Sintered ore production method

Abstract

A method for producing sintered ore includes: charging granules of a material mixture of a lower layer group into a sintering machine (100) to form a lower-layer material packed bed (10); charging granules of a material mixture of an upper layer group thereon to form an upper-layer material packed bed (20); and igniting surfaces of the respective material packed beds and introducing, at atmospheric pressure, an oxygen-containing gas into the respective material packed beds by downward suction (6), in which at least a part of the gas downwardly suctioned from a surface side of the upper-layer material packed bed after completion of the ignition thereof is an oxygen enriched gas having an oxygen concentration of 26 vol% or more and 46 vol% or less, and assuming that a middle position of a section from a point (X) immediately after an outlet of an upper-layer ignition furnace (2C) to a discharge end (Y) in a longitudinal direction of the sintering machine is defined as an intermediate position (Z) and a section from the point (X) to the intermediate position (Z) is defined as a former half section, an area where the oxygen enriched gas is supplied is an area that includes a part of the former half section.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for producing sintered ore used as a material in a blast furnace, in particular, to a double-layer charging and double-layer ignition sintering method.BACKGROUND ART

[0002] Sintered ore, a main material for production of pig iron in a blast furnace, is typically produced as follows. First, materials for producing sintered ore including iron materials such as iron ore (powder), iron-containing miscellaneous materials such as scale and steelmaking dust, CaO-containing flux such as limestone, return ore, carbonaceous materials (bonding agent) that serve as fuel to sinter (set) sintered ore using heat from combustion, and the like are mixed (blended) in a specified ratio. The blended materials (material mixture) are subjected to a granulation process (hereinafter simply referred to as granulation) to produce pseudo particles, which are aggregated primary particles of the materials, in order to adjust the particle size distribution. Next, the granulated material mixture (material mixture granules) is loaded from a hopper onto a pallet (sinter pallet) of a downward suction type Dwight-Lloyd (DL) sintering machine, forming a packed bed of the material mixture (hereinafter referred to as a material packed bed, or material bed). The carbonaceous material in the material packed bed is ignited by an ignition furnace (igniter) from the top (surface) of the formed material packed bed. Then, air is sucked from underneath the pallet while the pallet is continuously moved. Oxygen from the air is supplied into the material packed bed by suction, causing the carbonaceous material in the material packed bed to burn from the top to the bottom. The material packed bed is thus gradually sintered through the combustion heat of the carbonaceous material. The sintered portion (sinter cake) obtained by sintering is crushed to a specified particle size, is sized by sieving or the like, and becomes sintered ore, which is a material for blast furnaces.

[0003] For such a method for producing sintered ore using a DL-type sintering machine, Patent Literature 1 describes a multiple-layer charging and multiple-layer ignition sintering method in which formation of material packed beds and ignition are performed in multiple layers. In the double-layer charging and double-layer ignition sintering method (hereinafter also referred to as a double-layer charging and double-layer ignition method), which is an example of the multiple-layer charging and multiple-layer ignition sintering method, material mixture granules are charged into the sintering machine in two batches in a bed height direction of the sintering machine to form double-layer material packed beds (upper-layer material packed bed and lower-layer material packed bed), and a surface of each material packed bed is ignited and air is sucked from below, thereby allowing the sintering reaction in each bed to proceed in parallel.

[0004] In the double-layer charging and double-layer ignition sintering method, the material packed beds are formed in double layers and sintering proceeds simultaneously in the double layers, nearly doubling production volume. In addition, the exhaust gas used to sinter the upper-layer material packed bed (hereinafter referred to as an upper layer bed) is reused to sinter the lower-layer material packed bed (hereinafter referred to as a lower layer bed) by downward suction, which has an advantage of reducing (by half) the amount of exhaust gas. On the other hand, since the gas (exhaust gas) used to sinter the upper layer bed and with a reduced oxygen partial pressure is used to sinter the lower layer bed, sintering in the lower layer bed is performed under low oxygen partial pressure. This results in incomplete combustion of the carbonaceous material in the lower layer bed, which leads to an insufficient heat amount for sintering. The sintering reaction thus slows down, decreasing the strength of the sintered ore in the lower layer bed.

[0005] To address this issue, proposals have been made to perform oxygen enrichment in a suction gas.

[0006] Patent Literature 2 discloses a technique in which the oxygen concentration in a main exhaust gas sucked from the entire sintering machine is measured, and the oxygen concentration in a gas sucked downward from a surface side of a material bed (hereinafter referred to as suction gas) is adjusted so that the oxygen concentration is at 6% or more. In Examples, oxygen concentrations in the suction gas ranging from 21% to 25% were examined, and the effect of improving the strength of sintered ore by oxygen enrichment was confirmed.

[0007] Patent Literature 3 discloses a method of supplying an oxygen-containing gas using a differential pressure in the double-layer charging and double-layer ignition sintering method. Patent Literature 3 describes that the oxygen concentration of the oxygen-containing gas to be supplied is preferably 12 to 40%.

[0008] Patent Literature 4 discloses a technique for achieving a double-layer ignition sintering method in which a charging bed (material packed bed) is formed by single-layer charging, an upper surface of the charging bed is ignited by an ignition furnace, and a middle part of an upstream end of the charging bed is ignited from a side by a burner. Patent Literature 4 also describes that performing oxygen enrichment in a suction gas at a downstream side of the ignition furnace solves the insufficient combustion in a lower part of the charging bed. In Examples, oxygen concentrations in the suction gas ranging from 21% to 46% were examined, and an improvement in production rate and strength by oxygen enrichment were confirmed.CITATION LISTPATENT LITERATURE(S)

[0009] Patent Literature 1: JPS47-26304 A Patent Literature 2: JPH06-43618 B Patent Literature 3: JP 2000-17343 A Patent Literature 4: JP 2015-157980 A SUMMARY OF THE INVENTIONPROBLEM(S) TO BE SOLVED BY THE INVENTION

[0010] However, in the test of the double-layer charging and double-layer ignition method in Patent Literature 2, no consideration is given to areas where the oxygen concentration of the suction gas exceeds 25%. In the technique of Patent Literature 3, the oxygen-containing gas is supplied by differential pressure. Patent Literature 3 does not suggest a double-layer charging and double-layer ignition method in which the oxygen-containing gas is sucked in without using differential pressure.

[0011] Patent Literature 4 discloses the test result of applying the double-layer ignition technique to the single-layer charging method, in which materials are charged at once to form a single-layer charging bed. Patent Literature 4 does not disclose the test result of the double-layer charging and double-layer ignition method. The material mixture granules are charged into a pallet of the sintering machine through a charging chute with particle size segregation, with smaller particles tending to lie on an upper side of the material bed and the larger particles tending to lie on a lower side of the material bed. Thus, for example, the carbonaceous material with small particle sizes remain fine even after granulation and will be distributed in large quantities on the upper side of the material bed. A lower part of the charging bed in the single-layer charging method has a coarser particle size and a lower carbonaceous material concentration than the lower layer bed in the double-layer charging method, in which respective beds are formed in two batches. It is generally known that such differences in particle size segregation and carbonaceous material distribution in a bed thickness (bed height) direction change the firing conditions, such as the temperature within the bed and air permeability, during sintering, and affect yield and productivity.

[0012] In the technique of Patent Literature 4, a lower part of the charging bed is ignited by applying flame from a side to the middle part of the upstream end of the charging bed. Since the charging bed on the pallet moves toward a discharge end along with the pallet, the ignition time of this technique is inevitably shorter than that of ignition by an ignition furnace in the double-layer charging and double-layer ignition method. In addition, the material mixture granules supplied from the hopper get in between the lower part of the charging bed and the flame during the ignition. This may reduce the amount of heat input to the lower part during actual operation, retarding the sintering reaction. Furthermore, the flame is blown toward a slope at the upstream end of the charging bed, which may affect the particle size segregation or the like. Based on the above, the inventors concluded that the effect of the oxygen enrichment in the suction gas in the double-layer charging and double-layer ignition method cannot be expected from the findings of Patent Literature 4.

[0013] In view of the above problems, the inventors studied the effect on the productivity (production rate) when the oxygen concentration of a gas supplied to the lower layer bed and the upper layer bed by downward suction is set, at atmospheric pressure, to a high oxygen concentration range exceeding 25% in the double-layer charging and double-layer ignition method.

[0014] An object of the invention is to provide a method for producing sintered ore that enables an improvement in production rate in a double-layer charging and double-layer ignition method.MEANS FOR SOLVING THE PROBLEMS

[0015] [1] A method for producing sintered ore, the method including: charging granules of a material mixture of a lower layer group into a sintering machine to form a lower-layer material packed bed; charging granules of a material mixture of an upper layer group onto the lower-layer material packed bed to form an upper-layer material packed bed; and igniting a surface of the lower-layer material packed bed and a surface of the upper-layer material packed bed and introducing, at atmospheric pressure, an oxygen-containing gas into the lower-layer material packed bed and the upper-layer material packed bed by downward suction, in which at least a part of the gas that is downwardly suctioned from a surface side of the upper-layer material packed bed after completion of the ignition of the upper-layer material packed bed is an oxygen enriched gas having an oxygen concentration of 26 vol% or more and 46 vol% or less, and assuming that a middle position of a section from a point immediately after an outlet of an upper-layer ignition furnace to a discharge end in a longitudinal direction of the sintering machine is defined as an intermediate position and a section from the point immediately after the outlet of the upper-layer ignition furnace to the intermediate position in the longitudinal direction is defined as a former half section, an area where the oxygen enriched gas is supplied is an area that includes a part of the former half section. [2] The method for producing sintered ore according to [1], in which the part of the former half section is an upstream part of the former half section. [3] The method for producing sintered ore according to [1], in which assuming that a section from the intermediate position to the discharge end in the longitudinal direction of the sintering machine is defined as a latter half section, the area where the oxygen enriched gas is supplied at least includes a part corresponding to the former half section, and the part corresponding to the former half section is longer than a part corresponding to the latter half section. [4] The method for producing sintered ore according to [1], in which the area where the oxygen enriched gas is supplied is the former half section or the part of the former half section. [5] The method for producing sintered ore according to any one of [1] to [4], in which the material mixture of the lower-layer material packed bed includes a highly combustible carbonaceous material with a combustion rate at 700 degrees C of 0.0022 (1 / sec) or more. [6] The method for producing sintered ore according to [5], in which the highly combustible carbonaceous material includes char obtained by carbonizing coal with a Roga index of less than 10. [7] The method for producing sintered ore according to [5], in which the highly combustible carbonaceous material includes palm kernel shell charcoal.

[0016] According to the above aspect of the invention, the productivity in the double-layer charging and double-layer ignition method can be improved by using an oxygen enriched gas having an oxygen concentration of 26 vol% or more and 46 vol% or less as at least a part of gas that is downwardly suctioned from a surface side of an upper layer bed after completion of ignition of the upper layer bed and setting an area where the oxygen enriched gas is supplied, to an area that includes a part of a former half section of a section ranging from a point immediately after an outlet of an upper-layer ignition furnace to a discharge end.BRIEF DESCRIPTION OF DRAWINGS

[0017] Fig. 1 schematically illustrates sintered ore producing steps using a double-layer charging and double-layer ignition sintering method according to an exemplary embodiment of the invention. Fig. 2 is a graph illustrating a relationship between oxygen concentration of oxygen enriched gas and product yield. Fig. 3 is a graph illustrating a relationship between oxygen concentration of oxygen enriched gas and production rate. DESCRIPTION OF EMBODIMENT(S)

[0018] Referring to Fig. 1, a double-layer charging and double-layer ignition sintering method according to an exemplary embodiment of the invention will be described below.

[0019] Fig. 1 schematically illustrates sintered ore producing steps using the double-layer charging and double-layer ignition sintering method, in which granulated material mixtures are charged in double layers to form an upper-layer material packed bed (hereinafter referred to as an upper layer bed) and a lower-layer material packed bed (hereinafter referred to as a lower layer bed), and sintering is performed by igniting each of the upper layer bed and the lower layer bed.

[0020] First, an exemplary double-layer charging and double-layer ignition sintering method as a related art will be described below.

[0021] In the example illustrated in Fig. 1 (excluding an oxygen enriched gas supplying unit 7), an upper-layer material mixture for forming an upper layer bed 20 and a lower-layer material mixture for forming a lower layer bed 10 are prepared in separate groups (two groups) and charged onto a pallet (not illustrated in Fig. 1) of a sintering machine 100 in separate groups. Specifically, lower-layer materials are stored in material bins (1D 1 to 1D X ) of lower-layer material bins 1D, and required types and amounts of the materials are dispensed from the bins in predetermined proportions and blended. The blended lower-layer materials (lower-layer material mixture) are fed into a lower-layer drum mixer 1A and mixed, and then water is added and the mixture is granulated. Upper-layer materials are stored in material bins (2D 1 to 2D y ) of upper-layer material bins 2D, and required types and amounts of the materials are dispensed from the bins in predetermined proportions and blended. The blended upper-layer materials (upper-layer material mixture) are fed into an upper-layer drum mixer 2A and mixed, and then water is added and the mixture is granulated. Carbonaceous materials for the lower and upper layer materials include coke breeze and anthracite. For example, when both coke breeze and anthracite are used as materials, they may be stored in separate material bins, or the coke breeze and anthracite may be mixed in a specified ratio and stored in the same material bin.

[0022] The granulated lower-layer material mixture (lower-layer material mixture granules) is charged from a lower-layer hopper 1B onto a pallet covered with bedding ore, thus forming the lower layer bed 10 (lower-layer material packed bed). The lower layer bed 10 is moved to below a lower-layer ignition furnace 1C by moving the pallet in a pallet traveling direction 5, where the carbonaceous material on a surface of the lower layer bed 10 is ignited by the lower-layer ignition furnace 1C. After ignition, sintering of the lower layer bed 10 is started by downward suction 6, which sucks air from below through a wind box (not illustrated) under the pallet. The sintering of the lower layer bed 10 progresses downward by the downward suction 6 performed continuously, forming a lower-layer bed combustion zone 10A.

[0023] When the lower layer bed 10, for which sintering has begun, reaches below an upper-layer hopper 2B, the granulated upper-layer material mixture (upper-layer material mixture granules) is charged from the upper-layer hopper 2B onto the ignited lower layer bed 10 to form the upper layer bed 20 (upper-layer material packed bed). The upper layer bed 20 is moved to below an upper-layer ignition furnace 2C by moving the pallet in the pallet traveling direction 5, where the carbonaceous material on a surface of the upper layer bed 20 is ignited by the upper-layer ignition furnace 2C. After ignition, sintering of the upper layer bed 20 is started by the downward suction 6. The sintering of the upper layer bed 20 progresses downward by the downward suction 6 performed continuously, forming an upper-layer bed combustion zone 20A.

[0024] As described above, in the double-layer charging and double-layer ignition method, the lower layer bed 10 is formed in the sintering machine 100, the surface of the lower layer bed 10 is ignited, the upper layer bed 20 is formed on the ignited lower layer bed 10, and the surface of the upper layer bed 20 is ignited. When ignition for the lower layer bed 10 begins, the downward suction 6 is started to advance the sintering of the lower layer bed 10 in a bed thickness direction. By further performing the downward suction 6, after the ignition of the upper layer bed 20, the sintering of the lower-layer bed combustion zone 10A of the lower layer bed 10 and the sintering of the upper-layer bed combustion zone 20A of the upper layer bed 20 concurrently proceed downward. When the lower-layer bed combustion zone 10A and the upper-layer bed combustion zone 20A reach the bottom of their respective beds, sintering by combustion of the carbonaceous materials ends, and the lower layer bed 10 and the upper layer bed 20 become a sintered portion 3. Finally, the sintered portion 3 where sintering is completed is discharged from an end of the pallet (discharge end).

[0025] A method for producing sintered ore according to the exemplary embodiment of the invention includes: charging granules of a material mixture of a lower layer group into a sintering machine to form a lower-layer material packed bed; charging granules of a material mixture of an upper layer group onto the lower-layer material packed bed to form an upper-layer material packed bed; and igniting a surface of the lower-layer material packed bed and a surface of the upper-layer material packed bed and introducing, at atmospheric pressure, an oxygen-containing gas into the lower-layer material packed bed and the upper-layer material packed bed by downward suction, in which at least a part of the gas that is downwardly suctioned from a surface side of the upper-layer material packed bed after completion of the ignition of the upper-layer material packed bed is an oxygen enriched gas having an oxygen concentration of 26 vol% or more and 46 vol% or less, and assuming that a middle position of a section from a point immediately after an outlet of an upper-layer ignition furnace to a discharge end in a longitudinal direction of the sintering machine is defined as an intermediate position and a section from the point immediately after the outlet of the upper-layer ignition furnace to the intermediate position in the longitudinal direction is defined as a former half section, an area where the oxygen enriched gas is supplied (oxygen enriched area) is an area that includes a part of the former half section. As illustrated in Fig. 1, the sintering machine 100 used in the exemplary embodiment of the invention includes the oxygen enriched gas supplying unit 7 in addition to the components of the sintering machine used in the related arts described above. The oxygen enriched gas supplying unit 7 includes a hood 8 and a gas pipe 9 through which the oxygen enriched gas is supplied into the hood 8. The oxygen enriched gas supplying unit 7 supplies the oxygen enriched gas with an oxygen concentration of 26 vol% or more and 46 vol% or less to an upper side (surface side) of the upper-layer material packed bed. The supplied oxygen enriched gas is guided into the material packed bed by the downward suction 6 of the wind box to advance the sintering reaction, and is recovered as exhaust gas by the wind box. In areas other than the oxygen enriched area, the air above the surface of the upper-layer material packed bed is introduced into the upper-layer material packed bed and the lower-layer material packed bed from the surface side of the upper-layer material packed bed by downward suction.

[0026] Alternatively, the hood 8 may not be provided, and oxygen gas may be injected from the gas pipe 9 toward the surface of the upper-layer material packed bed and then sucked together with the air. At this time, the supply amount of oxygen gas injected from the gas pipe 9 is adjusted so that the oxygen concentration on the surface of the upper-layer material packed bed is 26 vol% or more and 46 vol% or less. Here, setting the oxygen concentration of the oxygen enriched gas at 26 vol% or more and 46 vol% or less is based on the results of Examples described later. More preferably, the oxygen concentration is in a range from 36 vol% to 46 vol% in order to rapidly advance the combustion of the carbonaceous materials in the lower layer bed and to avoid supplying unnecessary oxygen.

[0027] The range (area) in which the oxygen enriched gas is supplied will be described below, assuming that a middle position of a section (entire section) from a point X immediately after the outlet of the upper-layer ignition furnace to a discharge end Y in the longitudinal direction (pallet traveling direction 5) of the sintering machine 100 is defined as an intermediate position Z, a section from the point X immediately after the outlet of the upper-layer ignition furnace to the intermediate position Z in the longitudinal direction is defined as a former half section, and a section from the intermediate position Z to the discharge end Y in the longitudinal direction is defined as a latter half section. Here, the point X immediately after the outlet of the upper-layer ignition furnace refers to a most upstream position where the oxygen enriched gas supplying unit 7 can be installed. In the pallet traveling direction 5 of the sintering machine 100, the position where the oxygen enriched gas supplying unit 7 is provided, i.e., the area where the oxygen enriched gas is supplied to a surface side of a sintered layer and suctioned downward (oxygen enriched area), is provided downstream of the upper-layer ignition furnace 2C. In Fig. 1, a safety interval is provided between the upper-layer ignition furnace 2C and the oxygen enriched gas supplying unit 7. If it is necessary to provide the safety interval, the point X immediately after the outlet of the upper-layer ignition furnace is a position X1, which is an upstream end of the oxygen enriched gas supplying unit 7 installed leaving the safety interval only. If there are no safety issues, the upper-layer ignition furnace 2C and the oxygen enriched gas supplying unit 7 may be continuously arranged. In such a case, the point X immediately after the outlet of the upper-layer ignition furnace is a position X2, which is a downstream end of the upper-layer ignition furnace. Preferably, the oxygen enriched gas supplying unit 7 is configured to continuously supply the oxygen enriched gas in the pallet traveling direction 5. It should be noted that the safety may be ensured as follows: the upper-layer ignition furnace 2C and the oxygen enriched gas supplying unit 7 are continuously arranged, and the oxygen concentration is set low (e.g., 26 vol% or more and 35 vol% or less) within the range from 26 vol% to 46 vol% only on the upstream side of the oxygen enriched gas supplying unit 7 in the pallet traveling direction (a side close to the upper-layer ignition furnace 2C).

[0028] The section in which the oxygen enriched gas supplying unit 7 is provided, i.e., the area in which the oxygen enriched gas is supplied to the surface of the material packed bed (hereinafter also referred to as the oxygen enriched area), includes a part of the former half section (the section from the point X immediately after the outlet of the upper-layer ignition furnace to the intermediate position Z) in the longitudinal direction of the sintering machine 100. Here, the part of the former half section is preferably an upstream part of the former half section (e.g., a part corresponding to 0 to 0.30 assuming that a position of an upstream end of the former half section in the pallet traveling direction is set at 0 and a position of a downstream end thereof is set at 0.5). Furthermore, it is preferable that the oxygen enriched area at least includes a part corresponding to the former half section, and that the part corresponding to the former half section is longer than a part corresponding to the latter half section (the section from the intermediate position Z to the discharge end Y). Moreover, the oxygen enriched area may include the entire former half section and a part of the latter half. More preferably, the oxygen enriched area is the former half section or a part of the former half section.

[0029] The reason for specifying the oxygen enriched area as described above is as follows: in Examples described later, setting the range from the point X immediately after the outlet of the upper-layer ignition furnace to the intermediate position Z (former half section) or a part of that range (a part of the former half section) as the range in which the oxygen enriched gas was supplied was more effective than setting the range from the intermediate position Z to the discharge end Y (latter half section) as the range in which the oxygen enriched gas was supplied. The effect can thus be obtained if the oxygen enriched area is an area that includes the former half section or an area that includes a part of the former half section. Here, when the oxygen enriched area is defined as a part of the entire section, the reason why the oxygen enrichment in the former half section is more effective than the oxygen enrichment in the latter half section is thought to be as follows.

[0030] The oxygen enrichment is performed to address the situation where the combustion of carbonaceous materials in the lower layer bed is inactive (incomplete) due to a lack of oxygen. In the section where the oxygen enrichment is performed, the combustion of carbonaceous materials becomes active, and the temperature inside the sintering machine can be maintained at an appropriate high temperature. If the oxygen enrichment is performed in the former half section, maintaining a high temperature in the former half section allows the temperature inside the sintering machine to remain high and the sintering reaction to proceed even if the oxygen enrichment is not performed in the latter half section. On the other hand, if the oxygen enrichment is not performed in the former half section but performed in the latter half section, carbonaceous material combustion in the former half section remains inactive and the temperature inside the sintering machine decreases. Therefore, even if the oxygen enrichment is performed later in the latter half section, it is difficult to sufficiently recover the temperature inside the sintering machine. For this reason, the oxygen enrichment in the former half section (or the upstream part of the former half section) is thought to be effective.

[0031] In the sintering machine, particle size segregation is provided when the material mixture is charged, and the fine-grained carbonaceous materials have a higher concentration at an upper part of the bed compared to main materials such as iron ore. Thus, in the double-layer charging and double-layer ignition method, the amount of carbonaceous materials is greater in the upper part than in the lower part in both the lower layer bed and the upper layer bed. Since the greater the amount of carbonaceous materials, the greater the amount of oxygen required for combustion, it is preferable to perform the oxygen enrichment in the former half section, which corresponds to the combustion section at the upper part of the bed. When limiting the oxygen enriched area in order to reduce the cost of oxygen gas, for the reasons described above, it is preferable to set the oxygen enriched area to an area that at least includes a part of the former half section (each of the areas described in paragraph 0030).

[0032] The composition of the upper-layer material mixture and the composition of the lower-layer material mixture may be the same or different. If the upper-layer material mixture and the lower-layer material mixture have the same composition, they may be prepared in the same group rather than in separate groups (two groups).

[0033] As will be shown in Examples described later, in a method for producing sintered ore according to the exemplary embodiment of the invention, it is preferable to use a highly combustible carbonaceous material as part or all of lower-layer carbonaceous materials. The highly combustible carbonaceous material is a carbonaceous material (bonding agent) with a combustion rate at 700 degrees C of 0.0022 (1 / sec) or more, as shown in Table 1. The highly combustible carbonaceous material includes coal char, palm kernel shell charcoal (PKS charcoal), and wood charcoal produced by carbonizing wood. The combustion start temperature of the highly combustible carbonaceous material is lower than that of coke or anthracite. Table 1Coke breezeAnthraciteHighly combustible carbonaceous materialCoal charPKS charcoalWood charcoalCombustion rate (700°C) (1 / sec)0.001120.002150.002830.003150.00421

[0034] The palm kernel shell charcoal (PKS charcoal) is a solid carbide produced by heat treatment (carbonization) of palm kernel shell. The coal char is a carbonaceous material (char) for sintering produced by carbonizing low-fluidity coal (for example, coal with a Roga index of less than 10) as raw coal. The coal char is produced by carbonizing raw coal (including blended coal) in a pyrolysis furnace (e.g., a rotary kiln). It is possible to produce highly combustible coal char by using low-fluidity coal with a Roga index of less than 10 as raw coal. The fluidity of coal is a property resulting from the degree of degradation to lower molecular weights when heated, and the low-fluidity coal is less likely to degrade to lower molecular weights when heated.

[0035] The Roga index is calculated by a Roga test method specified in JIS-M8801 (2008). The Roga test method is described below.

[0036] First, 1 g of low-grade coal with a particle size of 200 µm or less and 5 g of standard anthracite are thoroughly mixed in a crucible. The standard anthracite used has an ash content (on a dry basis) of 4.0% or less, a volatile content (on a dry basis) of 5.0% to 6.5%, and a particle size of 300 µm to 400 µm. Subsequently, a heat-resistant steel weight is used to apply a constant load (59 N) to the low-grade coal and standard anthracite in the crucible for a predetermined time (at least 30 seconds).

[0037] Subsequently, the above-mentioned crucible is placed in an electric furnace with a furnace temperature set to 850±10 degrees C, and the low-grade coal and standard anthracite are heated (carbonized) for 15 minutes. The heated crucible is then placed on a heat-resistant plate and cooled for 45 minutes, after which the mass of the contents (hereinafter occasionally referred to as a carbonized material) of the crucible is measured and the mass of the carbonized material on a sieve is measured using a 1 mm circular hole plate sieve.

[0038] Subsequently, the contents (carbonized material) of the crucible are placed in a drum, and the drum is rotated at a predetermined rotation rate (50 rpm) for 5 minutes, thereby subjecting the carbonized material to a breaking treatment. The inner diameter of the drum is 200 mm, the depth of the drum is 70 mm, and two blades, each 70 mm long and 30 mm wide, are symmetrically arranged on an inner peripheral wall of the drum.

[0039] Subsequently, the carbonized material after the breaking treatment is sieved using the 1 mm circular hole plate sieve, and the mass on the sieve is measured. The above-mentioned breaking treatment is repeated three times, and the Roga index is calculated based on the following formula (1). In the formula (1), RI represents the Roga index, m 1 represents the total mass [g] of the crucible contents (carbonized material) after carbonization, m 2 represents the mass [g] of the carbonized material on the sieve before the first breaking treatment, m 3 represents the mass [g] of the carbonized material on the sieve after the first breaking treatment, m 4 represents the mass [g] of the carbonized material on the sieve after the second breaking treatment, and m 5 represents the mass [g] of the carbonized material on the sieve after the third breaking treatment. [Formula 1] RI = 100 3 m 1 m 2 + m 5 2 + m 3 + m 4

[0040] The combustion rate (700 degrees C) shown in Table 1 is calculated as follows.

[0041] First, 10 mg of a sample to be measured is placed on a thermobalance inside an apparatus, and after thoroughly purging the inside of the apparatus with nitrogen, the sample is heated at a temperature increase rate of 100 degrees C / min with nitrogen flowing at 200 ml / min. Immediately after the sample temperature reached 700 degrees C, the flowing gas is switched from nitrogen to air at 200 ml / min to measure the weight loss, and a reaction time t (a time elapsed since the flowing gas has switched from nitrogen to air) and data for reaction rate Xr (Xr = [Amount of weight loss at each time - Weight of unburned matter at the end of measurement] / [Initial weight of sample - Weight of unburned matter at the end of measurement]) are obtained therefrom. Then, a reaction speed dXr / dt for each reaction rate is calculated, an average value with Xr being 0 to 0.5 is calculated, and this average value is used as the combustion rate at 700 degrees C.

[0042] In the double-layer charging and double-layer ignition method, the oxygen concentration of the gas supplied to the lower layer bed is lower than that supplied to the upper layer bed. The highly combustible carbonaceous material having a low combustion start temperature can burn even in low temperature conditions caused by low oxygen environments, which can prevent poor combustion (unburned carbonaceous material). As shown in Examples below, the production rate is significantly improved when the oxygen enrichment is combined with the use of the highly combustible carbonaceous material in the lower layer bed. The reasons for this effect are thought to be as follows. As shown in Table 1, the combustion rate of the highly combustible carbonaceous material is fast. However, when the highly combustible carbonaceous material is used without performing the oxygen enrichment, poor combustion can be inhibited, but the combustion rate is not fast enough due to lack of oxygen, and the combustion is sluggish. As a result, it is difficult to maintain an appropriate high temperature inside the sintering machine. On the other hand, performing the oxygen enrichment adjusts the oxygen concentration, thereby making it possible to adjust the combustion rate of the highly combustible carbonaceous material. The oxygen enrichment increases the sintering rate, which stimulates the combustion of carbonaceous materials and maintains an appropriately high temperature inside the sintering machine. Furthermore, since the combustion rate at 700 degrees C of the highly combustible carbonaceous material is fast, when the highly combustible carbonaceous material is used in the sintering step, the time required for the entire amount of carbonaceous materials to burn completely is shortened, and the time required for sintering to be completed is also shortened. Shorting the time until the completion of sintering increases the amount of sintered ore produced per unit time, resulting in a high production rate (t representing sintered ore / day / m 2< (t / d / m 2< )). Therefore, actively using the highly combustible carbonaceous material in the lower layer bed is effective in improving productivity (improving the sintering rate). The percentage of the highly combustible carbonaceous material is preferably in a range from 30 mass% to 100 mass% based on the total amount of carbonaceous materials used. When the percentage of the highly combustible carbonaceous material is less than 30 mass%, the sintering rate does not increase because it depends on the combustion rate of the carbonaceous materials other than the highly combustible carbonaceous material. When the percentage of the highly combustible carbonaceous material is increased to 100 mass%, the combustion rate increases accordingly and the sintering rate increases.

[0043] The highly combustible carbonaceous material is incorporated into the lower layer bed as follows.

[0044] As illustrated in Fig. 1, the upper-layer material mixture for forming the upper layer bed 20 and the lower-layer material mixture for forming the lower layer bed 10 are prepared in separate groups (two groups). At least one of the material bins (1D 1 to 1D X ) of the lower-layer material bins 1D is used as a material bin for storing the highly combustible carbonaceous material. For example, the material bin 1D 1 (first carbonaceous material bin) of the lower-layer material bins 1D stores carbonaceous materials other than the highly combustible carbonaceous material (e.g., coke and / or anthracite), and the material bin 1D 2 (second carbonaceous material bin) stores the highly combustible carbonaceous material (e.g., coal char and / or PKS charcoal). When two or more types of carbonaceous materials other than the highly combustible carbonaceous material and / or two or more types of highly combustible carbonaceous materials are used, each of the material bins may be provided for a corresponding one type of the materials.Examples

[0045] Examples that demonstrate the effects of the invention will be described below. Note that the invention is not limited to Examples below.

[0046] The inventors conducted a sinter pot test (diameter: 300 mm) capable of simulating sintering using a DL-type sintering machine, and verified the effects of the invention. Unlike the DL-type sintering machine, a device for the sinter pot test does not move the material packed bed on the pallet. In the sinter pot test device, the material mixture is charged into a predetermined-size container and ignited from the top, and then sintering proceeds by downward suction.

[0047] As shown in Table 3 below, 14 tests were performed, including Comparatives 1 to 5 and Examples 1 to 9.Blend of Materials

[0048] Table 2 shows materials and blending proportions thereof. As shown in Table 2, two types of material mixtures were prepared: material mixture a and material mixture b. In the material mixture, new materials that were iron ores A to D, peridotite, quicklime, and limestone were blended in proportions shown in Table 2. The iron ores A to D used had mutually different production areas. The bonding agent (carbonaceous material) was blended at 4.5 mass% (not included in total mass) with the new materials at 100 mass%. The material mixture a contained coke breeze as the carbonaceous material, while the material mixture b contained half coke breeze and half PKS charcoal, which was the highly combustible carbonaceous material. As shown in Table 3 below, the material mixture b was used only in the lower layer bed in each of Comparative 5, Example 8, and Example 9. That is, in each of Comparative 5, Example 8, and Example 9, PKS charcoal was blended as the bonding agent in the lower layer bed. Table 2Material Mixture (mass%)New materialsCarbonaceous material (not included in total mass)Iron oreFluxTotalABCDPeridotiteQuicklimeLimestoneCokePKS charcoalMaterial Mixture a20.010.034.920.01.61.512.0100.04.50.0Material Mixture b20.010.034.920.01.61.512.0100.02.252.25 Granulation Method

[0049] The material for the upper layer bed and the material for the lower layer bed were granulated separately. To the material mixture for each of the upper and lower layer beds mixed for 4 minutes using a drum mixer (diameter 600 mm, rotation speed 25 rpm), 7.2 mass% of water was added, followed by granulation for further 4 minutes.Test Cases

[0050] Test cases are as follows. As shown in an upper row of Table 3, in Comparatives 1 to 5 and Examples 1 to 9, the double-layer charging and double-layer ignition method was performed by changing, at atmospheric pressure, the oxygen concentration of the suction gas supplied from the surface side of the upper layer bed and suctioned downward within a range of 21 vol% (without oxygen enrichment) to 50 vol%. Details will be described later, but in the sinter pot tests of Comparatives 2 and 4 and Examples 1 to 3 and 6 to 9, the oxygen enriched gas was supplied in a bed height range (position) corresponding to the former half section (the former half of the section from the point immediately after the outlet of the upper-layer ignition furnace to the discharge end) in the actual machine; in Comparative 3, the oxygen enriched gas was supplied in a bed height range corresponding to the latter half section (the latter half of the section from the point immediately after the outlet of the upper-layer ignition furnace to the discharge end); in Example 4, the oxygen enriched gas was supplied in a bed height range corresponding to a part of the former half section; and in Example 5, the oxygen enriched gas was supplied in a bed height range corresponding to both the former half section and the latter half section (all sections). In addition, "a part of the former half section" in Example 4 specifically refers to an upstream part of the former half section in the actual machine, and is an area where the length of the upstream part is 0.28 assuming that the length of the former half section is 0.5. In Comparatives 1 and 5, no oxygen enrichment was performed. Firing Conditions

[0051] The bed thickness of the double-layer charging was 500 mm for the lower layer bed and 300 mm for the upper layer bed. Two pots were prepared: a cylindrical lower-layer pot with a diameter of 300 mm and a height of 500 mm, and a cylindrical upper-layer pot with a diameter of 300 mm and a height of 300 mm.

[0052] First, the granulated lower-layer material mixture and upper-layer material mixture were charged into the lower-layer pot and the upper-layer pot, respectively, with the bed height of the lower layer bed being 500 mm and the bed height of the upper layer bed being 300 mm. Then, the lower-layer pot with a bed height of 500 mm was set and ignited on a surface of the lower layer bed for 1 minute. Then, the upper-layer pot with a bed height of 300 mm was placed on the lower-layer pot, and in order to achieve double-layer sintering, a surface of the upper layer bed was ignited for 1 minute after confirming the temperature rise at a position having a bed height of 320 mm (320 mm from a lower surface of the lower layer bed) (by measuring the temperature with a thermocouple, which will be described later). The suction pressure was kept constant at 1,200 mmAq (11.8 kPa) from the start of ignition.Sintering Time

[0053] Thermocouples were inserted at bed heights of 440 mm, 320 mm, 230 mm, and 170 mm to measure the temperature inside the beds. Since the later of the completion of sintering of the upper layer bed and the completion of sintering of the lower layer bed was considered to be the completion of sintering of the entire material packed bed (upper layer bed and lower layer bed), the longer of the time taken for the thermocouple at 440 mm to start the second temperature rise (completion of sintering of the upper layer bed) and the time taken for the exhaust gas temperature at the wind box position to reach a peak (completion of sintering of the lower layer bed) was defined as the sintering time of the entire material packed bed. Suction was stopped 3 minutes after the sintering was completed, and sintering was terminated.Oxygen Enrichment

[0054] As shown in Table 3, the oxygen enrichment was performed in four patterns: a part of the former half section, the former half section, the latter half section, and all of the sections. Under a condition for a part of the former half section, the oxygen enrichment was performed from immediately after the start of the upper layer ignition (within 2 seconds after 0 seconds) until a timing at which the temperature rose at the 230 mm position. Under a condition for the former half section, the oxygen enrichment was performed from immediately after the start of the upper layer ignition until a timing at which the temperature rose at the 170 mm position, which corresponded to about a halfway position of the upper layer bed height. Under a condition for the latter half section, the oxygen enrichment was performed from a timing at which the temperature rose at the 170 mm position until the end of the test. Under a condition for all of the sections, the oxygen enrichment was performed from immediately after the start of upper layer ignition until the end of the test.Yield

[0055] The yield was measured as follows. After sintering, the obtained sinter cake was dropped four times from a height of 2 m, particles with a particle size of +5 mm (exceeding 5 mm) were defined as a sintered product, and the mass of the sintered product was obtained. The percentage (mass%) of this sintered product to the total mass of the sinter cake was defined as the product yield (+5 mm%) here.Production Rate

[0056] The production rate was calculated based on the sintering time measured as described above using the following formula (2). Sintered Ore Strength

[0057] The sintered ore strength was obtained by measuring a cold strength (tumble index TI) based on JIS M8712 (2009). The mass of the test sample was set to 15 kg (15 mm-40 mm size). The strength measurement was performed only on the lower-layer sintered ore (sintered ore in the lower-layer pot). A device used for the measurement was a cylindrical container (diameter 1,000 mm, depth 500 mm), in which the test sample was placed and rotated at a rotation speed of 25 rpm for 8 minutes. The mass of +6 mm of the sintered ore recovered after rotation was determined, and the percentage (mass%) of this sintered ore to 15 kg of the test sample was defined as the cold strength.Test Results

[0058] The test results are shown in the lower part of Table 3. Figs. 2 and 3 are graphs showing the test results in Table 3. Fig. 2 is a graph illustrating a relationship between oxygen concentration of oxygen enriched gas (vol%) and product yield (mass%). Fig. 3 is a graph illustrating a relationship between oxygen concentration of oxygen enriched gas (vol%) and production rate (t / d / m 2< ). A dashed line in Fig. 3 is a line obtained by shifting a straight line connecting the plots of Comparative 1 and Comparative 2 in a plus direction by 0.5 (t / d / m 2< ) in a parallel manner, and the test examples located above this dashed line are Examples of the invention.

[0059] In the test results for cases where no highly combustible carbonaceous material was used, as shown in Table 3, Fig. 2, and Fig. 3, the yield was significantly improved and the production rate was also improved in Examples 1 to 7 compared to Comparatives 1 and 2. Regarding the strength, Example 1 was approximately the same as Comparatives 1 and 2, but Examples 2 to 7 were improved. Comparative 4 in which the oxygen concentration was 50 vol% had lower yield, strength, and production rate than Example 7 in which the oxygen concentration was 46 vol%. This revealed that excessive oxygen enrichment was unnecessary and an oxygen concentration of 26 vol% to 46 vol% was desirable. The oxygen enrichment is not cost-effective because it incurs costs to produce oxygen (for example, a method of separating oxygen from air requires air compression and cooling, which incur costs for electricity, etc.), and thus Comparative 4 in which an oxygen concentration was 50 vol%, was considered a comparative rather than an example of the invention. The results of Examples 3 to 5 and Comparative 3, in which the oxygen concentration was kept constant at 36 vol% and the oxygen enrichment position was changed, revealed as follows. The oxygen enrichment was more effective in the former half section (Example 3) than in the latter half section (Comparative 4). The values were lower in a part of the former half section (Example 4) than in the former half section (Example 3). However, when calculating the improvement rate of yield, strength, and production rate (based on Comparative 1) relative to the length of the section where the oxygen enrichment was performed, the effect was obtained more efficiently in the part of the former half section. In particular, in Example 4, the oxygen enrichment was performed in an upstream part of the former half section, and it has been found out that it is preferable to perform the oxygen enrichment in a certain section immediately after the outlet of the upper-layer ignition furnace.

[0060] The test results for cases using the highly combustible carbonaceous material were as follows. Comparative 5, in which the highly combustible carbonaceous material (PKS charcoal) was used in the lower layer bed and the oxygen enrichment was not performed, had lower yield and production rate than Comparative 1 in which PKS charcoal was not used and the oxygen enrichment was not performed. On the other hand, Example 8 in which PKS charcoal was used in the lower layer bed and the oxygen enrichment was performed had significantly improved production rate and yield than Comparative 5 in which the highly combustible carbonaceous material (PKS charcoal) was used in the lower layer bed and the oxygen enrichment was not performed and Comparative 1 in which PKS charcoal was not used and the oxygen enrichment was not performed. Example 9 in which the PKS charcoal was used and the oxygen enrichment was performed with an increased oxygen concentration of the supply gas had significantly improved production rate and yield than Comparative 5 in which the highly combustible carbonaceous material (PKS charcoal) was used in the lower layer bed and the oxygen enrichment was not performed. Example 9 (46 vol% oxygen concentration) had improved production rate and yield than Example 8 (26 vol% oxygen concentration) in which PKS charcoal was used in the lower layer bed and the oxygen enrichment was performed. Especially, Example 9 had the highest production rate among all the test examples. Similar effects were obtained not only with PKS charcoal, but also with coal char, which was the highly combustible carbonaceous material. These results revealed that combining the use of the highly combustible carbonaceous material with the oxygen enrichment was effective.EXPLANATION OF CODES

[0061] 100...sintering machine, 1A...lower-layer drum mixer, 1B...lower-layer hopper, 1C...lower-layer ignition furnace, 1D...lower-layer material bins (lower-layer material bins 1D 1 to 1D X ), 2A...upper-layer drum mixer, 2B...upper-layer hopper, 2C...upper-layer ignition furnace, 2D...upper-layer material bins (upper-layer material bins 2D 1 to 2D y ), 3...sintered portion, 5...pallet traveling direction, 6...downward suction, 7...oxygen enriched gas supplying unit, 8...hood, 9...gas pipe, 10...lower layer bed, 10A...lower-layer bed combustion zone, 20...upper layer bed, 20A...upper-layer bed combustion zone, X (X1, X2)...point immediately after outlet of upper-layer ignition furnace, Y...discharge end, Z...intermediate position

Claims

1. A method for producing sintered ore, the method comprising: charging granules of a material mixture of a lower layer group into a sintering machine to form a lower-layer material packed bed; charging granules of a material mixture of an upper layer group onto the lower-layer material packed bed to form an upper-layer material packed bed; and igniting a surface of the lower-layer material packed bed and a surface of the upper-layer material packed bed and introducing, at atmospheric pressure, an oxygen-containing gas into the lower-layer material packed bed and the upper-layer material packed bed by downward suction, wherein at least a part of the gas that is downwardly suctioned from a surface side of the upper-layer material packed bed after completion of the ignition of the upper-layer material packed bed is an oxygen enriched gas having an oxygen concentration of 26 vol% or more and 46 vol% or less, and assuming that a middle position of a section from a point immediately after an outlet of an upper-layer ignition furnace to a discharge end in a longitudinal direction of the sintering machine is defined as an intermediate position and a section from the point immediately after the outlet of the upper-layer ignition furnace to the intermediate position in the longitudinal direction is defined as a former half section, an area where the oxygen enriched gas is supplied is an area that includes a part of the former half section.

2. The method for producing sintered ore according to claim 1, wherein the part of the former half section is an upstream part of the former half section.

3. The method for producing sintered ore according to claim 1, wherein assuming that a section from the intermediate position to the discharge end in the longitudinal direction of the sintering machine is defined as a latter half section, the area where the oxygen enriched gas is supplied at least includes a part corresponding to the former half section, and the part corresponding to the former half section is longer than a part corresponding to the latter half section.

4. The method for producing sintered ore according to claim 1, wherein the area where the oxygen enriched gas is supplied is the former half section or the part of the former half section.

5. The method for producing sintered ore according to any one of claims 1 to 4, wherein the material mixture of the lower-layer material packed bed includes a highly combustible carbonaceous material with a combustion rate at 700 degrees C of 0.0022 (1 / sec) or more.

6. The method for producing sintered ore according to claim 5, wherein the highly combustible carbonaceous material includes char obtained by carbonizing coal with a Roga index of less than 10.

7. The method for producing sintered ore according to claim 5, wherein the highly combustible carbonaceous material includes palm kernel shell charcoal.

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