CN115354105B - A system and method for reducing exhaust gas circulation with gas-based direct reduction of iron - Google Patents

Abstract

The invention relates to a system and a method for reducing gas-based direct reduced iron of exhaust gas circulation. According to the invention, the reducing gas is prepared by gasifying carbon-rich raw materials such as coal or biomass, and the reducing exhaust gas with a certain reducing potential and heat development energy is subjected to the process of directly reducing iron according to the gas base, so that the heat and the quality of the reducing exhaust gas are recycled, and the recycling is returned to the process of directly reducing iron smelting, thereby reducing the energy consumption of the gas base short-flow iron making process.

Description

A system and method for reducing exhaust gas circulation with gas-based direct reduction of iron

Technical Field

The invention belongs to the technical field of metal smelting, and in particular relates to a system and method for gas-based direct reduction of iron by reducing a waste gas cycle.

Background technique

The information disclosed in the background of the invention is only intended to enhance the understanding of the overall background of the invention and should not be necessarily regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

At present, the steel production process is mainly based on the long process of sintering and blast furnace, and the operation process has problems such as complex process flow, high energy consumption, and large pollutant emissions. On the other hand, with the deepening of industrialization, the recycling rate of scrap steel has increased, and the demand for direct reduced iron (sponge iron) for the utilization of scrap steel has also increased significantly. Direct reduced iron is an industrial raw material, mainly used in electric furnace steelmaking, partially replacing scrap steel or used in combination with scrap steel to improve furnace charges.

The short-process ironmaking process of gas-based direct reduction can not only meet the demand for direct reduced iron production, but also has the advantages of short process flow and low pollutant emissions. However, the energy consumption of gas-based direct reduced iron is higher than that of blast furnace. The main reason is that the traditional blast furnace smelting process fully utilizes the reducing potential and countercurrent heat exchange of the reducing gas, and the discharged blast furnace gas has low calorific value and low temperature; while the reducing exhaust gas discharged from the short-process iron smelting process has high reducing potential and high temperature. Therefore, reducing the energy consumption of gas-based direct reduced iron is a problem that must be solved for the large-scale industrial application of short-process direct reduced iron.

Summary of the invention

In view of the current energy situation in my country and the high energy consumption of the gas-based direct reduction of iron process, the present invention provides a system and method for gas-based direct reduction of iron with a reduction exhaust gas cycle. The present invention proposes to prepare reducing gas by gasifying carbon-rich raw materials such as coal or biomass, and according to the gas-based direct reduction of iron process, the reduction exhaust gas with a certain reduction potential and sensible heat energy is recycled to realize the heat and quality recovery of the reduction exhaust gas and return it to the direct reduction of iron smelting process, thereby reducing the energy consumption of the gas-based short-process ironmaking process.

To achieve the above object, the present invention adopts the following technical solution:

In a first aspect, the present invention provides a system for reducing gas-spent-gas-circulated gas-based direct-reduced iron, comprising: a gasification device, a mixing unit, a ore powder reduction unit, a ore powder preheating unit, a heat recovery device, a waste heat boiler, a dust removal device, a pressure swing adsorption purification device, a reduced iron powder cooler, a magnetic separation device and a hot pressing device; the gasification device, the mixing unit, the ore powder reduction unit, the ore powder preheating unit, the heat recovery device, the waste heat boiler, the dust removal device and the pressure swing adsorption purification device are connected in sequence, and the ore powder preheating unit, the ore powder reduction unit, the reduced iron powder cooler, the magnetic separation device and the hot pressing device are connected in sequence.

Furthermore, the system also includes a combustion device; the inlet of the combustion device is connected to the dust removal device, and the outlet pipe of the combustion device is connected to the outlet pipe of the heat recovery device and merged into a pipe connected to the mixing unit.

The present invention provides a method for reducing gas-based direct reduction of iron by exhaust gas circulation. The method comprises the following steps:

(1) The carbon-rich raw material reacts with the gasifying agent in the gasification device to generate H ₂ and CO-rich gas, and the reduced exhaust gas with a lower outlet temperature of the dust removal device is returned to the gasification device for temperature adjustment;

(2) The gasification gas generated by the gasification device is mixed with the purified and heated circulating reducing gas in the mixing unit to form reducing gas, which then enters the ore powder reduction unit to undergo a reduction reaction of the iron ore powder; the iron ore powder is converted into a direct reduced iron powder product, which is cooled in an iron powder cooler and enters a magnetic separation device for primary screening and purification, and then is hot-pressed into blocks in a hot pressing device and transported to the next process;

(3) After the direct reduction reaction occurs, the reducing gas is converted into reducing exhaust gas; the reducing exhaust gas enters the ore powder preheating unit to preheat the iron ore powder raw material, and then the reducing exhaust gas enters the heat recovery device, where the reducing exhaust gas exchanges heat with the purified circulating reducing gas, and the temperature of the reducing exhaust gas drops to 200-500°C, and then enters the waste heat boiler to recover the remaining sensible heat energy;

(4) After dust removal, most of the reduced exhaust gas discharged from the outlet of the waste heat boiler enters the pressure swing adsorption purification device to remove _H2O and _CO2 in the reduced gas to obtain purified circulating reduced gas. The circulating reduced gas then passes through the heat recovery device to recover part of the sensible heat of the reduced exhaust gas. A part of the reduced exhaust gas is burned in the combustion device to increase the temperature of the circulating reduced gas from the heat recovery device, and is mixed with the gasified gas produced by the gasification device in the mixing unit; the other part of the reduced exhaust gas enters the gasification device to participate in the temperature control of the gasified gas.

Furthermore, the carbon-rich raw materials include coal, biomass, etc. The gasifying agent includes pure O ₂ , H ₂ O, CO ₂ .

Furthermore, in the gasification device, the carbon-rich raw material and the gasifying agent react in the high temperature range of 1200-2000°C; part of the reducing exhaust gas with a lower outlet temperature of the waste heat boiler is returned to the gasification device for temperature adjustment, and finally the temperature of the gasified gas at the outlet of the gasification device is 800-1300°C.

Furthermore, the composition of the gasification gas is: 30-60% by volume of CO, 20-40% by volume of _H2 , 0-15% by volume of _CO2 , and 0-10% by volume of _H2O .

Furthermore, the reduced iron ore powder passes through an iron powder cooler and its temperature drops to 25-700°C.

Further, the reducing gas composition is: CO volume percentage is 40-60%, H ₂ volume percentage is 30-40%, CO ₂ volume percentage is 0-5%, and H ₂ O volume percentage is 0-5%. The reducing gas temperature is 800-1300°C.

The reduction reaction temperature is controlled between 800 and 1100°C.

Furthermore, after the direct reduction reaction occurs, the reducing gas is converted into reducing exhausted gas, the temperature of which is 700-1000°C.

Furthermore, the reduction exhaust gas preheats the iron ore powder raw material at room temperature to 500-800°C.

Furthermore, the reduction exhaust gas from the ore powder preheating unit has a temperature of 600-900°C, and exchanges heat with the purified circulating reduction gas in the heat recovery device, so that the temperature of the reduction exhaust gas drops to 200-500°C.

Furthermore, the temperature of the reduction exhaust gas discharged from the outlet of the waste heat boiler is 100-300°C.

Furthermore, the temperature of the circulating reducing gas is increased to 800-1300°C by burning part of the reducing exhaust gas.

Furthermore, the volume percentages of CO ₂ and H ₂ O in the circulating reducing gas purified by pressure swing adsorption are 0-5%, the volume percentage of CO is 50-60%, and the volume percentage of H ₂ is 40-50%.

Furthermore, a combustion device is used to burn part of the reducing exhaust gas, and the heat of the high-temperature flue gas generated by the combustion is transferred to the circulating reducing gas, which can be achieved by using a heat storage heat exchanger or a high-temperature resistant shell and tube heat exchanger.

Furthermore, the particle size of the iron ore powder is 50 to 1000 microns.

Furthermore, the gas conveying process is powered by an induced draft fan or a forced draft fan.

Furthermore, the dust removal device may be a bag dust collector, a cyclone separator, an axial flow cyclone separator, an electrostatic precipitator, or the like.

Beneficial effects of the invention: The invention proposes a process and method for recycling reduction exhaust gas of gas-based direct reduction of iron. According to the characteristics of high reduction potential and temperature of reduction exhaust gas in the short-process direct reduction of iron process, by rationally arranging the purification and circulation mode of reduction exhaust gas, the heat/quality recycling of reduction gas is realized, the reduction processing capacity of iron ore powder is increased, the energy consumption per ton of iron of the system is reduced, and the economy of the system is improved, which has broad application prospects.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

FIG1 is a schematic diagram of the process of reducing exhaust gas circulation for gas-based direct reduction of iron according to the present invention.

Detailed ways

It should be noted that the following detailed descriptions are all illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

As shown in FIG. 1 , the present invention provides a system and method for reducing waste gas circulation to directly reduce iron.

The present invention provides a system for reducing exhaust gas circulation of gas-based direct reduced iron, comprising: a gasification device, a reducing gas mixing unit, a mineral powder reduction unit, a mineral powder preheating unit, a heat recovery device, a waste heat boiler, a dust removal device, a pressure swing adsorption purification device, a combustion device, a reduced iron powder cooler, a magnetic separation device and a hot pressing device. The gasification device, the mixing unit, the mineral powder reduction unit, the mineral powder preheating unit, the heat recovery device, the waste heat boiler, the dust removal device and the pressure swing adsorption purification device are connected in sequence, and the mineral powder preheating unit, the mineral powder reduction unit, the reduced iron powder cooler, the magnetic separation device and the hot pressing device are connected in sequence.

The present invention also provides a method for recycling reduction exhaust gas in gas-based direct reduction of iron.

First, carbon-rich raw materials such as coal or biomass react with gasifying agents such as pure O ₂ , H ₂ O, and CO ₂ at a high temperature range of 1200-2000°C to generate gasification gas rich in H ₂ and CO. The main reactions that occur are C+O ₂ =CO ₂ , C+O ₂ =2CO, C+CO ₂ =2CO, and C+H ₂ O =CO+H _2. Part of the reduced exhaust gas with a lower outlet temperature of the waste heat boiler is returned to the gasification device for temperature adjustment, and the temperature of the gasification gas at the outlet of the gasification device is finally 800-1300°C. Depending on the different carbon-rich raw materials, the concentration of the gasification gas produced by the gasification device varies within a certain range, wherein the volume percentage of CO is 30-60%, the volume percentage of H ₂ is 20-40%, the volume percentage of CO ₂ is 0-15%, and the volume percentage of H ₂ O is 0-10%.

The gasification gas produced by the gasification device is mixed with _the purified _and heated circulating reducing gas in the mixing unit _to form reducing gas _, and then enters the ore powder reduction unit to undergo reduction reaction of iron ore powder. The main reactions are _3Fe2O3 +CO＝2Fe3O4 _{+ CO2} , Fe3O4+CO＝ _3FeO + _CO2 , FeO+CO _＝ Fe _{+ CO2} , Fe2O3+CO＝ _2FeO + _CO2 , _3Fe2O3 + _H2 ＝ _2Fe3O4 + _H2O , _Fe3O4 + _{H2＝3FeO+H2O, FeO+H2 ＝ Fe + H2O} , _Fe2O3 + _H2 ＝2FeO _{+ H2O} . During the reaction, the effective components CO and H2 in the reducing gas eventually deprive the oxygen atoms in the iron ore powder to generate _CO2 and _H2O (CO and _H2 in the reducing gas are partially converted into _CO2 and _H2O , but CO and _H2 are still the main parts). At the same time, the iron ore powder is converted into a direct reduced iron powder product. The reduced iron ore powder passes through an iron powder cooler, and the temperature can be reduced to 25-700℃. The cooling function is to prevent the secondary oxidation of the direct reduced iron. The cooled direct reduced iron powder enters the magnetic separation device for primary screening and purification, and then is hot-pressed into blocks by a hot pressing device, and then transported to the next process.

After the direct reduction reaction occurs, the reducing gas is converted into reducing exhaust gas (the reduction potential of _H2 and CO is reduced), but it still has a certain reduction potential and sensible heat energy, and the temperature is 700-1000°C. Dissipation will cause direct waste of energy. However, since the reducing exhaust gas also has the characteristics of low calorific value and small gas volume, the energy-saving method of directly burning to generate electricity and recover energy is often not energy-saving. Therefore, the present invention proposes to realize heat/mass recovery of the reduced exhaust gas after reduction. To recover the sensible heat of the reducing exhaust gas, first preheat the iron ore powder raw material to 500-800°C at room temperature. The reducing exhaust gas from the ore powder preheating unit has a temperature of about 600-900°C. It exchanges heat with the purified circulating reducing gas in the heat recovery device, and the temperature of the reducing exhaust gas drops to 200-500°C, and then enters the waste heat boiler to recover the remaining sensible heat energy.

The temperature of the reduced exhaust gas discharged from the outlet of the waste heat boiler is about 100-300℃. After dust removal, most of the reduced exhaust gas enters the pressure swing adsorption purification device to remove _CO2 and _H2O in the reduced gas, improve the reduction potential of the circulating reduced gas, and then recovers part of the sensible heat of the reduced exhaust gas through the heat recovery device. The temperature of the circulating reduced gas is increased to 800-1300℃ by burning part of the reduced exhaust gas, and is mixed with the gasified gas produced by the gasification device in the mixing unit. The volume percentages of _CO2 and _H2O in the circulating reduced gas purified by pressure swing adsorption are about 0-5%, the volume percentage of CO is 50-60%, and the volume percentage of _H2 is 40-50%.

In some embodiments, a combustion device is used to burn part of the reducing exhaust gas, and the heat of the high-temperature flue gas generated by the combustion is transferred to the circulating reducing gas, which can be achieved by using a heat storage heat exchanger or a high-temperature resistant shell and tube heat exchanger.

In some embodiments, the iron ore powder has a particle size of 50 to 1000 microns.

In some embodiments, the gasification device may be in various forms, such as a rotary kiln, a moving bed, an entrained bed, a fluidized bed, an ebullating bed, a bubbling bed, a spouted bed, a settling bed, etc. The reactor structure of the ore powder preheating and reduction unit may be a rotary kiln, a moving bed, an entrained bed, a fluidized bed, an ebullating bed, a bubbling bed, a spouted bed, a settling bed, etc. The flow direction of the reducing gas and the iron ore powder is countercurrent as a whole, which increases the heat exchange temperature difference and improves the heat and mass exchange efficiency.

In some embodiments, the gas delivery process is powered by an induced draft fan or a forced draft fan.

In some embodiments, the dust removal device may be a bag dust collector, a cyclone separator, an axial flow cyclone separator, an electrostatic precipitator, or the like.

The whole process achieves zero external discharge of reduction exhaust gas. Most of the reduction exhaust gas enters the pressure swing adsorption purification device to be converted into circulating reduction gas, and a small part goes to the gasification device for temperature adjustment or is sent to the burner for combustion. Among them, the reduction exhaust gas entering the pressure swing adsorption purification device accounts for 85% to 95% of the total reduction gas volume/reduction exhaust gas volume; the reduction exhaust gas entering the burner and sent to the gasification device for temperature adjustment accounts for 5% to 15% of the total reduction gas volume/reduction exhaust gas volume.

The pressure swing adsorption purification device is used to remove most of the H ₂ O and CO ₂ in the circulating reducing gas. According to the design capacity of the gasification device and the requirements for the reducing gas composition, the removed H ₂ O and CO ₂ are sent to the gasification device as gasification agents to participate in the gasification reaction, realizing the H ₂ O/CO ₂ mass return cycle and reducing the external discharge volume.

The innovation of the present invention is to make full use of the high reduction potential and temperature of the reduction exhaust gas in the direct reduction iron system, recycle the heat/mass of the reduction exhaust gas, and thus reduce energy consumption.

Example 1

A system for reducing exhaust gas circulation of gas-based direct reduced iron comprises: a gasification device, a reducing gas mixing unit, a mineral powder reduction unit, a mineral powder preheating unit, a heat recovery device, a waste heat boiler, a dust removal device, a pressure swing adsorption purification device, a combustion device, a reduced iron powder cooler, a magnetic separation device and a hot pressing device. The gasification device, the mixing unit, the mineral powder reduction unit, the mineral powder preheating unit, the heat recovery device, the waste heat boiler, the dust removal device and the pressure swing adsorption purification device are connected in sequence, and the mineral powder preheating unit, the mineral powder reduction unit, the reduced iron powder cooler, the magnetic separation device and the hot pressing device are connected in sequence.

A method for recycling the reduction exhaust gas of gas-based direct iron reduction based on the above system comprises the following steps:

(1) Biomass reacts with oxygen in the gasification device to generate _H2 and CO-rich gas. Part of the reduced exhaust gas with a lower outlet temperature of the dust removal device is returned to the gasification device for temperature adjustment. In the gasification device, the carbon-rich raw material and the gasifying agent react at a high temperature range of 1200-2000°C. Part of the reduced exhaust gas with a lower outlet temperature of the waste heat boiler is returned to the gasification device for temperature adjustment. Finally, the temperature range of the gasified gas at the outlet of the gasification device is 800-1300°C.

(2) The gasification gas generated by the gasification device is mixed with the purified and heated circulating reduction gas in the mixing unit to form reduction gas, which enters the ore powder reduction unit to undergo a reduction reaction of the iron ore powder; the iron ore powder is converted into a direct reduced iron powder product, which is cooled by an iron powder cooler and enters a magnetic separation device for primary screening and purification, and then is hot-pressed into blocks by a hot pressing device and then transported to the next process; the reduced iron ore powder passes through an iron powder cooler and its temperature drops to about 100°C. After the direct reduction reaction occurs, the reduction gas is converted into reduced exhaust gas, the temperature of which is 700°C.

(3) After the direct reduction reaction occurs, the reducing gas is converted into reducing exhaust gas; the reducing exhaust gas enters the ore powder preheating unit to preheat the iron ore powder raw material, and then the reducing exhaust gas enters the heat recovery device, where the reducing exhaust gas exchanges heat with the purified circulating reducing gas, and the temperature of the reducing exhaust gas drops to 200°C, and then enters the waste heat boiler to recover the remaining sensible heat energy; the reducing exhaust gas preheats the iron ore powder raw material at room temperature to about 500°C.

(4) After dust removal, most of the reduced exhaust gas discharged from the outlet of the waste heat boiler enters the pressure swing adsorption purification device to remove H ₂ O and CO ₂ in the reduced gas to obtain the purified circulating reduced gas. Then, the circulating reduced gas passes through the heat recovery device to recover part of the sensible heat of the reduced exhaust gas. Part of the reduced exhaust gas is burned in the combustion device to increase the temperature of the circulating reduced gas from the heat recovery device, and is mixed with the gasification gas produced by the gasification device in the mixing unit; the other part of the reduced exhaust gas enters the gasification device to participate in the temperature adjustment of the gasification gas. The reduced exhaust gas discharged from the mineral powder preheating unit has a temperature of 600°C. It exchanges heat with the purified circulating reduced gas in the heat recovery device, and the temperature of the reduced exhaust gas drops to 200°C. The temperature of the reduced exhaust gas discharged from the outlet of the waste heat boiler is 100°C. The temperature of the circulating reduced gas is increased to 800°C by burning part of the reduced exhaust gas.

The induced draft fan provides the conveying power for the gas conveying process. The dust removal device is a bag dust removal device.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims (8)

1. A method for reducing gas-based direct iron reduction by exhaust gas circulation, characterized in that it comprises the following steps: (1) The carbon-rich raw materials react with the gasifying agent in the gasification device to generate gasification gas rich in H ₂ and CO. The reduced exhaust gas with a lower outlet temperature of the waste heat boiler is returned to the gasification device for temperature adjustment; The gasifying agent includes one or more of pure O ₂ , H ₂ O, and CO ₂ ; (2) The gasification gas generated by the gasification device is mixed with the purified and heated circulating reducing gas in the mixing unit to form reducing gas, which then enters the ore powder reduction unit to undergo a reduction reaction of the iron ore powder; the iron ore powder is converted into a direct reduced iron powder product, which is cooled in an iron powder cooler and enters a magnetic separation device for primary screening and purification, and then is hot-pressed into blocks in a hot pressing device and transported to the next process; (3) After the direct reduction reaction occurs, the reducing gas is converted into reducing exhaust gas; the reducing exhaust gas enters the ore powder preheating unit to preheat the iron ore powder raw material, and then the reducing exhaust gas enters the heat recovery device, where the reducing exhaust gas exchanges heat with the purified circulating reducing gas, and the temperature of the reducing exhaust gas drops to 200-500°C, and then enters the waste heat boiler to recover the remaining sensible heat energy; (4) After dust removal, most of the reduced gas discharged from the outlet of the waste heat boiler enters the pressure swing adsorption purification device to remove _H2O and _CO2 in the reduced gas to obtain the purified circulating reduced gas. The circulating reduced gas then passes through the heat recovery device to recover part of the sensible heat of the reduced gas. A part of the reduced gas is burned in the combustion device to increase the temperature of the circulating reduced gas from the heat recovery device, and is mixed with the gasified gas produced by the gasification device in the mixing unit; the other part of the reduced gas enters the gasification device to participate in the temperature adjustment of the gasified gas; The whole process achieves zero external discharge of reduction exhaust gas. Most of the reduction exhaust gas enters the pressure swing adsorption purification device to be converted into circulating reduction gas, and a small part goes to the gasification device for temperature adjustment or is sent to the burner for combustion. The volume percentages of CO ₂ and H ₂ O in the circulating reducing gas purified by pressure swing adsorption are 0~5%, the volume percentage of CO is 50~60%, and the volume percentage of H ₂ is 40~50%; The gas-based direct iron reduction system for reducing the spent gas cycle includes: a gasification device, a mixing unit, a ore powder reduction unit, a ore powder preheating unit, a heat recovery device, a waste heat boiler, a dust removal device, a pressure swing adsorption purification device, a reduced iron powder cooler, a magnetic separation device and a hot pressing device; the gasification device, the mixing unit, the ore powder reduction unit, the ore powder preheating unit, the heat recovery device, the waste heat boiler, the dust removal device and the pressure swing adsorption purification device are connected in sequence, and the ore powder preheating unit, the ore powder reduction unit, the reduced iron powder cooler, the magnetic separation device and the hot pressing device are connected in sequence. 2. The method according to claim 1 is characterized in that the system also includes a combustion device; the inlet of the combustion device is connected to the dust removal device, the outlet pipe of the combustion device is connected to the outlet pipe of the heat recovery device and merged into one pipe connected to the mixing unit. 3. The method according to claim 1 is characterized in that the reducing exhaust gas entering the pressure swing adsorption purification device accounts for 85% to 95% of the total reducing gas; the reducing exhaust gas entering the burner and sent to the gasification device for temperature adjustment accounts for 5% to 15% of the total reducing gas. 4. The method according to claim 1, characterized in that the carbon-rich raw material comprises coal and biomass; In the gasification device, the carbon-rich raw materials and the gasifying agent react at a high temperature range of 1200-2000°C; part of the reduced exhaust gas with a lower outlet temperature of the waste heat boiler is returned to the gasification device for temperature adjustment, and the temperature of the gasified gas at the outlet of the gasification device is finally 800-1300°C; The composition of the gasification gas is: 30-60% by volume of CO, 20-40% by volume of H ₂ , 0-15% by volume of CO ₂ , and 0-10% by volume of H ₂ O. 5. The method according to claim 1, characterized in that the temperature of the reduced iron ore powder is reduced to 25-700° C. by passing through an iron powder cooler; The reducing gas composition is: CO volume percentage is 40-60%, H ₂ volume percentage is 30-40%, CO ₂ volume percentage is 0-5%, and H ₂ O volume percentage is 0-5%; the reducing gas temperature is 800-1300°C; The reduction reaction temperature is 800~1100℃. 6. The method according to claim 1, characterized in that after the direct reduction reaction occurs, the reducing gas is converted into reducing exhaust gas, and the temperature thereof is 700-1000°C; The reduction gas preheats the iron ore powder raw material at room temperature to 500-800℃; The reduction exhaust gas from the ore powder preheating unit has a temperature of 600-900°C. It exchanges heat with the purified circulating reduction gas in the heat recovery device, and the temperature of the reduction exhaust gas drops to 200-500°C. The temperature of the reduced exhaust gas discharged from the waste heat boiler outlet is 100-300℃; The temperature of the circulating reducing gas is raised to 800-1300°C by burning part of the reducing exhaust gas. 7. The method according to claim 1 is characterized in that a combustion device is used to burn part of the reducing exhaust gas, and the heat of the high-temperature flue gas generated by the combustion is transferred to the circulating reducing gas, which is achieved by using a heat storage heat exchanger or a high-temperature resistant shell and tube heat exchanger. 8. The method according to claim 1 is characterized in that the particle size of the iron ore powder is 50-1000 microns; the gas conveying process is powered by an induced draft fan or a forced draft fan; and the dust removal device is a bag dust collector, a cyclone separator, an axial flow cyclone separator or an electrostatic precipitator.