GB679430A - Improvements in or relating to steam distillation - Google Patents

Abstract

<PICT:0679430/III/1> <PICT:0679430/III/2> In the distillation, e.g. of petroleum oils, in a steam stripped column operating under vacuum and comprising a reflux zone and an absorption zone above the reflux zone, part of the liquid is withdrawn from the reflux zone, cooled in a heat-exchanger and the major part returned to the reflux zone and into direct contact with the vapours therein to condense the heavier components of the vapours, the remainder being further cooled and returned to the absorption zone to condense the lighter components of the residual vapours, a liquid product and substantially product-free steam being withdrawn from the absorption zone. Large vapour condensers for the product are thus avoided. In Fig. 1 liquid is taken off a tray 18a, forced by pump 22 through heat exchanger 24 and the major part returned by valved line 26 to upper tray 18b. Uncondensed vapours and steam pass to the absorption zone formed by plates 30, 30a, and the remainder of the liquid taken from tray 18a is further cooled in heat exchanger 36 and returned to tray 30. Product is taken by line 44 from a tray on plate 30a. Steam passes overhead and is condensed at 38. The usual vacuum jet 40 and barometric condenser 42 are provided. The column may be controlled by automatic regulation of a valve 45 in product line 44 in response to the temperature at an intermediate point in the column, surplus liquid from tray 30a being returned by line 31 to tray 18b. Alternatively the valve 45 may be replaced by a flow control valve giving a constant output. In the modification (Fig. 2) the product from tray 30a goes to an accumulator 46 from which it may be pumped to product line 35 or, in part, by valved line 35a and cooler 36 to tray 30. A valved line 37 replaces line 31. Lines 37 and 35a may be used separately or together to control the temperature at the top of the column and the composition of the product. Crude oil may be introduced to the columns at 12, and one or more sidestreams may be removed from the columns, steam and vapours from the sidestream strippers being returned to the columns through one or more lines 16.