Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B1/00—Preliminary treatment of ores or scrap
  • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
  • C22B1/24—Binding; Briquetting ; Granulating
  • C22B1/2406—Binding; Briquetting ; Granulating pelletizing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
  • B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
  • B02C23/00—Auxiliary methods or auxiliary devices or accessories specially adapted for crushing or disintegrating not provided for in preceding groups or not specially adapted to apparatus covered by a single preceding group
  • B02C23/08—Separating or sorting of material, associated with crushing or disintegrating
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B1/00—Preliminary treatment of ores or scrap
  • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
  • C22B1/24—Binding; Briquetting ; Granulating
  • C22B1/2413—Binding; Briquetting ; Granulating enduration of pellets
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• the present disclosure relates to a method for producing iron ore pellets.
• Patent Document 1 JP 2000-273552A discloses a method for producing reducing agent mixed pellets.
• this method for producing pellets at least one of carboxymethylcellulose and polyvinyl alcohol or tar is added to powdered iron ore and coal as a reducing agent, and water is added using a granulator to form pellets. to produce reducing agent mixed pellets.
• the reducing agent mixed pellets are further dried in a dryer at an ambient temperature of 150°C to 170°C. It is said that by using a hydrocarbon binder such as carboxymethylcellulose, polyvinyl alcohol, or tar in this reducing agent mixed pellet, the drop strength of the dried pellet can be greatly improved.
• Patent Document 2 JP-A-2002-206120 discloses pellets for reduction furnaces, a method for manufacturing the same, and a method for reducing metal oxide.
• this method for producing pellets raw materials discharged from a raw material storage tank are kneaded in a kneading device, and pellets are produced in a pan-type granulator using fine powder containing metal oxide and carbon as raw materials. It is said that it is possible to prevent the raw material pellets from collapsing when these pellets are classified using a pellet sieving device, dried using a pellet drying device, and then fired and reduced in a rotary hearth type reduction furnace.
• Patent Document 3 discloses a method for producing carbon-containing non-fired pellets for blast furnaces.
• This pellet manufacturing method involves adding a hydraulic binder to a finely powdered iron-containing raw material and a finely divided carbonaceous material, and blending the finely divided carbonaceous material so that the carbon content in the total raw material is 15 to 25% by mass.
• This is a method for producing carbon-containing unfired pellets for blast furnaces with a cold crushing strength of 85 kg/cm 2 or more by adjusting the proportions, mixing and granulating while controlling the moisture content, and then curing the mixture.
• the curing treatment involves leaving the pellets after granulation in the atmosphere for 12 to 48 hours in a primary curing yard, then charging the pellets into a shaft furnace for secondary curing, and then loading the pellets into a shaft furnace for secondary curing.
• Steam blowing treatment is performed at a temperature of 60 to 90°C for a treatment time of 5 hours or more, followed by continuous drying treatment, and the total treatment time of steam blowing treatment and drying treatment is within 8 hours.
• bursting refers to a phenomenon in which the green pellets burst, explode, or become powder due to the pressure of the vapor of the volatile components generated inside the green pellets when the volatile components of the iron ore in the green pellets vaporize. be.
• the volatile matter of the iron ore in the green pellets is, for example, crystal water of the iron ore in the green pellets.
• the present disclosure has been made in view of such circumstances, and its purpose is to provide a method for producing pellets that can suppress bursting of green pellets.
• the method for producing iron ore pellets according to the present disclosure to achieve the above object is as follows.
• the method for producing iron ore pellets according to the present disclosure may be further as follows.
• the method for producing iron ore pellets of the present disclosure it is possible to provide a method for producing pellets that can suppress bursting of green pellets.
• the iron ore pellets according to this embodiment are so-called green pellets (pre-fired pellets).
• the method for producing iron ore pellets according to the present embodiment includes a pulverizing step of pulverizing iron ore (so-called low-grade ore) having an iron content of 63% by mass or less to obtain ore powder.
• iron ore with an iron content of 63% by mass or less is simply referred to as iron ore.
• the volatile content of iron ore for obtaining ore powder is 3.3% by mass or more.
• the cumulative 90% diameter of the ore powder in the volume-based particle size distribution is 150 ⁇ m or less.
• the ore powder has a particle size distribution index defined by the above formulas (1) to (4) of 14,700 or more and 510,000 or less.
• the particle proportion wi is the interval of the representative particle size di when evaluating the particle size distribution by dividing it into intervals within a predetermined particle size range. is the particle proportion in .
• bursting refers to a phenomenon in which the green pellet ruptures, explodes, or becomes powder due to the pressure of the vapor of the volatile content generated inside the green pellet when the volatile content of the iron ore in the green pellet evaporates. It is about.
• the iron ore pellets in this embodiment are pellets before firing, and are so-called green pellets.
• the iron ore pellets according to the present embodiment may be referred to as green pellets
• the pellets after firing may be referred to as fired pellets.
• the green pellets and the fired pellets may contain auxiliary materials other than iron ore (eg, bentonite).
• the method for producing iron ore pellets according to the present embodiment may further include a granulation step of granulating ore powder to obtain green pellets.
• the green pellets may then be fired in a firing step to form fired pellets.
• the type and composition (ore composition) of iron ore that is the raw material for green pellets are not particularly limited.
• the raw material for green pellets may be made of a single iron ore, or may be a mixture of a plurality of ores in any combination.
• the volatile matter of iron ore used as a raw material for green pellets refers to water adsorbed to iron ore and crystal water contained in crystals in iron ore. That is, the volatile matter of the iron ore in the green pellets is, for example, water adsorbed to the iron ore in the green pellets or crystallized water of the iron ore in the green pellets.
• the content of volatile matter can be measured as the amount of weight loss (LOI: Loss On Ignition) of iron ore when the iron ore is held at 1000° C. for 30 minutes.
• iron ore with a volatile content of 3.3% by mass or more is used as a raw material for green pellets. This allows the use of inexpensive or easily available iron ore raw materials.
• the volatile content of iron ore is preferably 12.0% by mass or less.
• the pulverizing process is a process of pulverizing iron ore to obtain ore powder (iron ore powder) in which iron ore is powdered.
• the method of crushing iron ore in the crushing process and the crushing time required for crushing are not particularly limited. Iron ore can be crushed using, for example, a ball mill, a hammer mill, a roll crusher, or the like.
• the shape of the ore powder is not particularly limited.
• the particle size (particle size) of the ore powder is preferably, for example, 250 ⁇ m or less (for example, passed through a 250 ⁇ m sieve, so-called 250 ⁇ m pass). If coarse particles with a particle size exceeding 250 ⁇ m are included in the ore powder, the strength of the green pellets may decrease.
• the particle size distribution of the ore powder is a value measured using laser diffraction particle size measurement (Mastersizer 3000, manufactured by Malvern). Water is used as a dispersion medium when measuring particle size distribution.
• the particle size distribution of the ore powder is such that the cumulative 90% diameter in the volume-based particle size distribution is 150 ⁇ m or less.
• the particle size distribution of the ore powder has a particle size distribution index defined by the above formulas (1) to (4), that is, a particle size distribution index based on the harmonic mean diameter of 14,700. 510,000 or less. These can suppress pellet bursting.
• bursting is a phenomenon in which the green pellets explode or become powder due to the volatile content of the iron ore in the green pellets evaporating when the green pellets are heated.
• bursting is a phenomenon in which the green pellet ruptures, explodes, or becomes powder due to the pressure of steam generated inside the green pellet when the green pellet dries or when crystallization water is detached from the iron ore crystals in the green pellet. This refers to the phenomenon of change.
• the harmonic mean diameter is often used, for example, when evaluating the air permeability of a particle layer or a packed bed. Therefore, it is considered suitable for evaluating the ease with which steam escapes from the inside of green pellets to the outside.
• the particle size distribution index which represents the spread of the particle size distribution, is considered to be suitable for evaluating the ease with which steam escapes from the inside of the green pellet to the outside.
• the particle size distribution of the ore powder is preferably such that the cumulative 50% diameter in the volume-based particle size distribution is less than 61 ⁇ m. Thereby, pellet bursting can be better suppressed. Further, the particle size distribution of the ore powder is preferably such that the cumulative 10% diameter in the volume-based particle size distribution is less than 7.1 ⁇ m. This also makes it possible to better suppress pellet bursting.
• the particle size distribution of the ore powder preferably has a harmonic mean diameter of less than 13 ⁇ m.
• the granulation process is a process of granulating ore powder to obtain iron ore pellets (green pellets).
• the granulation method in the granulation step is not limited.
• the ore powder may be granulated using a pelletizer.
• a pelletizer for example, a pan-type granulator (so-called pan pelletizer) may be used.
• the shape and size (for example, particle size and average particle size) of the iron ore pellets are not particularly limited, and may be set to any value.
• the size of the green pellet may be determined by, for example, measuring the major axis diameter and the minor axis diameter using a caliper, and evaluating the average value as the particle size of the green pellet.
• the particle size of the green pellets is preferably 16 mm from 9 mm, which is commonly used in this technical field.
• the green pellets are then subjected to a firing process and fired to produce fired pellets.
• the firing temperature in the firing step is, for example, 1200°C to 1350°C.
• the ease with which bursting occurs can be evaluated, for example, based on the temperature at which bursting occurs when the green pellet is gradually heated to increase the temperature of the green pellet. That is, when the temperature at which bursting occurs is low, bursting is likely to occur (bursting property is high), and it can be evaluated that it is not good from the viewpoint of suppressing bursting. Conversely, when the temperature at which bursting occurs is high, bursting is less likely to occur (bursting property is low), and it can be evaluated as being good from the viewpoint of suppressing bursting.
• Green pellets were produced using the following procedure, and the strength and bursting properties of the pellets were evaluated.
• Ore (A, B) having the chemical composition shown in Table 1 was used as the iron ore used as the raw material (raw material ore) for green pellets.
• "LOI” in Table 1 is shown as the content (mass %) of volatile components such as crystal water as described above.
• T.Fe represents the mass % of the iron content (total Fe content) in the iron ore. Note that “T.Fe” is a value determined based on the total iron determination method of iron ore specified in JIS M 8212:2022.
• Ore A and Ore B used as raw materials for green pellets are both T. It is iron ore (so-called low-grade ore) containing 63% by mass or less of Fe.
• the raw material for green pellets is ore A or only the case where ore B is used, but if ore A and ore B are mixed in an arbitrary composition, iron ore can be used as the raw material for green pellets.
• the volatile content of the stone can be changed or adjusted within the range of 3.3% by mass or more and 12.0% by mass or less.
• Ore A or Ore B shown in Table 1 was ground in a ball mill to produce production No. 1 with a particle size distribution shown in Table 2. 1 to No. 13 ore powders were obtained. In addition, in the crushing of ore A or ore B, the particle size distribution of ore powder was created differently by adjusting the crushing time and sieving.
• D10 indicates the volume-based cumulative 10% diameter
• D50 the volume-based cumulative 50% diameter (median diameter)
• D90 the volume-based cumulative 90% diameter
• Dp indicates the harmonic mean diameter
• Isp indicates the particle size distribution index (see formula 2) based on the harmonic mean diameter.
• the particle size distribution shown in Table 2 was derived based on the particle size of ore powder measured using laser diffraction particle size measurement (Mastersizer 3000, manufactured by Malvern). Note that the dispersion medium used in measuring the particle size distribution was water. The measurement range of particle size distribution was 0.01 ⁇ m or more and 3500 ⁇ m or less, and this range was divided into 101 sections for measurement. As shown in Table 2, production No. 1 to No. The ore powder No. 13 has a cumulative 90% diameter of 150 ⁇ m or less in the volume-based particle size distribution.
• manufacture No. 1 to No. The ore powder of No. 13 was granulated using a pan-type granulator (pelletizer, pan diameter 1.2 m) to obtain green pellets (granulation process).
• Granulation was carried out by gradually adding water while rolling the ore powder on a rotating pan (rotation speed: 10 times/s).
• the rolling ore powder was gradually granulated as it was hydrated and rolled, and when it grew into pellets with a diameter of 9.5 mm to 12 mm, the pellets were collected.
• the pellets, which had grown from 9.5 mm to 12 mm, were further rolled on a pan for 10 minutes to form approximately spherical green pellets. Note that the amount of water added during the above granulation is about 10% of the weight of the green pellets.
• Table 3 shows manufacturing no. 1 to No. The evaluation results of the strength (“falling strength” in Table 3) and bursting property (“bursting temperature” in Table 3) of No. 13 green pellets are shown. In Table 3, the same "Isp” as shown in Table 2 is listed again for convenience of viewing.
• drop strength indicates the strength evaluation result based on a drop test of green pellets.
• the drop test was conducted for each manufacturing No. Each green pellet was dropped from a height of 50 cm, and the number of falls until the green pellet cracked or the green pellet was destroyed was measured (number of falls), and the number of falls was adopted as the falling strength. . That is, the larger the value of the falling strength, the higher the strength of the green pellet. Moreover, the smaller the value of the falling strength, the lower the strength of the green pellet. Note that the number of falls adopted as the falling strength does not include the number of falls when the green pellet cracks or breaks. In other words, the drop strength is the number of times the green pellet can be dropped without cracking or breaking the green pellet. In this example, the average value (arithmetic average) of 10 green pellets was used as the drop strength.
• bursting temperature indicates the evaluation results related to bursting properties.
• the bursting temperature indicates the temperature at which bursting occurs when the green pellet is gradually heated to increase the temperature of the green pellet. That is, when the bursting temperature is low, the bursting property is high. Moreover, when the bursting temperature is high, the bursting property is low.
• the "bursting temperature" is the temperature measured as follows. First, 200 g of green pellets are charged into a vertical cylindrical furnace (diameter 50 mm). Then, hot air heated to 200° C. is passed through the green pellet layer from below to above at a wind speed of 1.0 m/sec (converted to 0° C./1 atm) for 10 minutes. After that, check whether the green pellet has burst. If the green pellets burst or become powder during the period in which air heated to 200°C is passed through the layer of green pellets, or at the end of that period, the bursting temperature of the green pellets will be 200°C. be identified.
• the temperature of the hot air is further increased by 20° C., and the hot air is vented for 10 minutes, and the presence or absence of bursting of the green pellets is confirmed. Thereafter, the temperature is repeatedly increased by 20°C in the same manner (that is, the green pellet is gradually heated), and the temperature at which the green pellet bursts is determined. After repeatedly increasing the temperature of the hot air, the temperature at which the green pellet bursts is determined as the bursting temperature of the green pellet, as described above.
• the green pellets have enough strength to suppress disintegration and powdering due to handling such as transportation (from the granulation process to the firing process) until the green pellets are made into fired pellets.
• the strength of the drop is 5 times or more, the strength is determined to be good, and if the strength of the drop is less than 5 times, the strength is determined to be poor.
• whether or not bursting was suppressed was determined by whether the bursting temperature was 250°C or higher or lower than 250°C. That is, if the bursting temperature is 250°C or higher, the bursting property is low and good, and if the bursting temperature is less than 250°C, the bursting property is high and it is judged to be poor.
• Tables 2 and 3 taking these evaluations into consideration, No. 1, 6, 7, and 13 are written as Comparative Examples 1 to 4 in this order. Also, No. Examples 2-5 and 8-12 are written as Example 1-9 in this order.
• both strength and bursting property can be achieved if the cumulative 50% diameter is 5.0 ⁇ m or more and 61.0 ⁇ m or less, and at least 5.2 ⁇ m or more and 60.1 ⁇ m. Furthermore, it can be determined that both strength and bursting properties can be achieved if the cumulative 10% diameter is at least 0.6 ⁇ m or more and 7.1 ⁇ m or less.
• the harmonic mean diameter if it is at least 1.7 ⁇ m or more and less than 13.0 ⁇ m, it can be judged that both strength and bursting property can be achieved.
• the present disclosure can be applied to a method for producing iron ore pellets.

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