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The Chemistry and Technology of Petroleum
from the vacuum flasher can be routed to fuel oil blending or can be used internally as refinery
fuel. The recycling of heavy gas oil from both the vacuum flasher and the combi tower to the distillate heater means that all of the heavy gas oil is converted. Light gas oil from the combi tower
is first stripped, and is then routed to a hydrotreater. Alternatively, the light gas oil can be used
as cutter stock.
TAR
Steam
Gas
Naphtha
Gasoil
Vacuum
flashed
1 Combi tower
2 Distillate heater
3 Shell vacuum flasher
1
3
2
Distillate
feed
FIGURE 18.9 The shell thermal distillate cracking technology.
LGO
HGO
or
VGO
Residue
Lighter
150°C–180°C
320°C–370°C
520°C–600°C
FIGURE 18.8 Basic principle of the shell thermal distillate cracking technology.