A method for improving the hydrodynamic performance of a vertical water-cooled wall by deep peak shaving

Abstract

The present invention provides a method for improving the hydrodynamic performance of a vertical water-cooled wall during deep peak shaving, which includes the following steps: The unit load enters the second-stage peak shaving; The small overflow manual valve is opened; During the peak period, the exhaust steam temperature of the low-pressure cylinder is monitored; During the deep peak shaving of the unit, the operation conditions of the low-pressure heaters and high-pressure heaters are closely monitored; When the unit load drops to 300 MW, the secondary auxiliary air dampers of the pulverized coal burners corresponding to each operating coal pulverizing system adopt a waist-shaped air distribution method; In cooperation with the overhaul, the small overflow control valve is modified by installing a speed reducer to increase the torque and prevent overcurrent jamming, and the water level control logic of the storage tank after starting the furnace water pump is set to ensure the safe and stable operation of the furnace water pump. The present invention solves the problem that the feed water flow is prone to divergence during deep peak shaving, ensures the safe operation of the unit during deep peak shaving, significantly improves the hydrodynamic uniformity, significantly improves the hydrodynamic performance, and reduces the thermal stress of the vertical water-cooled wall.

Description

Technical Field

[0001] The present invention relates to the technical field of energy conservation, and in particular to a method for improving the water dynamics of a vertical water wall by deep peak shaving. Background Art

[0002] The boilers of the 2×670MW supercritical unit in the power plant are Benson once-through boilers with supercritical parameters manufactured by Harbin Boiler Co., Ltd. The steam turbines and their auxiliary equipment of the 2×670MW domestic supercritical coal-fired units in the power plant are supercritical, once-through reheat, single-shaft, three-cylinder, and four-exhaust condensing steam turbines. The feed water system is equipped with two steam-driven feed water pumps with a capacity of 50% BMCR and one start-up electric fixed-speed feed water pump with a capacity of 30% BMCR. The boiler start-up system is equipped with an in-built start-up separation system with a furnace water circulation pump, which consists of a steam-water separator, a storage tank, a furnace water start-up circulation pump, a water level control valve, a stop valve, a drain expansion vessel, a drain tank, a boiler start-up drain pump, pipes, and accessories. The furnace water circulation pump is put into operation when the start-up and stop conditions are lower than the Benson load (35% BMCR). The water in the storage tank is sent into the inlet header of the economizer by the furnace water circulation pump, and the excess water is discharged into the drain expansion vessel through the overflow pipe. The living space of thermal power units is being compressed year by year, and deep peak shaving has become the norm during the low-load period of the night grid. It is necessary to change the peak shaving strategy of the unit and improve the deep peak shaving ability.

[0003] Through technical transformation, the unit load is gradually reduced from 250MW to 165MW for stable operation. It is planned to reduce the unit load to 110MW. During deep peak shaving, the flow rate at the inlet of the economizer, which cannot be avoided, cannot be guaranteed, increasing the probability of transverse cracks on the fire side of the vertical water wall due to fatigue stress. Therefore, it is necessary to optimize the feed water control strategy. Improve the water dynamics limitations: 1. It is difficult to control the water level in the storage tank at low loads. 2. During deep peak shaving, the temperature difference of the vertical water wall is relatively large, and the probability of transverse cracks caused by uneven expansion increases significantly. 3. The water dynamics deteriorates due to the low feed water flow rate. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for improving the water dynamics of a vertical water wall by deep peak shaving, which solves the problem that the feed water flow rate is prone to divergence during deep peak shaving, ensures the safe operation of the unit during deep peak shaving, significantly improves the water dynamics uniformity, significantly improves the water dynamics, reduces the thermal stress of the vertical water wall, and reduces the probability of transverse cracks on the fire side of the water wall caused by fatigue stress.

[0005] According to the purpose of the present invention, a method for improving the water dynamics of a vertical water wall by deep peak shaving is provided, including the following steps:

[0006] S1, when the unit load enters the second-stage peak shaving, the steam turbine is controlled by a single valve, the cold reheat has taken over the auxiliary steam, the pressure is maintained not lower than 0.45 Mpa, and the steam supply source of the small steam turbine is switched to the auxiliary steam;

[0007] S2. The small overflow manual valve is opened, and the opening of the small overflow electric valve is permitted.

[0008] S3. During the peak shaving period, closely monitor the exhaust steam temperature of the low-pressure cylinder.

[0009] S4. During the deep peak shaving of the unit, closely monitor the operation of the deaerator, condenser, low-pressure heaters, and high-pressure heaters to ensure normal water levels.

[0010] S5. When the unit load drops to 300 MW, adopt the "waist-shaped" air distribution method for the secondary auxiliary air dampers of the pulverized coal burners corresponding to each operating coal pulverizing system, and fully close the burnout air to ensure a high enough temperature in the combustion area and normal combustion of pulverized coal.

[0011] S6. Cooperate with maintenance to transform the small overflow control valve, install a speed reducer to increase the torque, prevent overcurrent jamming, and start the control logic of the water level in the storage tank after the boiler water pump to ensure the safe and stable operation of the boiler water pump.

[0012] Furthermore, for deep peak shaving, it is required that the steam-driven feed pump operates stably, the boiler water dynamics is good, the wall temperature of the boiler heating surface does not exceed the limit, and it can operate stably for a long time.

[0013] Furthermore, when the steam turbine adopts single-valve control, the steam-driven feed pump recirculation should be opened, and the turbine-driven feed pump should have a speed regulation range.

[0014] Furthermore, when the low-pressure cylinder of the steam turbine operates with zero output, it should meet the heating steam extraction volume, and the TSI parameters of the unit should not change significantly.

[0015] Furthermore, in S3, by adjusting the unit vacuum and regulating the offset of the inlet butterfly valve of the low-pressure cylinder to reasonably distribute the inlet steam volume of the two low-pressure cylinders, the exhaust steam temperature of the low-pressure cylinder is controlled not to exceed 50 °C.

[0016] Furthermore, if it cannot be controlled and the temperature is greater than 50 °C, the low-pressure cylinder spray water is put into operation, and the main engine TSI screen is closely monitored during the spray water operation.

[0017] Furthermore, the monitoring of the main engine TSI screen includes data on low expansion, vibration, and axial displacement.

[0018] Furthermore, in S3, closely monitor the change of the exhaust steam temperature of the low-pressure cylinder. If an abnormal rise is found, the unit load should be increased in time, and the inlet control valve of the low-pressure cylinder should be opened wider.

[0019] Furthermore, in S5, the opening of the sandwich air of the pulverized coal burners corresponding to each operating coal pulverizing system is controlled within the range of 5% - 10% to reduce the primary air stiffness, ensure early ignition, and maintain a good combustion condition in the furnace.

[0020] Furthermore, in S6, the reduction ratio of the speed reducer added to the small overflow control valve is 1:40.

[0021] The technical solution of the present invention is applicable to a 600MW unit with a furnace circulating pump for deep peak shaving. Under the condition of meeting the deep peak shaving operation, in order to better enable the vertical water wall to have good hydrodynamic performance, the temperature difference between the walls of the vertical water wall is significantly reduced, the temperature deviation of the water on each wall is decreased, the hydrodynamic uniformity is significantly improved, the hydrodynamic performance is significantly improved, the thermal stress of the vertical water wall is reduced, so that the probability of transverse cracks on the fire side of the water wall caused by fatigue stress is reduced, and the safety of boiler operation is improved. The safe operation time of the boiler is increased. Detailed implementation manners

[0022] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs.

[0023] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular forms also include the plural forms. In addition, 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.

[0024] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0025] Embodiment 1

[0026] A method for improving the hydrodynamic performance of the vertical water wall during deep peak shaving includes the following steps:

[0027] S1. Prepare well before starting work: The unit load enters the second gear for peak shaving, the steam turbine is controlled by a single valve, the cold reheat has received auxiliary steam, and the pressure is maintained not lower than 0.45 Mpa. The steam supply source of the small steam turbine is switched to the auxiliary steam;

[0028] S2. Open the small overflow manual valve, the opening of the small overflow electric valve is allowed, and the local personnel of the small overflow regulating valve keep in touch with the front panel.

[0029] During S3, closely monitor the exhaust steam temperature of the low-pressure cylinder during the peak period. The exhaust steam temperature of the low-pressure cylinder can be controlled not to exceed 50°C by adjusting the unit vacuum and regulating the bias of the inlet butterfly valve of the low-pressure cylinder to reasonably distribute the inlet steam volume of the two low-pressure cylinders. If it cannot be controlled and the temperature is greater than 50°C, the low-pressure cylinder spray water can be put into operation. During the spray water operation, strengthen the monitoring of the main engine TSI screen, such as low expansion, vibration, axial displacement, etc.

[0030] During S4, during the deep peak shaving period of the unit, closely monitor the operation conditions of the deaerator, condenser, low-pressure heaters, and high-pressure heaters to ensure normal water levels and prevent abnormal water levels. Closely monitor the change of the exhaust steam temperature of the low-pressure cylinder. If an abnormal rise is found, increase the unit load in a timely manner and open the inlet regulating valve of the low-pressure cylinder wider.

[0031] When the unit load drops to 300 MW, adopt the "waist-shaped" air distribution method for the secondary auxiliary air dampers of the pulverized coal burners corresponding to each operating pulverizing system. All burnout air is closed (try to open as little as possible during adjustment) to ensure a high enough temperature in the combustion area and ensure normal combustion of pulverized coal. Control the opening of the sandwich air of the pulverized coal burners corresponding to each operating pulverizing system within the range of 5% - 10% to reduce the rigidity of the primary air, ensure early ignition, and maintain a good combustion condition in the furnace.

[0032] To improve the deep peak shaving ability of the unit, according to the unit load limit conditions, change the deep peak shaving mode strategy and implement the following specific implementation plans: Cooperate with maintenance to transform the small overflow regulating valve, install a reducer to increase the torque and prevent overcurrent jamming. Conduct a special analysis on the water level control logic of the storage tank after starting the boiler water pump to ensure the safe and stable operation of the boiler water pump.

[0033] For deep peak shaving in this embodiment, it is required that the steam-driven feed pump operates stably, the boiler hydrodynamic conditions are good, the wall temperature of the boiler heating surface does not exceed the limit, and it can operate stably for a long time.

[0034] When the steam turbine adopts single-valve control in this embodiment, the steam-driven feed pump recirculation should be opened to ensure that the turbine-driven feed pump has a certain speed adjustment space, so that the feed water flow has a certain adjustment function to adapt to load changes.

[0035] This embodiment requires the zero output operation of the low-pressure cylinder of the steam turbine to meet the heating extraction steam volume, and there is no obvious change in the TSI parameters of the unit.

[0036] Embodiment 2

[0037] To increase the unit's deep peak shaving capacity, improve the hydrodynamic performance of the vertical water walls, and change the unit's deep peak shaving operation mode, a special analysis was conducted on the water level control logic of the storage tank behind the start-up boiler water pump. At the same time, relevant technical transformations were carried out on the small overflow control valve, adding a speed reducer (reduction ratio 1:40) to the small overflow control valve to ensure smooth operation of the small overflow. The operation department adopted the deep peak shaving start-up boiler water circulation pump and compared the wall temperature changes during the original peak shaving. The conclusions are as follows:

[0038] 1. Under the two working conditions, the temperature non-uniformity of the vertical water walls on each side increases in condition ①, especially at 19:00, 21:00, and 25:00, with obvious fluctuations. The temperature uniformity of each water wall improves significantly in condition ②. For the points at 19:00, 21:00, and 25:00 with large fluctuations, there are no fluctuations, and the fluctuations of the other 9 measuring points are small. The average temperature deviation drops from 4.78 °C to 2.56 °C.

[0039] 2. Under the two working conditions, the temperature deviation of each vertical water wall in condition ① and the temperature deviation of each wall in condition ② decrease significantly, and the average temperature deviation drops from 3.25 °C to 1.98 °C.

[0040] 3. Under the two working conditions, the temperature uniformity of the adjacent front wall water wall and the left wall water wall in condition ① and condition ② improves. The temperature difference between the front wall and the left wall is 4.38 °C in condition ① and 0.31 °C in condition ②, and the temperature difference between adjacent walls decreases significantly.

[0041] 4. Under the two working conditions, the temperature uniformity of the adjacent front wall water wall and the right wall water wall in condition ① and condition ② improves. The temperature difference between the front wall and the right wall is 1.97 °C in condition ① and 0.97 °C between the front wall and the left wall in condition ②, and the temperature difference between adjacent walls decreases significantly.

[0042] 5. Under the two working conditions, the temperature uniformity of the adjacent rear wall water wall and the right wall water wall in condition ① and condition ② improves. The temperature difference between the front wall and the right wall is 3.94 °C in condition ① and 1.89 °C between the front wall and the left wall in condition ②, and the temperature difference between adjacent walls decreases significantly.

[0043] 6. Under the two working conditions, the temperature uniformity of the adjacent rear wall water wall and the left wall water wall in condition ① and condition ② improves. The temperature difference between the rear wall and the left wall is 1.53 °C in condition ① and 0.61 °C between the front wall and the left wall in condition ②, and the temperature difference between adjacent walls decreases significantly.

[0044] Under the condition of meeting the deep peak shaving, in order to better ensure that the vertical water walls have good hydrodynamic performance, through the comparison of the above 6 working conditions, the temperature difference between the walls of the vertical water walls behind the start-up boiler water pump decreases significantly, the temperature deviation of each wall of the water decreases, the hydrodynamic uniformity is significantly improved, the thermal stress of the vertical water walls is reduced, the probability of transverse cracks on the fire side of the water walls caused by fatigue stress is reduced, and the safety of boiler operation is improved.

[0045] The present invention solves the problem that the unit load is limited to 185 MW during deep peak shaving, and the adjustable peak shaving is 110 MW. It solves the problem that the feed water flow rate is prone to divergence during deep peak shaving, ensuring the safe operation of the unit during deep peak shaving. Under the condition of deep peak shaving, in order to better enable the vertical water wall to have good hydrodynamic performance, the temperature difference between each wall of the vertical water wall is significantly reduced, the temperature deviation of the water on each wall is reduced, the hydrodynamic uniformity is significantly improved, the hydrodynamic performance is significantly improved, the thermal stress of the vertical water wall is reduced, and the probability of transverse cracks on the fire side of the water wall caused by fatigue stress is reduced.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for improving the hydrodynamic performance of a vertical water-cooled wall during deep peak shaving, characterized in that, it includes the following steps: S1. When the unit load enters the second-stage peak shaving, the turbine is controlled by a single valve. The cold reheat steam has taken over the auxiliary steam, and the pressure is maintained not lower than 0.45 Mpa. The steam supply source of the small steam turbine is switched to the auxiliary steam; S2. The small overflow manual valve is opened, and the small overflow electric valve is allowed to open; S3. During peak shaving, closely monitor the exhaust steam temperature of the low-pressure cylinder; S4. During the deep peak shaving of the unit, closely monitor the operation conditions of the deaerator, condenser, low-pressure heaters, and high-pressure heaters to ensure normal water levels; S5. When the unit load drops to 300 MW, adopt a "waist-shaped" air distribution method for the secondary auxiliary air doors of the pulverized coal burners corresponding to each operating coal pulverizing system. All burnout air doors are closed to ensure a sufficiently high temperature in the combustion area and ensure normal combustion of pulverized coal; S6. Cooperate with maintenance to transform the small overflow regulating valve, install a speed reducer to increase the torque, prevent overcurrent jamming, and start the control logic of the water level in the storage tank after the boiler water pump to ensure the safe and stable operation of the boiler water pump.

2. The method for improving the hydrodynamic performance of a vertical water-cooled wall during deep peak shaving according to claim 1, characterized in that, the deep peak shaving requires stable operation of the steam-driven feed pump, good boiler hydrodynamic conditions, no over-temperature of the boiler heating surface wall temperature, and the ability to operate stably for a long time.

3. The method for improving the hydrodynamic performance of a vertical water-cooled wall during deep peak shaving according to claim 1, characterized in that, when the steam turbine is controlled by a single valve, the steam-driven feed pump recirculation is opened, and the steam-driven feed pump for the feed water pump has a speed regulation space.

4. The method for improving the hydrodynamic performance of a vertical water-cooled wall during deep peak shaving according to claim 1, characterized in that, the low-pressure cylinder of the steam turbine operates with zero output, meets the heating steam extraction volume, and there is no obvious change in the unit's TSI parameters.

5. The method for improving the hydrodynamic performance of a vertical water-cooled wall during deep peak shaving according to claim 1, characterized in that, in S3, by adjusting the unit vacuum and regulating the bias of the inlet butterfly valve of the low-pressure cylinder to reasonably distribute the inlet steam volume of the two low-pressure cylinders, the exhaust steam temperature of the low-pressure cylinder is controlled not to exceed 50 °C.

6. The method for improving the hydrodynamic performance of a vertical water-cooled wall during deep peak shaving according to claim 5, characterized in that, in S3, if the temperature cannot be controlled not to exceed 50 °C, when the temperature is greater than 50 °C, the low-pressure cylinder spray water is put into operation, and the monitoring of the main engine TSI screen is strengthened during the spray water operation.

7. The method for improving the hydrodynamic performance of a vertical water-cooled wall during deep peak shaving according to claim 6, characterized in that, the monitoring of the main engine TSI screen in S3 includes low expansion, vibration, and axial displacement data.

8. The method for improving the hydrodynamic performance of a vertical water-cooled wall during deep peak shaving according to claim 1, characterized in that, in S3, closely monitor the change of the exhaust steam temperature of the low-pressure cylinder. If an abnormal rise is found, the unit load is increased in time, and the inlet regulating valve of the low-pressure cylinder is opened wider.

9. The method for improving the hydrodynamic performance of a vertical water-cooled wall during deep peak shaving according to claim 1, characterized in that, in S5, the opening of the sandwich air of the pulverized coal burners corresponding to each operating coal pulverizing system is controlled within the range of 5% - 10%, reducing the rigidity of the primary air, ensuring early ignition, and maintaining a better combustion condition in the furnace.

10. The method for improving the hydrodynamic performance of the vertical water-cooled wall by deep peak shaving according to claim 1, characterized in that, in S6, the reduction ratio of the reducer added to the small overflow valve is 1:40.