10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Numerical Study on Evaporation of Inherent Minerals during Combustion of a Char Particle
SIBO QU, Haiming Wang, Changfu You, Tsinghua University, China
Abstract Number: 88 Working Group: Combustion-Generated Aerosols: the Desirable and Undesirable
Abstract A large number of experimental studies were performed to investigate the formation of ultrafine particles during combustion of pulverized coal. An evaporation-nucleation-coagulation mechanism has been established to describe this process.
A theoretical model, considering heat and mass transfer between the particle and the surrounding gas, has been developed in transient conditions to study the kinetics of evaporation of inherent minerals, the trend of particle size and ash content evolution, with allowance for the temperature distribution in particle. A comprehensive model for the prediction of the combustion of a char particle includes combustion model and inherent minerals release model in turn. Combustion model is composed of ash sub-model, intrinsic kinetics sub-model, diffusion sub-model and heat balance sub-model. Ash sub-model is mainly used to calculate the evolution of ash film thickness, and the ash content, based on the law of conservation of mass. Intrinsic kinetics sub-model and diffusion sub-model is mainly used to calculate the evolution of coal core size, considering the effect of ash and porosity in the char particle, the overall burning rate, consisting of the combination of the internal and external burning rates of the char.The heat released through char oxidation in the char core is transferred to the ash film through conduction, and then is transferred to the surroundings through convection and radiation. Considering the radiation heat transfer, convection heat transfer, and conductive heat transfer, the particle temperature are computed in heat balance sub-model. Iron and alkali metals is distributed on the surface of particle with coal ash separate out during combustion, and then into the surrounding gas. Based on the law of conservation of mass and energy between solid and gas, and the surface ionization controlled by iron and alkali metals content in coal ash, inherent minerals release model is set up.
The experimental data of iron and alkali metals release in coal ash are compared with theoretical results. Results indicate that this approach permits to predict the extent of evaporation of inherent minerals from a mineral porous matrix.