The Engineered Mist Eliminator - AMACS Process Tower Internals

Table of ContentsIntroduction............................. 1Droplet Formation and Size Distributions .... 1Mechanisms of Droplet Removal ........... 2Types of Mist Eliminator Mesh & Materials ... 4Design Equations ........................ 6Predicting Pressure Drop ................. 7Inlet Diffusers ........................... 7Vessel Configuration ..................... 8Advanced Mist Eliminator Designs ........ 10Mesh -Vane Assemblies ................. 11Use of Geometry ....................... 11MultiPocket V anes .................... 11Case Studies & Examples ............... 12Plate-Pak and MistXpert are trademarks ofAMACS. MaxFlow ® is a registered trademarkof AMACS and Mistermesh ® is a registeredtrademark of AMACS. Ripple Tray ® is aregistered trademark of Stone & WebsterEngineering Corporation. Kynar ® is a registeredtrademark of ELF Atochem North America, Inc.Teflon ® is a registered trademark of E.I. du Pontde Nemours and Company. Hastelloy ® is aregistered trademark of Haynes International,Inc. Goodloe ® is a registered trademark ofKoch-Glitsch, LP. AMACS presents theinformation in this publication in good faith,believing it to be accurate. However, nothingherein is to be construed as an express orimplied warranty or guarantee regardingperformance, merchantability, fitness for aparticular purpose, non-infringement of patents,trademarks or copyrights.©Copyright 2012 by AMACS,Printed in USA 4-04 1000APThe Engineered Mist EliminatorMist elimination, or the removal of entrained liquid droplets from a vaporstream, is one of the most commonly encountered processes regardless ofunit operation. Unfortunately, mist eliminators are often considered commodityitems and are specified without attention to available technologiesand design approaches. The engineered mist eliminator may reduce liquidcarryover by a factor of one hundred or more relative to a standard unit, drophead losses by 50% or more, or increase capacity by factors of three or four.This manual summarizes cost effective approaches to reducing solventlosses or emissions, extending equipment life and maintenance cycles -using proven and cost effective technologies and techniques.Droplet Formation and Size DistributionsEntrained liquid does not consist of same-sized droplets, but as a broadrange of droplet sizes that may be characterized with a Normal or BellDistribution centered about some mean or average. The average dropletsize depends very much on the mechanism by which they are generated.Sizing equations are expressed in terms of the probability of removing adroplet of a given diameter, and mist eliminator performance is the inte -gration or cumulative sum of individual removal efficiencies. It is thereforecritical to know the approximate droplet size distribution in order toproperly design a mist elimination system. Figure 1 shows some typicalsize distribution curvesFIGURE 1from different sources.VOLUME FRACTION FREQUENCY DISTRIBUTIONSFOR DISPERSIONS OF VARIOUS MATURITIESIn practice, designersor engineers do notquantify or measuredroplet size distributions,rather they areassumed based onempirical data or experience.Fortunately, anexperienced engineercan assume anapproximate distribu -tion based on themeans or mechanismby which the droplets are generated. Typical examples from commonmist sources are given to illustrate these concepts.Fine droplet distributions, often called fogs (