Efficient coal-fired unit bypass valve temperature reduction water spraying control system and control method

Abstract

The invention provides an efficient coal-fired unit bypass valve desuperheating water spraying control system and method, and the system is characterized in that the system comprises a boiler superheater, a boiler reheater, a bypass valve, a desuperheating water isolation valve, a desuperheating water adjusting valve, an enthalpy value controller loop and a temperature controller loop; according to the method, temperature reduction water spraying control is carried out through a flow and temperature cooperative control mode. Compared with the prior art, a temperature control mode and a flow and temperature cooperative control mode are set. The switching conditions of the two control modes comprise the water spraying flow requirement, the bypass outlet steam superheat degree and the temperature reduction water spraying flow measuring element fault, the stable switching of the modes enables the outlet steam superheat degree to be high, and the flow temperature cooperative control mode is activated in the flow requirement large stage of temperature control target required temperature reduction water. The problem that temperature parameter inertia is large is solved, and it is avoided that steam at a bypass outlet is too high, and safe and stable operation of a system and equipment is affected.

Description

Technical Field

[0001] The present invention relates to a coal-fired unit superheating water spraying system, and in particular to a high-efficiency coal-fired unit bypass valve superheating water spraying control system and control method. Background Art

[0002] Coal-fired units occupy a very important position in my country's energy industry. In recent years, coal-fired power units have developed in the direction of high capacity and high parameters. At the same time, the demand for auxiliary services such as reliable capacity, peak load regulation and frequency regulation has also increased the demand for coal-fired power units for operational flexibility and reliability.

[0003] The bypass valve desuperheating water spray system of the coal-fired unit is an important part of it. The bypass system of the unit effectively coordinates the balance between the boiler and the steam turbine, adapts to the unit startup conditions, trip conditions and the needs of different conditions during the normal operation of the unit, making the boiler and the turbine an organically coordinated union to ensure the safe and stable operation of the system and equipment.

[0004] The traditional bypass valve cooling water spray control uses the bypass valve outlet steam temperature as the control parameter, and all disturbance factors that affect the bypass valve outlet parameters are included in the temperature control loop. When the bypass valve water spray cooling system is disturbed, the bypass valve outlet steam temperature deviates from the set value, and the temperature controller calculates the corresponding adjustment amount according to the temperature deviation, thereby controlling the water spray regulating valve to adjust the flow of cooling water spray, thereby adjusting the bypass valve outlet temperature to return it to the set value. This control method has a simple and convenient structure and a general control effect. The main reason is that the hysteresis and inertia of the bypass valve outlet temperature object are large. When the bypass valve changes the outlet pressure, its outlet temperature takes a certain amount of time to follow the change. In this way, although the water spray regulating valve remains unchanged according to the previous instruction, the bypass valve outlet temperature will lag for a period of time and change, so that the temperature controller detects the deviation and then controls the output. This situation causes the bypass valve outlet temperature control to be untimely, causing excessive overshoot and insufficient stability.

[0005] When a special operating condition such as a turbine trip occurs, the bypass valve performs a quick opening action. At this time, if the unit is operating in a higher load area, a large volume of high-temperature and high-pressure steam will quickly enter the reheater, which may easily cause the risk of overheating the reheater and affect the stability and life of the equipment. In view of this situation, the present invention proposes a control loop switching function to cope with this special operating condition, so as to reduce the thermal shock of the special operating condition on the reheater, etc., and reduce the damage to the equipment caused by the instantaneous large volume of high-temperature and high-pressure steam. Summary of the invention

[0006] The purpose of the present invention is to provide a high-efficiency coal-fired unit bypass valve temperature reduction water spray control system and control method thereof, which are applied to high-parameter ultra-supercritical high-efficiency coal-fired units. In order to coordinate the operation of the machine and boiler, improve the start-up conditions of the whole machine and the load characteristics of the unit under different operating conditions, adapt to rapid load increase and decrease, and enhance the flexibility of the unit, the unit is equipped with a high low-pressure two-stage series steam turbine start-up bypass system.

[0007] The present application discloses a high-efficiency coal-fired unit bypass valve desuperheating water spraying control system, the system comprising: a boiler superheater, a boiler reheater, a bypass valve, a desuperheating water isolation valve, a desuperheating water regulating valve, an enthalpy controller circuit and a temperature controller circuit; the enthalpy controller circuit and the temperature controller circuit are connected in series, the boiler superheater and the boiler reheater are connected through the bypass valve, the desuperheating water is input into the bypass valve through the desuperheating water isolation valve and the desuperheating water regulating valve, a first redundant pressure detection element and a first redundant temperature detection element are arranged between the boiler superheater and the isolation valve, a second redundant pressure detection element and a second redundant temperature detection element are arranged between the boiler reheater and the isolation valve, a third redundant pressure detection element, a third redundant temperature detection element and a redundant flow detection element are arranged between the desuperheating water inlet and the desuperheating water isolation valve; the enthalpy controller circuit is configured to establish a desuperheating water flow demand for achieving the bypass valve outlet temperature setting value target as a basic controller according to the desuperheating water spraying energy transfer relationship.

[0008] In a preferred example, the system further comprises a control switching module, wherein the control switching module is configured to execute a bypass valve cooling water spray regulating valve control instruction switch for a pulse time period (3 to 5 seconds) when a turbine trip signal appears.

[0009] In a preferred example, the system is configured such that when the water spray flow demand is low or the steam superheat at the bypass outlet is low, the attemperation water regulating valve performs single impulse control to directly control the steam temperature at the bypass valve outlet at a fixed value. When the water spray flow demand is not low and the steam superheat at the bypass valve outlet is not low, the attemperation water regulating valve performs three impulse control, which is implemented by a serial temperature controller and an enthalpy controller.

[0010] In a preferred example, the enthalpy controller and the temperature controller are configured with a PID controller.

[0011] In a preferred example, the method is to perform cooling water spray control through a flow-temperature coordinated control mode. The flow-temperature coordinated control mode introduces the cooling water flow parameter through the enthalpy controller, and establishes a flow demand function based on the energy transfer relationship between the cooling water spray and the bypass steam, thereby calculating the cooling water flow demand. The algorithm enables the control of the bypass valve outlet steam parameters to coordinate the causal parameters, namely the cooling water flow and the bypass valve outlet steam temperature, thereby improving the reliability of its control.

[0012] In a preferred embodiment, the flow demand function is as follows:

[0013]

[0014] in:

[0015] Q W It is the demand value of desuperheating water flow rate in the enthalpy control loop;

[0016] Q1 is the steam flow rate at the bypass inlet;

[0017] h1 is the steam enthalpy at the bypass inlet, which is calculated using the enthalpy calculation module with the main steam temperature and main steam pressure as input.

[0018] h2 is the enthalpy of the steam at the bypass outlet, which is calculated using the enthalpy calculation module S with the bypass outlet temperature control set value and the bypass outlet steam pressure as input.

[0019] h w The enthalpy value of bypass cooling water is calculated by using the enthalpy calculation module with cooling water temperature and cooling water pressure as input.

[0020] In a preferred example, the bypass inlet steam flow is calculated using the bypass valve position signal, the bypass valve inlet steam specific volume and the bypass valve inlet and outlet steam pressure parameters.

[0021] In a preferred example, the method also includes a temperature control mode, in which a single temperature controller is directly used to control the bypass valve outlet steam temperature to a set value when the water spray flow demand is low or the bypass outlet steam superheat is low or the cooling water spray flow measurement element fails and cannot be put into use.

[0022] In a preferred example, a tracking module is provided in the PID controller, and the tracking module is used to ensure that when switching between the temperature control mode and the flow-temperature coordinated control mode and between the automatic mode and the manual control mode, the controller automatically tracks the instruction value being executed to avoid control loop jitter caused by mode switching.

[0023] In a preferred embodiment, an adder is added after the selector after the output of the temperature controller and the enthalpy controller, and the adder accumulates the output of the temperature controller and the enthalpy controller to obtain the change rate of the bypass outlet steam pressure PT2. The change rate of the bypass outlet steam pressure PT2 is calculated according to the following formula:

[0024] PT2 change rate = (PT2 real-time - PT2 previous sampling period) / PT2 real-time * 100%

[0025] Compared with the prior art, the advantages of the present invention are:

[0026] (1) The present invention proposes a high-efficiency coal-fired unit bypass valve cooling water spray control method, which fully considers the different operating states of the bypass system and sets a temperature control mode and a flow-temperature coordinated control mode. The switching conditions of the two control modes include the water spray flow demand, the bypass outlet steam superheat and the cooling water spray flow measurement element failure. The smooth switching of the mode activates the flow-temperature coordinated control mode when the outlet steam superheat is high and the flow demand of the cooling water required by its temperature control target is high, so as to solve the problem of large inertia of temperature parameters and avoid the bypass outlet steam being too high and affecting the safe and stable operation of the system and equipment. In addition, running in the temperature control mode makes the control system simple and the control effect direct.

[0027] (2) The control method proposed in the present invention provides a control loop switching function for transient operating conditions such as turbine tripping, which switches the control command to a control command set within a specific time interval taking into account the equipment protection function, so as to reduce the thermal shock of special operating conditions on the reheater, etc. and protect the safety of system equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the bypass valve cooling water spray system;

[0029] Figure 2 It is a schematic diagram of the bypass valve desuperheating water spray desuperheating water flow demand control loop of the present invention;

[0030] Figure 3 It is a control diagram of the control circuit of the bypass valve temperature reduction water spray regulating valve described in the present invention;

[0031] Figure 4 The present invention Figure 1-3 Description of the legend symbols in .

[0032] Among them, 1-boiler superheater; 2-boiler reheater; 3-bypass valve; 4-cooling water isolation valve; 5-cooling water regulating valve; 6-first redundant pressure test element; 7-first redundant temperature test element; 8-second redundant pressure test element; 9-second redundant temperature test element; 10-third redundant pressure detection element; 11-third redundant temperature detection element; 12-third redundant flow detection element. DETAILED DESCRIPTION

[0033] The inventor of the present invention has invented a high-efficiency coal-fired unit bypass valve desuperheating water spray control system and a control method thereof. Compared with the prior art, the present invention is divided into a temperature control mode and a flow-temperature coordinated control mode. The switching conditions of the two control modes include the water spray flow demand, the bypass outlet steam superheat and the desuperheating water spray flow measurement element failure. The smooth switching of the mode makes the outlet steam superheat high and the flow demand of the desuperheating water required by its temperature control target to activate the flow-temperature coordinated control mode in the stage to solve the problem of large inertia of temperature parameters and avoid the bypass outlet steam being too high and affecting the safe and stable operation of the system and equipment. In addition, running in the temperature control mode makes the control system simple and the control effect direct. Not only that, the control method proposed in the present invention provides a control loop switching function for transient operating conditions such as turbine tripping, which switches the control command to the control command set in a specific time interval taking into account the equipment protection function to reduce special operating conditions.

[0034] The present invention is described in detail below in conjunction with the various embodiments shown in the accompanying drawings, but it should be noted that these embodiments are not limitations of the present invention, and any equivalent transformations or substitutions in functions, methods, or structures made by ordinary technicians in the field based on these embodiments are all within the scope of protection of the present invention.

[0035] The specific implementation process of the present invention is described below through embodiments.

[0036] Example:

[0037] An embodiment of the present invention Figures 1 to 3 As shown, it should be noted that the invention proposes a method for controlling the temperature reduction and water spraying of a bypass valve of a high-efficiency coal-fired unit, which can be applied to high-parameter ultra-supercritical high-efficiency coal-fired units. In order to coordinate the operation of the machine and boiler, improve the starting conditions of the whole machine and the load characteristics of the unit under different operating conditions, adapt to rapid load increases and decreases, and enhance the flexibility of the unit, the unit is provided with a high- and low-pressure two-stage series steam turbine starting bypass system. The bypass capacity is set according to the partial capacity bypass, and the drive mode is hydraulic or pneumatic. The safe and stable operation of the bypass system is an important guarantee for maintaining the energy balance of the boiler and steam turbine, and the stability and efficiency of the system. Optionally, in this embodiment, if Figure 1As shown, the bypass valve cooling water spray system is a high-pressure bypass cooling water spray system, and the method of this embodiment is also applicable to other bypass cooling water spray systems.

[0038] The bypass valve desuperheating water spraying system of this embodiment includes: a boiler superheater 1, a boiler reheater 2, a bypass valve 3, a desuperheating water isolation valve 4, a desuperheating water regulating valve 5, an enthalpy controller circuit and a temperature controller circuit, wherein the enthalpy controller circuit and the temperature controller circuit are connected in series, the boiler superheater 1 and the boiler reheater 2 are connected through the bypass valve 3, the desuperheating water is input into the bypass valve 3 through the desuperheating water isolation valve 4 and the desuperheating water regulating valve 5, and a first redundant pressure detection element 6 and a first redundant temperature are arranged between the boiler superheater 1 and the isolation valve 3. Detection element 7, a second redundant pressure detection element 8 and a second redundant temperature detection element 9 are arranged between the boiler reheater 1 and the isolation valve 3, and a third redundant pressure detection element 10, a third redundant temperature detection element 11 and a redundant flow detection element 12 are arranged between the desuperheating water inlet and the desuperheating water isolation valve 4; the enthalpy controller loop is configured to establish a desuperheating water flow demand to achieve the target of the outlet temperature setting value of the bypass valve 3 as the basic setting value of the controller according to the desuperheating spray water energy transfer relationship, which is arranged in the control loop of the desuperheating water regulating valve 5. The enthalpy controller and the temperature controller are configured with a PID controller.

[0039] Optionally, in one embodiment, the system further includes a control switching module, and the control switching module is configured to execute a bypass valve cooling water spray regulating valve control instruction switch for a pulse time period (3 to 5s) when a turbine trip signal appears. When a turbine trip accident occurs, the bypass valve opens quickly, causing a large amount of high-temperature and high-pressure steam to enter the reheater and other equipment, which will cause a great thermal shock to the reheater and other equipment, and shorten its service life. At this time, the selector module of this embodiment can be used to reduce the thermal shock to the heater and other equipment,

[0040] In this embodiment, the system is configured such that when the water spray flow demand is low or the steam superheat at the bypass outlet is low, the desuperheating water regulating valve performs single impulse control to directly control the steam temperature at the bypass valve outlet at a fixed value. When the water spray flow demand is not low and the steam superheat at the bypass valve outlet is not low, the desuperheating water regulating valve performs three impulse control, which is implemented by a serial temperature controller and an enthalpy controller.

[0041] The control method of the bypass valve cooling water spray system used in this embodiment is as follows: Figure 2 and Figure 3 As shown, Figure 2The method for realizing the cooling water flow demand in the enthalpy control loop is as follows: the enthalpy controller loop establishes the cooling water flow demand to achieve the bypass valve outlet temperature setting value target according to the cooling water spray energy transfer relationship as the basic setting value of the controller. At the same time, the control output caused by the difference between the temperature setting value and the feedback value in the temperature control loop is added to the basic setting value of the enthalpy controller loop, so that the enthalpy controller comprehensively processes the target parameter (bypass valve outlet steam temperature) and its directly affected parameter (cooling water spray flow rate). The enthalpy controller outputs the difference between its set flow target value and the cooling water detection element feedback value to the bypass water spray regulating valve through the calculation value of the PID controller to adjust it to meet the needs of the loop control.

[0042] The desuperheating water flow demand in the enthalpy control loop is established based on the energy transfer relationship between desuperheating water spray and bypass steam. The calculation function is as follows:

[0043]

[0044] in:

[0045] Q W It is the demand value of desuperheating water flow rate in the enthalpy control loop;

[0046] Q1 is the steam flow rate at the bypass inlet;

[0047] h1 is the steam enthalpy at the bypass inlet, which is calculated using the enthalpy calculation module STM-TBL SS with the main steam temperature TT1 and the main steam pressure PT1 as input.

[0048] h2 is the enthalpy of the steam at the bypass outlet, which is calculated using the enthalpy calculation module STM-TBL SS with the bypass outlet temperature control set value TT2sp and the bypass outlet steam pressure PT2 as input.

[0049] h w The enthalpy value of the bypass desuperheating water is calculated by using the enthalpy calculation module STM-TBL SS with the desuperheating water temperature TT3 and the desuperheating water pressure PT3 as input.

[0050] K is the adjustment coefficient of the required value of the desuperheating water flow rate. In order to prevent the steam temperature after the bypass valve from exceeding the upper limit and ensure the safe and stable operation of equipment such as the reheater, the adjustment coefficient of the required value of the desuperheating water flow rate is set to 1.05~1.1, which is determined according to the on-site commissioning. Among them, Q1 is the steam flow rate at the bypass inlet. Since the steam temperature and pressure parameters here are high, the flow measurement element is difficult to adapt. Therefore, the bypass valve position signal, the bypass valve inlet steam specific volume (calculated by the bypass valve inlet steam temperature and pressure parameters), and the bypass valve inlet and outlet steam pressure parameters are used to calculate. The specific function is proposed by the bypass valve manufacturer.

[0051] The bypass valve cooling water spray control method proposed in the present invention sets two automatic control modes, a temperature control mode and a flow-temperature coordinated control mode. When the water spray flow demand is low or the bypass outlet steam superheat is low or the cooling water spray flow measurement element fails and cannot be put into use, the temperature control after the bypass valve directly uses a single temperature controller to control the bypass valve outlet steam temperature to the set value. This method can directly act on the final control parameter to reach the target value, and the effect is direct. When the water spray flow demand is low or the bypass outlet steam superheat is low, the bypass operates in a stage with a high outlet steam superheat and its temperature control target requires the cooling water flow rate to be at a large stage. At this time, in order to solve the problem of large inertia of temperature parameters and avoid excessive bypass outlet steam affecting the safe and stable operation of the system and equipment, an enthalpy controller is added to the control loop of the bypass valve cooling water spray regulating valve, and the enthalpy controller introduces the cooling water flow parameter. Since the desuperheating water flow parameter directly affects the bypass valve outlet steam temperature and has the characteristic of quick response, the control of the bypass valve outlet steam parameter coordinates the causal parameters (desuperheating water flow and bypass valve outlet steam temperature), thus improving the reliability of its control. Figure 3 shown.

[0052] Optionally, in one embodiment, in order to ensure smooth switching between the temperature control mode and the flow-temperature coordinated control mode and avoid large disturbances caused by switching of the control mode, a tracking function of the temperature mode or the manual switching mode is set in the temperature control PID controller and the enthalpy control PID controller. The tracking module is used to ensure that when switching between the temperature control mode and the flow-temperature coordinated control mode and between the automatic mode and the manual control mode, the controller automatically tracks the command value being executed to avoid control loop jitter caused by mode switching.

[0053] Optionally, in one embodiment, there is a large coupling of control parameters in the bypass valve desuperheating water spray control system of the coal-fired unit, and the valve position adjustment of the bypass valve affects the change of the bypass outlet steam flow rate, and its pressure parameter changes with dynamic sensitivity. The change of the outlet pressure affects the real-time change of the outlet steam enthalpy value. In addition, the change of the bypass steam flow rate itself makes the set value of the desuperheating water demand in the desuperheating water control loop coupled with the state of the bypass valve, which increases the difficulty of control. The present invention regards the influence of the bypass valve position adjustment as a main disturbance parameter of the control function, and corrects the influence of the disturbance parameter on the control function by adding a disturbance compensation function. An adder is added after the selector after the output of the temperature controller and the enthalpy controller, and the adder accumulates the change rate of the bypass outlet steam pressure PT2 output by the temperature controller and the enthalpy controller. The change rate of PT2 is calculated according to the following formula:

[0054] PT2 change rate = (PT2 real-time - PT2 previous sampling period) / PT2 real-time * 100%

[0055] Formula 2

[0056] This embodiment adds a compensation function for the change of the bypass outlet steam pressure PT2, which will improve the suppression effect of the entire control system on the system disturbance variable, effectively improve the speed of the control response, and reduce the influence of the hysteresis of the bypass outlet temperature response. In order to avoid the system oscillation problem that may be caused by the continuous influence of the disturbance on the control loop, the conditional restriction function of the bypass outlet steam pressure change compensation function is added, that is, a switching module is added. When the difference between the bypass valve outlet steam temperature setting value and the feedback value is greater than a certain setting value, the bypass outlet steam pressure change compensation function is added to speed up the control response. When the difference between the bypass valve outlet steam temperature setting value and the feedback value is less than the setting value, the bypass outlet steam pressure change compensation function is exited to stabilize its control function.

[0057] The series of detailed descriptions listed above are only specific descriptions of feasible implementation methods of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent implementation methods or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

[0058] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0059] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A high-efficiency coal-fired unit bypass valve temperature reduction water spray control system, characterized in that: The system includes: a boiler superheater, a boiler reheater, a bypass valve, a desuperheating water isolation valve, a desuperheating water regulating valve, an enthalpy controller loop and a temperature controller loop; the enthalpy controller loop and the temperature controller loop are connected in series and are configured in the control loop of the bypass valve; the boiler superheater and the boiler reheater are connected through the bypass valve, and desuperheating water is input into the bypass valve through the desuperheating water isolation valve and the desuperheating water regulating valve, a first redundant pressure detection element and a first redundant temperature detection element are configured between the boiler superheater and the isolation valve, a second redundant pressure detection element and a second redundant temperature detection element are configured between the boiler reheater and the isolation valve, and a third redundant pressure detection element, a third redundant temperature detection element and a redundant flow detection element are configured between the desuperheating water inlet and the desuperheating water isolation valve; the enthalpy controller loop is configured to establish a desuperheating water flow demand for achieving a bypass valve outlet temperature setting value target as a basic setting value of the controller according to the desuperheating spray water energy transfer relationship, and is configured in the control loop of the desuperheating water regulating valve.

2. The control system according to claim 1, characterized in that: The system further comprises a control switching module, wherein the control switching module is configured to execute a bypass valve desuperheating water spray regulating valve control instruction switching for a pulse time period (3 to 5 seconds) when a turbine trip signal appears.

3. The control system according to claim 1, characterized in that: The system is configured such that when the water spray flow demand is low or the superheat of the steam at the bypass valve outlet is low, the attemperating water regulating valve performs single-impulse control to directly control the steam temperature at the bypass valve outlet at a fixed value; when the water spray flow demand is not low and the superheat of the steam at the bypass valve outlet is not low, the attemperating water regulating valve performs three-impulse control, and the three-impulse control is realized by a serial temperature controller and an enthalpy controller.

4. The control system according to claim 1, characterized in that: The enthalpy controller and the temperature controller are configured with a PID controller.

5. A high-efficiency coal-fired unit bypass valve temperature reduction water spray control method applicable to any one of claims 1-4, characterized in that: The method is to control cooling water spraying through a flow-temperature coordinated control mode. The flow-temperature coordinated control mode introduces cooling water flow parameters through the enthalpy controller, and establishes a flow demand function based on the energy transfer relationship between the cooling water spraying and the bypass steam, thereby calculating the cooling water flow demand. The algorithm enables the control of the bypass valve outlet steam parameters to coordinate the causal parameters, namely the cooling water flow and the bypass valve outlet steam temperature, thereby improving the reliability of its control.

6. The control method according to claim 5, characterized in that: The flow demand function is as follows: in: Q w It is the demand value of desuperheating water flow rate in the enthalpy control loop; Q1 is the steam flow rate at the bypass inlet; h1 is the steam enthalpy at the bypass inlet, which is calculated using the enthalpy calculation module with the main steam temperature and main steam pressure as input; h2 is the enthalpy of the steam at the bypass outlet, which is calculated by using the enthalpy calculation module S with the bypass outlet temperature control set value and the bypass outlet steam pressure as input; h w The bypass desuperheating water enthalpy is calculated by using the enthalpy calculation module, taking the desuperheating water temperature and desuperheating water pressure as input; K is the adjustment coefficient of the desuperheating water flow demand value. In order to prevent the steam temperature after the bypass valve from exceeding the upper limit and to ensure the safe and stable operation of equipment such as the reheater, the adjustment coefficient of the desuperheating water flow demand value is set to 1.05~1.1, which is determined based on on-site commissioning.

7. The control method according to claim 6, characterized in that: The bypass inlet steam flow is calculated using the bypass valve position signal, the bypass valve inlet steam specific volume and the bypass valve inlet and outlet steam pressure parameters.

8. The control method according to claim 5, characterized in that: The method also includes a temperature control mode, in which a single temperature controller is directly used to control the bypass valve outlet steam temperature to a set value when the water spray flow demand is low or the bypass outlet steam superheat is low or the desuperheating water spray flow measurement element fails and cannot be put into use.

9. The control method according to claim 5, characterized in that: The PID controller is provided with a tracking module, which is used to ensure that when switching between the temperature control mode and the flow-temperature coordinated control mode and between the automatic mode and the manual control mode, the controller automatically tracks the command value being executed to avoid control loop jitter caused by mode switching.

10. The control method according to claim 5, characterized in that: An adder is added after the selector after the output of the temperature controller and the enthalpy controller, and the adder accumulates the output of the temperature controller and the enthalpy controller and the rate of change of the bypass outlet steam pressure PT2; wherein the rate of change of the bypass outlet steam pressure PT2 is calculated according to the following formula The change rate of PT2 = (PT2 real time - PT2 previous sampling period) / PT2 real time * 100%.

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