Base case details: CDU products
Stream name
Unstab. naphtha
Heavy naphtha
Light kero
Heavy kero
LGO
Total mass rate, lb/hr Liquid std. density, lb/ft³
357,283
147,511
121,699
232,241
551,728
44.03
49.18
50.37
51.72
52.96
ASTM D86 at 760 mmHG (LV) vs ºF 5%
61.2
245.7 277.0 289.4 302.2 322.5 335.1
323.8 346.5 356.4 370.4 388.4 397.0
366.4 410.5 429.4 451.2 490.6 511.9
364.8 494.8 542.3 577.4 649.8 675.5
30% 50% 70% 90% 95%
132.3 183.2 203.0 231.8 246.4
Table 1
Case study: 172,000 bopd Bombay High crude A case study of a refinery operating with 172,000 bopd Bombay High crude is considered the base case. Operating conditions, including pressure, temperature, and flow rate, were maintained in line with the base case, with product yields held within ±1% to ensure comparability. The steam- free rectification and wash oil system was established to optimise operating conditions. The broad product distilla- tion and specification of the base case considered for the new design are shown in Table 1 (CDU products) and Table 2 (VDU products). Technical and economic depth The novel configuration delivered transformative results, as shown in Table 3 . It achieved a 40% steam reduction (from 77,162 lb/hr to 46,297 lb/hr) and a 16% power reduction (from 2,247 kW to 1,892 kW), translating into $2.05 mil- lion in annual Opex savings, as shown in Table 4 . Energy and environmental benefits The steam-free rectification reduces vapour dilution and column traffic, achieving ~7,400 MTOE/year in energy savings. It lowers the refinery’s carbon footprint by ~52.9 million pounds/year of CO₂ through reduced steam genera- tion, aiding emission compliance. Water use drops by 15% due to lower condenser duties, and demineralised water is saved by minimising steam wastage, supporting resource conservation. Eliminating steam in CDU and VDU rectification zones
cuts vapour-liquid traffic and pressure drops, boosting heat recovery. This raises tray temperatures by 18-45°F, enabling deeper crude preheating and allowing products and pumparounds to be drawn at higher temperatures than conventional designs. The increased temperature differential reduces exchanger sizes in the preheat sec- tion, reducing fired heater duty, and enhancing preheat efficiency. High-temperature heat from the stripper overhead is recovered for processing, while low-grade heat preheats wash oil for the rectification column. Condensing stripper vapour at its dew point, with minimal non-condensables, maximises heat transfer efficiency by reducing film resist- ance, as fresh vapour quickly contacts the heat transfer surface. Bottom pumparound (BPA) duty is shifted to the stripper condenser, where higher temperatures enable more efficient duty extraction in crude preheat compared to conventional BPA draw points. Steam savings/ejector system optimisation Condensing stripping steam in the VDU stripper overhead separates hydrocarbons (mainly HVGO with minimal lighter gases), leaving pure steam with less than 0.5% non-con- densable hydrocarbons. This steam is reused for stripping or heater purging. The absence of stripping steam reduces the VDU top vapour condensable load, cutting ejector motive steam demand by 15-30%. Additionally, integrating VDU stripping column steam into the CDU saves 5-10% of its stripping steam.
Base case details: VDU products
Stream name
RCO
Vac. diesel
LVGO
HVGO
VR
Total mass rate, lb/hr Liquid std. density, lb/ft³
740,272
67,913
299,222
238,209
111,148
56.26
53.79
54.80
55.86
63.25
ASTM D1160 at 760 mmHG vs ºF 5%
594.5 763.3 837.0 941.4
502.3 577.9 606.6 635.4 669.7 683.2
673.9 702.6 744.4 807.1 871.0 907.5
788.0 879.1 960.7 970.0
1,059.9 1,133.4 1,185.8 1,272.4 1,495.0 1,665.9
30% 50% 70% 90% 95%
1,129.8 1,239.6
1,036.0 1,063.6
Table 2
68
PTQ Q2 2026
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