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A theoretical analysis of single coal particle behavior during spontaneous devolatilization and combustion

Autor :Shabi Ulzama
Herkunft :OvGU Magdeburg, Fakultät für Verfahrens- und Systemtechnik
Datum :26.04.2007
 
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Typ :Dissertation
Format :Text
Kurzfassung :The objective of this work has been to systematically analyze coal devolatilization, the radiation and convection effect over combustion, internal conduction within coal particle, and the reaction rates in circumstances where highly reactive gases come in contact with coal particle. The modeling concept of coal devolatilization is similar to that of the liquid droplet combustion except that volatiles emitted from the coal particle which has a constant diameter during devolatilization unlike droplet burning. An analytical model based on an assumption of combined quasi-steady and transient behavior of the process is presented to exemplify the unsteady, sphero-symmetric single droplet combustion under microgravity. The modeling approach especially focuses on predicting; the variations of droplet and flame diameters with burning time, the effect of vaporization enthalpy on burning behavior, the average burning rates and the effect of change in ambient oxygen concentration on flame structure. The droplet combustion model has been successfully implemented for description of devolatilization of a coal particle where more restrictive assumptions were made. The model describes the heat and mass transfer mechanisms among the particle, the flame, and the external environment. The volatile diffusive transport has been explained with quasi-steady state behavior unlike unsteady diffusive transport of oxidant. Moreover, the data incongruity existing in estimation of kinetic coefficients for gasification of coke by CO2 has shown a need to perform experimental investigation. This work includes experimental targets for re-estimation of kinetic rate coefficient of Boudouard reaction, which depends on the type of coke. A new set of activation energies and pre exponential factors differs mostly from the values available in the literature. Moreover, theoretical analyses are reported to describe the importance of Boudouard reaction during those combustion processes where the value of excess air number is approximately 1. Both the experimental and computational results reported in the present study suggest that Boudouard reaction has a great influence on process (air excess number ¡Ü 1) and shows dependence on a type of coal used in the process. Simulations of single particle combustion have been conducted using a steady state model that includes a detailed description of transport phenomenon coupled with chemical reactions. The results of simulations are compared with experimental data available in the literature.
Schlagwörter :Combustion, Coal, Droplet Combustion, Boudouard Reaction
Rechte :Dieses Dokument ist urheberrechtlich geschützt.
Größe :VI, 106 S.
 
Erstellt am :23.03.2009 - 14:51:11
Letzte Änderung :22.04.2010 - 09:07:48
MyCoRe ID :HALCoRe_document_00006330
Statische URL :http://edoc.bibliothek.uni-halle.de/servlets/DocumentServlet?id=6330