Dryers, belt steam

Among the contact drying processes in the paper industry are steam heated centrifugal dryers and disk dryers. The types of convection dryers used are drum dryers, belt dryers or rack dryers. 

Drying with Changing Humidity of Air in a Tunnel Dryer A granular material deposited on trays or a belt is moved through a tunnel dryer countercurrently to air that is maintained at 170°F with steam-heated tubes. The stock enters at 14001bdry/hr with W = 1.16 lb/lb and leaves with O.llb/lb. The air enters at 5% relative humidity (Hg = 0.0125 lb/lb) and leaves at 60% relative humidity at 170°F Hg = 0.203 lb/lb). The air rate found by moisture balance is 7790 lb dry/hr ... 

In larger factories the fruit is steamed on the shelves of chamber dryers or on the belt of belt dryers. 

Continuous band crossflow <3-mm thick bed area 20 to 100 m evaporative capacity 2 to 13 g water evaporated/s m residence time 0.2 to 1.3 h steam 1.7 to 1.9 kg/kg water evaporated fan power 35 to 1300 kJ/kg belt drive power 1 kW/m belt. Continuous band gas flow through the bed 1 to 4 g water evaporated/s-m steam 2 to 5 kg steam/kg water evaporated 1.25 m/s gas velocity throngh the bed area 5 to 25 m. Rotary cascading dryer/kiln roto-louvre area 10 to 1000 nC evaporative capacity 18 g water evaporated/s m or 7 g water/s m of peripheral area 5 to 10% solids, residence time 0.1 V/volumetric feedrate gas velocity 1 to 1.5 m/s or 1/2 terminal velocity of particles peripheral velocity 0.1 to 0.5 m/s, 4 to 5 rpm rpm times diameter = 3 to 12 rpm m L/D = 4 to 15/1 average temperatnre of evaporation thronghont = 3°C above the inlet wet-bulb temperature. Countercurrent exit air temperature about 100°C for cocurrent exit air, temperature = 10 to... 

A continuous CFBD was further designed (Figure 29.4) with a dryer surface of approximately 21 ft in the form of a rotating perforated stainless steel cylinder (10 in. diameter and 100 in. long) with an open area of 45% and Teflon-coated inside [30]. The cylinder could be rotated at speeds up to 350 rpm (F = 17.4 x G) through a belt drive and tilted between 0° and 6° from the horizontal to help control the residence time of material that is dried. Centrifugal fans with steam heaters enabled air temperatures up to 140°C. 

A number of factors influence the selection of a dryer from the many different types available. These factors are dominated by the nature of the feed, whether it be granular solids, a paste, a slab, a film, a slurry, or a liquid. Other factors include the need for agitation, the type of heat source (convection, radiation, conduction, or microwave heating), and the degree to which the material must be dried. The most commonly employed continuous dryers include tunnel, belt, band, turbo-tray, rotary, steam-tube rotary, screw-conveyor, fluidized-bed, spouted-bed, pneumatic-conveyor, spray, and drum dryers. 

Stabaxol KE 7646 is used in PET-monofilaments for dryer-conveyor belts in paper making machines where it assists to multiply the service lifetime. For example, by as much as three times after accelerated aging in saturated steam (121C/250F). 

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