500
The Chemistry and Technology of Petroleum
for processing the heavy feedstocks as well as the ubiquitous vacuum or atmospheric residues to
maximizing the value of the heavy crude oil and bitumen.
18.4.1 AsPHAlt CokIng teCHnology (AsCot) ProCess
The ASCOT process is a residual oil upgrading process that integrates the delayed coking process
and the deep solvent deasphalting process (low energy deasphalting, LEDA) (Chapters 18 and 20;
Bonilla, 1985; Bonilla and Elliott, 1987). Removing the deasphalted oil fraction prior to delayed
coking has two benefits: (1) in the coking process, this fraction is thermally cracked to extinction,
degrading this material as an FCC feedstock; and (2) in addition, in thermally cracking, this material to extinction, a significant portion will convert to coke.
In the process, the vacuum residuum is brought to the desired extraction temperature and then
sent to the extractor where solvent (straight run naphtha, coker naphtha) flows upward, extracting
soluble material from the down-flowing feedstock. The solvent-deasphalted phase leaves the top of
the extractor and flows to the solvent recovery system where the solvent is separated from the deasphalted oil and recycled to the extractor. The deasphalted oil is sent to the delayed coker where it
is combined with the HCGO from the coker fractionator and sent to the HCGO stripper where
low-boiling hydrocarbons are stripped off and returned to the fractionator. The stripped deasphalted
oil/HCGO mixture is removed from the bottom of the stripper and used to provide heat to the naphtha stabilizer-reboiler before being sent to battery limits as a cracking stock. The raffinate phase
containing the asphalt and some solvent flows at a controlled rate from the bottom of the extractor
and is charged directly to the coking section.
The solvent contained in the asphalt and deasphalted oil is condensed in the fractionator overhead condensers, where it can be recovered and used as lean oil for a propane/butane recovery in
the absorber, eliminating the need to recirculate lean oil from the naphtha stabilizer. The solvent
introduced in the coker heater and coke drums results in a significant reduction in the partial pressure of asphalt feed, compared with a regular delayed coking unit. The low asphalt partial pressure
results in low coke and high liquid yields in the coking reaction.
With the ASCOT process, there is a significant reduction in by-product fuel as compared to
either solvent deasphalting or delayed coking (Table 18.6) and the process can be tailored to process
a specific quantity or process to a specific quality of cracking stock.
18.4.2 CHerry-P (ComPreHensIve HeAvy ends reFormIng reFInery) ProCess
The Cherry-P process is a process for the conversion of heavy crude oil or residuum into distillate
and a cracked residuum (Speight and Ozum, 2002). In this process, the principal aim is to upgrade
heavy petroleum residues at conditions between those of conventional visbreaking and delayed
coking. Although coal is added to the feedstock, it is mainly intended to act as a scavenger to prevent coke build-up on the reactor wall.
In the process, the feedstock is mixed with coal powder in a slurry mixing vessel, heated in the
furnace and fed to the reactor where the feedstock undergoes thermal cracking reactions for several
hours at a temperature higher than 400°C–450°C (750°F–840°F) and under pressure (70–290 psi).
The residence time is in the range 1–5 h. No catalyst or hydrogen is added. Gas and distillate from
the reactor are sent to a fractionator and the cracked residuum residue is extracted out of the system
after distilling low-boiling fractions by the flash drum and vacuum flasher to adjust its softening
point. Distillable product yields of 44% by weight on total feed are reported (Table 18.7). Since this
yield is obtained when using anthracite, the proportion that is derived from the coal is likely to be
very low.
The distillates produced by this process are generally lower in the content of olefin hydrocarbons
than the other thermal cracking processes, comparatively easy to desulfurize in hydrotreating units,
and compatible with straight run distillates.
The Chemistry and Technology of Petroleum
for processing the heavy feedstocks as well as the ubiquitous vacuum or atmospheric residues to
maximizing the value of the heavy crude oil and bitumen.
18.4.1 AsPHAlt CokIng teCHnology (AsCot) ProCess
The ASCOT process is a residual oil upgrading process that integrates the delayed coking process
and the deep solvent deasphalting process (low energy deasphalting, LEDA) (Chapters 18 and 20;
Bonilla, 1985; Bonilla and Elliott, 1987). Removing the deasphalted oil fraction prior to delayed
coking has two benefits: (1) in the coking process, this fraction is thermally cracked to extinction,
degrading this material as an FCC feedstock; and (2) in addition, in thermally cracking, this material to extinction, a significant portion will convert to coke.
In the process, the vacuum residuum is brought to the desired extraction temperature and then
sent to the extractor where solvent (straight run naphtha, coker naphtha) flows upward, extracting
soluble material from the down-flowing feedstock. The solvent-deasphalted phase leaves the top of
the extractor and flows to the solvent recovery system where the solvent is separated from the deasphalted oil and recycled to the extractor. The deasphalted oil is sent to the delayed coker where it
is combined with the HCGO from the coker fractionator and sent to the HCGO stripper where
low-boiling hydrocarbons are stripped off and returned to the fractionator. The stripped deasphalted
oil/HCGO mixture is removed from the bottom of the stripper and used to provide heat to the naphtha stabilizer-reboiler before being sent to battery limits as a cracking stock. The raffinate phase
containing the asphalt and some solvent flows at a controlled rate from the bottom of the extractor
and is charged directly to the coking section.
The solvent contained in the asphalt and deasphalted oil is condensed in the fractionator overhead condensers, where it can be recovered and used as lean oil for a propane/butane recovery in
the absorber, eliminating the need to recirculate lean oil from the naphtha stabilizer. The solvent
introduced in the coker heater and coke drums results in a significant reduction in the partial pressure of asphalt feed, compared with a regular delayed coking unit. The low asphalt partial pressure
results in low coke and high liquid yields in the coking reaction.
With the ASCOT process, there is a significant reduction in by-product fuel as compared to
either solvent deasphalting or delayed coking (Table 18.6) and the process can be tailored to process
a specific quantity or process to a specific quality of cracking stock.
18.4.2 CHerry-P (ComPreHensIve HeAvy ends reFormIng reFInery) ProCess
The Cherry-P process is a process for the conversion of heavy crude oil or residuum into distillate
and a cracked residuum (Speight and Ozum, 2002). In this process, the principal aim is to upgrade
heavy petroleum residues at conditions between those of conventional visbreaking and delayed
coking. Although coal is added to the feedstock, it is mainly intended to act as a scavenger to prevent coke build-up on the reactor wall.
In the process, the feedstock is mixed with coal powder in a slurry mixing vessel, heated in the
furnace and fed to the reactor where the feedstock undergoes thermal cracking reactions for several
hours at a temperature higher than 400°C–450°C (750°F–840°F) and under pressure (70–290 psi).
The residence time is in the range 1–5 h. No catalyst or hydrogen is added. Gas and distillate from
the reactor are sent to a fractionator and the cracked residuum residue is extracted out of the system
after distilling low-boiling fractions by the flash drum and vacuum flasher to adjust its softening
point. Distillable product yields of 44% by weight on total feed are reported (Table 18.7). Since this
yield is obtained when using anthracite, the proportion that is derived from the coal is likely to be
very low.
The distillates produced by this process are generally lower in the content of olefin hydrocarbons
than the other thermal cracking processes, comparatively easy to desulfurize in hydrotreating units,
and compatible with straight run distillates.