Krupp–Renn process
The Krupp-Renn process consumed mainly hard coal and had the unique characteristic of partially melting the charge.
This method is beneficial for processing low-quality or non-melting ores, as their waste material forms a protective layer that can be easily separated from the iron.
This process is based on using a 3-meter in diameter and similarly lengthy drum with a horizontal axis for blowing gases preheated by two regenerators.
[2] The metallurgy industry underwent much research regarding the implementation of rotary tubular furnaces, inspired by similar equipment used in cement works.
The process, named after the Krupp company that created it and the Rennfeuer, translating to "low furnace,"[7] displayed potential.
According to sources, the Red Army's destructive techniques in dismantling German industrial plants proved inappropriate and wasted valuable resources.
Travelers from Berlin to Moscow reported observing German machinery scattered, largely deteriorating, along every meter of track and shoulder, suffering from the harsh climatic conditions.
However, the dwindling of local ferruginous sand deposits, along with the low cost of scrap and imported ores, eventually resulted in the gradual discontinuation of the process.
The process was steadily improved by the Japanese, who developed it under various names for specialized products including ferroalloys[12] and the recycling of steelmaking by-products.
[9] The residence time of the product is influenced by the slope and speed of rotation of the rotary kiln, which is inclined at an angle of roughly 2.5 percent.
The iron ore is introduced into the furnace upstream and mixed with a small amount of fuel, typically hard coal.
[21] The fumes exiting the furnace's upper end attain temperatures ranging from 850 to 900 °C and are subsequently cooled and purged of dust by water injection before discharge through the chimney.
Overly high temperatures or unsuitable granulometry lead to the creation of rings of sintered material that accumulate on the walls of the furnace.
It transforms into a paste that guards the metal against oxidation when heated and simplifies both Luppen processing and furnace cleaning during maintenance shutdowns through vitrification when it gets cold.
Due to its ability to cause slag to become especially infusible and viscous, ores that contain this oxide cannot be used with blast furnaces as they must remove all their production in liquid form.
[21] For this reason, the preferred ores for this technique are those that would become uneconomical if they had to be modified with basic additives, usually those with a low iron content (between 35 and 51%), and whose gangue needs to be neutralized.
However, with the Krupp-Renn process, the high temperature of the fumes prevents condensation within the furnace, before they are retrieved by the dust-removal system.
Understanding the mechanism of lining formation is a complex process involving mineralogy, chemical reactions, and ore preparation.
To remedy this, increasing the supply of combustion air or interrupting the furnace charging process are effective solutions.
Unless otherwise specified, data are taken from ECSC (1960[35]), UNIDO (1963[14]), and Production étrangère de fer sans haut fourneau (Moscow, 1964[36]) publications.
(external or internal unknown) Ząbkowice Śląskie (Poland) Zakłady Górniczo-Hutnicze „Szklary” 2 × 275–300 1950–1953[39] 1982[39] Garnierite processing (9% iron, 61% SiO2 and 0.73% nickel).
[62] Developed in the 1970s, it is based on the general principles of the Krupp-Renn process with a lower temperature reduction, typically between 950 and 1,050 °C, which saves fuel but is insufficient to achieve partial melting of the charge.
In 1957, Krupp tested a furnace at Stürzelberg [fr][nb 20] for the treatment of roasted pyrites to extract iron (in the form of Luppen) and zinc (vaporized in the flue gases).
In the 1960s, Japanese steelmakers, sharing the observation that furnace plugging was difficult to control, developed their own low-temperature variants of the Krupp-Renn process.
[19] The production of ferronickel from laterites takes place in a context that is much more favorable to the Krupp-Renn process than to the steel industry.
The process is therefore attractive, but regardless of the metal extracted, mastering all the physical and chemical transformations in a single reactor is a real challenge.
As a result, lower-temperature reduction followed by electric furnace smelting allows each stage to have its own dedicated tool for greater simplicity and efficiency.
Only 5% of the iron is reduced to metal, leaving unburned coal as fuel for the subsequent melting stage in the electric furnace.
It retains its advantages, which are the concentration of all pyrometallurgical reactions in a single reactor and the use of standard (i.e. non-coking) coal, which covers 90% of the energy requirements of the process.
Coal consumption is only 140 kg per ton of dry laterite,[nb 22] and the quality of the ferronickel obtained is compatible with direct use by the steel industry.
