A method for starting and stopping peak load regulation of thermal power units under turbine bypass fault

Abstract

This invention discloses a start-up and shutdown peak-shaving method for thermal power units under turbine bypass faults, comprising the following steps: S1: Upon receiving the start-up and shutdown peak-shaving order, the unit load is reduced according to the procedures, and the pressure and temperature of the main steam and reheat steam are steadily reduced during the load reduction process; S2: The generator is disconnected without stopping the turbine or boiler; S3: After the generator is disconnected, the turbine maintains no-load operation, during which the main steam parameters on the boiler side are kept stable, awaiting the reconnection order; S4: After the reconnection order is issued, the unit is reconnected to the grid; S5: After the unit is reconnected to the grid, the unit load is increased to the target value according to the hot start-up procedure. This start-up and shutdown peak-shaving method avoids the problems of severe overheating of the boiler superheater and reheater heating surfaces and negative temperature difference start-up of the turbine, ensuring the safe start-up and shutdown of the unit and preventing damage to the unit.

Description

Technical Field

[0001] This invention belongs to the field of thermal power generation technology, specifically relating to a method for starting and stopping peak shaving of thermal power units under turbine bypass faults. Background Technology

[0002] To meet the requirements of energy conservation, emission reduction, and the absorption of new energy sources, coal-fired power plants often need to participate in deep peak shaving and start-up / shutdown peak shaving. The existing start-up / shutdown peak shaving process is as follows: 1. Upon receiving the dispatch order, prepare for shutdown; 2. Reduce the load to 0MW and shut down the unit normally: i.e., shut down the boiler, trip the turbine, and disconnect the generator; 3. Perform boiler ignition operation; 4. After successful boiler ignition, use the turbine bypass system to raise the temperature and pressure until the main steam temperature at the turbine inlet is 50-80℃ higher than the first-stage metal temperature of the turbine. Since the boiler cools much faster than the turbine, the boiler needs to start raising the temperature and pressure at least 3 hours before reconnection to the grid; 5. When the main steam temperature at the turbine inlet is more than 50℃ higher than the first-stage metal temperature of the turbine, and the main steam superheat is greater than 56℃, the turbine is tripped and started to run, increasing the speed to 3000r / min; 6. Upon receiving the reconnection dispatch order, perform generator and system grid connection operation; 7. After the unit's initial load warm-up is completed, increase the load to the target load value.

[0003] After the boiler is ignited, the heat generated by coal combustion continuously heats the superheater and reheater. Since the metal wall temperatures of the superheater and reheater cannot exceed their limits, sufficient steam flow is necessary for cooling in both systems. This steam circulation carries the heat to the turbine inlet, increasing the main steam temperature at the turbine inlet. The turbine bypass system (including high-pressure and low-pressure bypasses) provides a steam circulation channel for boiler heating and pressurization. The specific circulation flow is as follows: Boiler evaporation equipment -- Superheater -- Main steam pipeline -- High-pressure bypass -- Reheater inlet pipeline -- Reheater -- Reheater outlet pipeline -- Low-pressure bypass -- Condenser -- Boiler evaporation equipment. During this process, there is always steam flowing in the superheater and reheater for cooling, so they will not be damaged due to overheating. Therefore, the boiler can gradually increase the main steam temperature through combustion adjustment until the main steam temperature at the turbine inlet is more than 50°C higher than the first stage metal temperature of the turbine, and the main steam superheat is greater than 56°C, before starting the turbine. There is no need to start the turbine with a negative temperature difference (starting the turbine when the main steam temperature at the turbine inlet is lower than the turbine metal temperature).

[0004] When the turbine bypass system malfunctions or becomes unusable, after boiler ignition, the superheater can only maintain minimal steam flow using condensate drained from the turbine side pipes, while the reheater experiences no steam flow and is in a dry-burning state. Therefore, the boiler cannot increase the main steam temperature by increasing the fuel supply. Forcibly increasing the fuel supply will cause the superheater and reheater to overheat and be damaged. Without increasing the fuel supply, the main steam temperature at the turbine inlet will be significantly lower than the turbine's first-stage metal temperature, failing to meet the turbine's start-up temperature requirements. Forcibly starting the turbine with a negative temperature difference will damage the turbine due to the excessively large negative temperature difference, resulting in substantial economic losses.

[0005] In actual operation, the start-up and shutdown peak-shaving requirements necessitate an interval of only 6-8 hours between unit shutdown and reconnection to the grid. This necessitates hot or extremely hot turbine startup. However, in the event of a turbine bypass system failure or unavailability, starting and shutting down the thermal power unit for peak shaving will face significant challenges such as severe overheating of the boiler superheater and reheater surfaces, and turbine startup under negative temperature differences, potentially causing serious damage to the boiler and turbine. Therefore, it is necessary to develop a start-up and shutdown peak-shaving method for thermal power units under turbine bypass failure conditions. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a method for starting and stopping a thermal power unit under turbine bypass fault, so as to ensure the safe start-up and shutdown of the unit and avoid damage to the unit.

[0007] The present invention solves the above problems through the following technical means:

[0008] A method for starting and stopping peak load regulation of a thermal power unit under turbine bypass fault includes the following steps:

[0009] S1: After receiving the start-up and shutdown peak-shaving order, operate according to the procedures to reduce the unit load. During the load reduction process, steadily reduce the pressure and temperature of the unit's main steam and reheat steam.

[0010] S2: Disconnect the generator without stopping the steam turbine or boiler;

[0011] S3: After the generator is disconnected, the steam turbine maintains no-load operation, during which the main steam parameters on the boiler side remain stable, and waits for the dispatch order to reconnect to the grid;

[0012] S4: After the grid connection command is issued, the unit reconnects to the grid;

[0013] S5: After the unit is connected to the grid, increase the unit load to the target value according to the hot start-up procedure.

[0014] Furthermore, in S1, when the unit load drops to 5MW, the PCV valve at the superheater outlet is opened to discharge some steam, and the main steam pressure is controlled at 4.2±0.5Mpa, the main steam temperature is controlled at 460℃±5℃, the reheat steam temperature is controlled at 480℃±5℃, and the vacuum is maintained at -(90±2.0)Kpa.

[0015] Furthermore, in S1, the boiler combustion adjustment is strengthened, 3-4 small oil guns are put into operation, each with a flow rate of 0.2 tons, and 2-3 pulverizers are put into operation, with the pulverizers controlling the pulverizer feed at 10-20% opening.

[0016] Furthermore, in S3, during the no-load operation of the steam turbine, the main steam parameters on the boiler side are kept stable by adjusting combustion and regulating the boiler-side drain, the superheater outlet PCV valve, and the main and reheat steam pipeline drains.

[0017] Furthermore, in S3, the turbine body drain is turned off after 10 minutes, and then turned on for 5 minutes every hour thereafter, while the main and reheat steam pipeline drains are kept open.

[0018] Furthermore, in S3, the opening of the reheater flue gas damper is reduced to 10%, which controls the degree of contact between the flue gas at the tail end of the boiler and the reheater.

[0019] Furthermore, in S5, after the unit is connected to the grid, steam matching the temperature of the first stage metal of the turbine is first introduced to warm up the unit. After warming up, the superheater outlet PCV valve is closed, and the unit load is increased to the target value according to the procedure.

[0020] The beneficial effects of this invention are:

[0021] 1. When the load is reduced to 5MW, the superheater outlet PCV valve is opened to discharge some steam into the air. This not only ensures that there is always enough steam flow in the superheater to cool and protect it, but also ensures that the boiler maintains a certain heat load operation, thereby ensuring that the main steam temperature of the boiler is maintained above 460℃. In the early stage, the main steam slowly cools the metal parts of the turbine. In the later stage, the main steam temperature is close to the metal temperature of the turbine, which can maintain the safe operation of the turbine under no-load conditions.

[0022] 2. The steam turbine maintains no-load operation, and the exhaust steam enters the reheater to ensure that there is steam flow in the reheater to cool it;

[0023] 3. Further, reduce the opening of the reheater flue gas damper to 10%. This flue gas damper controls the contact between the flue gas at the tail of the boiler and the reheater, reduces the flow of flue gas on the reheater side, and prevents the reheater wall temperature from exceeding the limit.

[0024] 4. Maintain the main steam pressure at 4.2±0.5 MPa, the main steam temperature at 460℃±5℃, the reheat steam temperature at 480℃±5℃, and the vacuum at -(90±2.0) kPa, and keep them stable. Main functions: 1) If the steam parameters drop below these levels, it will cause severe water erosion of the turbine's last-stage blades and affect the turbine's lifespan; 2) Maintaining lower steam parameters and a lower vacuum can increase the steam intake to 24 tons / hour during no-load operation of the turbine (an increase of 10 tons / hour compared to normal no-load operation). The larger steam intake is conducive to uniform heating and cooling of all parts of the turbine, preventing internal dynamic and static friction caused by uneven expansion of various parts of the turbine. At the same time, it increases the steam flow in the reheater, which is beneficial to protecting the reheater. Detailed Implementation

[0025] The present invention will now be described in detail. The method for starting and stopping peak load regulation of thermal power units under turbine bypass faults of the present invention includes the following steps:

[0026] S1: After receiving the start-up and shutdown peak-shaving order, operate according to the procedures to reduce the unit load. During the load reduction process, steadily reduce the pressure and temperature of the unit's main steam and reheat steam.

[0027] S2: Disconnect the generator without stopping the steam turbine or boiler;

[0028] S3: After the generator is disconnected, the steam turbine maintains no-load operation, during which the main steam parameters on the boiler side remain stable, and waits for the dispatch order to reconnect to the grid;

[0029] S4: After the grid connection command is issued, the unit reconnects to the grid;

[0030] S5: After the unit is connected to the grid, increase the unit load to the target value according to the hot start-up procedure.

[0031] In S1, when the unit load drops to 5MW, the PCV valve at the superheater outlet is opened to discharge some steam, and the main steam pressure is controlled at 4.2±0.5Mpa, the main steam temperature is controlled at 460℃±5℃, the reheat steam temperature is controlled at 480℃±5℃, and the vacuum is maintained at -(90±2.0)Kpa.

[0032] In S1, strengthen boiler combustion adjustment, put 3-4 small oil guns into operation, each with a flow rate of 0.2 tons, and put 2-3 pulverizers into operation, controlling the pulverizer feed at 10-20% opening.

[0033] In S3, during the no-load operation of the steam turbine, the main steam parameters on the boiler side are kept stable by adjusting the combustion and regulating the boiler-side drain, the superheater outlet PCV valve, and the main and reheat steam pipeline drains.

[0034] In S3, the turbine body drain is turned off after 10 minutes, and then turned on for 5 minutes every hour thereafter. The main and reheat steam pipeline drains are kept open.

[0035] In S3, the opening of the reheater flue gas damper is reduced to 10%. This flue gas damper controls the degree of contact between the flue gas at the tail end of the boiler and the reheater.

[0036] In S5, after the unit is connected to the grid, steam matching the temperature of the first stage metal of the turbine is first introduced to warm up the unit. After warming up, the superheater outlet PCV valve is closed, and the unit load is increased to the target value according to the procedure.

[0037] During load reduction, the shaft seal pressure should be kept normal, and parameters such as turbine vibration, cylinder temperature difference, high and low pressure cylinder exhaust temperature, oil temperature, and oil pressure should be closely monitored. When the cylinder temperature difference increases, measures such as switching on / off drains, activating / deactivating the high-pressure heater, and controlling the rate of steam temperature change should be taken to prevent the turbine from receiving cold steam and cold water during load reduction.

[0038] Specific operating steps for disconnecting generators using the method of not shutting down the power plant and boiler:

[0039] Before shutting down, request to disable generator protection;

[0040] Start the main unit AC lubrication oil pump and the backup oil pump, reduce the generator reactive power to 0MVar, quickly reduce the unit load to 0MW, and immediately disconnect the generator;

[0041] After disconnection, the electrical equipment was checked and found to be operating normally, and the generator-transformer unit remained in normal hot standby status.

[0042] After disconnection, check if the shaft seal pressure is normal. The turbine should be maintained at 3000 RPM, and the boiler should maintain stable steam temperature and pressure. When the turbine speed is stable at 3000 RPM, engage the interlock of the backup oil pump and the main engine AC lubrication oil pump, and then shut down the backup oil pump and the main engine AC lubrication oil pump.

[0043] Precautions during no-load operation:

[0044] 1. After the generator is disconnected, maintain the turbine shaft seal and vacuum stability, and strengthen the monitoring and control of parameters such as turbine vibration, cylinder temperature difference, high and low pressure cylinder exhaust temperature, oil temperature, and oil pressure. The turbine body drain should be opened for 10 minutes and then closed. Thereafter, the drain should be opened for 5 minutes every hour. The main and reheat steam pipeline drains should be kept open to prevent the turbine from receiving cold steam or cold water during no-load operation.

[0045] 2. During the no-load operation of the steam turbine, the main steam parameters on the boiler side should be stabilized as much as possible, and the minimum main steam temperature on the boiler side should be controlled to be no less than 460℃ to reduce the cooling of the cylinder; and the monitoring and control of the superheater and reheater wall temperatures should be strengthened.

[0046] Upon receiving the reconnection order, reset the current alarm on the generator protection panel, activate generator protection, and complete the grid connection operation on the DCS according to the grid connection procedure. After the unit is connected to the grid, when it is carrying an initial load of 15MW, close the superheater outlet PCV valve.

[0047] Precautions during the load increase process:

[0048] 1. During the low-load warm-up process of the steam turbine, the steam temperature and pressure parameters are stable, and the vacuum is maintained at around -90 kPa to ensure the steam flow and warm-up effect.

[0049] 2. For units below 90MW, it is recommended to reduce the amount of desuperheating water in operation. The order of desuperheating water operation is to first operate the primary desuperheating water, then the secondary desuperheating water. If secondary desuperheating water is operated, the steam temperature after the secondary desuperheating water should not be lower than 420 degrees Celsius. The desuperheating water flow rate should be uniform to avoid fluctuations in flow rate that could cause sudden increases or decreases in steam temperature.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for starting and stopping peak load regulation of a thermal power unit under turbine bypass fault, characterized in that, Includes the following steps: S1: After receiving the start-up and shutdown peak-shaving order, reduce the unit load according to the procedure. During the load reduction process, steadily reduce the pressure and temperature of the main steam and reheat steam of the unit. In S1, when the unit load drops to 5MW, open the PCV valve at the superheater outlet to discharge part of the steam, and control the main steam pressure at 4.2±0.5Mpa, the main steam temperature at 460℃±5℃, the reheat steam temperature at 480℃±5℃, and the vacuum at -(90±2.0)Kpa. S2: Disconnect the generator without stopping the steam turbine or boiler; S3: After the generator is disconnected, the steam turbine maintains no-load operation, during which the main steam parameters on the boiler side remain stable, and waits for the dispatch order to reconnect to the grid; S4: After the grid connection command is issued, the unit reconnects to the grid; S5: After the unit is connected to the grid, increase the unit load to the target value according to the hot start-up procedure.

2. The start-up and peak-shaving method for thermal power units under turbine bypass faults according to claim 1, characterized in that, In S1, strengthen boiler combustion adjustment, put 3-4 small oil guns into operation, each with a flow rate of 0.2 tons, and put 2-3 pulverizers into operation, controlling the pulverizer feed at 10-20% opening.

3. The start-up and peak-shaving method for thermal power units under turbine bypass faults according to claim 1, characterized in that, In S3, during the no-load operation of the steam turbine, the main steam parameters on the boiler side are kept stable by adjusting the combustion and regulating the boiler-side drain, the superheater outlet PCV valve, and the main and reheat steam pipeline drains.

4. The start-up and peak-shaving method for thermal power units under turbine bypass faults according to claim 1, characterized in that, In S3, the turbine body drain is turned off after 10 minutes, and then turned on for 5 minutes every hour thereafter. The main and reheat steam pipeline drains are kept open.

5. The start-up and peak-shaving method for thermal power units under turbine bypass faults according to claim 1, characterized in that, In S3, the opening of the reheater flue gas damper is reduced to 10%. This flue gas damper controls the degree of contact between the flue gas at the tail end of the boiler and the reheater.

6. The start-up and peak-shaving method for thermal power units under turbine bypass faults according to claim 1, characterized in that, In S5, after the unit is connected to the grid, steam matching the temperature of the first stage metal of the turbine is first introduced to warm up the unit. After warming up, the superheater outlet PCV valve is closed, and the unit load is increased to the target value according to the procedure.