Raw Material In Iron Making

A

Nirjhar Chakravorti

Presentation

RAW MATERIAL PLANT FOR IRON MAKING

Nirjhar Chakravorti

Nirjhar, a Mechanical Engineer by profession, has completed engineering in the year 2000, from Jalpaiguri Government Engineering College, India.Nirjhar has experience in design, development, project and plant engineering.As an engineering professional Nirjhar has worked at different industries.Nirjhar’s interest is to know different technology and process engineering.

Where from iron produced?

Raw iron is found in earth’s crust, as an ore.Iron ore mostly found as Fe2O3 (the form of iron oxide found as the mineral hematite).


At present, blast furnace is most commonly used furnace to produce iron.The Blast furnace iron making process basically consists of the conversion of iron oxide to iron in liquid form . This requires reductant for reduction of iron oxide and heat for the above reduction reaction to take place. The primary source to fulfill both these requirements is carbon (in the form of coke).


The blast furnace is a vertical counter-current heat exchanger as well as a chemical reactor in which burden material charged from the top descend downward and the gasses generated at the tuyere level ascend upward.

Raw Material Section in iron making

Broadly a raw material section in iron making plant has the following sections:a. Iron Ore Handling Systemb. Coke & Coal Handling Systemc. Lime & Other Material Handling Systemd. Sinter Plant

Flow Diagram

Blast Furnace

Iron

Ore

Iron Ore Section

Ore crushed & Transported from mine to plant

Ste

el P

lan

t

Blast Furnace

Iron

Ore

Mine

Stack

Yard

Material Handling System

Iron Ore Section

Iron ore chunks dugs from the earth and taken to process plant.Chunks are crushed to small fractions, and impurities are removed by magnetic separator or other means. The small iron fractions are formed into marble sized pellets in forming drums and discs. Then the pellets are transported to stack yard of steel plant.

Iron Ore Section

Iron ore is collected from mines and crushed

Iron Ore Section

Stack Yard

Processed iron ore are dumped at stack yard

Iron Ore Section

Iron ore are transported through belt conveyor

Belt Conveyor

Iron Ore Section


Raw Materials are Stored and transported

inside steel plant and fed into

Blast Furnace through material handling system

Flow Diagram

Blast Furnace

Iron Ore

Coal Coke Oven Plant

Coke

Coal & Coke SectionProcessed & Transported from mine to plant

Ste

el P

lan

tBlast

Furnace

Coal Mine

Stack Yard

Coke Oven Plant

Transportation by Material Handling System

Coke

StackMaterial Handling System

Coal & Coke Section

Coal are collected from mines. Then they are washed & crushed to pieces. After that coal is transported to stack yard of steel plant. From stack through material handling section, they are transported to coke oven section, where coal is baked and converted into coke.

Coal & Coke Section

Coal is collected from mines

Coal & Coke Section

Coal is processed, washed and crushed and then transported into stack yard of steel plant

Coal & Coke Section

Processed coal is dumped at stack yard and transported to coke oven plant by material handling system

Coal & Coke Section: Coke Oven Plant

Coke is source of thermal energy inside the Blast Furnace, which burns and the converted heat melts the iron ore.


Conventional coke making is done in a coke oven battery. Inside oven battery coal is sandwiched between heating walls. They are carbonized (at a temperature around 1000o-1100o C) upto a certain degree of de-volatization to produce metallurgical coke of desired mechanical and thermo-chemical properties.


Coke StackStorage Bunker

(Coal Tower)Stamp

Charging Car

Coke Oven Battery

Quenching Car

Water

Sprayed


Coke Bridge

Waste

Coke lump collected under ground,

Crushed & Stacked

Coal Pushed in

Coke Pushed out

Liquid ChemicalOff gas

used as fuel

Waste Volatile Substance


Schematic View of Coke Oven battery. Here instead of collecting coal at stamp charging car, loose coal is directly fed into the oven from top.


Stamp Charging of Coal : Stamp charging involves formation of a stable coal cake with finely crushed coal (88-90% - 3mm) by mechanically stamping outside the oven and pushing the cake thus formed inside the oven for carbonisation. Coal moisture is maintained at 8-10% for the formation of cake. Due to stamping, bulk density of charge increases by 30-35% causing significant improvement of coke. Oven productivity increases by 10-12% & there is a possibility of using inferior coking coals to the extent of about 20%.


Stamp Charging Machine: Erection Stage


Stamped Coal cake ready for charging into the oven


Pictorial View

Pusher and Charging Car travels & stops in front of the oven, where coal cake needs to be pushed

Coke OvenOven Door

Coal cake box front door

Coal cake box

Coal cake

Charging plate

Coal pusher plate

Coal pusherPlate drive

Coal Charging

Car

Pusher and Charging Car

Rail


Stamped Coal cake pushed into the oven


Pictorial View

Charging (i.e. pushing) the coal cake inside the oven

Oven door in semi open condition

Coal cake boxFront door inOpen position

Qu

ench

ing C

ar

Sid

e

Sta

mp

ing &

Charg

ing C

ar

Sid

e


Coke Oven : During carbonization, coals undergo transformation into plastic state at around 350o-400o C, swell and then re-solidify at around 500o-550o C to give semi-coke and then coke. In coke ovens, after coal is charged inside the oven, plastic layers are formed adjacent to the heating walls, and gradually the plastic layers move towards the centre of oven from either side and ultimately meet each other at the centre.

The quality and quantity of plastic layer is of extreme importance and it determines the inherent strength of coke matrix. For producing coke of good quality, coals should have certain degree of maturity, good properties and wide range of fluidity.


Pictorial View

Coal cake is pushed inside the oven and charging plate is pulling back

Coal pusher plate holds back the coal cake inside the oven, while pulling

back the charging plate


Coke inside oven ready for push out from oven


Hot Coke pushed out from oven


Quenching of hot coke : Red hot coke formed inside oven pushed out by pusher car, and collected on quenching car.


Hot coke being pushed from an oven into a quench car.

Quenching Car

Locomotive engine of

quenching carCoke collected on quenching

car

Coke Oven


The Quenching car travels and placed below the quench tower. The coke is treated to high-pressure water jets to cool the coke while still in the quench car. The coke is discharged from car and crushed into

pieces and stacked.

Quench Tower

Quenching Carwith coke

Flow Diagram

Blast Furnace

Iron Ore

Coal

Coke Oven Plant

Coke

Flux

Flux Section

Flux crushed & Transported from source to plant

Ste

el P

lan

t

Blast Furnace


Flux Stack Yard

Flux Section

Flux is added in the blast furnace to remove impurities, by producing slag. Lime is the most commonly used flux material. Lime may be used as a flux in the form of CaO, limestone (CaCO3), dolomite (magnesium calcium carbonate) or dolomitic lime (product obtained from burning or roasting of dolomite).

Flux Section

Lime is used as a flux in solid, particulate form and reacts with impurities in the charge to form a slag.It is important that the slag be kept fluid, not only to increase its ability to scavenge impurities from molten metal, but also to permit the slag to be readily removed from the furnace.

Flux Section

Formation of slag has a adverse effect also.Lime in reaction with silica or silicates present in the ore forms dicalcium silicate, which has 38000C melting point. It form a coating on lime particles and prevent it from further reaction.Auxiliary flux is used for the purpose of facilitating the reaction between lime and silica or silicates. Fluorspar is a example of auxiliary flux.

Flow Diagram

Blast Furnace

Iron Ore

Coal

Coke Oven Plant

Coke

Flux

SinterFines from

different sources

Sinter Plant Section

In order to enhance the productivity of blast furnaces, a high percentage of sinter charge is a prerequisite. Sinter is an agglomeration of iron ore fines, coke and limestone in the form of cakes. To ensure sinter burden in the blast furnaces at 75 per cent, a total of 3 million tonnes of sinter was envisaged for a production of about 2 million tonnes of hot metal.


Sinter Plant


Sinter Plant


Simple Flow Diagram of Sinter Plant


The raw materials used are as follows - Iron ore fines (-10 mm), coke breeze (-3 mm), Lime stone & dolomite fines (-3mm) and other metallurgical wastes. The proportioned raw materials are mixed and moistened in a mixing drum. The mix is loaded on sinter machine through a feeder onto a moving grate (pallet) and then the mix is rolled through segregation plate so that the coarse materials settle at the bottom and fines onto the top.


The top surface of the mix is ignited through stationary burners at 1200oC. As the pallet moves forward, the air is sucked through wind box situated under the grate. A high temperature combustion zone is created in the charge -bed due to combustion of solid fuel of the mix and regeneration of heat of incandescent sinter and outgoing gases. Due to forward movement of pallet , the sintering process travels vertically down. The different zones created on a sinter-bed are shown in the simple flow diagram of sinter plant.


Sinter is produced as a combined result of locally limited melting , grain boundary diffusion and recrystallization of iron oxides. On the completion of sintering process, finished sinter cake is crushed and cooled. The cooled sinter is screened and + 6 mm fraction is dispatched to blast furnace through material handling system and -6 mm is re-circulated as return sinter.

Blast Furnace

All the raw material is charged into the blast furnace, from top, through variable throat armour or any other means. The purpose of a blast furnace is to chemically reduce and physically convert iron oxides into liquid iron called "hot metal".

Blast Furnace

The blast furnace is a huge, steel stack lined with refractory brick, where iron ore, coke and limestone are dumped into the top, and preheated air is blown into the bottom. The raw materials require 6 to 8 hours to descend to the bottom of the furnace where they become the final product of liquid slag and liquid iron. These liquid products are drained from the furnace at regular intervals.

Blast Furnace

The hot air that was blown into the bottom of the furnace ascends to the top in 6 to 8 seconds after going through numerous chemical reactions. Once a blast furnace is started it will continuously run for four to ten years with only short stops to perform planned maintenance.

Blast Furnace

Blast Furnace

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Raw Material In Iron Making