Iron ore is the most important raw material for iron-pellet production. Iron-Pellets – means pellets made from iron ore fines and other additives that are first crude and then cooked and hardened and used to revive the traditional method of producing iron in a blast furnace or through multiple methods of direct reduction. Iron-Pellets are the raw material for the production of crude iron and must have the desired chemical and thermal mechanical properties in resuscitation furnaces.
For the production of iron-pellets, iron ore fines, including additives with moisturizing solutions such as water to obtain a spherical shape, are rotated in pelletizing machines to produce Iron-pellets. When producing iron-pellets, additives and adhesives such as calcium hydroxide may be added to enhance the quality and metallurgical mechanical properties of the pellets. At this stage the pellets are produced in the desired size with sufficient mechanical strength and shipped for transportation to the baking machine. In the second stage, the raw pellets are carefully heated to a temperature below the softening temperature of the iron to soften in the oxidizing atmosphere, first drying and then cooked, so that their porosity is not reduced.
Mechanical and Physical Properties of Iron-Pellets:
It is important that pellets have to bear considerable mechanical loads during transportation, drying and hardening at high temperatures. Therefore, they must have sufficient abrasion resistance and compressive strength against crushing. Depending on the uses of the pellets, their properties may vary. Special additives are used to achieve these properties. Also the machine used for pellet production should be able to provide the required properties. The method of transferring them to the baking unit should be designed to minimize the impact on the pellets.
Changes in the pellets consumed in the blsat furnace or in direct regeneration processes may cause them to crumble and disintegrate, so it is important to examine the mechanical and physical properties of the pellets and their resuscitation. Experiments are required to determine pellet properties under standard conditions.
The quality of the pellets depends on their chemical, mechanical and metallurgical properties. Each of these properties are effective in producing pellets, resuscitation as well as melting and refining sponge iron and crude iron.
Physical Properties of Pellets:
Determinants of pellets are their dimensions, shape, special surface, dimension distribution, porosity, abrasion resistance and friction.
Dimensions of pellets:
Pellets divided into three groups by size:
– Small pellets with a diameter of 3 to 8 mm for agglomeration and hydrometallurgical process
– Normal pellets with a diameter of 10 to 15 mm for use in tall furnaces and reclamation units
– Large pellets of 20 to 30 mm diameter for use in steel making and raw materials for cement production
Porosity is one of the special properties of pellets and plays an important role in all stages of pelletization and its consumption. In iron-pellets, porosity is the result of uniform removal of water and evaporation. Porosity in pellets is very effective on the resuscitation property. With the increase in porosity, the pelletizing properties of many pellets increase under certain conditions. On the other hand, porosity is inversely correlated with pellet strength and its increase or decreases pellet strength, so in order to adjust these two factors, optimum condition should be chosen. The porosity depends on the size of the particles and the pelletization method and plays an important role in drying and cooking. During these stages, the evaporated moisture and phase transformation occur and the materials are recrystallized. Given the required strength, the best porosity of the pellets is about 20 to 30 percent. The total porosity of the pellets is defined as the volume of the pits relative to the total volume of the raw pellets and is calculated using the difference between the actual and apparent specific gravity.