Paul Wurth’s dry slag granulation process with energy recovery has won the Business Federation of Luxembourg’s (FEDIL) Environment Award 2013.

With traditional blast furnace slag handling a substantial amount of energy contained within the slag is lost, whether the process entails granulation by water quenching or pit dumping.

With environmental and energy issues in mind, Paul Wurth developed an alternative slag treatment process designed to recover the energy contained in the slag while maintaining unchanged the physical properties of the granulated slag. The process is known as ‘dry slag granulation with energy recovery’.

Steel spheres are injected evenly into the liquid slag providing a large contact surface for efficient heat transfer. The slag cools rapidly from about 1450°C to 650°C, ensuring vitreous solidification, which is required if the slag is to be used by the cement industry.

The resulting mixture of steel spheres and solidified slag is subjected to heat recovery within a counter-current heat exchanger. The energy is recovered in the form of hot air at a temperature of approximately 600°C and can be used directly as thermal energy, or converted to steam and subsequently to electrical energy.

Paul Wurth claims that the process enables important water savings when compared with wet granulation (700 litres per tonne of slag), a reduction of sulphur and CO2 emissions, and reduced costs for transportation and further treatment (drying) for cement production – due to the fact that the product is dry.

After a series of trials, an industrial pilot plant began construction in October 2012 in on the site of the Dillinger Hütte steel plant in Dillingen, Germany. Designed for a daily production of 80 tonnes of slag, the plant was commissioned last month (November).

According to Paul Wurth, the first operating results are “very promising and confirm the technical, energetic and environmental viability of this new development, which can also been applied to steelmaking, EAF or ferronickel slags”.