Predicting the Pressure Drop of Corrugated Sheet Structured Packings in Deep Vacuum Applications

Abstract

Advanced corrugated sheet structured packings are considered a natural choice for deep vacuum distillation. In many of these applications that occur at absolute pressures below 0.01 bar at the top of the column, the low density gas/vapor driven by pressure ascends through an irrigated packed bed under laminar flow conditions. This implies that the packing geometry features aiming to reduce the form drag of advanced packing may not be as effective, if at all, as experienced in common applications where turbulent flow prevails. To consider this appropriately, a theoretically founded expression for laminar flow friction factor has been incorporated into Delft model (DM). With this extension, the predicted pressure drop within laminar flow region approaches closely that estimated using well-established empirical model available in software package SULCOL. In absence of adequate experimental evidence, extended DM was validated using newest data obtained at FRI with an advanced wire gauze structured packing in total reflux experiments carried out with paraxylene/orthoxylene system at 0.02 and 0.1 bar top pressure in a column with internal diameter of 1.22 m.

Keywords

• distillation
• packed columns
• structured packings
• pressure drop