sponge iron.pptx

7/29/2019 sponge iron.pptx

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Sponge Iron is iron ore reduced directly in solid state

using coal gas, natrual gas or coal as reductants andis also known as Directly Reduced Iron (DRI).

Sponge Iron


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Sponge iron is the metallic product formed by the reduction (removal ofoxygen) of iron ore at temperature below the fusion point of iron while it

is still in solid state. It is also called direct reduced iron (DRI). Direct-reduced iron (DRI) is produced from direct reduction of iron ore (in theform of lumps, pellets or fines) by a reducing gas produced from natural gasor coal.

The reducing gas is a mixture of majority of hydrogen (H2) and carbonmonoxide (CO). This process of directly reducing the iron ore in solid formby reducing gases is called direct reduction.A broadly used iron source is also a product known as direct reduced iron("DRI") which is produced by the solid state reduction of iron ore to highlymetalized iron without the formation of liquid iron.

Sponge iron is the product created when iron ore is reduced to metallic

iron, in the presence of coal, at temperatures below the melting point ofiron. The external shape of the ore is retained with 30% reduction inweight due to oxide reduction resulting in change in true density from 4.4gm/cc to 7.8 gm/cc in this product

Sponge Iron or Direct Reduced Iron (DRI)


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Electric Arc Furnaces (EAFs) engaged in manufacturing steelstarted facing problems of availability of scrap of desiredquality.

First DRI plant in 1957 in Mexico

The reasons for the growth of the sponge iron industrycould be attributed to

the advantages of using sponge iron in electric arcfurnaces, partly substituting scrap, the conventional chargeto the furnaces.

The industry is gaining further importance due to provenutility of sponge iron in other steel manufacturing processeslike L.D. Converters, Open Hearth Furnaces (OHFs), Blast

Furnaces (BFs) & Basic Oxygen Furnaces (BOFs), InductionFurnaces (IFs) and Cupolas.


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ADVANTAGES OF USING SPONGE IRON IN STEEL MAKING [15]

Use of sponge iron:

Increases productivity through shorter tap-to-tap time and refining time.

Simultaneous melting and refining with continuous charging.

Faster metallurgical reactions and Improved as well as more stable power consumption

Less electrode consumption due to stable power.

More precise of steel compositions and quality advantages.

High degree of metallization (up to 92%) and consistent chemical composition.

Deep drawing steel grades can be produced in electric arc furnace (EAF).

Flat products and alloy steels of international standards can be made in electric arcfurnace (EAF).

Reduction in number of off-grade heats.


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The advantages of sponge iron use in EAFs are summarisedbelow:-

Uniform known composition

Low levels of residuals/tramp elements

Capability to maintain phosphorous level in steel within0.002%

Maintenance of sulphur in steel by its removal in sponge

manufacture.

Low content of dissolved gases

Uniform size and higher bulk density as compared to scrapCapability of forming protective cover of foamy slag in thebath

Lower refining requirements of steel produced

Potential of sensible heat recovery from waste gases

Possibility of producing variety of steels


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There are a few disadvantages of the use of spongeiron in the arc furnaces such as

lower liquid metal yield,

lower metallisation,

lower carbon content in sponge iron produced in coalbased plants, gangue content of the sponge ironresulting in additional requirement of electrical energyin its melting and higher meltdown time.

However, an ever widening gap between thedemand and availability of scrap clearly indicates abright future for the sponge iron industry


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The substitution of scrap by sponge iron has

some limitations depending on the furnace

operating conditions. Only 20% to 30% ofsponge iron can be used in the furnace

charge when feeding is done in batches. The

proportion of sponge iron in the charge canhowever be increased to 40-50% by providing

continuous feeding arrangements. A further

increase in sponge proportion is possible by

use of high power furnaces with highercapacity transformers.


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Various technologies developed for the manufacture of spongeiron may be classified as:

A. Gas Based TechnologiesFluidised Bed Technologies

Technologies using hydrogen as reductant

Technologies using carbon monoxide as reductant

Technologies using mixture of both hydrogen and carbon monoxide as

reductant.

Static bed technologies using mixed gas as reductant

Moving bed technologies using mixed gas as reductant

The gas based technologies were capable of using either naturalgas associated with oil or reducing gas derived from coal.


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Gas-Based Process:

This process utilizes natural gas as the reducing

agent. Natural gas is reformed to enrich with H2and CO mixture and this enriched and reformed gasmixture is preheated in gas-based process. Avertical retort is used for the reduction of iron oreas against a rotary kiln in coal based sponge iron

process. When the gases are travelling upwards thecharge moves downward by gravity. Gas-basedsponge iron is not subjected for magneticseparation, as no contamination with nonmagneticis possible either it can be cooled indirectly or

briquetted in hot condition to get hot briquettediron (HBI)


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B. Solid Reducant or Coal Based Technologies

This process utilizes non-coking coal as reducing agentalong with lumpy rich grade iron ore.

Rotary kiln processes (SL/RN, DRC, and ACCAR/OSIL)

Retort processes (Kinglor Metor)

Rotary hearth processes (Inmetco, FASTMET


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MidrexCoal Based Process Flowsheet


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sponge iron.pptx

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