Drying kinetics, power consumption, economic and environmental analysis of pomegranate peels drying using a hybrid solar dryer compared with oven dryer

Drying pomegranate peels, a by-product of juice production, preserves their beneficial properties and minimizes waste. Using optimal drying conditions, such as controlled temperatures and thin layers, improves efficiency and ensures high quality. These dried peels can then be utilized in various industries, including food, pharmaceuticals, and cosmetics. To our knowledge, there are no existing studies that detail the effects of hybrid solar drying, drying temperatures, and layer thickness on the drying kinetics, power consumption, and economic and environmental aspects. In this study, a hybrid indirect SD (HISD) with a temperature and humidity control unit was used to dry pomegranate peels at three different temperatures-50 °C, 60 °C, and 70 °C-and three different thicknesses-1, 2, and 3 cm. The HISD was then compared to a conventional oven drying system (CODS). The obtained results indicated that increasing the drying temperature increased the weight loss of pomegranate peels. Also, the average initial moisture content of pomegranate peels was 76.5% (w.b.). The final MC ranged from 2.67 to 2.10% and from 2.97 to 2.84% for the CODS and HISD, respectively. The higher drying rates of the pomegranate peels dried using CODS and HISD were 169.79 and 196 kg_{water/kgdrymatter}/h, respectively, at a layer thickness of 3 cm and a drying temperature of 70 °C. Additionally, using HISD led to a reduction in power consumption by about 64.28% to 75.75% compared to the CODS. Furthermore, the environmental analysis results showed that the embodied energy is about 1270.463 kW.h. The energy payback period for HISD ranges between 2.38 and 6.34 years. The earned carbon credit for drying pomegranate peels using the HISD ranged between 770.1 and 2207.2 USD. Based on economic analysis, the lowest drying cost using the HISD was 144.5 USD per ton of pomegranate peels, achieved at layer thicknesses of 1 cm and a drying temperature of 70 °C.