Ultralow-load stable combustion system and method for pulverized coal fired boiler

Abstract

The invention discloses an ultralow-load stable combustion system and method for a pulverized coal fired boiler. The ultralow-load stable combustion system comprises a pulverized coal concentration separator device, an oxygen preparation device, an oxygen storage tank, a heater, a thick pulverized coal burner, a thin pulverized coal burner and an oxygen-enriched combustion-supporting air nozzle. An inlet of the pulverized coal concentration separator device is connected with a primary air pulverized coal feeding pipeline, a thick pulverized coal outlet of the pulverized coal concentration separator device is connected with a thick pulverized coal burner through a first pipeline, and a thin pulverized coal outlet is connected with a thin pulverized coal burner through a second pipeline. The oxygen preparation device is connected with the oxygen storage tank, the oxygen storage tank is connected with the heater, and the heater is connected with the oxygen-enriched combustion-supporting air nozzle arranged above the dense pulverized coal burner. The method comprises the following steps: separating primary air into thick pulverized coal and thin pulverized coal; the thick pulverized coal is fed into a thick pulverized coal burner, and the thin pulverized coal is fed into a thin pulverized coal burner; preparing high-concentration oxygen, heating the high-concentration oxygen, and spraying the heated high-concentration oxygen to the upper part of the And stable combustion is maintained when the boiler load is lower than 20%. Continuous and stable combustion of the boiler under the load of 20% or below is achieved.

Description

Technical Field

[0001] This invention relates to the field of pulverized coal boiler combustion technology, specifically to a pulverized coal boiler ultra-low load stable combustion system and method for deep peak shaving conditions. Background Technology

[0002] In recent years, with the country's vigorous promotion of the development of new energy power generation technologies, the proportion of clean energy such as wind power, photovoltaic power, hydropower, and nuclear power in the power structure has been increasing year by year, while the utilization hours of thermal power units have continued to decline, and partial load operation has become the norm. At the same time, in order to ensure the safe and stable operation of the power grid, especially when the output of new energy power generation fluctuates greatly, large thermal power units are required to have stronger deep peak-shaving capabilities to adapt to the changing needs of the power grid load.

[0003] One of the key technical challenges in achieving deep peak shaving for coal-fired power units lies in the ability to maintain stable combustion under low loads. When the boiler load drops below 30% or even below 20%, the furnace temperature drops significantly, making it difficult for pulverized coal to ignite and resulting in poor flame stability. This can easily lead to flameout or unstable combustion, and in severe cases, may cause furnace fire extinguishing or even an explosion, threatening the safe operation of the unit.

[0004] Traditional low-load stable combustion technologies such as micro-oil ignition and plasma ignition have improved ignition capability to some extent, but under ultra-low load conditions (such as below 20%), it is still difficult to maintain continuous and stable combustion, and there are problems such as system complexity, high operating costs, and poor adaptability to coal quality.

[0005] To this end, this invention proposes an ultra-low load stable combustion system and method for pulverized coal boilers based on the combination of pulverized coal concentration and separation with oxygen-enriched combustion. By increasing the concentration of pulverized coal, the concentration of oxygen in the combustion air, and the temperature of the combustion air entering the burner, the combustion stability under low load is significantly improved without changing the existing main structure of the boiler and the pulverizing system, so as to achieve continuous and stable operation of the boiler under loads below 20%. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing boilers in terms of poor combustion stability and easy flameout when operating at ultra-low loads, and to provide a stable combustion system and method for pulverized coal boilers at ultra-low loads. Through the technical means of combining pulverized coal concentration and separation with oxygen-enriched combustion, continuous and stable combustion is achieved at loads below 20%.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A pulverized coal boiler ultra-low load stable combustion system includes: The coal powder thickener separator has its inlet connected to the primary air conveying pipeline to separate the coal powder in the primary air into concentrated coal powder and dilute coal powder. An oxygen preparation device used to produce high-concentration oxygen; An oxygen storage tank, connected to the oxygen preparation device, is used to store oxygen; A heater, connected to the oxygen storage tank, is used to heat the oxygen; The concentrated pulverized coal burner is connected to the concentrated pulverized coal outlet of the pulverized coal thickener / separator via a pipeline. The pulverized coal burner is connected to the pulverized coal outlet of the pulverized coal thickener / separator via a pipeline.

[0009] The oxygen-enriched combustion air nozzle is designed as an integral part of the burner's secondary combustion air nozzle, connected to the heater, and arranged above the pulverized coal burner. It is used to inject heated pure oxygen and hot secondary air to increase the oxygen content and temperature of the secondary combustion air adjacent to the burner. The oxygen concentration of the secondary combustion air is adjusted by the regulating valve set on the secondary air duct and the corresponding pure oxygen pipeline regulating valve to improve the combustion capability.

[0010] Furthermore, the pulverized coal thickener / separator includes:

[0011] Primary air inlet pipe, separation elbow, separator outer cylinder, separator inner cylinder and arc guide plate;

[0012] The primary air inlet pipe and the separation elbow are installed eccentrically.

[0013] The bending angle of the separation elbow is 45° to 90°.

[0014] Furthermore, the center lines of the inner cylinder and the outer cylinder of the separator are parallel but not collinear.

[0015] Furthermore, the bending radius of the separation elbow is 1.25 to 1.5 times the radius of the outer cylinder of the separator.

[0016] Furthermore, the ratio of the maximum to the minimum distance between the inner and outer cylinders of the separator is 2:1.

[0017] Furthermore, the arc-shaped guide plate has the same bending radius as the inner side of the separation elbow but is not concentric, and is connected to the inner cylinder of the separator.

[0018] Furthermore, the primary air conveying pulverized coal pipeline has two layers, and a pulverized coal concentration separator is installed on both layers of primary air conveying pulverized coal pipeline; the pipeline connected to the dilute pulverized coal outlet is equipped with an electrically adjustable shrinkage orifice.

[0019] Furthermore, an electric regulating valve is installed on the pipeline between the oxygen storage tank and the heater; the heater is an explosion-proof heater.

[0020] Furthermore, the light pulverized coal burner and the heavy pulverized coal burner are arranged separately; there are multiple pure oxygen combustion air nozzles, which are evenly arranged above the heavy pulverized coal burner.

[0021] A method for stable combustion of pulverized coal boilers under ultra-low load, applied to the aforementioned system, is characterized by comprising the following steps:

[0022] S1. Primary air is introduced into the coal powder thickener and separator to separate it into concentrated coal powder and light coal powder.

[0023] S2. Feed the concentrated pulverized coal into the concentrated pulverized coal burner and the light pulverized coal into the light pulverized coal burner;

[0024] S3. High-concentration oxygen is produced by an oxygen preparation device and stored in an oxygen storage tank;

[0025] S4. After the oxygen is heated by the heater, the heated pure oxygen and hot secondary air are injected to increase the oxygen content and temperature of the combustion secondary air adjacent to the burner; the oxygen concentration of the combustion secondary air is adjusted by the regulating valve set on the secondary air duct and the corresponding pure oxygen pipeline regulating valve to improve the combustion capability.

[0026] S5. When the boiler load is below 20%, maintain stable combustion of the pulverized coal burner to achieve stable combustion at ultra-low load.

[0027] Compared with the prior art, the beneficial effects of the present invention are: 1. Increase coal powder concentration: More than 90% of the coal powder in the primary air is separated by the coal powder thickener and sent to the concentrated coal powder burner, which significantly increases the coal powder concentration in the combustion zone, reduces the ignition heat required for the coal powder, and improves the ignition conditions; 2. Increase the oxygen concentration for combustion: By using oxygen-enriched combustion, the oxygen content in the combustion gases is significantly increased, thereby enhancing the combustion intensity; 3. Increase the temperature of the combustion air: By heating pure oxygen with a heater, the temperature of the combustion air is further increased, which promotes the ignition and stable combustion of pulverized coal; 4. Good system independence: The modification can be carried out without changing the existing main structure of the boiler and the pulverizing system, resulting in low investment costs and a short modification cycle; 5. Wide range of applications: Applicable to pulverized coal boilers of various capacities, especially suitable for large thermal power units that require deep peak shaving; 6. High operational safety: By improving combustion stability, it avoids flameout or explosion accidents during low-load operation, ensuring the safe operation of the unit. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of the pulverized coal boiler ultra-low load stable combustion system provided in an embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram of the coal powder thickener separator device in an embodiment of the present invention.

[0030] Explanation of reference numerals in the attached figures:

[0031] 1-Primary air conveying pipeline; 2-Pulverized coal thickener and separator device; 3-First pipeline; 4-Second pipeline; 5-Electrically adjustable constriction orifice; 6-Concentrated pulverized coal burner; 7-Depleted pulverized coal burner; 8-Oxygen-enriched combustion air nozzle; 9-Oxygen preparation device; 10-Oxygen storage tank; 11-Electrically regulating valve; 12-Heater; 13-Regulating valve; 14-Regulating valve; 21-Primary air inlet pipe; 22-Depleted pulverized coal outlet; 23-Concentrated pulverized coal outlet; 24-Separation elbow; 25-Separator outer cylinder; 26-Separator inner cylinder; 27-Arc-shaped guide plate. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] like Figure 1 As shown, this embodiment provides an ultra-low load stable combustion system for a pulverized coal boiler, including a pulverized coal thickener separator 2, an oxygen preparation device 9, an oxygen storage tank 10, a heater 12 (the heater can be a flue gas, steam, gas, or electric heater), a concentrated pulverized coal burner 6, a light pulverized coal burner 7, and an oxygen-enriched combustion air nozzle 8.

[0034] The inlet of the pulverized coal thickener / separator 2 is connected to the primary air conveying pipe 1 to separate the pulverized coal in the primary air into concentrated pulverized coal and diluted pulverized coal. The concentrated pulverized coal outlet 23 of the pulverized coal thickener / separator 2 is connected to the concentrated pulverized coal burner 6 via a first pipe 3, and the diluted pulverized coal outlet 22 is connected to the diluted pulverized coal burner 7 via a second pipe 4. The second pipe 4 is equipped with an electrically adjustable orifice 5 for adjusting the flow rate of diluted pulverized coal, thereby controlling the ratio of concentrated to diluted pulverized coal.

[0035] The oxygen preparation device 9 is a pressure swing adsorption (PSA) oxygen generator, connected to the oxygen storage tank 10 via a pipeline, for preparing and storing high-concentration oxygen (purity ≥90%). The oxygen storage tank 10 is connected to the heater 12 via a pipeline, and an electric regulating valve 11 is installed on the pipeline to control the oxygen flow rate. The heater 12 is an explosion-proof heater capable of heating oxygen to 150℃~300℃.

[0036] The heater 12 is connected to multiple oxygen-enriched combustion air nozzles 8 via pipes. The oxygen-enriched combustion air nozzles 8 are evenly arranged in the area above the pulverized coal burner 6 and are used to inject heated oxygen-enriched air into the pulverized coal combustion area to assist combustion.

[0037] like Figure 2As shown, the pulverized coal thickener separator 2 includes a primary air inlet pipe 21, a separation elbow 24, an outer separator cylinder 25, an inner separator cylinder 26, and an arc-shaped guide plate 27. The primary air inlet pipe 21 and the separation elbow 24 are installed eccentrically, causing centrifugal separation when the pulverized airflow enters the separation elbow. The bending angle of the separation elbow 24 is 45°~90°, and the bending radius is 1.5 times the radius of the outer separator cylinder 25. The centerlines of the inner separator cylinder 26 and the outer separator cylinder 25 are parallel but not collinear, and the ratio of their maximum to minimum distance is 2:1. The arc-shaped guide plate 27 has the same bending radius as the inner side of the separation elbow 24 but is not concentric, and is connected to the inner separator cylinder 26, further optimizing airflow guidance and improving separation efficiency.

[0038] In this embodiment, the primary air conveying pulverized coal pipeline 1 has 4 to 6 layers, and pulverized coal concentration separators 2 are installed on two of the layers of primary air conveying pulverized coal pipeline 1; the second pipeline 4 connected to the desalted pulverized coal outlet 22 is equipped with an electrically adjustable orifice 5, suitable for small and medium-sized boilers. Testing shows that this device can separate more than 90% of the pulverized coal in the primary air and send it to the concentrated pulverized coal burner 6, while the remaining approximately 10% of the desalted pulverized coal is sent to the desalted pulverized coal burner 7.

[0039] Meanwhile, this application also provides a method for stable combustion of pulverized coal boilers under ultra-low load, applied to the aforementioned pulverized coal boiler ultra-low load stable combustion system, comprising the following steps:

[0040] S1. Primary air is introduced into the coal powder thickener separator 2, and the coal powder in the primary air is separated into concentrated coal powder and light coal powder through centrifugal separation, wherein the concentrated coal powder accounts for more than 90% of the total coal powder.

[0041] S2. The concentrated coal powder is fed into the concentrated coal powder burner 6 through the first pipe 3, and the light coal powder is fed into the light coal powder burner 7 through the second pipe 4. The flow rate of light coal powder is adjusted by the electric adjustable constriction orifice 5 to control the ratio of concentrated to light coal powder.

[0042] S3. High-concentration oxygen is produced by oxygen preparation device 9 and stored in oxygen storage tank 10;

[0043] S4. After the oxygen is heated to a set temperature (e.g., 200°C) by the heater 12, the heated pure oxygen and hot secondary air are injected to increase the oxygen content and temperature of the combustion secondary air adjacent to the burner; the oxygen concentration of the combustion secondary air is adjusted by the regulating valve 13 set on the secondary air duct and the corresponding pure oxygen pipeline regulating valve 14 to improve the combustion capability.

[0044] S5. When the boiler load is below 20%, maintain stable combustion of the pulverized coal burner 6 to achieve stable combustion under ultra-low load.

[0045] The system and method of this invention were tested on a 600MW coal-fired power unit. The results showed that when the boiler load dropped to 15%, the pulverized coal burner area could still maintain stable combustion, the furnace temperature fluctuation range was less than ±20℃, NOx emissions did not increase significantly, and the system operation was safe and reliable. Compared with traditional low-load stable combustion technology, this invention has better stable combustion effect and higher economy at lower loads.

[0046] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A pulverized coal boiler ultra-low load stable combustion system, characterized in that, include: The coal powder thickener separator (2) has its inlet connected to the primary air conveying pipeline (1) and is used to separate the coal powder in the primary air into concentrated coal powder and light coal powder. Oxygen preparation device (9), used to prepare high-concentration oxygen; An oxygen storage tank (10) is connected to the oxygen preparation device (9) and is used to store oxygen; A heater (12) is connected to the oxygen storage tank (10) for heating oxygen; The pulverized coal burner (6) is connected to the pulverized coal outlet (23) of the pulverized coal thickener / separator device (2) via the first pipe (3); The light pulverized coal burner (7) is connected to the light pulverized coal outlet (22) of the pulverized coal thickener / separator device (2) via a second pipe (4); The oxygen-enriched combustion air nozzle (8) is designed as an integral part of the combustion secondary air nozzle of the burner, connected to the heater (12), and arranged above the pulverized coal burner (6). It is used to inject heated pure oxygen and hot secondary air to increase the oxygen content and temperature of the combustion secondary air adjacent to the burner. The oxygen concentration of the combustion secondary air is adjusted by the regulating valve (14) set on the secondary air duct and the corresponding pure oxygen pipeline regulating valve (13) to improve the combustion capability.

2. The pulverized coal boiler ultra-low load stable combustion system according to claim 1, characterized in that, The pulverized coal thickener / separator device (2) includes: Primary air inlet pipe (21), concentrated powder outlet (23), light powder outlet (22), separation elbow (24), separator outer cylinder (25), separator inner cylinder (26) and arc-shaped guide plate (27); The primary air inlet pipe (21) and the separation elbow (24) are installed eccentrically; The bending angle of the separation elbow (24) is 45° to 90°.

3. The pulverized coal boiler ultra-low load stable combustion system according to claim 2, characterized in that, The center lines of the separator inner cylinder (26) and the separator outer cylinder (25) are parallel but not collinear.

4. The pulverized coal boiler ultra-low load stable combustion system according to claim 2, characterized in that, The bending radius of the separation elbow (24) is 1.25 to 1.5 times the radius of the outer cylinder (25) of the separator.

5. The pulverized coal boiler ultra-low load stable combustion system according to claim 2, characterized in that, The ratio of the maximum distance to the minimum distance between the inner cylinder (26) and the outer cylinder (25) of the separator is 2:

1.

6. The pulverized coal boiler ultra-low load stable combustion system according to claim 2, characterized in that, The arc-shaped guide plate (27) has the same bending radius as the inner side of the separation elbow (24) but is not concentric, and is connected to the inner cylinder (26) of the separator.

7. The pulverized coal boiler ultra-low load stable combustion system according to claim 1, characterized in that, The primary air conveying pulverized coal pipeline (1) has 4 to 6 layers, and a coal powder concentration separator (2) is installed on two of the primary air conveying pulverized coal pipelines (1); the second pipeline (4) connected to the desalted coal outlet (22) is equipped with an electrically adjustable shrinkage orifice (5).

8. The pulverized coal boiler ultra-low load stable combustion system according to claim 1, characterized in that, An electric regulating valve (11) is provided on the pipeline between the oxygen storage tank (10) and the heater (12); the heater (12) is an explosion-proof heater.

9. The pulverized coal boiler ultra-low load stable combustion system according to claim 1, characterized in that, The light pulverized coal burner (7) and the heavy pulverized coal burner (6) are arranged separately; there are multiple pure oxygen combustion air nozzles (8), which are evenly arranged above the heavy pulverized coal burner (6).

10. A method for stable combustion of pulverized coal boilers under ultra-low load, applied to the system described in any one of claims 1 to 9, characterized in that, Includes the following steps: S1. Pass the primary air into the coal powder thickener separator (2) to separate it into concentrated coal powder and light coal powder; S2. The concentrated pulverized coal is fed into the concentrated pulverized coal burner (6), and the light pulverized coal is fed into the light pulverized coal burner (7). S3. High-concentration oxygen is produced by oxygen preparation device (9) and stored in oxygen storage tank (10); S4. After the oxygen is heated by the heater (12), the heated pure oxygen and hot secondary air are injected to increase the oxygen content and temperature of the combustion secondary air adjacent to the burner; the oxygen concentration of the combustion secondary air is adjusted by the regulating valve (14) set on the secondary air duct and the corresponding pure oxygen pipeline regulating valve (13) to improve the combustion capability. S5. When the boiler load is below 20%, maintain stable combustion of the pulverized coal burner (6) to achieve stable combustion under ultra-low load.

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