Column distillation stripping section

Ethylene Oxide Purification. The main impurities ia ethylene oxide are water, carbon dioxide, and both acetaldehyde and formaldehyde. Water and carbon dioxide are removed by distillation ia columns containing only rectifying or stripping sections. Aldehydes are separated from ethylene... 

Steam used in the sidestream strippers and in the stripping section of the main column is condensed in the overhead condenser. This water settles to the bottom of the distillate dmm and is drawn off through a small water pot in the bottom. In most installations, ammonia gas is injected into the overhead line to raise the pH of this water and reduce corrosion. 

The excess benzene is distilled over a column and used as recycled benzene in the alkylation. In the bottom of the stripping section of the column the raw alkylates, consisting of LAB, heavy alkylate, and excess paraffin, are separated. This mixture is fed to a second column in which the excess paraffin is separated off. The actual purification of the LAB follows in a third column. The bottom product, heavy alkylate, consisting mainly of dialkylbenzene is also separated. Heavy alkylates are used in various applications. Both the paraffin and the LAB column are operated under vacuum. 

The rectifying or stripping section of a column must operate somewhere between total reflux and minimum reflux conditions. The range of feasible operation of a column section can thus be defined for a given product composition. It can be seen in Figure 12.19 that these section profiles are bounded for a stage column by the distillation line and the pinch point curve. As noted previously, the pinch point curve provides a minimum reflux boundary for both staged and packed columns,... 

The component balance equations for reflux drum, column enriching section, feed plate, column stripping section and the column base and reboiler are very similar to those derived previously for the binary distillation example CONSTILL, but are now expressed in multicomponent terms as described in Section 3.3.3.4. 

The idea is best explained with an example. Suppose the base level in a distillation column is normally held by bottoms product withdrawal as shown in Fig. 8.4a. A temperature in the stripping section is held by steam to the rcboiler. Situations can arise where the base level continues to drop even with the bottoms flow at zero (vapor boilup is greater than the liquid rate from tray 1). if no corrective action is taken, the reboiler may boil dry (which could foul the tubes) and the bottoms pump could lose suction. 

Fig. 4.12. Design diagrams for isopropyl acetate (IPOAc) reactive distillation column and comparison with simulation results (solid curves simulated column profile markers = stage composition for column rectifying section + = stage composition for column stripping section).

In a Middle Vessel Batch Distillation Column (MVC) (Figure 2.2) the separation section is divided, as in the usual continuous distillation column, into rectifying and stripping sections, with a feed tray in the middle. The essential features of this type of column are ... 

Referring to Figure 2.2 for MVC column configuration, the model equations for the rectifying section are the same (except the reboiler equations) as those presented for conventional batch distillation column (Type III, IV, V in section 4.2). The model equations for the stripping section are the same (except the condenser equations) as those presented for inverted batch distillation column (Type III, IV, V in section 4.3.2). However, note that the vapour and liquid flow rates in the rectifying and stripping sections will not be same because of the introduction of the feed plate. 

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