Numerical Modeling of Fixed-Bed Cocombustion Processes through the Multiple Thermally Thick Particle Model

Fixed-bed cocombustion provides opportunities for utilizing various low-quality solid residues, but there still remain obstacles for quantitative numerical modeling. The difficulties originate from the particles in the thermally thick regime and the diverse properties of different fuels. This work presents the multiple thermally thick particle (MTTP) model that considers detailed transport processes and chemical reactions in subparticle and interparticle scales, and different fuels can be assigned with distinctive physical and chemical properties. The model was validated by cocombustion experiments using wood and potato as representatives of low- and high-moisture fuels. The predicted results showed satisfactory agreement with measured values, and the characteristics of asynchronous conversion were clearly revealed. For thermally thick fuels with high moisture content, the drying process extends almost across the whole conversion zone and is highly overlapped with devolatilization process. Consequently, the structure of the in-bed conversion zone is beyond the expectation of conventional fixed-bed combustion theory.