Alternative Ironmaking Methods

Chapter 5: Alternative Iron Making Technologies

The BF process remains the dominant method of making iron today

However alternative processes that do not depend on the use of metallurgical coke have been developed and currently account for

about 8% of global iron production

Development of alternative iron making processes has been necessitated by factors

which include the following:

Costly and scarce coking coal: Need to look beyond coking coal

Lecture 7: Alternative Iron Making

possibility to use iron ore fines directly

Environmental considerations (eliminate pollution-intensive sintering and coke-

making processes)

Large scale of economy (High capital cost of BF)

Scientific/ engineering knowledge to think/ design alternative processes


The alternative processes can be broadly

divided into two categories:

1. Production of solid iron through solid state

reduction (DR)

2. Production of liquid iron by combination of

solid and liquid state reduction (SR)


5.1 Production of solid iron (Direct reduction)

Direct reduction (DR) is a generic name of a family of processes that in which iron ore in the

form of fines, lumps or pellets is reduced to solid-

state Fe by use of solid or gaseous reducing agents.

The processes produce sponge iron (also called direct reduced iron (DRI)).

Natural gas products or non-coking coal is used as the reductant as well as energy source

The resultant solid Fe will have to be melted during steel making in EAFs.


Natural gas (if or when the Kudu gas project begins!) processes use shaft furnaces, fluidized beds or retorts as reactors

Coal-based processes use rotary kilns, rotary hearth furnaces and multi-hearth furnaces as reactors

In both cases the final sponge iron is porous, less dense and possesses larger surface due to the removal of oxygen during reduction

The high porosity and large surface area makes it prone to re-oxidation when it contacts moisture, a phenomenon called in-situ rusting


Although passivation techniques have been developed, there still remains some degree

of oxidation. Another disadvantage of DRI

production is that some gangue minerals

remain in the ore.

Despite these drawbacks several DRI technologies (producing sponge iron) have

been developed:



Process Basic Features Year Country Reductant Ore form Reactor

Wilberg Coke Pellets Shaft 1952 Sweden

HyL I Natural gas Pellets Retort 1953 Mexico

SL/RN Coal lump & fines

Lump Rotary kiln

1964 Canada

Midrex Natural gas Pellets Shaft 1967 USA

Fastmelt Coal fines Fines Rotary hearth

1974 USA, Japan

ITmk3 Coal fines Fines Rotary hearth

1996 Japan

Reduction occurs through a series of steps that start at 850oC.

3Fe2O3 + CO = 2Fe3O4 + CO2

Fe3O4 + CO = 3FeO + CO2

FeO +CO = Fe + CO2

The CO required for reduction is generated by the Boudard reaction

C + CO2 = 2CO

World production of DRI is about 60 million tpy (2014).


Case study: ITmk3 Process

Developed by Kobe Steel, Japan.

Raw material is ore + coal composite pellets (i.e. pellets containing iron fines and coal fines.

Reduction & melting occur at 1500oC in Rotary Hearth Furnace. It produces almost low sulphur pure iron nuggets (& slag globules)

Commercial applications include a 0.5 mtpy plant at Minnesota, USA.


5.2 Smelting Reduction the aim is to produce liquid iron (just like in

the BF) but using iron sources that are not

acceptable BF iron making (both for physical

and chemical reasons) and coal, oxygen

and/or electrical energy. Hence their

advantages include the following:

Production of hot metal which is ready for BOF based Integrated Steel Plants

Direct use of non-coking coal and Iron ore fines


need much less land as compared to conventional BF complex

Suitable for small scale production at lower costs

It operates like DR process up to the stage where FeO is produced. But there after the

FeO is reduced in molten state by CO.

This improves the transport rates due to convection thus improving the kinetics.

The more heat generated in this process is largely due to the increased amount of coal

used per unit mass of ore.


SR processes can be single stage or double stage

1-stage process


2-stage process:


Several SR technologies have been developed but the most prominent ones are:

COREX (Two stage) (commercially operating)

FINEX (Two stage) (commercially operating)

HISMELT (Single stage) (not yet operating commercially)

ROMELT (Single stage) (not yet operating commercially)


Case Study 1: COREX Process

Developed by Korf Stahl, Germany

Involves pre-reduction in shaft furnace followed by melting in a melter-gasifier.

Commercially operating in India, South Korea, China and South Africa

A single unit can produce up to 2 million tpy

Total fuel rate requirement = 950 kg/thm.

~ 100% pellets are charged


Oxygen requirement = 550 Nm3/thm (very high!)

Typical HM Composition: C~ 4%, Si=0.5-0.9%, S=0.025- 0.07%, P=0.13-0.19%, at temp=

1480-1520oC


Case Study 2: HISMELT Process

Developed by Hismelt Corporation, Australia

1-Stage hot air based Smelting Reduction Process using metal bath as primary reaction

medium which is unique

Bulk of smelting of ore takes place via dissolved carbon resulting in high reaction rate

Direct utilisation of ore fines (-0.6 mm) and non-coking coal fines (-0.3mm): feed material is

directly injected through water cooled lances

into metal bath.


No oxygen requirement only preheated air is used

Variety of coals containing 10 to 38 %VM can be used, Low coal rate (600-620 kg/thm

HM: Low P (0.02-0.05% based on ore of 0.12% P) and very low Si


First industrial Hismelt Plant (capacity 600,000 tpa) commenced operation in

Kwinana, Australia in 2005.

No other plant in the world reported


5.3 Mini Blast Furnaces Operate more like SR processes in terms of

tonnage, but are use a large proportion of

coke just like in normal BF. Size ranges from

50-350m3. HM quality same as normal BF.

Major drawback is low energy efficiency resulting in higher coke rate than normal BF.

They normally use 100% lump ore. In China

55 million tpy HM produced in MBFs. Other

countries that use this technology are India

and Brazil. MBFs compete with SR

technology for small scale production of pig

iron.


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Alternative Ironmaking Methods