Volume XXXII: Column Internals


The scope of this presentation is to present basic information and understanding of the ASME code for the design of pressure vessels for the chemical and process industry as applicable in the United States and most of North and South America. For more information about our productsheavy plate & custom fabrication services or fabrication capabilities contact us today! 


Distillation is a process in which a liquid or vapour mixture of two or more substances is separated into its component fractions of desired purity, by the application and removal of heat. This is a process used for centuries to separate compounds into their principal components. One such use comes to mind. Liquor stills to make “moonshine” were prevalent in the United States for many years.


Distillation columns are a device for performing this process in refineries. Just like other process equipment, there are several methods of performing the distillation process.

There are three types of distillation.  They are:

Fractional Distillation – The separation of key components in a mixture by the difference in their relative volatility or boiling points.

Extractive Distillation - An external solvent is added to the system to increase the separation. The external solvent changes the relative volatility between two ‘close’ components by extracting one of the components, forming a ternary mixture with different properties. The solvent is recycled into the system after the extracted component is separated from it.

Reactive Distillation - A distillation column may also have a catalyst bed and reaction occurring in it. This type of column is called a reactive distillation column. The targeted component reacts when it is in contact with the catalyst, thereby separated from the rest of the components in the mixture.


There are two main types of column internals, they are trays and packing,


  • Sieve
  • Bubble Cap
  • Valve


  • Random (Rings, saddles)
  • Structured

The choice between use of tray column or a packed column for a given mass transfer operation should, theoretically, be based on a detail cost analysis for the two types of contactors. However, the decision can be made on the basis of a qualitative analysis of relative advantages and disadvantages, eliminating the need for a detailed cost comparison.

Which are as follows:

  • Liquid dispersion difficulties
  • Capable of handling wide ranges liquid rates
  • Cleaning.
  • Non-foaming systems
  • Periodic cleaning
  • Weight of the column
  • Design information
  • Inter stage cooling
  • Temperature change
  • Diameters


  • Utilize a pressure and temperature differential to separate the products.
  • For most tray columns, the weir holds a liquid level of each tray. Liquid enters from the down-comer of the tray above.
  • The vapor must overcome this liquid head to move up the column.
  • On the tray the vapor and liquid are contacted becomes bubble or froth where the mass transfer takes place and then above the tray they are separated where froth flows over the outlet weir and vapor with the light volatile compound is disengaged


  • Tray column performs well in high liquid and vapor loading.
  • Trays have higher pressure drop than packed.
  • Trays also have high resistance to corrosion.


Five major types of tray column:

  • Bubble Cap
  • Sieve
  • Dual Flow
  • Valve
  • Baffle



This is presented to you as a service from BOARDMAN, LLC located in Oklahoma City, Oklahoma.

Since 1910, Boardman has been a respected custom fabricator. We take pride in our ability to take the most stringent specifications and requirements to provide a high quality solution to our customers. With more than 75 years of ASME Section VIII, Division I engineering experience, we have the unique ability to provide custom solutions to our customers.

Fabricated Projects Include:

  • Trayed Towers & Columns
  • ASME Pressure Vessels
  • Molecular Sieves
  • Rotary Dryers & Kilns
  • API Tanks
  • Acid settlers
  • Stacks, Scrubbers
  • Thermal Oxidizers
  • Accumulators, Condensers
  • Crystallizers
  • Ducting
  • Bins
  •  Large Diameter Piping

The sizes of these projects are up to 200’ in length, 350 tons, 16’ diameter and 4” thick.

BOARDMAN, LLC is available for shop tours and Pressure Vessel and Static Equipment Fabrication Classes.

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