Blast furnace technology is still the large scale indus-trial producer for hot metal and is expected to remain in the main stream for number of years. Coking coal reserves are depleting hence, there is a necessity for  developing alternative processes  using  abundantly  available  non-coking coal. The new iron making processes avoid the depe-ndency of high quality metallurgical coal hence the deve-lopment has resulted in  large  number  of  processes. The important amongst them are COREX, Direct Iron Ore Smelting Process  (DIOS), Hi Smelt Process etC, NML has developed a process  using  noncoking  coal  as  reductant  to produce sponge iron in a vertical retort direct  reduction furnace developed at NML And the sponge iron so  produced  is  hot charged to sub-merged arc furnace for production of liquid iron containing low sulphur  and  phosphorus. It  has been demonstrated that the liquid iron can be produced with low sulphur (less than 0.02 % and phosphorus less than 0.06% ) and can be successfully and economically produced by utili-sing  this process. The paper describes the details of the same

Gupta, K N

Vaish, A K

English

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PRODUCTION OF LIQUID IRON USING COAL Editors H.S. RAY, D.N. DEY R.K. PARAMGURU and A.K. JOUHARI PROCEEDINGS OF THE WORKSHOP ON PRODUCTION OF LIQUID IRON USING COAL August 24-25, 1994 Regional Research Laboratory (Council of Scientific & Industrial Research) Bhubaneswar, India Aft ALLIED PUBLISHERS LIMITED NEW DELHI BOMBAY CALCUTTA MADRAS NAGPUR AHMEDABAD BANGALORE HYDERABAD LUCKNOW ON THE POTENTIALITY OF PRODUCTION OF LOW S & P HOT METAL BY VRDR-SAF PROCESS K.N. Gupta and A.K. Vaish National Metallurgical Laboratory, Jamshedpur ABSTRACT  Blast furnace technology is still the large scale industrial producer for hot metal and is expected' to remain in the main stream for number of years. Coking coal rdsetve§ are depleting hence, there is a necessity for developing alternatiV@ pPOddt§eg Utgitig abundantly available non-coking coal. 	 The new iron making processes avoid the dependency of high quality metallurgical coal hence the development has resulted in large number of processes. The important amongst them are COREX, Direct Iron Ore Smelting Process (DIOS), Hi 	 Smelt Process etC, NML has developed a process using non- coking coal as reductant to produce sponge iron in a vertical retort direct reduction furnace developed at NML And the sponge iron so produced is hot charged to sub-merged arc furnace for production of liquid iron contai-ning low sulphur and phosphorus. It has been demonstrated that the liquid iron can be produced with low sulphur (less than 0.02 % and phosphorus less than 0.06% ) and can be successfully and economically produced by utilising this process. The paper describes the details of the same. INTRODUCTION Blast furnace technology has been developed continuously over decades, culminating in its current performance / capabilities and efficiency and many feels that it is at its maturity. The process is still competitive as the large scale, industrial way for obtaining hot metal and is expected to remain a mainstream of iron production through the future. 	 Processes involving scrap melting, smelting reduction or direct reduction have so far not succee ded in displacing the "black giants". But when one considers that it requires quality metallurgical coking coal and iron ores and large investment for replacing coke oven to forestall the imminent coke shortage, it is impera-tive to funnel resources into the development of new ironmaking processes 229 that can supplement the blast furnace process. In India the situation is even of more concern. India has large reserves of good quality. iron, fairly dispersed, but 	 adverse A1203/Si02 ratio creating problems. of high A1203 slags in blast furnaces. 	 Fast depleting coking coal reserves but abundant reserves of non-coking coal, higher total energy consumption of hot metal production due to high ash of coal/coke, higher refractory consumption, higher capital investment for blast furnace plant, all' these factors direct R&D workers to look • into alterliative processes and resources available elsewhere in the world or to develop one suitable under Indian conditions. Use of all ir.iported raw materials may not present a really viable solution under Ini•:an conditions. Due to high S & P of Indian pig iron the SG/CG foundry plant suffer additional problem. Most of them resort tomelting steel scrap in induction furnace then resiliconise, recarburise to produce SG/CG castings. EVOLUTION OF ALTERNATIVE PROCESSES. One aspect is common in all the development of new ironmaking processes is to avoid the dependency on high quality metallurgical coke as a reductant and fuel source. This is a response by the iron and steel industry to the economics of raw material supply and feed preparation, and in anticipation of increasing environmental processes(1). Thus, using coal, sc.me of the earlier desirable properties such as medium to high volatil3 content, high swelling index and strength are not relevant to these new processes. The new process, now being developed in the world can • be covered under three basic alternatives as in Fig.1. 	 A shows single stage iron bath coal gasif ication wherein all the reactants are injected in iron bath. 	 There is no direct utilisation of high value off gas, hence process can be viable only if this gas is used for some useful purpose. 	 B shows first generation processes(3). 	 In this smelting reactor is coupled. to direct reduction unit. 	 C shows second generation smelting reduction wherein the bath reaction gas is combusted by the injection of air or oxygen into the top space or slag region in the smelting vessel. 	 The heat so 230 produced can be utilised for preheating of incoming materials and thus ;4) making large fuel savings. • THE ALTERNATIVE PROCESSES. Large number of . processes are being developed in the world. 	 These are on pilot plant scale, semi-commercial or commercial scale. 	 The characte- ristics of some smelting reduction processes are given in Table I and classification of ironmaking processes by pre-reduction degree in Table II. The three processes that have gained some grounds are COREX, DIOS (japan) and Hi-Smelt (Australia). COREX (5) It is only commercially operating example of a first generation process. Schematically it is shown in Fig.2. 	 In a shaft type reactor coal is directly injected with oxygen and a gasification reaction takes place producing CO + H2. The reducing gases pass through another reactor con-taining iron bearing materials. The reduction takes place and the reduced material passes to the shaft where it gets smelted and produces iron and slag. DIOS (Direct Iron Ore Smelting Process) (6)  This is an example of second generation process as given in schematic diagram Fig.3. The off gas from the smelting reactions is post combusted with oxygen supply the process heat. The partially combusted gases are used for preheating and prereducing incoming iron ore fines. Coal, pre-reduced iron and flux are dropped onto the surface of foaming slag. Oxygen is blown in slag layer and thus iron is produced. (7) Hi-SMELT. This is also a second generation process. The major difference with other 231 process is that most of the smelting reactions are performed in an intensely agitated iron/carbon bath. 	 This is shown in diagram in Fig. 4. As shown in Figure the pulyerised coal is entrained in a flow of nitrogen and is injected directly into the smelting vessel through basal tuyeres. The hot metal and slag are tapped from the welt reduction vessel and sent for pig casting. LIQUID IRON PRODUCTION BY VRDR-SAF PROCESS(8). NMLillas developed a process of production of low S & P iron by using Vertical Direct Reduction and Submerged Arc Furnace Process (VRDR-SAF). VRDR-SAF Process is a combination of Vertical Retort Direct Reduction. Process - Sub-merged Arc Furnace Process as given in Fig.5. • The process comprises the reduction of iron ore with a carbonaceous mate-rial and smelting the reduced mass in a sub-merged arc furnace. The resul-tant high temperature hot metal is relatively low in S & P and is aptly suitable or SG/CG castings. Thus this process has two separate equipments coupled together (1) Vertical Retort Direct Reduction Unit (VRDR Unit) and (2) Submerged Arc Furnace (SAF). Vertical , Retort Direct Reduction (VRDR) Unit for Production of DRI.  - The process of production of DRI is based on the reduction of iron oxide by solid carbonaceous materials in a retort reactor. The sized iron ore lump mixed with sized non-coking coal and limestone is pre-determined proportion and fed into the charging hopper through self discharging container. From the charging hopper tie mixed in.FAterial is chargeo to i.ne retort rector intermittently. The charge material inside the retort passes through stages of preheating, reduction and cooling. This is achieved indirectly by burning liquid or liquid and gaseous fuel in a furnace built around the retort. The slow movement of the charge is controlled depending on time of reduction by controlling the discharge from the retort. The product from the retort is discharged through a screw discharge system and then magnetically separated to remove the non-metallics. The total reduction time . in the retort is 3i to 4i hours. The process has been developed on a pilot plant scale of single retort producing 1 - 1.3 tonnes/day of DRI. A commercial 232 • size retort will produce about 3 - 3.5 TPD of DRI and a module of 4 retorts can produce about 4200 TPA. If 8 - 10 retorts module is used, 10,000 TPA of. DRI can be produced, Submerged Arc Furnace (SAF). Normally the sponge iron produced in the VRDR furnace is cooled down from almost the bottom of the retort so that when it is discharged from the unit, it is at a temperature of 70°C. 	 In the case of VRDR-SAF, an intermediate system is used wherein the discharge from VRDR unit is hot screened at a temp. of 900°C thereby most of the fine char is sepa-rated and hot sponge iron at 800 - 900°C is discharged directly to the SAP. It may, however, be mentioned that so far NM has conducted experiments using cold DRI and not hot DRI. The advantage of this hot DRI is obvious, since there will be a distinct saving of power of about 200 KWH/tonne of DRI due to high temperature of the DRI. 	 This hot DRI along with a very small quantity of reductant is reacted in the SAF wherein the smelting takes place and the iron so produced contains nearly 3.2 to 3.8 percent C, 0.6 - 1.8 percent silicon, 0.02 - 0.03 percent S, 0.03 - 0.06 percent P and 0 - 0.025 percent Mn. The temperature of the hot metal ranges from 1350 - 1450°C depending on the quality of the DRI and initial power input. 	 On an average, about 1000 KWH/tonne of the hot metal is the power consumption. 	 This hot metal can be subsequently cast in the form of pigs for subsequent melting and converting to SG iron or can be directly converted to SG/CG iron castings because of appropriate chemical composi-tion and temperature. Coupling of VRDR unit with SAF. The schematic diagram is the flowsheet of the VRDR-SAF technology is given in Fig. 5 	 . 	 The coupling of the two units have to match in such a way that the discharge of the VRDR furnace would be able to be smelted 233 in the SAF. We have conducted experiments at NML in 500 KVA Sub-merged Arc Furnace which is giving about 9 - 10 tonnes of hot metal of low S & P quality. Thus, by employing a 500 KVA furnace, one can easily produce about 3000 tonnes hot metal per year. One KVA furnace can easily produce about 6000 tonnes/year. The matching VRDR unit can be easily put up based on the designs prepared by MECON. The physical feature as given in the diagram is a unique system wherein hot DRI and char is discharged from the VRDR unit and charged to SAF to 800 - 900°C. This gives an energy saving of about 200 KWH per tonne hot metal. 	 We envisage that this must be included in the commercial unit. We have conducted experiments by using cold DRI produced in VRDR at our pilot plant area and since the SAF is located in the main labo-ratory, we had no other alternative, but to conduct experiments with cold DRI. It can be logically and technically possible to couple these units and produce hot metal directly. Trials were conduCted in SAF with prereduced materials as given in Table 3. 	 The reductants used in the campaign is given in Table 4 Some of the results are given in Table 5 	 and Table 6. The trials concluded as :- 1. Possible to use fine fraction (-15 +1 mm) coal as reductant in VRDR furnace without adversely affecting VRDR operation. 2. Laboratory studies revealed some aspects of mechanism of smelting. of pre-reduced iron. 3. Low S & P iron (0.02 - 0.04% and 0.03 - 0.06% respectively) can be produced using DRI in SAF. 4. Desired levels of C, Si, S&P of hot metal possible. 5. 0 - 37% Fe0 containing pre-reduced material can be successfully smelted to produce low S & P hot metal. 6. Power consumption of 950 - 1400 KWH/tonne of HM can be achieved for different Fe0 content of raw materials. 234 7. 	 Petrocoke, nut coke and LTC can be used as reductant in SAF for producing low S & P iron. 8. 	 High temperature ( --#1400°C) HM is suitable for directly converting to SG iron. 9. Use of SAF top cover decreased heat loss and power consumption by about 100 KWH/tonne. 10. Development of thermochemical model for VRDR-SAF process assis-ted in predicting raw material behaviour. 11. Prototype hot screening and charging of hot DRI to SAF is likely to decrease power consumption. Status of the technology.  NML has conducted experiments with cold DRI obtained from NML's VRDR ffurnace, DRI from RDCIS, Ranchi-, DRI lump obtained from SIIL, DRI fines from SIIL and DRI from IPITATA. In all the campaigns together, NML has produced about 400 tonnes of hot metal of low S & P quality. As far as NML's VRDR unit is concerned, several campaigns have been conducted with various types of raw materials including the material from SIIL and successfully produced high grade, highly metallised DRI from raw materials. A plant is coming up in Madhya Pradesh with a capacity of 4200 tonnes/annum by a private entrepreneur and • trials for Sponge Iron India are being done or their plant. Four parties are seriously contem-plating to put up this unit based on our technology in order to produce SG • iron for SG castings, CG castings, ingot moulds and rolls from this unit. These indigenous efforts have led to the conclusion that liquid iron produ-ction with indigenously available quality of raw-materials requires a serious consideration. The commercial techno-economics can ofcourse be proved; only if some plants come at the earliest. Serious efforts are on to achieve the same and it is expected that plant may come up soon. 235 ACKNOWLEDGEMENTS The authors wish to express. their sincere thanks to Prof.P.Ramachandra Rao, Director, National Metallurgical Laboratory for permitting to present this paper. Their very sincere thanks are also due to authors whose work has been freely quoted in the paper, the names are somany that it is difficult to name here but is given in the references. However, authors have been fully involved in all the work cited above. REFERENCES. 1. R.J. Batterham and U.S. Conochie: IEA-OECD Symposium on Coal, The Environment and Development: Technologies to Reduce Greenhouse Gas Emissions, Sydney, IEA-OECD, 1991. 2. J.K: Wright: First Intl' Cong.Sc. & Tech. of Ironmaking, 1994, Sendai, ISIJ, P. 597. 3. B.L. Cusack, G.J. Hardie and P.D. Burke: Second European Ironmaking Conference Glasgow,Sept. 1991. 4. J.K. Wright: NI.W. Symp., Univ. of Mel., Ausxralip,6-8 July, 1992. 5. D. Siuka and C. Bohm - Steel Times International, March 1994,p.12. 6. T. Inatani: 50th Ironmaking Conference Procedgings, ISS-AIME, 1991, p.651-58. 7. John Innes, B.Cusack - Steel Times International, March 1994, p.21. 8. K.N. Gupta, Workshop on 'Emerging routes to liquid iron', April 23rd, 1993. 9. E. Kasai, Tohoku Univ. ICSTI '94 Workshop, Ironmakingfor 21st Cent. ISIJ, Japan. 236 Fine ores, Coal, Coal rate: 0.81 Ut--p Oxygen rate: 504 Nm/t-p Fine ores & coal, Coal rate: 0.64 Ut-p Air rate: 2,400 Nrrit-p Fluidized bed for pre-reduction • Smelter Gas modifier N2 blow, 0.3 MPa High-speed CFB for pro-reduction H. smelter (Bottom coal injection). Hot-blast stove (120ff C) 1993 180,000Uy National project started in 1988 DIOS (Japan) 4C-low Si- high S PC: 50% HI-smelt (Australia) 3.8-C-high S 1993 100,000t/y High-FeO slaR(cx. 5"6) PC: >60% •p,  Table 1. Characteristics of some smelting reduction processes (9)  Process Raw materials 	 Furnace 	 Quality 	 Present COREX (Voest Alpine) lumpy ores, Pellets, Sinter, Coal Coal rate: 1.05 t/t-p Oxygen rate: 540 Nnbt-p Shaft (moving bed) for pre-reduction Fine coal injection Oxygen blow 4.3C-0.3S1- 	 1981-88 60,0001/y 0.04S-0.09P 1989 300,000Uy PC: 5% 	(South Africa) 1995 600,000tfy (South Korea) Table 2. Classification of lronmaking Process by Pre-Reduction Degree (9) Process 	 P-R 	 P-R process Final Process 	 Pico 	 Gas tomp.(oC) degree(%) 	 P-R Final P-R Final Novollpetsk 	 0 	 Slag bath 	0.02 	 - 	 1500 Rectangular 	 -0.93 DIOS 	 30 	 Fluidized bed Iron bath 	 0.7 	 0.5 	 800 	 1700 HI-Smelt 	 30 	 Fluidized bed Iron bath 	 0.7 	 0.5 	 800 	 1690 horizontal type Plasma-Smelt 	 50 	Fluidized bed Coke bed + 	 0.7 	 0.4 Plasma Blast Furnace 	 75 	 Shaft 	 Coke bed 	0.5 	 0.01 	 200 	 1350 Oxygen BF 	75 	 Shaft 	Coke bed 	0.5 	 0.02 	 400 	 1400 COREX 	90 	 Shaft 	 Char bed 	 0.5 	 0.1 	 750 	 1600 FIOR 	 93 	 Fluidized bed Electric arc 	 0.2 	 900 Cupola 	 100 	 Scrap 	 Coke hod 	 0.5 	 1500 237 Table 3 - 	 Composition of DRI lumps and pre-reduced pellets. Constituents in 	 26 Lump I Lump II Lump III Lump IV Lump V Pellet I Pellet II Fe(T) 88.48 86.8 88.78 91.80 90.78 77.84 82.90 Fe(M) 61.04 62.7 64.96 70.50 79.09 56,56 64.90 FeO 35.29 30.98 28.60 27.26 15.00 26.98 24.43 C 0.30 0.20 0,38 0.30 0.233 1.37 0.48 S 0.02 0.019 0.02 0.026 0.016 0.044. 0.066 P 0.02 0.03 0.03 0.02 0.02 0.07 0.07 SiO2 3.32 2.35 1.64 1.90 2.92 5,48 7.89 CaO 0.33 0.36 0.15 0.30 0.77 0.97 MgO 0.30 0.80 0.43 0.83 1.10 0.15 1.90 A1203 0.66 1.32 0.52 2.56 5.16 0.97 Metallisation 69.00 72.00 73.00 77.00 87.00 73.00 78.00 Table 4 - Composition of reductants. Constituents in % Uncalcined Petro coke Calcined Petro coke Nut coke L.T.C. P.C. 90.81 97.20 73.68 61.58 V.M. 8.21 2.50 1.20 13.06 Ash 0.20 0.24 24.80 21.76 Moisture 0.28 0.06 0.32 3.60 S 0.50 0.66 0.11 0.23 P Trace Trace 0.26 0.35 238 Table 5 - Smelting of DRI lumps of 72% metallisation.  Charge   DRI Lumps Uncalcined petro coke Limestone Quartzite No. of charges Metal temperature speciic power consumption 100 kg 12 kg 14 kg 4 kg 10 1398°C 1300 KWH/THM Hot. metal composition 	 in % Slag composition , ire 	 % 3.53 Si02 	 28.60 Si 1.64 Ca0 31.10 S 0.02 MgO 2.15 0.03 A12 03 1 0.65  Mn 0.026 Fe0 3.62 0.020 Table 6 - Smelting of DRI lumps of 87% metallisation. Charge.  DRI lumps 	100 kg Calcined petro coke 	 10 kg Limestone 	 12 kg Quartzite 	 4 kg No. of charges 	 13 Metal temperature 	 1395°C Speciic power consumption 	 1200 KWH/THM Hot metal composition 	 in % 	 Slag composition in % C 4.10 SiO2 23.10 Si 1.40 Ca0 30.45 S Trace Mg0 5.65 P 0.025 A1203 26.14 Mn 0.001 FeO 15.50 P 0.014 239 Coal Sloam Oxygen Slag 	 Hot Metal Coal Oxygen Smutting Direct Roduction Gas 	IRoducod Iron Oro A Single stage iron bath coat, gasification Iron Oro 	 Gas Iron Oro Gas B 1st Generation Smelting Reduction Hot Metal C 2nd Generation Smelting Reduction Partially Roducod Iron Oro  Slag Iron Ore Pro- Reduction Olt Gas Gas Coal 	 Oiroct 	 Post 	 . 	 Air/Oxygen Oxygon—r Smelting 1 	  Combustion 1 	Heat  I---.- Hot Metal Slag Fig .1 : Evolution of Direct Smelting -Processes (2) 240 241 Cyclone Fine cre Iron ore Flux 	1485kg 56kg Coal Pr6eatilv furiuct C 0 keS4 Ctg t41 43 Pre Curbe—all AIT)NI4  6A 7  la.14. .9 504N trri Taphole open .r and rr.ucipir) Molten iron ,,,,,,,,, 21 Vh 4•V.0 1500t i Si 1, __ 100Ckg 17619 Cyclone Air 170NO Compresscr Fine cre 	Goal cli7er Gas•rufortninQ coal i0Okg —melting reduction furnzco PC5O% 1.9kg/cm2 G 200Nrn3 t•12 ca rrprg sSW Fig.3 : Schematic now sheet of aios Process (5) {eataj ve6mi Material hoppers Underground bunkers 714kg Pressers coud 4ve. PC. IA.,/ oPriiipill% •-044 L.L.Lexn C.9“ C r ;As AZ prow. lock.on cle-s-ve 242 Horizontal Vassal Hot Pro-roducad Ora lisfectIon Myers Cooling Water Bo(Ion, Tuyores Slag • IMO gain 	 A:eta! Rod Sittg Tipping Natural Gas Shroud Bottom Coal LS Oust injection.. Pro-roducod Ora Pre-roductlon System! Hof Alr Blast (120(1C) Fig.4 	 HIsmelt smelt reduction vessel. Vigorous bath agitation leads to the top space being an important reaction area (7) 243 VRDR - SAF PROCESS VRDR -  FURNACE\ RAW MATERIALS HOX MTALUCS \  HOT SCREEN \ now OE 	 X. C. COAL 	 WC STOIC Fig.5 	 Schematic VRDR — SAF Process (8) 244 

On the Potentiality of Production of Low S & P Hot Metal by VRDR-SAF Process

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On the Potentiality of Production of Low S & P Hot Metal by VRDR-SAF Process

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