Batch Agitated and Rotating Dryers

A similar example for batch dryers may be found in the section Batch Agitated and Rotating Dryers, including constant-rate and falling-rate kinetics and scale-up from an experimental test result. 

Filter Dryers Basically this is a Nutsche filter (Sec. 18, Liquid-Solid Operations and Equipment ) followed by a batch dryer, usually of vertical pan type (see Batch Agitated and Rotating Dryers section). They are popular in the pharmaceutical and specialty chemicals industries as two unit operations are performed in the same piece of equipment without intermediate solids transfer, and containment is good. 

Design, Scale-up, and Performance Like all batch dryers, agitated and rotating dryers are primarily sized to physically contain the required batch volume. Note that the nominal capacity of most dryers is significantly lower than their total internal volume, because of the headspace needed for mechanical drives, inlet ports, suction lines. 

Agitated and Rotating Batch Dryers Scale up from pilot-plant tests in a small-scale dryer at the same temperature and pressure and similar agitation conditions. As noted under scoping design, scale-up depends on the surface area/volume ratio, and hence normally to the one-third power of mass. Results from one dryer type may be extrapolated to a different type if assumptions are made on the heat transfer coefficients in both dryers obviously this is less reliable than measurements on the same dryer type. 

Paper is placed in a hydropulper, a large water tank equipped with a heavy motor-driven propeller at the bottom. The propeller agitates the water and wet paper and separates the paper fibers into a fiber slurry. Additives are added and mixed as needed at this point. This is a batch process and as such requires more than one hydropulper in order to be processing one tank as another is being emptied of slurry and refilled with water. The slurry is pumped into a box having a large-diameter cylinder covered by a wire screen rotating slowly within it. Fibers are deposited on the screen as water is pumped out of the screen and returned to the process. The fiber mat is carried up and over as the screen rotates and then transferred to a flat wire screen belt which moves the mat across suction boxes and onto the dryers. 

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