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2026 DIGEST TECHNOLOGY CONFERENCES LOGISTICS ANALYTICS GREEN STEEL Mysteel and SGX Commodities will jointly host the 2026 Singapore Iron Ore and Steel Forum on June 16, 2026. The Instituto Argentino de Siderurgia invites you to the: 26th IAS Steel Conference Held by ABM (Brazilian Metallurgy, Materials and Mining Association), the event takes place from September 8 to 10, 2026, at the Pro Magno Convention Center, in São Paulo, Brazil.

Drying of pellets The initial heat engineering stage of obtaining a fired pellet is pellet drying. The basic concept of drying is the removal of internal and external moisture in pellets without destroying them. The moisture contained in raw pellets evaporates under the influence of the heat of gases passing through the layer. Water can be contained in the pellet structure in various forms: a. water contained in the pores and capillaries between the particles and grains of the material (capillary); b. chemically bound water in minerals accompanying iron oxides (in the form of hydrate); c. water included in the composition of binders that tend to form gels, such as bentonite (in the form of hydrate Ca(OH)2); d. in the form of crystalline components in existing and added salts; Thus, the moisture of the green pellet is formed from the water that is directly in the material and the water added during the pelletizing process. Depending on the form of the content in the pellet structure, water evaporates at different temperatures during drying - capillary at a temperature of 100 C, salts and hydrate components at higher temperatures. Since this is the first stage of the technological process, it is the main link between the green pellet, pellet drying and subsequent stages of the process. Drying of the green pellet is accompanied by three main stages: the first is the evaporation of surface moisture, the second is the evaporation of capillary moisture from the inside of the granules (after this stage, the granules are usually dry), the third is hygroscopic and chemically bound water (hydrated). The main factor in obtaining a strong green pellet is the presence of strong interparticle bonds at the grain boundary due to the presence of a binding liquid in the pellet volume. During the drying process, there is another task – complete removal of the binding liquid (capillary and molecular moisture) from the pellet structure. During pellet drying, two processes of moisture release occur. The first is the movement of moisture in the pores from the center to the surface, the second is from the surface to the surrounding phase of the heat carrier. Naturally, the limiting stage is the internal process of transformation and movement of moisture, which is simultaneously in a liquid, vaporous and vapor-liquid state. Phase transformations of moisture form resistance to moisture diffusion on the pellet surface. During intensive heating of the pellet, excess pressure is formed inside due to the internal resistance of the layers to the movement of steam formed as a result of moisture evaporation. Heating of pellets should be carried out in such a way that the amount of steam formed is in balance with its movement and removal to the pellet surface and further into the surrounding gas phase. The higher the temperature gradient, the greater the volume of steam phase formed. An increase in the amount of steam phase inside the pellet and, as a consequence, an increase in pressure leads to damage to the pellet structure (cracks and ruptures) when the "shock" temperature is reached (the temperature at which such an amount of steam phase is formed and such excess steam pressure is created at which the pellet structure begins to collapse). The critical pressure at which pellets collapse depends on the size of the concentrate, the density of the pellets, the type of flux, the binder additive, and the strength of the ore frame. The cause of destruction is the development of a volumetric stress state above the maximum permissible value, and is determined by the gradient of moisture content and temperature. Explosive shock, leading to a complete loss of pellet shape, is observed in the final period of drying, therefore the critical drying rate is determined by the pellet shock temperature. The limit of the critical drying rate is the absence of cracks and ruptures in the pellet structure. If the strength of green pellets mainly depends on the surface tension and capillary expansion of the wetting agent, then the addition of binders, such as bentonite, has a decisive effect on the strength of a dry pellet. Its use increases the strength of dry pellets to 5-15kg/pellet due to the formation of rigid skeletal bridges in the pellet structure, increasing the adhesive forces. For this reason, there are certain limitations on the use of organic binders in the charge, which cannot create a strengthening bridge structure during drying and heating of pellets, since they burn out at a temperature of 250-300 C. This is especially critical if bentonite is not added. Therefore, in practice, a charge with the addition of both bentonite and an organic binder is often used. It is important to preserve the strength of dry pellets by means of a binder additive until the onset of solid-phase sintering, when other strengthening forces begin to act due to the adhesion of ore grains of charge materials. The addition of bentonite to the charge binds and strengthens the structure of pellets and increases the resistance to destruction, raising the "shock" temperature of pellets. The higher the quality of bentonite (swelling index and water absorption), the higher the destruction temperature of the pellet. Sometimes, calcium hydroxide or slaked lime - Ca(OH)2 is used as a binder. However, its use is limited by the following conditions: a. slaked lime should not contain inclusions of unslaked lime, which undergo a slaking process with an increase in volume during the pelletizing process and at the initial stages of drying, which leads to cracking of green pellets and, as a consequence, a violation of the technological mode of heating and firing and a decrease in the strength characteristics of the fired pellets; b. the binding capacity of slaked lime is lower than the binding capacity of bentonite (the addition of 0.5-1.0% bentonite to the batch as a binding component is equivalent to adding 2-3% Ca(OH)2); c. the "shock temperature" of calcium hydroxide is significantly lower than that of bentonite and is about 300-400 C; Numerous industrial experiments conducted recently show the inefficiency of using this binder in the production of pellets, due to a decrease in the strength characteristics of the fired pellets and a loss in the productivity of the firing machine. The fired pellets should not contain free CaO, since after some time it hydrates with the moisture of the environment and weakens the structure of the pellets. This is especially true: a. during long-term storage in open warehouses; b. in the autumn-winter period or in the season of increased precipitation; c. for fluxed pellets, the higher the degree of fluxing and, accordingly, the basicity modulus, the more the pellets are subject to destruction; d. during numerous reloads during transportation to the consumer; Green pellets obtained from finely ground concentrates with a high specific surface area and low porosity (due to a reduction in pore size) dry more slowly and have a lower "shock" temperature. The intensity of pellet drying is higher, the greater the value of the total and, in particular, open porosity and the average pore size. The main criteria leading to a decrease in the intensity of the drying process are the size of the pellets, low pellet strength, the presence of cracks, an over-moistened structure in relation to the type of concentrate used and charge additives and shock destruction during heating. A decrease in the amount of vapor phase from the parity and, as a consequence, the pressure inside the pellet slows down the process of moisture movement to the surface and slows down the pellet drying process, which ultimately affects the productivity of this operation and, in general, all subsequent technological zones of the firing machine. In practice, three periods of pellet drying are defined. In the first period (warming up), the pellet moisture changes insignificantly, the surface temperature and evaporation intensity increase. At the end of the period, a constant surface temperature is established. Thermal equilibrium occurs between the amount of heat perceived by the material and the heat consumption for moisture evaporation. As moisture is removed, the iron ore pellet changes from a plastic to a solid elastic-brittle state. The porosity of the pellet increases and the density of the body decreases, nonequilibrium stresses arise within the structure of the material, and the intensity of heat and moisture transfer changes. The second period is characterized by drying at a constant rate. The pellet temperature is practically in equilibrium with the temperature of the heat carrier saturated with moisture vapor. This period is accompanied by pellet shrinkage, the unevenness of which can cause cracks. Shrinkage occurs until a strong layer of bound matrix macromolecules and pores is formed. Pellets shrinkage depends on the moisture content, concentrate type and drying intensity. The main shrinkage of pellets occurs at the first and second stages of drying to a temperature of, 200 C; the wetter the pellet, the greater its shrinkage. Therefore, the pellet must be dried at a safe heating rate, depending on its moisture content, size and the temperature of the heat carrier supplied to the drying layer. In the third period (with decreasing drying rate), the intensity of the process is determined by the rate of heat and moisture supply to the evaporation surface, moving into the pellet body. A decrease in the evaporation rate is accompanied by a decrease in heat consumption and an increase in the average pellet temperature. When equilibrium moisture is reached on the pellet surface, the drying rate becomes zero, i.e. the process of moisture removal stops and all supplied heat is spent on further physical heating and increasing the pellet temperature. For optimal drying, it is necessary to have a significant component of the temperature difference between the coolant supplied to the vacuum chambers of drying zone 1 and the furnace hood of drying zone 2 and drying zone 3. The higher it is, the shorter the period of time required for drying pellets. The temperature of the coolant supplied to drying zone 1 and drying zones 2 and 3 must be maintained at 270-320 C. The temperature of the coolant supplied to the drying zones is also related to the final temperature of the coolant after drying, which is then released into the atmosphere through a dust cleaning system (electrostatic precipitator, wet and dry scrubber, bag filter). The value of the temperature of the exhaust gases after drying is especially critical for bag filters and electrostatic filters. It must be maintained at 140-190 C, preventing the formation of a "dew point" and condensation of moisture inside the dust cleaning devices. When producing pellets from magnetite concentrates with a high content of sulfur compounds, it is desirable to bring the exhaust gas temperature closer to the maximum permissible values, or to use a wet scrubber with the addition of a lime milk solution to neutralize sulfur. When heating pellets during drying, moisture evaporates and steam diffuses in the pellet volume. If the amount of steam formed is greater than its amount removed during diffusion by the coolant, stress concentration and cracks in the pellets occur. Therefore, the time of water evaporation and steam diffusion are the limiting factors of the drying process. When drying pellets, it is necessary to maintain a balance of three components - the temperature of the coolant, the drying time and the flow rate of the coolant passing through the layer of raw pellets. In the presence of a significant number of fired pellets with cracks, the coolant temperature is usually reduced or the drying time is increased. When drying pellets, due to the evaporation of moisture, the weight of the raw pellets is lost. Drying time takes up to 30% of the total time of pellets on the induration machine, and up to 10-15% of the heat required for pellet heat treatment is spent on moisture removal. The complexity of the moisture removal process is associated with the heterogeneity of moisture across the pellet cross-section and the pore structure (uneven distribution of pores and their shape). The main goal of pellet drying is to minimize the effect of the overmoistening zone in the layer. For this purpose, a two-section drying zone with a coolant reverser is organized on induration machines. In the first drying zone, the coolant is fed from below into the layer of raw pellets through the bed layer, which avoids overmoistening of the lower layer of pellets and eliminates or minimizes swelling, increased plasticity and aerodynamic resistance of the layer and, as a result, the destruction of pellets in this part by subsequent overlying layers of pellets. Overmoistening of the layer always limits the increase in the height of the layer of raw pellets, If it is necessary to increase the height of the layer of raw pellets, pellets with increased strength properties, reduced humidity and an initially elevated temperature - preliminary drying outside the machine, or primary drying by suction at the beginning of the firing machine (zero chamber) must be fed to the firing machine. The option of increasing the height of the raw pellet bed with a corresponding decrease in the speed of the incinerator allows for better accumulation of the heat of the recirculation gases passing through this bed in the drying, heating and incinerator zones. This solution allows for a decrease in the consumption of process fuel and the filtration rate of the coolant in the incinerator zone. However, any increase in the bed height on the incinerator trolley will lead to an increase in power consumption due to an increase in the resistance of the higher bed and, as a consequence, an increase in the loads on the drives of the main process fans. Therefore, when considering the implementation of this technical solution, it is necessary to understand - the presence of a power reserve for the drives of the process fans and the opening value of the control servo drive dampers in the basic operating mode (the degree of opening should not exceed 75-80%, with a greater degree of opening of the dampers, this option cannot be implemented without replacing the fan drive with a more powerful one). The parameters of the heat carrier in drying zones 1 and 2 must be maintained based on the properties of the original pellets in order to achieve maximum drying intensity while maintaining the integral structure of the pellets. The drying process can be improved by reducing the initial moisture content of the raw pellets as much as the technology of producing raw pellets allows and by increasing the heat carrier consumption. Drying of pellets is the main limiting process for increasing the productivity of the indurating machine; until the moisture in the pellets is completely removed, a subsequent increase in the pellet temperature and transition to the next heating stage without loss of quality due to the presence of residual moisture inside the pellet body is impossible. Over the past few decades, attempts have been made to partially remove moisture before the firing unit (heating and partial drying of pellets on a conveyor belt, roller stacker) in order to further eliminate over-moistening of pellets in the layer and accelerate the pellet drying process over time to increase productivity and reduce heat costs for drying pellets. However, to date, the proposed solutions have not been implemented on an industrial scale due to the high costs of heating and implementing heat supply for this operation, the insignificant residence time of pellets and multi-layer conical stacking during transportation from unloading from the pelletizer to loading onto firing trolleys. The main directions for optimizing pellet drying on the firing machine were aimed at modernizing the drying zone and partially heating with the organization of a zero additional chamber at the beginning of the firing machine, a three-section drying zone instead of a two-section one, increasing the filtration rate of the heat carrier in the ascending flow in drying zone 1, and the use of three-level roller screens to optimize the layer-bylayer stacking of raw pellets on the firing trolley. The main factors influencing the pellet drying process are divided into two groups. The first group includes external factors (temperature, consumption and moisture content of the heat carrier), the second - internal factors (pellet diameter, its density, composition and structure): a. specific surface area of concentrate (cm2/gram) – increasing the specific surface area of concentrate leads to increasing the drying time; b. pellet porosity (%) – increasing porosity leads to decreasing the drying time; c. pellet size (mm) – increasing the average pellet diameter leads to increasing the pellet drying time; d. uniformity of particle size distribution – increasing the uniformity of the particle size distribution reduces the drying time due to improving the gas permeability of the layer; e. moisture content in pellets – increasing the moisture content in pellets leads to increasing the pellet drying time; f. pellet bed height – increasing the height of the pellet bed leads to increasing the pellet drying time; g. bentonite, limestone content (kg/ton) – an increase in the addition of these materials to the batch leads to a decrease in the pellet drying rate and an increase in its duration due to the compaction of the pellet structure and an increase in the amount of bound water; h. heat carrier filtration rate (m/s) – an increase in the heat carrier filtration rate reduces the drying time; i. heat carrier temperature (degrees) – an increase in the heat carrier temperature reduces the drying time due to improved heat exchange and an increase in the moisture capacity of the heat carrier; j. content of class 0-5 mm in the bottom bed (%) – an increase in this class leads to an increase in the drying time due to an increase in the gas-dynamic resistance of the layer; 0 0 0 0 0 0

General overview The technology of iron ore pellet production is one of the most complex in metallurgy, which is due to the following circumstances: a. the initial materials being processed have a complex physical, chemical, mineralogical and granulometric composition, and the wet pellet is a porous body, the main carrier of strength in which the molecular and capillary forces that form this strength are interconnected; b. in the process of heat treatment of the initial pellets, it is necessary to obtain an agglomerated product with high mechanical strength and specified metallurgical properties. To do this, it is necessary to create conditions for the most complete development of physicochemical, mass transfer and structural processes in an individual pellet; c. heat treatment of the initial iron ore pellets is accompanied by a noticeable number of physicochemical, mineral-forming and structural processes, often occurring in the same temperature ranges, mutually influencing and hindering each other; d. heat treatment of pellets is carried out in a polydisperse layer due to the cross-flow of a gaseous heat carrier, which creates noticeable temperature, mass transfer and time unevenness, both in the height of the layer and in the width of the processed layer; e. in a single unit (annealing conveyor machine), several technological operations (drying, heating, annealing, cooling) are carried out sequentially, each of which has its own characteristics, and the efficiency of the subsequent operation depends on the previous one; The input parameters of the initial pellets – quantity, humidity, granulometry composition, chemical composition and strength properties affect the output parameters of the fired pellets and determine the operation of the charge preparation, pelletizing sections and the firing machine itself as a whole. To coordinate the input parameters and physical and chemical processes occurring in the thermal unit, automated process control systems (APCS) are used, operating according to certain specified control algorithms. Modern control systems for the operation of a firing machine must contain the following technological subsystems: a. automatic control of the operation of smoke exhausters, throttles of gas-air ducts and burners regulating the flow rate of process gases, temperature conditions and flow rate of natural gas (excluding overheating of the main process equipment and refractory lining); b. automatic control of the productivity of the firing machine allowing for prompt assessment and coordination of the operation of the heating unit taking into account the thermal capabilities, quality characteristics of raw (humidity, grain size composition and mechanical characteristics) and roasted pellets (strength, grain size composition); c. automatic control of the volume of exhaust gases (process gas flow sensors) and the composition of emissions (devices for determining the concentration of harmful substances) This chapter analyzes the main factors influencing the production of pellets with specified physicochemical and metallurgical properties. Pellets are produced in two types: pellets for blast furnace processing and direct reduction pellets. The requirements for pellets used in blast furnace processing are less critical, since some of the harmful elements that reduce the quality of the product in subsequent stages leave the process with blast furnace slag. The requirements for direct reduction pellets have strict restrictions on the content of harmful impurities, since all oxides, including harmful impurities, enter the final product and are then used in steel production in electric arc furnaces. The main requirement for the chemical composition of pellets is a maximum iron content of at least 67.5% and a minimum content of SiO2, Al2O3, P, S. The main properties of finished pellets begin to form at the stage of obtaining raw pellets from the moment of their placement on the firing machine and until the moment of cooling of the already finished roasted pellets. Raw pellets produced on pelletizers and loaded on the firing machine must have the appropriate fractional composition, the content of class 9-16mm of at least 95%, have the specified strength properties - crushing strength of at least 1.0kg/pellet, dropping strength of at least 4.0kg/pellet. It is generally accepted that the strength characteristics of an ideal green pellet should ensure its passage from the pelletizer to loading onto the firing machine and transportation in the firing machine until hardening. At the same time, the pellet should not be subject to destruction during the physical and chemical processes inside it. However, practice has shown that this is often not the case and in fact, in the total mass of fired pellets, there is a certain part of the pellets with strength indicators of less than 150kg/pellet, containing cracks, chips or even pieces of material that disintegrate into several parts, as well as an under-fired structure along the cross-section of the granules. There are several reasons - under-fired lower part of the pellet layer, bed pellets, green pellets, which from the very beginning of the firing process did not meet the requirements of strength characteristics and were destroyed during the thermal exposure. In order to understand the reason for the decrease in the quality characteristics of roasted pellets, it is necessary to analyze all possible factors influencing this process. It is necessary to evaluate the obtained quality characteristics of roasted pellets, starting from the composition of the charge materials to the operation of the firing machine itself. It is almost impossible to evaluate the influence of the mineralogical and phase composition of the concentrate and other components of the charge on the quality characteristics of finished pellets, especially in the operational control of the technological process due to the lack of the necessary laboratory equipment and the duration of the studies. The influence of various physical factors on the quality characteristics of pellets has been studied most - compressive strength, abrasion strength, impact strength, content of small classes. This assessment is constantly carried out at all factories producing pellets and almost all metallurgical enterprises consuming pellets, and their values serve as a guide for obtaining a pellet with specified properties. If the necessary equipment is available, operational control of the metallurgical indicator of pellet quality - low-temperature reduction strength LTD is also carried out. All other indicators related to the metallurgical properties of pellets are performed periodically in a specialized laboratory. Figure shows a generalized structural diagram of pellet production. The main operation following the receipt of raw pellets and their placement on the firing machine is heat treatment, as a result of which the pellets undergo various heat engineering operations: drying, heating, firing, recovery and cooling. As a result of passing these stages, the pellets obtain the necessary physical and metallurgical properties that meet the requirements of various consumers of prepared iron ore raw materials. All operations from drying to cooling are interconnected, and violation of the process parameters at one of the stages makes it practically impossible to correct deviations at subsequent stages without loss of productivity or quality characteristics of the pellets. The physicochemical properties and metallurgical characteristics of the roasted pellets depend on the mineralogical composition of the roasted pellets, which is formed as a result of reactions in the pellet volume between the ore particles, as well as between the ore particles and the gangue or flux particles during solidification. Thus, the size, chemical composition and mineralogical composition as well as the fluxing and firing conditions of the green pellets determine the mineralogical composition of the roasted pellets. Due to the differences in mineralogy, different types of pelletizing raw materials require very different fluxing and firing conditions, such as preheating temperature, preheating duration, oxygen potential, firing temperature and firing duration. Oxygen potential is especially important for the oxidation reactions of green pellets made from magnetite concentrates. Complete oxidation of magnetite minerals determines not only the quality of the roasted pellets, but also the energy intensity of the firing process. Since pellets are produced from different types of ore under different conditions, they will have different mineralogical compositions to achieve the required quality. A number of measures have been developed to optimize the effect of mineralogical composition on the properties of the produced pellets, such as blending different types of concentrates, using boron-containing additives and MgO-containing components, optimizing basicity, and pre-treating the concentrate with high-pressure rollers HPGR. Figure1

Iron ore concentrate Magnetite concentrates are the main iron ore part of the charge for pellet production. For a certain type of ore and a given quality (Fe and SiO2 content) of the enriched material, an appropriate concentrate production scheme is selected. The enrichment of ore coming from a quarry includes the following stages of the technological process: crushing, grinding, classification, separation and filtration. To obtain a concentrate of a given quality, the ore fed to enrichment must have certain quality indicators for enrichment and magnetic iron content. The ore enrichment index affects the iron content in the final concentrate, the higher its value, the higher the iron content in the concentrate. The magnetic iron index in the ore affects the amount of concentrate obtained during enrichment, the higher it is, the greater the volume of concentrate obtained during enrichment. When feeding the ore mass for enrichment, the optimal ratio of different types of ores is calculated to obtain the planned quality of concentrate and its quantity for the selected enrichment scheme. In order to obtain a higher iron content in the concentrate, ore processing schemes with separate enrichment of rich and poor ores are practiced, which leads to the production of two types of concentrate with an iron content (Fetotal≈67.5-68.5%) and an iron content (Fetotal≈64.5-65.5%). There are also options when, in the presence of free processing capacities, ore enrichment is carried out instead of a 3-stage enrichment scheme according to a 4-stage enrichment scheme, which allows involving in production an additional amount of ores with low enrichment without losing the iron content in the concentrate or enriching ore with high enrichment and obtaining a concentrate with an iron content (Fetotal≈69.5-70.5%). There are also classical enrichment schemes using flotation finishing or fine grinding screens to increase the iron content in the concentrate to (Fetotal≈69.5-70.5%). Below are the main technological schemes for enriching ore mass to obtain concentrate: a. WMS - wet magnetic separation; b. WMS - wet magnetic separation with an additional grinding stage; c. WMS - wet magnetic separation with separate ore enrichment; d. WMS + MFFC - wet magnetic separation and magnetic flotation finishing of concentrate; e. WMS + fine screening - wet magnetic separation and fine screening; In the production of iron ore concentrate for pelletizing, the priority quality characteristics are the content of the mass fraction of iron, silicon oxide, moisture content, specific surface area and grain size distribution. Also, concentrates should contain as little sulfur (S≈0.01-0.05%) and phosphorus (P≈0.003-0.008%) as possible. All these derivatives are directly or indirectly related to each other in relation to the existing enrichment technology and the need to supply concentrate of a given quality for pellet production. Concentrates obtained using different enrichment methods differ from each other in granulometry composition and specific surface area. These two parameters are related - the finer the concentrate is ground, the greater the specific surface area of the concentrate, which directly affects the moisture content in the material. The specific surface area is one of the main indicators for monitoring the fineness of the material during granulation. It is determined by measurement methods based on determining the air permeability of the porous layer of particles, developed by Blaine and Fisher. However, such methods do not take into account the shape factor of mineral particles, as well as roughness and porosity, which leads to some inaccuracies and measurement errors in different laboratories. The smaller the average diameter of the mineral particles, the higher the specific surface area, regardless of the type of material. With the same average particle diameter, the specific surface area value is higher for materials with a lower specific gravity. The optimum specific surface area for pelletizing depends on the concentrate type and the quality characteristics of the fired pellets. It varies between 1600-2200cm2/gram at different plants. In order to create a homogeneous batch, the additives used for pelletizing should be ground to the same average particle diameter as the iron ore raw material used. The specific surface area of the prepared limestone/bentonite additives is within 3800-5200cm2/gram, anthracite 5200-7000cm2/gram. An important characteristic of the concentrate is also the shape and surface of the grains of the material, which is determined by the mineralogical and chemical composition and the selected technological enrichment scheme. Concentrate grains may have different shapes – spherical, polyhedral, lamellar, dendritic. The strength of green pellets depends on the total contact area of concentrate grains. The higher the contact area, the greater the strength of green pellets. The polyhedral grain shape is characterized by the largest contact area, the smallest by the branched dendritic grain shape. Particles with a rough and developed surface have a higher degree of wetting and are better lumped. Magnetite concentrate particles in most cases have acute-angled grains. When obtaining the final concentrate using flotation technology, the hydrophilicity of the concentrate decreases due to the formation of reagent films, which somewhat worsens the pelletizing process and can lead to the inclusion of an additional stage in the process flow chart - concentrate washing. In some enrichment schemes, when producing concentrates with a low specific surface area and dendritic grain shape, roller presses (Köppern, KHD, Ecoplex, Polycom, Krupp-Polysius) are installed before feeding the concentrate for pelletizing. The schemes and equipment for filtration of concentrate are determined by the need to obtain a given moisture content of concentrate for the process of pelletizing raw pellets. The classic filtration scheme using vacuum filters allows working with a specific surface area of concentrate of 1500-2200cm2/gram and a granulometry composition of 95-98% of class 0.056mm and obtaining concentrate with a moisture content of 9.5% to 10.0%. Such schemes are used in a 3-stage grinding scheme and were practiced at all old enrichment plants. If more stringent requirements are required for the upper limit of moisture content in the concentrate, ceramic vacuum filters, vacuum filters with steam and bar filters are used, which provide concentrate moisture from 8.6 to 9.6% with a specific surface area of 1700-2400cm2/gram and a particle size distribution of 96-98.5% of class 0.056mm. Flotation enrichment schemes, the concentrates of which are characterized by a high specific surface area of 2400-2800cm2/gram and a grain size distribution of 99-99.8% of class 0.056mm, require the use of press filters for dehydration of the concentrate to a moisture content of 8.8-9.5%. At the beneficiation plants built in the 50-80s of the last century, in order to increase the iron content in the concentrate by 1.5-3%, the ore mass is re-crushed by reducing the productivity of the sections or by working according to a 4-stage grinding scheme, which leads to an increase in the specific surface area of the concentrate to 2400-2600cm2/gram and a decrease in the size of the material to 98-99.5% of the 0.056mm class. When filtering such concentrate on conventional vacuum filters, the moisture content at the outlet is from 11.0 to 12.5%, which does not meet the requirements of the pellet production process. Due to the lack of the necessary filtering equipment and in order to reduce the moisture content in the concentrate, various dehydrating reagents are used, which are added directly to the pulp separator before feeding the concentrate in the liquid phase for filtration. The use of these reagents allows obtaining a moisture content in the concentrate of about 9.3-9.8% and is justified for further shipment of the concentrate to the buyer. However, the use of a dehydrating reagent reduces the hydrophilic properties of the concentrate due to local binding of water in the volume of the concentrate sample and, as a result, reduces the lumpiness of the concentrate and worsens the process of pelletizing green pellets. For each type of concentrate obtained, based on the specific surface area of the concentrate, granulometry composition, mineralogy, added batch materials and pelletizing requirements, the appropriate moisture content should be selected to obtain optimal characteristics of green pellets during pelletizing. In most cases, magnetite concentrate used for pellet production has a basicity modulus of 0.04 to 0.1units. Some companies produce concentrates with a basicity modulus of 0.5-0.8units, mainly hematite concentrates. In general, the basicity modulus of a concentrate is a derivative of the content of the main calcium oxides CaO and magnesium oxides MgO in the ore used to obtain the concentrate.

Lime Lime is a derivative of the thermal decomposition of limestone and is calcium oxide CaO or quicklime. It has a dual purpose in pellet production – it introduces CaO into the batch and simultaneously acts as a binder component of the batch. When in contact with water, quicklime is converted into slaked lime Ca(OH)2. Lime slaking is accompanied by significant heat release. The use of slaked lime as a binder component of the batch is most attractive in the production of fluxed pellets, which require the addition of several percent of CaO and/or MgO to the pellets. In traditional fluxed pellets, flux is added in the form of limestone (CaCO3) or dolomite CaMg(CO3)2, neither of which has noticeable binding properties. However, if any of these flux components are calcined to CaO or (CaO+MgO) and then hydrated and added to the granules, they can be very effective binders. Only slaked lime should be used for pelletizing, since adding quicklime to the batch causes it to interact with the concentrate moisture and the moisture supplied to the process to form raw pellets. The lime slaking process starts directly in the pelletizer, which completely destabilizes the process of obtaining raw pellets of the required quality and grain size. Pelletizers work with a constant batch, the presence of many small fractions and huge rolled balls with a diameter of 50mm to 200mm, it is not possible to achieve a constant grain size in the 8-16mm class. With slaked lime, the situation is somewhat different: during slaking, it disintegrates into a very fine powder and is evenly distributed throughout the mixture. Such distribution of very fine particles over the surface of the concentrate grains during moistening helps to improve the cohesive ability of the particles and the formation of raw pellets. The experiments confirm that slaked lime allows partial replacement of bentonite in the pelletizing batch. However, compared to the use of bentonite, the use of slaked lime in pelletizing leads to a decrease in the homogeneity of the granulometry composition and the strength characteristics of raw and, as a consequence, fired pellets. The main reason for the decrease in strength is the formation of cracks in raw and dry pellets due to the loss of plasticity. This is especially pronounced with a significant addition of slaked lime. Slaked lime used for pelletizing should be carefully averaged in the volume of the batch, the degree of lime hydration should be 100% or close to this value in order to exclude the slaking process directly in the pelletizer. Addition of calcium hydroxide reduces the effectiveness of bentonite as a binding additive due to the replacement of the more effective sodium ion (Na) with the calcium ion (Ca ) in the bentonite structure, turning it into a more calcium and less effective component of the batch, which leads to deterioration of the pellet properties. In addition, complete or partial replacement of bentonite with slaked lime additionally reduces the shock temperature when heating pellets in the firing machine. This forces the temperature regimes in the furnace of the firing machine to be rebuilt to more gentle ones, which leads to a decrease in the plant productivity by 8-10%. If we consider the binding capacity of bentonite and slaked lime, then in order for raw pellets using slaked lime as a binder to have similar strength when falling and compressing, as well as resistance to thermal shock, the dosage of slaked lime should significantly exceed the consumption of bentonite (for example, an addition of 0.5% of bentonite to the batch should correspond to a 2.0% addition of slaked lime). For these reasons, pelletizing plants do not have lime production units, its slaking and introduction into the batch, and imported lime significantly increases the costs of pelletizing. Moreover, the increased requirements for the quality characteristics of pellets by consumers make its use increasingly problematic and ineffective. + +2

Properties of pellets by degree of importance If we consider the pellet properties in order of increasing importance, the hierarchy is as follows (figure). Metallurgical properties such as reducibility are important, but the chemical composition of the pellets and the physical characteristics (size, strength) are still of primary importance, since a highly reducible pellet with a low iron content, low strength and inappropriate size in a blast furnace and direct reduction plants will worsen the gas permeability of the bed and the efficiency of contact of the reducing gas with the charge material and will negate all the advantages inherent in its high reducibility. The quality of the pellet should maximally correspond to the requirements of subsequent processing stages (blast furnace or metallization furnaces). The following tests are used to assess the quality of pellets for a blast furnace (figure and ). Taking into account the specifics of metallization furnaces, the following tests are additionally carried out to assess the quality of pellets: ISO 11256 - method for determining the conglomeration index, ISO 11257 - determination of the degree of destruction and metallization of raw materials for processing during direct reduction, ISO 11258 - determination of the degree of reduction and metallization of raw materials for processing during direct reduction in gas reduction processes. Almost all tests require special equipment and can be performed only in specialized laboratories. Pellet factories conduct all types of physical tests of pellets and some factories have installations for testing LTD and swelling index. In addition to these definitions of pellet quality, an indicator of pellet yield was introduced. A certain pellet compressive strength limit was set for each pellet type and consumer requirement, below which pellets were considered substandard. By testing each pellet type and comparing yield, compressive strength, and LTD statistics, it is possible to determine with a high degree of probability the dependence of the LTD indicator on yield and pellet strength. For clarity, diagrams show the test results, where to obtain LTD +6.3mm of at least 70%, the pellet strength should be at least 275kg/pellet and the yield should be at least 67%. To work with this tool, it is necessary to develop statistics for each specific type of pellets with subsequent evaluation of the results. annex3

Colemanite To increase the mechanical strength of pellets during firing, boroncontaining materials are used. In particular, a boron - containing additive, calcined colemanite, has found its application. Colemanite has a chemical formula (Ca2B6O11 5H2O) with a melting point of 986 C and forms borosilicate slag bonds at relatively low temperatures (about 1000 C) in the presence of silica iron ore concentrate. Since the strength of pellets largely depends on the presence of a slag bond during pellet hardening, the mechanism of influence on the improvement of the quality characteristics of pellets is the shift of the onset of liquidphase hardening to the region of lower temperatures. As noted earlier, bentonite is the most common binder used in iron ore pelletizing. However, it is considered an impurity due to its high content of SiO2 and Al2O3 oxides. In recent years, numerous alternative organic binders that do not contain impurities have been tested in order to completely replace bentonite or reduce its dosage in the batch. Organic binders produce green and dry granules of good quality. However, they do not provide sufficient mechanical strength to preheated and calcined pellets due to insufficient slag binding. Addition of boron compounds to the batch is proposed as a potential solution to this problem in order to overcome the insufficient strength of pellets made with organic binders or to increase the strength when using bentonite and calcined colemanite together. The addition of calcined colemanite increases the strength of green pellets. The improvement in the strength properties of green pellets with calcined colemanite is due to the clayey nature of calcined colemanite and to the fact that during the pelletizing of the batch, colemanite is hydrated by the moisture of the batch, turning into the sassolite phase (boric acid B2O3 H2O). Fragments of B2O3 crystals turn into intergrowths of needleshaped sassolite crystals penetrating the body of the green granulated pellet. During the drying of pellets, sassolite at a temperature of 180-190 C again loses water, turning into boron oxide. The first borate melt appears at a temperature of, 450 C as a result of melting of boron oxide. The appearance of local volumes of borate solution leads to the development of the liquid-phase strengthening process. In the temperature range of 600-1000 C, the high-borate melt promotes sintering and recrystallization of ore grains in unfluxed pellets and ore and ferrite grains in fluxed pellets. This is especially important for unfluxed pellets containing refractory minerals of host rocks in the composition of the batch, which cannot form liquid-phase melts. At a temperature of 1000-1200 C, along with the primary melt, a silicate melt is formed due to the melting of silicon-containing phases of the iron ore concentrate. Both melts combine, absorbing the flux of the batch, the fine fraction of the concentrate and solid-phase ferrites. The more boron in the melt, the more intense the strengthening and recrystallization of the ore phase, which leads to an increase in the cold strength of the pellets compared to borate-free pellets. The main reason for the increase in the compressive strength of roasted pellets associated with calcined colemanite is the physical melting of calcined colemanite at the point of contact of iron oxide grains during heat treatment. The increase in the strength of roasted pellets is 13-30kg/pellet with a dosage of calcined calcium colemanite in the charge from 3kg/ton to 5kg/ton of concentrate, the yield of suitable pellets also increases and the number of pellets with a strength of less than 210kg/pellet decreases. The use of colemanite in such dosages increases the swelling index of pellets from 12% to 17%, but it is within acceptable values for blast furnace operation - no more than 20%. The use of boron oxide increases the pellet strength during reduction due to an increase in the amount of silicate binder, which reduces the formation of cracks in the pellet body, but at the same time reduces the pellet reducibility due to reduced access of the reducing gas to the ore grains. The optimal content of boron oxide is within 0.3-0.5%, which allows increasing the pellet strength during reduction while maintaining sufficient pellet reducibility. Colemanite calcined at a temperature of 500-550 C after removing chemically bound water is suitable for pelletizing. The addition of colemanite during pelletizing is practically not used due to its cost and the need for an additional calcination operation; in any case, it is necessary to calculate the economic feasibility of its use, taking into account the increase in the cost of pellets and the increase in the strength properties of pellets. The purposes of using binders and various additives are: a. obtaining high-quality raw pellets (compressive strength, drop strength, particle size distribution, shape, type); b. improving the strength of dry pellets at subsequent stages of heat treatment; c. improving the physical and chemical properties of fired pellets; d. binders should be relatively inexpensive and not have a negative impact on the chemical composition of pellets and the operation of the firing machine; All effects on the initial charge materials and raw pellets should be aimed at optimizing bentonite consumption and improving the physicochemical properties of pellets. 0 0 0 0 0 0 0 0 0 0 . .

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Features of the firing machine operation The performance of the firing machine plays one of the key roles in the pellet production volume and the degree of its influence on the quality characteristics of the pellets. The following main factors influence the performance: a. technical - the condition of the main process equipment that does not allow the process to be carried out with the specified productivity while maintaining the quality characteristics of the pellets (for example, the lack of sufficient compaction of the induration machine, the technical condition of the grate field and induration trolleys), downtime - they can be caused both by the condition of the equipment and by various other reasons (for example, power outages, lack of natural gas, supply of process water for cooling the furnace elements, or an emergency failure of the main equipment) associated with the shutdown of the induration machine equipment for a short or long period and returning to the operating mode after these stops; b. technological - the type of pellet produced (blast furnace or direct reduction pellet, non-fluxed or highly fluxed), the type of iron ore concentrate (magnetite, hematite, limonite), inadequate quality characteristics of the initial raw materials (high moisture content in the concentrate), raw pellets (high moisture content in the concentrate, low strength properties and inadequate particle size distribution by size classes); c. human factor - violation of the technological process by the plant personnel, failure to comply with the requirements of regulatory documentation (instructions, process maps, standard operating procedures) resulting in the shutdown of the firing machine or a decrease in productivity, insufficient training of personnel in the technological process; Since the firing machine is a thermal unit, any short-term shutdown for scheduled maintenance or emergency downtime is associated with a decrease in the temperature in the furnace to 750-800 C with reduced gas consumption and the operation of some burners, usually 4-6 pieces, at a reduced consumption of natural gas "low flame". It is also common practice to turn off all gas burner devices with a decrease in the temperature in the furnace to certain values, which are associated with the duration of the shutdown period. In this case, when subsequently supplying natural gas to the firing machine and igniting the burners, it is imperative to take a sample in the furnace for the absence of an explosive mixture. During longer cold shutdowns of the thermal unit, the temperature in the furnace decreases to the ambient temperature with gas consumption turned off and burners not working. The subsequent start-up and return to the previous value in terms of productivity is associated with the time intervals required for the temperatures in the furnace zones to reach the initially set values and the heating of the furnace (an example of returning to the mode after stopping for scheduled maintenance). The firing machine's entry into the mode with reduced productivity and the loss of part of the production volumes should be taken into account when planning production volumes. There can be two approaches: the first is to take into account the time of entering the mode during repair work, the second is to take into account part of the loss of production volumes after starting the firing machine into operation after repair. In fact, both the first and second options are used when planning production volumes. The effective productivity of the firing machine (or, more correctly, the technological line, including the firing machine and other related equipment directly involved in the technological process of pellet production) and, as a consequence, the production volumes are determined based on the total calendar operating time minus the downtime, regardless of their cause. On this basis, the equipment utilization rate EUR is calculated. EUR – equipment utilization rate, Ta – actual time worked by equipment, hour Тc – calendar operating time of equipment, hour There are some differences in calculating the EUR. At some enterprises, when calculating the actual EUR, only the readiness of the firing machine to produce pellets is taken into account, excluding all stops of other associated equipment, which naturally increases the values of this indicator in the reporting data. The productivity of the firing machine is defined as the ratio of the number of pellets produced (tons) for a certain amount of time (hour, day, month, year), for example - t/hour. Specific productivity is defined as the ratio of the number of pellets produced for a certain time to the useful sintering area of the firing machine, for example - t/m2hour or more often in calculations - t/m2day. The higher it is, the better the thermal unit works. The calculation formulas for determining the productivity of the firing machine are as follows: Qr - actual productivity of raw pellets, t/hour h - average height of the layer of raw pellets, m b - width of the layer of raw pellets, m v - speed of firing trolleys, m/min - bulk density of pellets, t/m3 Qf - actual productivity of fired pellets, t/hour Cf - the yield coefficient of roasted pellets (calculated on the basis of the material balance, example annex 2) is 0.9-0.93units Qs - actual productivity of suitable pellets, t/hour Cs - the coefficient of yield of suitable pellets (calculated based on the removal of dust and screenings of class 6.3mm after screening) is 0.98-0.95units Then the general formula for suitable pellets, The yield of suitable pellets increases with an increase in the iron content in the charge, a decrease in the basicity modulus, a decrease in the moisture content in the raw pellets, a decrease in the screening of fines during the screening of the roasted pellets and the removal of dust into the environment. Below are the actual approximate specific productivity of the firing machine for suitable pellets depending on the type of concentrates used: magnetite: - 19-32 t/m2day; hematite: - 16-26 t/m2day; limonite: - 12-18 t/m2day; An example of the material balance of non-fluxed blast furnace pellets is shown in figure 2. According to their hardening ability, all pellets can be divided into materials with heavy and lightened firing conditions. Lightened conditions are those in which the firing temperature does not exceed 1250-1280 C. This occurs when firing pellets from a charge with an increased content of slag-forming agents. To obtain high mechanical strength of pellets, it is sufficient to have a short firing zone in which the required temperatures are maintained. For severe firing conditions, temperatures in the range of 1300-1350 C are typical, and at the border with the bottom bed, it is necessary to maintain temperatures of about 1220-1250 C with a time interval of 1-4 minutes. There is no layer separation by temperature in the grate-tube furnace-ring cooler (GK) type of firing units; pellets move inside the rotary kiln from loading to unloading, being simultaneously roasted at temperatures of 1250-1280 C. If we compare the characteristics of the pellets obtained using the two technologies, then the pellets roasted using the GK technology, all other things being equal, have higher values for compressive strength, impact strength, and abrasion resistance. This is due to more uniform firing by the pellet volume, minimal presence of underroasted pellets and pellets with a two-zone hematite-magnetite structure, and the absence of re-firing of bed pellets. The main advantages of the GK technology are the flexibility of the technological process, the quality of the manufactured products, and the use of alternative types of fuel. The main disadvantages of this technology are the following: limitations on granulation of pure hematite raw materials, lower energy efficiency, increased costs for maintenance and refractories, limitations on the production of pellets with a basicity of more than 0.3units. If the production of pellets with a basicity modulus of up to 1.2units has been mastered on conveyor machines (SG), then the production of fluxed pellets using the GK technology is associated with the formation of accretions in the tube furnace, which leads to damage to the refractory lining, local overheating of the tube furnace casing, and long shutdowns. The schemes of pellet production using the GK and SG technologies are shown in figures. A comparison of the differences in the technological process of the grate-tube furnace-ring cooler and straight grate-type firing units is reflected in table. 0 Figure2 0 0 0 0