GB824111A - Improvements in and relating to evaporators - Google Patents

Abstract

<PICT:0824111/III/1> <PICT:0824111/III/2> <PICT:0824111/III/3> A multi-stage flash-type evaporator comprises a shell which is divided by a partition-walls 16 into a number of flash-chambers 10 arranged side by side in a straight line, the upper part of each chamber having an outlet 18 for the discharge of vapour; the lower portions of the walls 16 have orifices 14 for the passage of heated liquid through the chambers, and each chamber is provided with a weir 20 the top of which lies above the orifices through which the liquid enters and leaves the chamber, the horizontal distance of the upper edge of the weir from the inlet end of the chamber being equal to or less than its horizontal distance from the outlet end. The heated liquid enters the first chamber through pipe 12, and passes from chamber to chamber through orifices 14. For any given operating condition, from starting-up to full load, the liquid-level upstream of each orifice 14 adjusts itself so that the difference in static head across the opening plus the vapour-pressure difference on either side of the wall 16 are sufficient to transfer the liquid through the orifice and over the top of the weir lying downstream of the orifice. The liquid levels in the chambers on full load operation are shown at 24 and 26 in Fig. 1. Under low-load or no-load conditions, when the pressure difference from stage to stage is small or absent, the liquid levels in the chambers are higher, the levels on no-load being shown at 22. In the alternative embodiment shown in Fig. 3, each weir is arranged close to the upstream wall of the chamber and is bent over at the upper part to form, at the top of the weir, a secondary orifice 32 through which the liquid is projected upwards into the chamber. Baffle plates 34 are arranged above the orifices 32 in such a position that the liquid is projected on to them.