Radiant tube burner

Abstract

This technology provides a way to reduce NOx emissions when using hydrogen. [Solution] A radiant tube burner 10 comprises a radiant tube 100 and a burner 200, wherein the burner comprises a burner body 210, a hydrogen supply pipe 220 having a first supply port formed at the opening side of the radiant tube and a second supply port formed at the rear end, a primary air supply pipe 230 whose rear end is located further back than the first supply port and closer to the opening than the second supply port, and an ignition unit 240a.

Description

Technical Field

[0001] The present invention relates to a regenerative radiant tube burner. In this specification, for simplicity, the regenerative radiant tube burner is referred to as a radiant tube burner.

Background Art

[0002] Burners are installed at the openings at both ends of radiant tubes disposed in a heat treatment furnace, and fuel is alternately supplied from these pair of burners at regular intervals, the fuel is burned, and a radiant tube burner that heats the inside of the heat treatment furnace by radiant heat is known. For example, Patent Document 1 discloses a radiant tube burner using gas as fuel.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] It has been considered to use hydrogen as fuel for a radiant tube burner. However, it has been difficult to sufficiently suppress the NOx emission amount when using the conventional structure. The present invention has been made in view of the above problems, and an object thereof is to provide a technique for suppressing the NOx emission amount when using hydrogen.

Means for Solving the Problems

[0005] A radiant tube burner according to one embodiment comprises a radiant tube disposed in a heat treatment furnace and burners disposed at the openings at both ends of the radiant tube, wherein the burner comprises a burner body, a tubular hydrogen supply pipe extending from the burner body to the rear of the radiant tube inside the radiant tube and serving as a hydrogen flow path, the hydrogen supply pipe having a first supply port formed at the opening side inside the radiant tube and a second supply port formed at the rear end, the hydrogen supply pipe, a tubular primary air supply pipe surrounding the radially outer side of the hydrogen supply pipe and extending from the burner body to the rear inside the radiant tube and serving as a primary air flow path for primary air used in the primary combustion of the hydrogen, the primary air supply pipe having its rear end located further back than the first supply port and closer to the opening than the second supply port, and an ignition part located between the first supply port and the inner wall of the primary air supply pipe.

[0006] In other words, the hydrogen supply pipe, positioned inside the radiant tube, has a first supply port at one end of the radiant tube and a second supply port at the other end. Primary air is supplied between the outer wall of the hydrogen supply pipe and the inner wall of the primary air supply pipe. When hydrogen supplied to the outside of the hydrogen supply pipe from the first supply port is ignited by the ignition unit, the hydrogen burns between the outer wall of the hydrogen supply pipe and the inner wall of the primary air supply pipe (primary combustion).

[0007] On the other hand, in the hydrogen supply pipe, the second supply port opens on the far side of the radiant tube. Therefore, the second supply port can supply hydrogen to the far side of the radiant tube than the first supply port. The tip of the primary air supply pipe at the far side of the radiant tube is located further back than the first supply port and closer to the opening of the second supply port. As a result, the primary air is carried to the far side through the space between the outer wall of the hydrogen supply pipe and the inner wall of the primary air supply pipe. Consequently, the hydrogen supplied to the outside of the hydrogen supply pipe from the second supply port is combusted by this primary air.

[0008] With the above configuration, hydrogen mixed with primary air is ignited and combusted near the first supply port, and also combusts near the second supply port. Therefore, compared to a configuration in which hydrogen is supplied and combusted from only one of the first or second supply ports, the hydrogen can be combusted more slowly. Generally, NOx is generated in larger quantities as the combustion temperature increases and as the residence time of the combustion gas in the high-temperature range increases.

[0009] However, in this embodiment, since hydrogen burns slowly, the combustion temperature is lower compared to the case where combustion proceeds rapidly without slow combustion, and NOx emissions can be suppressed. Furthermore, in this embodiment, since hydrogen burns near the first and second supply ports, the residence time of hydrogen in the high-temperature range is shorter compared to a configuration in which the same amount of hydrogen burns only around one supply port. For this reason, NOx emissions can be suppressed compared to a configuration in which combustion occurs only around one supply port. [Brief explanation of the drawing]

[0010] [Figure 1] This diagram shows the components of a burner. [Figure 2] This diagram shows the overall configuration of a radiant tube burner. [Figure 3] This is a magnified view of the area around the hydrogen supply pipe that makes up the burner. [Figure 4] This graph shows the measured amount of NOx in Comparative Example 1, Example 1, and Example 2. [Figure 5] This graph shows the loudness of the sound produced in Comparative Example 1, Example 1, and Example 2. [Modes for carrying out the invention]

[0011] Here, embodiments of the present invention will be described in the following order. (1) Radiant tube burner configuration: (2) Combustion of hydrogen: (3) Examples: (4) Other embodiments:

[0012] (1) Radiant tube burner configuration: Figure 1 shows the components of a burner, and Figure 2 shows the overall configuration of a radiant tube burner. Figure 3 is an enlarged view of the area around the hydrogen supply pipe that constitutes the burner. The radiant tube burner 10 according to this embodiment comprises a radiant tube 100 and a burner 200. The radiant tube 100 is a tubular member, and Figures 1, 2, and 3 are cross-sectional views showing the radiant tube 100 cut in a plane including its axis.

[0013] As shown in Figure 2, the radiant tube 100 has straight sections 100a to 100d that extend in a straight line and curved sections 100e to 100g that extend in a semicircular shape and connect the straight sections. Straight sections 100a and 100b are connected to both ends of curved section 100e, and straight sections 100b and 100c are connected to both ends of curved section 100f. In addition, straight sections 100c and 100d are connected to both ends of curved section 100g.

[0014] The straight sections 100a to 100d and the curved sections 100e to 100g are connected to form a series of cylindrical bodies with a substantially constant inner diameter. Furthermore, it has a W-shape when viewed from the direction shown in Figure 2. In Figure 2, the flame is shown by a dashed line. In this specification, the direction in which the central axis of the straight sections 100a to 100d extends is called the axial direction, and the direction perpendicular to the axial direction is called the radial direction. Additionally, the direction approaching the central axis in the radial direction is called the radially inward direction, and the direction moving away from the central axis in the radial direction is called the radially outward direction. Furthermore, the direction of rotation around the central axis is called the circumferential direction.

[0015] In this embodiment, the radiant tube burner 10 is used to heat the interior of the heat treatment furnace H. The inside and outside of the heat treatment furnace H are separated by a wall surface W, and the radiant tube 100 is disposed inside the wall surface W, that is, inside the heat treatment furnace H. In this embodiment, holes into which the radiant tube 100 can be inserted are formed at two locations on the wall surface W, and the radiant tube 100 is inserted into the holes. Further, the openings 110 at both ends of the radiant tube 100 are disposed at the boundary between the wall surface W and the outside of the heat treatment furnace H.

[0016] The burner 200 is disposed at the openings 110 at both ends of the radiant tube 100. In this embodiment, the burner 200 is attached so as to close the openings 110 at both ends of the radiant tube 100.

[0017] The burner 200 includes a burner body 210, a hydrogen supply pipe 220, a primary air supply pipe 230, a spark plug 240, and a secondary air supply pipe 250. The burner body 210 is a component in which an air flow path 210a protrudes from a substantially rectangular parallelepiped portion. The inside of the burner body 210 is a cavity, and a plurality of heat storage bodies 210b are accommodated in the cavity.

[0018] In this embodiment, the heat storage body 210b is a substance having a function of storing heat, and is a substance that is less likely to cool than surrounding substances, such as metals. In this embodiment, it has a function of recovering a part of the heat generated by combustion in the radiant tube 100. The material, shape, and size of the heat storage body 210b are not limited, but in this embodiment, the heat storage body 210b is spherical ceramics. A plurality of heat storage bodies 210b are prepared and accommodated inside the burner body 210. Note that the heat storage body 210b may be a ceramic foam made of a porous body having a large number of holes, or a ceramic honeycomb formed by forming a large number of lattice-shaped cells.

[0019] The flow path 210a protruding from the burner main body 210 is a hollow cylindrical body, one side of which is open, and air A flows into the burner main body 210 from the opening portion. A pipe serving as a flow path for air A may be connected to the opening portion. Further, in the burner main body 210, the surface on the radiant tube 100 side, that is, the surface on the opening 110 side of the radiant tube 100 is open.

[0020] The hydrogen supply pipe 220 extends from the burner main body 210 to the inner side of the radiant tube 100 inside the radiant tube 100. Further, the hydrogen supply pipe 220 extends through the inside of the burner main body 210 in the axial direction to the side opposite to the radiant tube 100 and penetrates the burner main body 210.

[0021] In the present embodiment, the hydrogen supply pipe 220 is a tubular member. As shown in FIG. 1, one tip 220a of the hydrogen supply pipe 220 is present inside the radiant tube 100, and the other tip 220b of the hydrogen supply pipe 220 is present outside the burner main body 210. A connection portion 220e to which a pipe (not shown) is connected is attached to the tip 220b of the hydrogen supply pipe 220 present outside the burner main body 210. Hydrogen (H2 shown in FIG. 1) is supplied from a pipe (not shown) connected to the connection portion 220e. Therefore, the hydrogen supply pipe 220 is a tubular member serving as a flow path for hydrogen.

[0022] As described above, the hydrogen supply pipe 220 is a member that penetrates the burner main body 210 from the outside of the heat treatment furnace H and reaches the radiant tube 100. Here, attention is paid only to the portion of the hydrogen supply pipe 220 that exists inside the radiant tube 100. FIG. 3 is an enlarged view showing the hydrogen supply pipe 220, the primary air supply pipe 230, and the secondary air supply pipe 250 existing on the heat treatment furnace H side with respect to the boundary line Lb between the inside and the outside of the radiant tube 100 in the axial direction inside the radiant tube 100. In FIG. 3, since the opening 110 of the radiant tube 100 exists on the right side in the axial direction, it is the opening side. The left side in the axial direction is the inner side of the radiant tube 100.

[0023] The end of the hydrogen supply pipe 220 located inside the radiant tube 100, on the opening side, is supported by a disc-shaped primary air supply port forming portion 225. That is, the primary air supply port forming portion 225 is a disc-shaped member with a constant thickness in the axial direction, and is located between the radially inner surface of the primary air supply pipe 230 and the radially outer surface of the hydrogen supply pipe 220. A circular hole slightly larger than the outer shape of the hydrogen supply pipe 220 is formed on the radially inner side of the primary air supply port forming portion 225, and the hydrogen supply pipe 220 is inserted through this hole. Since this hole is formed at the center of the primary air supply port forming portion 225, when the hydrogen supply pipe 220 is inserted through this hole, the hydrogen supply pipe 220 is positioned radially in the center within the radially inner space of the primary air supply pipe 230.

[0024] The primary air supply port forming section 225 has multiple axially extending holes at various circumferential positions. An ignition plug 240 extending from the burner body 210 is inserted through one of these holes. The ignition plug 240 is a roughly cylindrical member that is long in the axial direction, with an ignition section 240a formed at its tip on the axially rear side. In the ignition plug 240, the part opposite to the ignition section 240a penetrates the burner body 210, and its tip is connected to a connector 240b (see Figure 1). Wiring (not shown) is connected to the connector 240b, and a predetermined voltage is applied through the wiring to generate a spark at the ignition section 240a. The ignition section 240a is located radially between the first supply port 220c (described later) and the inner wall of the primary air supply pipe 230. In the example shown in Figure 3, the ignition unit 240a is positioned in the radial extension direction of the first supply port 220c at a location where a spark is formed by the ignition unit 240a. The remaining holes of the multiple holes formed in the primary air supply port forming section 225 become primary air supply ports 225a that supply primary air into the interior of the radiant tube 100.

[0025] In the hydrogen supply pipe 220, a first supply port 220c, which is a hydrogen supply port, is formed at the opening side inside the radiant tube 100. Specifically, multiple holes are formed at the opening side end of the hydrogen supply pipe 220 located inside the radiant tube 100, and at a position further inside than the primary air supply port forming section 225, constituting the first supply port 220c. The first supply port 220c is a hole that penetrates from the radially outer surface to the radially inner surface of the hydrogen supply pipe 220, and multiple such holes are formed. As described above, the inside of the hydrogen supply pipe 220 becomes a hydrogen flow path, so when the hydrogen supplied from the piping connected to the connection section 220e reaches the vicinity of the first supply port 220c, some of it flows out of the first supply port 220c to the outside of the hydrogen supply pipe 220, and the remaining part moves to the back of the hydrogen supply pipe 220.

[0026] Since the hydrogen supply pipe 220 is a tubular member that penetrates in the axial direction, its inner end 220a is open, forming the second supply port 220d. When the hydrogen supplied from the piping connected to the connection part 220e reaches the second supply port 220d, hydrogen is supplied from the second supply port 220d to the inner side in the axial direction.

[0027] The primary air supply pipe 230 extends from the burner body 210 to the rear side of the radiant tube 100 inside the radiant tube 100. Furthermore, the primary air supply pipe 230 extends axially through the burner body 210, opposite to the radiant tube 100, and penetrates the burner body 210.

[0028] In this embodiment, the primary air supply pipe 230 is a tubular member that surrounds the radially outer side of the hydrogen supply pipe 220 inside the radiant tube 100. As shown in Figure 1, one end 230a of the primary air supply pipe 230 is located inside the radiant tube 100, and the other end 230b of the primary air supply pipe 230 is open on one side of the burner body 210. An attachment 230c for introducing primary air is attached to the end 230b of the primary air supply pipe 230, which is located outside the burner body 210. Primary air (A1 shown in Figure 1) is supplied from a pipe (not shown) connected to the attachment 230c. Therefore, the primary air supply pipe 230 is a tubular member that serves as a flow path for primary air, which is the air used for the primary combustion of hydrogen.

[0029] As shown in Figure 3, the inner end 230a of the primary air supply pipe 230 is located further in the axial direction than the first supply port 220c, and closer to the opening in the axial direction than the second supply port 220d. In this embodiment, the end 230a of the primary air supply pipe 230 is located closer to the second supply port 220d than to the first supply port 220c in the axial direction of the radiant tube 100. The distance Lg between the second supply port 220d and the inner end 230a of the primary air supply pipe 230 is not limited, but can be set to a value of approximately 15 mm, for example.

[0030] The secondary air supply pipe 250 extends from the burner body 210 to the rear of the radiant tube 100 inside the radiant tube 100. The end of the secondary air supply pipe 250 on the burner body 210 side is formed in a flange shape, and this flange-shaped portion 250b extends radially at the opening 110 of the radiant tube 100, and is positioned to close the opening 110.

[0031] In this embodiment, the secondary air supply pipe 250 is a tubular member that surrounds the radially outer side of the primary air supply pipe 230 inside the radiant tube 100. As shown in Figure 1, one end 250a of the secondary air supply pipe 250 is located inside the radiant tube 100, and the other end of the secondary air supply pipe 250 is a flange-shaped portion 250b.

[0032] As described above, the secondary air supply pipe 250 is a tubular member that surrounds the radially outer side of the primary air supply pipe 230, and its inner diameter D2 is approximately the same at each axial position. Therefore, as shown in Figure 3, the inner diameter of the opening 250c on the burner body 210 side of the flange-shaped portion 250b is larger than the outer diameter of the primary air supply pipe 230. The opening 250c is connected to a cavity inside the burner body 210. For this reason, the opening 250c becomes a secondary air supply port 250d that supplies air used for the secondary combustion of hydrogen from the burner body 210. With this configuration, the secondary air supply pipe 250 becomes a flow path for secondary air.

[0033] In the flange-shaped portion 250b, tertiary air supply ports 250e, which are holes extending in the axial direction, are formed at multiple positions in the circumferential direction. The tertiary air supply ports 250e are connected to the internal cavity of the burner body 210. Therefore, the tertiary air supply ports 250e serve as supply ports for air used in the tertiary combustion of hydrogen from the burner body 210. With this configuration, the space between the radially outer surface of the secondary air supply pipe 250 and the radially inner surface of the radiant tube 100 becomes a flow path for tertiary air. As shown in Figure 1, the innermost tip 250a of the secondary air supply pipe 250 is located further in the axial direction than the tip 230a of the primary air supply pipe 230.

[0034] (2) Combustion of hydrogen: The operation of the radiant tube burner 10 configured as described above when burning hydrogen will now be explained. In the radiant tube burner 10 according to this embodiment, the fuel is hydrogen, and the hydrogen is supplied to the hydrogen supply pipe 220 from a pipe connected to the connection part 220e. With hydrogen supplied to the hydrogen supply pipe 220, the burners 200 operate alternately. That is, when a predetermined voltage is applied to the spark plug 240 of one burner 200, a spark is generated at the ignition part 240a, and hydrogen burns. After combustion in the one burner 200 has occurred, a predetermined voltage is applied to the spark plug 240 of the other burner 200. As a result, a spark is generated at the ignition part 240a at the tip of the spark plug 240 of the other burner 200, and hydrogen burns. Figure 2 shows the state in which hydrogen is burning and a flame is formed on the burner 200 side shown on the lower side.

[0035] In a configuration in which hydrogen is alternately burned by a pair of burners 200, when combustion is performed by one burner 200, the exhaust gas passes through the radiant tube 100 and reaches the other burner 200. The waste heat from the exhaust gas is then recovered by the heat storage body 210b in the other burner 200. Therefore, when combustion is alternately performed by each burner 200 in the radiant tube burner 10, the temperature of the heat storage body 210b housed inside each burner 200 rises.

[0036] When waste heat is recovered by the heat storage body 210b and hydrogen combustion is performed using the other burner 200 while the heat is stored in the heat storage body 210b, the secondary air A2 and tertiary air A3 are supplied to the inside of the radiant tube 100 through the burner body 210 and thus come into contact with the heat storage body 210b.

[0037] Therefore, in the radiant tube burner 10, the secondary air A2 and tertiary air A3 are preheated by the heat storage body 210b. When hydrogen is burned using preheated air, the combustion efficiency increases. Therefore, it becomes possible to efficiently heat the heat treatment furnace H. In this embodiment, the primary air A1 is supplied into the radiant tube 100 without passing through the heat storage body 210b. Therefore, the primary air A1 is not preheated and is at a lower temperature than the secondary air and tertiary air A3. This prevents components such as the spark plug 240 and its surrounding circuitry from becoming excessively hot.

[0038] Here, referring to Figures 3 and 1, the combustion of hydrogen will be explained focusing on one burner 200. In this embodiment, hydrogen is supplied by a hydrogen supply pipe 220. Therefore, hydrogen is supplied into the radiant tube 100 from the first supply port 220c and the second supply port 220d formed in the hydrogen supply pipe 220. The space between the radially inner circumferential surface of the primary air supply pipe 230 and the radially outer circumferential surface of the hydrogen supply pipe 220 serves as a flow path for primary air A1 supplied axially to the inner side from the primary air supply port 225a formed in the primary air supply port forming section 225.

[0039] The space between the radially inner circumferential surface of the secondary air supply pipe 250 and the radially outer circumferential surface of the primary air supply pipe 230 serves as a flow path for secondary air A2 supplied axially inward from the secondary air supply port 250d. Furthermore, the space between the radially inner circumferential surface of the radiant tube 100 and the radially outer circumferential surface of the secondary air supply pipe 250 serves as a flow path for tertiary air A3 supplied axially inward from the tertiary air supply port 250e.

[0040] When hydrogen is being supplied from the first supply port 220c and a spark is generated by the ignition unit 240a, the hydrogen supplied from the first supply port 220c to the vicinity of the ignition unit 240a burns. In this specification, this combustion is referred to as primary combustion. Figure 1 schematically shows the region in which primary combustion C1 occurs.

[0041] Near the second supply port 220d, there is primary air A1 supplied through the primary air supply pipe 230 and secondary air A2 supplied through the secondary air supply pipe 250. Therefore, the hydrogen supplied from the second supply port 220d mixes with the primary air A1 and secondary air A2 and becomes combustible. In this state, when the range of primary combustion C1 reaches the vicinity of the second supply port 220d, the hydrogen supplied from the second supply port 220d burns. In this specification, this combustion is called secondary combustion. Figure 1 schematically shows the region where secondary combustion C2 occurs.

[0042] In this embodiment, the inner end 230a of the primary air supply pipe 230 is located further axially inward than the first supply port 220c and closer to the opening in the axial direction than the second supply port 220d. Therefore, a portion of the primary air A1 supplied from the primary air supply port 225a is supplied to the inner axial direction, i.e., near the second supply port 220d, by passing through the radially inner side of the primary air supply pipe 230.

[0043] With the above configuration, the primary air A1 is mixed with hydrogen present near the first supply port 220c and used for combustion, and also mixed with hydrogen present near the second supply port 220d and used for combustion. Therefore, hydrogen can be burned both near the first supply port 220c and near the second supply port 220d, and hydrogen can be burned more slowly compared to a configuration in which hydrogen is supplied and burned from only one of the first or second supply port 220c.

[0044] Furthermore, in this embodiment, the hydrogen supply pipe 220 has an axially elongated shape, and the tip 230a of the primary air supply pipe 230 is positioned near the second supply port 220d. As a result, as shown in Figure 1, primary combustion C1 can be generated in an axially elongated space. Consequently, after primary combustion C1 is generated in an axially elongated space, secondary combustion C2 can be generated, allowing for slow combustion of hydrogen.

[0045] Generally, NOx is generated in larger quantities as the combustion temperature increases and as the residence time of combustion gases in the high-temperature range increases. However, in this embodiment, because hydrogen burns slowly, the combustion temperature is lower compared to cases where combustion proceeds rapidly without slow combustion, and NOx emissions can be suppressed.

[0046] Furthermore, in this embodiment, since hydrogen burns near the first supply port 220c and the second supply port 220d, the residence time of hydrogen in the high-temperature range is shorter compared to a configuration in which the same amount of hydrogen burns only around one supply port. Therefore, NOx emissions can be suppressed compared to a configuration in which combustion occurs only around one supply port.

[0047] In this embodiment, the tip 230a of the primary air supply pipe 230 is located closer to the second supply port 220d than to the first supply port 220c in the axial direction of the radiant tube 100. If the length of the primary air supply pipe 230 is short, the primary air will dissipate radially outward before reaching the vicinity of the second supply port 220d. However, if the tip 230a of the primary air supply pipe 230 is located near the second supply port 220d, the primary air supply pipe 230 can more reliably supply the primary air A1 to the vicinity of the second supply port 220d.

[0048] A portion of the hydrogen supplied from the second supply port 220d moves to the far side of the radiant tube 100 through the radially inner side of the secondary air supply pipe 250. When this hydrogen reaches the tip 250a of the secondary air supply pipe 250, it mixes with the tertiary air A3 that has reached the vicinity of the tip 250a of the secondary air supply pipe 250, passing between the radiant tube 100 and the secondary air supply pipe 250. In this state, when the range of secondary combustion C2 reaches the vicinity of the tip 250a of the secondary air supply pipe 250, the hydrogen present in that vicinity burns. In this specification, this combustion is referred to as tertiary combustion. Figure 1 schematically shows the region in which tertiary combustion C3 occurs.

[0049] With the above configuration, hydrogen can be burned in three stages: primary combustion C1, secondary combustion C2, and tertiary combustion C3. Therefore, compared to burning hydrogen with fewer combustion stages, hydrogen can be burned more slowly. As a result, NOx generation can be suppressed more reliably.

[0050] Furthermore, in this embodiment, as shown in Figure 2, the length of the secondary air supply pipe 250 is sufficiently secured, and the tip 250a of the secondary air supply pipe 250 is positioned far from the tip 220a of the hydrogen supply pipe 220. As a result, as shown in Figure 1, secondary combustion C2 can be generated in a space that is long in the axial direction. Consequently, after secondary combustion C2 is generated in a space that is long in the axial direction, tertiary combustion C3 can be generated, allowing for slow combustion of hydrogen.

[0051] (3) Examples: Next, an embodiment of the radiant tube burner 10 will be described. In this embodiment, the inner diameter D1 (see Figure 1) of the radiant tube 100 is 125 mm and its thickness is 8 mm. The inner diameter D2 (see Figures 1 and 3) of the secondary air supply pipe 250 is 80 mm and its thickness is 5 mm. The inner diameter D3 (see Figure 3) of the primary air supply pipe 230 is 40 mm and its thickness is 5 mm. The inner diameter D4 (see Figure 3) of the hydrogen supply pipe 220 is 6 mm and its thickness is 5 mm.

[0052] In this example, Examples 1 and 2 and Comparative Example 1 were prepared. In Example 1, the length Lh of the hydrogen supply pipe 220 inside the boundary line Lb was 86 mm, and the axial distance Lg between the tip 220a of the hydrogen supply pipe 220 and the tip 230a of the primary air supply pipe 230 was 15 mm (see Figure 3). In Example 2, the length Lh was 136 mm and the distance Lg was 15 mm, and in Comparative Example 1, the length Lh was 36 mm and the distance Lg was 15 mm.

[0053] In other words, in Example 1, the length of the hydrogen supply pipe 220 inside the radiant tube 100 is 50 mm longer than in Comparative Example 1, and in Example 2, the length of the hydrogen supply pipe 220 inside the radiant tube 100 is 100 mm longer than in Comparative Example 1. Also, in all of Examples 1, 2, and Comparative Example 1, the axial distance Lg between the tip 220a of the hydrogen supply pipe 220 and the tip 230a of the primary air supply pipe 230 is 15 mm.

[0054] In Examples 1, 2, and Comparative Example 1, the hydrogen flow rate to the hydrogen supply pipe 220 was set to 280 L / min, the primary air A1 flow rate to 13 L / min, the secondary air A2 flow rate to 10 L / min, and the tertiary air A3 flow rate to 190 L / min. Furthermore, hydrogen was alternately burned in each burner 200 at these flow rates. The amount of NOx emissions (ppm) generated by the combustion of each burner 200 was measured using an exhaust gas analyzer. In addition, the sound level (dB) generated by the combustion of each burner 200 was measured using a sound level meter.

[0055] Figure 4 is a graph showing the measured amount of NOx in Comparative Example 1, Example 1, and Example 2. The graph shows the amount of NOx emitted as a result of combustion by the two burners 200 provided in Comparative Example 1, Example 1, and Example 2. In the graph, the horizontal axis is the length of the hydrogen supply pipe 220 inside the radiant tube 100, and the vertical axis is the NOx emission amount (ppm). In the figure, the emission amount from one burner 1 is shown by a black circle and a solid line, and the emission amount from the other burner 2 is shown by a black square and a dashed line. As shown in the figure, it can be seen that the longer the hydrogen supply pipe 220, the lower the NOx emission amount. From the graph, it can be seen that if the length of the hydrogen supply pipe 220 inside the radiant tube 100 is 80 mm or more, the NOx emission amounts from both burners 1 and 2 will be less than or equal to the NOx emission amounts from burners 1 and 2 in Comparative Example 1, and a radiant tube burner 10 with lower NOx emission amounts than Comparative Example 1 can be provided. Furthermore, if the length of the hydrogen supply pipe 220 inside the radiant tube 100 is 86 mm or more, NOx emissions can be suppressed to 180 ppm or less on average across the two burners 200.

[0056] In Examples 1 and 2, the inner diameter D1 of the radiant tube 100 is 125 mm. However, it is expected that the NOx emission levels will be equivalent to those in Examples 1 and 2 if the length of the hydrogen supply pipe 220 is changed in proportion to the change in inner diameter D1. Therefore, when the diameter (inner diameter) of the radiant tube 100 is D, it is conceivable to set the axial length of the hydrogen supply pipe 220 located inside the radiant tube 100 to 80 × D / 125 mm or more. Furthermore, in order to suppress the NOx emission level to 180 ppm or less on average for the two burners 200, it is conceivable to set it to 86 × D / 125 mm or more. With the above configuration, it is possible to suppress the NOx emission level to a desired value or less in a radiant tube burner 10 of any diameter.

[0057] Figures 5A, 5B, and 5C are graphs showing the loudness of the sound produced in Comparative Example 1, Example 1, and Example 2, respectively. In each graph, the horizontal axis represents time and the vertical axis represents loudness (dB), showing the loudness of the sound produced in Comparative Example 1, Example 1, and Example 2. In each graph, a loudness of 76 dB is shown with a thick line to serve as a reference for comparison. In these examples, ignition occurs with one burner 200 at 0 seconds, and thereafter, ignition occurs alternately with each burner 200 every 30 seconds.

[0058] When hydrogen is burned, a loud noise is generated when a spark is produced by the spark plug 240. In Figures 5A, 5B, and 5C, it can be seen that a loud noise occurs every 30 seconds, such as at 0 seconds, 30 seconds, and 60 seconds. However, when comparing the loudness of the noise in Comparative Example 1, Example 1, and Example 2, it is generally Comparative Example 1 > Example 1 > Example 2. In other words, it can be seen that the longer the hydrogen supply pipe 220 and the primary air supply pipe 230, the quieter the noise becomes.

[0059] This is thought to be due to the primary combustion C1 by the ignition unit 240a occurring between the radially outer circumferential surface of the hydrogen supply pipe 220 and the radially inner circumferential surface of the primary air supply pipe 230. In other words, the longer the axial length of the primary air supply pipe 230, the longer the wall surface surrounding the ignition unit 240a becomes. Therefore, the longer the axial length of the primary air supply pipe 230, the more noise can be reduced.

[0060] Furthermore, in this embodiment, slow combustion is achieved by burning hydrogen in three stages: primary combustion C1, secondary combustion C2, and tertiary combustion C3. As a result, the amount of hydrogen consumed in a single combustion cycle is reduced compared to a configuration in which the same amount of hydrogen as that burned in three stages is burned in one or two locations. Consequently, the noise generated during ignition by the ignition unit 240a is reduced.

[0061] (4) Other embodiments: The embodiments described above are merely examples for carrying out the present invention, and various other embodiments can be adopted. For example, the size, shape, etc., of each component constituting the radiant tube burner 10 may be in various forms.

[0062] The radiant tube only needs to be placed inside the heat treatment furnace. In other words, the radiant tube only needs to be able to regulate the temperature of the heat treatment furnace by the radiant heat generated by the combustion of hydrogen inside it. The heat treatment furnace can be any furnace that performs any heat treatment, and there are no limitations on its use or the material to be treated. For example, the heat treatment furnace can be used as a carburizing furnace, quenching furnace, nitriding furnace, annealing furnace, tempering furnace, etc. Furthermore, the material to be treated can be any material such as ferrous metals, non-ferrous metals, and various other metals.

[0063] The shape of the radiant tube is not limited to the shape of the embodiment described above. For example, the radiant tube may be U-shaped, with a pair of straight sections arranged parallel to each other and connected by a curved section.

[0064] The burner only needs to be positioned at the openings at both ends of the radiant tube. In other words, the burner only needs to be able to supply hydrogen from both ends of the radiant tube towards the inside of the radiant tube and burn it. The burner comprises at least a burner body, a hydrogen supply pipe, a primary air supply pipe, and an ignition unit, but it may also have other components. The burner is positioned at the opening of the radiant tube and is assumed to close the opening (the burner body is larger than the diameter of the opening), but of course, an air supply port may also be provided.

[0065] The burner body can be any part that is positioned at the opening of the radiant tube, and any part to which other components, such as the hydrogen supply pipe, primary air supply pipe, ignition unit, and secondary air supply pipe, are attached.

[0066] The hydrogen supply pipe is a tubular hydrogen supply pipe that extends from the burner body to the back of the radiant tube inside the radiant tube, serving as a hydrogen flow path. Furthermore, the hydrogen supply pipe only needs to have a first supply port at the opening end of the radiant tube and a second supply port at the back end. In other words, the hydrogen supply pipe only needs to be able to supply hydrogen to multiple different locations along the axial direction of the radiant tube.

[0067] While the length of the hydrogen supply pipe is not limited, longer pipes allow for greater reduction in NOx emissions. Therefore, by setting an upper limit for permissible NOx emissions, the minimum length of the hydrogen supply pipe can be set so that emissions remain below that limit. The maximum length of the hydrogen supply pipe can be set as the limit for hydrogen combustion near the second supply port. The length of the hydrogen supply pipe can be set within the range between the minimum and maximum values. Furthermore, the shape of the hydrogen supply pipe is not limited, and various shapes other than cylindrical can be used.

[0068] The first supply port only needs to be able to supply hydrogen to the opening side of the radiant tube and ignite it. Therefore, the first supply port only needs to be able to achieve slow combustion by burning both the hydrogen near the first supply port and the hydrogen near the second supply port. In this respect, the size, shape, and number of the first supply ports are not limited.

[0069] When setting the first supply port in relation to the second supply port, for example, a setting of approximately 1 to 10 for the ratio of the total area of ​​the second supply port to the total area of ​​the first supply port is possible.

[0070] The position of the opening on the hydrogen supply pipe can be any position on the opening side of the hydrogen supply pipe located inside the radiant tube. In other words, by positioning the first supply port on the opening side, primary combustion of hydrogen can occur at the position opposite the rear end of the hydrogen supply pipe. In order to separate the first supply port and the second supply port, a configuration can be adopted in which the first supply port is formed at the opening end of the hydrogen supply pipe 220, which is located further inside the radiant tube than the primary air supply port forming section 225. In other words, the first supply port 220c may be formed near the primary air supply port forming section 225, but further inside than the primary air supply port forming section 225. In this case, for example, an embodiment in which the first supply port 220c is formed within a range of 10 mm from the primary air supply port forming section 225 can be assumed.

[0071] The second supply port should supply hydrogen to the far end, which is the opposite end of the radiant tube opening, and should be able to generate secondary combustion near the first supply port and the other supply port. Therefore, the second supply port should be able to achieve slow combustion by burning both the hydrogen near the first supply port and the hydrogen near the second supply port. To this extent, the size, shape, and number of the second supply ports are not limited.

[0072] The far end of the hydrogen supply pipe can be near the far tip. The tip is the outermost part in a particular direction, and the end is the part that includes the tip. By positioning the second supply port at the far end of the hydrogen supply pipe, secondary combustion of hydrogen should occur near the tip on the opposite side of the opening. For example, the far end can be defined as an area within 10 mm of the tip of the hydrogen supply pipe.

[0073] The primary air supply pipe is a tubular component that surrounds the radially outer side of the hydrogen supply pipe, extends from the burner body towards the back inside the radiant tube, and serves as a flow path for the primary air, which is the air used for the primary combustion of hydrogen. In other words, the tubular hydrogen supply pipe is positioned radially inside the tubular primary air supply pipe. With this configuration, it is sufficient to create a space for primary air to flow between the radially inner wall of the primary air supply pipe and the radially outer wall of the hydrogen supply pipe.

[0074] The length of the primary air supply pipe is not limited, but the longer the primary air supply pipe, the closer the primary air can be directed to the space of the second supply port. Furthermore, the shape of the primary air supply pipe is not limited, and various shapes other than cylindrical can be used.

[0075] The far end of the primary air supply pipe should be located further back than the first supply port and closer to the opening than the second supply port. In other words, the far end of the primary air supply pipe should be located further back than the first supply port. With this configuration, it is sufficient that the hydrogen supplied from the first supply port can remain to some extent between the radially inner wall of the primary air supply pipe and the radially outer wall of the hydrogen supply pipe, preventing excessive dissipation.

[0076] Furthermore, the inner end of the primary air supply pipe is located closer to the opening than the second supply port. This configuration prevents the hydrogen supplied from the second supply port from accumulating only between the radially inner wall of the primary air supply pipe and the radially outer wall of the hydrogen supply pipe, and is sufficient if it is configured to allow combustion using the air located radially outside the primary air supply pipe, etc.

[0077] The ignition unit only needs to be located between the first supply port and the inner wall of the primary air supply pipe. In other words, the ignition unit only needs to be able to ignite the hydrogen supplied from the first supply port. Note that the axial position of the ignition unit is not limited to being exactly the same as the axial position of the first supply port; the axial position of the ignition unit can be arbitrarily selected as long as it can ignite the hydrogen supplied from the first supply port.

[0078] The secondary air supply pipe is a tubular pipe that surrounds the radially outer side of the primary air supply pipe, extends from the burner body towards the back inside the radiant tube, and serves as a flow path for the secondary air, which is the air used for the secondary combustion of hydrogen. In other words, a tubular primary air supply pipe is positioned radially inside the tubular secondary air supply pipe. With this configuration, it is sufficient to create a space for secondary air to flow between the radially inner wall of the secondary air supply pipe and the radially outer wall of the primary air supply pipe.

[0079] The length of the secondary air supply pipe is not limited, but the longer the secondary air supply pipe, the more the combustion caused by tertiary air can be delayed (moving the combustion area further away from the opening). Furthermore, the shape of the secondary air supply pipe is not limited, and various shapes other than cylindrical can be used.

[0080] The far end of the secondary air supply pipe only needs to be located further back than the end of the primary air supply pipe. The far end of the secondary air supply pipe may also be located further back than the end of the hydrogen supply pipe. This configuration is sufficient if the hydrogen supplied from the second supply port remains to some extent radially inside the secondary air supply pipe, allowing secondary combustion to proceed without excessive dissipation.

[0081] Furthermore, the space between the radially outer surface of the secondary air supply pipe and the radially inner surface of the radiant tube becomes a passage for tertiary air, which is the air used for the tertiary combustion of hydrogen. In other words, it is sufficient to supply tertiary air so that tertiary combustion occurs near the far end of the secondary air supply pipe. With this configuration, primary, secondary, and tertiary combustion can be generated inside the radiant tube, allowing for slow combustion of hydrogen. [Explanation of Symbols]

[0082] 10...Radiant tube burner, 100...Radiant tube, 100a~100d...Straight section, 100e~100g...Curved section, 110...Opening, 200...Burner, 210...Burner body, 210a...Flow path, 210b...Heat storage body, 220...Hydrogen supply pipe, 220a...Tip, 220b...Tip, 220c...First supply port, 220d...Second supply port, 220e...Connection section, 225. ...Primary air supply port forming section, 225a...Primary air supply port, 230...Primary air supply pipe, 230a...Tip, 230b...Tip, 230c...Attachment, 240...Spark plug, 240a...Ignition section, 240b...Connector, 250...Secondary air supply pipe, 250a...Tip, 250b...Flange-shaped section, 250c...Opening, 250d...Secondary air supply port, 250e...Tertiary air supply port

Claims

1. A radiant tube is installed inside the heat treatment furnace, A radiant tube burner comprising: burners disposed at the openings at both ends of the radiant tube, The aforementioned burner, The burner body and A tubular hydrogen supply pipe extending from the burner body to the rear of the radiant tube within the radiant tube, forming a hydrogen flow path, wherein a first supply port, which is the hydrogen supply port, is formed at the opening side within the radiant tube, and a second supply port, which is the hydrogen supply port, is formed at the rear end of the hydrogen supply pipe, A tubular primary air supply pipe that surrounds the radially outer side of the hydrogen supply pipe, extends from the burner body to the rear side inside the radiant tube, and serves as a flow path for primary air, which is air used for the primary combustion of the hydrogen, wherein the rear end of the primary air supply pipe is located further back than the first supply port and closer to the opening than the second supply port, The ignition part located between the first supply port and the inner wall of the primary air supply pipe, A radiant tube burner equipped with this feature.

2. The tip of the primary air supply pipe is closer to the second supply port than to the first supply port in the axial direction of the radiant tube. The radiant tube burner according to claim 1.

3. When the diameter of the radiant tube is D, The length of the hydrogen supply pipe located inside the radiant tube in the axial direction of the radiant tube is 80 × D / 125 mm or more. A radiant tube burner according to claim 1 or claim 2.

4. A tubular secondary air supply tube surrounds the radially outer side of the primary air supply tube, extends from the burner body to the rear side inside the radiant tube, and serves as a passage for secondary air, which is air used for the secondary combustion of hydrogen, wherein the rear end of the secondary air supply tube is located further rear than the end of the primary air supply tube, and the space between the radially outer surface of the secondary air supply tube and the radially inner surface of the radiant tube serves as a passage for tertiary air, which is air used for the tertiary combustion of hydrogen, further comprising the secondary air supply tube. A radiant tube burner according to claim 1 or claim 2.

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