Gases for Life


Super­conductivity for large consumers

By the Editorial Team

New forms of electricity transmission can save energy and help reduce CO₂ emissions. The goal of DEMO200 is to facilitate a high direct current flow to industrial consumers without losses.

Background picture: The Trimet aluminum smelter in Voerde, Germany, was selected as pilot project for a superconducting conductor rail system. The necessary high-current infrastructure is already in place here.

Aluminum smelting, chlorine alkali electrolysis or large data centers require huge amounts of electrical energy. However, some of the electricity is lost in the industrial power lines due to electrical resistance. The greater the flow of electricity, the greater the losses that have to be taken into account. This wastage drives up costs, and where the electricity is generated from fossil fuels, the transmission loss leads to an increase in CO₂ emissions.

Superconductivity for 200 kiloamps

Physics provides an effective way of minimizing resistance: superconductivity. It is associated with considerable technical complexity, however, and is currently only feasible over limited distances. This approach is therefore of particular interest for energy-intensive industries. The objective of the DEMO200 project is to develop a 200-kiloamp superconducting busbar which is ready to go into production. That is ten times more than what has been achieved so far. Huge currents are thus already required for the test runs. It was therefore decided to run the pilot project at the Trimet aluminum smelter in Voerde. The plant already has high-current infrastructure in place, which can also be used for the tests. Superconductivity pioneer Vision Electric Super Conductors is in charge of the project. Besides Trimet, the other partners in this development project are the Karlsruhe Institute of Technology (KIT) and the companies Theva Dünnschichttechnik, Deutsche Nanoschicht and Messer.

Low temperatures eliminate resistance

A very low temperature is the indispensable prerequisite for loss-free superconductivity. Messer has developed a new technical approach specifically for the purpose of cooling the busbar in Voerde. The busbar’s operating temperature is minus 206 degrees Celsius. At this extremely low temperature, the electrons move without any resistance, which means that there are no longer any transmission losses. The storage temperature of liquid nitrogen is close to its boiling point of minus 196 degrees. This means that the gas has to be “subcooled” to an even lower temperature for this application. To this end, the liquid gas is piped into a “sub cooler”. This is a vacuum-insulated vessel in which the nitrogen cools down to minus 209 degrees Celsius through expansion in sub-atmospheric pressure. The principle has already been used for the AmpaCity project in Essen, with the technology being further optimized for Demo200. One of the new features is that the pump for circulating the liquid gas is no longer required, making the technology even more efficient.

In addition, the cooling effect of the nitrogen is now reused to a certain extent after the gas has cooled the busbar. At this point it is still extremely cold, with a temperature of around minus 200 degrees Celsius. The nitrogen is conducted to the power supply, where it cools the junction between the conventional power line and the superconducting busbar. Heat is inevitably generated here. Keeping this disruptive factor away from the cryogenic superconductor is a core element of the new Demo200 development. And here Messer technology is making a vital contribution.