JPH0387502A - Device for controlling feedwater for waste heat recovery boiler - Google Patents

Abstract

PURPOSE:To enable satisfactorily controlling the feedwater to a high-pressure drum by means of a high-pressure feedwater pump of small capacity by throttling the flow in quantity of the feedwater to a drum by means of a flow- regulating valve to an extent not causing trouble to the control of the flow in quantity of the feedwater to the high-pressure system in the part beginning with a high-pressure economizer. CONSTITUTION:When the differential pressure at a feedwater-regulating valve 17 is larger than a prescribed valve, a signal '6' is transmitted by a transmitter 33 relating to the feedwater temperature at the inlet to a low-pressure economizer. For the signal '6', for example, approx. 60T/H may be set as a quantity of recirculation not exceeding the specified point of a high-pressure feedwater pump 15. When the differential pressure at the feedwater-regulating valve 17 has fallen below a prescribed point, a signal 'a' is transmitted by the transmitter 33 relating to the feedwater temperature at the inlet to a low-pressure economizer. For the signal 'a', approx. 40T/H may be set. The quantity of recirculation is thus throttled from 60T/H to 40T/H so that differential pressure can be ensured across the feedwater-regulating valve 17.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a water supply control device for an exhaust heat recovery boiler, and particularly to a water supply control device suitable for properly supplying water to a drum.

[Background Art] In recent years, construction of combined power generation plants has been progressing as part of high-efficiency power generation. This combined power plant generates electricity using a gas turbine.

The system uses an exhaust heat recovery boiler to recover the heat retained in the exhaust gas discharged from the gas turbine, and the steam generated by the exhaust heat recovery boiler activates a steam turbine to generate electricity.

In addition to the high-efficiency power generation mentioned above, this combined power generation plant also has features such as ease of rapid startup and high load response, which are characteristics of gas turbines, and is suitable for intermediate load operation in line with recent electricity demand patterns. It is a power generation plant. Such an exhaust heat recovery boiler will be explained with reference to the drawings.

FIG. 11 is a schematic diagram of a conventional combined cycle power plant. In FIG. 11, 1 is a gas turbine, 2 is a generator activated by the gas turbine 1, and 3 is an exhaust heat recovery boiler that introduces the exhaust gas G of the gas turbine 1 and recovers its exhaust heat.

The exhaust heat recovery boiler 3 includes a superheater 4. High pressure evaporator 5° High pressure economizer 6. Low pressure evaporator7. Low pressure energy saver8. Low pressure drum9.
It is composed of a high pressure drum 10 and the like.

12 is a steam turbine activated by steam from the superheater 4, and is connected to the generator 2. 13 is a condenser that condenses steam discharged from the steam turbine 12, and 14 is a condensate pump that supplies water W from the condenser 13 to the low-pressure economizer 8. 15 is a high-pressure water supply pump that guides the heated feed water at the outlet of the low-pressure economizer 8 to the high-pressure economizer 6 and mixes it with the water supplied to the low-pressure economizer 8; 16 is a temperature control valve; 17 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 power generation plant is well known, a description of its operation will be omitted. The reason why it is mixed with the water supply W at the inlet of No. 8 will be explained.

Recent combined cycle power plants have reduced installation costs,
The deaerator is omitted for reasons such as system simplification.

A condenser deaeration method is adopted in which the condenser 13 has a deaeration function. In the case of this condenser deaeration method, the feed water temperature T11 at the inlet of the low pressure economizer 8 of the waste heat recovery boiler 3 is approximately 30°C.
Since the temperature is low, low-temperature corrosion occurs in the low-pressure economizer 8 when water at the same water supply temperature (approximately 30° C.) is supplied to the low-pressure economizer 8.

As a countermeasure against this problem, as shown in Figure 1, the heated feed water WR at the outlet of the low-pressure economizer 8 mixes with the boiler feed water W (the water at the inlet of the low-pressure economizer 8) via the high-pressure water pump 15, causing low-temperature corrosion. Measures have been taken to raise the temperature to a temperature at which this does not occur. The water supply temperature is set to approximately 60°C, which is the temperature at which low-temperature corrosion does not occur during rated operation, and the temperature of this water supply is adjusted by the temperature/flow rate controller 19 based on the temperature detected by the temperature detector 18. It is kept constant by controlling valve 16.

By the way, in the past, the above-mentioned water supply temperature was set at a constant value (approximately 60°C) over the entire load, so the condenser 13
If the temperature of the boiler feed water W is low due to the decrease in seawater temperature at It is necessary to circulate (hereinafter abbreviated as recirculation flow rate WR).

Therefore, the capacity of the high-pressure water supply pump 15 is the high-pressure water pump flow rate Q, which is the sum of the winter recirculation flow rate WR and the high-pressure evaporation amount at that time (i.e., the water supply flow rate to the high-pressure economizer 6).
In order to determine the capacity with a margin of usually 10 to 20% in consideration of load fluctuations, gas turbine exhaust gas fluctuations, etc., it is necessary to use a large-capacity high-pressure water supply pump 15, which increases the auxiliary power. This resulted in the disadvantage that plant efficiency decreased.

An object of the present invention is to eliminate the drawbacks of the prior art described above, and to provide a small-capacity, high-pressure water supply pump that can efficiently supply water to a high-pressure drum even under winter load fluctuations, gas turbine exhaust gas fluctuations, etc. To provide boiler water supply control equipment.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a low-pressure economizer, a high-pressure economizer, and a low-pressure economizer installed between the low-pressure economizer and the high-pressure economizer. A high-pressure water pump that supplies water from the coal generator to the high-pressure economizer, a recirculation system that partially branches the outlet side of the high-pressure water pump and connects it to the inlet side of the low-pressure economizer, and a recirculation system that is installed in the middle of the recirculation system. In a water supply control device for an exhaust heat recovery boiler, which is equipped with a flow rate regulating valve that controls the inlet water temperature of the low-pressure economizer to a temperature that does not cause low-temperature corrosion, The present invention is characterized in that the flow rate adjustment valve is configured to restrict the flow rate to an extent that does not interfere with water supply flow rate control to the high-pressure system.

[Example] Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 1 is a schematic system diagram of a combined power generation plant according to a first embodiment of the present invention. In FIG. 1, parts that are the same as those shown in FIG. 11 are given the same reference numerals, and explanations thereof will be omitted. Reference numeral 20 denotes a differential pressure detector of the water supply regulating valve 17, and its differential pressure detection signal 26 controls the temperature regulating valve 16 in priority 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 occurs when moisture (Hld) in exhaust gas condenses. The dew point temperature of the condensation is H in the exhaust gas.
20 Depends on partial pressure. FIG. 2 shows the relationship between H,0 partial pressure and dew point temperature, and as is clear from FIG. 2, as H,0 partial pressure decreases, dew point temperature also decreases.

By the way, the relationship between the atmospheric temperature and the partial pressure of H,0 in the exhaust gas is as shown in FIG. From FIG. 3, the relationship between atmospheric temperature and dew point temperature is as shown in FIG. 4. Therefore, when the atmospheric temperature is low, the dew point temperature is also low.On the other hand, the water supply temperature of the low pressure energy saver 8 is set by simplifying the control and taking a margin for the dew point temperature when the atmospheric temperature is high. (for example, 60°C), and is kept constant regardless of the atmospheric temperature.

Figure 5 (a) shows the relationship between the atmospheric temperature and the temperature of the boiler feed water W. When the atmospheric temperature is low, the water supply temperature is also low. The recirculation flow rate for heating is the highest. Furthermore, Figure 5 (
As shown in b), the flow rate of water supplied to the high-pressure drum 10 is also highest when the atmospheric temperature is low. Therefore, as shown in FIG. 6, the high-pressure water supply pump flow rate Q of the high-pressure water supply pump 15 is maximum when the atmospheric temperature is low. Conventionally, high pressure water supply pump 1
The capacity of No. 5 is determined by taking 10 to 20% of the flow rate when the atmospheric temperature is low, taking into account load fluctuations, gas turbine exhaust gas fluctuations, etc., but in the present invention, the pump capacity is reduced by setting the margin to zero. It is up to you to decide. In this case, due to load fluctuations, gas turbine exhaust gas fluctuations, etc., the water supply flow rate to the high-pressure drum 10 increases, exceeding the capacity of the high-pressure water supply pump 15, and the discharge pressure of the high-pressure water pump 15 decreases, causing the difference in the water supply control valve 17. There is a possibility that the pressure will decrease and the control of water supply to the high-pressure drum 10 will be hindered.

In contrast, in the present invention, the differential pressure across the water supply control valve 17 is detected by the differential pressure detector 20, and when the differential pressure becomes smaller than the set differential pressure, the recirculation flow rate is throttled by the temperature control valve 16, and the high-pressure water supply pump 15 is activated. The flow rate is reduced and the discharge pressure is increased to ensure a differential pressure across the water supply control valve 17, thereby achieving good water supply control.

In this case, the rate of reduction of the recirculation flow rate WR is 20~
40%, but as a result, the water supply temperature for the eight low-pressure economizers is reduced from 60℃ to 55-50℃ as shown in Figure 4, which is a sufficient margin for the dew point temperature (40℃). There is no problem.

Here, a specific method of controlling the temperature control valve 16 will be explained as shown in FIG. 12. 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 is 6.
becomes. At this time, 6 is 1. For example, set the recirculation amount to about 60 T/H as the recirculation amount that does not exceed the specification point of the high pressure water supply pump 15, and when the differential pressure of the water supply control valve 17 becomes smaller than the set value, the low pressure saving Inlet water supply temperature transmitter 33
The signal from is a. A is set to about 40 T/H, and the recirculation amount is narrowed down from 60 T/H to 40 T/H to ensure the differential pressure of the water supply control valve 17.

In the figure, 28 is a proportional-integral circuit, 29 is a high signal limiter, 30 is a subtracter, 3 is a switching relay, 32 is a signal generator, 33 is an oscillator, 34 is a control signal, and 35 is a temperature setting device. It is.

FIG. 7 shows a temperature control valve 16 according to a second embodiment of the present invention.
The present invention relates to a control device. FIG. 7 shows a water supply system in place of the differential pressure detector 20 of the water supply control valve 17 of the above embodiment.
An opening degree detector 21 for detecting the opening degree of the Li moderation valve 17 is installed. The control signal 34 in FIG. 12 is the opening degree of the water supply control valve 17. That is, when the water supply flow rate to the high-pressure drum 10 increases and the opening degree of the water supply regulating valve 170 becomes larger than the set opening degree, the temperature regulating valve 16 is controlled with priority over the signal from the temperature sensor upper 8, This is to restrict the recirculation flow rate WR.

FIG. 8 shows a temperature control valve 16 according to a third embodiment of the present invention.
The present invention relates to a control device. FIG. 8 shows that the temperature control valve 16 is controlled by a gas turbine operating state detector 22 that detects a signal of the operating state of the gas turbine 1, that is, load, fuel amount, exhaust gas temperature, exhaust gas amount, or a combination thereof. Thus, the recirculation flow rate WR is throttled, and the control signal 34 in FIG. 12 is the signal from the gas turbine operating state detector 22.

FIG. 9 shows a temperature control valve 16 according to a fourth embodiment of the present invention.
The present invention relates to a control device. FIG. 9 shows that the temperature detector 18 is detected by the steam turbine operating state detector 23 which detects the operating state of the steam turbine 12, that is, the load, the opening of the control valve, the opening of the turbine bypass valve, or a combination thereof. The temperature control valve 16 is controlled with priority over the first signal to reduce the recirculation flow rate WR.
The control signal 34 in FIG. 2 is a signal from the steam turbine operating state detector 23.

FIG. 10 shows a temperature control valve 1 according to a fifth embodiment of the present invention.
This relates to the control device No. 6. FIG. 10 shows that when the flow rate exceeds the set flow rate by the flow rate detector 24 that detects the flow rate of the high-pressure water supply pump 15, the signal from the flow rate controller 25 controls the temperature and flow rate. The temperature control valve 16 is controlled with priority over the signal from the water supply pump 19 to reduce the recirculation flow rate WR, and the control signal 34 in FIG. It was used as a signal.

[Effects of the Invention] As described above, according to the present invention, a small-capacity high-pressure water supply pump can perform good high-pressure drum water supply control even under load fluctuations during the maximum water supply flow rate in winter, gas turbine exhaust gas fluctuations, etc. This makes it possible to suppress an increase in auxiliary machine power and prevent a decrease in plant efficiency.

A trial calculation of the annual reduction effect on auxiliary machine power is as follows.

Conventional high-pressure water supply pump movable crab 54OKW High-pressure water feed pump movable crab in case of the present invention 470KV Utilization rate 60%9 Power generation unit cost 10 yen/KW)I, (540-470)K
V x 24hr x 365 days x O, 6 x 10 yen/) IH = Savings of 3.679 million yen/year.

[Brief explanation of drawings]

Fig. 1 is a system diagram of a combined cycle power plant according to the first embodiment of the present invention, Fig. 2 is a characteristic diagram showing the relationship between H20 partial pressure and dew point temperature, and Fig. 3 is a diagram showing the relationship between atmospheric temperature and gas turbine A characteristic diagram showing the relationship between H,0 partial pressure in exhaust gas, Figure 4 is a characteristic diagram showing the relationship between atmospheric temperature and dew point temperature, and Figure 5 (a) is a characteristic diagram showing the relationship between atmospheric temperature and boiler feed water temperature. Figure 6 is a characteristic diagram showing the relationship between atmospheric temperature and the amount of water supplied to the high-pressure drum. Figure 6 is a characteristic diagram showing the relationship between atmospheric temperature and high-pressure water pump flow rate. , a system diagram of a combined power plant according to the second embodiment of the present invention, FIG.
The system diagram of the combined power generation plant according to the example of FIG. 9 is as follows.
FIG. 10 is a system diagram of a combined cycle plant according to the fourth embodiment of the present invention, and FIG. 11 is a system diagram of a conventional combined cycle plant according to the fifth embodiment of the present invention. System diagrams FIGS. 12(a) and 12(b) show control system diagrams of the temperature control valve of the present invention. 1...Gas turbine, 2...Exhaust heat recovery boiler. 6...High pressure economizer, 8...Low pressure economizer, 10...High pressure drum, 12...Steam turbine, 15...・High pressure water pump, 16...
... Temperature control valve, 18 ... Temperature detector, 1
9...Temperature, flow rate controller, 2o...Differential pressure detector, 21...Opening degree detector, 22...
... Gas turbine operating state detector, 23... Steam turbine operating state detector, 24... Group flow rate detector,
WR...Recirculation flow rate. Figure 2 Figure 3 Figure 4 Figure 9 Figure 12 (a)

Claims (6)

[Claims] (1) A low-pressure economizer, a high-pressure economizer, a high-pressure water supply pump that is installed between the low-pressure economizer and the high-pressure economizer and supplies water from the low-pressure economizer to the high-pressure economizer, and its high-pressure A recirculation system that partially branches the outlet side of the water pump and connects it to the inlet side of the low-pressure economizer, and a recirculation system that is installed in the middle of the recirculation system to ensure that the inlet water temperature of the low-pressure economizer does not cause low-temperature corrosion. In a water supply control device for an exhaust heat recovery boiler, the flow rate adjustment valve is provided with a flow rate adjustment valve that adjusts the opening so that A water supply control device for an exhaust heat recovery boiler, characterized by being configured to restrict the flow rate using a valve. (2) In claim (1), a water supply regulating valve and a differential pressure detector for detecting a differential pressure of the water supply regulating valve are provided between the high pressure economizer and the high pressure drum, and the differential pressure is detected. The water supply for a waste heat recovery boiler is characterized in that the flow rate regulating valve is configured to throttle the recirculation flow rate when the actual differential pressure detected by the device becomes smaller than a preset set differential pressure. Control device. (3) In claim (1), a water supply regulating valve and an opening degree detector for detecting the opening degree of the water supply regulating valve are provided between the high-pressure energy saver and the high-pressure drum, and detecting the opening degree. When the actual opening degree of the water supply regulating valve detected by the device is larger than the preset opening degree, the flow rate regulating valve is configured to throttle the recirculation flow rate. Recovery boiler water supply control device. (4) In claim (1), a gas turbine and a gas turbine operating state detector for detecting the operating state of the gas turbine are provided on the high-pressure system side of the high-pressure energy saver, and the detection from this detector is provided. A water supply control device for an exhaust heat recovery boiler, characterized in that the flow rate regulating valve is configured to throttle the recirculation flow rate based on a signal. (5) In claim (1), a steam turbine and a steam turbine operating state detector for detecting the operating state of the steam turbine are provided on the high-pressure system side of the high-pressure economizer, and the detection from this detector is provided. A water supply control device for an exhaust heat recovery boiler, characterized in that the flow rate regulating valve is configured to throttle the recirculation flow rate based on a signal. (6) In claim (1), when the high-pressure water supply pump is provided with a flow rate detector, and the measured flow rate of the high-pressure water supply pump detected by the flow rate detector exceeds a preset set flow rate, A water supply control device for an exhaust heat recovery boiler, characterized in that the flow rate adjustment valve is configured to throttle the recirculation flow rate.