CFD Modeling of char particle combustion in a Fluidized Bed

JOSÉ M. SORIA; MARIANA T. ZAMBON; ROSA A. RODRIGUEZ; STELLA MARIS UDAQUIOLA; DANIEL GAUTHIER; GILLES FLAMANT; GERMÁN D. MAZZA

Lille

Congreso; XIIIème Congrès de la Société Française de Génie des Procédés; 2011

SFGP

Combustion technologies are strongly developing over the world for two main reasons: they reduce the weight and volume of waste, while producing thermal energy. They can be used for eliminating all types of waste: Municipal Solid Waste (MSW) after sorting, as well as Hazardous Waste (HW), Medical Waste (MW), or Sewage Sludge. Although they are a good way of processing waste, their environmental impact is of great concern. Therefore, understanding the mechanisms and processes involved in the combustion of particles is of key importance in the development of more efficient combustion systems. The char combustion process is selected since this is the rate limiting stage in the overall process of combustion of coal particle in the Fluidized Bed and the char temperature during this stage is significantly higher than the temperature in the surroundings.In this work, Computational Fluid Dynamics tool is used for modeling the processes that take place in a single particle during Fluidized Bed combustion. The unsteady model comprises phenomena of heat and mass transfer through a porous char particle, thermal non-equilibrium between the phases, as well as heterogeneous reaction at the interior char surface along with the shrinkage of the particle. The only major simplification is the omission of volatiles evolution and combustion and heavy metal vaporization. Although these are important aspects for most practical wastes, the purpose here is to develop and validate a char model as a foundation on which to base later models of volatiles and pollutant processes. The results calculated via CFD are verified with experimental data, obtained in a laboratory scale bubbling fluidized bed incinerator, and also compared with a previous model developed by the group [1]. This model combines an asymptotic-combustion model for carbonaceous-solid combustion and a shrinking-core model to describe the heavy metal vaporization phenomenon, in which the particle is considered non-isothermal