MECO developed the vertical tube vapor compression evaporator after many years of research and trials on horizontal tube and vacuum plant designs. The early horizontal tube plants exhibited localized scaling and corrosion due to poor circulation of the brine within the evaporator tube bundle. In the horizontal configuration, the forced circulation of brine with proper distribution over the tube bundle, via spray nozzles, became critical (see figure 1).

Scaling within the bundle on the outside of the tubes proved difficult to clean. As a result, the horizontal concept was abandoned in favor of a vertical tube design with the brine evaporating evenly on the inside of the tubes (see figure 2).

The vertical tube natural circulation evaporator allowed any scale or foulants that formed to lay down evenly on the heat transfer surface. This facilitated their even removal by chemical means and, subsequently, less corrosion of bare metal surfaces which were traditionally present in the horizontal tube units. A by-product of the vertical tube design was the ability to mechanically brush or clean the I.D. of the tubes, if necessary. This option was not available in the early horizontal tube units.