JPH0933005A - Water feeding device for waste heat recovery boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of rusting due to a moisture content in exhaust gas by a method wherein delivery of a feed water pump is branched into a system passing through a heat-exchange part and a system not passing therethrough, which are joined together, and is fed to an economizer after regulation of temperature. SOLUTION: Exhaust gas from a gas turbine 4 is guided to a waste heat recovery boiler 6 and discharged through a chimney 12 after the exhaust gas is heat-exchanged with, in order, a superheater 7, a high pressure vaporizer 8, a high pressure economizer 9, a low pressure vaporizer 10, and a low pressure economizer 11. Further, generating high pressure steam is guided from a high pressure drum 13 to the high pressure side of a steam turbine 15 through the superheater 7 and a high pressure evaporation spill valve 14. Meanwhile, low pressure steam low pressure steam is guided from a low pressure drum 16 to a stem turbine 15 through a low pressure evaporation spill valve 17 and condensed by a condenser 18 and changed into condensate. After feed water from the condenser 18 is branched into a system wherein after the feed water is boosted by a low pressure water feed pump 19 and passes a heat-exchange part 16a arranged at the low pressure drum 16 and a system wherein the feed water does not pass the heatexchange part, which are joined together at a low pressure economizer inlet temperature regulating valve 24. A feed water temperature at the inlet of the economizer is stably controlled regardless of a difference in a season between a summer season and a winter season.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust heat recovery boiler water supply system in a combined cycle power generation plant, and more particularly to corrosion due to external dew condensation on a header of a coal economizer feed water of an exhaust heat recovery boiler and exhaust heat at the time of plant startup. The present invention relates to a waste heat recovery boiler water supply device for preventing an unstable operation phenomenon due to evaporation of water supply in a recovery boiler economizer.

[0002]

2. Description of the Related Art Generally, in this type of combined cycle power generation plant, in order to improve the plant efficiency, the exhaust heat recovery boiler is often of a double pressure type, and the exhaust gas flowing near the economizer, which is the most downstream part of the boiler. The temperature tends to be low.

Further, since the steam turbine has a relatively small capacity, a feed water heater is often not installed, and the feed water is slightly supercooled from the saturation temperature determined by the degree of vacuum of the steam turbine condenser, and the feed water is supplied. Therefore, if the feed water is not heated by about 15 to 20 ° C from the temperature in that state, the surface temperature of the header of the economizer inlet and the outer surface of the tube may be below the dew point, and the moisture in the exhaust gas will Condensation is formed on the outer metal surface of the charcoal inlet header and tube, causing rusting, which eventually leads to tube leakage from the outer surface corrosion, which interferes with plant operation.

Therefore, conventionally, the system is branched from the circulation pump discharge line installed in the system for circulating between the drum of the exhaust heat recovery boiler and the evaporator, and this branch pipe is provided with a control valve at the inlet of the economizer. The temperature of the feed water is adjusted so that the temperature of the inlet of the economizer is increased by mixing a part of the high-temperature water held in the drum with the feedwater, and the temperature of the outer metal surface of the economizer is higher than the dew point of the exhaust gas. I am adjusting.

FIG. 6 is a system diagram showing an example of a conventional combined cycle power generation plant. As shown in FIG.
When the starter 1 is started, the air compressed by the compressor 2 burns with the fuel in the combustor 3 to work in the gas turbine 4 to drive the generator 5 to generate electric power. . Exhaust gas from the gas turbine 4 is guided to the exhaust heat recovery boiler 6, and inside the exhaust heat recovery boiler 6, the superheater 7, the high pressure evaporator 8, the high pressure economizer 9, the low pressure evaporator 10 and the low pressure economizer 11 are discharged. After exchanging heat in order, it is discharged from the stack 12.

In the steam generated in the exhaust heat recovery boiler 6, the high-pressure steam is guided from the high-pressure drum 13 to the high-pressure side of the steam turbine 15 through the superheater 7 and the high-pressure steam control valve 14, while the low-pressure steam is discharged from the low-pressure drum 16. Low pressure steam control valve 1
After being guided to the low-pressure side of the steam turbine 15 via 7 and working in the steam turbine 15, they are condensed and liquefied in the condenser 18 to become condensed water, and this condensed water is boosted by the low-pressure water supply pump 19 to supply low-pressure water. The flow rate is adjusted by the flow rate control valve 20, and water is supplied to the inlet of the low pressure economizer 11 of the exhaust heat recovery boiler 6.

Further, the downstream side of the low-pressure water supply pump 19 is branched, a condensate recirculation valve 21 is installed in this branch pipe, and the condensate is recirculated to the condenser 18 through the condensate recirculation valve 21. It is like this. And the low pressure feed water flow rate control valve 2
The opening degree of 0 is adjusted by the control signal of the drum level control device 22.

Here, at the inlet of the low-pressure economizer 11, the low-pressure economizer inlet temperature control valve 2 is branched from the discharge side of the low-pressure circulation pump 23 together with the water supplied from the low-pressure feed pump 19.
The system via 4 is also connected, whereby a part of the high temperature drum-holding water is mixed with the feed water to raise the temperature. The temperature set value of the low-pressure economizer inlet temperature control valve 24 is usually set to about 45 to 47 ° C., which is slightly higher than the dew condensation temperature of the moisture in the exhaust gas. Is prevented, and as a result, the effect of preventing external corrosion is obtained.

That is, at the inlet of the low pressure economizer 11,
The temperature detector 25 is installed, the detection signal of this temperature detector 25 is output to the comparator 26, and the comparator 26 compares the temperature of the inlet portion of the low pressure economizer 11 with the temperature of the set value. The opening degree of the low pressure economizer inlet temperature control valve 24 is adjusted via 27.

The high-pressure economizer 9 includes a low-pressure drum 16
From the high pressure water supply pump 28, high temperature water is supplied through the high pressure water supply control valve 29. Then, the high-pressure evaporator 8 is supplied with high-temperature water from the high-pressure drum 13 by the high-pressure circulation pump 30.

In addition to the problem of low temperature corrosion as described above, generally, when the combined cycle power plant as described above is started up, the amount of steam generated in the exhaust heat recovery boiler 6 is small, so that the operation state in which the feed water flow rate is also small. The flow velocity becomes slow in the economizer, and the evaporation (steaming) phenomenon occurs, which may cause the fluctuation of the water level of the drum and the water hammer phenomenon of the water supply pipe, which may hinder the operation.

However, in the exhaust heat recovery boiler water supply system constructed as shown in FIG. 6, the low-pressure economizer inlet temperature control valve 24 is operated at the cold start time when the temperature of the water held in the drum is started from a state close to the atmospheric temperature. Due to the deviation from the temperature set value, the valve is initially opened, so that the system that circulates between the low-pressure drum 16 and the low-pressure economizer 11 ensures sufficient water supply to the low-pressure economizer 11 even at startup. , Avoiding the unstable operation phenomenon at cold start.

[0013]

In the water supply device for the waste heat recovery boiler economizer as described above, if a sufficient flow rate does not flow in the system for branching the drum holding water and mixing it with the feed water, the mixing is performed. The temperature rise of the supplied feed water cannot be expected, and this flow rate is determined by whether or not the differential pressure of the low pressure economizer inlet temperature control valve 24 is sufficiently secured, that is, the inlet pressure of the low pressure evaporator 10. Should be sufficiently higher than the inlet pressure of the low pressure economizer 11.

Since the outlet of the low pressure evaporator 10 and the outlet of the low pressure economizer 11 are connected to the low pressure drum 16, the inlet pressure of the low pressure evaporator 10 and the inlet pressure of the low pressure economizer 11 are different from each other. Low pressure evaporator determined by loss 1
The difference between the pressure loss at 0 and the pressure loss at the low pressure economizer 11 is 1 kg / cm ² or less at the maximum, and depending on the flow state inside the low pressure evaporator 10 and the low pressure economizer 11, the low pressure economizer inlet The differential pressure of the temperature control valve 24 becomes insufficient, and even if the temperature control valve 24 is fully opened, a sufficient flow rate does not flow, and there is a possibility that the temperature cannot be controlled to the target temperature.

Further, the temperature of water supplied from the low-pressure water supply pump 19 is about 7 to 8 ° C. in the winter season as compared with that in the summer season due to the difference in vacuum degree due to the temperature difference of the cooling water of the condenser 18 in the summer season and the winter season. Since it also decreases and the difference from the target temperature becomes large, in order to control the target temperature in the winter, it is necessary to flow a larger amount of flow in the system that mixes the water held in the drum than in the summer.

Further, as shown in FIG. 6, the steam turbine 1 is installed in the combustor 3 of the gas turbine as a nitrogen oxide reduction measure.
When steam injection is performed from No. 5 through the steam injection flow rate control valve 31, the dew condensation temperature changes by about 5 ° C. at maximum depending on the injected steam amount. In this case, when the amount of injected steam is large, the dew condensation temperature rises, so it is necessary to set the temperature setting value of the low-pressure economizer inlet temperature control valve 24 to a high value so that dew does not condense even at the maximum amount of injected steam. , In the end,
It is necessary to further increase the flow rate of the system that mixes the drum water.

After all, in the exhaust heat recovery boiler 6 constituted by the conventional system, a sufficient margin is expected for the differential pressure of the inlet temperature control valve 24 determined by the pressure loss of the low pressure evaporator 10 and the low pressure economizer 11. Therefore, the inlet temperature of the low pressure economizer 11 cannot be controlled to the target temperature in an operating state where the amount of steam injected to the gas turbine combustor is large in winter, and as a result, the corrosion prevention effect of the low pressure economizer 11 is sufficient. There was a problem that I could not get it.

Further, when the plant has a short stop interval since the last stop and the hot start is started from the state where the drum-holding water retains the residual temperature, the low-pressure feed water flow rate control valve 20 side is operated near the full close at the initial stage. Accordingly, the low-pressure economizer inlet temperature control valve 24 is also operated near the fully closed state, which is different from the cold start. As a result, an evaporation phenomenon occurs in the economizer and the operation becomes unstable. There was a problem.

The present invention has been made in consideration of the above-mentioned circumstances, and it is possible to perform stable feed water temperature control against the influence of the difference in the seasons in the summer and winter and the change in the amount of steam injected to the gas turbine combustor. This is a section to prevent corrosion in the economizer and to ensure operational stability even in an operation area where the feed water flow rate to the exhaust heat recovery boiler is small, such as when starting the plant, regardless of cold / hot start. It is an object of the present invention to provide an exhaust heat recovery boiler water supply device having a charcoal evaporation prevention function.

[0020]

In order to solve the above-mentioned problems, the first aspect of the present invention is to arrange an evaporator, a drum and a economizer in an exhaust heat recovery boiler using the exhaust gas of a gas turbine as a heat source. In the waste heat recovery boiler water supply device for supplying water to the drum via the coal economizer, the discharge system of the water supply pump for supplying water to the economizer, A system that passes through the heat exchange section provided in the drum and a system that does not pass through this heat exchange section are branched, and the feed water is joined to the economizer inlet feed water temperature adjusting means to adjust the temperature, It is characterized by supplying to a container.

According to a second aspect of the present invention, in the waste heat recovery boiler water supply device according to the first aspect, a water supply flow rate adjusting means for adjusting a water supply flow rate to the drum side is installed between the outlet of the economizer and the drum. A recirculation system for returning a part of the water supply from the water supply flow rate adjusting means to the water supply pump inlet is provided, and the ratio between the recirculation flow rate and the water supply flow rate to the drum side is adjusted based on the water supply flow rate request signal. To do.

According to a third aspect of the present invention, in the exhaust heat recovery boiler water supply apparatus according to the first aspect, when the combustor is injecting steam, the injected steam amount is detected by the detector, and the detected signal is detected. It is characterized in that it is added to the temperature control set value of the charcoal inlet temperature adjusting means.

[0023]

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

FIG. 1 is a system diagram showing a first embodiment of an exhaust heat recovery boiler water supply system according to the present invention. Parts that are the same as or correspond to those of the conventional configuration will be described using the same reference numerals as in FIG.

As shown in FIG. 1, when the starter 1 is started, the air compressed by the compressor 2 burns with the fuel in the combustor 3 and works in the gas turbine 4 to drive the generator 5. To generate electricity. Exhaust gas from the gas turbine 4 is guided to the exhaust heat recovery boiler 6, and inside the exhaust heat recovery boiler 6, the superheater 7, the high pressure evaporator 8, the high pressure economizer 9, the low pressure evaporator 10 and the low pressure economizer 11 are discharged. After exchanging heat in order, it is discharged from the stack 12.

In the steam generated in the exhaust heat recovery boiler 6, the high-pressure steam is guided from the high-pressure drum 13 to the high-pressure side of the steam turbine 15 through the superheater 7 and the high-pressure steam control valve 14, while the low-pressure steam is discharged from the low-pressure drum 16. Low pressure steam control valve 1
After being guided to the low-pressure side of the steam turbine 15 via 7 and working in the steam turbine 15, they are condensed and liquefied in the condenser 18 to be condensed water.

The water supplied from the condenser 18 is pressurized by the low-pressure water supply pump 19 and then branched into a system that passes through the heat exchange section 16a provided in the low-pressure drum 16 and a system that does not pass through the low-pressure drum 16. After that, they are joined by a low pressure economizer inlet temperature control valve 24 as a economizer inlet feed water temperature adjusting means having a three-way control valve structure.
Flow distribution between the system passing through the side and the system not passing is performed by controlling the opening degree of the low-pressure economizer inlet temperature control valve 24 as shown in FIG.

That is, at the inlet of the low pressure economizer 11,
A temperature detector 25 is installed, and a detection signal of the temperature detector 25 is output to a comparator 26. The comparator 26 outputs the temperature of the inlet portion of the low pressure economizer 11 and the low pressure economizer inlet temperature control valve 24.
The temperature set value of the low temperature economizer inlet temperature control valve 24 is compared via the controller 27 with the temperature added by the adder 32.
Is adjusted.

The feed water discharged from the low-pressure economizer inlet temperature control valve 24 is supplied to the low-pressure economizer 11, and the low-pressure feed water as a water supply flow rate adjusting means having a three-way control valve structure through the low-pressure economizer 11. The flow rate is adjusted by the flow rate control valve 20 to reach the low pressure drum 16. Here, the low-pressure feed water flow control valve 20 is also connected to a system for recirculation on the inlet side of the low-pressure feed pump 19, and when the feed water flow demand signal for controlling the level of the low-pressure drum 16 is small, this recirculation is performed. By mainly supplying water to the system, a minimum flow of the low-pressure water supply pump 19 is ensured, and at the same time, a necessary flow rate for preventing evaporation of the low-pressure economizer 11 is ensured.

On the other hand, when the feed water flow rate demand signal becomes large, the opening of the low pressure feed water flow rate control valve 20 is adjusted so that the flow rate of the recirculation system is reduced and the flow rate of the low pressure drum 16 is increased. To adjust to normal drum level control. Then, the opening degree of the low pressure feed water flow rate control valve 20 is adjusted by a control signal of the drum level control device 22. FIG. 3 shows an example of a method of controlling the opening degree of the low pressure feed water flow rate control valve 20 described above.

When steam is injected into the combustor 3, the flow rate of the injected steam is detected by the detector 33, and this detection signal is used as the temperature set value of the low pressure economizer inlet temperature control valve 24. By adding through the adder 32 to the above, it is possible to prevent the influence of the change in the condensation temperature due to the change in the amount of injected steam in advance and prevent the condensation in the low pressure economizer 11.

Next, the operation of the first embodiment will be described.

In the first embodiment, when controlling the inlet temperature of the low-pressure economizer 11 of the exhaust heat recovery boiler 6, a system in which the discharge system of the low-pressure feed pump 19 is heat-exchanged with the high-temperature drum-holding water, The temperature is adjusted by branching to a system where heat is not exchanged and adjusting the rate of flow through both by the low pressure economizer inlet temperature adjustment valve 24 and then mixing.

Further, a low pressure feed water flow rate control valve 20 as a feed water flow rate control means for the exhaust heat recovery boiler 6 is provided in the low pressure economizer 11.
It is installed between the outlet and the low-pressure drum 16 and is also connected to a recirculation system that returns to the low-pressure feed pump 19 inlet, and if the water supply request signal to the low-pressure drum 16 side is small, flow mainly to this recirculation system. As a result, the recirculation flow rate for preventing overheating of the low-pressure feed pump 19 and the required minimum flow rate of the economizer for preventing evaporation (steaming) of the low-pressure economizer 11 can be secured at the same time.

Further, when the gas turbine combustor is injecting steam, the amount of injected steam is detected by the detector 33, and the detection signal of this is added to the control set value of the feed water temperature at the economizer inlet. As a result, even if the dew condensation temperature of the exhaust gas changes due to a change in the amount of injected steam, this effect can be canceled out in advance, and the temperature can be controlled to a temperature at which dew condensation does not occur on the outer surface of the economizer inlet header or the tube.

As described above, according to the first embodiment, when adjusting the inlet temperature of the low pressure economizer 11 of the exhaust heat recovery boiler 6, it is necessary to adjust the pressure when mixing the high temperature feed water with the low temperature feed water. The problem goes away. Further, the required flow rate for preventing evaporation in the low-pressure coal economizer 11 is always secured, and at the same time the minimum flow of the water supply pump can be used at the time of plant startup. Further, even when steam is being injected into the combustor 3, this effect can be canceled in advance to prevent dew condensation in the economizer.

FIG. 4 is a system diagram showing a second embodiment of the waste heat recovery boiler water supply system according to the present invention. It should be noted that the same or corresponding parts as those of the first embodiment are designated by the same reference numerals in the following description. The same applies to the following embodiments.

In the second embodiment, the exhaust heat recovery boiler 6 is of a single pressure type, and the superheater 34, the evaporator 35 and the economizer 36 are provided in the exhaust heat recovery boiler 6 on the downstream side of the exhaust gas. And the evaporator 35 and the economizer 36 correspond to the low pressure evaporator 10 and the low pressure economizer 11 in the first embodiment, respectively. Then, the steam generated in the exhaust heat recovery boiler 6 is guided from the drum 37 to the steam turbine 15 via the superheater 34 and the steam control valve 38. Also in this second embodiment, the same effect as in the first embodiment can be obtained. Other configurations and operations are the same as those of the first aspect.
The description is omitted because it is similar to the embodiment.

FIG. 5 is a system diagram showing a third embodiment of the waste heat recovery boiler water supply system according to the present invention. In the third embodiment, a part of the feed water is heat-exchanged with the high-pressure drum 13 in order to adjust the inlet temperature of the low-pressure economizer 11.
That is, the water supplied from the condenser 18 is the low-pressure water supply pump 1
After the pressure is increased by 9, the system is branched into a system that passes through the heat exchange section 13a provided in the high-pressure drum 13 and a system that does not pass through the high-pressure drum 13, and then a low-pressure economizer inlet temperature control valve having a three-way control valve structure. Joined at 24.

The same effect as that of the first embodiment can be obtained in the third embodiment. Other configurations and operations are the same as those in the first embodiment, and therefore their explanations are omitted.

[0041]

As described above, according to the first aspect of the present invention.
According to, according to the discharge system of the water supply pump that supplies water to the economizer,
A system that passes through the heat exchange section provided in the drum and a system that does not pass through this heat exchange section are branched, and the feed water is joined to the economizer inlet feed water temperature adjusting means to adjust the temperature, By supplying the water to the economizer, the inlet water temperature of the economizer can be stably controlled regardless of the difference of seasons in summer and winter, and rusting due to moisture condensation in the exhaust gas in the economizer can be prevented. As a result, the possibility of tube leak in the economizer can be reduced.

According to a second aspect of the present invention, in the exhaust heat recovery boiler water supply apparatus according to the first aspect, a water supply flow rate adjusting means for adjusting the water supply flow rate to the drum side is installed between the outlet of the economizer and the drum. At the same time, by providing a recirculation system for returning a part of the water supply from the water supply flow rate adjusting means to the water supply pump inlet, by adjusting the ratio between the recirculation flow rate and the water supply flow rate to the drum side based on the water supply flow rate request signal. Regardless of whether the plant is cold or hot started, the flow rate required to prevent evaporation in the economizer is secured, and at the same time, the minimum flow is also secured, which causes fluctuations in drum level due to evaporation in the economizer and in the water supply piping. It is possible to avoid the water hammer phenomenon and prevent overheating of the water supply pump.

According to the third aspect, in the exhaust heat recovery boiler water supply apparatus according to the first aspect, when steam is injected into the combustor, the amount of injected steam is detected by the detector, and this detection signal is detected. Is added to the temperature control set value of the economizer inlet temperature adjusting means, the economizer inlet feed water temperature is controlled stably regardless of the difference in the amount of steam injected to the combustor. The same effect as can be obtained.

[Brief description of drawings]

FIG. 1 is a system diagram showing a first embodiment of an exhaust heat recovery boiler water supply apparatus according to the present invention.

FIG. 2 is a diagram showing an example of a method for controlling the opening degree of the low-pressure economizer inlet temperature control valve of FIG.

FIG. 3 is a diagram showing an example of an opening control method of the low-pressure feed water flow rate control valve of FIG. 1.

FIG. 4 is a system diagram showing a second embodiment of an exhaust heat recovery boiler water supply apparatus according to the present invention.

FIG. 5 is a system diagram showing a third embodiment of an exhaust heat recovery boiler water supply system according to the present invention.

FIG. 6 is a system diagram showing an example of a conventional combined cycle power generation plant.

[Explanation of symbols]

1 Starter 2 Compressor 3 Combustor 4 Gas turbine 5 Generator 6 Exhaust heat recovery boiler 7 Superheater 8 High pressure evaporator 9 High pressure economizer 10 Low pressure evaporator 11 Low pressure economizer 12 Chimney 13 High pressure drum 13a Heat exchange section 14 High Pressure Steam Control Valve 15 Steam Turbine 16 Low Pressure Drum 16a Heat Exchange Section 17 Low Pressure Steam Control Valve 18 Condenser 19 Low Pressure Water Supply Pump 20 Low Pressure Water Supply Flow Rate Control Valve (Supply Water Flow Rate Controlling Device) 21 Condensate Recirculation Valve 22 Drum Level Control Device 23 Low pressure circulation pump 24 Low pressure economizer inlet temperature control valve (coefficient economizer inlet feed water temperature adjusting means) 25 Temperature detector 26 Comparator 27 Regulator 28 High pressure water supply pump 29 High pressure water supply control valve 30 High pressure circulation pump 31 Steam injection Flow control valve 32 Adder 33 Detector

Claims (3)

[Claims] 1. An evaporator, a drum, and a economizer are provided in an exhaust heat recovery boiler that uses the exhaust gas of a gas turbine as a heat source.
In the waste heat recovery boiler water supply device that connects the drum to the evaporator and supplies water to the drum through the economizer, the discharge system of the water supply pump that supplies water to the economizer is provided in the drum. The system is divided into a system that passes through the heat exchange section and a system that does not pass through this heat exchange section, and these feed waters are joined to the economizer inlet feed water temperature adjusting means to adjust the temperature and then supplied to the economizer. Exhaust heat recovery boiler water supply device characterized by: 2. The exhaust heat recovery boiler water supply apparatus according to claim 1, wherein a water supply flow rate adjusting means for adjusting a water supply flow rate to the drum side is installed between the economizer outlet and the drum, and the water supply flow rate is provided. Exhaust heat characterized by providing a recirculation system for returning a part of the water supply from the adjusting means to the inlet of the water supply pump, and adjusting the ratio between the recirculation flow rate and the water supply rate to the drum side based on the water supply rate request signal. Recovery boiler water supply device. 3. The exhaust heat recovery boiler water supply system according to claim 1, wherein when steam is injected into the combustor, the amount of injected steam is detected by a detector, and the detection signal is input to the economizer inlet. An exhaust heat recovery boiler water supply device characterized by adding to a temperature control set value of a temperature adjusting means.