Fiuidized Bed Drying of Rice Using a Pilot-scale Drier

摘要

Fiuidized bed drying utilizes drying air temperatures that are much higher (90 deg C to 200 deg C) than those used in current commercial drying systems in the U.S. (approx 60 deg C). Consequently, the drying rate is much greater with these units, andthe stratification of moisture contents (MCs) across the drying bed is less than conventional, cross-flow driers. A pilot-scale, fluidized bed drier was used in this study to investigate the effects of various drying air temperatures and incoming rice MCs on various rice quality parameters, including the amount of MC reduction per pass, grain tempering and milling quality. Incoming and exiting rough rice temperatures and MCs were measured so as to allow plotting the drying process onto a phase diagram,which comprised a plot of rice glass transition temperature (Tg) vs. MC. Experiments were conducted at a commercial facility in September 2006 in Arkansas, USA. The temperature and MC data from the experiments were plotted onto state diagrams to track the drying process from a material property standpoint. Milling quality data from these tests were also plotted onto the state diagram in an attempt to understand the limits of high temperature drying on the various rice quality parameters. Results of thestudy showed that high temperature fluidized bed drying of up to 150 deg C at harvest moisture contents below 22% is feasible without substantial reductions in milling quality as long as the MC reduction does not exceed 4 to 5 percentage points. The feeding rate affects the kernel retention time in the drier which in turn determines the percentage point MC reduction.