Three-stage overheating desuperheating water cooperative control system and method for ultra-supercritical boiler

Abstract

The invention discloses an ultra-supercritical boiler three-stage overheating desuperheating water cooperative control system and method, and relates to the field of thermotechnical automatic control. The steam specific enthalpy of an outlet of a low-temperature superheater is controlled through first-stage desuperheating water; the second-stage desuperheating water mainly controls the steam temperature of an outlet of the platen superheater and assists in adjusting the opening range of a third-stage desuperheating water flow adjusting valve; and the third-stage desuperheating water still controls the superheated steam temperature of the boiler. In the scheme, compared with the method for controlling the steam temperature of the outlet of the low-temperature superheater through the first-stage superheated desuperheating water, the method for controlling the specific enthalpy of the steam of the outlet of the low-temperature superheater can keep high control precision during large-range variable-load operation of a unit, and the overall control effect is good. And the second-stage overheating desuperheating water is controlled through event driving, the opening degree of the third-stage overheating desuperheating water regulating valve can be kept within a reasonable range within the full-load range, and the overall control quality of the overheating steam temperature system within the full-load range is improved.

Description

Technical Field

[0001] This invention relates to the field of thermal automatic control, specifically to a three-stage superheated desuperheating water coordinated control system and method for an ultra-supercritical boiler. Background Technology

[0002] Coal-fired boilers are developing towards larger capacity and higher parameters. A 330MW unit equipped with a subcritical drum boiler has a rated evaporation capacity of 1080 t / h and a superheated steam temperature of 540℃; a 660MW unit equipped with a supercritical once-through boiler has a rated evaporation capacity of 1860 t / h and a superheated steam temperature of 570℃; and a 1000MW unit equipped with an ultra-supercritical once-through boiler has a rated evaporation capacity of 2700 t / h and a superheated steam temperature of 605℃. As superheated steam temperatures increase, the safety margin for superheater metal tube temperature decreases to near its limit, thus increasing the requirements for the precision of superheated steam temperature control at each stage.

[0003] With the large-scale grid connection of new energy sources such as photovoltaic and wind power, the power grid increasingly relies on thermal power units to provide capacity support and absorb various disturbances. For example, when the photovoltaic load rises rapidly in the morning, thermal power units need to quickly reduce their load; when photovoltaic power is at full load at noon, thermal power units need to operate at the minimum load for deep peak regulation; when the photovoltaic load decreases in the afternoon, thermal power units need to quickly increase their load; and when the photovoltaic load drops to zero in the evening, thermal power units need to operate at full load. Therefore, the key to thermal power units fulfilling their capacity support role is to increase the adjustment range and rate of power generation load. Current thermal power units are required to achieve an adjustment range of 35%–100% and a rate of 1.2–2.5% Pe / min, while the new generation of demonstration thermal power units is required to achieve an adjustment range of 25%–100% and a rate of 2.0–4.0% Pe / min. This wide-range, high-rate load change operation poses a more severe challenge to the control level of boiler steam temperature and pressure.

[0004] The fundamental task of boiler operation is to heat a certain amount of feedwater with a certain amount of fuel according to load demand, producing steam at a certain temperature. One of the core tasks of the boiler control system is to maintain a relatively stable water-fuel ratio. Excessive fuel will produce superheated steam with a temperature higher than the design value, which can easily lead to overheating of the heated surface metal and affect boiler safety; excessive feedwater flow will reduce the superheated steam temperature and affect the unit's thermal efficiency. Boilers generally use a method of coarse adjustment of the water-fuel ratio with feedwater and fine adjustment with superheated desuperheating water. However, the principle of coarse adjustment of the water-fuel ratio differs between subcritical drum boilers and ultra-supercritical once-through boilers: subcritical drum boilers store excess saturated water in the drum-downcomer-water-cooled wall system, and its evaporation rate depends only on the fuel quantity. When the fuel quantity increases, the evaporation rate naturally increases. Therefore, on the superheater side, an increase in fuel quantity will naturally lead to an increase in steam flow, making superheated steam temperature control relatively easy. Under normal operating conditions, ultra-supercritical once-through boilers do not have a large internal water storage capacity. They need to roughly control the feedwater flow rate to achieve an initial match with the heat generated by fuel combustion, and then correct the temperature using the steam temperature (or specific enthalpy and superheat) signal at the steam-water separator outlet. However, the control of the steam temperature (or specific enthalpy and superheat) at the steam-water separator outlet has a certain lag. Therefore, the superheater side does not show a situation where the steam flow rate naturally increases with the increase in fuel quantity, making it relatively difficult to control the superheated steam temperature.

[0005] The boiler controls the superheated steam temperature by injecting desuperheating water into the superheater. Specifically, the boiler is designed so that the heat absorbed by the superheating section is slightly greater than that absorbed by the evaporation section (vaporization section). The superheated steam temperature is then lowered to the rated value by injecting desuperheating water. After being injected into the superheater, the desuperheating water rapidly vaporizes, absorbing heat to lower the steam temperature, but simultaneously increasing the steam flow rate and raising the superheated steam pressure instantaneously. Superheated steam temperature control and superheated steam pressure control are coupled, and the coupling strength increases with the ratio of superheater desuperheating water flow rate to feedwater flow rate.

[0006] During wide-range load changes, the adjustability of supercritical once-through boilers for superheated steam temperature is greater than that of subcritical drum boilers. In subcritical drum boilers, the evaporation rate is determined by the fuel quantity, and the water-fuel ratio cannot be directly adjusted. At low loads, more heat from the boiler fuel is concentrated in the furnace, leading to increased heat absorption in the evaporation section and decreased heat absorption in the superheating section, resulting in excessive water evaporation. Even if the superheater desuperheating water is reduced to zero, it cannot meet the heat requirements for heating the excess evaporated water to the rated steam temperature, causing a decrease in superheated steam temperature. In contrast, supercritical once-through boilers can directly adjust the water-fuel ratio. Theoretically, at low loads, reducing the feedwater flow rate can decrease evaporation and thus increase steam temperature. However, at this time, the boiler water-cooled walls absorb a large amount of heat while the feedwater flow rate is small. Furthermore, the lack of an internal circulation loop results in poor hydrodynamic characteristics of the water-cooled walls, making the metal tube walls prone to overheating. Therefore, it is necessary to increase the feedwater flow rate to suppress overheating. Operators frequently adjust the feedwater flow rate to increase the superheated steam temperature and prevent the water-cooled wall metal tubes from overheating, which causes changes in the steam temperature at the steam-water separator outlet. Consequently, the superheated steam temperature fluctuates significantly, and in severe cases, this is coupled with the superheated steam pressure control to create oscillations.

[0007] Traditional boilers typically have two stages of superheater desuperheating water. The first stage superheater desuperheater is installed at the inlet of the front screen superheater to assist in controlling the superheated steam temperature at the boiler outlet and to protect the screen-type superheater. The second stage superheater desuperheater is installed at the inlet of the high-temperature superheater to control the superheated steam temperature at the boiler outlet. However, for ultra-supercritical units, the arrangement of the two stages of superheater desuperheating water is not reasonable. The reasons include: (1) Superheater desuperheating water can only be injected from two locations, resulting in poor uniformity of the desuperheating regulation effect and poor suppression of local overheating of the superheater metal tube wall. Especially during deep peak shaving and rapid load change operation of the boiler, the superheated steam temperature is often forced to be lowered. (2) Due to the limited number of injection points, the length of the heating surface pipes shared by each injection point increases, which increases the inertia and delay time of the desuperheating water regulating valve opening on the controlled objects of each stage of steam temperature, making the steam temperature more difficult to control. (3) The steam temperature control system needs to generate large The dynamic over-adjustment amount is used to overcome the inertia of the steam temperature object, resulting in a large instantaneous injection volume of desuperheating water and a large fluctuation range, which is seriously coupled with the superheated steam pressure; (4) Due to the small number of injection points, the desuperheating water flow rate shared by each injection point increases. During the adjustment process, a large change in the flow rate of a certain stage of desuperheating water will cause the inlet temperature of the heat receiving surface after the desuperheater to fluctuate violently, generating alternating thermal stress that affects the life of the metal; (5) The heat storage of the ultra-supercritical unit is relatively small, while the heat storage of the superheated section metal accounts for more than 30% of the total heat storage. The arrangement of the secondary desuperheating water is not conducive to making full use of the heat storage of the superheated section metal, and the steam pressure fluctuates greatly during the load change process.

[0008] To address the above problems, improvements have been made to the existing technology. The improved new ultra-supercritical boiler adopts a three-stage superheating desuperheating water arrangement, which can significantly improve the above problems. The advantages include: (1) the uniformity of the desuperheating regulation is improved, and the ability to suppress local overheating is enhanced; (2) the pipe length of each stage of superheating desuperheating water passing through the heating surface is shortened, the inertial delay is reduced, and the superheated steam temperature is easier to control; (3) the dynamic over-adjustment of the desuperheating water is reduced, and the coupling effect with the superheated steam pressure control is weakened; (4) the deviation of the heat absorption of the heating surface that each stage of desuperheating water is responsible for dissipating is reduced, and the overall fluctuation range of the superheating desuperheating water volume is reduced; (5) the control system design is more flexible. In addition to achieving the main control objective of maintaining the stability of the superheated steam temperature, the superheating desuperheating water can also take into account secondary control objectives such as using metal heat storage to reduce steam pressure fluctuations and suppressing overheating of the metal pipe wall of the heating surface.

[0009] For ultra-supercritical boilers, the heating surfaces in the vaporization section include: economizer, spiral water-cooled wall, and vertical water-cooled wall; the intermediate section includes: steam-water separator and water storage tank; the heating surfaces in the superheating section include: wall-mounted tube / roof / partition screen superheater, low-temperature superheater, front / rear screen superheater, and high-temperature superheater. A schematic diagram of the improved three-stage superheating and desuperheating system is shown below. Figure 1 As shown in the diagram, the first-stage superheated water spray desuperheater is located before the low-temperature superheater, the second-stage superheated water spray desuperheater is located before the screen-type superheater, and the third-stage superheated water spray desuperheater is located before the high-temperature superheater. Thus, the first-stage superheated steam temperature corresponds to the outlet steam temperature of the low-temperature superheater, the second-stage superheated steam temperature corresponds to the outlet steam temperature of the screen-type superheater, and the third-stage superheated steam temperature corresponds to the boiler outlet superheated steam temperature.

[0010] After adopting the three-stage superheating desuperheating water scheme, if the control method of the traditional superheated steam temperature control system is used, the first-stage superheating desuperheating water controls the outlet steam temperature of the low-temperature superheater; the second-stage superheating desuperheating water controls the outlet steam temperature of the screen-type superheater; the third-stage superheating desuperheating water controls the outlet steam temperature of the high-temperature superheater, i.e., the superheated steam temperature; the steam temperature setpoints of each stage are set by the operators. The disadvantages of this control method in the actual operation of the boiler are: (1) Due to the uncertainty of the functional relationship between the heat absorption of each stage of superheater and the boiler load, the operators need to frequently adjust the steam temperature setpoints of the first and second stages during large-scale load changes; (2) There is a lack of a coordinated scheduling strategy to evenly distribute the flow of desuperheating water at each stage, which may result in the situation where the flow regulating valve of a certain stage of desuperheating water is fully open while the flow regulating valve of another stage of desuperheating water is fully closed, thus limiting the overall regulation capacity; (3) All three stages of superheating desuperheating water are used to control the steam temperature, and their additional auxiliary ability to regulate the steam pressure is not utilized.

[0011] To address the aforementioned issues, existing literature, such as invention CN201310057004.9, discloses a two-stage coordinated predictive control method for superheated steam temperature in thermal power units. This method employs a generalized predictive-proportional (GPC-P) cascade control strategy with feedforward compensation. When the secondary desuperheating water valve is at its upper / lower limit, it fully utilizes the adjustment margin of the primary water spray to assist the secondary water spray in controlling the superheated steam temperature, thereby improving the system's control performance. Although the technical objective is the same as this invention, the problem-solving approach and method are completely different. Another example is invention CN202410983915.2, which discloses an optimization method for superheated steam temperature control in supercritical coal-fired boilers. Its core is the introduction of predicted intermediate-point enthalpy into the feedwater control system to improve superheated steam temperature stability, but the control signal and method are completely different from this invention. Summary of the Invention

[0012] To address the shortcomings of existing technologies, this invention aims to provide a three-stage superheated desuperheating water coordinated control system and method for ultra-supercritical boilers. Compared to the first-stage superheated desuperheating water controlling the outlet steam temperature of the low-temperature superheater, the method of controlling the specific enthalpy of the outlet steam of the low-temperature superheater in this invention can maintain high control accuracy and achieve good overall control performance during large-scale load changes of the unit.

[0013] This invention is achieved through the following technical solution:

[0014] A method for coordinated control of three-stage superheating and desuperheating water in an ultra-supercritical boiler includes the injection of an additional first-stage superheating and desuperheating water before the low-temperature superheater, and the control and regulation steps of the first-stage superheating and desuperheating water control system, the second-stage superheating and desuperheating water control system, and the third-stage superheating and desuperheating water control system, respectively.

[0015] The control and regulation steps of the first-stage superheated desuperheating water control system include using the steam enthalpy at the outlet of the low-temperature superheater as the controlled variable, and controlling and regulating the steam enthalpy at the outlet of the low-temperature superheater according to the steam enthalpy set value generated by logic.

[0016] The control and regulation steps of the second-stage superheated desuperheating water control system include using the steam temperature at the outlet of the screen-type superheater as the main controlled variable and the opening range of the third-stage superheated desuperheating water regulating valve as the auxiliary controlled variable, and controlling and regulating the steam temperature at the outlet of the screen-type superheater according to the set value of the steam temperature at the outlet of the screen-type superheater generated by logic.

[0017] Further optimization includes the following steps in generating the vapor specific enthalpy setpoint:

[0018] The boiler steam flow signal is filtered by the first-order inertial module LAG1 and then calculated by the multi-point piecewise linear function F(X)1 to obtain the reference value signal of the low-temperature superheater outlet steam specific enthalpy setpoint.

[0019] The steam pressure signal at the outlet of the steam-water separator is filtered by the first-order inertial module LAG2, and then the gain correction signal of steam pressure to steam specific enthalpy is calculated by the multi-point piecewise linear function module F(X)2.

[0020] The low-temperature superheater outlet steam temperature bias value set by the operator is multiplied by the gain correction signal through the multiplication module MUL1 to obtain the low-temperature superheater outlet steam specific enthalpy bias value signal. Then, the bias value signal is added to the reference value signal through the addition module SUM1 to obtain the steam specific enthalpy set value of the low-temperature superheater outlet in the first-stage superheating and desuperheating water control system.

[0021] For further optimization, the parameters of the multi-point piecewise linear function F(X)1, which are inputs and outputs, are obtained by fitting the design operating data based on the boiler steam flow rate and the specific enthalpy of the low-temperature superheater outlet steam.

[0022] For further optimization, the first-stage superheated desuperheating water control system adopts a cascade control system. The main loop of the cascade control system uses the dynamic correction signal of the steam specific enthalpy at the outlet of the low-temperature superheater as the feedback value, and the secondary loop of the cascade control system uses the dynamic correction signal of the steam specific enthalpy at the inlet of the low-temperature superheater as the feedback value.

[0023] Further optimization includes the following steps for calculating the dynamic correction feedback value of the low-temperature superheater outlet steam specific enthalpy:

[0024] The actual differential signal of the low-temperature superheater outlet steam temperature is obtained by subtracting the output signal after filtering by the first-order inertial module LAG3 from the subtraction module SUB1, and then multiplying it by a gain coefficient by the gain module K1.

[0025] The low-temperature superheater outlet steam temperature signal and the actual differential signal of the low-temperature superheater outlet steam temperature are added together by the summation module SUM2 to obtain the low-temperature superheater outlet steam temperature signal after advance compensation.

[0026] The low-temperature superheater outlet steam pressure signal is lag-compensated by the first-order inertial module LAG4, and then, together with the low-temperature superheater outlet steam temperature signal after advance compensation, is processed by the water vapor specific enthalpy calculation module ETHP1 to obtain the low-temperature superheater outlet steam specific enthalpy dynamic correction signal.

[0027] Further optimizations include setting the inertial time for first-order inertial modules LAG3 and LAG4, and setting the gain for gain module K1, specifically:

[0028] Make the inertial time of the first-order inertial module LAG3 and the first-order inertial module LAG4 the same, and set the range between 30s and 60s.

[0029] The gain of gain module K1 is set within the range of 1.25 to 2.5; and the smaller the inertia time of first-order inertial module LAG3 and first-order inertial module LAG4, the greater the gain of gain module K1, and the two are set in an inverse proportion.

[0030] Further optimization includes the following steps for calculating the dynamic correction feedback value of the inlet steam specific enthalpy of the low-temperature superheater:

[0031] The low-temperature superheater inlet steam temperature signal is obtained by subtracting the output signal after being filtered by the first-order inertial module LAG5 from the subtraction module SUB2, and then multiplying it by a gain coefficient by the gain module K2.

[0032] The low-temperature superheater inlet steam temperature signal and the actual differential signal of the low-temperature superheater inlet steam temperature are added together by the summation module SUM3 to obtain the low-temperature superheater inlet steam temperature signal after advance compensation.

[0033] The low-temperature superheater inlet steam pressure signal is lag-compensated by the first-order inertial module LAG6, and then, together with the low-temperature superheater inlet steam temperature signal after advance compensation, is processed by the water vapor enthalpy calculation module ETHP2 to obtain the low-temperature superheater inlet steam enthalpy dynamic correction signal.

[0034] Further optimizations include setting the inertial time for first-order inertial modules LAG5 and LAG6, and setting the gain for gain module K2, specifically:

[0035] The inertial time of the first-order inertial module LAG5 and the first-order inertial module LAG6 is the same, and the setting range is between 5s and 10s.

[0036] The gain setting range of gain module K2 is between 0.5 and 1.0; and the smaller the inertia time of first-order inertial module LAG5 and first-order inertial module LAG6, the greater the gain of gain module K2, and the two are set in an inverse proportional manner.

[0037] Further optimization includes the following steps for generating the setpoint for the outlet steam temperature of the screen-type superheater:

[0038] Based on the opening command signal of the third-stage superheated desuperheating water flow regulating valve, after filtering by the first-order inertial module LAG7, the bias value signal of the setpoint of the outlet steam temperature of the screen-type superheater is calculated by the event-driven control module DSCT.

[0039] The reference value signal of the steam temperature at the outlet of the screen-type superheater, set by the operator, is added to the bias value signal through the SUM4 addition module to obtain the set value of the steam temperature at the outlet of the screen-type superheater in the second-stage superheating and desuperheating water control system.

[0040] Further optimization includes the following internal control calculation steps for the event-driven control module DSCT:

[0041] In the event-driven control module DSCT, when the filtered third-stage superheated desuperheating water flow regulating valve opening command signal is less than the low threshold signal L and continues for a certain period of time, an input signal less than the low threshold event is generated, thereby triggering the output signal to increase the bias value of the control panel superheater outlet steam temperature setpoint by one temperature step.

[0042] After the filtered third-stage superheated desuperheating water flow regulating valve opening command signal is greater than the high threshold signal H and continues for a certain period of time, an input signal greater than the high threshold event is generated, thereby triggering the output signal to control the bias value of the outlet steam temperature setpoint of the screen superheater to decrease by one temperature step.

[0043] When the input signal is greater than the low threshold signal L and less than the high threshold signal H, the bias value of the setpoint for the outlet steam temperature of the screen-type superheater remains unchanged.

[0044] Further solutions:

[0045] This invention also provides a three-stage superheated desuperheating water coordinated control system for an ultra-supercritical boiler, comprising:

[0046] The unit's distributed control system includes a first-stage superheated desuperheating water control system, a second-stage superheated desuperheating water control system, and a third-stage superheated desuperheating water control system, all configured in a configurable manner.

[0047] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0048] 1. This invention provides a three-stage superheated desuperheating water coordinated control system and method for an ultra-supercritical boiler. Compared with the first-stage superheated desuperheating water controlling the outlet steam temperature of the low-temperature superheater, the method of controlling the specific enthalpy of the outlet steam of the low-temperature superheater in this invention can maintain high control accuracy during large-scale load changes of the unit, resulting in better overall control performance. Furthermore, the second-stage superheated desuperheating water, through event-driven control, can maintain the opening of the third-stage superheated desuperheating water regulating valve within a reasonable range with bidirectional adjustment margin across the entire load range, improving the overall control quality of the superheated steam temperature system across the entire load range.

[0049] 2. This invention provides a three-stage superheating and desuperheating water coordinated control system and method for an ultra-supercritical boiler. When the unit experiences large-scale load changes, the enthalpy of the steam at the outlet of the low-temperature superheater can more accurately reflect the water-fuel ratio and is easy to control with high precision. During rapid load changes, it can fully utilize the heat storage of the metal in the low-temperature superheater, reduce the fluctuation range of superheated steam pressure, and increase the rate of load increase and decrease. It can also maintain the adjustment margin of the three-stage superheating and desuperheating water regulating valves throughout the full load range to prevent them from entering the open saturation or closed saturation state, thereby ensuring the overall control quality of the superheated steam temperature system.

[0050] 3. This invention provides a three-stage superheating and desuperheating water coordinated control system and method for ultra-supercritical boilers. Targeting novel ultra-supercritical once-through boilers equipped with a three-stage superheating and desuperheating water system, it fully leverages the characteristics of each of the three desuperheating water control systems. While ensuring stable superheated steam temperature at the boiler outlet, it also compensates for and controls superheated steam pressure, thus improving the unit's load response rate. Furthermore, each controlled variable and key debugging parameter of the control logic in this method has a clear physical meaning, and the control logic is convenient to configure on-site, simple to debug, and easy to maintain. Attached Figure Description

[0051] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0052] Figure 1 This is a schematic diagram of the three-stage superheated desuperheating water system for an ultra-supercritical boiler provided by the present invention.

[0053] Figure 2 A logic diagram for generating the steam specific enthalpy setpoint of the first-stage superheated desuperheating water control system provided by the present invention;

[0054] Figure 3 The calculation logic diagram of the dynamic correction feedback value signal of the low temperature superheater outlet steam specific enthalpy of the first-stage superheated desuperheating water control system provided by the present invention is shown below.

[0055] Figure 4 The calculation logic diagram of the dynamic correction feedback value signal of the low temperature superheater inlet steam specific enthalpy for the first-stage superheating and desuperheating water control system provided by the present invention;

[0056] Figure 5 A logic diagram for generating the setpoint of the outlet steam temperature of the screen-type superheater in the second-stage superheating and desuperheating water control system provided by the present invention.

[0057] Figure 6 The internal control logic diagram of the event-driven control module DSCT provided by this invention.

[0058] The attached diagram shows the markings and corresponding component names:

[0059] 1-Separator inlet steam; 2-First-stage superheated desuperheating water; 3-Second-stage superheated desuperheating water; 4-Third-stage superheated desuperheating water; 5-Boiler superheated steam; 6-Steam-water separator; 7-Wall-insulating pipe / ceiling / partition screen superheater; 8-First-stage spray desuperheater; 9-Low-temperature superheater; 10-Second-stage spray desuperheater; 11-Screen-type superheater; 12-Third-stage spray desuperheater; 13-High-temperature superheater; 14-First-stage superheated desuperheating water flow regulating valve; 15-Second-stage superheated desuperheating water flow regulating valve; 16-Third-stage superheated desuperheating water flow regulating valve. Detailed Implementation

[0060] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0061] Example: This example provides a method for coordinated control of three-stage superheated desuperheating water in an ultra-supercritical boiler. The specific analysis steps regarding the selection of the controlled variable in the control system are as follows:

[0062] In existing technologies, due to the significant large inertia and large delay characteristics of the controlled object of boiler superheated desuperheating water control steam temperature, even with advanced control methods such as predictive control, the adjustment time of the superheated steam temperature control system is between 90s and 180s. This means that when the set value of a certain level of superheated steam temperature changes, the actual steam temperature feedback value will take 90s to 180s to approach the set value.

[0063] For the ultra-supercritical boiler with three-stage attemperation water for a 1000MW unit, the design and operating data of steam temperatures at all levels are shown in Table 1. It can be seen that within the full load range, only the steam temperature of the third stage of superheat, i.e., the steam temperature at the boiler outlet, does not change with the load. This means that the set value of its control system can be set as a constant without adjusting the steam temperature set value according to the load change. Although the steam temperature of the second stage of superheat, i.e., the steam temperature at the outlet of the platen superheater, changes with the load, the change range is small. Therefore, when the steam temperature set value is adjusted according to the load, the deviation between the set value and the feedback value will not be too large and will not have a significant impact on the overall steam temperature control. However, the steam temperature of the first stage of superheat, i.e., the steam temperature at the outlet of the low-temperature superheater, changes significantly with the load. The change range from the 35%THA condition to the 100%THA condition reaches 15.7%. This means that when the boiler changes load continuously and rapidly, the set value of the control system for the first stage of superheat steam temperature will also change significantly and rapidly. However, due to the characteristics of large inertia and large delay of the controlled object, the actual feedback value of the first stage of superheat steam temperature is difficult to follow the change of the set value, which will lead to a decline in the overall control quality of the steam temperature system.

[0064] Table 1 Corresponding relationship between steam-water working medium temperature and load of ultra-supercritical boiler

[0065]

[0066] The design and operating data of specific enthalpy of steam-water working medium at all levels of the ultra-supercritical boiler with three-stage attemperation water are shown in Table 2. The specific enthalpy of steam is jointly determined by steam temperature and pressure. It can be seen that within the full load range, the change range of the specific enthalpy of the first stage of superheat steam with the load is not large. The change range of the specific enthalpy value from the 35%THA condition to the 100%THA condition is only 3.1%. The change of the specific enthalpy of steam converted into the change range of temperature is only 20°C, while comparing with Table 1, it can be seen that the change range of temperature reaches 70°C. Therefore, for the first stage of attemperation water, the specific enthalpy signal of the steam at the outlet of the low-temperature superheater is more suitable as the controlled variable than the steam temperature signal. When the boiler operates with a large range of load changes, the adjustment range of the specific enthalpy set value with the load is very small, and the deviation between its set value and the feedback value is naturally very small, which will not have a significant impact on the control system.

[0067] Table 2 Corresponding relationship between steam-water working medium specific enthalpy and load of ultra-supercritical boiler

[0068]

[0069] In addition, the first-stage superheated desuperheating water 2, which controls the steam specific enthalpy, can also play a role in assisting in regulating the superheated steam pressure when the boiler rapidly changes load. Taking load reduction as an example: when load reduction begins, the control system will reduce the turbine regulating valve opening to decrease steam flow. At this time, the superheated steam pressure increases. According to the principle of energy conservation, the steam specific enthalpy does not change. As shown in Table 3, when the steam specific enthalpy remains constant, the increase in pressure leads to an increase in temperature. Therefore, when the first-stage desuperheating water is used to control the outlet steam temperature of the low-temperature superheater 9, the steam temperature feedback value will increase due to the increased pressure. At this time, the first-stage superheated desuperheating water flow regulating valve 14 automatically opens wider under the control system to reduce the steam temperature feedback value, thereby increasing the desuperheating water flow. The increased desuperheating water will absorb heat and rapidly vaporize in the low-temperature superheater 9, which in turn increases the steam pressure. In this case, the first-stage superheated steam temperature control system and the superheated steam pressure control system exhibit a "reverse coupling" effect, which is detrimental to the overall stability of the boiler control system. When using primary superheating water to control the enthalpy of the steam outlet at the low-temperature superheater 9, changes in steam pressure during load reduction do not lead to changes in the enthalpy of the steam outlet. The opening of the primary superheating desuperheating water flow regulating valve 14 and the desuperheating water flow rate remain essentially unchanged, thus avoiding the "reverse coupling" between the primary superheating steam temperature control system and the superheated steam pressure control system, and improving the overall stability of the boiler control system. Further analysis of Table 2 shows that the setpoint for the enthalpy of the steam outlet at the low-temperature superheater 9 will show a slight increasing trend during load reduction. The primary superheating steam temperature control system will then close the primary superheating desuperheating water flow regulating valve 14, which is more conducive to superheated steam pressure regulation.

[0070] Table 3. Correspondence between specific enthalpy of outlet steam of cryogenic superheater at 75% THA operating point and pressure and temperature.

[0071]

[0072] In summary, this invention controls the three-stage desuperheating water system for ultra-supercritical boilers by using the enthalpy of the steam outlet from the low-temperature superheater 9 as the controlled variable for the first-stage superheated desuperheating water 2, the steam outlet temperature from the screen-type superheater 11 as the controlled variable for the second-stage superheated desuperheating water 3, and the steam outlet temperature from the convective superheater 4 as the controlled variable. Specific improvements are described below:

[0073] I. Regarding the first-stage superheated desuperheating water control system:

[0074] The first-stage superheated desuperheating water 2 adopts a cascade control system. The main loop uses the dynamic correction value of the steam ratio enthalpy at the outlet of the low-temperature superheater 9 as feedback, and the secondary loop uses the dynamic correction value of the steam ratio enthalpy at the inlet of the low-temperature superheater 9 as feedback.

[0075] As described above, the method for generating the setpoints of the first-stage superheated desuperheating water 2 control system is as follows: Figure 2As shown. The boiler steam flow signal is filtered by the first-order inertial module LAG1, and then the reference value signal of the first-stage superheater outlet steam specific enthalpy setpoint is calculated by the multi-point piecewise linear function module F(X)1.

[0076] The steam pressure signal at the separator outlet is filtered by the first-order inertial module LAG2, and then the gain correction signal of steam pressure to steam specific enthalpy is calculated by the multi-point piecewise linear function module F(X)2.

[0077] The offset value of the steam temperature at the outlet of the low-temperature superheater 9, set by the operator, is multiplied by the gain correction signal of the steam pressure on the steam specific enthalpy through the multiplication module MUL1 to obtain the offset value signal of the steam specific enthalpy at the outlet of the first-stage superheater. Then, it is added by the reference value signal of the set value of the steam specific enthalpy at the outlet of the low-temperature superheater 9 through the addition module SUM1 to obtain the set value signal of the first-stage desuperheating water control system.

[0078] The actual working principle of the above logic is as follows: the reference value of the low-temperature superheated outlet steam specific enthalpy setpoint is calculated from the boiler steam flow signal, and the bias value signal of the low-temperature superheated outlet steam specific enthalpy setpoint is set by the operator. However, compared with the specific enthalpy signal, the operator's perception of temperature signal changes is more direct, so here the operator directly sets the bias value of the outlet temperature of the low-temperature superheater 9, and the bias value of the low-temperature superheated outlet steam specific enthalpy setpoint is obtained after steam pressure correction calculation. Among them, the inertia time of LAG1 and LAG2 modules is set to 5s; the parameters of the multi-point piecewise linear function input and output of F(X)1 are obtained by fitting the design operation data of boiler steam flow and low-temperature superheater 9 outlet steam specific enthalpy; the input and output parameter settings of the multi-point piecewise linear function of F(X)2 are shown in Table 4.

[0079] Table 4. Parameter settings for the multi-point polyline function module F(X)2

[0080]

[0081] In addition, there are many mature control schemes for controlling superheated steam temperature with desuperheating water, such as cascade PID control and cascade predictive control. Due to the large inertia and delay characteristics of the controlled object, the main controller of any control scheme must rely on a large differential control action to counteract the object's inertia and delay. However, this situation changes when using the specific enthalpy of superheated steam as the controlled variable, because the specific enthalpy of steam is affected by pressure in addition to temperature. When desuperheating water is injected, the superheated steam temperature decreases while the steam pressure increases. According to the thermodynamic properties of water and steam, a decrease in steam temperature leads to a decrease in specific enthalpy of steam, and an increase in steam pressure also leads to a decrease in specific enthalpy of steam. Since the amount of steam pressure change caused by the injection of desuperheating water is relatively small, the impact of pressure change on the specific enthalpy of steam is also relatively small compared to temperature change, accounting for only 4-8%. However, the propagation speeds of pressure and temperature in steam pipes differ significantly. For the low-temperature superheater 9, the steam pressure changes immediately after the desuperheating water is injected, with an overall response time of less than 30 seconds; while the steam temperature only begins to change after 60 to 120 seconds, resulting in an overall response time as long as 180 to 360 seconds. Therefore, compared to controlling steam temperature with desuperheating water, controlling steam enthalpy with desuperheating water presents an equivalent fast negative feedback channel: desuperheating water injection - steam pressure increase - steam enthalpy decrease. Thus, the impact of this situation on the control system must be considered.

[0082] In theory, the rapid feedback channel of steam pressure improves the response speed of the controlled object, thus benefiting control. However, due to the significant inertia and delay still present on the steam temperature side, and its influence on steam enthalpy being the primary factor, a large differential action is still required in the design of the main controller to offset these inertia and delay. This presents a contradiction in the design and debugging of the differential control logic of the control system: a strong differential control action can easily lead to differential oscillations in the control system due to the rapid feedback from the pressure side; a weak differential control action is insufficient to compensate for the large inertia and delay on the temperature side, resulting in a slow adjustment time for the control system.

[0083] To resolve this contradiction, in the first-stage superheated desuperheating water 2 control system, the control system feedback signal, namely the enthalpy signal of the steam at the outlet of the low-temperature superheater 9, and the control system internal loop feedback signal, namely the enthalpy signal of the steam at the inlet of the low-temperature superheater 9, are respectively adopted as follows: Figure 3 and Figure 4 The computational logic is shown.

[0084] exist Figure 3 In the process, the steam temperature signal at the outlet of the low-temperature superheater 9 is processed by the subtraction module SUB1, which subtracts the output signal after it has been filtered by the first-order inertial module LAG3. Then, it is multiplied by a gain coefficient by the gain module K1 to obtain the actual differential signal of the steam temperature at the outlet of the low-temperature superheater 9.

[0085] The outlet steam temperature signal of the low-temperature superheater 9 is obtained by adding the actual differential signal of the outlet steam temperature of the low-temperature superheater 9 after passing through the summation module SUM2.

[0086] The steam pressure signal at the outlet of the low-temperature superheater 9 is compensated for hysteresis by the first-order inertial module LAG4, and then combined with the steam temperature signal at the outlet of the low-temperature superheater 9 after advance compensation, and then processed by the water vapor specific enthalpy calculation module ETHP1 to obtain the steam specific enthalpy signal at the outlet of the low-temperature superheater 9.

[0087] In addition, such as Figure 4 As shown, the calculation process for the inlet steam specific enthalpy signal of the low-temperature superheater 9 is the same as that for the outlet steam specific enthalpy signal of the low-temperature superheater 9, and will not be repeated here.

[0088] The actual working principle of the above logic is as follows: After performing lead compensation on the steam temperature signal and lag compensation on the steam pressure signal, the steam specific enthalpy signal is calculated. By increasing the dynamic response speed of the temperature signal and decreasing the dynamic response speed of the pressure signal, the contradiction between the fast response speed of the pressure side and the slow response speed of the temperature side of the controlled object is overcome. Specifically: the inertia time setting range for LAG3 and LAG4 modules is 30–60 s, and the gain setting range for gain module K1 is 1.5–2.5. The smaller the inertia time of LAG3 and LAG4 modules, the larger the gain of gain module K1, and the two are inversely proportional. The inertia time setting range for LAG5 and LAG6 modules is 5–10 s, and the gain setting range for gain module K2 is 0.5–1.0. The smaller the inertia time of LAG5 and LAG6 modules, the larger the gain of gain module K2, and the two are inversely proportional.

[0089] II. Regarding the second-stage superheated desuperheating water control system:

[0090] Under full load conditions, all three stages of superheating and desuperheating water regulating valves have adjustment margins. The even injection of superheating and desuperheating water into each stage of the superheater is most beneficial for stable unit operation. However, during actual boiler operation, factors such as load, coal quality, air distribution method, and the operation mode of the coal mill and burners can affect the proportion of heat generated by fuel combustion distributed across different heating surfaces, leading to uneven heat absorption. When the heat absorption ratio of the low-temperature superheater 9, the screen-type superheater 11, and the high-temperature superheater 13 changes significantly, the steam temperature at the outlet of each superheater will deviate significantly from the normal operating value. At this time, the superheating and desuperheating water control system at each stage will adjust the desuperheating water flow to maintain stable steam temperature. When the difference in heat absorption is large, the desuperheating water regulating valves at different stages will operate in different directions until saturation is reached. For example, when the coal quality deteriorates and the primary air volume increases, the high heat output of the screen-type superheater 11 can cause the opening of the second-stage desuperheating water regulating valve to reach 100%, while the low heat absorption of the high-temperature superheater 13 can cause the opening of the third-stage desuperheating water regulating valve to drop to 0%. Furthermore, since both the low-temperature superheater 9 and the high-temperature superheater 13 primarily absorb convective heat, the use of steam specific enthalpy as the controlled variable for the first-stage desuperheating water can amplify this deviation to some extent. In this situation, the operator will appropriately increase the setpoint of the second-stage superheated steam temperature control system. Under the regulation of the control system, the opening of the second-stage desuperheating water regulating valve will decrease, reducing the desuperheating water flow. This increases the steam temperature at the outlet of the second-stage superheater, which in turn increases the steam temperature at the outlet of the third-stage superheater. Under the control system's action, the third-stage desuperheating water regulating valve will then open wider, ensuring that both the second and third-stage desuperheating water regulating valves have a regulating margin.

[0091] To reduce operator intervention and achieve balanced control of the superheated desuperheating water, the conventional control scheme for the two-stage superheated steam temperature control system is as follows: the second-stage desuperheating water controls the second-stage steam temperature, and the first-stage desuperheating water controls the temperature difference before and after the second-stage spray desuperheater 10. However, this scheme has the disadvantage of severe coupling between the two-stage desuperheating water control systems, resulting in poor overall stability and difficult on-site commissioning.

[0092] This embodiment addresses this problem by proposing an event-driven control method for the second-stage superheated desuperheating water 3, which primarily controls the outlet steam temperature of the superheater 11 and secondarily controls the opening range of the third-stage desuperheating water regulating valve. In this method, the setpoints for the second-stage superheated desuperheating water 3 control system are generated as follows: Figure 5 As shown.

[0093] exist Figure 5 In the process, the opening command signal of the third-stage superheated desuperheating water 4 regulating valve is filtered by the first-order inertial module LAG7, and then the event-driven control module DSCT calculates the setpoint bias signal of the second-stage superheater outlet steam temperature. This bias signal is then added to the second-stage superheater outlet steam temperature reference signal set by the operator through the addition module SUM4 to obtain the setpoint signal of the second-stage desuperheating water control system.

[0094] The inertial time of the first-order inertial module LAG7 is set to 60s.

[0095] The internal control logic of the event-driven control module DSCT is as follows: Figure 6 As shown, the input signal is compared with the low threshold signal L and the high threshold signal H by the less-than comparison module "<" and the greater-than comparison module ">", respectively, and outputs the signals "Input signal less than the low threshold" and "Input signal greater than the high threshold", respectively. The output signals of the delay-on modules TDON1 and TDON2 are inverted by the NOT1 and NOT2 modules, respectively, and then ANDed with the input signal less than the low threshold signal and the input signal greater than the high threshold signal by the AND1 and AND2 modules, respectively. After that, they are fed into the delay-on modules TDON1 and TDON2, respectively, to obtain the events "Input signal less than the low threshold" and "Input signal greater than the high threshold".

[0096] When the input signal is less than the low threshold, the switching module T selects an increased step signal "S+" when it is 1 and a zero signal 0.0 when it is OFF. When the input signal is greater than the high threshold, the switching module T selects a decreased step signal "S-" when it is 1 and a zero signal 0.0 when it is OFF. The output signals selected for the events where the input signal is less than the low threshold and the events where the input signal is greater than the high threshold are summed by the summing module SUM5, then summed with the event-driven control output signal by the summing module SUM6. Finally, the signal is limited by the high / low limiting module "H / / L" to obtain the event-driven control output signal.

[0097] The actual working principle of the above logic is as follows: When the input signal is less than the low threshold and persists for a certain period of time, an event indicating that the input signal is less than the low threshold is generated, which triggers the output signal to increase by one step. When the input signal is greater than the high threshold and persists for a certain period of time, an event indicating that the input signal is greater than the high threshold is generated, which triggers the output signal to decrease by one step. When the input signal is greater than the low threshold but less than the high threshold, the output remains unchanged. The delay modules TDON1 and TDON2 operate as follows: when the input signal is ON and the duration exceeds the set delay time, the output becomes ON; otherwise, the output is OFF.

[0098] In this embodiment, the low threshold signal L is set to 10%, and the high threshold signal is set to 70%. The delay times of the delay-on modules TDON1 and TDON2 are both 300s. The step-increasing signal "S+" is set to +0.5℃, and the step-decreasing signal "S-" is set to -0.5℃. The high and low limit modules "H / / L" have a high limit set to +5.0℃ and a low limit set to -5.0℃.

[0099] This embodiment applies the above scheme to an ultra-supercritical boiler with three-stage superheated desuperheating water. Each stage of desuperheating water includes left and right sides, and the control methods for both sides are exactly the same. The system setup and commissioning steps are as follows:

[0100] First, the controlled variables of each stage of the superheating water control system need to be determined. The controlled variable of the first-stage superheating desuperheating water 2 control system is the specific enthalpy of the steam at the outlet of the low-temperature superheater 9; the controlled variable of the second-stage superheating desuperheating water 3 control system is the steam temperature at the outlet of the screen-type superheater 11; and the controlled variable of the third-stage superheating desuperheating water 4 control system is the steam temperature at the boiler outlet.

[0101] Subsequently, the control logic for the first-stage superheated desuperheating water 2 control system was configured and built in the unit's distributed control system (DCS). The first-stage superheated desuperheating water 2 control system employs cascade control, with the improvement being that the setpoint follows... Figure 2 The logic shown is configured, and the inner loop feedback value and outer loop feedback value are respectively configured according to... Figure 3 Configure the logic shown. Figure 2 In the table, the inertia time of LAG1 and LAG2 modules is set to 5s; the parameters of the multi-point piecewise linear function input and output of F(X)1 are obtained by fitting the design operation data of boiler steam flow and the specific enthalpy of steam at the outlet of low-temperature superheater 9; the input and output parameter settings of the multi-point piecewise linear function of F(X)2 are shown in the table. Figure 3 In the diagram: The inertia time setting range for both LAG3 and LAG4 modules is 30–60 seconds, and the gain setting range for gain module K1 is 1.5–2.5. The smaller the inertia time of LAG3 and LAG4 modules, the greater the gain of gain module K1. Figure 4 In the model, the inertia time setting range for both LAG5 and LAG6 modules is 5–10 seconds, and the gain setting range for gain module K2 is 0.5–1.0. The smaller the inertia time of LAG5 and LAG6 modules, the greater the gain of gain module K2.

[0102] Subsequently, the control logic for the second-stage superheated desuperheating water 3 control system was configured and built into the unit's distributed control system. The second-stage superheated desuperheating water 3 control system employs cascade control, with the improvement being that the setpoint follows... Figure 5 Configure the logic shown. Figure 4 In this example, the inertial time of the first-order inertial module LAG5 is set to 60s. Figure 5 In the middle section, the low threshold signal L is set to 10%, and the high threshold signal is set to 70%. The delay times of delay-on modules TDON1 and TDON2 are both set to 300s. The step-increasing signal "S+" is set to +0.5℃, and the step-decreasing signal "S-" is set to -0.5℃. The high and low limit modules "H / / L" have their high limit set to +5.0℃ and low limit set to -5.0℃.

[0103] Finally, the control logic for the third-stage superheated desuperheating water control system was configured in the unit's distributed control system. The third-stage desuperheating water control system uses cascade control, which is existing technology and will not be elaborated here.

[0104] After configuring the control logic in the distributed control system of the unit, during unit operation, it is also necessary to debug each superheated desuperheating water control system separately, including the PID parameters of the secondary controller and the primary controller, the inertia time of modules LAG3, LAG4, LAG5, and LAG6, and the gain of gain modules K1 and K2. After debugging, the control system can be put into use.

[0105] In summary, this invention addresses the advantages of improved superheating and desuperheating water systems in ultra-supercritical once-through boilers, which offer more adjustment options and can accommodate multiple control objectives after the two-stage arrangement is changed to a three-stage arrangement. Therefore, it proposes a three-stage superheating and desuperheating water collaborative control system and its method for ultra-supercritical boilers.

[0106] The main features of the collaborative control system and its method are as follows: the first-stage desuperheating water controls the enthalpy of the steam at the outlet of the low-temperature superheater 9; the second-stage desuperheating water mainly controls the steam temperature at the outlet of the screen-type superheater 11 and assists in adjusting the opening range of the third-stage desuperheating water flow regulating valve; the third-stage desuperheating water still controls the temperature of the boiler superheated steam 5. The setpoint of the first-stage desuperheating water control system is obtained by adding the baseline value of the enthalpy of the steam at the outlet of the low-temperature superheater 9, calculated from the boiler steam flow rate, to the offset value of the enthalpy of the steam at the outlet of the low-temperature superheater 9, obtained after pressure correction by the operator. The feedback value of the first-stage superheated desuperheating water 2 control system, i.e., the enthalpy signal of the steam at the outlet of the low-temperature superheater 9, is calculated by the steam thermodynamic properties module through the superheated steam temperature signal after lead compensation and the low-temperature superheater 9 outlet steam pressure signal after lag compensation. The setpoint of the second-stage superheated desuperheating water 3 control system adopts the baseline value of the stable steam setpoint at the outlet of the screen-type superheater 11, set by the operator, plus the bias value calculated by the event-driven control logic based on the opening of the third-stage superheated desuperheating water flow regulating valve 16. Through this scheme, the specific enthalpy of the steam at the outlet of the low-temperature superheater 9 can more accurately reflect the water-fuel ratio and is easier to control during large-scale load changes, resulting in high control precision. During rapid load changes, it can fully utilize the metal heat storage of the low-temperature superheater 9, reducing the amplitude of superheated steam pressure fluctuations and increasing the rate of load increase and decrease. Furthermore, it can maintain adjustment margins for all three-stage superheated desuperheating water regulating valves across the entire load range, preventing them from entering open-saturation or closed-saturation states, thereby ensuring the overall control quality of the superheated steam temperature system.

[0107] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A triple-superheating desuperheating water coordinated control method of an ultra-supercritical boiler, characterized in that, The method comprises the steps of adding the injection of the first-stage superheating desuperheating water (2) before the low-temperature superheater (9) and the control and adjustment of the first-stage superheating desuperheating water control system, the second-stage superheating desuperheating water control system and the third-stage superheating desuperheating water control system, wherein: The control and adjustment step of the first-stage superheating desuperheating water control system comprises taking the steam specific enthalpy at the outlet of the low-temperature superheater (9) as the controlled variable, and controlling and adjusting the steam specific enthalpy at the outlet of the low-temperature superheater (9) according to the steam specific enthalpy set value generated by the logic. The control and adjustment step of the second-stage superheating desuperheating water control system comprises taking the steam temperature at the outlet of the screen superheater (11) as the main controlled variable and taking the third-stage superheating desuperheating water adjustment valve opening range as the auxiliary controlled variable, and controlling and adjusting the steam temperature at the outlet of the screen superheater (11) according to the steam temperature set value generated by the logic.

2. The triple-superheating desuperheating water coordinated control method of an ultra-supercritical boiler according to claim 1, characterized in that, The steam specific enthalpy set value generation step comprises: The boiler steam flow signal is filtered by a first-order inertia module LAG1, and then a base value signal of the steam specific enthalpy set value at the outlet of the low-temperature superheater (9) is calculated by a multi-point broken line function F(X)1. The steam pressure signal at the outlet of the steam-water separator (6) is filtered by a first-order inertia module LAG2, and then a gain correction signal of the steam pressure to the steam specific enthalpy is calculated by a multi-point broken line function module F(X)2. The steam temperature bias value at the outlet of the low-temperature superheater (9) set by the operator is multiplied by the gain correction signal by a multiplication module MUL1 to obtain a steam specific enthalpy bias value signal at the outlet of the low-temperature superheater (9), and then the bias value signal is added to the base value signal by an addition module SUM1 to obtain the steam specific enthalpy set value at the outlet of the low-temperature superheater (9) in the first-stage superheating desuperheating water control system.

3. The tertiary superheating desuperheating water coordinated control method of an ultra-supercritical boiler according to claim 2, characterized in that, The parameters of the multi-point broken line function input corresponding to the output of the multi-point broken line function F(X)1 are fitted according to the design operation data of the boiler steam flow and the steam specific enthalpy at the outlet of the low-temperature superheater (9).

4. The tertiary superheating desuperheating water coordinated control method of an ultra-supercritical boiler according to claim 2, characterized in that, The first-stage superheating desuperheating water control system adopts a cascade control system, and the main loop of the cascade control system takes the steam specific enthalpy dynamic correction signal at the outlet of the low-temperature superheater (9) as the feedback value, and the auxiliary loop of the cascade control system takes the steam specific enthalpy dynamic correction signal at the inlet of the low-temperature superheater (9) as the feedback value.

5. The three-stage superheating desuperheating water collaborative control method of the ultra-supercritical boiler according to claim 4, characterized in that: The calculation step of the steam specific enthalpy dynamic correction feedback value at the outlet of the low-temperature superheater (9) comprises: The steam temperature signal at the outlet of the low-temperature superheater (9) is subtracted from the filtered output signal of the steam temperature signal at the outlet of the low-temperature superheater (9) by a subtraction module SUB1, and then multiplied by a gain coefficient by a gain module K1 to obtain the steam temperature actual differential signal at the outlet of the low-temperature superheater (9); The steam temperature signal at the outlet of the low-temperature superheater (9) and the steam temperature actual differential signal at the outlet of the low-temperature superheater (9) are added by a summation module SUM2 to obtain the steam temperature signal at the outlet of the low-temperature superheater (9) after the lead compensation. The low-temperature superheater (9) outlet steam pressure signal is lagged after passing through a first-order inertia module LAG4, and then, together with the low-temperature superheater (9) outlet steam temperature signal after leading compensation, passes through a water-steam specific enthalpy calculation module ETHP1 to obtain a low-temperature superheater (9) outlet steam specific enthalpy dynamic correction signal.

6. The tertiary superheating desuperheating water coordinated control method of an ultra-supercritical boiler according to claim 5, characterized in that, Further comprising inertia time settings of the first-order inertia module LAG3 and the first-order inertia module LAG4 and gain settings of the gain module K1, specifically: The inertia time of the first-order inertia module LAG3 and the first-order inertia module LAG4 is the same, and the setting range is between 30s and 60s; The gain setting range of the gain module K1 is between 1.25 and 2.5; and the smaller the inertia time of the first-order inertia module LAG3 and the first-order inertia module LAG4, the greater the gain of the gain module K1, and the two are inversely proportional.

7. The method according to claim 4, characterized in that, The calculation steps of the low-temperature superheater (9) inlet steam specific enthalpy dynamic correction feedback value include: The low-temperature superheater (9) inlet steam temperature signal is subtracted from the output signal of the low-temperature superheater (9) inlet steam temperature signal after passing through a first-order inertia module LAG5, and then multiplied by a gain coefficient after passing through a gain module K2 to obtain a low-temperature superheater (9) inlet steam temperature actual differential signal; The low-temperature superheater (9) inlet steam temperature signal and the low-temperature superheater (9) inlet steam temperature actual differential signal are added after passing through a summation module SUM3 to obtain a low-temperature superheater (9) inlet steam temperature signal after leading compensation; The low-temperature superheater (9) inlet steam pressure signal is lagged after passing through a first-order inertia module LAG6, and then, together with the low-temperature superheater (9) inlet steam temperature signal after leading compensation, passes through a water-steam specific enthalpy calculation module ETHP2 to obtain a low-temperature superheater (9) inlet steam specific enthalpy dynamic correction signal.

8. The tertiary superheating desuperheating water coordinated control method of an ultra-supercritical boiler according to claim 6, characterized in that, Further comprising inertia time settings of the first-order inertia module LAG5 and the first-order inertia module LAG6 and gain settings of the gain module K2, specifically: The inertia time of the first-order inertia module LAG5 and the first-order inertia module LAG6 is the same, and the setting range is between 5s and 10s; The gain setting range of the gain module K2 is between 0.5 and 1.0; and the smaller the inertia time of the first-order inertia module LAG5 and the first-order inertia module LAG6, the greater the gain of the gain module K2, and the two are inversely proportional.

9. The coordinated control method of tertiary superheating desuperheating water of an ultra-supercritical boiler according to any one of claims 1-8, characterized in that, The generation steps of the screen superheater (11) outlet steam temperature set value include: Based on the third-stage superheating desuperheating water flow regulating valve (16) opening degree instruction signal, after filtering processing by a first-order inertia module LAG7, a bias value signal of the screen superheater (11) outlet steam temperature set value is calculated by an event-driven control module DSCT; The reference value signal of the screen superheater (11) outlet steam temperature set by the operator is added to the bias value signal through an addition module SUM4, and the screen superheater (11) outlet steam temperature set value in the second-stage superheating desuperheating water control system is obtained.

10. The tertiary superheating desuperheating water coordinated control method of an ultra-supercritical boiler according to claim 9, characterized in that, The internal control calculation steps of the event-driven control module DSCT include: In the event-driven control module DSCT, when the filtered third-stage superheating desuper spray valve (16) opening degree command signal is less than the low threshold signal L and lasts for a certain time, a one-time input signal less than the low threshold event is generated, thus triggering the output signal to control the bias value of the screen superheater (11) outlet steam temperature set value to increase by one temperature step; When the filtered third-stage superheating desuper spray valve (16) opening degree command signal is greater than the high threshold signal H and lasts for a certain time, a one-time input signal greater than the high threshold event is generated, thus triggering the output signal to control the bias value of the screen superheater (11) outlet steam temperature set value to decrease by one temperature step; When the input signal is greater than the low threshold signal L and less than the high threshold signal H, the bias value of the screen superheater (11) outlet steam temperature set value remains unchanged.

11. A triple-superheating desuperheating water coordinated control system of an ultra-supercritical boiler, characterized in that, The unit distributed control system comprises a first-stage superheating desuper spray control system, a second-stage superheating desuper spray control system and a third-stage superheating desuper spray control system built in a configuration mode; The ultra-supercritical boiler three-stage superheating desuper spray collaborative control system is used for realizing the ultra-supercritical boiler three-stage superheating desuper spray collaborative control method according to any one of claims 1-10. ​

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