Haoran Sun

Understanding the complex dynamics and spatial distribution of rising bubbles in fluidized bed gasifiers is crucial for designing, optimizing, and scaling up of the reactor. However, existing studies on bubble dynamics mainly focused on cold flow investigations, failing to capture the behavior of bubbles under the influence of chemical reactions and intricate coupling of heat transfer. Therefore, a reactive Lagrangian model is established to explore intricate bubble behaviors during biomass air gasification. The model is well validated with experiment, and the impact of operating parameters including bed temperature and equivalence ratio (ER) on the bubble behaviors is studied. The growth, coalescence, break, and eruption of rising bubbles are studied. A lower ER is recommended for better gasification performance. With an increase in the ER from 0.12 to 0.3, both the lower heating value and combustible gas concentration experienced a decrease of approximately 38.5% and 38.3%, respectively. The lateral feeding of biomass leads to asymmetrical distribution of bed temperature and bubble properties. Near the biomass inlet, a larger bubble aspect ratio is observed, possibly attributed to the hindrance in the lateral bubble growth due to the lateral biomass feeding. The bubble coordinate number is introduced to characterize the degree of bubble distribution density in a specific region. It is found that increasing the operating temperature results in a reduction in the density and an increase in the volume of bubbles at the bottom, resulting in a denser distribution of bubbles in this region. Although this concentrated bubble distribution may impact local heat and mass transfer, the differences in bubble distribution under temperature dominance gradually decrease along the reactor height. The impact of the operating conditions on the thermal properties and spatial distribution of bubbles obtained in this work can provide valuable guidance for practical gasification operations.

Biomass fast pyrolysis is a promising technology to produce available char and high‐value gas due to its green and sustainable ability. In the current work, the biomass fast pyrolysis in draft tube spouted bed has been numerically investigated via the multiphase particle‐in‐cell model. In this model, gas turbulence is calculated via large eddy simulation and particles are individually tracked in the Lagrangian manner. This model is successfully validated against experimental data. The particle‐scale information of sand and biomass feedstock has been discussed, and the influence of draft tube configuration on the pyrolysis performance has been studied. The results show that the equipment of draft tube prevents gas leakage from spout to annulus, leading to large axial gas flux in the spout. Biomass particles in the spout and freeboard have high temperature and heat‐transfer coefficient. Some biomass particles move along the outer wall of draft tube, indicating that the equipment of draft tube can avoid back‐mixing by preventing direct contact of particles in the spout and annulus. Increasing the height of draft tube results in larger axial gas flux and higher sand heat‐transfer coefficient, while decreases biomass temperature in the spout. The simulation results can offer valuable insights into comprehending intricate reactive gas–solid characteristics and conducting operation and design optimization of spouting apparatus.