October 2016 – Dividing wall column technology applied to a xylenes separation project delivered superior energy efficiency compared to a two-column arrangement.
As the global energy sector enters a new phase centered on energy reduction, dividing wall columns (DWC) are providing a unique way to meet the current challenges facing the refining and petrochemical industries. The concept of a dividing wall is not new; in fact, it has been utilized in the chemicals industry for some time. However, over the past decade, this concept has gained momentum following successful revamps of existing distillation columns. DWCs have produced tremendous savings in both capital and utility costs as compared to conventional distillation columns, and are now being used with advanced heat integration schemes.
This article will present a case study with the DWC process applied at a refinery in Japan. The goal of the project was to recover mix-xylenes from a full-range reformate feed. The original benzene extraction unit (BEU), operational since 1999, consisted of pre-cut and extraction sections for extraction of benzene from reformate produced by a catalytic reforming unit. The unit separated the feed into a light reformate, heavy reformate and a benzene-rich stream. The crude benzene was fed to the extraction section of the BEU. The light and heavy reformate were sent to the tankage offsite as mogas blendstocks. The heavy reformate contained a substantial amount of mix-xylenes along with toluene, which could be recovered as separate products.
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