Improved Metal Production

Abstract

A system (100) for producing metals includes: a reduction furnace (110) configured to receive metal ore (101) and process gas (102) and to discharge heated metal (115) and reduction furnace top gas (111); and a first thermochemical reactor (130) configured to, in a first mode, receive at least a portion (163) of the reduction furnace top gas (111), generate carbon monoxide from carbon dioxide in the portion (163) of the blast reduction furnace top gas (111) by oxidation of thermochemical compounds, and return at least a portion of the generated carbon monoxide (151) to the reduction furnace (110).

Description

[Technical Field]

[0001] SYSTEMS AND METHODS FOR PRODUCING LIQUID METAL FIELD OF THE INVENTION The present invention relates to systems and methods for producing liquid metal, and more particularly to systems and methods for producing metal with a reduced carbon footprint. [Background technology]

[0002] The steel sector is a major source of greenhouse gas emissions, producing up to 9% of global CO2 emissions. Steel is certainly among the difficult sectors to decarbonize, as its production is inherently energy- and carbon-intensive, involving very high-temperature processes. In fact, by weight, it emits more carbon dioxide than the steel produced, with 1.89 tonnes of CO2 released for every tonne of steel produced using current technology. The main reason for this is the use of coking coal as an energy source and structural support, which accounts for 74% of total energy feedstock and 15% of total global coal consumption.

[0003] Currently, there are two primary methods for producing steel: the blast furnace-basic oxygen furnace (BF-BOF) method accounts for 71% of production, and natural gas-based direct reduction of iron followed by electric arc furnace (DRI-EAF) accounts for the remaining 29%. The BF-BOF method is described in more detail below, but generally both methods consist of two steps: first, iron ore is reduced to metallic iron in the BF or DRI, which is then converted to steel in the BOF or EAF by reducing the carbon content of the metal.

[0004] Several technologies are being investigated to decarbonize the steel industry. The first option is to close old BF-BOFs and replace them with DRI-EAFs. Running EAFs on renewable electricity could potentially reduce CO2 emissions by 1.5 Gt per year. However, a typical large-scale DRI-EAF plant costs $1.1 billion to $1.7 billion to build. This cost, combined with the stranded assets of old BF-BOF plants, makes this conversion economically impractical in the short term required to meet the Paris 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, scrap accounted for 32% of all inputs. Scrap recycling reduces CO2 emissions by 90% and uses 70% less energy than using virgin iron ore in BF-BOFs. Additionally, each tonne of scrap steel recycled replaces 1,400 kg of iron ore, 740 kg of coal, and 120 kg of limestone. In EAF, the share of scrap steel in the input can be less than 100%, while for BF-BOF, the current maximum is 20-25%. It is estimated that the share of scrap in the input could increase to 46% by 2050, which, while not enough on its own to decarbonize the sector, could result in significant reductions in CO2 emissions.

[0005] Another decarbonization option is the use of hydrogen for direct reduced iron (HDRI) followed by an EAF. Using renewable electricity to power the electrolyzer to form green hydrogen could dramatically reduce emissions. However, this requires the construction of a new DRI plant to replace the BF-BOF, and the technology readiness level (TRL) is 5–7, meaning the technology is proven but not yet industrially operational. It has been estimated that a carbon price of $67 / tCO2 equivalent would be required to enable HDRI to produce steel at the same price as conventional blast furnaces, provided that sufficiently low-cost renewable electricity is provided. Furthermore, the reduction of iron with hydrogen is less efficient than with carbon monoxide at lower temperatures, and the reduction of Fe2O3 to Fe3O4 occurs more readily in the presence of CO. Conversely, the reduction of Fe3O4 to Fe at higher temperatures occurs more readily in the presence of hydrogen. Modelling suggests that a hydrogen-based DRI could reduce emissions in the EU steel industry by 35% at current grid emission levels, but would require 3.72 MWh per tonne of liquid steel produced. As a reference, BF-BOF uses 3.48 MWh / t. The costs of hydrogen production remain very high.

[0006] A related technology is natural gas DRI with carbon capture, utilization, and storage (CCUS), which also has a TRL of 5–7. Several CCUS methods have been demonstrated, and a few industrial CCUS facilities are in operation; however, costs are expected to be $100 per ton of CO2 for capture and $160 per ton for transportation and storage by 2030, with modest declines expected by 2050. The very high emissions from steelmaking facilities necessitate large-scale CCUS plants, but emissions reductions are estimated at 20–80%. Finally, another proposed solution is iron ore electrolysis, which has a TRL of 6. This technology is already used on a large scale in aluminum production; therefore, the technology has been demonstrated on an industrial scale, but it operates at significantly lower temperatures than the iron and steelmaking processes. Efficient reduction of iron ore requires high temperatures and optimized electrodes and electrolytes.

[0007] In summary, steel production accounts for 9% of global CO2 emissions and rapid decarbonization is essential to limit warming to 1.5°C. 70% of existing steel facilities rely on high-temperature BF-BOF processes, which are highly energy intensive and have high emissions. Most current approaches to decarbonizing the sector rely on phasing out these BF-BOF plants and introducing lower-carbon methods such as EAF and DRI plants, which comes at a very high cost.

[0008] The techniques applicable to iron and steel production are also potentially applicable to other production processes that use carbon monoxide as a reducing agent in reduction furnaces. Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, there is a need for a means to decarbonize metals production that at least ameliorates the problems noted above. [Means for solving the problem]

[0010] According to a first aspect of the present invention there is provided a system for producing metals, the system comprising: a reduction furnace configured to receive metal ore and process gas and to discharge heated metal and reduction furnace top gas; a first thermochemical reactor configured to, in a first mode, receive at least a portion of the reduction furnace top gas, generate carbon monoxide from carbon dioxide in the portion of the reduction furnace top gas by oxidation of a thermochemical compound, and return at least a portion of the generated carbon monoxide to the reduction furnace; Equipped with.

[0011] The reduction furnace may comprise a blast furnace or a DRI furnace.

[0012] The metal may be iron. The system may be for the production of iron and / or steel.

[0013] The first thermochemical reactor may comprise a series of sub-reactors, which may be operated in series so that CO from the first sub-reactor can be further reduced in a subsequent sub-reactor, and so on.

[0014] The system may further include a gas separator configured to receive the reduction furnace top gas, separate the 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.

[0015] 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.

[0016] The thermochemical compound may comprise (or consist essentially 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 It may also contain O3.

[0017] The first thermochemical reactor may be configured in a second mode to produce oxygen by reduction of a thermochemical compound. The reduction of the thermochemical compound may include the use of green hydrogen derived from renewable resources.

[0018] The system may further include a controller configured to switch or cycle between a first mode in which the first thermochemical reactor receives carbon dioxide from the reduction furnace top gas and produces carbon monoxide by oxidation of a thermochemical compound, and a second mode in which the first thermochemical reactor produces oxygen by reduction of a thermochemical compound.

[0019] The system may further include a second thermochemical reactor, wherein in a first mode, the second thermochemical reactor produces oxygen by reduction of a thermochemical compound, and in a second mode, the second thermochemical reactor receives carbon dioxide from the reduction furnace top gas and produces carbon monoxide by oxidation of a thermochemical compound. The system may be configured to operate the first and second thermochemical reactors in a cycle (repeated between the first and second modes) for a continuous supply of carbon monoxide and oxygen.

[0020] The system may further include a steel furnace (which may include a basic oxygen furnace or an electric arc furnace), the steel furnace configured to receive heated metal from the reduction furnace and oxygen from the first thermochemical reactor and / or the second thermochemical reactor, and to discharge molten steel and steel furnace gases.

[0021] The gas separator may be configured to separate nitrogen from the reduction furnace top gas and supply the nitrogen to the first thermochemical reactor and / or the second thermochemical reactor for reduction of thermochemical compounds.

[0022] The gas separator may be configured to separate carbon monoxide from the basic oxygen furnace gas for return to the reduction furnace.

[0023] The system may include a first thermochemical reactor gas separator configured to receive exhaust gas from the first thermochemical reactor in a first mode and separate carbon monoxide from the exhaust gas. The system may include a second thermochemical reactor gas separator configured to separate oxygen from the exhaust gas from the first thermochemical reactor in a second mode. The first thermochemical reactor gas separator may be configured to receive exhaust gas from the second thermochemical reactor in the second mode and separate carbon monoxide from the exhaust gas. The second thermochemical reactor gas separator may be configured to receive exhaust gas from the second thermochemical reactor in the first mode.

[0024] The system may include a regenerative heat exchanger configured to extract heat from the reduction furnace top gas and / or 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.

[0025] The system may include a heater (e.g., powered by a renewable or other zero-carbon energy, low-carbon source) configured to provide heat to the first thermochemical reactor and / or the second thermochemical reactor.

[0026] The system may include a heat exchanger for removing heat from the reduced process gas or for removing heat from the oxygen produced from the reduced process gas and supplying heat to at least one of the first and second thermochemical reactors, the CO storage tank, or the process gas.

[0027] The first thermochemical reactor and the second thermochemical reactor may together be configured to provide at least 50% (or at least 30%, or at least 70%, or at least 80%) of the carbon monoxide used in the reduction furnace to reduce the metal ore to heated metal.

[0028] The system may include an electric reduction furnace heater configured to heat the process gas and / or metal ore introduced into the reduction furnace using electrical power, which may be supplied from a carbon-neutral source.

[0029] According to a second aspect there is provided a method of producing a metal, the method comprising: reducing metal ores in a reduction furnace by reacting carbon monoxide with metal oxides to produce heated metals, thereby producing carbon dioxide; supplying at least a portion of the carbon dioxide produced from the reduction furnace to a first thermochemical reactor, and producing carbon monoxide from the carbon dioxide by oxidation of a thermochemical compound; Returning at least a portion of the produced carbon monoxide to the reduction furnace. Includes.

[0030] The reduction furnace can be a blast furnace or a DRI furnace.

[0031] The metal ore may include or consist essentially of iron ore, the metal oxide may include or consist essentially of iron oxide, and the heating metal may be iron.

[0032] The carbon dioxide from the reduction furnace that is supplied to the first thermochemical reactor may be obtained by separating carbon dioxide from the reduction furnace top gas produced by the reduction furnace.

[0033] The method may further include separating the carbon monoxide from the reduction furnace top gas and returning the carbon monoxide to the reduction furnace.

[0034] The thermochemical compound may include or consist essentially of a perovskite or a double perovskite. The thermochemical compound may include or consist essentially of a barium niobium ferrite double perovskite. The thermochemical compound may include Ba2Ca 0.66 Nb 0.34 It may also contain FeO6.

[0035] The method may include producing oxygen by reduction of a thermochemical compound in a first thermochemical reactor.

[0036] The method may further include switching or cycling between a first mode in which the first thermochemical reactor receives carbon dioxide from the reduction furnace top gas and produces carbon monoxide by oxidation of a thermochemical compound, and a second mode in which the first thermochemical reactor produces oxygen by reduction of a thermochemical compound.

[0037] In a first mode, the second thermochemical reactor may produce oxygen by reduction of thermochemical compounds, and in a second mode, the second thermochemical reactor may receive carbon dioxide from the reduction furnace top gas and produce carbon monoxide by oxidation of thermochemical compounds.

[0038] The method may include receiving heated metal and oxygen from the thermochemical reactor at a steel furnace (e.g., a basic oxygen furnace or an electric arc furnace) and discharging molten steel and steel furnace gases from the steel furnace.

[0039] The method may include separating nitrogen from the reduction furnace top gas and feeding the nitrogen to a thermochemical reactor for reduction of thermochemical compounds.

[0040] The method may include separating carbon monoxide from an exhaust gas from the first thermochemical reactor in a first mode, and separating oxygen from the exhaust gas in a second mode.

[0041] The method may include using a first thermochemical reactor and a second thermochemical reactor to provide at least 50% (or at least 30%, or at least 70%, or at least 80%) of the carbon monoxide used in a reduction furnace to reduce metal ore to heated metal.

[0042] The method may further include using electrical power to heat the process gas and / or the metal ore introduced into the reduction furnace.

[0043] The method may include reducing CO2 emissions associated with the reduction furnace by at least 50% by replacing coke used as input to the reduction furnace with gas-phase carbon monoxide obtained from exhaust gases (which may include carbon dioxide produced by the reduction furnace and flue gases from a steel furnace, such as a BOF or EAF). In some embodiments, CO2 emissions may be reduced by at least 20%, or at least 75%.

[0044] According to a third aspect, there is provided a method of decarbonizing a system for producing metals, the method comprising adding to a system comprising a reduction furnace a thermochemical reactor configured to produce carbon monoxide by reacting a thermochemical compound with carbon dioxide obtained from the reduction furnace top gas, and to supply at least a portion of the produced carbon monoxide to the reduction furnace for the reduction of iron oxide.

[0045] The reduction furnace can be a blast furnace or a DRI furnace.

[0046] The method may include adding a gas separator. The method may include adding any of the elements mentioned in relation to the first aspect, including any features thereof.

[0047] Features of each aspect may be combined with features of any other aspect. Any feature of any aspect may be combined with features of any other aspect. The operations that the system is configured to perform may include steps in methods according to embodiments.

[0048] The invention will now be described, by way of example only, with reference to the accompanying drawings in which: [Brief explanation of the drawings]

[0049] [Figure 1] FIG. 1 is a schematic diagram of a TC-BF system including a blast furnace and a thermochemical reactor for producing carbon monoxide from carbon dioxide produced in the blast furnace, according to an embodiment. [Figure 1a] FIG. 1a is a schematic diagram of a DRI system including a DRI furnace and a thermochemical reactor for producing carbon monoxide from carbon dioxide produced in the DRI furnace, according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram of an embodiment of a TC-BF-BOF system including a blast furnace, a basic oxygen furnace, and first and second thermochemical reactors, with mass flows shown. [Figure 3]FIG. 3 is a schematic diagram of a TC-BF-BOF system similar to that of FIG. 2, with heat flow indicated. [Figure 4] FIG. 4 shows a graph of carbon dioxide conversion versus oxidation time at different temperature ranges for an exemplary thermochemical compound. [Figure 5] FIG. 5 shows Hancock and Sharpe plots for exemplary thermochemical compounds. [Figure 6] FIG. 6a) is a plot of reaction rate constants at each temperature, and b) is an Arrhenius plot for the oxidation of an exemplary thermochemical compound. DETAILED DESCRIPTION OF THE INVENTION

[0050] Modern blast furnaces can produce over 10,000 tons of hot metal per day, with the largest furnaces measuring 6,000 m 3 The typical blast furnace has a furnace top temperature of approximately 200°C, while the bottom can reach temperatures exceeding 1600°C. In existing blast furnaces used for iron production, iron ore and coke are fed into the furnace in layers. Air or oxygen-enriched air, also known as blast, is preheated to 1100–1350°C in a regenerative heat exchanger known as a hot stove before being injected into the bottom of the furnace. This hot blast provides most of the heat required by the furnace. The hot blast reacts with the coke layer to produce large amounts of carbon monoxide (CO), which rises through the furnace, reducing the iron ore and transferring heat to the materials above it. Once the iron ore is reduced to metallic iron, the liquid metal accumulates at the bottom of the furnace and is tapped or removed from the furnace. To reduce coke consumption, crushed coal particles and / or combustible gases (e.g., natural gas, coke oven gas) can be injected through furnace tuyeres at the bottom of the furnace.

[0051] Iron ore often contains impurities, so limestone and other additives are used to separate these impurities from the liquid metal. For example, limestone removes sulfur from FeS, resulting in metallic iron and CaS. CaS, being less dense than metallic iron, rises in the furnace, forming a layer of molten slag that also contains other impurities such as SiO2, Al2O3, MgO, and CaO. The slag is tapped from the furnace at approximately 1650°C, and up to 65% of this heat can be recovered. Typically, about 0.275 tons of slag is generated per ton of steel produced. The process gas, which mixes with carbon monoxide and carbon dioxide in the furnace and rises to the top of the furnace, is known as top gas. This top gas leaves the furnace at approximately 200–300°C and typically has a molten content of 3–4 MJ / Nm 3 (standard cubic meters), most of which is recovered in a regenerative heat exchanger. This heat, together with additional heat obtained by burning this top gas, is used to heat the blast to above 1100°C as mentioned above.

[0052] Modern steel production using a BF-BOF furnace uses approximately 1,370 kg of iron ore, 780 kg of smelting coal, 270 kg of limestone, and 125 kg of recycled steel to produce 1,000 kg of crude steel. Blasting requires approximately 1,500 kg of air, which is supplied to the bottom of the furnace through a tuyere (nozzle). Before use in the BF, smelting coal must be treated and heated to approximately 1,250 °C for approximately 12 hours using heat from the furnace top gas and coke oven gas (COG). COG is a gas released during coal pretreatment after cooling and cleaning. Typically, COG contains 60% H2, 24% CH4, 6% CO, 6% N2, and 4% CO2. Because hydrogen and carbon monoxide are excellent reducing agents for iron ore, COG is also used in BF. After treatment, the coke has several major uses in a typical BF. First, coke is the primary energy source for BF, with 95% of the total energy provided by coke combustion during BF (and coke accounts for 20–40% of the total cost). Second, coke reacts with oxygen to produce carbon monoxide, an effective reducing agent for iron ore. It then reacts with carbon dioxide produced during reduction to form more carbon monoxide via the Boudouard reaction. Coke also adds carbon to metallic iron. Finally, coke serves as support for the iron ore bed and aids in gas transport within the furnace. To reduce the amount of coke required, other reducing agents, such as pulverized coal (cheaper than refinery coal), hydrocarbons, waste plastics, and biomass, can be added to the blast furnace. Natural gas can also replace part of the coke, provided that its methane content is greater than 80%, as it is cracked into carbon monoxide and hydrogen. A fuel value of 465 kg per tonne of heated metal produced is accepted as a theoretical minimum, and modern BF approaches this at 500 kg per tonne.

[0053] There are four main reactions in BF to reduce iron ore to iron. Iron ore is primarily composed of Fe2O3. Below 570°C, the following two reactions occur: [ka]

[0054] As the remaining iron ore begins to fall downward in the furnace and the temperature exceeds 570°C, two reactions become dominant: [ka]

[0055] Here, a CO concentration of at least 70% is required for the reduction of FeO (Eq. 4).

[0056] The so-called pig iron produced in the blast furnace is tapped from the BF and fed into the BOF. Scrap metal may also be fed into the BOF at up to 25-30 wt%. No heat is added to the BOF, but oxygen is blown into the molten metal, reacting with the carbon in the iron (often FeC) to form carbon monoxide and carbon dioxide, releasing heat. This reaction raises the temperature to approximately 1650°C. To be able to produce a wide range of steel products, the oxygen must be at least 99.9% pure. A total of 50-60 Nm 3 1 / tls (standard cubic meter per tonne of liquid steel) is blown into the hot metal through a lance at the top or bottom for 15-20 minutes, also known as blowing. Steel is tapped from the furnace approximately every 40 minutes. Basic oxygen furnace gas (BOF gas) leaves the furnace at about 1600°C and is released at a rate of approximately 100 Nm 3 The BOF gas is produced in a BOF reactor, which contains carbon dioxide, carbon monoxide, and nitrogen from the atmosphere. The temperature and composition of the BOF gas often change over time during the process. This BOF gas has a yield of approximately 8.8 MJ / Nm 3 of which over 90% can be recovered as thermal and chemical energy.

[0057] 1 shows an overview of an exemplary TC-BF system 100 according to an embodiment, including a reduction furnace 110 and a thermochemical reactor 130. The blast furnace 110 is operated similarly to the above example, except that at least a portion of the carbon monoxide used in the reduction of the iron ore is obtained by thermochemical reduction of carbon dioxide from blast furnace top gas 111, rather than by combustion of coke. The blast furnace 110 receives iron ore 101 and process gas 102 (e.g., air or oxygen-enriched air) along with a carbon source (e.g., pulverized coal or natural gas (not shown)), and produces heated metal 115 and blast furnace top gas 111. In this example, the reduction furnace 110 is a blast furnace 110, and the process gas 102 may be referred to as blast gas 102.

[0058] At least a portion 163 of the blast furnace top gas 111 that is enriched in carbon dioxide (e.g., containing at least 20%, 50%, 75%, 85%, or 95% carbon dioxide) is provided as input to the thermochemical reactor 130. A gas separator (not shown) may be used to separate the carbon dioxide from the top gas 111 to produce carbon dioxide 163 that is provided to the thermochemical reactor 130. Gas separation may use any suitable technique, such as (but not limited to): adsorption, membrane, or chemical acceptor.

[0059] The thermochemical reactor 130 reacts the carbon dioxide 163 with the thermochemical compound, thereby reducing / decomposing the carbon dioxide to produce carbon monoxide 151, which is now oxidized. The carbon monoxide 151 is provided as input to the blast furnace 110, for example mixed with the process gas 102 (or introduced directly and not mixed with the process gas 102), to reduce the iron oxides. The carbon source may include coke, charcoal, biomass, and / or waste plastics, and may be introduced at least in part into the process gas 102 (due to the lower mechanical strength of the materials and higher proportion of volatiles in this approach compared to traditional coke-based systems).

[0060] In embodiments, the carbon monoxide required for the reduction of iron ore in a blast furnace is provided, at least in part, by converting carbon dioxide from the blast furnace top gas 111 to carbon monoxide 151 via a thermochemical reaction. In some embodiments, at least 20%, 30%, 50%, 75%, or 85% of the carbon monoxide used in the blast furnace to reduce iron oxides can be provided by the thermochemical conversion of carbon dioxide to carbon monoxide (which may be in situ). This can significantly reduce the amount of coke required as input to the blast furnace 110 and significantly 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 in which all of the carbon monoxide in the blast furnace is derived from coke). For high coke reduction rates, alternative materials, such as inert (chemically compatible) ceramic materials, that act as structural support to ensure permeability and stability of BF operation may be required, and such materials may be reused in the process (e.g., the structural support may not be consumed by the chemical reactions in the BF).

[0061] Two major classes of materials capable of decomposing carbon dioxide to carbon monoxide via a thermochemical cycle are simple metal oxides or mixed metal oxides, such as perovskites. Ceria (cerium oxide) is an example of a metal oxide capable of decomposing carbon dioxide in good yield; however, high temperatures, such as 1400°C for reduction and 900°C for oxidation, are required. Ceria is a nonstoichiometric 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 oxide. Volatile metal oxides are stoichiometric oxygen carriers; the melting temperature of the pure metal is lower than the reduction temperature of the metal oxide.

[0062] Perovskites are non-stoichiometric mixed metal oxides with the ideal formula ABO3, where A and B are metallic elements. An example of a perovskite for thermochemical cycling is the La1-xSrxMnO3 system, which is reducible at about 1400°C and oxidizable at about 900°C, with a fuel yield ten times higher than ceria. Ba2Ca 0.66 Nb 1.34 -xFe x O6 (x=0, 0.34, 0.66, and 1) is a double perovskite that can be reduced at about 800°C to decompose CO2 and is particularly preferred for the embodiments.

[0063] Examples of perovskites suitable for decomposing carbon dioxide to carbon monoxide include those listed in Table 1 below (further examples are listed in Table 2).

[0064] [Table 1] Table 1: Examples of perovskites for carbon dioxide decomposition

[0065] In embodiments, the thermochemical reaction is reversible, reducing the thermochemical compound to produce oxygen, which can be disposed of as waste or recovered and sold.

[0066] In the context of a BF-BOF, oxygen produced by the reduction of a thermochemical compound can be used as input to the BOF to provide at least a portion of the oxygen gas required as input. In some embodiments, all of the oxygen for the BOF may be provided by the reduction of a thermochemical compound, and there may be a potential for excess oxygen.

[0067] Many materials are capable of undergoing thermochemical cycling; however, in the exemplary embodiment described herein, BaCa is used due to its high yield for the oxidation reaction, low reaction temperature, 100% selectivity to CO, and low activation energy.0.66 Nb 0.34 FeO6(BCNF1) will be used. BCNF1 is a double perovskite material. When BCNF1 is reduced at 700°C under a nitrogen atmosphere, oxygen is lost from the crystal structure, forming oxygen vacancies and releasing oxygen gas. [ka] where δ is equal to the degree of non-stoichiometry. Oxidation of BCNF1 occurs at 800 °C in a carbon dioxide atmosphere, decomposing CO2 to CO, which reincorporates oxygen into the lattice by filling oxygen vacancies, reforming the original perovskite. [ka]

[0068] This allows for repeated reduction and oxidation cycles to decompose CO2. BCNF1 has been found to convert 10.1% of CO2 to CO per cycle (average value over 5 cycles). 3 Producing CO at 1000kJ / hr requires 5700kWh of electricity with an 85% efficient electric heater. This plant can produce carbon monoxide at a cost of £0.19 / kg when the price of electricity is £0.11 / kWh. When the price of electricity is £0.05 (average US industrial electricity price), the cost of carbon monoxide is £0.11 / kg.

[0069] 1a shows an overview of an exemplary TC-DRI system according to an embodiment, including a direct reduced iron furnace 210 and a thermochemical reactor 230. The direct iron reduction furnace 210 is operated to reduce iron in the solid phase by contacting it with a process gas, such as hydrogen or carbon monoxide. The reaction is shown below. [ka]

[0070] At least a portion of the carbon monoxide used in the reduction of iron ore in the DRI furnace 210 is obtained by thermochemical reduction of carbon dioxide from top gas 211 discharged from the DRI furnace 210. The DRI furnace 210 receives iron ore 201 and process gas 202 (e.g., carbon monoxide and / or hydrogen) along with a carbon source (e.g., pulverized coal or natural gas (not shown)) to produce heated metal 215 and DRI top gas 211. At least a portion 263 of the DRI top gas 111 enriched in carbon dioxide (e.g., containing at least 20%, 50%, 75%, 85%, or 95% carbon dioxide) is provided as input to the thermochemical reactor 230. A gas separator (not shown) may be used to separate the carbon dioxide from the top gas 211 to produce carbon dioxide 263, which is provided to the thermochemical reactor 230. Gas separation may use any suitable technique, such as (but not limited to): adsorption, membrane, or chemical acceptor.

[0071] 1a, the thermochemical reactor 230 reacts carbon dioxide 263 with a thermochemical compound, thereby reducing / decomposing the carbon dioxide to produce carbon monoxide 251, which is now oxidized. Carbon monoxide 251 is provided as input to the DRI furnace 210, for example, mixed with the process gas 202 (or introduced directly and not mixed with the reducing gas 202), to reduce the iron oxide.

[0072] In embodiments, the carbon monoxide used in the reduction of iron ore in the DRI furnace is at least partially provided by converting carbon dioxide from the DRI furnace top gas 211 to carbon monoxide 251 via a thermochemical reaction. In some embodiments, at least 20%, 30%, 50%, 75%, or 85% of the carbon monoxide used in the DRI furnace to reduce iron oxides can be provided by the thermochemical conversion of carbon dioxide to carbon monoxide (which can be in situ). This can significantly reduce the amount of coke required as input to the DRI furnace 210 and can significantly reduce the carbon footprint of the DRI furnace 210.

[0073] 2, a schematic diagram of a system 100 according to an embodiment is shown. 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 O storage tank 190, and a controller 200. In this exemplary embodiment, the steel furnace 120 is a basic oxygen furnace / BOF 120, although in other embodiments, an EAF may be used as the steel furnace 120.

[0074] The mass and molar flows in system 100 are described with reference to the production of 1 ton of liquid steel (1000 kg). The mass and molar flows are illustrative of a specific example and should not be construed as limiting the scope of the invention. Other systems with different mass flows are possible.

[0075] The blast furnace 110 receives iron ore 101, process gas 102, and carbon monoxide 151 and supplies heating metal 115 to a basic oxygen furnace 120. Conventional slag formers may also be provided as input to the blast furnace 101, along with a carbon source (as described above). The basic oxygen furnace 120 receives the heating metal 115 and scrap steel 122, along with oxygen gas 191. The heating metal 115 and scrap steel 122 are converted to liquid steel by removal of carbon in reaction with the oxygen 191. To produce 1000 kg of liquid steel 125, the blast furnace 110 may be supplied with approximately 1600 kg of iron ore and approximately 1500 kg of process gas. This amount of iron ore 101 is based on the assumption of 95% Fe2O3 and 5% impurities. The blast furnace 110 discharges about 900 kg of hot metal and about 1500 kg of blast furnace top gas 111 .

[0076] BF 111 contains carbon dioxide, carbon monoxide, nitrogen, and hydrogen. BOF 120 produces BOX 121, which contains carbon monoxide and carbon dioxide. In this example, the heated metal is combined with about 125 kg of scrap steel in BOF 120, although higher or lower percentages of scrap metal may be used. BOF 120 is approximately 50 Nm 3of oxygen and approximately 100Nm 3 BOF gas 121 (containing CO and CO2) is discharged.

[0077] The gas separator 160 receives both the top gas 111 and the BOF gas 121 and separates them into three components: carbon monoxide 165, 166, carbon dioxide 163, 164, and nitrogen 161 / hydrogen 162. In this example, the top gas 111 proportions are assumed to be 5% CO, 45% CO, 2% H, and 48% N. These values ​​differ from those typical for prior art coke-based blast furnaces, where the proportions of CO and H are higher. The absence (or small amount) of coke is assumed to result in less CO in the top gas because the amount of CO added is substantially stoichiometric. In other embodiments, these proportions may be different. While this example is based on a near-stoichiometric supply of CO to the blast furnace, in some instances, an excess amount of CO may be present in the blast furnace. In this example, the BOF gas 121 proportions are 90% CO and 10% CO.

[0078] Gas separator 160 (and, optionally, gas separators 140, 180) may be operated using any suitable technology, such as (but not limited to): adsorption (including pressure swing adsorption), membrane, or chemical acceptor. Gas separator 160 supplies carbon monoxide components 165, 166 to carbon monoxide storage tank 150, carbon dioxide components 163, 164 to first thermochemical reactor 130, and nitrogen / hydrogen components 161, 162 to second thermochemical reactor 170.

[0079] The carbon dioxide 163, 164 from the gas separator 160 includes 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 significantly greater than the mass flow of the BOF gas 121, meaning that the majority of the carbon dioxide produced by the gas separator 160 will come from the top gas 111. In this example, approximately 21,200 moles of CO2 originate from the top gas 111, and only approximately 410 moles of CO2 originate from the BOF gas 121. It can therefore be seen that recovering carbon dioxide from the BOF gas is advantageous, but not required in all embodiments. The discharge of CO2 from the BOF may be periodic.

[0080] Similarly, the carbon monoxide 165, 166 from the gas separator 160 includes 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 proportion of CO than the BOF gas 121, meaning that the contribution of CO from the BOF gas is greater than that of CO. However, most of the CO 151 supplied to the blast furnace 110 (about 75% in this example, but typically greater than 50%) can be obtained from the decomposition of CO to form CO in the thermochemical reactor 130. In this example, 2600 moles of CO are obtained from the top gas 111 by the gas separator 160, and 3570 moles of CO are obtained from the BOF gas 121 by the gas separator 160 (this is in addition to the approximately 15,070 moles of CO obtained from the thermochemical reactor 130).

[0081] 2, the system 100 is operating in a first mode in which the reactor 130 receives CO 163, 164 from the gas separator 160 and the first thermochemical reactor 130 operates in an oxidation mode in which CO is produced by oxidation of the thermochemical compound. As noted above, the conversion of CO to CO is not 100% with each pass through the reactor 130 (approximately 10% may be converted with each pass). The reactor 130 produces an oxidation product gas (OPG) 131 in which at least a portion of the CO has been converted to CO. The OPG 131 is fed to the thermochemical reactor gas separator 140, where the CO is separated from the CO. The CO 142 is recycled to the reactor 130, and the CO 141 is stored in the CO storage tank 150.

[0082] In this example, 21,610 moles of CO are converted to 15,070 moles of CO. In some embodiments, about 80% of the moles of CO 163,164 input to the reactor 130 are converted and stored as CO ready for use in the blast furnace 110. In combination with the CO 165,166 streams from the gas separator, the CO storage tank 150 receives 21,400 moles of CO, which is supplied to the blast furnace 110. Preferably, the CO 151 is injected into the blast furnace 110 via a tuyere along with the process gas 102 (however, in some embodiments, other CO injection points may be used, optionally in combination with the injection of CO 151 with the process gas 102).

[0083] When the reduction of iron ore to metallic iron occurs via reactions (1) and (2), 3 moles of CO are required per mole of Fe2O3. When the reduction proceeds via reactions (1), (3), and (4), 2 moles of CO are required. Therefore, an approximation can be made in calculating the required stoichiometry, where 2.5 moles of CO are required per mole of Fe2O3. This corresponds to 23,800 moles of CO / tls.

[0084] In some embodiments, all of the CO required for iron ore reduction in the blast furnace 110 can be obtained from the top gas 111, the BOF gas 121, and the thermochemical reactor 141. In the exemplary embodiment of FIG. 2 , a portion of the CO required for iron ore reduction in the blast furnace is provided as a gas input, and coke (or charcoal, biomass, waste plastic, etc.) is used (not shown) to provide the remainder of the CO (as well as provide structure and act as a source of solid carbon). In embodiments where a high percentage of coke is replaced by CO, structural materials can be provided to the BF 110 to ensure operational permeability and stability. Such structural materials can be inert (e.g., chemically compatible ceramic balls or the like) and recyclable during the process. In some embodiments, less reactive engineered carbon materials (unlike porous coke) can be provided, with the primary function of providing structure. If the CO concentration is high enough, carbon oxidation can be thermodynamically unfavorable.

[0085] In the first system mode, the second thermochemical reactor 170 operates in a reduction mode, where it receives nitrogen 161 and hydrogen 162 from the gas separator 160 and produces O2 by the reduction of thermochemical compounds. Nitrogen 161 is supplied as an inert carrier / purge gas to provide the low oxygen concentration necessary for the thermal reduction of BCNF1. Hydrogen can improve the degree of reduction of thermochemical compounds and increase the oxygen yield. The reduction product gas (RPG) 171 exiting the reactor 170 is not pure O2 but also contains N2 and H2O (water produced by the oxidation of hydrogen). The RPG 171 is supplied to the thermochemical reactor gas separator 180 to separate the O2 from the nitrogen and condense the water. Nitrogen 182 is recycled to the reactor 170, and O2 181 is stored in the O2 storage tank 190.

[0086] In this example, 50 Nm of oxygen 181 3More oxygen is produced from the gas separator 180 into the oxygen storage tank 190. Therefore, all of the oxygen 191 for the BOF 120 can be supplied from the oxygen storage tank 190, and the remaining oxygen 192 is available for sale. The oxygen can also be used for oxy-combustion in the BF hot stove.

[0087] 2, 2580 kg of BCNF1 is fed to each of reactors 130, 170. 1 kg of BCNF1 produces approximately 5.8 moles of CO in 24 hours. In embodiments where all of the CO used in the iron ore reduction comes from the gas input, the input of thermochemical compounds (e.g., BCNF1) in reactors 130, 170 can be adjusted accordingly.

[0088] The reactions in the first thermochemical reactor 130 and the second thermochemical reactor 170 cannot continue indefinitely. In the example of BCNF1 material, the production rates of oxygen and carbon monoxide decrease after approximately 24 hours. Regardless of the material used, at some point, enough of the thermochemical compounds in the reactors 130, 170 will react to cause the production rates to decrease. This point can be determined empirically, for example, based on a threshold production rate (or based on a predetermined period, such as 24 hours or any other predetermined time), based on the partial pressure of the gas (e.g., CO or O) detected in the OPG 131 and / or RPG 171. Once the appropriate time is reached, the controller 200 can reconfigure the system to operate in a second mode, in which the first reactor 130 is in a reduction mode and the second reactor 170 is in an oxidation mode.

[0089] Reconfiguring the system may involve opening and closing various control valves so that: i) the first reactor 130 receives nitrogen 161 and hydrogen 162 from the gas separator 160, the first reactor 130 supplies reduction product gas 171 to the gas separator 180, and receives recycled nitrogen 182 from the gas separator 180; and ii) the second reactor 170 receives CO2 163, 164 from the gas separator 160 and recycled CO2 142 from the gas separator 140, and the second reactor supplies 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 can be increased from the reduction temperature (700°C for BCNF1) to the oxidation temperature (800°C for BCNF1).

[0090] Oxygen may be bubbled through the BOF 120 for 15-20 minutes, with the liquid steel 125 and slag (not shown) being tapped approximately every 40 minutes.

[0091] A system such as the one illustrated in Figure 2 has the potential to reduce CO2 emissions by 94% compared to a typical BF-BOF, since all of the carbon monoxide is produced from carbon dioxide recovered from the blast furnace 110 and BOF 120, with the only emissions coming from the solid carbon source fed to the blast furnace 110. This 94% reduction assumes that the solid carbon source is charcoal, biomass, or plastic. If coke is used as the solid carbon source, the CO2 emission reduction is approximately 90% (still a significant reduction). Even greater reductions are possible in embodiments using only gas-phase CO2.

[0092] As noted above, embodiments are possible in which only a portion of the carbon monoxide is obtained by decomposition of carbon dioxide recovered from the blast furnace 110 and / or BOF 120. Even relatively small amounts of CO2 captured / converted to CO can provide some benefit.

[0093] The energy flow for the system shown in Figure 2 is shown schematically in Figure 3. Figure 3 includes the arrangement described with reference to Figure 2 and additionally includes a regenerative heat exchanger 105 and a recycle coke oven 175. The recycle coke oven 175 may be used if coke is produced locally at the BF 110 site; otherwise, an alternative heat source may be suitable.

[0094] Removing coke from the BF110 reduces the energy available to heat the BF110 to the required temperature. The reaction of coke with oxygen in the BF110 is an exothermic reaction that releases heat. A solid carbon source (e.g., 10% biomass-based charcoal added to the BF110 as an alternative carbon source) can aid in this, but additional heat, for example from an electric heater, may be required to reach the required temperature. To assist with this, the iron ore 101 can be preheated. Such electric heaters can be powered by renewable (solar, wind) and / or other low / zero carbon (nuclear) sources.

[0095] The process gas 102 may be preheated using heat 107 obtained from the top gas 111 and the BOF gas 121. If 90% of the energy is recovered using the regenerative heat exchanger 105, the top gas 111 and the BOF gas 121 may provide 2.7 GJ / tls and 0.8 GJ / tls, respectively. This heat 107 is transferred from the effluent gases 106 from the regenerative heat exchanger 105 (including both the top gas 111 and the BOF gas 121) before they are fed to the gas separator 160.

[0096] In a conventional BF-BOF, after thermal energy is extracted, the coke off-gas, BF furnace gas, and BOF gas are often combusted to generate the power required for the BF-BOF. The coke off-gas may not be present in some embodiments (if coke cannot be used). In some embodiments, the furnace gas and BOF gas are completely recycled through the TC reactor, and power generation from the coke off-gas is no longer possible. In some embodiments, at least some of the power may need to be derived from, for example, renewable (solar, wind) and / or zero / low carbon sources (nuclear).

[0097] This situation is not necessarily applicable to all embodiments. In some embodiments, a small proportion of the coke may be replaced by CO obtained by decomposition of CO from the top gas and / or BOF gas. In some embodiments, only a portion of the top gas and / or BOF gas may be recovered and recycled, leaving a portion available for combustion and power generation.

[0098] The carbon monoxide exiting the thermochemical reactor 130 is at the oxidation temperature for the thermochemical compound (800°C for BNCF). Depending on the chemical compound being used, this temperature can be a significant fraction (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 produced in the reduction reactor 170, as there is no need to heat the oxygen 181 before introduction into the BOF 120. Because CO is continuously used by the BF 110, the amount of CO storage can be small, allowing it to be stored at intermediate temperatures (e.g., about 500-800°C, or at least 50% of the blast temperature). Alternatively, CO can be stored under pressure at ambient temperature, and thermal energy can be stored separately (not shown) to heat the CO before addition to the blast 102.

[0099] Because heat is generated by the reaction of oxygen with iron carbide (FeC), BOF120 does not require additional heat or fuel.

[0100] Liquid steel 125 exits BOF 120 at above 1500° C. After steel 125 is cast into its final shape, some of the heat can be recovered for use in system 100.

[0101] In this embodiment, coke ovens are no longer needed to prepare coke, saving 1.1 GJ / tls of primary energy. Operating the thermochemical (TC) reactors 130, 170 requires approximately 2.2 GJ / tls. This means that when reaction conditions are switched, the power and electric heaters previously used to heat coal to 1250°C for 12 hours can be reused (if on-site) to maintain the temperature in the TC reactors 130, 170 and heat the thermochemical compounds from reduction temperatures (700°C for BNCF1) to oxidation temperatures (800°C for BCNF1). Therefore, an additional 1.1 GJ / tls of power, used to power the electric heaters, is likely required to operate the TC reactors.

[0102] If the electricity required to power the electric heater and gas separator is obtained from renewable sources or a nuclear power plant, this does not add to 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 savings from replacing coke in the system.

[0103] In the above exemplary embodiment, a BF-BOF system is considered. The present invention is also applicable to a BF-EAF system in which the BOF is replaced by an EAF. The EAF also produces flue gas that can be separated and recycled. CO2 present in the EAF flue gas can be decomposed to CO by a thermochemical reaction, and CO that may be present in the EAF flue gas can be separated. At least a portion of the CO from the EAF flue gas can be fed to the BF.

[0104] Similarly, features described with reference to the BF-BOF system above also pertain to systems with 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 may contain at least 80% (by volume) CO and H. At least a portion of the process gas may be formed using a thermochemical reactor according to embodiments. For example, a gas separator may be configured to receive top gas from the DRI furnace and supply CO to the thermochemical reactor, as described herein. A pair of thermochemical reactors may be used that cycle between producing carbon monoxide from carbon dioxide and producing oxygen by reducing thermochemical compounds. The thermochemical reactor may be used in addition to, or instead of, a reformer configured to receive at least a portion of the top gas and reform CO from the CO in the top gas.

[0105] In one embodiment, Ba2Ca 0.66 Nb 0.34 FeO6(BCNF1) can be synthesized by mixing stoichiometric amounts of 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 was calcined in air at 1000°C for 12 hours and then re-ground into a fine powder. In the following examples, the perovskite was used as both a powder and a 10 mm pellet. To form the powder, the calcined fine powder was sintered at 1400°C for 24 hours. For the pellets, the calcined powder was compressed into a 10 mm pellet at an isostatic pressure of 120 MPa for 1 minute and then similarly sintered.

[0106] In a practical scale thermochemical reactor, the thermochemical compound may be configured as a highly porous structure and may include at least one of thin plates, mm-scale rods, or balls. The thermochemical compound may be packed to provide good heat transfer, fluid flow, and large contact area, and / or may be fluidized by the through flow of gas.

[0107] To demonstrate the TC reactor containing BCNF1, 100 g of BCNF1 was synthesized and placed in a 25.4 mm (1 inch) reactor. Nitrogen gas was flowed through the reactor at 40 ml / min during the reduction at 700 °C for 24 hours. For the oxidation, the temperature was increased to 800 °C, and the gas flow was changed to CO2 at 40 ml / min. This was repeated for five thermochemical cycles. In the first cycle, hourly samples were collected from 0 to 11 hours and analyzed by gas chromatography (GC). In cycles 2 to 5, hourly gas samples were collected from 12 to 23 hours and analyzed by GC. A 10.1% conversion of CO2 to CO per cycle was observed throughout the five cycles.

[0108] Figure 4(a) shows the carbon monoxide yield of BCNF1 over time at different oxidation temperatures. It is clearly evident that 800 °C is the optimum temperature, showing significantly higher CO production than lower temperatures across all time ranges. As the temperature decreases, the CO production also decreases. Using the maximum CO production of 498 μmol / g (800 °C, 24 h) as the reference, the conversion rate (Xa) at each time point was calculated and shown in Figure 5(b). Plotting ln(ln(1-Xa)) against ln(t), where t is time (seconds), yields a Hancock and Sharpe plot (Figure 5). The slope m of the plot (inset in Figure 5) provides information about the type of redox reaction mechanism. For example, if m is less than 1, the reaction is diffusion-dominated. Since m is greater than 1 for all oxidation temperatures, the reaction is phase-boundary-dominated. Therefore, to better understand the oxidation reaction, we applied a linear approximation method for different phase-boundary-dominated mechanisms.

[0109] The reaction at 800°C is based on the zero-order model (R 2= 0.9905) was found to be the best fit, suggesting that the decomposition 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 favorable because it suggests that at this temperature the decomposition reaction will proceed at its maximum rate regardless of the extent of the reaction. The best fit for the reaction at 700°C is the Avrami-Erofeyev model (R 2 = 0.9912), where the degree of conversion is low at the beginning and end of the period but accelerates midway through the period. The reaction occurs at the same rate in all directions, and the rate of conversion is independent of the degree of conversion. For the reaction at 750°C, no good approximation could be found with any of the models tested. Therefore, for the purposes of constructing the Arrhenius plot, the reaction at 750°C is a 50 / 50 mix of zero-order and Avrami-Erofeyev4.

[0110] Figure 6(a) shows the reaction rate constants at each temperature obtained with the above model. The Arrhenius plot for the oxidation reaction is shown in Figure 6(b), indicating an activation energy (Ea) of 46.6 kJ / mol. This is compared to the oxidation reactions of similar materials in Table 2. The activation energy of BCNF1 is found to be lower than all lanthanum manganates (LSMOs) examined except for La0.625Ca0.375Mn0.5Cr0.5O3, suggesting that the CO2 decomposition reaction is more favorable for BCNF1 than for most LSMOs. This is demonstrated by the temperature required for the oxidation reaction, which is 800 °C compared to at least 1050 °C for LSMO. Compared to barium magnesium iron niobate, the activation energy decreases with increasing iron content. BaMg 0.33 Nb 0.5 Fe 0.17 O3 has a higher Ea than BCNF1, while BaMg 0.33 Nb 0.34 Fe 0.33 O3 has almost half the Ea of BCNF1, suggesting that the CO2 decomposition reaction in this perovskite may be even more favorable than BCNF1.

[0111] [Table 2] Table 2: Activation energies of oxidation reactions under CO2

[0112] Thermochemical reactors according to embodiments may comprise perovskite particles or porous structures of suitable characteristic sizes provided as a packed bed or a fluidized bed, where a packed bed allows the carbon dioxide to contact a large surface area of ​​the perovskite, and a fluidized bed may result in a higher degree of conversion due to enhanced solid and gas mixing, as well as heat and mass transfer.

[0113] The TC-BF and TC-BF-BOF systems proposed herein have the potential to contribute to the decarbonization of the steel and other production metallurgical industries both in the UK and around the world. As an example, there are five steel producers in the UK: Tata Steel and British Steel, which operate BF-BOF systems, and British Steel, Liberty Steels, and Outokumpu, which operate EAF systems. Of the 7.65 million tons of steel products produced annually in the UK, 6 million tons are made using the BF-BOF process. In the UK, BF-BOF therefore accounts for approximately 94% of the total emissions from the UK steel sector, based on an emissions intensity of 1.89 tCO2 eq / tls (tonnes of CO2 equivalent per tonne of liquid steel) for the BF-BOF process and 0.44 tCO2 eq / tls for the EAF process. EAFs can be more easily decarbonized by using renewable electricity and / or 100% recycled steel. On the other hand, decarbonising BF-BOF is more challenging due to the inherent carbon-intensive nature of the process. Decarbonising these is crucial for the UK to meet its net-zero emissions target by 2050 and more broadly to avoid problematic climate change, which is a global issue.

[0114] Tata Steel and British Steel both produce approximately 3 million tonnes of steel per year at their respective Port Talbot and Scunthorpe sites. Because production volumes are similar, the same TC-BF-BOF system can be used in both of the above examples, as described below. Using BCNF1 as an example of a TC compound, 42,500 tonnes of BCNF1 would be required to generate the 124 million moles of carbon monoxide per day needed to replace 90% of the coke, with the remaining 10% being replaced by a solid carbon source such as biomass-based charcoal. The TC compound could be split into 10 TC reactors, each 15 m high and 9.5 m in diameter, with five reactors performing reduction and five reactors performing oxidation at any given time. The raw material required to produce the required amount of BCNF1 would cost £210 million, which would require replacement approximately every 5–10 years. In addition to CO, these reactors would generate 1.3 million m³ per day. 3 of oxygen produced, of which 420,000 m 3 is required at the BOF. Excess oxygen production could yield 35,000 lb / day. Replacing 90% of the coke with CO would save 187 million lbs per year.

[0115] The estimated energy requirement for running the TC cycle of the exemplary embodiment is 3.6 TJ per reactor for a complete reduction and oxidation cycle over 48 hours. The reduction reaction uses 85% of this energy due to the high endothermic enthalpy of reduction of 620 kJ / kg, while the enthalpy of oxidation is exothermic and therefore releases energy (-45.1 kJ / kg). Implementing a TC-BF-BOF system requires an additional 2.2 GJ / tls, where a typical BF-BOF requires 19.8-31.2 GJ / tls. Here, surplus coke oven heat can be recycled to generate 1.1 GJ / tls of heat. As noted above, the furnace and BOF gases contain a large amount of energy. If 90% of this energy is recovered via a regenerative heat exchanger, this amounts to 3.5 GJ / tls, exceeding the energy usage of the TC system. Alternatively, if the TC reactor were to run on electricity alone, it would require 607 kWh / tls, at a cost of approximately £42 / tls. This is significantly less than hydrogen direct reduced iron (HDRI), which requires 3.72 MWh / tls. If this were derived from the UK electricity grid, which has an emission factor of 212 g CO2 eq / kWh, it would produce 129 kg CO2 eq / tls, equivalent to 6.9% of current emissions per tonne of liquid steel. From both economic and environmental perspectives, it is beneficial to use as high a proportion of renewable electricity and / or nuclear power as possible.

[0116] Importantly, implementation of the exemplary TC-BF-BOF system would reduce emissions from 5.7 million tCO2 eq to 340,000 tCO2 eq per site. Even without any emissions improvements at operating EAF plants, implementation of this system would reduce UK steel emissions by 88%, lowering the share of emissions from BF from 94% to 48%. Currently, the UK steel industry emits 12 million tCO2 eq out of a total of 369 million tCO2 eq for the UK as a whole, meaning that steel accounts for approximately 3.3% of UK emissions. Implementation of the TC-BF-BOF system at Tata Steel and British Steel plants would reduce the share of UK emissions from steel to 0.38%. Therefore, a 2.9% reduction in UK emissions would be achievable with a capital expenditure of approximately £720 million, with ongoing expenditure of approximately £400 million every 5–10 years to replace used BCNF1 material after it has deactivated. Furthermore, the implementation of this system will achieve significant reductions in operating costs, primarily through the replacement of expensive mill coal. The capital expenditure will be fully repaid by these savings in 22 months, resulting in total savings of £1.28 billion after five years. Any potential slight increase in electricity consumption due to the implementation of this system will be easily absorbed by these savings. The system will also reduce the production price of steel, making steel produced with this approach more competitive in the global market.

[0117] While the above examples relate to implementations such as those shown in FIG. 2, it should be understood that benefits are also obtained in embodiments in which a smaller proportion of the coke is replaced with CO obtained by TC decomposition of CO produced by the blast furnace and / or BOF.

[0118] Embodiments may have several advantages over other methods for decarbonizing the steel sector. First, embodiments may utilize existing BF-BOFs, which account for 70% of steel production, thereby preventing the creation of stranded assets. Given that the global transition to a net-zero economy will likely create stranded assets in several sectors that are not net-zero compatible, any system that minimizes stranded assets while achieving significant emissions reductions should be prioritized. Furthermore, the continued operation of BF-BOFs around the world ensures the preservation of highly skilled jobs and potentially creates new jobs for the management and operation of TC reactors. Second, emission reductions are immediately apparent once a TC-BF or TC-BF-BOF retrofit is implemented, rather than waiting years for the construction of a new DRI-EAF or the decarbonization of the power grid to realize emission reductions. This system can operate a nearly completely carbon-closed loop, where all CO2 produced in the BF or BOF is fed to the TC reactor and decomposed into more carbon monoxide for use in the BF. The system also generates a small but additional income from selling the excess oxygen produced in the TC reactors (equivalent to approximately £13 million per year for each of the two UK BF-BOF plants).

[0119] Another important factor is that TC-BOF or TC-BF-BOF is economically viable and potentially lowers the cost of producing steel than conventional BF-BOF, potentially saving up to £600 million per plant over five years. In addition to producing lower-cost steel, the steel produced can also be considered carbon-neutral, potentially adding significant value as companies and governments work to reduce operational emissions across a wide range of sectors. The emissions intensity of steel produced via TC-BF-BOF could be up to four times lower than that of DRI-EAF plants. Most importantly, implementing a TC-BF-BOF system does not preclude other efforts toward decarbonizing the sector, such as improving efficiency, using renewable electricity, increasing scrap recycling, or improving DRI-EAF methods. In fact, to maximize the reduction in emissions across the sector, the majority of the scrap can be used in the EAF (where 100% of the scrap can be used), and the remainder of the scrap is used in the TC-BF-BOF.

[0120] The present invention is not limited to the above-described embodiments, which may be modified in construction and detail, and the scope of the present invention should be determined with reference to the appended claims.

Claims

1. 1. A system for metal production comprising: a blast furnace configured to receive metal ore and blast gases and to discharge heated metal and blast furnace top gases; and a first thermochemical reactor configured to, in a first mode, receive at least a portion of the reduction furnace top gas, generate carbon monoxide from carbon dioxide in the portion of the reduction furnace top gas by oxidation of a thermochemical compound, and return at least a portion of the generated carbon monoxide to the reduction furnace; wherein the first thermochemical reactor is configured to, in a second mode, produce oxygen by reduction of the thermochemical compound; and 10. The system of claim 9, further comprising: a controller configured to switch or cycle between a first mode in which the first thermochemical reactor receives carbon dioxide from the blast furnace top gas and produces carbon monoxide by oxidation of the thermochemical compound, and a second mode in which the first thermochemical reactor produces oxygen by reduction of the thermochemical compound.

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

4. The system of any one of claims 1 to 3, wherein the thermochemical compound comprises a metal oxide, a perovskite material, or a dual perovskite material.

5. 5. The system of claim 1, further comprising a second thermochemical reactor, wherein in the first mode, the second thermochemical reactor produces oxygen by reduction of the thermochemical compounds, and in the second mode, the second thermochemical reactor receives carbon dioxide from the blast furnace top gas and produces carbon monoxide by oxidation of the thermochemical compounds.

6. 6. The system of any one of claims 1 to 5, further comprising a steel furnace configured to receive the heated metal from the blast furnace and the oxygen from the first thermochemical reactor and / or the second thermochemical reactor, and to discharge molten steel and steel furnace gases.

7. 7. The system of claim 6, including 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 reduction of the thermochemical compounds.

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

9. 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 returned carbon monoxide.

10. 10. The system of any one of claims 1 to 9, comprising a first thermochemical reactor gas separator configured to receive exhaust gas from the first thermochemical reactor in the first mode and separate carbon monoxide from the exhaust gas; and optionally a second thermochemical reactor gas separator configured to separate oxygen from the exhaust gas from the first thermochemical reactor in the second mode, including the subject matter of claim 7.

11. 11. The system of any one of claims 1 to 10, including the subject matter of claim 5, wherein the first thermochemical reactor and the second thermochemical reactor together are configured to provide at least 50% of the carbon monoxide used in the blast furnace to reduce the metal ore to heated metal.

12. 12. The system of claim 1, further comprising an electric blast furnace heater configured to heat the blast gas and / or the metal ore introduced into the blast furnace using electrical power.

13. 1. A method for producing steel comprising: reducing metal ores in a blast furnace to produce heated metal by reacting carbon monoxide with metal oxides, thereby producing carbon dioxide; supplying at least a portion of the carbon dioxide produced from the blast furnace to a first thermochemical reactor and producing carbon monoxide from the carbon dioxide by oxidation of a thermochemical compound; Returning at least a portion of the produced carbon monoxide to the blast furnace; and further producing oxygen by reduction of the thermochemical compound in the first thermochemical reactor, and switching or repeating between a first mode in which the thermochemical reactor receives carbon dioxide from the blast furnace top gas and produces carbon monoxide by oxidation of the thermochemical compound, and a second mode in which the first thermochemical reactor produces oxygen by reduction of the thermochemical compound. A method comprising:

14. 14. The method of claim 13, wherein the carbon dioxide from the blast furnace supplied to the first thermochemical reactor is obtained by separating carbon dioxide from blast furnace top gas produced by the blast furnace.

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

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

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

18. A method according to any one of claims 13 to 17, comprising receiving the heated metal and the oxygen from the thermochemical reactor at a steel furnace and discharging molten steel and steel furnace gases from the steel furnace.

19. 20. The method of claim 18, further comprising separating nitrogen from the reduction furnace top gas and supplying the nitrogen to the first thermochemical reactor and / or the second thermochemical reactor for reduction of the thermochemical compounds.

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

21. 21. The method of any one of claims 13 to 20, comprising using the first and second thermochemical reactors to provide at least 50% of the carbon monoxide used in the reduction furnace to reduce the metal ore to heated metal.

22. 22. The method of any one of claims 13 to 21, further comprising using electrical power to heat the process gas and / or the metal ore introduced into the reduction furnace.

23. The coke used as input to the reduction furnace is replaced with gas phase carbon monoxide obtained from the exhaust gas, thereby reducing the CO ２ 23. The method of any one of claims 13 to 22, comprising reducing emissions by at least 50%.

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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