APV Dryer Handbook - Umbc

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8 POWDER TYPE D R Y E R S Fine Freeflow Dustless Granular Wettable Agglom Coated Lump SELECTION, SIZING, COSTS <strong>Dryer</strong> Selection Chart FEED TYPE Solution Thixotrop Dilatent Cohesive Friable Granules Powder Spray Spray or SBD Spray Bed Figure 1. A guide to dryer selection Spin Flash Flash Band Spin Flash + Fluid Bed Agglom. Fluid Bed Tray Band Granulation Throughout the food, dairy, chemical and process industries, there are various requirements for thermal drying. Some involve the removal of water or other volatiles from pasty materials such as pigments, clays, synthetic rubbers and fine chemicals. Others involve the drying of solutions or liquid suspensions such as whey, milk and coffee. To assist manufacturers in arriving at a reasonably accurate first assessment of the type, size and cost of equipment for a particular duty, this article describes the most widely used types of both batch and continuous dryers. Three basic methods of heat transfer are used in industrial dryers in various combinations. These are convection, conduction and radiation. In the processing industries the majority of dryers employ forced convection and continuous operation. With the exception of the indirectly heated rotary dryer and
the film drum dryer, units in which heat is transferred by conduction are suitable only for batch use. This limitation effectively restricts them to applications involving somewhat modest production runs. Radiant or so called “infra-red” heating is rarely used in drying materials such as fine chemicals, pigments, clays or synthetic rubbers. Its main application is in operations such as the drying of surface coatings on large plane surfaces, since efficient utilization generally requires a line of sight between the material being irradiated and the heat source or emitter. In all the dryers considered here, however, there is a radiant component in the heat transfer mechanism. E av = Evaporation (average) Evaporation rate Evaporation rate Fluids, Pastes, Granules, (lb/ft 2 hr) (kg/m 2 h) liquid dewatered Powders pellets, Operation Mean rate = Eav Mean rate =Eav suspension cake extrudates FORCED CONVECTION 0.15 - 0.25 .7 – 1.2 (cross-airflow) E av = 0.2 E av = 1 poor fair fair good batch FORCED CONVECTION 1.0 – 2.0 5 – 10 (throughflow) E av = 1.5 E av = 7.5 - - - good batch AGITATED PAN 1.0 – 5.0 5 – 25 (sub-atmospheric) E av = 3.0 E av = 15 fair fair fair poor batch AGITATED PAN 1.0 – 5.0 5 – 25 (atmospheric) E av = 3.0 E av = 15 fair fair fair poor batch DOUBLE CONE TUMBLER 1.0 - 3.0 5 – 15 (sub-atmospheric) E av = 2.0 E av = 10 - poor fair poor batch FLUIDIZED BED 2 – 50 10 – 250 (throughflow) E av = 26 E av = 130 - - good good continuous CONVEYOR BAND 2.0 – 10.0 10 – 50 (throughflow) E av = 6.0 E av = 30 - fair - good continuous FILM DRUM 3.0 – 6.0 15 – 30 (atmospheric) E av = 4.5 E av = 22 good fair - - continuous PNEUMATIC 50 – 250 250 – 1250 or FLASH E av = 150 E av = 750 - fair good fair continuous ROTARY 1.0 – 3.0* 15 – 50 (indirect) E av = 2.0 E av = 33 - poor good fair continuous ROTARY 2.0 – 6.0* 30 – 100 (direct) E av = 4.0 E av = 65 - fair fair good continuous SPIN FLASH 4.0 – 18* 70 – 300 E av = 11 E av = 185 - good good fair continuous SPRAY 0.3 – 1.6* 5 – 25 E av = 1.0 E av = 15 good - - - continuous *Note: Evaporation rates for rotary, Spin Flash, and spray dryers are expressed in lb/ft 3 hr. Table 1. Product classification and dryer types as an aid to selection 9
Page 1: Improving Process Profitability...C
Page 5: I N T R O D U C T I O N The drying
Page 10 and 11: 10 Direct heating is used extensive
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Page 18 and 19: 18 whether there is any need to re-
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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 48 and 49: 48 S P I N F L A S H D R Y E R S fo
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58 S P R A Y D R Y E R S SPRAY DRYE
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60 inwards towards the centerline o
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62 a high speed by a spinning disc.
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64 internal bowl diameter, radial d
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66 variations, some plants utilize
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68 Condensation deposits can freque
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70 HIGH FAT PRODUCTS If the powder
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72 INLET TEMPERATURE The powder coo
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74 POWDER DENSITY The density of sp
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76 chamber wall, tending to scour a
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