Sliding pressure rate self-adaptive control method in thermal power generating unit RB process

Abstract

The invention discloses a sliding pressure rate self-adaptive control method in the RB process of a thermal power generating unit, which comprises the following steps: step 1, judging whether a condition for triggering an RB function is met, and if so, entering step 2; step 2, outputting a new steam turbine total flow instruction fluu'by the steam turbine main control PI according to the main steam pressure deviation delta p, and obtaining a corresponding target opening degree of a steam turbine adjusting steam valve; step 3, calculating a sliding pressure target instruction descent rate a; step 4, calculating a sliding pressure target instruction descent rate alited after rate limitation, and transmitting the sliding pressure target instruction descent rate alited to a steam turbine and a boiler; and 5, judging whether the RB mode is exited or not. According to the method, the sliding pressure target instruction descent rate a is dynamically adjusted and corrected according to the main steam pressure deviation delta p and the steam turbine total flow instruction flu, so that the sliding pressure target instruction descent rate a adapts to the actual working condition; pI closed-loop control is adopted for steam turbine master control under the RB working condition, so that the system maintains all parameters within a safe range while rapidly reducing the load.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal power plant control, and more particularly to a method for adaptively controlling a sliding pressure rate during a RB process of a thermal power plant. Background Art

[0002] During the RB process of a thermal power unit, controlling the sliding pressure rate is crucial. When a single-side critical auxiliary unit, such as an induced draft fan or forced draft fan, fails and ceases operation, the unit must rapidly reduce its load to the capacity of the operating auxiliary units. During this process, a reasonable reduction in main steam pressure is crucial for maintaining energy balance between the boiler and turbine. A too rapid pressure drop can lead to a sudden drop in steam temperature and instability in the feedwater system; a too slow pressure drop can prevent the timely release of stored heat in the boiler, leading to the risk of overpressure. Accurate sliding pressure control is crucial for maintaining safe and stable unit operation.

[0003] Existing technology uses an open-loop control scheme to regulate the sliding pressure rate: After the RB is triggered, the system generates a sliding pressure target command based on the target load using a fixed function. This command is then processed by a rate limiter and an inertia link, and ultimately output to the turbine master control PI to control the total turbine flow. This method relies entirely on preset load-pressure curves and manual experience, and is essentially a static feedforward control method.

[0004] This traditional control method has significant drawbacks. First, the fixed sliding pressure rate cannot adapt to the dynamic changes in the boiler's actual heat load, often resulting in a mismatch between the set pressure and the actual pressure, leading to problems such as main steam temperature fluctuations and cylinder exhaust overheating. Second, there is a lack of real-time feedback on the turbine's flow capacity. When the total flow command is too low, it can easily lead to insufficient steam source pressure for the feedwater pump or insufficient cooling flow for the high-pressure cylinder. Summary of the Invention

[0005] The technical problem to be solved by the present application is to address the deficiencies in the above-mentioned prior art and provide a method for adaptively controlling the sliding pressure rate during the RB process of a thermal power unit. The method has a simple structure and a reasonable design. The sliding pressure target instruction decrease rate a is dynamically adjusted and corrected according to the main steam pressure deviation Δp and the turbine total flow instruction flu, so that the sliding pressure target instruction decrease rate a adapts to the actual working conditions. The PI closed-loop control is adopted to enable the system to maintain various parameters within a safe range while rapidly reducing the load, and the use effect is good.

[0006] To solve the above technical problems, the technical solution adopted in this application is: a method for adaptively controlling the sliding pressure rate during the RB process of a thermal power unit, characterized in that it includes the following steps:

[0007] Step 1: Monitor the status of the thermal power unit to determine whether the conditions for triggering the RB function are met. If so, proceed to step 2.

[0008] Step 2: Calculate the main steam pressure deviation Δp. The turbine master control outputs a new turbine total flow command flu' based on the main steam pressure deviation Δp, where the main steam pressure deviation Δp is the difference between the main steam pressure set value and the actual main steam pressure value. The target opening of the corresponding turbine regulating valve is obtained based on the new turbine total flow command flu'; the turbine regulating valve is driven to the target opening.

[0009] Step 3. Calculate the sliding pressure target command descent rate: the sliding pressure target command descent rate a, a = a3 + a1 × a2, where a1 represents the first rate correction coefficient, a1 = f1(Δp), f1(·) represents the first rate correction function, and Δp represents the main steam pressure deviation; a2 represents the second rate correction coefficient, a2 = f2(flu'), f2(·) represents the second rate correction function; a3 represents the preset sliding pressure descent rate corresponding to the RB type;

[0010] Step 4: Calculate the sliding pressure target instruction descent rate a after rate limitation limited ; Sliding pressure target instruction descent rate a limited Transmitted to the steam turbine and boiler to dynamically adjust the main steam pressure set point;

[0011] Step 5: Determine whether the exit condition is met. If so, proceed to step 6; otherwise, return to step 2.

[0012] Step 6. Exit RB mode and switch to normal sliding pressure control.

[0013] The above-mentioned method for adaptively controlling the sliding pressure rate during the RB process of a thermal power unit is characterized in that the first rate correction function f1(·) and the second rate correction function f2(·) are both broken line functions.

[0014] The above-mentioned method for adaptively controlling the sliding pressure rate during the RB process of a thermal power unit is characterized by:

[0015]

[0016] The above-mentioned method for adaptively controlling the sliding pressure rate during the RB process of a thermal power unit is characterized in that: in step 2, the specific method of "obtaining the corresponding target opening of the turbine regulating steam valve based on the new turbine total flow instruction flu'" is to check the opening-flow curve of the turbine regulating steam valve based on the new turbine total flow instruction flu' to obtain the corresponding target opening of the turbine regulating steam valve.

[0017] The above-mentioned method for adaptively controlling the sliding pressure rate during the RB process of a thermal power unit is characterized in that: the opening-flow curve of the turbine regulating steam valve includes the opening-flow curve of the ultra-high pressure regulating valve, the opening-flow curve of the high pressure regulating valve, and the opening-flow curve of the medium pressure regulating valve; the turbine regulating steam valve includes the ultra-high pressure regulating valve, the high pressure regulating valve, and the medium pressure regulating valve; the new turbine total flow instruction flu' is converted into the opening instruction of the ultra-high pressure regulating valve through the opening-flow curve of the ultra-high pressure regulating valve, the opening-flow curve of the high pressure regulating valve is converted into the opening instruction of the high pressure regulating valve, and the opening-flow curve of the medium pressure regulating valve is converted into the opening instruction of the medium pressure regulating valve.

[0018] The above-mentioned method for adaptively controlling the sliding pressure rate during the RB process of a thermal power unit is characterized in that the exit condition in step 5 includes:

[0019] Exit condition 1: main steam pressure fluctuation <±0.3MPa for duration t1;

[0020] Exit condition 2, load fluctuation <±2% rated value for duration t2;

[0021] Exit condition 3: main steam temperature fluctuation <±5℃ for duration t3;

[0022] Exit condition 4, feed water flow and steam flow balance duration t4;

[0023] When any of the exit conditions fluctuates beyond the limit, the timing of other exit conditions will be reset to zero and the process will return to step 2.

[0024] The above-mentioned method for adaptively controlling the sliding pressure rate during the RB process of a thermal power unit is characterized in that: in step three, where a t-k represents the initial drop rate of the kth control cycle, R max Indicates the maximum allowable rate of change, △t indicates the control period, a min Indicates the minimum descent rate, a max Indicates the maximum descent rate.

[0025] The above-mentioned method for adaptively controlling the sliding pressure rate during the RB process of a thermal power unit is characterized in that: in step 203, the RB types include primary fan RB, forced draft fan RB, induced draft fan RB, feed water pump RB, coal mill RB, and air preheater RB.

[0026] The above-mentioned method for adaptive control of sliding pressure rate during RB process of thermal power unit is characterized in that: in step 2, the main control of the steam turbine is PI controller, the proportional gain Kp=1.4, the integral time constant Ki=40s -1 , the rated main steam pressure base value is 310bar.

[0027] Compared with the prior art, this application has the following advantages:

[0028] 1. The structure of this application is simple, the design is reasonable, and it is easy to implement and use.

[0029] 2. The sliding pressure rate adaptive control method of the present application dynamically adjusts and corrects the sliding pressure target instruction decrease rate a according to the main steam pressure deviation Δp and the turbine total flow instruction flu, avoiding the one-sidedness of single parameter control, preventing pressure runaway caused by delayed boiler heat storage release, and avoiding the overheating risk caused by insufficient turbine flow, significantly improving the control accuracy and safety of the RB process, and making the sliding pressure target instruction decrease rate a adapt to actual working conditions.

[0030] 3. In the adaptive control of the sliding pressure rate during the RB process of a thermal power unit, the present application adopts PI control, outputs a new total turbine flow command flu' based on the deviation Δa, and in the next control cycle, calculates a second rate correction coefficient a2 based on the new total turbine flow command flu', thereby achieving closed-loop control. This allows the system to maintain various parameters within a safe range while rapidly reducing the load, achieving good results.

[0031] In summary, the present application dynamically adjusts and corrects the sliding pressure target instruction decrease rate a according to the main steam pressure deviation Δp and the turbine total flow instruction flu, so that the sliding pressure target instruction decrease rate a adapts to the actual working conditions; and adopts PI closed-loop control to enable the system to maintain various parameters within a safe range while rapidly reducing the load, with good use effect.

[0032] The technical solution of the present application is further described in detail below through the accompanying drawings and examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a flow chart of the method of this application.

[0034] Figure 2 This is the control logic diagram of PI for this application.

[0035] Figure 3 This is a flow chart of the method for calculating the sliding pressure target instruction descent rate in this application. DETAILED DESCRIPTION

[0036] The present application will be further described in detail below with reference to the accompanying drawings and embodiments of the present application.

[0037] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0038] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0039] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can, for example, be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0040] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used herein to describe the spatial positional relationship of a device or feature to other devices or features as shown in the figures. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figures. For example, if the device in the drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0041] like Figure 1 、 Figure 2 and Figure 3 As shown, a method for adaptively controlling the sliding pressure rate during the RB process of a thermal power unit of the present application comprises the following steps:

[0042] Step 1: Monitor the status of the thermal power unit to determine whether the conditions for triggering the RB function are met. If so, proceed to step 2.

[0043] Step 2: Calculate the main steam pressure deviation Δp. The turbine master control outputs a new turbine total flow command flu' based on the main steam pressure deviation Δp, where the main steam pressure deviation Δp is the difference between the main steam pressure set value and the actual main steam pressure value. Based on the new turbine total flow command flu', the corresponding target opening of the turbine regulating steam valve is obtained; the turbine regulating steam valve is driven to the target opening.

[0044] The turbine master control PI performs dynamic PI calculations based on the main steam pressure deviation Δp and outputs a new turbine total flow command flu'; the corresponding target opening of the turbine regulating valve is obtained based on the new turbine total flow command flu'; and the turbine regulating valve is driven to the target opening. Then, in the next control cycle, the first rate correction coefficient a1 is calculated based on the main steam pressure deviation Δp, and the second rate correction coefficient a2 is calculated based on the new turbine total flow command flu', thereby achieving closed-loop control. In step 2, the turbine master control is a PI controller with a proportional gain Kp = 1.4 and an integral time constant Ki = 40s. -1 , the rated main steam pressure base value is 310bar.

[0045] After the turbine master control PI output is the new total turbine flow command flu', the target opening of the turbine regulating valve corresponding to the new total turbine flow command flu' is obtained by checking the opening-flow curves of the turbine regulating valves. The opening-flow curves of the turbine regulating valves include the opening-flow curves of the ultra-high pressure regulating valve, the opening-flow curves of the high pressure regulating valve, and the opening-flow curves of the medium pressure regulating valve. The turbine regulating valves include the ultra-high pressure regulating valve, the high pressure regulating valve, and the medium pressure regulating valve. The new total turbine flow command flu' is converted to the opening command of the ultra-high pressure regulating valve using the opening-flow curve of the ultra-high pressure regulating valve, the opening-flow curve of the high pressure regulating valve into the opening command of the high pressure regulating valve, and the opening-flow curve of the medium pressure regulating valve into the opening command of the medium pressure regulating valve.

[0046] Table 1 shows the opening-flow curve for the ultra-high-pressure regulating valve. This shows the correspondence between the total turbine flow demand command flu' and the target opening demand CV Dmd of the high-pressure regulating valve under specific per-unit normalization rules (0-100 per-unit converted to a range of 0-1). For example, when flu' = 0.7476, CV Dmd = 0.2231, indicating that the turbine is operating at 74.76% of the rated flow and the ultra-high-pressure regulating valve is open to 22.31% of the rated opening.

[0047] Table 1 Opening-flow curve of ultra-high pressure regulating valve

[0048]

[0049] In the steam turbine control system, the turbine master control PI outputs a new total turbine flow command, flu', based on the main steam pressure deviation Δp. By increasing or decreasing flu', the control valve opening is adjusted, thereby controlling the rate of change of the main steam pressure. After receiving the ultra-high-pressure, high-pressure, and intermediate-pressure control valve opening commands, the servo valve actuates the control valve. By adjusting the control valve opening, the rate of boiler heat load reduction is matched to the turbine flow rate, thereby stabilizing the main steam temperature, preventing the turbine exhaust temperature from exceeding the limit, and maintaining the steam source pressure of the feedwater pump.

[0050] Step 3. Calculate the sliding pressure target instruction descent rate: the sliding pressure target instruction descent rate a, a=a3+a1×a2, a1 represents the first rate correction coefficient, a1=f1(Δp), f1(·) represents the first rate correction function, Δp represents the main steam pressure deviation; a2 represents the second rate correction coefficient, a2=f2(flu'), f2(·) represents the second rate correction function; a3 represents the preset sliding pressure descent rate corresponding to the RB type.

[0051] Regarding the first rate correction coefficient a1: the heat released by the boiler Q is mainly composed of the convection heat transfer Q dl And the radiation heat transfer Q fs Composition, Q = Q dl +Q fs After the thermal power unit RB triggers load reduction, the amount of fuel and air volume in the furnace decreases rapidly, resulting in the convective heat transfer Q dl Then it drops rapidly. Due to the delay in the temperature drop of the furnace wall and the heat exchange tube row wall, the radiation heat transfer Q fs The rate of decrease is slow. Due to the varying number and location of radiant heat exchange surfaces in different boilers, the type of coal burned, and the ash accumulation on the heat exchange tubes before RB occurs, the rate of decrease in heat release varies across different boiler types and at different times during RB. The decrease in heat release Q delays the unit's vaporization process, accelerating the decrease in the actual evaporation rate D. At this point, if the openings of the turbine's high-pressure and medium-pressure regulating valves remain unchanged, the boiler evaporation rate D is approximately proportional to the main steam pressure, and the rate of decrease in boiler evaporation rate is directly reflected in the actual rate of decrease in main steam pressure. The main steam pressure deviation Δp is the difference between the target and actual main steam pressure values. If the actual main steam pressure is lower than the target value (i.e., the main steam pressure deviation Δp > 0), it indicates that the boiler evaporation rate D is decreasing too rapidly, and the preset sliding pressure target command does not match the actual change in boiler heat release. Therefore, the preset sliding pressure decrease rate a3 needs to be increased to match the change in heat load.

[0052] Therefore, it is necessary to correct the current preset sliding pressure drop rate a3 in combination with the main steam pressure deviation Δp to make the sliding pressure control more suitable for the actual working conditions and avoid steam temperature fluctuations or turbine exhaust temperature exceeding the limit. In actual use, the main steam pressure deviation Δp is mapped to the first rate correction coefficient a1 through the first rate correction function f1(Δp), which is used to correct the preset sliding pressure drop rate a3. f1(Δp) is a broken line function. In one possible embodiment,

[0053] Taking a 1000MW double reheat unit as an example, the relationship between the main steam pressure deviation Δp and the first rate correction coefficient a1 is shown in Table 2:

[0054] Table 2 Comparison table of main steam pressure deviation and first rate correction coefficient of preset sliding pressure drop rate

[0055]

[0056] In one possible embodiment, taking a 1000MW unit as an example, when the load is 100%, the target main steam pressure is 30.0MPa; when the load is 80%, the target main steam pressure is 24.0MPa; when the load is 60%, the target main steam pressure is 18.0MPa; and when the load is 50%, the target main steam pressure is 15.0MPa.

[0057] Δp=0, indicating that the main steam pressure target value is consistent with the actual value and no correction is required. At this time, a1=f1(Δp)=0, and the sliding pressure rate is dominated by the preset sliding pressure drop rate a3; 0<Δp≤2, indicating that the actual value of the main steam pressure is too small, at this time the first rate correction coefficient a1 increases linearly according to 1.1Δp-0.7; 2<Δp≤3, indicating that the main steam pressure deviation Δp increases, and the correction coefficient is adjusted at an accelerated rate; Δp>3, indicating that the main steam pressure deviation Δp is too large, and the correction coefficient reaches the upper limit.

[0058] Regarding the second rate correction coefficient a2: The total turbine flow command flu represents the deviation between the preset sliding pressure drop rate a3 and the required flow capacity of the turbine. Its essence lies in the fact that flu directly reflects the dynamic regulation of the turbine control valve opening on the steam flow. If the total turbine flow command flu is too small, on the one hand, it will cause the opening of the turbine high-pressure control valve group to be too low, causing the exhaust temperature to exceed the limit or insufficient steam source pressure of the feedwater pump. The steam flow throttled into the turbine cannot meet the minimum cooling flow required by the turbine cylinder, resulting in excessive cylinder exhaust temperature. On the other hand, it will cause the opening of the intermediate-pressure control valve group to decrease, which will also cause the extraction pressure of the intermediate and low-pressure cylinders of the turbine to drop, further causing insufficient steam source pressure of the feedwater pump turbine, reducing the output and sensitivity of the feedwater flow regulation.

[0059] Therefore, it is necessary to correct the current preset sliding pressure decrease rate a3 in combination with the total steam turbine flow command flu, so that the sliding pressure control is more in line with the actual working conditions, ensure that the steam flow meets the requirements, and avoid the exhaust steam temperature exceeding the limit caused by the low opening of the high-pressure control valve and the decrease of the steam source pressure of the feed water pump caused by the insufficient opening of the intermediate-pressure control valve.

[0060] In actual use, the total steam turbine flow command flu is mapped into the second rate correction coefficient a2 through the second rate correction function a2 = f2(flu'), which is used to correct the preset sliding pressure decrease rate a3. a2 = f2(flu') is a piecewise function. In a possible embodiment,

[0061] Taking a certain 1000MW unit with double reheat as an example, the relationship between the total steam turbine flow command flu and the second rate correction coefficient a2 is shown in Table 3:

[0062] Table 3 Comparison table of the preset sliding pressure decrease rate, the total steam turbine flow command and the second rate correction coefficient

[0063]

[0064] When flu = 0, it means that the ultra-high pressure control valve, high-pressure control valve, and intermediate-pressure control valve are all closed, cutting off the steam inlet. The second rate correction coefficient a2 takes the maximum value, a2 = 5.0, and the preset sliding pressure decrease rate a3 is forced to accelerate to protect the steam turbine. When 0 < flu ≤ 70%, it means that the opening of the steam turbine control valve is too small, and there is a risk of the exhaust steam temperature exceeding the limit. It is necessary to increase the opening of the steam turbine control valve, and the value of the second rate correction coefficient a2 is greater than 1. When flu > 70%, it means that the flow command is sufficient and no correction is required, a2 = 0, and the sliding pressure rate is dominated by the preset sliding pressure decrease rate a3.

[0065] Regarding the preset sliding pressure decrease rate a3: The preset sliding pressure decrease rate a3 is set according to different types of RB. It should be noted that different types of RB include primary fan RB, forced draft fan RB, induced draft fan RB, feed water pump RB, coal mill RB, and air preheater RB. In a possible embodiment, taking a 1000MW unit as an example, when it is primary fan RB, the preset sliding pressure decrease rate a3 = 1.8 MPa / min; when it is forced draft fan RB, the preset sliding pressure decrease rate a3 = 1.5 MPa / min; when it is induced draft fan RB, the preset sliding pressure decrease rate a3 = 1.2 MPa / min; when it is feed water pump RB, the preset sliding pressure decrease rate a3 = 2.5 MPa / min; when it is coal mill RB, the preset sliding pressure decrease rate a3 = 3.0 MPa / min; when it is air preheater RB, the preset sliding pressure decrease rate a3 = 1.0 MPa / min.

[0066] The sliding pressure target command decrease rate a is calculated based on the second rate correction coefficient a1, the second rate correction coefficient a2, and the preset sliding pressure decrease rate a3, where a = a3 + a1 × a2. Through dynamic correction, the sliding pressure target command decrease rate a is adapted to the actual operating conditions to avoid parameter fluctuations.

[0067] Compared with using only the total turbine flow command flu correction, adding the main steam pressure deviation Δp correction can more accurately identify insufficient heat storage release or excessive pressure reduction; this dual-parameter collaborative control realizes the synchronous response of the thermal inertia on the boiler side and the flow restriction on the turbine side, avoiding the one-sidedness of single-parameter control, preventing pressure runaway due to delayed boiler heat storage release, and avoiding the overheating risk caused by insufficient turbine flow, significantly improving the control accuracy and safety of the RB process.

[0068] Step 4: Calculate the sliding pressure target instruction descent rate a after rate limitation limited ; Sliding pressure target instruction descent rate a limited The pressure is transmitted to the steam turbine and boiler to dynamically adjust the main steam pressure setting value. In the RB control process of the thermal power unit, the sliding pressure target instruction drop rate a after setting the rate limit is set. limited The core significance of this is to balance control response speed and equipment safety. By limiting the rate of change of the sliding pressure target command decrease rate a, the system can avoid drastic valve control movements caused by sudden command changes, thereby protecting the turbine valves and actuators from mechanical shock and preventing thermal stress damage to the boiler drum and piping caused by sudden drops in main steam pressure.

[0069] In one possible embodiment, where a t-k represents the initial drop rate of the kth control cycle, R max Indicates the maximum allowable rate of change, △t indicates the control period, a min Indicates the minimum descent rate, a max Indicates the maximum descent rate. min Usually set to 0, a max Usually set to 6 to 10.

[0070] If the calculation in step 3 yields a=3.0MPa / min, and the actual pressure drop rate a t =1.0MPa / min, the sliding pressure command suddenly changes from 1.0MPa / min to 3.0MPa / min, which may cause the turbine regulating steam valve to open instantly, resulting in a surge in steam flow, and thus threatening the safety of the unit. max The constraint makes the actual pressure drop rate a t With the maximum allowable change rate R maxThe smooth transition to a naturally matches the pressure change with the boiler heat load reduction rate, which not only ensures the life of the equipment but also maintains the stability of the control process.

[0071] Step 5: Determine whether the exit conditions are met. If so, proceed to step 6; otherwise, return to step 2. Exit conditions include:

[0072] Exit condition 1: main steam pressure fluctuation <±0.3MPa for duration t1;

[0073] Exit condition 2, load fluctuation <±2% rated value for duration t2;

[0074] Exit condition 3: main steam temperature fluctuation <±5℃ for duration t3;

[0075] Exit condition 4, feed water flow and steam flow balance duration t4;

[0076] If exit conditions 1-4 are met simultaneously, proceed to step 6 to exit RB mode. If any of the exit conditions fluctuates beyond the limit, the timing of the other exit conditions is reset to zero and the system returns to step 2.

[0077] In one possible embodiment, t1 = t2 = t3 = t4 = 30 s.

[0078] Taking the unit's primary fan RB test as an example, the parameters set before the test are: the target load of the primary fan after RB is 450MW, the load reduction rate is 2000MW / min, and the preset sliding pressure reduction rate a3 is 1.8MPa / min.

[0079] Before the test, the unit operating parameters were as follows: control mode: coordinated mode; unit load: 912.4MW; main steam pressure: 30.28MPa; primary air pressure: 10.15kPa; furnace negative pressure: -180.5Pa; coal feed rate: 339.8t / h; operating pulverizers: A, B, C, D, and E pulverizers.

[0080] The operator manually stops the primary fan on the B side before the panel to trigger the RB action. The coordination screen displays "primary fan RB" and the unit operation mode automatically switches from coordination to TF operation. After the RB action, the unit quickly reduces the load, and the load target value is 450MW. The boiler master control quickly reduces the air, coal, and water according to the RB target load and rate to control the boiler load. During the test, the actual change rate of the main steam pressure is a tThe main steam pressure deviation Δp is 1.79 to 2.28 MPa / min, and the maximum main steam pressure deviation Δp is 1.55 MPa, corresponding to the first rate correction coefficient a1 = 0.605. The total turbine flow command flu drops to a minimum of 61.05%. At this time, the opening of the ultra-high pressure control valve group is 21.91%, the opening of the high pressure control valve group is 34.63%, and the opening of the medium pressure control valve group is 34.30%, corresponding to the second rate correction coefficient a2 = 3.031. The corrected sliding pressure target command decrease rate a = 1.8 + 0.605 × 3.031 = 3.634 MPa / min. The PI accelerates pressure reduction by increasing the flu. The ultra-high pressure, high pressure, and medium pressure control valve groups gradually adjust their openings based on the flu' output of the PI, after cylinder flow calculation and flow curve conversion. The total turbine flow command gradually increases to 73.44% and ultimately remains stable, achieving rapid matching of boiler heat load and turbine inlet steam flow, effectively ensuring the stability of the main reheat steam temperature. During the test, the turbine ultra-high pressure cylinder exhaust temperature reached a maximum of 416.41°C, the high pressure cylinder exhaust temperature reached a maximum of 444.70°C, and the feedwater pump turbine inlet steam pressure reached a minimum of 0.8 MPa. No abnormalities such as high cylinder exhaust temperature alarms or tripping were observed. The steam source to the feedwater pump turbine was stable, ensuring the quality of feedwater flow regulation.

[0081] 6 minutes and 16 seconds after the primary wind turbine RB was triggered, the actual load of the unit dropped to 592.6MW. The parameters of the unit are shown in Table 3. The parameters are basically stable, and the primary wind turbine RB test is completed.

[0082] Table 3 Main parameter records of primary fan RB working condition unit

[0083]

[0084] By real-time correction of the sliding pressure target command descent rate a and the regulating valve opening, the main steam temperature dropped from an initial 597.5°C to a minimum of 567.2°C before recovering to 594.1°C, within a fluctuation range of ±5°C and well below the trip threshold. The main steam pressure decreased from the preset sliding pressure descent rate MPa of 30.28 to 21.61 MPa, with an actual rate of 1.79 to 2.28 MPa / min, without significant fluctuations, thus preventing thermal stress damage to the boiler. The sliding pressure target command descent rate a is dynamically adjusted based on the main steam pressure deviation Δp and the total turbine flow command flu, replacing traditional fixed-rate control and reducing the operational burden on operators.

[0085] The above description is merely an embodiment of the present application and does not constitute any limitation to the present application. Any simple modifications, changes, and equivalent structural changes made to the above embodiments based on the technical essence of the present application shall still fall within the scope of protection of the technical solution of the present application.

Claims

1. A method for adaptively controlling the sliding pressure rate during the RB process of a thermal power unit, characterized by: The following steps are involved: Step 1: Monitor the status of the thermal power unit to determine whether the conditions for triggering the RB function are met. If so, proceed to step 2. Step 2: Calculate the main steam pressure deviation Δp. The turbine master control outputs a new turbine total flow command flu' based on the main steam pressure deviation Δp, where the main steam pressure deviation Δp is the difference between the main steam pressure set value and the actual main steam pressure value. The target opening of the corresponding turbine regulating valve is obtained based on the new turbine total flow command flu'; the turbine regulating valve is driven to the target opening. Step 3. Calculate the sliding pressure target command descent rate: the sliding pressure target command descent rate a, a = a3 + a1 × a2, where a1 represents the first rate correction coefficient, a1 = f1(Δp), f1(·) represents the first rate correction function, and Δp represents the main steam pressure deviation; a2 represents the second rate correction coefficient, a2 = f2(flu'), f2(·) represents the second rate correction function; a3 represents the preset sliding pressure descent rate corresponding to the RB type; Step 4: Calculate the sliding pressure target instruction descent rate a after rate limitation limited ; Sliding pressure target instruction descent rate a limited Transmitted to the steam turbine and boiler to dynamically adjust the main steam pressure set point; Step 5: Determine whether the exit condition is met. If so, proceed to step 6; otherwise, return to step 2. Step 6. Exit RB mode and switch to normal sliding pressure control.

2. The method for adaptively controlling the sliding pressure rate during the RB process of a thermal power plant according to claim 1, characterized in that: The first rate correction function f1(·) and the second rate correction function f2(·) are both broken line functions.

3. A method for adaptively controlling sliding pressure rate during RB process of a thermal power plant according to claim 1 or 2, characterized in that:

4. The method for adaptively controlling the sliding pressure rate during the RB process of a thermal power plant according to claim 1, characterized in that: The specific method for "obtaining the corresponding target opening of the turbine regulating steam valve based on the new turbine total flow command flu'" in step 2 is to check the opening-flow curve of the turbine regulating steam valve based on the new turbine total flow command flu' to obtain the corresponding target opening of the turbine regulating steam valve.

5. The method for adaptively controlling the sliding pressure rate during the RB process of a thermal power plant according to claim 4, characterized in that: The opening-flow curve of the steam turbine regulating valve includes the opening-flow curve of the ultra-high pressure regulating valve, the opening-flow curve of the high pressure regulating valve, and the opening-flow curve of the medium pressure regulating valve; the steam turbine regulating valve includes the ultra-high pressure regulating valve, the high pressure regulating valve and the medium pressure regulating valve; the total flow instruction flu' of the new steam turbine is converted into the opening instruction of the ultra-high pressure regulating valve through the opening-flow curve of the ultra-high pressure regulating valve, is converted into the opening instruction of the high pressure regulating valve through the opening-flow curve of the high pressure regulating valve, and is converted into the opening instruction of the medium pressure regulating valve through the opening-flow curve of the medium pressure regulating valve.

6. The method for adaptively controlling the sliding pressure rate during the RB process of a thermal power plant according to claim 1, characterized in that: The exit conditions in step 5 include: Exit condition 1: main steam pressure fluctuation <±0.3MPa for duration t1; Exit condition 2, load fluctuation <±2% rated value for duration t2; Exit condition 3: main steam temperature fluctuation <±5℃ for duration t3; Exit condition 4, feedwater flow and steam flow balance duration t4; When any of the exit conditions fluctuates beyond the limit, the timing of other exit conditions will be reset to zero and the process will return to step 2.

7. The method for adaptively controlling the sliding pressure rate during the RB process of a thermal power plant according to claim 1, characterized in that: In step four, where a t-k represents the initial drop rate of the kth control cycle, R max Indicates the maximum allowable rate of change, △t indicates the control period, a min Indicates the minimum descent rate, a max Indicates the maximum descent rate.

8. The method for adaptively controlling the sliding pressure rate during the RB process of a thermal power plant according to claim 1, characterized in that: In step three, RB types include primary fan RB, forced draft fan RB, induced draft fan RB, feed water pump RB, coal mill RB, and air preheater RB.

9. The method for adaptively controlling the sliding pressure rate during the RB process of a thermal power plant according to claim 1, characterized in that: In step 2, the turbine master controller is a PI controller with a proportional gain Kp = 1.4 and an integral time constant Ki = 40s. -1 , the rated main steam pressure base value is 310bar.

Images