Experimental investigations on drying kinetics and modeling of two-phase olive pomace dried in a hybrid solar greenhouse dryer

Olive pomace is generated during the production of olive oil. The disposal of olive pomace presents a serious environmental issue to the agricultural community in Morocco. Among all actions devoted to the reduction of olive pomace waste, their revaluation seems to be the most efficient and advantageous from both environmental and economic points of view. Due to its high moisture content, solar drying constitutes an important and promising solution for a possible bio-fuel conversion of olive pomace. For this purpose, a modified uneven-span greenhouse dryer was designed and installed at the faculty of sciences Semlalia, Marrakech, Morocco. An experimental study of solar drying kinetics of the olive pomace was conducted to test the performances of the modified greenhouse dryer under a hybrid (solar/hot air) forced convection mode. The hot-air blower was supplied by electricity from a PV array installed near the greenhouse. The mean temperatures of air within the greenhouse and of the olive waste during the drying hours reached, respectively, 63 °C and 55 °C (from August 3rd to August 5th). The duration of the drying operation of 300 kg of waste from a moisture content of 50 mass% to 19 mass% was 27 h, which was low compared to the open sun drying. Therefore, hybrid forced mode enabled a considerable reduction in drying time, being an aspect to take into account for its use during low solar radiation. The drying kinetics of thin layer two-phase olive pomace was also investigated. The Two-term Gaussian model was found to be the most suitable model to describe the thin layer drying behavior of the two-phase olive pomace dried under hybrid forced convection greenhouse drying mode. In addition, the Fourier series was used to solve the diffusivity equation inside the two-phase olive pomace. The effective diffusivity was found to be 2.0 10 –09 m 2 s −1 and 2.3 10 –09 m 2 s −1 using the linear fit and the slope from two successive points methods, respectively.