FOCUS ON: ANODES 39
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Green anode plants -10 years of success Over the last 10 years, Fives’ Green Anode Plants have been based on the Rhodax® process, which allows a selective crushing for higher green and baked anode densities. By Christophe Bouche*
Fives develops three fields of expertise in the aluminium sector: � Carbon with Green Anode Plants, Carbon Butts Crushing and Recycling units, Firing Control Systems, Fume Treatment Centers, Furnace Tending Assemblies, Anode Rodding Shops, Bath Processing and Recycling Units � Reduction with Gas Treatment Center, Pot Tending Machines, cathode transport cranes, alumina transport systems � Casthouse with Melting & Holding Furnaces, Heat Treatment Furnaces and complete solutions for secondary aluminium casthouse Green Anode Plants are proposed with extended battery limits including a crushing and recycling unit, raw material storage, a paste plant, forming, a cooling tunnel and all associated utilities. Rhodax® History The Rhodax process is the result of two parallel developments started in early 90’s. On one side, Aluminium Pechiney (now Rio Tinto) was validating a new concept of high Grain/Sand ratio, which has been proven to be a key factor to minimise anode thermal shock problems. On the other side, Solios Carbone (Fives Solios) had developed a new crusher for
Green scrap
Fine grinding
Grains >300mm
To mixing & forming areas
Fig 1. Rhodax® key process features
the mineral processing applications, the Rhodax®, which key characteristics are linked to the in-bed compressive grinding principle: � The outlet particle size distribution (PSD) is almost insensitive to the inlet PSD � Selective crushing takes place by preserving the hard and coarse feed particles (mostly baked scraps) while crushing preferably the weaker, porous or pre-cracked particles (mostly raw coke). In carbon anodes application, it prevents also from producing fine particles from the baked scraps. Fig 2. Rhodax® dry mix preparation line
MIXING
Rhodax® flow sheet
Fines 70% < 32mm
Rhodax®
Much less spares Reduced maintenance COKE
MIXING
40% less items
<0.03mm
Two fractions only
Coke
Green & baked SCRAPS
>0.3mm
<0.3mm
15% reduction in main steel 20% less cranes 20% less electrical consumers
<0.3mm Ventilated classifyer
Ventilated classifyer
Recycl.
Conventional flow sheet
Coke
Baked scrap
>3mm
Screen
All raw materials mixed
In the early 2000’s, Fives and Aluminium Pechiney joined their R&D efforts and copatented the SCAP-RHODAX® process which consisted mainly in: � Mixing all solids (raw coke, green and baked scraps) to crush them all together at the same time without any detrimental impact on anode quality � Producing a recipe based on two size fractions only leading to a drastic flow sheet simplification Rhodax® key process features A full scale 35t/h industrial prototype was successfully tested from 2002 to 2004 at Aluminium Dunkerque in France. Design and operation concepts were validated and the achieved baked anode quality was found at least as good as with conventional process. Rhodax® Process Flow Sheet The Rhodax® dry mix preparation line consists mainly of one Rhodax® crusher (R), two TSV dynamic classifiers (C) (one for sand fraction, the other one for fine fraction), and one ball mill (B). Rhodax® dry mix preparation line The dry aggregate final product consists of two fractions only: grains from 0.3 to 30mm and fines from 0 to 80 µm, with a grain/sand (G/S) ratio above 5.
*Technical Director, Fives Solios and André Pinoncely, VP Technology, Fives Aluminium Division Aluminium International Today
Anode fives.indd 1
July/August 2017
19/07/2017 15:07:18