ISIJ International
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ONLINE ISSN: 1347-5460
PRINT ISSN: 0915-1559

ISIJ International Vol. 49 (2009), No. 5

  • Analysis of Raw Material Flow with Axial Direction in Continuous Drum Mixer for Sintering Process

    pp. 609-617

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    DOI:10.2355/isijinternational.49.609

    The granulation process is known to be important to achieve high productivity in sinter process because the granulation of sinter mixture is connected with permeability of sinter bed. Past studies on the granulation in the drum mixer for sintering process mostly used the batch type drum mixer, hence their studies were on the raw material behavior for cross-section of the drum mixer. In contrast there were few reported on the raw material behavior for a drum axial and a residence time in a continuous type drum mixer. The raw material flows and the residence times have been investigated experimentally by using a continuous type drum mixer, and results were compared to those by the theory predicts suggested by Saeman. In addition, the effects of the ring dam fitted to the discharge end on the residence time and granulation improvement were investigated. As a result, with the drum set at the low angle, the observed residence times were shorter than the theory predicts. This is due to the level of the raw material tapering off as it reaches the discharge end. Thus, by newly considering angle ψ between the raw material surface and the drum mixer, the residence time was accurately estimated. Also, with the drum set the low angle, the ring dam fitted to the discharge end prevented any tapering, resulting in the longer residence time and greatly improved granulation.
  • Effect of Moisture Absorption Behavior on Optimal Granulation Moisture Value of Sinter Raw Material

    pp. 618-624

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    DOI:10.2355/isijinternational.49.618

    In order to optimize the added moisture content to match the raw material mix conditions, the necessary moisture content for the iron ore in the raw materials and so on must be determined in advance. Accordingly, the authors conducted a study of the necessary moisture content for each brand of iron ore, in order to stabilize the granularity of the sinter ore raw material and the permeability of the packed bed and maintain these values at a high level regardless of the conditions of sinter mix.
    When the particle size distribution was constant, the added moisture volume such that the permeability of the packed bed (made up of quasi-particles) for each type of ore after granulation was the maximum value (=optimal moisture value) tended to be lower than the saturation moisture content for all types of ore. Moreover, when the quantity of coarse-grained particles in the ore increased, the optimal moisture value tended to shift to the low moisture side. The application of the optimal moisture value enables the added moisture content to be reduced as compared to the conventional method, without adversely affecting granularity or the permeability of the packed bed.
  • Effect of Granulation Condition and Property of Raw Material on Strength of Granulated Particle by Tumbling Granulation

    pp. 625-630

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    DOI:10.2355/isijinternational.49.625

    In order to clarify the factors on strength of granules for iron ore sinter, especially made of limonite iron ore, the effects of porosity, moisture and revolution speed of pelletizer on the strength of granules were examined with using reagent hematite. Moreover, using three kinds of commercial iron ores, the relationship between granule size and strength was examined. The strength measurement was undertaken before and after drying with a compression taster. The results obtained are follows:
    (1) In case of reagent hematite sample, the strength after drying became very low compared with that before drying. The compressive strength of sample just after granulation is determined by the adhesion force between hematite particles by liquid bridge of added water, but the strength after drying is maintained by the adhesion force by intertwined particles.
    (2) In case of commercial iron ores, the compressive strength after drying was very high compared with that in wet condition.
    (3) The cause for the different effect of drying on compressive strength between the commercial iron ore and reagent hematite seems to be the difference of gangue minerals that exist only in the iron ore and/or that of surface properties because the particle size distribution of reagent hematite and iron ores used is the same.
  • Study for Evaluation and Optimization of Iron Ore Granulation with Consideration of Dynamics and Particle Conditions

    pp. 631-636

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    DOI:10.2355/isijinternational.49.631

    Fundamental study was carried out to evaluate and optimize fine powder of iron ore granulation. In this study, the conditions of particle preparation and mechanism of granulation were discussed. As a conclusion of this study, for both fine and coarse iron ore sample, the optimum conditions for pellet growth, were defined by saturation degree value of approximately 0.9–1.0. Furthermore, it was found that wet pellet agglomerates were formed as a result of compaction and tumbling action under the condition of saturation degree S from S≧1 in particle preparation stage to S=0.9 (0.85) at final granulation stage, and that Stokes deformation number at that time indicates to determine optimal granulation condition. When introducing new granulation method to commercial agglomeration process for fine powder of iron ore, saturation degree and Stokes deformation number show a suitable operating point of new system to attain required quality of granulation.
  • Quantitative Effect of Micro-particles in Iron Ore on the Optimum Granulation Moisture

    pp. 637-644

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    DOI:10.2355/isijinternational.49.637

    Anionic polymer dispersant (APD) has been applied to the granulation process for enhancing sintering productivity. It is reported that APD accelerates micro-particle dispersion. In this study, the amount of micro-particles whose diameter was less than 10 μm has been surveyed by means of Andreasen pipette method. And in order to understand granulation mechanism focused on micro-particle, effect of micro-particles on granulation has been analyzed by granulation test with single ore. As results, total amount of micro-particle was in the range from 2 to 10% in all ores. The increase in amount of micro-particles by APD differed according to ores. These differences mostly could be explained with mineral characteristics of micro-particle. From the granulation test, the optimum moisture in wet state did not correspond with one in dry state. In wet state, micro-particles dispersed by APD increased effective volume of water, resulting in lowing water requirement for optimum granulation. Therefore, APD addition is seemed to enable optimum moisture of granulation to move wet optimum moisture closer to dry optimum moisture. In dry state, dispersing micro-particles may result in concentrating in contact point of iron ores and reinforces the strength of granules. This understanding based on this result can make comprehensive interpretation for granulation.
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  • Analysis of Granules Behavior in Continuous Drum Mixer by DEM

    pp. 645-649

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    DOI:10.2355/isijinternational.49.645

    A numerical simulation model was developed to analyze the behavior of iron ore granules in a continuous drum mixer by Discrete Element Method (DEM). The effects of the gradient angle of the drum mixer on the behavior of granules were investigated using the simulation. The granulation experiment of iron ore fine was also performed to observe the occupation ratio and retention time. The occupation ratio and retention time obtained by both the simulation and experiment decrease with an increase in the gradient angle. The effect of the length of the drum mixer on the behavior of granules was investigated using the DEM simulation. The retention time increases with an increase in the length of the drum mixer. If the occupation distributions in the direction of the rotational axis is based on the exit of the drum mixer, it will be the same regardless of the length of the drum mixer. This simulation model proposed will be useful to understand granules behavior and to design of granulators.
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  • Effect of High-phosphorous Iron Ore Distribution in Quasi-particle on Melt Fluidity and Sinter Bed Permeability during Sintering

    pp. 650-658

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    DOI:10.2355/isijinternational.49.650

    The effect of high P Brockman ore on the melt fluidity was investigated to make clear the mechanism for the deterioration of permeability of sinter bed during sintering.
    Blending high-P ore, characterized by the high porosity and fine size distribution, decreased melt fluidity by the absorption of melt into porous high P Brockman ore. As a result, the pressure drop of sinter bed increased during sintering by the suppression of pore growth, and the sinter productivity decreased.
    To improve the sinter productivity using high-P Brockman ore, JFE Steel has developed an advanced granulation process characterized by segregating high-P Brockman ore at the center of quasi-particle, which was coated by coke breeze and limestone. It is important to select the suitable coating thickness of dense hematite ore around porous iron ore for preventing from the melt absorption into iron ore. This process controls the excess melting reaction between iron ore and limestone, owing to the segregation of high-P ore within the quasi-particles.
    The commercial plant trials showed that the desirable melt fluidity, resulting from the segregation of high-P ore in a quasi-particle, enhanced the permeability of sinter bed at Fukuyama No. 4 Sinter Plant of JFE Steel. The application of new granulation process remarkably improved both the productivity and reducibility of sinter products, in spite of the recent inferior ore conditions.
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  • Granule Design for the Sintering with Less Amount of Liquid Phase Formation

    pp. 659-666

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    DOI:10.2355/isijinternational.49.659

    In order to clarify the conditions to produce a dense and large pellet required from the MEBIOS method, some basic sintering experiments were conducted. Consequently, the pellet having a sufficient strength as a blast furnace burden was able to be produced by selecting the composition of the pellet and the temperature so that the liquid phase ratio in the CaO–Fe2O3–SiO2 system was about 40 mass%. Moreover, it was confirmed by the sintering pot experiment using X-ray CT that a void was formed around the pellet when this pellet was placed in the sintering mixture. The crushing strength of the pellet collected from the sinter cake was low. However, increasing of the basicity of the pellet and extension of the retention time at high temperature were effective for improving the crushing strength of the pellet.
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  • Optimization of Coke Breeze Segregation in Sintering Bed under High Pisolite Ore Ratio

    pp. 667-675

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    DOI:10.2355/isijinternational.49.667

    Increased demand and the diminishing high grade resources have resulted in a shift to using low grade iron ore in Japanese steel mills. Especially, pisolite ore ratio is quite high. Therefore, decrease in sinter productivity became serious problem with increasing the amount of pisolite ore.
    To improve the sinter productivity, effective method at the charging device in sintering machine was investigated by laboratory experiments.
    The following results were obtained.
    1) It was expected that the holding time over 1200°C at the middle and bottom layer of the sintering bed decreased with high pisolite ore ratio. On the other hand, in order to preserve the sinter strength, it was suggested that the holding time over 1200°C in sintering must be extended under high pisolite ore ratio.
    2) There is the optimum coke segregation degree according to the pisolite ore ratio. It was decreased with increase of the pisolite ore ratio.
    3) To control the coke segregation in the sintering bed, Magnetic Braking Feeder (MBF) was introduced, and the operating conditions were investigated with the laboratory charging tests and sintering pot test.
    4) Based on the fundamental research, MBF has been applied to Keihin No. 1 sinter plant, and the productivity was improved by 4.2% under constant sinter strength.
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    3. Effect of Carbon Structure Crystallinity on Initial Stage of Iron Carburization ISIJ International Vol.50(2010), No.1
  • Use of Raw Petroleum Coke in Sinter Plants

    pp. 676-680

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    DOI:10.2355/isijinternational.49.676

    With the augmentation of sinter production in Jamshedpur works of Tata Steel, there was an acute shortage of coke breeze, the usual solid fuel for sintering. This required the use of alternate fuel for sinter making. Raw Petroleum Coke (RPC) was utilized in all three sinter plants of Tata Steel, Jamshedpur works since November 2005. RPC usage went as high as 50% of total carbonaceous fuel used for sinter making. A unique advantage of using RPC is its low ash (nearly 1.5%) compared to that of coke breeze with 22–25% ash. Thus it was possible to lower Al2O3 in sinter from 2.5 to 2.2% consistently. RPC is obtained as a by-product from the petroleum refinery. It is extremely fine in size having −0.25 mm nearly 60% and is highly reactive. RPC also contains volatile matter of about 6–7%, which has implications in suction system. Given the above conditions, it was really a challenge taken by the sinter making team of Tata Steel to adjust the process for using RPC to such a high extent without adversely affecting the quality productivity and equipment health. At some point of time deterioration in sinter quality, particularly in terms of RDI and certain loss in availability and productivity was observed. This paper is to share the experience of Tata Steel in using RPC for sinter making.
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    3. The Influence of Fuel Reactivity on Iron Ore Sintering ISIJ International Vol.49(2009), No.2
  • Heat Transfer Analysis of the Mosaic Embedding Iron Ore Sintering (MEBIOS) Process

    pp. 681-686

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    DOI:10.2355/isijinternational.49.681

    Using computational fluid dynamics software, two-dimensional (2D) and three-dimensional (3D) simulation models for simulating the mosaic embedding iron ore sintering (MEBIOS) process were developed on the basis of the concept of the multiply shared space (MUSES) method. When one pellet (diameter: 15 mm) was placed at the centre of a sintering bed, the estimated time variations of temperature at the centre and surface of the pellet by both the 2D and 3D simulations were similar to the corresponding experimental results. The calculated cooling rate of the pellet was comparatively high; however, it could be improved further by introducing the fraction of closed pore in the bed in the simulation model.
    It was supposed that the 2D simulation of the MEBIOS process was quite effective in decreasing calculation cost; therefore, in the case that several pellets were distributed in lattice and staggered alignments throughout the bed, the 2D model was used for calculating the time variations of temperature at the centre of the pellets. The calculated results showed that the sintering process could not continue when the pellets were distributed in the staggered alignment and the distance between pellet centres was 30 mm. On the other hand, changing the distance between the pellets distributed in the lattice alignment had little effect on the sintering process, and the process accelerated by approximately 300 s due to the high gas velocity around the pellets.
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  • Penetration Behavior of Calcium Ferrite Melts into Hematite Substrate

    pp. 687-692

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    DOI:10.2355/isijinternational.49.687

    Effects of adding SiO2 or Al2O3 on the penetration characteristics of calcium ferrite (CF) melts into hematite substrate with the different percentage of porosity were examined, and were discussed from the viewpoints of the relation to the solubility gap, ΔFe2O3 (mol%), viscosity and surface tension of the CF-based melts.
    In case of dense hematite substrate with 5% porosity, the penetration depth of CF melts into hematite substrate was depressed by the addition of SiO2 or Al2O3, and the addition of SiO2 was more effective than that of Al2O3. Moreover, the penetration of CF-based melts along grain boundaries into hematite substrate did not take place, and melts/hematite interface moved down by dissolution of solid hematite into these melts. The penetration depth of CF-based melts into hematite substrate was mostly determined by ΔFe2O3 (mol%), which meant that the dissolution of hematite into melts was rate-determine.
    In case of porous hematite substrate with 15% porosity, the penetration of CF-based melts along grain boundaries into hematite substrate occurred, and the penetration depth was 10 times deeper than the case of dense hematite substrate with 5% porosity for each slag. The penetration depth of CF melts was increased by the addition of SiO2 due to the decrease of melting temperature in the calcium ferrite system. The penetration depth of CF melts with the addition of Al2O3 was very similar to that of CF melts. These melts penetrated into hematite substrate with crystallization (solid) due to the increase of the melting temperature in calcium ferrite system by the dissolution of hematite into the liquid phase. The penetration depth of CF-based melts into hematite substrate was dominated by the ratio between the surface tension and viscosity of melts taking the suspension-corrected into consideration.
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  • Numerical Simulation of Particle Agglomeration and Bed Shrink in Sintering Process

    pp. 693-702

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    DOI:10.2355/isijinternational.49.693

    The motions of the particles and the gas in the actual scale sintering bed were simulated to elucidate the mechanism of the bed structure changes, the bed shrink and the local void formations by the simultaneous calculation of Navier–Stokes equations and the Lagrangian DEM equations based on the simple sintering model in which the phase change of particles and the cohesion forces due to the liquid bridges among particles were considered.
    The bed shrink rate decreased with the moving downward of the melting zone. This is mainly because the weight of the particle bed increases with increasing the bed height. The gap of the particle motions occurred between the zones of which the content and the contact number were largely different. The gap separates contact particles and the crack appears. The shrinks of the beds with the large particles (MEBIOS particle) were smaller than that of the bed without the large particles. The reasons are that the large particles do not change the particle volume and also the high void region around the large particles is formed. The crack did not occur in the particle bed placing the large particles. The large scale zones of which the content and the contact number are largely different are cut off by the large particles and the small crack originated from the separation of contact points between iron ore particles does not grow by the existence of the large particles. After the sintering the high number density areas on the large particles and the void areas under the large particles were formed. This is because the large particles with smaller particle density relatively ascend among the small particles with the larger particle density. The void areas under the large particles advance the aggregation among the small particles which do not contact with the large particles.
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    3. Factors Accelerating Dioxin Emission from Iron Ore Sintering Machines ISIJ International Vol.49(2009), No.5
  • A Novel Method for Quantifying the Composition of Mineralogical Phase in Iron Ore Sinter

    pp. 703-708

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    DOI:10.2355/isijinternational.49.703

    This paper presents a new method to calculate accurately the composition of the mineralogical phase in iron ore sinter, especially the minor phases. This model is based on the combined model of gray-level distribution for a multi-phase system. The composition of the mineralogical phase is calculated by minimizing the difference between the theoretical gray-level histogram and the actual gray-level histogram of a micrograph of the iron ore sinter. A genetic algorithm and an improved genetic algorithm are introduced to solve this extreme value problem. Suitable parameters for the algorithm were determined by comparing the solutions for each of several cases. The example provided demonstrates that this model is valid, especially for the minor phases, and the solution is credible.
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  • Relationship between Texture Features and Mineralogy Phases in Iron Ore Sinter Based on Gray-level Co-occurrence Matrix

    pp. 709-718

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    DOI:10.2355/isijinternational.49.709

    An intelligent recognition and quantification system for photomicrographs of iron ore sinter is useful and convenient; however, it is impossible to develop a successful intelligent system without adequate and accurate texture features of mineralogical phases. The gray-level co-occurrence matrix (GLCM) has been proved as an effective method for extracting the texture features in other fields, therefore, this work examines texture features for the main mineralogical phases, such as magnetite and calcium ferrite, based on GLCM. These features include contrast, energy, entropy, and inverse difference moment. Specifically, this study addresses the effect on these features of several parameters, including the gray levels, the size of the image window, and the distance between the co-occurrences, and the offset angle. When the gray levels equal 125, the size of image window equals 100, and the distance of the co-occurrence equals 15, the average values of the four offset angles indicated that the features of each phase were relatively constant. Space distance characterizes the differences between a known image and an image to be analyzed; it determines the texture pattern of the image and is calculated using the Canberra space distance equation. Further calculation validates the results, indicating that intelligent recognition and quantification systems can be developed based on this method.
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  • Effect of Variation of Alumina on the Microhardness of Iron Ore Sinter Phases

    pp. 719-721

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    DOI:10.2355/isijinternational.49.719

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  • Effect of Mineral Composition and Pore Structure on Reducibility of Composite Iron Ore Sinter

    pp. 722-728

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    DOI:10.2355/isijinternational.49.722

    Recently, a new agglomeration concept called MEBIOS (Mosaic EmBedding Iron Ore Sintering) process is proposed. In the process, to utilize the characteristic of the goethite effectively is aimed on the premise of the major use of the goethite ores as a raw material and the low slag content. This is the sintering technology in proportion to the property of the goethite, in which a composite iron ore sinter is formed by arranging the dense pre-granulated pellets properly in the porous induction bed. The use of pisolite and Marra Mamba ores are considered as main components of the porous induction bed and the dense pre-granulated pellets, respectively. In the present study, the composite iron ore sinter, which is composed of the dense pre-granulated pellet and the porous induction bed, is produced experimentally. Only a dense pre-granulated pellet is placed at the center of the porous induction bed. In order to examine what kind of mineral composition and pore structure are desirable from the viewpoint of the reducibility of the composite iron ore sinter, the hydrogen reduction experiments are conducted at 1173 K. The reduction rate of the composite iron ore sinter, which is composed of the dense pre-granulated pellet and the porous induction bed, is larger than the uniform pellet, of which the whole composition is identical. Moreover, the reduction becomes faster by considering the compositional design between the porous induction bed and the dense pre-granulated pellet. It is desirable to contain CaO and SiO2 more in the porous induction bed than in the dense pre-granulated pellet. From the measurement of the pore-size distribution by the mercury penetration style porosimeter, the reduction is faster for the samples, of which the accumulation pore volume over 10 μm is larger. From the components analysis of the mineral phase, the increase of calcium ferrite in the porous induction bed contributes to the improvement in the reducibility of the composite iron ore sinter.
  • Factors Accelerating Dioxin Emission from Iron Ore Sintering Machines

    pp. 729-734

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    DOI:10.2355/isijinternational.49.729

    Causal factors for dioxin (D) emission from iron ore sintering machines has been investigated by means of pot tests designed with the two-level seven-factor orthogonal array (L8(27)) and multiple regression analysis on commercial plant data.
    EP dust, BF dust and purchased scale were major D-accelerators; quick lime was a D-suppressor. D emission was not a sum but a product event of those factors, and their coefficients were 28, 4, 4 and 0.7 times for 5% EP dust, 5% BF dust, 5% purchased scale and 2% quick lime additions, respectively. As for operational conditions, bed height, coke content, gas velocity and after burning had insignificant effects whereas the increase of hearth layer and the decrease of BTP position increased D emission, which implied the hearth layer and wind boxes could be other synthesis sites.
  • Separation and Recovery of Potassium Chloride from Sintering Dust of Ironmaking Works

    pp. 735-742

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    DOI:10.2355/isijinternational.49.735

    Sintering plant in iron and steel making company generates very fine metal-containing dusts which can present major environmental problems. This paper describes experimental work on a relatively simple and inexpensive process for recovering the potassium chloride and upgrading the iron level of dust from a Chinese plant, to produce saleable potassium chloride product and environmentally safe waste products for reuse. The dust contained about 10–20% potassium as potassium chloride, 20% iron as iron oxides, plus small quantities of lead, copper, cadmium, zinc and other materials. Individual particles of the dust were commonly aggregates of various shapes. Multi-stage countercurrent leaching was taken to completely remove potassium chloride in the ESP dust, but leave iron in the leach residual. With the help of sodium sulfide precipitation, the leached heavy metals were removed from the leaching solutions and a mixture solution which can be perceived as system KCl–NaCl–CaCl2–H2O was left. Then potassium chloride in the system can be separated and recovered by fractional crystallization. At last the mother liquor was returned to the leaching process as leaching agent together with new tap water. This proposed flow sheet was proved feasible through construction of the demonstration unit in the lab, and KCl product with a purity of 96.5% was obtained.
  • Application of Orthogonal Array Tests Method to Optimize Operating Conditions for Iron Ore Sintering

    pp. 743-748

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    DOI:10.2355/isijinternational.49.743

    The objective of this study was to determine optimal operation parameters for increasing iron ore sinter productivity (SP) and sinter strength (SS) during sintering process by using the orthogonal array test method, and examine their emissions. Three operating parameters, including the water content (Wc; range=6.0–7.0 mass%), suction pressure (Ps; range=1000–1400 mmH2O), and bed height (Hb; rang=500–600 mm) were selected for conducting experiments in a pilot-scale sinter pot to simulate various sintering operating conditions of a real scale-sinter plant. We found the resultant optimal combination (Wc=7.0 mass%, Ps=1400 mmH2O, and Hb=500 mm) could increase SP up to 20.2% in comparison with the current operating condition of a real-scale sinter plant (Wc=6.5 mass%, Ps=1200 mmH2O, and Hb=550 mm). The results of the ANOVA analysis indicates that Wc and Ps were the two significant parameters (p<0.05) accounting for 50.3% and 36.7% of the total contribution of the three selected parameters, respectively. The SS of the resultant optimal combination shows no significant difference (only increased 2.2%) as compared with the current operating condition of the selected real-scale sinter plant. By examining the emissions of SOx, NOx, and particulate matters, the values obtained from the optimal combination were quite comparable to those of the current operating condition. The above results further confirm the applicability of the obtained optimal combination for the real-scale sinter production.
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