A low nox combustion system for ammonia fuel based on plasma X Generated staged ammonia gas combustion system

Abstract

The application discloses a low-NOx ammonia fuel combustion system based on plasma combustion support X The generated staged ammonia gas combustion system comprises a high-frequency high-voltage power supply, a dielectric barrier plasma generator, a gas distribution system (a blower and an ammonia storage tank), a combustion chamber and a swirler; the dielectric barrier plasma generator comprises a high-voltage electrode, an insulating medium, a swirler and a ground electrode; and the gas distribution system comprises a blower and an ammonia storage tank. The application utilizes dielectric barrier to generate ammonia gas plasma discharge, reduces the difficulty of ammonia gas combustion and improves the stability of ammonia gas combustion; utilizes the swirler to generate rotating airflow and improves the combustion efficiency; utilizes ammonia gas staged combustion to further reduce NOx emission; and the ideal staged ratio is that the volume ratio of ammonia gas plasma to side wall ammonia gas is 20% (10%-30%), so that the ammonia gas plasma can be fully discharged, and the ammonia sprayed from the side wall can also be fully combusted.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of combustion and the technical field of plasma application, and particularly relates to a staged ammonia combustion system based on plasma combustion-supporting low-NOx generation of ammonia fuel. BACKGROUND

[0002] In order to reduce the greenhouse effect, it is one of the necessary ways to replace or partially replace the existing fossil fuels with new fuels, and hydrogen energy is an important part of future energy systems and energy revolution. As a clean energy, its combustion process is stable, and the heat value released by combustion is high, but there are great problems and challenges in the transportation and storage of hydrogen energy. Therefore, it is necessary to find new clean energy, and ammonia, as a good hydrogen storage medium, is a very market-potential energy, which will not produce greenhouse gases in the combustion process and can reduce greenhouse gas emissions from the source. However, there are still some problems in the current ammonia combustion. Because the ignition point of ammonia is high and the flame propagation rate is slow, it is easy to burn unstably, the output power is small, and a large amount of NOx pollutants are generated in the combustion. Therefore, it is necessary to find new technical means to optimize ammonia combustion, improve combustion stability and reduce NOx generation.

[0003] Dielectric barrier plasma (DBD, Dielectric Barrier Discharge) refers to the discharge phenomenon of plasma generated by dielectric barrier high-voltage electric field. Its principle is to press a dielectric between metal electrodes, and when the voltage reaches a certain value, a non-thermal plasma is formed on the surface of the dielectric, realizing the chemical, physical, biological and material surface treatment of air and other media. Dielectric barrier plasma has the characteristics of low temperature, non-thermal equilibrium, high reaction rate, chemical reaction and biological degradation. Ionizing ammonia fuel by dielectric barrier discharge plasma can shorten the ignition delay time, stabilize and even control the combustion, improve the combustion speed, and reduce the emission of pollutants. Plasma has thermal effect, chemical kinetic effect and flow effect, and has great application prospect in auxiliary combustion. However, the effect of plasma combustion-supporting reduction of NOx emission still needs to be further improved.

[0004] In summary, how to improve the stability of ammonia combustion and the emission of NOx pollutants according to the characteristics of ammonia combustion is a technical problem to be solved in the prior art. SUMMARY

[0005] The main purpose of the present application is: (1) to realize stable combustion of ammonia by using plasma combustion-supporting, and to solve the problems of unstable and insufficient combustion of ammonia fuel; (2) to realize low emission of combustion pollutants NOx by using staged combustion of ammonia and taking advantage of the strong reducing property of ammonia fuel.

[0006] To achieve the above object, the application provides an ammonia fuel staged combustion system based on plasma combustion, wherein fuel ammonia is supplied in stages, a high electric field is provided by dielectric barrier discharge plasma, a large-area high-energy-density low-temperature non-equilibrium plasma is generated and sprayed by means of violent ammonia gas discharge, so that part of the ammonia gas is ignited and stably combusted.

[0007] The ammonia fuel staged combustion system based on plasma combustion comprises a dielectric barrier plasma generator, a high-frequency high-voltage power supply, a gas distribution system, a combustion chamber and a swirler.

[0008] The application adopts the following technical scheme:

[0009] The ammonia fuel staged combustion system based on plasma combustion comprises a dielectric barrier plasma generator, a high-frequency high-voltage power supply, a gas distribution system and a combustion chamber; the dielectric barrier plasma generator comprises a high-voltage electrode, an insulating medium and a grounded metal shell; the gas distribution system comprises a blower and an ammonia storage tank.

[0010] The high-voltage electrode is installed in the insulating medium but does not contact the insulating medium;

[0011] The high-frequency high-voltage power supply is connected to the high-voltage electrode of the dielectric barrier plasma generator through a high-voltage line, and simultaneously, the high-frequency high-voltage power supply leads out a grounding line connected to the grounded metal shell of the dielectric barrier plasma generator; the dielectric barrier plasma generator is installed at a top air inlet of the combustion chamber; a discharge gas inlet of the dielectric barrier plasma generator is connected to the ammonia storage tank; a staged ammonia gas inlet is coaxially arranged outside the dielectric barrier plasma generator at the top air inlet of the combustion chamber and is connected to the ammonia storage tank; a combustion air inlet is coaxially arranged outside the dielectric barrier plasma generator and the staged ammonia gas inlet at the top air inlet of the combustion chamber, and the combustion air inlet is connected to the blower.

[0012] Further, the combustion chamber is additionally provided with an air inlet in a side wall, ammonia gas discharged by the dielectric barrier plasma generator is introduced through the top air inlet, and ammonia gas combusted in stages is introduced through a sleeve outside the plasma generator tube or a side wall air inlet of the burner.

[0013] Further, the top air inlet is a coaxial structure and is provided with a cyclone, so that air and ammonia plasma are simultaneously introduced and a rotating airflow is generated, thereby improving combustion efficiency.

[0014] Further, the dielectric barrier plasma generator is installed at the top air inlet of the combustion chamber, and the dielectric barrier discharge device comprises a high-voltage electrode, an insulating medium, a cyclone and a grounded metal shell, and a ceramic tube is fixed to the inner side of the high-voltage electrode and the grounded electrode.

[0015] Further, the dielectric barrier plasma generator is a coaxial structure, thereby increasing the ionization efficiency of ammonia.

[0016] As a further improvement of the present application, ammonia is directly ionized by the dielectric barrier plasma generator, thereby generating products such as hydrogen (H2), nitrogen (N2), amino radical (NH2), amino radical ion (NH2 - ), amino ion (NH3 + ) and the like, and the temperature of the discharge area is increased to ignite the gas. Finally, the ignition difficulty of ammonia is reduced and the combustion stability is improved.

[0017] As a further improvement of the present application, a part of ammonia is introduced into the ammonia plasma flame through a grading from a concentric sleeve tube or a burner side wall, at this time, ammonia combustion further consumes oxygen to form a low-oxygen area, and the NOx generated in the flame is reduced under the action of low-oxygen ammonia, thereby effectively inhibiting the generation of NOx.

[0018] According to an embodiment of the present application, a method for controlling an ammonia fuel staged combustion system with plasma combustion support is provided, which specifically comprises the following steps:

[0019] Step (1): high-frequency high-voltage power supply setting step, in the setting unit of the high-frequency high-voltage power supply control system, the limited voltage and the limited power are adjusted according to the required plasma parameters;

[0020] Step (2): fuel source and air source flow setting step, in the flow setting unit of the ammonia storage tank, the air blower and the air blower, the ammonia gas entering the plasma generator inlet and the ammonia gas entering the grading inlet are set according to the grading ratio, and the flow value is adjusted according to the required gas flow;

[0021] Step (3): grading ratio optimization step, when the plasma combustion support system is normally working, the grading ratio is changed according to the actual combustion condition, and the best NOx emission low point is explored;

[0022] Step (4) grading ammonia injection position optimization step, when the plasma combustion support system is normally working, different grading ammonia injection positions are changed according to the actual combustion condition, that is, coaxial ammonia injection or side wall ammonia injection at different positions, and the best NOx emission low point is explored.

[0023] The above merely provides the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art, according to the technical scheme and the inventive concept of the present application, can make equivalent replacement or change within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.

[0024] The technical scheme provided by the present application has the following remarkable effects:

[0025] (1) The medium barrier is used to carry out ammonia plasma discharge, which reduces the difficulty of ammonia combustion and improves the stability of ammonia combustion;

[0026] (2) The rotating airflow is generated by the cyclone to improve the combustion efficiency;

[0027] (3) The ammonia staged combustion is used to further reduce the NOx emission. The ideal staged ratio is that the volume ratio of ammonia plasma to side wall ammonia is 20% (10%-30%), so that the ammonia plasma is fully discharged, and the ammonia sprayed from the side wall can also be fully combusted. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The figure is a NOx concentration distribution diagram of ammonia plasma staged combustion;

[0029] Figure 2 The figure is a schematic diagram of an ammonia fuel staged combustion system based on plasma combustion assistance according to the present application;

[0030] Figure 3 The figure is a schematic diagram of the position of ammonia injection port and side wall injection port on the combustion chamber according to the present application;

[0031] Figure 4 The figure is a schematic diagram of the medium barrier discharge plasma structure used in the present application.

[0032] In the figure, 100-high frequency high voltage power supply; 200-medium barrier plasma generator; 201-ground electrode; 202-insulating medium; 203-high voltage electrode; 204-cyclone; 205-discharge gas passage; 300-blower; 400-combustion chamber; 500-ammonia storage tank; 401-medium barrier plasma gas inlet; 404(1)-staged ammonia injection port; 402-air inlet; 403-cyclone; 404(2), 404(3)......404(n)-side wall staged ammonia injection position, sprayed at different heights on the side wall of the combustion chamber 400. DETAILED DESCRIPTION

[0033] The application will be described in detail below with reference to the drawings and specific embodiments. However, the following embodiments are only used to explain the application, and the protection scope of the application should include the entire content of the claims, and through the description of the following embodiments, those skilled in the art can fully realize the entire content of the claims of the application.

[0034] As Figure 1 shown is the NOx concentration distribution diagram obtained by actual experimental verification, which will be specifically analyzed in the following part.

[0035] As Figure 2 shown, the ammonia fuel staged combustion system based on plasma combustion of the application comprises a high-frequency high-voltage power supply 100, a dielectric barrier plasma generator 200, a blower 300, a combustion chamber 400 and an ammonia storage tank 500.

[0036] The high-frequency high-voltage power supply 100 is connected with the high-voltage electrode of the dielectric barrier plasma generator 200 through a high-voltage line, and at the same time, a grounding wire is led out and connected with the grounding metal shell of the dielectric barrier plasma generator 200. The dielectric barrier plasma generator 200 is installed at the top air inlet of the combustion chamber, so that the plasma can be directly sprayed into the combustion chamber 400. The top air inlet of the combustion chamber is connected with the dielectric barrier plasma air inlet 401. The discharge gas inlet of the dielectric barrier plasma generator 200 is connected with the ammonia storage tank 500 through a corrosion-resistant pipeline, and an ammonia gas flowmeter is connected in the pipeline to control the flow. The top air inlet of the combustion chamber 400 is coaxially provided with a staged ammonia gas inlet, i.e., a staged ammonia injection port 404(1) outside the dielectric barrier plasma generator 200, which is also connected with the ammonia storage tank 500 through a corrosion-resistant pipeline and connected with an ammonia gas flowmeter to control the flow. The top air inlet of the combustion chamber 400 is coaxially provided with a combustion-supporting air inlet outside the dielectric barrier plasma generator 200 and the staged ammonia gas inlet, and the air is provided by the blower 300, connected with the combustion-supporting air inlet through a pipeline and connected with an air gas flowmeter to control the flow.

[0037] As Figure 3 shown, the staged manner involved in the application is coaxial (side wall) staging, two-stage staging and multi-stage staging, and the staged manner is related to different ammonia injection positions and ammonia injection stages. The top of the combustion chamber 400 is provided with multiple coaxial air inlets, the center of which is the dielectric barrier plasma air inlet 401, the outside of which is the staged ammonia injection port 404(1), and the outside of which is the air inlet 402. The bottom of the air inlet is provided with a cyclone 403, and the side wall of the combustion chamber 400 is provided with multiple staged ammonia injection positions 404(2), 404(3) to 404(n). The ammonia injection positions 404(2)-(n) are arranged at different heights on the side wall of the combustion chamber 400. According to different staged manners, the corresponding ammonia staging scheme is selected:

[0038] Scheme one, coaxial staging, when using coaxial staging, the staged ammonia gas is injected from the staging ammonia injection port 404(1);

[0039] Scheme two, side wall staging, when using side wall staging, the staged ammonia gas is injected from the ammonia injection location 404(2);

[0040] Scheme three, two-stage staging, when using two-stage staging, the staged ammonia gas is injected from any two of the staging ammonia injection port 404(1) to the ammonia injection location 404(n);

[0041] Scheme four, multi-stage staging, when using multi-stage staging, the staged ammonia gas is injected from any multiple of the staging ammonia injection port 404(1) to the ammonia injection location 404(n);

[0042] As shown in Figure 4 The medium barrier plasma generator 200 used in the present application includes a ground electrode 201, an insulating medium 202, a high voltage electrode 203, a cyclone 204, and a discharge gas passage 205. The high voltage electrode 203 is installed in the insulating medium 202 but does not contact it; the gap between the ground electrode 201 and the insulating medium 202 is the discharge gas passage 205, and the discharge gas in the present system is ammonia gas; the cyclone 204 is installed at the front end of the generator outlet to generate plasma cyclone, and the insulating medium 202 and the high voltage electrode 203 pass through the center of the cyclone 204. The ground electrode 201 is a grounded metal shell. For example, the insulating medium 202 and the high voltage electrode 203 are located inside the ground electrode 201.

[0043] The use method of an ammonia fuel staged combustion system based on plasma combustion support of the present application is as follows:

[0044] 1. Design the working condition, design the high-frequency high-voltage power supply parameters according to the actual situation, design the parameters of the staging mode, the staging ratio, the staging ammonia injection location, the ammonia gas flow, and the combustion-supporting air flow;

[0045] 2. Connect the pipeline, connect the system components according to the schematic diagram and the required staging mode;

[0046] 3. Input parameters, turn on the power supply, and input the control parameters on the high-frequency high-voltage power supply and the gas flow controller;

[0047] 4. Run the system, open the gas distribution system, and input the ammonia gas and the combustion-supporting air for plasma discharge, then start the medium barrier plasma generator for discharge, and finally input the staged ammonia gas for combustion;

[0048] 5. Analysis and detection, for the detection of the combustion condition in the combustion chamber, a sampling tube is inserted into the combustion chamber to sample and analyze the flue gas, and the NOx pollutant emission is analyzed and detected.

[0049] The technical solution provided by the application has been verified in actual experimental research and ideal experimental results have been obtained. Table 1 is the experimental conditions used in the actual experimental research. In the experiment, ammonia gas is used as the discharge gas, and the fuel staging combustion technology is used. A part of the ammonia gas is discharged by the dielectric barrier discharge plasma generator, and the other part of the ammonia gas is directly injected from the sidewall (0.2 m or 0.45 m) of the combustion chamber. The total ammonia gas amount is controlled at 10 SLM, and the excess air coefficient is controlled at α = 1.2. The staging ratio is the percentage of the ammonia plasma flow to the total ammonia gas amount under the condition that the total ammonia gas amount is 10 SLM.

[0050] The ammonia injection position refers to the distance between the ammonia injection port of the sidewall ammonia injection and the vertical height of the horizontal plane between the top of the combustion chamber and the gas inlet port. The experiment is carried out at the ammonia injection position of 0.2 m and 0.45 m. The total ammonia flow is based on the required set value, aiming to study the combustion under different staging conditions by fixing the total flow of the ammonia gas. The excess air coefficient α refers to the ratio of the actual air amount supplied for combustion to the theoretical air amount. In order to ensure sufficient combustion of ammonia fuel, generally, excess air is supplied, that is, α > 1. In the experiment, α is set to 1.2. The air flow is calculated based on the theoretical combustion air requirement of the total ammonia flow and combined with the excess air coefficient. The air is provided by an air blower, and the flow size is controlled by an air gas flow meter. The plasma ammonia flow ratio refers to the ratio of the plasma ammonia flow to the total ammonia flow when the total ammonia flow is allocated to plasma discharge and sidewall ammonia injection. Different ratios determine the size of the ammonia flow through plasma discharge. In the experiment, the combustion in the combustion chamber under the conditions that the plasma ammonia flow ratio is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 is studied. The ammonia gas is provided by an ammonia storage tank, and the plasma ammonia flow and the sidewall ammonia injection flow are controlled by an ammonia gas flow meter.

[0051] Table 1 Ammonia plasma discharge assisted ammonia staging combustion condition table

[0052]

[0053] By sampling and analyzing the flue gas in the combustion chamber when the plasma assists ammonia combustion under different staging ratios and different ammonia injection positions (0.2 m or 0.45 m), the NOx concentration distribution diagram is obtained, as shown in Figure 1

[0054] Figure 1 ​​It can be clearly seen from the figure that when all the ammonia is combusted by plasma, the NOx generation is about 100 ppm; when the ammonia is combusted by plasma in stages, with the decrease of the plasma ratio of ammonia, the plasma NOx emission begins to decrease, and when the plasma ratio is 0.8, the NOx reaches the lowest value. When the ammonia is injected in different positions in stages, the NOx generation is also different. Injecting ammonia near the outlet of the combustor is beneficial to reduce the generation of NOx. When the ammonia is combusted in stages near the outlet of the combustor, the low point of NOx emission appears when the ratio is 0.8 in the two ammonia injection positions. At this time, the NOx concentrations are 32.4 mg / m 3 and 30.05 mg / m 3 (reduced to 6% O2), which reaches the standard of ultra-low NOx emission.

[0055] The part of the present application which is not described in detail belongs to the known technology of those skilled in the art. The above-described embodiments only describe the preferred embodiments of the present application, and the preferred embodiments do not describe all the details and limit the present application to the specific embodiments. Various modifications and improvements of the technical solutions of the present application made by those skilled in the art without departing from the design spirit of the present application shall fall within the protection scope of the present application defined by the claims.

Claims

1. A staged ammonia combustion system based on low NOx generation of ammonia fuel with plasma-assisted combustion, characterized in that, It comprises a dielectric barrier plasma generator, a high-frequency high-voltage power supply, a gas distribution system and a combustion chamber. The high-voltage electrode is installed in the insulating medium but not in contact with the insulating medium. The high-frequency high-voltage power supply is connected with the high-voltage electrode of the dielectric barrier plasma generator through a high-voltage line, and the high-frequency high-voltage power supply leads out a grounding line connected with the grounded metal shell of the dielectric barrier plasma generator. The discharge gas inlet of the dielectric barrier plasma generator is connected with the ammonia storage tank. The top inlet of the combustion chamber is coaxially provided with a staged ammonia gas inlet outside the dielectric barrier plasma generator, and the staged ammonia gas inlet is connected with the ammonia storage tank.

2. The system of claim 1, wherein, The combustion chamber is provided with a plurality of groups of coaxial inlets at the top thereof, the center of which is a dielectric barrier plasma inlet, and the outside of which is a staged ammonia and air inlet in sequence from the center to the outside.

3. The system of claim 1, wherein, The dielectric barrier plasma generator is of a coaxial structure, thereby increasing the ionization efficiency of ammonia gas.

4. The system of claim 1, wherein, Ammonia gas is directly ionized by a dielectric barrier plasma generator, thereby generating hydrogen (H2), nitrogen (N2), amino radical (NH2), amino radical ion (NH2 - ), and amino ion (NH3 + ) products, while the temperature of the discharge zone is raised to ignite the gas.

5. The system of claim 1, wherein, A part of ammonia gas is introduced into the ammonia plasma flame through the concentric sleeve pipe or the burner side wall, at this time, the ammonia gas combustion further consumes oxygen to form a low-oxygen region, and the NOx generated in the flame is reduced under the action of low-oxygen ammonia gas, thereby effectively inhibiting the generation of NOx.

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