JP2839195B2 - Waste heat recovery boiler water supply control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water supply control device for an exhaust heat recovery boiler, and more particularly, to a water supply control device suitable for performing good water supply to a drum.

[Prior Art] In recent years, as part of high-efficiency power generation, construction of a combined power generation plant has been promoted. This combined cycle power plant generates power using a gas turbine and collects the heat possessed by the exhaust gas discharged from the gas turbine with an exhaust heat recovery boiler.
The steam generated by the exhaust heat recovery boiler drives a steam turbine to generate power.

This combined cycle power plant has the features of gas turbines, such as easy start-up and high load responsiveness, in addition to the high-efficiency power generation as described above, and is suitable for intermediate load operation according to the recent power demand pattern. Power plant. Such an exhaust heat recovery boiler will be described with reference to the drawings.

FIG. 11 is a schematic system diagram of a conventional combined cycle power plant. In FIG. 11, 1 is a gas turbine and 2 is a gas turbine 1.
Is a waste heat recovery boiler for introducing exhaust gas G of the gas turbine 1 and recovering waste heat thereof.

The exhaust heat recovery boiler 3 includes a superheater 4, a high-pressure evaporator 5, a high-pressure economizer 6, a low-pressure evaporator 7, a low-pressure economizer 8, a low-pressure drum 9, and a high-pressure drum.
It is composed of 10 mag. Reference numeral 12 denotes a steam turbine driven by steam from the superheater 4, and is connected to the generator 2. 13 is a condenser for condensing steam discharged from the steam turbine 12, and 14 is a condensate pump for supplying water W of the condenser 13 to the low-pressure economizer 8. Reference numeral 15 denotes a high-pressure feed pump that guides heated feedwater at the outlet of the low-pressure economizer 8 to the high-pressure economizer 6 and mixes the feedwater with the feed to the low-pressure economizer 8.
Is a water supply control valve, 18 is a temperature detector, and 19 is a temperature / flow rate controller.

[Problems to be Solved by the Invention] Since the above-mentioned combined cycle power plant is well known, the description of its operation is omitted, and the feedwater WR at the outlet of the low-pressure economizer 8 is reduced by using the high-pressure water pump 15. The reason for mixing with the feed water W at the inlet 8 will be described.

In recent combined cycle power plants, equipment costs have been reduced,
The deaerator is omitted for reasons such as simplification of the system, and a condenser deaeration system in which the condenser 13 has a deaeration function is adopted. In the case of this condenser degassing method, the feedwater temperature T _S1 at the inlet of the low-pressure economizer 8 of the exhaust heat recovery boiler 3 is as low as about 30 ° C.
When the feedwater at the same feedwater temperature (about 30 ° C.) is fed to the low-pressure economizer 8, low-temperature corrosion occurs in the low-pressure economizer 8.

As a countermeasure, the heated feedwater WR at the outlet of the low-pressure economizer 8 is mixed with the boiler feedwater W (the feedwater at the inlet of the low-pressure economizer 8) via the high-pressure feed pump 15 as shown in the figure to prevent low-temperature corrosion. Means for raising the temperature to a temperature that does not occur is employed.
Then, the feedwater temperature is set to about 60 ° C., which is a temperature at which low-temperature corrosion does not occur during rated operation, and the feedwater temperature is adjusted by the temperature / flow controller 19 based on the temperature detected by the temperature detector 18. It is kept constant by controlling the valve 16.

By the way, conventionally, the feedwater temperature is set to a constant value (approximately 60 ° C.) over the entire load. Therefore, when the temperature of the seawater in the winter condenser 13 decreases, the temperature of the boiler feedwater W is low. In order to raise the feedwater temperature T _S1 at the inlet of the low-pressure economizer 8 to the set temperature (about 60 ° C.), it is necessary to recirculate an excessive flow rate (hereinafter abbreviated as a recirculation flow rate WR).

Accordingly, the capacity of the high-pressure water supply pump 15 is a high-pressure water supply pump flow rate Q that is the sum of the recirculation flow rate WR in winter and the high-pressure evaporation amount (that is, the water supply flow rate to the high-pressure economizer 6) at that time.
In addition, a large capacity high-pressure water supply pump 15 must be used in order to determine the capacity with a margin of 10 to 20% in consideration of load fluctuations, gas turbine exhaust gas fluctuations, and the like. And the disadvantage that the plant efficiency is reduced occurs.

SUMMARY OF THE INVENTION An object of the present invention is to provide a small-capacity high-pressure feed pump which can supply water to a high-pressure drum satisfactorily even in winter due to load fluctuations and gas turbine exhaust gas fluctuations. An object of the present invention is to provide a water supply control device for a boiler.

Means for Solving the Problems In order to achieve the above object, the present invention provides a low pressure economizer 8
A high-pressure economizer, a high-pressure water supply pump provided between the low-pressure economizer and the high-pressure economizer and supplying water from the low-pressure economizer to the high-pressure economizer, and a part of an outlet side of the high-pressure economizer. A recirculation system that branches off and connects to the low-pressure economizer inlet side, and the opening is adjusted so that the inlet water supply temperature of the low-pressure economizer is set to a temperature that does not cause low-temperature corrosion. Temperature control valve, a temperature detector for detecting the inlet feedwater temperature of the low-pressure economizer, and a controller for controlling the opening of the temperature control valve based on a temperature detection signal of the temperature detector. ,
For example, when the load changes in winter or when the gas turbine exhaust gas fluctuates, the above-mentioned temperature detector is prioritized over the temperature detection signal, and the flow rate of the water supply to the high-pressure system after the high-pressure economizer is not hindered. The flow rate is reduced by a temperature control valve.

[Example] Hereinafter, the present invention will be described based on an illustrated example.

FIG. 1 is a schematic system diagram of a combined cycle power plant according to a first embodiment of the present invention. In FIG. 1, the same portions as those shown in FIG. 11 are denoted by the same reference numerals, and description thereof will be omitted. Reference numeral 20 denotes a differential pressure detector of the water supply control valve 17, which controls the temperature control valve 16 with a differential pressure detection signal 26 prior to the temperature detection signal 27 of the temperature detector 18.

Here, low-temperature corrosion of the low-pressure economizer 8 will be considered. Low-temperature corrosion is caused by condensation of moisture (H ₂ O) in exhaust gas. And the dew point temperature of the condensation is H _{2 in the} exhaust gas.
ODepends on partial pressure. FIG. 2 shows the relationship between the H ₂ O partial pressure and the dew point temperature. As is clear from FIG. ₂ , as the H ₂ O partial pressure decreases, the dew point temperature also decreases.

Incidentally, the relationship between the atmospheric temperature and the partial pressure of H ₂ O in the exhaust gas is as shown in FIG. From FIG. 3, the relationship between the atmospheric temperature and the stall temperature is as shown in FIG. Therefore, when the atmospheric temperature is low, the stall temperature is also low. On the other hand, the feedwater temperature at the inlet of the low-pressure economizer 8 is set with a margin for the dew point temperature when the atmospheric temperature is high to simplify the control (for example,
60 ° C) and is constant regardless of the atmospheric temperature.

FIG. 5 (a) shows the relationship between the ambient temperature and the temperature of the boiler feedwater W. When the ambient temperature is low, the feedwater temperature is also low, so that the feedwater temperature at the low-pressure economizer 8 inlet reaches the set value (60 ° C.). The recirculation flow rate for raising the temperature is highest. Further, as shown in FIG. 5 (b), the flow rate of water supplied to the high-pressure drum 10 is largest when the atmospheric temperature is low. Accordingly, as shown in FIG. 6, the high-pressure water supply pump flow rate Q of the high-pressure water supply pump 15 becomes maximum when the atmospheric temperature is low. Conventionally, the capacity of the high-pressure feed pump 15 is determined by giving a margin of 10 to 20% to the flow rate when the atmospheric temperature is low, taking into account load fluctuations, gas turbine exhaust gas fluctuations, and the like. , The pump capacity is determined to be small. In this case, the flow rate of the water supply to the high-pressure drum 10 increases due to load fluctuations, fluctuations in the exhaust gas of the gas turbine, and the like, exceeding the capacity of the high-pressure water supply pump 15 and decreasing the discharge pressure of the high-pressure water supply pump 15, causing the water supply control valve 17 to decrease. , There is a risk that the restriction of water supply to the high-pressure drum 10 may be hindered.

On the other hand, in the present invention, the differential pressure of the water supply control valve 17 is detected by the differential pressure detector 20, and when the pressure becomes lower than the set differential pressure, the recirculation flow rate is reduced by the temperature control valve 16, and the high pressure water pump 15 The flow rate is reduced, the discharge pressure is increased, the differential pressure of the water supply control valve 17 is secured, and good water supply control is performed. In this case, the reduction rate of the recirculation flow rate WR is 20 to
As a result, the feedwater temperature at the inlet of the low-pressure economizer 8 drops from 60 ° C to 55 to 50 ° C, as shown in Fig. 4, and is lower than the dew point temperature (40 ° C). There is no problem.

Here, a specific control method of the temperature control valve 16 will be described with reference to FIG. In FIG. 12, the differential pressure of the water supply control valve 17 is used as the control signal A.

That is, when the differential pressure of the feed water control valve 17 is larger than the set value, the signal from the low pressure economizer inlet feed water temperature transmitter 33 becomes b. At this time, as b, for example, the high-pressure water supply pump 15
The recirculation amount should not exceed the specification point of about 60 T / H. When the pressure difference of the feed water control valve 17 becomes smaller than the set value, the signal from the low pressure economizer inlet feed water temperature transmitter 33 is a
Becomes a is set to about 40 T / H, the recirculation amount is reduced from 60 T / H to 40 T / H, and the differential pressure of the water supply control valve 17 is secured.

In the figure, 28 is a proportional integration circuit, 29 is a high signal limiter, 30 is a subtractor, 31 is a switching relay, 32 is a signal generator,
33 is a transmitter, 34 is a control signal, and 35 is a temperature setting device.

FIG. 7 shows a temperature control valve 16 according to a second embodiment of the present invention.
Related to the control device. FIG. 7 shows a water supply control valve instead of the differential pressure detector 20 of the water supply control valve 17 of the embodiment.
An opening detector 21 for detecting the opening of 17 is provided. The control signal 34 shown in FIG. 12 is the opening of the water supply control valve 17. That is, when the flow rate of the water supply to the high-pressure drum 10 increases and the opening of the water supply control valve 17 becomes larger than the set opening, the temperature control valve 16 is controlled in preference to the signal of the temperature detector 18, The recirculation flow rate WR is reduced.

FIG. 8 shows a temperature control valve 16 according to a third embodiment of the present invention.
Related to the control device. FIG. 8 shows the operation of the gas turbine 1, that is, a gas turbine operating state detector 22 for detecting a signal of any one of a load, a fuel amount, an exhaust gas temperature, and an exhaust gas amount, or a combination thereof.
Is controlled to reduce the recirculation flow rate WR, and the control signal 34 in FIG. 12 is a signal of the gas turbine operation state detector 22.

FIG. 9 shows a temperature control valve 16 according to a fourth embodiment of the present invention.
Related to the control device. FIG. 9 shows a temperature detection by the steam turbine operating state detector 23 which detects the operating state of the steam turbine 12, that is, any one of the load, the control valve opening, the turbine bypass valve opening, or a combination thereof. The temperature control valve 16 is controlled in preference to the signal of the device 18 to reduce the recirculation flow rate WR, and as the control signal 34 in FIG. 12, the signal of the steam turbine operating state detector 23 is used. Things.

FIG. 10 shows a temperature control valve 16 according to a fifth embodiment of the present invention.
Related to the control device. FIG. 10 shows a flow rate detector 24 that detects the flow rate of the high-pressure water supply pump 15, and when the flow rate exceeds the set flow rate, the signal of the flow rate controller 25 takes priority over the signal of the temperature detector 18 to adjust the temperature. The valve 16 is controlled to reduce the recirculation flow rate WR, and the control signal 34 in FIG. 12 is a signal from the flow rate detector 24 of the high-pressure feed pump 15.

[Effects of the Invention] As described above, according to the present invention, good pressure control of high-pressure drum water supply can be achieved with a small-capacity high-pressure water supply pump even in a load fluctuation at the time of the maximum water supply flow rate in winter and a gas turbine exhaust gas fluctuation. Becomes possible, and consequently suppresses the increase in auxiliary power,
A decrease in plant efficiency can be prevented.

The annual reduction effect of auxiliary equipment power is estimated as follows.

Conventional high-pressure feedwater pump power: 540KW High-pressure feedwater pump power in the case of the present invention: 470KW Assuming a utilization rate of 60% and a power generation unit price of 10 yen / KWH, (540-47
0) KW x 24hr x 365 days x 0.6 x 10 yen / KWH = 3.679 million yen / year.

[Brief description of the drawings]

FIG. 1 is a system diagram of a combined cycle power plant according to a first embodiment of the present invention, FIG. 2 is a characteristic diagram showing a relationship between H ₂ O partial pressure and dew point temperature, and FIG. FIG. 4 is a characteristic diagram showing the relationship between the H ₂ O partial pressure in the gas turbine exhaust gas, FIG. 4 is a characteristic diagram showing the relationship between the atmospheric temperature and the dew point temperature, and FIG. 5 (a) is the atmospheric temperature and the temperature of the boiler feed water W FIG. 6B is a characteristic diagram showing the relationship between the atmospheric temperature and the amount of water supplied to the high-pressure drum, FIG. 6 is a characteristic diagram showing the relationship between the atmospheric temperature and the flow rate of the high-pressure water supply pump, and FIG. FIG. 8 is a system diagram of a combined cycle power plant according to a second embodiment of the present invention, and FIG.
FIG. 9 is a system diagram of the combined cycle power plant according to the embodiment of FIG.
FIG. 10 is a system diagram of a combined cycle power plant according to a fourth embodiment of the present invention, FIG. 10 is a block diagram of a combined cycle power plant according to a fifth embodiment of the present invention, and FIG. 12 (a) and 12 (b) show a control system diagram of the temperature control valve of the present invention. 1 gas turbine 2 waste heat recovery boiler 6 high pressure economizer 8 low pressure economizer 10 high pressure drum 12
... Steam turbine, 15 ... High pressure feed pump, 16 ... Temperature control valve, 18 ... Temperature detector, 19 ... Temperature and flow controller, 20
…… Differential pressure detector, 21 …… Opening degree detector, 22 …… Gas turbine operating state detector, 23 …… Steam turbine operating state detector, 24 …… Flow detector, WR …… Recirculation flow rate.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Tetsuo Mimura 6-9 Takara-cho, Kure City, Hiroshima Pref. Inside the Kure Plant, Babkotsuk Hitachi Ltd. (56) References JP-A-63-118502 (JP, A) (58) Field surveyed (Int.Cl. ⁶ , DB name) F22D 1/12

Claims (6)

(57) [Claims] 1. A low-pressure economizer, a high-pressure economizer, a high-pressure water supply pump provided between the low-pressure economizer and the high-pressure economizer and supplying water from the low-pressure economizer to the high-pressure economizer. A recirculation system that partially branches the outlet side of the high-pressure feedwater pump and connects to the low-pressure economizer inlet side, and is installed in the middle of the recirculation system, and the low-pressure economizer inlet feedwater temperature causes low-temperature corrosion. A temperature control valve whose opening degree is adjusted so as not to have a temperature, a temperature detector that detects an inlet feedwater temperature of the low-pressure economizer, and an opening of the temperature control valve based on a temperature detection signal of the temperature detector. A controller for controlling the temperature, the temperature control valve, so as not to interfere with the control of the flow rate of water supply to the high-pressure system after the high-pressure economizer, in preference to the temperature detection signal of the temperature detector. The exhaust heat recovery boiler is characterized by being configured to reduce the flow rate Water supply control device. 2. A water supply control valve is provided between the high pressure economizer and the high pressure drum, and a differential pressure detector for detecting a differential pressure of the water supply control valve is provided, When the actually measured differential pressure detected by the differential pressure detector becomes smaller than a preset differential pressure, the recirculation flow rate is reduced by the temperature control valve. Water supply control device for recovery boiler. 3. A water supply control valve is provided between the high-pressure economizer and the high-pressure drum, and an opening detector for detecting an opening of the water supply control valve is provided. When the measured opening of the water supply control valve detected by the opening detector is larger than a preset opening, the recirculation flow rate is narrowed by the temperature control valve. Water supply control device for waste heat recovery boiler. 4. A gas turbine according to claim 1, further comprising a gas turbine and a gas turbine operation state detector for detecting an operation state of the gas turbine on a high pressure system side with respect to the high pressure economizer. Wherein the recirculation flow rate is reduced by the temperature control valve based on the detection signal of (1). 5. A steam turbine according to claim 1, further comprising a steam turbine and a steam turbine operating state detector for detecting an operating state of the steam turbine, provided on a high pressure system side of the high pressure economizer. Wherein the recirculation flow rate is reduced by the temperature control valve based on the detection signal of (1). 6. A high-pressure water supply pump according to claim 1, wherein a flow rate detector is provided in said high-pressure water supply pump, and an actual measured flow rate of said high-pressure water supply pump detected by said flow rate detector exceeds a preset flow rate. And a temperature control valve for narrowing a recirculation flow rate.