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The Adverse Effects of Air Inleakage on ESPs

By TRK Engineering Services, Inc.

Air infiltration is an obvious but often overlooked source of precipitator problems, and identifying and eliminating sources of air inleakage on negative draft systems can have a a profound effect on ESP performance.  We are often asked, "What is an acceptable level of air inleakage?"  The answer depends on your system and how much corrosion or performance related problems you are willing to live with.  Air inleakage not only promotes corrosion of the precipitator and internal components, it can adversely effect performance by increasing gas volume and velocity, distorting gas distribution, reducing treatment time, affecting gas temperature (particle resistivity), reducing moisture content of the flue gas and causing reentrainment of particulate.  Identifying and eliminating air inleakage should be a part of routine maintenance to maintain optimum performance of a precipitator.

Why Minimize Heat Losses?

Line air inleakage, heat losses can cause reduction in gas temperature that can alter resistivity. ESP oversizing, poor heat distribution or localized areas within the ESP where temperatures are lower than elsewhere.  A temperature gradient can lead to differences in particle resistivity within zones of the same electrical field, causing the performance of the whole field to be adversely affected.  This is often evident in the gas passages adjacent to the outside casing walls of an ESP.  The effects of heat loss are usually magnified in outlet fields because of heat loss through the steel structure and the normal reduction of particle loading from inlet to outlet.  Upgrades should include the evaluation, or possible replacement, of the existing insulation barrier.  The insulation barrier should utilize chimney stops for heat distribution.  All penetrations in the insulation barrier, such as support members for access stairways, should be sealed at the point of penetration to minimize heat loss.  In some instances, consideration should be given to use of a double wall casing design where heated air is circulated between the walls to maintain temperature and reduce corrosion.

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Last updated: May 10, 2009.
Copyright 1997 TRK Engineering Services, Inc. All rights reserved.
For more information contact: TRK Engineering Services - 95 Clarks Farm Road - Carlisle, MA 01741 - Telephone: 978-287-0550 - Fax: 978-287-0569 - email: