KR20100113177A - Iron ore briquetting - Google Patents

Abstract

A method of producing an iron one briquette that is suitable for use as a blast furnace or other direct reduction furnace feedstock which includes the steps of: (1) mixing: (i) ore having a predetermined particle size distribution with a top size of 4.0 mm or less; and (ii) a flux; to form an ore/flux; (2) adjusting the water content of the ore prior to or during mixing step (1) to optimise briquette quality and product yield; (3) pressing the ore/flux mixture into a green briquette; and (4) indurating the green briquette to from a fured briquette.

Description

Briquetting method of iron ore {IRON ORE BRIQUETTING}

The present invention relates to a process for the production of iron ore briquettes suitable for transportation and use in the iron production process.

Since the late 1800s, agglomerating methods have been developed. However, among the available methods only the method of pelletizing and sintering is currently considered important, but this method has some disadvantages.

Pelletization consists of two distinct processes of forming pellets from wet ore granules and then firing them at temperatures around 1300 ° C. In order to prepare suitable pellets it is important to grind the ore very finely with a particle size of about 60% ore passing through 45 μm. The pulverized ore is then formed into pellets in a horizontal drum or inclined disk, usually with the addition of suitable binders. The pellets thus formed are then fired in a process often referred to as induration, in a shaft kiln, horizontally movable grate, or a combination device of movable grate and rotary kiln. Pelletization is a practical and commercially attractive way to agglomerate fine concentrates, but to achieve the desired particle size requires a significant energy consuming grinding process. Pellets made from goethite-hematite ores require long curing times, which affects manufacturing costs. In order to reduce the curing time, coke-like solid fuels are often added, resulting in the generation of hazardous emissions (including dioxins, NOx, SOx).

Sintering consists of granulating wet iron ore and other particulates together with a solid fuel, usually coke coal dust, and loading the granulated mixture into a permeable mobile grate. As the temperature rises, air is vented downwards from the grate. After a short ignition period, external heating of the bed is stopped, and as the solid fuel in the bed burns, the narrow combustion zone moves downward through the bed, and each layer is heated to approximately 1300 ° C. in turn. Bonding between particles occurs during combustion, and strong agglomerates are formed. However, traditional sintering processes produce high levels of harmful emissions, especially sulfur dioxide and dioxins, and therefore for environmental reasons these processes are undesirable and cannot be sustained.

Briquetting is a process of commercial interest since the late 1800s and early 1900s, but the production of iron ore briquettes used as blast furnace feedstock has not reached a significant level, and has declined since 1950 until 1960. It was stopped at the time. The practical process involves crushing ore particles into blocks of some suitable size and shape and then curing the blocks. A wide range of binders and / or organic products such as tar and pitch, sodium silicates, ferrous sulfate, magnesium chloride, limestone and other additives such as cement have been tested. However, the first briquetting process, the Groendal process, involved only the process of mixing iron ore with water and pressing it into rectangular blocks of brick size. In this process, after pressing, blocks were hardened by passing through a tunnel-type kiln heated to 1350 ° C.

Advances in briquetting processes have generally been directed to the development of suitable binders, but Japanese Patent No. 60-243232 discloses briquettes having a flat shape to provide a stable distribution in a blast furnace. Specifically, the specification of the above Japanese patent discloses that flat briquettes are reduced much more easily at higher temperatures than conventional spherical pellets. The briquettes are made from 2 cc to 30 cc volume to balance inferior rotational or tumble strength and impact resistance with increasing dimension and relatively high compressive strength. The Japanese specification discloses that larger briquettes are reduced less easily in blast furnaces. However, apart from the dimensions and shape of the briquettes, there are no other factors other than the above-mentioned factors as important factors, and no other details are really described in connection with the production of briquettes.

The Applicant has conducted extensive research in the manufacture of briquettes from iron ore and invented a method for producing briquettes having properties suitable for use in blast furnaces and other direct reduction furnaces.

One of the important issues that applicants have focused on in this study is that a commercially viable iron ore briquetting plant must be able to handle a significant amount of material. To this end, the Applicant believes that briquetting presses should be able to process about 70-100 tonnes of iron ore per hour per press. Applicants have found in the study that it is possible to operate briquetting presses at surprisingly low roll pressures and to produce green briquettes with sufficient green strength to withstand subsequent handling. . This is a surprising finding because, according to the information provided by the briquetting press manufacturer, a roll pressure is required that is much greater than the pressure we found to be an appropriate pressure. The discovery that it is possible to operate at low roll pressures is important because low pressure operation allows the use of wider presses, resulting in higher production speeds at those presses.

The present invention relates to the selection of briquetting parameters.

According to the present invention, there is provided a process for producing iron ore briquettes suitable for use as a raw material for blast furnaces or other direct reducing furnaces, which process comprises: (a) mixing iron ore and flux to form an iron ore / flux mixture; Mixing step; (b) pressing the iron ore / flux mixture into a green briquette using a low roll pressure; (c) a curing step of curing the base briquettes to form fired briquettes.

Low pressure operation for briquetting the iron ore described in step (b) is important, which makes it possible to achieve high production rates by using wide rolls on briquetting machines up to 1.6 m in length.

The low roll pressure is preferably produced by a roll pressure sufficient to produce briquettes having a compressive strength of at least 2 kgf.

It is preferable that the holding compressive strength is 4 kgf or more.

As for the holding compressive strength, it is more preferable that it is 5 kgf or more.

As for the holding compressive strength, it is more preferable that it is 5-30 kgf.

The holding compressive strength is more preferably 15 to 30 kgf.

The low roll pressure is preferably produced by a roll compression force of 10 to 140 kN / cm for the iron ore / flux mixture.

The roll compression force is more preferably 10 to 60 kN / cm.

The roll compression force is more preferably 10 to 40 kN / cm.

Step (a) preferably comprises mixing the iron ore and flux particles with a predetermined particle size distribution of the iron ore particles.

The predetermined particle size distribution of the iron ore particles mixed with the flux in step (a) can be produced without the milling of the iron ore.

The method preferably comprises crushing and screening the iron ore to form a desired particle size distribution of the iron ore mixed with the flux in step (a).

The maximum particle size of the predetermined particle size distribution of the iron ore mixed with the flux in step (a) is preferably 4.0 mm or less.

The maximum particle size is more preferably 3.5 mm or less.

It is more preferable that the maximum particle size is 3.0 mm or less.

It is more preferable that the maximum particle size is 2.5 mm or less.

It is more preferable that the maximum particle size is 1.5 mm or less.

The maximum particle size is more preferably 1.0 mm or less.

The desired particle size distribution of iron ore mixed with the flux in step (a) is preferably less than 50% passing through a 45 μm screen.

The particle size distribution is more preferably less than 30% through a 45 μm screen.

The particle size distribution more preferably includes less than 10% passing through the 45 μm screen.

Iron ore is preferably a hydrated iron ore (hydrated iron ore).

Hydrated iron ore is preferably goethite-containing ore.

The flux preferably has a particle size distribution of less than 100 μm.

The particle size distribution of the flux is preferably 95% or more through the 250 μm screen.

The flux is preferably limestone.

The iron ore / flux mixture produced in step (a) is preferably chosen such that the basicity of calcined briquettes is greater than 0.2.

The basicity is more preferably greater than 0.6.

Here, "base degree" means (% CaO +% MgO) / (% SiO ₂ +% Al ₂ O ₃ ) of calcined briquettes.

The iron ore / flux mixture is preferably free of binders.

The method further comprises adjusting the water content of the iron ore before or during the mixing step (a) to optimize the quality of the briquettes and the product yield.

Preferably adjusting the water content of the ore comprises adjusting the water content of the iron ore such that the water content of the ore / flux mixture is from 2 to 12% by weight of the total weight of the ore / flux mixture.

The term "total weight of ore / flux mixture" means (a) the dry weight of the ore / flux mixture, (b) the weight of the intrinsic moisture of this mixture, and (c) (if any) It means the sum of the weights of added moisture.

The term "water content" is the sum of (b) and (c) above.

Preferably, the step of adjusting the moisture content of the ore, in the case of iron ore of high density hematite ore, the iron ore so that the moisture content of the iron ore / flux mixture is 2 to 5% by weight of the total weight of the iron ore / flux mixture It includes controlling the water content of.

Preferably, step (b) is for the iron ore containing 50% or less goothite, so that the moisture content of the iron ore / flux mixture is from 4 to 8% by weight of the total weight of the iron ore / flux mixture. Adjusting the.

Preferably, step (b) is characterized in that, for iron ore in which goethite ore predominates, i.e., iron ore containing more than 50% of goethite ore, the moisture content of the iron ore / flux mixture is 6 to 12 of the total weight of the iron ore / flux mixture. Adjusting the water content of the iron ore to be in weight percent.

Preferably the pressing step (c) produces briquettes with a volume of 10 cc or less.

More preferably, the pressing step (c) produces briquettes with a volume of 8.5 cc or less.

More preferably the pressing step (b) produces briquettes with a volume of 6.5 cc or less.

Preferably the step of indurating (c) comprises heating the briquettes to firing temperature within 40 minutes.

Preferably the curing step (d) comprises heating the briquettes to the firing temperature in 35 minutes.

More preferably the curing step (d) comprises heating the briquettes to the firing temperature within 30 minutes.

More preferably step (c) comprises heating the briquettes to the firing temperature within 20 minutes.

More preferably step (c) comprises heating the briquettes to the firing temperature within 15 minutes.

Preferably the firing temperature is at least 1200 ° C.

More preferably, the firing temperature is 1260 ° C or higher.

More preferably, the firing temperature is at least 1320 ° C.

More preferably, the firing temperature is at least 1350 ° C.

More preferably, the firing temperature is at least 1380 ° C.

The fired briquettes preferably have a fracture stress of at least 200 kgf.

The fired briquettes preferably have a fracture stress of at least 250 kgf.

Iron ore particulates are broadly classified into four groups based on petroleum properties such as mineralogy, mineral relatedity and particle texture, porosity, particle size distribution and chemical properties. The groups are as follows.

(a) HC-dense hematite / magnetite ore,

(b) GC-ore containing up to 50% goethite, and

(c) G-Ore containing more than 50% of goethite, such as gothite, pisolites, detritals, and channel iron deposits.

The following describes two specific sub-groups for GC ores. The two sub-groups are as follows.

(Iii) HG-goethite-containing ore in which hematite is dominant, and

(Ii) GH-ore with almost the same amount of hematite and goethite.

Not wishing to be bound by theory, the binding mechanisms of the briquettes involve the mechanical interbonding of particles, van der Waals forces, and hydrated iron contained in the GC and C forms of the raw material, for example, goethite. species) are thought to involve a combination of bonds comprising varying degrees of hydrogen bonding depending on the percentage. Several properties of the feed material have been found to have a significant impact on the formation of the aforementioned bonds, which affects the quality and processing performance of the briquettes and calcined briquettes. These features include the moisture content of the feedstock, the flow characteristics of the feedstock, the chemical composition of the iron ore, the particle size distribution and the mineralogy, and the porosity.

The feed material preferably has a particle size distribution as wide as possible in order to increase the packing density and increase the binding force of the ore particles. As mentioned above, the bonding mechanism of the briquettes is believed to be due to the combination of mechanical mutual bonding of the particles, van der Waals forces, and bonds resulting from hydrogen bonding in the case of GC and C type raw materials. Although wide size distribution increases packing density and improves the strength of the briquettes, iron ore with a narrow particle size distribution can also be produced as briquettes.

The maximum particle size of the particles is determined by the crushing treatment, but is preferably 2.5 mm or less in order to produce plastic briquettes of acceptable characteristics after the curing process. In general, iron ores in the form of HC and HG can be made into briquettes with a coarser maximum particle size due to the low heating requirements of such raw materials to achieve acceptable plastic strength. The maximum particle size of the raw material can be reduced by either crushing or screening treatment.

The minimum particle size of the particles does not have absolute limitations, but since this is an additional economic burden to be unnecessary by the present invention, it is not necessary or desirable to grind the iron ore into fine particles (as required for pelletization). It is preferred that less than 10% of the particles pass through a 45 μm sieve.

The pocket dimensions of the briqueting device should preferably be selected based on the appropriate curing performance as well as the maximum particle size to be brittled so that satisfactory briquettes can be achieved. The maximum particle size to achieve satisfactory briquetting is usually 25% to 30% of the minimum pocket dimension. If the maximum particle size exceeds that specification, it may be necessary to select a larger pocket size.

It is desirable to control the water supply to optimize the quality of the briquettes and the product yield. Liquid bridging should not exceed the level at which it is a major form of interparticle bonding. This reduces the body strength and adversely affects thermal stability. Insufficient moisture causes overpressure in the briquetting crimping step, adversely affecting the quality and yield of the briquettes possessed.

Depending on the feed properties of the iron ore to be treated, a water content of 2% to 12% by weight of the feed material is used to optimize the quality and yield of the briquettes in the possession. High density hematite concentrates generally have a low optimum briquette moisture content in the range of 2% to 5% by weight. These concentrates are often made up of particles of narrow particle size distribution with smooth surface textures resulting in low intensity briquettes due to the reduced mutual bonding of the particles. More porous goethite-containing ores (GCs) with less than 50% goethite are well brittle in the range of 4 to 8% by weight, and ores (G) dominated by the more porous goethite range from 6 to 12 wt%. Is well bridging at. These ores have a rough surface texture and shape that enhances briquetting properties.

Conventional briquetting devices can also be used in the method of the present invention. In essence, such a device has two adjacent rolls with pockets that meet together in the nip region to compress the feed material into adjacently aligned pockets to produce briquettes. In the case of the present invention, the rolls are preferably aligned horizontally to achieve the required output for economical possibilities.

Depending on the application, briquetting may be carried out over a wide range of roll pressures, but briquetting of iron ore is preferably carried out with a roll pressing force of 10 to 140 kN / cm, in the region below the range of 10 More preferably, it is performed at 60 kN / cm. As mentioned above, this low pressure operation is important for briquetting of iron ore, and the production speed can be increased by using wide rolls on briquetting machines up to 1.6 m in length.

The roll pressure is preferably carefully controlled within the low pressure range to optimize briquetting operations. If the roll pressure is too low, the rolls will be spaced apart, creating thick webs and crushed briquettes, which compromise the yield and quality of briquettes after curing. If the roll pressure exceeds the optimum value, poor clogging of briquettes occurs due to the clamshell effect when emitting briquettes from the pocket. The clamshell effect becomes more pronounced in the case of small diameter rolls and excess roll pressure, causing pocket binding / jamming. While the density and crush strength of the briquettes are increased, the impact resistance of the fired briquettes will be severely impaired.

The moisture level is preferably selected to affect the flow properties of the material through the feed system, with a moisture level of 2 to 12% by weight being generally suitable for the feed material. If the moisture level in the supply system is too high, the supply pressure is adversely affected, resulting in some damage to the quality of the briquettes, which results in low holding strength, and a decrease in yield. If there is too little moisture in the feed material in the feed system, the resulting feed pressure may result in a clamshell, resulting in lower yields, increased wear rate of the roll pockets and lowered properties of the calcined briquettes.

The briquetting device can be operated with a preliminary compressor supply system or a gravity supply system. Gravity feed systems are beneficial when the mass is briquettes, such as in the iron ore industry.

For briquetting processes, the diameter of the roll is chosen to ensure briquetting quality is obtained at an economical production rate. Larger diameters of rolls increase production speed but increase the area of the nip region. Careful control of the nip area facilitates formation of high quality briquettes and avoids the formation of briquettes with thick webs. Changing the roll diameter may also change the optimum moisture level for the feed material, in which case increasing the roll diameter increases the feed moisture. The diameter of the rolls can vary substantially in the range of 250 to 1200 mm. In order to maximize productivity, the rolls are preferably operated at the maximum speed possible while maintaining the quality of briquettes. However, very low roll speeds may be used where productivity is a secondary consideration.

Usually, a roll speed of 1 rpm to 20 rpm is used. To maintain feed quality, especially at high roll speeds, while providing feed to the rolls at a rate that matches the production rate of briquettes while matching the area of the nip area that generates the necessary force to form a good briquette. It is preferable.

Any suitable roller width can be selected if it is within the pressure tolerance of the briquetting machine. When briquetting of iron ore is a low pressure operation, wide rolls are preferred, and the capacity of briquetting machines is increased. The rolls are preferably horizontally aligned for use with gravity feed systems. Whether HC, GC (including HG and GH), or G, the flow characteristics of iron ore in the moisture ranges described above for each species are suitable for gravity feeding.

The shape of the pockets should not usually be sharply angled, but should be smoother and rounder to improve handling characteristics. For example, the ratio of length / width and width / depth is suitably about 0.65. The shape of the pocket also has a specific release angle of 110 ° to 120 ° to exclude the tendency to stick to the pocket.

The size of the pocket can be optimized according to the requirements for the curing process, the raw material particle size and the steelmaking blast furnace. Usually, the volume of briquettes is 2 to 30 cc. It is preferable that the said volume is 10 cc or less. More preferably, the volume is 8.5 cc or less. More preferably, the volume is 6.5 cc or less.

A staggered pocket structure is preferred because the available space on the roll surface can be optimally used, maximizing the yield.

Preferably, the curing method and conditions are selected taking into account the complex relationship between the impact of briquetting dimensions and the properties of the raw material.

Consideration should be given to the relationship between the volume of briquettes, their shape, and the petrochemical properties of the raw materials. The chemical composition of the feed material has a significant effect on the properties of the calcined briquettes. Apart from the moisture, the feed material contains iron ore consisting of iron oxide and gangue minerals, and the necessary flux is added to provide the basicity levels required for calcined briquettes. From the test results, the flux was found to pass through a sieve of finer particle size, typically 95% or more, in order to achieve the properties required for firing briquettes.

Although not intending to be bound by theory, it is believed that the bonding mechanism for plastic briquettes includes diffusion bonding, recrystallization of iron oxide particles, and slag bonding at higher flux levels. Therefore, the firing time up to a predetermined range as well as the flux level and firing temperature greatly affects the characteristics of briquettes. Due to the increase in the basicity level, reducing and curing strengths can be improved as higher flux levels promote the formation of a bonding phase that resists deformation in the reducing atmosphere.

Curing can be performed using a grate kiln or batch kiln process of a straight grating.

Green briquettes produced under optimal conditions have been found to be thermally very stable compared to pellets made from the same material. The feed ore for pelletization is of a fine particle size, typically having to be pulverized to pass 60% or less through a 45 μm sieve, and the pellets are slowly dried at low temperatures, typically below 200 ° C., to prevent cracking. Alternatively, as described above, the feed ore for the present invention that can be successfully cured can be much coarse with a top size, preferably up to 2.5 mm, and thus to the same extent as is necessary for producing pellets. No need to grind This feature represents a reduction in the main capital cost of briquetting operations compared to conventional pellet production plants.

An important feature of the briquettes of the present invention is their ability to withstand high temperatures during high speed heating, such as heating to a predetermined firing temperature within 30 minutes, more preferably within 20 minutes. This is in stark contrast to the conventional understanding of how goethite ore reacts in hardening situations, where it has conventionally been found to break up when heated too quickly through the dehydration and free water removal zones.

As mentioned above, the thermal stability of the briquettes of the present invention has been found to be much greater than the thermal stability of the pellets, and these briquettes can be heated much faster than the pellets without breaking. This makes the heating cycle much shorter. As a result, the productivity of briquettes can be significantly higher than the productivity of pellets using the same material. For example, the productivity of briquettes could potentially be 30 t / m 2 · day in a straight great kiln, whereas the productivity of pellets for HG ore in the same kiln could be 16 t / m 2 · day.

Although references in the prior art are referred to herein, it will be understood that such citations do not acknowledge that all documents form part of the common general knowledge of the art in Australia or any other country.

Preferred embodiments of the present invention will be described by way of example only with reference to the accompanying drawings.

According to the present invention it is possible to operate briquetting presses at low roll pressures and to produce green briquettes having a sufficient green strength to withstand subsequent handling.

1 is a schematic representation of a suitable compression supply system and 250 mm diameter rolls for implementing the process of the present invention.
2 is a schematic representation of a gravity feed system and a suitable apparatus with 450 mm diameter rolls for implementing the process of the present invention.
3 is a schematic illustration of a gravity feed system and a suitable apparatus with 650 mm diameter rolls for carrying out the process of the present invention.
FIG. 4 shows the production yield versus feed moisture for total briquettes for HG material when using 450 mm rolls with 4 cc long almond pockets and 6 cc almond shapes.
FIG. 5 shows the effect of feed moisture on the holding briquette strength on HG material on 450 mm rolls with varying pocket dimensions.
FIG. 6 shows the effect of feed moisture on the possessed briquette strength for HG material when using 650 mm rolls and a 7.5 cc 'pillow' shape. FIG.
FIG. 7 shows the influence of roll pressure on the properties of briquettes for the case of 450 mm rolls and 9 cc almond shape, ie thickness, holding strength and holding density.
FIG. 8 shows the effect of rule pressure on the holding strength for HG material when using 650 mm rolls and a 7.5 cc 'pillow' shape. FIG.
FIG. 9 shows the effect of rule pressure on holding strength for GH material when using 650 mm rolls and a 7.5 cc 'pillow' shape. FIG.
10 shows the effect of roll speed on the properties of briquettes using 450 mm rolls and 9 cc almond forms and at 6 wt% feed moisture and 90 kg / cm 2 roll pressure, ie thickness, holding strength, and holding density. Indicative drawing.
FIG. 11 shows an operating window for a briquetting machine with a preliminary compressor, 250 mm rolls, 4 cc almond shape and HG material.
FIG. 12 shows temperature profiles for briquetting curing in a 500 mm deep bed.
FIG. 13 shows a temperature profile for briquetting to produce briquettes at high productivity and a typical temperature profile for pellet curing to produce pellets at low productivity.
FIG. 14 shows the effect of average bed temperature on briquettes made of GH material using 650 mm rolls and 7.5 cc 'pillow' shape at the end of the great cycle of batch grate kiln. FIG.
FIG. 15 shows the effect of average bed temperature on briquettes made of GH material using 650 mm rolls and a 7.5 cc 'pillow' shape at the end of the great kiln firing cycle of the batch great kiln.
FIG. 16 shows the effect of time at firing temperature (1380 ° C.) for briquettes made of GH material using 650 mm rolls and 7.5 cc 'pillow' geometry during a test cycle in a batch great kiln.
FIG. 17 shows the effect of time at firing temperature (1380 ° C.) for briquettes made of GH material using 650 mm rolls and a 7.5 cc 'pillow' shape during a test cycle in a batch great kiln.
FIG. 18 shows the effect of residence time on 7.5 cc GH briquettes in a kiln during a test cycle only in the kiln.
FIG. 19 shows the effect of bad height and grate firing profile on briquettes made of GH material using 650 mm rolls and 7.5 cc 'pillow' geometry during a test cycle in a batch great kiln.
20 shows the effect of bad height and great plasticity profile on briquettes made of GH material using 650 mm rolls and 7.5 cc 'pillow' geometry during a test cycle in a batch great kiln.
FIG. 21 shows the influence of basicity and firing temperature on firing crush strength of briquettes made using HG material, 250 mm rolls and 4 cc almond shape.
FIG. 22 shows the effect of basicity on the reduction properties of briquettes such as reduction index, crush strength after reduction (CSAR), and swell of briquettes made using HG material, 250mm rolls and 4cc almond shape. A diagram showing.

(Example 1)

Briquetting was carried out using three different roll presses while modifying the roll diameter, width and feed system.

Initial testing was performed using a Taiyo K-102A double roll press with a nominal capacity of 300 kg / hr. The machine is equipped with a 36 mm wide 250 mm diameter roll and features a screw-type preliminary compressor. 1 is a schematic diagram showing its main components.

The resulting briquettes were of the pillow type with a nominal dimension of 13 x 19 x 28 mm and a volume of 4 mm 3. Thirty pockets were arranged in a row around each roll.

Among the two rolls, one roll was fixed and the other "floating roll" was held in contact with the fixed roll by a ram filled with oil and gas. Pressure was applied to the oil in the ram to provide the desired load force between the two rolls.

Briquetting was also performed using a Komarek BH400 double roll press with a roll diameter of 450 mm and a roll width of 75 mm. The feed material was gravity fed into the nip zone from the feed hopper on the roll. 2 is a schematic diagram showing main components thereof.

Briquettes with modified dimensions were produced with the following detailed specifications.

(1) Nominal dimensions 17.5 × 28 × 34.3 mm (volume 8.9 kPa). 48 pockets (9 kPa almonds) were arranged in two rows with staggered arrangement around each row.

(2) Nominal dimension 14.5 x 22 x 33.9 mm (volume 6.3 kPa). Sixty pockets (six almonds) were arranged in two rows with staggered arrangement around each roll.

(3) Nominal dimensions 15.2 × 21 × 22.9 mm (volume 3.9 kPa). 58 pockets (spherical spheres of 4 mm 3) were arranged in three rows with staggered arrangement around each row.

(4) Nominal dimensions 11.2 x 17.3 x 32.1 mm (volume 3.9 kPa). 72 pockets (4 mm square) were arranged in two rows in a symmetrical arrangement over each roll.

Of the two rolls, one roll was fixed and the other "floating roll" was held in contact with the fixed roll by a ram filled with oil and gas. Pressure was applied to the oil in the ram to provide the desired specific pressing force between the two rolls. In addition, briquetting treatment was performed using a Koppern 52 / 6.5 double roll press having a roll diameter of 650 mm and a roll width of 130 mm. The feed material was fed by gravity into the nip region from an arc located above the nip region. The area of the nip region was controlled via the 'nip region regulator'. 3 is a schematic diagram showing its main components.

The resulting briquettes were 'pillow' shaped with a nominal dimension of 30 × 24 × 16 mm and a volume of 7.5 mm 3. Along the face of each roll, 77 pockets were arranged symmetrically in four rows.

Of the two rolls, one roll was fixed and the other "floating roll" was held in contact with the fixed roll by a ram filled with oil and gas. Pressure was applied to the oil in the ram to provide the desired specific compressive force between the two rolls.

(Example 2)

The effect of the feed moisture content was investigated.

4 illustrates that the feed moisture has a significant effect on the yield of 6 cc briquettes and 4 cc briquettes produced by briquetting presses with a 450 mm roll as disclosed in Example 1. FIG. The feed material is gravity fed to the roll while the rolls are operating at a speed of a fixed roll of 20 rpm and a roll pressure of 90 kg / cm 2.

Feed moisture control is also important in that the change in moisture content affects the properties of the body, such as green strength, abrasion resistance and shatter strength. This is illustrated in FIGS. 5 and 6.

FIG. 5 illustrates the relationship between supply moisture level and intensity for briquettes composed of HG using 450 mm rolls, gravity feed systems, and various types of pocket sizes.

FIG. 6 shows the same relationship for briquettes consisting of a 650 mm roll and 7.5 cc pockets for HG material.

Body strength tended to increase maximally for an optimum moisture content of approximately 6%. At moisture levels above 7.5%, the body strength becomes unacceptably low.

The feed moisture has a low impact on brittle fracture strength and intrinsic wear resistance.

(Example 3)

As mentioned above, although briquetting operations can be carried out over a wide range of roll pressures, the briquetting operations are preferably carried out at low pressures. The low pressure operation described above for iron ore briquetting treatments is groundbreaking and opens up the possibility of achieving high productivity by wide rolls in briquetting machines.

However, as mentioned above, the roll pressure needs to be carefully adjusted within this low pressure range if briquetting operations are optimized. If the roll pressure is too low and the area of the nip area is not carefully controlled, the rolls will be spaced apart from one another, producing thick webs and crushed briquettes, which in particular impair the quality and production yield of briquettes after curing. If the roll pressure exceeds the optimum, poor clogging of briquettes is caused by the "clamshell" effect on the release of briquettes from the pocket. Although the density and breaking strength of the briquettes can be increased, the impact resistance of the calcined briquettes can be greatly impaired.

FIG. 7 shows the effect of roll pressure on briquette thickness and quality (measured with respect to fracture strength) for raw material HG made with a gravity fed machine having a 450 mm diameter roll with a nominal 9 cc pocket. 7 shows that acceptable holding strength can be obtained at low roll pressures of 60 kg / cm 2.

8 and 9 show the effect of the pressing force that can be obtained by using a 650 mm diameter roll and the resulting strength. The work was carried out on HG raw material and GH raw material types, and the relationship between roll pressure and holding strength appears to be similar to that using 450 mm diameter rolls. In particular, FIGS. 8 and 9 show that acceptable holding strength can be obtained at a compaction force of 20 kN / cm.

Pressing force has also been found to have a significant impact on brittle strength and brittle wear resistance of these briquettes, and these two variables increase with increasing roll pressure.

(Example 4)

Roll speed was also investigated.

It was found that the roll speed, measured in revolutions per minute (rpm), affects the amount of pressure applied to the feed material.

Since the residence time in the nip zone of the roll is shorter by increasing the roll speed, lower pressure is applied for a longer time. Roll pressure can be used primarily to control the magnitude of the pressure applied to the feed material, and the roll speed can be varied to maximize production speed. However, it is important to consider the influence of the roll speed on briquette thickness and body strength when optimizing the briquette production operation.

FIG. 10 shows the effect of roll speed on briquette thickness and quality (measured by breaking strength) in the case of raw material HG for a gravity feed machine with a roll diameter of 450 mm.

10, it is seen that the thickness and holding strength decrease as the roll speed is increased.

(Example 5)

The process variables of the briguetting machine described in Example 1, namely roll speed, precompressor speed and roll pressure, and briquetting density are used to determine the operating window of such a particular briquetting treatment system. do.

The diagram of FIG. 11 is an example of an operating region where briquetting with a 250 mm roll forms a nominal 4 cc briquette from HG material in a Taiyo press.

To simplify these curves, the roll pressure was fixed at 150 kg / cm 2 and the preliminary compressor speed was fixed at 20 rpm. A series of curves are shown for feed moisture from 4 wt% to 12 wt%. Each represents the conditions which form whole briquettes.

On the right side of the curve there is an area of low supply pressure where the pocket is not filled or briquettes are easily broken off. On the left side of the curves is an area where the supply pressure is too high. Briquetting shear and pocket blocking occurred. In the intensity range of 6 kgf or less, briquettes are so weak that they cannot tolerate opening the pocket, which may remain in the pocket or split upon opening. Above 30 kgf no further compaction could be achieved. The briquettes thickened, and the clam shell started. The intensity range of 6 to 30 kgf defines the outer limits of the range in which whole briquettes can be formed using sample materials and a Daiyo briquetting machine.

To determine its operating area, specific production and quality variables, including yield, density, crush strength and drop / crush strength, must be considered. Taking these characteristics into account, it is possible to define a narrow area which is the operating area of the briquetting process.

In FIG. 11, the area occurs at a roll speed of 5 to 9 rpm, green strength of 6 kgf to 18 kgf.

(Example 6)

Base steels produced under optimized conditions have been found to be very thermally stable compared to pellets formed from the same material. This is illustrated in FIGS. 12 and 13.

FIG. 12 shows the temperature profiles of three points in the briquette bed as well as the inlet and outlet gases during lab grade curing tests simulating a straight great process.

Bed temperature was measured with thermocouples located 100, 250 and 500 mm from the top of the bed.

Briquettes were found to be thermally stable when heated at the high speeds shown in the figures. The good drying performance allowed the incoming gas temperature to rise to 1340 ° C. in 10 minutes from ambient temperature without destroying briquettes.

FIG. 13 shows the temperature profile for briquetting to produce a nominal 4 cc briquette of HG ore with productivity of 32 t / m 2 · d and 25 t / m 2 · d. This figure also shows a curing temperature profile for a typical pellet as a comparative example. Pellet profiles are profiles that are optimized to minimize pellet breakage and maximize properties after firing. The pellet profile produced pellets with a productivity of 16 t / m 2 · d, which was relatively lower than that of briquettes. Briquettes and pellets were made from the same kind of ore.

The high productivity of briquettes is due to the thermal stability of the briquettes which allow briquettes to be heated at high speed.

It has been found that the thermal stability of briquettes is not limited to one curing method and one ore type.

(Example 7)

A test Great Kiln system was used to measure briquette characteristics as briquettes exited the Great before entering the kiln.

Such equipment consists of pot grate and batch kiln. In order to simulate moving greats, LGP gas burners were used to generate flame temperatures. Port Great allows for gas flow to flow up and down. The temperature of the material was measured throughout the bed using a thermocouple placed through the wall into the port wall. This measurement was assumed to be briquetting temperature during the firing cycle. Due to the size of the briquettes tested, the temperature measurements represent the outside temperature of briquettes, not the internal temperature. The temperature measured can usually be a mixture of the outside temperature of briquettes and the gas temperature at that point in the bed.

FIG. 14 shows a minimum at ˜700 ° C. after the temperature of briquettes prepared from GH material (d95 = 1 mm) having a nominal body size of 7.5 cc was initially increased to a maximum at an average bed temperature of approximately 300-400 ° C. FIG. It shows how it falls. At higher temperatures, the strength increased again. The strength drops to a minimum at ˜700 ° C., which is lower than the holding strength. This is an important factor for transporting material from the great to the kiln. Since the strength is the lowest in this temperature range, the maximum reduction can be expected when the firing profile includes transport from the great to the kiln at that temperature.

In the case of straight grate processes, the bed height selected for the curing process is not critical and has been found not to be inhibited by the gas permeability generally chosen to prevent deformation of briquettes at the bottom of the bed while achieving ideal productivity. In addition, at briquetting volumes exceeding 6 cc, the permeability of the bed was not significantly impaired by the bed height. Thus, the curing process is not limited by such variables as in the case of pelletizing operations. The briquetting bed depth can be selected to optimize productivity without compromising quality.

The great kiln process may provide certain advantages in terms of producing better plastic products over products obtained from other curing processes. In addition, the briquettes are heated more evenly over a high temperature range in a manner that reduces the temperature gradient in the briquettes and prevents differential shrinkage of the briquettes that may cause cracking. In addition, since all briquettes undergo similar firing temperatures and times in the rotary kiln, the briquette quality becomes more uniform compared to the straight grate process.

If a suitable grade of raw material is available, it is also possible to produce briquettes suitable for the direct reduction process.

(Example 8)

The firing temperature was studied.

Using all of the same firing profiles for the great sections, 7.5 cc of GH material (d95 = 1 mm) briquettes were fired in the grate-kiln test rig. After moving to the kiln, the same profile was applied to the firing, except that the firing temperature reached was changed as shown. The result is shown in FIG.

It can be clearly seen from FIG. 15 that the firing temperature in the kiln should be at least 1380 ° C. in order to achieve adequate firing strength in briquettes of such size.

15 also shows improved tumble strength (Tumble Index; TI) and abrasion resistance (Abrasion Index; AI) with firing temperature.

(Example 9)

Firing temperature and temperature time were studied.

Briquettes of GH material (d95 = 1 mm) with a nominal size of 7.5 cc were fired in a series of Great Kiln tests. The great firing profile was the same, only the firing time in the kiln of the firing temperature was changed from 6 minutes to 9 minutes. The overall firing time in the kiln remained the same, with additional time for firing from the heating rate in the kiln, the 9 minute firing time having a faster heating rate up to 1380 ° C. compared to the 6 minute firing time.

In addition, tests were also performed with 6.3cc GH bridging using the same profile used for 7.5cc.

The results are shown in FIGS. 16 and 17.

In the case of GH briquettes of nominal 7.55 cc size, the firing strength substantially increased with increasing firing time in the kiln. The reason is that the thermal penetration of briquettes is greater during the firing cycle.

The post-calcination properties for the 6.3 cc GH briquettes were better than those produced for 7.5 cc, suggesting that the problem of heat penetration is an important issue for the generation of post briquetting properties. This result also suggests that adequate strength will not occur in the fired product when heat penetration in briquettes is insufficient.

(Example 10)

The effect of residence time in the Great Kiln was studied.

Briquettes of nominal 7.5 cc of GH material (d95 = 1 mm) were calcined in a batch-type Great Kiln on a test scale. Briquettes were charged in the kiln preheated to 500 or 1000 ° C. Firing profiles were imposed on briquettes and the total residence time was recorded. The result is shown in FIG.

18 shows that the properties after firing have improved with longer residence times, implying that it is important to fully heat the product to achieve the required final properties.

The effect of the fast heating was not reduced by the greater bed depth of the grate. This is shown in FIGS. 19 and 20. The green briquette bed was highly permeable and did not result in the suppression of air flow as often occurs in the case of pellets. The maximum bed depth available is not limited but will be greater than 300 mm. This far exceeds the possible range for the best pallet beds in the grate-kiln system.

(Example 11)

The effect of briquette chemical properties was investigated. The effect of basicity and temperature on the properties of calcined briquettes made from HG materials was determined by firing briquettes in a muffle furnace at specific temperatures and times. The results are shown in FIG.

Chemical analysis of the resulting calcined briquettes with a gradual change in basicity ranging from 63.81% Fe with a basicity of 1.2 to 65.93% Fe with a basicity of 0.2 reflecting the level of flux additive.

As can be seen in Figure 21, the breaking strength increased with increasing temperature and the basicity increased with increasing from 0.2 to 0.8. This effect becomes more pronounced as the temperature increases over the range to be investigated, it is possible to achieve 300 kgf at 1295 ° C. with a basicity of 0.6 and 300 kgf at 1280 ° C. with a basicity of 0.8.

The explanation for the increase in basicity level resulting in increased strength is related to the binding mechanism variation. At low basicity levels, the binding of particles occurs as a result of recrystallization of iron oxide and the formation of iron oxide-iron oxide bonds. At increased basicity levels, melt formation occurs at low temperatures to improve the melting of iron oxide crystals, and slag bonds become more pronounced, providing higher strength for the same temperature.

(Example 12)

Total Briquettes and Standard Reduction Test Methods Reduction tests using JIS 8713 / IS07215 were performed on HG briquettes calcined at 1300 ° C. for 10 minutes. The results for reducibility, swell and crush strength after reduction (CSAR) are shown in FIG. 22.

Reduction index (RI) remained relatively stable over a range of basicity levels. RI varied from 53.8% at a basicity of 0.2 to levels above 62.2% at a basicity of 1.00.

The Swell Index was somewhat responsive and varied from 11% in the lowest basicity to 14.8% in the midrange and then to zero at the basicity of 1.2.

The crush strength (CSAR) after reduction showed a large response to fluctuations in the basicity level, starting from 22 kgf at a basicity of 0.20 to 121 kgf at a basicity of 1.20. This change in reducing strength reflects the fracture strength results after firing and is also related to the variation in the bonding phase of the ignited briquettes. Low basic briquettes are mainly bound by iron oxide-iron oxide bonds, but these bonds are weakened during reduction. At increased basicity levels, slag bonds become more pronounced. These bonds are more stabilized during reduction due to the absence or little swell at a basicity of 1.2 and the higher reduction strength. Slag bonds are also a more important form of bonding of briquettes made from GH and G, even if the SiO ₂ and Al ₂ O ₃ levels are higher resulting in increased flux additives. Such briquettes are generally stronger after reduction, unless the reduction process results in the destruction of the non-ferrous bonding phase. High grade ores, such as HC, which require low flux additions mostly rely only on oxide-oxide junctions, and thus have low strength values after reduction.

Many modifications may be made to the embodiments of the invention described above without departing from the spirit and scope of the invention.

Claims (21)

As a method of producing iron ore briquettes for use as a raw material for blast furnaces or other direct reduction furnaces,
(a) a mixing step of mixing iron ore and flux to form an iron ore / flux mixture, wherein the iron ore / flux mixture is free of binder;
(b) pressing the iron ore / flux mixture into a green briquette by using a roll pressure formed by applying a roll pressing force of 10 to 140 kN / cm to the iron ore / flux mixture;
(c) a curing step of curing the base briquettes to form fired briquettes
Iron ore briquette manufacturing method comprising a. The iron ore briquette manufacturing method of claim 1, wherein the roll pressure is generated by a roll pressing force that produces briquettes having a compressive strength of 2 kgf or more. The iron ore briquette manufacturing method of claim 2, wherein the base compressive strength is 5 to 30 kgf. The iron ore briquette manufacturing method of claim 1, wherein the roll compressive force is 10 to 60 kN / cm. The method of claim 1, wherein the mixing step (a) comprises mixing the iron ore and flux particles having a predetermined particle size distribution of the iron ore particles. The iron ore briquette manufacturing method of claim 5, wherein a predetermined particle size distribution of the iron ore particles mixed with the flux in the mixing step (a) can be generated without crushing the iron ore. 6. The method of claim 5, comprising crushing and screening the iron ore to form a predetermined particle size distribution of the iron ore mixed with flux in the mixing step (a). The iron ore briquette manufacturing method according to any one of claims 5 to 7, wherein a maximum particle size of a predetermined particle size distribution of the iron ore mixed with the flux in the mixing step (a) is 4.0 mm or less. The iron ore briquette manufacturing method according to claim 5, wherein the maximum particle size of a predetermined particle size distribution of the iron ore mixed with the flux in the mixing step (a) is 2.5 mm or less. The iron ore briquette manufacturing method according to claim 5, wherein the predetermined particle size distribution of the iron ore mixed with the flux in the mixing step (a) passes less than 50% through a 45 μm screen. The method of claim 10, wherein the predetermined particle size distribution passes less than 10% through a 45 μm screen. The method of claim 1, wherein the iron ore is a hydrated iron ore. 13. The method of claim 12, wherein the hydrated iron ore is goethite-containing iron ore. The iron ore briquette manufacturing method of claim 1, wherein the flux has a particle size distribution of less than 100 μm. 15. The method of claim 14, wherein the flux particle size distribution is at least 95% through a 250 μm screen. The iron ore briquette manufacturing method of claim 1, wherein the iron ore / flux mixture produced in the mixing step (a) is selected such that the basicity of the calcined briquette is greater than 0.2. The method of claim 1, further comprising adjusting the water content of the iron ore before or during the mixing step (a) to optimize briquetting quality and yield. 18. The method of claim 17, wherein adjusting the water content of the iron ore comprises adjusting the water content of the iron ore such that the water content of the iron ore / flux mixture is from 2 to 12% by weight relative to the total weight of the iron ore / flux mixture. Process for producing iron ore briquettes. The method of claim 1, wherein the pressing step (b) produces briquettes having a volume of 10 cc or less. The method of claim 1, wherein the curing step (c) comprises heating the briquette to a firing temperature of at least 1200 ° C. within 40 minutes. The method of claim 1 wherein the calcined briquettes have a breaking strength of at least 200 kgf.

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