Patent Application
20180320245
Production processes in the iron and steel industry involve the formation of large amounts of by-products that create waste streams governed by costly legal disposal requirements designed to prevent environmental pollution.
In an integrated iron and steel plant, one of the most important thermal operations is the sintering of raw iron ore. In a conventional sintering process, waste products from the iron making process (a mixture of iron bearing residues, such as blast furnace dust and filter cake, commonly referred to as “reverts”), are mixed with iron ores, coke breeze, and limestone to create a sinter blend composition. The sinter blend composition is then heated at high temperatures until it is sintered into a porous irregular shaped iron oxide—commonly known as a “sinter”—that is feedstock for a blast furnace used in the production of pig iron, and eventually the production of steel.
Conventional sinter blend compositions have some disadvantages. For example, the energy source for conventional sintering processes is the carbon contained in the sinter blend composition's coke breeze (dust and fines of coke). However, as a result of the rapid growth of the steel industry worldwide, coke breeze is becoming increasingly expensive and difficult to procure. Another issue with sinter blend compositions is that after the sintering process they generally must produce a sinter with an ISO 3271 tumble strength rating (“ISO tumble strength”) typically, greater than 72, that is capable of withstanding the rigors of the blast furnace iron-making process, which involves movement of the sinter on conveyor belts, and into shaft furnaces, under significant weight compression. Accordingly, not all iron making reverts are easily repurposed by incorporation into a sinter blend composition, in evaluating a typical sinter blend it may be necessary to estimate the total energy content of the sinter blend composition. Depending on the blend, any of the following energy sources may he present: coke breeze, component metallics and component carbon. If the combined energy content of the sinter blend composition is too high, excessive temperatures and slagging may develop during the sintering process.
Direct reduced iron (DRI), sometimes called sponge iron, is a commercial product widely used as a source material for making steel. The conventional techniques for making steel involve the use of an electric arc furnace (EAF) or a basic oxygen furnace (BOF). DRI is typically higher in iron units than taconite pellets and other sources of iron, and can be used as a partial substitute for scrap in the production of steel by EAF.
DRI is formed from beneficiated iron ore, such as taconite pellets. For example, taconite has been mined and crushed, and the iron containing portions magnetically separated from the non-iron containing portions to form a beneficiated product higher in iron content than mined taconite. The beneficiated iron ore portion may be formed into pellets by pelletizing, and heated in a linear hearth furnace in the presence of reducing agent (e.g., carbonaceous material) to a temperature below the melting point of iron using natural gas or coal, to promote the reduction of iron ore to metallic iron. DRI is typically above 90% metallic iron with the remainder gangue.
In the process to make DRI, the beneficiated and pelletized iron oxide containing material is moved through a furnace mixed with a reducing agent, such as coal, coke, or another for of carbonaceous material. A desulfurizing agent, such as limestone or dolomite, is also typically added. The carbon of the reducing agent and the oxygen of the iron oxide material react chemically in the reducing zone of the furnace, thereby partially reducing the iron oxide to form metallic iron. This, and other traditional reducing processes, are used to create the DRI.
DRI is difficult to transport because DRI and DRI fines are highly reactive with oxygen in air and moisture. Moisture, in particular, reacts with the iron forming FeO and H2. The DRI being sponge iron his many voids making it porous in nature. The porous nature of DRI also means that it has low compressive strength, and handling of DRI generates surface fines and dust. Additionally, when the DRI is stored, for example in the hold of a ship during transportation, some of the pellets have been prone to disintegrate under the weight of pellets above them further generating fines and small particles. The DRI lines and small particles increased the ability for reaction with moisture and oxygen around it. Additionally, the rough surface characteristics of the DRI pellets produce particulate matter and other fines having a high surface area, which also promoted the likelihood of the DRI reacting with oxygen. Such particulate matter and fines typically are produced throughout the storage and transportation of the DRI, making it difficult to transport DRI over long distances and to store DRI for long periods.
The porous, low internal strength, and flakey nature of DRI all increase the surface area of the nodule that is exposed to an oxidizing atmosphere and/or moisture, resulting in substantial and rapid oxidation and rusting. The reactions that occur during DRI oxidation produce heat and hydrogen making DRI susceptible to overheating and combustion. Increases in temperature in containers storing DRI, in which air is free to circulate, can reach 1200° F. Such combustion causes fires in the holds of ships during transportation of DRI and in the clam buckets of cranes when unloading DRI. These risks have substantially increased the cost of DRI delivered to a steel plant because of the losses during transportation and storage. Due to the difficulties and risks associated with transporting DRI, production of DRI has with a few exceptions been generally located near the steelmaking facilities and near the time of use in steelmaking, rather than in more economical locations and times. For these same reasons, the disposal of DRI fines and dusts is expensive and difficult.
While disposing of DRI reverts is expensive and environmentally challenging, it has now been determined that DRI fines and dust (DF blend) can be successfully repurposed by being incorporated and used as a replacement energy source to replace coke breeze in sinter blends. Accordingly, in cokeless sinter blends disclosed herein, the DRI reverts are used as a replacement fuel source for the coke breeze in the sintering process, while still producing sinter with an ISO tumble strength of at least 72. The cokeless sinter blends are inert, safe to transport, inexpensive to produce and provide sinter with the ISO tumble strength ratings necessary for use in conventional blast furnace iron-making processes.
As used herein, “cokeless” or “free of coke breeze” means no intentional addition of coke or coke breeze.
The invention described herein in multiple embodiments relates to sinter blend compositions for use in a sintering process that do not contain coke breeze (0.00% coke breeze), or contain only very small amounts of coke breeze. In particular, these sinter blend compositions are capable of repurposing a mixture of iron-making reverts, having high total and metallic iron levels that re-oxidize so as to become a replacement fuel source for the coke breeze typically used in sinter blend compositions for use in a sintering process, while still managing to produce a sinter with sufficient ISO tumble strengths.
In some embodiments, a sinter blend composition for use in a sintering process is a mixture of iron making reverts comprising a high metallic content blend, an oxide blend, a sludge blend, a dust blend, and a DF blend; wherein the sinter blend composition is free of coke breeze and is configured to produce a sinter with an ISO tumble strength of at least 72.
In some embodiments, a sinter blend composition for use in a sintering process is between 0.01% and 5.0% coke breeze and a mixture of iron making reverts, comprising a high metallic content blend, an oxide blend, a sludge blend, a dust blend, a DF blend; wherein the iron-making reverts contain, by weight, at least 10.0% metallic iron levels, and the sinter blend composition is configured to produce a sinter with an ISO tumble strength of at least 72.
Additional embodiments as well as the foregoing and other objects, features, and advantages of the examples will be apparent from the following more detailed descriptions of particular examples, as illustrated in the accompanying drawings wherein like reference numbers represent like parts of the examples.
In various embodiments, the inventive sinter blend compositions utilize a mixture of iron-making reverts such as DRI fines, dust and clarifier sludge, characterized by high metallic iron and total iron content levels in lieu of coke breeze, as the energy source in sinter blend compositions. In embodiments, the cokeless sinter blend composition may comprise a mixture of iron making reverts containing residues such as dust, fines and clarifier sludge resulting from the production of DRI and other additives that results—after the sintering process—in a sinter with an ISO tumble strength greater than 72.
Table 1 identifies the chemical compositions of various mixtures of iron-making reverts, which were tested as sinter blend compositions. Such test sinter blend compositions comprised various mixtures of iron-making reverts that included one or more of a high metallic content blend, oxide blend, sludge blend, dust blend, and DRI fines (hereafter, “DF blend”). Optionally, the sinter blend compositions also comprised additives such as limestone, silica sand, quick lime, and olivine. See Tables 1-4.
The component size distribution for the various blends is summarized in Table 2. The mixing and granulation processes employed in the production of the sinter blend compositions disclosed herein are conventional, and may include one or more of the addition of water to produce slurries, screening of blends to remove oversize pellets, and/or use of medium or high intensity mixing devices.
Disclosed herein is a cokeless sinter blend composition for use in a sintering process, which comprises a mixture of DRI making reverts. The DRI reverts may comprise one or more of a high metallic content blend, an oxide blend, a sludge blend, a dust blend, and a DF blend. In embodiments, the sinter blend composition may comprise only a mixture of iron-making reverts, be free of coke breeze, and be capable of producing a sinter with an ISO tumble strength of at least 72. In some embodiments, the quality of sinter produced from a coke free sinter blend composition may be characterized by having an ISO tumble strength of at least +6.35 mm: >75%; a reducibility of ISO 4695, R40: >1% and an [low temperature reduction-disintegration indices] ISO 4696, +6.36 mm: >66%. Unless otherwise indicated all compositions are given in weight percent.
In embodiments, the sinter blend composition may comprise between 38.0% and 44.0% high metallic content blend, between 27.0% and 34.0% oxide blend, between 4.0% and 8.0% sludge blend, between 0.5% and 4.5% dust blend and between 17.0% and 23.0% DF blend. The sinter blend composition may comprise, by weight, approximately 41.3% high metallic content blend, approximately 30.6% oxide blend, approximately 5.9% sludge blend, approximately 2.2% dust blend and approximately 20.0% DF blend.
In one embodiment, the sinter blend composition may comprise the composition, and corresponding characteristics, shown in Table 3. In embodiments, the cokeless sinter blend composition comprises, by weight, at least about 20.0% metallic iron. In embodiments, the cokeless sinter blend composition comprises 21.69% metallic iron, and 0.0% coke breeze, with a corresponding estimated mix chemical energy of 1.92 GJ/t. See Table 3 in case of a shortfall in the availability of DF Blend, the balance mix chemical energy may be met with the addition of low levels of coke breeze, as discussed infra. In embodiments, the cokeless sinter blend composition may additionally comprise one or more additives, including one or more of limestone, quick lime, olivine and silica sand.
40.74
39.62
42.27
1.04
0.87
0.97
1.15
In some embodiments, the sinter blend composition may be free (0.0%) of coke breeze (or other carbonaceous materials, including biomass) and comprise, by weight, between 33.0% and 40.0% high metallic content blend, between 25.0% and 30.0% oxide blend, between 0.0% and 5.0% sludge blend, between 0.0% and 2.2% dust blend, and between 14.0% and 18.0% DF blend, with the remainder comprising impurities and/or one or more fluxes in an amount necessary to meet target basicity, silica and MgO levels in sinter. In various embodiments, the fluxes may comprise one or more of limestone, dolo-stone, quick lime, hydrated lime, milk of lime, other calcareous materials, magnesite, olivine, serpentine, silica sand, or other such components known to persons of skill in the art. In one embodiment, the sinter blend composition may comprise between 10.00% and 14.00% limestone, between 0.50% and 4.00% quick lime, between 0.50% and 5.00% olivine and between 0.50% and 3.50% silica sand. In embodiments, the total iron metallics in the sinter blend may be less than or equal to 22.0%. In embodiments, the sinter blend compositions may be free of coke breeze and comprise, by weight, approximately 33.87% high metallic content blend, approximately 25.09% oxide blend, approximately 4.84% sludge blend, approximately 1.80% dust blend, approximately 16.40% DF blend, approximately 12.15% limestone, approximately 1.98% quick lime, approximately 2.56% olivine and approximately 1.31% silica sand, which resulted in sinter having an ISO tumble strength of between 79.2 and 83.9. See Table 3.
In embodiments, the chemical composition of the high metallic content blend of the sinter blend composition may comprise, at least, iron (Fe), silicon dioxide (SiO2), aluminum oxide (Al2O3), calcium oxide (CaO), magnesium oxide (MgO) and carbon (C). In embodiments, the high metallic content blend may comprise, by weight, between 68.0% and 74.0% total iron (FeTOT) levels, between 1.0% and 3% SiO2, between 0.05% and 2.0% Al2O3, between 0.50% and 2.50% CaO, between 0.05% and 1.50% MgO, and between 0.20% and 2.20% C, with the remainder being impurities. The high metallic content blend may also comprise, by weight, approximately 71.31% total iron (FeT0T) levels, approximately 1.89% SiO2, approximately 0.95% Al2O3, approximately 1.48% CaO, approximately 0.19% MgO, approximately 1.16% C, with the remainder being impurities.
In embodiments, the chemical composition of the oxide blend of the sinter blend composition may comprise, at least, iron (Fe), silicon dioxide (SiO2), aluminum oxide (Al2O3), calcium oxide (CaO), and magnesium oxide (MgO). In embodiments, the oxide blend may comprise, by weight, between 63.00% and 68.50% FeTOT, between 1.00% and 3.50% SiO2, between 0.50% and 2.50% Al2O3, between 0.05% and 2.00% CaO, and between 0.01% and 1.50% MgO, with the remainder being impurities. In embodiments, the oxide blend may comprise, by weight, approximately 66.34% FeT0T, approximately 2.28% SiO2, approximately 1.43% Al2O3, approximately 0.82% CaO, and approximately 0.03% MgO, with the remainder being impurities.
In embodiments, the chemical composition of the sludge blend of the sinter blend composition may comprise, at least, iron (Fe), silicon dioxide (SiO2), aluminum oxide (Al2O3), calcium oxide (CaO), magnesium oxide (MgO) and carbon (C). In embodiments, the sludge blend may comprise, by weight, between 53.00% and 59.00% total iron (FeTOT) levels, between 3.00% and 6.00% SiO2, between 0.50% and 3.00% Al2O3, between 8.00% and 12.00% CaO, between 0.05% and 2.00% MgO, and between 0.50% and 3.00% C, with the remainder being impurities. The sludge blend may also comprise, by weight, approximately 56.19% total iron (FeTOT) levels, approximately 4.34% SiO2, approximately 1.82% Al2O3, approximately 9.69% CaO, approximately 0.67% MgO, and approximately 1.92% C, with the remainder being impurities. In embodiments, the sludge blend may comprise between 10.0% and 20.0% water, or approximately 16.3% water.
In embodiments, the chemical composition of the dust blend of the sinter blend composition may comprise, at least, iron (Fe), silicon dioxide (SiO2), aluminum oxide (Al2O3), calcium oxide (CaO), magnesium oxide (MgO) and carbon (C). In embodiments, the dust blend may comprise, by weight, 76.00% and 82.00% total iron (FeTOT) levels, between 2.00% and 6.00% SiO2, between 1.00% and 3.50% Al2O3, between 5.00% and 9.500% CaO, between 0.05% and 1.50% MgO, and between 3.00% and 6.00% C, and the remainder impurities. The dust blend may also comprise, by weight, approximately 79.28% total iron (FeTOT) levels, approximately 4.05% SiO2, approximately 2.11% Al2O3, approximately 7.39% CaO, approximately 0.64% MgO, and approximately 4.59% C, with the remainder being impurities. In embodiments, the dust blend may comprise between 0.01% and 1.0% water, or approximately 0.3% water.
In embodiments, the chemical composition of the DF blend of the sinter blend composition may comprise, at least, iron (Fe), silicon dioxide (SiO2), aluminum oxide (Al2O3), calcium oxide (CaO), magnesium oxide (MgO ) and carbon (C). In embodiments, the DF blend may comprise, by weight, between 77.00% and 84.00% total iron (FeTOT) levels, between 1.00% and 5.00% SiO2, between 0.05% and 3.00% Al2O3, between 4.00% and 8.00% CaO, between 0.05% and 1.50% MgO, and between 4.00% and 8.50% C, with the remainder being impurities. The DF blend may also comprise, by weight, approximately 80.55% total iron (FeTOT) levels, approximately 2.99% SiO2, approximately 1.29% Al2O3, approximately 5.94% CaO, approximately 0.50% MgO, and approximately 6.41% C, with the remainder being impurities.
In still other embodiments, the sinter blend composition may comprise a mixture of iron-making reverts (including, at least, a DF blend) and coke breeze or other carbonaceous materials, including bio-mass. The relative relationship between the amount of metallics content to coke content is shown in
In embodiments, the high metallic content blend, an oxide blend, a sludge blend, a dust blend, DF blend and additives may additionally comprise varying levels of water (H2O).
indicates data missing or illegible when filed
Table 4 shows an exemplary cokeless sinter blend with return fines of 30% of wet mix that is fired to produce sinter. This composition comprises DRI reverts comprising, by weight, 33.87% high metallic content blend, 25.09% oxide blend, 4.84% sludge blend, 1.8% dust blend, 16.4% DF blend, and a calculated metallic blend percentage of 21.00%. The composition further comprises additives in the amount of 0.00% coke breeze, 12.15% limestone, 1.98% quick lime, 2.56% olivine and 1.31% silica sand.
Table 5 is an analysis of an exemplary cokeless sinter produced in accordance with the present invention, comprising, by weight, a total dry mix of metallics of 21.69%; a total dry mix flux of 18.00% with a mix moisture of 7.6%, a return fines weight percentage of 30% and an ISO tumble strength of 81.30.
In one embodiment, the sinter blend composition for use in a sintering process may comprise, by weight: 33.87% high metallic content blend, 25.09% oxide blend, 4.84% sludge blend, 1.8% dust blend, 16.4% DF blend, plus additives in the amount of 0.00% coke breeze, 12.15% limestone, 1.98% quick lime, 2.56% olivine and 1.31% silica sand; wherein the calculated metallics percentage is 21.69%, with a corresponding estimated mix chemical energy of 1.92 GJ/t, an ISO tumble strength of at least +6.35 mm 75%, a reducibility of ISO 4695, R40: >1%, and a low temperature reduction-disintegration indices ISO 4696, +6.36 mm: >66%.
In utilizing the sinter blend compositions disclosed herein, it can be appreciated that DRI reverts—that are effectively difficult and expensive to dispose of waste by-products—can be repurposed in a meaningful way to produce sinters with good quality mechanical properties (such as strong ISO tumble strength ratings), excellent transportation capabilities (because the DRI fines and dust have been rendered inert), and economical (because the expensive coke breeze has been replaced with waste materials).
While it has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made, and that combinations and equivalents of the above-described sinter blend composition component features may be combinable with other features, and may otherwise be substituted, re-arranged, and claimed in different ways without departing from scope. In addition, many modifications may be made to adapt a particular situation or material to the teachings without departing from its scope. Therefore, it is intended that it not be limited to the particular embodiments disclosed, but that it will include all embodiments falling within the scope of the detailed description and appended claims.
This application claims priority to, and the benefit of, U.S. Provisional Application No. 62/501,161 filed on May 4, 2017 with the United States Patent Office, which is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62501161 | May 2017 | US |
