US 6,305,178 B1 · Continuous system of freeze concentration for aqueous solutions

Abstract

Investigations on the formation and growth behavior of ice crystallization in aqueous solutions reveal an important phenomenon—ice crystal transformation. It leads to very rapid growth of ice crystals and result in grain-shaped and agglomerated large crystals without inside entrainment of solute. This provides a practical basis for a new technology of freeze concentration. The efficient physical process for freeze concentration of aqueous solutions comprises, mainly, refrigerating solutions to a supercooled status without ice nucleation, or without ice formation on the heat transfer surface, instantaneously nucleating the supercooled solution to generate fine ice crystals and make the solution concentrated, producing large, grain/sphere-shaped ice crystals at high rate by growth, transformation and agglomeration of ice crystals under environment of well-controlled endo/exothermal balances. Apparatus for performing the process including, mainly, refrigerating heat exchangers, nucleators, filters and multi-function crystallizers are described. Single-stage and multistage operations can be used for the process and the major steps can be flexibly arranged.

Claims24

Dependent claims

A method for freeze concentration of aqueous solutions comprising the steps of:

(a) preparing feed solution for supercooling;
(b) supercooling said feed solution to produce supercooled, metastable solution;
(c) generating fine ice crystals from the supercooled, metastable solution and concentrating the solution by instantaneous nucleation/crystallization;
(d) separating fine ice crystals from mother solution to obtain wet fine ice crystals and filtrate solution;
(e) transforming fine ice crystals having melting potential onto growing ice crystals, making growing ice crystals continue their growth and agglomerating growing ice crystals to produce large ice crystals without inside entrainment of solutes;
(f) precooling original solution to be concentrated to prepare precooled original solution by use of large ice crystals produced in step (g);
and
(g) removing surface-entrained solution from large ice crystals to produce substantially pure large ice crystals and to recover solutes by use of the precooled original solution and water from melted ice.

5 more elements

A system for freeze concentration of aqueous solutions comprising:

(a) a mixing tank equipped with an agitator and good insulation for preparing a feed solution for supercooling;
(b) a conventional shell and tube heat exchanger with the feed solution in the tube side and the coolant in the shell side in a counter-current manner for supercooling the feed solution to produce a supercooled, metastable solution;
(c) a nucleator having an agitator and good insulation for generating fine ice crystals from the supercooled, metastable solution and concentrating the solution by instantaneous nucleation/crystallization;
(d) a continuous filter for separating fine ice crystals from the concentrated solution produced by the nucleator to obtain wet fine ice crystals and filtrate solution;
(e) a multi-function crystallizer for transforming fine ice crystals onto growing ice crystals, making growing ice crystals continue their growth and agglomerating growing ice crystals to obtain large ice crystals;
(f) heat transfer means for precooling original solution to prepare precooled original solution by use of large ice crystals;
and
(g) separating/washing means for removing surface-entrained solution from large ice crystals by use of the precooled original solution and water from melted ice to obtain substantially pure ice crystals.

5 more elements

Dependencies are inferred from the claim text.

Continuous system of freeze concentration for aqueous solutions

Life of this patent

Continuous system of freeze concentration for aqueous solutions

Life of this patent

Abstract

Claims24