Fine ores need to be conditioned before they can be formed into pellets on disk pelletizers or in mixing drums. Added solids need to be mixed in optimally, and the moisture of the material needs to be as uniform as possible. To start with, simple mixers were used for the mixing process. In 1974, comparative trials performed with a company in Sweden showed that the use of an EIRICH mixer offers many different advantages. As a result, all production lines there were switched over to mixing technology from EIRICH. Since then, numerous iron ore producers all around the world have trusted in this mixing technology, including Ferrexpo Poltava Mining at their plant near Horischni Plawni. In 2013, older mixers here were replaced with an EIRICH mixer on one of the existing production lines. Based on the successful and cost-effective operation of this mixer in the years since, Ferrexpo has decided to equip other existing and new lines with EIRICH mixing technology. For a new plant, EIRICH will be supplying four of its largest mixers of type DW40 with a usable volume of 12 m³ each and a maximum design performance of 1400 t/h each. The nominal output of the four modernized lines will initially be around 3300 t/h of pellets, whereby the press filtration plant (18 filters) can process up to 3900 t/h of concentrate.
Iron – in its uses as steel or cast iron – is the most significant metal of our civilization. Natural ore deposits are usually made up of iron oxides, carbonates or sulfides, mixed with the gangue that needs to be separated during processing. To do this, the raw ore is broken down in several steps until it can be fed into a flotation stage as a fine powder, in which the gangue is then largely separated out. The remaining fine ore is pelletized, and the green pellets are thermally hardened. The pellets are the ideal feed material for iron production in a blast furnace process or via direct reduction. Alongside iron ore, they can also contain aggregates that are required for metallurgical reasons. Pelletizing plants are normally operated close to the ore mines.
Fine ore in itself does not have any bonding strength. In order to pelletize it, it is necessary to mix in binding agents (such as bentonite), aggregates (such as limestone or dolomite) and water. Uniform distribution of all these materials plays a very significant role for the subsequent yield of suitable pellets. Conventional mixing systems often have problems with this on account of their design. These mixers often have localized areas in which the moisture of the material is too high. As a result, undesirable large agglomerates – i.e. oversized grains – form on the disk pelletizer, and these then need to be screened out and re-processed.
By contrast, there are no problems with the distribution of solids and liquids when using an EIRICH mixer. Here, the material being mixed is not moved by mixing tools, but is instead transported to the mixing tools by means of a rotating pan. In addition, the entire content of the mixer is turned over in a single revolution of the mixing pan. The mixing tools, which are known as rotors, can run at tool speeds of more than 30 m/s. This makes it possible to generate high shear forces and distribute both solids and liquids quickly. The result: mixing qualities and levels of moisture distribution that normally cannot be matched by other mixing systems.
The production quantities of iron ore pellets are huge, so even minor improvements like savings in terms of binding agents can offer production sites annual cost advantages in the region of five to six-figure Euro amounts. In 1974, comparative trials showed that the use of an EIRICH mixer offers a number of advantages. Since the mixer is better at distributing the materials, significantly less bentonite is required in comparison to processing systems using simple mixers. In addition, it was also advantageous that slurries could be added to the mix. The homogeneity of the pellet feeds was better, and the green pellets were rounder and firmer. Energy demands were reduced, and the wear in the mixer was also lower. These results led to the introduction of EIRICH mixers – initially in a size of 7 m³ with throughput of up to 750 t/h. Since 2006, mixers have been developed especially for pellet feed processing with a usable volume of 12 m³ and throughput rates of up to 1500 t/h – often running for months on end in continuous operation without any downtime or repairs required due to wear.
Ferrexpo has also been using this technology since 2013 in a mixer running in continuous operation with a capacity of 7 m³. The company has been extracting, processing and selling high-quality iron ore pellets to the global steel industry for 40 years. They supply to steel mills in Austria, Germany, Japan, South Korea, Taiwan, China, Slovakia, the Czech Republic, Turkey, Vietnam and the USA. On its website, the company states the following: “Ferrexpo’s strategy is to produce and export high quality pellets to premium steel mills around the world who produce sophisticated steel products. It aims to be a low-cost efficient producer with a reliable logistics infrastructure.”
For Ferrexpo, the obvious choice was therefore to go for the best mixing technology available. For the new plant, EIRICH will be supplying four size DW40 mixers with a usable volume of 12 m³ each and a maximum combined design performance of 5600 t/h. The mixing tools will all be driven by highly efficient high-torque motors. The corresponding control systems will also be supplied by EIRICH.
The system, which is due to be taken into operation in 2021, will enable Ferrexpo to grow its output of high-quality pellets and supply to additional export markets.
Contact: Torsten Henk, e-mail: firstname.lastname@example.org