The SAF
The SAF (Submerged Arc Furnace) is a very special electric furnace for the production of ferro-alloys, pig iron, steel, silicon metal, calcium carbide, phosphorus, precious metals, mineral wool and for recycling processes. A small introduction to this technology is created at this point.
The SAF uses the electrical resistance of the raw material and/or the slag which is produced in the process as a heating medium. Through electrodes, electric current is passed through the heating medium, creating a kind of resistance heating.
In contrast to an electric arc furnace, the main focus of SAF is on reduction and slower metallurgical processes. Therefore, a SAF works much quieter and more stable than an EAF (Electric Arc Furnace) and is usually operated continuously. Batch processes are rather rare, but also possible in individual cases.
Since the process is more important than the melting capacity, SAFs are also characterized more according to the actual furnace nominal power in MW than according to the tonnage in t or the transformer power in MVA.
The SAF can - with identical electrical and process system - be designed with completely different power ratings and dimensions depending on the process and the production rate. Systems are possible from small pilot furnaces with 100 kVA to over 100 MVA, from round furnaces with a diameter of only 500 mm up to rectangular furnaces with side lengths of almost 50 m.
SAF can be designed with round and rectangular shells, with DC or AC systems, with three or 6 electrodes or with one top and one bottom electrode (as anode and cathode). Depending on the process and furnace size, graphite electrodes, carbon electrodes or self-baking Söderberg electrodes are used as electrodes. Depending on the performance, operating temperatures, process and mode of operation, the furnaces are designed with different refractory concepts and different cooling options can be considered; from air cooling to water trickle cooling and water channel cooling to copper cooling systems.
The SAF Submerged Arc Furanace
The "classic" SAF is used for the production of ferroalloys and metallurgical silicon as well as calcium carbide or phosphorus. It is carried out "openly" with combustion of the reducing gases at the Möller surface or "closed" with a sealed furnace chamber and removal of the unburned reducing gases. Both variants can be combined with energy recoveries. These ovens are filled with möller a few meters inside; depending on the size of the furnace, the electrodes are immersed e.B. 1.5 m deep in the möller. The actual melting and reduction zone is "covered" ("submerged") inside the furnace. The proportion of slag produced in relation to metal production is low to moderate. In the case of a very low slag content, e.g. in silicon metal production, a separate slag tapping is dispensed with.
The slag SAF Submerged Arc Furnace Smelter
Whenever the ores
contain only small amounts of metal (e.g. in nickel production) or pre-reduced
material with a high degree of metallization (DRI) is used or minerals are to
be (re)melted or slags are to be treated, the SAF is designed as a “slag
furnace”: with a slag bath height of about 1,000 mm to 1,500 mm, with
electrodes immersed in the slag and the use of the slag (and not the raw
material) as a resistance medium. In the case of particularly high outputs,
fine input material and/or low specific slag resistances, an arc can also be
"drawn". These modes of operation require a special design of the
furnace electrics and usually also of the furnace cooling. These furnaces can
also be designed "open" or "closed".
The dimensioning
of the SAF is always very specific and individual depending on the
metallurgical process, the production rate, the power requirement, the process
characteristics and the electrical boundary conditions. Bluemetals is looking
back on several decades of experience and follows the global developments and
trends by dynamic monitoring.
The technique
described here and the comparisons do not claim to be scientific complete and
universal. Rather, they serve to provide a very simplified overview of the SAF
technology in general. In detail, we are happy to help you to design YOUR submerged
arc furnace for YOUR process.
Electrode column
The electrode column is a main component of a SAF. Holding and regulating the electrodes it is important for the energy transfer from the transformer to the process area inside the furnace. The upper part of the electrode column enables the positioning and slipping of the Söderberg-, carbon- or graphite electrodes, the lower part is responsible for transmitting the electrical current from the high current cables and tubes to the electrodes by copper contact clamps. The columns are driven by hydraulic systems, sometimes also by electric drives. 3 electrodes are positioned 3 in line in rectangular furnaces and on a so named pitch circle diameter at round furnaces, 6 electrodes fit to rectangular furnaces.