Vertical shaft kilns

Deadburned magnesia production
QMAG’s specially designed vertical shaft kilns are key to our production process and ensure high-quality products.

Our kilns are used to convert reactive calcined magnesia to a significantly less reactive form: deadburned magnesia. This process involves heating the previously briquetted calcined magnesia to high temperatures (in excess of 2000 °C), during which its reactivity is killed.

The highly energy efficient vertical shaft kilns used at QMAG are over 10 m in height. Green (unfired) briquettes are fed into the top of the kiln at a controlled rate. As the briquettes travel downwards through the kiln, their temperature increases thanks to 20 natural gas and air burners per kiln. These burners drive the sintering process.

During sintering, the small MgO crystals in the calcined magnesia begin to coalesce and form large crystals of periclase (MgO). As this is a physical as well as a chemical process, each briquette will have shrunk to almost half its original size by the time it reaches optimum density.

As the briquettes reach the bottom of the kiln, they are met by large volumes of air in the product discharge area. This helps to cool them, while also providing additional air for to allow combustion to continue in higher tiers.

What makes our process different?
Our vertical shaft kilns are lined with multiple layers of different refractory materials to provide production consistency, long service life and excellent energy efficiency. These layers are all contained within a steel shell, which has to be airtight due to the kiln’s pressurisation.

Our kilns operate continuously and they can be used 24/7 for over nine months before requiring scheduled maintenance.

To ensure extremely consistent density and periclase crystal sizes, our sintering process is tightly controlled. Our deadburned magnesia goes to refractory companies all over the world, where our DBM’s specific physical properties, like density and crystal size, are highly valued.

Studies over the past 40 years have shown the clear relationships between refractory performance and high density, large crystal size and the correct chemical composition.

QMAG’s unique cryptocrystalline magnesite deposit is perfectly suited to the production of DBM as the small magnesite crystal structure is easier to sinter than many other magnesite deposits around the world. This means our DBM grades are highly consistent and are widely recognised to give the best performance.