Stripping operating line

Equation 32 represents the upper (or rectifying) operating line equation and equation 33 represents the lower (or stripping) operating line equation. The slopes L jV and L jV can vary, depending on heat effects. 

The McCabe-Thiele method employs the simplifying assumption that the molal overflows in the stripping and the rectification sections are constant. This assumption reduces the rectifying and stripping operating line equations to ... 

Condition of Feed (q Fine). The q line, which marks the transition from rectifying to stripping operating lines, is determined by mass and enthalpy balances around the feed plate. These balances are detailed in distillation texts (15). 

The stripping operating line can be drawn. It is a straight line with slope Ls/Vs that interacts the 45° line at the bottoms composition x. The proof of this construction can be derived by looking at the bottom of the column, as shown in Figure 2.5. Figure 2.6 shows the two operating lines. 

The equations of the rectifying and stripping operating lines are given below in terms of the point of intersection of the two lines at and Xi t-... 

The point of intersection of the enriching and the stripping operating-line equations on an xy plot can be derived as follows. Rewriting Eqs. (11.4-6) and (11.4-10) as follows without the tray subscripts ... 

For the correct method, the shift is made on step 2 to the stripping line, as shown in Fig. 11.4-8b. A total of only about 3.7 steps are needed with the feed on tray 2. To keep the number of trays to a minimum, the shift from the enriching to the stripping operating line should be made at the hrst opportunity after passing the operating-line intersection. 

The stripping operating line is drawn connecting the point y x = Xty = 0.10 with the intersection of the q line and the enriching operating line. Starting at the point y = x = Xj, the theoretical steps are drawn in as shown in Fig. 11.4-9. The number of theoretical steps is 7.6 or 7.6 steps minus a reboiler, which gives 6.6 theoretical trays. The feed is introduced on tray 5 from the top. 

In Fig. 11.4-14 the stripping operating-line equation (11.4-25) is plotted and the q line, Eq. (11.4-19), is also shown for q = 1.0. Starting atXf, the steps are drawn down the tower. 

The flows for a column with a liquid side stream removed above the feed inlet are shown in Fig. 11.4-17. The top enriching operating line above the liquid side stream and the stripping operating line below the feed are found in the usual way. The equation of the q line is also unaffected by the side stream and is found as before. The liquid side stream alters the liquid rate below it, and hence the material balance or operating line in the middle portion between the feed and liquid side stream plates. 

The / values for the first case (liquid feed at the boiling point) is zero, giving a vertical feed line. The intercept of the feed line and the rectifying operating line gives one intercept for stripping operating line (the other intercept is Xb = Yb). 

Draw stripping operating line from Xg point on 45° line to the intersection of the q line with the rectifying operating line. 

Check your calculations by seeing whether the slope of stripping operating line is Ls/V -... 

Start from the Xg point on the 45° line and step up the column from the stripping operating line to the VLB curve. The first step corresponds to the partial reboiler. Hie next step is tray 1, the next is tray 2, and so on. 

---