A New Drying Process of Dusts and Sludge by Employing Heat Storage Materials

Industries consisted of high temperature processes discharge a certain amount of waste heat in a wide temperature range. In such industries, on the other hand, a large amount of primary energy is still used for drying processes of raw materials and wastes such as wet dust and sludge. In this study, a new drying process was proposed by employing metallic heat storage materials (HSMs) as drying media, which can store waste heat from low to mid temperatures (250–500°C) as both sensible and latent heat. The process possesses several advantages that the process size and exhaust gas volume are significantly small and heat recovery from a dusty gas is possible. The cold model experiments understanding the motion of HSM balls and powder inside the rotary dryer and its numerical simulations were carried out. The behavior of HSM balls was simulated by using the friction coefficient as a fitting parameter. Further, assuming that a HSM ball forms a composite particle with a powder layer, the numerical simulations of its drying process were conducted. They confirmed that, drying time can be shortened significantly when the latent heat was considered. Design of the drying process of wet dust in a practical scale showed that the size of the dryer will be several times smaller than that of a conventional rotary dryer because of higher volumetric heat transfer coefficient between HSM and dusts. Since the heat exchange tower between waste gas and HSM balls is also compact, the proposed process shows a certain potential to be applicable as an actual drying process.