Chatchai Nimmol

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

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.

Moisture Content and Physical Properties of High-Moisture Agricultural Material Dried by Impinging Stream Dryer

The objective of this research was to study the drying of high-moisture agricultural material using an impinging stream dryer with multi-stage drying concept. Okara was used in this study as the test agricultural material. Experiments were performed in one-stage and two-stage drying. The final moisture content of the okara at several drying conditions was examined. The physical properties of dried okara were analyzed in terms of color and rehydration ability. It was found from the experiment that with the use of multi-stage drying concept the moisture content of okara could be significantly reduced within a very short period of time. In terms of physical properties, it was observed that the dried okara was darker, redder and more yellow than the fresh okara. Drying at higher temperatures led to higher color changes values of the dried okara. The effect of okara feed rate on the redness and yellowness was not significant, except for the lightness; drying at lower okara feed rates led to a darker dried okara. An increase in the drying temperature and a decrease in the okara feed rate led to a higher rehydration ability of the okara.