A while back I wrote about pressure processing which was driven by the “fresher flavour” of juice that is not heated. Freeze concentration is driven by the same quality concerns and is an alternative to concentration by boiling off water.
Interesting is that the energy needed to melt a kg of ice is several times lower than that required to evaporate a kg of water. In these days of high energy costs and carbon footprints this would seem to be an advantage. However, the freeze concentrator can not be run in mutiple effect plants which allows an evaporator with sufficient effects to use almost the same energy.
Even more disadvantageous, is that the freeze concentrator is often unable to reach the concentration required and a thermal evaporator has to be used as a finisher.
Falling Film Evaporators are designed for the production of concentrates from heat sensitive liquids.
(click image for full story online)
The text on the above image from a Wiegand brochure reads:
FALLING FILM EVAPORATORS
Vertical shell-and-tube heat exchanger, with laterally or con- centrically arranged centrifugal separator.
The liquid to be concentrated is supplied to the top of the heating tubes and distributed in such a way as to flow down the inside of the tube walls as a thin film. The liquid film starts to boil due to the external heating of the tubes and is partially evaporated as a result. The downward flow, caused initially by gravity, is enhanced by the parallel, downward flow of the vapour formed. Residual film liquid and vapour is separated in the lower part of the calandria and in the downstream centrifugal droplet separator. It is essential that the entire film heating surface, es- pecially in the lower regions, be evenly and sufficiently wetted with liquid. Where this is not the case, dry spots will result