STRUCTURAL EVOLUTION AND FRAGMENTATION PHENOMENA OF COAL PARTICLES IN COMBUSTION SYSTEMS

Fragmentation of coal particles during heat up, pyrolysis and combustion has been developed in Comsol Multiphysics environment. The model calculates the temperature and oxygen profiles within the particle, the evolution of internal porosity as a consequence of both devolatilization and carbon combustion, the mechanical stress caused by temperature gradients and by volatiles generated overpressure inside the particles. Eventually the model calculates the probability of rupture of the particle based on Weibull theory [1]. The validity of the model has been checked through comparison with results obtained in previous work [2-6]. A campaign of computational experiments has been carried out with reference to coals of given properties under a wide range of operating conditions, so as to address both traditional and most innovative combustion systems. The aim is to in investigate the evolution of porosity and structure of char upon a wide range of combustion conditions and to highlight situations where extensive fragmentation occurs, thus modifying significantly the particle size distribution and the residence time of coal in the reactor.