Drum driers

Figure 32. An atmospheric single drum drier with dip feed.

Figure 33. Atmospheric double-drum drier with center feed.

Trommel-ofcn, m. rotary furnace or oven cylinder roaster, -probe, /. (Coke, Ceram.) rattler test, -sieb, n. drum sieve, cylindrical screen, trommel, -trockner, m. drum drier, rotary drier. -versuch, m. = Trommel-probe. 

In the rotary drum driers, a liquid material, a solution, slurry, or paste is transferred in the form of a film to the surface of... 

Drum driers can operate either at atmospheric pressure or under vacuum... 

The simplest type of drum drier contains only one drum and is known as ... 

Atmospheric Twin-Drum Drier with Splash Feed is described in Perry, p 64-L and shown in Fig 64, which is reproduced here as Fig 9. 

All driers listed above are steam-heated Vacuum drum driers operate on the same principle as the corresponding atmospheric driers, except that the drums are enclosed in vacuum-tight casing and a vacuum is created either by a pump or a steam jet. They are used in drying materials which are heat-sensitive, easily oxidizable or when it. is desired to recover a volatile solvent... 

Vacuum Single-Drum Drier of Blaw-Knox Co. is described by Perry on p858 and shown in Fig 57. It is reproduced here as Fig 10 Vacuum Single-Drum Drier of Blaw-Knox Co with Patented Spray Film Feed is described in Perry, p864-R and shown in Fig 65, which is reproduced here as Fig 11... 

Procedure. The chlorosulfonic acid in a beaker is cooled to —15°. The thiophene is added, with stirring (manual stirring rod) over a period of eight minutes, during which time the temperature rises to —5°. This mixture is immediately poured into 100 g. of crushed ice and the temperature of the quenched mixture is held below 30° by means of external cooling. The mixture is then neutralized with 325 ml. of 20% sodium hydroxide solution at a temperature below 40°. The aqueous solution is extracted three times with petroleum ether and then evaporated to dryness on a drum drier. The residue is extracted with boiling anhydrous methanol to remove the product from sodium sulfate and the alcoholic solution is dried on the drum drier (or the alcohol is evaporated and the product dried in a vacuum desiccator). The product is a white hygro-... 

Although many types of continuous driers are available, the scale of the operation for which they are designed is rarely appropriate to pharmaceutical manufacture. As with most continuous operations, the cost is disproportionately high for small units. Spray and drum driers provide an exception, because residence times in the driers are short and thermal degradation is minimized. Under some conditions, freeze drying may be the only practicable alternative. 

Drying capacity is influenced by the speed of the drum and the temperature of the feed, which may be preheated. With the double-drum drier, the gap between the cylinders determines the thickness of the film. 

Drum driers, like spray driers, are relatively expensive in small sizes and their use in the pharmaceutical industry is largely confined to drying thermolabile materials where the short contact time is advantageous. Drums are normally fabricated from stainless or chrome-plated steel to reduce contamination. The heat treatment to which the solid is subjected is more intense than in spray drying and the physical form of the produce is often less attractive during drying, the liquid approaches its boiling point and the dry solids attain the temperature of the drum surface. 

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