System and method for ammonia-coal blending combustion of a pulverized coal boiler of a power plant

Abstract

The application discloses a system and method for ammonia-coal blending combustion of a pulverized coal boiler of a power station. The system and method utilize the heat of high-temperature flue gas to obtain high-temperature ammonia gas and coal pyrolysis gas, realize step-by-step utilization of energy, and are favorable for improving the energy utilization efficiency of the system. The boiler is divided into a pulverized coal ignition area, an ammonia-coal main combustion area, an ammonia gas reduction area and a burnout area. The coal pyrolysis gas burner is arranged in the pulverized coal ignition area, the pulverized coal burner, the secondary air injection port and the ammonia-coal burner are arranged on the ammonia-coal main combustion area, the ammonia gas burner is arranged on the ammonia gas reduction area, and the burnout air injection port is arranged on the burnout area, which is favorable for stable blending combustion of ammonia and coal and reduction of nitrogen oxide emission. The flue gas detection and feedback device and the ammonia gas flow adjusting valve are utilized to adjust the ammonia gas flow at the inlet of the ammonia gas burner, which is favorable for avoiding excessive nitrogen oxide generated by excessive NH3 combustion.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fuel combustion, and particularly relates to a system and method for ammonia-coal mixed combustion of a pulverized coal boiler of a power station. BACKGROUND

[0002] Coal-fired power generation provides about 29% of the world's primary energy, but compared with any other power generation method, the CO2 emissions of coal-fired boilers are also more. Therefore, there is considerable potential for reducing the CO2 emissions of coal-fired boilers of thermal power plants.

[0003] Ammonia, as an artificially synthesized energy storage material, has the characteristics of low liquefaction pressure, safe storage, and carbon-free and particle-free combustion products, and has similar storage and transportation characteristics as fossil fuels. It is a good hydrogen carrier and energy storage fuel, has the advantages of being safer and more economical than hydrogen, and is an ideal energy conversion carrier. Developing and utilizing high-efficiency and low-pollution combustion technology of ammonia can become one of the effective ways to solve the replacement of fossil energy and reduce carbon emissions of thermal power units. However, the combustion speed, flame structure, ignition temperature, NOx emission and other key parameters of ammonia fuel combustion under various conditions are still not perfect, and the reaction mechanism of ammonia combustion is not clear. Pure ammonia combustion cannot be used in the current coal-fired units, and ammonia cannot directly replace coal in the short term. Therefore, mixing coal and ammonia for combustion in coal-fired units is a key measure for the thermal power industry to reduce CO2 emissions. However, ammonia-coal mixed combustion has poor combustion characteristics, and the increase of the ammonia mixing ratio will reduce the combustion efficiency of the boiler, making it difficult to achieve large-scale ammonia mixing, and the NOx emission of the flue gas after ammonia combustion is high. x x SUMMARY

[0004] The purpose of the present application is to provide a system and method for ammonia-coal mixed combustion of a pulverized coal boiler of a power station to solve the problems of poor combustion stability, difficulty in achieving large-scale ammonia mixing, and high NOx emission of flue gas after combustion in ammonia-coal mixed combustion as described in the background. x

[0005] The present application is realized by adopting the following technical solutions:

[0006] A system for ammonia-coal mixed combustion of a pulverized coal boiler of a power station, comprising a boiler body, an air preheater, a liquid ammonia storage tank, a heat exchanger, a coal powder preheating decomposer, a coal supply device, a primary air fan and a secondary air fan, the boiler body is sequentially provided with a coal powder ignition zone, an ammonia-coal main combustion zone, an ammonia gas reduction zone and a burnout zone from bottom to top;

[0007] ​​​The coal pyrolysis gas burner is arranged on the side wall of the coal ignition zone, the coal burner, the first layer of secondary air injection port, the ammonia coal burner and the second layer of secondary air injection port are arranged on the side wall of the ammonia coal main combustion zone from bottom to top, the ammonia gas burner is arranged on the side wall of the ammonia gas reduction zone, and the three layers of burnout air injection ports are arranged on the side wall of the burnout zone.

[0008] The air preheater is arranged in the boiler tail flue, the primary air provided by the primary air fan is preheated by the air preheater, part of the primary air enters the coal ignition zone and the ammonia coal main combustion zone through the coal pyrolysis gas burner and the ammonia coal burner, and the other part of the primary air directly enters the ammonia coal main combustion zone through the coal burner; the secondary air provided by the secondary air fan is preheated by the air preheater and then enters the ammonia coal main combustion zone through the secondary air injection port.

[0009] The flue gas is led out from the air preheater to the heat exchanger to exchange heat with the liquid ammonia provided by the liquid ammonia storage tank, and the liquid ammonia is cooled to obtain low-temperature ammonia gas; the low-temperature ammonia gas is heated again in the air preheater to obtain high-temperature ammonia gas, and the high-temperature ammonia gas enters the ammonia coal main combustion zone and the ammonia gas reduction zone through the ammonia coal burner and the ammonia gas burner.

[0010] The coal provided by the coal supply device and the primary air preheated by the air preheater are introduced into the coal pyrolysis gas burner, and the high-temperature flue gas is led out from the end of the boiler horizontal flue to the coal pyrolysis gas burner for heat exchange, so that the coal pyrolysis gas is obtained.

[0011] The further improvement of the present application is that the ammonia gas flow adjusting valve is further included, which is used for adjusting the ammonia gas flow at the inlet of the ammonia gas burner according to the NOx content in the exhaust flue gas. x The further improvement of the present application is that the ammonia gas flow adjusting valve is further included, which is used for adjusting the ammonia gas flow at the inlet of the ammonia gas burner according to the NOx content in the exhaust flue gas.

[0012] The further improvement of the present application is that the flue gas detection and feedback device arranged at the boiler horizontal flue is further included, which is used for feeding the NOx content in the flue gas to the ammonia gas flow adjusting valve. x The further improvement of the present application is that the flue gas detection and feedback device arranged at the boiler horizontal flue is further included, which is used for feeding the NOx content in the flue gas to the ammonia gas flow adjusting valve.

[0013] The further improvement of the present application is that the coal supply device includes the coal bunker and the coal mill, and the coal is introduced into the coal mill from the coal bunker.

[0014] The further improvement of the present application is that the coal mill is used for grinding the coal into powder and then sending the powder into the coal pyrolysis gas burner or the coal burner.

[0015] The further improvement of the present application is that the number of each layer of burners is four, the burners are arranged at the four corners of the boiler, and the outlet angles of the burners are consistent.

[0016] The further improvement of the present application is that the main components of the coal pyrolysis gas are carbon monoxide, methane and hydrogen.

[0017] An ammonia coal blending combustion method of an ammonia coal blending combustion system of a power station coal powder boiler, comprising:

[0018] 1) Install a coal pyrolysis gas burner on the side wall of the pulverized coal ignition zone and introduce coal pyrolysis gas for ignition;

[0019] 2) An ammonia burner is installed on the side wall of the main combustion zone of ammonia coal, which introduces high-temperature ammonia gas and coal pyrolysis gas. The main components of the coal pyrolysis gas are CO and H2, which inhibits the reaction of NH3 and excess O2.

[0020] 3) An ammonia burner is installed in the ammonia reduction zone, and high-temperature ammonia gas is introduced to reduce the NO produced by combustion. x Unreacted ammonia gas passes through the combustion zone and reacts fully with the combustion air; based on the NO content in the flue gas detected and fed back by the flue gas detection and feedback device... x To reduce the amount of NH3, adjust the ammonia flow rate at the ammonia burner inlet to decrease the reaction of excess NH3 with the burnout air to generate NO. x ;

[0021] 4) Liquid ammonia is preheated twice to obtain high-temperature ammonia gas. The primary and secondary air are also preheated by air preheaters. Pulverized coal is pyrolyzed using the heat of high-temperature flue gas at the end of the boiler's horizontal flue.

[0022] The present invention provides a system and method for ammonia-coal co-firing in a power plant pulverized coal boiler, which has the following beneficial technical effects:

[0023] (1) A coal pyrolysis gas burner is installed on the side wall of the coal ignition zone. The pyrolysis gas after pyrolysis is introduced for ignition, which is easy to ignite and has good combustion stability.

[0024] (2) An ammonia-coal burner is installed on the side wall of the main combustion zone of the ammonia-coal, through which high-temperature ammonia gas and coal pyrolysis gas are introduced. The main components of the coal pyrolysis gas are CO and H2, and NH3 is mixed with CO. This can simultaneously improve the flame speed of CO and NH3, and CO combines with O2 more quickly, which can inhibit the reaction of NH3 with excess O2 and reduce NO. x content.

[0025] (3) An ammonia burner is installed in the ammonia reduction zone, and high-temperature ammonia gas is introduced to reduce the NO produced by combustion. x Unreacted ammonia gas passes through the combustion zone, where it reacts fully with the combustion air, preventing ammonia escape. The NO content in the flue gas is monitored based on feedback from the flue gas detection and feedback device. x To reduce the amount of NH3, adjust the ammonia flow rate at the ammonia burner inlet to decrease the reaction of excess NH3 with the burnout air to generate NO. x .

[0026] (4) The burner design enables fuel and air grading, which helps reduce the excess air coefficient in the main combustion zone, enhances the reducing properties of the main combustion zone, and reduces NO. x content.

[0027] (5) The liquid ammonia is preheated twice to obtain high-temperature ammonia gas, and the primary air and the secondary air are also preheated by the air preheater, and the pulverized coal is pyrolyzed by using the heat of the high-temperature flue gas at the end of the horizontal flue of the boiler, which is beneficial to improve the efficiency of the boiler and realizes the graded utilization of energy. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a system schematic diagram of the ammonia-coal mixed combustion of the pulverized coal boiler of the power station.

[0029] Mark explanation:

[0030] 1 is a boiler body, 2 is a pulverized coal ignition area, 3 is an ammonia-coal main combustion area, 4 is an ammonia gas reduction area, 5 is a burnout area, 6 is an air preheater, 7 is a coal pyrolysis gas burner, 8 is a pulverized coal burner, 9 is a secondary air injection port, 10 is an ammonia-coal burner, 11 is an ammonia gas burner, 12 is a burnout air injection port, 13 is a liquid ammonia storage tank, 14 is a heat exchanger, 15 is a pulverized coal pre-pyrolyzer, 16 is a flue gas detection and feedback device, 17 is an ammonia gas flow regulating valve, 18 is a coal supply device, 19 is a primary air blower, and 20 is a secondary air blower. DETAILED DESCRIPTION

[0031] The application will be further described in detail below with reference to the drawings:

[0032] Reference Figure 1 The application provides a system for ammonia-coal mixed combustion of a pulverized coal boiler of a power station, which comprises a boiler body 1, a pulverized coal ignition area 2, an ammonia-coal main combustion area 3, an ammonia gas reduction area 4, a burnout area 5, an air preheater 6, a coal pyrolysis gas burner 7, a pulverized coal burner 8, a secondary air injection port 9, an ammonia-coal burner 10, an ammonia gas burner 11, a burnout air injection port 12, a liquid ammonia storage tank 13, a heat exchanger 14, a pulverized coal pre-pyrolyzer 15, a flue gas detection and feedback device 16, an ammonia gas flow regulating valve 17, a coal supply device 18, a primary air blower 19 and a secondary air blower 20.

[0033] The flue gas is led out from the air preheater 6 to the heat exchanger 14 to exchange heat with the liquid ammonia provided by the liquid ammonia storage tank 13, and low-temperature ammonia gas is obtained after the liquid ammonia passes through the heat exchanger 14. The low-temperature ammonia gas is exchanged in the air preheater 6 to obtain high-temperature ammonia gas. The pulverized coal and the primary air passing through the air preheater 6 are introduced into the pulverized coal pre-pyrolyzer 15, and the high-temperature flue gas is led out from the end of the horizontal flue of the boiler to exchange heat with the pulverized coal pre-pyrolyzer 15, so that the coal pyrolysis gas can be obtained.

[0034] Further, the coal pyrolysis gas burner 7 is arranged on the side wall of the pulverized coal ignition area 2, and the coal pyrolysis gas is introduced to ignite, so that the ignition stability is improved.

[0035] Further, in the ammonia coal main combustion zone 3, from bottom to top, the pulverized coal burner 8, the secondary air nozzle 9, the ammonia coal burner 10, and the secondary air nozzle 9 are sequentially arranged. The high-temperature ammonia gas and the coal pyrolysis gas after pyrolysis are introduced into the ammonia coal burner 10, the main component of the coal pyrolysis gas is CO and H2, NH3 is mixed with CO, the flame speed of CO and NH3 can be improved at the same time, CO combines with O2 faster, the reaction of NH3 and excess O2 can be inhibited, and the content of NO x is reduced.

[0036] Further, the ammonia gas burner 11 is arranged in the ammonia gas reduction zone 4, and the high-temperature ammonia gas is introduced, so that the NO x generated by combustion can be reduced.

[0037] Further, the three layers of burnout air nozzles 12 are arranged in the burnout zone 5, react with the ammonia gas that is not reacted in the ammonia gas reduction zone 4, reduce the ammonia escape, and the air staging is beneficial to reduce the excess air coefficient of the main combustion zone, enhance the reduction of the main combustion zone, and reduce the content of NO x .

[0038] Further, the flue gas detection and feedback device 16 at the horizontal flue of the boiler can feed the content of NO x in the flue gas to the ammonia gas flow adjusting valve 17, adjust the ammonia gas flow at the inlet of the ammonia gas burner 11 according to the content of NO x in the exhaust flue gas, and avoid the NO x generated by the reaction of excess NH3 and the burnout air.

[0039] Referring to Figure 1 , the application provides a method for ammonia coal blending combustion of a power station pulverized coal boiler, which comprises the following steps:

[0040] (1) A coal pyrolysis gas burner is arranged on the side wall of the coal ignition zone, and the coal pyrolysis gas is introduced to ignite.

[0041] (2) The ammonia coal burner is arranged on the side wall of the ammonia coal main combustion zone, and the high-temperature ammonia gas and the coal pyrolysis gas are introduced, the main component of the coal pyrolysis gas is CO and H2, and the reaction of NH3 and excess O2 can be inhibited.

[0042] (3) The ammonia gas burner is arranged in the ammonia gas reduction zone, and the high-temperature ammonia gas is introduced, so that the NO x generated by combustion can be reduced. The unreacted ammonia gas passes through the burnout zone, can fully react with the burnout air, and avoids ammonia escape. According to the content of NO x in the flue gas fed by the flue gas detection and feedback device, the ammonia gas flow at the inlet of the ammonia gas burner is adjusted to reduce the NO x generated by the reaction of excess NH3 and the burnout air.

[0043] (4) The liquid ammonia is preheated twice to obtain high-temperature ammonia gas, and the primary air and the secondary air are also preheated by an air preheater, and the pulverized coal is pyrolyzed by using the heat of the high-temperature flue gas at the end of the horizontal flue of the boiler.

[0044] The above merely describes the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and other modifications or equivalent replacements to the technical solutions of the present application made by those skilled in the art should be covered in the protection scope of the present application.

Claims

1. A system for co-firing ammonia and coal in a power plant pulverized coal boiler, characterized in that, The boiler body (1) includes an air preheater (6), a liquid ammonia storage tank (13), a heat exchanger (14), a pulverized coal preheater (15), a coal supply device (18), a primary air fan (19), and a secondary air fan (20). The boiler body (1) is arranged from bottom to top as follows: a pulverized coal ignition zone (2), an ammonia-coal main combustion zone (3), an ammonia reduction zone (4), a burnout zone (5), an ammonia flow regulating valve (17), and a flue gas detection and feedback device (16) installed at the horizontal flue of the boiler. A coal pyrolysis gas burner (7) is installed on the side wall of the pulverized coal ignition zone (2). A pulverized coal burner (8), a first-layer secondary air nozzle (9), an ammonia coal burner (10), and a second-layer secondary air nozzle (9) are installed on the side wall of the ammonia reduction zone (4) from bottom to top. An ammonia burner (11) is installed on the side wall of the ammonia reduction zone (4). A three-layer burnout air nozzle (12) is installed on the side wall of the burnout zone (5). The air preheater (6) is arranged in the flue at the tail end of the boiler. The primary air provided by the primary air fan (19) is preheated by the air preheater (6), and part of it enters the pulverized coal ignition zone (2) and the ammonia coal main combustion zone (3) through the pulverized coal preheater (15), the coal pyrolysis gas burner (7) and the ammonia coal burner (10), while part of it directly enters the ammonia coal main combustion zone (3) through the pulverized coal burner (8). The secondary air provided by the secondary air fan (20) is preheated by the air preheater (6) and enters the ammonia coal main combustion zone (3) through the secondary air nozzle (9). Flue gas is drawn from the air preheater (6) to the heat exchanger (14) to exchange heat with the liquid ammonia supplied by the liquid ammonia storage tank (13). The liquid ammonia is then passed through the heat exchanger (14) to obtain low-temperature ammonia. The low-temperature ammonia is then exchanged again at the air preheater (6) to obtain high-temperature ammonia. The high-temperature ammonia passes through the ammonia coal burner (10) and the ammonia gas burner (11) and enters the ammonia coal main combustion zone (3) and the ammonia gas reduction zone (4). The pulverized coal supplied by the coal supply device (18) and the primary air passing through the air preheater (6) are introduced into the pulverized coal preheater (15), and high-temperature flue gas is drawn from the end of the boiler horizontal flue to the pulverized coal preheater (15) for heat exchange, so as to obtain coal pyrolysis gas. The coal pyrolysis gas is then introduced into the coal pyrolysis gas burner (7) and the ammonia coal burner (10). The ammonia flow regulating valve (17) is used to regulate the flow of NO in the exhaust gas. x The ammonia content is adjusted to regulate the ammonia flow rate at the inlet of the ammonia burner (11); the flue gas detection and feedback device (16) is used to detect NO in the flue gas. x The content is fed back to the ammonia flow regulating valve (17); Each layer of burners consists of four units, arranged at the four corners of the boiler, with the outlet angle of each burner remaining consistent.

2. The system for ammonia-coal co-firing in a power plant pulverized coal boiler according to claim 1, characterized in that, The coal supply device (18) includes a coal bunker and a coal mill, from which coal enters the coal mill.

3. A system for ammonia-coal co-firing in a power plant pulverized coal boiler according to claim 2, characterized in that, The coal mill is used to grind coal into powder and then feed it into the coal powder preheater (15).

4. A system for ammonia-coal co-firing in a power plant pulverized coal boiler according to claim 2, characterized in that, A coal mill is used to grind coal into powder and then feed it into a pulverized coal burner (8).

5. A system for ammonia-coal co-firing in a power plant pulverized coal boiler according to claim 1, characterized in that, The main components of coal pyrolysis gas are carbon monoxide, methane, and hydrogen.

6. The ammonia-coal co-firing method of a pulverized coal boiler system for power plants according to claim 1, characterized in that, include: 1) A coal pyrolysis gas burner (7) is installed on the side wall of the pulverized coal ignition zone (2) to introduce coal pyrolysis gas for ignition; 2) An ammonia coal burner (10) is installed on the side wall of the main combustion zone (3) of ammonia coal, which introduces high-temperature ammonia gas and coal pyrolysis gas. The main components of the coal pyrolysis gas are CO and H2, which inhibits the reaction of NH3 and excess O2. 3) An ammonia burner (11) is installed in the ammonia reduction zone (4) to introduce high-temperature ammonia gas, which reduces the NO produced by combustion. x Unreacted ammonia gas passes through the burnout zone (5) and reacts fully with the burnout air; the NO in the flue gas is detected and fed back by the flue gas detection and feedback device (16). x To reduce the amount of NH3, adjust the ammonia flow rate at the inlet of the ammonia burner (11) to decrease the reaction of excess NH3 with the burnout air to generate NO. x ; 4) Liquid ammonia is preheated twice to obtain high-temperature ammonia gas. The primary and secondary air are also preheated by air preheaters. Pulverized coal is pyrolyzed using the heat of high-temperature flue gas at the end of the boiler's horizontal flue.

Images