As can be seen, the use of lift gas as an alternative to steam gives:
• Lower hydrogen production
• Lower hydrogen/methane ratio
• Increase in liquid yield
Residuum Hydrocracking
Residuum hydrocracking is often combined with a thermal cracker to upgrade
the “bottom of the barrel” and provide high-quality light and middle distillates.
Figure 15 shows such a configuration for a fixed-bed cracking unit (there are also
fluid bed resid hydrocrackers not covered here).
Bitumen feed from the crude vacuum distillation unit enters the hydrocracker
section of the plant to be preheated by hot flash vapors in shell and tube
exchangers and finally in a fired heater. A recycle and makeup hydrogen stream
is similarly heated by exchange with hot flash vapors. The hydrogen stream is
mixed with the hot bitumen stream before entering the hydrocracker heater. The
feed streams are risen to the reactor temperature in the heater and leave to enter
the top of the reactor vessel. The feed streams flow downward through the catalyst
beds contained in the reactor. Additional cold hydrogen is injected at various
sections of the reactor to provide temperature control as the hydrocracking
process is exothermal.
The reactor effluent leaves the reactor to enter a hot flash drum. Here the
heavy bituminous portion of the effluent leaves from the bottom of the
drum while the lighter oil and gas phase leaves as a vapor from the top of
the drum. This vapor is subsequently cooled by heat exchange with the feed
and further cooled and partially condensed by an air cooler. This cooled
stream then enters a cold separator operating at a pressure only slightly lower
than that of the reactor. A rich hydrogen gas stream is removed from this drum to
be amine treated and returned as recycle gas to the process. The distillate liquid
leaves from the bottom of the separator to join a vapor stream from the hot flash
surge drum (thermal cracker feed surge drum). Both these streams enter the cold
flash drum which operates at a much lower pressure than the upstream equipment.
A gas stream is removed from the drum to be routed to an absorber unit.
The liquid distillate from the drum is routed to the debutanizer in a light-ends
recovery unit.
The thermal cracking section of the unit takes as feed the heavy bituminous
liquid from the hot flash drum. This enters the cracker heater via a surge drum. This
heater has two parallel coils. The oil feed enters these coils to be thermally cracked
to form some lighter products. The stream leaving the heater is quenched before
entering a flash chamber. This vessel contains some baffled trays and a light gas and
oil vapor stream leaves overhead. This stream is subsequently cooled and the
distillate formed routed to the cold flash drum. The bottoms from the flash chamber
Upgrading the Bottom of the Barrel
553
• Lower hydrogen production
• Lower hydrogen/methane ratio
• Increase in liquid yield
Residuum Hydrocracking
Residuum hydrocracking is often combined with a thermal cracker to upgrade
the “bottom of the barrel” and provide high-quality light and middle distillates.
Figure 15 shows such a configuration for a fixed-bed cracking unit (there are also
fluid bed resid hydrocrackers not covered here).
Bitumen feed from the crude vacuum distillation unit enters the hydrocracker
section of the plant to be preheated by hot flash vapors in shell and tube
exchangers and finally in a fired heater. A recycle and makeup hydrogen stream
is similarly heated by exchange with hot flash vapors. The hydrogen stream is
mixed with the hot bitumen stream before entering the hydrocracker heater. The
feed streams are risen to the reactor temperature in the heater and leave to enter
the top of the reactor vessel. The feed streams flow downward through the catalyst
beds contained in the reactor. Additional cold hydrogen is injected at various
sections of the reactor to provide temperature control as the hydrocracking
process is exothermal.
The reactor effluent leaves the reactor to enter a hot flash drum. Here the
heavy bituminous portion of the effluent leaves from the bottom of the
drum while the lighter oil and gas phase leaves as a vapor from the top of
the drum. This vapor is subsequently cooled by heat exchange with the feed
and further cooled and partially condensed by an air cooler. This cooled
stream then enters a cold separator operating at a pressure only slightly lower
than that of the reactor. A rich hydrogen gas stream is removed from this drum to
be amine treated and returned as recycle gas to the process. The distillate liquid
leaves from the bottom of the separator to join a vapor stream from the hot flash
surge drum (thermal cracker feed surge drum). Both these streams enter the cold
flash drum which operates at a much lower pressure than the upstream equipment.
A gas stream is removed from the drum to be routed to an absorber unit.
The liquid distillate from the drum is routed to the debutanizer in a light-ends
recovery unit.
The thermal cracking section of the unit takes as feed the heavy bituminous
liquid from the hot flash drum. This enters the cracker heater via a surge drum. This
heater has two parallel coils. The oil feed enters these coils to be thermally cracked
to form some lighter products. The stream leaving the heater is quenched before
entering a flash chamber. This vessel contains some baffled trays and a light gas and
oil vapor stream leaves overhead. This stream is subsequently cooled and the
distillate formed routed to the cold flash drum. The bottoms from the flash chamber
Upgrading the Bottom of the Barrel
553