JPH11223301A - Operating method of waste heat recovery boiler - Google Patents

Abstract

(57) [Problem] To provide an operation method of an exhaust heat recovery boiler that lowers steam pressure and drum water in a steam drum of an exhaust heat recovery boiler to keep them constant when a gas turbine is stopped. An operation method of an exhaust heat recovery boiler according to the present invention includes connecting a steam drum 9 of an exhaust heat recovery boiler 3 to a condenser 20 of a steam turbine plant 2 when shifting to hot banking when the gas turbine is stopped. The turbine bypass valve 21 provided in the turbine bypass pipe 22 is opened, the drum water remaining in the steam drum 9 is discharged to the condenser 20, and the steam pressure in the steam drum 9 is reduced. is there.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an operation method of an exhaust heat recovery boiler, and more particularly, to a waste heat recovery boiler which maintains a steam pressure and a water level in a steam drum at a constant value and waits for restart when a plant is stopped. Related to the driving method.

[0002]

2. Description of the Related Art In recent thermal power plants, combined cycle power plants have become the mainstream because of their higher plant thermal efficiency and better start-up characteristics than conventional power plants in which a steam turbine plant is combined with a boiler. It is occupying.

[0003] This combined cycle power plant is a combination of a gas turbine plant with a steam turbine plant and an exhaust heat recovery boiler, and uses exhaust gas (exhaust heat) that has completed expansion work from the gas turbine of the gas turbine plant as a heat source. Steam is generated by the recovery boiler, and the steam drives the steam turbine of the steam turbine plant to generate electric power.The exhaust heat from the gas turbine plant gas turbine is used as a heat source to generate steam from the exhaust heat recovery boiler This makes the plant thermal efficiency higher than that of a conventional power plant.

[0004] In recent years, the technical development of gas turbine plants has been remarkably advanced, and air compressors whose discharge pressure has been increased and whose discharge temperature has reached 400 ° C have been realized as actual machines. From the combustion gas temperature at the inlet of the gas turbine at 1100 ° C.
Research and development are being carried out so that the temperature can be raised to 1500 ° C. through 0 ° C.

As described above, as the capacity of the gas turbine plant increases, the capacity of the exhaust heat recovery boiler naturally increases, so that more steam can be generated. It is expected that further improvement of the plant thermal efficiency will be achieved by the results of the above.

[0006]

As the capacity of both the gas turbine plant and the exhaust heat recovery boiler has recently increased, the exhaust heat recovery boiler may have disadvantages and disadvantages.

[0007] Conventionally, the exhaust heat recovery boiler is kept in a so-called hot banking state in which exhaust gas from the gas turbine is confined in the vessel at the end of the operation of the gas turbine plant. Keep the supply water remaining in the vessel and the steam drum in hot banking water of relatively high temperature, and when restarting, circulate from the heat exchanger to the steam drum using the hot banking water to prevent dew point corrosion of the heat exchanger. The associated heat transfer tubes were prevented from being damaged.

However, as the capacity of a gas turbine plant increases, the temperature of exhaust gas is too high, and an abnormal phenomenon may occur in a steam drum of an exhaust heat recovery boiler during hot banking. Was.

FIG. 3 is a time chart showing fluctuations of hot banking water as drum water remaining in the steam drum of the exhaust heat recovery boiler when the operation of the gas turbine plant is stopped.

[0010] When the shutdown operation of the gas turbine plant is started (time A), the output of the combined cycle power plant gradually decreases, and accordingly, the water supply control valve for supplying water to the steam drum is closed. The steam pressure in the steam drum drops, and the water level of the drum water becomes the standard water level NW.
L is maintained.

When the operation of the gas turbine plant is stopped (time B), the exhaust heat recovery boiler traps the exhaust gas from the gas turbine of the gas turbine plant in the vessel and shifts to a hot banking state (stop of the exhaust heat recovery boiler). I do.
At this time, the exhaust heat recovery boiler abnormally increases the steam pressure in the steam drum as shown in the figure due to the high temperature of the exhaust gas enclosed in the vessel, and as a result, hot banking as drum water Water also apparently increases, causing so-called swelling. In addition, the exhaust heat recovery boiler, when the steam pressure of the steam drum exceeds the preset maximum pressure,
The safety valve is opened to release hot banking water to the atmosphere.

When the exhaust heat recovery boiler releases the hot banking state, specifically, opens a damper provided on the downstream side of the vessel and discharges exhaust gas trapped in the vessel to the atmosphere, the steam recovers steam. The steam pressure in the drum is lowered, and the level of the hot banking water is also lowered while repeating the swelling (time C).

However, when the capacity of the recent heat recovery steam generator is increased and the inertia force is increased as compared with the conventional heat recovery steam generator, the steam pressure in the steam drum cannot be rapidly reduced. Drum water as water may be much lower than the design water level. For this reason, the exhaust heat recovery boiler needs to recover the steam drum water that is significantly lower than the design water level when restarting, so the water supply control valve is opened (time D to E), and the steam drum is filled with water. Therefore, there is a problem that it takes a long time to restart the plant, and the load schedule and the time schedule of the rated load are hindered.

SUMMARY OF THE INVENTION The present invention has been made to address such a problem. After the operation of a gas turbine plant is stopped, the steam pressure and drum water in the steam drum are lowered while maintaining a hot banking state. An object of the present invention is to provide a method of operating an exhaust heat recovery boiler that maintains a constant value and hasten the restart time of a plant.

[0015]

In order to achieve the above object, a method for operating an exhaust heat recovery boiler according to the present invention is used when shifting to hot banking when a gas turbine is stopped. Opening a turbine bypass valve provided on a turbine bypass pipe connected to a condenser of a steam turbine plant from a steam drum of a waste heat recovery boiler, and discharging drum water remaining on the steam drum to the condenser. ,
This is a method of reducing the steam pressure in the steam drum.

According to a second aspect of the present invention, there is provided a method for operating an exhaust heat recovery boiler in order to achieve the above object. When the turbine bypass valve provided in the turbine bypass pipe connected from the steam drum to the condenser of the steam turbine plant is closed, and the drum water remaining in the steam drum is discharged to the condenser, In this method, a water supply control valve provided in a water supply system connected to the steam drum from the water dispenser is slightly opened to supply water to the steam drum from the condenser.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a method of operating an exhaust heat recovery boiler according to the present invention will be described. Prior to the description, an embodiment of a combined cycle power plant will be referred to the drawings and reference numerals attached to the drawings. I will explain.

FIG. 2 is a schematic system diagram showing an embodiment of a combined cycle power plant.

The combined cycle power plant according to the present embodiment has a configuration in which a gas turbine plant 1 is combined with a steam turbine plant 2 and an exhaust heat recovery boiler 3.

The gas turbine plant 1 includes an air compressor 4, a gas turbine combustor 5, and a gas turbine 6, and compresses the atmosphere AR sucked by the air compressor 4 to a high pressure.
The high-pressure air is supplied to the gas turbine combustor 5 together with the fuel F, where the combustion gas is generated and guided to the gas turbine 6, the expansion work is performed on the combustion gas to drive the gas turbine 6, and the expansion work is completed. Waste gas G from waste heat recovery boiler 3
To supply.

The exhaust heat recovery boiler 3 is provided with a superheater 8, an evaporator 10 having a steam drum 9 and the like in order along the flow of exhaust gas in a casing 7 formed in a horizontally long cylinder. Then, the water supplied from the steam turbine plant 2 to the steam drum 9 via the water supply system 11 and the water supply control valve 12 using the exhaust gas G from the gas turbine plant 1 as a heat source is allowed to flow through the evaporator 10 to evaporate the water. A two-phase flow is formed, the gas-liquid two-phase flow is separated into a gas and a liquid by a steam drum 9, and the separated saturated steam is superheated again by a superheater 8. To the steam turbine plant 2. The steam drum 9 is provided with a blow pipe 16 provided with a blow control valve 15 to blow impurities such as oxide scale out of the vessel.

On the other hand, the steam turbine plant 2 includes a high-pressure turbine 17, an intermediate-pressure turbine 18, a low-pressure turbine 19, and a condenser 20. The high-pressure turbine 17 expands the steam from a steam control valve 14 to a steam turbine driven steam whose flow rate is controlled. The steam turbine driven steam having completed the expansion work is expanded again by the medium-pressure turbine 18 and the low-pressure turbine 19 is also expanded, and the steam turbine driven steam having completed the expansion work is condensed as turbine exhaust. The condensate is condensed into condensed water, and the condensed water is supplied as water to the steam drum 9 via a water supply system 11 and a water supply control valve 12.

Further, the steam turbine plant 2 branches from the inlet side of the steam control valve 14, and is provided with a turbine bypass pipe 22 provided with a turbine bypass valve 21 on the way and connected to the condenser 20. During startup operation,
When the temperature of the exhaust gas G supplied from the gas turbine 6 to the exhaust heat recovery boiler 3 is low, the drum water of the steam drum 9 is returned to the condenser 20 via the steam pipe 13 and the turbine bypass pipe 22.

Next, an operation method of the exhaust heat recovery boiler according to the present invention will be described.

FIG. 1 is a time chart showing fluctuations of hot banking water as drum water left on the steam drum of the exhaust heat recovery boiler when the operation of the gas turbine plant is stopped.

When the shutdown operation of the gas turbine plant 1 is started (time F), the output of the combined cycle power plant gradually decreases, and accordingly, the water supply control valve 12 that supplies water to the steam drum 9. Is closed, the steam pressure in the steam drum 9 drops, and the level of the drum water is maintained at the standard level NWL.

When the operation of the gas turbine plant 1 is stopped (time G), the exhaust heat recovery boiler 3 traps the exhaust gas from the gas turbine 6 of the gas turbine plant 1 in a vessel, and enters a hot banking state (stop of the exhaust heat recovery boiler). ). However, at this time, the exhaust heat recovery boiler 3 abnormally increases the steam pressure in the steam drum 9 because the temperature of the trapped exhaust gas is high.

In the operation method of the exhaust heat recovery boiler according to the present embodiment, the abnormal increase in the steam pressure in the steam drum 9 is suppressed. By opening the bypass valve 21, hot banking water as drum water in the steam drum 9 is discharged to the condenser 20 of the steam turbine plant 2, and so-called de-lumping is performed to lower the steam pressure. During the de-ramping, the steam drum 9 causes the hot banking water as the drum water to swale,
The water supply control valve 12 is slightly opened, and the water supply system 11
, And the steam pressure is gradually reduced while keeping the swelling low.

When the steam drum 9 gradually lowers the steam pressure and the steam pressure becomes a constant value (time H), the exhaust heat recovery boiler 3 releases the hot banking. Note that the steam pressure is set high with a margin for the design pressure.

After releasing the hot banking, the exhaust heat recovery boiler 3 opens the water supply control valve 12 (time I), and the condenser 2
Water supply is performed from 0 to the steam drum 9 via the water supply system 11, that is, water filling is performed. After the water level of the steam drum 9 reaches a predetermined value, the water supply control valve 12 is closed (time J).
The water supply to the steam drum 9 is stopped, and the restart operation of the plant is waited.

As described above, in the operation method of the exhaust heat recovery boiler according to the present embodiment, when the gas turbine is stopped, the turbine bypass valve 21 is opened, and the hot banking water as the drum water in the steam drum 9 is condensed. The steam is discharged to the vessel 20 and the steam pressure is reduced. At this time, the water supply control valve 12 is slightly opened to supply the water to the steam drum 9, the swelling of the drum water is suppressed low, and the steam pressure is kept at a constant value. After that, the water supply control valve 12 is opened again,
Since water is supplied to and supplied with water to the steam drum 9, the restart operation of the plant can be performed earlier than before.

[0032]

As described above, the method of operating the exhaust heat recovery boiler according to the present invention allows the steam drum water in the steam drum to be discharged to the condenser when shifting to hot banking when the gas turbine is stopped. , The steam pressure is maintained at a constant value,
Since the stabilization of the drum water is made earlier than before, the plant can be restarted more quickly.

[Brief description of the drawings]

FIG. 1 is a time chart illustrating a variation of hot banging water as steam drum water left on a steam drum, for explaining an operation method of an exhaust heat recovery boiler according to the present invention.

FIG. 2 is a schematic system diagram of a combined cycle power plant applied to an operation method of an exhaust heat recovery boiler according to the present invention.

FIG. 3 illustrates an operation method of a conventional waste heat recovery boiler.
FIG. 5 is a time chart showing a variation of hot banging water as steam drum water left in the steam drum.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas turbine plant 2 Steam turbine plant 3 Exhaust heat recovery boiler 4 Air compressor 5 Gas turbine combustor 6 Gas turbine 7 Casing 8 Superheater 9 Steam drum 10 Evaporator 11 Water supply system 12 Water supply control valve 13 Steam pipe 14 Steam control valve 15 Blow control valve 16 Blow pipe 17 High pressure turbine 18 Medium pressure turbine 19 Low pressure turbine 20 Condenser 21 Turbine bypass valve 22 Turbine bypass pipe

Claims (2)

[Claims] When shifting to hot banking when a gas turbine is stopped, a turbine bypass valve provided in a turbine bypass pipe connected from a steam drum of an exhaust heat recovery boiler to a condenser of a steam turbine plant is opened. A method for operating an exhaust heat recovery boiler, comprising: discharging drum water remaining in a steam drum to the condenser to lower the steam pressure in the steam drum. 2. When the gas turbine is stopped, when shifting to hot banking, a turbine bypass valve provided in a turbine bypass pipe connected from a steam drum of an exhaust heat recovery boiler to a condenser of a steam turbine plant is closed. When discharging the drum water remaining in the steam drum to the condenser, the water supply control valve provided in the water supply system connected to the steam drum from the condenser is slightly opened, and the condenser is discharged from the condenser. An operation method of an exhaust heat recovery boiler, which supplies water to a steam drum.