Method for smelting direct reduction iron through electric furnace

Abstract

The invention discloses a method for smelting direct reduction iron through an electric furnace. The method comprises the following steps that S1, a direct reduction iron raw material with the high carbon content is obtained through a shaft furnace; s2, a molten pool is firstly formed in the electric furnace; s3, the direct reduction iron raw materials are added into an electric furnace molten pool in batches for electric furnace smelting; in each charging process, a direct reduction iron raw material is firstly put into an electric furnace molten pool, then scrap steel is put into the electric furnace molten pool to press the direct reduction iron into the molten pool, lime is added after the direct reduction iron is completely molten, and then charging is continued; and S4, after melting in the electric furnace molten pool is completed, blowing oxygen to stir the molten pool for continuous smelting until carbon in the molten steel reaches the standard. The melting efficiency of the direct reduction iron can be improved, and the power consumption cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of electric furnace smelting, and in particular to a method for smelting direct-reduced iron in an electric furnace. Background Art

[0002] Under the background of global carbon emission reduction, China is gradually promoting CO2 emission reduction actions in the steel industry in order to achieve the goal of reducing carbon dioxide emissions. From the perspective of reducing carbon emissions, changing the traditional process and adopting the gas-solid reaction of the vertical furnace to produce direct reduced iron can greatly reduce carbon dioxide emissions. However, one of the biggest problems with using electric furnaces to smelt direct reduced iron is the long melting time.

[0003] Due to the smelting characteristics of the electric arc furnace refining furnace, electric energy needs to be transmitted through ultra-high power electrode discharge during the smelting process. Due to the high temperature of the electric arc, the direct reduced iron is melted; however, direct reduced iron has problems such as low density, large voids, high FeO content, large slag volume, and poor conductivity. The reason for these problems is that direct reduced iron is generated by gas-solid reaction and has many pores inside. Due to the existence of these pores, its density is relatively small. After being placed in the electric furnace, it cannot be precipitated into the molten pool, which causes problems such as slow melting speed of direct reduced iron in electric furnace.

[0004] Many technical personnel in the industry have conducted relevant research on the problem of melting direct reduced iron. For example, Chinese patent publication No. CN101775460A proposes a method for quickly melting direct reduced iron. The technology adds direct reduced iron into an electric furnace, adds waste electrodes at 1-1.5% of the mass of the direct reduced iron, and then adds low-S coke or anthracite at 2.5-3.5% of the mass of the direct reduced iron. The electric furnace is powered on for heating and oxygen is blown to assist melting until all the direct reduced iron in the furnace is melted. Slag is made, P is removed, and the temperature is raised. After the steel is qualified, the steel is tapped. After tapping, the steel and slag are retained. The difficulties of tunnel kiln direct reduced iron being difficult to melt, the large amount of slag, and the low carbon content of the molten steel pool are effectively overcome, and the electric furnace achieves 100% smelting of low-quality tunnel kiln direct reduced iron, which is conducive to the promotion of direct reduction ironmaking technology. The core feature of this technology is carbon matching, which uses waste electrodes or coal to match the carbon, and the carbon is matched in place, and the melting of the direct reduced iron is promoted by the chemical heat of the reaction of oxygen and carbon. In response to the problem of low density and more voids in reduced iron, Chinese patent application No. CN105695654A proposes a method for preparing a clean steel base billet / mother liquor, which selects iron concentrate powder or iron-containing oxide according to the requirements of the product chemical composition, and controls the reduction to produce sponge iron through a direct reduction device; the reduced sponge iron is pressed into blocks to obtain pressed sponge iron; the pressed sponge iron is then smelted to obtain molten iron; and the C, S, and P in the molten iron are deeply refined through refining; the above scheme, in essence, is to reduce the voids and increase the density through the process of pressurization and molding; although this can partially solve the problem of low density of reduced iron, it causes heat loss of the reduced iron in a red-hot state, and requires an additional hot pressing molding process, which increases the fixed asset investment, and even if the hot pressing molding is performed, the direct reduced iron becomes a hot pressed block, and the problem of high FeO content in the reduced iron cannot be reduced. Chinese patent publication number CN102787196A proposes a method for smelting stainless steel using direct reduced iron, which belongs to the technical field of stainless steel smelting. The process steps are melting direct reduced iron in an electric furnace, refining and alloying in an AOD furnace, refining in a VOD furnace, and continuous casting. During the electric furnace smelting process, the requirements for reduced iron are that the C content is ≥2.0% and the metallization rate is ≥90%. This technology illustrates a key point, that is, the carbon content must be high, but no specific technical description is given on how to ensure the high carbon content.Regarding the scheme of adding high carbon content to direct reduced iron, international patent PCT / US2022 / 034129 proposes connecting a chute between the discharge outlet of the vertical furnace that discharges hot direct reduced iron and the inlet of the hot briquetting machine, and adding solid carbon-containing material and / or flux to the hot direct reduced iron discharged from the vertical furnace to produce a mixture of the discharged hot direct reduced iron and the solid carbon-containing material and / or flux before supplying it to the hot briquetting machine, thereby processing it in the hot briquetting machine to produce a hot briquetting iron product with an increased solid carbon-containing material content or an increased flux content greater than about 3 weight%; the carbon added by this technology is basically a mechanical mixture, and does not become dissolved carbon in the direct reduced iron; after mechanical mixing, it will float above the molten pool in the subsequent smelting process, and the carbon yield will be greatly affected.

[0005] From the above-mentioned existing technologies, the operability of the relevant technical solutions to the problem of the difficulty in melting reduced iron is relatively poor, and they have not fundamentally solved the problem of the difficulty in melting and provided specific solutions. In view of the above situation, it is urgent to develop a technology that can improve the melting efficiency of direct reduced iron in the electric furnace smelting process. Summary of the invention

[0006] In view of the defect of refractory melting of direct reduced iron in electric furnace smelting in the prior art, the present invention aims to provide a method for smelting direct reduced iron in an electric furnace, which can improve the melting efficiency of direct reduced iron and reduce electricity consumption cost.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] The present invention provides a method for smelting direct reduced iron in an electric furnace, comprising the following steps:

[0009] S1, using a vertical furnace to obtain direct reduced iron raw materials;

[0010] S2, a molten pool is first formed in the electric furnace;

[0011] S3, adding the direct reduced iron raw material and scrap steel into the electric furnace molten pool in batches for electric furnace smelting; in each feeding process, firstly adding the direct reduced iron raw material into the electric furnace molten pool, then adding the scrap steel to press the direct reduced iron into the molten pool, adding lime after the direct reduced iron is completely melted, and then continuing to add materials;

[0012] S4, after the melting of the molten pool in the electric furnace is completed, oxygen is blown to stir the molten pool and smelting continues until the carbon content of the molten steel reaches the standard.

[0013] Preferably, in step S1, the high-carbon content direct reduced iron raw material is obtained by grinding iron ore and then carbonizing it to obtain a shaft furnace raw material during vertical furnace production, and the shaft furnace raw material is pelletized and then put into the vertical furnace for gas-solid reaction to obtain the high-carbon content direct reduced iron raw material.

[0014] Preferably, the carbon content of the direct reduced iron raw material is 1.0-3.0 wt%.

[0015] Preferably, in step S2:

[0016] In the continuous electric furnace production process, 10-20wt% of the molten steel in the previous furnace is left in the furnace to form a molten pool; or

[0017] In the discontinuous electric furnace production process, scrap steel is put into the electric furnace, the amount of the scrap steel put in is 10-20wt% of the capacity of the electric furnace, and the scrap steel is melted by electrode heating to form a molten pool.

[0018] Preferably, in step S3, the direct reduced iron raw material is added into the electric furnace molten pool in 2 to 3 batches.

[0019] Preferably, in step S3, when the direct reduced iron is added to the electric furnace molten pool in three batches:

[0020] In the first batch, the input amount of the direct reduced iron raw material is 8-15wt% of the capacity of the electric furnace, and the input amount of the scrap steel is 8-15wt% of the capacity of the electric furnace;

[0021] In the second batch, the input amount of the direct reduced iron raw material is 15-22wt% of the capacity of the electric furnace, and the input amount of the scrap steel is 15-22wt% of the capacity of the electric furnace;

[0022] In the third batch, the input amount of the direct reduced iron raw material is 15-40wt% of the capacity of the electric furnace, and the input amount of the scrap steel is 15-40wt% of the capacity of the electric furnace.

[0023] Preferably, in the step S3, in each feeding process, the amount of lime added is 5-10% of the input amount of the direct-reduced iron raw material.

[0024] Preferably, in step S4, the flow rate of oxygen is 5000-9000 Nm 3 / h, the smelting temperature is 1590~1660℃.

[0025] Preferably, in step S4, the carbon content in the molten steel is 0.02-0.07wt%.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The method of smelting direct reduced iron in an electric furnace of the present invention can accelerate the melting speed of electric furnace smelting and reduce the electricity consumption cost, and is particularly suitable for the process of smelting high-quality steel products by using direct reduced iron on a large scale in an electric furnace;

[0028] 2. The method of smelting direct reduced iron in an electric furnace of the present invention can be widely used in the process of smelting high-quality steel in an electric furnace, and can smelt with high efficiency, thereby ensuring a high yield of direct reduced iron and a good purity of molten steel;

[0029] 3. The method for smelting direct reduced iron in an electric furnace of the present invention comprises the following steps: preparing high-carbon-content raw materials in a vertical furnace to obtain high-carbon-content direct reduced iron (i.e., high carbon content); forming a molten pool in an electric furnace (i.e., forming a molten pool by retaining steel or smelting part of scrap iron in an electric furnace); and adding direct reduced iron in batches (2 to 3 batches, the direct reduced iron can be added in 2 to 3 batches) into the molten pool, and then pressing the direct reduced iron in the molten pool with the aid of scrap steel for electric furnace smelting, thereby solving the problem of refractory direct reduced iron;

[0030] 4. The method of smelting direct reduced iron in an electric furnace of the present invention is suitable for promotion and use in the process of electric furnace smelting using scrap steel and direct reduced iron, and can solve the problem of slow melting during the electric furnace smelting process. DETAILED DESCRIPTION

[0031] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form.

[0032] In order to solve the problem of slow melting of direct reduced iron in the electric furnace smelting process, the present invention provides a method for smelting direct reduced iron in an electric furnace, which solves the problem of slow melting of direct reduced iron in an electric furnace smelting from two aspects: carbon content preparation technology of raw materials and charging technology of electric furnace molten pool, and specifically comprises the following steps:

[0033] S1, using a vertical furnace to obtain high carbon content direct reduced iron raw materials;

[0034] Specifically, the carbon content of the shaft furnace raw material is 1.0-3.5wt%, and the shaft furnace is used to obtain the direct reduced iron raw material with high carbon content; in the shaft furnace production process, the shaft furnace raw material for direct reduced iron is first produced, and the iron ore is ground and the carbon content is 1.0-3.5wt%, and then the shaft furnace raw material with a carbon content of 1.0-3.5wt% is pelletized and put into the shaft furnace, and the carbon component is retained due to the gas-solid reaction between the reducing gas and the ore. Only a small part of the carbon will undergo oxidation reaction, and most of the carbon does not participate in the reaction and is retained in the generated direct reduced iron, so a direct reduced iron raw material with a carbon content of 1.0-3.5wt% is obtained.

[0035] S2, forming a molten pool in the electric furnace first. This technical point can be viewed from two parts: in the continuous electric furnace production process, 10-20wt% of the molten steel in the previous furnace is left in the electric furnace to form a molten pool first; if it is discontinuous production, scrap steel is added to the electric furnace, the amount of scrap steel added is 10-20wt% of the electric furnace capacity, and it is melted by electrode heating to form a molten pool before the direct reduced iron raw material is added.

[0036] S3, adding the direct reduced iron raw materials into the electric furnace molten pool in batches for electric furnace smelting; in each charging process, the direct reduced iron raw materials are firstly charged into the electric furnace molten pool, and then the scrap steel is added to press the direct reduced iron into the molten pool, and after the direct reduced iron is completely melted, lime is added, and then the charging is continued;

[0037] The technical key points of this step are: adding materials in batches, with direct reduced iron at the bottom and scrap iron at the top each time. On the basis of the molten pool formed in the early stage of the electric furnace, the direct reduced iron raw materials are added to the electric furnace molten pool in batches for electric furnace smelting; in each charging process, the direct reduced iron raw materials are first put into the electric furnace, and then the scrap steel is pressed on the direct reduced iron raw materials, so that the direct reduced iron raw materials are pressed into the molten pool, and then the electrodes are heated to melt. Since the direct reduced iron is immersed in the molten pool, the internal gap of the direct reduced iron is soaked by molten steel, and the scrap steel above forms a current loop between the electrode and the molten pool below, which will quickly complete the melting of the direct reduced iron. After the melting is completed, lime is added and the next charging is continued. Among them, the direct reduced iron raw materials are added to the electric furnace molten pool in 2 to 3 batches; in each charging process, the amount of lime added is 5 to 10% of the amount of direct reduced iron raw materials input. When direct reduced iron is added to the electric furnace molten pool in three batches: in the first batch, the input amount of direct reduced iron raw material is 8-15wt% of the electric furnace capacity, and the input amount of scrap steel is 8-15wt% of the electric furnace capacity; in the second batch, the input amount of direct reduced iron raw material is 15-22wt% of the electric furnace capacity, and the input amount of scrap steel is 15-22wt% of the electric furnace capacity; in the third batch, the input amount of direct reduced iron raw material is 15-40wt% of the electric furnace capacity, and the input amount of scrap steel is 15-40wt% of the electric furnace capacity.

[0038] S4, after the melting of the molten pool in the electric furnace is completed, oxygen is blown to stir the molten pool and smelting continues until the carbon content of the molten steel reaches the standard.

[0039] Specifically, the technical key point of this step is to blow oxygen to stir the molten pool, wherein during the continued smelting process, the oxygen flow rate is 5000-9000Nm 3 / h, and the smelting temperature is 1590~1660℃. Due to the high carbon content in the front, the carbon-oxygen reaction in (1) and the carbon-FeO reaction in (2) are more fully carried out:

[0040] C+O=CO (1)

[0041] C+FeO=CO+Fe(2)

[0042] Due to the high carbon content, the FeO content in the molten pool can be quickly reduced, which improves the recovery rate of direct reduced iron. When the carbon content in the molten steel is 0.02-0.07wt%, deoxidation is required according to the type of steel, and then alloying is carried out to complete the smelting process.

[0043] A method for smelting direct reduced iron in an electric furnace is further introduced below with reference to specific examples.

[0044] Example 1

[0045] The method of smelting direct reduced iron in an electric furnace of this embodiment is implemented as follows according to the important steps of the technical description.

[0046] One day, in a 100-ton electric furnace, direct reduced iron was used to smelt plates. The operation steps are as follows:

[0047] (1) In a vertical furnace, the ore graphite powder is mixed with coal to 3.5%, and after being pelletized, it is put into the vertical furnace for gas-solid reaction to obtain a direct reduced iron raw material with a carbon content of 3.0 wt%.

[0048] (2) In a 100-ton electric furnace, retain 15% of the steel, leaving 15 tons of molten steel to form a molten pool first.

[0049] (3) First, add 15 tons of direct reduced iron raw material with a higher carbon content, and then add 15 tons of scrap steel on top of the added direct reduced iron to completely press the direct reduced iron into the molten pool.

[0050] (4) The electrodes are energized for smelting. After the molten pool is completely melted, 0.9 tons of lime is added at the same time.

[0051] (5) 15 tons of direct reduced iron raw material with a high carbon content is added, and 10 tons of scrap steel is added on top to completely press the direct reduced iron into the molten pool; after the molten pool is completely melted, 0.9 tons of lime is added at the same time.

[0052] (6) Add 20 tons of direct reduced iron raw material with a high carbon content, and add 10 tons of scrap steel on top to completely press the direct reduced iron into the molten pool. After the molten pool is completely melted, add 1.2 tons of lime at the same time.

[0053] (7) After the molten pool is melted, oxygen is blown to reduce carbon and increase temperature. The oxygen flow rate is 6000Nm 3 / h, the smelting temperature is 1570℃.

[0054] (8) After the carbon is in place (at this time, the carbon content in the molten steel is 0.04wt%), deoxidation is required depending on the type of steel, and then alloying is carried out to complete the smelting process.

[0055] Example 2

[0056] The method of smelting direct reduced iron in an electric furnace of this embodiment is implemented as follows according to the important steps of the technical description.

[0057] One day, in a 100-ton electric furnace, direct reduced iron was used to smelt plates. The operation steps are as follows:

[0058] (1) In a vertical furnace, the ore graphite powder is mixed with coal to 3.0%, pelletized and put into the vertical furnace for gas-solid reaction to obtain a direct reduced iron raw material with a carbon content of 2.5wt%.

[0059] (2) In a 100-ton electric furnace, 10% of the steel is retained, leaving 10 tons of molten steel.

[0060] (3) First add 10 tons of direct reduced iron raw material with a higher carbon content, and then add 10 tons of scrap steel on top of the added direct reduced iron to completely press the direct reduced iron into the molten pool.

[0061] (4) The electrodes are energized for smelting until the molten pool is completely melted. At the same time, 0.06 tons of lime is added.

[0062] (5) Add 20 tons of direct reduced iron raw material with a high carbon content, and add 15 tons of scrap steel on top to completely press the direct reduced iron into the molten pool. After the molten pool is completely melted, add 1.2 tons of lime at the same time.

[0063] (6) Add 20 tons of direct reduced iron raw material with a high carbon content, and add 15 tons of scrap steel on top to completely press the direct reduced iron into the molten pool. After the molten pool is completely melted, add 1.2 tons of lime at the same time.

[0064] (7) After the molten pool is completely melted, oxygen is blown to reduce carbon and increase the temperature. The oxygen flow rate is 6000 Nm3 / h and the smelting temperature is 1620°C.

[0065] (8) After the carbon is in place (at this time, the carbon content in the molten steel is 0.05wt%), deoxidation is required depending on the type of steel, and then alloying is carried out to complete the smelting process.

[0066] Example 3

[0067] The method of smelting direct reduced iron in an electric furnace of this embodiment is implemented as follows according to the important steps of the technical description.

[0068] One day, in a 100-ton electric furnace, direct reduced iron was used to smelt plates. The operation steps are as follows:

[0069] (1) In a vertical furnace, the ore graphite powder is mixed with coal to 3.0%, pelletized and put into the vertical furnace for gas-solid reaction to obtain a direct reduced iron raw material with a carbon content of 2 wt%.

[0070] (2) In a 100-ton electric furnace, 12% of the steel is retained, leaving 12 tons of molten steel.

[0071] (3) First add 8 tons of direct reduced iron raw material with a higher carbon content, and then add 8 tons of scrap steel on top of the added direct reduced iron to completely press the direct reduced iron into the molten pool.

[0072] (4) The electrodes are energized for smelting until the molten pool is completely melted. At the same time, 0.025 tons of lime are added.

[0073] (5) Add 22 tons of direct reduced iron raw material with a high carbon content, and add 20 tons of scrap steel on top to completely press the direct reduced iron into the molten pool. After the molten pool is completely melted, add 1.5 tons of lime at the same time.

[0074] (6) Add 30 tons of direct reduced iron raw material with a high carbon content, and add 15 tons of scrap steel on top to completely press the direct reduced iron into the molten pool. After the molten pool is completely melted, add 1.8 tons of lime at the same time.

[0075] (7) After the molten pool is completely melted, oxygen is blown to reduce carbon and increase the temperature. The oxygen flow rate is 6000 Nm3 / h and the smelting temperature is 1650°C.

[0076] (8) After the carbon is in place (at this time, the carbon content in the molten steel is 0.07wt%), deoxidation is required depending on the type of steel, and then alloying is carried out to complete the smelting process.

[0077] In summary, the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for smelting direct reduced iron in an electric furnace, characterized in that: The following steps are involved: S1, using a vertical furnace to obtain direct reduced iron raw materials; S2, a molten pool is first formed in the electric furnace; S3, adding the direct reduced iron raw material and scrap steel into the electric furnace molten pool in batches for electric furnace smelting; in each feeding process, firstly put the direct reduced iron raw material into the electric furnace molten pool, then put the scrap steel into the molten pool to press the direct reduced iron into the molten pool, and then add lime after the direct reduced iron is completely melted, and then continue the next feeding; S4, after the melting of the molten pool in the electric furnace is completed, oxygen is blown to stir the molten pool and smelting continues until the carbon content of the molten steel reaches the standard.

2. The method for smelting direct reduced iron in an electric furnace according to claim 1, characterized in that: In step S1, the method for obtaining the high-carbon content direct reduced iron raw material is: during vertical furnace production, the iron ore is ground and carbonized to obtain vertical furnace raw material, and the vertical furnace raw material is pelletized and then put into the vertical furnace for gas-solid reaction to obtain the high-carbon content direct reduced iron raw material.

3. The method for smelting direct reduced iron in an electric furnace according to claim 1 or 2, characterized in that: The carbon content of the direct reduced iron raw material is 1.0-3.0 wt%.

4. The method for smelting direct reduced iron in an electric furnace according to claim 1, characterized in that: In step S2: In the continuous electric furnace production process, 10-20wt% of the molten steel in the previous furnace is left in the furnace to form a molten pool; or In the discontinuous electric furnace production process, scrap steel is put into the electric furnace, the amount of the scrap steel put in is 10-20wt% of the capacity of the electric furnace, and the scrap steel is melted by electrode heating to form a molten pool.

5. The method for smelting direct reduced iron in an electric furnace according to claim 1, characterized in that: In the step S3, the direct reduced iron raw material is added into the electric furnace molten pool in 2 to 3 batches.

6. The method for smelting direct reduced iron in an electric furnace according to claim 5, characterized in that: In step S3, when the direct reduced iron is added to the electric furnace molten pool in three batches: In the first batch, the input amount of the direct reduced iron raw material is 8-15wt% of the capacity of the electric furnace, and the input amount of the scrap steel is 8-15wt% of the capacity of the electric furnace; In the second batch, the input amount of the direct reduced iron raw material is 15-22wt% of the capacity of the electric furnace, and the input amount of the scrap steel is 15-22wt% of the capacity of the electric furnace; In the third batch, the input amount of the direct reduced iron raw material is 15-40wt% of the capacity of the electric furnace, and the input amount of the scrap steel is 15-40wt% of the capacity of the electric furnace.

7. The method for smelting direct reduced iron in an electric furnace according to claim 1, characterized in that: In the step S3, during each feeding process, the amount of lime added is 6% of the input amount of the direct-reduced iron raw material.

8. The method for smelting direct reduced iron in an electric furnace according to claim 1, characterized in that: In step S4, the flow rate of oxygen is 5000-9000 Nm 3 / h, the smelting temperature is 1590~1660℃.

9. The method for smelting direct reduced iron in an electric furnace according to claim 1, characterized in that: In the step S4, the carbon content in the molten steel is 0.02-0.07wt%.