Non-isothermal effectiveness factors in thermo-chemical char conversion

• Main Authors: Markus Bösenhofer, Michael Harasek
• Format: Article
• Language: English
• Published: KeAi Communications Co., Ltd. 2021-01-01
• Series: Carbon Resources Conversion
• Subjects: Reaction-diffusion equation; Non-isothermal char conversion; Gas-solid reactions; Shooting method; Non-linear boundary value problem
• Online Access: http://www.sciencedirect.com/science/article/pii/S2588913321000120

Modeling heterogeneous combustion and gasification at large or industry scale is important in ongoing research and development activities. These simulations rely on comprehensive, accurate, and efficient solid conversion models. Pore diffusion is an important sub-process of gas–solid reactions and is often approximated by effectiveness factors. Analytic expressions for isothermal effectiveness factors are usually used, due to the numerical effort of determining non-isothermal ones. The consequences of this simplification are evaluated by determining non-isothermal effectiveness factors for typical combustion conditions for the reactions of carbon with O2,CO2,H2O, and H2. The results show that exothermal reaction rates are under-estimated, while endothermal are over-estimated at low and intermediate temperatures for Thiele moduli between 0.1 and 100. In addition, the reaction zone relocates towards the outer particle layers under these conditions. Cross-sensitivity effects between the four reactions are neglected in this study. A reasonable approximation is the superposition of the individual reactions, because the oxidation reaction is dominant under typical combustion conditions.