The forced circulation evaporator is suitable for processing liquors, which are susceptible to scaling or crystallizing. Liquid is circulated at a high rate through the calandria, boiling being prevented within the unit by virtue of a hydrostatic head maintained above the top tube plate. As the liquid enters the separator where the absolute pressure is slightly less than in the tube bundle, the liquid flashes to form a vapor.
The main applications for a forced circulation evaporator are in the concentration of inversely soluble materials, crystallizing duties, and in the concentration of thermally degradable materials, which result in the deposition of solids.
Forced circulation evaporators normally are more expensive than film evaporators because of the need for large bore circulating pipe work and large recirculating pumps. Operating costs of such a unit also are considerably higher. |
