Briquetting of Ferro Manganese Fines & Use in Steel Making

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Ferro Manganese(FeMn) is used for alloying & refining of steel. During manufacture of FeMn fines are generated which are not useable (except in small induction furnaces). This paper describes a …

Ferro Manganese(FeMn) is used for alloying & refining of steel. During manufacture of FeMn fines are generated which are not useable (except in small induction furnaces). This paper describes a process for agglomeration of FeMn fines and its use in steel making.

Paper submitted for NMD 2012.

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  • 1. Ferro Manganese Briquettes - A New & Promising Product for Steel MakingAuthors Prabhash Gokarn, V Singh, A Kumar, B D Nanda & A Bhattcharjee Tata Steel Ltd., India.1. Introduction Manganese alloys are added as deoxidizing agents and additives to increasestrength, elasticity and abrasion resistance of steel. Manganese is usually added inthe form of lumps of high carbon ferro manganese, silico manganese and manganesemetal. In steelmaking, overall consumption is (on an average) 6 to 7 kgs ofmanganese (Mn content in Mn alloys) per ton of steel. According to the National Steel Policy, 2005, projected steel production inIndia is likely to double within a decade. With this background, there is likely to be ahuge gap between the availability and demand of Manganese alloys, if theproduction of ferro alloys fails to match the growth in production of steel. Manganese ferro alloys are made by carbo-thermic reduction of manganese oresin electric arc furnace. Liquid hot metal is cast into cakes and crushed into 10mm to60mm size lumps. The fines generated during the sizing of metal cake cannot beused in the LD steel making process. These fines get oxidized quickly and reduce theoverall manganese recovery during steel making [1-2]. Though, ferro manganese inthe size range of 3 to 20mm has better dissolution characteristics, the higher surfacearea (due to small size) also transports undesirable gases and moisture into thefurnace. Small alloy size also increases dust losses and leads to handling difficulties[3-6]. Briquetting is the best method to utilize these fines. Binder composition andphysical strength of the agglomerate are two main constraints to develop a costeffective method. Various attempts have been made in the past to agglomerate thesefines using conventional binders like molasses, tar, resin, etc [6-10]. A briquettingprocess has been developed in this study to utilize high carbon ferro manganesefines in the steel making process. The suitability of the produced briquettes wastested in the laboratory as well as in the plant. The developed product will improvethe utilization of manganese resources, while minimizing the environmentalpollution caused by steel industry.Gokarn et al Ferro Manganese Briquettes for Steel Making Page 1 of 12
  • 2. 2. Lab Scale Studies2.1. Characterization of Fines: Samples of ferro manganese fines were collectedfrom Ferro Alloy Plant (FAP), Joda, India. These were classified into three differentsize ranges (>10mm; -10+3mm; -3mm). Five important constituents (Mn, C, S, P, andSi) were analyzed using ICP-OES (Spectro-Analytical Instruments; Ciros) to find thechemical composition of the prepared agglomerate. Particle shape and surfacecharacteristics were also analyzed using scanning by electron microscope to studythe agglomeration behavior of fines.2.2 Briquetting of Fines: Selection of binder for alloy fines determines the strengthof briquettes and thus is most important. The binders should not add any unwantedingredient like sulphur, phosphorus, nitrogen etc. in the steel, and it should be costeffective. Molasses and other conventional organic binders were rejected becausethese binders contain sulphur and phosphorus. Sodium silicate, Bentonite, Acrylicresins and Phenolic resins were tried as binders and tested, and the results aregiven in Table-1. The experimental work plan is described in Table 1 and Fig. 1.Fines and binder were mixed properly. Sixty to seventy grams of the mixture werecompacted in cylindrical die of diameter 3cm at different loads and compact wascured at different temperatures (100˚ and 150˚ C) for one hour. Briquette density,compressive strength, tumbling index, abrasion index, shatter index and dissolutioncharacteristics were studied. Binder % Load (ton) Curing Condition Sodium Silicate 5, 7.5 & 10 1&5 100 C, 1 hour Sodium Silicate+ Bentonite 5+2, 7.5+2 & 10+2 1 100 C, 1 hour Acrylic Resin 5, 8 & 10 1&3 100 C, 1 hour Phenol formaldehyde Resin 5, 8 & 10 1&5 100 & 150 C, 1 hour Table-1: Briquetting conditionsGokarn et al Ferro Manganese Briquettes for Steel Making Page 2 of 12
  • 3. Sample Preparation (0-3mm) FeMn fine) Mixing Binder Pressing (1-5ton) Curing (100 & 150° C, 60 minutes) Compressive strength Test Figure-1: Process Methodology for Binder Selection 2.3. Smelting of Briquettes: Twenty kilograms of steel scrap was melted in a 25 kginduction furnace and 5 kg of ferro manganese (FeMn) lumps were added.Experiments were repeated for FeMn fines and FeMn briquettes under the same testconditions for comparison. The mixing behavior of the materials was observed. Slagand metal samples were collected and the manganese recovery was calculated.Figure-2 shows the lab scale setup to test the dissolution behavior of lumps, finesand briquettes. (a) (b) (c)Figure-2: Lab Scale trials in Induction furnace (a) Induction furnace (25kg) (b) Melting of scrap (c) Sample collection before and after the additionGokarn et al Ferro Manganese Briquettes for Steel Making Page 3 of 12
  • 4. 3. Results and Discussions3.1 Characterization Studies: Chemical analysis of various size fractions is given inTable-2. Despite the slightly lower percentage of silicon (Si) and manganese (Mn) infines compared to lumps, fines are suitable for use in steel making. Size analysis ofthe samples of ferro manganese fines (0-10mm) was carried out and it was foundthat ~70 % fines are of 0 to 3mm size (fines) and 30 % are of 3 to 10mm size(chips). Particle size and shape analysis is shown in Figure-3 and 4. Finer particlesizes are preferred for briquetting, but presence of significant amount of veryangular particles makes the agglomeration process more challenging. Very angularparticles enhance the mechanical interlocking but require high pressurecompaction. 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 1.33 Table-2: Size and Size wise chemical analysis of Ferromanganese fines 100 80 Comm.Pass %, Passed 60 40 20 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Particle Size (mm) Figure-3: Particle Size AnalysisGokarn et al Ferro Manganese Briquettes for Steel Making Page 4 of 12
  • 5. Figure-4: Particle Shape AnalysisGokarn et al Ferro Manganese Briquettes for Steel Making Page 5 of 12
  • 6. SEM analysis shown in Figure 5 reveals that these fines are not oxidized. Some smallslag inclusions were also seen in the briquetted samples. Pt-1 Pt-2 Pt-1 Pt-2Figure-5: SEM micrograph of Lumps (Pt1-High carbon Phase, Pt2-Low Carbon Phase) and Briquettes (Pt1-High carbon Phase, Pt2- Slag particle)Gokarn et al Ferro Manganese Briquettes for Steel Making Page 6 of 12
  • 7. 3.2 Briquetting Studies: Metallic fines show a different binding behavior comparedto conventional ore particles. Figure 6 shows surface of manganese ore and ferromanganese metal particles. The ore particles usually contain small cracks andcleavages which play important role in binder absorption and binding of theparticles. (a) Mn Ore Particle (b) FeMn Particle Figure-6: Surface Roughness of Mn ore and FeMn Metal Particle Three different combination of sodium silicate were tried and it was found that theprepared agglomerate does not attain the suitable compressive strength and itvaries between 90 and 240 kgf/sample. The strength achieved by machinecompaction was 700-1150 kgf/sample. The strength of the briquettes is not suitablefor handling and presence of alkalis and silicon are a concern which prevents its usein the steel making process. Acrylic resins and phenol based resins were then used and it was found thatacrylic resins produce an agglomerate of strength of 650-1050 kgf/sample and 720to 1100 kgf/sample at 1 ton and 3 ton loads, respectively. Thermosetting resin produces the best agglomerate with minimumcompressive strength of 1050 kgf/sample. Agglomerate strength varies between1600 and 2000 kgf by machine compaction with a 15 MPa load. This binderproduces good strength with manual compaction also and strength varies between1050 to 1440 kgf/ sample for 5 and 10 % binder content, respectively. Acomparative analysis of maximum cold compressive strength achieved usingdifferent binders is given in Figure-7 and it shows that phenolic resin basedagglomerate achieves maximum strength. Handling properties of these briquetteswere tested and shown in Table 3 for the briquettes produced with the mostsuitable binder combination. The physical characteristics of briquettes areacceptable to existing LD steel making process.Gokarn et al Ferro Manganese Briquettes for Steel Making Page 7 of 12
  • 8. 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 Figure-7: Maximum Cold Compressive Strength of Briquettes Achieved using Different Binders3.3 Smelting Studies: Initially these briquettes were tested in laboratory andsubsequently larger trials (0.5, 10 & 100 ton) were conducted at the plant. Mixingand other operational performance parameters were observed during the lab scaleinduction furnace operations. It was observed that fines do not mix properly in theliquid steel but get trapped in the foam on top of the liquid steel. It also generates asignificant amount of slag. The slag generation was lowest for lumps and highest forfines. Mn recovery was lowest for the fines but it was similar for lumps andGokarn et al Ferro Manganese Briquettes for Steel Making Page 8 of 12
  • 9. briquettes. A comparison is given in Figure 8. Mn recovery was also observed fordifferent types of briquettes tested for tumbling test. The best recovery wasobserved for the briquettes of 30mm diameter and 20mm thickness (Weight: 65gm)and same were used for the plant trial. Figure-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 Plantadds 150 to 600 kg of ferro manganese in ladles of heat size of 155 tons to producedifferent grades of steel. 200 kg and 300 kg ferro manganese briquettes were addedin two heats. It was found that the Mn recovery was 5 to 10% higher when usingbriquettes (over lumps) compensating the lower Mn content of fines. The improveddissolution characteristic is the likely reason for improved Mn recovery. Nitrogenlevel did not show any unexpected variation (and was within ~13ppm). In secondphase 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. Thesetrials too were found satisfactory and in further trials 100 tons of FeMn briquetteswere filled in the working chute and added through the actual plant feeding system.These results, presented in figure 9, confirm the results of the previous trials.Gokarn et al Ferro Manganese Briquettes for Steel Making Page 9 of 12
  • 10. After successful implementation at the plant scale, a vendor was identifiedand developed for supply of 200 tpm of ferro manganese briquettes. Metal Analysis Slag Analysis Figure-9: Slag-Metal Analysis During Plant Trials5. ConclusionsHigh carbon ferro manganese fines cannot be used in LD steel making process as thesmall size increases losses, reduces recovery and could act as carrier for moistureand gasses. High quality briquettes can be produced by mixing the resin binder,compaction and by curing at 150˚ C temperature. The process flow sheet developedfor briquetting is shown in Figure-10. The developed product was tested in the laband commercialized after successful plant trials. Tata Steel produces 25kTPA highcarbon ferro manganese fines. In the current market scenario the developedproduct can save Rs 1.2 crore/annum including the improved process performanceand cost difference between lumps and agglomerate. Use of briquettes isenvironment friendly and it can significantly reduce the amount of metallic dust andfines added to environment by foundries using the fines.A similar method of briquetting can be explored for SiMn fines, noble ferro alloyfines and manganese metal which will further reduce costs of steel making andincrease competitiveness.Gokarn et al Ferro Manganese Briquettes for Steel Making Page 10 of 12
  • 11. Figure-10: Process flow Sheet to Agglomerate the FeMn Fines5. AcknowledgementsThe authors express their sincere thanks to Dr. D. Bhattachrjee, Director, RD&T,TATA Steel, Mr. Rajeev Singhal, EIC, FAMD and Mr. Debashis Das Chief LD#1, TataSteel for their keen interest and guidance in the present study.6. References [1] K.D. Peaslee, D.S. Webber, S. Lekakh and B. Randall: 58th SFSA Technical and Operating Conference, 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).Gokarn et al Ferro Manganese Briquettes for Steel Making Page 11 of 12
  • 12. 7. Abbreviations Mn Manganese Fe Ferro / Iron Si Silicon C Carbon P Phosphorus kg Kilograms mm Millimeters kgf Kilogram-forceGokarn et al Ferro Manganese Briquettes for Steel Making Page 12 of 12