Energy Reports (Nov 2022)
Energetic and exergetic performances during drying of freshly harvested peanut with industrial mixed-flow dryer
Abstract
Rapid drying of peanut is very important to maintain quality and reduce the risk of mildew, especially for peanut harvested in high moisture content in China. The modified mixed-flow dryer can dry freshly harvested peanut efficiently and evenly which is not available for traditional fixed-bed drying. However, the performances of energy and exergy of peanut drying using modified mixed-flow dryer are not clear, lacking of relevant data for equipment improvement and process formulation. Therefore the relevant investigation was carried out to evaluate the performance of fresh harvested peanut drying using industrial mixed-flow dryer with heat-pump full power heating and waste heat recovery The results show that the energy consumption is mainly consumed by heat-pump and centrifugal fan, accounting for 73.5% and 24.2% of all energy consumed respectively. The overall specific energy consumption and specific heat consumption are 1494.5 kJ/kg and 4706.1 kJ/kg respectively. The thermal efficiency and the energy efficiency are affected by the change of the temperature of airflow entering the drying chamber, both fluctuate over time, increase earlier then decrease later and rise again until the material temperature reach to a relatively steady temperature. And the energy efficiency of dryer (178.9%) is approximately triple of thermal efficiencies of drying chamber (56.1%) and dryer (59.4%) for the overall drying. The heat utilization ratio decreases gradually over drying time, with the overall value of 50.0% for drying chamber and 52.9% for dryer. The exergy efficiency of drying process earlier increases then decreases in the overall trend with the overall value of 51.3%. The exergy efficiencies of the drying chamber and whole dryer are both increased gradually with the overall value of 34.5% and 31.8% respectively. However, the variation tendencies of energy improvement potential rates are opposite to exergy efficiencies.
