IRON ORE FINES UTILIZATION via PELLETIZATION

World Wide Trend for Blast Furnace Burden

Availability and Cost are the major factors.Lump Ore and Sinter popular in countries like India, Brazil where Rich ores are available .

Pellets are popular in USA, Canada, China, Europe due to low Fe magnetite ores

Almost all combinations and proportions of Lump ore, Sinter and Pellets are used

Some Canadian/US furnaces use 100% pellets While some Japanese furnaces use 100 % sinter

No Big Size furnace operates without Sinter or Pellets

PELLETIZATION OF IRON ORES

It is one of the major agglomeration techniques usedfor preparing Iron Ore Fines to a form suitable for charging in BF. Pellets produced are generally 9 to16mm dia.The iron ore used for pelletization needs to becrushed to finer sizes (generally -300 mesh). The pellets produced are much stronger than sinterand can be transported with many falls without breakages. Due to their spherical shape and greater uniformityin size pellets improve the gas permeability in BF. They can be stored for months together.

Pelletization Process DescriptionPelletization Process Description

The pelletization process consists of forming green balls out of a very finely ground mixture of Iron ore fines, flux, coke breeze and a binder like bentonite.

These balls are then fired in an indurating furnace to get hardened balls called pellets. The fired pellets are then segregated for size and the fraction between 9 to 16 mm is sent to Blast furnace as the finished product.

The Raw Materials used in Pellet Making

Iron ore Fines/concentrateFlux

Coke Breeze Binder like Bentonite

All Iron Bearing Waste materials produced in Integrated Steel Plants

Like Mill Scale, Sludge, Flue Dust etc.

Different Units of Pellet Plant

1.Raw Material Receiving Section 2.Proportioning 3.Drying & Grinding Unit 4.Ground Material Storage 5.Mixing Unit 6.Balling Unit 7.Induration furnace/machine 8.Pellet segregation & Hearth Layer Separation 9.Product Storage/Dispatch

Raw Material Receiving Section

It consists of a few Receiving Conveyors and Bins for receiving and storage of the different raw materials.

Proportioning Section

Proportioning of the different Raw materials is accomplished using weigh feeders of suitable capacities.These weigh feeders are placed under respective bunkers and are controlled throgh a PLC.

A typical raw material proporyion could be:Iron Ore Fines 439.8 T/h 965 Kg/T of pelletsSludges 18.2 T/h 40 “CokeBreeze 9.1 T/h 20 “Bentonite 3.2 T/h 7 “L.S. 11.4 T/h 25 “

Drying & Grinding Unit

Typically the input material sizes are as under: Ore Fines -8 mmSludges -1 mmCoke -25 mmL.S. -10 mm Bentonite -5 mm The drier cum grinder unit consists of two parts the first part being the drier.Drying is done using a hot gas generator burning mixed gas.

After drying, the moisture level is less than 1 %.The grinding section uses steel balls as the grinding medium.

Closed circuit grinding uses air separators for separating coarse particles from the output.Air slides and bucket conveyors carrythe ground material to silos.

Ground Material Storage The output from drying and grinding unit is stored in silos. The silos are equipped with aeration equipment, electrically operated gates and air lock valves at the outlet. Belt weigh feeders are provided below the silo for drawing out material at desired rate.

Mixing UnitPaddle Mixers are used to produce a thoroughly uniform mix after adding water.The ground material from the silos is charged to the mixer. Bulk of water addition is done here.The mixed material from the mixer is then carried to the green pellet forming unit.

BALLING UNIT

To form green pellets with sufficient strength which can be loaded onto the induration

machine without breakage.

Pelletizers consist of inclined (at 45 to 50 deg) rotating discs , rotating between 5 -12 rpm.

Controlled quantity of water is added to adjust the final moisture .

Induration of Green Balls

1. It is the thermal treatment of green pellets through stages of Drying, Preheating, Firing, After Firing & Cooling

2. It is the main unit of the Pellet Plant.

3. Two types of indurations units are popular: Traveling Grate type:(70%). Grate Kiln type : (30%).

Principle of Travelling Grate M/cPelletization as opposed to sintering uses

gas as the main fuel.The consumption of gas is very high

compared to that in Sintering.Hence recirculation of hot waste gases is

highly important.An elaborate scheme is devised to utilize the sensible heat of waste gases to the

maximum.

Indurated Pellets

Pellet plantPellet plant

Pellets with their higher Fe content(63 %) as opposed to sinter with Fe Content of max 54% offer an attractive solution easing the transportation problem considerably.

Pellets are considerably stronger than sinter, the size does not degrade during transportation.Hence the "PELLET RETURNS" if at all are NEGLIGIBLE.

Due to their higher strength dust pollution is negligible. This will reduce Air Pollution in High lines area to a great extent.

If an effort is made to divert ore fines with higher -1 mm fraction to Pellet Plant and the ore fines with lesser -1 mm fraction sent to Sinter Plant,benefits will accrue to both Sinter Plant and Pellet Plant.Pellet Plant will spend less energy on crushing and grinding while the productivityand quality of Sinter will improve due to better raw material quality. This will ultimately benefit Blast Furnaces and BSP.