Vol 7 No 3 APRIL 2013Gokarn et al Agglomeration of Ferro Alloy Fines for Use in Bulk Steel Making Process Page 1 of 10
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Agglomeration of Ferroalloy Fines for use in Bulk Steelmaking Processes

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International Paper Published in STEEL TECH (ISSN 0976-4232) Vol:7 No:3 in April 2013

Ferroalloys are added as deoxidizing agents and additives to increase strength, elasticity and abrasion & corrosion resistance of steel. The preferred size of ferroalloy lumps for steel making is 10mm – 80 mm to optimize the operational efficiency. Ferroalloy lumps are produced by manual breaking of casted alloy cakes which generates 5-10% fines which cannot be used in bulk steel making process (like the commonly used LD process) because of handing and operational difficulties. Therefore, we at Tata Steel developed an agglomeration process for ferroalloy fines and used the briquettes thus produced for making steel. The developed process described in the paper is an economic, environment friendly and efficient way to utilize the ferroalloy fines in steel making.

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Agglomeration of Ferroalloy Fines for use in Bulk Steelmaking Processes

  1. 1. Vol 7 No 3 APRIL 2013Gokarn et al Agglomeration of Ferro Alloy Fines for Use in Bulk Steel Making Process Page 1 of 10
  2. 2. Vol 7 No 3 APRIL 2013Gokarn et al Agglomeration of Ferro Alloy Fines for Use in Bulk Steel Making Process Page 2 of 10Agglomeration of Ferro Alloy Fines for Use in Bulk Steel Making ProcessAuthorsPrabhash Gokarn*, Veerendra Singh, A Kumar, B D Nanda & A Bhattcharjee, Tata Steel Ltd., India.(*corresponding author - prabhash@tatasteel.com)AbstractFerroalloys are added as deoxidizing agents and additives to increase strength, elasticity and abrasion& corrosion resistance of steel. The preferred size of ferroalloy lumps for steel making is 10mm – 80mm to optimize the operational efficiency. Ferroalloy lumps are produced by manual breaking ofcasted alloy cakes which generates 5-10% fines which cannot be used in bulk steel making process(like the commonly used LD process) because of handing and operational difficulties. Therefore, we atTata Steel developed an agglomeration process for ferroalloy fines and used the briquettes thusproduced for making steel. The developed process described in the paper is an economic, environmentfriendly and efficient way to utilize the ferroalloy fines in steel making.1. IntroductionFerroalloys are used in Steel Making as deoxidizing agents and additives to increase mechanicalproperties (strength, toughness, wear resistance, springiness), high temperature properties(creepstrength, hardness), electrical properties or corrosion resistance.Most bulk ferroalloys - like FeMn, SiMn, FeSi and FeCr manufactured by carbo-thermic reduction ofores in submerged arc furnaces. Noble ferroalloys like FeMo, FeV, FeTi etc. manufactured throughthe Alumino-Thermic process. In both cases, the ferroalloy is produced in form of liquid metal.The liquid metal is cast into cakes and crushed into ~10mm to ~60mm size lumps, with co-generation of fines during sizing.The fines generated during the sizing of metal cake cannot be used in the bulk steel makingprocesses like the BOF(LD) process, as these fines get oxidized quickly and this reduces the overallrecovery during steel making [1-2]. Though, ferroalloy fines in the size range of 3 to 20mm havebetter dissolution characteristics, the higher surface area (due to small size) also transportsundesirable gases and moisture into the furnace. Small alloy size also increases dust losses andleads to handling difficulties [3-6].Agglomeration into lumps is the best method to utilize these fines. Binder composition and physicalstrength of the agglomerate are two main constraints to develop a cost effective method. Variousattempts have been made in the past to agglomerate these fines using conventional binders likemolasses, tar, resin, etc [6-10], which failed due to a variety of reasons and could not be adoptedcommercially.A briquetting process has been developed in this study to utilize ferroalloy fines of manganesealloys (ferro-manganese and silico-manganese) in the steel making process. The briquettesproduced by the patented process developed was tested in the laboratory as well as incommercially in the LD shops of Tata Steel.2. Lab Scale Studies2.1. Characterization of Fines: Samples of ferroalloy fines were collected from Ferro Alloy Plantsbeing operated by Tata Steel (viz FeMn at Joda, FeCr at Cuttack and SiMn under tolling atDurgapur). These were classified into three different size ranges (>10mm; -10+3mm; -3mm). Fiveimportant constituents (Mn/Cr, Si C, S, and P) were analyzed using ICP-OES (Spectro-AnalyticalInstruments; Ciros) to find the chemical composition of the prepared agglomerate. Particle shape
  3. 3. Vol 7 No 3 APRIL 2013Gokarn et al Agglomeration of Ferro Alloy Fines for Use in Bulk Steel Making Process Page 3 of 10and surface characteristics were also analyzed using scanning by electron microscope to study theagglomeration behavior of fines.2.2 Briquetting of Fines: Selection of binder for alloy fines determines the strength of briquettesand thus is most important. The binders should not add any unwanted ingredient like sulphur,phosphorus, nitrogen etc. in the steel, and it should be cost effective. Molasses and otherconventional organic binders were rejected because these binders contain sulphur and phosphorus.Sodium silicate, Bentonite, Acrylic resins and Phenolic resins were tried as binders and tested, andthe results are given in Table-1. The experimental work plan is described in Table 1 and Fig. 1.Ferroalloy fines were mixed thoroughly with the binder in a muller mixer. Sixty to seventy grams ofthe mixture was compacted in a cylindrical die of diameter 3cm at different loads and the greencompact was cured at different temperatures (100˚ and 150˚ C) for one hour. Briquette density,compressive strength, tumbling index, abrasion index, shatter index and dissolution characteristicswere studied.Binder % Load (ton) Curing ConditionSodium Silicate 5, 7.5 & 10 1 & 5 100 C, 1 hourSodium Silicate+ Bentonite 5+2, 7.5+2 & 10+2 1 100 C, 1 hourAcrylic Resin 5, 8 & 10 1 & 3 100 C, 1 hourPhenol formaldehyde Resin 5, 8 & 10 1 & 5 100 & 150 C, 1 hourTable-1: Briquetting conditionsFigure-1: Process Methodology for Binder Selection2.3. Smelting of Briquettes: Twenty kilograms of steel scrap was melted in a 25 kg inductionfurnace and 5 kg of ferro manganese (FeMn) lumps were added. Experiments were repeated forFeMn fines and FeMn briquettes under the same test conditions for comparison. The mixingbehavior of the materials was observed. Slag and metal samples were collected and the manganeserecovery was calculated. Figure-2 shows the lab scale setup to test the dissolution behavior oflumps, fines and briquettes. Similar trials were conducted for SiMn and FeCr fines, for reasons ofspace and clarity trials with FeMn fines have been described in detail in this paper.Sample Preparation(0-3mm) FeMn fine)MixingPressing(1-5ton)Curing(100 & 150° C, 60 minutes)Compressive strength TestBinder
  4. 4. Vol 7 No 3 APRIL 2013Gokarn et al Agglomeration of Ferro Alloy Fines for Use in Bulk Steel Making Process Page 4 of 10(a) (b) (c)Figure-2: Lab Scale trials in Induction furnace (a) Induction furnace (25kg) (b) Melting of scrap (c) Samplecollection before and after the addition3. Results and Discussions3.1 Characterization Studies: Chemical analysis of various size fractions is given in Table-2.Despite the slightly lower percentage of silicon (Si) and manganese (Mn) in fines compared tolumps, fines are suitable for use in steel making. Size analysis of the samples of ferro manganesefines (0-10mm) was carried out and it was found that ~70 % fines are of 0 to 3mm size (fines) and30 % are of 3 to 10mm size (chips). Particle size and shape analysis is shown in Figure-3 and 4.Finer particle sizes are preferred for briquetting, but presence of significant amount of very angularparticles makes the agglomeration process more challenging. Very angular particles enhance themechanical interlocking but require high pressure compaction.Size Range % C Mn S P Si>10mm 93 6 >68 0.01 0.193 0.54-10, +3mm 2 6.75 66.30 0.01 0.175 1.72<3mm 5 6.7 65.90 0.01 0.188 1.33Table-2: Size and Size wise chemical analysis of Ferromanganese fines0.0 0.5 1.0 1.5 2.0 2.5 3.0020406080100Comm.Pass%,PassedParticle Size (mm)Figure-3: Particle Size Analysis
  5. 5. Vol 7 No 3 APRIL 2013Gokarn et al Agglomeration of Ferro Alloy Fines for Use in Bulk Steel Making Process Page 5 of 10Figure-4: Particle Shape AnalysisSEM analysis shown in Figure 5 reveals that these fines are not oxidized. Some small slag inclusionswere also seen in the briquetted samples.Figure-5: SEM micrograph of Lumps (Pt1-High carbon Phase, Pt2-Low Carbon Phase) and Briquettes (Pt1-High carbon Phase, Pt2- Slag particle)Pt-1Pt-2Pt-1Pt-2
  6. 6. Vol 7 No 3 APRIL 2013Gokarn et al Agglomeration of Ferro Alloy Fines for Use in Bulk Steel Making Process Page 6 of 103.2 Briquetting Studies: Metallic fines show a different binding behavior compared toconventional ore particles. Figure 6 shows surface of manganese ore and ferro manganese metalparticles. The ore particles usually contain small cracks and cleavages which play important role inbinder absorption and binding of the particles.Figure-6: Surface Roughness of Mn ore and FeMn Metal ParticleThree different combination of sodium silicate were tried and it was found that theprepared agglomerate does not attain the suitable compressive strength and it varies between 90and 240 kgf/sample. The strength achieved by machine compaction was 700-1150 kgf/sample. Thestrength of the briquettes is not suitable for handling and presence of alkalis and silicon are aconcern which prevents its use in the steel making process.Acrylic resins and phenol based resins were then used and it was found that acrylic resinsproduce an agglomerate of strength of 650-1050 kgf/sample and 720 to 1100 kgf/sample at 1 tonand 3 ton loads, respectively.Thermosetting resin produces the best agglomerate with minimum compressive strength of1050 kgf/sample. Agglomerate strength varies between 1600 and 2000 kgf by machine compactionwith a 15 MPa load. This binder produces good strength with manual compaction also and strengthvaries between 1050 to 1440 kgf/ sample for 5 and 10 % binder content, respectively.A comparative analysis of maximum cold compressive strength achieved using differentbinders is given in Figure-7 and it shows that phenolic resin based agglomerate achieves maximumstrength. Handling properties of these briquettes were tested and shown in Table 3 for thebriquettes produced with the most suitable binder combination. The physical characteristics ofbriquettes are acceptable to existing LD steel making process.Properties BriquetteSize & Shape Diameter : 30mm, L : 20mmApparent Density 5200 kg/m3Compressive Strength 55MpaTensile Strength (Load Applied in radial direction) 15MpaTumbler Index (Wt 15kg, rpm 200@25) 95% (>6.3mm)Abrasion Index (Wt: 15kg, rpm 200@25) 3%( <0.5mm)Shatter Index (Wt : 10 kg, No of Drops : 4, Height : 2m) 98%(<5mm)Table-3: Properties of briquettes(a) Mn Ore Particle (b) FeMn Particle
  7. 7. Vol 7 No 3 APRIL 2013Gokarn et al Agglomeration of Ferro Alloy Fines for Use in Bulk Steel Making Process Page 7 of 10Figure-7: Maximum Cold Compressive Strength of Briquettes Achieved using Different Binders3.3 Smelting Studies: Initially these briquettes were tested in laboratory and subsequentlylarger trials (0.5, 10 & 100 ton) were conducted at the plant. Mixing and other operationalperformance parameters were observed during the lab scale induction furnace operations. It wasobserved that fines do not mix properly in the liquid steel but get trapped in the foam on top of theliquid steel. It also generates a significant amount of slag. The slag generation was lowest for lumpsand highest for fines. Mn recovery was lowest for the fines but it was similar for lumps andbriquettes. A comparison is given in Figure 8. Mn recovery was also observed for different types ofbriquettes tested for tumbling test. The best recovery was observed for the briquettes of 30mmdiameter and 20mm thickness (Weight: 65gm) and same were used for the plant trial.
  8. 8. Vol 7 No 3 APRIL 2013Gokarn et al Agglomeration of Ferro Alloy Fines for Use in Bulk Steel Making Process Page 8 of 10Figure-8: Comparative Analysis of Mn Recovery from Lumps, Briquettes and Fines4. Product ValidationFirst phase plant trials were carried out using 500 kg of FeMn briquettes. The Plant adds150 to 600 kg of ferro manganese in ladles of heat size of 155 tons to produce different grades ofsteel. 200 kg and 300 kg ferro manganese briquettes were added in two heats. It was found that theMn recovery was 5 to 10% higher when using briquettes (over lumps) compensating the lower Mncontent of fines. The improved dissolution characteristic is the likely reason for improved Mnrecovery. Nitrogen level did not show any unexpected variation (and was within ~13ppm). Insecond phase of plant trials, 10 ton of ferro manganese briquettes were prepared and addedmanually in 20 different heats of different grades of steel in varied quantities. These trials too werefound satisfactory and in further trials 100 tons of FeMn briquettes were filled in the working chuteand added through the actual plant feeding system. These results, presented in figure 9, confirm theresults of the previous trials.After successful implementation at the plant scale, a vendor was identified and developedfor supply of 200 tpm of ferro manganese briquettes. Later after successful lab and plant scale trialswith briquetting of silico-manganese fines, the capacity at the vendor was increased andbriquetting of silico manganese fines for use at the LD Shops(BOF Steelmaking) was commerciallyundertaken. Lab scale trials have also successfully been completed using FeCr fines.
  9. 9. Vol 7 No 3 APRIL 2013Gokarn et al Agglomeration of Ferro Alloy Fines for Use in Bulk Steel Making Process Page 9 of 10Figure-9: Slag-Metal Analysis During Plant Trials5. ConclusionsFerroalloy fines cannot be used in bulk steel making processes like BOF(LD) as the smallsize increases losses, reduces recovery and can act as carrier for moisture and gasses. High qualitybriquettes can be produced by mixing the resin binder, compaction and by curing at 150˚ Ctemperature. The process flow sheet developed for briquetting is shown in Figure-10. Thedeveloped product was tested in the lab and commercialized after successful plant trials.Apart from financial benefits of using ferroalloy fines, use of briquettes is environmentfriendly and it can significantly reduce the amount of metallic dust and fines generated duringhandling and use of ferroalloy fines in smaller furnaces.The method of briquetting developed by Tata Steel for bulk ferroalloys (FeMn, SiMn andFeCr) can be extended to noble ferro alloy fines and fines of manganese metal which will furtherreduce costs of steel making and increase competitiveness.Figure-10: Process flow Sheet to Agglomerate the FeMn Fines5. AcknowledgementsThe authors express their sincere thanks to Dr. D. Bhattacharjee, Director, RD&T, TATASteel, Mr. Rajeev Singhal, EIC, FAMD and Mr. Debashis Das Chief LD#1, Tata Steel for their keeninterest and guidance during the development of the process and its commercialization.Metal Analysis Slag Analysis
  10. 10. Vol 7 No 3 APRIL 2013Gokarn et al Agglomeration of Ferro Alloy Fines for Use in Bulk Steel Making Process Page 10 of 106. References[1] K.D. Peaslee, D.S. Webber, S. Lekakh and B. Randall: 58th SFSA Technical and OperatingConference, 4.1, (2005).[2] P.G. Sismanis and S. A. Argyropoulos: Proc. of the 69th Steelmaking Conf., 69(1986), 315.[3] Y. Lee, H Berg, B. Jensen, and J. Sandberg: Iron and Steel Society, 54(1996), 237.[4] M. Tanaka, M. Mazumdar and R.I. L. Guthrie: Metall. Trans. B, 24B, 4, (1993), 639.[5] H. Berg, H. Laux,, S. T. Johansen and O. S. Klevan: Ironmaking Steelmaking, 26,2, (1999),127.[6] V Singh, S M Rao, B D Nanda and D Srinivas: International Patent Application No. 2009-PCT/IN2009/000532.[7] Vance, L Calbert. : United States Patent 1946-2405278.[8] Saunders, R. Earle, Pope, L. Richard: United States Patent 1960- 2935397.[9] L. Robert and Ranke: United States Patent 1975-3898076.[10] J.P.Beukes, J. Nell and S. D McCullough: South Africa Patent: 2001-4091.[11] A Ramu, P K Banerjee and B Roy Choudhury: Unpublished Report, R&D Tata Steel, India,R&D-INV-011-96-1-13-97(1997).7. AbbreviationsMn ManganeseCr ChromeFe Ferro / IronSi SiliconC CarbonP Phosphoruskg Kilogramsmm Millimeterskgf Kilogram-forceBOF/LD Basic Oxygen Furnace Processes like LD

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