Column distillation rectifying section

Weak nitric acid (normally 60 wt% HNO3) and concentrated magnesium nitrate solution (72 wt% Mg(NC>3)2) enter at the feed point of an extractive distillation column. The rectifying section above the feed point has a water-cooled... 

The rectifying section contains three or four bubble cap (wine) plates in the top section of the stiU to produce distillates up to 160° proof. Whiskey stills are usually made of copper, especially in the rectifying section, which often yields a superior product. Additional copper surface in the upper section of the column may be provided by a demister, a flat disk of copper mesh. Stainless steel is also used in some stills. 

In the use of temperature measurement for control of the separation in a distillation column, repeatability is crucial but accuracy is not. Composition control for the overhead product would be based on a measurement of the temperature on one of the trays in the rectifying section. A target would be provided for this temperature. However, at periodic intervals, a sample of the overhead product is analyzed in the laboratory and the information provided to the process operator. Should this analysis be outside acceptable limits, the operator would adjust the set point for the temperature. This procedure effectively compensates for an inaccurate temperature measurement however, the success of this approach requires good repeatability from the temperature measurement. 

For the stripping and rectifying sections to become a feasible column, the two operation leaves must overlap. Figure 12.20 shows the system chloroform, benzene and acetone. The operation leaf for a distillate composition D intersects with the operation leaf for a bottoms composition... 

In the use of temperature measurement for control of the separation in a distillation column, repeatability is crucial but accuracy is not. Composition control for the overhead product would be based on a measurement of the temperature on one of the trays in the rectifying section. A target would be provided for this temperature. However, at... 

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. 

Figure 6.12 illustrates this effect. As more LLK component comes in with the feed stream, more depression occurs in the rectifying section temperature profile. If we control a tray temperature near the top and the amount of LLK in the feed increases, the temperature on this tray will start to go down. We will increase heat input to drive it back to its setpoint value, and this will push more HK component out the top. Therefore holding a constant temperature on a tray near the top of the column w ould result in significant variations in the amount of heavy key component in the distillate product. All of the LLK components must go out the top of the column, and there is nothing we can do about it once these components enter the column. Action must be taken in the upstream column to keep LLK components out of this column. Similar effects occur in the stripping section and near the base when variations occur in the amount of HHK components in the feed. Now temperatures rise as more heavy components enter the column, and we drop more LK component into the bottoms product if we hold a constant temperature on a tray near the base of the column. 

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