Gas / oil selectable burner

Abstract

To provide a gas / oiling switching mono-fuel combustion burner capable of obtaining a high turndown ratio and promoting low NOx while suppressing CO generation.SOLUTION: A gas / oiling switching mono-fuel combustion burner 100 includes: a combustion cylinder 10 composed so that combustion air flows inside; an oil burner unit 20 inside a combustion cylinder which has a plurality of oil spray nozzles including two low combustion nozzles, a middle combustion nozzle, and a high combustion nozzle, and a baffle plate 24 having a central opening; a frame funnel 30 which has an enlarged diameter cylinder part 32 enlarged forward and an end opening 30a and are arranged in front of the combustion cylinder and the oil burner unit; and a plurality of gas nozzles 40 which are provided so that they go through an inside an insertion hole 32a formed in the enlarged cylinder part 32 of the frame funnel from outside and a gas jet port 42 is located inside the frame funnel.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a gas / oil switching dedicated burner, and particularly to a gas / oil switching dedicated burner that can achieve low NOx and low CO while achieving a high turndown ratio.

Background Art

[0002] Conventionally, as combustion devices used in water heaters, steam boilers, etc., gas burners and oil burners are widely and commonly used. As an oil burner, a pressure spray type oil burner (hydraulic spray combustion device) equipped with a plurality of fuel spray nozzles is known. In this type of oil burner, multi-stage combustion can be performed by appropriately selecting the nozzles for spraying fuel and adjusting the overall spray amount.

[0003] Patent Documents 1 and 2 by the present applicant disclose a pressure spray type oil burner including four oil spray nozzles: two low combustion nozzles, a medium combustion nozzle, and a high combustion nozzle. In these oil burners, the two low combustion nozzles are arranged opposite to each other across the burner central axis, and the medium combustion nozzle and the high combustion nozzle are arranged opposite to each other across the burner central axis.

[0004] In this configuration, primary air is supplied through the central opening of the flame retention plate, and fuel is sprayed from the two low combustion nozzles so as to evenly overlap, thereby enabling more stable low combustion. As a result, while suppressing the generation of CO (carbon monoxide), a high turndown ratio of, for example, 1:4 or less can be achieved. Also, by appropriately selecting the nozzles for spraying fuel, three-stage combustion of low, medium, and high can be performed.

[0005] The turndown ratio refers to the ratio of the minimum fuel flow rate or minimum combustion amount that can be stably controlled to the rated fuel flow rate or rated combustion amount of the combustion device. Here, a smaller ratio (for example, 1:4 or 1:5 compared to the conventional 1:2) is described as a high turndown ratio or an improved turndown ratio.

[0006] Furthermore, a gas / oil switching burner is also known as a combustion device, which is configured to allow switching between fuel gas and fuel oil for combustion (for example, Patent Documents 3 and 4). In such a switching burner, multiple fuel gas nozzles are provided at intervals along the circumferential direction around a fuel oil spray nozzle located near the burner's central axis. The gas / oil switching burner can switch between gas-only combustion and oil-only combustion in the same combustion range by selecting the fuel to be used. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2019-211095 [Patent Document 2] Patent No. 6679471 [Patent Document 3] Japanese Patent Application Publication No. 5-280716 [Patent Document 4] Japanese Patent Application Publication No. 62-26412 [Patent Document 5] Patent No. 4963621 [Patent Document 6] Japanese Patent Publication No. 2010-249425 [Patent Document 7] Japanese Patent Publication No. 2008-032381 [Overview of the project] [Problems that the invention aims to solve]

[0008] In recent years, there has been an increasing demand for reducing NOx (nitrogen oxides) and CO emissions in all types of burners, including gas burners, oil burners, and gas / oil switching burners, as part of environmental protection measures. Patent documents 5 to 7 disclose gas burners or oil burners to which various technologies are applied to control combustion and achieve low NOx and low CO emissions.

[0009] NOx generated during combustion includes thermal NOx, which is produced when nitrogen and oxygen in the air react at high temperatures, and fuel NOx, which is produced when nitrogen components in the fuel are oxidized during combustion. To suppress the generation of NOx associated with combustion, it is effective to take measures such as lowering the flame temperature to eliminate localized high-temperature regions, lowering the oxygen concentration in the combustion zone, or shortening the residence time of combustion gases in high-temperature regions.

[0010] However, in conventional oil-fired burners in particular, in order to achieve a high turndown ratio while suppressing CO generation, it was necessary to design the burner configuration in a way that made it easier for the flame temperature to rise, which led to the problem of increased NOx generation. Therefore, it was beneficial to provide a gas / oil-switchable dedicated burner that could enable oil-fired combustion at a high turndown ratio, as well as gas-fired combustion, and further reduce NOx emissions.

[0011] The present invention was made to solve the above problems, and its objective is to provide a gas / oil switching dedicated burner that can achieve a high turndown ratio while also reducing CO and NOx emissions. [Means for solving the problem]

[0012] A gas / oil switching dedicated burner according to an embodiment of the present invention comprises: a combustion cylinder configured such that combustion air flows through the inside; an oil burner unit disposed inside the combustion cylinder, comprising a plurality of oil spray nozzles including two low-combustion nozzles, a medium-combustion nozzle, and a high-combustion nozzle; a flame-holding plate having a central opening and provided so as not to cover the spray ports of the plurality of oil spray nozzles; a flame funnel disposed in front of the combustion cylinder and the oil burner unit, comprising an enlarged diameter cylindrical portion that expands toward the front and having a tip opening; and a plurality of gas nozzles disposed on the outer circumference of the oil burner unit, comprising a plurality of insertion holes formed in the enlarged diameter cylindrical portion of the flame funnel, each penetrating from the outside to the inside of the flame funnel, such that the gas injection port is located inside the flame funnel.

[0013] In one embodiment, a gap is provided between an insertion hole formed in the frame funnel and a gas nozzle that passes through it, and the circulating gas is configured to pass through the gap.

[0014] In one embodiment, the protruding length of each of the plurality of gas nozzles, which is the length in front of the combustion cylinder in the burner axis direction, is set to be 0.3 to 0.4 times the length of the flame funnel in the burner axis direction, and the diameter of the gas nozzle arrangement circle where the nozzle centers of the plurality of gas nozzles are located is set to be larger than the diameter of the combustion cylinder.

[0015] In one embodiment, the gas injection section at the tip of each of the plurality of gas nozzles, where the gas injection port is formed, is provided with a protruding portion positioned further forward and a base portion positioned further back than the protruding portion, wherein the base portion is positioned closer to the burner central axis than the protruding portion.

[0016] In one embodiment, a step is formed between the protruding portion and the base portion of the gas ejection section.

[0017] In one embodiment, a flow restricting portion for improving the flow velocity by locally reducing the gas passage cross-sectional area is provided inside each of the plurality of gas nozzles.

[0018] In one embodiment, inside the combustion cylinder, a swirling blade for swirling the primary air passing through the central opening of the flame holding plate of the oil burner unit is further provided, which is disposed behind the flame holding plate of the oil burner unit.

[0019] In one embodiment, the frame funnel further includes a same-diameter cylinder portion disposed in front of the enlarged-diameter cylinder portion, and an annular throttle portion disposed in front of the same-diameter cylinder portion and having the tip opening on the inside.

[0020] In one embodiment, the diameter of the gas nozzle arrangement circle at the center of the nozzles of the plurality of gas nozzles is larger than or equal to the diameter of the tip opening provided inside the annular throttle portion.

[0021] In one embodiment, the two low-combustion nozzles are opposed to each other across the burner central axis, the medium-combustion nozzle and the high-combustion nozzle are opposed to each other across the burner central axis, the plurality of oil spray nozzles are evenly arranged along the circumferential direction around the burner central axis, and the plurality of gas nozzles are evenly spaced along the circumferential direction on the outer peripheral side of the oil burner unit.

[0022] In one embodiment, the plurality of gas nozzles are eight gas nozzles, and are configured to be capable of three-stage combustion when using either fuel of oil or gas.

Advantages of the Invention

[0023] According to the gas / oil switching dedicated burner according to the embodiment of the present invention, it is possible to arbitrarily switch and use both gas and oil as fuels, and to achieve low NOx and low CO while realizing a high turndown ratio.

Brief Description of the Drawings

[0024] [Figure 1] This is a cross-sectional view showing the overall configuration of a gas / oil switching dedicated burner according to an embodiment of the present invention. [Figure 2] This figure shows the positional relationships of each component when viewed from the flame direction (along the burner's central axis) of a gas / oil switching dedicated burner according to an embodiment of the present invention. [Figure 3] This figure shows the combustion section of an oil burner unit in a gas / oil switching dedicated burner according to an embodiment of the present invention, where (a) is a side view and (b) is a diagram showing the positional relationship of each component when viewed from the direction of the flame. [Figure 4] This is a side view showing the gas nozzle, which is fixed to the burner body, and the flame funnel of a gas / oil switching dedicated burner according to an embodiment of the present invention, separated. [Figure 5] This is a cross-sectional view showing the gas-fired operation using a gas / oil-switchable dedicated burner according to an embodiment of the present invention. [Figure 6] These diagrams illustrate design examples for the tip position of the gas nozzle and the radius position of the arrangement circle. (a) is a cross-sectional view along the burner axis, and (b) is a diagram showing the arrangement of the gas nozzles as viewed from the burner axis. [Figure 7] This figure shows the detailed configuration of the gas nozzle in a gas / oil switching dedicated burner according to an embodiment of the present invention, where (a) is a perspective view and (b) is a cross-sectional view. [Figure 8] This figure shows the arrangement of each gas nozzle as viewed from the burner's central axis direction. [Modes for carrying out the invention]

[0025] The embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to the following embodiments.

[0026] Figure 1 is a cross-sectional view showing a gas / oil switching dedicated burner 100 according to an embodiment of the present invention. Figure 2 is a diagram showing the arrangement of each component when the gas / oil switching dedicated burner 100 is viewed from the flame direction (from bottom to top of the paper in Figure 1).

[0027] As shown in Figures 1 and 2, the gas / oil switching dedicated burner 100 comprises a combustion cylinder 10 that forms a flow path for combustion air, an oil burner unit 20 positioned inside the combustion cylinder 10, a flame funnel 30 positioned in front of the combustion cylinder 10 and the oil burner unit 20, and a plurality of gas nozzles 40 provided such that the gas injection port 42 at the tip is located inside the flame funnel 30. The combustion cylinder 10 is sometimes called a blast tube or draft tube.

[0028] The oil burner unit 20 is connected to a fuel oil supply line and can spray fuel oil in front of the combustion chamber 10, particularly inside the flame funnel 30, for combustion. In addition, multiple gas nozzles 40 are connected to a fuel gas supply line and can inject fuel gas in front of the combustion chamber 10, particularly inside the flame funnel 30.

[0029] The combustion chamber 10 is connected to a combustion air supply path from a blower via a wind box 12 for rectification, allowing combustion air to be supplied to the front of the combustion chamber 10 for mixing with fuel. The amount of combustion air supplied can be adjusted using an air damper or the like installed in the air supply line, and this adjustment allows for the generation of a suitable mixture for combustion in front of the combustion chamber 10.

[0030] In the gas / oil switching dedicated burner 100, oil spraying and gas injection into the flame funnel 30 can be easily switched with a single switch by controlling the opening and closing of valves provided in each fuel supply line. In this way, the gas / oil switching dedicated burner 100 is configured to easily switch between oil-only combustion and gas-only combustion in the same combustion area formed in front of the combustion cylinder 10 or inside the flame funnel 30.

[0031] In this specification, the direction downward in Figure 1, i.e., the direction in which fuel is injected from the fuel nozzle and a flame is formed, is referred to as "forward," and the opposite direction (i.e., upward in Figure 1) is referred to as "rearward." The "burner central axis" is an axis located inside the combustion chamber 10 and extending along the forward-rear direction, and is typically assumed to coincide with the central axis of the combustion chamber 10 and / or the oil burner unit 20.

[0032] The following describes the configuration of the gas / oil switching dedicated burner 100 in more detail. First, the detailed configuration of the oil burner unit 20 will be described.

[0033] As shown in Figures 3(a) and (b), the oil burner unit 20 of the gas / oil switching dedicated burner 100 of this embodiment includes a plurality of oil spray nozzles 22, a flame-holding plate 24 positioned in front of the oil spray nozzles 22 and having a central opening 24a so as not to cover the spray ports of the oil spray nozzles 22, and a swivel vane 26 positioned behind the spray ports of the oil spray nozzles 22 and the flame-holding plate 24, on the rear side.

[0034] The oil burner unit 20 may have a configuration similar to that of an oil-fired burner described in, for example, Patent Document 2. In this embodiment, four nozzles are provided as multiple oil spray nozzles 22: two low-combustion nozzles 22L, one medium-combustion nozzle 22M, and one high-combustion nozzle 22H.

[0035] Each oil spray nozzle 22 is an on / off control nozzle (full-flow nozzle or non-return nozzle) without a flow rate adjustment mechanism, and can spray fuel oil in a conical shape. The spray angle of each oil spray nozzle 22 is designed to be, for example, 30° to 60°. In this embodiment, by spraying high-pressure fuel oil (for example, fuel oil pressurized to 0.5 to 2.0 MPa by a fuel pump) from a selected nozzle among the plurality of oil spray nozzles 22, the fuel oil can be atomized without the need for an atomizing medium such as air or steam, and the resulting mixture can be burned by mixing it with combustion air.

[0036] The oil burner unit 20 configured as described above can perform three-stage combustion (low, medium, and high) (or four-position combustion: combustion stop, low combustion, medium combustion, and high combustion). Low combustion is performed by simultaneously spraying fuel from only two low-combustion nozzles 22L, medium combustion is performed by simultaneously spraying fuel from the two low-combustion nozzles 22L and the medium-combustion nozzle 22M, and high combustion is performed by simultaneously spraying fuel from all four oil spray nozzles 22. Which oil spray nozzles the fuel is sprayed from can be arbitrarily determined by controlling the opening and closing of on-off valves (such as solenoid valves) provided in each fuel supply line.

[0037] Furthermore, in this embodiment, the spray volume (corresponding to the nozzle diameter, etc.) of the two low-combustion nozzles 22L is designed to be equivalent, while the spray volume of the medium-combustion nozzle 22M and the high-combustion nozzle 22H is designed to be greater than the spray volume of the low-combustion nozzle 22L. The spray volume of the high-combustion nozzle 22c may be set to be greater than the spray volume of the medium-combustion nozzle 22M. More specifically, the spray volume of the two low-combustion nozzles 22L is set to, for example, 10% to 15% of the rated volume, the spray volume of the medium-combustion nozzle 22M is set to, for example, 20% to 40% of the rated volume, and the spray volume of the high-combustion nozzle 22H is set to, for example, 40% to 50% of the rated volume.

[0038] For example, the spray volume of each low-combustion nozzle 22L can be set to 10%, the spray volume of the medium-combustion nozzle 22M to 30%, and the spray volume of the high-combustion nozzle 22H to 50%. In this example, three-stage combustion at 20%, 50%, and 100% load is possible, and the turndown ratio can be set to 1:5 (minimum combustion amount is 20% of the rated combustion amount). However, the above example is not limited, and the spray volume of each nozzle can be set arbitrarily.

[0039] Furthermore, in the oil burner unit 20, the two low-combustion nozzles 22L are positioned opposite each other across the burner central axis 20x, and the medium-combustion nozzle 22M and the high-combustion nozzle 22H are also positioned opposite each other across the burner central axis 20x. These oil spray nozzles 22 are arranged evenly along the circumferential direction around the burner central axis, that is, equidistant and point-symmetric with respect to the burner central axis 20x. In addition, the tip of the ignition rod 28 for ignition is located near one of the spray ports of the low-combustion nozzles 22L.

[0040] In this configuration, as can be seen by referring to Figures 1 to 3, fuel oil is sprayed into the forward flame funnel 30 from each oil spray nozzle 22 along with primary air (combustion air supplied around the fuel injection port) through the central opening 24a of the flame holder plate 24. The central opening 24a typically has a circular planar shape, but is not limited to this and may have other planar shapes such as polygons.

[0041] On the other hand, secondary air (combustion air supplied to the combustible gasified fuel) is supplied from the outside of the flame holder plate 24, that is, from the gap between the combustion cylinder 10 and the flame holder plate 24, to the inner surface of the base of the flame funnel 30. By adopting this method of supplying combustion air in two stages, primary air and secondary air, and achieving complete combustion throughout the entire system, it is possible to reduce the oxygen concentration and flame temperature in the primary air supply region, which tends to be oxygen-deficient. Therefore, the amount of NOx generated can be suppressed to some extent.

[0042] Furthermore, in low-combustion conditions, the oil burner unit 20 supplies primary air through the central opening 24a and simultaneously sprays fuel in an overlapping manner from two opposing low-combustion nozzles 22L. This improves the fuel-air mixture balance even when the spray volume is small, compared to using a single nozzle in low-combustion conditions, thereby ensuring combustion stability. In addition, even in low-combustion conditions, high-pressure fuel oil can be sprayed from the nozzles to ensure sufficient atomization of the fuel, thus stabilizing combustion. By arranging the two low-combustion nozzles 22L opposite each other across the burner central axis 20x in this way, the high turndown ratio described above can be achieved while suppressing CO generation.

[0043] Furthermore, the oil burner unit 20 of this embodiment is provided with swirling vanes 26 located inside the combustion cylinder 10, behind the spray nozzle of the oil spray nozzle 22 and the flame holder plate 24, for swirling the primary air passing through the central opening 24a of the flame holder plate 24. This allows for improved mixing of the spray fuel and primary air in front of the flame holder plate 24.

[0044] The swirl vanes 26 are not limited to the six-bladed configuration shown in the figure, but may be provided in any other configuration as long as they can swirl the primary air. The number of blades of the swirl vanes 26 can be set to, for example, 4 to 12. Each blade of the swirl vanes 26 is usually positioned at an angle of, for example, 30 to 60° with respect to the burner central axis when viewed from the normal direction.

[0045] Furthermore, as shown in Figures 3(a) and 3(b), in this embodiment, the flame-holding plate 24 is provided with 4 to 12 (in this case, 8) slits 24b that extend radially from the central opening 24a. The slits 24b are provided, for example, as elongated end face openings at one side edge portion of the slit cover 24b' that extends radially from the central opening 24a. The slits 24b may be formed separately from the central opening 24a.

[0046] In the above configuration, the combustion air flowing into the combustion chamber 10 is given a certain degree of swirling motion by the swirling vanes 26, and then passes through the central opening 24a or slit 24b of the flame holder plate 24, where it is supplied intensively to the front of the flame holder plate 24 as primary air in a state of increased agitation. By supplying primary air in this manner, the spray fuel and primary air can be sufficiently and uniformly mixed in the negative pressure region, making it possible to obtain a more easily combustible gas. As a result, low combustion can be performed more stably while suppressing CO emissions, and the high turndown ratio described above can be achieved more easily.

[0047] In particular, as shown in the illustrated embodiment, by designing the diameter of the tip circle of the swivel vane 26 when viewed from the direction of the burner's central axis and the diameter of the circle formed at the tip of the slit 24b of the flame holder plate 24 to be approximately the same (within an error of 10%), the primary air flowing forward of the oil spray nozzle 22 can be effectively swirled.

[0048] In this way, by swirling the primary air using the swirling vanes 26 and slits 24b, it becomes possible to mix the primary air with the fuel sprayed from the oil spray nozzle 22 more uniformly, and at the same time, secondary air can be smoothly supplied DC-flow from the outside of the flame holder plate 24. As a result, stable combustion with better ignition stability and flame retention can be achieved. In addition, since uniform mixing of fuel and primary air is promoted, smoke generation at ignition is suppressed, incomplete combustion is suppressed and CO generation is reduced. With the oil burner unit 20, despite its compact design, three-stage stable combustion (low, medium, and high combustion) is possible, and it is possible to achieve a high turndown ratio while suppressing CO generation.

[0049] However, in the oil burner unit 20, in order to stabilize low combustion, the atomized fuel and primary air are concentrated near the burner's central axis and thoroughly mixed before stable combustion. Therefore, although the two-stage supply of combustion air can reduce the temperature somewhat, the flame temperature still tends to be high. Consequently, while a high turndown ratio can be obtained by using the oil burner unit 20 alone, it was not easy to sufficiently suppress NOx emissions.

[0050] Therefore, the gas / oil switching dedicated burner 100 of this embodiment is equipped with multiple gas nozzles 40 in addition to the oil burner unit 20 to enable gas firing in the same combustion range within the flame funnel 30. Furthermore, it enables three-stage combustion with a high turndown ratio even when switching to gas firing with a single switch, and achieves low CO and low NOx emissions. By using the gas / oil switching dedicated burner 100, both gas and oil can be used as fuel, and multi-stage combustion with a high turndown ratio is possible regardless of which fuel is used, and particularly improved low NOx emissions can be achieved when using gas firing.

[0051] Furthermore, three-stage combustion in gas-fired combustion can be easily achieved by switching the total gas flow rate injected from multiple gas nozzles 40 in three stages using a flow control valve installed in the gas supply line. In particular, by automatically switching the gas flow rate control to match the flow rate of combustion air (the amount of combustion air from a blower adjusted by a damper, etc.), it is possible to continuously perform three-stage combustion with the same heat output and a high turndown ratio by switching only the fuel when switching between oil-fired and gas-fired combustion.

[0052] Furthermore, gas-fired combustion is easier to achieve compared to oil-fired combustion, as it allows for more homogeneous and efficient combustion and relatively stable low-burnout conditions. This makes it easier to achieve low NOx emissions while maintaining a high turndown ratio. The gas / oil-switchable dedicated burner 100 can be operated primarily using gas-fired combustion, and can be switched to oil-fired combustion as a supplement when gas-fired combustion fails. This allows for the achievement of low NOx emissions while also obtaining the assurance of oil-fired combustion, providing continuous and stable appropriate burner function.

[0053] The following describes in more detail the configuration for low-NOx gas firing using multiple gas nozzles 40 in the gas / oil switching dedicated burner 100.

[0054] As can be seen from Figures 1 and 2, the multiple gas nozzles 40 for gas firing are evenly arranged along the circumferential direction on the outer circumference of the oil burner unit 20 (the side furthest from the burner central axis 20x). Furthermore, each gas nozzle 40 is positioned to penetrate the flame funnel 30 from the outside to the inside, such that the gas injection port 42 is located inside the flame funnel 30.

[0055] As shown in Figure 2, in this embodiment, eight gas nozzles 40 are used and are evenly arranged at 45° intervals around the burner central axis 20x (outside the flame holder plate 24). Also, as shown in the figure, in this embodiment, the gas nozzles 40 are provided so as to penetrate the flame funnel 30 near its base, such that their gas injection ports 42 are located on the outer circumference side of the combustion cylinder 10 (and the base cylindrical portion of the flame funnel 30). Furthermore, in this embodiment, the gas injection ports 42 of the gas nozzles 40 are located slightly outward from the tip opening 30a of the flame 30 when viewed from the burner axis direction.

[0056] The number of gas nozzles 40 is not limited to 8; for example, it may be 4 to 16. However, if the number is small, there is a risk of uneven distribution of gas from each nozzle, which could lead to variations in the concentration of the combustion gas and raise concerns about an increase in the combustion temperature and the temperature of the flame funnel 30. Also, if the number is large, an increase in manufacturing costs can be expected. For this reason, it is preferable to set the number of gas nozzles 40 to, for example, 6 to 12.

[0057] Figure 4 shows the state when the flame funnel 30 has been removed from the burner body to which the multiple gas nozzles 40 are fixed. In the burner body, the multiple gas nozzles 40 are commonly connected to a gas manifold 44 (formed integrally with the combustion cylinder 10 in this embodiment), and fuel gas is supplied commonly via a gas pipe 46. The burner body and the flame funnel 30 can be easily fixed together by screws or the like.

[0058] As shown in Figure 4, in this embodiment, the flame funnel 30 includes an enlarged diameter cylindrical portion 32 that expands in diameter toward the front, and has a tip opening 30a. Furthermore, the flame funnel 30 in the illustrated embodiment includes a cylindrical portion 34 of the same diameter positioned in front of the enlarged diameter cylindrical portion 32, and an annular constricted portion 36 positioned in front of the cylindrical portion 34 and having the tip opening 30a on its inner side. The inclination angle of the enlarged diameter cylindrical portion 32 with respect to the burner central axis 20x is set, for example, to 20° to 60°, more specifically to 30° to 45°, and the angle can be arbitrarily selected according to the required size of the combustion chamber.

[0059] In the examples shown in Figures 4 and 5, the constricted portion 36 of the frame funnel 30 has a shape in which it bends at approximately a right angle at the opening. However, as in the frame funnel 30 shown in Figure 1, the constricted portion 36 may be formed to include a curved portion, and the shape of the constricted portion 36 can be designed arbitrarily as long as it has a tip opening 30a on the inside. Furthermore, although the frame funnel 30 requires an enlarged diameter cylindrical portion 32, the cylindrical portion 34 of the same diameter and the constricted portion 36 are not necessarily provided.

[0060] Furthermore, as shown in Figure 4, the enlarged diameter cylindrical portion 32 of the frame funnel 30 is provided with multiple insertion holes 32a, each corresponding to a gas nozzle 40, at positions corresponding to the gas nozzles 40. When using eight gas nozzles 40 arranged evenly in the circumferential direction as described above, the enlarged diameter cylindrical portion 32 of the frame funnel 30 will also be provided with eight insertion holes 32a arranged evenly in the circumferential direction.

[0061] Each gas nozzle 40 is positioned so as to penetrate the flame funnel 30 from the outside to the inside through each insertion hole 32a formed in the enlarged diameter cylindrical portion 32, and the gas injection port 42 of each gas nozzle 40 is located inside the flame funnel 30. In the illustrated embodiment, each gas nozzle 40 has a shape that extends linearly parallel to the burner central axis 20x, but is not limited to this, and may be formed to extend in a direction that is slightly inclined inward, or may have a shape in which the tip is slightly curved inward.

[0062] Furthermore, each insertion hole 32a is formed to be larger than each gas nozzle 40, creating a gap between them. Gas can pass through this gap to the inside and outside of the flame funnel 30. If the outer diameter of the gas nozzle 40 is, for example, about 12 mm, the cross-sectional diameter of the insertion hole 32a (diameter in the plane perpendicular to the nozzle axis) is set to, for example, about 14 to 20 mm (gap width about 1 to 4 mm). Typically, the gas nozzle 40 is positioned to penetrate the center of the insertion hole 32a, with a gap evenly distributed around it.

[0063] Figure 5 shows the gas-fired operation in the gas / oil-switchable dedicated burner 100. Gas is uniformly ejected from each gas nozzle 40 into the flame funnel 30, where it burns and forms a flame F that extends to the front of the flame funnel 30. At this time, the combustion gas discharged to the front of the flame funnel 30 can be returned to the flame funnel 30 as circulating gas G through the gap between the insertion hole 32a and the gas nozzle 40. This enables self-recirculating combustion.

[0064] Generally, slow combustion is preferable for reducing exhaust gas NOx emissions, but poor mixing of fuel and air can easily generate unburned components such as CO gas. In contrast, with the gas / oil switching dedicated burner 100, the circulating gas G that returns inside the flame funnel 30 mixes well with the fuel gas and air, thus suppressing CO generation and maintaining stable combustion. Furthermore, by mixing the circulating gas G (exhaust gas) with the supplied combustible fuel gas, rapid combustion can be suppressed while preventing CO generation. Therefore, by introducing circulating gas G, it is possible to perform slow combustion appropriately, achieving low exhaust gas NOx and low CO combustion.

[0065] Furthermore, while the flame funnel 30 promotes the vaporization of oil fuel and quickly completes combustion in oil-fired combustion, in gas-fired combustion, combustion within the flame funnel 30 is prone to inducing high temperatures, which can increase NOx emissions and also increase the possibility of the flame funnel 30 burning out.

[0066] In contrast, in this embodiment, the protrusion length of the gas nozzle 40 (the length in front of the combustion cylinder 10) is adjusted to prevent excessive temperature rise of the flame funnel while achieving stable combustion, especially at low combustion levels. If the protrusion length of the gas nozzle 40 is long, the flame is more likely to exit the flame funnel, thus lowering the funnel temperature, but conversely, combustion stability decreases. On the other hand, if the protrusion length of the gas nozzle 40 is made too short, the flame is less likely to exit the flame funnel, and although the funnel temperature is more likely to rise, stable combustion becomes easier. The protrusion length of the gas nozzle 40 must be designed to be at least longer than the distance to the funnel so that the gas injection port is positioned inside the funnel.

[0067] Figure 6(a) is a diagram illustrating a design example of the ratio of the protruding length of the gas nozzle 40 to the length H of the flame funnel 30 in the burner axial direction (hereinafter sometimes referred to as the funnel length H). As shown in Figure 6, the distance h from the tip of the gas nozzle 40 to the opening of the flame funnel 30 (hereinafter sometimes referred to as the nozzle front space distance h) is set to approximately 0.6 to 0.7 times the funnel length H, that is, the protruding length (Hh) of the gas nozzle 40 is set to approximately 0.3 to 0.4 times the funnel length H.

[0068] By designing the protrusion length (Hh) of the gas nozzle 40 or the space distance h in front of the nozzle as described above, the gas injection port 42 is positioned within the flow of swirling combustion air produced by the swirling vanes 26 and slits 24b. This allows for a cooling effect on the flame funnel 30 by the swirling combustion air, while also ensuring sufficient fuel mixing without excessive forward flame projection, resulting in stable combustion with low CO emissions, especially during low combustion. Furthermore, in this embodiment, since circulating gas G can be drawn in through the insertion hole 32a, stable combustion due to fuel agitation by the circulating gas G and slow combustion due to exhaust gas mixing can be expected, enabling low NOx and low CO emissions with the nozzle arrangement described above.

[0069] Furthermore, in this design example, the diameter D of the arrangement circle C40 of the multiple gas nozzles 40 shown in Figure 6(b) is set to be larger than the diameter d3 of the combustion cylinder 10 shown in Figure 6(a). Also, the diameter D of the gas nozzle arrangement circle C40 is set to be greater than or equal to the funnel opening diameter d1. Here, the gas nozzle arrangement circle C40 is a virtual circle defined on a plane perpendicular to the burner axis, and represents the circle in which the nozzle center of each gas nozzle 40 is located.

[0070] This configuration facilitates the supply of combustion air from the combustion chamber 10 to the inner circumference of the gas nozzle 40. Furthermore, the injection port 42 of the gas nozzle 40 is prevented from being positioned inside the tip opening 30a of the flame funnel 30, thus suppressing gas diffusion. By appropriately setting the radial arrangement of the gas nozzle 40 in this way, gas can be properly injected into the combustion space within the funnel to obtain a suitable mixture, making it easier to achieve the desired gas combustion.

[0071] Furthermore, the outer diameter d2 of the gas nozzle 40 may be designed to be approximately 0.065 to 0.085 times the diameter D of the gas nozzle arrangement circle C40. Considering the amount of gas sprayed when using a nozzle with a predetermined outer diameter d2, if the diameter D of the gas nozzle arrangement circle C40 (and the size of the flame funnel 30) is set to satisfy the above relationship, gas can be injected relatively uniformly in the combustion space, and better gas combustion can be achieved.

[0072] Next, with reference to Figures 7 and 8, specific configuration examples of the gas nozzle 40 will be described. As shown in Figures 7(a) and (b), in this embodiment, the gas injection section at the tip of each gas nozzle 40, where the gas injection port 42 is formed, is provided with a projection 42H located further forward and a base 42L located further rear.

[0073] In this embodiment, the protruding portion 42H and the base portion 42L are stepped, and for example, in a gas nozzle 40 with an outer diameter d2 of approximately 12 mm (inner diameter d4 of approximately 9.8 mm), a step (step b) of 5 mm in the axial direction is formed. Step b is set to, for example, approximately 0.35 to 0.5 times the outer diameter d2 of the nozzle. However, the protruding portion 42H and the base portion 42L do not necessarily have to be provided to form a step, and for example, the tip shape may have a diagonal cut from the base portion 42L to the protruding portion 42H.

[0074] As shown in Figure 8, multiple (eight in this case) gas nozzles 40 are evenly arranged around the burner's central axis, with the base 42L of each gas nozzle 40 located on the inner circumference closer to the burner's central axis 20x, and the protrusion 42H located on the outer circumference. By having the protrusion 42H on the outer circumference, the contact area between the central airflow and the fuel gas is increased, thereby promoting the mixing of combustion air and fuel gas. This helps to stabilize combustion. In addition, since the gas injection tends to be directed slightly toward the central airflow, the flame is less likely to spread outwards, and the temperature rise of the flame funnel 30 can be suppressed.

[0075] Furthermore, as shown in Figures 7(a) and (b), in this embodiment, a flow limiting section 43 is provided inside each gas nozzle 40, which locally reduces the gas passage cross-sectional area in the form of an orifice. The flow limiting section 43 is provided, for example, by arranging an orifice plate with an opening diameter d5: 5.8 mm at a position 25 mm behind the nozzle outlet when the nozzle inner diameter d4 is 9.8 mm.

[0076] By providing a flow limiting section 43 just before the outlet 42 of the gas nozzle 40, the gas flow velocity is increased in this section, and then the gas flows again through a flow path with a larger cross-sectional area. This allows for a more uniform and continuous gas flow at the nozzle outlet, further improving flame retention.

[0077] As described above, the gas-fired configuration allows for the suppression of red-hot (temperature rise) of burner components through self-combustion gas recirculation and appropriate adjustment of the gas nozzle length. Furthermore, the improved nozzle tip shape enhances combustion stability, resulting in improved low NOx and low CO combustion. In addition, it prevents burnout of the flame funnel 30, which was previously difficult to avoid, resulting in a highly durable and convenient burner that can be used for both oil and gas-fired combustion.

[0078] Although embodiments of the present invention have been described above, various modifications are possible. For example, in the oil burner unit 20, a flow straightening plate having a porous structure or a honeycomb lattice structure may be provided between the flame-holding plate 24 and the swivel blades 26. [Industrial applicability]

[0079] The gas / oil switching dedicated burner according to the embodiment of the present invention is suitably used as a combustion device in various steam boilers and water heaters, and is suitably used as a combustion device in, for example, a multi-tube once-through boiler. [Explanation of symbols]

[0080] 10. Combustion tube (blast tube) 12 Window Box 20 Oil burner unit 22L Low-combustion nozzle 22M Medium Combustion Nozzle 22H High-Combustion Nozzle 24 Flame holding plate 24a center opening 24b Slit 26 Swivel blades 28 Lighting stick 30 Frame Funnel 32 Expanding cylinder part 34 Same diameter cylinder part 36 Annular constriction section 40 Gas Nozzles 42 Gas nozzles 42L base 42H protrusion 43 Flow limiting section 44 Gas Manifold 46 Gas pipes 100 Gas / Oil Switchable Dedicated Burner

Claims

1. A combustion cylinder configured so that combustion air flows through the inside, An oil burner unit disposed inside the combustion cylinder, comprising a plurality of oil spray nozzles including two low-combustion nozzles, a medium-combustion nozzle, and a high-combustion nozzle, and a flame-holding plate having a central opening and provided so as not to cover the spray ports of the plurality of oil spray nozzles, A flame funnel positioned in front of the combustion cylinder and the oil burner unit, comprising a diameter-expanding cylindrical portion that widens toward the front, and having a tip opening, A plurality of gas nozzles arranged on the outer circumference of the oil burner unit, wherein the gas injection ports are located inside the flame funnel, and the plurality of insertion holes formed in the enlarged cylindrical portion of the flame funnel are provided so as to penetrate from the outside to the inside of the flame funnel. Equipped with, A gas / oil switching dedicated burner is configured such that a gap is provided between an insertion hole formed in the frame funnel and a gas nozzle passing through it, allowing circulating gas to pass through the gap.

2. The gas / oil switching dedicated burner according to claim 1, wherein the protruding length of each of the plurality of gas nozzles, which is the length in front of the combustion cylinder in the burner axis direction, is set to be 0.3 to 0.4 times the length of the flame funnel in the burner axis direction, and the diameter of the gas nozzle arrangement circle in which the nozzle centers of the plurality of gas nozzles are located is set to be larger than the diameter of the combustion cylinder.

3. The gas / oil switching dedicated burner according to claim 1 or 2, wherein in the gas injection section where the gas injection ports are formed at the tips of each of the plurality of gas nozzles, a protruding portion is provided that is positioned further forward, and a base portion is provided that is positioned further back than the protruding portion, and the base portion is positioned closer to the burner central axis than the protruding portion.

4. The gas / oil switching dedicated burner according to claim 3, wherein a step is formed between the protruding portion and the base portion in the gas injection portion.

5. The gas / oil switching dedicated burner according to claim 1 or 2, wherein a flow limiting section is provided inside each of the plurality of gas nozzles to improve the flow velocity by locally reducing the gas passage cross-sectional area.

6. The gas / oil switching dedicated burner according to claim 1 or 2, further comprising a swirling vane positioned inside the combustion cylinder, behind the flame-holding plate of the oil burner unit, for swirling primary air passing through the central opening of the flame-holding plate.

7. The gas / oil switching dedicated burner according to claim 1 or 2, wherein the frame funnel further includes a cylindrical portion of the same diameter disposed in front of the enlarged cylindrical portion and an annular constricted portion disposed in front of the cylindrical portion of the same diameter and having the tip opening facing inward.

8. The gas / oil switching dedicated burner according to claim 7, wherein the diameter of the gas nozzle arrangement circle where the nozzle centers of the plurality of gas nozzles are located is greater than or equal to the diameter of the tip opening provided inside the annular constriction portion.

9. The two low-combustion nozzles are positioned opposite each other across the burner's central axis, the medium-combustion nozzle and the high-combustion nozzle are positioned opposite each other across the burner's central axis, and the plurality of oil spray nozzles are evenly arranged along the circumferential direction around the burner's central axis. The gas / oil switching dedicated burner according to claim 1 or 2, wherein the plurality of gas nozzles are arranged at equal intervals along the circumferential direction on the outer circumference of the oil burner unit.

10. The gas / oil switching dedicated burner according to claim 9, wherein the plurality of gas nozzles are eight gas nozzles and are configured to enable three-stage combustion when using either oil or gas as fuel.

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