Industrial furnace and fuel supply method for industrial furnace

Abstract

To provide a highly safe industrial furnace for efficiently burning hydrogen by using a simple facility and a fuel supply method for the industrial furnace.SOLUTION: In an industrial furnace, a burner 10 provided on a furnace wall 3 is supplied with hydrogen via first piping 11 with a first on-off valve 31, gas fuel via second piping 12 with a second on-off valve 32 and combustion air via air piping 13 with an air on-off valve 33, so as to burn the hydrogen and the gas in a mixed manner. Third piping 15 with a third on-off valve 35 is branched from the second piping 12, and the third piping 15 is connected to a portion between the burner 10 and the first on-off valve 31 provided in the first piping 11. Before fire is extinguished in the burner 10, the first on-off valve 31 is turned off and the second on-off valve 32 and the third on-off valve 35 are turned on to replace the hydrogen between the burner 10 and the first on-off valve 31 in the first piping 11 with the gas fuel so as to discharge the hydrogen into the furnace.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an industrial furnace that burns hydrogen and gas together and a fuel supply method for the industrial furnace. [Background technology]

[0002] In recent years, from the viewpoint of curbing global warming, hydrogen, which does not produce carbon dioxide when burned, has attracted attention as a new fuel, and mixtures of hydrogen with fossil fuels are known (see, for example, Patent Document 1).

[0003] The invention described in Patent Document 1 (claim 5) involves the inclusion of hydrogen in the gas fuel, but as shown in Figure 4, there is also a known system in which the gas fuel and hydrogen are sent to the burner in separate systems and mixed-fired.

[0004] 4 shows a configuration in which hydrogen (H2), gas fuel, and combustion air are supplied to a burner 10 provided on a side wall 3 of a furnace body 2 of an industrial furnace 1. Hydrogen (H2) is sent from a hydrogen supply device 21 to the burner 10 via a first pipe 11, which is provided with a first on-off valve (solenoid valve) 31 along the way. The gas fuel, consisting of an existing gas (conventional fuel) such as city gas or propane gas, is sent from a gas supply device 22 to the burner 10 via a second pipe 12, which is provided with a second on-off valve (solenoid valve) 32 along the way. As combustion air, outside air is sent by a blower 23 to the burner 10 via an air pipe 13, which is provided with an air on-off valve (solenoid valve) 33 along the way.

[0005] In an industrial furnace that uses hydrogen, when the hydrogen combustion is stopped and the fire is extinguished, hydrogen remains in the pipe (in this case, the first pipe 11). In particular, hydrogen burns quickly and has a wide flammable range, so it may backfire in the pipe and produce a loud noise. Furthermore, hydrogen has a small molecular weight and density, so it may leak from piping, and if it does leak, there is a risk of a hydrogen explosion.

[0006] Therefore, as shown in FIG. 5, a method is known in which the hydrogen in the first pipe 11 is replaced with nitrogen. This is done by connecting the end of the nitrogen piping 14, which supplies nitrogen (N2) from the nitrogen supply device 24, between the burner 10 and the first on-off valve 31 of the first piping 11, and when stopping the hydrogen combustion and extinguishing the fire, turning off (closing) the first on-off valve 31 and turning on (opening) the nitrogen on-off valve 34 provided on the nitrogen piping 14, and filling nitrogen (N2) from the first on-off valve 31 of the first piping 11 to the burner 10 side, thereby replacing the hydrogen with nitrogen. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 7183343 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the method of replacing hydrogen with nitrogen, it is necessary to newly provide nitrogen together with the nitrogen supply device 24 . Furthermore, when restarting the combustion of hydrogen, it is necessary to first discharge the nitrogen filled in the first pipe 11, which poses the problem of taking time to ignite the hydrogen.

[0009] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an industrial furnace and a fuel supply method for an industrial furnace that are highly safe and that can efficiently burn hydrogen using simple equipment. [Means for solving the problem]

[0010] In order to achieve the above object, the present invention provides an industrial furnace (1) for co-firing hydrogen and gas by supplying hydrogen through a first pipe (11) equipped with a first on-off valve (31), gas fuel through a second pipe (12) equipped with a second on-off valve (32), and combustion air through an air pipe (13) equipped with an air on-off valve (33) to a burner (10) provided on a furnace wall (3), A third pipe (15) with a third on-off valve (35) is branched from the second pipe (12), and the third pipe (15) is connected between the burner (10) and a first on-off valve (31) provided on the first pipe (11).

[0011] The present invention also provides a fuel supply method for an industrial furnace (1) for co-firing hydrogen and gas by supplying hydrogen to a burner (10) provided on a furnace wall (3) through a first pipe (11) having a first on-off valve (31), gas fuel through a second pipe (12) having a second on-off valve (32), and combustion air through an air pipe (13) having an air on-off valve (33), a third pipe (15) with a third on-off valve (35) branched from the second pipe (12), and the third pipe (15) connected between the burner (10) and a first on-off valve (31) provided on the first pipe (11); Before the burner (10) is extinguished, the first on-off valve (31) is turned off, and the second on-off valve (32) and the third on-off valve (35) are turned on, so that hydrogen in the first pipe (11) between the burner (10) and the first on-off valve (31) is replaced with gas fuel and the hydrogen is discharged into the furnace. Note that turning on the second on-off valve (32) here includes not only turning on from off but also maintaining the on state. Normally, the second on-off valve (32) is in the on state during combustion before extinguishing.

[0012] Furthermore, the present invention is characterized in that after the hydrogen is replaced with the gas fuel, the second on-off valve (32) and the third on-off valve (35) are turned off to extinguish the fire.

[0013] Furthermore, the present invention is characterized in that, before ignition of the burner (10), the first on-off valve (31) is turned off, the air on-off valve (33) is turned on, and the second on-off valve (32) and the third on-off valve (35) are turned on, so that only gas fuel flows through the first pipe (11) between the burner (10) and the first on-off valve (31), and after ignition, the first on-off valve (31) is turned on and the third on-off valve (35) is turned off to supply hydrogen into the furnace. Here, turning off the first on-off valve (31) includes not only turning off the on-off valve but also maintaining the off state. The first on-off valve (31) is turned off during fire extinguishing, and is therefore normally in the off state.

[0014] The present invention also provides a fuel supply method for an industrial furnace (1) for co-firing hydrogen and gas by supplying hydrogen through a first pipe (11) equipped with a first on-off valve (31), gas fuel through a second pipe (12) equipped with a second on-off valve (32), and combustion air through an air pipe (13) equipped with an air on-off valve (33) to a burner (10) provided on a furnace wall (3), the method comprising: a third pipe (15) with a third on-off valve (35) branched from the second pipe (12), and the third pipe (15) connected between the burner (10) and a first on-off valve (31) provided on the first pipe (11); Before ignition of the burner (10), the first on-off valve (31) is turned off, the air on-off valve (33) is turned on, and the second on-off valve (32) and the third on-off valve (35) are turned on, so that only gas fuel flows through the first pipe (11) between the burner (10) and the first on-off valve (31), and after ignition, the first on-off valve (31) is turned on and the third on-off valve (35) is turned off to supply hydrogen into the furnace. Here, turning off the first on-off valve (31) includes not only turning off the on-off valve but also maintaining the off state. The first on-off valve (31) is turned off during fire extinguishing, and is therefore normally in the off state.

[0015] The symbols in parentheses above indicate corresponding elements or items described in the drawings and in the detailed description of the invention to be described later. [Effects of the Invention]

[0016] The industrial furnace of the present invention is an industrial furnace in which hydrogen and gas are mixed and burned by supplying hydrogen to a burner via a first pipe equipped with a first on-off valve, gas fuel via a second pipe equipped with a second on-off valve, and combustion air via an air pipe equipped with an air on-off valve, and a third pipe equipped with a third on-off valve branches off from the second pipe and is connected between the burner and the first on-off valve provided on the first pipe.Therefore, by turning off (closing) the first on-off valve and turning on (opening) the third on-off valve, the hydrogen between the burner and the first on-off valve in the first pipe can be easily replaced with gas fuel. In other words, when replacing hydrogen with nitrogen as in the conventional method, it is necessary to install a new nitrogen piping along with a nitrogen supply device, but with the present invention, it is only necessary to modify the existing gas fuel second piping so that a third piping branched off from the second piping is connected to the first piping, thereby reducing equipment costs. Furthermore, replacing existing gas fuel with hydrogen provides peace of mind by preventing the highly explosive hydrogen leak and avoiding the distress caused by hydrogen backfiring in the piping and the loud noise it produces. Furthermore, the gas fuel that replaces hydrogen has larger molecules than hydrogen and is less likely to leak, and it has been used for a long time. Therefore, even if it does leak from the piping, it will have an odor and existing gas leak detection means can be used, making it safe to handle.

[0017] Furthermore, according to the fuel supply method for industrial furnaces of the present invention, before the burner is extinguished, the first on-off valve is turned off and the second and third on-off valves are turned on to replace the hydrogen in the first piping between the burner and the first on-off valve with gaseous fuel and discharge the hydrogen into the furnace, so that after extinguishing the burner, i.e., when the industrial furnace is not in operation, hydrogen, which has a high possibility of flashback, does not remain in the first piping or the furnace, ensuring safety. Since gaseous fuel has a slower combustion rate than hydrogen, it does not flash back and produce a loud noise.

[0018] Furthermore, according to the fuel supply method for an industrial furnace of the present invention, before the burner is ignited, the first on-off valve is turned off, the air on-off valve is turned on, and the second on-off valve and the third on-off valve are turned on, so that only gas fuel is present between the burner and the first on-off valve in the first piping. Therefore, hydrogen is not sent before ignition, and there is no need to worry about hydrogen leaking, which is highly explosive. After ignition, the first valve is turned on and the third valve is turned off to supply hydrogen into the furnace. As the hydrogen is sent to the burner side, the gas fuel filled in the first pipe is gradually pushed out toward the burner, and the inside of the first pipe is replaced with hydrogen, making it easy to control combustion. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a partial cross-sectional view showing a main part and a fuel supply system of an industrial furnace according to an embodiment of the present invention. [Figure 2] 2 is a flowchart showing a fuel supply method during a fire extinguishing operation in the industrial furnace shown in FIG. [Figure 3] 2 is a flowchart showing a fuel supply method during an ignition operation in the industrial furnace shown in FIG. [Figure 4] FIG. 10 is a partial cross-sectional view showing the main parts and fuel supply system of a conventional industrial furnace. [Figure 5] FIG. 10 is a partial cross-sectional view showing a main part of an industrial furnace according to a conventional example and another fuel supply system. DETAILED DESCRIPTION OF THE INVENTION

[0020] An industrial furnace 1 according to an embodiment of the present invention will be described with reference to Fig. 1. Note that the same components as those in the conventional example are given the same reference numerals.

[0021] As shown in FIG. 1, an industrial furnace 1 according to this embodiment (here, a metal heating furnace will be described as an example) has a generally rectangular cross section, and burners 10 are provided on furnace walls 3 that constitute a furnace body 2. Hydrogen (H) is mixed with gas fuel and burned using flames from the burners 10.

[0022] Hydrogen (H2) is sent from a hydrogen supply device 21 to the burner 10 via a first pipe 11, which is provided with a first on-off valve (solenoid valve) 31. The gas fuel, which is made up of existing gases such as city gas or propane gas, is sent from a gas supply device 22 to the burner 10 via a second pipe 12, which is provided with a second on-off valve (solenoid valve) 32. As combustion air, outside air is sent by a blower 23 to the burner 10 via an air pipe 13, which is provided with an air on-off valve (solenoid valve) 33.

[0023] A third pipe 15 equipped with a third on-off valve 35 branches off from the second pipe 12 that sends fuel gas, and the third pipe 15 is connected between the burner 10 and the first on-off valve 31 provided on the first pipe 11 that sends hydrogen. The third on-off valve 35 is an electromagnetic valve, and a check valve 25 is provided between the third on-off valve 35 and the first on-off valve to prevent hydrogen or gas fuel from flowing from the first pipe 11 side to the second pipe 12 side. Here, the third pipe 15 branches off between the second on-off valve 32 provided on the second pipe 12 and the gas supply device 22, but it may also branch off between the second on-off valve 32 and the burner 10. The first pipe 11, the second pipe 12 and the air pipe 13 are provided with throttle valves capable of changing the flow rate in addition to the on-off valves 31, 32 and 33, but are not shown in the drawings.

[0024] The opening and closing of each of the on-off valves (solenoid valves) 31, 32, 33, and 35 is controlled by a control device 500 that controls the entire electrical system of the industrial furnace 1. The control device 500 has a CPU which is a control unit, a memory unit consisting of a ROM in which a control program is stored and a RAM for writing and retrieving data, and is connected to a timer T. Here, an external timer T is shown, but an internal timer may also be used.

[0025] During combustion, the control device 500 keeps the first on-off valve 31, the second on-off valve 32, and the air on-off valve 33 in an on state (open state) and the third on-off valve 35 in an off state (closed state), but during extinguishing, it executes the operation shown in Figure 2.

[0026] More specifically, before extinguishing the burner 10, the CPU of the control device 500 first turns off (i.e., closes) the first on-off valve 31 (step S101: hereinafter, the word "step" will be omitted). This prevents hydrogen from flowing into the burner 10 from the hydrogen supply device 21.

[0027] Next, the CPU of the control device 500 sets a timer T for a certain time and then turns it on (S102), and turns on the second on-off valve 32 and the third on-off valve 35 (i.e., opens them) (S103). Note that turning on the second on-off valve 32 here includes not only turning it from off to on, but also maintaining it in the on state. During combustion before extinguishing, the second on-off valve 32 is in the on state. As a result, the hydrogen remaining between the burner 10 and the first on-off valve 31 in the first pipe 11 is discharged into the furnace, and the hydrogen is completely replaced with the gas fuel.

[0028] Thereafter, when the timer T is up (S104), the second on-off valve 32 and the third on-off valve 35 are turned off (i.e., closed) (S105), and the inflow of gas fuel to the burner 10 side is cut off to extinguish the flame (S106).

[0029] This method replaces hydrogen with gaseous fuel, preventing the highly explosive hydrogen from leaking, providing peace of mind. It also prevents the severe stress caused by hydrogen backfiring in the piping and the loud noise it produces. Furthermore, the gas fuel that replaces hydrogen has larger molecules than hydrogen and is less likely to leak, and it has been used for a long time. Therefore, even if it does leak from the piping, it will have an odor and existing gas leak detection means can be used, making it safe to handle.

[0030] Furthermore, the control device 500 executes the operation shown in FIG. 3 at the time of ignition.

[0031] More specifically, before igniting the burner 10, the CPU of the control device 500 first turns off the first on-off valve 31 (i.e., closes it) (step S201: hereinafter, the word "step" will be omitted). Note that turning off the first on-off valve 31 here includes not only turning it off from on to off, but also maintaining the off state. The first on-off valve 31 is turned off during extinguishing, and is therefore normally in the off state. Next, after setting the timer T to a certain time, it is turned on (S202), and the air on-off valve 33 is turned on (that is, opened) (S203). As a result, combustion air flows to the burner 10.

[0032] Next, when the timer T expires (S204), the CPU of the control device 500 turns on the second on-off valve 32 and the third on-off valve 35 (i.e., opens them) (S205, S206). As a result, gas fuel is sent to the burner 10, and the first pipe 11 on the burner 10 side from the first on-off valve 31, the second pipe 12, and the third pipe 15 are filled with gas fuel.

[0033] Then, the CPU of the control device 500 commands ignition (spark) without delay (S207), and when ignition is completed (S208), it turns on the first opening / closing valve 31 (i.e., opens it) and turns off the third opening / closing valve 35 (i.e., closes it) to supply hydrogen into the furnace (S209, S210).

[0034] Thereafter, the CPU of the control device 500 performs temperature control (S211) and starts combustion in the industrial furnace 1.

[0035] According to this, hydrogen is not sent to the burner 10 before ignition, but is sent to the burner 10 side after the gas fuel has been sent and reliably ignited. As hydrogen is sent to the burner 10 side in this way, the gas fuel filled in the first pipe 11 is gradually pushed out toward the burner 10 side and the inside of the first pipe 11 is replaced with hydrogen, making it possible to easily control combustion.

[0036] In this embodiment, an example has been described in which the industrial furnace 1 is applied to a metal heating furnace, but it can be widely used in combustion-type thermal equipment such as heat treatment furnaces, forging furnaces, melting furnaces, and ladle preheaters. [Explanation of symbols]

[0037] 1. Industrial furnace 2 Furnace body 3 side wall 10 Burner 11 First piping 12 Second piping 13 Air piping 14 Nitrogen piping 15 Third piping 21 Hydrogen supply device 22 Gas supply equipment 23 Blois 24 Nitrogen supply device 25 Check valve 31 First shut-off valve 32 Second shut-off valve 33 Air on-off valve 34 Nitrogen on-off valve 35 Third shut-off valve 500 control device T-Timer

Claims

1. An industrial furnace in which hydrogen and gas are mixed and burned by supplying hydrogen through a first pipe having a first on-off valve, gas fuel through a second pipe having a second on-off valve, and combustion air through an air pipe having an air on-off valve to a burner provided on a furnace wall, an industrial furnace, characterized in that a third pipe equipped with a third on-off valve is branched from the second pipe, and the third pipe is connected between the burner and the first on-off valve provided on the first pipe.

2. A fuel supply method for an industrial furnace for co-firing hydrogen and gas by supplying hydrogen through a first pipe having a first on-off valve, gas fuel through a second pipe having a second on-off valve, and combustion air through an air pipe having an air on-off valve to a burner provided on a furnace wall, the method comprising: a third pipe having a third on-off valve branched from the second pipe, and the third pipe connected between the burner and the first on-off valve provided on the first pipe; a first valve that is turned off and a second valve that is turned on before the burner is extinguished, and a third valve that is turned on to replace the hydrogen in the first piping between the burner and the first valve with gas fuel and discharge the hydrogen into the furnace.

3. 3. The fuel supply method for an industrial furnace according to claim 2, wherein after the hydrogen is replaced with the gas fuel, the second and third on-off valves are turned off to extinguish the fire.

4. 4. The fuel supply method for an industrial furnace according to claim 2, wherein before ignition of the burner, the first on-off valve is turned off, the air on-off valve is turned on, and the second and third on-off valves are turned on so that only gas fuel flows through the first piping between the burner and the first on-off valve, and after ignition, the first on-off valve is turned on and the third on-off valve is turned off to supply hydrogen into the furnace.

5. A fuel supply method for an industrial furnace for co-firing hydrogen and gas by supplying hydrogen through a first pipe having a first on-off valve, gas fuel through a second pipe having a second on-off valve, and combustion air through an air pipe having an air on-off valve to a burner provided on a furnace wall, the method comprising: a third pipe having a third on-off valve branched from the second pipe, and the third pipe connected between the burner and the first on-off valve provided on the first pipe; a first valve for supplying hydrogen to the furnace; a second valve for supplying hydrogen to the furnace; a third valve for supplying hydrogen to the furnace; a gas fuel supply system for supplying hydrogen to the furnace; a gas supply system for supplying hydrogen to the furnace; a gas supply system for supplying hydrogen to the furnace; a gas supply system for supplying hydrogen to the furnace;

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