A system for promoting low temperature ignition of ammonia fuel using nitrogen oxides

Abstract

The present invention belongs to the field of energy utilization, and specifically relates to a system that utilizes nitrogen oxides to promote the low-temperature ignition of ammonia fuel, including a storage unit, an ammonia combustion unit, a flue gas catalytic oxidation unit and an adsorption regeneration unit connected in sequence, and the output end of the adsorption regeneration unit is also connected to the ammonia combustion unit. The ammonia fuel is transported from the storage unit to the ammonia combustion unit, and the ammonia fuel is mixed with an oxygen source and a promoter for combustion. The flue gas generated by the combustion enters the flue gas catalytic oxidation unit and is processed into circulating gas. Part of the circulating gas is returned to the ammonia combustion unit as a promoter, and the remaining part of the circulating gas is concentrated in the adsorption regeneration unit and returned to the ammonia combustion unit as a promoter. The promoter is a NO / NO2 mixed gas. Compared with the prior art, the present invention effectively solves the problems of difficult ignition of ammonia fuel combustion, low flame propagation speed and NO x It can solve the problems of emission, reduce the ignition temperature of ammonia, and increase the flame propagation speed, thereby significantly improving the comprehensive utilization performance of ammonia fuel.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of energy utilization, and particularly relates to a system for promoting low-temperature ignition of ammonia fuel by using nitrogen oxides. BACKGROUND

[0002] Under the background of global response to climate change, the greenhouse gas emission problem of the shipping industry has attracted global attention. Compared with other industries, due to the difficulty of adopting electrification in the energy and power system of ocean shipping, the dependence on oil-based fuel is relatively strong, resulting in greater difficulty in carbon emission reduction than other industries. At present, the clean alternative fuels for ship energy mainly include low-carbon fuels such as liquefied natural gas, methanol, biomass mixed fuel, and zero-carbon alternative fuels such as hydrogen and ammonia. In the long run, under the background of double carbon emission reduction, only the use of fossil fuels without carbon can achieve clean energy utilization for ocean-going ships. Since ammonia is easy to liquefy, the energy density of liquid ammonia is almost twice that of liquid hydrogen, and it is expected to become a competitive choice for zero-carbon emission ships. Large-scale storage and utilization of ammonia on ships is one of the future development trends.

[0003] The potential application value of ammonia as fuel in the field of ships has attracted widespread attention. Ammonia not only has the function of zero-carbon fuel, but also plays an important role in the reduction and resource utilization of NO x . However, when using traditional combustion methods, there are two major bottleneck problems in the direct use of ammonia fuel: one is the difficulty in ignition due to the low chemical activity of ammonia, the low flame propagation speed, and the need for ignition with other fuels; the other is that due to the presence of nitrogen atoms in ammonia molecules, ammonia combustion will produce a large amount of NO x emission and ammonia escape, which will also generate N2O with strong greenhouse effect. In order to solve the problems of difficult ignition of ammonia fuel and high NO x emission, it is necessary to strengthen ammonia fuel combustion and coordinate the generation of pollutants. Therefore, it is necessary to develop efficient strengthening technology and post-processing process for ammonia fuel combustion.

[0004] Most of the existing technologies for fuel systems or combustion devices are focused on traditional fossil fuels, such as CN202010289078.5, CN201811489800.9, etc. A small part of the research focuses on the combustion of biomass fuel, such as CN201710115255.6, CN201010500581.7, etc. There is no suitable system and device for ammonia or ammonia fuel combustion. Therefore, in order to cooperate with the use of ammonia fuel, it is urgent to propose a suitable combustion system. SUMMARY

[0005] The purpose of the present application is to provide a system for promoting low-temperature ignition of ammonia fuel by using nitrogen oxides, in order to solve the problems of difficult ignition, low flame propagation speed, and NO xThe system realizes the effect of reducing the ammonia ignition temperature by 200-300 DEG C and increasing the flame propagation speed by more than 5 times, so that the comprehensive utilization performance of the ammonia fuel is obviously improved.

[0006] The object of the present application is achieved by the following technical solutions.

[0007] A system for promoting low-temperature ignition of ammonia fuel by nitrogen oxides, comprising a storage unit, an ammonia combustion unit, a flue gas catalytic oxidation unit and an adsorption regeneration unit connected in sequence; the output end of the adsorption regeneration unit is also connected with the ammonia combustion unit;

[0008] The ammonia fuel is delivered from the storage unit to the ammonia combustion unit, and the ammonia fuel is mixed with an oxygen source and a promoter to combust, and the flue gas generated by combustion is treated in the flue gas catalytic oxidation unit to become a circulating gas, part of the circulating gas is returned to the ammonia combustion unit as a promoter, and the remaining part of the circulating gas is returned to the ammonia combustion unit as a promoter after being concentrated by the adsorption regeneration unit; the promoter is a NO / NO2 mixed gas.

[0009] Preferably, the ammonia fuel is ammonia gas or a mixed gas formed by ammonia gas and natural gas; the volume content of oxygen in the oxygen source is 10-40 vol%; the addition amount of the promoter is 5-15 vol% of the amount of the ammonia fuel, and the content of NO2 is 20-50 vol%.

[0010] Preferably, the ammonia combustion unit comprises an ignition zone and a main combustion zone, and the oxygen source and the promoter are added to the ammonia combustion unit from the ignition zone, and the ammonia fuel is added to the ammonia combustion unit from the ignition zone and the main combustion zone respectively; when the combustion temperature is lower than 850 DEG C, NO2 in the mixed gas plays a main combustion promoting role, and when the combustion temperature is higher than 850 DEG C, NO in the mixed gas also plays a combustion promoting role.

[0011] In the ignition zone, in the low-temperature initial combustion stage (<850 DEG C), the fast reaction rule and mechanism of NO2 and ammonia fully play the chain transmission role and the heat release self-sustaining ignition effect of the combustion promoting reaction, and at a slightly high temperature (>850 DEG C), NO2 can continuously promote the ammonia combustion. In the presence of nitrogen oxides, the ammonia combustion in the main combustion zone is obviously accelerated, while ensuring the combustion output power, the generation of NO x , N2O and other pollutants is reduced.

[0012] When the ammonia fuel is liquid ammonia, it should be stored in a storage tank with a temperature lower than 50 DEG C and a working pressure not greater than 2.5 MPa; the liquid ammonia is warmed and vaporized after passing through a gasification heat exchanger, and then is sent to the combustion ignition zone device, and part of the input to the main combustion zone can use vaporized ammonia or directly spray liquid ammonia as fuel.

[0013] Preferably, the flue gas catalytic oxidation unit uses an oxidation catalyst and a common dielectric barrier discharge or pulsed corona discharge to treat the flue gas, decompose a small amount of N2O, and convert NO into NO2, which is easy to adsorb, adjust the ratio of NO2 / NO, and adjust the promoter concentration to 0.5-5 vol% of the total concentration of the circulating gas, with the content of NO2 being 20-50 vol%.

[0014] Preferably, the system further comprises an ammonia catalytic oxidation unit, which catalytically oxidizes 2-10 vol% of ammonia fuel into a promoter before inputting the ammonia combustion unit.

[0015] Preferably, the flue gas catalytic oxidation unit uses one of Pt / CeO2, Pt / Al2O3, Ru / CeO2, and Ru / Al2O3 as the catalyst; the ammonia catalytic oxidation unit uses a noble metal catalyst, and one of the Pt and Ru composite catalysts described above as the catalyst, with the reaction temperature being 300-500℃, and the heat released by the reaction being used for preheating of the ammonia fuel and the oxygen source.

[0016] Preferably, 50-70 vol% of the circulating gas is directly returned to the ammonia combustion unit, and the remaining circulating gas is input into the adsorption regeneration unit.

[0017] Preferably, the adsorption regeneration unit is Pd-SSZ-13 molecular sieve; when the adsorption regeneration unit is saturated to 70-80 vol%, it is regenerated, and the desorbed circulating gas is returned to the ammonia combustion unit.

[0018] The promoter returned to the ammonia combustion unit by the adsorption regeneration unit and the additional promoter input into the ammonia combustion unit by the ammonia catalytic oxidation unit ensure sufficient content of the promoter in the ammonia combustion unit.

[0019] Preferably, the system further comprises a waste heat recovery unit, which is connected between the ammonia combustion unit and the flue gas catalytic oxidation unit, and is used for recovering waste heat in the flue gas.

[0020] Preferably, the waste heat recovery unit reduces the temperature of the flue gas from 700-1000℃ to 350℃ before inputting the flue gas into the flue gas catalytic oxidation unit.

[0021] The principle of the accelerator is that nitrogen oxides accelerate the chain transfer of the reaction between ammonia and oxygen, and in the process, nitrogen oxides are also gradually reduced by ammonia to harmless nitrogen. There are two sources of nitrogen oxides in the complete system, one is that when the combustion temperature is high, part of the ammonia is over-oxidized to produce a certain amount of nitrogen oxides (mainly NO), which can be converted into NO2 for recycling and utilization during the exhaust emission process; the second is to convert 2-10% of the ammonia fuel into NO and NO2 in advance through a catalytic oxidation unit to ensure a stable and sufficient supply of nitrogen oxides.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] The present application adopts NO x As an ammonia combustion accelerator, it overcomes the problems of high ignition temperature and low flame propagation speed of ammonia fuel. At the same time, with the help of catalytic oxidation and adsorption storage, NO2 in the exhaust gas of ammonia fuel combustion is separated, enriched and adsorbed for recycling, thereby realizing efficient combustion and zero pollutant emission of ammonia fuel simultaneously. With the help of NO2 accelerator, a low-temperature ignition combustion system of NH3 fuel can be constructed, which can improve the mixed combustion efficiency, promote the innovative breakthrough of pollution reduction and carbon neutralization, and form a green energy system for ships under the background of double carbon reduction in China. The related technical methods will provide support for the energy system of the ship industry, effectively promote the development of energy structure adjustment, pollution control and resource utilization of ships, and have good economic and environmental benefits.

[0024] Through the above promotion, the ammonia ignition temperature can be reduced by 200-300 DEG C, and the flame propagation speed can be increased by more than 5 times, so that the comprehensive utilization performance of ammonia fuel is significantly improved.

[0025] The system proposed in the present application not only breaks through the bottleneck problem of ammonia fuel combustion, but also has good application potential in the fields of natural gas, ammonia / natural gas mixed combustion, etc.

[0026] The present application realizes the comprehensive utilization of ammonia fuel raw materials and effectively improves the low-temperature combustion performance.

[0027] In the present application, ammonia not only has the function of zero-carbon fuel, but also realizes the end-of-pipe nitrogen oxides emission reduction and recycling.

[0028] The present application has the advantages of simple and compact overall structure, economy and practicality, can realize zero emission of air pollutants and greenhouse gases, reasonably recycles the waste heat of combustion, and has good application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a structural schematic diagram of the system;

[0030] Figure 2Structure schematic diagram for the internal combustion engine in Example 1;

[0031] In the figure: 1 - storage unit; 2 - ammonia combustion unit; 3 - flue gas catalytic oxidation unit; 4 - adsorption regeneration unit; 5 - ammonia catalytic oxidation unit; 6 - waste heat recovery unit. DETAILED DESCRIPTION

[0032] The present application will be described in detail below with reference to the accompanying drawings and specific examples.

[0033] A system for promoting low-temperature ignition of ammonia fuel by nitrogen oxides, as shown in the figure, comprises a storage unit 1, an ammonia combustion unit 2, a flue gas catalytic oxidation unit 3 and an adsorption regeneration unit 4 connected in sequence; the output end of the adsorption regeneration unit 4 is also connected to the ammonia combustion unit 2. Figure 1

[0034] The ammonia fuel is delivered from the storage unit 1 to the ammonia combustion unit 2, where it is mixed with an oxygen source and a promoter and combusted, and the flue gas generated by the combustion is treated in the flue gas catalytic oxidation unit 3 to become circulating gas, part of which is returned to the ammonia combustion unit 2 as a promoter, and the remaining part is concentrated by the adsorption regeneration unit 4 and then returned to the ammonia combustion unit 2 as a promoter.

[0035] The promoter is a mixture of NO and NO2.

[0036] More specifically,

[0037] ​The system and method for promoting ammonia fuel low-temperature ignition by using nitrogen oxides mainly includes the following steps: (1) liquid ammonia is sent into the ignition zone of the combustion device after gasification as fuel, air or oxygen-containing gas stream is used as the oxygen source required for combustion, and a certain amount of NO / NO2 is mixed as a combustion promoter (nitrogen oxides recovered from ammonia combustion tail gas, or nitrogen oxides prepared by catalytic oxidation of ammonia, and the ratio of NO2 / NO is adjusted by a suitable oxidation method, which is used as an ammonia combustion ignition promoter), so that the fuel can be smoothly ignited in the combustion device and fully combusted in the main combustion zone. (2) After the flue gas (or tail gas) after combustion is cooled by a high-temperature waste heat boiler, it is subjected to control processes such as catalytic oxidation and adsorption storage, and part of it is recycled as flue gas, which is sent back to the combustion device by a fan. By reasonable grading and proportioning of the fuel and flue gas recirculation, the generation of nitrogen oxides in the flue gas is reduced, and efficient combustion of ammonia fuel is realized. (3) The tail gas after full combustion of ammonia is discharged from the burner, when the ammonia combustion temperature is high, a certain amount of NO is generated by the excessive oxidation of ammonia, which can be further catalytically oxidized to NO2 by a suitable method during the discharge process, and then recovered by adsorption and recycled as a combustion promoter. Mainly using the effects of oxidation catalyst and discharge plasma, a small amount of N2O is decomposed, and NO is converted into NO2 which is easy to adsorb. (4) An appropriate amount of adsorbent is used at the tail of the combustion to adsorb and store nitrogen oxides. With the help of molecular sieve adsorbent, NO2 produced by combustion is adsorbed and stored. When the storage amount of NO2 reaches 70-80 vol. % of the saturation value, the molecular sieve adsorbent is regenerated to obtain high-concentration NO2 gas, which is recycled to promote low-temperature combustion of ammonia fuel. (5) In order to ensure a stable and sufficient supply of nitrogen oxides, ammonia fuel can be pre-oxidized to NO and NO2 by an ammonia catalytic oxidation unit 5. The catalyst required for this process is a noble metal catalyst such as Pt and Ru, and the reaction temperature is 300-500℃. The heat released by the reaction can be used for preheating of the fuel or air. (6) Through the above promotion, the ammonia ignition temperature can be reduced by 200-300℃, and the flame propagation speed can be increased by more than 5 times, so that the comprehensive utilization performance of ammonia fuel is significantly improved.

[0038] Ammonia combustion refers to the combustion process of ammonia or ammonia / natural gas mixture as fuel by mixing with a certain amount of air or oxygen-containing gas stream, including combustion in internal combustion engines, gas turbines or gas boilers, etc. There is an ignition stage or ignition zone in the combustion process.

[0039] When the ammonia fuel is liquid ammonia, it should be stored in a storage tank (storage unit 1) with a temperature below 50°C and a working pressure of no more than 2.5 MPa. The liquid ammonia in the liquid ammonia tank is sent to the combustion pilot area device after being warmed and gasified by the gasification heat exchanger. The main combustion area can use the gasified ammonia gas or directly inject liquid ammonia into the main combustion area as fuel.

[0040] The oxygen source for combustion is mainly air (the air in the atmosphere can be directly taken without setting an oxygen source storage unit 1), or an oxygen-containing gas stream (an oxygen source storage tank needs to be set in the storage unit 1). The oxygen content is 10-40 vol.%, and the rest can be nitrogen. The residual oxygen concentration in the flue gas after combustion is 1-5 vol.%, and the rest is nitrogen and water vapor except a small amount of nitrogen oxides generated during combustion.

[0041] The ammonia gas to be combusted is premixed with air during the process of entering the ammonia combustion unit 2, and according to the characteristics of the ammonia combustion unit 2, a gas stream containing a nitrogen oxide promoter is quickly injected into the ignition area or the pilot area before ignition.

[0042] The amount of nitrogen oxide promoter added in the pilot area is 5-15 vol.% of the amount of ammonia fuel in the area, and the NO2 content in the total nitrogen oxides is 20-50 vol.%, and the rest is NO. There are two sources of nitrogen oxides, one is that when the combustion temperature is high, part of the ammonia gas is over-oxidized to produce a certain amount of nitrogen oxides (mainly NO), which can be converted to NO2 for recycling and utilization during the exhaust emission process; the second is to convert 2-10% of the ammonia fuel through an ammonia catalytic oxidation unit 5 to NO and NO2 to ensure a stable and sufficient supply of nitrogen oxides.

[0043] The ammonia combustion unit 2 can use one of a gas-fired boiler, an internal combustion engine, or a gas turbine, or a combination thereof, to reduce the concentration of nitrogen oxides in the exhaust flue gas by partial flue gas recirculation combustion.

[0044] The addition of nitrogen oxides can be different for different ammonia combustion units 2. For gas-fired boilers or gas turbines, they can be directly mixed into the primary air or recirculated flue gas to play a role in the pilot area. For internal combustion engines, they can be injected into the ignition area and mixed quickly before the end of compression and ignition.

[0045] The ammonia combustion unit 2 mainly comprises an ignition zone and a main combustion zone. In the ignition zone, a low-temperature initial combustion stage (<850°C), the ammonia reacts rapidly with oxygen under the excitation of NO2, realizing rapid ignition and temperature rise, the rapid reaction rule and mechanism of NO2 and ammonia, fully exerting the chain transfer effect and the self-sustaining ignition effect of the combustion promoting reaction; at a slightly higher temperature (>850°C), NO can promote the continuous combustion of ammonia, and under the continuous action of the two, the combustion rate and flame propagation speed are further improved. In the presence of nitrogen oxides, the ammonia combustion in the main combustion zone is significantly accelerated, which reduces the generation of NO x and N2O and other pollutants while ensuring the output power of the combustion.

[0046] The flue gas discharged from the ammonia combustion unit 2 passes through the waste heat recovery unit 6, which can use a conventional waste heat recovery boiler to reduce the flue gas temperature from 700-1000°C to about 350°C. The tail gas after recovering waste heat passes through the oxidation catalyst and the action of the discharge plasma in the flue gas catalytic oxidation unit 3 to decompose a small amount of N2O therein and convert NO into NO2 that is easy to adsorb, adjust the ratio of NO2 / NO, and adjust the total concentration of nitrogen oxides after adjustment to 0.5-5vol.%, and NO2 accounts for 20-50vol.% thereof.

[0047] Thereafter, 50-70% of the flue gas is returned to the combustion device through the induced draft fan for flue gas recirculation. The remaining 30-50% of the flue gas is stored and treated by the molecular sieve adsorbent in the adsorption regeneration unit 4. When the storage amount of NO2 reaches 70-80vol.% of the saturation value, the adsorbent is regenerated to obtain high-concentration NO2 gas, which is returned to the combustion device through the induced draft fan for recycling.

[0048] The noble metal catalytic material required for the conversion of NO to NO2 is any one of Pt / CeO2, Pt / Al2O3, Ru / CeO2, and Ru / Al2O3; the ammonia catalytic oxidation unit 5 uses ammonia catalytic oxidation to prepare NO x The required catalyst is any one of the noble metal catalysts such as Pt and Ru as described above, the reaction temperature is 300-500°C, and the heat released by the reaction can be used for preheating of fuel or air; the NO2 adsorption material in the tail gas is a molecular sieve adsorption material, the composition of which can be a commercially available product Pd-SSZ-13.

[0049] The purified tail gas can be directly discharged or partially used as circulating flue gas for the burner.

[0050] In addition, a buffer tank that can be shared after the adsorption regeneration unit 4 and after the ammonia catalytic oxidation unit 5 can be provided for storage, buffering, and mixing of the circulating gas and the promoter.

[0051] Example 1

[0052] As shown in Figure 2 A kind of internal combustion engine system using nitrogen oxide promotes low temperature ignition of ammonia fuel, mainly includes: fuel supply device (corresponding storage unit 1, only show supply passage in the figure), combustion device (ammonia internal combustion engine, corresponding ammonia combustion unit 2), NO 2 Capture / regeneration unit (corresponding to flue gas catalytic oxidation unit 3 and adsorption regeneration unit 4), NH 3 Catalytic oxidation unit (corresponding to ammonia catalytic oxidation unit 5) and so on.

[0053] In the internal combustion engine system:

[0054] After gasification, liquid ammonia is sent into ammonia internal combustion engine as fuel, uses air as the oxygen source required for combustion, is drawn into ammonia internal combustion engine by air compression pump, while mixing a certain amount of NO / NO 2 as combustion promoter, so that ammonia fuel can be ignited smoothly and fully combusted in ammonia internal combustion engine. After the flue gas (or exhaust gas) after combustion is cooled by high-temperature waste heat boiler, it is subjected to control processes such as catalytic oxidation and adsorption storage, part of it is recycled as flue gas, which is sent back to ammonia internal combustion engine by fan. Through reasonable grading and proportioning of fuel and flue gas recirculation, the generation of nitrogen oxides in flue gas is reduced, and efficient combustion of ammonia fuel is realized.

[0055] When the ammonia combustion temperature is high, part of the ammonia gas is over-oxidized to generate NO emissions, which can be further catalytically oxidized to NO 2 by oxidation catalyst and discharge plasma for recycling and recycling; at the tail of the combustion, with the help of molecular sieve adsorbent, the combustion product NO 2 is adsorbed and stored, and when the storage amount of NO 2 reaches 70-80vol.% of the saturation value, the molecular sieve adsorbent is regenerated to obtain high-concentration NO 2 gas and is recycled to promote low-temperature combustion of ammonia fuel. The molecular sieve adsorbent needs to be connected in parallel with at least one pair, so that the system can be operated continuously, and when one or more molecular sieve adsorbents are desorbed and regenerated, the other one or more molecular sieve adsorbents are adsorbed.

[0056] To ensure stable and sufficient supply of nitrogen oxides, ammonia fuel is oxidized to NO and NO 2 by a catalytic oxidation unit in advance, the catalyst required for this process is a noble metal catalyst such as Pt or Ru, and the reaction temperature is about 450°C; the NO 2 adsorption material in the exhaust gas is a molecular sieve adsorption material, and the main component is Pd-SSZ-13.

[0057] Application example 1

[0058] The internal combustion engine system provided in Example 1 is used.

[0059] For the use of ammonia fuel in the internal combustion engine (such as Figure 2The liquid ammonia is stored in a tank at a temperature <50℃ and a working pressure <2.5MPa. The liquid ammonia is warmed and vaporized by a vaporization heat exchanger, and then is sent into the combustion device together with air. The oxygen content in the ignition zone is 10% (volume concentration). The amount of nitrogen oxide promoter added in the ignition zone is 5% of the total amount of ammonia fuel, in which the proportion of NO2 in the nitrogen oxide is 20%, and the rest is NO. The flue gas discharged from the combustion device is passed through a waste heat recovery boiler to reduce its temperature from 700℃ to 350℃. 50% of the flue gas is returned to the combustion device by an induced draft fan to further catalytically oxidize the NO produced by the excessive oxidation of ammonia gas into NO2 for recycling and utilization. The remaining 50% of the flue gas is stored and treated by a molecular sieve adsorbent. When the storage amount of NO2 reaches 70%, the adsorbent is regenerated to obtain high-concentration NO2 gas, which is returned to the combustion device by an induced draft fan for recycling. In order to ensure a stable and sufficient supply of nitrogen oxides, the ammonia fuel is pre-oxidized into NO and NO2 by a catalytic oxidation unit. The catalyst required for this process is a Pt noble metal catalyst, and the reaction temperature is 450℃. The heat released by the reaction is used for preheating the fuel or air. The generated NO is adjusted to a total concentration of 0.5% by catalysis and pulsed discharge plasma, and the proportion of NO2 is 20%.

[0060] Through the above technical implementation process of strengthening the promotion effect, the ignition temperature of NH3 / O2 oxidation reaction is reduced to below 800℃, the ignition rate is increased by 5 times, the NO2 recovery rate of tail gas is greater than 85%, and the NO x The emission concentration is <15mg / m 3 .

[0061] Application Example 2

[0062] The internal combustion engine system provided in Example 1 is adopted.

[0063] Liquid ammonia stored at temperature below 50℃ and pressure below 2.5MPa is vaporized by a vaporization heat exchanger, and then is sent into a combustion device together with air. The oxygen content in the ignition zone is 40%(volume concentration). The amount of nitrogen oxide promoter added in the ignition zone is 15% of the total amount of ammonia fuel, in which NO2 accounts for 50% of the nitrogen oxides, and the rest is NO. The flue gas discharged from the combustion device is cooled by a waste heat recovery boiler from 1000℃ to 350℃. 70% of the flue gas is sent back to the combustion device by an induced draft fan to further catalyze the NO produced by the excessive oxidation of ammonia into NO2 for recycling and utilization. The remaining 30% of the flue gas is stored by a molecular sieve adsorbent. When the storage amount of NO2 reaches 80%, the adsorbent is regenerated to obtain high-concentration NO2 gas, which is sent back to the combustion device by an induced draft fan for recycling. In order to ensure a stable and sufficient supply of nitrogen oxides, the ammonia fuel is pre-oxidized into NO and NO2 by a catalytic oxidation unit. The catalyst required for this process is a Pt noble metal catalyst, and the reaction temperature is 450℃. The heat released by the reaction is used for preheating the fuel or air. The generated NO is adjusted to a total concentration of 5% by catalysis and pulsed discharge plasma, and NO2 accounts for 50% of it.

[0064] Through the above-mentioned technical implementation process of strengthening the promotion effect, the ignition temperature of NH3 / O2 oxidation reaction is reduced to below 600℃, the ignition rate is increased by 10 times, the NO2 recovery rate of tail gas is greater than 90%, and the NO x The emission concentration is less than 10mg / m 3 .

[0065] The above description of the embodiments is for the convenience of those skilled in the art to understand and use the invention. Those skilled in the art can obviously make appropriate modifications to these embodiments, and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above-mentioned embodiments, and the improvements and modifications made by those skilled in the art according to the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A system for promoting low-temperature ignition of ammonia fuel using nitrogen oxides, characterized in that: It comprises a storage unit (1), an ammonia combustion unit (2), a flue gas catalytic oxidation unit (3) and an adsorption regeneration unit (4) which are connected in sequence; the output end of the adsorption regeneration unit (4) is also connected to the ammonia combustion unit (2); Ammonia fuel is transported from a storage unit (1) to an ammonia combustion unit (2), where it is mixed with an oxygen source and a accelerator and combusted. The flue gas generated by the combustion enters a flue gas catalytic oxidation unit (3) and is processed into circulating gas. Part of the circulating gas is returned to the ammonia combustion unit (2) as a accelerator, and the remaining circulating gas is concentrated in an adsorption regeneration unit (4) and returned to the ammonia combustion unit (2) as a accelerator. The accelerator is a NO / NO2 mixed gas. In the flue gas catalytic oxidation unit (3), the flue gas is catalytically oxidized by an oxidation catalyst and a pulse discharge plasma, and the concentration of the promoter is adjusted to 0.5-5 vol% of the total concentration of the circulating gas, wherein the content of NO2 is 20-50 vol%; The system further comprises an ammonia catalytic oxidation unit (5), which catalytically oxidizes 2-10 vol% of ammonia fuel into a promoter, and then inputs the promoter into the ammonia combustion unit (2); The flue gas catalytic oxidation unit (3) and the ammonia catalytic oxidation unit (5) use one of Pt / CeO2, Pt / Al2O3, Ru / CeO2 and Ru / Al2O3 as a catalyst, the reaction temperature is 300-500°C, and the heat released by the reaction is used to preheat the ammonia fuel and the oxygen source; 50-70 vol% of the circulating gas is directly returned to the ammonia combustion unit (2), and the remaining circulating gas is input to the adsorption regeneration unit (4); The adsorption regeneration unit (4) is a Pd-SSZ-13 molecular sieve; when the adsorption regeneration unit (4) adsorbs to a saturation value of 70-80 vol%, it is regenerated, and the desorbed circulating gas returns to the ammonia combustion unit (2).

2. The system for promoting low-temperature ignition of ammonia fuel by utilizing nitrogen oxides according to claim 1, characterized in that: The ammonia fuel is ammonia or a mixture of ammonia and natural gas; the volume content of oxygen in the oxygen source is 10-40 vol%; the amount of the accelerator added is 5-15 vol% of the ammonia fuel, of which the content of NO2 is 20-50 vol%.

3. The system for promoting low-temperature ignition of ammonia fuel by utilizing nitrogen oxides according to claim 2, characterized in that: The ammonia combustion unit (2) comprises an ignition zone and a main combustion zone, an oxygen source and a promoter are added to the ammonia combustion unit (2) from the ignition zone, and ammonia fuel is added to the ammonia combustion unit (2) from the ignition zone and the main combustion zone respectively.

4. A system for promoting low-temperature ignition of ammonia fuel using nitrogen oxides according to claim 1 or 2, characterized in that: The system further comprises a waste heat recovery unit (6), which is connected between the ammonia combustion unit (2) and the flue gas catalytic oxidation unit (3) and is used to recover waste heat in the flue gas.

5. The system for promoting low-temperature ignition of ammonia fuel by utilizing nitrogen oxides according to claim 4, characterized in that: The waste heat recovery unit (6) reduces the temperature of the flue gas from 700-1000°C to 350°C before inputting the flue gas into the flue gas catalytic oxidation unit (3).

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