A method for increasing the scrap steel ratio of converter using hydrothermal carbon

Abstract

The invention relates to a method for improving the scrap steel ratio of a converter by using hydrothermal carbon. The method comprises the following steps: adding a binder to specific hydrothermal carbon powder to make balls, clamping the balls between two batches of scrap steel and adding the balls into a converter, and then adding molten iron to carry out specific converter smelting. The method realizes the smelting of a converter with a large scrap steel ratio by using hydrothermal carbon, greatly improving the scrap steel ratio, and not adding harmful elements to the molten steel.

Description

Technical Field

[0001] The invention relates to the field of industrial environmental protection, and in particular to a method for increasing the scrap steel ratio of a converter by using hydrothermal charcoal. Background Art

[0002] In my country, the annual industrial energy consumption of the steel industry accounts for about 16% of the total national industrial energy consumption. 2 Emissions also account for about 15% of the country's total industrial carbon emissions. Increasing the proportion of scrap steel in the converter smelting process is not only a resource reuse of scrap steel itself, but also can reduce the overall carbon emissions of steel mills.

[0003] There are many methods for increasing the scrap ratio in the prior art, but the existing methods such as molten iron insulation and scrap preheating have an upper limit on the increase of the scrap ratio of the converter. If the scrap ratio of the converter is to be further increased, it is necessary to add a heat supplement to the converter. The heat supplement used in the converter is divided into two categories: metal heat supplement and carbon heat supplement. Metal heat supplements include ferrosilicon alloys and aluminum, which use the oxidation heat of Si and Al to increase the converter temperature. However, due to the SiO generated after the oxidation of Si and Al, the converter temperature is increased. 2 and Al 2 O 3 To reduce the basicity of the slag, CaO is needed to adjust the basicity of the slag to prevent the dephosphorization and desulfurization capabilities of the slag from decreasing and reduce the rate of lining erosion, thereby increasing the amount of slag in the converter and resulting in a decrease in the recovery rate of iron and manganese. Carbon-based heat supplements include gaseous or liquid hydrocarbons, such as natural gas, heavy oil and diesel, as well as solid ones such as carbide, coke, anthracite and graphite. The products of carbon-based heat supplements are mainly CO and CO 2 Gas can improve the dynamic conditions of the molten pool to a certain extent, and there is no problem of increasing the amount of slag. At present, there is an industrial practice of adding coal or coke in converter smelting, but the sulfur content of coal and coke is high, and 40-50% of the sulfur in the heat supplement will remain in the molten steel, increasing the cost of subsequent desulfurization and affecting the quality of steel.

[0004] In a subcritical water environment at medium pressure and temperature, biomass undergoes a series of complex chemical reactions such as hydrolysis, dehydration, decarboxylation, and polycondensation to form hydrothermal char similar to coal. This is the process of biomass hydrothermal carbonization. At present, biomass hydrothermal carbonization technology has gradually been industrialized from the experimental research stage. It has been used for harmless treatment of sludge in China, and there are also demonstration projects for industrial continuous production abroad. However, whether the carbon-based heat supplement can be fully burned and heat-transferred in the converter is the key to its heat supplement effect. The way to add biomass hydrothermal charcoal to the converter and the supporting process operation still need further research and exploration.

[0005] Chinese invention patent publication CN110904299A discloses a method for using a carbon-based heating agent to supplement heat in a converter, which uses a heating agent to supplement heat in a converter, thereby reducing electrodes and power consumption in a refining furnace, thereby relatively reducing costs. However, the carbon-based heating agent is obtained by configuration, which increases costs, and the component content is not perfect. Summary of the invention

[0006] Aiming at the shortcomings of high sulfur content and limited addition amount of traditional converter carbon-based heat supplement agents mainly composed of coke and coal, the present invention proposes a method for increasing the scrap steel ratio of the converter by using hydrothermal carbon.

[0007] The specific implementation is through the following technical solutions:

[0008] A method for increasing the scrap steel ratio of a converter using hydrothermal carbon comprises the following steps:

[0009] (1) Hydrothermal carbon particle molding: 97-98.5 parts by weight of hydrothermal carbon powder and 1.5-3 parts by weight of a binder are added to a mixer and mixed for 15-30 minutes to obtain a hydrothermal carbon particle mixture; the water content of the hydrothermal carbon powder is 20-33wt%; the obtained hydrothermal carbon particle mixture is then added to an extruder to form strips with a diameter of 7-15 mm, which are then sheared into particles of 20-40 mm to obtain wet hydrothermal carbon particles; the obtained wet hydrothermal carbon particles are then placed in a drying device for drying at a drying temperature of 180-240° C. to obtain hydrothermal carbon particles with a moisture content of less than 1%.

[0010] (2) Material preparation: 150-250 kg / ton of steel scrap, 750-850 kg / ton of steel molten iron, and 6-30 kg / ton of steel hydrothermal carbon particles prepared in step (1) are prepared.

[0011] (3) Smelting preparation: Use an oxygen top-blown converter. After the steel is tapped and the slag splashing operation is completed, close the tapping port.

[0012] (4) Adding materials: adding 45-55wt% of the total amount of scrap steel, then adding all the hydrothermal carbon particles, and then adding the remaining scrap steel, and then adding the molten iron prepared in step (2) into the top-blown converter, the temperature of the molten iron being 1280-1400°C, and then shaking the converter back and forth to completely bury the hydrothermal carbon particles in the scrap steel, and then straightening the converter body.

[0013] (5) Blowing: Lower the oxygen lance to the blowing position for blowing.

[0014] (6) Charging: 1 to 3 minutes after the start of blowing, charging is carried out, specifically, lime: 12 to 13 kg / ton of molten iron, light-burned dolomite: 12 to 13 kg / ton of molten iron, and iron oxide scale: 4.5 to 5.5 kg / ton of molten iron.

[0015] (7) Enhanced stirring: 1.5 to 2.5 minutes after adding the materials, the oxygen lance is lowered to 15 to 35 cm below the blowing position, and oxygen is used to enhance the stirring of the melt.

[0016] (8) Adding materials during blowing: Continue blowing for 4 to 6 minutes, add the remaining materials in batches during blowing, and then raise the top oxygen lance to the blowing position.

[0017] (9) Evenly dissolving molten steel in the later stage of blowing: After the addition of material in step (8) is completed, the blowing process begins in the later stage. At this time, the oxygen lance is kept in the blowing position. After 4 to 6 minutes, the oxygen lance is lowered to 25 to 45 cm below the blowing position, and the blowing process is continued for 2 to 3 minutes.

[0018] (10) Steel tapping: Raise the oxygen lance, stop blowing oxygen, and tap the steel in the furnace. The tapping temperature is 1650-1700°C. During the tapping process, ferroalloy is added to the ladle for deoxidation and alloying. Slag is left in the converter and nitrogen is sprayed to splash the slag to protect the furnace.

[0019] Preferably, in step (8), the adding of the remaining materials comprises: adding 4.5-5.5 kg / ton of molten iron scale to the top-blown converter, continuing blowing for 1-2 min, and then adding 4.5-5.5 kg / ton of molten iron scale to the top-blown converter; then adding 12-13 kg / ton of molten iron lime; then adding 4.5-5.5 kg / ton of molten iron scale after an interval of 0.5-1.5 min; then adding 4.5-5.5 kg / ton of molten iron scale after an interval of 0.5-2 min; and then adding 9.5-10.5 kg / ton of molten iron lime after an interval of 0.2-0.8 min.

[0020] Preferably, the molten iron has a carbon content of 3.5-4.5wt%, a silicon content of 0.3-0.6wt%, a manganese content of 0.2-0.6wt%, a phosphorus content of ≤0.2%, and a sulfur content of ≤0.05%.

[0021] Preferably, the hydrothermal carbon powder in step (1) has a particle size of 0.1-0.8 mm, a moisture content of 20-30 wt%, an ash content of ≤5 wt%, a sulfur content of ≤0.2 wt%, a carbon content of 60-75 wt% on a dry ash-free basis, a sulfur content of ≤0.2 wt%, Na+K ≤0.1 wt%, and a low calorific value of 23-26 MJ / kg on a dry basis.

[0022] Preferably, the hydrothermal carbon particles obtained in step (1) have a particle size of 15 to 38 mm, an ash content of 2.5 to 5.5 wt%, a carbon content of 60 to 75 wt% on a dry ash-free basis, a sulfur content of ≤0.2 wt%, Na+K ≤0.1 wt%, and a lower calorific value of 23 to 26 MJ / kg on a dry basis.

[0023] Preferably, the mixer is a wheel-type mixer, the extruder is a screw extruder granulator, and the drying device is a rotary kiln.

[0024] Preferably, the binder in step (1) is one or more organic binders selected from the group consisting of coal tar, phenolic resin, modified starch and syrup.

[0025] Preferably, the total amount of iron oxide scale added is 2.3-2.7 wt % of the total mass of molten iron.

[0026] Preferably, the hydrothermal carbon powder is prepared by the following steps:

[0027] 1) The biomass raw material is crushed by a crushing device until the maximum particle size of the biomass is 26 to 33 mm, and then the crushed biomass particles are transported to a stirring device, water is added for stirring, and a biomass raw material slurry with a moisture content of 70 to 85 wt% is obtained by stirring.

[0028] 2) The biomass raw material slurry obtained in step 1) is discharged into a preheating tube and pressurized to 2.1-4 MPa, and a heating liquid is flowed outside the preheating tube to preheat the biomass raw material slurry in the preheating tube to 55-200°C.

[0029] 3) Add the pressurized and preheated biomass raw material slurry in step 2) to the hydrothermal reactor of the hydrothermal reaction device, control the temperature in the hydrothermal reactor to 200-250°C, the reaction pressure to 2.9-4.5MPa, and maintain the water content of the slurry in the hydrothermal reactor to 80-90wt%, the hydrothermal carbonization reaction time to 2-5h, and obtain a high-temperature hydrothermal carbon slurry with a temperature of 220-250°C.

[0030] 4) The high-temperature hydrothermal carbon slurry obtained in step 3) is discharged into the preheating tube of step 2) as a heating liquid to preheat the biomass raw material slurry in the preheating tube, and then the hydrothermal carbon slurry is depressurized and crushed to 0.1-0.8 mm, and hydrothermal carbon powder is obtained after flotation and filter pressing.

[0031] Preferably, in step 2), the preheating tube is a double-layer structure, the inner layer is for biomass raw material slurry to pass through, and the outer layer is for high-temperature hydrothermal carbon slurry obtained in step 4) as heating liquid to pass through, and the flow directions of the inner and outer layers are opposite.

[0032] The technical effects of the present invention are:

[0033] (1) The present invention uses biomass hydrothermal carbon powder that is bonded and then pelletized as a heat supplement for the converter. Since the hydrothermal carbon powder obtained by this treatment method has a high carbon content, high calorific value, and low content of harmful elements such as ash, sulfur, sodium, and potassium, the biomass hydrothermal carbon can be added to the converter for steelmaking, which can greatly increase the amount of scrap steel added and will not bring harmful elements to the converter smelting. For every 1 kg of hydrothermal carbon particles added, the amount of scrap steel added can be increased by 4 to 6 kg / t. In addition, the biomass hydrothermal carbon is carbon neutral and will not increase the carbon emissions of the converter.

[0034] (2) The hydrothermal carbon particles of the present invention are directly granulated with hydrothermal carbon powder with a moisture content of 30% after filter pressing and dehydration as raw material, and the hydrothermal carbon cake prepared by a specific method is directly used as the granulation raw material, which simplifies the conventional granulation process of "powder drying→water granulation→granule drying", reduces energy consumption and the amount of dust in the drying process, and when added to the converter, the particle size meets the specific addition method of the present invention.

[0035] (5) The present invention adopts the method of burying the hydrothermal carbon particles directly in the scrap steel in the converter, and starts to supply heat from the beginning of blowing when the molten pool temperature is the lowest, so that the thermal efficiency is high, the carbon loss is small, and the transcription smelting with a larger scrap steel ratio can be achieved. If the hydrothermal carbon particles are added by sinking them into the molten iron under load, although a shorter converter smelting cycle can be obtained, the increase in scrap steel is limited. The present invention can significantly increase the increase in scrap steel by adding the hydrothermal carbon particles between the two additions of scrap steel. DETAILED DESCRIPTION

[0036] Example 1

[0037] This embodiment is an embodiment of using hydrothermal carbon particles as a supplementary heat agent to achieve a large proportion of scrap steel smelting in a converter. Garden prunings are used as raw materials and are processed through crushing, pulping, preheating, hydrothermal carbonization, refining, dehydration and other steps to produce biomass hydrothermal carbon powder. Its component analysis and calorific value are shown in Table 1:

[0038] Table 1

[0039]

[0040] The hydrothermal carbon powder and the modified starch binder were added to a wheel mixer at a mass ratio of 100:1.5 and mixed for 15 to 30 minutes to obtain a mixture of hydrothermal carbon particles. The obtained mixture was added to a screw extruder granulator to form a long strip with a diameter of 10 mm, and then sheared into 30 mm particles. The wet particles were then added to a rotary kiln for drying at a drying temperature of 180 to 240 ° C to obtain composite hydrothermal carbon particles with a moisture content of less than 1%. The composition analysis and calorific value are shown in Table 2:

[0041] Table 2

[0042]

[0043] First, add 6 tons of scrap steel into a top-bottom double-blown converter with a nominal volume of 50 tons, then add 1.2 tons of hydrothermal carbon particles, and then add 6 tons of scrap steel. Slightly shake the converter back and forth to bury the hydrothermal carbon particles in the scrap steel, then add 38 tons of molten iron (the scrap steel ratio is 31.6% at this time), and blow oxygen to start smelting. The scrap steel meets the standard of "GB / T4223-2017 Scrap Steel", and the composition and temperature of the molten iron are shown in Table 3:

[0044] Table 3

[0045] C (wt%) Si (wt%) Mn (wt%) P (wt%) S (wt%) Temperature(℃) Example 1 Molten Iron 4.33 0.40 0.30 0.097 0.043 1300

[0046] After the loading of scrap steel and molten iron is completed, the converter is straightened, the height of the oxygen lance is lowered from 1.8m to 1.4m, oxygen is sprayed and ignited, and blowing begins.

[0047] The position of the oxygen lance during the blowing process is: 0-3min at 1.4min, 3-8 at 1.2m, 8-13min at 1.4m, and 13-15min at 1.1m.

[0048] The time and amount of material addition during the blowing process are: add 500kg of lime, 500kg of light-burned dolomite, and 200kg of iron oxide in 1.3min; add 200kg of iron oxide in 3min; add 200kg of iron oxide in 4.5min; add 500kg of lime in 5min; add 200kg of iron oxide in 6min; add 200kg of iron oxide in 7.5min; add 400kg of lime in 8min.

[0049] Under this condition, the smelting cycle of the converter is 31 minutes, and the tapping temperature is about 1680°C. The earlier the heat supplement is added, the higher the thermal efficiency. In this embodiment, the hydrothermal carbon and scrap steel are added at the same time, and the heat supply starts when the oxygen lance is blown. At this time, the molten pool temperature is the lowest and the hydrothermal carbon heating efficiency is the highest. In addition, the hydrothermal carbon particles and scrap steel are immersed in the molten pool together, and the hydrothermal carbon will not be wrapped by materials such as lime, dolomite and iron oxide, and the proportion of hydrothermal carbon participating in the heating is higher.

[0050] Example 2

[0051] This example illustrates the preparation process of hydrothermal carbon powder in Example 1.

[0052] 1) The biomass raw material is crushed by a crushing device until the maximum particle size of the biomass is 30 mm, and then the crushed biomass particles are transported to a stirring device, water is added for stirring, and a biomass raw material slurry with a water content of 80 wt% is obtained by stirring.

[0053] 2) The biomass raw material slurry obtained in step 1) is discharged into a preheating tube and pressurized to 3 MPa, and a heating liquid is flowed outside the preheating tube to preheat the biomass raw material slurry in the preheating tube to 125°C.

[0054] 3) Add the pressurized and preheated biomass raw material slurry in step 2) to the hydrothermal reactor of the hydrothermal reaction device, control the temperature in the hydrothermal reactor to 240°C, the reaction pressure to 4.0 MPa, and maintain the water content of the slurry in the hydrothermal reactor to 85wt%, the hydrothermal carbonization reaction time to 3h, and obtain a high-temperature hydrothermal carbon slurry with a temperature of 240°C.

[0055] 4) The high-temperature hydrothermal carbon slurry obtained in step 3) is discharged into the preheating tube of step 2) as a heating liquid to preheat the biomass raw material slurry in the preheating tube, and then the hydrothermal carbon slurry is depressurized and crushed to 0.5 mm, and hydrothermal carbon powder is obtained after flotation and filter pressing.

[0056] Comparative Example 1

[0057] This comparative example is a conventional converter smelting example without using a supplementary heat agent. The difference from Example 1 is that the amount of scrap steel added is 6 tons, the amount of molten iron added is 44 tons (the scrap steel ratio is 13.64%), and the other settings are the same as Example 1. The converter smelting cycle under this condition is about 27 minutes, and the tapping temperature is about 1690°

[0058] C. The carbon, phosphorus and sulfur elements in the molten steel all meet the requirements.

[0059] Comparative Example 2

[0060] This comparative example is a converter smelting example using a large scrap ratio without using a supplementary heat agent. The difference from Example 1 is that 12t of scrap steel is added first, and then 38t of molten iron is added. No hydrothermal carbon particles are added. The other settings are the same as Example 1. Under this working condition, the average smelting cycle of the converter is about 33min, and the tapping temperature is lower than 1600℃. Compared with Comparative Example 1, when the amount of scrap steel increases and the amount of molten iron decreases, if no supplementary heat agent is added, the overall heat input of the converter smelting is reduced due to the reduction of physical heat brought into the molten iron and oxidation heat of carbon, sulfur, manganese, etc. in the molten iron. In addition, the amount of scrap steel that absorbs heat increases, resulting in slower melting of scrap steel, longer smelting cycle, and too low terminal temperature of molten steel, which is not conducive to later casting. The effects of dephosphorization and decarburization are also poor, and the carbon and phosphorus content of molten steel is high, affecting the quality of steel products.

[0061] Comparative Example 3

[0062] This comparative example is an example of using coal as a heat supplement for converter smelting. The other settings are the same as those in Example 1. The difference from Example 1 is that the hydrothermal carbon particles are replaced with 200 kg of iron oxide scale and 800 kg of coal. The coal particle size is 6 to 25 mm, and the component analysis and calorific value are shown in Table 4:

[0063] Table 4

[0064]

[0065] Under this condition, the average smelting cycle of the converter is 28 minutes, and the tapping temperature is about 1680°C. Compared with Example 1, although the calorific value of coal is slightly higher than that of hydrothermal coal, the ash content is also higher, and the slag amount of the converter is slightly increased, so the tapping temperature is not much different. However, due to the high sulfur content in the coal powder, part of the sulfur remains in the molten steel, causing the sulfur content of the molten steel to increase from about 0.019% in Example 1 to about 0.027% in Comparative Example 3, affecting the quality of the molten steel.

[0066] Comparative Example 4

[0067] This comparative example is an example of using hydrothermal carbon powder as a heat supplement and adding it directly. The difference from Example 1 is that hydrothermal carbon powder with a moisture content of less than 1% after drying is not added between the two batches of scrap steel. The average smelting cycle of the converter under this condition is 35 minutes, and the tapping temperature is about 1620°C. Due to the low density and small particles of hydrothermal carbon powder, it will float on the surface of the molten pool. During blowing, a large amount of hydrothermal carbon powder is carried away by the airflow and is not burned in the molten pool for heat supply, resulting in a longer smelting cycle and a lower tapping temperature.

[0068] Comparative Example 5

[0069] This comparative example is an example of adding hydrothermal carbon particles to the converter before adding scrap steel. The difference from Example 1 is that the hydrothermal carbon particles are added first, and then the scrap steel and molten iron are added. Since the lining temperature is high after the slag splashing furnace protection, the hydrothermal carbon particles will directly smoke and burn after being added to the converter, causing safety accidents.

[0070] Comparative Example 6

[0071] This comparative example is an example in which hydrothermal carbon particles are added to the converter after scrap steel. The difference from Example 1 is that all the scrap steel is added first, then the hydrothermal carbon particles are added, and finally the molten iron is added. The average smelting cycle of the converter under this condition is 33 minutes, and the tapping temperature is about 1650°C. Since the hydrothermal carbon particles have a low density, they will float on the surface of the molten iron in large quantities. The high-temperature CO generated during blowing is directly discharged above the molten pool, and the heating efficiency of the hydrothermal carbon particles is low, the smelting cycle is extended, and the tapping temperature is reduced. In Example 1, the hydrothermal carbon particles are buried in the scrap steel, and the high-temperature CO generated can fully heat the molten pool during the rising process in the molten pool, and the hydrothermal carbon particles have a high heat supplement efficiency.

[0072] Comparative Example 7

[0073] This comparative example is an example of adding hydrothermal carbon particles to the converter along with lime, dolomite and other furnace materials. The difference from Example 1 is that all scrap steel and molten iron are added first, and the hydrothermal carbon particles are added to the converter along with the first batch of lime, light-burned dolomite and iron oxide scale 1.3 minutes after the start of blowing. The average smelting cycle of the converter under this condition is 31 minutes, and the tapping temperature is about 1650°C. Although this comparative example simplifies the charging method and shortens the charging time compared with Example 1, this charging method also has the problems of low density of hydrothermal carbon particles, easy floating on the surface of the molten pool, and reduced thermal efficiency, and the tapping temperature of this comparative example is low.

Claims

1. A method for increasing the scrap ratio of converter using hydrothermal carbon, characterized in that: The steps include: (1) Hydrochar particle molding: 97-98.5 parts by weight of hydrochar powder and 1.5-3 parts by weight of a binder are added to a mixer and mixed for 15-30 minutes to obtain a hydrochar particle mixture; the water content of the hydrochar powder is 20-33wt%; the obtained hydrochar particle mixture is then added to an extruder to form strips with a diameter of 7-15 mm, which are then sheared into particles of 20-40 mm to obtain wet hydrochar particles; the obtained wet hydrochar particles are then placed in a drying device for drying at a drying temperature of 180-240°C to obtain hydrochar particles with a moisture content of less than 1%; (2) Material preparation: 150-250 kg / ton of steel scrap, 750-850 kg / ton of steel molten iron, and 6-30 kg / ton of steel hydrothermal carbon particles prepared in step (1); (3) Smelting preparation: Use an oxygen top-blown converter, close the tapping port after the steel is tapped and the slag splashing operation is completed; (4) Adding materials: adding 45-55 wt% of the total amount of scrap steel, then adding all the hydrothermal carbon particles, and then adding the remaining scrap steel, and then adding the molten iron prepared in step (2) into the top-blown converter, the temperature of the molten iron being 1280-1400° C., and then shaking the converter back and forth to completely bury the hydrothermal carbon particles in the scrap steel, and then shaking the converter body straight; (5) Blowing: Lower the oxygen lance to the blowing position for blowing; (6) Charging: 1 to 3 minutes after the start of blowing, charging is carried out, specifically, lime: 12 to 13 kg / ton of molten iron, light-burned dolomite: 12 to 13 kg / ton of molten iron, and iron oxide scale: 4.5 to 5.5 kg / ton of molten iron; (7) Enhanced stirring: 1.5 to 2.5 minutes after adding the material, lower the oxygen lance to 15 to 35 cm below the blowing position, and use oxygen to enhance the stirring of the melt; (8) Adding materials during blowing: Continue blowing for 4 to 6 minutes, add the remaining materials in batches during blowing, and then raise the top-blown oxygen lance to the blowing position; the specific addition of the remaining materials is as follows: add 4.5 to 5.5 kg of iron oxide per ton of molten iron into the top-blown converter, continue blowing for 1 to 2 minutes, and then add 4.5 to 5.5 kg of iron oxide per ton of molten iron into the top-blown converter; then add 12 to 13 kg of lime per ton of molten iron; then add 4.5 to 5.5 kg of iron oxide per ton of molten iron after an interval of 0.5 to 1.5 minutes; then add 4.5 to 5.5 kg of iron oxide per ton of molten iron after an interval of 0.5 to 2 minutes; then add 9.5 to 10.5 kg of lime per ton of molten iron after an interval of 0.2 to 0.8 minutes; (9) Evenly dissolving the molten steel in the late stage of blowing: After the addition of material in step (8) is completed, the late stage of blowing begins. At this time, the oxygen lance is kept in the blowing position. After 4 to 6 minutes, the oxygen lance is lowered to 25 to 45 cm below the blowing position and the blowing is continued for 2 to 3 minutes. (10) Steel tapping: Raise the oxygen lance, stop blowing oxygen, and tap the steel in the furnace. The tapping temperature is 1650~1700℃. During the tapping process, ferroalloy is added to the ladle for deoxidation and alloying. Slag is left in the converter and nitrogen is sprayed to splash the slag to protect the furnace.

2. The method for increasing the scrap steel ratio of converter using hydrothermal carbon according to claim 1, characterized in that: The molten iron has a carbon content of 3.5-4.5wt%, a silicon content of 0.3-0.6wt%, a manganese content of 0.2-0.6wt%, a phosphorus content of ≤0.2%, and a sulfur content of ≤0.05%.

3. The method for increasing the scrap steel ratio of converter using hydrothermal carbon according to claim 1, characterized in that: The hydrothermal carbon powder in step (1) has a particle size of 0.1-0.8 mm, a moisture content of 20-30 wt%, an ash content of ≤5 wt%, a sulfur content of ≤0.2 wt%, a carbon content of 60-75 wt% on a dry ash-free basis, a sulfur content of ≤0.2 wt%, Na+K ≤0.1 wt%, and a low calorific value of 23-26 MJ / kg on a dry basis.

4. The method for increasing the scrap ratio of converter using hydrothermal carbon according to claim 1, characterized in that: The hydrothermal carbon particles obtained in step (1) have a particle size of 15-38 mm, an ash content of 2.5-5.5 wt %, a carbon content of 60-75 wt % on a dry ash-free basis, a sulfur content of ≤0.2 wt %, Na+K ≤0.1 wt %, and a low calorific value of 23-26 MJ / kg on a dry basis.

5. The method for increasing the scrap ratio of converter using hydrothermal carbon according to claim 1, characterized in that: The mixer is a wheel-rolling mixer, the extruder is a screw extruder granulator, and the drying device is a rotary kiln.

6. The method for increasing the scrap ratio of converter using hydrothermal carbon according to claim 1, characterized in that: The binder in step (1) is one or more organic binders selected from the group consisting of coal tar, phenolic resin, modified starch and syrup.

7. The method for increasing the scrap ratio of converter using hydrothermal carbon according to claim 1, characterized in that: The total amount of iron oxide scale added is 2.3~2.7wt% of the total mass of molten iron.

8. The method for increasing the scrap ratio of converter using hydrothermal carbon according to claim 1, characterized in that: The hydrothermal carbon powder is prepared by the following steps: 1) The biomass raw material is crushed by a crushing device until the maximum particle size of the biomass is 33 mm, and then the crushed biomass particles are transported to a stirring device, and water is added for stirring to obtain a biomass raw material slurry with a moisture content of 70-85wt%; 2) The biomass raw material slurry obtained in step 1) is discharged into a preheating tube and pressurized to 2.1-4 MPa, and a heating liquid is flowed outside the preheating tube to preheat the biomass raw material slurry in the preheating tube to 55-200° C.; 3) Add the pressurized and preheated biomass raw material slurry in step 2) to the hydrothermal reactor of the hydrothermal reaction device, control the temperature in the hydrothermal reactor to 200-250°C, the reaction pressure to 2.9-4.5MPa, and maintain the water content of the slurry in the hydrothermal reactor to 80-90wt%, the hydrothermal carbonization reaction time to 2-5h, and obtain a high-temperature hydrothermal carbon slurry with a temperature of 220-250°C; 4) The high-temperature hydrothermal carbon slurry obtained in step 3) is discharged into the preheating tube of step 2) as a heating liquid to preheat the biomass raw material slurry in the preheating tube, and then the hydrothermal carbon slurry is depressurized and crushed to 0.1-0.8 mm, and hydrothermal carbon powder is obtained after flotation and filter pressing.

9. The method for increasing the scrap ratio of converter using hydrothermal carbon according to claim 8, characterized in that: In step 2), the preheating tube is a double-layer structure, the inner layer is for biomass raw material slurry to pass through, and the outer layer is for high-temperature hydrothermal carbon slurry obtained in step 4) as heating liquid to pass through, and the inner and outer layers flow in opposite directions.

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