The naphthas. There are usually two naphtha cuts produced from most crudes.
These are:
• Light naphtha (sometimes called light gasoline)
• Heavy naphtha
Both these streams are the bottom product of the debutanizer unit. They are
separated in a naphtha splitter tower. The light naphtha contains most of the crude’s
C 5 s and much of the paraffin portion of the crude’s C 6 s. The purpose of making
such a division is to produce a satisfactory heavy naphtha which will contain the
heavier naphthenes and will be a suitable feed for a catalytic reformer (see the
chapter on “▶ Catalytic Reforming in Petroleum Processing”).
The light naphtha has a TBP distillation range of C 5 to around 190
F. The
heavy naphtha is the feed to the catalytic reformer and is a cut on crude of about
190–360
F. This cut point of 360
F can vary depending on the operating severity
of the catalytic reformer, the volatility specification of the finished gasoline for
which the reformate will be a major precursor, and the refinery’s production
requirements. In this latter case, for example, the refinery’s operating plan may
call for maximizing kerosene in which case the atmospheric distillation unit
would be operated to decrease the amount of overhead distillate in order to increase
the kerosene (top side stream) fraction. Of course, if the refinery plan is to
maximize gasoline, the atmospheric tower would be operated to increase the
overhead distillate at the expense of the kerosene fraction.
Straight run kerosene. This fraction is usually the first side stream of a conventional atmospheric distillation unit. It may be cut to meet a burning oil specification
or become a component in Jet Fuel finished product. Its cut range is usually between
360
F and 480
F. Again this cut range may vary with the required heavy end of the
naphtha and the front end of the gas oils. In most cases, this Kero fraction must meet
a flash point specification after it has been steam stripped, and its end cut point is
usually set to meet a smoke point specification. Usually the sulfur content restriction is met by hydrodesulfurization; in some cases too, the smoke point is reduced
by other processes. These subsequent processes are aimed at removing or
converting the aromatic content of the fraction. It can also be routed to the gas oil
pool as a precursor for a diesel finished product.
The atmospheric straight run gas oils. Usually there will be two gas oil side
streams, a light gas oil side stream and, below this take off, a heavy gas oil side
stream. Both these side streams are steam stripped to meet their respective flash
point specification (usually 150
F minimum). The lighter side stream (cut of about
480–610
F on crude) is the principal precursor for the automotive diesel grade
finished product. This side stream is desulfurized to meet the diesel sulfur specification in a hydrotreater (see the chapter “▶ Hydrotreating in Petroleum
Processing”). The lower gas oil stream is really a guard stream to correct the diesel
distillation end point. This heavy gas oil may also be hydrodesulfurized and routed
to either the fuel oil pool (e.g., as a precursor for marine diesel) or to a finished
heating oil product from the gas oil pool.
Petroleum Products and a Refinery Configuration
57
These are:
• Light naphtha (sometimes called light gasoline)
• Heavy naphtha
Both these streams are the bottom product of the debutanizer unit. They are
separated in a naphtha splitter tower. The light naphtha contains most of the crude’s
C 5 s and much of the paraffin portion of the crude’s C 6 s. The purpose of making
such a division is to produce a satisfactory heavy naphtha which will contain the
heavier naphthenes and will be a suitable feed for a catalytic reformer (see the
chapter on “▶ Catalytic Reforming in Petroleum Processing”).
The light naphtha has a TBP distillation range of C 5 to around 190
F. The
heavy naphtha is the feed to the catalytic reformer and is a cut on crude of about
190–360
F. This cut point of 360
F can vary depending on the operating severity
of the catalytic reformer, the volatility specification of the finished gasoline for
which the reformate will be a major precursor, and the refinery’s production
requirements. In this latter case, for example, the refinery’s operating plan may
call for maximizing kerosene in which case the atmospheric distillation unit
would be operated to decrease the amount of overhead distillate in order to increase
the kerosene (top side stream) fraction. Of course, if the refinery plan is to
maximize gasoline, the atmospheric tower would be operated to increase the
overhead distillate at the expense of the kerosene fraction.
Straight run kerosene. This fraction is usually the first side stream of a conventional atmospheric distillation unit. It may be cut to meet a burning oil specification
or become a component in Jet Fuel finished product. Its cut range is usually between
360
F and 480
F. Again this cut range may vary with the required heavy end of the
naphtha and the front end of the gas oils. In most cases, this Kero fraction must meet
a flash point specification after it has been steam stripped, and its end cut point is
usually set to meet a smoke point specification. Usually the sulfur content restriction is met by hydrodesulfurization; in some cases too, the smoke point is reduced
by other processes. These subsequent processes are aimed at removing or
converting the aromatic content of the fraction. It can also be routed to the gas oil
pool as a precursor for a diesel finished product.
The atmospheric straight run gas oils. Usually there will be two gas oil side
streams, a light gas oil side stream and, below this take off, a heavy gas oil side
stream. Both these side streams are steam stripped to meet their respective flash
point specification (usually 150
F minimum). The lighter side stream (cut of about
480–610
F on crude) is the principal precursor for the automotive diesel grade
finished product. This side stream is desulfurized to meet the diesel sulfur specification in a hydrotreater (see the chapter “▶ Hydrotreating in Petroleum
Processing”). The lower gas oil stream is really a guard stream to correct the diesel
distillation end point. This heavy gas oil may also be hydrodesulfurized and routed
to either the fuel oil pool (e.g., as a precursor for marine diesel) or to a finished
heating oil product from the gas oil pool.
Petroleum Products and a Refinery Configuration
57