Low consumption and high efficiency smelting method of a consteel electric arc furnace

Abstract

The application discloses a low-consumption and high-efficiency smelting method of a Consteel electric arc furnace, which comprises a slagging system, a power supply system, a carbon powder and oxygen injection system, a slagging system, a charging system, a furnace door control system, a steel retaining system and a bottom blowing system; the slagging system is as follows: if the content of FeO in the slag is less than 20 wt%, oxygen blowing is first performed, and then carbon powder is injected; if the content of FeO in the slag is more than 30 wt%, carbon powder is first injected, lime and light-burned dolomite are added to adjust the slag, and then oxygen blowing is performed to form foamed slag; the power supply system is as follows: at the beginning of the smelting of a furnace, arc smelting is started by using a voltage of 800-840 V and an arc length of 76-80 cm, and after the foamed slag is formed, the gear is raised to perform smelting; the power supply gear is adjusted according to the feeding speed of the scrap steel, and the gear is raised according to the feeding speed of the scrap steel; after the scrap steel is completely added, long-arc smelting is performed by using a voltage of 960-1040 V. The method reduces the power consumption of the electric arc furnace smelting and shortens the smelting period.

Description

Technical Field

[0001] This invention relates to an electric arc furnace metallurgical technology, and more particularly to a low-consumption and high-efficiency smelting method using a Consteel electric arc furnace. Background Technology

[0002] Electric arc furnace (EAF) steelmaking is one of the main steelmaking methods currently available. EAF steelmaking offers advantages such as lower investment, shorter construction period, smaller footprint, energy efficiency, environmental friendliness, low energy consumption, and low carbon emissions. The carbon emissions of EAF steelmaking using all-scrap steel are approximately one-third of those of the long-process method, making it a major low-carbon steelmaking route. In recent years, my country's EAF steel industry has made significant progress. However, there is still a gap between my country's high-efficiency, low-consumption EAF steelmaking technology and advanced foreign technologies. The cost of EAF steel is typically 100-500 yuan higher than that of converter steel. Therefore, EAF steelmaking requires low-consumption, high-efficiency production processes. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a low-consumption and high-efficiency smelting method for Consteel electric arc furnace, so as to reduce the cost of electric arc furnace steel.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention includes a slag-making system, a power supply system, a carbon powder and oxygen injection system, a slag discharge system, a feeding system, a furnace door control system, a steel retention system, and a bottom blowing system.

[0005] The slag-making process is as follows: at the beginning of each smelting, if the FeO content in the slag is <20wt%, oxygen is blown first, followed by carbon powder injection; if the FeO content in the slag is >30wt%, carbon powder is injected first, and lime and lightly calcined dolomite are added to adjust the slag, followed by oxygen blowing to create foamy slag.

[0006] The power supply system is as follows: at the beginning of each furnace smelting, the voltage is 800-840V and the arc length is 76-80cm to start the arc smelting. After the foamy slag is made, the voltage is increased to carry out smelting. During the smelting process, the power supply voltage is adjusted according to the scrap steel addition speed and the voltage is increased according to the scrap steel addition speed. After all the scrap steel is added, the voltage is 960-1040V for long arc smelting.

[0007] The carbon powder and oxygen injection regime is as follows: for steel grades with a carbon content not exceeding 0.03 wt% at the end of the electric arc furnace, the carbon powder injection rate is 20-25 kg / t, and the oxygen injection rate is 30-40 Nm³. 3 / t; steel grade with final carbon content of 0.03-0.08wt%, carbon powder injection rate of 20-25kg / t, oxygen blowing rate of 25-35Nm 3 / t; For steel grades with a final carbon content greater than 0.08wt%, the carbon powder injection rate is 20-30 kg / t, and the oxygen blowing rate is 20-30 Nm. 3 / t;

[0008] The slag discharge system is as follows: avoid slag discharge during the addition of scrap steel, and discharge 80-100 kg / t of slag per ton of steel;

[0009] The feeding system is as follows: heavy and medium scrap steel are added in the early stage of smelting, small and medium-sized heavy and medium scrap steel are added in the middle stage of smelting, and small scrap steel and light and thin materials are added in the later stage of smelting.

[0010] The furnace door control system is as follows: the furnace door should be kept closed unless absolutely necessary.

[0011] The steel retention system is as follows: 50% to 60% of the steel is retained per furnace.

[0012] The bottom blowing system is as follows: the bottom blowing flow rate is 0-500 NL / min during the scrap steel addition stage, and the bottom blowing flow rate is 500-2000 NL / min during the heating and temperature rise stage after the scrap steel is added.

[0013] Furthermore, regarding the slag-forming process, if the FeO content in the slag is <20wt%, oxygen blowing is performed for 1-3 minutes at a blowing rate of 100-200 Nm. 3 / min; if the FeO content in the slag is >30wt%, first inject carbon powder for 1-3 minutes at a carbon injection rate of 50-100kg / min, and add 500-1000kg of lime and 500-1000kg of lightly calcined dolomite to adjust the slag.

[0014] Furthermore, the slag discharge system begins 3-5 minutes after the scrap steel is added.

[0015] Furthermore, the feeding system ensures that the scrap steel is added within 20 to 30 minutes during the smelting process.

[0016] The beneficial effects of adopting the above technical solution are as follows: This invention reduces the power consumption of electric arc furnace smelting by controlling the slag-making system, power supply system, carbon powder and oxygen injection system, slag discharge system, charging system, furnace door control system, steel retention system, and bottom blowing system during the electric arc furnace smelting process, shortens the smelting cycle, reduces the average power consumption per ton of steel by 10-30 kWh / t, shortens the smelting cycle by 3-5 min, reduces smelting costs, improves production efficiency, and realizes low-consumption and high-efficiency smelting of the Consteel electric arc furnace. Detailed Implementation

[0017] The present invention will now be described in further detail with reference to specific embodiments.

[0018] The main idea behind this low-consumption and high-efficiency smelting method using the Consteel electric arc furnace is to strengthen the control of the slag-making system, power supply system, carbon powder and oxygen injection system, slag discharge system, charging system, furnace door control system, steel retention system, and bottom blowing system during the electric arc furnace smelting process. It is applicable to all steel grades using the Consteel electric arc furnace.

[0019] The slag-forming process is as follows: At the beginning of each smelting cycle, slag is adjusted according to the slag quality. If the FeO content in the slag is <20wt%, i.e., the slag is viscous, the slag's oxidizing power is not high. In this case, oxygen should be blown for 1-3 minutes at a blowing rate of 100-200 Nm. 3 At a rate of 50-100 kg / min, the oxygen blowing process will produce the following reaction: [Fe] + (O) = (FeO); then, carbon powder will be injected, and the following reactions will occur: C + (FeO) = [Fe] + CO, CO + (FeO) = [Fe] + CO2; otherwise, if carbon powder is injected first, there will not be enough oxygen to react with the carbon, and a large number of CO and CO2 bubbles cannot be formed quickly, which is not conducive to the rapid formation of foamy slag and cannot achieve a good submerged arc effect. If the FeO content in the slag is >30 wt%, that is, the slag is relatively thin, and the FeO content in the slag is high, carbon powder will be injected for 1-3 minutes at a carbon injection rate of 50-100 kg / min, and 500-1000 kg of lime and 500-1000 kg of lightly calcined dolomite will be added to adjust the slag, and then oxygen will be blown to quickly form foamy slag. When the FeO content in the slag is 20-30 wt%, the slag is normal, and oxygen and carbon are injected at the same time, with an oxygen blowing rate of 100-200 Nm. 3 The carbon injection rate is 50-100 kg / min, and 500-1000 kg of lime and 500-1000 kg of lightly calcined dolomite are added to quickly create foamy slag. The total amount of lime added during the smelting process is 20-25 kg / t, and the total amount of lightly calcined dolomite added is 15-20 kg / t. The amount of lime and lightly calcined dolomite added is evenly distributed according to the amount of scrap steel added, and the lime and lightly calcined dolomite are added in batches. The last batch of lime and lightly calcined dolomite is added after all the scrap steel has been added.

[0020] The power supply system is as follows: The Consteel electric arc furnace has a total of 21 power supply levels. At the start of each furnace smelting operation, a low level (levels 6-8) is used, with a voltage of 800-840V and an arc length of approximately 76-80cm. At this stage, the slag thickness is not high. If a higher level is used with a longer arc, the slag cannot completely cover the arc, resulting in greater energy loss. Simultaneously, the exposed arc corrodes the furnace lining, reducing its lifespan. After creating a foamed slag layer to ensure a good submerged arc effect, the power level is increased for smelting. The power supply setting during the smelting process is adjusted according to the scrap steel addition speed. A lower setting is used when the scrap steel addition speed is slow to avoid excessive heat loss when the setting is high; a higher setting is used when the scrap steel addition speed is fast to avoid insufficient heat supply when the setting is low, resulting in incomplete melting of the scrap steel and accumulation of scrap steel. After all the scrap steel has been added, setting 14 to 18 (long arc smelting, i.e., voltage 960 to 1040V) is used to rapidly heat the molten steel. The relationship between the scrap steel addition speed, power supply setting, and power supply voltage is shown in Table 1.

[0021] Table 1: Scrap Steel Addition Rate and Corresponding Power Supply Level and Voltage

[0022]

[0023] The carbon powder and oxygen injection system is as follows: the carbon powder and oxygen injection rates during the smelting process are adjusted according to the final composition requirements of the electric arc furnace for different steel grades. For steel grades with a carbon mass fraction not exceeding 0.03% at the final stage of the electric arc furnace, the carbon powder injection rate is 20-25 kg / t, and the oxygen injection rate is 30-40 Nm³ / t. 3 / t; For steel grades with a final carbon mass fraction of 0.03-0.08%, the carbon powder injection rate per ton of steel is 20-25 kg / t, and the oxygen blowing rate per ton of steel is 25-35 Nm. 3 / t; For steel grades with a final carbon mass fraction greater than 0.08%, the carbon powder injection rate per ton of steel is 20-30 kg / t, and the oxygen blowing rate per ton of steel is 20-30 Nm³. 3 / t. In this way, by strengthening the control of oxygen blowing and carbon injection, the chemical energy of the carbon-oxygen reaction can be used to replace part of the electrical energy, effectively reducing power consumption.

[0024] The slag removal system is as follows: to avoid removing too much heat during the scrap steel addition process, slag removal begins 3-5 minutes after the scrap steel is added, with a slag removal rate of 80-100 kg / t of steel. This reduces the amount of slag in the furnace while ensuring an appropriate amount of slag left in each furnace, preventing excessive slag from affecting oxygen blowing and carbon injection effects, and facilitating process control and rapid foam slag formation. For some furnaces with difficult slag removal, forced slag removal is implemented. The forced slag removal process involves adding 200-400 kg of lightly calcined dolomite and using carbon lances on both sides of the furnace door to inject carbon powder for forced slag removal. The principle is that the "cold boiling" effect produced by adding lightly calcined dolomite is beneficial for slag removal. At the same time, the addition of lightly calcined dolomite and the injection of carbon powder generate a large amount of CO and CO2 gas, which rapidly increases the foam volume of the slag, allowing for rapid slag removal. The reaction formulas are as follows: MgCO3=MgO+CO2, C+(FeO)=[Fe]+CO, C+CO2=2CO, CO+(FeO)=[Fe]+CO2.

[0025] The feeding system is as follows: Heavy scrap steel with a thickness greater than 6mm and medium scrap steel with a thickness of 3-6mm are added in the early stage of smelting, as their melting time is longer, and adding them later would result in them being difficult to melt and thus increasing the smelting cycle. Small and medium-sized heavy and medium scrap steel are added in the middle stage of smelting. The small and medium-sized heavy and medium scrap steel refers to other scrap steel that does not belong to heavy scrap steel, medium scrap steel, small scrap steel, or thin and light scrap. In the later stage, small scrap steel with a thickness of 1-3mm and thin and light scrap steel with a thickness of less than 1mm are mainly added. Small scrap steel and thin and light scrap steel melt faster, and adding them later will not increase the smelting cycle. The scrap steel is added at a consistent rate during the smelting process, ensuring that the scrap steel is added within 20-30 minutes, avoiding a longer addition time that would increase the smelting cycle and power consumption. The scrap steel is added at a stable rate to avoid frequent changes in the feeding speed that would increase power consumption.

[0026] The furnace door control system is as follows: strengthen the operation of closing the furnace door, and keep the furnace door closed as much as possible unless necessary. For example, during the smelting process, when waiting for steel tapping after temperature sampling, during the steel tapping process, during sand filling and electrode replacement, etc., keep the furnace door closed as much as possible to reduce heat loss.

[0027] The steel retention system is as follows: the steel retention ratio for each furnace is 50% to 60%, which avoids a small amount of steel retention leading to a slow melting rate of scrap steel, and at the same time avoids a large amount of steel retention leading to increased heat loss.

[0028] The bottom blowing system is as follows: the bottom blowing flow rate is 0-500 NL / min during the scrap steel addition stage, and the flow rate is 500-2000 NL / min during the heating and temperature rise stage after the scrap steel is added. In this way, the bottom blowing stirring during the heating and temperature rise stage is strengthened, and the composition and temperature of the molten steel are quickly and evenly distributed, thereby shortening the smelting cycle.

[0029] Example 1: The low-consumption and high-efficiency smelting method of this Consteel electric arc furnace is described in detail below.

[0030] A 150t Consteel electric arc furnace was used, with a total steel capacity of 230-250t, producing Q195 steel. 153.5t of steel was tapped from the eccentric bottom tap, leaving a 52% steel residue. Smelting began with a low-level (6th gear) power supply and a bottom blowing flow rate of 300 NL / min. The initial FeO content was 18wt%, and the slag was viscous. Oxygen was first blown for 2 minutes at a blowing rate of 150 Nm. 3 The flow rate is 6.3 t / min, followed by carbon powder injection to quickly create foamy slag. Larger and medium-sized heavy and medium-sized scrap steel is added in the early stages of smelting, smaller and medium-sized heavy and medium-sized scrap steel is added in the middle stages, and small and light scrap steel is added mainly in the later stages. The average scrap steel addition rate is 6.3 t / min, and the power supply setting is 15. The lime and light-burned dolomite addition rates are 22 kg / t and 16 kg / t, respectively, evenly distributed according to the scrap steel addition. The final batch of lime and light-burned dolomite is added after all scrap steel has been added. The furnace door is kept closed during smelting to reduce heat loss and avoid slag discharge. Scrap steel addition is completed 27 minutes after smelting begins, and the bottom blowing flow rate is adjusted to 800 NL / min. Slag discharge begins at 29 minutes, with 88 kg / t of slag discharged per ton of steel. Temperature is measured and steel samples are taken in preparation for tapping. The final carbon content of Q195 steel produced by electric arc furnace is ≤0.03%, with a carbon powder injection rate of 22.3 kg / t and an oxygen blowing rate of 34.5 Nm³ / t during the smelting process. 3 / t. In this embodiment, the final carbon content of the electric arc furnace is 0.017%, the power consumption per ton of steel is 349 kWh / t, and the smelting cycle is 39 min.

[0031] Example 2: The low-consumption and high-efficiency smelting method of this Consteel electric arc furnace is described in detail below.

[0032] A 150t Consteel electric arc furnace is used, with a total steel capacity of 230-250t, producing Q215 steel. 151.3t of steel is tapped from the eccentric bottom tap, leaving 55% of the steel. Smelting begins with a low-level (8th gear) power supply and a bottom blowing flow rate of 100NL / min. The initial FeO content is 31wt%, and the slag is relatively thin. Carbon powder is injected for 1 minute at a rate of 100kg / min, along with 1 ton of lime and 500kg of lightly calcined dolomite to adjust the slag. Oxygen blowing begins 1 minute after carbon injection to quickly create foamy slag. Larger and medium-sized heavy and medium-sized scrap are added in the early stages of smelting, smaller and medium-sized heavy and medium-sized scrap are added in the middle stages, and small and light scrap are added mainly in the later stages. The average scrap addition rate is 6.8t / min, and the power supply level is set to 16. During the smelting process, 20 kg / t of lime and 20 kg / t of lightly calcined dolomite were added. The lime and lightly calcined dolomite were added evenly based on the scrap steel input. The final batch of lime and lightly calcined dolomite was added after all the scrap steel had been added. The furnace door was kept closed during the smelting process to minimize heat loss and avoid slag discharge. Scrap steel was added 25 minutes after the start of smelting, and the bottom blowing flow rate was adjusted to 1000 NL / min. At the 28th minute, the furnace door was opened to begin slag discharge. Due to difficulties in slag discharge, 200 kg of lightly calcined dolomite was added, and carbon powder was injected using carbon lances on both sides of the furnace door to force slag discharge. The slag discharge rate was 92 kg / t per ton of steel. Temperature was measured, steel samples were taken, and preparation for tapping was made. The final carbon content of the Q215 steel electric arc furnace was 0.04%–0.08%. The carbon powder injection rate per ton of steel during the smelting process was 23.6 kg / t, and the oxygen blowing rate per ton of steel was 29.7 Nm³. 3 / t. In this embodiment, the final carbon content of the electric arc furnace is 0.057%, the power consumption per ton of steel is 358 kWh / t, and the smelting cycle is 41 min.

[0033] Example 3: The low-consumption and high-efficiency smelting method of this Consteel electric arc furnace is described in detail below.

[0034] A 150t Consteel electric arc furnace was used, with a total steel capacity of 230-250t, producing steel grade 82B. 155.4t of steel was tapped from the eccentric bottom tap, leaving 58% of the steel. Smelting began with a low-speed (level 7) power supply and a bottom blowing flow rate of 500 NL / min. Initial FeO content was 26wt%, slag was normal, and oxygen and carbon were injected simultaneously at a blowing rate of 160 Nm. 3The carbon injection rate is 70 kg / min, with 500 kg of lime and 500 kg of lightly calcined dolomite added to quickly create foamy slag. Larger and medium-sized heavy and medium-sized scrap steel is added in the early stages of smelting, smaller and medium-sized heavy and medium-sized scrap steel is added in the middle stages, and small and light scrap steel is added mainly in the later stages. The average scrap steel addition rate during smelting is 7.2 t / min, and the power supply setting is 17. The lime addition rate is 25 kg / t, and the lightly calcined dolomite addition rate is 17 kg / t. The lime and lightly calcined dolomite addition amounts are evenly distributed according to the scrap steel addition. The final batch of lime and lightly calcined dolomite is added after all the scrap steel has been added. The furnace door was kept closed during the smelting process to avoid slag discharge. Scrap steel was added 23 minutes after smelting began, and the bottom blowing flow rate was adjusted to 1600 NL / min. Slag discharge began at the 26th minute. Due to difficulties, 200 kg of lightly calcined dolomite was added, and carbon powder was injected using carbon lances on both sides of the furnace door to force slag removal. The slag discharge rate was 92 kg / t of steel. Temperature was measured, steel samples were taken, and preparation for tapping was completed. The final carbon content of the 82B steel electric arc furnace was greater than 0.08%. The carbon powder injection rate was 28.6 kg / t of steel, and the oxygen blowing rate was 29.7 Nm³ / t of steel. 3 / t. In this embodiment, the final carbon content of the electric arc furnace is 0.081%, the power consumption per ton of steel is 345 kWh / t, and the smelting cycle is 37 min.

Claims

1. A low-consumption and high-efficiency smelting method using a Consteel electric arc furnace, characterized in that: It includes slag-making system, power supply system, carbon powder and oxygen injection system, slag discharge system, charging system, furnace door control system, steel retention system and bottom blowing system; The slag-making process is as follows: at the beginning of each smelting, if the FeO content in the slag is <20wt%, oxygen is blown first, followed by carbon powder injection; if the FeO content in the slag is >30wt%, carbon powder is injected first, and lime and lightly calcined dolomite are added to adjust the slag, followed by oxygen blowing to create foamy slag. The power supply system is as follows: at the beginning of each furnace smelting, the voltage is 800-840V and the arc length is 76-80cm for arc smelting. After the foamy slag is made, the voltage is increased to a higher level for smelting. During the smelting process, the power supply level is adjusted according to the scrap steel addition speed and the level is increased according to the scrap steel addition speed. After all the scrap steel is added, the voltage is 960-1040V for long-arc smelting. The carbon powder and oxygen injection regime is as follows: for steel grades with a carbon content not exceeding 0.03 wt% at the end of the electric arc furnace, the carbon powder injection rate is 20-25 kg / t, and the oxygen injection rate is 30-40 Nm³. 3 / t; for steel grades with 0.03wt% < final carbon ≤ 0.08wt%, carbon powder injection rate is 20-25kg / t, and oxygen blowing rate is 25-35Nm. 3 / t; For steel grades with a final carbon content greater than 0.08wt%, the carbon powder injection rate is 20-30 kg / t, and the oxygen blowing rate is 20-30 Nm. 3 / t; The slag discharge system is as follows: avoid slag discharge during the addition of scrap steel, and discharge 80-100 kg / t of slag per ton of steel; The feeding system is as follows: heavy and medium-sized scrap steel is added in the early stage of smelting, small and medium-sized heavy and medium-sized scrap steel is added in the middle stage of smelting, and small scrap steel and light and thin materials are added in the later stage of smelting; the small and medium-sized heavy and medium-sized scrap steel refers to other scrap steel that does not belong to heavy scrap steel, medium scrap steel, small scrap steel and light and thin materials. The furnace door control system is as follows: the furnace door should be kept closed unless necessary. The steel retention system is as follows: 50% to 60% of the steel is retained per furnace. The bottom blowing system is as follows: the bottom blowing flow rate is 0-500 NL / min during the scrap steel addition stage, and the bottom blowing flow rate is 500-2000 NL / min during the heating and temperature rise stage after the scrap steel is added.

2. The low-consumption and high-efficiency smelting method of a Consteel electric arc furnace according to claim 1, characterized in that: The aforementioned slag-forming process, if the FeO content in the slag is <20wt%, involves oxygen blowing for 1–3 minutes at a blowing rate of 100–200 Nm. 3 / min; if the FeO content in the slag is >30wt%, first inject carbon powder for 1-3 minutes at a carbon injection rate of 50-100kg / min, and add 500-1000kg of lime and 500-1000kg of lightly calcined dolomite to adjust the slag.

3. The low-consumption and high-efficiency smelting method of the Consteel electric arc furnace according to claim 1, characterized in that: The slag discharge procedure begins 3-5 minutes after the scrap steel is added.

4. A low-consumption and high-efficiency smelting method for a Consteel electric arc furnace according to claim 1, 2, or 3, characterized in that: The feeding system ensures that scrap steel is added within 20-30 minutes during the smelting process.

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