ABSTRACT
Figure 28.1 presents the schematic of a hybrid dryer where a spray dryer (SD) is integrated with a fl uidized bed (FB) dryer, and such a unit is combined with a vibrated fl uid bed (VFB) dryer/cooler (Tang et al., 1999). Filtered ambient heated to 150°C in a fi nned heat exchanger is drawn to the air distributor of a concurrent SD. The homogenized dairy feed with 50% solid content is pumped at 15 MPa into the pressure nozzle located axially at the top of a drying chamber. The semidry product of ~8% moisture content falls onto the dryer bottom, whereas spent air at 90°C is fi ltered off in a bag fi lter surrounding the drying chamber and discharged to the atmosphere. Up to this point, such a classical SD with a volumetric evaporation rate of ~5.5 kg/m3 h is considered as the fi rst drying stage. To arrange for FB drying (the second stage of the process), the perforated conical grid is attached to the conical bottom of the SD. Here, the semidry granules are dried by 120°C air supplied to the gas plenum formed by the perforated grid and the dryer cone. The product at ~4% moisture content falls through the central overfl ow to the VFB to agglomerate and complete drying at 90°C. Cooling of the product before packaging is performed at the last section of the VFB by blowing dehumidifi ed air at 50°C. Drying and cooling in the VFB at a bed height from 200 to 300 mm take ~2 to 3 min.
