Revamping CDU-VDU configurations
A cost-effective retrofit for enhanced efficiency and net-zero ambitions in Indian refineries
Ramanayya Gorle, Grandhi Srivardhan, Narendra Kumar Paladugu, and Anil Kumar Engineers India Limited
I ndia’s r efining sector plays a critical role in supporting economic growth, processing a wide spectrum of crudes – from light Bombay High to heavy imported blends. Crude distillation units (CDU) and vacuum distillation units (VDU) form the core, fractionating more than 50% of the output into naphtha, kerosene, diesel, and vacuum gas oil (VGO). However, these units consume nearly 30% of the total refinery energy, posing a significant challenge to the country’s net-zero emission ambitions by 2070. In a typical CDU-VDU configuration, the CDU separates lighter fractions at atmospheric pressure, while the VDU processes heavier
residues under vacuum to recover vacuum diesel (VD), vacuum gas oil (VGO), and vacuum residue (VR) without inducing thermal cracking, as shown in Figure 1 . Crude oil is preheated to 250-300°C through a heat exchanger network using heat recovered from product streams and pumparound circuits. It is then heated to 340- 370°C in the CDU furnace before being flashed in a single column, where vapours rise and atmospheric residue settles. The integrated rectification section refines vapours into naphtha, kerosene, and diesel using reflux, while side strippers remove lighter components. Steam injection at the column bottom strips lighter hydrocarbons
Water cooler
Gas
Heat recovery
Air cooler
Separator
Wash water
Wild naphtha-re ux pump
Crude charge pump
Re ux
(In case of Pre-frac.)
Crude
SS1
Heavy naphtha Steam
Sour water pump
PA1
Crude column
Steam
SS2
PA2
Preheat-1
Steam
Kerosene
PA3
(In case of Pre-frac.)
Vac. diesel
SS3
PA4
Steam
Gas
Diesel
Vacuum column
Desalter
Pre- ash drum/ Pre-fractionator
CDU Over ash
Hot well
(Absence of Pre- ash/Pre-frac.)
LVGO
PA5
Steam
Sour water pump
Slop oil pump
HVGO
PA6
VDU Over ash
Fired heater
Fired heater
Coil steam
Steam
Preheat-2
VR
RCO pump
(In case of Pre- ash/Pre-frac.)
Figure 1 Typical CDU-VDU configuration
Refining India
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