Pelletizing is the process of compressing or molding a material into the shape of a pellet. A wide range of different materials are pelletized including

chemicals A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., wit ...

iron ore Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the fo ...

, animal

compound feed Animal feed is food given to domestic animals, especially livestock, in the course of animal husbandry. There are two basic types: fodder and forage. Used alone, the word ''feed'' more often refers to fodder. Animal feed is an important input to ...

, plastics, waste materials, and more. The process is considered an excellent option for the storage and transport of said materials. The technology is widely used in the powder metallurgy engineering and medicine industries.

Pelletizing of iron ore

Pelletizing iron ore is undertaken due to the excellent physical and metallurgical properties of

pellets. Iron ore pellets are spheres of typically to be used as raw material for

blast furnace A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally pig iron, but also others such as lead or copper. ''Blast'' refers to the combustion air being "forced" or supplied above atmospheric ...

s. They typically contain 64–72% Fe and various additional material adjusting the chemical composition and the metallurgic properties of the pellets. Typically

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

and

olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...

is added and

Bentonite Bentonite () is an absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelling capacity than Ca-mon ...

is used as binder. The process of pelletizing combines mixing of the raw material, forming the pellet and a thermal treatment baking the soft raw pellet to hard spheres. The raw material is rolled into a ball, then fired in a kiln or in travelling grate to sinter the particles into a hard sphere. The configuration of iron ore pellets as packed spheres in the blast furnace allows air to flow between the pellets, decreasing the resistance to the air that flows up through the layers of material during the smelting. The configuration of iron ore powder in a blast furnace is more tightly-packed and restricts the air flow. This is the reason that iron ore is preferred in the form of pellets rather than in the form of finer particles. The quality of the iron ore pellets depends on different factors, which include feed particle size, amount of water used, disc rotating speed, inclination angle of the disc bottom, residence time in the disc as well as the quality and quantity of the binder(s) used.

Preparation of raw materials

Additional materials are added to the iron ore (pellet feed) to meet the requirements of the final pellets. This is done by placing the mixture in the pelletizer, which can hold different types of ores and additives, and mixing to adjust the chemical composition and the metallurgic properties of the pellets. In general, the following stages are included in this period of processing: concentration / separation,

homogenization Homogeneity is a sameness of constituent structure. Homogeneity, homogeneous, or homogenization may also refer to: In mathematics *Transcendental law of homogeneity of Leibniz * Homogeneous space for a Lie group G, or more general transformati ...

of the substance ratios, milling, classification, increasing thickness, homogenization of the pulp and filtering.

Formation of the raw Pellets

The formation of raw iron ore pellets, also known as pelletizing, has the objective of producing pellets in an appropriate band of sizes and with mechanical properties high usefulness during the stresses of transference, transport, and use. For example, waste materials are ground before being heated and introduced into a press for compression. Both mechanical force and thermal processes are used to produce the correct pellet properties. From an equipment point of view there are two alternatives for industrial production of iron ore pellets: the drum and the pelletizing disk.

Thermal processing

In order to confer to the pellets high resistance metallurgic mechanics and appropriate characteristics, the pellets are subjected to thermal processing, which involves stages of drying, preheating, firing, after-firing and cooling. The duration of each stage and the temperature that the pellets are subjected to have a strong influence on the final product quality.

Pharmaceutical industry

In the field of medicine, pelletization is referred to as the agglomeration process that converts fine powders or granules into more or less spherical pellets. The use of the technology increased because it allows for the controlled release of dosage form, which also lead to a uniform absorption with less mucosal irritation within the gastrointestinal tract. There are different pelletization processes applied in the pharmaceutical industry and these typically vary according to the bonding forces. Some examples of the processes include balling, compression, and spray congealing. Balling is similar to the wet (or green) pelletization used in the iron ore industry.

Pelletizing of animal feeds

Pelletizing of animal feeds can result in pellets from (shrimp feeds), through to (poultry feeds) up to (stock feeds). The pelletizing of stock feed is done with the

pellet mill A pellet mill, also known as a pellet press, is a type of mill or machine press used to create pellets from powdered material. Pellet mills are unlike grinding mills, in that they combine small materials into a larger, homogeneous mass, rather t ...

machinery, which is done in a

feed mill A gristmill (also: grist mill, corn mill, flour mill, feed mill or feedmill) grinds cereal grain into flour and middlings. The term can refer to either the grinding mechanism or the building that holds it. Grist is grain that has been separat ...

Preparation of raw ingredients

Feed ingredients are normally first hammered to reduce the particle size of the ingredients. Ingredients are then batched, and then combined and mixed thoroughly by a feed mixer. Once the feed has been prepared to this stage the feed is ready to be pelletized.

Pelletizing of wood

Wood pellets made by compressing sawdust or other ground woody materials are used in a variety of energy and non-energy applications. In the energy sector, wood pellets are often used to replace coal with power plants such as Drax, in England, replacing most of their coal use with woody pellet. As sustainably harvested wood does not lead to a long-term increase in atmospheric carbon dioxide levels, wood fuels are considered to be a low-carbon form of energy. Wood pellets are also used for domestic and commercial heating either in the form of automated boilers or pellet stoves. Compared to other fuels made from wood, pellets have the advantage of higher energy density, simpler handling as it flows similar to grain, and low moisture. Concerns have been raised about the short-term carbon balance of wood pellet production, particularly if it is driving the harvesting of old or mature harvests that would otherwise not be logged. Areas of concern include the inland rainforests of British Columbia These claims are contested by the pellet and forest industries.

Formation of the feed pellets

Pelletizing is done in a

, where feed is normally conditioned and thermal-treated in the fitted conditioners of a pellet mill. The feed is then pushed through the holes and exit the pellet mill as pelleted feed.

After pelleting processes

After pelleting, the pellets are cooled with a cooler to bring the temperature of the feed down. Other post pelleting applications include post-pelleting conditioning, sorting via a screen, and maybe coating if required.

Gallery

References

{{Authority control Iron Livestock Metallurgical processes