Dual-fuel flameless combustion device for mixing superfine pulverized coal with ammonia

Abstract

The invention discloses a superfine pulverized coal and ammonia mixed dual-fuel flameless combustion device which comprises a combustion chamber, primary air spray pipes and secondary air spray pipes, the secondary air spray pipes are used for conveying high-temperature and high-speed oxidant airflow into the combustion chamber, and the primary air spray pipes are symmetrically distributed around the secondary air spray pipes. The primary air spray pipe comprises a conventional pulverized coal spray pipe, an ammonia gas spray gun and a superfine pulverized coal spray pipe which are respectively used for conveying conventional pulverized coal airflow, ammonia gas and superfine pulverized coal airflow into the combustion chamber, and the conventional pulverized coal spray pipe, the ammonia gas spray gun and the superfine pulverized coal spray pipe are coaxially arranged from outside to inside; therefore, a high-temperature combustion area with conventional pulverized coal, ammonia gas and superfine pulverized coal sequentially from outside to inside is formed at an outlet of the primary air spray pipe. According to the low-nitrogen-emission ammonia-coal mixed combustion device, internal and external combustion distribution of conventional coal powder, ammonia gas and superfine coal powder is utilized, a unique combustion mode of flameless combustion is supplemented, accordingly, low-nitrogen emission of ammonia-coal mixed combustion is achieved, and the low-nitrogen-emission ammonia-coal mixed combustion device has the advantages of being simple in structure, convenient to install, low in cost, wide in applicability and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of coal-fired boiler ammonia-blended combustion, and in particular relates to a dual-fuel flameless combustion device of ultra-fine coal powder mixed with ammonia. Background Art

[0002] At present, the use of green ammonia in coal-fired units for power generation has gradually become an important way to promote the low-carbon transformation of coal-fired power generation and reduce the carbon emission level of coal-fired power generation. However, the main problems faced by ammonia-coal co-firing technology are: 1) Compared with pulverized coal solid fuel, ammonia preferentially burns, resulting in a large amount of oxygen around pulverized coal particles being consumed, thus affecting the ignition and burnout of pulverized coal; 2) The nitrogen content in ammonia is much higher than that in pulverized coal. As the ammonia ratio increases, the nitrogen content in the fuel increases rapidly, and ammonia-coal co-firing faces the risk of excessive nitrogen oxide (NOx) emissions. Because the characteristics of ammonia fuel are very different from those of pulverized coal solid fuel, it is difficult to achieve both high combustion efficiency and low NOx emissions using conventional combustion technology and traditional pulverized coal burners. Therefore, it is urgent to develop new combustion technologies or design new low-nitrogen dual-fuel burners to solve the problems of pulverized coal burnout and high NOx emissions in ammonia-coal co-firing.

[0003] Applying the flameless combustion (MILD combustion) technology with high combustion stability and low NOx emissions to ammonia-coal co-combustion is a new idea to achieve stable, low-nitrogen combustion of ammonia-coal. In the flameless combustion mode, the internal circulation entrainment of high-temperature flue gas caused by high-speed jets preheats and dilutes the reactants, reduces the peak temperature in the furnace, dilutes the oxygen concentration in the reaction zone, and inhibits the generation of NOx. In addition, ultra-fine coal powder has superior combustion characteristics and strong reduction performance, which is conducive to further reducing the NOx emission level of ammonia-coal co-combustion. Summary of the invention

[0004] Purpose of the invention: In order to solve the above problems, the present invention provides a dual-fuel flameless combustion device of ultra-fine coal powder mixed with ammonia, which utilizes the internal and external combustion distribution of conventional coal powder-ammonia-ultra-fine coal powder, supplemented by the unique combustion mode of flameless combustion, thereby achieving low NOx emissions from ammonia-coal co-combustion.

[0005] Invention content: To achieve the above-mentioned objectives, the present invention provides a dual-fuel flameless combustion device of ultra-fine coal powder mixed with ammonia, comprising a combustion chamber, a primary air nozzle and a secondary air nozzle, wherein the secondary air nozzle is used to convey a high-temperature, high-speed oxidant gas flow into the combustion chamber, the primary air nozzle is symmetrically distributed around the secondary air nozzle, the primary air nozzle comprises a conventional coal powder nozzle, an ammonia spray gun and an ultra-fine coal powder nozzle, which are respectively used to convey a conventional coal powder gas flow, ammonia gas and an ultra-fine coal powder gas flow into the combustion chamber, the conventional coal powder nozzle, ammonia spray gun and ultra-fine coal powder nozzle are coaxially arranged from outside to inside, thereby forming a high-temperature combustion zone at the outlet of the primary air nozzle, which is conventional coal powder-ammonia gas-ultra-fine coal powder from outside to inside.

[0006] The present invention adopts the combustion distribution of conventional coal powder-ammonia-ultrafine coal powder from the outside to the inside. The reason for this arrangement is: 1) the local reducing environment formed by the combustion of the outer layer of conventional coal powder is used to prevent NH 3 With O 2 1) The outermost layer of ultrafine coal powder has a reducing atmosphere that is not conducive to the combustion of the inner layer fuel. If ordinary coal powder is used, it may burn incompletely. However, ultrafine coal powder has better ignition and burnout characteristics, which is conducive to reducing the possibility of incomplete combustion of coal powder. Therefore, this arrangement is selected for the above two reasons.

[0007] It should be noted that the combustion distribution from outside to inside does not mean that it burns sequentially from outside to inside, because the three are injected into the furnace at the same time. Generally speaking, the inner layer is easier to burn because NH 3 As a gas, it is easier to burn, and ultrafine coal powder is easier to ignite than conventional coal powder, so the combustion distribution here is formed after the combustion reaches stability. This distribution method is conducive to reducing NOx emissions in the subsequent ammonia-coal co-combustion process.

[0008] Specifically, the air inlet end of the ammonia spray gun is provided with an ammonia air inlet, and the air outlet end of the ammonia spray gun is provided with an ammonia nozzle, and the ammonia nozzle is evenly distributed along the circumference at the end edge of the ammonia spray gun, and the opening angle is 30° to 45°, and the aperture is 6mm to 8mm. It should be noted that the opening angle of the ammonia nozzle should not be too large or too small to ensure that the ammonia jet is located inside the conventional coal powder jet, and most of the ultra-fine coal powder jet is located inside the ammonia flame.

[0009] Specifically, the ammonia spray gun runs through the conventional pulverized coal nozzle arrangement, and the gas outlet of the ammonia spray gun extends into the combustion chamber to ensure that the ammonia jet is located inside the conventional pulverized coal jet, and most of the ultrafine pulverized coal jet is located inside the ammonia flame.

[0010] Specifically, a separation block is provided in the conventional pulverized coal nozzle to separate the conventional pulverized coal airflow into a concentrated pulverized coal airflow and a light pulverized coal airflow, wherein the concentrated pulverized coal airflow is closer to the inner ammonia jet to prevent the O 2 and NH 3 Molecular contact, inhibition of NH 3 Oxidation.

[0011] Specifically, the separation block is symmetrically arranged on the inner walls of both sides of the conventional pulverized coal nozzle, namely, the side close to the secondary air nozzle and the side away from the secondary air nozzle, and at the same time, axially closer to the outlet end of the conventional pulverized coal nozzle to avoid affecting the intake stability.

[0012] Specifically, the separation block has a triangular cross-section, and thus has an upper slope α and a lower slope β relative to the inner wall of a conventional pulverized coal nozzle, wherein the upper slope α is closer to the inlet end of the conventional pulverized coal nozzle, α is 135° to 150°, and β is 150° to 160°.

[0013] Specifically, the conventional pulverized coal nozzle, ammonia spray gun and ultrafine pulverized coal nozzle are detachably connected from the outside to the inside, which facilitates the loading, unloading and replacement of the ammonia spray gun, thereby adapting to different furnace types and combustion conditions.

[0014] Specifically, the weight ratio of the conventional coal powder to the ultrafine coal powder is 2:1 to 3:1 to ensure the reduction effect and control the combustion cost.

[0015] Beneficial effects:

[0016] On the one hand, the present invention sets an ammonia nozzle inside a conventional coal powder nozzle to achieve combustion of ammonia in a local reduction zone formed by coal powder combustion, effectively improving the stability of coal powder combustion, while inhibiting the oxidation process of ammonia and reducing the generation of NOx; on the other hand, the ultrafine coal powder nozzle is set inside the ammonia nozzle to promote heterogeneous reduction of NOx by utilizing the superior reduction performance of ultrafine coal powder, further reducing NOx emissions. In addition, the present invention has a simple structure and is easy to install. At the same time, there is no need to add other auxiliary nitrogen reduction devices, the cost is low, the applicability is wide, and it is conducive to large-scale industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural schematic diagram of a dual-fuel flameless combustion device in an embodiment of the present invention;

[0018] Figure 2 a, 2b are respectively a structural schematic diagram and a partial enlarged diagram of an ultra-fine coal powder mixed with ammonia burner in an embodiment of the present invention;

[0019] Figure 3 a~3d are schematic structural diagrams of two ammonia spray guns in embodiments of the present invention;

[0020] Figure 4 Schematic diagram of the structure of a conventional pulverized coal nozzle in an embodiment of the present invention;

[0021] Figure 5 It is a structural schematic diagram of a separation block in an embodiment of the present invention;

[0022] Figure 6 Schematic diagram of flue gas circulation of a dual-fuel flameless combustion device in an embodiment of the present invention;

[0023] The figure includes: 1. ultra-fine coal powder nozzle, 2. ammonia spray gun, 3. conventional coal powder nozzle, 4. separation block, 5. secondary air nozzle. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0025] Reference Figure 1 The present embodiment provides a dual-fuel flameless combustion device of ultra-fine coal powder mixed with ammonia, which mainly includes a combustion chamber, a primary air nozzle and a secondary air nozzle 5, wherein the secondary air nozzle 5 is used to convey a high-temperature and high-speed oxidant airflow (secondary air) into the combustion chamber, and the primary air nozzle includes a conventional coal powder nozzle 3, an ammonia spray gun 2 and an ultra-fine coal powder nozzle 1, which are respectively used to convey a conventional coal powder airflow, ammonia and an ultra-fine coal powder airflow into the combustion chamber.

[0026] Specifically, the primary air nozzle and the secondary air nozzle 5 are both arranged at the top of the combustion chamber, wherein the primary air nozzle is symmetrically distributed around the secondary air nozzle 5; the conventional coal powder nozzle 3, the ammonia spray gun 2 and the ultra-fine coal powder nozzle 1 are coaxially arranged from outside to inside, thereby forming a high-temperature combustion zone of conventional coal powder-ammonia-ultra-fine coal powder from outside to inside at the outlet of the primary air nozzle. Exemplarily, there are two primary air nozzles, which are symmetrically arranged on both sides of the secondary air nozzle 5.

[0027] Specifically, the ultrafine coal powder nozzle 1 is used to transport part of the primary air and ultrafine coal powder particles (particle size less than 20 μm) into the combustion chamber, and its inlet end receives ultrafine coal powder particles and a small amount of primary air, and the outlet end is connected to the combustion chamber to inject the ultrafine coal powder airflow into the combustion chamber at high speed. Furthermore, the ultrafine coal powder nozzle 1 is coaxially assembled inside the ammonia spray gun 2, so that the ultrafine coal powder particles near its outlet are burned inside the ammonia flame, and the large amount of unburned coke produced in the oxygen-deficient area is conducive to the heterogeneous reduction of NOx produced by ammonia combustion by coal coke particles, thereby inhibiting the generation of NOx.

[0028] Specifically, the ammonia spray gun 2 is used to deliver pure ammonia to the combustion chamber. The ultra-fine coal powder nozzle 1 is installed inside the ammonia spray gun 2, and the conventional coal powder nozzle 3 is nested outside. Therefore, a high-temperature flame zone of conventional coal powder, ammonia and ultra-fine coal powder is formed at the burner outlet (i.e., the primary air nozzle) from the outside to the inside. Figure 6 Ammonia is burned in the oxygen-poor area formed by the combustion of conventional pulverized coal particles, reducing the NH 3 With O 2 Contact inhibits the oxidation process of ammonia, thereby reducing the generation of NOx. Figure 2a. The ammonia spray gun 2 and the ultra-fine coal powder nozzle 1 are independent of each other and can be assembled together after being processed and manufactured separately, thereby forming an ultra-fine coal powder mixed with ammonia dual-fuel burner. At the same time, the ammonia spray gun 2 and the conventional coal powder nozzle 3 are also independent of each other and can be sleeved together to facilitate the loading and unloading and replacement of the ammonia spray gun 2, thereby adapting to different furnace types and combustion conditions.

[0029] In order to ensure that most of the ammonia jet is located between the conventional coal powder jet and the ultra-fine coal powder jet, thereby suppressing the NH 3 To oxidize and promote NO reduction, it is necessary to optimize the structure of the ammonia spray gun 2, especially the opening angle and aperture of the ammonia nozzle. Figure 2 a, 2b, the air inlet end of the ammonia spray gun 2 is provided with an ammonia air inlet, and the air outlet end of the ammonia spray gun 2 is provided with an ammonia nozzle, which is evenly distributed along the circumference at the end edge of the ammonia spray gun 2, and its opening angle (i.e. the angle formed by the center line of the nozzle) is 30° to 45°, and the aperture is 6mm to 8mm. The reasons for this arrangement are: 1) the local oxygen-poor area formed by the combustion of conventional coal powder is used to create a local reducing environment for ammonia combustion, reducing the contact between ammonia and oxygen, thereby inhibiting the generation of NOx; 2) a large amount of unburned ultra-fine coal char particles are used to heterogeneously reduce NOx, thereby reducing NOx emissions. Through the combined effect of the two, the emission level of NOx in ammonia-coal co-combustion can be reduced as much as possible.

[0030] For example, two spray gun structures are provided here, one is a No. 1 spray gun with a nozzle opening angle of 45°, an aperture of 8 mm, and a number of 6 (see Figure 3 a, 3b), the other is a No. Ⅱ spray gun with a nozzle opening angle of 30°, an aperture of 6 mm, and 8 nozzles (see Figure 3 c, 3d), the appropriate spray gun structure can be selected according to the specific combustion furnace type and conditions. If the diameter of the conventional pulverized coal nozzle 3 is larger, the oxygen-depleted area it forms is wider, and a No. Ⅰ spray gun with an opening angle of 45° can be selected; if the diameter of the conventional pulverized coal nozzle 3 is smaller, the corresponding oxygen-depleted area is narrower, and a No. Ⅱ spray gun with an opening angle of 30° can be selected.

[0031] Further, refer to Figure 6 The ammonia spray gun 2 is arranged through the conventional pulverized coal nozzle 3, and the outlet end of the ammonia spray gun 2 extends into the combustion chamber instead of being flush with the outlet end of the conventional pulverized coal nozzle 3. This is because the NH 3 As a gas fuel, it has a stronger diffusion ability, so the outlet end of the ammonia spray gun 2 needs to extend into the combustion chamber to avoid premature diffusion of ammonia, thereby ensuring that most of the ammonia jet is located between the conventional coal powder jet and the ultra-fine coal powder jet. In addition, the outlet end of the ultra-fine coal powder nozzle 1 can be flush with the ammonia spray gun 2 to ensure that the ultra-fine coal powder particles are burned inside the ammonia flame, and a large number of unburned ultra-fine coal coke particles are used to heterogeneously reduce NOx, thereby reducing NOx emissions.

[0032] Specifically, the conventional pulverized coal nozzle 3 is used to transport part of the primary air and conventional pulverized coal particles into the combustion chamber. Furthermore, a separation block 4 is provided in the conventional pulverized coal nozzle 3 to achieve the separation of dense and thin pulverized coal, so that the dense pulverized coal airflow is closer to the ammonia jet side, ensuring that the local reducing atmosphere formed by the combustion of the dense pulverized coal airflow blocks the combustion of the ammonia jet. 2 and NH 3 contact, inhibiting NH 3 oxidation process, reducing the generation of fuel-type NOx.

[0033] For example, refer to Figure 4 The separation block 4 is symmetrically arranged on the inner walls of both sides of the conventional pulverized coal nozzle 3, namely, the side close to the secondary air nozzle 5 and the side away from the secondary air nozzle 5, and at the same time, it is closer to the outlet end of the conventional pulverized coal nozzle 3 in the axial direction to avoid affecting the intake stability; refer to Figure 5 The cross section of the separation block 4 is triangular, and thus has an upper slope α and a lower slope β relative to the inner wall of the conventional pulverized coal nozzle 3, wherein the upper slope α is closer to the inlet end of the conventional pulverized coal nozzle 3, α is 135°~150°, and β is 150°~160°.

[0034] Specifically, the primary air and secondary air account for approximately 20% and 80%, respectively, of which the primary air is a normal temperature and low-speed jet (temperature is about 303K, jet speed is about 26m / s), and the secondary air is a high-temperature and high-speed jet (preheating temperature is about 1573K, jet speed is about 65m / s).

[0035] Furthermore, the weight ratio of conventional coal powder to ultrafine coal powder is 2:1 to 3:1. The reason is that although ultrafine coal powder has good combustion characteristics and high reducibility, there is a cost problem of coal grinding power consumption in actual applications, so conventional coal powder is mainly used in the present invention, and ultrafine coal powder is used as a supplement. Of course, the appropriate ratio between ultrafine coal powder and conventional coal powder can be selected according to the different types of coal. If low-volatile coal is used, the proportion of ultrafine coal powder can be increased as much as possible, which is conducive to the combustion of coal powder; if high-volatile coal is used, it depends on the actual combustion situation. NH 3 The proportion is mainly determined by the actual carbon emission reduction needs. If the power plant hopes to reduce CO 2 emissions, more NH 3 Replace part of the coal powder.

[0036] In summary, the present invention utilizes a combination of conventional particles + ultrafine particles to achieve low NOx emissions in ammonia-coal co-combustion, thereby reducing the process cost of flue gas denitrification. At the same time, by setting a separation block 4 in the pulverized coal nozzle, the thick and thin separation of pulverized coal is achieved, which can further improve the combustion stability and flexibility. In addition, the present invention has a simple structure and wide applicability, and is less expensive than other burner modifications.

[0037] As a solid fuel, the combustion process of coal powder needs to go through processes such as devolatilization, volatile combustion, and coke combustion. Since the coal powder particles need to be preheated to a relatively high temperature before the devolatilization process occurs, and then the subsequent processes such as volatile combustion are carried out, for low-volatile coal, a blunt body is provided in the conventional coal powder nozzle 3 so that the concentrated coal powder airflow is quickly preheated by the internal ammonia flame, promoting the precipitation and combustion of volatiles, thereby alleviating the problem of the difficulty of ignition of low-volatile coal powder.

[0038] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A dual-fuel flameless combustion device of ultra-fine coal powder mixed with ammonia, characterized in that: It includes a combustion chamber, a primary air nozzle and a secondary air nozzle, wherein the secondary air nozzle is used to convey a high-temperature and high-speed oxidant gas flow into the combustion chamber, the primary air nozzle is symmetrically distributed around the secondary air nozzle, the primary air nozzle includes a conventional coal powder nozzle, an ammonia spray gun and an ultra-fine coal powder nozzle, which are respectively used to convey conventional coal powder gas flow, ammonia gas and ultra-fine coal powder gas flow into the combustion chamber, the conventional coal powder nozzle, ammonia spray gun and ultra-fine coal powder nozzle are coaxially arranged from outside to inside, thereby forming a high-temperature combustion zone at the outlet of the primary air nozzle, which is conventional coal powder-ammonia gas-ultra-fine coal powder from outside to inside.

2. The dual-fuel flameless combustion device according to claim 1, characterized in that: The air inlet end of the ammonia spray gun is provided with an ammonia air inlet, and the air outlet end of the ammonia spray gun is provided with an ammonia nozzle, which is evenly distributed along the circumference at the end edge of the ammonia spray gun, has an opening angle of 30° to 45°, and a hole diameter of 6mm to 8mm.

3. The dual-fuel flameless combustion device according to claim 1, characterized in that: The ammonia spray gun is arranged through a conventional pulverized coal spray pipe, and the gas outlet end of the ammonia spray gun extends into the combustion chamber.

4. The dual-fuel flameless combustion device according to claim 1, characterized in that: A separation block is provided in the conventional pulverized coal nozzle for separating the conventional pulverized coal airflow into a concentrated pulverized coal airflow and a lean pulverized coal airflow, wherein the concentrated pulverized coal airflow is closer to the inner ammonia jet.

5. The dual-fuel flameless combustion device according to claim 5, characterized in that: The separation block is symmetrically arranged on the inner walls of both sides of the conventional pulverized coal nozzle, namely, the side close to the secondary air nozzle and the side away from the secondary air nozzle, and is axially closer to the outlet end of the conventional pulverized coal nozzle.

6. The dual-fuel flameless combustion device according to claim 6, characterized in that: The separation block has a triangular cross section, and has an upper slope α and a lower slope β relative to the inner wall of a conventional pulverized coal nozzle, wherein the upper slope α is closer to the inlet end of the conventional pulverized coal nozzle, α is 135° to 150°, and β is 150° to 160°.

7. The dual-fuel flameless combustion device according to claim 1, characterized in that: The conventional coal powder nozzle, the ammonia spray gun and the superfine coal powder nozzle are detachably connected in sequence from the outside to the inside.

8. The dual-fuel flameless combustion device according to claim 1, characterized in that: The weight ratio of the conventional coal powder to the ultrafine coal powder is 2:1 to 3:1.

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