Multi-effect film evaporator - has evaporator surfaces, in effects where heat flux is critical, increased in area

摘要

Multi-effect film evaporator plant has evaporator surfaces, in those effects where the heat flux is critical in terms of scale formation or liq. film dry out, increased in area relative to the other effects. The risk of scale formation due to critical heat flux is greatest at the highest temp. effect evaporator surface and a reduction of overall temp. operating range may be avoided by having an enlarged evaporator surface area in that effect relative to the majority of the effects. The risk of dry out, i.e. complete diapperarance of liq. film, is greatest at the lowest temp. effect evaporator surface and the area of this surface is pref. enlarged relative to the majority of the effects. If the heat flux in any effect is too high instead of reducting the temp. range across the whole plant the surface area in that effect is enlarged. This reduces the temp. driving force within that effect and permits the evapn. temp. range to be restored to its full value. An overall saving in total area of evaporator surface can be achieved even through the surface area in one effect is increased.