Pelletizing

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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, iron ore, animal compound feed, plastics, waste materials, and more. The process is considered an excellent option for the storage and transport of said materials. [1] The technology is widely used in the powder metallurgy engineering and medicine industries. [2]

Contents

Pelletizing of iron ore

Edward W Davis of the University of Minnesota is credited for devising the process of pelletizing iron ore.

Processed Taconite pellets as used in the steelmaking industry, with a US Quarter shown to scale. TaconitePellet.JPG
Processed Taconite pellets as used in the steelmaking industry, with a US Quarter shown to scale.

Pelletizing iron ore is undertaken due to the excellent physical and metallurgical properties of iron ore pellets. [1] Iron ore pellets are spheres of typically 6–16 mm (0.24–0.63 in) to be used as raw material for blast furnaces. They typically contain 64–72% Fe and various additional material adjusting the chemical composition and the metallurgic properties of the pellets. [3] Typically limestone, dolomite and olivine is added and Bentonite 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. [4]

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. [5] 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. [1]

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

Formation of the raw Pellets

Disc Pelletizer PELLETIZER.jpg
Disc Pelletizer

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. [6] 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. [7] 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. [7] There are different pelletization processes applied in the pharmaceutical industry and these typically vary according to the bonding forces. [8] Some examples of the processes include balling, compression, and spray congealing. [8] Balling is similar to the wet (or green) pelletization used in the iron ore industry. [9]

Pelletizing of animal feeds

animal pellets PelletRation.jpg
animal pellets

Pelletizing of animal feeds can result in pellets from 1.2 mm (0.047 in) (shrimp feeds), through to 3–4 mm (0.12–0.16 in) (poultry feeds) up to 8–10 mm (0.31–0.39 in) (stock feeds). The pelletizing of stock feed is done with the pellet mill machinery, which is done in a feed mill.

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.

Formation of the feed pellets

Pelletizing is done in a pellet mill, 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.

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. [10] 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. [11] Areas of concern include the inland rainforests of British Columbia These claims are contested by the pellet and forest industries.

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.

See also

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Wrought iron is an iron alloy with a very low carbon content in contrast to that of cast iron. It is a semi-fused mass of iron with fibrous slag inclusions, which give it a wood-like "grain" that is visible when it is etched, rusted, or bent to failure. Wrought iron is tough, malleable, ductile, corrosion resistant, and easily forge welded, but is more difficult to weld electrically.

<span class="mw-page-title-main">Sintering</span> Process of forming and bonding material by heat or pressure

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<span class="mw-page-title-main">Steelmaking</span> Process for producing steel from iron ore and scrap

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<span class="mw-page-title-main">Slag</span> By-product of smelting ores and used metals

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<span class="mw-page-title-main">Blast furnace</span> Type of furnace used for smelting to produce industrial metals

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<span class="mw-page-title-main">Mill (grinding)</span> Device that breaks solid materials into smaller pieces by grinding, crushing, or cutting

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Comminution is the reduction of solid materials from one average particle size to a smaller average particle size, by crushing, grinding, cutting, vibrating, or other processes. In geology, it occurs naturally during faulting in the upper part of the Earth's crust. In industry, it is an important unit operation in mineral processing, ceramics, electronics, and other fields, accomplished with many types of mill. In dentistry, it is the result of mastication of food. In general medicine, it is one of the most traumatic forms of bone fracture.

Sinter plants agglomerate iron ore fines (dust) with other fine materials at high temperature, to create a product that can be used in a blast furnace. The final product, a sinter, is a small, irregular nodule of iron mixed with small amounts of other minerals. The process, called sintering, causes the constituent materials to fuse to make a single porous mass with little change in the chemical properties of the ingredients. The purpose of sinter are to be used converting iron into steel.

<span class="mw-page-title-main">Feed manufacturing</span>

Feed manufacturing refers to the process of producing animal feed from raw agricultural products. Fodder produced by manufacturing is formulated to meet specific animal nutrition requirements for different species of animals at different life stages. According to the American Feed Industry Association (AFIA), there are four basic steps:

  1. Receive raw ingredients: Feed mills receive raw ingredients from suppliers. Upon arrival, the ingredients are weighed, tested and analyzed for various nutrients and to ensure their quality and safety.
  2. Create a formula: Nutritionists work side by side with scientists to formulate nutritionally sound and balanced diets for livestock, poultry, aquaculture and pets. This is a complex process, as every species has different nutritional requirements.
  3. Mix ingredients: Once the formula is determined, the mill mixes the ingredients to create a finished product.
  4. Package and label: Manufacturers determine the best way to ship the product. If it is prepared for retail, it will be "bagged and tagged," or placed into a bag with a label that includes the product's purpose, ingredients and instructions. If the product is prepared for commercial use, it will be shipped in bulk.
<span class="mw-page-title-main">Metallurgical coal</span> Grade of coal

Metallurgical coal or coking coal is a grade of coal that can be used to produce good-quality coke. Coke is an essential fuel and reactant in the blast furnace process for primary steelmaking. The demand for metallurgical coal is highly coupled to the demand for steel. Primary steelmaking companies often have a division that produces coal for coking, to ensure a stable and low-cost supply.

References

  1. 1 2 3 Totten, George E.; Colas, Rafael (2016). Encyclopedia of Iron, Steel, and Their Alloys (Online Version). Boca Raton, FL: CRC Press. p. 118. ISBN   978-1-4665-1108-8.
  2. ↑ Ulitsky, V. M.; Lisyuk, M. B.; Shashkin, A. G. (2014). Soil-Structure Interaction, Underground Structures and Retaining Walls: Proceedings of the ISSMGE Technical Committee 207 International Conference on Geotechnical Engineering. Amsterdam: IOS Press. p. 124. ISBN   978-1-61499-463-3.
  3. ↑ Advanced Explorations Inc.:Iron Ore Products Archived 2014-10-31 at the Wayback Machine
  4. ↑ National Steel Pellet Company:Iron Ore Processing for the Blast Furnace Archived 2010-12-31 at the Wayback Machine
  5. ↑ Pelletizing of Iron Ores:[Meyer, Kurt. Pelletizing of Iron Ores. Springer-Verlag Berlin, Heidelberg, Verlag Stahleisen mBH, Dusseldorf, 1980.]
  6. ↑ Api (2000). Polyurethanes Conference 2000: Defining the Future Through Technology. APC. p. 45. ISBN   978-1-58716-038-7.
  7. 1 2 Sandell, Erik (1992). Industrial Aspects of Pharmecuticals. Boca Raton, FL: CRC Press. p. 200. ISBN   978-91-86274-46-7.
  8. 1 2 Ghebre-Selassie, Isaac (2022). Pharmaceutical Pelletization Technology. Boca Raton, FL: CRC Press. pp. 3, 133. ISBN   9780824780852.
  9. ↑ Drew, Thomas (1978). Advances in Chemical Engineering, Volume 10. New York: Academic Press. p. 56. ISBN   978-0-08-056557-6.
  10. ↑ "Drax fires up biomass power – Wood Pellet Association of Canada".
  11. ↑ "B.C. Giving millions to transform rainforest into wood pellets for export, new report documents".
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