Slag aging method

Abstract

To provide a steam aging method that reduces steam segregation resulting from grain size segregation of slag after stacking in order to prevent expansion and collapse of slag used as roadbed material.SOLUTION: A method for aging slag that comprises, in this order, a pre-treatment step for crushing slag as raw material and adjusting the particle size thereof, a water sprinkling step for sprinkling and adding water, a stacking step for loading the slag into aging treatment facilities, and an aging step. It is preferable to have a stirring step after the water sprinkling step and before the stacking step, and further a heating and drying step after the stacking step and before the aging step, in which the raw material slag is heated and dried.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for aging slag, and more particularly to a steam aging method that reduces steam drift in order to prevent the expansion and collapse of slag used as roadbed material. [Background technology]

[0002] One of the most important issues is how to recycle the large amounts of steel slag (hereafter simply referred to as "slag") generated from converters and other processes in the steelmaking process. Because slag has a hard, stony quality, it is used as a roadbed material and aggregate for roads and other uses. However, steelmaking slag, in particular, contains free lime, which can cause it to expand when exposed to moisture, such as rainwater. For slag to be used for roads, JIS A 5015 "Iron and Steel Slag for Roads" stipulates that it must meet certain expansion characteristics (a water immersion expansion ratio of 1.0% or less). Therefore, steelmaking slag requires a process, known as an aging process, in which the free lime is allowed to react with moisture before use.

[0003] A widely known method for efficiently aging slag is the steam aging method, which uses steam to promote a reaction with water at high temperatures. Regarding this steam aging method, for example, Patent Document 1 discloses a technique in which water is added to steelmaking slag until the water content of the slag reaches 10% by weight or more, and then steam aging is performed. Furthermore, Patent Documents 2 and 3 disclose techniques in which water is sprayed onto the steelmaking slag to uniformly apply water, and then steam aging is performed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-12384 [Patent Document 2] Japanese Patent Application Publication No. 2017-149637 [Patent Document 3] JP 2017-7880 A Summary of the Invention [Problem to be solved by the invention]

[0005] The particle sizes of individual slag particles in slag for roadbed materials range widely, from several micrometers to several tens of millimeters. Therefore, in the aging method for slag, a slope is formed in the pile when the slag is transported to the aging equipment, filled, and stacked. This slope causes particle size segregation in the layer of slag packed into the aging equipment (hereinafter also referred to as the "slag packed layer"), where larger slag particles tend to roll to the edge of the pile and smaller slag particles concentrate in the center. In the steam aging method, this particle size segregation results in a large porosity in the areas where the coarse slag particles are concentrated, allowing steam to pass easily through, while the areas where the fine slag particles are concentrated restrict steam passage. This particle size segregation causes steam drift, resulting in the presence of insufficiently reacted slag after steam aging. The presence of such unreacted slag is one of the factors affecting the quality variation of roadbed materials.

[0006] The aforementioned Patent Documents 1, 2, and 3 describe that the efficiency of steam aging is improved by adding moisture before steam aging to promote the reaction in advance and then contacting the material with water vapor. However, no consideration is given to the effect of the above-mentioned particle size segregation on improving the efficiency of steam aging.

[0007] The present invention has been made to address the above-mentioned problems, and aims to provide a steam aging method that reduces steam drift caused by particle size segregation of slag after stacking in order to prevent the expansion and collapse of slag used as roadbed material. [Means for solving the problem]

[0008] As a result of extensive research into solving the above-mentioned problems, the inventors have discovered that in the steam aging method, controlling the particle size segregation during the slag stacking process as described above is important for quality control of roadbed material products.

[0009] The present invention was completed based on these findings and further investigations, and the gist of the present invention is as follows. [1] A method for aging slag, comprising: A pre-processing process in which the raw material slag is crushed and particle size adjusted; a watering step of adding moisture by watering; a loading step of loading the products into an aging treatment facility; An aging process; A method for aging slag, characterized in that: [2] The slag aging method according to [1], characterized in that it includes a stirring step after the water spraying step and before the stacking step. [3] In the above [1] or [2], a slag aging method characterized by including a temperature-rising drying step of heating and drying after the stacking step and before the aging step. [4] A method for aging slag according to [1] or [2], characterized in that the moisture content of the slag immediately before the loading process is set to 6 wt% to 12 wt%. [5] A method for aging slag, characterized in that in the temperature-rising drying process described in [3], the slag after the stacking process is heated and dried using high-temperature gas of 100°C or higher. [6] A method for aging slag according to any one of [1] to [5], wherein the slag is steelmaking slag, and the aging step comprises performing steam aging treatment using water vapor. [7] In any one of [1] to [6], the raw material slag has a particle size characteristic in which the particle size distribution index k calculated by the following formula (2) is 0.4 or more.

[0010]

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[0011]

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[0012] [8] In any one of [1] to [7], a slag aging method characterized in that the particle size segregation degree coefficient Iseg of the slag after the stacking process, calculated by the following equation (5), is controlled to a range of 1.0 to 1.5.

[0013]

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[0014]

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[0015]

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[0016] where aij is the division area (i: 1 to m, j: 1 to n), m is the number of division areas along the x direction, n is the number of division areas along the y direction, Nk(aij) is the number of k-component particles in the division area aij, Ck(aij) is the number concentration of k-component particles in the division area aij,

[0017]

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[0018] According to the present invention, when performing the aging treatment, spraying water on the slag before piling it increases the porosity in the slag packed bed and reduces particle size segregation of the slag. Furthermore, suppressing the uneven flow of steam in steam aging and stirring after spraying water significantly reduces particle size segregation, allowing the slag to react more uniformly. Furthermore, heating and drying the slag before aging shortens the aging treatment time. In the case of steam aging, the amount of water vapor can be reduced, resulting in the excellent effect of further improving productivity. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a flow chart showing steps of a slag aging method according to the present invention. [Figure 2] FIG. 1 is a diagram showing the relationship between the moisture content of slag and adhesiveness. [Figure 3] FIG. 1 is a diagram showing the relationship between the particle size distribution index and the particle size segregation coefficient for each moisture content of slag. [Figure 4] FIG. 1 is a diagram showing the relationship between the moisture content and the average porosity for each particle size distribution index of slag. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the slag aging method according to the present invention will be described in detail with reference to the drawings, but the present invention is not limited to these.

[0021] [Slug] First, we will explain the slag that is the subject of this invention. Steel slag includes blast furnace slag, which is produced when pig iron is produced in a blast furnace, and steelmaking slag, which is produced when steel is produced from pig iron in a converter or the like, or when scrap iron is melted and refined in an electric furnace. The steel slag used as roadbed material is made from blast furnace slag and steelmaking slag, either alone or in combination, and various types of slag are available depending on the application and quality.

[0022] The slag that is the target of the slag aging method of the present invention is not particularly limited, but it is preferable to apply it to steelmaking slag, from the viewpoint that the excellent effect of the present invention, which can prevent the expansion and collapse of slag, is best exhibited.

[0023] [Slag aging method] The outline of the slag aging method according to the present invention will be explained with reference to Fig. 1. Fig. 1 is a flow chart showing the flow of steps in the aging method according to the present invention.

[0024] The slag aging method according to the present invention is characterized by having the following basic steps in the following order: (1) The "pre-processing process" involves crushing and adjusting the particle size of the raw material, slag. <2> The "watering process" involves spraying water on the slag after the pre-treatment process to add moisture. (3) The "loading process" involves loading the slag after the watering process into the aging treatment facility. (4) Aging process: aging the slag after the loading process Furthermore, if necessary, <5> The "mixing process" is performed after the watering process and before the loading process, in which the slag is mixed after the watering process. or <6> After the loading process and before the aging process, the slag is heated and dried in the "heating and drying process." The present invention is characterized by having the following.

[0025] [〈1〉Pre-treatment process] First, the pre-processing process involves collecting slag generated from converters and other furnaces, adjusting it to an appropriate particle size using a crusher, and then piling the slag in a stockyard for storage. The crusher used here is, for example, an impact crusher. The particle size distribution of the slag is standardized in JIS A 5015, "Iron and Steel Slag for Road Use," and adjustments are made based on this standard.

[0026] Specifically, the solidified slag is crushed using a crusher or the like, and then passed through a sizing device to adjust the particle size to a predetermined range.

[0027] [Slag particle size distribution index k] The present inventors have found that using the "particle size distribution index k" described below is an effective method for pre-adjusting the particle size of slag.

[0028] The results of the inventors' investigation into slag particle size adjustment are shown in Figure 3. This figure shows the particle size segregation coefficient Iseg after stacking and filling for different moisture contents of slag with a particle size distribution index k that is applicable to roadbed materials.

[0029] Here, the particle size distribution index k is an index that indicates the fineness of the slag particle size, and is calculated by the following equation (2).

[0030]

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[0031]

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[0032] Here, Ds is the average particle diameter based on the specific surface area calculated by the above formula (1), wi is the weight ratio of particle group i, and di is the particle diameter of particle group i. Ds f : The average particle size based on the specific surface area of ​​the finest particle size distribution, Dmax and Dmin: The maximum and minimum particle sizes in the particle size distribution.

[0033] The slag used as the raw material in the present invention preferably has a particle size characteristic in which the particle size distribution index k is 0.4 or more. If k is less than 0.4, the particle size of the slag is too large and it is not suitable for use as a roadbed material.

[0034] The particle size distribution was measured using a sieving device according to JIS Z 8801 and in accordance with the particle size distribution measurement method of JIS Z 8815.

[0035] Specifically, the average particle size based on the specific surface area is measured by classifying sampled slag particles, assuming that the slag particles are spherical, and calculating the average particle size using the particle size of the classified slag and the slag density. The maximum and minimum particle sizes are the maximum and minimum mesh sizes of the classification sieve, and can be determined from these.

[0036] [〈2〉Watering process] The steps from this water spraying step to the aging step described below are the basic steps that characterize the present invention.

[0037] The water sprinkling process is a process for sprinkling water on the slag piled up in the stockyard in the above-mentioned pre-treatment process to provide an appropriate amount of moisture to the entire slag. The sprinkling device is not particularly limited, and any device or machine that can provide or supply moisture to the entire piled slag may be used. The amount of water to be sprinkled may be determined so as to achieve an appropriate moisture content for the amount of piled slag.

[0038] [Moisture content] The reason for spraying water on the slag before the next loading process is to impart adhesiveness to the slag through the liquid bridging force of water. Figure 2 shows the change in adhesiveness of slag used for roadbed construction after water spraying. If the adhesiveness is set to 1.0 when the moisture content is 0.4 wt% or less (i.e., almost moisture-free), adhesiveness increases with increasing moisture content, reaching a maximum (approximately 1.6 times the adhesiveness of the moisture-free state) at a moisture content of approximately 10 wt%. At higher moisture contents, the slag becomes supersaturated and adhesiveness decreases. By imparting adhesiveness to the slag, fine particles adhere to coarse particles, thereby reducing particle size segregation within the slag-packed bed. Therefore, the adhesiveness of the slag is preferably at least 1.5 times that of the dry (moisture-free) state, and the moisture content is preferably 5 wt% to 12 wt%. A moisture content of 6 wt% to 10 wt% is more preferable.

[0039] The moisture content was measured by measuring the sampled slag particles with a moisture meter, and the adhesiveness was evaluated by measuring the angle of repose of sampled slag particles having different moisture contents.

[0040] [<3> Loading process] The stacking process involves transporting the moistened slag to an aging facility using a transport device, filling the facility, and then performing stacking operations such as leveling the top surface. Specific methods for filling and leveling the top surface are not particularly limited, but include, for example, using heavy machinery to level the top surface.

[0041] [Grain size segregation coefficient Iseg] The present inventors have further found that it is effective to use the "particle size segregation coefficient Iseg" described below as an index of the particle size of the slag after the stacking process.

[0042] The grain size segregation coefficient Iseg is an index (coefficient) that indicates the grain size segregation state, and the smaller this coefficient, the greater the degree of segregation. This Iseg can be calculated using equation (5), which is derived from equations (3) and (4) below.

[0043]

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[0044]

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[0045]

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[0046] where aij is the division area (i: 1 to m, j: 1 to n), m is the number of division areas along the x direction, n is the number of division areas along the y direction, Nk(aij) is the number of k-component particles in the division area aij, Ck(aij) is the number concentration of k-component particles in the division area aij,

[0047]

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[0048] The number concentration mentioned above refers to the proportion of particles of each particle size in the region aij after classification. It can be calculated from the relationship between the mass and particle size of the particle group of each particle size in the region aij, assuming that the slag particles are spherical.

[0049] In the present invention, the particle size segregation coefficient Iseg of the slag after the stacking process is preferably controlled to a range of 1.0 to 1.5. This is because Iseg has a minimum value of 1.0, and if it exceeds 1.5, the degree of particle size segregation becomes large, causing significant steam drift in the subsequent aging process. It is more preferably 1.0 to 1.3.

[0050] As can be seen from Figure 3, even for slag with different particle size distribution indices k, when the moisture content is within the preferred range of 8.3 wt%, for example, the particle size segregation coefficient Iseg after slag loading is 1.5 or less, which is clearly reduced.

[0051] [〈4〉Aging process] Aging is a process that stabilizes the volume of slag by reacting it with water to prevent it from expanding and collapsing. There are two types of aging: atmospheric aging, in which the slag is exposed to the air (open air) for several months, and accelerated aging, in which steam or hot water is used to promote the hydration reaction. In the present invention, steam aging is preferably used, particularly when applied to steelmaking slag. Steam aging involves injecting steam into the bottom of a packed slag bed to bring the steam into contact with the free lime in the steelmaking slag, thereby preventing the slag from expanding and collapsing and stabilizing the slag.

[0052] The amount of steam used and the injection time depend on the amount of slag to be loaded and the specifications and processing capacity of the aging equipment. As an example, the amount of steam used is preferably 360 tons / treatment to 720 tons / treatment, and the injection time is preferably 48 to 96 hours.

[0053] The aged slag is discharged outside the facility by a discharge device and sent to, for example, a facility for producing roadbed material or a storage location.

[0054] [<5> Stirring process] The stirring step can be carried out after the water spraying step as needed, but it is preferable to carry out the stirring step first, since stirring the water-sprayed slag allows the slag to be uniformly saturated with water. Stirring methods include, for example, using heavy machinery or transporting the slag to a mixer and stirring it.

[0055] The moisture content of the slag after the stirring step is preferably 5 wt% to 12 wt%, similar to the moisture content after the water spraying step described above, and more preferably 6 wt% to 10 wt%.

[0056] [〈6〉 Temperature-rising drying process] If steam aging is performed in the next aging step while the slag layer is still moist, the air permeability will be reduced due to the decrease in voids in the slag layer. In addition, more heat will be required to evaporate the moisture. This will increase the amount of steam used in the steam aging process, resulting in an increase in the steam consumption rate.

[0057] Therefore, it is preferable to carry out a steam aging process in which high-temperature gas of 100°C or higher is uniformly blown into the bottom of the slag packed bed to evaporate the moisture inside and dry the slag packed bed, followed by a temperature-rising drying process in which water vapor is blown in.

[0058] Here, Ar gas, for example, is used as the high-temperature gas at 100°C or higher. High-temperature gas blown from equipment outside the aging equipment (for example, a hot air furnace) is blown into the aging equipment. The temperature of the gas blown in at this time is preferably 100°C or higher, more preferably 100°C to 120°C. The airflow rate and airflow time may be adjusted appropriately depending on the amount of aging treatment and the capacity of the treatment equipment. For example, the airflow rate is preferably 200,000 to 1,200,000 L / min, and the airflow time is preferably 6 to 24 hours.

[0059] As described above, by blowing high-temperature gas into the slag packed bed to heat and dry it, the temperature rise time in the subsequent aging process can be shortened, and the amount of steam used in the steam aging process can be reduced, making the steam aging process more efficient.

[0060] In the steam aging treatment, it is desirable that the slag packed layer have a large porosity so that steam can pass smoothly through the slag packed layer.

[0061] However, in the slag packed layer after the stacking process, the moisture content causes some of the voids between the slag particles to be filled with moisture, resulting in a reduction in the voids.

[0062] This decrease in porosity (Δε) can be expressed by the following formula (7).

[0063]

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[0064] where Δε: decrease in void ratio in the slag packed bed, ε: void ratio of the slag before water sprinkling, ε': void ratio of the slag after water sprinkling, mw: mass of water sprinkled (kg), ρw: density of water, V: volume of the slag packed bed (m 3 ).

[0065] If steam aging is performed by injecting steam into slag that already contains moisture, the amount of steam used in the steam aging process increases due to the reduced air permeability caused by the reduction in porosity and the additional heat required to evaporate the moisture. Therefore, by injecting high-temperature gas at 100°C or higher into the slag packed bed, the moisture inside the packed bed can be evaporated. Then, by injecting steam into the slag packed bed after drying it, the steam consumption can be reduced. [Example]

[0066] Hereinafter, the embodiments of the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0067] The relationship between the moisture content and the porosity of the slag packed bed during steam aging was investigated. Three types of steelmaking slag with particle size distribution index k suitable for roadbed materials (sample a: k = 0.4, sample b: k = 0.6, sample c: k = 1.0) were prepared. The water sprinkling and stirring processes were adjusted for each sample so that the moisture content in the slag packed bed was 0.4 wt%, 3.3 wt%, and 8.3 wt%. The slag samples were then sampled, and the average porosity of each sample was measured. The average porosity was calculated using the apparent volume, mass, and density of the packed slag.

[0068] The results are shown in Table 1 and FIG.

[0069] [Table 1]

[0070] It was found that for all three types of steelmaking slag, the average porosity was significantly improved when the moisture content was 8.3 wt%.

[0071] As described above, according to an embodiment of the present invention, by adjusting the particle size of the slag and performing water spraying and stirring, the moisture content of the stacked slag packed bed can be adjusted and the porosity of the slag packed bed can be improved. This reduces particle size segregation and improves permeability during steam aging. Furthermore, by injecting high-temperature gas before aging, the temperature rise time during steam aging can be shortened, preventing steam drift and reducing the steam consumption rate during steam aging.

Claims

1. 1. A method for aging slag, comprising: A pre-processing process in which the raw material slag is crushed and particle size adjusted; a watering step of adding moisture by watering; a loading step of loading the products into an aging treatment facility; An aging process; in that order, The moisture content of the slag immediately before the loading process is set to 5 wt% to 12 wt%, A method for aging slag, characterized in that the raw material slag has particle size characteristics in which the particle size distribution index k calculated by the following equation (2) is 0.4 or more. [Equation 1] [Equation 2] where Ds is the average particle size based on the specific surface area calculated by the above formula (1), wi is the weight ratio of particle group i, di is the particle size of particle group i, Dsf is the average particle size based on the specific surface area of ​​the finest particle size distribution, and Dmax and Dmin are the maximum and minimum particle sizes in the particle size distribution.

2. 2. The slag aging method according to claim 1, further comprising a stirring step of stirring the slag after the water sprinkling step and before the stacking step.

3. 3. The slag aging method according to claim 1, further comprising a temperature-raising and drying step of heating and drying the slag after the stacking step and before the aging step.

4. 4. The slag aging method according to claim 3, wherein in the temperature-rising and drying step, the slag after the stacking step is heated and dried using high-temperature gas at 100°C or higher.

5. 3. The slag aging method according to claim 1, wherein the slag is steelmaking slag, and the aging step comprises performing steam aging treatment using water vapor.

6. 4. The slag aging method according to claim 3, wherein the slag is steelmaking slag, and the aging step comprises performing steam aging treatment using water vapor.

7. 5. The slag aging method according to claim 4, wherein the slag is steelmaking slag, and the aging step comprises performing steam aging treatment using water vapor.

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