Pilot Scale Simulation of Ash Deposition on an Isolated Convective Tube: The Effect of Temperature on Deposit Growth

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Title Pilot Scale Simulation of Ash Deposition on an Isolated Convective Tube: The Effect of Temperature on Deposit Growth
Creator Walsh, Peter M.; Sayre, Alan N.; Loehden, David ; Beer, Janos M.; Sarofim, Adel F.
Publisher Digitized by J. Willard Marriott Library, University of Utah
Date 1988
Spatial Coverage presented at Pittsburgh, Pennsylvania
Abstract Fouling deposits were collected on a steam cooled tube at the exit of a pilot scale (1.5 MW thermal) furnace during combustion of Upper Freeport bituminous coal. The tube surface temperature was 1000°F. The objective of the work is to identify coal properties and combustion conditions with which one may anticipate fouling behavior of coal ash in electric utility boilers. Because of the high fusion temperature of the ash investigated (initial deformation temperature in oxidizing atmosphere 2630° F), deposition on a time scale practical for an experiment was observed only at furnace exit gas temperatures near 2700°F, above the temperatures expected at a radiant superheater or slag screen. A model is needed to make the results of these experiments applicable in the field. In order to model the process of deposit formation, the probability that incoming slag droplets and ash particles will stick on collision with a tube or deposit surface was related to their melting temperature or viscosity. The deposition rate and the structure of the deposit changed markedly when the deposit became thick enough, and its surface temperature high enough, that some of the incoming particles remained sticky on the deposit surface. Two deposit removal processes may compete with deposition to determine the net rate of deposit growth: 1. Erosion of nonsticky deposit by nonsticky particles, and 2. Shedding of large pieces of deposit due to vibration, temperature change, etc. The model provides an explanation for the observed sensitivity of deposit growth to temperature, a predictive capability which cannot be achieved using conventional measurements of ash fusion temperatures. The ability to make such calculations opens the way to quantitative estimates of improvements in plant availability associated with changes in coal preparation or operating conditions.
Type Text
Format application/pdf
Language eng
Rights This material may be protected by copyright. Permission required for use in any form. For further information please contact the American Flame Research Committee.
Conversion Specifications Original scanned with Canon EOS-1Ds Mark II, 16.7 megapixel digital camera and saved as 400 ppi uncompressed TIFF, 16 bit depth.
Scanning Technician Cliodhna Davis
Metadata Cataloger Kendra Yates
ARK ark:/87278/s6tx3hxq
Setname uu_afrc
Date Created 2012-04-20
Date Modified 2012-09-20
ID 5215
Reference URL https://collections.lib.utah.edu/ark:/87278/s6tx3hxq