APV Dryer Handbook - Umbc

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48 S P I N F L A S H D R Y E R S for continuous powder production from pastes and filter cakes While mechanical dewatering of a feed slurry is significantly less expensive than thermal drying, this process results in a paste or filter cake that cannot be spray dried and can be difficult to handle in other types of dryers. This article describes the Spin Flash dryer, shown in Figure 21, as one option available for continuous powder production from pastes and filter cakes without the need for grinding. Powder production generally involves some form of drying operation. There are several generic types of dryers but all must involve the evaporation of water, which can take anywhere from 1000 to 2500 BTU/lb (555 to 1390 Kcals/kg), depending on dryer type. Due to its ability to produce a uniform powder at relatively low temperatures, the spray dryer is probably the most common of these dryers. However, by its definition, a spray dryer requires a fluid feed material to allow its atomization device to be employed. Generally, there is a maximum viscosity limitation in the range of 250 to 300 Centipoise. Figure 22 (on page 49) illustrates the amount of water which must be evaporated to produce one pound of bone dry powder from a range of different feed solids. It can be clearly seen that even a 5% increase in total solids will reduce the water evaporation and hence, the dryer operating costs by about 20%. If this water removal can be done mechanically by, for example, filtration or centrifuging, the cost will be significantly lower than that required to heat and evaporate the same water. The direct energy cost can be calculated as equivalent to 3-8 BTU/lb (1.7-4.5 Kcals/kg) compared to an average 1500 BTU/lb (830 Kcals/kg) for evaporation. This increase in Figure 21. Spin Flash dryer solids, however, inevitably will result in an
POUNDS WATER PER POUND DRY PRODUCT W E 2.5 2.0 1.5 1.22 1.0 .539 .429 18.6% 20.4% increase in viscosity, which may exceed the limitations of a spray dryer. Available options for drying these higher viscosity feed materials are listed in Table 6. The subject of this paper is the Spin Flash dryer, which is among the newest of the dryer options and has the capability of drying most materials ranging from a dilatent fluid to a cohesive paste. SPIN FLASH DRYER WE = 100 - %TS %TS 30 35 40 45 50 55 60 65 70 75 80 % TOTAL SOLIDS TO DRYER (TS) Figure 22. Water evaporation vs. total solids ratio The Spin Flash dryer was developed and introduced in 1970 in response to a demand by the chemical industry to produce a uniform powder on a continuous basis from high viscosity fluids, cohesive pastes and sludges. DRYER OPTIONS FOR HIGH VISCOSITY MATERIALS DIRECT SUSPENSION DRYERS • Pneumatic or flash dryers • Spin Flash dryers • Fluid bed dryers DIRECT NON-SUSPENSION DRYERS • Tray dryers • Tunnel dryers • Belt dryers • Rotary dryers INDIRECT DRYERS • Screw conveyor dryers • Vacuum pan dryers • Steam tube rotary dryers Table 6. 49
Page 1: Improving Process Profitability...C
Page 5: I N T R O D U C T I O N The drying
Page 8 and 9: 8 POWDER TYPE D R Y E R S Fine Free
Page 10 and 11: 10 Direct heating is used extensive
Page 12 and 13: 12 corresponding number of conventi
Page 14 and 15: 14 Two particular types are the dou
Page 16 and 17: 16 particular application and the m
Page 18 and 19: 18 whether there is any need to re-
Page 20 and 21: 20 material comes into contact with
Page 22 and 23: 22 together since both share simila
Page 24 and 25: 24 circulation. Alternatively, and
Page 26 and 27: 26 Each of the types available are
Page 28 and 29: 28 At this time Pulse Drying techno
Page 30 and 31: 30 E F F I C I E N T E N E R G Y U
Page 32 and 33: 32 DRYER FEED MOISTURE CONTENT (% W
Page 34 and 35: 34 DRYING COLUMN SCREW FEEDER PARAM
Page 36 and 37: 36 way a dryer can be turned down i
Page 38 and 39: 38 3. The wetted particles sink int
Page 40 and 41: 40 TEMPERATURE (°C) 150 100 50 0 4
Page 42 and 43: 42 flow patterns, residence time di
Page 44 and 45: 44 As indicated by this partial lis
Page 46 and 47: 46 FEED HP PUMP COMPRESSED AIR AGGL
Page 50 and 51: 50 PROCESS DESCRIPTION The Spin Fla
Page 52 and 53: 52 Figure 24 illustrates the very r
Page 54 and 55: 54 The drying chamber would be main
Page 56 and 57: 56 COST BENEFITS In comparison to a
Page 58 and 59: 58 S P R A Y D R Y E R S SPRAY DRYE
Page 60 and 61: 60 inwards towards the centerline o
Page 62 and 63: 62 a high speed by a spinning disc.
Page 64 and 65: 64 internal bowl diameter, radial d
Page 66 and 67: 66 variations, some plants utilize
Page 68 and 69: 68 Condensation deposits can freque
Page 70 and 71: 70 HIGH FAT PRODUCTS If the powder
Page 72 and 73: 72 INLET TEMPERATURE The powder coo
Page 74 and 75: 74 POWDER DENSITY The density of sp
Page 76 and 77: 76 chamber wall, tending to scour a
Page 80: Local Office APV Separations Produc

APV Dryer Handbook - Umbc

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