A steam-driven starting and mode switching method for a steam-electric dual-driven unit

Abstract

The present invention relates to a steam-driven start-up and mode switching method for a steam-electric dual-drive unit, wherein the steam-electric dual-drive unit includes a small steam turbine, an asynchronous motor and an induced draft fan, and the method includes the following steps: step S1, optimizing the control strategy of the small steam turbine, improving the conditions for allowing the lock to be locked, and having the function of independently running the small steam turbine; step S2, subdividing the protection type of the induced draft fan, and optimizing the related logic of the small steam turbine; step S3, comprehensively judging the operating state of the induced draft fan; step S4, optimizing the valve control mode of the small steam turbine, newly setting the valve position control mode of the small steam turbine, improving the speed control strategy, and adding the low speed protection function; step S5, designing the control scheme when the induced draft fan motor trips and switches to the pure steam drive mode, and needs to be restored online. Compared with the prior art, the present invention has the advantages of being able to improve the reliability of the power source of the suction fan of this type of unit, flexible suction fan starting mode, reasonably reducing the small machine protection action, and reducing the probability of triggering the unit suction fan RB.

Description

Technical Field

[0001] The invention relates to the field of automatic control of thermal power generating sets, and in particular to a steam-driven starting and mode switching method for a steam-electric dual-driven set. Background Art

[0002] As an important auxiliary machine of thermal power plants, suction fans have always been one of the equipment with the largest power consumption. Saving energy and reducing consumption, and reasonably reducing the power consumption rate of thermal power plants are important ways to improve the economic benefits of power generation companies. Among them, the application of steam-electric dual-drive suction fans has become one of the important means to reduce the power consumption rate of thermal power plants.

[0003] Different from the steam-driven suction fan technology, in the existing steam-electric dual-drive technology, the suction fan control mode designs are: pure electric drive, steam-electric dual drive, steam-driven power generation and steam-driven mode. The design chooses the electric drive mode to start, that is, when starting, the small steam turbine (hereinafter referred to as the small machine) supporting the suction fan is disconnected from the asynchronous motor and the suction fan. The asynchronous motor is powered by the factory power and started as an electric motor to drive the fan to run stably. At the same time, the small machine slowly increases the speed to near the synchronous speed and then runs in parallel with the motor and fan. Driven by the small machine, the speed of the asynchronous motor increases steadily, and after exceeding the synchronous speed, it runs as a generator. At the same time, the design directly switches to pure electric drive after the small machine trips, and the tripping of the suction fan motor directly interlocks the tripping of the small machine. There are problems that need to be solved urgently, and the working conditions are as follows:

[0004] 1. The design does not include the startup and operation of the suction fan in pure steam drive mode, nor does it include the plan to switch to other operation modes online after steam drive startup.

[0005] (1) During the unit startup phase, the suction fan did not consider the function of first starting the small machine. If there is a non-mechanical fault in the suction fan electrical switch, but it does not affect the safety of the fan shaft system, the suction fan cannot be started, affecting the commissioning of the wind and smoke system and even the normal startup process of the unit.

[0006] (2) During the unit commissioning and maintenance phase, the adjustment and testing of the small unit is involved. According to the existing design, the small unit must wait until the relevant work of the suction fan motor is completed, the air and smoke system of the unit is randomly started, and the steam source parameters of the small unit are met before the work can be carried out. In the case where there is a spare steam source that can meet the steam source requirements of the small unit, it will not only waste a lot of time, but also increase the risk of online operation.

[0007] 2. The control strategy of the small machine tripping due to the failure of the suction fan motor is not perfect

[0008] Existing settings: When the suction fan electrical switch is off, the suction fan small unit will be tripped. In actual operation, it is not only easy to trigger the small unit to trip, but also increases the probability of the suction fan RB action.

[0009] The type of protection related to the suction fan motor is not distinguished. For electrical faults or tripping signals that do not affect the operation of the suction fan shaft system, after the suction fan electrical switch is tripped, the pure steam drive mode can be maintained in theory, that is, a small machine is used to drive the suction fan. However, there is no relevant supporting design at present. Summary of the invention

[0010] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a steam-driven starting and mode switching method for a steam-electric dual-driven unit.

[0011] The purpose of the present invention can be achieved by the following technical solutions:

[0012] According to one aspect of the present invention, a method for steam-driven starting and mode switching of a steam-electric dual-drive unit is provided, wherein the steam-electric dual-drive unit comprises a small steam turbine, an asynchronous motor and an induced draft fan, and the method comprises the following steps:

[0013] Step S1, optimizing the control strategy of the small steam turbine, improving the conditions for allowing the lock to be engaged, and having the function of independently starting the small steam turbine;

[0014] Step S2, subdividing the induced draft fan protection type and optimizing the small steam turbine related logic;

[0015] Step S3, comprehensively judging the operation status of the induced draft fan;

[0016] Step S4, optimizing the small steam turbine valve control mode, setting up a new small steam turbine valve position control mode, improving the speed control strategy, and adding a low speed protection function;

[0017] Step S5, designing a control scheme for when the induced draft fan motor trips and switches to pure steam drive mode and needs to be restored online.

[0018] As a preferred technical solution, the conditions for allowing the lock to be engaged in step S1 are improved to have the function of independently starting the small steam turbine as follows:

[0019] One of the conditions in the lock-in condition, "the suction fan is already running", is removed, that is, the small steam turbine is allowed to start without judging whether the suction fan is running, thus optimizing the preconditions for the start-up of the small steam turbine.

[0020] As a preferred technical solution, the optimization logic related to the small steam turbine in step S2 includes:

[0021] S201) For mechanical faults of the shaft system, the small steam turbine needs to be tripped after the induced draft fan switch is tripped. If such fault signal exists, the small steam turbine is not allowed to start;

[0022] S202) For electrical faults that do not affect the operation of the shaft system, after the induced draft fan switch is tripped, the pure steam drive mode is maintained. If such fault signal exists, the small machine is allowed to start.

[0023] As a preferred technical solution, the mechanical faults of the shaft system in S201) include faults of the high-speed shaft, the low-speed shaft, and the gearbox, wherein the high-speed shaft is the output shaft of the small steam turbine and the low-speed shaft is the output shaft of the asynchronous motor.

[0024] As a preferred technical solution, the electrical fault in S202) includes main transformer fault, bus fault, generator fault and induced draft fan motor electrical equipment fault.

[0025] As a preferred technical solution, the step S3 of comprehensively judging the operation status of the induced draft fan is specifically as follows:

[0026] The operating status of the induced draft fan is comprehensively judged based on the status of the induced draft fan motor incoming line switch, clutch engagement, tripping signal, steam drive mode and speed of the small steam turbine operating status signal.

[0027] As a preferred technical solution, the step S4 optimizes the small steam turbine valve control mode, and the newly set small steam turbine valve position control mode is specifically:

[0028] S401) In the steam-driven power generation mode, the small steam turbine regulating valve overrides and automatically and quickly closes to the set value, and at the same time, switches to the pure steam-driven mode;

[0029] S402) In the steam-electric dual drive mode, if the small steam turbine regulating valve is throttled, it will be instantly opened to the set value, and at the same time, it will be switched to the pure steam drive mode.

[0030] As a preferred technical solution, the step S5 is specifically as follows:

[0031] When the induced draft fan motor trip ends and needs to be restored online in pure steam drive mode, there are two control methods:

[0032] Method 1: Steam drive-pure electric drive-steam-electric dual drive-steam drive power generation;

[0033] Method 2: Steam drive - steam-electric dual drive - steam drive power generation method.

[0034] As a preferred technical solution, the method 1 specifically comprises the following steps:

[0035] Step 5011: Under the steam drive mode, control the speed of the small steam turbine to be close to the synchronous speed, slightly lower than the synchronous speed;

[0036] Step 5012, the induced draft fan electrical switch is closed to switch to pure electric drive mode;

[0037] Step 5013, gradually increase the speed of the small steam turbine to the meshing speed, the clutch automatically meshes the small steam turbine with the asynchronous motor, and the unit is switched from pure electric drive to steam-electric dual drive mode;

[0038] Step 5014, gradually open the large and small steam turbine regulating valves to increase the motor power output, and the asynchronous motor switches to generator operation. At this time, the small steam turbine drives the asynchronous motor and the induced draft fan to enter the steam-driven power generation mode, completing online recovery.

[0039] As a preferred technical solution, the second method specifically comprises the following steps:

[0040] Step 5021, in steam drive mode, control the speed of the small steam turbine to near the synchronous speed, and stabilize it slightly higher than the synchronous speed;

[0041] Step 5022, the induced draft fan electrical switch is closed, the clutch is engaged, and the fan is switched to steam-electric dual drive or steam drive power generation mode;

[0042] Step 5023, gradually open the large and small turbine regulating valves to increase the motor power output and complete online recovery.

[0043] Compared with the prior art, the present invention has the following advantages:

[0044] 1. The present invention is equipped with a separate small steam turbine start-up function in the non-start-up stage of the unit; a flexible starting mode is added, so that the steam-electric dual-drive induced draft fan unit can choose electric drive start or directly start the induced draft fan system by the matching induced draft fan small unit; the start-up time of the wind and smoke system is saved and the safe operation level of the unit is improved.

[0045] 2. The present invention refines the control strategy of the induced draft fan protection and small unit tripping, reasonably reduces the frequency of small unit protection action, and reduces the probability of triggering the unit RB.

[0046] 3. The present invention adds a control method for switching the induced draft fan to a pure steam drive mode without stopping the induced draft fan when a non-mechanical fault occurs in the induced draft fan motor.

[0047] 4. The present invention adds a control scheme for online recovery to the steam-electric dual drive or steam-driven power generation mode after the induced draft fan motor fails and switches to the pure steam-driven mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a schematic diagram of the steam-electric dual-drive arrangement of the induced draft fan;

[0049] Figure 2 A schematic diagram of mode switching in the gas-electric dual-drive mode of the present invention;

[0050] Figure 3 It is a schematic diagram of mode switching in the steam-driven power generation mode of the present invention;

[0051] Figure 4 It is a specific flow chart of the present invention. DETAILED DESCRIPTION

[0052] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0053] A steam-driven starting and mode switching method for a steam-electric dual-driven unit specifically includes: improving the conditions for allowing the switch to be switched on, designing a function for independently starting a small steam turbine; improving the pure steam-driven control mode, distinguishing the types of motor fault protection of a suction fan system, and improving the comprehensive operation criterion of the suction fan system; optimizing the small steam turbine control mode, improving the suction fan motor non-mechanical fault tripping electrical switch to drive the suction fan to operate by the small steam turbine, and switching the steam drive to other control modes.

[0054] The present invention can improve the reliability of the power source of the suction fan of this type of unit, flexibly start the suction fan, reasonably reduce the small turbine protection action, and reduce the probability of triggering the suction fan RB of the unit. In this way, while ensuring the safety and stability of the unit, economic operation is achieved, which is helpful to further promote energy conservation and emission reduction of thermal power units.

[0055] Pure steam drive state criterion, the following conditions are all met:

[0056] 1) Small steam turbine speed (after 3 selections)∈[the minimum speed that can satisfy the operation of the small steam turbine, meshing speed];

[0057] 2) Open the electrical switch of the suction fan.

[0058] Among them, after 3 selections, an optimal measurement point is selected using three measurement points.

[0059] like Figure 4 As shown, the steam-driven starting and mode switching method of the steam-electric dual-driven unit of the present invention specifically includes the following steps:

[0060] Step S1, optimize the control strategy of the small steam turbine, improve the conditions for allowing the shutdown, and have the function of independently starting the small steam turbine.

[0061] In the prior art, the small steam turbine system can be started only after the induced draft fan has been running. That is, the prior art sets one condition for the lock to be allowed: the suction fan has been running. The present invention allows the small steam turbine to be started without judging whether the suction fan is running, thus optimizing the preconditions for starting the small steam turbine.

[0062] Step S2: Subdivide the protection type of the suction fan and optimize the related logic of the small steam turbine

[0063] (1) For mechanical faults that affect the "suction fan-motor-small steam turbine" shaft system, the small steam turbine needs to be tripped after the suction fan switch is tripped. If such a signal exists, the small steam turbine is not allowed to start.

[0064] (2) For electrical faults that do not affect the operation of the shaft system, the suction fan switch is tripped and the operation is maintained in pure steam drive mode. Among them, electrical system faults mainly include: main transformer (plant high-voltage transformer) fault, busbar fault, generator fault, suction fan motor electrical equipment fault. If such signals exist, the small steam turbine is allowed to start.

[0065] Step S3, comprehensively judge the operating status of the suction fan, change the original judgment of only the state of the suction fan motor incoming switch to a comprehensive judgment, including the state of the suction fan motor incoming switch, clutch engagement, tripping signal, including the small steam turbine system operating status signal such as steam drive mode and speed.

[0066] Step S4, optimize the small steam turbine valve control mode, set up a new small steam turbine valve position control mode, improve the speed control strategy, and add low speed protection function. Designed when the suction fan motor trips:

[0067] (1) In the steam-driven power generation mode, the small steam turbine regulating valve overrides and automatically and quickly closes to the set value, and at the same time, switches to the pure steam-driven mode.

[0068] (2) In the steam-electric dual-drive mode, if the small steam turbine regulating valve is throttled, it will be instantly opened to the set value and at the same time, it will be switched to the pure steam drive mode.

[0069] Step S5, designing a control scheme for when the suction fan motor trips and switches to pure steam drive mode and needs to be restored online.

[0070] (1) Scheme 1: Steam drive-electric drive-steam-electric dual drive-steam drive power generation

[0071] First, in steam drive mode, control the speed of the small steam turbine to near the synchronous speed, slightly lower than the synchronous speed. Second, close the electrical switch of the induced draft fan and switch to electric drive mode. Third, gradually increase the speed of the small steam turbine to the meshing speed, the clutch automatically meshes the small steam turbine with the asynchronous motor, and the unit switches from pure electric drive to steam-electric dual drive mode. Fourth, gradually open the regulating valves of the large and small steam turbines to increase the power generation output of the motor, and the asynchronous motor switches to the generator operation state. At this time, the small steam turbine drives the asynchronous motor and the induced draft fan to operate, enter the steam drive power generation mode, and complete the online recovery.

[0072] (2) Option 2: Steam drive-steam-electric dual drive-steam drive power generation

[0073] First, in steam drive mode, control the speed of the small steam turbine to near the synchronous speed, and stabilize it slightly higher than the synchronous speed. Second, close the electrical switch of the induced draft fan, engage the clutch, and switch to steam-electric dual drive or steam drive power generation mode. Third, gradually open the throttle valves of the large and small steam turbines to increase the power generation output of the motor and complete the online recovery. Specific embodiments

[0075] like Figure 1 As shown in the figure, for a certain 1000MW ultra-supercritical steam turbine generator set, two 50%BMCR steam-electric dual-drive induced draft fans are installed, and the exhaust steam heat recovery system of the induced draft fan adopts the configuration of "back pressure steam turbine + constant speed ratio gearbox + asynchronous motor + dynamic fan". At the same time, each induced draft fan is equipped with a small steam turbine (hereinafter referred to as small steam turbine) equipped with a set of clutch reduction gearbox, lubricating oil system, shaft seal system, small steam turbine steam supply and exhaust system, etc. The steam source of the small steam turbine uses the medium-pressure steam inlet of the unit, that is, the steam outlet of the first-stage reheater of the boiler, and the exhaust steam returns to the main engine No. 6 low-pressure heater. The unit usually adopts the economic mode of sliding pressure operation with the high-pressure regulating valve fully opened.

[0076] Modify the conditions for small steam turbines to allow shutdown. The following conditions are all met (take a single turbine as an example for explanation), as follows:

[0077] 1) Small steam turbine oil system meets the requirements

[0078] 2) The main steam valve of the small steam turbine is fully closed

[0079] 3) The main regulating valve of the small steam turbine is closed (opening degree < 5%)

[0080] 4)ETS first output has been reset

[0081] 5) The exhaust passage of the small steam turbine is unobstructed (OR)

[0082] (1) PCV isolation valve fully open and PCV valve fully open

[0083] (2) Unobstructed waterways

[0084] like Figure 2 As shown, during normal operation,

[0085] 1) In the steam-driven power generation mode, if an electrical fault occurs in the induced draft fan but does not affect the normal operation of the fan, the steam inlet regulating valve of the small steam turbine will be overrun and quickly closed to a certain set value. The set value is generated based on the load corresponding function and corrected, and the speed of the small steam turbine is controlled to maintain the normal operation of the induced draft fan and switch to the pure steam-driven mode.

[0086] 2) In the steam-electric dual-drive mode, when this condition occurs, the small steam turbine regulating valve instantly opens to a certain set value, controls the speed of the small steam turbine, and switches to pure steam drive mode at the same time.

[0087] When the induced draft fan motor trip ends and needs to be restored online in pure steam drive mode, the control scheme is as follows:

[0088] (1) Scheme 1: Steam drive-electric drive-steam-electric dual drive-steam drive power generation

[0089] First, in steam drive mode, control the speed of the small steam turbine to near the synchronous speed, slightly lower than the synchronous speed. Second, close the electrical switch of the induced draft fan and switch to electric drive mode. Third, gradually increase the speed of the small steam turbine to the meshing speed, the clutch automatically meshes the small steam turbine with the asynchronous motor, and the unit switches from pure electric drive to steam-electric dual drive mode. Fourth, gradually open the regulating valves of the large and small steam turbines to increase the power generation output of the motor, and the asynchronous motor switches to the generator operation state. At this time, the small steam turbine drives the asynchronous motor and the induced draft fan to operate, enter the steam drive power generation mode, and complete the online recovery.

[0090] (2) Option 2: Steam drive-steam-electric dual drive-steam drive power generation

[0091] First, in steam drive mode, control the speed of the small steam turbine to near the synchronous speed, and stabilize it slightly higher than the synchronous speed. Second, close the electrical switch of the induced draft fan, engage the clutch, and switch to steam-electric dual drive or steam drive power generation mode. Third, gradually open the throttle valves of the large and small steam turbines to increase the power generation output of the motor and complete online recovery. Mode switching, see Figure 2 and 3 shown.

[0092] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for steam-driven starting and mode switching of a steam-electric dual-drive unit, wherein the steam-electric dual-drive unit comprises a small steam turbine, an asynchronous motor and an induced draft fan, characterized in that: The method comprises the following steps: Step S1, optimizing the control strategy of the small steam turbine, improving the conditions for allowing the lock to be engaged, and having the function of independently starting the small steam turbine; Step S2, subdividing the induced draft fan protection type and optimizing the small steam turbine related logic; Step S3, comprehensively judging the operation status of the induced draft fan; Step S4, optimizing the small steam turbine valve control mode, setting up a new small steam turbine valve position control mode, improving the speed control strategy, and adding a low speed protection function; Step S5, designing a control scheme for when the induced draft fan motor trips and switches to pure steam drive mode and needs to be restored online; The optimization logic of the small steam turbine in step S2 includes: S201) For mechanical faults of the shaft system, the small steam turbine needs to be tripped after the induced draft fan switch is tripped. If such fault signal exists, the small steam turbine is not allowed to start; S202) For electrical faults that do not affect the operation of the shaft system, after the induced draft fan switch is tripped, the pure steam drive mode is maintained. If such fault signal exists, the small steam turbine is allowed to start.

2. A method for steam-driven starting and mode switching of a steam-electric dual-driven unit according to claim 1, characterized in that: The conditions for allowing the switch-on in step S1 are improved to have the function of independently starting the small steam turbine. Specifically, one of the conditions in the switch-on conditions, "the suction fan is already running", is removed. That is, the small steam turbine is allowed to start without judging whether the suction fan is running, thereby optimizing the preconditions for starting the small steam turbine.

3. A method for steam-driven starting and mode switching of a steam-electric dual-driven unit according to claim 1, characterized in that: The mechanical faults of the shaft system in S201) include faults of the high-speed shaft, the low-speed shaft, and the gear box, wherein the high-speed shaft is the output shaft of the small steam turbine and the low-speed shaft is the output shaft of the asynchronous motor.

4. A method for steam-driven starting and mode switching of a steam-electric dual-driven unit according to claim 1, characterized in that: The electrical faults in S202) include main transformer faults, busbar faults, generator faults and induced draft fan motor electrical equipment faults.

5. The method for steam-driven starting and mode switching of a steam-electric dual-driven unit according to claim 1, characterized in that: The step S3 of comprehensively judging the operation status of the induced draft fan is specifically as follows: The operating status of the induced draft fan is comprehensively judged based on the status of the induced draft fan motor incoming line switch, clutch engagement, tripping signal, steam drive mode and speed of the small steam turbine operating status signal.

6. A steam-driven starting and mode switching method for a steam-electric dual-driven unit according to claim 1, characterized in that: The step S4 optimizes the small steam turbine valve control mode, and the newly set small steam turbine valve position control mode is specifically: S401) In the steam-driven power generation mode, the small steam turbine regulating valve overrides and automatically and quickly closes to the set value, and at the same time, switches to the pure steam-driven mode; S402) In the steam-electric dual drive mode, if the small steam turbine regulating valve is throttled, it will be instantly opened to the set value, and at the same time, it will be switched to the pure steam drive mode.

7. The method for steam-driven starting and mode switching of a steam-electric dual-driven unit according to claim 1, characterized in that: The step S5 is specifically as follows: When the induced draft fan motor trip ends and needs to be restored online in pure steam drive mode, there are two control methods: Method 1: Steam drive-pure electric drive-steam-electric dual drive-steam drive power generation; Method 2: Steam drive - steam-electric dual drive - steam drive power generation method.

8. A steam-driven starting and mode switching method for a steam-electric dual-driven unit according to claim 7, characterized in that: The method 1 specifically comprises the following steps: Step 5011: Under the steam drive mode, control the speed of the small steam turbine to be close to the synchronous speed, slightly lower than the synchronous speed; Step 5012, the induced draft fan electrical switch is closed to switch to pure electric drive mode; Step 5013, gradually increase the speed of the small steam turbine to the meshing speed, the clutch automatically meshes the small steam turbine with the asynchronous motor, and the unit is switched from pure electric drive to steam-electric dual drive mode; Step 5014, gradually open the large and small steam turbine regulating valves to increase the motor power output, and the asynchronous motor switches to generator operation. At this time, the small steam turbine drives the asynchronous motor and the induced draft fan to enter the steam-driven power generation mode, completing online recovery.

9. A steam-driven starting and mode switching method for a steam-electric dual-driven unit according to claim 7, characterized in that: The second method specifically comprises the following steps: Step 5021, in steam drive mode, control the speed of the small steam turbine to near the synchronous speed, and stabilize it slightly higher than the synchronous speed; Step 5022, the induced draft fan electrical switch is closed, the clutch is engaged, and the fan is switched to steam-electric dual drive or steam drive power generation mode; Step 5023, gradually open the large and small turbine regulating valves to increase the motor power output and complete online recovery.

Images