A method for preventing nitrogen and hydrogen increase during LF refining process

Abstract

The present invention discloses a method for preventing nitrogen and hydrogen increase during LF refining, belonging to the technical field of steel metallurgy refining furnace equipment. The device includes a water-cooled furnace cover installed at the upper port of the ladle, and is characterized in that: a secondary dust removal pipeline horizontally communicated with the water-cooled furnace wall of the furnace cover is provided on the furnace cover; gas spray holes are provided along the furnace cover below the secondary dust removal pipeline; a telescopic spray gun is provided on the water-cooled furnace wall of the furnace cover; a tertiary dust removal cover is installed on the furnace cover, and a tertiary dust removal pipeline is provided on the tertiary dust removal cover. By adopting the above technical solution, the original process of producing a slightly positive pressure in the LF refining furnace is changed. On the premise of retaining the useful functions of heating, uniform composition and inclusion removal, through the research and development of methods of gas replacement and protection and positive pressure smelting production, the harmful effects of nitrogen and hydrogen increase during the heating process of the LF refining furnace are completely removed, thereby improving the quality of molten steel.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel metallurgy refining furnace equipment, and particularly relates to a method for preventing nitrogen and hydrogen increase during LF refining. Background Technique

[0002] The LF refining furnace, as a mainstream secondary refining equipment, is widely used in the steel industry. Its main functions include useful functions such as adjusting temperature, homogenizing composition, and removing inclusions. At the same time, during the arc heating process in refining, due to the impact of the arc, it is inevitable that the molten steel in the arc impact area is exposed. The temperature in the arc impact area is above 3000K. Under the condition of high-temperature ionization, the N2 molecules in the air are ionized into nitrogen atoms and the H2O molecules in the air and materials are ionized into hydrogen atoms, resulting in the phenomenon of nitrogen and hydrogen increase in the molten steel, thus having a negative impact on the quality of the molten steel.

[0003] The existing publicly disclosed methods mainly adopt two ways of submerged arc heating and ensuring slightly positive pressure in the furnace to slow down the negative effects of LF refining. For example, Chen Bingchun. Research on Nitrogen Control Countermeasures during Refining Process [J]. Lianyuan Steel Science and Technology & Management. 2022(01) mentioned that "for the same steel grade, the heating time is 9 minutes. With different submerged arc effects, when the submerged arc is good, the nitrogen increase in the molten steel is less, and the average nitrogen increase is only 4.1ppm, while when the submerged arc is poor, the nitrogen absorption in the molten steel is serious, and the average nitrogen absorption is 20.5ppm". Therefore, submerged arc heating and adjusting the arc length can reduce the effect of nitrogen absorption but cannot eliminate nitrogen absorption. Patent No. 201610506127.X, a method for removing hydrogen in steelmaking, also mentioned that "controlling the submerged arc operation during the refining process, increasing the amount of submerged arc slag to 1.3 kg / ton steel to 1.8 kg / ton steel to reduce the addition amount of alloy and slag-making materials, and extending the weak stirring time to more than 10 minutes to increase the adsorption time of gas inclusions and reduce the hydrogen content in the steel". The above hydrogen and nitrogen control both adopt the submerged arc heating process to control the gas absorption of the molten steel. However, since the above method cannot solve the condition that the foam slag cannot be effectively generated during the poor melting stage of the furnace slag at the initial stage of heating, and overly relies on the judgment of the thickness of the foam slag by people to adjust the power supply parameters, it is impossible to effectively and completely avoid the nitrogen and hydrogen increase caused by the ionization of N2 and H2O in the air. And for the concept of slightly positive pressure during the refining process, it is mainly a compromise method selected considering the environmental protection requirement that the soot in the furnace cover area cannot overflow. Due to environmental protection pressure and the fluctuation of the flue gas generation amount at different stages in the furnace, the slightly positive pressure smelting cannot be effectively implemented. Summary of the Invention

[0004] In view of the problems existing in the prior art, the present invention provides a method for preventing nitrogen and hydrogen increase during LF refining.

[0005] The present invention is implemented as follows

[0006] A method for preventing nitrogen and hydrogen increase during LF refining is as follows:

[0007] Step 1: During the tapping process of the converter, add 2.5 - 3.5 Kg / t of lime with the alloy. After the tapping is completed, blow argon for 1 - 3 minutes and then close the argon gas, waiting to enter the LF refining furnace station;

[0008] Step 2: After the ladle enters the LF refining furnace station, confirm the normal argon gas and then close the bottom blowing argon and enter the heating station, and turn on the three - stage dust removal pipeline. At this time, the opening degree of the dust removal valve installed on the three - stage dust removal pipeline is set to 100%;

[0009] Step 3: After the ladle enters the heating station, use the device for preventing nitrogen and hydrogen increase to replace the air in the space formed by the molten steel in the ladle and the furnace cover with inert gas atmosphere. Open the valves for supplying argon to 12 gas nozzles and the telescopic lance, and set the flow rate of each gas nozzle to 1000 NL / min, and the argon gas flow rate of the telescopic lance to 100 Nm 3 / min; The replacement time is 2 - 3 minutes, and then close the valves for supplying argon to the gas nozzles and the telescopic lance;

[0010] Step 4: After the replacement is completed, the bottom blowing argon gas flow rate of the ladle is 800 NL / min. After blowing argon for 2 minutes, select a foaming agent with a particle size of 0.01 - 0.2 mm at 0.25 - 0.45 Kg / t. The foaming agent is composed by weight of:

[0011] CaCO3 55 - 65%, CaC2 15 - 20%, MgCO3 20 - 25%; Use the telescopic lance to spray at a speed of 0.15 - 2.0 Kg / S ; The height of the lance outlet from the steel - slag surface is 450 mm, ensuring that the best coverage area of the ladle slag surface is 55 - 65%;

[0012] The uniformly sprayed small - particle foaming agent reacts with the slag to produce fine and dispersed CO2 bubbles, so that the bubbles slowly overflow in the slag, thus forming a honeycomb - like structure between the slag and the gas. The dense bubbles are separated from the slag by a liquid slag film, forming a foam slag with good metallurgical properties. The specific reactions are as follows:

[0013] CaCO3 = CaO + CO2

[0014] CaC2 + 5FeO = CaO + 5Fe + 2CO2

[0015] MgCO3 = MgO + CO2

[0016] Step Five: After the injection is completed, open the secondary dust removal valve position to 20 - 35%, open the flow rate of the annular gas holes on the furnace cover to 650 NL / min, and then use the heating system of the LF refining furnace to heat the molten steel; observe through the industrial camera set on the LF furnace platform. There should be obvious overflow of flue gas at the gap between the furnace cover and the ladle to ensure positive pressure inside the furnace and prevent air from entering. Use the tertiary dust removal cover to absorb the overflowing flue gas to meet the environmental protection requirements.

[0017] Step Six: Observe through the camera. During the power supply process, adjust the secondary dust removal valve on the secondary dust removal pipeline according to the overflow situation of the flue gas, and the opening degree is controlled at 0 - 25%; when the flue gas overflows significantly, close the valves of the 12 gas injection holes.

[0018] Step Seven: When the secondary dust removal is completely closed and the condition of obvious flue gas overflow still cannot be ensured, open the valve supplying argon gas to the 12 gas injection holes again, and set the flow rate of each gas injection hole to 300 - 650 NL / min; make an argon protection atmosphere form above the molten steel surface during the power supply process, and at the same time prevent air from entering.

[0019] Step Eight: When the ladle is about to be taken out of the heating position, adjust the bottom blowing argon gas of the ladle to 50 - 150 NL / min to ensure that the entire slag surface is wriggling but the molten steel is not exposed.

[0020] Preferably, the device for preventing nitrogen and hydrogen increase includes a water-cooled furnace cover installed at the upper port of the ladle. There is a secondary dust removal pipeline horizontally arranged on the furnace cover and connected to the water-cooled furnace wall of the furnace cover. Gas injection holes are arranged along the furnace cover below the secondary dust removal pipeline. A telescopic spray gun is arranged on the water-cooled furnace wall of the furnace cover; a tertiary dust removal cover is installed on the furnace cover, and a tertiary dust removal pipeline is arranged on the tertiary dust removal cover.

[0021] Preferably, there are 12 gas injection holes, and the 12 gas injection holes are evenly distributed along the circumference of the furnace cover.

[0022] Preferably, the gas injection holes form a 45° angle with the water-cooled furnace wall of the furnace cover.

[0023] Preferably, the telescopic spray gun includes a central spray pipe, and the central spray pipe is connected to a foaming agent supply pump; an argon supply pipe is sleeved outside the central spray pipe, and an air channel is formed between the central spray pipe and the argon supply pipe; sealing caps are arranged at the ends of the central spray pipe and the argon supply pipe. A foaming agent injection port is arranged at the center of the sealing cap, and argon injection holes are evenly distributed around the foaming agent injection port.

[0024] Advantages and technical effects of the present invention: By adopting the above technical solution, the original process of producing slightly positive pressure in the LF refining furnace is changed. On the premise of retaining the useful functions of heating, homogenizing the composition, and removing inclusions, through the research and development of the methods of gas replacement and protection and positive pressure smelting production, the harmful effects of nitrogen and hydrogen increase during the heating process of the LF refining furnace are completely removed, thereby improving the quality of molten steel. Brief Description of the Drawings

[0025] Figure 1 is a schematic structural diagram of the present invention;

[0026] Figure 2 is a schematic structural diagram of the telescopic spray gun.

[0027] In the figure: 1, ladle; 2, furnace cover; 2-1, gas spray hole; 3, secondary dust removal pipeline; 4, telescopic spray gun; 4-1, central spray pipe; 4-2, argon supply pipe; 4-3, sealing cover; 4-30, foaming agent injection port; 4-31, argon injection hole; 5, tertiary dust removal cover; 6, tertiary dust removal pipeline. Detailed Embodiments

[0028] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following embodiments are used to further elaborate on the present invention in detail. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] Please refer to Figure 1 and Figure 2 , the method for preventing nitrogen and hydrogen increase during the LF refining process using the above device is as follows:

[0030] Step 1: During the tapping process of the converter, 2.5 - 3.5 Kg / t of lime is added along with the alloy. After the tapping is completed, argon is blown for 1 - 3 minutes and then the argon is closed, waiting to enter the LF refining furnace station;

[0031] Step 2: After the ladle enters the LF refining furnace station, after confirming that the argon is normal, the bottom blowing argon is closed and then it enters the heating station, and the tertiary dust removal pipeline is opened. At this time, the opening degree of the dust removal valve installed on the tertiary dust removal pipeline is set to 100%;

[0032] Step 3: After the ladle enters the heating station, using the modified furnace cover, the air in the space formed by the molten steel in the ladle and the furnace cover is replaced to form an inert gas atmosphere. The valves for supplying argon to 12 gas spray holes and the telescopic spray gun are opened, and the flow rate of each gas spray hole is set to 1000 NL / min, and the argon flow rate of the telescopic spray gun is set to 100 Nm 3 / min; The replacement time is 2 - 3 min, then close the valves for supplying argon gas to the gas injection holes and the telescopic lance; Step Four: After the replacement is completed, the bottom blowing argon gas flow rate of the ladle is 800 NL / min. After blowing argon gas for 2 min, 0.25 - 0.45 Kg / t of foaming agent with a particle size of 0.01 - 0.2 mm is selected. The foaming agent is composed of by weight: 55 - 65% CaCO3, 15 - 20% CaC2, and 20 - 25% MgCO3; Use the telescopic lance to spray at a speed of 0.15 - 2.0 Kg / S ; Select the optimal height of the lance outlet from the steel - slag surface to be 450 mm, and ensure that the optimal coverage area of the ladle slag surface is 55 - 65%;

[0033] The uniformly sprayed small - particle foaming agent reacts with the slag to produce fine and dispersed CO2 bubbles, causing the bubbles to slowly overflow in the slag, so that the slag and gas form a honeycomb - like structure. The dense bubbles and the slag are separated by a liquid slag film, forming a foamed slag with good metallurgical properties; The specific reactions are as follows:

[0034] CaCO3 = CaO + CO2

[0035] CaC2 + 5FeO = CaO + 5Fe + 2CO2

[0036] MgCO3 = MgO + CO2

[0037] Step Five: After the spraying is completed, open the secondary dust removal valve position to 20 - 35%, open the flow rate of the annular gas holes on the furnace cover to 650 NL / min, and then use the heating system of the LF refining furnace to heat the molten steel; Observe through the industrial camera set on the LF furnace platform. There should be obvious smoke overflow at the gap between the furnace cover and the ladle to ensure positive pressure inside the furnace and no air enters, and use the tertiary dust removal cover to absorb the overflowing smoke to meet environmental protection requirements;

[0038] Step Six: Observe through the camera. During the power supply process, adjust the secondary dust removal valve on the secondary dust removal pipeline according to the smoke overflow situation, and the opening degree is controlled at 0 - 25%; When there is obvious smoke overflow, close the valves of 12 injection holes.

[0039] Step Seven: When the secondary dust removal is completely closed and still cannot ensure the condition of smoke overflow, open the valves for supplying argon gas to the 12 gas injection holes again, and set the flow rate of each gas injection hole to 300 - 650 NL / min; Make an argon - protection atmosphere form above the molten steel surface during the power supply process, and at the same time prevent air from entering;

[0040] Step Eight: When the ladle is about to be taken out of the heating position, adjust the bottom blowing argon gas of the ladle to 50 - 150 NL / min to ensure that the entire slag surface is wriggling but the molten steel is not exposed.

[0041] The device for preventing nitrogen and hydrogen increase used above includes a water-cooled furnace cover 2 installed at the upper port of the ladle 1. A secondary dust removal pipe 3 horizontally communicating with the water-cooled furnace wall of the furnace cover is provided on the furnace cover. Gas injection holes 2-1 are provided along the furnace cover below the secondary dust removal pipe. A telescopic spray gun 4 is provided on the water-cooled furnace wall of the furnace cover. A tertiary dust removal cover 5 is installed on the furnace cover, and a tertiary dust removal pipe 6 is provided on the tertiary dust removal cover.

[0042] Preferably, there are 12 gas injection holes, and the 12 gas injection holes are evenly distributed along the periphery of the furnace cover.

[0043] Preferably, the gas injection holes form an angle of 45° with the water-cooled furnace wall of the furnace cover.

[0044] Preferably, the telescopic spray gun 4 includes a central spray pipe 4-1, and the central spray pipe is connected to a foaming agent supply pump. An argon supply pipe 4-2 is sleeved outside the central spray pipe, and an air duct is formed between the central spray pipe and the argon supply pipe. Sealing caps 4-3 are provided at the ends of the central spray pipe and the argon supply pipe. A foaming agent injection port 4-30 is provided at the center of the sealing cap, and argon injection holes 4-31 are evenly distributed around the foaming agent injection port.

[0045] This method changes the original process of producing slightly positive pressure in the LF refining furnace. On the premise of retaining the useful functions of heating, uniforming composition, and removing inclusions, through the research and development of the methods of gas replacement and protection and positive pressure smelting production, the harmful effects of nitrogen and hydrogen increase during the heating process of the LF refining furnace are completely removed, thereby improving the quality of molten steel.

[0046] By using the above method, the nitrogen increase amount during the heating process is reduced from 3.5 ppm to 0.3 ppm, and the hydrogen increase amount (in the rainy season) is reduced from 1.5 ppm to 1 ppm.

[0047] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention, such as by adjusting the combination of the opening degrees of different secondary dust removal and tertiary dust removal valves and increasing or decreasing the number and flow rate of the injection holes, shall be included in the protection scope of the present invention.

Claims

1. A method for preventing nitrogen and hydrogen increase during LF refining is as follows: Step 1: During the tapping process of the converter, add 2.5 - 3.5 Kg / t of lime with the alloy. After the tapping is completed, blow argon for 1 - 3 minutes and then close the argon gas, waiting to enter the LF refining furnace station; Step 2: After the ladle enters the LF refining furnace station, after confirming that the argon gas is normal, close the bottom blowing argon and enter the heating station, and turn on the three - stage dust removal pipeline. At this time, the opening degree of the dust removal valve installed on the three - stage dust removal pipeline is set to 100%; Step 3: After the ladle enters the heating station, use the nitrogen and hydrogen addition prevention device to replace the air in the molten steel in the ladle and the space formed by the furnace cover with inert gas atmosphere. The nitrogen and hydrogen addition prevention device includes a water-cooled furnace cover installed on the upper port of the ladle. The furnace cover is provided with a secondary dust removal pipeline horizontally connected to the water-cooled furnace wall of the furnace cover. Gas spray holes are arranged along the furnace cover below the secondary dust removal pipeline. A telescopic spray gun is arranged on the water-cooled furnace wall of the furnace cover. A tertiary dust removal cover is installed on the furnace cover, and a tertiary dust removal pipeline is arranged on the tertiary dust removal cover. There are 12 gas spray holes, and the 12 gas spray holes are evenly distributed along the circumference of the furnace cover. Open the valves for supplying argon to the 12 gas spray holes and the telescopic spray gun, and set the flow rate of each gas spray hole to 1000 NL / min, and the argon flow rate of the telescopic spray gun to 100 Nm 3 / min; The replacement time is 2 - 3 min, and then close the valves for supplying argon to the gas spray holes and the telescopic spray gun; Step 4: After the replacement, the bottom argon flow rate of the ladle is 800 NL / min. After blowing argon for 2 minutes, 0.25 - 0.45 Kg / t of a foaming agent with a particle size of 0.01 - 0.2 mm is selected. The weight composition of the foaming agent is: CaCO3 55 - 65%, CaC2 15 - 20%, MgCO3 20 - 25%; A telescopic spray gun is used to spray at a speed of 0.15 - 2.0 Kg / S The height of the spray gun outlet from the steel-slag surface is 450 mm, ensuring that the best coverage area of the ladle slag surface is 55 - 65%; The uniformly sprayed small - particle foaming agent reacts with the slag to produce fine and dispersed CO2 bubbles, causing the bubbles to slowly overflow in the slag, so that the slag and gas form a honeycomb - like structure. The dense bubbles and the slag are separated by a liquid slag film to form a foam slag with good metallurgical properties. The specific reactions are as follows: CaCO3 = CaO + CO2 CaC2 + 5FeO = CaO + 5Fe + 2CO2 MgCO3 = MgO + CO2 Step 5: After the spraying is completed, open the secondary dust removal valve to an opening degree of 20 - 35%, open the flow rate of the annular gas holes on the furnace cover to 650 NL / min, and then use the heating system of the LF refining furnace to heat the molten steel; Observe through the industrial camera set on the LF furnace platform. There should be obvious smoke overflow at the gap between the furnace cover and the ladle to ensure positive pressure in the furnace and no air enters, and use the three - stage dust removal cover to absorb the overflowing smoke to meet the environmental protection requirements; Step 6: Observe through the camera. During the power supply process, adjust the secondary dust removal valve on the secondary dust removal pipeline according to the smoke overflow situation, and control the opening degree within 0 - 25%; When the smoke overflows significantly, close the valves of 12 gas injection holes; Step 7: When the secondary dust removal is completely closed and still cannot ensure the condition of smoke overflow, open the valve for supplying argon to the 12 gas injection holes again, and set the flow rate of each gas injection hole to 300 - 650 NL / min; Make an argon protection atmosphere form above the molten steel surface during the power supply process, and at the same time prevent air from entering; Step 8: When the ladle is ready to leave the heating position, adjust the bottom blowing argon of the ladle to 50 - 150 NL / min to ensure that the entire slag surface wriggles but does not expose the molten steel.

2. The method for preventing nitrogen and hydrogen increase in the LF refining process according to claim 1, characterized in that: The gas injection hole forms a 45° angle with the water - cooled furnace wall of the furnace cover.

3. The method for preventing nitrogen and hydrogen increase during LF refining according to claim 1, characterized in that: The telescopic spray gun includes a central spray pipe, and the central spray pipe is connected to a foaming agent supply pump; An argon supply pipe is sleeved outside the central spray pipe, and an air channel is formed between the central spray pipe and the argon supply pipe; Sealing caps are provided at the ends of the central spray pipe and the argon supply pipe. A foaming agent injection port is provided at the center of the sealing cap, and argon injection holes are evenly distributed around the foaming agent injection port.

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