A rapid cooling process for a gas-steam combined cycle power generation unit

Abstract

The present invention discloses a rapid cooling process for a gas-steam combined cycle power generation unit, which relates to the technical field of gas-steam combined cycle power generation. In the rapid cooling process for a gas-steam combined cycle power generation unit of the present invention, while the high-pressure rotor is cooled by steam in the gas turbine, the steam parameters of the steam turbine are reduced by adopting the sliding parameter shutdown mode of the steam turbine to rapidly cool the steam turbine. During the temperature reduction process, the temperature reduction rate of each metal component of the steam turbine is uniform and controllable, thereby shortening the shutdown cooling time, reducing the maintenance period, and improving the operation utilization rate of the unit; during the cooling and starting process of the gas turbine at 600 rpm, the desuperheater and desuperheating and pressure-reducing device in the starting steam system are started to successively reduce the starting steam parameters to the superheated steam temperature at the pressures of 1.4 MPa and 1.0 MPa, so that there is no need to additionally increase a dedicated rapid cooling device, and the influence of the reliability of the rapid cooling device on the safety of the steam turbine is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of gas-steam combined cycle power generation, and more specifically to a rapid cooling process for a gas-steam combined cycle power generation unit. Background Art

[0002] For the M701S(DA) type gas-steam combined cycle power generation unit, the cooling waiting time after shutdown is long. Although the Mitsubishi high-pressure rotor cooling strategy is adopted for gas turbine cooling after shutdown, the Mitsubishi cooling strategy is only effective for the gas turbine and ineffective for the steam turbine cooling. Due to the asynchronous temperature drop between the gas turbine and the steam turbine, the cooling time of the steam turbine is still very long, seriously affecting the maintenance period of the unit.

[0003] In the existing design, as Figure 1 shown, the shutdown cooling process flow is as follows: First, the gas turbine reduces the load to 4.6 MW. When the metal temperature of the balance ring < 430 °C, the generator is disconnected and the gas turbine stops. After the gas turbine stops for 2 hours, the steam turbine (turbine) is restarted by starting steam to perform high-pressure rotor cooling on the gas turbine, and then the gas turbine and the steam turbine are cooled naturally after shutdown. Summary of the Invention

[0004] 1. Technical Problems to be Solved by the Invention

[0005] Aiming at the problems of asynchronous temperature drop between the gas turbine and the steam turbine of the existing steam combined cycle power generation unit, resulting in long cooling shutdown waiting time, etc., the present invention proposes a rapid cooling process for a gas-steam combined cycle power generation unit. While performing high-pressure rotor cooling on the gas turbine with steam, the steam parameters are reduced by adopting the sliding parameter shutdown mode of the steam turbine to rapidly cool the steam turbine, so as to shorten the shutdown cooling time, reduce the maintenance period, and improve the operation utilization rate of the unit.

[0006] 2. Technical Solutions

[0007] To achieve the above object, the technical solution provided by the present invention is:

[0008] A rapid cooling process for a gas-steam combined cycle power generation unit. While performing high-pressure rotor cooling on the gas turbine with steam, the sliding parameter shutdown mode of the steam turbine is adopted to reduce its steam parameters, so as to rapidly cool the steam turbine. During the temperature reduction process, the temperature drop rate of each metal component of the steam turbine is uniform and controllable, thereby shortening the shutdown cooling time, reducing the maintenance period, and improving the operation utilization rate of the unit.

[0009] A further technical solution is that the steam turbine cooling specifically includes the following steps:

[0010] Step 1. Preliminary cooling: The unit is preliminarily cooled by reducing the load with sliding parameters. The unit reduces the load with sliding parameters to the minimum load of 4.6 MW. The waste heat boiler reduces the pressure and temperature accordingly. When the metal temperature of the steam turbine gland packing ring drops to 430°C - 440°C and remains basically unchanged, the unit stops. Immediately after the rotor coasts to a stop, continuous low-speed turning gear is put into operation for natural cooling for 2 hours.

[0011] Step 2. Re-cooling: After 2 hours of natural cooling with low-speed turning gear, the metal temperature of the steam turbine gland packing ring is 410°C - 420°C. Immediately, the gas turbine body is cooled by using the gas turbine cooling and turning program, and the unit stops when it is cooled to the superheated steam temperature at a pressure of 1.0 MPa.

[0012] Step 3. Deep cooling: Instrument air is introduced through the main steam drain bypass to deeply cool the steam turbine until the metal temperature of the steam turbine gland packing ring (the metal temperature of the inner wall of the high-pressure inner cylinder of the steam turbine) drops to 180°C.

[0013] For a further technical solution, in Step 2, during the cooling and turning process of the gas turbine at 600 rpm, the desuperheater and desuperheating and pressure-reducing device in the start-up steam system are used to successively reduce the turning steam parameters to the superheated steam temperature at pressures of 1.4 MPa and 1.0 MPa, so that there is no need to additionally increase a dedicated fast cooling device, avoiding the impact of the reliability of the fast cooling device on the safety of the steam turbine, reducing equipment reinvestment, saving energy, realizing the fast and safe cooling of the gas-steam combined cycle generating unit, improving the annual utilization rate of the unit, and having good economic benefits.

[0014] For a further technical solution, first start the desuperheater to reduce the turning steam temperature to the superheated steam temperature at a pressure of 1.4 MPa at a temperature reduction rate of 0.5 - 1°C / min, and its superheated steam temperature is 245°C; then start the desuperheating and pressure-reducing device to reduce the turning steam parameters to the superheated steam temperature at a pressure of 1.0 MPa at a pressure reduction rate of 0.05 - 0.1 MPa / min and a temperature reduction rate of 0.2 - 0.5°C / min, and its superheated steam temperature is 230°C, so as to make full use of the principle of the steam turbine shutting down with sliding parameters, obtain the superheated steam at a required lower temperature by reducing the pressure, make the temperature reduction rate of each metal component of the steam turbine uniform and controllable during the temperature reduction process, not increase the life loss of the steam turbine, accelerate the cooling speed of the unit, greatly reduce the waiting time for unit maintenance, and shorten the maintenance period.

[0015] For a further technical solution, in Step 3, the cooling speed is 3°C - 4°C / h.

[0016] 3. Beneficial effects

[0017] Adopting the technical solution provided by the present invention, compared with the prior art, it has the following beneficial effects:

[0018] (1) A rapid cooling process for a gas - steam combined cycle power generation unit of the present invention, while cooling the high - pressure turbine of the gas turbine with cooling steam, adopts the sliding - parameter shutdown mode of the steam turbine to reduce its steam parameters, so as to rapidly cool the steam turbine, thereby shortening the shutdown cooling time, reducing the maintenance period, and improving the operation utilization rate of the unit; making the temperature - drop rate of each metal component of the steam turbine uniform and controllable during the temperature - reduction process, without increasing the life loss of the steam turbine, accelerating the cooling speed of the unit, greatly reducing the waiting time for unit maintenance, and shortening the maintenance period.

[0019] (2) A rapid cooling process for a gas - steam combined cycle power generation unit of the present invention first starts the desuperheater in the steam system to reduce the impulse steam temperature to the superheated steam temperature at a pressure of 1.4 MPa; then starts the desuperheating and pressure - reducing valve in the steam system to reduce the impulse steam parameters to the superheated steam temperature at a pressure of 1.0 MPa, thereby obtaining superheated steam at a lower required temperature by reducing the pressure.

[0020] (3) A rapid cooling process for a gas - steam combined cycle power generation unit of the present invention does not require additional dedicated rapid - cooling devices, avoids the impact of the reliability of the rapid - cooling device on the safety of the steam turbine, reduces equipment reinvestment, saves energy, realizes the rapid and safe cooling of the gas - steam combined cycle power generation unit, improves the annual utilization rate of the unit, and has good economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a process flow chart of the existing high - pressure turbine cooling process of the gas turbine;

[0022] Figure 2 is a process flow chart of the rapid cooling process for the gas - steam combined cycle power generation unit of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] To further understand the content of the present invention, the invention will be described in detail with reference to the accompanying drawings.

[0024] Embodiment 1

[0025] A rapid cooling process for a gas - steam combined cycle power generation unit of this embodiment, as Figure 2 shown, while cooling the gas turbine with high - pressure turbine cooling steam, adopts the sliding - parameter shutdown mode of the steam turbine to reduce its steam parameters, so as to rapidly cool the steam turbine. During the temperature - reduction process, the temperature - drop rate of each metal component of the steam turbine is uniform and controllable, thereby shortening the shutdown cooling time, reducing the maintenance period, and improving the operation utilization rate of the unit.

[0026] The cooling of the steam turbine specifically includes the following steps:

[0027] Step 1. Preliminary cooling: Adopt sliding parameter load reduction for preliminary cooling. The unit reduces load with sliding parameters to the minimum load of 4.6 MW. The waste heat boiler reduces pressure and temperature accordingly. When the metal temperature of the steam turbine gland packing ring drops to 430°C - 440°C and remains basically unchanged, the unit shuts down. Immediately after the rotor coasts to a stop, continuous low-speed turning gear is engaged for natural cooling for 2 hours.

[0028] Step 2. Re-cooling: After 2 hours of natural cooling with low-speed turning gear, the metal temperature of the steam turbine gland packing ring is 410°C - 420°C. Immediately adopt the gas turbine cooling and turning program to cool the gas turbine body. Stop when it cools to the superheated steam temperature at a pressure of 1.0 MPa.

[0029] Step 3. Deep cooling: Connect instrument air through the main steam drain bypass to deeply cool the steam turbine. Control the cooling rate at 3°C - 4°C / h until the metal temperature of the steam turbine gland packing ring (the metal temperature of the inner wall of the high-pressure inner cylinder of the steam turbine) drops to 180°C.

[0030] In this embodiment, compared with the existing situation where it takes 60 hours for the metal temperature of the steam turbine gland packing ring to cool naturally from 430°C to 180°C, after adopting the fast cooling technology of the present invention, it only takes 25 hours, which is 35 hours earlier than natural cooling.

[0031] Calculated based on saving 35 hours for each shutdown and maintenance, with additional power generation at 150,000 kWh per hour and electricity price at 0.38 yuan per kWh (purchased electricity price), the annual additional power generation benefit is:

[0032] 35 hours × 150,000 kWh / hour × 0.38 yuan / kWh = 1.995 million yuan

[0033] That is: The annual economic benefit is 1.995 million yuan.

[0034] Embodiment 2

[0035] A fast cooling process for a gas-steam combined cycle power generation unit in this embodiment has the same basic structure as Embodiment 1. The differences and improvements are as follows: As Figure 2 shown, in Step 2, during the cooling and turning process of the gas turbine at 600 rpm, by starting the desuperheater and desuperheating and pressure reducing valve in the start-up steam system, the turning steam parameters are successively reduced to the superheated steam temperature at pressures of 1.4 MPa and 1.0 MPa, thus eliminating the need to additionally install a dedicated fast cooling device, avoiding the impact of the reliability of the fast cooling device on the safety of the steam turbine, reducing equipment reinvestment, saving energy, achieving fast and safe cooling of the gas-steam combined cycle power generation unit, improving the annual utilization rate of the unit, and having good economic benefits.

[0036] In this embodiment, during the cooling start-up process of the gas turbine at 600 rpm, first start the desuperheater to reduce the temperature of the starting steam at a temperature drop rate of 0.5 - 1 °C / min to 245 °C (this temperature is the superheated steam temperature at a pressure of 1.4 MPa); then start the desuperheating and pressure-reducing valve to reduce the parameters of the starting steam at a pressure drop rate of 0.05 - 0.1 MPa / min and a temperature drop rate of 0.2 - 0.5 °C / min to 1.0 MPa and 230 °C (this temperature is the superheated steam temperature at a pressure of 1.0 MPa), so as to make full use of the principle of sliding parameter shutdown of the steam turbine, obtain superheated steam at a lower required temperature by reducing the pressure, ensure that the temperature drop rate of each metal component of the steam turbine is uniform and controllable during the temperature reduction process, do not increase the life loss of the steam turbine, accelerate the cooling speed of the unit, greatly reduce the waiting time for unit maintenance, and shorten the maintenance period.

[0037] The above has schematically described the present invention and its implementation manners. This description is not restrictive. What is shown in the drawings is only one of the implementation manners of the present invention, and the actual structure is not limited thereto. Therefore, if those of ordinary skill in the art are inspired by it and design, without creative efforts, structural manners and embodiments similar to the technical solution without departing from the purpose of the present invention, they shall fall within the protection scope of the present invention.

Claims

1. A rapid cooling process for a gas-steam combined cycle power generation unit, characterized in that: Adopt the sliding parameter shutdown mode of the steam turbine to reduce its steam parameters for rapid cooling of the steam turbine. The cooling of the steam turbine specifically includes the following steps: Step 1, preliminary cooling: Adopt sliding parameter load reduction for preliminary cooling. The unit reduces the load by sliding parameters to the minimum load of 4.6 MW. The waste heat boiler reduces the pressure and temperature accordingly. When the metal temperature of the steam turbine packing ring drops to 430°C - 440°C and remains basically unchanged, the unit shuts down. After the rotor coasts to a stop, immediately start continuous low-speed turning gear for natural cooling for 2 hours; Step 2, re-cooling: After 2 hours of natural cooling with low-speed turning gear, the metal temperature of the steam turbine packing ring is 410°C - 420°C. Immediately adopt the gas turbine cooling and turning program to cool the gas turbine body until it shuts down when the superheated steam temperature under a pressure of 1.0 MPa is reached. The cooling and turning program is as follows: During the cooling and turning process of the gas turbine at 600 rpm, first start the desuperheater to reduce the turning steam temperature at a temperature drop rate of 0.5 - 1°C / min to the superheated steam temperature under a pressure of 1.4 MPa, and its superheated steam temperature is 245°C; then start the desuperheating and pressure reducing valve to reduce the turning steam parameters at a pressure drop rate of 0.05 - 0.1 MPa / min and a temperature drop rate of 0.2 - 0.5°C / min to the superheated steam temperature under a pressure of 1.0 MPa, and its superheated steam temperature is 230°C; Step 3, deep cooling: Connect instrument air through the main steam drain bypass to conduct deep cooling of the steam turbine until the metal temperature of the steam turbine packing ring drops to 180°C.

2. A rapid cooling process for a gas-steam combined cycle power generation unit according to claim 1, characterized in that: In Step 3, the cooling rate is 3°C - 4°C / h.

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