| dc.description.abstract | In the contemporary energy landscape, the escalating demand for energy has driven efforts to develop solutions for extracting energy from renewable sources. Among various technologies, fluidized beds are notably efficient for energy extraction through biomass gasification and combustion. This efficiency is attributed to their superior mixing, enhanced heat transfer and uniform temperature distribution. CFB technology is particularly applied in processes like pyrolysis, gasification and waste firing to produce high-quality producer gas, thereby meeting emission limits. In a single reactor CFB, particles are carried by the gas flow, separated using a cyclone and returned to the riser through a gas sealing mechanism such as a loop seal or valves. The efficient design and operation of CFB reactors depend on the gas-particle flow behavior and particle circulation rate under different process conditions.
This study investigates the dynamic flow behavior of Geldart A and Geldart B particles in a CFB using both experimental and computational simulation methods. Sand particles ranging from 63-200 µm in size were used as the bed material. A CPFD model was developed using the MP-PIC approach in a Barracuda virtual reactor. The CPFD model results were validated against experimental data obtained from pressure sensor readings at different reactor zones. The optimal velocities for smooth particle circulation were identified as 1.954 m/s in the riser and 0.0531 m/s in the loop seal. The results demonstrated that the Wen-Yu Ergun drag models predicted the flow dynamics behavior closely matching the experimental measurements among the several drag models tested.
Furthermore, different simulations were conducted under various design considerations, including changes in cyclone diameter and height, the angle of the downcomer (return pipe), the height of the return pipe and the transition from a double riser to a single riser configuration. These simulations were performed using CPFD software and the impact on the particle circulation rate was observed as design changes were implemented. Finally, a new design was developed based on individual design changes that maximized the circulation rate and the percentage increase in the circulation rate was evaluated. The final design showed 20.40 % increase in circulation rate. | |
