World current   prereduction  capacity  of about 5 million tons is expected to rise to over 60 million tons by end of the decade. The paper briefly reviews the major prereduction processes and  outlines  uses  of  products. Attempts is made to define the broad parameters  of  iron ores used for prereduction. Adoption of  prereduction  by solid reductant process seems to  hold  our  promise  for Indian conditions. Application of prereduction as a means of producing steel directly or  as  an ancilliary process for stretching capacity of  existing  and  future  blast furnaces. Possibility of estabilishing a number of small centers for providing raw materials for founders and rero-lling mills. Recommends  experimental  industrial  appli-cation of prereduction during  5th plan  period  towards gaining experience for wider application for increasing iron and steel capacity in the 6th and subsequent plans

Engineer, B B

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IRON ORE PRE - REDUCTION B. B. ENGINEER National Iranian Steel Corp. Abstract World current prereduction capacity of about S million tons is expected to rise to over 60 million tons by end of the decade. The paper briefly reviews the major prereduction processes and outlines uses of products. Attempt is made to define the broad parameters of iron ores used for prereduction. Adoption of prereduction by solid reductant process seems to hold our promise for Indian conditions. Application of prereduction as a means of producing steel directly or as an ancilliary process for stretching capacity of existing and future blast furnaces. Possibility of establishing a number of small centers for providing raw materials for foundries and rerolling mills. Recommends experimental industrial application of prereduction during 5th plan period towards gaining experience for wider applications for increasing iron and steel capa-city in the 6th and subsequent plans. General Growth • SEARCH for production of iron by means other than the expensive blast furnace complex requiring increasingly expensive coal /coke con-sumption has been in progress for a very long time. Though the principle of direct reduction was worked upon about a 100 years ago the com-mercial application of this principle has been established only very recently. Term direct re-duction or prereduction envisages operations by which oxygen from iron ore in the solid state is removed— at temperatures below 2200°F—with-out going through the • smelting stage. Reduction is achieved either reducing gases- or through a solid reductant (non-coking coal). At the end of 1972 total world capacity for production is estimated at about 5 million tons p.m. a highly accelerated growth rate during the current decade is anticipated 5 years ago, Miller and Lorig predicted the world capacity of pre-reduction in 1980 at about 30 million tons but in 1971 Miller's new estimates indicated 1980 capa-city at about 62 million tons and for 1975 at about 10 million tons. Compared to these the total crude steel figures for 1975 and 1980 are 730/760 million tons and over 900 million tons  respectively of which -electric steel may be 106 and 180 million tons respectively. Figure I shows the anticipated trend of pre-reduction capacities and Table 1 shows compari-son of total crude steel, electric furnace steel and prereduction anticipated capacities. TABLE I (Figures in Million Metric Tons) Years 	 Total 	B.F. Crude 	 Tons 	 % Prereduction 1970 590 81 13.8 3 1972 620 __ 87 14. 5 1975 735 106 14.4 10 1980 915 183 20.0 62 Processes Several prereduction methods have been considered in the past but the Mowing are amongst the better known in the industry : — viz. HYL., Midrex, ARMCO., US. Steel Nu-Iron (fluidised bed) and the SL/RN. The first 4 are gaseous reductions while the 5th one is a solid carbon reductant process. Capacity 	 Year (tonsfannum) 115,000 240,000 270,000 400,000 lam_ L-2-13;000-  c 400,000 400,000 800,000 Prcbably over I million "Process" Under Reconsideration. 11000$000 	 1967 	1,000,000 	 1973 	65,000 	 1972 I:fEklEw  1972 	koo,000 	 1971 	250,000 	 1972 	165,000 	 1969 800,000 Under Planning 5G0,000 	 1972 212922_ 1972 M7656-  1957 1960  1969 1973 1967 1969 1971 1973 1972 TABLE II WORLD PRE-REDUCTION COUNTRY-WISE CAPACITY Ho. 6ountry Company and Location Process 1 Hojalata Y Lamina S.A. Monterrey HYL 2 - Do Monterrey HYL 3 - Do Puebla HYL - Do Monterrey HYL 5 Mexico TW)os 80 Acero de Vera Cruz HYL Mexico S.A. 6 Oregon Steel Co. Portland Miami 7 U.S.A. George Town Steel Georgetown Midrex 8 Midland Ross Batonrouge Midren 9 Armco Steel Texas 10 Canada Falconbridge Nickel Sudbury SL/AB Minea Ltd, adbec (Ontario) Contrecour Midrex (ltiebec) 12 south- U.S. Steel Corp Ciudnd Guayana America Veneznels MU-,Iron 13 Acos tiros Piratini S.A, Usiba Brazil Brasil MOM Ma 14 Europe Korf Indu5triv Handel Hamburg Midrez GmbH W.Germany 15 Skopje Yougoslavia 510114 16 South- Inchon Iron *orris Inchon SW EN Korea 17 New New Senlard steel Cos New Zealand MOM Zealand 18 Japan Osaka Midrex 19 Iran Bandar Abas 20 Australia Samersley 21 S. Africa Witbank 311/HN (Early Version) 267 rums I rrobabl• trfoad 	 P•raductian Capacity have attracted much attention in the U.S.A. and elsewhere in a short span of time. Reduction is achieved in a vertical furnace on iron oxide pel- f 	 lets by a counter current of hot reformed natu- ral gas. 	 is reported to produce 92-95 per cent metallization from 65-66 per cent Fe oxide pel-lets. Energy requirements at the established Portland Plant is in the region of 3.5 million ICcals/ton product which is considered favour-able. Earlier established plants are slowly incre, asing capacity towards the rated level, but still have to approach it. Teats 60 •o 23 to HYL process — this is perhaps the 1st to establish itself successfully in industry. The first HYL plant established at Monterry — Mexico in mid-fifties has since produced serveral million tons of prereduced material. Further additions made at Peublo and Vera Cruz. Basically a static bed batch process in which reduction is achieved in vertical retorts. Ore and reformed natural gas (74% 14-13% CO) enter the reactor at higher end. Reduction time about 12 hrs. Re-duction temperature between 870-1050°C. Lump ore or pellets mainly in the size range 1/4" to 1/2" are fed in batches at top of retort. The earliest installations fed on approximately 60 per cent Fe ore gave products at about 82 per cent metallization or 88 per cent reduction. The newer plant at Peublo has better results, Oxide pellets at 65-66 per cent Fe and a gangue rang-ing from 4-8 per cent; P-0.02 to 0.04 per cent S-0.02 to 0.04 per cent and carrying almost equal proportions of hematite and magnetite and magnetite give about 91 per cent metallization. Practically all plants run near rated capacities. Although the Midrex process is also a gase-ous reduction process much the same as HYL, it is a continuous charge system. It seems to The ARMCO batch process is somewhat simi-lar to the Midrex process is that it is a gaseous countercurrent reduction but the main difference is in its gas reforming method. It is expected to reduce a 63 per cent Fe oxide pellets to a 95 per cent metallization product. Not much is known about the process as the first MOO ton] day plant is expected to start production this year (1973). Orinoco 'Fluidized bed' Nu Iron or High-Iron Briquette (HIB) gaseous reduction is perhaps the only known successful industrial application of iron ore fines below 10 mesh. It too is a counter current reduction achieved in a tall multistage reactor. The first and perhaps the only known plant (1 million t.p.y.) is expected to go on stream early 1973 at Ciudad Guyana-Venezuela although planned for operations in mid 1971. The process consists of 4 basic stages. Ore preparation: —Fine ore from mines is dried, crushed and screened to 10 mesh size. Gas reformation is achieved by mixing na-tural gas with superheated steam in pre-sence of a nickel catalytic agent at 1500°F. Gas then cooled to remove excess water vapour. Actual reduction achieved in tall reactors —dry preheated ore (600°F) pneumatically injected into top of reactors: Prereduced material under inert nitrogen-ous atmosphere is pressed into small bri-quettes of about 5.5 to 5.7 density at high temperature of about 2700°F. With 58 per cent Fe natural ore and dried iron content of over Fe 63 per cent a prereduced pro-. duct of 86 per cent total Fe with 75 per cent of its oxygen removed is obtained. Briquettes are planned specially for use in blast furnaces. The main advantage of the briquettes would be uniformity of size and quality enabling use as scrap substi-tute to enrich burden. 268 Reduction % 75 - 80   85 .  90 9:     100 100 	 95 	 90 	 85 	 80 	 75 	70 ketellizetion % SL/RN—solid reductant process. Iron ores — natural lumps (up to 20 m.m.) or pellets (18- 15m.m.) are directly reduced at about 1100°C in a slightly inclined rotary shaft kiln in presence of coal. The special kiln is provided with a series of burners throughout the full length of the kiln. Limestone/dolomite is used as a sul-phur-binder to prevent excess sulphur from coal finding its way into the metallized product. Kiln product is cooled in special cooler and separated by magnets and screens. The ability to use a wide range of solid carbon reductants •is the main inherent advantage of the process. It is well suited to production of low sulphur di-rect-reduced pellets or sponge of 93-95 per cent metallization. Oxide pellets at 68 per cent Fe give a product at 95 per cent total Fe with about 95 per cent metallization; Sulphur is about 0.03 per cent to 0.01 per cent. In heat energy require-ments at about 3.5 million K cal/M.T. product is comparable to the better amongst the gaseous reduction processes. Power consumption is of the order of 55 KlArh/M.T. product. From the point of view of industrial opera-tions SL/RN is newer than the well established HYL. Start-up difficulties are encountered but these are more in the nature of insufficient engi-neering and operational problems than process problems. Engineering problems of such nature are normally encountered on nearly all industries particularly where the processes involved are comparatively new. Problems were also found by the HYL gaseous reduc-tion processes, which needed as much as 30 months of experience after start-ups to arrive at satisfactory engineering solutions. Whilst some of the gaseous reduction processes have had time the solid reductant process should be able to hold its own. A year or so from now should see most of the 'problems' re-moved enabling industry to welcome not only the solid reductant process but prereduction as a whole on a more readily acceptable basis than hitherto. Use of prereduced material Broadly depending on the degree of metalliz-ation, gangue content etc. the main uses are i) Electric steel making furnace — charged with scrap. Recent studies indicate a mixed charge of prereduced pellets and scrap in appro-ximately 60:40 ratio is more easily processed than a charge wholly of either. As indicated in forecasts given above about 20 per cent of world crude steel — i.e. over 180 million tons -- are  expected to be electric furnace steel by end/ of decade. In view of economics, as currently predictable, a very, fast growth of use of prere-duced ore in electric steel making is strongly in-dicated. Thus a large percentage of 62 million tons tof world prereduced ores will be used di-rectly in electric steel making by 1980. ii) Basic Oxygen Furnace. With a much lower degree of metallization, down to 75 per cent or 70 per cent. and less stringent specifica-tions for gangue, use in oxygen converters is possible. Although technically any coolant—iron ore with 0% metallzation—can be used the use of prereduced ores will depend on economic eva-luation of the numerous factors involved. iii) Blast Furnace. Number of tests have been made, on commercial and non-commercial scale, using prereduced iron ores in the blast furnace. Although at one time great emphasis was placed on the use of such ores in blast fur-naces interested in European and American con-tinents now seems to be largely away from this direction. Nevertheless serious research on this aspect is currently receiving attention in Japan. Japan's interest may be attributed to its unique position in the world as a steel producer very largely dependnt on long distance ocean trans-port of iron ore and increasingly expensive cok-ing coal. Experiments in Japan have indicated Timms rI Reduction - MetalAisation 269 F Fe Percent Gangue in Ores re* Megnetit2_, aconite n n 	 nn•  	 dr. n  n nn nn •  6 7 6 n 43 68,5_ 391.2 3$, 	 5* 	 10% B.O.F. - B.F. area 	 area 7 SiO2 4, A1203 III Fe that a 10 per cent increase in burden metalliza-tion decreases coke rate by about 6 per cent. Studies by U.S. Bureau of Mines in experi-mental blast furnace indicate that with an 80 per cent reduced burden instead of normal pellets burden lowered coke rate by 53 per cent and increased production rate by 175 per cent. The main question of the use of prereduced ores is of economics; balancing of cost of prereduction against reduction of coal/coke cost and increas-ed pig production. With the current difficulties in supply and production of coking coals and its increasing cost as experienced in India perhaps the use of a supplementary process — use of pre-reduced ore in B.F. — which decrease the pres-sure on coking coal /coke is worthy of a syste-matic study. Added advantage would be increas- ed production at blast furnace. Specifications of ore and prereduced product Specifications of iron ore used for prereduc-tion would be guided by the end use of the pro.. duct (E.F. or B.O.F. or B:F,) and also to some extent on the process used for prereduction. The prereduction industry is still very young and no clear cut specifications for ores to be used have been established. A fairly wide range of iron ores have been used in the commercial and non-commercial plants in the past. On the basis of available data, metallurgical and other consi-derations and attempt is made below to define the broad parameters of ores for optimum oper-ating conditions under economic environment currently understood. 270 Broad range of ores to be used in a) Electric Furnace Electric arc steel furnace is basically not a reduction but a melting furnace. Some reduc-tion is achieved at cost of increased electrical energy and increased use of carbon electrodes. Slag derived from gangue Si02 + A1203 in ore will need extra electric energy for slag off. Very low P and S are required to meet steel quality. Thus desirable:--- Degree of metallization over 90 per cent or reduction over 93 per cent. Residual oxygen less than 0.03 ton /ton steel. Low Fe slag with basi-city of under 5% A1203 + Si02/Fe gives gangue in ore at 3.4 to 3.5 per cent (for hematite and magnetite ores respectively). Ores under 3.5 per cent Si02 + A1203 and generally under 3 per cent would appear preferable. To achieve this end superconcentrates with under 2 per cent SiOz being experimented upon in U.S.A. To match above conditions Fe in Hematite ores at 67.6 per cent and at 70 per cent in Magnetites and about 61 per cent in limonites. b) B.O.F. Metallization down to 75 70 per cent. Oxygen up to 0 A1203 + SiOz ratio below Fe works out to Si02 + A1203 a)  Hematite at 6.5% : Fe 65.41, b)  Magnetite at 6.75% : Fe 67.75% and c) Limonite at 5.7% : Fe 59.2% c) Blast Furnace Broadly similar to that used in B.O.F. but lower metallisation 70 — 50%, and larger gangue contents are tolerated. Optimum degree of me-tallization basically a question of balancing eco- nomies and will thus have to be worked out sepa-rately for individual conditions. While the above is an attempt at generally defining parameters of ores for optimization of production economies it must be noted that these vary with conditions of economy and availability of resources from country to country. Ores (oxide and prereduced) of less rigid specifications have been successfully used in the past. For instance HYL prereduced ores at 85 per cent metallization and over 6.5' per cent SiO2i have been used in electric steel furnaces, in a ratio of 60:40 with scrap, for years. Application under Indian conditions It is obvious that in view of shortage of na-tural gas, in most cases, the solid reductant pro-cess should hold out promise of greater interest than the gaseous reductant methods. The pre-sent problems facing individual plants using the former process need not be cause for pessimism as these do not appear unsurmountable. Mainly three broad fields of application of prereduction appear possible and to that extent one sees .a strong potential, subject to solid re-ductant process successfully ironing out Tugs'. i) Application to existing and future inte-grated steel plants as an ancillary (complimen-tary) process for increasing production of hot metal/ingot steel. High along volumes and high coke rates arising out of fundamentally high ash in 'Indian coal /coke are contributory factors to low blast furnace productivity; below 1.5 ton/ m3 furnace volume. Introduction of prereduced burden, in blast furnace, with a suitable degree of metallization can substantially decrease coke rate and increase blast furnace production. Viewed like a sinter/pellet plant as a means of making a high prepared burden (prereduced Burden) and using more readily available and less expen-sive reductant (non-coking coal) capacities of existing blast furnaces stand to be stretched' If technology/economies permit, use of preredu-ced ore directly in B.O.F. is indicated. Second condition would permit some increase in steel per cent or even .07 ton/ton steel. 10 percent which in: d) Size specifications Sized ore or natural pellets (12 m.m 	 25 m.m.) Pellets 12 m.m. Fines Below 10 mesh static bed. shaft furnace or Rotary Kiln (solid reductant). Fluidised bed process. 271 capacity in integrated steel works without going through major investments in blast furnace/ coke over complex stage. One would think a solid re-ductant process judiciously used with above ob-jectives would well demand serious considerations and techno-economic evaluation studies to ex-plore new avenues. • ii) Establishment of new small centres for small scale steel production — mini steel plants — and foundries. Prereduced ore to be used as supplement to or in lieu of scrap in electric fur-naces. Centres established near ports viz. Visha-kapaatnam, Goa, Madras. Mangalore can have added advantage of using alternative processes based on LNG from Persian Gulf area if justified. Gases from nearby refineries offer another possi-bility. iii) Manufacture of prereduced ore/pellet for export. Kudremukh iron ores have already been well studied for export. If the present pro-posals of collaborations in the area are not found acceptable a modified proposal based on manu-facture of prereduced product from Kudremukh ores would be well worth a pragmatic look. Over 500 million tons of fully explored and studied ores so close to the port call for a bold futuristic approach instead of remaining unused over years. Summary and Conclusions In spite of numerous difficulties faced, there is no doubt prereduction has come to stay. It is however, not likely, in the foreseeable future, to replace the well established large scale blast furnace method of pig iron manufacture. Used as a method of taking a highly prepared (prere-duced) burden for blast furnace or as method of manufacture of sponge for direct use in steel mak-ing furnaces prereduction is likely to have noti-ceable consequences on the future economics of iron and steel making. It probably is likely to aid expansion of world iron and steel capacity. , Once the solid reductant method of prereduction is able to remove the present 'bugs' it is likely to find wide application in this country. One, however, need not wait for all these bugs to be removed. If positive steps are straight away taken the prereduction method can be introduc-ed during the 5th or 6th Plan Periods to help in- crease and probably at a lower cost than other-wise the country's iron and probably at a lower it be too optimistic to think in terms of possibi-lity of establishing one or two small/medium sized prereduction plants for the existing or pro-posed integrated steel works during the 5th plan, not so much from the point of view of immediate production/economic gains as the 6th and. subse-quent Plans. 272 

Iron Ore Pre-Reduction

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Iron Ore Pre-Reduction

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