed water W on the feed water inlet side of the gas low pressure feed water heater 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for controlling feedwater temperature in an exhaust gas reburning combined cycle plant. More specifically, the present invention relates to a method for controlling the temperature of feedwater supplied to a boiler body at a feedwater inlet side of a gas low-pressure feedwater heater. The present invention relates to a method and apparatus for controlling a feedwater temperature in an exhaust gas reburning combined cycle plant capable of maintaining a required temperature.

[0002]

2. Description of the Related Art In recent years, in order to improve thermal efficiency, a turbine exhaust gas after driving a generator and a compressor is fed to a boiler as a combustion gas, and is used for combustion of fuel in the boiler. Combined cycle plants are being put into practical use, and an example of such a plant is shown in FIG.

In FIG. 6, reference numeral 1 denotes a boiler main body having a furnace 1a and a sub-side wall 1b and a rear heat transfer section 1c as well as a boiler main body 1.
The burner is installed below the furnace 1a. In the furnace 1a, the combustion gas G2 is generated by the combustion of the fuel F injected from the burner 2.

A gas turbine 3 is driven by combustion gas supplied from a combustor 4 to drive a generator 5 and a compressor 6. 6 and can be mixed and burned.

[0005] Reference numeral 7 denotes a duct provided with an airway evaporator 23 in the middle and for feeding turbine exhaust gas discharged from the gas turbine 3 into the furnace 1a as combustion gas G1, and reference numeral 8 denotes a rear transmission of the boiler body 1. This is an exhaust gas duct connected to the lower part of the heating unit 1c to supply the boiler exhaust gas G3 to a subsequent process.

Reference numeral 9 denotes a water supply W sent through a water supply pipe 10.
So that the water can be heated by the economizer stored in the lower part of the rear heat transfer section 1c. The feed water W heated by the economizer 9 is transferred to the lower part of the furnace wall tube forming the wall of the furnace 1a of the boiler body 1. A water supply pipe for feeding, 12 is a superheater stored in the sub-side wall 1b so as to superheat the steam generated by heating the feedwater with a furnace wall tube or the like, and 13 is a superheated steam generated by the superheater 12 A superheated steam pipe 15 for supplying V to the steam turbine 14 is a generator driven by the steam turbine 14, and steam extracted from the steam turbine 14 is condensed by a condenser (not shown). After that, the water can be returned to the water supply pipe 10 as the water supply W.

Reference numeral 16 denotes a water supply pipe which is connected to an intermediate portion between the exhaust gas duct 8 and the water supply pipe 10 so as to be located on the upstream side in the flow direction of the boiler exhaust gas G3. Water W which was sent 10
A high-pressure gas feed water heater 17 capable of heating the gas is connected to an intermediate portion between the exhaust gas duct 8 and the water supply pipe 10 so as to be located downstream of the gas high-pressure feed water heater 16 in the flow direction of the boiler exhaust gas G3. By the boiler exhaust gas G3 sent from the gas high-pressure feed water heater 16 through the exhaust gas duct 8, the feed water W sent from the feed pipe 10 is supplied to the feed water W by the gas high-pressure feed water heater 16 more. This is a gas low-pressure feedwater heater that can be heated on the upstream side in the flow direction.

Reference numeral 18 denotes a high-pressure ventilator connected to a middle part of the exhaust gas duct 8 downstream of the gas low-pressure feed water heater 17 in the flow direction of the boiler exhaust gas G3, and 19 denotes a flow direction of the boiler exhaust gas G3 in the exhaust gas duct 8. A chimney connected to the downstream end.

A condensate pump 20 is connected to a middle part of the water supply pipe 10 so as to be located upstream of the gas low-pressure water heater 17 in the flow direction of the water supply W, and 21 is a gas low-pressure water supply in the middle part of the water supply pipe 10. Heater 17 and gas high pressure feed water heater 1
A deaerator 22 connected between the deaerator 21 and the gas high-pressure water heater 16 is provided in the middle of the water supply pipe 10. .

[0010] In the above-described exhaust reburning combined cycle plant, the combined cycle operation in which only the steam turbine 14 is operated and the steam turbine 14 is operated only when the steam turbine output rises to a predetermined output. Is performed.

[0011] During the sole power operation, the operation is performed with the gas turbine 3 stopped. That is, the fuel F is injected from the burner 2 into the furnace 1a of the boiler main body 1, and air is supplied into the furnace 1a from a line (not shown). Combustion gas G
2 is generated.

The combustion gas G2 rises in the furnace 1a, passes through the sub-wall 1b and the rear heat transfer section 1c, is discharged as boiler exhaust gas G3 into the exhaust gas duct 8, passes through the exhaust gas duct 8, and is discharged into the atmosphere from the chimney 19. You. At this time, the combustion gas G2
Heats fluids such as water and steam in each furnace wall tube, the superheater 12 and the economizer 9 of the boiler body 1, and the boiler exhaust gas G3 is exhaust gas duct 8, gas high pressure feed water heater 16, gas low pressure feed water In the gas high-pressure feed water heater 16 and the gas low-pressure feed water heater 17 passing through the heater 17, the feed water W sent through the feed pipe 10 by the feed water pump 22 and the condensate pump 20 is heated.

On the other hand, the superheated steam V generated by being superheated by the superheater 12 passes through a superheated steam pipe 13 and a steam turbine 14.
And the steam turbine 14 is driven, and the steam extracted from the steam turbine 14 is condensed by a condenser,
Return to the condensate pump 20. In addition, a generator 15 is driven by the steam turbine 14 to generate power.

When the steam turbine output rises to a predetermined output, the gas turbine 3 is also driven to start the combined cycle operation. That is, the combustion gas generated by burning in the combustor 4 is introduced into the gas turbine 3 to drive the gas turbine 3, is discharged from the gas turbine 3, passes through the duct 7, and evaporates in the middle of the duct 7 in the wind path. Vessel 2
3 to generate steam, and then the combustion gas G
1 is fed into the furnace 1a of the boiler body 1. For this reason, the fuel F injected from the burner 2 into the furnace 1a is burned by the oxygen in the combustion gas G1 from the gas turbine 3, and the combustion gas G2 is generated. At this time, the supply of air from another line to the furnace 1a is stopped in advance.

The flow of the generated combustion gas G1 in the boiler main body 1 and the flow of the boiler exhaust gas G3 in the exhaust gas duct 8 are the same as those in the case of the above-described aerodynamic single operation.

The compressor 6 and the generator 5 are driven by driving the gas turbine 3, and the compressed air generated by the compressor 6 is used for combustion of fuel in the combustor 4.

[0017]

In the exhaust gas reburning combined cycle plant described above, LNG containing no sulfur is used as the fuel F. However, sulfur is contained as the fuel F in view of cost and the like. The use of heavy oil is being considered.

[0018] However, in the above-described exhaust reburning combined cycle plant, for example, when starting the boiler,
The temperature of the feedwater W on the feedwater inlet side of the gas low-pressure feedwater heater 17 is low and the feedwater inlet end of the gas low-pressure feedwater heater 17 is SO
_{(3) The} temperature is lower than the dew point of 115 ° C. Therefore, when heavy oil is used as the fuel F, SO ₃ acid adheres to the inlet end of the gas low-pressure feed water heater 17 and the inlet of the gas low-pressure feed water heater 17 Corrosion may occur on the side.

Further, even during the normal operation of the exhaust reburn type combined cycle plant, the gas low pressure feed water heater 17
If the feedwater temperature at the feedwater inlet side of the boiler becomes low for some reason, SO ₃ condensation will occur as in the case of starting the boiler.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to prevent the occurrence of SO ₃ dew condensation on the feed water inlet side of a gas low-pressure feed water heater.

[0021]

SUMMARY OF THE INVENTION According to the present invention, there is provided an exhaust system in which exhaust gas of a gas turbine is used as a fuel combustion gas in a boiler body, and a feed water heater heats water supplied to the boiler body by the boiler exhaust gas. In the reburning combined cycle plant, when the temperature of the feedwater sent from the feedwater heater is lower than a predetermined temperature, the feedwater circulates from the feedwater outlet side of the feedwater heater to the feedwater inlet side of the feedwater heater via the feedwater circulation pipe. The flow rate of the circulating water flowing through the feed water circulation pipe is controlled so that the flow rate of the circulating water becomes a predetermined flow rate set in advance, and when the temperature of the feed water sent from the feed water heater rises to a predetermined temperature, circulation is performed. The feed water circulation pipe is set so that the temperature at the feed water heater inlet side of the feed water introduced into the feed water heater together with the feed water from the condensate pump becomes a predetermined temperature set in advance. And controls the flow rate of the circulating water to the ring.

Further, according to the present invention, when the temperature of the feed water sent from the feed water heater is lower than the predetermined temperature, light oil is used as the fuel, and the temperature of the feed water sent from the feed water heater becomes the predetermined temperature. It is good to use heavy oil as fuel when

The present invention relates to a boiler body using exhaust gas from a gas turbine as fuel combustion gas, a feedwater heater for heating feedwater to be fed to the boiler body by boiler exhaust gas discharged from the boiler body, In an exhaust gas recirculation type combined cycle plant provided with a feed water circulation pipe for circulating a part of feed water sent from a heater to a feed water inlet side of a feed water heater, the flow rate of circulating water flowing through the feed water circulation pipe and the feed water A first controller for processing a difference in the flow rate of circulating water set to flow in the circulation pipe to obtain a valve opening adjustment command; A second regulator for processing the difference between the temperature of the feed water introduced into the heater and the set feed water temperature to obtain a valve opening adjustment command, and a flow of the feed water to the boiler body determined from the generator output command And a feedwater correction flow rate determined from the temperature of the feedwater downstream of the feedwater heater in the feedwater flow direction corresponding to the generator output command and the temperature of the feedwater detected downstream of the feedwater heater in the feedwater flow direction. An adder that gives a valve opening degree adjustment command to a first flow control valve provided downstream of the feedwater heater in the feedwater flow direction with respect to the feedwater heater; and that the temperature of the feedwater downstream of the feedwater heater in the feedwater flow direction is a predetermined value. A monitor switch for outputting a switching command when the temperature is reached, and a valve opening adjustment command from the first controller when the switching command is not given from the monitor switch, and is provided in the water supply circulation pipe. To the second flow control valve, and when a switch command from the monitor switch is provided, the switch is switched to output a valve opening degree adjustment command from the second regulator, and the second flow control valve is Give to It is provided with a and exchanger.

In the present invention, when the feed water temperature at the feed water outlet side of the feed water heater is lower than a predetermined temperature,
The temperature of the feedwater is raised by circulating a predetermined amount of feedwater as circulating water from the feedwater heater outlet side to the inlet side, and when the feedwater temperature downstream of the feedwater heater outlet becomes higher than the predetermined temperature, the feedwater heater inlet is increased. Since the flow rate of the circulating water is controlled so that the temperature of the feedwater on the upstream side becomes a predetermined temperature, the temperature on the feedwater inlet side of the feedwater heater can be kept high. Therefore, even when heavy oil is used as fuel, SO condensation of ₃ acid can be prevented.

When the temperature of the feed water sent from the feed water heater is lower than a predetermined temperature, light oil is used as fuel,
If heavy oil is used as fuel when the temperature of the feed water sent from the feed water heater reaches a predetermined temperature, the dew condensation of SO ₃ can be prevented even when the plant is started.

[0026]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIGS. 1 to 5 show an embodiment of the present invention.

As shown in FIG. 4, the exhaust gas reburning type combined cycle plant in the present embodiment has substantially the same configuration as the conventional exhaust gas reburning type combined cycle plant shown in FIG. And the description is omitted.

Thus, in the exhaust gas refueling type combined cycle plant according to the embodiment of the present invention, one end is connected between the gas low-pressure feed water heater 17 of the feed pipe 10 and the deaerator 21 and the other end is supplied with water. Gas low pressure feed water heater 1 for pipe 10
Feed water circulation pipe 26 connected between the pump 7 and the condensate pump 20
The inside of the feed water circulation pipe 26 is directed from the feed water outlet side of the gas low-pressure feed water heater 17 to the feed water inlet side, and the circulating water WC is provided.
Can be circulated.

Further, the circulating water pump 2 is provided with the circulating water pump 2 sequentially from the upstream side to the downstream side in the flow direction of the circulating water WC.
7, a flow detector 28 and a flow control valve 29 are connected.

Gas low pressure feed water heater 1 in feed pipe 10
7, a temperature detector 30 is provided at a position between the gas low-pressure feed water heater 17 and the upstream connection portion X1 of the feed water circulation pipe 26 to the feed pipe 10.

Gas low pressure feed water heater 1 in feed pipe 10
7, the temperature is sequentially detected from the upstream side to the downstream side in the flow direction of the feed water W so as to be located between the deaerator 21 and the downstream connection portion X2 of the feed water circulation pipe 26 to the feed pipe 10 at the feed water outlet side. The vessel 31 and the flow control valve 32 are connected.

The deaerator 21 is connected to an auxiliary steam supply pipe 34 provided with an on-off valve 33 at an intermediate position.
From 4, auxiliary steam of a predetermined pressure (for example, 3 ata) can be supplied to the deaerator 21. The reason why the auxiliary steam is supplied to the deaerator 21 is that the inside of the deaerator 21 is set to a saturated steam temperature corresponding to the pressure.

FIG. 1 shows the details of the feed water temperature control device applied to the exhaust gas reburning combined cycle plant shown in FIG.

Reference numeral 35 denotes a feed water inlet side of the gas low pressure feed water heater 17 and a gas low pressure feed water heating temperature TI detected by the temperature detector 30 and the gas low pressure feed water supplied from the signal generator 36. Subtractor that calculates the difference between the inlet water supply set temperature TS (for example, 115 ° C.) and obtains a gas low pressure feed water heater inlet water temperature deviation ΔTI (= TI−TS).
Reference numeral 7 denotes a proportional-integral controller for proportionally adjusting the gas supply pressure difference ΔTI at the inlet of the gas low-pressure feedwater heater supplied from the subtractor 35 to obtain a valve opening adjustment command VS1.

Numeral 38 represents a difference between the flow rate (detected circulating water flow rate) QWC of the circulating water WC flowing in the feed water circulation pipe 26 detected by the flow rate detector 28 and the set circulating water flow rate QS given from the signal generator 39. Circulating water flow rate deviation ΔQ (= QWC-
QS) is a proportional-integral adjuster for obtaining a valve opening adjustment command VS2 by proportional-integrally adjusting the circulating water flow rate deviation ΔQ given from the subtractor 38.

Reference numeral 41 denotes a switch, which is a proportional-integral controller 37
Of the valve opening degree adjustment command VS1 given from the controller or the valve opening degree adjustment command VS2 given from the proportional-integral controller 40, and gives it to the flow rate control valve 29 provided in the water supply circulation pipe 26, 29 can be adjusted.

Reference numeral 42 denotes a function for outputting the flow rate (water flow rate at the outlet of the gas low-pressure feed water heater) QM of the feed water W corresponding to the generator output command MWD, which should flow out of the gas low-pressure feed water heater 17 and be sent to the feed pipe 10. The generator 43 feeds water W to be sent out of the gas low pressure feed water heater 17 and through the feed pipe 10
A function generator that outputs a temperature (water supply temperature at the outlet of the gas low-pressure water supply heater) TM corresponding to the generator output command MWD,
4 is a gas low-pressure feedwater heater outlet feedwater temperature TM from the function generator 43 and a gas low-pressure feedwater heater outlet feedwater detection temperature TO in the feed pipe 10 on the outlet side of the gas low-pressure feedwater heater 17 detected by the temperature detector 31. Is a subtractor for calculating the gas supply pressure deviation ΔTO (= TM−TO) at the outlet of the gas low pressure feed water heater at the gas low pressure feed water heater, and 45 is a gas low pressure by proportionally integrating the gas supply pressure deviation ΔTO of the gas low pressure feed water heater from the subtractor 44. 46 is a proportional-integral controller for obtaining the feedwater correction flow rate QC, and 46 is a gas low-pressure feedwater heater outlet feedwater flow QM from the function generator 42.
And the gas low-pressure feedwater heater feedwater correction flow rate QC from the proportional-integral controller 45, and the valve is opened to the flow control valve 32 provided downstream of the gas low-pressure feedwater heater 17 of the feed pipe 10 in the flow direction of the feedwater W. This is an adder that gives the degree adjustment command VS3 (= QM + QC).

Reference numeral 47 denotes a gas low-pressure feed water heater outlet water supply detection temperature TO in the water supply pipe 10 on the outlet side of the gas low-pressure feed water heater 17 detected by the temperature detector 31 which is higher than a predetermined temperature (for example, 127 ° C.). This is a high / low monitor switch that outputs a switching command Y when the switching command Y is given to the switching device 41 through the set / reset device 48. When the switching command Y is given to the switching device 41, the switching device 41 switches from the a side to the b side. It has become.

Functions F1 (x) and F2 (x) as shown in FIGS. 2 and 3 are set in the function generators 42 and 43 described above. In any case, when the generator output command MWD is 30% or less, the gas low-pressure feedwater heater outlet feedwater flow rate QM and the gas low-pressure feedwater heater outlet feedwater temperature TM are minimum even if the generator output command MWD changes. When the generator output command MWD exceeds 30%, the flow rate of the feed water at the outlet of the gas low-pressure feed water heater QM, the feed water temperature at the outlet of the gas low-pressure feed water heater TM
Rise linearly as the generator output command MWD increases.

Next, the operation of the embodiment of the present invention will be described.

In the embodiment of the present invention, when operating the exhaust gas reburning type combined cycle plant, the on-off valve 33 is opened to supply auxiliary steam from the auxiliary steam supply pipe 34 into the deaerator 21, A predetermined pressure (for example, 3
ata (saturated steam temperature of 133 ° C. in this case)).

The operation procedure of the exhaust reburning type combined cycle plant in this embodiment of the present invention in the independent power operation and in the combined cycle operation is the same as that of the conventional case, and the description thereof will be omitted.

During operation, the generator output command MW
D is given to the function generators 42 and 43, and the function generator 42
, The gas low-pressure feedwater heater outlet feedwater flow rate QM corresponding to the generator output command MWD is output and provided to the adder 46.

The function generator 43 outputs a gas low pressure feed water heater outlet feed water temperature T corresponding to the generator output command MWD.
M is output and provided to the subtractor 44, and at the same time, the temperature detector 31 provided on the water supply outlet side of the gas low-pressure feed water heater 17 detects the gas low-pressure feed water heater outlet feed water detection temperature TO, and the subtractor 44 and the high-low It is given to the monitor switch 47.

In the subtracter 44, the difference between the gas supply pressure TM at the outlet of the gas low pressure feed water heater and the detected temperature TO at the gas outlet of the gas low pressure feed water heater TO is obtained, and the deviation ΔTO of the gas supply pressure at the gas low pressure feed water heater exit is obtained. Then, the gas low-pressure feedwater heater outlet feedwater temperature deviation ΔTO is proportionally integrated and adjusted by the proportional-integral controller 45, and is supplied to the adder 46 as the gas low-pressure feedwater heater feedwater correction flow rate QC.

The adder 46 adds the gas low-pressure feed water heater outlet feed flow rate QM and the gas low-pressure feed water heater feed water correction flow rate QC to obtain a valve opening adjustment command VS3, and obtains the obtained valve opening adjustment command VS3. VS3 is given to the flow control valve 32, and the opening of the flow control valve 32 is adjusted in accordance with the valve opening adjustment command VS3. Therefore, the gas low pressure feed water heater 1
The flow rate of the feed water W flowing out of the feed pipe 7 and supplied from the feed pipe 10 to the economizer 9 in the boiler main body 1 is adjusted.

The gas supply pressure TM at the outlet of the gas low-pressure supply water heater detected by the temperature detector 31 is a predetermined temperature (for example, 127).
° C), the high-low monitor switch 47
Since the switching command Y is not output from the switching device 41, the switching device 41 is switched to the side a in FIG.

Therefore, the flow rate of the circulating water WC flowing through the feed water circulation pipe 26 detected by the flow rate detector 28 is given to the subtractor 38 as a detected circulating water flow rate QWC. The difference from the preset circulating water flow rate QS given by the signal generator 39 is obtained to determine the circulating water flow rate deviation ΔQ, and the circulating water flow rate deviation ΔQ is supplied to the proportional-integral controller 40.

In the proportional integral controller 40, the circulating water flow rate deviation ΔQ is proportionally integrated to obtain a valve opening adjustment command VS2, and the obtained valve opening adjustment command VS2 is sent to the flow control valve 29 via the switch 41. Then, the opening of the flow control valve 29 is adjusted. Therefore, the circulating water WC pressurized by the circulating water pump 27 is supplied to the flow control valve 2 so as to have a constant flow rate.
9 circulates through the water supply circulation pipe 26, the water supply pipe 10, the gas low-pressure water supply heater 17, the water supply pipe 10, and the water supply circulation pipe 26. In this case, the operation is performed such that the circulation amount of the circulating water WC becomes the set circulating water flow rate QS set by the signal generator 39.

While a part of the feedwater W is circulating in this way, the boiler exhaust gas G3 continuously passes through the exhaust gas duct 8, passes through the gas high pressure feedwater heater 16, the exhaust gas duct 8, and the gas low pressure feedwater heater 17 The exhaust gas passes through the exhaust gas duct 8 and is discharged into the atmosphere by the high pressure ventilator 18 through the chimney 19.

When the boiler exhaust gas G3 passes through the gas low-pressure feed water heater 17, the feed water W mixed with the feed water from the condensing pump 20 and the circulating water WC from the circulating water pump 27 is heated. The temperature of the feed water W is determined by the gas low pressure feed water heater 1
7, the temperature gradually increases with the passage of time, and accordingly, the temperature of the feed water W sent to the economizer 9 by the feed pump 22 through the feed pipe 10 also gradually increases.

When the temperature TO detected at the outlet of the gas low-pressure feed water heater detected by the temperature detector 31 exceeds a predetermined temperature, a switching command Y is issued from the high / low monitor switch 47.
Is output to the switching unit 41 via the set / reset unit 48.
And the switch 41 switches to the b side.

Therefore, the temperature of the feed water W at the inlet side of the gas low-pressure feed water heater 17 is detected by the temperature detector 30 and given to the subtractor 35 as a gas low-pressure feed water heater inlet feed water detection temperature TI. At 35, the gas low pressure feed water heater inlet feed water detection temperature TI and the gas low pressure feed water heater inlet feed water set temperature TS given by the signal generator 36 in advance.
The difference between the two is taken as the gas low pressure feedwater heater inlet feedwater temperature deviation Δ
TI is determined, and the determined gas low-pressure feedwater heater inlet feedwater temperature deviation ΔTI is provided to a proportional-integral controller 37, which performs proportional-integral adjustment to obtain a valve opening degree adjustment command VS1. The circulating water flowing through the feed water circulation pipe 26 is adjusted by adjusting the opening of the flow control valve 29 so that the temperature of the feed water W on the inlet side of the gas low-pressure feed water heater 17 becomes a predetermined temperature (for example, 115 ° C.). The flow rate of the WC is controlled.

As described above, when the temperature of the feed water W at the feed water outlet side of the gas low-pressure feed water heater 17 is lower than a predetermined temperature, the flow rate of the circulating water WC is controlled to be a constant flow rate. The temperature of the WC is raised and the gas low pressure feed water heater 17
When the temperature of the feedwater W on the feedwater outlet side is higher than a predetermined temperature, the flow rate of the circulating water WC is controlled so that the temperature of the feedwater W on the inlet side of the gas low-pressure feedwater heater 17 becomes the predetermined temperature. The temperature of the feedwater W at the feedwater inlet side of the gas low-pressure feedwater heater 17 can be maintained at 115 ° C. or higher, which is the SO ₃ dew point, and therefore, the feedwater inlet side (gas outlet side) of the gas low-pressure feedwater heater 17 can be maintained. Corrosion due to adhesion of SO ₃ acid can be prevented.

When the detected temperature TO at the outlet of the gas low-pressure feed water heater is lower than a predetermined value and the switch 41 is switched to the side a, light oil is used as the fuel F, and the gas low-pressure feed water is heated. When the temperature at the outlet water supply detection temperature TO becomes a predetermined value and the switch 41 is switched to the b side, the use of heavy oil as the fuel F can prevent the SO ₃ condensation more effectively.

Further, as a general example of the case where such an operation is performed, there is a boiler startup, and the relationship between the elapse of the time and the boiler exhaust gas temperature, feed water temperature, feed water flow rate, and steam turbine load is shown in FIG. Is shown in On the left side of the point A, the switch 41 in FIG. 1 is switched to the a side, and at the point A, the switch 41 is switched to the b side.

It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that various changes can be made without departing from the spirit of the present invention.

[0059]

In the feed water temperature control method and apparatus in repowering-shaft combined cycle plant of the present invention exhibits, in any of the claims, to hold the feed water temperature in the feed water inlet side of the feedwater heater than SO ₃ dew point Therefore, it is possible to prevent corrosion due to adhesion of SO ₃ acid on the gas outlet side of the feed water heater.

[Brief description of the drawings]

FIG. 1 is a block diagram of a control system of a feedwater temperature control method and apparatus in an exhaust gas reburning combined cycle plant of the present invention.

FIG. 2 is a function F1 set in a function generator 42 of FIG. 1;
It is a graph which shows (x).

FIG. 3 is a function F2 set in a function generator 43 of FIG. 1;
It is a graph which shows (x).

FIG. 4 is a flowchart showing an outline of an exhaust gas reburning combined cycle plant to which the present invention is applied.

FIG. 5 is a graph showing a relationship between a lapse of time when the present invention is applied at the time of starting the boiler, a boiler exhaust gas temperature, a feedwater temperature, a feedwater flow rate, and a steam turbine load.

FIG. 6 is a flowchart showing an outline of a conventional exhaust gas reburning combined cycle plant.

[Description of Signs] 1 Boiler main body 3 Gas turbine 10 Water supply pipe 17 Gas low pressure feed water heater (feed water heater) 20 Condensate pump 26 Feed water circulation pipe 29 Flow control valve (second flow control valve) 32 Flow control valve ( (First flow control valve) 37 Proportional integral controller (second controller) 40 Proportional integral controller (first controller) 41 Switcher 46 Adder 47 High-low monitor switch (monitor switch) F Fuel G1 For combustion Gas G3 Boiler exhaust gas W Feedwater WC Circulating water TI Gas low-pressure feedwater heater inlet feedwater detection temperature (temperature) TS Gas low-pressure feedwater heater inlet feedwater set temperature (temperature) ΔTI Gas low-pressure feedwater heater inlet feedwater temperature deviation (difference) VS1, VS2, VS3 Valve opening adjustment command MWD Generator output command TO Gas low-pressure feedwater heater outlet feedwater detection temperature (temperature) TM Gas low-pressure feedwater heater outlet supply Water temperature (Temperature) QM Gas low pressure feed water heater outlet feed flow rate (flow rate) QC Gas low pressure feed water heater feed water correction flow rate (feed water correction flow rate) QS Set circulating water flow rate (flow rate) QWC Detection circulating water flow rate (flow rate) ΔQ Circulating water Flow deviation (difference) Y switching command

Claims (3)

[Claims] An exhaust gas recirculation type combined cycle plant in which exhaust gas from a gas turbine is used as fuel combustion gas in a boiler body and feed water to a boiler body is heated by a boiler exhaust gas by a feed water heater. When the temperature of the feedwater sent from the heater is lower than a predetermined temperature, the flow rate of the circulating water circulating from the feedwater outlet side of the feedwater heater to the feedwater inlet side of the feedwater heater via the feedwater circulation pipe is set to a predetermined predetermined value. The flow rate of the circulating water flowing through the feed water circulation pipe is controlled so that the flow rate of the feed water circulation pipe is increased. When the temperature of the feed water sent from the feed water heater rises to a predetermined temperature, the feed water is heated together with the feed water from the condensing pump. The flow rate of the circulating water circulating through the feed water circulation pipe is controlled such that the temperature of the feed water introduced at the inlet of the feed water heater becomes a predetermined temperature. A method for controlling a feedwater temperature in an exhaust gas reburning combined cycle plant, characterized in that: 2. When the temperature of the feed water sent from the feed water heater is lower than a predetermined temperature, light oil is used as fuel, and when the temperature of the feed water sent from the feed water heater reaches the predetermined temperature, the fuel The feedwater temperature control method for an exhaust gas reburning combined cycle plant according to claim 1, wherein heavy oil is used as the fuel cell. 3. A boiler body that uses exhaust gas of a gas turbine as a fuel combustion gas, a feedwater heater that heats feedwater supplied to the boiler body by boiler exhaust gas discharged from the boiler body, and a feedwater heater. In an exhaust gas recirculation type combined cycle plant equipped with a water supply circulation pipe that circulates a part of the supplied water to the water supply inlet side of the water supply heater, the flow rate of circulating water flowing through the water supply circulation pipe and the inside of the water supply circulation pipe A first controller for processing a difference in the flow rate of the circulating water set to flow to obtain a valve opening adjustment command; and circulating through the water supply circulation pipe and introducing water from the condensate pump to the water heater. A second regulator for processing the difference between the supplied water supply temperature and the set supply water temperature to obtain a valve opening degree adjustment command; a flow rate of water supply to the boiler body determined from a generator output command; Add the feedwater temperature on the downstream side of the feedwater flow direction of the feedwater heater corresponding to the output command and the feedwater correction flow rate determined from the detected feedwater temperature on the downstream side of the feedwater flow direction of the feedwater heater, and feed the feedwater to the feedwater pipe. An adder that gives a valve opening degree adjustment command to a first flow control valve provided on the downstream side of the feedwater flow direction with respect to the heater, when the temperature of the feedwater on the downstream side of the feedwater flow direction of the feedwater heater reaches a predetermined temperature. A monitor switch for outputting a switching command; and a second switch provided in the water supply circulation pipe by outputting a valve opening adjustment command from the first controller when no switching command is given from the monitor switch. When given to the flow control valve, when a switching command from the monitor switch is given, it is switched to output a valve opening adjustment command from the second regulator,
A feeder temperature control device for an exhaust gas reburning type combined cycle plant, further comprising a switch for giving the flow rate to the second flow control valve.