BG1-18 Turndown Operation of a Vertical Tubeside Thermosiphon Reboiler

S. Talapatra

This report provides a comprehensive look at the turndown operation of a vertical tubeside thermosiphon reboiler (VTTR), including predictions of thermal and hydraulic performance and quantitative criteria for turndown limits. Data were collected for water, n-pentane, p-xylene, and n-pentane/p-xylene mixtures in an industrially relevant VTTR flow loop. The unit was systematically turned down by lowering the hot and cold stream temperature difference while maintaining constant column pressure and column liquid height. Heat transfer and pressure drop measurements indicated increased deviation from Xist predictions at reduced mass and heat flux conditions. For some pure fluids and mixtures, we observed a threshold heat flux below which “normal” thermosiphon operation (i.e., liquid recirculating back to the column) was not possible. This report discusses the modes of unit shutdown with pure fluids and mixtures, evaluates existing guidelines for VTTR shutdown, and presents new data-based criteria for turndown limits.