GB632580A - Improvements in or relating to the evaporation of water from concentrated solutions of calcium nitrate - Google Patents

Abstract

A saturated or nearly saturated aqueous solution of calcium nitrate is heated under a pressure high enough to prevent boiling and then expanded to a pressure below the vapour pressure of the heated solution before the expansion. The expansion gives rise to violent evaporation and a pasty mass containing solid calcium nitrate is formed. This pasty mass is preferably dried by mixing it with dry calcium nitrate, i.e. part of the final product, so that the mixture contains less than 10 per cent water and then using a drying drum. Calcium <PICT:0632580/III/1> nitrate solution containing 45 per cent water is concentrated in evaporator 1, and the concentrated solution (25.5 per cent water) is stored in tank 2. The concentrated solution is pumped through tube-furnace 4 where it is heated to 260 DEG C. under a pressure of 19 atm., and is then injected tangentially against the wall of vessel 6 which is at atmospheric pressure. The solution descends along the wall in a helical line and a pasty mass containing 14.7 p per cent water discharges from the bottom of vessel 6 into trough 7 where it is mixed with dry calcium nitrate introduced at 8, the ratio of salt to paste being 11 to 10. The mixture is dried in drum 9 at about 230 DEG C., and the solid obtained which contains 1.5 per cent water, is cooled in drum 10. The solid is separated into three fractions by sieves 11, 12, and the middle fraction of grain size between 3 to 4 mm. constitutes the final product. The mixture of the coarser and finer fractions, the former after being ground by mill 13, introduced into trough 7.