CN113864756A - Main steam pressure variable rate control method for assisting RB process steam drum water level control - Google Patents
Main steam pressure variable rate control method for assisting RB process steam drum water level control Download PDFInfo
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Abstract
The invention relates to a main steam pressure variable rate control method for assisting RB process steam drum water level control, which comprises the following steps: carrying out differential calculation on the steam drum water level value to obtain the change rate of the steam drum water level; and respectively designing model functions of main steam pressure rate and steam pressure instruction generation inertia time corresponding to the water level change rate of the steam drum when the water feeding pump RB and the non-water feeding pump RB are used, and correcting the main steam pressure rate and the steam pressure instruction generation inertia time through the model functions. The invention has the beneficial effects that: on the basis of correcting the sliding pressure rate and the inertia time by the advancing time of the RB process, the sliding pressure rate and the inertia time in the RB process are corrected in real time by combining the advancing time of the RB process, the RB action preload and the dynamic characteristics of the steam drum water level, and the auxiliary stable steam drum water level is controlled by utilizing the variable speed of the main steam pressure, so that the fluctuation of the steam drum water level in the RB process of various auxiliary machines is effectively reduced, and the running safety and the running state recovery of the unit are ensured.
Description
Technical Field
The invention belongs to the field of equipment faults of thermal power generating units, and particularly relates to a main steam pressure variable rate control method for assisting RB process steam drum water level control.
Background
When important auxiliary equipment faults occur in the thermal power generating unit, the adopted rapid load reduction control strategy is called RUNBACK, called RB for short. A thermal power generating unit has corresponding main steam pressure parameters according to design capacity, a main steam pressure set value is automatically controlled according to a unit load value, a designed speed and inertia time when the unit normally operates, the purpose of inertia time setting is to simulate a pressure starting process of actual main steam pressure, in the current RB control strategy design of the unit, in order to achieve rapid balance of unit load and auxiliary machine load carrying capacity, a steam pressure sliding rate and inertia time of the unit in the RB process are switched from a fixed value set in normal operation to a fixed value set in RB action until the load and the main steam pressure are reduced to a target value, the action rate of a steam-water system under an RB working condition is high, the sliding pressure rate and the inertia time parameters are obtained according to tests and actual operation experience, and obvious differences exist among various types of units.
Common RB is fuel RB, a primary air fan RB, a sending/induced draft fan RB, a water feeding pump RB and the like. In the current common control strategy, after RB action is triggered, the control mode of the unit is switched from a coordinated control mode (CCS) to a turbine following mode (TF). In the TF mode, the main steam pressure is controlled by a steam turbine regulating valve on the steam turbine side, a large regulating valve is opened when the actual value of the main steam pressure is higher than a set value, a small regulating valve is closed when the actual value of the main steam pressure is lower than the set value, and a boiler instruction value is directly determined by RB target load of a unit. Different sliding pressure rates are designed for RB actions caused by faults or tripping of different auxiliary equipment, the main steam pressure is controlled to rapidly follow and drop, and the disturbance of a primary fan and a water supply pump RB on combustion and water supply is the most severe, so that the designed RB actions are faster in sliding pressure rate and shorter in inertia time.
In addition, the inventor of the application researches an auxiliary machine RB method for controlling the variable speed rate of a steam-water system in the previous work, corrects the sliding pressure rate, the steam pressure and the water supply inertia time in the RB process through the RB propulsion time and the unit load before RB action, enables the control of the main steam pressure to accord with the actual trend under each RB working condition, can effectively improve the precision and the stability of the RB control of the thermal power unit, and the control method is shown as the attached figure 1, and the design steps are briefly described as follows:
1. the sliding pressure set speed and inertia time under different RB working conditions are designed, and the sliding pressure speed and the inertia time are corrected through the advancing time of the RB process. And comprehensively considering the RB preload of the unit and the RB propulsion process time point, and designing the sliding pressure rate and the inertia time of the pressure set value of each stage.
2. In order to play the role of adjusting the main steam temperature by the main steam pressure, the compensation role of the main steam temperature is added in the inertia time setting link.
However, in the current RB control, the setting mode of the constant rate and the constant inertia time generally adopted by the main steam pressure setting value cannot well conform to the change of actual parameters, not only affects the control of important parameters of a unit part in the RB process, but also is not beneficial to the recovery of the running state of a subsequent unit, particularly the control of the steam drum water level in the sub-critical unit RB process; the inventor only considers the variable speed control (sliding pressure rate) of the main steam pressure in the RB process in the auxiliary RB method for controlling the variable speed of the steam-water system, designs the speed which is consistent with the actual trend in each stage according to the advancing step of the RB process, but does not consider the mechanism relation among the associated operation parameters, designs the sliding pressure rate and the inertia time of each stage according to the advancing of the RB time, cannot accurately adapt to the real-time working condition change of the unit, and particularly does not consider the influence of the steam pressure on other operation parameters of the unit.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides a main steam pressure variable rate control method for assisting RB process steam drum water level control.
The main steam pressure variable speed control method for assisting RB process steam drum water level control comprises the following steps:
step 1, carrying out differential calculation on a steam drum water level value to obtain the change rate of the steam drum water level;
Preferably, the step 2 specifically comprises the following steps:
step 2.1, designing a model function of inertia time generated by a main steam pressure rate and a steam pressure instruction corresponding to a steam drum water level change rate when a water-supply pump RB is not used, and correcting the inertia time generated by the main steam pressure rate and the steam pressure instruction through the model function;
step 2.1.1, the first stage of the non-feedwater pump RB is a stage of lowering of the water level of the steam drum, and the main steam pressure rate and the steam pressure command generation inertia time are corrected according to the lowering rate of the water level of the real-time steam drum; the model function corrects the main steam pressure rate in an offset manner: correcting and generating a main steam pressure rate set value through the falling rate of the steam drum water level, and adding the main steam pressure rate set value and an offset value; the model function corrects the steam pressure command generation inertia time in a gain mode: multiplying the steam pressure command generation inertia time by the gain;
step 2.1.2, starting to rise again after the water level of the steam drum is reduced to the lowest value, and entering a second stage of a non-water-feeding pump RB; the model function corrects the main steam pressure rate and the steam pressure command generation inertia time by adopting the same correction mode as the first stage in the step 2.1.1 according to the descending rate of the real-time steam drum water level; slowing down the correction speed of the main steam pressure rate in the second stage along with the advancing of RB time;
step 2.1.3, when the water level of the steam drum rises to the highest value and the water level of the steam drum begins to fall, entering a third stage of a non-water-feeding pump RB; the model function does not correct the inertia time generated by the main steam pressure rate and the steam pressure instruction any more, the water level of the steam drum is not adjusted through the main steam pressure any more, the bias value of the output main steam pressure rate is 0, and the gain of the inertia time generated by the output steam pressure instruction is 1;
step 2.2, designing a model function of inertia time generated by a main steam pressure rate and a steam pressure instruction corresponding to the water level change rate of the steam drum during the water feeding pump RB, and correcting the inertia time generated by the main steam pressure rate and the steam pressure instruction through the model function;
2.2.1, a stage of lowering the water level of the steam drum when the water feeding pump RB enters the steam drum is a first stage of the water feeding pump RB; setting a bias value of a main steam pressure rate corresponding to the first stage of the feed water pump RB and a gain of steam pressure instruction generation inertia time by combining the propulsion time of the feed water pump RB;
step 2.2.2, the feed pump RB enters a steam drum water level rising stage, namely a second stage of the feed pump RB, and the second stage of the feed pump RB does not correct the main steam pressure rate and the steam pressure instruction generation inertia time;
and 2.2.3, enabling the water feeding pump RB to enter a stable recovery stage of the steam drum water level, wherein the stable recovery stage is a third stage of the water feeding pump RB, and the third stage of the water feeding pump RB does not correct the main steam pressure rate and the steam pressure instruction generation inertia time.
Preferably, the model function in the step 2 is set according to the RB process propulsion time and the drum water level rate; and fitting the model function according to the unit operation test data to obtain a more reasonable range of the water level rate in the RB process, and using the range as a control dead zone.
Preferably, when the drum water level variation rate is within the dead zone range in step 2, the offset output of the drum water level variation rate is 0, and the main steam pressure rate is not corrected; when the drum water level change rate is within the dead zone range, the gain output of the drum water level change rate is 1, and the steam pressure command generation inertia time is not corrected.
Preferably, the control dead zone of the model function is different between the feed water pump RB and the non-feed water pump RB in step 2.
Preferably, the bias or gain of the rate of change of the drum level in step 2 is:
Y＝aX+b
wherein X is the input steam drum water level rate value, Y is the output offset or gain, and a and b are constants.
The invention has the beneficial effects that:
the control of the main steam pressure in the RB process is crucial to the stability of the steam drum water level, the sliding pressure rate and the inertia time in the RB process are corrected in real time by combining the RB propulsion time, the RB action preload and the steam drum water level dynamic characteristics and aiming at a subcritical unit on the basis of the correction of the RB process propulsion time to the sliding pressure rate and the inertia time, and the auxiliary stable steam drum water level is controlled by using the main steam pressure variable rate, so that the fluctuation of the steam drum water level in the RB process of various auxiliary machines is effectively reduced, and the running safety and the running state recovery of the unit are ensured.
The method is used as a supplement to a main steam pressure variable rate control method in the RB process of a subcritical unit, the RB process propulsion time design conforms to the change characteristics of the steam drum water level, the requirements of the unit on steam pressure control in all time periods are different along with the propulsion of the RB process, and generally speaking, the fluctuation of the steam drum water level at the RB initial stage is severe, and the main steam pressure is required to realize quick auxiliary control on the steam drum water level so as to stabilize related parameters; RB later combustion tends to be stable, and the fluctuation of the drum water level is obviously reduced, so the correction effect of the drum water level is properly weakened, and the water level stabilization is mainly completed by a water supply system. And fitting the bias function, the gain coefficient function and the steam drum water level rate value in advance, and further accurately obtaining the values through tests and analysis.
Drawings
FIG. 1 is a logic diagram of a conventional main steam pressure variable speed control method;
FIG. 2 is a logic diagram of the main steam pressure variable rate control method for assisting RB process drum water level control according to the present invention.
Description of reference numerals: the method comprises the following steps of fuel RB action 1, pump feeding RB action 2, unit load set value 3, air and air feeding fan RB action 4, sliding pressure set value 5, primary air fan RB action 6, main steam pressure set value 7, unit load before RB 8, RB action 9, main steam temperature 10, RB action (not including water feeding RB)11 and steam drum water level 12.
Detailed Description
The present invention will be further described with reference to the following examples. The following examples are set forth merely to aid in the understanding of the invention. It should be noted that, for a person skilled in the art, several modifications can be made to the invention without departing from the principle of the invention, and these modifications and modifications also fall within the protection scope of the claims of the present invention.
Non-feed water pump RB: RB action is triggered, the operation mode of the unit is switched to a turbine following mode (TF mode), the load of a boiler is reduced to a target value according to a certain speed, a coal mill trips according to a designed sequence and interval time, a large amount of fuel is lost in a short time, the water level of a steam drum is caused to show a descending trend firstly due to the fact that the quantity of bubbles of steam-water mixture in the steam drum is reduced by evaporation weakening, but the water level is not caused by the fact that the evaporation quantity is larger than the water supply flow at the moment, but is transient state descending caused by combustion change, and therefore the water level is called as 'false water level'. Along with the rapid reduction of the main steam pressure, on one hand, the specific volume of the steam-water mixture is increased, on the other hand, the reduction of the saturation temperature enables the evaporated metal and the furnace water to release heat to generate more steam, the volume of the steam-water mixture expands to promote the water level to rise rapidly, along with the propulsion of the RB process, the loading capacity of the operating auxiliary machine is adapted to the load of a unit, all main operating parameters tend to be stable, the volume of the steam-water mixture is reduced when the steam amount is reduced, and the water level of a steam pocket is gradually reduced to be within a normal range. The method can be summarized into a process that the water level of a steam drum in a non-feed water pump RB firstly drops, then rises and finally drops to a stable value, the influence of various auxiliary machines RB on combustion is different, and the dynamic characteristics of each stage are slightly different. Since the change of the water level does not actually reflect the supply and demand relation of the water supply in the process, how to solve the influence of the false water level on the water supply control is the key of the success of the RB control.
A water supply pump RB:
1. the electric pump is started automatically:
a. the capacity of the electric pump is equal to that of the steam pump, the electric pump is quickly started after the steam pump RB, the electric pump is quickly recovered after the steam drum water level possibly drops a little at the initial stage of the starting process, the RB action is not triggered by the unit, the load of the boiler is not changed, and the correction of the steam drum water level to the sliding pressure rate is not considered in the working condition;
b. the capacity of the electric pump is smaller than that of the steam pump (for example, a 30% capacity electric pump, the capacity of the 30% electric pump is the rated power of the electric pump, the requirement of the generator set for 30% rated power can be met when the electric pump operates, two steam pumps are configured for a single unit, each steam pump can meet the requirement of the generator set for 50% rated power), the unit triggers RB action, the boiler is reduced to a target value according to a designed speed, the water level of a steam drum is reduced firstly, the electric pump is quickly raised after being started, the water level of the steam drum is quickly raised after being reduced for a very short time due to quick starting of the hot standby electric pump, the RB target load value is higher and is generally about 75% rated load, the steam pressure parameter is reduced less, the RB process is relatively short, the fluctuation of the water level of the steam drum is smaller, and the consideration is avoided;
2. the electric pump does not self-start (failed start):
because the unit water supply system loses half of the loading capacity, the main steam pressure and the steam drum water level are decreased at a higher rate, when the output of the water supply pump operated at one side is increased to be suitable for the unit load and the steam-water mixture caused by the decrease of the pressure parameter is expanded, the steam drum water level begins to rise back, meanwhile, the decreasing rate of the main steam pressure is slowed down, and finally, the dynamic characteristic is recovered stably, and the most main difference of the main steam pressure and the non-water supply pump RB is as follows: the initial water level drop of the feed pump RB is mainly caused by the limited water supply capacity of the feed pump RB, which is larger in magnitude and longer in duration, and therefore, a certain distinction needs to be made in the control.
In conclusion, the RB action initial stage is the stage with the highest failure risk, and the boiler combustion or water supply disturbance in the stage is severe; therefore, the control of the main steam pressure in the RB process is important to the stability of the steam drum water level; on the basis of correcting the sliding pressure rate and the inertia time by the advancing time of the existing RB process, the invention corrects the sliding pressure rate and the inertia time of the steam pressure by performing auxiliary control on other parameters such as the steam pressure and the like in real time according to the dynamic characteristics of the water level of the steam drum, thereby effectively reducing the fluctuation of the water level of the steam drum in the RB process of various auxiliary machines and ensuring the running safety and the recovery of the running state of the unit.
As shown in fig. 1, the conventional main steam pressure speed control method is to advance a set speed and an inertia time of a set variable value according to RB time, set corresponding speeds and inertia times for operating conditions of various auxiliary machines RB, and multiply and add function blocks corresponding to a pump RB, a fuel RB, a feed/suction fan RB, and a primary fan RB. The invention adds the correction of the steam drum water level of the subcritical generator set to the main steam pressure set rate and the inertia time on the original basis, corrects the generation of the main steam pressure set value through the change rate of the steam drum water level, adds the main steam pressure set rate and the offset value, and multiplies the inertia time and the gain coefficient.
The function blocks in the DCS system are simple broken line functions, the DCS system function blocks of different manufacturers are basically the same, the setting mode is that a one-dimensional linear function with the function formula of Y-aX + b is arranged between every two points, X is an input water level rate value, Y is output offset or gain, as shown in the following table 1, no fixed expressions (X1, Y1) to (X2 and Y2) are a section of function, the control system automatically calculates the expression of the section of function according to the set values of the two points, and the like, (X2, Y2) and (X3 and Y3) are a section of function, and 4 points are set in the following table and comprise 3 sections of broken line functions. The function functions applied in the DCS system comprise the functions of bias and gain, the water level rate is input X, and the output Y is corresponding bias or gain.
TABLE 1 table of values obtained without fixed expression to which offset and gain belong
| X | Y |
| X1 | Y1 |
| X2 | Y2 |
| X3 | Y3 |
| X4 | Y4 |
Example one
On the basis of the RB process main steam pressure variable rate control method, starting from the mechanism relationship between the drum water level dynamic characteristic and the main steam pressure variation trend in the RB process, the embodiment of the present application provides a main steam pressure variable rate control method for assisting the drum water level control in the RB process as shown in fig. 2, which is divided into a water supply pump RB working condition and a non-water supply pump RB working condition:
step 1, carrying out differential calculation on a steam drum water level value to obtain the change rate of the steam drum water level;
the model function is set according to the RB process propulsion time and the drum water level rate; fitting the model function according to the unit operation test data to obtain a reasonable range of the water level rate in the RB process, and taking the reasonable range as a control dead zone; when the drum water level change rate is in the dead zone range, the bias output of the drum water level change rate is 0, and the main steam pressure rate is not corrected; when the steam drum water level change rate is in the dead zone range, the gain output of the steam drum water level change rate is 1, and the steam pressure instruction generation inertia time is not corrected; dead zone: the method is characterized in that the method is also called as a neutral zone or an inactive zone, an input signal range with zero corresponding output in a transfer function of a control system has no special function formula, a dead zone mentioned in the invention is an inactive zone of offset and gain, the offset is addition, and the gain is multiplication; the control dead zones of the model functions are different when the water feeding pump RB and the non-water feeding pump RB are used;
the bias or gain in the drum level rate of change is:
Y＝aX+b
wherein X is the input steam drum water level rate value, Y is the output offset or gain, and a and b are constants;
step 2.1, designing a model function of inertia time generated by a main steam pressure rate and a steam pressure instruction corresponding to a steam drum water level change rate when a water-supply pump RB is not used, and correcting the inertia time generated by the main steam pressure rate and the steam pressure instruction through the model function;
step 2.1.1, the first stage of the non-feedwater pump RB is a steam drum water level descending stage, the main steam pressure rate and the steam pressure instruction generation inertia time are corrected according to the descending rate of the real-time steam drum water level, the descending rate of the main steam pressure can be adjusted rapidly, and the continuous descending of the RB initial-stage steam drum water level is slowed down; the model function corrects the main steam pressure rate in an offset manner: correcting and generating a main steam pressure rate set value through the falling rate of the steam drum water level, and adding the main steam pressure rate set value and an offset value; the model function corrects the steam pressure command generation inertia time in a gain mode: multiplying the steam pressure command generation inertia time by the gain;
step 2.1.2, starting to rise again after the water level of the steam drum is reduced to the lowest value, and entering a second stage of a non-water-feeding pump RB; the model function corrects the main steam pressure rate and the steam pressure command generation inertia time by adopting the same correction mode as the first stage in the step 2.1.1 according to the descending rate of the real-time steam drum water level; however, as the operation of the second-stage unit gradually tends to be stable, in order to prevent the water level of the steam drum from being too high, the correction speed of the main steam pressure rate of the second stage is integrally reduced along with the advancing of RB time;
step 2.1.3, when the water level of the steam drum rises to the highest value and the water level of the steam drum begins to fall, entering a third stage of a non-water-feeding pump RB; the model function does not correct the inertia time generated by the main steam pressure rate and the steam pressure instruction any more, the water level of the steam drum is not adjusted through the main steam pressure any more, the bias value of the output main steam pressure rate is 0, and the gain of the inertia time generated by the output steam pressure instruction is 1;
step 2.2, designing a model function of inertia time generated by a main steam pressure rate and a steam pressure instruction corresponding to the water level change rate of the steam drum during the water feeding pump RB, and correcting the inertia time generated by the main steam pressure rate and the steam pressure instruction through the model function;
2.2.1, the feed pump RB enters a stage of lowering the water level of the steam drum, namely a first stage of the feed pump RB, the boiler loses a large amount of feed water flow instantly after the action of the first stage RB is triggered, the load of the boiler is lowered rapidly, the reduction of the steam flow causes the main steam pressure to drop rapidly, the water level of the steam drum is lowered at a faster rate, and the lowering rate is faster than that of other auxiliary machines RB; setting a bias value of a main steam pressure rate corresponding to the first stage of the feed water pump RB and a gain of steam pressure instruction generation inertia time by combining the propulsion time of the feed water pump RB;
step 2.2.2, when the output of the water supply pump is matched with the load, the water level stops falling and starts rising again to enter a second stage, the water supply pump RB enters a rising stage of the steam drum water level and is the second stage of the water supply pump RB, the water supply pump RB gradually stabilizes after entering the second stage, and the water supply pump RB does not correct the main steam pressure rate and the steam pressure instruction generation inertia time in the second stage;
step 2.2.3, the feed pump RB enters a stage of recovering the water level of the steam drum, and is a third stage of the feed pump RB, and the third stage of the feed pump RB does not correct the main steam pressure rate and the steam pressure instruction generation inertia time;
Example two
On the basis of the first embodiment, the second embodiment of the present application provides an application of the method of the first embodiment to a certain 330MW subcritical unit:
designing model functions of main steam pressure rate and inertia time corresponding to steam drum water level change rate, and respectively specifying non-water-feeding pump RB working condition and water-feeding pump RB working condition;
1. RB condition of non-feed pump
The disturbance to the drum water level comes from boiler combustion, the drum water level shows a trend of firstly descending and then ascending and finally descending to a stable value, and the three stages are divided into a first stage which is a descending stage, a second stage which is an ascending stage and a third stage which is a stable value gradually recovered after ascending according to the change characteristics of the drum water level.
In the first stage, the quantity of bubbles of steam-water mixture in the steam drum is reduced due to evaporation weakening, the water level is reduced, the influence on combustion in the furnace is larger when the quantity of jumping mills is larger and the interval time of the jumping mills is shorter, the falling rate of the water level of the steam drum is higher, and the falling rate of the main steam pressure is higher. The sliding pressure rate and the steam pressure command generation inertia time are corrected according to the real-time water level reduction rate, the steam pressure command reduction rate can be adjusted rapidly, and continuous reduction of the RB initial steam drum water level is slowed down. For example, the fault tripping of the primary fan influences the feeding of pulverized coal into a hearth, the influence on the combustion of a boiler is the largest, the main steam pressure in the non-water-feeding pump RB falls the fastest, and the drop rate of the water level of the steam drum and the main steam pressure in the first stage is higher than that of other non-water-feeding pumps RB.
The water level drops to the lowest value and begins to rise again, enters the second stage, because the RB process has impeld a period of time, the load is fallen fast to the boiler, compares and tends to steadily gradually in first stage unit operating mode, because the main steam pressure parameter falls fast in the short time and directly influences steam pocket pressure, and steam-water mixture's volume expansion causes the water level to rise, and the unit has the too high risk of steam pocket water level. The rising rate of the water level is closely related to the falling rate of the main steam pressure, the rising rate is slower than that of the first stage, the correction mode is similar to that of the first stage, but the unit operation of the stage gradually tends to be stable, the sliding pressure rate of the stage is integrally slowed down along with the adjustment of the RB advancing time, and the adjustment of the second stage aims to prevent the water level of the steam drum from being too high.
The water level rises to the highest value and begins to fall, and the third stage is entered, at this moment, the unit load is gradually close to the target load, the operation process is basically stable, the volume of the steam-water mixture is reduced, the steam drum water level slowly falls to the vicinity of the set value, the stage does not need to be corrected, the steam drum water level is not adjusted through the main steam pressure after the third stage is entered, the bias output is 0, and the gain coefficient output is 1.
2. RB operating mode of feed pump
In the water supply pump RB, only the condition that the electric pump is not started automatically after the action of the water supply pump RB is triggered is described, and the water supply pump RB is also divided into three stages, wherein the first stage is a water level descending stage, the second stage is a water level rising stage, and the third stage is a water level recovery and stabilization stage. The method comprises the steps that after RB action in the first stage is triggered, a large amount of water supply flow is lost instantly by a boiler, load of the boiler is reduced rapidly, the reduction of steam flow causes rapid drop of main steam pressure, the water level of a steam drum is dropped at a relatively rapid rate, the dropping rate is faster than that of other auxiliary machines RB, when the output of a running water supply pump is adaptive to the load, the water level stops dropping and starts rising back to enter the second stage, the water supply pump RB is gradually stable after entering the second stage, the second stage and the third stage are not corrected, corresponding sliding pressure rate offset and inertia time gain of the first stage of the water supply pump RB are set by combining RB advancing time, when the dropping rate of the water level of the steam drum is too fast, the sliding pressure rate is increased, the inertia time is reduced, the dropping rate of a steam pressure set value is accelerated, a steam turbine throttle is opened, actual main steam pressure is dropped, and steam-water mixture expansion slows down the dropping rate of the water level. Meanwhile, the main steam pressure is quickly reduced, so that the water outlet of the water feeding pump is smooth, and the output of the water feeding system can be quickly recovered.
The model and the operation condition of each unit are different, the parameters suitable for each unit are required to be debugged and optimized, a 330MW subcritical unit is tested for multiple times, the suitable range of the steam drum water level rate change value of each RB action is determined to be less than 80mm/min, the steam pressure change rate is 0.25MPa/min when the unit operates normally, the inertia time is set to be one-order 120s, when a primary fan RB action is triggered, the steam pressure rate is switched to 0.4MPa/min, the inertia time is switched to 60s, and the data of the embodiment are set as follows:
the bias function for the rate of change of the primary fan RB is shown in table 2 below, with the "-" symbol representing the deceleration rate:
TABLE 2 bias function value-taking table for primary air fan RB change rate
| X | Y | X | Y |
| 0 | 0 | 0 | 0 |
| 80 | 0 | -80 | 0 |
| 85 | 0.05 | -85 | 0.04 |
| 90 | 0.07 | -90 | 0.05 |
| 100 | 0.11 | -100 | 0.10 |
| 120 | 0.15 | -120 | 0.13 |
The gain function for the inertia time of the primary fan RB is shown in table 3 below, with the "-" symbol representing the deceleration rate:
TABLE 3 gain function value-taking table for RB inertia time of primary air fan
| X | Y | X | Y |
| 0 | 1 | 0 | 1 |
| 80 | 1 | -80 | 1 |
| 85 | 0.95 | -85 | 0.95 |
| 90 | 0.92 | -90 | 0.92 |
| 100 | 0.88 | -100 | 0.86 |
| 120 | 0.8 | -120 | 0.8 |
Taking the design parameters in the tables 2 and 3 as reference, assuming that the actual speed of the drum water level reaches 100mm/min, the steam pressure speed is corrected to be 0.51MPa/min, the inertia time is 52.8, and the set value curve of the main steam pressure is obviously accelerated compared with the original design;
the bias function for the rate of change of the induced draft fan RB is shown in table 4 below:
TABLE 4 bias function value-taking table for RB change rate of air-sending/draught fan
| X | Y | X | Y |
| 0 | 0 | 0 | 0 |
| 80 | 0 | -80 | 0 |
| 85 | 0.04 | -85 | 0.04 |
| 90 | 0.05 | -90 | 0.05 |
| 100 | 0.08 | -100 | 0.08 |
| 120 | 0.10 | -120 | 0.10 |
The gain function for the inertia time of the induced/induced draft fan RB is shown in table 5 below:
TABLE 5 gain function value-taking table for RB inertia time of air-sending/draught fan
| X | Y | X | Y |
| 0 | 1 | 0 | 1 |
| 80 | 1 | -80 | 1 |
| 85 | 0.97 | -85 | 0.97 |
| 90 | 0.93 | -90 | 0.93 |
| 100 | 0.9 | -100 | 0.9 |
| 120 | 0.85 | -120 | 0.85 |
The fuel RB is set in a similar manner and the description will not be repeated.
Because the water level is mainly prevented from dropping too fast in the process of the water supply pump RB, the water level does not need to be increased and the bias function value of the change rate of the water supply pump RB is shown in the following table 6:
TABLE 6 bias function value-taking table for RB change rate of water-feeding pump
| X | Y | X | Y |
| 0 | 0 | 0 | 0 |
| 80 | 0 | -80 | 0 |
| 85 | 0 | -85 | 0.06 |
| 90 | 0 | -90 | 0.08 |
| 100 | 0 | -100 | 0.12 |
| 120 | 0 | -120 | 0.18 |
The gain function of the inertia time of the primary air fan RB is shown in table 7 below:
TABLE 7 gain function value-taking table for RB inertia time of primary air fan
| X | Y | X | Y |
| 0 | 1 | 0 | 1 |
| 80 | 1 | -80 | 1 |
| 85 | 1 | -85 | 0.92 |
| 90 | 1 | -90 | 0.87 |
| 100 | 1 | -100 | 0.80 |
| 120 | 1 | -120 | 0.75 |
In fig. 1 and 2: the dotted line represents the switching value, which is 0 or 1; the solid line represents the analog quantity; (x) is a relation function, and in the two forms in the graph, one input corresponds to one output, and two inputs correspond to one output; Σ denotes addition, and x denotes multiplication; v is not more than the change rate of the setting, LAG is a LAG time function block which is used for setting the inertia time in the text, the LAG time function block is set to be three-order in the figure, the LAG time function block is a common function of a DCS (distributed control system), the rate and the inertia time are combined to be a method commonly adopted in the thermal power control industry, and the change trend of the actual pressure is simulated to set a main steam pressure set value; M/A represents a main controller (manual operator), and a unit operator can set a manual automatic state; TIME is a timer, and the TIME is started when the RB action signal is triggered; d/dt is a differential link, and the change rate of the steam drum water bit value is calculated; t represents a switching formula, and when the switching value is 1, the side of Y (Yes) is selected by the output, and when the switching value is 0, the side of N (NO) is selected by the output; in fig. 1 and 2, a is a constant and is a value of 1.
Claims (6)
1. A main steam pressure variable rate control method for assisting RB process steam drum water level control is characterized by comprising the following steps:
step 1, carrying out differential calculation on a steam drum water level value to obtain the change rate of the steam drum water level;
step 2, respectively designing a main steam pressure rate and a steam pressure instruction generation inertia time model function corresponding to the water level change rate of the steam drum when the water feeding pump RB and the non-water feeding pump RB are used, and correcting the main steam pressure rate and the steam pressure instruction generation inertia time through the model function;
step 3, when the dropping rate of the water level of the steam drum is too fast, increasing the pressure rate of main steam, reducing the inertia time generated by a steam pressure instruction, accelerating the dropping rate of a steam pressure set value, opening a steam turbine regulating valve, reducing the actual main steam pressure, and slowing down the dropping rate of the water level through expansion of a steam-water mixture;
step 4, when the rising rate of the water level of the steam drum is too fast, reducing the pressure rate of the main steam and slowing down the falling rate of the set value of the main steam pressure; the pressure of the main steam is delayed to drop by closing the steam turbine regulating valve, and the water level is slowed down to rise.
2. The main steam pressure variable rate control method for assisting RB process drum water level control according to claim 1, wherein the step 2 specifically comprises the following steps:
step 2.1, designing a model function of inertia time generated by a main steam pressure rate and a steam pressure instruction corresponding to a steam drum water level change rate when a water-supply pump RB is not used, and correcting the inertia time generated by the main steam pressure rate and the steam pressure instruction through the model function;
step 2.1.1, the first stage of the non-feedwater pump RB is a stage of lowering of the water level of the steam drum, and the main steam pressure rate and the steam pressure command generation inertia time are corrected according to the lowering rate of the water level of the real-time steam drum; the model function corrects the main steam pressure rate in an offset manner: correcting and generating a main steam pressure rate set value through the falling rate of the steam drum water level, and adding the main steam pressure rate set value and an offset value; the model function corrects the steam pressure command generation inertia time in a gain mode: multiplying the steam pressure command generation inertia time by the gain;
step 2.1.2, starting to rise again after the water level of the steam drum is reduced to the lowest value, and entering a second stage of a non-water-feeding pump RB; the model function corrects the main steam pressure rate and the steam pressure command generation inertia time by adopting the same correction mode as the first stage in the step 2.1.1 according to the descending rate of the real-time steam drum water level; slowing down the correction speed of the main steam pressure rate in the second stage along with the advancing of RB time;
step 2.1.3, when the water level of the steam drum rises to the highest value and the water level of the steam drum begins to fall, entering a third stage of a non-water-feeding pump RB; the model function does not correct the inertia time generated by the main steam pressure rate and the steam pressure instruction any more, the water level of the steam drum is not adjusted through the main steam pressure any more, the bias value of the output main steam pressure rate is 0, and the gain of the inertia time generated by the output steam pressure instruction is 1;
step 2.2, designing a model function of inertia time generated by a main steam pressure rate and a steam pressure instruction corresponding to the water level change rate of the steam drum during the water feeding pump RB, and correcting the inertia time generated by the main steam pressure rate and the steam pressure instruction through the model function;
2.2.1, a stage of lowering the water level of the steam drum when the water feeding pump RB enters the steam drum is a first stage of the water feeding pump RB; setting a bias value of a main steam pressure rate corresponding to the first stage of the feed water pump RB and a gain of steam pressure instruction generation inertia time by combining the propulsion time of the feed water pump RB;
step 2.2.2, the feed pump RB enters a steam drum water level rising stage, namely a second stage of the feed pump RB, and the second stage of the feed pump RB does not correct the main steam pressure rate and the steam pressure instruction generation inertia time;
and 2.2.3, enabling the water feeding pump RB to enter a stable recovery stage of the steam drum water level, wherein the stable recovery stage is a third stage of the water feeding pump RB, and the third stage of the water feeding pump RB does not correct the main steam pressure rate and the steam pressure instruction generation inertia time.
3. The main steam pressure variable rate control method for assisting RB process drum water level control according to claim 1, wherein: setting a model function according to the RB process propulsion time and the drum water level rate in the step 2; and fitting the model function according to the unit operation test data to obtain a more reasonable range of the water level rate in the RB process, and using the range as a control dead zone.
4. The main steam pressure variable rate control method for assisting RB process drum water level control according to claim 1 or 3, wherein: when the steam drum water level change rate is in the dead zone range in the step 2, the bias output of the steam drum water level change rate is 0, and the main steam pressure rate is not corrected; when the drum water level change rate is within the dead zone range, the gain output of the drum water level change rate is 1, and the steam pressure command generation inertia time is not corrected.
5. The main steam pressure variable rate control method for assisting RB process drum water level control according to claim 3, wherein: and in the step 2, the control dead zones of the model functions are different when the water feeding pump RB and the non-water feeding pump RB are used.
6. The method of claim 3, wherein the offset or gain of the drum level change rate in step 2 is:
Y＝aX+b
wherein X is the input steam drum water level rate value, Y is the output offset or gain, and a and b are constants.
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