The production of cement has remained largely unchanged for 175 years, and only fossil fuels have been able to deliver the high temperatures required. In broad terms, production relies on limestone combined with iron, aluminium and silicate materials, which are fired at around 1,450 °C in a long, rotating kiln. The fired material is then ground into a fine powder and mixed with gypsum and other additives before the finished cement is ready for sale.
During firing, the limestone releases half of its weight as CO₂. The remaining CO₂-emissions come from the large amounts of fossil energy used in the process.

Green production

A green solution has long been sought by the cement industry. However, providing high-temperature process heat of up to 1,500 °C without fossil fuels has been one of several major obstacles. In addition, there has been uncertainty about changes to the complex production flow when introducing a new energy source – including how hot air is distributed and recirculated in the kiln – and how a new process could enable the capture of pure CO₂.
These challenges have now been solved by the two Danish engineers through a combination of well-known technologies, electrification and heat recovery. A validated solution, supported by leading experts in the field.

“The process takes place entirely without combustion, using electricity as the sole energy source. At the same time, the CO₂ extracted has a purity that allows it to be directly cooled, compressed and stored underground without the need for subsequent capture or chemical purification,” says Morten Drivsholm, expert in cement decarbonisation at COWI.
“In the future, cement production will be established where there is a surplus of green electricity and access to CO₂ storage. This marks a new, decentralised and sustainable business model for the cement industry,” Morten Drivsholm adds.

The solution

A key element in the green production of cement is the developed e-UltraHeater, which can deliver process heat of more than 3,000 °C using green electricity. Production can also be ramped up or down, allowing it to adapt to electricity prices and interact with the production of other renewable energy sources.

“The new production method will make it easier to control cement production flexibly. It will also make it possible to use the captured CO₂ for the production of other sustainable products,” notes Mads Pagh Nielsen, Professor at Aalborg University.

For the new production method, the two engineers from Northern Jutland have developed and patented an upright kiln – the e-VerticalKiln – whose function is tailored to the use of the e-UltraHeater in cement production and to the extraction of CO₂ from the firing process.

The perspective

From being one of the world’s major CO₂ emitters, cement production using the invention developed by the two Danes could become a zero-emission process – or very close to it.
This would enable the construction sector to take a major step towards meeting the stringent CO₂ requirements looming on the horizon.

“If this technology is realised, it will represent a breakthrough for an industry that lacks effective solutions. Current methods are expensive to operate and maintain and are energy-intensive, as they require complex systems for heating and cooling,” says Mads Pagh Nielsen, Professor at Aalborg University.

Føns Transformers and the Department of Energy at Aalborg University have already successfully tested several of the core concepts at laboratory scale. The next important step is to scale the technology and test it in a real operating environment.

“We are ready to begin production as soon as testing of the demo models is completed. The commitment of financial support from EUDP and Energy Cluster Denmark for this work is invaluable.
Of course, we would like to make some money from the product. But the most important thing is that our technology is put to work. Given the massive CO₂ emissions from cement production, every new plant will be a positive contribution to the fight against climate change,” conclude Flemming Buus Bendixen and Mogens Juhl Føns.

The two engineers

The two engineers behind the invention are both specialists with extensive experience in their respective fields.

Mogens Juhl Føns is a mechanical engineer, graduating from DTU in 1989. He has spent most of his engineering career working within the global cement industry, where he has gained extensive knowledge and experience with high-temperature processes. He is co-owner of a major production and sales unit in Turkey, supplying the FonsDelta clinker cooler to customers worldwide. To date, more than 100 units have been sold, and more than 200 cement plants in China have installed the clinker cooler under licence.

Flemming Buus Bendixen is a power engineering graduate from Aalborg University (1997). He holds a PhD in motor design and control and is also a specialist in magnetic systems. Throughout his career, he has been employed by or affiliated with several of Denmark’s largest companies.

Info box – about the two inventors

Mogens Juhl Føns

• Mechanical Engineer, DTU, 1989
• Former positions: Rambøll, FLSmidth
• Consultant since 1996 for, among others, Alfa Laval and FLSmidth
• Co-owner of CemGreen, 2020–2023
• Involved in the construction of cement plants in China
• Co-owner of Føns Technology International since 2010 – developed, produced and delivered more than 300 clinker coolers to the global cement industry
• Filed more than 20 patent applications
• Co-inventor of the e-UltraHeater and e-VerticalKiln

Flemming Buus Bendixen

• Power Engineer, Aalborg University, 1997
• PhD in motor design and control, 2005
• Specialist in magnetic systems for transformers
• Former positions: Grundfos, Vestas and Sintex
• Consultant since 1999 for, among others, Alfa Laval, Bang & Olufsen, Dali, Nano Nord and R&D Testsystems
• Chairman of the Danish Magnetic Society since 2022
• Filed more than 25 patent applications
• Co-inventor of the e-UltraHeater and e-VerticalKiln