| 摘要 |
PURPOSE:To concentrate a caustic soda solution with saved energy in a relatively simple process without using high-class materials, by heating the caustic soda solution within a specific low temperature region and stirring the deposited crystals in concentrating the solution while heating under reduced pressure. CONSTITUTION:A caustic soda solution is concentrated while heating under reduced pressure. In the process, temperature is kept within a range where only anhydrous crystals are crystallized and the deposited crystals are stirred. The concentrating and stirring while heating are preferably carried out in two stages in a centrifugal thin film evaporation apparatus having a rotating stirring device in the interior of a heat transfer drum within a low concentration region of the caustic soda solution and in a conductive heating type stirring dryer or kneading dryer within a high concentration region. For example, the concentrating in the first stage is initially carried out in the centrifugal thin film evaporator 2 having rotating and sliding blades on the inner wall surface of a jacketed heat transfer drum 5 under reduced pressure and the concentrating in the second stage is subsequently carried out in a paddle dryer 7 having paddles 6.
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