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Research Papers: Power Engineering

Combined Effects of Overheating and Soot-Blower Erosion on Reheater Tubing in a Gas-Fired Large Capacity Boiler

[+] Author and Article Information
Nasr M. Hosny

Higher Institute of Engineering, Thebes Academy, P.O. Box 2075, Cairo 11511, Egypt

J. Eng. Gas Turbines Power 130(2), 023002 (Jan 22, 2008) (4 pages) doi:10.1115/1.2795769 History: Received May 28, 2006; Revised June 10, 2007; Published January 22, 2008

In a large capacity tangentially fired boiler, the final reheater tubing sustained abnormal oxidation and localized excessive metal wastage in a short time of the unit operation. The root causes of the problem are identified by test data analysis. The test data indicated that the reheater tubing metal temperatures in the affected areas exceeded the recommended limit of the metal oxidation temperature due to higher than expected local gas temperatures and velocities. A soot-blower facing the overheated portion of the reheater leading tubes accelerated the process of metal wastage by periodically removing the oxide layer. The configuration of the boiler internals upstream of the reheater section is found to be the main cause of the localized overheating. Side-to-side gas flow/temperature stratification due to tangential firing contributed to a lesser degree to the problem. The results and conclusions presented in this paper should be a beneficial guide to the designer of large capacity boilers.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 7

Calculated scale thickness as a function of time for the measured tube-metal temperatures of 563°C, 571°C, and 613°C (based on the approximated equation of French (8))

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Figure 5

Tube-metal temperatures and the front-tube outlet-steam temperatures

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Figure 6

Flue-gas temperature partial profiles

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Figure 3

Leading tube-thickness readings across the boiler width at the soot-blower elevation

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Figure 1

A side view of the upper section of the boiler shows the final reheater and upstream installations: a soot blower, water-tube screen, and the final superheater

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Figure 2

(a) Front-side external appearance of a tube sample removed from the leading tube of assembly 181 at the soot-blower level. (b) Microstructure of the same tube sample as appeared on the transverse section of the tube-wall front side.

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Figure 4

Reduction in tube thickness along the leading tube of each of the assemblies 8 and 179

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