Influence of gas and solid phase thermo-physical and transport properties on the thermo-chemical conversion of char in reacting media: intra-particle, microscopic and temporal mass loss-based sensitivity analysis

The article addresses the implications of adopting (a) non-kinetic theory-based correlations for the estimation of thermodynamic and transport properties and (b) over-simplifying assumptions, as reported in literature, in the numerical simulation of thermo-chemical conversion of char. A one-dimensional char thermo-chemical conversion model with discretisation to capture intra-particle gradients of temperature and species is developed. Species and mixture property estimations are based on kinetic theory approaches, and all extraneous assumptions are eliminated. Simulation results indicate char conversion in air and CO2 to be near diffusion (tc∼d01.8) and near kinetic (tc∼d01.05) limit, respectively, while char conversion in H2O has a competitive influence of both diffusion and kinetics (tc∼d01.35). Literature-specific correlations yield an order of magnitude deviation (up to 800%) in the properties (thermal conductivity, specific heat, mass diffusivity). Adopting mole/mass fraction weighted averaging for mixture transport properties results in variations to the extent of 85%. Unity Lewis number assumption introduces one order magnitude deviation in presence of H2. It is observed that the deviations introduced in conversion process can be surmounted by using correction factor in the kinetic rate parameters, a prevalent practice. Such an approach is however thermodynamically untenable.