Column trayed, HETP value

HETP is another quantity that is used to express the efficiency of a device for carrying out a separation, particularly in which mass is transferred by a stage-wise action rather than a differential contact. For example, in a tray column, the HETP value is the tray spacing divided by the fractional overall tray efficiency. 

A similar HETP value can be obtained for a plate column if the tray spacing is known... 

Height Equivalent to a Theoretical Plate. Provided both the equilibrium and operating lines are straight, HETP values may be estimated by combining the HG and HL values predicted by the above correlations and by translating the resulting HQG into HETP by combining equations 47, 51, and 56 with equation 85, which is discussed under bubble tray absorption columns ... 

Packed columns maintain a high separation efficiency in both liquid-film-controlled and gas-film-controlled systems. For many years, packed columns have been used for absorption systems that characteristically are liquid-film-controlled. As an example, the HETP value for a trayed column might be twice as great in an absorption operation as compared to a distillation operation. For the same systems, the HETP value for IMTP packing in the absorption operation typically would be only one-third greater than for the distillation operation. 

---