Composite materials containing iron oxides and biomass

Abstract

The composite material is composed of a lignocellulose-based biomass having a moisture content of 5 to 10 weight% and an iron material comprising at least 30% iron oxides, and the molar ratio Fe / C of the composite material is 3 to 6.5.

Description

Technology Field

[0001] The present invention relates to a composite material comprising iron oxides and biomass, a method for manufacturing such a composite material, and a method for ironmaking using such a composite material. Background Technology

[0002] Steel can currently be manufactured on an industrial scale through two major production routes. Today, the most widely used manufacturing route involves producing pig iron in blast furnaces, 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 require sintering plants and coke plants for production, respectively, and these two plants are major sources of CO2 and, furthermore, pollutants worldwide.

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

[0004] To reduce its own environmental footprint, the steel industry is seeking solutions to manufacture iron and carbon-containing materials without requiring sintering and coking processes and to promote the use of renewable carbon materials. The problem to be solved

[0005] Therefore, there is a need for composite iron-carbon materials to be used in ironmaking or steelmaking with a reduced environmental footprint. means of solving the problem

[0006] This problem is solved by a composite material comprising a lignocellulose-based biomass having a moisture content of 5 to 10 weight% and an iron material comprising at least 30 weight% of iron oxides, wherein the molar ratio Fe / C of the composite material is 3 to 6.5.

[0007] The composite material of the present invention may also include the following optional features, which are considered individually or according to all possible technical combinations:

[0008] - The above iron material is selected from at least one of iron ore, direct reduction powder, oily mill sludge, iron mine tailings, electric arc furnace dust, and sintered powder.

[0009] - The biomass is selected from at least one of straw, miscanthus, waste wood, or sawdust.

[0010] - Composite materials are in the form of extruded pellets, and

[0011] - The composite material consists of 25% to 65% by weight of biomass and 35% to 75% by weight of iron material.

[0012] - The molar ratio Fe / C is 3 to 4.4,

[0013] - The molar ratio Fe / C is 4.5 to 5.9,

[0014] - The molar ratio Fe / C is 6.0 to 6.5.

[0015] The present invention also relates to a method for producing a composite material, comprising the steps of providing a lignocellulosic biomass having a moisture content of 5 to 10 weight%, providing an iron material comprising at least 30 weight% of iron oxides, mixing the biomass and the iron material in appropriate amounts to obtain a predetermined molar ratio of Fe / C in the range of 3 to 6.5, and aggregating the obtained mixture to form a composite material.

[0016] Other features and advantages of the present invention will become apparent from the description given below, which is non-limiting and illustrated with reference to the accompanying drawings. Brief explanation of the drawing

[0017] FIG. 1 illustrates a composite material according to the present invention in the form of pellets. Specific details for implementing the invention

[0018] The elements of the drawings are exemplary and may not be depicted to scale.

[0019] The pellets shown in FIG. 1 are made of a ferrous material comprising lignocellulose-based biomass having a moisture content of 5 to 10 weight% and at least 30 weight% of iron oxides, and the molar ratio Fe / C of the composite material is 3 to 6.5.

[0020] In this document, the term 'lignocellulose-based' is understood to mean any several closely related materials that are essentially composed of cellulose and hemicellulose in a lignin backbone. These lignocellulose-based biomass may be found in forestry products and byproducts, agricultural products and byproducts (including residues such as straw and bran waste from crop harvesting) and / or energy crops such as sorghum, switchgrass, and sugarcane (as sugarcane bagas).

[0021] These biomass materials are preferably selected from straw, miscanthus, sawdust, eucalyptus, apple bagas, or waste wood.

[0022] One advantage of using biomass is that it has a higher proportion of volatile matter (VM) compared to fossil carbon. VM is the component of coal / biomass that is driven off when it is rapidly heated without contact with air. The emitted gases are generally a mixture of short-chain and long-chain hydrocarbons, aromatic hydrocarbons, and sulfur. VM is the percentage of mass loss, adjusted for moisture, when coal is heated without contact with air under standard conditions.

[0023] The iron material containing at least 30 weight percent of iron oxides may be iron ore concentrate, direct reduction fines, oily mill sludge, iron mine tailings, electric arc furnace dust, sintered fines, or a mixture of any of these materials. The iron oxides may be hematite Fe2O3, magnetite Fe3O4, goethite FeO(OH), limonite FeO(OH)n(H2O), siderite FeCO3, or a mixture of such different oxides. In a preferred embodiment, the iron material is a low-quality material containing less than 67 weight percent of iron oxides.

[0024] The inventors discovered, surprisingly, that when such biomass materials having a specific moisture content are mixed with iron oxides without the use of any binders or additional fluxes, the resulting mixture is suitable for forming a composite material of the strength required for handling and transport. Furthermore, this composite material has been proven suitable for a direct reduction process having a percentage of metallization of at least 93%, compared to an average metallization rate of 92 to 95% for DRIs produced by existing technologies such as Midrex® or HYL®. The metallization rate of DRI is the degree of conversion of iron oxides to metallic iron during reduction. It is defined as the percentage of the mass of metallic iron divided by the total mass of iron.

[0025] A method for manufacturing such a composite material comprises the steps of supplying an iron material and biomass having a required moisture content, and preparing a mixture of the biomass and the iron material to obtain a predetermined ratio. The mixture is then aggregated to form a composite material. Aggregation is, for example, extrusion.

[0026] The molar ratio Fe / C of the composite material according to the present invention is set in the range of 3 to 6.5. If it is less than 3, the Fe / C ratio is too low to have a reducing effect. If it exceeds 6.5, the iron content will be excessively low for subsequent steelmaking and / or ironmaking steps.

[0027] The main role of carbon addition to composite materials is to have a reducing effect on iron oxides, which means that the Fe / C ratio is predetermined depending on the type of oxides present in the iron material, particularly containing at least 30 weight percent of iron oxides.

[0028] Different reduction reactions can be considered, and their general formula is as follows:

[0029] (1) FexOy + zC → x Fe + CzOy

[0030] In the case of hematite Fe2O3, the following reactions may occur:

[0031] (2) Fe2O3 + 3C → 2 Fe + 3CO

[0032] (3) Fe2O3 + 2C → 2 Fe + CO + CO2

[0033] (4) 2 Fe2O3 + 3C → 4 Fe + 3CO2

[0034] The molar ratio of Fe / C also depends on the subsequent use of the composite material. In fact, carbon can also be used for functions other than reducing iron oxides. In particular, when used in a direct reduction process performed in the solid state, this carbon can enrich the obtained DRI product. Such direct reduction can be carried out in a standard DRI furnace, such as a Midrex® or HYL® furnace, preferably operated with hydrogen as the reducing gas. The use of the composite material not only allows for providing carbon for reduction in such cases but also allows for increasing the carbon content of the resulting DRI product. In fact, one of the problems when operating with an H2 DRI process is that the resulting DRI product has a low carbon content, and this low carbon content can cause problems in subsequent stages of the steelmaking process.

[0035] This solid reduction is carried out by heating the composite materials to a temperature of 800°C to 1000°C, but without the use of any reducing gas, to remove carbon and oxygen by combustion and thus reduce iron oxides to metallic iron. In such cases, the molar ratio Fe / C can be customized so that the carbon of the composite material can also be used to provide heat to the process in addition to the reduction of iron oxides. This solid reduction can be carried out in a Rotary Hearth Furnace (RHF), preferably in an inert atmosphere. If the Fe / C ratio is selected solely to meet the requirements for the reduction reactions to occur, the heating energy required for this process can be provided by electric heating and not by the combustion of carbon.

[0036] This solid-state reduction process can be carried out at lower temperatures of 550 to 600°C to directly reduce magnetite to iron with the support of catalysts such as cobalt or nickel materials.

[0037] When added to an electric arc furnace (EAF), electric smelting furnace (ESF), immersion arc furnace (SAF), or oxygen bath smelting furnace (OSBF), briquettes produced by the method according to the present invention are melted alone or in combination with steel scrap and / or DRI products. If the briquettes are dense enough to reach the molten metal beneath the slag, the use of such briquettes allows, in particular, to provide carbon to the molten metal, which is essential for carburizing the molten metal and forms CO bubbles upon reaction with oxygen. These bubbles can agitate the bath and promote the reduction of impurities. If the composite material has a lower density and remains in the slag, due to its significant volatile content, such briquettes may also generate more gases than standard DRI, which will enhance slag foaming. Slag foaming is essential to the energy efficiency of the electric arc furnace.

[0038] The density of the composite material can be significantly adjusted by changing the molar ratio Fe / C.

[0039] An Fe / C molar ratio of 3 to 4.4 allows for the reduction of more iron oxides, and thus allows for a higher metallization yield to be achieved after reduction. This also allows for the production of reduced iron products with high carburization potential for subsequent steelmaking steps.

[0040] An Fe / C molar ratio of 4.5 to 5.9 means that the reduction output is lower compared to the previous ratio, but a high metallization yield can still be obtained through the participation of carbon.

[0041] An Fe / C molar ratio of 6.0 to 6.5 allows for an increase in the density of the composite and the density of the resulting reduced iron product, but the risk of re-oxidation during the reduction step is higher due to the generation of CO2.

[0042] The use of these composite materials in iron or steelmaking processes also allows for a reduction in the use of sintered ore and coke, thereby reducing emissions of NOx, SOx, and PAHs associated with sintering and coking plants. Furthermore, when used as a coke substitute, the use of these composite materials enables a reduction in the CO2 footprint of the steelmaking process by replacing fossil carbon with renewable carbon. Additionally, this allows for a reduction in the sulfur content of the molten metal produced as a result. Coke is produced from coal, which contains sulfur, and this sulfur remains in the coke and must be removed in specific desulfurization steps.

[0043] test

[0044] In the first example (Pellet 1), 2 kg of straw with 5 wt% moisture was mixed with 3 kg of Mount Wright iron ore, which is gangue containing 67 wt% iron oxides, the remainder being alumina, silica, phosphorus, and sulfur, and 90 wt% of the iron oxides being hematite. The mixture was extruded in a 7.5 kW extruder to produce composite extruded pellets with a diameter of 6 mm and a length of 30 mm. These composite pellets have an Fe / C molar ratio of 3.11. Analysis of these composites was performed, and the results are exemplified in Table 1.

[0045] Volatile matter is determined as a loss in mass, adjusted for moisture, when the sample is heated at 900 degrees Celsius for a time period of 7 minutes. This procedure is performed without contact with air under standardized conditions specified by the European standard EN15148-2009 ("Solid biofuels - Determination of the content of volatile matter").

[0046] The content of other components is indicated on a dry basis, which means that the moisture content of the analyzed material is excluded from the weight calculation. In this case, the pellets were heated to 105°C until a constant weight was observed, which means that all water evaporated prior to chemical analysis of the remaining components.

[0047]

[0048] Table 1

[0049] 1.68 kg dry weights of these pellets underwent a direct reduction step in the solid state, where the pellets were placed in an oven and heated to 1020°C at a heating lamp of 3°C / min under an inert atmosphere. This inert atmosphere was used to avoid the re-oxidation of iron, which is associated with small-scale testing. For the same process applied to composite materials exceeding 100 kilograms, re-oxidation is essentially prevented by the gases produced by the reduction reaction.

[0050] A dry standard of 1.06 kg of DRI with 74% Fe metal and 96% metallization was obtained.

[0051] In Example 2 (Pellet 2), a mixture comprising 60 wt% straw with a moisture content of 5 wt% and 40 wt% Mount Wright iron ore, comprising 67 wt% iron oxides, wherein 90 wt% of the iron oxides are hematite, was subjected to an extrusion step in a 7.5 kW pelletizer to produce composite extruded pellets having a diameter of 6 mm and a length of 30 mm. These composite pellets have an Fe / C molar ratio of 4.67. The obtained composite pellets underwent a direct reduction step in the solid state, where the extruded pellets were placed in a crucible and heated in an oven at 1000°C under an inert atmosphere with ramping of 350°C / hour to 1000°C and a dwelling time of 1 hour at 1000°C. The metallization rate of the produced DRI is 96%.

Claims

Claim 1 A composite material comprising a lignocellulose-based biomass having a moisture content of 5 to 10 weight% and an iron material comprising at least 30 weight% of iron oxides, wherein the molar ratio Fe / C of the composite material is 3 to 6.

5. Claim 2 In claim 1, the iron material is a composite material selected from at least one of iron ore, direct reduction fines, oily mill sludge, iron mine tailings, electric arc furnace dust, and sintered fines. Claim 3 In paragraph 1 or 2, the biomass is a composite material selected from at least one of straw, miscanthus, waste wood, or sawdust. Claim 4 A composite material according to any one of claims 1 to 3, wherein the composite material is in the form of extruded pellets. Claim 5 A composite material comprising 25% to 65% by weight of biomass and 35% to 75% by weight of iron material, in any one of claims 1 to 4. Claim 6 A composite material according to any one of claims 1 to 5, wherein the molar ratio Fe / C is 3 to 4.

4. Claim 7 A composite material according to any one of claims 1 to 5, wherein the molar ratio Fe / C is 4.5 to 5.

9. Claim 8 A composite material according to any one of claims 1 to 5, wherein the molar ratio Fe / C is 6.0 to 6.

5. Claim 9 A method for manufacturing a composite material according to any one of claims 1 to 8, comprising the following steps: a. providing a lignocellulosic biomass having a moisture content of 5 to 10 weight%; b. providing an iron material comprising at least 30 weight% of iron oxides; c. mixing the biomass and the iron material in appropriate amounts to obtain a predetermined molar ratio Fe / C in the range of 3 to 6.5; and d. aggregating the obtained mixture to form a composite material. Claim 10 A method for manufacturing a composite material, wherein the agglomerating step in paragraph 12 is an extrusion step.

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