Evaporators long-tube: climbing-film

Although the methods proposed for scale control relate specifically to spray evaporation, the strippable film technique may well be applicable to other types of evaporator, and this requires further investigation. The other two methods are practicable as a result of the very low liquid holdup in spray evaporation, so that interruption of the feed leads to elimination of the holdup in a matter of seconds. The same process should be applicable to conventional evaporators of low holdup—e.g., long-tube climbing and falling film types—if entrainment steam were admitted at the same time as the feed is interrupted, and this possibility would well repay further investigation. 

The preferred types in use today are (1) climbing-film long-tube vertical type, (2) forced-circulation type, and (3) falling-film long-tube vertical type. Examples of these types are shown in Fig. 4-3. Mechanical compression and multiple effect are favored where high evaporation temperatures and relatively high fuel costs exist. 

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