Soderberg electrodes

Fig. 4. Top view of Soderberg electrode showiag reinforcing fins and steel casiag with hoUow electrode pipe at the center.

The calcium oxide is produced immediately prior to reduction from high purity limestone. This enthalpy of the reaction is +465.6kJ/mol and is provided by electric power and results in the consumption of Soderberg electrodes made from anthracite. The cell is tapped to release the molten carbide which is produced in 80% purity. The off-gas from the cell is typically 80% carbon monoxide and about 10% hydrogen. Following the production of calcium carbide, acetylene is produced by addition of water to the carbide ... 

Aluminium Production. Primary aluminium production is based on two different technologies basically using Soderberg or prebaked anodes. PAH are emitted from the carbon electrodes containing tar and pitch as binder (22). The emissions from the prebaked electrodes are usually 1-10% of that of the Soderberg electrodes. 

In the ferro-alloy industry the PAH emission is due to contact between hot metal and tarry products in electrodes and shutters. Only data for PAH emissions to water has been found for this source (29). However, assuming equal emission to water and air (50% efficiency in the wet scrubbers), this source has an emission factor of 10 g PAH per ton alloy. In a study in a Norwegian iron work, emissions to water were determined (29). PAH emission is due to the use of Soderberg electrodes. Making the same assumptions as above with the scrubber efficiency, the iron works emit 60 g PAH per ton produced iron. 

Anthracite is calcined at appreciably higher temperatures (1800—2000°C). The higher calcining temperatures for anthracite are necessary to complete most of the shrinkage and to increase the electrical conductivity of the product for use in either Soderberg or prebaked carbon electrodes for aluminum, siHcon, or phosphoms manufacture. 

Sources/Uses. Occur as emissions from coke ovens, from coking of coal tar pitch, and ftom Soderberg aluminum reduction electrolytic cells used for base coatings and paints for roofing and paving and as a binder for carbon electrodes... 

The use of electrodes in aluminum reduction operations is associated with the generation of several types of wastes (Dinman 1983 IARC 1984). In aluminum reduction facilities using the prebake process, PAHs are generated. In aluminum reduction operations using the Soderberg cell process, considerable amounts of volatiles from coal tar pitch, petroleum coke, and pitch, including PAHs, are generated. 

Soderberg anode (or electrode) — This electrode is named to honor the Swedish-Norwegian engineer Carl Wilhelm Soderberg (1876-1955). It is a continuously... 

Gulf Canada has been active in this area for sometime and recently has developed a process that produces a high quality electrode binder pitch from a petroleum-based feedstock (7). This pitch has been used on a commercial scale by the aluminum industry in both vertical stud Soderberg and prebaked electrodes. 

Figure 3.55, Double layer on mercury. Contribution of anions to the countercharge. Temperature 25°C. electrolyte concentration 0.1 M. Potentials with respect to a normal calomel electrode. (Redrawn from D.C. Grahame and B.A. Soderberg, J. Chem. Phys. 22 (19541 449.)...

The ca. 80% carbide produced, the rest being mainly calcium oxide, is formed as a liquid and is removed as blocks. Crucial in the economics of calcium carbide production is, in addition to the price of the raw materials, the electricity price, because the process is very energy intensive, 2.8 to 3.1 MWh being required per t. Calcium carbide furnaces with power demands up to 70 MW generally have to be operated with three-phase current and utilize Soderberg hollow carbon electrodes dipped deeply into the reaction mixture. 

Anode characteristics For prebaked Resistivity Current density For Soderberg Resistivity Current density Electrode spacing... 

The electrochemical production of aluminum utilizes pre-baked or Soderberg anodes. Pre-baked anodes are manufactured by mixing petroleum or pitch coke with around 20% of electrode binder (see Chapter 13.1.2), followed by molding, as is also usual for the production of graphite electrodes. The green electrodes are baked in a ring furnace at a temperature of 1200 °C. 

Fig. 5.7 - The charge attributed to cations z FV+) and anions (z-FT ) in the electrical double layer for 0.1 mol dm aqueous solutions at a mercury electrode. Data taken from D. C. Grahame B. A. Soderberg, J. Chem. Phys., 22 (1954), 449.

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