Method for operating a boiler and control device for a boiler

Abstract

To provide a boiler operation method which starts supplying an ammonia fuel under a condition that generation of NOx can be suppressed, and a control device for boiler.SOLUTION: A boiler operation method includes steps of: combusting a fuel other than an ammonia fuel inside of a furnace (S11); determining whether or not a determination condition that an air ratio which is a ratio of an air supply amount to the furnace with respect to a theoretical air amount required for combusting the other fuel supplied to the furnace is an upper limit value or less and a representative temperature in the furnace is a lower limit value or more is satisfied (S13); and starting supplying the ammonia fuel to the furnace in a case where at least the determination condition is satisfied (S15). The upper limit value of the air ratio constituting the determination condition is 0.8 or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a method of operating a boiler and a control device for a boiler. [Background technology]

[0002] Conventionally, boilers in which ammonia is supplied as fuel into a furnace are known. When ammonia is used as fuel, it is necessary to suppress the emission of nitrogen oxides (NOx). For example, in the boiler disclosed in Patent Document 1, ammonia fuel is not supplied to the upper burners among the multiple burners, thereby suppressing the emission of NOx. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-112280 Summary of the Invention [Problem to be solved by the invention]

[0004] According to the knowledge of the inventors, in order to suppress NOx emissions, it is preferable to optimize the combustion environment in the boiler by using another fuel before starting to supply ammonia fuel. However, Patent Document 1 does not specifically disclose such a configuration.

[0005] The present disclosure relates to a boiler operation method that starts the supply of ammonia fuel under conditions that can suppress the generation of NOx, and a boiler control device. [Means for solving the problem]

[0006] A method for operating a boiler according to at least one embodiment of the present invention includes: burning a fuel other than ammonia fuel in a furnace; a step of determining whether or not a determination condition is satisfied that an air ratio, which is a ratio of an amount of air supplied to the furnace to a theoretical amount of air required to combust the other fuel supplied to the furnace, is equal to or less than an upper limit value, and a representative temperature in the furnace is equal to or greater than a lower limit value; starting the supply of the ammonia fuel to the furnace when at least the determination condition is satisfied; Equipped with The upper limit of the air ratio constituting the determination condition is 0.8 or less.

[0007] A control device for a boiler according to at least one embodiment of the present invention comprises: 1. A control device for a boiler having a furnace and a supply system configured to supply ammonia fuel and other fuels into the furnace, comprising: a combustion command generating unit that generates an other fuel combustion command for burning the other fuel in the furnace; a determination unit for determining whether or not a determination condition is satisfied in which an air ratio, which is a ratio of an amount of air supplied to the furnace to a theoretical amount of air required to combust the other fuel supplied to the furnace, is equal to or less than an upper limit value, and a representative temperature in the furnace is equal to or greater than a lower limit value; an ammonia supply command generation unit configured to generate an ammonia supply start command to cause the supply system to start supplying the ammonia fuel to the furnace when the determination unit determines that at least the determination condition is satisfied; Equipped with The upper limit of the air ratio constituting the determination condition is 0.8 or less. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a boiler operation method that starts the supply of ammonia fuel under conditions that can suppress the generation of NOx, and a boiler control device. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a conceptual diagram of a boiler operation system according to an embodiment. [Figure 2] 3 is a flowchart illustrating a method for operating a boiler according to one embodiment. [Figure 3] 1 is a cross-sectional view showing the configuration of an ammonia burner according to one embodiment. [Figure 4] FIG. 2 is an explanatory diagram of a specific configuration of a burner unit according to one embodiment. [Figure 5] 1 shows a specific configuration of a boiler operation system according to an embodiment. [Figure 6] 4 is a flowchart illustrating a boiler operation control process according to an embodiment. [Figure 7] 4 is a graph showing the relationship between the burner air ratio and NOx emissions according to one embodiment. [Figure 8] 1 is a graph showing the relationship between gas temperature and required residence time of ammonia according to one embodiment. [Figure 9] 10 is a graph showing the relationship between nose temperature and gas temperature in a burner section according to one embodiment. [Figure 10] 1 is a graph showing the relationship between the ammonia co-firing ratio in terms of calorific value and NOx emissions according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, several embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present invention.

[0011] FIG. 1 is a conceptual diagram of a boiler operation system 1 according to one embodiment. The boiler operation system 1 includes a boiler 2 incorporated in, for example, a thermal power plant (not shown), a supply system 15 for supplying air and fuel to the boiler 2, and a measurement system 9 for measuring parameters related to the operation of the boiler 2. The fuel supplied from the supply system 15 to the boiler 2 includes ammonia fuel. The ammonia fuel may be either liquid ammonia or ammonia gas. An embodiment in which the ammonia fuel is liquid ammonia will be exemplified below. In one embodiment, the liquid ammonia is supplied to the boiler 2 in a liquid state. The liquid ammonia does not contain gases such as hydrogen gas, but may contain impurities (e.g., urea) to an extent that does not affect combustion in the boiler 2. The liquid ammonia vaporizes into ammonia gas within the boiler 2. Furthermore, the fuel supplied from the supply system 15 to the boiler 2 includes fuel other than ammonia fuel. For example, after combustion using other fuel is performed in the boiler 2, ammonia is mixed with the other fuel or ammonia is exclusively combusted. The carbon-containing fuel, which is an example of a fuel other than ammonia, is a biomass fuel or a fossil fuel. The fossil fuel is liquefied natural gas, oil such as heavy oil or light oil, or coal such as pulverized coal. In the following, an embodiment in which the carbon-containing fuel is oil and pulverized coal will be exemplified.

[0012] The boiler 2 of one embodiment includes a furnace 20 including a furnace wall 19 and at least one burner unit 30 provided on the furnace wall 19 . The furnace 20 is a cylindrical hollow body in which fuel injected by the burner unit 30 reacts with combustion air and burns, and can take various shapes, for example, a cylindrical shape or a square pillar shape. Furthermore, the furnace 20 of one embodiment includes a nose 11 that protrudes into the furnace 20. The nose 11 is configured so that gases (e.g., combustion gases and unburned gases) generated in the combustion space 7 of the furnace 20 properly flow into a flow path located downstream of the furnace 20. The flow path located downstream of the furnace 20 is, for example, a flue 8. At least one burner unit 30 is configured to combust fuel in the combustion space 7 of the furnace 20. In the embodiment illustrated in FIG. 1, the burner units 30 are arranged in three stages along the direction in which gas generated in the combustion space 7 flows (arrow A in FIG. 1). Hereinafter, the burner units 30 in each stage, from the downstream side in the gas flow direction, may be referred to as the first burner unit 31, the second burner unit 32, and the third burner unit 33, and these three stages of burners may be collectively referred to as the burner unit 30. The burner units 30 may also be arranged in two or four stages, etc. The boiler 2 in one embodiment is a swirl combustion boiler, and the burner units 30 provided in each stage are arranged at equal intervals along the circumferential direction of the furnace 20. The number of burner units 30 in each stage is, for example, four, but only one burner unit 30 is shown in Fig. 1. Note that the number of burner units 30 in each stage may be three or five or more. The boiler 2 according to another embodiment is an opposed-fire boiler, in which at least a pair of burner units 30 are provided at positions facing each other.

[0013] Each burner unit 30 includes at least one burner. In at least one burner unit 30, the burner is an ammonia burner 50 configured to inject liquid ammonia in liquid form into the interior of the furnace 20. The ammonia burner 50 may be configured to inject only liquid ammonia. Alternatively, the ammonia burner 50 may be configured to inject a carbon-containing fuel and then inject liquid ammonia together with (or instead of) the carbon-containing fuel. In one embodiment, the first burner unit 31 includes an ammonia burner 50. The second burner unit 32 and the third burner unit 33 may or may not include an ammonia burner 50. In other embodiments, the ammonia burner 50 may be included only in the second burner unit 32 or the third burner unit 33. Additionally, any of the burner units 30 may include a fuel burner 35 (see FIG. 4) for injecting a carbon-containing fuel into the furnace 20, as will be described in more detail below.

[0014] In one embodiment, the supply system 15 is configured to supply primary air and fuel to the burner units 30. The fuel (liquid ammonia and carbon-containing fuel in this example) supplied to the burner units 30 may be switched. For example, the burner units 30 of any stage may be supplied with a carbon-containing fuel (e.g., oil) followed by liquid ammonia. The supply system 15 of one embodiment is configured to supply secondary air (additional air) via a supply unit 4 provided on the furnace wall 19 downstream of the burner unit 30.

[0015] The measurement system 9 in one embodiment includes a plurality of flow meters for measuring the flow rate of air or fuel supplied from the supply system 15, and a furnace thermometer 6 for measuring a representative temperature inside the furnace 20. The representative temperature inside the furnace 20 is a temperature correlated with the gas temperature, which is the temperature of gas in the combustion space 7 of the furnace 20. As an example, the representative temperature inside the furnace 20 is the temperature of the inner wall surface of the nose 11 described above (hereinafter referred to as the nose temperature). The nose temperature is measured by the furnace thermometer 6. Note that the representative temperature inside the furnace 20 may be, for example, the gas temperature.

[0016] The boiler operation system 1 may be operated by an operator, or may be operated under the control of a control device 5 (see FIG. 5) described later, or may be operated by a combination of these. In the furnace 20 of one embodiment, the supply of ammonia fuel may be started after a fuel other than ammonia fuel (in this example, a carbon-containing fuel) has been combusted, and the ammonia fuel may be mixed and combusted with the other fuel.

[0017] In one embodiment, a determination condition is used as a condition for starting the supply of ammonia fuel. The determination condition is satisfied when the air ratio is equal to or lower than an upper limit and the representative temperature in the furnace 20 is equal to or higher than a lower limit. The air ratio that constitutes the determination condition is the ratio of the amount of air supplied to the furnace 20 to the theoretical amount of air required to combust other fuels supplied to the furnace 20. In one embodiment, the amount of air supplied to the furnace 20 does not include secondary air (additional air). In other words, in this example, the air ratio that constitutes the determination condition is also the value obtained by multiplying the total air ratio by the supply proportion of air other than secondary air out of the total air supplied to the furnace 20. Specifically, the air ratio that constitutes the determination condition (hereinafter sometimes referred to as the burner section air ratio) is defined by the following formula (1): λ b =λ×(100-AA) / 100 Equation (1) In equation (1), λ b is the burner air ratio, λ is the total air ratio, and AA is the proportion of secondary air supplied to the total air supply to boiler 2. The total air ratio (λ) is defined by equations (2), (3), and (4). λ=Q Air / Q x ...Equation (2) Q x =Q mf ×A mf ...Equation (3) A mf =(100-X) / 100×A car +X / 100×A NH3 ...Equation (4) In equations (2) to (4), Q Air is the total air supply. Also, Q mf Q is the amount of ammonia fuel and other fuel (carbon-containing fuel in this example) supplied when the combustion performed in the furnace 20 is ammonia co-firing (co-firing ratio in weight conversion: X%). x is the air flow rate required for the air ratio to be 1 during mixed combustion. mf is the theoretical air amount of the fuel (in this example, ammonia fuel and carbon-containing fuel) when the above-mentioned mixed combustion is performed, and A car is the theoretical air amount for carbon-containing fuel, and A NH3 is the theoretical air amount for ammonia fuel. The formulas (1) to (3) are also applicable to the mixed combustion of ammonia fuel and carbon-containing fuel. In order to calculate the air ratio that constitutes the judgment condition (i.e., the burner air ratio before the start of the supply of ammonia fuel), X and A NH3 Set each to 0, and Q mf is set to the supply amount of only the carbon-containing fuel, and formulas (1) to (3) are applied. Note that, in the following, λ defined by formula (1) is used not only before the start of ammonia fuel supply, but also when ammonia mixed combustion or ammonia mono-combustion is performed. b is sometimes called the burner air ratio.

[0018] In one embodiment, the upper limit of the burner section air ratio constituting the judgment condition is 0.8 or less. If the supply of ammonia fuel to the furnace 20 is started under the condition that the burner section air ratio is 0.8 or less, the burner section air ratio at the start of combustion of the ammonia fuel will also be 0.8 or less. This effectively reduces NOx generated in the furnace 20. The upper limit of the burner air ratio constituting the determination condition may be 0.7 or less. In this case, combustion of ammonia fuel is started under the condition that the air ratio is 0.7 or less, and excess generation of NOx is suppressed. In addition, in a boiler 2 having a typical size used in a thermal power plant, it is not realistic for the burner air ratio to be less than 0.6. Therefore, the burner air ratio constituting the judgment condition is preferably 0.6 or more and 0.8 or less, and more preferably 0.6 or more and 0.7 or less.

[0019] In one embodiment, the representative temperature in the furnace 20 that constitutes the judgment condition is the nose temperature described above. The lower limit of the nose temperature is 1120°C or higher. According to the findings of the inventors, it has been found that if the nose temperature is 1120°C or higher, the gas temperature is 1400°C or higher, and the thermal decomposition of ammonia is sufficiently carried out in a relatively short residence time in the furnace. Therefore, by starting the supply of ammonia fuel when the nose temperature is 1120°C or higher, it is possible to suppress the generation of NOx. The residence time in the furnace is the time from when the fuel is charged into the furnace 20 until it reaches the nose 11. The residence time in the furnace can be calculated based on, for example, the air flow rates of the primary air and secondary air, the supply flow rate of the carbon-containing fuel, the cross-sectional area (constant value) of the furnace 20, and the height (constant value) of the furnace 20. Therefore, the residence time in the furnace can be obtained based on the measurement results of multiple flow meters included in the measurement system 9.

[0020] In one embodiment, the determination conditions may include that the residence time of the other fuel (carbon-containing fuel in this example) in the furnace is 0.5 seconds or more. According to the findings of the inventors, it has been found that if the residence time of ammonia in the furnace is 0.5 seconds or more, the ammonia fuel charged into the furnace 20 is sufficiently thermally decomposed. Since the supply of ammonia fuel starts when the residence time of the other fuel in the furnace is 0.5 seconds or more, the residence time of ammonia in the furnace can also be made 0.5 seconds or more, and the amount of NOx generated can be reduced. The longer the residence time in the furnace, the more favorable the combustion environment for the thermal decomposition of ammonia fuel is formed. However, in a boiler 2 having a typical size used in a thermal power plant, the residence time of fuel (including other fuels and ammonia fuel) in the furnace is, for example, 2.0 to 3.0 seconds at most. Therefore, the residence time in the furnace that constitutes the judgment condition may be 0.5 seconds or more and 3.0 seconds or less, or 0.5 seconds or more and 2.0 seconds or less.

[0021] 2 is a flowchart showing a method for operating the boiler 2 according to one embodiment. Hereinafter, "step" may be abbreviated as "S."

[0022] In an operation method of a boiler 2 according to one embodiment, first, combustion of a fuel other than ammonia fuel is started in the furnace 20 (S11). In one embodiment, when the load of the boiler 2 increases (for example, when the boiler 2 is started), the supply system 15 supplies a fuel other than ammonia fuel (a carbon-containing fuel in this example) to the burner unit 30. Note that the load of the boiler 2 is, for example, the heat amount of steam generated by the boiler 2.

[0023] Next, it is determined whether the above-mentioned determination conditions are satisfied (S13). In one embodiment, in S13, it is determined whether the burner air ratio is 0.8 or less and the nose temperature, which is a representative temperature inside the furnace 20, is 1120°C or more. Whether the determination conditions are satisfied is determined based on the measurement results of the measurement system 9. In one embodiment, when the load of the boiler 2 increases, combustion using another fuel is performed in the furnace 20 until the determination condition is met (S13: NO). This causes the temperature in the furnace 20 to rise. According to the findings of the inventors, when the thermal load of the boiler 2 increases, the gas temperature in the furnace 20 is relatively low, and it has been found that if ammonia fuel is supplied to the furnace 20 at this time, excessive NOx is generated. Since the supply of ammonia fuel does not start until the determination condition is met when the load of the boiler 2 increases, the generation of NOx can be suppressed. Note that when the load of the boiler 2 increases, this concept includes the time when the thermal load of the boiler 2 increases after decreasing. In another embodiment, in S13, instead of determining whether the burner section air ratio is 0.8 or less, it may be determined whether the burner section air ratio is 0.7 or less. Also, the determination conditions in S13 may include that the residence time of the other fuel in the furnace is 0.5 seconds or more. In this case, the residence time of the other fuel in the furnace is acquired based on the measurement results of the measurement system 9. Also, in S13, it may be determined whether a condition other than the determination conditions is satisfied.

[0024] If it is determined that at least the determination conditions are satisfied (S13: YES), the supply of ammonia fuel is started (S15). In one embodiment, the supply system 15 supplies ammonia fuel to the burner unit 30 together with the carbon-containing fuel, and the ammonia fuel and the carbon-containing fuel are mixed and burned in the furnace 20. At this time, the ammonia mixed-combustion ratio in terms of calorific value is, for example, 20% or more. According to the findings of the inventors, when the mixed-combustion ratio of ammonia and other fuel in terms of calorific value is 20% or more, the amount of NOx generated in the furnace 20 is likely to increase. Therefore, it is very significant to reduce the amount of NOx generated when ammonia mixed-combustion is performed at a mixed-combustion ratio of 20% or more. In one embodiment, the burner air ratio during ammonia co-firing is 0.6 or more and 0.7 or less. According to the findings of the inventors, by performing ammonia co-firing under the condition of a burner air ratio of 0.6 or more and 0.7 or less, NOx emissions can be suppressed.

[0025] FIG. 3 is a cross-sectional view showing the configuration of an ammonia burner 50 according to one embodiment. As described above, one example of the ammonia fuel supplied to the boiler 2 is liquid ammonia. The ammonia burner 50 includes an ammonia supply path 52 configured to receive liquid ammonia from the supply system 15 (see FIG. 1), and an ammonia injection nozzle 54 configured to inject the liquid ammonia supplied from the ammonia supply path 52 into the furnace 20 while it is still in liquid form. The ammonia burner 50 is a one-fluid nozzle for injecting liquid ammonia in liquid form without using an assist fluid. More specifically, the ammonia burner 50 is a swirl injection nozzle (swirl atomizer) configured to inject liquid ammonia in the form of a liquid film that diverges toward the end. Alternatively, the ammonia burner 50 may be a fan spray nozzle configured to inject liquid ammonia in the form of a sheet-like liquid film, or a plain jet atomizer configured to inject liquid ammonia in the form of a simple liquid jet. In either embodiment, the liquid ammonia injected into the furnace 20 is easily atomized, and the liquid ammonia is easily vaporized in the combustion space 7.

[0026] The ammonia burner 50 according to one embodiment further includes a flame-holding mechanism 60 configured to hold the combustion flame generated in the furnace 20 . When flame-retardant liquid ammonia is used as fuel, there is a possibility of misfire occurring in the furnace 20. In order to avoid misfire, the liquid ammonia needs to be vaporized and further thermally decomposed in the furnace 20. In this regard, by using the mechanism 60 having the flame-stabilizing effect to stabilize the combustion flame, the liquid ammonia can obtain heat for vaporization and thermal decomposition, thereby suppressing misfire in the furnace 20.

[0027] The flame-holding mechanism 60 according to one embodiment is a swirler type. As a more specific example, the flame-holding mechanism 60 includes an inner cylinder 62 with the ammonia injection nozzle 54 disposed therein, an outer cylinder 64 disposed to surround the inner cylinder 62, and a swirler 65. The outer cylinder 64 according to one embodiment includes a first outer cylinder 64A surrounding the inner cylinder 62 and a second outer cylinder 64B surrounding the first outer cylinder 64A. An air supply passage 63A communicating with the interior of the furnace 20 is formed between the first outer cylinder 64A and the inner cylinder 62. Similarly, an air supply passage 63B communicating with the interior of the furnace 20 is formed between the first outer cylinder 64A and the second outer cylinder 64B. The air flowing through the air supply passages 63A and 63B is primary air supplied from the supply system 15 (see FIG. 1). The swirler 65 is provided in the air supply passage 63A and is configured to impart a swirling force to the air flowing through the air supply passage 63A. A swirling force is applied by the swirler 65 to the air supplied from the air supply passage 63A to the furnace 20 (arrow B). This promotes mixing of the air with the liquid ammonia injected from the ammonia injection nozzle 54. This promotes diffusion of the liquid ammonia inside the furnace 20, facilitating thermal decomposition of the liquid ammonia in the furnace 20. In other embodiments, the mechanism 60 having the flame holding effect may be a diffuser type instead of a swirler type. Also, the ammonia burner 50 does not have to be provided with the mechanism 60 having the flame holding effect.

[0028] FIG. 4 is an explanatory diagram of a specific configuration of the burner unit 30 according to one embodiment. The burner unit 30 shown in FIG. 4 is configured to switch to ammonia mono-combustion after the ammonia co-combustion ratio reaches approximately 50% in terms of heat amount. The burner unit 30 is, for example, an existing burner unit. Therefore, some components of the burner unit 30 may be unused. Alternatively, the components may be used only during ammonia co-firing and unused during ammonia mono-firing. Each stage of burner unit 30 includes five injection means 40. Each injection means 40 is configured to supply fuel or air to furnace 20. As an example, each injection means 40 is either the ammonia burner 50 described above, a fuel burner 35 for injecting a carbon-containing fuel, or an air nozzle 42 for injecting primary air. The first burner unit 31, second burner unit 32, and third burner unit 33 of the burner unit 30 all have the same configuration. Specifically, the two outermost injection means 40 are both air nozzles 42, and the central injection means 40 is an ammonia burner 50. The injection means 40 between the ammonia burner 50 and the upper air nozzle 42 is a fuel burner 35, and the remaining injection means 40 is not used. In the example of FIG. 4, all fuel burners 35 of burner unit 30 are coal burners configured to inject pulverized coal as the carbon-containing fuel. In one embodiment, the fuel injected from the ammonia burner 50 of the first burner unit 31 is liquid ammonia only, and the fuel injected from the ammonia burners 50 of the second burner unit 32 and the third burner unit 33 is oil and liquid ammonia.

[0029] The burner unit 30 operates, for example, as follows. First, combustion using a carbon-containing fuel is performed. Specifically, the air nozzle 42 injects primary air, and the fuel burner 35 injects pulverized coal. At this time, the ammonia burner 50 of the first burner unit 31 is not activated, and the ammonia burners 50 of the second burner unit 32 and the third burner unit 33 each inject oil. Thereafter, liquid ammonia is injected from the ammonia burner 50 of the first burner unit 31, and the fuel injected from the remaining two ammonia burners 50 is switched from oil to liquid ammonia. As a result, ammonia mixed combustion is performed in the furnace 20. Thereafter, the injection of pulverized coal from the three fuel burners 35 of the burner unit 30 is stopped, and the only fuel injected into the furnace 20 is liquid ammonia from the three ammonia burners 50. As a result, combustion in the furnace 20 is switched from ammonia mixed combustion to ammonia exclusive combustion.

[0030] 5 shows a specific configuration of a boiler operation system 1 according to one embodiment. The boiler operation system 1 includes a control device 5 for controlling the operation of the boiler 2, in addition to the boiler 2, supply system 15, and measurement system 9 described above. In one embodiment, the control device 5 includes a processor 91 , a ROM 92 , a RAM 93 , and a memory 94 . The processor 91 is configured to read the boiler operation program stored in the ROM 92, load it into the RAM 93, and execute instructions included in the boiler operation program. The processor 91 is a CPU, GPU, MPU, DSP, various other arithmetic devices, or a combination of these. The processor 91 may be realized by an integrated circuit such as a PLD, ASIC, FPGA, or MCU. The memory 94 stores various data associated with the execution of the boiler operation program. One example of the memory 94 is a flash memory. The processor 91 is electrically connected to the supply system 15 and the measurement system 9. In one embodiment, the processor 91 is configured to generate an other fuel combustion command for burning a fuel other than ammonia fuel in the furnace 20, an ammonia supply start command for starting the supply of ammonia fuel to the supply system 15, and an ammonia mono-combustion start command for starting the mono-combustion of ammonia in the furnace 20. In one embodiment, these control commands are sent to the supply system 15. In one embodiment, the processor 91 generates an ammonia supply start command when it determines that the above-described determination conditions are satisfied based on the measurement results of the measurement system 9. Furthermore, in one embodiment, the processor 91 initiates an ammonia combustion command when it determines that the ammonia combustion conditions for starting ammonia combustion are satisfied. The ammonia combustion conditions include, for example, that the representative temperature in the furnace 20 has reached a specified temperature, that a specified time has elapsed since ammonia co-combustion started, that a specified parameter has reached a set value after a specified input operation has been performed by the operator, or a combination of these.

[0031] The supply system 15 includes a primary air supply system 110 for supplying primary air, a secondary air supply system 120 for supplying secondary air, an ammonia supply system 100 for supplying liquid ammonia, an oil supply system 80 for supplying oil, and a pulverized coal supply system 70 for supplying pulverized coal. The oil supply system 80 and the pulverized coal supply system 70 are each an example of a system for supplying a carbon-containing fuel. Primary air, liquid ammonia, pulverized coal, and oil are supplied to a burner unit 30, and secondary air is supplied to a supply section 4 provided in a furnace wall 19. The supply system 15 is configured to be controlled by a control device 5.

[0032] An air supply line 112 of the primary air supply system 110 is connected to all of the burner units 30. The air supply line 112 is provided with a flow rate adjustment valve 116 for adjusting the flow rate of the primary air, and a switching valve 118 for switching the communication state of the air supply line 112. An air supply line 122 of the secondary air supply system 120 is connected to the supply unit 4. The air supply line 122 is provided with a flow rate adjustment valve 126 for adjusting the flow rate of the secondary air, and a switching valve 128 for switching the communication state of the air supply line 122. The flow rate adjusting valves 116 and 126 and the switching valves 118 and 128 are configured to operate in response to control commands sent from the control device 5.

[0033] The ammonia supply system 100 includes the above-mentioned ammonia burner 50, an ammonia tank 101 in which liquid ammonia is stored, an ammonia supply line 102 connecting the ammonia tank 101 and the ammonia burner 50, a pump 103 provided in the ammonia supply line 102, a pressure regulating valve 105 for regulating the pressure in the ammonia supply line 102, a switching valve 107 provided in the ammonia supply line 102 and for switching the communication state between the ammonia tank 101 and the ammonia burner 50, and a flow rate regulating valve 108 for regulating the flow rate of liquid ammonia flowing through the ammonia supply line 102. The pressure regulating valve 105, the switching valve 107, and the flow rate regulating valve 108 are configured to operate in response to a control command from the processor 91. This allows the ammonia supply system 100 to change between a supply stop state in which liquid ammonia is not supplied to any of the ammonia burners 50, and a supply state in which liquid ammonia is supplied to all of the ammonia burners 50. As will be described later, when the ammonia supply system 100 is in the supply stop state, oil is supplied from the oil supply system 80 to the ammonia burners 50 of the second burner unit 32 and the third burner unit 33.

[0034] An oil supply system 80 of one embodiment includes an oil supply device 81, an oil supply line 82 connecting the oil supply device 81 and the ammonia burner 50, an oil flow rate regulating valve 86 for regulating the flow rate of oil flowing through the oil supply line 82, and a switching valve 88 for switching the communication state of the oil supply line 82. The oil supply line 82 of this example is connected to the ammonia burners 50 of the second burner unit 32 and the third burner unit 33. In one embodiment, the oil supply device 81, the oil flow rate adjustment valve 86, and the switching valve 88 are configured to operate in response to a control command from the control device 5. This allows the oil supply system 80 to change between a supply state in which oil is supplied to the ammonia burner 50 connected to the oil supply line 82, and a supply stop state in which the supply of oil is stopped. In another embodiment, the oil supply line 82 may be connected to the fuel burner 35 for injecting oil. The oil supply line 82 may also be configured to allow atomized steam to flow in. In this case, oil and atomized steam are supplied to the burner unit 30.

[0035] A pulverized coal supply system 70 of one embodiment includes a pulverized coal supply device 71 for supplying pulverized coal using a carrier gas, a pulverized coal supply line 72 connecting the pulverized coal supply device 71 and the burner unit 30, a pulverized coal flow rate adjustment valve 76 for adjusting the flow rate of pulverized coal flowing through the pulverized coal supply line 72, and a switching valve 78 for switching the communication state of the pulverized coal supply line 72. The pulverized coal supply line 72 of this example is connected to the fuel burners 35 of each of the first burner unit 31, the second burner unit 32, and the third burner unit 33. The pulverized coal supply device 71, the pulverized coal flow rate adjustment valve 76, and the switching valve 78 are configured to operate in response to control commands from the control device 5. This allows the pulverized coal supply system 70 to change between a supply stop state in which the supply of pulverized coal is stopped, and a supply state in which pulverized coal is supplied to the burner unit 30. When the pulverized coal supply system 70 is in the supply state, pulverized coal is supplied to the fuel burner 35 (see FIG. 4) that functions as a coal burner.

[0036] The measurement system 9 includes an air flow meter 114 for measuring the flow rate of primary air supplied by the primary air supply system 110, an air flow meter 124 for measuring the flow rate of secondary air supplied by the secondary air supply system 120, an ammonia flow meter 109 for measuring the flow of ammonia fuel supplied by the ammonia supply system 100, an oil flow meter 84 for measuring the flow rate of oil supplied by the oil supply system 80, a pulverized coal flow meter 74 for measuring the flow rate of pulverized coal supplied by the pulverized coal supply system 70, and the furnace thermometer 6 described above. These flow meters are configured to send measurement results to processor 91. This allows processor 91 in one embodiment to determine whether a determination condition is met.

[0037] The boiler operation system 1 operates, for example, as follows in response to a control command sent from the processor 91. First, a command to combust other fuels is sent from processor 91 to supply system 15. As a result, primary air supply system 110 and secondary air supply system 120 each supply air. At this time, ammonia supply system 100 is in a supply stop state, and oil supply system 80 and pulverized coal supply system 70 are both in a supply state. Therefore, oil and pulverized coal are supplied to burner unit 30. At this time, ammonia burner 50 of first burner unit 31 is stopped, and ammonia burners 50 of second burner unit 32 and third burner unit 33 inject oil. After that, in response to the determination condition being satisfied, processor 91 sends an ammonia supply start command to supply system 15. Oil supply system 80 changes to a supply stop state, and ammonia supply system 100 changes to a supply state. As a result, first burner unit 31 injects liquid ammonia, and the fuel injected from second burner unit 32 and third burner unit 33 is switched from oil to liquid ammonia. Pulverized coal supply system 70 maintains the supply state. As a result, ammonia and pulverized coal are mixed and burned in boiler 2. After that, in response to the ammonia combustion conditions being satisfied, the control device 5 sends an ammonia combustion command to the supply system 15. The pulverized coal supply system 70 changes to a supply stop state, and the fuel burner 35, which had been functioning as a coal burner, stops. In addition, the ammonia supply system 100 increases the amount of liquid ammonia supplied. As a result, ammonia combustion is performed in the boiler 2. In another embodiment, the supply system 15 that has received the other fuel combustion command from the processor 91 may first supply oil to the burner unit 30, and then supply oil and pulverized coal to the burner unit 30. After the ammonia supply start command is sent to the supply system 15, mixed combustion of ammonia fuel and oil may be performed, or mixed combustion of ammonia fuel, pulverized coal, and oil may be performed.

[0038] 6 is a flowchart showing a boiler operation control process according to one embodiment. The boiler operation control process is started, for example, when an operator of the boiler operation system 1 inputs a start instruction.

[0039] In the boiler operation control process, first, the processor 91 generates an other fuel combustion command (S51). In one embodiment, the processor 91 executes S51 when the load on the boiler 2 increases (for example, when the boiler 2 is started). The generated other fuel combustion command is sent to the supply system 15, thereby starting combustion using a carbon-containing fuel, which is an example of a fuel other than ammonia fuel. As a specific example, the supply system 15 and the burner unit 30 operate as described above, and combustion using oil and a carbon-containing fuel is started. The processor 91 that executes S51 is an example of an other fuel combustion command unit that generates an other fuel combustion command for burning another fuel (carbon-containing fuel in this example) in the furnace 20.

[0040] Next, the processor 91 determines whether the determination condition is met based on the measurement result of the measurement system 9 (S53). The processor 91 that executes S53 is an example of a determination unit that determines whether or not the determination condition is satisfied. The determination conditions in one embodiment include the following conditions (A) to (C), and when all of (A) to (C) are satisfied, the processor 91 determines that the determination conditions are satisfied. (A) The air ratio, which is the ratio of the amount of air supplied to the furnace 20 to the theoretical amount of air required to combust the other fuel (carbon-containing fuel in this example), is 0.8 or less. (B) The nose temperature, which is the representative temperature inside the furnace 20, is 1120°C or higher. (C) The residence time of other fuels in the furnace 20 is 0.5 seconds or more. Whether or not condition (A) is satisfied is determined based on equations (1) to (3) and the measurement results of the measurement system 9. Whether or not condition (B) is satisfied is determined based on the measurement results of the furnace thermometer 6. Whether or not condition (C) is satisfied is determined based on the measurement results of the measurement system 9. The processor 91 waits until the determination condition is satisfied (S53: NO). In one embodiment, during the period when the load on the boiler 2 increases and until the determination condition is satisfied, other combustion occurs in the furnace 20. In another embodiment, the upper limit of the air ratio specified by condition (A) may be 0.7.

[0041] When it is determined that the determination condition is satisfied (S53: YES), the processor 91 generates an ammonia supply start command (S55). The generated ammonia supply start command is sent to the supply system 15. At this time, the supply system 15 and the burner unit 30 operate as described above. The processor 91 that executes S55 is an example of an ammonia supply command generating unit configured to generate an ammonia supply start command for causing the supply system 15 to start supplying ammonia fuel to the furnace 20. In one embodiment, the ammonia co-firing ratio (calorific value) in the boiler 2 is 20% or more and 50% or less. In addition, the burner air ratio in the furnace 20 at this time is 0.7 or less.

[0042] Subsequently, the processor 91 determines whether or not an ammonia combustion condition for performing ammonia combustion in the boiler 2 is satisfied (S57). In one embodiment, the ammonia combustion condition is, for example, that a certain time has elapsed since the start of S53. The processor 91 waits until the ammonia mono-combustion condition is satisfied (S57: NO). During this time, ammonia is mixed with other fuel and combusted in the boiler 2.

[0043] If it is determined that the ammonia combustion condition is satisfied (S57: YES), the processor 91 generates an ammonia combustion command. The generated ammonia combustion command is sent to the supply system 15. The supply system 15 and the burner unit 30 operate as described above, and ammonia combustion is performed. In one embodiment, the burner air ratio during ammonia combustion is 0.9 or less, which makes it possible to suppress the amounts of carbon dioxide and NOx emitted during ammonia combustion.

[0044] (summary) Below, an overview will be given of a method for operating a boiler 2 and a control device 5 for a boiler according to some embodiments.

[0045] (1) At least one embodiment of the present invention relates to a method for operating a boiler (2), Steps (S11, S51) of burning fuel other than ammonia fuel in a furnace (20); a step (S13, S53) of determining whether or not a determination condition is satisfied that an air ratio (burner air ratio), which is a ratio of an amount of air supplied to the furnace (20) to a theoretical amount of air required for combusting the other fuel supplied to the furnace (20), is equal to or less than an upper limit value and a representative temperature in the furnace (20) is equal to or greater than a lower limit value; Steps (S15, S55) of starting the supply of the ammonia fuel to the furnace (20) when at least the determination condition is satisfied; Equipped with The upper limit of the air ratio constituting the determination condition is 0.8 or less.

[0046] According to the findings of the inventors, it has been found that when ammonia is burned in the furnace (20) under the condition that the air ratio (burner section air ratio) constituting the determination condition is 0.8 or less, the amount of NOx generated in the furnace (20) is effectively reduced. It has also been found that thermal decomposition of ammonia in the furnace (20) is necessary to suppress the generation of NOx, and that this thermal decomposition is promoted when the gas temperature in the furnace (20) is equal to or higher than a certain temperature. The representative temperature in the furnace (20) correlates with the gas temperature in the furnace (20). The configuration of (1) above realizes a method for operating a boiler (2) that starts the supply of ammonia fuel under conditions that can suppress the generation of NOx.

[0047] (2) In some embodiments, in the configuration of (1), When the heat load of the boiler (2) increases, the other fuel is combusted until the determination condition is satisfied (S13: NO, S53: NO), and after the determination condition is satisfied, the supply of the ammonia fuel to the furnace (20) is started.

[0048] According to the findings of the inventors, when the heat load of the boiler (2) increases, the gas temperature in the furnace (20) is relatively low, and it has been found that if ammonia fuel is supplied to the furnace (20) at this time, excessive NOx is generated. In this regard, according to the configuration (2), when the load of the boiler (2) increases, the supply of ammonia fuel is not started until the determination condition is satisfied, and therefore, the amount of NOx emissions can be suppressed.

[0049] (3) In some embodiments, in the configuration of (1) or (2), The upper limit of the air ratio constituting the determination condition is 0.7 or less.

[0050] According to the findings of the inventors, it has been found that when the burner air ratio is 0.7 or less, the proportion of oxygen in the furnace (20) is reduced, and the amount of NOx generated when ammonia fuel is supplied into the furnace (20) is reduced. It has also been found that when the burner air ratio is 0.7 or less, the reduction reaction between ammonia and NOx in the furnace (20) is promoted, and the amount of NOx emissions is reduced. Therefore, the configuration (3) above can suppress the amount of NOx emissions.

[0051] (4) In some embodiments, in any of the configurations (1) to (3), The lower limit of the nose temperature of the furnace (20) as the representative temperature constituting the judgment condition is 1120°C or higher.

[0052] According to the findings of the inventors, when the gas temperature in the furnace (20) is 1400°C or higher, it has been found that the thermal decomposition of ammonia is sufficiently carried out in a relatively short residence time in the furnace. Furthermore, it has been found that when the nose temperature is 1120°C or higher, the gas temperature reaches 1400°C or higher. According to the configuration (4) above, when the nose temperature reaches 1120°C or higher, the supply of ammonia fuel starts, thereby suppressing NOx emissions.

[0053] (5) In some embodiments, in any of the configurations (1) to (4) above, The determination condition is that the residence time of the other fuel in the furnace (20) from when it is charged into the furnace (20) until it reaches the nose (11) of the furnace (20) is 0.5 seconds or more.

[0054] According to the findings of the inventors, it has been found that if the residence time of ammonia in the furnace is 0.5 seconds or more, 80 percent or more of the ammonia fuel fed into the furnace (20) is thermally decomposed. According to the configuration of (5) above, the supply of ammonia fuel is started when the residence time of other fuels in the furnace is 0.5 seconds or more, so that the residence time of ammonia in the furnace at the start of combustion can also be 0.5 seconds or more. This makes it possible to suppress NOx emissions.

[0055] (6) In some embodiments, in any of the configurations (1) to (5) above, In the furnace (20), the mixed combustion ratio of the supplied ammonia fuel and the other fuel is 20% or more in terms of heat amount.

[0056] According to the findings of the inventors, when the mixed combustion ratio of ammonia and other fuel is 20% or more, the amount of NOx generated in the furnace (20) is likely to increase. Therefore, it is significant to reduce the amount of NOx generated under the condition where the mixed combustion ratio is 20% or more. According to the configuration of (6), the determination condition is satisfied before combustion with a mixed combustion ratio of 20% or more is started. Therefore, even when the mixed combustion ratio is 20% or more, the amount of NOx generated can be reduced.

[0057] (7) In some embodiments, in any of the configurations (1) to (6) above, In the step (S15, S55) of starting the supply of ammonia fuel, the supply of the ammonia fuel is started so that the ammonia mixed combustion ratio is 50% or less in terms of heat amount and the air ratio in the furnace (20) is 0.7 or less; The method includes a step (S59) of performing mono-combustion of the ammonia fuel so that the air ratio in the furnace (20) becomes 0.9 or less after starting the supply of the ammonia fuel.

[0058] According to the findings of the inventors, when ammonia co-firing is performed under conditions where the co-firing ratio in terms of calorific value is 50% or less and the burner air ratio is 0.7 or less, NOx emissions are reduced. Furthermore, according to the findings of the inventors, ammonia mono-firing under conditions where the burner air ratio is 0.9 or less can further reduce NOx emissions. According to the configuration (7) above, ammonia co-firing and ammonia mono-firing can be performed sequentially while reducing NOx emissions. Furthermore, mono-firing of ammonia can suppress carbon dioxide emissions. Furthermore, by setting the burner air ratio at 0.7 or less during ammonia co-firing, it is possible to prioritize suppressing an increase in NOx emissions over suppressing an increase in the amount of unburned ammonia produced, and therefore, it is possible to effectively suppress NOx emissions even during ammonia co-firing.

[0059] (8) At least one embodiment of the boiler control device (5) according to the present invention comprises: 1. A control device for a boiler (2) having a furnace (20) and a supply system configured to supply ammonia fuel and other fuels into the furnace (20), comprising: a combustion command generating unit (91) that generates an other fuel combustion command for burning the other fuel in the furnace (20); a determination unit (91) for determining whether or not a determination condition is satisfied, the determination condition being that an air ratio, which is a ratio of an amount of air supplied to the furnace (20) to a theoretical amount of air required for combusting the other fuel supplied to the furnace (20), is equal to or less than an upper limit value, and a representative temperature in the furnace (20) is equal to or greater than a lower limit value; an ammonia supply command generation unit (91) configured to generate an ammonia supply start command to cause the supply system to start supplying the ammonia fuel to the furnace (20) when the determination unit determines that at least the determination condition is satisfied (YES in S53); Equipped with The upper limit of the air ratio constituting the determination condition is 0.8 or less.

[0060] According to the configuration (8), for the same reason as in the configuration (1), a boiler control device (5) is realized that starts the supply of ammonia fuel under conditions that can suppress the generation of NOx.

[0061] Example 1 The results of identifying the relationship between the burner air ratio and the amount of NOx emissions through a combustion test will be described with reference to Fig. 7. Fig. 7 is a graph showing the relationship between the burner air ratio and the amount of NOx emissions. The combustion tests were conducted in a vertical drop tube furnace (DTF) and a single burner test furnace. The combustion tests conducted in the DTF included mono-combustion of ammonia, co-combustion of ammonia and pulverized coal, and mono-combustion of pulverized coal. The co-combustion ratio for ammonia co-combustion was 25% or 50% in terms of heat value. The combustion tests conducted in the single burner test furnace were mono-combustion of pulverized coal.

[0062] First, we examine the relationship between the burner air ratio and NOx emissions during ammonia combustion. As shown in Figure 7, NOx emissions from ammonia combustion with a burner air ratio of 1.0 are more than six times higher than those from pulverized coal combustion in a DTF or single-burner test furnace. On the other hand, NOx emissions from ammonia combustion with a burner air ratio of 0.9 or less were found to be lower than those from pulverized coal combustion. In particular, NOx emissions from ammonia combustion with a burner air ratio of 0.8 were found to be the lowest in this combustion test. Furthermore, NOx emissions from ammonia combustion with a burner air ratio of less than 0.8 are predicted to be lower than those from a burner air ratio of 0.8. This is because the lower the burner air ratio, the less oxygen is available for combustion in the combustion space 7. As a result, the thermal decomposition of ammonia gas is promoted over the oxidation of nitrogen, and the reduction of NOx is also promoted (a similar trend is expected to emerge when ammonia co-firing or ammonia combustion is performed). From the above considerations, it can be seen that in order to reduce NOx emissions in ammonia mono-combustion, the upper limit of the burner air ratio is preferably 0.9 or less, more preferably 0.8 or less, and even more preferably 0.7 or less. When operating a boiler 2 having a typical size used in thermal power generation, it is not realistic for the burner air ratio to be less than 0.6 (this also applies when ammonia co-firing or pulverized coal mono-combustion is performed). Therefore, the lower limit of the burner air ratio is 0.6 or more.

[0063] Next, we will examine the relationship between the burner air ratio and NOx emissions during ammonia co-firing. As shown in Figure 7, ammonia co-firing with a burner air ratio of 0.8 (co-firing ratios: 25% and 50%) results in higher NOx emissions compared to pulverized coal mono-firing. However, it was found that these emissions are significantly lower than those during ammonia mono-firing with a burner air ratio of 1.0. Furthermore, it was found that ammonia co-firing with a burner air ratio of 0.7 or less (co-firing ratio: 50%) results in lower NOx emissions compared to those during pulverized coal mono-firing with a burner air ratio of 0.8. NOx emissions during ammonia co-firing with a burner air ratio of 0.7 (co-firing ratio: 25%) have not been measured. However, it can be predicted that NOx emissions will be lower when the ammonia co-firing ratio is 25% than when it is 50%. This is because the lower the ammonia co-firing ratio, the less ammonia fuel, which generates NOx, is supplied to the furnace 20. Therefore, in order to reduce NOx emissions, it is clear that the upper limit of the burner air ratio during ammonia co-firing is preferably 0.8 or less, and more preferably 0.7 or less. Also, as mentioned above, the lower limit of the burner air ratio during ammonia co-firing is 0.6 or more.

[0064] Example 2 Next, with reference to FIGS. 8 and 9, the relationship between the representative temperature inside the furnace 20, the residence time of ammonia inside the furnace, and the amount of NOx emissions will be described. Figure 8 is a graph showing the relationship between gas temperature and the required residence time of ammonia. The gas temperature is an example of a representative temperature inside the furnace 20. The required residence time is the residence time inside the furnace that is required for 80% of the ammonia fuel supplied into the furnace 20 to be thermally decomposed in the combustion space 7. The thermal decomposition of ammonia is expressed by the following (chemical formula A). 2NH3→N2+3H2...(chemical formula A) As the proportion of ammonia that thermally decomposes increases, the proportion of ammonia that converts to NOx decreases, resulting in a reduction in NOx emissions. In the graph shown in FIG. 8, the required residence time is 0.741 seconds when the gas temperature is 1400°C, 0.569 seconds when the gas temperature is 1500°C, and 0.452 seconds when the gas temperature is 1600°C. As can be seen from Figure 8, when the gas temperature is 1400°C or higher, 80% of the ammonia fuel is thermally decomposed in the furnace 20 even if the required residence time is less than 1 second. On the other hand, when the gas temperature is 1300°C, the required residence time is predicted to be 2 seconds or more, and particularly when the gas temperature is 1200°C, the required residence time is approximately 10 seconds. Even if the boiler 2 is operated under such conditions, it is understood that it will be difficult to thermally decompose 80% of the ammonia fuel. From the above, it can be seen that in order for 80% of the ammonia fuel supplied to the furnace 20 to be thermally decomposed in the combustion space 7, it is preferable that the gas temperature be 1400° C. or higher. The required residence time shown in Fig. 8 is a calculated value. In a boiler 2 having a typical size used in a thermal power plant, the gas temperature is actually sufficiently higher than 1200°C even when the boiler load is extremely small.

[0065] Figure 9 is a graph showing the relationship between nose temperature and gas temperature in the burner section. It can be seen that when the gas temperature is 1400°C, the nose temperature is 1113°C. Therefore, if the nose temperature is 1120°C or higher, the gas temperature will be 1400°C or higher, and NOx emissions will be reduced.

[0066] Example 3 The relationship between the ammonia co-firing ratio and NOx emissions will be described with reference to Fig. 10. Fig. 10 is a graph showing the relationship between the ammonia co-firing ratio and NOx emissions. The graph shown in Fig. 10 shows NOx emissions when the ammonia co-firing ratios are 0%, 25%, 50%, and 100% under the same combustion conditions of boiler 2. Note that the ammonia co-firing ratios shown in the graph of Fig. 10 are ratios converted into heat amounts, and an ammonia co-firing ratio of 100% is synonymous with mono-fuel combustion of ammonia. As can be seen from Figure 10, when the ammonia co-firing ratio exceeds 20%, NOx emissions increase. Therefore, it is clear that reducing NOx emissions is highly significant when the ammonia co-firing ratio exceeds 20%. It is also clear that when the ammonia co-firing ratio is 50%, NOx emissions increase significantly. Therefore, it is clear that reducing NOx emissions is highly significant when the ammonia co-firing ratio is between 20% and 50%.

[0067] The above describes an embodiment of the present invention, but the present invention is not limited to the above-described embodiment, and also includes forms in which the above-described embodiment is modified, or forms in which these forms are appropriately combined.

[0068] In this specification, expressions expressing relative or absolute arrangement such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial" not only express such an arrangement strictly, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. For example, expressions such as "identical," "equal," and "homogeneous" that indicate that something is in an equal state not only indicate a state of strict equality, but also indicate a state in which there is a tolerance or a difference to the extent that the same function is obtained. Furthermore, in this specification, expressions representing shapes such as a rectangular shape or a cylindrical shape not only represent rectangular shapes or cylindrical shapes in the strict geometric sense, but also represent shapes including uneven portions, chamfered portions, etc., to the extent that the same effect can be obtained. Furthermore, in this specification, the expressions "comprise," "include," or "have" a component are not exclusive expressions that exclude the presence of other components. [Explanation of symbols]

[0069] 2: Boiler 5: Control device 11: Nose 15: Supply system 20: Furnace 91: Processor

Claims

1. burning a fuel other than ammonia fuel in a furnace; a step of determining whether a determination condition is satisfied that an air ratio, which is a ratio of an amount of air supplied to the furnace to a theoretical amount of air required to combust the other fuel supplied to the furnace, is equal to or less than an upper limit value, and a representative temperature in the furnace is equal to or greater than a lower limit value; starting the supply of the ammonia fuel to the furnace when at least the determination condition is satisfied; Equipped with the upper limit of the air ratio constituting the determination condition is 0.8 or less, In the step of starting the supply of the ammonia fuel, the ammonia fuel is injected into the furnace in a liquid state. How to operate a boiler.

2. When the heat load of the boiler increases, the other fuel is burned for a period until the determination condition is satisfied, and after the determination condition is satisfied, the supply of the ammonia fuel to the furnace is started. A method for operating a boiler according to claim 1.

3. The upper limit of the air ratio constituting the judgment condition is 0.7 or less. A method for operating a boiler according to claim 1 or 2.

4. The lower limit of the nose temperature of the furnace as the representative temperature constituting the judgment condition is 1120°C or higher. A method for operating a boiler according to any one of claims 1 to 3.

5. A method of burning a fuel other than ammonia fuel in a furnace; a step of determining whether a determination condition is satisfied that an air ratio, which is a ratio of an amount of air supplied to the furnace to a theoretical amount of air required to combust the other fuel supplied to the furnace, is equal to or less than an upper limit value, and a representative temperature in the furnace is equal to or greater than a lower limit value; starting the supply of the ammonia fuel to the furnace when at least the determination condition is satisfied; Equipped with the upper limit of the air ratio constituting the determination condition is 0.8 or less, The determination condition is that the residence time of the other fuel in the furnace from when it is charged into the furnace until it reaches the nose of the furnace is 0.5 seconds or more. How to operate a boiler.

6. 6. The boiler operating method according to claim 1, wherein a mixed combustion ratio of the supplied ammonia fuel and the other fuel in the furnace is 20% or more in terms of calorific value.

7. A method of burning a fuel other than ammonia fuel in a furnace; a step of determining whether a determination condition is satisfied that an air ratio, which is a ratio of an amount of air supplied to the furnace to a theoretical amount of air required to combust the other fuel supplied to the furnace, is equal to or less than an upper limit value, and a representative temperature in the furnace is equal to or greater than a lower limit value; starting the supply of the ammonia fuel to the furnace when at least the determination condition is satisfied; Equipped with the upper limit of the air ratio constituting the determination condition is 0.8 or less, In the step of starting the supply of ammonia fuel, the supply of the ammonia fuel is started so that an ammonia co-firing ratio is 50% or less in terms of heat amount and the air ratio in the furnace is 0.7 or less; A boiler operation method comprising: after starting the supply of the ammonia fuel, performing mono-combustion of the ammonia fuel so that the air ratio in the furnace is 0.9 or less.

8. 1. A control device for a boiler having a furnace and a supply system configured to supply ammonia fuel and other fuels into the furnace, comprising: a combustion command generating unit that generates an other fuel combustion command for burning the other fuel in the furnace; a determination unit for determining whether the following determination conditions are satisfied: an air ratio, which is a ratio of the amount of air supplied to the furnace to the theoretical amount of air required to combust the other fuel supplied to the furnace, is equal to or less than an upper limit value; a representative temperature in the furnace is equal to or greater than a lower limit value; and the residence time of the other fuel in the furnace from when it is introduced into the furnace until it reaches the nose of the furnace is 0.5 seconds or more; an ammonia supply command generation unit configured to generate an ammonia supply start command to cause the supply system to start supplying the ammonia fuel to the furnace when the determination unit determines that at least the determination condition is satisfied; Equipped with The upper limit of the air ratio constituting the judgment condition is 0.8 or less. Control device for boiler.

Images