Industrial furnace

Abstract

[Problem] To provide an industrial furnace which burns ammonia effectively while achieving a reduction in nitrogen oxides, without a particular increase in cost. [Solution] In an industrial furnace 100 equipped with a regenerative burner comprising a pair of burners 10, 20: air nozzles 11, 21 for discharging combustion air into the furnace are provided in furnace walls 101, 102 in positions at the centers of the burners 10, 20; fuel nozzles 12, 22 for discharging a fossil fuel into the furnace are provided on one of two sides sandwiching the air nozzles 11, 21, and ammonia nozzles 13, 23 for discharging ammonia into the furnace are provided on the other side; and the ammonia is burned using the burners 10, 20.

Description

Technical Field

[0001] The present invention relates to industrial furnaces such as heating furnaces, heat treatment furnaces, forging furnaces, melting furnaces, and ladle preheating devices.

Background Art

[0002] In recent years, from the perspective of suppressing global warming, ammonia that does not generate carbon dioxide even when burned has attracted attention as a new fuel. In industrial furnaces, ammonia is hardly used as a fuel, and ammonia combustion using a normal burner is being put into practical use through research and development by various research institutions and companies, but there is no use in high-temperature air combustion burners such as regenerative burners. A regenerative burner alternately burns a pair of burners, stores the waste heat obtained by the combustion of one burner in the regenerator of the other burner, and uses this waste heat when burning the other burner (for example, see Patent Document 1), but there is no case of using ammonia as a fuel.

[0003] Especially when ammonia is mixed with existing fossil fuels or burned alone, the amount of nitrogen oxides (NO X ) generated as combustion products increases 5 to 10 times compared to the case of exclusive burning of fossil fuels, so its use in general industrial furnaces is prohibited due to environmental regulations.

[0004] Therefore, if a denitration facility is installed in the flue or exhaust gas duct of an industrial furnace, it will increase the installation space and significantly increase the equipment cost, and ultimately increase the product price.

[0005] Also, in the co-combustion of fossil fuels and ammonia, it is necessary to consider the effects on the heated object to be processed (product), and heat-resistant steel and refractories in the furnace due to the generation and corrosion of nitrides by nitrogen oxides (NO X ) and unburned ammonia contained in the combustion exhaust gas. Furthermore, since combustion becomes unstable at low furnace temperatures, it is conceivable to start by burning only existing fossil fuels to raise the furnace temperature, and then switch to co-firing with ammonia once a certain temperature is reached. However, from a decarbonization perspective, it is preferable to achieve ammonia co-firing from as low a temperature as possible. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2015-132408 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Therefore, the object of the present invention is to provide an industrial furnace that effectively burns ammonia while reducing nitrogen oxides without particularly increasing costs. [Means for solving the problem]

[0008] To achieve the above objective, the present invention provides a metal or non-ferrous metal industrial furnace (100) equipped with a regenerative burner that alternately burns at least one pair of burners (10, 20), stores the waste heat obtained from the combustion of one burner (10) in a heat regenerator (25) of the other burner (20), and uses that waste heat when burning the other burner (20), The invention is characterized by providing an air nozzle (11, 21) in the furnace wall (101, 102) located in the center of the burner (10, 20) for discharging combustion air into the furnace, and providing a fuel nozzle (12, 22) on one side of the air nozzle (11, 21) for discharging fossil fuel into the furnace, and an ammonia nozzle (13, 23) on the other side for discharging ammonia into the furnace, and burning the ammonia in the burner (10, 20).

[0009] Furthermore, in the present invention, on one burner (10) side, the fuel nozzle (12) is provided above the air nozzle (11), and the ammonia nozzle (13) is provided below it. On the other burner (20) side, the ammonia nozzle (23) is provided above the air nozzle (21), and the fuel nozzle (22) is provided below it.

[0010] Furthermore, in the present invention, on one burner (10) side, the ammonia nozzle (13) is provided on the left side when viewed from the air nozzle (11) towards the inside of the furnace, and the fuel nozzle (12) is provided on the right side. On the other burner (20) side, the ammonia nozzle (23) is provided on the left side and the fuel nozzle (22) is provided on the right side when viewed from the air nozzle (21) towards the inside of the furnace.

[0011] Furthermore, the present invention is characterized by providing a mechanism for varying the angle of both or one of the fuel nozzles (12, 22) and the ammonia nozzles (13, 23).

[0012] Furthermore, the present invention is characterized in that a second ammonia nozzle (14, 24) for discharging ammonia into the furnace is provided between the air nozzle (11, 21) and the ammonia nozzle (13, 23).

[0013] The symbols in parentheses above indicate the corresponding elements or items shown in the drawings and the embodiments for carrying out the invention described later. [Effects of the Invention]

[0014] According to the industrial furnace of the present invention, in each pair of burners, the fuel nozzle is positioned opposite the ammonia nozzle with the air nozzle in the center, so that the combustion air blocks the flame of the existing fossil fuel and prevents the flame from coming into contact with the ammonia discharged from the ammonia nozzle. Existing fossil fuels do not begin to burn immediately after being discharged from the fuel nozzle, but rather after a certain period of time has passed since discharge, that is, after a certain distance has passed from the discharge point towards the burner opposite it.

[0015] Furthermore, ammonia burns more slowly than existing fossil fuels, and is therefore burned downstream of the flames from the combustion of existing fossil fuels. When ammonia is burned in an air-fuel ratio, it produces nitrogen oxides (NOx). X Although the amount of nitrogen oxides (NOx) generated by ammonia combustion becomes large, in the downstream part of the flame of this existing fossil fuel, the air ratio is low due to the entrainment effect of the furnace gas, so the amount of nitrogen oxides (NOx) generated by ammonia combustion becomes large. X The amount of ) can be significantly reduced. Thus, according to the present invention, ammonia can be effectively burned while reducing nitrogen oxides by utilizing a regenerative burner. Furthermore, it eliminates the need to equip industrial furnaces with denitrification equipment in flues and exhaust gas ducts, thus reducing costs.

[0016] Furthermore, in this invention, the fuel nozzle and ammonia nozzle can be provided in the vertical direction relative to the air nozzle, or in the horizontal direction relative to the air nozzle, and the air nozzle, fuel nozzle and ammonia nozzle can be arranged in a straight line vertically or horizontally.

[0017] Furthermore, in this invention, on one burner side, a fuel nozzle is placed above the air nozzle and an ammonia nozzle is placed below it, and on the other burner side, an ammonia nozzle is placed above the air nozzle and a fuel nozzle is placed below it. This arrangement causes the line connecting the two fuel nozzles and the line connecting the two ammonia nozzles to cross, thus canceling out differences in combustion conditions and making the temperature distribution more uniform compared to a configuration where the line connecting the two fuel nozzles and the line connecting the two ammonia nozzles are parallel.

[0018] In the present invention, on one burner side, when viewing the inside of the furnace from the air nozzle, an ammonia nozzle is provided on the left side of the air nozzle and a fuel nozzle is provided on the right side. On the other burner side, when viewing the inside of the furnace from the air nozzle, an ammonia nozzle is provided on the left side of the air nozzle and a fuel nozzle is provided on the right side. By arranging them in such a way that the line connecting the two fuel nozzles and the line connecting the two ammonia nozzles cross each other, compared with the case where the line connecting the two fuel nozzles and the line connecting the two ammonia nozzles are parallel, the difference in combustion states can be offset and the temperature distribution can be made uniform. In terms of offsetting the difference in combustion states and making the temperature distribution uniform, it is more preferable to arrange the fuel nozzle and the ammonia nozzle in the horizontal direction with respect to the air nozzle than to arrange the fuel nozzle and the ammonia nozzle in the vertical direction with respect to the air nozzle.

[0019] In the present invention, a mechanism for varying the angle of both or one of the fuel nozzle and the ammonia nozzle is provided, so that the directivity of the flame can be changed, or unburned ammonia during combustion can be prevented from being exposed to the heated object (not shown). The method of varying the angle may be manual or automatic. In particular, in the case of automatically varying the nozzle angle, it can be varied according to changes in the temperature inside the furnace, differences in the type and shape of the heated object, etc. during the operation of the industrial furnace, and it can also be varied in a direction to suppress the generation amount of nitrogen oxides (NO X ).

[0020] In the present invention, a second ammonia nozzle for discharging ammonia into the furnace is provided between the air nozzle and the ammonia nozzle. According to this, combustion stability can be ensured in accordance with the heating process. For example, when the temperature inside the furnace is low at 800°C or less, ammonia is difficult to burn, so ammonia is discharged from the second ammonia nozzle closer to the air nozzle. When the temperature rises to 800°C or more at high temperature, it can be easily switched from the second ammonia nozzle to the ammonia nozzle to discharge ammonia.

Brief Description of the Drawings

[0021] [Figure 1] This is a cross-sectional view showing the main part of an industrial furnace according to an embodiment of the present invention. [Figure 2] This is a cross-sectional view along line AA shown in Figure 1. [Figure 3] Figure 1 is a schematic diagram showing the fluid supply system to the burner 10. [Figure 4] Figure 1 is a partial cross-sectional view showing the mechanism for varying the angle of the ammonia nozzle 13. [Figure 5] This is a schematic diagram showing a fluid supply system to a burner 10 provided in an industrial furnace according to another embodiment of the present invention. [Figure 6] This shows an industrial furnace according to yet another embodiment of the present invention, where (a) is a cross-sectional view and (b) is a cross-sectional view of (a) along line BB. [Modes for carrying out the invention]

[0022] An industrial furnace 100 according to an embodiment of the present invention will be described with reference to Figures 1 to 3. Here, a metal heating furnace 100 for heating metal will be used as an example of the industrial furnace 100.

[0023] As shown in Figure 1, the metal heating furnace 100 according to this embodiment has a substantially rectangular cross-section, and a pair of regenerative burners, consisting of burners 10 and 20, are installed on the opposing first side wall 101 and second side wall 102. The regenerative burner alternately burns a pair of burners 10 and 20, storing the waste heat obtained from the combustion of one burner 10 in a heat accumulator 25 provided on the other burner 20, and using that waste heat when burning the other burner 20. Furthermore, the waste heat obtained from the combustion of the other burner 20 is stored in a heat accumulator 15 provided on one burner 10, and using that waste heat when burning the other burner 10.

[0024] An air nozzle 11 for discharging combustion air into the furnace is provided in the center of the burner 10 installed on the first side wall 101 of the metal heating furnace 100. On one side of the air nozzle 11, a fuel nozzle 12 for discharging existing fossil fuels into the furnace is provided, and on the other side, an ammonia nozzle 13 for discharging ammonia into the furnace is provided. The air nozzle 11, fuel nozzle 12, and ammonia nozzle 13 are installed on the first side wall 101, aligned horizontally at arbitrary distances (here, they are assumed to be at equal intervals, but this is not limited to them). That is, the air nozzle 11, fuel nozzle 12, and ammonia nozzle 13 are parallel, with the ammonia nozzle 13 located on the left side (arrow S1 side in Figure 1: third side wall 103 side) and the fuel nozzle 12 located on the right side (arrow S2 side in Figure 1: fourth side wall 104 side) when viewed from the air nozzle 11 towards the inside of the reactor.

[0025] Furthermore, an air nozzle 21 for discharging combustion air into the furnace is provided in the center of the burner 20 installed on the second side wall 102 of the metal heating furnace 100. On one side of the air nozzle 21, a fuel nozzle 22 for discharging existing fossil fuels into the furnace is provided, and on the other side, an ammonia nozzle 23 for discharging ammonia into the furnace is provided. The air nozzle 21, fuel nozzle 22, and ammonia nozzle 23 are installed on the second side wall 102, aligned horizontally at arbitrary distances (here, they are assumed to be at equal intervals, but this is not limited to them). That is, the air nozzle 21, fuel nozzle 22, and ammonia nozzle 23 are parallel, with the ammonia nozzle 23 located on the left side (arrow S3 in Figure 1: towards the fourth side wall 104) and the fuel nozzle 22 located on the right side (arrow S4 in Figure 1: towards the third side wall 103) when viewed from the air nozzle 21 towards the inside of the reactor.

[0026] As shown in Figure 2, an exhaust tower 110 is provided in the center of the ceiling wall 105 of the metal heating furnace 100.

[0027] As shown in Figure 3, on the burner 10 side, combustion air is supplied to the air nozzle 11 via the on-off valve 31, existing fossil fuel is supplied to the fuel nozzle 12 via the on-off valve 32, and ammonia is supplied to the ammonia nozzle 13 via the on-off valve 33. Similarly, on the burner 20 side, combustion air is supplied to the air nozzle 21 via the on-off valve 41, existing fossil fuel is supplied to the fuel nozzle 22 via the on-off valve 42, and ammonia is supplied to the ammonia nozzle 23 via the on-off valve 43. The on / off valves 31-33 and 41-43 may be of any form, such as solenoid valves or control valves. Existing fossil fuels include natural gas, petroleum-based gases (propane / butane, etc.), and coal-based gases (blast furnace gas), and in this embodiment, natural gas is used.

[0028] In the metal heating furnace 100 configured in this way, the burners 10 and 20 have fuel nozzles 12 and 22 positioned on the opposite side of the ammonia nozzles 13 and 23, with the air nozzles 11 and 21 in the center, and at a certain distance from the air nozzles 11 and 21. This prevents the combustion air from blocking the flame of the existing fossil fuel and from coming into contact with the ammonia discharged from the ammonia nozzles 13 and 23. Existing fossil fuels do not begin to burn immediately after being discharged from the fuel nozzles 12 and 22, but rather after a certain period of time has passed since discharge, that is, after a certain distance has passed from the discharge point towards the burner side (approximately midway between the first side wall 101 and the second side wall 102).

[0029] Furthermore, ammonia burns more slowly than existing fossil fuels, and is burned downstream of the flame from the combustion of existing fossil fuels (i.e., in the case of combustion in burner 10, the part closer to burner 20). When ammonia is burned in an air-fuel ratio, it produces nitrogen oxides (NOx). X Although the amount of nitrogen oxides (NOx) generated by ammonia combustion becomes large, in the downstream part of the flame of this existing fossil fuel, the air ratio is low due to the entrainment effect of the furnace gas, so the amount of nitrogen oxides (NOx) generated by ammonia combustion becomes large. X The amount of ) can be significantly reduced.

[0030] Furthermore, on the burner 10 side, when viewed from the air nozzle 11 into the furnace, an ammonia nozzle 13 is provided on the left side (arrow S1 in Figure 1: side of the third side wall 103) and a fuel nozzle 12 is provided on the right side (arrow S2 in Figure 1: side of the fourth side wall 104). Conversely, on the burner 20 side, when viewed from the air nozzle 21 into the furnace, an ammonia nozzle 23 is provided on the left side (arrow S3 in Figure 1: side of the fourth side wall 104) and a fuel nozzle 22 is provided on the right side (arrow S4 in Figure 1: side of the third side wall 103). Thus, the lines connecting the fuel nozzles 12 and 22 and the lines connecting the ammonia nozzles 13 and 23 cross each other. Compared to a configuration where the lines connecting the fuel nozzles 12 and 22 and the ammonia nozzles 13 and 23 are parallel, the differences in combustion state can be offset and the temperature distribution can be made more uniform.

[0031] While it is possible to arrange the fuel nozzles 12 and 22 and the ammonia nozzles 13 and 23 so that they intersect with the lines connecting the fuel nozzles 12 and 22 and the ammonia nozzles 13 and 23, respectively, by placing the fuel nozzle 12 and 22 above the air nozzle 11 and the ammonia nozzle 13 below it on one burner 10 side, and the ammonia nozzle 23 above the air nozzle 21 and the fuel nozzle 22 below it on the other burner 20 side, it is preferable to arrange the fuel nozzles 12 and 22 and the ammonia nozzles 13 and 23 horizontally with respect to the air nozzles 11 and 21, as shown in Figure 1, in order to cancel out the differences in combustion state and equalize the temperature distribution.

[0032] In the metal heating furnace 100 shown in Figure 1, 80% of the exhaust gas is discharged from the burners 10 and 20, and the remaining 20% ​​of the exhaust gas is discharged directly from the exhaust tower 110 installed in the ceiling wall 105.

[0033] In this embodiment, the air nozzles 11, 21, fuel nozzles 12, 22, and ammonia nozzles 13, 23 are all fixed to the first side wall 101 and second side wall 102 of the metal heating furnace 100. However, as shown in Figure 4, a variable mechanism 200 can also be provided to change the angle of both or one of the fuel nozzles 12, 22 and the ammonia nozzles 13, 23.

[0034] The variable mechanism 200 can be of any form and may be manual or automatic. For example, as shown in Figure 4, the ends of the fuel nozzles 12 and 22 are rotatably mounted on a horizontally extending shaft 201, so that the tips of the fuel nozzles 12 and 22 can be directed upward or downward. According to this, by changing the nozzle angle (discharge angle) in the vertical direction, the directionality of the flame can be changed, or unburned ammonia during combustion can be prevented from being exposed to the object being heated (not shown). In particular, with systems that automatically vary the nozzle angle, it is possible to adjust the angle during operation of the metal heating furnace 100 in accordance with changes in the furnace temperature, differences in the type and shape of the object being heated, and furthermore, nitrogen oxides (NOx) X It can also be varied to suppress the amount of () generated.

[0035] Furthermore, as shown in Figure 5, second ammonia nozzles 14 and 24 for discharging ammonia into the furnace may be provided between the air nozzles 11 and 21 and the ammonia nozzles 13 and 23 via on-off valves 34 and 44. Note that the number of additional ammonia nozzles (in this case, second ammonia nozzles 14 and 24) may be one or more. According to this, combustion stability can be ensured in accordance with the heating process. For example, when the temperature inside the furnace is low, below 800°C, ammonia is difficult to burn, so ammonia is discharged from the second ammonia nozzles 14 and 24, which are closer to the air nozzles 11 and 21. When the temperature rises to a high temperature of 800°C or higher, it is easy to switch from the second ammonia nozzles 14 and 24 to ammonia nozzles 13 and 23 to discharge ammonia. Also, at low temperatures, ammonia can be discharged from both ammonia nozzles 13 and 23 and the second ammonia nozzles 14 and 24.

[0036] Furthermore, either without providing the second ammonia nozzles 14 and 24, or in combination with providing the second ammonia nozzles 14 and 24, at low temperatures, the variable mechanism 200 shown in Figure 4 may be used to change the angle of the ammonia nozzles 13 and 23 so that ammonia is discharged from a position closer to the air nozzles 11 and 21, and at high temperatures the angle may be returned to its original position.

[0037] Furthermore, in this embodiment, a metal heating furnace 100 with a substantially rectangular cross-section is provided with one set of a pair of burners 10, 20, but it is also possible to provide multiple sets of a pair of burners 10, 20. Furthermore, this method is not limited to furnaces with a roughly rectangular cross-section; it can also be applied to any furnace equipped with at least one set of a pair of burners 10, 20. For example, it may be a dome-shaped furnace with a circular top view, as shown in Figure 6. Here, a metal heating furnace 100 equipped with two sets of a pair of burners 10, 20 is shown.

[0038] The industrial furnace 100 according to this embodiment is not limited to a metal heating furnace 100, but may be a furnace for heating non-ferrous metals such as aluminum. Furthermore, it is not limited to heating furnaces, but can also be applied to industrial furnaces such as heat treatment furnaces, forging furnaces, melting furnaces, and ladle preheating devices. [Explanation of Symbols]

[0039] 10 burners 11 Air nozzle 12 Fuel nozzles 13 Ammonia nozzle 14. Second ammonia nozzle 15 Heat storage 20 burners 21 Air nozzle 22 Fuel nozzles 23 Ammonia nozzle 24. Second ammonia nozzle 25 Heat storage 31. Shut-off valve 32 Shut-off valves 33. Shut-off valves 34. Shut-off valves 41 Shut-off valve 42 Shut-off valves 43. Shut-off valve 44 Shut-off valves 100 Metal heating furnace (industrial furnace) 101 First side wall 102 Second side wall 103 Third side wall 104 Fourth side wall 105 Ceiling and Wall 110 Exhaust tower 200 Variable Mechanism 201 axis (horizontal axis)

Claims

1. A metal or non-ferrous metal industrial furnace is equipped with a regenerative burner that alternately burns at least one pair of burners, stores the waste heat obtained from the combustion of one burner in a heat regenerator of the other burner, and uses that waste heat when burning the other burner, An industrial furnace characterized by having an air nozzle for discharging combustion air into the furnace located in the center of the burner, a fuel nozzle for discharging fossil fuel into the furnace on one side of the air nozzle, and an ammonia nozzle for discharging ammonia into the furnace on the other side, and burning the ammonia in the burner.

2. On one of the burner sides, the fuel nozzle is provided above the air nozzle, and the ammonia nozzle is provided below it. The industrial furnace according to claim 1, characterized in that the other burner side is provided with the ammonia nozzle above the air nozzle and the fuel nozzle below the air nozzle.

3. On one of the burner sides, the ammonia nozzle is provided on the left side and the fuel nozzle on the right side when viewed from the air nozzle towards the inside of the furnace. The industrial furnace according to claim 1, characterized in that, on the other burner side, the ammonia nozzle is provided on the left side and the fuel nozzle is provided on the right side when viewed from the air nozzle into the furnace.

4. The industrial furnace according to claim 2 or 3, characterized in that it is provided with a mechanism for varying the angle of both or one of the fuel nozzle and the ammonia nozzle.

5. The industrial furnace according to claim 2 or 3, characterized in that a second ammonia nozzle for discharging ammonia into the furnace is provided between the air nozzle and the ammonia nozzle.

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