JPH076601B2 - Exhaust heat recovery boiler feed water temperature controller - Google Patents

Description

The present invention relates to a feed water temperature control device for an exhaust heat recovery boiler in a combined cycle power plant.

[Conventional technology]

As a plant most suitable for high-efficiency power generation and intermediate load operation, a combined power generation plant has recently received attention. This plant is equipped with an exhaust heat recovery boiler that recovers the heat of the exhaust gas discharged from this gas turbine while generating electricity with a gas turbine, and drives the steam turbine with the steam generated in the exhaust heat recovery boiler to generate electricity. Is. Such an exhaust heat recovery boiler will be described with reference to the drawings.

FIG. 11 is a system diagram of a conventional combined cycle power plant. In the figure, 1 is a gas turbine, 2 is a generator driven 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 the 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. A steam turbine 12 is driven by steam from the superheater 4 and is connected to the generator 2. Reference numeral 13 is a condenser for condensing steam discharged from the steam turbine 12, and 14 is a condensate pump for supplying the water W of the condenser 13 to the low pressure economizer 8. Reference numeral 15 is a boiler transfer 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, and 16 is a flow control valve. Reference numeral 17 is a temperature detector for detecting the feed water temperature T _S1 at the inlet of the low pressure economizer 8, and 18 is a temperature / flow rate controller.

Since the combined power generation plant is well known, description of its operation will be omitted, and the reason why the feed water at the outlet of the low pressure economizer 8 is mixed with the feed water at its inlet will be described. In recent complex power plants, the deaerator is removed and the condenser 13 is equipped with a deaerator system with a deaerating function for reasons such as facility cost reduction and system simplification. . In the case of this method, the feed water temperature T _S1 at the inlet of the low pressure economizer 8 of the boiler 3 is about
Since it is as low as 30 ℃, low-pressure economizer 8
When the water is supplied to the low pressure economizer 8, low temperature corrosion occurs. As a countermeasure against this, as shown in the figure, the heated feed water at the outlet of the low-pressure coal economizer 8 is supplied to the boiler feed water W via the boiler transfer pump 15.
(Means for supplying water at the inlet of the low pressure economizer 8) is used to raise the temperature to a temperature at which low temperature corrosion does not occur. The temperature is set to about 60 ° C, which is the temperature at which low temperature corrosion does not occur during rated operation, and this temperature is adjusted by the temperature / flow controller 18 based on the temperature detected by the temperature detector 17.
It is held constant by controlling 16.

[Problems to be Solved by the Invention]

By the way, conventionally, the above temperature was set to a constant value (about 60 ° C.) over the entire load. Therefore, at startup, when the feed water temperature T _{S1 at the} outlet of the low pressure economizer 8 is low, In order to raise the feed water temperature T _S1 at the inlet of the reactor 8 to the set temperature, it is necessary to recirculate an excessive flow rate above the evaporation amount at the rated load. As a result, a large capacity pump is used for the boiler transfer pump 15. However, there is a drawback in that the power of the auxiliary machinery is increased and the plant efficiency is reduced.

An object of the present invention is to provide a feed water temperature control device for an exhaust heat recovery boiler, which is capable of preventing low temperature corrosion without increasing the amount of recirculation to the low pressure economizer at the time of startup, except for the above-mentioned drawbacks of the prior art. There is.

[Means for Solving the Problems]

In order to achieve the above object, the present invention provides a low-pressure economizer supplied from a condensate pump, and a boiler transfer pump that recirculates the water supply that has passed through the low-pressure economizer to the water supplied from the condensate pump. In the exhaust heat recovery boiler equipped with a regulating valve for adjusting the amount of recirculation by the boiler transfer pump, a temperature detector for detecting the feed water temperature at the inlet of the low pressure economizer,
Temperature setting means for setting a set value of the feed water temperature according to a value related to H ₂ O partial pressure in exhaust gas introduced into the exhaust heat recovery boiler, and a temperature set by the temperature setting means and the temperature detection. And a control means for controlling the regulating valve based on the temperature detected by the vessel.

[Action]

In order to prevent corrosion of the low-pressure economizer due to the low temperature of the water supplied from the condensate pump to the low-pressure economizer, the heated feedwater at the outlet of the low-pressure economizer is supplied to the condensate pump by the boiler transfer pump. Recycle. In this case, the set value of the feed water temperature is determined according to the value related to the H ₂ O partial pressure in the exhaust gas introduced into the exhaust heat recovery boiler. This eliminates the need for extra recirculation and allows the boiler transfer pump to have a smaller capacity.

〔Example〕

 Hereinafter, the present invention will be described based on the illustrated embodiments.

FIG. 1 is a system diagram of a combined cycle power plant according to a first embodiment of the present invention. In the figure, those parts that are the same as those corresponding parts in FIG. 11 are designated by the same reference numerals, and a description thereof will be omitted. 20 is a temperature / flow rate controller, the configuration of which is shown in FIG. 11.
Different from 18 configurations. Reference numeral 21 denotes a gas turbine load signal transmitter, which outputs a signal proportional to the gas turbine load to the temperature / flow rate controller 20.

Now consider low temperature corrosion. Low temperature corrosion is caused by condensation of water (H ₂ O) in exhaust gas. The dew point temperature of the condensation depends on the H ₂ O partial pressure in the exhaust gas. Figure 2 shows the relationship between H ₂ O partial pressure and dew point temperature. In FIG. 2, the horizontal axis shows the H ₂ O partial pressure, and the vertical axis shows the dew point temperature.
As is clear from the figure, when the H ₂ O partial pressure is small, the dew point temperature is low, and when the H ₂ O partial pressure is large, the dew point temperature is high. Therefore, if the H ₂ O partial pressure in the exhaust gas is low, it is not necessary to maintain the feed water temperature T _S1 of the low pressure economizer 8 at a high temperature.

By the way, the relationship between the gas turbine load, the H ₂ O partial pressure in the exhaust gas, and the low-pressure economizer outlet feed water temperature is shown in FIG.
The relationship is as shown in (b). In each figure, the horizontal axis shows the gas turbine load, and the vertical axis shows the low-pressure economizer outlet feed water temperature and H ₂
O partial pressure is available. From the figure, it can be seen that the lower the gas turbine load (including no load), the smaller the H ₂ O partial pressure.

From the above, it can be seen that the dew point temperature is lower at the time of starting the gas turbine and at the time of low load than at the time of rated operation. Therefore, at the time of starting the gas turbine and at the time of low load, the feed water temperature T _S1 of the low pressure economizer 8 is There is no need to raise it.

The temperature / flow rate controller 20 includes a temperature setting circuit composed of a function generator, and sets the feed water temperature of the low pressure economizer 8 in accordance with the signal output from the gas turbine load signal transmitter 21. FIG. 4 (a) shows a first concrete example of the characteristic of the function generator, and FIG. 4 (b) shows a second concrete example. In each figure, the horizontal axis shows the gas turbine load, and the vertical axis shows the set value. In the case of the first specific example, when the signal from the gas turbine load signal transmitter 21 is 25% or less of the gas turbine load, the function generator outputs a signal corresponding to a temperature of 40 ° C., which is the set temperature. Also, the gas turbine load exceeds 25%
When it is less than 50%, the function generator outputs a signal proportional to the gas turbine load.
When it is 50% or more, the function generator outputs a signal corresponding to 60 ° C. The set temperature output from this function generator according to its characteristics is compared with the feed water temperature T _S1 detected by the temperature detector 17, and the flow rate adjusting valve is adjusted so that the set temperature and the feed water temperature T _S1 match. 16 are controlled. In the case of the second specific example, when the gas turbine load is less than 50%, the flow rate adjustment valve
When 16 is set to a certain fixed opening and the opening is not controlled, and when the gas turbine load is 50% or more, a signal corresponding to 60 ° C. is output and this becomes the set temperature.

FIGS. 5 (a), (b), and (c) show an embodiment in which the control means of the present embodiment is used, in which the horizontal axis represents time, the vertical axis represents the recirculation amount, and the set temperature. , Gas turbine speed, and gas turbine load. FIG. 5 (a),
The dashed-dotted line shown in (b) shows the case where the conventional apparatus is used. As is clear from FIG. 5 (a), when the set temperature is kept constant even in the starting process as in the conventional case, the maximum recirculation amount becomes about 380 T / H as shown by the hatched portion, whereas in the present implementation The example can be reduced to about 40 T / H and about 1/10.

As described above, in this embodiment, the temperature of the feed water at the low pressure economizer inlet is set according to the gas turbine load, and the flow rate control valve is controlled based on the set temperature and the detected actual temperature. As a result, it is possible to prevent low temperature corrosion without increasing the amount of recirculation to the low-pressure coal economizer at start-up, and it is not necessary to use a large capacity pump for the boiler transfer pump. It is possible to suppress an increase in force and prevent a decrease in plant efficiency.

6 (a) and 6 (b) are characteristic diagrams of a function generator used in the feed water temperature control device for the exhaust heat recovery boiler according to the second embodiment of the present invention. In the above-described first embodiment, the set temperature of the inlet feed water of the low pressure economizer 8 is set according to the gas turbine load. However, as is clear from FIG. 3 (a), since the gas turbine load and the low-pressure economizer outlet feed water temperature have a predetermined relationship, the setting of the set temperature does not depend on the gas turbine load, and Obviously, it can be set by the outlet water supply temperature. That is, from FIGS. 3A and 3B, when the low-pressure coal economizer outlet feed water temperature is low, it means that the gas turbine load is low.
The H ₂ O partial pressure is low, and conversely, when the low-pressure economizer outlet feed water temperature is high, the H ₂ O partial pressure is also high. From this, in place of the gas turbine load signal transmitter 21 shown in FIG. 1, a temperature detector for detecting the outlet water supply load of the low-pressure coal economizer is provided, and the detection signal of this temperature detector is supplied to the temperature / flow controller. If input to the function generator, the set temperature can be obtained as in the first embodiment. The first of the characteristics of the function generator used in this case
A specific example is shown in FIG. 6 (a), and a second specific example is shown in FIG. 6 (b). In each figure, the horizontal axis shows the outlet water temperature of the low-pressure coal economizer, and the vertical axis shows the set temperature.

In the case of the first concrete example, when the low-pressure economizer outlet feed water temperature is 70 ° C or lower, the set temperature is 40 ° C, and the low-pressure economizer outlet feed water temperature is 70 ° C.
When the temperature is higher than ℃ and less than 125 ℃, the set temperature is proportional to the feed water temperature at the outlet of the low-pressure economizer, and the set temperature is constant at 60 ℃ when the feed water temperature at the low-pressure economizer outlet is 125 ℃ or higher. In the case of the second specific example, when the low-pressure economizer outlet feed water temperature is less than 125 ° C, control is not performed (the flow rate adjusting valve 16 is set to a certain constant opening), and the low-pressure economizer outlet feed water temperature is set. When is over 125 ℃, the set temperature is constant at 60 ℃. By defining the characteristics of the function generator in this way, almost the same results as the experimental results shown in FIGS. 5A to 5C can be obtained in this embodiment as well.

It should be noted that the can water temperature of the low pressure drum 9 may be detected as the outlet water temperature of the low pressure economizer.

As described above, in this embodiment, the set temperature is set according to the low-pressure economizer outlet feed water temperature, and the flow control valve is controlled so that the low-pressure economizer inlet feed water temperature matches the set temperature. Therefore, the same effect as the first embodiment is obtained.

FIG. 7 is a characteristic diagram of a function generator used in a feed water temperature control device for an exhaust heat recovery boiler according to a third embodiment of the present invention. This characteristic diagram shows the characteristic of the gas turbine load at the base load. In the present embodiment, the atmospheric temperature is detected instead of the gas turbine load and the low-pressure coal economizer outlet feed water temperature in each of the preceding embodiments, and this is used as the set temperature setting means. Here, the drive source of the gas turbine 1 is air, so that the amount of exhaust gas of the gas turbine 1 changes depending on the atmospheric temperature. Therefore, the partial pressure of H ₂ O in the exhaust gas also changes depending on the atmospheric temperature. This is shown in FIG. FIG. 8 is a characteristic diagram when the gas turbine load is constant,
Atmospheric temperature is plotted on the horizontal axis, and H ₂ O partial pressure is plotted on the vertical axis.
Based on such characteristics, a function generator having the characteristics shown in FIG. 7 is used. In this case, a temperature detector for detecting the atmospheric temperature is used instead of the gas turbine load signal generator 21 shown in FIG.

As described above, in this embodiment, the set temperature is set according to the atmospheric temperature, and the flow control valve is controlled so that the low-pressure economizer inlet feed water temperature matches the set temperature. The same effect as the embodiment is achieved.

FIG. 9 is a characteristic diagram of a function generator used in the feed water temperature control device for the exhaust heat recovery boiler according to the fourth embodiment of the present invention. This characteristic diagram shows the characteristic of the gas turbine load at the base load. In the present embodiment, the condensate pump outlet feed water temperature is used in place of the gas turbine load, low pressure economizer outlet feed water temperature, and atmospheric temperature in each of the preceding embodiments. In the case of the condenser deaeration system, the outlet water supply temperature of the condenser pump 14 depends on the degree of vacuum of the condenser 13, that is, the seawater temperature (atmosphere temperature) for cooling. This is shown in FIG. FIG. 10 shows the case where the gas turbine load is constant, and the horizontal axis shows the atmospheric temperature and the vertical axis shows the condensate pump outlet feed water temperature.
As shown in FIG. 8, since the atmospheric temperature and the H ₂ O partial pressure have a predetermined relationship, the condensate pump outlet feed water temperature and the H ₂ O partial pressure eventually have a predetermined relationship. Based on such characteristics, the function generator having the characteristics shown in FIG. 9 is used. In this case, instead of the gas turbine load signal generator shown in FIG. 1, a temperature detector for detecting the condensate pump outlet feed water temperature is used.

As described above, in the present embodiment, the set temperature is set according to the condensate pump outlet feed water temperature, and the flow control valve is controlled so that the low pressure economizer inlet feed water temperature matches the set temperature. The same effect as the first embodiment is obtained.

In the description of each of the above embodiments, an example in which the function generator is used for setting the set temperature has been described. However, when the temperature / flow rate controller is configured by a microcomputer, the characteristic of the function generator is ROM (read only).・ It will be stored in memory.

〔The invention's effect〕

As described above, in the present invention, the set temperature is set according to the value related to the H ₂ O partial pressure in the exhaust gas introduced into the exhaust heat recovery boiler, and the low pressure economizer inlet feed water temperature is set to this set temperature. Since the flow rate adjustment valve is controlled so that
At startup, low temperature corrosion can be prevented without increasing the amount of recirculation to the low pressure economizer, which in turn can suppress an increase in auxiliary machine power and prevent a decrease in plant efficiency.

[Brief description of drawings]

FIG. 1 is a system diagram of a complex plant according to a first embodiment of the present invention, FIG. 2 is a characteristic diagram of dew point temperature, FIG. 3 (a),
(B) is a characteristic diagram of the low-temperature coal economizer outlet feed water temperature and H ₂ O partial pressure with respect to the gas turbine load.
The characteristic diagram of the function generator used in the temperature / flow rate controller shown in the figure, and FIGS. 5 (a), (b), and (c) show changes in recirculation amount, set temperature, gas turbine load, and gas turbine speed. 6 (a), (b) and FIG. 7 are graphs showing the function generation used in the feed water temperature control device for the exhaust heat recovery boiler according to the second and third embodiments of the present invention. vessels of characteristic diagrams, FIG. 8 is a characteristic diagram of the H ₂ O partial pressure with respect to ambient temperature, 9
FIG. 10 is a characteristic diagram of a function generator used in a feed water temperature control device for an exhaust heat recovery boiler according to a fourth embodiment of the present invention, FIG. 10 is a characteristic diagram of condensate pump outlet feed water temperature with respect to atmospheric temperature,
FIG. 11 is a system diagram of a conventional combined cycle power plant. 1 ... Turbine, 2 ... Generator, 3 ... Exhaust heat recovery boiler, 8 ... Low pressure economizer, 12 ... Steam turbine, 13 ... Condenser, 14 ... Condensate pump, 15 ... Boiler transfer pump, 16
...... Flow rate adjusting valve, 17 ...... Temperature detector, 20 ...... Temperature / flow rate controller, 21 ...... Gas turbine load signal transmitter.

Claims (6)

[Claims] 1. A low-pressure economizer supplied from a condensate pump,
In a waste heat recovery boiler equipped with a boiler transfer pump that recirculates the feed water that has passed through this low-pressure coal economizer to the feed water from the condensate pump, and an adjustment valve that adjusts the amount of recirculation by this boiler transfer pump, A temperature detector that detects the feed water temperature at the inlet of the low-pressure economizer, and a temperature that determines the set value of the feed water temperature according to the value related to the H ₂ O partial pressure in the exhaust gas introduced into the exhaust heat recovery boiler. Supply water temperature of an exhaust heat recovery boiler, characterized by comprising setting means and control means for controlling the regulating valve based on the temperature set by the temperature setting means and the temperature detected by the temperature detector. Control device. 2. The temperature setting means according to claim 1, wherein the temperature setting means determines the set value of the feed water temperature according to the load of the gas turbine that supplies the exhaust gas to the exhaust heat recovery boiler. Water temperature control device for exhaust heat recovery boiler. 3. The exhaust heat recovery boiler according to claim 1, wherein the temperature setting means determines the set value of the feed water temperature according to the temperature of the feed water at the outlet of the low pressure economizer. Water temperature controller. 4. The exhaust heat recovery boiler according to claim 1, wherein the temperature setting means determines a set value of the feed water temperature in accordance with a drum can water temperature of the exhaust heat recovery boiler. Water temperature control device. 5. The exhaust heat recovery boiler according to claim 1, wherein the temperature setting means determines the set value of the feed water temperature according to the temperature of the feed water at the outlet of the condensate pump. Water temperature control device. 6. The feed water temperature control device for an exhaust heat recovery boiler according to claim 1, wherein the temperature setting means sets the set value of the feed water temperature according to the atmospheric temperature.