Water cooler
Gas
Heat recovery
Air cooler
Separator
Wash water
Wild naphtha-re ux pump
Crude column
Crude charge pump
Re ux
(In case of Pre-frac.)
Crude
3 stage ejectors + LRVP
SS1
Sour water pump
Heavy naphtha Steam
Steam
PA1
Vacuum column
SS2
Pre- ash drum/ Pre-fractionator
PA2
Preheat-1
Vac. diesel
PA4
Steam
Kerosene
Gas
PA3
(In case of Pre-frac.)
SS3
Steam
Hot well
LVGO
PA5
Separator
Diesel
CDU Over ash
Desalter
HVGO
(Absence of Pre- ash/Pre-frac.)
PA6
Sour water pump
Slop oil pump
Heat recovery
Steam
CDU wash oil pump
Sour water
VDU Over ash
Partition Plate with downpipe/ downcomer
CDU ash drum
(Self draining)
Fired heater
Fired heater
Steam
VR
Coil steam
Single stage ejectors
Preheat-2
VDU wash oil pump
RCO pump
(In case of Pre- ash/Pre-frac.)
Figure 4 Novel CDU-VDU configuration suits revamp scenario of existing refinery with minimum modifications
to ~370°C in the furnace and initially flashed in a CDU flash drum, where the separated vapours are routed to the CDU rectification section above the partition plate, while the liquid stream is introduced below the partition into the stripping section. The vapours undergo steam-free (dry) rectification, yielding naphtha, kerosene, and diesel, while the RCO in the lower section is contacted with LP steam (2-3 bar) to recover lighter components. This dual- flash arrangement minimises entrainment by segregating vapour-liquid traffic across the partition, thereby improving separation efficiency. The CDU stripper overheads from below the partition are condensed in shell-and-tube exchangers, providing heat integration to the preheat train. The condensed hydrocarbon fraction (wash oil) is routed to the section above the flash zone in the rectification zone, ensuring improved liquid distribution and effective scrubbing of entrained metals and heavy components before carryover into lighter fractions. This is particularly evident in improved diesel quality. The RCO is subsequently routed to the VDU furnace, where it is heated to a controlled COT
of up to ~400°C to minimise thermal cracking and prevent loss of valuable distillates. It is then initially flashed in a VDU flash drum, where vapours are routed above the partition into the rectification section, while the remaining liquid is introduced below the partition into the stripping section. The vapours undergo steam-free (dry) rectification to produce VD, LVGO, and HVGO, while the bottom stream is contacted with LP stripping steam to yield VR. This dual-flash and partition-based arrangement, analogous to the CDU configuration, delivers similar benefits in terms of reduced entrainment and improved separation efficiency. The VDU stripper overhead vapours are condensed in baffle condensers, where the significant boiling point difference between hydrocarbons and steam enables near-complete condensation of hydrocarbon components. The condensed hydrocarbon fraction (wash oil) is routed above the flash zone, enhancing scrubbing efficiency and reducing entrainment of metals into HVGO. This improved recovery of hydrocarbons significantly reduces slop generation and enhances overall distillate recovery. The uncondensed steam is recovered and routed through an ejector system to
Refining India
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