Industrial furnace equipped with ammonia burner

Abstract

To provide a positive pressure operable industrial furnace with an ammonia burner.SOLUTION: Provided is an industrial furnace 10 with an ammonia burner using ammonia as a fuel, which comprises: an ammonia combustion apparatus 2 having a burner for combusting ammonia at an air ratio less than 1; a duct 3 for receiving a hot wind from the ammonia combustion apparatus 2; and a furnace body 4 for receiving the hot wind from the duct 3 and combusting the same.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an industrial furnace equipped with an ammonia burner that uses ammonia as fuel.

Background Art

[0002] As industrial furnaces using a hot air generator that utilizes the flame of a burner, there are furnaces such as those shown in Patent Documents 1 and 2. Here, in an industrial furnace, the pressure inside the furnace is generally maintained at a slightly positive pressure (above atmospheric pressure) so that outside air does not enter the furnace through the gaps in the furnace wall, causing the temperature inside the furnace to drop or the temperature distribution inside the furnace to change.

[0003] Separately from the above, due to recent demands for decarbonization, as an ammonia burner that uses ammonia as fuel, a burner such as that shown in Patent Document 3 has been developed. And a technique for heating ammonia to a high temperature and decomposing it into hydrogen and nitrogen, and making the hard-to-burn ammonia easier to burn with its hydrogen component, is shown in Patent Document 4.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0005] When using ammonia burners, a challenge arises because the nitrogen component of ammonia tends to cause NOx emissions. However, it is now known that burning ammonia with an air-fuel ratio of less than 1 can reduce NOx emissions. However, burning ammonia with an air-fuel ratio of less than 1 results in unburned ammonia being included in the exhaust. When applied to industrial furnaces with positive pressure, as described above, this can lead to ammonia leaking to the outside, emitting a foul odor and degrading the living environment. Therefore, combining ammonia burners with positive-pressure industrial furnaces has been difficult.

[0006] Therefore, the objective of the present invention is to provide an industrial furnace equipped with an ammonia burner that is capable of positive pressure operation. [Means for solving the problem]

[0007] The present invention relates to an industrial furnace equipped with an ammonia burner that uses ammonia as fuel, An ammonia combustion apparatus having a burner that burns ammonia at an air ratio of less than 1, A duct that receives hot air from the ammonia combustion device, The system includes a furnace body that receives and burns hot air from the aforementioned duct.

[0008] According to the above configuration, by burning ammonia at an air ratio of less than 1, NOx generation is reduced, and the unburned ammonia contained in the exhaust is decomposed in the duct. As a result, no ammonia is contained in the furnace body, and the furnace body can be operated under positive pressure. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an industrial furnace equipped with an ammonia burner that can be operated under positive pressure. [Brief explanation of the drawing]

[0010] [Figure 1] This is a conceptual diagram of an industrial furnace according to an embodiment of the present invention. [Modes for carrying out the invention]

[0011] Figure 1 is a conceptual diagram of an industrial furnace 10 according to an embodiment of the present invention. As shown in Figure 1, the industrial furnace 10 comprises an ammonia combustion device 2 having an ammonia burner 20 that uses ammonia as fuel, a duct 3 that receives hot air from the ammonia combustion device 2, and a furnace body 4 that receives the hot air from the duct 3 and burns it. The industrial furnace 10 further comprises a control unit 11 that controls the operation of the industrial furnace 10.

[0012] Industrial furnaces 10 are a general term for devices used to melt, heat, and heat treat materials at a desired temperature. By heating materials, they alter their physical, chemical, and mechanical properties, and are used to process products to suit specific purposes. Industrial furnaces 10 include many types of furnaces, each suited to its respective use and purpose, such as heat treatment furnaces for heat treating materials and automobile / machine parts, heating furnaces for heating steel materials, and melting furnaces for melting aluminum materials.

[0013] The ammonia combustion apparatus 2 comprises an ammonia pipe 21 for supplying ammonia, an air supply pipe 22 for supplying air, an ammonia burner 20 that mixes the ammonia supplied from the ammonia pipe 21 and the air supplied from the air supply pipe 22 to form a flame, and an ammonia combustion furnace 23 to which the ammonia burner 20 is installed and which surrounds the area where the flame is formed. The ammonia burner 20 is configured to adjust the amount of ammonia supplied from the ammonia pipe 21 and the amount of air supplied from the air supply pipe 22 so that the ammonia burns at an air-to-air ratio of less than 1. The ammonia pipe 21 is provided with an on-off valve 211 for opening and closing the ammonia pipe 21, and the air supply pipe 22 is provided with an on-off valve 221 for opening and closing the air supply pipe 22. The combustion air ratio is adjusted by adjusting the opening degree of the on-off valve 211 and the on-off valve 221, thereby adjusting the amount of ammonia supplied from the ammonia pipe 21 and the amount of air supplied from the air supply pipe 22.

[0014] Duct 3 is connected to the ammonia combustion furnace 23 and is designed to receive hot air from inside the ammonia combustion furnace 23. The opening 31 of duct 3 to the ammonia combustion furnace 23 is located opposite the ammonia burner 20. Duct 3 has a straight cylindrical shape, with the opening 31 at one end of the cylindrical shape and the opening 32 of duct 3 to the furnace body 4 at the other end of the cylindrical shape. That is, the opening 32 is located opposite the opening 31.

[0015] A sensor 33 for measuring the hydrogen concentration inside the duct 3 is provided near the connection point with the furnace body 4. The control unit 11 of the industrial furnace 10 adjusts the amount of air supplied to the supply pipe 42, which will be described later, using the detection results of the sensor 33.

[0016] High-temperature exhaust gas, produced by the combustion of ammonia and air, flows through duct 3 as hot air, causing unburned ammonia in the exhaust gas to decompose into hydrogen and nitrogen due to its high temperature. To maintain a high-temperature environment inside duct 3, the outer surface of duct 3 is covered with insulating material 34. To decompose ammonia inside duct 3, it is preferable to maintain the temperature inside duct 3 at 1000°C or higher. Furthermore, the size of duct 3 is preferably such that the residence time of ammonia is 1 second or more. The diameter, length, and shape of duct 3 are specified to ensure the temperature inside duct 3 and the residence time of ammonia necessary for the decomposition of ammonia inside duct 3. For example, if the flow velocity of typical exhaust gas is approximately 10 m / s, the length of duct 3 is preferably 10 m or more in order to ensure a residence time of ammonia of 1 second or more. In this embodiment, the duct 3 has a straight pipe shape, and generally the inner diameter 3d of the duct 3 is about 100 to 1000 mm, which is smaller than the vertical length 23d of the inner cross-section of the ammonia combustion furnace 23 (for example, about 500 to 5000 mm), and further smaller than the vertical length 4d of the inner cross-section of the furnace body 4 (for example, about 5000 to 10000 mm).

[0017] The furnace body 4 is connected to the duct 3 and is configured to receive the hot air in the duct 3. Near the opening 41 of the furnace body 4 to the duct 3, a supply pipe 42 for supplying air is provided. The hydrogen component in the hot air from the opening 41 and the air supplied from the supply pipe 42 are mixed, and a flame is formed inside the furnace body 4. Thereby, the hydrogen component after decomposition inside the furnace body 4 is burned. A workpiece W is disposed inside the furnace body 4, and the workpiece W is heat-treated by the heat from this flame.

[0018] The supply pipe 42 is provided with an adjustment valve 421 for opening and closing the supply pipe 42. According to the detection result of the hydrogen concentration by the sensor 33, the opening degree of the adjustment valve 421 is adjusted, and the air supply amount to the supply pipe 42 for burning the hydrogen component is adjusted. The adjustment valve 421 is an electric valve.

[0019] The furnace body 4 is provided with a pressure gauge 43 for measuring the pressure inside the furnace body 4. The control unit 11 of the industrial furnace 10 uses the detection result of the pressure gauge 43 to control the opening and closing valves 211 and 221, adjust the combustion amount, increase or decrease the exhaust gas, and other means to adjust the hot air introduction amount from the duct 3 into the furnace body 4 and maintain the pressure inside the furnace body 4 at a positive pressure.

[0020] An exhaust port 44 for exhausting the atmosphere inside the furnace is provided on the wall surface of the furnace body 4 facing the wall surface provided with the opening 41 to the duct 3. The exhaust port 44 is connected via an exhaust pipe 51 and an exhaust stack 5, and the atmosphere inside the furnace is discharged to the outside from the exhaust stack 5 according to the internal pressure inside the furnace.

[0021] The industrial furnace 10 operates as follows.

[0022] First, a workpiece W to be heat-treated in the industrial furnace 10 is placed inside the furnace body 4.

[0023] Next, in the ammonia combustion device 2, ammonia is supplied from the ammonia pipe 21 and air is supplied from the air supply pipe 22 so that the air ratio is less than 1. The ammonia and air are mixed, and the ammonia is burned by the ammonia burner 20, forming a flame in the ammonia combustion furnace 23. When ammonia burns, nitric oxide and water vapor are produced. Here, by burning the ammonia at an air ratio of less than 1, the generation of NOx is suppressed, but unburned ammonia remains.

[0024] The flame formed by the ammonia burner 20 generates hot air (exhaust gas) inside the ammonia combustion furnace 23. The hot air inside the ammonia combustion furnace 23 is sent into the duct 3 through the opening 31.

[0025] Inside duct 3, the high temperature of the hot air decomposes the unburned ammonia into nitrogen and hydrogen. Based on the detection result of the amount of hydrogen after decomposition by sensor 33, control unit 11 confirms that the unburned ammonia in duct 3 has been decomposed into hydrogen, and adjusts the amount of air supplied to supply pipe 42 by adjusting the opening of control valve 421 so that the hydrogen burns inside furnace body 4, based on the hydrogen concentration inside duct 3.

[0026] After the unburned ammonia in duct 3 is decomposed into nitrogen and hydrogen, the hot air in duct 3 is sent into the furnace body 4 through opening 41. The hot air in duct 3 mainly contains nitrogen, hydrogen, nitrogen oxides (NOx), and water vapor.

[0027] Inside the furnace body 4, hot air from duct 3 and air from supply pipe 42 mix, hydrogen burns, and a flame is formed. The workpiece W placed inside the furnace body 4 is heated by the combustion gases from the flame. Based on the detection result of the pressure gauge 43, the control unit 11 adjusts the amount of hot air introduced from duct 3 into the furnace body 4 so that the pressure inside the furnace body 4 becomes positive pressure (pressure greater than atmospheric pressure).

[0028] The combustion gases that contribute to heating the workpiece W are discharged to the outside from the exhaust pipe 5 through the exhaust port 44 and exhaust pipe 51. The combustion gases discharged from the exhaust pipe 51 include nitrogen, nitrogen oxides (NOx), water vapor, etc. Since ammonia is not contained in the furnace body 4, ammonia will not be released to the outside even if the inside of the furnace body 4 is maintained at positive pressure.

[0029] The industrial furnace 10 with the above configuration can achieve the following effects.

[0030] (1) By burning ammonia at an air ratio of less than 1, NOx generation is reduced, and the unburned ammonia contained in the exhaust is decomposed in the duct, so that no ammonia is contained in the furnace body 4, and the furnace body 4 can be made to have positive pressure.

[0031] (2) By covering the outer surface of the duct 3 with the insulating material 34, the temperature inside the duct 3 is maintained at a high temperature, which promotes the decomposition of ammonia inside the duct 3.

[0032] (3) The furnace body 4 is provided with a supply pipe 42 for supplying air into the furnace, and by mixing the hydrogen produced by the decomposition of ammonia with the air from the supply pipe 42 and burning it, the hydrogen produced by the decomposition of ammonia can be used as fuel.

[0033] (4) The duct 3 is equipped with a sensor 33 for measuring the hydrogen concentration inside the duct 3, and by using the detection results of the sensor 33 to adjust the mixing ratio of the air supplied to the furnace and the hydrogen produced by the decomposition of ammonia, combustion inside the furnace can be made more efficient.

[0034] (5) The control unit 11 adjusts the amount of hot air introduced from the duct 3 using the detection result of the pressure gauge 43, thereby making the pressure inside the furnace body 4 positive. This prevents outside air from entering the furnace through gaps in the furnace wall, which would lower the temperature inside the furnace or change the temperature distribution inside the furnace. Furthermore, since there is no ammonia in the furnace, the inside of the furnace can be made positive.

[0035] (6) By making the inner diameter 3d of the duct 3 smaller than the vertical length 23d of the inner cross-section of the ammonia combustion device 2 and the vertical length 4d of the inner cross-section of the furnace body 4, a constriction of the flow occurs at high temperatures, increasing turbulence, which further promotes the decomposition of ammonia in the duct 3.

[0036] In the above embodiment, the duct 3 has a straight pipe shape, but it may have a bent shape in order to shorten the overall length of the industrial furnace while ensuring the residence time of ammonia inside the duct 3.

[0037] In the above embodiment, the decomposition of ammonia in the duct 3 is ensured by the ambient temperature inside the duct and the shape of the duct 3, but an ammonia sensor may be installed near the outlet of the duct 3 to confirm that ammonia is being decomposed inside the duct 3.

[0038] In the above embodiment, the decomposition of ammonia inside the duct 3 is promoted by covering the outer surface of the duct 3 with an insulating material 34, but a heater for heating the inside of the duct 3 may be attached to the duct. Alternatively, an ammonia decomposition catalyst that promotes the decomposition of ammonia may be placed inside the duct 3.

[0039] In the above embodiment, after burning ammonia, the unburned ammonia is decomposed into hydrogen and nitrogen by heating with hot air. However, the amount of unburned ammonia may be reduced by heating the ammonia beforehand before burning it.

[0040] The present invention and its embodiments are summarized as follows.

[0041] (1) One embodiment of the present invention is an industrial furnace equipped with an ammonia burner that uses ammonia as fuel, An ammonia combustion apparatus having a burner that burns ammonia at an air ratio of less than 1, A duct that receives hot air from the ammonia combustion device, The system includes a furnace body that receives and burns hot air from the aforementioned duct.

[0042] According to the above configuration (1), by burning ammonia at an air ratio of less than 1, the generation of NOx is reduced, and the unburned ammonia contained in the exhaust is decomposed in the duct, so that no ammonia is contained in the furnace and the furnace can be made to have positive pressure.

[0043] (2) In the above configuration (1), the outer surface of the duct is covered with an insulating material.

[0044] According to the above configuration (2), by covering the outer surface of the duct with an insulating material, the temperature inside the duct can be maintained at a high temperature, thereby promoting the decomposition of ammonia inside the duct.

[0045] (3) In the configuration (1) or (2) above, the furnace body is provided with a supply pipe for supplying air into the furnace.

[0046] According to the above configuration (3), the hydrogen produced by the decomposition of ammonia can be mixed with air from the supply pipe and burned, thereby allowing the hydrogen produced by the decomposition of ammonia to be used as fuel.

[0047] (4) In the above configuration (3), the duct is provided with a sensor for measuring the hydrogen concentration inside the duct. The amount of air supplied to the supply pipe is adjusted using the detection results from the sensor.

[0048] According to the above configuration (4), by adjusting the mixing ratio of the air supplied into the furnace and the hydrogen produced by the decomposition of ammonia, combustion in the furnace can be made more efficient.

[0049] (5) In any one of the above configurations (1) to (4), the furnace body is provided with a pressure gauge for measuring the internal pressure inside the furnace, The control unit of the industrial furnace adjusts the amount of hot air introduced from the duct using the detection result of the pressure gauge to make the pressure inside the furnace positive.

[0050] According to the above configuration (5), by making the internal pressure inside the furnace positive, it is possible to prevent outside air from entering the furnace through gaps in the furnace wall, which would cause the temperature inside the furnace to drop or the temperature distribution inside the furnace to change.

[0051] (6) In any one of the above configurations (1) to (5), the duct has a cylindrical shape, and the inner diameter of the duct is smaller than the vertical length of the inner cross-section of the ammonia combustion device and the vertical length of the inner cross-section of the furnace body.

[0052] According to the above configuration (6), by making the inner diameter of the duct smaller than the vertical length of the inner cross-section of the ammonia combustion device and the vertical length of the inner cross-section of the furnace body, flow contraction occurs at high temperatures, increasing turbulence, which further promotes the decomposition of ammonia in the duct.

[0053] Various modifications and alterations can be made without departing from the spirit and scope of the invention as described in the claims. [Industrial applicability]

[0054] The present invention provides an industrial furnace equipped with an ammonia burner that can be operated under positive pressure, thus having great industrial value. [Explanation of symbols]

[0055] 10 Industrial Furnaces 11 Control Unit 2. Ammonia combustion device 20 Ammonia burner 21 Ammonia pipe 211 Shut-off valve 22 Air supply pipe 221 Shut-off valve 23 Ammonia combustion furnace 3 ducts 31 Opening 32 Opening 33 Sensor 34 Insulation 4 Furnace body 41 Opening 42 Supply pipe 421 Control valve 43 Pressure gauge 44 Exhaust port 5 Exhaust stack 51 Exhaust pipe Double job

Claims

1. An industrial furnace equipped with an ammonia burner that uses ammonia as fuel, An ammonia combustion apparatus having a burner that burns ammonia at an air ratio of less than 1, A duct that is in communication with the ammonia combustion device and receives the hot air generated by the combustion of ammonia in the ammonia combustion device, The system comprises a furnace body that is in communication with the aforementioned duct, receives hot air from the duct, and burns the hot air and the supplied air, The duct has a cylindrical shape, the inner diameter of the duct is smaller than the vertical length of the inner cross-section of the ammonia combustion device and the vertical length of the inner cross-section of the furnace body, and the length of the duct is set so as to ensure that the residence time of the hot air within the duct is 1 second or more. The furnace body is equipped with a pressure gauge for measuring the internal pressure inside the furnace. The control unit of the industrial furnace adjusts the amount of hot air introduced from the duct using the detection result of the pressure gauge to make the pressure inside the furnace positive.

2. The industrial furnace according to claim 1, wherein the outer surface of the duct is covered with an insulating material.

3. The industrial furnace according to claim 1, wherein the furnace body is provided with a supply pipe for supplying air into the furnace.

4. The duct is equipped with a sensor for measuring the hydrogen concentration inside the duct. The industrial furnace according to claim 3, wherein the amount of air supplied to the supply pipe is adjusted using the detection result of the sensor.

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