pool for blending to meet motor gasoline specifications. Part of the gas leaving the
flash drum is recycled to the reactors as the unit’s recycle stream. The remaining gas
is normally sent to the naphtha hydrotreater for use in that process. There is also a
continuous version of this process available.
Details of the catalytic reforming process are described and discussed further in
the chapter entitled “▶ Catalytic Reforming in Petroleum Processing.”
The Hydrotreating Units (de-sulfurization)
Most streams from the crude distillation units contain sulfur and other impurities
such as nitrogen and metals in some form or other. By far the most common of these
impurities is sulfur, and this is also the least tolerable of these impurities. Its
presence certainly lowers the quality of the finished products and, in the processing
of the crude oil, its presence invariably affects the performance of the refining
processes. Hydrotreating the raw distillate streams removes a significant amount of
the sulfur impurity by reacting the sulfur molecules with hydrogen to form hydrogen sulfide (H 2 S); this is then removed as a gas.
Several types of hydrotreaters are described in this book. The two most common
types found are:
• Naphtha hydrotreating – once through or recycle hydrogen
• Diesel hydrotreating – recycle hydrogen
In naphtha hydrotreating the naphtha from the naphtha splitter is mixed with the
hydrogen-rich gas from the catalytic reformer unit and preheated to about 700
F by
heat exchange and a fired heater. On leaving the fired heater, the stream enters a
reactor containing a desulfurizing catalyst (often Co Mo – cobalt molybdenum – on
an alumina base). The sulfur components of the feed combine with the hydrogen to
form H 2 S. The effluent from the reactors is cooled and partially condensed before
being flashed in a separator drum. The gas phase from this drum is still high in
hydrogen content and is usually routed to other downstream hydrogen-using processes. This stream contains most of the H 2 S produced in the reactors; the remainder leaves the flash drum with the desulfurized naphtha liquid to be removed in the
hydrotreater’s stabilizer column as an H 2 S-rich gas.
Diesel hydrotreating has very much the same process configuration as the
naphtha unit. The main difference is that this unit will almost invariably have a
rich hydrogen stream recycle. The recycle is provided by the flashed gas stream
from the flash drum. This is returned to mix with the feed and a fresh hydrogen
make up stream before entering the preheater system. The recycle gas stream in
these units is often treated for the removal of H 2 S before returning to the reactors.
A detailed discussion and description of these processes are given in the chapter
entitled “▶ Hydrotreating in Petroleum Processing.”
36
D.S.J. Jones
flash drum is recycled to the reactors as the unit’s recycle stream. The remaining gas
is normally sent to the naphtha hydrotreater for use in that process. There is also a
continuous version of this process available.
Details of the catalytic reforming process are described and discussed further in
the chapter entitled “▶ Catalytic Reforming in Petroleum Processing.”
The Hydrotreating Units (de-sulfurization)
Most streams from the crude distillation units contain sulfur and other impurities
such as nitrogen and metals in some form or other. By far the most common of these
impurities is sulfur, and this is also the least tolerable of these impurities. Its
presence certainly lowers the quality of the finished products and, in the processing
of the crude oil, its presence invariably affects the performance of the refining
processes. Hydrotreating the raw distillate streams removes a significant amount of
the sulfur impurity by reacting the sulfur molecules with hydrogen to form hydrogen sulfide (H 2 S); this is then removed as a gas.
Several types of hydrotreaters are described in this book. The two most common
types found are:
• Naphtha hydrotreating – once through or recycle hydrogen
• Diesel hydrotreating – recycle hydrogen
In naphtha hydrotreating the naphtha from the naphtha splitter is mixed with the
hydrogen-rich gas from the catalytic reformer unit and preheated to about 700
F by
heat exchange and a fired heater. On leaving the fired heater, the stream enters a
reactor containing a desulfurizing catalyst (often Co Mo – cobalt molybdenum – on
an alumina base). The sulfur components of the feed combine with the hydrogen to
form H 2 S. The effluent from the reactors is cooled and partially condensed before
being flashed in a separator drum. The gas phase from this drum is still high in
hydrogen content and is usually routed to other downstream hydrogen-using processes. This stream contains most of the H 2 S produced in the reactors; the remainder leaves the flash drum with the desulfurized naphtha liquid to be removed in the
hydrotreater’s stabilizer column as an H 2 S-rich gas.
Diesel hydrotreating has very much the same process configuration as the
naphtha unit. The main difference is that this unit will almost invariably have a
rich hydrogen stream recycle. The recycle is provided by the flashed gas stream
from the flash drum. This is returned to mix with the feed and a fresh hydrogen
make up stream before entering the preheater system. The recycle gas stream in
these units is often treated for the removal of H 2 S before returning to the reactors.
A detailed discussion and description of these processes are given in the chapter
entitled “▶ Hydrotreating in Petroleum Processing.”
36
D.S.J. Jones