A method and system for stepwise reduction of non-blast furnace produced steel

Abstract

The present application belongs to the technical field of metallurgical processing, and more particularly relates to a method and system for stepwise reduction of non-blast furnace production of steel. First, iron ore powder is mixed with non-metallurgical coke reducing material and solvent to form a mixed raw material, and then low-temperature pre-reduction is carried out in a tubular fluidized bed reducer to reduce the oxygen content in the iron oxide and increase the metallization rate, obtaining a solid pre-reduced product. Then, the pre-reduced product-iron concentrate, whose metallization rate has been increased, is heated in a melting furnace for high-temperature reduction. In the reaction product after high-temperature reduction, carbon has been almost completely consumed, so the carbon content is already very low. Therefore, after the reduction is completely finished, when the solid iron is continued to be converted into molten iron, there is no carbon source for carburization, and the carbon content of the molten iron can fall within the carbon content range of steel, thereby achieving the purpose of directly smelting target steel products from iron ore.

Description

TECHNICAL FIELD

[0001] The present invention belongs to the technical field of metallurgical processing, and more particularly, to a method and system for stepwise reduction of non-blast furnace production of steel. BACKGROUND

[0002] Currently, steel smelting in the world mainly relies on the process of blast furnace ironmaking, converter or electric furnace steelmaking, which is a dominant process. However, blast furnace ironmaking has its own shortcomings that are difficult to overcome. First, the iron ore raw material used in the blast furnace, except for high-grade lump ore that can be directly smelted in the furnace, must be pre-processed into pellets, then sintered and hardened to 1200 Newtons per ball, in order to ensure that the raw material pellets have sufficient strength to ensure smooth ventilation in the blast furnace under the condition of being close to the molten state at the lower part of the blast furnace. Fine powder with a particle size less than 5mm cannot be smelted in the blast furnace. They will block the ventilation gap in the blast furnace, causing serious smelting accidents.

[0003] Secondly, in the lower part of the blast furnace, in order to maintain the permeability, even if the molten iron drops on the reducing agent, the reducing agent still needs to have sufficient strength. Therefore, the reducing agent used in the blast furnace is expensive metallurgical coke. The coking process is a high-energy consumption and high-pollution process. The coking plant is also a large investment unit. Generally speaking, the investment of the coking plant accounts for about 1 / 4 of the total investment of the iron plant.

[0004] Thirdly, blast furnace ironmaking has high requirements for the grade of ore. If the grade of the iron ore entering the furnace is too low, not only the economic benefit cannot be guaranteed, but also the separation of slag and iron may be difficult. In theory, when the grade of the ore reaches a certain lower limit, slag and iron cannot be separated. Therefore, lean ore cannot be directly smelted in the blast furnace.

[0005] Finally, some difficult-to-smelt ores cannot be smelted in the blast furnace. For example, as everyone knows, vanadium-titanium magnetite cannot be smelted in the blast furnace. Under the smelting conditions of the blast furnace, titanium dioxide in the iron ore will form titanium carbide with carbon in the reducing agent, and will also form titanium nitride with nitrogen in the air. These are substances with very high melting points. They cannot dissolve in the slag, but are suspended in the slag in the form of fine particles, causing the slag to be very viscous. These slags will block the ventilation gap of the blast furnace, causing the blast furnace to be blocked, and even causing a catastrophic accident of blast furnace explosion!

[0006] There is another problem, which is also the reason for the current ironmaking and steelmaking two-step approach: in the lower part of the blast furnace (mainly in the softening zone and the dripping zone), the molten iron and the hot coke are in close contact. This makes the smelted iron passively carburized, so that its carbon content is as high as 3% to 4.5%. Such a high carbon content limits its range of use. Therefore, people use oxygen to oxidize these carbon, which is called steelmaking.

[0007] In order to solve the series of disadvantages of the above-mentioned blast furnace ironmaking, the state clearly stipulates that non-blast furnace ironmaking is an encouraged project. However, up to now, the progress in non-blast furnace ironmaking is still not very obvious. Some people can also smelt iron by non-blast furnace method. However, among various methods, there are either technical problems or economic problems, and they cannot be widely promoted. Most patents are to make balls in advance by mixing ore and reducing agent, etc. to meet the "internal carbon" condition. In fact, the "internal carbon" itself leads people into a misunderstanding. "External carbon" can completely meet the needs of the reduction reaction. Some technologies deliberately heat-press the materials into balls during the preheating process of non-blast furnace ironmaking, and increase the strength of individual balls, which is more inclined to the blast furnace ironmaking process of sintering and sintering.

[0008] Therefore, the task in front of us is how to find a completely alternative method of blast furnace ironmaking, and the prerequisite is that the economic and technical indicators are better than those of blast furnace ironmaking. SUMMARY

[0009] The purpose of the present application is to provide a step-by-step reduction non-blast furnace steel production method and system, to solve the problems of severe carburization reaction, long reduction time, and the need to equip a converter or electric furnace for steelmaking in the prior art non-blast furnace ironmaking, and to overcome the technical problems of complex process and high steelmaking cost.

[0010] To achieve the above-mentioned purpose, the present application provides a step-by-step reduction non-blast furnace steel production method, which comprises the following steps:

[0011] (1) mixing iron ore powder, reducing agent and solvent to form mixed raw materials; the reducing agent is a non-metallurgical coke carbonaceous reducing agent;

[0012] (2) carrying out first reduction of the mixed raw materials in the fluidized bed dilute phase zone; in the first reduction process, the iron oxides in the iron ore powder are partially reduced by the reducing agent, to obtain a first reduction solid product;

[0013] (3) the first reduced solid product is subjected to a second reduction in the dense phase zone of the fluidized bed; iron oxides in the first reduced solid product are further reduced by the reducing agent, and a fine iron concentrate is obtained, in which the oxygen element is further reduced, but iron still mainly exists in the form of oxides;

[0014] (4) the fine iron concentrate is fed into a smelting furnace, the smelting furnace is heated, and the remaining reducing agent reduces the iron oxides in the fine iron concentrate to solid iron particles during the heating process; the temperature is continuously raised until the iron particles are melted into molten iron, the dross on the upper layer of the smelting furnace is discharged, and a crude steel or crude iron product is obtained.

[0015] Preferably, the reducing agent in step (1) is biomass, coal, petroleum, or natural gas; and the solvent is calcium carbonate and / or fluorite.

[0016] Preferably, the mixed raw material in step (1) is a mixed powder; and the size of the mixed powder is greater than or equal to 0.18 mm, and is further preferably 0.18-5 mm.

[0017] Preferably, the first reduction process and the second reduction process are carried out in a fluidized bed, and the reduction temperature is 700-790°C; the fluidized bed includes a dilute phase zone at the upper part and a dense phase zone at the lower part, fuel gas is introduced from the bottom of the dilute phase zone, so that the mixed raw material is subjected to the first reduction in the fluidized bed in a dilute phase state, and the reduction time of the first reduction is less than or equal to 2 minutes; the dense phase zone is not introduced with the fuel gas, and the first reduced solid product falls into the dense phase zone to be subjected to the second reduction, and the heat required by the second reduction process is provided by the residual heat of the first reduction, and the reduction time of the second reduction is 1-30 minutes.

[0018] Preferably, the height-diameter ratio of the fluidized bed is 2-10.

[0019] Preferably, the smelting furnace in step (4) is a gas type smelting furnace or an electric smelting furnace, and is further preferably an electric smelting furnace, and the electric smelting furnace is a medium frequency induction furnace or an electric arc furnace, and is more preferably a medium frequency induction furnace.

[0020] Preferably, the residence time of the fine iron concentrate in the smelting furnace in step (4) is 0.5-1 hour.

[0021] Preferably, the reducing furnace gas generated during the process of melting into molten iron in step (4) is treated by a coal gas recovery system and supplied as part of the fuel to the fluidized bed.

[0022] Preferably, the molar ratio of C element in the reducing agent to O element in the iron ore powder in step (1) is 1.05-1.15:1; step (4) continues to increase the temperature until the iron particles are reduced into molten iron, and when the carbon content reaches the required carbon content range of the target steel product, the slag on the upper layer of the molten furnace is discharged, and the molten iron is contacted with air to undergo desulfurization, dephosphorization and decarburization reactions to obtain a crude steel product.

[0023] Preferably, the method further comprises the steps of:

[0024] (5) refining the crude steel product in step (4) in a refining furnace or a refining ladle to obtain a target steel product, which is directly used as a casting raw material in a casting plant; or directly using the crude steel or crude iron product in step (4) as a casting raw material in a casting plant.

[0025] According to another aspect of the present application, a system for producing steel and iron by using the method is provided, comprising a fluidized bed and a melting furnace, wherein,

[0026] The fluidized bed comprises an upper dilute phase section and a lower dense phase section, and a mixed raw material inlet and a fluidized bed flue gas outlet are arranged at the top of the fluidized bed, and a fuel gas inlet is arranged between the upper dilute phase section and the lower dense phase section;

[0027] The iron concentrate outlet arranged at the bottom of the fluidized bed is connected to the iron concentrate inlet of the melting furnace, the melting furnace is provided with a melting furnace flue gas outlet at the top, the melting furnace flue gas outlet is connected to the flue gas treatment system, the flue gas treatment system is connected to the fuel gas inlet, and the melting furnace is further provided with a slag outlet at the upper side and a molten steel or molten iron discharge port at the bottom.

[0028] Overall, compared with the prior art, the above technical solutions conceived by the present application have the following beneficial effects:

[0029] (1) The present application provides a method for producing steel and iron by stepwise reduction without a blast furnace. First, the reducing agent, iron ore powder and various solvents are mixed before pre-reduction, and then enter the tubular pre-reduction reactor with a delayed reduction reaction section (fluidized bed dense phase section). This approach has the following advantages:

[0030] First, under the same conditions of providing reducing gas, the reducing agent and iron ore are contacted in advance, increasing the carbon concentration of the reactants. From the mechanism of chemical reactions, it is known that this facilitates the acceleration of the reduction reaction.

[0031] Secondly, after the reaction in the "dilute phase zone" of the upper part of the pipe reactor, the reaction products will fall into the "dense phase zone" of the delay reduction section of the lower part of the pipe reactor. Since the reactants still contain carbon and have a high temperature, the reactants will continue to reduce when they are in the "dense phase zone" of the delay reduction section. It is well known that reaction temperature and reaction time are the two most important parameters of a chemical reaction. Under the same temperature conditions, extending the reaction time will facilitate the chemical reaction. Raw materials without pre-carbon cannot achieve this delay reduction process. None of the existing technologies for non-blast furnace ironmaking using the "fluidization method" have pre-carbon in the final reduction reactor.

[0032] Thirdly, the large height-diameter ratio of the pipe reactor reduces the degree of "back mixing" of the material. That is, the high oxidation state ore that initially enters the reactor meets the high-carbon reducing agent, increasing the "driving force" of the reduction reaction, allowing the reduction reaction to proceed quickly after the temperature is reached. After the reaction in the "dilute phase zone" of the upper part of the pipe reactor, the carbon concentration in the reactants will decrease to some extent. The invention ingeniously keeps them in the "dense phase zone" of the delay reduction section to continue the reaction. The problem of carbon concentration reduction and low reduction temperature is solved by extending the time.

[0033] Fourthly, in the upper part of the pipe reactor, the flue gas is used to preheat the reaction material sufficiently, so that the heat energy in the flue gas is fully utilized. The final exhaust gas temperature can be reduced to below 200°C.

[0034] Fifthly, in existing non-blast furnace ironmaking processes, high-temperature, flammable, explosive, and toxic reducing gases such as carbon monoxide are produced in the final reduction reactor. However, the invention first performs two-step pre-reduction in the fluidized bed pipe reactor. The reducing gases such as carbon monoxide produced during the two-step reduction process can be used as fuel gas in the fluidized bed. Compared to the reducing gases produced directly in the final reduction reactor, the amount of reducing gases produced in the third reduction in the final reduction reactor after two-step pre-reduction in the invention is greatly reduced, reducing the burden on the reducing gas treatment system caused by the production of large amounts of high-temperature, flammable, explosive, and toxic reducing gases in the final reduction reactor.

[0035] Sixthly, the pre-reduction pipe reactor fluidized bed and the final reduction reactor melting furnace of the invention jointly undertake the task of reducing iron ore. Since the pipe reactor undertakes more reduction tasks than the usual pre-reduction reactor, the final electric melting furnace needs to undertake less reduction reaction tasks, which allows the use of low-value fuel to replace expensive electricity.

[0036] (2) The present application carries out low-temperature (below 800 degrees Celsius) pre-reduction of iron ore, first carries out first reduction in the fluidized bed dilute phase section, reduces the oxygen content in the iron oxide of the iron ore, and increases the metallization rate thereof; then carries out second reduction in the delayed reduction section (dense phase section), further reduces the carbon content and oxygen content therein, and finally, after the iron ore completes final reduction in the intermediate frequency electric furnace, the reducing agent carbon has been consumed. When the molten iron is formed, there is no carburizing agent, so that the carbon content of the molten iron reaches the carbon content range of the target steel product, and the target steel product is directly obtained after appropriate removal of impurities. In the first step and the second step of the pre-reduction process, non-metallurgical coke is used as the carbonaceous reducing agent, and the reducing agent carbon is consumed in the third step of the final reduction process in the melting furnace. In the present application, the "carbon starvation" strategy (C / O molar ratio in the mixed raw materials = 1.05-1.15) is adopted when the carbon is mixed in the raw materials in the step-by-step reduction non-blast furnace steel production method, so that the carbon content in the reducing agent is greatly reduced at the end of the pre-reduction reaction. The iron oxide in the iron ore is partially reduced, and since the iron oxide is not directly reduced to iron in the pre-reduction step, but is still an iron oxide (such as it may be reduced from ferric oxide to ferriferrous oxide or ferrous oxide), the carburization reaction does not occur. In the third reduction process, the pre-reduction product completes the third reduction in the process of heating, and then is converted into molten iron after complete reduction. At this time, the carbon content is very low, and the carburization reaction does not occur. Moreover, the carbon content is within the carbon content range of the steel product, and does not need to be supplemented with oxygen blowing. Therefore, the step-by-step reduction non-blast furnace ironmaking method of the present application can directly obtain a steel product.

[0037] (3) The present application uses non-metallurgical coke as the reducing agent for pre-reduction, which can greatly save electric energy and cost, and the pre-reduction process can consume the carbon in the reducing agent, avoiding the occurrence of carburization reaction during ironmaking.

[0038] (4) The blast furnace ironmaking must first make the iron ore powder into pellets, and the pellets need to be sintered to make their strength reach 1200 Newtons per ball. In order to ensure the strength of the sintered pellets, the reducing agent cannot be mixed in the pellets. However, the present application directly mixes the reducing agent in the non-blast furnace step-by-step reduction method, and does not need to sinter the iron ore powder to make it hard. The iron ore raw material used in the low-temperature pre-reduction of the present application is a powdery material, with a particle size greater than 0.18 mm and less than 5 mm, or a certain particle size range selected within this range.

[0039] (5) Blast furnace ironmaking can only use expensive metallurgical coke as a reducing agent, and coking is also a high-energy-consuming and high-polluting process. The stepwise reduction non-blast furnace ironmaking method of this invention has no requirements on the strength of the reducing agent. Theoretically speaking, as long as it can be cracked and burned and the impurities are not too high, it can be used as a reducing agent. Therefore, the selection of reducing agents in this invention is relatively broad. In this invention, biomass is mixed with iron ore powder as a reducing agent, and the biomass is cracked and carbonized. The combustion of the cracked gas can provide fuel for the pre-reduction reactor, and the carbon produced by carbonization is used as a reducing agent, which can make full use of the function of biomass.

[0040] (6) Blast furnace ironmaking requires a very high grade of iron ore. The iron ore grade required by this invention is very low, reaching below 40% or even lower. The method of this invention can smelt vanadium-titanium magnetite, which blast furnaces cannot.

[0041] (7) The carbon content of iron produced in blast furnaces is as high as 3% to 4.5%, resulting in severe carburization within the blast furnace, necessitating oxygen blowing for decarburization during further steelmaking. This invention, however, consumes almost all the reducing agent carbon before the iron is molten, effectively eliminating the carbon source for iron carburization. This ensures that the carbon content of the iron we produce falls within the range of steel carbon content. This truly achieves a leap from a two-step ironmaking and steelmaking process to a one-step direct steelmaking process! Of course, conventional electric arc furnace steelmaking requires a refining furnace at the rear. This invention can also conventionally be used with a refining furnace after a medium-frequency electric furnace, where adjustments to individual elements are handled—a common steelmaking refining method.

[0042] (8) The pre-reduction process of the present invention is a low-temperature reduction process with a temperature below 800 degrees Celsius. It has low requirements for the fire resistance of the equipment. The pre-reduction can be carried out in a protected stainless steel reactor, that is, it can be carried out in a hot-wall reactor. Attached Figure Description

[0043] Figure 1 This is a flowchart of the method for stepwise reduction of steel production in a non-blast furnace according to the present invention.

[0044] Figure 2 This is a schematic diagram of the system for the stepwise reduction of steel production in a non-blast furnace according to the present invention.

[0045] Figure 3 These are images of the third reduction process of iron concentrate in a medium-frequency induction furnace in Embodiment 5 of the present invention.

[0046] Figure 4 This is a photograph of the crude steel product obtained in Embodiment 5 of the present invention.

[0047] Figure 5 These are photographs of iron (steel) ingots obtained by cooling crude steel products under different conditions in different embodiments of the present invention.

[0048] In all the drawings, like reference numerals will be used to depict like structural elements or components throughout the several views. In all the drawings, like reference numerals will be used to depict like structural elements or components throughout the several views.

[0049] 1 - dilute phase section; 2 - dense phase section; 3 - mixed feedstock inlet; 4 - fuel gas inlet; 5 - fluidized bed flue gas outlet; 6 - iron concentrate outlet; 7 - iron concentrate inlet; 8 - smelting furnace; 9 - smelting furnace flue gas outlet; 10 - flue gas treatment system; 11 - tapping hole; 12 - molten steel or iron outlet. DETAILED DESCRIPTION

[0050] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific examples described herein are merely intended to explain the present application and not to limit the present application.

[0051] The present application provides a method for producing steel and iron in a non-blast furnace in steps, as shown in the following steps: Figure 1

[0052] (1) mixing iron ore powder, a reducing agent and a solvent to form a mixed feedstock; the reducing agent is a carbonaceous reducing agent other than metallurgical coke;

[0053] (2) performing a first reduction on the mixed feedstock in a dilute phase zone of a fluidized bed; during the first reduction, iron oxides in the iron ore powder are partially reduced by the reducing agent to obtain a first reduction solid product;

[0054] (3) performing a second reduction on the first reduction solid product in a dense phase zone of the fluidized bed; during the second reduction, iron oxides are further reduced by the reducing agent to obtain an iron concentrate, in which the oxygen element is further reduced, but iron still mainly exists in the form of oxides;

[0055] (4) sending the iron concentrate into a smelting furnace for smelting, and heating the smelting furnace; during the heating, the remaining reducing agent performs a third reduction on the iron concentrate, and reduces iron oxides in the iron concentrate into solid iron particles; continue heating until the iron particles are melted into molten iron, and the scum on the upper layer of the smelting furnace is discharged to obtain a crude steel or iron product.

[0056] In some embodiments, the reducing agent in step (1) is biomass, coal, petroleum or natural gas; and the solvent is one or more of calcium carbonate and fluorite.

[0057] ​The iron ore powder applicable to the method for producing steel and iron by non-blast furnace includes but is not limited to iron ore powder, and can also be other metal oxides that can be reduced by blast furnace or electric furnace, such as vanadium iron ore powder, vanadium-titanium magnetite powder, hematite powder, manganese ore powder, etc., all of which can fall within the scope of the present application. The reducing agent can be non-metallurgical coke such as biomass, coal, petroleum or natural gas. The biomass can be rice husk, sawdust, plant straw, coconut shell, cassava residue, etc. In use, the biomass can be first compressed into blocks and then broken to obtain biomass powder of appropriate particle size, and then mixed with the iron ore powder. In a preferred embodiment, the particle size of the powder in the mixed raw materials is 0.18-5 mm.

[0058] The carbon-oxygen ratio in the mixed raw materials can be adjusted to control the product to be steel or iron by the step-by-step reduction method for non-blast furnace production. When the carbon-oxygen ratio is high, molten iron can be obtained. In some embodiments, the molar ratio of C element in the reducing agent to O element in the iron ore powder (abbreviated as C / O ratio in the present application) in the mixed raw materials of the present application is 1.05-1.15:1, preferably 1.05-1.12:1. The molar amount of C element refers to the fixed carbon content in the reducing agent, which can be obtained by pyrolysis analysis of the reducing agent; and the molar amount of O element is 4 / 3 times the content of O element obtained by analyzing the Fe grade of the iron ore powder and then converting the Fe content into Fe3O4. At this C / O ratio, it is found that crude steel products can be directly obtained. The C / O ratio in the existing blast furnace or other non-blast furnace ironmaking method is greater than 1.2, so the strategy adopted by the method for one-step production of steel products by non-blast furnace in the present application is called "carbon starvation" strategy.

[0059] The mixed raw materials of the present application also contain a solvent, which can contain calcium carbonate. During the process of partial reduction of the iron ore powder in the fluidized bed of the present application, calcium carbonate decomposes to produce calcium oxide which can be used as a slagging agent, saving energy. In addition, the biomass reducing agent used in the present application produces carbon by pyrolysis and carbonization in the fluidized bed, which is used as a reducing agent to reduce the iron ore powder, and the cracking gas produced during the cracking process can also provide heat for the reduction process.

[0060] In some embodiments, the mixed raw materials of step (1) are mixed powders; the size of the mixed powders is greater than or equal to 0.18 mm, preferably 0.18-5 mm. It is found that the particle size of the mixed raw materials should not be less than 0.18 mm, otherwise it is easy to splash out during smelting in the melting furnace.

[0061] In some embodiments, the first reduction process and the second reduction process are performed in a fluidized bed, and the reduction temperature is 700-790°C; the fluidized bed comprises a dilute phase zone in the upper part and a dense phase zone in the lower part, fuel gas is introduced from the bottom of the dilute phase zone, so that the mixed raw material is subjected to the first reduction in the dilute phase state of the fluidized bed, and the reduction time of the first reduction is determined according to the height-diameter ratio of the fluidized bed and the flow rate of the fuel gas, and depends on the time of the material falling, and is generally less than or equal to 2 minutes; the dense phase zone is not introduced with the fuel gas, and the solid product of the first reduction falls into the dense phase zone to be subjected to the second reduction, and the heat required by the second reduction process is provided by the residual heat of the first reduction, and the reduction time of the second reduction is 1-30 minutes. In use, the mixed raw material is first placed in the dilute phase zone to be subjected to the rapid first reduction, and the reduction time is less than or equal to 2 minutes, and is preferably controlled within 30 seconds; after the first reduction is completed, the solid product of the first reduction falls into the dense phase zone to continue the reduction, and the iron concentrate is obtained. One of the important reasons why the present application selects the temperature within 800 degrees Celsius to perform the pre-reduction in the fluidized bed is that the pre-reduction product is controlled to be the iron concentrate containing iron oxides instead of iron particles, so as to facilitate the feeding to the melting furnace of the next reduction reactor. Therefore, in the actual production process, the metallization rate of the iron ore powder can also be judged in combination with the form of the solid product of the second reduction, and if the pre-reduction degree is too high to cause the reduction to be the iron particles, the pre-reduction product may be bonded to cause the material to be unable to be discharged.

[0062] In some embodiments, the height-diameter ratio of the fluidized bed is 2-10. The total height of the fluidized bed is the sum of the height of the dense phase section (also referred to as the dense phase zone) and the height of the dilute phase section (also referred to as the dilute phase zone). The present application performs two-step reduction on the mixed raw material in the temperature range of 700-790°C, and the temperature is lower than 800°C, so as to control the reduction product from being bonded and facilitate the smooth feeding to the melting furnace of the third reduction; the first reduction is the reduction process in the dilute phase state of the fluidized bed, at this time, the carbon content and the oxygen content in the iron ore powder are relatively high, and the reduction efficiency is relatively high, and the first reduction time can be controlled within 2 minutes; the second reduction is performed in the dense phase fluidized bed in the lower part of the fluidized bed, and in order to make up for the shortage of the reduction temperature, the second reduction improves the reduction degree by prolonging the reduction time. At the end of the second reduction, the metallization rate of the iron ore powder is increased to 60-80% to become the iron concentrate, but the iron in the iron concentrate still exists in the form of oxides.

[0063] In some embodiments, the present application performs the first reduction in the dilute phase section, and by controlling the flow rate of the fuel gas and the feeding amount of the mixed raw material, the solid material amount in the dilute phase section is within 100 kg per cubic meter (the volume of the dilute phase section reactor), and is preferably 30-60 kg / m 3 , and more preferably 30-50 kg / m 3The material after the first reduction falls into the dense phase section to undergo the second reduction, the dense phase section does not blow fuel gas, and the solid material density is 800-1800 kg / m 3 .

[0064] The present application adopts a tubular fluidized bed reactor comprising an upper dilute phase zone and a lower dense phase zone, and the "height-diameter ratio" is 2-10 to perform two-step pre-reduction, and has the following advantages: (1) the large height-diameter ratio of the tubular reactor reduces the degree of "back mixing" of the material; (2) the first reduction is performed in the upper dilute phase fluidized bed, at this time, the carbon content and the oxygen content in the iron ore powder are high, the reduction reaction rate is fast, the reduction efficiency is high, the first reduction time is short, and can be controlled within 2 minutes; (3) in the same tubular fluidized bed reactor, the upper dilute phase zone and the lower dense phase zone share a heating system, the solid product after the first reduction directly falls into the dense phase fluidized bed to perform the second reduction, the second reduction is performed by utilizing the waste heat of the dilute phase fluidized bed, and energy consumption is saved.

[0065] In some embodiments, the melting furnace of step (4) is a gas type melting furnace or an electric melting furnace, preferably an electric melting furnace, which includes but is not limited to, for example, a medium frequency induction furnace or an electric arc furnace, and preferably a medium frequency induction furnace. The gas type melting furnace can use coal, liquefied gas, petroleum, etc. as fuel.

[0066] The present application sends the iron concentrate obtained through two-step pre-reduction into a melting furnace for smelting, heats the iron concentrate in the melting furnace, and reduces the remaining reducing agent to the iron concentrate during the heating process, and reduces the iron oxides in the iron concentrate into solid iron particles; in some embodiments, the temperature is continuously increased until the iron particles are melted into molten iron, and at this time, the carbon content reaches the required carbon content range of the target steel product; at this time, the upper floating dross is discharged to obtain a crude steel product. The molten iron surface can also be exposed to air in the melting furnace after the dross is discharged, and the sulfur, phosphorus and carbon elements in the molten iron can be removed by oxidation reaction with oxygen in the air. This process can be considered as a preliminary steelmaking operation, and a crude steel product is obtained. The present application ingeniously realizes two completely different reaction processes in the same furnace body of the melting furnace, first, the reduction process of the iron concentrate to molten iron, and the formation of the upper floating dross maintains the reduction process; then the dross is discharged, the molten iron is exposed to air, and the sulfur, phosphorus and carbon in the molten iron are oxidized and removed, which is a preliminary steelmaking process. Therefore, the present application can realize the process of smelting iron first and then smelting steel in the same furnace body of the melting furnace.

[0067] In some embodiments, the residence time of the iron concentrate in the melting furnace of step (4) is 30-60 minutes. Among them, the third reduction to molten iron generally takes 25-50 minutes, and the dross discharge and preliminary steelmaking process generally takes 5-10 minutes.

[0068] In some embodiments, the reducing furnace gas generated in the process of converting the molten iron in step (4) is treated by a gas recovery system and used as part of the fuel for the fluidized bed.

[0069] In some embodiments, the crude steel product in step (4) is refined in a refining furnace or a refining ladle to obtain a target steel product, which is directly used as a casting raw material in a casting plant; or the crude steel or crude iron product in step (4) is directly used as a casting raw material in a casting plant.

[0070] The present application also provides a system for producing steel and iron by using the method, as shown in Figure 2 In the following embodiments of the present application, a system for producing steel and iron by a non-blast furnace step-by-step reduction one-step method includes a fluidized bed and a melting furnace, wherein the fluidized bed includes an upper dilute phase section 1 and a lower dense phase section 2, a mixed raw material inlet 3 and a fluidized bed flue gas outlet 5 are arranged at the top of the fluidized bed, a fuel gas inlet 4 is arranged between the upper dilute phase section 1 and the lower dense phase section 2, an iron concentrate outlet 6 arranged at the bottom of the fluidized bed is in communication with an iron concentrate inlet 7 of the melting furnace 8, a melting furnace flue gas outlet 9 is arranged at the top of the melting furnace 8, the melting furnace flue gas outlet 9 is in communication with a flue gas treatment system 10, the flue gas treatment system 10 is in communication with the fuel gas inlet 4, and a slag outlet 11 is further arranged on the upper side of the melting furnace 8, and a molten steel or molten iron outlet 12 is arranged at the bottom of the melting furnace 8.

[0071] When the system is used, the mixed raw material enters the dilute phase section 1 of the fluidized bed through the mixed raw material inlet 3 arranged at the top of the fluidized bed, the fuel gas required for the fluidized bed reduction process enters the fluidized bed through the fuel gas inlet 4 arranged between the upper dilute phase section 1 and the lower dense phase section 2, so that the mixed raw material becomes a dilute phase state in the dilute phase section 1 and a first reduction process is carried out in the dilute phase section; the first reduction solid product falls into the dense phase section 2 after reduction, a second reduction process is carried out in the dense phase section, and iron concentrate is obtained; the flue gas generated by low-temperature pre-reduction in the fluidized bed flows out from the fluidized bed flue gas outlet 5. The iron concentrate obtained by the second reduction is transported from the iron concentrate outlet 6 arranged at the bottom of the fluidized bed to the iron concentrate inlet 7 arranged at the top of the melting furnace, a temperature rising process is carried out in the melting furnace, and a third reduction of the iron concentrate, iron melting, and slagging are sequentially completed, and the obtained crude steel product is discharged from the molten steel or molten iron outlet 12 arranged at the bottom of the melting furnace; the floating slag is discharged from the slag outlet 11 arranged on the melting furnace; the flue gas generated by reduction in the melting furnace enters the flue gas treatment system 10 through the melting furnace flue gas outlet 9, and is transported to the fuel gas inlet 4 of the fluidized bed after being removed, cooled, and compressed in the flue gas treatment system 10, and is used as part of the fuel for the fluidized bed.

[0072] The fuel gas inlet 4 of the present application is connected to a mixture of combustible gas and air, part of the combustible gas comes from the flue gas outlet 9 of the melting furnace, which contains carbon monoxide and other combustible gas, and the combustible gas after treatment by the flue gas treatment system; another part can be externally supplemented, such as biomass fuel cracking gas, natural gas, liquefied petroleum gas, coal gas, etc. The fuel gas produced by biomass fuel cracking can be collected according to the existing conventional cracking and collection method, and used as the combustible gas of the fluidized bed reduction fuel gas of the present application.

[0073] Since the present application can directly smelt iron ore into steel by controlling the carbon content, the iron ore can be smelted into iron by increasing the carbon content. In other words: the present application can decide to smelt iron or steel according to our needs. In addition, since the present application can directly smelt iron or steel from iron ore, there is no need to use iron or steel as raw material in the foundry, and the crude steel product obtained by the production method of the present application can be directly used as raw material for the foundry.

[0074] The method for step-by-step reduction of non-blast furnace steel production in some embodiments of the present application is actually a method for step-by-step reduction of non-blast furnace smelting into steel using iron ore powder. Iron ore powder and reducing agent powder are directly mixed as raw materials, especially using a "lean high" fluidized bed as a low-temperature pre-reduction reactor, combined with a "carbon starvation" strategy, to first perform a first rapid reduction in the dilute phase zone of the fluidized bed, and then use the residual heat in the dilute phase zone to perform a second reduction in the dense phase zone of the lower fluidized bed. The iron concentrate obtained after reduction is sent to a melting furnace, and the third reduction, molten iron, slagging, and partial desulfurization, dephosphorization, and decarburization steelmaking operations are sequentially completed in the same furnace body during the heating process. In some embodiments, the crude steel water obtained has reached the requirements of medium carbon steel or even low carbon steel products, and the iron (steel) yield can be as high as 96% or more, achieving unexpected technical effects. In some embodiments, in order to obtain a lower carbon content, when the C / O ratio is small, the carbon starvation strategy seems to affect the iron yield, and the iron yield is only 91%. However, it should be noted that for a blast furnace, even if the carbon content is reduced, sacrificing part of the iron yield, it cannot be smelted into steel in one step like the method of the present application. The principle of blast furnace ironmaking determines that once molten iron is generated, carburization reaction will inevitably occur.

[0075] The present application provides a method for producing steel by stepwise reduction. Specifically, first, low-temperature pre-reduction of metal oxides reduces the oxygen content and increases the metallization rate, which is suitable for the smelting process of iron-making in an intermediate frequency induction furnace, and then producing steel and other metals. It is well known that the entire iron-making process is a process in which the ore gradually loses oxygen. While the ore gradually loses oxygen, its metallization rate is also increased. The benefits of pre-reducing iron ore at low temperature are: low-value fuel can be used for heating, and even we can use biomass fuel for heating. The low-temperature reduction process saves a lot of high-priced electricity. This pre-reduction process is also a preheating process of raw materials. Moreover, when we use biomass fuel, we can achieve zero carbon emissions. Because when we burn biomass fuel, the carbon dioxide emitted is exactly the same amount of carbon dioxide absorbed from the atmosphere during their growth process through photosynthesis.

[0076] Then, in the low-temperature pre-reduction stage, the oxygen content in the iron ore is greatly reduced, and the metallization rate is significantly increased. In our experiment, we weighed the solid material obtained in the low-temperature pre-reduction stage in the fluidized bed. Their weight is not only lower than the original feed weight, but also lower than the individual weight of the iron ore. This shows that the carbon and oxygen in the reactants form carbon monoxide and carbon dioxide, which are discharged into the air. This leads to a decrease in the total weight of the solid material. It is because the oxygen content in the iron ore is reduced that the metallization rate is increased to the level that can be used for iron-making in an induction furnace. Before the iron-making process, the concentrate powder and the remaining reducing agent continue to be reduced as the temperature in the furnace rises. Before the molten iron is formed, all the concentrates have completed the reduction process. This cleverly realizes the final reduction of the concentrate and the iron-making process in the iron-making process.

[0077] Finally, the induction furnace uses electric current to apply a magnetic field to the inducted metal or low-oxidation state ore to achieve the purpose of heating. This process saves a lot of electricity. The current general steel smelting is using an electric arc furnace, also known as a submerged arc furnace. This electric furnace does not rely on the induction of metal to heat, but relies on the discharge between the electrodes to generate an electric arc to heat the raw materials. The temperature of the electric arc is as high as 3000 degrees Celsius. Using an electric arc furnace to smelt steel consumes more electricity than using an induction furnace. Moreover, at high temperatures, the consumption of electrodes in the electric arc furnace is also a non-negligible expense. The present application greatly improves the metallization rate of the iron ore in the first two pre-reduction processes, so the third reduction can be carried out using a low-energy intermediate frequency induction furnace, which greatly saves energy compared to the existing technology of electric arc furnace or submerged arc furnace.

[0078] The present application first mixes iron ore with non-metallurgical coke-like reducing material and additives to form a mixture, and then performs low-temperature pre-reduction to reduce the oxygen content in the iron oxide and increase the metallization rate, thereby obtaining a solid pre-reduction product. Then, the pre-reduction product, whose metallization rate has been increased, is heated in a melting furnace to perform high-temperature reduction. In the reaction product after high-temperature reduction, carbon has been almost completely consumed, and thus the carbon content is very low. Therefore, after the reduction is completed, when the solid iron is continuously converted into molten iron, there is no carbon source for carburization, so that the carbon content of the molten iron falls within the range of the carbon content of steel, thereby achieving the purpose of directly smelting target steel products from iron ore.

[0079] The following examples produce steel and iron in the production system as described above. The present application is a step-by-step reduction method for producing steel and iron by a non-blast furnace process, which is locally discontinuous and overall continuous. The mixed raw materials are continuously fed into the dilute phase section from the top raw material inlet of the fluidized bed to perform the first reduction. After the reduction is completed, the mixed raw materials fall into the dense phase section to perform the second reduction. After the reduction is completed, the iron concentrate that meets the reduction degree requirement is taken out from the bottom iron concentrate outlet of the fluidized bed in batches and fed into the intermediate frequency induction furnace for smelting. Of course, multiple intermediate frequency induction furnaces can be used to meet the production requirements. Figure 2

[0080] The following is an example:

[0081] Example 1

[0082] In a magnetite with a grade of 67wt% (representing a Fe content of 67wt%), 18wt% of anthracite coal with a calorific value of 5500 kcal (the amount added is 18wt% of the total mass of the magnetite, the same below) and 10wt% of straw are added, 9wt% of calcium carbonate and 6wt% of fluorite are added. The C / O molar ratio in the mixed raw materials is 1.11. The above raw materials are mixed uniformly in a mixer and sieved to obtain powder raw materials with a particle size in the range of 1-3 mm, which are added from the upper mixed raw material inlet of the tubular reduction reactor with a height-diameter ratio of 4. The mixed raw materials first perform the first reduction in the dilute phase section of the tubular reduction reactor, and then fall into the dense phase section to perform the second solid-state reduction. The mixed gas of liquefied petroleum gas and air (volume ratio 1:50) is introduced into the fuel gas inlet of the reduction reactor, and the furnace temperature is controlled at 700-750 degrees Celsius (the furnace temperature is controlled in this range by controlling the amount of fuel gas and the amount of fuel gas). The average reduction reaction time in the "dilute phase section" is 15 seconds, and the solid material density in the dilute phase section is 35 kg / m 3 . In the dense phase delayed reduction section, the average reduction time is 20 minutes, and the solid material density in the dense phase section is 1000 kg / m 3 ​The reaction product is taken out from the lower part of the reactor. The product of the pre-reduction reaction is directly put into the intermediate frequency induction furnace and heated to the temperature of molten iron (1400-1450 degrees Celsius). During the heating process, the third reduction and the molten iron are formed, the slag is discharged, and the desulfurization and dephosphorization reactions of S, P and C in the molten iron with oxygen in the air are carried out for 8 minutes to obtain the crude steel product. The test shows that the conversion rate of iron is 96.45%, and the carbon content of the molten iron is 0.94%.

[0083] Comparative Example 1

[0084] The other conditions are the same as in Example 1, except that the particle size of the mixed raw materials is less than 80 mesh (0.18 mm) by sieving. The mixed raw materials are solid-state reduced in the reduction reactor. The fuel gas of the reduction reactor is the mixed gas of liquefied petroleum gas and air (volume ratio 1:50), and the hearth temperature is controlled at 700-750 degrees Celsius. The average reduction reaction time in the "dilute phase section" is 15 seconds, and the solid material density in the dilute phase section is 35 kg / m 3 . In the delayed reduction section, the average reduction time is 20 minutes, and the solid material density in the dense phase section is 1000 kg / m 3 . The reaction product is taken out from the lower part of the reactor. The product of the pre-reduction reaction is directly put into the induction furnace, and the material is splashed out from the crucible of the intermediate frequency furnace during the iron melting process. It can be seen that the iron ore with too small particle size, especially the iron ore with particle size less than 80 mesh, is difficult to process by this method if it is not agglomerated.

[0085] Example 2

[0086] In order to verify the effect of the "carbon starvation" strategy, we deliberately added extra carbon in the experiment. We want to see what changes will occur to the carbon content of the molten iron obtained according to the method of Example 1 without providing "carbon starvation".

[0087] The other conditions are the same as in Example 1, except that the amount of straw added is replaced from 10wt% in Example 1 to 15wt%, and the molar ratio of C / O in the mixed raw materials is 1.2. The final product is tested and it is found that the conversion rate of iron is 96.88%, and the carbon content of the molten iron is 3.57%. It can be completely seen from this example that "carbon starvation" is indeed an effective way to reduce the carbon content of the molten iron. In other words, the iron ore can be directly smelted into steel or into iron by the present application.

[0088] Example 3

[0089] Vanadium titanium magnetite of 50wt% grade with particle size of 0.18-1 mm, 16.5wt% of carbonized coconut shell, 6wt% of fluorite and 6wt% of calcium carbonate are added. The C / O molar ratio in the mixed raw materials is 1.09. The above raw materials are mixed in a blender and sieved to obtain mixed raw materials with particle size of 0.8-5 mm, which are added from the top of a tubular reduction reactor with a height-diameter ratio of 3. The mixed raw materials are reduced in solid state in the reduction reactor. The fuel gas of the reduction reactor is a mixture of straw gas produced by carbonization cracking of biomass and air (volume ratio 1:40), and the hearth temperature is controlled at 750-790 degrees Celsius. The average reduction time in the "dilute phase section" is 10 seconds, and the solid material density in the dilute phase section is 40 kg / m 3 . In the delayed reduction section, the average reduction time is 25 minutes, and the solid material density in the dense phase section is 1200 kg / m 3 . The reaction-generated iron concentrate is taken out from the lower part of the reactor. The product of the pre-reduction reaction is directly put into a medium-frequency induction furnace to be heated to the temperature of molten iron (1400-1450 degrees Celsius). In the heating process, the third reduction is completed and the molten iron is formed. The slag is discharged, and the S, P and C in the molten iron react with oxygen in the air for 10 minutes to achieve desulfurization, dephosphorization and decarburization, thereby obtaining a crude steel product. The conversion rate of iron in the test is 96.01%. The carbon content of the iron (steel) water is 0.45%. This carbon content is the carbon content of medium carbon steel (such as 45 steel).

[0090] Example 4

[0091] Magnetite of 67% grade, 21wt% of carbonized coconut shell, 9wt% of calcium carbonate and 6wt% of fluorite are added. The above raw materials are mixed in a blender and sieved to obtain mixed powder raw materials with particle size of 0.18-2 mm, which are added from the upper part of a tubular pre-reduction reactor with a height-diameter ratio of 6. The C / O molar ratio in the mixed raw materials is 1.03. The raw materials are pre-reduced in solid state in the pre-reduction reactor. The average reduction time in the "dilute phase section" is 20 seconds, and the solid material density in the dilute phase section is 45 kg / m 3 . In the delayed reduction section, the average reduction time is 30 minutes, and the solid material density in the dense phase section is 1200 kg / m 3The fuel gas for the pre-reduction reactor is a mixture of liquefied petroleum gas and air (volume ratio 1:50), and the hearth temperature is controlled at 750-790 degrees Celsius. The solid concentrate produced by the reaction is taken out from the lower part of the reactor. The product of the pre-reduction reaction is directly put into a medium-frequency induction furnace and heated to the temperature of molten iron (1400-1450 degrees Celsius). In the heating process, the third reduction is completed and the molten iron is formed. The slag is discharged, and the S, P and C in the molten iron react with oxygen in the air for 10 minutes to produce the crude steel product. The yield of the iron (steel) reaches 91.74%, and the carbon content is as low as 0.05%, which is close to the national requirement for the carbon content of ultra-low carbon steel.

[0092] Example 5

[0093] The iron ore with a grade of 40wt% is mixed with 15wt% carbonized coconut shell, 5wt% fluorite and 5wt% calcium carbonate in a blender. The mixed powder with a particle size range of 1-5mm is obtained by sieving and is added from the upper part of the reduction reactor. The C / O molar ratio in the mixed material is 1.08. The solid-state pre-reduction of the material is carried out in a tubular pre-reduction reactor with a height-diameter ratio of 6. The fuel for the pre-reduction reactor is a mixture of liquefied petroleum gas and air (volume ratio 1:50), and the hearth temperature is controlled at 700-750 degrees Celsius. The average reduction time in the "dilute phase section" is 20 seconds, and the solid material density in the dilute phase section is 45kg / m 3 . In the delayed reduction section, the average reduction time is 30 minutes, and the solid material density in the dense phase section is 1200kg / m 3 . The solid concentrate produced by the reaction is taken out from the lower part of the reactor. The product of the pre-reduction reaction is directly put into a medium-frequency induction furnace and heated to the temperature of molten iron (1400-1450 degrees Celsius). In the heating process, the third reduction is completed and the molten iron is formed. The third reduction process is shown in Figure 3 . During the reduction process, the flame can be observed, indicating that combustible gases such as carbon monoxide are produced in the reduction process. After the molten iron is fully formed, the slag is discharged, and the S, P and C in the molten iron react with oxygen in the air for 5 minutes to produce the crude steel product, as shown in Figure 4 . The yield of the iron (steel) reaches 95.18%, and the carbon content is as low as 0.2%, which meets the requirement for the carbon content of low-carbon steel. In addition, the S content is measured to be 0.028%, the P content is 0.030%, the Si content is 0.639%, and the Mn content is 0.345%.

[0094] The iron (steel) ingot obtained by cooling the crude steel product in the experimental process is shown in Figure 5 . In actual production, the crude steel product obtained in the examples can be directly sent to a refining furnace for refining to obtain the final target steel product.

[0095] Those skilled in the art can easily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for the stepwise reduction of non-blast furnace produced steel iron, characterized in that, The method comprises the following steps: (1) mixing iron ore powder, a reducing agent and a solvent to form a mixed raw material; the reducing agent is a non-metallurgical coke-like carbonaceous reducing agent; the molar ratio of C element in the reducing agent to O element in the iron ore powder is 1.05-1.15:1; the mixed raw material is a mixed powder; the size of the mixed powder is greater than or equal to 0.18 mm; (2) performing first reduction on the mixed raw material in a dilute phase zone of a fluidized bed; during the first reduction process, iron oxides in the iron ore powder are partially reduced by the reducing agent to obtain a first reduction solid product; (3) performing second reduction on the first reduction solid product in a dense phase zone of the fluidized bed; iron oxides in the first reduction solid product are further reduced by the reducing agent to obtain iron concentrate, in which the content of oxygen element is further reduced, but iron still mainly exists in the form of oxides; (4) sending the iron concentrate into a melting furnace for smelting; the melting furnace is heated, and the remaining reducing agent performs third reduction on the iron concentrate during the heating process, so that iron oxides in the iron concentrate are reduced to solid iron particles; the temperature is continuously raised until the iron particles are melted into molten iron; the scum in the upper layer of the melting furnace is discharged to obtain a crude steel or iron product; The first reduction process and the second reduction process are performed in the fluidized bed, and the reduction temperature is 700-790 ℃; the fluidized bed comprises a dilute phase zone in the upper part and a dense phase zone in the lower part; fuel gas is introduced from the bottom of the dilute phase zone, so that the mixed raw material is subjected to the first reduction in the fluidized bed in a dilute phase state; the dense phase zone is not introduced with the fuel gas, and the first reduction solid product falls into the dense phase zone to perform the second reduction; the heat required by the second reduction process is provided by the waste heat of the first reduction.

2. The method of claim 1, wherein, In step (1), the reducing agent is biomass, coal, petroleum or natural gas; and the solvent is calcium carbonate and / or fluorite.

3. The method of claim 1, wherein, In step (1), the mixed raw material is a mixed powder; and the size of the mixed powder is 0.18-5 mm.

4. The method of claim 1, wherein, The reduction time of the first reduction is less than or equal to 2 minutes; and the reduction time of the second reduction is 1-30 minutes.

5. The method of claim 1, wherein, The height-diameter ratio of the fluidized bed is 2-10.

6. The method of claim 1, wherein, In step (4), the melting furnace is a gas-fired melting furnace or an electric melting furnace.

7. The method of claim 1, wherein, In step (4), the temperature is continuously raised until the iron particles are melted into molten iron, and the carbon content reaches the required carbon content range of the target steel product at this time; after the scum in the upper layer of the melting furnace is discharged, the molten iron is contacted with air to perform desulfurization, dephosphorization and decarburization reactions, and a crude steel product is obtained.

8. The method of claim 7, wherein, The method further comprises the following step: (5) refining the crude steel product in step (4) in a refining furnace or a refining molten iron ladle to obtain a target steel product; the target steel product is directly used as a casting raw material in a foundry; or the crude steel or iron product in step (4) is directly used as a casting raw material in a foundry.

9. A system for producing steel using the method according to any one of claims 1 to 8, characterized in that, The method comprises a fluidized bed and a melting furnace, wherein The fluidized bed comprises an upper section dilute phase section (1) and a lower section dense phase section (2), the fluidized bed top is provided with a mixed raw material inlet (3) and a fluidized bed flue gas outlet (5), the upper section dilute phase section (1) and the lower section dense phase section (2) are provided with a fuel gas inlet (4) therebetween; The fluidized bed bottom provided with a concentrate outlet (6) is communicated with the concentrate inlet (7) of the smelting furnace (8), the smelting furnace (8) top is provided with a smelting furnace flue gas outlet (9), the smelting furnace flue gas outlet (9) is communicated with a flue gas treatment system (10), the flue gas treatment system (10) is communicated with the fuel gas inlet (4); the smelting furnace (8) upper portion side is further provided with a slag outlet (11), and the bottom is provided with a molten steel or molten iron discharge port (12); When the system is used, the mixed raw material enters the dilute phase section (1) of the fluidized bed from the mixed raw material inlet (3) provided at the top of the fluidized bed, and the fuel gas required in the fluidized bed reduction process enters the fluidized bed from the fuel gas inlet (4) between the upper section dilute phase section (1) and the lower section dense phase section (2), so that the mixed raw material becomes a dilute phase state in the dilute phase section (1), and the first reduction process is carried out in the dilute phase section; the first reduction solid product after reduction falls into the dense phase section (2), and the second reduction process is carried out in the dense phase section, and the concentrate is obtained; the concentrate is transported from the concentrate outlet (6) at the bottom of the fluidized bed to the concentrate inlet (7) at the top of the smelting furnace, and the third reduction, molten iron and slagging operations of the concentrate are sequentially completed in the smelting furnace, and the obtained crude steel or crude iron product is discharged from the molten steel or molten iron discharge port (12) at the bottom of the smelting furnace; wherein the dross is discharged from the slag outlet (11) provided at the top of the smelting furnace; the flue gas produced by reduction in the smelting furnace (8) enters the flue gas treatment system (10) from the smelting furnace flue gas outlet (9), and is transported to the fuel gas inlet (4) of the fluidized bed after being removed, cooled and compressed in the flue gas treatment system (10), and is supplied to the fluidized bed as part of the fuel.

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