Distributed high-temperature flue gas circulation oxygen-deficient combustion system and method

Abstract

The invention relates to the field of industrial furnace combustion, in particular to a distributed high-temperature flue gas circulation oxygen-deficient combustion system and method.The side, facing a hearth, of a burner is provided with a primary air pipe nozzle (17), a gas pipe nozzle (16) and a secondary air pipe outlet (13), and the primary air pipe nozzle (17), the gas pipe nozzle (16) and the secondary air pipe outlet (13) are sequentially distributed from inside to outside; the primary air pipe nozzle (17) is positioned in the center of the burner; the primary air pipe nozzle (17), the gas pipe nozzle (16) and the secondary air pipe outlet (13) are concentric circles; a primary air pipe nozzle (17) is communicated with a primary air pipe (10), a gas pipe nozzle (16) is communicated with a gas pipe (9), and a Laval pipe is arranged between a secondary air pipe (11) and a secondary air pipe outlet (13). The method has the advantages that the generation of NOx can be effectively inhibited, the emission of NOx is reduced, and the pollution to the environment is reduced; and high-temperature flue gas circulation is adopted, so that the problem of equipment corrosion caused by low-temperature flue gas condensation is avoided.

Description

Technical Field

[0001] This invention relates to the field of industrial furnace combustion, and more particularly to a decentralized high-temperature flue gas recirculation oxygen-deficient combustion system and method. Background Technology

[0002] Nitrogen oxides (NOx), as one of the key pollutants under control, are a major source of acid rain and photochemical smog, causing significant harm to human health, crops, and the ecological environment. Besides directly harming human health as a primary pollutant, NOx also generates various secondary pollutants. The steel industry has numerous high-temperature industrial furnaces and kilns, where the high-temperature combustion of carbon (C) and hydrogen (H) fuels produces large amounts of high-temperature NOx-containing waste gas, a significant component of NOx pollution. Therefore, controlling the oxygen content in fuels is a crucial means of controlling NOx formation during combustion.

[0003] In the prior art, application number 201020668557.X discloses a "novel flue gas self-recirculation oxygen-deficient burner," which has a combustion air duct (4) inside the burner shell (5), the combustion air duct (4) is connected to the combustion air inlet on one side of the burner shell, a fuel spray gun (3) is set in the center of the combustion air duct (4), the combustion air duct (4) is connected to the fire channel (6) of the shaped refractory brick above the combustion air duct, and a cyclone separator (8) is set at the outlet of the combustion air duct (4); a flue gas passage (7) is set on the shaped refractory brick (1), and the flue gas passage (7) is connected to the fire channel (6) of the shaped refractory brick. This patent's self-recirculation device in the furnace cannot effectively control the oxygen content, resulting in unstable combustion.

[0004] Application number 202010051097.4 discloses a "self-circulating high-temperature, low-oxygen regenerative self-preheating burner for flue gas," comprising: a main housing, a heat storage housing, and two air / flue gas inlets arranged sequentially from bottom to top; a combustion nozzle and two telescopic pipe assemblies connected to the main housing; a fuel channel within the main housing, with left and right heat storage channels on either side of the fuel channel, each front end containing a left nozzle and a right nozzle; a premixing chamber connected to the fuel channel and combustion nozzle within the main housing, with the left and right nozzles connected to the premixing chamber via left and right mixing channels; and left and right return flue ducts within the left and right telescopic pipe assemblies, with the left return flue connected to the left nozzle and left mixing channel, and the right return flue connected to the right nozzle and right mixing channel. This patent employs low-temperature flue gas circulation, which makes it difficult to guarantee the circulating heat sufficient for low-oxygen combustion, resulting in reduced efficiency. Furthermore, the low-temperature flue gas causes problems such as dew point corrosion.

[0005] Application number 201920979429.8 discloses a "high-temperature, low-oxygen, low-NOx burner," comprising a burner shell consisting of a front section and a volute-type rear section. An insulation layer is provided on the inner wall of the burner shell. A flame tube is located inside the front section of the shell. Several outer gas guns embedded in the insulation layer are arranged around the flame tube in the front section of the shell. An ignition gun extending into the flame tube is installed on the rear side wall of the rear section of the shell. A central gas gun is spaced out from the ignition guns, and cooling ducts are spaced out from the central gas guns. This patent cannot effectively control the amount of flue gas mixed in, nor can it effectively control the stable combustion of the flame.

[0006] In summary, achieving oxygen-deficient combustion through flue gas recirculation in heating furnaces presents two main challenges: firstly, how to recirculate high-temperature flue gas, and secondly, how to effectively control the oxygen content of the combustion aids to ensure stable combustion. Currently, most flue gas recirculation technologies can only recirculate low-temperature flue gas (<300℃), failing to effectively compensate for the temperature loss caused by reduced oxygen-deficient combustion efficiency. High-temperature flue gas recirculation, manifested as flue gas reflux within the furnace, cannot effectively control the mixing concentration, resulting in unstable combustion. Summary of the Invention

[0007] The purpose of this invention is to provide a decentralized high-temperature flue gas recirculation and oxygen-deficient combustion system and method. By realizing high-temperature flue gas recirculation and changing the burner structure, the high-temperature flue gas is directly returned to the combustion air for mixing, achieving controllable and stable oxygen-deficient combustion of the burner. This significantly reduces NOx generation in the flue gas while greatly reducing energy consumption.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A decentralized high-temperature flue gas recirculation oxygen-deficient combustion system includes a burner, which includes a gas pipe, a primary air pipe, a secondary air pipe, and burner bricks. The primary air pipe, gas pipe, and secondary air pipe are assembled from the inside out in one continuous process.

[0010] The burner has a primary air duct nozzle, a gas duct nozzle, and a secondary air duct outlet arranged on the furnace side. The primary air duct nozzle, gas duct nozzle, and secondary air duct outlet are distributed from the inside to the outside. The primary air duct nozzle is located at the center of the burner, and the primary air duct nozzle, gas duct nozzle, and secondary air duct outlet are concentric circles.

[0011] The primary air duct nozzle is connected to the primary air duct, the gas pipe nozzle is connected to the gas pipe, and a Laval tube is installed between the secondary air duct and the secondary air duct outlet; the circulating flue gas inlet is inserted into the Laval tube.

[0012] A Laval tube consists of a tapering section, a constricted section, and a widening section. The tapering section, constricted section, and widening section are connected in sequence to form a Laval tube. The central axes of the tapering section, constricted section, and widening section are located on the same horizontal plane. The tapering section and the widening section have the same structure, both being frustum-shaped.

[0013] The burner brick extends from the outside of the furnace wall to the inlet of the shrink tube section. On the burner brick side of the furnace, with the primary air nozzle as the center and a radius of 2-10cm outside the burner brick nozzle, several holes are evenly distributed in a circle to serve as the circulating flue gas inlet.

[0014] The circulating flue gas inlet is inserted into the constricted section via a high-temperature flue gas circulation channel.

[0015] The outlet of the high-temperature flue gas circulation channel in the constricted section is sloped with a slope angle of 5° to 60°, and the direction of the circulating flue gas outlet in the constricted section is the same as the direction of the air outlet.

[0016] The primary air duct is an L-shaped channel. The horizontal outlet section of the primary air duct is inserted into the gas pipe, and one end of the horizontal inlet section of the primary air duct is connected to the vertical inlet section of the primary air duct.

[0017] A control valve is installed on the inlet side of the secondary air duct, and a gas sensor is installed on the outlet side of the secondary air duct. The gas sensor is used to detect the gas composition at the high-temperature oxygen-deficient combustion-supporting sampling point. A gas sensor is installed inside the furnace to detect the gas composition of the furnace flue gas.

[0018] The burner brick nozzle faces the furnace side, the primary air duct nozzle faces the furnace side, and the burner brick is connected to the furnace wall.

[0019] A decentralized high-temperature flue gas recirculation and oxygen-deficient combustion method is described below:

[0020] The gas is initially mixed and burned with the primary air supplied by the primary air pipe at the gas pipe nozzle;

[0021] Combustion products and secondary air brought in by the secondary air duct are further combusted at the outlet of the secondary air duct to form high-temperature flue gas which is injected into the furnace through the burner brick nozzle to heat the materials.

[0022] The pressurization effect of the Laval tubes arranged on the secondary air duct is used to increase the secondary air velocity and pressure in the constricted section of the Laval tube;

[0023] By inserting a high-temperature flue gas circulation channel into the shortened section of the Laval tube, and utilizing the sloping outlet of the high-temperature flue gas circulation channel, with the outlet direction of the high-temperature flue gas circulation channel facing away from the gas flow direction in the secondary air duct, the high-pressure secondary air formed in the shortened section of the Laval tube blows across the outlet of the high-temperature flue gas circulation channel to form a negative pressure, drawing the high-temperature flue gas in the furnace into the secondary air duct and mixing it thoroughly with the secondary air to form a high-temperature oxygen-deficient combustion-supporting gas.

[0024] The high-temperature, oxygen-deficient combustion gas is further mixed and burned with the combustion products of primary air and coal gas at the outlet of the secondary air duct to form high-temperature flue gas which is then sent into the furnace.

[0025] It also includes the control of oxygen deficiency concentration, as follows:

[0026] The concentration of oxygen deficiency in the gas at the high-temperature oxygen-deficient combustion-supporting gas sampling point was detected and compared with the target oxygen deficiency concentration.

[0027] When the oxygen concentration of the gas at the high-temperature oxygen-deficient combustion-supporting sampling point is higher than the target oxygen concentration, the opening of the control valve on the inlet side of the secondary air duct is increased to increase the secondary air volume and reduce the primary air volume until the oxygen concentration of the gas at the high-temperature oxygen-deficient combustion-supporting sampling point reaches the target oxygen concentration.

[0028] When the oxygen content of the flue gas in the furnace is lower than 0.5%, the opening of the control valve on the inlet side of the secondary air duct is stopped to stop the increase of secondary air volume, and the current oxygen-deficient concentration is recorded as the lowest value as the target oxygen-deficient concentration.

[0029] When the oxygen concentration at the high-temperature oxygen-deficient combustion-supporting gas sampling point is lower than the target oxygen concentration, the opening of the control valve on the inlet side of the secondary air duct is reduced to decrease the secondary air volume and increase the primary air volume. If the NOx generation does not meet the requirements, the reduction of the secondary air ratio is stopped, and the current oxygen concentration is recorded as the lowest value as the target oxygen concentration.

[0030] The formula for calculating oxygen deficiency concentration is as follows:

[0031] ①

[0032] In formula ①, This indicates the oxygen-deficient concentration of the mixed combustion-supporting gas, expressed in % (%). This indicates the oxygen concentration in the combustion flue gas, expressed in % (%). This refers to the flue gas recirculation rate, measured in meters (m). 3 / h;

[0033] The formula for calculating the flue gas recirculation flow rate is as follows:

[0034]

[0035] ②

[0036] In formula ②, , These represent the diameter of the combustion air duct, the diameter of the Laval tube at the contraction point, and the equivalent diameter of the flue gas return pipe, respectively, in mm; , These represent the specific gravity of air and flue gas at room temperature, respectively, in kg / Nm³. 3 ; These represent the main air pipe pressure and the furnace internal pressure, respectively, in mmH2O. This indicates the proportion of secondary air, where V1 and V2 represent the primary air volume and secondary air volume, respectively, in Nm³. 3 / h; t represents the furnace temperature, in K; This represents the conversion factor, with a value of 1 / 273; This represents the acceleration due to gravity, with a value of 9.8 m / s². 2 ; This represents pi, with a value of 3.14.

[0037] The average oxygen content in the high-temperature oxygen-deficient combustion-supporting gas is 15%~18%, the air pressure in the secondary air duct is 10~20kPa, and the distribution ratio of primary air to secondary air is 1:(2~50).

[0038] Compared with the prior art, the beneficial effects of the present invention are:

[0039] 1. This invention achieves high-temperature flue gas recirculation, directly mixing high-temperature flue gas with combustion air to form high-temperature oxygen-deficient combustion gas, thereby reducing the oxygen content during combustion. Since NOx formation is closely related to high temperature and high oxygen concentration during combustion, reducing the oxygen content can effectively inhibit NOx formation, reduce NOx emissions, and reduce environmental pollution. Furthermore, using high-temperature flue gas (rather than low-temperature flue gas) recirculation avoids equipment corrosion problems caused by low-temperature flue gas condensation, extending the burner's service life.

[0040] 2. By adopting oxygen-deficient combustion technology, the oxygen content in the combustion-supporting gas is controlled (15%~18%), which inhibits the formation of NOx under high-temperature conditions, reduces NOx emissions, reduces environmental pollution, and meets environmental protection requirements;

[0041] 3. By utilizing the pressurizing effect of the secondary air Laval tubes arranged on the secondary air duct, the flow rate and pressure of the secondary air are increased. At the same time, by rationally designing the outlet structure of the high-temperature flue gas circulation channel, the high-temperature flue gas and secondary air are fully mixed to form a high-temperature oxygen-deficient combustion-supporting gas. When this mixed gas is further mixed and burned with the primary air and coal gas, it can release heat more efficiently. While reducing the oxygen content, it ensures the stability and efficiency of combustion, improves combustion efficiency, reduces energy waste, and lowers production costs. Stable combustion control is achieved by enhancing the secondary air flow rate through the Laval tube structure and using the negative pressure effect to precisely regulate the circulation volume of high-temperature flue gas, ensuring a stable combustion process and avoiding combustion instability or flameout problems caused by fluctuations in oxygen content.

[0042] 4. The ratio of primary to secondary air (1:2~1:50) and the pressure of secondary air (10~20kPa) can be adjusted according to different fuel types and furnace conditions to optimize combustion effect and is suitable for a variety of industrial furnaces.

[0043] 5. By monitoring the oxygen content of high-temperature oxygen-deficient combustion-supporting gas and the composition of flue gas in the furnace in real time, the air volume ratio is dynamically adjusted to ensure the best balance between combustion efficiency and environmental performance, while preventing incomplete combustion or excessive NOx.

[0044] 6. The burner has a simple structural design. The high-temperature flue gas circulation channel is combined with the Laval tube, which can realize flue gas circulation without the need for an additional power unit, reducing the complexity of the equipment and maintenance costs. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of a decentralized high-temperature flue gas recirculation oxygen-deficient combustion system.

[0046] Figure 2 This is a view from direction A of a decentralized high-temperature flue gas recirculation oxygen-deficient combustion system.

[0047] Figure 3 This is a schematic diagram of the flue gas circulation in a decentralized high-temperature flue gas recirculation and oxygen-deficient combustion system.

[0048] Figure 4 This is a front view of the circulating flue gas outlet.

[0049] Figure 5 This is a left-facing view of the circulating flue gas outlet.

[0050] In the diagram: 1. High-temperature flue gas circulation channel; 2. Furnace wall; 3. Burner brick; 4. High-temperature oxygen-deficient combustion-supporting gas sampling point; 5. Meter; 6. Circulating flue gas outlet; 7. Widening section; 8. Secondary air control valve; 9. Gas pipe; 10. Primary air duct; 11. Secondary air duct; 12. Contraction section; 13. Secondary air duct outlet; 14. Flue gas sampling point; 15. Burner brick nozzle; 16. Gas nozzle; 17. Primary air duct nozzle; 18. Circulating flue gas inlet; 19. Contraction section; 20. Vertical inlet section of gas pipe; 21. Vertical inlet section of primary air duct. Detailed Implementation

[0051] The present invention will now be described in detail with reference to the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0052] The following embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments. Unless otherwise specified, the methods used in the following embodiments are conventional methods.

[0053] Example 1

[0054] See Figure 1A decentralized high-temperature flue gas recirculation oxygen-deficient combustion system includes a burner, which comprises a gas pipe 9, a primary air pipe 10, a secondary air pipe 11, and a burner 3. The primary air pipe 10, gas pipe 9, and secondary air pipe 11 are assembled in a single, continuous manner from the inside out. Figure 1 .

[0055] The burner brick 3 has a primary air duct nozzle 17, a gas duct nozzle 16, and a secondary air duct outlet 13 respectively arranged at one end leading into the burner brick furnace. See Figure 2 The primary air duct nozzle 17, gas duct nozzle 16, and secondary air duct outlet 13 are distributed sequentially from the inside out. The primary air duct nozzle 17 is located at the center of the burner, and the primary air duct nozzle 17, gas duct nozzle 16, and secondary air duct outlet 13 are concentric circles. The primary air duct nozzle 17 faces the furnace side. The burner brick is connected to the furnace wall, and the burner brick nozzle faces the furnace side. The primary air duct nozzle 17 is connected to the primary air duct 10, which is an L-shaped channel. The horizontal outlet section of the primary air duct 10 is inserted into the gas duct 9, and one end of the horizontal inlet section of the primary air duct 10 is connected to the vertical inlet section 21 of the primary air duct. The secondary air duct outlet 13 is connected to the secondary air duct 11, and the secondary air duct 11 is connected to the secondary air duct... A secondary air Laval pipe is installed between outlets 13; the gas pipe nozzle 16 is connected to the gas pipe 9, the gas pipe 9 is an L-shaped channel, the horizontal outlet section of the gas pipe 9 is inserted into the secondary air Laval pipe, and one end of the horizontal inlet section of the gas pipe 9 is connected to the vertical inlet section 20 of the gas pipe; a control valve is installed on the inlet side of the secondary air pipe 11, and a gas sensor is installed on the outlet side of the secondary air pipe 11. The gas sensor is used to detect the gas composition of the high temperature oxygen-deficient combustion-supporting sampling point (4). A gas sensor is installed in the furnace. The gas sensor is used to detect the flue gas composition of the furnace flue gas sampling point (14), including the gas composition (specifically including O2, N2, CO2, CO, H2, etc.).

[0056] The secondary air Laval tube includes a converging section 19, a contracting section 12, and a widening section 7. These sections are sequentially connected to form the secondary air Laval tube. The central axes of the converging section 19, contracting section, and widening section 7 are located on the same horizontal plane. The converging section 19 and widening section 7 have the same structure, both being frustum-shaped. The burner rotor 3 extends from the outside of the furnace wall to the inlet of the contracting section 12. Sixteen circular holes are evenly distributed on the burner rotor 3 on the burner brick furnace side, centered on the primary air nozzle and with a radius of 2-10 cm outside the burner brick nozzle, serving as the circulating flue gas inlet 18. The circulating flue gas inlet 18 is inserted into the contracting section 12 via the high-temperature flue gas circulation channel 1. The outlet 6 of the high-temperature flue gas circulation channel within the contracting section 12 is sloped with an angle of 5°-60°. The direction of the circulating flue gas outlet 6 within the contracting section 12 is the same as the air outlet direction. Figures 3-5 .

[0057] A decentralized high-temperature flue gas recirculation and oxygen-deficient combustion method is described below:

[0058] S1. The gas is initially mixed and burned with the primary air supplied by the primary air pipe 10 through the gas pipe nozzle 16 via the gas pipe 9.

[0059] S2. Combustion products and secondary air brought in by secondary air duct 11 are further combusted at the outlet 13 of secondary air duct. The air pressure of secondary air duct is 10~20kPa. The ratio of primary air to secondary air is 1:(2~10). High-temperature flue gas is formed and injected into the furnace through burner nozzle 15 to heat the material under the action of the burner brick to stabilize the flame. The oxygen content of the flue gas in the furnace is 0%~5%.

[0060] S3. The pressurization effect of the secondary air Laval tube arranged on the secondary air duct 11 is used to increase the secondary air velocity and pressure in the constricted section of the secondary air Laval tube.

[0061] S4. By inserting the high-temperature flue gas circulation channel 1 into the shortened section of the secondary air Laval tube, and utilizing the sloping outlet 6 of the high-temperature flue gas circulation channel, with the outlet 6 facing away from the flue gas flow direction, the high-pressure secondary air formed in the shortened section of the secondary air Laval tube blows through the high-temperature flue gas circulation channel 1 to form a negative pressure, drawing the high-temperature flue gas in the furnace into the secondary air duct 11 and mixing it fully with the secondary air to form a high-temperature oxygen-deficient combustion-supporting combustion.

[0062] S5. The high-temperature oxygen-deficient combustion gas and the combustion products of primary air and coal gas are further mixed and burned at the outlet 13 of the secondary air duct to form high-temperature flue gas which is then sent into the furnace.

[0063] S6. Oxygen deficiency concentration control, details are as follows:

[0064] S61. Detect the oxygen deficiency concentration of the gas at the high-temperature oxygen-deficient combustion-supporting gas sampling point. The average oxygen content in the high-temperature oxygen-deficient combustion-supporting gas ranges from 15% to 18%. Compare the oxygen deficiency concentration of the gas at the high-temperature oxygen-deficient combustion-supporting gas sampling point with the target oxygen deficiency concentration:

[0065] S62. When the oxygen concentration of the gas at the high-temperature oxygen-deficient combustion-supporting sampling point is higher than the target oxygen concentration, increase the opening of the control valve on the inlet side of the secondary air duct 11 to increase the secondary air volume and reduce the primary air volume until the oxygen concentration of the gas at the high-temperature oxygen-deficient combustion-supporting sampling point reaches the target oxygen concentration.

[0066] S63. When the oxygen content of the flue gas in the furnace is lower than 0.5%, stop increasing the opening of the control valve on the inlet side of the secondary air duct 11 to stop increasing the secondary air volume, and record the current oxygen-deficient concentration as the lowest value as the target oxygen-deficient concentration.

[0067] S64. When the oxygen concentration of the gas at the high-temperature oxygen-deficient combustion-supporting gas sampling point is lower than the target oxygen concentration, reduce the opening of the control valve on the inlet side of the secondary air duct 11 to reduce the secondary air volume and increase the primary air volume. If the NOx generation does not meet the requirements, stop reducing the secondary air ratio and record the current oxygen concentration as the lowest value as the target oxygen concentration.

[0068] The formula for calculating oxygen deficiency concentration is as follows:

[0069] ①

[0070] In formula ①, This indicates the oxygen-deficient concentration of the mixed combustion-supporting gas, expressed in % (%). This indicates the oxygen concentration in the combustion flue gas, expressed in % (%). This refers to the flue gas recirculation rate, measured in meters (m). 3 / h;

[0071] The formula for calculating flue gas recirculation flow rate is as follows:

[0072] ②;

[0073] In formula ②, , These represent the diameters of the combustion air duct, the Laval tube at its contraction point, and the flue gas return duct, respectively, in meters (m). , These represent the specific gravity of air and flue gas at room temperature, respectively, in kg / Nm³. 3 ; , , represent the main air pipe pressure and the furnace internal pressure, respectively, in mmH2O; n represents the secondary air ratio. V1, V2 primary and secondary air volumes, Nm 3 / h; t represents the furnace temperature, in K; This represents the conversion factor, with a value of 1 / 273; This represents the acceleration due to gravity, with a value of 9.8 m / s². 2 ; This represents pi, with a value of 3.14.

[0074] Example 2

[0075] A thick-plate heating furnace in a certain factory burns a mixed gas with a calorific value of 2000 kcal / Nm3, an average gas consumption of 20000 Nm3 / h, an air-fuel ratio of 2.1, a furnace temperature of 1210℃, an original unit energy consumption of 1.53 GJ / t, and a NOx emission value of 220 mg / Nm3. 3 This method is used to design a high-temperature flue gas recirculation oxygen-deficient burner, with a secondary air ratio n of 10 / 1 and a secondary air inlet pressure of [missing information]. 1200 mmH2O, furnace pressure The amount of H2O is 1 mmH2O, and the diameter of the combustion-supporting air duct is... The diameter at the contraction point of the Laval tube is 0.4m, designed according to the return flow rate. The diameter of the flue gas return pipe is 0.2m. The specific gravity of air and flue gas at room temperature is 0.05m. , They are 1.273 kg / Nm 3 0.427 kg / Nm 3 The furnace temperature t is controlled at 1473K, and the oxygen content of the flue gas inside the furnace is controlled. The preheating gas temperature is 2%. Based on formulas ① and ②, the flue gas recirculation volume is 20.9% of the secondary air volume. The temperature of the mixed combustion-supporting gas reaches above 538℃. The actual oxygen-deficient concentration is 17.7%. Assuming a 5% reduction in furnace fuel consumption by increasing the preheating gas temperature by 100℃, the furnace fuel consumption is 1.42 GJ / t, with an energy saving rate of 6.95%. Assuming a 1% reduction in oxygen concentration and a 3% reduction in NOx, the NOx emission concentration is 189 mg / Nm³. 3 It decreased by 9.88%.

[0076] Example 3

[0077] A billet heating furnace in a certain factory burns a mixed gas with a calorific value of 2200 kcal / Nm3. The average gas consumption is 10000 Nm3 / h, the air-fuel ratio is set at 2.3, the furnace temperature is 1300℃, the original unit energy consumption is 1.29 GJ / t, and the NOx emission value is 260 mg / Nm3. 3 This method is used to design a high-temperature flue gas recirculation oxygen-deficient burner with a secondary air ratio n of 20 / 1 and a secondary air inlet pressure of [missing information]. 1200 mmH2O, furnace pressure The concentration of H2O is 1.5 mmH2O, and the diameter of the combustion-supporting air duct is... The diameter at the contraction point of the Laval tube is 0.45m, designed according to the return flow rate. The diameter of the flue gas return pipe is 0.18m. The specific gravity of air and flue gas at room temperature is 0.04m. , They are 1.273 kg / Nm 3 0.427 kg / Nm 3 The furnace temperature t is controlled at 1363K, and the oxygen content of the flue gas inside the furnace is controlled. Assuming a 1% reduction, the flue gas recirculation volume, calculated using formulas ① and ②, is 26.97% of the secondary air volume. With the mixed combustion gas temperature exceeding 609℃, the calculated oxygen-deficient concentration is 16.75%. Assuming a 5% reduction in furnace fuel consumption due to a 100℃ increase in preheated gas temperature, the furnace fuel consumption is 1.19 GJ / t, resulting in an energy saving rate of 7.96%. Furthermore, assuming a 1% reduction in oxygen concentration and a 3% reduction in NOx, the NOx emission concentration is 226 mg / Nm³. 3 This represents a decrease of 12.75%.

[0078] This invention achieves high-temperature flue gas circulation by directly mixing high-temperature flue gas with combustion air to form a high-temperature, oxygen-deficient combustion gas, thereby reducing the oxygen content during combustion. Since NOx formation is closely related to high temperature and high oxygen concentration during combustion, reducing the oxygen content effectively inhibits NOx formation, reduces NOx emissions, and minimizes environmental pollution. Using high-temperature flue gas (rather than low-temperature flue gas) circulation avoids equipment corrosion problems caused by low-temperature flue gas condensation, extending the burner's service life. Employing oxygen-deficient combustion technology, the oxygen content in the combustion gas is controlled (15%~18%), inhibiting NOx formation under high-temperature conditions, reducing NOx emissions, minimizing environmental pollution, and meeting environmental protection requirements. The pressurization effect of the secondary air Laval tubes arranged on the secondary air duct increases the secondary air velocity and pressure. Simultaneously, through a rationally designed outlet structure of the high-temperature flue gas circulation channel, the high-temperature flue gas and secondary air are fully mixed to form a high-temperature, oxygen-deficient combustion gas. This mixed gas is then combined with primary air and coal gas. Further mixing and combustion allows for more efficient heat release, reducing oxygen content while ensuring combustion stability and efficiency, improving combustion efficiency, reducing energy waste, and lowering production costs. Stable combustion control is achieved through a Laval tube structure that enhances secondary air velocity and utilizes negative pressure to precisely regulate the high-temperature flue gas circulation volume, ensuring stable combustion and preventing combustion instability or flameout due to oxygen content fluctuations. The primary and secondary air ratio (1:2~1:50) and secondary air pressure (10~20kPa) can be adjusted according to different fuel types and furnace conditions to optimize combustion performance, making it suitable for various industrial furnaces. Real-time monitoring of the oxygen content of high-temperature oxygen-deficient combustion-supporting gases and furnace flue gas composition dynamically adjusts the air volume ratio, ensuring the optimal balance between combustion efficiency and environmental performance, while preventing incomplete combustion or NOx exceedances. The burner's simple structural design, with the high-temperature flue gas circulation channel integrated with the Laval tube, eliminates the need for additional power units, reducing equipment complexity and maintenance costs.

Claims

1. A decentralized high-temperature flue gas recirculation oxygen-deficient combustion system, characterized in that, It includes a burner, which consists of a gas pipe, a primary air pipe, a secondary air pipe, and burner bricks. The primary air pipe, gas pipe, and secondary air pipe are assembled from the inside out in one continuous process. The burner has a primary air duct nozzle, a gas duct nozzle, and a secondary air duct outlet arranged on the furnace side. The primary air duct nozzle, gas duct nozzle, and secondary air duct outlet are distributed from the inside to the outside. The primary air duct nozzle is located at the center of the burner, and the primary air duct nozzle, gas duct nozzle, and secondary air duct outlet are concentric circles. The primary air duct nozzle is connected to the primary air duct, the gas pipe nozzle is connected to the gas pipe, and a Laval tube is installed between the secondary air duct and the secondary air duct outlet; the circulating flue gas inlet is inserted into the Laval tube.

2. The decentralized high-temperature flue gas recirculation oxygen-deficient combustion system according to claim 1, characterized in that, The Laval tube includes a tapered section, a constricted section, and a widening section, which are connected sequentially to form the Laval tube. The central axes of the tapered section, constricted section, and widening section are located on the same horizontal plane. The tapered section and the widening section have the same structure, both being frustum-shaped. The burner brick extends from the outside of the furnace wall to the inlet of the shrink tube section. On the burner brick side of the furnace, with the primary air nozzle as the center and a radius of 2-10cm outside the burner brick nozzle, several holes are evenly distributed in a circle to serve as the circulating flue gas inlet. The circulating flue gas inlet is inserted into the constricted section via a high-temperature flue gas circulation channel.

3. The decentralized high-temperature flue gas recirculation oxygen-deficient combustion system according to claim 2, characterized in that, The outlet of the high-temperature flue gas circulation channel in the constricted section is sloped with a slope angle of 5° to 60°, and the direction of the circulating flue gas outlet in the constricted section is the same as the direction of the air outlet.

4. The decentralized high-temperature flue gas recirculation oxygen-deficient combustion system according to claim 1, characterized in that, The primary air duct is an L-shaped channel, with the horizontal outlet section of the primary air duct inserted into the gas pipe, and one end of the horizontal inlet section of the primary air duct connected to the vertical inlet section of the primary air duct.

5. A decentralized high-temperature flue gas recirculation oxygen-deficient combustion system according to claim 1, characterized in that, The secondary air duct is equipped with a control valve at the inlet side and a gas sensor 1 at the outlet side. The gas sensor 1 is used to detect the gas composition at the high-temperature oxygen-deficient combustion-supporting sampling point. A gas sensor 2 is installed inside the furnace to detect the gas composition of the furnace flue gas.

6. A decentralized high-temperature flue gas recirculation oxygen-deficient combustion system according to claim 1, characterized in that, The burner brick nozzle faces the furnace side, the primary air duct nozzle faces the furnace side, and the burner brick is connected to the furnace wall.

7. A decentralized high-temperature flue gas recirculation oxygen-deficient combustion method for implementing the system described in any one of claims 1-6, characterized in that, The content is as follows: The gas is initially mixed and burned with the primary air supplied by the primary air pipe at the gas pipe nozzle; Combustion products and secondary air brought in by the secondary air duct are further combusted at the outlet of the secondary air duct to form high-temperature flue gas which is injected into the furnace through the burner brick nozzle to heat the materials. The pressurization effect of the Laval tubes arranged on the secondary air duct is used to increase the secondary air velocity and pressure in the constricted section of the Laval tube; By inserting a high-temperature flue gas circulation channel into the shortened section of the Laval tube, and utilizing the sloping outlet of the high-temperature flue gas circulation channel, with the outlet direction of the high-temperature flue gas circulation channel facing away from the gas flow direction in the secondary air duct, the high-pressure secondary air formed in the shortened section of the Laval tube blows across the outlet of the high-temperature flue gas circulation channel to form a negative pressure, drawing the high-temperature flue gas in the furnace into the secondary air duct and mixing it thoroughly with the secondary air to form a high-temperature oxygen-deficient combustion-supporting gas. The high-temperature, oxygen-deficient combustion gas is further mixed and burned with the combustion products of primary air and coal gas at the outlet of the secondary air duct to form high-temperature flue gas which is then sent into the furnace.

8. The decentralized high-temperature flue gas recirculation oxygen-deficient combustion method according to claim 7, characterized in that, It also includes the control of oxygen deficiency concentration, as follows: The concentration of oxygen deficiency in the gas at the high-temperature oxygen-deficient combustion-supporting gas sampling point was detected and compared with the target oxygen deficiency concentration. When the oxygen concentration of the gas at the high-temperature oxygen-deficient combustion-supporting sampling point is higher than the target oxygen concentration, the opening of the control valve on the inlet side of the secondary air duct is increased to increase the secondary air volume and reduce the primary air volume until the oxygen concentration of the gas at the high-temperature oxygen-deficient combustion-supporting sampling point reaches the target oxygen concentration. When the oxygen content of the flue gas in the furnace is lower than 0.5%, the opening of the control valve on the inlet side of the secondary air duct is stopped to stop the increase of secondary air volume, and the current oxygen-deficient concentration is recorded as the lowest value as the target oxygen-deficient concentration. When the oxygen concentration at the high-temperature oxygen-deficient combustion-supporting gas sampling point is lower than the target oxygen concentration, the opening of the control valve on the inlet side of the secondary air duct is reduced to decrease the secondary air volume and increase the primary air volume. If the NOx generation does not meet the requirements, the reduction of the secondary air ratio is stopped, and the current oxygen concentration is recorded as the lowest value as the target oxygen concentration.

9. A decentralized high-temperature flue gas recirculation oxygen-deficient combustion method according to claim 8, characterized in that, The formula for calculating the oxygen deficiency concentration is as follows: ① In formula ①, This indicates the oxygen-deficient concentration of the mixed combustion-supporting gas, expressed in % (%). This indicates the oxygen concentration in the combustion flue gas, expressed in % (%). This refers to the flue gas recirculation rate, measured in meters (m). 3 / h; The formula for calculating the flue gas recirculation flow rate is as follows: ② In formula ②, , These represent the diameter of the combustion air duct, the diameter of the Laval tube at the contraction point, and the equivalent diameter of the flue gas return pipe, respectively, in mm; , These represent the specific gravity of air and flue gas at room temperature, respectively, in kg / Nm³. 3 ; These represent the main air pipe pressure and the furnace internal pressure, respectively, in mmH2O. This indicates the proportion of secondary air, where V1 and V2 represent the primary air volume and secondary air volume, respectively, in Nm³. 3 / h; t represents the furnace temperature, in K; This represents the conversion factor, with a value of 1 / 273; This represents the acceleration due to gravity, with a value of 9.8 m / s². 2 ; This represents pi, with a value of 3.

14.

10. A decentralized high-temperature flue gas recirculation oxygen-deficient combustion method according to claim 7, characterized in that, The average oxygen content in the high-temperature oxygen-deficient combustion-supporting gas is 15%~18%, the air pressure in the secondary air duct is 10~20kPa, and the distribution ratio of primary air to secondary air is 1:(2~50).

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