Special continuous flow dryer types, which are used as first stage dryers in two-stage drying systems, are the rotary drum dryers in the Philippines and the fluidized bed dryers which were successfully commercialized in Thailand in the nineties. Both types use extremely high temperatures (up to 110-120°C) for rapid removal of the surface moisture and can only dry down to 18% MC without damaging the grains (see also "Two stage drying"). While the rotary drum dryers were mainly disseminated through government programs the fluidized bed dryers in Thailand were accepted by the private sector and are well integrated in combination drying systems that include either large scale in-store drying facilities with several hundred tons capacity or mixed flow heated air dryers for second stage drying to storage MC.
The fluidized bed dryer consists of a drying chamber with an air speed of around 2.3 m/s, a bed thickness of 10 cm in which the grain is exposed to the drying air for 10-15 minutes. Capacities of commercial units range from 1-10 t/h. A diesel burner or a rice hull furnace is used as heat source and a system for re-cycling 50-70% of the drying air is provided to improve energy efficiency. Typically head rice yields are reported to be up to 5% reduced compared to samples dried at ambient air while the effect on whiteness is minimal.