Here, we present criteria needed for the intelligent, effective specification of trays for a distillation or stripping column.
Among the key parameters and accessories during specification are column diameter, tray spacing, number of trays, number of passes, type of downcomers, weir heights, provision of downcomer backups, tray pressure drops, design of bottom seal pan, column bottom arrangement, and nozzle location and orientation.
The vertical distance between adjacent trays varies from 450 to 900 mm in the columns generally employed in the chemical process industries (CPI), as seen in Table 1.
Spacing involves a tradeoff between column height and column diameter; with greater tray spacing, the column height increases, while the required diameter decreases.
Height/diameter ratios greater than 25 – 30 are generally not recommended.
Set the number of passes such that liquid loads do not exceed 70 m 3 /h per meter weir length.
After the number of passes has been selected, if necessary, adjust the column diameter in order to arrive at a minimum path length of 400 mm.
For a column diameter of 1,200 to 2,100 mm: use two passes at maximum
For a diameter of 2,100 to 3,000 mm: use three passes at…