Spiral countercurrent reinforced iron ore reduction system and smelting method

Abstract

The invention relates to the technical field of ferrous metallurgy, in particular to a spiral countercurrent reinforced iron ore reduction system and a smelting method. Comprising a reduction furnace body and a spiral conveyor arranged in the reduction furnace body, the reduction furnace body is vertically arranged, a feeding pipeline is arranged at the top of the reduction furnace body, a discharging pipeline is arranged at the bottom or the lower part, and a reducing gas inlet is formed in the lower part of the side wall of the furnace body; the spiral conveyor comprises a vertically arranged spiral rod main shaft and a spiral blade fixed on the spiral rod main shaft; and the screw rod main shaft is driven by a driving device to rotate, so that iron ore raw materials can spirally descend, and reducing gas can be guided to spirally ascend. And the retention time of the coal gas in the furnace can be effectively prolonged, and the contact and mixing between the gas phase and the solid phase are strengthened, so that the utilization efficiency of the coal gas is fundamentally improved, and the more flexible and accurate control on the reduction process is realized.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, specifically to a spiral countercurrent enhanced iron ore reduction system and smelting method. Background Technology

[0002] In the iron and steel metallurgy industry, the reduction smelting of iron ore is a core technological process. Currently, the main equipment for large-scale industrial pig iron production is the blast furnace, while direct reduced iron production mostly uses reactors such as vertical shaft furnaces. Whether it is a blast furnace's bulk belt furnace or a dedicated reduction vertical shaft furnace, the internal materials (iron ore, pellets, etc.) and reducing gas (mainly composed of CO and H2) generally adopt a simple counter-current contact method: that is, the furnace charge moves from top to bottom under the action of gravity, while the gas flow passes through the material layer from bottom to top under pressure.

[0003] While this traditional counter-current contact method is simple and reliable in terms of process, its inherent drawbacks limit further improvements in technical and economic indicators. The primary problem lies in the low gas utilization efficiency. Due to the relatively straight gas flow path and low resistance, the actual gas velocity within the furnace is high, resulting in a short residence time. This leads to insufficient heat and mass transfer (reduction reaction) between the gas and the solid charge, causing a large amount of CO and H2 with reduction potential to escape from the furnace top without participating in the reaction. Public data and production practice show that the gas utilization rate of blast furnace block furnaces and typical vertical shaft furnaces is generally only 30% to 35%, which not only results in a huge waste of energy but also increases the load on subsequent gas purification and treatment.

[0004] In addition, traditional vertical shaft furnaces or blast furnaces with blocky zones have relatively simple and crude methods for controlling the reduction process. They mainly rely on adjusting the overall gas flow, temperature and pressure, making it difficult to precisely intervene in the reaction process in specific areas of the furnace and to flexibly adjust the degree of reduction of the final product in real time according to changes in the properties of the raw materials. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a spiral countercurrent enhanced iron ore reduction system and smelting method. This system effectively prolongs the residence time of the gas in the furnace, enhances the contact and mixing between the gas and solid phases, thereby fundamentally improving gas utilization efficiency and enabling more flexible and precise control of the reduction process.

[0006] To achieve the above objectives, the present invention employs the following technical solution: A spiral countercurrent enhanced iron ore reduction system includes: a reduction furnace body and a spiral conveyor disposed inside the reduction furnace body; the reduction furnace body is vertically arranged, with a feeding pipe at the top and a discharge pipe at the bottom or lower part, and a reducing gas inlet at the lower part of the side wall of the furnace body; the spiral conveyor includes a vertically arranged spiral shaft and spiral blades fixed thereon; the spiral shaft is driven to rotate by a drive device, which can simultaneously realize the spiral descent of iron ore raw material and guide the reducing gas spiral upward.

[0007] Furthermore, an annular gap is provided between the outer edge of the spiral blade and the inner wall of the reduction furnace body, and the width of the annular gap is no more than 2mm.

[0008] Furthermore, the main shaft of the screw is hinged to the reduction furnace body via a head bearing and a tail bearing; the drive device includes a variable frequency motor and a reducer connected in sequence.

[0009] Furthermore, the system also includes a discharge system connected to the discharge pipe, the discharge system including a high-pressure tank, a variable-pressure tank and an atmospheric-pressure tank to achieve continuous discharge; the system also includes a feeding system connected to the feeding pipe, the feeding system including an atmospheric-pressure tank, a variable-pressure tank and a high-pressure tank to achieve continuous feeding.

[0010] Furthermore, the system also includes a reducing gas circulation system, which includes, in sequence via pipelines: a purification unit for purifying the flue gas discharged from the top of the reducing furnace; a compressor for compressing the purified gas; a buffer tank for storing the compressed gas; and a heating furnace for heating the circulating gas; wherein the outlet of the heating furnace is connected to the reducing gas inlet, and the buffer tank is provided with a replenishing reducing gas interface.

[0011] Furthermore, the reducing gas circulation system is also equipped with at least one of a cyclone heat exchanger and a dust collector.

[0012] Furthermore, the main shaft and the helical blades are made of high-temperature resistant alloy steel.

[0013] A method for smelting iron ore using the above system includes the following steps: S1: Introduce reducing gas A reducing gas heated to 750-800°C is introduced into the reduction furnace. The reducing gas is H2, CO, or a mixture of both.

[0014] S2: Start the screw conveyor Start the drive unit to rotate the screw conveyor.

[0015] S3: Add and restore materials Iron ore raw materials are continuously fed into the reduction furnace through a feeding system and feeding pipes. The iron ore raw materials are any one or a combination of pellets, sinter, and lump ore. Inside the reduction furnace, the iron ore raw materials spiral down under the action of rotating spiral blades. At the same time, the reducing gas spirals up under the guidance of rotating spiral blades and undergoes a countercurrent contact reduction reaction with the spirally descending iron ore raw materials.

[0016] S4: Excretion of waste products The reduced product is continuously discharged through the discharge pipe and discharge system.

[0017] S5: The high-temperature flue gas discharged from the top of the reduction furnace will be processed sequentially through a cyclone heat exchanger, dust collector, purification unit, compressor, buffer tank and heating furnace.

[0018] S6: The gas processed and reheated in step S5 is circulated into the reduction furnace (1) as a reducing gas; wherein, fresh H2, CO or a mixture of both is added to the buffer tank.

[0019] Furthermore, in steps S2 and / or S3, the descent speed of the iron ore raw material in the reduction furnace is controlled by adjusting the rotation speed of the drive device, thereby controlling the degree of reduction and discharge speed of the product.

[0020] Compared with existing methods, the beneficial effects of the present invention are: 1. Significantly improve gas utilization efficiency and achieve energy conservation and consumption reduction. Because this invention employs a built-in screw conveyor, its rotation forces the reducing gas to rise along a spiral path. Compared to the near-linear upward path of gas in traditional vertical furnaces, this significantly extends the flow path and residence time of the gas within the furnace. Simultaneously, the solid charge descends spirally under the propulsion of the screw blades, further increasing the contact opportunities and area between the gas and solid phases. This "spiral counter-current" contact method ensures more thorough contact between the reducing components (CO and H2) in the gas and the iron ore, significantly improving mass transfer and reaction efficiency. Therefore, this invention can dramatically increase the gas utilization rate from approximately 30%–35% in traditional systems to a higher level, effectively reducing excessive consumption of reducing gas, achieving significant energy savings, and lowering the fuel cost per ton of iron.

[0021] 2. Achieve flexible and precise control over the reduction process. Because this invention controls the screw rotation speed via a variable frequency motor, it directly transforms the key process parameter of "reduction time" into a directly adjustable and precise operational variable. Operators can flexibly adjust the screw rotation speed according to different raw material types or varying requirements for product reduction levels (such as metallization rate), thereby controlling the residence time of the material in the high-temperature reduction zone. Compared to traditional vertical shaft furnaces that rely primarily on methods that are difficult to precisely control, such as changing the height of the feed column or the amount of gas, this invention achieves precise and flexible control over the final product quality, enhancing process adaptability and product consistency.

[0022] 3. Enhance heat transfer within the furnace to improve reaction efficiency. As the reducing gas ascends in a spiral, it mixes and collides more vigorously with the spiral blades and the furnace charge, which greatly enhances the heat transfer process between the gas and solid phases. The heat carried by the high-temperature gas can be transferred to the low-temperature furnace charge more efficiently, allowing the furnace charge to reach and maintain the optimal reaction temperature (750~800℃) more quickly. This accelerates the kinetics of the reduction reaction and helps to improve the yield per unit time of the entire unit.

[0023] 4. Achieve continuous, stable, and efficient closed-loop production. Because this invention combines a screw conveyor reduction device with a continuous feeding and discharging system including multi-stage material tanks and a complete gas circulation system, it achieves truly continuous and closed-loop operation throughout the entire process. This not only avoids pressure and gas volume fluctuations caused by traditional intermittent operation, ensuring the stability and efficiency of the reaction, but also completely solves the gas leakage problem that may occur during feeding and discharging in traditional devices, fundamentally improving the working environment, eradicating fugitive emissions, and demonstrating outstanding environmental benefits.

[0024] 5. Improve the economic efficiency and environmental friendliness of the entire system. The integrated gas circulation system of this invention can purify, compress, replenish with fresh gas, and reheat the exhaust gas from the furnace top for reuse. This maximizes the utilization of residual reducing gases and sensible heat in the exhaust gas, further reducing the purchase cost of fresh reducing gas (saving raw materials) and reducing the energy consumption of the heating furnace by recovering waste heat through equipment such as cyclone heat exchangers. The entire system forms a low-consumption, low-emission circular process. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure and process principle of the present invention.

[0026] In the diagram: 1. Reduction furnace body; 2. Screw main shaft; 3. Screw blade; 4. Head bearing; 5. Reducer; 6. Variable frequency motor; 7. Tail bearing; 8. Discharge pipe; 9. Feeding pipe. Detailed Implementation

[0027] The embodiments of the present invention are described in detail below. To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0029] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0030] In the description of this invention, it should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0031] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0032] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0033] Example: like Figure 1 As shown, this embodiment provides a spiral countercurrent enhanced iron ore reduction system, the specific configuration of which is as follows: The reduction furnace body 1 is designed as a vertical cylindrical structure with an inner diameter of 1.5m and a height of 2.5m. The inner wall is constructed of high-temperature resistant refractory material to withstand the high-temperature environment inside.

[0034] Inside the reduction furnace body 1, a screw conveyor is coaxially mounted. This screw conveyor is welded together from a screw shaft 2 and screw blades 3. Both the screw shaft 2 and the screw blades 3 are made of high-temperature resistant alloy steel to ensure sufficient high-temperature strength and oxidation resistance under a reducing atmosphere of 750~800℃. The outer diameter of the screw blades 3 is precisely designed to be slightly smaller than the inner diameter of the reduction furnace body 1, so that the width of the annular gap between the outer edge of the blades and the inner wall of the furnace body is controlled within the range of 1~2mm. This gap is small enough to force most of the reducing gas to rise along the spiral channel, avoiding short-circuiting of the gas flow, while also ensuring that the screw does not rub against or get stuck against the furnace wall when it expands due to heat and undergoes slight deformation.

[0035] The upper end of the screw shaft 2 is hinged to and supported on the reduction furnace body 1 via a head bearing 4 and a tail bearing 7, ensuring stable rotation. The head bearing 4 is a high-temperature bearing capable of withstanding axial thrust and radial load. The lower end of the screw shaft 2 extends outside the furnace and is sequentially connected to a reducer 5 and a variable frequency motor 6. The rotational speed of the screw shaft can be steplessly adjusted via the variable frequency motor 6.

[0036] The top right sidewall of the reduction furnace body 1 is connected to a feeding pipe 9, which is connected to an external continuous feeding system (not fully shown in the figure). This feeding system includes an atmospheric pressure tank, a variable pressure tank, and a high pressure tank. By alternating the tank pressure, the iron ore raw material (pellets are used in this embodiment) is continuously and stably added to the furnace without interrupting the high-pressure process inside the reduction furnace.

[0037] A discharge pipe 8 is connected to the bottom right side of the reduction furnace body 1. This discharge pipe 8 is connected to an external continuous discharge system (not fully shown in the figure). The discharge system includes a high-pressure tank, a variable-pressure tank, and an atmospheric-pressure tank. Its working principle is similar to that of the feeding system. It is used to continuously and stably discharge the reduced product (direct reduced iron) from the high-pressure reduction furnace to maintain the continuity of production.

[0038] A reducing gas inlet is located on the lower left side wall of the reduction furnace body 1, positioned higher than the discharge pipe 8. This inlet is connected to a reducing gas circulation system via a pipe. This system, along the gas flow direction, includes, in sequence: a cyclone heat exchanger, a dust collector, a purification unit, a compressor, a buffer tank, and a heating furnace. The high-temperature flue gas (approximately 300-500°C) discharged from the top of the reduction furnace body 1 first enters the cyclone heat exchanger, where it indirectly exchanges heat with the cold coal gas to recover waste heat. It then passes through the dust collector to remove solid dust, and then enters the purification unit (such as a desulfurization and decarbonization device) for deep purification. The purified coal gas is pressurized by the compressor and sent to the buffer tank for storage and pressure stabilization. Finally, the coal gas is reheated to 800°C in the heating furnace and returned to the reduction furnace body 1 through the reducing gas inlet, completing the cycle. The buffer tank is equipped with a reducing gas replenishment interface, used to replenish fresh H2 into the system according to process requirements to maintain the reducing potential and pressure balance within the system.

[0039] The method for iron ore smelting using the above system specifically includes the following steps: S1: Introduce reducing gas. Start the system and heat the circulating reducing gas (pure H2 in this embodiment) to 800°C through the heating furnace, and introduce it into the reducing furnace body 1 through the reducing gas inlet.

[0040] S2: Start the screw conveyor. Start the variable frequency motor 6, which, after being reduced in speed by the reducer 5, drives the screw shaft 2 to rotate at an initial speed of 5 rpm.

[0041] S3: Adding and Reducing Materials. Pellet ore is continuously added to the reduction furnace 1 at a rate of 10 t / h via a continuous feeding system and feeding pipe 9. After entering the furnace, the pellet ore is captured and propelled by the rotating screw blades 3, forming a spiral downward trajectory. Simultaneously, high-temperature H2 reducing gas enters from the bottom of the furnace and is guided by the rotating screw blades 3, forming a spiral upward airflow that matches the material's downward trajectory. During this process, the gas and solid phases come into full contact, and the pellet ore is efficiently reduced to direct reduced iron.

[0042] S4: Product Discharge. The reduced direct reduced iron product, pushed by the spiral blades, finally enters the continuous discharge system through the discharge pipe 8 and is continuously discharged at a rate basically matching the feeding rate, entering the next process.

[0043] S5 and S6: Flue gas recirculation. The exhaust gas, at approximately 400°C, discharged from the top of the reduction furnace 1, sequentially passes through a cyclone heat exchanger (recovering waste heat and preheating the circulating gas to approximately 300°C), a dust collector, a purification unit, a compressor, a buffer tank, and a heating furnace (finally heated to 800°C) before being recycled as reducing gas. During this process, based on process analysis results, a small amount of fresh H2 is continuously added to the buffer tank to maintain the system's hydrogen concentration.

[0044] Throughout the smelting process, operators adjust the speed of the variable frequency motor 6 in real time based on the results of rapid quality analysis of the discharged direct reduced iron products. For example, if the metallization rate of the product is detected to be low, the screw speed can be appropriately reduced to 4 rpm to prolong the reduction time of the material in the furnace, thereby improving the degree of reduction; conversely, the speed can be increased to increase output. In this way, precise and flexible control over product quality and production efficiency is achieved.

[0045] Using the system and method of this embodiment, calculations show that the utilization rate of coal gas (H2) can be stably increased to over 50%, which is significantly more energy-efficient than that of traditional vertical furnaces (approximately 35%), and the product quality is stable and controllable. This invention effectively extends the residence time of coal gas in the furnace, enhances the contact and mixing between the gas and solid phases, thereby fundamentally improving coal gas utilization efficiency and enabling more flexible and precise control of the reduction process.

[0046] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A spiral countercurrent enhanced iron ore reduction system, characterized in that, include: The reduction furnace body (1) and the screw conveyor disposed inside the reduction furnace body (1); The reduction furnace body (1) is vertically arranged, with a feeding pipe (9) at the top and a discharge pipe (8) at the bottom or lower part. A reducing gas inlet is provided at the lower part of the side wall of the furnace body. The screw conveyor includes a vertically arranged screw shaft (2) and screw blades (3) fixed thereon; The main shaft (2) of the screw rod is driven to rotate by the drive device, which can simultaneously realize the spiral descent of iron ore raw materials and guide the reducing gas spiral upward.

2. The spiral countercurrent enhanced iron ore reduction system according to claim 1, characterized in that, An annular gap is provided between the outer edge of the spiral blade (3) and the inner wall of the reduction furnace body (1), and the width of the annular gap is no more than 2 mm.

3. The spiral countercurrent enhanced iron ore reduction system according to claim 1, characterized in that, The main shaft (2) of the screw rod is hinged to the reduction furnace body (1) through the head bearing (4) and the tail bearing (7); the driving device includes a variable frequency motor (6) and a reducer (5) connected in sequence.

4. The spiral countercurrent enhanced iron ore reduction system according to claim 1, characterized in that, The system also includes a discharge system connected to the discharge pipe (8), the discharge system including a high-pressure tank, a variable-pressure tank and an atmospheric pressure tank to achieve continuous discharge; the system also includes a feeding system connected to the feeding pipe (9), the feeding system including an atmospheric pressure tank, a variable-pressure tank and a high-pressure tank to achieve continuous feeding.

5. The spiral countercurrent enhanced iron ore reduction system according to claim 1, characterized in that, The system also includes a reducing gas circulation system, which comprises components connected sequentially via pipelines: A purification unit for purifying the flue gas discharged from the top of the reduction furnace body (1); A compressor used to compress purified gas; Buffer tanks used to store compressed gas; And a heating furnace for heating the circulating gas; The outlet of the heating furnace is connected to the inlet of the reducing gas, and the buffer tank is provided with a replenishing reducing gas interface.

6. The spiral countercurrent enhanced iron ore reduction system according to claim 5, characterized in that, The reducing gas circulation system is also equipped with at least one of a cyclone heat exchanger and a dust collector.

7. The spiral countercurrent enhanced iron ore reduction system according to claim 1, characterized in that, The main shaft (2) and the spiral blade (3) are made of high-temperature resistant alloy steel.

8. A method for smelting iron ore using the system described in any one of claims 1-7, characterized in that, Includes the following steps: S1: Introduce reducing gas A reducing gas heated to 750~800°C is introduced into the reduction furnace body (1). The reducing gas is H2, CO or a mixture of both. S2: Start the screw conveyor Start the drive unit to rotate the screw conveyor; S3: Add and restore materials Iron ore raw materials are continuously fed into the reduction furnace body (1) through the feeding system and feeding pipe (9). The iron ore raw materials are any one or a combination of pellets, sintered ore, and lump ore. Inside the reduction furnace (1), the iron ore raw material spirals downward under the action of the rotating spiral blades (3), while the reducing gas spirals upward under the guidance of the rotating spiral blades (3) and undergoes a countercurrent contact reduction reaction with the spirally descending iron ore raw material. S4: Excretion of waste products The reduced product is continuously discharged through the discharge pipe (8) and the discharge system.

9. The iron ore smelting method according to claim 8, characterized in that, In steps S2 and / or S3, the descent speed of the iron ore raw material in the reduction furnace body (1) is controlled by adjusting the rotation speed of the drive device, thereby controlling the degree of reduction and discharge speed of the product.

10. A method for smelting iron ore according to claim 8, characterized in that, The method also includes the step of circulating the flue gas from the furnace top: S5: The high-temperature flue gas discharged from the top of the reduction furnace body (1) is processed sequentially through a cyclone heat exchanger, a dust collector, a purification unit, a compressor, a buffer tank, and a heating furnace; S6: The gas processed and reheated in step S5 is circulated into the reduction furnace (1) as a reducing gas; The buffer tank is replenished with fresh H2, CO, or a mixture of both gases.

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