An Improved Model for Heat Transfer at Particle Surfaces During Heterogeneous Char Combustion

摘要

In this work, the impact of char oxidation rate and its produced heat on the coal combustion process is studied through simulation. In the gas phase, a detailed kinetics model based on GRI 3.0 is applied. A Lagrangian formulation for the coal particle phase is fully coupled with the gas phase where the evolution of coal constituents are modeled through evaporation, devolatilization (chemical percolation devolatilization model) and char gasification/oxidation. Two different models for char oxidation namely, the n~(th)-Order Langmiur-Hinshelwood (LH) and the Char Conversion (CCK) models are utilized. The exothermic char oxidation has a major impact on the coal combustion process. A fraction (α) of the heat produced through char oxidation transfers to the gas phase is while the remainder is absorbed by the coal particle. In this work, a dynamic model for α is proposed and its prediction is compared with experimental results for single-particle time-temperature histories. The proposed model for α shows significant improvement in agreement with the experimental data relative to previous models which assumed constant α. The gasification rate using the LH model is significantly affected by applying the dynamic α model at high oxygen concentration, whereas the CCK model does not show considerable sensitivity.