Steam preheating and tempering pulverized coal ammonia-doped combustion device and method

Abstract

The invention belongs to the field of pulverized coal ammonia-doped combustion, and provides a pulverized coal ammonia-doped combustion device and method for steam preheating and tempering, and the device comprises a spray head and a pipeline assembly connected with the spray head; the pipeline assembly comprises an ammonia gas pipeline, and a water vapor channel, a pulverized coal and primary air channel, a rotational flow secondary air channel and a tertiary air channel are sequentially arranged outwards in an axial symmetry mode along the two sides of the ammonia gas pipeline. The ammonia gas pipeline and the water vapor channel are respectively provided with a spray head plate, and the spray head plate is provided with a nozzle; and ammonia gas in the ammonia gas pipeline and water vapor in the water vapor channel are converged near the central axis of the combustor and are fully mixed. The device can promote pre-decomposition of ammonia gas, improve temperature distribution of a hearth and achieve the aim of coal-ammonia stratified combustion.

Description

Technical Field

[0001] The invention belongs to the field of coal powder mixed with ammonia combustion, and in particular relates to a coal powder mixed with ammonia combustion device and method for steam preheating and tempering. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Considering that ammonia contains 82.35% nitrogen by mass, if the combustion method is not appropriate, nitrogen will be converted into atmospheric pollutants such as NOx in large quantities during the combustion process. In order to meet environmental protection requirements, these pollutants need to be treated with SCR and other technologies for denitrification, which greatly increases the power generation cost of coal-fired power plants. In addition, the flue gas from ammonia combustion contains a large amount of high-temperature water vapor, and direct emission causes energy waste. Therefore, utilizing high-temperature water vapor and tempering pulverized coal with ammonia combustion through high-temperature water vapor can synergistically reduce NOx emissions and improve combustion efficiency. However, the existing technologies mostly use water vapor to improve combustion performance under pure coal combustion conditions or to achieve energy storage. None of them combines extraction steam with ammonia-coal mixed combustion. Water vapor is only regarded as an energy storage medium, and none of them achieves the purpose of using water vapor for preheating and tempering to promote the full combustion of ammonia and coal. Summary of the Invention

[0004] In order to solve the technical problems existing in the above-mentioned background technology, the present invention proposes a coal-ammonia combustion device and method with steam preheating and tempering, which can promote the predecomposition of ammonia, improve the furnace temperature distribution, and achieve the goal of coal-ammonia stratified combustion.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A steam preheated and tempered pulverized coal mixed with ammonia combustion device, comprising: A nozzle and a pipe assembly connected to the nozzle; The pipeline assembly includes an ammonia pipeline, and a water vapor channel, a pulverized coal and primary air channel, a swirl secondary air channel and a tertiary air channel are symmetrically arranged along both sides of the ammonia pipeline. The ammonia pipeline and the water vapor channel are both provided with nozzle plates, and the nozzle plates are provided with nozzles; the ammonia in the ammonia pipeline and the water vapor in the water vapor channel converge near the central axis of the burner and are fully mixed.

[0006] As an embodiment, the nozzle plate is of shower head type.

[0007] As an embodiment, a guide baffle is provided in the tertiary air channel.

[0008] As an implementation form, the cyclone secondary air channel is in a cyclone structure, so that the air entering is fully cyclone, forming a cyclone secondary air to promote the mixing of the pulverized coal and the air.

[0009] As an implementation form, the pulverized coal and the primary air in the primary air channel are mixed in the mixing area of the primary air and the secondary air at the outlet of the primary air channel, forming a high-temperature backflow area.

[0010] As an implementation form, the nozzles are uniformly arranged on the nozzle plate.

[0011] As an implementation form, the proportions of the primary air in the pulverized coal and primary air channel, the secondary air in the cyclone secondary air channel, and the tertiary air in the tertiary air channel are 2:5:3.

[0012] As an implementation form, the air speeds of the primary air in the pulverized coal and primary air channel, the secondary air in the cyclone secondary air channel, and the tertiary air in the tertiary air channel are sequentially increased.

[0013] As an implementation form, the cross-sectional area of the nozzles on the nozzle plate in the ammonia gas channel is greater than the cross-sectional area of the nozzles on the nozzle plate in the water vapor channel.

[0014] The second aspect of the present application provides a working method of a pulverized coal ammonia-doped combustion device with steam preheating and conditioning.

[0015] A working method of a pulverized coal ammonia-doped combustion device with steam preheating and conditioning, comprising: The water vapor transfers part of the heat to the ammonia gas, and a part of the ammonia gas is pre-decomposed to generate NH2 and NH, and another part of the pre-decomposed ammonia gas is sprayed into the burner from the nozzles of the nozzle plate; The ammonia gas is pre-decomposed or under-oxygen combustion in the furnace, and the water vapor outside the ammonia gas is sprayed through the water vapor nozzles, at this time, the high-temperature water vapor plays a role of isolating the ammonia gas and the pulverized coal, and achieves the purpose of ammonia-coal layered combustion; The pulverized coal outside the water vapor channel forms a local backflow area at the junction of the primary air and the secondary air outside the outlet under the action of the trumpet-shaped flared portion, and the high-temperature secondary air is sucked to promote the pyrolysis and combustion of the pulverized coal; The secondary air outside the pulverized coal fully reacts with the pulverized coal outside the burner, forming a lean combustion zone to further reduce the generation of NO; the tertiary air is introduced to stabilize the flame shape and protect the inner wall of the burner.

[0016] The present application has the following advantages: (1) The present application exchanges heat between water vapor and ammonia gas, so that the ammonia gas is partially pre-decomposed after entering the combustion chamber, generating free NH2, NH and H free radicals, reducing the difficulty of subsequent ammonia gas ignition and combustion, improving the poor combustion performance of ammonia gas, and improving the energy utilization efficiency of the system.

[0017] (2) The present application realizes the conditioning effect of water vapor. Water is a three-atom molecule, and has a large specific heat capacity, which makes the temperature distribution in the furnace more uniform, avoiding the occurrence of local overheating areas. In addition, water vapor will decompose into H, OH and other free radicals at high temperatures. These free radicals can inhibit the oxidation of key intermediates HCN, HNO and the like to NO x in the ammonia-coal blending combustion process, thereby reducing the amount of NO x generation, reducing the cost of subsequent selective non-catalytic reduction denitrification process, and improving the economic benefit of coal-fired power plants.

[0018] (3) The present application realizes ammonia-coal layered combustion through the isolation effect of water vapor. Ammonia is pre-combusted and decomposed near the axis of the burner, and coal is pyrolyzed and combusted on the outside. The two are separated by water vapor to avoid the generation of a large amount of NO x in the coupled combustion process. The coal powder on the periphery is combusted first, and part of the heat released during coal combustion provides a reliable heat atmosphere for the decomposition and combustion of ammonia through heat conduction. The peripheral coal can quickly consume the oxygen in the secondary air, making the ammonia combustion area exhibit lean combustion characteristics. In this working condition, the nitrogen element in ammonia tends to generate non-toxic and harmless N2, rather than NO x in the rich combustion condition. This design further reduces the generation of pollutants NO x while ensuring the reduction of CO2 emissions, and improves the operation stability and flexibility compared to direct ammonia-coal blending combustion.

[0019] The advantages of the additional aspects of the present application will be partially given in the following description, partially will become apparent from the following description, or will be understood through the practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0020] The drawings accompanying the specification of the present application serve to provide a further understanding of the present application, and the illustrative embodiments of the present application and their descriptions serve to explain the present application, and do not constitute an improper limitation of the present application.

[0021] Figure 1 is a high-temperature steam preheating conditioning coal powder ammonia blending combustion device of an embodiment of the present application; Figure 2 is a nozzle cross section of an embodiment of the present application; Figure 3 is a cross section of a cyclone secondary air passage of an embodiment of the present application. DETAILED DESCRIPTION

[0022] The present application will be further described below in conjunction with the drawings and embodiments.

[0023] It should be noted that the following detailed description is illustrative only, and is intended to provide further description in order to provide a thorough understanding of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the application pertains.

[0024] It is also important to note that the terms used herein are not intended to limit the particular embodiments of the present application disclosed in this specification. Rather, any person of ordinary skill in the art will recognize that many changes can be made thereto without departing from the spirit and scope of the present application. Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the application pertains.

[0025] In the present application, the terms such as "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "side", "bottom", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, which is only a relationship word determined for the convenience of describing the structural relationship of the components or elements of the present application, and cannot be understood as a limitation on the present application.

[0026] In the present application, the terms such as "fixedly connected", "connected", "connected" and the like should be understood broadly, which means that it can be fixedly connected, integrally connected or detachably connected, and it can be directly connected or indirectly connected through an intermediate medium. For relevant researchers or technicians in the art, the specific meaning of the above terms in the present application can be determined according to the specific circumstances, and cannot be understood as a limitation on the present application.

[0027] According to Figure 1 , the embodiment of the present application provides a pulverized coal ammonia blending combustion device for steam preheating and conditioning, which comprises a nozzle and a pipeline assembly connected with the nozzle. The pipeline assembly comprises an ammonia gas pipeline, and water vapor channels, pulverized coal and primary air channels, rotational flow secondary air channels and tertiary air channels are sequentially arranged outward in an axisymmetric manner on both sides of the ammonia gas pipeline. The ammonia gas pipeline and the water vapor channel are both provided with a nozzle plate, and the nozzle plate is uniformly provided with a nozzle.

[0028] Among them, the nozzle plate is a shower head type. A flow guide baffle is arranged in the tertiary air channel.

[0029] The periphery of the ammonia gas pipeline of the embodiment of the present application is surrounded by the water vapor pipeline (the water vapor can be derived from the exhaust steam of the low-pressure cylinder of the steam turbine, and the temperature is about 100-200 DEG C). The small holes on the nozzle plate at the end of the water vapor pipeline improve the rigidity of the water vapor jet. The periphery of the water vapor pipeline is the pulverized coal pipeline, and the coal enters the burner through the pipeline. The periphery of the pulverized coal pipeline is the secondary air pipeline and the tertiary air pipeline, respectively.

[0030] The cross section of the device is concentric circles, as shown, from inside to outside, ammonia, water vapor, coal powder and primary air, secondary air, tertiary air. Figure 2

[0031] The combustion details of the material are as follows: In the conveying pipeline, the water vapor outside the ammonia can preheat the ammonia, and the presence of a large amount of water vapor will form hydrogen bonds with the ammonia, thereby reducing the N-H bond dissociation energy and improving the poor combustion characteristics of ammonia. After passing through the conveying pipeline, the ammonia and water vapor converge near the central axis of the burner and mix thoroughly.

[0032] Further, due to the insulating effect of water vapor, the coal powder on the outside is not easy to contact with the ammonia on the inside, and the heat generated by coal pyrolysis and combustion can provide a reliable heat atmosphere for ammonia combustion, achieving the purpose of ammonia-coal layered combustion and reducing the generation of nitrogen oxides.

[0033] Figure 3 The cross section of the swirl secondary air nozzle. The cross section design makes the air flowing in fully swirl, forming swirl secondary air to promote the mixing of fuel and air, and establishing a high-temperature backflow area at the primary air and secondary air mixing area at the outlet to improve flame stability.

[0034] The outermost tertiary air serves to stabilize the flame shape and protect the inner wall of the burner.

[0035] In the specific implementation process, the swirl secondary air channel is in a swirl structure to make the air flowing in fully swirl, forming swirl secondary air to promote the mixing of coal powder and air. The primary air and secondary air mixing area at the outlet of the coal powder and primary air channel forms a high-temperature backflow area.

[0036] In this embodiment, the ratio of primary air in the coal powder and primary air channel, secondary air in the swirl secondary air channel, and tertiary air in the tertiary air channel is 2:5:3. The air speed in the primary air in the coal powder and primary air channel, secondary air in the swirl secondary air channel, and tertiary air in the tertiary air channel increases in turn.

[0037] In this embodiment, the nozzles are uniformly arranged on the nozzle plate. The cross-sectional area of the nozzles on the nozzle plate in the ammonia pipe is larger than that of the nozzles on the nozzle plate in the water vapor channel.

[0038] The proportioning details of each nozzle are as follows: ​With a 600 MW coal-fired boiler as an example, the ammonia mixing ratio is 20 cal.%, the boiler thermal efficiency is 93%, the low heat value of ammonia is 18.60 MJ / kg, the low heat value of coal is 20.9 MJ / kg, the excess air coefficient is 1.2, the primary air, secondary air and tertiary air account for 20%, 50% and 30% respectively, and the steam is calculated as 5% of the ammonia flow. In addition, in order to avoid the material from being too fast to cause pipeline corrosion, and at the same time to make the material fully mixed, according to the experience value, the ammonia injection speed into the furnace is about 30-60 m / s, the steam is about 25-35 m / s, the coal powder and the primary air speed is about 15-25 m / s, the secondary air speed is about 40-60 m / s, and the tertiary air speed is about 60-80 m / s. According to the above-mentioned experience value and the distribution ratio of the primary air, the secondary air and the tertiary air, the ammonia injection port, the steam injection port, the primary air injection port, the secondary air injection port and the tertiary air injection port can be designed. It is calculated that the total cross-sectional area of the ammonia injection port is 0.149-0.298 m 2 , the total cross-sectional area of the steam injection port is 0.018-0.030 m 2 , the cross-sectional area of the coal powder and the primary air injection port is 1.72-2.87 m 2 , the cross-sectional area of the secondary air injection port is 1.79-2.69 m 2 , and the cross-sectional area of the tertiary air injection port is 0.806-1.075 m 2 .

[0039] The operation process of the combustion device is as follows: When the device is running, the water vapor transfers part of the heat to the ammonia, and part of the ammonia is pre-decomposed to produce NH2 and NH. Part of the pre-decomposed ammonia is injected into the burner from the small holes in the injection head plate. These small holes can increase the jet speed and thus improve the flame rigidity. The ammonia is pre-decomposed or under-oxygen combustion in the furnace. The water vapor around the ammonia is injected into the furnace through the water vapor injection port at a high speed. At this time, the high-temperature water vapor plays a role in isolating the ammonia and the coal powder, achieving the purpose of ammonia-coal layered combustion. The coal powder outside the water vapor pipeline can form a local recirculation zone at the outlet of the trumpet-shaped expansion under the action of the trumpet-shaped expansion, and the high-temperature secondary air is sucked to promote the pyrolysis and combustion of the coal powder. The outer periphery of the coal powder is the secondary air pipeline, and the secondary air fully reacts with the coal powder outside the burner to form a poor combustion zone near the central axis with less oxygen, further reducing the generation of NO. The outermost pipeline of the pipeline is the tertiary air, which stabilizes the flame shape and protects the inner wall of the burner.

[0040] The above only describes the preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A steam preheated and tempered coal powder mixed with ammonia combustion device, characterized in that: include: A nozzle and a pipe assembly connected to the nozzle; The pipeline assembly includes an ammonia pipeline, and a water vapor channel, a pulverized coal and primary air channel, a swirl secondary air channel and a tertiary air channel are symmetrically arranged along both sides of the ammonia pipeline. The ammonia pipeline and the water vapor channel are both provided with nozzle plates, and the nozzle plates are provided with nozzles; the ammonia in the ammonia pipeline and the water vapor in the water vapor channel converge near the central axis of the burner and are fully mixed.

2. The steam preheated and tempered pulverized coal mixed with ammonia combustion device according to claim 1, characterized in that: The nozzle plate is of shower head type.

3. The steam preheated and tempered pulverized coal mixed with ammonia combustion device according to claim 1, characterized in that: A guide baffle is provided in the tertiary air channel.

4. The steam preheated and tempered pulverized coal mixed with ammonia combustion device according to claim 1, characterized in that: The swirl secondary air channel is of a swirl structure, so that the air introduced therein can fully swirl, forming swirl secondary air to promote the mixing of pulverized coal and air.

5. The steam preheated and tempered pulverized coal mixed with ammonia combustion device according to claim 1, characterized in that: The primary air and secondary air mixing area at the outlet of the pulverized coal and the primary air channel forms a high-temperature reflux area.

6. The steam preheated and tempered pulverized coal mixed with ammonia combustion device according to claim 1, characterized in that: The nozzles are evenly arranged on the nozzle plate.

7. The steam preheated and tempered pulverized coal mixed with ammonia combustion device according to claim 1, characterized in that: The ratio of pulverized coal to primary air in the primary air channel, secondary air in the swirl secondary air channel and tertiary air in the tertiary air channel is 2:5:

3.

8. The steam preheated and tempered pulverized coal mixed with ammonia combustion device according to claim 1, characterized in that: The wind speeds of the pulverized coal and the primary air in the primary air channel, the secondary air in the swirl secondary air channel, and the tertiary air in the tertiary air channel increase sequentially.

9. The steam preheated and tempered pulverized coal mixed with ammonia combustion device according to claim 1, characterized in that: The cross-sectional area of ​​the nozzles on the nozzle plate in the ammonia pipeline is greater than the cross-sectional area of ​​the nozzles on the nozzle plate in the water vapor channel.

10. A method for operating a pulverized coal-ammonia combustion device using steam preheating and tempering according to any one of claims 1 to 9, characterized in that: include: The water vapor transfers part of the heat to the ammonia gas, part of the ammonia gas is pre-decomposed to produce NH2 and NH, and the other part of the pre-decomposed ammonia gas is sprayed into the burner from the nozzle of the nozzle plate; Ammonia undergoes pre-combustion decomposition or oxygen-deficient combustion in the furnace, and water vapor surrounding the ammonia passes through the steam nozzle. At this time, the high-temperature steam acts to isolate the ammonia and coal powder, achieving the purpose of ammonia-coal stratified combustion; The pulverized coal on the outside of the steam pipe forms a local recirculation zone at the junction of the primary air and the secondary air outside the outlet under the effect of the trumpet-shaped expansion, which draws in the high-temperature secondary air to promote the pyrolysis and combustion of the pulverized coal. The secondary air outside the pulverized coal fully reacts with the pulverized coal outside the burner to form a lean combustion zone to further reduce the generation of NO; ​​the tertiary air is introduced into the outermost area to stabilize the flame shape and protect the inner wall of the burner.

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