Study of a solar installation for olive mill sludge treatment

Olive mill sludge treatment was performed using a parabolic trough solar collector (PTC) to supply thermal energy. The proposed prototype, composed of a drying chamber coupled with a heat exchanger and a PTC, allows the treatment of up to 80 kg of wet olive oil pomace in about 1 hour and 40 min, the equivalent of 112 tons during the post-production period of olive oil. Due to the presence of oil, which delays evaporation, the drying process was studied at relatively high temperatures between 120 and 140 degrees C. The obtained results show that the effective diffusivities varied from 2.59 10-7 to 1.36 10-6 m2/s with an activation energy of 27.9 kJ/mol. The sludge dryer performance has also been analyzed and optimized numerically with MATLAB software. The indirect solar dryer using a PTC showed a relevant level of stability, fewer temperature fluctuations, and better control of the drying parameters compared to the direct solar dryer. The overall analysis reveals that the maximum thermal efficiency of 43% was recorded with total thermal energy produced throughout the year of 23,909 kWh, while the Levelized cost of heat was 0.34 $/kWhth. The proposed system leads to the avoidance of about 15,900 kg of CO2 emissions.