Energy efficiency and paddy quality during drying of paddy with impinging stream dryer

Abstract

Impinging stream dryer (ISD) is the energy effi cient dryer for removing surface moisture of particulate materials including freshly-harvested paddy. However, energy effi ciency of ISD can still be improved. One of the possible methods that can be used to reduce the net energy supply to the ISD is the reuse of exhaust air leaving a drying system. In this study, an impinging stream dryer with exhaust air recycle system was therefore developed. The overall performance and speci fi c energy consumption of the drying system at various conditions was investigated. The quality of dried paddy was also evaluated. It was found that the moisture content of paddy was reduced from its original value by 3.30 to 6.00% (d.b.) within a very short period of time (less than 2.1 s). The maximum value of the volumetric water evaporation rate was found to be about 144 kg water /m3 h, while the maximum value of the volumetric heat transfer coeffi cient was about 6871 W/m3 K. The lowest total speci fi c energy consumption of the process was 4.2 MJ/kgwaterwhen using inlet air temperature of 100 oC, particle fl ow rate of 120 kgdry solid/h and air recycle ratio of 40%. With the use of exhaust air recycle, the energy consumption of the drying process could be reduced by 20%. The head rice yield signi fi cantly decreased only with an increase in the inlet air temperature. The effects of inlet air temperature, paddy feed fl ow rate and air recycle ratio on whiteness of the product was not signi fi cant, however.