This work is designed to arrive at a slag composition through the present experiments which will ensure the reduction of the cohesive zone of the blast furnace with the simultaneous reduction of the difference between the softening temperature (ST) and the flow temperature (FT) of the slag. The composition of the slag must be controlled or else it may affect the quality of the products. As the charge descends down the furnace, the quality of the iron obtained depends on the formation of slag and its transformations.
The cohesive zone in the blast furnace would be lower if there is a high softening and melting temperature of the iron bearing materials. This is done by crushing and grinding the coal and then loading it into the furnace. The cooking of coal is done in a furnace and the volatile matter is removed and the product obtained is called coke.
The reduction of iron ore, pellet and sinter takes place in the sinter by a series of chemical reactions. The above reactions are simultaneously followed by the softening and melting of iron, which eventually seeps down as the liquid iron through the layers of coke present at the bottom of the blast furnace.
BLAST FURNACE REACTIONS
REACTIONS IN THE UPPER ZONE
It is also possible for carbon monoxide to reduce steam in the upper zone of the furnace.
REACTIONS IN THE MIDDLE ZONE
REACTIONS IN THE LOWER ZONE
DIFFENT ZONES OF BLAST FURNACE
COHESIVE ZONE
- GAS PERMEABILITY
- EXTENT OF INDIRECT REDUCTION
- Si CONTENT OF PIG IRON
The region of softening and melting of the filler materials is referred to as the cohesive zone. The performance and efficiency of the blast furnace is determined by the two factors which are position and thickness of the cohesive zone. Cohesive zone consists of alternate impermeable, semi-fluid layers that resist the flow of rising gases.
The wind volume is related to the viscosity, the length of the coke gap and the band volume of the melt. And by lowering the continuous zone, the coke consumption for 1 ton of pig iron is greatly reduced. By lowering the location of the cohesive zone in the blast furnace, the Si content of the pig iron is reduced, as silicon oxide has less chance to reduce.
BLAST FURNACE SLAG
- ORIGIN
- BLAST FURNACE SLAG STRUCTURE
- SLAG COMPOSITION
- SLAG VISCOSITY
- FLOW CHARACTERISTICS OF SLAG
- INITIAL DEFORMATION TEMPERATURE (IDT)
- SOFTENING TEMPERATURE (ST)
- HEMISPHERICAL TEMPERATURE (HT)
- FLOW TEMPERATURE (FT)
Crystal structure analysis of solid silica shows that the silicon ion is located in the center of a tetrahedron, which is bounded by four oxygen atoms, one at each corner. Symmetry is obtained in the structure of the tetrahedral arrangement of the silicon and oxygen atoms. In the molten state, the deformed structure is observed, but almost all corners are shared.
The attraction between silicon and oxygen is the driving force for breaking down the silicon-oxygen network, which depends on their valencies and ionic radii. Blast furnace slag must be essentially homogeneous liquid at the operating temperatures to be most efficient and practical. It must also have enough fluidity to allow it to run unconditionally from the hearth without any loss of manufacturing time.
The quality of hot metal is greatly influenced by the development of slag and the mineralogical conversion that the slag undergoes during the descent of the load inside the furnace. Viscosity of the slag is increased by the presence of components such as silica and alumina, while calcium oxide reduces it. The cohesive zone is determined by the melting zone, therefore the melting and flow properties of slag play a very important role in the blast furnace productivity.
Silica and alumina from the ash generated by the combustion of coke are assimilated as the slag trickles through the blast furnace. Because the reduction of iron ore and also the formation of slag takes place in the blast furnace, the basicity and FeO percentage in the slag often change compared to the initial composition of the sintered ore. The main causes of the slag formation problem are the relatively high C/S ratio of the slag in the bosh areas.
When the sample has melted to hemispherical shape, the temperature responsible for the above change is referred to as HT.
LITERATURE STUDY
B.Ozturk and R.J.Fruehan: “The Reaction of SiO (g) with liquid slags”
Results based on the rates obtained from the slag-metal reaction show that the rate of silicon transfer is too low to obtain the actual silicon content in the blast furnace. The SiO-generated travels in the blast furnace react with carbon-saturated iron droplets and also with slag droplets. The kinetics of the reaction between SiO(g) and carbon dissolved in iron is controlled by mass transfer in the gas phase.
The viscous behavior of blast furnace slag plays an equally important role in influencing efficiency, as the flow nature of molten slag has a major influence on heat transfer, gas permeability, SiO2 and FeO reduction. Repolymerization of a silicate network, in which the silicate structure changes from 30 to discrete anionic groups containing simple chains, resulting in a decrease in basicity. Paulo Nogueira, Richard Fruehen: “Blast Furnace Load Softening and Melting Phenomena” – Part I Observation of Pellet Bulk Interactions, Metallurgical and.
Paulo Nogueira, Richard Fruehen: “Blast Furnace Burden Softening and Melting Phenomena”- Part I Pellet Bulk Interaction Observation, Metallurgical and
The softening and melting temperature from the displacement versus temperature curves were close enough for both pellets reduced to 80.
P.F.Noguira and R.J Fruehen: “Blast Furnace Softening and Melting Phenomenon”
EXPERIMENTAL DETAILS
- EXPERIMENTAL PROCEDURE
- EXPERIMENTAL APPARATUS .1 HEATING MICROSCOPE
- PLANETARY BALL MILL
- EXPERIMENTAL RESULTS AND DISCUSSION .1 FLOW CHARACTERISTICS MEASUREMENT
- RESULT
- XRD AND MICROSCOPIC ANALYSIS
- PHASE DIAGRAM STUDY
The samples are placed in one of the dirty and numerous balls are added as indicated. The bowls are independent of the rotatable platform and the direction of rotation of the bowls is opposite to the direction of the rotatable platform. The movement resembles the teacup and saucer as seen in some of the theme parks.
Due to the alternating addition and subtraction of the centrifugal forces, the grinding balls roll halfway into the repulsive and then thrown over the repulsive walls and then collide with the opposite walls. As with any grinding method, contamination of the sample with the grinding medium is a problem. The chemical composition of the synthetic slags is determined approximately that of the slags obtained from the industry, as far as the main oxides are concerned.
The MgO content is kept at 10% in all these cases because it is reported that a high MgO content is not favorable from the point of view of the viscosity of the blast furnace slag [22]. This would increase the size of the granular zone with the possibility of a simultaneous increase in the degree of indirect reduction in the furnace, resulting in energy savings. Furthermore, the small difference between FT and HT will result in improved mobility of the slag and provide better separation between slag and metal.
These facts should be kept in mind while determining the constituents of the slag for better results in terms of energy saving, smooth operation and quality of pig iron. This aspect needs to be further investigated, taking into account that the industrial slags also contain minor components that are not taken into account in the case of the synthetic slags prepared in the laboratory. Similarly, in industrial slag, the best results are obtained at the lowest MgO content (10.4%) of the slag.
To know the chemical properties of the minor phases present in the slag, XRD analysis was carried out. The traces found may not be the actual cause for the variation in the result, but are the cause for the variation in the melting point. Since the cause of the lowering of the difference between the HT and FT cannot be known until and unless the main compound responsible for this is found, further investigation must be done before reaching a conclusion.
CONCLUSION
CONCLUSION
With our result obtained from our work, we conclude that with an appropriate choice of raw materials, desired slag can be obtained which leads to lower coke consumption and gives a greater control over metal composition through control of slag-metal reaction. The flow characteristics obtained after the experiment and concluded that addition of MgO content around 9.80 % is beneficial for a thin cohesive zone along the blast furnace. The result of the XRD analysis showed the presence of some large and small oxides.
The data obtained was used to draw the corresponding phase diagram and the phase diagram gave the idea of the slag composition that can be used in reducing the cohesive zone. The future perspective of the project is to use the provided data and change the composition in the slag to decrease the cohesive zone. This can be done by preparing synthetic slags of different compositions and weight percentages and then studying their flow characteristics.
The properties obtained should be compared with slag from various Indian steel mills. From the data obtained, the related phase diagram must be deduced and then used to reduce the difference between HT and FT and thus determine the characteristics for the narrow cohesive zone.
REFRENCES
Viscous behavior of CaO-SiO2-Al2O3-MgO-FeO slag”: VII International Conference on Molten Slag Fluxes and Salts, The South African Institute of Mining and Metallurgy, 2004. Slag on the Blast Furnace Operations”, ISIJ International, Vol. 14) Li ZHANG, Linnan ZHANG, Mingyu WANG, Guangqiang and Zhitong; "Dynamic oxidation of the Ti-bearing blast furnace slag", ISIJ International, Vol. Sorbents for flue gas desulphurisation”, Ind. 18) Kiichi NARITA, Shin-ichi INABA, Masakata SHIMIZU, Arata YAMAGUCHI, Isao KOBAYASHI and Ken-ichi OKIMOTO; "Burden and Gas Distribution Considering Blast Furnace Aerodynamics", ISIJ Journal, Vol.21, No.6(1981)pp.405-413.
A Blast Furnace Model to Optimize the Burden Distribution”, http://www.crm-eur.com/F- PUBLICATIONS/media/BF_MODEL.pdf, retrieved at 04:05:10. Proceedings of VIII international conference on molten slag, fluids and salts, The South African Institute of Mining and Metallurgy, 2004, p.225.
