Improved metal production

Abstract

A system (100) for metal production, the system comprising: a reduction furnace (110) configured to receive metal ore (101) and process gas (102) and to output hot metal (115) and reduction furnace top gas (111); and a first thermochemical reactor (130) configured, in a first mode, to receive at least a portion (163) of the reduction furnace top gas (111) and to produce carbon monoxide from carbon dioxide in the portion (163) of the blast furnace reduction furnace top gas (111) by oxidizing a thermochemical compound, and to return at least a portion of the produced carbon monoxide (151) into the reduction furnace (110).

Description

[0001] Objective

[0002] The present invention relates to systems and methods for producing liquid metal. In particular, the present invention relates to systems and methods for metal production with a reduced carbon footprint. Background Art

[0003] The iron and steel industry is a major emitter of greenhouse gases, with emissions accounting for up to 9% of global CO2 emissions. Due to the inherent energy and carbon intensity of steel production, which involves very high-temperature processes, steel is indeed an industry that is difficult to decarbonize. In fact, by weight, more carbon dioxide is released than the steel produced, with 1.89 tons of CO2 released per ton of steel produced using current technologies. The main reason is that coking coal is used as both energy and structural support, accounting for 74% of the total energy raw materials and 15% of the total global coal consumption.

[0004] Currently, there are two main methods of steel production. The blast furnace-basic oxygen furnace (BF-BOF) route accounts for 71% of production, and the natural gas-based direct reduced iron followed by an electric arc furnace (DRI-EAF) accounts for the other 29%. The BF-BOF route will be discussed in detail below, but generally both methods consist of two parts. First, iron ore is reduced to metallic iron in the BF or DRI, and then it is converted to steel by reducing the carbon content in the metal in the BOF or EAF.

[0005] Currently, several technologies for decarbonizing the steel industry are being studied. The first option is to shut down old BF-BOFs and replace them with DRI-EAFs. If the EAF is powered by renewable electricity, it is possible to save 1.5 Gt of CO2 emissions per year. However, the construction cost of a typical large DRI-EAF plant ranges from $1.1 billion to $1.7 billion. Combined with the stranded assets of old BF-BOF plants, the cost makes this conversion economically unfeasible in the short term required to meet the Paris Climate Agreement. The second option is to increase scrap recycling. Steel is already one of the most recycled materials, with a recycling rate of 84% in 2017. In 2019, 32% of the total input was scrap. Compared with virgin iron ore in the BF-BOF, scrap recycling reduces CO2 emissions by 90% and saves 70% of the energy. Additionally, each ton of recycled scrap steel displaces 1400 kg of iron ore, 740 kg of coal, and 120 kg of limestone. In the EAF, the proportion of scrap steel in the input can reach 100%, while the maximum input in the current BF-BOF is 20-25%. It is expected that by 2050, the share of scrap in the input may increase to 46%. Although this is not sufficient to decarbonize the industry alone, it may significantly reduce CO2 emissions.

[0006] Another decarbonization option is to use hydrogen direct reduced iron (HDRI), followed by an EAF. If renewable electricity is used to power electrolyzers to produce green hydrogen, this can significantly reduce emissions. However, this requires building new DRI plants to replace BF-BOF, and its technology readiness level (TRL) is 5-7, meaning the technology has been demonstrated but not yet in industrial operation. It is estimated that if there is sufficient low-cost renewable electricity, HDRI requires a carbon price of $67 per tonne of CO2 equivalent to produce steel at the same price as a traditional blast furnace. Additionally, at lower temperatures, reducing iron with hydrogen is less efficient than with carbon monoxide, and it is easier to reduce Fe2O3 to Fe3O4 under CO. Conversely, at higher temperatures, it is easier to reduce Fe3O4 to Fe under hydrogen. Modeling shows that at current grid emission levels, hydrogen-based DRI can reduce emissions in the EU steel industry by 35%, while requiring 3.72 MWh per tonne of liquid steel produced. For reference, BF-BOF uses 3.48 MWh / t. The cost of hydrogen production remains prohibitively high.

[0007] A related technology is natural gas DRI with carbon capture, use, and storage (CCUS), which also has a TRL of 5-7. Although several CCUS methods have been demonstrated and some industrial CCUS facilities are operating, the cost of capturing each tonne of CO2 is expected to be $100 by 2030, while transportation and storage costs are expected to be $160 per tonne, with a modest decline in cost by 2050. Given the extremely high emissions from steel facilities, large CCUS plants will be required, but emission reductions are estimated to be between 20-80%. Finally, another proposed solution is iron ore electrolysis, which has a TRL of 6. This technology has been used on a large scale in aluminum production, so the technology has been demonstrated at an industrial scale, although the temperature is much lower than in iron and steelmaking processes. To efficiently reduce iron ore, high temperatures and optimization of electrodes and electrolytes are required.

[0008] In summary, steel production accounts for 9% of global CO2 emissions and must be rapidly decarbonized to limit warming to within 1.5°C. 70% of existing steel facilities rely on the extremely energy-intensive and emission-intensive high-temperature BF-BOF route. Most current decarbonization methods in the industry rely on phasing out these BF-BOF plants and implementing low-carbon methods such as EAF and DRI plants. This will be very expensive.

[0009] Technologies applicable to steel production may also be applicable to other production processes that use carbon monoxide as a reducing agent in reduction furnaces.

[0010] Therefore, a way to decarbonize metal production that at least ameliorates the above problems is needed. SUMMARY OF THE INVENTION

[0011] According to a first aspect of the present invention, there is provided a system for metal production, the system comprising:

[0012] A reduction furnace configured to receive metal ore and process gas and output hot metal and reduction furnace top gas;

[0013] A first thermochemical reactor configured to receive at least a portion of the reduction furnace top gas in a first mode and produce carbon monoxide from carbon dioxide in this portion of the reduction furnace top gas by oxidizing a thermochemical compound, and return at least a portion of the produced carbon monoxide to the reduction furnace.

[0014] The reduction furnace may include a blast furnace or a DRI furnace.

[0015] The metal may be iron. The system may be used for iron and / or steel production.

[0016] The first thermochemical reactor may include a series of sub-reactors. The sub-reactors may be operated in series such that CO2 from the first sub-reactor may be further reduced in subsequent sub-reactors (etc.).

[0017] The system may further include a gas separator configured to: receive the reduction furnace top gas, separate carbon dioxide from other components of the reduction furnace top gas, and supply the carbon dioxide portion of the reduction furnace top gas to the first thermochemical reactor.

[0018] The gas separator may be further configured to separate carbon monoxide from other components of the reduction furnace top gas for return to the reduction furnace.

[0019] The thermochemical compound may comprise, consist essentially of, or consist of a metal oxide, a perovskite material, or a double perovskite material. The thermochemical compound may comprise barium calcium iron niobate double perovskite or barium magnesium iron niobate perovskite. The thermochemical compound may comprise Ba2Ca 0.66 Nb 0.34 FeO6 or BaMg 0.33 Nb 0.34 Fe 0.33 O3.

[0020] The first thermochemical reactor may be configured to produce oxygen by reducing the thermochemical compound in a second mode. Reducing the thermochemical compound may include using green hydrogen from renewable resources.

[0021] The system may further include a controller configured to switch or cycle between the first mode and the second mode, in the first mode, the first thermochemical reactor receives carbon dioxide from the reduction furnace top gas and produces carbon monoxide by oxidizing the thermochemical compound, and in the second mode, the first thermochemical reactor produces oxygen by reducing the thermochemical compound.

[0022] The system may further include a second thermochemical reactor, wherein, in a first mode, the second thermochemical reactor produces oxygen by reducing a thermochemical compound, and in a second mode, the second thermochemical reactor receives carbon dioxide from the top gas of the reduction furnace and produces carbon monoxide by oxidizing the thermochemical compound. The system may be configured to operate the first and second thermochemical reactors in a cycle (cycling between the first mode and the second mode) for continuous supply of carbon monoxide and oxygen.

[0023] The system may further include a steel furnace (which may include a basic oxygen furnace or an electric arc furnace), which is configured to receive hot metal from the reduction furnace and receive oxygen from the first thermochemical reactor and / or the second thermochemical reactor, and output molten steel and steel furnace gas.

[0024] The gas separator may be configured to separate nitrogen from the top gas of the reduction furnace and supply the nitrogen to the first thermochemical reactor and / or the second thermochemical reactor for reducing the thermochemical compound.

[0025] The gas separator may be configured to separate carbon monoxide from the basic oxygen furnace gas for returning to the reduction furnace.

[0026] The system may include a first thermochemical reactor gas separator, which is configured to receive the output gas from the first thermochemical reactor in the first mode and separate carbon monoxide from the output gas. The system may include a second thermochemical reactor gas separator, which is configured to separate oxygen from the output gas from the first thermochemical reactor in the second mode. The first thermochemical reactor gas separator may be configured to receive the output gas from the second thermochemical reactor in the second mode and separate carbon monoxide from the output gas. The second thermochemical reactor gas separator may be configured to receive the output gas from the second thermochemical reactor in the first mode.

[0027] The system may include a regenerative heat exchanger, which is configured to extract heat from the top gas of the reduction furnace and / or from the steel furnace gas. The regenerative heat exchanger may be configured to supply heat to the process gas and / or the first thermochemical reactor and / or the second thermochemical reactor.

[0028] The system may include a heater (e.g., powered by renewable energy or other zero-carbon, low-carbon energy), which is configured to supply heat to the first thermochemical reactor and / or the second thermochemical reactor.

[0029] The system may include a heat exchanger, which is used to remove heat from the reduction process gas or from the oxygen produced with the reduction process gas, and supply the heat to at least one of the following: the first and second thermochemical reactors, the CO storage tank, or the process gas.

[0030] The first thermochemical reactor and the second thermochemical reactor may be configured together to provide at least 50% (or at least 30%, or at least 70% or at least 80%) of the carbon monoxide for reducing metal ore to hot metal in a reduction furnace.

[0031] The system may include a reduction furnace electric heater configured to heat the process gas and / or metal ore introduced into the reduction furnace using electricity. The electricity may be sourced from a carbon-neutral source.

[0032] According to a second aspect, there is provided a method of producing metal, comprising:

[0033] Reducing a metal ore in a reduction furnace to produce hot metal by reacting carbon monoxide with a metal oxide, thereby producing carbon dioxide;

[0034] Providing at least some of the carbon dioxide produced from the reduction furnace to a first thermochemical reactor and producing carbon monoxide from carbon monoxide by oxidizing a thermochemical compound;

[0035] Returning at least a portion of the produced carbon monoxide to the reduction furnace.

[0036] The reduction furnace may be a blast furnace or a DRI furnace.

[0037] The metal ore may include iron ore or consist essentially of iron ore. The metal oxide may include iron oxide or consist essentially of iron oxide. The hot metal may be iron.

[0038] The carbon dioxide from the reduction furnace provided to the first thermochemical reactor may be obtained by separating carbon dioxide from the reduction furnace top gas produced from the reduction furnace.

[0039] The method may further include separating carbon monoxide from the reduction furnace top gas and returning the carbon monoxide to the reduction furnace.

[0040] The thermochemical compound may comprise a perovskite or a double perovskite, or consist essentially of them. The thermochemical compound may comprise barium niobate ferrite double perovskite, or consist essentially of it. The thermochemical compound may comprise Ba2Ca 0.66 Nb 0.34 FeO6.

[0041] The method may include producing oxygen by reducing a thermochemical compound in a first thermochemical reactor.

[0042] The method may further include switching or cycling between a first mode and a second mode, in the first mode, the first thermochemical reactor receives carbon dioxide from the reduction furnace top gas and produces carbon monoxide by oxidizing a thermochemical compound, and in the second mode, the first thermochemical reactor produces oxygen by reducing a thermochemical compound.

[0043] In a first mode, the second thermochemical reactor can produce oxygen by reducing a thermochemical compound, and in a second mode, the second thermochemical reactor can receive carbon dioxide from the top gas of the reduction furnace and produce carbon monoxide by oxidizing the thermochemical compound.

[0044] The method can include receiving hot metal and oxygen from a thermochemical reactor at a steel furnace (e.g., a basic oxygen furnace or an electric arc furnace) and outputting molten steel and steel furnace gas from the steel furnace.

[0045] The method can include separating nitrogen from the top gas of the reduction furnace and providing the nitrogen to the thermochemical reactor for reducing the thermochemical compound.

[0046] The method can include separating carbon monoxide from the output gas from the first thermochemical reactor in the first mode and separating oxygen from the output gas in the second mode.

[0047] The method can include using the first thermochemical reactor and the second thermochemical reactor to provide at least 50% (or at least 30%, or at least 70% or at least 80%) of the carbon monoxide for reducing metal ore to hot metal in a reduction furnace.

[0048] The method can further include using electricity to heat the process gas and / or the metal ore introduced into the reduction furnace.

[0049] The method can include reducing at least 50% of the CO2 emissions associated with the reduction furnace by replacing the coke used as the input to the reduction furnace with gaseous carbon monoxide obtained from the output gas (the output gas can include carbon dioxide produced by the reduction furnace and flue gas from a steel furnace such as a BOF or EAF). In some embodiments, at least 20% or at least 75% of the CO2 emissions can be reduced.

[0050] According to a third aspect, a method for decarbonizing a system for producing metal is provided, including adding a thermochemical reactor to a system including a reduction furnace, the thermochemical reactor being configured to: produce carbon monoxide by reacting a thermochemical compound with carbon dioxide obtained from the top gas of the reduction furnace and provide at least a portion of the produced carbon monoxide to the reduction furnace for reducing iron oxide.

[0051] The reduction furnace may be a blast furnace or a DRI furnace.

[0052] The method can include adding a gas separator. The method can include adding any element mentioned with reference to the first aspect, including its optional features.

[0053] The features of each aspect can be combined with the features of any other aspect. The optional features of any aspect can be combined with the features of any other aspect. The actions that the system is configured to perform can include the steps in the method according to the embodiments. Detailed implementation manners

[0054] The present invention will be described by way of example only with reference to the accompanying drawings, wherein:

[0055] Figure 1 is a schematic diagram of a TC-BF system according to an embodiment, the TC-BF system including a blast furnace and a thermochemical reactor for producing carbon monoxide using carbon dioxide produced by the blast furnace;

[0056] Figure 1a is a schematic diagram of a DRI system according to an embodiment, the DRI system including a DRI furnace and a thermochemical reactor for producing carbon monoxide using carbon dioxide produced by the DRI furnace;

[0057] Figure 2 is a schematic diagram of a TC-BF-BOF system according to an embodiment, the TC-BF-BOF system including a blast furnace, a basic oxygen furnace, and first and second thermochemical reactors, Figure 2 showing the mass flow;

[0058] Figure 3 is similar to the system of Figure 2 a schematic diagram of a TC-BF-BOF system, Figure 3 showing the heat flow;

[0059] Figure 4 shows a graph of carbon dioxide conversion versus oxidation time in different temperature ranges for an exemplary thermochemical compound;

[0060] Figure 5 shows a Hancock-Sharpe diagram for an exemplary thermochemical compound; and

[0061] Figure 6 a) plots the rate constant at each temperature, and Figure 6 b) is an Arrhenius diagram of the oxidation of an exemplary thermochemical compound.

[0062] Modern blast furnaces can produce more than 10,000 tons of hot metal per day, and the size of the largest furnace is 6000m 3。The top of a typical blast furnace is about 200 °C, while the bottom can reach temperatures exceeding 1600 °C. In existing blast furnaces used for iron production, iron ore and coke are added to the furnace in layers. Air or oxygen-enriched air (also known as blast) is injected at the bottom of the furnace, which has been preheated to 1100 - 1350 °C by a regenerative heat exchanger called a stoves. This hot blast provides most of the heat required in the furnace. The hot blast reacts with the layers of coke to produce large amounts of carbon monoxide (CO) that rise through the furnace, reduce the iron ore, and transfer heat to the materials higher up in the furnace. When the iron ore is reduced to metallic iron, the liquid metal accumulates at the lower part of the furnace to be drawn off or removed from the furnace. To reduce coke consumption, pulverized coal particles and / or combustible gases (such as natural gas, coke oven gas) can be injected through the tuyeres at the bottom of the furnace.

[0063] Iron ore is usually impure, and thus, limestone and other additives are used to separate these impurities from the liquid metal. For example, limestone removes sulfur from FeS to obtain metallic iron and CaS. CaS has a lower density than metallic iron and rises in the furnace to form a layer of slag, which also contains other impurities such as SiO2, Al2O3, MgO, and CaO. The slag is drawn off from the furnace at about 1650 °C, and up to 65% of this heat can be recovered. Typically, about 0.275 tons of slag are produced per ton of steel produced. The process gas, which is a mixture of carbon monoxide and carbon dioxide in the furnace, rises to the top of the furnace and is called top gas. This top gas leaves the furnace at about 200 - 300 °C and has a generally low calorific value of 3 - 4 MJ per Nm 3 (standard cubic meter), most of which is recovered by the regenerative heat exchanger. This heat, together with the additional heat obtained by the combustion of this top gas, is used to heat the blast to over 1100 °C, as described above.

[0064] Modern steel production via BF-BOF uses (approx.) 1370 kg of iron ore, 780 kg of metallurgical coal, 270 kg of limestone, and 125 kg of recycled steel to produce 1000 kg of crude steel. Blowing requires approximately 1500 kg of air, which is fed into the bottom of the furnace via the tuyeres (nozzles). The metallurgical coal must be processed before it can be used in the BF, heating it for approximately 12 hours to reach approximately 1250 °C using heat obtained from the top gas and coke oven gas (COG). COG is the gas released during the pretreatment of coal during quenching and purification. Typically, COG contains 60% H2, 24% CH4, 6% CO, 6% N2, and 4% CO2. COG is also used in the BF because hydrogen and carbon monoxide are excellent reducing agents for iron ore. After processing, the coke has several main uses in a typical BF. First, the coke is the main energy source for the BF, with 95% of the total energy originating from the combustion of coke in the BF (and the coke accounts for 20 - 40% of the total cost). Subsequently, the coke reacts with oxygen to produce carbon monoxide (an effective reducing agent for iron ore), and then reacts with the carbon dioxide produced during reduction to form more carbon monoxide according to the Boudouard reaction. The coke also adds carbon to the metallic iron. Finally, the coke serves as a carrier for the multi-layer iron ore and helps the gas move through the furnace. Other reducing agents can also be injected into the blast furnace to reduce the amount of coke required, such as pulverized coal (cheaper than metallurgical coal), hydrocarbons, waste plastics, and biomass. Additionally, if natural gas has a methane content higher than 80%, natural gas can replace some of the coke because natural gas decomposes into carbon monoxide and hydrogen. The recognized minimum theoretical fuel value is 465 kg per ton of hot metal produced, with modern BFs approaching this value at 500 kg per ton.

[0065] Four main reactions occur in the BF to reduce iron ore to iron. Iron ore mainly consists of Fe2O3. Two reactions occur below 570 °C.

[0066] 3Fe2O3 + CO → 2Fe3O4 + CO2 (1)

[0067] ΔH 843K = -30.050 kJ / mol

[0068] Fe3O4 + 4CO → Fe + 4CO2 (2)

[0069] ΔH 843K = -44.478 kJ / mol

[0070] Once the remaining iron ore starts to descend in the furnace and the temperature rises above 570 °C, the following two reactions mainly occur:

[0071] Fe3O4 + CO → 3FeO + CO2 (3)

[0072] ΔH 1073K = +9.707 kJ / mol

[0073] FeO + CO → Fe + CO2 (4)

[0074] ΔH 1273K = -15.653 kJ / mol, ΔH 1473K = -16.484 kJ / mol

[0075] Reducing FeO (Equation 4) requires a CO concentration of at least 70%.

[0076] The so-called pig iron produced in the blast furnace is withdrawn from the BF and poured into the BOF. By weight, up to 25 - 30% scrap metal can also be added to the BOF. No heat is added to the BOF, but oxygen is blown through the molten metal, reacting with the carbon in the iron (usually FeC) to form carbon monoxide and carbon dioxide while releasing heat. This reaction raises the temperature to approximately 1650 °C. The oxygen must be at least 99.9% pure to enable the production of a wide range of steel products. A total of 50 - 60 Nm 3 / tls (standard cubic meters per ton of molten steel) is blown in from above or below the hot metal through a lance for 15 to 20 minutes, also known as blowing. Steel is withdrawn from the furnace approximately every 40 minutes. Basic oxygen furnace gas (BOF gas) leaves the furnace at approximately 1600 °C, generating approximately 100 Nm 3 / tls, containing carbon dioxide, carbon monoxide, and nitrogen from the environment. During this process, the temperature and composition of the BOF gas usually change over time. This BOF gas has a calorific value of approximately 8.8 MJ / Nm 3 and more than 90% of the BOF gas can be recovered as heat and chemical energy.

[0077] Figure 1 FIG. shows an overview of a TC - BF exemplary system 100 according to an embodiment, the system including a reduction furnace 110 and a thermochemical reactor 130. The blast furnace 110 operates in a manner similar to the above example, except that at least some of the carbon monoxide used to reduce the iron ore is obtained not by burning coke but by thermochemical reduction of carbon dioxide from the blast furnace top gas 111. The blast furnace 110 receives iron ore 101 and process gas 102 (such as air or oxygen - enriched air) and a carbon source (such as pulverized coal or natural gas, not shown), and produces hot metal 115 and blast furnace top gas 111. In this example, the reduction furnace 110 is the blast furnace 110, and the process gas 102 can refer to the blast gas 102.

[0078] At least a portion 163 of the carbon dioxide-rich blast furnace top gas 111 (e.g., containing at least 20%, 50%, 75%, 85% or 95% carbon dioxide) is provided as an input to the thermochemical reactor 130. A gas separator (not shown) can be used to separate carbon dioxide from the top gas 111 to produce the carbon dioxide 163 provided to the thermochemical reactor 130. Any suitable technique can be used for gas separation, such as but not limited to: adsorption, membranes or chemical receptors.

[0079] The thermochemical reactor 130 reacts the carbon dioxide 163 with a thermochemical compound that reduces / splits the carbon dioxide to produce carbon monoxide 151, while the thermochemical compound is in turn oxidized. The carbon monoxide 151 is provided as an input to the blast furnace 110 for reducing iron oxides, e.g., by mixing with the process gas 102 (or being introduced directly, without mixing with the process gas 102). The carbon source can include coke, charcoal, biomass and / or waste plastics, and can be introduced at least in part together with the process gas 102 (due to the lower mechanical strength of the materials in the BF and the higher proportion of volatiles in this mode compared to traditional coke-based systems).

[0080] In embodiments, at least part of the carbon monoxide required to reduce iron ore in the blast furnace is provided by converting carbon dioxide from the blast furnace top gas 111 to carbon monoxide 151 by means of a thermochemical reaction. In some embodiments, at least: 20%, 30%, 50%, 75% or 85% of the carbon monoxide used to reduce iron oxides in the blast furnace can be provided by the thermochemical conversion of carbon dioxide to carbon monoxide (which can be on-site conversion). This can significantly reduce the amount of coke required as an input to the blast furnace 110 and greatly reduce the carbon footprint of the blast furnace 110. The amount of coke required by the blast furnace 110 can be reduced by at least 20%, 30%, 50%, 75%, 85%, 90% or even 100% (compared to a system where all the carbon monoxide in the blast furnace is obtained from coke). A high percentage reduction in coke may require alternative materials to act as structural supports, such as inert (chemically compatible) ceramic materials, so as to ensure permeability and the stability of BF operation, and such materials can be reused in the process (e.g., the structural support may not be consumed by chemical reactions in the BF).

[0081] The two main types of materials capable of thermochemical cycling to split carbon dioxide into carbon monoxide are simple metal oxides or mixed metal oxides, such as perovskites. Cerium dioxide (ceria) is an example of a metal oxide that can split carbon dioxide in good yield; however, it requires high temperatures, such as a reduction temperature of 1400 °C and an oxidation temperature of 900 °C. Ceria is a non-stoichiometric oxygen carrier, meaning that less than one mole of oxygen is released per mole of ceria. Other metal oxides include volatile metal oxides and iron oxides. Volatile metal oxides are stoichiometric oxygen carriers, and the melting temperature of their pure metal is lower than the reduction temperature of the metal oxide.

[0082] Perovskites are non-stoichiometric mixed metal oxides with the ideal chemical formula ABO3, where A and B are metal elements. An example of a perovskite for thermochemical cycling is the La1-xSrxMnO3 family, which can be reduced at approximately 1400 °C and oxidized at about 900 °C, with a fuel yield up to ten times higher than that of ceria. Ba2Ca 0.66 Nb 1.34 -xFe x O6 (x = 0, 0.34, 0.66, and 1) are double perovskites and can be reduced and decompose CO2 at approximately 800 °C and are thus particularly suitable for the examples.

[0083] Examples of suitable perovskites for splitting carbon dioxide include those listed in Table 1 below (Table 2 lists further examples).

[0084] Table 1: Example perovskites for splitting carbon dioxide

[0085]

[0086]

[0087] In an example, the thermochemical reaction is reversible, reducing the thermochemical compound to produce oxygen. This oxygen can be vented as a waste product or captured and sold.

[0088] In the case of BF - BOF, the oxygen produced by reducing the thermochemical compound can be used as an input to the BOF to provide at least a portion of the oxygen required for the input. In some examples, all of the oxygen for the BOF can be provided by reducing the thermochemical compound, and excess oxygen is also possible.

[0089] Many materials are capable of thermochemical cycling. However, Ba2Ca 0.66 Nb 0.34FeO6(BCNF1) will be used in the exemplary embodiments described herein because it has a high yield, a low reaction temperature, 100% selectivity for CO, and a low activation energy for the oxidation reaction. BCNF1 is a double perovskite material. When BCNF1 is reduced under nitrogen at 700 °C, oxygen is lost from the crystal structure, forming oxygen vacancies and releasing oxygen.

[0090]

[0091] where δ is equal to the degree of non-stoichiometry. The oxidation of BCNF1 is carried out under carbon dioxide at 800 °C such that CO2 is split into CO, oxygen is re-included in the lattice by filling the oxygen vacancies, and the original perovskite is reorganized.

[0092]

[0093] This allows the cycle of reduction and oxidation to be repeated, splitting the CO2. It has been found that BCNF1 converts 10.1% of the CO2 into CO per cycle (average over five cycles). Producing 150 m 3 / hr of CO would require 5700 kWh of electricity and an 85% efficient electric heater. At an electricity price of £0.11 / kWh, such a plant could produce carbon monoxide at a cost of £0.19 per kilogram. At an electricity price of £0.05 (average US industrial electricity price), carbon monoxide would cost £0.11 per kilogram.

[0094] Figure 1a An overview of a TC-DRI example system according to one embodiment is shown, the system including a direct iron reduction furnace 210 and a thermochemical reactor 230. The direct iron reduction furnace 210 is used to reduce iron in the solid phase by contacting the solid phase with a process gas (such as hydrogen or carbon monoxide). The reactions are listed below:

[0095] 3Fe2O3 + CO / H2 → 2Fe3O4 + CO2 / H2O

[0096] Fe3O4 + CO / H2 → 3FeO + CO2 / H2O

[0097] FeO + CO / H2 → Fe + CO2 / H2O

[0098] At least some of the carbon monoxide used to reduce iron ore in the DRI furnace 210 is obtained by the thermochemical reduction of carbon dioxide in the top gas 211 output from the DRI furnace 210. The DRI furnace 210 receives iron ore 201 and process gas 202 (such as carbon monoxide and / or hydrogen) and a carbon source (such as pulverized coal or natural gas, not shown), and produces hot metal 215 and DRI top gas 211. At least a portion 263 of the DRI top gas 111 rich in carbon dioxide (e.g., containing at least 20%, 50%, 75%, 85% or 95% carbon dioxide) is provided as an input to the thermochemical reactor 230. A gas separator (not shown) can be used to separate carbon dioxide from the top gas 211 to produce carbon dioxide 263 provided to the thermochemical reactor 230. Any suitable technique can be used for gas separation, such as but not limited to: adsorption, membranes or chemical receptors.

[0099] As referenced Figure 1a As described, the thermochemical reactor 230 reacts carbon dioxide 263 with a thermochemical compound that reduces / splits the carbon dioxide to produce carbon monoxide 251, while the thermochemical compound is in turn oxidized. The carbon monoxide 251 is provided as an input to the DRI furnace 210 for reducing iron oxides, such as being mixed with the process gas 202 (or being introduced directly without being mixed with the reducing gas 202).

[0100] In an embodiment, at least part of the carbon monoxide used to reduce iron ore in the DRI furnace is provided by converting carbon dioxide from the DRI furnace top gas 211 to carbon monoxide 251 by means of a thermochemical reaction. In some embodiments, at least: 20%, 30%, 50%, 75% or 85% of the carbon monoxide used to reduce iron oxides in the DRI furnace can be provided by the thermochemical conversion of carbon dioxide to carbon monoxide (which can be in-situ conversion). This can significantly reduce the amount of carbon required as an input to the DRI furnace 210 and greatly reduce the carbon footprint of the DRI furnace 210.

[0101] Reference Figure 2 , shows a schematic diagram of a system 100 according to one embodiment. The system includes a blast furnace 110, a steel furnace 120, gas separators 140, 160, 180, a first thermochemical reactor 130, a second thermochemical reactor 170, a CO storage tank 150, an O2 storage tank 190 and a controller 200. The steel furnace 120 in this exemplary embodiment is a basic oxygen furnace / BOF 120, but in other embodiments, an EAF may be used as the steel furnace 120.

[0102] The mass flow and molar flow within the system 100 will be discussed with reference to the production of 1 ton of liquid steel (1000 kg). The mass flow and molar flow are illustrative of a specific example and should not be construed as limiting the scope of the present invention. Other systems are possible with different mass flows.

[0103] The blast furnace 110 receives iron ore 101, process gas 102, and carbon monoxide 151, and supplies hot metal 115 to the basic oxygen furnace 120. Useful slag formers can also be provided as an input to the blast furnace 110 together with the carbon source (as described above). The basic oxygen furnace 120 receives hot metal 115, scrap steel 122, and oxygen 191. The hot metal 115 and scrap steel 122 are converted into molten steel by removing carbon in a reaction with oxygen 191. To produce 1000 kg of molten steel 125, approximately 1600 kg of iron ore and approximately 1500 kg of process gas can be provided to the blast furnace 110. This amount of iron ore 101 is based on the assumption of 95% Fe2O3 and 5% impurities. The blast furnace 110 outputs approximately 900 kg of hot metal and approximately 1500 kg of blast furnace top gas 111.

[0104] The blast furnace top gas 111 contains carbon dioxide, carbon monoxide, nitrogen, and hydrogen. The basic oxygen furnace 120 produces basic oxygen furnace gas 121, which contains carbon monoxide and carbon dioxide. In this example, the hot metal is combined with approximately 125 kg of scrap steel in the BOF 120, but higher or lower scrap metal ratios can also be used. The BOF 120 receives approximately 50 Nm 3 of oxygen and outputs approximately 100 Nm 3 of BOF gas 121 (containing CO and CO2).

[0105] The gas separator 160 receives both the top gas 111 and the BOF gas 121 and separates these gases into three components: carbon monoxide 165, 166, carbon dioxide 163, 164, and nitrogen 161 / hydrogen 162. In this example, it is assumed that the top gas 111 has a composition of 5% CO, 45% CO2, 2% H2, and 48% N2. These values are different from those typically used for coke-based blast furnaces in the prior art, which produce higher proportions of CO and H2. Assuming the absence of coke (or a reduced amount) results in less CO in the top gas because the amount of added CO is substantially stoichiometric. In other embodiments, these ratios may be different. Although this example is based on supplying approximately stoichiometric CO to the blast furnace, in some examples, there may be an excess of CO in the blast furnace. In this example, the BOF gas 121 has a composition of 90% CO and 10% CO2.

[0106] The gas separator 160 (optionally, gas separators 140, 180) can operate using any suitable technique, such as but not limited to: adsorption (including pressure swing adsorption), membranes, or chemical receptors. The gas separator 160 supplies carbon monoxide components 165, 166 to the carbon monoxide storage tank 150, supplies carbon dioxide components 163, 164 to the first thermochemical reactor 130, and supplies nitrogen / hydrogen components 161, 162 to the second thermochemical reactor 170.

[0107] The carbon dioxide 163, 164 from the gas separator 160 contains two components: a first component 163 obtained from the top gas 111 and a second component 164 obtained from the BOF gas 121. The mass flow of the top gas 111 is much higher than the mass flow of the BOF gas 121, which means that most of the carbon dioxide produced by the gas separator 160 will be sourced from the top gas 111. In this example, approximately 21,200 moles of CO2 are from the top gas 111, and only approximately 410 moles of CO2 are from the BOF gas 121. Thus, it can be seen that collecting carbon dioxide from the BOF gas is advantageous but not necessary for all embodiments. Outputting CO2 from the BOF may be periodic.

[0108] The carbon monoxide 165, 166 from the gas separator 160 similarly contains two components: a first component 165 obtained from the top gas 111 and a second component 166 obtained from the BOF gas 121. The mass flow of the top gas 111 has a lower CO ratio than the BOF gas 121, which means that the contribution of CO from the BOF gas is more significant than in the case of CO2. However, most (in this example, approximately 75%, but generally higher than 50%) of the CO 151 supplied to the blast furnace 110 can be obtained by splitting CO2 in the thermochemical reactor 130 to form CO. In this example, 2,600 moles of CO are obtained from the top gas 111 by the gas separator 160, and 3,570 moles of CO are obtained from the BOF gas 121 by the gas separator 160 (adding it to the approximately 15,070 moles of CO obtained from the thermochemical reactor 130).

[0109] In Figure 2In the example, system 100 operates in a first mode, in which the first thermochemical reactor 130 operates in an oxidation mode. In the oxidation mode, the reactor 130 receives CO2 163, 164 from the gas separator 160 and produces CO by oxidizing a thermochemical compound. As described above, the conversion of CO2 to CO is not 100% each time through the reactor 130 (about 10% can be converted each time). The reactor 130 produces an oxidation product gas (OPG) 131 in which at least some of the CO2 has been converted to CO. The OPG 131 is provided to the thermochemical reactor gas separator 140, which separates CO2 from the CO. The CO2 142 is recycled to the reactor 130, and the CO 141 is stored in the CO storage tank 150.

[0110] In this example, 21,610 moles of CO2 are converted to 15,070 moles of CO. In some embodiments, approximately 80% of the moles of CO2 163, 164 input to the reactor 130 are converted and stored as CO for use in the blast furnace 110. Combining the flow of CO 165, 166 from the gas separator, the CO storage tank 150 receives 21,400 moles of CO, which are provided to the blast furnace 110. Preferably, the CO 151 is injected into the blast furnace 110 via the tuyeres together with the process gas 102 (but in some embodiments, other CO injection points can also be used, optionally in combination with the injection of CO 151 and the process gas 102).

[0111] If iron ore is reduced to metallic iron via reactions (1) and (2), three moles of CO are required for each mole of Fe2O3. If the reduction is carried out via (1), (3), and (4), two moles of CO are required. Therefore, an approximation can be made when calculating the required stoichiometric amount, where 2.5 moles of CO are required for each mole of Fe2O3. This is equal to 23,800 moles of CO / tls.

[0112] In some embodiments, all of the CO necessary for reducing iron ore in the blast furnace 110 can be obtained from the top gas 111, the BOF gas 121, and the thermochemical reactor 141. In Figure 2In an example embodiment, some of the CO necessary for reducing iron ore in a blast furnace is provided as a gas input, and coke (or charcoal, biomass, waste plastics, etc.) is used (not shown) to provide the remaining CO (and to provide structure and to act as a solid carbon source). In embodiments where a large percentage of the coke is replaced by CO, a structural material can be provided to BF 110 to ensure permeability and operational stability. Such a structural material can be inert (e.g., chemically compatible ceramic balls or the like) and recycled in the process. In some embodiments, a less reactive engineered carbon material (as opposed to porous coke) can be provided, whose main function is to provide structure. If the CO concentration is high enough, it is possible to make carbon oxidation thermodynamically less favorable.

[0113] In a first system mode, the second thermochemical reactor 170 operates in a reduction mode, in which the reactor 170 receives nitrogen 161 and hydrogen 162 from the gas separator 160 and produces O2 by reducing a thermochemical compound. Nitrogen 161 is provided as an inert carrier / purge gas, thus providing the low oxygen concentration necessary for thermally reducing BCNF1. Hydrogen can increase the degree of reduction of the thermochemical compound and increase the oxygen yield. The reduction product gas (RPG) 171 leaving the reactor 170 is not pure O2: it will also contain N2 and H2O (water produced by oxidizing hydrogen). RPG 171 is provided to the thermochemical reactor gas separator 180, which separates O2 from nitrogen and condenses out water. Nitrogen 182 is recycled to the reactor 170, and O2 181 is stored in the O2 storage tank 190.

[0114] In this example, more than 50 Nm 3 of oxygen 181 is produced from the gas separator 180 to the oxygen storage tank 190. Thus, all of the oxygen 191 for the BOF 120 can be provided from the oxygen storage tank 190, and the remaining oxygen 192 is available for sale. Oxygen can also be used for oxy-fuel combustion in the BF hot stoves.

[0115] In Figure 2 the example, 2580 kg of BCNF1 is provided in each of the reactors 130, 170. One kilogram of BCNF1 produces approximately 5.8 moles of CO in 24 hours. In embodiments where all of the CO used for reducing iron ore comes from a gas input, the loading of the thermochemical compound (e.g., BCNF1) in the reactors 130, 170 can be adjusted accordingly.

[0116] The reactions in the first thermochemical reactor 130 and the second thermochemical reactor 170 cannot continue indefinitely. For example, for the BCNF1 material, after about 24 hours, the production rates of oxygen and carbon monoxide decrease. Regardless of the material used, at some point, enough thermochemical compounds in the reactors 130, 170 will have reacted to slow down the production rate. This can be sensed empirically based on the partial pressure of the gas (such as CO or O2) detected in the OPG 131 and / or RPG 171, for example, based on a threshold production rate (or based on a predetermined duration, such as 24 hours, or any other predetermined time period). When the appropriate time is reached, the controller 200 can reconfigure the system to operate in a second mode, where the first reactor 130 is in the reduction mode and the second reactor 170 is in the oxidation mode.

[0117] Reconfiguring the system can include closing and opening the respective control valves such that: i) the first reactor 130 receives nitrogen 161 and hydrogen 162 from the gas separator 160, and the first reactor 130 provides the reduction product gas 171 to the gas separator 180 and receives the recycled nitrogen 182 from the gas separator 180; and ii) the second reactor 170 receives CO2 163, 164 from the gas separator 160 and recycles the CO2 142 from the gas separator 140, and the second reactor provides the oxidation product gas 131 to the gas separator 140. In addition to operating the control valves, the temperature of the first thermochemical reactor 130 can be reduced from the oxidation temperature (800 °C for BCNF1) to the reduction temperature (700 °C for BCNF1), and the temperature of the second thermochemical reactor 170 can be increased from the reduction temperature (700 °C for BCNF1) to the oxidation temperature (800 °C for BCNF1).

[0118] Oxygen can be blown into the BOF 120 for 15 - 20 minutes, during which the molten steel 125 and slag (not shown) are withdrawn approximately every 40 minutes.

[0119] Compared with a typical BF - BOF, as Figure 2 shown, the system has the potential to reduce CO2 emissions by 94%, where there are only emissions from the solid carbon source input to the blast furnace 110, because all the carbon monoxide produced by the carbon dioxide is recovered from the blast furnace 110 and the BOF 120. To achieve this 94% emission reduction, it is assumed that the solid carbon source is charcoal, biomass, or plastic. If coke is used as the solid carbon source, then the CO2 emission reduction is approximately 90% (which is still a huge emission reduction). In embodiments using only gaseous CO, even higher emission reductions may be achieved.

[0120] As described above, embodiments are possible in which only some carbon monoxide is obtained by splitting the carbon dioxide captured from the blast furnace 110 and / or the BOF 120. Even if a relatively low amount of CO2 is captured / converted to CO, some benefits are achieved.

[0121] Figure 3 is schematically shown Figure 2 the energy flow of the system shown. Figure 3 including the features Figure 2 described, and further including a regenerative heat exchanger 105 and a retrofitted coke oven 175. The retrofitted coke oven 175 can be used if coke is produced on-site at the BF 110 site. If not, an alternative heat source may be appropriate.

[0122] Removing coke from the BF 110 reduces the energy available to heat the BF 110 to the required temperature. The reaction of coke with oxygen in the BF 110 is exothermic, releasing heat. A solid carbon source (e.g., 10% biomass-based charcoal added to the BF 110 as an alternative carbon source) will help achieve this, but additional heat (e.g., heat from an electric heater) may be required to reach the required temperature. The iron ore 101 can be preheated to help achieve this. Such an electric heater can be powered by renewable resources (solar, wind) and / or other low-carbon / zero-carbon (nuclear) sources.

[0123] The heat 107 obtained from the top gas 111 and the BOF gas 121 can be used to preheat the process gas 102. If 90% of the energy is recovered using the regenerative heat exchanger 105, the top gas 111 and the BOF gas 121 can provide 2.7 GJ / tls and 0.8 GJ / tls, respectively. This heat 107 will be transferred from these gases before the effluent gas 106 (containing both the top gas 111 and the BOF gas 121) from the regenerative heat exchanger 105 is fed into the gas separator 160.

[0124] In a conventional BF-BOF, the coke waste gas, the BF top gas, and the BOF gas are typically burned after the thermal energy has been extracted to generate the electricity required for the BF-BOF. In some embodiments (where coke may not be used), the coke waste gas may not be present. In some embodiments, all of the top gas and the BOF gas are recycled through the TC reactor, making it no longer possible to generate electricity from the coke waste gas. In some embodiments, it may be necessary to introduce at least some electricity, e.g., from renewable resources (solar, wind) and / or zero-carbon / low-carbon sources (nuclear).

[0125] This situation may not apply to every embodiment. In some embodiments, a smaller proportion of coke can be replaced with CO obtained by splitting CO2 from top gas and / or BOF gas. In some embodiments, only some of the top gas and / or BOF gas can be captured and recycled, leaving some available for combustion and power generation.

[0126] The carbon monoxide leaving the thermochemical reactor 130 is at the oxidation temperature for the thermochemical compound (800 °C for BNCF1). Depending on the thermochemical compound used, this temperature can be a significant portion (e.g., at least 50%) of the desired blast temperature of 1200 °C. The temperature in the CO storage tank 150 can be maintained at the oxidation temperature for the thermochemical compound. This can be achieved by heat transfer (not shown) from the oxygen 181 generated in the reduction reactor 170, since the oxygen 181 does not need to be heated before being introduced into the BOF 120. Since CO is always used by the BF 110, the CO storage can be small, such that it can be stored at a moderate temperature (e.g., about 500 - 800 °C, or at least 50% of the blast temperature). CO can also be stored pressurized at ambient temperature, where a thermal energy storage (not shown) next to it is used to heat the CO before adding it to the blast 102.

[0127] The BOF 120 does not require any additional heat or fuel, as heat is generated by the reaction between oxygen and iron carbide (FeC).

[0128] The molten steel 125 leaves the BOF 120 at a temperature above 1500 °C. Once the steel 125 is cast into its final shape, some heat can be recovered for use in the system 100.

[0129] In this embodiment, there will no longer be a need for a coke oven to produce coke, saving 1.1 GJ / tls of primary energy. Approximately 2.2 GJ / tls is required to power the thermochemical (TC) reactors 130, 170. This means that the electricity and electric heaters previously used to heat coal to 1250 °C in 12 hours can be retrofitted (if on-site) to maintain the temperature in the TC reactors 130, 170 and to heat the thermochemical compound from the reduction temperature (700 °C for BNCF1) to the oxidation temperature (800 °C for BCNF1) when switching reaction conditions. Therefore, an additional 1.1 GJ / tls of electricity may be required to power the electric heaters to operate the TC reactors.

[0130] If the electricity required to power the electric heaters and the gas separator is obtained from renewable resources or a nuclear power plant, this will not increase the emissions of the system 100. The cost of this electricity plus the cost of the electricity required to power the gas separator can be at least partially offset by the cost savings from replacing coke in the system.

[0131] In the above exemplary embodiment, a BF-BOF system is considered. The present invention can be similarly applied to a BF-EAF system, where the BOF is replaced by an EAF. The EAF will similarly generate flue gas, which can be separated and recycled. The CO2 present in the EAF flue gas can be split into CO by a thermochemical reaction, and any CO present in the EAF flue gas can be separated. At least a portion of any CO derived from the EAF flue gas can be provided to the BF.

[0132] Similarly, the features described with reference to the above BF-BOF system are relevant to a system including DRI. In one example of a DRI system, a DRI furnace receives iron ore and a process gas for reducing the iron ore. The process gas can contain at least 80% (by volume) of CO and H2. At least some of the process gas can be formed using a thermochemical reactor according to an embodiment. For example, a gas separator can be configured to receive top gas from the DRI furnace and provide CO2 to the thermochemical reactor as described herein. A pair of thermochemical reactors can be used, which cycle between producing carbon monoxide using carbon dioxide and producing oxygen by reducing thermochemical compounds. The thermochemical reactor can be used as a supplement or alternative to a reformer that is configured to receive at least some of the top gas and reform the CO from the CO2 in the top gas.

[0133] In one example, Ba2Ca 0.66 Nb 0.34 FeO6 (BCNF1) can be synthesized by mixing stoichiometric amounts of the precursors BaCO3, CaCO3, Nb2O5, and Fe2O3. The solid-state reaction can be carried out by grinding and mixing the powders to form a well-mixed powder. In one example, the resulting powder is air calcined at 1000 °C for 12 hours before being ground again into a fine powder. In the following examples, perovskite is used as a powder and as 10 mm pellets. To form the powder, the calcined fine powder is sintered at 1400 °C for 24 hours, while for the pellets, the calcined powder is compressed for 1 minute at an isostatic pressure of 120 MPa to form 10 mm pellets before being sintered in the same manner.

[0134] In a full-scale thermochemical reactor, the thermochemical compound can be configured as a highly porous structure and can include at least one of the following: thin plates, millimeter-scale rods, or spheres. The thermochemical compound can be packed to provide good heat transfer, fluid flow, and a high contact area, and / or be fluidized by the flow of gas.

[0135] To demonstrate the TC reactor containing BCNF1, 100 g of BCNF1 was synthesized and placed in a 25.4 mm (1 inch) reactor. During the 24-hour reduction at 700 °C, nitrogen passed through the reactor at 40 ml / min. For oxidation, the temperature was 800 °C and the gas flow was changed to 40 ml / min of CO2. This was repeated for five thermochemical cycles. For the first cycle, samples were collected every hour between 0 and 11 hours and analyzed by gas chromatography (GC). For the second to fifth cycles, gas samples were collected every hour between 12 and 23 hours and analyzed by GC. In all five cycles, the conversion rate of CO2 to CO was found to be 10.1% in each cycle.

[0136] Figure 4 (a) shows the carbon monoxide production rate of BCNF1 over time at different oxidation temperatures. It can be clearly seen that 800 °C is the optimal temperature because, in all time domains, the CO production is significantly higher than that at lower temperatures. The same is true for the carbon monoxide production as the temperature decreases. The maximum CO production, i.e., 498 μmol / g (800 °C, 24 hours), was used as the baseline to calculate the conversion rate (Xa) at each point, as Figure 5 (b) shows. A plot of ln(ln(1 - Xa)) versus ln(t), where t is the time in seconds, gives the Hancock-Sharpe plot ( Figure 5 ). The slope m of the plot ( Figure 5 inset) gives information about the type of redox reaction mechanism. For example, when m is less than one, the reaction is diffusion-controlled. Since m is greater than one for all oxidation temperatures, the reaction is phase-boundary-controlled. Therefore, a linear best-fit method applying different phase-boundary control mechanisms was used to gain more insight into the oxidation reaction.

[0137] The reaction at 800 °C was found to best fit the zero-order model (R 2 = 0.9905), indicating that the splitting of carbon dioxide to carbon monoxide at this temperature depends only on time and not on the concentration of carbon dioxide or the non-stoichiometry or degree of conversion of the perovskite. This is advantageous because it shows that at this temperature, the splitting reaction will occur at the maximum rate regardless of how far the reaction has progressed. The Avrami-Erofeyev 4 model (R 2At 700 °C (R² = 0.9912), the best fit for the reaction was found, where the conversion was low at the start and end of the time period but accelerated in the middle of the time period. The reaction occurred at the same rate in all directions, and the conversion did not depend on the degree of conversion. No best fit was found for the model of the reaction tested at 750 °C. Therefore, to plot the Arrhenius plot, the reaction at 750 °C was considered as a 50 / 50 mixture of a zero-order reaction and Avrami-Erofeyev 4.

[0138] Figure 6 (a) shows the rate constants at each temperature obtained from the above model. The Arrhenius plot for the oxidation reaction is shown in Figure 6 (b) and gives an activation energy (Ea) of 46.6 kJ / mol. This was compared with the oxidation reactions of similar materials in Table 2. It can be seen that the activation energy of BCNF1 is lower than that of all lanthanum manganites (LSMO) studied, except for La 0.625 Ca 0.375 Mn 0.5 Cr 0.5 O3, which indicates that the CO2 splitting reaction is more favorable with BCNF1 than with most LSMO. This is demonstrated by the temperature required for the oxidation reaction, which is 800 °C compared to at least 1050 °C for LSMO. When compared with barium magnesium niobate ferrite, an increase in iron content reduces the activation energy. BaMg 0.33 Nb 0.5 Fe 0.17 O3 has a higher Ea than BCNF1, while the Ea of BaMg 0.33 Nb 0.34 Fe 0.33 O3 is almost half of the Ea of BCNF1, indicating that the CO2 splitting reaction on this perovskite may be even more favorable than BCNF1.

[0139] Table 2: Activation energies for oxidation reactions under CO2

[0140]

[0141] According to one embodiment, a thermochemical reactor may include perovskite particles or a porous structure with an appropriate characteristic size, provided as a packed bed or a fluidized bed. The packed bed allows carbon dioxide to contact the perovskite with a large surface area, and due to enhanced solid and gas mixing and heat and mass transfer, the fluidized bed can provide an even higher conversion rate.

[0142] The TC-BF system and the TC-BF-BOF system proposed in this paper have the potential to contribute to the decarbonization of the UK and global steel industries and other extractive metallurgical industries. As an example, there are five steel production companies in the UK; Tata Steel and British Steel operate BF-BOF, and British Steel, Liberty Steel, and Outokumpu operate EAF. The UK produces 7.65 million tons of steel products annually, of which six million tons are produced through the BF-BOF route. Therefore, based on the emission intensity of 1.89 tCO 2eq / tls (tons of CO2 equivalent per ton of liquid steel) for the BF-BOF route and 0.44 tCO 2eq / tls for the EAF route, the BF-BOF in the UK accounts for approximately 94% of the total emissions of the UK steel industry. The EAF can be more easily decarbonized by using renewable electricity and / or 100% recycled steel. On the other hand, due to the inherently carbon-intensive nature of the process, it is much more difficult to decarbonize the BF-BOF. Their decarbonization is crucial for the UK to achieve its net-zero emissions target by 2050 and, more broadly, for avoiding the global problem of climate change.

[0143] Tata Steel and British Steel produce approximately three million tons of steel per year at their Port Talbot and Scunthorpe plants respectively. Due to similar production values, the same TC-BF-BOF system can be used in both cases, as described below. Taking BCNF1 as an example of a TC compound, 42,500 tons of BCNF1 are required per day to produce 124 million moles of carbon monoxide to replace 90% of the coke, with the remaining 10% replaced by a solid carbon source such as biomass-based charcoal. The TC compound can be divided into ten TC reactors, 15 m high and 9.5 m in diameter, with five reactors undergoing reduction and five undergoing oxidation at any given time. The raw materials required to produce the required amount of BCNF1 will cost £210 million, which may need to be replaced every five to ten years or so. In addition to CO, these reactors will also produce 1.3 million m 3 of oxygen per day, of which 420,000 m 3 will be required by the BOF. The excess oxygen production can generate £35,000 per day. Replacing 90% of the coke with CO will save £187 million per year.

[0144] For the entire reduction and oxidation cycle within 48 hours, the approximate energy requirement to power the TC cycle for the exemplary embodiment is 3.6 TJ per reactor. Due to the high endothermic reduction enthalpy of 620 kJ / kg, 85% of this energy is used for the reduction reaction, while the oxidation enthalpy is exothermic and thus releases energy (-45.1 kJ / kg). The implementation of the TC-BF-BOF system requires an additional 2.2 GJ / tls, while a typical BF-BOF requires 19.8 to 31.2 GJ / tls. The now redundant coke ovens can be retrofitted to produce 1.1 GJ / tls of heat. As mentioned above, there is a large amount of energy in the top gas and BOF gas. If 90% of this energy is recovered through a regenerative heat exchanger, this is equivalent to 3.5 GJ / tls, which is higher than the energy utilization of the TC system. Alternatively, if the TC reactor is fully powered by electricity, 607 kWh / tls is required, at a cost of approximately £42 / tls. This is far lower than that of hydrogen direct reduced iron (HDRI), which requires 3.72 MWh / tls. If this is obtained from the UK grid with an emission factor of 212 gCO 2eq / kWh, this will produce 129 kgCO 2eq / tls, equal to 6.9% of the current emissions per tonne of liquid steel. In terms of both finance and the environment, it is beneficial to use as much renewable electricity and / or nuclear energy as possible.

[0145] It is worth noting that the implementation of the exemplary TC-BF-BOF system will reduce emissions per site from 5.7 million tonnes of CO 2eq to 340,000 tonnes of CO 2eq . Even if the emissions of the operating EAF plants do not improve, the implementation of this system will reduce UK steel emissions by 88%, and the share of BF emissions will drop from 94% to 48%. Currently, the UK steel industry emits 12 million tonnes of CO 2eq , and the UK as a whole totals 369 million tonnes of CO 2eq , which means that steel accounts for nearly 3.3% of UK emissions. Implementing the TC-BF-BOF system at Tata Steel and British Steel plants will reduce the UK's steel-based emissions share to 0.38%. Therefore, a 2.9% reduction in UK emissions can be achieved through capital expenditure of approximately £720 million, with ongoing expenditure of approximately £400 million every 5 - 10 years to replace used BCNF1 materials once activities decrease. Additionally, after implementing the system, operating expenditure is significantly reduced, mainly due to the replacement of expensive metallurgical coal. The capital expenditure can be fully repaid from these savings within 22 months, with total savings of £1.28 billion after 5 years. The small increase in electricity consumption that may occur after implementing the system will be easily absorbed by these savings. The system will also reduce the price of steel production and enhance the competitiveness of steel produced in this way in the global market.

[0146] Although the above examples relate to Figure 2 the type of embodiments shown, it should be understood that embodiments in which coke portions that are reduced are replaced by CO obtained by TC splitting of CO2 generated by blast furnaces and / or BOFs also have advantages.

[0147] Compared with other methods of decarbonizing the steel industry, the embodiments may have several advantages. First, the embodiments can utilize existing BF-BOFs that account for 70% of steel production, thereby preventing the formation of stranded assets. Given that the global shift to a net-zero economy may create stranded assets in multiple industries that are incompatible with net-zero, any system that minimizes stranded assets while achieving significant emissions reduction should be prioritized. In addition, the continued operation of global BF-BOFs will ensure the retention of highly skilled jobs and create new job opportunities for the management and operation of TC reactors. Second, once a TC-BF or TC-BF-BOF retrofit is installed, emissions reduction is evident, rather than waiting for years to build new DRI-EAFs or decarbonize the power grid to achieve emissions reduction. The system can operate a nearly perfect closed-loop carbon circuit in which any CO2 generated in the BF or BOF is fed into the TC reactor to be split into more carbon monoxide for use in the BF. Additionally, the system provides additional revenue in the form of selling the extra oxygen generated in the TC reactor, although the revenue is small (equivalent to approximately £13 million per year for each of two BF-BOF plants in the UK).

[0148] Another important factor is that since TC-BOF or TC-BF-BOF is economically viable and each plant may save up to £600 million within five years, the cost of producing steel may be lower than that of traditional BF-BOF. In addition to cheaper steel production, the steel produced can also be regarded as carbon-neutral steel, which may command a premium as companies and governments seek to reduce in-operation and entrenched emissions across a wide range of industries. The emission intensity of steel produced by TC-BF-BOF may be up to four times lower than that of DRI-EAF plants. Most importantly, the implementation of the TC-BF-BOF system does not preclude other efforts to decarbonize the industry, such as improving efficiency, using renewable electricity, increasing scrap recycling, or methods to improve the DRI-EAF route. In fact, to minimize emissions across the industry, most of the scrap can be used in the EAF (which can use 100% scrap), and the remaining scrap is used in TC-BF-BOF.

[0149] The present invention is not limited to the embodiments described above, and its structure and details may vary. The scope of the present invention should be determined with reference to the appended claims.

Claims

1. A system for metal production, the system comprising: A blast furnace configured to receive metal ore and blast gas and output hot metal and blast furnace top gas; And A first thermochemical reactor configured to receive at least a portion of the reducing furnace top gas in a first mode and produce carbon monoxide from carbon dioxide in the portion of the reducing furnace top gas by oxidizing a thermochemical compound, and return at least a portion of the produced carbon monoxide to the reducing furnace; Wherein the first thermochemical reactor is configured to produce oxygen by reducing the thermochemical compound in a second mode, and The system further comprises a controller configured to switch or cycle between the first mode and the second mode, in the first mode, the first thermochemical reactor receives carbon dioxide from the blast furnace top gas and produces carbon monoxide by oxidizing the thermochemical compound, and in the second mode, the first thermochemical reactor produces oxygen by reducing the thermochemical compound.

2. The system according to claim 1, further comprising: A gas separator configured to: receive the blast furnace top gas, separate carbon dioxide from other components of the blast furnace top gas, and supply the carbon dioxide portion of the blast furnace top gas to the first thermochemical reactor.

3. The system according to claim 1 or 2, wherein The gas separator is further configured to separate carbon monoxide from other components of the blast furnace top gas for return to the blast furnace.

4. The system according to any one of the preceding claims, wherein, The thermochemical compound includes a metal oxide, a perovskite material or a double perovskite material.

5. The system according to any one of the preceding claims 1, wherein, The system further comprises a second thermochemical reactor, wherein in the first mode, the second thermochemical reactor produces oxygen by reducing the thermochemical compound, and in the second mode, the second thermochemical reactor receives carbon dioxide from the blast furnace top gas and produces carbon monoxide by oxidizing the thermochemical compound.

6. The system according to any one of the preceding claims, further comprising a steel furnace configured to receive the hot metal from the blast furnace and receive the oxygen from the first thermochemical reactor and / or the second thermochemical reactor, and output molten steel and steel furnace gas.

7. The system according to claim 6, comprising the subject matter of claim 2, wherein, The gas separator is configured to separate nitrogen from the blast furnace top gas and supply the nitrogen to the first thermochemical reactor and / or the second thermochemical reactor for reducing the thermochemical compound.

8. The system according to claim 6 or 7, wherein, The gas separator is configured to separate carbon monoxide from the steel furnace gas for return to the blast furnace.

9. The system according to any one of claims 6 to 8, further comprising a regenerative heat exchanger configured to receive the steel furnace gas and supply heat from the steel furnace gas to the blast gas and / or the returned carbon monoxide.

10. The system according to any one of the preceding claims, comprising a first thermochemical reactor gas separator configured to receive an output gas from the first thermochemical reactor in the first mode and to separate carbon monoxide from the output gas; and optionally comprising the subject matter of claim 7, wherein, The system includes a second thermochemical reactor gas separator configured to separate oxygen from the output gas from the first thermochemical reactor in the second mode.

11. The system according to any one of the preceding claims, comprising the subject matter of claim 5, wherein, The first thermochemical reactor and the second thermochemical reactor are jointly configured to provide at least 50% of the carbon monoxide used in the blast furnace for reducing the metal ore to hot metal.

12. The system according to any one of the preceding claims, further comprising a blast furnace electric heater configured to heat the blast gas and / or the metallic ore introduced into the blast furnace using electricity.

13. A method for producing steel, comprising: reducing a metallic ore in a blast furnace to produce hot metal by reacting carbon monoxide with a metal oxide, thereby producing carbon dioxide; providing at least some of the carbon dioxide produced from the blast furnace to a first thermochemical reactor and producing carbon monoxide from the carbon dioxide by oxidizing a thermochemical compound; returning at least a portion of the produced carbon monoxide to the blast furnace; and the method further comprises producing oxygen by reducing the thermochemical compound in the first thermochemical reactor and switching or cycling between a first mode and a second mode, in the first mode, the thermochemical reactor receives carbon dioxide from the blast furnace top gas and produces carbon monoxide by oxidizing the thermochemical compound, in the second mode, the first thermochemical reactor produces oxygen by reducing the thermochemical compound.

14. The method according to claim 13, wherein, Obtaining the carbon dioxide from the blast furnace provided to the first thermochemical reactor by separating carbon dioxide from the blast furnace top gas produced from the blast furnace.

15. The method according to claim 14, wherein, The method further comprises separating carbon monoxide from the blast furnace top gas and returning the carbon monoxide to the blast furnace.

16. The method according to any one of claims 13 to 15, wherein, The thermochemical compound comprises a metal oxide, a perovskite material or a double perovskite material.

17. The method according to any one of claims 13 to 16, wherein In the first mode, a second thermochemical reactor produces oxygen by reducing the thermochemical compound, and in the second mode, the second thermochemical reactor receives carbon dioxide from the reducing furnace top gas and produces carbon monoxide by oxidizing the thermochemical compound.

18. The method according to any one of claims 13 to 17, comprising receiving the hot metal and the oxygen from the thermochemical reactor at the steel furnace and outputting molten steel and a steel furnace gas from the steel furnace.

19. The method according to claim 18, further comprising separating nitrogen from the reducing furnace top gas and providing the nitrogen to the first thermochemical reactor and / or the second thermochemical reactor for reducing the thermochemical compound.

20. The method according to any one of claims 13 to 19, comprising separating carbon monoxide from the output gas from the first thermochemical reactor in the first mode and separating oxygen from the output gas in the second mode.

21. The method according to any one of claims 13 to 20, comprising using the first thermochemical reactor and the second thermochemical reactor to provide at least 50% of the carbon monoxide used in the reducing furnace for reducing the metallic ore to hot metal.

22. The method according to any one of claims 13 to 21, further comprising heating the process gas and / or the metallic ore introduced into the reducing furnace using electricity.

23. The method according to any one of claims 13 to 22, comprising: Reducing at least 50% of the CO2 emissions associated with the reducing furnace by replacing coke used as an input to the reducing furnace with gaseous carbon monoxide obtained from the output gas.

24. The system according to any one of claims 1 to 12, or the method according to any one of claims 13 to 23, wherein The reduction furnace is a DRI furnace.

25. The system according to any one of claims 1 to 12, or the method according to any one of claims 13 to 23, wherein, The reduction furnace is a blast furnace.

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