Axial multi-stage combustion system that suppresses the generation of nitrogen oxides from ammonia or hydrogen flames.

Abstract

The present invention relates to a gas turbine using a carbon-free fuel such as hydrogen or ammonia, and more specifically, to an axial multi-stage combustion system that suppresses the generation of nitrogen oxides from ammonia or hydrogen flames, thereby reducing nitrogen oxides in the exhaust gas after combustion of the gas turbine. [Solution] The combustion system includes a first combustion section in which a primary combustion region is formed where a first fuel gas is supplied and primary combustion takes place; a second combustion section in which a secondary combustion region is formed, with its front end connected to the rear end of the first combustion section, and to which the primary combustion gas burned in the first combustion section is supplied; and a second fuel gas supply section that supplies a second fuel gas to the secondary combustion region so that it is mixed with the primary combustion gas and secondary combustion takes place.

Description

Technical Field

[0001] The present invention relates to a gas turbine using a carbon-free fuel such as hydrogen or ammonia. More specifically, the present invention relates to an axial multi-stage combustion system that suppresses the generation of nitrogen oxides in an ammonia or hydrogen flame, which reduces nitrogen oxides in exhaust gas after combustion of the gas turbine.

Background Art

[0002] With the exacerbation of global warming due to greenhouse gas emissions, gas turbine engines using hydrocarbon fuels are cited as a major cause of environmental problems. To solve this, it is necessary to convert conventional gas turbine engines to carbon-free fuels such as hydrogen and ammonia.

[0003] In particular, ammonia has lower transportation and storage costs compared to hydrogen, can significantly reduce carbon dioxide emissions through production using renewable energy, and can also serve as an effective hydrogen carrier containing three hydrogens in its molecule. Therefore, it has attracted attention as a next-generation gas turbine fuel.

[0004] However, in order to apply ammonia to a gas turbine system, problems related to reactivity and exhaust gas emissions must be solved in terms of combustion technology. In particular, ammonia contains nitrogen in its fuel composition and can generate a large amount of fuel nitrogen oxides (Fuel NOx). Therefore, the development of technologies to reduce this is required.

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention has been derived to solve the above problems. The present invention aims to provide an axial multi-stage combustion system that improves thermal efficiency by suppressing nitrogen oxides by fuel-rich combustion in the upstream region of the combustor and inducing further combustion of unburned fuel in the downstream region to increase the turbine inlet temperature.

[0006] In particular, the objective is to provide an axial multi-stage combustion system that further reduces nitrogen oxide generation by injecting hydrogen / air into the secondary combustion chamber. [Means for solving the problem]

[0007] A combustion system according to one embodiment of the present invention includes a first combustion section in which a primary combustion region is formed where a first fuel gas is supplied and primary combustion takes place; a second combustion section in which a secondary combustion region is formed, with its front end connected to the rear end of the first combustion section, and to which the primary combustion gas burned in the first combustion section is supplied; and a second fuel gas supply section that supplies a second fuel gas to the secondary combustion region so as to be mixed with the primary combustion gas and subjected to secondary combustion.

[0008] Furthermore, the first fuel gas comprises a mixture of ammonia and air, and the second fuel gas comprises a mixture of hydrogen and air so as to spontaneously ignite when mixed with a high-temperature primary combustion gas.

[0009] Furthermore, the combustion system is further provided with a fuel nozzle section, which includes a first dump section connected to the front end of the first combustion section and having a number of first nozzles formed therein for injecting fuel gas into the primary combustion region.

[0010] Furthermore, the second fuel gas supply unit is connected to the front end of the secondary combustion region and includes a second dump unit in which a number of second nozzles are formed, the number of second nozzles being less than the number of first nozzles.

[0011] Furthermore, the second dump section is connected to the side surface of the second combustion section so as to supply the second fuel gas to the secondary combustion region and to inject the second fuel gas perpendicular to the flow direction of the primary combustion gas.

[0012] Furthermore, the combustion system further includes a sampling unit for collecting exhaust gas discharged from the second combustion unit, and an analysis unit for analyzing the components of the exhaust gas collected by the sampling unit.

[0013] Furthermore, the combustion system further includes a control unit that calculates the supply amount of a second fuel gas or the mole fraction of hydrogen that minimizes the nitrogen oxides analyzed by the analysis unit.

[0014] Furthermore, the control unit calculates the distance between the front end of the first combustion section and the front end of the second combustion section at which the nitrogen oxides analyzed by the analysis unit are minimized.

[0015] Furthermore, the diameter of the first nozzle is 6.0 to 7.0 mm, and the diameter of the second nozzle is the same as that of the first nozzle.

[0016] Furthermore, the first fuel gas contains hydrogen. [Effects of the Invention]

[0017] The axial multi-stage combustion system of the present invention, which suppresses the generation of nitrogen oxides from ammonia or hydrogen flames with the above configuration, has the effect of suppressing the generation of nitrogen oxides that may be contained in the exhaust gas of a combustion system using ammonia or hydrogen as fuel, thereby reducing environmental pollution.

[0018] Furthermore, it provides fundamental information regarding combustion conditions in the secondary region of axial multi-stage combustion systems, which can be useful in revitalizing ammonia combustion systems. [Brief explanation of the drawing]

[0019] [Figure 1] This is a side view of a combustion system according to one embodiment of the present invention. [Figure 2] This is a rear view showing the end portion of the fuel nozzle section of the present invention. [Figure 3] This is a side view of the second combustion section of the present invention. [Figure 4] This is a plan view of the end portion of the second nozzle of the second combustion section of the present invention. [Figure 5] This graph shows the results of exhaust gas component measurements during single-combustion. [Figure 6]It is a graph showing the results of component measurement of exhaust gas during multi-stage combustion with additional air injection. [Figure 7] It is a graph showing the results of component measurement of exhaust gas during multi-stage combustion with additional injection of a premixed hydrogen / air mixture.

Mode for Carrying Out the Invention

[0020] Hereinafter, an embodiment of the present invention as described above will be described in detail with reference to the drawings.

[0021] In FIG. 1, a side view of a combustion system 1000 according to an embodiment of the present invention is illustrated. Also, in FIG. 2, a rear view showing an end portion of a fuel nozzle portion 100 of the present invention is illustrated. In FIG. 3, a side view of a second combustion portion 300 of the present invention is illustrated, and in FIG. 4, a plan view of an end portion of a second damper portion of the second combustion portion 300 of the present invention is illustrated.

[0022] As illustrated in FIG. 1, the combustion system 1000 can be configured to include a fuel nozzle portion 100, a first combustion portion 200, a second combustion portion 300, a flame tube 400, a sampling portion 500, and a gas analysis portion 600. A first inflow portion 110 is formed at the front end of the fuel nozzle portion 100, and a first damper portion 120 is formed at the rear end. The rear end of the fuel nozzle portion 100 can be connected to the first combustion portion 200. The fuel nozzle portion 100 and the first combustion portion 200 are configured to be integrally formed or independently formed and bonded and sealed with room temperature vulcanizing (RTV) silicone. Also, a second combustion portion 300 is provided at the rear end of the first combustion portion 200, and a flame tube 400 is provided at the rear end of the second combustion portion 300. The second combustion portion 300 and the flame tube 400 are each independently formed and can be bolted together.

[0023] The fuel nozzle section 100 is configured to receive a supply of first fuel gas G1 via a first inlet section 110 and supply it to the first combustion section 200 via a first dump section 120. The first inlet section 110 and the first dump section 120 can be connected via a number of transfer pipes 150. Therefore, the first dump section 120 can have a number of first nozzles 125, each connected to the rear ends of the number of transfer pipes 150.

[0024] Referring to Figure 2, multiple first nozzles 125 are formed in the first dump section 120 so as to be connected to each of the multiple transfer pipes 150, and can be spaced apart in the radial and circumferential directions. The first dump section 120 has 60 first nozzles 125 with a diameter of 6.5 mm, arranged at intervals of 15 mm. If the diameter of the first nozzle 125 exceeds 6.5 mm, flashback may occur when burning fuel gas with a hydrogen fraction above a predetermined level. Also, if it is less than 6.5 mm, the flow velocity of the fuel gas increases rapidly, and under high ammonia fraction conditions, a scattering phenomenon may occur without the flame adhering to the first dump section 120 of the fuel nozzle section 100. The first fuel gas G1 injected into the first combustion section 200 via the first nozzle 125 is ignited and burned by an igniter 121 provided in the first dump section 120, generating a flame.

[0025] Referring to Figure 1, the first combustion section 200 is located at the rear end of the fuel nozzle section 100 and is configured to provide a space for primary combustion by receiving the supply of the first fuel gas G1 injected through the first nozzle 125. Therefore, the first combustion section 200 has a primary combustion region 201 formed inside it, and the front end of the primary combustion region 201 can communicate with the rear end of the first dump section 120 in which the first nozzle 125 is formed. On the other hand, the first combustion gas G1 may be a mixed gas in which ammonia, hydrogen, and air are premixed. In the case of ammonia fuel, since its reactivity is very low, a portion of hydrogen, which is a highly reactive fuel, is added to increase the reactivity of the first combustion gas G1.

[0026] The first fuel gas G1 injected into the primary combustion region 201 of the first combustion section 200 is ignited and burned by an igniter 121 provided in the first dump section 120, generating a flame and producing a primary combustion gas G11. The primary combustion gas G11 can be supplied to the second combustion section 200 connected to the rear end of the first combustion section 100.

[0027] The second combustion section 300 has a secondary combustion region 301 formed inside it. The secondary combustion region 301 is configured to receive primary combustion gas G11 generated in the first combustion section 200, and then receive a second fuel gas G2 to perform secondary combustion. The second combustion section 300 can be positioned 400 mm from the front end to the rear end of the first combustion section 200. If it is less than 400 mm, the reaction residence time decreases, and the nitrogen oxide reduction efficiency in the downstream region may decrease. This is because, in the ammonia flame, above a certain fuel-to-air ratio, the degree to which the ammonia reactor and nitrogen oxides react with each other in the downstream region increases, thus reducing nitrogen oxides. Also, if it exceeds 400 mm, the primary combustor region expands too much, which may increase cost problems in terms of combustor shape design.

[0028] Referring to Figure 3, a second inlet 320 is formed at the front end of the second combustion section 300, and a second outlet 320 is formed at the rear end. The second inlet 320 can be connected to and communicate with the first outlet 210 formed at the rear end of the first combustion section 200. Therefore, the primary combustion gas G11 from the first combustion section 200 is discharged through the first outlet 210 and supplied to the secondary combustion region 301 through the second inlet 320 of the second combustion section 300. On the other hand, the second combustion section 300 may be equipped with a second fuel gas supply section 350 for receiving a second fuel gas G2. The second fuel gas supply section 350 has a second fuel inlet 351 formed at its front end to receive the second fuel gas G2, and a second dump section 352 including a second nozzle 355 formed at its rear end to inject the second fuel gas G2 into the secondary combustion region 301. The second dump section 352 is connected to the side surface above the front end of the second combustion section 300 and can be configured to inject the second fuel gas G2 perpendicular to the primary combustion gas G11 flowing along the longitudinal direction. Supplying the second fuel gas G2 perpendicular to the flow direction of the primary combustion gas G11 has the advantage of forming a shear layer between the main flow and the injection region of the second fuel gas G2, thereby improving mixing efficiency as the recirculation region further develops.

[0029] Referring to Figure 4, the second dump section 352 includes a plurality of second nozzles 355, each having a diameter of 6.5 mm, similar to the first nozzle 115 of the first combustion section 200, and a total of nine nozzles can be arranged in a grid pattern with 9 mm spacing. Thus, the second fuel gas G2 can be injected into the secondary combustion region 301 via the plurality of second nozzles 355.

[0030] The second dump section 352, as a transition piece connecting the first combustion section 200 and the secondary combustion section 300, can be rectangular in shape for the sake of flow optimization, structural advantages, and ease of maintenance. On the other hand, the reason why there are fewer second nozzles 355 than first nozzles 115 is related to the injection momentum ratio supplied from the second nozzles 355. The flow rate of the second fuel gas G2 supplied in this region is generally significantly less than the flow rate of the primary combustion gas G11, so if the number of nozzles is the same, the flow velocity may decrease. When the flow velocity decreases, the injection momentum of the second nozzles 355 decreases, and mixing may not occur effectively during the reaction process with the primary combustion gas G11.

[0031] The second fuel gas G2 can consist of a mixture of hydrogen and air. When injected into the secondary combustion region 301, the second fuel gas G2 comes into contact with the high-temperature primary combustion gas G11 and spontaneously ignites, producing exhaust gas G3 with reduced nitrogen oxides through secondary combustion.

[0032] The exhaust gas G3 generated in the secondary combustion region 301 is supplied to a flame tube 400 connected to the rear end of the second combustion section 300 via a second outlet 320. Cooling air passages and cooling water passages can be formed on the flame tube 400 to cool the exhaust gas through heat exchange with the exhaust gas.

[0033] On the other hand, as illustrated in Figure 1, a sampling unit 500 is provided at the front end of the flame tube 400, configured to collect a portion of the secondary combustion gas G21. The sampling unit 500 may be a conventional sampling probe. The secondary combustion gas G21 collected by the sampling unit 500 is transmitted to the analysis unit 600 for analysis and measurement of the gas's components. The analysis unit 600 may include a first analyzer 610 and a second analyzer 620. The first analyzer 610 receives the secondary combustion gas G21 from the sampling unit 500 and analyzes and measures nitrogen oxides, hydrogen, ammonia, and oxygen components, while the second analyzer 620 receives the secondary combustion gas G21 from the sampling unit 500 and analyzes and measures nitrous oxide and oxygen components. The first analyzer 610 may, for example, be an Ecom J2KN Pro instrument, and the second analyzer 620 may be a Gasmet DX4000.

[0034] Furthermore, the secondary combustion gas G21 transmitted to the first analyzer 610 can be configured to be diluted with nitrogen by the nitrogen diluent 615 before being supplied to the first analyzer 610.

[0035] In the case of the above-mentioned analyzer, since there is a maximum measurable concentration for a specific chemical type, it is preferable to dilute nitrogen to lower the measurable concentration and conduct the experiment in order to prevent exceeding that concentration range under specific experimental conditions. This allows the true experimental value to be recalculated through a post-processing step after the experiment is completed.

[0036] The system is configured to allow for the calculation of the optimal amount of second fuel gas that minimizes nitrogen oxides, the hydrogen-to-air mixture ratio of the second fuel gas, and the optimal distance from the front of the first combustion chamber 200 to the second fuel gas supply chamber 350, based on the component analysis of the secondary combustion gas G21 as described above. If a chemical species is detected above a certain value, the system can be configured to adjust the concentration using a nitrogen dilution device for measurement.

[0037] The following are the results of an experiment measuring the exhaust emission characteristics of a premixed ammonia / hydrogen flame using a multi-stage combustor. The detailed experimental conditions are as follows.

[0038] To determine the optimal primary combustion conditions for multi-stage combustion, an experiment was first conducted under primary combustion conditions without multi-stage combustion. In this experiment, the primary combustion conditions were an ammonia / hydrogen mole fraction of 80% / 20%, an equivalent ratio fixed at 1.25, and a temperature set at 450K under atmospheric pressure.

[0039] Next, in the multi-stage combustion experiment, air was injected into the secondary reaction region at 20% intervals, from 20% to 80% of the primary region's airflow rate, while the temperature was kept fixed at 450K.

[0040] Furthermore, the conditions for injecting the premixed hydrogen / air mixture were fixed at 10 kW based on the hydrogen flow rate, and the secondary equivalent ratio was adjusted from 0.20 to 0.35 in increments of 0.05 during the experiment. The temperature in the secondary region was fixed at room temperature to maintain the momentum ratio. The combustor used in the experiment was a tunable combustor rig structure, which is used in industry for the purpose of combustor development. Exhaust gas analysis was performed using an Ecom J2KN Pro instrument to measure nitrogen oxides, hydrogen, ammonia, and oxygen, and a Gasmet DX4000 to measure nitrous oxide and oxygen.

[0041] Figure 5 shows a graph illustrating the results of exhaust gas component measurements during single combustion.

[0042] As shown in the diagram, in the case of single combustion using only the first combustion section 200, it was confirmed that a high concentration of nitrogen oxides of approximately 3030 ppmvd was generated under the condition of an equivalence ratio of 1.05. As the equivalence ratio increased, the concentration of nitrogen oxides gradually decreased, and it was confirmed that it decreased to a minimum of 57 ppmvd in the equivalence ratio interval of 1.25. Furthermore, it was found that almost no nitrous oxide was generated under these conditions. However, in this interval, there was a problem of a small amount of unburned ammonia being generated and a large amount of hydrogen being generated.

[0043] Figure 6 shows a graph illustrating the results of exhaust gas component measurements during multi-stage combustion with additional air injection.

[0044] As illustrated, when air is further injected into the secondary combustion region 301 in the multi-stage combustion system, the unburned ammonia completely reacts, and hydrogen also tends to gradually decrease. Here, the generation of nitrous oxide was hardly observed, similar to the single-combustion conditions. However, it was confirmed that a large amount of nitrogen oxides, approximately 1000-1600 ppmvd, was generated by the secondary reaction. These results indicate that multi-stage combustion using air can reduce the amount of unburned ammonia and hydrogen generated and improve combustion efficiency, but it shows low efficiency in terms of nitrogen oxide generation.

[0045] Figure 7 shows a graph illustrating the results of exhaust gas component measurements during multi-stage combustion with additional injection of a premixed hydrogen / air mixture. When hydrogen-mixed air is added to the secondary combustion region 301, the unburned ammonia in the secondary combustion region reacts completely, and the hydrogen decreases from 25816 ppmvd to 70-140 ppmvd. Under these conditions, nitrous oxide was not significantly generated. The most noteworthy result from the above is the nitrogen oxide concentration, which was confirmed to be around 360-400 ppmvd. This is approximately 64% lower than the minimum generation amount during multi-stage combustion using air. This result confirms that the multi-stage combustion technique using a premixed hydrogen / air mixture is a better alternative to air-based combustion in reducing nitrogen oxide generation.

[0046] The technical idea of ​​the present invention should not be interpreted as being limited to the above embodiments. Needless to say, the scope of application is diverse, and various modifications can be made at the level of a person skilled in the art without departing from the gist of the invention as claimed. Therefore, such improvements and modifications are within the scope of protection of the present invention, insofar as they are obvious to a person skilled in the art.

Claims

1. A first combustion section is formed in which a primary combustion region is created where a first fuel gas is supplied and primary combustion takes place, A second combustion section is formed in which the front end is connected to the rear end of the first combustion section and a secondary combustion region is formed to which the primary combustion gas burned in the first combustion section is supplied, An axial multi-stage combustion system, comprising: a second fuel gas supply unit that supplies a second fuel gas to the secondary combustion region so as to be mixed with the primary combustion gas and subjected to secondary combustion.

2. The first fuel gas is It contains a mixture of ammonia and air, The second fuel gas is The axial multi-stage combustion system according to claim 1, comprising a mixture of hydrogen and air that spontaneously ignites when mixed with a high-temperature primary combustion gas.

3. The aforementioned combustion system, The axial multi-stage combustion system according to claim 1, further comprising a fuel nozzle section including a first dump section connected to the front end of the first combustion section and having a plurality of first nozzles formed therein for injecting fuel gas into the primary combustion region.

4. The second fuel gas supply unit is, It includes a second dump section connected to the front end of the secondary combustion region and having a number of second nozzles formed thereon, The axial multi-stage combustion system according to claim 3, wherein the number of second nozzles is less than the number of first nozzles.

5. The second dump section is, The axial multi-stage combustion system according to claim 4, wherein a second fuel gas is supplied to the secondary combustion region and the second fuel gas is injected perpendicular to the flow direction of the primary combustion gas, and is connected to the side surface of the second combustion section.

6. The aforementioned combustion system, A sampling unit for collecting exhaust gas discharged from the second combustion unit, The axial multi-stage combustion system according to claim 1, further comprising an analysis unit for analyzing the components of exhaust gas collected by the sampling unit.

7. The aforementioned combustion system, The axial multi-stage combustion system according to claim 6, further comprising a control unit that calculates the supply amount of a second fuel gas or the mole fraction of hydrogen that minimizes the nitrogen oxides analyzed by the analysis unit.

8. The control unit, The axial multi-stage combustion system according to claim 7, wherein the distance between the front end of the first combustion section and the front end of the second combustion section is calculated so that the nitrogen oxides analyzed by the analysis section are minimized.

9. The axial multi-stage combustion system according to claim 4, characterized in that the diameter of the first nozzle is 6.0 to 7.0 mm, and the diameter of the second nozzle is the same as that of the first nozzle.

10. The first fuel gas is The axial multi-stage combustion system according to claim 2, further comprising hydrogen.

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