Auxiliary steam self-supply system and method for gas-steam combined cycle unit

Abstract

The present invention discloses an auxiliary steam self-supply system and method for a gas-steam combined cycle unit, wherein the auxiliary steam self-supply system for the gas-steam combined cycle unit comprises: a high-pressure drum, a medium-pressure drum, a supplementary steam pipeline, a steam supply pipeline, a medium-pressure superheated steam outlet manifold and an auxiliary steam system, wherein the high-pressure drum is connected to the medium-pressure drum via a supplementary steam pipeline, and the medium-pressure drum is connected to the medium-pressure superheated steam outlet manifold and the auxiliary steam system via a steam supply pipeline. The present invention proposes to modify the shaft seal pressure during the startup phase and before the steam turbine enters the steam during the auxiliary steam self-supply process, so as to reduce the amount of high-quality steam consumed by the shaft seal steam supply as much as possible under the premise of ensuring the safety of the unit; at the same time, in order to prevent abnormalities such as CV sudden closure and medium-pressure drum overpressure that may be caused during the auxiliary steam self-supply process, protection logic is set for the high-pressure to medium-pressure supplementary steam electric valve and the high-pressure to medium-pressure supplementary steam regulating valve related to the auxiliary steam self-supply.

Description

Technical Field

[0001] The present invention relates to the field of power generation in power plants, and in particular to a system and method for self-supplying auxiliary steam for a gas-steam combined cycle unit. Background Art

[0002] In the patent application document with application number: CN201911039584.2, it is mentioned: With the change of my country's electricity consumption structure, the peak-to-valley difference of the power grid is increasing. In order to ensure the stability of the power system, the gas-steam combined cycle system participates in the operation of the power grid as a peak-shaving unit due to its fast start-stop speed and good economy. At the same time, in order to improve energy utilization efficiency, the gas-steam combined cycle system adopts a cogeneration energy supply method.

[0003] At present, the 9FA gas-steam combined cycle unit needs to be supplied with auxiliary steam required before starting by the startup boiler. After a certain modification of the boiler system, the residual steam after the waste heat boiler is shut down can be used for self-supply of auxiliary steam. However, in addition to the modification of the equipment, the original start-up and shutdown operation method is difficult to adapt to the higher steam quality requirements required for the self-supply of auxiliary steam. The shutdown procedure of the unit does not fully consider the insulation and pressure maintenance of the waste heat boiler. The insulation and pressure maintenance effect of the waste heat boiler actually not only affects the load loading speed when the unit is restarted, but also determines the success rate of the unit's auxiliary steam self-supply. The original shutdown operation needs to wait for the unit trip oil to be lost, and then shut down the unit bypass system and break the vacuum. This makes a large amount of high-parameter steam enter the condenser through the bypass system and be condensed during a long idling time, so that the steam-water parameters of the waste heat boiler after the final shutdown are low, which fundamentally limits the insulation and pressure maintenance effect of the waste heat boiler. In addition, since the water supply pump of my driver team is equipped with a reverse warming pipeline, a large amount of high-parameter steam and water will be reversed from the high-pressure system to the low-pressure system through this pipeline after shutdown, which also reduces the insulation and pressure maintenance effect of the residual furnace to a certain extent. Summary of the invention

[0004] Based on this, the purpose of the present invention is to solve the problem that the original 9FA gas-steam combined cycle unit start-up and shutdown operation method is difficult to adapt to the higher steam quality requirements required for auxiliary steam self-supply.

[0005] To achieve the above-mentioned purpose, the present invention proposes an auxiliary steam self-supply system for a gas-steam combined cycle unit, wherein the auxiliary steam self-supply system for the gas-steam combined cycle unit comprises: a high-pressure steam drum, a medium-pressure steam drum, a supplementary steam pipeline, a steam supply pipeline, a medium-pressure superheated steam outlet manifold and an auxiliary steam system, wherein the high-pressure steam drum is connected to the medium-pressure steam drum through the supplementary steam pipeline, and the medium-pressure steam drum is connected to the medium-pressure superheated steam outlet manifold and the auxiliary steam system through the steam supply pipeline.

[0006] The supplementary steam pipeline is provided with a supplementary steam electric valve and a supplementary steam regulating valve.

[0007] The auxiliary steam self-supply system of the gas-steam combined cycle unit also includes a medium-pressure superheater, which is arranged on the steam supply pipeline from the medium-pressure steam drum to the medium-pressure superheated steam outlet manifold and the auxiliary steam system.

[0008] The auxiliary steam self-supply system of the gas-steam combined cycle unit also includes a high-pressure bypass system, which is connected to the high-pressure steam drum and is provided with a high-pressure bypass valve and a high-pressure combined valve seat front steam trap.

[0009] The auxiliary steam self-supply system of the gas-steam combined cycle unit also includes an isolation valve, which is arranged on the steam supply pipeline from the medium-pressure steam drum to the auxiliary steam system.

[0010] The auxiliary steam self-supply method for a gas-steam combined cycle unit comprises the following steps:

[0011] S1: Control the high-pressure to medium-pressure steam supply electric valve and the high-pressure to medium-pressure steam supply regulating valve to control the medium-pressure steam drum pressure to always be between 1.2-1.4Mpa;

[0012] S2: Control the high-pressure drum pressure not lower than 1.5Mpa, and the medium-pressure drum pressure not higher than 2.0Mpa;

[0013] S3: gradually close the high-pressure to medium-pressure steam supply electric valve and the high-pressure to medium-pressure steam supply regulating valve;

[0014] S4: The high-pressure to medium-pressure steam supplement electric valve and the high-pressure to medium-pressure steam supplement regulating valve are completely closed, and the auxiliary steam self-supply operation is completed.

[0015] The auxiliary steam self-supply method for the gas-steam combined cycle unit further comprises the following parallel steps:

[0016] S5: When the high-pressure drum pressure is lower than 1.5MPa and / or the medium-pressure drum pressure is higher than 2.0MPa and / or the isolation valve from the medium-pressure drum to the auxiliary steam system is closed: the steam supplement electric valve and the steam supplement regulating valve are forced to close;

[0017] The method for self-supplying auxiliary steam for a gas-steam combined cycle unit further comprises the following steps:

[0018] S6: When the auxiliary steam self-supply system of the gas-steam combined cycle unit is shut down: determine the unit speed; when the unit speed drops to 600r / min, disable the bypass system; when the unit speed drops to 300 r / min, close the drain in front of the high-pressure main steam combined valve seat; after stopping water replenishment, close the high-pressure feedwater main pipe electric valve, and close the high-pressure feedwater pump reverse warming valve.

[0019] The method for self-supplying auxiliary steam for a gas-steam combined cycle unit further comprises the following steps:

[0020] S7: When the auxiliary steam self-supply system of the gas-steam combined cycle unit is started: before the shaft seal is put into operation, the water drainage is strengthened, and after the shaft seal is put into operation, it is determined whether the steam superheat condition is met. If it is met, the water drainage is closed; after the shaft seal is put into operation, the pressure is set to 0.17kg / cm 2 , until the auxiliary steam self-supply operation is completed; delay opening of the high-pressure bypass drain valve.

[0021] Beneficial effects of this application:

[0022] 1. Make appropriate improvements to the shutdown operation process to reduce the steam loss during the unit shutdown and idling process, and improve the steam-water parameters of the residual boiler after shutdown; formulate an operation method for early shutdown of the bypass system to reduce the steam loss of the bypass system; select the optimal speed for shutting down the bypass system to prevent the risk of overpressure in each steam drum after shutdown, while minimizing the loss of high-quality steam due to the bypass system during idling, and also ensure the safety of equipment after the unit is shut down;

[0023] 2. After shutdown, formulate an operation method to close the reverse heating valve to stop reverse heating, so as to reduce the loss of high-quality steam and water due to the reverse heating pipeline; take measures such as closing the high-pressure joint valve seat front drain in advance during shutdown and delaying the opening of the high-pressure bypass drain during startup to reduce the steam loss caused by the drain system;

[0024] 3. During the auxiliary steam self-supply process, the shaft seal pressure during the startup phase and before the steam turbine enters the steam turbine is modified to minimize the amount of high-quality steam consumed by the shaft seal steam supply while ensuring the safety of the unit;

[0025] 4. In order to prevent abnormalities such as CV sudden closure and medium-pressure steam drum overpressure that may be caused during the auxiliary steam self-supply process, protection logic is set for the high-pressure to medium-pressure steam supplement electric valve and high-pressure to medium-pressure steam supplement regulating valve related to the auxiliary steam self-supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the auxiliary steam self-supply system structure;

[0027] Figure 2 The shutdown flow chart of the auxiliary steam self-supply system is shown in FIG.

[0028] Figure 3 This is the flow chart of auxiliary steam from the supply system to the grid connection;

[0029] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0030] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described with reference to the accompanying drawings.

[0031] like Figure 1 As shown, in this embodiment, a gas-steam combined cycle unit auxiliary steam self-supply system is provided, and the auxiliary steam self-supply system of the gas-steam combined cycle unit includes: a high-pressure steam drum, a medium-pressure steam drum, a supplementary steam pipeline, a steam supply pipeline, a medium-pressure superheated steam outlet manifold and an auxiliary steam system. The high-pressure steam drum is connected to the medium-pressure steam drum through the supplementary steam pipeline, and the medium-pressure steam drum is connected to the medium-pressure superheated steam outlet manifold and the auxiliary steam system through the steam supply pipeline.

[0032] The supplementary steam pipeline is provided with a supplementary steam electric valve and a supplementary steam regulating valve.

[0033] The auxiliary steam self-supply system of the gas-steam combined cycle unit also includes a medium-pressure superheater, which is arranged on the steam supply pipeline from the medium-pressure steam drum to the medium-pressure superheated steam outlet manifold and the auxiliary steam system.

[0034] The auxiliary steam self-supply system of the gas-steam combined cycle unit also includes a high-pressure bypass system, which is connected to the high-pressure steam drum and is provided with a high-pressure bypass valve and a high-pressure combined valve seat front steam trap.

[0035] The auxiliary steam self-supply system of the gas-steam combined cycle unit also includes an isolation valve, which is arranged on the steam supply pipeline from the medium-pressure steam drum to the auxiliary steam system.

[0036] The auxiliary steam self-supply method for a gas-steam combined cycle unit comprises the following steps:

[0037] S1: Control the high-pressure to medium-pressure steam supplement electric valve and the high-pressure to medium-pressure steam supplement regulating valve to control the medium-pressure drum pressure to always be between 1.2-1.4Mpa to meet the auxiliary steam pressure requirement of 0.8Mpa;

[0038] S2: During the whole operation, the high-pressure drum pressure should be controlled not lower than 1.5Mpa, and the medium-pressure drum pressure should be controlled not higher than 2.0Mpa to prevent the protection action from causing the auxiliary steam to be cut off;

[0039] S3: As the heat of the waste furnace increases after startup, when the medium-pressure drum pressure rises, the high-pressure to medium-pressure steam supplement electric valve and the high-pressure to medium-pressure steam supplement regulating valve are gradually closed;

[0040] S4: When the high-pressure to medium-pressure steam supply electric valve and the high-pressure to medium-pressure steam supply regulating valve are completely closed, the auxiliary steam self-supply operation ends.

[0041] The method for self-supplying auxiliary steam for a gas-steam combined cycle unit further comprises the following parallel steps:

[0042] S5: When the high-pressure drum pressure is lower than 1.5MPa and / or the medium-pressure drum pressure is higher than 2.0MPa and / or the isolation valve from the medium-pressure drum to the auxiliary steam system is closed: the steam supplement electric valve and the steam supplement regulating valve are forced to close to prevent abnormalities such as low high-pressure drum pressure, CV closure, and / or medium-pressure drum overpressure;

[0043] The method for self-supplying auxiliary steam for a gas-steam combined cycle unit further comprises the following steps:

[0044] S6: When the auxiliary steam self-supply system of the gas-steam combined cycle unit is shut down: determine the unit speed; when the unit speed drops to 600r / min, disable the high, medium and low pressure bypass systems to reduce the loss of high-quality steam through the bypass system during the shutdown process; when the unit speed drops to 300 r / min, close the drain in front of the high-pressure main steam combined valve seat to reduce the loss of high-quality steam in the high-pressure system during the shutdown process; after stopping water replenishment, close the high-pressure water supply main pipe electric valve, and close the two high-pressure water supply pumps’ one, two and three reverse warming valves to reduce the loss of high-pressure and high-quality steam after shutdown.

[0045] The method for self-supplying auxiliary steam for a gas-steam combined cycle unit further comprises the following steps:

[0046] S7: When the auxiliary steam self-supply system of the gas-steam combined cycle unit is started: before the shaft seal is put into operation, the water drainage is strengthened. After the shaft seal is put into operation, it is determined whether the steam superheat condition is met. If it is met, the water drainage is closed to reduce unnecessary steam loss. After the shaft seal is put into operation, the pressure is set to 0.17kg / cm 2 , which is 0.25kg / cm below the normal value 2 , until the auxiliary steam self-supply operation is completed; delay opening of the high-pressure bypass drain valve to reduce the loss of high-quality steam during the auxiliary steam self-supply process.

[0047] The above is only a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art shall not deviate from the spirit and scope of the present invention, and shall be within the scope of protection of the claims attached to the present invention.

Claims

1. A method for self-supplying auxiliary steam for a gas-steam combined cycle unit, the method comprising the following steps: S1: Control the high-pressure to medium-pressure steam supply electric valve and the high-pressure to medium-pressure steam supply regulating valve to control the medium-pressure steam drum pressure to always be between 1.2-1.4Mpa; S2: Control the high-pressure drum pressure not lower than 1.5Mpa, and the medium-pressure drum pressure not higher than 2.0Mpa; S3: gradually close the high-pressure to medium-pressure steam supply electric valve and the high-pressure to medium-pressure steam supply regulating valve; S4: The high-pressure to medium-pressure steam supplement electric valve and the high-pressure to medium-pressure steam supplement regulating valve are completely closed, and the auxiliary steam self-supply operation is completed; S5: When the high-pressure drum pressure is lower than 1.5MPa and / or the medium-pressure drum pressure is higher than 2.0MPa and / or the isolation valve from the medium-pressure drum to the auxiliary steam system is closed: the steam supplement electric valve and the steam supplement regulating valve are forced to close; S6: When the auxiliary steam self-supply system of the gas-steam combined cycle unit is shut down: determine the unit speed; when the unit speed drops to 600r / min, disable the bypass system; when the unit speed drops to 300r / min, close the drain in front of the high-pressure main steam joint valve seat; after stopping water replenishment, close the high-pressure feedwater main pipe electric valve and the high-pressure feedwater pump reverse warming valve; S7: When the auxiliary steam self-supply system of the gas-steam combined cycle unit is started: before the shaft seal is put into operation, the water drainage is strengthened, and after the shaft seal is put into operation, it is determined whether the steam superheat condition is met. If it is met, the water drainage is closed; after the shaft seal is put into operation, the pressure is set to 0.17kg / cm 2 , until the auxiliary steam self-supply operation is completed; delay opening of the high-pressure bypass drain valve.

2. A method for self-supplying auxiliary steam for a gas-steam combined cycle unit according to claim 1, characterized in that: It also includes an auxiliary steam self-supply system for a gas-steam combined cycle unit, which is implemented based on an auxiliary steam self-supply method for a gas-steam combined cycle unit. The system includes: a high-pressure steam drum, a medium-pressure steam drum, a supplementary steam pipeline, a steam supply pipeline, a medium-pressure superheated steam outlet manifold and an auxiliary steam system. The high-pressure steam drum is connected to the medium-pressure steam drum through a supplementary steam pipeline, and the medium-pressure steam drum is connected to the medium-pressure superheated steam outlet manifold and the auxiliary steam system through a steam supply pipeline.

3. A method for self-supplying auxiliary steam for a gas-steam combined cycle unit according to claim 2, characterized in that: The supplementary steam pipeline is provided with a supplementary steam electric valve and a supplementary steam regulating valve.

4. A method for self-supplying auxiliary steam for a gas-steam combined cycle unit according to claim 2, characterized in that: The system further comprises a medium-pressure superheater, which is arranged on a steam supply line from a medium-pressure steam drum to a medium-pressure superheated steam outlet manifold and an auxiliary steam system.

5. A method for self-supplying auxiliary steam for a gas-steam combined cycle unit according to claim 2, characterized in that: The system also includes a high-pressure bypass system, which is connected to the high-pressure steam drum and is provided with a high-pressure bypass valve and a high-pressure combined valve seat front drain valve.

6. A method for self-supplying auxiliary steam for a gas-steam combined cycle unit according to claim 2, characterized in that: The system further comprises an isolation valve, which is arranged on a steam supply pipeline from the medium-pressure steam drum to the auxiliary steam system.

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