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Title: Predicting slag viscosity from coal ash composition

Abstract

Management of slag flow from cyclone-fired utility boilers requires accurate prediction of viscosity. Cyclones tend to build up slag when the cyclone combustion temperature is less than the temperature required to melt and tap the ash from the coal being fired. Cyclone-fired boilers designed for lignite are equipped with predry systems, which remove 6-9% of the moisture from the coal. Cyclones tend to slag when the as-received heating value of the fuel is less than 6350 Btu/lb and T250 (temperature where viscosity equals 250 poise) is greater than 2350 F. The T250 value, as well as the rest of the viscosity-temperature relationship, can be predicted using models based on coal ash composition. The focus of this work is to evaluate several models in terms of their agreement with measured viscosities. Viscosity measurements were made for ten samples, including nine lignite coals and one lignite-derived slag. Model performance is related to the SiO{sub 2}, CaO, and Fe{sub 2}O{sub 3} contents of the slag. The Sage and McIlroy and Kalmanovitch models worked best for high SiO{sub 2} and low Fe{sub 2}O{sub 3} fuels. The Senior model worked best when Fe{sub 2}O{sub 3} content was moderate to high.

Authors:
; ; ; ;
Publication Date:
Research Org.:
Microbeam Technologies Inc., Grand Forks, ND (US)
OSTI Identifier:
20082332
Resource Type:
Conference
Resource Relation:
Conference: Sixteenth Annual International Pittsburgh Coal Conference, Pittsburgh, PA (US), 10/11/1999--10/15/1999; Other Information: 1 CD-ROM. Operating systems required: Windows 95/98; Windows 3.X, Macintosh; PBD: 1999; Related Information: In: Sixteenth annual international Pittsburgh Coal Conference: Proceedings, [2000] pages.
Country of Publication:
United States
Language:
English
Subject:
01 COAL, LIGNITE, AND PEAT; SLAGS; VISCOSITY; ASH CONTENT; CHEMICAL COMPOSITION; CYCLONE COMBUSTORS; LIGNITE; CALORIFIC VALUE; MATHEMATICAL MODELS; PERFORMANCE

Citation Formats

Laumb, J., Benson, S.A., Katrinak, K.A., Schwalbe, R., and McCollor, D.P.. Predicting slag viscosity from coal ash composition. United States: N. p., 1999. Web.
Laumb, J., Benson, S.A., Katrinak, K.A., Schwalbe, R., & McCollor, D.P.. Predicting slag viscosity from coal ash composition. United States.
Laumb, J., Benson, S.A., Katrinak, K.A., Schwalbe, R., and McCollor, D.P.. 1999. "Predicting slag viscosity from coal ash composition". United States. doi:.
@article{osti_20082332,
title = {Predicting slag viscosity from coal ash composition},
author = {Laumb, J. and Benson, S.A. and Katrinak, K.A. and Schwalbe, R. and McCollor, D.P.},
abstractNote = {Management of slag flow from cyclone-fired utility boilers requires accurate prediction of viscosity. Cyclones tend to build up slag when the cyclone combustion temperature is less than the temperature required to melt and tap the ash from the coal being fired. Cyclone-fired boilers designed for lignite are equipped with predry systems, which remove 6-9% of the moisture from the coal. Cyclones tend to slag when the as-received heating value of the fuel is less than 6350 Btu/lb and T250 (temperature where viscosity equals 250 poise) is greater than 2350 F. The T250 value, as well as the rest of the viscosity-temperature relationship, can be predicted using models based on coal ash composition. The focus of this work is to evaluate several models in terms of their agreement with measured viscosities. Viscosity measurements were made for ten samples, including nine lignite coals and one lignite-derived slag. Model performance is related to the SiO{sub 2}, CaO, and Fe{sub 2}O{sub 3} contents of the slag. The Sage and McIlroy and Kalmanovitch models worked best for high SiO{sub 2} and low Fe{sub 2}O{sub 3} fuels. The Senior model worked best when Fe{sub 2}O{sub 3} content was moderate to high.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1999,
month = 7
}

Conference:
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  • Since 1980, Bituminous Coal Research, Inc., (BCR) has been conducting measurements on the viscosity of western U.S. low-rank coal slags under a contract with the Grand Forks Energy Technology Center (GFETC), U.S. Department of Energy. This work has been motivated by the realization that very few data exist in the literature on the viscosity of low-rank-coal slags; published correlations relating slag viscosity to coal ash composition were derived from work with bituminous-coal slags, and attempts to apply them to data from low-rank coal slags generally have been unsuccessful; and, from a practical standpoint, data on slag rheology are of considerablemore » interest in support of the operation of a slagging fixed-bed lignite gasifier at GFETC. As a matter of related interest, BCR's slag viscometer was originally put into operation in 1976 to obtain data on the slagging properties of coals intended for use in the BI-GAS coal gasification pilot plant at Homer City, Pennsylvania; the BI-GAS process incorporates an entrained-bed, slagging gasifier. Although the data obtained in these studies have been valuable in interpreting the slagging phenomena observed in the Grand Forks gasifier tests, a more fundamental objective of the current work is to develop correlations that can be used to predict a priori the viscosity behavior of low-rank-coal slags from a knowledge of the ash or slag composition.« less
  • With the advent of advanced coal-fired power systems operating at higher working fluid temperatures, slag corrosion, erosion, and fouling of heat exchanger surfaces will become even more of a problem than in today`s systems. Laboratory experiments have shown excessive corrosion of candidate alloy and ceramic heat exchanger materials by both calcium-rich subbituminous and iron-rich bituminous coal slags. The viscosity of the slag greatly affects the corrosion rate since it determines the rate of transfer of corrosive species to the materials and corrosion product away from the materials. Slag viscosity is controlled by the composition of the slag and surrounding atmospheremore » as well as its temperature. In this paper we report the results of investigations of the viscosities and critical temperatures of three coal slags in three atmospheres: air, air plus water vapor, and reducing gas. In addition, the effects of additions of alumina, magnesia, and copper oxide on viscosity, crystallization, and critical temperature of the slags are reported. Conclusions are drawn about appropriate test conditions for determining slag corrosion rates and about ways of modifying slag viscosity to reduce corrosion rates.« less
  • This is part of a study of the slagging operation in the fixed-bed slagging coal gasification pilot plant. The equation log/sub 10/ eta = 10/sup 7/M/(T-150)/sup 2/ + C was used to calculate the viscosity eta from the temperature T(/sup 0/C); values of the constants C and M were computed by linear regression from the slag composition. Equations were derived for the feldspar and pyroxene normative slags: (feldspar) C = -4.5413 - 0.2158(K/sub 2/O) + 0.0883(SiO/sub 2/) + 0.0091(Al/sub 2/O/sub 3/) and M = 0.3676 + 0.0783(K/sub 2/O) - 0.0043(Al/sub 2/O/sub 3/); (pyroxene) C = 0.8143(Fe/sub 2/O/sub 3/) - 4.8749more » and M = 0.1135(Fe/sub 2/O/sub 3/) - 0.5219. (DLC)« less
  • The viscosities of 21 synthetic coal slags (30 to 50 wt % SiO/sub 2/) were measured as a function of temperature under oxygen partial pressures (about 10/sup -8/ to 10/sup -9/ atm) and, in some cases, under an ambient air environment. The viscosity of any given slag composition is a single-valued function of the temperature and oxygen partial pressure and does not exhibit a hysteresis effect. The measured viscosities were significantly different from the viscosities one would predict from two of the more commonly used viscosity-temperature-composition correlations. The sensitivity of viscosity to oxygen partial pressure was greatest for the slagsmore » with high iron content. An examination of log reciprocal viscosity versus reciprocal absolute temperature indicates that many slags went through a transition near temperatures corresponding to final solidification in a related ternary phase equilibrium diagram. 5 figures.« less