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- Raschig - Dual Flow Trays
Raschig - Dual Flow Trays
Dual flow trays are essentially sieve trays without down comers such that the entire tray active area is perforated with holes. Hole sizes range between 12.5 to 25 mm in diameter. Tray action occurs through the continuous counter current passage of vapour and liquid through the tray holes. As the liquid and vapour load are increased, the tray liquid head increases up to a point where a pulsating liquid seal is established at sufficiently high loads. At these conditions, liquid momentarily leaks through holes in areas of wave crests, while vapour surges through holes in the area between crests. As a result dual flow trays only have a very narrow efficient operating range.
High open hole area dual flow trays have a higher capacity and lower pressure drop compared to conventional distillation trays at the same tray spacing and are best suited for processing fluids that form polymers or have a high solids content. The majority of commercial applications are common in small to moderate sized columns. They are seldom used in larger diameter columns because of difficulties in achieving the desired tray tolerances for levelness. Trays that suffer from out-of-levelness, are prone to segregation of the vapour-liquid flows which results in large scale liquid and vapour maldstribution.