Evaporation

A.  Most popular types are long tube vertical with natural or forced circulation.  Tubes range from 3/4" to 2.5" (19-63 mm) in diameter and 12-30 ft (3.6-9.1 m) in length.
B.  Forced circulation tube velocities are generally in the 15-20 ft/s (4.5-6 m/s) range.
C.  Boiling Point Elevation (BPE) as a result of having dissolved solids must be accounted for in the differences between the solution temperature and the temperature of the saturated vapor.
D.  BPE's greater than 7 °F (3.9 °C) usually result in 4-6 effects in series (feed-forward) as an economical solution.  With smaller BPE's, more effects in series are typically more economical, depending on the cost of steam.
E.  Reverse feed results in the more concentrated solution being heated with the hottest steam to minimize surface area.  However, the solution must be pumped from one stage to the next.
F.  Interstage steam pressures can be increased with ejectors (20-30% efficient) or mechanical compressors (70-75% efficient).