Combustion method for mixed-fuel and single-fuel burner, and mixed-fuel and single-fuel burner

Abstract

To provide a combustion method for a mixed-fuel and single-fuel burner, capable of switching a kind of fuel from single firing of hydrocarbon fuel to mix firing of hydrocarbon and hydrogen or single firing of hydrogen during an operation using the same burner, while maintaining a safe combustion state.SOLUTION: There is provided a combustion method for a mixed-fuel and single-fuel burner in which fuel is hydrocarbon gas, hydrogen gas or mixture gas thereof, and a combustion state can be successively changed among single firing of hydrocarbon gas, mix firing of hydrocarbon gas and hydrogen gas and single firing of hydrogen. A jet flow rate of fuel is a first flow speed V1 of 7 m / s or more when single firing of hydrocarbon gas and a second flow speed V2 of 28 m / s or more when single firing of hydrogen gas, and a lower limit value is the first flow speed V1 and an upper limit value is the second flow speed V2 in mix firing.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a combustion method for a dual-fuel combustion burner and a dual-fuel combustion burner. [Background technology]

[0002] Conventionally, a mixed combustion burner that mixes hydrogen with city gas, which is mainly composed of methane, and burns the mixture has been known as a burner that suppresses carbon dioxide emissions in combustion exhaust gas (see, for example, Patent Document 1). Patent Document 1 describes a hydrogen mixed combustion burner that has a structure in which city gas and hydrogen gas are ejected from separate nozzles. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-025713 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, if the velocity of gas ejected from the burner is slow, there is a risk of backfire. Alternatively, if the jet is weak, it may be prone to misfire due to external disturbances. On the other hand, if the velocity of the ejected gas is too fast, the flame may rise, making it prone to misfire. For these reasons, it is necessary to control the ejection velocity to an appropriate level.

[0005] Furthermore, when using hydrogen as fuel, its laminar burning speed is known to be about five times faster than that of typical hydrocarbon fuels such as methane and natural gas, making burners using hydrogen even more susceptible to backfire.Also, because the flame tends to form upstream, the heat load at the tip of the burner is large, which can lead to melting or other damage.

[0006] Generally, hydrogen gas has a lower lower heating value—one-third to one-quarter—than methane or city gas, requiring three to four times the flow rate to obtain the same energy. Considering the future fuel conversion process from hydrocarbons to hydrogen, it is expected that furnaces will need to switch from mono-fuel combustion using methane or natural gas to hydrogen-mixed combustion and then mono-fuel combustion during operation. Because it is difficult to replace burners and burner nozzles during operation, it is desirable to be able to use the same burners and burner nozzles for a wide range of combustion scenarios, from mono-fuel combustion using methane or natural gas to hydrogen-mixed combustion and then mono-fuel combustion. Therefore, there was a need to maintain a sufficiently stable combustion state even when the fuel type was changed and the jet flow rate changed by three to four times. Even in the case of Patent Document 1 mentioned above, when using hydrogen-only combustion, there is a risk that hydrogen will flow back into the city gas nozzle and form a flame inside the nozzle. In other words, it is difficult to switch from city gas-only combustion to hydrogen-mixed combustion or to hydrogen-only combustion, and there is room for improvement in this regard.

[0007] Therefore, the present invention has been made in consideration of the above circumstances, and provides a combustion method for a dual-fuel, single-fuel burner and a dual-fuel, single-fuel burner that can switch the fuel type from hydrocarbon fuel combustion to hydrocarbon-hydrogen mixed combustion or hydrogen fuel combustion during operation with the same burner while safely maintaining a combustion state. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention employs the following means. That is, the combustion method for a dual-fuel, mono-fuel burner according to the present invention is a combustion method for a dual-fuel, mono-fuel burner in which the fuel is hydrocarbon gas, hydrogen gas, or a mixture of these, and the combustion state can be continuously switched between hydrocarbon gas mono-fuel combustion, dual-fuel combustion of hydrocarbon gas and hydrogen gas, and mono-fuel combustion, and is characterized in that the fuel ejection flow velocity is a first flow velocity of 7 m / s or more when dual-fuel combustion is used, and a second flow velocity of 28 m / s or more when dual-fuel combustion is used, and the first flow velocity is a lower limit value and the second flow velocity is an upper limit value.

[0009] In this combustion method for a dual-fuel burner configured as described above, the fuel ejection velocity from the burner tip is set to a first velocity of 7 m / s or more when using hydrocarbon gas exclusively, and to a second velocity of 28 m / s or more when using hydrogen gas exclusively, with the lower limit being the first velocity and the upper limit being the second velocity when using dual-fuel combustion.This makes it possible to maintain a safe combustion state even when switching from hydrocarbon fuel exclusively combustion to hydrocarbon-hydrogen dual combustion or to hydrogen exclusively combustion during operation with the same burner without replacing the dual-fuel burner or nozzle, and enables safe and stable use of the dual-fuel burner.If the velocity is outside the range of 7 m / s or more and 28 m / s or less during dual-fuel combustion, the combustion state will be poor and stable combustion will not be maintained.

[0010] In addition, in the combustion method for a dual-fuel / single-fuel burner according to the present invention, it is preferable to adjust the ejection flow velocities of the hydrocarbon gas and the hydrogen gas so that the heat value of the flame is constant.

[0011] In the combustion method for the dual-fuel burner configured as described above, the ejection flow velocity of the mixed gas can be maintained by adjusting the ejection flow velocity of the hydrocarbon gas and the hydrogen gas to maintain the calorific value, thereby suppressing misfires and thereby reducing the impact of fluctuations in the calorific value on the heated object.

[0012] In the combustion method for a dual-fuel / monofuel burner according to the present invention, the mixed gas may be supplied to the burner in a state in which the hydrocarbon gas and the hydrogen gas are mixed together.

[0013] In the combustion method of the dual-fuel mono-fuel burner configured in this manner, the hydrocarbon gas and hydrogen gas fuels are supplied to a single fuel supply path to produce a mixed gas, and therefore backfire caused by fuel flowing into the other fuel path in the mono-fuel state, as occurs in conventional burners in which the hydrocarbon gas and hydrogen gas fuel paths are separate, can be prevented.

[0014] Furthermore, in the combustion method for a dual-fuel / single-fuel burner according to the present invention, the injection speed of the combustion-supporting gas injected around the fuel injected at the center may be not more than 1 / 2 and not less than 1 / 8 of the injection speed of the fuel.

[0015] In the combustion method of the dual-fuel burner configured in this way, even when the thermal load on the nozzle increases due to radiation from the furnace, it is possible to achieve a good flame shape that does not interfere with the flame while keeping the hole diameter to a minimum, which promotes mixing of the combustion-supporting gas and fuel, allowing the combustion reaction to proceed in a short interval and achieving efficient combustion.

[0016] In the combustion method for a dual-fuel / single-fuel burner according to the present invention, the combustion-supporting gas injected around the injected fuel may be oxygen alone.

[0017] In the combustion method of the dual-fuel burner configured in this way, by using a combustion-supporting gas that is pure oxygen with a 100% oxygen content, the higher the oxygen concentration in the oxidizer, the less heat loss caused by the exhaust gas and the better the thermal efficiency, which can reduce fuel consumption. In particular, it can reduce the cost of hydrogen fuel, which is expensive and difficult to secure in supply.

[0018] Furthermore, the dual-fuel combustion burner according to the present invention is a dual-fuel combustion burner used in the combustion method of the dual-fuel combustion burner described above, characterized in that it has a double-tube structure with a fuel outlet located in the center and a combustion-supporting gas outlet located around the fuel outlet, and at least two staging nozzles for injecting the combustion-supporting gas are provided on the outer periphery of the combustion-supporting gas outlet.

[0019] In a dual-fuel burner configured in this way, the oxidizer supplied is split between the center burner and the staging nozzle, allowing the fuel to burn in stages, reducing localized high-temperature areas in the flame and suppressing NOx generation. This is particularly effective for hydrogen combustion, and can be applied to both hydrocarbon and hydrogen fuels. In the present invention, the ejection flow velocity of the fuel ejected from the burner tip is set to a first flow velocity of 7 m / s or more when hydrocarbon gas is exclusively fired, a second flow velocity of 28 m / s or more when hydrogen gas is exclusively fired, and a lower limit value for the first flow velocity and an upper limit value for the second flow velocity when mixed combustion is performed.This makes it possible to safely maintain a combustion state even when the fuel type is switched from hydrocarbon fuel exclusive combustion to hydrocarbon-hydrogen mixed combustion or hydrogen exclusive combustion during operation with the same burner, without replacing the mixed-combustion burner or nozzle, and enables the safe and stable use of the mixed-combustion burner.

[0020] Furthermore, the combustion method for a dual-fuel combustion burner according to the present invention is the combustion method for a dual-fuel combustion burner described above, characterized in that the ratio of the flow rate of the combustion-supporting gas supplied to the staging nozzle to the total flow rate of the combustion-supporting gas supplied to the combustion-supporting gas outlet and the staging nozzle is 50% or more.

[0021] In the combustion method of the dual-fuel mono-fuel burner configured in this way, hydrogen combustion tends to produce higher NOx emissions than hydrocarbon fuels. However, by supplying 50% or more of the oxygen to the staging nozzle during the staging combustion, it is possible to reduce NOx emissions to levels equal to or lower than those of conventional hydrocarbon fuels. [Effects of the Invention]

[0022] According to the combustion method for a dual-fuel, mono-fuel burner and the dual-fuel, mono-fuel burner of the present invention, it is possible to switch the fuel type from mono-fuel hydrocarbon fuel combustion to mono-fuel hydrocarbon-hydrogen hybrid combustion or mono-fuel hydrogen combustion during operation using the same burner while safely maintaining a combustion state. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a side cross-sectional view showing a schematic configuration of a center burner according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a side cross-sectional view showing a schematic configuration of a dual-fuel / exclusive combustion burner according to a second embodiment of the present invention. [Figure 3]FIG. 10 is a diagram showing the NOx suppression effect by staging in the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0024] The following describes in detail a combustion method for a dual-fuel combustion burner and a dual-fuel combustion burner according to an embodiment of the present invention, with reference to the accompanying drawings. Note that the drawings used in the following description may show enlarged portions of the burner's features for ease of understanding, and the dimensional proportions of the components may not necessarily be the same as those of the actual burner.

[0025] (First embodiment) A center burner 1 (multi-fuel combustion burner) according to the first embodiment is shown in Fig. 1. As shown in Fig. 1, the combustion method of the center burner 1 is a combustion method in which the fuel is hydrocarbon gas, hydrogen gas, or a mixed gas of these, and the combustion state can be continuously switched between hydrocarbon gas combustion, mixed combustion of hydrocarbon gas and hydrogen gas, and hydrogen combustion.

[0026] The fuel for the center burner 1 is hydrocarbon gas, hydrogen gas, or a mixture of these. In this embodiment, a mixture of hydrocarbon gas and hydrogen gas is used as the fuel. The hydrocarbon gas is, for example, city gas or natural gas such as methane gas.

[0027] In the combustion method of the center burner 1, a combustion-supporting gas is injected around the injected fuel. The combustion-supporting gas used in the center burner 1 of this embodiment can use any of air, oxygen-enriched air, and pure oxygen as an oxidant. Here, the pure oxygen may be 100% oxygen or about 90 vol% oxygen produced by a VPSA or the like.

[0028] The configuration of the center burner 1 of the first embodiment will be specifically described. As shown in Fig. 1, the center burner 1 comprises a burner body 10 with a double-pipe structure having a fuel nozzle 20 forming a fuel flow path to which fuel consisting of a mixed gas is supplied, and a combustion-supporting gas nozzle 30 provided coaxially around the fuel nozzle 20 and forming a combustion-supporting gas flow path to which a combustion-supporting gas is supplied. The center burner 1 further comprises a mixing section 40 to which hydrogen gas and hydrocarbon gas (city gas) are supplied and mixed. Here, in Fig. 1, the left side of the paper is the ejection side of the center burner 1, and the right side of the paper is the upstream side of the center burner 1.

[0029] The inner tube nozzle 2 forming the fuel outlet 20 and the outer tube nozzle 3 forming the combustion supporting gas outlet 30 are both hollow cylindrical. The outer tube nozzle 3 has a larger diameter than the inner tube nozzle 2.

[0030] The inner tube nozzle 2 is arranged coaxially inside the outer tube nozzle 3. A fuel supply port 21, to which fuel is supplied from the mixing section 40, is provided on the upstream side of the inner tube nozzle 2. The fuel supply port 21 protrudes upstream from the base end of the burner body 10.

[0031] A combustion-supporting gas supply port 31, through which a combustion-supporting gas is supplied, is provided on the upstream side of the outer tube nozzle 3. A first gas valve 33, which can adjust the amount of combustion-supporting gas supplied, is connected to a combustion-supporting gas supply line 32 connected to the combustion-supporting gas supply port 31.

[0032] The mixing section 40 mixes hydrocarbon fuel and hydrogen fuel into a mixed gas and supplies it to the fuel outlet 20, which is the fuel flow path of the center burner 1. The mixing section 40 is the confluence of a hydrocarbon gas supply line 41, to which hydrocarbon gas is supplied, and a hydrogen gas supply line 42, to which hydrogen gas is supplied. The mixing section 40 may be a mixing chamber having a certain amount of space. In this case, for example, a pipe having an inner diameter larger than those of the supply lines 41 and 42 can be used as the mixing chamber. A second gas valve 43 capable of adjusting the amount of hydrocarbon gas supplied is connected to the hydrocarbon gas supply line 41. A third gas valve 44 capable of adjusting the amount of hydrogen gas supplied is connected to the hydrogen gas supply line 42.

[0033] Next, a method for generating a combustion flame using the center burner 1 will be described. 1, hydrocarbon gas is supplied to a mixing section 40 through a hydrocarbon gas supply line 41, and hydrogen gas is supplied to the mixing section 40 through a hydrogen gas supply line 42. Then, in the mixing section 40, a fuel consisting of a mixed gas obtained by mixing the hydrocarbon gas and the hydrogen gas is ejected from the fuel ejection port 20 of the inner tube nozzle 2 of the center burner 1.

[0034] The fuel jet flow velocity V at this time is set such that the first flow velocity V1 in the case of hydrocarbon gas mono-combustion is set to 7 m / s or more. The second flow velocity V2 in the case of hydrogen gas mono-combustion is set to 28 m / s or more. The jet flow velocity in the case of hydrocarbon gas and hydrogen gas co-combustion is set such that the lower limit is the first flow velocity V1 and the upper limit is the second flow velocity V2. The fuel jet flow velocity V is adjusted so that the heat value of the flame remains constant.

[0035] Generally, hydrogen gas has a lower heating value of 10.78MJ / Nm 3 and 35.9MJ / Nm of methane gas. 3 and city gas 40MJ / Nm 3 Since the flow rate is 1 / 3 to 1 / 4 of that of the conventional fuel, 3 to 4 times the flow rate is required to obtain the same energy, but by setting the fuel injection flow velocity V as above, this required flow rate can be ensured.

[0036] The ejection speed of the combustion supporting gas ejected around the fuel ejected from the fuel ejection port 20 is set to be not more than 1 / 2 and not less than 1 / 8 of the ejection speed of the fuel.

[0037] The combustion method of the center burner 1 configured in this manner uses hydrocarbon gas, hydrogen gas, or a mixture of these gases as fuel, and the combustion state can be continuously switched between hydrocarbon gas combustion, mixed combustion of hydrocarbon gas and hydrogen gas, and hydrogen gas combustion. The fuel jet flow velocity is a first flow velocity V1 of 7 m / s or more when hydrocarbon gas combustion is used exclusively. When hydrogen gas combustion is used exclusively, the second flow velocity V2 is 28 m / s or more. When mixed combustion is used, the lower limit is the first flow velocity V1 and the upper limit is the second flow velocity V2. In this way, in the combustion method of the center burner 1, the ejection flow velocity of the fuel ejected from the burner tip is set to a first flow velocity V1 of 7 m / s or more when using hydrocarbon gas exclusively, a second flow velocity V2 of 28 m / s or more when using hydrogen gas exclusively, and a lower limit value of the first flow velocity V1 and an upper limit value of the second flow velocity V2 when using mixed combustion, so that a safe combustion state can be maintained even when the fuel type is switched from hydrocarbon fuel exclusively combustion to hydrocarbon-hydrogen mixed combustion or hydrogen exclusively combustion during operation with the same burner without replacing the center burner 1 or nozzle, and the center burner 1 can be used safely and stably. If the velocity is outside the range of 7 m / s or more and 28 m / s or less when using mixed combustion, the combustion state becomes poor and stable combustion cannot be maintained.

[0038] In this embodiment, the ejection flow velocities of the hydrocarbon gas and hydrogen gas are adjusted so that the heat value of the flame is constant. Therefore, by adjusting the ejection flow speeds of the hydrocarbon gas and the hydrogen gas to maintain the calorific value, the ejection flow speed of the mixed gas can be maintained and misfires can be suppressed, thereby reducing the impact of fluctuations in the calorific value on the heated object.

[0039] In this embodiment, the mixed gas is supplied to the burner in a state where hydrocarbon gas and hydrogen gas are mixed together. Therefore, since the hydrocarbon gas and hydrogen gas fuels are supplied to a single fuel supply path to form a mixed gas, backfire caused by fuel flowing into the other fuel path in a mono-fuel state can be prevented, as is the case with conventional burners in which the hydrocarbon gas and hydrogen gas fuel paths are separate.

[0040] In this embodiment, the ejection speed of the combustion-assisting gas ejected around the fuel ejected at the center is not more than 1 / 2 and not less than 1 / 8 of the ejection speed of the fuel. Therefore, even if the thermal load on the nozzle increases due to radiation from the furnace, it is possible to achieve a good flame shape without flame interference while keeping the hole diameter to a minimum, promoting the mixing of the combustion-supporting gas and fuel, and allowing the combustion reaction to proceed in a short section, thereby achieving efficient combustion. This prevents problems that occurred in the past, such as a short flame length, which reduces direct radiant heat transfer from the flame to the furnace wall and glass, and a short, thick flame that causes the flame to interfere with the hole in the burner tile into which the burner is inserted.

[0041] In this embodiment, the combustion-supporting gas injected around the injected fuel is oxygen alone. Therefore, by using a combustion-supporting gas that is pure oxygen with a 100% oxygen content, the higher the oxygen concentration in the oxidizer, the less heat loss caused by exhaust gases and the better the thermal efficiency, which can reduce fuel consumption. In particular, it can reduce the cost of hydrogen fuel, which is expensive and difficult to secure in supply.

[0042] (Second embodiment) As shown in FIG. 2, a dual-fuel combustion burner 1A according to the second embodiment includes the center burner 1 of the first embodiment and a staging nozzle 50 provided on the outer periphery of the center burner 1.

[0043] The dual-fuel / single-fuel burner 1A includes a cylindrical burner block 11 made of refractory material. The burner block 11 has a central insertion hole 12 formed along the center of the burner block 11 and an outer peripheral insertion hole 13 with a circular (cylindrical) cross section formed on the outer periphery of the central insertion hole 12. The central insertion hole 12 and the outer peripheral insertion hole 13 each pass through the burner block 11 in the axial direction. A portion of the center burner 1 is inserted into the central insertion hole 12. At least two (two in this embodiment) staging nozzles 50 (50A, 50B) are inserted into the outer peripheral insertion hole 13.

[0044] The center burner 1 comprises an inner tube nozzle 2 having a fuel outlet 20 arranged at the center, and an outer tube nozzle 3 having combustion supporting gas outlets 30 arranged around the fuel outlet 20 and from which a first combustion supporting gas is ejected. A mixing section 40 is connected to the fuel outlet 20 of the center burner 1. A hydrocarbon gas supply line 41 to which hydrocarbon gas is supplied and a hydrogen gas supply line 42 to which hydrogen gas is supplied converge at the mixing section 40. The center burner 1 configured in this manner has the same configuration as the first embodiment described above, so a detailed description will be omitted here. The combustion method of the center burner 1 is also the same as that of the first embodiment described above.

[0045] Two staging nozzles 50 (50A, 50B) are provided on the outer periphery of the center burner 1, i.e., on the outer periphery of the combustion supporting gas outlet 30, for ejecting a second combustion supporting gas that is supplied via a route different from that of the first combustion supporting gas.

[0046] In the dual-fuel combustion burner 1A according to the second embodiment, the oxidizer to be supplied is divided into two parts: an oxidizer (first combustion supporting gas) ejected from the center burner 1 and an oxidizer (second combustion supporting gas) ejected from the staging nozzles 50 (50A, 50B). This allows the fuel to burn in stages, reducing local high-temperature areas in the flame and suppressing NOx generation. This is particularly effective in hydrogen combustion, and can be applied to fuels ranging from hydrocarbon fuels to hydrogen fuels.

[0047] In the dual-fuel combustion burner 1A of the second embodiment, the ejection flow velocity of the fuel ejected from the burner tip is set to a first flow velocity V1 of 7 m / s or more when using hydrocarbon gas exclusively, and to a second flow velocity V2 of 28 m / s or more when using hydrogen gas exclusively, and by setting the lower limit value to the first flow velocity V1 and the upper limit value to the second flow velocity V2 when using dual-fuel combustion, it is possible to maintain a safe combustion state even when switching the fuel type from hydrocarbon fuel exclusively combustion to hydrocarbon-hydrogen dual combustion or to hydrogen exclusively combustion during operation with the same burner without replacing the center burner 1 or nozzle, and the dual-fuel combustion burner 1A can be used safely and stably.

[0048] In addition, in the combustion method of the dual-fuel combustion burner 1A of the second embodiment, the flow rate of the second combustion-supporting gas supplied to the staging nozzle 50 (50A, 50B) is adjusted to be 50% or more of the total flow rate of the combustion-supporting gas (first combustion-supporting gas and second combustion-supporting gas) supplied to the combustion-supporting gas outlet 30 and the staging nozzle 50 (50A, 50B). Therefore, when burning hydrogen, NOx emissions tend to increase compared to hydrocarbon fuels. However, by supplying 50% or more of the oxygen to the staging nozzles 50 (50A, 50B) when performing the staging combustion, it is possible to reduce NOx emissions to levels equal to or lower than those of conventional hydrocarbon fuels.

[0049] Next, an example will be described below that was carried out to verify the combustion method of the dual-fuel combustion burner and the effects of the dual-fuel combustion burner according to the above-described embodiment.

[0050] (First Example) In Example 1, the combustion conditions were observed when using the dual-fuel combustion burner (see Figure 1) in the first embodiment described above, and its effectiveness was confirmed. In Example 1, the staging nozzle of the second embodiment described above was not used, and burner combustion evaluation was performed using only the center burner.

[0051] As shown in Table 1, two types of nozzles (Nozzles 1 and 2) were used, each designed to have a fuel injection velocity as shown in Table 1 when the combustion scale was 200 kW. The fuel injection velocity of Nozzle 1 was 40 m / s for natural gas and 150 m / s for hydrogen gas. The fuel injection velocity of Nozzle 2 was 10.6 m / s for natural gas and 40 m / s for hydrogen gas. All of the oxygen, which is the combustion-supporting gas, was ejected from the center burner, and the oxygen injection velocity was adjusted to be 10 m / s.

[0052] [Table 1]

[0053] In the first example, the combustion status was observed while changing the combustion scale based on the conditions shown in Table 1. The observation results are shown in Table 2. As shown in Table 2, the combustion scale was changed in the range of 60 to 240 kW and evaluated in 20 kW increments. Table 2 shows the flow velocity (m / s) and evaluation results for both natural gas and hydrogen gas combustion for nozzles 1 and 2, respectively.

[0054] The evaluation criteria were based on visual observation of the combustion state, and a good combustion state in which stable combustion was maintained was judged as "Good", while a poor combustion state in which the nozzle was red hot and there was a risk of melting was judged as "Poor".

[0055] [Table 2]

[0056] When Nozzle 1 was used, it was visually confirmed that stable combustion was maintained at all fuel inputs from 60kW to 240kW for both natural gas and hydrogen combustion, and the evaluation result was "Good combustion".

[0057] When Nozzle 2 was used, visual inspection confirmed that stable combustion was maintained at 140kW to 240kW for both natural gas and hydrogen firing, resulting in an evaluation of good combustion (good). However, when using hydrogen firing with a flow velocity of 26m / s or less, visual inspection confirmed that the nozzle was red-hot, raising concerns about melting, resulting in an evaluation of poor combustion (poor). Furthermore, when using natural gas firing with a flow velocity of 6.9m / s or less, visual inspection confirmed that the flame was weak and curved significantly upwards. Therefore, when used inside a furnace, this could result in a combustion state that could interfere with the furnace walls and ceiling, resulting in an evaluation of poor combustion (poor).

[0058] From these results, it was found that in the first embodiment, it is desirable to set the flow velocity to 7 m / s or more when using natural gas exclusively and 28 m / s or more when using hydrogen exclusively.

[0059] (Second Example) In the second example, the nozzle 1 used in the first example was used to evaluate the combustion conditions using a mixed combustion gas of hydrocarbon gas and hydrogen gas. Table 3 shows the mixed combustion conditions and results for each of Tests 1 to 12. As shown in Table 3, in the second example, 12 cases (Tests 1 to 12) were conducted, in which the natural gas flow rate (m / s), hydrogen gas flow rate (m / s), total fuel flow rate (m / s), and flame heat value (kW) were varied. Regarding the total fuel flow rate in Table 3, the notation "29>28" for Test 8 indicates that the flow rate in Test 8 was 29 m / s, which is greater than the preferred upper limit of 28 m / s, which will be described later. Similarly, for Tests 11 and 12, the flow rate in Test 11 was 6 m / s, and the flow rate in Test 12 was 5 m / s, which is less than the lower limit of 7 m / s, which will be described later.

[0060] [Table 3]

[0061] The evaluation method was the same as in the first example, in which the combustion state was observed visually, and a good combustion state in which stable combustion was maintained was judged as "Good", and a poor combustion state in which the nozzle was red-hot and there was a risk of melting was judged as "Poor".

[0062] As shown in Table 3, in Tests 1 to 4, the flow rates of natural gas and hydrogen gas were changed to maintain a constant heat output from the flame, and co-firing evaluation was performed. In Tests 1 to 4, it was visually confirmed that the flame combustion state was stable, and the evaluation results were good combustion (good).

[0063] In Tests 5 to 8, the flow rates of natural gas and hydrogen gas were changed to increase the heat generation rate of the flame, and a mixed combustion evaluation was conducted. In Tests 5 to 7, it was confirmed by visual inspection that the flame combustion state was stable, and the evaluation result was good combustion (good). In Test 8, it was confirmed by visual inspection that the flame combustion state was unstable, and the evaluation result was poor combustion (poor).

[0064] In Tests 9 to 12, the flow rates of natural gas and hydrogen gas were changed to reduce the heat generation rate of the flame, and a mixed combustion evaluation was conducted. In Tests 9 and 10, it was visually confirmed that the flame combustion state was stable, and the evaluation result was "Good combustion" (○). In Tests 11 and 12, the flame combustion state was unstable and misfires occurred, resulting in an evaluation result of "Poor combustion" (×).

[0065] From these results, in the mixed combustion evaluation of the second embodiment, poor combustion occurred at a total fuel flow velocity of 29 m / s or more in Test 8, and at a total fuel flow velocity of 6 m / s or less in Tests 11 and 12. Therefore, it was confirmed that the lower limit of the total fuel flow velocity is 7 m / s and the upper limit is 28 m / s, i.e., it is desirable to set the total fuel flow velocity between 7 m / s and 28 m / s.

[0066] (Third Example) In the third example, an evaluation experiment was conducted to measure the amount of NOx generated by a test furnace using a dual-fuel combustion burner 1A (see Figure 2) equipped with the staging nozzle of the second embodiment described above, and its effectiveness was confirmed.

[0067] Table 4 shows the operating conditions. The dual-fuel burner used in Example 3 has a structure with a center burner and two staging nozzles as shown in Figure 2, and its rated combustion capacity is 200 kW. The fuel injection flow velocity under rated conditions is as shown in Table 4. That is, the fuel injection velocity from the nozzle is 40 m / s for natural gas and 150 m / s for hydrogen gas. The oxygen flow rate to the staging nozzle (the ratio of staging oxygen flow rate to total oxygen flow rate) was varied within a range of 20 to 80% of the total. In Example 3, under the above test conditions, the effect of the flow rate distribution of the oxygen flow rate to the staging nozzle was evaluated in terms of the Nox emission concentration (ppm) in the exhaust gas.

[0068] [Table 4]

[0069] Figure 3 shows the test results for Example 3, illustrating the NOx emission concentration in the exhaust gas. In Figure 3, the horizontal axis represents the ratio (%) of staging oxygen flow rate to total oxygen flow rate, and the vertical axis represents the NOx concentration (ppm, converted to 15% oxygen). In Example 3, evaluation was performed using the regulated value of 360 ppm, which is converted to 15% oxygen, as a standard, in accordance with standards for glass melting furnaces, for example.

[0070] As shown in Figure 3, when using natural gas exclusively and a 50% hydrogen mixture, NOx concentrations below the regulated value were emitted when the ratio of staging oxygen flow rate to total oxygen flow rate was in the range of 20 to 80%. On the other hand, when using hydrogen exclusively, NOx levels above the regulated value were emitted when the ratio of staging oxygen flow rate to total oxygen flow rate was 20%, but by increasing the distribution ratio of staging oxygen to 50% or more of the total, NOx emissions were below the regulated value.

[0071] From these results, it was found that in the third embodiment, it is desirable to set the ratio of staging oxygen flow rate / total oxygen flow rate to 50% or more.

[0072] The shapes and combinations of the components shown in the above-described embodiment are merely examples, and various modifications can be made based on design requirements, etc., within the scope of the present invention.

[0073] For example, in the embodiment described above, a combustion method is adopted in which the ejection flow rates of hydrocarbon gas and hydrogen gas are adjusted so that the heat generation value of the flame is constant, but the present invention is not limited to adjusting the heat generation value to be constant in this way.

[0074] In addition, in this embodiment, the mixing section 40 is provided upstream of the center burner 1, but it is also possible to use the pipeline where the hydrocarbon gas supply line 41 and the hydrogen gas supply line 42 join as the mixing section.

[0075] The combustion method used for the dual-fuel burner is such that the velocity of the combustion-supporting gas ejected around the fuel ejected at the center is between 1 / 2 and 1 / 8 of the velocity of the fuel, but this method can also be omitted.

[0076] The configurations of the shape, size, quantity, etc. of the center burner 1 and the dual-fuel combustion burner 1A equipped with the staging nozzle 50 in the above-described embodiment are merely examples, and the configuration is not limited to this as long as it can realize a combustion method in which the fuel ejection flow velocity is a first flow velocity of 7 m / s or more when hydrocarbon gas is exclusively combusted, a second flow velocity of 28 m / s or more when hydrogen gas is exclusively combusted, and a lower limit value of the first flow velocity and an upper limit value of the second flow velocity when dual-fuel combustion is used. [Explanation of symbols]

[0077] 1 Center burner (mixed-fuel / exclusive combustion burner) 1A Dual-fuel / Single-fuel burner 2 Inner pipe nozzle 3 Outer tube nozzle 10 Burner body 11 Burner Block 12 Center insertion hole 13 Outer peripheral insertion hole 20 Fuel spout 21 Fuel supply port 30 Combustion-supporting gas outlet 31 Combustion-supporting gas supply port 40 Mixing section 41 Hydrocarbon gas supply line 42 Hydrogen gas supply line V1 1st flow velocity V2 2nd flow rate

Claims

1. A combustion method for a dual-fuel burner in which the fuel is hydrocarbon gas, hydrogen gas, or a mixed gas thereof, and the combustion state can be continuously switched between hydrocarbon gas mono-fuel, mixed combustion of hydrocarbon gas and hydrogen gas, and hydrogen mono-fuel, comprising: The injection flow velocity of the fuel is When hydrocarbon gas is exclusively fired, the first flow velocity is 7 m / s or more, When hydrogen gas is exclusively burned, the second flow velocity is 28 m / s or more. A combustion method for a dual-fuel / exclusive-fuel burner, wherein, during dual-fuel combustion, the lower limit value is the first flow rate and the upper limit value is the second flow rate.

2. 2. The combustion method for a dual-fuel / single-fuel burner according to claim 1, wherein the ejection flow rates of the hydrocarbon gas and the hydrogen gas are adjusted so that the heat value of the flame is constant.

3. 2. The combustion method for a dual-fuel / single-fuel burner according to claim 1, wherein the mixed gas is supplied to the burner in a state in which the hydrocarbon gas and the hydrogen gas are mixed together.

4. 2. The combustion method for a dual-fuel / single-fuel burner according to claim 1, wherein the ejection speed of the combustion-supporting gas ejected around the fuel ejected at the center is not more than 1 / 2 and not less than 1 / 8 of the ejection speed of the fuel.

5. 2. The combustion method for a dual-fuel / single-fuel burner according to claim 1, wherein the combustion-supporting gas injected around the injected fuel is oxygen alone.

6. A dual-fuel combustion burner used in the combustion method for a dual-fuel combustion burner according to any one of claims 1 to 5, a centrally disposed fuel outlet; a combustion-supporting gas outlet disposed around the fuel outlet, The dual-fuel / single-fuel burner is provided with at least two staging nozzles for ejecting the combustion-supporting gas on the outer periphery of the combustion-supporting gas outlet.

7. A combustion method for a dual-fuel / single-fuel burner according to claim 6, A combustion method for a dual-fuel / single-fuel burner, wherein the ratio of the flow rate of the combustion-supporting gas supplied to the staging nozzle to the total flow rate of the combustion-supporting gas supplied to the combustion-supporting gas outlet and the staging nozzle is 50% or more.

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