EP4715069A1 - Zero-oxygen injection low-carbon ironmaking method - Google Patents

Zero-oxygen injection low-carbon ironmaking method

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Publication number
EP4715069A1
EP4715069A1 EP24878660.0A EP24878660A EP4715069A1 EP 4715069 A1 EP4715069 A1 EP 4715069A1 EP 24878660 A EP24878660 A EP 24878660A EP 4715069 A1 EP4715069 A1 EP 4715069A1
Authority
EP
European Patent Office
Prior art keywords
gas
furnace
reducing gas
oxygen
free injection
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP24878660.0A
Other languages
German (de)
French (fr)
Inventor
Yun Huang
Zhiquan Huang
Mansheng CHU
Xian Gan
Shufang LU
Jue TANG
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Pangang Group Xichang Steel&vanadium Co Ltd
Northeastern University China
Original Assignee
Pangang Group Xichang Steel&vanadium Co Ltd
Northeastern University China
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Pangang Group Xichang Steel&vanadium Co Ltd, Northeastern University China filed Critical Pangang Group Xichang Steel&vanadium Co Ltd
Publication of EP4715069A1 publication Critical patent/EP4715069A1/en
Pending legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B13/00—Making spongy iron or liquid steel, by direct processes
    • C21B13/004—Making spongy iron or liquid steel, by direct processes in a continuous way by reduction from ores
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B13/00—Making spongy iron or liquid steel, by direct processes
    • C21B13/0073—Selection or treatment of the reducing gases
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B13/00—Making spongy iron or liquid steel, by direct processes
    • C21B13/02—Making spongy iron or liquid steel, by direct processes in shaft furnaces
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B13/00—Making spongy iron or liquid steel, by direct processes
    • C21B13/02—Making spongy iron or liquid steel, by direct processes in shaft furnaces
    • C21B13/023—Making spongy iron or liquid steel, by direct processes in shaft furnaces wherein iron or steel is obtained in a molten state
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B13/00—Making spongy iron or liquid steel, by direct processes
    • C21B13/14—Multi-stage processes processes carried out in different vessels or furnaces
    • C21B13/143—Injection of partially reduced ore into a molten bath
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B2100/00—Handling of exhaust gases produced during the manufacture of iron or steel
    • C21B2100/60—Process control or energy utilisation in the manufacture of iron or steel
    • C21B2100/64—Controlling the physical properties of the gas, e.g. pressure or temperature
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B2100/00—Handling of exhaust gases produced during the manufacture of iron or steel
    • C21B2100/60—Process control or energy utilisation in the manufacture of iron or steel
    • C21B2100/66—Heat exchange

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Manufacture And Refinement Of Metals (AREA)

Abstract

The present invention relates to the technical field of non-blast furnace low-carbon metallurgy, and relates to a zero-oxygen injection low-carbon ironmaking method. The method comprises: loading hot-state self-fluxing oxidized pellets into a gas-based shaft furnace from the top of the furnace, injecting cold reducing gas into the gas-based shaft furnace from the bottom of the gas-based shaft furnace, and meanwhile, injecting hot reducing gas into the gas-based shaft furnace from the junction of a reducing section and a cooling section of the gas-based shaft furnace, wherein the cold reducing gas is heated in the rising process and mixed with the hot reducing gas, then the mixed gas undergoes a pre-reduction reaction with the self-fluxing oxidized pellets to obtain hot-state direct reduced iron, and the hot-state direct reduced iron is cooled by the cold reducing gas in the cooling section to obtain direct reduced iron; and loading a solid carbon material and the direct reduced iron into a zero-oxygen injection furnace from the top of the furnace, injecting superhot reducing gas into the zero-oxygen injection furnace, and the direct reduced iron undergoing reduction melting to obtain liquid slag and molten iron. The present invention reduces gas heating energy consumption, and significantly reduces carbon emission compared with a blast furnace.

Description

    FIELD
  • The present disclosure relates to the technical field of non-blast furnace low-carbon metallurgy, and in particular to a method for oxygen-free injection low-carbon ironmaking.
    • BACKGROUND
  • At present, mature ironmaking processes primarily include blast furnace ironmaking, smelting reduction (HIsmelt, COREX, Finex), direct reduction (gas-based direct reduction, coal-based direct reduction), and the like. The existing processes have their own advantages and disadvantages, mainly as follows:
    1. 1. The blast furnace ironmaking process is mature and can achieve an annual production capacity of more than one million tonnes per unit. However, its disadvantages include an excessive reliance on high-quality metallurgical coke, with the average solid fuel consumption in the industry being 0.55kg/t molten iron. The requirement for supporting coking, sintering, and pelletizing facilities results in significant system investment. The blast furnace is difficult to operate and difficult to recover after furnace conditions of disruption and fluctuation. The cost, carbon emissions and energy consumption are high.
    2. 2. Smelting reduction
      1. (1) The HIsmelt process has poor heat transfer effect. The temperature of molten iron in the molten iron pool is low, only 1400°C to 1450°C. The flue gas flow rate is as high as 2700 Nm3/t iron and the flue gas temperature reaches 1600°C. A large amount of physical heat is discharged from the furnace along with the flue gas, resulting in energy losses. The iron loss is high, the fuel consumption is high, and the carbon emissions are high.
      2. (2) In the COREX or Finex process, the silicon content in molten iron is excessively high, accompanied by excessive gas generation and high primary carbon consumption.
      3. (3) The chemical energy utilization rate of carbon is insufficient, and a part of the carbon element escapes with the gas in the form of CO, and its chemical energy cannot be further utilized.
    3. 3. Direct reduction
  • Direct reduction method is a process of smelting iron ore into iron through solid-state reduction at a temperature lower than the melting point of the ore. The iron produced by the method is called direct reduced iron (DRI). Depending on the reducing agent, direct reduction can be classified into two categories: gas-based direct reduction and coal-based direct reduction. Herein, the gas-based reduction process is the mainstream and dominant process worldwide.
  • Coal-based direct reduction requires solid fuel, so the carbon consumption is high. From the perspective of green and low-carbon development of the steel industry, coal-based direct reduction cannot address the issue of reducing carbon emissions in ironmaking, and imposes high requirements on ore quality.
  • Gas-based shaft furnace is the process with the greatest carbon reduction potential at present, accounting for 75.3% of the total direct reduction output (herein, MIDREX accounts for 60.0%, HYL accounts for 12.4%, and PERED accounts for 2.9%). However, the existing gas-based shaft furnace process has the following disadvantages:
    1. (1) The raw material cost is high and the difficulty in promotion is large. The existing gas-based shaft furnace process utilizes electric furnace for deep melting-separation of direct reduced iron, which requires iron ore pellets with TFe>67% and SiO2<3.0%. If high-grade pellets are not guaranteed, a large amount of electric furnace slag will be generated in the subsequent electric furnace smelting. Unlike the blast furnace which employs substantial gas injection for agitation, the electric furnace production process suffers from inferior kinetic conditions during production. The increased slag amount may result in slow heat transfer, low electric furnace production efficiency, long smelting cycle, high energy consumption and high cost. In China, the iron ore is mainly lean ore. The strict requirements of current gas-based shaft furnace for raw ore not only result in high raw material procurement costs, but also hinder the widespread of the gas-based shaft furnace in China.
    2. (2) The gas production costs are high and the safety risks are high. In existing gas-based shaft furnace process, pellets are charged cold into the shaft furnace, and the heat required for the reaction in the furnace is brought in by heated reducing gas. In order to expand the high-temperature zone of 600°C to 1100°C in the furnace, a higher gas temperature and a larger gas volume are required. On the other hand, in order to prevent the generated sponge iron from sticking in the furnace, the volume ratio of H2 to CO in the furnace should be controlled to be greater than 1:1, and the upper limit of the reducing gas temperature should be controlled to be less than 1100°C. Since the reduction of iron oxides by H2 is an endothermic reaction, which exacerbates the temperature drop in the furnace and requires a larger amount of gas. The higher cost of obtaining H2 than that of CO, the higher cost of heating H2 at high temperature, and the high power cost for circulating and pressurizing a large amount of gas in the system are some of the reasons for the high cost and high safety risks of the gas-based shaft furnace.
    3. (3) The gas-based shaft furnace-electric furnace melting-separation process exhibits low operation efficiency and faces significant challenges in scaling up. The high gas volume, high temperature, and high hydrogen content of shaft furnaces require twenty days of annual downtime for inspection of all pipelines. Continuous charging and slag iron discharge of electric furnaces are difficult, the large-scale capacity of the electric furnace is difficult, and the reaction rate of the electric furnace is slow.
  • In summary, the operating cost of existing gas-based shaft furnaces is 600 yuan/tonne higher than that of blast furnace ironmaking, and the cost differential may increase to approximately 1,000 yuan/tonne in electric furnace steelmaking. Therefore, the development of a low-cost, safe, and efficient gas-based direct reduction process, tailored to China's iron ore and energy resources, is crucial for achieving carbon peak and carbon neutrality in the China's steel industry.
    • SUMMARY
  • To address the above issues, the present disclosure provides a method for oxygen-free injection low-carbon ironmaking. The method utilizes self-fluxing pellets that are hot-charged into a gas-based shaft furnace. Gas flows into the reducing section as a reducing agent from the cooling section of the gas-based shaft furnace. A portion of hot reducing gas is added to the reducing section of the shaft furnace to obtain cold direct reduced iron (DRI) with a metallization rate of at least 92%. The DRI and solid carbon material are added into the oxygen-free injection furnace through a furnace top, and superheated reducing gas is injected into the furnace hearth of the oxygen-free injection furnace. The DRI is further reduced and heated within the oxygen-free injection furnace to produce high-temperature molten iron and slag, which are then discharged from the furnace through slag outlet. The gaseous products generated in the gas-based shaft furnace and the oxygen-free injection furnace are subjected to heat recovery via a heat exchanger, followed by further removal of dust, CO2, and H2O, and are then recycled as the reducing gas for the system. The method effectively reduces the heating temperature and heating amount of the reducing gas in the gas-based shaft furnace, reduces the cost and energy consumption of deep reduction and melting-separation, and improves system availability.
  • A first object of the present disclosure is to provide a method for oxygen-free injection low-carbon ironmaking, comprising:
    • charging hot self-fluxing oxidized pellets into a gas-based shaft furnace from a furnace top, injecting cold reducing gas into the gas-based shaft furnace from a bottom of the gas-based shaft furnace, and simultaneously injecting hot reducing gas into the gas-based shaft furnace from a junction of a reducing section and a cooling section of the gas-based shaft furnace, where the cold reducing gas is heated and mixed with the hot reducing gas during a rising process to perform a pre-reduction reaction with the self-fluxing oxidized pellets to obtain hot direct reduced iron, and the hot direct reduced iron is cooled by the cold reducing gas in the cooling section to obtain direct reduced iron;
    • charging solid carbon material and the direct reduced iron at a mass ratio of 0.03 to 0.1: 1 into an oxygen-free injection furnace from a furnace top, injecting superheated reducing gas with a flow rate of 900 to 1500 Nm3/t Fe at a temperature of 1800°C to 2350°C into the oxygen-free injection furnace, where the direct reduced iron is reduced and melted to obtain liquid slag and molten iron.
  • When the hot self-fluxing oxidized pellets are charged into the gas-based shaft furnace, the temperature is 600°C to 1100°C. The self-fluxing oxidized pellets are obtained by high-temperature treatment of iron ore, flux, and bentonite. The high-temperature treatment is a well-known process in the art and will not be described in detail in embodiments of the present disclosure. The high-temperature treatment does not include cooling of the self-fluxing oxidized pellets. The temperature of the self-fluxing oxidized pellets, 600°C to 1100°C, is produced during the high-temperature treatment process, not by secondary heating.
  • Furthermore, when the flux (primarily composed of CaCO3) is added to the gas-based shaft furnace or the oxygen-free injection furnace, it causes the CaCO3 to decompose and absorb heat, affecting the system temperature and reaction rate. Therefore, the self-fluxing pellets are required. Therefore, a mass ratio of CaO to SiO2 in the self-fluxing oxidized pellets is 0.9 to 1.3, and a mass percent of Fe in the pellets is 50% to 69%.
  • Furthermore, the mass percent of Fe element in the self-fluxing oxidized pellets is 50% to 69%, the direct reduced iron obtained after the hot direct reduced iron is cooled by the cold reducing gas in the cooling section has a temperature of less than 250°C and a metallization rate of ≥92%, the solid carbon material is any one or more of coke, semi-coke, and molded coke, and a fixed carbon content in the solid carbon material is greater than 75%; and a temperature of the cold reducing gas is less than 50°C.
  • Furthermore, the hot reducing gas and the superheated reducing gas are reducing gas from a reduction gas holder, and the cold reducing gas is reducing gas from the reduction gas holder and/or coke oven gas.
  • The reducing gas from the reduction gas holder comprises purified gas and newly replenished reducing gas, and the reducing gas from the reduction gas holder comprises CO, H2, N2, and impurity gases, and a sum of a volume percentage of CO and a volume percentage of H2 is greater than 92%.
  • The purified gas is the gas recovered after heat exchange, heat recovery and purification of top gas from the gas-based shaft furnace and the oxygen-free injection furnace.
  • The hot reducing gas is a portion of the reducing gas from the reduction gas holder that is pressurized, preheated via a heat exchange system, and then heated to a desired temperature.
  • The superheated reducing gas is another portion of the reducing gas from the reduction gas holder that is pressurized, preheated via the heat exchange system, and then heated to a desired temperature.
  • Furthermore, a total gas flow rate in the gas-based shaft furnace comprises a cold reducing gas flow rate and a hot reducing gas flow rate, where a ratio of the cold reducing gas flow rate to the hot reducing gas flow rate is K.
  • In a case that a H2 to CO ratio of reducing gas injected into the gas-based shaft furnace is greater than 5, a charging temperature of the self-fluxing oxidized pellets is 1050°C to 1100°C, and in the gas-based shaft furnace, a total flow rate of the reducing gas is 1800 to 1900 Nm3/t Fe, a value of K ranges from 1.7 to 2.1, and a temperature of the hot reducing gas is 1050±20°C.
  • In a case that the H2 to CO ratio of the reducing gas injected into the gas-based shaft furnace is greater than 1.5 and less than or equal to 5, the charging temperature of the self-fluxing oxidized pellets is 1000°C to 1050°C, and in the gas-based shaft furnace, the total flow rate of the reducing gas is 1900 to 2000 Nm3/t Fe, the value of K ranges from 1.5 to 1.8, and the temperature of the hot reducing gas is 1000°C to 1050°C.
  • In a case that the H2 to CO ratio of the reducing gas injected into the gas-based shaft furnace is greater than 0.6 and less than or equal to 1.5, the charging temperature of the self-fluxing oxidized pellets is 950°C to 1000°C, and in the gas-based shaft furnace, the total flow rate of the reducing gas is 2000 to 2100 Nm3/t Fe, the value of K ranges from 1.3 to 1.6, and the temperature of the hot reducing gas is 980±20°C.
  • In a case that the H2 to CO ratio of the reducing gas injected into the gas-based shaft furnace is greater than 0.2 and less than or equal to 0.6, the charging temperature of the self-fluxing oxidized pellets is 900°C to 950°C, and in the gas-based shaft furnace, the total flow rate of the reducing gas is 2100 to 2200 Nm3/t Fe, the value of K ranges from 1.2 to 1.4, and the temperature of the hot reducing gas is 950±20°C.
  • In a case that the H2 to CO ratio of the reducing gas injected into the gas-based shaft furnace is less than or equal to 0.2, the charging temperature of the self-fluxing oxidized pellets is 880°C to 920°C, and in the gas-based shaft furnace, the total flow rate of the reducing gas is 2200 to 2300 Nm3/t Fe, the value of K ranges from 1.1 to 1.3, and the temperature of the hot reducing gas is 930±20°C.
  • During descending process of the hot self-fluxing oxidized pellets in the gas-based shaft furnace, they come into contact with and undergo reduction reactions with the gas formed by mixture of the hot reducing gas and the heated cold reducing gas in the gas-based shaft furnace: Fe2O3 + CO → Fe3O4 + CO2, Fe3O4 + CO → FeO + CO2, FeO + CO → Fe + CO2, and reactions: Fe2O3 + H2 → Fe3O4 + H2O (gas), Fe3O4 + H2 → FeO + H2O (gas), and FeO + H2 → Fe + H2O (gas), so hot solid direct reduced iron (DRI) and gaseous CO2 and H2O are produced. The process is called a pre-reduction of the self-fluxing oxidized pellets, and the product of the pre-reduction of the self-fluxing oxidized pellets is called DRI (direct reduced iron).
  • Thereafter, the hot DRI continues to descend and encounters the ascending cold reducing gas, resulting in heat exchange. This causes a temperature of the cold reducing gas to rise and a temperature of the hot DRI to drop, accompanied by reactions as follows: FeO + H2 → Fe + H2O (gas), FeO + CO → Fe + CO2, and/or CH4 = C + H2, and/or C + 3Fe = Fe3C, to obtain cold DRI. Simultaneously, the temperature of the cold reducing gas rises, the cold reducing gas continues to ascend, mixes with the hot reducing gas, and comes into contact with the self-fluxing oxidized pellets to reduce them.
  • Finally, the cold DRI is discharged from a discharge outlet at the bottom of the gas-based shaft furnace, and the furnace charge at the upper portion of the gas-based shaft furnace moves downward in sequence. The gases generated by the chemical reactions within the gas-based shaft furnace and the unreacted reducing gas are collectively referred to as shaft furnace gas, which is discharged from the gas outlet pipe at the top of the shaft furnace.
  • Furthermore, an inlet flow rate and an inlet temperature of the superheated reducing gas injected into the oxygen-free injection furnace are controlled within the following ranges:
    • when the inlet flow rate of the superheated reducing gas is 900 to 1200 Nm3/t Fe, the inlet temperature of the superheated reducing gas is controlled within a range of 2130°C to 2320°C;
    • when the inlet flow rate of the superheated reducing gas is 1200 to 1500 Nm3/t Fe, the inlet temperature of the superheated reducing gas is controlled within a range of 1850°C to 2250°C.
  • In the oxygen-free injection furnace, the solid carbon material and the direct reduced iron come into contact with the reducing gas, where the direct reduced iron is deeply reduced to produce molten iron and slag. The gas generated by the chemical reactions within the oxygen-free injection furnace and the unreacted reducing gas are collectively referred to as oxygen-free injection furnace gas. The oxygen-free injection furnace gas is discharged from the oxygen-free injection furnace gas outlet pipe at the top of the oxygen-free injection furnace.
  • A second object of the present disclosure is to provide an apparatus for oxygen-free injection low-carbon ironmaking, wherein the apparatus is configured to implement the aforementioned method for oxygen-free injection low-carbon ironmaking. The apparatus comprises the gas-based shaft furnace and the oxygen-free injection furnace.
  • The gas-based shaft furnace is divided into a reducing section and a cooling section from top to bottom along an internal vertical direction.
  • A plurality of hot reducing gas injection inlets are symmetrically arranged on a same horizontal cross-section at the junction of the reducing section and the cooling section, and the reducing section is for the pre-reduction reaction of self-fluxing oxidized pellets to obtain hot direct reduced iron.
  • A plurality of cold reducing gas injection inlets are symmetrically arranged on a same horizontal cross-section inside a lower portion of the cooling section, and the cooling section is for cooling the hot direct reduced iron to obtain cold direct reduced iron.
  • The direct reduced iron discharged from the bottom of the cooling section is transported to the oxygen-free injection furnace, the oxygen-free injection furnace is neither an electric furnace nor a blast furnace, with zero oxygen injection volume, an interior of the oxygen-free injection furnace is divided into a furnace shaft and a furnace hearth from top to bottom along its vertical center line, and the oxygen-free injection furnace is for reducing and melting the direct reduced iron to obtain liquid slag and molten iron.
  • Furthermore, an interior of the furnace shaft is divided into a solid material layer and a soft melt droplet zone from top to bottom along the vertical direction, and an interior of the furnace hearth is divided into a gas recirculation zone, a liquid slag layer and a liquid molten iron layer from top to bottom along the vertical direction.
  • Furthermore, a plurality of reducing gas injection inlets is symmetrically distributed along the circumference at a same horizontal cross-section as the gas recirculation zone of the furnace hearth. A plurality of slag outlets is symmetrically distributed along the circumference at a same horizontal cross-section as the liquid slag layer of the furnace hearth. A plurality of iron outlets is symmetrically distributed along the circumference at a same horizontal cross-section as the liquid molten iron layer of the furnace hearth.
  • Furthermore, a diameter of the furnace hearth of the oxygen-free injection furnace adopts an adjustable sleeve design. And a diameter of the furnace hearth of the oxygen-free injection furnace and a flow rate of the superheated reducing gas injected are controlled as follows:
    • In a case that the diameter d of the furnace hearth is less than 10m, the flow rate of the superheated reducing gas injected is 150m/s to 350m/s;
    • In a case that the diameter d of the furnace hearth is greater than 10m, the flow rate of the superheated reducing gas injected is 250m/s to 450m/s.
  • Furthermore, a ratio of an inner diameter of a horizontal cross-section of a lower portion of the reducing section of the gas-based shaft furnace to the diameter of the furnace hearth of the oxygen-free injection furnace is 1.0 to 1.3, a height of a material layer in the reducing section of the gas-based shaft furnace is 5 to 8 meters, a ratio of a height to the diameter of the furnace hearth in the oxygen-free injection furnace is 0.35 to 0.6, and a ratio of a height of the furnace shaft to the diameter of the furnace hearth in the oxygen-free injection furnace is 0.8 to 1.3.
  • The present disclosure has beneficial effects:
    1. (1) The present disclosure adopts hot charging of self-fluxing oxidized pellets into the gas-based shaft furnace, so that all the ore in the furnace is in the high-temperature zone. That is, the reaction zone is expanded and the metallization rate is improved, so as to reduce the gas heating temperature or/and reduce the flow rate of the heated gas, thereby reducing energy consumption.
    2. (2) The present process adopts cold reducing gas, which after exchanging heat with hot DRI to increase temperature, enters the reducing section of the shaft furnace to participate in the pre-reduction reaction of the self-fluxing oxidized pellets. The beneficial effects of the design are reflected in two aspects: on the one hand, the total gas flow rate of the reducing gas and cooling gas in the gas-based shaft furnace is reduced, thereby reducing the power cost of gas transportation. On the other hand, the cold reducing gas acts as a carrier to transfer the physical heat of the hot DRI to the reducing section of the gas-based shaft furnace, and the physical heat of the DRI is recycled and utilized, thereby further reducing the energy consumption of the system.
    3. (3) In the present disclosure, the gas source is not limited, and requirements for the ratio of H2 to CO in the reducing gas are low, and the reducing gas with any ratios of H2:CO is applicable. In the existing gas-based shaft furnace processes, due to the mass and heat transfer method of "hot gas and cooled ore", and "lower temperature in the upper portion and higher temperature in the lower portion", when the pellets descend to the lower-middle portion of the reducing section and the metallization rate rises above 80% in the gas-based shaft furnace, it is necessary to control the ratio of H2:CO of the reducing gas to >1.2, to prevent pellets from sticking together at high temperature and high metallization rate, which would cause unsmooth feeding in the shaft furnace. The gas-based shaft furnace of the present disclosure utilizes hot ore and medium-temperature gas, with a temperature distribution of "higher temperature in the upper portion and lower temperature in the lower portion" in the furnace. When the self-fluxing oxidized pellets descend to the lower-middle portion of the reducing section, and the metallization rate rises above 80%, the temperature of the pellets has dropped to below 800°C. Furthermore, the temperature of the mixed gas formed by the cold reducing gas and the hot reducing gas is significantly lower than that of existing gas-based shaft furnace processes. By simply controlling the flow rate and temperature of the hot reducing gas according to the parameters claimed in the claims, the test results show that even when the ratio of H2 to CO in the reducing gas approaches zero, it can still effectively prevent pellet adhesion from causing unsmooth production in the shaft furnace.
    4. (4) The process utilizes the oxygen-free injection furnace instead of an electric furnace to achieve deep reduction of DRI and melting separation of slag iron. The beneficial effects are as follows:
      Compared with the gas-based shaft furnace-electric furnace deep reduction and melting-separation process, the beneficial effects of the present disclosure are as follows: ① The cost of consumables such as electrodes is low. The oxygen-free injection furnace is not an electric furnace and do not require insertion of electrodes, thus avoiding the cost of electrode consumption during the production process. ② The oxygen-free injection furnace has higher thermal efficiency. The oxygen-free injection furnace utilizes the superheated reducing gas as the carrier to transfer heat into the furnace from the reducing gas injection inlet of the furnace hearth. The injection inlet is located below the solid material layer and the soft melt droplet zone, that is, the heat transfer method in the oxygen-free injection furnace is that the heat source is at the bottom and the heated material is at the top. In the electric furnace, the electrodes are inserted from the top, so the heating method is top heating. Therefore, the oxygen-free injection furnace has higher thermal efficiency. ③ The oxygen-free injection furnaces are suitable for smelting high-grade, medium-grade, and low-grade ores. Electric furnace typically does not have or only have a small amount of gas injection, resulting in extremely uneven heat transfer within the furnace. Especially when smelting the low-grade ores, the large amount of slag and low slag thermal conductivity result in slow and uneven heat transfer in the molten pool, ultimately leading to high power consumption and low yields. Therefore, the current gas-based shaft furnace-electric furnace melting-separation process is unsuitable for smelting medium-grade and low-grade iron ores. The oxygen-free injection furnace utilizes the superheated reducing gas at a rate of 900 to 1500 Nm3/t Fe. The larger the furnace hearth diameter, the higher the gas flow rate. Even when smelting low-grade ores, the powerful airflow agitation enables rapid and sufficient reaction of slag iron, which then drips into the furnace hearth for separation. ④ The oxygen-free injection furnace offers a higher metal recovery rate. The DRI reduction process in the oxygen-free injection furnace primarily occurs in the solid material layer, the soft melt droplet zone, and the recirculation zone, while the slag and iron separation process occurs in the slag layer and molten iron layer. The injection inlet is located in the recirculation zone. As the injected reducing gas ascends, the "stirring" effect of the reducing gas promotes rapid and sufficient reduction reactions in the upper portion. As the injected reducing gas does not pass through the slag-iron layer, the resulting molten slag-iron mixture is in a relatively static state, which facilitates slag and iron stratification and separation, thereby improving the metal recovery rate. ⑤ The oxygen-free injection furnace is suitable for smelting specialty ores. When smelting ores that are difficult to beneficiate and separate, such as vanadium-titanium magnetite, the oxygen-free injection furnace offers excellent kinetic conditions, and enables rapid DRI reduction and rapid slag and iron separation, thus avoiding the formation of foamy slag. In contrast, during the smelting of vanadium-titanium ore using the gas-based shaft furnace-electric furnace melting-separation process, rapid slag and iron separation cannot be achieved in the furnace, resulting in foamy slag, unsmooth slag discharge, and unsmooth iron tapping. ⑥ The oxygen-free injection furnace utilizes continuous charging and continuous slag-iron discharge operations. The furnace capacity can be expanded to 5,000 m3 or more. The annual output of a single unit can reach more than 3.5 million tonnes of molten iron, demonstrating significant promotion and application value.
  • Compared to the blast furnace, the following benefits are achieved: ① The carbon emission is significantly reduced. In traditional blast furnaces, the oxygen injection volume through the tuyere is 350 to 370 Nm3/t molten iron. This injected oxygen reacts with solid carbon at the tuyere to generate high-temperature CO. The higher the oxygen injection volume, the higher the carbon consumption and carbon emissions. The oxygen-free injection furnace is not a blast furnace with zero oxygen injection. The oxygen-free injection furnace recycles the CO at the furnace top, resulting in zero actual CO2 emission. ② The temperature inside the oxygen-free injection furnace is controlled by the temperature of the superheated reducing gas at the injection inlet. The injection inlet is located in the furnace hearth, allowing for rapid and flexible heat regulation. The heat in a blast furnace hearth is determined by the amount of solid carbon material burned per tonne of charge. Adjusting the heat in the furnace hearth requires adjusting the amount of coke charged from the furnace top or the amount of pulverized coal injection through the tuyere. The effect of such adjustment has a lag of approximately 2 to 5 hours, and is affected by slag and iron discharge, which can easily lead to uncontrolled furnace hearth temperature. ③ It is conductive to the smelting of special ores such as vanadium-titanium magnetite. The nitrogen content of the injection gas in the oxygen-free injection furnace is less than 8% (compared to 79% in conventional blast furnace), and the solid carbon material consumption is less than 0.1 kg/t molten iron (compared to 0.55 kg/t molten iron in blast furnace). The oxygen-free injection furnace effectively suppresses the formation of Ti(C,N) during the smelting of vanadium-titanium ores. Additionally, due to the rapid and flexible adjustment of hearth temperature, the oxygen-free injection furnace can reduce the frequency of low furnace temperatures, which is beneficial to vanadium recovery.
  • Other features and advantages of the present disclosure will be set forth in the subsequent description and will become apparent from the description or learned through practice of the present disclosure. The objectives and other advantages of the present disclosure may be realized and obtained through the structure pointed out in the description, claims and drawings.
    • BRIEF DESCRIPTION OF THE DRAWINGS
  • To illustrate embodiments of the present disclosure or technical solutions in the prior art more clearly, hereinafter drawings required for use in the embodiments or descriptions of the prior art are introduced briefly. Apparently, the drawings described below are some embodiments of the present disclosure. Other drawings may be obtained by those skilled in the art without creative efforts based on the provided drawings.
    FIG. 1 shows a schematic structural diagram of an apparatus for oxygen-free injection low-carbon ironmaking according to an embodiment of the present disclosure.
  • Reference numerals:
    10: gas-based shaft furnace; 11: reducing section;
    12: cooling section; 13: shaft furnace charging assembly;
    14: cold reducing gas injection inlet; 15: discharge outlet;
    16: hot reducing gas injection inlet; 17: shaft furnace gas outlet pipe;
    18: first gravity dust collector; 20: oxygen-free injection furnace;
    21: solid material layer; 22: soft melt droplet zone;
    23: gas recirculation zone; 24: slag layer;
    25: molten iron layer; 26: oxygen-free injection furnace charging assembly;
    27: slag outlet; 28: iron outlet;
    29: oxygen-free injection furnace gas outlet pipe; 210: oxygen-free injection furnace reducing gas injection inlet;
    211: second gravity dust collector; 30: reduction gas holder;
    31: first compressor; 32: first heat exchanger;
    40: first heating furnace; 50: second compressor;
    51: second heat exchanger; 60: second heating furnace;
    70: gas purification system.
    • DETAILED DESCRIPTION OF EMBODIMENTS
  • To further clarify objectives, technical solutions, and advantages of embodiments of the present disclosure, hereinafter the technical solutions in the embodiments of the present disclosure are explained clearly and completely in conjunction with the drawings. Apparently, the described embodiments are only a part, not all of the embodiments of the present disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of the present disclosure without creative effort are within the scope of protection of the present disclosure.
  • Reference is made to FIG. 1, the oxygen-free injection low-carbon ironmaking apparatus according to an embodiment of the present disclosure comprises a gas-based shaft furnace 10 and an oxygen-free injection furnace 20.
  • The gas-based shaft furnace 10 is divided into a reducing section 11 and a cooling section 12 from top to bottom along an internal vertical direction.
  • A plurality of hot reducing gas injection inlets 16 are symmetrically arranged on a same horizontal cross-section at the junction of the reducing section 11 and the cooling section 12, and the reducing section 11 is for the pre-reduction reaction of self-fluxing oxidized pellets to obtain hot direct reduced iron.
  • A plurality of cold reducing gas injection inlets 14 are symmetrically arranged on a same horizontal cross-section inside a lower portion of the cooling section 12, and the cooling section 12 is for cooling the hot direct reduced iron to obtain cold direct reduced iron. In one embodiment, the cold reducing gas injection inlets 14 are located at a height of 0.5m to 2.5m above the bottom of the cooling section 12.
  • The cold direct reduced iron discharged from the bottom of the cooling section 12 is transported to the oxygen-free injection furnace 20. The oxygen-free injection furnace 20 is a non-electric furnace that does not require insertion of electrodes and is a non-blast furnace with zero oxygen injection volume. The oxygen-free injection furnace 20 is divided into a furnace shaft and a furnace hearth from top to bottom along a vertical direction. The oxygen-free injection furnace 20 is for reducing and melting the direct reduced iron to obtain liquid slag and molten iron.
  • In one embodiment, the cooling section 12 utilizes an inverted frustum design, with the lower cross-sectional diameter being smaller than the upper cross-sectional diameter.
  • In one embodiment, a discharge outlet 15 is provided at the bottom of the cooling section 12, and the cold directly reduced iron is discharged from the discharge outlet 15. The discharge outlet 15 is located below the cold reducing gas injection inlet 14.
  • In one embodiment, in order to facilitate charging, a shaft furnace charging assembly 13 is provided at the top of the gas-based shaft furnace 10, and an oxygen-free injection furnace charging assembly 26 is provided at the top of the oxygen-free injection furnace 20. The shaft furnace charging assembly 13 and the oxygen-free injection furnace charging assembly 26 are well known to those skilled in the art and will not be described in detail herein.
  • In one embodiment, in order to facilitate the discharge of shaft furnace gas and oxygen-free injection furnace gas, a shaft furnace gas outlet pipe 17 is provided at the top of the gas-based shaft furnace 10, and an oxygen-free injection furnace gas outlet pipe 29 is provided at the top of the oxygen-free injection furnace 20.
  • In one embodiment, the interior of the furnace shaft is divided into a solid material layer 21 and a soft melt droplet zone 22 from top to bottom along the vertical direction, and the interior of the furnace hearth is divided into a gas recirculation zone 23, a slag layer 24, and a molten iron layer 25 from top to bottom along the vertical direction.
  • A plurality of reducing gas injection inlets 210 of the oxygen-free injection furnace is symmetrically distributed along the circumference at a same horizontal cross-section as the gas recirculation zone 23 of the furnace hearth. A plurality of slag outlets 27 is symmetrically distributed along the circumference at a same horizontal cross-section as the liquid slag layer 24 of the furnace hearth. A plurality of iron outlets 28 is symmetrically distributed along the circumference at a same horizontal cross-section as the liquid molten iron layer 25 of the furnace hearth.
  • For example, in one embodiment, the longitudinal cross-section of the furnace hearth is rectangular.
  • In one embodiment, a diameter of the reducing gas injection inlets 210 of the oxygen-free injection furnace adopts an adjustable sleeve design to control the flow rate of the superheated reducing gas injected from the reducing gas injection inlets 210 of the oxygen-free injection furnace.
  • A diameter of the furnace hearth of the oxygen-free injection furnace 20 and a flow rate of the superheated reducing gas injected are controlled as follows:
    • When the diameter d of the furnace hearth is less than 10m, the flow rate of the superheated reducing gas injected is 150m/s to 350m/s;
    • When the diameter d of the furnace hearth is greater than 10m, the flow rate of the superheated reducing gas injected is 250m/s to 450m/s.
  • The reaction process of the direct reduced iron within the oxygen-free injection furnace 20 (DRI undergoes deep reduction, melting, and slag-iron separation within the oxygen-free injection furnace 20) is as follows:
    In the oxygen-free injection furnace 20, the DRI and solid carbon material are charged into the oxygen-free injection furnace 20 through the charging equipment at its top and distributed on the surface of the solid material layer 21. The super-high-temperature (1800°C to 2350°C) reducing gas (i.e., superheated reducing gas) is injected from the oxygen-free injection furnace reducing gas injection inlet 210 into the gas recirculation zone 23 in the furnace hearth under high pressure and at a high flow rate (flow rate of 900 to 1500 Nm3/t Fe). That is, the superheated reducing gas injected from the oxygen-free injection furnace reducing gas injection inlet 210 does not directly enter the liquid molten iron layer 25 and slag layer 24.
  • At the front end of the reducing gas injection inlet 210, when the high-pressure, high-flow-rate superheated reducing gas is injected into the furnace hearth, the material at the front end of the reducing gas injection inlet 210 is blown away to form a high-temperature gasdominated space, which is the gas recirculation zone 23. The gas recirculation zone 23 is located between the liquid slag layer 24 and the soft melt droplet zone 22. The airflow generated by the gas recirculation zone 23 is for stirring the material passing through the horizontal cross-section of the gas recirculation zone 23, ensuring even distribution of the material and temperature within the furnace hearth and promoting more efficient physical and chemical reactions within the furnace hearth.
  • After passing through the gas recirculation zone 23, the superheated reducing gas ascends into the soft melt droplet zone 22. In the soft melt droplet zone 22, intense heat exchange occurs between the superheated reducing gas, the DRI, and the solid carbon material, which causes the DRI to heat up, soften, and melt into a liquid slag-iron mixture. Under the influence of gravity, the liquid slag-iron mixture begins to drip through the gas recirculation zone 23 into the liquid molten pool of the furnace hearth. Within the molten pool, the molten slag-iron mixture are automatically separated into layers due to their different densities. The molten iron sinks to the bottom to form the liquid molten iron layer 25, and the slag floats above the molten iron to form the liquid slag layer 24.
  • The liquid slag and molten iron in the furnace hearth are discharged from the furnace through the slag outlet 27 and the iron outlet 28, respectively. For ores with less slag, the slag outlet may be eliminated and the slag may be discharged through the iron outlet 28.
  • The discharge of liquid slag and iron from the furnace hearth frees up space in the furnace, allowing the slag and iron in the soft melt droplet zone 22 to continuously drip into the furnace hearth. The materials in the solid material layer 21 move downward sequentially and enter the soft melt droplet zone 22. The oxygen-free injection furnace charging assembly 26 continuously feeds new materials onto the surface of the solid material layer 21, maintaining the thickness of the solid material layer 21.
  • The superheated reducing gas, after heat exchange with the DRI and solid carbon material in the soft melt droplet zone 22, enters the solid material layer 21 to preheat the DRI and solid carbon material and undergo a reduction reaction with the incompletely reduced iron oxides in the DRI: FeO + CO = Fe + CO2 and/or FeO + H2 = Fe + H2O. The gaseous product is discharged from the oxygen-free injection furnace gas outlet pipe 29 at the top of furnace 20.
  • The melting point of carbon in the solid carbon material is as high as 4000°C. During the smelting process, the solid carbon material is continuously heated but remains solid as the charge descends until it enters the soft melt droplet zone 22, gas recirculation zone 23, slag layer 24, and molten iron layer 25, forming a solid material column.
  • Affected by the high-flow-rate reducing gas in the gas recirculation zone 23, the solid material column is mainly distributed at the center of the furnace hearth on a horizontal cross-section of gas recirculation zone 23, and after entering the molten slag-iron mixture, the solid material column gradually diffuses to other zones of the furnace hearth.
  • In the molten iron layer 25, a part of the carbon in the solid material column dissolves in the molten iron, which causes molten iron carburization.
  • In the liquid slag layer 24 and soft melt droplet zone 22, the part of the carbon in the solid material column undergoes a direct reduction reaction with incompletely reduced iron oxides: FeO + C = Fe + CO. The gaseous product CO rises and then is discharged through the oxygen-free injection furnace gas outlet pipe 29 at the top of the furnace.
  • Molten iron carburization and direct reduction continuously "consume" the solid material column, and the descending materials from the upper portion continuously provides new solid material columns, which ensures the permanent existence and continuous replacement of the solid material column.
  • The solid material column and the high-pressure airflow within the gas recirculation zone 23 support the solid material layer 21 in the furnace shaft.
  • The gases produced by the chemical reactions within the oxygen-free injection furnace 20, as well as the unreacted gases injected into the furnace, are collectively referred to as oxygen-free injection furnace gas. The oxygen-free injection furnace gas is discharged through the oxygen-free injection furnace gas outlet pipe 29 at the top of the furnace.
  • In some embodiments, in order to improve the coordination of pre-reduction and deep reduction in the gas-based shaft furnace 10 and the oxygen-free injection furnace 20, as well as the reduction efficiency of the entire ironmaking apparatus, the inner diameter of the horizontal cross-section of the furnace hearth of the oxygen-free injection furnace 20 (hereinafter referred to as the diameter of the furnace hearth in the oxygen-free injection furnace 20) is an important parameter determining the molten iron production capacity of the system. In order to ensure that the ore pre-reduction system production capacity matches the slag iron smelting-separation production capacity, a ratio of the inner diameter of the horizontal cross-section at the lower portion of the reducing section 11 of the gas-based shaft furnace 10 to the diameter of the furnace hearth of the oxygen-free injection furnace 20 is 1.0 to 1.3. A height of the material layer in the reducing section 11 of the gas-based shaft furnace 10 is 5m to 8m. A ratio of the height of the furnace hearth of the oxygen-free injection furnace 20 to the diameter of the furnace hearth of the oxygen-free injection furnace 20 is 0.35 to 0.6, and a ratio of the height of the furnace shaft of the oxygen-free injection furnace 20 to the diameter of the furnace hearth of the oxygen-free injection furnace 20 is 0.8 to 1.3.
  • In some embodiments, in order to save energy consumption in the ironmaking apparatus, the apparatus for oxygen-free injection low-carbon ironmaking further comprises a gas and heat recovery system.
  • The gas and heat recovery system comprises a shaft furnace gas and heat recovery sub-system and an oxygen-free injection furnace gas and heat recovery sub-system.
  • The shaft furnace gas and heat recovery sub-system and the oxygen-free injection furnace gas and heat recovery sub-system may be independent or partially or fully shared.
  • The gas output from the top of the shaft furnace has a temperature of 700°C to 900°C, undergoes coarse dust removal by a gravity dust collector to remove large particles of dust, then enters a heat exchange system to transfer heat to the heated medium, and the gas is then output from the heat exchange system, and then enters a gas purification system 70 to further remove fine particles of dust, CO2, and H2O to obtain purified gas. The sum of the volume percentages of CO2 and H2O in the purified gas is less than 1.5%. The purified gas is then transported to a reduction gas holder for recycling.
  • The gas output from the top of the oxygen-free injection furnace has a temperature of 500°C to 700°C, undergoes coarse dust removal by a gravity dust collector to remove large particles of dust, then enters a heat exchange system to transfer heat to the heated medium, and the gas is then output from the heat exchange system, and then enters the gas purification system 70, where fine dust particles are first removed, then CO2 and H2O are selectively removed depend on the gas composition, or the gas is directly discharged. The oxygen-free injection furnace gas output from the gas purification system 70 is called purified gas. The sum of the volume percentages of CO2 and H2O in the purified gas is less than 1.5%. The purified gas is then transported to a reduction gas holder for recycling.
  • In one embodiment, the shaft furnace gas and heat recovery sub-system comprises a first gravity dust collector 18 and a reduction gas holder 30. The first gravity dust collector 18 is connected to the shaft furnace gas outlet pipe 17 to remove dust and other impurities from the shaft furnace gas.
  • The reduction gas holder 30 is connected to a first compressor 31, which is connected to a first heating furnace 40 via a first heat exchanger 32.
  • The first gravity dust collector 18 is connected to a port of the reduction gas holder 30 via the first heat exchanger 32. The port is different from another port of the reduction gas holder 30 connecting to the first gravity dust collector 18.
  • The shaft furnace gas (high temperature) is discharged from the shaft furnace gas outlet pipe 17, passes through the first gravity dust collector 18 and then undergoes heat exchange with the reducing gas pressurized by the first compressor 31 from the reduction gas holder 30 in the first heat exchanger 32 to obtain purified shaft furnace gas, which is returned to the reduction gas holder 30.
  • To further remove dust, carbon dioxide, and water vapor from the shaft furnace gas, the first gravity dust collector 18 is connected to the reduction gas holder 30 via the first heat exchanger 32 and the gas purification system 70 (for fine dust removal, CO2 removal, and H2O removal). That is, after the shaft furnace gas undergoes dust removal, heat exchange, and purification (fine dust removal, CO2 removal, and H2O removal), the purified shaft furnace gas is obtained and returned to the reduction gas holder 30. The purification system 70 is well known to those skilled in the art and will not be described in detail herein.
  • Furthermore, the reducing gas within the reduction gas holder 30 is preheated by heat exchange with the shaft furnace gas (high-temperature) to serve as a source of the hot reducing gas. The reducing gas is then heated by the first heating furnace 40 (connected to the hot reducing gas injection inlet 16) and then enters the gas-based shaft furnace 10 through the hot reducing gas injection inlet 16.
  • The above sub-system not only fully recycles the thermal and chemical energy of the shaft furnace gas but also purifies the shaft furnace gas for reuse as the reducing gas, achieving dual recycling of gas and heat.
  • The oxygen-free injection furnace gas and heat recovery sub-system comprises a second gravity dust collector 211 and a reduction gas holder 30. The second gravity dust collector 211 is connected to the oxygen-free injection furnace gas outlet pipe 29 to remove impurities such as dust from the oxygen-free injection furnace gas.
  • The reduction gas holder 30 is connected to a second compressor 50 (with a connection port different from another connection port connecting the reduction gas holder 30 to the first compressor 31). The second compressor 50 is connected to a second heating furnace 60 via a second heat exchanger 51.
  • The second gravity dust collector 211 is connected to the reduction gas holder 30 via the second heat exchanger 51.
  • The oxygen-free injection furnace gas (high-temperature) is discharged from the oxygen-free injection furnace gas outlet pipe 29, passes through the second gravity dust collector 211, and undergoes heat exchange with the reducing gas pressurized by the second compressor 50 from the reduction gas holder 30 in the second heat exchanger 51 to obtain the oxygen-free injection furnace purified gas, which is returned to the reduction gas holder 30.
  • To further remove dust from the oxygen-free injection furnace gas, the second gravity dust collector 211 is connected to the reduction gas holder 30 via the second heat exchanger 51 and the gas purification system 70 (primarily for fine dust removal). That is, the oxygen-free injection furnace gas undergoes dust removal, heat exchange, and purification (fine dust removal) to obtain the oxygen-free injection furnace purified gas, which is returned to the reduction gas holder 30. The reduction gas holder 30 is a device well known to those skilled in the art and will not be described in detail herein.
  • Furthermore, the reducing gas in the reduction gas holder 30 is preheated by heat exchange with the (high-temperature) oxygen-free injection furnace gas to serve as the source of the hot reducing gas. The gas is then heated by the second heating furnace 60 (connected to the oxygen-free injection furnace reducing gas injection inlet 210), and then enters the oxygen-free injection furnace 20 through the oxygen-free injection furnace reducing gas injection inlet 210.
  • To illustrate the effectiveness of the method and apparatus for oxygen-free injection low-carbon ironmaking provided by an embodiment of the present disclosure, three types of typical China's iron ores of different grades listed in Table 1 are tested under different atmospheres. The components in Table 1 are all expressed in mass ratios (unit: %). Table 1
    Specie s TFe Fe2O3 FeO SiO2 TiO2 Al2O3 CaO MgO Other impuritie s Total
    Iron ore A 70.00 89.11 9.80 0.64 0.02 0.18 0.03 0.02 0.20 100
    Iron ore B 62.00 88.17 0.36 5.44 0.17 4.10 0.70 0.76 0.30 100
    Iron ore C 55.00 41.68 33.20 4.49 11.50 4.03 0.53 4.07 0.50 100
    • Example 1
  • A method for oxygen-free injection low-carbon ironmaking was for smelting China's high-grade iron ore:
    1.1 The ore blending was performed based on the chemical compositions of iron ore, flux, and bentonite. The composition of each material was shown in Table 2 (mass ratio, unit: %). Table 2
    Species TFe Fe2O3 FeO SiO2 TiO2 Al2O3 CaO MgO Other impurities Total
    Iron ore A 70.00 89.11 9.80 0.64 0.02 0.18 0.03 0.02 0.20 100
    Flux 3.37 0.18 92.91 3.55
    Bentonite 66.14 28.11 2.87 2.87 100
  • A balanced ore blending was performed at a bentonite ratio of 1.5% and a mass ratio of CaO/SiO2 in the pellets of 1.2, the calculated mass proportions of the materials were as follows:
    Iron ore A: flux: bentonite = 96.4%: 2.1%: 1.5%.
  • The composition of the self-fluxing oxidized pellets produced using the above blending ratios was shown in Table 3 (mass ratio, units: %). Table 3
    Species TFe Fe2O3 FeO SiO2 TiO2 Al2O3 CaO MgO Other impuritie s Total
    Pellets 67.48 85.91 9.45 1.68 0.02 0.60 2.02 0.14 0.19 100
  • 1.2 The gas-based shaft furnace 10 and the oxygen-free injection furnace 20 were operated based on economic composition of the reducing gas.
  • In certain regions, H2 resources were abundant, or the cost of obtaining H2 was lower than that of CO. In this case, when the composition of the reducing gas was primarily H2, the production cost of the gas-based shaft furnace was lower. Therefore, production may be performed with a higher H2:CO ratio. Herein, an H2:CO ratio of 5 (volume ratio, the same below) was taken as an example.
  • The composition of the reducing gas was detailed in Table 4 (volume ratio, unit: %). Table 4
    H2 CO N2 Total
    79.2 15.8 5.0 100
  • The charging temperature of pellets was 1000°C, a total flow rate of the reducing gas in the gas-based shaft furnace 10 was 2000 Nm3/t Fe, and K (cold reducing gas flow rate: hot reducing gas flow rate) was selected as 1.62, the cold reducing gas flow rate was 1237 Nm3/t Fe, the cold reducing gas temperature was 25°C, the hot reducing gas flow rate was 763 Nm3/t Fe, and the hot reducing gas temperature was 1000°C. Based on the ore grade, the total reducing gas flow rate in the gas-based shaft furnace 10 was 1832 Nm3/t DRI, the cold reducing gas flow rate was 1133 Nm3/t DRI and the hot reducing gas flow rate was 699 Nm3/t DRI.
  • The reducing gas at a flow rate of 699 Nm3/t DRI was output from the reduction gas holder, passed through the first compressor 31, and was then blown into the gas first heat exchanger 32 , where the reducing gas was preheated to 300°C. The reducing gas was then blown into the first heating furnace 40, where it was heated to 1000°C to become the hot reducing gas, which was then injected from the hot reducing gas injection inlet 16.
  • The DRI discharged from the bottom of the gas-based shaft furnace 10 had a temperature of 250°C. The composition was shown in Table 5 (mass ratio, unit: %). Table 5
    TFe MFe FeO SiO2 TiO2 Al2O3 CaO MgO Other impurities Total
    91.6 84.3 9.4 2.3 0.0 0.8 2.7 0.2 0.3 100
  • The cold reducing gas was injected into the cooling section 12 through the cold reducing gas injection inlet 14 of the gas-based shaft furnace 10. When the reducing gas reached the reducing section 11, its temperature was 514°C. After mixing with the hot reducing gas injected from the hot reducing gas injection inlet 16, the formed mixed reducing gas had a temperature of 700°C. In the reducing section 11, the mixed reducing gas reacted with iron oxides in the pellets to produce metallic iron and shaft furnace gas. The composition of the shaft furnace gas was shown in table 6 (volume ratio, unit: %). The shaft furnace gas was discharged from the shaft furnace gas outlet pipe 17 at a flow rate of 1832 Nm3/t DRI and a temperature of 750°C. After passing through the first heat exchanger 32, the temperature of the shaft furnace gas was lowered, and further fine dust removal, CO2, and H2O removal were performed to produce shaft furnace purified gas. The amount of CO2 removed was 189 kg/t Fe. The composition of the shaft furnace purified gas was shown in table 7 (volume ratio, unit: %). The shaft furnace purified gas had a flow rate of 1332 Nm3/t DRI, which is equivalent to 1454 m3/t Fe. Table 6
    H2 CO H2O CO2 N2
    56.7% 11.0% 22.5% 4.8% 5.0%
    Table 7
    H2 CO N2
    78.0% 15.2% 6.9%
  • The solid carbon material was coke with a fixed carbon content of 85%. The coke and direct reduced iron (DRI) produced in the shaft furnace were added through the charging assembly 26 at the top of the oxygen-free injection furnace 20 at a mass ratio of 0.064:1. The reducing gas, at a flow rate of 1000 Nm3/t Fe, was blown into the second heat exchanger 51 through the second compressor 50. The gas was preheated to 300°C in the second heat exchanger 51 and then entered the second heating furnace 60, where it was further heated to 2250°C to become the superheated reducing gas. The superheated reducing gas was blown into the oxygen-free injection furnace 20 through the oxygen-free injection furnace reducing gas injection inlet 210.
  • In the oxygen-free injection furnace 20, the superheated reducing gas underwent intense heat exchange with the solid direct reduced iron in the furnace to produce the liquid mixed slag and iron at a temperature of 1400°C to 1600°C. The superheated reducing gas temperature dropped from 2250°C to a temperature of 1800°C to 2000°C. During its upward movement, the superheated reducing gas continued to preheat the direct reduced iron in the furnace shaft, finally its temperature dropped to approximately 600°C, and the gas was then discharged from the oxygen-free injection furnace gas outlet pipe 29 at the furnace top. The high-temperature liquid mixed slag and iron chemically reacted with the hot reducing gas and the solid coke: FeO + H2 = H2O + Fe, H2O + C = H2 + CO, FeO + CO = CO2 + Fe, CO2 + C = 2CO, and FeO + C = CO + Fe. The gaseous products within the furnace were discharged through the oxygen-free injection furnace gas outlet pipe 29 at the furnace top. The output gas was oxygen-free injection furnace gas. The oxygen-free injection furnace gas had a flow rate of 1032 Nm3/t molten iron. The composition of the oxygen-free injection furnace gas was shown in table 8 (volume ratio, unit: %). Table 8
    H2 CO N2 Total
    76.71 18.44 4.84 100
  • Since the gas does not contain H2O and CO2, only dust removal was required to obtain the oxygen-free injection furnace purified gas.
    • 1.3 Implementation Results
  • Based on market prices from January to August 2023, the above production process costs 2,093 yuan per tonne of molten iron, which was shown in table 9 for details. The cost was 717 yuan per tonne lower than the 2,810 yuan per tonne cost of molten iron produced in a traditional blast furnace, thus the cost was reduced by 25.5%. Table 9
    Item Unit Unit Price(RMB) Consumption per Tonne of Iron Cost (RMB/Tonne of Iron)
    Iron ore A Tonne 920 1.429 1,314
    Coke Tonne 2,700 0.070 188
    Bentonite Tonne 700 0.022 15.6
    Flux Tonne 550 0.031 17.1
    Reducing gas m3 0.70 3000 2,100
    Purified gas m3 0.70 -2486 -1740
    Energy consumption for gas heating kgce (kilogram of standard coal equivalent) 0.52 123 63.9
    Electricity consumption for gas pressurization KWH (kilowatthour) 0.56 240 134.4
    Total 2,093
  • The actual CO2 emission in the above production process was 189 kg CO2/t molten iron, a 34% reduction compared to the actual CO2 emission of 287 kg/t molten iron in the existing gas-based shaft furnace process. The energy and material consumption of the production process were converted into the CO2 emissions according to their respective carbon emission factors, and the CO2 emission during the production process was 771.4 kg CO2/ t molten iron, which was shown in table 10 for details. The CO2 emission was 878.6kg CO2/ t molten iron lower than the 1,650 kg CO2/ t molten iron from smelting high-grade ore using the traditional blast furnace process, representing a reduction of 53.2% in CO2 emission. Table 10
    Item name Unit Carbon emission factor Consumption Carbon emission (kgCO2)
    Pellet Production kgce 2.69 34.1 91.7
    Coke Production kgce 2.69 7.5 20.2
    Reducing Gas Heating kgce 2.69 122.6 329.7
    Coke kg 3.26 69.6 226.6
    Electricity kwh 0.57 240.0 136.9
    Reducing Gas m3 0.31 3,000.0 933.0
    Shaft Furnace Purified Gas m3 0.30 -1,453.8 -432.8
    Oxygen-free Injection Furnace Purified Gas m3 0.36 -1,032.0 -373.9
    Molten Iron kg 0.16 -1,000.0 -160.0
    Total 771.4
    • Example 2
  • A method for oxygen-free injection low-carbon ironmaking was for smelting China's medium-grade iron ore.
  • 2.1 The ore blending was performed based on the chemical compositions of iron ore, flux, and bentonite. The composition of each material was shown in Table 11. All components in Table 11 were expressed in mass ratios (unit: %). Table 11
    Species TFe Fe2O3 FeO SiO2 TiO2 Al2O3 CaO MgO Other impurities Total
    Iron ore B 62.00 88.71 0.36 5.44 0.17 4.10 0.70 0.76 0.30 100
    Flux 3.37 0.18 92.91 3.55
    Bentonite 66.14 28.11 2.87 2.87 100
  • A balanced ore blending was performed at a bentonite ratio of 1.5% and a mass ratio of CaO/SiO2 in the pellets of 1.2, the calculated mass proportions of the materials were as follows:
  • Iron ore A: flux: bentonite = 91.2%: 7.3%: 1.5%.
  • The composition of the self-fluxing oxidized pellets produced using the above blending ratios was shown in Table 12 (mass ratio, units: %). Table 12
    TFe Fe2O3 FeO SiO2 TiO2 Al2O3 CaO MgO Other impurities Total
    56.56 80.43 0.33 6.20 0.15 4.18 7.44 0.99 0.27 100
  • 2.2 The gas-based shaft furnace 10 was operated based on economic composition of the reducing gas.
  • In certain regions, due to resource and price constraints, the reducing gas H2:CO within a certain range is most economical. Production is performed based on the most economical approach. Herein, an H2:CO ratio of 1.0 was taken as an example, and the reducing gas composition is detailed in Table 13 (volume ratio, unit: %). Table 13
    H2 CO N2 Total
    47.5 47.5 5.0 100
  • Herein a charging temperature of pellets was 980°C, a total flow rate of the reducing gas in the gas-based shaft furnace 10 was 2100 Nm3/t Fe, and K (cold reducing gas flow rate: hot reducing gas flow rate) was selected as 1.47, the cold reducing gas flow rate was 1249 Nm3/t Fe, the cold reducing gas temperature was 25°C, the hot reducing gas flow rate was 851 Nm3/t Fe, and the hot reducing gas temperature was 980°C. Based on the ore grade, the total reducing gas flow rate in the gas-based shaft furnace 10 was 1541 Nm3/t DRI, the cold reducing gas flow rate was 917 Nm3/t DRI and the hot reducing gas flow rate was 624 Nm3/t DRI.
  • The reducing gas at a flow rate of 624 Nm3/t DRI was output from the reduction gas holder, passed through the first compressor 31, and was then blown into the gas first heat exchanger 32, where the reducing gas was preheated to 300°C. The reducing gas was then blown into the first heating furnace 40, where it was heated to 980°C to become the hot reducing gas, which was then injected from the hot reducing gas injection inlet 16.
  • The DRI discharged from the bottom of the gas-based shaft furnace 10 had a temperature of 250°C. The composition was shown in Table 14 (mass ratio, unit: %). Table 14
    TFe MFe FeO SiO2 TiO2 Al2O3 CaO MgO Other impurities Total
    73.4 67.5 7.5 8.0 0.2 5.4 9.7 1.3 0.4 100
  • The cold reducing gas was injected into the cooling section 12 through the cold reducing gas injection inlet 14 of the gas-based shaft furnace 10. When the reducing gas reached the reducing section 11, its temperature was 521°C. After mixing with the hot reducing gas injected from the hot reducing gas injection inlet 16, the formed mixed reducing gas had a temperature of 700°C. In the reducing section 11, the mixed reducing gas reacted with iron oxides in the pellets to produce metallic iron and shaft furnace gas. The composition of the shaft furnace gas was shown in table 15 (volume ratio, unit: %). The shaft furnace gas was discharged from the shaft furnace gas outlet pipe 17 at a flow rate of 1541 Nm3/t DRI and a temperature of 750°C. After passing through the first heat exchanger 32, the temperature of the shaft furnace gas was lowered, and further fine dust removal, CO2, and H2O removal were performed to produce shaft furnace purified gas. The amount of CO2 removed was 577 kg/t Fe. The composition of the shaft furnace purified gas was shown in table 16 (volume ratio, unit: %). The shaft furnace purified gas had a flow rate of 1125 Nm3/t DRI, which is equivalent to 1533 m3/t Fe. Table 15
    H2 CO H2O CO2 N2
    34.5% 33.5% 13.0% 14.0% 5.0%
    Table 16
    H2 CO N2
    47.2% 45.9% 6.8%
  • The solid carbon material was coke with a fixed carbon content of 85%. The coke and direct reduced iron (DRI) produced in the shaft furnace were added through the charging assembly 26 at the top of the oxygen-free injection furnace 20 at a mass ratio of 0.051:1. The reducing gas, at a flow rate of 1100 Nm3/t Fe, was blown into the second heat exchanger 51 through the second compressor 50. The gas was preheated to 300°C in the second heat exchanger 51 and then entered the second heating furnace 60, where it was further heated to 2200°C to become the superheated reducing gas. The superheated reducing gas was blown into the oxygen-free injection furnace 20 through the oxygen-free injection furnace reducing gas injection inlet 210.
  • In the oxygen-free injection furnace 20, the superheated reducing gas underwent intense heat exchange with the solid direct reduced iron in the furnace to produce the liquid mixed slag and iron at a temperature of 1400°C to 1600°C. The superheated reducing gas temperature dropped from 2200°C to a temperature of 1800°C to 2000°C. During its upward movement, the superheated reducing gas continued to preheat the direct reduced iron in the furnace shaft, finally its temperature dropped to approximately 600°C, and the gas was then discharged from the oxygen-free injection furnace gas outlet pipe 29 at the furnace top. The high-temperature liquid mixed slag and iron chemically reacted with the hot reducing gas and the solid coke: FeO + H2 = H2O + Fe, H2O + C = H2 + CO, FeO + CO = CO2 + Fe, CO2 + C = 2CO, and FeO + C = CO + Fe. The gases generated by the reactions were output through the oxygen-free injection furnace gas outlet pipe 29 together with the unreacted superheated reducing gas. The output gas was oxygen-free injection furnace gas. The oxygen-free injection furnace gas had a flow rate of 1132 Nm3/t molten iron. The composition of the oxygen-free injection furnace gas was shown in table 17 (volume ratio, unit: %). Table 17
    H2 CO N2 Total
    46.16 48.98 4.86 100
  • Since the gas does not contain H2O and CO2, only dust removal was required to obtain the oxygen-free injection furnace purified gas.
    • 2.3 Implementation Results
  • Based on market prices from January to August 2023, the above production process costs 1,998 yuan per tonne of molten iron, which was shown in table 18 for details. The cost was 812 yuan per tonne lower than the 2,810 yuan per tonne cost of molten iron produced in a traditional blast furnace, thus the cost was reduced by 28.9%. Table 18
    Item Unit Unit Price(RMB) Consumption per Tonne of Iron Cost (RMB/Tonne of Iron)
    Iron ore B Tonne 800 1.429 1,143
    Coke Tonne 2,700 0.070 188
    Bentonite Tonne 700 0.023 16.4
    Flux Tonne 550 0.114 62.7
    Reducing gas m3 0.70 3200 2,240
    Purified gas m3 0.70 -2665 -1865
    Energy consumption for gas heating kgce 0.52 134 70.0
    Electricity consumption for gas pressurization KWH 0.56 256 143.4
    Total - - 1,998
  • The actual CO2 emission in the above production process was 577 kg CO2/t molten iron. The energy and material consumption of the production process were converted into the CO2 emissions according to their respective carbon emission factors, and the generalized CO2 emission during the production process was 1216.8 kg CO2/ t molten iron, which was shown in table 19 for details. The CO2 emission was 580.2kg CO2/ t molten iron lower than the 1,797 kg CO2/ t molten iron from smelting medium-grade ore using the traditional blast furnace process, representing a reduction of 32.3% in CO2 emission. Table 19
    Item name Unit Carbon emission factor Consumption Carbon emission (kgCO2)
    Pellet Production kgce 2.69 40.7 109.4
    Coke Production kgce 2.69 7.5 20.2
    Reducing Gas Heating kgce 2.69 134.2 360.9
    Coke kg 3.26 69.6 226.6
    Electricity kwh 0.57 256.0 146.0
    Reducing Gas m3 0.93 3200.0 2985.7
    Shaft Furnace Purified Gas m3 0.90 -1532.9 -1382.8
    Oxygen-free Injection Furnace Purified Gas m3 0.96 -1132.0 -1089.2
    Molten Iron kg 0.16 -1000.0 -160.0
    Total 1216.8
    • Example 3
  • A method for oxygen-free injection low-carbon ironmaking was for smelting China's low-grade iron ore that is difficult to beneficiate and smelt.
  • Low-grade iron ore that is difficult to beneficiate and smelt in China presented an iron ore resource with the greatest challenge and daunting task in reducing carbon emissions. During the smelting process, CO2 emissions can reach as high as 2,150 kgCO2/t molten iron. Prior to the present disclosure, no economically effective technical measures for reducing carbon emissions had been found.
  • 3.1 The ore blending was performed based on the chemical compositions of iron ore, flux, and bentonite. The composition of each material was shown in Table 20. All components in Table 20 are expressed in mass ratios (unit: %). Table 20
    Species TFe Fe2O3 FeO SiO2 TiO2 Al2O3 CaO MgO Other impurities Total
    Iron ore C 55.00 41.68 33.20 4.49 11.50 4.03 0.53 4.07 0.50 100
    Flux 3.37 0.18 92.91 3.55
    Bentonite 66.14 28.11 2.87 2.87 100
  • A balanced ore blending was performed at a bentonite ratio of 1.5% and a mass ratio of CaO/SiO2 in the pellets of 1.05, the calculated mass proportions of the materials were as follows:
    Iron ore A: flux: bentonite = 93.0%: 5.5%: 1.5%.
  • The composition of the self-fluxing oxidized pellets produced using the above blending ratios was shown in Table 21 (mass ratios, units: %). Table 21
    TFe Fe2O3 FeO SiO2 TiO2 Al2O3 CaO MgO Other impurities Total
    51.16 38.77 30.88 5.35 10.70 4.18 5.63 4.03 0.47 100
  • 3.2 The gas-based shaft furnace was operated based on economic composition of the reducing gas.
    • 3.2.1 Smelting and effects of low H2:CO ratio
    1. (1) Operation of the gas-based shaft furnace 10 and the oxygen-free injection furnace 20 with a H2:CO ratio of 0.2
  • In certain regions, H2 resources were relatively scarce, or the cost of obtaining H2 was higher than the cost of CO. In this case, production can be performed at a low H2:CO ratio. Herein, an H2:CO ratio of 0.2 was taken as an example, and the composition of the reducing gas was shown in Table 22 (volume ratio, unit: %). Table 22
    H2 CO N2 Total
    15.8 79.2 5.0 100
  • Herein a charging temperature of pellets was 930°C, a total flow rate of the reducing gas in the gas-based shaft furnace 10 was 2200 Nm3/t Fe, and K (cold reducing gas flow rate: hot reducing gas flow rate) was selected as 1.26, the cold reducing gas flow rate was 1227 Nm3/t Fe, the cold reducing gas temperature was 25°C, the hot reducing gas flow rate was 973 Nm3/t Fe, and the hot reducing gas temperature was 930°C. Based on the ore grade, the total reducing gas flow rate in the gas-based shaft furnace 10 was 1361 Nm3/t DRI, the cold reducing gas flow rate was 759 Nm3/t DRI and the hot reducing gas flow rate was 602 Nm3/t DRI.
  • The reducing gas at a flow rate of 602 Nm3/t DRI was output from the reduction gas holder, passed through the first compressor 31, and was then blown into the gas first heat exchanger 32, where the reducing gas was preheated to 300°C. The reducing gas was then blown into the first heating furnace 40, where it was heated to 930°C to become the hot reducing gas, which was then injected from the hot reducing gas injection inlet 16.
  • The DRI discharged from the bottom of the gas-based shaft furnace 10 had a temperature of 250°C. The composition is shown in Table 23 (mass ratio, unit: %). Table 23
    TFe MFe FeO SiO2 TiO2 Al2O3 CaO MgO Other impurities Total
    61.9 56.9 6.4 6.5 12.9 5.1 6.8 4.9 0.6 100
  • The cold reducing gas was injected into the cooling section 12 through the cold reducing gas injection inlet 14 of the gas-based shaft furnace 10. When the reducing gas reached the reducing section 11, its temperature was 518°C. After mixing with the hot reducing gas injected from the hot reducing gas injection inlet 16, the formed mixed reducing gas had a temperature of 700°C. In the reducing section 11, the mixed reducing gas reacted with iron oxides in the pellets to produce metallic iron and shaft furnace gas. The composition of the shaft furnace gas was shown in table 24 (volume ratio, unit: %). The shaft furnace gas was discharged from the shaft furnace gas outlet pipe 17 at a flow rate of 1361 Nm3/t DRI and a temperature of 750°C. After passing through the first heat exchanger 32, the temperature of the shaft furnace gas was lowered, and further fine dust removal, CO2, and H2O removal were performed to produce shaft furnace purified gas. The amount of CO2 removed was 787 kg/t Fe. The composition of the shaft furnace purified gas was shown in table 25 (volume ratio, unit: %). The shaft furnace purified gas had a flow rate of 1068 Nm3/t DRI, which is equivalent to 1726 m3/t Fe. Table 24
    H2 CO H2O CO2 N2
    12.5% 60.9% 3.3% 18.2% 5.0%
    Table 25
    H2 CO N2
    15.9% 77.7% 6.4%
  • The solid carbon material was coke with a fixed carbon content of 85%. The coke and direct reduced iron (DRI) produced in the shaft furnace were added through the charging assembly 26 at the top of the oxygen-free injection furnace 20 at a mass ratio of 0.043:1. The reducing gas, at a flow rate of 1200 Nm3/t Fe, was blown into the second heat exchanger 51 through the second compressor 50. The gas was preheated to 300°C in the second heat exchanger 51 and then entered the second heating furnace 60, where it was further heated to 2150°C to become the superheated reducing gas. The superheated reducing gas was injected through the oxygen-free injection furnace reducing gas injection inlet 210.
  • In the oxygen-free injection furnace 20, the superheated reducing gas underwent intense heat exchange with the solid direct reduced iron in the furnace to produce the liquid mixed slag and iron at a temperature of 1400°C to 1600°C. The superheated reducing gas temperature dropped from 2150°C to a temperature of 1800°C to 2000°C. During its upward movement, the superheated reducing gas continued to preheat the direct reduced iron in the furnace shaft, finally its temperature dropped to approximately 600°C, and the gas was then discharged from the oxygen-free injection furnace gas outlet pipe 29 at the furnace top. The high-temperature liquid mixed slag and iron chemically reacted with the hot reducing gas and the solid coke: FeO + H2 = H2O + Fe, H2O + C = H2 + CO, FeO + CO = CO2 + Fe, CO2 + C = 2CO, and FeO + C = CO + Fe. The gases generated by the reactions were output through the oxygen-free injection furnace gas outlet pipe 29 together with the unreacted superheated reducing gas. The output gas was oxygen-free injection furnace gas. The oxygen-free injection furnace gas had a flow rate of 1232 Nm3/t molten iron. The composition of the oxygen-free injection furnace gas was shown in table 26 (volume ratio, unit: %). Table 26
    H2 CO N2 Total
    15.42 79.71 4.87 100
  • Since the gas does not contain H2O and CO2, only dust removal was required to obtain the oxygen-free injection furnace purified gas.
    • (2) Implementation effect
  • Based on market prices from January to August 2023, the above production process costs 1,288 yuan per tonne of molten iron, which was shown in table 27 for details. The cost was 1522 yuan per tonne lower than the 2,810 yuan per tonne cost of molten iron produced in a traditional blast furnace, thus the cost was reduced by 54.2%. Table 27
    Item Unit Unit Price(RMB) Consumption per Tonne of Iron Cost (RMB/Tonne of Iron)
    Iron ore C Tonne 350 1.429 500
    Coke Tonne 2700 0.070 188
    Bentonite Tonne 700 0.023 16.1
    Flux Tonne 550 0.084 46.3
    Reducing gas m3 0.70 3400 2380
    Purified gas m3 0.70 -2958 -2071
    Energy consumption for gas heating kgce 0.52 145 75.7
    Electricity consumption for gas pressurization KWH 0.56 272 152.3
    Total - - 1288
  • The actual CO2 emission in the above production process was 787 kg CO2/t molten iron. The energy and material consumption of the production process were converted into the CO2 emissions according to their respective carbon emission factors, and the CO2 emission during the production process was 1477.7 kg CO2/ t molten iron, which was shown in table 28 for details. The CO2 emission was 672.3kg CO2/ t molten iron lower than the 2,150 kg CO2/ t molten iron from smelting low-grade ore using the traditional blast furnace process, representing a reduction of 31.3% in CO2 emission. Table 28
    Item name Unit Carbon emission factor Consumption Carbon emission (kgCO2)
    Pellet Production kgce 2.69 44.96 120.9
    Coke Production kgce 2.69 7.51 20.2
    Reducing Gas Heating kgce 2.69 145 390.2
    Coke kg 3.26 70 226.6
    Electricity kwh 0.57 272 155.1
    Reducing Gas m3 1.56 3,400 5,287.2
    Shaft Furnace Purified Gas m3 1.53 -1,726 -2,633.7
    Oxygen-free Injection Furnace Purified Gas m3 1.57 -1,232 -1,928.9
    Molten Iron kg 0.16 -1,000 -160.0
    Total - - 1,477.7
    • 3.2.2 Smelting and effects of high H2:CO ratio
    1. (1) The gas-based shaft furnace 10 and oxygen-free injection furnace 20 were operated with full hydrogen gas as the effective reducing gas component. The composition of the reducing gas was shown in Table 29 (volume ratio, unit: %).
    Table 29
    H2 CO N2 Total
    95 0 5.0 100
  • Herein a charging temperature of pellets was 1050°C, a total flow rate of the reducing gas in the gas-based shaft furnace 10 was 1800 Nm3/t Fe, and K (cold reducing gas flow rate: hot reducing gas flow rate) was selected as 2.02, the cold reducing gas flow rate was 1204 Nm3/t Fe, the cold reducing gas temperature was 25°C, the hot reducing gas flow rate was 596 Nm3/t Fe, and the hot reducing gas temperature was 1050°C. Based on the ore grade, the total reducing gas flow rate in the gas-based shaft furnace 10 was 1114 Nm3/t DRI, the cold reducing gas flow rate was 745 Nm3/t DRI and the hot reducing gas flow rate was 369 Nm3/t DRI.
  • The reducing gas at a flow rate of 369 Nm3/t DRI was output from the reduction gas holder, passed through the first compressor 31, and was then blown into the first heat exchanger 32 (a gas heat exchanger), where the reducing gas was preheated to 300°C. The reducing gas was then blown into the first heating furnace 40, where it was heated to 1050°C to become the hot reducing gas, which was then injected from the hot reducing gas injection inlet 16.
  • The DRI discharged from the bottom of the gas-based shaft furnace 10 had a temperature of 250°C. The composition is shown in Table 30 (mass ratio, unit %). Table 30
    TFe MFe FeO SiO2 TiO2 Al2O3 CaO MgO Other impurities Total
    61.9 56.9 6.4 6.5 12.9 5.1 6.8 4.9 0.6 100
  • The cold reducing gas was injected into the cooling section 12 through the cold reducing gas injection inlet 14 of the gas-based shaft furnace 10. When the reducing gas reached the reducing section 11, its temperature was 527°C. After mixing with the hot reducing gas injected from the hot reducing gas injection inlet 16, the formed mixed reducing gas had a temperature of 700°C. In the reducing section 11, the mixed reducing gas reacted with iron oxides in the pellets to produce metallic iron and shaft furnace gas. The composition of the shaft furnace gas was shown in table 31 (volume ratio, unit: %). The shaft furnace gas was discharged from the shaft furnace gas outlet pipe 17 at a flow rate of 1114 Nm3/t DRI and a temperature of 750°C. After passing through the first heat exchanger 32, the temperature of the shaft furnace gas was lowered, and further fine dust removal, CO2, and H2O removal were performed to produce shaft furnace purified gas. The amount of CO2 removed was 0 kg/t Fe. The composition of the shaft furnace purified gas was shown in table 32 (volume ratio, unit: %). The shaft furnace purified gas had a flow rate of 821 Nm3/t DRI, which is equivalent to 1326 m3/t Fe. Table 31
    H2 CO H2O CO2 N2
    68.7% 0.0% 26.3% 0.0% 5.0%
    Table 32
    H2 CO N2
    93.2% 0.0% 6.8%
  • The solid carbon material was coke with a fixed carbon content of 85%. The coke and direct reduced iron (DRI) produced in the shaft furnace were added through the charging assembly 26 at the top of the oxygen-free injection furnace 20 at a mass ratio of 0.043:1. The reducing gas, at a flow rate of 1200 Nm3/t HM, was blown into the second heat exchanger 51 through the second compressor 50. The gas was preheated to 300°C in the second heat exchanger 51 and then entered the second heating furnace 60, where it was further heated to 2150°C to become the superheated reducing gas. The superheated reducing gas was injected through the oxygen-free injection furnace reducing gas injection inlet 210.
  • In the oxygen-free injection furnace 20, the superheated reducing gas underwent intense heat exchange with the solid direct reduced iron in the furnace to produce the liquid mixed slag and iron at a temperature of 1400°C to 1600°C. The superheated reducing gas temperature dropped from 2150°C to a temperature of 1800°C to 2000°C. During its upward movement, the superheated reducing gas continued to preheat the direct reduced iron in the furnace shaft, finally its temperature dropped to approximately 600°C, and the gas was then discharged from the oxygen-free injection furnace gas outlet pipe 29. The high-temperature liquid mixed slag and iron chemically reacted with the hot reducing gas and the solid coke: FeO + H2 = H2O + Fe, H2O + C = H2 + CO, FeO + CO = CO2 + Fe, CO2 + C =2CO, and FeO + C = CO + Fe. The gases generated by the reactions were output through the oxygen-free injection furnace gas outlet pipe 29 together with the unreacted superheated reducing gas. The output gas was the oxygen-free injection furnace gas with a flow rate of 1232 Nm3/t molten iron. The composition of the oxygen-free injection furnace gas was shown in table 33 (volume ratio, unit: %). Table 33
    H2 CO N2 Total
    92.53 2.60 4.87 100
  • Since the gas does not contain H2O and CO2, only dust removal was required to obtain the oxygen-free injection furnace purified gas.
    • (2) Implementation effect
  • The recovery rate of iron in the production process was 98.4%, which was 2.6% higher than 95.8% of the blast furnace process and 29.7% higher than the 68.7% of the gas-based shaft furnace-electric furnace smelting-separation process. The recovery rate of V element was 71.2%, which was 1.9% higher than the 69.3% of the blast furnace process and 21.5% higher than the 47.8% of the gas-based shaft furnace-electric furnace smelting-separation process.
  • Based on market prices from January to August 2023, the above production process costs 1,260 yuan per tonne of molten iron, which was shown in table 34 for details. The cost was 1550 yuan per tonne lower than the 2,810 yuan per tonne cost of molten iron produced in a traditional blast furnace, thus the cost was reduced by 55.2%. Table 34
    Item Unit Unit Price(RMB) Consumption per tonne of Iron Cost (RMB/tonne of Iron)
    Iron ore C Tonne 350 1.429 500
    Coke Tonne 2700 0.070 188
    Bentonite Tonne 700 0.023 16.1
    Flux Tonne 550 0.084 46.3
    Reducing gas m3 0.70 3000 2100
    Purified gas m3 0.70 -2558 -1791
    Energy consumption for gas heating kgce 0.50 127 66.1
    Electricity consumption for gas pressurization KWH 0.56 240 134.4
    Total - - 1260
  • The actual CO2 emission in the above production process was 0 kg CO2/t Fe. The energy and material consumption of the production process were converted into the CO2 emissions according to their respective carbon emission factors, and the CO2 emission during the production process was 622.34 kg CO2/ t molten iron, which was shown in table 35 for details. The CO2 emission was 1527.7kg CO2/ t molten iron lower than the 2,150 kg CO2/ t molten iron from smelting low-grade ore using the traditional blast furnace process, representing a reduction of 71.1% in CO2 emission. Table 35
    Item name Unit Carbon emission factor Consumption Carbon emission (kgCO2)
    Pellet Production kgce 2.69 44.96 120.93
    Coke Production kgce 2.69 7.51 20.21
    Reducing Gas Heating kgce 2.69 126.60 340.55
    Coke kg 3.26 69.58 226.62
    Electricity kwh 0.57 240.00 136.87
    Reducing Gas m3 0.00 3000.00 0.00
    Shaft Furnace Purified Gas m3 0.00 -1325.90 0.00
    Oxygen-free Injection Furnace Purified Gas m3 0.05 -1232.00 -62.86
    Molten Iron kg 0.16 -1000.00 -160.00
    Total - - 622.34
  • Although the present disclosure has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments can still be modified, or equivalent replacements for some of the technical features therein can be made. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present disclosure.

Claims (10)

  1. A method for oxygen-free injection low-carbon ironmaking, comprising:
    charging hot self-fluxing oxidized pellets into a gas-based shaft furnace (10) from a furnace top, injecting cold reducing gas into the gas-based shaft furnace (10) from a bottom of the gas-based shaft furnace (10), and simultaneously injecting hot reducing gas into the gas-based shaft furnace (10) from a junction of a reducing section (11) and a cooling section (12) of the gas-based shaft furnace (10), wherein the cold reducing gas is heated and mixed with the hot reducing gas during a rising process to perform a pre-reduction reaction with the self-fluxing oxidized pellets to obtain hot direct reduced iron, and the hot direct reduced iron is cooled by the cold reducing gas in the cooling section (12) to obtain direct reduced iron;
    charging solid carbon material and the direct reduced iron at a mass ratio of 0.03 to 0.1: 1 into an oxygen-free injection furnace (20) from a furnace top, injecting superheated reducing gas with a flow rate of 900 to 1500 Nm3/t Fe at a temperature of 1800°C to 2350°C into the oxygen-free injection furnace (20), wherein the direct reduced iron is reduced and melted to obtain liquid slag and molten iron.
  2. The method for oxygen-free injection low-carbon ironmaking according to claim 1, wherein a temperature of the hot self-fluxing oxidized pellets is 600°C to 1100°C, a mass ratio of CaO to SiO2 in the self-fluxing oxidized pellets is 0.9 to 1.3, a mass percent of Fe in the self-fluxing oxidized pellets is 50% to 69%, a temperature of the cold reducing gas is less than 50°C, the direct reduced iron, obtained after the hot direct reduced iron is cooled by the cold reducing gas in the cooling section (12), has a temperature of less than 250°C and a metallization rate of ≥92%, and a fixed carbon content in the solid carbon material is greater than 75%.
  3. The method for oxygen-free injection low-carbon ironmaking according to claim 1, wherein the hot reducing gas and the superheated reducing gas are reducing gas from a reduction gas holder, and the cold reducing gas is reducing gas from the reduction gas holder and/or coke oven gas;
    the reducing gas from the reduction gas holder comprises purified gas and newly replenished reducing gas, and the reducing gas from the reduction gas holder comprises CO, H2, N2, and impurity gases, and a sum of a volume percentage of CO and a volume percentage of H2 is greater than 92%;
    the purified gas is gas recovered after heat exchange, heat recovery and purification of top gas from the gas-based shaft furnace (10) and the oxygen-free injection furnace (20).
  4. The method for oxygen-free injection low-carbon ironmaking according to claim 1, wherein a total gas flow rate in the gas-based shaft furnace (10) comprises a cold reducing gas flow rate and a hot reducing gas flow rate, wherein a ratio of the cold reducing gas flow rate to the hot reducing gas flow rate is K;
    in a case that a H2 to CO ratio of the reducing gas injected into the gas-based shaft furnace (10) is greater than 5, a charging temperature of the self-fluxing oxidized pellets is 1050°C to 1100°C, and in the gas-based shaft furnace (10), a total flow rate of the reducing gas is 1800 to 1900 Nm3/t Fe, a value of K ranges from 1.7 to 2.1, and a temperature of the hot reducing gas is 1050±20°C;
    in a case that the H2 to CO ratio of the reducing gas injected into the gas-based shaft furnace (10) is greater than 1.5 and less than or equal to 5, the charging temperature of the self-fluxing oxidized pellets is 1000°C to 1050°C, and in the gas-based shaft furnace (10), the total flow rate of the reducing gas is 1900 to 2000 Nm3/t Fe, the value of K ranges from 1.5 to 1.8, and the temperature of the hot reducing gas is 1000°C to 1050°C;
    in a case that the H2 to CO ratio of the reducing gas injected into the gas-based shaft furnace (10) is greater than 0.6 and less than or equal to 1.5, the charging temperature of the self-fluxing oxidized pellets is 950°C to 1000°C, and in the gas-based shaft furnace (10), the total flow rate of the reducing gas is 2000 to 2100 Nm3/t Fe, the value of K ranges from 1.3 to 1.6, and the temperature of the hot reducing gas is 980±20°C;
    in a case that the H2 to CO ratio of the reducing gas injected into the gas-based shaft furnace (10) is greater than 0.2 and less than or equal to 0.6, the charging temperature of the self-fluxing oxidized pellets is 900°C to 950°C, and in the gas-based shaft furnace (10), the total flow rate of the reducing gas is 2100 to 2200 Nm3/t Fe, the value of K ranges from 1.2 to 1.4, and the temperature of the hot reducing gas is 950±20°C;
    in a case that the H2 to CO ratio of the reducing gas injected into the gas-based shaft furnace (10) is less than or equal to 0.2, the charging temperature of the self-fluxing oxidized pellets is 880°C to 920°C, and in the gas-based shaft furnace (10), the total flow rate of the reducing gas is 2200 to 2300 Nm3/t Fe, the value of K ranges from 1.1 to 1.3, and the temperature of the hot reducing gas is 930±20°C.
  5. The method for oxygen-free injection low-carbon ironmaking according to any one of claims 1 to 3, wherein an inlet flow rate and an inlet temperature of the superheated reducing gas injected into the oxygen-free injection furnace are controlled within the following ranges:
    when the inlet flow rate of the superheated reducing gas is 900 to 1200 Nm3/t Fe, the inlet temperature of the superheated reducing gas is controlled within a range of 2130°C to 2320°C;
    when the inlet flow rate of the superheated reducing gas is 1200 to 1500 Nm3/t Fe, the inlet temperature of the superheated reducing gas is controlled within a range of 1850°C to 2250°C.
  6. An apparatus for oxygen-free injection low-carbon ironmaking, wherein the apparatus is configured to implement the method for oxygen-free injection low-carbon ironmaking according to any one of claims 1 to 4, and the apparatus comprises a gas-based shaft furnace (10) and an oxygen-free injection furnace (20);
    the gas-based shaft furnace (10) is divided into a reducing section (11) and a cooling section (12) from top to bottom along an internal vertical direction;
    a plurality of hot reducing gas injection inlets (16) are symmetrically arranged on a same horizontal cross-section at the junction of the reducing section (11) and the cooling section (12), and the reducing section (11) is for the pre-reduction reaction of self- fluxing oxidized pellets to obtain hot direct reduced iron;
    a plurality of cold reducing gas injection inlets (14) are symmetrically arranged on a same horizontal cross-section inside a lower portion of the cooling section (12), and the cooling section (12) is for cooling the hot direct reduced iron to obtain cold direct reduced iron;
    the direct reduced iron discharged from the bottom of the cooling section (12) is transported to the oxygen-free injection furnace (20), the oxygen-free injection furnace (20) is neither an electric furnace nor a blast furnace, with zero oxygen injection volume, an interior of the oxygen-free injection furnace (20) is divided into a furnace shaft and a furnace hearth from top to bottom along its vertical center line, and the oxygen-free injection furnace (20) is for reducing and melting the direct reduced iron to obtain liquid slag and molten iron.
  7. The apparatus for oxygen-free injection low-carbon ironmaking according to claim 6, wherein an interior of the furnace shaft is divided into a solid material layer (21) and a soft melt droplet zone (22) from top to bottom along the vertical direction;
    an interior of the furnace hearth is divided into a gas recirculation zone (23), a liquid slag layer (24) and a liquid molten iron layer (25) from top to bottom along the vertical direction.
  8. The apparatus for oxygen-free injection low-carbon ironmaking according to claim 7, wherein a plurality of reducing gas injection inlets (210) is symmetrically distributed along the circumference at a same horizontal cross-section as the gas recirculation zone (23) of the furnace hearth,
    a plurality of slag outlets (27) is symmetrically distributed along the circumference at a same horizontal cross-section as the liquid slag layer (24) of the furnace hearth,
    a plurality of iron outlets (28) is symmetrically distributed along the circumference at a same horizontal cross-section as the liquid molten iron layer (25) of the furnace hearth.
  9. The apparatus for oxygen-free injection low-carbon ironmaking according to claim 8, wherein a diameter of the reducing gas injection inlets (210) of the oxygen-free injection furnace adopts an adjustable sleeve design, and a diameter of the furnace hearth of the oxygen-free injection furnace (20) and a flow rate of the superheated reducing gas injected are controlled as follows:
    in a case that the diameter d of the furnace hearth is less than 10m, the flow rate of the superheated reducing gas injected is 150m/s to 350m/s;
    in a case that the diameter d of the furnace hearth is greater than 10m, the flow rate of the superheated reducing gas injected is 250m/s to 450m/s.
  10. The apparatus for oxygen-free injection low-carbon ironmaking according to any one of claims 7 to 9, wherein a ratio of an inner diameter of a horizontal cross-section of a lower portion of the reducing section (11) of the gas-based shaft furnace (10) to the diameter of the furnace hearth of the oxygen-free injection furnace (20) is 1.0 to 1.3;
    a height of a material layer in the reducing section (11) of the gas-based shaft furnace (10) is 5 to 8 meters;
    a ratio of a height to the diameter of the furnace hearth in the oxygen-free injection furnace (20) is 0.35 to 0.6, and a ratio of a height of the furnace shaft to the diameter of the furnace hearth in the oxygen-free injection furnace (20) is 0.8 to 1.3.
EP24878660.0A 2023-10-20 2024-08-15 Zero-oxygen injection low-carbon ironmaking method Pending EP4715069A1 (en)

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