Batch Direct Dryers

Most direct batch dryers are fluid bed types such as those which retain the batch on a screen while pneumatically fluidizing the product. Mechanically agitated or tumble rotary dryers also exist. If the product is temperature 

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Accompanying the above advantages of indirect dryers are several limitations such as their limited ability to enhance the drying rates due to their limited availability of the heat transfer areas, especially in large-scale equipment. Indirect dryers also possess lower maximum drying temperature and maximum throughput when compared to direct dryers. Many types of indirect dryers can only be operated in batch mode hence they have lower production capabilities than direct dryers. In addition, indirect dryers have typically higher... 

Laboratory testing of small samples of the product can be very useful in determining the required size of a conveyor dryer. The continuous, conveyor dryer process can be simulated in the laboratory by a small, static batch tray dryer. The temperature and airflow direction can be changed with time to simulate the progression of the product from one zone to the other in the continuous conveyor dryer. The turnovers (transfer of the product from one conveyor to the other), however, are difficult to simulate in the static tray dryer. For this reason, some products are test run in a continuous laboratory conveyor dryer. This requires significantly more product than for the tray dryer testing, however the simulation is closer to the real-life production situation. 

Industrial dryers may be broadly classified by heat-transfer method as being either direct or indirect heat. Dryers evolved from material handling equipment and thus most types of industrial dryers are specially suited for certain forms of material. Dryers are also classified as being batch or continuous. 

Batch thi ough-cii culation. Direct type, hatch operation Not apphcahle Not apphcahle Suitable only if material can he preformed. Suited to hatch operation. Shorter drying time than tray dryers Not apphcahle... 

Once a group of possible dryers has been selected, the choice may be narrowed by deciding whether batch or continuous operation is to be employed and, in addition to restraints imposed by the nature of the material, whether heating by contact with a solid surface or directly by convection and radiation is preferred. 

The CIP and SIP cycle was performed according to the SOP and process was simulated according to the media fill batch manufacturing directions. The CIP, SIP, leak test, and process results of the freeze dryer for media fill run 1, run 2, and run 3 are found satisfactory. 

Figure 9.4. Types of dryers cited in Tables 9.1 and 9.2. (a) Tray or compartment, (b) Vacuum tray, (c) Vertical agitated batch vacuum drier, (d) Continuous agitated tray vertical turbo, (e) Continuous through circulation, (f) Direct rotary, (g) Indirect rotary, (h) Agitated batch rotary (atmos or vacuum), (i) Horizontal agitated batch vacuum drier, (j) Tumble batch dryer, (k) Splash dryer. (I) Single drum, (m) Spray, (n) Fluidized bed dryer, (o) Pneumatic conveying (mostly after Nonhebel and Moss, 1971).

Once the cores are compressed, one to three sealing coats may be applied by the process operator. The third coat was never required, however. All 19 batches were completed with two coats of shellac. The volume of shellac applied was always 350 mL for both steps, as required by the batch record, and the record further indicates that the temperature of the air directed into the coating pan was always set at 40°C. There is no record of the temperature being monitored, however. The shellacked cores were dried overnight at 35°C. The dryer temperature was tracked and automatically recorded no variablity was encountered when the temperature chart was reviewed. 

Various Types of Steam Dryers.—simple apparatus is a jacketed shallow pan which is shown in Fig. 31. A number of such pans are frequently placed in one chamber, the outlet of which is connected to an exhauster or chimney. The material rests directly on the pan surface or is placed in metallic trays which can easily be handled. Figure 32 describes a trough dryer which may be used in batches or continuously. Here the material is agitated by paddles or screws and the capacity per square foot is therefore much higher than in tray dryers. Steam consumption is high, i,e., from 1.6 to 2.0 lb. per pound of evaporation. 

Batch Dryers If the batch size is stipulated, the requirement is simply that the dryer be able to physically contain the volume of the solids, and the dryer volume and dimensions can thus be calculated directly. Solids residence time must then be calculated. Equation (12-61) can be reversed and modified to give... 

Continuous fluid beds may be even more varied than batch fluid beds. The main distinction between continuous fluid beds will be according to the solids flow pattern in the dryer. The continuous fluid bed will have an inlet point for moist granular material to be dried and an outlet for the dried material. If the moist material is immediately fluidizable, it can be introduced directly onto the plate and led through the bed in a plug-flow pattern that will enhance control of product residence time and temperature control. If the moist granular material is sticky or cohesive due to surface moisture and therefore needs a certain degree of drying before fluidization, it can be handled by a backmix fluid oed, to be described later. 

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