Computational modeling of oxy-coal combustion with intrinsic heterogeneous char reaction models

- Models for char reaction in oxy-coal combustion, based on intrinsic n-th order and LH mechanisms, were proposed.
- Model parameters, like pre-exponential factor, roughness factor, and tortuosity factor are sensitive to reaction rate.
- Gas penetration, ash inhibition and specific reaction rate were analyzed using single particle conversion model.
- CO2 gasification promotes gas or particle temperature at flame zone of furnace.
- Correlation that oxidation reactivity with coal type was proposed.

This paper simulated single char particle conversion and oxy-coal combustion in furnaces using modified intrinsic char reaction models that accounted for CO2 gasification. Firstly, modified char reaction models were exhibited, which encompassed intrinsic reaction mechanism, optimized ratio of primary char oxidation products, specific surface area and char density submodel, and effectiveness factor for reactants' diffusion. Then, simulations for single char particle conversion were conducted to explore the sensitivities of model parameters, and also to analyze the effects of conversion fraction on reaction rate and reactants' diffusion; the results showed that the pre-exponential factor, tortuosity factor, and roughness factor had the largest effect on reaction rate, meanwhile, oxidation rate and O2 diffusion were not greatly affected by conversion fraction until a high value (above 0.9), whereas gasification rate and CO2 diffusion were hardly influenced. Finally, the availability of the modified model was validated by several CFD calculations (maximal deviation of burnout < 2% compared with experimental data), and a correlation that related reactivity with coal type was proposed through linear regression of experimental data. Besides, the study of the effects of CO2 gasification on overall temperature and char burnout revealed that the reaction temperature was crucial.