Drying of High-Moisture Paddy Using a Combined Impinging Stream and Pneumatic Drying System

Abstract

A system combining the principles of impinging stream drying and pneumatic drying (ISD-PD) for high-moisture paddy was developed to increase the energy efficiency of the drying process. The effects of inlet air temperature and paddy feed flow rate on the overall performance, in terms of the volumetric water evaporation rate and volumetric heat transfer coefficient, and energy consumption of the system were then investigated. The dried paddy quality in terms of the head rice yield and whiteness was also assessed. The results were compared with those obtained from a system consisting only of a pneumatic dryer. It was found that an increase in the inlet air temperature and paddy feed flow rate led to an increase in the volumetric water evaporation rate. The volumetric heat transfer coefficient varied insignificantly with the inlet air temperature but increased with the paddy feed flow rate. The moisture content of paddy was reduced from its original value by 6.6 to 9.7% (db) within a very short period of time. The mean residence time of the paddy was increased by 33 to 41% via the use of the ISD-PD system, leading to moisture reduction rates 55-166% higher than those for the pneumatic dryer. The head rice yield decreased with an increase in the inlet air temperature and paddy feed flow rate. On the other hand, the effects of inlet air temperature and paddy feed flow rate on whiteness was not significant. © 2012 Copyright Taylor and Francis Group, LLC.