Coal-fired power generation unit and its control method

Abstract

The present invention discloses a coal-fired power generation unit and its control method. Among them, the coal-fired power generation unit includes a boiler, a steam turbine, and a feed water accumulator. The steam turbine includes a cylinder group, a condenser, and a deaerator. The deaerator is configured with a first outlet water pipeline, and the first outlet water pipeline is connected to the feed water accumulator. The feed water accumulator is configured with a second outlet water pipeline and a first steam extraction pipeline. The second outlet water pipeline is connected to the boiler, and the first steam extraction pipeline is configured to be able to partially introduce the steam generated by the boiler into the feed water accumulator. The above-mentioned coal-fired power generation unit can have a lower dry-state deep load regulation capacity, can maintain a dry-state operating condition within a wider load range, which is beneficial to ensuring the safety and stability of equipment operation. At the same time, it can also be used to improve the load change rate, improve the operating stability, and improve the economy and rapidity of the unit start-stop peak regulation.

Description

Technical Field

[0001] The present invention relates to the technical field of coal-fired power generation, and particularly to a coal-fired power generation unit and a control method thereof. Background Art

[0002] With the transformation and upgrading of the power industry, the demand for flexible operation of coal-fired power generation units has gradually increased, specifically manifested as new requirements for the deep peak shaving ability of the units.

[0003] Currently, the benchmark point for deep peak shaving of coal-fired power generation units has been lowered to 40% of the rated load. Only when the unit operates below 40% of the rated load can it obtain the deep peak shaving grid-connected electricity price. For (ultra) supercritical coal-fired power generation units, during deep peak shaving operation, between 40% of the rated load and the designed Benson load of the boiler (about 25%-30% of the rated load), it is in a dry operating condition. If we want to further explore the deep peak shaving ability of the unit and continue to lower to 20% of the rated load or even 15% of the rated load, it is necessary to perform the dry-wet conversion of the boiler and switch the boiler to the wet operating condition to ensure the safety of the water-cooled wall.

[0004] However, compared with the dry operating condition, in the wet operating condition of the boiler, the steam temperature at the steam separator is low, and the main steam and reheat steam temperature levels are also low, resulting in a significant reduction in the economy of the unit. Moreover, during the dry-wet conversion of the boiler, it will also cause large fluctuations in the temperature of the steam separator and the subsequent superheater, affecting the safe operation of the equipment.

[0005] Therefore, how to provide a solution to overcome or alleviate the above defects is still a technical problem that needs to be urgently solved by those skilled in the art. Summary of the Invention

[0006] The object of the present invention is to provide a coal-fired power generation unit and a control method thereof. Among them, the coal-fired power generation unit can have a lower dry-state deep peak shaving load capacity, can maintain a dry operating condition within a wider load range, which is beneficial to ensuring the safety and stability of equipment operation. At the same time, it can also be used to improve the load change rate, improve the operation stability, and improve the economy and rapidity of unit start-stop peak shaving.

[0007] To solve the above technical problems, the present invention provides a coal-fired power generation unit, including a boiler, a steam turbine, and a feed water accumulator. The steam turbine includes a cylinder group, a condenser, and a deaerator. The deaerator is configured with a first outlet water pipe, and the first outlet water pipe is connected to the feed water accumulator. The feed water accumulator is configured with a second outlet water pipe and a first steam extraction pipe. The second outlet water pipe is connected to the boiler, and the first steam extraction pipe is configured to be able to partially introduce the steam generated by the boiler into the feed water accumulator.

[0008] In the embodiment of the present invention, a feed water accumulator is added between the deaerator and the boiler. When the real-time load of the coal-fired power generation unit drops to the set load and the load change trend is still in a downward trend, the first steam extraction pipeline of the feed water accumulator can be opened to input a part of the steam generated by the boiler into the feed water accumulator. In this way, the inlet flow rate of the water wall can correspond to the steam inlet flow rate of the cylinder group and the steam extraction flow rate of the first steam extraction pipeline, and the water wall can still maintain the required flow rate, such as the minimum safety flow rate, so that the coal-fired power generation unit can still operate under the dry operating condition. Due to the introduction of the first steam extraction pipeline, the steam inlet flow rate of the cylinder group can be reduced, so that the coal-fired power generation unit can still perform load reduction operation. And as the steam extraction flow rate of the first steam extraction pipeline increases, the real-time load of the coal-fired power generation unit can gradually be less than the designed Benson load, which is equivalent to reducing the actual Benson load of the coal-fired power generation unit, so that the coal-fired power generation unit can maintain the dry operating condition in a wider load range, and the coal-fired power generation unit can have a lower dry state deep load regulation capacity, which is beneficial to ensuring the safety and stability of equipment operation.

[0009] In addition, the coal-fired power generation unit provided by the embodiment of the present invention can also be used to improve the load change rate, improve the operation stability, and improve the economy and rapidity of unit start-stop peak regulation.

[0010] Optionally, the first steam extraction pipeline includes a first steam extraction branch, and the first steam extraction branch is connected to the boiler.

[0011] Optionally, the boiler includes a superheater, the superheater includes a plurality of heating components, and each of the heating components is arranged along the steam flow direction. The connection point of the first steam extraction branch and the boiler is located between two adjacent heating components.

[0012] Optionally, an air heater is arranged on the first steam extraction branch.

[0013] Optionally, the first steam extraction pipeline further includes a second steam extraction branch, and the second steam extraction branch is connected to the cylinder group.

[0014] Optionally, a high-pressure heater is arranged on the first water outlet pipeline.

[0015] Optionally, the condenser is configured with a third water outlet pipeline, the third water outlet pipeline is connected to the deaerator, and a low-pressure heater is arranged on the third water outlet pipeline.

[0016] The present invention also provides a control method for a coal-fired power generation unit, which is applicable to the above-mentioned coal-fired power generation unit. The control method includes: a first acquisition step of acquiring the real-time load of the coal-fired power generation unit and the load change trend of the coal-fired power generation unit; a first judgment step of judging whether the real-time load is less than the set load and the load change trend is a downward trend. If so, execute the following first control step; a first control step of controlling to open the first steam extraction pipeline.

[0017] The present invention also provides a control method for a coal-fired power generation unit, which is applicable to the above-mentioned coal-fired power generation unit. The condenser is configured with a third water outlet pipeline, and the third water outlet pipeline is connected to the deaerator. The control method includes: a second acquisition step of acquiring the load change command of the coal-fired power generation unit; a second judgment step of judging whether the load change command is a load increase command. If so, execute the following second control step; or judge whether the load change command is a load decrease command. If so, execute the following third control step; a second control step of reducing the flow rates of the first water outlet pipeline and the third water outlet pipeline; a third control step of increasing the flow rates of the first water outlet pipeline and the third water outlet pipeline.

[0018] The present invention also provides a control method for a coal-fired power generation unit, which is applicable to the above-mentioned coal-fired power generation unit. The control method includes: controlling to open the first steam extraction pipeline when the coal-fired power generation unit is initially started. Description of the Drawings

[0019] Figure 1 It is a schematic structural diagram of an implementation manner of the coal-fired power generation unit provided by the present invention;

[0020] Figure 2 It is a schematic structural diagram of another implementation manner of the coal-fired power generation unit provided by the present invention;

[0021] Figure 3 It is a schematic flowchart of an implementation manner of the control method for the coal-fired power generation unit provided by the present invention;

[0022] Figure 4 It is a schematic flowchart of another implementation manner of the control method for the coal-fired power generation unit provided by the present invention.

[0023] The description of the reference numerals is as follows:

[0024] 100 Boiler, 110 Economizer, 120 Water Wall, 130 Steam-Water Separator, 140 Superheater, 141 Heat-Receiving Component, 150 Storage Tank, 160 Steam Supply Pipeline;

[0025] 200 steam turbine, 210 cylinder block, 220 condenser, 221 third outlet pipeline, 230 deaerator, 231 first outlet pipeline, 232 second extraction pipeline, 240 high-pressure heater, 241 third extraction pipeline, 250 low-pressure heater, 251 fourth extraction pipeline, 260 condensate pump, 270 first feed water pump;

[0026] 300 feed water accumulator, 310 second outlet pipeline, 311 second feed water pump, 320 first extraction pipeline, 321 first extraction branch, 321a air heater, 322 second extraction branch. Detailed implementation manners

[0027] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] In the embodiments of the present invention, the terms "first", "second", "third", and "fourth" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first", "second", "third", and "fourth" may explicitly or implicitly include one or more of such features.

[0029] In the description of the embodiments of the present invention, the term "plurality" means two or more. And when using "plurality" to describe the quantities of different components, it does not indicate the mutual relationship in quantity of these components.

[0030] In the description of the embodiments of the present invention, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of another identical element in the process, method, article or device including that element.

[0031] Please refer to Figure 1 and Figure 2 , Figure 1 which is a schematic structural diagram of an implementation manner of the coal-fired power generation unit provided by the present invention, Figure 2 which is a schematic structural diagram of another implementation manner of the coal-fired power generation unit provided by the present invention.

[0032] As Figure 1 shown, the present invention provides a coal-fired power generation unit, including a boiler 100 and a steam turbine 200.

[0033] The boiler 100, also known as a coal-fired boiler, is a component used to heat water into steam. The boiler 100 includes a furnace body, and a combustion chamber can be formed inside the furnace body. Fuels such as coal can be burned in the combustion chamber to generate flames.

[0034] A water-cooled wall 120 is also provided inside the furnace wall of the furnace body. Boiler feed water passes through the water-cooled wall 120. The water-cooled wall 120 is the core heat exchange device of the boiler 100 and is used to absorb the heat of the flame so as to heat at least part of the boiler feed water inside it into steam. The specific structural form of the water-cooled wall 120 is not limited. In practical applications, those skilled in the art can select according to specific needs. Generally speaking, the water-cooled wall 120 can include multiple heat exchange pipes, and each heat exchange pipe can be arranged at different positions on the furnace wall of the furnace body.

[0035] An economizer 110 can be provided upstream of the water-cooled wall 120. The economizer 110 can utilize the heat of the flue gas at the tail of the boiler to preheat the boiler feed water before it enters the water-cooled wall 120, which can effectively save boiler fuel.

[0036] In addition, the boiler 100 can also include a steam-water separator 130, a superheater 140, a water storage tank 150, and a steam supply pipeline 160. The steam-water separator 130 is located downstream of the water-cooled wall 120 and is used to separate the steam (which may carry a certain amount of water) discharged from the water-cooled wall 120. The separated water can be discharged into the water storage tank 150, and the separated steam can enter the superheater 140 for further heating to form main steam. The main steam can be supplied to the steam turbine 200 through the steam supply pipeline 160 for the steam turbine 200 to do work and generate electricity.

[0037] The superheater 140 can include multiple heating components 141, and each heating component 141 can be arranged in sequence. Correspondingly, the steam can pass through each heating component 141 in sequence to increase the temperature step by step; for example Figure 1 as shown, the superheater 140 can include two heating components 141. Of course, the superheater 140 can also include only one heating component 141, which can be determined specifically in combination with the usage requirements, etc. In some implementation manners, the superheater 140 can also be called the boiler heating surface. In short, it can reheat the steam after leaving the steam-water separator 130 to further increase the temperature of the steam.

[0038] The steam turbine 200 includes a cylinder block 210, a condenser 220, and a deaerator 230.

[0039] The cylinder block 210 is a core component of the steam turbine 200, which is used to isolate steam from the atmosphere and form a closed space for steam to complete energy conversion. The cylinder block 210 may include multiple cylinders. In some implementations, the cylinder block 210 may include a high-pressure cylinder, an intermediate-pressure cylinder, and two low-pressure cylinders. In other implementations, the cylinder block 210 may also adopt other structural forms; for example, the cylinder block 210 may include a high-pressure cylinder, an intermediate-pressure cylinder, and a low-pressure cylinder, or the cylinder block 210 may include a combined high- and intermediate-pressure cylinder and a low-pressure cylinder, etc.

[0040] The condenser 220 may be located on the lower side of the low-pressure cylinder. The condenser 220 and the low-pressure cylinder may share a housing to improve the integration of the equipment; of course, the condenser 220 and the low-pressure cylinder may also be independent of each other. In short, the condenser 220 and the low-pressure cylinder may be connected, and the steam can be discharged into the condenser 220 after doing work in the low-pressure cylinder, and condensation can occur in the condenser 220 to form condensate. The condenser 220 may be configured with a third outlet pipe 221, and the third outlet pipe 221 may be connected to the deaerator 230 to introduce the condensate in the condenser 220 into the deaerator 230 for thermal deaeration in the deaerator 230.

[0041] The third outlet pipe 221 may also be provided with a low-pressure heater 250 and a condensate pump 260. The condensate pump 260 may be located upstream of the low-pressure heater 250 to provide power for the condensate in the third outlet pipe 221, drive the condensate in the third outlet pipe 221 to flow, and adjust the flow rate of the condensate in the third outlet pipe 221. The low-pressure heater 250 may be configured with a fourth extraction pipe 251, and the fourth extraction pipe 251 may be connected to any cylinder in the cylinder block 210 to extract the steam in the cylinder block 210, so as to heat the condensate in the third outlet pipe 221 and relieve the temperature rise pressure of the deaerator 230. The number of low-pressure heaters 250 is not limited here.

[0042] The deaerator 230 may be configured with a first outlet pipe 231 and a second extraction pipe 232. The second extraction pipe 232 may be connected to any cylinder in the cylinder block 210 to directly introduce the steam in the cylinder block 210 into the deaerator 230 to heat up and deaerate the condensate. The first outlet pipe 231 is used to lead out the condensate heated and deaerated in the deaerator 230 for discharge.

[0043] The first outlet water pipe 231 may be provided with a high-pressure heater 240 and a first feed water pump 270. The first feed water pump 270 may be located upstream of the high-pressure heater 240, and is used to provide power for the condensate water in the first outlet water pipe 231, can drive the condensate water in the first outlet water pipe 231 to flow, and can adjust the flow rate of the condensate water in the first outlet water pipe 231. The high-pressure heater 240 may be configured with a third extraction steam pipe 241, and the third extraction steam pipe 241 may be connected to any cylinder in the cylinder group 210 to lead out the steam in the cylinder group 210, so as to realize heating of the condensate water in the first outlet water pipe 231. The number of high-pressure heaters 240 is also not limited.

[0044] In the conventional solution, the above-mentioned first outlet water pipe is directly connected to the boiler, that is, the condensate water in the deaerator can be directly used as boiler feed water and supplied to the boiler. In this way, when the coal-fired power generation unit is at low load, the flow rate of the first outlet water pipe will be greatly reduced. Correspondingly, the flow rate of the water wall will also be greatly reduced, which is likely to cause the problem of hydrodynamic multiplicity, that is, the flow rate deviation of the boiler feed water entering each heat exchange channel of the water wall is large, and there is even a stagnant or reverse flow state of the boiler feed water in some heat exchange channels; since the water wall is located in the internal combustion area of the boiler, the temperature level in this area is the highest. Once the problem of hydrodynamic multiplicity occurs, it may cause dangerous situations such as dry burning and pipe explosion in some heat exchange pipelines, seriously threatening the safe operation of the unit. In order to ensure the safe operation of the water wall, it is necessary to maintain a relatively high flow rate of the water wall at low load. However, due to the low load demand of the unit and the large flow rate of the water wall, the water-coal ratio will be unbalanced. At this time, the steam at the outlet of the water wall is wet steam. When passing through the steam-water separator, a considerable amount of water will be separated, and the remaining dry saturated steam can enter the superheater for heating. This operating condition is the wet operating condition of the boiler.

[0045] Based on this situation, coal-fired power generation units, especially (ultra) supercritical coal-fired power generation units, will have to face the problem of the minimum safe flow rate of the water wall when operating from the dry operating condition to a lower load. The load corresponding to the minimum safe flow rate under the dry operating condition of the boiler is the designed Benson load of the boiler. Generally speaking, the value of the designed Benson load is clearly given. When the real-time load of the coal-fired power generation unit is higher than the designed Benson load, the boiler can operate safely under the dry operating condition; when the real-time load of the coal-fired power generation unit is lower than the designed Benson load, in order to ensure the safety of the water wall, the minimum safe flow rate mentioned above still needs to be maintained at the inlet of the water wall, and the boiler has to switch to the wet operating condition, and part of the saturated water of the water wall will circulate inside the system.

[0046] However, as described in the background art section, under wet operating conditions, the steam temperature at the steam-water separator is low, and the main steam and reheated steam temperature levels are also relatively low. Moreover, during the dry-wet state conversion of the boiler, it will also cause large fluctuations in the temperatures of the steam-water separator and the superheater, affecting the safe operation of the equipment.

[0047] Therefore, if the load point corresponding to the dry-wet state conversion can be reduced, it is beneficial for ensuring the dry-state deep load regulation capacity of the unit and the safe and stable operation of the equipment. However, the focus of related technologies generally is on how to ensure the smoothness during the dry-wet state switching process, rather than on how to reduce the above-mentioned load point.

[0048] In view of this, the coal-fired power generation unit provided by an embodiment of the present invention further includes a feedwater accumulator 300. The feedwater accumulator 300 is arranged between the deaerator 230 and the boiler 100. The water-side inlet of the feedwater accumulator 300 can be connected to the aforementioned first outlet pipeline 231. At the same time, the feedwater accumulator 300 is configured with a second outlet pipeline 310 and a first steam extraction pipeline 320. The second outlet pipeline 310 is connected to the boiler 100, and the first steam extraction pipeline 320 is configured to be able to partially introduce the steam generated by the boiler 100 into the feedwater accumulator 300.

[0049] With the above solution, when the real-time load of the coal-fired power generation unit drops to the set load and the load change trend is still in a downward trend, the first steam extraction pipeline 320 can be opened to inject a part of the steam generated by the boiler 100 into the feedwater accumulator 300. In this way, the inlet flow rate of the water wall 120 can correspond to the steam inlet flow rate of the cylinder group 210 and the steam extraction flow rate of the first steam extraction pipeline 320. The water wall 120 can still maintain the required flow rate, such as the aforementioned minimum safety flow rate, so that the coal-fired power generation unit can still operate under dry operating conditions. And due to the introduction of the first steam extraction pipeline 320, the steam inlet flow rate of the cylinder group 210 can be reduced, enabling the coal-fired power generation unit to still perform load reduction operation. Moreover, as the steam extraction flow rate of the first steam extraction pipeline 320 increases, the real-time load of the coal-fired power generation unit can gradually be less than the above-mentioned designed Benson load, which is equivalent to reducing the actual Benson load of the coal-fired power generation unit, enabling the coal-fired power generation unit to maintain a dry operating condition in a wider load range, and the coal-fired power generation unit can have a lower dry-state deep load regulation capacity, which is beneficial for ensuring the safety and stability of equipment operation.

[0050] The above-mentioned set load can be the designed Benson load, that is, when the real-time load drops to the designed Benson load, the first steam extraction pipeline 320 is opened again. For example, when the designed Benson load is 25% of the rated load, the coal-fired power generation unit in the embodiment of the present invention can control the first steam extraction pipeline 320 to open when the real-time load drops to 25% of the rated load.

[0051] Alternatively, the above set load can also be a load value greater than the designed Benson load. In this way, the coal-fired power generation unit can control the opening of the first steam extraction pipeline 320 before the real-time load drops to the designed Benson load, so as to reserve the response time of the unit, which is beneficial to ensuring the stable operation of the unit. In a specific example, the difference between the above set load and the designed Benson load can be less than or equal to 7.5% of the rated load. For example, when the designed Benson load is 25% of the rated load, the set load can be 30% of the rated load. The coal-fired power generation unit in the embodiment of the present invention can control the opening of the first steam extraction pipeline 320 when the real-time load drops to 30% of the rated load.

[0052] Through research and testing, the coal-fired power generation unit provided by the embodiment of the present invention can reduce the dry deep regulation load capacity by about 5% of the rated load. Specifically, if the designed Benson load is 25% of the rated load, the actual Benson load of the coal-fired power generation unit provided by the embodiment of the present invention can drop to 20% of the rated load; if the designed Benson load is 20% of the rated load, the actual Benson load of the coal-fired power generation unit provided by the embodiment of the present invention can drop to 15% of the rated load.

[0053] The first steam extraction pipeline 320 may include a first steam extraction branch 321, and the first steam extraction branch 321 may be connected to the boiler 100 to directly obtain steam from the boiler 100.

[0054] In some implementation manners, as Figure 1 shown, the connection point between the first steam extraction branch 321 and the boiler 100 may be located between two adjacent heating components 141. In this way, the temperature of the steam in the first steam extraction branch 321 can be effectively controlled to avoid the situation of too high steam temperature; at the same time, for the heating component 141 on the downstream side of the connection point of the first steam extraction branch 321, the steam flow rate inside it will be reduced, the heat exchange pressure will drop, and correspondingly, the steam temperature inside it can be increased, which is also beneficial to ensuring the temperature of the main steam in the steam supply pipeline 160.

[0055] Of course, in some other implementation manners of the embodiment of the present invention, it is also possible to directly set the connection point between the first steam extraction branch 321 and the boiler 100 downstream of the superheater 140. At this time, the steam temperatures in the first steam extraction branch 321 and the steam supply pipeline 160 are basically the same.

[0056] In the embodiment of the present invention, the first steam extraction pipeline 320 may further include a second steam extraction branch 322, and the second steam extraction branch 322 may be connected to the cylinder block 210 to directly obtain steam from the cylinder block 210. In this way, the amount of steam provided by the boiler 100 to the steam turbine 200 can also be effectively reduced.

[0057] Both the first steam extraction branch 321 and the second steam extraction branch 322 can be configured with regulating valves to adjust the steam extraction flow rates of the two. Of course, it is also possible not to provide regulating valves. In this case, the steam flow rates inside the two can be adjusted by regulating valves at other positions inside the unit, such as the regulating valve at the inlet of the cylinder block 210; or, the first steam extraction branch 321 and the second steam extraction branch 322 can also operate in a non-adjustable steam extraction mode.

[0058] As Figure 2 shown, in some other implementation manners of the embodiments of the present invention, an air supply heater 321a can also be provided on the first steam extraction branch 321 to heat the primary air and secondary air of the boiler 100 through steam, which can increase the air temperature entering the boiler 100 and is beneficial to improving the combustion stability in the boiler 100. At the same time, the inlet flue gas temperature of the Selective Catalytic Reduction (SCR) reactor can also be ensured, which is beneficial to the safe input of denitrification under the ultra-low load condition of the coal-fired power generation unit.

[0059] In addition to obtaining the lower dry-state deep regulation load capacity as described above, the coal-fired power generation unit provided by the embodiments of the present invention can also be used to improve the load change rate, improve the operation stability, and improve the economy and rapidity of unit start-stop peak regulation.

[0060] <Improve the load change rate>

[0061] When the load change command received by the coal-fired power generation unit is a load increase command, the flow rate of the first water outlet pipe 231 is reduced, specifically, it can be reduced to the minimum safe flow rate. The specific reduction method can be to operate the first feed water pump 270. At this time, all the boiler feed water required by the boiler 100 is provided by the high-temperature water stored in the feed water accumulator 300; in this way, the flow rate of the condensate flowing through the high-pressure heater 240 is greatly reduced, and the steam extraction flow rate in the third steam extraction pipe 241 of the high-pressure heater 240 decreases accordingly, so that more steam can do work in the cylinder block 210. At the same time, the flow rate of the third water outlet pipe 221 can also be reduced, specifically, it can be achieved by operating the condensate pump 260 to control the water level in the deaerator 230; in this way, the flow rate of the condensate flowing through the low-pressure heater 250 is greatly reduced, and the steam extraction flow rate in the fourth steam extraction pipe 251 of the low-pressure heater 250 also decreases accordingly, so that more steam can do work in the cylinder block 210. And for the deaerator 230, the reduction of the flow rates of the first water outlet pipe 231 and the third water outlet pipe 221 also greatly reduces the renewal speed of the condensate in the deaerator 230, and the steam extraction flow rate in the second steam extraction pipe 232 of the deaerator 230 can also be reduced accordingly, so that more steam can do work in the cylinder block 210. In this way, the load increase rate of the coal-fired power generation unit can be improved.

[0062] When the load change command received by the coal-fired power generation unit is a load reduction command, increase the flow rate of the first water outlet pipeline 231, which can be specifically achieved by operating the first feed water pump 270, and then reduce the flow rate of the second water outlet pipeline 310, which can be specifically achieved by operating the second feed water pump 311; the additional condensate water brought about by the flow rate difference between the first feed water pump 270 and the second feed water pump 311 can be stored in the feed water accumulator 300. Contrary to the aforementioned load increase process, after the flow rate of the first water outlet pipeline 231 increases, the extraction steam flow rate of the third extraction steam pipeline 241 of the high-pressure heater 240 will increase accordingly; at the same time, in order to maintain the liquid level stability in the deaerator 230, the flow rate of the third water outlet pipeline 221 also increases synchronously, and the extraction steam flow rate of the fourth extraction steam pipeline 251 of the low-pressure heater 250 also increases correspondingly; moreover, the update speed of the condensate water in the deaerator 230 is greatly accelerated, and the extraction steam flow rate of the second extraction steam pipeline 232 of the deaerator 230 can also increase accordingly. In this way, the steam in the cylinder group 210 is reduced, and the load reduction rate of the coal-fired power generation unit is increased.

[0063] That is to say, the load change rate of the coal-fired power generation unit provided by the embodiment of the present invention can be relatively fast.

[0064] In addition, similar to the above load increase and decrease rate ideas, the coal-fired power generation unit provided by the embodiment of the present invention can also improve the primary frequency regulation ability. Specifically, if the primary frequency regulation command is a load increase command, then reduce the flow rates of the first water outlet pipeline 231 and the third water outlet pipeline 221, so that the extraction steam flow rates of the third extraction steam pipeline 241 of the high-pressure heater 240, the fourth extraction steam pipeline 251 of the low-pressure heater 250, and the second extraction steam pipeline 232 of the deaerator 230 all decrease, and more steam can do work in the cylinder group 210, and the coal-fired power generation unit can quickly increase the load to meet the primary frequency regulation load demand; if the primary frequency regulation command is a load reduction command, then increase the flow rates of the first water outlet pipeline 231 and the third water outlet pipeline 221, so that the extraction steam flow rates of the third extraction steam pipeline 241 of the high-pressure heater 240, the fourth extraction steam pipeline 251 of the low-pressure heater 250, and the second extraction steam pipeline 232 of the deaerator 230 all increase, and the steam volume in the cylinder group 210 decreases, and the coal-fired power generation unit can quickly reduce the load to meet the primary frequency regulation load demand.

[0065] During the above load change process, the flow rate changes of the condensate pump 260, the first feed water pump 270, and the second feed water pump 311 can be changed in a stepwise manner, or can also be changed in a linear manner, which is not clearly limited here.

[0066] <Improve operating stability>

[0067] Based on the coal-fired power generation unit provided by the embodiments of the present invention, when it enters the low load, whether it is in the dry operating condition or the wet operating condition, the first steam extraction pipeline 320 can be opened to input steam into the feed water accumulator 300. After the steam is input into the feed water accumulator 300, the internal water temperature of the feed water accumulator 300 can be significantly increased. Compared with the conventional scheme, the feed water temperature of the boiler entering the economizer 110 can be greatly increased; in a specific example, the feed water temperature of the boiler at the inlet of the economizer 110 is increased by about 50 °C. Correspondingly, the water temperature entering the water wall 120 can be increased, which is beneficial to the internal temperature field of the boiler 100 and the stability of combustion.

[0068] Moreover, in addition to the economizer 110 being provided in the boiler flue, an air preheater (not shown in the figure) is usually also provided, and the air preheater is located downstream of the economizer 110. The temperature of the boiler feed water in the economizer 110 is relatively high, so less heat of the boiler flue gas can be utilized, enabling more heat in the boiler flue gas to be utilized at the air preheater. As a result, the inlet air temperature of the boiler 100 can be increased to a certain extent, which is also extremely beneficial to improving the combustion stability of the boiler 100. At the same time, the inlet flue gas temperature of the SCR reactor can be ensured, which is conducive to the safe input of denitration under the ultra-low load condition of the coal-fired power generation unit.

[0069] The increase in the air temperature is more obvious in the implementation mode with the air supply heater 321a provided, and correspondingly, the beneficial effects brought about by the increase in the air temperature will also be more significant.

[0070] <Improving the economy and rapidity of unit start-stop peak regulation>

[0071] To ensure the start-stop peak regulation benefits of the enterprise, it is necessary to scientifically and effectively reduce the operating costs of start-stop peak regulation. For the overall physical shutdown of the boiler 100 and the steam turbine 200, the operating costs of start-stop peak regulation are mainly the costs of unit startup. In terms of startup costs, it is mainly reflected in two aspects: time and efficiency. In terms of time, in order to meet the safe inlet steam temperature, it takes a certain amount of time to increase the main reheat steam temperature, which means an increase in coal consumption and auxiliary machine power consumption. In terms of efficiency, during the startup process, steam mainly enters the condenser 220 through the high and low bypasses (bypassing the cylinder group 210), and the heat is mainly transferred to the circulating water system and wasted. Therefore, it is necessary to improve the economy of start-stop from the aspects of efficiency and time during the startup process.

[0072] In the embodiment of the present invention, during the shutdown process of the coal-fired power generation unit, the feed water accumulator 300 can be utilized to achieve water filling and heat storage while shutting down. When the coal-fired power generation unit starts to make startup preparations, the hot water stored in the feed water accumulator 300 can be used to feed water to the boiler 100, increasing the water temperature entering the boiler 100 and ensuring that the boiler 100 can rapidly increase in temperature and pressure after ignition. Moreover, after the boiler 100 increases in temperature and pressure, the boiler steam can be drawn into the feed water accumulator 300 through the first steam extraction pipeline 320. On the one hand, it can further heat the hot water in the feed water accumulator 300 and recover a part of the heat that would otherwise be wasted in the high and low bypasses. On the other hand, for the implementation mode where the connection point of the first steam extraction branch 321 and the boiler 100 is located between two adjacent heating components 141, when the first steam extraction branch 321 is opened, the steam flow rate in the steam supply pipeline 160 can be reduced, and the heat exchange pressure of the heating component 141 on the downstream side of the connection point of the first steam extraction branch 321 is relatively small, which can increase the temperature level of the main steam in the steam supply pipeline 160. In this way, during the shutdown and restart process of the coal-fired power generation unit, the thermal utilization efficiency is relatively high, energy waste can be reduced, and at the same time, the temperature rise is relatively fast. Both in terms of time and efficiency, the economic efficiency of the coal-fired power generation unit can be improved.

[0073] In the embodiment of the present invention, the control of each component can be achieved by a control device, and the specific structural form of the control device is not limited herein.

[0074] Please refer to Figure 3 , Figure 3 which is a schematic flow diagram of an implementation mode of the control method for the coal-fired power generation unit provided by the present invention.

[0075] As Figure 3 shown, the embodiment of the present invention also provides a control method for the coal-fired power generation unit, which is applicable to the coal-fired power generation unit involved in the foregoing implementation modes. The control method may specifically include the following steps.

[0076] The first acquisition step S110, acquiring the real-time load of the coal-fired power generation unit and the load change trend of the coal-fired power generation unit.

[0077] The first judgment step S120, judging whether the real-time load is less than the set load and the load change trend is a downward trend. If so, execute the following first control step S130. The set load can be the designed Benson load or greater than the designed Benson load.

[0078] The first control step S130, controlling to open the first steam extraction pipeline 320.

[0079] With such a setting, by extracting a part of the steam supplied from the boiler 100 to the steam turbine 200, the real-time load of the coal-fired power generation unit can remain in the dry operating condition when it is less than the designed Benson load. This is equivalent to reducing the actual Benson load of the coal-fired power generation unit, enabling the coal-fired power generation unit to maintain the dry operating condition within a wider load range, endowing the coal-fired power generation unit with a lower dry deep load regulation capacity, and being conducive to ensuring the safety and stability of equipment operation. Through research and testing, the coal-fired power generation unit provided by the embodiment of the present invention can reduce the dry deep load regulation capacity by about 5% of the rated load.

[0080] Please refer to Figure 4 , Figure 4 which is a schematic flow chart of another implementation manner of the control method for the coal-fired power generation unit provided by the present invention.

[0081] As Figure 4 shown, the embodiment of the present invention further provides another control method for the coal-fired power generation unit, which is applicable to the coal-fired power generation units involved in the foregoing implementation manners. The control method may specifically include the following steps.

[0082] The second acquisition step S210: acquiring a load change command of the coal-fired power generation unit.

[0083] The second judgment step S220: judging whether the load change command is a load increasing command. If so, execute the following second control step S230; or, judging whether the load change command is a load decreasing command. If so, execute the following third control step S240.

[0084] In specific practice, it may be to first judge whether it is a load increasing command. If not, then judge whether it is a load decreasing command; or, it may also be to first judge whether it is a load decreasing command. If not, then judge whether it is a load increasing command; or, the judgment of the load increasing command and the load decreasing command may also be carried out synchronously.

[0085] The second control step S230: reducing the flow rates of the first water outlet pipe 231 and the third water outlet pipe 221. In this way, the extraction steam flow rates of the third extraction steam pipe 241 of the high-pressure heater 240, the fourth extraction steam pipe 251 of the low-pressure heater 250, and the second extraction steam pipe 232 of the deaerator 230 can be reduced, enabling more steam to do work in the cylinder group 210, and the coal-fired power generation unit can quickly increase the load.

[0086] The third control step S240 is to increase the flow rates of the first outlet water pipe 231 and the third outlet water pipe 221. In this way, the extraction steam flow rate of the third extraction steam pipe 241 of the high-pressure heater 240, the extraction steam flow rate of the fourth extraction steam pipe 251 of the low-pressure heater 250, and the extraction steam flow rate of the second extraction steam pipe 232 of the deaerator 230 can be increased, so that the amount of steam in the cylinder group 210 is reduced, and the coal-fired power generation unit can quickly reduce the load.

[0087] The above control method can achieve rapid load increase and rapid load decrease, and can be used for primary frequency modulation to improve the primary frequency modulation ability of the unit.

[0088] The present invention also provides another control method for a coal-fired power generation unit, which is applicable to the coal-fired power generation units involved in the foregoing implementation manners. The control method specifically includes: when the coal-fired power generation unit is initially started, controlling to open the first extraction steam pipe 320.

[0089] This control method can reduce the waste of steam in the high and low bypasses when the coal-fired power generation unit stops and restarts, and can increase the temperature level of the main steam in the steam supply pipe 160, which is beneficial to improving the economy and rapidity of the unit's start-stop peak regulation.

[0090] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art of the present technology, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A control method for a coal-fired power generation unit, characterized in that: The coal-fired power generation unit comprises a boiler, a steam turbine and a feedwater heat accumulator, the steam turbine comprises a cylinder group, a condenser and a deaerator, the deaerator is provided with a first water outlet pipeline, the first water outlet pipeline is connected to the feedwater heat accumulator, the feedwater heat accumulator is provided with a second water outlet pipeline and a first steam extraction pipeline, the second water outlet pipeline is connected to the boiler, the first steam extraction pipeline is configured to be able to partially pass the steam generated by the boiler into the feedwater heat accumulator; the first steam extraction pipeline comprises a first steam extraction branch, the first steam extraction branch is connected to the boiler; the boiler comprises a superheater, the superheater comprises a plurality of heat receiving components, each of the heat receiving components is arranged along the flow direction of the steam, and the connection point between the first steam extraction branch and the boiler is located between two adjacent heat receiving components, and the control method comprises: A first acquisition step is to acquire the real-time load of the coal-fired power generation unit and the load change trend of the coal-fired power generation unit; The first judgment step is to judge whether the real-time load is less than the set load and the load change trend is a downward trend. If so, the following first control step is performed; the set load is the load corresponding to the minimum safe flow rate under the dry operation of the boiler; The first control step is to control opening of the first steam extraction pipeline.

2. The control method of the coal-fired power generation unit according to claim 1, characterized in that: An air supply heater is provided on the first steam extraction branch line.

3. The control method of the coal-fired power generation unit according to claim 1, characterized in that: The first steam extraction pipeline further includes a second steam extraction branch, and the second steam extraction branch is connected to the cylinder group.

4. The control method of the coal-fired power generation unit according to claim 1, characterized in that: The first water outlet pipeline is provided with a high-pressure heater.

5. The control method of the coal-fired power generation unit according to claim 1, characterized in that: The condenser is equipped with a third water outlet pipeline, the third water outlet pipeline is connected to the deaerator, and a low-pressure heater is arranged on the third water outlet pipeline.

6. The control method of a coal-fired power generation unit according to any one of claims 1 to 5, characterized in that: The condenser is provided with a third water outlet pipeline, and the third water outlet pipeline is connected to the deaerator. The control method comprises: A second acquisition step is to acquire a load change instruction of the coal-fired power generation unit; A second judging step, judging whether the load change instruction is a load increase instruction, if so, executing the following second control step; or judging whether the load change instruction is a load reduction instruction, if so, executing the following third control step; A second control step is to reduce the flow rates of the first water outlet pipeline and the third water outlet pipeline; The third control step is to increase the flow rates of the first water outlet pipeline and the third water outlet pipeline.

7. The control method of a coal-fired power generation unit according to any one of claims 1 to 5, characterized in that: The control method comprises: when the coal-fired power generation unit is initially started, controlling to open the first steam extraction pipeline.

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