Boiler

Abstract

A boiler according to the present invention includes: a burner for burning hydrogen fuel and combustion air to generate combustion gas; and a rectangular can body in which a plurality of water pipes are arranged at predetermined intervals in a gas flow space. The water pipes are arranged so that a longitudinal direction thereof is a vertical direction in the gas flow space, and are configured so that water is supplied from a lower end part thereof and steam is discharged from an upper end part thereof. The burner is disposed at a position biased downward in the vertical direction of the gas flow space, and ejects the combustion air or a premixed gas of the combustion air and the hydrogen fuel so as to form a main flow direction of the combustion gas in a direction perpendicular to the longitudinal direction of the water pipes facing the burner. An expansion region for expanding the flow of the combustion gas in the upward direction of the gas flow space is provided between the water pipes on the downstream side of the water pipe in the first row adjacent to the burner.

Description

Boiler

[0001] This application claims priority based on Japanese Patent Application No. 2024-170434 filed in Japan on September 30, 2024, and incorporates its content herein. The present invention relates to a boiler that burns hydrogen fuel.

[0002] Conventionally, boilers that use hydrogen fuel mainly composed of hydrogen as fuel are known. Boilers that burn hydrogen fuel have attracted attention in that they do not generate carbon dioxide by combustion. On the other hand, since hydrogen fuel has a faster combustion rate and a higher combustion temperature than hydrocarbon gas, suppression of NOx generation during combustion has become an important issue. For example, in Patent Document 1, a technique for suppressing NOx generation by adding moisture to hydrogen fuel has been devised. Also, in boilers that use hydrocarbon gas as fuel, NOx reduction techniques for adjusting the combustion gas temperature (the temperature of the combustion flame) by cold bodies near the burner are known (for example, Patent Document 2).

[0003] Japanese Patent Application Laid-Open No. 2020-26921, Patent Publication No. 2824619

[0004] In the boiler with a rectangular can body structure that uses hydrocarbon gas as fuel shown in Patent Document 2, the combustion gas directly heats the water pipe group to generate steam, and the combustion gas temperature is kept low by cooling the combustion gas in the water pipe group, and it has been shown that generation of harmful exhaust substances such as NOx can be suppressed. However, in a boiler in the form shown in Patent Document 2, if hydrogen fuel is burned, since the combustion gas temperature near the burner becomes high, there is concern about overheating of the water pipes and an increase in thermal NOx generation.

[0005] An object of the present invention is to provide a boiler that can suppress NOx generation while preventing problems due to overheating of the water pipes and can maintain heat exchange performance.

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

[0007] The boiler of the present invention comprises a burner that burns hydrogen fuel and combustion air to generate combustion gas, and a rectangular boiler body in which a plurality of water tubes are arranged at predetermined intervals within a gas flow space, wherein the water tubes are arranged so that their longitudinal direction is in the vertical direction within the gas flow space, water is supplied from the lower end and steam is released from the upper end, wherein the burner is positioned at a lower-biased position in the vertical direction within the gas flow space, and the combustion air or a premixed gas of combustion air and hydrogen fuel is ejected perpendicular to the longitudinal direction of the water tubes facing the burner so as to form the main flow direction of the combustion gas, and an expansion region is provided between the water tubes downstream of the first row of water tubes adjacent to the burner, which expands the flow of the combustion gas upward within the gas flow space.

[0008] Furthermore, it is preferable that the burner ejects at least a portion of the combustion air and at least a portion of the hydrogen fuel from one or more different nozzles, thereby causing diffusion combustion of the combustion air and the hydrogen fuel.

[0009] Furthermore, it is preferable that at least some of the water tubes are arranged in a staggered pattern, and that the enlarged region is formed by omitting one or more of the water tubes.

[0010] Furthermore, it is preferable that the upper end of the nozzle for the combustion air or the premixed gas of the combustion air and the hydrogen fuel is positioned within 70% of the vertical dimension of the gas flow space relative to the lower end of the burner.

[0011] According to the present invention, it is possible to provide a boiler that can suppress the generation of NOx while preventing malfunctions caused by overheating of water tubes, and while maintaining heat exchange performance.

[0012] This is a diagram illustrating the boiler of the first embodiment. It is a cross-sectional view of the boiler body. This is a diagram illustrating an enlarged area.

[0013] 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.

[0014] (First Embodiment) Figure 1 is a diagram illustrating a boiler 1 of the first embodiment. Figure 2 is a cross-sectional view of the boiler body 10. The boiler 1 of this embodiment is a boiler that uses hydrogen fuel F1 as fuel, and is, for example, a once-through boiler. The boiler 1 comprises a boiler body 10 and a burner 20. The boiler 1 also comprises an exhaust stack 40, a hydrogen fuel supply line L100 and an air supply line L200. In this specification, "line" is a general term for a flow path, route, pipeline, etc.

[0015] In this specification and in the claims, hydrogen fuel F1 includes not only hydrogen gas consisting solely of hydrogen, but also mixed gases mainly composed of hydrogen and other gases. In the case of mixed gases, it is preferable that the volume concentration of hydrogen is 50% or more (hydrogen ratio of 0.5 or more). In the case of a mixed gas of hydrocarbon fuel and hydrogen, the combustion rate increases sharply when the hydrogen ratio exceeds 0.5. On the other hand, when the hydrogen ratio is small, the combustion temperature and combustion rate tend to become closer to those of hydrocarbon fuels (combustion temperature is lower and combustion rate is lower compared to the combustion of hydrogen alone) (see reference: "Ekenechukwu C. Okafor, Yukihide Nagano, Toshiaki Kitagawa, “Experimental and theoretical analysis of cellular instability in lean H2-CH4-air flames at elevated pressures”, International Journal of Hydrogen Energy 41 (2016) p6581-6592"). Therefore, when using a hydrogen-based mixed gas as the hydrogen fuel F1, a hydrogen volume concentration of 50% or more is preferable, and from the viewpoint of achieving the combustion temperature and combustion rate of a hydrogen combustion boiler, a hydrogen volume concentration of 70% or more is more preferable. In this embodiment, an example in which hydrogen gas is used as the hydrogen fuel F1 will be described.

[0016] The boiler body 10 generates steam by heating water supplied to water pipes 11 inside the boiler body 10. The boiler body 10 is rectangular in shape, and as shown in Figure 2, it has a rectangular cross-section, with multiple water pipes 11 arranged at predetermined intervals within a rectangular gas flow space S in plan view. The boiler body 10 also includes a lower header 12, an upper header 13, etc. The boiler body 10 may be approximately rectangular or cubic in shape, and the gas flow space S may also be approximately rectangular. A burner 20 is arranged on one side of the boiler body 10, and an exhaust pipe 40 is connected to the side opposite to the side on which the burner 20 is arranged. In Figures 1 and 2, the vertical direction of the gas flow space S is indicated by arrow d1, and the direction parallel to the main flow direction of the combustion gas is indicated by arrow d2. In this embodiment, we will explain using an example where the directions of arrows d1 and d2 are orthogonal, but the angle between the directions of arrows d1 and d2 may be approximately orthogonal (an angle that can be considered orthogonal), and is not limited to this. Also, in the main flow direction of the combustion gas (direction of arrow d2), the burner 20 side is the upstream side and the exhaust pipe 40 side is the downstream side.

[0017] The water pipe 11 is positioned between the upper header 13 and the lower header 12 such that its longitudinal direction is vertical in the gas flow space S. Water is supplied to the water pipe 11 from its lower end, which is connected to the lower header 12, and steam is released from its upper end, which is connected to the upper header 13. The steam released from the water pipe 11 is supplied to a steam-using facility (not shown) via a steam extraction means (not shown) connected to the upper header 13.

[0018] Furthermore, as shown in Figure 2, in this embodiment, within the boiler body 10, the water tube 11 located on the outermost side in the short direction of the water tube group is connected in the longitudinal direction (direction of arrow d2) by a connecting part 14, forming a water tube wall 15. The boiler body 10 has a gas flow space S formed by this pair of water tube walls 15, the lower header 12, and the upper header 13.

[0019] As shown in Figure 2, the water pipes 11 are arranged in a staggered pattern at predetermined intervals within the gas flow space S inside the boiler 10. Furthermore, if we designate the row of water pipes from the row closest to the burner 20 towards the exhaust pipe 40 as the 1st row, 2nd row, and so on, an expanded region E is formed within the water pipe group downstream of the 1st row of water pipes 11, which is closest to the burner 20. This expanded region E has the function of expanding the flow of combustion gas upwards within the boiler 10. In Figure 2, the expanded region E is the area shaded.

[0020] This expanded region E is formed, for example, by removing one or more water pipes 11 from a group of water pipes arranged in a staggered pattern. In this embodiment, the expanded region E is shown as being formed by removing water pipes 11 located in the fourth row from the burner 20 side and some water pipes 11 located in the fifth row in the main gas flow direction (direction of arrow d2). The rows and number of water pipes removed may be selected as appropriate, as long as they can adequately fulfill the function of the expanded region E.

[0021] The burner 20 burns hydrogen fuel F1 and combustion air A1 to generate combustion gas. The burner 20 is a premixed burner with a planar premixed gas ejection surface 20a, and multiple nozzles for ejecting premixed gas are arranged on this premixed gas ejection surface 20a. The hydrogen fuel F1 supplied from the hydrogen fuel supply line L100 and the combustion air A1 supplied from the air supply line L200 are supplied to the burner 20 as a premixed gas. In this embodiment, the hydrogen fuel supply line L100 is connected to the air supply line L200 near the burner 20, and the hydrogen fuel F1 and combustion air A1 are mixed in the air supply line L200 downstream of this connection point. The premixed gas ejected from the premixed gas ejection surface 20a of the burner 20 is ignited by an ignition means such as a pilot burner (not shown), and a combustion gas accompanied by a flame F is formed in the burner 20.

[0022] The burner 20 is positioned at a location that is biased downward in the vertical direction of the gas flow space S of the boiler body 10. With the burner 20 positioned as described above, the flame F generated by the combustion of the hydrogen fuel F1 strikes the lower side of the water pipe 11, particularly in the vicinity of the burner 20. Furthermore, it is preferable that the uppermost end of the premixed gas nozzle at the premixed gas nozzle surface 20a is positioned within 70% of the vertical dimension of the gas flow space S from the lower end of the gas flow space S in the vertical direction (direction of arrow d1) of the gas flow space S.

[0023] Furthermore, the burner 20 injects a premixed gas of hydrogen fuel F1 and combustion air A1 in a direction perpendicular to the longitudinal direction of the water tube 11 (direction of arrow d1 in Figure 1) (direction of arrow d2 in Figure 1). Note that the angle that the direction in which the burner 20 injects the premixed gas makes with the longitudinal direction of the water tube 11 may be strictly perpendicular, or it may be inclined at an angle that can be considered perpendicular. Also, when the premixed gas of hydrogen fuel F1 and combustion air A1 is injected in a direction that makes a certain angle (for example, 45 degrees or less) with respect to the longitudinal direction of the water tube 11, it is sufficient that the main flow direction of the combustion gas is formed perpendicular to the longitudinal direction of the water tube facing the burner 20 (direction of arrow d1) (direction of arrow d2).

[0024] The exhaust pipe 40 has its inlet on the side of the boiler 10 facing the burner 20 and is located at the downstream end of the boiler 10. The combustion gas generated by the burner 20 comes into contact with the water pipes 11 that make up the boiler 10 to exchange heat, and is then discharged as exhaust gas to the outside of the boiler 1 through the exhaust pipe 40.

[0025] The boiler 1 of this embodiment is configured as described above, and based on this configuration, the following combustion state is formed inside the boiler 1. The premixed gas of hydrogen fuel F1 and combustion air A1 is ejected from the burner 20 in a direction perpendicular to the longitudinal direction of the water tubes 11 inside the boiler body 10. The combustion gas accompanied by a flame F undergoes heat exchange with the multiple water tubes 11 inside the boiler body 10, and further, after the combustion is completed, the combustion gas undergoes heat exchange with the multiple water tubes 11 before becoming exhaust gas. The exhaust gas is discharged to the outside of the boiler 1 through an exhaust pipe 40 provided on the downstream side of the boiler body 10. As shown in Figure 1, the flame F from the combustion of hydrogen fuel F1 extends downstream of the first row of water tubes 11 facing the burner 20 in the gas flow direction (direction of arrow d2). The flame F generated at the burner 20 undergoes heat exchange with the water tubes 11 near the burner 20 simultaneously with the combustion reaction. As the flame F strikes the water pipe 11, the combustion gas G is cooled, which lowers the combustion gas temperature and suppresses the generation of harmful exhaust substances such as NOx.

[0026] Furthermore, the burner 20 is positioned on the lower side in the vertical direction of the gas flow space S, and the flame F strikes the lower side of the water pipe 11 in the vicinity of the burner 20. Since the water pipe 11 is supplied with water from its lower end and releases steam from its upper end, the upper side tends to become hot. Because the burner 20 is positioned in a location biased towards the lower side of the gas flow space S, the flame F mainly heats the lower side of the water pipe 11 in the vicinity of the burner 20, which contains water, and less heat is applied to the upper side, which tends to become hot. This prevents the upper part of the water pipe 11, which tends to become hot, from being heated by the flame F and suffering damage due to overheating.

[0027] As mentioned above, the water tube 11 is supplied with water from its lower end and releases steam from its upper end. In such a water tube, the degree of dryness of the steam increases as it approaches the water tube outlet at the upper end, and the heat transfer coefficient from the tube wall deteriorates. Therefore, it is common practice to slightly lower the degree of dryness at the water tube outlet to prevent overheating of the tube and to separate the moisture using a steam-water separator installed downstream of the boiler. Overheating of the water tube due to excessive dryness, resulting in insufficient liquid to wet the inner wall, should be prevented from the standpoint of preventing malfunctions, regardless of which water tube outlet is at. Furthermore, the range of water levels in the water tubes that allows for sufficient liquid to wet the tube wall while keeping the degree of dryness at the water tube outlet low is narrow, and this appropriate water level changes depending on the boiler operating conditions (boiler pressure, combustion rate, etc.).

[0028] As in this embodiment, in a burner 20 that burns hydrogen fuel F1, which has a high combustion temperature and a fast combustion speed, it is necessary to form the flame F while avoiding the upper part of the water tube 11 where overheating is likely to occur, and to ensure wetting of the inner wall of the water tube 11, direct heating by the flame must be limited to near the control water level. For this reason, it is preferable that in the vertical direction (direction of arrow d1) of the gas flow space S, the upper end of the premixed gas ejection surface 20a of the burner 20 is positioned at a location that is 70% of the vertical dimension of the gas flow space S from the lower end of the gas flow space S. In this embodiment, by positioning the burner 20 at a location that satisfies this condition, damage to the water tube 11 due to overheating can be effectively suppressed.

[0029] The combustion gas, accompanied by a flame F from the burning of hydrogen fuel F1, spreads within the water tube group as it moves downstream, and in the expanded region E, it spreads further upward in the gas flow space S. The water in the water tubes 11 is heated by heat exchange with the combustion gas and turns into steam. This steam is supplied to steam-using equipment (not shown) via steam extraction means (not shown) connected to the upper header 13. The combustion gas spreads within the water tube group of water tubes 11 arranged in a staggered pattern within the boiler body 10, and after heat exchange with the water tubes 11, it is discharged outside the boiler 1 as exhaust gas from the exhaust stack 40 located at the downstream end of the boiler body 10.

[0030] Figure 3 is a diagram illustrating the expanded region E. Figure 3(a) schematically shows a part of the boiler body 10 of this embodiment that has the expanded region E, and Figure 3(b) schematically shows a comparative example boiler body 10B that does not have the expanded region. In the comparative example boiler body 10B shown in Figure 3(b), similar to the boiler body 10 shown in Figure 3(a), the burner 20 is located on the lower side in the vertical direction of the gas flow space S. In Figure 3, for ease of understanding, the shape of the burner 20 and the like are simplified, the flow of combustion gas G is indicated by arrows, and the water pipe 11 is shaded. In the comparative example boiler body 10B shown in Figure 3(b), because the burner 20 is located on the lower side in the vertical direction of the gas flow space S, the combustion gas G generated by the burner 20 is located on the lower side of the gas flow space S near the burner 20, and gradually spreads upward as it moves downstream in the gas flow direction. Therefore, the upper portion of the upstream water pipes 11 does not contribute effectively to heat exchange, and although this tendency gradually improves as you move to downstream water pipes 11, it still extends over a wide area of ​​the water pipe group.

[0031] In contrast, in the boiler body 10 of this embodiment shown in Figure 3(a), the premixed gas ejected from the burner 20 burns in the combustion region near the burner 20 and is located below the gas flow space S. The combustion gas G flows into the expanded region E where the water tubes 11 have been removed and the vertical flow resistance caused by the water tubes 11 has decreased, and spreads upward in the space of the expanded region E. Downstream of the expanded region E, the combustion gas G spreads throughout the entire gas flow space S and flows downstream. As a result, the entire surface of the water tubes 11 can be effectively used as a heat transfer surface to perform heat exchange. Therefore, in the boiler body 10, heat exchange in the water tubes 11 downstream of the expanded region E in the gas flow space S can be promoted, and the efficiency of heat exchange can be improved.

[0032] Furthermore, since the expanded region E does not have water pipes 11, the cooling effect on the combustion gas G is reduced, and the flow cross-sectional area of ​​the combustion gas G is increased, resulting in a slower flow velocity of the combustion gas G. Consequently, in the expanded region E, the residence time of the combustion gas G at the temperature at which the hydrogen combustion reaction continues is increased, and the combustion gas G that has flowed through different flow paths formed by the water pipes 11 mixes. As a result, in the expanded region E, the unburned hydrogen remaining upstream of the expanded region E can be sufficiently burned, thereby suppressing the generation of unburned hydrogen. Normally, when the temperature of the combustion gas is lowered to suppress the generation of NOx, unburned substances such as unburned hydrogen remain in the exhaust gas. In order to reduce unburned hydrogen, it is necessary to raise the temperature of the combustion gas, but in that case, the generation of NOx increases. As in this embodiment, by providing the expanded region E downstream of the first row, which is closest to the burner 20 in the water pipe group, the remaining unburned hydrogen can be suppressed and NOx can be reduced.

[0033] Furthermore, it is preferable that the expansion region E be located downstream of the first row of water tubes, which is closest to the burner 20, in the group of water tubes arranged within the gas flow space S, at a position where the flame temperature is approximately 1000 to 1300°C. If the flame temperature is 1300°C or higher when it enters the expansion region E, the long residence time of the combustion gas G in the expansion region E will generate a large amount of NOx. Therefore, by positioning the expansion region E at a position where the flame temperature is approximately 1000 to 1300°C, the generation of NOx can be suppressed. In addition, by positioning the expansion region E as described above, the combustion gas G spreads upward in the gas flow space S while maintaining a temperature sufficient for heat exchange, thereby improving the efficiency of heat exchange in the downstream water tube 11. Furthermore, even when the combustion gas G spreads upward in the gas flow space S and comes into contact with the upper part of the water tube 11 downstream of the expansion region E, the temperature of the combustion gas G is sufficiently lower than the temperature of the high-temperature part of the flame, thus suppressing overheating of the upper part of the water tube 11.

[0034] As described above, this embodiment provides the following effects: (1) The boiler 1 comprises a burner 20 that burns hydrogen fuel F1 and combustion air A1 to generate combustion gas G, and a rectangular boiler body 10 in which a plurality of water tubes 11 are arranged at predetermined intervals within the gas flow space S. The water tubes 11 are arranged so that their longitudinal direction is in the vertical direction in the gas flow space S, with water supplied from the lower end and steam released from the upper end. The burner 20 is positioned at a lower-biased position in the vertical direction of the gas flow space S, and injects combustion air A1 or a premixed gas of combustion air A1 and hydrogen fuel F1 (in this embodiment, premixed gas) perpendicular to the longitudinal direction of the water tubes 11 facing the burner 20 so as to form the main flow direction of the combustion gas G. Downstream of the first row of water tubes 11 adjacent to the burner 20, between the water tubes 11, an expansion region is provided that expands the flow of the combustion gas G upward in the gas flow space S.

[0035] In boiler 1, the burner 20 injects a premixed gas of combustion air A and hydrogen fuel F1 perpendicular to the longitudinal direction of the water tube 11, and the main flow direction of the combustion gas G is formed perpendicular to the longitudinal direction of the water tube 11 facing the burner 20. As a result, the combustion gas G flows quickly to the downstream side of the gas flow space S, and the flame from the burner 20 hits the water tube 11, cooling the combustion gas G, so that the temperature of the combustion gas is kept low and the generation of harmful exhaust substances such as NOx is suppressed. Furthermore, the burner 20 is positioned at a lower-biased position in the vertical direction of the gas flow space S and is located facing the lower side of the water tube 11 which contains water. As a result, the upper part of the water tube 11 near the burner 20, which tends to become hot, is not heated by the high-temperature combustion gas and is prevented from being damaged by overheating. In addition, since boiler 1 has an expansion region E, the flow of combustion gas G can be expanded upward in the gas flow space S downstream of the expansion region E. As a result, boiler 1 can promote heat exchange in the water tubes 11 downstream of the expanded region E, and maintain a sufficiently high heat exchange efficiency. In addition, boiler 1 can effectively burn hydrogen fuel F1 in the expanded region E, reducing unburned hydrogen in the exhaust gas.

[0036] (2) In the boiler 1, the multiple water tubes 11 are arranged such that at least some of them are in a staggered pattern, and the expanded region E is formed by missing one or more water tubes 11. By providing the expanded region E and arranging the water tubes 11 in a staggered pattern, the combustion gas G spreads upward in the gas flow space S, promoting heat exchange in the water tubes 11 downstream of the expanded region E. In addition, the mixing of the combustion gas G is further promoted, the combustion reaction progresses, and heat exchange (cooling of the flame) occurs simultaneously with the combustion reaction effectively. This makes it possible to more efficiently achieve both a reduction in unburned hydrogen and a suppression of NOx.

[0037] (3) In the boiler 1, the burner 20 is positioned such that the upper end of the nozzle for the combustion air A1 or the premixed gas of combustion air A1 and hydrogen fuel F1 (in this embodiment, the nozzle for the premixed gas) is located within 70% of the vertical dimension of the gas flow space S from the lower end. By positioning the burner 20 in this manner, the flame formed by the combustion air A1 and hydrogen fuel F1 ejected from the burner 20 hits the lower side of the water tube 11 located near the burner 20 where water is present, and is less likely to hit the upper part of the water tube 11, which tends to become hot due to the presence of water vapor inside. This suppresses problems such as damage to the water tube 11 due to overheating.

[0038] (Second Embodiment) The boiler of the second embodiment is similar in form to the boiler 1 of the first embodiment, except that the burner is a diffusion combustion burner. Therefore, parts that perform the same functions as those of the first embodiment described above are given the same reference numerals or the same reference numerals at the end, and redundant explanations are omitted as appropriate. The burner of this embodiment is a diffusion combustion burner that ejects at least a portion of the combustion air A1 and at least a portion of the hydrogen fuel F1 from one or more different nozzles, and diffusely combusts the combustion air A1 and the hydrogen fuel F1.

[0039] In this embodiment, the burner is connected to a hydrogen fuel supply line L100, and multiple hydrogen fuel nozzles for ejecting hydrogen fuel F1 are regularly arranged on substantially the same plane. The hydrogen fuel F1 is ejected from each hydrogen fuel nozzle at approximately the same flow velocity. In addition, the burner in this embodiment is connected to an air supply line L200, and multiple air nozzles for ejecting combustion air A1 are regularly arranged on substantially the same plane. The combustion air A1 is ejected from each air nozzle at approximately the same flow velocity. In this embodiment, the multiple hydrogen fuel nozzles and the multiple air nozzles are arranged on different planes.

[0040] The burner of this embodiment ejects combustion air A1 from multiple air nozzles perpendicular to the longitudinal direction of the water tube 11 (direction of arrow d1 in Figure 1) (direction of arrow d2 in Figure 1), and ejects hydrogen fuel F1 from multiple hydrogen fuel nozzles to promote mixing with the combustion air A1. The direction of ejection of combustion air A1 may be strictly perpendicular to the longitudinal direction of the water tube 11, or it may be inclined at an angle that can be considered perpendicular. Furthermore, when combustion air A1 is ejected in a direction that forms a certain angle (for example, 45 degrees or less) with respect to the longitudinal direction of the water tube 11, it is sufficient that the main flow direction of the combustion gas is formed perpendicular to the longitudinal direction of the water tube facing the burner 20 (direction of arrow d1) (direction of arrow d2). Furthermore, the injection direction of the hydrogen fuel F1 is preferably in a direction that promotes mixing with the combustion air A1, and is intersecting with the injection direction of the combustion air A1, which in this embodiment is perpendicular to it.

[0041] The boiler 2 of this embodiment is configured as described above, and based on this configuration, the following combustion state is formed inside the boiler 1. First, hydrogen fuel F1 is injected from a plurality of hydrogen fuel nozzles, and combustion air A1 is injected from a plurality of air nozzles. At least a portion of the injected hydrogen fuel F1 mixes with the injected combustion air A1 and is ignited by an ignition device (not shown), forming a combustion gas with a flame F in the burner 20.

[0042] As described above, the burner of the present embodiment is a diffusion combustion burner, in which the hydrogen fuel F1 and the combustion air A1 are ejected from different ejection ports and burn while being mixed. Therefore, compared with a premixed burner in which the hydrogen fuel F1 and the combustion air A1 are mixed in advance, flashback is less likely to occur in the hydrogen fuel supply line L100, and the safety of the boiler can be improved.

[0043] In addition, since the hydrogen fuel F1 ejected from the plurality of hydrogen fuel ejection ports burns while being mixed with the combustion air A1, the flame F spreads over a wider range between the water pipes 11 arranged in the gas flow space S compared to a premixed burner. At this time, in the hydrogen fuel F1, which has a higher combustion rate and flammability compared to general hydrocarbon fuels, diffusion combustion continues while the hydrogen fuel F1 and the combustion air A1 are mixed, and at the same time, heat exchange occurs between the combustion gas G containing unburned hydrogen and the water pipes 11 arranged in the combustion space, the temperature of the combustion gas decreases, and the generation of harmful exhaust gases such as NOx can be suppressed. Further, in the expansion region E, the cooling effect on the combustion gas G in the space where the water pipes 11 are removed is small, and in addition to the flow velocity of the combustion gas G becoming slow, the combustion gases G flowing through different flow paths formed by the water pipes 11 are mixed. As a result, the expansion region E can expand the flow of the combustion gas G upward in the gas flow space S, suppress the generation of NOx, and promote the combustion of unburned hydrogen remaining upstream of the expansion region E.

[0044] As described above, according to the present embodiment, similar to the first embodiment described above, it is possible to suppress the generation of NOx while preventing problems due to overheating of the water pipes 11, and to maintain sufficient heat exchange performance.

[0045] According to the present embodiment, in addition to the effects of (1) to (3) described above, the following effects can be achieved. (4) In the boiler, the burner ejects at least a part of the combustion air A1 and at least a part of the hydrogen fuel F1 from different one or more ejection ports, and the combustion air A1 and the hydrogen fuel F1 are subjected to diffusion combustion.

[0046] The burner of this embodiment is a diffusion combustion burner, in which the ejected hydrogen fuel F1 burns while mixing with combustion air A1. Therefore, compared with a premixed burner, the burner of this embodiment has a larger flame spread, can perform heat exchange (cooling of the flame) simultaneously with the combustion reaction, can reduce the combustion temperature, and suppress the generation of NOx. In addition, when burning hydrogen fuel F1 with a premixed burner, there is a risk of flashback. However, since the burner of this embodiment is a diffusion combustion burner, flashback can be prevented and the safety of the boiler can be improved.

[0047] (Modified form) Without being limited to the embodiments described above, various modifications and changes are possible, and they are also within the scope of the present invention. In this embodiment, an example of using hydrogen gas as the hydrogen fuel F1 is shown. However, it is not limited to this, and a mixed gas with a hydrogen volume concentration of 50% or more may be used. Also, in this embodiment, an example in which the water pipes 11 are arranged in a staggered pattern is shown. However, a form in which a part of the water pipe group is arranged in a staggered pattern and the rest are arranged in a lattice pattern may also be used.

[0048] In the first embodiment, an example in which the premixed gas of hydrogen fuel F1 and combustion air A1 is ejected in a direction perpendicular to the longitudinal direction of the water pipe 11 has been described. However, it is not limited to this, and it may be ejected in a direction forming an angle of 45 degrees or less in a direction perpendicular to the longitudinal direction of the water pipe 11. In the second embodiment as well, the combustion air A1 may be ejected in a direction forming an angle of 45 degrees or less in a direction perpendicular to the longitudinal direction of the water pipe 11.

[0049] In the second embodiment, an example in which a plurality of air ejection ports for ejecting combustion air A1 are regularly arranged on substantially the same plane has been described. However, it is not limited to this, and the combustion air A1 may be ejected from a single air ejection port.

[0050] Each embodiment and modified form can be used in appropriate combination, but detailed description is omitted. In addition, the present invention is not limited by the embodiments described above.

[0051] Furthermore, since the present invention promotes the use of hydrogen, which does not emit carbon dioxide as a fuel, it can contribute, for example, to United Nations Sustainable Development Goal (SDG) 7, "Ensure access to affordable, reliable, sustainable and modern energy."

[0052] 1 Boiler 10 Boiler body 11 Water tube 12 Lower header 13 Upper header 20 Burner 40 Exhaust stack S Gas flow space E Enlarged area

Claims

1. A boiler comprising: a burner that burns hydrogen fuel and combustion air to generate combustion gas; and a rectangular boiler body in which a plurality of water tubes are arranged at predetermined intervals within a gas flow space, wherein the water tubes are arranged so that their longitudinal direction is in the vertical direction within the gas flow space, with water supplied from the lower end and steam released from the upper end, wherein the burner is positioned at a lower-biased position in the vertical direction within the gas flow space, and injects the combustion air or a premixed gas of the combustion air and hydrogen fuel in a direction perpendicular to the longitudinal direction of the water tubes facing the burner so as to form the main flow direction of the combustion gas, and an expansion region is provided between the water tubes downstream of the first row of water tubes adjacent to the burner, which expands the flow of the combustion gas upward within the gas flow space.

2. The boiler according to claim 1, wherein the burner ejects at least a portion of the combustion air and at least a portion of the hydrogen fuel from one or more different nozzles, and diffusely combusts the combustion air and the hydrogen fuel.

3. The boiler according to claim 1, wherein at least a portion of the plurality of water tubes are arranged in a staggered pattern, and the enlarged region is formed by the absence of one or more water tubes.

4. The boiler according to claim 1, wherein the upper end of the nozzle for the combustion air or a premixed gas of the combustion air and the hydrogen fuel is positioned within 70% of the vertical dimension of the gas flow space in the vertical direction of the gas flow space.

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