GB789710A - Vacuum evaporator for concentrating juices and other liquids - Google Patents

Abstract

<PICT:0789710/III/1> <PICT:0789710/III/2> An evaporator, for the concentration under vacuum of liquids such as citrus juices, comprises three or four up-right cylindrical or frustoconical heat - exchange surfaces disposed coaxially within each other, the first evaporating surface being formed by the inner wall of an outer heat-exchanger and the other surfaces being formed by the outer and inner walls of one or two internal heat-exchangers, means for supplying liquid to be concentrated to the upper end of the outermost heat-exchange surface, down which it flows as a film, and means for causing the liquid to flow in the form of a film up the outer surface(s) of the inner heat-exchanger(s). The apparatus shown comprises a heat-exchange surface 1 surrounded by a jacket 2 which is supplied with high-pressure steam through inlet 17. The upper part of the apparatus leads to a hood connected to a vacuum duct. Within the apparatus is a heat-exchanger 9 comprising an annular body having a vertical outer wall 10 and a sloping inner wall 11. The interior of heat-exchanger 9 may be connected in series with jacket 2, or it may be supplied with heating fluid independently. A shaft 22, driven by motor 25, extends up through the evaporator; and a circular plate 30 and eight radial blades 31 are connected to the hub 29 of the shaft. Four radial blades 34, disposed in vertical register with alternating blades 31, are connected to hub 33 of the shaft. The outer edges of blades 34 are in close proximity to surface 1, with a gap of 2 mm. or less. A sleeve 38, connected by spokes 36 to hub 361, surrounds heat-exchanger 9, and the bottom edge of this sleeve carries on its inner face a plurality of curved vanes 39. Radial blades 41, in vertical register with blades 34, are secured to the outer face of the sleeve. Liquid is delivered on to rotating plate 30, and is thrown as a fine spray towards wall 3. Some of the liquid does not reach wall 3 directly, but drops on to annular plate 32 and is delivered to wall 3 by rotating blades 31. The liquid runs down the hot surface 1 where it is spread out as a thin film by blades 34 and 41. When the liquid reaches trough 7, the sideward component of its movement is suppressed by baffles 15. From the trough 7, the liquid is taken up by the vanes 39 of sleeve 38 and, with a spiral movement, is raised up along surface 10 of heat-exchanger 9, i.e. sleeve 38 serves as a centrifugal pump. On reaching the top of surface 10 the liquid is directed inwards by rim 37 of sleeve 38, and its flow is now guided by baffles 16 so that it descends down surface 11 in a straight and gentle flow. The concentrated liquid collects in pit 12, and is withdrawn via conduit 19, the degree of concentration being measured by refractometer 21. When the apparatus is used as a second-stage evaporator it may be mounted directly at the bottom end of the first-stage evaporator.