Home to the Valley of the Muses, Greece’s Mount Helicon has been hailed by Ovid and Hesiod as the font of inspiration and poetry. But today, the plains between Helicon’s foothills and the cool blue waters of the Gulf of Corinth are yielding a more prosaic kind of material: aluminum. Instead of verse, raw red bauxite — a mixture of aluminum oxides — flows freshly mined from the hills to a large smelter operated by Aluminium of Greece (AoG) in the town of Agios Nikolaos. On the other end, 185,000 tons of the pure silvery metal comes out every year, ready to be shipped all over the world.
The smelter’s location may be unique, but its owner, Mytilineos Group, is dealing with a global challenge affecting the entire smelting industry: The price of aluminum has dropped by almost half in the last 10 years, while the cost of production has dropped by only about 30 percent. Electricity is the biggest single contributor to cost, accounting for between 30 and 40 percent of production costs. Like other smelters, AoG found ways to become more efficient and remain profitable by putting in place successive cost-reduction programs.
“The key variables AoG is continuously looking to improve include energy use, raw-material consumption and preview of pot leakages,” says Bhanu Shekhar, chief digital officer for GE Power in the Middle East and Africa. “GE’s digital smelter solutions, data mixed with analytics, and physics can help them do just that and more.”
Top and above: AoG has three potlines consisting of 780 smelting pots running around the clock. Images credit: AoG
Current efficiency, or the relationship between the current intensity and the amount of aluminum a smelter produces, is the most important element of the smelting process. “Generally in a smelter, current efficiency runs around 93 to 94 percent, but just 1 percent increase in efficiency per year could be $2 million to $3 million in savings,” Shekhar says.
This benchmark is closely ties to “specific energy consumption”— a rate that describes how many kilowatt-hours it takes to produce a ton of aluminum. To improve it, AoG needed to find a way to optimize its smelting process.
The smelter is using a variant of the Hall-Héroult process, an industrial technique that has changed remarkably little since it was developed in 1886. AoG makes pure aluminum by first dissolving aluminum oxide, or alumina, in electrolytic cells filled with the molten aluminum compound cryolite. This bath lowers pure aluminum’s melting temperature from more than 2,000 degrees Celsius to about 940 degrees.
AoG has three potlines consisting of 780 smelting pots running around the clock. Each cell is insulated with a layer of high-silica bricks and lined with stainless steel and carbon, which serves as the cathode. There are also carbon anodes immerse in the metallic bath. When workers run a strong electric current through the bath, the reaction, called electrolysis, separates pure aluminum from the solution and pulls the metal towards the cathode on the bottom, where it can be periodically siphoned off.
These are high temperatures and extreme voltages, and slight mistakes can lead to major problems. The overheating of the pots, for example, can damage the brick lining and steel sheet and cause “pot leakage.” On the the other hand, a prolonged break in energy supply can potentially ruin the potline by “freezing” the molten bath and the aluminum.
To limit these problems and increase efficiency, AoG is deploying the world’s first digital smelter technology built on Predix, GE’s platform for the Industrial Internet. “As the largest vertically integrated bauxite, alumina and aluminum production and trading unit in the European Union, we are constantly looking at innovative technologies to enhance performance standards,” says Dimitris Stefanidis, CEO of AoG.
Opting for GE’s digital smelter solutions seemed like an obvious choice to Stefanidis. “After all, there is no potential downside of adopting these solutions, but if they work, the upside gains are tremendous.”
The digital smelter will use virtual sensors to “facilitate the ongoing collection and evaluation of parameters such as temperature and chemistry that are not ordinarily monitored continuously,” says Ammar Bustami, general manager for GE Power’s Digital Smelter Global COE. “We’re measuring almost 100 parameters per pot, and the digital solutions can explain why there is a variance between different pots and optimize the values within.” Bustami says that “physics models and analytics are applied to the data to not only understand what is happening in the pots but also to predict how they will react under a variety of circumstances and stimuli.”
Using the digital smelter solutions, AoG can accurately estimate a variety of conditions in the pots. It can then predict how they will function in the short and long term and recommend adjustments to maximize efficiency.
The system can be constantly adjusted. For example, as pots are taken offline, repaired and returned to use, they can quickly incorporate the new parameters, not only maximizing the efficiency of each pot, but also integrating them with the rest of the production line, Bustami says.
Constructing these first-of-their-kind digital smelter solutions isn’t an easy undertaking, but Bustami estimates that it will bring AoG a more than tenfold return on the investment needed to create them.
The solutions are a product of the GE Store, being created by a team of software engineers and developers based in San Ramon, California; GE Power’s Digital Smelter Center of Excellence (COE) in Dubai, United Arab Emirates; and GE’s Global Research Center in Bangalore, India.