Pretreated full-steel-scrap low-carbon electric arc furnace steelmaking foaming carburant and application thereof

Abstract

The invention belongs to the field of solid waste recovery, and particularly relates to a pretreated full-steel-scrap low-carbon electric arc furnace steelmaking foaming carburant and application thereof. In order to avoid the phenomena of adhesion and pipeline blockage caused by melting of the waste plastics or the waste tires, the interaction between the iron oxide and the waste plastics or the waste tires is utilized, and a mixture of the waste plastics or the waste tires and the iron oxide is heated and pretreated within the temperature range of 300-500 DEG C; the heating speed is 5-100 DEG C / min, and the heat preservation time is 0-120 minutes, specifically depending on the pretreatment temperature. In the temperature range, carbon chains of the waste plastics or the waste tires are not broken, part of H elements on the carbon chains react with ferric oxide to generate H2O, finally, the waste plastics or the waste tires lose viscosity due to partial carbonization, and it is guaranteed that the injection process is conducted smoothly. And then spraying into the steelmaking slag of an electric arc furnace at 1500-1600 DEG C, releasing a gas product to blister the slag, and reducing iron oxide into carbon saturated metal iron to recarburize the molten steel.

Description

Technical Field

[0001] The invention belongs to the field of solid waste recycling, and in particular relates to a pretreated all-scrap low-carbon electric arc furnace steelmaking foaming recarburizer and application thereof. Background Art

[0002] Compared with the long-process steelmaking process of blast furnace-converter, the short-process electric arc furnace steelmaking process using scrap steel as raw material has the advantages of low energy consumption and flexible operation, and is one of the important measures for the steel industry to reduce carbon emissions. However, when using all scrap steel for electric arc furnace steelmaking, due to the extremely low carbon content in the raw materials, in order to achieve operations such as stable arc and impurity removal, it is necessary to spray foam slag foaming agent and recarburizer. The current routine operation is to add lime and spray coke / coal powder, which has high carbon emissions.

[0003] Waste plastics are mainly composed of H and C elements, both of which can be oxidized to produce gaseous products. Tires are made of natural rubber / synthetic rubber, carbon black, steel wire and sulfur. Similar to plastics, the main elements of rubber are C and H. At present, there are a lot of waste plastics and waste tires that cannot be recycled. In 2019, the domestic emission of waste plastics was nearly 40 million tons, and currently only about 50% can be recycled. Waste plastics and waste tires are secondary resource treasures that need to be developed. As an alternative carbon source for electric arc furnace steelmaking, they have great potential, and the gaseous products produced by their decomposition enter the slag, which helps to form stable foam slag.

[0004] Plastics and rubber have low melting points and high viscosity after melting, so waste plastics and tires need to be mixed with high melting point substances before spraying to prevent clogging of the spray gun. A simpler approach is to replace part of the coke / coal powder with waste plastics or waste tires and mix them with the mixture and then spray them into the electric arc furnace, as shown in patents CN102216473A and CN106350635B. However, coke / coal powder is a fossil carbon resource, which is not conducive to carbon neutralization. In order to increase the amount of gas generated, oxygen-enriched operation is also required (CN106350635B).

[0005] Patent CN115478127A proposes to spray waste plastics / waste tires with biomass into an electric arc furnace, abandoning the use of coke / coal powder, and the effect is good. Biomass is a zero-carbon resource, which is conducive to reducing carbon in electric arc furnace steelmaking. However, due to the high water content of biomass, a large amount of energy needs to be invested, and the low density of biomass is not conducive to mixing into slag.

[0006] Iron oxide is abundant in reserves and is one of the main raw materials for the steel industry. It has a high melting point (Fe2O3: 1565℃, Fe3O4: 1595℃, FeO: 1369℃) and a specific gravity greater than 5g / cm 3 (The specific gravity of coke / coal powder is about 1.7g / cm 3), it is easy to mix into slag and molten steel, stays there for a long time and reduces the melting point of slag, and reacts with the cracking products of waste plastics and waste tires during the heating process and under high temperature conditions to generate gaseous products H2O and CO / CO2, which are beneficial to the stability of foamed slag; and the carbon-saturated metallic iron generated afterwards enters the molten steel, which increases the carbon content of the molten steel while improving the metal yield of the steelmaking process, thereby achieving the dual goals of stable formation of foamed slag and carbon increase of molten steel.

[0007] US Patent US5554207 uses plastic as a binder and reducing agent to recover metal resources from industrial secondary resources such as electric furnace dust, and has achieved good results. The typical operation is to mix 1 part of plastic with 5 parts of dust (the plastic content in the mixture is 16.7%), and use the plastic to bind the dust and extrude it into pellets at a temperature range of 300-500°F, that is, 150-260°C, and use it as a steelmaking raw material to recover the metal components. In this temperature range, the plastic is in a molten state but has not yet begun to decompose. It is mainly used as a binder for dust. Therefore, the amount of plastic added is small to ensure that the pellets will not cause pipeline blockage due to the melting of the plastic components, and cannot be used as a foaming agent and recarburizer in the steelmaking process.

[0008] Patent CN117587192A mixes waste tire rubber powder with used magnesium carbon bricks, blast furnace dust and limestone powder, adds water and stirs, uses a binder to granulate, and uses it as an arc furnace slag foaming agent after drying, with good results. However, the waste tire rubber powder has not been carbonized before spraying, and it needs to be bonded by an external binder and water, and then sprayed into the arc furnace after granulation, drying and other processes. The evaporation of water will increase energy consumption, and the magnesium oxide in the magnesium carbon brick will increase the melting point of the slag. Summary of the invention

[0009] In order to solve the above-mentioned technical problems, this application provides the following technical solutions:

[0010] The present invention provides a pre-treated all-scrap steel low-carbon electric arc furnace steelmaking foaming and recarburizing agent, comprising solid waste and a substance containing iron oxide; the solid waste is selected from one or both of waste plastics and waste tires. The catalytic effect of iron oxide is utilized to pre-treat and remove part of the hydrogen element at a temperature lower than the cracking temperature of the solid waste, so that the solid waste is partially carbonized and the blowing performance is improved.

[0011] Preferably, the substance containing iron oxide includes one or more of hematite powder, magnetite powder and other substances containing iron oxide.

[0012] Preferably, the waste plastics include one or more of chlorine-free waste plastics and polyhydrocarbons obtained by dechlorination of chlorine-containing waste plastics by iron oxide.

[0013] Furthermore, the waste plastics include chlorine-free waste plastics and polyhydrocarbons of chlorine-containing waste plastics after dechlorination by iron oxide; the iron oxide includes iron ore powder (hematite powder and magnetite powder) and all substances containing iron oxide.

[0014] Preferably, the content of solid waste is 33-75wt%.

[0015] Preferably, the size of the solid waste in any direction is less than 1 cm.

[0016] The pretreatment conditions of the pretreated all-scrap low-carbon arc furnace steelmaking foaming carburizer of the present invention are temperature 300-500°C, heat preservation 0-120min; the pretreated mixture is sprayed into 1500-1600°C arc furnace steelmaking slag for mixing reaction.

[0017] Preferably, in step S11, the heating rate during heating is 5-100°C / min.

[0018] Preferably, the mixture after heat preservation comprises ferroferric oxide, silicon dioxide, ferric oxide and hydrocarbons.

[0019] Preferably, the electric arc furnace steelmaking slag includes CaO, SiO2, MgO, Al2O3, Fe2O3 and MnO.

[0020] Furthermore, the mass ratio of CaO, SiO2, MgO, Al2O3, Fe2O3 and MnO is 30:13:11:6:34:6.

[0021] The technical solution of the present invention has the following advantages over the prior art:

[0022] The invention increases the amount of solid waste mixed with iron oxide, improves the C and H contents in the mixture, sprays waste plastics or waste tires into an electric arc furnace after appropriate pretreatment to make them lose viscosity due to partial dehydrogenation and carbonization, and plays the role of bubbling and carbonization in the steelmaking process of the electric arc furnace.

[0023] The invention sets the mass ratio of waste plastic or waste tire to iron oxide in the range of 3:1 to 1:2 (that is, the content of plastic or waste tire in the mixture is in the range of 75%-33%) and applies it to the electric arc furnace steelmaking process.

[0024] In order to avoid the phenomenon of adhesion and pipe clogging during the blowing process caused by the melting of waste plastics or waste tires, the present invention utilizes the interaction between iron oxide and waste plastics or waste tires to quickly heat and pretreat the mixture of waste plastics or waste tires and iron oxide in the temperature range of 300-500°C. The heating rate of the mixture is 5-100°C / min, and the insulation time is 0-120min. The specific heating rate and insulation time depend on the temperature of the above-mentioned pretreatment. Within this temperature range, the carbon chain in the waste plastics or waste tires has not yet broken, and part of the H element on the carbon chain reacts with iron oxide to generate H2O and is removed. The final result is that the waste plastics or waste tires lose viscosity due to the retention of C and partial carbonization, which ensures the smooth progress of the blowing process. The pretreated foaming carburizer is sprayed into the arc furnace slag at 1500-1600°C. Under the action of high temperature, the iron oxide is reduced to carbon-saturated metallic iron to increase the carbon of the molten steel, and the gas phase product causes the slag to foam. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a diagram of the steps for pretreatment of foaming carburizer for low-carbon electric arc furnace steelmaking with all scrap steel.

[0026] Figure 2 This is a step diagram of the process of spraying the foaming recarburizer for low-carbon electric arc furnace steelmaking with all scrap steel into the electric arc furnace and mixing it with steel slag after pretreatment.

[0027] Figure 3 This is the XRD (X-ray diffraction) spectrum of the mixture after pretreatment in Example 3.

[0028] Figure 4 This is a diagram showing the promotion of electric furnace slag foaming behavior at high temperature in the pretreated mixture in Example 3. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0030] Example 1

[0031] The large pieces of waste plastic and the waste tires from which the steel wires have been extracted are cut into blocks with a size of less than 1 cm in any direction, and the waste plastic film is rolled into a ball with a diameter of less than 1 cm. The waste plastic and the rubber in the waste tires are mixed with iron oxide at a heating rate of 5°C / min in a temperature range of 300°C for 120 minutes, during which the rubber in the waste plastic and the waste tires undergoes melting and interacts with the iron oxide, the hydrogen element in the waste plastic and the waste tire rubber is partially removed, and the ferric oxide is reduced to ferric oxide, and finally a premix of waste plastic and waste tires and iron oxide whose main component is ferric oxide is obtained, such as Figure 1 shown.

[0032] The premix of waste plastics and waste tires with iron oxide can be sprayed into the 1500℃ electric arc furnace steelmaking slag. The water and CO / CO2 generated by the reaction of the pyrolysis products of waste plastics and waste tires with iron oxide, together with the gas phase pyrolysis products of waste plastics and waste tires, enter the slag phase to promote the foaming of steel slag; the iron oxide is reduced to carbon-containing metallic iron under high temperature conditions, and enters the molten steel to increase carbon and metal recovery rate, such as Figure 2 The composition of the electric furnace slag used is 30CaO+13SiO2+11MgO+6Al2O3+34Fe2O3+6MnO.

[0033] Example 2

[0034] Large pieces of waste plastic and waste tires with steel wires extracted are cut into blocks with a size of less than 1 cm in any direction, and waste plastic films are rolled into balls with a diameter of less than 1 cm. They are mixed with iron oxide at a heating rate of 100°C / min in a temperature range of 500°C for 10 minutes, during which the rubber in the waste plastic and waste tires undergoes melting and interacts with the iron oxide, the hydrogen element in the waste plastic and waste tire rubber is partially removed, and the ferric oxide is reduced to ferric oxide, and finally a premix of waste plastic and waste tires and iron oxide whose main component is ferric oxide is obtained.

[0035] The premix of waste plastics and waste tires with iron oxide can be sprayed into the 1600℃ electric arc furnace steelmaking slag. The water and CO / CO2 generated by the reaction of the pyrolysis products of waste plastics and waste tires with iron oxide, together with the gas phase pyrolysis products of waste plastics and waste tires, enter the slag phase to promote the foaming of steel slag; the iron oxide is reduced to carbon-containing metallic iron under high temperature conditions, and enters the molten steel to increase carbon and metal recovery. The composition of the electric furnace slag used is 30CaO+13SiO2+11MgO+6Al2O3+34Fe2O3+6MnO.

[0036] Example 3

[0037] Large pieces of waste plastic and waste tires with steel wires extracted are cut into blocks with a size of less than 1 cm in any direction, and waste plastic films are rolled into balls with a diameter of less than 1 cm. The resulting PE (polyethylene) is mixed with hematite powder at a ratio of 1:2 for 30 minutes, and then pretreated at 420°C for 30 minutes. The components of the obtained premix are ferroferric oxide, silicon dioxide, ferric oxide and hydrocarbons. After the prepared premix interacts with electric furnace slag at 1500°C, the electric furnace slag foams, and part of the iron oxide is reduced to carbon-saturated metallic iron, achieving the goal of foaming and carbon increase. The composition of the electric furnace slag used is 30CaO+13SiO2+11MgO+6Al2O3+34Fe2O3+6MnO.

[0038] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A pre-treated all-scrap low-carbon electric arc furnace steelmaking foaming recarburizer, characterized in that: It comprises solid waste and substances containing iron oxide; the solid waste is selected from one or both of waste plastics and waste tires.

2. The pretreated all-scrap low-carbon electric arc furnace steelmaking foaming and recarburizing agent as claimed in claim 1, characterized in that: The substance containing iron oxide includes one or more of hematite powder and magnetite powder or other substances containing iron oxide.

3. The pretreated all-scrap low-carbon electric arc furnace steelmaking foaming recarburizer as claimed in claim 1, characterized in that: The waste plastics include one or more of chlorine-free waste plastics and polyhydrocarbons obtained by dechlorination of chlorine-containing waste plastics by iron oxide.

4. The pretreated all-scrap low-carbon electric arc furnace steelmaking foaming and recarburizing agent as claimed in claim 1, characterized in that: The content of solid waste in the all-scrap low-carbon electric arc furnace steelmaking foaming and recarburizing agent is 33-75wt%.

5. The pretreated all-scrap low-carbon electric arc furnace steelmaking foaming recarburizer as claimed in claim 1, characterized in that: The size of the solid waste in any direction is less than 1 cm.

6. The use of the pretreated all-scrap low-carbon electric arc furnace steelmaking foaming recarburizer according to any one of claims 1 to 5, characterized in that: The steps include: S11: pretreatment condition is 300-500℃, heat preservation time is 0-120min; S12: spraying the pretreated mixture into electric arc furnace steelmaking slag at 1500-1600° C. for mixing reaction.

7. The use according to claim 6, characterized in that In the step S11, the heating rate during heating is 5-100°C / min.

8. The use according to claim 6, characterized in that The heat-insulated mixture comprises ferroferric oxide, silicon dioxide, ferric oxide and hydrocarbons.

9. The use according to claim 6, characterized in that The electric arc furnace steelmaking slag includes CaO, SiO2, MgO, Al2O3, Fe2O3 and MnO.

10. The use according to claim 9, characterized in that The mass ratio of CaO, SiO2, MgO, Al2O3, Fe2O3 and MnO is 30:13:11:6:34:6.

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