Comparison of base case and optimum case (utilities): Opex
Savings in utilities
Savings
Utility
MTOE
Parameters
Base case
Optimum case
Steam, TPH Power, kWh
29,854 (MP)
2,183 (LP)
CDU stripping steam, lb/hr VDU stripping steam, lb/hr VDU ejector steam, lb/hr CDU & VDU pump duty, kW
19,401 14,330 43,122
18,739
355
0.071
0
Fuel oil eq. saving, MTOE/hr
0.92
27,602
Ton/annum
7,384
2,247
1,182
Savings in INR, $/ton
273
Total Steam, lb/hr Power, kW
Million $/year
~2.05
77,162
46,297 (-40%) 1,892 (-16%)
CO₂ savings, CO₂ eq. million lb/year
52.9
2,247
Note: The conversion factors considered are as: steam: 14 tons/MTOE, power: 5,000 kw/MTOE, cooling water: 20,000 m³/MTOE.
Table 3
Distillation operation/efficiency Top vapour generation is reduced in both CDU and VDU, enhancing efficiency as the absence of steam improves rectification zone fractionation by avoiding irrelevant mate - rial dilution. Approximately 8% additional vacuum diesel is recovered, reducing slop rerouting. More over-flash liquid is drawn without extra energy (at the same COT as the base case), eliminating metering issues when pumped mechani - cally instead of relying on gravity flow. The stripper can be operated at lower pressure than the rectification zone, improving stripping efficiency and utilis - ing excess LP steam (instead of MP steam) while lowering fired heater COT. As it adds an additional fractionation stage to the flash zone with good wetting rates, overflash and COT can be reduced. The stripper can be isolated for main - tenance for replacing the tray panels for efficient stripping while the rectification column continues operating. Unlike dry fractionation, effective stripping means it does not depend on higher overflash or COT to minimise slippage of lighter distillates into the bottom residue. Successive dual flash zones (optional), one in the flash drum and one in the rectification column, optimise separa - tion. Reduced lighter components in bottoms lessen down - stream unit loads, and VDU stripper bottom temperatures drop by ~18°F due to low-pressure operation, minimising quenching needs to prevent coking. Vapour load distribu - tion between rectification and stripper overheads enhances equipment sizing flexibility. The present shift to reboiler side strippers from steam side strippers for dry distillate prod - ucts and operational stability further enables a steam-free rectification section. Wash bed performance and coking mitigation The closed-loop wash oil system, deployed above the CDU and VDU flash zones, addresses operational bottlenecks by optimising overflash at the same COT. Using high-tem - perature wash oil, it ensures consistent wetting, reduces temperature variations, boosts HVGO yield by 2-3%, low - ers coil outlet temperatures, minimises slop formation, and enhances stability, especially with high-asphaltene crudes. Recycled wash oil outperforms slop, which can reduce HVGO yield or introduce contaminants, requiring higher COT. The closed-loop system maintains effective wetting without impacting HVGO yield or raising COT, improving process performance. At the same COT, increased over - flash indicates better wetting, while improved end-point
Table 4
distillation of diesel and HVGO reflects enhanced fractiona - tion and metal washing. The system replaces traditional overflash washing, reduc - ing coking risks by minimising metal, solids, and colouring compound build-up. The unique closed loop self-washes with condensed water and fresh stripping zone vapour (by adding additional fractionation stage), preventing metal, salt, and colouring compound accumulation. Hydraulic and operational enhancements Reduced vapour-liquid traffic decreases jet flood by 15-20% and pressure drop by 20-25%, allowing smaller column diameters or 5-10% throughput increases (see Table 5 ). In the VDU, the hydrocarbon vapour load to ejectors drop by 20-30%, cutting motive steam demand from 26,455 lb/ hr to 17,637 lb/hr (15-30% reduction), improving vacuum efficiency. Dual flash zones, one in the flash drum and one in the rectification column, optimise separation and minimise entrainment. Additionally, the VDU recovers 20-30% of vapour load as vacuum diesel, enhancing pumparound duty. Corrosion and reliability Eliminating steam in rectification raises the CDU top dew point by 18-27°C, reducing water condensation and cor - rosion, thus extending equipment life. The wash oil system minimises wash zone fouling, enhancing reliability, and
Comparison of base case and optimum case: Capex
Parameter
Base case
Optimum case
Column size (dia. x height) CDU-top section, ft CDU-bottom section, ft
22.0 x 187.5 12.5 x 32.8 1,433,003 22.3 x 31.7 32.8 x 137.8 22.3 x 18.0
21.3 x 187.5 12.5 x 32.8
1,395,524 (~2.6%)
CDU weight, lb
VDU-top section, ft VDU-middle section, ft VDU-bottom section, ft
22.3 x 31.7 30.5 x 137.8 22.3 x 18.0
1,399,934 (~4.2%)
VDU weight, lb
1,461,663
Separators (dia. x length) CDU stripper separator, ft
- -
4.9 x 11.8
Stripper weight, lb
13,228
Table 5
69
PTQ Q2 2026
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