Case Study 2: Naphtha splitter revamp at a South Asian refinery
Case study 3: Naphtha splitter revamp at a South Asian refinery
Conventional
Middle DWC
Conventional
Middle DWC
design
design
design
design
(Naphtha splitter
(only Naphtha
Feed rate, kg/hr
330,000 180,000
330,000 160,000
I and II) 308,000 105,400
Splitter I) 308,000 109,700
Side draw rate, kg/hr
Feed rate, kg/hr
Side cut D86 (IBP/FBP), °C
106 to 191
111 to 180
Side cut C 8 /C 9 rate, kg/hr Side cut C 8 /C 9 content, wt% Side cut C 8 /C 9 recovery, %
Overla p (middle naphtha D86 95% - heavy naphtha D86 5%), °C
63.9
66.5
55
8
95
98
Ene rgy savings, %
–
25%
a
Light naphtha
b
Light naphtha
Heart cut naphtha
Feed
Middle naphtha
Feed
Heart cut naphtha
Heavy naphtha 2
Heavy naphtha
Figure 4 Retrofitted naphtha splitter with a middle DWC
original column struggled to deliver the required separation between light, middle, and heavy naphtha, resulting in off- spec products and operational challenges such as exces- sive C₆ and C1₀+ in the middle cut. These issues threatened catalyst life and product yields in downstream units. Conventional upgrade strategies, including reboiler duty shifts and feed location changes, proved insufficient, and installing a second column was ruled out due to high capital costs. To address these chal- lenges, the column was successfully upgraded using a mid- dle DWC configuration within a tight 20-day turnaround. The revamp involved replacement of the conventional trays by high-performance ones, custom-designed DWC internals, changes to the side draw location, and a new reboiler with minimal changes to the control system. Post- revamp, the column achieved a sharp 25°C gap between light and heavy naphtha and reduced the overlap between middle and heavy cuts from 55°C to just 8°C. The revamped unit delivered improved product quality and operational stability, running reliably for more than seven years without major issues. This transformation demon- strated the effectiveness of DWC technology in achieving high-performance separation within existing infrastructure. In another case study, a South Asian refinery originally used two separate distillation columns to fractionate naph- tha into light, heart-cut (C8 /C 9 ), and heavy naphtha to meet stringent product quality requirements (see Figure 5 ). The first column received feed from the depentaniser and produced preliminary light, heart-cut, and heavy naphtha Figure 5 Upgrade of a naphtha splitter into a DWC: (a) Naphtha splitter I revamped to DWC, (b) Naphtha splitter II idled
subsequently processed in a reformate splitter to isolate C 6 hydrocarbons. These C 6 components, which include ben- zene, are then sent to the benzene extraction unit for fur- ther purification. Each of these separation steps presents opportunities for DWC integration to improve separation efficiency, reduce energy use, and increase product value. Naphtha splitter revamp opportunity A key opportunity for DWC implementation lies in revamp- ing the naphtha splitter for octane boost, where naphtha is split into an iC₅-rich top product, a normal paraffins-rich C₅-C₆ middle cut, and a C₇+ bottom product (see Figure 3 ). This approach raises isomerate octane, increases ISOM unit capacity by maximising normal paraffins in the feed, and delivers a 20-30% energy saving. A case study from a Middle East refinery highlights the performance improvements achieved by converting a con- ventional naphtha splitter into a middle-wall DWC (Figure 3). The DWC design significantly enhanced the separa - tion of iC₅ and nC₅ components, improving iC₅ purity in the overhead from 70% to 85% and reducing nC₅ con - tamination. Additionally, the side draw saw improved nC₅ concentration, while maintaining low C₇+ and C₆ content in undesired fractions. Most notably, the revamp delivered a 30% reduction in energy consumption, underscoring the thermodynamic efficiency of the DWC configuration. In a separate case study in a South Asian refinery, a con - ventional naphtha splitter at an FCC unit was repurposed to meet more demanding product specifications, particu - larly for the middle naphtha cut, which was redirected to downstream aromatics recovery units (see Figure 4 ). The
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