Development and experimental results of a thermal oil based roasting system for decentralized processing of groundnuts

Abstract

The current research has been conducted to investigate the capacity of an indigenously developed thermal oil based continuous solar roaster (CSR) for groundnuts roasting. A 10m2 standing Scheffler fixed focus concentrator is used to target the incoming direct normal irradiance at casted aluminum surface of a heat receiver which transfers this heat energy to the roasting unit by means of thermal oil circulation. The roasting unit comprises a cylindrical shell (2000 mm in length and 450 mm in diameter) attached beneath a semi-circular oil flow jacket and equipped with a ribbon type screw conveyer with 6 mm thick paddles. Optimizing for maximum energy utilization and feeding capacity using response surface methodology, roasting time for light, medium and dark quality was found to be 14 + 0.1, 20 + 0.1 and 29 + 0.1 min respectively. In terms of roasting quality, CSR has shown quite satisfactory results. The study revealed that continuous solar roaster has the capability to roast 140 to 288 kg groundnuts per day subjected to dark to light roasting quality with average direct normal irradiance ranging from 650-800 Wm-2. The overall thermal efficiency of the system was found to be 37.8%. The payback period of CSR was estimated to be 2450-5250 useful working hours.