Simulation of drying aggregate in asphalt plants

Lowering production temperature in warm mix asphalt technology may lead to inadequate drying of aggregates, resulting in low-quality asphalt production. Due to difficulty in direct observation of drying and heating process and measurement of aggregate temperature inside the dryer, numerical analysis offers an alternative way to study heat transfer and aggregate temperature evolution. In this paper, coupled Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) is used to simulate aggregate movement and heat transfer in a simple drum. The effects of aggregate size and drum rotation speed on aggregate temperature evolution and fluid temperature on the heating efficiency are studied. The results show that coupled CFD-DEM technique is an appropriate approach to study aggregate movement and temperature evolutions in the drum directly. Small particles can be heated more easily than large particles. Determination of optimal drum rotation speed needs to consider particle movement models as well as resident time in a real drum with inclined angle. High fluid temperature could reduce heating time of particles to reach the target mixing temperature. The preliminary results may provide some guidelines for operating the mixing drum efficiently and designing drum to control quality of asphalt mixes and save energy.