Low-carbon-dioxide-emission high-density carbon spheres for steelmaking and preparation method thereof

Abstract

The invention discloses a low-carbon-dioxide-emission high-density carbon sphere for steelmaking and a preparation method thereof. The carbon sphere comprises the following chemical components in percentage by mass: 3-10% of oxide, 35-50% of C, 40-50% of Fe, 1-5% of St, and the balance of Fe. 0.1%, Plt; the water content is 0.03%, and the moisture content is 1t; 1%, 3-6% of an adhesive, and the balance of unavoidable impurities. The high-density carbon balls can suspend on a steel slag interface, the recarburization efficiency of the carbon balls to molten steel can be greatly improved, energy needed for steelmaking is ensured, the molten steel is stirred, denitrification is promoted, the steelmaking process gets rid of dependence on molten iron or pig iron raw materials with high carbon emission in the production process, and the overall reduction of carbon dioxide emission in the steelmaking process is achieved.

Description

Technical Field

[0001] The invention relates to a carbon-containing pellet for steelmaking and a preparation method thereof, and in particular to a high-density carbon pellet for low carbon dioxide emission steelmaking and a preparation method thereof. Background Art

[0002] At present, the steel metallurgical production mainly adopts the blast furnace-converter long process with iron ore as the main raw material and the electric furnace short process with scrap steel as the main raw material. In recent years, with the proposal of the "dual carbon" development goal, the steel industry is moving towards a green and low-carbon emission trend. The carbon emission of blast furnace production of molten iron reaches 1.7tCO2 / t 铁 , then reducing the proportion of molten iron (or pig iron) raw materials used in the steelmaking process can significantly reduce the carbon emissions of the entire manufacturing process. For example, the carbon emissions of electric furnaces using all scrap steel smelting or using direct reduced iron smelting are only 1 / 3 of the blast furnace-converter long process. Theoretical calculations show that the CO2 emissions of the steelmaking process caused by the addition of external carbon to the steelmaking process is 8% of the total CO2 emissions of the same amount of carbon in the molten iron or pig iron strip in the steelmaking process plus the CO2 emissions of the molten iron or pig iron preparation process. Therefore, the replacement of molten iron carbon or pig iron carbon by external carbon in the steelmaking process can significantly reduce the CO2 emissions of the entire manufacturing process.

[0003] However, in order to reduce carbon dioxide emissions in the steelmaking process, in the case of using less or no molten iron or pig iron as raw materials, in order to stir the molten pool and speed up steelmaking efficiency, necessary oxygen blowing and related chemical energy release are indispensable. This requires a certain amount of carbon to be added to the steelmaking process to ensure that CO or CO2 bubbles are generated during the oxygen blowing process to release chemical energy to increase the temperature of the molten steel, stir the molten pool and remove nitrogen. The common method of adding carbon to the electric furnace is to add electrodes, coke blocks or spray carbon powder to the raw materials, but because the density of carbon block raw materials is relatively light, less than 1g / cm 3 During the smelting process, most of the carbon will float on the slag surface and react with the air to burn. The actual amount of carbon added to the molten steel to react with the blown oxygen is relatively small, and the carbon addition efficiency is less than 30%. As a result, it is difficult for the carbon combustion release capacity to enter the molten steel pool. It is also difficult to ensure that the carbon powder enters the molten steel by spraying carbon powder. The above carbon addition method is difficult to achieve actual metallurgical effects. Carbon addition in converter smelting is even more difficult. People have tried to spray powder from the bottom of the converter for high carbon injection, but because the carbon powder causes great wear on the injection tuyere, there are safety risks in spraying carbon powder from the bottom.

[0004] Chinese patent 200510134295.2 provides a composite carbon-containing pellet, the chemical composition (wt%) of the composite carbon-containing pellet is: 40-80% carbon-containing material, 10-42% metal oxide, 5-30% rare earth oxide, 2-10% binder, 1-5% reinforcing agent, 1-5% expander, and 1-4% steel processing chips. The composite carbon-containing pellet of the invention has high strength, and the compressive strength of a single sphere reaches more than 5Mpa, so that it will not break during transportation, storage and use, and maintain the inherent properties of the pellet. The strength of the carbon ball is improved by adding metal raw materials and rare earth oxides to ensure the carbon matching effect. However, the preparation cost of this method is relatively high. At the same time, due to the high oxide content (including metal oxides and rare earth oxides), these oxides are useless for steelmaking. The steelmaking process also consumes a lot of energy to melt these oxides. Because the oxides are difficult to melt, the amount of carbon in the carbon ball entering the molten steel is relatively small, and the reaction of carbon with these metal oxides is generally an endothermic reaction, so the carbon matching cannot release energy to heat the molten steel to meet the normal metallurgical process. Chinese Patent 200510117645.4 provides a method and device for manufacturing composite carbon-containing pellets. The carbon-containing pellets prepared by the method have a high density of 3.0 g / cm 3 The above has a large pressure-bearing strength, and a single sphere can withstand a pressure of more than 5 MPa. It is particularly suitable for metallurgical by-raw materials used as a carburizer in electric furnace steelmaking. However, the preparation process of this method is complicated, resulting in a high cost of the prepared carbon balls. Summary of the invention

[0005] The purpose of the present invention is to provide a high-density carbon ball for low-carbon dioxide emission steelmaking and a preparation method thereof. The high-density carbon ball can be suspended at the interface of steel slag, which can greatly improve the efficiency of carbon addition to molten steel by the carbon ball, ensure the energy required for steelmaking, stir the molten steel and promote denitrification, so that the steelmaking process is free from dependence on molten iron or pig iron raw materials with high carbon emissions in the production process, and achieve an overall reduction in carbon dioxide emissions in the steelmaking process.

[0006] In order to achieve the above technical objectives, the present invention adopts the following technical solutions: A high-density carbon ball for low carbon dioxide emission steelmaking, wherein the chemical composition of the carbon ball is as follows by mass percentage: oxide: 3-10%, C: 35-50%, Fe: 40-50%, S<0.1%, P<0.03%, moisture<1%, adhesive: 3-6%, and the rest are unavoidable impurities.

[0007] The oxide is any one of CaO, SiO2, Al2O3, FeO, and Fe2O3, or the sum of any two or more thereof.

[0008] The adhesive comprises sodium silicate, dry powder of papermaking waste liquid and cement clinker.

[0009] The adhesive comprises: 20-25% sodium silicate, 30-40% dry powder of papermaking waste liquid, and 40-50% cement clinker.

[0010] The carbon ball density is 2.5-3.5 g / cm 3 .

[0011] The compressive strength of a single carbon sphere is above 10 MPa.

[0012] A method for preparing high-density carbon balls for steelmaking with low carbon dioxide emissions, the steps of which are: Step 1: crush the scrap iron powder, carbonaceous materials and oxides and use them as materials for future use; Step 2: Stir and mix the material and the binder in a ratio, wherein the material ratio is: scrap iron powder 42-52%, carbonaceous material: 37-50%, oxide: 1-7%, and binder: 3-6%; Step 3: Add appropriate amount of water, stir and cold press into a flat ball shape to make a flat ball-shaped material; Step 4: transport the oblate spherical material to a heating furnace, heat and dry it at 100-200°C for 20-40 hours to form carbon balls; Step 5: Cool the carbon balls to obtain carbon ball products.

[0013] The particle size of the scrap iron powder, carbonaceous materials and oxides in step 1 is less than 0.2 mm.

[0014] The carbon-containing material is one or both of earthy graphite powder and blue carbon powder.

[0015] The high-density carbon balls for low carbon dioxide emission steelmaking of the present invention comprehensively consider the carbon ball density and carbon increase efficiency, thereby determining the range of carbon content and iron content. The setting of the carbon ball density must ensure that the carbon balls sink below the slag surface after being added to the steelmaking molten pool and contact with the molten steel, and it is necessary to consider that there are inevitably gaps inside the carbon balls during the pressing process. After comprehensive consideration, the high-density carbon balls of the present invention are finally set to have a C content of 35-50% and an Fe content of 40-50%, thereby satisfying the carbon ball density of 2.5-3.5g / cm after production. 3 The density of the carbon balls just meets the requirement that the carbon balls sink to the slag interface. If the density of the carbon balls is higher, more iron will be added to the carbon balls, and the carbon content will inevitably be lower. On the contrary, if the density of the carbon balls is lower, it will be difficult for the carbon balls to sink.

[0016] The oxide content of the high-density carbon sphere of the present invention is set mainly considering that the carbon sphere processing process may contain a small amount of oxides or inevitably contain oxides, and the oxides are any one or the sum of any two or more of CaO, SiO2, Al2O3, FeO, and Fe2O3. A small amount of oxides is beneficial to the pressing and bonding of carbon spheres, but the content of this part of oxides cannot be too high, and the oxide content is within 10% after comprehensive consideration.

[0017] The requirements for the S and P contents in the high-density carbon spheres of the present invention are mainly to ensure that the carbon spheres do not excessively pollute the molten steel during the steelmaking application process and increase the dephosphorization and desulfurization loads of the molten steel.

[0018] The main components of the high-density carbon balls of the present invention are iron and carbon. When the carbon balls are suspended at the interface of steel slag, the interface of the carbon balls in contact with the molten steel can be effectively melted, while the interface of the carbon balls in contact with the slag melts slowly because the melting rate of iron in the slag is low. The design concept of the carbon balls of the present invention ensures that the carbon balls can effectively add carbon to the molten steel after melting, thereby improving the carbon increase efficiency. Even if the carbon in the carbon balls reacts with the slag FeOx to generate CO2, the energy released can be effectively attracted by the molten steel and plays a key role in maintaining the foam slag in the slag, which is more easily absorbed by the molten steel than the energy released by the sprayed carbon powder reacting only on the slag surface.

[0019] The high-density carbon balls of the present invention also include a binder, which is sodium silicate, papermaking waste liquid dry powder, and cement clinker. Sodium silicate is selected because of its strong water-soluble ability, which is beneficial to improving the bonding uniformity of powdered materials. Papermaking waste liquid dry powder is selected because it has a certain bonding ability to carbon powder and metallic iron. Cement clinker is selected because it can quickly improve the strength of high-density carbon balls during the drying process.

[0020] The high-density carbon balls of the present invention can be suspended at the interface of steel slag. The use of the carbon balls can greatly improve the efficiency of carbon addition to molten steel, and the carbon addition efficiency of ordinary carbon balls is increased from less than 30% to 60% or more, thereby ensuring normal oxygen blowing in steelmaking, releasing required energy, stirring molten steel and promoting denitrification, so that the steelmaking process is freed from dependence on molten iron or pig iron raw materials with high carbon emissions in the production process, and achieving an overall reduction in carbon dioxide emissions in the steelmaking process.

[0021] The method for preparing high-density carbon balls for low carbon dioxide emission steelmaking of the present invention comprises the following steps: mixing powdered scrap iron, carbon-containing materials, oxides and a binder in a uniform ratio, adding a proper amount of water, stirring, cold pressing into an oblate ball shape, and then transporting the mixture to a heating furnace, heating and drying at 100-200° C. for 20-40 hours to form carbon balls.

[0022] The material ratio of the high-density carbon ball preparation method of the present invention is: 42-52% scrap iron powder, 37-50% carbonaceous material, 1-7% oxide, and 3-6% adhesive. The carbonaceous material is one or two of earthy graphite powder and blue charcoal powder. The particle size of the scrap iron powder, the carbonaceous material and the oxide is less than 0.2 mm, which is convenient for stirring and mixing evenly. The main component of the scrap iron powder is iron, and the main component of the earthy graphite powder is carbon, which has good quality. The oxide is mainly configured with a small amount of iron oxide powder and lime powder, and the scrap iron powder and the carbonaceous material contain inevitable oxides. If the high-density carbon ball of the present invention is used in electric furnace smelting of ordinary construction steel, the molten steel has low requirements for sulfur, phosphorus and nitrogen content. For cost considerations, cheap carbonaceous materials such as blue charcoal powder can be selected. The material ratio of the high-density carbon ball of the present invention is mainly selected to meet the final carbon ball composition: oxide: 3-10%, C: 35-50%, Fe: 40-50%, S<0.1%, P<0.03%, moisture<1%, adhesive: 3-6%.

[0023] The test shows that the high-density carbon ball prepared by the preparation method of the present invention has a compressive strength of more than 10 MPa for a single ball, and the carbon ball does not break when dropped from a height of 5 meters, and does not break when a single ball presses a 50 kg weight. The prepared carbon ball is an oblate spherical shape with a diameter of 3 to 5 cm and a thickness of 2 to 4 cm.

[0024] Compared with the prior art, the high-density carbon spheres of the present invention have the following beneficial effects: 1) The carbon emissions from the steelmaking process can be reduced from the current 2tCO2 / t steel to 0.7t CO2 / t steel or below, thereby reducing CO2 emissions from the steelmaking process.

[0025] 2) For electric furnace applications, the high-density carbon balls of the present invention can reduce power consumption and shorten the smelting cycle. After the electric furnace is added with the carbon balls of the present invention, the smelting chemical energy can be improved and the foam slag can be better maintained. Adding 1% of the carbon balls of the present invention to steel raw materials can reduce power consumption by 30-40 KWh / t. When power consumption is relatively expensive, the addition of the carbon balls has the advantage of reducing costs.

[0026] For converter applications, the high-density carbon balls of the present invention can increase the scrap steel ratio of the converter. Adding 1% of the carbon balls of the present invention to steel raw materials can increase the scrap steel ratio by 3%. When scrap steel is relatively cheap, the use of the carbon balls of the present invention can reduce the cost of converter smelting.

[0027] The carbon balls can also meet the requirements of low-nitrogen steel smelting, achieving a nitrogen content of less than 30ppm in steel produced by an electric furnace. Implementation

[0028] The present invention will be further described below in conjunction with specific embodiments. Example

[0029] The high-density carbon balls used for electric furnace steelmaking have the following main chemical components: CaO: 1%, SiO2: 1%, Al2O3: 1%, FeO+Fe2O3: 3%, C: 42%, Fe: 48%, S<0.05%, P<0.025%, moisture<1% and adhesive: 4%. The high-density carbon balls of the present invention are made by mixing 50% scrap iron powder with a particle size less than 0.2mm, 44% earthy graphite powder and 2% oxide, and 4% adhesive. The adhesive is synthesized with sodium silicate, papermaking waste liquid dry powder and cement clinker, wherein the adhesive contains 20% sodium silicate, 30% papermaking waste liquid dry powder and 50% cement clinker. After adding appropriate amount of water and stirring, it is cold pressed into shape, and then dried to improve the strength of the carbon balls. The drying temperature is 200℃, the drying time is 20 hours, and the drying is completed and then air-dried. After testing, it is found that the density of the carbon balls is 2.8g / cm 3 , compressive strength 12MPa, shape is oblate spherical, diameter 4cm, thickness 2.5cm.

[0030] The carbon balls of the present invention are used in the 150t traditional electric furnace using all scrap steel smelting process, wherein 25 tons of molten steel are retained at the beginning of smelting, 3.5 tons of carbon balls of the present invention are added together with the scrap steel charge during smelting, added to the lower middle part of the basket, then powered on and oxygen blown for smelting, when slag is formed in the middle of smelting, 1.5 tons of carbon balls of the present invention are added from the silo, which can be added in three batches, 0.5 tons per batch, with an interval of 2 minutes, and other operations of the electric furnace are carried out in the existing normal way. After the molten steel is melted, the carbon content of the molten steel is measured to be 0.35%, and the carbon balance calculation shows that the carbon distribution efficiency is 80%, oxygen blowing and power on are continued, and finally qualified molten steel is smelted, and the oxygen consumption of the electric furnace is 30Nm 3 / t, the power consumption is reduced from 460KWh / t of conventional smelting of all scrap steel with ordinary carbon powder to 350KWh / t, the T.Fe content of slag is 18%, and under the condition that the electricity is green electricity, the CO2 emissions per ton of steel smelted by the electric furnace are 112 kgCO2 / t steel, which is close to the carbon neutrality level. Compared with the traditional electric furnace that uses scrap steel + pig iron or scrap steel + molten iron as raw materials and also uses green electricity, the carbon emissions are about 650 kgCO2 / t steel, which has been greatly reduced. Example

[0031] The high-density carbon balls used for electric furnace steelmaking have the following main chemical components: CaO: 1%, SiO2: 1%, Al2O3: 1%, FeO+Fe2O3: 4%, C: 47%, Fe: 40%, S<0.05%, P<0.025%, moisture<1% and adhesive: 5%. The high-density carbon balls of the present invention are made by mixing 42% scrap iron powder with a particle size less than 0.2mm, 50% earthy graphite powder and 3% oxide, and 5% adhesive. The adhesive is synthesized with sodium silicate, papermaking waste liquid dry powder and cement clinker. The adhesive contains 25% sodium silicate, 30% papermaking waste liquid dry powder and 45% cement clinker. After adding appropriate amount of water and stirring, it is cold pressed into shape, and then dried to improve the strength of the carbon balls. The drying temperature is 150°C, the drying time is 30 hours, and the carbon balls are dried after drying. After testing, it is found that the density of the carbon balls is 2.5g / cm 3 , compressive strength 15MPa, shape is oblate spherical, diameter 3cm, thickness 2cm.

[0032] The carbon balls of the present invention are used in a 150t continuous charging electric furnace using all scrap steel smelting process, wherein 45 tons of molten steel are retained at the beginning of smelting, and 1.5 tons of the carbon balls of the present invention are added from the silo in advance after the start of smelting, and then the preheating channel is opened to enter the scrap steel silo door, and the scrap steel immediately falls into the electric furnace smelting pool, and then power is turned on and oxygen is blown for smelting. After the slag is formed in the early stage of smelting, 3.2 tons of the carbon balls of the present invention are added from the silo, which can be divided into four batches, with 0.8 tons added in each batch, and an interval of 1.5 minutes. Other operations of the electric furnace are carried out in a normal manner. After the molten steel was melted, the carbon content of the molten steel was measured to be 0.41%. After carbon balance calculation, the carbon efficiency was 75%. Continuous oxygen blowing and power supply were used to finally smelt qualified molten steel. The oxygen consumption of the electric furnace was 32Nm3 / t, and the power consumption was reduced from 430KWh / t of conventional all-scrap steel and ordinary carbon powder smelting to 300KWh / t. The T.Fe content of the slag was 16%, and the nitrogen content was 35ppm. Under the condition that the electricity is green electricity, the CO2 emissions per ton of steel smelted by the electric furnace were 128 kgCO2 / t steel, which is close to the carbon neutrality level. Compared with the traditional electric furnace that uses scrap steel + pig iron or scrap steel + molten iron as raw materials and also uses green electricity, the carbon emissions of about 650 kgCO2 / t steel have been greatly reduced. Example

[0033] The high-density carbon balls used in electric furnace steelmaking have the following main chemical components: CaO: 0.5%, SiO2: 1%, Al2O3: 0.5%, FeO+Fe2O3: 1%, C: 49%, Fe: 41%, S<0.05%, P<0.025%, moisture<1% and adhesive: 6%. The high-density carbon balls of the present invention are made by mixing 42% scrap iron powder with a particle size less than 0.2mm, 50% earthy graphite powder and 2% oxide, and 6% adhesive. The adhesive is synthesized with sodium silicate, papermaking waste liquid dry powder and cement clinker, wherein the adhesive contains 20% sodium silicate, 40% papermaking waste liquid dry powder and 40% cement clinker. After adding appropriate amount of water and stirring, cold pressing is performed, and then drying is performed to improve the strength of the carbon balls. The drying temperature is 120℃, the drying time is 40 hours, and the carbon balls are dried after drying. After testing, it is found that the density of the carbon balls is 2.7g / cm 3 , compressive strength 13MPa, shape is oblate spherical, diameter 3cm, thickness 2cm.

[0034] The carbon balls of the present invention are used in a 150t continuous charging electric furnace using scrap steel and direct reduced iron (the proportion of direct reduced iron reduced by natural gas is 30%) for smelting, wherein 40 tons of molten steel are retained at the beginning of smelting, 2 tons of the carbon balls of the present invention are added from the silo in advance after the smelting starts, and then the preheating channel is opened to enter the scrap steel silo door, and the scrap steel immediately falls into the electric furnace smelting pool, and then power is turned on and oxygen is blown for smelting. 5 minutes after the start of blowing, direct reduced iron is continuously added from a special feeding channel, and when the slag is formed in the early stage of smelting, the carbon balls of the present invention are added from the silo in four times. common 3.2 tons, 0.8 tons are added in each batch, with an interval of 1.5 minutes, and other operations of the electric furnace are carried out in a normal manner. After the molten steel is melted, the carbon content of the molten steel is measured to be 0.27%, and the carbon balance calculation shows that the carbon efficiency is 76%. Continuous oxygen blowing and power supply are applied, and finally qualified molten steel is smelted. The oxygen consumption of the electric furnace is 25Nm 3 / t, the power consumption is reduced from 450KWh / t of conventional all-scrap steel smelting with ordinary carbon powder to 320KWh / t, the T.Fe content of the slag is 22%, the nitrogen content is 25ppm, and under the condition that the electricity is green electricity, the CO2 emission of this smelting electric furnace per ton of steel is 478 kgCO2 / t steel, which is significantly lower than the carbon emission of about 650 kgCO2 / t steel of traditional electric furnaces that use scrap steel + pig iron or scrap steel + molten iron as raw materials and also use green electricity. Example

[0035] The high-density carbon balls used in electric furnace steelmaking have the following main chemical components: CaO: 1%, SiO2: 3%, Al2O3: 1%, FeO+Fe2O3: 4%, C: 35%, Fe: 50%, S<0.05%, P<0.025%, moisture<1% and adhesive: 5%. The high-density carbon balls of the present invention are made by mixing 52% scrap iron powder with a particle size less than 0.2mm, 38% earthy graphite powder and 5% oxide, and 5% adhesive. The adhesive is synthesized with sodium silicate, papermaking waste liquid dry powder and cement clinker, wherein the adhesive contains 22% sodium silicate, 30% papermaking waste liquid dry powder and 48% cement clinker. After adding appropriate amount of water and stirring, it is cold pressed into shape, and then dried to improve the strength of the carbon balls. The drying temperature is 180℃, the drying time is 24 hours, and the carbon balls are dried after drying. After testing, it is found that the density of the carbon balls is 3.5g / cm 3 , compressive strength 20MPa, shape is oblate spherical, diameter 5cm, thickness 3cm.

[0036] The carbon balls of the present invention are used in a 150t continuous charging electric furnace using all scrap steel smelting process. The steel produced is high-carbon bearing steel with a carbon content of about 1%. At the beginning of smelting, 35 tons of molten steel are retained. After the start of smelting, 2 tons of the carbon balls of the present invention are added from the silo in advance, and then the preheating channel is opened to enter the scrap steel silo door. The scrap steel then falls into the smelting pool of the electric furnace, and then the power is turned on and oxygen is blown for smelting. After the slag is formed in the early stage of smelting, a total of 2.0 tons of the carbon balls of the present invention are added from the silo. It can be added in two batches, 1 ton is added in each batch, with an interval of 2 minutes, and other operations of the electric furnace are carried out in a normal manner. After the molten steel is melted, the carbon content of the molten steel is measured to be 0.2%. The carbon balance calculation shows that the carbon distribution efficiency is 90%, and oxygen blowing and power are continued. 1.5 tons of the carbon balls of the present invention are added again, which can be added in three times, 0.5 tons each time, with an interval of 4 minutes. When the temperature of the molten steel reaches the steel-making requirement of 1610°C, qualified molten steel is finally smelted, and the oxygen consumption of the electric furnace is 28Nm 3 / t, the power consumption is reduced from 400KWh / t of conventional scrap steel smelting with ordinary carbon powder to 310KWh / t, the T.Fe content of the slag is 14%, and the carbon content is 0.52%. Under the condition that the electricity is green electricity, the CO2 emissions per ton of steel smelted by the electric furnace are 148 kgCO2 / t steel, which is close to the carbon neutrality level. Compared with the traditional electric furnace that uses scrap steel + pig iron or scrap steel + molten iron as raw materials and also uses green electricity, the carbon emissions are about 650 kgCO2 / t steel, which has been greatly reduced. Example

[0037] The high-density carbon balls used for electric furnace steelmaking have the following main chemical components: CaO: 2%, SiO2: 1%, Al2O3: 1%, FeO+Fe2O3: 3%, C: 36%, Fe: 50%, S<0.1%, P<0.03%, moisture<1% and adhesive: 5%. The high-density carbon balls of the present invention are made by mixing 52% scrap iron powder with a particle size less than 0.2mm, 38% blue carbon powder and 4% oxides, and 6% adhesive. The adhesive is synthesized with sodium silicate, papermaking waste liquid dry powder and cement clinker, wherein the adhesive contains 22% sodium silicate, 30% papermaking waste liquid dry powder and 48% cement clinker. After adding appropriate amount of water and stirring, they are cold pressed into shape, and then dried to improve the strength of the carbon balls. The drying temperature is 180°C, the drying time is 24 hours, and the carbon balls are air-dried after drying. After testing, it is found that the density of the carbon balls is 3.0g / cm 3 , compressive strength 20MPa, shape is oblate spherical, diameter 4.5cm, thickness 3cm.

[0038] The carbon balls of the present invention are used in a 150t continuous charging electric furnace using all scrap steel smelting process. The steel produced is ordinary rebar with a carbon content of about 0.2%. The sulfur content and phosphorus content of the molten steel are required to be low. At the beginning of smelting, 35 tons of molten steel are kept. After smelting starts, 2 tons of the carbon balls of the present invention are added from the silo in advance. Then, the preheating channel is opened to enter the scrap steel silo door. The scrap steel then falls into the smelting pool of the electric furnace. Then, power is turned on and oxygen is blown for smelting. After the slag is formed in the early stage of smelting, a total of 2.2 tons of the carbon balls of the present invention are added from the silo. They can be added in two batches, with 1.1 tons added in each batch, at an interval of 2 minutes. Other operations of the electric furnace are carried out in a normal manner. After the molten steel is melted, the carbon content of the molten steel is measured to be 0.2%. The carbon balance calculates the carbon efficiency to be 68%. Oxygen blowing and power on are continued. 0.9 tons of carbon balls of the present invention are added again, which can be added three times, 0.3 tons each time, with an interval of 4 minutes. When the molten steel temperature reaches 1610°C required for steel production, qualified molten steel is finally smelted, and the oxygen consumption of the electric furnace is 28Nm 3 / t, the power consumption is reduced from 410KWh / t of conventional scrap steel smelting with ordinary carbon powder to 320KWh / t, the T.Fe content of the slag is 14%, and the carbon content is 0.21%. Under the condition that the electricity is green electricity, the CO2 emissions per ton of steel smelted by the electric furnace are 195kgCO2 / t steel, which is close to the carbon neutrality level. Compared with the traditional electric furnace that uses scrap steel + pig iron or scrap steel + molten iron as raw materials and also uses green electricity, the carbon emissions are about 650 kgCO2 / t steel, which has been greatly reduced. Example

[0039] The main chemical components of high-density carbon balls for converter steelmaking are: CaO: 1%, SiO2: 1%, Al2O3: 1%, FeO+Fe2O3: 6%, C: 38%, Fe: 50%, S<0.05%, P<0.025%, moisture<1% and adhesive: 3%. The high-density carbon balls of the present invention are made by mixing 52% scrap iron powder with a particle size less than 0.2mm, 40% earthy graphite powder and 5% oxide, and 3% adhesive. The adhesive is synthesized with sodium silicate, papermaking waste liquid dry powder and cement clinker, wherein the adhesive contains 25% sodium silicate, 30% papermaking waste liquid dry powder and 45% cement clinker. After adding appropriate amount of water and stirring, it is cold pressed into shape, and then dried to improve the strength of the carbon balls. The drying temperature is 200℃, the drying time is 20 hours, and the drying is completed and then air-dried. After testing, it is found that the density of the carbon balls is 3g / cm 3 , compressive strength 11MPa, shape is oblate spherical, diameter 5cm, thickness 4cm.

[0040] The 300t converter started smelting, including the total addition ratio of scrap steel raw materials such as the preheating of the molten iron ladle, from the conventional 10% to 20% to 45%. After 6 minutes of converter blowing, 30t of the carbon balls of the present invention were added in six batches, with a time interval of 1.5 minutes. Then, normal oxygen blowing and decarburization smelting were carried out. The carbon balls released a large amount of energy by reacting with oxygen to melt the scrap steel and increase the temperature of the molten steel. Finally, the converter smelting oxygen consumption was 58Nm 3 / t, slag T.Fe 25%, carbon balance calculation shows that the carbon efficiency is nearly 100%. Compared with conventional smelting, the carbon emission of converter smelting is reduced by nearly 500kgCO 2 / t, and under the condition that scrap steel is relatively cheap, the production cost of the converter is greatly reduced.

[0041] Embodiments 1 to 5 of the present invention are applied in electric furnaces. After adding the carbon balls of the present invention, the carbon addition efficiency reaches more than 65%. If the carbon balls of the present invention are applied on a large scale, the carbon emission of the steelmaking process can be reduced from about 650kgCO2 / t in the current electric furnace process (adding part of the molten iron or pig iron smelting) to 500t CO2 / t steel or less (carbon emission calculated based on green electricity), thereby reducing CO2 emissions in the steelmaking process.

[0042] Example 6 is a converter application. After adding the carbon balls of the present invention, the carbonization efficiency reaches more than 95%. Compared with conventional smelting, the carbon emission of converter smelting is reduced by nearly 500kgCO 2 / t, thereby reducing CO2 emissions in the steelmaking process.

[0043] In terms of economic benefits: Examples 1 to 5 are applied in electric furnaces. The high-density carbon balls of the present invention can reduce power consumption and shorten the smelting cycle. After the carbon balls of the present invention are added to the electric furnace, the smelting chemical energy can be improved and the foam slag can be better maintained. Adding 1% of the carbon balls of the present invention to the steel raw materials can reduce power consumption by 30-40 KWh / t. In the case of expensive power consumption, the addition of the carbon balls has the advantage of reducing costs. At the same time, the corresponding power-on time will also be reduced due to the reduction in power consumption, thereby shortening the smelting cycle and improving production efficiency, and better meeting the requirements of high production rhythm of continuous casting.

[0044] Example 6 is a converter application. The high-density carbon balls of the present invention can increase the scrap steel ratio of the converter. Adding 1% of the carbon balls of the present invention to the steel raw materials can increase the scrap steel ratio by 3%. When scrap steel is relatively cheap, the use of the carbon balls of the present invention can reduce the cost of converter smelting.

[0045] The carbon balls of the present invention can also meet the smelting requirements of low-nitrogen steel (corresponding to Example 3), achieving a nitrogen content of steel tapped from an electric furnace of less than 30 ppm.

Claims

1. A high-density carbon ball for low carbon dioxide emission steelmaking, characterized by: The chemical composition of the carbon sphere is as follows by mass percentage: oxide: 3-10%, C: 35-50%, Fe: 40-50%, S<0.1%, P<0.03%, moisture<1%, adhesive: 3-6%, and the rest are unavoidable impurities.

2. The high-density carbon spheres for low carbon dioxide emission steelmaking according to claim 1 are characterized by: The oxide is any one of CaO, SiO2, Al2O3, FeO, and Fe2O3, or the sum of any two or more thereof.

3. The high-density carbon spheres for low carbon dioxide emission steelmaking according to claim 1 are characterized by: The adhesive comprises sodium silicate, dry powder of papermaking waste liquid and cement clinker.

4. The high-density carbon spheres for low carbon dioxide emission steelmaking according to claim 3 are characterized by: The adhesive comprises: 20-25% sodium silicate, 30-40% dry powder of papermaking waste liquid, and 40-50% cement clinker.

5. The high-density carbon spheres for low carbon dioxide emission steelmaking according to claim 1 are characterized by: The carbon ball density is 2.5-3.5 g / cm 3 .

6. The high-density carbon spheres for low carbon dioxide emission steelmaking according to claim 1 are characterized by: The compressive strength of a single carbon sphere is above 10 MPa.

7. A method for preparing high-density carbon balls for steelmaking with low carbon dioxide emissions, characterized by: Step 1: crush the scrap iron powder, carbonaceous materials and oxides and use them as materials for future use; Step 2: Stir and mix the material and the binder in a ratio, wherein the material ratio is: scrap iron powder 42-52%, carbonaceous material: 37-50%, oxide: 1-7%, and binder: 3-6%; Step 3: Add appropriate amount of water, stir and cold press into a flat ball shape to make a flat ball-shaped material; Step 4: transport the oblate spherical material to a heating furnace, heat and dry it at 100-200°C for 20-40 hours to form carbon balls; Step 5: Cool the carbon balls to obtain carbon ball products.

8. The method for preparing high-density carbon balls for low carbon dioxide emission steelmaking according to claim 7 is characterized by: The particle size of the scrap iron powder, carbonaceous materials and oxides in step 1 is less than 0.2 mm.

9. The method for preparing high-density carbon balls for low carbon dioxide emission steelmaking according to claim 7 is characterized by: The carbon-containing material is one or both of earthy graphite powder and blue carbon powder.