PROCEDE ET DISPOSITIF PERMETTANT DE CONCENTRER UNE LESSIVE ALCALINE

L'INVENTION SE RAPPORTE A UN PROCEDE DANS LEQUEL LA LESSIVE ALCALINE EST CONCENTREE A LA PRESSION ATMOSPHERIQUE, SOUS LA FORME D'UN FILM CHAUFFE S'ECOULANT DE HAUT EN BAS, DE MANIERE A OBTENIR UNE SOLUTION PRATIQUEMENT EXEMPTE D'EAU, LA SOLUTION ALCALINE S'ECOULANT DU SUPPORT DU FILM EST RECUEILLIE ET EVACUEE SEPAREMENT DES BUEES.DANS LE DISPOSITIF, LA FACE EXTREME INFERIEURE 13 DE CHAQUE TUBE D'EVAPORATION 1 EST BISEAUTEE CONIQUEMENT A ANGLE AIGU VERS L'EXTERIEUR, SELON LE MEME ANGLE QUE LA FACE EXTREME 12 DE LA PAROI INTERNE DE CHAQUE CANAL COLLECTEUR, L'ANGLE DELIMITANT LES DEUX FACES EXTREMES 12, 13 MESURANT ENTRE 16 ET 45, ET AVANTAGEUSEMENT 27. A method and apparatus for the concentration of an alkaline solution to an approximately anhydrous melt using the falling-film principle under atmospheric pressure wherein the solution to be concentrated is conducted along the internal surface of evaporator tubes (1). Each tube (1) is surrounded by a heating jacket (2). The heating jackets (2) are fed with heat-transfer fluid from a conduit (6) which is common to all jackets. An annular collecting trough (8) is associated with the lower end of each evaporator tube (1). The metal running off from the tube (1) is collected by the trough (8) separately from the vapors. All of the troughs (8) are connected to a melt discharge line (9) which is also common to all troughs. The vapors descending in the tube (1), in contrast thereto, pass through the opening (8a) of the collecting troughs (8) into a collecting duct (10) which is common to all troughs. By the separation of the melt and vapors at the tube end portions, a renewed drop in the alkali concentration is avoided.