heated to remove the “kerosene” fraction. The residue from this still is a very light fuel
oil which may be further heated and partially vaporized to give a pitch of sorts as a
residue and a distillate which could be used as fuel. This distillate would later become
the diesel or gas oil fraction and be used in the development of the diesel engine.
The vapor from each still passes through a small packed wash section before
being condensed and collected in a condensate drum. A portion of the condensate is
returned to the top of the wash section as the wash liquid, similar to the reflux
stream in modern distillation towers. Usually steam was injected through the liquid
phase of each still to facilitate vaporization and to strip out the light ends.
This type of crude distillation was superseded by the continuous fractionation
tower used in modern petroleum refining. This type of crude “still” remained in
operation well after World War II in some oil refineries. The author recalls such a still
in operation as late as 1956 in the refinery where he was employed, although there
were also in operation three other modern crude oil fractionating units. Indeed, one
major oil company even today calls the crude distillation unit a “pipestill.” This
chapter now continues with the description of a present-day atmospheric and vacuum
crude oil distillation units. It will be divided into two parts:
• The atmospheric crude distillation unit (CDU)
• The vacuum crude distillation unit (VDU)
Both parts will contain a process description with a schematic flow sheet, a
discussion on the development of the material balance, a description and discussion
on the design characteristics of the units, and finally a worked design example.
It is common to use process simulation software (HYSYS, Pro/II, and others) to
perform the design calculations for crude and vacuum units. This allows case
studies to optimize the process design. The details of the computer simulations
are beyond the scope of this Handbook.
The manual approach to the calculations is described here. It is helpful to
understand this approach to establish the background and limitations behind the
computerized calculations.
The Atmospheric Crude Distillation Unit
Process Description
The first process encountered in any conventional refinery is the atmospheric crude
distillation unit. In this unit the crude oil is distilled to produce distillate streams
which will be the basic streams for the refinery product slate. These streams will
either be subject to further treating downstream or become feedstock for conversion
units that may be in the refinery configuration. A schematic flow diagram of an
atmospheric crude unit is shown in Fig. 2.
Crude oil is pumped from storage to be heated by exchange against hot overhead
and product side streams in the Crude Unit. At a preheat temperature of about
Atmospheric and Vacuum Crude Distillation Units in Petroleum Refineries
127
oil which may be further heated and partially vaporized to give a pitch of sorts as a
residue and a distillate which could be used as fuel. This distillate would later become
the diesel or gas oil fraction and be used in the development of the diesel engine.
The vapor from each still passes through a small packed wash section before
being condensed and collected in a condensate drum. A portion of the condensate is
returned to the top of the wash section as the wash liquid, similar to the reflux
stream in modern distillation towers. Usually steam was injected through the liquid
phase of each still to facilitate vaporization and to strip out the light ends.
This type of crude distillation was superseded by the continuous fractionation
tower used in modern petroleum refining. This type of crude “still” remained in
operation well after World War II in some oil refineries. The author recalls such a still
in operation as late as 1956 in the refinery where he was employed, although there
were also in operation three other modern crude oil fractionating units. Indeed, one
major oil company even today calls the crude distillation unit a “pipestill.” This
chapter now continues with the description of a present-day atmospheric and vacuum
crude oil distillation units. It will be divided into two parts:
• The atmospheric crude distillation unit (CDU)
• The vacuum crude distillation unit (VDU)
Both parts will contain a process description with a schematic flow sheet, a
discussion on the development of the material balance, a description and discussion
on the design characteristics of the units, and finally a worked design example.
It is common to use process simulation software (HYSYS, Pro/II, and others) to
perform the design calculations for crude and vacuum units. This allows case
studies to optimize the process design. The details of the computer simulations
are beyond the scope of this Handbook.
The manual approach to the calculations is described here. It is helpful to
understand this approach to establish the background and limitations behind the
computerized calculations.
The Atmospheric Crude Distillation Unit
Process Description
The first process encountered in any conventional refinery is the atmospheric crude
distillation unit. In this unit the crude oil is distilled to produce distillate streams
which will be the basic streams for the refinery product slate. These streams will
either be subject to further treating downstream or become feedstock for conversion
units that may be in the refinery configuration. A schematic flow diagram of an
atmospheric crude unit is shown in Fig. 2.
Crude oil is pumped from storage to be heated by exchange against hot overhead
and product side streams in the Crude Unit. At a preheat temperature of about
Atmospheric and Vacuum Crude Distillation Units in Petroleum Refineries
127