JP7661602B2 - Ammonia fuel boiler - Google Patents

Description

This disclosure relates to an ammonia-fueled boiler.

Conventionally, boilers are known in which ammonia is supplied as fuel into the furnace. 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 burner stages, thereby suppressing the emission of NOx.

JP 2020-112280 A

According to the inventors' findings, 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.

The objective of this disclosure is to provide an ammonia-fueled boiler that can suppress the generation of NOx.

At least one embodiment of the ammonia-fueled boiler of the present invention comprises:
a furnace including a furnace wall;
A burner unit provided on the furnace wall;
a supply system for supplying fuel to the burner unit;
The burner unit includes:
a fuel burner for injecting a carbon-containing fuel into the furnace;
an ammonia burner including an ammonia supply passage configured to supply liquid ammonia, and an ammonia injection nozzle configured to inject the liquid ammonia supplied from the ammonia supply passage into the furnace while it is in a liquid state,
The supply system supplies the liquid ammonia to the burner unit together with the carbon-containing fuel as fuel, and the liquid ammonia is injected from the ammonia injection nozzle into the furnace in which combustion using the carbon-containing fuel is performed, thereby co-combusting the carbon-containing fuel and ammonia.

This disclosure provides an ammonia-fueled boiler that can suppress the generation of NOx.

FIG. 1 is a conceptual diagram of a boiler operation system according to one embodiment. 4 is a flowchart illustrating a method of operating a boiler according to one embodiment. FIG. 1 is a cross-sectional view showing a configuration of an ammonia burner according to one embodiment. FIG. 2 is an explanatory diagram of a specific configuration of a burner unit according to one embodiment. 1 illustrates a specific configuration of a boiler operation system according to an embodiment. 4 is a flowchart showing a boiler operation control process according to one embodiment. 4 is a graph showing a relationship between a burner section air ratio and NOx emissions according to one embodiment. 1 is a graph showing the relationship between gas temperature and required residence time of ammonia according to one embodiment. 4 is a graph showing the relationship between nose temperature and gas temperature of a burner section according to one embodiment. 1 is a graph showing a relationship between an ammonia co-firing ratio in terms of heat amount and NOx emissions according to one embodiment.

Below, several embodiments of the present invention will be described with reference to the attached drawings. However, the dimensions, materials, shapes, relative positions, etc. of the components described as the embodiments or shown in the drawings are not intended to limit the scope of the present invention and are merely illustrative examples.

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 that is 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. In the following, an embodiment in which the ammonia fuel is liquid ammonia is illustrated. 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 in the boiler 2.
Furthermore, the fuel supplied from the supply system 15 to the boiler 2 includes fuel other than ammonia fuel. For example, in the boiler 2, after combustion using other fuel is performed, 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 is exemplified.

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 the fuel injected by the burner unit 30 reacts with the combustion air and is burned, and can have various shapes, for example, a cylindrical shape or a square prism shape.
Moreover, 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 flow appropriately to a flow path on the downstream side of the furnace 20. The flow path on the downstream side of the furnace 20 is, for example, a flue 8.
At least one burner unit 30 is configured to burn 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 may be referred to as a first burner unit 31, a second burner unit 32, and a third burner unit 33 in order from the downstream side in the gas flow direction, and these three stages of burners may be collectively referred to as a burner unit 30. The burner units 30 may be arranged in two or four stages, for example.
The boiler 2 in one embodiment is a swirl combustion boiler, and a plurality of burner units 30 provided in each stage are disposed 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 Fig. 1 illustrates only one burner unit 30 in each stage. 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 firing boiler. In this case, at least a pair of burner units 30 are provided in each stage at positions opposed to each other.

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 a liquid state 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 liquid ammonia together with (or instead of) the carbon-containing fuel after injecting 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.

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.
In one embodiment, the supply system 15 is configured to supply secondary air (additional air) via a supply 4 provided in the furnace wall 19 downstream of the burner unit 30 .

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 in the furnace 20. The representative temperature in the furnace 20 is a temperature that correlates with the gas temperature, which is the temperature of the gas in the combustion space 7 of the furnace 20. As an example, the representative temperature in 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 in the furnace 20 may be, for example, the gas temperature.

The boiler operation system 1 may be operated by operation by an operator, or may be operated under the control of a control device 5 (see FIG. 5 ) described below, 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) is combusted, and the ammonia fuel may be mixed and combusted with the other fuel.

In one embodiment, a judgment condition is used as a condition for starting the supply of ammonia fuel. The judgment 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 above-mentioned air ratio constituting the judgment 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 above-mentioned amount of air supplied to the furnace 20 does not include secondary air (additional air). In other words, in this example, the air ratio constituting the judgment condition is also a value obtained by multiplying the total air ratio by the supply ratio of air other than secondary air to the total air supplied to the furnace 20. Specifically, the air ratio constituting the judgment condition (hereinafter, sometimes referred to as the burner air ratio) is defined by the following formula (1).
λ _b =λ×(100-AA)/100...Formula (1)
In formula (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 the boiler 2.
In addition, the total air ratio (λ) is defined by equations (2), (3), and (4).
λ=Q _Air /Q _x ...Formula (2)
Q _x =Q _mf ×A _mf ...Formula (3)
A _mf = (100-X)/100×A _car +X/100×A _NH3 ...Formula (4)
In formulas (2) to (4), Q _Air is the total air supply amount. Q _mf is the supply amount of ammonia fuel and other fuel (carbon-containing fuel in this example) when the combustion performed in the furnace 20 is ammonia co-combustion (co-combustion rate in weight conversion: X%). Q _x is the air flow rate for the air ratio to be 1 during the co-combustion. _{A mf} is the theoretical air amount of the fuel (ammonia fuel and carbon-containing fuel in this example) when the co-combustion is performed, A _car is the theoretical air amount of the carbon-containing fuel, and A _NH3 is the theoretical air amount of the ammonia fuel.
Formulas (1) to (3) are also applicable to the mixed combustion of ammonia fuel and carbon-containing fuel. To obtain the air ratio constituting the judgment condition (i.e., the burner section air ratio before the start of the supply of ammonia fuel), X and A _NH3 are each set to 0, and Q _mf is set to the supply amount of only the carbon-containing fuel, and formulas (1) to (3) are applied. In the following, λ _b defined by formula (1) may be referred to as the burner section air ratio, not only before the start of the supply of ammonia fuel, but also when ammonia mixed combustion or ammonia mono-combustion is performed.

In one embodiment, the upper limit of the burner 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 air ratio is 0.8 or less, the burner 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 judgment 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.

In one embodiment, the representative temperature in the furnace 20 constituting 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 performed 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, the generation of NOx can be suppressed.
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 of the furnace 20 (a constant value), and the height of the furnace 20 (a constant value). 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.

The judgment conditions in one embodiment 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 was found that if the residence time of ammonia in the furnace is 0.5 seconds or more, the ammonia fuel fed into the furnace 20 is sufficiently thermally decomposed. Since the supply of ammonia fuel is started 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 the ammonia fuel is formed. However, in a boiler 2 having a typical size used in a thermal power plant, the residence time of the 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 constituting 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.

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

In one embodiment of the method for operating the boiler 2, 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 (e.g., when the boiler 2 is started), the supply system 15 supplies the fuel other than ammonia fuel (in this example, a carbon-containing fuel) to the burner unit 30. Note that the load of the boiler 2 is, for example, the heat amount of the steam generated by the boiler 2.

Next, it is determined whether the above-mentioned judgment 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 as the representative temperature in the furnace 20 is 1120° C. or more. Whether the judgment 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 is increased, combustion using another fuel is performed in the furnace 20 until the judgment condition is satisfied (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 is increased, 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 is not started until the judgment condition is satisfied when the load of the boiler 2 is increased, the generation of NOx can be suppressed. Note that when the load of the boiler 2 is increased, this concept includes the time when the thermal load of the boiler (2) increases after decreasing.
In another embodiment, instead of determining whether the burner air ratio is 0.8 or less in S13, it may be determined whether the burner air ratio is 0.7 or less. 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. It may also be determined in S13 whether a condition other than the determination conditions is satisfied.

When 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 heat amount 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 heat amount 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 with a mixed-combustion ratio of 20% or more is performed.
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.

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 passage 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 passage 52 into the furnace 20 while it is in liquid form.
The ammonia burner 50 is a one-fluid nozzle for injecting liquid ammonia in a liquid state without using an assist fluid. More specifically, the ammonia burner 50 is a swirl injection nozzle (swirl atomizer) configured so that the injected liquid ammonia becomes a liquid film that spreads toward the end. Alternatively, the ammonia burner 50 may be a fan spray nozzle configured so that the injected liquid ammonia becomes a sheet-like liquid film, or a plain jet type atomizer configured to inject liquid ammonia in a simple liquid jet state. 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.

The ammonia burner 50 according to one embodiment further comprises 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 that misfire may occur in the furnace 20. In order to avoid misfire, the liquid ammonia needs to be vaporized and further pyrolyzed in the furnace 20. In this regard, the mechanism 60 having the flame-holding effect described above holds the combustion flame, so that the liquid ammonia can obtain heat for vaporization and pyrolysis, thereby suppressing misfire in the furnace 20.

The mechanism 60 having a flame-holding effect according to one embodiment is a swirler type. As a more specific example, the mechanism 60 having a flame-holding effect includes an inner cylinder 62 in which an ammonia injection nozzle 54 is disposed, 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 inside 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 inside 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 to the air supplied from the air supply passage 63A to the furnace 20 by the swirler 65 (arrow B). This promotes mixing of the liquid ammonia injected from the ammonia injection nozzle 54 with the air. 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 include the mechanism 60 having the flame-holding effect.

FIG. 4 is an explanatory diagram of a specific configuration of the burner unit 30 according to one embodiment.
Burner unit 30 shown in FIG. 4 is configured to switch to ammonia mono-fuel combustion after the ammonia co-fuel combustion ratio reaches about 50% in terms of heat amount.
The burner unit 30 is, for example, an existing burner unit. Therefore, some of the 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 burner unit 30 includes five injection means 40. Each injection means 40 is configured to supply fuel or air to the furnace 20. By way of example, each injection means 40 is either the previously mentioned ammonia burner 50, a fuel burner 35 for injecting a carbon-containing fuel, or an air nozzle 42 for injecting primary air.
The first burner unit 31, the second burner unit 32, and the 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 one injection means 40 is not used.
In the example of FIG. 4, all of the fuel burners 35 of the burner units 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 only liquid ammonia, 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.

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 operated, 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 is stopped from the three fuel burners 35 of the burner unit 30, and the fuel injected into the furnace 20 is only liquid ammonia from the three ammonia burners 50. As a result, the combustion in the furnace 20 is switched from ammonia mixed combustion to ammonia exclusive combustion.

5 is a specific configuration of a boiler operation system 1 according to an 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, the supply system 15, and the 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 out 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, a GPU, an MPU, a DSP, various other arithmetic devices, or a combination of these. The processor 91 may be realized by an integrated circuit such as a PLD, an ASIC, an FPGA, and an 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.
The processor 91 in one embodiment 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.
The processor 91 in one embodiment generates an ammonia supply start command when it is determined that the above-mentioned determination conditions are satisfied based on the measurement results of the measurement system 9. The processor 91 in one embodiment also initiates an ammonia mono-combustion command when it is determined that an ammonia mono-combustion condition for starting ammonia mono-combustion is satisfied. The ammonia mono-combustion condition is, for example, that a representative temperature in the furnace 20 has reached a specified temperature, that a specified time has elapsed since ammonia co-combustion was started, that a specified parameter has reached a set value after a specified input operation has been performed by an operator, or a combination of these.

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.
The primary air, liquid ammonia, pulverized coal, and oil are supplied to a burner unit 30, and the 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.

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 adjustment valves 116 , 126 and the switching valves 118 , 128 are configured to operate in response to control commands sent from the control device 5 .

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 adjusting the pressure of 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 adjusting 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 described later, when the ammonia supply system 100 is in a 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.

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 regulating 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 the oil. The oil supply line 82 may also be configured to receive atomized steam. In this case, the oil and atomized steam are supplied to the burner unit 30.

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 regulating valve 76 for regulating the flow rate of the 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 each of the fuel burners 35 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 a control command 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 the pulverized coal is supplied to the burner unit 30. When the pulverized coal supply system 70 is in the supply state, the pulverized coal is supplied to the above-mentioned fuel burner 35 (see FIG. 4 ) functioning as a coal burner.

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 the processor 91. This allows the processor 91 in one embodiment to determine whether a determination condition is met.

The boiler operation system 1 operates, for example, as follows, in response to control commands sent from the processor 91.
First, a command to burn other fuels is sent from the processor 91 to the supply system 15. As a result, the primary air supply system 110 and the secondary air supply system 120 each supply air. At this time, the ammonia supply system 100 is in a supply stop state, and the oil supply system 80 and the pulverized coal supply system 70 are both in a supply state. Therefore, oil and pulverized coal are supplied to the burner unit 30. At this time, the ammonia burner 50 of the first burner unit 31 is stopped, and the ammonia burners 50 of the second burner unit 32 and the third burner unit 33 inject oil.
Thereafter, in response to the determination condition being satisfied, an ammonia supply start command is sent from the processor 91 to the supply system 15. The oil supply system 80 changes to a supply stop state, and the ammonia supply system 100 changes to a supply state. As a result, the first burner unit 31 injects liquid ammonia, and the fuel injected from the second burner unit 32 and the third burner unit 33 is switched from oil to liquid ammonia. The pulverized coal supply system 70 maintains the supply state. As a result, mixed combustion of ammonia and pulverized coal is performed in the boiler 2.
After that, in response to the ammonia combustion condition 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 that 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 an ammonia supply start command is sent to the supply system 15, ammonia fuel and oil may be mixed and burned, or ammonia fuel, pulverized coal, and oil may be mixed and burned.

Figure 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 command.

In the boiler operation control process, first, the processor 91 generates an other fuel combustion command (S51). In one embodiment, when the load of the boiler 2 increases (for example, when the boiler 2 is started), the processor 91 executes S51. The generated other fuel combustion command is sent to the supply system 15, and combustion using a carbon-containing fuel, which is an example of a fuel other than ammonia fuel, is started. 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 a other fuel combustion command for combusting another fuel (in this example, a carbon-containing fuel) in the furnace 20.

Next, the processor 91 determines whether or not the determination condition is satisfied based on the measurement result of the measurement system 9 (S53).
The processor 91 that executes S53 is an example of a determination section that determines whether or not a determination condition is satisfied.
In one embodiment, the judgment conditions include the following conditions (A) to (C), and if all of (A) to (C) are satisfied, the processor 91 judges that the judgment 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 another fuel (in this example, a carbon-containing fuel), is 0.8 or less.
(B) The nose temperature, which is the representative temperature inside the furnace 20, is 1,120° 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 until the determination condition is satisfied when the load of the boiler 2 increases, other combustion is performed in the furnace 20.
In still another embodiment, the upper limit of the air ratio defined by condition (A) may be 0.7.

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 rate (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.

Next, 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-fuel combustion condition is satisfied (S57: NO). During this time, the ammonia is mixed with other fuel and combusted in the boiler 2.

When 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. This makes it possible to suppress the amounts of carbon dioxide and NOx emitted during ammonia combustion.

(summary)
Below, an overview is given of a method for operating a boiler 2 and a control device 5 for a boiler according to several embodiments.

(1) A method for operating a boiler (2) according to at least one embodiment of the present invention includes the steps of:
A step (S11, S51) of burning a 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 lower than an upper limit value, and a representative temperature in the furnace (20) is equal to or higher than a lower limit value;
A step (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 value of the air ratio constituting the judgment condition is 0.8 or less.

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 judgment condition is 0.8 or less, the amount of NOx generated in the furnace (20) is effectively reduced. It has also been found that in order to suppress the generation of NOx, thermal decomposition of ammonia in the furnace (20) is necessary, and this thermal decomposition is promoted when the gas temperature in the furnace (20) is at or above a certain temperature. The representative temperature in the furnace (20) correlates with the gas temperature in the furnace (20). According to the configuration of (1) above, a method of operating a boiler (2) that starts the supply of ammonia fuel under conditions that can suppress the generation of NOx is realized.

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

The inventors have found that when the heat load of the boiler (2) increases, the gas temperature in the furnace (20) is relatively low, and if ammonia fuel is supplied to the furnace (20) at this time, excessive NOx is generated. In this regard, according to the configuration of (2) above, when the load of the boiler (2) increases, the supply of ammonia fuel is not started until the judgment condition is satisfied, so that NOx emissions can be suppressed.

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

According to the findings of the inventors, 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 by supplying ammonia fuel into the furnace (20) is reduced. In addition, when the burner air ratio is 0.7 or less, the reduction reaction between ammonia and NOx in the furnace (20) is promoted, and NOx emissions are reduced. Therefore, according to the above configuration (3), NOx emissions can be suppressed.

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

The inventors have found that when the gas temperature in the furnace (20) is 1400°C or higher, the thermal decomposition of ammonia is sufficient with 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 becomes 1400°C or higher. According to the above configuration (4), when the nose temperature becomes 1120°C or higher, the supply of ammonia fuel begins, thereby suppressing NOx emissions.

(5) In some embodiments, in any one of the configurations (1) to (4) above,
The judgment condition is that the residence time of the other fuel in the furnace 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.

The inventors have 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 begins 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.

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

According to the findings of the inventors, when the ratio of ammonia and other fuels mixed 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 conditions where the ratio of ammonia mixed is 20% or more. According to the configuration of (6) above, the judgment condition is satisfied before combustion with a ratio of 20% or more is started. Therefore, even when the ratio of ammonia mixed is 20% or more, the amount of NOx generated can be reduced.

(7) In some embodiments, in any one of the configurations (1) to (6) above,
In the step (S15, S55) of starting the supply of the 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 further includes a step (S59) of performing mono-combustion of the ammonia fuel so that the air ratio in the furnace (20) is 0.9 or less after starting the supply of the ammonia fuel.

According to the findings of the inventors, when ammonia co-combustion is performed under conditions where the co-combustion ratio in terms of heat amount is 50% or less and the burner air ratio is 0.7 or less, NOx emissions are reduced. Also, according to the findings of the inventors, ammonia mono-combustion under conditions where the burner air ratio is 0.9 or less can further reduce NOx emissions. According to the above configuration (7), ammonia co-combustion and ammonia mono-combustion can be performed in sequence while reducing NOx emissions. Also, by performing ammonia mono-combustion, carbon dioxide emissions can be suppressed.
In addition, by setting the burner air ratio at 0.7 or less during ammonia co-firing, it is possible to prioritize suppression of an increase in NOx emissions over suppression of an increase in the amount of unburned ammonia produced. Therefore, even during ammonia co-firing, NOx emissions can be effectively suppressed.

(8) At least one embodiment of the present invention relates to a boiler control device (5),
A control device for a boiler (2) comprising 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 a 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 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 lower than an upper limit value, and a representative temperature in the furnace (20) is equal to or higher than a lower limit value;
an ammonia supply command generation unit (91) configured to generate an ammonia supply start command for causing 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 (S53: YES);
Equipped with
The upper limit value of the air ratio constituting the judgment condition is 0.8 or less.

The configuration of (8) above, for the same reason as (1) above, realizes a boiler control device (5) that starts the supply of ammonia fuel under conditions that can suppress the generation of NOx.

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.
In this combustion test, a vertical drop tube furnace (DTF) and a single burner test furnace were used. The combustion tests conducted in the DTF were ammonia mono-combustion, ammonia and pulverized coal co-combustion, and pulverized coal mono-combustion. The co-combustion ratio in ammonia co-combustion was 25% or 50% in terms of heat value. The combustion test conducted in the single burner test furnace was pulverized coal mono-combustion.

First, we will consider the relationship between the burner air ratio and NOx emissions during ammonia combustion. As shown in Figure 7, the NOx emissions from ammonia combustion with a burner air ratio of 1.0 are more than six times the NOx emissions from pulverized coal combustion in a DTF or single burner test furnace. On the other hand, it was found that the NOx emissions from ammonia combustion with a burner air ratio of 0.9 or less are lower than those from pulverized coal combustion. In particular, it was found that the NOx emissions from ammonia combustion with a burner air ratio of 0.8 were the lowest in this combustion test. Furthermore, it is predicted that the NOx emissions from ammonia combustion with a burner air ratio of less than 0.8 will be lower than the emissions when the burner air ratio is 0.8. This is because the lower the burner air ratio, the less oxygen is used for combustion in the combustion space 7, and as a result, the thermal decomposition of ammonia gas is promoted rather than the oxidation reaction of nitrogen, and the reduction reaction of NOx is also promoted (it is believed that a similar tendency will appear when ammonia co-firing or ammonia mono-firing is performed). From the above considerations, it can be seen that in order to reduce the amount of NOx emissions from ammonia mono-firing, 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. Note that when a boiler 2 having a typical size used in thermal power generation is operated, 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-firing is performed). Therefore, the lower limit of the burner air ratio is 0.6 or more.

Next, the relationship between the burner air ratio and NOx emissions in ammonia co-firing will be examined. As shown in FIG. 7, in ammonia co-firing with a burner air ratio of 0.8 (co-firing ratios: 25% and 50%), the NOx emissions are higher than in pulverized coal mono-firing, but are significantly lower than in ammonia mono-firing with a burner air ratio of 1.0. In addition, in ammonia co-firing with a burner air ratio of 0.7 or less (co-firing ratio: 50%), the NOx emissions are lower than in pulverized coal mono-firing with a burner air ratio of 0.8. The NOx emissions in 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 the 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 the amount of ammonia fuel supplied to the furnace 20, which is a factor in generating NOx. Therefore, in order to reduce NOx emissions, it is preferable that the upper limit of the burner air ratio during ammonia co-firing is 0.8 or less, and it is even more preferable that it is 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.

Example 2
Next, the relationship between the representative temperature in the furnace 20, the residence time of ammonia in the furnace, and the amount of NOx emissions will be described with reference to Figs.
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 in the furnace 20. The required residence time is the residence time of ammonia fuel in the furnace 20 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 represented by the following (chemical formula A).
2NH ₃ →N ₂ +3H ₂ ... (chemical formula A)
As the proportion of ammonia that undergoes thermal decomposition increases, the proportion of ammonia that is converted to NOx decreases, and therefore NOx emissions decrease.
In the graph shown in FIG. 8, the required residence time when the gas temperature is 1400° C. is 0.741 seconds, when the gas temperature is 1500° C. is 0.569 seconds, and when the gas temperature is 1600° C. is 0.452 seconds.
As can be seen from Fig. 8, if 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. It can be seen that even if the boiler 2 is operated under such conditions, 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 value obtained by calculation. 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 if the boiler load is extremely small.

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 it can be seen that NOx emissions will be reduced.

Example 3
The relationship between the ammonia co-firing ratio and the amount of 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 the amount of NOx emissions. The graph shown in Fig. 10 shows the amount of NOx emissions when the ammonia co-firing ratios are 0%, 25%, 50%, and 100% under the same combustion conditions of the boiler 2. Note that the ammonia co-firing ratio shown in the graph of Fig. 10 is a ratio converted into heat amount, and an ammonia co-firing ratio of 100% is synonymous with mono-combustion of ammonia.
As can be seen from Fig. 10, when the ammonia co-firing ratio exceeds 20%, the amount of NOx emissions increases. Therefore, it is very significant to reduce the amount of NOx emissions in ammonia co-firing with ammonia co-firing ratio exceeding 20%. In addition, it is seen that when the ammonia co-firing ratio is 50%, the amount of NOx emissions increases significantly. Therefore, it is very significant to reduce the amount of NOx emissions in ammonia co-firing with ammonia co-firing ratio between 20% and 50%.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and also includes variations on the above-described embodiments and appropriate combinations of these embodiments.

In this specification, expressions expressing relative or absolute configuration, such as "in a certain direction,""along a certain direction,""parallel,""orthogonal,""center,""concentric," or "coaxial," do not only strictly represent such a configuration, but also represent 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 indicating that things are in an equal state, such as "identical,""equal," and "homogeneous," 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 describing shapes such as a rectangular shape or a cylindrical shape do not only refer to shapes such as a rectangular shape or a cylindrical shape in the strict geometric sense, but also refer to shapes that include uneven portions, chamfered portions, etc., to the extent that the same effect is obtained.
In addition, in this specification, the expressions "comprise,""include," or "have" a certain element are not exclusive expressions that exclude the presence of other elements.

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

Claims (19)

a furnace including a furnace wall;
A burner unit provided on the furnace wall;
a supply system for supplying fuel to the burner unit;
The burner unit includes:
a fuel burner for injecting a carbon-containing fuel into the furnace;
an ammonia burner including an ammonia supply passage configured to supply liquid ammonia, and an ammonia injection nozzle configured to inject the liquid ammonia supplied from the ammonia supply passage into the furnace while it is in a liquid state,
The supply system supplies the liquid ammonia to the burner unit together with the carbon-containing fuel as fuel, and injects the liquid ammonia from the ammonia injection nozzle into the furnace in which combustion using the carbon-containing fuel is performed, thereby achieving co-combustion of the carbon-containing fuel and ammonia in an ammonia-fueled boiler. The ammonia fuel boiler according to claim 1, characterized in that the liquid ammonia is injected from the ammonia injection nozzle into the furnace, where the gas temperature due to combustion using the carbon-containing fuel is 1400°C or higher, and the carbon-containing fuel and ammonia are mixed and combusted. The ammonia fuel boiler according to claim 1 or 2, characterized in that the liquid ammonia is injected from the ammonia injection nozzle into the furnace, the nose temperature of which is 1120°C or higher due to combustion using the carbon-containing fuel, and the carbon-containing fuel and ammonia are mixed and combusted. the ammonia injection nozzle is any one of a swirl injection nozzle configured to inject liquid ammonia in a divergent liquid film, a fan spray nozzle configured to inject liquid ammonia in a sheet-like liquid film, and a plain jet type atomizer configured to inject liquid ammonia in a liquid jet state;
4. The ammonia-fueled boiler according to claim 1, wherein the liquid ammonia injected by the ammonia injection nozzle is vaporized into ammonia gas inside the furnace and combusted. The ammonia fuel boiler according to any one of claims 1 to 4, wherein the ammonia injection nozzle is a one-fluid nozzle for injecting the liquid ammonia in liquid form without using an assist fluid. An ammonia fuel boiler according to any one of claims 1 to 5, wherein the ammonia injection nozzle is a dual-purpose nozzle capable of injecting both start-up fuel and the liquid ammonia. An ammonia-fueled boiler according to any one of claims 1 to 6, wherein the ammonia burner is provided with a mechanism having a flame-holding effect configured to hold the combustion flame generated in the furnace. The mechanism having a flame-holding effect is
an inner cylinder having the ammonia injection nozzle disposed therein;
An outer cylinder is arranged to surround the inner cylinder, and an air supply passage communicating with the inside of the furnace is formed between the outer cylinder and the inner cylinder;
8. The ammonia-fueled boiler according to claim 7, further comprising: a swirler provided in the air supply passage and configured to impart a swirling force to air flowing through the air supply passage. An ammonia-fueled boiler according to any one of claims 1 to 8, wherein the supply system supplies the fuel and primary air to the burner unit. The ammonia-fueled boiler according to claim 9, wherein the burner unit includes an air nozzle for injecting the primary air into the furnace. The supply system includes a supply unit provided on the furnace wall downstream of the burner unit and configured to supply secondary air.
An ammonia-fueled boiler according to any one of claims 1 to 10. An ammonia-fueled boiler according to any one of claims 1 to 11, wherein the carbon-containing fuel is a biomass fuel or a fossil fuel. An ammonia fuel boiler according to any one of claims 1 to 12, characterized in that when the gas temperature resulting from combustion using the carbon-containing fuel reaches 1400°C or higher, the liquid ammonia is injected from the ammonia injection nozzle into the furnace, and the carbon-containing fuel and ammonia are mixed and combusted. An ammonia-fueled boiler according to any one of claims 1 to 13, characterized in that when the nose temperature of the furnace reaches 1120°C or higher due to combustion using the carbon-containing fuel, the liquid ammonia is started to be injected into the furnace from the ammonia injection nozzle, and the carbon-containing fuel and ammonia are mixed and combusted. An ammonia-fueled boiler as described in any one of claims 1 to 14, characterized in that the liquid ammonia injected from the ammonia injection nozzle contains urea. An ammonia-fueled boiler according to any one of claims 1 to 15, comprising a plurality of the burner units. The ammonia-fueled boiler according to claim 16, wherein a plurality of the burner units are arranged along the circumferential direction of the furnace. An ammonia-fueled boiler according to any one of claims 1 to 17, characterized in that the mixed combustion ratio of the liquid ammonia and the carbon-containing fuel in terms of calorific value is 20% or more. The ammonia-fueled boiler according to claim 18, characterized in that the mixed-fuel ratio is 50% or less.

Images