Patent ID: 7637965

Claim:
A process for controlling a hydraulic wash column which has a cylindrical shell ( 1 ) which delimits the column and within which one or more filter tubes ( 2 ) extend through the column parallel to the cylinder axis and have, in the vicinity of the second end of the column, at least one filter ( 3 ) in the filter tube wall which forms the sole direct connection between the filter tube interior under the pressure P 1 and the interior of the column, in which at least one stream of a suspension ( 4 ) which comprises crystals of a substance to be purified suspended in a mother liquor is fed continuously into the first end of the column ( 5 ) with a pressure P 2 which is greater than P 1 , mother liquor ( 7 ) is conducted through the filters into the filter tube interior and out of the column via the filter tubes, optionally control liquor ( 9 ) is fed into the wash column at the first end of the column and/or between this end and the start of the filter, the mother liquor and, optionally control liquor flow in the column form a crystal bed ( 10 ) of the substance to be purified, said crystal bed having a buildup front ( 11 ) which faces the first end of the column and at which crystals of the introduced suspension add continuously to the crystal bed, the crystal bed, by virtue of the force resulting from the hydraulic flow pressure drop of the mother liquor and, optionally control liquor flow in the column, is transported ( 13 ) past the filters into the wash zone disposed between the filters and the second end of the wash column ( 12 ), crystals are removed ( 14 ) continuously at the opposite end of the crystal bed to the buildup front, the removed crystals are melted ( 15 ) and a portion of the melt is passed ( 16 ) through the crystal bed as a wash liquid stream coming from the second end of the column against the transport direction of the crystals and the position of the buildup front is controlled with the aid of the flow rate of control liquor conducted into the wash column and/or with the aid of the flow rate of the suspension ( 4 ) conducted into the wash column, wherein the flow rates of the control liquor and/or suspension ( 4 ) conducted into the wash column are determined by utilizing at least one pressure difference ΔP SK which exists in the column between at least one point in the suspension zone ( 17 ) disposed in front of the buildup front and at least one point in the zone projecting from the buildup front up to the end of the crystal bed.