Single Stage Solution Evaporation

A solvent mass balance gives the solvent flow rate t ( vapor flow rate ) to be evaporated in order to concentrate the solution from iv to 

A heat balance over the evaporator gives the required steam flow rate Dff to evaporate D 

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Figure 7-10 shows a schematic of a single stage solution evaporator, to evaporate a solution flow rate F with an initial mass fraction of soluted solid to the final concentration of... 

Fig. 7-10. Balance scheme to determine the solvent vapor flow and steam consumption (a) and heat flow diagram for single stage solution evaporation (b).

The urea solution is evaporated in a two-stage system (99.8%) if the final product is prills, and a single-stage system (+95%) if granules are to be provided. 

The urea solution stream is then fed to the vacuum concentrator unit which operates at 17.3 kPa (130 mm Hg abs) and produces 88.7 wt % urea. It then goes to either two-stage evaporators if prills are made, or a single-stage unit for granule production. 

Since all scale-forming constituents of saline waters have inverted solubility-temperature relationships, the scale problem can be alleviated, if not wholly solved, by evaporation at high vacuum and hence low temperature. Some small single-stage units for household and other uses boil the solution at a temperature as low... 

If recapture from air takes place on an activated carbon bed, it is likely that the ethyl acetate arising from regeneration of the bed will be mostly in aqueous solution with a small upper layer of water-saturated solvent. As the VLE diagram (Fig. 16.31) shows, ethyl acetate is very readily stripped from water in a single-stage evaporation to yield the water azeotrope. Since, whatever the method of stripping, some hydrolysis will have occurred, the recovered mixture will consist of a mixture presenting complex separation problems (Table 16.19). 

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