Steel Mill Residues
A vast range of residual substances is found in steel mills, varying tremendously in volume and composition. Briquetting allows a wide variety of these residues to be processed. It is generally possible to tailor a briquetting plant to the specific needs of a steel mill while still offering the capability of processing a broad feed range.
Both cold and hot briquetting can be applied to steel mill residues.
Feed materials that are fully oxidized and hydrated can be briquetted by adding a binding agent. Oil and water content must be limited (oil is a separating agent, water is incompressible) - the admissible content varies depending on size distribution and feed. Usually, molasses and hydrated lime are used as binders. These are readily available at reasonable prices and the dosing procedure is unproblematic. This binder system also tolerates feed fluctuations to a certain extent. As an example, one steel mill has reached a capability of around 26 t/h for feeding residual material into a blast furnace.
The service life of the briquetting tools is an important aspect, as steel mill residues may contain substances of a highly abrasive nature. Based on Köppern’s comprehensive experience and backed by relevant research, we can offer you specific technical solutions that significantly extend tool service life, such as our exclusive RESIDUR® wear protection system for briquetting and compaction applications.
Fines from Direct Reduced Iron (DRI)
Fines ranging from 6 to 40% arise when iron ore is directly reduced. These fines are difficult to handle and to process in a melting vessel. Thus size enlargement is required. In the briquetting process, fines are usually bound using water glass with hydrated lime. There are alternatives of equivalent quality, such as sulfite lye or molasses.
For the cold briquetting of sponge iron, specific pressing forces in the range of 100 to 120 kN/cm are required, with similar forces being applied in the hot briquetting process (HBI). Cold briquetting combines the “forging” phenomenon without a binding agent - as seen in hot briquetting - with the “gluing” action caused by the binder. Product density is around 4 g/cm3, with typical throughput ranging between 10 and 40 t/h.
Reduction in the Rotary Hearth Furnace
An option for mill residue recovery is to reduce material using rotary hearth furnaces. This process can generate metallic iron by separating volatile constituents such as zinc and lead in such a way that it makes economic sense to put the residual materials to further use.
Size-enlarged material is needed for the rotary hearth. But using a pelletizing system means that certain granulometric requirements must be met that limit the feed selection. So plant owners have substituted pelletizing with briquetting, because handling the green pellets and distributing them on the hearth could not be solved satisfactorily.
Köppern has achieved the objective of producing high-temperature resistant, reducible briquettes with a minimum of binding agents on an industrial scale. The output from the rotary hearth can be subjected to hot briquetting with a view to increasing density to around 4.5 g/ccm and improving size enlargement with the intention of optimizing the melting operation. Such briquettes may, for example, also be used in a blast furnace.
Further Applications for Cold Briquetting
Chrome ore - Ferrochrome, which is an important raw material for the production of stainless steel, is gained from chrome ore using submerged arc furnaces. With the help of binders, the fines resulting from the ore processing can be briquetted and returned to the production cycle. Typical capacities are around 30 t/h per briquetting line.
Quicklime/Dolomite - Carbon dioxide is extracted from limestone or dolomite by calcination. The fines produced during the process can be briquetted to make them suitable for use in steelmaking. Both quicklime and dolomite can be briquetted without binders. Typical capacities lie between 5 and 20 t/h per briquetting line.
Sodium cyanide - Sodium cyanide is used in the leaching of gold ores. The chemically processed, fine-grained powder tends to become clumpy, however this can be effectively avoided by briquetting. The briquetting press is specially sealed to prevent the poisonous material from escaping. Typical capacities are around 4-8 t/h per briquetting line.
Coal - Hard coal processing is the classic briquetting application. In the process, dried coal dust is formed into egg-shaped briquettes using binders such as molasses or bitumen. Köpperm has delivered complete plants up to a capacity of 1.5 million t/a. Nowadays, the significance of hard-coal briquettes for home heating has declined in Europe. However, major efforts are being made to further the development of briquetting of brown coal in order to make the vast supplies of fines of this form of coal available for energy recovery.
Fireproof products - Raw materials for the production of fireproof products (e.g. clays) can be briquetted prior to firing. The greater density of the briquetted material allows the firing process to take place at a lower temperature and in a shorter time. Depending on the material, a lower pressure is used with water as a binder, or a higher pressure is used in a dry process.
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