MODELING IN-BIN RICE DRYING USING NATURAL AIR AND CONTROLLED AIR DRYING STRATEGIES

Uncontrolled air conditions during natural air drying (NAD) often result in over-dried rice, especially in the bottom layers of bins. In order to reduce such over-drying and associated economic loss for farmers, some control of the inlet air temperature and relative humidity is needed. In this study, a software program, Post-Harvest Aeration Simulation Tool (PHAST), based on the Thompson equilibrium moisture content model, was used to simulate NAD of rice at four representative rice-growing locations in Arkansas (Jonesboro, West Memphis, Stuttgart, and Monticello). Hourly weather data, including ambient air temperature and relative humidity, were downloaded from the National Climatic Data Center website for each location. Different combinations of controlled and uncontrolled NAD strategies were simulated using three levels of initial rice moisture content (16%, 18%, and 20%), four airflow rates (0.6, 1.1, 1.7, and 2.2 m(3) min(-1) t(-1)), four bin diameters (7.3 m (24 ft), 9.1 m (30 ft), 11.0 (36 ft), and 12.8 m (42 ft)), three varieties of rice (Jupiter, Wells, and CL XL 730), and three harvesting dates (August 15, September 15, and October 15). It was found that drying strategy, airflow rate, harvest date, and initial grain moisture content had significant effects on NAD of rice. An airflow rate of 1.1 m(3) min(-1) t(-1) (1.0 cfm bu(-1)) was found to be optimum in terms of minimizing drying cost, which included over-drying and dry matter loss costs. The controlled drying strategy was found to be superior in terms of drying and fan operating costs.