Method and apparatus for fluidized production of chromium stainless steel

Abstract

A method for preparing chromium-based stainless steel using fluidized bed refining includes: 1) conveying iron oxide to the upper middle part of a fluidized bed furnace tube and chromium oxide to the lower middle part of the fluidized bed furnace tube; 2) introducing a first reducing gas from the middle of the fluidized bed furnace tube and a second reducing gas from the bottom of the fluidized bed furnace tube, where the iron oxide and chromium oxide move downwards within the fluidized bed furnace tube and undergo a reduction reaction with the first and second reducing gases moving upwards to generate elemental iron and chromium; 3) conveying the reduced elemental metals to a vacuum refining furnace to produce chromium-based stainless steel. This invention, based on the reaction characteristics of the smelting raw materials, utilizes the different reduction reaction temperatures and reducing media of iron oxide and chromium oxide to propose a novel two-step process of fluidized bed reduction + vacuum melting, significantly shortening the process flow and reducing system energy consumption.

Description

Technical Field

[0001] This invention relates to the preparation technology of chromium-based stainless steel, specifically to a method and apparatus for fluidized bed preparation of chromium-based stainless steel, belonging to the field of iron and steel smelting technology. Background Technology

[0002] Stainless steel generally refers to iron-based corrosion-resistant alloy steel containing nickel and chromium. It encompasses a range of steels exhibiting high chemical stability in air, water, aqueous salt solutions, acids, and other corrosive media. Stainless steel can be classified by chemical composition into chromium-based stainless steel and chromium-nickel-based stainless steel. Based on its metallographic structure, it can be further classified into austenitic stainless steel, ferritic stainless steel, duplex stainless steel, martensitic stainless steel, and precipitation-hardening stainless steel. Due to its excellent corrosion resistance, formability, machinability, and toughness, stainless steel is an indispensable special steel material in civilian, military, nuclear power, and aerospace fields. In 2020, global stainless steel production exceeded 50 million tons, and my country's annual stainless steel production also increased from 450,000 tons in 1980 to 30.14 million tons in 2020, accounting for more than half of the global annual stainless steel production. With the rapid development of the national economy, my country will continue to have a large demand for stainless steel materials in the future.

[0003] Stainless steel smelting initially employed the crucible method, later evolving to electric furnace smelting. The emergence of new ladle refining technologies such as AOD and VOD in the 1960s ushered in a new era for stainless steel smelting. Since the 1970s, stainless steel smelting processes have developed rapidly, gradually entering the three-step steelmaking stage. Currently, there are various stainless steel smelting methods worldwide. Large and medium-sized enterprises generally use the three-step method, while small and medium-sized enterprises typically use the double-step ladle refining method. The three-step method consists of: primary refining furnace (step one) → refining furnace (step two) → vacuum refining furnace (step three).

[0004] (1) Primary refining furnace

[0005] The primary refining furnace serves only as a melting and initial refining furnace, responsible for supplying the primary molten steel, also known as stainless steel mother liquor, to the refining furnace. Depending on the raw material conditions and specifications, an induction furnace, electric furnace, or converter can be selected. When recycled scrap steel is used as the main raw material, both induction furnaces and electric furnaces can be used as primary refining furnaces, but induction furnaces are generally used for small-scale production. When ordinary scrap steel is used as the main raw material, an electric furnace is chosen as the primary refining furnace to melt the scrap steel and alloys. When blast furnace iron is used as the main raw material, converters such as LD, OTB, AOD, and K-OBM-S are chosen as primary refining furnaces for dephosphorization and initial decarburization, as well as melting small amounts of scrap steel and alloys.

[0006] If the raw materials contain a large amount of scrap steel and a high proportion of alloys, an electric furnace should be selected to melt the alloys and scrap steel, providing the function of mixing the composition and temperature of the stainless steel mother liquor. If the alloys in the raw materials are largely derived from ores, such as chromium ore, iron ore and nickel ore, a converter can be used as a primary smelting furnace to reduce the alloying elements in the ore. For example, Kawasaki in Japan used chromium ore reduction to obtain metallic chromium.

[0007] It is generally considered uneconomical to use a converter as a primary smelting furnace. This is because it requires blast furnace molten iron to provide the mother liquor and heat source, extending the process route and increasing initial investment. A converter should only be considered as a primary smelting furnace when electricity is scarce.

[0008] (2) Refining furnace

[0009] The main function of a refining furnace is to reduce carbon and retain chromium, while simultaneously carrying out desulfurization. The most commonly used refining furnace is the converter, including AOD, K-BOP, K-OBM-S, MRP, CLU, KCR-S, etc.

[0010] Argon-oxygen oxidizing (AOD) furnaces, commonly known as argon-oxygen furnaces, are the most common refining furnaces, accounting for approximately 70% of stainless steel refining furnaces. They are widely used in two-step and three-step smelting processes. Traditional AOD furnaces use side-blowing nozzles installed at the bottom of the converter to inject oxygen and argon for decarburization and refining. Currently, adding a top lance and injecting oxygen and a mixed gas to the AOD converter creates an AOD-L refining furnace, which can accelerate decarburization, shorten the smelting cycle, and increase production capacity. Daido Steel Corporation of Japan has added a vacuum system to its AOD converter, defining it as an AOD-VCR refining furnace, which can be used to produce low-carbon stainless steel and also reduces argon and ferrosilicon consumption, further shortening the smelting cycle.

[0011] K-BOP is a top-blown basic oxygen converter (BOF) developed by Kawasaki Steel Corporation, with the addition of bottom-blown nozzles. It can spray oxygen and the cooling medium methane, as well as lime.

[0012] K-OBM-S is a technology improved and developed by Voestalpine (VA1) based on K-BOP. It adds bottom-blowing nozzles or side-blowing nozzles to the top-blown basic oxygen converter (BOF). In fact, both K-BOP and K-OBM-S were originally top-and-bottom combined blowing basic oxygen converters. Recently, K-OBM-S has added side-blowing nozzles, making it very similar to AOD-L. K-BOP and K-OBM-S are suitable for existing top-and-bottom combined blowing basic oxygen converters, and with partial modifications, they can produce stainless steel.

[0013] GOR was developed in Ukraine for a top-and-bottom blown alkaline oxygen converter. The bottom blown nozzles are protected with natural gas or hydrocarbons, and it is comparable to K-BOP and K-OBM-S.

[0014] MRP is an abbreviation for Metal Refining Process, developed by Mannesmann Demag Hut-tentechnik based on a bottom-blown converter. Early versions used bottom-blown nozzles to alternately inject oxygen and inert gas. Later, top lances were added, with oxygen injected from the top and inert gas injected from the bottom, forming the MRP-L type refining furnace.

[0015] CLU is similar to AOD, but the bottom-blown dilution gas has been changed to water vapor, and it is blown in from the bottom.

[0016] KCB-S is an abbreviation for Krupp combined blowing stainless steel, developed by Krupp Stahl AG, which adds top blowing to the AOD furnace and is equivalent to AOD-L.

[0017] (3) Vacuum oxygen blowing refining furnace

[0018] Vacuum oxygen blowing refining furnaces (mainly VOD and RH-OB / RH-KTB, etc.) function to further decarburize under vacuum conditions, completing the fine-tuning of the final composition and control of purity. This method was initially used to produce ultra-low carbon and ultra-low nitrogen stainless steel. When the Ar gas source cannot be guaranteed or is insufficient, a vacuum oxygen blowing refining furnace is often added after the two-step process to reduce Ar gas consumption and achieve the same refining effect.

[0019] VOD and RH-OB / RH-KTB are based on the VD vacuum furnace and RH vacuum furnace, with the addition of an oxygen lance. RH-OB has an oxygen lance installed on the side wall of the vacuum chamber, while VOD and RH-KTB have an oxygen lance installed on the top of the vacuum chamber. The purpose of both is to inject oxygen into the molten steel inside the vacuum chamber.

[0020] The three-step process has gradually become the main method for smelting stainless steel at present. However, the three-step process has disadvantages such as long process flow, complex equipment system, large footprint, high system energy consumption, large carbon emissions, and high investment and production costs, which does not conform to the national industrial policy of low carbon and low energy consumption. Summary of the Invention

[0021] To address the shortcomings of existing technologies, this invention proposes a method and apparatus for fluidized bed preparation of chromium-based stainless steel. First, iron oxide and chromium oxide are introduced into the fluidized bed furnace from different positions within the furnace tube. Then, a first reducing gas and a second reducing gas are introduced into the furnace tube from different positions. The iron oxide and chromium oxide react with the first and second reducing gases respectively to generate elemental iron and chromium. The elemental metals are then transferred to a vacuum refining furnace for smelting to obtain chromium-based stainless steel. Based on the reaction characteristics of the smelting raw materials, this invention proposes a novel two-step process of fluidized bed reduction followed by vacuum smelting. This new process reduces the initial melting and refining steps in the existing three-step process, significantly shortening the process flow and simultaneously improving the reduction efficiency of the two metal oxides, thus increasing the yield of the elemental metals.

[0022] According to a first embodiment of the present invention, a method for preparing chromium-based stainless steel by fluidization is provided.

[0023] A method for preparing chromium-based stainless steel by fluidization, the method comprising the following steps:

[0024] 1) Raw material feeding: Iron oxide is fed to the upper middle part of the fluidized bed furnace tube, and chromium oxide is fed to the lower middle part of the fluidized bed furnace tube.

[0025] 2) Fluidized reduction: A first reducing gas is introduced from the middle of the fluidized furnace tube, and a second reducing gas is introduced from the bottom of the fluidized furnace tube. Iron oxides and chromium oxides move from top to bottom in the fluidized furnace tube and react with the first and second reducing gases moving from bottom to top to produce metallic elements of iron and chromium.

[0026] 3) Vacuum melting: The elemental metal generated in step 2) is transported to a vacuum refining furnace to produce chromium-based stainless steel.

[0027] In this invention, in step 2), the first reducing gas is H2 or a mixture of multiple reducing gases including H2. The second reducing gas is CO or a mixture of multiple reducing gases including CO.

[0028] Preferably, in the first reducing gas, the concentration of H2 is greater than 80%, more preferably greater than 85%, and even more preferably greater than 90%. In the second reducing gas, the concentration of CO is greater than 60%, more preferably greater than 65%, and even more preferably greater than 70%.

[0029] In this invention, in step 1), the iron oxide is Fe2O3 or a mixture of various iron oxides including Fe2O3. The chromium oxide is Cr2O3 or a mixture of various chromium oxides including Cr2O3.

[0030] Preferably, in the iron oxide, the Fe2O3 content is greater than 80%, more preferably greater than 85%, and even more preferably greater than 90%. In the chromium oxide, the Cr2O3 content is greater than 50%, more preferably greater than 60%, and even more preferably greater than 70%.

[0031] In this invention, the concentration of H2 in all the reducing gases introduced into the fluidized bed furnace tube is greater than 70%, preferably greater than 75%, and more preferably greater than 80%.

[0032] In this invention, among all the metal oxides added in the fluidized bed furnace tube, the amount of iron oxide added is 70% to 90% of the total amount of metal oxides added, preferably 72% to 88%, and more preferably 75% to 85%.

[0033] In this invention, step 1) specifically involves: grinding iron oxide and chromium oxide into powder respectively, then conveying the iron oxide powder obtained after grinding to the upper middle part of the fluidized bed furnace tube, and conveying the chromium oxide powder obtained after grinding to the lower middle part of the fluidized bed furnace tube.

[0034] Preferably, the particle size ratio of the chromium oxide powder to the iron oxide powder is 1:(0.98-1). The particle size of the chromium oxide powder is 0.1-1 mm, preferably 0.15-0.9 mm.

[0035] In this invention, in step 2), the flow rates of the first and second reducing gases are adjusted to control the iron oxide powder to be suspended in the upper middle part of the fluidized bed furnace tube, and the chromium oxide powder to be suspended in the lower middle part of the fluidized bed furnace tube. In step 3), the reduced elemental metal is blown by the gas flow into a vacuum refining furnace to produce chromium-based stainless steel.

[0036] Preferably, in the fluidized bed furnace tube, the flow rates of the first reducing gas and the second reducing gas are 0.2 to 2 m / s, and more preferably 0.3 to 1.8 m / s.

[0037] In this invention, the reduction reaction temperature of iron oxide in the upper middle part of the fluidized bed furnace tube is 1000–1300°C, preferably 1050–1280°C. The reduction reaction time of iron oxide is 0.5–4 h, preferably 1–3.5 h; and / or

[0038] In this invention, the reduction reaction temperature of chromium oxide in the lower middle part of the fluidized bed furnace tube is 1300–1600°C, preferably 1350–1580°C. The reduction reaction time of chromium oxide is 0.5–4 h, preferably 1–3.5 h.

[0039] According to a second embodiment of the present invention, an apparatus for fluidized bed preparation of chromium-based stainless steel is provided.

[0040] An apparatus for the fluidized bed preparation of chromium-based stainless steel, or an apparatus for preparing chromium-based stainless steel using the method described in the first embodiment, the apparatus comprising a fluidized bed furnace tube and a vacuum refining furnace. The fluidized bed furnace tube is provided with a first material inlet, a second material inlet, a first gas inlet, a second gas inlet, and a material outlet. The first material inlet is located in the upper-middle part of the sidewall of the fluidized bed furnace tube. The second material inlet is located in the lower-middle part of the sidewall of the fluidized bed furnace tube. The first gas inlet is located in the middle of the sidewall of the fluidized bed furnace tube. The second gas inlet is located at the bottom of the fluidized bed furnace tube. The material outlet is located in the upper part or at the top of the fluidized bed furnace tube. The material outlet of the fluidized bed furnace tube is connected to the material inlet of the vacuum refining furnace.

[0041] In this invention, the device further includes a first feed pipe and a second feed pipe. The first feed pipe is disposed outside the fluidized bed furnace tube and connected to the first material inlet of the fluidized bed furnace tube. The second feed pipe is disposed outside the fluidized bed furnace tube and connected to the second material inlet of the fluidized bed furnace tube.

[0042] Preferably, the lower part of the fluidized furnace tube has a double-layer concentric furnace tube structure.

[0043] In this invention, the first feed pipe extends obliquely downwards through the first material inlet into the fluidized bed furnace tube. The second feed pipe extends obliquely downwards through the second material inlet into the fluidized bed furnace tube.

[0044] Preferably, the first feed pipe has a first material discharge hole. The second feed pipe has a second material discharge hole. Preferably, the diameter of the first material discharge hole is smaller than the diameter of the second material discharge hole.

[0045] In this invention, the angle between the first feed pipe and the axial direction of the fluidized bed furnace tube is 5–80°, preferably 10–70°. The angle between the second feed pipe and the axial direction of the fluidized bed furnace tube is 5–80°, preferably 10–70°.

[0046] In this invention, the diameter of the first material feeding hole is 1-3 mm, preferably 1.2-2.8 mm. The diameter of the second material feeding hole is 2-4 mm, preferably 2.2-3.8 mm.

[0047] In this invention, the vacuum refining furnace is one of the VOD, RH-OB, or RH-KTB type vacuum oxygen blowing refining furnaces.

[0048] To address the problems of long process flow, high energy consumption, and large carbon emissions in existing stainless steel smelting processes, this invention proposes a fluidized bed method for preparing chromium-based stainless steel. This method first introduces iron oxide and chromium oxide into the furnace through the upper and lower parts of the fluidized bed furnace tube, respectively. Then, a first reducing gas and a second reducing gas are introduced into the furnace through the middle and bottom parts of the fluidized bed furnace tube, respectively. Under the influence of the reducing gas flow, the iron oxide and chromium oxide are fluidized, with the iron oxide mainly concentrated in the upper part of the fluidized bed furnace tube and the chromium oxide mainly concentrated in the lower part. The first reducing gas, entering from the middle, moves upwards and reacts with the iron oxide suspended in the upper part to produce elemental iron; while the second reducing gas, entering from the bottom, moves upwards and reacts with the chromium oxide suspended in the lower part to produce elemental chromium. The generated elemental metals, due to reduction and weight loss, are blown by gas flow into a vacuum refining furnace to produce chromium-based stainless steel. Based on the reaction characteristics of the smelting raw materials, this invention proposes a novel two-step process of fluidized bed reduction followed by vacuum melting, utilizing the different reduction reaction temperatures and reducing media of iron oxides and chromium oxides. This new process reduces the melting and initial refining steps in the existing three-step process, significantly shortening the process flow and reducing system energy consumption. Simultaneously, in this process, the two metal oxides are reduced by different reducing media at different temperature ranges within the fluidized bed furnace tubes, improving the reduction efficiency of both metal oxides, thus increasing the yield of elemental metals.

[0049] In existing technologies, stainless steel smelting generally uses iron ore, chromite, and other similar raw materials. This often requires melting and initial refining of these materials, or mixing and pelletizing various ores before smelting to obtain stainless steel products. Therefore, existing stainless steel smelting technologies suffer from long processes, high energy consumption, and large carbon emissions. To address these issues, this application breaks with convention by directly using iron oxides and chromium oxides as smelting raw materials. These two metal oxides directly react with reducing gases to obtain elemental metals, which are then smelted under vacuum to obtain stainless steel products. This application obtains the iron and chromium sources required for smelting stainless steel through the direct reduction of metal oxides. On the one hand, it eliminates the lengthy steps of melting and primary refining or mixing and pelletizing in existing technologies, shortening the process flow and reducing energy consumption. On the other hand, the metal oxides directly react with reducing gases, significantly improving reduction efficiency and increasing the yield of elemental metals. Furthermore, in this application, the two metal oxides undergo their respective reduction reactions, allowing for better matching and control of the reduction reaction temperature and reduction medium based on the reaction characteristics of each metal oxide, ensuring the effectiveness of the reduction reaction. Finally, this application replaces various ores with metal oxides as the existing smelting raw materials, thereby reducing carbon generation and emissions at the source and protecting the environment.

[0050] Furthermore, if multiple ores such as iron ore and chromite are mixed and pelletized before reduction, it will affect the reduction reaction rate of each substance in the pellet, which is not conducive to the reduction of each substance in the pellet. At the same time, due to the mixing of multiple substances, the required reduction reaction temperature is higher (the temperature in the system needs to be raised to the reduction temperature of the most difficult substance to reduce in the pellet), which greatly increases the system energy consumption. Its reduction reaction effect is far inferior to the effect of the two metal oxides in this application being directly reduced by reducing gas.

[0051] In this invention, the iron oxide is Fe2O3 or a mixture of various iron oxides including Fe2O3. That is, the iron oxide can be pure Fe2O3 or a mixture of Fe2O3 and other iron oxides (e.g., Fe3O4, FeO). In this case, the Fe2O3 content is greater than 80%, preferably greater than 85%, and more preferably greater than 90%. Obviously, when the iron oxide is pure Fe2O3, the Fe2O3 content is 100%. In other words, considering the reaction characteristics of each oxide, Fe2O3 is the primary iron source for the final smelting of stainless steel. The chromium oxide is Cr2O3 or a mixture of various chromium oxides including Cr2O3. That is, the chromium oxide can be pure Cr2O3 or a mixture of Cr2O3 and other chromium oxides (e.g., CrO2). In this case, the Cr2O3 content is greater than 50%, preferably greater than 60%, and more preferably greater than 70%. Obviously, when the chromium oxide is pure Cr2O3, the Cr2O3 content is 100%. In other words, considering the reaction characteristics of each oxide, Cr2O3 is the main source of chromium for the final smelting of stainless steel. When both iron oxide and chromium oxide enter the fluidized bed furnace tube, based on the specific iron and chromium content required in the chromium-based stainless steel, the amount of iron oxide added in the furnace is 70% to 90% (preferably 72% to 88%, more preferably 75% to 85%) of the total metal oxides added, while the amount of chromium oxide added is 10% to 30% of the total metal oxides added.

[0052] In this invention, the first reducing gas is H2 or a mixture of multiple reducing gases including H2. That is, the first reducing gas can be pure H2 or a mixture of H2 and other reducing gases (e.g., CO). In this case, the concentration of H2 is greater than 80%, preferably greater than 85%, and more preferably greater than 90%. Obviously, when the first reducing gas is pure H2, the concentration of H2 is 100%. In other words, in this invention, H2 is used as the primary reducing medium. The second reducing gas is CO or a mixture of multiple reducing gases including CO. That is, the second reducing gas can be pure CO or a mixture of CO and other reducing gases (e.g., H2). In this case, the concentration of CO is greater than 60%, preferably greater than 65%, and more preferably greater than 70%. Obviously, when the second reducing gas is pure CO, the concentration of CO is 100%. In other words, in this invention, CO is used as the primary reducing medium. When both the first and second reducing gases enter the fluidized bed furnace tube, the concentration of H2 in all the reducing gases introduced into the furnace is greater than 70%, preferably greater than 75%, and more preferably greater than 80%. This invention uses two metal oxides for direct reduction, thus reducing carbon emissions. Furthermore, by using H2 as the main reducing medium, a significant reduction in carbon emissions is further ensured, aligning with the national low-carbon and low-energy consumption industrial policy.

[0053] Based on the characteristics of the smelting raw materials, this invention proposes a novel two-step process combining fluidized bed reduction and vacuum smelting. The fluidized bed reduction involves controlling the flow rate of the reducing gas entering the fluidized bed furnace tube, thereby suspending the two metal oxides in this application within a set temperature range: iron oxide in the upper-middle part of the furnace, and chromium oxide in the lower-middle part. To ensure successful fluidization of both iron and chromium oxides, they must be ground separately before entering the furnace to meet the particle size requirements for fluidized bed reduction. Generally, the flow rates of the reducing gases entering the fluidized bed furnace tubes are the same, i.e., the flow rates of the first and second reducing gases are identical. Under the same gas flow rate, considering the different specific gravities of iron oxide and chromium oxide (for example, the specific gravity of iron oxide Fe2O3 is greater than that of chromium oxide Cr2O3), the particle size of the ground iron oxide is smaller than that of the chromium oxide. This allows the two metal oxides with different specific gravities to be fluidized smoothly under the same gas flow rate. Based on the specific gravities of iron oxide and chromium oxide, the particle size ratio of the ground chromium oxide powder to the iron oxide powder is 1:(0.98~1). For example, the particle size of the chromium oxide powder is 0.1~1 mm (preferably 0.15~0.9 mm). Based on the aforementioned particle size ratio of the two powders, the particle size of the iron oxide powder can be obtained. Accordingly, based on the particle size of the two metal oxides after grinding, this application adjusts the flow rates of the first reducing gas and the second reducing gas to control the iron oxide powder to be suspended in the upper middle part of the fluidized bed furnace tube, and the chromium oxide powder to be suspended in the lower middle part of the fluidized bed furnace tube. For example, the flow rates of the first reducing gas and the second reducing gas are 0.2 to 2 m / s (preferably 0.3 to 1.8 m / s).

[0054] Iron oxides and chromium oxides have different reaction characteristics. For example, the reduction reaction temperatures of iron oxides and chromium oxides are different, and the reduction of chromium oxides often requires a higher temperature. In this invention, the upper and middle parts of the fluidized bed furnace tube are low-temperature zones (relative to the high-temperature zones), while the lower and middle parts are high-temperature zones. Therefore, in this application, iron oxides and chromium oxides enter the furnace from the upper and lower parts of the fluidized bed furnace tube, respectively. After entering the fluidized bed furnace tube, under the action of the reducing gas flow, iron oxides mainly concentrate in the upper and middle parts of the fluidized bed furnace tube, while chromium oxides mainly concentrate in the lower and middle parts. The temperature of the upper-middle low-temperature zone of the fluidized bed furnace tube, i.e., the reduction reaction temperature range of iron oxide, is 1000–1300℃ (preferably 1050–1280℃); the temperature of the lower-middle high-temperature zone of the fluidized bed furnace tube, i.e., the reduction reaction temperature range of chromium oxide, is 1300–1600℃ (preferably 1350–1580℃). The reduction reaction time of iron oxide and chromium oxide is 0.5–4 hours (preferably 1–3.5 hours). Therefore, this application introduces iron oxide and chromium oxide into the furnace from different positions within the fluidized bed furnace tube to better match the reaction characteristics of different metal oxides, enabling the two metal oxides to complete the reduction more efficiently within their respective reduction reaction temperature ranges. Furthermore, this application divides the fluidized bed furnace tube into two different temperature zones, upper-middle and lower-middle. Iron oxide, with its lower reduction reaction temperature, can be reduced in the upper-middle low-temperature zone, eliminating the need to consider the higher temperature required for the reduction of chromium oxide and thus reducing the overall temperature within the fluidized bed furnace tube, thereby lowering system energy consumption.

[0055] It should be noted that iron oxides and chromium oxides have their own distinct reaction characteristics. For example, iron oxides and chromium oxides have different levels of stability, thus requiring different reduction reaction temperatures and reduction media. As mentioned earlier, the reduction reaction temperature of chromium oxide (Cr₂O₃) is higher than that of iron oxide (Fe₂O₃). Iron oxides (mainly Fe₂O₃) can undergo reduction reactions with H₂ or CO to produce elemental iron. While chromium oxides (mainly Cr₂O₃) can undergo reduction reactions with CO to produce elemental chromium, they are difficult to reduce with H₂. Therefore, this application separately transports iron oxides and chromium oxides to the upper-middle low-temperature zone and the lower-middle high-temperature zone of the fluidized bed furnace tube, ensuring that both oxides can be reduced within their respective reduction reaction temperature ranges. This application also introduces the first reducing gas (mainly H2) and the second reducing gas (mainly CO) into the furnace from the middle and bottom of the fluidized bed furnace tube, respectively. This ensures that the H2 entering from the middle moves upward and can reduce the iron oxides in the upper middle part, while the CO entering from the bottom moves upward and can reduce the chromium oxides in the lower middle part. This ensures that both the iron oxides and chromium oxides are compatible with the reducing medium, thereby ensuring the formation of elemental iron and chromium.

[0056] In this application, although the fluidized bed furnace tube is divided into two different temperature zones, the upper and lower sections, they are not completely separated. Therefore, cross-flow of the two metal oxides is possible; a small amount of chromium oxide may be present in the upper section, and a small amount of iron oxide may be present in the lower section. Correspondingly, cross-flow of the first and second reducing gases is also possible. Furthermore, the first reducing gas is primarily H2, but may also contain a small amount of CO, and the second reducing gas is primarily CO, but may also contain a small amount of H2. Firstly, from a chemical equilibrium perspective, when the reducing medium is entirely CO, the concentration of generated CO2 is high, which can affect the reduction reaction to some extent. Therefore, the simultaneous participation of CO and H2 in the reduction of iron oxides is beneficial to the reduction reaction of iron oxides. Chromium oxides, such as Cr₂O₃, are extremely stable and remain unchanged even when H₂ is introduced at red heat. However, when the reducing medium includes both CO and H₂, CO can first reduce Cr₂O₃ to a certain extent, altering its crystal lattice and weakening its stability, making it easier to reduce. Then, it can continue to react with H₂, allowing for greater utilization of H₂ as the reducing gas and significantly reducing carbon emissions. Therefore, CO and H₂, as reducing media, can be mutually utilized in the reduction of iron and chromium oxides, accelerating the reaction rate and promoting the reduction process.

[0057] As mentioned above, if only CO is used as the reducing medium in this application, on the one hand, it increases carbon emissions, which is inconsistent with the national industrial policy of low-carbon emission reduction; on the other hand, the high concentration of CO2 generated when only CO is used as the reducing medium will inevitably affect the forward chemical reaction, i.e., the reduction reaction. If only H2 is used as the reducing medium in this application, since chromium oxide is extremely stable, it is difficult to react with hydrogen, thus failing to obtain the chromium source required for the final smelting of stainless steel. Obviously, the reduction effect of using a single reducing medium is far inferior to the effect of using both H2 and CO as reducing media to reduce iron oxide and chromium oxide in this invention. Moreover, in this invention, H2 is used as the main reducing medium among the two, effectively solving the problem of high carbon emissions in the prior art.

[0058] Based on the above-described method for preparing stainless steel using fluidized bed technology, this invention also proposes an apparatus for preparing stainless steel using fluidized bed technology. The apparatus includes a fluidized bed furnace tube and a vacuum refining furnace. The upper middle section of the fluidized bed furnace tube has a first material inlet for conveying iron oxides. The lower middle section of the fluidized bed furnace tube has a second material inlet for conveying chromium oxides. The middle section of the fluidized bed furnace tube has a first gas inlet for conveying a first reducing gas. The bottom of the fluidized bed furnace tube has a second gas inlet for conveying a second reducing gas. The upper or top section of the fluidized bed furnace tube has a material outlet for discharging the reduced elemental metal. The material outlet of the fluidized bed furnace tube is connected to the material inlet of the vacuum refining furnace, meaning the reduced elemental metal enters the vacuum refining furnace to produce chromium-based stainless steel.

[0059] To facilitate the delivery of the ground oxide powders to different locations within the fluidized bed furnace tube, this application further includes a first feed pipe and a second feed pipe disposed on the outer side of the fluidized bed furnace tube. The first feed pipe is connected to the first material inlet of the fluidized bed furnace tube, and the second feed pipe is connected to the second material inlet of the fluidized bed furnace tube. Preferably, considering that chromium oxide requires a higher reduction reaction temperature than iron oxide, and that concentric tubes can concentrate heat and increase the temperature of the reaction zone, this application sets the lower middle part of the fluidized bed furnace tube as a double-layer concentric furnace tube structure.

[0060] Further optimized, to prevent the two materials from adhering together upon entering the fluidized bed furnace tube, resulting in excessive weight and hindering fluidization, a first feed pipe extends obliquely downwards through a first material inlet into the fluidized bed furnace tube. Correspondingly, a second feed pipe extends obliquely downwards through a second material inlet into the fluidized bed furnace tube. A first material discharge hole is provided on the first feed pipe. A second material discharge hole is provided on the second feed pipe. The angle between the first or second feed pipe and the axis of the fluidized bed furnace tube can be adjusted as needed (e.g., based on the flow rate of the reducing gas and the particle size of the oxide powder after grinding), for example, an angle of 5–80° (preferably 10–70°).

[0061] In this invention, the specific gravity of iron oxide (mainly Fe2O3) is greater than that of chromium oxide (mainly Cr2O3). To ensure smooth fluidization of both materials at the same airflow velocity, the aperture of the first material discharge orifice is smaller than that of the second material discharge orifice. For example, the aperture of the first material discharge orifice is 1–3 mm (preferably 1.2–2.8 mm), and the aperture of the second material discharge orifice is 2–4 mm (preferably 2.2–3.8 mm).

[0062] In this invention, multiple first material inlets can be provided, evenly distributed in the upper-middle part of the sidewall of the fluidized bed furnace tube. Correspondingly, multiple first feed pipes are provided, each passing through one first material inlet. Each first feed pipe has multiple first material discharge holes evenly distributed on it. Similarly, multiple second material inlets can be provided, evenly distributed in the lower-middle part of the sidewall of the fluidized bed furnace tube. Correspondingly, multiple second feed pipes are provided, each passing through one second material inlet. Each second feed pipe has multiple second material discharge holes evenly distributed on it.

[0063] In this invention, the vacuum refining furnace is one of the VOD, RH-OB, or RH-KTB type vacuum oxygen blowing refining furnaces.

[0064] Compared with the prior art, the present invention has the following beneficial technical effects:

[0065] 1. Based on the reaction characteristics of smelting raw materials, this invention proposes a new two-step process of fluidized bed reduction + vacuum melting by utilizing the different reduction reaction temperatures and reduction media of iron oxide and chromium oxide. This greatly shortens the process flow and reduces system energy consumption. At the same time, in this process, the two metal oxides are reduced by different reduction media in different temperature ranges within the fluidized bed furnace tube, which improves the reduction efficiency of the two metal oxides, that is, improves the yield of elemental metals.

[0066] 2. This invention obtains the iron and chromium sources required for smelting stainless steel through the direct reduction of metal oxides. On the one hand, it eliminates the lengthy steps of melting and primary smelting or mixing and pelletizing in existing technologies, shortening the process flow. On the other hand, the metal oxides directly react with reducing gases, significantly improving the reduction efficiency and thus increasing the yield of elemental metals. Furthermore, in this application, the two metal oxides undergo their respective reduction reactions, allowing for better matching and control of the reduction reaction temperature and reduction medium based on the reaction characteristics of each metal oxide, ensuring the effectiveness of the reduction reaction. Finally, this application replaces various ores with metal oxides as the existing smelting raw materials, thereby reducing carbon production and emissions at the source and protecting the environment.

[0067] 3. This invention introduces iron oxide and chromium oxide into the furnace from different positions within the fluidized bed furnace tube, better matching the reaction characteristics of the different metal oxides. This allows the two metal oxides to complete their reduction more efficiently within their respective reduction reaction temperature ranges. Furthermore, this application divides the fluidized bed furnace tube into two distinct temperature zones: an upper-middle section and a lower-middle section. Iron oxide, with its lower reduction reaction temperature, can be reduced in the lower-temperature upper-middle zone, eliminating the need to consider the higher temperature required for the reduction of chromium oxide. This increases the overall temperature within the fluidized bed furnace tube, thereby reducing system energy consumption.

[0068] 4. This invention uses two reducing media, H2 and CO, to reduce iron oxides and chromium oxides. H2 and CO can be mutually utilized to accelerate the reaction rate and promote the reduction reaction. Moreover, this invention uses H2 as the main reducing medium, which effectively solves the problem of high carbon emissions in the prior art.

[0069] The promotion of this invention has good economic and environmental benefits, and is expected to open up a more stable and efficient way for stainless steel smelting. Attached Figure Description

[0070] Figure 1 This is a schematic diagram of the apparatus for fluidized preparation of chromium-based stainless steel according to the present invention;

[0071] Figure 2 This is a schematic diagram of the lower part of the fluidized bed furnace tube in this invention, which is a double-layer concentric furnace tube structure.

[0072] Figure 3 This is a schematic diagram of the structure of the first feed pipe and the second feed pipe extending into the fluidized bed furnace tube in this invention.

[0073] Figure label:

[0074] 1: Fluidized bed furnace tube; 101: First material inlet; 102: Second material inlet; 103: First gas inlet; 104: Second gas inlet; 105: Material outlet; 2: Vacuum refining furnace; 3: First feed pipe; 301: First material discharge hole; 4: Second feed pipe; 401: Second material discharge hole. Detailed Implementation

[0075] The technical solution of the present invention will be illustrated below with examples. The scope of protection sought by the present invention includes, but is not limited to, the following embodiments.

[0076] According to a second embodiment of the present invention, an apparatus for fluidized bed preparation of chromium-based stainless steel is provided.

[0077] An apparatus for the fluidized bed preparation of chromium-based stainless steel, or an apparatus for preparing chromium-based stainless steel using the method described in the first embodiment, the apparatus comprising a fluidized bed furnace tube 1 and a vacuum refining furnace 2. The fluidized bed furnace tube 1 is provided with a first material inlet 101, a second material inlet 102, a first gas inlet 103, a second gas inlet 104, and a material outlet 105. The first material inlet 101 is located in the upper-middle part of the side wall of the fluidized bed furnace tube 1. The second material inlet 102 is located in the lower-middle part of the side wall of the fluidized bed furnace tube 1. The first gas inlet 103 is located in the middle of the side wall of the fluidized bed furnace tube 1. The second gas inlet 104 is located at the bottom of the fluidized bed furnace tube 1. The material outlet 105 is located in the upper part or top of the fluidized bed furnace tube 1. The material outlet 105 of the fluidized bed furnace tube 1 is connected to the material inlet of the vacuum refining furnace 2.

[0078] In this invention, the device further includes a first feed pipe 3 and a second feed pipe 4. The first feed pipe 3 is disposed on the outside of the fluidized bed furnace tube 1 and is connected to the first material inlet 101 of the fluidized bed furnace tube 1. The second feed pipe 4 is disposed on the outside of the fluidized bed furnace tube 1 and is connected to the second material inlet 102 of the fluidized bed furnace tube 1.

[0079] Preferably, the lower part of the fluidized furnace tube 1 has a double-layer concentric furnace tube structure.

[0080] In this invention, the first feed pipe 3 extends obliquely downward through the first material inlet 101 into the fluidized bed furnace tube 1. The second feed pipe 4 extends obliquely downward through the second material inlet 102 into the fluidized bed furnace tube 1.

[0081] Preferably, the first feed pipe 3 has a first material discharge hole 301. The second feed pipe 4 has a second material discharge hole 401. Preferably, the diameter of the first material discharge hole 301 is smaller than the diameter of the second material discharge hole 401.

[0082] In this invention, the angle between the first feed pipe 3 and the axial direction of the fluidized furnace tube 1 is 5–80°, preferably 10–70°. The angle between the second feed pipe 4 and the axial direction of the fluidized furnace tube 1 is 5–80°, preferably 10–70°.

[0083] In this invention, the diameter of the first material feeding hole 301 is 1-3 mm, preferably 1.2-2.8 mm. The diameter of the second material feeding hole 401 is 2-4 mm, preferably 2.2-3.8 mm.

[0084] In this invention, the vacuum refining furnace 2 is one of the VOD, RH-OB, or RH-KTB type vacuum oxygen blowing refining furnaces.

[0085] Example 1

[0086] like Figure 1 As shown, an apparatus for fluidized bed preparation of chromium-based stainless steel includes a fluidized bed furnace tube 1 and a vacuum refining furnace 2. The fluidized bed furnace tube 1 is provided with a first material inlet 101, a second material inlet 102, a first gas inlet 103, a second gas inlet 104, and a material outlet 105. The first material inlet 101 is located in the upper-middle part of the side wall of the fluidized bed furnace tube 1. The second material inlet 102 is located in the lower-middle part of the side wall of the fluidized bed furnace tube 1. The first gas inlet 103 is located in the middle of the side wall of the fluidized bed furnace tube 1. The second gas inlet 104 is located at the bottom of the fluidized bed furnace tube 1. The material outlet 105 is located at the top of the fluidized bed furnace tube 1. The material outlet 105 of the fluidized bed furnace tube 1 is connected to the material inlet of the vacuum refining furnace 2. The vacuum refining furnace 2 is a VOD type vacuum oxygen blowing refining furnace.

[0087] Example 2

[0088] The same method as Embodiment 1 is used, except that the device further includes a first feed pipe 3 and a second feed pipe 4. The first feed pipe 3 is disposed on the outside of the fluidized bed furnace tube 1 and is connected to the first material inlet 101 of the fluidized bed furnace tube 1. The second feed pipe 4 is disposed on the outside of the fluidized bed furnace tube 1 and is connected to the second material inlet 102 of the fluidized bed furnace tube 1.

[0089] Example 3

[0090] like Figure 2 As shown, Example 2 is repeated, except that the lower part of the fluidized furnace tube 1 is a double-layer concentric furnace tube structure.

[0091] Example 4

[0092] like Figure 3 As shown, Embodiment 2 is repeated, except that the first feed pipe 3 extends obliquely downward through the first material inlet 101 into the fluidization furnace tube 1. The second feed pipe 4 extends obliquely downward through the second material inlet 102 into the fluidization furnace tube 1.

[0093] Example 5

[0094] Example 4 is repeated, except that the first feed pipe 3 has a first material discharge hole 301. The second feed pipe 4 has a second material discharge hole 401.

[0095] Example 6

[0096] Example 5 is repeated, except that the diameter of the first material discharge hole 301 is smaller than the diameter of the second material discharge hole 401.

[0097] Example 7

[0098] Example 6 is repeated, except that the angle between the first feed pipe 3 and the axis of the fluidized furnace tube 1 is 60°. The angle between the second feed pipe 4 and the axis of the fluidized furnace tube 1 is also 60°.

[0099] Example 8

[0100] Example 6 is repeated, except that the angle between the first feed pipe 3 and the axis of the fluidized furnace tube 1 is 50°, and the angle between the second feed pipe 4 and the axis of the fluidized furnace tube 1 is 60°.

[0101] Example 9

[0102] Example 6 is repeated, except that the angle between the first feed pipe 3 and the axis of the fluidized furnace tube 1 is 30°, and the angle between the second feed pipe 4 and the axis of the fluidized furnace tube 1 is 40°.

[0103] Example 10

[0104] Example 7 is repeated, except that the diameter of the first material discharge hole 301 is 2 mm, and the diameter of the second material discharge hole 401 is 3 mm.

[0105] Example 11

[0106] Example 9 is repeated, except that the diameter of the first material discharge hole 301 is 1.5 mm, and the diameter of the second material discharge hole 401 is 2.5 mm.

[0107] Example 12

[0108] Repeat Example 10, except that the vacuum refining furnace 2 is an RH-OB type vacuum oxygen blowing refining furnace.

[0109] Example 13

[0110] Example 11 is repeated, except that the vacuum refining furnace 2 is an RH-KTB type vacuum oxygen blowing refining furnace.

[0111] Example 14

[0112] A method for preparing chromium-based stainless steel by fluidization, the method comprising the following steps:

[0113] 1) Raw material feeding: Iron oxide is conveyed to the upper middle part of fluidized furnace tube 1, and chromium oxide is conveyed to the lower middle part of fluidized furnace tube 1.

[0114] 2) Fluidized reduction: A first reducing gas is introduced from the middle of the fluidized furnace tube 1, and a second reducing gas is introduced from the bottom of the fluidized furnace tube 1. Iron oxides and chromium oxides move from top to bottom in the fluidized furnace tube 1 and react with the first and second reducing gases moving from bottom to top to produce metallic elements of iron and chromium.

[0115] 3) Vacuum melting: The elemental metal generated in step 2) is transported to vacuum refining furnace 2 to produce chromium-based stainless steel.

[0116] Example 15

[0117] A method for preparing chromium-based stainless steel by fluidization, the method comprising the following steps:

[0118] 1) Raw material feeding: Iron oxide and chromium oxide are ground into powder separately. The iron oxide powder obtained after grinding is then conveyed to the upper middle part of the fluidized furnace tube 1, and the chromium oxide powder obtained after grinding is conveyed to the lower middle part of the fluidized furnace tube 1.

[0119] The iron oxide is Fe2O3, and the chromium oxide is Cr2O3. Of all the metal oxides added in the fluidized bed furnace tube 1, Fe2O3 accounts for 80% of the total metal oxide addition, and Cr2O3 accounts for 20%. The particle size of the chromium oxide powder obtained after grinding is 0.5 mm, and the particle size of the iron oxide powder is 0.49 mm.

[0120] 2) Fluidized reduction: A first reducing gas is introduced from the middle of the fluidized furnace tube 1, and a second reducing gas is introduced from the bottom of the fluidized furnace tube 1. Iron oxides and chromium oxides move from top to bottom in the fluidized furnace tube 1 and react with the first and second reducing gases moving from bottom to top to produce metallic elements of iron and chromium.

[0121] The first reducing gas is H2. The second reducing gas is CO. Of all the reducing gases introduced into the fluidized bed furnace tube 1, the concentration of H2 is 78% and the concentration of CO is 22%.

[0122] 3) Vacuum melting: The elemental metal generated in step 2) is transported to vacuum refining furnace 2 to produce chromium-based stainless steel.

[0123] In step 2), the flow rates of the first and second reducing gases are adjusted to 1 m / s, thereby controlling the iron oxide powder to be suspended in the upper and middle parts of the fluidized bed furnace tube 1, and the chromium oxide powder to be suspended in the lower and middle parts of the fluidized bed furnace tube 1. In the upper and middle parts of the fluidized bed furnace tube 1, the reduction reaction temperature of the iron oxide is 1200℃, and the reduction reaction time is 1.5 h. In the lower and middle parts of the fluidized bed furnace tube 1, the reduction reaction temperature of the chromium oxide is 1450℃, and the reduction reaction time is 1.5 h. At this time, in step 3), the reduced elemental iron and chromium are blown by the gas flow into the vacuum refining furnace 2 to produce chromium-based stainless steel.

[0124] Example 16

[0125] Example 15 is repeated, except that in step 1), the iron oxide is a mixture of Fe2O3, Fe3O4, and FeO. The chromium oxide is a mixture of Cr2O3 and CrO2. The Fe2O3 content in the iron oxide is 96%. The Cr2O3 content in the chromium oxide is 86%. Of all the metal oxides added in the fluidized bed furnace tube 1, the amount of iron oxide added is 84% ​​of the total amount of metal oxides added, and the amount of chromium oxide added is 16% of the total amount of metal oxides added.

[0126] Example 17

[0127] Example 15 is repeated, except that in step 2), the first reducing gas is a mixture of H2 and CO. The second reducing gas is a mixture of CO and H2. In the first reducing gas, the concentration of H2 is 90% and the concentration of CO is 10%. In the second reducing gas, the concentration of CO is 70% and the concentration of H2 is 30%. Of all the reducing gases introduced into the fluidized bed furnace tube 1, the concentration of H2 is 82% and the concentration of CO is 18%.

[0128] Example 18

[0129] Example 15 is repeated, except that in step 1), the particle size of the chromium oxide powder obtained after grinding is 0.8 mm and the particle size of the iron oxide powder is 0.79 mm. In step 2), the flow rates of the first reducing gas and the second reducing gas are adjusted to 1.4 m / s, thereby controlling the iron oxide powder to be suspended in the upper middle part of the fluidized bed furnace tube 1 and the chromium oxide powder to be suspended in the lower middle part of the fluidized bed furnace tube 1.

[0130] Example 19

[0131] Example 16 was repeated, except that in the upper middle part of the fluidized bed furnace tube 1, the reduction reaction temperature of iron oxide was 1100°C and the reduction reaction time of iron oxide was 2 hours. In the lower middle part of the fluidized bed furnace tube 1, the reduction reaction temperature of chromium oxide was 1400°C and the reduction reaction time of chromium oxide was 2 hours.

Claims

1. A method for preparing chromium-based stainless steel by fluidization, the method comprising the following steps: 1) Raw material feeding: Iron oxide is fed to the upper middle part of the fluidized furnace tube (1), and chromium oxide is fed to the lower middle part of the fluidized furnace tube (1); 2) Fluidized reduction: A first reducing gas is introduced from the middle of the fluidized furnace tube (1), and a second reducing gas is introduced from the bottom of the fluidized furnace tube (1). Iron oxide and chromium oxide move from top to bottom in the fluidized furnace tube (1) and react with the first and second reducing gases moving from bottom to top to generate metallic elements of iron and chromium. The flow rates of the first and second reducing gases are adjusted to control the iron oxide to be suspended in the upper middle part of the fluidized furnace tube (1) and the chromium oxide to be suspended in the lower middle part of the fluidized furnace tube (1). 3) Vacuum melting: The elemental metal generated in step 2) is transported to a vacuum refining furnace (2) to produce chromium-based stainless steel.

2. The method according to claim 1, characterized in that: In step 2), the first reducing gas is H2 or a mixture of multiple reducing gases including H2; the second reducing gas is CO or a mixture of multiple reducing gases including CO.

3. The method according to claim 2, characterized in that: In the first reducing gas, the concentration of H2 is greater than 80%; in the second reducing gas, the concentration of CO is greater than 60%.

4. The method according to claim 3, characterized in that: In the first reducing gas, the concentration of H2 is greater than 85%; in the second reducing gas, the concentration of CO is greater than 65%.

5. The method according to claim 4, characterized in that: In the first reducing gas, the concentration of H2 is greater than 90%; in the second reducing gas, the concentration of CO is greater than 70%.

6. The method according to claim 1, characterized in that: In step 1), the iron oxide is Fe2O3 or a mixture of various iron oxides including Fe2O3; the chromium oxide is Cr2O3 or a mixture of various chromium oxides including Cr2O3.

7. The method according to claim 6, characterized in that: In iron oxides, the Fe2O3 content is greater than 80%; in chromium oxides, the Cr2O3 content is greater than 50%.

8. The method according to claim 7, characterized in that: In iron oxides, the Fe2O3 content is greater than 85%; in chromium oxides, the Cr2O3 content is greater than 60%.

9. The method according to claim 8, characterized in that: In iron oxides, the Fe2O3 content is greater than 90%; in chromium oxides, the Cr2O3 content is greater than 70%.

10. The method according to claim 1, characterized in that: In all reducing gases introduced into the fluidized bed furnace tube (1), the concentration of H2 is greater than 70%; and / or Of all the metal oxides added in the fluidized furnace tube (1), the amount of iron oxide added is 70% to 90% of the total amount of metal oxides added.

11. The method according to claim 10, characterized in that: In all reducing gases introduced into the fluidized bed furnace tube (1), the concentration of H2 is greater than 75%; and / or Of all the metal oxides added in the fluidized bed furnace tube (1), the amount of iron oxide added is 72% to 88% of the total amount of metal oxides added.

12. The method according to claim 11, characterized in that: In all reducing gases introduced into the fluidized bed furnace tube (1), the concentration of H2 is greater than 80%; and / or Of all the metal oxides added in the fluidized furnace tube (1), the amount of iron oxide added is 75% to 85% of the total amount of metal oxides added.

13. The method according to any one of claims 1-12, characterized in that: Step 1) Specifically, iron oxide and chromium oxide are ground into powder respectively, and then the iron oxide powder obtained after grinding is conveyed to the upper middle part of the fluidized furnace tube (1), and the chromium oxide powder obtained after grinding is conveyed to the lower middle part of the fluidized furnace tube (1).

14. The method according to claim 13, characterized in that: The particle size ratio of the chromium oxide powder to the iron oxide powder is 1:(0.98~1); wherein the particle size of the chromium oxide powder is 0.1~1mm.

15. The method according to claim 14, characterized in that: The particle size of the chromium oxide powder is 0.15~0.9mm.

16. The method according to claim 13, characterized in that: In step 2), the flow rates of the first reducing gas and the second reducing gas are adjusted to control the iron oxide powder to be suspended in the upper middle part of the fluidized furnace tube (1) and the chromium oxide powder to be suspended in the lower middle part of the fluidized furnace tube (1); in step 3), the reduced metal element is blown by the gas flow to the vacuum refining furnace (2) to produce chromium stainless steel.

17. The method according to claim 16, characterized in that: In the fluidized bed furnace tube (1), the flow rates of the first reducing gas and the second reducing gas are 0.2~2m / s.

18. The method according to claim 17, characterized in that: In the fluidized bed furnace tube (1), the flow rates of the first reducing gas and the second reducing gas are 0.3~1.8 m / s.

19. The method according to claim 16, characterized in that: In the upper middle part of the fluidized bed furnace tube (1), the reduction reaction temperature of iron oxide is 1000~1300℃; the reduction reaction time of iron oxide is 0.5~4h; and / or In the middle and lower part of the fluidized furnace tube (1), the reduction reaction temperature of chromium oxide is 1300~1600℃; the reduction reaction time of chromium oxide is 0.5~4h.

20. The method according to claim 19, characterized in that: In the upper middle part of the fluidized bed furnace tube (1), the reduction reaction temperature of iron oxide is 1050~1280℃; the reduction reaction time of iron oxide is 1~3.5h; and / or In the middle and lower part of the fluidized bed furnace tube (1), the reduction reaction temperature of chromium oxide is 1350~1580℃; the reduction reaction time of chromium oxide is 1~3.5h.

21. An apparatus for preparing chromium-based stainless steel by the method according to any one of claims 1-20, characterized in that: The device includes a fluidized bed furnace tube (1) and a vacuum refining furnace (2); the fluidized bed furnace tube (1) is provided with a first material inlet (101), a second material inlet (102), a first gas inlet (103), a second gas inlet (104), and a material outlet (105); wherein, the first material inlet (101) is located in the upper middle part of the side wall of the fluidized bed furnace tube (1); the second material inlet (102) is located in the lower middle part of the side wall of the fluidized bed furnace tube (1); the first gas inlet (103) is located in the middle part of the side wall of the fluidized bed furnace tube (1); the second gas inlet (104) is located at the bottom of the fluidized bed furnace tube (1); the material outlet (105) is located in the upper part or top of the fluidized bed furnace tube (1); the material outlet (105) of the fluidized bed furnace tube (1) is connected to the material inlet of the vacuum refining furnace (2).

22. The apparatus according to claim 21, characterized in that: The device also includes a first feed pipe (3) and a second feed pipe (4); the first feed pipe (3) is located outside the fluidized furnace tube (1) and is connected to the first material inlet (101) of the fluidized furnace tube (1); the second feed pipe (4) is located outside the fluidized furnace tube (1) and is connected to the second material inlet (102) of the fluidized furnace tube (1).

23. The apparatus according to claim 22, characterized in that: The lower part of the fluidized furnace tube (1) has a double-layer concentric furnace tube structure.

24. The apparatus according to claim 22, characterized in that: The first feed pipe (3) passes through the first material inlet (101) and extends obliquely downward into the fluidized furnace tube (1); the second feed pipe (4) passes through the second material inlet (102) and extends obliquely downward into the fluidized furnace tube (1).

25. The apparatus according to claim 24, characterized in that: The first feed pipe (3) has a first material discharge hole (301); the second feed pipe (4) has a second material discharge hole (401).

26. The apparatus according to claim 25, characterized in that: The diameter of the first material discharge hole (301) is smaller than the diameter of the second material discharge hole (401).

27. The apparatus according to claim 25, characterized in that: The angle between the first feed pipe (3) and the axis of the fluidized bed tube (1) is 5~80°; the angle between the second feed pipe (4) and the axis of the fluidized bed tube (1) is 5~80°; and / or The diameter of the first material discharge hole (301) is 1~3mm; the diameter of the second material discharge hole (401) is 2~4mm.

28. The apparatus according to claim 27, characterized in that: The angle between the first feed pipe (3) and the axis of the fluidized bed tube (1) is 10~70°; the angle between the second feed pipe (4) and the axis of the fluidized bed tube (1) is 10~70°; and / or The diameter of the first material discharge hole (301) is 1.2~2.8mm; the diameter of the second material discharge hole (401) is 2.2~3.8mm.

29. The apparatus according to any one of claims 21-28, characterized in that: The vacuum refining furnace (2) is one of the VOD, RH-OB, or RH-KTB type vacuum oxygen blowing refining furnaces.

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