Washcolumn separation

Step 3 The washfront

The crystals enter the column in equilibrium with the mother liquor and will be at the same temperature as this slurry feed - ( Tcry). The wash front is the zone where the crystals go from being surrounded by the impurity rich mother liquor to pure product.
The crystals above the wash front are in equilibrium with the surrounding wash liquid - (Twash), which is the melting temperature of pure water (0°C).
This change in temperature occurs at the washfront in a bed depth of just a few centimeters.
This sharp separation can be easily seen through the clear cylinder in a screw type wash column.These columns are separating ice crystals from the concentrated liquid. The dark liquid provides a clear view of the wash front. A simple photo cell provides an indication for the wash front position with the lamp used as part of the wash front control.

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