JP5389308B2 - 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

  The present invention relates to the production of iron ore briquettes suitable for transport and use in iron making processes.

  Iron ore agglomeration methods have been developed since the late 1800s. However, among all available methods, only the pellet method and the sintering method are currently meaningful, but there are certain disadvantages to these methods.

Pelletization consists of two different operations: forming pellets from wet ore fines and then firing it at a temperature on the order of 1300 ° C. In order to prepare suitable pellets, it is generally important that the ore be very finely crushed to a size such that 60% of the ore passes through 45 μm. This is then formed into pellets, either in a horizontal drum or tilted disc, generally with the addition of a suitable binder. The formed pellets are then fired in a shaft kiln, a horizontal movable grid, or a combination of movable grid and rotary kiln, in a process sometimes referred to as induration. Pelletization is a practical and commercially attractive way to agglomerate fine concentrates, but requires substantial grinding to achieve the required particle sizing, It is an energy intensive method. Pellets made from goethite-hematite ore require long setting times that affect the economics of the process. Solid fuels in the form of coke, often added to reduce curing time, but this leads to generation of (dioxins, including NO _x and SO _x) harmful emissions.

  Sintering consists of granulating wet iron ore fines and other fine raw materials with solid fuel, usually powdered coke, and loading the granulated mixture onto a breathable moving grid. As the temperature rises, air is drawn down through the grid. After a short burning time, heating from outside the bed is turned off, and as the solid fuel in the bed burns, a narrow combustion zone moves down through the bed and each layer is heated in turn to approximately 1300 ° C. Bonding occurs between the particles during combustion and a strong agglomerate is formed. However, traditional sintering processes result in high levels of harmful emissions, particularly sulfur oxides and dioxins, and thus the sintering process is undesirable from an environmental standpoint and cannot be maintained.

  Agglomeration was a method of commercial interest in the late 1800s and early 1900s, but the production of iron ore ores for use as blast furnace feedstock was never to a significant level. Without reaching it, it decreased after 1950, and by 1960, it had stopped. The process performed included pressing the ore fines into blocks of some appropriate size and shape and then curing the blocks. A wide range of binders and / or organics such as tar and pitch, other additives such as sodium silicate, iron sulfate, magnesium chloride, limestone and cement have been tested. However, the Glendal process, an early briquetting process, simply involved mixing iron ore with water and pressing it into a rectangular block of construction brick size. They were then solidified by passing through a tunnel kiln heated to 1350 ° C.

  While the development of briquetting processes has generally been directed to the development of suitable binders, JP 60-243232 describes briquettes having a flat shape to provide a stable distribution in a blast furnace. Specifically, the Japanese patent specification discloses that flat shaped briquettes are reduced much more easily at high temperatures than ordinary spherical pellets. The briquette is made in a volume of 2 to 30 cc to balance a relatively large compressive strength against rotational or tumble strength and impact resistance that weakens with increasing size. The Japanese patent specification discloses that larger briquettes are more difficult to reduce in a blast furnace. However, except for the size and shape of the briquette, there are no other factors listed as important, and indeed there is no detailed description of any other aspect of briquette production.

  Applicants have conducted extensive research on the production of briquettes from iron ore and have invented methods that can produce briquettes with properties suitable for use in blast furnaces and other direct reduction furnaces.

  One notable issue that the researchers must address in their research is that a commercially viable iron ore ore plant must be able to process a sufficient throughput of raw material. is there. In order to do so, the applicant believes that the briquetting press will be able to process 70-100 tonnes of iron ore per hour per press. Applicant will operate a briquette press at surprisingly low roll pressures in the study to produce green briquettes with sufficient green strength to withstand subsequent handling I found that it was possible. This was a surprising discovery. This is because the information provided by the briquetting press manufacturer indicated that it would be appropriate pressure and that a roll pressure significantly higher than the pressure found by the applicant would be required. is there. The discovery that low roll pressure operation is possible is significant. This is because the low pressure operation makes it possible to use a wider press, thereby having a higher production rate for the press.

  The present invention relates to the selection of briquette formation parameters.

According to the present invention,
(A) mixing the ore and the flux to form an ore / flux mixture;
(B) pressing the ore / flux mixture into a green ore using low roll pressure;
(C) Producing iron ore briquettes that are suitable for use as feedstock for blast furnaces or other direct reduction furnaces that include the step of indulating the green briquettes to form calcined briquettes A method is provided.

  The low pressure operation for iron ore aggregate mineralization described in step (b) above is significant and achieves high production rates by using wide rolls on the aggregate mineralization machine up to 1.6 m in length. Make it possible.

  Preferably, the low roll pressure is generated by a roll pressure that is sufficient to produce briquettes having a green compressive strength of at least 2 kgf.

  Preferably, the raw compressive strength is at least 4 kgf.

  More preferably, the raw compressive strength is at least 5 kgf.

  More preferably, the raw compressive strength is 5 to 30 kgf.

  More preferably, the raw compressive strength is 15 to 30 kgf.

  Preferably, the low roll pressure is generated by a roll pressing force of 10 to 140 kN / cm for the ore / flux mixture.

  More preferably, the roll press force is 10 to 60 kN / cm.

  More preferably, the roll press force is 10 to 40 kN / cm.

  Preferably, step (a) comprises mixing ore having a predetermined particle size distribution of ore particles and flux particles.

  A predetermined particle size distribution of the ore particles mixed with the flux in step (a) can be obtained without grinding the ore.

  Preferably, the method includes crushing or sieving the ore to produce a predetermined particle size distribution that is mixed with the flux in step (a).

  Preferably, the ore having a predetermined particle size distribution of the ore mixed with the flux in step (a) has a maximum ore size of 4.0 mm or less.

  More preferably, the maximum size is 3.5 mm or less.

  More preferably, the maximum size is 3.0 mm or less.

  More preferably, the maximum size is 2.5 mm or less.

  More preferably, the maximum size is 1.5 mm or less.

  More preferably, the maximum size is 1.0 mm or less.

  Preferably, the predetermined particle size distribution of the ore mixed with the flux in step (a) is such that less than 50% passes through a 45 μm screen.

  More preferably, the particle size distribution is such that less than 30% passes through a 45 μm screen.

  More preferably, the particle size distribution is such that less than 10% passes through a 45 μm screen.

  Preferably, the ore is a hydrated iron ore.

  Preferably, the hydrated ore is a goethite-containing ore.

  Preferably, the flux has a particle size distribution that is primarily less than 100 μm.

  Preferably, the particle size distribution of the flux is such that greater than 95% passes through a 250 μm screen.

  Preferably, the flux is limestone.

  Preferably, the ore / flux mixture produced in step (a) is selected such that the basicity of the calcined briquette exceeds 0.2.

  More preferably, the basicity is greater than 0.6.

The term “basicity” is taken here to mean (% CaO +% MgO) / (% SiO ₂ +% Al ₂ O ₃ ) of the calcined briquette.

  Preferably, no binder is present in the ore / flux mixture.

  Preferably, the method includes adjusting the moisture content of the ore prior to or during the mixing step (a) to optimize briquette quality and product yield.

  Preferably, the step of adjusting the water content of the ore includes adjusting the water content such that the water content of the ore / flux mixture is 2-12% by weight of the total weight of the ore / flux mixture.

  The term “total weight of the ore / flux mixture” refers to (a) the dry weight of the ore / flux mixture, (b) the inherent moisture weight of this mixture, and (c) (if any) ) Means the total weight of water added to the mixture in the process.

  The term “moisture content” is the sum of (b) and (c) above.

  Preferably, the step of adjusting the water content of the ore is such that the water content of the ore / flux mixture is 2-5% by weight of the total weight of the ore / flux mixture for ores that are dense hematite ores. Including adjusting the content.

  Preferably, step (b) comprises the ore moisture content such that the ore / flux mixture moisture content is 4 to 8% by weight of the ore / flux mixture total weight for ores containing up to 50% goethite. Including adjusting the content.

  Preferably, step (b) is carried out at an amount of 6-12% by weight of the total weight of the ore / flux mixture, for ores where the water content of the ore / flux mixture is primarily greater than 50% and includes goethite ore. Including adjusting the moisture content of the ore.

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

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

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

  Preferably, the curing step (c) comprises heating the briquette to the firing temperature in 40 minutes.

  Preferably, the curing step (d) comprises heating the briquette to the firing temperature within 35 minutes.

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

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

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

  Preferably, the firing temperature is at least 1200 ° C.

  More preferably, the firing temperature is at least 1260 ° C.

  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.

  Preferably, the fired briquette has a crush strength of at least 200 kgf.

  Preferably, the calcined briquette has a crush strength of at least 250 kgf.

  Iron ore fines are broadly characterized into four groups based on petrological properties such as mineralogy, mineral association and particle texture, porosity, size distribution and chemical properties. These groups are as follows:

Iron ore fines are broadly characterized into four groups based on petrological properties such as mineralogy, mineral association and particle texture, porosity, size distribution and chemical properties. Those groups are
(A) HC-dense hematite / magnetite ore,
(B) ores containing up to GC-50% goethite, and (c) containing mainly goethite such as G-beanite, derritals and channel iron deposits, It is an ore containing more than 50% goethite.

Hereinafter, the specification will refer to two specific subgroups of GC ores:
Reference is made to (i) goethite-containing ores that are dominated by HG-hematite and (ii) GH--ores with approximately equal amounts of hematite and goethite.

  Although not wishing to be bound by theory, the cohesive ore coalescence mechanism includes a combination of particles mechanically interlocking, including van der Waals forces, for types GC and G raw materials It is believed that the varying degree of hydrogen bonding depends on the percentage of hydrated ionic species present, such as goethite. Several properties of the feedstock have been identified as having a significant impact on the formation of such bonds that affect the quality and processing performance of green and calcined briquettes. These properties are the moisture level of the feedstock and its flow properties, the ore chemical composition, its size distribution and petrological properties and porosity.

  Preferably, the feedstock is of the widest possible size distribution to achieve high packing density and improved ore particle bonding. As mentioned above, the cohesive ore coalescence mechanism is through a combination of particle mechanical interlocking, van der Waals forces, and, in the case of type GC and G feedstocks, bonds resulting from hydrogen bonding. It is believed. Although a wide size distribution increases the packing density and increases the strength of the green ore, it is possible to nominate narrow size iron ores.

  The maximum size of the particles is determined by the crushing process, but is preferably less than 2.5 mm to produce a fired property briquette that is acceptable after the curing process. In general, ore types HC and HG can be aggregated with a coarser maximum size due to the lower thermal requirements for their feedstock to achieve acceptable firing strength. The maximum size of the raw material can be reduced by either a crushing or sieving process. There is no absolute limit to the minimum particle size. However, it is unnecessary and undesirable to grind the ore into very fine particles (as required for pelleting). This is because this is an additional economic burden that is not required by the present invention. Preferably, less than 10% of the particles pass through a 45 μm sieve.

  Advantageously, the pocket dimension of the briquetting equipment is based on the maximum particle size to be brittled to ensure that satisfactory briquetting can be achieved, as well as of the appropriate hardening performance. Should be selected for. Typically, the maximum particle size that achieves satisfactory briquetting is 25-30% of the minimum pocket dimension. If the maximum particle size exceeds this specification, it may be necessary to select a larger pocket size.

  It is desirable to control the water supply in order to optimize the quality and product yield of the dynamite. The addition of moisture should not exceed the level at which the liquid bridge becomes a meaningful form of interparticle bonding. This results in a reduction in green strength and in addition has an adverse effect on thermal stability. Insufficient moisture can lead to over-pressurization in the briquetting press process and adversely affect the raw briquette quality and yield.

  Depending on the feed characteristics of the ore to be processed, a moisture content of 2 to 12 wt% is used for the feedstock to optimize the quality and yield of the green ore. Dense hematite concentrate has a low optimum nodulated moisture, generally in the range of 2-5 wt%. These concentrates are often made of narrow sized particles with a smooth surface texture that produces low strength briquettes due to reduced particle engagement. More porous goethite-containing ores (GC) with up to 50% goethite are well aggregated in the range of 4-8 wt% moisture, and the more porous mainly goethite ores (G) Good mineralization in the range of 6-12 wt% moisture. Such ores have a rough surface texture and shape that enhances their briquetting properties.

  In the method of the present invention, a normal briquetting apparatus can be used. In essence, such a device uses two adjacent rolls with pockets that come together in the nip area to compress the feed material into adjacent aligned pockets to produce briquettes. Including. In the case of the present invention, the rolls are preferably arranged horizontally to achieve the throughput required for economic feasibility.

  Although briquetting can be performed over a wide range of roll pressures depending on the application, briquetting of iron ore is preferably 10-140 kN / cm, more preferably on the lower side of this range. The roll pressing force is 10 to 60 kN / cm. As mentioned above, such a low pressure operation for iron ore briquetting is meaningful and achieves high production speeds by using wide rolls on briquetting machines up to 1.6m in length It is possible to do.

  Preferably, the roll pressure is carefully controlled within the low pressure range to optimize the briquetting operation. If the roll pressure is too low, the rolls are pulled apart, producing a thick web and distorted briquettes that detract from briquette yield and quality, especially after hardening. If the roll pressure is above optimum, a poor closure of the briquette occurs due to the “clamshell” effect upon the release of the briquette from the pocket. For small roll diameters and excessive roll pressure, the clamshell effect is more pronounced, which also causes pocket bonding / clogging. Although the density and crushing strength of the green briquettes will increase, the impact resistance of the fired briquettes will be severely impaired.

  Preferably, the moisture level is selected to affect the flow properties of the material through the feed system, with a moisture level of 2-12 wt% being generally appropriate for the feed. If the moisture level is too high for the feed system, the feed pressure will be adversely affected, resulting in reduced yield and reduced briquette quality characterized by low green strength. If the feed is too low for the feed system, the resulting feed pressure will cause clamshelling, which will result in reduced yield, increased roll pocket wear rate and poor post-fire characteristics. obtain.

  The briquetting apparatus can be operated with a pre-compactor supply system or with a gravity supply system. Gravity supply systems are advantageous when large weights are aggregated as in the iron ore industry.

  For the briquetting press, the roll diameter is selected to ensure that briquetting quality is ensured at a production rate that is economically reasonable. Large diameter rolls increase production speed, however, such rolls also increase the area of the nip area. Careful control of the nip area facilitates the formation of high quality green ore and avoids formation of briquettes with excessively thick webs. Changing the roll diameter also changes the optimal moisture level for the feed, where an increase in roll diameter represents an increase in feed moisture. The roll diameter typically has a range of 250 mm to 1200 mm. In order to maximize production, preferably the rolls are operated at the highest possible speed while maintaining briquette quality. However, very low roll speeds can be used if productivity is a secondary problem.

  Typically, roll speeds in the range of 1 rpm to 20 rpm are used. In order to maintain quality, especially at high roll speeds, the feedstock will have a nip area that creates the force required to form a high quality briquette at a speed that matches the briquetting production speed. It is desirable to be supplied to a roll.

  Any suitable roll width can be selected as long as it is within the pressure tolerance of the briquetting machine. Wide rolls that increase the capacity of the machine are preferred when iron ore briquetting is in low pressure operating conditions. The rolls are preferably arranged horizontally to allow use in a gravity supply system. The flow properties of either HC, GC (including HG and GH) or G iron ores are appropriate for gravity supply in the water ranges specified above for each taxon.

  The pocket shape should generally not be of a sharp angle, but is more smooth and rounded to improve handling characteristics. As an example, a length / width and width / depth ratio of approximately 0.65 is appropriate. The shape of the pocket also has a specific release angle of 110-120 ° that counteracts the tendency to stick within the pocket.

  The pocket size can be optimized according to the hardening process and the maximum size of the material and the requirements for the ironmaking blast furnace. Typically, briquettes have a volume of 2 to 30 cc. Preferably, the volume is 10 cc or less. More preferably, the volume is 8.5 cc or less. More preferably, the volume is less than 6.5 cc.

  A pocket shape with a staggered arrangement is preferred. This is because it makes optimal use of the available space on the surface of the roll and thus maximizes throughput.

  Preferably, the curing method and conditions are selected in relation to a complex relationship between raw material properties and briquette size effects.

  Consideration of the relationship between briquette volume, shape and petrological properties of raw materials is required. The chemical composition of the feedstock can have a significant impact on the properties of the calcined briquette. Apart from moisture, the feedstock contains iron ore made of iron oxide and gangue with the required flux added to give the required basicity level in the calcined briquette. Test results show that to achieve the required properties for the calcined briquettes, the flux should preferably be sized to a fines size typically> 95% passing 250 μm. It was.

  Although not wishing to be bound by theory, the bonding mechanism for calcined briquettes appears to include diffusion bonding and recrystallization of iron oxide and slag bonding at higher flux levels. Therefore, flux level and firing temperature and to some extent firing time have a strong influence on briquette properties. Increasing the basicity level can improve the reduced strength as well as the cure strength. This is because higher flux levels promote the formation of a binder phase that resists deformation under reducing conditions.

  Curing can be performed using a straight grid, grid-kiln or continuous kiln type process.

  It has been found that conglomerate produced under optimal conditions is thermally very stable compared to pellets prepared from the same material. The feed ore for pelleting must be ground to a fine size, typically up to 60% passing 45 μm, and the pellet is typically <200 ° C. to avoid spalling It must be dried slowly at low temperatures. In contrast, as described above, the feed ore for the present invention that can be hardened can be much coarser, preferably with a maximum size of up to 2.5 mm and is therefore necessary to produce pellets. There is no need to grind to the same extent as it is. This feature provides major capital cost savings for briquetting operations for conventional pellet manufacturing plants.

  An important property of the briquettes of the present invention is the ability to withstand high temperatures during heating at high speeds, such as heating to a calcination temperature within 30 minutes, more preferably within 20 minutes. This is in stark contrast to previous understandings of how goethite ores respond in the hardening situation that has been shown to cause briquette flaking off when rapidly heated through the dewatering and free water removal zone. Is.

As mentioned above, the thermal stability of the briquettes of the present invention has been found to be much better than pellets, and briquettes can be heated much faster than pellets without flaking. This allows a much shorter heating cycle. As a result, briquetting productivity will be significantly higher than for pellets using the same material. For example, compared to 16 t / m ² · day pellet productivity for HG ore in a straight grate kiln, potentially 30 t / m ² · day briquette productivity is achieved in the same kiln. Can be done.

  Although prior art publications are referred to herein, this specification forms part of the common general knowledge of the art either in Australia or any other country. It will be clearly understood that this does not constitute a license.

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

Example 1
The briquetting was carried out using three different roll presses with varying roll diameters, widths and feed systems.

  Initial testing was performed using a Taiyo K-102A double roll press with a nominal capacity of 300 kg / hr. This machine has a 36 mm wide 250 mm diameter roll and is equipped with a screw-type precompactor. A schematic diagram showing the main components can be seen in FIG.

  The briquette produced was pillow-shaped and had a nominal dimension of 13 × 19 × 28 mm and a volume of 4 cc. There were 30 single pockets around each roll.

  For the two rolls, one was fixed while the other “floating roll” was held against a roll fixed by a ram filled with oil and gas. The oil in the ram was pressurized to provide the desired loading force between the rolls.

  The briquetting was also carried out using a Komalek BH400 double roll press with a roll diameter of 450 mm and a roll width of 75 mm. Feedstock was gravity fed from the feed hopper located on the roll to the nip area. A schematic diagram of the main parts can be seen in FIG.

  Various sizes of briquettes were produced according to the following details.

  (1) Nominally 17.5 x 28 x 34.3 mm with a volume of 8.9 cc. There were two rows of 48 pockets arranged in a staggered pattern around each row (9 cc almond type).

  (2) Nominally 14.5 x 22.1 x 33.9 mm with a volume of 6.3 cc. There were two rows of 60 pockets arranged in a staggered pattern around each roll (6 cc almond type).

  (3) Nominally 15.2 × 21.7 × 22.9 mm with a volume of 3.9 cc. There were 3 rows of 58 pockets arranged in a staggered pattern around each row (4 cc sphere).

  (4) Nominally 11.2 x 17.3 x 32.1 mm with a volume of 3.9 cc. There were two rows of 72 pockets arranged in a symmetrical row around each roll (4 cc portrait).

  One of the two rolls was fixed, and the other “floating roll” was held in contact with a roll fixed by a ram filled with oil and gas. The oil in the ram was pressurized to provide the specific pressing force desired between the rolls.

  The briquetting was also carried out using a Kepan 52 / 6.5 double roll press with a diameter of 650 mm and a roll width of 130 mm. Feedstock was gravity fed from the hopper located above to the nip area. The nip area was controlled using a “nip area adjuster”. A schematic diagram of the main components can be seen in FIG.

  The created ore has a nominal dimension of 30 × 24 × 16 mm and is “pillow” shaped and has a volume of 7.5 cc. There were four rows of 77 pockets arranged in contrast across the face of the roll.

  One of the two rolls was fixed, and the other “floating roll” was held in contact with a roll fixed by a ram filled with oil and gas. The oil in the ram was pressurized to provide the specific pressing force desired between the rolls.

Example 2
The effect of water supply content was studied.

FIG. 4 illustrates that the feed moisture had a significant effect on the yield of 6 cc and 4 cc briquettes produced by the briquetting press with the 450 mm roll described in Example 1. The feedstock was gravity fed to the rolls while the rolls was operated at a fixed roll pressure of roll speed and 90 kg / cm ² for 20 rpm.

  Control of water supply is also important because fluctuations in moisture content affect green properties such as green strength, abrasion resistance and crush strength. This is illustrated in FIGS. 5 and 6.

  FIG. 5 shows the relationship between feed moisture level and strength for briquettes made with HG using 450 mm rolls, gravity feed system, and various pocket sizes.

  FIG. 6 shows the same relationship for briquettes made with 650 mm rolls and 7.5 cc pockets for HG material.

  The green strength tended to increase to the highest value for an optimal moisture content of approximately 6%. At moisture levels above 7.5%, the green strength is unacceptably low.

  The water supply had less influence on the crushing strength and raw wear resistance of briquettes.

Example 3
As mentioned above, the briquetting operation can be carried out over a wide range of roll pressures, but the briquetting is preferably carried out at low pressure. Such low pressure operation for iron ore briquetting is meaningful and opens up the possibility of achieving high production rates with wide rolls for briquetting machinery.

  However, as mentioned above, if the briquetting operation should be optimized, the roll pressure should be carefully controlled in its low pressure range. If the roll pressure is too low and the nip area is not carefully controlled, the rolls are pulled apart, creating thick webs and distorted briquettes, especially after hardening and degrading the production yield and briquette quality. If the roll pressure exceeds the optimum, brittle closure of the briquette occurs due to the “clamshell” effect in the ejection of briquette from the pocket. Although the density and crushing strength of raw briquettes will increase, the impact resistance of the calcined briquettes will be severely impaired.

FIG. 7 shows the effect of roll pressure on briquette thickness and quality (measured in terms of crush strength) for raw material HG produced on a gravity feed machine with a 450 mm diameter roll with a nominal 9 cc pocket. Indicates. The figure shows that an acceptable green strength was obtained with a roll pressure as ^high as 60 kg / cm ² .

  Figures 8 and 9 show the effect of the pressing force obtained using a 650 mm diameter roll and the resulting green strength. Work is performed on HG and GH raw material types to illustrate the relationship between roll pressure and green strength similar to 450 mm work. Specifically, the figure shows that acceptable green strength was obtained with a pressing force of 20 kN / cm.

  Pressing force has also been found to have a significant effect on briquetting crush strength and raw wear resistance, both of which increase in response to increasing roll pressure.

Example 4
The roll speed was also studied.

  It has been found that the roll speed measured in rpm affects the degree of pressure applied to the feedstock.

  An increase in roll speed results in a reduction in residence time in the nip area of the roll, thus resulting in a low pressure over an extended period of time. Roll pressure can be used primarily to control the degree of pressure exerted on the feedstock, and roll speed can be varied to maximize production speed. However, when optimizing livestock ore production operations, it is important to consider the effect of roll speed on briquette thickness and green strength.

  The effect of roll speed on briquette thickness and quality (measured in terms of crush strength) for the raw material HG is shown in FIG. 10 for a gravity feed machine with a 450 mm diameter roll.

  The figure shows that the thickness and green strength decreased as the roll speed increased.

Example 5
Determine the process variables of the briquetting machine described in Example 1, namely roll speed, precompactor speed and roll pressure, and briquette density, and determine the operating window for that particular system for briquetting Used to do.

  The diagram shown in FIG. 11 is an example of an operating window for bridging with a 250 mm roll to form a nominal 4 cc briquette from HG material on a Taiyo press.

To simplify the curve, the roll pressure was fixed at 150 kg / cm ² and the precompactor speed was fixed at 20 rpm. A series of curves are shown for 4 to 12 wt% feed moisture. Each represents a condition that leads to the formation of the entire ore.

  On the right side of the curve is a region of low supply pressure where the pockets are not filled or the briquettes are weak and easily split. On the left side of the curve is a region where the pressure on the feed is too high. The briquettes were sheared and clogged with pockets. Over the strength range below 6 kgf, briquettes are too fragile to withstand release from the pocket and remain in the pocket or split upon release. Beyond 30 kgf, further compacting would not be achieved. The ore was thick and began to become a “clamshell”. The strength range of 6-30 kgf defines the outer limit at which all briquettes could be formed by the sample material and the Taiyo briquetting machine.

  In order to determine the operating window, certain product and quality parameters must be considered, including yield, density, crush strength and drop / shatter strength. Once those characteristics are taken into account, a narrower region can be defined which is the operating region of the briquetting process.

  In FIG. 11, the region exists at a roll speed of 5-9 rpm and a raw strength of 6 kgf-18 kgf.

Example 6
It has been found that the conglomerate produced under optimized conditions is thermally very stable compared to pellets formed from the same material. This is illustrated in FIGS. 12 and 13.

  FIG. 12 shows the temperature profile for the inlet and outlet gases and three locations in the briquette bed during a lab-scale hardening trial simulating a straight grid process.

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

  The briquette was found to be thermally stable when heated at the high rate shown in the figure. Its good drying performance allowed the inlet gas temperature to rise from ambient temperature to 1340 ° C. in 10 minutes without stripping the briquette.

FIG. 13 shows 32 t / m ² . d and 25 t / m ² . Figure 2 shows the temperature profile for hardening of a briquette produced a nominal 4cc briquette of HG ore with a productive of d. The figure also shows a typical curing temperature profile for the pellets as a comparison. The pellet profile was an optimized profile that minimized pellet flaking and maximized post-firing properties. The pellet profile is 16 t / m ² . Pellets were produced with a productivity of d, which is significantly lower than the productivity of briquettes. The briquette and pellets were made from the same ore type.

  The high productivity of briquettes was due to the thermal stability of the raw briquettes that allowed the briquettes to be heated at high speed.

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

Example 7
A pilot scale grid-kiln system was used to determine the characteristics of briquettes as they exit the grid before they enter the kiln.

  The apparatus consisted of a pot lattice and a batch kiln. In order to simulate the moving grid, an LGP gas burner was used to generate the flame temperature. The pot grid was able to raise and lower the draft gas flow. The temperature of the material was measured across the floor using a thermocouple installed through the pot wall. These measurements were estimated to be briquette temperatures during the firing cycle. Depending on the size of the briquette being tested, the temperature measurement will indicate the temperature outside the briquette and not the internal temperature. The temperature measured is most likely the sum of the temperature outside the briquette and the gas temperature at that location in the bed.

  FIG. 14 shows that the temperature of briquettes made from GH material (d95 = 1 mm) having a raw nominal size of 7.5 cc initially increased to a maximum with an average bed temperature of approximately 300-400 ° C. Then, it shows whether it falls to minimum temperature at about 700 degreeC. At higher temperatures, the intensity increased again. The intensity drops to a minimum value at approximately 700 ° C. and then becomes lower than the raw intensity. This is an important requirement for the transport of material from the lattice to the kiln. Since the strength was lowest in this temperature range, the highest degree of degradation could have been expected if the firing profile included migration from the lattice to the kiln at this temperature.

  For straight grid processes, the floor height selected for the curing process is not critical and generally to avoid deformation of the floor bottom briquettes while achieving reasonable productivity It has been found that it is not inhibited by the selected gas permeability. In addition, for briquetting volumes greater than 6 cc, the permeability of the floor was not greatly compromised by the floor height. As a result, the curing process is not constrained by this variable as it is for the pelletizing operation. The depth of the conglomerate ore can be selected to optimize productivity without compromising on quality.

  The lattice-kiln process can provide certain advantages in terms of producing a product that has been fired better compared to products obtained from other curing processes. It also heats the briquette more uniformly throughout the high temperature range in a manner that reduces the temperature gradient in the briquette and avoids the differential shrinkage of the briquette that can result in crack formation. Also, in a rotary kiln, the briquette quality is more uniform compared to the straight grid process because all briquettes are subjected to similar firing temperatures and firing times.

  There is also a possibility for the production of briquettes where a direct reduction process is suitable if appropriate grade raw materials are used.

Example 8
The firing temperature was studied.

  7.5 cc briquette of GH material (d95 = 1 mm) was fired in a lattice-kiln pilot rig, all using the same combustion profile for the lattice section. After moving to the kiln, the same profile was applied for firing except that the firing temperature achieved was changed as indicated. The results are shown in FIG.

  There is a clear suggestion in FIG. 15 that the firing temperature in the kiln should be at least 1380 ° C. to achieve adequate fired strength with this size briquette.

  FIG. 15 also shows that the tumble strength (tumble index-TI) and wear resistance (wear index-AI) were improved by the firing temperature.

Example 9
The firing temperature and the time at that temperature were studied.

  Briquettes made from GH material with a nominal size of 7.5 cc (d95 = 1 mm) were fired in a series of lattice-kiln tests. The firing profile in the lattice was the same, only the firing time in the kiln at that firing temperature was changed from 6 to 9 minutes. Firing from the rate of heating in the kiln so that the total firing time in the kiln was the same, but the 9 minute firing time had a faster heating rate to 1380 ° C compared to the 6 minute firing time. Took extra time for.

  The test was also performed on a 6.3 cc GH ore using the same firing profile used in the 7.5 cc case.

  The results are shown in FIGS.

  For GH briquettes with a nominal size of 7.5 cc, the firing strength increased significantly with longer firing times in the kiln. This is due to the greater thermal penetration of briquettes during the firing cycle.

  The firing characteristics for the 6.3 cc GH briquettes are superior to those produced for the 7.5 cc case, and the heat penetration problem is an important issue for the formation of the briquette fired characteristics. I mean. This result also suggests that adequate strength may not be obtained with a fired product when the thermal penetration of briquettes is insufficient.

Example 10
The effect of residence time in the lattice kiln was studied.

  Made from GH material (d95 = 1 mm), a nominal 7.5 cc briquette was fired in a pilot scale batch grid kiln. They were loaded raw into kilns preheated to either 500 or 1000 ° C. The firing profile was loaded on briquettes and the total residence time was reported. The results are shown in FIG.

  FIG. 18 shows that extended residence time improves firing characteristics and suggests the importance of thoroughly heating the product to achieve the required final properties.

  The effect of fast heating was not diminished by the depth of the deep lattice floor. This is illustrated in FIGS. 19 and 20. As often happens with pellets, the conglomerate bed was very permeable and did not restrict the air flow. The maximum floor depth that could be used was not specified, but could exceed 300 mm. This is far beyond what is possible even with the best pellet bed in a lattice-kiln system.

Example 11
The influence of briquette chemistry was studied.

  The effect of basicity and temperature on the properties of fired briquettes made from HG material was measured by firing briquettes in a muffle furnace for a specific temperature and time. The results are shown in FIG.

  The results for the chemical analysis of the calcined briquettes made at various basicities were 65.93% for 63.81% Fe to 0.2 basicity at 1.2 basicity. It resulted in calcined briquettes varying in grades up to Fe, reflecting the level of flux addition.

  As can be seen in FIG. 21, the crush strength increased as the temperature increased and in addition the basicity increased from 0.2 to 0.8. This effect became more significant as the temperature increased over the range studied, and it was possible to achieve 300 kgf at 1295 ° C. for 0.6 basicity and 1280 ° C. for 0.8 basicity.

  The explanation for increased basicity levels resulting in increased strength relates to changes in binding mechanisms. At low basicity levels, particle bonding occurs as a result of iron oxide recrystallization and the formation of iron oxide-iron oxide bonds. At high basicity levels, melt formation occurs at low temperatures, promotes melting of iron oxide crystals, and slag bonding becomes more pronounced, giving higher strength at the same temperature.

Example 12
Reduction tests using all briquettes and standard reduction test method JIS8713 / IS07215 were conducted on HG briquettes calcined at 1300 ° C. for 10 minutes. The results of reducibility, swelling and crush strength after reduction (CSAR) are shown in FIG.

  The reducing index (RI) remained relatively stable over a range of basicity levels. The RI varied from 53.8% at a basicity of 0.20 to slightly over 62.2% at a basicity of 1.00.

The swelling index shows several responses, varying from 11% at the lowest basicity to 14.8% in the middle range and decreasing to zero at the basicity of 1.20. Crush strength after reduction (CSAR) showed a large response to changes in basicity level, ranging from 22 kgf at 0.20 basicity to 121 kgf at 1.20 basicity. This change in reduced strength reflects the result of the calcined crush strength and is also related to the change in the binder phase of the calcined briquette. Low basicity briquettes are bound mainly by iron oxide-iron oxide bonds, which bonds decrease during the reduction. As the basicity level increases, the slag bond becomes more significant. These bonds become more stable during the reduction, explaining that there is little or no swelling with greater reduction strength and basicity of 1.20. Slag bonds are also a more important form for bonds in briquettes made from GH and G, where higher SiO ₂ and Al ₂ O ₃ levels increase fluxing. Such briquettes are generally found to be stronger after reduction. This is because the reduction process does not cause destruction of the non-ferrous binder phase. Higher ores such as HC that require less flux addition rely mostly on oxide-oxide bonds and therefore have less strength after reduction has been effected.

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

FIG. 1 is a schematic illustration of a suitable apparatus having a 250 mm diameter roll and a pre-compacted feed system for carrying out the method of the present invention. FIG. 2 is a schematic illustration of a suitable apparatus having a 450 mm diameter roll and a gravity feed system for carrying out the method of the present invention. FIG. 3 is a schematic illustration of a suitable apparatus having a 650 mm diameter roll and a gravity feed system for carrying out the method of the present invention. FIG. 4 is a plot of overall briquette yield versus feed moisture for HG material on a 450 mm roll with 6 cc almond type and 4 cc elongated almond pockets. FIG. 5 is a plot showing the effect of feed moisture on the strength of dynamite for HG material on 450 mm rolls with various pocket dimensions. FIG. 6 is a plot showing the effect of water supply on the strength of biome ore for HG material using a 650 mm roll and a 7.5 cc “pillow”. FIG. 7 shows the effect of roll pressing force on briquette properties such as thickness, green strength, and green density on a 450 mm roll and 9 cc almond mold. FIG. 8 is a plot showing the effect of roll press on green strength for HG material using a 650 mm roll and 7.5 cc “pillow”. FIG. 9 is a plot showing the effect of roll press force on green strength for GH materials using 650 mm rolls and 7.5 cc “pillows”. FIG. 10 shows roll speed versus briquette characteristics such as thickness, green strength, and green density for 90 kg / cm ² roll pressure and 6 wt% feed moisture using a 450 mm roll and 9 cc almond mold. The influence of FIG. 11 is an operating window for a briquetting machine with a precompacter, 250 mm roll, 4 cc almond type and HG material. FIG. 12 shows the temperature profile for briquetting hardening in a 500 mm deep bed. FIG. 13 shows a temperature profile for briquetting hardening with high productivity producing briquettes and a typical temperature profile for pellet hardening with pellets produced with low productivity. FIG. 14 is a plot showing the effect of average bed temperature on briquettes made of GH material using a 650 mm roll and 7.5 cc “pillow” at the end of the lattice cycle in a batch lattice kiln. FIG. 15 is a plot showing the effect of average bed temperature on briquettes made of GH material using a 650 mm roll and 7.5 cc “pillow” at the end of the lattice kiln combustion cycle in a batch lattice kiln. FIG. 16 is a plot showing the effect of time at calcination temperature (1380 ° C.) for briquettes made of GH material using a 650 mm roll and 7.5 cc “pillow” during the test cycle of a batch grid kiln. is there. FIG. 17 shows the effect of time at calcination temperature (1380 ° C.) on briquettes made of GH material using a 650 mm roll and 7.5 cc “pillow” during a test cycle in a batch lattice kiln. It is a plot to show. FIG. 18 is a plot showing the effect of residence time on a 7.5 cc GH ore in the kiln during a test cycle in the kiln alone. FIG. 19 is a plot showing the effect of bed height and grid combustion profile on briquettes made of GH material using a 650 mm roll and 7.5 cc “pillow” during a test cycle in a batch grid kiln. It is. FIG. 20 is a plot showing the effect of bed height and grid combustion profile on briquettes made of GH material using a 650 mm roll and 7.5 cc “pillow” during a test cycle in a batch grid kiln. It is. FIG. 21 shows the effect of basicity and firing temperature on the firing crush strength of briquettes made of HG material, 250 mm roll and 4 cc almond type. FIG. 22 shows the bases for properties of reduced briquettes such as swelling, reduced reduction crush strength (CSAR) and reducibility index of briquettes made of HG material, 250 mm roll and 4 cc almond type. Shows the effect of gender.

Claims (11)

(A) mixing an ore containing hematite and / or goethite and a limestone flux to form an ore / flux mixture, wherein no binder is present in the ore / flux mixture;
(B) pressing the ore / flux mixture into green ore using a low roll pressure generated by a roll pressing force of 10-40 kN / cm for the ore / flux mixture, Generating by roll pressure that is sufficient to produce briquettes having a raw compressive strength of at least 5 kgf,
(C) adjusting the moisture content before or during the mixing step (a) such that the moisture content of the ore / flux mixture is 2-12% by weight of the total weight of the ore / flux mixture;
(D) Basicity exceeding 0.2 (where basicity is (mass% CaO + mass% MgO) / (mass% SiO ₂ + mass% Al ₂ O ₃ ) of the calcined briquette ) Curing a green ore to form a calcined briquette having a crush strength of at least 200 kgf
To produce iron ore briquettes suitable for use as feedstock for blast furnaces or other direct reduction furnaces containing The method according to claim 1, wherein the raw compressive strength is 5 to 30 kgf. The method according to claim 1 or 2, wherein the maximum size of the ore having a predetermined particle size distribution mixed with the flux in the step (a) is 4.0 mm or less. The method according to any one of claims 1 to 3, wherein the ore having a predetermined particle size distribution mixed with the flux in step (a) passes less than 50% by weight of the ore particles through a 45 µm screen. The ore / flux mixture produced in step (a) is selected such that the basicity of the calcined briquette is greater than 0.2, where the basicity is ( by mass% CaO + wt% MgO) / (mass% SiO ₂ + wt% _Al 2 _{O 3),} any one method according to claims 1 to 4. The step of adjusting the moisture content of the ore is to adjust the moisture content so that the ore / flux mixture moisture content is 2-5% by mass of the ore / flux mixture total weight for ores that are dense hematite ores. 6. The method according to any one of claims 1 to 5, comprising: The ore moisture content is adjusted so that the process of adjusting the ore moisture content is 4-8% by weight of the total weight of the ore / flux mixture for ores containing goethite with a moisture content of the ore / flux mixture of up to 50% by weight. 6. The method according to any one of claims 1 to 5, comprising adjusting the water content. The step of adjusting the water content of the ore is 6-12% by weight of the total weight of the ore / flux mixture for ores containing ore / flux mixture containing more than 50% by weight of goethite. 6. A method according to any one of claims 1 to 5, comprising adjusting the water content as follows. The method according to any one of claims 1 to 8, wherein the pressing step (c) produces briquette having a volume of 10 cc or less. The method according to any one of claims 1 to 9, wherein the curing step (c) comprises heating the briquette to the firing temperature in 40 minutes. The method according to any one of claims 1 to 10, wherein the firing temperature is at least 1200 ° C.

Images