Prediction method for reheat steam temperature regulation

Abstract

The invention discloses a prediction method for reheat steam temperature adjustment, and the method comprises the steps: S1, collecting a measurement value of the reheat steam temperature, and carrying out the preprocessing; s2, inputting the preprocessed measurement value into a first-order differential loop and a second-order differential loop of a T1 period, and performing piecewise function conversion to obtain a variable speed data value and a variable acceleration data value under the T1 period; s3, obtaining a changed speed data value and a changed acceleration data value in the T2 period; s4, the calculation results in the step S2 and the step S3 and the measured value of the reheat steam temperature are sent into an accumulator 1 to be accumulated, and a predicted value 1 of the reheat steam temperature and a predicted value 2 of the reheat steam temperature are obtained; the predicted value 1 of the reheat steam temperature and the predicted value 2 of the reheat steam temperature serve as process variables to be sent into a PID regulator 1 and a PID regulator 2 respectively; a result obtained by the PID regulator is sent to an accumulator 2; and a result obtained by the accumulator 2 is converted by a piecewise function and then is sent to a reheated flue gas baffle plate to control the action of the reheated flue gas baffle plate.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal automatic control in thermal power plants. Specifically, it relates to a prediction method for reheated steam temperature regulation. Background Art

[0002] In power generation enterprises, the economy of equipment is an important factor affecting the operation of the enterprise, and the reheated steam temperature is one of the economic indicators of the generator set. If the reheated steam temperature is too low, it will increase the humidity of the last-stage blades of the steam turbine and reduce the efficiency of the thermal cycle. If the reheated steam temperature is too high, it will affect the safety of the reheater and is prone to tube burst. Therefore, we need to control the reheated steam temperature in a suitable state to improve the economy and safety of the unit.

[0003] The current steam reheater used in thermal power plants is an intermediate reheater, and its heat transfer effect is affected by factors such as the furnace flue gas temperature, flow rate, and flow. The control mainly uses changing the flue gas flow as the main means. Using this conventional PID control loop will have problems such as large overshoot, poor robustness, and slow adjustment speed, with a large lag. Summary of the Invention

[0004] Aiming at the problem that the existing reheated steam temperature control loop has a large lag, the present invention provides a prediction method for reheated steam temperature regulation, enabling the adjustment loop to act in advance, so that the reheated steam temperature changes within the allowable range during the dynamic process and is equal to the set value at steady state, avoiding parameter imbalance caused by excessive lag.

[0005] To achieve the above technical objectives, the technical solution adopted by the present invention is as follows:

[0006] A prediction method for reheated steam temperature regulation, comprising the steps of:

[0007] S1. Collect the measured value of the reheated steam temperature through a thermocouple thermometer and preprocess the measured value of the reheated steam temperature;

[0008] S2. Input the preprocessed measured value of the reheated steam temperature into the first-order and second-order differential circuits with a T1 period, and after conversion by a piecewise function, obtain the velocity data value of the reheated steam temperature change and the acceleration data value of the reheated steam temperature change under the T1 period;

[0009] S3. Input the preprocessed measured value of the reheated steam temperature into the first-order and second-order differential circuits with a T2 period, and after conversion by a piecewise function, obtain the velocity data value of the reheated steam temperature change and the acceleration data value of the reheated steam temperature change under the T2 period;

[0010] S4. Feed the calculation results in steps S2 and S3 and the measured value of the reheated steam temperature itself into accumulator 1 for accumulation to obtain predicted value 1 of the reheated steam temperature and predicted value 2 of the reheated steam temperature;

[0011] S5. Feed predicted value 1 of the reheated steam temperature as a process variable into PID regulator 1;

[0012] S6. Feed predicted value 2 of the reheated steam temperature as a process variable into PID regulator 2;

[0013] S7. Feed the result obtained by the PID regulator into accumulator 2;

[0014] S8. At the same time, according to the correspondence between the load and the reheated steam temperature, convert the load through a piecewise function and feed it as feedforward 1 into accumulator 2;

[0015] S9. According to the influence of the variable load feedforward on the reheated steam temperature, convert the variable load feedforward through a piecewise function and feed it as feedforward 2 into accumulator 2;

[0016] S10. The result obtained by accumulator 2, after being converted through a piecewise function, is sent to the reheated flue gas damper to control its action.

[0017] Further, use the predicted value as a process variable to control the desuperheating water spray valve of the reheated steam.

[0018] Further, the period of T1 is 60 s and the period of T2 is 30 s.

[0019] Further, the reheated steam is at 600 °C.

[0020] Further, the magnitudes, amplitudes, directions, and rates of change of the predicted value of the reheated steam and the reheated steam temperature value are the same.

[0021] Further, the change in the predicted value of the reheated steam temperature precedes the temperature value itself. It is equivalent to the reheated steam temperature changing in advance.

[0022] Further, use the predicted value of the reheated steam temperature to replace the measured value of the reheated steam temperature as the controlled variable to participate in the control.

[0023] The present invention has the following beneficial effects compared with the prior art:

[0024] By using the predicted value of the reheated steam temperature to replace the measured value of the reheated steam temperature as the controlled variable to participate in the control, this method improves the hysteresis of the reheated steam temperature regulation system, controls the reheated steam temperature in a suitable state, increases the service life of the boiler reheater, and improves the safety and economy of the unit.

[0025] This method finally realizes the regulation of the reheated steam temperature by controlling the reheated flue gas damper. Description of the Drawings

[0026] Figure 1 It is the overall flowchart of a prediction method for reheated steam temperature regulation in an embodiment of the present invention;

[0027] Figure 2 It is the schematic diagram of logical control of a prediction method for reheated steam temperature regulation in an embodiment of the present invention;

[0028] Figure 3 It is the schematic curve diagram of the reheated steam temperature and the predicted value of the reheated steam temperature provided by an embodiment of the present invention;

[0029] Figure 4 It is the schematic diagram of the regulation effect of the reheated steam temperature and the predicted value of the reheated steam temperature provided by an embodiment of the present invention. Detailed Embodiment

[0030] For the convenience of those skilled in the art to understand, the present invention will be further described below in conjunction with the embodiments and the drawings. The content mentioned in the embodiments does not limit the present invention.

[0031] As Figure 1 and 2 shown, this embodiment provides a prediction method for reheated steam temperature regulation, including the steps:

[0032] S1. Collect the measured value of the reheated steam temperature through a thermocouple thermometer, and preprocess the measured value of the reheated steam temperature;

[0033] S2. Input the preprocessed measured value of the reheated steam temperature into the first-order and second-order differential circuits with a period of T1, and obtain the speed data value of the change in the reheated steam temperature and the acceleration data value of the change in the reheated steam temperature after conversion by a piecewise function; the transfer function of the differential circuit is:

[0034]

[0035] where K is the gain, T1 is the lead time, and T2 is the lag time. 1 + T1S is the differential link, and its characteristic is the strengthening of lead and start. 1 + T2S is the first-order inertia link, and its characteristic is lag.

[0036] S3. Input the preprocessed measured value of the reheated steam temperature into the first-order and second-order differential circuits with a period of T2, and obtain the speed data value of the change in the reheated steam temperature and the acceleration data value of the change in the reheated steam temperature after conversion by a piecewise function; the piecewise function is built according to the debugging experience, and the broken line function interval is adjusted according to the actual operating conditions on site.

[0037] S4. Feed the calculation results in steps S2 and S3 and the measured value of the reheated steam temperature itself into accumulator 1 for accumulation to obtain predicted value 1 of the reheated steam temperature and predicted value 2 of the reheated steam temperature;

[0038] S5. Use predicted value 1 of the reheated steam temperature as a process variable and feed it into PID regulator 1;

[0039] S6. Use predicted value 2 of the reheated steam temperature as a process variable and feed it into PID regulator 2;

[0040] S7. Feed the result obtained by the PID regulator into accumulator 2;

[0041] S8. At the same time, according to the corresponding relationship between the load and the reheated steam temperature, convert the load through a piecewise function and feed it as feedforward 1 into accumulator 2;

[0042] S9. According to the influence of the variable load feedforward on the reheated steam temperature, convert the variable load feedforward through a piecewise function and feed it as feedforward 2 into accumulator 2;

[0043] S10. The result obtained by accumulator 2 is sent to the reheated flue gas damper after being converted through a piecewise function to control its action.

[0044] Detailed steps for preprocessing the measured value of the reheated steam temperature:

[0045] Replace the out-of-limit abnormal values of the measured value of the reheated steam temperature with the mean value;

[0046] Complement the missing values of the measured value of the reheated steam temperature with the mean value.

[0047] The change curves of the predicted value of the reheated steam temperature and the measured value of the reheated steam temperature are as Figure 3 shown. It can be seen that after the prediction model is reasonably tuned, at the inflection point where the predicted value increases or decreases, the error from the measured value is within ±1°C, and the time is advanced by 2 - 3 minutes, achieving a good prediction effect.

[0048] When it is put into use in a certain ultra-supercritical reheated thermal power unit, the reheated damper can act approximately 2 - 3 minutes in advance. While ensuring the safety of the system, the regulation speed is increased, the overshoot is reduced, and the regulation hysteresis is weakened. The specific results are as Figure 4 shown.

[0049] Use the predicted value as a process variable to control the spray valve of the reheated steam desuperheating water.

[0050] The period of T1 is 60 s, and the period of T2 is 30 s.

[0051] The reheated steam is at 600°C.

[0052] The magnitude, amplitude, direction, and rate of change of the predicted value of the reheated steam are the same as those of the reheated steam temperature value.

[0053] The change in the predicted value of the reheated steam temperature precedes the temperature value itself. This is equivalent to the reheated steam temperature changing in advance.

[0054] The predicted value of the reheated steam temperature is used to replace the measured value of the reheated steam temperature as the controlled variable and participate in the control.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] By using the predicted value of the reheated steam temperature to replace the measured value of the reheated steam temperature as the controlled variable and participating in the control, this method improves the hysteresis of the reheated steam temperature regulation system, controls the reheated steam temperature in a suitable state, increases the service life of the boiler reheater, and improves the safety and economy of the unit.

[0057] This method ultimately realizes the regulation of the reheated steam temperature by controlling the reheated flue gas damper.

[0058] The working principle is that the result of the first derivative (representing its change speed) and the second derivative (representing its change acceleration) of the measured value in a certain period can predict the inflection point of the change of the measured value. By performing a certain conversion and accumulation on the results of different periods, the result can be matched with the change amplitude of the measured value, and the change trajectory of the measurement point several minutes in advance can be predicted to achieve the prediction function.

[0059] The above provides a detailed introduction to a prediction method for reheated steam temperature regulation provided by this application. The description of specific embodiments is only used to help understand the method and its core idea of this application. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of this application, several improvements and modifications can be made to this application, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A prediction method for reheat steam temperature regulation, characterized in that, Including the steps: S1. Collect the measured value of the reheated steam temperature through a thermocouple thermometer and preprocess the measured value of the reheated steam temperature; S2. Input the preprocessed measured value of the reheated steam temperature into the first-order and second-order differential circuits of the T1 period, and through piecewise function conversion, obtain the velocity data value of the reheated steam temperature change and the acceleration data value of the reheated steam temperature change under the T1 period; S3. Input the preprocessed measured value of the reheated steam temperature into the first-order and second-order differential circuits of the T2 period, and through piecewise function conversion, obtain the velocity data value of the reheated steam temperature change and the acceleration data value of the reheated steam temperature change under the T2 period; S4. Send the calculation results in steps S2 and S3 and the measured value of the reheated steam temperature itself into accumulator 1 for accumulation to obtain the predicted value 1 of the reheated steam temperature and the predicted value 2 of the reheated steam temperature; S5. Use the predicted value 1 of the reheated steam temperature as the process variable and send it into PID regulator 1; S6. Use the predicted value 2 of the reheated steam temperature as the process variable and send it into PID regulator 2; S7. Send the result obtained by the PID regulator into accumulator 2; S8. At the same time, according to the corresponding relationship between the load and the reheated steam temperature, convert the load through a piecewise function and send it into accumulator 2 as feedforward 1; S9. According to the influence of the variable load feedforward on the reheated steam temperature, convert the variable load feedforward through a piecewise function and send it into accumulator 2 as feedforward 2; S10. The result obtained by accumulator 2 is sent to the reheated flue gas damper after piecewise function conversion to control its action.

2. The predictive method for reheated steam temperature regulation according to claim 1, wherein Detailed steps for preprocessing the measured value of the reheated steam temperature: Perform mean value replacement on the out-of-limit abnormal values of the measured value of the reheated steam temperature; Perform mean value supplementation on the missing values of the measured value of the reheated steam temperature.

3. A prediction method for reheated steam temperature regulation according to claim 2, characterized in that, Use the predicted value as the process variable to control the spray valve of the reheated steam desuperheating water.

4. A prediction method for reheated steam temperature regulation according to claim 3, characterized in that, The T1 period is 60s, and the T2 period is 30s.

5. A prediction method for reheated steam temperature regulation according to claim 4, characterized in that, The reheated steam is 600°C.

6. A prediction method for reheated steam temperature regulation according to claim 5, characterized in that The magnitude, amplitude, direction, and rate of change of the predicted value of the reheated steam temperature and the reheated steam temperature value are the same.

7. A prediction method for reheated steam temperature regulation according to claim 6, characterized in that The change of the predicted value of the reheated steam temperature precedes the temperature value itself.

8. A prediction method for reheated steam temperature regulation according to claim 7, characterized in that, Use the predicted value of the reheated steam temperature to replace the measured value of the reheated steam temperature as the regulated variable to participate in the control.

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