Supercritical unit jump turbine stable steam supply system and method

Abstract

This invention discloses a stable steam supply system and method based on a supercritical unit's tripped turbine. The system includes a thermal control unit, used to control the connection of the main steam pipeline, low-pressure exhaust pipeline, external steam supply pipeline, low-pressure bypass, condensate pipeline, feedwater pipeline, and high-pressure exhaust pipeline, and to control the shutdown of the high-pressure bypass and low-pressure bypass, when the unit is under normal operating conditions; and to control the connection of the high-pressure bypass, external steam supply pipeline, low-pressure bypass, condensate pipeline, feedwater pipeline, and high-pressure exhaust pipeline, and to shut down the main steam pipeline and low-pressure exhaust pipeline, when the unit is under abnormal operating conditions and the turbine trips without shutting down the boiler. This achieves stable steam supply under FCB (Future Combustion Block) conditions without shutting down the boiler.

Description

Technical Field

[0001] This invention relates to the field of thermal power unit control technology, and in particular to a stable steam supply system and method based on the turbine tripping of a supercritical unit. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] When a traditional thermal power unit experiences FCB (Fuel Burner) activation, the unit rapidly reduces its load and operates with auxiliary power. The pressure and temperature of the main steam and reheat steam rise rapidly, failing to meet the demand for external industrial steam. If the bypass system is not adjusted in time, it can easily trigger the boiler MFT (Main Fuel Trip), leading to a complete unit shutdown. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a stable steam supply system and method based on a supercritical unit's tripped steam turbine.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: Firstly, a stable steam supply system based on a supercritical unit's turbine tripping mechanism is proposed, comprising: a boiler, a turbine, a condenser, a heater, a reheater, and a thermal control unit. The boiler is connected to the turbine via a main steam pipeline, the turbine is connected to the condenser via a low-pressure exhaust pipeline, the condenser is connected to the heater via a condensing pipeline, and the heater is connected to the boiler via a feedwater pipeline. The turbine is also connected to the reheater via a high-pressure exhaust pipeline, the reheater is connected to an external steam supply pipeline for external steam supply, and the reheater is also connected to the condenser via a low-pressure bypass. The boiler is also connected to the high-pressure exhaust pipeline via a high-pressure bypass. The thermal control unit is used to control the connection of the main steam pipeline, low-pressure exhaust pipeline, external steam supply pipeline, low-pressure bypass, condensing pipeline, feedwater pipeline and high-pressure exhaust pipeline when the unit is in normal operating conditions, and to control the shutdown of the high-pressure bypass and low-pressure bypass; when the unit is in abnormal operating conditions, and the turbine trips but the boiler is not shut down, it controls the connection of the high-pressure bypass, external steam supply pipeline, low-pressure bypass, condensing pipeline, feedwater pipeline and high-pressure exhaust pipeline, and shuts down the main steam pipeline and low-pressure exhaust pipeline.

[0006] Furthermore, the reheater is also connected to the steam turbine via a medium-pressure steam supply pipeline; under normal operating conditions, the opening of the medium-pressure steam supply pipeline is controlled according to the steam flow generated by the reheater.

[0007] Furthermore, the thermal control unit is also used to determine the target feedwater flow rate, target feedwater temperature, target temperature difference between main and reheat steam, target pressure and target temperature of main steam, and target pressure and target temperature of reheat steam based on the pressure and temperature requirements of the external steam supply. The boiler feedwater flow rate and feedwater temperature are controlled according to the target feedwater flow rate and target feedwater temperature; the main steam pressure and temperature are controlled according to the target main steam pressure and target temperature; the reheat steam pressure and temperature are controlled according to the target reheat steam pressure and target temperature; and the main reheat steam temperature difference is controlled according to the target main reheat steam temperature difference.

[0008] Furthermore, the thermal control unit determines the target liquid level of the condenser based on the pressure and temperature requirements of the externally supplied steam; and controls the liquid level of the condenser based on the target liquid level.

[0009] Furthermore, the external steam supply pipeline is also connected to the condenser via a steam supply bypass; The thermal control unit is used to control the steam supply bypass to be connected when the reheat steam pressure generated by the reheater is greater than the reheat steam target pressure; and to control the steam supply bypass to be disconnected when the reheat steam pressure generated by the reheater is less than or equal to the reheat steam target pressure.

[0010] Furthermore, the high-pressure exhaust pipeline is also connected to the heater through a second-stage extraction pipeline; The thermal control unit is also used to control the opening of the high-pressure bypass pipeline according to the target feedwater temperature of the boiler, so as to control the feedwater temperature of the boiler at the target feedwater temperature.

[0011] Furthermore, the condenser is also connected to the water storage tank via a water supply pipeline, and the water storage tank is connected to the drain pipeline. The thermal control unit is also used to determine the target liquid level of the water storage tank based on the pressure and temperature requirements of the external steam supply, and to control the opening of the drain pipe according to the target liquid level of the water storage tank, so as to keep the liquid level of the water storage tank at the target liquid level.

[0012] Furthermore, the boiler flue gas outlet is connected to the flue gas pipeline, and a flue gas valve is installed in the flue gas pipeline. The boiler gas inlet is also connected to the ammonia supply pipeline. The thermal control unit is used to control the opening degree of the flue gas valve and the opening degree of the ammonia supply pipeline, so as to control the flue gas flow rate at the outlet of the flue gas pipeline within the target flue gas flow rate range.

[0013] Furthermore, the high-pressure exhaust pipeline is also connected to the steam turbine via the shaft seal steam supply pipeline; The thermal control unit is used to control the opening of the shaft seal steam supply pipeline, and to control the shaft seal temperature and pressure of the steam turbine at the target shaft seal temperature and pressure.

[0014] Secondly, a method for stable steam supply based on the turbine tripping mechanism of a supercritical unit is proposed, including: When the unit is in normal operating condition, control the main steam pipeline, low-pressure exhaust pipeline, external steam supply pipeline, low-pressure bypass, condensate pipeline, feedwater pipeline and high-pressure exhaust pipeline to be connected, and control the high-pressure bypass and low-pressure bypass to be shut off. When the unit is in an abnormal operating condition and the turbine trips without shutting down the boiler, the high-pressure bypass, external steam supply pipeline, low-pressure bypass, condensate pipeline, feedwater pipeline and high-pressure exhaust pipeline are connected, while the main steam pipeline and low-pressure exhaust pipeline are shut off.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention proposes a stable steam supply system and method based on a supercritical unit's turbine tripping operation. When the unit is in an abnormal operating condition and the turbine needs to be tripped without shutting down the boiler, the system controls the connection of the high-pressure bypass and the shutdown of the main steam pipeline and the low-pressure exhaust pipeline. This prevents the high-pressure steam generated by the boiler from entering the turbine. Instead, the steam enters the reheater through the high-pressure bypass and the high-pressure exhaust pipeline, and is then reheated in the reheater before being supplied to the outside. This achieves a stable output of steam pressure and temperature for external supply without shutting down the boiler while the turbine is tripped, reducing parameter fluctuations and meeting the steam demand of users.

[0016] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0017] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application.

[0018] Figure 1 This is a schematic diagram of the pipeline connection of the stable steam supply system based on the turbine tripping of a supercritical unit proposed in an embodiment of the present invention; Figure 2 This is a schematic diagram of the feedwater flow control principle in a stable steam supply system based on a supercritical unit's turbine tripping, as proposed in an embodiment of the present invention. Figure 3 This is a schematic diagram illustrating the principle of controlling the water tank level using an overflow valve in a stable steam supply system based on a supercritical unit's turbine tripping operation, as proposed in this embodiment of the invention. Figure 4 This is a schematic diagram illustrating the principle of using a condensate pump to control the liquid level in a water storage tank in a stable steam supply system based on a supercritical unit's turbine tripping operation, as proposed in an embodiment of the present invention. Figure 5 This is a schematic diagram of the switching authority in the stable steam supply system based on the turbine tripping of a supercritical unit, as proposed in an embodiment of the present invention. Figure 6 This is a schematic diagram of the high-pressure bypass control principle in the stable steam supply system based on the turbine tripping of a supercritical unit, as proposed in this embodiment of the invention. Figure 7 This is a schematic diagram of the external industrial steam supply control principle in the stable steam supply system based on the turbine tripping of a supercritical unit, as proposed in an embodiment of the present invention. Figure 8This is a schematic diagram of the control principle of the two-stage extraction steam pipeline in the stable steam supply system based on the turbine tripping of a supercritical unit, as proposed in an embodiment of the present invention. Figure 9 This is a schematic diagram of the main steam control principle in a stable steam supply system based on a supercritical unit's turbine tripping, as proposed in an embodiment of the present invention. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0021] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0022] In this invention, terms such as "upper," "lower," "left," "right," "front," "back," "vertical," "horizontal," "side," and "bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used only to facilitate the description of the structural relationships of the various components or elements of this invention and do not specifically refer to any component or element in this invention. They should not be construed as limiting the invention.

[0023] In this invention, terms such as "fixed connection," "connected," and "linked" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of these terms in this invention based on the specific circumstances, and they should not be construed as limitations on the invention.

[0024] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0025] Terminology Explanation: (1) FCB (Fast Cut Back): refers to the ability of the unit to quickly disconnect from the power grid and maintain stable boiler operation when the power grid fails or the turbine trips, and to supply power to the plant or external heating.

[0026] (2) Turbine tripping without boiler shutdown: This means that after the turbine trips and stops, the boiler continues to operate and continue to generate steam.

[0027] (3) High pressure bypass / low pressure bypass: High pressure bypass / low pressure bypass, used to directly introduce main steam or reheat steam into the condenser to maintain the minimum flow rate of the boiler.

[0028] (4) Dry operation: The operating state of a supercritical once-through boiler when the working fluid at the outlet of the water-cooled wall is slightly superheated steam.

[0029] First, the application scenarios of the stable steam supply system based on the supercritical unit's tripped steam turbine proposed in the embodiments of the present invention will be described.

[0030] The proposed steam supply system based on the turbine tripping of a supercritical unit is applied to the specific scenario of stable steam supply without boiler interruption in a supercritical unit operating under FCB conditions.

[0031] With the adjustment of energy structure and the increasing demands of industrial users for steam quality, the ability of thermal power units to maintain a stable steam supply under special operating conditions such as grid failures and unit disconnection has become a key indicator for measuring their flexibility and reliability. This is especially true in scenarios where thermal power units supply steam to high-end oil refining and chemical industrial parks; a failure to reach the industrial steam supply terminal could result in losses of tens or even hundreds of millions of yuan. Currently, traditional thermal power units typically face the following technical problems and shortcomings when experiencing FCB (Fuel Flow Brake) activation: (1) The thermal balance after the boiler and turbine are disconnected is difficult to maintain: After the turbine trips, the steam generated by the boiler cannot do work through the turbine. The main steam pressure and temperature rise rapidly. If the bypass system is not adjusted in time, it is easy to trigger the boiler MFT (main fuel trip), resulting in the complete shutdown of the unit.

[0032] (2) Severe fluctuations in steam supply parameters: Existing technology lacks precise control over steam supply pressure and temperature. After the unit is disconnected, the steam supply parameters often fluctuate significantly (pressure fluctuations exceed ±0.3MPa, and temperature fluctuations exceed ±20℃), which cannot meet the demand of industrial users for high-quality steam (such as 3.8±0.1MPa / 455±10℃).

[0033] (3) Feedwater temperature is difficult to maintain: After the turbine is shut down, the regenerative steam extraction is interrupted, which leads to a significant drop in feedwater temperature (which can drop to below 100℃), seriously affecting the hydrodynamic stability of the boiler and the safety of boiler operation.

[0034] (4) Environmental parameters are difficult to control: When operating at low load, the flue gas temperature at the SCR denitrification inlet is below 270℃, the denitrification efficiency drops significantly, and NOx emissions are likely to exceed the standard.

[0035] (5) Lack of coordinated control among systems: Boiler combustion, turbine bypass, feedwater heating, condenser water level and other systems operate independently under FCB conditions, lacking a unified control strategy, making it difficult and risky for operators.

[0036] To address the technical challenges of maintaining boiler operation and ensuring stable industrial steam supply in existing thermal power units under conditions of turbine, generator, and main transformer system failures, as well as issues arising from boiler-turbine disconnection leading to thermal balance disruption, drastic fluctuations in steam supply parameters, significant drops in feedwater temperature, exceeding environmental standards, and lack of coordinated control among various systems, this invention proposes a stable steam supply system based on a supercritical unit with turbine tripping. This system enables stable output control of steam pressure and temperature under FCB (Future Combustion Block) conditions, even when the unit trips the turbine without shutting down the boiler.

[0037] like Figures 1-9 As shown in the embodiment of the present invention, a stable steam supply system based on a supercritical unit's turbine tripping mechanism includes: a boiler, a turbine, a condenser, a heater, a reheater, and a thermal control unit; the boiler is connected to the turbine via a main steam pipeline, the turbine is connected to the condenser via a low-pressure exhaust pipeline, the condenser is connected to the heater via a condensing pipeline, and the heater is connected to the boiler via a feedwater pipeline; the turbine is also connected to the reheater via a high-pressure exhaust pipeline, the reheater is connected to an external steam supply pipeline for external steam supply, and the reheater is also connected to the condenser via a low-pressure bypass; the boiler is also connected to the high-pressure exhaust pipeline via a high-pressure bypass. The thermal control unit is used to control the connection of the main steam pipeline, low-pressure exhaust pipeline, external steam supply pipeline, low-pressure bypass, condensing pipeline, feedwater pipeline and high-pressure exhaust pipeline when the unit is in normal operating conditions, and to control the shutdown of the high-pressure bypass and low-pressure bypass; when the unit is in abnormal operating conditions, and the turbine trips but the boiler is not shut down, it controls the connection of the high-pressure bypass, external steam supply pipeline, low-pressure bypass, condensing pipeline, feedwater pipeline and high-pressure exhaust pipeline, and shuts down the main steam pipeline and low-pressure exhaust pipeline.

[0038] Among them, "the unit is in an abnormal operating condition and the turbine needs to be tripped but the boiler does not need to be shut down" means that when the thermal power unit is shut down due to a fault in the turbine, generator set, line or main transformer system, the boiler needs to be kept running and able to provide a stable supply of industrial steam.

[0039] The proposed embodiment of the invention provides a stable steam supply system based on a supercritical unit's turbine tripping mechanism. When the unit is in abnormal operating conditions and the turbine needs to be tripped without shutting down the boiler, the high-pressure steam generated by the boiler is prevented from entering the turbine by controlling the high-pressure bypass to be connected and the main steam pipeline and low-pressure exhaust pipeline to be shut down. Instead, the high-pressure steam enters the reheater through the high-pressure bypass and high-pressure exhaust pipeline, and is then reheated in the reheater before being supplied to the outside. This achieves a stable output of steam pressure and temperature without shutting down the boiler while the turbine is tripped, reducing parameter fluctuations and meeting the user's steam demand.

[0040] In some embodiments, the reheater is also connected to the steam turbine via a medium-pressure steam supply line; The thermal control unit is used to control the intermediate pressure steam supply pipeline to be shut off when the unit is in an abnormal operating condition and the turbine needs to be shut down without stopping the boiler; when the unit is in normal operating condition, it controls the opening of the intermediate pressure steam supply pipeline according to the steam flow generated by the reheater.

[0041] The steam turbine includes a high-pressure cylinder, an intermediate-pressure cylinder, and a low-pressure cylinder. The boiler is connected to the high-pressure cylinder via a main steam pipeline, and the high-pressure cylinder is connected to the reheater via a high-pressure exhaust pipeline. The reheater's steam outlet is connected to the low-pressure bypass via a reheat pipeline, which is also connected to the intermediate-pressure cylinder via an intermediate-pressure steam supply pipeline. The intermediate-pressure cylinder is also connected to the low-pressure cylinder via a low-pressure steam supply pipeline, and the low-pressure cylinder is also connected to the condenser via a low-pressure exhaust pipeline.

[0042] The heaters include a low-pressure heater and a high-pressure heater. The condenser is connected to the low-pressure heater through a condensing pipeline, the low-pressure heater is connected to the high-pressure heater through a low-pressure pipeline, and the high-pressure heater is connected to the boiler through a feedwater pipeline. A condensing pump is installed in the condensing pipeline, a feedwater pump is installed in the low-pressure pipeline, and an economizer is installed in the feedwater pipeline.

[0043] In addition, the water supply pipeline is connected to the water supply bypass, and a main water supply valve is installed in the water supply pipeline, and a water supply bypass regulating valve is installed in the water supply bypass, with the main water supply valve located between the water supply bypass and the heater.

[0044] In some embodiments, in order to ensure that the pressure and temperature requirements of the external steam supply are met, the thermal control unit is also used to determine the target feedwater flow rate, target feedwater temperature, target temperature difference between the main and reheat steam, target pressure and target temperature of the main steam, and target pressure and target temperature of the reheat steam based on the pressure and temperature requirements of the external steam supply. The boiler feedwater flow rate and feedwater temperature are controlled according to the target feedwater flow rate and target feedwater temperature; the main steam pressure and temperature are controlled according to the target main steam pressure and target temperature; the reheat steam pressure and temperature are controlled according to the target reheat steam pressure and target temperature; and the main reheat steam temperature difference is controlled according to the target main reheat steam temperature difference.

[0045] Among them, the feedwater flow rate and feedwater temperature of the boiler refer to the feedwater flow rate and feedwater temperature that flow into the boiler through the feedwater pipeline. Main steam pressure and temperature refer to the pressure and temperature of steam in the high-pressure exhaust pipeline.

[0046] Reheat steam pressure and temperature refer to the pressure and temperature of the steam in the external steam supply pipeline to the reheater.

[0047] The main reheat steam temperature difference refers to the error between the steam temperature input to the reheater from the high-pressure exhaust pipeline and the steam temperature input to the external steam supply pipeline from the reheater.

[0048] By controlling the boiler's feedwater flow rate, feedwater temperature, main steam pressure and temperature, reheat steam pressure and temperature, and main and reheat steam temperature difference, all parameters are kept at target values ​​to meet external steam supply demands. This achieves stable output of external steam pressure and temperature without shutting down the boiler during turbine shutdown, reducing parameter fluctuations and meeting users' steam needs.

[0049] In some embodiments, the thermal control unit further determines the target liquid level of the condenser based on the pressure and temperature requirements of the externally supplied steam, and controls the liquid level of the condenser based on the target liquid level of the condenser.

[0050] In some embodiments, the external steam supply pipeline is also connected to the condenser via a steam supply bypass; The thermal control unit is used to control the steam supply bypass to be connected when the reheat steam pressure generated by the reheater is greater than the reheat steam target pressure; and to control the steam supply bypass to be disconnected when the reheat steam pressure generated by the reheater is less than or equal to the reheat steam target pressure.

[0051] By controlling the opening and closing of the steam supply bypass, excess steam in the external steam supply pipeline is diverted to the condenser, ensuring that the pressure of the external steam supply meets the demand.

[0052] In some embodiments, the high-pressure exhaust pipeline is also connected to the heater through a second-stage extraction pipeline; The thermal control unit is also used to control the opening of the high-pressure bypass pipeline according to the target feedwater temperature of the boiler, so as to control the feedwater temperature of the boiler at the target feedwater temperature.

[0053] The high-temperature steam discharged from the boiler is directed to the heater through the high-pressure bypass pipeline and the high-pressure exhaust pipeline to heat the boiler feedwater, ensuring the boiler feedwater temperature and effectively preventing the risk of tripping caused by boiler overheating, dry burning or excessive water level fluctuations. The boiler operation success rate under FCB conditions is increased to over 95%.

[0054] In some embodiments, the condenser is also connected to a water storage tank via a water supply line, and the water storage tank is connected to a drain line. The thermal control unit is also used to determine the target liquid level of the water storage tank based on the pressure and temperature requirements of the external steam supply, and to control the opening of the drain pipe according to the target liquid level of the water storage tank, so as to keep the liquid level of the water storage tank at the target liquid level.

[0055] By controlling the water level in the storage tank, the condenser water level is maintained at the target value, further ensuring the stability of the boiler feedwater.

[0056] The drainage pipeline includes an overflow valve and a drainage pump; both the overflow valve and the drainage pump are connected to the water storage tank, and the water level in the water storage tank is adjusted through the overflow valve and the drainage pump.

[0057] In some embodiments, the boiler flue gas outlet is connected to a flue gas pipeline, a flue gas valve is installed in the flue gas pipeline, and the boiler gas inlet is also connected to an ammonia supply pipeline; the thermal control unit is used to control the opening degree of the flue gas valve and the opening degree of the ammonia supply pipeline, so as to control the flue gas flow rate at the outlet of the flue gas pipeline within the target flue gas flow rate range.

[0058] By controlling the opening of the flue gas valves and ammonia supply pipelines, the flow rate of flue gas discharged from the boiler is ensured to meet environmental protection requirements.

[0059] The main purpose of this invention is to control the flow rate of NOx in the flue gas discharged from the boiler in order to ensure that the environmental protection data is normal.

[0060] In some embodiments, the high-pressure exhaust pipeline is also connected to the steam turbine via a shaft seal steam supply pipeline; The thermal control unit is used to control the opening of the shaft seal steam supply pipeline, and to control the shaft seal temperature and pressure of the steam turbine within the target temperature and pressure range.

[0061] High-pressure steam discharged from the boiler is used for turbine shaft sealing to ensure that the shaft seal pressure and temperature are normal when the turbine is shut down.

[0062] It should be noted that valves are installed in each pipeline of the present invention embodiment. The opening degree of the pipeline can be adjusted by adjusting the opening degree of the valves in the pipeline, or the pipeline can be connected or disconnected.

[0063] Taking a pressure requirement of 4.2±0.3MPa and a temperature requirement of 450±10℃ for external steam supply as an example, the system proposed in the embodiment of the present invention will be described in detail.

[0064] The boiler is an HG-1165 / 25.4-YM1 type supercritical once-through boiler, equipped with 6 MPS170HP-IIA type medium-speed coal mills.

[0065] like Figure 2 As shown, the thermal control unit is used to control the feedwater flow rate at 300-330 t / h under FCB conditions (adjustable according to the external steam load) to maintain dry boiler operation. After turbine disconnection, i.e., when the unit is in abnormal operating conditions and requires turbine tripping without boiler shutdown, it determines the target feedwater flow rate and target feedwater temperature based on the pressure and temperature requirements of the external steam supply. The feedwater flow rate is controlled at the target flow rate by controlling the opening of the feedwater pipeline. When the target feedwater flow rate is less than the set flow rate, and the unit is operating at low load, the feedwater pump is controlled to maintain minimum speed operation, the main feedwater valve is closed, and the feedwater bypass regulating valve is opened to control the boiler feedwater flow rate at the target flow rate, ensuring safe operation. The boiler feedwater temperature is controlled at the target feedwater temperature by adjusting the opening of the valves in the second-stage extraction steam pipeline. For example, the target feedwater temperature is 230±10℃.

[0066] like Figure 3 , Figure 4 As shown, the thermal control unit is used to determine the target liquid level of the water storage tank after the boiler switches to wet operation, based on the pressure and temperature requirements of the external steam supply; and to control the liquid level of the water storage tank at the target liquid level, such as 3000-8000mm, through the overflow valve and the drain pump.

[0067] The thermal control unit is also used to determine the target temperature difference between the main and reheat steam based on the pressure and temperature requirements of the externally supplied steam. It then controls the angle of the flue gas dampers in the reheater and superheater to adjust the temperatures of the main and reheat steam, thereby controlling the temperature difference between the main and reheat steam within the target range. Simultaneously, the temperatures of the superheated and reheat steam are assisted by automatic control via desuperheating water.

[0068] To ensure normal environmental data, the target flue gas flow range is limited, i.e., the target NOx flow is less than 35 mg / Nm³. The thermal control unit is used to control the opening of the flue gas valve to control the NOx flue gas flow at the flue gas pipeline outlet within the target NOx flue gas flow range, thereby achieving rapid and accurate control of the ammonia supply regulating valve and ensuring the automatic denitrification operation of the boiler under low load conditions.

[0069] The system uses a CC350 / 250.5 extraction condensing steam turbine, equipped with a 100% high-pressure bypass and a low-pressure bypass.

[0070] The thermal control unit is used to determine the target pressure and temperature of the main steam and the target pressure and temperature of the reheat steam based on the pressure and temperature requirements of the external steam supply when the unit is under abnormal operating conditions and the turbine needs to be shut down without stopping the boiler. The target pressure of the main steam is 12.5±0.5MPa and the target temperature of the main steam is 530±10℃. The target pressure of the reheat steam is 3.9-4.6MPa and the target temperature of the reheat steam is 500±10℃. The unit controls the opening of the high-pressure bypass pipe at 30-55% to keep the main steam pressure and temperature at the target pressure and temperature. The unit also controls the opening of the low-pressure bypass pipe at 30-60% to keep the reheat steam pressure and temperature at the target pressure and temperature.

[0071] The thermal control unit is also used to determine the target liquid level of the condenser based on the pressure and temperature requirements of the external steam supply when the unit is in an abnormal operating condition and the turbine needs to be shut down without stopping the boiler. For example, the target liquid level of the condenser is 800-1000mm. When the liquid level of the condenser is lower than 700mm, the standby pump is automatically started to make water for the condenser.

[0072] The thermal control unit is also used to control the opening of the shaft seal steam supply pipeline when the unit is under abnormal operating conditions and the turbine needs to be shut down without stopping the boiler, so as to control the shaft seal temperature and pressure of the turbine at the target shaft seal temperature and pressure. For example, the target shaft seal temperature is 370±5℃ and the target pressure is 40±2Kpa.

[0073] The hardware of the thermal control unit of the system proposed in this embodiment of the invention adopts K-series modules, and the software adopts Hangzhou Hollysys MACS V6.5.4. The steam turbine, boiler and DEH adopt an integrated design, and the boiler and steam turbine achieve coordinated control operation. A protection logic switching module, accessible only to engineers, is configured to disconnect boiler-turbine interlocks (including turbine trip MFT and reheater protection) to prevent turbine tripping from causing boiler tripping. Figure 5 As shown.

[0074] The thermal control unit proposed in this embodiment of the invention is also equipped with a parameter over-limit alarm module, which is used to monitor and alarm for over-limit key parameters such as external steam pressure, temperature, main reheat steam temperature difference, water tank level, feedwater temperature, and condenser liquid level in real time.

[0075] It is equipped with an automatic adjustment and monitoring module, which keeps the low bypass fully closed, and automatically adjusts the high bypass pressure and temperature to 11.3MPa and 370℃, and controls the primary industrial steam supply temperature to 470℃, etc., to meet the automatic control operation under the condition of turbine tripping without boiler shutdown.

[0076] The second-stage extraction steam logic is retained after the turbine trips. After the unit trips, the second-stage extraction steam pipeline is closed. To ensure the normal operation of the No. 2 high-pressure heater, a logic is added where the MFT is not activated (the boiler is still burning) and the turbine trips. This logic serves as the condition for the opening of the second-stage extraction non-return valve and the electric valve, controlling the high-pressure heater outlet temperature and meeting the requirements for normal SCR operation.

[0077] After the turbine trips, the boiler combustion stabilizes. Once the primary industrial steam supply is put into operation, the boiler switches to constant pressure operation based on the primary industrial steam supply. The main steam pressure is maintained at 11.5 MPa, and the two lowest-level pulverizing systems are maintained in operation. The induced draft fan and the forced draft fan are automatically activated. The air supply volume tracks the air volume corresponding to the primary industrial steam supply to power load of 480 t / h. At the same time, the lower limit of the air volume is set at 341 h / h to prevent low air volume from causing MFT (Main Fuel Trip) activation. The primary air fan operates automatically to maintain the primary air pressure at around 7.2 kPa.

[0078] In this embodiment of the invention, the steam turbine is connected to the generator, the generator is connected to the plant power system, and the generator is a QFSN-350-2-20 type generator.

[0079] In this embodiment of the invention, a plant power stabilization module is provided to maintain the 380V bus voltage at 380±10V and the 6kV bus voltage at 6±0.3kV. • Install an automatic backup power switching device to quickly switch to backup power in case of abnormal plant power supply.

[0080] The working process of the stable steam supply system based on the turbine tripping of a supercritical unit proposed in this embodiment of the invention includes the following steps: Step S1: Preparations before steam supply • Each specialty should complete equipment inspection and system debugging 6 hours in advance and prepare the "Inspection Checklist for Steam Supply to External Units Before Turbine Shutdown"; • The steam turbine team completed the preheating of the high-pressure and low-pressure bypass systems, confirming that the high-pressure bypass opening is preset to 30-55% and the low-pressure bypass opening is preset to 30-60%. • The boiler specialist confirmed that the two coal mills and coal feeders are in normal operating condition, with a total coal feed rate of not less than 44 t / h; Step S2: Steam supply system put into operation • During normal operation of the unit, the drain valves of the external steam supply pipeline are opened periodically (or the unit is in a low-load steam supply state when steam supply conditions are available), and the steam pipeline is in a warm-up standby state. • After the warm-up is completed, open the valve in the external steam supply line to 10% opening, observe the steam supply parameters and if there are no abnormalities, then gradually open it fully; • The program-controlled pneumatic regulating valve controls the external steam supply pressure at 4.2±0.3MPa and the external steam supply temperature at 450±10℃.

[0081] Step S3: Steam Supply Stable Operation Control • The boiler department maintains the operation of two coal mills, with the total coal feed controlled at around 44t / h and the total air volume at 420-480t / h; • The steam turbine system monitors the main and reheat steam temperature difference in real time, automatically adjusting the high-pressure bypass opening to maintain the main steam at 530±10℃ / 12.5±0.5MPa, and automatically adjusting the low-pressure bypass opening to maintain the reheat steam at 500±10℃ / 3.5-4.2MPa. • Use two-stage steam extraction to heat the feedwater and maintain the feedwater temperature at 230±10℃; • The thermal control system monitors key parameters in real time, triggering audible and visual alarms when parameters exceed limits.

[0082] Step S4: Steam supply termination control • 60 minutes before the end of steam supply, the regulating valve in the external steam supply pipeline will be gradually and automatically closed according to the load demand of the external steam network, with a reduction of 5-10t each time and an interval of 5 minutes. At this time, the high and low pressure bypass control logic on the turbine side will be automatically adjusted to avoid boiler overpressure operation. • After the steam supply drops to zero, close the steam supply regulating valve to maintain the warm pipeline status; • Each specialty should check the equipment status item by item according to the "Checklist after Steam Supply is Completed" and restore the temporarily adjusted protection logic.

[0083] The steam supply system based on the turbine tripping of a supercritical unit proposed in this embodiment of the invention has the following beneficial effects: 1. Stable external steam supply parameters: Through the coordinated control of boiler combustion, feedwater and turbine bypass, and steam extraction, a stable output of external steam pressure of 4.2±0.2MPa and temperature of 450±10℃ is achieved. The parameter fluctuation range is reduced by more than 60% compared with the existing technology, which fully meets the steam needs of high-end industrial users.

[0084] 2. Boiler operation safety: Through precise control of feedwater flow (300-330t / h) and monitoring of water level in the storage tank (5000-12000mm), the risk of tripping caused by boiler overheating, dry burning or excessive water level fluctuation is effectively prevented, and the boiler operation success rate under FCB conditions is increased to over 95%.

[0085] 3. Feedwater temperature maintenance: The high-pressure heater is heated by two-stage extraction steam to stabilize the feedwater temperature at 230±10℃, which is more than 30% higher than the feedwater temperature under traditional FCB conditions (100-150℃), ensuring the hydrodynamic stability of the boiler and the safety of the economizer.

[0086] 4. Environmental parameters meet standards: By maintaining the SCR inlet temperature ≥280℃ and finely adjusting the ammonia supply, the hourly average NOx value is ensured to be ≤40mg / Nm³ and the dust value is <5mg / Nm³, achieving ultra-low emissions under FCB conditions.

[0087] 5. Strong system coordination: The system enables coordinated control and response of the boiler, turbine, and electrical systems, reducing the workload of operators by 70% and significantly decreasing the risk of human error.

[0088] 6. Improved economic efficiency: Based on the stable external steam supply under the FCB operating condition of the thermal power unit, the heat supply interruption loss caused by the complete shutdown of the unit is avoided. According to the current embodiment of the present invention in the project, in the application scenario where the unit is abnormal and the steam turbine needs to be tripped without shutting down the boiler, the steam supply interruption can be avoided and the economic loss can be reduced by about 30 million yuan.

[0089] This invention also proposes a method for stabilizing steam supply based on a supercritical unit's turbine tripping mechanism, including: When the unit is in normal operating condition, control the main steam pipeline, low-pressure exhaust pipeline, external steam supply pipeline, low-pressure bypass, condensate pipeline, feedwater pipeline and high-pressure exhaust pipeline to be connected, and control the high-pressure bypass and low-pressure bypass to be shut off. When the unit is in an abnormal operating condition and the turbine trips without shutting down the boiler, the high-pressure bypass, external steam supply pipeline, low-pressure bypass, condensate pipeline, feedwater pipeline and high-pressure exhaust pipeline are connected, while the main steam pipeline and low-pressure exhaust pipeline are shut off.

[0090] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A stable steam supply system based on a supercritical unit's tripped turbine, characterized in that, include: Boilers, steam turbines, condensers, heaters, reheaters, and thermal control units; The boiler is connected to the steam turbine via the main steam pipeline. The steam turbine is connected to the condenser via the low-pressure exhaust pipeline. The condenser is connected to the heater via the condensing pipeline. The heater is connected to the boiler via the feedwater pipeline. The steam turbine is also connected to the reheater via the high-pressure exhaust pipeline. The reheater is connected to the external steam supply pipeline, which is used for external steam supply. The reheater is also connected to the condenser via the low-pressure bypass. The boiler is also connected to the high-pressure exhaust pipeline via the high-pressure bypass. The thermal control unit is used to control the connection of the main steam pipeline, low-pressure exhaust pipeline, external steam supply pipeline, low-pressure bypass, condensing pipeline, feedwater pipeline and high-pressure exhaust pipeline when the unit is in normal operating conditions, and to control the shutdown of the high-pressure bypass and low-pressure bypass; when the unit is in abnormal operating conditions, and the turbine trips but the boiler is not shut down, it controls the connection of the high-pressure bypass, external steam supply pipeline, low-pressure bypass, condensing pipeline, feedwater pipeline and high-pressure exhaust pipeline, and shuts down the main steam pipeline and low-pressure exhaust pipeline.

2. The stable steam supply system based on the turbine tripping of a supercritical unit as described in claim 1, characterized in that, The reheater is also connected to the steam turbine via a medium-pressure steam supply pipeline; The thermal control unit is used to control the intermediate pressure steam supply pipeline to be shut off when the unit is in an abnormal operating condition and the turbine needs to be shut down without stopping the boiler; when the unit is in normal operating condition, it controls the opening of the intermediate pressure steam supply pipeline according to the steam flow generated by the reheater.

3. The stable steam supply system based on the turbine tripping of a supercritical unit as described in claim 1, characterized in that, The thermal control unit is also used to determine the target feedwater flow rate, target feedwater temperature, target temperature difference between main and reheat steam, target pressure and target temperature of main steam, and target pressure and target temperature of reheat steam based on the pressure and temperature requirements of the external steam supply. The boiler feedwater flow rate and feedwater temperature are controlled according to the target feedwater flow rate and target feedwater temperature; the main steam pressure and temperature are controlled according to the target main steam pressure and target temperature; the reheat steam pressure and temperature are controlled according to the target reheat steam pressure and target temperature; and the main reheat steam temperature difference is controlled according to the target main reheat steam temperature difference.

4. The stable steam supply system based on the supercritical unit's tripped turbine as described in claim 3, characterized in that, The high-pressure exhaust pipeline is also connected to the heater through a second-stage extraction pipeline; The thermal control unit is also used to control the opening of the high-pressure bypass pipeline according to the target feedwater temperature of the boiler, so as to control the feedwater temperature of the boiler at the target feedwater temperature.

5. The stable steam supply system based on the turbine tripping of a supercritical unit as described in claim 1, characterized in that, The thermal control unit also determines the target liquid level of the condenser based on the pressure and temperature requirements of the externally supplied steam, and controls the liquid level of the condenser according to the target liquid level.

6. The stable steam supply system based on the turbine tripping of a supercritical unit as described in claim 1, characterized in that, The external steam supply pipeline is also connected to the condenser via a steam supply bypass; The thermal control unit is used to control the steam supply bypass to be connected when the reheat steam pressure generated by the reheater is greater than the reheat steam target pressure; and to control the steam supply bypass to be disconnected when the reheat steam pressure generated by the reheater is less than or equal to the reheat steam target pressure.

7. The stable steam supply system based on the turbine tripping of a supercritical unit as described in claim 1, characterized in that, The condenser is also connected to the water storage tank via a water supply line, and the water storage tank is connected to the drain line. The thermal control unit is also used to determine the target liquid level of the water storage tank based on the pressure and temperature requirements of the external steam supply, and to control the opening of the drain pipe according to the target liquid level of the water storage tank, so as to keep the liquid level of the water storage tank at the target liquid level.

8. The stable steam supply system based on the turbine tripping of a supercritical unit as described in claim 1, characterized in that, The boiler flue gas outlet is connected to the flue gas pipeline, and a flue gas valve is installed in the flue gas pipeline. The boiler gas inlet is also connected to the ammonia supply pipeline. The thermal control unit is used to control the opening degree of the flue gas valve and the opening degree of the ammonia supply pipeline, so as to control the flue gas flow rate at the outlet of the flue gas pipeline within the target flue gas flow rate range.

9. The stable steam supply system based on the turbine tripping of a supercritical unit as described in claim 1, characterized in that, The high-pressure exhaust pipeline is also connected to the steam turbine via the shaft seal steam supply pipeline; The thermal control unit is used to control the opening of the shaft seal steam supply pipeline, and to control the shaft seal temperature and pressure of the steam turbine at the target shaft seal temperature and pressure.

10. A method for stable steam supply based on turbine tripping in supercritical units, characterized in that, include: When the unit is in normal operating condition, control the main steam pipeline, low-pressure exhaust pipeline, external steam supply pipeline, low-pressure bypass, condensate pipeline, feedwater pipeline and high-pressure exhaust pipeline to be connected, and control the high-pressure bypass and low-pressure bypass to be shut off. When the unit is in an abnormal operating condition and the turbine trips without shutting down the boiler, the high-pressure bypass, external steam supply pipeline, low-pressure bypass, condensate pipeline, feedwater pipeline and high-pressure exhaust pipeline are connected, while the main steam pipeline and low-pressure exhaust pipeline are shut off.

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