Sinter Cake Research Articles

Scientific and technical support for the devel-opment of sinter plant no. 5 of PJSC MMK

The design characteristics of the sinter plant No. 5 of PJSC MMK, commissioned in 2019, are presented. The results of studies of the processes of homogenization, mixing, moistening and pelletizing of the burden, its burdening on the sintering machine, ignition, sintering and cooling of the sinter cake are presented. The erroneousness of the design solutions for installing the pelletizing drum at the zero level and the charge bunker with a volume of 60 m3 in the sintering body without an intermediate bunker is shown. Technical solutions are presented to prevent a discrete charge descent of the charge from the drum feeder of the loading unit and to form the profile of the charge layer on the sintering machine, which increases the uniformity of the process of its sintering along the width of the pallets. The operation of a multi-roll charge stacker, first used at sinter plants in the CIS, was studied. Industrial experiments were carried out on sintering a conditionally “dense” and loosened by a special device batch layer, the advantage of the latter in terms of the speed of the sintering process was established. A technical solution has been developed and accepted for implementation to reduce the length of the hearth by 40%, which will increase the sintering area of the sintering machine by 3%. The operation of the energy-consuming exhaust gas recirculation system based on their selection from eight vacuum chambers of the sinter machine out of twenty with the installation of a smoke exhauster with a drive capacity of 3.1 MW and gas cleaning from dust was stopped. Vacuum chambers of the recirculation system are connected to two parallel collectors of the sintering machine; an analysis of the impact of these measures on the operation of the sintering machines has been carried out. The possibility of using gas recirculation with the installation of a smoke exhauster with a drive power of 400 kW without additional purification of gases from dust is shown. In the future, it is proposed to increase the open section of the collectors by making them from three sections of different sections. It was found that the area of linear coolers was overestimated due to the use of “direct” loading of sinter on them, in which the cooling of the material is limited by its large lumps located in the upper part of the layer. A sinter back loading system was proposed and implemented in the project, which allows to reduce the cooling area by 30% (turn off two of the six blowers), it was decided to implement it. As a result of development of AF-5, for the first time in the practice of sintering plants in the CIS, the height of sintered charge layer of 700 mm was established. The specific productivity of sintering machines during the sintering of the charge based on the Sokolovsko-Sarbaisky concentrate was achieved, equal to 1.10 t/(m2•h); the cold strength of the sinter according to GOST 15137–77 for impact is on average 82.5%, for abrasion ‒ 4.5%.

STUDY OF THE EFFECT OF EXPERIMENTAL 70%-IRON CONCENTRATE ON TECHNOLOGICAL PERFORMANCE INDICATORS AND SINTER QUALITY

One of the main functional properties of iron-ore sinter is iron content, which mainly determines the technical and economic parameters of iron production. Metallurgists are ever striving to increase the iron content in sinter. At present, the majority of Russian steelmakers produce sinter from concentrates with iron content of 65‒66%. OJSC Stoilensky GOK has been searching for new enrichment methods to increase iron content in the iron ore concentrate, and it has managed to obtain an experimental concentrate containing 70% iron. Studies conducted in Japan have shown that the productivity of sintering machines deteriorates when the iron content in concentrate rises and the SiO2 content lowers. With increasing iron in sinter, Russian scientists have established a decrease in strength and higher breaking. This required further study, so research was conducted to determine how partial and full replacement of the current iron-ore concentrate with experimental concentrate (70 % Fe) in sinter charge influences technological parameters and sinter strength. Increasing the share of experimental concentrate in sinter charge causes increase in iron content in sinter and decrease in SiO2 content. With this, metallurgical value of sinter goes up, while strength, yield of good sinter, productivity of sintering machines and sinter strength deteriorate. The main reason for the reduction in strength is the reduced amount of melt during the sintering of charge. As a result, the sinter cake structure gets areas of poorly sintered charge material, and vitreous phase is found in the binder along with strong ferrites. These factors are the main drivers of sinter strength reduction observed when the share of experimental concentrate in the charge increases.

Simulation model for the selection of technological parameters to obtain a sinter with high consumer properties based on the committee method

To control the quality characteristics of the agglomerate, a simulation model based on the committee method has been proposed. A generalized model of committee structures is presented in the form of a linear programming problem with partially integer variables. The model has been tested on real data. The minimum number of informative features is determined, in the space of which it is possible to construct a decision rule that separates agglomerate areas with high consumer characteristics from areas with satisfactory quality indicators. A high-quality agglomerate had to simultaneously meet the specified limits in terms of yield and strength. As a result of the calculations, a decision rule was built in the form of a seniority committee of five members in the space of 43 features. Geometrically, this is a convex region obtained from a hyperparallelepiped when it is truncated by five hyperplanes. This decision rule can be easily programmed with simple tools and integrated into the sinter quality control system. The practical importance lies in reducing the yield of structural fines during the destruction of the sinter cake, i.e., increasing the yield of a suitable agglomerate while keeping the technological parameters within the convex region.Contributors to the preparation of the article: A. A. Eliseev, Raw Material Research Manager of PJSC Severstal, aaeliseev@severstal.com, Yu. A. Malygin, Director of Ferrox Ltd., y.malygin@ferrox.org,N. P. Chernavin, Assistant of the Dept. of Big Data Analytics and Video Analysis Methods of Ural Federal University, ch_k@mail.ru, F. P. Chernavin, Cand. Econ., Associate Professor of the Dept. of Controlled Systems Modeling of Ural Federal University, chernavin_fedor@mail.ru.

Analysis and prediction of sinter yield and strength based on mathematical programming model

This article proposes a method for a comprehensive analysis of the controlled parameters of the technological process and the dynamics of sinter cake disintegration during mechanical processing, taking into account the transport lag of the measured output characteristics (fines yield 0-5 mm when sinter cake is destroyed within the sinter plant and along the conveyor path for transporting sinter to the blast furnace shop) from the current composition of the charge and the parameters of the sintering process. On the basis of the specified output characteristics, an assessment of the sinter yield and strength was carried out. To analyze and predict the physical and mechanical properties of iron ore sinter, a new method of constructing regression equations based on linear programming problems with partially Boolean variables was used. The most significant drawback of the standard approach is the strong dependence of the regression equation coefficients on random anomalous observations (outliers), which in practical problems can be quite large and it is impossible to filter them out. The proposed MILP Regression method improves the forecast quality by automatically excluding atypical observations from consideration. The method is compared with other regression models. The method of mixed integer linear programming (MLIP) was used to process the current information about the operation of the sinter shop No. 3. The most significant parameters that affect the formation of the total amount of fines during the destruction of sinter were established: the component composition of the charge, sinter machine pallets speed, pressure gas and temperature in collectors, temperature in ignition furnaces and behind them, temperature in last vacuum chambers of sintering machines. The obtained regression equations quite accurately reflect the influence of the initial data array on the yield of recycled sintering products and they can be used to predict the output parameters of the sinter quality. A. A. Eliseev, manager on raw materials research (PJSC Severstal), Yu. A. Malygin, director (JSC Ferroks), N. P. Chernavin, assistant of the department “Big data analytics and video analysis methods” (Ural federal university), F. P. Chernavin, associate professor, department “Simulation of managing systems” (Ural federal university) participated in preparation of this article.

Bulk Raw Materials Handling and Blending Techniques of Sinter Plant: A Case Study of Ajaokuta Steel Company Limited, Kogi State, Nigeria

Bulk raw materials handling plant and sintering plant preparatory plants are established to receive, blend, stockpile, prepare and supply specified grades of raw materials for smooth operations of iron making plant (Blast furnace), steel making plant (Basic oxygen converter) and lime Plant(calcinations plant). The study discusses bulk raw materials handling and some general problem of scientific analysis and documentation of basic equipment details, stockyard facilities, bulk materials transport systems and sinter processes, for the general knowledge and operational procedures of these plant for effective and efficient operational processes for optical results. Iron ore concentrate supplied from the mines to some extent fluctuate in their chemical composition as a result of the nature of the deposit with various factors controlling beneficiation processes and addition of metal-bearing materials collected as a waste product from the Rolling Mills, Blast Furnace and Sinter Plant which must be recycled through Iron ore concentrate stockyard. The part of the sinter mixture is melted at a temperature about 1300-1480 ° C and a sequence of reactions shaping the sinter cake to be loaded into the blast furnace to produce iron from a pig.

(Ti,Cr)C-Based Cermets with Varied Nicr Binder Content via Elemental SHS for Perspective Cutting Tools

The effects of granulation of reactive mixtures Ti-Cr-C and Ti-Cr-C-Ni on the combustion temperature and velocity, as well as phase composition and mechanical properties (crushing ability) of combustion products, were studied. Granulation was associated with a 1.5-fold increase in combustion velocity, caused by a nearly 10-fold increase in gas permeability. Secondary reactions between TiC, Cr7C3, and molten Ni led to the formation of (Ti,Cr)C FCC solid solution and Ni2.88Cr1.12 intermetallics. After the combustion of Ti-Cr-C-Ni mixtures, prolonged fluorescence was registered, suggesting the exothermic nature of secondary phase formation reactions. The introduction of the nickel binder decreased the content of Cr in the solid solution (Ti,Cr)C owing to the formation of the Ni2.88Cr1.12 phase. To prevent the Cr depletion from the carbide solid solution, Ni-20%Cr binder was added to the granulated 80%(Ti + C)/20%(3Cr + 2C) mixture. Combustion of granulated mixture yielded brittle porous sinter cake, which was easy to crush and mill, whereas the combustion products from the powdered mixtures were more ductile and harder to crush.

On the Applicability of the Evaluation Techniques of the Properties of Iron-Ore Sinter

Referring to the hierarchical structure of sinter cake, the applicability of various methods for controlling sinter properties has been studied. The technique has been proposed for evaluation of quality yield and strength for sinter using the parameters characterizing structural fines yield and strength of macroblocks under destruction.

Study of stand-support sintering to achieve high oxygen potential in iron ore sintering to enhance productivity and reduce CO content in exhaust gas

Abstract Coarse coke particles, thick combustion zone, and poor thermal permeability during sintering have been widely reported to lead to incomplete solid fuel combustion and low oxygen potential, which induces the formation of harmful gas and decreases the energy efficiency. To solve these problems, stand-support sintering with an ultrathick 1000 mm bed was first proposed in this paper. The influences of the stand height and coke size on the process parameters and sinter quality were studied through a series of experiments. The results showed that the average gas flow velocity increased from 0.24 m/s to 0.32 m/s and the maximum combustion zone thickness decreased from 202 mm to 140 mm, which indicated that stand-support sintering could substantially improve the thermal permeability and enhance the oxidizing atmosphere. The fuel consumption was reduced by 1.28 kg/t (2.25%), the generated CO in exhaust gas was reduced, and the production efficiency increased by 17.4% when the stand height increased from 0 to 500 mm. Moreover, a 3D high-energy X-ray computerized tomography (CT) scanner was first used to quantitatively confirm the effect of the stand on the distribution and size of the pores in the whole sinter cake. Research findings showed that the porosity increased by 7.1% when the height of the stand increased from 0 to 500 mm, which further illustrated the effect of stand-support sintering. The present study provided an effective way to optimize the energy efficiency and reduce the CO content in exhaust gas.

Self-propagating high-temperature synthesis of single-phase binary tantalum-hafnium carbide (Ta,Hf)C and its consolidation by hot pressing and spark plasma sintering

Manufacturing of the single-phase binary carbide (Ta,Hf)C by self-propagating high-temperature synthesis (SHS) from a mechanically activated (MA) reaction mixture is discussed. The effect of mechanical activation conditions on the microstructure and phase composition of the reaction mixtures and the SHS products was studied. The measured combustion temperature (2127°C) was significantly lower than the calculated adiabatic temperature (3001°C), which is related to the intensive gas release during combustion and the possible loss of thermal contact between a thermocouple and a briquette. After MA in the air, the SHS product was a virtually single-phase carbide with the lattice parameter a = 0.4487nm, which corresponds to 18.0at% of dissolved HfC; HfO2 content was less than 1%. The SHS product was a high-porosity sinter cake with a carbide grain size of less than 10µm. The resulting product was refined in a planetary ball mill. Dense samples with relative density up to 90.0 ± 5.0%, the hardness of 24.0–27.4GPa, Young’s modulus of 423.6–484.4GPa, and elastic recovery values of 44.3–46.1 were fabricated by hot-pressing and spark plasma sintering methods using the SHS micron-sized (Ta,Hf)C powders.

High resolution X-ray microtomography for the characterization of pore structure and effective thermal conductivity of iron ore sinter

Thoroughly understanding of the thermophysical properties of porous sinter is especially important for operation optimization and energy saving in integrated steel mills. Under this prospect, nondestructive X-ray microtomography was applied to characterize the pore structure and following simulations for estimating the sinter effective thermal conductivity were performed. Three sinter cakes produced from pilot-scale sinter pot tests under three granulation moisture levels were scanned with resolution ratio of 42µm. The reconstructed sinter cakes have various complex pore distributions, leading to remarkable anisotropic thermal conductivities and complicated temperature field. The pores smaller than 300µm dominate the number frequency in sinter cake, while a small amount of pores larger than 1mm account for ∼94% of the total pore volume, which determine the thermal behavior greatly. The estimated effective thermal conductivities of three samples are 0.847, 0.865, 0.558W/mK, corresponding to the porosity of 48.1%, 49.1% and 59.4% respectively. Comparing these values with values of similar iron agglomerates in the literature, some empirical correlations and analytical models, the results proved that CT-simulation is a valid approach for capturing the peculiar details of the real sinter porous structure, thus to predict thermal behavior with higher accuracy than the simplified geometric models.

Optimization of coke ratio for the second proportioning phase in a sintering process base on a model of temperature field of material layer

Abstract Coke ratio for a sintering process is often determined by experience because models of calculating a coke ratio are very complicated, and are hard to be used in practice. This paper presents a three-step optimization method to find a coke ratio that meets the requirements for commercial operations. First, a back-propagation neural network (BPNN) for temperature field of the material layer (TFML) is built to calculate a mass of sinter cake of a sintering process. Then, the energy flow in a sintering process is analyzed, and a theoretical value of the coke ratio is calculated. Finally, the optimization problem for the second portioning phase is formulated that takes into consideration of the conventional constraints, such as material balance, chemical composition, required quality, etc., and a coke ratio constraint based on the theoretical value. This benefits the reduction of CO 2 for the sintering process. Numerical verification has shown the validity of the method.

Experimental study and X-ray microtomography based CFD simulation for the characterization of pressure drop in sinter bed

In this study, pilot-scale sinter pot tests under three granulation moisture conditions were conducted. Porous structures of the sampled sinter cakes were reconstructed by X-ray microtomography and CFD simulations were applied based on the real geometry. The pressure drop of serial subzones along the sinter bed including sintered zone, high-temperature zone and humidified zone were discussed by analyzing the experimental measured airflow rate and CFD simulation results together. The results show that sinter cake porosity increases from 0.48 at 6.3wt% H2O to 0.59 at 7.3wt% H2O. The reconstructed sinter cakes show various complex porous structures, resulting in remarkable flow heterogeneity and complicated velocity field. A high porosity bed has many more gas channels and the flow distribution is developed better. The pressure drop in sintered zone is ∼1.5kPa/m, which is much lower compared to the high-temperature zone and humidified zone. The high-temperature zone where main reactions and bed structure changes happen has a controlling effect on the pressure drop across the sinter bed. The sintering bed permeability greatly determines the final productivity, which is affected by the bed temperature profile and bed porous structure.

Failure Analysis of Wear Block of Crush Deck Used in Sinter Plant

Failure analysis of wear block used in the crush deck of a Sinter Plant was carried out. Crush deck acts as a platform to transfer the hot sinter cake from sinter machine to crushing unit. Hot sinter cake with a temperature around 800 °C falls on the crush deck from the discharging end of rotating sinter machine. This investigation consists of visual observation, chemical analysis, characterization of microstructures, energy dispersive spectroscopy, and measurement of hardness. Analysis revealed that this is an iron-based material with Cr–Ni alloying with higher hardness and lower toughness, which was due to improper microstructure. Microstructure revealed a large number of primary carbides along with needle-shaped carbides, which drastically reduce the toughness of the material. Application point of view the wear block should have optimum combination of toughness and wear resistance at elevated temperature; however, analyses showed the actual wear block had with higher wear resistance and lower toughness. This was reflected in the undesirable microstructure observed during metallographic study. It was thus concluded that the component failed before a proper life cycle was achieved due to poor material properties. Based on the failure analysis suitable heat treatment process was recommended. Metallurgical study carried out on the suggested material, showed significant improvements in material property. Trial of recommended wear block was taken at the plant level and life of the recommended material improved twice than that of previous one.

Extraction of Rare-Earth Metals During the Systematic Processing of Diaspore-Boehmite Bauxites

An integrated technology is proposed for processing diaspore-boehmite bauxites and extracting their useful components. It is established that sintering bauxite with a caustic alkali increases the quantities of rare-earth metals that are recovered. Experiments showed that the sintering of bauxite with a caustic alkali must be done with no more than 10–15% moisture in the charge at the optimum temperature of 200°C. Leaching of the sinter cake with water or a dilute aluminate solution forms high-iron red mud with low concentrations of alkali and alkaline-earth metals. Leaching the mud with a dilute inorganic acid makes it possible to extract up to 90% of the rare-earth metals, including scandium oxide.

Failure of metallurgical sinter

Strength tests of sinter associated with the optimization of sinter production have certain deficiencies, whose analysis calls for models of sinter failure. The theory of melt mixing in sintering and structure formation in the sinter cake is reviewed. A model for the failure of metallurgical sinter is proposed on the basis of a model of the stress state of the solid inclusions in the matrix and a failure model based on the Rittinger law. The load in the sinter pieces in the test drum is determined, and a method is proposed for adapting the model of sinter failure by means of granulometric data regarding the test products. The adaptation employs the probability distributions of the model parameters. The dependence of these parameters on the sinter basicity, the carbon content in the batch, and the size of the limestone pieces is determined.

FRACTURE MODEL OF METALLURGICAL SINTER

The paper covers specifi c features of up-to-date test methods for metallurgical sinter strength, defi ciencies of these methods, related to issues of overall improvement of sintering and blast-furnace production processes requiring application of sinter fracture models. Theories of liquid melt migration upon sintering as well as features of sinter cake formation are reviewed; a model of metallurgical sinter fracture is suggested as well, which is based on combined use of the model for hard inclusion tension in the matrix along with the fracture model based on Rittinger’s law. Forces applied to sinter lumps in a test drum are determined and a method for adjustment of the sinter fracture model is suggested with use of granulometric properties of products under testing. It is suggested to use probability distribution of fracture model parameters for the purpose of adjustment. Dependences of these parameters from sinter basicity, carbon content in the charge material and limestone lump size are determined.

Experimental Analysis of the Process Performance and Quality Index in the Waste Gas Recovery Iron Ore Sintering—Based on a Plant Test

Effects of different waste gas recovery sintering (WGRS) methods on the quality index and process performance of the iron ore sinter were studied by a plant test, compared to the conventional sintering (CS). Two key operational parameters, namely, the temperature and oxygen content of the recycling gas, were selectively discussed. The values of these two parameters were measured in the gas‐mixing chamber. The sintering mixture with a constant proportion was obtained ensuring the similar mass averaged particle sizes. The changes in the sintering process performance, such as the exhaust emission regulation, productivity, energy consumption, and sintering efficiency of the system, were analyzed. The quality indexes including the yield, chemical composition and size distribution of the sinter cake, the tumbler index (TI), and the reducibility (RI) in different methods of WGRS were also analyzed. Systematic analyses demonstrate the feasibility of replacing the CS production with the WGRS technology. The optimal temperature range of the recycling gas was 200 °C∼250 °C, and the suggested values of oxygen content was closed to 21%.

Three-Dimensional Mathematical (Dynamic) Model of the Sintering Process. Part II*

This article presents a three-dimensional mathematical (dynamic) model of the sintering process. The model was developed to solve theoretical and practical problems. It allows real-time determination of the distributions of the temperatures and the chemical compositions of the charge, the melt, the sinter cake, and the gas in the bed of charge materials with allowance for transients. The model also permits real-time determination of the temperatures in the pallets and the parameters of the gas flow (including infiltrating air) in the flue system of the sintering machine.

Chemical Dispersion as a Method for Segregation of Ultrafine and Nanosized Powders of SHS Refractory Compounds

Overviewed are some results of our recent works aimed at the synthesis of ultrafine and nanosized refractory powders by self-propagating high-temperature synthesis (SHS) combined with chemical dispersing of combustion products. The possible application of SHS for preparing ultrafine and nanosized powders of refractory compounds is examined. Specific features of SHS afford to affect not only the chemical/phase composition of products but also the morphology and size of synthesized particles. Quenching experiments have shown that the primary product particles formed in the combustion wave may have a size of below 0.1-0.2 μm. By etching a ground SHS cake with appropriate solutions, one can dissolve the defect-rich layers between the crystallites and remove impurities. As a result, the sinter cake breaks into crystalline particles of the same size as the primary crystallites, without compositional changes. This process was termed chemical dispersion. The phase and chemical composition, specific surface and grain size of SHS refractory compounds powders are detected before and after treatment. The influence of the synthesis conditions and the dispersion agent on the morphology and particle size of the resultant powders are ascertained. Successive chemical dispersing of raw products (carbides, nitrides, silicides, borides, oxides of metals and nonmetals) with solutions of different acids, alkalis, and salts leads to an additional grinding of the product, an increase in the specific surface and a decrease in the particle size. So, the possibility to control the SHS processes allows changing the particle size and structure of the synthesized compounds and provides obtaining high-quality products of the preset structure. The following thermochemical treatment of the ground cake by special solutions (chemical dispersion) allows to segregate ultra- and nanosized powders of refractory compounds. Our experience<br />in preparation, separation, and purification of SHS-produced nanopowders can be used as a basis for elaboration of general methodology for pilot-scale production of nanostructured compounds and composites.

Chemical profile identification of fugitive and confined particle emissions from an integrated iron and steelmaking plant

The aim of this study is to obtain the characteristic inorganic chemical profile of important particle sources identified in the integrated iron and steel process: sintering, blast furnace, steelmaking and desulfurization slag processing. A complete chemical and physical characterization program was developed: particle size distribution, chemical analysis, XRD, SEM-EDX and TGA/DTA. The sample collected from the sinter stack showed high levels of K and Cl−, followed by Fe, NH4+, Ca, Na and Pb. The profile of the dust samples taken from the sinter cake discharge zone was quite different, showing higher amounts of Fe, Ca and Al, and lower amounts of K, Cl−, Na and Pb. Dust samples collected from the blast furnace (BF) and steelmaking cast house may be distinguished from each other based on the higher levels of Fe (hematite and magnetite) and lower levels of Ca, Zn and C (graphite) found in BF dust. High levels of Ca and Fe were found in samples taken from the desulfurization slag processing area. Such information can be useful for source apportionment studies at receptor sites that could be influenced by iron and steelmaking plant emissions.