HETP is numerically equal to HTU, only when the operating line

ANS:C - and equilibrium lines are parallel.

The Height Equivalent to a Theoretical Plate (HETP) and the Height of a Theoretical Unit (HTU) are parameters used to quantify the efficiency of a distillation column. They are measures of the height of packing or the length of a theoretical plate required to achieve a certain degree of separation. HETP is the physical height of packing material (or theoretical plate) required to achieve the same separation efficiency as one theoretical plate. HTU, on the other hand, is the theoretical height of packing material (or theoretical plate) required to achieve the same separation efficiency as one theoretical plate. When HETP is numerically equal to HTU, it implies that the physical and theoretical heights of packing material (or theoretical plates) are the same, indicating a certain level of efficiency in the column. However, this condition is generally true only under specific circumstances, which are:

• lies below the equilibrium line: When the operating line lies below the equilibrium line, indicating that the actual concentrations of components in the column are lower than their equilibrium concentrations.