liquefaction pathways of bituminous subbituminous coals andtheir
liquefaction pathways of bituminous subbituminous coals andtheir liquefaction pathways of bituminous subbituminous coals andtheir
~ Firmre 1 : Visualization of fluidized coal particles using fluorescence microscopy, Coal particles appear dark on the otherwise bright background of fluorescent liquid. (a) Near top of column, the bed consists of only smaller particles (b) near bottom of column, the bed is a mixture of large and small coal particles. Video digitization, filtering and edge detection algorithms will be implemented to provide area fraction and particle size information from such images. 638
Dynamics of the Extract Molecular-Weight Distribution in supercritical Thermolysis of Coal: continuous-Mixture Kinetics Chunjie zhang, Ming Wang, J. M. Smith, Ben J. McCoy Department of Chemical Engineering University of California Davis, CA 95616 Keywords: coal, thermolysis, kinetics Introduction In this paper experimental molecular-weight distribution data for coal thermolysis at 340 OC and 360 OC in a differential flow reactor are interpreted by assuming that decomposition reaction rate expressions are continuous with molecular weight. Three groups of chemical species, representing polyaromatic compounds bound in the coal network by one, two, or more chemical linkages, are extracted simultaneously during the thermolysis reaction. The three groups are gamma distributions in molecular weight (Darivakis et al., 1990). The data support the hypothesis that the first-order rate coefficient is independent of molecular weight, and that as a consequence the MWD has a similar shape during the time of extraction. When the number of chemical species involved in a chemical process reaches a large number, e.g., 102-103, it is convenient to consider a property of the components to be a continuous variable. For example, the molecular weight, the number of carbon or oxygen atoms, or the boiling point of the different species can be considered a continuum of values, rather than discrete numbers. One line of inquiry is to formulate and solve the equations governing the chemical kinetics, or thermodynamics, of the continuous mixture, and to test the theory by experimentally measurinq the frequency of occurrence of the continuous variable (e.g., the molecular weight distribution). Another possible program is to average the governing equations to obtain relations for lumped variables that can be measured experimentally for the bulk mixture. Both these approaches have been explored for continuous-mixture the-. The theoretical issues of continuous mixture and lumping kinetics for chemical reactions have been addressed in numerous mathematical studies, but their use to interpret experimental data has been limited. In the present work we wish to apply concepts from continuous-mixture kinetics to thermolytic coal extraction. Some essential ideas of continuous-mixture kinetics provide a framework for the theoretical analysis of the data given below. The averaging, or lumping procedure shows how the kinetics governing the MWDs can lead to overall, lumped rate expressions used in most earlier studies of coal thermolysis. The overlapping groups of extractable compounds in the coal matrix present, in some cases, complications for lumping mathematics. The low temperature data (T 5 360 OC) are readily explained by first-order expressions with rate coefficients that are independent ‘of molecular weight and identical for the three groups of extractable compounds. The lumping in this case provides overall first-order rate expressions with the same rate coefficient. 639 1
- Page 113 and 114: EFFECT OF TEMPERATURE, SAMPLE SI2E
- Page 115 and 116: of some of the thermobalance runs.
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- Page 145 and 146: substructure have been identified a
- Page 147 and 148: Pyridine extraction showed that 60
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- Page 155 and 156: increased from 120°C to 135”C, r
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~<br />
Firmre 1 : Visualization <strong>of</strong> fluidized coal particles using fluorescence microscopy,<br />
Coal particles appear dark on the otherwise bright background <strong>of</strong> fluorescent<br />
liquid. (a) Near top <strong>of</strong> column, the bed consists <strong>of</strong> only smaller particles (b) near<br />
bottom <strong>of</strong> column, the bed is a mixture <strong>of</strong> large and small coal particles. Video<br />
digitization, filtering and edge detection algorithms will be implemented to provide<br />
area fraction and particle size information from such images.<br />
638
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