Non-Isothermal Effectiveness Factors in Coal Combustion

Abstract

Thermo-chemical conversion of porous solids like coal is often modeled using generic approaches capable to reproduce chemical kinetic and mass transfer limitations of the conversion rate. The effectiveness factor (η) is used to describe the intraparticle mass transfer limitations in these models. Since a non-linear second order reaction-diffusion equation has to be solved to obtain the effectiveness factors for exothermic reactions, analytic solutions for the isothermal case are often used instead of solving the reaction diffusion equation. For highly exothermic reactions, this approach might underestimates the conversion rates. Therefore, this work investigates the influence of non‑isothermal effectiveness factors on conversion rates under coal combustion conditions.The results indicate that non-isothermal effectiveness factors cause a change in the conversion characteristics from progressive core to shrinking particle. Moreover, the conversion rates might be significantly under-estimated by the isothermal effectiveness factors for the investigated conditions.