Process and installation are for the concn. by evapn. of a soln. having a high boiling point rise. The soln. is preheated by passage through a heat exchanger and then passed to an evaporator for partial evapn. of the solvent. Vapour from the evaporator is put through a compressor serving as a heat pump. The compressed vapour is passed to a contactor to be absorbed by a satd. soln. having a high b.pt. rise. This raises the temp. of the soln. to the satn. temp. of the vapour plus the b.pt. rise of the soln., and this increased temp. soln. is employed as the heating fluid in the preheater. Pref. the soln. employed in the absorption circuit is of a higher b.pt. rise than the soln. to be evapd. The higher the b.pt. rise of the soln. in the absorption circuit, the less compression of vapour required, if any. Used in concn. of solns. of high b.pt. rise, e.g. sodium chloride soln. An energy saving of 50% because the vapour need not be compressed to such a high degree as when the absorption stage is omitted.
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