Boiler combustion system capable of reducing nitrogen oxide emission

Abstract

The utility model provides a boiler combustion system capable of reducing nitrogen oxide emission, and relates to the technical field of boiler combustion, the boiler combustion system comprises a boiler, a flue gas chamber, a chimney, a circulating flue gas pipeline, a mixing tank, a mixed gas pipeline, an air pipeline and an oxygen pipeline, the gas outlet end of the boiler is connected with the chimney through the flue gas chamber; the gas outlet end of the mixing tank is connected with the gas inlet end of the boiler through the mixed gas pipeline, one end of the circulating flue gas pipeline is connected with the flue gas chamber, and the other end of the circulating flue gas pipeline is connected with the gas inlet end of the mixing tank; the air pipeline and the oxygen pipeline are both connected with the air inlet end of the mixing tank; the flue gas generated by the boiler and the pure oxygen are mixed to serve as the combustion-supporting gas of the fuel gas in the boiler hearth, nitrogen can be prevented from being brought in due to the fact that air is adopted for supporting combustion, emission of nitric oxide is effectively reduced, and the situation that the boiler is damaged due to the fact that pure oxygen is adopted for supporting combustion and the pure oxygen and the fuel gas are combusted violently can be prevented.

Description

Technical Field

[0001] This application relates to the technical field of boiler combustion, and more particularly, to a boiler combustion system for reducing nitrogen oxide emissions. Background Art

[0002] A boiler is an energy converter that uses the heat energy released by fuel combustion or other heat energy to heat the working medium water or other fluids to a certain parameter. Existing boilers use air as an oxygen-supplying combustion aid. Since the nitrogen content in air accounts for about 78%, when the fuel gas burns at high temperature in the boiler furnace, it will react with nitrogen to generate nitrogen oxides, resulting in a high content of nitrogen oxides in the flue gas discharged from the boiler, which cannot meet the environmental protection requirements. If pure oxygen is used as the combustion aid, due to the high combustion intensity of pure oxygen, it will damage the boiler body and is not conducive to the safe operation of the boiler. Summary of the Invention

[0003] The purpose of the embodiments of this application is to provide a boiler combustion system for reducing nitrogen oxide emissions, which can solve the technical problems that existing boilers use air as an oxygen-supplying combustion aid, resulting in a high content of nitrogen oxides in the flue gas discharged from the boiler and not meeting the environmental protection requirements. If pure oxygen is used as the combustion aid, due to the high combustion intensity of pure oxygen, it will damage the boiler body and is not conducive to the safe operation of the boiler.

[0004] The embodiments of this application provide a boiler combustion system for reducing nitrogen oxide emissions, including a boiler, a flue gas chamber, a chimney, a circulating flue gas pipeline, a mixing tank, a mixed gas pipeline, an air pipeline, and an oxygen pipeline. The outlet end of the boiler is connected to the chimney through the flue gas chamber. The outlet end of the mixing tank is connected to the inlet end of the boiler through the mixed gas pipeline. One end of the circulating flue gas pipeline is connected to the flue gas chamber, and the other end of the circulating flue gas pipeline is connected to the inlet end of the mixing tank. The air pipeline and the oxygen pipeline are both connected to the inlet end of the mixing tank.

[0005] Among them, a suction fan and a first regulating valve are provided on the circulating flue gas pipeline, a second regulating valve is provided on the mixed gas pipeline, a blower and a third regulating valve are provided on the air pipeline, a fourth regulating valve and a first quick-opening valve are provided on the oxygen pipeline, and the oxygen pipeline is connected to an external oxygen supply device.

[0006] Among them, a first flowmeter and a first analyzer are provided on the circulating flue gas pipeline, a second analyzer is provided on the mixed gas pipeline, and a second flowmeter is provided on the oxygen pipeline.

[0007] Among them, it further includes a first gas pipeline, the first gas pipeline is connected to the inlet end of the boiler, and the first gas pipeline is connected to an external gas supply device. A fifth regulating valve is provided on the first gas pipeline.

[0008] Among them, a second quick-opening valve, a first pressure switch and a third quick-opening valve are arranged on the first gas pipeline. The fifth regulating valve is located between the boiler and the second quick-opening valve. The third quick-opening valve is located between the fifth regulating valve and the second quick-opening valve. The first pressure switch is located between the second quick-opening valve and the third quick-opening valve.

[0009] Among them, it further includes a second gas pipeline, an igniter and a flame detector. The second gas pipeline, the igniter and the flame detector are all connected to the air inlet end of the boiler. The second gas pipeline is connected to an external gas supply device. An electromagnetic valve is arranged on the second gas pipeline.

[0010] Among them, a second pressure switch is arranged on the mixed gas pipeline. A fourth pressure switch is arranged on the second gas pipeline. The electromagnetic valve is located between the boiler and the fourth pressure switch.

[0011] Among them, a third pressure switch is arranged on the first gas pipeline. The second quick-opening valve is located between the first pressure switch and the third pressure switch.

[0012] Among them, a first pressure gauge is arranged on the oxygen pipeline. A second pressure gauge is arranged on the first gas pipeline.

[0013] Among them, an economizer is arranged between the air outlet end of the boiler and the flue gas chamber.

[0014] Advantages of the present utility model:

[0015] A boiler combustion system for reducing nitrogen oxide emissions provided by the present utility model, when in use, first conveys air to the boiler via an air pipeline, and at the same time conveys gas to the boiler via a first gas pipeline. The flue gas generated by the combustion of air and gas in the boiler enters the flue gas chamber. Subsequently, the flue gas in the flue gas chamber is pumped into a mixing tank via a circulating flue gas pipeline, and at the same time oxygen is conveyed to the mixing tank via an oxygen pipeline. The flue gas and oxygen are mixed in the mixing tank to form a mixed gas. The mixed gas is conveyed into the boiler via a mixed gas pipeline. The flue gas generated by the combustion of the mixed gas and gas in the boiler enters the flue gas chamber for recycling; this system mixes the flue gas generated by the boiler with pure oxygen as the combustion-supporting gas for the gas in the boiler furnace, which can not only prevent the introduction of nitrogen due to using air for combustion support, effectively reduce nitrogen oxide emissions, but also prevent damage to the boiler caused by the violent combustion of pure oxygen and gas due to using pure oxygen for combustion support. Description of the drawings

[0016] To more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the accompanying drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present application and should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0017] Figure 1 It is a schematic diagram of the overall structure in some embodiments of the present application.

[0018] The reference numerals are respectively:

[0019] 1, boiler;

[0020] 2, flue gas chamber;

[0021] 3, chimney;

[0022] 4, circulating flue gas pipeline; 401, induced draft fan; 402, first regulating valve; 403, first flowmeter; 404, first analyzer;

[0023] 5, mixing tank;

[0024] 6, mixed gas pipeline; 601, second regulating valve; 602, second analyzer; 603, second pressure switch;

[0025] 7, air pipeline; 701, blower; 702, third regulating valve;

[0026] 8, oxygen pipeline; 801, fourth regulating valve; 802, first quick-opening valve; 803, second flowmeter; 804, first pressure gauge;

[0027] 9, first gas pipeline; 901, fifth regulating valve; 902, second quick-opening valve; 903, first pressure switch; 904, third quick-opening valve; 905, third pressure switch; 906, second pressure gauge;

[0028] 10, second gas pipeline; 1001, solenoid valve; 1002, fourth pressure switch;

[0029] 11, ignition gun;

[0030] 12, flame detector;

[0031] 13, economizer. Detailed implementation manners

[0032] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this application. Apparently, the described embodiments are some, but not all, of the embodiments of this application. The components of the embodiments of this application usually described and illustrated in the drawings here can be arranged and designed in various different configurations.

[0033] Therefore, the detailed description of the embodiments of this application provided in the drawings below is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application without creative efforts belong to the scope of protection of this application.

[0034] It should be noted that like reference numerals and letters denote like items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0035] In the description of this application, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of this application is usually placed when in use. It is only for the convenience of describing this application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. In addition, the terms "first", "second", "third", etc. are only used for descriptive distinction and should not be construed as indicating or implying relative importance.

[0036] In addition, terms such as "horizontal", "vertical", "overhanging", etc. do not mean that the components are required to be absolutely horizontal or overhanging, but may be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but may be slightly inclined.

[0037] In the description of this application, it should also be noted that unless otherwise clearly specified and limited, the terms "set", "installed", "connected", "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific situations.

[0038] Such as Figure 1As shown in the figure, an embodiment of the present application provides a boiler combustion system for reducing nitrogen oxide emissions, which includes a boiler 1, a flue gas chamber 2, a chimney 3, a circulating flue gas pipeline 4, a mixing tank 5, a mixed gas pipeline 6, an air pipeline 7, and an oxygen pipeline 8. The outlet end of the boiler 1 is connected to the chimney 3 through the flue gas chamber 2. The outlet end of the mixing tank 5 is connected to the inlet end of the boiler 1 through the mixed gas pipeline 6. One end of the circulating flue gas pipeline 4 is connected to the flue gas chamber 2, and the other end of the circulating flue gas pipeline 4 is connected to the inlet end of the mixing tank 5. Both the air pipeline 7 and the oxygen pipeline 8 are connected to the inlet end of the mixing tank 5.

[0039] During use, first, air is supplied to the boiler 1 via the air pipeline 7, and at the same time, gas is supplied to the boiler 1 via the first gas pipeline 9. The flue gas generated by the combustion of air and gas in the boiler 1 enters the flue gas chamber 2. Subsequently, the flue gas in the flue gas chamber 2 is pumped into the mixing tank 5 via the circulating flue gas pipeline 4, and at the same time, oxygen is supplied to the mixing tank 5 via the oxygen pipeline 8. The flue gas and oxygen are mixed in the mixing tank 5 to form a mixed gas, and the mixed gas is transported into the boiler 1 via the mixed gas pipeline 6. The flue gas generated by the combustion of the mixed gas and gas in the boiler 1 enters the flue gas chamber 2 and is recycled. By mixing the flue gas generated by the boiler 1 with pure oxygen and using it as the combustion-supporting gas for the gas in the furnace of the boiler 1, this system can not only prevent the introduction of nitrogen due to using air for combustion support, effectively reducing nitrogen oxide emissions, but also prevent damage to the boiler 1 caused by the intense combustion of pure oxygen and gas.

[0040] As Figure 1 shown in the figure, in this embodiment, a suction fan 401 and a first regulating valve 402 are provided on the circulating flue gas pipeline 4, a second regulating valve 601 is provided on the mixed gas pipeline 6, a blower 701 and a third regulating valve 702 are provided on the air pipeline 7, a fourth regulating valve 801 and a first quick-opening valve 802 are provided on the oxygen pipeline 8, and the oxygen pipeline 8 is connected to an external oxygen supply device.

[0041] During use, first, the blower 701 and the third regulating valve 702 are opened, and air is supplied to the boiler 1 via the air pipeline 7. At the same time, gas is supplied to the boiler via the first gas pipeline 9. The flue gas generated by the combustion of air and gas in the boiler 1 enters the flue gas chamber 2. Subsequently, the suction fan 401 and the first regulating valve 402 are opened, and the flue gas in the flue gas chamber 2 is pumped into the mixing tank 5 via the circulating flue gas pipeline 4. At the same time, the fourth regulating valve 801 and the first quick-opening valve 802 are opened, and oxygen is supplied to the mixing tank 5 via the oxygen pipeline 8. The flue gas and oxygen are mixed in the mixing tank 5 to form a mixed gas. The second regulating valve 601 is opened, and the mixed gas is transported into the boiler 1 via the mixed gas pipeline 6. The flue gas generated by the combustion of the mixed gas and gas in the boiler 1 enters the flue gas chamber 2 and is recycled.

[0042] AsFigure 1 As shown, in this embodiment, a first flowmeter 403 and a first analyzer 404 are provided on the circulating flue gas pipeline 4, a second analyzer 602 is provided on the mixed gas pipeline 6, and a second flowmeter 803 is provided on the oxygen pipeline 8.

[0043] During use, the second analyzer 602 is used to measure the oxygen concentration in the mixed gas. It is preferably about 21% oxygen content. The oxygen content in the mixed gas is similar to that in the air, which can prevent damage to the boiler 1 caused by the intense combustion of oxygen and fuel gas due to the use of oxygen with too high purity, and can also prevent poor combustion effect of oxygen and fuel gas due to the use of oxygen with too low purity. The first flowmeter 403 is used to measure the flue gas flow rate flowing through the circulating flue gas pipeline 4, and the second flowmeter 803 is used to measure the oxygen flow rate flowing through the oxygen pipeline 8, which is convenient for controlling the sizes of the first regulating valve 402 and the fourth regulating valve 801 according to the measurement situation to adjust the ratio of flue gas to oxygen, and then adjust the oxygen concentration in the mixed gas to the target value. The first analyzer 404 is used to measure the oxygen concentration in the flue gas and can provide a reference for the ratio of flue gas to oxygen.

[0044] As Figure 1 shown, in this embodiment, it further includes a first fuel gas pipeline 9. The first fuel gas pipeline 9 is connected to the intake end of the boiler 1 and is also connected to an external fuel gas supply device. A fifth regulating valve 901 is provided on the first fuel gas pipeline 9.

[0045] During use, open the fifth regulating valve 901 to supply fuel gas to the boiler 1 via the first fuel gas pipeline 9. The fuel gas can be coal gas or natural gas.

[0046] As Figure 1 shown, in this embodiment, a second quick-opening valve 902, a first pressure switch 903 and a third quick-opening valve 904 are provided on the first fuel gas pipeline 9. The fifth regulating valve 901 is located between the boiler 1 and the second quick-opening valve 902, the third quick-opening valve 904 is located between the fifth regulating valve 901 and the second quick-opening valve 902, and the first pressure switch 903 is located between the second quick-opening valve 902 and the third quick-opening valve 904.

[0047] During use, before supplying fuel gas to the boiler 1 via the first fuel gas pipeline 9, it is necessary to check for leaks in the second quick-opening valve 902 and the third quick-opening valve 904 to ensure that no fuel gas enters the boiler 1 when the second quick-opening valve 902 and the third quick-opening valve 904 are closed. The second quick-opening valve 902 and the third quick-opening valve 904 are provided to quickly cut off the fuel gas when situations such as the boiler 1 going out of flame or the steam drum overpressure occur, so that the boiler 1 stops operating and prevent the risk of explosion of the boiler 1.

[0048] The specific inspection method is as follows:

[0049] Check whether the third quick-opening valve 904 leaks: Open the second quick-opening valve 902 and then quickly close it. At this time, the space between the second quick-opening valve 902 and the third quick-opening valve 904 is filled with gas. After waiting for 5 seconds, use the first pressure switch 903 to determine whether the third quick-opening valve 904 leaks. If the first pressure switch 903 is not turned on, it means the third quick-opening valve 904 leaks, then stop the start-up procedure of the boiler 1. If the first pressure switch 903 is turned on, it means the third quick-opening valve 904 does not leak, then proceed to the next procedure normally.

[0050] Check whether the second quick-opening valve 902 leaks: Open the third quick-opening valve 904 and then quickly close it. At this time, the gas filled between the second quick-opening valve 902 and the third quick-opening valve 904 is depressurized. After waiting for 5 seconds, use the first pressure switch 903 to determine whether the second quick-opening valve 902 leaks. If the first pressure switch 903 is turned on, it means the second quick-opening valve 902 leaks, then stop the start-up procedure of the boiler 1. If the first pressure switch 903 is not turned on, it means the second quick-opening valve 902 does not leak, then proceed to the next procedure normally.

[0051] After the leakage inspections of the second quick-opening valve 902 and the third quick-opening valve 904 are confirmed normal, the fifth regulating valve 901, the second quick-opening valve 902 and the third quick-opening valve 904 can be opened, and gas is supplied to the boiler 1 through the first gas pipeline 9. The gas can be coal gas or natural gas.

[0052] As Figure 1 shown in the figure, in this embodiment, it further includes a second gas pipeline 10, a spark igniter 11 and a flame detector 12. The second gas pipeline 10, the spark igniter 11 and the flame detector 12 are all connected to the intake end of the boiler 1. The second gas pipeline 10 is connected to an external gas supply device, and a solenoid valve 1001 is provided on the second gas pipeline 10.

[0053] During use, turn on the spark igniter 11, then turn on the solenoid valve 1001, supply gas to the boiler 1 through the second gas pipeline 10. After waiting for 5 seconds, turn off the spark igniter 11, and use the flame detector 12 to determine whether the small fire is lit. If the flame detector 12 has no flame signal, it means that lighting the small fire is not successful, then stop the start-up procedure of the boiler 1 and conduct purging. If the flame detector 12 continuously has a flame signal, it means that lighting the small fire is successful, then proceed to the next procedure normally.

[0054] When the boiler 1 experiences normal shutdown, fault shutdown, interlock shutdown, shutdown due to unsuccessful ignition of small fire, shutdown due to unsuccessful ignition of large fire, etc., purging should be carried out. Purging means turning on the blower 701 to purge the furnace of the boiler 1 with air to purge the gas in the furnace of the boiler 1. Because the gas ignition in the furnace of the boiler 1 requires ignition first and then gas supply. If gas is supplied first and then ignition, there may be a risk of explosion.

[0055] As Figure 1 shown, in this embodiment, a second pressure switch 603 is provided on the mixed gas pipeline 6, a fourth pressure switch 1002 is provided on the second gas pipeline 10, and the solenoid valve 1001 is located between the boiler 1 and the fourth pressure switch 1002.

[0056] During use, the second pressure switch 603 is used to detect the blast pressure. If the second pressure switch 603 shows no pressure, indicating a malfunction or shutdown of the blower 701, the operation of the boiler 1 is stopped; the fourth pressure switch 1002 is used to detect the ignition gas pressure. If the second pressure switch 603 shows no pressure, indicating that there is no ignition gas flowing in the second gas pipeline 10, the ignition procedure cannot be completed.

[0057] As Figure 1 shown, in this embodiment, a third pressure switch 905 is provided on the first gas pipeline 9, and the second quick-opening valve 902 is located between the first pressure switch 903 and the third pressure switch 905; during use, the third pressure switch 905 is used to detect the gas pressure. When the gas pressure is low, it indicates that the gas volume in the first gas pipeline 9 is small, which is likely to cause the boiler 1 to go out or explode.

[0058] As Figure 1 shown, in this embodiment, a first pressure gauge 804 is provided on the oxygen pipeline 8, and a second pressure gauge 906 is provided on the first gas pipeline 9; during use, the first pressure gauge 804 is used to observe and refer to the oxygen pressure provided externally during debugging; the second pressure gauge 906 is used to observe and refer to the gas pressure provided externally during debugging.

[0059] As Figure 1 shown, in this embodiment, an economizer 13 is provided between the outlet end of the boiler 1 and the flue gas chamber 2; during use, the economizer 13 is used to recover the waste heat of the flue gas, reduce the exhaust temperature of the flue gas, save energy, and improve efficiency.

[0060] Working principle: The method of using the boiler combustion system for reducing nitrogen oxide emissions provided by this application is as follows:

[0061] Step S1. Check whether the third quick-opening valve 904 leaks: Open the second quick-opening valve 902 and then quickly close it. At this time, the space between the second quick-opening valve 902 and the third quick-opening valve 904 is filled with gas. After waiting for 5 seconds, judge whether the third quick-opening valve 904 leaks through the first pressure switch 903. If the first pressure switch 903 is not turned on, indicating that the third quick-opening valve 904 leaks, the startup procedure of the boiler 1 is stopped. If the first pressure switch 903 is turned on, indicating that the third quick-opening valve 904 does not leak, the next procedure is carried out normally.

[0062] Step S2: Check whether the second quick-opening valve 902 leaks. Open the third quick-opening valve 904 and then quickly close it. At this time, the gas filled between the second quick-opening valve 902 and the third quick-opening valve 904 is depressurized. After waiting for 5 seconds, judge whether the second quick-opening valve 902 leaks through the first pressure switch 903. If the first pressure switch 903 is turned on, it means the second quick-opening valve 902 leaks, and then stop the boiler 1 startup program. If the first pressure switch 903 is not turned on, it means the second quick-opening valve 902 does not leak, and then proceed to the next program normally.

[0063] Step S3: Purge the furnace of the boiler 1. Open the second regulating valve 601, the third regulating valve 702 and the blower 701. Deliver air to the boiler 1 via the air pipeline 7, the mixing tank 5 and the mixed gas pipeline 6, and purge the furnace of the boiler 1 with air to purge the gas in the furnace of the boiler 1 completely, for 60 seconds continuously.

[0064] Step S4: Prepare to ignite the pilot flame. Adjust the second regulating valve 601 to an opening of about 5%, adjust the third regulating valve 702 to an opening of about 30%, and open the fifth regulating valve 901 to an opening of about 5%.

[0065] Step S5: Ignite the pilot flame. Turn on the igniter 11, and then turn on the solenoid valve 1001. Deliver gas to the boiler 1 via the second gas pipeline 10. After waiting for 5 seconds, turn off the igniter 11. Judge whether the pilot flame is ignited through the flame detector 12. If the flame detector 12 has no flame signal, it means that igniting the pilot flame is not successful, and then stop the boiler 1 startup program and conduct purging. If the flame detector 12 continuously has a flame signal, it means that igniting the pilot flame is successful, and then proceed to the next program normally.

[0066] Step S6: Ignite the main flame. Open the second quick-opening valve 902 and the third quick-opening valve 904, and then turn off the solenoid valve 1001. After waiting for 5 seconds, judge whether the main flame is ignited through the flame detector 12. If the flame detector 12 has no flame signal, it means that igniting the main flame is not successful, and then stop the boiler 1 startup program and conduct purging. If the flame detector 12 continuously has a flame signal, it means that igniting the main flame is successful, and then proceed to the next program normally.

[0067] Step S7: Switch air combustion support to combustion support with a mixture of flue gas and pure oxygen. First, turn on the blower 701 to supply air to the boiler 1 via the air pipeline 7, the mixing tank 5, and the mixed gas pipeline 6. At the same time, turn on the second quick-opening valve 902 and the third quick-opening valve 904 to supply fuel gas to the boiler 1 via the first fuel gas pipeline 9. The flue gas generated by the combustion of air and fuel gas in the boiler 1 enters the flue gas chamber 2. Subsequently, turn on the first quick-opening valve 802 and slowly open the fourth regulating valve 801 to supply oxygen to the mixing tank 5 via the oxygen pipeline 8. At the same time, turn on the induced draft fan 401 and slowly open the first regulating valve 402 to pump the flue gas in the flue gas chamber 2 to the mixing tank 5 via the circulating flue gas pipeline 4. At the same time, slowly close the third regulating valve 702 until it is completely closed to stop supplying air. The flue gas and oxygen are mixed in the mixing tank 5 to form a mixed gas, and the mixed gas is transported to the boiler 1 via the mixed gas pipeline 6. The flue gas generated by the combustion of the mixed gas and the fuel gas in the boiler 1 enters the flue gas chamber 2 and is recycled.

[0068] The above are only the preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A boiler (1) combustion system for reducing nitrogen oxide emissions, characterized in that: It includes a boiler (1), a flue gas chamber (2), a chimney (3), a circulating flue gas pipeline (4), a mixing tank (5), a mixed gas pipeline (6), an air pipeline (7) and an oxygen pipeline (8). The outlet end of the boiler (1) is connected to the chimney (3) through the flue gas chamber (2). The outlet end of the mixing tank (5) is connected to the inlet end of the boiler (1) through the mixed gas pipeline (6). One end of the circulating flue gas pipeline (4) is connected to the flue gas chamber (2), and the other end of the circulating flue gas pipeline (4) is connected to the inlet end of the mixing tank (5). The air pipeline (7) and the oxygen pipeline (8) are both connected to the inlet end of the mixing tank (5).

2. The boiler (1) combustion system for reducing nitrogen oxide emissions according to claim 1, characterized in that: A draft fan (401) and a first regulating valve (402) are arranged on the circulating flue gas pipeline (4). A second regulating valve (601) is arranged on the mixed gas pipeline (6). A blower (701) and a third regulating valve (702) are arranged on the air pipeline (7). A fourth regulating valve (801) and a first quick-opening valve (802) are arranged on the oxygen pipeline (8), and the oxygen pipeline (8) is connected to an external oxygen supply device.

3. The boiler (1) combustion system for reducing nitrogen oxide emissions according to claim 1, characterized in that: A first flowmeter (403) and a first analyzer (404) are arranged on the circulating flue gas pipeline (4). A second analyzer (602) is arranged on the mixed gas pipeline (6). A second flowmeter (803) is arranged on the oxygen pipeline (8).

4. The boiler (1) combustion system for reducing nitrogen oxide emissions according to claim 1, characterized in that: It further includes a first gas pipeline (9). The first gas pipeline (9) is connected to the inlet end of the boiler (1), and the first gas pipeline (9) is connected to an external gas supply device. A fifth regulating valve (901) is arranged on the first gas pipeline (9).

5. The boiler (1) combustion system for reducing nitrogen oxide emissions according to claim 4, characterized in that: A second quick-opening valve (902), a first pressure switch (903) and a third quick-opening valve (904) are arranged on the first gas pipeline (9). The fifth regulating valve (901) is located between the boiler (1) and the second quick-opening valve (902). The third quick-opening valve (904) is located between the fifth regulating valve (901) and the second quick-opening valve (902). The first pressure switch (903) is located between the second quick-opening valve (902) and the third quick-opening valve (904).

6. The boiler (1) combustion system for reducing nitrogen oxide emissions according to claim 1, characterized in that: It further includes a second gas pipeline (10), a spark igniter (11) and a flame detector (12). The second gas pipeline (10), the spark igniter (11) and the flame detector (12) are all connected to the inlet end of the boiler (1). The second gas pipeline (10) is connected to an external gas supply device. A solenoid valve (1001) is arranged on the second gas pipeline (10).

7. The boiler (1) combustion system for reducing nitrogen oxide emissions according to claim 6, characterized in that: A second pressure switch (603) is arranged on the mixed gas pipeline (6). A fourth pressure switch (1002) is arranged on the second gas pipeline (10). The solenoid valve (1001) is located between the boiler (1) and the fourth pressure switch (1002).

8. The boiler (1) combustion system for reducing nitrogen oxide emissions according to claim 5, characterized in that: A third pressure switch (905) is provided on the first gas pipeline (9), and the second quick-opening valve (902) is located between the first pressure switch (903) and the third pressure switch (905).

9. The boiler (1) combustion system for reducing nitrogen oxide emissions according to claim 4, characterized in that: A first pressure gauge (804) is provided on the oxygen pipeline (8), and a second pressure gauge (906) is provided on the first gas pipeline (9).

10. The boiler (1) combustion system for reducing nitrogen oxide emissions according to claim 1, characterized in that: An economizer (13) is provided between the outlet end of the boiler (1) and the flue gas chamber (2).

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