METHOD FOR PREPARING AN AQUEOUS SOLUTION, IN PARTICULAR SODIUM HYDROXIDE SOLUTION, BY MEANS OF A MULTI-STAGE EVAPORATION

摘要

The invention relates to a method for preparing an aqueous solution, in particular a sodium hydroxide solution by means of a multi-stage evaporation. Product streams (4, 5), in particular concentrate streams or vapour condensate are produced from the aqueous solution, (in the form of a hot feed solution (L)). The feed solution stream is divided between two evaporation devices A and B. During the multi-stage evaporation, the feed solution that is supplied to device A is concentrated to form a first concentrated product solution (C1). Preferably, device A represents a last stage of the multi-stage evaporation and the feed solution is conducted through additional evaporation stages (10) in the opposite direction to the vapour (Bi). Vapours (Bi) of the multi-stage evaporation are liquefied to produce vapour condensates (Ki). A fraction of said vapours (B5) is liquefied in device B to provide heating energy. A second concentrated product solution (C2) is produced in device B. According to the invention, the concentrations of said product solutions (C1, C2) do not differ by more than 20 % in relation to the higher concentration. Preferably, the first concentrated product solution (C1) has a lower concentration.