Agglomeration

Agglomeration
Points : Agglomeration, Definition Definition Iron ores are benefited to improve chemical and physical properties. When iron-content of the ore is increased, the process is termed concentration, and when physical structure is improved, by making larger particles out of smaller particles, the process is termed as agglomeration.

Some ores can be concentrated simply by crushing, screening and washing. Others need to be ground to very small particle sizes before the iron oxide could be separated from extraneous materials by flotation. Magnetite ores can be separated magnetically. These ores contain 25-30 % iron as mined. They are ground to 75µm (200 mesh) or finer size and then concentrated by magnetic separating drums. The final concentrate has 60-65 % iron and 2-8% silica. This concentrate quality is acceptable but they need to be agglomerated into suitable size that the blast furnace can easily accept. Fine particles of iron ore and concentrates are undesirable for blast furnace feed for which the desired size is 6- 25 mm. This is achieved by sintering and pelleting. A mixture of iron-ore fines, concentrates and coke fines is deposited on a travelling grate. The travelling grate is shaped like an endless loop of conveyor-belt forming a shallow trough with small holes in the bottom. The bed of the material on the grate is ignited by an ignition burner (that is fired with natural gas and air), and then as the grate moves slowly towards the charge-end, air is pulled down through the bed. As the coke fines burn in the bed, the heat sinters the small particles. At the discharge end of the machine the sinter is crushed to remove large lumps and then cooled and screened. Addition of limestone and dolomite fines to the sinter feed, produces a self-fluxing sinter. In modern integrated steel plant, most of the iron-bearing dusts and slag’s are recycled by adding then to sinter plant feed-mix.