217
Fractional Composition
The vacuum distillation unit (vacuum pipe still) is a distillation unit that contains a smaller
number of theoretical plates than the atmospheric distillation unit and, again, the side streams are
taken off at different heights up the distillation tower. The atmospheric residuum fractionated to
produce overhead fractions such as vacuum gas oils and lubricating oil distillates, and the bottoms
is a vacuum residuum with an initial boiling point of about 565°C (1050°F), calculated to atmospheric pressure.
The amounts of the various fractions obtained by distillation depend on the nature of the crude
oil, which is reflected in the boiling point profile (Figure 9.2). Clearly, petroleum character is very
important to the refiner in meeting the product demands of customers as well as in determining
what further processing the distillation products may require. For example, the distillates from one
crude oil (e.g., Louisiana crude oil) are suitable feedstocks for lubricating oils and specialty products. On the other hand, the distillates from another crude oil (e.g., Bachaquero crude oil) are more
suitable for use as fuel oil. Thus, the boiling range of petroleum along with its quality is so important to a refiner in meeting the product slate that most refineries must be able to meet any changes
in feedstock quality by adapting the refining options.
In the laboratory (but not always practical in the refinery), lower pressures can be attained
by use of an empty column or a spinning band column. With these, the pressure drop is small
enough that low pressures can be maintained in the reboiler. For instance, with a distillate
pressure of 0.1 mmHg, one may have a pressure of 0.5–1 mmHg in the reboiler that, theoretically, allows the collection of distillates with an AET cut point of as high as 560°C (1050°F).
0
0
2 0
100
200
300
400
500
600
40
60
Louisiana
(a)
Bachaquero
Boiling point, °C
80
100
Volume % distilled
Properties of the 565°C
+ residua:
Louisiana
Gravity, API
Bachaquero
2.8
3.71
0.6
27.5
100
900
55
13.1
0.9
0.4
15.8
20
8
Nitrogen, wt.%
Conradson carbon, wt.%
Nickel, ppm
Vanadium, ppm
Pour point, °C
Sulfur, wt.%
(b)
FIGURE 9.2 (a) Distillation profiles and (b) residua properties for Louisiana and Bachaquero crude oils.
Fractional Composition
The vacuum distillation unit (vacuum pipe still) is a distillation unit that contains a smaller
number of theoretical plates than the atmospheric distillation unit and, again, the side streams are
taken off at different heights up the distillation tower. The atmospheric residuum fractionated to
produce overhead fractions such as vacuum gas oils and lubricating oil distillates, and the bottoms
is a vacuum residuum with an initial boiling point of about 565°C (1050°F), calculated to atmospheric pressure.
The amounts of the various fractions obtained by distillation depend on the nature of the crude
oil, which is reflected in the boiling point profile (Figure 9.2). Clearly, petroleum character is very
important to the refiner in meeting the product demands of customers as well as in determining
what further processing the distillation products may require. For example, the distillates from one
crude oil (e.g., Louisiana crude oil) are suitable feedstocks for lubricating oils and specialty products. On the other hand, the distillates from another crude oil (e.g., Bachaquero crude oil) are more
suitable for use as fuel oil. Thus, the boiling range of petroleum along with its quality is so important to a refiner in meeting the product slate that most refineries must be able to meet any changes
in feedstock quality by adapting the refining options.
In the laboratory (but not always practical in the refinery), lower pressures can be attained
by use of an empty column or a spinning band column. With these, the pressure drop is small
enough that low pressures can be maintained in the reboiler. For instance, with a distillate
pressure of 0.1 mmHg, one may have a pressure of 0.5–1 mmHg in the reboiler that, theoretically, allows the collection of distillates with an AET cut point of as high as 560°C (1050°F).
0
0
2 0
100
200
300
400
500
600
40
60
Louisiana
(a)
Bachaquero
Boiling point, °C
80
100
Volume % distilled
Properties of the 565°C
+ residua:
Louisiana
Gravity, API
Bachaquero
2.8
3.71
0.6
27.5
100
900
55
13.1
0.9
0.4
15.8
20
8
Nitrogen, wt.%
Conradson carbon, wt.%
Nickel, ppm
Vanadium, ppm
Pour point, °C
Sulfur, wt.%
(b)
FIGURE 9.2 (a) Distillation profiles and (b) residua properties for Louisiana and Bachaquero crude oils.