Method for manufacturing sintered ore

Abstract

The present invention provides a method for producing sintered ore that can reduce carbon dioxide emissions from the sintering machine. [Solution] The present invention is a method for producing sintered ore using a Dwightroid sintering machine, which uses a granulation raw material that is a mixture of powdered iron ore, a solvent for adjusting the composition, return ore, and carbon material, wherein the CaO-based auxiliary raw material among the solvent for adjusting the composition is blended into the granulation raw material such that the total amount is CaO-based decarboxylation raw material such as quicklime, slaked lime, lightly calcined dolomite, or digested dolomite, which are derived from CaO-based rock raw materials such as limestone or dolomite, or such that the simple sum of the CaO mass equivalent value and the CaO·MgO mass equivalent value exceeds that of the CaO-based rock raw material.

Description

Technical Field

[0001] The present invention relates to a method for producing sintered ore, and particularly to a method for producing sintered ore capable of suppressing the amount of carbon dioxide emissions from a sintering machine.

Background Art

[0002] The production of sintered ore using a downward suction type sintering machine such as a Dwight Lloyd type sintering machine in a steelworks is carried out as follows. The sintering raw material is formed by blending an iron-containing raw material (also referred to as powdered iron ores) such as iron ore as the main raw material and iron dust generated in the steelmaking process, a subsidiary raw material (also referred to as a flux for component adjustment) such as limestone and silica required for the sintering reaction, and a carbonaceous material such as coke powder as a heat source. The subsidiary raw material is not only used to adjust the sinterability of the sintered ore, but also used to increase the fluidity of the slag in the blast furnace by making the subsidiary raw material a gangue component of the sintered ore and a source of the blast furnace slag.

[0003] Before the sintering raw material is charged into the downward suction type sintering machine, it is mixed and granulated while adding water using a mixing and granulating machine such as a drum type mixer, and mainly made into pseudo-particles composed of core particles having a particle size of 1 mm or more and adhering powder having a particle size of 0.5 mm or less adhering to the periphery thereof. Thereby, after charging into the sintering machine, the air permeability in the raw material filling layer formed in the sintering pallet can be maintained, the sintering reaction of the sintering raw material can be promoted, and high productivity can be ensured. Note that the sintering raw material may be referred to as a granulation raw material before granulation.

[0004] The pseudo-particle formed sintering raw material is charged into the sintering pallet in the feeding section of the sintering machine to form a raw material filling layer. Then, in the ignition furnace, the coke powder on its surface is ignited, and by sucking air into the lower layer of the sintering machine, the combustion point (also referred to as the combustion zone) of the coke powder is moved downward.

[0005] The sintering reaction proceeds sequentially from the top to the bottom of the raw material packing bed due to the heat of combustion, and sintering is completed by the time the sintering pallet moves and reaches the ore discharge section. After the sintered cake (lump) in the sintering pallet is discharged from the ore discharge section, it is crushed to produce sintered ore of a predetermined particle size for the blast furnace. Sintered ore powder with a particle size smaller than the predetermined particle size for the blast furnace, which is generated during the production of sintered ore, is mixed into the sintering raw materials as return ore and sintered again.

[0006] Reducing carbon dioxide emissions is an urgent issue from the perspective of preventing global warming, and the steel industry is also developing technologies to reduce carbon dioxide emissions. Methods for reducing carbon dioxide emissions include (x) reducing the amount of carbon in the input, (y) capturing carbon dioxide in the output, and (z) replacing conventional coal, oil, etc. with carbon-free carbon sources.

[0007] As described above, conventional downward-suction sintering machines, such as the Dwight-Royd sintering machine, use large amounts of coal (anthracite) or powdered coke as carbonizing material, thus generating large amounts of carbon dioxide. However, since the carbonizing material used here is an essential raw material as a heat source for the sintering reaction that occurs at high temperatures, reducing the amount of carbon in the input (x) above was not an easy way to reduce carbon dioxide emissions.

[0008] In relation to (y) above, common industrial and large-scale methods for removing carbon dioxide emitted from sintering machines include chemical absorption, physical adsorption, and cryogenic separation. Patent Document 1 discloses a method for separating and recovering carbon dioxide from by-product gases generated at steel mills using the chemical absorption method. According to the document, by-product gases such as blast furnace gas generated at steel mills have a high carbon dioxide concentration of over 20% to over 30%, unlike exhaust gases from the combustion of fossil fuels. Therefore, when separating and recovering carbon dioxide using the chemical absorption method, the equipment can be made significantly smaller compared to thermal power plants.

[0009] Furthermore, Patent Document 2 discloses an invention in which, as a carbon material to be blended into the sintering raw material, oil palm kernel shell char is used, which is obtained by carbonizing oil palm kernel shells, a biomass, by dry distillation. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2004-292298 [Patent Document 2] Japanese Patent Publication No. 2013-237876 [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] Incidentally, the sintering reaction is ignited on the surface of the raw material packed layer on the sintering pallet and moves from the surface to the lower layers as air is drawn in from below. Since it occurs in a combustion zone that is only a very small part of the entire raw material packed layer, the carbon dioxide concentration in the exhaust gas of the sintering machine is low, less than 10%. For this reason, applying conventional industrial methods described in Patent Document 1, which are based on the recovery of high concentrations of carbon dioxide gas of 15% or more, to the recovery of carbon dioxide from the exhaust gas generated by the sintering machine is inefficient and would require large-scale recovery equipment, making it impractical.

[0012] Furthermore, while the invention described in Patent Document 2, which uses carbon-free carbon material for sintering, is a promising technology for reducing carbon dioxide emissions in the steel industry, the demand for biomass-derived carbon material is increasing globally across all industrial sectors, and the development of alternative methods is also required.

[0013] Therefore, the present invention aims to provide a method for producing sintered ore that can suppress carbon dioxide emissions from a sintering machine. [Means for solving the problem]

[0014] [1] A method for producing sintered ore using a Dwightroid sintering machine, comprising granulation raw materials blended with powdered iron ore, a solvent for adjusting the composition, return ore, and carbon material, (A) Among the solvents for adjusting the components, as a CaO-based auxiliary material, (a) limestone; (a1) Quicklime, and, (a2) Slaked lime, Each of the raw materials is considered to be a blended raw material that can be equivalently substituted for the others in terms of CaO mass, (b) Dolomite, (b1) Lightly calcined dolomite, and (b2) Digestive dolomite, Each of these raw materials is considered to be a blended raw material that can be equivalently substituted for the others in terms of CaO·MgO mass, (B) The CaO-based auxiliary raw material, (a) The limestone and, (b) The dolomite, A CaO-based rock raw material consisting of one or two of the following blended raw materials, (a1) The quicklime mentioned above, (a2) the slaked lime; (b1) The light-calcined dolomite and, (b2) The digested dolomite, A CaO-based decarboxylation raw material consisting of one or more of the following blended raw materials, When classifying, (C) The CaO-based auxiliary raw materials are (c1) The entire amount consists of the CaO-based decarboxylation raw material, or (c2) When the CaO-based rock raw material or the CaO-based decarboxylated raw material is simply summed up, the CaO mass equivalent value and the CaO·MgO mass equivalent value of the constituent blended raw materials are such that the simple sum of the CaO-based decarboxylated raw material exceeds the simple sum of the CaO-based rock raw material. A method for producing sintered ore, wherein the aforementioned blending raw materials are prepared.

[0015] [2] The carbon material blended into the granulation raw material includes: The CaO-based decarboxylation raw material comprises, (a1) the quicklime, (a2) the slaked lime, (b1) the lightly burned dolomite, and (b2) the slaked dolomite, do not include the amount of carbonaceous material that generates heat equivalent to the reaction heat required in the decarbonation reaction from (a) the limestone or (b) the dolomite as the raw material for each production, and the method for producing sintered ore according to [1].

[0016] [3] Constituting the CaO-based decarbonation raw material, (a1) the quicklime, (a2) the slaked lime, (b1) the lightly burned dolomite, and (b2) the slaked dolomite, are those in which all or part of the carbon dioxide generated in the decarbonation reaction from (a) the limestone or (b) the dolomite as the raw material for each production is recovered, and the method for producing sintered ore according to [1] or [2].

Advantages of the Invention

[0017] According to the present invention, since the CaO-based decarbonation raw material as the CaO-based auxiliary raw material is formulated so that the total simple sum value of the mass conversion values of CaO and CaO·MgO contained exceeds the total amount or is compared with the CaO-based rock raw material, the CO2 emissions in the sintering machine can be significantly reduced compared to the conventional method. Further, according to the present invention, by changing the CaO-based auxiliary raw material from a CaO-based rock raw material such as limestone to a CaO-based decarbonation raw material such as quicklime, the carbonaceous material corresponding to the heat required for the decarbonation reaction in the sintering machine becomes unnecessary, and the CO2 emissions in the sintering machine can be further reduced. Further, according to the present invention, by changing the CO2 recovery process generated in the decarbonation reaction of limestone or the like from the sintering process with a low CO2 concentration in the exhaust gas to the firing process of limestone or the like where it is easy to increase the CO2 concentration, the substantial CO2 recovery efficiency combining the firing process and the sintering process can be highly efficient. As described above, according to the present invention, it is possible to provide a method for producing sintered ore that can suppress CO2 emissions from the sintering machine.

Brief Description of the Drawings

[0018] [Figure 1] This is a flowchart illustrating a method for producing sintered ore according to an embodiment of the present invention. [Modes for carrying out the invention]

[0019] The method for producing sintered ore according to an embodiment of the present invention will be described below with reference to the attached drawings. However, the present invention is not limited to the following embodiments.

[0020] As shown in Figure 1, the sintered ore according to the embodiment of the present invention is produced by a Dwightroid sintering machine using granulated raw materials that are a mixture of powdered iron ore, a solvent for adjusting the composition, return ore, and carbon material. The solvent for adjusting the composition here generally consists of SiO2-based auxiliary materials and CaO-based auxiliary materials, and as will be explained later, is mainly added to control the basicity (CaO / SiO2) of the melt generated during sintering within a predetermined range.

[0021] In this embodiment, (C) the CaO-based auxiliary raw material is primarily composed of (c1) an entire amount of CaO-based decarboxylated raw material, or (c2) the CaO-based decarboxylated raw material exceeds the CaO-based rock raw material in a simple sum of the CaO mass equivalent value and CaO·MgO mass equivalent value of the blended raw materials. In this embodiment, for the convenience of formulating raw materials for adjusting basicity, (a) limestone, (a1) quicklime, and (a2) slaked lime are all considered equivalently substituted raw materials in terms of CaO mass, since they melt in the molten liquid during sintering as the same CaO. Similarly, (b) dolomite, (b1) lightly calcined dolomite, and (b2) smoldered dolomite are also considered equivalently substituted raw materials in terms of CaO·MgO mass. Furthermore, in this embodiment, for the convenience of raw material formulation, CaO-based auxiliary raw material A is classified as CaO-based rock raw material if it consists of one or two of either (a) limestone and (b) dolomite. Similarly, CaO-based auxiliary raw material B is classified as CaO-based decarboxylated raw material if it consists of one or more of either (a1) quicklime, (a2) slaked lime, (b1) lightly calcined dolomite and (b2) digested dolomite.

[0022] In this embodiment, when comparing CaO-based rock raw materials and CaO-based decarboxylated raw materials, we will explain that the CaO mass equivalent value and the CaO·MgO mass equivalent value are simply added together for comparison, regardless of the type of constituent raw material. The CaO-based rock raw materials (a) limestone CaCO3 and (b) dolomite CaCO3·MgCO3 contain approximately equivalent amounts of CO2, about 44% by mass and about 47% by mass, respectively, as can be calculated from Table 1 shown below. From this, it can be easily estimated that, although (a) limestone CaCO3 and (b) dolomite CaCO3·MgCO3 have different chemical formulas, if the mass of CO2 in the raw materials is the same, the mass of the remaining CaO and the mass of CaO·MgO in the raw materials will also be the same. Therefore, for convenience, when formulating raw materials for basicity adjustment, it is considered possible to treat the CaO mass equivalent value and the CaO·MgO mass equivalent value as equivalent and simply add them together. This equivalence treatment of CaO mass equivalent values ​​and CaO·MgO mass equivalent values ​​in CaO-based rock raw materials also applies to CaO-based decarboxylated raw materials obtained by decarboxylating CaO-based rock raw materials. In other words, among CaO-based decarboxylated raw materials, the CaO mass equivalent values ​​and CaO·MgO mass equivalent values ​​can be treated as equivalent between (a1) quicklime or (a2) slaked lime derived from limestone and (b1) lightly calcined dolomite or (b2) sieved dolomite derived from dolomite. Furthermore, the equivalence of CaO mass equivalent values ​​and CaO·MgO mass equivalent values, which has been shown to hold true within CaO-based rock raw materials and CaO-based decarboxylated raw materials, also holds true between CaO-based rock raw materials and CaO-based decarboxylated raw materials, since the blended raw materials are common. Thus, when comparing CaO-based rock raw materials and CaO-based decarboxylated raw materials, treating the CaO mass equivalent of limestone-derived raw materials and the CaO·MgO mass equivalent of dolomite-derived raw materials as equivalent without distinction simplifies the consideration of raw material formulation, which is preferable. In other words, when determining the usage ratio, such as whether the CaO-based decarboxylated raw material of the CaO-based auxiliary raw material exceeds the CaO-based rock raw material, there is no major problem in treating the raw materials as the same type and adding up their masses without distinguishing between limestone-derived and dolomite-derived raw materials; rather, it becomes simpler and clearer.

[0023] Aside from the main components of this embodiment described above, the manufacturing method of sintered ore is the same as that of a normal sintered ore. Therefore, we will first briefly explain the general method of manufacturing sintered ore, which is the premise of this embodiment.

[0024] (Granulated raw material for sintering) As shown in Figure 1, powdered iron ore, a solvent for adjusting the composition, return ore (powdered sintered ore with a finished size that cannot be used as raw material for blast furnaces), and carbon material are blended and granulated in a drum-type mixer while adjusting the moisture content to produce pseudo-particles. By using pseudo-particles as the granulation raw material for sintering, the permeability when charging into a sintering machine such as a Dwightroid sintering machine is improved, allowing for good sintering to proceed.

[0025] These pseudo-particles are primarily composed of granular iron ore with a particle size of approximately 10 mm or less and 1 mm or more, used as the core particle. Furthermore, these pseudo-particles are formed by the adhesion of powdered iron ore with a particle size of 1 mm or less, solvents for adjusting the composition, powdered sintered ore from the return ore, and powdered coke, etc., due to added moisture, etc., around the core particle.

[0026] Iron ore powder refers to raw materials containing a large amount of iron, such as iron ore powder, iron-containing dust generated during the steelmaking process, and scale. The iron ore within iron ore powder is usually a blend of multiple types of powder to average out the different compositional properties of ore from each mine. As shown in Figure 1, the solvents for adjusting the composition (auxiliary raw materials) generally consist of SiO2-based auxiliary raw materials made from silica and various smelting slags, and CaO-based auxiliary raw materials mainly prepared from limestone. In this embodiment, in addition to auxiliary raw materials such as limestone or dolomite that have carbonate groups (referred to as CaO-based auxiliary raw material A or CaO-based rock raw material), decarboxylated auxiliary raw materials (referred to as CaO-based auxiliary raw material B or CaO-based decarboxylated raw material) are used as CaO-based auxiliary raw materials. CaO-based auxiliary raw material B (CaO-based decarboxylated raw material) will be described in detail later. Carbonized material serves as fuel for the combustion reaction in sintering, and powdered coke, anthracite, and other similar materials are used.

[0027] In this embodiment, minerals and other materials used as solvents for adjusting the composition may be represented by their main constituent minerals or main components, which are also industrial raw materials, in order to aid in understanding their constituent components. For example, in relation to SiO2-based auxiliary materials, silica may be represented as SiO2. In relation to CaO-based auxiliary materials, limestone may be represented as CaCO3, quicklime as CaO, slaked lime as Ca(OH)2, dolomite as CaCO3·MgCO3, calcined dolomite as CaO·MgO, and scavenged dolomite as Ca(OH)2·Mg(OH)2, etc. However, it goes without saying that actual minerals, as shown in Table 1 with examples of limestone and dolomite compositions, contain gangue components in addition to the main constituent minerals or main components represented here. Furthermore, in this embodiment, the secondary raw materials, limestone and dolomite, may be calcined (decarboxylated) to produce quicklime and lightly calcined dolomite, and these may be further slaked to produce slaked lime and slaked dolomite. In this embodiment, the manufacturing methods for calcination and scalding are not particularly limited, and existing methods may be used.

[0028] [Table 1]

[0029] Hoppers for adding auxiliary materials are usually separated for each material, such as limestone and dolomite. However, in cases where some limestone is replaced with quicklime, it may be acceptable to mix them in the existing limestone hopper. However, it is often preferable to prepare a separate quicklime hopper. This is because using different hoppers allows for precise modification, adjustment, and monitoring of the amount of limestone and quicklime used. This is especially desirable when the amount of charcoal required differs between limestone and quicklime. When adding quicklime to an existing limestone hopper, it is desirable to introduce the limestone and quicklime in a way that ensures a uniform mixture. This is because limestone and quicklime require different amounts of carbonaceous material, and uneven mixing can lead to localized excesses or shortages of carbonaceous material, resulting in a deterioration of sintered ore quality and a decrease in yield. The above explanation of the divided and mixed feeding into the hopper was given using the relationship between limestone and quicklime as an example, but the same principles apply to the relationship between dolomite and calcined dolomite, and further to the relationship when slaked lime and smoldered dolomite are added to these materials.

[0030] The main component composition of typical granulation raw materials for sintering is, for example, T.Fe: 55-57% by mass, CaO: 9-10% by mass, SiO2: 5-5.3% by mass, Al2O3: 1.7-1.8% by mass, and MgO: 1-20% by mass. Here, T.Fe is the total amount of Fe in all granulation raw materials, mainly consisting of powdered iron ore. CaO is the total amount of CaO by mass in all granulation raw materials, mainly consisting of auxiliary materials such as limestone CaCO3 and dolomite CaCO3·MgCO3. MgO is the total amount of MgO by mass in all granulation raw materials, mainly consisting of auxiliary materials such as dolomite CaCO3·MgCO3. The same applies to SiO2 and Al2O3, as they represent the total amounts in all granulation raw materials, including iron ore and auxiliary materials. The amount of carbon material added as a heat source is approximately 5% by mass relative to the granulation raw material.

[0031] (Sintering process) The pseudo-particle sintering raw material is charged and packed onto a pallet of a grate-moving sintering machine, and the carbon material such as coke present on the surface of the packed bed is ignited by a burner in the ignition furnace on the inlet side. In a downward suction type sintering machine, air is drawn in from the top of the packed bed and vented downwards, and the heat of combustion of the carbon material is transferred from the upper layer to the lower layer, causing sintering to proceed. Sintering is completed when the pallet moves to the outlet side of the sintering machine. The resulting sintered cake is crushed and sized to produce sintered ore with an average particle size of 5 to 75 mm.

[0032] In sintering raw materials with the above-described component composition, during heating and sintering, CaO and iron oxide Fe2O3 first react at around 1200°C to generate an initial melt. Subsequently, as the temperature rises, gangue (slag) components such as SiO2, Al2O3, and MgO, as well as iron oxide, melt (assimilate) into the melt, and the coarse iron ore particles bond together through this melt, resulting in sintering.

[0033] As mentioned above, the main reaction in the sintering reaction is the generation of an initial melt by the reaction of Fe2O3 in iron ore with CaO in limestone, etc., and further, the melting reaction of this melt with auxiliary raw materials, gangue components such as SiO2 in the iron ore, and iron oxide, which is called the assimilation reaction. For example, if the assimilation reaction proceeds excessively and the amount of melt generated increases drastically, uneven burning occurs due to poor ventilation in the sintered layer, which significantly worsens the yield and strength of the sintered ore. On the other hand, if the assimilation reaction does not proceed, the amount of melt that binds the unmelted iron ore particles together decreases, leading to a decrease in the yield and strength of the sintered ore. Such sintering reactions can be controlled by managing the basicity (CaO / SiO2) of the melt generated during sintering within a predetermined range using a solvent for adjusting the components in the granulation raw materials.

[0034] Incidentally, ensuring air permeability and fluid permeability around the fusion zone is one of the most important control matters in blast furnace operation. Therefore, normally, the amount of auxiliary materials such as limestone and silica added to the sintering raw materials is increased or decreased so that the basicity (CaO / SiO2) of the molten raw material of all raw materials charged into the blast furnace falls within a predetermined range. Furthermore, in this embodiment, it is preferable to control the amount of the solvent used for component adjustment so that the basicity (CaO / SiO2) of the molten raw material in the blast furnace is within a predetermined range even with sintered ore alone. Therefore, the adjustment is made while prioritizing the adjustment of the basicity of the molten raw material during the assimilation reaction of sintered ore, while also considering the basicity of the molten raw material in the blast furnace.

[0035] The overall basicity (CaO / SiO2) of the sintering raw materials can be adjusted by adjusting the blending pattern of each raw material so that the basicity, determined from the total amount of CaO and SiO2 contained in each of the powdered iron ore and the solvent for adjusting the composition, falls within a predetermined range.

[0036] (Fluent material for component adjustment; CaO-based auxiliary raw material B) Next, in the method for producing sintered ore according to this embodiment, as shown in Figure 1, we will explain how to blend CaO-based auxiliary raw material B (CaO-based decarboxylated raw material), which is decarboxylated from limestone or dolomite, into the granulation raw material as a CaO-based auxiliary raw material among the solvents for adjusting the composition.

[0037] The CaO-based decarboxylation raw material B referred to here shall consist of one or more of the following: quicklime CaO, slaked lime Ca(OH)2, calcined dolomite CaO·MgO, and digested dolomite Ca(OH)2·Mg(OH)2.

[0038] Generally, quicklime CaO is produced by heating (calcining) limestone CaCO3 to remove carbon dioxide CO2 (decarboxylation). Similarly, calcined dolomite CaO·MgO is produced by calcining dolomite CaCO3·MgCO3 to remove carbon dioxide CO2 (decarboxylation). Since these quicklime CaO and calcined dolomite CaO·MgO are decarboxylated raw materials as described above, in this embodiment they may be referred to as CaO-based decarboxylated raw materials.

[0039] Furthermore, quicklime CaO is reacted (scalded) with water to produce slaked lime Ca(OH)2. Similarly, calcined dolomite CaO·MgO is reacted (scalded) with water to produce scalded dolomite Ca(OH)2·Mg(OH)2. Thus, since the reaction from limestone CaCO3 to quicklime CaO and then to slaked lime Ca(OH)2 involves a decarboxylation reaction, we will include slaked lime Ca(OH)2 in addition to quicklime CaO as a CaO-based decarboxylation raw material. Similarly, digested dolomite Ca(OH)2·Mg(OH)2, produced from dolomite CaCO3·MgCO3 via calcined dolomite CaO·MgO, will also be included as a CaO-based decarboxylation raw material along with calcined dolomite CaO·MgO. The above describes a typical method for producing the CaO-based decarboxylation raw material used in this embodiment. However, this embodiment is not limited to these methods, and the final CaO-based decarboxylation raw material used in this embodiment may be obtained by passing through other compounds.

[0040] (CO2 emission reduction effect of sintering machine 1; equivalent to the amount of decarboxylation during the production of CaO-based auxiliary raw material B) In this embodiment, as described above, it is important to adjust the amount of CaO-based decarboxylation raw material (CaO-based auxiliary raw material B) blended into the granulation raw material as a CaO-based auxiliary raw material among the solvents for adjusting the composition. Specifically, in this embodiment, (C) the CaO-based auxiliary raw material is (c1) made entirely of CaO-based decarboxylation raw material, or (c2) the CaO-based decarboxylation raw material exceeds the CaO-based rock raw material in the simple sum of the CaO mass equivalent value and CaO·MgO mass equivalent value of the blended raw material. By replacing the conventional CaO-based rock raw material with the CaO-based decarboxylation raw material in this way, it is possible to reduce the amount of carbon dioxide generated in the sintering machine from the CaO-based rock raw material before substitution without affecting the basicity (CaO / SiO2) of the sintered ore. Reducing the amount of carbon dioxide generated in the sintering machine in this way is an effective means of reducing carbon dioxide in the sintering machine without carbon dioxide recovery, especially when the carbon dioxide concentration in the exhaust gas of the sintering machine is low (10% or less) and it is difficult to apply conventional industrial methods such as chemical absorption.

[0041] (CO2 emission reduction effect of sintering machine 2; equivalent to carbon material used as a decarbonization heat source during the production of CaO-based auxiliary raw material B) In this embodiment, which uses CaO-based auxiliary raw material B (CaO-based decarboxylation raw material), the amount of carbon material to be blended into the granulation raw material for sintering does not need to be the amount of carbon material equivalent to the heat source already used in the pre-decarboxylation treatment before the sintering process, which is derived from limestone and other raw materials that make up each of the blending raw materials that constitute the CaO-based decarboxylation raw material. Therefore, in this embodiment, the amount of carbon material in the sintering raw material may be reduced so that the amount of carbon material that is necessary with CaO-based auxiliary material A before substitution but becomes unnecessary when substituted with CaO-based auxiliary material B is reduced. This reduction in carbon material in the granulation raw material has the direct effect of reducing carbon dioxide caused by the decarboxylation reaction in the sintering machine by substituting with CaO-based auxiliary material B, as well as the secondary effect of reducing the carbon dioxide generated by the carbon material before the reduction. Furthermore, in this embodiment, in addition to the carbon dioxide reduction effect associated with the reduction of carbon material, there is also an effect that focuses on the type of carbon material. That is, the carbon dioxide reduction effect here is offset by the carbon dioxide generation during the production of CaO-based auxiliary material B, from the perspective of carbon material for the decarboxylation reaction alone. However, considering that anthracite or powdered coke used as sintering carbon material are special carbon materials that do not generate volatile matter during use, this is useful. This is because the carbon material used in the production stage of CaO-based auxiliary material B does not need to be anthracite or powdered coke that do not generate volatile matter during use, thus expanding the range of fuel choices and reducing fuel costs.

[0042] (CO2 recovery during the manufacturing process of CaO-based auxiliary material B) As mentioned above, in conventional methods for producing sintered ore, the carbon dioxide concentration in the exhaust gas is 10% or less, making it difficult to apply conventional industrial methods such as chemical absorption, and resulting in a situation where recovery is unavoidable. Furthermore, in this embodiment, as mentioned above, by using CaO-based auxiliary material B as the CaO-based auxiliary material, the carbon dioxide concentration in the exhaust gas of the sintering machine is further reduced, making it even more difficult to apply conventional industrial methods such as chemical absorption to the sintering machine.

[0043] On the other hand, even if carbon dioxide recovery is difficult in the sintering process alone, if carbon dioxide can be recovered through a decarboxylation reaction in the manufacturing process of CaO-based auxiliary material B, this can be considered as recovery in the sintering process, thereby effectively enabling the recovery of carbon dioxide from the CaO-based auxiliary material. Therefore, after examining a firing furnace capable of increasing the concentration of carbon dioxide generated during firing (decarboxylation) in the manufacturing of CaO-based auxiliary material B, it was determined that the desired objective can be achieved, for example, by using the quicklime production apparatus disclosed in Japanese Patent Application Publication No. 2013-180940.

[0044] In this embodiment, it is preferable to use a blending material from which all or part of the carbon dioxide generated in the decarboxylation reaction at each manufacturing step has been recovered for the CaO-based auxiliary material B (CaO-based decarboxylation material). This is because, at least all, or at least part, of the carbon dioxide generated in the decarboxylation reaction during firing when CaO-based auxiliary material B is manufactured is preferably recovered in the blending material manufacturing step before the sintering step, indirectly contributing to the reduction of carbon dioxide in the sintering machine. Furthermore, since the concentration of carbon dioxide generated in the manufacturing step of CaO-based auxiliary material B can be made sufficiently high for carbon dioxide recovery here, it can be recovered using conventional industrial methods such as chemical absorption.

[0045] (Estimated CO2 emission reduction effect when using CaO-based auxiliary material B as the sintering raw material) Next, we will give specific examples of the CaO-based auxiliary raw material B used in the method for producing sintered ore according to this embodiment, and explain the results of our calculations regarding the carbon dioxide reduction effect of each. For the calculations, the typical compositions of limestone and dolomite were taken from the values ​​in Table 1, and the decomposition heat and carbon dioxide emissions were taken from the values ​​in Table 2. Furthermore, the lower heating value and carbon dioxide emissions of the carbon materials were taken from the values ​​in Table 3. The calculation results are summarized in Table 4. Table 4 shows a comparative example of a conventional method that uses CaO-based rock raw materials (CaO-based auxiliary raw material A), namely limestone and dolomite, as CaO-based auxiliary raw materials, but does not use CaO-based decarboxylation raw materials (CaO-based auxiliary raw material B). Furthermore, the calculation results according to this embodiment are shown in Calculations 1 to 4 in Table 4. Specifically, Calculation 1 is the calculation result when the entire amount of CaO-based auxiliary raw materials is replaced from CaO-based rock raw materials to CaO-based decarboxylation raw materials, quicklime and light-calcined dolomite. Calculation 2 is the calculation result when, in addition to Calculation 1 in which the entire amount of CaO-based auxiliary raw materials is replaced from CaO-based rock raw materials to CaO-based decarboxylation raw materials, quicklime and light-calcined dolomite, is reduced by anthracite equivalent to the surplus heat energy due to the elimination of the decarboxylation treatment. Calculation 3 is the calculation result when the entire amount of CaO-based auxiliary raw materials is replaced from CaO-based rock raw materials to CaO-based decarboxylation raw materials, slaked lime and smoldered dolomite, and anthracite equivalent to the surplus heat energy due to the elimination of the decarboxylation treatment is reduced. Calculation 4 shows the results of a calculation in which more than half of the CaO-based rock raw material used as a CaO-based auxiliary raw material is replaced with quicklime and light-calcined dolomite, which are CaO-based decarboxylation raw materials, thereby reducing the amount of anthracite coal equivalent to the excess thermal energy that would otherwise be required for decarboxylation treatment.

[0046] [Table 2]

[0047] [Table 3]

[0048] (Calculation 1: When all of the CaO-based auxiliary materials are replaced with quicklime and light-calcined dolomite) First, in order to minimize CO2 emissions in the sintering machine, we will explain an example calculation where the entire amount of limestone and dolomite in CaO-based auxiliary raw material A (CaO-based rock raw material) is replaced with quicklime and calcined dolomite in CaO-based auxiliary raw material B (CaO-based decarboxylated raw material).

[0049] The substitutions here were carried out according to the following reasoning: Based on the composition of limestone, 1 kg of limestone contains 0.438 kg of CO2, so the amount of quicklime needed to replace 1 kg of limestone is 1 - 0.438 = 0.562 kg. The same applies to dolomite; 1 kg of dolomite contains 0.466 kg of CO2, so the amount of lightly calcined dolomite needed to replace 1 kg of dolomite is 0.534 kg. Before substitution (comparative example), the amount of sintering raw materials charged per ton of sintered ore produced was 104.5 kg of limestone and 47.5 kg of dolomite. Therefore, 58.7 kg of quicklime and 25.4 kg of lightly calcined dolomite are needed to replace them. This results in a reduction of 45.8 kg and 22.1 kg of CO2 emissions caused by limestone and dolomite, respectively. Consequently, when these CO2 emission reductions are totaled, a reduction of 68 kg of CO2 emissions per ton of sintered ore produced is possible. While it is possible to carry out sintering with this formulation, since the proportions of powdered coke and anthracite used remain constant, as mentioned above, an excess of thermal energy is supplied for the decarboxylation of CaCO3 and MgCO3. The following calculation 2 shows an improvement on this point.

[0050] (Calculation 2: If all CaO-based auxiliary materials are replaced with quicklime and light-calcined dolomite, and anthracite is reduced) Next, in order to minimize CO2 emissions in the sintering machine, we will explain an example of a calculation that reduces the amount of anthracite equivalent to the surplus thermal energy obtained by eliminating the need for decarboxylation treatment, in addition to the calculation in Calculation 1 in which the entire amount of CaO-based rock raw material, a CaO-based auxiliary raw material, is replaced with CaO-based decarboxylated raw material.

[0051] The substitutions here were carried out according to the following reasoning: Based on the composition of limestone, 1 kg of limestone contains 0.438 kg of CO2, so the amount of quicklime needed to replace 1 kg of limestone is 1 - 0.438 = 0.562 kg. The same applies to dolomite; 1 kg of dolomite contains 0.466 kg of CO2, so the amount of lightly calcined dolomite needed to replace 1 kg of dolomite is 0.534 kg. Before substitution (comparative example), the amount of sintering raw materials charged per ton of sintered ore produced was 104.5 kg of limestone and 47.5 kg of dolomite. Therefore, 58.7 kg of quicklime and 25.4 kg of lightly calcined dolomite were needed to replace them. As a result, the reduction in CO2 emissions caused by limestone and dolomite was 45.8 kg and 22.1 kg, respectively. Next, the amount of thermal energy required to decompose 1 kg of limestone into quicklime is 1.77 MJ. Similarly, the amount of thermal energy required to decompose 1 kg of dolomite into calcined dolomite is 1.53 MJ. Therefore, the amount of thermal energy that can be saved before and after substitution is 184.5 MJ for limestone and 72.7 MJ for dolomite per ton of sintered ore produced, for a total of 257.2 MJ. This reduction in thermal energy can be achieved using either powdered coke or anthracite, but here we will use anthracite. Since the calorific value of 1 kg of anthracite is 29.88 MJ, 8.6 kg of anthracite can be saved per ton of sintered ore produced. Furthermore, since burning 1 kg of anthracite coal generates 2.936 kg of CO2, reducing anthracite coal production can reduce CO2 emissions by 25.3 kg. Therefore, when these CO2 reductions are added together, it is possible to reduce CO2 emissions by 93 kg per ton of sintered ore produced.

[0052] (Calculation 3: If all CaO-based auxiliary materials are replaced with slaked lime and digested dolomite, and anthracite coal is reduced) It is generally pointed out that quicklime (CaO) is highly reactive, increasing the risk of accidents during handling. Furthermore, quicklime (CaO) can absorb CO2 during transport and storage, reverting back to limestone (CaCO3). From this perspective, it is effective to use quicklime (CaO) as slaked lime (Ca(OH)2) before use. The same applies to dolomite; it is preferable to calcine dolomite (CaCO3·MgCO3) to obtain lightly calcined dolomite (CaO·MgO), and then use it as slaked dolomite (Ca(OH)2·Mg(OH)2). Therefore, this section will explain an example of calculations when limestone, a CaO-based rock raw material, is replaced with slaked lime, a CaO-based decarboxylation raw material, and dolomite, a CaO-based rock raw material, is replaced with digested dolomite, a CaO-based decarboxylation raw material.

[0053] The substitutions here were carried out according to the following reasoning: Based on the composition of limestone, 1 kg of limestone is converted to 0.741 kg of slaked lime. The same applies to dolomite; 1 kg of dolomite is converted to 0.725 kg of slaked dolomite. Before substitution (comparative example), the amount of sintering raw materials charged per ton of sintered ore produced was 104.5 kg of limestone and 47.5 kg of dolomite. Therefore, the amount of slaked lime and digested dolomite required to replace them is 77.4 kg and 34.5 kg, respectively. The reduction in CO2 emissions caused by limestone and dolomite in this case is the same as in calculations 1 and 2, at 45.8 kg and 22.1 kg, respectively. Next, the amount of thermal energy required to decompose 1 kg of slaked lime into quicklime is 1.46 MJ. Therefore, the amount of thermal energy that can be reduced before and after substitution is the difference between the amount of thermal energy required to decompose limestone into quicklime and the amount required to decompose limestone into quicklime, which is 0.68 MJ per kg of limestone. Similarly, the amount of thermal energy required to decompose 1 kg of slaked dolomite into light-calcined dolomite is 1.41 MJ. Therefore, the amount of thermal energy that can be reduced before and after substitution is the difference between the amount of thermal energy required to decompose dolomite into light-calcined dolomite and the amount required to decompose dolomite into light-calcined dolomite, which is 0.51 MJ per kg of dolomite. Thus, the amount of thermal energy that can be reduced before and after substitution is 71.5 MJ for limestone and 24.0 MJ for dolomite per ton of sintered ore produced, for a total of 95.5 MJ. If we assume that this reduction in thermal energy is achieved by using anthracite coal, then 3.2 kg of anthracite coal can be reduced per ton of sintered ore produced. In addition, the amount of CO2 that can be reduced by reducing anthracite coal is 9.4 kg. Therefore, when these reductions in CO2 emissions are added together, a total reduction of 77 kg of CO2 emissions is possible per ton of sintered ore produced.

[0054] (Calculation 4: If more than half of the CaO-based rock raw material used as a CaO-based auxiliary raw material is replaced with CaO-based decarboxylated raw material, and anthracite is reduced.) In Calculation 4, we show an example where limestone and dolomite, which are CaO-based rock raw materials, are replaced with quicklime and light-calcined dolomite, which are CaO-based decarboxylation raw materials, in such a way that the simple sum of their respective CaO equivalent values ​​and CaO·MgO equivalent values ​​shows that the CaO-based decarboxylation raw materials outweigh the others. The calculation methods for the changes in the amount of blended raw materials, the reduction in CO2 emissions, the difference in thermal energy, etc., are the same as in Calculations 1 to 3, so an explanation is omitted here. In this case, the reduction in CO2 emissions is 47 kg-CO2 / t-sintered ore.

[0055] [Table 4]

Claims

1. A method for producing sintered ore using a Dwightroid sintering machine, comprising granulation raw materials blended with powdered iron ore, a solvent for adjusting the composition, return ore, and carbon material, (A) Among the solvents for adjusting the components, as a CaO-based auxiliary material, (a) limestone; (a1) Quicklime, and (a2) Slaked lime, Each of the raw materials is considered to be a blended raw material that can be equivalently substituted for the others in terms of CaO mass, (b) Dolomite, (b1) Lightly calcined dolomite, and (b2) Digestive dolomite, Each of these raw materials is considered to be a blended raw material that can be equivalently substituted for each other in terms of CaO and MgO mass, (B) The CaO-based auxiliary raw material, (a) The limestone and, (b) The dolomite, A CaO-based rock raw material consisting of one or two of the following blended raw materials, (a1) The quicklime mentioned above, (a2) the slaked lime; (b1) The light-calcined dolomite, and (b2) The digested dolomite, A CaO-based decarboxylation raw material consisting of one or more of the following blended raw materials, When classifying, (C) The CaO-based auxiliary raw material is (c1) The entire amount consists of the CaO-based decarboxylation raw material, or (c2) In the CaO-based rock raw material, or in the CaO-based decarboxylated raw material, when the CaO mass equivalent value and the CaO・MgO mass equivalent value of the constituent blended raw materials are simply summed, the simple sum of the CaO-based decarboxylated raw material is greater than the simple sum of the CaO-based rock raw material. A method for producing sintered ore, wherein the aforementioned blending raw materials are prepared.

2. The carbon material blended into the granulation raw material includes, The CaO-based decarboxylation raw material comprises, (a1) The quicklime mentioned above, (a2) the slaked lime; (b1) The light-calcined dolomite, and (b2) The digested dolomite, The method for producing sintered ore according to claim 1, wherein the amount of carbon material is not such that it generates an amount of heat equivalent to the heat of reaction required for the decarboxylation reaction from (a) the limestone or (b) the dolomite of each of the raw materials for production.

3. The CaO-based decarboxylation raw material comprises, (a1) The quicklime mentioned above, (a2) the slaked lime; (b1) The light-calcined dolomite, and (b2) The digested dolomite, The method for producing sintered ore according to claim 1 or claim 2, wherein all or part of the carbon dioxide generated in the decarboxylation reaction from (a) the limestone or (b) the dolomite of each of the manufacturing raw materials is recovered.

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