of super fractionating units with over a hundred trays in many cases, this has to be a
primary consideration.
There are many light ends tower computer simulation packages in the market,
and most of these calculate vapor and liquid traffic in the tower on a tray-to-tray
basis. The input for these programs however does require a fairly accurate estimate
of these values for easy convergence and subsequent use of the program. The
following procedure with the equations used can provide details of tower loading
and tray criteria at critical trays in the tower. A linear correlation between these
points will then provide a reasonable loading profile over the tower sufficient for
good computer input.
Tower Loading and Overall Tower Diameter
The diameter of a fractionating tower is usually based on the vapor loading on two
critical trays. These are the tower top tray which will set the diameter for the
rectifying section (i.e., the trays above the feed tray) and the tower bottom tray. This
lower tray sets the tower diameter for the stripping section of the tower (i.e., the
feed tray and the trays below the feed tray). These two sections may have different
diameters.
The vapor loading is based on the rate of vapor passing through the tray and the
density of the vapor and the liquid on the tray through which the vapor bubbles.
This relationship is given by the Brown and Souders equation. There are several
400
390
370
350
330
310
290
270
250
230
210
190
170
150
130
1
F
3
5
7
9 11 13
TRAY NUMBER
15 17 19 21 23 25 27 2930
TRAY 30
TEMP =
357F
REBOILER
AND TOWER
BOTTOM
Fig. 4 Tower temperature profile
Distillation of the ‘‘Light Ends´´ from Crude Oil in Petroleum Processing
217
primary consideration.
There are many light ends tower computer simulation packages in the market,
and most of these calculate vapor and liquid traffic in the tower on a tray-to-tray
basis. The input for these programs however does require a fairly accurate estimate
of these values for easy convergence and subsequent use of the program. The
following procedure with the equations used can provide details of tower loading
and tray criteria at critical trays in the tower. A linear correlation between these
points will then provide a reasonable loading profile over the tower sufficient for
good computer input.
Tower Loading and Overall Tower Diameter
The diameter of a fractionating tower is usually based on the vapor loading on two
critical trays. These are the tower top tray which will set the diameter for the
rectifying section (i.e., the trays above the feed tray) and the tower bottom tray. This
lower tray sets the tower diameter for the stripping section of the tower (i.e., the
feed tray and the trays below the feed tray). These two sections may have different
diameters.
The vapor loading is based on the rate of vapor passing through the tray and the
density of the vapor and the liquid on the tray through which the vapor bubbles.
This relationship is given by the Brown and Souders equation. There are several
400
390
370
350
330
310
290
270
250
230
210
190
170
150
130
1
F
3
5
7
9 11 13
TRAY NUMBER
15 17 19 21 23 25 27 2930
TRAY 30
TEMP =
357F
REBOILER
AND TOWER
BOTTOM
Fig. 4 Tower temperature profile
Distillation of the ‘‘Light Ends´´ from Crude Oil in Petroleum Processing
217