Fluidized bed grain dryers are now commercially available in several countries.In particular, it is suitable for high moisture grains such as paddy, parboiled rice, maize, and soybeans.Compared to conventional grain dryers, its drying rate is very fast.As a result, the dryingunit is very compact relative to its capacity. Its energy consumption is relatively low while grain quality is maintained. A comprehensive reviewoffluidized bed dryers has been done by Soponronnarit (2003), with the emphasis on research and development efforts on fluidized bed grainprocessing,especially in Thailand, starting with an experimental batch dryer and culminating with a commercial continuous-flow dryer.This paper presents a mathematical model of the fluidized bed grain drying system including a series of drying, tempering, and ambient air circulation steps.
Fluidized bed paddy dryers are competitive with conventional hot air dryers at high moisture levels, i.e. low energy consumption, low cost, and acceptable paddy quality.Some valuableoperating parameters are: drying air temperature of 140°C–150°C, fraction of air recycled of 0.8, air velocity around 2.0–2.3 m/s, and bed thickness of 10–15 cm. Under proper conditions such as high initial moisture content of paddy (higher than 30%) and high air temperature (140°C–150°C), head yield can beincreased by upto 50% compared with ambient air drying. For consumer acceptance, tested rice with fluidized bed drying is not significantly different from that dried by ambient air. For other grains, thefluidbed dryer hassubstantialpotential for commercialization.There have been many units used in rice mills, as well as in the maize and soybean industries.Results obtained from commercial fluidized bed dryers indicate high performance and high product quality, with a significant spin-off that urease activity in soybean kernels can be reduced to levels acceptable to the feed industry.