Air impingement drying of digestate: Experimental and modelling study

Abstract Few studies have been interested in the drying process of digestate and no information is available on the modelling. This research work consisted in modelling the drying kinetics and determining the moisture diffusivity. Experiments were performed using an air impingement dryer under 6 air velocities (1, 5, 7, 13, 17 and 19 m s -1 ) and 2 temperatures (40 °C and 70 °C). The time required to achieve a residual moisture content of 20% varied between 240 min and 140 min at 40 °C, and between 96 min to 60 min at 70 °C for 1 m s -1 and 19 m s -1 , respectively. Experimental data were fitted to different curve fitting equations: the Lewis, the Modified Page and the Logarithmic equations. The analytical solution was also applied to identify the apparent moisture diffusivity. The effective moisture diffusivity at infinite air velocity, D e f f , was varied with the temperature and the values were equal to 1.70 × 10 - 9  m 2 s -1 at 40 °C and 3.98 × 10 - 9  m 2 s -1 at 70 °C. Predictive equations for the apparent moisture diffusivity versus air velocity and temperature were determined.