Drying Characteristics of the Solid By-product of Olive Oil Extraction

Olive cake, the solid by-product of olive oil extraction, consists of pit and pulp of the olive fruit, and has significant oil content. Although the initial moisture content of olive cake is 44·78%±0·5 by weight (wet basis), the material has quite a high-energy content that enables it to be used for direct burning in bakeries and olive oil mills after sun drying in Turkey. When the latter manufacturing processes such as pomace oil production, bio-oil production by using thermal conversion processes were used, the effect of drying should be considered. Therefore, drying behaviour of olive cake in a cabinet type dryer was examined using heated ambient air at temperatures from 80 to 110°C and constant air velocity of 1·2 m s−1 in this study. In addition, the effects of sample thickness on the drying characteristics, drying time and energy quality of dried product were also determined. The experimental data was compared with values predicted by the Page model, and by the Henderson and Pabis model, good agreement being obtained with Page model. A diffusion model was used to describe the moisture transfer and the effective diffusivity at each temperature was determined. The effective diffusivity varied between 489·2 and 998·4 μm2 s−1. The temperature dependence of the diffusivity coefficient was also described by the Arrhenius type relationship. The activation energy was found to be 26·71 kJ mol−1.