Quarry Southern Africa November 2017 - Page 27

motors with fixed speed and, therefore, the drying time is fixed, regardless of the aggregates’ characteristics. However, more porous aggregates should remain in the drying environment longer so that all the moisture can be removed and then heated, according to the project. This happens during the creation of the project in which the aggregates are dried and heated in a kiln until all the moisture is eliminated. A new concept of an asphalt plant drying system was developed to adjust the aggregates’ drying time according to the characteristics of those inputs, mainly due to adhesiveness and absorbed moisture. To do this, the engines that make the drying drum rotate vary the speed of rotation, thanks to a frequency inverter. With this technology, aggregates that are more porous spend more time receiving heat from the flame of the burner for complete drying, while less porous aggregates go through the dryer faster, without altering the plant’s production. Intelligent combustion system Traditional burners applied to asphalt plants use the air from the environment (sucked in by an exhaust fan with constant TECHNOLOGY The latest combustion technology in plants accurately and automatically control the optimum air-to-fuel ratio by supplying all combustion air mechanically through two fans: a blower and an axial fan. QUARRY SA | NOVEMBER 2017 _ 25