Nested multi-nozzle ammonia-coal dual-fuel flameless burner

Abstract

The nested multi-nozzle ammonia-coal dual-fuel flameless burner comprises a tapered high-temperature oxidant spray pipe 1, an ammonia gas preheating chamber 2, a pulverized coal preheating chamber 3, a pulverized coal spray pipe 4 and an ammonia gas spray pipe 5, the tapered high-temperature oxidizing agent spraying pipe 1 penetrates through the pulverized coal and ammonia gas spraying device and is used for conveying secondary air, the ammonia gas preheating chamber 2 is coaxially assembled on the outer side of the tapered high-temperature oxidizing agent spraying pipe 1, the pulverized coal preheating chamber 3 is coaxially assembled on the outer side of the ammonia gas preheating chamber, the pulverized coal spraying pipe 4 is used for conveying primary air and pulverized coal, and the ammonia gas spraying pipe 5 is used for conveying NH3. On the basis of the outer spraying type nozzle structure of outer side coal spraying and inner side ammonia spraying and the spraying mode that the outer side deviates from oxidizing agent jet flow, NOx generated in ammonia coal flameless combustion can be remarkably reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of flameless combustion, and particularly to a nested multi-nozzle ammonia-coal dual-fuel flameless burner. Background Art

[0002] Driven by the dual-carbon goal, the combustion of ammonia in coal-fired units is an effective way to rapidly reduce CO2 emissions. Different from fossil fuels such as pulverized coal, problems such as poor flame stability and easy exceedance of nitrogen oxide emissions exist during the combustion of the zero-carbon fuel - ammonia (NH3). Conventional combustion technologies and traditional pulverized coal burners are difficult to balance the efficient combustion and low nitrogen emissions of the ammonia-coal gas-solid two-phase, so there is an urgent need to develop new combustion technologies or design low-nitrogen burners for the characteristics of ammonia-coal fuels to achieve stable, efficient, and clean combustion of ammonia-coal.

[0003] In recent years, the flameless combustion technology (flameless combustion) has been favored due to its inherent advantages of high combustion stability and low nitrogen emissions. Flameless combustion usually adopts the method of high-speed jet + high-temperature preheating to achieve mild combustion of different fuels. Different from conventional combustion, in the flameless combustion mode, the strong recirculating flue gas fully entrains the fuel and oxidant, making them evenly dispersed throughout the furnace, and the reaction area expands from the traditional flame front to the entire furnace. The lower peak temperature, uniform heat flux distribution, and diluted oxygen concentration in the flameless combustion mode effectively inhibit the formation of thermal and fuel-type NOx. Therefore, combining flameless combustion with ammonia-coal co-combustion, taking advantages of each other, can achieve stable, efficient, and clean combustion of ammonia-coal.

[0004] In view of the above problems, the applicant conducted research based on a certain megawatt-scale flameless combustion device, and analyzed the effects of different injection positions and injection methods on NO generation in ammonia-coal flameless combustion. At the same time, it was found that the nozzle structure of "injecting coal on the outside + injecting ammonia on the inside" and the injection method of the outside jet deviating from the oxidant can significantly reduce NOx generation in ammonia-coal flameless combustion. Based on the above findings, the present invention proposes a nested multi-nozzle ammonia-coal dual-fuel flameless burner in which the ammonia nozzle is coaxially assembled inside the pulverized coal nozzle, and at the same time, the ammonia and pulverized coal are preheated by the high-temperature oxidant. Summary of the Invention

[0005] The nested multi-nozzle ammonia-coal dual-fuel flameless burner described in the present invention includes: a tapered high-temperature oxidant nozzle, an ammonia preheating chamber, a pulverized coal preheating chamber, a pulverized coal nozzle, and an ammonia nozzle; the tapered high-temperature oxidant nozzle penetrates through the ammonia and pulverized coal injection devices for delivering secondary air, the ammonia preheating chamber is coaxially assembled outside the tapered high-temperature oxidant nozzle, the pulverized coal preheating chamber - 3 is coaxially assembled outside the ammonia preheating chamber, the pulverized coal nozzle is used for delivering primary air and pulverized coal, and the ammonia nozzle is used for delivering NH3.

[0006] The described tapered high-temperature oxidant nozzle is used to inject high-temperature preheated air (>1300K) as secondary air into the furnace. The upper end of the tapered high-temperature oxidant nozzle connects to the high-temperature preheating device and the air compressor, and the lower end communicates with the furnace combustion chamber. The described tapered high-temperature oxidant nozzle is divided into three sections. The diameter D1 of the first section is 125mm, and the height L1 is 200mm, and its height is the same as that of the ammonia preheating chamber. The diameter D2 of the second section is 90mm, and the height L2 is 300mm, and its height is the vertical distance between the bottom of the ammonia preheating chamber and the bottom of the pulverized coal preheating chamber 3. The diameter D3 of the third section is 60mm, and the height L3 is 400mm, and its height is the same as that of the pulverized coal nozzle. The greater the injection speed of the oxidant jet, the higher the level of flue gas recirculation in the furnace, and the easier it is to achieve the flameless combustion state. The described tapered high-temperature oxidant nozzle adopts a tapered nozzle. By gradually reducing the pipe diameter, the injection speed of the oxidant before entering the furnace is further increased, the internal flue gas recirculation in the furnace is strengthened, the dilution level of the circulating flue gas to the fuel and the oxidant is increased, and the realization of the flameless combustion state is promoted.

[0007] The described ammonia preheating chamber is coaxially assembled outside the tapered high-temperature oxidant nozzle 1 and is used to collect NH3 transported by the upstream ammonia pipeline. The tapered high-temperature oxidant nozzle in the center of the ammonia preheating chamber is used to preliminarily preheat NH3. The preheated NH3 enters the ammonia nozzle through the nozzle at the bottom of the ammonia preheating chamber. The first section of the tapered high-temperature oxidant nozzle preliminarily preheats NH3 while transporting high-temperature air, increasing the initial jet temperature of NH3 to promote its rapid ignition and stable combustion at the outlet of the described nested multi-nozzle ammonia-coal dual-fuel flameless burner.

[0008] The described pulverized coal preheating chamber is used to collect primary air and pulverized coal. The second section of the tapered high-temperature oxidant nozzle is used to preliminarily preheat the pulverized coal and primary air between the bottom of the ammonia preheating chamber and the bottom of the pulverized coal preheating chamber. The preheated primary air and pulverized coal enter the pulverized coal nozzle through multiple nozzles at the bottom of the pulverized coal preheating chamber. The pulverized coal preheating chamber is coaxially assembled outside the ammonia preheating chamber. Its upper end receives the pulverized coal and primary air transported by the boiler system feeding device, and its lower end is connected to the pulverized coal nozzle. The second section of the tapered high-temperature oxidant nozzle preheats the pulverized coal particles and primary air to promote the ignition of the pulverized coal particles.

[0009] The described pulverized coal nozzle is used to transport pulverized coal and primary air particles into the furnace. Its upper end receives the primary air and pulverized coal particles transported from the pulverized coal preheating chamber, and its lower end is connected to the furnace. The diameter of the pulverized coal nozzle is 40 mm and the height is 400 mm. Different from the conventional directly fired pulverized coal nozzle, the pulverized coal nozzle adopts an inclined and diverging tapered high-temperature oxidant nozzle, that is, the pulverized coal nozzle uses a structure that is inclined and diverges from the oxidant jet to transport pulverized coal and primary air. Its advantage is that when the pulverized coal nozzle, i.e., the pulverized coal jet, diverges from the oxidant jet, the contact between pulverized coal and the oxidant can be effectively avoided, thus suppressing the oxidation of fuel nitrogen. The applicant's previous research found that when the included angle (α) between the pulverized coal jet and the oxidant jet is +10°, the NOx emissions in ammonia-coal flameless combustion decrease rapidly, but as α further increases, most of the pulverized coal jets will directly impact the furnace wall, which is not conducive to the burnout of pulverized coal. Therefore, in the present invention, the included angle between the pulverized coal nozzle and the tapered high-temperature oxidant nozzle is set to +10°, that is, the "outer spray type" nozzle structure. As attached Figure 2 , two layout schemes of the pulverized coal nozzle are proposed: one is to arrange six pulverized coal nozzles at equal intervals circumferentially around the pulverized coal preheating chamber, and the other is to arrange four pulverized coal nozzles at equal intervals circumferentially around the pulverized coal preheating chamber. The advantages of such an arrangement are as follows: The six pulverized coal nozzles arranged at equal intervals circumferentially around the pulverized coal preheating chamber split the NH3 jet in the ammonia nozzle coaxially arranged inside it into more small NH3 jets, and each small NH3 jet is tightly wrapped by the pulverized coal jet to fully isolate the contact between NH3 and the high-temperature oxidant, more effectively reducing NOx emissions, and is suitable for large-scale ammonia blending combustion (ammonia blending ratio exceeds 50 cal.%); while the four pulverized coal nozzles arranged at equal intervals circumferentially around the pulverized coal preheating chamber 3 are suitable for ammonia-coal co-combustion with a relatively low blending ratio, and can be selected according to different blending ratios in actual applications.

[0010] The described ammonia nozzle is used to transport NH3 from the ammonia preheating chamber into the furnace. Its upper end receives the ammonia preheating chamber 2, and its lower end communicates with the furnace. The diameter of the ammonia nozzle 5 is 20 mm and the length is 400 mm. The ammonia nozzle is coaxially assembled inside the pulverized coal nozzle, adopting a "coal-wrapped ammonia" structure of "spraying coal on the outside + spraying ammonia on the inside". The advantages of such an arrangement are as follows: The external flame formed by the combustion of the pulverized coal jet hinders the full contact between oxygen and NH3, enabling more NH3 to burn in the internal oxygen-deficient zone formed by the combustion of the pulverized coal jet. The oxidation process of NH3 is significantly inhibited, and the generation of fuel-type NOx is rapidly reduced. In the "coal-wrapped ammonia" spraying mode, although the NOx generated by the combustion of pulverized coal slightly increases, compared with the NOx emissions brought by the combustion of NH3, the overall NOx emissions are still significantly reduced.

[0011] Beneficial effects:

[0012] 1. The nested multi-nozzle ammonia-coal dual-fuel flameless burner of the present invention has a simple structure and is easy to install. It adopts a "coal-wrapped ammonia" nozzle structure of "spraying coal on the outside + spraying ammonia on the inside" and a spraying method where the fuel jet deviates from the oxidant jet, and couples with the strong flue gas entrainment characteristics of flameless combustion, which can significantly reduce NOx emissions in ammonia-coal flameless combustion. The specific technical principle is as follows: on the one hand, the NH3 jet burns in the internal oxygen-deficient zone formed by the combustion of the pulverized coal jet, effectively inhibiting the contact between NH3 and oxygen and avoiding the large generation of fuel-type NO. On the other hand, the local reducing atmosphere (CO and H2) generated by the pulverized coal under the flameless combustion mode and the reducing ability of unburned coke (C + 2NO → N2 + CO2) are utilized to promote the homogeneous and heterogeneous reduction of NO, further reducing NOx emissions.

[0013] 2. The nested multi-nozzle ammonia-coal dual-fuel flameless burner of the present invention adopts a nested assembly structure, coaxially assembling the three-stage tapered oxidant nozzle with the ammonia preheating chamber and the pulverized coal preheating chamber, giving full play to the characteristic that the oxidant needs high-temperature preheating in flameless combustion, preliminarily preheating the pulverized coal and NH3, and promoting the rapid ignition and stable combustion of NH3 and pulverized coal.

[0014] 3. The nested multi-nozzle ammonia-coal dual-fuel flameless burner of the present invention does not require other auxiliary nitrogen reduction devices. To adapt to ammonia-coal co-firing with different ammonia blending ratios, the present invention provides two arrangements of pulverized coal nozzles. For high-proportion ammonia-coal co-firing, a burner with six pulverized coal nozzles arranged equidistantly in the circumferential direction of the pulverized coal preheating chamber 3 is adopted, separating the incident NH3 into multiple small NH3 jets, and each NH3 jet is wrapped by the pulverized coal jet, greatly avoiding the oxidation of NH3; for lower-proportion ammonia-coal co-firing, a burner with four pulverized coal nozzles arranged equidistantly in the circumferential direction of the pulverized coal preheating chamber 3 can be adopted. Description of the Drawings

[0015] Figure 1 Schematic structural diagram of a nested multi-nozzle ammonia-coal dual-fuel flameless burner;

[0016] Figure 2 Schematic diagram of the fuel nozzle arrangement of a nested multi-nozzle ammonia-coal dual-fuel flameless burner;

[0017] Among them, (a) is a schematic diagram of the arrangement of six pulverized coal nozzles arranged equidistantly in the circumferential direction of the pulverized coal preheating chamber 3,

[0018] (b) is a schematic diagram of the arrangement of four pulverized coal nozzles arranged equidistantly in the circumferential direction of the pulverized coal preheating chamber 3,

[0019] Figure 3 Tapered high-temperature oxidant nozzle;

[0020] Figure 4 Cross-sectional view of the pulverized coal injection device;

[0021] Figure 5 Cross-sectional view of ammonia injection device;

[0022] Figure 6 Effect of different burners on NO formation in ammonia-coal flameless combustion (a 0.58MWth flameless combustion furnace);

[0023] Figure 7 Schematic diagram of burner structure optimization. Reference numerals: 1 - Converging high-temperature oxidant nozzle, 2 - Ammonia preheating chamber, 3 - Pulverized coal preheating chamber, 4 - Pulverized coal nozzle, 5 - Ammonia nozzle Specific implementation method

[0024] The nested multi-nozzle ammonia-coal dual-fuel flameless burner of the present invention includes: a converging high-temperature oxidant nozzle 1, an ammonia preheating chamber 2, a pulverized coal preheating chamber 3, a pulverized coal nozzle 4 and an ammonia nozzle 5; the converging high-temperature oxidant nozzle 1 penetrates through the pulverized coal and ammonia injection device for transporting secondary air, the ammonia preheating chamber 2 is coaxially assembled outside the converging high-temperature oxidant nozzle 1, the pulverized coal preheating chamber 3 is coaxially assembled outside the ammonia preheating chamber 2, the pulverized coal nozzle 4 is used for transporting primary air and pulverized coal, and the ammonia nozzle 5 is used for transporting NH3.

[0025] The assembly and working method among the components of the nested multi-nozzle ammonia-coal dual-fuel flameless burner of the present invention are as follows:

[0026] (1) The converging high-temperature oxidant nozzle 1 is used to inject high-temperature preheated air (>1300K) as secondary air into the furnace. The upper end of the converging high-temperature oxidant nozzle 1 receives the high-temperature preheating device and the air compressor, and the lower end communicates with the furnace combustion chamber. The converging high-temperature oxidant nozzle 1 is divided into three sections. The diameter D1 of the first section is 125mm, and the height L1 is 200mm, and its height is the same as that of the ammonia preheating chamber 2; the diameter D2 of the second section is 90mm, and the height L2 is 300mm, and its height is the vertical distance between the bottom of the ammonia preheating chamber 2 and the bottom of the pulverized coal preheating chamber 3; the diameter D3 of the third section is 60mm, and the height L3 is 400mm, and its height is the same as that of the pulverized coal nozzle 4.

[0027] (2) The ammonia preheating chamber 2 is coaxially assembled outside the converging high-temperature oxidant nozzle 1, and is used to collect NH3 transported by the upstream ammonia pipeline, and use the converging high-temperature oxidant nozzle 1 in the center of the ammonia preheating chamber 2 to preheat NH3 preliminarily. The preheated NH3 enters the ammonia nozzle 5 through the nozzle at the bottom of the ammonia preheating chamber 2.

[0028] (3) The pulverized coal preheating chamber 3 is used to collect primary air and pulverized coal. The pulverized coal and primary air between the bottom of the ammonia preheating chamber 2 and the bottom of the pulverized coal preheating chamber 3 are preliminarily preheated by using the second section of the tapered high-temperature oxidant nozzle 1. The preheated primary air and pulverized coal enter the pulverized coal nozzle 4 through multiple nozzles at the bottom of the pulverized coal preheating chamber 2. The pulverized coal preheating chamber 3 is coaxially mounted outside the ammonia preheating chamber 2. The upper end of the pulverized coal preheating chamber 3 receives the pulverized coal and primary air delivered by the boiler system feeding device, and the lower end is connected to the pulverized coal nozzle 4.

[0029] (4) Pulverized coal nozzle 4 is used to transport pulverized coal and primary air particles into the furnace. Its upper end receives the primary air and pulverized coal particles transported by the pulverized coal preheating chamber 3, and its lower end is connected to the furnace. The diameter of the pulverized coal nozzle 4 is 40 mm and the height is 400 mm. The pulverized coal nozzle 4 adopts a structure that is inclined away from the tapered high-temperature oxidizer nozzle 1, that is, the pulverized coal nozzle 4 is inclined away from the oxidizer jet to transport pulverized coal and primary air. In the present invention, the angle between the pulverized coal nozzle 4 and the tapered high-temperature oxidizer nozzle 1 is set to +10°, that is, an "external spray" nozzle structure. As shown in the attached Figure 2 Two arrangements of the pulverized coal nozzles 4 are proposed: one is to arrange six pulverized coal nozzles at equal intervals along the circumference of the pulverized coal preheating chamber 3, and the other is to arrange four pulverized coal nozzles 4 at equal intervals along the circumference of the pulverized coal preheating chamber 3. The six pulverized coal nozzles 4 at equal intervals along the circumference of the pulverized coal preheating chamber 3 are suitable for large-proportion ammonia combustion (ammonia ratio exceeding 50 cal.%); while the four pulverized coal nozzles 4 at equal intervals along the circumference of the pulverized coal preheating chamber 3 are suitable for ammonia-coal mixed combustion with relatively low mixing ratios. In actual applications, the selection can be made according to different mixing ratios.

[0030] (5) Ammonia nozzle 5, used to transport NH3 from ammonia preheating chamber 2 into the furnace. Its upper end is connected to ammonia preheating chamber 2, and its lower end is connected to the furnace. The diameter of ammonia nozzle 5 is 20 mm and the length is 400 mm. Ammonia nozzle 5 is coaxially mounted inside pulverized coal nozzle 4, and adopts a "coal-enclosed ammonia" structure of "coal injection on the outside + ammonia injection on the inside".

[0031] Example

[0032] Based on a pilot scale (0.58MW th The numerical simulation of ammonia-coal blending in a pulverized coal flameless combustion furnace was carried out. The NO generation characteristics of conventional ammonia-coal premixed direct-fired burners, "coal-ammonia" composite burners and external-spray "coal-ammonia" composite burners were compared at a 40 cal.% ammonia blending ratio. The distribution of NO in the furnace is shown in Figure 2. Figure 6 As shown. It can be seen that compared with the conventional premixed direct-fired burner, the NO concentration in the furnace is significantly reduced after the latter two burners are used. When the "coal-enclosed ammonia" composite burner is used, the NO concentration at the furnace outlet (converted to 6% oxygen concentration) decreases by 33.8%. On this basis, after the external spray "coal-enclosed ammonia" composite burner is used, the outlet NO emission concentration is further reduced by 40.2%.

[0033] Based on the above two findings, the nested multi-nozzle ammonia-coal dual-fuel flameless burner of the present invention combines an external injection type "coal-in-ammonia" composite burner with an injection mode in which the fuel jet deviates from the oxidant jet. By adding a pulverized coal preheating chamber and an ammonia preheating chamber, a nested multi-nozzle ammonia-coal dual-fuel flameless burner is designed, which not only makes full use of the waste heat of the high-temperature oxidant to increase the initial temperature of the fuel and promote the rapid ignition and stable combustion of the fuel, but also can significantly reduce NO x emissions.

Claims

1. A nested multi-nozzle ammonia-coal dual-fuel flameless combustor, characterized in that Including: A tapered high-temperature oxidant nozzle 1, an ammonia preheating chamber 2, a pulverized coal preheating chamber 3, a pulverized coal nozzle 4 and an ammonia nozzle 5; the tapered high-temperature oxidant nozzle 1 penetrates through the pulverized coal and ammonia injection device for transporting secondary air, the ammonia preheating chamber 2 is coaxially assembled outside the tapered high-temperature oxidant nozzle 1, the pulverized coal preheating chamber 3 is coaxially assembled outside the ammonia preheating chamber 2, the pulverized coal nozzle 4 is used to transport primary air and pulverized coal, and the ammonia nozzle 5 is used to transport NH3.

2. The nested multi-nozzle ammonia-coal dual fuel flameless burner according to claim 1, wherein, The tapered high-temperature oxidant nozzle 1 is used to inject high-temperature preheated air (>1300K) as secondary air into the furnace. The upper end of the tapered high-temperature oxidant nozzle 1 receives the high-temperature preheating device and the air compressor, and the lower end communicates with the furnace combustion chamber.

3. The nested multi-nozzle ammonia-coal dual-fuel flameless burner according to claim 1, wherein The tapered high-temperature oxidant nozzle 1 is divided into three sections. The height of the first section is the same as the height of the ammonia preheating chamber 2; the height of the second section is the vertical distance between the bottom of the ammonia preheating chamber 2 and the bottom of the pulverized coal preheating chamber 3; the height of the third section is the same as the height of the pulverized coal nozzle 4.

4. The nested multi-nozzle ammonia-coal dual-fuel flameless burner according to claim 3, wherein The diameter D1 of the first section of the tapered high-temperature oxidant nozzle 1 is 125mm, and the height L1 is 200mm; the diameter D2 of the second section is 90mm, and the height L2 is 300mm; the diameter D3 of the third section is 60mm, and the height L3 is 400mm.

5. The nested multi-nozzle ammonia-coal dual-fuel flameless combustor according to claim 1, wherein The ammonia preheating chamber 2 is used to collect NH3 transported by the upstream ammonia pipeline, and the tapered high-temperature oxidant nozzle 1 in the center of the ammonia preheating chamber 2 is used to preheat NH3 preliminarily. The preheated NH3 enters the ammonia nozzle 5 through the nozzle at the bottom of the ammonia preheating chamber 2.

6. The nested multi-nozzle ammonia-coal dual-fuel flameless combustor according to claim 1, wherein The upper end of the pulverized coal preheating chamber 3 receives the pulverized coal and primary air transported by the boiler system feeding device, and the lower end is connected to the pulverized coal nozzle 4; the second section of the tapered high-temperature oxidant nozzle 1 is used to preheat the pulverized coal and primary air between the bottom of the ammonia preheating chamber 2 and the bottom of the pulverized coal preheating chamber 3 preliminarily. The preheated primary air and pulverized coal enter the pulverized coal nozzle 4 through multiple nozzles at the bottom of the pulverized coal preheating chamber 2.

7. The nested multi-nozzle ammonia-coal dual-fuel flameless burner according to claim 1, characterized in that, The pulverized coal nozzle 4, its upper end receives the primary air and pulverized coal particles transported by the pulverized coal preheating chamber 3, and the lower end is connected to the furnace; the pulverized coal nozzle 4 is inclined away from the tapered high-temperature oxidant nozzle 1, that is, the pulverized coal nozzle 4 is inclined away from the oxidant jet to transport pulverized coal and primary air; the included angle between the pulverized coal nozzle 4 and the tapered high-temperature oxidant nozzle 1 is set to +10°, that is, the "outer spray type" nozzle structure.

8. The nested multi-nozzle ammonia-coal dual-fuel flameless combustor according to claim 1, characterized in that, The layout scheme of the pulverized coal nozzle 4 is as follows: one is to arrange six pulverized coal nozzles at equal circumferential intervals along the circumference of the pulverized coal preheating chamber 3, and the other is to arrange four pulverized coal nozzles 4 at equal circumferential intervals along the circumference of the pulverized coal preheating chamber 3. Arranging six pulverized coal nozzles 4 at equal circumferential intervals along the circumference of the pulverized coal preheating chamber 3 is suitable for large-scale ammonia-doped combustion (ammonia doping ratio exceeds 50cal.%); while arranging four pulverized coal nozzles 4 at equal circumferential intervals along the circumference of the pulverized coal preheating chamber 3 is suitable for ammonia-coal co-combustion with a relatively low doping ratio. In actual application, it can be selected according to different doping ratios.

9. The nested multi-nozzle ammonia-coal dual-fuel flameless burner according to claim 1, characterized in that, The ammonia nozzle 5, its upper end receives the ammonia preheating chamber 2, and the lower end communicates with the furnace; the ammonia nozzle 5 is coaxially assembled inside the pulverized coal nozzle 4, adopting the "coal-wrapped ammonia" structure of "spraying coal on the outside + spraying ammonia on the inside".

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