JPH06265103A - Discharged gas recombustion type combined cycle power generating plant - Google Patents

Abstract

PURPOSE:To prevent an abnormal increasing of temperature of condensed water at an outlet port of a lower pressure gas heater and further to prevent an overheating of a lower pressure gas heater itself by a method wherein a deaerator water level adjusting valve is installed at a downstream side of a merging point of the condensed water passing through the low pressure feedwater heater and the low pressure gas heater. CONSTITUTION:Condensed water passed through a low pressure feedwater heater 16 and condensed water passed through a lower pressure gas heater 7 are merged from each other, thereafter the merged water is fed into a deaerator 17 through a deaerator water level adjusting valve 29 and the water of which gas is deaerated by the deaerator 17 is fed. Then, a pressure of the feedwater from the deaerator 17 is increased by a feedwater pump 18, enters a feedwater distribution valve 19 and then the water is distributed by a feedwater distributing valve 19 into a high pressure feedwater heater 20 and a high pressure gas heater 6. With such an arrangement as above, the deaerator water level is varied due to a reduction in flow rate of the condensed water caused by a reduction of load, the deaerator water level adjusting valve is varied and even if the valve is fully closed, the condensed water can be recovered to the condensor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas re-combustion combined cycle power plant, and more particularly, when the plant has a low load, deaerator water level control, condensate overheating (steaming) prevention, and boiler exhaust gas at the chimney inlet. The present invention relates to those suitable for temperature control.

[0002]

2. Description of the Related Art FIG. 2 shows a part of a cycle configuration of a conventional exhaust gas re-combustion combined power plant mainly used in Europe. About 13 to 15% of O ₂ remains in the exhaust gas from the gas turbine 1, and the exhaust gas is introduced into the boiler wind box 4 as the steam generator 4 and the steam generating boiler 3 to be used as combustion air. By
Generates steam. Exhaust gas from the steam generating boiler 3 is 3
The temperature is as high as 50 ° C., and heat is recovered through the high pressure gas heater 6 and the low pressure gas heater 7 connected in parallel (or series) with the high pressure feed water heater 20 and the low pressure feed water heater 16 of the steam turbine cycle. By doing 10
After being cooled to about 0 to 150 ° C., it is discharged into the atmosphere from the chimney 9 through the induced draft fan 8.

On the other hand, the condensate from the condenser 10 is boosted by the condensate pump 11, passes through the gland steam condenser 12, the condensate flow rate transmitter 13 and the deaerator water level adjusting valve 14, and the condensate distribution valve 1
5, the distribution valve 15 distributes the mixture to the low-pressure feed water heater 16 side and the low-pressure gas heater 7 side for heating. Then, the heated condensate is joined and then guided to the deaerator 17.

In the deaerator 17, dissolved oxygen and carbon dioxide gas in the condensate are removed in order to prevent the boiler or the like from being corroded, and the removed condensate is boosted by the feed water pump 18 and is used as a feed water distribution valve. It is distributed to the high-pressure feed water heater 20 side and the high-pressure gas heater 6 side by 19. In this case, the feed water heated by the high pressure feed water heater 20 on the one hand and the feed water heated by the high pressure gas heater 6 on the other hand join together and are guided to the steam generating boiler 3 to generate steam.

In the minimum flow operation of the condensate pump 11 and the gland steam condenser 12, the condensate flow rate transmitter 13 is used.
The condensate flow rate is detected by the condensate recirculation valve 21, and the minimum flow of the condensate pump 11 and the gland steam condenser 12 is recovered by the condensate recirculation line 22 to the condenser.

[0006]

In the prior art described above, the exhaust gas from the steam generating boiler 3 is recovered by the high pressure gas heater 6 into the feed water, and the low pressure gas heater 7 is recovered into the condensate. By doing so, it has higher thermal efficiency than a general steam engine plant.

However, in the exhaust gas re-combustion type combined plant of the prior art, when the load of the steam turbine is lowered, the amount of condensed water passing through the low pressure gas heater 7 is reduced, but the low pressure gas Since the amount of decrease in the amount of heat exchange of the heater 7 is small, there is a problem that the low pressure gas heater 7 overheats the condensate.

More specifically, when the steam turbine load decreases, the condensate flow rate decreases on both the low pressure gas heater 7 side and the low pressure feed water heater 16 side, as shown in FIG. Further, the amount of heat exchanged in the low-pressure gas heater 7 also decreases as shown in FIG. However, as shown in FIGS. 3 and 4, the amount of decrease in the amount of heat exchanged by the low-pressure gas heater 7 is smaller than the amount of decrease in the condensate flow rate.
As a result of the amount of heat exchanged not decreasing accordingly, the condensate passing through the low-pressure gas heater 7 is overheated, so that the temperature of the condensate at the inlet of the deaerator 17 and the temperature inside the deaerator 17 are increased. It becomes difficult to secure the difference (ΔT) at the desired value,
There is a problem that the deaeration effect decreases, and there is a problem that steaming occurs at the inlet of the deaerator 17. Furthermore, if the feedwater flow rate and condensate flow rate are extremely reduced due to the decrease in steam turbine load, the gas heater itself will also be overheated, and especially in the condensate system, if the water level of the deaerator becomes high, degassing will occur. There is also a problem that the low-pressure gas heater 7 is abnormally overheated because the condensate flow rate is drastically reduced by temporarily closing the air level control valve.

Further, since the heat recovery amount of the condensed water in the low-pressure gas heater 7 becomes smaller as the supply / condensed water amount decreases, the boiler exhaust gas is discharged from the chimney to the atmosphere at a high temperature, which causes a problem in environmental regulation.

As a countermeasure for this, there is a method of providing a line for recovering a part of the condensate to the condenser 10 at the outlet of the low-pressure gas heater 7. The condensate recovery line 34 shown in FIG. Since it is installed on the downstream side of the valve 14, there is a problem that the required recovery amount does not flow even if the condensate recovery valve 33 is opened.

An object of the present invention is to prevent the condensate from being overheated to a desired value or more when the flow rate of the condensate passing through the low-pressure gas heater 7 decreases, and to prevent the temperature of the boiler exhaust gas at the chimney inlet. (EN) An exhaust gas re-combustion combined cycle power plant capable of reliably preventing the exhaust gas from being discharged into the atmosphere at the maximum operating temperature of the chimney or above the environmental regulation temperature and being suitable for the deaerator water level control.

[0012]

According to the present invention, when the flow rate of condensate passing through the low pressure gas heater 7 decreases, overheating and environmental regulation values exceeding a desired value of the condensate passing through the low pressure gas heater 7 are achieved. As described above, in order to reliably prevent the exhaust gas of the boiler from being emitted from the chimney to the atmosphere, condensate recirculation and deaerator at the outlet of the low-pressure gas heater 7 so that part of the condensate can be smoothly collected in the condenser. A water level adjustment valve is installed.

[0013]

When the flow rate of the condensate flowing through the low pressure gas heater 7 decreases as the steam turbine load decreases, the low pressure gas heater 7
The temperature of the condensate that passes through will be overheated abnormally, and the temperature of the exhaust gas from the boiler cannot be suppressed below the maximum operating temperature of the chimney.

Here, by installing the deaerator water level adjusting valve 29 after the condensate recirculation line 27, a part or all of the outlet condensate of the low-pressure gas heater 7 is recovered to the condenser as described above. (Recirculation circulation) and by controlling the amount of condensate flowing to the low-pressure gas heater 7, it is possible to prevent condensate from overheating. Also, in order to withstand the temperature of the chimney, the boiler exhaust gas temperature is desired to be lowered. It can be reduced to the value. Further, even if the deaerator water level fluctuates and the opening degree of the deaerator water level adjustment valve 29 fluctuates and is fully closed, stable recovery of the condensate to the condenser is possible, and further, to the condenser. Even if the amount of recovered condensate fluctuates, it does not disturb the deaerator water level control.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of an exhaust gas reburn type combined cycle power plant according to the present invention will be described below with reference to FIG.

In the embodiment shown in the figure, the exhaust gas discharged from the gas turbine 1 is guided to a boiler wind box 4 as a steam generator, and inside the steam generating boiler 3 together with the fuel charged into the steam generating boiler 3. Will be burned again. Then, the exhaust gas from the steam generating boiler 3 passes through the boiler exhaust gas duct 5 and is heat-recovered by the high-pressure gas heater 6 by the feed water, and is further recovered by the low-pressure gas heater 7 by the condensate, so that the temperature is about 100 to 150 ° C. After being lowered, it is discharged to the atmosphere from the chimney 9 through the induction draft fan 8.

Condensate from the condenser 10 is boosted by the condensate pump 11, passes through the gland steam condenser 12 and the condensate flow rate transmitter 13, enters the condensate distribution valve 15, and is condensed. 15, the low-pressure feed water heater 16 side and the low-pressure gas heater 7
Distributed to the side. At this time, the condensate distribution valve 15 is provided in the low-pressure feed water heater 1 in order to reduce thermal stress at the confluent confluence.
Condensate is distributed so that the temperature of the condensate that has passed through 6 and the temperature of the condensate that has passed through the low-pressure gas heater 7 are the same. When the turbine load decreases, the condensate flow rate distribution ratio to the low-pressure gas heater 7 side increases, and when the turbine load further decreases, the entire amount of condensate is passed through the low-pressure gas heater 7.

The condensate that has passed through the low-pressure feed water heater 16 and the condensate that has passed through the low-pressure gas heater 7 are combined and then sent to the deaerator 17 via the deaerator water level adjusting valve 29, and the deaerator 17 Water degassed in. Then, the water supply from the deaerator 17 is increased in pressure by the water supply pump 18 and the water supply distribution valve 1
9, the water is distributed to the high-pressure water heater 20 and the high-pressure gas heater 6 by the water supply distribution valve 19. At this time, the feed water distribution valve 19 determines the temperature of the feed water that has passed through the high-pressure feed water heater 20,
The distribution amount is adjusted and distributed so that the temperature of the feed water that has passed through the high-pressure gas heater 6 becomes the same. Further, the feed water that has passed through the high-pressure feed water heater 20 and the feed water that has passed through the high-pressure gas heater 6 are combined and then guided to the steam generation boiler 3.

The deaerator water level adjusting valve 29 for adjusting the water level of the deaerator includes a low pressure feed water heater 16 and a low pressure gas heater 7.
The low-pressure gas heater 7 is installed after the condensate confluence at the outlet.
It has a condensate recirculation line 27 for collecting the condensate that has passed through to the condenser 10. A condensate recirculation valve 28 is provided on the condensate recirculation line 27, and the condensate recirculation valve 28 adjusts the amount of condensate recirculation.

The degree of opening of the condensate recirculation valve 28 is selected by the selector 26. The selector 26 includes the condensate temperature detector 23 of the outlet side condensate system of the low pressure gas heater 7 and the condensate flow rate. Signals from the transmitter 13 and the boiler exhaust gas temperature detector 30 at the outlet of the low-pressure gas heater 7 are connected through the respective arithmetic units.

Next, the operation will be described.

When the plant is started (after the completion of water filling), first, the condensate pump 11 is started, but the deaerator water level adjusting valve 29 is in a closed state, and the condensate flow rate transmitter 13 detects the amount of condensed water and the calculator 25. Then, the condensate recirculation valve 28 is controlled to open so as to secure the required minimum flow of the condensate pump 11 and the gland steam condenser 12. At this time, the temperature difference between the internal temperature of the deaerator 17 and the outlet condensate temperature (ΔT) of the low-pressure gas heater 7 is set to be the required temperature difference for maintaining good deaerating performance of the deaerator 17. Signals from the water temperature detector 23 and the deaerator temperature detector 32 are calculated by the calculator 24 to open the condensate recirculation valve 28, but the deaerator 17 is not in operation, so low pressure gas heating is performed. Since there is no need to control the outlet condensate temperature of the condenser 7, the signal from the condensate flow transmitter 13 is selected by the selector 26 so as to secure the required minimum flow of the condensate pump 11 and the gland steam condenser 12. To do.

At the time of ignition of the gas turbine 1, the internal pressure of the deaerator 17 is set to a predetermined pressure by the auxiliary steam. Here, since the low-pressure gas heater 7 starts heat exchange between the exhaust gas of the gas turbine 1 and the condensate, the outlet condensate temperature of the low-pressure gas heater 7 rises above the condensate allowable temperature as shown in FIG. Since the difference between the temperature inside the deaerator 17 and the condensate temperature at the outlet of the low-pressure gas heater 7 decreases and steaming occurs when the condensate temperature further rises, good deaeration performance of the deaerator 17 is obtained. The effector 24 controls the condensate recirculation adjusting valve 28 so that the required temperature difference for maintaining the condensate recirculation operation is started, and the condensate recirculation operation shown in FIG. 1 is started to lower the condensate temperature. At this time, the larger one of the signals from the calculator 24 and the calculator 25 is selected by the selector 26 to control the condensate recirculation valve 28.

Further, the deaerator water level adjusting valve 2 when the load changes suddenly.
9 Even if the opening degree fluctuates, the deaerator water level adjusting valve 29 is installed after the condensate confluent passing through the low pressure gas heater 7 and the low pressure feed water heater is installed, and the condensate recirculation line 27 is provided in the deaerator. Since it is taken out from the upstream side of the water level adjusting valve 29, no great disturbance is given to the condensate recirculation flow rate control.

Since the displacement of the steam turbine increases as the load increases, the internal pressure / temperature of the deaerator 17 increases and the condensate flow rate increases. Therefore, as shown in FIG. 5, as the temperature of the outlet condensate of the low-pressure gas heater 7 rises, the increase in the temperature inside the deaerator 17 increases, and the amount of condensate recirculation to the condenser decreases. However, as the load increases, the difference between the internal temperature of the deaerator 17 and the outlet condensate temperature of the low-pressure gas heater 7
Since (ΔT) becomes equal to or greater than the required value, the condensate recirculation valve 28 is closed, and the condensate recirculation collected from the outlet of the low pressure gas heater 7 to the condenser is stopped. In addition, as the load increases, the condensate pump 11 and the gland steam condenser 12 are able to secure a flow rate greater than the minimum flow shown in FIG. The condensate recirculation valve 28 is closed by a signal from the condensate flow rate transmitter 13 provided on the outlet side of the device 12.

On the other hand, when the boiler exhaust gas temperature causes problems due to environmental regulations and the temperature resistance of the chimney, the low pressure gas heater 7
It is possible to reduce the boiler exhaust gas temperature by performing condensate recirculation control with the calculator 31 and the selector 26 based on the signal detected by the boiler exhaust gas temperature detector 30 installed on the outlet side of the boiler exhaust gas system. Is.

[0027]

According to the first, second and third aspects of the present invention, the deaerator water level fluctuates due to a decrease in the condensate flow rate due to a decrease in load,
Even if the deaerator water level control valve fluctuates and is fully closed, it is possible to recover the condensate to the condenser, and even if the amount of condensate recovered to the condenser fluctuates, disturbance to the deaerator water level control Because it does not give, it has the effect of increasing reliability.

According to claim 4, the condensate recirculation system according to claims 2 and 3 can prevent the degassing effect from being reduced due to the overheating of the condensate in the low pressure gas heater, and the steaming at the deaerator inlet can be prevented. Also, the minimum flow of the condensate pump and the gland steam condenser can be secured. According to the fifth aspect, in addition to the effect of the fourth aspect, it is possible to surely suppress the boiler exhaust gas temperature within the maximum operating temperature of the chimney, so that there is an effect of improving safety and maintainability.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of an exhaust gas re-combustion combined cycle power plant according to the present invention.

FIG. 2 is a system diagram showing a conventional example.

FIG. 3 is an explanatory diagram showing a relationship between a steam turbine load and a condensate flow rate.

FIG. 4 is an explanatory diagram showing the relationship between steam turbine load and low-pressure gas heater exchange heat quantity.

FIG. 5 is an explanatory view showing a temperature relationship around a steam turbine load and a low-pressure gas feed water heater.

[Explanation of symbols]

1 ... Gas turbine, 2 ... Gas turbine exhaust gas duct, 3
... Boiler wind box, 4 ... Steam generating boiler, 5 ... Boiler exhaust gas duct, 6 ... High pressure gas heater, 7 ... Low pressure gas heater, 8
… Induction draft fan, 9… Chimney, 10… Condenser, 11… Condensate pump, 12… Grand steam condenser, 13… Condensate flow transmitter, 14… Deaerator water level control valve, 15… Condensate Distribution valve,
16 ... Low-pressure feed water heater, 17 ... Deaerator, 18 ... Water feed pump, 19 ... Water feed distribution valve, 20 ... High pressure feed water heater, 21 ...
Condensate recirculation line, 22 ... Condensate recirculation valve, 23 ... Condensate temperature detector, 24, 25, 31 ... Arithmetic unit, 26 ... Selector,
27 ... Condensate recirculation valve line, 28 ... Condensate recirculation valve, 29
… Deaerator water level control valve, 30… Boiler exhaust gas temperature detector,
32 ... Deaerator temperature detector.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Hiroshi Arase 3-2-1, Saiwaicho, Hitachi, Ibaraki Hitachi Engineering Co., Ltd. (72) Inventor, Akihiro Kawauchi 3-chome, Saiwaicho, Hitachi, Ibaraki No. 1 Stock company Hitachi Ltd. Hitachi factory

Claims (5)

[Claims] 1. A gas turbine, a steam generator for injecting fuel into exhaust gas from the gas turbine to reburn the steam, a steam turbine driven by steam from the steam generator, and a condensate and a feed water, respectively. In the exhaust gas re-combustion combined cycle power plant having a gas heater for heating the condensate and the feed water respectively by the exhaust gas from the steam generator, a deaerator water level adjusting valve for adjusting the water level of the deaerator is supplied at a low pressure. An exhaust gas re-combustion combined cycle power plant, which is installed after the condensate water passing through the heater and the low-pressure gas heater is joined. 2. The low pressure gas heater according to claim 1, or
An exhaust gas re-combustion combined cycle power plant in which a condensate recirculation line for recovering a part or all of the condensate to a condenser is installed between the low-pressure feed water heater and the deaerator water level adjusting valve. 3. The exhaust gas re-combustion combined cycle power plant according to claim 2, wherein a flow rate adjusting device is installed on the condensate recirculation line. 4. A condensate recirculation line is used for the purpose of preventing abnormal temperature rise of condensate, ensuring a minimum flow of condensate pump and gland steam condenser, and controlling boiler exhaust gas temperature at the chimney inlet. An exhaust gas re-combustion combined cycle power plant characterized by having a control device. 5. An exhaust gas reburning type combined reactor, characterized in that a temperature detector is installed in the boiler exhaust gas system on the outlet side of the low pressure gas heater to control the boiler exhaust gas temperature in order to lower the boiler exhaust gas temperature at the chimney inlet. Cycle power plant.