The Crude Vacuum Distillation Unit
Further breakup of the crude is often required to meet the refinery’s product slate.
This is usually required to produce low-cost feed to cracking units or to produce the
basic stocks for lubricating oil production. To achieve this, the residue from the
atmospheric unit is distilled under subatmospheric conditions in the crude vacuum
distillation unit. This unit is similar to the atmospheric unit in so much as the feed is
heated by heat exchange with hot products and then in a fired heater before entering
the distillation tower. In this case, however, the tower operates under reduced
pressure (vacuum) conditions. These units operate at overhead pressures as low
as 10 mmHg. Under these conditions the hot residue feed is partially vaporized on
entering the tower. The hot vapors rise up the tower to be successively condensed
by a cooled internal reflux stream moving down the tower as was the case in the
atmospheric distillation unit. The condensed distillate streams are taken off as side
stream distillates. There is normally no overhead distillate stream in this case.
The high vacuum required in these units is produced by a series of steam ejectors
attached to the unit’s overhead system. Typical product streams from this unit are as
follows:
Top side stream
Light vacuum gas oil
690–750
F
2nd side stream
Heavy vacuum gas oil
750–985
F
Residue
Bitumen
+985
F
This unit is further described and discussed in the chapter entitled
“▶ Atmospheric and Vacuum Crude Distillation Units in Petroleum Refineries.”
The Light Ends Units
The full-range naphtha distillate as the overhead product from the atmospheric
crude unit is further split into the basic components of the refinery’s volatile and
light oil products. This is accomplished in the light ends plant, which usually
contains four separate distillation units. These are:
• The de-butanizer (or debutanizer)
• The de-propanizer (or depropanizer)
• The de-ethanizer (or deethanizer)
• The naphtha splitter
The most common routing of the full-range naphtha from the atmospheric crude
overhead is first to the debutanizer unit. This feed stream is heated by heat exchange
with hot products before entering the feed tray of the debutanizer column. This is a
distillation column containing between 30 and 40 trays. Separation of butanes and
lighter gas from the naphtha occurs in this tower by fractionation. The butanes and
34
D.S.J. Jones
Further breakup of the crude is often required to meet the refinery’s product slate.
This is usually required to produce low-cost feed to cracking units or to produce the
basic stocks for lubricating oil production. To achieve this, the residue from the
atmospheric unit is distilled under subatmospheric conditions in the crude vacuum
distillation unit. This unit is similar to the atmospheric unit in so much as the feed is
heated by heat exchange with hot products and then in a fired heater before entering
the distillation tower. In this case, however, the tower operates under reduced
pressure (vacuum) conditions. These units operate at overhead pressures as low
as 10 mmHg. Under these conditions the hot residue feed is partially vaporized on
entering the tower. The hot vapors rise up the tower to be successively condensed
by a cooled internal reflux stream moving down the tower as was the case in the
atmospheric distillation unit. The condensed distillate streams are taken off as side
stream distillates. There is normally no overhead distillate stream in this case.
The high vacuum required in these units is produced by a series of steam ejectors
attached to the unit’s overhead system. Typical product streams from this unit are as
follows:
Top side stream
Light vacuum gas oil
690–750
F
2nd side stream
Heavy vacuum gas oil
750–985
F
Residue
Bitumen
+985
F
This unit is further described and discussed in the chapter entitled
“▶ Atmospheric and Vacuum Crude Distillation Units in Petroleum Refineries.”
The Light Ends Units
The full-range naphtha distillate as the overhead product from the atmospheric
crude unit is further split into the basic components of the refinery’s volatile and
light oil products. This is accomplished in the light ends plant, which usually
contains four separate distillation units. These are:
• The de-butanizer (or debutanizer)
• The de-propanizer (or depropanizer)
• The de-ethanizer (or deethanizer)
• The naphtha splitter
The most common routing of the full-range naphtha from the atmospheric crude
overhead is first to the debutanizer unit. This feed stream is heated by heat exchange
with hot products before entering the feed tray of the debutanizer column. This is a
distillation column containing between 30 and 40 trays. Separation of butanes and
lighter gas from the naphtha occurs in this tower by fractionation. The butanes and
34
D.S.J. Jones