In the evaporation of aqueous solutions, the ratio of heating steam to generated vapors is in the region of 1.2. By preheating the fresh feed solution by condensing a small portion of the vaporized solvent, it is possible to achieve efficiency improvement, of the order of 10 to 15% [ 15]. A diagram representing the principle of introducing this technique is presented on the Figure 7.19. A small portion of the vapor preheats the feed by condensing in the preheater. A cooling medium is used to condense the residual vapors in the condenser.
Single [ stage evaporators are not often used because of their low thermal efficiency. Their application is limited to systems of small capacity, or those in which the product requires short residence time due to temperature sensitivity .
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