Dividing-wall columns are a cost-effective option to increase capacity and meet tighter product specifications in naphtha processing.
Over the past several years, refineries have worked to minimize emissions and reduce their carbon footprint. Many naphtha processing refineries were refurbished with new technologies and have transformed their original operations. A few of these changes were enforcement driven, such as compliance with benzene-content restrictions for gasoline, while the impetus for others was to maximize the research octane number (RON) of the gasoline pool. Generating fuel with a high RON has become the new target because it can be used in high-efficiency engines.
Because the RON can be increased through isomerization and reforming, these two units have become an integral part of the naphtha “block” of the refinery. Full-range naphtha (FRN) is a mixture of C5–C12 hydrocarbons. The isomerization unit is used to boost the RON of light naphtha (C5 and C6), while the reforming unit improves the RON of heavy naphtha (C8+).
Refineries with both isomerization and reforming units cannot economically utilize all of the molecules in FRN. These low-RON streams are predominantly composed of C7 hydrocarbons, which cannot be processed in isomerization and reforming units and are difficult to dispose of. Improving the performance of the naphtha splitting column and other distillation columns within the refinery can reduce the flowrates of these low-value streams.
This article describes how dividing-wall columns (DWCs) can improve naphtha processing and presents three case studies demonstrating the importance of DWCs in the naphtha block.
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