The study on the relation between coal structure and its reactivity is of importance in understanding the mechanisms of coal combustion.  In this thesis, different from previous studies on coal combustion characteristics, the emphases are placed on petrographic structure and physical structure of coal, and their effects on the whole process of coal combustion.

The petrographic influences on coal combustion characteristics are studied in detail.  The morphology and reactivity studies of different maceral-rich coals with varied ranks are carried out based on gas adsorption, SEM and TG analysis. Moreover, a grey correlation method is used to analyze the key factors which affect the reactivity and morphology.

A new petrographic factor, which combines the influence of both the maceral and the rank together, is proposed to describe the variation of maceral with rank.  Taking account of the effects of maceral and rank on reactivity, while focusing on the essential aspects and main factors and leaving aside minor details or secondary factors which have shown to be obstacles to the application of petrography on coal combustion, the petro-factor is considered as a new concept and an improvement in the application of petrography on coal combustion.  The reason why study of maceral in coal combustion field did not get much progress in the past two decades is that more attention was paid on details of petrography instead of coal combustion itself.

The physical structure of coal/char is studied on three levels: the macro-level, the submicro- level and the micro-level.  On the macro-level, the influence of particle size on the burning rate of pulverized coal is studied.  The swelling of coal, which changes particle size, is also studied.  On the submicro-level, the features of the surface area and pore distribution are studied.  On the micro level, micro-crystallite  parameters obtained from XRD are studied along with active site.  TGA is presented to measure relative active site since it is concluded that the mass increase during the early stage is related with oxygen chemical adsorption.  The differences in oxygen chemical adsorption between coal, char and petroleum coke are used to at least partially explain the different reactivity of coal, coal char and petroleum coke.

The surface area of coal is an uncertain concept since it changes with different adsorbates. This phenomenon can be easily explained by fractal.  It is the first time to point out that fractal features of coal particle can be found from two different viewpoints.  One is caused by the distribution of pores and the irregularity of pore surface, which can be measured by gas adsorption. The fractal dimension shows the compound information of inner-pore.  A larger dimension of pore structure implies a more irregular surface and a larger diffusion obstacle.  Another is caused by the morphology of outer surface of coal/char particle.   Image processing technology is employed to analyze the texture of photographs of SEM.  A fractal dimension of morphology is obtained by calculating the subimage of grey level image, which can describe the change of outer-surface during the combustion process quantitatively.  Distinguishing the two fractal dimensions facilitates discussion the factors affecting the fractal dimension D, and the effect of D on reality.   The role of fractal dimension in reaction and diffusion has been theoretically discussed based on governing equations of diffusion reaction in this thesis.  The result shows there exists a best fractal dimension for reaction, which can be used to analyze and explain some experimental results got by previous studies, and will be a guide for fractal application on coal combustion and lead it from description to further analysis.

With the accumulation of knowledge on coal combustion, and the detailed study of structure and reactivity, it is the time to predict coal combustion behavior based on essential parameters of coal.  It has proved successful in predicting the ignition temperature from the proximate analysis using ANN technology in this thesis.  Furthermore, by involving petro-factor into ANN training, a better correlation between prediction value and experimental value can be obtained.  The prediction of ash fusion temperature based on ANN is also satisfactory.  A comparison between ANN and traditional regression method shows that ANN has superiority over the latter one.  The use of ANN in coal combustion research has formed a bridge between laboratory study and its application.

Based on above studies of relation between structure and reactivity, the effect of coal type and coal structure on coal combustion is evolved in the numerical simulation in this thesis.  Heterogeneous reaction model of char in a three-dimensional computational model of full-scale furnace is developed which is capable of reflecting changes in coal types.  A method to judge the combustion regime based on the oxygen content of the particle surface is put forward.  The evaluation of control step in reaction and the use of pore criterion to separate the physical and chemical factors affecting coal combustion are breakthroughs in the numerical simulation of coal combustion, which make it possible to implement in practice.  Moreover, it is closer to the practical prediction of the reactivity, which is the overall objective of coal combustion research.

Key words: coal/char, structure, reactivity, maceral, rank, petro factor, fractal, image processing, ANN, numerical simulation