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Corrosion in lower furnace of kraft recovery boilers--in-situ characterization of corrosive environments.

APPLICATION: Fireside corrosion in kraft recovery boilers in lower and mid furnace is a continuing problem in the pulp and paper industry. This paper describes some of the reasons for higher corrosion in localized areas of waterwall in the lower furnace. Findings from this study can be used to mitigate some of the lower furnace corrosion problems by making changes in operating conditions to avoid intentional or unintentional spray of black liquor on waterwalls.

Fireside corrosion in kraft recovery boilers is a continuing problem, especially in the boilers using carbon steel tubes in lower furnace areas. Certain areas in the lower furnace of kraft recovery boilers consistently have higher corrosion rates than the nearby areas. As the tube material in these areas is the same, differences in the corrosion rate suggest that the local environmental conditions in the two areas are different. Corrosive environments were characterized in a kraft recovery boiler, which had well-defined areas with high corrosion rates and low corrosion rates. Three important variables, tube surface temperature, gas composition at the waterwall surface, and smelt composition were monitored in the selected areas. Recovery boiler gases were analyzed using an on-line gas chromatograph. Temperature and smelt did not have any effect on differences in the corrosion rate in the two areas. Smelt was not present in either the low or the high corrosion rate areas. Gas compositions were found to be significantly different in the high corrosion area compared to the low corrosion area. This study demonstrated that direct pyrolysis of black liquor on the waterwall surface results in significantly higher concentrations of sulfur containing gases in the high corrosion areas, leading to higher corrosion rates of the waterwall. View this paper online at http://www.tappi.org/index.asp?pid=28651

Preet M. Singh is with the School of Materials, Science & Engineering, Georgia Institute of Technology, Atlanta; Safaa J. Al-Hassan, Sloane Stalder, and Greg Fonder are with the Institute of Paper Science and Technology, 500 10th Street., NW, Atlanta, GA, 30318. Email Singh at preet.singh@ipst.edu.
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Title Annotation:Corrosion
Publication:Solutions - for People, Processes and Paper
Date:Feb 1, 2004
Words:340
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Summaries of July 2005 peer-reviewed papers.

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