Process Description :
In a process called beneficiation, many mine mouth processing plants crush and grind the ore to very fine particles. These iron rich fines are then separated from the rock either magnetically or by flotation and made into pellets a process called palletizing. At the iron and steel plants, fines are recovered from ore handling and from the blast furnace itself. These fines are partially fused and then broken up into a uniform size in a process called sintering that allows the material to be fed into the blast furnace.

Sintering Line


Equipments :
In the pelletizing process, fine ore concentrate is mixed with a binder (Bentonite) and formed into green balls in the balling drums. These green balls are then fed into traveling grate kiln furnaces where they are dried and heated and then pass into a rotary kiln for final heating to a point just below fusion (2400°F).
In the sintering process, ore, limestone, and coke fines are mixed and deposited on a traveling grate. Burners ignite the mixture at the feed end of the grate. Air is pulled down through the bed to cause the burning zone to move through the bed until the sintering of the mixture has taken place throughout the entire depth of the bed. The porous, clinker-like sinter is cooled and broken up for use in the blast furnace. The use of sinter reduces coke requirements in the blast furnace, because the limestone is pre-reduced in the sinter bed.

Balling Drum Mixer


Combustion Technology :
The grate kiln system (graphic) consists of a straight grate for drying and preheating the pellets to 1900° F, a rotary kiln for heating to the final hardening temperature of 2400°F and a horizontal rotary hearth for cooling and heat recuperation. Either oil, gas, or a coal burner is placed at the discharge end of the kiln. Hot gases produced in the kiln are used for downdraft drying and preheating of the pellets. Hot air from the cooling zone is used for combustion.
The sinter plant uses a radiant hood ignition furnace over the bed with the combustion air preheated cooling the finished sinter. This ignition hood is up to 25% of the length of the sinter bed. Temperature in the hood starts at 2100°F at the start of the hood to about 1500°F at the exit. Wind-boxes beneath the grate create down-draft combustion that ignites the coke breeze in the mixture and ensures even heating of the entire bed.




Energy Consumption Statistics :
The graphic show the energy and materials requirements for palletizing and sintering. In palletizing, the furnaces require 0.5 to 1.0 million Btu per ton of ore pellets produced depending on the type and quality of ore produced. Sintering requires an ignition source fuel which in turn produces combustion in the coke breeze. The ignition fuel requirements are about 1.5 million Btu/ton of sinter produced. A nearly equivalent amount of energy is contained in the coke breeze that is mixed with the ore fines prior to firing.


Glossary:
BTU: British thermal unit (1 btu = 1055.05585 joules)
Coke Breeze: Coke breeze is fine coke particles, dust, etc. too small to be charged in the blast furnace.