Batch drier

ScroU centrifuges discharge soHds continuously and usuaUy drier than disk and imperforate batch types. GeneraUy disk centrifuges have the highest values of Z or for a given size and therefore the best abUity to coUect fine particles at a high rate. 

Driers are used in the forest products industry to lower the moisture content of the wood product being processed. Drying of dimension lumber gives it dimensional stability. This type of drying is done in steam kilns and is a batch process. No appreciable pollutants are released. 

A 1.3 t batch of off-spec, material had been redried in a rotating double cone vacuum drier heated by steam to around 120-130°C for 23 h. It was left in the... 

A 100 kg batch of granular solids containing 30 per cent moisture is to be dried in a tray drier to 15.5 per cent of moisture by passing a current of air at 350 K tangentially across its surface at a velocity of 1.8 m/s. If the constant rate of drying under these conditions is 0.0007 kg/s m2 and the critical moisture content is 15 per cent, calculate the approximate drying time. Assume the drying surface to be 0.03 m2/kg dry mass. 

Additional supporting documents are also included in the manufacturing records. These may include computerized print-outs from weighing equipment used to dispense chemical raw materials, or recorder charts obtained, e.g. from a freeze-drier upon completion of freeze-drying that batch of product. 

Brattice driers, incorporating a device for removing the dried material (Fig. 44) have been used in Germany. The moist material, spread in a thin layer over cloth stretched on wooden frames (1), is dried in warm air supplied via the ducting (2) at a rate of about 0.5 m/sec. Next to the frame on which the material is dried there is a tin funnel (3) with a built-in sieve in its base. This funnel is connected with the ventilating duct by a flexible tube. Each frame (7) contains about 1.2 kg of fulminate (dry substance). To dry a batch of fulminate at 65-70°C takes... 

The product was dried in a drier (as described for mercury fulminate) at temperatures from 65 to 70°C in batches of 1.2 kg at a time it was then sieved as described above. A sieve analysis of the product showed, for example, the following sizes of crystals ... 

Toluene and olefinic stock from storage are pumped (at 80°F) separately through individual driers and filters into the alkylation reactor. The streams combine just before they enter the reactor. The reactor is batch operated 4 hr/cycle it is equipped with a single impeller agitator and a feed hopper for solid aluminum chloride which is charged manually from small drams. The alkylation... 

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).

Continuous hoi air driers are used to prepare most of the high quality, dried, piece-furm fruits and vegetables produced in the United States. Liquids and pastes arc commonly dried in spray, drum, or feeze dryers. Particulate foods can be dried in batch or continuous air-fluidized beds or freeze dryers. Many agricultural commodities are sun-dried when weather conditions at harvest provide low humidity, warm temperatures, and good air circulation. 

The S88 approach to batch control provides a framework for the architecture of the system, having essentially four layers of control that operate on plant units (e.g., reactors, filters, driers) within a process cell (a collection of plant units within a facility or used for a process stage). 

In applications, where aluminum powder is requested (e.g. in powder coatings) or where the rest of the remaining mineral spirit would not be compatible with the application medium (e.g. in printing inks, waterborne coatings and inks, master-batches etc.), the mineral spirit of the press cake is removed in vacuum driers and substituted by any kind of solvent, water, plasticizer, mineral oil or other liquids. 

A flow diagram for the production of aspirin is shown in Fig. 10.6 [9]. A mixture of salicylic acid powder, acetic anhydride, and a small amount of sulfuric acid is charged into a batch reactor. The mixture is stirred for 2 to 3 hours and then transferred to a crystallizing kettle. A portion of the mother liquor is recycled in the next run, and the other part of the slurry is centrifuged. The resulting crystalline material is dried in a rotary drier to yield acetylsalicylic acid (aspirin). Excess mother liquor is distilled and the excess of acetic anhydride is recycled. 

---