Boiler low load in-furnace nox generation control system and boiler combustion system

Abstract

The application discloses a boiler low-load in-furnace NOx generation control system and a boiler combustion system, and belongs to the field of boiler combustion control technology.The boiler low-load in-furnace NOx generation control system comprises a coal mill, a boiler, a pulverized coal separator, a pulverized coal bin, a powder feeder and a mixed flue gas box.The coal mill is provided with a coal mill outlet and a coal mill inlet, and the coal mill inlet is used for the entry of cold primary air and hot primary air.The boiler is provided with a burner.The coal mill outlet is communicated with the burner and the pulverized coal separator.The pulverized coal separator is provided with a gas outlet used for the discharge of gas.The pulverized coal bin inlet is communicated with the pulverized coal separator outlet, and the pulverized coal bin outlet is communicated with the burner.The powder feeder is used for feeding the pulverized coal into the pulverized coal bin.The mixed flue gas box is provided with a flue gas inlet and a flue gas outlet.The boiler low-load in-furnace NOx generation control system can realize the regulation of steam temperature, ensure the burner nozzle wind speed, ensure the safety of the system, control the oxygen content of the mixed flue gas, and be beneficial to the inhibition of NOx generation in the initial stage of combustion.

Description

Technical Field

[0001] This invention relates to the field of combustion technology for pulverized coal boilers in large-scale coal-fired power plants, and particularly to a low-load in-furnace NOx generation control system and a boiler combustion system. Background Technology

[0002] Currently, the control of NOx generation in coal-fired power plant boilers mainly adopts low-NOx burners and air-stage combustion technology.

[0003] However, when the boiler is operating at low load, the following problems exist:

[0004] 1. The organizational methods required for low-NOx combustion under low load contradict the adjustment methods required for steam temperature regulation: To ensure a balance between the heat absorption of radiant and convective heat transfer surfaces in the boiler and to guarantee that the main steam and reheat steam temperatures meet requirements under low load, the amount of air entering the furnace is generally increased to increase the flue gas volume, thereby lowering the furnace flue gas temperature and increasing the flue gas volume in the convective heat transfer area, thus achieving a match between radiant and convective heat transfer within the furnace. This disrupts the low-oxygen reducing atmosphere required for low-NOx combustion in the furnace, hindering the conversion of fuel N during pulverized coal combustion. Furthermore, when the unit's peak load is reduced to below 30%, the oxygen content in the furnace is very high under low load due to the minimum output of the forced draft fan, induced draft fan, and primary air fan. For example, in a 600MW unit, the oxygen content at the furnace outlet is 12% at 20% load. This also makes it difficult to control NOx formation in the furnace under low load.

[0005] 2. The oxygen-deficient, low-NOx combustion conditions required in the initial stage of combustion under low load contradict the low output and high flow rate of the pulverizing system: Under low load, especially below 60%, to ensure the safety of unit operation, three or more coal mills are generally used, resulting in lower output per mill. To ensure the burner nozzle velocity and control the ignition distance of pulverized coal, the primary air velocity is not reduced compared to the full-load output. This leads to an increase in the air-to-coal ratio of the primary air at each burner nozzle, resulting in a higher oxygen content in the initial stage of pulverized coal combustion, which cannot effectively inhibit NOx formation. Summary of the Invention

[0006] This invention aims to solve the technical problems existing in the prior art. To this end, this invention proposes a low-load in-furnace NOx generation control system for boilers. This system, operating under low-load conditions, regulates steam temperature while maintaining burner nozzle velocity, ensuring system safety. Furthermore, it can control the oxygen content of the mixed flue gas, which helps suppress NOx generation in the initial stages of combustion.

[0007] The present invention also proposes a boiler combustion system, including the aforementioned low-load in-furnace NOx generation control system.

[0008] According to an embodiment of the present invention, a low-load in-furnace NOx generation control system for a boiler includes: a coal mill having a coal mill outlet and a coal mill inlet, the coal mill inlet being used for the intake of cold primary air and hot primary air; a boiler having a burner; a pulverized coal separator having one coal mill outlet connected to the burner and another connected to the inlet of the pulverized coal separator, the pulverized coal separator having an exhaust port for the discharge of gas; a pulverized coal silo having a pulverized coal silo inlet and a pulverized coal silo outlet, the pulverized coal silo inlet being connected to the outlet of the pulverized coal separator, and the pulverized coal silo outlet being connected to the burner; a pulverized coal feeder having an inlet connected to the outlet of the pulverized coal silo, and the pulverized coal feeder outlet being connected to the burner; and a mixing flue gas box having an inlet and an outlet, the inlet being used for the intake of flue gas, cold primary air, and hot primary air, and the outlet being connected to the outlet of the pulverized coal feeder.

[0009] According to an embodiment of the present invention, the boiler low-load in-furnace NOx generation control system includes a coal mill with a coal mill outlet and a coal mill inlet, the coal mill inlet being used for the intake of cold primary air and hot primary air; the boiler has a burner, the coal mill outlet being connected to the burner in one direction and to the inlet of a pulverized coal separator in another direction, the pulverized coal separator having an exhaust port for gas discharge; the pulverized coal silo has a pulverized coal silo inlet and a pulverized coal silo outlet, the pulverized coal silo inlet being connected to the outlet of the pulverized coal separator, and the pulverized coal silo outlet being connected to the burner; the mixing flue gas box has a flue gas inlet and a flue gas outlet, the flue gas inlet being used for the intake of flue gas, cold primary air, and hot primary air, and the outlet of the pulverized coal feeder being connected to the burner, so that when the boiler low-load in-furnace NOx generation control system is under low-load conditions, the mixed flue gas in the mixing flue gas box can replace the hot and cold primary air to transport pulverized coal, thereby achieving steam temperature regulation while ensuring the burner nozzle velocity, controlling the pulverized coal ignition distance, and ensuring system safety. On the other hand, it can control the oxygen content of the mixed flue gas, so that the pulverized coal combustion has good oxygen-deficient reducing atmosphere combustion conditions in the early stage, which is conducive to suppressing NOx generation in the early stage of combustion.

[0010] In some embodiments of the present invention, a first shut-off valve is provided between the burner and the outlet of the coal mill; and / or, a second shut-off valve is provided between the outlet of the coal mill and the inlet of the pulverized coal separator; and / or, a regulating valve is provided between the flue gas outlet and the outlet of the pulverizer.

[0011] In some embodiments of the present invention, the smoke inlet of the mixing smoke box is multiple and includes a first smoke inlet, a second smoke inlet and a third smoke inlet. The first smoke inlet is used for the entry of flue gas, the second smoke inlet is used for the entry of cold primary air, and the third smoke inlet is used for the entry of hot primary air.

[0012] In some embodiments of the present invention, the system further includes: an air preheater; the boiler having an economizer outlet and a desulfurization tower outlet; the flue gas including a first flue gas and a second flue gas, the temperature of the first flue gas being higher than the temperature of the second flue gas; the first flue gas being taken from the economizer outlet of the boiler; the second flue gas being taken from the air preheater and / or the desulfurization tower outlet of the boiler; the boiler low-load in-furnace NOx generation control system further includes: an ejector having a first inlet, a second inlet, and a first outlet; the first inlet being used for the entry of the first flue gas; the second inlet being used for the entry of the second flue gas; and the first outlet being connected to the first flue gas inlet; and a booster fan for pressurizing the second flue gas taken from the air preheater outlet and / or the desulfurization tower outlet of the boiler; the pressurized second flue gas then drawing the first flue gas from the economizer outlet of the boiler after passing through the ejector.

[0013] In some embodiments of the present invention, the ejector further has a second outlet, and the boiler includes a boiler body and a secondary air box connected to each other, wherein the second outlet is connected to the inlet of the secondary air box.

[0014] In some embodiments of the present invention, the boiler includes a boiler body and a burnout air box connected to each other. The boiler body has a furnace, the burnout air box has a burnout air nozzle, the exhaust gas port is connected to the burnout air nozzle, and the burnout air nozzle is connected to the furnace.

[0015] In some embodiments of the present invention, the burnout air nozzle includes a direct flow nozzle and a swirl nozzle. The burnout air box is provided with a direct flow nozzle pipe and a swirl nozzle pipe for burnout air. The swirl nozzle pipe is sleeved outside the direct flow nozzle pipe for burnout air. The swirl nozzle pipe for burnout air is provided with blades. The swirl nozzle is formed between the direct flow nozzle pipe and the swirl nozzle pipe for burnout air. The direct flow nozzle is formed inside the direct flow nozzle pipe for burnout air. The direct flow nozzle pipe and the swirl nozzle pipe for burnout air are connected to the boiler body.

[0016] In some embodiments of the present invention, the coal mill outlet, the coal powder separator inlet, and the burner are connected by a three-way valve.

[0017] In some embodiments of the present invention, an airlock valve is provided between the pulverized coal bin and the burner.

[0018] The boiler combustion system according to an embodiment of the present invention includes the above-described boiler low-load in-furnace NOx generation control system.

[0019] According to an embodiment of the present invention, the boiler combustion system, by setting up the aforementioned low-load in-furnace NOx generation control system, includes a coal mill with a coal mill outlet and a coal mill inlet, the coal mill inlet being used for the entry of cold primary air and hot primary air; a boiler with a burner connected to the coal mill outlet; a pulverized coal separator with an inlet connected to the coal mill outlet, and a pulverized coal separator with a waste gas outlet for gas discharge; a pulverized coal silo with a pulverized coal silo inlet and a pulverized coal silo outlet, the pulverized coal silo inlet being connected to the outlet of the pulverized coal separator, and the pulverized coal silo outlet being connected to the burner; and a mixing flue gas box with a flue gas inlet and a flue gas outlet, the flue gas inlet being used for the entry of flue gas, cold primary air, and hot primary air, and the flue gas outlet being connected to the burner. This allows the mixed flue gas in the mixing flue gas box to replace the hot and cold primary air for conveying pulverized coal when the low-load in-furnace NOx generation control system is operating at a low load. This achieves both steam temperature regulation and ensures the burner nozzle velocity, controlling the pulverized coal ignition distance and guaranteeing system safety. On the other hand, it can control the oxygen content of the mixed flue gas, so that the pulverized coal combustion has good oxygen-deficient reducing atmosphere combustion conditions in the early stage, which is conducive to suppressing NOx generation in the early stage of combustion.

[0020] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0021] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0022] Figure 1 This is a schematic diagram of a boiler low-load in-furnace NOx generation control system according to an embodiment of the present invention;

[0023] Figure 2 This is a perspective view of a boiler with a low-load in-furnace NOx generation control system according to an embodiment of the present invention.

[0024] Figure 3 This is a partial structural diagram of a boiler according to an embodiment of the present invention, which shows the combustion air box and the boiler body.

[0025] Figure label:

[0026] 10. Boiler low-load in-furnace NOx generation control system;

[0027] 1. Coal mill; 11. Coal mill outlet; 12. Coal mill inlet;

[0028] 2. Boiler; 22. Burner; 23. Boiler body; 231. Furnace; 24. Secondary air box; 25. Combustion air box; 251. Combustion air direct nozzle; 252. Combustion air swirl nozzle;

[0029] 3. Pulverized coal separator; 31. Exhaust gas inlet;

[0030] 4. Pulverized coal silo; 41. Pulverized coal silo inlet; 42. Pulverized coal silo outlet;

[0031] 5. Mixing smoke box; 51. Smoke inlet; 511. First smoke inlet; 512. Second smoke inlet; 513. Third smoke inlet; 52. Smoke outlet;

[0032] 61. First shut-off valve; 62. Second shut-off valve; 63. Regulating valve; 64. Airlock valve;

[0033] 7. Ejector; 71. First inlet; 72. Second inlet; 73. First outlet; 74. Second outlet;

[0034] 8. Powder feeder;

[0035] 91. Primary cold air duct; 92. Primary hot air duct; 93. First flue gas duct; 94. Second flue gas duct; 95. Secondary air duct. Detailed Implementation

[0036] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0037] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, features defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0038] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0039] The following is for reference. Figures 1-3 A boiler low-load in-furnace NOx generation control system 10 is described according to an embodiment of the present invention.

[0040] like Figures 1-3 As shown, the boiler low-load in-furnace NOx generation control system 10 according to an embodiment of the present invention includes: a coal mill 1, a boiler 2, a pulverized coal separator 3, a pulverized coal silo 4, and a mixing flue gas box 5.

[0041] Specifically, refer to Figure 1 The coal mill 1 has a coal mill outlet 11 and a coal mill inlet 12, with the inlet 12 for the intake of cold primary air and hot primary air. The boiler 2 has a burner 22, with one path of the coal mill outlet 11 connected to the burner 22 and another path connected to the inlet of the pulverized coal separator 3. The pulverized coal separator 3 has an exhaust port 31 for the discharge of gas. The pulverized coal silo 4 has a pulverized coal silo inlet 41 and a pulverized coal silo outlet 42, with the inlet 41 connected to the outlet of the pulverized coal separator 3 and the outlet 42 connected to the burner 22. The mixing flue gas box 5 has a flue gas inlet 51 and a flue gas outlet 52, with the inlet 51 for the intake of flue gas, cold primary air, and hot primary air, and the outlet 52 connected to the outlet of the pulverized coal feeder 8. The inlet of the pulverized coal feeder 8 is connected to the outlet 42 of the pulverized coal silo, and the outlet of the pulverized coal feeder 8 is connected to the burner 22. Therefore, the pulverized coal from the pulverized coal bin outlet 42 can be conveyed at a constant speed and in a fixed quantity by the pulverizer 8, thereby achieving the accuracy of the control system 10 for NOx generation in the boiler under low load.

[0042] It should be noted that hot primary air and cold primary air are formed and transported by a primary air fan. The hot primary air is blown by the primary air fan and then passes through an air preheater. It is then transported to the coal mill inlet 12 and the flue gas inlet 51 via a primary hot air duct 92. The cold primary air is blown by the primary air fan and then transported to the coal mill inlet 12 and the flue gas inlet 51 via a primary cold air duct 91. The hot and cold primary air provide power for the conveying of pulverized coal and oxygen for its combustion, ensuring uniform mixing. Furthermore, the mixing of hot and cold primary air allows for temperature control, facilitating better combustion of the pulverized coal. The boiler low-load in-furnace NOx generation control system 10 also includes a burner 22, located inside the boiler 2, used to mix and ignite pulverized coal and air (including primary and secondary air).

[0043] Understandably, when the boiler's low-load in-furnace NOx generation control system 10 is under high-load (greater than 60% of the boiler's rated output) conditions, the burner 22 is directly connected to the coal mill outlet 11. The pulverized coal from the coal mill 1 is directly fed into the boiler 2 for combustion through the hot primary air and cold primary air conveyors. The temperature of the air entering the coal mill 1 is adjusted by adjusting the shut-off valves on the primary cold air pipe 91 and the primary hot air pipe 92 to ensure that the drying output of the coal mill 1 and the temperature of the outlet air-coal mixture meet the requirements.

[0044] When the boiler low-load in-furnace NOx generation control system 10 is under low load (less than 60% of the boiler's rated output), the pulverized coal from the pulverizer 1 enters the pulverized coal separator 3 through the inlet of the pulverized coal separator 3 after being conveyed by hot primary air and cold primary air. Through the air-pulverized coal separation of the pulverized coal separator 3, the pulverized coal can enter the pulverized coal silo 4 from the pulverized coal silo inlet 41, and the air can be discharged from the exhaust port 31. In this way, the relationship between pulverized coal combustion and the wind speed and flow rate of cold primary air and hot primary air is decoupled, avoiding the pulverized coal carrying a large amount of air into the boiler 2. This is conducive to the formation of the conditions required for oxygen-deficient and low-NOx combustion, thereby reducing NOx generation.

[0045] Simultaneously, the mixed flue gas in the mixing flue gas box 5 can provide power for the pulverized coal exiting the pulverizer 8, allowing the pulverized coal to be fed into the boiler 2 for combustion. By controlling the ratio of hot primary air, cold primary air, and flue gas entering the mixture (e.g., through a shut-off valve), the oxygen content (e.g., 10%–20% in this invention), temperature (e.g., 60–200°C in this invention), and flow rate (which can be adjusted by pressure) of the mixed flue gas can be controlled. This ensures that the flow rate and velocity of the pulverized coal and mixed flue gas mixture are at appropriate levels. On the one hand, while regulating the steam temperature (achieved by adjusting the mixed flue gas flow rate), the burner 22 nozzle velocity is maintained, controlling the pulverized coal ignition distance and ensuring system safety. On the other hand, by controlling the oxygen content of the mixed flue gas, a favorable oxygen-deficient reducing atmosphere combustion condition is provided for the initial stage of pulverized coal combustion, which helps suppress NOx formation in the early stages of combustion.

[0046] For example, when the oxygen content is too high, the amount of flue gas entering the furnace can be increased, while the amount of hot and cold primary air entering the furnace can be reduced; when the oxygen content is too low, the amount of flue gas entering the furnace can be reduced, while the amount of hot and cold primary air entering the furnace can be increased; when the steam temperature is too low, the flow rate of the mixed flue gas can be increased, at which point the furnace flue gas temperature drops (because a large amount of flue gas carries away the heat in the furnace), while the amount of flue gas flowing through the convective heating surface increases, which helps to increase the convective heat transfer, thereby increasing the steam temperature; when the steam temperature is too high, the flow rate of the mixed flue gas can be reduced, while the amount of flue gas flowing through the convective heating surface decreases, reducing the convective heat transfer, thereby lowering the steam temperature.

[0047] Therefore, when the NOx generation control system 10 in the boiler is operating at low load, the mixed flue gas in the mixed flue gas box 5 replaces the hot and cold primary air to transport pulverized coal. On the one hand, this achieves steam temperature regulation while ensuring the nozzle velocity of the burner 22, controlling the ignition distance of the pulverized coal, and ensuring system safety. On the other hand, by controlling the oxygen content of the mixed flue gas, a favorable oxygen-deficient reducing atmosphere combustion condition is achieved in the initial stage of pulverized coal combustion, which helps to suppress NOx generation in the early stage of combustion.

[0048] According to an embodiment of the present invention, a low-load in-furnace NOx generation control system 10 for a boiler includes a coal mill 1 with a coal mill outlet 11 and a coal mill inlet 12, the coal mill inlet 12 being used for the intake of cold primary air and hot primary air; a boiler 2 with a burner 22, the coal mill outlet 11 being connected to the burner 22 in one direction and to the inlet of a pulverized coal separator 3 in another direction, the pulverized coal separator 3 having an exhaust port 31 for the discharge of gas; and a pulverized coal silo 4 with a pulverized coal silo inlet 41 and a pulverized coal silo outlet 42, the pulverized coal silo inlet 41 being connected to the inlet of the pulverized coal separator 3. The outlet is connected to the pulverized coal bin outlet 42, which is connected to the burner 22. The mixing flue gas box 5 has an inlet 51 and an outlet 52. The inlet 51 is used for the entry of flue gas, cold primary air, and hot primary air, and the outlet 52 is connected to the outlet of the pulverized coal feeder 8. This allows the mixed flue gas in the mixing flue gas box 5 to replace the hot and cold primary air for conveying pulverized coal when the NOx generation control system 10 is operating at a low load in the boiler. On the one hand, this achieves steam temperature regulation while ensuring the nozzle velocity of the burner 22, controlling the ignition distance of the pulverized coal, and ensuring the safety of the system. On the other hand, it can control the oxygen content of the mixed flue gas, so that the pulverized coal has good oxygen-deficient reducing atmosphere combustion conditions in the early stage of combustion, which is conducive to suppressing NOx generation in the early stage of combustion.

[0049] In some embodiments of the present invention, such as Figure 1 As shown, there are multiple pulverized coal separators 3, which improves the efficiency of air-coal separation and thus improves the efficiency of the NOx generation control system 10 in the boiler at low load. For example, in Figure 1 In the example shown, there are two coal powder separators 3, but the present invention is not limited to this. There can be more coal powder separators 3, such as 3, 4, 5 or 6, etc.

[0050] In some embodiments of the present invention, such as Figure 1 As shown, each pulverized coal separator 3 has multiple inlets, thereby improving the efficiency of the incoming coal in each pulverized coal separator 3, and further improving the efficiency of the boiler low-load in-furnace NOx generation control system 10. For example, in Figure 1 In the example shown, each pulverized coal separator 3 has two inlets, but the present invention is not limited to this. Each pulverized coal separator 3 may have more inlets, such as 3, 4, 5 or 6, etc.

[0051] In some embodiments of the present invention, such as Figure 1As shown, the coal mill 1 has multiple coal mill outlets 11, the boiler 2 has multiple burners 22 corresponding to the multiple coal mill outlets 11, and the pulverized coal silo 4 has multiple pulverized coal silo outlets 42 corresponding to the multiple burners 22. This improves the pulverized coal transport efficiency, thereby further improving the efficiency of the boiler's low-load in-furnace NOx generation control system 10. For example, in... Figure 1 In the example shown, there are four outlets: 11 of the coal mill, 22 of the burner, and 42 of the pulverized coal bin. However, the present invention is not limited to this. The number of outlets: 11 of the coal mill, 22 of the burner, and 42 of the pulverized coal bin can also be other, such as two, three, five, or six.

[0052] In some embodiments of the present invention, such as Figure 1 As shown, there are multiple smoke outlets 52, which improves the smoke discharge efficiency of the mixing smoke box 5, thereby further helping to ensure wind speed, better regulate steam temperature, and further ensure the wind speed at the burner 22 nozzle, control the ignition distance of the pulverized coal, and ensure the safety of the system. For example, in this invention, there are two smoke outlets 52, but the invention is not limited to this; there can be more smoke outlets 52, such as 3, 4, 5, or 6.

[0053] In some embodiments of the present invention, such as Figure 1 As shown, a first shut-off valve 61 is provided between the burner 22 and the coal mill outlet 11. On the one hand, the direction of coal powder transportation can be controlled by opening and closing the first shut-off valve 61. For example, when the first shut-off valve 61 is closed, coal powder flows from the coal mill outlet 11 to the inlet of the coal powder separator 3; when the first shut-off valve 61 is open, coal powder flows from the coal mill outlet 11 to the burner 22. On the other hand, the degree of opening and closing of the first shut-off valve 61 can be controlled, thereby controlling the flow rate and speed of air and coal entering the boiler 2.

[0054] In some embodiments of the present invention, such as Figure 1 As shown, a second shut-off valve 62 is provided between the coal mill outlet 11 and the inlet of the pulverized coal separator 3. On the one hand, the direction of pulverized coal transportation can be controlled by opening and closing the first shut-off valve 61. For example, when the second shut-off valve 62 is open, pulverized coal flows from the coal mill outlet 11 to the inlet of the pulverized coal separator 3; when the second shut-off valve 62 is closed, pulverized coal flows from the coal mill outlet 11 to the burner 22. On the other hand, the degree of opening and closing of the second shut-off valve 62 can be controlled, thereby controlling the flow rate and velocity of air-coal entering the inlet of the pulverized coal separator 3.

[0055] In some embodiments of the present invention, such as Figure 1 As shown, there is a regulating valve 63 between the flue gas outlet 52 and the outlet of the pulverizer 8; thereby, the flow rate and speed of the mixed flue gas and pulverized coal entering the burner 22 can be controlled by adjusting the opening and closing degree of the valve 63.

[0056] In some embodiments of the present invention, the pulverizer outlet 11, the inlet of the pulverized coal separator 3, and the burner 22 are connected by a three-way valve (not shown). This allows the coal to enter the pulverized coal separator 3 from either the pulverizer outlet 11 or the burner 22, thereby enabling different flow directions of pulverized coal under different operating conditions of the boiler low-load in-furnace NOx generation control system 10.

[0057] In some embodiments of the present invention, such as Figure 1 As shown, the mixing flue gas box 5 has multiple flue gas inlets 51, including a first flue gas inlet 511, a second flue gas inlet 512, and a third flue gas inlet 513. The first flue gas inlet 511 is used for flue gas entry, the second flue gas inlet 512 is used for cold primary air entry, and the third flue gas inlet 513 is used for hot primary air entry. Thus, different gases enter through the first flue gas inlet 511, the second flue gas inlet 512, and the third flue gas inlet 513 respectively, thereby avoiding mutual interference between different gases and their corresponding pipelines.

[0058] In some embodiments of the present invention, such as Figure 1 As shown, the low-load NOx generation control system 10 in the boiler also includes: an air preheater (not shown), the boiler 2 has an economizer outlet (not shown) and a desulfurization tower outlet (not shown), the flue gas includes a first flue gas and a second flue gas, the temperature of the first flue gas is higher than the temperature of the second flue gas, the first flue gas is taken from the economizer outlet of the boiler, and the second flue gas is taken from the air preheater and / or the desulfurization tower outlet of the boiler. The low-load NOx generation control system 10 in the boiler also includes: an ejector 7, the ejector 7 has a first inlet 71, a second inlet 72 and a first outlet 73, the first inlet 71 is used for the entry of the first flue gas, the second inlet 72 is used for the entry of the second flue gas, and the first outlet 73 is connected to the first flue gas inlet 511.

[0059] It should be noted that the second flue gas is low-temperature flue gas, taken from the outlet flue of the air preheater. It can be taken from the flue before and after the dust collector, or from the outlet of the desulfurization tower. The second flue gas is transported through the second flue gas pipe 94. The first flue gas is high-temperature flue gas, taken from the flue before the air preheater. It can be taken from the inlet and outlet flue of the economizer, or from the furnace outlet. The first flue gas is transported through the first flue gas pipe 93.

[0060] Understandably, the low-temperature flue gas is ejected at high speed through the ejector 7, creating a low-pressure zone at the nozzle. This low-pressure zone attracts and mixes with the high-temperature flue gas, thereby reducing the difficulty of extracting the high-temperature flue gas. At the same time, after the high-temperature flue gas mixes with the low-temperature flue gas, the temperature of the mixed flue gas decreases. Furthermore, due to the increase in the total amount of mixed gas, the flow rate of the mixed flue gas decreases, which is beneficial for heat transfer and improving combustion efficiency.

[0061] In addition, direct contact between high-temperature flue gas and the heating surfaces at the tail end of boiler 2 (such as air preheaters and economizers) can lead to overheating and corrosion of these surfaces. Low-temperature flue gas injection can reduce the temperature of these heating surfaces and decrease the risk of corrosion.

[0062] Furthermore, the low-load in-furnace NOx generation control system 10 also includes a booster fan (not shown), which pressurizes the second flue gas taken from the air preheater outlet and / or the boiler desulfurization tower outlet. The pressurized second flue gas then draws the first flue gas from the boiler economizer outlet through an ejector. The booster fan may be located inside the second flue gas pipe 94.

[0063] In some embodiments of the present invention, such as Figure 1 As shown, the ejector 7 also has a second outlet 74. The boiler 2 includes a boiler body 23 and a secondary air box 24 connected to each other. The second outlet 74 is connected to the inlet of the secondary air box 24. It should be noted that the secondary air is usually injected into the furnace at a certain stage of pulverized coal combustion (such as after the pulverized coal is ignited). The secondary air is transported to the inlet of the secondary air box 24 through the secondary air duct 95.

[0064] It is understandable that the second outlet 74 is connected to the inlet of the secondary air box 24, so that some of the first flue gas and the second flue gas can be mixed and enter the secondary air box 24. Since the oxygen content of the first flue gas and the second flue gas is low, the oxygen content of the secondary air is also low. This further ensures that when the NOx generation control system 10 in the boiler is at a low load, the pulverized coal combustion has good oxygen-deficient reducing atmosphere combustion conditions in the early stage, which is conducive to suppressing NOx generation in the early stage of combustion.

[0065] In some embodiments of the present invention, such as Figures 1-3 As shown, boiler 2 includes a boiler body 23 and a burnout air box 25 connected to each other. The boiler body 23 contains a furnace 231, and the burnout air box 25 has a burnout air nozzle. Exhaust gas inlet 31 is connected to the burnout air nozzle, and the burnout air nozzle is connected to the furnace 231. It is understood that the connection between the exhaust gas inlet 31 and the burnout air nozzle allows the gas separated from the pulverized coal separator 3 to be recycled, avoiding waste and thus improving the energy efficiency of the primary air fan and the working efficiency of the boiler's low-load in-furnace NOx generation control system 10. Simultaneously, the gas separated by the pulverized coal separator 3 contains a small amount of pulverized coal. The connection between the exhaust gas inlet 31 and the inlet of the burnout air box 25 allows any unseparated pulverized coal to enter the furnace 231 for combustion, thereby reducing pulverized coal loss.

[0066] In some embodiments of the present invention, such as Figure 2 and Figure 3As shown, the burnout air nozzle includes a direct flow nozzle and a swirl nozzle. The burnout air box 25 is equipped with a burnout air direct flow nozzle pipe 251 and a burnout air swirl nozzle pipe 252. The burnout air swirl nozzle pipe 252 is sleeved outside the burnout air direct flow nozzle pipe 251. The burnout air swirl nozzle pipe 252 is equipped with blades. A swirl nozzle is formed between the burnout air direct flow nozzle pipe 251 and the burnout air swirl nozzle pipe 252. A direct flow nozzle is formed inside the burnout air direct flow nozzle pipe 251. The burnout air direct flow nozzle pipe 251 and the burnout air swirl nozzle pipe 252 are connected to the boiler body 23.

[0067] Understandably, when the airflow passes through the burnout air direct nozzle 251, it generates a highly linear airflow that enters the boiler body 23 in a straight direction, resulting in high airflow velocity and rapid mixing. When the airflow passes through the burnout air swirl nozzle 252, it generates a rotating airflow that enters the boiler body 23 in a spiral direction, resulting in relatively lower airflow velocity but good mixing and combustion. Thus, through the interaction of the burnout air direct nozzle 251 and the burnout air swirl nozzle 252, both high airflow velocity and high combustion efficiency are achieved, along with good airflow mixing and combustion, reducing NOx formation.

[0068] In some embodiments of the present invention, such as Figure 1 As shown, there is an airlock valve 64 between the pulverized coal bin 4 and the burner 22, which can control the speed and flow rate of pulverized coal entering the burner 22 from the pulverized coal bin 4.

[0069] Furthermore, the airlock valve 64 is located between the coal powder bin outlet 42 and the inlet of the coal feeder 8. Thus, the airlock valve 64 controls the flow rate and speed of coal powder entering the coal feeder 8 from the coal powder bin outlet 42, preventing excessive coal powder accumulation in the coal feeder 8 and causing blockages. This ensures smooth coal powder transport and guarantees the efficiency of the boiler low-load in-furnace NOx generation control system 10.

[0070] The following describes a boiler combustion system according to an embodiment of the present invention.

[0071] The boiler combustion system according to an embodiment of the present invention includes the above-described boiler low-load in-furnace NOx generation control system 10.

[0072] According to an embodiment of the present invention, the boiler combustion system includes a low-load in-furnace NOx generation control system 10. The coal mill 1 has a coal mill outlet 11 and a coal mill inlet 12, with the inlet 12 for the intake of cold primary air and hot primary air. The boiler 2 has a burner 22, with one path of the coal mill outlet 11 connected to the burner 22 and another path connected to the inlet of the pulverized coal separator 3. The pulverized coal separator 3 has a waste gas outlet 31 for gas discharge. The pulverized coal silo 4 has a pulverized coal silo inlet 41 and a pulverized coal silo outlet 42. The pulverized coal silo inlet 41 is connected to the coal... The outlet of the pulverized coal separator 3 is connected, and the outlet 42 of the pulverized coal silo is connected to the burner 22. The mixing flue gas box 5 has an inlet 51 and an outlet 52. The inlet 51 is used for the entry of flue gas, cold primary air, and hot primary air, and the outlet 52 is connected to the outlet of the pulverized coal feeder 8. This allows the mixed flue gas in the mixing flue gas box 5 to replace the hot and cold primary air for conveying pulverized coal when the NOx generation control system 10 is operating at a low load in the boiler. On the one hand, this achieves steam temperature regulation while ensuring the nozzle velocity of the burner 22, controlling the ignition distance of the pulverized coal, and ensuring the safety of the system. On the other hand, it can control the oxygen content of the mixed flue gas, so that the pulverized coal has good oxygen-deficient reducing atmosphere combustion conditions in the early stage of combustion, which is conducive to suppressing NOx generation in the early stage of combustion.

[0073] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0074] Although embodiments of the invention have been shown and described, those skilled in the art will understand 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 claims and their equivalents.

Claims

1. A boiler low load in-furnace NOx generation control system characterized by, Comprising: a coal mill having a coal mill outlet and a coal mill inlet for the entry of cold primary air and hot primary air; a boiler having a burner; a pulverized coal separator, the coal mill outlet being in communication with the burner and the pulverized coal separator inlet, the pulverized coal separator having a spent gas outlet for the exit of gas; a pulverized coal bin having a pulverized coal bin inlet and a pulverized coal bin outlet, the pulverized coal bin inlet being in communication with the pulverized coal separator outlet, the pulverized coal bin outlet being in communication with the burner; a coal feeder, the coal feeder inlet being in communication with the pulverized coal bin outlet, the coal feeder outlet being in communication with the burner; a mixed flue gas box having a flue gas inlet and a flue gas outlet, the flue gas inlet being for the entry of flue gas, cold primary air and hot primary air, the flue gas outlet being in communication with the coal feeder outlet, the mixed flue gas in the mixed flue gas box replacing the hot primary air and cold primary air to transport the pulverized coal; the flue gas inlet of the mixed flue gas box being multiple and comprising a first flue gas inlet, a second flue gas inlet and a third flue gas inlet, the first flue gas inlet being for the entry of flue gas, the second flue gas inlet being for the entry of cold primary air, the third flue gas inlet being for the entry of hot primary air.

2. The system for controlling the generation of NOx in a low load boiler according to claim 1, characterized by a first shut-off door between the burner and the coal mill outlet; and / or, a second shut-off door between the coal mill outlet and the pulverized coal separator inlet; and / or, a regulating valve between the flue gas outlet and the coal feeder outlet.

3. The system for controlling the generation of NOx in a low load furnace of a boiler according to claim 1, characterized by Further comprising: an air preheater, the boiler having an economizer outlet and a desulfurization tower outlet, the flue gas comprising a first flue gas and a second flue gas, the first flue gas having a higher temperature than the second flue gas, the first flue gas being taken from the economizer outlet of the boiler, the second flue gas being taken from the air preheater and / or the desulfurization tower outlet of the boiler, the boiler low load in-furnace NOx generation control system further comprising: an ejector having a first inlet, a second inlet and a first outlet, the first inlet being for the entry of the first flue gas, the second inlet being for the entry of the second flue gas, the first outlet being in communication with the first flue gas inlet; a booster fan for pressurizing the second flue gas taken from the air preheater outlet and / or the desulfurization tower outlet of the boiler, the pressurized second flue gas sucking the first flue gas from the economizer outlet of the boiler through the ejector.

4. The system for controlling the generation of NOx in a low load boiler according to claim 3, wherein the ejector further having a second outlet, the boiler comprising a boiler body and a secondary air box connected to each other, the second outlet being in communication with the secondary air box inlet.

5. The system for controlling low load NOx generation in a boiler according to claim 1, wherein the boiler comprising a boiler body and an overfire air box connected to each other, the boiler body having a furnace, the overfire air box having an overfire air injection port, the spent gas outlet being in communication with the overfire air injection port, the overfire air injection port being in communication with the furnace.

6. The system for controlling the generation of NOx in a low load furnace of a boiler according to claim 5, characterized by The overfire air nozzle comprises a straight flow nozzle and a rotational flow nozzle, the overfire air box is internally provided with an overfire air straight flow nozzle pipe and an overfire air rotational flow nozzle pipe, the overfire air rotational flow nozzle pipe is sleeved outside the overfire air straight flow nozzle pipe, the overfire air rotational flow nozzle pipe is internally provided with blades, the overfire air straight flow nozzle pipe and the overfire air rotational flow nozzle pipe form the rotational flow nozzle, the overfire air straight flow nozzle pipe forms the straight flow nozzle, and the overfire air straight flow nozzle pipe and the overfire air rotational flow nozzle pipe are connected with the boiler body.

7. The system for controlling low load NOx generation in a boiler according to claim 1, wherein The outlet of the coal mill, the inlet of the coal powder separator and the burner are communicated through a three-way valve.

8. The system for controlling low load NOx generation in a boiler according to claim 1, wherein The coal powder bin is provided with a gas locking valve between the coal powder bin and the burner.

9. A boiler combustion system characterized by, A boiler low-load in-furnace NOx generation control system comprising the boiler low-load in-furnace NOx generation control system according to any one of claims 1-8.

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