Powered by low-emission electricity, the kiln also enables capturing of pure CO2 when lime is burned in the precalcination phase of cement production. The production of cement, the world’s most used building material, causes around 7% of all CO2 emissions. VTT’s electric kiln is capable of making cement production close to carbon neutral.
VTT has announced the successful completion of several experiments with different feedstocks of its electrically heated rotary kiln that will revolutionise the cement, quicklime and pulp production industries. The experiments were done between November 2021 and October 2022.
Cement and quicklime production causes significant emissions for two reasons. First, the process requires a temperature of about 1,000 degrees Celsius, which releases emissions into the atmosphere when fuel is burned to create these temperatures. Secondly, as limestone – the main raw material of cement and quicklime – is heated, the carbonate it contains decomposes into carbon dioxide, causing even further emissions.
Until now, carbon-neutral production of industrial-quality burnt lime mix has been an elusive goal. However, the importance of finding a solution has become a top global priority.
“Limestone is one of the most used raw materials in the world, so it is urgent we find ways to use it in a more environmentally friendly way. At VTT, we have been able to make the crucial calcination phase more sustainable. With tests of our electric kiln, we have proven that replacing combustion processes with electricity-based solutions is an effective means of curbing climate change. Furthermore, the quality of the burnt lime product is good,” says Eemeli Tsupari, Principal Scientist at VTT.
The captured CO2 can also be used for industrial purposes, from synthetic fuels to novel materials, like plastic replacements, or it can be permanently trapped if it is mixed into the concrete that is used for sidewalks, roads and bridges.
The pilot kiln has been designed with convenient transport in mind. Housed inside of a cargo container, it can be easily transported to industrial plants to be used in different production processes, including chemical pulping in the paper industry.
“With proof of concept for the electric kiln in the precalcination phase, we are on the path towards fully decarbonising the second burn process by considering new carbon-free heat sources, such as hydrogen, to reach the necessary temperatures,” says Tsupari.
The current global energy crisis has made electricity an even more desirable source of energy due to the high prices of fossil fuels.
“The current high cost of natural gas makes electricity a more viable option for heating processes using gas. Solving this challenge globally could be the equivalent of taking millions of cars off the road each year. We are now looking for partnerships with major industrial players to take this solution to the next level,” states Tsupari.
“The raw meal of cement production was successfully treated in the trial runs to an intermediate product which is fully calcined but not yet reacted with silica, which is exactly what is wanted to achieve in a calciner,” says Mathias Frankenhaeuser, Technical Manager at Finnsementti.
“It’s exciting to see that properties of calcium oxide produced in the best experiment points are very near to product-grade burnt lime,” says Erkka Uuttu, Energy Manager at Nordkalk.
The kiln is located at a VTT facility in Central Finland in the city of Jyväskylä.
“Next, we would love to find a technology partner to help us build a large kiln to scale the output,” concludes VTT’s Tsupari.