Boiler

Abstract

An ammonia mixed-combustion boiler device (1) serving as a boiler comprises a burner (10) to which oil fuel (F1) and ammonia fuel (F2) are supplied, a can body (30) that recovers heat from combustion gas in which the fuel injected from the burner (10) is combusted, and a control unit (70). The control unit (70) is provided with a combustion control unit (71) that enables combustion of the oil fuel (F1) at a plurality of stepwise combustion positions and enables combustion of the ammonia fuel (F2) by continuously changing the combustion amount of the ammonia fuel (F2) within a prescribed range.

Description

boiler

[0001] This application claims priority from Japanese Patent Application No. 2023-202751, filed on November 30, 2023, the contents of which are incorporated herein by reference. The present invention relates to a boiler.

[0002] It is expected that carbon dioxide emissions will be reduced by replacing part of the hydrocarbon fuels used as burner fuel, such as natural gas and petroleum fuel, with ammonia, which does not generate carbon dioxide (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2021-185122

[0004] Ammonia is known to be a fuel with low combustibility, with an extremely slow combustion speed and a narrow flame-holding range compared to other hydrocarbon fuels such as methane, the main component of city gas. For this reason, in boilers that recover heat from combustion gas to a heated medium, the combustion gas is quickly cooled in the heat exchanger, and unburned ammonia is likely to be generated due to changes in combustion conditions such as the combustion amount and air ratio.

[0005] In addition, industrial boilers that supply heat to demand units in food factories, chemical plants, etc., control the combustion amount by increasing or decreasing it to supply heat according to the load (demand). For example, in the case of a steam boiler that can control the combustion amount at four combustion positions - combustion stop, low combustion position, medium combustion position, and high combustion position - if the steam pressure drops below a predetermined pressure during combustion at the low combustion position, the combustion amount is increased from the low combustion position to the medium combustion position. During this transition period, the combustion state becomes unstable, and the generation of unburned material increases.

[0006] In ammonia co-firing boilers that control the amount of oil fuel combustion in stages, there is a problem that the generation of unburned ammonia increases due to combustion instability when the amount of oil fuel combustion is increased or decreased in stages. Therefore, there is a demand for a boiler that can supply heat quickly and flexibly in response to fluctuations in required load, and can burn ammonia stably to suppress the generation of unburned ammonia.

[0007] An object of the present invention is to provide a boiler that co-combustes oil fuel and ammonia, which can control the heat supply by ammonia combustion so as to continuously correspond to the load required by the load equipment, suppresses the generation of unburned ammonia, and enables stable combustion.

[0008] The present invention relates to a boiler comprising: a burner to which oil fuel and ammonia fuel are supplied; a boiler body that recovers heat from combustion gas resulting from the combustion of fuel ejected from the burner; a control unit; an oil fuel supply line that supplies the oil fuel to the burner; an ammonia supply line that supplies the ammonia fuel to the burner; a combustion air supply line that supplies combustion air to the burner; and an exhaust gas line that is connected to the boiler body and through which combustion gas generated by the combustion of the oil fuel and the ammonia fuel in the boiler body flows, wherein the control unit enables the oil fuel to be combusted at a plurality of staged combustion positions, and also comprises a combustion control unit that enables the combustion of the ammonia fuel by continuously changing the combustion amount of the ammonia fuel within a predetermined range.

[0009] Moreover, it is preferable that the combustion control unit changes the combustion position of the oil fuel after stopping the supply of the ammonia fuel.

[0010] In addition, it is preferable that the combustion control unit changes the combustion position of the oil fuel after stopping the supply of the ammonia fuel when the total combustion amount of the oil fuel and the ammonia fuel reaches a combustion amount corresponding to a combustion rate set according to the combustion position.

[0011] In addition, it is preferable that the combustion control unit changes the combustion position of the oil fuel to a higher combustion position when the total combustion amount reaches a combustion amount corresponding to a combustion rate set according to the combustion position due to an increase in the combustion amount of the ammonia fuel.

[0012] Furthermore, it is preferable that the ammonia fuel mixing ratio of the upper limit of a range in which the combustion amount of the ammonia fuel can be continuously changed at a combustion position of the oil fuel with the ammonia fuel at the maximum combustion rate among the plurality of stepwise combustion positions is larger than the ammonia fuel mixing ratio of the upper limit of a range in which the combustion amount of the ammonia fuel can be continuously changed at a combustion position of the oil fuel with the minimum combustion rate among the plurality of stepwise combustion positions.

[0013] Moreover, it is preferable that the ammonia supply line includes an ammonia flow rate adjustment valve and an ammonia shutoff valve, and the combustion control unit closes the ammonia shutoff valve when changing the combustion position of the oil fuel.

[0014] According to the present invention, it is possible to provide a boiler that co-fires oil fuel and ammonia, which can be controlled to continuously respond to the load required by the load equipment, suppresses the generation of unburned ammonia, and enables stable combustion.

[0015] Fig. 1 is a longitudinal sectional view of an ammonia-coal-fired boiler apparatus of a first embodiment according to the present invention; Fig. 2 is a graph showing the relationship between a predetermined combustion rate at a certain time and the ammonia-coal-fired ratio at the predetermined combustion rate for an ammonia-coal-fired boiler apparatus of a first embodiment according to the present invention; Fig. 3 is a graph showing the relationship between a predetermined combustion rate at a certain time and the ammonia-coal-fired ratio at the predetermined combustion rate for an ammonia-coal-fired boiler apparatus of a second embodiment according to the present invention; Fig. 4 is a graph showing the relationship between a predetermined combustion rate at a certain time and the ammonia-coal-fired ratio at the predetermined combustion rate for an ammonia-coal-fired boiler apparatus of a third embodiment according to the present invention;

[0016] (First embodiment) A boiler according to a first embodiment of the present invention will be described below with reference to the drawings. An ammonia-mixed combustion boiler system 1 as a boiler of this embodiment is a steam boiler that heats water to generate steam and supplies the steam to load equipment (not shown). Figure 1 is a vertical cross-sectional view of the ammonia-mixed combustion boiler system 1 of the first embodiment of the present invention.

[0017] As shown in FIG. 1 , the ammonia co-firing boiler apparatus 1 includes a boiler body 30, a burner 10, a control unit 70, a fuel supply line 100, and a combustion air supply line 200. The boiler body 30 includes a plurality of water tubes 40, a lower header 50, and an upper header 60. A combustion chamber 32 surrounded by the plurality of water tubes 40 is formed inside the boiler body 30. The fuel supply line 100 includes an oil fuel supply line 130 and an ammonia supply line 140. In this embodiment, the ammonia co-firing boiler apparatus 1 ejects oil fuel and ammonia fuel from the burner 10 to which the oil fuel and ammonia fuel are supplied, and co-firing the oil fuel and ammonia fuel in the combustion chamber 32. The boiler body 30 recovers heat from the combustion gas resulting from the combustion of the fuel ejected from the burner 10. Heavy oil, light oil, kerosene, or the like can be used as the oil fuel.

[0018] The can body 30 is cylindrical and constitutes the main part of the exterior of the ammonia co-firing boiler apparatus 1. The shape of the can body 30 of this embodiment will be described below, but this is merely an example, and the shape of the can body 30 and the shape of the water tubes 40 provided in the can body 30 are not limited to this example. The can body 30 is arranged so that its height direction is along the vertical direction. An exhaust port 31 is formed in the upper part of the circumferential surface of the can body 30. The exhaust port 31 is connected to an exhaust gas line 33 through which combustion gas obtained by co-firing oil fuel and ammonia fuel by the burner 10 flows.

[0019] The plurality of water tubes 40 are arranged to extend vertically inside the boiler body 30. As shown in Fig. 1 , the plurality of water tubes 40 constitute an inner water tube group 41 and an outer water tube group 42 arranged outside the inner water tube group 41. The inner water tube group 41 is configured by arranging the plurality of water tubes 40 in an annular shape so that they are coaxial with the jet central axis X of the burner 10, which will be described later. In this embodiment, the water tubes 40 constituting the inner water tube group 41 are arranged so that adjacent water tubes 40 abut against each other. Furthermore, the lower portions of the plurality of water tubes 40 constituting the inner water tube group 41 have a small diameter, and at this lower portion, a gap is formed between adjacent water tubes 40.

[0020] The outer water tube group 42 is configured by arranging a plurality of water tubes 40 in an annular shape so that they are coaxial with the jet central axis X of the burner 10. The outer water tube group 42 is also arranged so that a predetermined space is formed between it and the inner water tube group 41. In this embodiment, the water tubes 40 constituting the outer water tube group 42 are arranged so that adjacent water tubes 40 are in contact with each other. The upper portions of the plurality of water tubes 40 constituting the outer water tube group 42 have a small diameter, and at this upper portion, a gap is formed between adjacent water tubes 40.

[0021] The burner 10 extends in the vertical direction of the ammonia co-firing boiler apparatus 1 and is disposed on top of the boiler body 30. As shown in Fig. 1, the burner 10 of this embodiment includes an oil-fuel flow path L1, a first air flow path L2, an ammonia flow path L3, and a second air flow path L4. The burner 10 also includes a wind box 28, which includes a combustion air inlet 29 for introducing combustion air A0. The combustion air inlet 29 is connected to a combustion air supply line 200, which will be described later, and the combustion air A0 is fed from the combustion air supply line 200.

[0022] The oil fuel flow path L1 includes two oil fuel supply pipes 11 (a first supply pipe 11a and a second supply pipe 11b), an oil fuel inlet 21 (a first inlet 21a and a second inlet 21b) for introducing the oil fuel F1, and an oil fuel ejection portion 15 (a first ejection portion 15a and a second ejection portion 15b) for ejecting the oil fuel F1. In this embodiment, an example will be described in which a total of two oil fuel supply pipes 11, the first supply pipe 11a and the second supply pipe 11b, are arranged.

[0023] The oil fuel inlet 21 (first inlet 21a, second inlet 21b) is a portion into which the oil fuel F1 flowing through the oil fuel supply line 130 is sent, and is provided at the end of the base end side (opposite the combustion chamber 32) of the oil fuel supply pipe 11. As shown in FIG. 1, the first supply pipe 11a is provided with the first inlet 21a, and the second supply pipe 11b is provided with the second inlet 21b. At the tip of the oil fuel supply pipe 11 on the combustion chamber 32 side, an oil fuel ejection section 15 (first ejection section 15a, second ejection section 15b) and a baffle plate (not shown) are provided. As shown in FIG. 1, the first supply pipe 11a is provided with the first ejection section 15a, and the second supply pipe 11b is provided with the second ejection section 15b. The oil fuel ejection section 15 is, for example, a nozzle tip.

[0024] The first air flow path L2 includes a first combustion air inlet 22 for introducing the first combustion air A1, a first air flow path pipe 12, and a first air ejection unit 16. The first combustion air inlet 22 is a portion into which a portion of the combustion air A0 sent to the wind box 28 is sent as the first combustion air A1. The first air flow path pipe 12 is a tubular member through which the first combustion air A1 flows, and in this embodiment, has a larger diameter than the oil fuel supply pipe 11, shares the same central axis as the oil fuel supply pipe 11, and is provided so as to house the oil fuel supply pipe 11. The first air ejection unit 16 is disposed at the tip of the first air flow path L2 on the combustion chamber 32 side, and ejects the first combustion air A1 that has flowed through the first air flow path L2.

[0025] The ammonia flow path L3 includes an ammonia inlet 23 for introducing the ammonia fuel F2, an ammonia flow path pipe 13, and an ammonia fuel ejection unit 17. The ammonia inlet 23 is a portion into which the ammonia fuel flowing through the ammonia supply line 140 is fed. The ammonia flow path pipe 13 is a tubular member for circulating the ammonia fuel F2, and in this embodiment, has a larger diameter than the first air flow path pipe 12, shares the same central axis as the first air flow path pipe 12 and the oil fuel supply pipe 11, and is provided so as to house these. The ammonia fuel ejection unit 17 is disposed at the tip of the ammonia flow path pipe 13 on the combustion chamber 32 side, and ejects the ammonia fuel F2.

[0026] The second air flow path L4 includes a second combustion air inlet 24 serving as a second combustion air introduction section, a swirl section 20, a second air flow path pipe 14, and a second air ejection section 18. The second combustion air inlet 24 is a section that sends a portion of the combustion air A0 sent to the wind box 28 as the second combustion air A2. The swirl section 20 is a section that swirls the second combustion air A2. In this embodiment, the second combustion air A2 that flows into the second air flow path L4 from the second combustion air inlet 24 is swirled by the swirl section 20 and becomes a swirling flow centered on the ejection central axis X from the second air ejection section 18, and is ejected through the second air flow path L4. The second air flow path pipe 14 is a tubular member through which the second combustion air A2 flows, and in this embodiment, has a larger diameter than the ammonia flow path pipe 13, and is provided so as to have the same central axis as the first air flow path pipe 12, the oil fuel supply pipe 11, and the ammonia flow path pipe 13 and to house these. The second air ejection part 18 is disposed at the tip of the second air flow path pipe 14 on the combustion chamber 32 side, and ejects the second combustion air A2.

[0027] 1, the combustion chamber 32 is formed by a space surrounded by the inner water tube group 41 inside the boiler body 30. In this combustion chamber 32, oil fuel F1 ejected from the oil fuel ejection portion 15 of the burner 10, first combustion air A1 ejected from the first air ejection portion 16, ammonia fuel F2 ejected from the ammonia fuel ejection portion 17, and second combustion air A2, which is a swirling flow ejected from the second air ejection portion 18, are mixed and burned. Combustion gas flows from the combustion chamber 32 through gaps formed between adjacent water tubes 40 below the inner water tube group 41 and rises in the space formed between the inner water tube group 41 and the outer water tube group 42. The combustion gas that rises in the space formed between the inner water tube group 41 and the outer water tube group 42 flows through the gaps formed between adjacent water tubes 40 at the top of the outer water tube group 42 to the exhaust port 31 formed at the top of the boiler body 30, and is discharged to the outside through the exhaust gas line 33 connected to this exhaust port 31.

[0028] As described above, the fuel supply line 100 includes the oil fuel supply line 130 and the ammonia supply line 140. The oil fuel supply line 130 supplies oil fuel F1 from an oil fuel supply source (not shown) to the burner 10. The upstream side of the oil fuel supply line 130 is connected to the oil fuel supply source (not shown), and the downstream side of the oil fuel supply line 130 is connected to the burner 10. The oil fuel supply line 130 includes a first oil fuel supply line 110 and a second oil fuel supply line 120. The first oil fuel supply line 110 and the second oil fuel supply line 120 include, from the upstream side, pumps (first pump 111, second pump 121), on-off valves (first on-off valve 112, second on-off valve 122), and fuel supply valves (first fuel supply valve 113, second fuel supply valve 123). The first oil fuel supply line 110 is connected to a first supply pipe 11 a of the burner 10 , and the second oil fuel supply line 120 is connected to a second supply pipe 11 b of the burner 10 .

[0029] The first pump 111 and the second pump 121 discharge the oil fuel F1 supplied from an oil fuel supply unit (not shown) toward the first jetting portion 15a and the second jetting portion 15b of the oil fuel jetting portion 15, respectively. The first on-off valve 112 and the second on-off valve 122 and the first fuel supply valve 113 and the second fuel supply valve 123 are configured by electromagnetic valves or air-driven valves. The first on-off valve 112 and the first fuel supply valve 113 supply or cut off the oil fuel F1 between the first pump 111 and the first jetting portion 15a, and can doubly cut off the supply of the oil fuel F1 from the first oil fuel supply line 110. In addition, the second on-off valve 122 and the second fuel supply valve 123 supply or cut off the oil fuel F1 between the second pump 121 and the second jetting portion 15b, and can doubly cut off the second oil fuel supply line 120.

[0030] The ammonia supply line 140 supplies ammonia fuel F2 from an ammonia fuel supply source (not shown) to the burner 10. The upstream side of the ammonia supply line 140 is connected to the ammonia fuel supply source, and the downstream side of the ammonia supply line 140 is connected to the burner 10. The ammonia supply line 140 is equipped with, from the upstream side, an ammonia fuel flow rate sensor 141, a first shutoff valve 142 serving as an ammonia shutoff valve, a flow rate adjustment valve 143 serving as an ammonia flow rate adjustment valve, and a second shutoff valve 144 serving as an ammonia shutoff valve.

[0031] The ammonia fuel flow rate sensor 141 detects the flow rate of the ammonia fuel F2 flowing through the ammonia supply line 140. The first shutoff valve 142 and the second shutoff valve 144 are configured by electromagnetic valves, and open and close the flow path of the ammonia supply line 140 to supply or stop the ammonia fuel F2. The flow rate adjustment valve 143 is an adjustment valve that adjusts the flow rate of the ammonia fuel F2 supplied to the burner 10 by adjusting the valve opening based on the detection result of the ammonia fuel flow rate sensor 141.

[0032] The combustion air supply line 200 supplies combustion air A0 to the burner 10. In this embodiment, the combustion air A0 is supplied to the wind box 28 of the burner 10. The upstream side of the combustion air supply line 200 is connected to a blower 201, and the downstream side of the combustion air supply line 200 is connected to the wind box 28. The combustion air supply line 200 is equipped with, from the upstream side, the blower 201, an air flow sensor 202, and a damper 203.

[0033] The blower 201 supplies combustion air A0 to the burner 10. The blower 201 includes a fan and a motor that rotates the fan, and the rotation speed of the motor can be adjusted by controlling the frequency using an inverter 204. The air flow sensor 202 detects the flow rate of the combustion air A0 flowing through the combustion air supply line 200. The damper 203 adjusts the flow rate of the combustion air A0 supplied to the burner 10 by adjusting its opening. Specifically, the damper 203 is arranged to be rotatable between a closed state in which the flow path of the combustion air supply line 200 is blocked and an open state in which the damper 203 rotates from the closed state by a predetermined angle (e.g., 90 degrees) to open the flow path of the combustion air supply line 200.

[0034] The control unit 70 includes a combustion control unit 71 and a memory unit 72. The control unit 70 is configured with an arithmetic processor such as a programmable logic controller (PLC), a digital signal processor (DSP), or a field-programmable gate array (FPGA). 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 by a combination of hardware and software, or may be realized only by hardware (electronic circuits). The memory unit 72 stores various types of information. For example, the memory unit 72 may store a database of flow rates corresponding to the combustion rate of oil fuel F1 and a database of flow rates corresponding to the combustion rate of ammonia fuel F2.

[0035] The control unit 70 monitors the steam usage load based on the steam pressure of a steam header (not shown) and controls the steam pressure to control the ammonia-mixed combustion boiler apparatus 1. In this embodiment, the combustion in the ammonia-mixed combustion boiler apparatus 1 is controlled by a combustion control unit 71 of the control unit 70. The combustion control unit 71 enables the combustion of oil fuel F1 at a plurality of staged combustion positions, and controls the combustion amount of ammonia fuel F2 to be continuously changed within a predetermined range so as to enable the combustion of ammonia fuel F2.

[0036] In the ammonia-mixed combustion boiler system 1 of this embodiment, the combustion control unit 71 controls the oil fuel F1 in three stepwise combustion states (combustion position, combustion rate) shown in the following (A) to (C). The combustion rate indicates the ratio of the combustion amount (based on the calorific value) when the maximum combustion amount of the ammonia-mixed combustion boiler system 1 is set to 100%. (A) Combustion stop position (first combustion position: combustion rate 0%), (B) Low combustion position L (second combustion position: for example, set to a combustion rate of 25%), (C) Medium combustion position M (third combustion position: for example, set to a fuel rate of 50%)

[0037] In the ammonia co-firing boiler apparatus 1 of this embodiment, when oil fuel F1 is burned at the low combustion position L (combustion rate 25%), the combustion control unit 71 continuously controls the co-firing ratio of ammonia fuel F2 in the range of 0% to 50%. When oil fuel F1 is burned at the low combustion position L (combustion rate 25%) and ammonia fuel F2 is burned at a co-firing rate of 50%, the combustion rate of the ammonia co-firing boiler apparatus 1 is 50%. The combustion control unit 71 continuously adjusts the co-firing rate of ammonia fuel F2, so that the ammonia co-firing boiler apparatus 1 continuously controls the combustion amount in the combustion range from the low combustion position L to the medium combustion position M. The ammonia co-firing ratio indicates the proportion of the combustion amount of ammonia fuel F2 in the combustion amount of the ammonia co-firing boiler apparatus 1.

[0038] Furthermore, in the ammonia co-firing boiler apparatus 1 of this embodiment, when oil fuel F1 is burned at the medium combustion position M (combustion rate 50%), the combustion control unit 71 continuously controls the co-firing ratio of ammonia fuel F2 in the range of 0% to 50%. When oil fuel F1 is burned at the medium combustion position M (combustion rate 50%) and ammonia fuel F2 is burned at a co-firing ratio of 50%, the combustion rate of the ammonia co-firing boiler apparatus 1 is 100% (high combustion position H). By the combustion control unit 71 continuously adjusting the co-firing ratio of ammonia fuel F2, the ammonia co-firing boiler apparatus 1 continuously controls the combustion amount in the combustion range from the medium combustion position M to the high combustion position H (combustion amount 100%).

[0039] Furthermore, when the total combustion amount of the oil fuel F1 and the ammonia fuel F2 reaches a combustion amount corresponding to a combustion rate set according to the combustion position, the combustion control unit 71 changes the combustion position of the oil fuel F1 after stopping the supply of the ammonia fuel F2. At this time, the total combustion amount of the oil fuel F1 and the ammonia fuel F2 before stopping the supply of the ammonia fuel F2 and the combustion amount at the combustion position of the oil fuel F1 changed after stopping the supply of the ammonia fuel F2 may be the same or may be the same within a predetermined tolerance range. For example, a difference in combustion amount of about ±5% of the fuel rate while the combustion of the ammonia fuel F2 is stopped does not significantly affect the combustion state of the oil fuel F1, and can be set to a combustion amount that makes it easy to stabilize combustion in the ammonia co-firing boiler apparatus 1.

[0040] When the oil fuel F1 is combusted at the low combustion position L in the ammonia co-firing boiler apparatus 1, the combustion control unit 71 controls the supply of the oil fuel F1 only from either the first oil fuel supply line 110 or the second oil fuel supply line 120. For example, the combustion control unit 71 controls the supply of the oil fuel F1 only from the first oil fuel supply line 110 and cuts off the supply of the oil fuel F1 from the second oil fuel supply line 120. At this time, the combustion control unit 71 opens the first on-off valve 112 and the first fuel supply valve 113, closes the second on-off valve 122 and the second fuel supply valve 123, and operates the first pump 111. As a result, the oil fuel F1 is injected from the first injection part 15a of the first supply pipe 11a to which the first oil fuel supply line 110 is connected. Furthermore, when the combustion control unit 71 controls so that the oil fuel F1 is supplied only from the second oil fuel supply line 120 and the supply of the oil fuel F1 from the first oil fuel supply line 110 is cut off, the combustion control unit 71 closes the first on-off valve 112 and the first fuel supply valve 113, opens the second on-off valve 122 and the second fuel supply valve 123, and operates the second pump 121. As a result, the oil fuel F1 is injected from the second injection part 15b of the second supply pipe 11b to which the second oil fuel supply line 120 is connected.

[0041] When shifting the combustion position of the oil fuel F1 from the low combustion position L to the medium combustion position M, the combustion control unit 71 maintains the low combustion state, opens the on-off valve on the oil fuel supply line side where the supply of the oil fuel F1 has been stopped and the fuel supply valve, operates the pump, and injects the oil fuel F1 from the oil fuel injection unit 15. For example, if the supply of the oil fuel F1 from the first oil fuel supply line 110 has been stopped at the low combustion position L, the combustion control unit 71 opens the first on-off valve 112 and the first fuel supply valve 113, operates the first pump 111, and injects the oil fuel F1 from the first injection unit 15a, thereby controlling the amount of combustion of the burner 10 to increase.

[0042] Furthermore, the combustion control unit 71 burns the oil fuel F1 at a predetermined combustion rate in the ammonia co-firing boiler apparatus 1, and when a required load exceeding this predetermined combustion rate is requested from the load equipment, opens the first shutoff valve 142 and the second shutoff valve 144 of the ammonia supply line 140. At this time, the combustion control unit 71 adjusts the valve opening of the flow rate adjustment valve 143 based on the detection result of the ammonia fuel flow rate sensor 141 so that the combustion rate of the ammonia fuel F2 corresponds to the combustion amount that is the difference between the combustion amount of the oil fuel F1 and the combustion amount of the required load. As a result, combustion of the ammonia fuel F2 begins, and the combustion rate of the ammonia fuel F2 is continuously controlled in accordance with the required load.

[0043] The combustion control unit 71 changes the opening of the damper 203 according to each combustion position to control the flow rate of combustion air supplied to the combustion chamber 32. For example, the combustion control unit 71 injects oil fuel F1 from the oil fuel injection unit 15 (first injection unit 15a) and controls the opening of the damper 203 so as to increase the combustion air A0 after a predetermined time delay. The predetermined time delay for increasing the combustion air A0 is set in advance through experiments, etc.

[0044] 2 is a graph showing the combustion rate and the ammonia fuel combustion rate at a certain time in the ammonia-mixed combustion boiler apparatus 1 of the first embodiment according to the present invention. As shown in Fig. 2, in the first embodiment, the low combustion position L of the oil fuel F1 is set to a combustion rate of 25%, and the medium combustion position M is set to a combustion rate of 50%. As shown in Fig. 2, the combustion control unit 71 opens the first on-off valve 112 and the first fuel supply valve 113 of the first oil fuel supply line 110, closes the second on-off valve 122 and the second fuel supply valve 123 of the second oil fuel supply line 120, and operates the first pump 111 to inject the oil fuel F1 from the first injection part 15a, thereby burning the oil fuel F1 at the low combustion position L. At this time, if a required load exceeding a combustion rate of 25% of the oil fuel F1 is requested from the load equipment, the combustion control unit 71 opens the first shutoff valve 142 and the second shutoff valve 144, and adjusts the aperture of the flow rate adjustment valve 143 based on the detection result of the ammonia fuel flow rate sensor 141 so that the amount of combustion of the ammonia fuel F2 corresponds to the combustion rate that is the difference between the combustion rate of the required load and the combustion rate at the low combustion position L. Note that the aperture of the flow rate adjustment valve 143 may be adjusted based on a database of flow rates that correspond to the combustion rates of the ammonia fuel F2, which is stored in the memory unit 72.

[0045] Furthermore, the combustion control unit 71 performs control to continuously increase the combustion amount of ammonia fuel F2 by adjusting the valve opening of the flow rate control valve 143 while maintaining the combustion position of oil fuel F1 at the low combustion position L until the total combustion amount of oil fuel F1 and ammonia fuel F2 reaches the medium combustion position M set at 50% (combustion rate 50%) of the maximum combustion amount of the ammonia co-firing boiler apparatus 1. At this time, the co-firing rate of ammonia fuel F2 gradually increases to 50%.

[0046] As a result, the amount of ammonia fuel F2 is continuously changed within a predetermined range of combustion amount, and it is possible to avoid starting and stopping the combustion of the ammonia fuel F2 in the burner 10, thereby suppressing the amount of unburned ammonia that increases when the combustion of the ammonia fuel starts and stops. Furthermore, since the combustion amount of the ammonia mixed-fuel boiler apparatus 1 is continuously changed according to the required load from the load equipment, it is possible to respond quickly and flexibly to fluctuations in the required load.

[0047] Furthermore, when the total combustion amount of the oil fuel F1 and the ammonia fuel F2 reaches a combustion amount corresponding to the combustion rate at which the combustion position of the oil fuel F1 is changed, the combustion control unit 71 stops the supply of the ammonia fuel F2, and then changes the combustion position of the oil fuel F1. Furthermore, when the combustion amount of the ammonia fuel F2 increases so that the total combustion amount of the oil fuel F1 and the ammonia fuel F2 reaches a combustion amount corresponding to the combustion rate at which the combustion position of the oil fuel F1 is changed, the combustion control unit 71 changes the combustion position of the oil fuel F1 to a next higher combustion position. Furthermore, when changing the combustion position of the oil fuel F1, the combustion control unit 71 closes the first shutoff valve 142 and the second shutoff valve 144 as ammonia shutoff valves.

[0048] Specifically, the combustion control unit 71 performs the following control: As shown in Fig. 2 , the combustion control unit 71 adjusts the valve opening of the flow rate control valve 143 so as to increase the combustion amount of the ammonia fuel F2 while maintaining the combustion position of the oil fuel F1 at the low combustion position L. When the total combustion amount of the oil fuel F1 and the ammonia fuel F2 converted based on the calorific value of the oil fuel F1 reaches a combustion amount corresponding to the intermediate combustion position M set at a combustion rate of 50% by increasing the combustion amount of the ammonia fuel F2, the combustion control unit 71 closes the first shutoff valve 142 and the second shutoff valve 144 to stop the supply of the ammonia fuel F2, and opens the first on-off valve 112 and the first fuel supply valve 113 so that the combustion amount of the oil fuel F1 corresponds to the intermediate combustion position M, and while keeping the first pump 111 in operation, opens the second on-off valve 122 and the second fuel supply valve 123 of the second oil fuel supply line 120 where the supply of the oil fuel F1 has stopped, and operates the second pump 121 to inject the oil fuel F1 from the second injection unit 15b. As a result, the combustion control unit 71 changes the combustion position of the oil fuel F1 to a higher combustion position. Here, when the combustion position of the oil fuel F1 is changed from the low combustion position L to the medium combustion position M, the mixed combustion rate of the ammonia fuel F2 is 0%.

[0049] When the total combustion amount of the oil fuel F1 and the ammonia fuel F2 is changed and the combustion rate corresponding to the combustion position of the oil fuel F1 is reached, the supply of the ammonia fuel F2 is temporarily stopped and the combustion position of the oil fuel F1 is changed. Since the supply of the ammonia fuel F2 is resumed after the combustion position of the oil fuel F1 is changed, the ammonia fuel F2 is not burned when combustion becomes unstable due to the change in the combustion position of the oil fuel F1, and it is possible to avoid the generation of unburned ammonia.

[0050] Furthermore, when the total combustion amount of the oil fuel F1 and the ammonia fuel F2 reaches a combustion rate at which the combustion position of the oil fuel F1 is changed due to an increase in the combustion amount of the ammonia fuel F2, the combustion position of the oil fuel F1 is changed to a combustion position one step higher, thereby making it possible to continuously change the combustion amount of the ammonia co-firing boiler apparatus 1 over a wide range of combustion amounts, from the low combustion position L (combustion rate 25%) of the oil fuel F1 to the maximum combustion amount (combustion rate 100%) of the ammonia co-firing boiler apparatus 1. Furthermore, by closing the first shutoff valve 142 and the second shutoff valve 144 as ammonia shutoff valves, it is not necessary to wait for the closing operation of the flow control valve 143 as an ammonia flow rate control valve, which takes time to close, and the combustion position of the oil fuel F1 can be changed in a short time.

[0051] 2, thereafter, the combustion control unit 71 continuously controls the combustion position of the oil fuel F1 to be maintained at the intermediate combustion position M and the combustion amount of the ammonia fuel F2 to be continuously increased until the total combustion amount of the ammonia co-firing boiler system 1 corresponding to the required load reaches a combustion amount equivalent to 100% (combustion rate 100%) of the maximum combustion amount of the ammonia co-firing boiler system 1. At this time, the combustion rate of the ammonia fuel F2 gradually increases to 50%, and accordingly the co-firing rate gradually increases to 50%.

[0052] Specifically, the combustion control unit 71 burns the oil fuel F1 at the intermediate combustion position M, and opens the first shutoff valve 142 and the second shutoff valve 144 when a required load exceeding a combustion rate of 50% is requested from the load equipment. Furthermore, the combustion control unit 71 adjusts the aperture of the flow rate control valve 143 based on the detection result of the ammonia fuel flow rate sensor 141 so that the combustion amount of the ammonia fuel F2 corresponds to a combustion rate that is the difference between the combustion rate of the required load and the combustion rate at the intermediate combustion position M. The aperture of the flow rate control valve 143 may be adjusted based on a database of flow rates corresponding to the combustion rates of the ammonia fuel F2 stored in the storage unit 72. Furthermore, the combustion control unit 71 performs control to continuously increase the combustion amount of the ammonia fuel F2 by adjusting the aperture of the flow rate control valve 143 while maintaining the combustion position of the oil fuel F1 at the intermediate combustion position M until the total combustion amount of the oil fuel F1 and the ammonia fuel F2 reaches a combustion amount corresponding to a combustion rate of 100%.

[0053] 2 , when the total combustion amount of the ammonia-mixed combustion boiler system 1 corresponding to the required load decreases after reaching a combustion rate of 100%, the combustion control unit 71 maintains the combustion position of the oil fuel F1 at the medium combustion position M until the combustion amount reaches a combustion amount corresponding to a combustion rate of 50%. The combustion control unit 71 also controls the combustion amount of the ammonia fuel F2 to continuously decrease by adjusting the aperture of the flow rate adjustment valve 143. As a result, the combustion rate of the ammonia fuel F2 gradually decreases from 50% to 0%. When the total combustion amount of the ammonia-mixed combustion boiler system 1 reaches a combustion rate of 50%, the combustion control unit 71 closes the first shutoff valve 142 and the second shutoff valve 144 to stop the supply of the ammonia fuel F2.

[0054] 2, when the total combustion amount of the ammonia co-firing boiler apparatus 1 is further reduced from the combustion rate of 50% in response to a reduction in the required load, the combustion control unit 71 keeps the first on-off valve 112 and the first fuel supply valve 113 open and the first pump 111 in operation, and continues to supply oil fuel F1 from the first jetting unit 15a. On the other hand, the combustion control unit 71 closes the second on-off valve 122 and the second fuel supply valve 123, stops the second pump 121, and stops the supply of oil fuel F1 from the second jetting unit 15b.

[0055] At the same time, the combustion control unit 71 continuously controls the combustion amount of the ammonia fuel F2 so that the total combustion amount of the ammonia-mixed combustion boiler system 1 corresponds to the required load. As shown in Fig. 2 , the combustion position of the oil fuel F1 is maintained at the low combustion position L, and the combustion amount of the ammonia fuel F2 is controlled to be continuously increased so that the total combustion amount of the ammonia-mixed combustion boiler system 1 reaches a combustion rate of 50% from a combustion rate of 25%.

[0056] Specifically, the combustion control unit 71 opens the first shutoff valve 142 and the second shutoff valve 144 when a required load exceeding a combustion rate of 25% is requested by the load equipment. The combustion control unit 71 also adjusts the aperture of the flow rate control valve 143 based on the detection result of the ammonia fuel flow rate sensor 141 so that the combustion amount of the ammonia fuel F2 corresponds to the combustion rate difference between the combustion rate of the required load and the combustion rate at the low combustion position L. The aperture of the flow rate control valve 143 may be adjusted based on a database of flow rates corresponding to the combustion rates of the ammonia fuel F2 stored in the storage unit 72. In FIG. 2 , the combustion control unit 71 maintains the aperture of the flow rate control valve 143 based on the detection result of the ammonia fuel flow rate sensor 141 so that the combustion amount of the ammonia fuel F2 corresponds to 15% of the maximum combustion amount of the ammonia co-firing boiler apparatus 1 (combustion rate of 15%) when the total combustion amount of the oil fuel F1 and the ammonia fuel F2 reaches a combustion amount corresponding to a combustion rate of 40%.

[0057] When the total combustion amount of the ammonia co-firing boiler system 1 corresponding to the required load reaches a combustion amount corresponding to a combustion rate of 40%, the oil fuel F1 is burned at a combustion amount corresponding to a combustion rate of 25%, and the ammonia fuel F2 is burned at a combustion amount corresponding to 15% of the maximum combustion amount of the ammonia co-firing boiler system 1. At this time, the co-firing rate of the ammonia fuel F2 is 37.5%.

[0058] The ammonia-mixed combustion boiler system 1 described above provides the following effects.

[0059] (1) The ammonia co-firing boiler apparatus 1 of this embodiment includes a burner 10 to which oil fuel F1 and ammonia fuel F2 are supplied, a boiler body 30 that recovers heat from combustion gas resulting from the combustion of fuel ejected from the burner 10, a control unit 70, an oil fuel supply line 130 that supplies oil fuel F1 to the burner 10, an ammonia supply line 140 that supplies ammonia fuel F2 to the burner 10, a combustion air supply line 200 that supplies combustion air A0 to the burner 10, and an exhaust gas line 33 that is connected to the boiler body 30 and through which combustion gas generated by the combustion of the oil fuel F1 and the ammonia fuel F2 in the boiler body 30 flows. The control unit 70 enables the oil fuel F1 to be combusted at a plurality of staged combustion positions, and also includes a combustion control unit 71 that enables the ammonia fuel F2 to be combusted by continuously changing the combustion amount of the ammonia fuel F2 within a predetermined range. As a result, the amount of ammonia fuel F2 continuously changes within a predetermined range of combustion amount, and therefore the amount of ammonia fuel F2 supplied to the burner 10 does not increase abruptly, making it possible to suppress the generation of unburned ammonia in the burner 10. Furthermore, the combustion amount of the ammonia-mixed combustion boiler apparatus 1 continuously changes in accordance with the required load from the load equipment, making it possible to respond quickly and flexibly to fluctuations in the required load.

[0060] (2) In the ammonia co-firing boiler apparatus 1 described in (1) above, the combustion control unit 71 changes the combustion position of the oil fuel F1 after stopping the supply of the ammonia fuel F2. As a result, when combustion is likely to become unstable due to a gradual change in the combustion position of the oil fuel F1, the ammonia fuel F2 is not burned, and it is possible to avoid the generation of unburned ammonia.

[0061] (3) In the ammonia co-firing boiler apparatus 1 described in (1) and (2) above, when the total combustion amount of the oil fuel F1 and the ammonia fuel F2 reaches a combustion amount corresponding to a combustion rate set in accordance with the combustion position, the combustion control unit 71 stops the supply of the ammonia fuel F2 and then changes the combustion position of the oil fuel F1. When the total combustion amount of the oil fuel F1 and the ammonia fuel F2 reaches a combustion rate corresponding to the combustion position of the oil fuel F1 by changing the total combustion amount of the oil fuel F1 and the ammonia fuel F2, the supply of the ammonia fuel F2 is temporarily stopped and the combustion position of the oil fuel F1 is changed. As a result, the supply of the ammonia fuel F2 is resumed after the combustion position of the oil fuel F1 is changed, and therefore the ammonia fuel F2 is not burned when combustion is likely to become unstable due to a gradual change in the combustion position of the oil fuel F1, and therefore it is possible to avoid the generation of unburned ammonia.

[0062] (4) In the ammonia co-firing boiler system 1 described in (1) to (3) above, when the total combustion amount of the oil fuel F1 and the ammonia fuel F2 reaches a combustion amount corresponding to a combustion rate set according to the combustion position due to an increase in the combustion amount of the ammonia fuel F2, the combustion control unit 71 shifts the combustion position of the oil fuel F1 to a next higher combustion position. As a result, when the total combustion amount of the oil fuel F1 and the ammonia fuel F2 reaches a combustion rate set according to the combustion position due to an increase in the combustion amount of the ammonia fuel F2, the combustion position of the oil fuel F1 is shifted to a next higher combustion position, thereby making it possible to continuously change the combustion amount of the ammonia co-firing boiler system 1 over a wide range of combustion amounts.

[0063] (5) In the ammonia co-firing boiler apparatus 1 described in (1) to (4) above, the ammonia supply line 140 includes a flow control valve 143 as an ammonia flow control valve and a first shutoff valve 142 and a second shutoff valve 144 as ammonia shutoff valves, and the combustion control unit 71 closes the first shutoff valve 142 and the second shutoff valve 144 as ammonia shutoff valves when changing the combustion position of the oil fuel F1. By closing the first shutoff valve 142 and the second shutoff valve 144 as ammonia shutoff valves, it is not necessary to wait for the closing operation of the flow control valve 143 as an ammonia flow control valve, which takes time to close, and the combustion position of the oil fuel F1 can be changed in a short time.

[0064] Second Embodiment Next, a second embodiment of the present invention will be described. In this embodiment, the same configuration of the ammonia co-firing boiler apparatus 1 as in the first embodiment is used. Note that in the second embodiment, the combustion rates of the oil fuel F1 at the low combustion position L and the medium combustion position M are different from those in the first embodiment. Accordingly, in the second embodiment, the maximum value of the ammonia co-firing rate when the oil fuel F1 is burned at the combustion position of the medium combustion position M is larger than that in the first embodiment. In the following description, emphasis will be placed on the differences from the first embodiment, and a description of the commonalities with the first embodiment may be omitted.

[0065] Fig. 3 is a graph showing the combustion rate and ammonia fuel combustion rate at a certain time in the ammonia-fuel-fuel boiler apparatus 1 of the second embodiment according to the present invention. In the graph shown in Fig. 3, the combustion rate and ammonia fuel combustion rate on the vertical axis are the same as those on the vertical axis of the graph in Fig. 2. In the second embodiment, the low combustion position L of the oil fuel F1 is set to a combustion rate of 20%, and the medium combustion position of the oil fuel F1 is set to a combustion amount of 40%.

[0066] In this embodiment, when oil fuel F1 is combusted at the low combustion position L, the combustion control unit 71 continuously controls the co-combustion ratio of ammonia fuel F2 within a range of 0% to 50%, and continuously controls the combustion amount within a combustion range of 20% or more of the maximum combustion amount of the ammonia co-combustion boiler apparatus 1 (combustion rate 20%, corresponding to the low combustion position L of oil fuel F1) to 40% or less of the maximum combustion amount (combustion amount 40%). Here, the combustion amount of ammonia fuel F2 refers to the combustion amount converted based on the calorific value of oil fuel F1. Furthermore, when co-combustion is performed with ammonia fuel F2 while oil fuel F1 is being combusted at the medium combustion position M, the combustion control unit 71 continuously changes the co-combustion ratio of ammonia fuel F2 within a range of 0% to 60%.

[0067] 3 , the combustion control unit 71 burns the oil fuel F1 at the low combustion position L, and when a required load exceeding a combustion rate of 20% is requested from the load equipment, starts the combustion of the ammonia fuel F2 so that the combustion amount of the ammonia fuel F2 corresponds to the combustion rate difference between the combustion rate of the required load and the combustion rate at the low combustion position L. The combustion control unit 71 also performs control to continuously increase the combustion amount of the ammonia fuel F2 while maintaining the combustion position of the oil fuel F1 at the low combustion position L until the total combustion amount of the oil fuel F1 and the ammonia fuel F2 reaches a combustion amount corresponding to the middle combustion position M set at 40% (combustion rate 40%) of the maximum combustion amount of the ammonia co-firing boiler apparatus 1. At this time, the combustion amount of the ammonia fuel F2 increases to 20% of the maximum combustion amount of the ammonia co-firing boiler apparatus 1, and the co-firing rate of the ammonia fuel F2 increases to 50%.

[0068] When the combustion amount of ammonia fuel F2 is increased and the total combustion amount of the combustion amount of oil fuel F1 and the combustion amount of ammonia fuel F2 reaches the combustion amount corresponding to the medium combustion position M set at a combustion rate of 40%, the combustion control unit 71 stops the supply of ammonia fuel F2 and controls the supply of oil fuel F1 so that the combustion amount of oil fuel F1 corresponds to the medium combustion position M. In this way, the combustion control unit 71 changes the combustion position of oil fuel F1 to a combustion position one step higher. Here, when the combustion position of oil fuel F1 is changed from the low combustion position L to the medium combustion position M, the mixed combustion rate of ammonia fuel F2 is 0%.

[0069] Thereafter, the combustion control unit 71 continuously controls the combustion position of the oil fuel F1 to be maintained at the intermediate combustion position M and the combustion amount of the ammonia fuel F2 to be continuously increased until the total combustion amount of the ammonia co-firing boiler system 1 corresponding to the required load reaches a combustion amount equivalent to 100% of the maximum combustion amount of the ammonia co-firing boiler system 1. At this time, the co-firing ratio of the ammonia fuel F2 increases to 60%.

[0070] 3, the upper limit of the co-firing ratio of ammonia fuel F2 when oil fuel F1 is at the medium combustion position M is 60%, which is higher than the 50% co-firing ratio of ammonia fuel F2 when oil fuel F1 is at the low combustion position L. When oil fuel F1 is at the medium combustion position M, the total combustion amount of oil fuel F1 and ammonia fuel F2 combined is larger and the combustion state is more stable than when oil fuel F1 is at the low combustion position L, so stable combustion can be achieved even if the ammonia co-firing ratio is increased. Furthermore, by increasing the ammonia co-firing ratio at the maximum combustion amount, the effect of reducing carbon dioxide emissions can be increased.

[0071] That is, in the second embodiment, the upper limit of the ammonia fuel co-firing ratio in the range in which the combustion amount can be continuously changed is set higher at the combustion position (medium combustion position M) of oil fuel F1 where the combustion rate is maximum when co-firing with ammonia fuel F2, compared to the combustion position (low combustion position L) of oil fuel F1 where the combustion rate is minimum when co-firing with ammonia fuel F2. As a result, according to this embodiment, the ammonia co-firing ratio at the maximum combustion amount can be increased, and the effect of reducing carbon dioxide emissions can be enhanced.

[0072] Furthermore, according to this embodiment, among the combustion positions of the oil fuel F1 that are set in stages, the combustion amount at the combustion position that results in the smallest combustion amount is reduced, for example, by setting the combustion amount at the low combustion position L to 10% of the maximum combustion amount, the TDR (turndown ratio) is increased, and the load following capability and the stability of the ammonia fuel can be improved.

[0073] The ammonia-mixed combustion boiler system 1 described above provides the following effects.

[0074] (6) In the ammonia co-firing boiler system 1 described in (1) to (5) above, the upper limit of the ammonia co-firing ratio in the range in which the combustion amount of the ammonia fuel F2 can be continuously changed at the combustion position with the highest combustion rate among the plurality of combustion positions of the oil fuel F1 for co-firing with the ammonia fuel F2 is higher than the upper limit of the ammonia co-firing ratio in the range in which the combustion amount of the ammonia fuel F2 can be continuously changed at the combustion position with the lowest combustion rate among the plurality of combustion positions of the oil fuel F1 for co-firing with the ammonia fuel F2. This increases the ammonia co-firing ratio at the maximum combustion amount, thereby enhancing the effect of reducing carbon dioxide emissions. Furthermore, by reducing the combustion amount at the combustion position with the lowest combustion amount among the combustion positions of the oil fuel F1 that are set in stages, for example, by setting the combustion amount at the low combustion position L to 10% of the maximum combustion amount, the turndown ratio (TDR) is increased, thereby simultaneously achieving both load following and stable combustion of the ammonia fuel F2.

[0075] Third Embodiment Next, a third embodiment of the present invention will be described. In this embodiment, the same configuration as in the first embodiment is used for the ammonia-mixed combustion boiler system 1. In the following description, differences from the first embodiment will be emphasized, and descriptions of commonalities with the first embodiment may be omitted. FIG. 4 is a graph showing the combustion rate and ammonia fuel mixing rate at a certain time in the ammonia-mixed combustion boiler system 1 of the third embodiment of the present invention. In the graph shown in FIG. 4, the combustion rate and ammonia mixing rate on the vertical axis are the same as those on the vertical axis of the graph in FIG. 2 described above. In this embodiment, the combustion control unit 71 controls the combustion position of the oil fuel F1 in three stages: a combustion stop position (combustion rate 0%), a medium combustion position M (combustion rate 50%), and a high combustion position H (combustion rate 100%).

[0076] In this embodiment, when the oil fuel F1 is at the intermediate combustion position M, the combustion control unit 71 continuously changes the combustion amount of the ammonia fuel F2 within a range of 0% to 50% of the maximum combustion amount of the ammonia co-firing boiler apparatus 1, and burns the ammonia fuel F2. Here, the combustion amount of the ammonia fuel F2 refers to the combustion amount converted based on the calorific value of the oil fuel F1. Furthermore, when the oil fuel F1 is being burned at the intermediate combustion position M and the ammonia fuel F2 is to be co-fired, the combustion control unit 71 continuously changes the co-firing ratio of the ammonia fuel F2 within a range of 0% to 50%.

[0077] 4 shows an example in which the ammonia co-firing boiler apparatus 1 in a cold state receives a boiler combustion start command. The combustion control unit 71 receives the boiler combustion start command and changes the combustion position of the oil fuel F1 from the combustion stop position to the high combustion position H. The combustion control unit 71 starts combustion of the oil fuel F1 at the high combustion position H and continues for a predetermined time. Here, when the combustion position of the oil fuel F1 is the high combustion position H, the co-firing ratio of the ammonia fuel F2 is 0%.

[0078] 4, when the total combustion amount of the ammonia co-firing boiler apparatus 1 is controlled within a combustion rate range lower than 100% in response to a decrease in the required load, the combustion control unit 71 changes the combustion position of the oil fuel F1 to a combustion position one step lower so that the combustion amount of the oil fuel F1 corresponds to the medium combustion position M (combustion rate of 50%). When the combustion position of the oil fuel F1 is changed from the high combustion position H to the medium combustion position M, the co-firing rate of the ammonia fuel F2 is 0%.

[0079] Thereafter, the combustion control unit 71 maintains the combustion position of the oil fuel F1 at the intermediate combustion position M and continuously controls the combustion amount of the ammonia fuel F2 so that the total combustion amount of the ammonia co-firing boiler apparatus 1 corresponds to the required load. As a result, the total combustion amount quickly reaches the combustion rate corresponding to the previous decrease in the required load. Here, if the total combustion amount corresponding to the previous decrease in the required load is, for example, an 80% combustion rate, the total combustion amount is maintained at an 80% combustion rate if the required load continues to be constant. At this time, the ammonia co-firing ratio is maintained at 37.5%. FIG. 4 illustrates a case where the required load increases after the previous decrease in the required load. The total combustion amount increases beyond the 80% combustion rate, and the ammonia co-firing ratio increases beyond 37.5%. Note that the control of the flow rate of the ammonia fuel F2 by the combustion control unit 71 when a required load exceeding a combustion rate of 50% is requested by the load equipment is the same as in the first embodiment.

[0080] 4, the present embodiment illustrates a case in which the combustion control unit 71 controls the combustion state of the oil fuel F1 at three combustion positions: the combustion stop position (combustion rate 0%), the medium combustion position M (combustion rate 50%), and the high combustion position H (combustion rate 100%). However, for example, the control may be at four stages: the combustion stop position (combustion rate 0%), the low combustion position L (25%), the medium combustion position M (combustion rate 50%), and the high combustion position H (combustion rate 100%). Increasing the number of combustion positions for the oil fuel F1 reduces the difference in combustion rate between the respective combustion positions, thereby improving the responsiveness to the required load.

[0081] The ammonia-mixed combustion boiler system 1 of this embodiment described above has the same effects as the ammonia-mixed combustion boiler system 1 described in the above (1) to (5). In addition, the ammonia-mixed combustion boiler system 1 of this embodiment can have the following effects.

[0082] (7) In the ammonia co-firing boiler apparatus 1, if combustion is started with the heat exchanger, heat insulating material, etc. cooled to the ambient temperature or a predetermined temperature or below, the flame is cooled and unburned ammonia is likely to be generated. However, according to this embodiment, the oil fuel F1 is burned at a combustion rate of 100% during cold start-up, so the preheating time required to stably start ammonia co-firing can be shortened and ammonia co-firing can be started earlier.

[0083] Although a preferred embodiment of the ammonia co-firing boiler apparatus 1 as a boiler according to the present invention has been described above, the present invention is not limited to the above embodiment and can be modified as appropriate. Modified embodiments of the boiler according to the present invention will be described below.

[0084] (Modifications) The ammonia fuel is a gas fuel containing ammonia as a main component, and may be an ammonia decomposition gas containing ammonia.

[0085] In each embodiment, an example has been shown in which the flow rate of the ammonia fuel F2 and the flow rate of the combustion air A0 are detected by a flow sensor (ammonia fuel flow sensor 141, air flow sensor 202), but the present invention is not limited to this. The flow rate sensor may be a combination of a pressure loss section (an orifice or the like) and a pressure measurement section (a pressure gauge, a differential pressure gauge or the like) provided in each flow path.

[0086] In each embodiment, the ammonia co-fuel boiler apparatus 1 according to the present invention includes a burner 10, a boiler body 30 including multiple water tubes 40, a lower header 50, and an upper header 60, and the combustion chamber 32 is surrounded by the multiple water tubes 40. Examples of such boilers include small-scale once-through boilers, and for ships, marine water tube boilers and marine composite boilers. The boiler according to the present invention may also be a fire-tube boiler in which multiple pipes through which combustion gases burned in a combustion furnace circulate are arranged underwater, and steam is generated by heat exchange between the multiple pipes and the water. The present invention may also be applied to furnaces without water-cooled walls, such as heating furnaces and incinerators. In these boilers and combustion apparatuses, the combustion amount is controlled (the combustion amount fluctuates) in response to fluctuations in the required load or control of heating conditions, thereby effectively suppressing the generation of unburned material due to changes in the combustion amount.

[0087] In the first and second embodiments, cases where the combustion rate of the oil fuel F1 is switched to the "combustion stop position," "low combustion position L," and "medium combustion position M" are shown, and in the third embodiment, cases where the combustion rate of the oil fuel F1 is switched to the "combustion stop position," "medium combustion position M," and "high combustion position H" are shown, but the setting of the combustion rate of the oil fuel F1 is not limited to this. The combustion rate of the oil fuel F1 may be switched to three or more stages. For example, by providing a third oil fuel supply line (not shown) and controlling the supply of oil fuel from these three supply lines, the combustion rate of the oil fuel F1 can be controlled in more stages. For example, if the combustion rates when the first to third oil fuel supply lines are burned alone are 20%, 30%, and 50%, the combustion rate of the oil fuel F1 can be set to 20%, 30%, 50%, and 100% by combining the oil fuel supply lines to be opened.

[0088] Furthermore, in each embodiment, an example has been shown in which, when the oil fuel F1 burns at the low combustion position L, the oil fuel F1 is injected from only one of the two oil fuel ejection portions 15, and when the oil fuel F1 burns at the medium combustion position M, the oil fuel F1 is injected from both oil fuel ejection portions 15. However, this is not limiting, and even when the oil fuel F1 burns at the medium combustion position M, a configuration may be adopted in which the oil fuel F1 equivalent to the combustion amount at the medium combustion position M is injected from only one oil fuel ejection portion 15. In this case, a flame is formed from a single oil fuel ejection portion 15 at both the low combustion position L and the medium combustion position M. Therefore, compared to a case in which a flame is formed from two oil fuel ejection portions 15, a uniform flame is formed with no overlapping portions of the oil combustion flame, and unburned ammonia can be further suppressed.

[0089] Furthermore, since the present invention promotes the use of ammonia as a fuel, which does not emit carbon dioxide, it can contribute to, for example, Goal 7 of the Sustainable Development Goals (SDGs) led by the United Nations, which is to "ensure access to affordable, reliable, sustainable and modern energy."

[0090] REFERENCE SIGNS LIST 1 Ammonia co-firing boiler apparatus 10 Burner 15 Oil fuel ejection section 17 Ammonia fuel ejection section 30 Boiler body 33 Exhaust gas line 70 Control section 71 Combustion control section 130 Oil fuel supply line 140 Ammonia supply line 200 Combustion air supply line A0 Combustion air F1 Oil fuel F2 Ammonia fuel L1 Oil fuel flow path L3 Ammonia flow path

Claims

1. A boiler comprising: a burner to which oil fuel and ammonia fuel are supplied; a boiler body for recovering heat from combustion gas produced when fuel sprayed from the burner is combusted; a control unit; an oil fuel supply line for supplying the oil fuel to the burner; an ammonia supply line for supplying the ammonia fuel to the burner; a combustion air supply line for supplying combustion air to the burner; and an exhaust gas line connected to the boiler body through which combustion gas generated by combustion of the oil fuel and the ammonia fuel in the boiler body flows, wherein the control unit enables the oil fuel to be combusted at a plurality of staged combustion positions, and also comprises a combustion control unit for enabling the combustion of the ammonia fuel by continuously changing the amount of combustion of the ammonia fuel within a predetermined range.

2. The boiler according to claim 1, wherein the combustion control unit changes the combustion position of the oil fuel after stopping the supply of the ammonia fuel.

3. The boiler as described in claim 1, wherein the combustion control unit changes the combustion position of the oil fuel after stopping the supply of the ammonia fuel when a total combustion amount of the oil fuel and the ammonia fuel reaches a combustion amount corresponding to a combustion rate set according to the combustion position.

4. The boiler as described in claim 3, wherein the combustion control unit changes the combustion position of the oil fuel to a higher combustion position when the total combustion amount reaches a combustion amount corresponding to a combustion rate set according to the combustion position due to an increase in the combustion amount of the ammonia fuel.

5. The boiler as described in claim 1, wherein an upper limit ammonia fuel co-combustion ratio of a range in which the combustion amount of the ammonia fuel can be continuously changed at a combustion position of the maximum combustion rate for co-combustion with the ammonia fuel among the plurality of stepwise combustion positions of the oil fuel is greater than an upper limit ammonia fuel co-combustion ratio of a range in which the combustion amount of the ammonia fuel can be continuously changed at a combustion position of the minimum combustion rate for co-combustion with the ammonia fuel among the plurality of stepwise combustion positions of the oil fuel.

6. The boiler as described in claim 1, wherein the ammonia supply line is provided with an ammonia flow rate control valve and an ammonia shutoff valve, and the combustion control unit closes the ammonia shutoff valve when the combustion position of the oil fuel is changed.

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