CN109654475B - Reheating steam temperature control method for double reheating unit - Google Patents
Reheating steam temperature control method for double reheating unit Download PDFInfo
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- CN109654475B CN109654475B CN201811418931.8A CN201811418931A CN109654475B CN 109654475 B CN109654475 B CN 109654475B CN 201811418931 A CN201811418931 A CN 201811418931A CN 109654475 B CN109654475 B CN 109654475B
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F22—STEAM GENERATION
- F22G—SUPERHEATING OF STEAM
- F22G5/00—Controlling superheat temperature
- F22G5/04—Controlling superheat temperature by regulating flue gas flow, e.g. by proportioning or diverting
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Abstract
The invention discloses a reheating steam temperature control method of a double reheating unit, which comprises a variable frequency control method of a flue gas recirculation fan and an opening control method of a flue gas adjusting baffle; the two control methods comprise a leading differential feedforward unit of the reheated steam temperature after water spraying and a feedforward unit in load change, and meanwhile, an override and locking control unit under special conditions is arranged in the two control loops. The invention solves the problems of mutual coupling between the primary and secondary reheating steam temperatures of the ultra-supercritical secondary reheating unit, slow adjustment speed and the like, respectively controls the total heat absorption capacity of the primary and secondary reheaters by using the frequency converter of the flue gas recirculation fan, controls the primary and secondary reheating steam temperatures by using the flue gas adjusting baffle of the reheater, adopts control measures of feedforward, override, locking and the like, realizes the control precision and response speed of the primary and secondary reheating steam temperatures of the ultra-supercritical secondary reheating unit, and simultaneously ensures the safe and stable operation of the unit.
Description
Technical Field
The invention belongs to the technical field of control over ultra-supercritical secondary reheating units, relates to a method for controlling the temperature of reheated steam of a secondary reheating unit, and particularly relates to a method for controlling the temperature of reheated steam of a boiler of a secondary reheating thermal power unit.
Background
According to the national sustainable development strategy and the requirements of energy conservation and emission reduction, in recent years, the thermal power industry is developed towards higher parameters, supercritical, ultra-supercritical and even secondary reheating thermal power generating units come up to work, the number of the secondary reheating thermal power generating units which are put into operation and reported in China at present is small, and the design of a reheating steam temperature control scheme is still a difficulty in controlling the secondary reheating thermal power generating units.
For a secondary reheating unit, the current temperature control scheme mainly adopts a swinging burner to simultaneously coordinate and control the temperature of primary reheating steam and the temperature of secondary reheating steam, and meanwhile, smoke baffles are arranged on the primary reheater side and the secondary reheater side of a secondary reheating boiler tail flue to respectively control the temperature of the primary reheating steam and the temperature of the secondary reheating steam, so that the overheating of a reheater is further prevented, the safety of unit equipment is ensured, and a reheater trace water spray is designed for a backup measure under an emergency condition; such a control scheme suffers from the following problems:
primary and secondary side reheat steam temperature intercoupling, if certain one side reheat steam temperature is on the high side or on the low side, adopt baffle regulation then to lead to the boiler tail portion to flow the flue gas volume of once re-heater and secondary re-heater flue and change, must lead to the fluctuation of opposite side reheat steam temperature, both sides flue gas baffle action is frequent, and the governing speed is slower moreover.
When primary and secondary side reheat steam temperature all deviate from the normal value, boiler afterbody flue gas baffle can move simultaneously, and the action at this moment can lead to further worsening of boiler afterbody flue gas heat transfer, hardly accomplishes the purpose of adjusting reheat steam temperature smoothly, and adjusts then response speed through the swing combustor and difficultly satisfies actual operation demand.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a method for controlling the temperature of the reheated steam of a boiler of an ultra-supercritical secondary reheating thermal power generating unit.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a reheating steam temperature control method of a double reheating unit comprises a variable frequency control method of a flue gas recirculation fan and an opening control method of a flue gas adjusting baffle;
(1) the frequency conversion control method of the flue gas recirculation fan comprises the following steps:
1.1) respectively acquiring a high-pressure side reheat steam temperature signal, a low-pressure side reheat steam temperature signal, a water spray desuperheating rear high-pressure side reheat steam temperature signal and a water spray desuperheating rear low-pressure side reheat steam temperature signal of an ultra-supercritical double reheat unit; acquiring the load variation of the unit and carrying out differential processing to obtain a differential value;
1.2) respectively solving the deviation of the high-pressure side reheated steam temperature signal and the low-pressure side reheated steam temperature signal from respective set values, averaging the two deviations, and using the two deviations as the input of a first PID (proportion integration differentiation) controller of the frequency converter of the flue gas recirculation fan to generate a basic control instruction of the frequency converter of the flue gas recirculation fan;
1.3) averaging and differentiating the high-pressure side reheated steam temperature signal after water spraying and temperature reduction and the low-pressure side reheated steam temperature signal after water spraying and temperature reduction to obtain a differential value serving as a reheated steam temperature control feedforward signal;
1.4) adding the differential value of the temperature and the differential value of the load fluctuation amount after water spraying into a basic control instruction of a frequency converter of the flue gas recirculation fan respectively to generate an intermediate instruction of frequency conversion control of the recirculation fan;
1.5) carrying out related optimization by adopting locking and override control logic according to the basic operation conditions of the boiler and the recirculation fan, and finally generating a variable frequency control instruction of the flue gas recirculation fan;
(2) the method for controlling the opening of the flue gas adjusting baffle comprises the following specific steps:
2.1) respectively acquiring a high-pressure side reheat steam temperature signal, a low-pressure side reheat steam temperature signal, a water spray desuperheating rear high-pressure side reheat steam temperature signal and a water spray desuperheating rear low-pressure side reheat steam temperature signal of the ultra-supercritical double reheat unit; acquiring the load variation of the unit and carrying out differential processing to obtain a differential value;
2.2) taking the deviation value of the high-pressure side reheat steam temperature and the low-pressure side reheat steam temperature as the input of a PID controller of the reheater side flue gas adjusting baffle plate to generate a basic control instruction of the reheater side flue gas adjusting baffle plate;
2.3) adding the differential value of the temperature after water spraying and the differential value of the load fluctuation amount into a basic control instruction of a flue gas adjusting baffle at the reheater side respectively;
and 2.4) simultaneously setting reverse action logics of the flue gas baffles at the high-pressure side and the low-pressure side of the reheater according to the basic operation condition of the boiler, and finally generating opening instructions of the flue gas adjusting baffles at the high-pressure side and the low-pressure side of the reheater.
As a further improvement of the invention, the step 1.2) comprises the following specific steps:
and performing first difference operation on the filtered high-pressure side reheated steam temperature signal and a high-pressure side reheated steam temperature set value to obtain a deviation, performing second difference operation on the filtered low-pressure side reheated steam temperature signal and a low-pressure side reheated steam temperature set value to obtain a deviation, performing first averaging operation on results of the first difference operation and the second difference operation to obtain an average, wherein the result of the first averaging operation is used as the input of a first PID controller, and is used as a basic instruction of the flue gas recirculation fan frequency converter after being operated by the first PID controller.
As a further improvement of the invention, the specific steps of steps 1.3) and 1.4) are as follows:
and carrying out second averaging operation on the filtered water spraying high-pressure side reheated steam temperature signal and the water spraying low-pressure side reheated steam temperature signal set value to average, wherein the result of the second averaging operation is subjected to differential calculation through first differential operation, is used as a feedforward value of a basic instruction of the frequency converter of the flue gas recirculation fan together with a differential value of the load variation amount, and is used as a middle instruction of the frequency converter of the flue gas recirculation fan after being subjected to first summation operation calculation.
As a further improvement of the invention, the specific steps of step 1.5) are as follows:
after limiting the generated middle instruction of the frequency converter of the flue gas recirculation fan by the upper limit value and the lower limit value of the frequency converter of the flue gas recirculation fan, performing first switching operation:
when the boiler generates MFT, the output of the first switching operation is the value of the filtered steam-water separator pressure after the first conversion function operation;
when the MFT does not occur, the output of the first switching operation is a middle instruction of the frequency converter of the smoke recirculation fan; and performing second switching operation on the result of the first switching operation, wherein the result of the second switching operation is the output of the first switching operation when the recirculation fan normally operates, and the result of the second switching operation is a first fixed value when the recirculation fan stops operating.
As a further improvement of the present invention, the method for determining the first reduction function and the first fixed value is as follows:
the input of the first folding function is the pressure of the steam-water separator, and a reasonable frequency converter instruction of the flue gas recirculation fan is obtained through calculation;
when the smoke recirculation fan stops running, the value of the first fixed value output by the switching module in an operation mode is 0%.
As a further improvement of the invention, the specific steps of step 2.2) are as follows:
and performing third difference operation on the filtered high-pressure side reheated steam temperature signal and the high-pressure side reheated steam temperature set value to obtain a deviation, performing fourth difference operation on the filtered low-pressure side reheated steam temperature signal and the low-pressure side reheated steam temperature set value to obtain a deviation, performing fifth difference operation on the deviation value of the third difference operation and the fourth difference operation, and using the result of the fifth difference operation as the input of a second PID controller and the basic instruction of the reheater side flue gas adjusting baffle after the operation of the second PID controller.
As a further improvement of the invention, the specific steps of step 2.3) are as follows:
and carrying out third averaging operation on the filtered water spraying high-pressure side reheated steam temperature signal and a water spraying low-pressure side reheated steam temperature signal set value to average, wherein the operation result of the third averaging operation is subjected to differential calculation through second differential operation, is used as a feedforward value of a basic instruction of the reheater side flue gas adjusting baffle together with a differential value of a load variation amount, and is calculated through second summation operation to be used as a middle instruction of the reheater side flue gas adjusting baffle.
As a further improvement of the invention, the specific steps of step 2.4) are as follows:
the generated value of the middle instruction of the flue gas adjusting baffle after the second conversion function operation is used as the instruction of the flue gas adjusting baffle at the high-pressure side reheater side through the operation of a third switching operation algorithm; when the MFT occurs, the output of the third switching operation is a second constant value; when the MFT does not occur, the output of the third switching operation is a value calculated by the second reduction function;
the generated value of the middle instruction of the flue gas adjusting baffle after the third conversion function operation is used as the instruction of the flue gas adjusting baffle at the high-pressure side reheater side after the fourth switching operation, and when the MFT occurs, the output of the fourth switching operation is a third fixed value; when the MFT does not occur, the output of the fourth switching operation is a value calculated by the third folding function.
As a further improvement of the present invention, the method for determining the second and third reduction functions and the second and third fixed values is as follows:
the second folding function and the third folding function are a pair of folding lines which are in opposite trend, the total smoke flux is unchanged, the smoke quantity of one side is increased, and the smoke quantity of the other side is reduced;
when the boiler generates MFT, the smoke passing through the high-pressure side reheater and the low-pressure side reheater are evenly distributed, so that the second fixed value and the third fixed value are both 50%.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides a method for controlling the reheating steam temperature of a secondary reheating steam unit, which solves the problems of mutual coupling between the primary reheating steam temperature and the secondary reheating steam temperature of the ultra-supercritical secondary reheating steam unit, slow adjustment speed and the like, respectively controls the total heat absorption capacity of a primary reheater and a secondary reheater by using a flue gas recirculation fan, controls the primary reheating steam temperature and the secondary reheating steam temperature by using a reheater flue gas adjusting baffle, adopts control measures such as feedforward, override, locking and the like, realizes the control precision and the response speed of the primary reheating steam temperature and the secondary reheating steam temperature of the ultra-supercritical secondary reheating steam unit, and simultaneously ensures the safe and stable operation of the unit.
Drawings
Fig. 1 is a schematic flow chart of a method for controlling the reheat steam temperature of a double reheat unit according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a control loop of a variable frequency control system of a flue gas recirculation fan according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of a control loop of the primary/secondary side flue gas damper control system according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a reheating steam temperature control method of a double reheating unit, which is applied to a flue gas recirculation variable frequency regulation loop of the total flue gas amount of a reheating steam temperature control system of the double reheating unit and a primary/secondary side flue gas baffle control system control loop for regulating the temperature of high-pressure side reheating steam and low-pressure side reheating steam.
As shown in fig. 1, a method for controlling the reheated steam temperature of a double reheating unit includes a method for controlling the frequency of a flue gas recirculation fan and a method for adjusting the opening of a flue gas damper.
(1) The method for controlling the frequency conversion of the flue gas recirculation fan comprises the following specific steps:
1.1) respectively acquiring a high-pressure side reheat steam temperature signal, a low-pressure side reheat steam temperature signal, a water spray desuperheating rear high-pressure side reheat steam temperature signal and a water spray desuperheating rear low-pressure side reheat steam temperature signal of an ultra-supercritical double reheat unit; and carrying out filtering treatment;
acquiring the load variation of the unit and carrying out differential processing to obtain a differential value;
1.2) respectively solving the deviation of the high-pressure side reheated steam temperature signal and the low-pressure side reheated steam temperature signal from respective set values, averaging the two deviations, and using the two deviations as the input of a first PID controller of a frequency converter of the flue gas recirculation fan to generate a basic control instruction of the frequency converter of the flue gas recirculation fan;
1.3) averaging and differentiating the high-pressure side reheated steam temperature signal after water spraying and temperature reduction and the low-pressure side reheated steam temperature signal after water spraying and temperature reduction to obtain a differential value serving as a reheated steam temperature control feedforward signal;
1.4) adding the differential value of the temperature and the differential value of the load fluctuation amount after water spraying into a basic control instruction of a frequency converter of the flue gas recirculation fan respectively to generate an intermediate instruction of frequency conversion control of the recirculation fan and ensure the response speed and the control precision of a control system of the flue gas recirculation fan;
1.5) according to the basic operation conditions of the boiler and the recirculation fan, adopting locking and override control logic to carry out relevant optimization, and finally generating a variable frequency control instruction of the flue gas recirculation fan.
The method for determining the first fixed value, the second fixed value, the third fixed value and the upper and lower limit values of the frequency converter of the flue gas recirculation fan comprises the following steps:
when the flue gas recirculation fan is stopped, the second switching output first fixed value is 0%; when the boiler generates MFT, the second fixed value and the third fixed value are both 50%; when the temperature of the reheating steam of the boiler is too high, the flue gas recirculation volume at the side of a reheater is not increased so as to prevent the reheater from being overheated; when the temperature of the reheat steam of the boiler is too low, the recirculation quantity of the flue gas at the reheater side is not reduced to prevent the temperature of the reheat steam from being too low and the superheat degree is not enough; these two limits can be obtained by thermodynamic calculations.
As shown in fig. 2, the specific steps of the method for controlling the frequency conversion of the flue gas recirculation fan are described in detail by combining the schematic structural diagram of the flue gas recirculation frequency conversion regulating loop of the total flue gas amount of the reheating steam temperature control system of the double reheating unit:
acquiring high-pressure side reheated steam temperature, low-pressure side reheated steam temperature, steam temperature after water spraying of a high-pressure side reheater, steam temperature after water spraying of a low-pressure side reheater, steam-water separator pressure and unit power change signals from a DCS (distributed control system) of a thermal generator set, and filtering;
carrying out difference operation on the filtered high-pressure side reheated steam temperature signal and a high-pressure side reheated steam temperature set value, carrying out difference operation on the filtered low-pressure side reheated steam temperature signal and a low-pressure side reheated steam temperature set value, carrying out averaging operation on the output of the difference calculation, wherein the output of the averaging operation is used as the input of a PID (proportion integration differentiation) controller, and is used as a basic instruction of a frequency converter of the flue gas recirculation fan after being operated by the PID controller;
averaging the filtered water spray high-pressure side reheated steam temperature signal and the water spray low-pressure side reheated steam temperature signal set value, wherein the averaging result is subjected to differential calculation processing, is used as a feedforward value of a basic variable frequency control instruction of the flue gas recirculation fan together with a differential value of a load variation amount, and is used as an intermediate instruction of the variable frequency control of the flue gas recirculation fan after summation calculation;
after the generated intermediate command of the frequency conversion control of the flue gas recirculation fan is limited by the upper limit module and the lower limit module, the generated intermediate command is operated by the first switching module, when MFT (main fuel trip) occurs in the boiler, the switching module operates and outputs a value obtained by operating the pressure of the filtered steam-water separator through a first conversion function, and when the MFT does not occur, the switching module operates and outputs the intermediate command of the frequency converter of the flue gas recirculation fan; and the output after the operation of the switching module is calculated by a second switching module, when the recirculation fan normally operates, the output of the control system is the output value calculated by the switching module, and when the recirculation fan stops operating, the output of the control system is a first fixed value.
(2) The method for adjusting the opening degree of the baffle plate by using the flue gas comprises the following specific steps:
2.1) respectively acquiring a high-pressure side reheat steam temperature signal, a low-pressure side reheat steam temperature signal, a water spray desuperheating rear high-pressure side reheat steam temperature signal and a water spray desuperheating rear low-pressure side reheat steam temperature signal of the ultra-supercritical double reheat unit; and carrying out filtering treatment;
acquiring the load variation of the unit and carrying out differential processing to obtain a differential value;
2.2) taking the deviation value of the high-pressure side reheat steam temperature and the low-pressure side reheat steam temperature as the input of a PID controller of the reheater side flue gas adjusting baffle plate to generate a basic control instruction of the reheater side flue gas adjusting baffle plate;
2.3) respectively adding the differential value of the temperature and the differential value of the load fluctuation amount after water spraying into a basic control instruction of the reheater side flue gas adjusting baffle plate to ensure the response speed and the control precision of a reheater side flue gas adjusting baffle plate control system;
and 2.4) simultaneously setting reverse action logics of the flue gas baffles at the high-pressure side and the low-pressure side of the reheater according to the basic operation condition of the boiler, and finally generating opening instructions of the flue gas adjusting baffles at the high-pressure side and the low-pressure side of the reheater.
The boiler swinging burner is controlled by adopting conventional open-loop control; the reheat water spray desuperheating control is only used as emergency water spray control.
As shown in fig. 3, the specific steps of the method for adjusting the opening of the baffle by using flue gas are described in detail in conjunction with the schematic structural diagram of the control loop of the primary/secondary side flue gas baffle control system:
acquiring high-pressure side reheated steam temperature, low-pressure side reheated steam temperature, steam temperature after water spraying of a high-pressure side reheater, steam temperature after water spraying of a low-pressure side reheater, steam-water separator pressure and unit power change signals from a DCS (distributed control system) of a thermal generator set, and filtering;
performing difference operation on the filtered high-pressure side reheated steam temperature signal and a high-pressure side reheated steam temperature set value, performing difference operation on the filtered low-pressure side reheated steam temperature signal and a low-pressure side reheated steam temperature set value, performing difference operation on the output of the two difference operations, and taking the calculated final difference result as the input of a PID (proportion integration differentiation) controller and the calculated final difference result as a basic instruction of a reheater side flue gas adjusting baffle after the calculation of the PID controller;
carrying out averaging calculation on the filtered water spray high-pressure side reheated steam temperature signal and the water spray low-pressure side reheated steam temperature signal set value, carrying out differential operation on the result of averaging calculation, taking the result of averaging calculation as a feedforward value of a reheater side flue gas adjusting baffle basic instruction together with a differential value of a load variation amount, and taking the result of summing calculation as a middle instruction of the reheater side flue gas adjusting baffle;
taking the value of the generated middle command of the flue gas adjusting baffle after the second conversion function operation as the command of the flue gas adjusting baffle at the high-pressure side reheater side through the operation of the third switching module algorithm, wherein when the MFT occurs, the output of the third switching module algorithm is a second constant value; when the MFT does not occur, the output of the third switching module algorithm is a value calculated by the second reduction function. The value of the generated middle command of the flue gas adjusting baffle after the operation of the third conversion function is used as the command of the flue gas adjusting baffle at the high-pressure side reheater side through the operation of the fourth switching module algorithm, and when the MFT occurs, the output of the fourth switching module is a third fixed value; when the MFT does not occur, the output of the fourth switching module is a value calculated by the third folding function.
The method for controlling the reheated steam temperature of the double reheating unit provided by the embodiment of the invention simultaneously considers the total heat absorption capacity of the high-pressure side reheater side and the low-pressure side reheater side, adopts the variable frequency regulation of the flue gas recirculation fan to the total flue gas quantity passing through the reheater side, and ensures that the reheated steam temperature can reach a reasonable range; while adjusting the total smoke amount, the locking logic and the differential feedforward logic of the temperature after water spraying and the unit load variation are adopted, and the equipment safety, the adjusting precision and the response speed of the unit are considered. Respectively adjusting a high-pressure side flue gas adjusting baffle and a low-pressure side flue gas adjusting baffle, distributing the heat of the total flue gas, ensuring the temperature of reheated steam to be within a reasonable range, and utilizing different conversion functions to ensure that the total opening degree of the high-pressure side flue gas adjusting baffle and the low-pressure side flue gas adjusting baffle is unchanged, thereby realizing decoupling control; in the two control loop designs, a switching module algorithm is adopted to realize the override logic under the fault or emergency condition, so that the safe and stable operation of the unit is ensured.
The invention provides a structural schematic diagram of a flue gas recirculation variable frequency regulating loop of the total flue gas amount of a reheating steam temperature control system of a double reheating unit, and the structural schematic diagram is specifically shown in figure 2.
Carrying out first difference operation on the filtered high-pressure side reheated steam temperature signal and a high-pressure side reheated steam temperature set value, carrying out second difference operation on the filtered low-pressure side reheated steam temperature signal and a low-pressure side reheated steam temperature set value, outputting results of the first difference operation and the second difference operation to a first averaging operation, wherein the output of the first averaging operation is used as the input of a first PID (proportion integration differentiation) controller, and is used as a basic instruction of a flue gas recirculation fan frequency converter after being operated by the first PID controller;
carrying out second averaging operation on the filtered water spraying high-pressure side reheated steam temperature signal and the water spraying low-pressure side reheated steam temperature signal set value, wherein the result of the second averaging operation is calculated through first differential operation, is used as a feedforward value of a basic instruction of a frequency converter of the flue gas recirculation fan together with a differential value of a load variation amount, and is calculated through first summation operation and then is used as a middle instruction of the frequency converter of the flue gas recirculation fan;
after the middle instruction of the flue gas recirculation fan frequency converter generated by the method is limited by the upper limit module and the lower limit module, the operation is carried out through the first switching module:
when the boiler has MFT (namely main fuel trip), the output of the first switching module is the value of the filtered steam-water separator pressure after the operation of a first conversion function;
when the MFT does not occur, the output of the first switching module is an intermediate instruction of the frequency converter of the smoke recirculation fan; the output of the first switching module is sent to the second switching module for operation, when the recirculation fan operates normally, the output of the second switching module is the output of the first switching module, and when the recirculation fan stops operating, the output of the second switching module is a first fixed value.
And performing third difference operation on the filtered high-pressure side reheated steam temperature signal and the high-pressure side reheated steam temperature set value, performing fourth difference operation on the filtered low-pressure side reheated steam temperature signal and the low-pressure side reheated steam temperature set value, sending the output of the third difference operation and the output of the fourth difference operation to fifth difference operation, and taking the output of the fifth difference operation as the input of a second PID (proportion integration differentiation) controller and the basic instruction of the reheater side flue gas adjusting baffle after the operation of the second PID controller.
Exemplarily, the determination of the first reduction function, the first fixed value and the upper and lower limit values of the frequency converter of the flue gas recirculation fan of the flue gas recirculation frequency conversion regulating loop is as follows:
the input of the first folding function is the pressure of the steam-water separator, the pressure can reflect the actual heat in the boiler from one side surface, and a reasonable instruction of the frequency converter of the flue gas recirculation fan is obtained through calculation, and the folding function can be corrected by professional technicians in the later engineering implementation process so as to achieve the best operation effect;
considering the operation safety of the frequency converter and the undisturbed operation of the control system, when the smoke recirculation fan stops operating, the value of a first fixed value output by the operation of the switching module is 0%; when the boiler generates MFT, the smoke passing through the high-pressure side reheater and the low-pressure side reheater is equal, so that the second fixed value and the third fixed value are both 50%;
when the temperature of the reheating steam of the boiler is too high, the flue gas recirculation volume at the side of a reheater is not increased so as to prevent the reheater from being overheated; when the temperature of the reheat steam of the boiler is too low, the recirculation quantity of the flue gas at the reheater side is not reduced to prevent the temperature of the reheat steam from being too low and the superheat degree is not enough; the two limits can be obtained through thermodynamic calculation, and in the later engineering implementation stage, a professional can partially adjust the two limits according to the actual performance of the equipment.
The embodiment of the invention also provides a schematic structural diagram of a control loop of the primary/secondary side flue gas baffle control system, which is specifically shown in fig. 3.
Carrying out third averaging operation on the filtered water spray rear high-pressure side reheated steam temperature signal and a water spray rear low-pressure side reheated steam temperature signal set value, wherein the operation result of the third averaging operation is calculated through second differential operation, is used as a feedforward value of a reheater side flue gas adjusting baffle basic instruction together with a differential value of a load variation amount, and is calculated through a second summation operation algorithm and is used as a middle instruction of the reheater side flue gas adjusting baffle;
the generated value of the middle instruction of the flue gas adjusting baffle after the second conversion function operation is used as the instruction of the flue gas adjusting baffle at the high-pressure side reheater side through the operation of the algorithm of the third switching module, and when the MFT occurs, the output of the third switching module is a second fixed value; when the MFT does not occur, the output of the third switching module is a value calculated by the second reduction function.
The generated value of the middle instruction of the flue gas adjusting baffle after the operation of a third conversion function is used as the instruction of the flue gas adjusting baffle at the high-pressure side reheater side through the operation of a fourth switching module algorithm, and when the MFT occurs, the output of the fourth switching module is a third fixed value; when the MFT does not occur, the output of the fourth switching module is a value calculated by the third folding function.
For example, the determination of the second and third fold functions and the second and third constants of the reheater side flue gas conditioning damper control loop:
the second and third folding function is a pair of folding lines which are opposite to each other, the total smoke flux is unchanged, the purpose is to ensure that the smoke flux on one side is increased and the smoke flux on the other side is reduced, and in the later engineering implementation process, a professional can adjust according to the specific performance of the equipment to realize the optimal control effect.
When the boiler generates MFT, the smoke passing through the high-pressure side reheater and the low-pressure side reheater should be evenly distributed, so that the second fixed value and the third fixed value are both 50%; in the later engineering implementation process, the professional can adjust according to the specific performance of the equipment to realize the optimal control effect.
The control unit of the reheating steam temperature of the ultra-supercritical double reheating unit provided by the embodiment of the invention is more suitable for large pulverized coal fired boilers and can be realized by DCS control system configurations designed and produced by different companies; in order to realize convenience, the high-pressure side reheated steam temperature, the low-pressure side reheated steam temperature, the high-pressure side reheater water spray rear steam temperature, the low-pressure side reheater water spray rear steam temperature, the steam-water separator pressure and the unit power change signal are all from a DCS control system of the thermal power generating unit.
The invention discloses a reheating steam temperature control system of an ultra-supercritical secondary reheating unit, which comprises a secondary reheating unit flue gas recirculation fan frequency converter instruction generation control loop and a reheater side flue gas regulation baffle instruction generation control loop, wherein the flue gas recirculation fan frequency converter and the flue gas regulation baffle instruction generation control loop respectively comprise a leading differential feedforward unit for reheating steam temperature after water spraying and a feedforward unit for load change, and meanwhile, an override and locking control unit under special conditions is respectively arranged in the two control loops. The invention solves the problems of mutual coupling between the primary and secondary reheating steam temperatures of the ultra-supercritical secondary reheating unit, slow adjustment speed and the like, respectively controls the total heat absorption capacity of the primary and secondary reheaters by using the frequency converter of the flue gas recirculation fan, controls the primary and secondary reheating steam temperatures by using the flue gas adjusting baffle of the reheater, adopts control measures of feedforward, override, locking and the like, realizes the control precision and response speed of the primary and secondary reheating steam temperatures of the ultra-supercritical secondary reheating unit, and simultaneously ensures the safe and stable operation of the unit.
The above embodiments are only for illustrating the invention and are not to be construed as limiting the invention, and those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention, therefore, all equivalent technical solutions also belong to the scope of the invention, and the scope of the invention is defined by the claims.
Claims (7)
1. A reheating steam temperature control method of a double reheating unit is characterized by comprising a variable frequency control method of a flue gas recirculation fan and an opening control method of a flue gas adjusting baffle;
(1) the frequency conversion control method of the flue gas recirculation fan comprises the following steps:
1.1) respectively acquiring a high-pressure side reheat steam temperature signal, a low-pressure side reheat steam temperature signal, a water spray desuperheating rear high-pressure side reheat steam temperature signal and a water spray desuperheating rear low-pressure side reheat steam temperature signal of an ultra-supercritical double reheat unit; acquiring the load variation of the unit and carrying out differential processing to obtain a differential value;
1.2) respectively solving the deviation of the high-pressure side reheated steam temperature signal and the low-pressure side reheated steam temperature signal from respective set values, averaging the two deviations, and using the two deviations as the input of a first PID (proportion integration differentiation) controller of the frequency converter of the flue gas recirculation fan to generate a basic control instruction of the frequency converter of the flue gas recirculation fan;
1.3) averaging and differentiating the high-pressure side reheated steam temperature signal after water spraying and temperature reduction and the low-pressure side reheated steam temperature signal after water spraying and temperature reduction to obtain a differential value serving as a reheated steam temperature control feedforward signal;
1.4) adding the differential value of the temperature and the differential value of the load fluctuation amount after water spraying into a basic control instruction of a frequency converter of the flue gas recirculation fan respectively to generate an intermediate instruction of frequency conversion control of the recirculation fan;
1.5) carrying out related optimization by adopting locking and override control logic according to the basic operation conditions of the boiler and the recirculation fan, and finally generating a variable frequency control instruction of the flue gas recirculation fan;
the step 1.5) comprises the following specific steps:
after limiting the generated middle instruction of the frequency converter of the flue gas recirculation fan by the upper limit value and the lower limit value of the frequency converter of the flue gas recirculation fan, performing first switching operation:
when the boiler generates MFT, the output of the first switching operation is the value of the filtered steam-water separator pressure after the first conversion function operation;
when the MFT does not occur, the output of the first switching operation is a middle instruction of the frequency converter of the smoke recirculation fan; performing second switching operation on the result of the first switching operation, wherein the result of the second switching operation is the output of the first switching operation when the recirculation fan normally operates, and the result of the second switching operation is a first fixed value when the recirculation fan stops operating;
(2) the method for controlling the opening of the flue gas adjusting baffle comprises the following specific steps:
2.1) respectively acquiring a high-pressure side reheat steam temperature signal, a low-pressure side reheat steam temperature signal, a water spray desuperheating rear high-pressure side reheat steam temperature signal and a water spray desuperheating rear low-pressure side reheat steam temperature signal of the ultra-supercritical double reheat unit; acquiring the load variation of the unit and carrying out differential processing to obtain a differential value;
2.2) taking the deviation value of the high-pressure side reheat steam temperature and the low-pressure side reheat steam temperature as the input of a PID controller of the reheater side flue gas adjusting baffle plate to generate a basic control instruction of the reheater side flue gas adjusting baffle plate;
2.3) adding the differential value of the temperature after water spraying and the differential value of the load fluctuation amount into a basic control instruction of a flue gas adjusting baffle at the reheater side respectively;
2.4) setting reverse action logics of the flue gas baffles at the high-pressure side and the low-pressure side of the reheater at the same time according to the basic operation condition of the boiler, and finally generating opening instructions of the flue gas adjusting baffles at the high-pressure side and the low-pressure side of the reheater;
the specific steps of step 2.4) are as follows:
the generated value of the middle instruction of the flue gas adjusting baffle after the second conversion function operation is used as the instruction of the flue gas adjusting baffle at the high-pressure side reheater side through the operation of a third switching operation algorithm; when the MFT occurs, the output of the third switching operation is a second constant value; when the MFT does not occur, the output of the third switching operation is a value calculated by the second reduction function;
the generated value of the middle instruction of the flue gas adjusting baffle after the third conversion function operation is used as the instruction of the flue gas adjusting baffle at the high-pressure side reheater side after the fourth switching operation, and when the MFT occurs, the output of the fourth switching operation is a third fixed value; when the MFT does not occur, the output of the fourth switching operation is a value calculated by the third folding function.
2. The reheat steam temperature control method of the double reheat unit as claimed in claim 1, wherein the step 1.2) comprises the following steps:
and carrying out first difference operation on the filtered high-pressure side reheated steam temperature signal and the high-pressure side reheated steam temperature set value to obtain deviation, carrying out second difference operation on the filtered low-pressure side reheated steam temperature signal and the low-pressure side reheated steam temperature set value to obtain deviation, carrying out first averaging operation on results of the first difference operation and the second difference operation to obtain average, taking the result of the first averaging operation as the input of a first PID (proportion integration differentiation) controller, and taking the result of the first averaging operation as a basic instruction of the flue gas recirculation fan frequency converter after the operation of the first PID controller.
3. The reheat steam temperature control method of the double reheat unit as claimed in claim 1, wherein the steps 1.3) and 1.4) are as follows:
and carrying out second averaging operation on the filtered water spraying high-pressure side reheated steam temperature signal and the water spraying low-pressure side reheated steam temperature signal set value to average, wherein the result of the second averaging operation is subjected to differential calculation through first differential operation, is used as a feedforward value of a basic instruction of the frequency converter of the flue gas recirculation fan together with a differential value of the load variation amount, and is used as a middle instruction of the frequency converter of the flue gas recirculation fan after being subjected to first summation operation calculation.
4. The reheat steam temperature control method of a double reheat unit as claimed in claim 1, wherein the method for determining the first reduction function and the first fixed value is as follows:
the input of the first folding function is the pressure of the steam-water separator, and a reasonable frequency converter instruction of the flue gas recirculation fan is obtained through calculation;
when the smoke recirculation fan stops running, the value of the first fixed value output by the switching module in an operation mode is 0%.
5. The reheat steam temperature control method of the double reheat unit as claimed in claim 1, wherein the specific steps of step 2.2) are as follows:
and performing third difference operation on the filtered high-pressure side reheated steam temperature signal and the high-pressure side reheated steam temperature set value to obtain a deviation, performing fourth difference operation on the filtered low-pressure side reheated steam temperature signal and the low-pressure side reheated steam temperature set value to obtain a deviation, performing fifth difference operation on the deviation value of the third difference operation and the fourth difference operation, and using the result of the fifth difference operation as the input of a second PID controller and the basic instruction of the reheater side flue gas adjusting baffle after the operation of the second PID controller.
6. The reheat steam temperature control method of the double reheat unit as claimed in claim 1, wherein the specific steps of step 2.3) are as follows:
and carrying out third averaging operation on the filtered water spraying high-pressure side reheated steam temperature signal and the water spraying low-pressure side reheated steam temperature signal set value to average, wherein the operation result of the third averaging operation is subjected to differential calculation through second differential operation, is used as a feedforward value of a basic command of the reheater side flue gas adjusting baffle together with a differential value of a load variation amount, and is calculated through second summation operation to be used as a middle command of the reheater side flue gas adjusting baffle.
7. The reheat steam temperature control method of the double reheat unit as claimed in claim 1, wherein the determination method of the second and third calculation functions and the second and third fixed values is as follows:
the second folding function and the third folding function are a pair of folding lines which are in opposite trend, the total smoke flux is unchanged, the smoke quantity of one side is increased, and the smoke quantity of the other side is reduced;
when the boiler generates MFT, the smoke passing through the high-pressure side reheater and the low-pressure side reheater are evenly distributed, so that the second fixed value and the third fixed value are both 50%.
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| CN110274219B (en) * | 2019-07-12 | 2020-09-29 | 浙江浙能兰溪发电有限责任公司 | Supercritical boiler reheat steam temperature adjusting system and method |
| CN111486441B (en) * | 2020-04-17 | 2022-01-28 | 湛江电力有限公司 | Control method for boiler superheated steam temperature override loop |
| CN112146083B (en) * | 2020-09-28 | 2021-11-16 | 华能国际电力股份有限公司上海石洞口第二电厂 | Trace water spraying control method for power plant boiler |
| CN112648606A (en) * | 2020-10-29 | 2021-04-13 | 北京国电智深控制技术有限公司 | Steam temperature cooperative control system of double-reheating ultra-supercritical boiler |
| CN114253315B (en) * | 2022-03-02 | 2022-05-27 | 天津国能津能滨海热电有限公司 | Control method for reheating steam temperature of boiler, electronic equipment and storage medium |
| CN115095848B (en) * | 2022-06-21 | 2023-02-28 | 西安交通大学 | Steam temperature control method considering dynamic characteristics and variable load rate of secondary reheating unit |
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