How to Design and Construct A Distillation Column along with Mechanical Parameters? What Are The Stepwise Procedures For Designing The Distillation Column?

For separation and purification of chemical compounds the most commonly used equipment is distillation column. Which have its application in every petrochemical and refining industries along with food and pharmaceutical industries, it is an option for separation by creation of phase in the mixture of chemical compounds, it is employed anywhere when there is a necessity of separation or purification operations. If it doesn’t work during the designing than other unit operation are chosen for desired separations.

Designing a distillation column is most important skill of a chemical engineer because it covers all the concepts of the course. For graduates who are at their project work and plant personals who want to learn from basis or just want a simple rough procedure which are used as thumb rule by experiences from the industrial personal, they can follow the below procedure for their start up.

Initial we must make lot of discussion before design because to avoid the confusion and clear the layers of concepts which overlap on each other, which helps to finding out the relation of each concept. For any design their will a “basis, skeleton structure, balancing , mathematical model, analysis, pilot plant trail, modifying, reanalysis, optimize” and then final design come out from the drawing board, right now we stick with the column design only we study about the mechanical designing part later.
Let start for a binary distillation column:

This means that two components solution is selected as feed mixture to the distillation column no other impurities or trace will exist. Now we should gather all the data required which are

  • Heat of vaporization at normal boiling point
  • Data of Heat capacities
  • Data of Vapor pressure
  • Vapor and liquid equilibrium data of the selected compounds

Equations and calculation which are required are:

  • Antoine equation
  • Fenske equation
  • Stage equation
  • Dew points and bubble points
  • Equilibrium flash calculations
  • Q-line calculation
  • Design methods
  • McCabe-Thiele method (Graphical method)
  • Low product concentrations
  • The Smoker equations
  • Plate efficiency
  • Prediction of plate efficiency
  • O'Connell's correlation
  • Van Winkle's correlation
  • AIChE method
  • Entrainment
In some problems, methods adopted for calculation are of
1. Analytical Method: which is known by Sorel-Lewis method and involves plate to plate calculations involving material and energy balance equations.
2. Graphical Method:
     i) Based on equilibrium relation and material balance we use Mc-Cabe-Thiele method.
     ii) Based on equilibrium relation and energy balance we use Ponchon-Savarit method.

Column sizing:

  • Selection of plate type in distillation column
  • Plate material of construction
  • Plate and inner column flow path hydraulic design

Plate-design procedure

  • Plate occupying areas calculation
  • Diameter of the column and degree of narrowing
  • Liquid-flow arrangement up and bottom of the tray
  • Entrainment cause and prevention parameters
  • Weep point calculation by optimizing
  • Weir liquid crest designing from the standard data
  • Weir dimensions which depend on the plate diameter and liquid flow rate
  • Perforated area of the tray which help in contact of the liquid and vapor
  • Hole size on the sieve tray which determine the area of opening for liquid and vapor to flow
  • Hole pitch which depends on the distance between the centers of the hole and provide enough gaps
  • Hydraulic gradient which make the liquid flow from top to bottom of the column and pass from weir to plates
  • Plate pressure drop caused by the liquid which flow over from plate to plate
  • Down comer design [back-up] where liquid flow from sides of the column and liquid hold up for continuous flow
  • Cooling water quantity required at top of the column for condensing the vapors
  • Condenser duty which depends on the quantity of  vapors produced
  • Reboiler steam consumption which add the driving force of temperature gradient to the mixture present in the column
distillation column diagram and image which is used for separation of ammonia and carbon dioxide from waste water using low pressure steam in ammonia production
Distillation column used for
of NH3 and CO2 from waste water
By using this calculator you can calculate how many theoretical stages are required to separate a binary mixture, this calculator uses Fenske,Underwoods and Gilland Correlation as above said along with the famous McCabe-Thiele method. 

All above are some of the basis topic which are to be covered and  must be known for designing a distillation column.

Literature which can help to understand about
Distillation calculations and formulas
Distillation control design