Page 339 - Distillation theory

P1: JPJ/FFX P2: FCH/FFX QC: FCH/FFX T1: FCH
0521820928c08 CB644-Petlyuk-v1 June 11, 2004 20:20

8.7 Petroleum Mixtures 313

a)
D
N

N f
F
T
st B

b) V/F, %
1
2

st/F, %
Figure 8.30. A temperature profile of column with steam
stripping (a) and fraction of feed vaporized V/F as function
of mass flow rate of steam st/F (b). 1, steam-heated reboiler;
2, live steam.

temperature is achieved, not in the bottom, but in feed cross-section
(Fig. 8.30).
2. It is necessary to keep in the feed cross-section the lowest possible pressure,
which provides the possibility to obtain a maximum fraction of vapor phase
in the feeding and a maximum vapor flow rate in the column.
3. It is necessary to increase the number of theoretical trays in sections ad-
jacent to feed cross-section, where the most valuable products are being
separated from the less valuable ones.
4. In feeding of the column, where the most valuable products are being
separated from the less valuable ones, the fraction of light components
that have stripping influence on the rest of components should be as large
as possible.
Figure 8.31 shows the calculation dependence of the output of light oil products
(benzine + kerosene + diesel oil) on the pressure in the column and on the number
of trays in the first section above the feed cross-section (West Siberian petroleum).
The above-listed methods of separability increase require some increase of
capital expenditures (an increase in the column diameter – item 1, 2, and 4, an
increase in the column height – item 3).

8.7.3. The Best Distillation Complex for Petroleum Refining

Columns with side stripping sections were used for petroleum separation already
in the first decades of twentieth century. This choice is quite grounded by the main
purposes of designing: increase of separability, and decrease of energy and capital
expenditures on separation.