Low-combustion fuel combustion device

Abstract

The low-combustibility fuel is mixed with primary combustion air for primary combustion, and the low-combustibility fuel contained in the combustion gas after primary combustion is mixed with secondary combustion air for secondary combustion. This suppresses the generation of NOx, ensures stable combustion of the low-combustibility fuel, and prevents the tip of the fuel supply pipe from melting due to primary combustion. [Solution] The low-combustibility fuel G is injected from a fuel nozzle 11 provided in a fuel supply pipe 10, which supplies low-combustibility fuel G, and mixed with primary combustion air A1 guided through a primary air guide passage R1 to perform primary combustion in a primary combustion cylinder 50. The low-combustibility fuel contained in the combustion gas after primary combustion is mixed with secondary combustion air A2 guided through a secondary air guide passage R2 to perform secondary combustion in a secondary combustion pipe 60. A flow rate control means 44 is provided to control the ratio of the flow rate of primary combustion air guided through the primary air guide passage to the flow rate of secondary combustion air guided through the secondary air guide passage.

Description

Technical Field

[0001] The present invention relates to a low-flammability fuel combustion device, which is provided with a primary air guide passage for guiding primary combustion air on the outer periphery of a fuel supply pipe for supplying low-flammability fuel, and a secondary air guide passage for guiding secondary combustion air on the outer periphery of the primary air guide passage. The low-flammability fuel ejected from a fuel jet provided in the fuel supply pipe is mixed with the primary combustion air guided through the primary air guide passage and subjected to primary combustion in a primary combustion cylinder. The low-flammability fuel contained in the combustion gas after the primary combustion is mixed with the secondary combustion air guided through the secondary air guide passage and subjected to secondary combustion in a secondary combustion pipe. Particularly, when suppressing the generation of NOx during combustion by mixing low-flammability fuel with primary combustion air for primary combustion and then mixing the low-flammability fuel contained in the combustion gas after primary combustion with secondary combustion air for secondary combustion, ammonia, which is a low-flammability fuel, is sufficiently mixed with the primary combustion air and the secondary combustion air and stably burned, and the tip of the fuel supply pipe and the like are prevented from being damaged by melting due to primary combustion.

Background Art

[0002] In a combustion device that mixes fuel with combustion air for combustion, generally, a device using a hydrocarbon-based fuel as fuel is used.

[0003] However, when such a hydrocarbon-based fuel is mixed with combustion air and burned in a combustion device, there is a problem that a large amount of greenhouse gases such as carbon dioxide is generated.

[0004] Therefore, in recent years, there has been a demand to reduce greenhouse gases such as carbon dioxide, and the use of fuels other than hydrocarbon-based fuels has been studied.

[0005] Furthermore, it has been known for some time that ammonia, a low-combustibility fuel, is used as fuel in combustion devices. However, ammonia has problems with poor flammability compared to hydrocarbon fuels, is prone to misfires during combustion, and generates NOx during combustion.

[0006] Conventionally, when burning ammonia, a low-combustibility fuel with poor flammability, Patent Document 1 shows that a primary air guide passage is provided on the outer circumference of a fuel supply pipe that supplies a low-combustibility fuel such as ammonia, a secondary air guide passage is provided on the outer circumference of the primary air guide passage that guides secondary combustion air, the low-combustibility fuel injected from a fuel nozzle provided in the fuel supply pipe is mixed with the primary combustion air guided through the primary air guide passage and subjected to primary combustion in the primary combustion cylinder, and the low-combustibility fuel contained in the combustion gas after primary combustion is mixed with secondary combustion air guided through the secondary air guide passage and subjected to secondary combustion in the secondary combustion cylinder.

[0007] However, in the aforementioned Patent Document 1, it is difficult to burn the low-combustibility fuel ammonia sufficiently stably. Therefore, an auxiliary burner section is provided, which includes an auxiliary fuel supply pipe for supplying auxiliary fuel and a tubular auxiliary fuel nozzle connected to the auxiliary fuel supply pipe for ejecting auxiliary fuel. The auxiliary fuel supply pipe of the auxiliary burner section is provided inside the fuel supply pipe and fuel nozzle, and the auxiliary fuel nozzle of the auxiliary burner section protrudes forward from the front end of the fuel nozzle, forming numerous flame holes in the circumferential wall of the pipe, and ejecting auxiliary fuel radially from the flame holes.

[0008] Therefore, in the case of the aforementioned Patent Document 1, the structure of the low-combustion fuel combustion device becomes very complex, and because two types of fuel are used separately, the combustion control also becomes complex, among other problems.

[0009] Furthermore, in the aforementioned Patent Document 1, when combustion of the low-combustibility fuel ammonia begins and the temperature inside the primary combustion chamber rises, and some of the ammonia is decomposed to generate hydrogen, there were problems such as the combustion of the generated hydrogen causing melting damage to the fuel nozzle of the fuel supply pipe and the auxiliary fuel nozzle of the auxiliary burner. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Patent No. 7545764 [Disclosure of the Invention] [Problems that the invention aims to solve]

[0011] The present invention aims to solve the aforementioned problems in a low-combustibility fuel combustion device, which involves providing a primary air guide passage on the outer circumference of a fuel supply pipe that supplies a low-combustibility fuel such as ammonia, providing a secondary air guide passage on the outer circumference of the primary air guide passage that guides secondary combustion air, mixing the low-combustibility fuel injected from a fuel nozzle provided in the fuel supply pipe with the primary combustion air guided through the primary air guide passage to perform primary combustion in the primary combustion cylinder, and mixing the low-combustibility fuel contained in the combustion gas after primary combustion with secondary combustion air guided through the secondary air guide passage to perform secondary combustion in the secondary combustion cylinder.

[0012] In other words, the present invention aims to suppress the generation of NOx during combustion in a low-combustibility fuel combustion device as described above, by first mixing a low-combustibility fuel with primary combustion air and performing primary combustion, and then mixing the low-combustibility fuel contained in the combustion gas after primary combustion with secondary combustion air and performing secondary combustion, thereby ensuring that the low-combustibility fuel is sufficiently mixed with the primary and secondary combustion air and burns stably, and also to prevent the tip of the fuel supply pipe from melting due to primary combustion. [Means for solving the problem]

[0013] In the low-combustibility fuel combustion device according to the present invention, in order to solve the above-mentioned problems, a primary air guide passage is provided on the outer circumference of a fuel supply pipe that supplies low-combustibility fuel to guide primary combustion air, a secondary air guide passage is provided on the outer circumference of the primary air guide passage to guide secondary combustion air, low-combustibility fuel injected from a fuel nozzle provided in the fuel supply pipe is mixed with primary combustion air guided through the primary air guide passage to perform primary combustion in the primary combustion cylinder, and the low-combustibility fuel contained in the combustion gas after primary combustion is mixed with secondary combustion air guided through the secondary air guide passage to perform secondary combustion in the secondary combustion cylinder, and in the low-combustibility fuel combustion device according to the present invention, a flow rate control means for controlling the ratio of the flow rate of primary combustion air guided through the primary air guide passage to the flow rate of secondary combustion air guided through the secondary air guide passage As such, a control valve is installed in the combustion air supply pipe that supplies primary and secondary combustion air, to control the ratio of the flow rate of primary combustion air supplied to the primary air guide passage to the flow rate of secondary combustion air supplied to the secondary air guide passage. A system was established.

[0014] Furthermore, in the low-combustibility fuel combustion device according to the present invention, the low-combustibility fuel injected from a fuel nozzle provided in the fuel supply pipe is mixed with primary combustion air guided through the primary air guide passage and subjected to primary combustion in the primary combustion cylinder. Subsequently, the low-combustibility fuel contained in the combustion gas after primary combustion is mixed with secondary combustion air guided through the secondary air guide passage and subjected to secondary combustion in the secondary combustion cylinder. In the initial stages of starting the combustion of the low-combustibility fuel, the flow rate control means increases the proportion of primary combustion air supplied to the primary air guide passage, thereby facilitating primary combustion by thoroughly mixing the low-combustibility fuel injected from the fuel nozzle with the primary combustion air.

[0015] On the other hand, if the combustion of the low-combustibility fuel progresses, causing the temperature inside the primary combustion chamber and at the tip of the fuel supply pipe to rise, and the low-combustibility fuel decomposes to generate hydrogen, etc., and the combustion of the low-combustibility fuel progresses rapidly, the proportion of primary combustion air flow rate supplied to the primary air guide passage is reduced to suppress combustion by the primary combustion air and prevent the temperature inside the primary combustion chamber and at the tip of the fuel supply pipe from rising. At the same time, the proportion of secondary combustion air flow rate supplied to the secondary air guide passage is increased to supply a large amount of secondary combustion air into the secondary combustion pipe, and the low-combustibility fuel contained in the combustion gas after primary combustion is thoroughly mixed with the secondary combustion air, enabling secondary combustion with a longer flame and a more uniform temperature distribution.

[0016] Furthermore, in the low-combustion fuel combustion device according to the present invention, as the flow rate control means, a control valve is provided in the combustion air supply pipe that supplies primary combustion air and secondary combustion air, which controls the ratio of the flow rate of primary combustion air supplied to the primary air guide passage and the flow rate of secondary combustion air supplied to the secondary air guide passage. I did that.

[0017] Furthermore, in the low-combustibility fuel combustion device according to the present invention, ammonia can be used as the low-combustibility fuel. Even when ammonia is used as the low-combustibility fuel, as described above, in the initial stages of combustion, the ammonia is sufficiently mixed with the primary combustion air to facilitate primary combustion. As combustion progresses and the temperature inside the primary combustion cylinder and at the tip of the fuel supply pipe rises, combustion by the primary combustion air is suppressed, preventing the temperature inside the primary combustion cylinder and at the tip of the fuel supply pipe from rising. At the same time, the low-combustibility fuel contained in the combustion gas after primary combustion is sufficiently mixed with the secondary combustion air in the secondary combustion pipe, enabling secondary combustion with a longer flame and a more uniform temperature distribution.

[0018] Furthermore, in the low-combustion fuel combustion device according to the present invention, if the secondary combustion tube is made of a radiant tube, a long flame is generated by the primary and secondary combustion, the inside of the radiant tube is sufficiently heated, and the inside of the furnace can be indirectly heated more uniformly.

[0019] Furthermore, in the low-combustibility fuel combustion device according to the present invention, a fuel nozzle for injecting low-combustibility fuel can be provided on the outer circumference of the fuel supply pipe. When low-combustibility fuel is injected from the fuel nozzle provided on the outer circumference of the fuel supply pipe, the injected low-combustibility fuel is efficiently mixed with the primary combustion air flowing through the primary air guide passage on the outer circumference of the fuel supply pipe.

[0020] Furthermore, in the low-combustibility fuel combustion device according to the present invention, it is preferable to provide a primary combustion swirling vane in the primary air guide passage, and to swirl the primary combustion air while mixing it with the low-combustibility fuel and guiding it into the primary combustion cylinder.

[0021] Furthermore, if a fuel nozzle for injecting low-combustibility fuel is provided on the outer circumference of the fuel supply pipe as described above, and a primary combustion swirling vane is provided downstream of the fuel nozzle in the primary air guide passage, the low-combustibility fuel injected from the fuel nozzle will be swirled and thoroughly mixed with the primary combustion air flowing around the outer circumference of the fuel supply pipe before being guided into the primary combustion cylinder.

[0022] Furthermore, in the low-combustibility fuel combustion device according to the present invention, a secondary combustion swirling vane is provided in the secondary air guide passage, and the secondary combustion air is guided to the secondary combustion tube while swirling, so that the secondary combustion air is thoroughly mixed with the low-combustibility fuel contained in the combustion gas after primary combustion in the secondary combustion tube and secondary combustion occurs. In this way, the secondary combustion air is thoroughly mixed with the low-combustibility fuel contained in the combustion gas after primary combustion in the secondary combustion tube and secondary combustion occurs.

[0023] Further, in the low-flammability fuel combustion device according to the present invention, a stabilizer for pre-burning and maintaining combustion of the low-flammability fuel ejected from the fuel ejection port provided on the outer peripheral portion of the fuel supply pipe and the primary combustion air guided through the primary air guide passage can be provided on the downstream side of the fuel ejection port. By doing so, the low-flammability fuel ejected from the fuel ejection port is pre-burned and maintained in combustion with the primary combustion air guided through the primary air guide passage in the stabilizer, and at the initial stage of starting the combustion of the low-flammability fuel, the low-flammability fuel can be reliably burned in the primary combustion cylinder.

[0024] Further, if primary combustion swirling blades are also provided on the outer periphery of the stabilizer, the primary combustion air flowing through the outer periphery of the stabilizer and the low-flammability fuel are swirled and mixed by the primary combustion swirling blades and guided into the primary combustion cylinder, so that the low-flammability fuel is sufficiently mixed with the primary combustion air and is reliably burned in the primary combustion cylinder.

Advantages of the Invention

[0025] In the low-flammability fuel combustion device of the present invention, when the low-flammability fuel ejected from the fuel ejection port provided in the fuel supply pipe as described above is mixed with the primary combustion air guided through the primary air guide passage and burned primarily in the primary combustion cylinder, and the low-flammability fuel contained in the combustion gas after the primary combustion is mixed with the secondary combustion air guided through the secondary air guide passage and burned secondarily in the secondary combustion pipe, flow rate control means for controlling the ratio of the flow rate of the primary combustion air guided through the primary air guide passage and the flow rate of the secondary combustion air guided through the secondary air guide passage As such, a control valve is provided in the combustion air supply pipe that supplies primary combustion air and secondary combustion air, which controls the ratio of the flow rate of primary combustion air supplied to the primary air guide passage and the flow rate of secondary combustion air supplied to the secondary air guide passage, and the control valve is used to The ratio of the flow rate of primary combustion air guided through the primary air guide channel to the flow rate of secondary combustion air guided through the secondary air guide channel. perform control.

[0026] And in the low-flammability fuel combustion device of the present invention, at the initial stage of starting the combustion of the low-flammability fuel, The aboveThe flow rate control means increases the proportion of primary combustion air supplied to the primary air guide path so that the low-combustibility fuel injected from the fuel nozzle is sufficiently mixed with the primary combustion air for primary combustion. On the other hand, if the combustion of the low-combustibility fuel progresses and the temperature inside the primary combustion cylinder and at the tip of the fuel supply pipe rises, causing the low-combustibility fuel to decompose and generate hydrogen, and the combustion of the low-combustibility fuel proceeds rapidly, the proportion of primary combustion air supplied to the primary air guide path is reduced to suppress combustion by the primary combustion air and prevent the temperature inside the primary combustion cylinder and at the tip of the fuel supply pipe from rising. At the same time, the proportion of secondary combustion air supplied to the secondary air guide path is increased to supply a large amount of secondary combustion air to the secondary combustion pipe, allowing the low-combustibility fuel contained in the combustion gas after primary combustion to be sufficiently mixed with the secondary combustion air for secondary combustion.

[0027] As a result, in the low-combustibility fuel combustion device of the present invention, when low-combustibility fuel is mixed with primary combustion air for primary combustion, and then the low-combustibility fuel contained in the combustion gas after primary combustion is mixed with secondary combustion air for secondary combustion, the low-combustibility fuel is sufficiently mixed with the primary and secondary combustion air and burns stably, NOx generation during combustion is suppressed, the tip of the fuel supply pipe is prevented from melting due to primary combustion, and furthermore, the low-combustibility fuel contained in the combustion gas after primary combustion is sufficiently mixed with the secondary combustion air, enabling secondary combustion with a longer flame and a more uniform temperature distribution. [Brief explanation of the drawing]

[0028] [Figure 1] This is a schematic cross-sectional diagram illustrating the initial operating state when combustion of a low-combustibility fuel begins in a low-combustibility fuel combustion device according to one embodiment of the present invention. [Figure 2] This is a schematic longitudinal cross-sectional view showing the operating state of the low-combustibility fuel combustion device according to the same embodiment, when the combustion of the low-combustibility fuel has progressed and the temperature inside the primary combustion cylinder and at the tip of the fuel supply pipe has risen. [Best Mode for Carrying Out the Invention]

[0029] Hereinafter, a low-combustibility fuel combustion device according to an embodiment of the present invention will be specifically described with reference to the attached drawings. It should be noted that the low-combustibility fuel combustion device according to the present invention is not limited to those shown in the embodiments below, and can be implemented with appropriate modifications without altering the essence of the invention.

[0030] In this embodiment of the low-combustibility fuel combustion device, ammonia is used as the low-combustibility fuel G. As shown in Figures 1 and 2, a primary guide pipe 20 is provided on the outer circumference of the fuel supply pipe 10 that supplies the low-combustibility fuel G, and a secondary guide pipe 30 is provided on the outer circumference of the primary guide pipe 20. Primary combustion air A1 is supplied from the combustion air supply pipe 40 through the supply hole 21 to the primary air guide passage R1 in the primary guide pipe 20, and secondary combustion air A2 is supplied from the combustion air supply pipe 40 to the secondary air guide passage R2 between the primary guide pipe 20 and the secondary guide pipe 30.

[0031] In this embodiment, when supplying primary combustion air A1 from the combustion air supply pipe 40 to the primary air guide passage R1 and secondary combustion air A2 to the secondary air guide passage R2, a partition 41 is provided between the combustion air supply pipe 40 and the primary guide pipe 20 and the secondary guide pipe 30 to separate and guide the primary combustion air A1 and the secondary combustion air A2. The primary combustion air A1 is supplied from the primary air supply section 42 of the combustion air supply pipe 40 to the primary air guide passage R1 through a plurality of supply holes 21 provided in the primary guide pipe 20, while the secondary combustion air A2 is supplied from the secondary air supply section 43 of the combustion air supply pipe 40 to the secondary air guide passage R2 between the primary guide pipe 20 and the secondary guide pipe 30. Furthermore, a retaining member 25 is provided in the middle of the secondary air guide passage R2 to maintain the distance between the primary guide pipe 20 and the secondary guide pipe 30, and multiple through holes 26 are opened around its entire circumference for the secondary combustion air A2 to flow through.

[0032] Furthermore, in this embodiment, a control valve 44 is provided in the combustion air supply pipe 40 as a flow rate control means 44 for controlling the ratio of the flow rate of primary combustion air A1 guided through the primary air guide passage R1 to the flow rate of secondary combustion air A2 guided through the secondary air guide passage R2. By rotating this control valve 44, the ratio of the flow rate of primary combustion air A1 supplied to the primary air guide passage R1 to the flow rate of secondary combustion air A2 supplied to the secondary air guide passage R2 is controlled.

[0033] In this embodiment, the fuel supply pipe 10 is provided with a plurality of fuel nozzles 11 on the outer surface downstream of the supply direction for injecting low-combustibility fuel G, and the low-combustibility fuel G injected from each fuel nozzle 11 is mixed with the primary combustion air A1 flowing through the primary air guide passage R1.

[0034] Furthermore, in this embodiment, a stabilizer 22 with a larger diameter than the fuel supply pipe 10 is provided in the primary air guide passage R1 downstream of the fuel nozzle 11 in the fuel supply pipe 10. Between the stabilizer 22 and the fuel supply pipe 10, a plurality of primary swirling vanes 23a are provided to swirl and mix the primary combustion air A1 and the low-combustibility fuel G, and a spark plug 24 is also provided. The low-combustibility fuel G mixed with the primary combustion air A1 by the primary swirling vanes 23a is ignited by the spark plug 24, causing the low-combustibility fuel G to be pre-combusted within the stabilizer 22. In this case, the stabilizer 22 itself becomes hot when it receives heat from the combustion, and by raising the temperature around the flame F, it stabilizes the combustion state of the flame F and has the effect of making the flame F less likely to go out (flame-sustaining).

[0035] Furthermore, in this embodiment, a plurality of primary swirling vanes 23b are provided on the outer circumference of the stabilizer 22 to swirl and mix the primary combustion air A1 and the low-combustibility fuel G. The low-combustibility fuel G mixed with the primary combustion air A1 by these primary swirling vanes 23b is guided downstream of the stabilizer 22 and, together with the low-combustibility fuel G that has been pre-combusted as described above, is subjected to primary combustion in the primary combustion cylinder 50 provided downstream of the primary guide pipe 20. In this embodiment, the primary combustion cylinder 50 has a shape with a contracted middle section, but the shape of the primary combustion cylinder 50 is not limited and may be a cylindrical shape with the same diameter as the primary guide pipe 20.

[0036] Furthermore, in this embodiment, a radiant tube 60 is provided inside the furnace 1 through the furnace wall 1a so as to be continuous with the secondary guide tube 30, and a secondary swirling vane 51 is provided on the outer circumference of the primary combustion cylinder 50, as a secondary combustion tube 60 for secondary combustion of the low-combustibility fuel G contained in the combustion gas after primary combustion as described above.

[0037] In this embodiment, the secondary combustion air A2 flowing through the secondary air guide passage R2 between the radiant tube 60 and the primary combustion cylinder 50 is swirled by the secondary swirling vane 51 and guided from the outer circumference of the primary combustion cylinder 50 to the downstream side of the primary combustion cylinder 50. The low-combustibility fuel G contained in the combustion gas after primary combustion in the primary combustion cylinder 50 is mixed with the secondary combustion air A2 and secondary combustion is performed in the radiant tube 60.

[0038] In this embodiment, by using a radiant tube 60 as the secondary combustion tube 60, the inside of the radiant tube 60 is heated by the primary and secondary combustion, and the workpiece (not shown) inside the furnace 1 is not exposed to flames, allowing the workpiece to be indirectly heated through the radiant tube 60. Note that the secondary combustion tube 60 is not limited to the radiant tube 60; although not shown, a pipe material with an open downstream end can also be used as the secondary combustion tube 60, allowing flames to be injected into the furnace 1.

[0039] In this embodiment, in the initial stage of starting the combustion of the low-combustibility fuel G, as shown in Figure 1, the control valve 44 provided in the combustion air supply pipe 40 is rotated in a direction that reduces the gap with the secondary air supply unit 43, thereby reducing the flow rate of secondary combustion air A2 supplied to the secondary air guide passage R2 through the secondary air supply unit 43, while increasing the proportion of the flow rate of primary combustion air A1 supplied to the primary air guide passage R1 through the primary air supply unit 42.

[0040] In this way, by increasing the proportion of the flow rate of primary combustion air A1 guided to the primary air guide passage R1, the low-combustibility fuel G ejected from each fuel nozzle 11 provided on the outer surface of the fuel supply pipe 10 is sufficiently mixed with the large amount of primary combustion air A1 guided through the primary air guide passage R1. The mixed primary combustion air A1 and low-combustibility fuel G are then guided into the stabilizer 22 while being rotated by the primary swirl vanes 23 provided between the stabilizer 22 and the fuel supply pipe 10, and are ignited by the spark plug 24. The low-combustibility fuel G mixed with the primary combustion air A1 is then pre-combusted in the stabilizer 22. At the same time, the mixed primary combustion air A1 and low-combustibility fuel G are guided downstream of the stabilizer 22 while being rotated by the primary swirl vanes 23 provided on the outer surface of the stabilizer 22, and together with the pre-combusted low-combustibility fuel G, they are reliably primary-combusted in the primary combustion cylinder 50. Therefore, even with a low-combustibility fuel G using ammonia, the low-combustibility fuel G injected from each of the fuel nozzles 11 is reliably subjected to primary combustion within the primary combustion chamber 50.

[0041] Furthermore, in this embodiment, if the combustion of the low-combustibility fuel G progresses, the temperature inside the primary combustion chamber 50 and the tip of the fuel supply pipe 10 rises, the low-combustibility fuel G decomposes and hydrogen is generated, and the combustion of the low-combustibility fuel G progresses rapidly, then, as shown in Figure 2, the control valve 44 provided in the combustion air supply pipe 40 is rotated in a direction that reduces the gap with the primary air supply unit 42, thereby reducing the proportion of the flow rate of primary combustion air A1 supplied to the primary air guide passage R1 through the primary air supply unit 42, while increasing the proportion of the flow rate of secondary combustion air A2 supplied to the secondary air guide passage R2 through the secondary air supply unit 43.

[0042] In this way, by reducing the proportion of the flow rate of primary combustion air A1 guided to the primary air guide passage R1, the amount of low-combustibility fuel G that is primary combusted in the stabilizer 22 and primary combustion chamber 50 is reduced, which suppresses the temperature rise of the primary combustion chamber 50 and the tip of the fuel supply pipe 10 due to primary combustion, and prevents the tip of the fuel supply pipe 10 from melting due to primary combustion.

[0043] Furthermore, as described above, increasing the flow rate of secondary combustion air A2 supplied to the secondary air guide passage R2 through the secondary air supply section 43 in the combustion air supply pipe 40 increases the flow rate of secondary combustion air A2 flowing through the secondary air guide passage R2 between the radiant tube 60 and the primary combustion cylinder 50. As a result, the flow rate of secondary combustion air A2 guided from the outer circumference of the primary combustion cylinder 50 to the downstream side of the primary combustion cylinder 50 increases as it is swirled by the secondary swirling vanes 51 provided on the outer circumference of the primary combustion cylinder 50. The low-combustibility fuel G contained in the combustion gas after primary combustion in the primary combustion cylinder 50 is mixed with the secondary combustion air A2 guided to the downstream side of the primary combustion cylinder 50 at an increased flow rate, and undergoes secondary combustion in the radiant tube 60.

[0044] In this way, by mixing the low-combustibility fuel G contained in the combustion gas after primary combustion with the increased flow rate of secondary combustion air A2 and performing secondary combustion in the radiant tube 60, the flame from the secondary combustion in the radiant tube 60 becomes longer, the temperature distribution in the radiant tube 60 becomes more uniform, and the efficiency of indirect heating is improved by preventing the flame from coming into contact with the workpiece (not shown) in the furnace 1. [Explanation of symbols]

[0045] 1: Furnace 1a: Furnace wall 10:Fuel supply pipe 11:Fuel spout 20:Primary guide pipe 21: Supply hole 22: Stabilizer 23, 23a, 23b: Primary swivel vanes 24: Spark plug 25: Retaining member 26: Through hole 30: Secondary guide tube 40: Combustion air supply pipe 41: Partition 42: Primary air supply unit 43: Secondary air supply unit 44: Flow control means (control valve) 50: Primary combustion chamber 51: Secondary swivel vane 60: Secondary combustion tube (radiant tube) A1: Primary combustion air A2: Air for secondary combustion G: Low-combustion fuel (ammonia) F:Flame R1: Primary air guide channel R2: Secondary air guide channel

Claims

1. Low-combustibility fuel combustion device comprising: a fuel supply pipe for supplying low-combustibility fuel, a primary air guide passage for guiding primary combustion air on the outer circumference of the fuel supply pipe for supplying low-combustibility fuel, a secondary air guide passage for guiding secondary combustion air on the outer circumference of the primary air guide passage, a low-combustibility fuel injected from a fuel nozzle provided in the fuel supply pipe, mixed with primary combustion air guided through the primary air guide passage for primary combustion in a primary combustion cylinder, and low-combustibility fuel contained in the combustion gas after primary combustion, mixed with secondary combustion air guided through the secondary air guide passage for secondary combustion in a secondary combustion cylinder, wherein a control valve is provided in the combustion air supply pipe that supplies primary and secondary combustion air, to control the ratio of the flow rate of primary combustion air supplied to the primary air guide passage and the flow rate of secondary combustion air supplied to the secondary air guide passage as a flow rate control means for controlling the ratio of the flow rate of primary combustion air guided through the primary air guide passage and the flow rate of secondary combustion air guided through the secondary air guide passage.

2. A low-combustibility fuel combustion device according to Claim 1, characterized in that the low-combustibility fuel is ammonia.

3. A low-combustion fuel combustion device according to claim 1 or claim 2, characterized in that the secondary combustion tube is a radiant tube.

4. A low-combustibility fuel combustion device according to claim 1 or claim 2, characterized in that a fuel nozzle for injecting low-combustibility fuel is provided on the outer circumference of the fuel supply pipe.

5. A low-combustibility fuel combustion device according to claim 1 or claim 2, characterized in that a primary combustion swirling vane is provided in the primary air guide passage, and primary combustion air is mixed with the low-combustibility fuel while swirling and guided into the primary combustion cylinder.

6. A low-combustibility fuel combustion device according to Claim 4, characterized in that a primary combustion swirling vane is provided downstream of the primary air guide passage from a fuel injection port provided on the outer circumference of the fuel supply pipe, for mixing primary combustion air with low-combustibility fuel while swirling it.

7. A low-combustibility fuel combustion device according to claim 1 or claim 2, characterized in that a secondary combustion swirling vane is provided in the secondary air guide passage, and secondary combustion air is guided to the secondary combustion tube while swirling, and mixed with the low-combustibility fuel contained in the combustion gas after primary combustion in the secondary combustion tube to perform secondary combustion.

8. A low-combustibility fuel combustion device comprising: a fuel supply pipe for supplying low-combustibility fuel, a primary air guide passage for guiding primary combustion air on the outer circumference of the fuel supply pipe, a secondary air guide passage for guiding secondary combustion air on the outer circumference of the primary air guide passage, a low-combustibility fuel injected from a fuel nozzle provided in the fuel supply pipe, a primary combustion in which the low-combustibility fuel guided through the primary air guide passage is mixed with primary combustion air guided through the primary air guide passage and subjected to primary combustion in a primary combustion cylinder, and a secondary combustion in which the low-combustibility fuel contained in the combustion gas after primary combustion is mixed with secondary combustion air guided through the secondary air guide passage and subjected to secondary combustion in a secondary combustion cylinder. A low-combustibility fuel combustion device is characterized by providing a flow rate control means for controlling the ratio of the flow rate of primary combustion air guided through the primary air guide passage to the flow rate of secondary combustion air guided through the secondary air guide passage, a fuel nozzle for injecting low-combustibility fuel is provided on the outer circumference of the fuel supply pipe, and a stabilizer is provided downstream of the fuel nozzle on the outer circumference of the fuel supply pipe in the primary air guide passage for pre-combusting the low-combustibility fuel injected from the fuel nozzle and the primary combustion air guided through the primary air guide passage to maintain the flame.

9. A low-combustibility fuel combustion device according to Claim 8, characterized in that the primary combustion swirling vanes are also provided on the outer circumference of the stabilizer.

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