A low-nox catalytic burner for ammonia fuel

Abstract

The application provides a low-NOx catalytic burner for ammonia fuel, which comprises a catalyst fixing device, three air supply pipes and a burner fixing device, and the ammonia gas combustion of the burner is divided into three stages, including an ignition stage, a mixed combustion stage and a stable combustion stage; the combustible gas ethylene is used for combustion, the ammonia gas is introduced after the flame is stabilized, the gas flow ratio of each stage is controlled, and thus the ammonia gas can be stably combusted; the ammonia gas combustion process is carried out in a special nickel modified iron-based catalyst, the ammonia gas conversion rate and nitrogen selectivity can be improved after the ammonia gas is catalytically combusted, the emission of nitrogen oxides such as NO and NO2 is greatly reduced, and finally the product is basically nitrogen and water. The application can make the ammonia gas combustion safer and more reliable, is convenient to operate and green and environmentally-friendly, and provides a possibility for the ammonia gas as a carbon-free alternative energy.

Description

Technical Field

[0001] This invention relates to the field of ammonia combustion technology, and more specifically to a low-NOx catalytic combustor for ammonia fuel. Background Technology

[0002] Ammonia, as a carbon-free fuel, does not produce large amounts of CO2 during combustion. Furthermore, compared to H2, ammonia is easier to store, transport, and produce, thus it is considered one of the most promising fuels. In terms of combustion performance, ammonia's volumetric energy density is comparable to that of conventional fuels. Therefore, ammonia combustion has attracted widespread attention, and using it as a fuel could alleviate our dependence on fossil fuels.

[0003] Ammonia combustion presents numerous problems: low combustion rate, high ignition temperature, poor flame stability, and NO content. x Issues such as emissions exist. Therefore, using ammonia as a single fuel in practical combustion devices still faces many challenges. Currently, many scholars have proposed a combustion method that co-fires ammonia with hydrocarbon fuels, seeking an optimal balance between reducing greenhouse gas emissions and improving flame stability. Much research currently focuses on the co-fired combustion of NH3 with H2 or CH4; due to the low reactivity and difficulty in ignition of NH3, research on the combustion of pure NH3 remains relatively scarce.

[0004] Catalytic combustion has been applied to gas turbines, boilers, and jet engines since the 1980s. By applying a novel catalytic combustion system to NH3 fuel, it is hoped that low-temperature ignition and low NO content can be achieved. x Emissions. Regarding catalyst selection, some scholars have proposed CuO as an effective choice for ammonia catalytic combustion. Copper oxide catalysts exhibit good N2 selectivity in NH3 combustion. Studies have shown that CuO exhibits high NO and NO2 selectivity under lean combustion conditions; however, at an equivalence ratio of 1, the production of NO and NO2 decreases. An increase in N2 selectivity was observed with increasing O2 content, but the specific reason remains unclear. Based on this research, it is recommended to use optimized support materials to enable the NH3-NO reaction on CuO to overcome... The combustion of NH3-O2 produces N2O and NO. x The problem.

[0005] Furthermore, in order to achieve high catalytic oxidation performance from NH3 to N2, CuO x CuO-based catalysts have also been extensively studied. x It can be combined with other catalysts such as Pt, Al₂O₃, and RuO₂ to form binary catalysts. Furthermore, related reaction mechanisms, such as CuO, have been proposed. x The reaction mechanism of Al2O3, with the initial reaction as follows:

[0006] 4NH3 + 3O2 → 2N2 + 6H2O (1)

[0007] 4NH3 + 5O2 → 4NO + 6H2O (2)

[0008] Subsequently, the kinetically generated NO(2) is selectively reduced to N2(3) or N2O(4) by the unreacted NH3 in the initial reaction and is absorbed by the catalyst.

[0009] 4NH3 + 4NO + O2 → 4N2 + 6H2O (3)

[0010] 4NH3 + 4NO + 3O2 → 4N2O + 6H2O (4)

[0011] However, relevant studies have shown that during the high-temperature catalytic oxidation of NH3, some CuO is oxidized to Cu2O, leading to oxidant deactivation and affecting the catalytic combustion of ammonia. Therefore, a more effective catalyst is needed for the combustion of ammonia. Fe2O3, as a catalyst, has increased active sites due to the small size of iron oxide particles, a large surface area, different bond and electronic states compared to the interior particles, and different atomic coordination on the surface. Compared to copper oxide, iron oxide is more stable and less prone to deactivation, making it worthy of further investigation. Summary of the Invention

[0012] The purpose of this invention is to provide a low-NOx catalytic combustor for ammonia fuel.

[0013] This invention provides an ammonia catalytic combustor, comprising the following various devices:

[0014] A catalyst tightening device is embedded in the porous media catalyst fixing device and connected to the burner tube protective sleeve. The burner tube protective sleeve and column are embedded inside the fixing disc. Oxygen and nitrogen vent pipes are respectively embedded at the lower left and right ends of the burner tube protective sleeve, and the main fuel pipe is embedded at the bottom end. The oxygen and nitrogen vent pipes are connected to the main fuel pipe.

[0015] This burner divides ammonia combustion into three stages: ignition stage, co-combustion stage, and stable combustion stage. In the ignition stage, ethylene is introduced through the main fuel pipe, nitrogen through the nitrogen inlet pipe, and oxygen through the oxygen inlet pipe. The main fuel pipe mixes these three gases before ignition and combustion. Once the flame stabilizes, ammonia is slowly introduced through the main fuel pipe, and the ethylene flow rate is reduced to enter the co-combustion stage. By observing the flame pattern and controlling the ethylene flow rate in the main fuel pipe to the minimum required for stable combustion, the catalyst is placed inside the porous media catalyst fixing device. The catalyst tightening device then tightens and fixes the catalyst, covering the flame, ultimately achieving the stable combustion stage.

[0016] Preferably, the length of the porous media catalyst fixing device needs to allow the ammonia gas to fully contact within it. Based on the experimental gas flow rate of 1200 ml / min and the main fuel pipe diameter of 4 cm, it is necessary to stay in the porous media for at least 2 to 4 seconds to achieve the catalytic effect.

[0017] Preferably, the porous media catalyst stationary portion is loaded with a nickel-modified iron-based catalyst (NiO / Fe2O3), which can be made into honeycomb, spherical, cylindrical, etc.

[0018] Preferably, the diameter of the main fuel pipe ignition hole is 4 cm, which allows the gas inside the pipe to be in a laminar flow state, thereby generating a laminar flame;

[0019] Preferably, both the oxygen inlet pipe and the nitrogen inlet pipe are connected to the left and right sides of the main fuel pipe.

[0020] Preferably, the ignition stage is as follows: First, ethylene, a readily combustible gas, is introduced into the main fuel pipe, while oxygen and nitrogen are introduced into the side vent pipes for combustion, and the flame is allowed to stabilize. The volume ratio of ethylene to oxygen is 1:3; the oxygen and nitrogen are introduced in a volume ratio of 21:79 to simulate air.

[0021] Preferably, the combustible gas that is easy to burn is not limited to ethylene, but can also be methane, hydrogen, etc.

[0022] Preferably, the co-combustion stage is as follows: after the flame stabilizes during the ignition stage, the ethylene flow rate is gradually reduced and ammonia is slowly introduced into the main fuel pipe, and the flame stability is controlled by adjusting the oxygen and nitrogen flow rates.

[0023] Preferably, in the stable combustion stage: while adjusting the flow rates of ethylene and ammonia during the co-combustion stage, the flow rates of oxygen and nitrogen must be continuously adjusted to prevent backfire and flame lifting, thereby controlling the flame stability.

[0024] This invention has significant advantages over existing technologies:

[0025] 1. In practical applications, the size of this burner can be reduced or enlarged at any ratio. The device has a simple structure, low equipment and operating costs, and safe operation, making ammonia combustion more efficient, energy-saving, and economical.

[0026] 2. This burner mixes nitrogen and oxygen in the same proportion as air, allowing ammonia to burn in air. Furthermore, the ammonia flame is designed to be a laminar flow flame through the size of the burner orifice, which improves safety and stability.

[0027] 3. Compared with previous catalysts, the nickel-modified iron-based catalyst installed in this burner can greatly improve the conversion rate of ammonia and the selectivity of nitrogen, thereby significantly reducing the emission of nitrogen oxides such as NO and NO2. It is green and environmentally friendly, reduces the harm to the environment, and provides the possibility of ammonia as an alternative energy source. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a low-NOx catalytic combustor for ammonia fuel.

[0029] Among them are: (1) a porous medium catalyst fixing device; (2) a catalyst tightening device; (3) a burner tube protective sleeve; (4) a fixing disc; (5) a column; (6) an oxygen inlet pipe; (7) a nitrogen inlet pipe; and (8) a main fuel pipe. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the accompanying drawings. The specific details are intended to explain, but not limit, the present invention.

[0031] A low-NOx catalytic combustor for ammonia fuel according to the present invention includes:

[0032] The catalyst tightening device 2 is embedded in the porous media catalyst fixing device 1;

[0033] It is connected to the burner tube protective sleeve 3, and the burner tube protective sleeve 3 and column 5 are embedded inside the fixed disc 4;

[0034] The lower left and right ends of the burner tube protective sleeve 3 are respectively embedded with oxygen vent pipe 6 and nitrogen vent pipe 7, and the bottom end is embedded with main fuel pipe 8; oxygen vent pipe 6 and nitrogen vent pipe 7 are connected to main fuel pipe 8.

[0035] During the ignition phase, ethylene is introduced into the main fuel pipe 8, nitrogen is introduced into the nitrogen inlet pipe 7, and oxygen is introduced into the oxygen inlet pipe 6. The main fuel pipe 8 mixes the three together and then ignites and burns them.

[0036] After the flame stabilizes, ammonia is slowly introduced into the main fuel pipe 8 and the ethylene flow rate is reduced to enter the co-combustion stage;

[0037] After observing the flame pattern and controlling the ethylene flow rate in the main fuel pipe 8 to decrease to the minimum flow rate required for stable combustion, the catalyst is placed inside the porous media catalyst fixing device 1, and the catalyst tightening device 2 is tightened and fixed to cover the flame, finally achieving the stable combustion stage.

[0038] Furthermore, the length of the porous media catalyst fixing device 1 must be sufficient to allow for adequate contact of ammonia gas within it. Based on the experimental gas flow rate of 1200 ml / min and the main fuel pipe 8 diameter of 4 cm, the gas needs to remain within the porous medium for at least 2–4 seconds to achieve the catalytic effect. The porous media catalyst 1 is a nickel-modified iron-based catalyst, NiO / Fe2O3, manufactured in honeycomb, spherical, or cylindrical shapes. The diameter of the main fuel pipe's flame hole 8 is 4 cm, ensuring laminar flow of the gas within the pipe, thereby generating a laminar flame.

[0039] The present invention discloses a low-NOx catalytic combustor for ammonia fuel. The implementation process is as follows: first, ammonia gas is introduced into the nitrogen gas inlet pipe for two minutes to purge the gas in the pipe. Then, according to the air ratio, the nitrogen:oxygen ratio is 79:21, and oxygen gas of the corresponding ratio flow rate is introduced into the oxygen gas inlet pipe. After the two are completely mixed to simulate the air condition, combustion is prepared.

[0040] The first step is the ignition stage: Ethylene, a combustible gas that is easy to burn, is introduced into the main fuel pipe. According to the combustion chemical formula C2H4(g) + 3O2(g) == 2CO2(g) + 2H2O, the ratio of ethylene flow rate to oxygen flow rate is determined to be 1:3. After the ethylene is introduced, it mixes with oxygen and nitrogen in the pipe and then ignites. After ignition, the proportion of each gas can be adjusted as needed until a stable ethylene flame is obtained.

[0041] Next, the co-combustion phase begins: Once the ethylene flame stabilizes and the flame temperature reaches approximately 1000 degrees Celsius, which is the ignition temperature of ammonia, ammonia is slowly introduced into the main fuel pipe while gradually reducing the ethylene flow rate, maintaining a constant flow rate for nitrogen and oxygen. The ammonia flow rate is determined according to the total flow rate specified in the combustion chemical formula 4NH3 + 3O2 = 2N2 + 6H2O, and is added in a predetermined proportion. At this stage, the gas in the pipe is a mixture of ethylene and ammonia undergoing co-combustion. During the co-combustion phase, the ammonia introduction rate or the ethylene reduction rate can be adjusted appropriately to maintain flame stability and prevent safety hazards, ultimately waiting until the ethylene flow rate is reduced to zero.

[0042] Finally, the pure ammonia stable combustion stage begins: after only ammonia remains in the main fuel pipe, the ammonia flow rate, oxygen flow rate, and nitrogen flow rate are adjusted to meet the ratios required by the chemical equation. Once the ammonia flame is stable, the prepared nickel-modified iron-based catalyst is placed in a porous media catalyst fixing device. Using a catalyst tightening device, the catalyst is positioned directly above the flame and moved downwards until it completely covers the flame. This allows the ammonia to fully contact and catalytically combust within the porous media. This catalyst improves the conversion rate of ammonia and the selectivity of nitrogen, significantly reducing emissions of nitrogen oxides such as NO and NO2.

[0043] In the ignition stage of this invention, compared with modern traditional burners that use an igniter as the ignition source, this burner uses an ethylene flame as the ammonia ignition source, which can provide sufficient ignition energy and eliminates the risk of ammonia leakage, making it safe, efficient and convenient.

[0044] In the co-combustion stage of this invention, by adopting the mode of ignition first and then gas adjustment, not only can the flow rate of the ignition gas ethylene be adjusted to the minimum, thereby maximizing the proportion of ammonia, there is no waste of gas resources and energy utilization can be significantly improved. Moreover, adjusting the gas flow rate while maintaining flame stability can effectively prevent dangerous situations such as backfire and flame lifting, greatly increasing safety and reliability.

[0045] In the stable combustion stage of this invention, based on the formation of a stable ammonia flame, the required catalyst is installed using the catalyst fixing device of the burner and closely attached to the main fuel pipe port. This can significantly increase the contact area and contact time between ammonia and the catalyst, thereby maximizing catalytic efficiency and achieving the goal of green combustion.

[0046] By using ethylene, a readily combustible gas, to ignite ammonia, and controlling the proportions of each gas in each stage to obtain a stable ammonia flame, compared to the current method of igniting ammonia using premixed combustion, not only can the combustion of ammonia be guaranteed to proceed smoothly, but safety is also greatly improved.

[0047] This invention involves three successive combustion stages, ultimately achieving catalytic combustion in which ammonia accounts for up to 70% of the volume of the mixed fuel. This reduces NOx emissions in the exhaust gas by 39.6% to 72.5% and CO generation by 5.3% to 66.4%, promoting the rapid development of low-carbon energy—ammonia—and laying the foundation for its future energy utilization.

Claims

1. A method of using a low-NOx catalytic combustor for ammonia fuel, characterized in that, The burner includes: A catalyst tightening device (2) is embedded in a porous media catalyst fixing device (1); The porous media catalyst fixing device (1) is connected to the burner tube protective sleeve (3), and the burner tube protective sleeve (3) and the column (5) are embedded inside the fixing disc (4). The lower left and right ends of the burner tube protective sleeve (3) are respectively embedded with oxygen inlet pipe (6) and nitrogen inlet pipe (7), and the bottom end is embedded with main fuel pipe (8); oxygen inlet pipe (6) and nitrogen inlet pipe (7) are connected to main fuel pipe (8); The method is as follows: when entering the ignition stage, the combustible gas ethylene is introduced into the main fuel pipe (8), nitrogen is introduced into the nitrogen inlet pipe (7), and oxygen is introduced into the oxygen inlet pipe (6). The main fuel pipe (8) mixes the three together and then ignites and burns them. After the flame stabilizes, ammonia is slowly introduced into the main fuel pipe (8) and the flow rate of ethylene, a combustible gas, is reduced to enter the co-combustion stage; After observing the flame pattern and controlling the flow rate of ethylene gas in the main fuel pipe (8) to reduce to the minimum flow rate required for stable combustion, the catalyst is placed inside the porous media catalyst fixing device (1), and the catalyst tightening device (2) is tightened and fixed and then covered on the flame, finally reaching the stable combustion stage. The length of the porous media catalyst fixing device (1) needs to be sufficient for ammonia to fully contact within it; The porous media catalyst is a nickel-modified iron-based catalyst NiO / Fe2O3, which is made into honeycomb, spherical or cylindrical shapes; The main fuel tube has a 4cm diameter orifice, which keeps the gas in the tube in a laminar flow state, thereby generating a laminar flame. During the co-combustion stage, while adjusting the flow rates of ethylene and ammonia, it is necessary to continuously adjust the flow rates of oxygen and nitrogen to prevent backfire and flame lifting, thereby controlling the flame stability.

2. The method of use according to claim 1, characterized in that, The oxygen inlet pipe (6) and the nitrogen inlet pipe (7) are respectively connected to the left and right sides of the main fuel pipe (8).

3. The method of use according to claim 1, characterized in that, During the ignition stage, ethylene, a flammable gas that is easy to burn, is first introduced into the main fuel pipe, while oxygen and nitrogen are introduced into the two side vent pipes for combustion, and the flame is allowed to stabilize. The volume ratio of ethylene to oxygen is 1:3, and the volume ratio of oxygen to nitrogen is 21:79 to simulate the state of air.

4. The method of use according to claim 1, characterized in that, The flammable gas ethylene can also be selected as methane or hydrogen.

5. The method of use according to claim 3, characterized in that, Stable combustion stage: After the ethylene flow rate drops to the minimum flow rate required for stable combustion, and the ammonia flame stabilizes, control the mass flow rate ratio of ammonia to oxygen to be 4:

3. At the same time, adjust the flow rates of each gas in real time according to the oxygen to nitrogen ratio described in the ignition stage.

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