Tower Flooding Definitions

Lili Lyddon

January 3, 2007

There are several definitions of trayed column flooding, and a number of correlations used to calculate flooding. Fraction Flooding in ProMax is calculated by Fair’s correlation which is generally conservative and includes both jet and downcomer flood data in its development. This correlation is described in Perry’s Chemical Engineers Handbook, 6th ed., pages 18-6 and 18-7. Some vendors calculate jet and downcomer flood separately. Perry’s basically describes two types of flooding as follows:

Entrainment Flooding - For a constant liquid rate, increasing the gas rate results eventually in excessive entrainment and flooding. At the flood point it is difficult to obtain net downward flow of liquid, and any liquid fed to the column is carried out with the overhead gas. Furthermore, the column inventory of liquid increases, pressure drop across the column becomes quite large, and control becomes difficult.

Downflow Flooding - Flooding may also be brought on by increasing the liquid rate while holding the gas rate constant. Excessive liquid flow can overtax the capacity of downcomers or other passages, with the ultimate result of increased liquid inventory, increased pressure drop, and the other characteristics of a flooded column.

Authored by Lili Lyddon - BR&E Technical Support / Help Author