There are three rotary kilns as well as two shaft kilns with a combined calcination capacity of 550 tpd. Kiln feed magnesite is fired in the kilns to produce either caustic calcined magnesia (at about 900°C) or deadburned magnesia (at about 1.800°C). During calcination magnesite (MgCO3) is decomposed to Magnesia by release of Carbon dioxide. The calcination process which controls the formation of magnesia crystals as well as the location and behavior of impurities is a key driver of the characteristics of the final products (e.g. specific gravity, reactivity, specific surface area, loss on ingition, etc.).
The most critical aspect of calcination, both in terms of quality and efficiency, is the control of the temperature profile in the kiln. Control is achieved by varying several parameters such as fuel/air ratio, primary and secondary air flow and flame shape.
The rotary kilns are equipped with PLCs for motor control and monitoring of several parameters. All kilns are also equipped with electrostatic filters, the most effective and expensive devices for the prevention of fine particles escaping to the atmoshere as dust. Electrostatic filter operation is complex and controlled by numerous parameters such as gas temperature, pressure and entry speed, electrode voltage and coolant flow.
Rotary kilns have integrated coolers where the calcined material’s temperature is allowed to drop in a controlled fashion. Output material is screened to remove over-burned material and leftover impurities. Then the material is transferred to warehouses via conveyor belts. The material processed in the shaft kilns is extracted by special mechanical devices and wagons and piled next to the kilns to cool down. It is then trucked to storage or directly fed to the final processing plant.