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Title: Spectroscopic research on infrared emittance of coal ash deposits

Abstract

This paper deals with thermal radiation characteristics of ash deposits on a pulverized coal combustion boiler of an electric power plant. Normal emittance spectra in the near to medium infrared (2.5-25 {mu}m) region and total normal emittances were measured on four kinds of ground ash deposits. Measurements were conducted in the 570-1460 K temperature range which is common for boiler furnaces, by both heating and cooling the ash samples, with the aim to study the effect of their thermal history. Dependence of emittance on wavelength, temperature and chemical composition was studied, too. Samples were tested for transparency (opacity) to verify the accuracy of results. It was determined that the thicknesses used for the ash powders are opaque for infrared radiation for thicknesses in the order of a millimeter. Tests have shown that spectral emittance increases with an increase of wavelength with a characteristic pattern common for all samples. Spectral normal emittance increases strongly with temperature at shorter wavelengths and remains high and unchanged at longer ones. Emittance spectra are not very sensitive to chemical composition of ashes especially beyond {lambda} {approx} 5 {mu}m. With an increase of temperature, total emittance of the powdered sample decreases to a minimum value aroundmore » 1200 K. Further temperature rise induces an increase of total emittance due to sintering in the ash. On cooling, the emittance increases monotonically following the hysteresis. Quantitative directions for evaluating thermal radiation characteristics of ash deposits for the merits of the safety design of boiler furnaces were proposed. That comprises correlating the experimentally obtained emittance spectra with curves of simple analytical form, i.e., a continuous function of minimum emittance vs. wavelength. The proposed method can be extended to other specimens from the same furnace and used to determine correlations for thermal calculation of old and design of new furnaces - with similar geometry and combusting similar coal. The method is potentially applicable to completely different boiler furnaces combusting different coal, and the authors recommend running the tests with new deposit samples. The data will then be applicable to the thermal design of a whole new class of furnaces, having similar geometry and combusting similar coal. This is expected to greatly enhance the accuracy and precision of thermal calculation as well as the efficiency of thermal design of steam boilers. (author)« less

Authors:
; ;  [1];  [2];  [3];  [4]
  1. Department of Thermomechanics, Faculty of Mechanical Engineering, University of Belgrade, Kraljice Marije 16, 11120 Belgrade 35 (RS)
  2. Laboratory for Thermal Engineering, Institute of Nuclear Sciences VINCA, P.O. Box 522, Belgrade 11001 (RS)
  3. Faculty of Chemistry and Chemical Engineering, University of Maribor, Smetanova 17, Maribor 2000 (Slovenia)
  4. Faculty of Mining and Geology, University of Belgrade, Dusina 7, 11120 Belgrade 35 (RS)
Publication Date:
OSTI Identifier:
21227404
Resource Type:
Journal Article
Resource Relation:
Journal Name: Experimental Thermal and Fluid Science; Journal Volume: 33; Journal Issue: 8; Other Information: Elsevier Ltd. All rights reserved
Country of Publication:
United States
Language:
English
Subject:
20 FOSSIL-FUELED POWER PLANTS; COAL; ASHES; THERMAL RADIATION; DEPOSITS; FURNACES; OPACITY; BOILERS; DESIGN; WAVELENGTHS; INFRARED RADIATION; THICKNESS; ACCURACY; COMBUSTION; EMISSION SPECTRA; CHEMICAL COMPOSITION; COOLING; DIAGRAMS; SINTERING; TEMPERATURE RANGE 0400-1000 K; CORRELATIONS; FUNCTIONS; HEATING; POWDERS; FOSSIL-FUEL POWER PLANTS; TEMPERATURE RANGE 1000-4000 K; TEMPERATURE DEPENDENCE; Heat radiation; Spectroscopy; Emittance; Ash deposit; Boiler furnace

Citation Formats

Saljnikov, Aleksandar, Komatina, Mirko, Gojak, Milan, Vucicevic, Biljana, Goricanec, Darko, and Stevanovic, Zoran. Spectroscopic research on infrared emittance of coal ash deposits. United States: N. p., 2009. Web. doi:10.1016/J.EXPTHERMFLUSCI.2009.07.002.
Saljnikov, Aleksandar, Komatina, Mirko, Gojak, Milan, Vucicevic, Biljana, Goricanec, Darko, & Stevanovic, Zoran. Spectroscopic research on infrared emittance of coal ash deposits. United States. doi:10.1016/J.EXPTHERMFLUSCI.2009.07.002.
Saljnikov, Aleksandar, Komatina, Mirko, Gojak, Milan, Vucicevic, Biljana, Goricanec, Darko, and Stevanovic, Zoran. Sun . "Spectroscopic research on infrared emittance of coal ash deposits". United States. doi:10.1016/J.EXPTHERMFLUSCI.2009.07.002.
@article{osti_21227404,
title = {Spectroscopic research on infrared emittance of coal ash deposits},
author = {Saljnikov, Aleksandar and Komatina, Mirko and Gojak, Milan and Vucicevic, Biljana and Goricanec, Darko and Stevanovic, Zoran},
abstractNote = {This paper deals with thermal radiation characteristics of ash deposits on a pulverized coal combustion boiler of an electric power plant. Normal emittance spectra in the near to medium infrared (2.5-25 {mu}m) region and total normal emittances were measured on four kinds of ground ash deposits. Measurements were conducted in the 570-1460 K temperature range which is common for boiler furnaces, by both heating and cooling the ash samples, with the aim to study the effect of their thermal history. Dependence of emittance on wavelength, temperature and chemical composition was studied, too. Samples were tested for transparency (opacity) to verify the accuracy of results. It was determined that the thicknesses used for the ash powders are opaque for infrared radiation for thicknesses in the order of a millimeter. Tests have shown that spectral emittance increases with an increase of wavelength with a characteristic pattern common for all samples. Spectral normal emittance increases strongly with temperature at shorter wavelengths and remains high and unchanged at longer ones. Emittance spectra are not very sensitive to chemical composition of ashes especially beyond {lambda} {approx} 5 {mu}m. With an increase of temperature, total emittance of the powdered sample decreases to a minimum value around 1200 K. Further temperature rise induces an increase of total emittance due to sintering in the ash. On cooling, the emittance increases monotonically following the hysteresis. Quantitative directions for evaluating thermal radiation characteristics of ash deposits for the merits of the safety design of boiler furnaces were proposed. That comprises correlating the experimentally obtained emittance spectra with curves of simple analytical form, i.e., a continuous function of minimum emittance vs. wavelength. The proposed method can be extended to other specimens from the same furnace and used to determine correlations for thermal calculation of old and design of new furnaces - with similar geometry and combusting similar coal. The method is potentially applicable to completely different boiler furnaces combusting different coal, and the authors recommend running the tests with new deposit samples. The data will then be applicable to the thermal design of a whole new class of furnaces, having similar geometry and combusting similar coal. This is expected to greatly enhance the accuracy and precision of thermal calculation as well as the efficiency of thermal design of steam boilers. (author)},
doi = {10.1016/J.EXPTHERMFLUSCI.2009.07.002},
journal = {Experimental Thermal and Fluid Science},
number = 8,
volume = 33,
place = {United States},
year = {Sun Nov 15 00:00:00 EST 2009},
month = {Sun Nov 15 00:00:00 EST 2009}
}
  • The effective thermal conductivity of coal ash deposits strongly influences heat transfer in pulverized coal-fired boilers. In this study thermal conductivity measurements were performed over a wide range of temperatures for fly ash, slagging deposits, and fouling deposits. The effects of ash particle size, thermal history, and physical structure of the deposit are discussed. Thermal history and deposit structure were observed to have the greatest influence on the local thermal conductivity, which increased by an order of magnitude with particle melting. Conductivities for solid-porous deposits were twice those of the same sample in particulate form.
  • Thermal desorption spectrometry (TDS) and Fourier transform infrared photoacoustic spectroscopy (FT-IR/PAS) have been used in combination to analyze the water and hydroxyl groups associated with four coal fly ashes. Measurements using the former technique on these ashes resulted in identification of three water desorption regions in the temperature range from 25/sup 0/ to 1100/sup 0/C. The regions consisted of a small desorption peak at 50/sup 0/, a broad band from 180/sup 0/ to 400/sup 0/, and an intense peak from 400/sup 0/ to 590/sup 0/. No additional water desorption was observed up to 1100/sup 0/. A fourth ash gave amore » similar spectrum except that it lacked the intense last peak. The TDS spectra together with FT-IR/PAS spectra taken on samples exposed to pre- and post-desorption peak temperatures allowed the first TDS peak to be assigned to the desorption of physically adsorbed water, the broad band to desorption of hydrogenbonded surface hydroxyls, and the intense last peak to the decomposition of Ca(OH)/sub 2/.« less
  • Historically, two primary roles have emerged for infrared spectroscopy in stratospheric research. The first is to obtain data pertinent to the problems of radiative transfer and inversion within the terrestrial atmosphere, and the second is to obtain detailed information on the identification of a large number of minor constituents in the atmosphere and their concentration profiles with height. The three types of ir spectrometers used in laboratory studies are the prism and grating spectrometers and the moving-mirror Michelson interferometer system. Advantages and disadvantages of the last two for stratospheric research are discussed. Experience with the following systems for stratospheric researchmore » is also discussed: transmission spectroscopy, emission spectroscopy, emission interferometry, and He-cooled emission instruments. (JGB)« less