Method for producing sintered ore

Abstract

Provided is a method for producing a sintered ore, with which there can be prevented a decrease in yield when using a carbonaceous material(s) with a low combustion start temperature. The method includes: preparing a granulated raw material for sintering by granulating a mixture of raw materials for sintering that contains a carbonaceous material as a solid fuel; and sintering the granulated raw material for sintering to obtain a sintered ore, wherein the carbonaceous material is a carbonaceous material prepared by combining at least two kinds of carbonaceous materials, and a weighted average of combustion start temperatures of the carbonaceous materials combined is 550°C or higher. Preferably, as part of the at least two kinds of carbonaceous materials, there are used those with combustion start temperatures of lower than 550°C.

Description

Technical Field

[0001] The present invention relates to a method for producing a sintered ore, in which a granulated raw material for sintering is prepared by granulating a mixture of raw materials for sintering that contains a carbonaceous material as a solid fuel, followed by sintering such granulated raw material for sintering to obtain a sintered ore.Background Art

[0002] In the production process of a sintered ore, a mixture of an iron ore, flux, and a carbonaceous material as a solid fuel is sintered in a sintering machine via the combustion heat of such carbonaceous material, thereby obtaining a sintered ore. Usually, coke breeze is used as a carbonaceous material; there may also be used anthracite or the like other than coke breeze in terms of risk diversification for, for example, price fluctuations of raw material coal, and troubles in a coke production equipment.

[0003] Meanwhile, in response to the growing awareness of environmental protection in recent years, carbonaceous materials have progressively diversified with the intention of reducing the burden on the environment, aside from the idea of risk diversification or the like. As one example thereof, Patent Literature 1 provides a carbonaceous material to be used for the production of a sintered ore, assuming the use of subbituminous coal and brown coal. The properties of this carbonaceous material are such that a reaction start temperature is 550°C or lower; a volatile matter (VM) is 1.0% or more; an atomic number ratio between hydrogen and carbon (H / C) is 0.040 or higher, and a pore quantity of pores with pore sizes of 0.1 to 10 µm is 50 mm 3< / g or larger when measured by the mercury intrusion technique. Further, in Patent Literature 2, proposed is the use of a raw material for sintering containing 10% by mass or more of a solid fuel with a combustion start temperature of lower than 450°C, when using 30% or more of a high crystal water iron ore that contains 4.0% by mass or more of crystal water.

[0004] However, there is imposed an upper limit on the reaction start temperature in each of the above cases; no consideration is made to the impact of yield worsening in a sintered ore production process. In this regard, the method provided by Patent Literature 3 is a double combustion sintering method where there are formed two layers of sintering charged layers whose surfaces are each ignited when performing sintering, in which a raw material used on the lower layer side includes coke and / or anthracite as well as carbonaceous materials with combustion start temperatures lower than those of coke and anthracite. Further, Patent Literature 4 provides a method where, as a coagulating material, carbonaceous materials with low combustion start temperatures are combined with coke breeze and anthracite so that the carbon content of such carbonaceous materials will be at a ratio of 25 to 75% with respect to the total carbon content of the coagulating material, and at least one of the low-combustion start temperature carbonaceous material and high-combustion start temperature carbonaceous material is added in the latter half of the granulation step.Citation ListPatent Literature

[0005] Patent Literature 1: Japanese Patent No.4681688 Patent Literature 2: Japanese Patent No.4837799 Patent Literature 3: JP-A-2020-186436 Patent Literature 4: JP-A-2022-033594 Summary of InventionTechnical Problem

[0006] However, the method disclosed in Patent Literature 3 is performed on the premise that a double combustion sintering method is used, which makes it impossible to utilize the method in a general sintering method. Further, with regard to the method disclosed in Patent Literature 4, there are different types of low-combustion start temperature carbonaceous materials with various combustion start temperatures, which makes controlling solely based on carbon content risky to a certain extent.

[0007] It is an object of the present invention to solve the abovementioned problems by providing a sintered ore production method capable of preventing a decrease in yield when using a carbonaceous material(s) with a low combustion start temperature, the sintered ore production method being the type of method including: preparing a granulated raw material for sintering by granulating a mixture of raw materials for sintering that contains a carbonaceous material as a solid fuel; and obtaining a sintered ore by sintering the granulated raw material for sintering.Solution to Problem

[0008] The method of the present invention for producing a sintered ore includes: preparing a granulated raw material for sintering by granulating a mixture of raw materials for sintering that contains a carbonaceous material as a solid fuel; and sintering the granulated raw material for sintering to obtain a sintered ore, wherein the carbonaceous material is prepared by combining at least two kinds of carbonaceous materials, and a weighted average of combustion start temperatures of the carbonaceous materials combined is 550°C or higher.

[0009] Here, it is considered that more preferable solutions can be brought when (1) the carbonaceous materials combined include a carbonaceous material having a combustion start temperature of lower than 550°C; (2) the carbonaceous material having a combustion start temperature of lower than 550°C includes an organic resource other than a fossil fuel, or a carbonaceous material produced by using said organic resource as a raw material; (3) the carbonaceous material having a combustion start temperature of lower than 550°C is coke whose raw material includes at least one selected from a group consisting of biomass charcoal, anthracite, waste plastic charcoal, brown coal, and subbituminous coal; and (4) the whole amount of the carbonaceous material prepared by combining is added before a granulation step. Advantageous Effects of Invention

[0010] According to the method of the present invention for producing a sintered ore, sintering is performed using a carbonaceous material prepared by combining at least two kinds of carbonaceous materials, in which a weighted average of the combustion start temperatures of these carbonaceous materials combined is 550°C or higher, thereby making it possible to suppress yield reduction when the carbonaceous material is combined and used in a sintered ore.Brief Description of Drawings

[0011] [Fig.1] is a schematic diagram showing an embodiment of a sintered ore production equipment used in the method of the present invention for producing a sintered ore. [Fig.2] is a graph showing a correlation between a product yield and a weighted average of combustion start temperatures in Examples. [Fig.3] is a graph showing and comparing product yields in both cases of adding a carbonaceous material before and in the latter half of granulation. Description of Embodiments

[0012] An embodiment of the present invention is described in detail hereunder. Here, the following embodiment is a set of examples of a device and / or method embodying the technical concept of the present invention and is not to limit the configuration of the present invention to those shown below. That is, various modifications can be made to the technical concept of the present invention within the technical scope described in the claims.<Sintered ore production equipment used in the method of the present invention for producing a sintered ore>

[0013] Fig.1 is a schematic diagram showing an embodiment of a sintered ore production equipment 1 that is used in the method of the present invention for producing a sintered ore. The sintered ore production equipment 1 has a drum mixer 2 as a granulator, a sintering machine 3, a crushing machine 4, a cooler 5, and a sieving device 6. A raw material for sintering containing an iron-containing raw material, an auxiliary raw material, and a coagulating material such as a carbonaceous material and a coke breeze is subjected to granulation in the drum mixer 2 with a granulation water being added thereto. The granulated raw material for sintering is then transferred to the sintering machine 3.

[0014] The sintering machine 3 is, for example, a Dwight-Lloyd type sintering machine. The sintering machine 3 has a raw material for sintering feeding device 11, a continuous-type pallet carriage 12, an ignition furnace 13, and a wind box 14. The granulated raw material for sintering is charged into the pallet carriage 12 from the raw material for sintering feeding device 11 to form a charged layer of the granulated raw material for sintering. The coagulating material contained in the surface layer of the charged layer is ignited by the ignition furnace 13, and the air in the charged layer is sucked downward through the wind box 14, thereby causing the combustion molten zone in the charged layer to be moved to the lower region of the charged layer. Due to such movement of the combustion molten zone, the charged layer is sintered to form a sintered cake.

[0015] When sucking the air in the charged layer downward through the wind box 14, a gas fuel and / or an oxygen-enriched air enriched with oxygen may be supplied from the upper region of the charged layer. The gas fuel is any combustible gas selected from a blast furnace gas, a coke oven gas, a converter gas, a city gas, a natural gas, a methane gas, an ethane gas, a propane gas, and a mixed gas of these gases.

[0016] The sintered cake is crushed by the crushing machine 4 and is cooled by the cooler 5. The sieving device 6 is then used to sieve the crushed product of the sintered cake into a sintered ore having a particle size of 5 mm or larger and a return fine having a particle size of smaller than 5 mm. The return fine is again used as the raw material for sintering. The sintered ore is produced in such manner.<Method of the present invention for producing a sintered ore>

[0017] The method of the present invention for producing a sintered ore is characterized in that sintering is performed using a carbonaceous material, being a carbonaceous material as a solid fuel, that is prepared by combining at least two kinds of carbonaceous materials, and in which a weighted average of the combustion start temperatures of these carbonaceous materials is 550°C or higher. Described hereunder is a carbonaceous material used in the method of the present invention for producing a sintered ore, the carbonaceous material constituting the characteristic of the present invention.

[0018] Biomass-derived carbonaceous materials (referred to as biomass charcoal hereunder) are gathering attention in terms of carbonaceous material diversification intended to reduce environmental load. Biomass charcoal absorbs carbon dioxide gas until a plant as its raw material has grown; thus, from the perspective of carbon neutrality, in the case of a fuel using such biomass charcoal, the discharge amount of carbon dioxide gas outside the system can be counted as none. Therefore, the use of biomass charcoal is under consideration even in an iron ore sintering process employing a normal coke breeze. One feature of biomass charcoal is that it has a combustion start temperature of roughly 550°C or lower, which is lower than that of coke (600 to 750°C).

[0019] In a sintering step performed by the sintering machine 3, flux and the carbonaceous material are added to an iron ore, followed by continuously charging them onto the sintering machine 3 to form a sintering bed composed of the charged layer of the raw material for sintering. By sucking an exhaust gas from the lower end of the sintering bed after igniting the upper end thereof, the combustion of the carbonaceous material will propagate from the upper end of the bed to the lower end thereof, thereby causing the iron ore and flux to react and agglomerate with each other via such heat. The exhaust gas suction from the lower layer is carried out with a blower, whereby the exhaust gas sucked is then ejected from a chimney after passing through the inner side of a duct, a dust collector, and a desulfurization and denitration equipment.

[0020] As mentioned above, the feature of a biomass charcoal is that it has a low combustion start temperature. The reason for that is considered as such that since biomass charcoal has a significantly large surface area due to its porosity as compared to coke breeze (fossil fuel-derived) that is used in a general sintering process, a high combustion rate can be achieved even at a low temperature. Thus, while biomass charcoal has a low combustion start temperature, it shows a trend of exhibiting a high combustion rate thereafter.

[0021] The combustion reaction of a carbonaceous material is a gas-solid reaction. A carbonaceous material burns by reacting with the oxygen in a surrounding gas. In a gas-solid reaction performed under a condition where a gas is flowing as is the case with sintering, an extremely thin-layered region called gas film is present on the solid surface. The gas film has its laminar flow maintained without being affected by the turbulent flow outside. The combustion of a carbonaceous material takes place in such a manner that oxygen is diffused in the gas film from outside the gas film and is consumed for combustion upon reaching the surface of the carbonaceous material. Here, when the combustion rate of the carbonaceous material is extremely high, and also when the surrounding oxygen concentration is high, there will be observed a higher oxygen consumption rate on the surface that is attributed to the combustion of the carbonaceous material with respect to an oxygen supply rate that is associated with the oxygen diffusion in the gas film, thereby resulting in a lower oxygen concentration in the gas film. In this way, the amount of carbon monoxide generated will increase due to the incomplete combustion of the carbonaceous material. Therefore, when the combustion rate is extremely high, part of the combustion heat as the carbonaceous material will be discharged out of the system as carbon monoxide, thus resulting in an impaired yield due to a reduced reaction heat used for sintering. Here, by lowering the combustion rate of the carbonaceous material used and setting the combustion start temperature to 550°C or higher, in-gas film diffusion controlling associated with oxygen supply in the combustion reaction can be resolved whereby part of the combustion heat can be restricted from being discharged out of the system as carbon monoxide.

[0022] It is considered that the combustion rate of a carbonaceous material is susceptible to, for example, the lowering of a burning rate constant per unit area of the carbonaceous material, and the lowering of the surface area; the burning rate constant is a value determined by the properties of a carbonaceous material and is thus difficult to control. The lowering of the surface area can be resolved by methods of, for example, increasing the particle size of the carbonaceous material, or coating the surface thereof. However, it is difficult to control the surface area to a target value because if increasing the particle size, the particle size needs to be increased to a size that is difficult to be used with an existing process, and if performing coating, coating a powder is technically difficult.

[0023] In view of the abovementioned facts, it is realistic to collectively control the combustion rate by mixing a carbonaceous material with a low combustion rate when using a carbonaceous material with a high combustion rate. For this reason, in the present invention, especially when using a carbonaceous material with a combustion start temperature of lower than 550°C such as a biomass charcoal other than a fossil fuel, carbonaceous materials with high combustion start temperatures are added and combined therewith so that a weighted average of the combustion start temperatures of the carbonaceous materials combined is 550°C or higher. Thus, yield reduction of a sintered ore can be suppressed; and from the perspective of carbon neutrality, the amount of CO 2 discharged out of the system can be suppressed as well.

[0024] Further, as a preferable embodiment, it is preferred that the whole amount of the carbonaceous material that has been prepared by combining at least two kinds of carbonaceous materials be added before the granulation step. In this way, the segregation of the carbonaceous materials combined can be suppressed, whereby variations in the combustion start temperatures of the carbonaceous materials combined in the sintering granulation raw material can be reduced so that variations in the yield of the sintered ore can be suppressed as a result.

[0025] Here, as a carbonaceous material with a combustion start temperature of lower than 550°C, there can be preferably employed an organic resource other than a fossil fuel, or a carbonaceous material produced by using such organic resource as a raw material, more specific examples of which include coke whose raw material includes at least one selected from a group consisting of biomass charcoal, anthracite, waste plastic charcoal, brown coal, and subbituminous coal.Examples<Example 1>

[0026] Using a batch-wise sintering test device, there was employed a carbonaceous material prepared by combining at least two kinds of carbonaceous materials with different combustion start temperatures, and a sintered ore was produced by performing sintering under a condition with the same amount of heat input. As the carbonaceous materials, there were used coke breeze and anthracite that are generally used; as well as a biomass charcoal and brown coal whose combustion start temperatures are lower than 550°C. Reference Examples 1 to 4 are examples where only one kind of the above carbonaceous materials was used; Comparative Examples 1 to 3 are examples where at least two kinds of the above carbonaceous materials were combined, and a weighted average of their combustion start temperatures was lower than 550°C; and Examples 1 to 6 are examples where at least two kinds of the above carbonaceous materials were combined, and a weighted average of their combustion start temperatures was 550°C or higher. At that time, raw materials other than the carbonaceous material(s) were added in a fixed amount. Next, the yield of a sintered ore produced using the carbonaceous material(s) of each example was obtained as a ratio of those with a size of 5 mm or larger after dropping the entire sintered sample from a height of 2 m four times. The results are shown in Table 1; based on these results, a correlation between the product yield and the weighted average of the combustion start temperatures is shown in Fig.2.

[0027] Here, the combustion start temperature was obtained by the following method. A target carbonaceous material was measured and taken by an amount of 10 mg, followed by heating the same in a differential thermal analytical function-equipped electric furnace at a rate of 10°C / min while flowing air at a rate of 200 ml / min. The carbonaceous material will start burning and rapidly generate heat upon reaching the combustion start temperature. Here, time was taken as the horizontal axis, a thermal change in the differential thermal analysis was taken as the vertical axis, and there was plotted a relation line between time and the thermal change. The combustion start temperature was defined as an intersection point between an extension of a thermal change line immediately before detecting the rapid heat generation in the differential thermal analysis, and an extension of a thermal change line immediately after detecting the rapid heat generation in the analysis. [Table 1]Reference Example 1Reference Example 2Comparative Example 1Comparative Example 2Comparative Example 3Example 1Reference Example 3Example 2Example 3Example 4Example 5Example 6Reference Example 4Coke Breeze (mass%)001010304004050607090100Anthracite (mass%)00202030301004030202000Biomass Charcoal (mass%)1000700403002001010100Brown Coal (mass%)010007000002010000Combustion Start Temperature(°C) (Weighted Average)430440480487537558570572582588609624645Product Yield (%)48527377768685828385838787

[0028] As is clear from the results shown in Table 1 and Fig.2, it was found that the product yield increased as the weighted average of the combustion start temperatures after combining increased. Further, it was found that low values of product yield were observed in the Comparative Examples 1 to 3 where the weighted average of the combustion start temperatures after combining was lower than 550°C. In contrast, as for the Examples 1 to 6 where the weighted average of the combustion start temperatures after combining at least two kinds of carbonaceous materials was 550°C or higher, it was found that the product yields in these examples were higher than those of the Comparative Examples 1 to 3, and that an increase in product yield saturated from around 550°C. Moreover, in the cases of biomass charcoal and brown coal each having a combustion start temperature of lower than 550°C, low values of product yield were exhibited when used alone (Reference Examples 1 and 2). However, it was found that higher product yields were achieved by mixing these carbonaceous materials with other carbonaceous materials so that the weighted average of the combustion start temperatures would be 550°C or higher (Examples 1 to 6). In view of the above results, it was made clear that even in the case of a carbonaceous material(s) having a combustion start temperature of lower than 550°C and resulting in a product yield so low that the carbonaceous material(s) is unusable if used alone, the carbonaceous material(s) can be used as a carbonaceous material when combined with other carbonaceous materials so that the weighted average of the combustion start temperatures becomes 550°C or higher.<Example 2>

[0029] The following standards were each performed multiple times, and variations in product yield were studied with regard to each standard. The standards are a standard where a carbonaceous material prepared by combining under the conditions of the Example 1 in Table 1 was added before the granulation step; and a standard where such carbonaceous material was added in the latter half of the granulation step. The results are shown in Fig.3. As a result, as for the standard where the carbonaceous material was added before granulation, there was observed a variation of about 8% in product yield, and an average value thereof was 87%. In contrast, as for the standard where the carbonaceous material was added in the latter half of granulation, there was observed a variation of about 17%, and there was also a standard in which the product yield exceeded 85%; however, the average value thereof was lower than that of the standard where the carbonaceous material was added before granulation. From these facts, it was made clear that a preferable embodiment is one in which the whole amount of the carbonaceous material prepared by combining is added before the granulation step.Industrial Applicability

[0030] According to the method of the present invention for producing a sintered ore, by using a given carbonaceous material, there can be prevented a decrease in yield when using a carbonaceous material(s) with a low combustion start temperature, which makes the production method of the present invention industrially useful.Reference Signs List

[0031] 1 Sintered ore production equipment 2 Drum mixer 3 Sintering machine 4 Crushing machine 5 Cooler 6 Sieving device 11 Raw material feeding device 12 Pallet carriage 13 Ignition furnace 14 Wind box

Claims

1. A method for producing a sintered ore, comprising: preparing a granulated raw material for sintering by granulating a mixture of raw materials for sintering that contains a carbonaceous material as a solid fuel; and sintering the granulated raw material for sintering to obtain a sintered ore, characterized in that the carbonaceous material is prepared by combining at least two kinds of carbonaceous materials, and a weighted average of combustion start temperatures of the carbonaceous materials combined is 550°C or higher.

2. The method for producing a sintered ore according to claim 1, wherein the carbonaceous materials combined include a carbonaceous material having a combustion start temperature of lower than 550°C.

3. The method for producing a sintered ore according to claim 2, wherein the carbonaceous material having a combustion start temperature of lower than 550°C includes an organic resource other than a fossil fuel, or a carbonaceous material produced by using said organic resource as a raw material.

4. The method for producing a sintered ore according to claim 3, wherein the carbonaceous material having a combustion start temperature of lower than 550°C is coke whose raw material includes at least one selected from a group consisting of biomass charcoal, anthracite, waste plastic charcoal, brown coal, and subbituminous coal.

5. The method for producing a sintered ore according to any one of claims 1 to 4, wherein the whole amount of the carbonaceous material prepared by combining is added before a granulation step.

Images