Method of producing a composite compact and related composite compact

Abstract

A method of producing a composite briquette, comprising the steps of: providing biochar (2) and an iron material (1) comprising at least 30% iron oxides; mixing the biochar (2) and the iron material (1) in appropriate amounts to obtain a predefined Fe / C molar ratio in the range of 3 to 6.5; and briquetting the obtained mixture to form a composite briquette (6).

Description

Technical Field

[0001] This invention relates to a method for producing composite material briquettes comprising iron oxide and biochar, and the uses of such briquettes. Background Technology

[0002] Currently, steel can be produced on an industrial scale via two main manufacturing routes. The most common route today involves producing pig iron in a blast furnace, a process that relies on two main raw materials: sintered iron ore to be reduced and coke as a reducing agent. These two raw materials are produced in sintering plants and coking plants, respectively, both of which are significant sources of CO2 and, more broadly, pollutants.

[0003] An alternative route involves the direct reduction of iron ore in the solid state using carbon monoxide and hydrogen derived from natural gas or coal. This direct reduction process also requires fossil-based carbon and is a source of CO2 emissions.

[0004] In order to reduce its environmental footprint, the steel industry is looking for solutions to produce iron and carbon-containing materials without sintering and coking processes, and to promote the use of renewable carbon materials.

[0005] Therefore, there is a need for methods to produce composite iron-carbon materials for ironmaking or steelmaking that have a reduced environmental footprint. Summary of the Invention

[0006] This problem is solved by a method according to the invention, which includes the following steps: providing biochar and an iron material containing at least 30% iron oxide; mixing the biochar and the iron material in appropriate amounts to obtain a predefined Fe / C molar ratio in the range of 3 to 6.5; and pressing the obtained mixture into a composite material briquette.

[0007] The method of the present invention may also include the following optional features, either individually or according to all possible combinations of techniques:

[0008] - The iron material is selected from at least one of the following: iron ore, iron oxide concentrate, direct reduction fine powder, oily steel rolling sludge, iron ore tailings, electric arc furnace dust, and sintering fine powder.

[0009] The mixing step also includes adding a binder to the biochar and the iron material.

[0010] The method also includes a preliminary step of pyrolyzing biomass to produce biochar, biogas, and pyrolysis oil, and then providing the biochar in step A.

[0011] - This biomass is lignocellulose biomass.

[0012] - The lignocellulose biomass is selected from wheat straw, miscanthus, sawdust, eucalyptus, apple pomace, or waste wood.

[0013] - The adhesive contains pyrolytic oil.

[0014] - The Fe / C ratio is 3 to 4.4.

[0015] - The Fe / C ratio is 4.5 to 5.9.

[0016] - The Fe / C ratio is 6.0 to 6.5.

[0017] - Before step A, the biochar undergoes a crushing step.

[0018] - The biochar is provided with 90% of the particles having a size of less than 3 mm.

[0019] The present invention also relates to a briquette consisting of biochar and an iron material comprising at least 30% by weight of iron oxide, wherein the amount of biochar and iron material in the briquette is such that the Fe / C molar ratio of the briquette is 3 to 6.5. Attached Figure Description

[0020] Other features and advantages of the invention will become apparent from the following description, which is given by way of indication and not limitation, with reference to the accompanying drawings, in which:

[0021] - Figure 1 A method for producing briquettes according to the present invention is shown.

[0022] - Figure 2 Another embodiment of the method according to the invention is shown.

[0023] - Figure 3 Images are of solidified slag samples produced in steelmaking processes without specific additives.

[0024] - Figure 4 Images are of solidified slag samples produced in a steelmaking process including the addition of composite material briquettes according to the invention.

[0025] The components in the attached diagram are schematic and may not be drawn to scale. Detailed Implementation

[0026] In such Figure 1 In the method shown, iron material 1 containing at least 30% by weight of iron oxide and biochar 2 are fed together into the hopper 3 of the briquetting machine 4.

[0027] The amount of each material loaded into the hopper depends on a predefined Fe / C molar ratio in the range of 3 to 6.5.

[0028] The mixture of iron material 1 and biochar 2 is then forced through the gap between two cylindrical rollers 5 that rotate horizontally in opposite directions around parallel axes. The two rollers are arranged such that a small gap exists between them, and this gap depends on factors such as the type of mixture, particle size, moisture content, and optional binder addition. The mixture is then pressed into a mold to form a briquette 6, which exits from the exit side of the rollers. The type of rollers or mold used determines the shape of the briquette 6. A roller press is described in this embodiment, but other briquetting techniques may also be used.

[0029] The iron material containing at least 30% by weight of iron oxide can be iron ore, iron oxide concentrate, direct reduction fine powder, oily steel rolling sludge, iron ore tailings, electric arc furnace dust, sintering fine powder, or a mixture of any of these materials. The iron oxide can be hematite Fe2O3, magnetite Fe3O4, goethite FeO(OH), limonite FeO(OH)n(H2O), siderite FeCO3, or a mixture of these different oxides. In a preferred embodiment, the iron material is a low-quality material containing less than 67% by weight of iron oxide.

[0030] Biochar refers to charcoal produced through the pyrolysis of biomass under anaerobic conditions. Biomass is a renewable organic material derived from plants and animals. Biomass sources used for energy include wood and wood processing waste—firewood, wood pellets, and sawdust; sawdust and waste from wood and furniture factories; and black liquor from pulp and paper mills; agricultural crops and waste—corn, soybeans, sugarcane, switchgrass, woody plants, and algae; and agricultural and food processing residues; biomaterials in municipal solid waste paper, cotton, and wool products; as well as food, yard, and wood waste, and animal manure and human sewage.

[0031] In a preferred embodiment, the biomass is lignocellulose biomass. The term "lignocellulose" is understood herein to mean any of several closely related substances that consist essentially of cellulose and hemicellulose in a lignin skeleton. Such lignocellulose biomass can be found in forestry products and byproducts, agricultural products and byproducts (including residues such as straw and husk waste from harvested crops), and / or energy crops such as sorghum, switchgrass, and sugarcane (as bagasse).

[0032] The biomass material is preferably selected from wheat straw, miscanthus, sawdust, eucalyptus, apple pomace, or waste wood.

[0033] Preferably, the biochar is supplied with a particle size of 90% less than 3 mm (90% < 3 mm). This allows the biochar to have a uniform distribution within the briquetting machine. To achieve this particle size, a crushing step can be performed on the biochar before it is fed to the briquetting machine 4.

[0034] In another embodiment of the invention, such as Figure 2 As shown, biomass 10 is pyrolyzed in pyrolysis reactor 11. This pyrolysis of biomass produces biochar 2, biogas 12, and pyrolysis oil 13. The pyrolysis oil 13 is used at least partially as a binder in the briquetting process of biochar 2 and iron material 1. Figure 1 All features described in the embodiments are applicable Figure 2 An example is provided. When the mixture of materials to be agglomerated does not have sufficient compressive and impact resistance after agglomeration, a binder is added to the mixture.

[0035] Using pyrolysis oil 13 as a binder allows for the recovery of byproducts from the pyrolysis process, thereby further reducing the overall environmental footprint of the process. Pyrolysis oil 13 is preferably derived from the production of biochar used in the mixture, but may also be derived from other biochar production depending on availability.

[0036] In all the previously mentioned embodiments, the amount of each material to be loaded into hopper 3 depends on the predefined Fe / C molar ratio to be obtained.

[0037] The Fe / C molar ratio of the briquettes produced using the method according to the invention is set in the range of 3 to 6.5. Below 3, the Fe / C ratio will be too low to produce a reduction effect. Above 6.5, the iron content will be too low for subsequent steelmaking and / or ironmaking steps.

[0038] The main purpose of adding carbon to the briquettes is to reduce iron oxides, which means that the Fe / C ratio is specifically predefined based on the type of oxides present in iron materials containing at least 30% iron oxides.

[0039] Different reduction reactions may occur, and their general expression is:

[0040] (1) FexOy + zC → xFe + CzOy

[0041] For hematite Fe2O3, the following reaction may occur:

[0042] (2) Fe2O3 + 3C → 2Fe + 3CO

[0043] (3) Fe2O3 + 2C → 2Fe + CO + CO2

[0044] (4) 2Fe2O3 + 3C → 4Fe + 3CO2

[0045] The Fe / C molar ratio also depends on the subsequent use of the briquettes. In fact, carbon can be used for purposes other than reducing iron oxides. Specifically, when used in a solid state in the direct reduction step, such carbon can enrich the resulting DRI product. Such direct reduction can be carried out in standard DRI furnaces such as Midrex® or HYL® furnaces, preferably using hydrogen as the reducing gas. In this case, the use of briquettes not only allows for the supply of carbon for reduction but also increases the carbon content of the resulting DRI product. In fact, one of the problems when operating with the H2 DRI process is that the resulting DRI product will have a low carbon content, which can cause problems in subsequent steps of the steelmaking process.

[0046] This solid reduction can also be carried out without the use of any reducing gas, by heating the briquettes to a temperature of 800°C to 1000°C to burn off the carbon and oxygen, thereby reducing iron oxide to metallic iron. In this case, the Fe / C molar ratio can be adjusted so that the carbon in the briquettes, in addition to being used to reduce the iron oxide, can also provide heat for the process. This solid reduction can be carried out in a rotary hearth furnace (RHF), preferably in an inert atmosphere. If the Fe / C ratio is chosen solely to meet the requirements for the reduction reaction, the heating energy required to drive the process can be provided by electric heating, rather than by the combustion of carbon.

[0047] This solid-state reduction process can be carried out at lower temperatures of 550°C to 600°C to directly reduce magnetite to iron with the aid of catalysts such as cobalt or nickel.

[0048] When added to an electric arc furnace (EAF), electric melting furnace (ESF), submerged arc furnace (SAF), or oxygen bath melting furnace (OSBF), the briquettes produced according to the method of the invention will melt alone or in combination with scrap steel and / or DRI products. If the briquettes are dense enough to reach the molten metal beneath the slag, using these briquettes will particularly allow the supply of carbon to the melt, which is essential for carburizing molten metal, and forms CO bubbles by reacting with oxygen. These bubbles can stir the molten pool and promote the reduction of impurities. If the composite material has a low density and remains in the slag, the briquettes can also generate more gas than standard DRI due to their significant volatile matter content, which will enhance slag foaming. Slag foaming is essential for the energy efficiency of electric arc furnaces.

[0049] The density of the briquettes can be specifically adjusted by changing the Fe / C molar ratio.

[0050] A Fe / C molar ratio of 3 to 4.4 allows for the reduction of more iron oxides, resulting in higher metallization yields after reduction. Furthermore, this allows for the production of reduced iron products with high carburizing potential for subsequent steelmaking steps.

[0051] A Fe / C molar ratio of 4.5 to 5.9 means a lower reduction output than the previous ratio, but a high metallization yield can still be obtained due to the involvement of carbon.

[0052] A Fe / C molar ratio of 6.0 to 6.5 allows for an increase in the density of the briquettes, thereby increasing the density of the resulting reduced iron product, but also presents a higher risk of re-oxidation during the reduction step due to the generation of CO2.

[0053] The use of briquettes produced using the method according to the invention in ironmaking or steelmaking processes also allows for a reduction in the use of sinter and coke, thereby reducing NOx, SOx, and PAH emissions associated with sintering and coking plants. Furthermore, when used as a coke substitute, the use of this composite material makes it possible to reduce the CO2 footprint of steelmaking processes by replacing fossil carbon with renewable carbon. It also allows for a reduction in the sulfur content of the resulting molten metal. Coke is made from coal, which contains sulfur, which is retained in the coke and must be removed in a special desulfurization step.

[0054] test

[0055] In the first example, biochar crushed to a particle size of less than 3 mm (90% < 3 mm) was mixed with fine-grained (< 1 mm) iron ore concentrate containing 65.8 wt% iron oxide (94 wt% of which was Fe2O3) and an organic bio-binder. Straw pellets, used as biomass material, were pyrolyzed to produce biochar. Pyrolysis oil from beech wood pyrolysis was mixed with 15 wt% expanded polystyrene (EPS) to produce the organic bio-binder. The Fe / C molar ratio was set to 3.11.

[0056] The material mixture containing 15 wt% bio-binder, 19.55 wt% biochar and 65.45 wt% iron was compacted at a pressure of 1.3 t / cm² to obtain a coarse composite material briquette with dimensions of 45×55×35 mm and a weight of 100 g. The briquettes were then analyzed to determine their mechanical properties.

[0057] The briquette has a compressive strength of 1600 N and an apparent density of 1.80 g / cm³. 3 This strength is sufficient to handle and load briquettes in subsequent ironmaking / steelmaking steps.

[0058] Experiment A – Direct Reduction

[0059] These 1.68 kg dry-based pellets were subjected to a direct reduction step in a solid state, wherein the pellets were placed in an oven and heated to 1020 °C at a heating rate of 3 °C / min under an inert atmosphere. The inert atmosphere was added to prevent re-oxidation of iron, which is relevant to the small scale of the experiment. For the same process applied to more than one hundred kg of composite material, this inertization would be inherently generated by the gases produced by the reduction reaction.

[0060] After 3 hours at 1020°C, 1.06 kg of dry-basis DRI was obtained, which had 74% metallic Fe and a metallization rate of 97%. The metallization rate of DRI is the degree to which iron oxides are converted into metallic iron during reduction. It is defined as the percentage of the mass of metallic iron divided by the mass of total iron.

[0061] Experiment B – Smelting

[0062] These 360 ​​kg briquettes were loaded into a 6-ton melting furnace. The briquettes were able to penetrate the slag layer and descend into the molten metal pool. A carburizing yield of 38% to 49% was observed for the briquettes according to the invention, compared to 21% for the addition of coke. Furthermore, as... Figure 3 and Figure 4 As shown, strong slag foaming was observed during the briquetting test compared to when no specific additives were used. Figure 3 The image shows a sample of solidified slag without any additives. Figure 4 Images are of solidified slag samples obtained by loading briquettes produced using the method according to the invention. It can be observed that the second slag sample has a higher porosity, which is due to foaming.

Claims

1. A method for producing composite material briquettes, comprising the following steps: A. Provide biochar (2) and iron material (1) containing at least 30% by weight of iron oxide; B. The biochar (2) and the iron material (1) are mixed in appropriate amounts to obtain a predefined Fe / C molar ratio in the range of 3 to 6.5; C. Press the obtained mixture into a composite material block (6).

2. The method according to claim 1, wherein, The iron material (1) is selected from at least one of iron ore, iron oxide concentrate, direct reduction fine powder, oil-containing steel rolling sludge, iron ore tailings, electric arc furnace dust and sintering fine powder.

3. The method according to any one of claims 1 or 2, wherein, The mixing step further includes adding a binder to the biochar (2) and the iron material (1).

4. The method according to any one of claims 1 to 3, comprising a preliminary step of pyrolyzing biomass (10) to produce biochar (2), biogas (12) and pyrolysis oil (13), and then providing said biochar (2) in step A.

5. The method according to claim 4, wherein, The biomass (10) is lignocellulose biomass.

6. The method according to claim 5, wherein, The lignocellulose biomass (10) is selected from wheat straw, miscanthus, sawdust, eucalyptus, apple pomace or waste wood.

7. The method according to any one of claims 4 to 6 in conjunction with claim 3, wherein, The binder contains pyrolysis oil (13).

8. The method according to any one of claims 1 to 7, wherein, The Fe / C ratio is 3 to 4.

4.

9. The method according to any one of claims 1 to 7, wherein, The Fe / C ratio is 4.5 to 5.

9.

10. The method according to any one of claims 1 to 7, wherein, The Fe / C ratio is 6.0 to 6.

5.

11. The method according to any one of the preceding claims, wherein, Before step A, the biochar is crushed.

12. The method according to any one of the preceding claims, wherein, The biochar is provided with 90% of the particles having a particle size of less than 3 mm.

13. A briquette comprising biochar and an iron material containing at least 30% by weight of iron oxide, wherein the amounts of biochar and iron material in the briquette are such that the Fe / C molar ratio of the briquette is 3 to 6.

5.

14. The pressing block according to claim 13, wherein, The Fe / C molar ratio of the compressed block is 3 to 4.

4.

15. The pressing block according to claim 13, wherein, The Fe / C molar ratio of the compressed block is 4.5 to 5.

9.

16. The pressing block according to claim 13, wherein, The Fe / C molar ratio of the compressed block is 6.0 to 6.5.

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