| 摘要 |
PURPOSE:To manufacture high-purity caustic soda by cooling slowly a high-temp. concentrated caustic soda soln. formed by the electrolysis of brine in two steps to make the separation of NaC which is contained as impurities easy in the succeding stage. CONSTITUTION:An NaOH soln. formed by the electrolysis of an aq. soln. of NaCl is concentrated, and the concentrated NaOH soln. at 85-90 deg.C from the concentration step is sent to a cooling tank 1 in the preceding stage through a line 10, passed through an indirect heat exchanger 3 from the tank 1 by a circulation pump 5, and cooled with cooling water at ordinary temp. Then the soln. is transferred to a cooling tank 2 in the succeeding stage through a pipe line 11, cooled in an indirect heat exchanger 4 with cold water at about 4 deg.C through a circulation pump 6, and then transferred to the next step by a pump 9 to crystallize out the impurities of NaCl which are filtered and removed to obtain the high-purity concentrated NaOH soln. In this way, the concentrated NaOH soln. is cooled slowly in two steps to make the separation of NaCl crystal from the NaOH soln. easy.
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