duty while preserving product quality. Steam utilisation is optimised through recovery of near-pure steam from VDU stripper overheads (hydrocarbon content <0.5%), enabling reuse across CDU-VDU operations. The reduction in steam demand directly lowers demineralised water consumption and associated boiler blowdown losses. In parallel, reduced VDU top vapour load decreases ejector motive steam requirement and interstage condenser duty, leading to lower cooling water demand – an important advantage under high ambient conditions typical of Indian refineries, where cooling water systems are often capacity- constrained. The condensation of
Comparison of base case and optimum case (utilities) – Opex
Parameters
Base case
Optimum case
CDU stripping steam, TPH VDU stripping steam, TPH VDU ejector steam, TPH CDU and VDU pump duty, KW
8.8 6.5
8.5
0
19.56 2,247 98.69
12.52 1,182 100.34
Total duty (CDU and VDU), MMKcal/hr
Total Steam, TPH Power, KW
35
21 (~40%)
2,247
1,892 (-16%)
Heat duty, MMKcal/hr 100 (~-1.5%) Note: The conversion factors considered are: steam: 14 tons/MTOE; power: 5,000 kw/MTOE; cooling water: 20,000 m³/MTOE. 98.7
Table 3
Savings of utilities
Savings Steam Power
Unit TPH kWh
Utility
MTOE
13.543 (MP)
0.99 (LP)
355
0.071 -0.14
Heat duty
MMKcal/hr MTOE/hr
-1.65
Fuel oil eq. saving
0.92
Ton/yr Rs/ton
7,384 24,000
Savings in INR
INR Crore/yr CO 2 eq ton/yr
~18
CO 2 savings
~23,000
Table 4
high-temperature stripper overhead vapours further enhances heat integration, as phase- change heat transfer provides a higher effective heat transfer coefficient compared to conventional sensible heat exchange. This improves heat recovery within the preheat train, increasing feed preheat temperatures by 5-10°C and reducing furnace duty. Elevated tray temperatures (10-25°C higher) further support deeper heat integration and improved thermal efficiency. Improved control of flash-zone dynamics and reduced entrainment enable higher distillate recovery while minimising slop generation, particularly for opportunity crudes with high asphaltene content (>6%). The configuration mitigates slop formation challenges associated with such crudes, reducing throughput losses and enhancing operational flexibility across varying crude slates. Reduced vapour traffic (20-25%) improves hydraulic performance, increasing jet flood margins by 15-20% and reducing pressure
improving by 10-20°C and HVGO yield increasing by ~2-3%. Enhanced scrubbing of metals and colour bodies reduces downstream catalyst deactivation, lowering regeneration frequency and improving overall unit reliability. In the VDU, elimination of steam from the rectification section reduces vapour dilution and entrainment of vacuum diesel into the overhead ejector system. This enables recovery of hydrocarbon vapours as valuable product, resulting in additional vacuum diesel recovery of ~8%, while also allowing associated pumparound and product cooling heat to be effectively recovered within the process rather than being lost to the vacuum system. The independent operation of the stripping section allows optimisation at lower pressures, resulting in reduced bottom temperatures (~10°C lower) and minimised thermal severity. This decreases the requirement for quenching to control residue cracking and enables operation at lower furnace coil outlet temperatures (reduction of ~5-10°C), thereby reducing fired
Refining India
36
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