Boiler control device, power plant, boiler control method, and boiler control program

Abstract

This invention provides a boiler control device, a power plant, a boiler control method, and a boiler control program that appropriately control the recirculation flow rate and make it usable as regulated power. [Solution] The boiler control device 50 has a switching unit 52 that switches between a once-through operation state and a circulating operation state, which has lower thermal efficiency than the once-through operation state, depending on the load. The switching unit 52 performs switching control to switch from the once-through operation state to the circulating operation state when the load falls below the first load, and when operating in the circulating operation state, it performs control to add a bias flow rate to the feedwater flow rate of the boiler so that the feedwater flow rate is appropriate to the boiler load.

Description

Technical Field

[0001] The present disclosure relates to a boiler control device, a power generation plant, a boiler control method, and a boiler control program.

Background Art

[0002] Large boilers such as power generation boilers have a furnace installed vertically in a hollow shape, and a plurality of burners are arranged along the circumferential direction of the furnace on the furnace wall. In addition, a large boiler has a flue connected above the furnace in the vertical direction, and a heat exchanger for generating steam is arranged in this flue. Then, a flame is formed by the burner injecting a mixture of fuel and air (oxidizing gas) into the furnace, combustion gas is generated and flows into the flue. A heat exchanger is installed in the region where the combustion gas flows, and water and steam flowing in the heat transfer tubes constituting the heat exchanger are heated to generate superheated steam.

[0003] In recent years, power generation using renewable energy has been carried out. However, renewable energy has problems in the stable supply of electric power, and there may be a gap between the power demand and the power generation amount by renewable energy. Thermal power plants, for example, coal-fired thermal power plants, etc., are required to shift from the previous base load operation to an operation used for adjusting the gap between the power demand and the power generation amount by renewable energy. In particular, although coal-fired power generation using a supercritical pressure boiler (once-through boiler) can be considered to be utilized as regulating power, there are load operation restrictions such as the minimum load at which operation is possible.

[0004] For once-through boilers, there are two operating states, a dry operating state and a wet operating state, which will be described later, depending on the operating load. The normal operation when the boiler load (evaporation amount) is above a predetermined value is a dry operating state (once-through operating state) in which the water supply to the boiler is equal to the evaporation amount. On the other hand, in the operation at a low load where the boiler load (evaporation amount) is smaller than the minimum water supply flow rate set for furnace wall protection, it is a wet operating state (circulation operating state) in which a part of the water supply circulates.

[0005] For example, Patent Document 1 discloses a method for increasing the water supply flow rate command based on a load command by the required amount from low load to medium load to obtain a minimum water supply flow rate command. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2002-106804 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, the invention described in Patent Document 1 involves increasing the required amount of the minimum water supply flow rate command compared to the normal minimum water supply flow rate command, resulting in an increase in both the water supply flow rate and the recirculation flow rate compared to the normal state, thus increasing energy loss. Furthermore, the invention described in Patent Document 1 uses a function to calculate the required amount of water supply to be increased.

[0008] This disclosure is made in view of these circumstances and aims to provide a boiler control device, a power plant, a boiler control method, and a boiler control program in which the feedwater flow rate and recirculation flow rate are appropriately controlled and can be used as regulated power. [Means for solving the problem]

[0009] To solve the above problems, the boiler control device, power plant, boiler control method, and boiler control program of this disclosure employ the following means. The boiler control device of this disclosure has a switching unit that switches the boiler between a once-through operation state and a circulating operation state which has lower thermal efficiency than the once-through operation state, depending on the load. The switching unit performs switching control to switch from the once-through operation state to the circulating operation state when the load falls below a first load, and when operating in the circulating operation state, it performs control to add a bias flow rate to the feedwater flow rate of the boiler so that the feedwater flow rate is appropriate to the boiler load.

[0010] The power plant of this disclosure is equipped with the boiler control device described above.

[0011] The boiler control method of this disclosure is a boiler control method that switches between a once-through operation state and a circulating operation state which has lower thermal efficiency than the once-through operation state, depending on the load, and performs switching control to switch from the once-through operation state to the circulating operation state when the load falls below a first load, wherein when operating in the circulating operation state, a computer performs control to add a bias flow rate to the feedwater flow rate of the boiler so that the feedwater flow rate is appropriate to the boiler load.

[0012] The boiler control program of this disclosure causes a computer to execute the boiler control method described above. [Effects of the Invention]

[0013] According to this disclosure, when the recirculation flow rate is appropriately controlled and renewable energy is used in combination with power generation equipment, and power generated by the power generation facility is used as regulating power, the load can be maintained at a lower load than the normal operating range, which is designated as a load-holding prohibited range. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram showing a boiler in some embodiments of the present disclosure. [Figure 2] This is a schematic diagram showing the water and steam system of a boiler in some embodiments of the present disclosure. [Figure 3] This figure shows an example of the hardware configuration of a control device in several embodiments of the present disclosure. [Figure 4] This figure illustrates an example of the functions of a boiler control device in several embodiments of the present disclosure. [Figure 5] This is a schematic diagram illustrating the control system used for conventional switching. [Figure 6] This diagram shows the conventional water supply flow rate setting. [Figure 7]It is a schematic diagram showing switching control by a boiler control device in some embodiments of the present disclosure. [Figure 8] It is a diagram showing the feed water flow rate setting by a boiler control device in some embodiments of the present disclosure. [Figure 9] It is a diagram showing a setting circuit of a constant load switching mode in some embodiments of the present disclosure. [Figure 10] It is a diagram showing a setting circuit of feed water bias and mill automatic stop in some embodiments of the present disclosure. [Figure 11] It is a diagram showing a switching control circuit by a constant load switching mode in some embodiments of the present disclosure. [Figure 12] It is a diagram showing a setting circuit of dedicated parameters when using a constant load switching mode in some embodiments of the present disclosure. [Figure 13] It is a diagram showing the relationship between a load index and a steam temperature setting in some embodiments of the present disclosure. [Figure 14] It is a diagram showing a timing chart when using a constant load switching mode in some embodiments of the present disclosure.

Mode for Carrying Out the Invention

[0015] Hereinafter, an embodiment according to the present disclosure will be described with reference to the drawings. Note that the present disclosure is not limited by this embodiment, and when there are multiple embodiments, the combination of each embodiment is also included. In the following description, "upper" or "above" indicates the upper side in the vertical direction, and "lower" or "below" indicates the lower side in the vertical direction. The vertical direction is not strict and includes errors.

[0016] FIG. 1 is a schematic configuration diagram showing a boiler in some embodiments of the present disclosure.

[0017] The boiler 10 of this embodiment is a boiler capable of generating superheated steam by burning fine fuel, which is obtained by crushing solid fuel, in a burner 21, and exchanging the heat generated by this combustion with feedwater or steam. As the solid fuel, biomass fuel or coal can be used.

[0018] The boiler 10 has a furnace 11, a combustion device 20, and a combustion gas passage 12. The furnace 11 has a hollow rectangular shape and is installed vertically. The furnace wall 101 that makes up the inner wall surface of the furnace 11 is composed of a plurality of heat transfer tubes and fins that connect the heat transfer tubes to each other, and recovers the heat generated by the combustion of pulverized fuel by heat exchange with water or steam circulating inside the heat transfer tubes, while also suppressing the temperature rise of the furnace wall 101.

[0019] The combustion device 20 is installed in the lower region of the furnace 11. In this embodiment, the combustion device 20 has a plurality of burners 21A, 21B, 21C, 21D, 21E, and 21F (hereinafter sometimes collectively referred to as "burners 21") mounted on the furnace wall 101. The burners 21 are arranged in multiple rows along the vertical direction, with each set consisting of burners 21 arranged at equal intervals along the circumferential direction of the furnace 11 (for example, four burners installed at each corner of a rectangular furnace 11). In Figure 1, for illustrative purposes, only two burners from one set of burners 21 are shown, and each set is labeled with the reference numerals 21A, 21B, 21C, 21D, 21E, and 21F. The shape of the furnace 11, the number of rows of burners 21, the number of burners 21 in one row, and the arrangement of the burners 21 are not limited to this embodiment.

[0020] Burners 21A, 21B, 21C, 21D, 21E, and 21F are each connected to multiple mills 31A, 31B, 31C, 31D, 31E, and 31F (hereinafter collectively referred to as "mills 31") via multiple fine fuel supply pipes 22A, 22B, 22C, 22D, 22E, and 22F (hereinafter collectively referred to as "fine fuel supply pipes 22"). Mills 31 crush solid fuel to produce fine fuel, and are, for example, vertical roller mills configured such that a crushing table (not shown) is supported inside so as to be rotatable, and multiple crushing rollers (not shown) are supported above the crushing table so as to be rotatable in conjunction with the rotation of the crushing table. The solid fuel crushed by the cooperation of the crushing rollers and the crushing table is conveyed to a classifier (not shown) equipped in mill 31 by primary air (conveying gas, oxidizing gas) supplied to mill 31. In the classifier, the crushed solid fuel is classified into fine fuel particles with a particle size suitable for combustion in the burner 21 and coarse fuel particles with a particle size larger than that. The fine fuel particles that pass through the classifier are supplied to the burner 21 via the fine fuel supply pipe 22 along with primary air. The coarse fuel particles that do not pass through the classifier fall onto the crushing table inside the mill 31 due to their own weight and are crushed again.

[0021] An air register 23 is provided on the outside of the furnace 11 where the burner 21 is installed, and one end of an air duct 24 is connected to this air register 23. A forced draft fan (FDF) 32 is connected to the other end of the air duct 24. The air supplied from the forced draft fan 32 is heated by an air preheater 42 installed in the air duct 24 (details will be described later), and is supplied to the burner 21 as secondary air (combustion air, oxidizing gas) via the air register 23 and introduced into the furnace 11.

[0022] The combustion gas passage 12 is connected to the upper vertical part of the furnace 11. The combustion gas passage 12 is equipped with superheaters 102A, 102B, 102C (hereinafter sometimes collectively referred to as "superheater 102"), reheaters 103A, 103B (hereinafter sometimes collectively referred to as "reheater 103"), and an economizer 104 as heat exchangers for recovering heat from the combustion gas. Heat exchange takes place between the combustion gas generated in the furnace 11 and the feedwater or steam circulating inside each heat exchanger. Note that the arrangement and shape of each heat exchanger are not limited to the configuration shown in Figure 1.

[0023] Downstream of the combustion gas passage 12 is a flue 13 through which the combustion gas, whose heat has been recovered by the heat exchanger, is discharged. An air preheater (air heater) 42 is installed between the flue 13 and the air duct 24, and heat exchange takes place between the air flowing through the air duct 24 and the combustion gas flowing through the flue 13. By heating the primary air supplied to the mill 31 and the secondary air supplied to the burner 21, heat is further recovered from the combustion gas after heat exchange with water or steam.

[0024] Furthermore, a denitrification device 43 may be provided in the flue 13 at a position upstream of the air preheater 42. The denitrification device 43 supplies a reducing agent, such as ammonia or urea solution, which has the effect of reducing nitrogen oxides, to the combustion gas flowing through the flue 13. The reaction between the nitrogen oxides (NOx) in the combustion gas to which the reducing agent has been supplied and the reducing agent is promoted by the catalytic action of a denitrification catalyst installed in the denitrification device 43, thereby removing and reducing nitrogen oxides in the combustion gas. A gas duct 41 is connected downstream of the air preheater 42 in the flue 13. The gas duct 41 is equipped with dust collection devices 44, such as an electrostatic precipitator, to remove ash and other particles from the combustion gas, and environmental devices such as a desulfurization device 46 to remove sulfur oxides, as well as an induced draft fan (IDF) 45 to guide the exhaust gas to these environmental devices. The downstream end of the gas duct 41 is connected to the chimney 47, and the combustion gas treated by the environmental devices is discharged outside the system as exhaust gas.

[0025] In the boiler 10, when multiple mills 31 are driven, the crushed and classified pulverized fuel is supplied to the burner 21 via the pulverized fuel supply pipe 22 along with primary air. In addition, secondary air heated by the air preheater 42 is supplied to the burner 21 from the air duct 24 via the wind box 23. The burner 21 blows a pulverized fuel mixture, which is a mixture of pulverized fuel and primary air, into the furnace 11, and also blows secondary air into the furnace 11. The pulverized fuel mixture blown into the furnace 11 ignites and reacts with the secondary air to form a flame. The flame is formed in the lower region of the furnace 11, and the high-temperature combustion gas rises inside the furnace 11 and flows into the combustion gas passage 12. In this embodiment, air is used as the oxidizing gas (primary air, secondary air), but a gas with a higher or lower oxygen content than air may also be used, and stable combustion in the furnace 11 can be achieved by adjusting the ratio of oxygen to the supplied fuel amount to an appropriate range.

[0026] Furthermore, above the mounting position of the burner 21 in the furnace 11, a number of additional air ports (AA ports) 25 are provided to supply additional combustion air (AA) into the furnace 11. The ends of additional air ducts (AA ducts) 26, which branch off from the air duct 24, are connected to the additional air ports 25, and a portion of the air supplied from the forced draft fan 32 can be supplied to the additional air ports 25 as additional combustion air via the additional air ducts 26.

[0027] In region A inside the furnace 11 shown in Figure 1 (the region corresponding to the height range of installation of the wind box 23), a flame is formed by the combustion of a mixture of primary air and pulverized fuel with secondary air. Here, the air ratio in region A is set to 1 or less. Specifically, the amount of air supplied to the burner 21 (the total amount of primary and secondary air) is set to be less than the theoretical amount of air relative to the amount of fuel supplied to the burner 21. As a result, regions A and B inside the furnace 11 (the region between the top of the burner 21 and the bottom of the additional air port 25) become a reducing atmosphere, and nitrogen oxides (NOx) generated by combustion are reduced inside the furnace 11. Subsequently, in region C (the region above the bottom of the additional air port 25), additional combustion air is supplied from the additional air port 25 to the combustion gas from which NOx has been reduced, and combustion is completed. However, the amount of NOx generated is reduced by the reduction effect in regions A and B.

[0028] The combustion gas flowing into the combustion gas passage 12 undergoes heat exchange with water and steam in the superheater 102, reheater 103, and economizer 104 located inside the combustion gas passage 12, before being discharged into the flue 13. There, nitrogen oxides are removed in the denitrification device 43, and after heat exchange with primary and secondary air in the air preheater 42, it is further discharged into the gas duct 41. Ash and other contaminants are removed in the dust collector 44, and sulfur oxides are removed in the desulfurization device 46 before being discharged out of the system through the chimney 47. Note that the arrangement of each heat exchanger in the combustion gas passage 12 and each device from the flue 13 to the gas duct 41 does not necessarily have to be in the order described above with respect to the combustion gas flow.

[0029] Next, we will describe in detail the superheater 102, reheater 103, and economizer 104, which are installed in the combustion gas passage 12 as heat exchangers. Figure 2 is a schematic diagram showing a heat exchanger provided in a coal-fired boiler in some embodiments of the present disclosure. Note that Figure 1 does not accurately show the positions of each heat exchanger (superheaters 102A, 102B, 102C, reheaters 103A, 103B, and economizer 104) within the combustion gas passage 12, and the arrangement order of each heat exchanger relative to the combustion gas flow is not limited to that shown in Figure 1.

[0030] As shown in Figure 2, the power plant 1 of this embodiment includes a heat exchanger installed in a boiler 10, a steam turbine 111 that is rotationally driven by the steam generated in the boiler 10, and a generator 113 connected to the steam turbine 111 that generates electricity using the rotational force of the steam turbine 111.

[0031] The steam turbine 111, which is rotationally driven by steam generated in the boiler 10, is composed of, for example, a high-pressure turbine 111A, an intermediate-pressure turbine 111B, and a low-pressure turbine 111C. After the steam superheated in the superheater 102 of the boiler 10 rotates the high-pressure turbine 111A, it is re-superheated in the reheater 103 of the boiler 10 and rotates the intermediate-pressure turbine 111B and the low-pressure turbine 111C. A condenser 112 is connected to the low-pressure turbine 111C, and the steam that rotates the low-pressure turbine 111C condenses into condensate in this condenser 112 through heat exchange with cooling water (for example, seawater or river water). The condenser 112 is connected to an economizer 104 via a feedwater line L1. The feedwater line L1 is equipped with, for example, a condensate pump (CP) 121, a low-pressure feedwater heater 122, a boiler feedwater pump (BFP) 123, and a high-pressure feedwater heater 124. A portion of the steam that drives the steam turbine 111 is extracted from the low-pressure feedwater heater 122 and the high-pressure feedwater heater 124 and supplied as a heat source via an extraction line (not shown), which heats the feedwater supplied to the economizer 104.

[0032] Boiler 10 is a once-through boiler. The economizer 104 is connected to the heat transfer tubes that make up the furnace wall 101. The feedwater heated in the economizer 104 is heated by radiation from the flames in the furnace 11 as it passes through the heat transfer tubes that make up the furnace wall 101, and is then led to the steam-water separator 125. The steam separated in the steam-water separator 125 is supplied to the superheater 102, and the condensate separated in the steam-water separator 125 flows into the steam-water separator drain tank 126 and is led to the condensate 112 via the drain water line L2 equipped with a drain water valve 128.

[0033] Furthermore, during startup or low-load operation of the once-through boiler, the feedwater supplied from the economizer 104 may not evaporate completely as it passes through the heat transfer tubes constituting the furnace wall 101, resulting in a wet operation state (circulation operation state) where a water level exists in the steam-water separator 125. In this wet operation state, the drain water separated in the steam-water separator 125 and discharged into the steam-water separator drain tank 126 may be recirculated and supplied from the economizer 104 to the heat transfer tubes constituting the furnace wall 101 by using a boiler circulation pump (BCP) 127 to join the feedwater line L1 via a circulation line L6.

[0034] As combustion gas flows through the combustion gas passage 12, heat is recovered from this combustion gas in the superheater 102, reheater 103, and economizer 104. Meanwhile, feedwater supplied from the boiler feedwater pump (BFP) 123 is preheated in the economizer 104, then heated to steam as it passes through the heat transfer tubes that make up the furnace wall 101, and is led to the steam-water separator 125. The steam separated in the steam-water separator 125 is introduced into the first superheater 102A, the second superheater 102B, and the third superheater 102C, where it is superheated by the combustion gas. The superheated steam generated in superheater 102 is supplied to the high-pressure turbine 111A via the steam line L3, which rotates the high-pressure turbine 111A. The steam discharged from the high-pressure turbine 111A is introduced into the first reheater 103A and the second reheater 103B, where it is re-superheated. The reheated steam is supplied to the low-pressure turbine 111C via the steam line L5, passing through the intermediate-pressure turbine 111B, and rotating both the intermediate-pressure turbine 111B and the low-pressure turbine 111C. The rotating shaft of the steam turbine 111 rotates the generator 113, generating electricity. The steam discharged from the low-pressure turbine 111C is cooled in the condenser 112 to become condensate, which is then sent back to the economizer 104 via the feedwater line L1. As it passes through the heat transfer tubes that make up the furnace wall 101, the entire amount evaporates, becoming dry steam, resulting in a dry operation state (through-flow operation state) where there is no water level in the steam-water separator 125.

[0035] The superheater 102 and reheater 103 may be provided with means for controlling the temperature of the steam superheated in each heat exchanger (hereinafter, the temperature of the superheated steam at the outlet of the third superheater 102C will be referred to as the "main steam temperature," and the temperature of the superheated steam at the outlet of the second reheater 103B will be referred to as the "reheat steam temperature"). For example, a superheater spray valve (not shown) and a reheater spray valve (not shown) may be provided to control the steam temperature by adjusting the amount of water mixed and injected into the superheated steam (hereinafter, the water injected for main steam temperature control will be referred to as "superheater spray water," and the water injected for reheat steam temperature control will be referred to as "reheater spray water"). The superheater spray water and reheater spray water are supplied, for example, by branching off a portion of the feedwater to the boiler 10 from the outlet of the boiler feedwater pump 123. Furthermore, the location where the superheater spray water is mixed and injected is not limited to the outlet of the third superheater 102C, but can be any location where the main steam temperature can be controlled, for example, it can be installed at any location between the outlet of the steam separator 125 and the inlet of the high-pressure turbine 111A. Similarly, the location where the reheater spray water is mixed and injected is not limited to the outlet of the second reheater 103B, but can be any location where the reheat steam temperature can be controlled, for example, it can be installed at any location between the outlet of the high-pressure turbine 111A and the inlet of the intermediate-pressure turbine 111B.

[0036] Furthermore, suit blowers (ash removal devices), not shown, may be placed in the gaps between the heat transfer tubes constituting each heat exchanger, such as the superheater 102, reheater 103, and economizer 104, or in the gaps between each heat exchanger. The suit blowers are positioned extending in a direction substantially perpendicular to the wall surface of the combustion gas passage 12. The suit blowers are injection devices that inject steam (gas) in a direction perpendicular to the axial direction, with the direction perpendicular to the wall surface of the combustion gas passage 12 as their axial direction, and the injection direction can also be varied. The steam injected from the suit blowers toward the heat exchangers, such as the superheater 102, reheater 103, and economizer 104, removes combustion ash adhering to and accumulated on the surface of the heat transfer tubes constituting the heat exchangers, thereby suppressing a decrease in the heat exchange efficiency of the heat transfer tubes.

[0037] As mentioned above, boiler 10 has two operating states: dry operation (through-flow operation) and wet operation (circulation operation). In wet operation, some of the feedwater heated by the furnace wall 101 circulates inside boiler 10 without being discharged outside the system, resulting in lower thermal efficiency of boiler 10 compared to dry operation. In dry operation, superheated steam (dry steam) is produced at the outlet of the furnace wall 101 of the boiler 10. On the other hand, in wet operation, saturated steam (moist steam) is produced at the outlet of the furnace wall 101. In wet operation, condensate in the moist steam is separated by the steam-water separator 125 and discharged into the steam-water separator drain tank 126. Boiler 10 is supplied with the necessary feedwater flow rate according to the load (evaporation rate, main steam flow rate supplied from boiler 10 to external systems such as high-pressure turbine 111A). During boiler 10 operation, the feedwater flow rate must always be above a predetermined amount to protect the furnace wall 101. This lower limit of feedwater flow rate is defined as the minimum feedwater flow rate. The lower limit of the load at which a stable dry operation state can be maintained while ensuring the minimum feedwater flow rate is defined as the first load (dry operation lower limit load, once-through operation lower limit load). Above the first load, operation is performed in a dry operation state, and the feedwater flow rate supplied is according to the load (evaporation rate). The first load is, for example, 30% ECR (ECR: Economical Continuous Rating, economic load, turbine rated load). The value of the first load is set according to the specifications of boiler 10.

[0038] Figure 3 is a diagram showing an example of the hardware configuration of a control device in some embodiments of the present disclosure. As shown in Figure 3, the boiler control device (Controller) 50 is a computer system and includes, for example, a CPU (Central Processing Unit: processor) 1100, a secondary storage device (ROM, Secondary storage: memory) 1300, a main memory device (RAM, Main Memory) 1200, a communication interface 1400 for connecting to a network, and an input / output unit 1500. A large-capacity storage device (HDD) may be provided (not shown), or a solid-state drive (SSD) may be used as the large-capacity storage device. These parts are connected via a bus 1800.

[0039] The CPU 1100 controls the entire boiler control device 50 using an OS (Operating System) stored in a secondary storage device 1300 connected via a bus 1800, and also performs various processes by executing various programs stored in the secondary storage device 1300. One or more CPUs 1100 may be provided and may cooperate with each other to perform processing.

[0040] The main memory 1200 consists of writable memory such as cache memory and RAM (Random Access Memory), and is used as a work area for reading the CPU 1100's executable program and writing processing data by the executable program.

[0041] The secondary storage device 1300 is a non-transitory computer-readable storage medium. Examples of secondary storage devices 1300 include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, and semiconductor memory. Examples of secondary storage devices 1300 include ROM (Read Only Memory), HDD (Hard Disk Drive), SSD (Solid State Drive), and flash memory. The secondary storage device 1300 stores, for example, an OS for controlling the entire information processing device such as Windows®, iOS®, and Android®, a BIOS (Basic Input / Output System), various device drivers for hardware operation of peripheral devices, various application software, and various data and files. Furthermore, the secondary storage device 1300 stores programs for implementing various processes and various data required to implement those processes. Multiple secondary storage devices 1300 may be provided, and the aforementioned programs and data may be divided and stored in each secondary storage device 1300.

[0042] Furthermore, the boiler control device 50 may include an input unit consisting of a keyboard or mouse, and a display unit consisting of a liquid crystal display device for displaying data. It may also include a notification unit that includes a display unit and outputs lamps, sounds, and especially alarm sounds, such as a speaker.

[0043] Figure 4 is a diagram illustrating an example of the functions of a boiler control device in several embodiments of the present disclosure. As shown in Figure 4, the boiler control device 50 includes a selection unit 51 and a switching unit 52.

[0044] The series of processes required to realize the functions of the boiler control device 50 are stored, for example, in the form of a program in the secondary storage device 1300 (see Figure 3). The CPU (processor) 1100 (see Figure 3) reads this program into the main memory 1200 (see Figure 3) and performs information processing and calculations to realize various functions. The program may be pre-installed in the secondary storage device 1300, provided stored in other non-temporary computer-readable storage media, or distributed via wired or wireless communication. Examples of non-temporary computer-readable storage media include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, and semiconductor memory.

[0045] The selection unit 51 shown in Figure 4 selects between a normal mode for normal control and a constant load switching mode. Here, normal control is a control that operates in a dry operation state (once-through operation state) when the load is equal to or greater than the first load, and switches the boiler 10 from a dry operation state (once-through operation state) to a wet operation state (circulation operation state), which has lower thermal efficiency than the dry operation state, when the load falls below the first load. The constant load switching mode is a control that adjusts the bias of the boiler feedwater amount and switches between the dry operation state and the wet operation state while maintaining a constant load on the boiler 10.

[0046] The selection between normal mode and constant load switching mode is made by load reduction commands and load increase commands (load change commands) described later, or by user judgment. The selection unit 51 selects either normal mode or constant load switching mode based on the load reduction commands and load increase commands (load change commands) or user selection.

[0047] When the constant load switching mode is selected by the selection unit 51, the switching unit 52 performs switching control to switch between dry operation and wet operation states.

[0048] Figure 5 is a schematic diagram illustrating a conventional control system for switching. As shown in Figure 5, in conventional control systems, a load-holding prohibition zone is provided as a band of transient operating conditions during switching between operating states. The region between the first load (lower limit load for dry operation, lower limit load for once-through operation) and the third load, which is a load smaller than the first load, is a region where the control of the boiler 10 is unstable, and this region is designated as the load-holding prohibition zone. When the load of the boiler 10 enters the load-holding prohibition zone, control is performed to change the load so that it operates at either the first or third load, and load holding at an intermediate value between the first and third loads is not performed. In addition, in the load-holding prohibition zone, a switch is made between the dry operation state and the wet operation state, and this switch is performed based on the once-through operation state / circulation operation state determination circuit 94, which will be described later. Thus, in conventional control systems, if the load is greater than or equal to the first load, the dry operation state is performed; in the load-holding prohibition zone between the first and third loads, a switch is made between the dry operation state and the wet operation state by the determination circuit; and if the load is less than the third load, the wet operation state is performed. The third load is, for example, 20% ECR. The third load is set to a value according to the specifications of boiler 10. Furthermore, during the switching between dry and wet operation states, the state of the steam flowing through the furnace wall 101 of the boiler 10 transitions between saturated steam and superheated steam. This raises concerns that a localized temperature difference (the difference between saturated steam temperature and superheated steam temperature) may occur, leading to excessive thermal stress.

[0049] Figure 6 shows a conventional water supply flow rate setting. In Figure 6, the vertical axis represents feedwater flow rate, the horizontal axis represents boiler load, and the solid line indicates the feedwater flow rate setting. As shown in Figure 6, in the conventional feedwater flow rate setting, the feedwater flow rate setting corresponding to the second load, which is smaller than the first load and larger than the third load, is set as the minimum feedwater flow rate. The second load is, for example, 25% ECR. The value of the second load is set according to the specifications of boiler 10.

[0050] In conventional control systems, as shown in Figure 6, the control system switches between dry and wet operation states based on the presence or absence of superheating of the boiler outlet steam while changing the load in the load range from the first to the third load (load holding prohibited zone). At this time, the feedwater flow rate is set to at least the minimum feedwater flow rate corresponding to the second load, regardless of the actual load, for the purpose of protecting the furnace wall 101. Thus, in conventional control systems, the load holding prohibited zone between the first and third loads is a transient operating state for the boiler 10, and an increase in thermal stress on the furnace wall 101 due to the mixing of saturated steam and superheated steam, as well as control instability, is possible, making it impossible to maintain the boiler load.

[0051] Furthermore, in conventional control systems, boiler feedwater in load ranges below the second load is supplied at the minimum feedwater flow rate corresponding to the second load, resulting in a surplus relative to the evaporation rate and operation with low thermal efficiency. Consequently, the steam flowing through the furnace wall 101 of the boiler 10 maintains its saturation temperature.

[0052] Figure 7 is a schematic diagram illustrating switching control by a boiler control device in several embodiments of the present disclosure. In the embodiments of this disclosure, as shown in Figure 7, the boiler 10 is switched between a dry operation state and a wet operation state when the load is at the first load state.

[0053] Specifically, the boiler load is maintained at the first load (lower limit load for dry operation, lower limit load for once-through operation), i.e., the feedwater bias is adjusted while the load remains constant, and the system switches from dry operation to wet operation, or vice versa. This control eliminates the need for the conventional load-holding prohibition zone where the boiler 10 enters a transient operating state, and allows load holding even in the load range between the first and third loads. The feedwater bias adjustment is shown in Figure 8.

[0054] Figure 8 shows the feedwater flow rate setting by a boiler control device in several embodiments of the present disclosure. In Figure 8, the vertical axis represents the feedwater flow rate, the horizontal axis represents the boiler load, the solid line represents the feedwater flow rate setting, and the thick solid line represents the feedwater flow rate command value, which is the feedwater flow rate setting plus a bias flow rate. As shown in Figure 8, the feedwater flow rate setting shown by the solid line is a flow rate proportional to the boiler load. However, as mentioned above, in order to protect the furnace wall 101, it is necessary to ensure a feedwater flow rate of a predetermined amount or more. Therefore, in the embodiment of this disclosure, the bias flow rate added to the feedwater flow rate is adjusted. For example, when the boiler load is detected to be the first load in the dry operation state, the switching unit 52 adds the bias flow rate to the feedwater flow rate setting and performs a switching operation from the dry operation state to the wet operation state while the load remains at the first load (constant load). In the embodiment of this disclosure, since the bias flow rate to be added is adjusted according to the load (amount of heat input to the boiler 10), near the lower limit load for stable operation of the boiler 10 (loads below the third load, which is the lower limit of the load holding band in conventional control), the feedwater flow rate command value, which is the sum of the feedwater flow rate setting and the bias flow rate, is lower than the conventional minimum feedwater flow rate.

[0055] The control logic in some embodiments of this disclosure is described below. Figure 9 shows a setting circuit for a constant load switching mode in some embodiments of the present disclosure.

[0056] As shown in Figure 9, the load index 60 is input to the H / L (large / small determination circuit) 61. The load index 60 is, for example, the required generator output (MWD, Mega Watt Demand) for power plant 1. H / L 61 is turned ON if the load index 60 is a value other than the first load. The output of H / L 61 is NOT (negated) by the logic unit 62 and input to the on-delay timer 63. In other words, H / L 61 and the logic unit 62 are circuits that are set to be true (ON) only when the load index 60 is the first load. When the output of the logic unit 62 is ON, the on-delay timer 63 functions. The on-delay timer 63 is a circuit that functions to prevent the condition from being met immediately after the load index 60 reaches the first load (the condition is met after a predetermined time has elapsed since the first load was reached). The output of the on-delay timer 63 is input to the logic unit 64. The output of the on-delay timer 63 is also input to the logic unit 75.

[0057] The load reduction command 65 and the feedwater bias activation operation 66, initiated by the user, are subjected to an OR (logical disjunction) operation by the logic unit 67. That is, if at least one of the load reduction command 65 or the feedwater bias activation operation 66 is ON, the output of the logic unit 67 becomes ON. The load reduction command 65 is a command to reduce the boiler load based on MWD, etc. The feedwater bias activation operation 66 indicates an operation that is turned ON when the user decides to apply a bias flow rate. The output of the logic unit 67 is input to the logic unit 64.

[0058] The logic unit 64 performs an AND operation, and if both the output of the on-delay timer 63 and the output of the logic unit 67 are ON, then the S / R (signal switch) 68 outputs ON. The S / R 68 switches its output to OFF (resets), that is, it cancels the constant switching mode, when the input from the logic unit 71 is ON (at least one of the unit trip 70 or mill start 77 is ON).

[0059] The logic unit 74 performs an OR (logical disjunction) operation between the load increase command 72 and the feedwater bias release operation 73 performed by the user. That is, if at least one of the load increase command 72 or the feedwater bias release operation 73 performed by the user is ON, the output of the logic unit 74 becomes ON. The load increase command 72 is a command to increase the boiler load based on MWD, etc. The feedwater bias release operation 73 is an operation that is turned ON when the user decides to release the bias flow rate (stop the supply of bias flow rate). The output of the logic unit 74 is input to the logic unit 75.

[0060] The logic unit 75 performs an AND operation, and if both the output of the on-delay timer 63 and the output of the logic unit 74 are ON, an ON signal is output to the mill automatic start command 76. The mill automatic start command 76 is a command to restart the mill 31 when it is stopped in the constant load switching mode 69 (details will be described later). When the mill automatic start command 76 is ON, the mill 31 is started. When the mill 31 is started, the ON output of the mill start 77 is input to the S / R 68, and the constant load switching mode 69 is reset (OFF).

[0061] The unit trip 70 is turned ON when a unit trip occurs during the operation of power plant 1. When unit trip 70 is ON, it is input to S / R68 and the constant load switching mode 69 is reset (turned OFF).

[0062] The logic unit 71 performs an OR (logical disjunction) operation between the unit trip 70 and the mill start 77. That is, if at least one of the unit trip 70 or the mill start 77 is ON, the output of the logic unit 71 is reset (OFF), and the constant load switching mode 69 is released.

[0063] Figure 10 shows the water supply bias and mill automatic stop setting circuits of several embodiments of the present disclosure. When the constant load switching mode 69 in Figure 9 is turned ON, it is input to the logic unit 79 along with the wet operation state 78, which is turned ON when the boiler is in a wet operation state. The load index 60 is also input to the function unit 81, which converts it into a bias flow rate and outputs it. In this way, the feedwater flow rate command value with the bias flow rate added is not a fixed amount (minimum feedwater flow rate) as in conventional control, but rather a flow rate that matches the load (heat input to the boiler 10) is set using a function. The bias flow rate, which is the output of the function unit 81, is the amount of excess feedwater necessary to maintain the wet operation state when the boiler 10 is under a specific load. The function that defines the bias flow rate is set so that the amount of excess feedwater is as small as possible. The bias flow rate, which is the output of the function unit 81, is input to the TRF (transversal filter) circuit 82. At this time, the bias flow rate input to the TRF circuit 82 may be changed at a constant rate (rate of change) in order to avoid sudden changes in the water supply flow rate. In the TRF circuit 82, when the constant load switching mode 69 is ON, the bias flow rate input from the function unit 81 is output, and when the constant load switching mode 69 is OFF, 0% input from the constant 83 is output. Thus, when the constant load switching mode 69 is OFF, the bias flow rate is not added to the water supply flow rate command value.

[0064] The bias flow rate, which is the output of the function unit 81, is input to the ΔH / L (difference determination circuit) 84. The ΔH / L 84 outputs ON when the difference between each input is 0, and turns ON when the output of the TRF circuit 82 and the output of the function unit 81 are equal. In other words, when the output of the ΔH / L 84 is ON, it means that the bias flow rate, which is the output of the function unit 81, is added to the water supply flow rate command value.

[0065] The logic unit 79 performs an AND operation on the wet operation state 78, the constant load switching mode 69, and ΔH / L 84. That is, if the wet operation state 78, the constant load switching mode 69, and ΔH / L 84 are all ON, the output of the logic unit 79 becomes ON, and ON is output to the mill automatic stop command 80. The mill automatic stop command 80 is a command to stop the mill 31 as needed when the constant load switching mode 69 is ON, the machine is in wet operation mode, and the bias flow rate is added to the water supply flow rate command value. This is because stopping the mill 31 could cause a significant disturbance in the operation control of the boiler 10, so the purpose is to stop the mill 31 when the addition of the bias flow rate to the feedwater flow rate command value is complete and the system is stable.

[0066] The feedwater flow rate setting 85 is input to the adder 86, and a bias flow rate corresponding to the value of the load index 60 is added. The feedwater flow rate setting 85 is set to the feedwater flow rate corresponding to the boiler load (evaporation rate) (i.e., the flow rate required in dry operation).

[0067] The minimum water supply flow rate setting 89 is input to the TRF (Transversal Filter) circuit 90. In the TRF circuit 90, 0% of the constant 91 is output when the constant load switching mode 69 is ON, and the minimum water supply flow rate setting 89 is output when the constant load switching mode 69 is OFF. In other words, when operating in constant load switching mode 69, the conventional control method of minimum water supply flow rate setting 89 is not used (0%).

[0068] The comparator 87 compares the output of the adder 86 with the output of the TRF circuit 90 and sets the larger value as the water supply flow rate command 88. In other words, when the constant load switching mode 69 is OFF, the conventional control method, the minimum water supply flow rate setting 89, is enabled.

[0069] In wet operation, the feedwater flow rate passing through the furnace wall 101 is high, resulting in a relatively stable operating state. However, the thermal efficiency of the boiler 10 decreases because heat is required to heat the excess feedwater and power is needed to circulate it back to the furnace wall 101. Therefore, by using the control circuit of this disclosure, the feedwater flow rate can be adjusted using a bias flow rate corresponding to the actual heat input to the boiler 10, thereby minimizing the amount of excess feedwater and suppressing the decrease in thermal efficiency.

[0070] Figure 11 shows a circuit diagram for switching control using a constant load switching mode in some embodiments of the present disclosure. As shown in Figure 11, the load index 60, load change 92, and boiler outlet superheat 93 are input to the once-through operation state / circulation operation state determination circuit 94. Load change 92 indicates whether the load on the boiler 10 is changing or not. The boiler outlet superheat 93 is a value that indicates the dryness of the steam (main steam) supplied from the superheater 102 of the boiler 10 to the high-pressure turbine 111A, and is calculated, for example, from the values ​​of the main steam thermometer and pressure gauge (not shown). Based on these values, the once-through operation state / circulation operation state determination circuit 94 determines whether the boiler 10 is in a dry operation state (once-through operation state) or a wet operation state (circulation operation state).

[0071] The once-through operation / circulation operation state determination circuit 94 outputs a switching signal to the dry operation state to the logic unit 95 when it determines that the boiler 10 should be in a dry operation state (for example, when it is currently in a wet operation state and a load increase command to the first load or higher is input). On the other hand, if the once-through operation state / circulation operation state determination circuit 94 determines that the boiler 10 should be in a wet operation state (for example, if it is currently in a dry operation state and a load reduction command to the first load or lower is input), it outputs a switching signal to the wet operation state to the logic unit 98.

[0072] On the other hand, when the constant load switching mode 69 is ON, the boiler outlet superheat level 93 is used to switch between once-through operation and circulating operation as follows. As shown in Figure 11, the boiler outlet superheat level 93 is input to the H / L (large / small determination circuit) 201. The H / L 201 is turned ON if the boiler outlet superheat level 93 is below a predetermined threshold. The output of the H / L 201 is input to the logic unit 202 along with the constant load switching mode 69, and an AND (logical conjunction) operation is performed. That is, if the boiler outlet superheat level 93 is below a predetermined threshold and the constant load switching mode 69 is ON, the output of the logic unit 202 is turned ON. When the output of the logic unit 202 is ON, the on-delay timer 203 functions. The output of the on-delay timer 203 is input to the logic unit 98 as a switching signal to the wet operation state.

[0073] The boiler outlet superheat level 93 is also input to the H / L (large / small determination circuit) 204. The H / L 204 is turned ON if the boiler outlet superheat level 93 is greater than or equal to a predetermined threshold. The output of the H / L 204 is input to the logic unit 206 along with the output of the constant load switching mode 69, which has been NOT calculated by the logic unit 205, and an AND (logical conjunction) operation is performed. That is, if the boiler outlet superheat level 93 is greater than or equal to a predetermined threshold, and the constant load switching mode 69 is OFF, the output of the logic unit 206 is turned ON. When the output of the logic unit 206 is ON, the on-delay timer 207 functions. The output of the on-delay timer 207 is input to the logic unit 95 as a switching signal to the dry operation state.

[0074] The logic unit 95 performs an OR (logical disjunction) operation, and if at least one of the switching signal to the dry operation state output from the through-flow operation state / circulation operation state determination circuit 94, or the output of the on-delay timer 207 is ON, the S / R (signal switch) 96 is set, i.e., the switch to the dry operation state is set.

[0075] The logic unit 98 performs an OR (logical disjunction) operation, and if at least one of the switching signal to the wet operation state output from the through-flow operation state / circulation operation state determination circuit 94, or the output of the on-delay timer 203 is ON, the S / R (signal switch) 96 is reset, i.e., the switch to the wet operation state is set.

[0076] If S / R96 is set to switch to dry operation state, the once-through operation state switch 97 is executed, and the logic unit 99 calculates NOT (negation), so the circulating operation state switch 100 is not executed. On the other hand, if S / R96 is set to switch to wet operation state, the once-through operation state switch 97 is not executed, and the logic unit 99 calculates NOT (negation) and the circulating operation state switch 100 is executed.

[0077] Figure 12 shows a dedicated parameter setting circuit when using the constant load switching mode in some embodiments of the present disclosure. The various settings of the boiler 10 are set based on the load index 60. The load index 60 is an index that indicates the magnitude of the boiler load, and is expressed, for example, as power generation MW or required power generation MWD. ​​The acquired load index 60 is processed by the function unit 213 to output the various settings of the boiler 10 corresponding to the load index 60, and these settings are then configured in the various setting value setting unit 216.

[0078] In response, when the constant load switching mode 69 shown in Figure 9 is set, it is input to the TRF (transversal filter) circuit 215 shown in Figure 12. When the constant load switching mode 69 is input to the TRF circuit 215, the TRF circuit 215 outputs the processing result of the function unit 214 to the various setting value settings 216, and the various setting values ​​of the boiler 10 are set.

[0079] The function unit 214 has dedicated parameters set for various settings of the boiler 10 that correspond to a predetermined constant load switching mode. The load index 60 is input to the function unit 214, processed, and the dedicated parameters corresponding to the constant load switching mode are output as various settings of the boiler 10. Examples of various settings include fuel flow rate setting, feedwater flow rate setting, air flow rate setting, and various steam temperature settings.

[0080] In this way, dedicated parameters are output as various setting values ​​for the boiler 10 according to the setting of the constant load switching mode, and these are output to the various setting value setting 216, thereby setting each of the settings for the boiler 10.

[0081] Figure 13 shows the relationship between load index and steam temperature setting in some embodiments of the present disclosure. In Figure 13, the vertical axis represents the steam temperature setting (°C), and the horizontal axis represents the load index (%ECR). The solid line shows the conventional steam temperature setting, and the dashed line shows the steam temperature setting of the embodiment of this disclosure.

[0082] The steam temperature setting in this embodiment of the disclosure, as set by the various setting values ​​216 in Figure 12, tends to be lower than conventional settings when the load index is below the first load. This is because, when the constant load switching mode is performed, the feedwater flow rate is greater than the fuel input to the boiler 10, resulting in a lower steam temperature setting than conventional settings.

[0083] Figure 14 shows a timing chart when using a constant load switching mode in some embodiments of the present disclosure. In Figure 14, the horizontal axis represents time, and the following are shown: ON / OFF status of the constant load switching mode, load index value (%ECR), bias flow rate value, boiler superheat value, operating mode (dry operation state / wet operation state), and the number of operating mills 31. The number of operating mills 31 is an example of when adjustment of the number of units is necessary, and in this disclosure, for example, it shows a case where three units are operating under the first load.

[0084] At time t0, power plant 1 is under normal control. The load indicator is, for example, the first load. The bias flow rate is 0 (t / h) because it is under normal control, the operating state is dry operation, and mill 31 is operating with, for example, three units when the first load is loaded.

[0085] At time t1, the constant load switching mode 69 is turned ON. The constant load switching mode 69 is turned ON when at least one of the load reduction command 65 shown in Figure 9 or the feedwater bias operation 66 performed by the user is ON. At this time, bias control of the feedwater flow rate is started, and a bias flow rate of feedwater is added to make the feedwater flow rate corresponding to the boiler load. The heat input to the boiler 10 becomes insufficient, and the boiler superheat level decreases in accordance with the increase in bias flow rate. The load index is maintained at the first load until time t5. In addition, the conventional minimum feedwater flow rate setting is not used because it would be a disturbance.

[0086] At time t2, when the increase in bias flow rate stops, the decrease in boiler superheating also stops.

[0087] At time t3, if the boiler superheating level is below a predetermined threshold and the on-delay timer 203 in Figure 11 has functioned for a certain period of time, it is determined that the switch to the wet operation state is complete. At the same time, an automatic stop command is issued to the mill 31. The automatic stopping of the mill 31 is performed according to the output of the mill automatic start / stop determination circuit 210, which takes additional conditions into account, and may not be performed depending on the conditions.

[0088] At time t4, Mill 31 receives an automatic Mill stop command and stops one of the three Mill 31 units currently in operation, changing to operation with two units.

[0089] Between times t5 and t6, the load index of boiler 10 decreases, and the bias flow rate also decreases, so that at time t6, the load index of boiler 10 decreases to the third load.

[0090] From time t6 to t7, the load index of boiler 10 is maintained at the third load, and the bias flow rate is also maintained at a constant value.

[0091] At time t7, the load index of boiler 10 begins to rise from the third load to the first load, and the bias flow rate also increases accordingly.

[0092] At time t8, the load indicator of boiler 10 reaches and is maintained at the first load, and the bias flow rate is also maintained at a constant value accordingly.

[0093] At time t9, if at least one of the load increase command 72 shown in Figure 9 or the water supply bias release operation 73 performed by the user is turned ON, the mill automatic start command is issued. The automatic startup of the mill 31 is performed according to the output of the mill automatic startup / stop determination circuit 210, which takes additional conditions into account, and may not be performed depending on the conditions.

[0094] At time t10, the load indicator remains at the first load while the system switches to dry operation. Also, upon receiving the automatic mill start command, mill 31 starts one of its stopped units, changing to three-unit operation. Furthermore, the feedwater bias is stopped, and the bias flow rate of the feedwater begins to be removed. The boiler superheat level increases in response to the decrease in bias flow rate.

[0095] At time t11, the bias flow rate becomes 0, and the increase in boiler superheating stops.

[0096] At time t12, if the boiler superheat level is above a predetermined threshold and the on-delay timer 207 in Figure 11 has functioned for a certain period of time, it is determined that the switch to the dry operation state is complete.

[0097] By using the boiler control device of this disclosure, there is an advantage in that load increases are not required even when using a deslagger. Ash from the fuel (coal) adheres to the furnace 11 of the boiler 10, so it is necessary to periodically remove the ash adhering to the furnace wall 101. A device that removes ash by blowing a medium such as steam onto the furnace wall 101 is called a deslugger. Removing ash with a deslugger increases the heat absorption of the furnace wall 101, but when the load on the boiler 10 is low, the amount of feedwater passing through the furnace wall 101 is relatively small, so there is a concern that the temperature of the heat transfer tubes that make up the furnace wall 101 will rise rapidly, causing thermal stress. For this reason, conventional control methods do not allow the use of a deslugger when the load is low. In some cases, the load may be increased to use the deslugger, for example, several times a day.

[0098] When using the boiler control device of this disclosure, the feedwater flow rate is increased by the bias flow rate, resulting in a wet operation state. Therefore, the temperature of the feedwater passing through the furnace wall 101 does not exceed the saturation temperature, and thermal stress is less likely to occur. Thus, the deslugger can be used even under low load conditions.

[0099] <Note> The boiler control device, power plant, boiler control method, and boiler control program described in the embodiments above can be understood, for example, as follows.

[0100] A boiler control device (50) in a first aspect of the present disclosure has a switching unit (52) that switches the boiler (10) between a once-through operation state and a circulating operation state which has lower thermal efficiency than the once-through operation state, depending on the load. The switching unit performs switching control to switch from the once-through operation state to the circulating operation state when the load falls below a first load, and when operating in the circulating operation state, it performs control to add a bias flow rate to the feedwater flow rate of the boiler so that the feedwater flow rate is in accordance with the boiler load (heat input).

[0101] By controlling the boiler feedwater flow rate by adding a bias flow rate to ensure that the feedwater flow rate corresponds to the boiler load, when using the power generated by the boiler power generation facility as adjustment power in conjunction with renewable energy, it is possible to maintain the load at a lower load than the normal operating range, which was previously considered a load-holding prohibited zone. This expands the range of operation for adjustment power. Furthermore, the use of the deslagger, which was previously unusable below normal operating ranges, will no longer require a load increase for its use. Since a load increase for the deslagger is not necessary, flexible load management of the boiler power generation facility becomes possible, facilitating the acceptance of renewable energy.

[0102] In the boiler control device of a second aspect of the present disclosure, in the first aspect, the feedwater flow rate may be the amount of feedwater evaporation required for the boiler load, and the bias flow rate may be the amount of excess feedwater required to maintain the circulating operation state, and a flow rate derived by a predetermined function with respect to the load.

[0103] Since the sum of the water supply flow rate and the bias flow rate fluctuates according to the load, excess water supply can be suppressed. In a circulating operation state, excess water supply reduces efficiency, but the excess can be minimized by adjusting the water supply flow rate.

[0104] A boiler control device according to a third aspect of the present disclosure, in the second aspect, the minimum feedwater flow rate of the boiler is the lower limit of the feedwater flow rate of the boiler that is secured to protect the furnace wall (101) of the boiler, and is the feedwater flow rate corresponding to a second load in which the boiler load is smaller than the first load, the minimum feedwater flow rate is a constant value regardless of the boiler load, and when operating in the circulating operation state, the bias flow rate may be added such that the sum of the feedwater flow rate and the bias flow rate is less than the minimum feedwater flow rate, at least near the lower limit load for stable operation of the boiler.

[0105] Unlike conventional systems where the minimum feedwater flow rate is constant, this system allows the feedwater flow rate to fluctuate according to the load, thus suppressing excess feedwater. In particular, near the lower limit load for stable boiler operation, the feedwater flow rate can be reduced compared to conventional systems.

[0106] In the boiler control device of the fourth aspect of this disclosure, in any of the first to third aspects, the switching unit may, during the switching control, add the bias flow rate to the feedwater flow rate while maintaining the first load, and switch from the once-through operation state to the circulating operation state.

[0107] This prevents transient operating conditions during switching control. It also suppresses increased thermal stress on the furnace wall due to the mixing of saturated and superheated steam, as well as control instability.

[0108] In the fifth aspect of the present disclosure, the boiler control device, in the fourth aspect, may switch from the circulating operation state to the once-through operation state when the load exceeds the first load, and during the switching control, the switching unit may switch from the circulating operation state to the once-through operation state while maintaining the first load and removing the bias flow rate that was added to the feedwater flow rate.

[0109] In switching control, it is possible to control the system from a circulating operation state back to a once-through operation state. When returning to the once-through operation state, the system can be returned to normal control except for the bias flow rate.

[0110] In the sixth aspect of the present disclosure, the boiler control device may, in any of the first to fifth aspects, have the first load be the lower limit load for once-through operation, which is the lower limit of the load in the once-through operation state.

[0111] Since the switching control is switched at the lower limit load for through-flow operation, normal control in the through-flow operation state is performed in the load range up to the lower limit load for through-flow operation, and the system can operate in a circulating operation state in the load range below the lower limit load for through-flow operation. This makes it possible to operate without setting a load holding prohibition zone.

[0112] A power plant (1) according to the seventh aspect of the present disclosure includes a boiler control device according to any of the first to sixth aspects.

[0113] A boiler control method according to an eighth aspect of the present disclosure is a boiler control method that switches between a once-through operation state and a circulating operation state with lower thermal efficiency than the once-through operation state depending on the load, and performs switching control to switch from the once-through operation state to the circulating operation state when the load falls below a first load, wherein when operating in the circulating operation state, a computer performs control to add a bias flow rate to the feedwater flow rate of the boiler so that the feedwater flow rate is corresponding to the boiler load.

[0114] The boiler control program of the ninth aspect of this disclosure causes a computer to execute the boiler control method described in the eighth aspect. [Explanation of Symbols]

[0115] 1. Power plant 10 Boilers 11 Furnace 12 Combustion gas passage 13 Flue 20 Combustion device 21 Burner 22 Fine fuel supply pipe 23. Air register 24. Air ducts 25 Additional Air Ports 26 Additional air ducts 31. Mill (Grinder) 32 Forced draft fan (FDF) 41 Gas duct 42 Air preheater 43 Denitration equipment 44 Dust collection device 45. Induced Draft Fan (IDF) 46 Desulfurization equipment 47 Chimney 50 Boiler control device 51 Selection Section 52 Switching section 101 Furnace wall 102 Superheater 102A 1st superheater 102B 2nd superheater 102C 3rd superheater 103 Reheater 103A 1st reheater 103B 2nd reheater 104 Economizer 111 Steam Turbine 111A High-Pressure Turbine 111B Intermediate Pressure Turbine 111C Low-Pressure Turbine 112 Condenser 113 Generator 121 Condensate pump (CP) 122 Low-pressure water supply heater 123 Boiler feedwater pump (BFP) 124 High-pressure water supply heater 125 Brackish water separator 126 Brackish water separator drain tank 127 Boiler circulation pump (BCP) L1 Water supply line L2 Drain water line L3~L5 Steam Line L6 Circulation Line 1100 CPU 1200 Main storage 1300 Secondary storage 1400 Communication I / F 1500 Input / output section 1800 Bus

Claims

1. It has a switching unit that switches between a boiler's once-through operation state and a circulating operation state which has lower thermal efficiency than the once-through operation state, depending on the load. The switching unit performs switching control to switch from the through-flow operation state to the circulating operation state when the load falls below the first load. A boiler control device that, when operating in the aforementioned circulating operation state, controls the boiler by adding a bias flow rate to the feedwater flow rate so that the feedwater flow rate corresponds to the boiler load.

2. The feedwater flow rate is the amount of feedwater corresponding to the evaporation rate in the boiler load. The boiler control device according to claim 1, wherein the bias flow rate is the amount of excess feedwater necessary to maintain the circulating operation state and is a flow rate derived by a predetermined function with respect to the load.

3. The minimum feedwater flow rate of the boiler is the lower limit of the feedwater flow rate of the boiler that is ensured to protect the furnace wall of the boiler, and is the feedwater flow rate corresponding to a second load where the boiler load is smaller than the first load. The minimum feedwater flow rate is a constant value regardless of the boiler load. The boiler control device according to claim 2, wherein, when operating in the aforementioned circulating operation state, the bias flow rate is added such that, at least near the lower limit load of stable operation of the boiler, the sum of the feedwater flow rate and the bias flow rate is less than the minimum feedwater flow rate.

4. The boiler control device according to claim 1, wherein the switching unit, during the switching control, adds the bias flow rate to the feedwater flow rate while maintaining the first load, and switches from the once-through operation state to the circulating operation state.

5. The switching unit switches from the circulating operation state to the through-flow operation state when the load exceeds the first load. The boiler control device according to claim 4, wherein the switching unit, during the switching control, removes the bias flow rate that was added to the feedwater flow rate while maintaining the first load, and switches from the circulating operation state to the once-through operation state.

6. The boiler control device according to claim 1, wherein the first load is the lower limit load for once-through operation, which is the lower limit of the load in the once-through operation state.

7. A power plant comprising the boiler control device described in claim 1.

8. Depending on the load, the boiler switches between a once-through operation state and a circulating operation state, which has lower thermal efficiency than the once-through operation state. A boiler control method that performs switching control to switch from the once-through operation state to the circulating operation state when the load falls below the first load, A boiler control method in which, when operating in the aforementioned circulating operation state, a computer performs control to add a bias flow rate to the feedwater flow rate of the boiler so that the feedwater flow rate corresponds to the boiler load.

9. A boiler control program for causing a computer to execute the boiler control method described in claim 8.

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