A method for controlling nitrogen content in a low-slag smelting process of direct-reduced iron in an electric arc furnace

Abstract

The present invention provides a method for controlling nitrogen content in an electric arc furnace (EAF) direct reduced iron (DRI) low-slag smelting process. The method comprises: loading scrap steel into an EAF and starting power; supplying oxygen into the furnace using a carbon-oxygen lance at the EAF door and oxygen lances on the furnace walls; continuously adding DRI and adjusting the oxygen supply intensity after a molten pool is formed in the EAF; adding limestone to the surface of the molten pool after all the DRI has entered the molten pool; continuing to add limestone to the EAF; spraying oxygen and calcium carbide powder into the molten pool using the carbon-oxygen lance at the EAF door; spraying oxygen and carbon powder into the molten pool using the oxygen lances on the EAF walls; spraying oxygen and calcium carbide powder into the molten pool using the carbon-oxygen lance at the EAF door; and spraying oxygen, carbon powder, and carrier gas-lime powder into the molten pool using the oxygen lances on the EAF walls. The method reduces the nitrogen content of molten steel by spraying calcium carbide powder into the molten pool during the final melting and oxidation phases of the DRI in the EAF, thereby facilitating dephosphorization of the molten steel.

Description

Technical Field

[0001] The invention relates to a method for controlling nitrogen content in a low-slag smelting process of direct-reduced iron in an electric arc furnace, and belongs to the technical field of electric arc furnace steelmaking. Background Art

[0002] Electric arc furnace steelmaking is an important steelmaking method, using scrap steel as its primary raw material. It boasts a short process, low energy consumption, and is energy-efficient and environmentally friendly. Direct-reduced iron (DRI) has a stable chemical composition and low impurity content, making it a viable alternative to scrap steel as a raw material for EAF steelmaking when scrap steel resources are scarce. However, DRI contains high levels of gangue, particularly SiO₂, which can reach 3-6%. During the smelting process, all of the SiO₂ in the DRI is absorbed into the slag. To maintain the alkalinity of the slag, large amounts of lime must be added, which increases the slag volume and smelting energy consumption. Therefore, the low-slag smelting of DRI in EAFs has long been a research topic of interest to metallurgists.

[0003] However, under the low-slag smelting conditions of an electric arc furnace, the arc easily ionizes nitrogen in the air, causing it to be absorbed by the molten steel. Nitrogen precipitates into iron nitride in the steel, causing aging and blue brittleness. Excessive nitrogen forms bubbles and porosity defects in the steel, affecting its processing and performance. Therefore, nitrogen is considered an impurity element for most steel grades, and its content must be controlled below 0.008%.

[0004] There are also many reports on denitrification and nitrogen control in the electric arc furnace steelmaking process. For example, CN112981038A discloses a method for reducing the nitrogen content in steel to obtain low-nitrogen steel during the electric arc furnace steelmaking process. This method uses rapid slag making technology during the electric arc furnace smelting process and uses measures such as LF refining, VD vacuum treatment, and protective pouring during the continuous casting process to control the nitrogen content of the product to within 30ppm. CN113416812A discloses a method for reducing nitrogen in high-alloy, high-vanadium steel. This method uses argon to form a protective atmosphere and sealing measures in the electric arc furnace smelting process. Argon is blown in stages during the LF refining process and VD vacuum treatment process to prevent the molten steel from absorbing nitrogen, thereby controlling the nitrogen content of the molten steel. CN107502702A discloses a method for clean and rapid smelting of all-scrap steel in an electric arc furnace. This method strengthens the molten pool decarburization by injecting a large flow of O2 or an O2-CO2 mixed gas into the molten pool during the middle and late stages of the electric arc furnace smelting process, and uses CO bubbles to remove nitrogen from the molten steel.

[0005] However, the technical solutions provided by the above-mentioned prior art still have some shortcomings. For example, in addition to adopting nitrogen control and denitrification means in the electric arc furnace smelting process, the above-mentioned technical solutions must also use LF refining, VD vacuum treatment, continuous casting protective pouring and other processes to denitrify the molten steel. It is difficult to achieve the expected denitrification effect by relying solely on denitrification in the electric arc furnace smelting process, and blowing a large amount of argon into the molten pool will cause the temperature of the molten steel to drop, making it difficult to achieve the smelting effect.

[0006] CN110317926A discloses a method for reducing nitrogen gain during steel tapping by using silicon carbide for deoxidation. This method involves adding silicon carbide to the ladle during the converter tapping process to form a foamy slag and a CO gas curtain, thereby inhibiting nitrogen absorption by the molten steel. However, adding silicon carbide to the molten bath is not feasible for electric arc furnace steelmaking using direct reduced iron (DRI). This is primarily due to the high SiO2 content in DRI. The SiO2 generated by the SiC reaction would further increase the SiO2 content of the electric arc furnace slag, affecting the acidity and alkalinity of the slag and, in turn, its ability to dephosphorize and desulfurize.

[0007] Therefore, developing a novel method for controlling nitrogen content in the low-slag smelting process of direct reduced iron in an electric arc furnace remains one of the problems to be solved urgently in this field. Summary of the Invention

[0008] To address the above technical issues, the present invention provides a method for controlling nitrogen content during the low-slag smelting process of direct-reduced iron (DRI) in an electric arc furnace (EAF). This method reduces the nitrogen content of molten steel by injecting calcium carbide powder into the molten pool using a furnace door carbon-oxygen lance during the final melting and oxidation phases of the DRI in the EAF.

[0009] In order to achieve the above object, the present invention provides a method for controlling nitrogen content in an electric arc furnace direct reduced iron low-slag smelting process, which comprises the following steps:

[0010] (1) Arcing period and main melting period

[0011] The smelting raw materials including scrap steel are loaded into the electric arc furnace and the power is turned on. Oxygen is supplied to the furnace through the carbon oxygen lance at the furnace door and the oxygen lance on the furnace wall. When a molten pool is formed in the electric arc furnace, direct reduced iron is continuously added and the oxygen supply intensity is adjusted. After all the direct reduced iron has entered the molten pool, limestone is added to the surface of the molten pool.

[0012] (2) End of melting

[0013] Continue to add limestone into the electric arc furnace; use the carbon oxygen lance on the electric arc furnace door to spray oxygen and calcium carbide powder into the molten pool; use the oxygen lance on the electric arc furnace wall to spray oxygen and carbon powder into the molten pool;

[0014] (3) Oxidation period

[0015] The carbon-oxygen lance on the door of the electric arc furnace is used to spray oxygen and calcium carbide powder into the molten pool; the oxygen lance on the wall of the electric arc furnace is used to spray oxygen, carbon powder, and carrier gas-lime powder into the molten pool.

[0016] In the above method, preferably, in step (1), the smelting raw material further comprises molten iron. The ratio of molten iron to scrap steel can be conventionally adjusted by those skilled in the art.

[0017] In the above method, preferably, in step (1), the power supply intensity of the power supply is 0.7 to 1.0 MVA / t steel.

[0018] In the above method, preferably, in step (1), the intensity of oxygen supplied to the furnace by the carbon oxygen lance at the furnace door and the oxygen lance at the furnace wall is 0.8 to 2.0 Nm 3 / (min·t steel); When a molten pool is formed in the electric arc furnace, direct reduced iron is continuously added and the oxygen supply intensity is adjusted to 0.6~1.5Nm 3 / (min·t steel).

[0019] In the above method, preferably, in step (1), the amount of direct reduced iron added is 20-50%, based on the total weight of the smelting raw materials after adding the direct reduced iron being 100%.

[0020] In the above method, preferably, in step (1), the amount of limestone added to the surface of the molten pool is 20-25 kg / t steel.

[0021] In the above method, preferably, in step (2), the amount of limestone added to the electric arc furnace is 10-15 kg / t steel.

[0022] In the above method, preferably, in step (2), when oxygen and calcium carbide powder are sprayed into the molten pool using the carbon oxygen gun at the door of the electric arc furnace, the oxygen spraying rate is 0.4 to 0.9 Nm 3 / (min·t steel), the injection rate of calcium carbide powder is 0.1~0.5kg / (min·t steel).

[0023] In the above method, preferably, in step (2), when oxygen and carbon powder are sprayed into the molten pool by using the oxygen lance on the wall of the electric arc furnace, the oxygen spraying rate is 0.6 to 1.2 Nm 3 / (min·t steel), the blowing rate of carbon powder is 0.1~0.6kg / (min·t steel).

[0024] In the above method, preferably, in step (3), when oxygen and calcium carbide powder are sprayed into the molten pool using the carbon oxygen gun at the door of the electric arc furnace, the oxygen spraying rate is 0.7 to 1.5 Nm 3 / (min·t steel), the injection rate of calcium carbide powder is 0.1~0.5kg / (min·t steel).

[0025] In the above method, preferably, in step (3), when oxygen, carbon powder, carrier gas-lime powder are sprayed into the molten pool by using the oxygen lance on the wall of the electric arc furnace, the oxygen spraying rate is 0.6-1.5Nm 3 / (min·t steel), the carbon powder spraying rate is 0.1~0.6kg / (min·t steel), and the carrier gas flow rate is 0.6~1.5Nm 3 / (min·tsteel), the flow rate of lime powder is 0.5-5 kg / (min·tsteel). More preferably, the carrier gas is argon or nitrogen.

[0026] The technical solution of the present invention has at least the following beneficial effects:

[0027] (1) The method of the present invention utilizes the method of spraying calcium carbide powder into the molten pool during the final melting stage and the oxidation stage. The calcium carbide powder reacts with oxygen in the molten steel to generate a large number of CO bubbles, forming a reducing gas curtain on the surface of the electric arc furnace molten pool, isolating the molten steel from contact with air, and preventing the molten steel from absorbing nitrogen; and the calcium carbide powder reacts with oxygen in the molten steel to generate CaO slag. The CO gas generated by the reaction prompts the CaO slag to form foamed slag, which can further control the nitrogen absorption of the molten steel under the condition of low slag smelting in the electric arc furnace, thereby avoiding the increase of energy consumption of the electric arc furnace under the condition of large slag smelting.

[0028] (2) The method of the present invention also helps dephosphorize molten steel. The direct reduced iron entering the electric arc furnace contains 3-6% SiO2, which increases the SiO2 content in the slag, reduces the basicity of the slag, and thus affects the dephosphorization ability of the slag. However, the calcium carbide powder sprayed into the molten pool at the end of the melting and oxidation stages reacts with oxygen in the molten steel to form CaO, which helps to increase the basicity of the slag and thus enhance the dephosphorization ability of the slag.

[0029] The present invention provides a method for controlling nitrogen content in a low-slag smelting process of direct-reduced iron in an electric arc furnace. The method of the present invention includes three stages: an arc starting period and a main melting period, a final melting period, and an oxidation period. The method of the present invention utilizes a furnace door carbon-oxygen gun to spray calcium carbide powder into a molten pool during the final melting period and the oxidation period of direct-reduced iron in an electric arc furnace. The calcium carbide powder reacts with oxygen in the molten steel to generate a large amount of CO gas. During the floating process in the molten pool, the CO bubbles can carry inclusions and gases to the slag, which helps to purify the molten steel. The CO bubbles float to the surface of the electric arc furnace molten pool to form a reducing gas curtain, which isolates the molten steel from the air and prevents the molten steel from absorbing nitrogen in the air. In addition, the calcium carbide powder reacts with oxygen in the molten steel to generate CaO slag. The generated CO gas prompts the CaO slag to form foamed slag, which can further control the nitrogen absorption of the molten steel under the low-slag smelting conditions of the electric arc furnace, reduce smelting energy consumption, and avoid the increase in energy consumption of the electric arc furnace under the conditions of large slag smelting. In addition, the CaO generated by the reaction of calcium carbide powder helps increase the basicity of the slag and enhance the slag's dephosphorization capacity. The method for controlling nitrogen content in the electric arc furnace low-slag smelting process provided by the present invention has the advantages of simple operation, low cost, and helps improve the cleanliness of the molten steel. The method for controlling nitrogen content in the electric arc furnace low-slag smelting process of the present invention reduces the nitrogen content in the molten steel to below 45 ppm, achieving a dephosphorization rate of over 90%.

[0030] In view of the above advantages of the method for controlling nitrogen content in the electric arc furnace direct reduced iron low-slag smelting process of the present invention, it has good application prospects in the field of steelmaking. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic structural diagram of the equipment used in the method for controlling nitrogen content in the low-slag smelting process of direct-reduced iron in an electric arc furnace provided in a specific embodiment of the present invention.

[0032] Explanation of the accompanying numbers: 1-control system; 2-gas supply system; 3-powder spraying system; 4-gas tank; 5-air flow control device; 6-powder storage tank; 7-powder flow control device; 8-gas and / or powder conveying pipeline; 9-furnace wall oxygen gun; 10-arc furnace; 11-electrode; 12-furnace door carbon oxygen gun. DETAILED DESCRIPTION

[0033] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be understood as limiting the scope of implementation of the present invention.

[0034] According to a specific embodiment of the present invention, the method for controlling nitrogen content in the electric arc furnace direct reduced iron low-slag smelting process of the present invention comprises the following steps:

[0035] (1) Arcing period and main melting period

[0036] The smelting raw materials including scrap steel are loaded into the electric arc furnace, and the power supply is started with a power supply intensity of 0.7 to 1.0 MVA / t steel;

[0037] The carbon oxygen lance at the furnace door and the oxygen lance on the furnace wall are used to supply oxygen to the furnace for cutting and melting scrap steel. The oxygen supply intensity is 0.8~2.0Nm 3 / (min·t steel);

[0038] When a molten pool is formed in the electric arc furnace, direct reduced iron is continuously added. Based on the total weight of the smelting raw materials after adding direct reduced iron as 100%, the amount of direct reduced iron added is 20-50%. At this time, the oxygen supply intensity is adjusted to 0.6-1.5Nm 3 / (min·t steel);

[0039] After all the direct reduced iron has entered the molten pool, limestone is added to the surface of the molten pool at a rate of 20-25 kg / t steel.

[0040] (2) End of melting

[0041] Continue to add limestone into the electric arc furnace at a rate of 10-15 kg / t steel;

[0042] Use the carbon oxygen gun on the door of the electric arc furnace to spray oxygen and calcium carbide powder into the molten pool. The oxygen injection rate is 0.4-0.9Nm 3 / (min·t steel), the injection rate of calcium carbide powder is 0.1~0.5kg / (min·t steel);

[0043] Use the oxygen lance on the wall of the electric arc furnace to spray oxygen and carbon powder into the molten pool. The oxygen injection rate is 0.6~1.2Nm 3 / (min·t steel), the blowing rate of carbon powder is 0.1~0.6kg / (min·t steel);

[0044] (3) Oxidation period

[0045] Use the carbon oxygen gun on the door of the electric arc furnace to spray oxygen and calcium carbide powder into the molten pool. The oxygen injection rate is 0.7~1.5Nm 3 / (min·t steel); the injection rate of calcium carbide powder is 0.1~0.5kg / (min·t steel);

[0046] Use the oxygen lance on the wall of the electric arc furnace to spray oxygen, carbon powder, carrier gas-lime powder into the molten pool. The oxygen spray rate is 0.6~1.5Nm 3 / (min·t steel), the carbon powder blowing rate is 0.1~0.6kg / (min·t steel), the carrier gas is argon or nitrogen, and the carrier gas flow rate is 0.6~1.5Nm 3 / (min·tsteel), the flow rate of lime powder is 0.5~5kg / (min·tsteel).

[0047] According to a specific embodiment of the present invention, based on the different proportions of direct reduced iron added to the electric arc furnace, the flow ratios of oxygen, carrier gas, calcium carbide powder, lime powder, etc. can be dynamically adjusted as long as they are within the above range defined by the present invention.

[0048] According to a specific embodiment of the present invention, the structure of the equipment used in the method for controlling nitrogen content in the electric arc furnace direct reduced iron low slag smelting process of the present invention is as follows: Figure 1 As shown, the device includes:

[0049] Control system 1, gas supply system 2, powder spraying system 3, gas and / or powder delivery pipeline 8 and electric arc furnace 10;

[0050] The control system 1 may be a computer for monitoring and controlling various process parameters in the method for controlling nitrogen content in the electric arc furnace direct reduced iron low-slag smelting process;

[0051] The air supply system 2 includes an air tank 4 and an air flow control device 5;

[0052] The powder spraying system 3 includes a powder storage tank 6 and a powder flow control device 7;

[0053] The electric arc furnace 10 is provided with at least a number of furnace wall oxygen lances 9, electrodes 11 and a number of furnace door carbon oxygen lances 12;

[0054] The gas tank 4 and the powder storage tank 6 are connected to the gas and / or powder delivery pipeline 8 through the airflow control device 5 and the powder flow control device 7 respectively; the gas and / or powder delivery pipeline 8 is connected to several furnace wall oxygen guns 9 and several furnace door carbon oxygen guns 12.

[0055] The technical solution of the present invention is described in detail below with reference to embodiments and comparative examples.

[0056] Example 1

[0057] This embodiment provides a method for controlling nitrogen content in a low-slag smelting process of direct reduced iron in an electric arc furnace.

[0058] For a 130t shaft scrap preheating electric arc furnace, the transformer capacity is 140MVA, 30% direct reduced iron is used for smelting, two furnace door carbon oxygen lances 12 and six furnace wall oxygen lances 9 are configured, the power of the lance is 4MW and the flow rate is 3200Nm 3 / h, steel tapping temperature>1610℃.

[0059] The method of this embodiment adopts Figure 1 The device shown comprises the following steps:

[0060] (1) During the 0-15 min smelting cycle of the electric arc furnace 10, 40 tons of molten iron and 50 tons of scrap steel were added to the furnace, and the power supply was started with a power supply intensity of 0.8 MVA / t steel. Oxygen was supplied to the furnace using the furnace door carbon oxygen lance 12 and the furnace wall oxygen lance 9 with an oxygen supply intensity of 1.5 Nm 3 / (min·t steel); After the molten pool is formed in the electric arc furnace 10, 40t of direct reduced iron is added, and the oxygen supply intensity is adjusted to 1.2Nm 3 / (min·t-steel); after all the direct reduced iron has entered the molten pool, limestone is added to the surface of the molten pool at a rate of 20kg / t-steel;

[0061] (2) During the smelting period of 16 to 22 minutes in the electric arc furnace 10, limestone is continuously added into the electric arc furnace 10 at a rate of 12 kg / t steel; oxygen and calcium carbide powder are sprayed into the molten pool using the furnace door carbon oxygen gun 12 at a rate of 0.5 Nm 3 / (min·t steel), the injection rate of calcium carbide powder is 0.3kg / (min·t steel); oxygen and carbon powder are injected into the molten pool using the furnace wall oxygen gun 9, and the oxygen injection rate is 0.7Nm 3 / (min·t steel), the blowing rate of carbon powder is 0.4kg / (min·t steel);

[0062] (3) During the smelting period of 23 to 39 minutes in the electric arc furnace 10, oxygen and calcium carbide powder are sprayed into the molten pool using the furnace door carbon oxygen gun 12. The oxygen spray rate is 1.1 Nm 3 / (min·t steel), the injection rate of calcium carbide powder is 0.4kg / (min·t steel); oxygen, carbon powder, carrier gas-lime powder are injected into the molten pool by using the furnace wall oxygen gun 9, and the oxygen injection rate is 0.9Nm 3 / (min·t steel), the carbon powder blowing rate is 0.4kg / (min·t steel), the carrier gas is argon, and the flow rate is 1.0Nm 3 / (min·tsteel), the flow rate of lime powder is 3.5kg / (min·tsteel);

[0063] (4) The electric arc furnace 10 produces steel after a smelting cycle of 40 to 43 minutes.

[0064] After adopting the method of this embodiment, the nitrogen content of the molten steel at the smelting end point is controlled below 38ppm, the phosphorus content is less than 0.01%, the dephosphorization rate is more than 92%, and the carbon content is less than 0.10%.

[0065] Example 2

[0066] This embodiment provides a method for controlling nitrogen content in a low-slag smelting process of direct reduced iron in an electric arc furnace.

[0067] For a 130t shaft scrap preheating electric arc furnace, the transformer capacity is 140MVA, 50% direct reduced iron is used for smelting, two furnace door carbon oxygen lances 12 and six furnace wall oxygen lances 9 are configured, the lance power is 4MW and the flow rate is 3200Nm 3 / h, steel tapping temperature>1610℃.

[0068] The method of this embodiment adopts Figure 1 The device shown comprises the following steps:

[0069] (1) During the 0-18 min smelting cycle of the electric arc furnace 10, 25 tons of molten iron and 40 tons of scrap steel were added to the furnace, and the power supply was started with a power supply intensity of 0.95 MVA / t steel. Oxygen was supplied to the furnace using the furnace door carbon oxygen lance 12 and the furnace wall oxygen lance 9 with an oxygen supply intensity of 2.0 Nm 3 / (min·t steel); When a molten pool is formed in the electric arc furnace 10, 65t of direct reduced iron is added, and the oxygen supply intensity is adjusted to 1.2Nm 3 / (min·t-steel); after all the direct reduced iron has entered the molten pool, limestone is added to the surface of the molten pool at a rate of 25kg / t-steel;

[0070] (2) During the smelting period of the electric arc furnace 10 for 19 to 26 minutes, limestone is continuously added into the electric arc furnace 10 at a rate of 15 kg / t steel; oxygen and calcium carbide powder are sprayed into the molten pool using the furnace door carbon oxygen gun 12 at a rate of 0.8 Nm 3 / (min·t steel), the injection rate of calcium carbide powder is 0.5kg / (min·t steel); oxygen and carbon powder are injected into the molten pool using the furnace wall oxygen gun 9, and the oxygen injection rate is 1.0Nm 3 / (min·t steel), the blowing rate of carbon powder is 0.5kg / (min·t steel);

[0071] (3) During the smelting period of 27 to 43 minutes in the electric arc furnace 10, oxygen and calcium carbide powder are sprayed into the molten pool using the furnace door carbon oxygen gun 12. The oxygen spray rate is 1.4 Nm 3 / (min·t steel), the injection rate of calcium carbide powder is 0.5kg / (min·t steel); oxygen, carbon powder, carrier gas-lime powder are injected into the molten pool by using the furnace wall oxygen gun 9, and the injection rate of oxygen is 1.3Nm 3 / (min·t steel), the carbon powder blowing rate is 0.4kg / (min·t steel), the carrier gas is nitrogen, and the flow rate is 0.8Nm 3 / (min·tsteel), the flow rate of lime powder is 4.5kg / (min·tsteel);

[0072] (4) During the smelting period of 44 to 47 minutes in the electric arc furnace 10, steel is discharged from the electric arc furnace 10.

[0073] After adopting the method of this embodiment, the nitrogen content of the molten steel at the end point of smelting is controlled below 45 ppm, and the dephosphorization rate reaches above 90%.

[0074] Example 3

[0075] This embodiment provides a method for controlling nitrogen content in a low-slag smelting process of direct reduced iron in an electric arc furnace.

[0076] For a 150t top-loading electric arc furnace, the transformer capacity is 81.4MVA, 30% direct reduced iron is used for smelting, two furnace door carbon oxygen lances 12 and four furnace wall oxygen lances 9 are configured, the power of the lance is 5MW, and the flow rate is 3360Nm 3 / h, steel tapping temperature>1620℃.

[0077] The method of this embodiment adopts Figure 1 The device shown comprises the following steps:

[0078] (1) During the smelting cycle 0 to 23 minutes of the electric arc furnace 10, 55 tons of molten iron and 50 tons of scrap steel were added to the furnace, and the power supply was started with a power supply intensity of 1.0 MVA / t steel. Oxygen was supplied to the furnace using the furnace door carbon oxygen lance 12 and the furnace wall oxygen lance 9 with an oxygen supply intensity of 2.0 Nm 3 / (min·t steel); After the molten pool is formed in the electric arc furnace 10, 45t of direct reduced iron is added, and the oxygen supply intensity is adjusted to 1.4Nm 3 / (min·t-steel); after all the direct reduced iron has entered the molten pool, limestone is added to the surface of the molten pool at a rate of 25kg / t-steel;

[0079] (2) During the smelting period of 24 to 29 minutes in the electric arc furnace 10, limestone is continuously added into the electric arc furnace 10 at a dosage of 15 kg / t steel; oxygen and calcium carbide powder are sprayed into the molten pool using the furnace door carbon oxygen gun 12 at a rate of 0.8 Nm 3 / (min·t steel), the injection rate of calcium carbide powder is 0.5kg / (min·t steel); oxygen and carbon powder are injected into the molten pool using the furnace wall oxygen lance 9, and the oxygen injection rate is 1.1Nm 3 / (min·t steel), the blowing rate of carbon powder is 0.5kg / (min·t steel);

[0080] (3) During the smelting period of 30 to 58 minutes in the electric arc furnace 10, oxygen and calcium carbide powder are sprayed into the molten pool using the furnace door carbon oxygen gun 12. The oxygen spray rate is 1.4 Nm 3 / (min·t steel), the injection rate of calcium carbide powder is 0.5kg / (min·t steel); oxygen, carbon powder, carrier gas-lime powder are injected into the molten pool by using the furnace wall oxygen gun 9, and the injection rate of oxygen is 1.4Nm 3 / (min·t steel), the carbon powder blowing rate is 0.5kg / (min·t steel), the carrier gas is nitrogen, and the flow rate is 1.2Nm 3 / (min·tsteel), the flow rate of lime powder is 3.8kg / (min·tsteel);

[0081] (4) During the smelting period of 59 to 63 minutes in the electric arc furnace 10, steel is discharged from the electric arc furnace 10.

[0082] After adopting the method of this embodiment, the nitrogen content of the molten steel at the end point of smelting is controlled below 45 ppm, and the dephosphorization rate reaches above 91%.

[0083] Comparative Example 1

[0084] For a 150t top-loading electric arc furnace, the transformer capacity is 81.4MVA, 30% direct reduced iron is used for smelting, two furnace door carbon oxygen lances 12 and four furnace wall oxygen lances 9 are configured, the power of the lance is 5MW, and the flow rate is 3360Nm 3 / h, steel tapping temperature>1620℃.

[0085] The method of this comparative example adopts Figure 1 The device shown comprises the following steps:

[0086] (1) During the smelting cycle 0 to 27 minutes of the electric arc furnace 10, 50 tons of molten iron and 55 tons of scrap steel were added to the furnace, and the power supply was started with a power supply intensity of 0.55 MVA / t steel. Oxygen was supplied to the furnace using the furnace door carbon oxygen lance 12 and the furnace wall oxygen lance 9 with an oxygen supply intensity of 0.37 Nm 3 / (min·t steel); After the molten pool is formed in the electric arc furnace 10, 45t of direct reduced iron is added. At this time, the oxygen supply intensity is 0.37Nm 3 / (min·t-steel); after all the direct reduced iron has entered the molten pool, limestone is added to the surface of the molten pool at a rate of 30kg / t-steel;

[0087] (2) During the smelting period of 28 to 34 minutes in the electric arc furnace 10, limestone is continuously added into the electric arc furnace 10 at a rate of 19 kg / t steel; oxygen is sprayed into the molten pool using the furnace door carbon oxygen gun 12 at a rate of 0.33 Nm 3 / (min·t steel); oxygen and carbon powder are sprayed into the 9 molten pool using the furnace wall oxygen lance, and the oxygen spray rate is 0.36Nm 3 / (min·t steel), the blowing rate of carbon powder is 0.29kg / (min·t steel);

[0088] (3) During the 35-65 min smelting cycle of the electric arc furnace 10, oxygen is sprayed into the molten pool using the furnace door carbon oxygen gun 12 at a rate of 0.30 Nm 3 / (min·tsteel); oxygen, carbon powder, carrier gas-lime powder are sprayed into the molten pool using the furnace wall oxygen lance 9, and the oxygen spray rate is 0.32Nm 3 / (min·t steel), the carbon powder blowing rate is 0.3kg / (min·t steel), the carrier gas is argon, and the flow rate is 0.30Nm 3 / (min·tsteel), the flow rate of lime powder is 1.8kg / (min·tsteel);

[0089] (4) The electric arc furnace 10 produces steel after a smelting cycle of 66 to 70 minutes.

[0090] In this comparative example, calcium carbide powder was not sprayed into the molten pool of the electric arc furnace 10 through the furnace door carbon-oxygen lance 12 during the late melting and oxidation periods. The nitrogen content of the molten steel at the end of the smelting process was 62 ppm, the phosphorus content was <0.015%, the dephosphorization rate was 85%, and the carbon content was <0.10%.

[0091] Comparative Example 2

[0092] For a 130t shaft scrap preheating electric arc furnace, the transformer capacity is 140MVA, 50% direct reduced iron is used for smelting, two furnace door carbon oxygen lances 12 and six furnace wall oxygen lances 9 are configured, the lance power is 4MW and the flow rate is 3200Nm 3 / h, steel tapping temperature>1610℃.

[0093] The method of this comparative example adopts Figure 1 The device shown comprises the following steps:

[0094] (1) During the 0-18 min smelting cycle of the electric arc furnace 10, 25 tons of molten iron and 40 tons of scrap steel were added to the furnace, and the power supply was started with a power supply intensity of 0.95 MVA / t steel. Oxygen was supplied to the furnace using the furnace door carbon oxygen lance 12 and the furnace wall oxygen lance 9 with an oxygen supply intensity of 2.0 Nm 3 / (min·t steel); When a molten pool is formed in the electric arc furnace 10, 65t of direct reduced iron is added, and the oxygen supply intensity is adjusted to 1.2Nm 3 / (min·t-steel); after all the direct reduced iron has entered the molten pool, limestone is added to the surface of the molten pool at a rate of 25kg / t-steel;

[0095] (2) During the smelting period of the electric arc furnace 10 for 19 to 26 minutes, limestone is continuously added into the electric arc furnace 10 at a rate of 15 kg / t steel; oxygen is sprayed into the molten pool using the furnace door carbon oxygen gun 12 at a rate of 0.8 Nm 3 / (min·tsteel); oxygen and carbon powder are sprayed into the molten pool using the furnace wall oxygen lance 9, and the oxygen spray rate is 1.0Nm 3 / (min·t steel), the blowing rate of carbon powder is 0.5kg / (min·t steel);

[0096] (3) During the smelting period of 27 to 43 minutes in the electric arc furnace 10, oxygen is sprayed into the molten pool using the furnace door carbon oxygen gun 12 at a rate of 1.4 Nm 3 / (min·tsteel); oxygen, carbon powder, carrier gas-lime powder are sprayed into the molten pool using the furnace wall oxygen lance 9, and the oxygen spray rate is 1.3Nm 3 / (min·t steel), the carbon powder blowing rate is 0.4kg / (min·t steel), the carrier gas is nitrogen, and the flow rate is 0.8Nm 3 / (min·tsteel), the flow rate of lime powder is 4.5kg / (min·tsteel);

[0097] (4) During the smelting period of 44 to 47 minutes in the electric arc furnace 10, steel is discharged from the electric arc furnace 10.

[0098] In this comparative example, calcium carbide powder was not sprayed into the molten pool of the electric arc furnace 10 using the furnace door carbon oxygen lance 12 during the late melting and oxidation stages. The nitrogen content of the molten steel at the end of smelting was 54 ppm, and the dephosphorization rate was 87%.

[0099] Finally, it should be noted that the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all implementation methods here. Any obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for controlling nitrogen content in an electric arc furnace direct reduced iron (DRI) low-slag smelting process, comprising the following steps: (1) Arcing period and main melting period The smelting raw materials including scrap steel are loaded into the electric arc furnace and the power is turned on. Oxygen is supplied to the furnace through the carbon oxygen lance on the furnace door and the oxygen lance on the furnace wall. When a molten pool is formed in the electric arc furnace, direct reduced iron is continuously added and the oxygen supply intensity is adjusted. After all the direct reduced iron has entered the molten pool, limestone is added to the surface of the molten pool; (2) End of melting Continue to add limestone into the electric arc furnace; use the carbon oxygen lance on the electric arc furnace door to spray oxygen and calcium carbide powder into the molten pool; use the oxygen lance on the electric arc furnace wall to spray oxygen and carbon powder into the molten pool; (3) Oxidation period The carbon-oxygen lance on the door of the electric arc furnace is used to spray oxygen and calcium carbide powder into the molten pool; the oxygen lance on the wall of the electric arc furnace is used to spray oxygen, carbon powder, and carrier gas-lime powder into the molten pool.

2. The method according to claim 1, wherein In step (1), the power supply intensity of the power supply is 0.7 to 1.0 MVA / t steel.

3. The method according to claim 1, wherein In step (1), the intensity of oxygen supply to the furnace by using the carbon oxygen lance at the furnace door and the oxygen lance at the furnace wall is 0.8 to 2.0 Nm 3 / (min·t steel); When a molten pool is formed in the electric arc furnace, direct reduced iron is continuously added and the oxygen supply intensity is adjusted to 0.6~1.5Nm 3 / (min·t steel).

4. The method according to claim 1, wherein In step (1), the amount of direct reduced iron added is 20-50%, based on the total weight of the smelting raw materials after adding direct reduced iron as 100%.

5. The method according to claim 1, wherein In step (1), the amount of limestone added to the surface of the molten pool is 20-25 kg / t steel.

6. The method according to claim 1, wherein In step (2), the amount of limestone added to the electric arc furnace is 10-15 kg / t steel.

7. The method according to claim 1, wherein In step (2), when oxygen and calcium carbide powder are sprayed into the molten pool using the carbon oxygen gun at the door of the electric arc furnace, the oxygen spraying rate is 0.4 to 0.9 Nm 3 / (min·t steel), the injection rate of calcium carbide powder is 0.1~0.5kg / (min·t steel).

8. The method according to claim 1, wherein In step (2), when oxygen and carbon powder are sprayed into the molten pool by using the oxygen lance on the wall of the electric arc furnace, the oxygen spraying rate is 0.6-1.2 Nm 3 / (min·t steel), the blowing rate of carbon powder is 0.1~0.6kg / (min·t steel).

9. The method according to claim 1, wherein In step (3), when oxygen and calcium carbide powder are sprayed into the molten pool using the carbon oxygen gun at the door of the electric arc furnace, the oxygen spraying rate is 0.7 to 1.5 Nm 3 / (min·t steel), the injection rate of calcium carbide powder is 0.1~0.5kg / (min·t steel).

10. The method according to claim 1, wherein In step (3), when oxygen, carbon powder, carrier gas-lime powder are sprayed into the molten pool by using the oxygen lance on the wall of the electric arc furnace, the oxygen spraying rate is 0.6-1.5Nm 3 / (min·t steel), the carbon powder spraying rate is 0.1~0.6kg / (min·t steel), and the carrier gas flow rate is 0.6~1.5Nm 3 / (min·tsteel), the flow rate of lime powder is 0.5~5kg / (min·tsteel).

11. The method according to claim 1 or 10, wherein: In step (3), the carrier gas is argon or nitrogen.

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