Influences of far-infrared radiation on the energy efficiency of stepwise jet spouted bed drying system

Abstract

       The objective of this research was to investigate the use of drying concept combining the stepwise jet spouted bed and FIR for drying of an agricultural product. A laboratory-scale of a combined stepwise jet spouted bed and FIR drying system is developed and tested. The effects of various operating parameters, i.e., drying temperatures (70, 80 and 90 oC), and stepwise drying patterns on the drying kinetics of a selected agricultural product (pepper grain) and energy consumption of the process as well as qualities of dried product are then investigated. In this work, stepwise supply of air velocity to the system (SV) and combination of continuous drying with stepwise drying (CSV) at different on:off periods were selected as the stepwise drying schemes. It was found from the experiments that combination of stepwise drying and FIR could reduce the energy consumption during the drying process expressed in terms of specific energy consumption (SEC). Based on the results obtained in this work it was found that energy saving in the case of combining SV drying scheme with FIR, at the drying temperature of 70 oC, was found to be around 31 to 36% compared to that of continuous drying. In terms of the dried product quality it was observed that drying temperature was the main factor influencing the color changes of the dried product. Drying at higher temperatures yielded redder and darker pepper than drying at lower temperatures. In addition, the value of broken-grain percentage of dried pepper in the case of continuous drying and stepwise drying was not significantly different.