The performance of the sintering process can be increased by means of various procedures. One of the options is increasing
the permeability of the sintering charge and improving the gas-dynamic conditions during the combustion.
This can be achieved by dosing coarse sinter on the sintering strands. This article analyzes a research conducted in order
to experimentally verify the impact of the use of coarse sinter on the performance of the sintering process.Web of Science561-213413

Besta, Petr

Wicher, Pavel

DSpace at VSB Technical University of Ostrava

131METALURGIJA 56 (2017) 1-2, 131-134P. BESTA, P. WICHERTHE OPTIMIZATION OF THE PRODUCTION OF SINTER AS THE FEEDSTOCK OF THE BLAST FURNACE PROCESSReceived – Prispjelo: 2016-04-25Accepted – Prihvaćeno: 2016-07-30Preliminary Note – Prethodno priopćenjeP. Besta, P. Wicher, Faculty of Metallurgy and Materials Engineering, VŠB – Technical University of Ostrava, Czech RepublicThe performance of the sintering process can be increased by means of various procedures. One of the options is in-creasing the permeability of the sintering charge and improving the gas-dynamic conditions during the combustion. This can be achieved by dosing coarse sinter on the sintering strands. This article analyzes a research conducted in or-der to experimentally verify the impact of the use of coarse sinter on the performance of the sintering process.Key words: blast furnace, iron, ore, sintering, productionINTRODUCTIONThe sintering of iron ores means heating the powder sintering mixture to such a temperature to achieve the surface melting of the individual charge grains: The re-sulting melt creates liquid bridges among the grains which, after solidification, facilitate the formation of a solid porous material [1].Charge for the production of sinter consists of sinter ore with the grain size below 10 mm, coke with the grain size below 3 mm and alkaline additives with the grain size below 3 mm [2]. After mixing and pre-pelletizing of the mixture, the layer is ignited on the surface, forming combustion and sintering zone (combustion front) which is moving towards the grate as a result of the air flow. As soon as the combustion front reaches the sintering grate, the sinter production process ends [3].The sintered material is discharged from the sinter-ing unit; it is further crushed, sorted, cooled and con-veyed to blast furnace storage containers. The sorting leaves certain part of tiny and dust fraction, which is called return sinter. This return sinter is added to the sintering mixture and re-sintered.The produced sinter is the dominant metal-bearing feedstock into the blast furnace process and as such it fundamentally affects the costs. Higher performance of the ore sintering process can significantly affect the price of the produced metal [4].We can influence the sintering process in terms of its physical, thermal or chemical conditions [5]. One op-tion is to increase the permeability of the charge and to improve the combustion front penetration. This can be done by adding coarse sinter, which is dosed on the sin-tering strands. This article evaluates the results of a re-search conducted by Best Industrial Company, which is engaged in the area of the sintering processes in metal-ISSN 0543-5846METABK 56(1-2) 131-134 (2017)UDC – UDK 669.162.2:669.1:669.051:622.781:669.15=111lurgical enterprises in the Czech Republic. The ana-lyzed data are based on the results of measurements car-ried out during one year in a sintering section for two sintering strands.INCREASING THE SINTERING EFFICIENCYAfter the sintering, the produced sintered material is subsequently crushed, cooled, and sorted. The sorting leaves certain part of tiny and dust fraction, which is called return sinter [6]. This return sinter is added to the sintering mixture and its ratio in the produced sinter should be in the range of 20 – 30 % [7].The higher amount of return sinter reduces the yield and performance of the sintering unit. At the same time, the sintering process can also lead to the formation of sinter of higher grain size (12 – 22 mm), which is called grate sinter [8]. This over-the-limit sinter can be used during the fol-lowing production of the sintering mixture as the bol-stering material, which is dosed on the sintering strands.The method of intensification of the sintering pro-cess is based on increasing the speed of the filtration of air passing through the sintered layer [9]. The sintered layer consists of several zones which have different gas-dynamic properties. The key aspect is to act on those zones that show the highest resistance and to increase their permeability. This can be achieved by means of: suitable mixture moisture, correct thickness of the layer where the air flows, removing the effect of false air in-take and also by reducing the number of technological downtimes.One of the alternative ways to improve the technical and economic parameters of the sintering process is to put the finished sinter with the grain size of 12 - 22 mm into the charge together with return sinter. This coarse material is then dosed on the sintering strands. The in-put sintering mixture intended for sintering is subse-quently dosed on this finished sinter. The coarse pieces 132P. BESTA et al.: THE OPTIMIZATION OF THE PRODUCTION OF SINTER AS THE FEEDSTOCK OF THE BLAST... METALURGIJA 56 (2017) 1-2, 131-134of sinter should improve the gas-dynamic conditions and the mixture combustion rate as well [10].This research has also experimentally verified the impact of the use of grate sinter on the performance of the sintering process. First, a layer of 25 to 30 mm of coarse finished agglomerate was placed on the sintering strands, and the sintering mixture intended for sintering was placed on top of that layer. The research was carried out over the period of one year, during which the performances of the sintering strands and the amount of produced sinter were checked.EXPERIMENTAL PARTThe research has also monitored the impact of coarse sinter dosing on the sintering process. The sintering pro-cess was analyzed for two sintering strands. Grate sinter was used alternatively as the base layer on both of the sintering strands. The performances of both sintering strands were monitored during the monitoring period of time, both with the use of grate sinter and without the use of this base layer during the mixture sintering. Detailed continuous measurements of the performance indicators were carried out for both sintering strands. The composi-tion of the input sintering mixture was continuously monitored in order to carry out an objective evaluation.Table 1 shows the concrete data of its composition for both sintering strands. The data related to feedstock were subsequently converted into a tone of finished sinter.The production with grate sintered and without grate sinter was run on both of the sintering strands. The pro-duction was usually switched after several days. In case of the use of grate sinter, the finished sinter was dosed as the base material on the sintering strands. The sintering mixture was dosed on this material. In case of feedstock, there was a maximum effort to keep the same composition which would allow a clear com-parison of the results and performances. Table 1 illus-trates that the differences in the composition of the feedstock are very little for both sintering strands. In most key raw materials, these differences range within the maximum interval of 1 - 2 %.The key aspects of the research were primarily as-sociated with the established performance and the pro-duced amount of sinter. The output side of the process in terms of immediate performance included the moni-toring of the amount of produced finished sinter, return sinter, the amount of sludge and the total losses. Table 2 shows the established statistically evaluated production indicators with the use of grate sinter and without this base layer. In case of dosing of grate sinter on the sinter-ing strands, we can clearly see a larger amount of pro-duced sinter.In case of using grate sinter (93,96 t/h), the perfor-mance increase is 2,83 % compared to the production without the use of finished sinter (91,30 t/h). There is a simultaneous increasing share of return sinter in the produced material (5,46 %). The experiment with coarse material was performed simultaneously on two sintering strands. The evaluation of the potential benefit was based on the determination of the total volume of produced material.Table 1 Mixture composition for both sintering strandsCharge Sintering strand 1 Sintering strand 2Without grate sinter With grate sinter Without grate sinter With grate sinterkg/t kg/t kg/t kg/tSinter 314,20 358,10 315,10 361,10Fine sinter 118,35 106,40 116,90 108,59Ore concentrate 469,10 474,70 474,29 473,10Slag 43,34 42,10 45,98 40,82Scale 7,80 9,60 7,98 9,06Flue-dust 8,41 6,15 7,32 5,86Sludge 2,10 1,30 2,01 1,21Dolomite 48,50 51,98 47,12 52,98Dolomitic limestone 83,10 80,15 82,81 79,70Limestone 3,58 1,910 3,15 1,71Lime 21,10 22,20 20,83 22,48Fuel 53,20 54,03 54,90 54,20Ore 913,20 910,10 911,20 914,16Wastes 62,30 63,10 64,50 63,70Table 2 Measured production indicatorsProduction performance Without grate sinter With grate sintert/h t/hFinished sinter 91,30 93,96Return sinter 38,90 41,15Sludge in the form of dry residue 4,10 3,50Losses 14,10 12,37∑ 148,4 159,30133P. BESTA et al.: THE OPTIMIZATION OF THE PRODUCTION OF SINTER AS THE FEEDSTOCK OF THE BLAST...METALURGIJA 56 (2017) 1-2, 131-134The evaluation concerned primarily the produced finished sinter and return sinter, which is repeatedly re-turned to the sintering process. Tables 3, 4 show the re-sults for both of the monitored sintering strands. During the monitored period, the first sintering strand produced 23 007 tons more sinter when grate sinter was used. Table 3 Results measured on the first sintering strand Sintering strand 1 Produced sinter Return sintert tWith grate sinter 1 210 987 498 785Without grate sinter 1 187 980 450 917Diff erence 23 007 47 868At the same time, the volume of return sinter in-creased by 47 868 tons. The second sintering strand produced 18 650 tons more sinter when grate sinter was used, while increasing the share of return sinter by 36 389 tons.Table 4 Results measured on the second sintering strand Sintering strand 2 Produced sinter Return sintert tWith grate sinter 1 180 610 485 690Without grate sinter 1 161 960 449 301Diff erence 18 650 36 389RESULTS AND DISCUSSIONSThe main aim of this research was to identify the ef-fect of the presence of grate sinter on the performance of the sintering process. In case of grate sinter dosing on the sintering strand, there was an increase in the perfor-mance of both strands (1,89 % and 1,58 %). At the same time, the volume of return sinter on sintering strand 1 increased by 9,59 % and by 7,49 % on sintering strand 2. The overall evaluation is shown in Figure 1. There was a higher incidence of incomplete sinter-ing of the charge, which ultimately means the formation of smaller fractions with a grain size below 4 mm. This material cannot be used in the blast furnace process and must go through the process of sintering once more. The amount of return sinter is a key factor, because its high ratio during repeated sintering can lead to the re-duction of the ore fraction (FeO). This naturally affects the process efficiency and the technical and economic indicators during the subsequent production of iron. The critical limit for the amount of return sinter in the sintering process is 30 %. Despite the identified in-crease in the amount of return sinter in both sintering strands, it cannot be considered as a negative fact, be-cause its ratio during the measurement varied in the in-terval of 18 - 23 %. These values  can be regarded as adequate from the technological point of view. The use of grate sinter can therefore be seen as positive from this point of view as well.The secondary consequence of the use of grate sinter can be identified in relation to a decrease in the amount of sludge. This is mainly due to the fact that the feed-stock into the sintering process using grate sinter is transformed into the finished or return sinter to a higher extent, while sludge dry residues are formed to a lesser extent. In case of production of sinter without the use of grate sinter, the production of sludge dry residues was 4,1 tons per hour. When grate sinter was used, the pro-duction of these sludge dry residues was reduced to 3,5 tons per hour. The overall production of this ballast component was therefore decreased by 14,63 %. This is a fundamental aspect from the long term point of view. The dosing of grate sinter therefore clearly contributes to the transition of feedstock into the finished and return sinter.CONCLUSIONSThe conducted research and the measured values show that grate sinter has a crucial effect on the perfor-mance of the sintering process. Coarse bedding layer was used as the base layer below the sintering mixture on the sintering strands during the research.The use of grate sinter has lead to an increase in the production volume of finished sinter per hour, as well as to a significant increase in the total production volume during the monitored period. This fact confirms an im-provement in the permeability of the mixture leading to an increased intensification of the sintering process. The dosing of coarse bedding layer improves the per-formance of the sintering unit, but also the production of return sinter, which is returned back into the sintering process. The amount of return sinter, however, corre-sponds to the technological requirements and does not increase the costs resulting from the re-entry of the raw materials back into the process.There has been an increase in the amount of pro-duced sinter on both sintering strands by 41 657 tons, which represents a relatively large increase; although it is actually a difference of only between 1 - 2 % of the total volume of sinter produced on both sintering strands. However, when we take into consideration the required amount of sinter for the blast furnace process in one year, even this increase in performance is impor-tant. In case of long-term use of grate sinter in the pro-Figure 1  Evaluation of the difference in the production of sinter134P. BESTA et al.: THE OPTIMIZATION OF THE PRODUCTION OF SINTER AS THE FEEDSTOCK OF THE BLAST... METALURGIJA 56 (2017) 1-2, 131-134duction of sinter, it is possible to gain a fundamental competitive advantage. This can be seen as an essential aspect with regards to the ever increasing pressures on the price of the produced metal.AcknowledgementThe work was supported by the specific university research of Ministry of Education, Youth and Sports of the Czech Republic No. SP2016/107.REFERENCES[1] M. Shamsuddin, Physical Chemistry of Metallurgical Pro-cesses, John Wiley & Sons, 2016, 340-341. [2] R. E. Smallman, A. H. W. Ngan, Physical Metallurgy and Advanced Materials, Butterworth-Heinemann, 2011, 99-101.[3] R. Yin, Metallurgical Process Engineering, Springer Scien-ce & Business Media, 2011, 268-269.[4] S. Seetharaman, Treatise on Process Metallurgy Newnes, 2013, 311-312.[5] J. J. Moore, Chemical Metallurgy, Elsevier, 2013, 174-175. [6] F. Ibbotson, The chemical analysis of Steel-Works Mate-rials, Hardprees 2012, 301-302.[7] C. Vliet, Modern Blast Furnace Ironmaking, IOS Pres, 2011, 148-149.[8] R. E. Smallman, A. H. W. Ngan, Modern Physical Metal-lurgy, Butterworth-Heinemann, 2013, 601-602.[9] A. Vignes, Extractive Metallurgy 1: Basic Thermodyna-mics and Kinetics, John Wiley & Sohn, 2013, 314.[10] B. Zhou, H. Ye, H. Zhang, M. Li, Process monitoring of iron-making process in a blast furnace with PCA-based methods, Control engineering practice 1 (2016) 1-14. DOI: 10.1016/j.conengprac.2015.11.006.Note:  The responsible translator for English language is Petr Jaroš (English Language Tutor at the College of Tourism and Foreign Trade, Goodwill - VOŠ, Frýdek-Místek, the Czech Republic). Revised by John Vlcek (Literacy Tutor at West Suffolk College, Bury St Edmunds, England)

The optimization of the production of sinter as the feedstock of the blast furnace process

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The optimization of the production of sinter as the feedstock of the blast furnace process

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