Combustion device

Abstract

The present invention provides a combustion device that can suppress ammonia emissions in a combustion device that burns ammonia fuels such as ammonia and ammonia decomposition gas. [Solution] The combustion apparatus comprises a burner having a main burner for burning ammonia fuel and a sub-burner for burning a first fuel which burns faster than ammonia; an ammonia fuel supply line for supplying the ammonia fuel; an ammonia fuel shut-off valve; an inert gas supply line connected downstream of the ammonia fuel shut-off valve and supplying inert gas to the ammonia fuel supply line; an inert gas shut-off valve; a first fuel supply line for supplying the first fuel to the sub-burner; and a control unit for controlling the combustion of the main burner and the sub-burner. The control unit includes a combustion stop control unit that, when the combustion of the main burner is to be stopped, initiates combustion of the sub-burner, opens the inert gas shut-off valve, and closes the ammonia fuel shut-off valve.

Description

Technical Field

[0001] The present invention relates to a combustion device that burns ammonia fuel containing ammonia.

Background Art

[0002] In recent years, from the perspective of reducing carbon dioxide emissions, the use of ammonia fuel that does not emit carbon dioxide during combustion has been spreading. Among combustion devices that use ammonia fuel, there are also those that decompose ammonia into ammonia decomposition gas consisting of nitrogen and hydrogen, and mix this with combustion air for combustion (see Patent Document 1). In the ammonia decomposition gas, in addition to hydrogen and nitrogen, there is also about several percent of undissociated ammonia.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a combustion device that uses ammonia fuel such as ammonia or ammonia decomposition gas as fuel, when stopping combustion, after stopping the supply of ammonia fuel, in order to discharge the ammonia fuel remaining in the pipe that supplies ammonia fuel, purging is performed with an inert gas or the like. The inert gas discharged by purging contains ammonia fuel, and the discharge of ammonia outside the system is not preferable from the perspective of danger to the human body and the like. The management standard value for ammonia concentration is low, at 1-2 ppm at the site boundary (the boundary between the factory site and the outside). Therefore, diluting the ammonia remaining in the piping to below the management standard value using inert gases requires a large amount of inert gas, making dilution difficult. Although methods such as equipping combustion equipment with abatement equipment to suppress ammonia emissions are known, this leads to increased installation costs for the combustion equipment, which is undesirable.

[0005] The present invention aims to provide a combustion device that can suppress ammonia emissions in a combustion device that burns ammonia fuels such as ammonia or ammonia decomposition gas. [Means for solving the problem]

[0006] The present invention solves the above problem by the following means.

[0007] The present invention relates to a combustion apparatus comprising: a burner having a main burner for burning ammonia fuel, which is a fuel containing ammonia; a sub-burner for burning a first fuel having a faster combustion rate than ammonia; an ammonia fuel supply line connected to the main burner for supplying the ammonia fuel to the burner; an ammonia fuel shut-off valve located in the ammonia fuel supply line for opening and closing the flow path of the ammonia fuel supply line; an inert gas supply line connected downstream of the ammonia fuel shut-off valve for supplying an inert gas to the ammonia fuel supply line; an inert gas shut-off valve located in the inert gas supply line for opening and closing the flow path of the inert gas; a first fuel supply line for supplying the first fuel to the sub-burner; and a control unit for controlling the combustion of the main burner and the sub-burner, wherein the control unit includes a combustion stop control unit that, when the combustion of the main burner is to be stopped, initiates combustion of the sub-burner, opens the inert gas shut-off valve, and closes the ammonia fuel shut-off valve.

[0008] Furthermore, it is preferable that the main burner comprises an ammonia fuel flow path pipe arranged around the sub-burner and forming a flow path for the ammonia fuel, and an ammonia fuel injection section arranged at the tip of the ammonia fuel flow path pipe and for injecting the ammonia fuel.

[0009] Furthermore, it is preferable that the main burner comprises an ammonia fuel flow path pipe that forms a flow path for the ammonia fuel, and an ammonia fuel injection unit located at the tip of the ammonia fuel flow path pipe that injects the ammonia fuel into the flame of the sub-burner.

[0010] Furthermore, it is preferable that the combustion apparatus includes an air supply line for supplying combustion air to the burner, a main burner air supply line located downstream of the air supply line for supplying combustion air to the main burner, and a sub-burner air supply line branching off from the air supply line for supplying combustion air to the sub-burner.

[0011] Furthermore, it is preferable that the combustion stop control unit starts combustion of the sub-burner, opens the inert gas shutoff valve, and then closes the ammonia fuel shutoff valve.

[0012] Furthermore, the combustion apparatus includes a main burner air supply line that supplies combustion air to the main burner, and an air flow rate adjustment unit that adjusts the flow rate of the combustion air in the main burner air supply line. Preferably, when the combustion stop control unit stops the combustion of the burner, it continues to supply the combustion air at a first air flow rate for a predetermined time, and then controls the air flow rate adjustment unit to set the flow rate to a second air flow rate that is different from the first air flow rate.

[0013] Furthermore, the inert gas supply line is equipped with an inert gas flow rate control valve for adjusting the flow rate of the inert gas, and the combustion stop control unit preferably adjusts the opening degree of the inert gas flow rate control valve so that the flow rate of the inert gas is in the range of 70 to 130% of the flow rate of the ammonia fuel at the time of receiving the combustion stop signal or immediately before receiving the combustion stop signal.

[0014] Furthermore, the inert gas supply line is preferably equipped with an inert gas flow rate control valve for adjusting the flow rate of the inert gas, and the combustion stop control unit preferably adjusts the opening degree of the inert gas flow rate control valve so that the amount of inert gas supplied is within a range in which hydrogen can be combusted. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a combustion device that can suppress the emission of ammonia in a combustion device that burns ammonia fuel such as ammonia or ammonia decomposition gas. [Brief explanation of the drawing]

[0016] [Figure 1] This is a diagram illustrating the configuration of a combustion device and a boiler equipped therewith according to an embodiment. [Figure 2] This is a diagram illustrating the shape of the burner in the embodiment. [Figure 3] This figure shows the relationship between the volume concentrations of hydrogen, nitrogen, and air and combustion when ammonia fuel is used as ammonia decomposition gas and nitrogen is used as the inert gas. [Modes for carrying out the invention]

[0017] Embodiments of the present invention will be described below with reference to the drawings and other figures. Note that the following figures, including Figure 1, are schematic representations, and the size and shape of each part have been exaggerated as appropriate for ease of understanding.

[0018] (Embodiment) Figure 1 is a diagram illustrating the configuration of the combustion device 10 and the boiler 1 equipped therewith according to this embodiment. The combustion device 10 of this embodiment is a combustion device that burns ammonia fuel F1 in the main burner 22 of the burner 21, and is applied to the boiler 1. However, the combustion device 10 is not limited to the boiler 1, and may also be applied to industrial furnaces, etc. As shown in FIG. 1, the combustion device 10 includes a burner 21, a control unit 70, an ammonia fuel supply line L100, an inert gas supply line L200, a first fuel supply line L300, an air supply line L400 (main burner air supply line L410, sub - burner air supply line L420), and an exhaust line (not shown). The boiler 1 includes the combustion device 10, a can body 20, a water supply line (not shown), a steam supply line (not shown), and the like. Note that the "line" in this specification is a general term for a flow path, a route, a pipeline, etc.

[0019] The ammonia fuel F1 is a fuel containing ammonia. In this specification and the claims, in addition to those consisting only of ammonia, it also includes a mixed gas mainly composed of ammonia, an ammonia decomposition gas generated by decomposing ammonia, and the like. In this embodiment, an example of using an ammonia decomposition gas as the ammonia fuel F1 will be described. This ammonia decomposition gas contains hydrogen, nitrogen, and about several percent of undissociated ammonia.

[0020] The can body 20 includes a lower header, a plurality of water pipes, an upper header (both not shown), a combustion chamber 25, etc., and heats the water supplied to the can body 20 to generate steam. The burner 21 is disposed above the can body 20. The burner 21 includes a main burner 22 and a sub - burner 23, a window box 24, a main flame detection unit and a sub - flame detection unit (not shown). The main burner 22 burns the ammonia fuel F1 in the combustion chamber 25 of the can body 20. For ease of understanding, in FIG. 1, the flame - holding part and the like of each burner are omitted.

[0021] The main burner 22 is a burner that burns the ammonia fuel F1 as fuel. The sub-burner 23 is a burner that burns the first fuel F2. In this embodiment, the sub-burner 23 and the main burner 22 share the same fuel discharge direction axis, and the sub-burner 23 is positioned inside the main burner 22. Furthermore, the sub-burner 23 in this embodiment has the function of a pilot burner that ignites the main burner 22, and the function of a decontamination burner that burns the ammonia fuel F1 remaining in the piping when the main burner 22 stops burning.

[0022] Figure 2 illustrates the shape of the burner 21 in this embodiment. In this embodiment, the burner 21 is configured such that the sub-burner 23 is located inside the main burner 22, as described above. The main burner 22 includes an ammonia fuel flow path pipe 221, an ammonia fuel injection section 222, and a combustion air flow path pipe 224. The ammonia fuel flow channel 221 is positioned around the sub-burner 23 and forms a flow channel for the ammonia fuel F1. The ammonia fuel injection section 222 is positioned at the tip of the ammonia fuel flow channel 221 and injects the ammonia fuel F1. During the inert gas purging described later, the ammonia fuel injection section 222 injects the ammonia fuel F1 discharged by the purging into the flame of the sub-burner 23. A flame-holding section 223 is formed at the lower end of the ammonia fuel flow channel pipe 221. Multiple through holes 223a are formed at predetermined intervals on the circumferential surface of the flame-holding section 223.

[0023] A combustion air passage pipe 224 is arranged around the ammonia fuel passage pipe 221 through which combustion air A1 flows. The combustion air passage pipe 224 is located on the outer circumference side of the ammonia fuel passage pipe 221, and the flow path for combustion air A1 is formed by the outer surface of the ammonia fuel passage pipe 221 and the inner surface of the combustion air passage pipe 224.

[0024] The sub-burner 23 comprises a first fuel passage pipe 231 and a first fuel injection unit 232. The first fuel passage pipe 231 forms a passage for a mixture of first fuel F2 and combustion air A2. The first fuel injection unit 232 is located at the tip of the first fuel passage pipe 231 and injects the mixture of first fuel F2 and combustion air A2. The first fuel flow path pipe 231 and the ammonia fuel flow path pipe 221 share the same fuel injection direction axis.

[0025] In the combustion device 10, the main burner 22 burns ammonia fuel F1 supplied from the ammonia fuel supply line L100, and the sub-burner 23 burns first fuel F2 supplied from the first fuel supply line L300, which has a faster burning rate than ammonia fuel F1. First fuel F2 is a gaseous fuel such as LNG or city gas 13A.

[0026] The window box 24 is connected to the main burner air supply line L410, which will be described later, and is supplied with combustion air A1 necessary for combustion of the main burner 22. A main flame detection unit (not shown) detects the flame of the main burner 22 and transmits it to the combustion stop control unit 71 of the control unit 70, which will be described later. A sub-flame detection unit (not shown) detects the flame of the sub-burner 23 and transmits it to the combustion stop control unit 71 of the control unit 70. These flame detection units can use optical sensors such as ultraviolet flame detectors that can detect flames.

[0027] Returning to Figure 1, the ammonia fuel supply line L100 supplies ammonia fuel F1 to the main burner 22. The ammonia fuel supply line L100 is connected to the main burner 22 on its downstream side and to a supply source (not shown) that supplies ammonia fuel F1 on its upstream side. The ammonia fuel supply line L100 is equipped with ammonia fuel shut-off valves V12 and V14, and an ammonia fuel flow rate control valve V13.

[0028] The ammonia fuel shut-off valves V12 and V14 are installed in the ammonia fuel supply line L100 and are composed of solenoid valves that open and close the flow path of the ammonia fuel supply line L100. The ammonia fuel shut-off valves V12 and V14 are connected to the control unit 70 via wired or wireless communication and are controlled based on signals transmitted from the control unit 70. In this embodiment, the ammonia fuel shut-off valve V12 is located upstream of the ammonia fuel shut-off valve V14.

[0029] The ammonia fuel flow control valve V13 is installed in the ammonia fuel supply line L100 and adjusts the flow rate of ammonia fuel F1 flowing through the ammonia fuel supply line L100 by adjusting the valve opening. The ammonia fuel flow control valve V13 is connected to the control unit 70 via wired or wireless communication, and the valve opening is controlled based on signals transmitted from the control unit 70. In this embodiment, the ammonia fuel flow control valve V13 is positioned between the ammonia fuel shut-off valve V12 and the ammonia fuel shut-off valve V14.

[0030] The inert gas supply line L200 is a line that supplies inert gas G1 into the combustion chamber 25 of the boiler body 20 via the ammonia fuel supply line L100. The upstream side of the inert gas supply line L200 is connected to a source of inert gas G1 (not shown), and the downstream side is connected to the downstream side of the ammonia fuel shut-off valve V14 in the ammonia fuel supply line L100, and is in the vicinity of the ammonia fuel shut-off valve V14. In this embodiment, an example in which nitrogen is used as the inert gas G1 will be described.

[0031] The inert gas supply line L200 is equipped with inert gas shut-off valves V22 and V24, and an inert gas flow rate control valve V23. The inert gas shut-off valves V22 and V24 are composed of solenoid valves and open and close the flow path of the inert gas supply line L200. The inert gas shut-off valves V22 and V24 are connected to the control unit 70 via wired or wireless communication and are controlled based on signals transmitted from the control unit 70. In this embodiment, the inert gas shut-off valve V22 is located upstream of the inert gas shut-off valve V24. The inert gas flow control valve V23 adjusts the flow rate of the inert gas G1 flowing through the inert gas supply line L200 by the degree to which it is opened. The inert gas flow control valve V23 is connected to the control unit 70 via wired or wireless communication and is controlled based on signals transmitted from the control unit 70.

[0032] The first fuel supply line L300 is a line that supplies the first fuel F2 to the sub-burner 23. In this embodiment, an example is given in which city gas 13A, a gaseous fuel, is used as the first fuel F2. However, LNG, LPG, or the like may also be used as the first fuel F2. The first fuel supply line L300 is connected to a fuel source (not shown) on its upstream side and to a sub-burner 23 on its downstream side. The first fuel supply line L300 is also equipped with first fuel shut-off valves V32 and V34 and a first fuel flow control valve V33.

[0033] The first fuel shut-off valves V32 and V34 are composed of solenoid valves and open and close the flow path of the first fuel supply line L300. The first fuel shut-off valves V32 and V34 are connected to the control unit 70 via wired or wireless communication and are controlled based on signals transmitted from the control unit 70. In this embodiment, the first fuel shut-off valve V32 is located upstream of the first fuel shut-off valve V34. The first fuel flow control valve V33 adjusts the flow rate of the first fuel F2 flowing through the first fuel supply line L300 depending on its opening degree. The first fuel flow control valve V33 is communicated with the control unit 70 by wire or wireless means and is controlled based on signals transmitted from the control unit 70.

[0034] The air supply line L400 comprises a main burner air supply line L410 and a sub-burner air supply line L420. The upstream side of the air supply line L400 is connected to the blower 41, and the downstream side is the main burner air supply line L410, with the sub-burner air supply line L420 branching off upstream of the main burner air supply line L410. The main burner air supply line L410 supplies combustion air A1 to the main burner 22. The main burner air supply line L410 is equipped with a damper 43 and its downstream side is connected to the window box 24.

[0035] The sub-burner air supply line L420 supplies combustion air A2 to the sub-burner 23. The sub-burner air supply line L420 branches off from the air supply line L400 upstream of the damper 43 located on the main burner air supply line L410. In this embodiment, the downstream side of the sub-burner air supply line L420 is connected to the first fuel supply line L300. Therefore, the sub-burner 23 is supplied with the first fuel F2 and combustion air A2 from the first fuel supply line L300 in a pre-mixed state. In other words, the sub-burner 23 in this embodiment is a pre-mixed type burner.

[0036] The blower 41 supplies air A0 to the air supply line L400. The blower 41 includes a fan (not shown) and a motor (not shown) that rotates the fan. The motor speed of the blower 41 can be adjusted by controlling the frequency of the inverter 42, thereby controlling the amount of air A0 supplied to the air supply line L400. Depending on the opening of the damper 43, a portion of the air A0 flows into the main burner air supply line L410 as combustion air A1, and the remaining air A0 flows into the sub-burner air supply line L420 as combustion air A2. The inverter 42 is connected to the control unit 70 via wired or wireless communication and is controlled based on signals transmitted from the control unit 70.

[0037] The damper 43 adjusts the amount of combustion air A1 supplied from the main burner air supply line L410 to the main burner 22 by adjusting the damper's opening. Specifically, the damper 43 is rotatably provided to operate between a closed state, which blocks the flow path of the main burner air supply line L410, and an open state, which rotates by a predetermined angle (e.g., 90 degrees) from this closed state to open the flow path of the main burner air supply line L410. The damper 43 is communicated with the control unit 70 by wire or wireless means and is controlled based on signals transmitted from the control unit 70. In the combustion device 10 of this embodiment, the air volume adjustment unit that adjusts the amount of combustion air A1 supplied to the main burner 22 is an inverter 42 and a damper 43. The amount of combustion air A1 supplied to the main burner 22 is controlled by a combination of the frequency of the inverter 42 and the opening degree of the damper 43.

[0038] The control unit 70 controls the combustion of the main burner 22 and the sub-burner 23. The control unit 70 includes a combustion stop control unit 71 and a storage unit 72. The control unit 70 is composed of an arithmetic processor such as a PLC (Programmable Logic Controller), DSP (Digital Signal Processor), or FPGA (Field Programmable Gate Array). The various functions of the control unit 70 are realized, for example, by executing predetermined software (programs) stored in the memory unit 72. The various functions of the control unit 70 may be realized through the cooperation of hardware and software, or they may be realized by hardware (electronic circuits) alone.

[0039] When the combustion stop control unit 71 stops the combustion of the main burner 22, it starts the combustion of the sub-burner 23, opens the inert gas shut-off valves V22 and V24, and closes the ammonia fuel shut-off valves V12 and V14. The combustion stop control unit 71 opens the first fuel shut-off valves V32 and V34 of the first fuel supply line L300 to start supplying the first fuel F2 (city gas 13A in this embodiment) to the sub-burner 23, and starts combustion of the sub-burner 23 by igniting it with an ignition device (not shown). Furthermore, the combustion stop control unit 71 stops the combustion of the sub-burner 23 by closing the first fuel shut-off valves V32 and V34 of the first fuel supply line L300 and stopping the supply of the first fuel F2 to the sub-burner 23.

[0040] Furthermore, the combustion stop control unit 71 stops the combustion of the main burner 22 by closing the ammonia fuel shut-off valves V12 and V14 of the ammonia fuel supply line L100, thereby stopping the supply of ammonia fuel F1 to the main burner 22.

[0041] Furthermore, the combustion stop control unit 71 opens the inert gas shut-off valves V22 and V24 of the inert gas supply line L200 and starts supplying inert gas G1 (nitrogen in this embodiment), thereby initiating an inert gas purge to the ammonia fuel supply line L100. At this time, the combustion stop control unit 71 controls the amount of inert gas G1 supplied by adjusting the opening degree of the inert gas flow rate control valve V23. Furthermore, the combustion stop control unit 71 closes the inert gas shut-off valves V22 and V24 to stop the supply of inert gas G1, thereby ending the inert gas purge to the ammonia fuel supply line L100.

[0042] Furthermore, the combustion stop control unit 71 starts and stops the blower 41. When starting the blower 41, it controls the flow rate of combustion air A1 and A2 supplied to the main burner 22 and sub-burner 23 by changing the frequency of the inverter 42 to control the rotation speed of the blower 41 motor and by adjusting the opening of the damper 43. When the combustion stop control unit 71 stops the combustion of the main burner 22, it controls the damper 43 and inverter 42, which are air volume adjustment units, to supply a second air flow rate different from the first air flow rate to the main burner 22 after maintaining a first air flow rate, which is a predetermined flow rate, for a predetermined time.

[0043] In this embodiment, the first air flow rate is the flow rate of combustion air A1 during combustion, that is, the flow rate of combustion air A1 when the combustion stop signal is received or immediately before the combustion stop signal is received, and the second air flow rate is a smaller flow rate than the first air flow rate. When the combustion stop control unit 71 receives a combustion stop signal, it may maintain the first air flow rate at that time, or it may store the state immediately before (for example, 1 second ago) in the storage unit 72 at each hour, and when it receives a combustion stop signal, it may read the state immediately before (1 second ago) from the storage unit 72 and control the damper 43 and inverter 42.

[0044] The memory unit 72 stores various setting information. The memory unit 72 also stores the first air flow rate, the second air flow rate, and the time for which the first air flow rate is maintained when the combustion of the main burner 22 is stopped. Furthermore, the control unit 70 is not limited to the above example, and may also be configured to include a separate memory unit for storing the duration of the first airflow rate and the second airflow rate, in addition to the memory unit 72.

[0045] In this embodiment, when the combustion of the main burner 22 stops, the combustion device 10 performs an inert gas purge (pipe purge) by purging the ammonia fuel F1 remaining downstream of the ammonia fuel shut-off valve V14 in the ammonia fuel supply line L100, that is, downstream of the connection point with the inert gas supply line L200, with inert gas G1. Furthermore, in this embodiment, the combustion device 10 starts combustion of the sub-burner 23 before the start of the inert gas purge, and the sub-burner 23 continues combustion for a predetermined time even during the inert gas purge. As a result, the ammonia fuel F1 discharged from the ammonia fuel supply line L100 by inert gas purging is burned together with the combustion air A1 supplied from the main burner air supply line L410, using the sub-burner 23 as an ignition source. Therefore, the combustion device 10 of this embodiment can burn the ammonia fuel F1 remaining in the piping of the ammonia fuel supply line L100, thereby suppressing the leakage of ammonia to the outside of the system (outside the combustion device 10 and boiler 1).

[0046] The following describes the control of the combustion stop control unit 71 when combustion stops in the combustion device 10 of this embodiment. When the main burner 22 is in combustion mode, the control unit 70 opens the ammonia fuel shut-off valves V12 and V14 of the ammonia fuel supply line L100, adjusts the opening of the ammonia fuel flow rate control valve V13, and supplies ammonia fuel F1 to the main burner 22. The control unit 70 also controls the frequency of the inverter 42 and the opening of the damper 43 to supply the main burner 22 with the necessary flow rate of combustion air A1. As a result, the main burner 22 burns ammonia fuel F1. When the main burner 22 is in combustion, the control unit 70 closes the inert gas shut-off valves V22 and V24 provided in the inert gas supply line L200 and the first fuel shut-off valves V32 and V34 provided in the first fuel supply line L300.

[0047] When the control unit 70 receives a combustion stop signal from the main burner 22, the combustion stop control unit 71 performs the following controls related to the combustion stop of the main burner 22: starting combustion in the sub-burner 23, starting the supply of inert gas G1, and closing the ammonia fuel shut-off valves V12 and V14. In this embodiment, the combustion stop control unit 71 first initiates combustion of the sub-burner 23. The combustion stop control unit 71 opens the first fuel shut-off valves V32 and V34 of the first fuel supply line L300 and starts supplying the first fuel F2 (city gas 13A in this embodiment) to the sub-burner 23. It controls the frequency of the inverter 42 and the opening degree of the damper 43 to supply a predetermined flow rate of combustion air A2 to the sub-burner 23 and ignites it using an ignition device (not shown) to start combustion of the sub-burner 23.

[0048] Furthermore, the combustion stop control unit 71 continues to supply the main burner air supply line L410 with the first air flow rate, which is the flow rate of combustion air A1 that was supplied to the main burner air supply line L410 when the combustion stop signal from the main burner 22 was received, for a predetermined time even after the combustion stop signal has been received. Next, the combustion stop control unit 71 controls the frequency of the inverter 42 and the opening degree of the damper 43 so that the amount of air supplied to the main burner air supply line L410 becomes the second air flow rate read from the memory unit 72.

[0049] In this embodiment, the second airflow rate is the airflow rate for furnace purging and is smaller than the first airflow rate. The first airflow rate is the airflow rate for burning the ammonia fuel F1 discharged from the piping of the ammonia fuel supply line L100 by purging with inert gas G1. It is preferable to switch from the first airflow rate to the second airflow rate at a timing when it is considered that all of the ammonia fuel F1 remaining in the piping has been pushed out by the inert gas purging, that is, after a flow rate of inert gas G1 has flowed that is considered to have purged all of the ammonia fuel F1 remaining in the piping. Therefore, it is preferable that the duration for which the first airflow rate is continuously supplied is sufficient time for purging by inert gas G1 to be performed from the connection point between the ammonia fuel supply line L100 and the inert gas supply line L200 to the main burner 22. The duration for which the first air flow rate is continuously supplied may be stored in advance in the memory unit 72, or it may be calculated by the combustion stop control unit 71, or the like.

[0050] The combustion stop control unit 71 controls the flow rate of the first fuel F2 supplied to the sub-burner 23 by adjusting the opening degree of the first fuel flow rate adjustment valve V33 of the first fuel supply line L300. The combustion stop control unit 71 also supplies the amount of combustion air A1 necessary for combustion to the main burner 22 from the main burner air supply line L410, and further supplies the amount of combustion air A2 necessary for combustion to the sub-burner 23 via the sub-burner air supply line L420, by controlling the frequency of the inverter 42 and the opening degree of the damper 43. The first fuel flow path pipe 231 of the sub-burner 23 is supplied in the first fuel supply line L300 in a state in which the first fuel F2 and combustion air A2 have been mixed in advance.

[0051] The sub-burner flame detection unit (not shown) transmits a detection signal to the combustion stop control unit 71 when it detects a flame from the sub-burner 23. When the combustion stop control unit 71 receives a detection signal indicating the presence of a flame from the sub-burner 23, it starts purging with inert gas. After combustion of the sub-burner 23 begins, the combustion stop control unit 71 opens the inert gas shut-off valves V22 and V24 provided in the inert gas supply line L200 to start supplying inert gas G1 to the ammonia fuel supply line L100. Next, the combustion stop control unit 71 closes the ammonia fuel shut-off valves V12 and V14 of the ammonia fuel supply line L100 to stop the supply of ammonia fuel F1 to the main burner 22.

[0052] The sub-burner 23 is started to burn, and the supply of inert gas G1 to the ammonia fuel supply line L100 is started before the supply of ammonia fuel F1 is stopped. As a result, any ammonia fuel F1 remaining in the piping of the ammonia fuel supply line L100 is pushed out by the inert gas G1 without interruption of flow. Furthermore, upon the start of the supply of inert gas G1, the ammonia fuel F1 pushed out by the inert gas G1 continues to burn in the main burner 22 for a predetermined time. When the supply of ammonia fuel F1 is stopped, any remaining ammonia fuel F1 in the piping is pushed out by the inert gas G1 and burned by the sub-burner 23. Therefore, the ammonia fuel F1 contained in the inert gas G1 can be sufficiently burned, and the emission of ammonia outside the system can be suppressed.

[0053] Furthermore, the combustion stop control unit 71 may simultaneously open the inert gas shut-off valves V22 and V24 and close the ammonia fuel shut-off valves V12 and V14 after the start of combustion of the sub-burner 23, or it may open the inert gas shut-off valves V22 and V24 after closing the ammonia fuel shut-off valves V12 and V14. In addition, the combustion stop control unit 71 may simultaneously open the first fuel shut-off valves V32 and V34, open the inert gas shut-off valves V22 and V24, and close the ammonia fuel shut-off valves V12 and V14.

[0054] When the inert gas shut-off valves V22 and V24 installed in the inert gas supply line L200 are opened, inert gas G1 is supplied to the downstream side of the connection point between the ammonia fuel supply line L100 and the inert gas supply line L200, and to the main burner 22, and inert gas purging (pipe purging) is started. The combustion stop control unit 71 adjusts the opening degree of the inert gas flow control valve V23 so that the flow rate of the inert gas G1 is 70-130% of the flow rate of the ammonia fuel F1 immediately before combustion stop, i.e., when the combustion stop signal is received or immediately before the combustion stop signal is received. In this embodiment, the combustion stop control unit 71 will be described with an example in which it adjusts the opening degree of the inert gas flow control valve V23 so that the flow rate of the inert gas G1 is 70-130% of the flow rate of the ammonia fuel F1 when the combustion stop signal is received. The combustion stop control unit 71 can obtain the flow rate of the ammonia fuel F1 from the opening degree of the ammonia fuel flow control valve V13 of the ammonia fuel supply line L100. The inert gas purging with inert gas G1 is performed at the flow rate described above for a predetermined time.

[0055] In this embodiment, as shown in Figure 2, the main burner 22 is positioned to surround the sub-burner 23, and during inert gas purging (pipe purging) with inert gas G1, the inert gas G1 containing ammonia fuel F1 flows out in a manner that surrounds the sub-burner 23. As a result, the combustion device 10 can effectively burn the ammonia fuel F1 remaining in the piping with the sub-burner 23. Furthermore, during inert gas purging (pipe purging), inert gas G1 containing ammonia fuel F1 is injected from the ammonia fuel injection section 222 into the flame of the sub-burner 23, so the combustion device 10 can burn the ammonia fuel F1 remaining in the piping using the sub-burner 23 as an ignition source.

[0056] By setting the flow rate of inert gas G1 during inert gas purging to a flow rate equivalent to 70-130% of the flow rate of ammonia fuel F1 when a combustion stop signal is received, the ammonia fuel F1 in the piping of the ammonia fuel supply line L100 can be sufficiently discharged to the main burner 22. In addition, changes in flow rate and the effects caused by the change in the fluid flowing through the piping of the ammonia fuel supply line L100 from ammonia fuel F1 to inert gas G1 can be suppressed.

[0057] Furthermore, when performing an inert gas purge, the combustion stop control unit 71 adjusts the opening of the inert gas flow control valve V23 so that the flow rate of the inert gas G1 is within a range in which the hydrogen contained in the ammonia decomposition gas, which is the ammonia fuel F1, can be burned. This allows the hydrogen contained in the ammonia fuel F1 that is pushed out by the inert gas G1 to be burned sufficiently, the ammonia contained in the ammonia fuel F1 to be incinerated and detoxified, and the discharge of ammonia outside the system to be suppressed.

[0058] When ammonia fuel F1 remaining in the piping is burned to incinerate and detoxify ammonia, if the flow rate of the inert gas G1 (nitrogen in this embodiment) used for inert gas purging is not properly balanced with the remaining ammonia fuel F1, insufficient incineration may occur, potentially leading to the discharge of ammonia outside the system. Therefore, it is important that the flow rate of the inert gas G1 is sufficient to incinerate and detoxify the ammonia. Furthermore, if the flow rate of the inert gas G1 used for inert gas purging is too high, the temperature inside the combustion chamber 25 will decrease, leading to heat loss. Furthermore, during inert gas purging, the combustion stop control unit 71 controls the frequency of the inverter 42 and the damper opening so that the flow rate of the combustion air A1 supplied to the main burner 22 is sufficient to allow for adequate combustion of the ammonia fuel F1 that is purged by the inert gas G1 and discharged from the piping.

[0059] Figure 3 is a triangular diagram showing the relationship between the volume concentrations of hydrogen, nitrogen, and air and combustion, when ammonia fuel F1 is ammonia decomposition gas and inert gas G1 is nitrogen. For simplicity, Figure 3 shows the volume concentrations of hydrogen, nitrogen, and air excluding undecomposed ammonia, and assumes that the volume concentration of undecomposed ammonia is negligibly small for the combustion of hydrogen. In Figure 3, arrow A indicates the volume concentration of hydrogen, arrow B indicates the volume concentration of nitrogen, and arrow C indicates the volume concentration of air. These volume concentrations are those near the burner 21 in the combustion space. In Figure 3, the shaded area indicates the range in which hydrogen can burn (explosion zone). If the intersection of the volume concentrations of hydrogen, nitrogen, and air is located within the burnable range, hydrogen is combustible; if it is located outside the burnable range, hydrogen is not combustible. The same flammability range is defined for cases where the flammable gas is ammonia instead of hydrogen. Furthermore, in the case of mixed gases containing multiple types of flammable gases, such as ammonia decomposition gas containing undecomposed ammonia, or ammonia fuel containing flammable gases other than ammonia, the flammability range of the mixed gas is defined by the flammability range and volume concentration of each component.

[0060] For example, when burning only ammonia fuel F1 and without inert gas purging, ammonia fuel F1 and combustion air A1 are supplied to the combustion chamber 25. If the composition of ammonia fuel F1 is 75% hydrogen and 25% nitrogen, and the ammonia fuel F1 is burned at an air ratio of 1 (the theoretical amount of hydrogen air is 2.381 m³), ​​then... 3 N / m 3 N) The volume concentration of hydrogen is 26.9%, the volume concentration of nitrogen is 9.0%, and the volume concentration of air is 64.1%. This state is shown in Figure 3 as point t1, which is the intersection of the volume concentrations of hydrogen, nitrogen, and air. This point t1 is located within the combustible range. As the flow rate of inert gas G1 is increased, the volume concentration of nitrogen increases, and the point moves along the dashed line L1 shown in Figure 3. Point t2 indicates the state where the flow rate of inert gas G1 (nitrogen) is 4.5 times the flow rate of ammonia fuel F1 (ammonia decomposition gas) discharged from the piping. Point t2 is where the volume concentration of hydrogen is 10.3%, the volume concentration of nitrogen is 65.2%, and the volume concentration of air is 24.5%, and it is located at the upper limit of the combustible range.

[0061] From the above, if the flow rate of inert gas G1 (nitrogen) exceeds 4.5 times the flow rate of ammonia decomposition gas discharged from the ammonia fuel F1 piping by inert gas purging, it will deviate from the upper limit of the combustible range. Therefore, when nitrogen is used as inert gas G1, it is preferable to keep the flow rate of inert gas G1 during inert gas purging at 4.5 times or less the flow rate of ammonia fuel F1 discharged, from the viewpoint of ensuring sufficient combustion of the hydrogen and ammonia contained in the ammonia fuel F1 pushed out by the inert gas G1 while maintaining a suitable combustion state.

[0062] Here, if the flow rate of combustion air A1 supplied to the main burner 22 for in-furnace purging (post-purging) is increased during inert gas purging (pipe purging), if the flow rate of combustion air A1 exceeds 13.3 times the flow rate of ammonia fuel F1 (ammonia decomposition gas) discharged from the ammonia fuel F1 piping, the combustion will deviate from the lower limit of the combustible range, even if the flow rate of inert gas G1 (nitrogen) is 4.5 times or less the flow rate of ammonia fuel F1. Point t3 in Figure 3 represents the state before inert gas purging, where the flow rate of combustion air A1 is 13.3 times that of ammonia fuel F1. At point t3, the volume concentration of hydrogen is 5.2%, the volume concentration of nitrogen is 1.7%, and the volume concentration of air is 93.0%.

[0063] When inert gas G1 is supplied here for inert gas purging, the point moves along the dashed line L2 shown in Figure 3, reaching point t4 when the flow rate of inert gas G1 increases to 4.5 times the flow rate of ammonia fuel F1 (ammonia decomposition gas). Point t4 is located at the lower limit of the combustible range, where the volume concentration of hydrogen is 3.99%, the volume concentration of nitrogen is 25.27%, and the volume concentration of air is 70.74%. Based on the above, it is desirable that the combustion air A1 supplied to the main burner 22 during inert gas purging be at a flow rate that does not fall below the lower combustion limit range of the ammonia fuel F1.

[0064] Based on the above, when ammonia decomposition gas is used as the ammonia fuel F1 as in this embodiment, the combustion stop control unit 71 adjusts the opening of the inert gas flow control valve V23 so that when supplying the inert gas G1, the flow rate of the inert gas G1 is less than 4.5 times the flow rate of the ammonia fuel F1 discharged from the piping of the ammonia fuel supply line L100, and is 70-130% of the flow rate of the ammonia fuel F1 at the time of or immediately before the combustion stop signal is received. Furthermore, the limit value for the flow rate of inert gas G1 can be derived similarly not only in the above example, but also when the air ratio is other than 1, or when the composition of ammonia fuel F1 is different.

[0065] The ammonia fuel F1, discharged from the piping of the ammonia fuel supply line L100 along with the inert gas G1 by the inert gas purge, is burned in the main burner 22 before the ammonia fuel shut-off valves V12 and V14 are closed. When the ammonia fuel shut-off valves V12 and V14 are closed by the combustion stop control unit 71, the ammonia fuel F1, discharged from the piping along with the inert gas G1 by the inert gas purge, continues to burn using the sub-burner 23 as an ignition source.

[0066] Furthermore, while inert gas purging is being performed, the combustion stop control unit 71 controls the frequency of the inverter 42 and the opening of the damper 43 so that the flow rate of combustion air A1 supplied to the main burner 22 is sufficient to allow for adequate combustion of the ammonia fuel F1 that is purged by inert gas G1 and discharged from the piping. Also, while inert gas purging is being performed, the combustion stop control unit 71 controls the frequency of the inverter 42 and other parameters so that the flow rate of combustion air A2 supplied to the sub-burner 23 is sufficient to allow for stable and continuous combustion of the first fuel F2 in the sub-burner 23.

[0067] A predetermined time after the closing of the ammonia fuel shut-off valves V12 and V14, the combustion stop control unit 71 closes the first fuel shut-off valves V32 and V34, stops the supply of the first fuel F2 to the sub-burner 23, and stops the combustion of the sub-burner 23. Furthermore, the combustion stop control unit 71 closes the inert gas shut-off valves V22 and V24 of the inert gas supply line L200, stops the supply of inert gas G1, and completes the inert gas purging. The completion of the inert gas purging is preferably simultaneous with or after the combustion stop of the sub-burner 23. Furthermore, the combustion stop control unit 71 controls the frequency of the inverter 42 to supply the second airflow to the main burner 22. The combustion stop control unit 71 continues to supply air to the burners 21 (main burner 22 and sub-burner 23) even after the combustion of the sub-burner 23 has stopped, performing a purging (post-purge) of the furnace. After performing post-purging for a predetermined time, the combustion stop control unit 71 stops the operation of the blower 41 and ends the post-purge.

[0068] Ammonia fuel F1 contains a few percent of ammonia, which has a significant impact on human health and the environment. However, by performing the above-described control with the combustion stop control unit 71, the combustion device 10 can sufficiently burn the ammonia fuel F1 remaining in the piping of the ammonia fuel supply line L100 when the main burner 22 stops burning. Therefore, the combustion device 10 can incinerate and detoxify the ammonia contained in the ammonia fuel F1, suppressing the discharge of ammonia outside the system and safely stopping combustion.

[0069] As described above, in this embodiment, when the combustion of the main burner 22 is stopped, the combustion of the sub-burner 23 is started, an inert gas purge (pipe purge) is performed, and the supply of ammonia fuel F1 is stopped. As a result, a flame is maintained in the combustion chamber 25, and the ammonia fuel F1 discharged into the combustion chamber 25 by the inert gas purge is burned by the sub-burner 23, thereby suppressing the discharge of ammonia outside the system. In particular, the combustion device 10 of this embodiment starts combustion in the sub-burner 23 and begins supplying inert gas G1 before closing the ammonia fuel shut-off valves V12 and V14. As a result, the ammonia fuel F1 remaining in the piping of the ammonia fuel supply line L100 is pushed out by the inert gas G1 without interrupting the flow. Furthermore, the ammonia fuel F1 pushed out by the inert gas G1 continues to burn in the main burner before the ammonia fuel shut-off valves V12 and V14 are closed, and then burns in the sub-burner 23 after the ammonia fuel shut-off valves V12 and V14 are closed. Therefore, the combustion device 10 can sufficiently burn the ammonia fuel F1 contained in the inert gas G1 and suppress the discharge of ammonia contained in the ammonia fuel F1 outside the system.

[0070] According to the embodiment described above, the following effects can be achieved. (1) According to the combustion device 10 of this embodiment, when the main burner 22 that burns the ammonia fuel F1 stops burning, the combustion device 10 burns a sub-burner 23 which has functions such as a pilot burner and a decontamination burner and burns the first fuel F2, and also performs an inert gas purge with an inert gas G1 inside the piping of the ammonia fuel supply line L100, thereby enabling the combustion device 10 to burn the ammonia fuel F1 remaining inside the piping of the ammonia fuel supply line L100. As a result, the combustion device 10 can suppress the discharge of undecomposed ammonia contained in the ammonia fuel F1 outside the system.

[0071] (2) According to the combustion device 10 of this embodiment, the main burner 22 is arranged so as to surround the sub-burner 23, and when piping is purged with inert gas G1, the inert gas G1 containing ammonia fuel F1 flows out so as to surround the sub-burner 23, so that the ammonia fuel F1 remaining in the piping can be effectively burned in the sub-burner 23. As a result, the combustion device 10 can suppress the discharge of ammonia outside the system.

[0072] (3) According to the combustion device 10 of this embodiment, when piping is purged with inert gas G1, inert gas G1 containing ammonia fuel F1 is injected from the ammonia fuel injection section 222 into the flame of the sub-burner 23, so that the ammonia fuel F1 remaining in the piping can be effectively burned in the sub-burner 23. As a result, the combustion device 10 can suppress the discharge of ammonia outside the system.

[0073] (4) According to the combustion device 10 of this embodiment, combustion air A2 for the sub-burner is supplied to the sub-burner 23 by the sub-burner air supply line L420, so that even when the main burner 22 stops burning, the sub-burner 23 can maintain its flame and burn stably.

[0074] (5) According to the combustion device 10 of this embodiment, the combustion stop control unit 71 starts combustion of the sub-burner 23, opens the inert gas shut-off valves V22 and V24, and then closes the ammonia fuel shut-off valves V12 and V14. Therefore, when the combustion device 10 is stopped, the ammonia fuel F1 remaining in the piping of the ammonia fuel supply line L100 is pushed out by the inert gas G1 without the flow stopping. Furthermore, the ammonia fuel F1 pushed out by the inert gas G1 is burned in the main burner 22 for a predetermined time, and after the combustion of the main burner 22 is stopped by closing the ammonia fuel shut-off valves V12 and V14, combustion can be switched to the sub-burner 23. Therefore, the combustion device 10 can sufficiently burn the ammonia fuel F1 contained in the inert gas G1 and suppress the discharge of ammonia outside the system.

[0075] (6) According to the combustion device 10 of this embodiment, when the combustion stop control unit 71 stops the combustion of the burner 21, it continues to supply the combustion air A1 at a first air flow rate for a predetermined time, and then controls the damper 43 and inverter 42, which are air flow rate adjustment units, so that the flow rate becomes a second air flow rate different from the first air flow rate. As a result, the combustion device 10 can sufficiently burn the ammonia fuel F1 discharged by the inert gas purge.

[0076] (7) According to the combustion device 10 of this embodiment, the combustion stop control unit 71 adjusts the opening of the inert gas flow rate control valve V23 so that the flow rate of the inert gas G1 is in the range of 70 to 130% of the flow rate of the ammonia fuel F1 at the time of receiving the combustion stop signal or immediately before receiving the combustion stop signal. As a result, the ammonia fuel F1 in the ammonia fuel supply line L100 can be pushed to the main burner 22 with inert gas G1 at a flow rate equivalent to 70-130% of the ammonia fuel F1's combustion flow rate, and the combustion device 10 can sufficiently burn any remaining ammonia fuel F1 in the sub-burner 23. Furthermore, it can suppress changes in the flow rate of the fluid flowing through the L100 ammonia fuel supply line and the resulting effects.

[0077] (8) According to the combustion device 10 of this embodiment, the combustion stop control unit 71 adjusts the opening of the inert gas flow rate control valve V23 so that the amount of inert gas G1 supplied is within the range in which hydrogen can be burned. Therefore, when the ammonia fuel F1 is ammonia decomposition gas, the amount of inert gas supplied can be set to an amount that does not deviate from the range in which hydrogen contained in the ammonia fuel F1 can be burned, and the combustion device 10 can sufficiently burn the ammonia fuel F1 that is pushed out by the inert gas G1.

[0078] (Transformed form) The present invention is not limited to the embodiments described above, and various modifications and changes are possible, all of which fall within the scope of the present invention. In this embodiment, the sub-burner 23 is shown as a pre-mixed type burner in which the first fuel F2 and combustion air A1 are supplied in a pre-mixed state. However, it is not limited to this, and for example, the first fuel F2 and combustion air A2 may be mixed in a pre-mixed type burner in the flame-holding section (not shown) at the lower end of the sub-burner 23.

[0079] In this embodiment, a configuration in which the sub-burner 23 is arranged inside the main burner 22 is shown, but the configuration is not limited to this, and the sub-burner 23 may be arranged outside the main burner 22 and in the vicinity of the main burner 22. In this case, it is preferable that the sub-burner 23 is arranged on the tip side of the ammonia fuel flow pipe, and that the ammonia fuel injection section 222 of the main burner 22 is configured to inject ammonia fuel F1 into the flame of the sub-burner 23.

[0080] In this embodiment, an example is shown in which the sub-burner 23 stops combustion after the inert gas purging is completed. However, the embodiment is not limited to this, and the sub-burner 23 may continue to burn even when the main burner 22 has stopped burning, until the main burner 22 resumes combustion. By adopting this configuration, the sub-burner 23 continues to burn even when the combustion device 10 is stopped, so the temperature drop of the combustion chamber 25 can be suppressed and heat loss can be reduced.

[0081] In this embodiment, an example was given in which ammonia decomposition gas is used as the ammonia fuel F1. However, the embodiment is not limited to this, and for example, ammonia may be used as the ammonia fuel F1, and the ammonia fuel F1 may be co-fired with a fuel that burns faster than ammonia, such as hydrogen.

[0082] In this embodiment, the combustion stop control unit 71 may adjust the opening degree of the inert gas flow rate control valve V23, and when the supply of inert gas G1 is started, set its flow rate to, for example, 10% of the flow rate of ammonia fuel F1 immediately before receiving the combustion stop signal, and gradually or continuously increase the flow rate until it is finally adjusted to be in the range of 70 to 130% of the flow rate of ammonia fuel F1 immediately before receiving the combustion stop signal.

[0083] In this embodiment, after the supply of ammonia fuel F1 is stopped, the combustion stop control unit 71 may control the flow rate of the inert gas G1 to decrease in stages or continuously in accordance with the decrease in the hydrogen concentration in the gas supplied to the main burner 22.

[0084] In this embodiment, the first airflow rate is set to be greater than the second airflow rate, but this is not limited to this configuration. The first airflow rate may be smaller than the second airflow rate and may be different from the flow rate at the time of or immediately before the combustion stop signal is received. In this configuration, the combustion stop control unit 71 can perform control such as setting a small airflow rate (first airflow rate) to prevent the flame from being extinguished while the ammonia fuel F1 remaining in the ammonia fuel supply line L100 is being purged with inert gas G1, and then setting a large airflow rate (second airflow rate) to ventilate the furnace after the inert gas purging is complete.

[0085] In this embodiment, the combustion stop control unit 71 may, from the viewpoint of preventing the flame of the sub-burner 23 from being extinguished and combustion from stopping due to the inert gas G1 during inert gas purging, control the opening degree of the first fuel flow rate control valve V33 of the first fuel supply line L300, the frequency of the inverter 42, and the opening degree of the damper 43, and adjust the flow rate of the first fuel F2 and the flow rate of the combustion air A2 so that the flame of the sub-burner 23 is larger than the normal flame of the sub-burner 23 when used for ignition of the main burner 22, etc.

[0086] In this embodiment, the sub-burner air supply line L420 may be equipped with a flow control valve, a shut-off valve, etc., and when combustion of the sub-burner 23 starts, the opening degree of these valves is controlled by the combustion stop control unit 71 to adjust the flow rate of combustion air A2 supplied to the sub-burner 23.

[0087] The embodiments and variations of this invention can be used in combination as appropriate, but a detailed explanation is omitted. Furthermore, the present invention is not limited to the embodiments described above.

[0088] Furthermore, since the present invention promotes the use of ammonia as a fuel that does not emit carbon dioxide, it can contribute, for example, to United Nations Sustainable Development Goal (SDG) 7, "Ensure access to affordable, reliable, sustainable and modern energy." [Explanation of Symbols]

[0089] 1 Boiler 10 Combustion device 20 can body 21 Burner 22 Main Burner 23 Sub-burner 221 Ammonia fuel flow path pipe 222 Ammonia fuel injection section 231 First fuel flow tube 232 1st fuel injection section 41 Blower 42. Inverter (Air volume adjustment unit) 43. Damper (air volume adjustment section) 70 Control Unit 71 Combustion Stop Control Unit L100 Ammonia Fuel Supply Line L200 Inert Gas Supply Line L300 No. 1 Fuel Supply Line L400 Air Supply Line L410 Main Burner Air Supply Line L420 Sub-burner air supply line V12, V14 Ammonia Fuel Shut-off Valve V13 Ammonia Fuel Flow Control Valve V22, V22 Inert Gas Shut-off Valve V23 Inert Gas Flow Control Valve V32, V34 First Fuel Shut-off Valve V33 No. 1 Fuel Flow Control Valve

Claims

1. A burner comprising a main burner that burns ammonia fuel, which is a fuel containing ammonia, and a sub-burner that burns a first fuel with a faster burning rate than ammonia, An ammonia fuel supply line connected to the main burner and supplying the ammonia fuel to the main burner, An ammonia fuel shut-off valve is placed in the ammonia fuel supply line and opens and closes the flow path of the ammonia fuel supply line, An inert gas supply line connected downstream of the ammonia fuel shutoff valve and supplying inert gas to the ammonia fuel supply line, An inert gas shut-off valve is placed in the inert gas supply line and opens and closes the flow path of the inert gas, A first fuel supply line that supplies the first fuel to the sub-burner, A control unit for controlling the combustion of the main burner and the sub-burner, Equipped with, The control unit, When stopping the combustion of the main burner, The start of combustion in the aforementioned sub-burner, The opening of the aforementioned inert gas shutoff valve, Closing of the ammonia fuel shutoff valve, It includes a combustion stop control unit that performs the following: Combustion device.

2. The aforementioned main burner is, An ammonia fuel flow path pipe is arranged around the sub-burner and forms a flow path for the ammonia fuel, An ammonia fuel injection unit is located at the tip end of the ammonia fuel flow path pipe and ejects the ammonia fuel, Equipped with, The combustion apparatus according to claim 1.

3. The aforementioned main burner is an ammonia fuel flow path pipe that forms the flow path of the ammonia fuel, An ammonia fuel injection unit is located at the tip end of the ammonia fuel flow tube and injects the ammonia fuel into the flame of the sub-burner, Equipped with, The combustion apparatus according to claim 1.

4. An air supply line that supplies combustion air to the burner, A main burner air supply line is located downstream of the aforementioned air supply line and supplies combustion air to the main burner, A sub-burner air supply line that branches off from the aforementioned air supply line and supplies combustion air to the sub-burner, Equipped with, The combustion apparatus according to claim 1.

5. The combustion stop control unit starts combustion of the sub-burner, opens the inert gas shutoff valve, and then closes the ammonia fuel shutoff valve. The combustion apparatus according to claim 1.

6. A main burner air supply line that supplies combustion air to the main burner, An air flow rate adjustment unit for adjusting the flow rate of the combustion air in the main burner air supply line, Equipped with, The combustion stop control unit, when stopping the combustion of the burner, continues to supply the combustion air at a first air flow rate for a predetermined time, and then controls the air flow rate adjustment unit to set the air flow rate to a second air flow rate that is different from the first air flow rate. The combustion apparatus according to claim 1.

7. The inert gas supply line includes an inert gas flow control valve for adjusting the flow rate of the inert gas, The combustion stop control unit adjusts the opening of the inert gas flow rate control valve so that the flow rate of the inert gas is in the range of 70 to 130% of the flow rate of the ammonia fuel at the time of receiving the combustion stop signal or immediately before receiving the combustion stop signal. The combustion apparatus according to claim 6.

8. The inert gas supply line includes an inert gas flow control valve for adjusting the flow rate of the inert gas, The combustion stop control unit adjusts the opening of the inert gas flow rate control valve so that the supply amount of the inert gas is within the range in which hydrogen can be combusted. The combustion apparatus according to claim 1.

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