THE HEAT CAPACITY OF COAL CHARS.
Item
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Title
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THE HEAT CAPACITY OF COAL CHARS.
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Identifier
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AAI8203339
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identifier
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8203339
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Creator
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WANG, WEI-YEONG.
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Contributor
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Leslie L. Isaacs
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Date
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1982
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Language
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English
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Publisher
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City University of New York.
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Subject
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Engineering, Chemical
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Abstract
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During pyrolysis, the solid phase of coal is transformed into a microcrystalline structure with some extent of graphite-like orderliness. It is of interest to determine the thermodynamics of this structure which is believed to be process and coal origin dependent.;This study has been undertaken to elucidate the effect of the various factors on the heat capacity of coal chars. In order to assess the effect of coal rank and impurity content, several coals were obtained from the Pennsylvania State University Coal Bank. These selected starting materials were, a North Dakota lignite, an Illinois No.6 bituminous and a Virginia coking coal. The carbon content of these coals ranged from 59 to 75 wt% (mineral matter included). Half of each of the received coal sample was demineralized using a standard procedure. Chars were prepared from the received and demineralized coals by pyrolysis. Prior to pyrolysis, the coals were ground to less than 250 mesh size in a ball mill. A relatively slow heating rate of 5(DEGREES)C/minute was employed for the pyrolysis under dry nitrogen gas atmosphere. Both the pyrolysis temperature and the "soak time" (length of time the sample is kept at the pyrolysis temperature) were varied. The pyrolysis temperatures were 700, 900 and 1100(DEGREES)C. The soak times were 0.1, 1 and 24 hours. The char samples were characterized by chemical composition analysis, X-ray diffraction and porosimetry. Heat capacity data were collected over 75 to 300(DEGREES)K temperature range using an adiabatic calorimeter. The experimental specimens were vacuum dried for one hour at 110(DEGREES)C prior to loading into the calorimeter.;The heat capacity of these samples increases, in general, with increasing temperature and moisture content, and its behavior and order of magnitude are very similar to pure carbons when compared on a moisture free basis.;A modified Debye theory is presented to correlate the heat capacity behavior with the pyrolysis temperature T(,p) and chemical composition for the chars prepared from the selected coals. The correlation indicates that the heat capacity of coal chars is not a function of T(,p) alone, but it is also dependent on the coal from which it originates. This correlation model has been used to extend the heat capacity data of a gasifier char to lower temperatures. "Equilibrium" constants for methane formation from this char by hydrogenation gives an upper limit about six times higher than equilibrium over graphite in the temperature range of 1000 to 1200(DEGREES)K.;The mineral matter content also affects the measured heat capacity. The thermally transformed mineral matter (ash) contributes differently to the total heat capacity than the mineral matter in its original form.;The moisture-containing coal seems to have a higher heat capacity than expected by simple additive principle and shows a broad phase transition around ice point.;Due to the uncertainties of the chemical forms of the mineral matter and the water phase below room temperature, all the heat capacity data are analyzed on a dry mineral matter free basis.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
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Program
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Engineering
