CN118856329A - Automatic control method for full-course water supply of deep peak regulation of once-through boiler - Google Patents
Automatic control method for full-course water supply of deep peak regulation of once-through boiler Download PDFInfo
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Abstract
The invention relates to a method for automatically controlling water supply in the whole process of deep peak shaving of a once-through boiler, which adopts the same set of control strategies to control water supply in a dry state and a wet state of the boiler; and simultaneously, load control and dry-wet state conversion control are combined to realize continuous load control in the dry-wet state conversion process. Compared with the prior art, the invention has the advantages of improving the whole depth peak regulation capacity of the unit and the like.
Description
Technical Field
The invention relates to a deep peak regulation control technology of a once-through boiler of a coal-fired thermal power unit, in particular to a full-process water supply automatic control method for the deep peak regulation of the once-through boiler.
Background
The new energy power generation has intermittence, randomness and fluctuation, and causes disturbance to the safe and stable operation of the power grid frequency. The peak regulation capability of the basic energy power taking the coal-fired power generation as a main body has important help for improving the flexible operation capability of a power grid, and a large amount of intermittent energy power grid connection can force the coal-fired power generation unit to participate in deep peak regulation more comprehensively, so that the deep peak regulation of the coal-fired unit is normalized, and the frequency of entering a wet operation mode of the direct-current boiler unit in an operation stage is gradually increased.
The control of the water supply system is one of the core control of the once-through boiler of the supercritical (super) coal-fired unit, and the control performance of each stage directly influences the economy and the safety of the unit operation. Because of the complexity of the once-through boiler water supply system, the once-through boiler water supply system needs to operate near or below the transition point under the deep peak shaving ultra-low load working condition, and therefore needs to have a wet state control mode, a dry state control mode and a dry-wet state conversion control mode. The automatic control of water supply in the dry running mode of the current direct current boiler is mature, the effect of the automatic control of the water supply system in the wet running mode and the dry-wet conversion process is relatively not ideal, and the automatic input rate is low.
The retrieved China patent publication No. CN117553289A discloses a method and a system for controlling the dynamic optimization of the depth peak shaving water coal coordination of a supercritical unit, and specifically discloses the method which comprises the following steps: acquiring unit load and a boiler main control instruction; obtaining a fuel instruction and a water supply instruction according to a boiler main control instruction; judging the stage of the unit load; according to the lag time and inertia order corresponding to the stage where the unit load is, differential correction is carried out on the water supply command to obtain a corrected water supply command; controlling coal feeding through a fuel command; and controlling the water supply through the corrected water supply command. However, the technology does not consider the dry and wet state of once-through boiler feedwater systems.
In addition, the prior art has the following problems:
(1) And a manual water supply control strategy in the process of deep peak regulation dry-wet state conversion and wet state operation. The system such as a water supply bypass valve, a rotating speed instruction of a steam feed pump, a water circulation pump outlet valve of the furnace and the like is operated in real time by an operator, and the monitoring parameters comprise water supply flow fluctuation conditions, liquid level stability of the separator, water circulation pump outlet flow, water supply pressure and the like, and a large amount of operations are included in the system, so that the operation burden of the operator is increased. In addition, because the operation level of operators cannot be ensured, the problems of dry state and wet state frequent switching, long state switching time, over-temperature of a water cooling wall, large fluctuation of water supply flow and liquid level of a separator and the like are easily caused to frequently occur, and the stable operation of the unit is influenced.
(2) The once-through boiler in partial wet running adopts a water supply bypass to adjust the minimum safe flow of the water cooling wall, and the rotation speed of the water supply pump is controlled to adjust the front-rear differential pressure of the water supply control door. However, the control mode has the condition that a water supply bypass is mutually coupled with the rotating speed of a water supply pump, and water supply oscillation is easy to occur when control parameters are unreasonable, so that the safety of wet running of the unit is endangered.
Therefore, the problems that the automatic input rate is not high, the wet state control strategy is complex and difficult, the dry and wet state conversion disturbance is large, the load control break point exists, the dry and wet state is difficult to accurately judge, the automatic control of the water supply is affected and the like in the conventional once-through boiler water supply control are solved, and the problems are solved.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a full-process water supply automatic control method for deep peak regulation of a once-through boiler.
The aim of the invention can be achieved by the following technical scheme:
according to one aspect of the invention, a method for automatically controlling the water supply in the whole process of deep peak shaving of a once-through boiler is provided, wherein the method adopts the same set of control strategies to control the water supply in a dry state and a wet state of the boiler; and simultaneously, load control and dry-wet state conversion control are combined to realize continuous load control in the dry-wet state conversion process.
As a preferred technical solution, the method specifically comprises the following steps:
Step S1, determining a lower limit value G gs of the water supply flow in the boiler depth peak regulation operation;
step S2, under the wet running mode of the boiler, the water supply system still maintains the automatic control mode of dry water supply;
step S3, setting a set value of steam temperature or enthalpy value of an outlet of the separator and a set value of coal water ratio under a wet working condition;
Step S4, triggering corresponding control measures when a water supply flow set value G sp output by the cooperative control system is lower than a water supply flow lower limit G gs in the unit depth peak regulation process;
Step S5, triggering a corresponding control strategy when the boiler enters a wet state operation condition or a dry state operation condition;
and S6, in the deep peak shaving process of the unit, the boiler changes the combustion rate according to load control and main steam pressure control.
As a preferable technical solution, the automatic control mode of the dry water supply in the step S2 specifically includes:
And controlling the water supply flow through the rotating speed of the steam pump, and still maintaining the automatic control of the steam temperature or the enthalpy value of the outlet of the separator, wherein the set value of the water supply flow is determined by the control of the steam temperature or the enthalpy value of the outlet of the separator and the water-coal ratio.
As a preferable technical solution, the triggering the corresponding control measure in step S4 includes:
41 A) sending the lower feed water flow limit G gs as a set value to the feed water flow controller;
42 Triggering a 1s water supply flow set value tracking signal, tracking a water supply flow set value G sp of the cooperative control system to a lower limit G gs of the water supply flow, and outputting tracking deviation for tracking the water supply flow set value by a separator outlet steam temperature or enthalpy value controller.
In the step S5, when the boiler enters the wet running condition, the load-reducing adjustment rate correction signal of the unit is triggered, and the load-changing rate is corrected according to the boiler pressure control deviation.
In the step S5, when the boiler enters the dry running condition, the unit is triggered to load the adjustment rate correction signal, and the variable load rate is corrected according to the boiler pressure control deviation.
As a preferable technical solution, the step S6 specifically includes:
When the set value G sp of the water supply flow is lower than the lower limit G gs of the water supply flow, the unit continuously reduces the load, the water supply flow is reduced at the moment to maintain the lowest limit, the combustion rate is reduced along with the reduction of the load, and the boiler is switched from a dry state to a wet state to operate;
When the load is increased in a wet running mode, the combustion rate output of the boiler is increased, the water supply flow is controlled by the steam temperature or enthalpy value of the outlet of the separator, and the water supply flow continues to maintain the minimum limit value until the boiler is switched to dry running.
Compared with the prior art, the invention has the following advantages:
1) The invention realizes the full-process automatic control of water supply in the deep peak regulation process of the once-through boiler of the supercritical (supercritical) coal-fired thermal power unit, has uniform control method, is convenient to realize, does not need to switch different control modes according to the dry and wet state working conditions of the boiler, and improves the safety and stability of water supply control in the deep peak regulation process of the unit.
2) According to the invention, load control and dry-wet state conversion control are combined, so that continuous load control in the dry-wet state conversion process is realized, and the integral depth peak regulation capacity of the unit is improved.
Drawings
FIG. 1 is a schematic diagram of a specific control process of the method of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.
Aiming at the problems that the automatic input rate is not high, the wet state control strategy is complex and difficult, the dry-wet state conversion disturbance is large, the load control break point exists, the dry-wet state is difficult to accurately judge, the automatic water supply control is affected, and the like in the water supply control of the existing once-through boiler, the invention provides a novel full-course water supply automatic control method for the once-through boiler. Meanwhile, load control and dry-wet state conversion control are combined, continuous load control in the dry-wet state conversion process is realized, the problem of AGC investment in the dry-wet state conversion process is solved, and the integral depth peak regulation capacity of the unit is improved.
A certain 660MW ultra-supercritical coal-fired thermal power unit daily needs deep peak shaving to 25% Pe (rated load), a 30% Pe load working condition of the unit is close to a dry-wet state conversion point, and a 25% Pe deep peak shaving boiler system needs to be subjected to dry-wet state conversion and wet state operation modes. The whole-course water supply control implementation method of the unit is as follows:
(1) According to a fixed value list provided by a boiler manufacturer, considering the requirements of safe and stable operation of deep peak shaving of a unit boiler, and determining the lower limit value G gs of the water supply flow in the deep peak shaving operation of the boiler to be 587t/h;
(2) Under the wet running mode of the boiler, the water supply system still maintains the automatic control mode of dry water supply: the rotating speed of the steam pump controls the water supply flow, the set value of the water supply flow is determined by the steam temperature control of the outlet of the separator and the water-coal ratio, and the automatic control of the steam temperature of the outlet of the separator is still maintained;
The set water supply flow set value G sp＝GBM+GST+GFF, wherein G BM is a water supply flow value corresponding to a boiler main control instruction, G ST is a water supply flow correction value output by separator outlet steam temperature control, and G FF is a feed-forward value of water supply flow such as variable load, primary frequency modulation, steam temperature correction and the like.
(3) Setting a separator outlet temperature set value and a coal water proportioning set value under a wet working condition; wherein, the outlet temperature set value of the separator is set to be 5 ℃ higher than the saturated steam temperature under the load working condition of less than 30%Pe; after the water supply flow set value reaches the minimum flow, the water supply flow set value is maintained unchanged, and the specific functional relation is as follows:
TABLE 1
(4) In the unit depth peak regulation process, when the water supply flow set value G sp output by the coordination control system is lower than the water supply flow lower limit G gs, the following control measures are triggered:
the lower limit G gs of the water supply flow is taken as a set value to be sent to a water supply flow controller;
Triggering a 1s water supply flow set value tracking signal, tracking a water supply flow lower limit G gs by a water supply flow set value G sp of the cooperative control system, and outputting tracking deviation of tracking the water supply flow set value by a separator outlet steam temperature controller, namely G ST＝Ggs-GBM-GFF.
(5) Triggering a unit load reduction adjustment rate correction signal when the boiler starts to enter a wet running condition, and correcting a variable load rate according to the boiler pressure control deviation; triggering a unit load adjustment rate correction signal when the boiler starts to enter a dry running condition, and correcting a variable load rate according to the boiler pressure control deviation;
(6) In the deep peak regulation process of the unit, the boiler changes the combustion rate according to load control and main steam pressure control. When the feedwater flow set point G sp is lower than the lower feedwater flow limit G gs, the unit continues to reduce the load, the reduced feedwater flow maintains the lowest limit at this time, the combustion rate is reduced along with the reduction of the load, and the boiler is switched from dry state to wet state operation. When the load is increased in a wet running mode, the combustion rate output of the boiler is increased, the water supply flow is controlled by the steam temperature at the outlet of the separator, and the water supply flow continues to maintain the minimum limit value until the boiler is switched to dry running.
D.c. boiler: the once-through boiler is a boiler in which water is fed sequentially through an economizer, an evaporation heating surface (water-cooled wall), and a superheater by the pressure of a water feed pump and is entirely changed into superheated steam. Because the water is heated, evaporated and overheated in the heating surface continuously after entering the boiler, steam-water separation is not needed in the middle of heating. Therefore, it does not have a drum of the natural circulation boiler. There is no fixed boundary point between the heating surface of the economizer, the evaporating heating surface and the superheater heating surface, and the boundary point changes along with the boiler load change.
Deep peak shaving: the method is greatly influenced by the peak-valley difference of the load of the power grid, so that the output of the thermal power plant is reduced, and the generator set is operated in a mode of peak regulation beyond the basic peak regulation range.
Dry/wet state: dry running of the boiler: the steam generated by the boiler is equal to the flow of the water-cooled wall, so that the superheated steam flows through the steam-water separator, and no water exists in the steam-water separator, so that the boiler is called dry running. Wet running of the boiler: in contrast to dry running, the steam generated in the boiler is smaller than the flow of the water-cooled wall, at the moment, the steam-water separator is internally provided with a steam-water mixture, redundant saturated water in the steam-water separator is separated and reused through the steam-water separator, and the saturated steam is continuously heated by a subsequent heating surface to become superheated steam.
While the invention has been described with reference to certain preferred embodiments, it will be understood by those skilled in the art that various changes and substitutions of equivalents may be made and equivalents will be apparent to those skilled in the art without departing from the scope of the invention. Therefore, the protection scope of the invention is subject to the protection scope of the claims.
Claims (7)
1. The method is characterized in that the method adopts the same set of control strategies to control the water supply in the dry state and the wet state of the boiler; and simultaneously, load control and dry-wet state conversion control are combined to realize continuous load control in the dry-wet state conversion process.
2. The method for automatically controlling the full-range water supply of the deep peak shaving of the once-through boiler according to claim 1, which is characterized by comprising the following steps:
Step S1, determining a lower limit value G gs of the water supply flow in the boiler depth peak regulation operation;
step S2, under the wet running mode of the boiler, the water supply system still maintains the automatic control mode of dry water supply;
step S3, setting a set value of steam temperature or enthalpy value of an outlet of the separator and a set value of coal water ratio under a wet working condition;
Step S4, triggering corresponding control measures when a water supply flow set value G sp output by the cooperative control system is lower than a water supply flow lower limit G gs in the unit depth peak regulation process;
Step S5, triggering a corresponding control strategy when the boiler enters a wet state operation condition or a dry state operation condition;
and S6, in the deep peak shaving process of the unit, the boiler changes the combustion rate according to load control and main steam pressure control.
3. The method for automatically controlling the full-range water supply of the once-through boiler by deep peak shaving according to claim 2, wherein the method for automatically controlling the dry water supply in step S2 is specifically as follows:
And controlling the water supply flow through the rotating speed of the steam pump, and still maintaining the automatic control of the steam temperature or the enthalpy value of the outlet of the separator, wherein the set value of the water supply flow is determined by the control of the steam temperature or the enthalpy value of the outlet of the separator and the water-coal ratio.
4. The method for automatically controlling the full-range water supply of the once-through boiler by deep peak shaving according to claim 2, wherein the triggering of the corresponding control measure in the step S4 includes:
41 A) sending the lower feed water flow limit G gs as a set value to the feed water flow controller;
42 Triggering a 1s water supply flow set value tracking signal, tracking a water supply flow set value G sp of the cooperative control system to a lower limit G gs of the water supply flow, and outputting tracking deviation for tracking the water supply flow set value by a separator outlet steam temperature or enthalpy value controller.
5. The method for automatically controlling the full-range water supply of the once-through boiler by deep peak shaving according to claim 2, wherein in the step S5, when the boiler enters a wet running condition, a unit load reduction adjustment rate correction signal is triggered, and the load change rate is corrected according to the boiler pressure control deviation.
6. The method for automatically controlling the full-range water supply of the once-through boiler by deep peak shaving according to claim 2, wherein in the step S5, when the boiler enters a dry running condition, a unit load adjustment rate correction signal is triggered, and the variable load rate is corrected according to the boiler pressure control deviation.
7. The method for automatically controlling the full-range water supply of the once-through boiler by deep peak shaving according to claim 2, wherein the step S6 is specifically:
When the set value G sp of the water supply flow is lower than the lower limit G gs of the water supply flow, the unit continuously reduces the load, the water supply flow is reduced at the moment to maintain the lowest limit, the combustion rate is reduced along with the reduction of the load, and the boiler is switched from a dry state to a wet state to operate;
When the load is increased in a wet running mode, the combustion rate output of the boiler is increased, the water supply flow is controlled by the steam temperature or enthalpy value of the outlet of the separator, and the water supply flow continues to maintain the minimum limit value until the boiler is switched to dry running.
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