Industrial furnace

Abstract

To provide an industrial furnace for effectively burning ammonia while reducing nitrogen oxide without increasing cost specifically.SOLUTION: A metallic or non-ferrous metallic industrial furnace 100 includes: an air nozzle 11 disposed at a center of a burner 10 provided on a furnace wall 101 to discharge combustion air into the furnace; and an ammonia nozzle 12 for discharging ammonia into the furnace. The air nozzle 11 and the ammonia nozzle 12 are disposed on the furnace side wall 101 so that the ammonia nozzle 12 is located on a vertical lower side of the air nozzle 11, leaving a fixed distance with respect to the air nozzle 11. Compared to a case where the ammonia nozzle 12 is provided horizontally by the fixed distance relative to the air nozzle 11, generation of nitrogen oxide (NOX) is suppressed.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an industrial furnace that burns ammonia as fuel.

Background Art

[0002] In recent years, from the perspective of suppressing global warming, ammonia, which does not generate carbon dioxide even when burned, has attracted attention as a new fuel. However, when ammonia is mixed with fossil fuels or burned only with ammonia, the emission amount of nitrogen oxides (NO X ) is known to increase (see, for example, Patent Document 1).

[0003] The combustion device described in Patent Document 1 solves the problem of an increase in nitrogen oxides when ammonia is added to coal and burned.

[0004] Although ammonia has attracted attention as a new fuel, there has been no industrial furnace that effectively uses ammonia as fuel so far, and currently it is in the research and development stage. That is, generally, the combustion rate of ammonia is about 25% of that of natural gas, and when burned, the emission amount of nitrogen oxides (NO X ) increases and exceeds the regulatory value (180 ppm, O2 = 11% conversion), resulting in it not being usable as fuel. When ammonia is used as fuel and burned in existing equipment, the emission amount of nitrogen oxides (NO X ) may exceed three times the regulatory value. In addition, nitrous oxide (N2O), whose global warming potential, which is a trigger for decarbonization, is said to be 250 to 300 times that of carbon dioxide, may also be generated.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In contrast, in order to suppress the emission of nitrogen oxides (NO X ), the inventors of the present invention conducted experiments focusing on the arrangement positions of an air nozzle that discharges combustion air into the furnace and an ammonia nozzle that discharges ammonia into the furnace. As a result, when the ammonia nozzle is arranged below the air nozzle, the emission of nitrogen oxides (NO X ) can be suppressed more effectively than when the air nozzle and the ammonia nozzle are arranged horizontally.

[0007] Therefore, an object of the present invention is to provide an industrial furnace that can effectively burn ammonia while suppressing the emission of nitrogen oxides by a simple method without particularly increasing costs.

Means for Solving the Problems

[0008] In order to achieve the above object, the present invention provides an industrial furnace (100) made of metal or non-ferrous metal, in which an air nozzle (11) is arranged at the center of a burner (10) provided on a furnace wall (101) and discharges combustion air into the furnace, and an ammonia nozzle (12) that discharges ammonia into the furnace is provided. The air nozzle (11) and the ammonia nozzle (12) are arranged on the side wall (101) of the furnace, and the ammonia nozzle (12) is arranged at a certain distance directly below the air nozzle (11) with respect to the air nozzle (11). The generation of nitrogen oxides (NO X ) is suppressed more than when the ammonia nozzle (12) is provided in the horizontal direction by the certain distance with respect to the air nozzle (11).

[0009] Further, in the present invention, when the diameter of the air nozzle (11) is D and the distance between the centers of the air nozzle (11) and the ammonia nozzle (12) is L, the ammonia nozzle (12) is arranged with respect to the position of the air nozzle (11) such that the value of L / D is 1.50 or more.

[0010] Further, in the present invention, when the diameter of the air nozzle (11) is D and the distance between the centers of the air nozzle (11) and the ammonia nozzle (12) is L, the ammonia nozzle (12) is arranged with respect to the position of the air nozzle (11) such that the value of L / D is 2.00 or more and 4.00 or less.

[0011] Further, in the present invention, only ammonia is discharged from the ammonia nozzle (12).

[0012] Further, in the present invention, a mixture of ammonia and fossil fuel is discharged from the ammonia nozzle (12).

[0013] Note that the symbols in the parentheses above indicate corresponding elements or corresponding matters described in the drawings and the embodiments for carrying out the invention described later.

Advantages of the Invention

[0014] According to the industrial furnace of the present invention, in an industrial furnace for metal or non-ferrous metal provided with an air nozzle and an ammonia nozzle, the ammonia nozzle is arranged at a certain distance directly below the air nozzle with respect to the air nozzle. Compared with the case where the ammonia nozzle is provided horizontally with respect to the air nozzle by a certain distance, nitrogen oxides (NO X ) generation is suppressed. Therefore, ammonia can be effectively burned while suppressing nitrogen oxide emissions in a simple method without particularly increasing costs. It has been clarified by the experiments of the present inventors that the generation of nitrogen oxides (NO X ) can be suppressed more effectively when the ammonia nozzle is provided directly below the air nozzle than when it is provided horizontally with respect to the air nozzle. Although the ammonia nozzle for discharging ammonia has existed conventionally, it was not known that there is an arrangement of an air nozzle and an ammonia nozzle that can suppress the generation of nitrogen oxides (NO X ).

[0015] More specifically, when the diameter of the air nozzle is D and the distance between the centers of the air nozzle and the ammonia nozzle is L, it is required to arrange the ammonia nozzle with respect to the position of the air nozzle such that the value of L / D is 1.50 or more. When the value of L / D is less than 1.50, the concentration of nitrogen oxides (NO X ) becomes higher than the regulated value (converted from 180 ppm, O2 = 11%).

[0016] Therefore, it is preferable to arrange the ammonia nozzle with respect to the position of the air nozzle such that the value of L / D is 2.00 or more and 4.00 or less. Note that the ammonia nozzle is not limited to the one that discharges only ammonia, and even if a mixture of ammonia and fossil fuel is discharged from the ammonia nozzle, it has been found to be effective in reducing the concentration of nitrogen oxides (NO X ).

[0017] This is because the flame ejected from the air nozzle becomes a flow that rises by buoyancy, and at the lower part of the flame, the air is in a state where it forms a large vertical vortex. When ammonia is discharged from the ammonia nozzle below the air nozzle, the residence time of ammonia in the furnace becomes longer, and as a result, nitrogen oxides (NO X ) are decomposed and the concentration becomes lower. There has never been anything in the past that considers the arrangement of the ammonia nozzle with respect to the air nozzle based on such an idea.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0019] Referring to FIGS. 1 to 3, the industrial furnace 100 according to an embodiment of the present invention will be described. Here, as the industrial furnace 100, a metal heating furnace 100 for heating metal will be described as an example.

[0020] As shown in FIG. 1, the metal heating furnace 100 according to the present embodiment has a substantially rectangular cross-section (composed of a first side wall 101, a second side wall 102, a third side wall 103, a fourth side wall 104, a ceiling wall 105, and a bottom wall 106). Among the opposing first side wall 101 and second side wall 102, the first side wall 101 is provided with a burner 10, and a flame F is ejected. As a result, the inside of the furnace is in a state exceeding 1000°C.

[0021] At the center of the burner 10 provided on the first side wall 101 of the metal heating furnace 100, an air nozzle 11 for discharging combustion air into the furnace is provided, and on the bottom wall 106 side directly below the air nozzle 11, an ammonia nozzle 12 for discharging ammonia into the furnace is provided.

[0022] In the present embodiment, 100% of ammonia, that is, only ammonia is discharged from the ammonia nozzle 12, but it can also be discharged in a state where fossil fuel is mixed with ammonia. Examples of existing fossil fuels include natural gas, petroleum-based gas (such as propane / butane), coal-based gas (such as blast furnace gas), and city gas.

[0023] In addition, an exhaust duct 110 is provided at the center of the second side wall 102 of the metal heating furnace 100.

[0024] In the burner 10, combustion air is supplied to the air nozzle 11 via an on-off valve (not shown), and ammonia is also supplied to the ammonia nozzle 13 via an on-off valve (not shown). These on-off valves may be in any form such as solenoid valves, regulating valves, etc.

[0025] As shown in FIG. 3, the arrangement of the ammonia nozzle 12 with respect to the position of the air nozzle 11 is such that the ammonia nozzle 12 is located below the air nozzle 11 in the vertical direction. When the diameter of the air nozzle 11 is D and the distance between the centers of the air nozzle 11 and the ammonia nozzle 12 is L, the value of L / D is set to be 1.50 or more. Specifically, it is more preferable that the value of L / D is 2.00 or more and 4.00 or less. In this embodiment, the value of L / D is set to 4.00. In this embodiment, since the diameter D of the air nozzle 11 is 70.3 mm, when the value of L / D is 4.00, the distance L between the centers of the air nozzle 11 and the ammonia nozzle 12 is 281.2 mm.

[0026] The value of L / D is derived from the graph shown in FIG. 5, which shows the relationship between L / D and the concentration of nitrogen monoxide (NO) generated in the furnace, obtained by repeating experiments using the industrial furnace 100 shown in FIG. 4. Here, the air nozzle 11 with a diameter D of 70.3 mm was also used.

[0027] In the graph of FIG. 5, The black circle ● indicates the concentration of nitrogen monoxide (NO) when the ammonia nozzle 12 is provided on the ceiling wall 105 and 30% ammonia (NH3) is co-fired with city gas. The white circle ○ indicates the concentration of nitrogen monoxide (NO) when the ammonia nozzle 12 is provided on the ceiling wall 105 and 100% ammonia is burned exclusively. The black square ■ indicates the concentration of nitrogen monoxide (NO) when the ammonia nozzle 12 is provided horizontally on the first side wall 101 and 30% ammonia (NH3) is co-fired with city gas. The white square □ mark indicates the concentration of nitrogen monoxide (NO) when 100% ammonia (NH3) is specially combusted in the case where the ammonia nozzle 12 is horizontally provided on the first side wall 101. Each of them is shown.

[0028] Also, "under" indicates the case where the ammonia nozzle 12 is arranged below the position of the air nozzle 11 provided at the center of the first side wall 101, and "side" indicates the case where the ammonia nozzle 12 is arranged horizontally shifted from the position of the air nozzle 11 provided at the center of the first side wall 101. "♯a", "♯b", "♯c" indicate the case where the distance between the air nozzle 11 and the ammonia nozzle 12 is changed. The value of L / D is the value obtained by dividing the distance L between the centers of the air nozzle 11 and the ammonia nozzle 12 by the diameter D of the air nozzle 11. Also, "♯1" to "♯6" indicate the case where the ammonia nozzle 12 is provided on the ceiling wall 105 and the distance from the air nozzle 11 is changed. The value of L / D is the value obtained by dividing the distance L between the center of the air nozzle 11 and the point where the line horizontally extending the center of the air nozzle 11 intersects the line vertically extending the center of the ammonia nozzle 12 by the diameter D of the air nozzle 11.

[0029] (1) When discharging a mixture of 30% ammonia (NH3) in city gas from the ammonia nozzle 12 located at "♯1" (in this case, L / D = 4.27), the concentration of nitrogen monoxide (NO) was 490 ppm. (2) When discharging a mixture of 30% ammonia (NH3) in city gas from the ammonia nozzle 12 located at "♯2" (in this case, L / D = 12.80), the concentration of nitrogen monoxide (NO) was 245 ppm. (3) When discharging a mixture of 30% ammonia (NH3) in city gas from the ammonia nozzle 12 located at "♯5" (in this case, L / D = 38.41), the concentration of nitrogen monoxide (NO) was 170 ppm. (4) When discharging the mixture of 30% ammonia (NH₃) and city gas from the ammonia nozzle 12 located at 「♯6」 (in this case, L / D = 46.94), the concentration of nitrogen monoxide (NO) was 134 ppm. (5) When discharging the specialized combustion of 100% ammonia (NH₃) from the ammonia nozzle 12 located at 「♯1」 (in this case, L / D = 4.27), the concentration of nitrogen monoxide (NO) was 473 ppm. (6) When discharging the specialized combustion of 100% ammonia (NH₃) from the ammonia nozzle 12 located at 「♯6」 (in this case, L / D = 46.94), the concentration of nitrogen monoxide (NO) was 316 ppm.

[0030] (7) When discharging the mixture of 30% ammonia (NH₃) and city gas from the ammonia nozzle 12 located on the 「♯a」 side (in this case, L / D = 1.92), the concentration of nitrogen monoxide (NO) was 369.99 ppm. (8) When discharging the mixture of 30% ammonia (NH₃) and city gas from the ammonia nozzle 12 located on the 「♯b」 side (in this case, L / D = 4.02), the concentration of nitrogen monoxide (NO) was 420.01 ppm. (9) When discharging the mixture of 30% ammonia (NH₃) and city gas from the ammonia nozzle 12 located on the 「♯c」 side (in this case, L / D = 5.16), the concentration of nitrogen monoxide (NO) was 487.36 ppm. (10) When discharging the mixture of 30% ammonia (NH₃) and city gas from the ammonia nozzle 12 located under 「♯b」 (in this case, L / D = 4.00), the concentration of nitrogen monoxide (NO) was 194.7 ppm. (11) When discharging the mixture of 30% ammonia (NH₃) and city gas from the ammonia nozzle 12 located under 「♯c」 (in this case, L / D = 2.00), the concentration of nitrogen monoxide (NO) was 219.85 ppm.

[0031] When 100% ammonia (NH₃) was specially combusted and discharged from the ammonia nozzle 12 (in this case, L / D = 1.92) located on the "♯a" side, the concentration of nitrogen monoxide (NO) was 369.99 ppm. (13) When 100% ammonia (NH₃) was specially combusted and discharged from the ammonia nozzle 12 (in this case, L / D = 4.02) located on the "♯b" side, nitrogen monoxide (NO X ) had a concentration of 390.34 ppm. (14) When 100% ammonia (NH₃) was specially combusted and discharged from the ammonia nozzle 12 (in this case, L / D = 5.16) located on the "♯c" side, the concentration of nitrogen monoxide (NO) was 543.74 ppm. (15) When 100% ammonia (NH₃) was specially combusted and discharged from the ammonia nozzle 12 (in this case, L / D = 4.00) located under the "♯b", the concentration of nitrogen monoxide (NO) was 170.84 ppm. (16) When 100% ammonia (NH₃) was specially combusted and discharged from the ammonia nozzle 12 (in this case, L / D = 2.00) located under the "♯c", the concentration of nitrogen monoxide (NO) was 168.11 ppm.

[0032] From this, it can be seen from the results of (1) to (6) above that the concentration of nitrogen monoxide (NO) is lower when it is farther away from the air nozzle 11. Also, from the results of (7) to (15) above, it can be seen that the concentration of nitrogen monoxide (NO) is lower when the ammonia nozzle 12 is arranged under, that is, vertically below the air nozzle 11, rather than arranging the ammonia nozzle 12 horizontally, that is, on the side of the air nozzle 11. In particular, in FIG. 5, in the region indicated by X, that is, in the region where the value of L / D is 2.00 or more and 4.00 or less, it can be seen that arranging the ammonia nozzle 12 vertically below the air nozzle 11 results in a much lower value than arranging the ammonia nozzle 12 horizontally with respect to the air nozzle 11. This indicates that arranging the ammonia nozzle 12 vertically below the air nozzle 11 is effective in reducing the generation of nitrogen monoxide (NO), whether it is a mixed combustion of ammonia and city gas or a dedicated combustion of ammonia.

[0033] This is because the flame F ejected from the air nozzle 11 forms a flow that rises due to buoyancy. At the lower part of the flame F, the air forms a large vertical vortex or flows in vertical or horizontal directions formed under the flow rising due to buoyancy. When ammonia is discharged from below the air nozzle 11 from the ammonia nozzle 12 or the ammonia nozzles of "#5" and "#6", it is considered that the residence time of ammonia in the furnace becomes longer, and as a result, nitrogen monoxide (NO) is decomposed and the concentration decreases. Also, as for nitrogen oxides (NOx), a tendency for a lower concentration has been confirmed.

[0034] When the ammonia nozzle 12 is arranged vertically below the air nozzle 11 at a position where the value of L / D is less than 1.50, the concentration of nitrogen oxides (NO X ) is lower than when it is arranged horizontally, but it is higher than the regulated value (180 ppm, converted from O2 = 11%). Therefore, it is required that the value of L / D is 1.50 or more, and further preferably, the value of L / D is 2.00 or more and 4.00 or less.

[0035] Also, although the ammonia nozzle 12 extends horizontally, its tip side may be configured to swing in the vertical or horizontal direction around the base side.

[0036] According to the industrial furnace configured as described above, in the industrial furnace 100 for metals or non-ferrous metals provided with the air nozzle 11 and the ammonia nozzle 12, the ammonia nozzle 12 is arranged at a certain distance directly below the air nozzle 11. Compared with the case where the ammonia nozzle 12 is provided horizontally relative to the air nozzle 11 by a certain distance, the generation of nitrogen oxides (NO X ) is suppressed. Therefore, ammonia can be effectively burned while suppressing the emission of nitrogen oxides by a simple method without particularly increasing costs.

[0037] The industrial furnace 100 according to the present embodiment has a substantially rectangular cross-section, but is not limited to a furnace with a substantially rectangular cross-section. For example, it may be a dome-shaped furnace with a circular plan view. Further, it is not limited to the metal heating furnace 100, and it may be a furnace for heating non-ferrous metals such as aluminum. Also, it is not limited to heating furnaces, and it is applicable to industrial furnaces such as heat treatment furnaces, forging furnaces, melting furnaces, and ladle preheating devices.

Explanation of reference numerals

[0038] 10 Burner 11 Air nozzle 12 Ammonia nozzle 100 Metal heating furnace (industrial furnace) 101 First side wall 102 Second side wall 103 Third side wall 104 Fourth side wall 105 Ceiling wall 106 Bottom wall 110 Exhaust duct F Flame

Claims

Claim 1 An industrial furnace made of metal or non-ferrous metal, provided with an air nozzle disposed at the center of a burner provided on a furnace wall for discharging combustion air into the furnace, and an ammonia nozzle for discharging ammonia into the furnace, wherein the air nozzle and the ammonia nozzle are provided on a side wall of the furnace, and the ammonia nozzle is disposed at a certain distance vertically below the air nozzle with respect to the air nozzle, An industrial furnace characterized in that the generation of nitrogen oxides (NO X ) is suppressed as compared with the case where the ammonia nozzle is provided horizontally at the fixed distance from the air nozzle. Claim 2 The industrial furnace according to Claim 1, wherein when the diameter of the air nozzle is D and the distance between the centers of the air nozzle and the ammonia nozzle is L, the ammonia nozzle is disposed with respect to the position of the air nozzle such that the value of L / D is 1.50 or more. Claim 3 The industrial furnace according to Claim 1, wherein when the diameter of the air nozzle is D and the distance between the centers of the air nozzle and the ammonia nozzle is L, the ammonia nozzle is disposed with respect to the position of the air nozzle such that the value of L / D is 2.00 or more and 4.00 or less. Claim 4 The industrial furnace according to any one of Claims 1 to 3, wherein only ammonia is discharged from the ammonia nozzle. Claim 5 The industrial furnace according to any one of Claims 1 to 3, wherein a mixture of ammonia and fossil fuel is discharged from the ammonia nozzle.

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