ASSESSMENT OF FAN CONTROL STRATEGIES FOR NATURAL AIR IN-BIN ROUGH RICE DRYING IN ARKANSAS LOCATIONS

摘要

There is a critical need to determine conditions of natural air, in-bin drying that maintain quality of dried rice. In this study, simulations were performed to determine the effects of typically used fan control strategies for natural air, in-bin drying of rough rice. The evaluated fan control strategies comprised of running the drying fan continuously (CNA), only at night (NO), only during the day (DO), at a set window of equilibrium moisture content of natural air (EMC-NA), and at set window of air EMC with supplemental heating (EMC-H). Specifically, the effects of fan control strategies on rice drying duration, rice dry matter loss (DML), percent overdrying, and total drying energy consumption were studied. The drying simulations were performed with air flowrates at 0.69, 1.39, 2.08, and 2.77 m(3) min-t(-1) and rough rice initial moisture contents (IMC) at 16%, 18%, 20%, and 22% (wet basis). Analyses were pooled from a 20-year (1995 to 2014) hourly weather data set of temperature and relative humidity at four Arkansas rice-growing locations. It was determined that accurate guidelines of air flowrate, fan control strategy, and IMC of the rough rice are key to timely drying of the rice to achieve the recommended average moisture content (MC) of 13% (or a maximum MC of 14%). The NO strategy resulted in the longest rice drying duration while using EMC-H resulted in the shortest drying duration. At rice IMC of 22%, air flowrates 1.39 to 2.08 m(3) min-t(-1) and 1.39 to 2.77 m(3) min-t(-1) were required for the EMC-NA and EMC-H strategies, respectively, to guarantee percent overdrying of 10% or less, maximum MC of rice in the bin of 14% or less, and DML of less than 0.5%. For NO, DO, and CNA strategies, drying with air flowrates of 1.39 to 2.77 m(3) min-t(-1) achieved DML less than 0.5%, but resulted in percent overdrying greater than 10%, and had maximum MC of rough rice in the bin exceeding 14%. Drying energy consumption escalated as the air flowrate increased. For the EMC-H strategy, more energy was used at the lowest air flowrate of 0.69 m(3) min-t(-1) compared to 1.39 m(3) min-t(-1) to dry rough rice at IMC of 20% and 22%. The study provided information that is vital to maintaining rice quality and safety during on-farm, in-bin drying.