aromatics and olefins) by solvent extraction. This is accomplished prior to the
stream being dewaxed and routed to storage. The heavy vacuum residue from the
vacuum tower is routed to a propane deasphalting unit. Here, the very thick
bituminous asphaltenes are removed by extraction with liquid propane. The
raffinate from this extraction process is the heaviest lube oil blending stream
commonly called bright stock. This stream is also routed to the solvent extraction
unit and the dewaxing process before storage.
Solvent extraction is accomplished in a trayed column by contacting the oil feed
and solvent countercurrently in the tower. The lighter raffinate stream leaves the top
of the tower to be stripped free of the solvent in an associated stripper column,
before entering the dewaxing unit. The extracted components leave the bottom of
the tower also to be stripped free of the solvent in an associated stripper column.
The extract in this case may be routed to the propane deasphalting unit or simply
sent to the refinery fuel supply. The solvent in modern refineries is either furfural,
phenol, or a proprietary solvent based on either of these chemicals. In earlier plants
oleum or liquid SO 2 was used for this purpose.
The oil streams routed to the dewaxing plant are contacted and mixed with a
crystallizing agent such as methyl-ethyl-ketone (MEK) before entering a series of
chiller tubes. Here the oil/MEK mix is reduced in temperature to a degree that the wax
contained in the oil crystallizes out. The stream with the wax now in suspension enters
a series of drum filters where the wax and oil are separated. Both streams are stripped
free of the MEK in separate columns. The MEK is recycled while the dewaxed oil is
sent to storage and blending. The wax may be retained as a solid in a suitably
furnished warehouse or remelted and stored in special tanks with inert gas cover.
The asphalt from the propane deasphalting unit is stripped free of propane and any
other light ends using inert gas as the stripping agent. It leaves the unit to proceed
either directly to the bitumen pool or to be further treated by air blowing. The
air-blowing process increases the hardness of the bitumen where this is required to
meet certain specifications. It is accomplished either as a batch process or on a
continuous basis. The hot stripped asphalt from the deasphalting unit enters the air
blower reactor under level control (if the process is continuous). Air is introduced via a
small compressor to the bottom of the reactor vessel and allowed to bubble up through
the hot oil phase. The air removes some of the heavy entrained oils in the asphalt and
reacts mildly to partially oxidize the asphaltenes. The hot oil vapors and the unused air
leaves the top of the reactor to be burned in a suitably designed incinerator. The blown
asphalt leaves the reactor as a side stream to bitumen storage or blending.
The production of lube oils usually takes place in a section of an energy refinery.
The various grades of the oils are also produced in a blocked operation using
storage facilities between the units. This is feasible as the amount of lube oils
required to be produced is relatively small and normally does not justify separate
treating facilities for each grade.
The lube oil refinery is further detailed in the chapter “▶ Non-energy Refineries
in Petroleum Processing.”
46
D.S.J. Jones
stream being dewaxed and routed to storage. The heavy vacuum residue from the
vacuum tower is routed to a propane deasphalting unit. Here, the very thick
bituminous asphaltenes are removed by extraction with liquid propane. The
raffinate from this extraction process is the heaviest lube oil blending stream
commonly called bright stock. This stream is also routed to the solvent extraction
unit and the dewaxing process before storage.
Solvent extraction is accomplished in a trayed column by contacting the oil feed
and solvent countercurrently in the tower. The lighter raffinate stream leaves the top
of the tower to be stripped free of the solvent in an associated stripper column,
before entering the dewaxing unit. The extracted components leave the bottom of
the tower also to be stripped free of the solvent in an associated stripper column.
The extract in this case may be routed to the propane deasphalting unit or simply
sent to the refinery fuel supply. The solvent in modern refineries is either furfural,
phenol, or a proprietary solvent based on either of these chemicals. In earlier plants
oleum or liquid SO 2 was used for this purpose.
The oil streams routed to the dewaxing plant are contacted and mixed with a
crystallizing agent such as methyl-ethyl-ketone (MEK) before entering a series of
chiller tubes. Here the oil/MEK mix is reduced in temperature to a degree that the wax
contained in the oil crystallizes out. The stream with the wax now in suspension enters
a series of drum filters where the wax and oil are separated. Both streams are stripped
free of the MEK in separate columns. The MEK is recycled while the dewaxed oil is
sent to storage and blending. The wax may be retained as a solid in a suitably
furnished warehouse or remelted and stored in special tanks with inert gas cover.
The asphalt from the propane deasphalting unit is stripped free of propane and any
other light ends using inert gas as the stripping agent. It leaves the unit to proceed
either directly to the bitumen pool or to be further treated by air blowing. The
air-blowing process increases the hardness of the bitumen where this is required to
meet certain specifications. It is accomplished either as a batch process or on a
continuous basis. The hot stripped asphalt from the deasphalting unit enters the air
blower reactor under level control (if the process is continuous). Air is introduced via a
small compressor to the bottom of the reactor vessel and allowed to bubble up through
the hot oil phase. The air removes some of the heavy entrained oils in the asphalt and
reacts mildly to partially oxidize the asphaltenes. The hot oil vapors and the unused air
leaves the top of the reactor to be burned in a suitably designed incinerator. The blown
asphalt leaves the reactor as a side stream to bitumen storage or blending.
The production of lube oils usually takes place in a section of an energy refinery.
The various grades of the oils are also produced in a blocked operation using
storage facilities between the units. This is feasible as the amount of lube oils
required to be produced is relatively small and normally does not justify separate
treating facilities for each grade.
The lube oil refinery is further detailed in the chapter “▶ Non-energy Refineries
in Petroleum Processing.”
46
D.S.J. Jones