THE EFFECT OF QUALITY OF FERROUS BURDEN MATERIALS ON THE QUALITY OF PIG IRON

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1 THE EFFECT OF QUALITY OF FERROUS BURDEN MATERIALS ON THE QUALITY OF PIG IRON Edyta KARDAS Czestochowa University of Technology, Abstract: To produce goods of sufficient quality and at the lowest possible cost is the main goal of each production process. In case of production of blast furnace pig iron, the quality can be defined as the chemical composition and temperature on accordance with relevant customer s requirements and standards. The important factor to the quality of this product is that these parameters should be kept on constant level, which is one of basic requirements of blast furnace receiver, steelmaking plant. The quality of pig iron can be affected by many factors, among which should be mentioned theses associated with: quality of ferrous burden materials, quality of coke and alternative fuels used in blast furnace process, methods of blast furnace working. The topic of this paper was part of the research related to the problem of the effect of production factors on the quality of pig iron. The analysis of the quality of ferrous burden materials and its effect on the quality of the finished product, pig iron will be presented in this paper. The research was done in collaboration with one of Polish blast furnace divisions and was based on the results coming from the industrial plant. Keywords: Pig iron, blast furnace, burden materials, quality 1. INTRODUCTION The chemical composition is the primary qualitative factor of pig iron, specifying its class and meets the requirements set by the steelplant. The important thing is that the chemical composition of pig iron was as stable as possible. In addition, pig iron temperature is very important parameter of the quality, it is a fundamental property important for steelworkers. Many factors have the influence on the temperature of pig iron e.g.: the size of the blast furnace, since the higher volume of the blast furnace, the higher temperature of pig iron; charge quality, fuel quality, temperature of blast and its humidity [1]. Besides the basic element, iron, pig iron also contains other various alloying elements. The general quality requirements of pig iron (on the individual alloying elements) are shown in Tab. 1. Table 1 General requirements for the content of individual alloying elements in the pig iron [2, 3] Element Content, % Si Mn >0.20 S <0.030 P <0.11 for the production of rail steel 0.14 for other kind of steel The quality of pig iron is influenced by many various factors, which can be divided into three basic groups: - The quality of ferrous burden materials, - The quality of coke and alternative fuels, - Parameters of blast furnace process.

2 Ferrous materials are the basic raw materials used in blast furnace process [4]. They are the primary source of iron, which is the main component of pig iron. The statement of iron rich, well prepared, in terms of chemical and physical characteristics, burden materials determines achieving the optimum values of technical and economic indexes, allows the uniform working of blast furnace [5] and to obtain a product with appropriate quality. In the blast furnace process, besides iron ores and their concentrates, a variety of waste materials are used, which significantly affects the economic results of this process [4]. It is possible, because the fact that metallurgical waste materials often contains more iron than iron ores used in process [6]. Determining the quality of ferrous burden materials used in blast furnace process, the following properties should be evaluated [7]: - The chemical composition of material, - Physical properties, - Metallurgical properties. In this paper, the analysis of chosen qualitative properties of ferrous burden materials, their chemical composition, is made. The research are done with collaboration with one of Polish Blast Furnace Division and are based on the results coming from the industrial plants. The analysis includes monthly results of 8 consecutive calendar years 2. CHARACTERISTICS AND QUANLITATIVE ANALYSIS OF FERROUS BURDEN MATERIALS USED IN BLAST FURNACE PROCESS IN EXAMINED STEELPLANT In Blast Furnace Department under study, following groups of ferrous burden materials are used: - Sinters, - Pellets, - Rich iron ores, - Converter slags, - Iron ores concentrates. Ferrous sinter, which is product of sintering process of fine ferrous materials, is the main component of ferrous blast furnace burden materials in Steelwork under study [8]. It is prepared from a mixture of fine iron ores, concentrates and wastes from metallurgical processes [9]. In conditions of studied Steelwork it is used in amount of over 80% of total ferrous burden materials [2]. Pellets, which are produced in process of agglomeration of fine concentrates of iron ores by burning or chemical reactions, are the second group of ferrous materials used in blast furnace process. Additionally, as ferrous burden materials directly used in blast furnace process, ferrous concentrates can be used. As a part of blast furnace burden materials the furnace additives of converter slags, which is waste from steelmaking process, are also used. It is burden addition, containing useful component as phosphorous and manganese, which increases the amount of these elements in pig iron [10 12]. The quantitative analysis of ferrous burden materials consumption was done. The results of this analysis ape presented in Tab. 2. In the analyzed blast furnace department many types of materials are used, however in the paper only 7 types were taken into consideration, because only these types were used during study period. Based on the results presented in Tab. 2. it can be concluded that to produce 1 Mg of pig iron in examined process almost 1650 kg of various ferrous burden materials are used on the average during study period. Sinter, which is produced in examined steelpant, is the basic material. It was more than 92% of ferrous burden materials in total used in this process. Other materials was used only in small amount, their average percentage was less than 8% of ferrous burden materials in total. It means that quality of sinter have the greatest importance for the quality of the finished products, pig iron. However, it should be noted that some materials (e.g. converter slags) are used in process to change the amount of certain elements in pig iron.

3 Table 2 The structure of consumption of ferrous burden materials used in blast furnace process in study period Component Percentage in total ferrous burden materials, % Sinter Poltawskie Pellets 5.03 Michajlowskie Pellets 0.78 Liebiedenskie Pellets 0.46 J-GOK agglomerates 0.10 Converter slags 1.10 Ferrous Concentrate 0.35 The average unit consumption ferrous burden materials, kg/1 Mg pig iron The analysis of chemical composition of ferrous burden materials used in analyzed blast furnace department ware made. The analysis of changes of individual compounds in all ferrous burden materials in study period was made. Table 3 shows the content of individual compounds in ferrous burden materials in study period. Table 3 Content of elements in ferrous burden materials during study period Elements and compounds in ferrous burden materials H 2 O, % Fe, % FeO, % SiO 2, % CaO, % MgO, % Al 2 O 3, % Mn, % P 2 O 5, % Na 2 O, % K 2 O, % Zn, % S, % C, % Based on the results presented in Tab. 3 it can be concluded that: - The moisture content varied in range %. The highest value was recorded in the second and the last months, the lowest in the sixth month. - The iron content during first four month was lower than 57.5%, while in subsequent period of time content of this element increased and was at the level of 58 59%. - In case of the iron oxide content any trend of changes was not observed, but its quantity was varied and ranged from 5 to 6.2%. - The content of silicon oxide in ferrous burden materials during study period systematically decreased. In the first month it was on level of 7%, in the last approximately 5.74%. - Similar trend was observed for calcium oxide. The content of this component decreased from 9.4% in the first month to 7.8% in the last month. - No trend in content was observed for magnesium oxide, it also underwent only minor fluctuations in range %. - The content of aluminium oxide on the beginning of study period was slightly lower than in the remaining period and was at the level 0.7%. In remaining months the content ranged from %.

4 - During study period significant increase of the magnesium content was observed (form 0.15 to 0.28%). Only in the last month the decrease of this element content to 0.22% was noted. - The content of phosphorus oxide underwent very slight fluctuations in range %. No trend in changes of content of this element was observed. - The content of sodium content was characterized only by periodic changes, during some period of time it was on constant level: during first three months it was on the level of ca. 0.07%, during next three months 0.06%, during last two months 0.08%. - The content of potassium oxide fluctuated within %. Only in the last month was much higher and it was at the level of 0.055%. - The zinc content in ferrous burden materials slightly decreased during study period from to 0.033%. Low content of this element was also observed in the third month at the level of 0.032%. - For the content of sulfur in the first three months significant decrease was observed (from to 0.010%), in the following the content slightly increase up to 0.017%. - The dawn ward trend of the carbon content was observed. The content decreased from 0.2 to 0.2%. - The content of major element on ferrous burden materials, iron, is the most important for main product of blast furnace process. The quantity and quality of pig iron and the quantity of by-products (eg. slag) depend on the content of this element. The content of such elements as: silicon, manganese, sulfur and phosphorus, also have a great importance for quality of pig iron, because the content of these element in pig iron depends from their content in the ferrous burden materials. 3. THE QUALITY ANALYSIS OF PIG IRON PRODUCED IN ANALYSED STEELPANT The analysis of selected quantitative parameters of pig iron was made. Chemical composition is the basic parameter. It shows content of the elements, such as: iron, silicon, manganese, sulfur, phosphorus and carbon. Also temperature of product was analyzed. The average value of pig iron parameters during study period, standard deviation, the highest and the lowest value of content of these elements were presented in Tab. 4. Cpk indexes was also calculated for three elements. Table 4 Analysis of chemical composition of pig iron in each month of study period Elements, % Fe Si Mn S P C Temperature, o C Average Standard deviation Coefficient of variation, % Minimum Maksimum Cpk Based on the results of analysis presented in Tab. 4 it can be concluded that: - During study period average iron content was approximately on the level of 94.4%, while content of the other elements respectively: silicon 0.4%, manganese 0.28%, sulfur 0.016, phosphorus 0.093% and carbon 4.7%. - The content of three elements was characterized by considerable variability: Mn 18.9%, P 14%, S 12.5% compared to the average. - Comparing the chemical composition of pig iron with the requirements of the standards it can be said that these requirements were maintained, limits of were not exceeded. - Cpk index values obtained for Mn (0.51) and P (0.43) reached very low values. It means that content of these elements were very variable, what may contribute to exceed the limit. In case of S high value of Cpk index was obtained (2.45), Despite wide variation, Cpk index indicates very low probability of exceeding the limit.

5 4. EFFECT OF QUALITY OF FERROUS BURDEN MATERIALS ON THE QUALITY OF PIG IRON IN ANALYSED STEELPANT The value of quantitative indicators of ferrous burden materials (their chemical composition) has an influence on the chemical composition of finished pig iron. Chemical compounds, which are contained in burden materials, go to products of blast furnace process, including basic product, pig iron. The analysis of influence of content of individual elements in ferrous burden materials on the content of these elements in pig iron was made. The correlation coefficient for these parameters was used in this analysis. The results of this analysis are presented in Tab. 5. The analysis includes these elements which were taken into account in the quality analysis of pig iron. Since in each month the volume of pig iron production and consumption of burden materials ware different, in order to determine accurately the dependences of factors, they were calculated with the total amount of element in burden materials and pig iron. Table 5 The effect of chosen qualitative parameters of ferrous burden materials on the quality of pig iron Factors of analysis Correlation coefficient Regression model The effect of amount of Fe and FeO in ferrous 0.99 burden materials on amount of Fe in pig iron ˆ y 0.93 X Fe 0.09 X FeO The effect of amount of SiO2 in ferrous burden materials on amount of Si in pig iron The effect of amount of Mn in ferrous burden materials on amount of Mn in pig iron The effect of amount of S in ferrous burden materials on amount of S in pig iron The effect of amount of P 2 O 5 in ferrous burden materials on amount of P in pig iron The effect of amount of C in ferrous burden materials on amount of C in pig iron 0.49 ˆ y 0.018X ˆ y 0.819X Based on the results of analysis presented in Tab. 5 it can be concluded that: - The more content of iron compounds in ferrous burden materials, the more content of this element in pig iron. Regression analysis indicates that that changes in Fe content in pig iron are caused mainly by Fe and FeO content in burden materials. On the basis of created regression model it can be said that changes in Fe content in burden materials at level of 1 g indicates the increase in Fe content in pig iron at the level of 0,93 g, while in case of FeO the increase of 0,09 g. It should be noted that the content of this element in ferrous burden materials also effects blast furnace process parameters: reduces the unit amount of slag and other wastes per tonne of pig iron (r=-0.97) and lower unit fuel consumption per tonne of pig iron (r = -0.95). - There is significant dependence between the content of SiO 2 in ferrous burden materials and the Si content in pig iron. However, it should be noted that content of this element in pig iron also depends on the content of Si in fuels supplied to the blast furnace process. Regression analysis showed that in constructed model other factors affecting Si content in pig iron (such as temperature) should have been taken into account. These factors, however, were not included in previous analysis. It is suggested, therefore, further studies to detects other factors which should be included in the model. - The more Mn content in ferrous burden materials, the more Mn content in pig iron. In this case, it should be noted that manganese to the process is supplied with converter slag, which is used in process just to increase of Mn content in pig iron. Regression analysis indicates that changes in Mn content in pig iron is affected, in addition to content of this element in burden materials, by many other factors (e.g. Content of this element in the fuels). On the basis of created regression model than in study case the increase of Mn content in burden materials at level of 1g caused the increase of Mn content in pig iron at the level of 0,819g. Si Mn

6 - During study period there was no functional dependence between sulfur content in ferrous burden materials and pig iron. This probably was due to the fact that S content in ferrous burden materials was very low, while high S content in fuels was recorded ( %), what had significant effect on the content of this element in the product. - There is significant effect of P 2 O 5 content in ferrous burden materials on P content in pig iron. However, in this case, as in case of silicon, content of this element depends also on phosphorus content in fuels. - Effect of C content in ferrous burden materials on C content in pig iron was not specified. This is due to the fact that carbon content in burden materials is very low, the majority of carbon included in pig iron passes from fuels supplied to the process. 5. CONCLUSION The quality of pig iron is influenced by many different factors, which can be divided into three main groups: quality of ferrous burden materials, quality of coke and alternative fuels, parameters of blast furnace process. This paper presents preliminary analysis of pig iron quality, ferrous burden materials quality and the effect of these materials quality on pig iron quality. This analysis includes only chemical composition of these materials, which does not represent all quality parameters of these materials, which can affect on pig iron quality. For this reason, it is difficult to build a model, which can describe such relations. Therefore, it can be suggested that further studies to complete this analysis should be one. LITERATURA: [1] SABELA W., BRZEZIŃSKI P., BUZEK J., Factors affecting on the cost of obtianing metallic iron, Metallurgy Metal Engineering, vol. 10/2005, pp [2] Technological instruction of blast furnace process. Internal print (unpublished) [3] PN EN 10001:1996: Pig iron definition and classification, Polish Committee of Standardization, [4] NIESLER M.: The central charge of coke as a method of improving the operation of blast furnaces, from Conference Proceedings : Management and Production in Metallurgy, Ustroń Jaszowiec 2004, Czestochowa Univeristy of technology, pp [5] NIESLER M.: The research on the influence of coke grain in the blend used with ferrous burden materials on the run of the reduction of blast furnace charge, Institute of Ferrous Metallurgy Works, vol. 2/2003, pp [6] RZESZOWSKI M., ZIELIŃSKI K., CHACHLOWSKI A, MOSTOWIK W.: Methods for recovery of iron from metallurgical slags and possibility of their use, Metallurgy Metal Engineering, vol. 1/2004, pp [7] MRÓZ J.: Methods for testing the properties of ferrous burden materials used in blast furnace process, Metallurgy Metal Engineering, vol. 2/2004, pp [8] NIESLER M.: Rationalization ot waste management in blast furnace department, Institute of Ferrous Metallurgy Works, vol. 3/2001, pp [9] FRANCIK P., BEDNARSKI W.: Zinc in blast furnace process and the reduction of sludge and dust, from Conference Proceedings : Management and Production in Metallurgy, Ustroń Jaszowiec 2004, Czestochowa Univeristy of technology, pp [10] SABELA W, KONSTANCIAK A: Waste in ferrous metallurgy and their use, Metallurgy Metal Engineering, vol. 12/1999, pp [11] KONSTANCIAK A.: Waste management in iron metallurgy, from Conference Proceedings: Recycling of metal waste, Ostrava 2006, VSB Technicka Univerzita Ostrava, pp [12] SVJAŻIN A.: Recycling of slags in iron metallurgy, Metallurgy Metal Engineering, vol. 2/1996, pp