JP2000297611A - Exhaust heat recovery system and operation method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce thermal stress generated in a merge portion by allowing, via a second adjusting valve, a part of the steam in the middle step of a high- temperature heater on the upstream side of exhaust gas to merge into a steam pipe, which allows part of the steam at the outlet of a heater on the downstream side of the exhaust gas to merge into the high-temperature heater outlet on the upstream side of the exhaust gas. SOLUTION: A part of the steam extracted from the middle step of a high- pressure secondary heater 10 is merged into a high-pressure secondary heater bypass pipe 27 via a high-pressure secondary heater middle step communication pipe 30 and high-pressure secondary heater middle step flow rate adjusting vale 31, so as to adjust the steam temperature inside the high-pressure secondary heater bypass pipe 27. In this way, by merging steam into the high-pressure secondary heater bypass pipe 27 by means of the high-pressure secondary heater middle step communication pipe 30 so as to adjust the steam temperature inside the bypass pipe 27, the steam temperature difference is decreased. Therefore, thermal stress and thermal shock in the merge portion pipe can be relaxed.

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 apparatus for recovering heat of exhaust gas of a combined cycle power plant using a combination of a gas turbine and a steam turbine and a method of operating the same. The present invention relates to an exhaust heat recovery device that can be supplied as steam for driving a turbine and steam for cooling a gas turbine, and an operation method thereof.

[0002]

2. Description of the Related Art In a combined cycle power plant combining a gas turbine and a steam turbine, the inlet temperature of the gas turbine can be improved by improving the material of the high temperature portion of the gas turbine and the cooling technology. It is becoming. As part of increasing the efficiency of combined cycle power generation, the use of steam as a cooling medium for high-temperature parts of gas turbines, especially blades, has been studied. -019528
No. etc. The gas temperature at the inlet of the gas turbine is still reaching 1300 ° C, and is expected to exceed 1500 ° C in the future.

At such a high temperature, the cooling effect of the conventional blade cooling using air is insufficient. Therefore, a gas turbine using blade cooling using steam has been developed, and a gas turbine using the same has been developed. A steam turbine combined cycle power plant is being planned. The above document describes a combined cycle power generation facility using such a steam-cooled gas turbine.

[0004] When steam is used as a cooling medium for a gas turbine, what is problematic is the steam temperature and steam properties for cooling. Since the gas flows through the blades of a high-temperature gas turbine and flows through extremely fine channels, it is possible to prevent the impurities in the minute steam from adhering to the fine channels on the inner surface of the blade at high temperatures. Once the impurities are attached, it may cause blade cooling failure due to the complicated channel shape, which may lead to blade damage. For this reason, steam for cooling the blades of the gas turbine requires a high degree of cleanliness.Steam temperature control, which was conventionally performed by spraying feedwater into steam, cannot be used. A method of controlling the steam temperature by bypassing the superheater has been adopted. Hereinafter, an outline of a conventional gas turbine steam turbine combined cycle power generation facility will be described with reference to FIG.

[0005] In FIG. 4, air taken into the compressor 1 from the atmosphere is compressed by the compressor 1, then burns together with fuel in a combustor, flows into a gas turbine 2 as high-temperature gas. The gas leaving the gas turbine becomes a gas having a temperature of about 600 ° C. and flows into the exhaust heat recovery boiler 8. The gas that has been absorbed by the heat recovery steam generator 8 and has dropped in temperature becomes about 100 ° C. and flows out of the heat recovery steam generator 8 into the atmosphere.

On the other hand, water is supplied from the condenser 7 to the low-pressure feed pump 41.
Thus, water is supplied to the exhaust heat recovery boiler 8. First, water is supplied to the low-pressure economizer 21. After the temperature rises, part of the water is supplied to the low-pressure drum 24, and after evaporation, the low-pressure saturated steam pipe
After passing through the low-pressure superheater 17 from 45, the low-pressure superheater outlet connecting pipe
It is supplied to the low-pressure steam turbine 6 by 46.

The other water is supplied to the medium pressure drum 23 and the high pressure drum 22 after the pressure is increased by the medium pressure water supply pump 43 and the high pressure water supply pump 44, respectively. The feedwater supplied to the medium-pressure drum 23 becomes steam in the medium-pressure evaporator 18, passes through the medium-pressure superheater 15 through the medium-pressure saturated steam pipe 36, and then is reheated in the low-temperature reheat steam pipe 34. After being mixed with the steam, it is supplied as gas turbine blade cooling steam from a gas turbine cooling steam pipe 38 to a gas turbine steam cooling line 39, and after cooling the gas turbine blades and the like, is reheated by a reheater 12. It becomes high-temperature steam and joins the high-temperature reheat steam pipe 40 and flows into the medium-pressure steam turbine 5.

Further, the water supplied to the high-pressure steam drum 22 is evaporated in the high-pressure evaporators 13 and 14, and then the high-pressure saturated steam
It flows into the high pressure primary superheater 11 from 25. After being superheated by the high-pressure primary superheater, the steam flows into the high-pressure secondary superheater 10. Some of the steam joins the high-pressure secondary superheater outlet connecting pipe 29 through the high-pressure secondary superheater bypass pipe 27 that bypasses the high-pressure secondary superheater 10 and the high-pressure secondary superheater bypass flow control valve 28, After lowering the steam temperature at the outlet of the high-pressure secondary superheater 10,
The steam flows into the high-pressure tertiary superheater 9 from the high-pressure tertiary superheater inlet connection pipe 32 and is supplied to the high-pressure steam turbine 4 as 540 ° C. steam as steam turbine inlet steam. The steam expanded by the high-pressure steam turbine 4 flows into the low-temperature reheat pipe 34.

A part of the low-temperature reheated steam is supplied to the gas turbine cooling steam pipe 38 together with the medium-pressure steam as steam for cooling the gas turbine.
From the gas turbine steam cooling pipe 39. Further, a part of the steam is raised in temperature by the reheater 12, becomes high-temperature reheat steam, and flows into the medium-pressure steam turbine 5 from the high-temperature reheat steam pipe 40. Eventually, the steam expanded and worked by the steam turbine is condensed by the condenser 7 and supplied to the cycle again.

[0010]

In the gas turbine / steam turbine combined cycle power plant having the above-described structure, the high-pressure secondary superheater bypass pipe 27 and the high-pressure secondary superheater outlet connecting pipe 29 have a steam converging section. Since the steam temperature difference between the two is about 180 ° C to 190 ° C at the maximum, there is a problem that very large thermal stress and thermal shock occur at the junction of the pipes.

The steam flow rate passing through the high-pressure secondary superheater bypass pipe 27 is such that bypass steam is not required at the design planning point (rated load), but is required at partial load. Since the operating condition changes depending on the operating condition, when the operating condition changes and the steam flow rate in the bypass pipe changes rapidly, there is a problem that a large thermal stress and thermal shock are generated at the pipe junction in a short time.

As shown in FIG. 5, the characteristic of the gas turbine is that the gas temperature becomes high at a partial load,
In addition, since the heat transfer surface becomes excessive due to the decrease in the steam flow rate and the superheater outlet steam temperature becomes high, the steam cooling by the bypass of the secondary economizer is controlled to control the high pressure tertiary superheater outlet steam temperature. This is because the steam temperature at the outlet of the high-pressure secondary superheater further increases as the amount increases.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and includes a bypass pipe of a high-pressure superheater and an outlet of a high-pressure superheater installed on the exhaust gas upstream side of the high-pressure superheater. An object of the present invention is to provide an exhaust heat recovery device that reduces thermal stress generated at a junction thereof due to a difference in steam temperature of a communication pipe, and an operation method thereof.

[0014]

According to a first aspect of the present invention, an evaporator and a superheater are provided in an exhaust heat recovery boiler for recovering heat of exhaust gas from a combined cycle power plant having a gas turbine and a steam turbine. The outlet steam of the superheater disposed on the exhaust gas upstream side of the evaporator, in the middle of the evaporator or on the exhaust gas downstream side of the evaporator, with the high-temperature superheater outlet steam disposed on the exhaust gas upstream side and the first steam. In the exhaust heat recovery device that adjusts the superheater outlet steam temperature by mixing through the control valve, to a steam pipe that joins a part of the exhaust gas downstream side superheater outlet steam to the exhaust gas upstream side high temperature superheater outlet, A part of the steam in the middle stage of the exhaust gas upstream-side high-temperature superheater is combined via the second control valve.
A second aspect of the present invention is characterized in that at least one of the first control valve and the second control valve is operated at a predetermined opening degree or more.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. In the figure, the same parts as those in FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 1, a high-pressure primary superheater 11 is disposed between a high-pressure evaporator (# 1) 13 and a high-pressure evaporator (# 2) 14. High pressure primary superheater
The steam leaving 11 is connected to the high pressure primary superheater outlet connecting pipe 26 and the high pressure 2 superheater.
The system which goes to the high pressure secondary superheater outlet communication pipe 29 via the secondary superheater 10 and the high pressure secondary superheater outlet communication via the high pressure secondary superheater bypass pipe 27 and the high pressure secondary superheater bypass flow rate control valve 28 After branching into a system leading to the pipe 29, they join at a high pressure secondary superheater outlet connecting pipe 29 so that the steam temperature at the inlet of the high pressure tertiary superheater 9 can be adjusted. Further, a part of the steam extracted from the middle stage of the high-pressure secondary superheater 10 is supplied to the high-pressure secondary superheater bypass pipe 27, and the high-pressure secondary superheater middle-stage communication pipe 30 and the high-pressure secondary superheater middle-stage flow control valve 31. To adjust the steam temperature in the bypass pipe of the high-pressure secondary superheater.

As shown in FIG. 2, the steam is joined to the high-pressure secondary superheater bypass pipe 27 by the high-pressure secondary superheater middle connecting pipe 30, and the steam temperature in the bypass pipe is adjusted.
In conventional systems, the maximum temperature is about 180 ° C to 190 ° C at the steam junction.
The steam temperature difference, which was ℃, can be reduced,
Thermal stress and thermal shock generated in the junction pipe can be reduced.

As shown in FIG. 3, the high-pressure secondary superheater bypass flow control valve 28 is always operated at a certain opening degree or more, so that a rapid temperature change at the pipe junction when the valve is closed to open. , And as shown in "Function 1 according to the present invention" in the figure, thermal stress and thermal shock can be reduced as compared with the conventional one.

Also, by constantly operating the high-pressure secondary superheater middle stage flow control valve 31 at a fixed opening or more, a sudden temperature change at the pipe junction when the control valve is closed to open can be suppressed. As shown in “Function 2 according to the present invention”, thermal stress and thermal shock can be further reduced.

[0019]

According to the exhaust heat recovery apparatus and the operation method of the present invention, it is possible to reduce the temperature difference between the combined steams at the outlet of the high-pressure superheater and to reduce the thermal stress generated at the pipe junction. Can be. Therefore, there is an effect that it is not necessary to upgrade the piping material, thermal stress is relaxed, and the life is extended. In addition, with respect to the shape of the junction, the reduction of the thermal stress broadens the selection range, and it can be expected that there is no need to adopt a special shape of the junction for reducing the thermal stress.

[Brief description of the drawings]

FIG. 1 is a diagram of a combined cycle power plant including an exhaust heat recovery device according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating the operation of the exhaust heat recovery device and the operation method thereof according to the embodiment of the present invention.

FIG. 3 is a diagram illustrating the operation of the exhaust heat recovery device and the operation method thereof according to the embodiment of the present invention.

FIG. 4 is a diagram of a combined cycle power plant equipped with a conventional exhaust heat recovery device.

FIG. 5 is an explanatory diagram showing outlet temperatures of primary and secondary superheaters and a bypass flow rate ratio.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Compressor, 2 ... Gas turbine, 3 ... Generator, 4 ... High pressure steam turbine, 5 ... Medium pressure steam turbine, 6 ... Low pressure steam turbine, 7 ... Condenser, 8 ... Exhaust heat recovery boiler, 9 ... High pressure 3
Secondary superheater, 10 high-pressure secondary superheater, 11 high-pressure primary superheater,
12 ... reheater, 13 ... high pressure evaporator (# 1), 14 ... high pressure evaporator (# 2), 15 ... medium pressure superheater, 16 high pressure economizer, 17 ... low pressure superheater, 18 ... medium pressure evaporation Vessel, 19: medium pressure economizer, 20: low pressure evaporator, 21: low pressure economizer, 22: high pressure drum, 23: medium pressure drum, 24: low pressure drum, 25: high pressure saturated steam pipe, 26: high pressure 1
Secondary superheater outlet connection pipe, 27 ... High pressure secondary superheater bypass pipe,
28 high-pressure secondary superheater bypass flow control valve, 29 high-pressure secondary superheater outlet connection pipe, 30 high-pressure secondary superheater middle connection pipe, 31
... High pressure secondary superheater middle stage flow control valve, 32 ... High pressure tertiary superheater inlet connection pipe, 33 ... High pressure main steam pipe, 34 ... Low temperature reheat steam pipe,
35… Reheater inlet connection pipe, 36… Medium pressure saturated steam pipe, 37… Medium pressure superheater outlet connection pipe, 38… Gas turbine cooling steam pipe, 39…
Gas turbine steam cooling line, 40… High temperature reheat steam line, 41…
Low pressure water supply pump, 42… Low pressure water supply pipe, 43… Medium pressure water supply pump, 44… High pressure water supply pump, 45… Low pressure saturated steam pipe, 46… Low pressure superheater outlet connection pipe.

Claims (2)

[Claims] 1. An exhaust heat recovery boiler for recovering heat of exhaust gas of a combined cycle power plant equipped with a gas turbine and a steam turbine has an evaporator and a superheater. Alternatively, the superheater is formed by mixing a part of the outlet steam of the superheater disposed on the exhaust gas downstream side of the evaporator with the high-temperature superheater outlet vapor disposed on the exhaust gas upstream side via the first control valve. In the exhaust heat recovery device that adjusts the outlet steam temperature, part of the steam in the middle stage of the exhaust gas upstream high-temperature superheater to the steam pipe that joins part of the exhaust gas downstream superheater outlet steam to the exhaust gas upstream high-temperature superheater outlet Are combined via a second control valve. 2. The operation of the exhaust heat recovery apparatus according to claim 1, wherein at least one of the first control valve and the second control valve is operated at a predetermined opening degree or more. Method.