The top recovery turbines (TRT) technology reuses high-pressure gases (known as flue gases) from the blast furnaces to drive electricity generators.

TRT turbines generate energy by exploiting a property that is common to all gases - they expand as pressure drops. Fine particles are removed from the flue gas using dry and wet scrubbing systems. During the scrubbing process, the gas cools and its pressure drops. Before it can be used in the gas pipe network, the gas needs to be reduced to 0.1 bar (a standard unit of pressure). The most energy efficient way to do this is to lead the gas through a turbine, where it activates a generator to produce electricity.

TRT does not have an impact on the blast furnace operations. As blast furnace gas is very combustible, it is normally used in other parts of the plant to generate heat or energy for other processes. With the TRT system, the flue gas generates energy twice – first in the turbine and also when it is burnt for its usual purpose.

TRT is a proven technology, with very limited risks: if the system fails, the expanding gas is accommodated in the existing scrubber. This is what happens in any blast furnace that is not equipped with the TRT technology.

The technology has great potential, as each TRT has the same capacity as three to four land-based wind turbines. To date, six blast furnaces at four of our sites have been equipped with such turbines and are generating more than 482 Gigawatt hours (GWh) of electricity each year. As a result, FCE's energy bill has already been cut by more than 3% a year. TRT also provides ArcelorMittal with security over the sustainability of our long-term energy supply, and reduces our exposure to rising energy prices.

ArcelorMittal is actively looking for energy partners to help the company increase the amount of electricity we produce via TRT. An additional eight blast furnaces in Europe have been identified as being suitable for conversion. Together they have the potential to produce another 475 GWh/year using existing TRT technology.

The company is also looking to expand the technology to its blast furnaces beyond Europe. Significant efforts are already underway at our plants in Brazil and South Africa. With wider implementation of the TRT technology, ArcelorMittal will be able to sustainably secure even more of our energy supply needs.

Want to know more?

For more information, visit the Flat Carbon Europe website (http://www.arcelormittal.com/fce/trt)

For more detail on how flue gases are utilised in ArcelorMittal's Gent mill, click here (http://www.arcelormittal.com/corp/news-and-media/news/2012/jun/20-06-2012)