CN118159671A - Process and method for producing steel and iron - Google Patents

Abstract

The present invention provides an externally heated vertical reactor for the reduction of iron ore, the reactor comprising: (a) a reactor tube positioned vertically adjacent the furnace; (b) An external furnace positioned vertically adjacent to at least one wall of the reactor tube to provide heat to be conducted through the at least one wall; (c) An input port at the base of the reactor tube, wherein the reducing gas is heated and injected into the input port such that the reducing gas rises upward through the reactor tube; (d) An exhaust port positioned adjacent a top surface of the reactor; (e) A gas filter positioned adjacent an inlet of the exhaust port; and (f) a bed positioned at the base of the reactor tube, wherein reduced iron powder product is collected in the bed at the base of the reactor tube.

Description

Process and method for producing steel and iron

Technical Field

The present invention broadly relates to providing a variety of means for the manufacture of steel products. In general, the process described herein is a method of producing iron from a variety of iron ore powders (such as hematite, magnetite and goethite) by an iron direct reduction process using indirect heating of a DRI reactor, and in particular, the process is directed to using hydrogen as the reductant of an indirectly heated H-DRI reactor, preferably using renewable electricity for indirect heating to reduce CO ₂ emissions from steel production. The use of these reactors to upgrade low grade iron ore and passivated iron for steelmaking is also described, as well as the integration of such indirectly heated reactors into both ironmaking and steelmaking.

Background

The steel industry accounts for about 6% to 8% of the global CO ₂ emissions, and the steel industry needs to reduce CO ₂ emissions to mitigate global warming. The world steel association reports that CO ₂ emissions of about 1,800kg CO ₂ per ton of steel in 2019 and energy intensity to produce 11 million tons of steel is about 19.84 Ji Jiao per ton. Since 2010, CO ₂ emissions increased from 1,800 to 1,830 and energy intensity dropped slightly from 20.13 gigajoules/ton to 19.84 gigajoules/ton. The steel process generally includes iron and steel making steps from iron ore, which may be closely integrated for making steel directly from iron ore.

It will be appreciated by those skilled in the art that the prior art of steel is greatly sophisticated and that most of the patents relating to processes used in these industries have progressed through iterative improvements to processes employed more than 30 years ago. Today, the energy intensity of the current process is very high, while the high emission intensity is a result of these process developments using treated coal for combustion, reduction, electrodes and incorporation of carbon steel. This prior art is limited by specific techniques developed over a long period of time, not by patents and publications.

There are three main iron-making processes, namely sponge iron production in which gangue is not removed from iron ore and pig iron production, smelting reduction in which gangue is removed by slagging.

There are three main steelmaking processes that can use this iron or scrap, namely flat melting furnaces, oxygen top-blown converter furnaces (BOF) and electric arc melting furnaces (EAF). Steelmaking is followed by casting, hot rolling and cold rolling processes. BOF and EAF processes are currently dominant in the industry. To mitigate climate change, it is desirable to reduce the emission intensity of steel production. Most desirably, the process does not increase the overall energy density of the overall steelmaking process, including the sequestration costs of any captured CO ₂. The invention disclosed herein relates generally to low emission steel production.

The reduction in emission intensity can be achieved initially by using low-emission iron instead of iron ore in the existing process. Flat melters and oxygen top-blown converter melters (BOFs) can typically replace 30% of the DRI sponge iron. The BOF process uses carbon (typically in the form of coke from metallurgical grade coal) for both the reduction and heating processes of iron ore and as a carbon source in carbon steel. CO ₂ generated during steelmaking is formed during the reduction of iron ore to molten iron. The CO ₂ produced is present as part of the furnace off-gas, called Blast Furnace Gas (BFG), produced by the use of coal.

Retrofitting existing BOF processes to produce low emission steels typically reduces emissions by only about 30% using H-DRI as feed. The emission intensity can be reduced by using natural gas instead of coal. Emissions may be reduced to about 600 kg CO ₂/ton. This is insufficient to achieve the goals of mitigating climate change and achieving zero emissions by 2050.

The substitution rate of DRI for scrap in EAF processes can be as high as 100%, but the substitution rate is currently limited to DRI produced from high grade ore, as EAF cannot tolerate large amounts of gangue from low grade ore. New EAF designs, such as Submerged Arc Furnaces (SAFs), are being developed to overcome this limitation. In order to meet current market needs and reduce emissions, it is preferred to use low grade ore with a low carbon DRI process.

The production of carbon steel requires the addition of carbon to produce sufficient cementite Fe ₃ C to obtain strength. There is also a need to reduce cementite production emissions to reduce CO ₂ emissions during steelmaking. Another source of CO ₂ emissions in steelmaking is the use of lime from limestone and Ca from what is commonly used to optimize slag formation: emissions of other carbonates in Mg proportions (such as dolomite). Another source of CO ₂ emissions is transportation or iron ore. There are many sources of CO ₂ emissions in the steelmaking supply chain. However, the greatest contribution of CO ₂ emissions comes from the use of fossil fuels in current DRI and BOF processes.

Over time, new steelmaking processes will be developed to produce low emissions steels driven by the need to reduce emissions to meet the zero emissions objectives required to mitigate climate change. The invention disclosed herein relates to low emission iron for both iron production and steel production.

The global supply of high grade iron ore is being reduced, so any development that reduces the strength of emissions and maintains energy efficiency should preferentially enable the production of steel using low grade iron ore. The invention disclosed herein may be employed to beneficiate low grade ores for both iron and steel making.

Strategies for producing low emission strength steels are mainly based on the use of low emission power and hydrogen gas in the iron reduction process. Furthermore, this strategy acknowledges that low-grade iron ore is unavoidable due to the increasing scarcity of high-grade iron ore. In the steelmaking process, it is fundamental why the main BOF process using coke is not suitable for producing low-emission steel. This strategy does not involve "end" processes such as Carbon Capture and Sequestration (CCS) for steelmaking or ironmaking, as such processes are generally found to be uneconomical for commodity products such as steel. Thus, the main means of producing low emission steel is to modify the current DRI process, using low emission hydrogen instead of mixed hydrogen and carbon monoxide in natural gas, synthesis gas, to produce sponge iron in a process called H-DRI. The intended route for H-DRI production of low-emission steel from sponge iron is to operate the EAF process using renewable power. This generally means that the concentration of low-grade iron ore can be achieved. A number of H-DRI processes have been developed.

Contemplated H-DRI processes can be categorized by two processes:

(a) And (5) reducing the granules. The first process developed for low emission DRI processes was to employ successful DRI processes such as MIDREX (low pressure) and hyt (high pressure) processes. This pellet DRI process uses a vertical furnace in which iron ore pellets are slowly reduced to sponge iron pellets. This is a validated technique for DRI. Low emissions can be achieved using hydrogen instead of synthesis gas as a reducing agent. Such a process is called H-DRI and the HYBRIT process in Sweden is an example (https:// www.hybritdevelopment.se/en /) where hot H-DRI pellets are prepared from high grade ore, directly injected into the EAF process for steel. Process variations must take into account the conversion of the process from an exothermic reaction using synthesis gas to an endothermic reaction using hydrogen.

(B) And (5) reducing particles. The second approach to the H-DRI process is particle flash reduction using particles, the benefit of which is the elimination of the pelletization process used in (a).

One example of particle reduction is the flash iron making technology (FIT), which was developed on a laboratory scale on the basis of using a suspension reactor in which preheated iron ore powder (typically less than 30 microns) is entrained in downward co-current flow of hydrogen and oxygen. The combustion of the hydrogen heats the powder to a sufficiently high temperature, typically above 1300 ℃, such that the reduction process is substantially complete within a residence time of about 5 seconds. The U.S. department of energy efficiency and renewable energy office 2018, "A Novel Flash Ironmaking Process (new flash ironmaking process)" reported the FIT process using a flash reactor. The short residence time is due to a number of factors, namely co-current flow of solids and gas, where the flow of particles is fast due to entrainment in the downwardly flowing gas; the high temperature of the process produces very high gas velocities; the mixing of the combustion gas and the reducing gas stream further increases the gas velocity; and the steam generated by the combustion drives the reaction to a high temperature because the steam drives the reverse reaction. The end result of the high temperature and gas velocity is that a residence time of about 5 seconds can be achieved in a reactor of about 19m high. Although the FIT process temperature is below the melting point of iron, there is reported to be strong sintering of the particles, which closes the pores in the particles and increases the reaction time, as the hydrogen gas is prevented from reaching the reduction reaction front in the particles.

Another example of particle reduction is the production of hydrogen using the HIsmelt process. The HISmelt process is a commercial EAF ironmaking process in which molten droplets of sponge iron produced by the combustion of oxygen and synthesis gas and the reduction of the synthesis gas are injected into a pool of molten steel. Molten sponge iron droplets are produced from iron ore particles injected into a hot cyclone collector where the cyclone is developed from the combustion of synthesis gas with oxygen to activate the reduction process with hydrogen and carbon monoxide, and the temperature is high enough to produce molten sponge iron. In the bath, gangue is removed by slagging to produce iron, or if the iron ore is of high grade, molten iron may be injected into the EAF. The HIsarna process replaces synthesis gas with hydrogen.

Another example of particle reduction is the FINEX process, which uses a fluidized bed (typically two three beds in series), heating the particles of <70 μm by combusting synthesis gas and oxygen and reducing by excess synthesis gas to produce iron. Modifying the process by modifying the particle size distribution can mitigate the effects of agglomeration. The conversion of such fluidized bed pathways to hydrogen is being developed in many processes, such as the HYFOR (< 150 μm) technology, CICORED (100-2,000 μm) technology and FINMET (50-8000 μm) technology, which differ primarily in the different particle sizes as shown. Notably, particles in the <250 μm range are often referred to as ultrafine particles.

In summary, all of the known techniques of H-DRI disclosed above use oxygen for combustion for heating and excess hydrogen for reduction in the reactor.

In the H-DRI process, low emission hydrogen (referred to as blue hydrogen) can be produced from fossil fuels to produce hydrogen and carbon monoxide; steam is used to convert carbon monoxide to CO ₂ and hydrogen; separating CO ₂ gas from hydrogen; CO ₂ is compressed to about 100 bar or liquefied; and this CO ₂ is transported and sequestered in the geological reservoir where it ₂ is converted to carbonate over time. Each of these process steps is a proven technology, but they increase production costs.

Alternatively, low-emission hydrogen (referred to as green hydrogen) can be produced from renewable power such as solar, wind and hydroelectric generation by electrolysis of water. According to the current trend, green hydrogen will become the lowest cost, as its process is simpler and the cost of the electrolyzer is decreasing, and the cost of wind and solar renewable power is also decreasing. Green hydrogen is making progress in item HYBRIT.

The challenge faced in retrofitting processes using fossil fuels is that the additional cost of producing hydrogen is generally not offset by process modifications. In addition, many such processes are not suitable for use with low grade ores, such as those required for EAF use. The cost for pelletization of iron ore for processing in a vertical furnace is not insignificant, for example, bentonite or biomass is required to be used as a binder to inhibit breakage of pellets in the bed of the vertical furnace.

Notably, the DRI process can produce hot sponge iron, which can be used in iron making to produce sponge iron briquettes using the Hot Briquette Iron (HBI) process. HBI treatment serves to limit oxidation of the briquettes, including inhibiting oxidation and spontaneous ignition during transportation of the steel grade iron. HBI sponge iron is a product sold to steel mills as a feedstock to a steelmaking process. Thus, any of the above discussed processes for producing HBI using H-DRI can be used to reduce the emission intensity of steel production. It is known that H-DRI can be processed into low emission sponge iron pieces using the HBI process.

HBI is not required if the H-DRI product is directly injected into molten iron for slagging to produce pig iron ingots for use in BOF or EAF or directly into EAF in the case of high grade ore to produce steel. Many of the iron produced by the particle-based H-DRI process considered above can be directly injected into the EAF steelmaking process, provided that high grade iron ore is used to produce H-DRI.

Notably, EAF technology was developed primarily for batch reprocessing of scrap steel. The development of a continuous EAF process allows hydrogen H-DRI pellets, briquettes or ingots to be continuously processed into steel.

As described above, the reduction process is converted to an endothermic reaction using hydrogen iron ore reduction, whereas the reaction is typically slightly exothermic when using carbon-based fuels. It will be appreciated by those skilled in the art that the hydrogen-based processes described above for iron and steel making are understood in their various forms to be energy intensive in the production of hydrogen. There is a need to develop processes that minimize hydrogen consumption.

In the present invention, an indirectly heated reactor will be disclosed that can be used to treat iron ore in a hydrogen-carbon monoxide/syngas (DRI reactor) and can preferably be a hydrogen (H-DRI reactor). H-DRI reduces the CO ₂ emissions intensity.

Sceats et al previously describe indirectly heated reactors for:

(a) Sceats et al, see WO2016/077863″Process and Apparatus for Manufacture of Calcined Compounds for the Production of Calcined Products( processes and apparatus for manufacturing calcined compounds for producing calcined products)' and references therein; and AU2020904492 and AU20201902810"Process and Methods for the Calcination AND MINERALS (processes and methods of calcining and mineral)" and references therein; WO2015/077818"Process and Apparatus for Manufacture of Portland Cement (process and apparatus for making portland cement)" and WO2021 references therein.

(B) Treatment of powders exhibiting phase transition in AU2020902858 "A Method for Pyroprocessing of Powers (powder high temperature treatment method)" and references thereto, and

(C) In "Processes and Methods of Calcination of Minerals (mineral calcination process and method)" of AU2021902040, the treatment of materials to prepare materials for batteries,

Wherein these inventions recognize that indirect heating means that heat is generated from outside the reactor vessel and may be generated by combustion reactions in a furnace surrounding the reactor, or electrical elements using resistive heating or inductive heating; and heat transfer into the reactor may be performed from such furnaces by steel or other heat conducting elements to separate heating and processing. This prior art on indirectly heated reactors does not disclose the use and benefits of using such indirectly heated reactors for iron or steel making.

This indirectly heated prior art does disclose the manufacture of low emission lime or lime fines that can be used in place of conventional lime or lime fines for use in low emission slagging processes to remove gangue from ironmaking or steelmaking processes.

It may be an object of the present invention to provide one or more means of optimizing the indirectly heated reactor design to produce DRI iron (preferably H-DRI iron).

It may be another object of the present invention to provide one or more means for using electric power to provide indirect heat to the DRI or H-DRI reactor.

Another object of the invention may be to describe the use of such indirectly heated DRI or H-DRI reactors to upgrade low grade iron ore.

Another object of the invention may be to describe a process for carburization of iron particles with the aim of passivating the iron and providing carbon in the iron for production of low carbon steel and carbon steel, thereby enabling carbon sequestration in carbon steel, especially if the carbon source is from CO ₂ that would otherwise be emitted. The low carbon steel comprises about 0.03 to 0.15% carbon and the carbon steel comprises 0.3 to 1.5% carbon by weight. Notably, stephens in US 5,869,018 discloses a process for iron carburization using carbon monoxide CO.

It may be another object of the present invention to provide a means to scale up indirectly heated DRI or H-DRI reactors to increase throughput.

Another object of the invention may be to describe the integration of indirectly heated DRI or H-DRI reactors into ironmaking processes.

It may be another object of the present invention to describe the integration of an indirectly heated DRI or H-DRI reactor into a steelmaking process.

Any discussion of the prior art throughout the specification should not be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.

Disclosure of Invention

The invention of this patent is generally associated with indirectly heated Direct Reduced Iron (DRI) reactors and hydrogen direct reduced iron (H-DRI) reactors for iron and steel making, respectively, using carbon monoxide/syngas or hydrogen as a reductant. The use of hydrogen is preferred to reduce CO ₂ emissions. Any reference to a DRI reactor with respect to the disclosed invention includes a reference to an H-DRI reactor, where the context permits.

Such inventions include:

(a) An indirectly heated DRI or H-DRI reactor for reducing iron ore fines, which is capable of controlling the reactor temperature profile along the reactor wall to initiate and maintain the reaction so that the reduction process is fully completed within the residence time of the fines in the reactor.

(B) Such indirectly heated DRI or H-DRI reactors are agnostic to the fuel used for heating and may be powered by indirect combustion of gases without the usual limitations of direct combustion in which iron ore also reacts with combustion gases and impurities therein.

(C) Such indirectly heated DRI or H-DRI reactors can be heated using electric power, using resistive, inductive or microwave heating. Such reactors may be explicitly referred to as indirectly heated e-DRI reactors or e-H-DRI reactors. Preferably, such reactors have the ability to operate at variable power throughput to enable rapid shut down and start up to handle typical renewable power variable feeds and to enable load balancing of the grid with variable feed rates of iron ore and reducing gas, or to operate at near constant power using energy storage systems (such as batteries, heated fluids or solids) to provide heat or power when renewable power generation is low.

(D) The modules of such indirectly heated DRI or H-DRI reactors are used to scale up the process while preferably allowing each reactor to be controlled by controlling the powder input, the reducing gas input and any selected indirect heating input if desired.

(E) A multistage indirectly heated DRI or H-DRI reactor is used and if desired crushed to enable upgrading of the powder in terms of iron content, with the gangue magnetically separated from the partially treated iron powder before the final stage of reduction to high grade iron described above.

(F) Indirectly heated DRI or H-DRI reactor sections are used to enable passivation of iron surfaces by forming carbon coatings, to increase oxidation resistance and pyrophoricity, and to provide carbon to carbon steel and thereby enable carbon to be encapsulated in the steel.

(G) Such indirectly heated DRI or H-DRI reactors are integrated with a furnace for melting iron powder and the molten iron is mixed with a slag former such as low emission lime/white lime to produce high grade pig iron ingots.

(H) An apparatus for integrating such indirectly heated DRI or H-DRI reactor consuming high grade iron in the form of briquettes or ingots with an EAF process comprising an added flux to produce steel.

Problems to be solved

The reactor was controlled by indirect heating. There is a need to provide improved reactor control for reduction of iron. The invention described herein discloses that indirectly heating the fines and gas in a DRI or H-DRI reactor process provides improved control of the DRI or H-DRI process compared to prior art DRI or H-DRI treatments for iron and steel making, wherein combustion and reduction occur simultaneously within the reactor vessel.

And (5) reducing by hydrogen. There is a need to reduce the amount of hydrogen used in the H-DRI process. The cost of producing green or blue hydrogen is high, so it is preferable to develop an H-DRI process that minimizes the use of hydrogen. It will be shown that the use of indirect heating reduces the need for hydrogen and oxygen. An example developed in the present disclosure is that hydrogen is to be used for iron reduction, and indirect heating may be provided by low cost combustion or preferably electrical heating. Such cost reductions may offset the energy required to grind raw ore into powder sizes for processing in such indirectly heated reactors.

And (3) treating iron ore fine particles. There is a need for an iron ore reduction process that can be used to treat iron ore fines, preferably less than about 200 μm. Such fines are produced in many stages from mining to ironmaking and steelmaking and provide a convenient source of powder that is not easily handled in a vertical furnace or fluidized bed.

And (5) treating the low-grade iron ore. There is a need to develop an iron treatment that can use low-grade iron ore as a feedstock and upgrade the quality of iron by removing gangue for steelmaking. The present disclosure includes processes for such beneficiation of iron ore using indirectly heated DRI or H-DRI reactors.

Carbon in the steel is sequestered. Carbon is required to be added to iron to produce low carbon steel. The present disclosure includes a process of carburized or partially carburized DRI or H-DRI during the manufacture of iron in which carbon is enabled to be encapsulated in the steel.

The reactor scale is enlarged. It is necessary to scale up the indirectly heated DRI or H-DRI reactor to process large amounts of iron ore.

In summary, the inventive content of the present disclosure relates to the use of an indirectly heated DRI or H-DRI reactor, which may use any means for indirectly heating and reducing gas, which indirectly heated DRI or H-DRI reactor may also use the following benefits: reactor control, high thermal efficiency, treatment of iron ore fines, upgrading of low grade iron ore, benefits of carburizing and passivating iron with carbon, and means of scale-up of modules using such reactors.

Reducing CO ₂ emission. The general object of the present invention is to reduce CO ₂ emissions in the production of iron or steel, wherein the H-DRI reactor uses renewable power heating and green hydrogen with the benefits described above, and uses zero emission lime and white lime for slag formation, and additionally uses carburization of iron for carbon sequestration.

Means for solving the problems

Indirectly heated reactors, such as droppers, have been accepted for laboratory assessment of materials. However, sceats et al have demonstrated that indirectly heated reactors can be deployed on an industrial scale for a variety of applications.

The present invention relates to the industrial application of indirectly heated DRI and H-DRI reactors, including the use of electric power to heat e-DRI and e-H-DRI reactors (referred to herein as e-DRI and e-H-DRI reactors).

According to a first aspect, the present invention provides an externally heated vertical reactor for the reduction of iron ore, the reactor comprising:

(a) A reactor tube positioned vertically adjacent to the melting furnace, wherein input powder of iron ore is injected into a hopper adjacent to a top end of the reactor tube, and the input powder drops downward through the reactor tube; wherein the input of the reducing gas is injected at the base of the reactor tube;

(b) An external furnace positioned vertically adjacent to at least one wall of the reactor tube to provide heat to be conducted through the at least one wall, wherein the conducted heat increases the temperature of the falling input powder;

(C) An input port at the base of the reactor tube, wherein a reducing gas is heated and injected into the input port such that the reducing gas rises upwardly through the reactor tube to further raise the temperature of the falling input powder such that the iron ore is reduced by the rising reducing gas, wherein a reaction temperature between 700 ℃ and 900 ℃ is reached such that the reducing gas is consumed by the iron ore in the reduction reaction, resulting in the formation of reduced iron powder products at the reactor base; wherein external heat is controlled along the length of the reactor tube to maintain a reaction temperature profile to reduce the iron ore.

(D) A vent positioned adjacent to a top surface of the reactor, wherein the gas exiting at the top of the reactor forms a gas stream and entrains unreacted input powder particles, wherein unreacted particles are extracted from the gas stream and re-injected into the reactor;

(e) A gas filter positioned adjacent to the inlet of the exhaust port, wherein the gas extracted from the reactor tube is scrubbed of gaseous reaction products comprising steam and carbon dioxide, and the scrubbed extracted gas is re-injected into the input gas stream; and

(F) A bed positioned at the base of the reactor tube, wherein the reduced iron powder product is collected in the bed at the base of the reactor tube and discharged from the reactor for subsequent processing.

The reducing gas preferably comprises carbon monoxide, hydrogen, methane or mixtures thereof.

The external heat source is formed in the furnace by combustion of a solid or gaseous fuel, or by electrical power generated using electric resistance, induction or microwaves, and distributed along the length of the reactor to provide a reactor wall temperature distribution wherein the volume fraction of the radiation penetration depth of about one meter is about 1x 10 ^-4 when wall, gas and particle emissions are considered, and wherein the reactor wall is heated to a temperature between 1100 ℃ and 1700 ℃.

The iron ore powder may be hematite, magnetite, goethite, siderite or other iron-based minerals, and mixtures thereof, requiring reduction of iron to treat the minerals.

At least one wall of the reactor tube is preferably made of steel or ceramic that is stable to hydrogen at about 1050 ℃.

Preferably, the reducing gas is hydrogen and the heat source is renewable power so as to minimize the CO ₂ emissions intensity of the product.

The input powder preferably has a particle diameter range of greater than 25 μm and less than about 250 μm. The diameter of the reactor tube is preferably not more than about 2m and the length of the reactor tube is between 10m and 35m, wherein the residence time of the downward flowing iron ore particles is about 10 seconds to 50 seconds, wherein the residence time depends on the direction of the gas flow and the formation of clusters of the iron ore particles.

The heat exchange between the reactor walls is preferably less than about 100kW/m. The average velocity of the input powder during its falling through the reactor tube is preferably less than 3.0m/s and more than 0.2m/s. Preferably, the flux of the input powder in the reactor is in the range of 0.5kg m ^-2s^-1 to 1.0kg m ^-2s^-1.

The input powder and the input reducing gas are preferably preheated by waste heat from other processes such as a water condenser and other processes associated with the use of reduced iron products.

Unreacted input powder particles extracted from the gas stream are preferably re-injected into the reactor tube with hydrogen through a metal tube passing through the center of the reactor tube so that the particles are heated and reduced during their transport to the base of the reactor.

The degree of reduction of iron is preferably 95% or more.

According to a second aspect, the present invention provides a method for reducing input iron ore powder using the externally heated vertical reactor according to the present invention, wherein the input iron ore powder is low grade hematite or goethite, wherein

(A) Controlling the method to substantially limit the extent of reduction, thereby producing ferromagnetic material (such as magnetite); and

(B) The powder cooling method is a flash quenching method; and

(C) Using

(D) Using a magnetic separator to separate gangue from magnetic iron ore products; and

(E) The magnetic iron ore product is injected into the second reactor according to any one of claims 1 to 15 for treatment to iron.

According to a third aspect, the present invention provides a process for reducing input iron ore powder using a reactor according to the present invention, wherein (a) low grade iron ore particles are treated to hot iron powder; and (b) injecting hot iron powder into the heated vat to produce molten iron; and (c) mixing the molten iron and a slag former (such as lime) in the heated vat so as to form a slag, wherein the slag floats to the top of the vat and is discharged and cooled; and (d) the molten iron is tapped from the heated vat and cooled and processed to produce high grade ingots.

According to a fourth aspect, the present invention provides a method of activating watertight iron ore, wherein:

(a) Oxidizing iron ore to produce porous hematite ore;

(b) Porous hematite ore is reduced in an externally heated vertical reactor according to the present invention to produce iron ore. Preferably, the oxidation process uses an externally heated vertical reactor according to the invention, wherein the reducing gas is replaced with air.

According to a fifth aspect, the present invention provides a process for producing cementite, wherein

(A) Reducing iron ore using the externally heated vertical reactor according to the present invention to produce iron particles; and

(B) If desired, the process of the fourth aspect may be combined to produce a high grade iron powder, and

(C) Iron powder can be used as feed to an externally heated vertical reactor according to any of claims 1 to 15, wherein CO ₂ and H ₂ are used as gaseous feed, and

(D) The reactor temperature and the relative composition fraction of CO ₂ are selected to convert a portion of the iron to cementite.

According to a sixth aspect, the present invention provides an externally heated vertical reactor according to the present invention for beneficiating iron, activating watertight iron ore or producing a desired fraction of cementite in iron by using a module consisting of about 8 such reactors, in which module an input iron ore feed is distributed from a central silo into the reactor, a reducing gas is distributed from a suitable gas source to the reactor, and heat can be exchanged independently of other elements of the industrial process to heat the powder or gas.

In another aspect of the invention, an apparatus for reducing iron ore using an indirectly heated DRI or H-DRI reactor is disclosed. This aspect includes the preferred means of reducing with hydrogen and indirectly heating with renewable electric power that together reduce the emission intensity to almost zero, such as a DRI reactor.

In another aspect of the invention, an apparatus for beneficiation of low grade iron ore using an indirectly heated DRI or H-DRI reactor configuration is disclosed.

In another aspect of the invention, an apparatus for sequestering CO ₂ in iron for use in the production of carbon steel and passivated iron is provided.

In another aspect of the invention, an apparatus for scaling up the process of the first aspect using a module of a plurality of such indirectly heated DRI or H-DRI reactors for iron and steel making is disclosed.

Other forms of the invention will become apparent from the description and drawings.

Drawings

Embodiments of the invention will be better understood and apparent to those skilled in the art from the following written description, by way of example only, in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an exemplary embodiment of an indirectly heated DRI reactor operating on a commercial scale. In this example, the indirect heating is a combustion furnace system using any fuel, and the reducing gas in the reactor is CO, H ₂, or a mixture, such as syngas. FIG. 2 is a schematic diagram of an exemplary embodiment of an indirectly heated DRI reactor in which indirect heat is provided by electric power and hydrogen gas is used as the reducing gas (e-H-DRI reactor). The embodiment of fig. 2 may achieve near zero emissions when renewable power is used.

FIG. 3 is a schematic process flow for upgrading low grade iron ore using a staged indirectly heated DRI or H-DRI reactor, wherein a first stage is used to produce magnetic iron material to effect magnetic separation of gangue, and a second stage is used to complete reduction of iron.

Fig. 4 is a schematic process flow for upgrading low grade iron ore, wherein iron powder from an indirectly heated DRI or H-DRI reactor is prepared into DRI powder, which is injected into a vat of molten iron, into which a slag former is injected to extract gangue, and then pig iron ingots are produced.

FIG. 5 is a schematic process flow for passivating iron ore with cementite and providing carbon for low carbon steel and carbon steel production using a staged indirectly heated DRI or HDI reactor, wherein DRI is produced in a first stage and iron coatings are produced by injecting gases of CO ₂ and hydrogen to deposit a layer of cementite Fe ₃ C. CO ₂ can be used to sequester carbon in the steel and reduce the CO ₂ footprint of the steel.

Fig. 6 is a schematic process flow in which iron powder from a module of an indirectly heated DRI or H-DRI reactor is used to produce DRI powder that is injected into a vat of molten iron into which a slag former (such as lime) is injected to extract gangue and produce pig iron ingots for steelmaking.

Detailed Description

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings and non-limiting examples.

Indirectly heated DRI and H-DRI reactor

In the production of steel using the known DRI treatment technique and the disclosed technique described in the experiments for developing H-DRI treatment, the reducing gas always plays two roles. The first function is to burn with the injected oxygen to provide heat to raise the temperature of the gas and solids, thereby initiating the reduction reaction, and to supply additional heat as needed for reducing iron ore to iron by hydrogen; and the second function is to provide a gas for reduction. In some cases, the combustion/reduction process includes coal as a fuel.

Current DRI processes are developed for iron and steel making processes, with those processes most commercially developed using pellet ore or fine iron ore/lump iron ore as a feedstock. In these DRI reactors, a slowly moving bed of pellets is reduced by a reducing gas in a shaft kiln. Heat from combustion is adsorbed on the surface of the pellets and diffusion of heat and the passage of reducing gases through the pellets is generally a rate limiting process of the reduction reaction. Typical residence times in such packed beds are on the order of a few hours for uniform reduction.

The primary disclosure of the present disclosure is that heat may be delivered to the reactants from the walls of an indirectly heated reactor rather than from combustion within the reactor. However, the penetration of heat from the heated reactor surface to the moving packed bed is limited to the area near the hot surface and the resulting temperature gradient is so high that indirect heating is not useful for a packed bed reactor. To produce such DRI in an H-DRI reactor, iron ore should be injected in particles, wherein a particle size distribution of less than about 250 μm should be used and a volume solids fraction of the particles of about 10 ^-4 to achieve uniform reduction across the reactor.

Such low volume solids fraction desirably equates the penetration depth of the radiation to a reactor tube radius of about 1m of the present invention so that the temperature distribution across the reactor is preferably nearly uniform. In the prior art of Sceats et al, it has been found that many chemical and physical reactions are sufficiently fast in such small particles because the heat and mass transfer in the particles is sufficiently fast, and the increase in reaction rate using small particles compared to pellets counteracts the lower volume fraction. Thus, the flux of the product is similar to that of a packed bed of pellets or a fluidized bed of pellets with combustion gases in the reactor. The residence time of the powder particles in the indirectly heated reactor is preferably less than about 50 seconds. The fast reaction time is such that the mass flow of iron ore in an indirectly heated reactor, where small particles flow in the reactor, is similar to the moving bed of pellets used in a conventional DRI reactor, and thus the flux of product through the reactor cross section is similar.

The benefit of indirect heating is that the tendency of the bed to collapse due to fluctuations is eliminated compared to a fluidized bed, which in particular makes the fluidized bed very susceptible to particle agglomeration. It is recognised that indirectly heated reactors may be higher than fluidised beds for equivalent heat transfer. When the indirectly heated reactor is operated with falling powder and rising gas, there is the same tendency for fine particles to be elutriated from the reactor, which is overcome by re-injecting such particles into the reactor for the circulating fluidized bed. The advantage of an indirectly heated reactor is that the extent of elutriation is small because there is no rising combustion gas and the gas flow rate is reduced.

The invention disclosed herein is premised on that the flux of iron from an indirectly heated reactor with a reducing gas is similar to the reduction of a packed bed or fluidized bed of particles of directly heated iron ore pellets where combustion from a portion of the reducing gas within the reactor is used. This process has been validated by treating various iron ores in indirectly heated reactors.

In terms of energy efficiency, the heat radiated from the indirect melting furnace into the reactor is offset by some radiation loss from the furnace outer wall to the ambient air which loses heat. This can be minimized by surrounding the exterior surfaces of the furnace with refractory material. The thick refractory stores energy which can lead to a delay in the response of the system to changes in heater temperature. In some applications, a fast response is required so that low thermal mass refractory materials can be used. Thus, indirectly heated DRI and H-DRI reactors have energy efficiencies comparable to existing processes.

The benefit is that these reactors provide for a more flexible operation for treating variations in heat, iron ore fines or reducing gas mass flow rates, and that thermal energy may be generated by any combustion process and electrical power or combination thereof.

Consider the first aspect of the present invention. A means for reducing iron ore on an industrial scale using an indirectly heated DRI or H-DRI reactor is disclosed. The basic principle of iron ore reduction is that iron ore must be heated in a reducing gas such as carbon monoxide or hydrogen to initiate the reduction reaction. The prior art heats iron oxide by injecting oxygen into the reducing gases of H ₂ and CO to cause combustion of the reducing gases to provide heat. At a specific temperature set by the characteristics of the iron ore, the iron ore reduction process with excess CO and H ₂ starts. The reduction of iron ore with CO is exothermic, while the reduction with H ₂ is endothermic, so equilibrium can be achieved by controlling the gas composition. In general, the result of combining an oxidative combustion process and a reductive process in the same reactor places constraints on the control of the process. In addition, it is also desirable to introduce iron ore as a particulate material to limit fines discharge in the exhaust gas stream or complex fluidized bed. The iron and steel industry has developed energy efficient means of operating the process and has expanded the scale of the process in large reactors such as BOF for many years.

The use of indirect heating of the iron ore eliminates the need to conduct a combustion process within the reactor to provide heat. Heat generated by combustion in an external furnace is transferred through a heat conducting medium such as steel or ceramic walls. The ability to control the temperature profile along the reactor enhances process control, which in conventional processes would require injection of reducing gas or oxygen at different points along the reactor.

One consequence of indirect heating is that the reduction process is independent of the heat source so that low grade fuels can be used for combustion in the external furnace, which would adversely affect the quality of the iron if used in an internal combustion reduction process. Another result is that air can be used for fuel combustion rather than an expensive oxy-fuel burner.

Ideally, the particle size in the indirectly heated reactor should be less than 250 μm, which can be achieved by crushing and grinding the ore, and the preferred range of 250 μm can be easily achieved using low cost crushers and grinders of raw ore. Preferably, the fraction of particles smaller than about 25 μm should be small, and this fraction can be reduced by mechanical fusion during milling.

In fig. 1, a schematic diagram of a DRI or H-DRI reactor is shown for producing sponge iron powder from iron ore powder injected from the top of the reactor and reducing gas injected at the base to provide indirect heating of the gas countercurrent. The reducing gas may be CO, or H ₂, or a mixture thereof. The reactor mainly comprises a reactor tube 101 and a combustion furnace 102, which combustion furnace 102 may be powered by a gas or gas-solid combustion process. Preferably the dried and preheated iron ore concentrate powder input 103 is injected into a hopper 104 to form a powder bed which is injected into an injection pipe 106 at the top of the reactor by a rotary valve 105 to form a downward plume of powder. At the base of the reactor, the reducing gas stream 107 was injected tangentially into the reactor as a swirl at a pressure of about 105 kPa. The gas may preferably be preheated. The rising gases and falling powders are heated by an external combustion furnace through the reactor walls. The staged burner can provide a desired reaction temperature along the reactor such that the iron ore consumes reducing gas at a controlled rate in this configuration. This is important because the reduction gas composition and the reduction kinetic reaction may be endothermic, exothermic, or a mixture of both, depending on any point in the reactor. By the reduction process, the reducing gas is converted to steam and CO ₂ as the gas rises through the reactor. As described above, the reducing gas injected into the reactor exceeds the consumed amount so that the reduction reaction can be performed to completion. At the top of the reactor, the exhaust gas vapors exit the top of the reactor and carry with it fines which are separated from the gas by cyclone 108 and filter 109 to obtain exhaust gas vapors 110. The exhaust gas is cooled by the falling powder. The gas is cooled by the falling powder. Entrained fines are collected in a bed in cone 111 and re-injected into the reactor through fines re-injection pipe 113 using rotary valve 112. All the treated powder, such as sponge iron, is cooled by the gas injected at the base of the reactor and is collected in a cone 114 in the bed at the base of the reactor and released from the reactor as sponge iron 116 by a rotary valve 115. The exhaust gas stream 110, which typically contains steam, CO ₂ and unreacted reducing gas, is cooled and water and CO ₂ are extracted using known processes used in the petrochemical industry. The excess reducing gas is recycled to the reactor as part of the reducing gas stream 107. The desired process temperature should preferably be low so that the reaction rate is not inhibited by sintering of the surface area of the particles or melting of the iron that would slow down the diffusion of hydrogen to the oxide. The residence time in the reactor is preferably less than 50 seconds and is typically in the range of 10-50 seconds. The degree of preheating of the powder and gas can be determined by minimizing the energy loss of the integrated system, and also by suppressing the process requirements of adverse reactions.

The rapid processing time of the reactor is such that the amount of material in the reactor is of the order of tens of kilograms, so that the feed rates of the iron feed ore and the reducing gas can be changed very rapidly to meet the energy available from the heat production.

Thus, the disclosed invention is direct heating of iron ore particles flowing downwardly through a reactor in a dilute flow state, wherein the volume fraction of particles is small enough that radiation from the reactor walls can penetrate the dust of powders and gases. When the wall, gas and particle emissions are considered at a temperature of about 700-1100 c, the radiation penetration depth is about in the order of meters and the volume solids fraction is about 10 ^-4. The need for a low solids volume fraction of particles in the powder means that the residence time of the particles in the reactor at a height of 8-30m is about 10-50 seconds for particles flowing down in countercurrent to the reducing gas. Thus, it is a primary consideration that the reaction rate of reduction of iron is such that the reaction can be completed within the desired residence time.

The short residence time considered above has certain benefits. Once formed at the process temperature of interest, the iron can rapidly diffuse through the particles and "hairs" of iron are known to form, which lead to agglomeration of the iron particles. This is a known risk that results in challenges for fluidized bed reactors because agglomeration or "sticking" can cause the bed to collapse, thus the reactor is shut down and the time to reestablish flow conditions is too long for commercial operation. The invention disclosed herein describes a process that is not a fluidized bed.

From the above, the criteria applied is whether the iron ore particles can be processed to sponge iron in about 10-50 seconds. The process temperature should preferably be in the range of 700-900 c for the following reasons. Such low temperatures prevent the "sticking phenomenon" common in gas-based DRI reactors such as fluidized beds. The kinetics of iron ore reduction have been intensively studied. It is well known that the kinetics of the direct reduction reactions of hematite to magnetite and magnetite to wustite occur very fast, in contrast to the slow reduction reactions of wustite to iron, which is then the rate determining step. Liu (W.Liu),. J.Y.lim, M.A.Sausedo, A.N.Hayhurst, S.A.Scott and J.S.Dennis et al in Kinetics of the reduction ofThe explicit study in by hydrogen and carbon dioxide for THE CHEMICAL looping production of hydrogen (kinetics of hydrogen and carbon dioxide reduction of wurtzite in hydrogen chemical looping production) (chem. Eng. Sci.120, 149-166 (2014)) considered the kinetics of reduction. This work shows that the reaction at this temperature regime is very fast even in about 5% hydrogen, with the result that it is ensured that the reaction is completed in less than 5-10 seconds for particles up to about 250 μm when pushing out to the base of the reactor initially 100% hydrogen to about 60% hydrogen at the top of the reactor. This reaction rate is fast enough to be used in a dilute flow reactor for treating iron ore particles in hydrogen. More detailed calculations indicate that the heat exchange between the hotter walls of the reactor is less than about 100kW/m, which is less than the rate of about 200kW/m required for highly endothermic reactions. It can be concluded that neither the chemical kinetics of the reduction nor the heat transfer from the thermal reactor wall are limitations of the process described herein. Experiments conducted in indirectly heated reactors confirm these conclusions.

The above considerations require that the reactor be limited to tubes up to about a few meters in diameter. The very fast reaction rate in the order of seconds is such that the flux of sponge iron discharged from the tube (in terms of tube cross section) is similar to that of a typical DRI reactor using a moving bed of pellets, since the reaction rate in such a bed is in the order of hours. It will be appreciated by those skilled in the art that a diluted powder stream having a velocity of less than about 3ms ^-1 will have a much lower attrition on reactor material formation than a moving bed of pellets. It will be apparent to those skilled in the art that indirectly heated DRI or H-DRI plants have the benefit of simplifying the steel production process by eliminating the need for granulation equipment. In order to change the high carbon emission production process of steel, it is important that the cost can be reduced by eliminating the manufacturing process such as granulation. The ability to produce iron or steel from iron ore concentrate has many such benefits.

The example of fig. 1 is an indirectly heated DRI or H-DRI reactor that does not explicitly address the need to reduce CO ₂ emissions in iron production. Emission reduction in a furnace can be achieved by using hydrogen as an injected reducing gas or low emission fuel such as biomass or waste. However, for large industrial plants, large amounts of biomass or waste are generally not available. An alternative way to simplify the heating process is to use renewable electric power for heating. This will be considered below.

In fig. 2, a schematic diagram of a preferred embodiment of an indirectly heated e-H-DRI reactor for producing sponge iron powder from iron ore powder using hydrogen as reducing gas is shown. The reducing gas is H ₂. The reactor mainly comprises a reactor tube 201 and an array 202 of electric melter elements. The preferably dried and preheated iron ore concentrate powder input 203 is injected into a hopper 204 to form a powder bed which is injected into an injection pipe 206 at the top of the reactor by a rotary valve 205 to form a downward plume of powder. Along the reactor, the hydrogen stream 207 is tangentially injected into the reactor as a vortex at a pressure of about 105 kPa. In this embodiment, the electric melter has a plurality of such injector elements 202 which can also be combined with deflector plates 208 which deflect the gases and particles to preheat the hydrogen gas injected into the reactor. Turbulence can assist in breaking up the gas and particle streams, thereby inhibiting the formation of powder agglomerates, enhancing gas-particle heat exchange and increasing residence time. The rising gases and falling powder are heated by the electric melter through the reactor walls so that the desired reaction temperature is reached, so that the reducing gases are consumed by the iron ore in the reduction process, which results in the formation of sponge iron at the base of the reactor. Through the reduction process, the hydrogen gas is converted to steam as it rises through the reactor. As described above, the hydrogen gas always exceeds the consumed amount so that the reduction reaction can proceed to completion. At the top of the reactor, the gas stream exits the top of the reactor and carries with it powder fines that are separated from the gas by cyclone 209 and filter 210 to obtain an exhaust stream 211. Fines are collected in the bed in cone 212 and re-injected into the reactor through fines re-injection pipe 214 using rotary valve 213. All the treated powder, such as sponge iron, is collected in a cone 215 in the bed at the base of the reactor and released from the reactor by rotary valve 216, releasing hot sponge iron 217. The off-gas vapor 211 of steam and hydrogen is cooled and water is easily extracted by cooling to form liquid water, leaving the hydrogen gas with minimal steam. The excess hydrogen is recycled to the reactor as part of the reducing gas stream 207. The desired reactor temperature should preferably be low so that the reaction rate is not inhibited by sintering of the surface area or melting of the iron. The degree of preheating of the powder and gas can be determined by minimizing the energy loss of the integrated system, and also by suppressing the process requirements of adverse reactions.

The use of an injection gas stream along the reactor and a plate deflector can be used in any application of an indirectly heated reactor. It is well known that countercurrent gas and powder flows will organize in the reactor tube to minimize interactions such that downwardly flowing particles tend to accumulate near the wall and the gas moves upwardly at high velocity in the middle of the tube. This means that the benefits of raising the gas to reduce the velocity of the powder and thereby increase the residence time and enhance the gas to particle heat transfer are lost. At the top of the reactor, such separation can reduce entrainment of fines in the off-gas and is useful. Particles and gases may be deflected by the plates within the tube, but the plates may become contaminated. A simple approach (such as an inner tube) may break the symmetry to form a loop reactor and the tube may be used to inject gas in a different manner than that described in fig. 2. The injection of hydrogen does not deflect the particles significantly because the momentum of the hydrogen is small. As shown in fig. 2, the most desirable approach is to use deflector plates purged with hydrogen jets to prevent plate fouling. Pulsed gas systems are commonly used in filtration systems and may be used for this purpose. The spacing between such devices should be less than the length of the steady state flow re-established in the pipeline. These details depend on the process details.

The use of electrically powered elements as in the embodiment of fig. 2 makes it possible to achieve very rapid shut-down or start-up. This reactor is designed to use renewable power and such power is not constantly generated. In the case of the strongest sunlight or wind, the cost is very low. This enables the throughput of the reactor to be adjusted up or down to meet the availability and cost of power, and green hydrogen will also have a similar response.

One way to regulate variable energy is to use a reactor design that can be switched between combustion power or renewable power or respective variable mixtures.

Another approach is to store electricity in a battery, or store heat and convert the heat to power, as needed, to maintain the required power over a period of time, particularly to fill renewable power gaps in solar and wind power plants. The average cost of renewable electric power (on a megawatt-hour basis) is expected to be lower than that of fossil fuels in the long term, so electric power can be used for 24 hours per day operation for 7 days per week to heat the reactor and produce hydrogen by electrolysis. In this case, it is always advantageous to use electricity for electric heating instead of using electrolysis to prepare hydrogen for combustion to generate heat by combustion.

In fig. 1 and 2, the hot wall for heat transfer may be any of the following:

(a) A metal alloy of steel, which has negligible carbon that may lead to hydrogen attack, which leads to embrittlement and failure of the carbon steel, and which exhibits strength at a temperature of about 1100 ℃ so that it can support its own weight as a vertical reactor tube, and which may preferably be an alloy with nickel and chromium and added with silicon dioxide, wherein the steel forms a passivation layer of chromium and silicon dioxide under appropriate conditions. Notably, the presence of a small amount of steam in the reactor stabilizes such oxide layers in hydrogen. In addition, the alloy should be an austenite phase that inhibits hydrogen diffusion. When such metals are used for heat transfer, electrical components are deployed in the furnace to illuminate the steel, and the static gas conditions are such that an oxidizing environment is maintained. Such systems may change rapidly with temperature and the steel pipe is installed so that it can be easily replaced, bellows and counterweights are used to reduce stress on the steel and to cope with thermal expansion and creep, and the gas pressure within the reactor needs to be maintained at positive gauge pressure to inhibit bending.

(B) Ceramic materials may be used in the reactor design, with the additional benefit of being able to encapsulate the electrical heating elements. Such elements may be subjected to thermal shock such that the operation of the reactor should be considered.

Fig. 1 depicts an embodiment using indirect heating from combustion, while fig. 2 depicts an embodiment using indirect heating with electrical power. It should be noted that the indirectly heated reactor described above (particularly the indirectly heated H-DRI reactor) may be applied to treat a variety of iron-containing or iron ores that contain elements such as manganese, nickel, copper, chromium, etc. that require an initial iron reduction step. Subsequent processes may include hydrometallurgical extraction processes or more advanced reduction processes such as thermite reduction. The advantages of the indirectly heated reactor described herein are: the product from this initial reduction step is a powder typically used in flotation and acid-base extraction processes and is porous, allowing for efficient extraction.

Another example of DRI or HDRI treatment is to modify the fines re-injection from the filter to the reactor. Figures 1 and 2 inject these particles into the top of the reactor together with the incoming particle stream, and thus fines in the cyclone and filter may become overloaded. Alternatively, the fines may be injected into the central heat transfer tube in a co-current configuration with some reducing gas in the reactor. As the gases and particles flow down the reactor they are heated by radiation/convection from the walls of the reactor, which are heated by radiation from the walls of the reactor, and when the reduction conditions are met, the reaction will take place. The mass flow of the fines and particles is set so that when the gas and fines are injected near the base of the reactor, the particles are sufficiently reduced. The fines are sprayed towards the cone of the product and the heated gas is led upwards into the reactor together with the injected reducing gas, which may be preheated externally. A preferred configuration to achieve this is a cyclone at the base of the reactor. It follows that by implementing this embodiment the loading of fines sprayed into the top cyclone and filter can be significantly reduced.

CO ₂ emissions reduction

The inventive examples described herein to reduce CO ₂ emissions in steel production may be based on indirect heating. Near zero emission intensity can be achieved by using the following method:

(a) Iron ore fines having a particle size preferably less than about 250 μm; and

(B) Green hydrogen or blue hydrogen with CCS for direct reduction of iron ore to iron; and

(C) Renewable electric power should be used to indirectly heat the reactants and products to initiate the reduction reaction and to provide energy to drive the endothermic hydrogen reduction that reduces iron ore to iron.

Because indirect heating is independent of the heat source, there are many ways to configure the reactor between the embodiment of fig. 1 (combustion heating) and the embodiment of fig. 2 (electrical heating) to achieve the desired degree of emission reduction, such as:

Concentrating iron ore and using indirectly heated DRI or H-DRI reactor

The beneficiation of the low grade iron ore can be achieved by grinding the low iron ore into small particles and extracting gangue by using a density difference between the iron ore and standard materials based on known techniques or, in the case of magnetite, by various processes using magnetic separators. This section describes a process for beneficiation of iron ore, including the use of indirectly heated DRI or H-DRI reactors.

It is well known that the reductive roasting of low grade hematite ore can be used to enhance the magnetic separation of gangue from magnetite produced by the roasting, as magnesite is a ferromagnetic material with high magnetic susceptibility. Thus, reduction of hematite to magnetite may improve gangue separation. Because the magnetic properties of iron ore depend on the thermal history of the grain morphology and grain size, the detailed process flow of beneficiation varies greatly. Conventional magnetic reduction roasting is performed on a time scale of several hours. Considering that the particle size for particle reduction is less than about 250 μm, the firing time is very short, on the order of seconds, and the temperature is maintained below the temperature at which magnetite is reduced to wustite, and a temperature of about 600 ℃ is selected for flash firing. When the product is cooled by flash quenching (preferably in an inert atmosphere to inhibit reoxidation), the curie temperature is reached and the magnetic susceptibility increases as the temperature decreases. Flash quenching may cause strain in the powder particles, so that further grinding steps of the finely porous magnetite may release additional gangue.

Fig. 3 shows a schematic process flow for upgrading low grade hematite ore 301, the low grade hematite ore 301 being ground to a size by a breaker/grinder 302 to be injected into a first section 303 of an indirectly heated H-DRI reactor, in which section it is operated to produce a hot magnetite 304 powder using hydrogen as a reducing agent, which reduces the hematite to magnetite, flash-cools the magnetite (not shown) in nitrogen and is injected into a second grinder 305 to release gangue and magnetite, and this powder is injected into a magnetic separator 306 to release a gangue stream 307 and a high grade porous magnetite stream 308. Porous magnetite is reduced in the second H-DRI stages 309 to 310 to produce high grade hot iron 311. The initial size of the crushing and grinding circuit may be greater than <250 μm specified for iron production, because the reduction process of hematite to magnetite is very fast compared to the overall reduction of iron. Thus, the process described in fig. 3 may be repeated to release gangue during the comminution stage.

The energy requirements for the hematite to magnetite conversion are low and standard heat recovery systems can be used to recover energy if required. The reactor may be an indirectly heated DRI reactor, which negates the benefits of reducing CO ₂ emissions when hydrogen is used in place of syngas. The energy consumption of the hematite to magnetite reaction is low, so the main benefit of using an indirectly heated reactor is the fine control of the process, mainly to ensure that sintering of the magnetite is minimized, especially to inhibit any thermal reaction of iron with gangue to form inseparable iron silicate. Flash quenching is desirable to increase the stress in the cooled magnetite particles to facilitate particle bursting and gangue release during magnetite grinding. It will be appreciated that the process will separate out gangue particulate material released in the hematite ore or in the initial crushing/grinding step. The pulse stream may contain insufficient magnetite for magnetic separation, and this feed may be further processed to remove such residual iron, including multiple passes through the magnetic separation process depicted in fig. 3. The comminution and heat treatment process described in fig. 3 may be repeated until the desired ore grade is achieved.

Hematite is selected as the iron ore to be treated in the two-stage reactor system depicted in fig. 3 because it is typically a low grade iron ore, but other ores such as goethite and siderite may also be treated.

Magnetite is found in nature and is generally found as a non-porous mineral, which is often associated with geological effects. As for hematite, high grade magnetite is depleting and the beneficiation of such ores is increasingly required. Magnetic separation is used, but this is incomplete because magnetite has low porosity and gangue is tightly bound within the particles. The small particle size required for the H-DRI process and H-DRI process described above helps to release such tightly bound gangue prior to injection into the indirectly heated reactor described in fig. 1 and 2.

Although the small particle size of magnetite facilitates the release of tightly held gangue, it is observed that the rate of reduction of low porosity gangue is slower, and therefore the indirectly heated DRI and H-DRI reactors are longer than high porosity iron ores, such as hematite and goethite. The porosity of such minerals may be enhanced by the process of oxidizing magnetite to hematite in an indirectly heated reactor, in which oxygen or preferably air is introduced into the indirectly heated reactor described above by replacing the reducing gas. During oxidation of magnetite to hematite, the particles burst, expand and break to produce a material with sufficient porosity that can be injected as synthetic hematite into the DRI or HDI reactor described above for iron reduction. The energy required to oxidize magnetite is small and the oxygen demand is also low. The oxidation of iron is performed in an indirectly heated reactor to maximize porosity and surface area, resulting in a material that reduces faster than the original magnetite, which means that the reactor is more compact.

The oxidation of magnetite to porous synthetic hematite can release the previously tightly held gangue. Synthetic hematite may be injected into the beneficiation process described in fig. 3 above to further beneficiate the rock as described, thereby producing a higher grade iron product.

It will be appreciated by those skilled in the art that the process described above is generally an irreversible process depending on the mineralogy of the iron ore. The process described above will vary depending on the mineralogy of the iron ore and the need for high grade iron, especially sponge iron which can be directly injected into EAF with a low emission footprint. Often ore beneficiation is required to remove phosphorus, in which case the beneficiation process described above can be integrated into known phosphorus extraction techniques.

It will be appreciated by those skilled in the art that the benefit of the beneficiation process described above is that the indirectly heated DRI or H-DRI reactor uses particles instead of pellets, making the particle-based beneficiation process based on magnetic separation of particles easy to integrate into the production of iron using such indirectly heated reactors.

Another route of beneficiation is to use a flash slagging route on the iron powder produced by the DRI or H-DRI reactor. This approach is illustrated in fig. 4. The hot iron particles 401 are injected into a heated vat 402, which heated vat 402 melts the particles that are formed into slag by injection of a slag forming agent 403 (preferably composed of lime, white lime or a mixture of both, rather than a carbonate material). Most preferably, this material is prepared by calcination of limestone, dolomite or magnesite, which captures CO ₂ as a pure gas stream for sequestration, as described in the prior art to Sceats et al, and thus the process described herein is a low emission process. The Ca/Mg ratio can be optimized to extract gangue using the best known ratio known from chemical analysis of gangue. Slag rises to the top of the vat and is extracted as stream 404, and molten iron is tapped from the vat as stream 405 using known slag forming techniques to extract the streams and mix the molten iron and slag former. In a subsequent process (not shown), the slag is cooled using a heat recovery process, and any iron may be recovered using known techniques, and the molten iron is preferably cooled and drawn to produce ingots and cooled to iron. The ingot is a form of pig iron. If desired, coke may be added to the process to facilitate subsequent carbon steel production.

The most desirable use of pig iron is to inject into EAF to produce steel because the gangue remaining in the pig iron is low enough, if desired, 100% of the pig iron can be treated in EAF, thereby reducing the need for scrap steel. It will be appreciated that this process may desirably be performed as a batch process. An advantage of using hot sponge iron powder from the DRI and H-DRI reactors is that the slag former is in intimate contact with the iron powder such that "flash slag formation" occurs because the diffusion length of the gangue and the reactive components of the slag former are minimized.

Carbon sequestration in iron

Carbon extracted from coal is used to produce certain grades of low carbon steel or carbon steel to maximize the strength of the steel while maintaining ductility for the manufacture and use of the steel. Therefore, low carbon steel and carbon steel are characterized by a large amount of cementite Fe ₃ C. Historically, pig iron feedstock has been provided with significant amounts of carbon. There is another reason for adding carbon to HBI and this is to passivate the surface. The surrounding air or moisture oxidizes cementite slowly, so the cementite coating can slow down the oxidation. In addition, hot iron spontaneously ignites due to rapid oxidation and presents a safety hazard for the treatment of DRI. This can be eliminated via HBI processes that reduce the iron surface area to inhibit uncontrolled oxidation, but this process does not inhibit oxidation of the exposed surfaces after compression. From these viewpoints, it is advantageous to coat the surface of iron with cementite. Importantly, if carbon is extracted from the otherwise emitted CO ₂, the emission intensity of the steelmaking process will be reduced. Such CO ₂ represents only a small portion of current steel emissions, but as previously mentioned, even with H-DRI there are other sources of CO ₂ emissions. One example of emissions is the CO ₂ emissions from lime, dolomite or magnesite, which CO ₂ emissions can be captured as a pure CO ₂ stream using the prior art of Sceats et al.

The prior art of Stephens teaches that the CO ₂ stream can be injected with hydrogen to convert iron to cementite by the following reaction mechanism:

3Fe+H₂+CO→Fe₃C+H₂O

Wherein it is assumed that the H ₂ O gas shift reaction is at equilibrium and that the H ₂ O partial pressure is such that oxidation of iron is inhibited. This technique teaches that if an attempt is made to reduce with iron ore to form cementite, the reaction rate is too slow. The H ₂、CO、CO₂ stream may be a tail gas from a steelmaking process.

In fig. 5, a means of coating the surface of the iron particles is considered. In this process, hot DRI 501 from the indirectly heated DRI or H-DRI reactor described above is injected into a second indirectly heated reactor 502, in this case heated by electric power 503, and the desired hydrogen/CO ₂ gas mixture 504 is injected at the base. The external heating is controlled to produce a rapid reaction of cementite for the hydrogen/CO ₂/CO/H₂ O partial pressure developed in the reactor and to ensure that the input temperature for a given iron and gas feed meets the conditions of the cementite reaction mechanism. The exhaust gas 505 is cooled in a condenser 506 to extract water as stream 507 and a residual gas stream 508 of CO, H ₂ and CO ₂ is recycled. The extent of reaction of iron with cementite in the product 509 will depend on the residence time of the particles in the reactor and the characteristics of the input iron stream (such as porosity and pore distribution) as the cementite product layer resistance will hinder the reaction rate. The solid product 509 is processed according to the needs of the next process in iron and steel making.

The extent of reaction of iron with cementite in the product will depend on the residence time of the particles in the reactor and the characteristics of the input iron stream (such as porosity and pore distribution) as the cementite product layer resistance can hinder the reaction rate. Ideally, the cementite product layer at ambient conditions is thick enough to inhibit spontaneous combustion of the iron so that the powder can be sufficiently stable that transportation to steel equipment is not required, making the HBI process ideal. For the production of mild steel or carbon steel, the amount of carbon to be added in steelmaking may be reduced, preferably to zero.

The beneficiation of low grade iron can be achieved together with a combination of cementite conversion and carbon sequestration levels to reduce the process costs of steel production and reduce the carbon footprint of the steel.

The production scale is enlarged.

A potential disadvantage of indirectly heated reactors for motive gas treatment is the need to ensure that radiation from the walls is able to penetrate the cloud of gas and particles. Typically, this limits the diameter of the single tube reactor to about 2 meters. While the throughput of the reactor may be the same as a conventional DRI reactor, the need for iron or steel equipment is such that multiple tubes are required to achieve a throughput of up to 5,000,000 tons of iron per year. The simplicity of the reactor design allows the development of modules of reactor tubes. For large devices, multiple modules may be used.

In FIG. 6, a top view of an indirectly heated H-DRI reactor module coupled to an EAF is shown. The 8-pipe module 601 contains 8 indirectly heated reactor units, such as the reactor of fig. 1 or fig. 2. Each reactor may preferably be operated independently. Each reactor delivers hot sponge iron and lime powder to a pool of molten steel in EAF 603. EAF is designed as a three-electrode unit with electrodes 604. The EAF is preferably a continuous EAF being developed in the industry, wherein molten steel 605 is withdrawn from the base of the EAF and slag 606 is withdrawn from the top of the molten steel. Various means are used to mix materials in the EAF and add additional materials, such as carbon and other alloying metals, as needed. Modifications to the upgrading including iron and cementite may be included in the modular design of the steelmaking.

The tube modules depicted in fig. 6 can also be applied to the production of low emission strength iron briquettes, where the powder at each reactor vent is collected and injected into the HBI apparatus. Modifications to the upgrading including iron and cementite may be included in the module design for ironmaking.

In modules for iron and steel making, each reactor can be operated independently controlled on each tube, or the power input powder can be distributed to multiple groups of tubes, and the hot iron powder streams can be clustered together. This option for module operation also draws power for production when the cost of electricity and hydrogen is low. A similar approach can be used to preheat the input stream of powder and reducing gas into the reactor. Such preheating is a known technique and the optimal preheating means will depend on the integrated design.

Claims (21)

1. An externally heated vertical reactor for the reduction of iron ore, the reactor comprising:

(a) A reactor tube positioned vertically adjacent to the furnace, wherein an input powder of iron ore is injected into a hopper adjacent to a top end of the reactor tube, and the input powder falls downward through the reactor tube; wherein an input of a reducing gas is injected at the base of the reactor tube;

(b) An external furnace positioned vertically adjacent to at least one wall of the reactor tube to provide heat to be conducted through the at least one wall, wherein the conducted heat increases the temperature of the falling input powder;

(C) An input port at a base of the reactor tube, wherein the reducing gas is heated and injected into the input port such that the reducing gas rises upward through the reactor tube to further raise the temperature of the falling input powder such that the iron ore is reduced by the rising reducing gas,

Wherein a reaction temperature between 700 ℃ and 900 ℃ is reached such that the reducing gas is consumed by the iron ore in a reduction reaction, resulting in the formation of reduced iron powder product at the reactor base; wherein external heat is controlled along the length of the reactor tube to maintain a reaction temperature profile to reduce the iron ore;

(d) A vent positioned adjacent to a top surface of the reactor, wherein the gas exiting at the top of the reactor forms a gas stream and entrains unreacted input powder particles, wherein unreacted particles are extracted from the gas stream and re-injected into the reactor;

(e) A gas filter positioned adjacent to the inlet of the exhaust port, wherein the gas extracted from the reactor tube is scrubbed of gaseous reaction products comprising steam and carbon dioxide and the scrubbed extracted gas is re-injected into the input gas stream; and

(F) A bed positioned at the base of the reactor tube, wherein the reduced iron powder product is collected in the bed at the base of the reactor tube and discharged from the reactor for subsequent processing.

2. The externally heated vertical reactor of claim 1 wherein the reducing gas comprises carbon monoxide, hydrogen, methane or mixtures thereof.

3. The externally heated vertical reactor of claim 1 or 2, wherein the volume fraction of the radiation penetration depth of about one meter is about 1 x 10 ^-4 when considering wall, gas and particle emissions, and wherein the reactor wall is heated to a temperature between 1100 ℃ and 1700 ℃.

4. An externally heated vertical reactor according to any of claims 1 to 3 wherein an external heat source is formed in the furnace by combustion of a solid or gaseous fuel, or generated by electrical power generated using resistance, induction or microwaves, and distributed along the length of the reactor to provide a reactor wall temperature distribution wherein the volume fraction of the radiation penetration depth of about one meter is about 1 x 10 ^-4 when wall, gas and particle emissions are considered, and wherein the reactor wall is heated to a temperature between 1100 ℃ and 1700 ℃.

5. The externally heated vertical reactor of any of claims 1 to 4, wherein the iron ore powder can be hematite, magnetite, goethite, siderite or other iron-based minerals, and mixtures thereof, requiring reduction of iron to treat the minerals.

6. The externally heated vertical reactor of any preceding claim wherein at least one wall of the reactor tube is made of steel or ceramic that is stable to hydrogen at about 1050 ℃.

7. The externally heated vertical reactor of any of claims 3 to 5 wherein the reducing gas is hydrogen and the heat source is renewable power so as to minimize CO ₂ emissions intensity of the product.

8. An externally heated vertical reactor according to any preceding claim in which the input powder has a particle diameter range of greater than 25 μm and less than about 250 μm.

9. The externally heated vertical reactor of any preceding claim wherein the reactor tube has a diameter of no greater than about 2m and a length of between 10m and 35m, wherein the residence time of downwardly flowing iron ore particles is from about 10 seconds to 50 seconds, wherein the residence time is dependent on the direction of gas flow and cluster formation of the iron ore particles.

10. Externally heated vertical reactor according to any of the preceding claims wherein the heat exchange between the walls of the reactor is less than about 100kW/m.

11. An externally heated vertical reactor according to any preceding claim in which the average velocity of the input powder during its fall through the reactor tube is less than 3.0m/s and greater than 0.2m/s.

12. An externally heated vertical reactor according to any preceding claim wherein the flux of the input powder in the reactor is in the range 0.5kg m ^-2s^-1 to 1.0kgm ^-2s^-1.

13. The externally heated vertical reactor of any preceding claim wherein the input powder and input reducing gas are preheated by waste heat from other processes such as a water condenser and other processes associated with the use of the reduced iron product.

14. An externally heated vertical reactor according to any preceding claim in which unreacted input powder particles extracted from the gas stream are re-injected into the reactor tube with hydrogen through a metal tube passing through the centre of the reactor tube so that these particles are heated and reduced during their delivery to the base of the reactor.

15. The externally heated vertical reactor of any preceding claim, the degree of reduction being 95% or greater.

16. A method of reducing input iron ore powder using the externally heated vertical reactor of any of claims 1 to 15, wherein the input iron ore powder is low grade hematite or goethite, wherein:

(a) Controlling the method to substantially limit the degree of reduction to produce a ferromagnetic material such as magnetite; and

(B) The powder cooling method is a flash quenching method; and

(C) Using

(D) Using a magnetic separator to separate gangue from magnetic iron ore products; and

(E) Injecting the magnetic iron ore product into a second reactor according to any one of claims 1 to 15 for treatment to iron.

17. A method of reducing input iron ore powder using the reactor of any one of claims 1 to 15, wherein:

(a) Treating the low-grade iron ore particles into hot iron powder; and

(B) Injecting the hot iron powder into a heated vat to produce molten iron; and

(C) The molten iron and a slag former such as lime are mixed in a heated vat so as to form slag, wherein the slag floats to the top of the vat and is discharged and cooled; and

(D) The molten iron is tapped from the heated vat and cooled and processed to produce high grade iron ingots.

18. A method of activating watertight iron ore, wherein:

(a) Oxidizing iron ore to produce porous hematite ore;

(b) Reducing the porous hematite ore in the externally heated vertical reactor of any one of claims 1 to 15 to produce iron ore.

19. The method of claim 18, wherein the oxidation process uses an externally heated vertical reactor according to any one of claims 1 to 15, wherein the reducing gas is replaced with air.

20. A method of producing cementite, wherein:

(a) Reducing iron ore to produce iron particles using the externally heated vertical reactor of any one of claims 1 to 15; and

(B) If desired, high grade iron powder can be produced in combination with the method according to claim 17, and

(C) The iron powder can be used as a feed to an externally heated vertical reactor according to any of claims 1 to 15, wherein CO ₂ and H ₂ are used as gaseous feeds, and

(D) The reactor temperature and the relative composition fraction of CO ₂ are selected to convert a portion of the iron to cementite.

21. An externally heated vertical reactor according to any of claims 1 to 15 for beneficiating iron, activating watertight iron ore or producing a desired fraction of cementite in iron by using a module of about 8 such reactors in which an input iron ore feed is distributed to the reactor from a central silo, the reducing gas is distributed to the reactor from a suitable gas source, and heat can be exchanged to heat the powder or gas independently of other elements of the industrial process.