Steam theoretical plates

The hot feed enters the fractionator, which normally contains 30-50 fractionation trays. Steam is introduced at the bottom of the fractionator to strip off light components. The efficiency of separation is a function of the number of theoretical plates of the fractionating tower and the reflux ratio. Reflux is provided by condensing part of the tower overhead vapors. Reflux ratio is the ratio of vapors condensing back to the still to vapors condensing out of the still (distillate). The higher the reflux ratio, the better the separation of the mixture. 

An oil containing 2.55 mole per cent of a hydrocarbon is stripped by running the oil down a column up which live steam is passed, so that 4 kmol of steam are used/100 kmol of oil stripped. Determine the number of theoretical plates required to reduce the hydrocarbon content to 0.05 mole per cent, assuming that the oil is non-volatile. The vapour-liquid relation of the hydrocarbon in the oil is given by ye = 33x, where ye is the mole fraction in the vapour and x the mole fraction in the liquid. The temperature is maintained constant by internal heating, so that steam does not condense in the tower. 

A column vacuum was produced with the eductor, and the operating pressure set to the desired test conditions. Water and steam flows were initiated, and the column was allowed to reach steady state. Steady state was determined by careful monitoring of column temperatures at the reboiler, mid-column, and top of column and confirmed by analysis of vapor and liquid samples drawn from the column sample ports over a 2- to 3-hour period. The height of an equivalent theoretical plate (HETF) of the packing was 19 in., as calculated from vapor and liquid sample compositions. 

It is fed to an absorber where 75% of the propane is recovered. The total amount absorbed is 50 mol/hr. The absorber has four theoretical plates and operates at 135psig and 100°F. All of the absorbed material is recovered in a steam stripper that has a large number of plates and operates at 25 psig and 230°F. 

Why are spinning bands so effective at increasing the number of theoretical plates in distillation columns 5-15. Why is steam distillation often used to isolate and purify naturally occurring plant substances ... 

According to the diagram, tower 1 requires a still and 15 theoretical plates. Since the bottoms of this tower are essentially water, live steam could be used, but if the same phenol recovery (99.99 per cent) were obtained, a total of 20 theoretical plates would be required. The large increase in the number of plates is due to dilution by the large amount of vapor used. If the same bottoms composition had been maintained instead of the same recovery, 16 theoretical plates would be required and the recovery would be 98.9 per cent. 

Fig. 7-3. Approximate steam required to strip when using only a bath of liquid, i.e., only one theoretical plate.

Fig. 7-4. Appro.ximate steam required to strip with three theoretical plates.

Preparation of the urethane, CgHj. NH. COOC,gH,7. A mixture of 2 or 3 grams of the alcohol is mixed with rather more than the theoretical amount of phenyl-isocyanate, and allowed to stand in a stoppered flask for a week. It is then mixed with water, and a current of steam passed through the mixture, in order to remove the unaltered linalol. The crystalline mass which remains is collected, dried on a porous plate, and extracted with ether, which dissolves the phenyl-urethane. The ethereal solution is aflowed to evaporate spontaneously when crystals of the urethane separate, which melt at 65°. 

Nn = Number of theoretical trays above feed, or reference plate, n, but not including n Nm = Number of theoretical trays before feed tray Njra = Mols of immiscible liquid No = Mols of non-volatile material present or, number of theoretical trays/stages in column only, not reboiler or condenser Ng = Mols of steam... 

About 200 g. of solid sodium chloride (Note 7) is added to the flask and the butyl alcohol is removed by steam distillation (Note 8). The alcohol layer is separated while still hot (Note 9), transferred to a t-1. beaker, and heated on a hot plate with stirring until the temperature reaches about 160°. By this time all the water is removed and foaming has stopped (Note 10). The hot liquid is transferred to a i-l. Claisen flask having a 25-cm. fractionating side arm and distilled at 3 mm. After a small fore-run of 5-10 g., the main fraction boils at 177-183°/3 mm. and amounts to 330-340 g. (82-84 per cent of the theoretical amount) (Note 11). 

In a 3-I. beaker are placed 750 cc. of 95 per cent ethyl alcohol and 1.5 g. of finely ground copper sulfate, and the mixture is heated on a hot plate or steam bath to 70°. Ihe diazonium slurry is added in about 30-cc. portions to the well-stirred alcohol the temperature is kept between 60° and 70°, and the nitrogen evolution is allowed to subside considerably between additions. The final traces of diazonium slurry are washed into the alcohol with small amounts of the decanted solution, the remainder of which is then added to the alcohol in loo-cc. portions. The reaction mixture is heated and stirred at 65-70° for half an hour, and then cooled without agitation to 5°. The ffi-iodobenzoic acid which separates is filtered with suction on a Buchner funnel, washed with three 50-cc. portions of cold water, and dried at 90-110°. There is obtained 107-116 g. of crude, brown w-iodobenzoic acid (86-93 per cent of the theoretical amount) (Note r). 

Lower distillation temperatures can be obtained by the use of steam. In this case the steam does not usually condense in the tower, and the plates contain only the high boiling organic material. The steam acts as an inert carrier that is easily condensed and does not have to pass through the vacuum pump. In some cases the temperature gradient in the distillation column may be so great that the steam will condense in the upper portions, and it should be withdrawn. If too much water collects on a plate, it may seriously interfere with the fractionation if the water runs down the tower, it will vaporize on the lower plates and this steam recycle in the tower can overload the unit and seriously interfere with the fractionation. Theoretically it is possible to fractionate a material with a very low vapor pressure by the use of steam distillation, but the steam consumption increases as the vapor pressure on the component decreases. Reduction of the total pressure reduces the steam consumption, but if the vapor pressure of the com-... 

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