Diameter rectification column

Fig. 38. (a, b) Kubierschky columns and (c) Raschig column. Diameter of columns is 99-120 cm. height, 8-16 m. The upper portion (1-2 m.) is cooled externally in rectification operations the rest of the column (7—15 m.) is well insulated and the top opening is closed. 

For many years up to the late 1960s, the use of packed columns in rectification and absorption processes was limited to relatively small plants with column diameters of up to 1 m. This was due to the properties of Raschig rings, commonly used at the time, which became less effective as the column diameter increased. It was not until Pall rings were introduced by BASF in the 1960s, that these limitations were partly reduced. In addition, little consideration was given to an even distribution of liquid at the column top and the pre-distribution of gas on inlet below the packed bed. 

Figure 6-5. Diagram of test plant for investigation of packings used for vacuum rectification. Column diameter ds = 150 and 220 mm, packed bed height H = 1.0-1.7m... 

Lewis and Smoley (Ref. 22) studied the plate efficiency in the rectification of mixtures of (1) benzene-toluene, (2) benzene-toluene-xylene, and (3) naphtha and mixtures of pinene and aniline in naphtha. An experimental column 8 in. in diameter with 10 plates spaced 16 in. apart was used. The bubble cap was rectangular, being 2 in. high and 2 in. wide, and extended across the column. There were 24 slots % by Ke on each side of the cap, giving a ratio of slot area to superficial area of about 0.16. The investigators found average plate efficiencies of 60 per cent for the benzene-toluene mixture, 76 per cent for the ternary mixture, and 80 to 95 per cent for the naphtha mixtures. 

Peavy and Baker (Ref. 27) investigated the rectification of ethanol-water mixtures in an 18-in.-diameter column, and obtained plate vapor efficiency from 80 to 120 per cent for superficial vapor velocities between 1 and 3 f.p.s. For other data on plate efficiency, see Refs. 7, 8, 13, 18, 25, 26, 28. 

Schmidt [9] introduced a concept for the design of columns packed with randomly filled 8—50 mm ceramic Raschig rings. He performed elaborate rectification tests in a column with a diameter of 0.3 m and a packing height of 2 m, using 7 binary mixtures at top pressures ranging between 66 and 1000 mbar, and used the results of... 

In the case of larger packing elements, used for rectification, with diameters of 35, 50 and 80 mm, it can often be assumed that the column operates in the turbulent range and the resistance coefficient / is only marginally dependent on the Reynolds number Rey of the vapour phase. 

The experimental constants are obtained for rectification of the stem chlorobenzene/ ethylbenzene at 66.7 mter in columns with diameters 220 and 300 nun. Because the Ferfactor in Eq. (17) takes into account the gas (vapour) density, the constants are practically indqiendent of the pressure. 

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