Industrial furnace

Abstract

OBJECT To provide an industrial furnace that burns ammonia efficiently decreasing nitrogen oxides without need for higher cost. MEANS OF REALIZING THE OBJECT An industrial furnace is equipped with a regenerative burner which includes a pair of first and second burners. The first and second burners burn ammonia. Air nozzles, used to expel combustion air into the furnace, are provided at a center of the first and second burners. Fuel nozzles, used to expel fossil fuel into the furnace, are provided on one of both sides that sandwich the air nozzles. Ammonia nozzles, used to expel ammonia into the furnace, are provided on another one of the both sides of the air nozzles.

Description

TECHNICAL FIELD

[0001] The present invention generally relates to an industrial furnace, which includes a heating furnace, a heat treatment furnace, a forging furnace, a melting furnace, and a ladle preheating device.BACKGROUND ART

[0002] The recent trend toward prevention of global warming has drawn attention to ammonia as new fuel, which emits no carbon dioxide under combustion.

[0003] Ammonia, which the industrial furnace hardly burnt, has increased its practical use in an ordinary burner owing to research and development by research institutes and companies. But no burner for high-temperature air combustion, which includes a regene burner (regenerative burner), has burnt ammonia.

[0004] The regenerative burner includes a pair of first and second burners, which produce flames alternately. A heat reservoir of the second burner stores and uses exhaust heat from the first burner for combustion (see, for example, Patent document 1). But no regenerative burner has burnt ammonia.

[0005] Ammonia, especially when mixed with conventional fossil fuel or burnt alone, is known to emit nitrogen oxides (NO x ) as a combustion product 5 to 10 times as much as fossil fuel solely burnt. Use of ammonia in the ordinary industrial furnace, therefore, is prohibited by environmental regulations.

[0006] Equipping a flue or an exhaust gas duct of the industrial furnace with a denitration facility increases an installation space and an equipment expense significantly. This finally leads to an increase in product price.

[0007] Nitrogen oxides (NO x ) or unburnt ammonia contained in a combustion exhaust gas, which is emitted under mixed combustion of fossil fuel and ammonia, may produce nitride or resultant corrosion. This can have a harmful effect on a heated object as a processed object (product), or heat-resistant steel or a refractory in the furnace.

[0008] Furthermore, to prevent an unstable combustion under a lower furnace temperature, burning solely the conventional fossil fuel first, to increase a furnace temperature up to a predetermined temperature, and then switching to mixed combustion of fossil fuel and ammonia has been proposed. But mixed combustion from a lower possible temperature is more preferable aiming at decarbonization.RELATED ART DOCUMENTSPATENT DOCUMENTS

[0009] Patent document 1: Japanese Unexamined Patent Application Publication No. 2015-132408DISCLOSURE OF THE INVENTIONPROBLEMS TO BE SOLVED BY THE INVENTION

[0010] To solve the above problems, it is an object of the present invention to provide an industrial furnace that burns ammonia efficiently decreasing nitrogen oxides without need for higher cost.MEANS OF SOLVING THE PROBLEMS

[0011] To achieve the above object, an aspect of the present invention provides an industrial furnace (100). The industrial furnace (100) is used for metal or nonferrous metal and is equipped with a regenerative burner. The regenerative burner includes at least a pair of first and second burners (10, 20), heat reservoirs (15, 25) integrated with the first and second burners (10, 20), air nozzles (11, 21), fuel nozzles (12, 22), and ammonia nozzles (13, 23).

[0012] The pair of the first and second burners (10, 20) produce flames alternately. The first and second burners (10, 20) burn ammonia.

[0013] The heat reservoir (25) of the second burner (20) stores and uses exhaust heat from the first burner (10) for combustion.

[0014] The air nozzles (11, 21) are provided on furnace walls (101, 102) at a center of the first and second burners (10, 20). The air nozzles (11, 21) are used to expel combustion air into the furnace.

[0015] The fuel nozzles (12, 22) are provided on one of both sides that sandwich the air nozzles (11, 21). The fuel nozzles (12, 22) are used to expel fossil fuel into the furnace.

[0016] The ammonia nozzles (13, 23) are provided on another one of the both sides of the air nozzles (11, 21). The ammonia nozzles are used to expel ammonia into the furnace.

[0017] In addition, according to an aspect of the present invention, the air nozzle (11) of the first burner (10) has the fuel nozzle (12) provided on an upper side part and the ammonia nozzle (13) on a lower side part, and the air nozzle (21) of the second burner (20) has the ammonia nozzle (23) provided on an upper side part and the fuel nozzle (22) on a lower side part.

[0018] In addition, according to an aspect of the present invention, the air nozzle (11) of the first burner (10) has the ammonia nozzle (13) provided on the left and the fuel nozzle (12) on the right with an inside of the furnace seen from the air nozzle (11), and the air nozzle (21) of the second burner (20) has the ammonia nozzle (23) provided on the left and the fuel nozzle (22) on the right with the inside of the furnace seen from the air nozzle (21).

[0019] In addition, according to an aspect of the present invention, the furnace further includes a mechanism, which changes an angle of both or one of the fuel nozzles (12, 22) and the ammonia nozzles (13, 23).

[0020] In addition, according to an aspect of the present invention, the furnace further includes extra ammonia nozzles (14, 24) provided between the air nozzles (11, 21) and the ammonia nozzles (13, 23). The extra ammonia nozzles (14, 24) are used to expel ammonia into the furnace.

[0021] Symbols in parentheses show constituents or items corresponding to the drawings.

[0022] According to the present invention, the pair of the first and second burners of the industrial furnace has the fuel nozzles provided opposite the ammonia nozzles with the air nozzles at a center. With this configuration, the combustion air cuts off flames of the conventional fossil fuel and prevents the flames from coming into contact with ammonia expelled from the ammonia nozzles.

[0023] Combustion of the conventional fossil fuel begins after a predetermined period of time, not immediately, from discharge from the fuel nozzle, that is after passage by a predetermined distance toward the opposite first or second burner.

[0024] Ammonia, which has a lower burning speed than the conventional fossil fuel, is burnt at a downstream part of the combustion flame of the conventional fossil fuel.

[0025] Burning ammonia under a higher air ratio emits a larger amount of nitrogen oxides (NO x ). But burning ammonia under a lower air ratio at the downstream part of the combustion flame of the conventional fossil fuel alongside of gas entrainment effect inside the furnace controls emission of a substantial amount of nitrogen oxides (NO x ).

[0026] The present invention burns ammonia efficiently decreasing nitrogen oxides with the regenerative burner. Also, the invention eliminates the need for equipping a flue or an exhaust gas duct of the industrial furnace with a denitration facility, and lowers cost.

[0027] In addition, the fuel nozzles and the ammonia nozzles are provided in an upper and lower direction relative to the air nozzles such that the air nozzles, the fuel nozzles, and the ammonia nozzles are aligned in the upper and lower direction. Alternatively, the fuel nozzles and the ammonia nozzles are provided in a horizontal direction to the right and left relative to the air nozzles such that the air nozzles, the fuel nozzles, and the ammonia nozzles are horizontally aligned.

[0028] In addition, the air nozzle of the first burner has the fuel nozzle provided on the upper side part and the ammonia nozzle on the lower side part, and the air nozzle of the second burner has the ammonia nozzle provided on the upper side part and the fuel nozzle on the lower side part. In other words, a line between the fuel nozzles and a line between the ammonia nozzles cross each other. This counterbalances difference in combustion condition and homogenizes a temperature distribution as compared with a configuration in which the line between the fuel nozzles and the line between the ammonia nozzles are parallel with each other.

[0029] In addition, the air nozzle of the first burner has the ammonia nozzle provided on the left and the fuel nozzle on the right with the inside of the furnace seen from the air nozzle, and the air nozzle of the second burner has the ammonia nozzle provided on the left and the fuel nozzle on the right with the inside of the furnace seen from the air nozzle. In other words, the line between the fuel nozzles and the line between the ammonia nozzles cross each other. This counterbalances the difference in the combustion condition and homogenizes the temperature distribution as compared with the configuration in which the line between the fuel nozzles and the line between the ammonia nozzles are parallel with each other.

[0030] To counterbalance the difference in the combustion condition and homogenize the temperature distribution, providing the fuel nozzles and the ammonia nozzles in the horizontal direction relative to the air nozzles is more preferable than providing the fuel nozzles and the ammonia nozzles in the upper and lower direction relative to the air nozzles.

[0031] In addition, the furnace further includes the mechanism, which changes the angle of both or one of the fuel nozzles and the ammonia nozzles. This changes directivity of the flame or prevents exposure of unburnt ammonia in the middle of the combustion to a heated object (illustration omitted).

[0032] The angle of the nozzles may be changed manually or automatically. The automatic mechanism, especially, changes the angle in conformance with change in a furnace temperature or a difference, for example, in kind or shape of the heated object in the operation of the industrial furnace. Also, the automatic mechanism changes the angle in a direction to control amount of nitrogen oxides (NO x ) to be emitted.

[0033] In addition, the furnace further includes the extra ammonia nozzles provided between the air nozzles and the ammonia nozzles. The extra ammonia nozzles are used to expel ammonia into the furnace. This keeps combustion stable in conformance with a heating process. More specifically, the extra ammonia nozzles closer to the air nozzles are used to expel ammonia, which is hard to burn, under the lower furnace temperature of not more than 800°C, and ammonia flow is switched to the ammonia nozzles under the higher temperature of not less than 800°C, to expel ammonia easily.BRIEF DESCRIPTION OF THE DRAWINGS

[0034] [Fig. 1] It is a lateral cross-sectional view of the main components of an industrial furnace according to an embodiment of the present invention in section. [Fig. 2] It is a cross-sectional view taken along line A-A of Fig. 1. [Fig. 3] It is a schematic diagram of a supply system of a fluid relative to a burner 10 illustrated in Fig. 1. [Fig. 4] It is a partial cross-sectional view of a mechanism that changes an angle of an ammonia nozzle 13 illustrated in Fig. 1. [Fig. 5] It is a schematic diagram of a supply system of a fluid relative to a burner 10 of an industrial furnace according to another embodiment of the present invention. [Fig. 6] It is an illustration of an industrial furnace according to still another embodiment of the present invention, in which (a) is a lateral cross-sectional view, and (b) is a cross-sectional view taken along line B-B of (a). MODE FOR CARRYING OUT THE INVENTION

[0035] Referring to Fig. 1 to Fig. 3, an industrial furnace 100 according to an embodiment of the present invention will be described. In this embodiment, a metal heating furnace 100, which heats metals, is used as an example of the industrial furnace 100.

[0036] As illustrated in Fig. 1, the metal heating furnace 100 of this embodiment has a substantially rectangular-shaped cross section, and is equipped with a regenerative burner. The regenerative burner includes a pair of first and second burners 10, 20 provided on first and second side walls 101, 102. The first side wall 101 is opposite the second side wall 102.

[0037] The regenerative burner includes the pair of the first and second burners 10, 20, which produce flames alternately. A heat reservoir 25 of the second burner 20 stores and uses exhaust heat from the first burner 10 for combustion. Next, a heat reservoir 15 of the first burner 10 stores and uses exhaust heat from the second burner 20 for combustion.

[0038] An air nozzle 11 is provided at a center of the first burner 10 on the first side wall 101 of the metal heating furnace 100. The air nozzle 11 is used to expel combustion air into the furnace. A fuel nozzle 12 is provided on one of both sides that sandwich the air nozzle 11. The fuel nozzle 12 is used to expel conventional fossil fuel into the furnace. An ammonia nozzle 13 is provided on another one of the both sides. The ammonia nozzle 13 is used to expel ammonia into the furnace.

[0039] The air nozzle 11, the fuel nozzle 12, and the ammonia nozzle 13 are horizontally aligned at freely-selected intervals (regular intervals in this embodiment, but not limited) and are provided on the first side wall 101. In other words, the air nozzle 11, the fuel nozzle 12, and the ammonia nozzle 13 are parallel with each other. The air nozzle 11 has the ammonia nozzle 13 provided on the left (closer to arrow S1 in Fig. 1: closer to third side wall 103) and the fuel nozzle 12 on the right (closer to arrow S2 in Fig. 1: closer to fourth side wall 104) with an inside of the furnace seen from the air nozzle 11.

[0040] An air nozzle 21 is provided at a center of the second burner 20 on the second side wall 102 of the metal heating furnace 100. The air nozzle 21 is used to expel the combustion air into the furnace. A fuel nozzle 22 is provided on one of both sides that sandwich the air nozzle 21. The fuel nozzle 22 is used to expel the conventional fossil fuel into the furnace. An ammonia nozzle 23 is provided on another one of the both sides. The ammonia nozzle 23 is used to expel ammonia into the furnace.

[0041] The air nozzle 21, the fuel nozzle 22, and the ammonia nozzle 23 are horizontally aligned at freely-selected intervals (regular intervals in this embodiment, but not limited) and are provided on the second side wall 102. In other words, the air nozzle 21, the fuel nozzle 22, and the ammonia nozzle 23 are parallel with each other. The air nozzle 21 has the ammonia nozzle 23 provided on the left (closer to an arrow S3 in Fig. 1: closer to fourth side wall 104) and the fuel nozzle 22 on the right (closer to an arrow S4 in Fig. 1: closer to third side wall 103) with the inside of the furnace seen from the air nozzle 21.

[0042] As illustrated in Fig. 2, the industrial furnace 100 has an exhaust tower 110 provided at a center of a ceiling wall 105.

[0043] As illustrated in Fig. 3, the air nozzle 11 of the first burner 10 is supplied with the combustion air through an on-off valve 31, the fuel nozzle 12 is supplied with the conventional fossil fuel through an on-off valve 32, and the ammonia nozzle 13 is supplied with ammonia through an on-off valve 33.

[0044] In the same manner, the air nozzle 21 of the second burner 20 is supplied with the combustion air through an on-off valve 41, the fuel nozzle 22 is supplied with the conventional fossil fuel through an on-off valve 42, and the ammonia nozzle 23 is supplied with ammonia through an on-off valve 43.

[0045] The on-off valves 31 to 33, 41 to 43 may have any shape including a solenoid valve and a regulating valve.

[0046] Examples of the conventional fossil fuel include natural gas, petroleum gas (e.g. propane / butane), and coal gas (blast furnace gas). In this embodiment, natural gas is used.

[0047] The first and second burners 10, 20 of the metal heating furnace 100 have the fuel nozzles 12, 22 provided opposite the ammonia nozzles 13, 23 with the air nozzles 11, 21 at a center and with a predetermined interval from the air nozzles 11, 21. With this configuration, the combustion air cuts off flame of the conventional fossil fuel and prevents the flame from coming into contact with ammonia expelled from the ammonia nozzles 13, 23.

[0048] Combustion of the conventional fossil fuel begins after a predetermined period of time, not immediately, from discharge from the fuel nozzle 12, 22, that is after passage by a predetermined distance (around the midpoint between the first side wall 101 and the second side wall 102) toward the opposite burner.

[0049] Ammonia, which has a lower burning speed than the conventional fossil fuel, is burnt at a downstream part (part closer to the second burner 20 when the first burner 10 is burning) of the combustion flame of the conventional fossil fuel.

[0050] Burning ammonia under a higher air ratio emits a larger amount of nitrogen oxides (NO x ). But burning ammonia under a lower air ratio at the downstream part of the combustion flame of the conventional fossil fuel alongside of gas entrainment effect inside the furnace controls emission of a substantial amount of nitrogen oxides (NO x ).

[0051] In addition, the air nozzle 11 of the first burner 10 has the ammonia nozzle 13 provided on the left (closer to arrow S1 in Fig. 1: closer to third side wall 103) and the fuel nozzle 12 on the right (closer to arrow S2 in Fig. 1: closer to fourth side wall 104) with the inside of the furnace seen from the air nozzle 11. The air nozzle 21 of the second burner 20, to the contrary, has the ammonia nozzle 23 provided on the left (closer to an arrow S3 in Fig. 1: closer to fourth side wall 104) and the fuel nozzle 22 on the right (closer to an arrow S4 in Fig. 1: closer to third side wall 103) with the inside of the furnace seen from the air nozzle 21. In other words, a line between the fuel nozzles 12, 22 and a line between the ammonia nozzles 13, 23 cross each other. This counterbalances difference in combustion condition and homogenizes a temperature distribution as compared with a configuration in which the line between the fuel nozzles 12, 22 and the line between the ammonia nozzles 13, 23 are parallel with each other.

[0052] In some embodiments, the air nozzle 11 of the first burner 10 has the fuel nozzle 12 provided on the upper side part and the ammonia nozzle 13 on the lower side part, and the air nozzle 21 of the second burner 20 has the ammonia nozzle 23 provided on the upper side part and the fuel nozzle 22 on the lower side part. In other words, the line between the fuel nozzles 12, 22 and the line between the ammonia nozzles 13, 23 cross each other. To counterbalance the difference in the burnt condition and homogenize the temperature distribution, providing the fuel nozzles 12, 22 and the ammonia nozzles 13, 23 in the horizontal direction relative to the air nozzles 11, 21 as illustrated in Fig. 1 is more preferable.

[0053] The metal heating furnace 100, illustrated in Fig. 1, discharges 80% of exhaust gas through the first and second burners 10, 20, and 20 % of exhaust gas through the exhaust tower 110 provided on the ceiling wall 105 directly.

[0054] In this embodiment, the air nozzles 11, 21, the fuel nozzles 12, 22, and the ammonia nozzles 13, 23 are fixed on the first side wall 101 or the second side wall 102 of the metal heating furnace 100. Alternatively, as illustrated in Fig. 4, the furnace may further include a changeable mechanism 200, which changes an angle of both or one of the fuel nozzles 12, 22 and the ammonia nozzles 13, 23.

[0055] The changeable mechanism 200 may have any mode including a manual mechanism and an automatic mechanism. More specifically, ends of the fuel nozzles 12, 22 under the changeable mechanism 200 illustrated in Fig. 4 are rotatably coupled to an axis 201, which extends in the horizontal direction such that top ends of the fuel nozzles 12, 22 turn upward or downward.

[0056] In this modification, changing the angle of the nozzles (angle for expelling) in an upper and lower direction changes directivity of the flame or prevents exposure of unburnt ammonia in the middle of the combustion to a heated object (illustration omitted).

[0057] The automatic mechanism, especially, changes the angle in conformance with change in a furnace temperature or difference, for example, in kind or shape of the heated object in the operation of the metal heating furnace 100. Also, the automatic mechanism changes the angle in a direction to control amount of nitrogen oxides (NO x ) to be emitted.

[0058] Alternatively, as illustrated in Fig. 5, the furnace further may have extra ammonia nozzles 14, 24 provided between the air nozzles 11, 21 and the ammonia nozzles 13, 23 through on-off valves 34, 44. The extra ammonia nozzles 14, 24 are used to expel ammonia into the furnace. One or plural extra ammonia nozzles (extra ammonia nozzles 14, 24 in this modification) may be added.

[0059] This keeps combustion stable in conformance with a heating process. More specifically, the extra ammonia nozzles 14, 24 closer to the air nozzles 11, 21 are used to expel ammonia, which is hard to burn, under the lower furnace temperature of not more than 800°C, and ammonia flow is switched to the ammonia nozzles 13, 23 under the higher temperature of not less than 800°C, to expel ammonia easily. Alternatively, the ammonia nozzles 13, 23 and the extra ammonia nozzles 14, 24 may be used to expel ammonia under the lower temperature.

[0060] Alternatively, the angle of the ammonia nozzles 13, 23 may be changed using the changeable mechanism 200 illustrated in Fig. 4, to expel ammonia on a position closer to the air nozzles 11, 21 under the lower temperature, and then the angle is restored to an original position under the higher temperature. In this modification, the first and second extra ammonia nozzles 14, 24 may be provided or omitted.

[0061] In this embodiment, the metal heating furnace 100, which has the substantially rectangular-shaped cross section, is equipped with the pair of the first and second burners 10, 20, which makes one set. Alternatively, plural sets of the pair of the first and second burners 10, 20 may be provided.

[0062] Shape of the metal heating furnace 100 is not limited to the substantially rectangular-shaped cross section. It is only required that the metal heating furnace 100 has at least one set of the pair of the first and second burners 10, 20. For example, the metal heating furnace 100 illustrated in Fig. 6 is dome-shaped and is circular in plan view. In this modification, the metal heating furnace 100 has two sets of the pair of the first and second burners 10, 20.

[0063] The industrial furnace 100 in this embodiment is not limited to the metal heating furnace 100, and is applicable to a furnace that heats nonferrous metal including aluminum. Also, the industrial furnace 100 is not limited to a heating furnace, and is applicable to an industrial furnace including a heat treatment furnace, a forging furnace, a melting furnace, and a ladle preheating device.DESCRIPTION OF NUMERALS

[0064] 10burner 11air nozzle 12fuel nozzle 13ammonia nozzle 14extra ammonia nozzle 15heat reservoir 20burner 21air nozzle 22fuel nozzle 23ammonia nozzle 24extra ammonia nozzle 25heat reservoir 31on-off valve 32on-off valve 33on-off valve 34on-off valve 41on-off valve 42on-off valve 43on-off valve 44on-off valve 100metal heating furnace (industrial furnace) 101first side wall 102second side wall 103third side wall 104fourth side wall 105ceiling wall 110exhaust tower 200changeable mechanism 201axis (horizontal axis)

Claims

1. An industrial furnace for metal or nonferrous metal, the industrial furnace being equipped with a regenerative burner, the regenerative burner comprising: at least a pair of first and second burners configured to produce flames alternately, the first and second burners being configured to burn ammonia; heat reservoirs integrated with the first and second burners, the heat reservoir of the second burner being configured to store and use exhaust heat from the first burner for combustion; air nozzles provided on furnace walls at a center of the first and second burners, the air nozzles being configured to expel combustion air into the furnace; fuel nozzles provided on one of both sides that sandwich the air nozzles, the fuel nozzles being configured to expel fossil fuel into the furnace; and ammonia nozzles provided on another one of the both sides of the air nozzles, the ammonia nozzles being configured to expel ammonia into the furnace.

2. The industrial furnace as claimed in Claim 1, wherein the air nozzle of the first burner has the fuel nozzle provided on an upper side part and the ammonia nozzle on a lower side part, and the air nozzle of the second burner has the ammonia nozzle provided on an upper side part and the fuel nozzle on a lower side part.

3. The industrial furnace as claimed in Claim 1, wherein the air nozzle of the first burner has the ammonia nozzle provided on the left and the fuel nozzle on the right with an inside of the furnace seen from the air nozzle, and the air nozzle of the second burner has the ammonia nozzle provided on the left and the fuel nozzle on the right with the inside of the furnace seen from the air nozzle.

4. The industrial furnace as claimed in Claim 2 or Claim 3, further comprising a mechanism, the mechanism being configured to change an angle of both or one of the fuel nozzles and the ammonia nozzles.

5. The industrial furnace as claimed in Claim 2 or Claim 3, further comprising extra ammonia nozzles provided between the air nozzles and the ammonia nozzles, the extra ammonia nozzles being configured to expel ammonia into the furnace.

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