Low-oxygen scrap iron ladle heating system

Abstract

The application discloses a scrap iron and low-oxygen steel ladle heating system which comprises a steel ladle, a steel ladle cover, a central combustor and a secondary air inlet device arranged on the steel ladle cover, wherein the central combustor is internally provided with a gas pipe, and the secondary air inlet device comprises a secondary air main pipe and a secondary air branch pipe. The gas enters the steel ladle through the gas pipe arranged in the central combustor, the primary combustion-supporting gas enters the steel ladle through the channel formed between the inner wall of the central combustor and the outer wall of the gas pipe, and the secondary combustion-supporting gas enters the steel ladle through the secondary air main pipe and the secondary air branch pipe arranged outside the central combustor. Based on the structural design, the paths of the gas and the primary combustion-supporting gas entering the steel ladle are different from the path of the secondary combustion-supporting gas entering the steel ladle, so that the secondary combustion-supporting gas enters the steel ladle later than the gas, the oxygen in the secondary combustion-supporting gas is consumed by the gas before reaching the surface of the scrap iron, and thus the direct high-speed impact of the secondary combustion-supporting gas on the scrap iron is avoided, and the oxidation of the scrap iron is reduced.

Description

Technical Field

[0001] This utility model relates to a scrap steel heating device, specifically a low-oxidation steel ladle heating system for scrap steel elements, belonging to the field of iron and steel metallurgy technology. Background Technology

[0002] Statistics show that using 1 ton of scrap steel as a raw material can save 1.7 tons of iron concentrate and reduce the mining of 4.25 tons of primary ore. Scrap steel, as a recyclable resource, typically has a cycle life of 8 to 30 years and can be reused indefinitely. Compared to iron ore, using scrap steel to produce the same amount of steel can save 60% of energy, 40% of water, and reduce emissions of exhaust gas by 86%, wastewater by 76%, and waste residue by 97%.

[0003] By adding a certain amount of scrap steel to the ladle, the sensible heat of the molten steel and the electric heating of the refining furnace can be used to increase the amount of scrap steel used in the steelmaking process and improve the scrap steel ratio.

[0004] Therefore, steel companies generally use ladle baking machines to bake scrap steel. For example... Figure 1 As shown, preheating scrap steel using a ladle preheater involves loading scrap steel into a ladle or scrap hopper and placing it under the burner of the ladle preheater for preheating. Once preheated, the scrap steel is poured into a converter for smelting. Alternatively, the ladle preheater carries the hot scrap steel to the converter / electric furnace to collect molten steel, which then enters the refining furnace for the refining process. This preheating method is technically simple and convenient, but to ensure preheating efficiency, the flow rate of the combustion gas and combustion air is usually high, directly impacting the surface of the scrap steel. Scrap steel is highly susceptible to oxidation at temperatures exceeding 550℃. Existing scrap steel preheating devices often reach temperatures of 700 or even 800℃ in the upper layer, resulting in the formation of large amounts of iron oxide scale, which leads to the following problems in the subsequent refining process: 1. Increased slag volume and refining agent consumption The main component of iron oxide scale is iron oxide, which reacts with other furnace materials during refining to generate more slag. This not only increases the amount of slag but also alters its composition and properties, affecting its fluidity and stability. To adjust the slag's composition and properties, more refining agents, such as lime and fluorite, need to be added, thus increasing the consumption of refining agents.

[0005] 2. Affects the quality of molten steel Excessive iron oxide scale increases the oxygen content in molten steel, reducing its purity. This can cause various defects in the steel, such as porosity and inclusions, thus reducing its mechanical and processing properties.

[0006] 3. Reduce refining efficiency Iron oxide scale requires heat to melt and react during the refining process, which increases energy consumption, prolongs refining time, and reduces refining efficiency. Excessive iron oxide scale can also form an oxide film on the surface of molten steel, hindering sufficient contact and reaction between the molten steel and the refining agents, further reducing refining efficiency.

[0007] 4. Increased equipment burden Increased slag volume leads to more frequent slag removal from the refining furnace, increasing equipment operating time and maintenance costs. Iron oxide scale may corrode the furnace lining during refining, shortening its service life and increasing equipment repair and replacement costs. Utility Model Content

[0008] To address the problem of severe oxidation of scrap steel during ladle heating in existing technologies, which affects subsequent processes, this invention proposes a low-oxidation ladle heating system for scrap steel. In this invention, the ladle heating system includes a ladle, a ladle furnace cover installed on top of the ladle, and a central burner and a secondary air intake device mounted on the furnace cover. The central burner contains a gas pipe, and the secondary air intake device includes a main secondary air pipe and secondary air branch pipes. Gas enters the ladle through the gas pipe inside the central burner, primary combustion-supporting gas enters the ladle through a channel formed between the inner wall of the central burner and the outer wall of the gas pipe, and secondary combustion-supporting gas enters the ladle through the main and branch pipes of the secondary air system located outside the central burner. Based on this structural design, both the combustion gas and the primary combustion-supporting gas are directly fed into the ladle through the vertical channel of the central burner. The secondary combustion-supporting gas, on the other hand, needs to enter the ladle through multiple indirect channels, such as the secondary air main pipe and secondary air branch pipes. Therefore, the secondary combustion-supporting gas enters the ladle later than the combustion gas. This allows the oxygen in the secondary combustion-supporting gas to be consumed by the combustion gas before it reaches the surface of the scrap steel, thereby avoiding the direct high-speed impact of the secondary combustion-supporting gas on the scrap steel, effectively reducing the oxidation of the scrap steel, and ensuring the smooth operation of subsequent processes.

[0009] According to the first embodiment of this utility model, a low-oxidation steel ladle heating system for scrap iron and steel elements is provided.

[0010] A low-oxidation steel ladle heating system for scrap iron includes a ladle with a top opening and a ladle furnace cover installed on top of the ladle. A central burner is mounted on the ladle furnace cover. The lower end of the central burner passes through the ladle furnace cover and communicates with the ladle. A gas pipe is installed inside the central burner. The upper end of the gas pipe has a gas inlet, and the lower end passes through the ladle furnace cover and communicates with the ladle. A primary air inlet pipe is connected to the upper part of the central burner. The primary air inlet pipe has a primary air inlet. The system also includes a secondary air inlet device. The secondary air inlet device includes a secondary air main pipe and secondary air branch pipes. The secondary air main pipe is located above the ladle furnace cover. The upper end of the secondary air branch pipe is connected to the secondary air main pipe, and the lower end passes through the ladle furnace cover and communicates with the ladle. A secondary air inlet pipe is also connected to the secondary air main pipe, and the secondary air inlet pipe has a secondary air inlet.

[0011] In this invention, the secondary air main pipe has a ring structure and is arranged around the central burner. Preferably, the secondary air main pipe, the central burner, and the gas pipe are arranged coaxially.

[0012] Preferably, the secondary air main pipe is connected to multiple secondary air branch pipes. Preferably, the multiple secondary air branch pipes are arranged in a ring or evenly distributed along the circumference at the lower part of the secondary air main pipe.

[0013] In this invention, the secondary air branch pipe includes a vertical section and an inclined section connected to the vertical section. The vertical section is connected to the main secondary air pipe, and the inclined section passes through the ladle furnace cover and communicates with the ladle.

[0014] Preferably, each secondary air branch pipe includes a vertical section and an inclined section. The inclined sections of multiple secondary air branch pipes are inclined to the same side along the circumferential direction.

[0015] In this invention, the central burner is a swirl burner. Preferably, the swirl direction of the central burner is opposite to the swirl direction formed by the inclined section of the secondary air branch pipe.

[0016] In this invention, the inclination angle α of the inclined section of the secondary air branch pipe is 15°~45°, preferably 20°~35°.

[0017] In this invention, a primary air guide vane and a primary air swirl vane are provided inside the central burner and located between the central burner and the gas pipe. Preferably, the primary air swirl vane is positioned near the outlet of the central burner. The primary air guide vane is located between the primary air inlet and the primary air swirl vane.

[0018] In this invention, a gas guide vane and a gas swirl vane are provided inside the gas pipe. A positioning shaft is located at the lower center of the gas pipe. The gas guide vane and the gas swirl vane are respectively mounted on the positioning shaft. Preferably, the gas swirl vane is positioned near the outlet of the gas pipe. The gas guide vane is located between the gas inlet and the gas swirl vane.

[0019] In this invention, the swirling directions of the primary air swirl vane and the gas swirl vane are the same, and their swirling directions are opposite to the swirling direction formed by the inclined section of the secondary air branch pipe.

[0020] Preferably, the spiral angle of the primary air swirl vane is 50°~60°, more preferably 50°~55°. The spiral angle of the gas swirl vane is 35°~50°, more preferably 42°~45°.

[0021] In this invention, a gap Δd1 is left between the ladle furnace cover and the top of the ladle. The value of Δd1 ranges from 0.05 to 0.2 m, preferably from 0.05 to 0.1 m.

[0022] According to a second embodiment of the present invention, a method for heating low-oxidation steel ladles of scrap iron is provided.

[0023] A method for heating a low-oxidation steel ladle from scrap iron, or a heating method using the system described in the first embodiment, the method comprising the following steps: S1. Add scrap steel to the ladle, then transport the ladle to the baking station, and lower the ladle furnace cover to the designated position above the ladle.

[0024] S2. Turn on the flue gas exhaust fan located outside the ladle, introduce gas into the gas pipe through the gas inlet, introduce primary combustion gas into the central burner through the primary air inlet, and introduce secondary combustion gas into the secondary air intake device through the secondary air inlet. Ignite the gas and start the scrap steel baking process.

[0025] S3. The gas and the primary combustion-supporting gas flow downwards. After mixing, they ignite. The combustion of the gas releases a large amount of heat, and the resulting high-temperature gas flow heats the scrap steel in the ladle.

[0026] S4. Secondary combustion-supporting gas enters the ladle, mixes and burns with the fuel gas, and the resulting high-temperature gas flow continues to heat the scrap steel, achieving efficient preheating of the scrap steel.

[0027] In this invention, in step S3, the flow rate of the primary combustion-supporting gas is controlled so that the high-temperature gas flow after the gas and the primary combustion-supporting gas are mixed and ignited is a fuel-rich gas flow.

[0028] Preferably, controlling the flow rate of the primary combustion-supporting gas specifically includes the following sub-steps: S301. Calculate the gas flow rate Q entering the gas pipe. fuel Nm 3 / h.

[0029] Q fuel =k1×m…………(1).

[0030] In the formula: m is the mass of scrap steel added to the ladle, in tons (t). k1 is an adjustment coefficient, with a value ranging from 25 to 50 Nm. 3 / (h·t).

[0031] S302, based on gas flow rate Q fuel Calculate the total amount of combustion-supporting gas required, Q. a Nm 3 / h.

[0032] Q a = k2×j×Q fuel …………(2).

[0033] In the formula: j is the amount of oxygen required for the complete combustion of a unit volume of fuel gas. k2 is the excess oxidizing gas system number. When the oxidizing gas is oxygen, the value of k2 ranges from 1.1 to 1.4, preferably from 1.1 to 1.15. When the oxidizing gas is compressed air, the value of k2 ranges from 1.1 / 0.21 to 1.5 / 0.21, preferably from 1.1 / 0.21 to 1.2 / 0.21.

[0034] S303, based on the total amount of combustion-supporting gas Q a Determine the flow rate of the combustion-supporting gas Q1, Nm 3 / h.

[0035] Q1 = k3 × Q a …………(3).

[0036] In the formula: k3 is the proportionality coefficient, and the value of k3 ranges from 0.05 to 0.25.

[0037] Adjust the primary combustion gas flow rate to Q1 to ensure smooth ignition of the gas. At the same time, the high-temperature gas flow after the gas and primary combustion gas mix and ignite is a fuel-rich gas flow.

[0038] In this invention, in step S4, the flow rate of the secondary combustion-supporting gas and the gas outlet speed are controlled so that the flow rate of the secondary combustion-supporting gas is lower than the gas outlet speed.

[0039] Preferably, controlling the flow rate of the secondary combustion-supporting gas and the gas outlet velocity specifically includes the following sub-steps: S401. Calculate the flow velocity v2 of the secondary combustion-supporting gas, m / h.

[0040] v2 =Q2 / (n×1 / 4×π×D1 2 ) …………(4).

[0041] And: Q2 = Q a - Q1…………(5).

[0042] In the formula: Q2 is the flow rate of the secondary combustion-supporting gas, Nm 3 / h. n is the number of secondary air branch pipes. D1 is the inner diameter of the inclined section of the secondary air branch pipe, in meters.

[0043] S402, based on the gas flow rate Q entering the gas pipe fuel Calculate the gas outlet velocity v fuel , m / h.

[0044] v fuel = Q fuel / [1 / 4π(D2 2 -D3 2 )]…………(6).

[0045] In the formula: D2 is the inner diameter of the gas inlet, in meters (m). D3 is the outer diameter of the positioning shaft, in meters (m).

[0046] S403, Adjust the flow rate v2 of the secondary combustion-supporting gas and the gas outlet velocity v fuel This satisfies the following relationship between the two: v2 ≤ v fuel / γ a …………(7).

[0047] In the formula: γ a This represents the system safety factor. Specifically, when the combustion-supporting gas is oxygen, γ... a The value range is 8~12. When the combustion-supporting gas is compressed air, γ a The value range is 1.8 to 3.

[0048] Adjust the flow rate of the secondary combustion-supporting gas to v2, and the gas outlet velocity to v. fuel This causes the flow rate of the secondary combustion-supporting gas to be lower than the gas outlet velocity.

[0049] To address the problem of severe oxidation of scrap steel during ladle heating in existing technologies, which affects subsequent processes, this invention proposes a low-oxidation ladle heating system for scrap steel. In this invention, the ladle heating system includes a ladle, a ladle furnace cover installed on top of the ladle, a central burner and a secondary air intake device mounted on the furnace cover. The central burner contains a gas pipe, and the secondary air intake device includes a main secondary air pipe and secondary air branch pipes. Gas is introduced into the ladle through the gas pipe located within the central burner and the furnace cover. Primary combustion-supporting gas enters the ladle through the furnace cover via a channel formed between the inner wall of the central burner and the outer wall of the gas pipe. Secondary combustion-supporting gas enters the ladle through the main and branch pipes of the secondary air system located outside the central burner and the furnace cover. Based on this structural design, both the combustion gas and the primary combustion-supporting gas are directly fed into the ladle through the vertical channel of the central burner. The secondary combustion-supporting gas, however, enters the ladle through multiple interconnected, indirect channels, including the secondary air main pipe and branch pipes. Therefore, the secondary combustion-supporting gas enters the ladle later than the combustion gas and primary combustion-supporting gas. During system operation, the primary combustion-supporting gas and a sufficient amount of combustion gas first enter the ladle and mix for combustion. The secondary combustion-supporting gas that subsequently enters the ladle mixes with the unreacted combustion gas to achieve complete combustion. In short, most of the oxygen in the primary or secondary combustion-supporting gas is consumed by the combustion gas before reaching the surface of the scrap steel, avoiding direct, high-speed impact on the scrap steel. This makes it difficult for oxygen molecules in the combustion-supporting gas to come into contact with the scrap steel, effectively reducing the degree of oxidation of the scrap steel during heating, thereby improving the efficiency of subsequent processes and product quality.

[0050] Furthermore, this invention, based on an optimized ladle heating system structure, precisely controls the flow rates of the combustion gas and the secondary combustion-supporting gas. Utilizing the velocity difference between the combustion gas and the secondary combustion-supporting gas, it prevents most oxygen molecules from contacting the heated scrap steel, thereby significantly reducing the oxidation level of the scrap steel. In addition, the chemical energy of the combustion gas is completely released in the space above the scrap steel, which is simultaneously heated by convection and radiation from the high-temperature airflow, achieving highly efficient preheating of the scrap steel under low-oxidation heating conditions.

[0051] Preferably, during the ladle heating process, this invention can also precisely control the flow rate of the primary combustion-supporting gas, so that the gas can be successfully ignited. At the same time, the high-temperature gas flow after the gas and the primary combustion-supporting gas are mixed and ignited is a fuel-rich gas flow (i.e., the gas is sufficient, but the oxygen in the primary combustion-supporting gas is insufficient to consume all the gas), which is in a reducing state. The fuel-rich gas flow will not oxidize the iron element of the scrap steel, but can instead react chemically with the oxidizing impurities on the surface of the scrap steel, release heat, remove some impurities, reduce the consumption of auxiliary materials in subsequent refining processes, and improve refining efficiency.

[0052] Specifically, the low-oxidation steel ladle heating system for scrap steel elements described in this utility model includes a steel ladle, a ladle cover, a central burner mounted on the ladle cover, and a secondary air intake device. The lower end of the central burner passes through the ladle cover and communicates with the steel ladle (the outer diameter of the central burner is the same as the burner orifice diameter on the ladle cover to ensure no gas leakage after the central burner is installed on the ladle cover). A gas pipe is installed inside the central burner, with a gas inlet at its upper end and a gas outlet at its lower end passing through the ladle cover and communicating with the steel ladle. A primary air intake pipe is connected to the upper part of the central burner, and a primary air inlet is provided on the primary air intake pipe. That is, the gas pipe located inside the central burner provides a channel for gas to enter the steel ladle, while the space between the inner wall of the central burner and the outer wall of the gas pipe provides a channel for primary combustion-supporting gas to enter the steel ladle. The secondary air intake device provides a channel for secondary combustion-supporting gas to enter the steel ladle. The secondary air intake device includes a secondary air main pipe and secondary air branch pipes. The secondary air main pipe is located above the ladle cover. The upper end of the secondary air branch pipe is connected to the secondary air main pipe, and the lower end passes through the ladle furnace cover and connects to the ladle. A secondary air inlet pipe is also connected to the secondary air main pipe, and a secondary air inlet is provided on the secondary air inlet pipe. It should be noted that the outer diameter of the secondary air inlet pipe and the outer diameter of the secondary air branch pipe are slightly smaller than the outer diameter of the secondary air main pipe to ensure that the secondary combustion-supporting gas can be input normally. As mentioned earlier, the paths of the primary combustion-supporting gas and the secondary combustion-supporting gas into the ladle are different from those of the secondary combustion-supporting gas, causing the secondary combustion-supporting gas to enter the ladle later than the primary combustion-supporting gas, thereby reducing the oxidation of the scrap steel. In addition, in this invention, the primary combustion-supporting gas, the secondary combustion-supporting gas, and the secondary combustion-supporting gas each enter the ladle independently through their respective channels. This structural design also helps to independently and precisely control the airflow rate and velocity of the three gases during the scrap steel heating process, achieving efficient preheating of the scrap steel within the heating system while ensuring that the scrap steel is not oxidized by the combustion-supporting gas, thus guaranteeing the smooth operation of subsequent refining processes.

[0053] Preferably, the secondary air main pipe has a ring structure and is arranged around the central burner. The secondary air main pipe, the central burner, and the gas pipe are coaxially arranged. This arrangement ensures that the gas entering the ladle via the gas pipe, the primary combustion-supporting gas entering the ladle via the central burner, and the secondary combustion-supporting gas entering the ladle via the secondary air intake device are all evenly distributed within the ladle, improving the heating efficiency of the scrap steel. Furthermore, multiple secondary air branch pipes are connected to the secondary air main pipe. These branch pipes are arranged in a ring or evenly distributed along the circumference at the lower part of the secondary air main pipe (generally, 2 to 12 secondary air branch pipes are evenly connected to the secondary air main pipe, preferably 3 to 8, for example, the number of secondary air branch pipes is 2, 3, 4, 6, 8, 10, or 12, etc.). This design ensures that the secondary combustion-supporting gas enters the ladle evenly from different points and is distributed more uniformly after entering the ladle. This design allows for more thorough mixing of the secondary combustion-supporting gas and the combustion gas, resulting in more complete combustion. This effectively slows down and reduces the contact between oxygen in the secondary combustion-supporting gas and the scrap steel, further reducing the oxidation of the scrap steel. It also avoids local overheating or underheating of the scrap steel.

[0054] Preferably, each secondary air branch pipe includes a vertical section and an inclined section, and the inclined sections of multiple secondary air branch pipes are inclined to the same side along the circumference. The inclined section design at the bottom of the secondary air branch pipe allows the secondary combustion-supporting gas to form a swirling flow within the ladle, further enhancing the heating effect on the scrap steel and reducing its oxidation level. The multiple inclined sections tilting to the same side ensures that the swirling flow direction of the secondary combustion-supporting gas at all secondary air outlets (i.e., the outlets of each inclined section, connected to the ladle) is consistent. Simultaneously, the inclination angle of each inclined section is optimized (here, the inclination angle refers to the angle between the straight line containing the inclined section and the vertical direction; generally, the inclination angle is 15°~45°, preferably 20°~35°, for example, inclination angles of 15°, 20°, 25°, 30°, 35°, 40°, or 45°, etc.), which can reduce the energy consumption of the secondary combustion-supporting gas while ensuring heating effect.

[0055] In this invention, the central burner is preferably a swirl burner, and its swirl direction is opposite to the swirl direction formed by the inclined section of the secondary air branch pipe. This design allows the combustion gas and the secondary combustion-supporting gas to form convection within the ladle, greatly increasing the mixing rate between the two. This results in oxygen molecules in the secondary combustion-supporting gas being consumed by the combustion gas molecules in the space above the scrap steel, making it difficult for oxygen molecules to contact the heated scrap steel material, thus significantly reducing the amount of oxidation in the scrap steel. Furthermore, the use of the swirl burner enhances the combustion effect of the combustion gas, improves the heat release efficiency, and further improves the heating efficiency of the scrap steel.

[0056] Specifically, this invention includes a primary air guide vane and a primary air swirl vane located within the central burner and between the central burner and the gas pipe (i.e., within the channel through which the primary combustion gas enters the ladle). The primary air swirl vane is positioned near the outlet of the central burner (i.e., the end of the central burner that connects to the ladle). The primary air guide vane is located between the primary air inlet and the primary air swirl vane. Correspondingly, this invention also includes a gas guide vane and a gas swirl vane within the gas pipe. A positioning shaft is located at the lower center of the gas pipe. The gas guide vane and the gas swirl vane are respectively mounted on the positioning shaft. The gas swirl vane is positioned near the outlet of the gas pipe (i.e., the end of the gas pipe that connects to the ladle). The gas guide vane is located between the gas inlet and the gas swirl vane. After the primary combustion-supporting gas enters the central burner, it passes through the primary air guide vanes and primary air swirl vanes before exiting the central burner. The gas enters the gas pipe and passes through the gas guide vanes and gas swirl vanes before exiting the gas pipe. The design of these guide vanes and swirl vanes allows the primary combustion-supporting gas and gas to form a swirling flow before mixing, further enhancing the mixing and combustion effects. Simultaneously, the swirl directions of the primary air and gas swirl vanes are the same. The primary combustion-supporting gas and gas flow downwards through the central burner and gas pipe respectively. After mixing, they ignite, and the resulting high-temperature gas flow heats the scrap steel in the ladle. With both swirl directions in the same direction, this invention can also precisely control the flow rate of the primary combustion-supporting gas, ensuring that the number of oxygen molecules in the primary combustion-supporting gas is insufficient to consume the fuel molecules in the gas. Therefore, the high-temperature gas flow after mixing and ignition is a fuel-rich gas flow, exhibiting a reducing state. It will not oxidize the iron in the scrap steel; instead, it can chemically react with oxidizing impurities on the surface of the scrap steel, releasing heat and removing some impurities.

[0057] The swirling direction of the gas swirl vane is opposite to that formed by the inclined section of the secondary air branch pipe. This means the rotation direction of the gas flow is opposite to that of the secondary combustion-supporting gas, significantly increasing the mixing rate within the ladle space. The better the mixing effect and the faster the reaction, the more oxygen molecules in the secondary combustion-supporting gas are consumed by the gas molecules before reaching the scrap steel surface. Therefore, oxygen molecules have difficulty contacting the scrap steel, reducing its oxidation. With the significantly increased mixing rate due to the opposite swirling directions, this invention can further precisely control the gas outlet velocity and the flow rate of the secondary combustion-supporting gas, ensuring that the flow rate of the secondary combustion-supporting gas is lower than the gas outlet velocity. This means the secondary combustion-supporting gas reaches the scrap steel surface later than the gas, further consuming most of the oxygen molecules in the secondary combustion-supporting gas before reaching the scrap steel surface, further reducing the possibility of oxygen molecules contacting the scrap steel and significantly lowering the amount of scrap steel oxidation.

[0058] Generally, the helical angle of the primary air swirl vane is 50°~60°, preferably 50°~55°, for example, the helical angle of the primary air swirl vane is 50°, 53°, 55°, or 60°, etc.; the helical angle of the gas swirl vane is 35°~50°, preferably 42°~45°, for example, the helical angle of the gas swirl vane is 35°, 40°, 42°, 45°, or 50°, etc. This invention sets the swirl angles of the primary air swirl vane and the gas swirl vane to be different, which helps to mix the gas and the primary combustion-supporting gas, improving ignition stability.

[0059] In this invention, a gap Δd1 is left between the ladle furnace cover and the top of the ladle. The value of Δd1 ranges from 0.05 to 0.2 m, preferably from 0.05 to 0.1 m. For example, the gap Δd1 between the ladle furnace cover and the top of the ladle can be 0.05 m, 0.07 m, 0.1 m, 0.15 m, or 0.2 m, etc. This distance, or gap, between the ladle furnace cover and the top of the ladle serves as the flue gas outlet of the ladle heating system. It should be noted that this invention requires controlling the flue gas outlet position to be at a negative pressure, for example, the pressure at the flue gas outlet position can be controlled to be -(30~100) Pa, thereby ensuring smooth flow of flue gas so that the flue gas that has entered the scrap steel and exchanged heat with the scrap steel can be discharged from the flue gas outlet.

[0060] Based on the above-mentioned low-oxidation steel ladle heating system for scrap steel elements, this utility model also proposes a method for using the steel ladle heating system, specifically including the following steps: S1. Scrap steel is added to the ladle, and then the ladle is transported to the baking station. The ladle furnace cover is lowered to a designated position above the ladle. This designated position is defined as a gap or distance Δd1 left between the ladle furnace cover and the top of the ladle as a flue gas outlet.

[0061] S2. Turn on the flue gas exhaust fan located outside the ladle (the flue gas outlet is connected to the external flue gas pipeline, and the flue gas exhaust fan is installed on the flue gas pipeline). Introduce gas into the gas pipeline from the gas inlet, introduce primary combustion gas into the central burner through the primary air inlet, and introduce secondary combustion gas into the secondary air intake device through the secondary air inlet. Ignite the gas and begin the scrap steel baking process.

[0062] S3. The gas and the primary combustion-supporting gas flow downwards. After mixing, they ignite. The combustion of the gas releases a large amount of heat, and the resulting high-temperature gas flow heats the scrap steel in the ladle.

[0063] In step S3, the flow rate of the primary combustion-supporting gas is controlled so that the high-temperature gas flow after the combustion gas and the primary combustion-supporting gas mix and ignite is a fuel-rich gas flow. Specifically, controlling the flow rate of the primary combustion-supporting gas includes the following sub-steps: S301, based on gas flow rate Q fuelCalculate the gas flow rate Q in the gas pipe based on the relationship between the mass m of scrap steel added to the ladle and the gas flow rate m. fuel Nm 3 / h.

[0064] Q fuel =k1×m…………(1).

[0065] In the formula: m is the mass of scrap steel added to the ladle, in tons (t). k1 is an adjustment coefficient, with a value ranging from 25 to 50 Nm. 3 / (h·t). Generally, when the combustion-supporting gas is oxygen, the value of k1 ranges from 25 to 35 Nm. 3 / (h·t); When the combustion-supporting gas is compressed air, the value of k1 ranges from 35 to 50 Nm. 3 / (h·t).

[0066] S302, based on gas flow rate Q fuel Calculate the total amount of combustion-supporting gas required, Q. a Nm 3 / h.

[0067] Q a = k2×j×Q fuel …………(2).

[0068] In the formula: j represents the amount of oxygen required for the complete combustion of a unit volume of fuel gas. The value of j depends on the type of fuel gas; for example, j=2 when the fuel gas is CH4, and j=0.78 when the fuel gas is coke oven gas. k2 is the excess oxidizing gas system number. Specifically, when the oxidizing gas is oxygen, the value of k2 ranges from 1.1 to 1.4, preferably from 1.1 to 1.15. When the oxidizing gas is compressed air, the value of k2 ranges from 1.1 / 0.21 to 1.5 / 0.21, preferably from 1.1 / 0.21 to 1.2 / 0.21.

[0069] S303, based on the total amount of combustion-supporting gas Q a Determine the flow rate of the combustion-supporting gas Q1, Nm 3 / h.

[0070] Q1 = k3 × Q a …………(3).

[0071] In the formula: k3 is a proportionality coefficient, and the value of k3 ranges from 0.05 to 0.25. Generally, when the combustion-supporting gas is oxygen, the value of k3 ranges from 0.05 to 0.15; when the combustion-supporting gas is compressed air, the value of k3 ranges from 0.12 to 0.25; in this case, the flow rate of the combustion-supporting gas can ensure smooth ignition of the gas.

[0072] Adjust the primary combustion gas flow rate to Q1 to ensure smooth ignition of the gas. At the same time, the high-temperature gas flow after the gas and primary combustion gas mix and ignite is a fuel-rich gas flow.

[0073] At this point, the number of O2 molecules in the primary combustion-supporting gas is insufficient to consume the fuel molecules in the combustion gas. Therefore, the high-temperature gas flow after ignition is a fuel-rich gas flow, such as... Figure 10 The airflow indicated by the dark gray arrow is in a reducing state. The fuel-rich airflow will not oxidize the iron in the scrap steel. Instead, it can react chemically with the oxidizing impurities on the surface of the scrap steel, releasing heat and removing some of the impurities.

[0074] S4. Secondary combustion-supporting gas enters the ladle, mixes and burns with the fuel gas, and the resulting high-temperature gas flow continues to heat the scrap steel, achieving efficient preheating of the scrap steel.

[0075] In step S4, the flow rate of the secondary combustion-supporting gas and the gas outlet velocity are controlled so that the flow rate of the secondary combustion-supporting gas is lower than the gas outlet velocity. Specifically, controlling the flow rate of the secondary combustion-supporting gas and the gas outlet velocity includes the following sub-steps: S401. Calculate the flow velocity v2 of the secondary combustion-supporting gas, m / h.

[0076] v2 =Q2 / (n×1 / 4×π×D1 2 ) …………(4).

[0077] The total amount of combustion-supporting gas Q a It is the sum of the flow rates of the primary combustion-supporting gas Q1 and the secondary combustion-supporting gas Q2, that is: Q2 = Q a - Q1…………(5).

[0078] In the formula: Q2 is the flow rate of the secondary combustion-supporting gas, Nm 3 / h. n is the number of secondary air branch pipes. D1 is the inner diameter of the inclined section of the secondary air branch pipe, in meters.

[0079] S402, based on the gas flow rate Q entering the gas pipe fuel Calculate the gas outlet velocity v fuel , m / h.

[0080] v fuel = Q fuel / [1 / 4π(D2 2 -D3 2 )]…………(6).

[0081] In the formula: D2 is the inner diameter of the gas inlet, in meters (m). D3 is the outer diameter of the positioning shaft, in meters (m).

[0082] S403, Adjust the flow rate v2 of the secondary combustion-supporting gas and the gas outlet velocity v fuel This satisfies the following relationship between the two: v2 ≤ v fuel / γ a …………(7).

[0083] In the formula: γ a This represents the system safety factor. Specifically, when the combustion-supporting gas is oxygen, γ... a The value range is 8~12. When the combustion-supporting gas is compressed air, γ a The value range is 1.8 to 3.

[0084] In step S403, if the flow velocity v2 of the secondary combustion-supporting gas and the gas outlet velocity v2 are calculated from the aforementioned steps S401 and S402 respectively... fuel If the relationship between the two does not meet the requirements of the above formula (7), then it is necessary to adjust the relevant parameters in formulas (4)-(6) (for example, the number of secondary air branch pipes n, the inner diameter D1 of the inclined section of the secondary air branch pipe, etc.) to obtain the adjusted new flow velocity v2 and gas outlet velocity v of the secondary combustion-supporting gas. fuel Ultimately, this makes the relationship between the two satisfy formula (7).

[0085] Adjust the flow rate of the secondary combustion-supporting gas to v2, and the gas outlet velocity to v. fuel This causes the flow rate of the secondary combustion-supporting gas to be lower than the gas outlet velocity (based on the system safety factor).

[0086] At this point, because the system strictly controls the flow rates of the secondary combustion-supporting gas and the combustion gas, the velocity of the secondary combustion-supporting gas, which provides the main combustion-supporting oxygen or air, is lower than the combustion gas outlet velocity. This means the secondary combustion-supporting gas will reach the scrap steel surface later than the combustion gas. Furthermore, because the rotation direction of the combustion gas flow is opposite to that of the secondary combustion-supporting gas in this embodiment, the mixing rate between the two in space is increased. Therefore, most of the secondary combustion-supporting gas is continuously consumed by combustion gas molecules before reaching the scrap steel surface. Figure 10 The light gray arrow indicates the airflow. Therefore, oxygen molecules in the secondary combustion-supporting gas have difficulty contacting the scrap steel, greatly reducing its oxidation.

[0087] In this application, the volume height of the ladle is 0.2-100m, preferably 0.3-50m, more preferably 0.5-40m, more preferably 0.8-30m, and even more preferably 1-25m.

[0088] In this application, the top inner diameter of the ladle is 0.1-30m, preferably 0.3-25m, more preferably 0.5-20m, more preferably 0.8-18m, and even more preferably 1-15m.

[0089] Compared with the prior art, the present invention has the following beneficial technical effects: 1. Significantly Reduced Oxidation of Scrap Steel During Effective Heating: Traditional ladle preheaters preheat scrap steel using high-velocity and high-flow-rate combustion gases to ensure preheating efficiency. This direct impact on the scrap steel surface leads to rapid oxidation and the generation of large amounts of iron oxide scale. Consequently, subsequent refining processes experience increased slag and refining agent consumption, decreased steel quality, reduced refining efficiency, and increased equipment load. This invention optimizes the ladle heating system structure by precisely controlling the flow rates of the combustion gases and secondary combustion gases. Utilizing the velocity difference between these gases, oxygen molecules are less likely to contact the heated material, significantly reducing the oxidation of the scrap steel. Simultaneously, the chemical energy of the combustion gases is completely released in the space above the scrap steel, allowing it to be effectively preheated through both convective and radiative heating by the high-temperature flue gas.

[0090] 2. Counter-current swirling of the gas and secondary combustion-supporting gas further reduces the oxidation of scrap steel: In this invention, the rotation direction of the gas flow is opposite to that of the secondary combustion-supporting gas flow, which greatly improves the mixing rate of the two in the ladle space. The better the mixing effect of the gas and the secondary combustion-supporting gas, the faster the reaction, so that most of the oxygen molecules in the secondary combustion-supporting gas are consumed by the gas molecules before reaching the surface of the scrap steel. Therefore, it is difficult for oxygen molecules to come into contact with the scrap steel, further reducing the oxidation of the scrap steel.

[0091] 3. Effectively removes oxidizing impurities from the surface of scrap steel: This invention precisely controls the flow rate of the primary combustion-supporting gas, so that the high-temperature gas flow after the combustion gas and the primary combustion-supporting gas are mixed and ignited is a fuel-rich gas flow, which is in a reducing state and will not cause oxidation of the iron element in the scrap steel. Instead, it can chemically react with the oxidizing impurities on the surface of the scrap steel, release heat, remove some impurities, reduce the consumption of auxiliary materials in subsequent refining processes, and improve refining efficiency.

[0092] This invention proposes a low-oxidation steel ladle heating system and method for scrap steel. By optimizing the structure of the ladle heating system and controlling the flow rate and velocity of the combustion gas, primary combustion-supporting gas, and secondary combustion-supporting gas during the scrap steel heating process, low-oxidation heating and efficient preheating of scrap steel are achieved. This heating system and method can be widely applied in the scrap steel heating process of the steel industry, and is of great significance for improving steel production efficiency and product quality. Attached Figure Description

[0093] Figure 1 This is a schematic diagram of a ladle preheater for preheating scrap steel in the prior art; Figure 2 This utility model is a perspective view of a steel ladle furnace cover equipped with a central burner, a primary air inlet pipe, and a secondary air inlet device. Figure 3This is a top view of the low-oxidation steel ladle heating system for scrap steel elements in this utility model; Figure 4 for Figure 3 AA section view; Figure 5 for Figure 3 BB section view; Figure 6 for Figure 3 CC section view; Figure 7 This is a schematic diagram of the structure of the central burner of this utility model; Figure 8 This is a bottom view of the central burner of this utility model; Figure 9 This is a schematic diagram of scrap steel being filled into a steel ladle in this utility model; Figure 10 This is a schematic diagram of the working state of the low-oxidation steel ladle heating system for scrap steel elements in this utility model; in, Figure 10 The dark gray arrows represent the high-temperature gas flow after the gas and primary combustion-supporting gas mix and ignite, while the light gray arrows represent the high-temperature gas flow after the gas and secondary combustion-supporting gas mix and ignite.

[0094] Figure label: 1: Steel ladle; 2: Steel ladle furnace cover; 3: Central burner; 4: Gas pipe; 401: Gas inlet; 402: Positioning shaft; 5: Primary air inlet pipe; 501: Primary air inlet; 6: Secondary air inlet device; 601: Secondary air main pipe; 602: Secondary air branch pipe; 60201: Vertical section; 60202: Inclined section; 603: Secondary air inlet pipe; 604: Secondary air inlet; 7: Primary air guide vane; 8: Primary air swirl vane; 9: Gas guide vane; 10: Gas swirl vane. Detailed Implementation

[0095] The technical solution of this utility model is illustrated below. The scope of protection of this utility model includes, but is not limited to, the following embodiments.

[0096] According to the first embodiment of this utility model, a low-oxidation steel ladle heating system for scrap iron and steel elements is provided.

[0097] A low-oxidation steel ladle heating system for scrap iron includes a ladle 1 with a top opening and a ladle furnace cover 2 installed on top of the ladle 1. A central burner 3 is mounted on the ladle furnace cover 2. The lower end of the central burner 3 passes through the ladle furnace cover 2 and communicates with the ladle 1. A gas pipe 4 is installed inside the central burner 3. The upper end of the gas pipe 4 has a gas inlet 401, and the lower end passes through the ladle furnace cover 2 and communicates with the ladle 1. A primary air inlet pipe 5 is connected to the upper part of the central burner 3. The primary air inlet pipe 5 has a primary air inlet 501. The system also includes a secondary air inlet device 6. The secondary air inlet device 6 includes a secondary air main pipe 601 and secondary air branch pipes 602. The secondary air main pipe 601 is located above the ladle furnace cover 2. The upper end of the secondary air branch pipe 602 is connected to the secondary air main pipe 601, and the lower end passes through the ladle furnace cover 2 and communicates with the ladle 1. The secondary air main pipe 601 is also connected to a secondary air inlet pipe 603, and the secondary air inlet pipe 603 is equipped with a secondary air inlet 604.

[0098] In this invention, the secondary air main pipe 601 has a ring structure and is arranged around the central burner 3. Preferably, the secondary air main pipe 601, the central burner 3, and the gas pipe 4 are arranged coaxially.

[0099] Preferably, the secondary air main pipe 601 is connected to multiple secondary air branch pipes 602. Preferably, the multiple secondary air branch pipes 602 are arranged in a ring or evenly distributed along the circumference at the lower part of the secondary air main pipe 601.

[0100] In this invention, the secondary air branch pipe 602 includes a vertical section 60201 and an inclined section 60202 connected to the vertical section 60201. The vertical section 60201 is connected to the secondary air main pipe 601, and the inclined section 60202 passes through the ladle furnace cover 2 and communicates with the ladle 1.

[0101] Preferably, each secondary air branch pipe 602 includes a vertical section 60201 and an inclined section 60202. The inclined sections 60202 of multiple secondary air branch pipes 602 are inclined to the same side along the circumferential direction.

[0102] In this invention, the central burner 3 is a swirl burner. Preferably, the swirl direction of the central burner 3 is opposite to the swirl direction formed by the inclined section 60202 of the secondary air branch pipe 602.

[0103] In this invention, the inclination angle α of the inclined section 60202 of the secondary air branch pipe 602 is 15°~45°, preferably 20°~35°.

[0104] In this invention, a primary air guide vane 7 and a primary air swirl vane 8 are provided inside the central burner 3 and located between the central burner 3 and the gas pipe 4. Preferably, the primary air swirl vane 8 is located near the outlet of the central burner 3. The primary air guide vane 7 is located between the primary air inlet 501 and the primary air swirl vane 8.

[0105] In this invention, a gas guide vane 9 and a gas swirl vane 10 are provided inside the gas pipe 4. A positioning shaft 402 is located at the lower center of the gas pipe 4. The gas guide vane 9 and the gas swirl vane 10 are respectively mounted on the positioning shaft 402. Preferably, the gas swirl vane 10 is positioned near the outlet of the gas pipe 4. The gas guide vane 9 is located between the gas inlet 401 and the gas swirl vane 10.

[0106] In this invention, the swirling directions of the primary air swirl vane 8 and the gas swirl vane 10 are the same, and their swirling directions are opposite to those formed by the inclined section 60202 of the secondary air branch pipe 602.

[0107] Preferably, the spiral angle of the primary air swirl vane 8 is 50°~60°, more preferably 50°~55°. The spiral angle of the gas swirl vane 10 is 35°~50°, more preferably 42°~45°.

[0108] In this invention, a gap Δd1 is left between the ladle furnace cover 2 and the top of the ladle 1. The value of Δd1 ranges from 0.05 to 0.2 m, preferably from 0.05 to 0.1 m. Example 1

[0109] like Figure 2 and 10 A low-oxidation steel ladle heating system for scrap iron includes a ladle 1 with a top opening and a ladle furnace cover 2 installed on top of the ladle 1. A central burner 3 is mounted on the ladle furnace cover 2. The lower end of the central burner 3 passes through the ladle furnace cover 2 and communicates with the ladle 1. A gas pipe 4 is installed inside the central burner 3. The upper end of the gas pipe 4 has a gas inlet 401, and the lower end passes through the ladle furnace cover 2 and communicates with the ladle 1. A primary air inlet pipe 5 is connected to the upper part of the central burner 3. The primary air inlet pipe 5 has a primary air inlet 501. The system also includes a secondary air inlet device 6. The secondary air inlet device 6 includes a secondary air main pipe 601 and secondary air branch pipes 602. The secondary air main pipe 601 is located above the ladle furnace cover 2. The upper end of the secondary air branch pipe 602 is connected to the secondary air main pipe 601, and the lower end passes through the ladle furnace cover 2 and communicates with the ladle 1. The secondary air main pipe 601 is also connected to a secondary air inlet pipe 603, and the secondary air inlet pipe 603 is equipped with a secondary air inlet 604. Example 2

[0110] The embodiment 1 is repeated, except that the secondary air main pipe 601 is a ring structure and is arranged around the central burner 3. Example 3

[0111] like Figure 3 As shown, Example 2 is repeated, except that the secondary air main pipe 601, the central burner 3, and the gas pipe 4 are arranged coaxially. Example 4

[0112] Example 3 is repeated, except that four secondary air branch pipes 602 are connected to the secondary air main pipe 601. The four secondary air branch pipes 602 are evenly distributed along the circumference at the lower part of the secondary air main pipe 601. Example 5

[0113] Example 3 is repeated, except that three secondary air branch pipes 602 are connected to the secondary air main pipe 601. The three secondary air branch pipes 602 are evenly distributed along the circumference at the lower part of the secondary air main pipe 601. Example 6

[0114] Example 3 is repeated, except that six secondary air branch pipes 602 are connected to the secondary air main pipe 601. The six secondary air branch pipes 602 are evenly distributed along the circumference at the lower part of the secondary air main pipe 601. Example 7

[0115] like Figure 6 As shown, Embodiment 4 is repeated, except that the secondary air branch pipe 602 includes a vertical section 60201 and an inclined section 60202 connected to the vertical section 60201. The vertical section 60201 is connected to the secondary air main pipe 601, and the inclined section 60202 passes through the ladle furnace cover 2 and communicates with the ladle 1. Example 8

[0116] Example 7 is repeated, except that each secondary air branch pipe 602 includes a vertical section 60201 and an inclined section 60202. The inclined sections 60202 of the four secondary air branch pipes 602 are inclined to the same side along the circumferential direction. Example 9

[0117] Example 8 is repeated, except that the central burner 3 is a swirl burner. The swirl direction of the central burner 3 is opposite to the swirl direction formed by the inclined section 60202 of the secondary air branch pipe 602. Example 10

[0118] Repeat Example 9, except that the inclination angle α of the inclined section 60202 of the secondary air branch pipe 602 is 20°. Example 11

[0119] Example 9 is repeated, except that the inclination angle α of the inclined section 60202 of the secondary air branch pipe 602 is 35°. Example 12

[0120] Example 9 is repeated, except that the inclination angle α of the inclined section 60202 of the secondary air branch pipe 602 is 28°. Example 13

[0121] like Figure 7 As shown, embodiment 12 is repeated, except that a primary air guide vane 7 and a primary air swirl vane 8 are provided inside the central burner 3 and located between the central burner 3 and the gas pipe 4. Example 14

[0122] Example 13 is repeated, except that the primary air swirl vane 8 is positioned closer to the outlet of the central burner 3. The primary air guide vane 7 is located between the primary air inlet 501 and the primary air swirl vane 8. Example 15

[0123] The embodiment 14 is repeated, except that the gas pipe 4 is equipped with a gas guide vane 9 and a gas swirl vane 10. A positioning shaft 402 is located at the lower center of the gas pipe 4. The gas guide vane 9 and the gas swirl vane 10 are respectively mounted on the positioning shaft 402. Example 16

[0124] Example 15 is repeated, except that the gas swirl vane 10 is positioned closer to the outlet of the gas pipe 4. The gas guide vane 9 is located between the gas inlet 401 and the gas swirl vane 10. Example 17

[0125] Example 16 is repeated, except that the swirling directions of the primary air swirl vane 8 and the gas swirl vane 10 are the same, and their swirling directions are opposite to the swirling direction formed by the inclined section 60202 of the secondary air branch pipe 602. Example 18

[0126] Example 17 is repeated, except that the spiral angle of the primary air swirl vane 8 is 50°, and the spiral angle of the gas swirl vane 10 is 35°. Example 19

[0127] Example 17 is repeated, except that the spiral angle of the primary air swirl vane 8 is 60°, and the spiral angle of the gas swirl vane 10 is 50°. Example 20

[0128] Example 17 is repeated, except that the spiral angle of the primary air swirl vane 8 is 55°, and the spiral angle of the gas swirl vane 10 is 45°. Example 21

[0129] Repeat Example 20, except that a gap Δd1=0.08m is left between the ladle furnace cover 2 and the top of the ladle 1.

[0130] The method for using the low-oxidation steel ladle heating system for scrap steel elements described in this embodiment includes the following steps: S1. Add scrap steel to ladle 1, then transport ladle 1 to the baking station, and lower ladle furnace cover 2 to the designated position above ladle 1.

[0131] S2. Turn on the flue gas exhaust fan located outside the ladle 1, introduce gas into the gas pipe 4 through the gas inlet 401, introduce primary combustion gas into the central burner 3 through the primary air inlet 501, and introduce secondary combustion gas into the secondary air intake device 6 through the secondary air inlet 604. Ignite and start the scrap steel baking.

[0132] S3. The gas and the primary combustion-supporting gas flow downwards. After mixing, they ignite. The combustion of the gas releases a large amount of heat, and the resulting high-temperature gas flow heats the scrap steel inside the ladle 1.

[0133] In step S3, the flow rate of the primary combustion-supporting gas is controlled so that the high-temperature gas stream after ignition of the gas and the primary combustion-supporting gas is a fuel-rich gas stream. At this time, the number of O2 molecules in the primary combustion-supporting gas is insufficient to consume the fuel molecules in the gas, therefore the high-temperature gas stream after ignition is a fuel-rich gas stream, such as... Figure 10 The airflow indicated by the dark gray arrow is in a reducing state. The fuel-rich airflow will not oxidize the iron in the scrap steel. Instead, it can react chemically with the oxidizing impurities on the surface of the scrap steel, releasing heat and removing some of the impurities.

[0134] S4. Secondary combustion-supporting gas enters ladle 1, mixes and burns with the fuel gas, and the resulting high-temperature gas flow continues to heat the scrap steel, achieving efficient preheating of the scrap steel.

[0135] In step S4, the flow rate of the secondary combustion-supporting gas and the gas outlet velocity are controlled so that the flow rate of the secondary combustion-supporting gas is lower than the gas outlet velocity. At this time, the secondary combustion-supporting gas will arrive at the scrap steel surface later than the gas. Furthermore, since the rotation direction of the gas flow is opposite to the rotation direction of the secondary combustion-supporting gas in this embodiment, the mixing rate between the two in space is increased. Therefore, most of the secondary combustion-supporting gas is continuously consumed by gas molecules before reaching the scrap steel surface. Figure 10 The light gray arrow indicates the airflow. Therefore, oxygen molecules in the secondary combustion-supporting gas have difficulty contacting the scrap steel, reducing its oxidation.

Claims

1. A low-oxidation steel ladle heating system for scrap iron, the system comprising a steel ladle (1) with a top opening and a ladle furnace cover (2) installed on top of the steel ladle (1); characterized in that: A central burner (3) is provided on the ladle furnace cover (2); the lower end of the central burner (3) passes through the ladle furnace cover (2) and communicates with the ladle (1); a gas pipe (4) is provided inside the central burner (3); a gas inlet (401) is provided at the upper end of the gas pipe (4), and the lower end passes through the ladle furnace cover (2) and communicates with the ladle (1); a primary air inlet pipe (5) is connected to the upper part of the central burner (3); a primary air inlet (501) is provided on the primary air inlet pipe (5); the system also includes a secondary air inlet device. The secondary air intake device (6) includes a secondary air main pipe (601) and a secondary air branch pipe (602). The secondary air main pipe (601) is located above the ladle furnace cover (2). The upper end of the secondary air branch pipe (602) is connected to the secondary air main pipe (601), and the lower end passes through the ladle furnace cover (2) and is connected to the ladle (1). The secondary air main pipe (601) is also connected to a secondary air intake pipe (603), and the secondary air intake pipe (603) is provided with a secondary air inlet (604).

2. The system according to claim 1, characterized in that: The secondary air main pipe (601) has an annular structure and is arranged around the central burner (3).

3. The system according to claim 2, characterized in that: The secondary air main pipe (601), the central burner (3), and the gas pipe (4) are arranged coaxially.

4. The system according to claim 2, characterized in that: Multiple secondary air branch pipes (602) are connected to the main secondary air pipe (601).

5. The system according to claim 4, characterized in that: The multiple secondary air branch pipes (602) are arranged in a ring or evenly distributed along the circumference at the lower part of the secondary air main pipe (601).

6. The system according to claim 1, characterized in that: The secondary air branch pipe (602) includes a vertical section (60201) and an inclined section (60202) connected to the vertical section (60201); wherein, the vertical section (60201) is connected to the secondary air main pipe (601), and the inclined section (60202) passes through the ladle furnace cover (2) and is connected to the ladle (1).

7. The system according to claim 6, characterized in that: Each secondary air branch pipe (602) includes a vertical section (60201) and an inclined section (60202); wherein the inclined sections (60202) of multiple secondary air branch pipes (602) are inclined to the same side along the circumferential direction.

8. The system according to claim 6, characterized in that: The central burner (3) is a swirl burner.

9. The system according to claim 8, characterized in that: The swirl direction of the central burner (3) is opposite to the swirl direction formed by the inclined section (60202) of the secondary air branch pipe (602); and / or The inclination angle α of the inclined section (60202) of the secondary air branch pipe (602) is 15°~45°.

10. The system according to claim 9, characterized in that: The inclination angle α of the inclined section (60202) of the secondary air branch pipe (602) is 20°~35°.

11. The system according to claim 1, characterized in that: A primary air guide vane (7) and a primary air swirl vane (8) are provided inside the central burner (3) and between the central burner (3) and the gas pipe (4); and / or The gas pipe (4) is provided with a gas guide vane (9) and a gas swirl vane (10); wherein, a positioning shaft (402) is provided at the lower center of the gas pipe (4); the gas guide vane (9) and the gas swirl vane (10) are respectively set on the positioning shaft (402).

12. The system according to claim 11, characterized in that: The primary air swirl vane (8) is positioned near the outlet of the central burner (3); the primary air guide vane (7) is located between the primary air inlet (501) and the primary air swirl vane (8); and / or The gas swirl vane (10) is located near the outlet of the gas pipe (4); the gas guide vane (9) is located between the gas inlet (401) and the gas swirl vane (10).

13. The system according to claim 11, characterized in that: The swirling direction of the primary air swirl vane (8) and the gas swirl vane (10) is the same, and the swirling direction of the two is opposite to the swirling direction formed by the inclined section (60202) of the secondary air branch pipe (602).

14. The system according to claim 11, characterized in that: The spiral angle of the primary air swirl vane (8) is 50°~60°; the spiral angle of the gas swirl vane (10) is 35°~50°.

15. The system according to claim 14, characterized in that: The spiral angle of the primary air swirl vane (8) is 50°~55°; the spiral angle of the gas swirl vane (10) is 42°~45°.

16. The system according to any one of claims 1-15, characterized in that: A gap Δd1 is left between the ladle furnace cover (2) and the top of the ladle (1); wherein: the value of Δd1 ranges from 0.05 to 0.2m.

17. The system according to claim 16, characterized in that: The value of Δd1 ranges from 0.05 to 0.1 m.

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