Aluminum, a truly valuable metal with a dynamic future has an excellent combination of light weight, high strength, superior corrosion resistance and excellent electrical conductivity
Aluminum lowers the weight of trains, planes, automobiles, structures and transmission lines, increasing their energy efficiency, lowering vehicle emissions and promoting a better environment. Many consider aluminum a ‘green metal’ for its ability to reduce vehicle fuel consumption.
Seventy percent of all primary aluminum ever produced is still in use. For the rest, it is very easy to recycle – only five percent of energy required to produce one ton of primary aluminum is required to recycle the same quantity.
Rain Carbon Inc. (RCI) is the leading, single-point, global supplier of both Calcined Petroleum Coke (CPC) and Coal Tar Pitch (CTP). Our Rain CII and RÜTGERS production facilities are innovators in the production of Calcined Petroleum Coke (CPC) and Coal Tar Pitch (CTP), which are both essential products in the manufacture of primary aluminum. RCI understands the critical roles played by both CPC and CTP in the aluminum industry, and we supply these products to numerous smelters around the world. We understand that supply interruptions and inconsistent quality can disrupt aluminum smelting operations, and emerging supply and quality constraints can threaten a smelter’s very existence. We have the resources, global diversity of production facilities, expertise and commitment to meet these challenges and help aluminum producers take advantage of new opportunities.
Aluminum is produced using the electrolytic Hall-Héroult process. Alumina (Al2O3) powder is dissolved in a molten bath of sodium aluminum fluoride known as cryolite. The temperature of operation in modern cells is about 950-960˚C (~1740-1760˚F). Electrical current is passed between carbon anodes and a carbon cathode in the cell, reducing alumina to aluminum metal which deposits on the cathode surface. Carbon anodes are consumed in this process, generating CO2 gas. The basic chemical reaction is:
2Al2O3+ 3C → 4Al + 3CO2
A modern electrolysis line, or ‘potline’, is shown above. Cells are connected in series and high-amperage DC current drives the electrolysis reaction. Modern cells operate at currents ranging from 200-500kA, but higher amperage cells are in development. Cells operate at a voltage of 3.8-4.5V; the energy required to produce 1 kg of aluminum is typically 12.5-14 DCkwhr. Aluminum smelting is energy intensive, and access to competitively priced electric power is critical for low-cost production.
The Aluminum Association is an excellent source for additional information on aluminum and its many applications and benefits.
Carbon Anode Production
Carbon anodes are essential to the production of aluminum, as described above.
Anodes used in the Hall-Héroult aluminum process are made from CPC and CTP. Most smelters operate their own anode-producing carbon plant. A handful of stand-alone anode plants supply pre-baked anodes to smelters without plants and to smelters who need anodes because of production shortfalls or maintenance shutdowns.
Pre-baked carbon anodes made from CPC and CTP are used to produce aluminum. In addition, spent anodes or ‘butts’ are used in the anode recipe. A typical breakdown is 67 percent CPC, 20 percent butts and 13 percent CTP. Green anodes are produced first and then baked in large furnaces to a final temperature of approximately 1,150˚C (2,100 ˚F). They are then rodded and used in electrolysis cells. Since anodes are consumed in the smelting process, they must be replaced every 20-30 days, depending on the size and cell design.
CPC and CTP quality directly influences anode quality and performance, so smelters accordingly set critical quality parameters such as sulfur and trace metal impurities (vanadium, nickel, calcium, iron, silicon and sodium). The physical properties of CPC such as bulk density, real density and particle size are also important when making anodes. Because of its lower thermal expansion coefficient, CPC with a sponge coke structure is favored over a shot coke structure.
A modern smelter producing 300,000 MT per year of aluminum requires the production of approximately 500 anodes per day, so consistent CPC and CTP quality from shipment to shipment is very important. Many green petroleum cokes sold to the fuel market are unsuitable for calcination for anode production due to those green cokes’ high impurity levels and undesirable structure.