505
Thermal Cracking
carbon monoxide (CO), hydrogen (H 2 ), carbon dioxide (CO 2 ), and hydrogen sulfide (H 2 S) with steam
and air. Regenerated hot particles are returned to the cracker.
Excess coke formation due to the presence of nickel and vanadium in the feedstock is effectively
avoided by the low pressure.
18.4.7 HIgH ConversIon soAker CrACkIng ProCess
The high conversion soaker cracking process (HSC process) is a cracking process designed for
moderate conversion, higher than visbreaking but lower than coking (Table 18.11; Watari et al.,
1987; Washimi, 1989). The process features less gas make and a higher yield of distillate compared
to other thermal cracking processes. The process can be used to convert a wide range of feedstocks
with high sulfur and metals content, including heavy oils, oil sand bitumen, residua, and visbroken
residua.
The process utilizes the unique technology of the original Eureka process, such as the injection
of superheated steam into the reaction atmosphere and the handling of pitch in a molten state. It also
combines a cracking heater with a high conversion rate and a single flow-type reactor. In comparison with the original Eureka process, the advantages offered by the ET-II process are lower capital
investment; lower operating cost; higher yield of lighter distillates. The cracked oil products can
also be processed in secondary upgrading processes and the pitch can then be utilized as a form of
pitch water slurry fuel. The HSC process both employs continuous reactors, whereas the original
Eureka process uses two batch reactors.
The preheated feedstock enters the bottom of the fractionator, where it is mixed with the recycle
oil. The mixture is pumped up to the charge heater and fed to the soaking drum (ca. atmospheric
pressure, steam injection at the top and bottom), where sufficient residence time is provided to complete the thermal cracking. In the soaking drum, the feedstock and some product flows downward
passing through a number of perforated plates while steam with cracked gas and distillate vapors
flow through the perforated plates counter-currently.
The volatile products from the soaking drum enter the fractionator where the distillates are fractionated into desired product oil streams, including a heavy gas oil fraction. The cracked gas product is
TABLE 18.10
Feedstock and Product Data for the FTC Process
Feedstock: Bachaquero, Khafji, and Maya Vacuum Residua Mix
API
6.4
Sulfur, % w/w
4.5
Carbon residue, % w/w
21.9
Nickel + vanadium, ppm
500.0
Products
Naphtha (C5-150°C, C5-300°F), % w/w
14.9
API
57.1
Sulfur, % w/w
0.4
Middle distillate (150°C–310°C, 300°F–590°F), wt.%
34.4
API
39.5
Sulfur, % w/w
1.4
Heavy distillate (310°C–525°C, 590°F–975°F), wt.%
21.8
API
18.7
Sulfur, % w/w
3.1
Nitrogen, % w/w%
0.2
Coke
19.0 (estimate)
Thermal Cracking
carbon monoxide (CO), hydrogen (H 2 ), carbon dioxide (CO 2 ), and hydrogen sulfide (H 2 S) with steam
and air. Regenerated hot particles are returned to the cracker.
Excess coke formation due to the presence of nickel and vanadium in the feedstock is effectively
avoided by the low pressure.
18.4.7 HIgH ConversIon soAker CrACkIng ProCess
The high conversion soaker cracking process (HSC process) is a cracking process designed for
moderate conversion, higher than visbreaking but lower than coking (Table 18.11; Watari et al.,
1987; Washimi, 1989). The process features less gas make and a higher yield of distillate compared
to other thermal cracking processes. The process can be used to convert a wide range of feedstocks
with high sulfur and metals content, including heavy oils, oil sand bitumen, residua, and visbroken
residua.
The process utilizes the unique technology of the original Eureka process, such as the injection
of superheated steam into the reaction atmosphere and the handling of pitch in a molten state. It also
combines a cracking heater with a high conversion rate and a single flow-type reactor. In comparison with the original Eureka process, the advantages offered by the ET-II process are lower capital
investment; lower operating cost; higher yield of lighter distillates. The cracked oil products can
also be processed in secondary upgrading processes and the pitch can then be utilized as a form of
pitch water slurry fuel. The HSC process both employs continuous reactors, whereas the original
Eureka process uses two batch reactors.
The preheated feedstock enters the bottom of the fractionator, where it is mixed with the recycle
oil. The mixture is pumped up to the charge heater and fed to the soaking drum (ca. atmospheric
pressure, steam injection at the top and bottom), where sufficient residence time is provided to complete the thermal cracking. In the soaking drum, the feedstock and some product flows downward
passing through a number of perforated plates while steam with cracked gas and distillate vapors
flow through the perforated plates counter-currently.
The volatile products from the soaking drum enter the fractionator where the distillates are fractionated into desired product oil streams, including a heavy gas oil fraction. The cracked gas product is
TABLE 18.10
Feedstock and Product Data for the FTC Process
Feedstock: Bachaquero, Khafji, and Maya Vacuum Residua Mix
API
6.4
Sulfur, % w/w
4.5
Carbon residue, % w/w
21.9
Nickel + vanadium, ppm
500.0
Products
Naphtha (C5-150°C, C5-300°F), % w/w
14.9
API
57.1
Sulfur, % w/w
0.4
Middle distillate (150°C–310°C, 300°F–590°F), wt.%
34.4
API
39.5
Sulfur, % w/w
1.4
Heavy distillate (310°C–525°C, 590°F–975°F), wt.%
21.8
API
18.7
Sulfur, % w/w
3.1
Nitrogen, % w/w%
0.2
Coke
19.0 (estimate)