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Separator Design for Liquid Removal from Gas Streams

John Pietranski, P.E., Ph.D.

Course Outline

This 3 hour course will focus on deriving the general Application Equations used for calculating equipment size requirements for removing entrained liquids from gas streams. Equipment requirement is based on a relationship of the gas stream properties as well as the liquid characteristics.

In order to discuss the subject of separation design it will be necessary to define the various terms and descriptions used to characterize liquids in gas streams. In particular, particle size will be discussed relative to separation design limits as covered by this course.

Following the calculation development for separation several Application Equation derivations are presented from the open literature. These correlations define the methodology for calculating the size of separation vessels based on specific stream data and desired results for both separators.

Two industrial examples follow the Application Equation development and the correlation review. The examples demonstrate how to design a horizontal and vertical separator.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

At the conclusion of the course the student will:

Intended Audience

It is the intention of this course to enable process engineers or other similar plant operations personnel to be able to calculate the vessel size for gravity separation. 

Benefit for Attendee

Separation design has been developed that takes theory and empirical methodology to define cause-and-effect parameters. The parameters can be used so that required aspects of desired separation can be determined.  In particular and where desired, acceleration of the liquid from gas separation can be designed to occur.

Course Introduction

Collection mechanisms will be covered following the review of particle size and its effect on separation. The mechanism reviewed in this course centers on gravity separation. Gravity separation relationships will be developed from Stokes law and will utilize stream properties and liquid droplet size to relate settling velocity to removal requirements.

Two industrial examples are presented in order to demonstrate the calculation techniques for horizontal separator requirements versus vertical design.  The examples calculate the size of each vessel that is needed to remove liquid from a defined inlet vapor stream in order to meet downstream process conditions.

Course Content

The course content is contained in the following PDF file:

Separator Design for Liquid Removal from Gas Streams

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Course Summary

This course provided a step-by-step development for the design of two types of liquid-in-gas separation devices: horizontal and the vertical gravity separators. These two types of process vessels are utilized throughout the chemical process industry to remove liquids from vapor streams.

Two sizing procedures were presented from the open literature for horizontal separators. The first is the procedure published by the American Institute of Chemical Engineers, (AIChE), through their Center for Chemical Process Safety (CCPS) group. The second procedure is published through the American Petroleum Institute, (API).

Examples of the design for horizontal as well as the vertical gravity separator were given. The calculation techniques required by the examples utilized the background covered in the Application Equations and correlation development. 

Related Links

For additional technical information related to this subject, please visit the following websites or web pages: Click on the links to API RP 521 5th edition.  Search under DIERS (Design Institute for Emergency Relief Systems) subheading for “Guidelines for Pressure Relief and Effluent Handling Systems” or “Emergency Relief System Design Using DIERS Technology: DIERS Project Manual” publications.


Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

Take a Quiz

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.