OVERVIEW_ •••• _

Innovative Iron and Steelmaking - __________ K. Upadhya

This paper addresses the need for radically new innovative technology to produce liquid iron and steel. The sa-lient features of these so called "direct smelting" processes are also discussed, as are the developments in iron blast furnaces and steelmaking technology and processes. The energy required for a direct smelting process, based on in-jection of coal and domestic iron ores and other raw materials, has been cal-culated and compared with various similar direct smelting processes as well as existing blast furnaces. Finally, the future trends in the liquid iron and steelmaking technology and processes have been speculated.

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INTRODUCTION Over the last few decades, the. existing ferrous industry developed in a

primarily empirical fashion. The extensive research work carried out dur-ing that time mainly deals with refining established processing routes. Much developmental activity has focused on the stepwise correction of failures in our existing processes to meet quality demands, increase productivity, optimize energy consumption, and improve both labor and environmental conditions. Advancement in contemporary iron and steel process technology has reached a critical limit. Any further savings, espe-cially in energy consumed and increased productivity, will be realized by adopting radically new innovations in ferrous industry. For example, the blast furnace for iron production has probably reached its maximum size of 13.5-15.0 meter hearth diameter, and, consequently, a certain limit has been imposed regarding both the blast furnace construction size and the production capacity which is currently a maximum of up to 10,000 metric tons per day per unit. Also, coke consumption of up to 0.46kg/kg of hot metal has been achieved in Japan and Europe by using increased blast temperatures and oxygen enrichment, high top pressure, humidified blast, hydrocarbon and coal injection, and computerized process control. On the other hand, from thermodynamic consideration, the coke consumption rate for oxide burden is 0.38kg/kg of hot metal at a blast temperature of 1200°C. Thus, a further theoretical savings in coke consumption of only 0.08kg/kg of hot metal could be expected. However, the required capital outlay needed to exploit this last reserve capacity may exceed the savings achieved. From these considerations, it appears that any further large energy savings in producing liquid iron or steel will be realized from a completely new, radically innovative process and not from modifying and improving iron blast furnaces.

There are few such processes being investigated today. Most of these "direct smelting" alternatives are still in their conceptual stages. To com-pete seriously with BF/BOF steelmaking, direct smelting processes must: • Use fine ore without any agglomeration as raw material and coal as

reductant. • In some processes, plasma is used as a heat source in conjunction with

coal, making the exit gas temperature very high. Hence, either the volume of gas generated must be kept at minimum or the heat content of these waste gases must be fully utilized.

• Because of high operating temperatures, refractory wear could be a serious problem. The processing conditions should be arranged so that refractory wear will be minimal.

• The total energy consumed must be kept at a minimum level by apply-ing co generative principles.

• The processes should have low capital investment and maximum pollu-tion control. They must also be continuous and operate at high specific output. Recently, several radically different "direct smelting" processes have

emerged. Only a few, however, are operating on a commercial scale. Most are still on either the laboratory research or pilot plant scale.

DEVELOPMENTS IN IRON BLAST FURNACES During the last two decades, enormous improvements in blast furnaces

have been made and are well documented, especially in a recent excellent article by Heinrich et aLl Basically, most of the changes or improvements can be categorized into four groups: reduced energy consumption; improved metal quality through uniform furnace operation; reduced down time and increased output/BF; and improved labor and environmental factors.

The factors contributing most to energy reduction in blast furnaces are high blast temperature, the use of well screened and prepared burden materials, and improvements in materials distribution at the top.2 Another area currently under scrutiny for further energy savings are blast furnace ancilliary plants.3,4,5 Further potentials for energy savings through dry

JOURNAL OF METALS· March, 1986

granulation of blast furnace slag with integrated heat recovery area also currently being examined.6 The heat contained in the slag, approximately 1.8 MJ/ton,6 represents an attractive source of energy recovery. This are must be vigorously pursued in the near future.

Through various improvements, tuyeres damage, a major factor in downtime, has almost been eliminated. These improvements are well documented in an article by Leuger et a1. 7 Also, the introduction of higher blast and dome temperatures, as well as higher blast pressure, has almost eliminated stress corrosion cracking, especially in stoves, hot blast mains, and expansion joints. A reduction in downtimes has also been achieved by employing preventive maintenance and a computerized, automated system.

There has been significant advancement towards improving labor condi-tions and reducing the environment pollution. Assisting in environmental control are: stockhouse and charging operations, blast furnace cooling, casthouses, and slag utilization. Environmental pollution has been reduced by slag granulation using vapor stack and stack spraying equipment, covering slag bins or pits, and reducing noise by using high top pressure furnaces, changing from septum valves to annular-gap scrubbers in gas cleaning system.

NEW PROCESSES FOR IRON MAKING Kawasaki Steel has reported development of a process in which iron

blast furnaces have split into two separate small units designed for processing fine ore and low grade coke as a reductant and heat supply source.8 This furnace can be used in producing liquid iron as well as ferro-alloys production. In the case of ferro-alloys production, the process requires supplementary injection of hydrocarbons, such as methane. Figure 1 features a schematic diagram of this furnace arrangement. In this process, the fine iron ore is injected into the pre-reduction furnaces and reduced by a combination of gases. Low grade coke is top charged through the center of the furnace. The coke reacts with hot blast of air or oxygen at the tuyere level to generate the necessary process heat and to form a strong reducing atmosphere inside the furnace. In the process, excess gas is generated, mainly as hydrogen or carbon monoxide. To make the concept commercially viable, this by-product gas must be further utilized in the power generating plant or sold to other utility companies. This particular process incorporates a dual tuyere design. Kawasaki claims that the design enhances the reducibility of chromium ores during ferro-alloy production. As an alternative source of energy, the main furnace is equipped to switch to fuel oil or natural gas.

Export gas

JOURNAL OF METALS· March, 1986

Prt!!l-rt!duclion Lrnace

~:;. Flneorech:atf18d :'~'. ' IftIOlhOturr«e ,:. " wrthOulpnot .:.; .. ~rab<Jn :' . :

~p!pelof 1I1I.c:\ICM"IOI tKlIblM101p

Slog>

.... " ..

Molten ~Feuo "JIOy$

furnace

-- OuIl !Uyt'r1'S

NOI'M'ntttJIUtgtellllcoal aJ!OIr1j~~1or

CCke-sa\'lng purpose

Figure 1. A schematic representation of the Kawasaki proposed iron making process.8

Figure 2. A schematic diagram of the KR process for liquid iron production.9

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Process

Dored

Eketorp-V allak (EV)

CIP

Direct-convector Smelting

KTH/u ddacon

McDowell-Wellman

Conred

Elkem

Elred

Inred

Plasmasmelt

Strategic Udy

ORCARB

VOEST

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According to Kawasaki, the furnaces' greater efficiency results from dichotomizing the phases of blast furnace operation into prereduction and smelting. Since the removal of oxygen is carried out in the prereduction furnace, while melting and refining is performed in another separate smelting furnace, there is an extra degree of freedom for more efficient operation. The energy consumption is less than in an iron blast furnace. Pollution control improves by eliminating the coke oven and sintering processes. The ore and reductant can be used in the inexpensive forms; i.e. fine ore and low grade coke. The operating cost, in the case of iron production, is reduced by 15 percent. When producing ferrochromium, the energy savings are 50 percent.

A novel technique, the KR process, for producin~ molten iron has been jointly developed by Korf and VOEST in Austria. The KR process is a new ironmaking technology for producing hot metal which replaces expen-sive coke with a wide range of coals for heating and generating reducing gases. In the dual reactor KR process, there are essentially two main process sequences for liquid iron production: reduction of iron ore, and producing reducing gases and melting reduced iron. Iron ore is reduced in

Table I. Direct Smelting Processes for Liquid Iron Production

Process Concept

One stage process; reduction and smelting of preheated fine iron ores in a rotary kiln.

One stage; Injection of oil and fine ore, secondary combustion with O2

One stage; injection of fine ore carbon and and oxygen in rotating horizontal cylinder type reactor.

One stage; oxygen, coal dust, and iron ore fines are injected into the side of a convector containing molten iron.

One stage; injection of fine ore or dust, carbon and oxygen into the side of a convector with a channel-type Two stage process; iron ore, coal dust and flux were mixed and pelletized. The pelletized hot charge was continuously fed to submerged electric arc furnace. Two stage; iron ore was pre-reduced in a fluidized bed and then final reduction and smelting was carried out in a convector by injection of carbon and oxygen.

Two stage, employing rotary kiln and Tysland-Hole electric ironmaking furnace.

Two stage pre-reduction in fluidized bed and final reduction and smelting in a single electrode electric arc furnace.

Two stage, preheating of fine ore and coal dust followed by flash smelting, and final reduction and smelting in an electric arc furnace.

Two stage, pre-reduction with gas in a fluidizied bed follow by final reduction and smelting using plasma in a coke filled shaft furnace. Two stage, employing rotary kiln and electric furnace. Two stage, reduction in rotary kiln and smelting in electric furnace.

Two stage, pre-reduction of ore in a shaft by reducing gases and smelting in electric furance.

Parent Company (Country)

Stora -Kopparberg, Sweden

Metallurgical Research Station, Lulea, Sweden

BSC UK

Royal Institute of Technology, Stockholm, Sweden

Royal Technical University,· Stockholm, Sweden Mewani Cast-Iron Pipe Co. Alabama, U.S.A.

Stora Kopparberg, Sweden

Industrial plants in Japan, South Africa and Yugoslavia

STORAIASEA

Boliden A.B. Sweden

SKF Sweden

Inter alia CVG, Venezuela

Swindell and Dresslar, U.S.A.

VOEST, Austria

Remarks

Industrial plant abandoned in 1969.

Discontinued after pilot test in 1970

Discontinued after experi-mental test in 1980.

Proposed process by Eketorp et.al.

Tests have been carried out with Mo oxide and steelmaking dust at Hagfors.

Abandoned after one year of initial test in 1970.

Proposed process.

Operation with Titanium manganese and vanadium containing ores.

Successful industrial tests have been conducted for several years.

Industrial tests carried out with calcined pyrite ores.

Pilot plant at Hofors, Sweden.

Industrial plants.

No industrial plants.

After initial test now abandoned.

JOURNAL OF METALS· March, 1986

Table II. Direct Reduction/Smelting of U.S. Iron Ore

Mass Balance

Charge Materials:

a) 1600 kg iron ore with 62% Fe (1417 kg Fe20a) 10% Si02 (160 kg) 1% Mno (16 kg) 0.44% A120 a (7.0 kg)

b) 568 kg coke breeze wi th 88% C (500 kg carbon) + 43 kg sulfur + 25 kg miscellaneous

c) 270 kg CaO

d) 577 + 36 = 613 kg oxygen 429 rna

a) + b) + c) + d) Total mass = 1600 + 568 + 270 + 613 = 3051 kg

Yield:

a) 1000 kg Fe with 4.5%C

b) 500 kg slag with 9.4% Feo (47 kg) 32% Si02 (160 kg) 3.2% MnO (16 kg) 1.4% A120 a (7.0 kg)

c) 1551 kg gas with

CO CO2

Miscellaneous: S2

43.26% 39.59% 14.38%

2.77%

100%

a) + b) + c) = 100 + 500 + 1551 = 3051 kg

671 kg 614 kg 223 kg 43 kg

1551 kg

(= 23970 mol) (= 13946 mol) (= 12389 mol)

a shaft furnace while the reducing gases are produced and sponge iron melting is performed in a "me Iter gasifier." A schematic arrangement of this process is shown in Figure 2.

The process can be operated by employing high pressures up to 5 bar. The raw materials, i.e. iron ore, coal and fluxes, are charged into the melter gasifier via a lock system. In the top section of this unit, the coal comes in contact with a gas at approximately 1l00°C, and thus coal is dried, degasified and transformed into coke. This coke is further degasified by the oxygen which is blown in via side nozzles. The gas flow rate in the cylindrical portion of the gasifier is selected so that a stable fluidized bed is maintained. The oxygen blown via the side nozzle will react with coke to produce CO2 , which in turn will further react with the coke to produce CO. ·The temperature in the fluidized bed is maintained at 1600-1700°C. This relatively high temperature in the fluidized bed, as well as in the gasifier dome, produces a highly reducing gas which consists of 95% CO and H2, approximately 2% CO2 and a balance of CH4 and N 2.

In the reduction shaft, the iron ore is reduced to metallic iron in a fashion very similar. to conventional iron blast furnaces when using coun-ter flow principles of solid charge and reducing gases. The hot reduced iron is discharged from the reduction shaft and enters the melter gasifier. The rate of fall, however, is extremely slow within fluidized bed section. In the fluidized bed, the sponge iron is further heated and melted. Finally, a liquid metal and liquid slag bath is formed in the gasifier hearth. Analo-gous to the blast furnace, iron and slag are periodically discharged at about three hour intervals. The tapped liquid metal temperature is in the range of 1400-1500°C. The carbon content of liquid iron is between 2% to 5%, depending on the charge materials used and modes of furnace operation. The excess gas produced during the KR process may be used either in other sections of steel plants, such as rolling mill, or for producing electricity in the power plant. Since 1981, a KR demonstration plant has operated in Kehl with an annual production capacity of 60,000 tons. It is claimed that the coal consumption in this process is 650-800kg of fixed carbon per ton of hot metal produced.

DIRECT SMELTING PROCESSES Because of the high capital investment in a BF/BOF integrated steel

plant, blast furnaces depend on decreasing coking coal resources for energy, reductant, and improved pollution control. This necessitates development of radically new, alternative technology for directly producing liquid iron or

JOURNAL OF METALS· March, 1986

Table III. Heat Balance

Heat Generated Meal % --Combustion of Coke 1950.9 72.2% CO,C02 Oxidation of other 729.7 27.0% Compound in Coke breeze Solution of C 20.3 0.8%

2700.9 100.0%

Heat Absorbed Decomposition of 1700.0 62.9% Iron Oxide Sensible heat of pig 242.6 9.0% iron (Fe&C) Sensible heat of slag 164.9 6.1% Sensible heat of gases 223.1 8.3% Heat losses by conduction 370.3 13.7% and radi~tion

2700.9 100.0%

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Table IV. Energy Consumed in Per Metric Ton of Liquid Iron Produced

Direct Smelting

Plasma (Proposed Blast Energy Used Elred Smelt Process) Furnace Coal 700 kg 200 kg 568 100 kg in (sintering

(22,692 kJ/kg) plant)

GJ 15.89 4.54 12.89 2.23 Coke

(25,786 kJ/kg) 50 460

GJ 1.29 11.9 Oxygen

(9670 kJ/kg) 613 Blast preheating

GJ 5.9 =2.4

Electricity 700 KWH 1120 (9584 kJ/KWHl produced in

the system

GJ 10.73

Remarks Electricity Waste gas Top gas credit (Credit Credit 5.5GJ 2.88 GJ) (Unknown)

15.89 GJ 16.56 GJ 18.79 GJ 16.53 GJ (3.78 G Cal) (3.96 G Cal) (4.49 G Cal) (3.95 G Cal)

steel by using fine iron ore and less expensive coal. Some new processes use coal or coke breeze as a heat supply as well as for reducing oxide ores. Few rely on the plasma to supply the necessary heat required or on carbon or coke as the reducing agents. The major features of these processes are listed in the Table I. The calculated energy requirement for a "direct smelting" process, based on injecting coal, domestic iron ores, and other raw materials, is shown in Tables II and III. Plasma-red, plasma-smelt and direct injection smelting convertor processes are discussed in Reference 10, and the Elred and Inred processes are examined in an excellent article by Moore.ll It is worth mentioning that out of all these processes, only plasma-smelt, the Elred and the earlier mentioned KR processes have a good potential to seriously challenge blast furnaces in the near future. The success of these processes will primarily depend on the total energy con-sumed per ton of liquid iron produced. It will also rely on the energy source, i.e., coal vs. electricity, or a combination of both. The approximate value of the total energy consumed while producing one metric ton of liquid iron shown in Table IV for several processes. The net energy re-quired in any process must take into account the credits for waste gas utilization outside the process, such as for preheating/reduction of ores or for the generation of electricity.

STEELMAKING Recent developments and trends in oxygen steelmaking have been exam-

ined by several authors, including an article by Chatterjee et aJ.l2 Suffice to say, the advantages offered by the hybrid processes are enormous, and they have already shown superiority to both top and bottom blown processes. Table V summerizes their main features. In the bottom of the converter either oxidizing gases, such as O2 , CO2, air, or inert gases, through porous bricks or tuyeres, are injected in conjunction with oxygen blowing from the top of converter.

Hybrid processes (mixed blown) offer advantages compared with flexible top blown processes: slopping can be largely reduced, even by a weak stirring rates; concentration and temperature gradients in the metal bath can be eliminated; and lower temperature differences between the metal and slag bath and higher ferro-alloy recovery can be achieved. The hybrid processes also offer advantages compared to bottom blown processes: a higher percentage of scrap can be melted; and the number of tuyeres in the bottom of the converter is reduced by 60-70% when only inert gas is blown through the bottom (in turn, it offers noise control as opposed to only bottom blowing process).

JOURNAL OF METALS· March, 1986

Table V. Steelmaking Processes

Parent Company Injection Materials Gas Flow Rate,

Process (Country) Method Injected Nm3 /min

LD VOEST Water cooled 3.0·3.5 (Austria) lance

LD·AC ARBED·CRM O2 + lime 3.0·3.5 (Belgium) powder

LD·KG Kawasaki Steel Tuyeres O2 as well as 3.0·3.5 (Japan) Ar/N2 0.01·0.05

KMS·KS Klockner· Tuyeres Coal + oil 4.5·5.0 Maxhutte + O2 + lime

OBM·S Tuyeres O2 , CnHn AOB Inland· U.C. Lance O2 + Ar 3.0·3.50

(U.S.A.)

LD·CL Nippon.Kokan Lance O2 3.0·3.50 (Japan) Circulated

NK·CB Nippon·Kokan Tuyeres and O2 3.0·3.3 (Japan) porrous plus Ar/Co2/N2 0.04·0.1

OBM Maxhutte Tuyeres O2 + lime (Germany)

Q·BOP U.S. Steel Tuyeres Oz + lime + (U.S.A.) Hydrocarbons

LW8 Creusot·Loire Tuyeres LiquidCnHm (France) + O2

AOD Union Carbide Tuyeres Ar + Oz (U.S.A.)

LBE IRSID Porous N2/Ar 0.1·0.5 (France) plugs

LD·HC CRM Tuyeres OzlNzlAr 0.2·0.3 (Belgium)

BSC BSC Tuyeres 02/N2 0.035·0.21 (England)

8TB Sumitomo Tuyeres 02/N 2/ Ar/C02 0.1·0.15 (Japan)

LD·OB Nippon Steel Tuyeres 02/Ar/CnHm = 0.3 (Japan)

LD·AB Nippon Tuyeres N 2/Ar 0.025·0.3 (Japan)

K·BOP Kawasaki Tuyeres °2/CnHm 1.6·2.1 (Japan)

LD·OTP Kobe Steel Tuyeres 02/Ar 0.25·0.1 (Japan)

It is worth mentioning that the hybrid processes in steelmaking have become extremely popular and a converter of 350 ton capacity has been operating over the last few years in Japan.13,14

In summary, more steelmaking companies are converting their existing facilities to the hybrid processes and are taking advantage of higher effi· ciency in terms of yield and production rates. They are also developing better process control and higher alloy recovery.

CONCLUSIONS Because of the high capital cost involved with an BF/BOF integrated

steel plant, prime considerations include the deceasing coke coal resources for both energy and reductant, and the need for improved pollution control. These conditions should spur thoughts about alternative methods of iron and steel production. There are several proposed techniques being tested and some have been commercially developed. One such process is SKF plasmadust, based on coal and plasma. Another such process is Elred, currently being marketed by ASEA. Several other "direct smelting" processes are now under investigation, and the future shape of iron and steelmaking will largely depend on their successful commercialization in the coming years.

JOURNAL OF METALS • March, 1986

References 1. P. Heinrich and W. Rettweiler, "Recent Develop·

ment in Blast Furnace Technology," Steel Times, Dec. 1984.

2. M. Higuchi, T. Shibuya and S. Kishimoto, paper presented at IntI. Blast Furnace Congress, Arles;France t979, cf Revde Metallurgtc, 77, (1980) p. 937. 3. S. Shiroda, paper at lISI 12th Committee on Tech·

nology Technical Exchange Session, Brussels, June (1980).

4. H. Fujimori and M. Inubushi, Iron and Steel Engineer, 53, No. 10 (1976).

5. "Top Pressure Recovery Turbine of Blast Furnace," Bull. Sumitomo Metal Industnes, Ltd., Japan.

6. Steel Times, 208, (1980) p. 469. 7. F. Leuger and J. Luttgens, Stahl und Eiesen, 96,

(1976) p. 153. 8. Steel Times, April (1984). 9. G. Papst and H. Rolf, "KR·Process Means Hot

Metal Production on the Basis of Coal," paper presented in the ISS conference 1985, Detroit, U.S.A. 10. K. Upadhya, J.J. Moore and KJ. Reid, "Application of Plasma Technology in Iron anq Steelmaking," JOM, Vol. 36, No. 2 (1984). 11. J.J. Moore, "An Examination of New Direct Smelting Processes for Iron and Steelmaking," Vol. 34 (1982). 12. A. Chatterjee, C. Manque and P. Nilles, "Overview of Present Status of Oxygen Steelmaking and its Expected Future Trends," I ro"making and Steelmaking, vol. 11, No. 3 (1984). 13. "The STB Process," Sumitomo Metals Industries, Sept. 1981. 14. K. Taquch, M. Hannyo, J. Shinatani and T. Hasagawa, Iron and Steel Eng., (1983) p. 26.

ABOUT THE AUTHOR _____ _

K. Upadhya received his Ph.D. in metallurgy from the University of Strathclyde in the Unit· ed Kingdom. He is currently Assistant Profes· sor in the Department of Civil Engineering, Mechanics and Metallurgy for the University of Illinois at Chicago. Dr. Upadhya is also a member of TMS.

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