Low-load stable combustion system for pulverized coal boilers

Abstract

This application provides a low-load stable combustion system for a pulverized coal boiler, comprising a boiler connected in sequence to a high-pressure steam turbine, a heat exchanger, a high-pressure heater, and an economizer installed in the boiler's flue. The gas inlet of the heat exchanger is also connected in sequence to an air preheater and an induced draft fan, and the gas outlet of the heat exchanger is also connected in sequence to a coal mill and a burner installed at the primary air inlet. A steam valve is installed between the high-pressure steam turbine and the heat exchanger. In this application, when the boiler is operating at low load, the device uses a heat exchanger to introduce a portion of the steam extracted from the high-pressure steam turbine as a heating medium to heat the primary air preheated by the air preheater, thereby increasing the primary air inlet temperature and maintaining stable combustion in the furnace under low-load operating conditions. This overcomes the drawbacks caused by unstable combustion in the furnace during low-load boiler operation.

Description

Technical Field

[0001] This application relates to the field of coal-fired boiler technology, and in particular to a low-load stable combustion system for pulverized coal boilers. Background Technology

[0002] With the advancement of carbon peaking and carbon neutrality, the accelerated planning and construction of a new energy system, and the promotion of clean and low-carbon transformation in key sectors, new energy sources, primarily solar, hydro, and wind power, have become the primary development targets for both the nation and the market. However, the current market development of new energy is extremely unstable, and its utilization rate and capacity still need improvement. Fossil fuels, mainly coal, oil, and natural gas, still dominate the market, especially coal. Due to the intermittent and fluctuating nature of new energy sources, large-scale grid connection will impact the power grid. Thermal power plants bear the heavy responsibility of peak power regulation, switching to low-load operation during peak new energy generation periods to enhance the grid's capacity to absorb new energy. However, when coal-fired boilers operate at low loads, the furnace temperature decreases, leading to problems such as incomplete combustion of pulverized coal or even flameout. Therefore, improving the combustion rate of pulverized coal under low loads and achieving stable combustion at low loads has become a major research objective.

[0003] When pulverized coal cannot burn completely in the boiler furnace, it not only affects the boiler's thermal efficiency but also increases the mechanical and chemical incomplete combustion losses of pulverized coal, increases coal fuel consumption, and unburned pulverized coal particles easily form ash accumulation on the tail heating surface, threatening the safe operation of the boiler, shortening equipment life, and producing a large amount of carbon monoxide gas and harmful substances, causing serious environmental pollution. Utility Model Content

[0004] This application provides a low-load stable combustion system for pulverized coal boilers to solve the problems caused by unstable combustion of pulverized coal in the furnace when the boiler is operating at low load, as described in the background art.

[0005] This application provides a low-load stable combustion system for a pulverized coal boiler, including a boiler, which is sequentially connected to a high-pressure steam turbine unit, a heat exchanger, a high-pressure heater, and an economizer installed in the boiler's flue.

[0006] The gas inlet of the heat exchanger is connected in sequence to the air preheater and the induced draft fan, and the gas outlet of the heat exchanger is connected in sequence to the coal mill and the burner located at the primary air inlet.

[0007] A steam valve is installed between the high-pressure steam turbine unit and the heat exchanger.

[0008] Optionally, the high-pressure turbine unit is also connected in sequence to a condenser, a water pump, and a high-pressure heater;

[0009] The air preheater is also connected to the boiler flue and flue gas treatment device.

[0010] Optionally, the boiler's secondary air inlet is also connected to the oxygen supply device via an oxygen supply valve.

[0011] Optionally, the oxygen supply device is also electrically connected to the furnace temperature detector.

[0012] Optionally, the oxygen supply device includes an oxygen generator and an oxygen storage cylinder;

[0013] The oxygen storage cylinder is connected to the oxygen supply valve;

[0014] The oxygen generator is connected to the oxygen storage cylinder via the first valve and to the oxygen supply valve via the second valve.

[0015] Optionally, a flame detector is installed at the outlet of the burner;

[0016] The flame detector is electrically connected to the controller.

[0017] Optionally, an electric heater is also provided between the air preheater and the induced draft fan.

[0018] This application provides a low-load stable combustion system for pulverized coal boilers. When the boiler is running at low load, a heat exchanger is installed to introduce steam extracted from the high-pressure turbine unit into the heat exchanger as a heating medium to heat the primary air preheated by the air preheater, thereby increasing the primary air inlet temperature and maintaining stable combustion in the furnace under low-load operating conditions. This overcomes the drawbacks caused by unstable combustion in the furnace due to the low flue gas temperature during low-load boiler operation, which prevents the air preheater from reaching the preset inlet temperature after preheating the primary air. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of a low-load stable combustion system for a pulverized coal boiler provided in an embodiment of this application;

[0021] Figure 2 This is a schematic diagram of a low-load stable combustion system for a pulverized coal boiler provided in another embodiment of this application;

[0022] Figure 3 A schematic diagram of a pulverized coal boiler low-load stable combustion system provided in yet another embodiment of this application;

[0023] Figure 4A schematic diagram of an oxygen supply device provided in an embodiment of this application;

[0024] Figure 5 A schematic diagram of a pulverized coal boiler low-load stable combustion system provided in another embodiment of this application;

[0025] Figure 6 This is a schematic diagram of a pulverized coal boiler low-load stable combustion system provided in an embodiment of this application.

[0026] Explanation of reference numerals in the attached figures:

[0027] 1. Boiler; 2. Heat exchanger; 3. Coal mill; 4. Condenser; 5. Flue gas treatment device; 6. Oxygen supply device; 10. Water pump; 11. High-pressure steam turbine unit; 12. High-pressure heater; 13. Economizer; 14. Air preheater; 15. Induced draft fan; 16. Burner; 17. Furnace temperature detector; 18. Controller; 19. Electric heater; 61. Oxygen generator; 62. Oxygen storage cylinder; 100. Steam valve; 161. Flame detector; 200. Oxygen supply valve; 300. First valve; 400. Second valve. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are also within the scope of protection of this application.

[0029] like Figure 1 As shown, this application provides a low-load stable combustion system for a pulverized coal boiler, including a boiler 1, which is sequentially connected to a high-pressure steam turbine unit 11, a heat exchanger 2, a high-pressure heater 12, and an economizer 13 installed in the flue of the boiler 1.

[0030] The gas inlet of heat exchanger 2 is connected in sequence to air preheater 14 and induced draft fan 15, and the gas outlet of heat exchanger 2 is connected in sequence to coal mill 3 and burner 16 located at primary air inlet.

[0031] A steam valve 100 is installed between the high-pressure steam turbine unit 11 and the heat exchanger 2.

[0032] During operation, the steam generated by boiler 1 needs to be transported to high-pressure turbine unit 11 to drive the turbine to perform work. When boiler 1 is operating at low load, the flue gas temperature may be low due to the low load operation of the entire boiler system. This can lead to a low temperature of the primary air after heat exchange in air preheater 14, affecting stable combustion in the furnace. In this case, steam valve 100 should be opened to extract a portion of the high-pressure steam (also known as exhaust steam) after it has been used in high-pressure turbine unit 11. After being depressurized through steam valve 100, this steam is transferred to heat exchanger 2 as a heat exchange medium to further heat the primary air preheated in air preheater 14 (drawn in by induced draft fan 15) to increase the primary air inlet temperature. The heated primary air is then mixed with pulverized coal ground by coal mill 3 and transported to burner 16, from which it is injected into the furnace of boiler 1 for combustion.

[0033] This application provides a low-load stable combustion system for a pulverized coal boiler. When the boiler is running at low load, a portion of the steam extracted from the high-pressure turbine unit 11 is introduced into the heat exchanger 2 as a heating medium to heat the primary air preheated by the air preheater 14. This increases the inlet temperature of the primary air, thereby maintaining stable combustion in the furnace under low-load operating conditions. This overcomes the drawback of unstable combustion in the furnace caused by the low flue gas temperature during low-load operation of the boiler 1, which results in the air preheater 14 not reaching the preset inlet temperature after preheating the primary air.

[0034] like Figure 1 As shown, optionally, the high-pressure turbine unit 11 is also connected in sequence to the condenser 4, the water pump 10 and the high-pressure heater 12;

[0035] The air preheater 14 is also connected to the flue of the boiler 1 and the flue gas treatment device 5.

[0036] After the exhaust steam from the high-pressure turbine unit 11 has been used for work, it enters the condenser 4 for cooling and condensation after being used by the medium-pressure turbine unit and the low-pressure turbine unit. The condensate produced by the condensation of steam is transferred to the high-pressure heater 12 by a water pump (before entering the high-pressure heater 12, the steam condensate is heated by passing through the low-pressure heater and the medium-pressure heater in sequence). It exchanges heat with the steam after the primary air is heated in the heat exchanger 2. The heated condensate enters the economizer 13, and then enters the water-cooled wall in the furnace of the boiler 1 to absorb heat and generate steam.

[0037] The flue gas discharged from boiler 1 into the flue gas duct exchanges heat with economizer 13 and then enters air preheater 14 as a heat exchange medium to exchange heat with the primary air drawn by induced draft fan 15. The temperature of the flue gas after heat exchange is reduced, and then it is fed into flue gas treatment device 5 for purification through dust removal, desulfurization and other methods until it meets the standards before being discharged into the chimney.

[0038] like Figure 2 As shown, optionally, the secondary air inlet of boiler 1 is also connected to oxygen supply device 6 via oxygen supply valve 200.

[0039] In this application, when the boiler 1 is running at low load, the combustion in the furnace is prone to be unstable, which means that the fuel is prone to incomplete combustion. At this time, the oxygen supply device 6 is configured to supply sufficient oxygen through the secondary air inlet when the combustion in the furnace is in an unstable combustion state, so as to support the full combustion of the fuel in the furnace, i.e., pulverized coal, and make the combustion in the furnace stable.

[0040] like Figure 3 As shown, the oxygen supply device 6 is optionally also electrically connected to the furnace temperature detector 17.

[0041] In this application, the furnace temperature detector 17 is used to monitor the combustion state in the furnace. When the fuel in the furnace is in an unstable combustion state, its temperature will drop. Therefore, the furnace temperature detector 17 can detect the temperature in the furnace to determine the combustion state in the furnace, thereby determining whether oxygen needs to be supplied to the furnace to support stable combustion in the furnace.

[0042] like Figure 4 As shown, optionally, the oxygen supply device 6 includes an oxygen generator 61 and an oxygen storage cylinder 62;

[0043] The oxygen storage cylinder 62 is connected to the oxygen supply valve 200;

[0044] The oxygen generator 61 is connected to the oxygen storage cylinder 62 via the first valve 300 and to the oxygen supply valve 200 via the second valve 400.

[0045] When the primary air with increased temperature carries pulverized coal into the boiler furnace for combustion, the furnace temperature detector 17 monitors the furnace temperature in real time. When the furnace temperature is equal to or greater than the theoretical stable combustion temperature of boiler 1 under the current load, the oxygen supply valve 200 is closed. When the furnace temperature is less than the theoretical stable combustion temperature of boiler 1 under the current load, the pulverized coal combustion in the furnace is in an unstable state. Therefore, the oxygen supply valve 200 can be opened to supply oxygen (purity ≥98%) supplied by the oxygen supply device 6 through the burner 16 into the primary air inlet and into the furnace to increase the oxygen concentration inside the furnace, allowing the pulverized coal to burn more completely and gradually become stable. When oxygen is supplied by oxygen supply device 6, the second valve 400 and the first valve 300 are closed, and the oxygen supply valve 200 is opened to output the oxygen in oxygen storage cylinder 62 into the secondary air duct. When the oxygen production rate and content of oxygen generator 61 reach the set value, the second valve 400 is gradually opened, while the exhaust valve of oxygen storage cylinder 62 is gradually closed. The oxygen produced by oxygen generator 61 takes over the output of oxygen from oxygen storage cylinder 62 until the temperature in the furnace is monitored to be within the theoretical temperature range of stable combustion of boiler 1 under the current load. At this time, the boiler furnace is in a stable combustion state under low load, and the pulverized coal is burning stably.

[0046] Optionally, the furnace temperature detector 17 is connected to the oxygen supply device 6 via a control device (such as a DCS system in a thermal power plant). The furnace temperature detector 17 sends the real-time detected temperature value to the control device, which determines whether to activate the oxygen supply valve 200 based on the temperature value. If the oxygen supply valve 200 is activated, the control device sends an activation signal to the oxygen supply valve 200. Additionally, the opening of the first valve 300, the second valve 400, the oxygen storage cylinder 62, and the oxygen generator 61 can also be controlled by the control device.

[0047] like Figure 5 As shown, optionally, a flame detector 161 is provided at the outlet position of the burner 16;

[0048] Flame detector 161 is electrically connected to controller 18.

[0049] Because the primary air temperature rise can cause premature combustion of pulverized coal, it may cause the flame to get close to burner 16, resulting in a local temperature increase. This temperature increase can easily lead to slagging and blockage at the outlet. Therefore, a flame detector 161 is installed at the outlet section of burner 16 to monitor specific characteristics of the flame during pulverized coal combustion, such as ultraviolet light, flicker frequency, and visible light intensity, to determine the relative position of the flame from the burner outlet. This data is then fed back to the controller 18 in real time (the controller 18 is, for example, a DCS system in a thermal power plant; the flame detector 161 is existing technology and will not be described further here). If the detected relative position of the flame from the burner outlet is less than the safe distance set for burner 16, the controller 18 can control the opening of the adjustable damper installed in the primary air duct. By reducing the opening, the effective flow area is reduced, thereby increasing the primary air velocity and ensuring that the relative position of the flame from the burner outlet is within the set safe distance range.

[0050] like Figure 6 As shown, optionally, an electric heater 19 is also provided between the air preheater 14 and the induced draft fan 15.

[0051] Correspondingly, when it is winter or the temperature is low, the temperature of the primary air drawn by the induced draft fan 15 is low. The excessively low inlet air temperature will cause cold end corrosion of the air preheater 14. Therefore, an electric heater 19 is installed to preheat the primary air drawn by the induced draft fan 15 before it is introduced into the air preheater 14 for heat exchange, so as to reduce the probability of cold end corrosion of the air preheater 14 and thus protect the air preheater 14.

[0052] A low-load stable combustion system for a pulverized coal boiler operates as follows:

[0053] During operation, the steam generated by boiler 1 needs to be transported to high-pressure turbine unit 11 to drive the turbine to perform work. When boiler 1 is operating at low load, the flue gas temperature may be low due to the low load operation of the entire boiler system. This can lead to a low temperature of the primary air after heat exchange in air preheater 14, affecting stable combustion in the furnace. In this case, steam valve 100 should be opened to extract a portion of the high-pressure steam (also known as exhaust steam) after it has been used in high-pressure turbine unit 11. After being depressurized through steam valve 100, this steam is transferred to heat exchanger 2 as a heat exchange medium to further heat the primary air preheated in air preheater 14 (drawn in by induced draft fan 15) to increase the primary air inlet temperature. The heated primary air is then mixed with pulverized coal ground by coal mill 3 and transported to burner 16, from which it is injected into the furnace of boiler 1 for combustion.

[0054] Correspondingly, when it is winter or the temperature is low, the temperature of the primary air drawn by the induced draft fan 15 is low. The low inlet air temperature will cause cold end corrosion of the air preheater 14. Therefore, an electric heater 19 is installed to preheat the primary air drawn by the induced draft fan 15 before it is introduced into the air preheater 14 for heat exchange, so as to reduce the probability of cold end corrosion of the air preheater 14 and thus protect the air preheater 14.

[0055] After the exhaust steam from the high-pressure turbine unit 11 has been used for work, it enters the condenser 4 for cooling and condensation after being used by the medium-pressure turbine unit and the low-pressure turbine unit. The condensate produced by the condensation of steam is transferred to the high-pressure heater 12 by a water pump (before entering the high-pressure heater 12, the steam condensate is heated by passing through the low-pressure heater and the medium-pressure heater in sequence). It exchanges heat with the steam after the primary air is heated in the heat exchanger 2. The heated condensate enters the economizer 13, and then enters the water-cooled wall in the furnace of the boiler 1 to absorb heat and generate steam.

[0056] The flue gas discharged from boiler 1 into the flue gas duct exchanges heat with economizer 13 and then enters air preheater 14 as a heat exchange medium to exchange heat with the primary air drawn by induced draft fan 15. The temperature of the flue gas after heat exchange is reduced, and then it is fed into flue gas treatment device 5 for purification through dust removal, desulfurization and other methods until it meets the standards before being discharged into the chimney.

[0057] Because the primary air temperature rise can cause premature combustion of pulverized coal, it may cause the flame to get close to burner 16, resulting in a local temperature increase. This temperature increase can easily lead to slagging and blockage at the outlet. Therefore, a flame detector 161 is installed at the outlet section of burner 16 to monitor specific characteristics of the flame during pulverized coal combustion, such as ultraviolet light, flicker frequency, and visible light intensity, to determine the relative position of the flame from the burner outlet. This data is then fed back to the controller 18 (e.g., the DCS system of a thermal power plant) in real time. If the relative position of the flame from the burner outlet is detected to be less than the safe distance set for burner 16, the controller 18 can control the opening of the adjustable damper installed in the primary air duct. By reducing the opening, the effective flow area is reduced, thereby increasing the primary air velocity and ensuring that the relative position of the flame from the burner outlet is within the set safe distance range.

[0058] When the primary air with increased temperature carries pulverized coal into the boiler furnace for combustion, the furnace temperature detector 17 monitors the furnace temperature in real time. When the furnace temperature is equal to or greater than the theoretical stable combustion temperature of boiler 1 under the current load, the oxygen supply valve 200 is closed. When the furnace temperature is less than the theoretical stable combustion temperature of boiler 1 under the current load, the pulverized coal combustion in the furnace is in an unstable state. Therefore, the oxygen supply valve 200 can be opened to supply oxygen (purity ≥98%) supplied by the oxygen supply device 6 through the burner 16 into the primary air inlet and into the furnace to increase the oxygen concentration inside the furnace, allowing the pulverized coal to burn more completely and gradually become stable. When oxygen is supplied by oxygen supply device 6, the second valve 400 and the first valve 300 are closed, and the oxygen supply valve 200 is opened to output the oxygen in oxygen storage cylinder 62 into the secondary air duct. When the oxygen production rate and content of oxygen generator 61 reach the set value, the second valve 400 is gradually opened, while the exhaust valve of oxygen storage cylinder 62 is gradually closed. The oxygen produced by oxygen generator 61 takes over the output of oxygen from oxygen storage cylinder 62 until the temperature in the furnace is monitored to be within the theoretical temperature range of stable combustion of boiler 1 under the current load. At this time, the boiler furnace is in a stable combustion state under low load, and the pulverized coal is burning stably.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A pulverized coal boiler low load stable combustion system comprising a boiler (1), characterized in that, The boiler (1) is connected in sequence to the high-pressure steam turbine unit (11), the heat exchanger (2), the high-pressure heater (12) and the economizer (13) installed in the flue of the boiler (1); The gas input end of the heat exchanger (2) is connected in sequence to the air preheater (14) and the induced draft fan (15), and the gas output end of the heat exchanger (2) is connected in sequence to the coal mill (3) and the burner (16) located at the primary air inlet. A steam valve (100) is provided between the high-pressure steam turbine unit (11) and the heat exchanger (2).

2. The pulverized coal boiler low load stable combustion system according to claim 1, characterized in that, The high-pressure steam turbine unit (11) is also connected in sequence to the condenser (4), the water pump (10) and the high-pressure heater (12); The air preheater (14) is also connected to the flue of the boiler (1) and the flue gas treatment device (5), respectively.

3. The pulverized coal boiler low load stable combustion system according to claim 1, characterized in that, The secondary air inlet of the boiler (1) is also connected to the oxygen supply device (6) via an oxygen supply valve (200).

4. The pulverized coal boiler low load stable combustion system according to claim 3, characterized in that, The oxygen supply device (6) is also electrically connected to the furnace temperature detector (17).

5. The pulverized coal boiler low load stable combustion system according to claim 4, characterized in that, The oxygen supply device (6) includes an oxygen generator (61) and an oxygen storage cylinder (62). The oxygen storage cylinder (62) is connected to the oxygen supply valve (200); The oxygen generator (61) is connected to the oxygen storage cylinder (62) via the first valve (300) and to the oxygen supply valve (200) via the second valve (400).

6. The pulverized coal boiler low load stable combustion system according to claim 1, characterized in that, A flame detector (161) is provided at the outlet position of the burner (16). The flame detector (161) is electrically connected to the controller (18).

7. The low load stable combustion system of pulverized coal boiler according to any one of claims 1-6, characterized in that, An electric heater (19) is also provided between the air preheater (14) and the induced draft fan (15).

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