Authors : Kaushik Ghosh, Dr.-Ing. Thomas Hanstein, Dr.-Ing Jörg Oligmüller, [Maschinenfabrik Köppern GmbH & Co. KG, Germany] Translator : Bahadır Ürkmez [Turbo Makina]
It all started in 1898 with a humble beginning, when Wilhelm Köppern, a mining Director, acquired the ’Berninghaus-Hütte’ and started manufacturing briquetting presses primarily for the coal industry as the region was famous for coal mining. Coal fines were needed to be used not only industrially but also for household purposes. Due to industrial development, slowly roller press was used also for briquetting of other industrial fines.
Further development and expansion was done by the next generations namely Leopold Köppern, Otto Schäfer, Helmut Schäfer and presently by Christopher Schäfer.
In the early 1980’s Prof. Schönert (University Clausthal-Zellerfeld) researched, that roller presses or High Pressure Grinding Rollers (HPGR’s) build up a particle bed by feeding material from a filled hopper into the gap between two counter-rotating rollers. The movable roller is hydraulically pressed against the material bed and the fixed roller. Within the particle bed compression and shear forces cause mechanical interactions of the individual drawn in particles responding with fracture or crack initiation [1,2]. Due to the high pressure acting in the roller gap the feed material is densified to an agglomerate (flake). Using this indirect crushing operation in HPGR’s results in a remarkably lower specific energy consumption compared to other conventional methods for comminution such as ball mills or vertical roller mills [3,4]. Ball mills were the only means of grinding in the past, though being simpler technology but bottleneck were capacity and energy consumption. So this was overcome by use of Roller press as pre-grinder and semi finish grinder in combination with ball mill as well as finish grinder.
Fig.1 – Typical HPGR grinding circuit as pregrinder or flake recycling system
As pre-grinder, the fresh feed is fed to the HPGR once and the output from the HPGR is directly forwarded to the ball mill without any separation. One-step forward was made when the discharge of the HPGR, especially the edge tailings, were re-circulated to the HPGR. By recycling the flakes, energy consumption was reduced but still cannot be compared to the modern semi finish or finish grinding systems using HPGR’s.
Energy cost is a major part of the total cost of cement production, so upgradations of older grinding systems are explored worldwide. Such brown field projects are known to be more profitable due to comparable low investment cost and quicker ROI. In most cases a combined separator is installed, which does not only break the flakes but can also separate fines from coarse. The major bottleneck is lack of space for installation of a combined separator.
Upgrading of grinding circuit with combined KOESEP®-Separator
In 2015 Maschinenfabrik Köppern GmbH & Co. KG successfully upgraded a HPGR with flake recycling grinding system to semi finish grinding system, Fig 2.
Fig 2- Conversion of flake recycling circuit to semi finish grinding with combined separator from Köppern (KOESEP®). Equipment’s within the green boundary were existing and dotted lines are indicating the flow of material before upgradation.
After installation of the KOESEP®-separator, which includes two separation stages in only one housing, the HPGR output is now fed to the static part for de-agglomeration and coarse separation. Coarse rejects of the static stage, so called coarse grits, are discharged and fed back to the HPGR for regrinding. Finer material enters the dynamic stage by air draft. Particles, that are rejected by the rotating cage, are discharged as fine grits for regrinding in the ball mill or in both ball mill and HPGR. The ball mill’s discharge material is directly fed onto a dispersion plate in the dynamic stage of the KOESEP®. All material of defined product fineness passes the rotating cage and is discharged together with the separation air.
(In our next issue we will discuss the advantages of this upgrade and the working principles of HPGRs)
References:
[1] Schönert, K.: „Energetische Aspekte des Zerkleinerns spröder Stoffe“, ZKG 32 (1979) 1, 1-9 [2] Schönert, K.; Knobloch, O.: „Mahlen von Zement in der Gutbett-Walzenmühle“, ZKG 37 (1984) 11, 563-568
[3] Kellerwessel, H.: „Betriebsergebnisse von Hochdruck-Rollenpressen“,Aufbereitungstechnik 27 (1986) 10, 555-559
[4] Rosemann, H.; Ellerbrock, H.-G.: „Mahltechnik für die Zementherstellung – Entwicklung, Stand und Ausblick“, ZKG-International 51 (1998) 2, 51-62
