lighter are taken off as an overhead distillate, while the naphtha is removed as the
column’s bottom product. The overhead distillate is then heated again by heat
exchange with hot streams and fed into a depropanizer column. This column also
has about 30–40 distillation trays and separates a butane stream from the propane
and lighter material stream by fractionation. The butanes leave as the column’s
bottom product to become the butane LPG product after further “sweetening”
treatment (sulfur removal). The column’s overhead distillate is fed to a deethanizer
column after preheating. Here the propane is separated from the lighter materials
and leaves the column as the bottom product. This stream becomes part of the
refinery’s propane LPG product after some further “sweetening” treatment. There
will be no overhead distillate product from this unit. The material lighter than
propane leaves the overhead drum as a vapor containing mostly ethane and is
normally routed to the refinery’s fuel gas system.
The debutanized naphtha leaving the bottom of the debutanizer is subsequently
fractionated in the naphtha splitter to give a light naphtha stream as the overhead
distillate and a heavy naphtha as the column’s bottom product. The light naphtha is
essentially C5s and nC6s; this stream is normally sent to the refinery’s gasoline pool
as blending stock. The heavy naphtha stream contains the cycloparaffin components
and the higher paraffin isomers necessary to make good catalytic reformer feed.
This stream therefore is sent to the catalytic reformer after it has been hydrotreated
for sulfur and nitrogen removal.
The light end units are further described and discussed in the chapter entitled
“▶ Distillation of the “Light Ends” from Crude Oil in Petroleum Processing.”
The Catalytic Reformer Unit
The purpose of the catalytic reformer plant is to upgrade low-octane naphtha to the
high-octane material suitable for blending into motor gasoline fuel. It achieves this
by reforming some of the hydrocarbons in the feed to hydrocarbons of high-octane
value. Notably among those reactions is the conversion of cycloparaffin content of
the feed to aromatics. This reaction also gives up hydrogen molecules which are
subsequently used in the refinery’s hydrotreating processes.
The feed from the bottom of the naphtha splitter is hydrotreated in the naphtha
hydrotreater for the removal of sulfur and nitrogen. It leaves this unit to be
preheated to the reforming reaction temperature by heat exchange with products
and by a fired heater. The feed is mixed with a recycle hydrogen stream before
entering the first of (usually) three or four reactors. The reforming reactions take
place in these reactors and the reactor temperatures are sustained and controlled by
intermediate fired heaters. The effluent leaves the last reactor to be cooled and
partially condensed by heat exchange with cold feed and a condenser. This cooled
effluent is routed to a flash drum from which a hydrogen-rich stream is removed as a
gas while reformate is removed as a liquid stream and sent to a stabilizer column.
The bottom from this column is debutanized reformate and is routed to the gasoline
Introduction to Crude Oil and Petroleum Processing
35
column’s bottom product. The overhead distillate is then heated again by heat
exchange with hot streams and fed into a depropanizer column. This column also
has about 30–40 distillation trays and separates a butane stream from the propane
and lighter material stream by fractionation. The butanes leave as the column’s
bottom product to become the butane LPG product after further “sweetening”
treatment (sulfur removal). The column’s overhead distillate is fed to a deethanizer
column after preheating. Here the propane is separated from the lighter materials
and leaves the column as the bottom product. This stream becomes part of the
refinery’s propane LPG product after some further “sweetening” treatment. There
will be no overhead distillate product from this unit. The material lighter than
propane leaves the overhead drum as a vapor containing mostly ethane and is
normally routed to the refinery’s fuel gas system.
The debutanized naphtha leaving the bottom of the debutanizer is subsequently
fractionated in the naphtha splitter to give a light naphtha stream as the overhead
distillate and a heavy naphtha as the column’s bottom product. The light naphtha is
essentially C5s and nC6s; this stream is normally sent to the refinery’s gasoline pool
as blending stock. The heavy naphtha stream contains the cycloparaffin components
and the higher paraffin isomers necessary to make good catalytic reformer feed.
This stream therefore is sent to the catalytic reformer after it has been hydrotreated
for sulfur and nitrogen removal.
The light end units are further described and discussed in the chapter entitled
“▶ Distillation of the “Light Ends” from Crude Oil in Petroleum Processing.”
The Catalytic Reformer Unit
The purpose of the catalytic reformer plant is to upgrade low-octane naphtha to the
high-octane material suitable for blending into motor gasoline fuel. It achieves this
by reforming some of the hydrocarbons in the feed to hydrocarbons of high-octane
value. Notably among those reactions is the conversion of cycloparaffin content of
the feed to aromatics. This reaction also gives up hydrogen molecules which are
subsequently used in the refinery’s hydrotreating processes.
The feed from the bottom of the naphtha splitter is hydrotreated in the naphtha
hydrotreater for the removal of sulfur and nitrogen. It leaves this unit to be
preheated to the reforming reaction temperature by heat exchange with products
and by a fired heater. The feed is mixed with a recycle hydrogen stream before
entering the first of (usually) three or four reactors. The reforming reactions take
place in these reactors and the reactor temperatures are sustained and controlled by
intermediate fired heaters. The effluent leaves the last reactor to be cooled and
partially condensed by heat exchange with cold feed and a condenser. This cooled
effluent is routed to a flash drum from which a hydrogen-rich stream is removed as a
gas while reformate is removed as a liquid stream and sent to a stabilizer column.
The bottom from this column is debutanized reformate and is routed to the gasoline
Introduction to Crude Oil and Petroleum Processing
35