Drying of parboiled paddy using an impinging stream dryer

Abstract

In order to reduce the time for drying parboiled paddy, animpinging stream drying technique is proposed. Different strategies for drying parboiled paddy via the use of an impinging stream dryer were also evaluated. The effects of drying air temperature and tempering time on the head rice yield (HRY) and whiteness index (WI) of the dried parboiled rice were studied; parboiled rice was prepared from Suphan Buri 1 with an initial moisture content in the range of 46-50% d.b. The drying experiments were carried out at drying air temperatures of 130, 150 and 170 degree Celsius, inlet air velocity of 20 m/s, impinging distance of 5 cm and paddy feed rate of 40 kgdry_paddy/h. Parboiled paddy was dried for two cycles; after each cycle of drying, paddy was tempered either for 15, 30, 60 and 120 min. After impinging stream drying, paddy was ventilated by ambient airflow until the final moisture content reached 16% d.b. Moisture reduction of paddy during each cycle of drying was noted to increase with an increase in the drying temperature. The HRY of paddy undergone any number of drying cycle at any drying temperature and tempering time was still maintained at a similar level to that of the reference rice. However, the WI of paddy was relatively lower than that of the reference rice when the paddy was tempered for longer than 60 min.