What is an effective boosting ratio

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Column parameters

The rectification apparatus basically has the following structure:

  1. Column with trays, random packings or packing
  2. Overhead condenser with device for overhead product removal
  3. Evaporator with device for removing bottom product
  4. Feed device for the starting mixture

Theoretical and practical separation levels

In the steady state, there is a thermodynamic equilibrium between the rising vapor and the flowing liquid on a theoretical floor. A column is assessed according to the number of its theoretical plates (also referred to as the number of plates). The number of theoretical trays must be determined experimentally in a rectification test for a given column and for a specific mixture with a known equilibrium diagram. The evaluation of the experiment shows the following relationships for tray columns and packed columns:

Bottom columns:

Number of practical trays (n) = number of theoretical trays (nth) / average amplification ratio (sm)

The mean reinforcement ratio (also referred to as the exchange ratio or degree of land use) practically represents the degree of efficiency of a floor. The following applies: sm <1. The values ​​sm and nth do not represent constants, as they are dependent on several variable influencing variables. These influencing variables are the construction, the distance between the trays and the operating conditions of the column. The operating conditions again include the following parameters: loading of the column, operating pressure, reflux ratio and the type of composition of the bubble mixture.

Packed columns:

Height of the packing bed (h) = number of theoretical trays (nth) HETP value (height equiv. Of theo. Plate)

The HETP value (height equivalent of a theoretical plate) depends in particular on the type and size of the packing. Effective fillers (e.g. coils) result in small HETP values ​​and thus also small bed heights.

In the continuous operation of rectification columns, 3 stationary states can arise:

Tab. 1
Stationary conditions
State 1Equilibrium with an infinite reflux ratio in the head and evaporator (state without withdrawal)=0=0=0
State 2Constant mixture composition in the evaporator (xB.) and constant withdrawal of product with xD. (finite reflux ratio). The distillate is returned directly to the still. State 2 is only used to determine column parameters!=0=0
State 3Equilibrium at a finite reflux ratio. Removal of top and bottom product (xD., xB.) and feeding an inlet with xZ.