An Examination of the New Direct Smelting Processes for Iron and Steelmaking

J. J. Moore

SUMMARY This paper discusses the need for a radical technological

change to take place in the production of iron and steel and suggests the salient features that should be addressed. In this respect, five new direct smelting steelmaking systems which, at least in part, provide some measure of meeting these salient features, have been examined and compared with the present blast furnace/basic oxygen furnace route. It is suggested that future ministeel plants may benefit from adopting one of these new direct smelting units when used in conjunction with converter steelmaking and continuous­casting facilities.

INTRODUCTION

The major incentives in developing new steelmaking processes are concerned with reducing energy and labor costs and capital expenditure, maximizing pollution con­trol, and optimizing production flexibility. Extensive tech­nological modifications over the past 30 years have resulted in a considerable reduction in the overall energy consumed in the blast furnacelbasic oxygen furnace route. However, it is still well above the thermodynamic equilibrium value, and it appears that any further dramatic reduction in energy consumption in the overall production of one metric ton of steel from iron ore will more likely result from more radical process changes than modifications to the blast furnace process. Added to this, the capital cost of coke ovens, ore processing (pelletizing and sintering), hot blast stoves, gas cleaning equipment, and the blast furnace itself is over one billion dollars. At the same time, the blast­furnace process relies on expensive metallurgical coke as a reductant, heat producer, and as a charge support in the shaft.

There are several radically new direct smelting (D.S.) processes which are emerging as contenders to both the blast furnace (B.F.) and the so called "direct reduction" (D.R.) processes for ironmaking and steelmaking. These D.S. processes have the following salient features: • coal used as the reductant; • minimum iron ore processing (pelletizing and sintering)

-preferably direct use of concentrate; • minimum ancillary plant and material handling; • low capital investment; • molten iron product that can be readily processed into

required steel composition; • maximum continuous processing; • maximum pollution control; and • minimum energy consumption and application of

cogenerative principles. Each of these new D.S. processes is characterized by a

two-stage continuous operation of 1) preheating and prereduction, followed by 2) final reduction. The resulting high-carbon molten iron can be readily processed via a converter into the required steel grade.

JOURNAL OF METALS· June 1982

This paper examines the need for development of radi­cally new iron and steelmaking processes, describes five of such processes that have recently been developed on at least pilot-plant basis and discusses how and under what conditions such processes may be implemented.

THE NEED FOR RADICAL TECHNOLOGICAL CHANGE

The developments that have taken place in the ironmaking process over the past 100 years have done so largely by modifying the same original process of reducing iron ore with coke in a shaft furnace. In this respect, considerable process improvements have taken place in the blast fur­nace process over the past 30 years. For example, increased blast preheat temperature and oxygen enrichment, high top pressure, humidified blast, hydrocarbon and coal injec­tion, and larger hearth diameters coupled with more pre­cise process control with the aid of computers have resulted in a production improvement from 1,000 metric tons per day to over 10,000 metric tons per day. However, it appears that this technological advancement is approaching the maximum degree of modification and refinement for the blast furnace process and that any further significant improvements in ironmaking will require far more radical changes and rethinking.

Steelmaking developments have followed more diverse paths than ironmaking since Bessemer first blew air into his converter of molten iron in 1855. The development of the open-hearth process was largely initiated due to the poor refining control of the Bessemer process and, although the open hearth operated with much longer refining times, open-hearth steelmaking capacity increased to an all-time high until the 1950s. The development of the top-blown oxygen converters in the 1950s permitted much faster bulk steel production rates than were possible in the open hearth. At the same time, the need to melt and refine increasing quantities of scrap accelerated the development of electric arc steelmaking. The development and improvement of the electric arc process, the top-blown and, more recently, the bottom-blown oxygen converter processes, have resulted in the replacement of the open hearths by electric arcs for scrap charges and by oxygen converters for molten-iron charges (Figure 1).

It is evident from these data that the frequency of implementing steelmaking technological developments, inno­vations, and changes has steadily increased over the past 30 years. It is reasonable to assume that this frequency will continue and even increase, and that an extremely important consideration for new steelworks will be the new and emerging technologies.

There is a great reluctance to change in all capital inten­sive industries. This has been largely evident in the ironmaking industry. However, the constraints on this con­dition are changing. The developed countries have largely

39

consumed their richer iron ores and are now being forced to use much leaner ores and to upgrade these by more expensive (with respect to both processing and energy costs) concentrating and agglomerating processes in an effort to retain their market share. On the other hand, the richer iron ores presently being processed are largely available in the developing countries of South America, Africa, India, and Australia.

This change in condition:;; has led to two important approaches to iron and steelmaking. The first approach is one of reducing processing and energy costs to a minimum by maximizing production rates, using the most modern and proven technology presently available, coupled with the imposition of stringent quality control procedures and utilization of a high level of technically qualified personnel and computer control to monitor the processes. Inevitably, this has meant modern blast furnace operation with its ancillary ore pretreatment and agglomeration cycles, coke ovens, and gas-cleaning plants followed by converter steel­making (i.e., BF/BOF). This approach is pertinent to the developed countries with a large market share of steel products and has been most eloquently demonstrated by Japan (Figure 2) with its emphasis on production rates and quality.

The second approach largely applies to the developing countries which possess the richer iron ores, but which also have a much lower demand and market for steel products. These countries have taken advantage of the lower capital expenditure, but usually increased energy consumptions, associated with the relatively new direct reduction/electric arc process routes (D.R.lE.A.F.l. These

PRODUCTION T .10.'

12

10

" " 6 "

" 4 / ••••••

" .' //._.-.L,. •.••. 2, , ....... , .... . ..... /. ................ . ..... ., ......... ... ........ . 1960 1970 1980 1990 2000

----TOTAL

_____ .BOF

••••••••••• ARC

_._._._._ OPEN HEARTH

•••••••• BESSEMER

Figure 1. World steelmaking capacity by process.

~ .. .. ,.. ~ 500 II E ::: .. ! 400 1/1 .. ... ~ u 300

" 2 ~ 200 "> -u

" ~ 100 .L

o 1960 1965 1970 1975 1980

Figure 2. Comparison of steel productlvHy for various countries.1

40

take the form of gas (e.g., CO + H2) or solid (e.g., coal, char, anthracite) reductants used in shaft furnaces (e.g., Midrex, NSC, HYL III), fluidized beds (e.g., Fior) , static bed retorts (e.g., HYL II) and rotary kilns (e.g., SLRN, DRC, Krupp Codir, Accar) as outlined in Figures 3 and 4 and Table I. Extensive reviews of direct reduction processes have recently been prepared.2,3.4

Thus, it has been left largely to these resource-rich devel­oping countries to pilot the direct reduction processes into full commercialization. However, 87% of the presently availa­ble direct reduction capacity uses reformed natural gas as reductant (Table I). This is particularly important since most of these developing countries also have a natural gas resource. For those that do not, the obvious answer is coal, but the use of a coal reductant in rotary kilns has not met with a large degree of success due to problems associated with coal reactivity and accretion build-up on the sides of the kiln created from the coal ash. Nevertheless, processes

Table I: Distribution of World Direct Reduction Capacity, 19804

Midrex HYL SLRN Purofer Others

Natural gas Coal Gas/fuel oil

Shaft furnace Static bed Rotary kiln Fluidized bed

Venezuela Iran Mexico Canada United States Japan Others

By Process, %

By Reductant Source, %

By Process Type, %

By Country, %

38.5 38.1

5.6 4.2

13.6

87.4 11.1

1.5

44.6 38.9 12.6 3.9

24.8 14.2 10.7

8.7 6.1 6.1

29.4

which efficiently utilize coal rather than natural gas will provide considerable economic advantages. This is particu­larly the case in the United States where coal reserves are very high, which has led to the development of the new coal-based shaft D.R. process recently developed by Midrex (i.e., Midrex E.D.R.) and SKF (i.e., SKF Plasmared). How­ever, both these new coal-based shaft D.R. processes rely on a pelletized charge and produce a solid "sponge" iron which must be cooled and charged to an electric arc fur­nace for reheating and melting.5

Further important considerations in assessing these new processes will be pollution control and the use of a cogenerative energy system that efficiently utilizes the process energy generated, such as the chemical and sensi­ble heats in the offgases. Both these areas are not strong points in favor of the BF/BOF route, and the need for a more radically innovative approach has been ably argued by Szekely6 and Eketorp.7

Five direct smelting processes have recently been developed and demonstrated on semicommercial, pilot plant, or large experimental bases. These are the ELRED process,B,9 the INRED process,lO,n the SKF Plasmasmelt process,12-14 the McDowell-Wellman process,15 and a converter smelting process.16.17 These processes adhere relatively closely to

JOURNAL OF METALS· June 1982

the salient features outlined earlier and, as such, ,will provide suitable exampl'es of the radical rethinking that presently is being pursued. It is of particular interest that four of these processes have been developed in Sweden, a country that has a considerable reputation in steelmaking development and one that relies on producing high-quality steels from relatively small steelworks complexes.

THE ELRED PROCESS

The ELRED (Electric Reduction) process was developed jointly by Stora Kopparberg and ASEA in Sweden in the early 1970s. A pilot plant has been operated at a capacity of 12 metric ton/day at ASEA. A diagram of the ELRED process (prereduction and final reduction stages) is given in Figure 5. This is an ideal example of the principle of a fully cogenerative system.

A two-stage process is used incorporating prereduction in a fluidized bed and final reduction in a D.C. arc furnace. Iron ore fines are pre reduced with coal dust and air in a circulating fast fluidized bed at 950°C. The prereducing unit operates with a high gas velocity, producing a cyclone effect which is claimed to offer a high degree of control over the reactions and a throughput of 500 kg/h. A stoichi­ometric excess of coal powder is also used which, in combi­nation with the high gas velocity, reduces the problem of sticking in the fast fluidized bed. The exit gas comprising CO, C02, and N2 is cleaned, the dust returned to the prereducer, and the sensible heat of the offgas used to

OFFGAS A

IRON ORE FEED

A. REDUCTION B. COOLING

preheat the iron ore and air prior to the prereduction stage. The chemical energy of the offgas is used to gener­ate electricity for the subsequent final reduction stage after removal of C02. The electrical process produced from combustion of the gas is generated using gas and steam turbines. In this way, the reducing gas for the final reduc­tion stage is generated in situ in the fast fluidized bed which also provides prereduction and preheating of the charge. This obviates the need for expensive coal gasifica­tion facilities.

The final reduction is conducted in a D.C. electric arc furnace at 1450°C with one hollow graphite electrode. The prereduced iron ore of 60-70% metallization is removed from the bottom of the fluidized· bed, cooled to about 700°C, and fed with slag-forming constituents into the hollow electrode of the D.C. electric arc furnace. The latter is operated with a foaming slag to aid separation of the slag from the metal. This improves penetration of the prereduced material into the liquid melt of the D.C. arc furnace and also aids the protection of the melt from the environment. The exit gas from the final reduction stage is also used to generate electricity in the steam turbine plant, but is not as rich as that from the prereducer. The tap-out analysis gives an iron of approximately 3.5% C, 0.05% Si, 0.5% S. The D.C. arc furnace is fed continuously from the prereducer and is tapped at regular intervals in order to ease the smooth continuation of processing in the final reduction stage; 30-50% of the molten product is retained in the D.C. arc furnace from each tap to initiate the melt in the next

r;;l CHARGE

I AND I CHARGE

'--..... ~ C. GAS REFORMER ~ NATURAL

GAS -_ ...... -DRI

a) MIDREX SHAFT

FUEL

DRI

c) SLRN ROTARY KILN

Figure 3. Diagrams of conventional direct reduction processes.3

JOURNAL OF METALS· June 1982

DRI

FEED

AIR--~

NATURAL GAS

b) HYL II STATIC BED RETORTS

a) FIOR FLUIDIZED BEDS

DRI

OFF GAS

MAKE-UP HYDROGEN

41

CURRENT DR PROCESSES

HYL HOEGANAES MIDREJ( ARMCO PUROFER NSC WIBERG HYL III

MIDREX EDR KINGLOR-METOR WIBERG SKF PLASMARED

ACCAR SLIRN DRC KRUPP CODIR HIGHVELD KAWASAKI SDR SPM TISCO

Figure 4. Classification of worldwide direct reduction processes.

FLUE GASES

PREREDUCTION STAGE

_ REC'CULATED GAS

SLAG

PRE-REDUCED I CHARGE LIME

+ DC ARC FURNACE

Figure 5. The ELRED process.

-.

FINAL REDUCTION STAGE

LIQUID IRON

ORE---"

COAL---,

PRE-REDUCED CARBONACEOUS

MATERIAL

DUST --~ SLAG ---\

LIQUID IRON

CO

ELEC­TRICITY

a. PRE-REDUCTION 950°C b. CLEANING AND HEATING c. GAS TURBINE d. STEAM TURBINE e. DC ARC 1450°C

FIOR HIB

DUST

AIR

CLEAN WATER FLUE GAS

42 JOURNAL OF METALS· June 1982

seql.lence. Owing to the high reducing conditions at 1450°C in the smelting reduction stage, most of the phosphorus is reduced into the molten product. Therefore, a separate step must be used for desulfurization and dephosphorization.

The electrical power generated by the process offga,ses is sufficient to supply the needs of the D.C. arc furnace and also a small amount (e.g., 300 kWh/metric ton Fe) can be sold for external use. The process consumes a total of approximately 600 kg of non-coking coal per metric ton of iron produced.

THE INRED PROCESS

The INRED (Instant Reduction) process (Figure 6) was developed in the early 1970s by Boliden A.B., Sweden, and run on a pilot trial basis at MEFOS at Lulea. The pilot plant facility at 5 metric ton/day is being replaced by a demonstration plant of 8 metric tonlh at MEFOS, Lulea. . The process sequence involves high-temperature preheating

of the ore fines and coal dust followed by prereduction in a flash smelting unit and final reduction in an electric arc furnace. The flash smelting unit is situated directly above the arc furnace and the process offgases from this com­bined smelting-reduction unit are used to preheat the ore fines.

The prereduction stage incorporates flash smelting of the iron oxide fines with coal dust and air, which results in

ORE COAL

LIMESTONE

ORE LIMESTONE COAL CONC.

DRYING

RETURNS

FLASH SMELTER

Figure 6. The INRED process.

ELECTRIC ARC

JOURNAL OF METALS· June 1982

FLASH SMELTER

reduction of the iron oxides to FeO. The prereduced mate­rial, after about 0.2-0.3 sec residence time, falls into an electric arc furnace which acts as the final reduction unit. The walls of the prereducing unit are covered with the downward flowing stream of liquid FeO. Pulverized lime­stone is also added with the charge in the flash smelting unit to aid slag formation. The flash smelter is water cooled and incorporates heat recovery from the 'waste gases to produce steam generation and electricity which is used in the electric arc. The granulated coke produced from the unburnt coal in the flash smelter is used in the electric arc to reduce any remaining iron oxides.

There is a cyclone effect in the prereducing or flash smelting unit due to vortexing of the input materials, and secondary and tertiary oxygen is injected into the flash smelter from the sille walls in order to control the combus­tion and superheating processes. Only 8% of the offtake gas is solid particles, which are removed and returned to the prereducing unit. Endothermic reduction of iron oxides results in a solid or pasty product entering the final reduc­tion unit. Therefore, an electric arc is used for this stage. The electrical energy is totally produced from the offtake gas in the prereducing unit. Initially, an induction furnace was tried, but proved impractical due to energy input requirements.

The sponge iron is melted around the electrodes where

ELECTRIC ARC

POWER PLANT

WASTE HEAT BOILERS

SECONDARY OXYGEN

STEAM ~J----TURBINE

43

CO is also produced due to the reduction of any remaining oxides with coke produced from the prereducing stage. This acts as a protective blanket around the electrode, thereby reducing wear and electrode consumption, e.g., 3 kg graphite electrodes/metric ton Fe, 4.5 kg Soederberg elec­trodes/metric ton Fe. Electrode penetration in the melt aids control over carbon and silicon content and melt tempera­ture is easily controlled by power input to electrodes.

The sensible heat of the process offgases (mainly C02), after preheating the charge materials, is fully utilized in generating electricity from steam as is the steam generated from water cooling systems of the flash smelting unit. A large. proportion of the energy required for the overall process is consumed in the final reduction stage. This energy is replaced by combustion of the coke, from the electrodes, the superheated sides, and radiation from the flame zone.

The highest temperature is in the combustion zone of the flash smelter (1900°C) while the final reduction stage operates at about 1400°C. Flash smelting produces a vis­cous mass ofwustite, coke particles, lime, and some reduced iron, which moves smoothly down the walls of the flash smelter.

Molten iron is tapped at regular intervals from the final reduction unit with a typical composition of 3-4% C, 0.5-1.0%

CO2 CO PLASMA

Si, 0.5-1 % Mn, and a high phosphorus content. As with the ELRED process, all the phosphorus in the ore is reduced into the molten iron and therefore necessitates a separate de sulfurizing and dephosphorizing operation.

The process consumes a total of approximately 600 kg of non-coking coal per metric ton Fe produced and produces sufficient electrical energy for the final reduction stage, i.e., approximately 400 kWh/metric ton Fe.

THE SKF PLASMASMELT PROCESS

The SKF Plasmasmelt process was developed by SKF Steel in Sweden in the mid 1970s. Trials have been completed with a 1.5 MW plasma unit and a semicommercial plant is planned consisting of a 15 MW plasma generator capable of producing 60,000 metric ton/yr.

Reduction of iron ore fines occurs in two stages, prereduction in two fluidized beds to approximately 50-60% metallization followed by final reduction in a coke-filled shaft producing a high-carbon iron (Figure 7).

The prereduction stage consists of two fluidized beds placed in series and fired by the process offgas from the final reduction stage. Prereduction occurs at a tempera­ture of 700-800°C to a degree of reduction of 50-60%. The

FLUIDIZED CO SHAFT kW POWER ORE BEDS

FeO

COKE

CAS

Figure 7. The SKF Plasmasmelt process.13

44

FURNACE

LIQUID

PRESSURE CONTROL

Fe

CRUDE IRON

PLANT

kW

TO ORE DRIER

COAL POWDER

JOURNAL OF METALS· June 1982

offgas from the fluidized beds contains 10-15% CO plus hydrogen and can be used for drying and preheating incom­ing concentrate. The carbon monoxide/hydrogen mixture from the final reduction shaft is cooled to the prereduction temperature, i.e., 700-800°C, purified in a cyclone and fed consecutively through the two fluidized beds countercur­rent to the flow of ore fines.

The final reduction to molten iron is accomplished in a coke-filled shaft furnace. The hot (700°C) prereduced ore concentrate is injected into the smelt reduction zone together with powdered slag formers and pulverized coal powder or atomized heavy oil as reducing agents. Heat energy is added by means of a plasma arc heater which is fed with a small portion of the process offgas bled off from the top of the reduction shaft. The point of injection of the prereduced iron ore is coincident with the plasma-heated process gas, providing superheating of the charge.

The gas temperature in the plasma arc heater is 3000-5000°C, but it sinks rapidly to 1700-2000°C in the reduction zone itself on account of the strongly endother­mic reduction reactions.

The gas that is formed during final reduction consists chiefly of carbon monoxide and hydrogen together with small amounts of carbon dioxide and water vapor. Carbon dioxide and water vapor are reduced by the coke higher up in the shaft, and the gas leaves as a mixture of carbon monoxide and hydrogen at a temperature of 1000-1200°C. This is used in the fluidized bed prereducers and a small portion is preheated in the plasma arc heat~r and recycled through the shaft.

The principal reducing agent is coal or oil. The purpose of the coke is to form a reaction space in the shaft permea­ble to gases and liquids and able to withstand high tem­peratures. In addition, coke is needed to ensure reducing conditions at the refractory walls, to even out small fluc­tuations in the feed of reducing agent, and to give a uni­form carbon content to the hot metal. The heating require­ment for both prereduction and final reduction is supplied by the process offgas. The entire energy content of the process offgases from both stages is fully utilized, which simplifies the design and energy requirements of the whole process since this eliminates any need for process gas cir­culation to a power plant. However, a large amount of electrical energy is required for the plasma arc heater (approximately 11 00 kWh/metric ton). Replacing some of the powdered coal with powdered coke and/or oil helps to reduce the electrical requirement to a small extent as shown in Table II.

As the smelting/reduction stage consists of a completely gas-proof closed system, the pressure of the gas can be raised to the necessary level in the shaft itself suitable for direct use in the fluidized bed prereduction units.

THE McDOWELL-WELLMAN PROCESS

The McDowell-Wellman process was developed in the mid 1960s. A 250,000 metric ton/yr plant was installed at McWane Cast Iron Pipe Company, Mobile, Alabama in 1969, but was shut down approximately one year later. However, with certain modifications, this process could well compete with the foregoing processes for the smaller steelworks complex and production of special steels. It falls short of one of the main salient features outlined earlier in that it uses a pellet charge. Nevertheless, it was thought to be worthwhile including here.

Iron ore fines and coal dust are mixed with flux fines and pelletized. The composite pellets are dried, preheated to approximately 1000°C, prereduced (50-60%) on an in-line liquid-sealed Dwight-Lloyd traveling grate machine, and continuously fed hot directly to a submerged electric arc furnace (Figure 8). The liquid iron produced is of a compa­rable composition to blast-furnace pig iron. The process offgas from the submerged arc furnace is rich in carbon

JOURNAL OF METALS· June 1982

Table II: Energy Requirements for the Various Modes of Operation of the SKF Plasmasmelt Process

Coke, Coal. Oil, Electricity. kg ~ ~ kWh

Plasma, coke 185 30 1,020 Plasma, coal 50 170 1,120 Plasma, oil 50 135 1,080

monoxide. This is allowed to ascend the permeable charge columns above the bath and is recycled to the traveling grate machine to effect drying of the pellets in the initial zone followed by high-temperature firing. This converts the coal to char, limestone to lime, and produces preheated, bonded composite pellets which are prereduced to 50-60%. The submerged arc furnace is operated under a slight pressure to minimize air infiltration and, therefore, dilu­tion of the high calorific offgas. They also operate with low charge columns (Figure 8) which do not impose rigid struc­tural requirements. A three-electrode (circular furnace shell) submerged arc furnace can be used for capacities up to 200-400 metric ton/day. Increased production requirements necessitate a six or even nine in-line electrode system in a rectangular furnace shell. I5

Submerged arc smelting of rotary-kiln, pre reduced iron ores is being successfully used at the Highveld Steel and Vanadium Corporation in Witbank, South Africa. ls Although there was an initial two-year period of problems, Highveld Steel is currently making a profit at approximately 400,000 metric ton/yr. The operation is aided by the economics ofre-

IRON OAE COAl.. FLUX

k.~ J VY'wI

'R"",,RTIONING 2. GRINDING

Q\FlLnRI G OtNERAL REQUIREMENTS \

(PER TON OF METAL) , IRON ORE , ... , 9 TONS COAl 0 6-0 9 TONS e: ~~~TROOES •. ,~2~ TONS -='=-----r ELECTRICITY 75().,OOO KWH

10001 C - CO Fe

t

DEPTH

2CaO 5102 AI20J ~ CaO AI20a + CaO 5102 3Fe + C = F~C

Figure 8. The McDowell-Wellman process.2, 15

45

CO TO POWER PLANT

f

CO TO POWER PLANT AFTER H20 REMOVAL

covering the vanadium from the ore by oxygen blowing van­adium-rich slag in a converter.

THE DIRECT CONVERTER SMELTING PROCESS

- . IRON ORE ~

COAL.--.y'" ~((t 'RON -\ \.>~ IC ORE

\'~lf' ;~~~~

Oxygen, coal dust, and iron-ore fines are injected into the side of a converter containing molten ironP The coal is burnt directly to CO and the iron ore reduced to iron (Figure 9a). The strongly endothermic nature of the reduc­tion of iron ore necessitates extra energy input in the form of either electrical energy or a high coal consumption. Electrical heating in a converter presents some difficult practical problems and, therefore, excess coal combustion is preferred. In this case, there is a high volume of carbon monoxide and hydrogen generated which can be utilized for prereduction of the iron ore and power generation. This power may be used, in part, to aid oxygen generation in an on-site oxygen plant. The process offgas so produced has been found to be almost free from gaseous sulfur com­pounds and with a typical gas analysis of: 73.2% CO, 2.9% C02, 17% H2, and 17 ppm total 8 (analyzed as 802 in process gas burnt in oxygen) .

OXYGEN '-...-~ ./' TORCH

LIQUID IRON

a t 1

!-' 1600

.. ~ 1500 ;. 6 - IRON' LIQ UID

- OX I DE S

§ 1400~==~~====~ l- IRON t WllSTITE

c Ie 20 22 24 26 liE IGHT PERCE NT OXYGE N (7.)

Most of the sulfur present in the coal is retained in the molten iron, necessitating desulfurization. The coal require­ment is similar to that consumed in the ELRED and INRED processes, i.e., approximately 600 kg of carbon equivalent per metric ton of iron produced.

Figure 9. Direct converter smelting process,16, 17 a) using coal, oxygen injection, b) using hydrogen plasma injection, and c) Fe-O phase diagram.

Another variation on the same idea is that of injecting hydrogen gas by means of a plasma torch into an oxygen­saturated melt of 0.2% oxygen (Figure 9b).l6 The iron ore is injected into the bath of the converter and ensures the necessary high oxygen level. In this way hydrogen is used as a deoxidizer. It is also proposed that a CaO-saturated calcium ferrite slag be used in conjunction with a CaO­lined converter in order to minimize any problems that might arise from refractory lining attack due to the high activity of iron oxide. Injection of iron ore results in a

Table III: Comparison of Capital Costs, CapaCity, and Energy Consumed in the New Direct Smelting Processes

Process ELRED

LNRED

SKF Plasmasmelt

McDowell­Wellman Process

Blast Furnace and Coke Oven. ete.

46

Capacity. million

metric tonlyr 1.30

0.45

1.00

0.25

3.65

Capital Co t

Total 396.5

million

130.5 million

205 million

56.25 million

1.5 billion

$lMetric Ton 305

290

205

225

411

Energy Requirements Per Ton Fos il Fuel Equivalent,

Fuel U d G a l 600 kg coal 3.39

600 kg coal

50 kg coke 170 kg coal

1120 kWh electl'icity

50 kg coke 135 kg oil

10 0 kWh electricity

185 kg coke 30 kg oil

1020 kWh electricity 600 kg coal

1000 kWh electricity

900 kg coal 750 kWh electricity 440 kg coke

40 kg oil 75 kWh electricity

4.17

4.42

4.52

4.23

675 1 .1

3.67

ufficient electrical energy enerated from ofTga e to operate D.C. arc furnace for final reduction and supply 300 kWh/metric ton- I of credit

ufficient electrical energy generated from ofTga es to operate electric arc fina l reduction meltin Pia rna arc heater u ed to uperheat portion of proce ofTga which i injected with coal du t and iron ore fines at lag-metal int rface.

Small amount of coke u ed in shaft.

es composite pellet charge.

Standard blast furnace practice-lO,OOO metric ton/day

JOURNAL OF METALS· June 1982

liquid oxide melt composition in the two-liquid (immisci­ble) region, shaded in Figure 9c.

In this phase region at 1600°C, a 0.25% oxygen iron melt is in equilibrium with 23% oxygen iron oxide melt. Injec­tion of hydrogen reduces the iron oxide to produce an oxygen-saturated liquid iron which is tapped from the bottom of the converter, deoxidized with carbon, and alloying addi­tions made to give the required specification. Coal injec­tion may also be used. Developments similar to this are also being pursued in Japan and Germany.

The utilization of scrap melting in such converters offers considerable benefits with respect to process economics. Recent trials in Germany have successfully melted scrap and/or sponge iron using only coal and oxygen injection into the molten iron in a converter.19

ENERGY AND CAPITAL COST COMPARISONS

Sufficient operational data from pilot plant and semi­commercial operation of the ELRED, INRED, Plasmasmelt, and McDowell-Wellman processes have been obtained to provide approximate capital costs and energy requirements. These are presented in Table III and compared with a modem blast furnace operation (10,000 metric ton/day) and all its ancillary plant. Fossil fuel equivalent is used as the yardstick since it is thought that this will be a more realistic comparison. In this case, electrical energy require­ments are multiplied by a factor of three. This has also been applied for credit electrical power. It is apparent that the blast furnace is still very competitive at the large tonnages that it can produce. However, these new direct smelting processes offer considerable savings in capital costs and, presumably, energy requirements for ministeel plant operations.

No accurate data are available for the direct converter smelting process since this is largely conceptual, with only limited large scale experimental work having been conducted. Nevertheless, an approximate estimate of the energy requirements on the same basis as used in Table III indi­cates that there would be an overall credit of between 1 to 8 Gcal per metric ton of iron produced, depending on how much electrical energy was used; i.e., for converter melt heating or for oxygen production only.

CONCLUSIONS

Owing to the general lack of substantial quantities of natural gas and oil in the developed countries, it becomes clear that any new direct smelting processes suitable for iron and steel production from the leaner iron ores should be essentially coal-based. Coal gasification is, of course, a possibility, but the excessive capital expenditure, e.g., in excess of $120 million for a 0.5-1 million metric tons per year steel plant, will largely prohibit this potential route, even though operating costs may be competitive. There­fore, direct smelting systems which utilize coal as a reduc­tant and heat producer and which are highly energy cogenerative in character, are most likely to find eventual application. Further requirements of such new processes should be that they utilize mineral and coal fines, obviating the need for expensive agglomerating processes, and that they produce a molten iron product which may be readily refined, deoxidized, degassed, and alloyed to the required steel specifications. In this respect, the most suitable final refining/alloying unit would be an A.O.D.-type converter. This would allow oxidation of phosphorus and carbon to the required limit and desulfurization down to 0.005% S with a suitable basic slag mix.2o A considerable level of degassing could also be achieved in this unit which is capable of producing the full range of steels from plain carbon to stainless. A further favorable factor is that side blowing used in the A.O.D. produces less severe pollution problems than top-blown oxygen converters which would

JOURNAL OF METALS· June 1982

ORE COAL FLUX OFFGASES

r OFFGAS~ -1- -----

A.O.D. LIQUID DIRECT

Fe POWER CONVERTER SMELTING PLANT

UNIT kW

1 LIQUID STEEL 1 CREDIT kW

CONTINUOUS CASTER

.J, BILLET BLOOM

OR SLAB

Figure 10. Flow process diagram for hypothetical direct smelting and continuous caster ministeel plant.

also require desulfurization and degassing treatments. Each of the five direct melting processes described offer

increased continuity of processing and a potential reduc­tion in pollution problems compared with the BF/BOF route. However, it will be necessary to provide considerable com­puterized control in each processing stage. Reduced capital expenditure and labor requirements make these new D.S. processes suitable for steelmaking operations which pro­duce up to one million metric ton/yr.

The substantially improved profitability of the ministeel works is evidence that a relatively small, efficient opera­tion which caters for a specific market outlet is a viable competitor to the large integrated BF/BOF route. As high­quality scrap becomes less available due to increased proc­ess efficiency and continuous casting, and the level of con­taminants increases, the numerous minimills already in existence will need to examine the possibilit of producing their own iron feed to the steelmaking unit and, indeed, will need to reexamine their total technology system. They could decide to use conventional direct reduced iron (DRI) as a feed for their electric arc furnaces, but direct smelting followed by an A.O.D.-type converter steelmaking offers a favorable alternative. An example of such a system is given in Figure 10.

References 1. H. Takano, "Productivity of the Japanese Iron and Steel Industry-Technology for Manpower Saving," Tetsu·to.Hagane, 67, (19811 1111, pp. 1867·1875. 2. C.G. Davis, J.F. McFarlin, and H.R. Pratt. "Compilation of Reports on Direct Reduc­tion Technology and Economics," United States Steel Corporation Research Laboratory, under sponsorship of U.S. Department of Energy, Washington, 1981, VI-16. 3. J.J. Moore, "The Potential for Direct Reduction Steelmaking in the Upper Great Lakes Region," Chapter 4, edited by K.J. Reid, 1981, sponsored by the Upper Great Lakes Regional Commission. 4. RJ. Goodman, "Direct Reduction Processing-State of the Art," Skillings' Mining Review, 68, (10) (1979). 5. J.J. Moore and K.J. Reid, "Novel Direct Reduction Technology," Final Report submitted to the Legislative Commission on Minnesota Resources, July 1981, p. 16. 6. J. Szekely, "The Role of Innovative Steelmaking Technologies," Iron and Steel­maker, 1, (12) (1979), pp. 25-30. 7. S. Eketorp, "Thoughts about Metallurgy Facing Year 2000," Stahl und Eisen, 101, m 13114), (1981), pp. 82-89. 8. P,H. Colin and H. Stickler, "ELRED--A New Process for the Less Expensive Produc­tion of Liquid Iron," Iron and Steel Engineer, March 1980. 9. E. Bergtsson and B. Widall, "The Chemistry of the ELRED Process," Iron and Steelmaker, 8, (10) (1981), pp. 30-34. 10. H.I. Elvander, I.A. Edenwall, and S.C.J. Hellstam, "The Boliden INRED Process for Smelting Reduction of Fine Grained Iron Oxides and Concentrates," Third Int. Iron and Steel Congo Proc., April 1978, Chicago, Illinois, pp. 195-200. 11. RR Irving, "The INRED Process: An Ironmaking Option," Iron Age, 6, (July 1981),

47

pp.21-23. 12. S. Santen, "Plasma Technology Gives New Lease of Life to Swedish DR Plant." Iron and Steel Int., 53, (1), (1980), pp. 347-350. 13. "SKF Steel 's 'Flash of Genius' Will Mean Brighter Prospects for the Steel Indus­try," SKF Steel Division Publication, Steel Market News, March, 1980, pp. 1-8. 14. "SKF Steel Plasmasmelt," SKF Steel Publication, 1981. 15. T.E. Ban, "Direct Electric Smelting of Hot Prereduced Iron Ore," Proceedings of the 46th Annual Meeting, Minnesota Section AIME and 34th Annual Mining Sympo­sium of University of Minnesota. 1973, pp. 95-102. 16. "The Future Steel Plant-A Study of Energy Consumption," Summary Report for Natural Swedish Board for Technical Development, No. 135, 1979. 17. S. Eketorp, O. Wijk, and S. Fukagawa, "Direct Use of Coal for Production of Molten Iron," in Proceedings. Extraction Metallurgy 81. I.M.M., 1981, London. pp. 184-192.

ABOUT THE AUTHOR

John J_ Moore, Associate Professor, Metal­lurgical Engineering, Mineral Resources Research Center, University of Minnesota, 56 East River Road, Minneapolis, Minnesota 55455.

Dr. Moore received his BSc in metallurgy from the University of Surrey, England and PhD in industrial metallurgy from the University of Birmingham, England. He has worked as a steel­works metallurgist and an industrial engineering­

18. "South African Mini Steelworks Smelts 420.000 tpy Plus," 33 - The Magazine of Metals Producing, 8, (4 ) (1970). 19. J. Hartwig, D. Radke. and H. Seelig, "Development of a Melt Down Process with Combined Direct Reduction Using Any Type of Small Coa!." Stahl und Eisen, 100, (10) (1980), pp. 535-543. 20. J.J. Moore, "The Case for Rare Earth Desulfurization of Acid Steel in Steel Casting Production." Trans. A.F.S., 1981.

production control manager. At the University of Minnesota, he is responsible for the Process Technology Division of the Mineral Resources Research Center. He is a member of The Metallurgical Society of AIME.

(Continued from page 21)

High-Strain-Rate Deformation

Abstracts are due by August 15, 1982 for two sessions sponsored by the TMS-AIME Shaping and Fonning Committee at the 1983 AIME Annual Meeting, Topics will cover experimental techniques; material properties; deformation mechanisms at strain rates greater than 1 S-I, including the shock wave regime; experimental or theoretical studies of strain localization; and fracture at high­strain rates,

Submit abstracts of up to 200 words on the appropriate TMS form to P.S. Follansbee or S,S, Hecker, Los Alamos National Labo­ratory, Mail Stop G730, Los Alamos, New Mexico 87545; telephone (505) 677-4591.

High-Temperature .Protective Coatings

Abstracts are due by July 15 1982 for a four-session symposium sponsored by the Corrosion and Environmental Effects Com­mittee of TMS-AIME at the 1983 AIME Annual Meeting.

Papers are sought in the areas of coating deposition techniques; characterization of coatings; physical, chemical, and mechani­cal properties of coatings; and behavior of coatings in energy conversion devices.

Submit abstracts on the appropriate TMS­AIME form to Subhash C. Singhal, Manag­er, High Temperature Metallurgy, Westing­house Research and Development Center, 1310 Beulah Road, Pittsburgh, Pennsylvania 15235; telephone (412) 256-3129.

Heterogeneities in Castings

Abstracts are due by July 15, 1982 for a two-session symposium, "Heterogeneities in Castings - Cause and Cure," sponsored by the Solidification Committee of TMS-AIME at the 1983 AIME Annual Meeting.

Papers are sought in the areas of inclu­sion formation and removal; porosity for­mation and prevention; and the control of macrosegregation and microsegregation in castings,

Submit abstracts on the appropriate TMS form to D. Apelian, Materials Engineering Dept., Drexel University, 32nd and Chest-

48

nut, Bldg. 3/261 , Philadelphia, Pennsylvania 19103; telephone (215) 895-2327.

Image Processing in Materials Characterization

Abstracts are due by August 1, 1982 for a four-session meeting on Image Processing in Materials Evaluation and Characterization sponsored by the TMS-AIME Structural Mate­rials Committee at the 1983 AIME Annual Meeting, Papers can address either current applications or research in image processing of materials characterization. Topics of inter­est include but are not limited to microscopic characterization, nondestructive evaluation and 3-D characterization,

Submit abstracts of 150 words or less on the appropriate TMS form to James F, Mancuso, Materials Engineering Department, Westinghouse R&D Center, Pittsburgh, Pennsylvania 15235; telephone (412) 256-3652.

Intermetallic Compounds for Potential Use as Structural Materials

Abstracts are due by July 30, 1982 for the session sponsored by the TMS-AIME Committee on Alloy Phases at the 1983 AIME Annual Meeting. Emphasis will be on mechanical property-structure relation­ships including influence of crystal struc­ture, grain boundary structure, and the effect of trace impurities on grain boundary fracture.

Submit 150-word abstracts on the appro­priate TMS form to Carl C. Koch, Metals and Ceramics Division, Oak Ridge National Laboratory, P .O. Box X, Oak Ridge, Ten­nessee 37830; telephone (615) 574-5156.

Lead-Zinc-Tin

Abstracts are due by August 9, 1982 for a general session on lead-zinc-tin extractive metallurgy sponsored by the TMS-AIME Lead-Zinc-Tin Committee at the 1983 AIME Annual Meeting. Review papers or papers on research, development, and operational aspects are sought.

Submit abstracts to H.E. Hirsch, Techni-

cal Research, COMINCO, Ltd., Trail, British Columbia VIR 4L8, Canada; telephone (604) 364-4426.

Metal Matrix Composites

Abstracts are due by August 1, 1982 for two sessions on Metal Matrix Composites­Particulate and Dispersion Strengthened Sys­tems, sponsored by the Metal Matrix Com­posites Committee at the 1983 AIME Annual Meeting.

Submit abstracts on the required TMS form to Ashok Dhingra, Experimental Sta­tion, E302, E.I. duPont, Wilmington, Delaware 19898, telephone (302) 772-3663; or Herb A. Newborn, Naval Surface Weapons Center, Code R34, White Oak, Silver Springs, Mary­land 20910, telephone (202) 394-1484.

Metallurgical Process Economics

Abstracts are due by August 1, 1982 for two sessions sponsored by the TMS-AIME Metallurgical Process Economics Committee at the 1983 AIME Annual Meeting. Abstracts should be submitted on the appropriate TMS form. Send abstracts for topics on selection of research and development projects to Noel Jarrett, Assistant Director, Alcoa, Alcoa Center, Pennsylvania 15069; telephone (412) 337-2109 or to Gordon Geiger, Vice Presi­dent and Technical Director, Chase Man­hattan Bank, Mining & Metals Division, 1 Chase Manhattan Plaza, 3rd Floor, New York, New York 10081; telephone (212) 552-2560. Send abstracts for topics on proc­ess economic tools for successful projects to Roger Kust, Manager, Minerals Processing, Exxon Minerals, 244 Park Avenue, Florham Park, New Jersey 07932; telephone (201) 765-4720 or to John Cigan, Director, Environmental Control, St. Joe Minerals Corp., P .O. Box A, Monaca, Pennsylvania 15061; telephone (412) 774-1020.

Physical Chemistry and Process Technology

Abstracts are due by August 1, 1982 for

JOURNAL OF METALS· June 1982