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From: Walter Bierwerth, Tabellenbuch Chemietechnik, 11th edition, Verlag EUROPA-LEHRMITTEL, Europe No. 70717, p. 439 ff.

Task:

In a mixture of benzene and toluene, the mass fraction of benzene is to be enriched by continuous rectification.

The plant is shown in the flow diagram (flow chart).

The mixture (pure two-substance mixture, ϑV = 20 °C) accumulates for separation with the following composition:

Operating specifications:

Desired enrichment: w1 = 0.95 (column head), the sump effluent should still contain a maximum of w1 = 0.05 benzene.

Feed to the column: boiling liquid

Outlet from the head condenser: boiling liquid

Cooling of the distillate in the distillate cooler to ϑ = 40 °C

Cooling water is available with a relative constant inlet temperature of ϑ = 20 °C and should not be warmer than ϑ = 30 °C when leaving the plant.

The column is operated at normal pressure.

Components to be designed:

Centrifugal pump (feed pump): Required pump capacity via pressure drop in the feed line

Mixture preheater (electric pipe heating, inductive): required heating power?

Separation column (packed column): required number of theoretical stages according to McCabe-Thiele

Head condenser (shell and tube heat exchanger): required exchange area

Distillate cooler (shell-and-tube heat exchanger): required exchange area

Distillate receiver (horizontal cylindrical buffer vessel with dished ends): Level diagram qV = f(h)

Required fittings and other piping parts in the feed line:

2 bends (elbows) 90°, R/d = 4

1 Globe valve (DIN valve)

1 Shut-off valve (ball valve), 50 % open

1 Check valve

1 Vortex counter

Calculation of the required number of separation stages for the rectification column p. 256/257

Boiling temperatures of the pure substances:

ϑB = 80.1 °C and ϑT = 111 °C (p. 110/111).

Boiling temperatures in Kelvin:

TB = 80.1 + 273.15 = 353.25 K

TT = 111 + 273.15 = 384.15 K

Separation factor according to Rose (p. 256):

Function equation for the equilibrium curve (p. 256):

z. e.g. for the stock consistency in the feed:

Minimum return ratio (p. 257):

Selected (p. 256): v = 2 - vmin = 2 - 2.39 = 4.78

Function equation for the gain line (p. 256):

or straight line between the ordinate intersection point and the intersection point of the perpendicular across x D with the diagonal line

For the ordinate intersection (p. 256):

Intersection with the diagonal: yD = xD

The intersection point line is the perpendicular over xZ , since the feed is boiling liquid. The output line is constructed between the intersection point of the intersection point line with the amplification line and the intersection point of the perpendicular across xB with the diagonal line.

Draw in the steps between the equilibrium curve and the amplification straight line and the equilibrium curve and the output straight line, starting above xD and ending above xB . This results in 7 theoretical steps in the amplifier part and 4 steps in the output part (without considering efficiency and buffer bottoms)