Case study 4: Deisohexaniser revamp at a South Asian refinery
Case study 5: Reformate splitter revamp
Conventional
Middle DWC
design
design
Conventional
Dual DWC
design 26,800
design 26,800
Overhead product rate, ton/hr
10 50
15 40 22 85 20
LI+HI isomerate, kg/hr
Side draw rate, ton/hr
Pharma-grade hexane, kg/hr
-
5,000
Benzene purity in side draw, wt% 17.6
DIH recycle, kg/hr
35,700 >88.7
30,700 >88.7
Bottoms product rate, ton/hr Side draw rate reduction, %
80
LI+HI isomerate RON Energy savings, %
–
–
20
C -
Light isomerate
DIH feed
DIH recycle to ISOM unit
Reformate
Concentrated C cut
Food/Pharma-grade hexane
Reformate bottoms
Heavy isomerate
Figure 7 Revamp of a reformer into a DWC
Figure 6 Revamp of a deisohexaniser into a DWC
Reformate splitter Beyond these, additional revamp opportunities exist that can deliver both operational and economic benefits, such as in the reformate splitter. In typical configurations, benzene control in the gasoline pool is achieved using a benzene extraction unit (BEU) or a benzene saturation unit, both of which are fed by the reformate splitter’s regular liquid side draw, which often includes a ‘sloppy cut’ containing signif - icant amount of C₅s and C₇s/toluene, components that are not desirable in the downstream unit. A DWC retrofit ena - bles the production of a benzene-concentrated C6 mid-cut that has little C₅s and C₇s/toluene, reducing the BEU feed rate by at least 20% and thereby improving overall process efficiency (see Figure 7 ). A case study in Figure 7 illustrates how a middle-wall DWC retrofit in a reformate splitter improved benzene concentration in the side draw from 17.6% to 22% while reducing the side draw rate by 20%. This more selective cut reduces the load on the downstream BEU, enhancing overall process efficiency. The revamp also increased the overhead and bottoms product rates, further contributing to operational gains. Debutaniser column A further strategic application of DWC technology lies in revamping the debutaniser column, which can signifi - cantly enhance separation efficiency and product recovery. A DWC retrofit in this case improves iC₄ recovery in the overhead, maximises nC₄ concentration in the side draw, and reduces the total feed to the downstream isomerisa- tion unit, effectively debottlenecking it (see Figure 8 ). This revamp also enhances blending flexibility for the isomerate
streams. The heart-cut stream was then routed to a second column for further purification to achieve the desired spec - ifications. However, this two-column setup was energy- intensive and operationally complex. To streamline operations and reduce costs, the first col - umn was revamped into a DWC, enabling it to perform the full separation in a single shell. This eliminated the need for the second column, which was subsequently taken offline. The DWC retrofit successfully met all performance objec - tives, delivering the required product purities while improv - ing energy efficiency and reducing equipment footprint (Figure 5). Deisohexaniser column Another high-impact revamp opportunity lies in the deisohexaniser column, which can be modified using the dual DWC design to recover an additional high-value hexane stream suitable for food-grade or pharmaceutical use, while minimising impact on the octane quality of the isomerate product (see Figure 6 ). Additionally, this revamp delivers 20-30% energy savings and increases the overall capacity of the ISOM unit. In a South Asian refinery case, the deisohexaniser was revamped into a dual DWC to enable the recovery of a high-purity hexane stream suitable for pharmaceutical applications (Figure 6). The new configuration maintained the same isomerate throughput and octane rating while introducing a valuable 5,000 kg/hr pharma-grade hexane stream. It also reduced the DIH recycle load and achieved 20% energy savings, demonstrating the dual DWC’s ability to unlock new product value without compromising exist - ing operations.
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Revamps 2025
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