Pilot-Scale Evaluation of Concentrating Solar Thermal Technology for Essential Oil Extraction and Comparison with Conventional Heating Sources for Use in Agro-Based Industrial Applications.

Abstract

The conventional steam-distillation method requires a high amount of saturated steam and as a result, a lot of energy. Besides being energy-intensive, conventional steam-distillation processes emit carbon dioxide into the atmosphere. The energy demand in essential oils processing and related agro-based processes can be alleviated by using concentrating solar thermal (CST) technologies. Most of the solar plants installed in South Africa use flat plate collectors and evacuated tube collector systems with temperatures below 100 °C, which is ideal for only a low-temperature process application. This paper investigates the use of a low-cost CST technology, the parabolic trough collector (PTC), for steam-distillation in an extraction process. The PTC-powered system was built and tested for extracting essential oil from citrus peels. For comparison, the extraction process was carried out on a laboratory scale, a pilot gas-powered system, and PTC. Essential oil yields for orange, lemon, and mandarin were 0.65, 0.44, and 1.17%, respectively, using gas-powered steam-distillation. The yields for PTC were 0.67, 0.53, and 1.09%, which were all within the expected ranges. Gas chromatography results for the PTC experiment showed the presence of key components such as limonene (90%) in the essential oils. The PTC achieved a significant overall system efficiency of 54.99%, even though some parts of the device were not thermally insulated. The results showed that PTC can compete with gas-powered systems. Furthermore, the essential oil yields were comparable to those obtained in laboratory experiments. All of this demonstrates that PTC is suitable for use in agro-based industrial applications.