Freeze concentration of milk and saline solutions in a liquid–solid fluidized bed: Part I. Experimental

Fluidized bed freeze concentration is a novel technique that uses a fluidized bed heat exchanger (FBHE) to concentrate liquids through the process of freeze concentration. Ice formed on the cooled surface of the vertical heat exchanger is removed by particles fluidized inside the FBHE. In this paper, the operating conditions are reported for freeze concentration of saline solutions and milk in FBHE. The operation was tested with equilateral 4 mm and then 5 mm particles at different bed porosities, cooling rates and NaCl and milk concentrations. Experiments with NaCl solutions showed that the 5 mm particles were more aggressive than 4 mm in removing ice from the heat exchanger wall. Whilst particle size was considered responsible for this, the particle shape could have played a major role. A theoretical analysis on effect of FBHE parameters showed the size of particles to exert influence on FBHE performance. The result from experiments with skim milk and whole milk maintained the conclusions formed previously with NaCl experiments with regard to the effect of tested parameters on operational stability. However, the ice formed from milk was more difficult to remove than the ice formed from NaCl solutions. Whole milk showed even more resistance to ice removal. Skim milk was freeze concentrated from 13% to 27% TS content in these experiments. Installing a wash screen further improved the purity of separated ice.