Two dimensional fluidized bed dynamics

• Autores: Sergio Sánchez Delgado
• Directores de la Tesis: Domingo Santana Santana (dir. tes.)
• Lectura: En la Universidad Carlos III de Madrid ( España ) en 2010
• Idioma: inglés
• Tribunal Calificador de la Tesis: Jorge Xiberta Bernat (presid.), Javier Villa Briongos (secret.), Juan José Hernández Adrover (voc.), Pedro Antonio Ollero de Castro (voc.), David Pallarès Tella (voc.)
• Materias:
  • Física
    • Química física
      • Termoquímica
  • Ciencias tecnológicas
    • Tecnología energética
      • Fuentes no convencionales de energía
    • Procesos tecnológicos
      • Fluidificación de sólidos
• Enlaces
  • Tesis en acceso abierto en: e-Archivo
• Resumen

  • There are different equipments where solid-gas reactions can take place. One of the most used equipments for these processes, are the uidized beds due to their high reaction rate per unit reactor volume. This complex gas-solid flow is often difficult to model because of the very different length scales that are present, so that additional fundamental investigations are needed before reliable models can be developed for the performance of fluidized beds. Among the different aspects in need of additional research, this PhD thesis focuses on the experimental investigation of the uid dynamics of the fluidized bed by use of pressure probes as well as nonintrusive measurements, based on Particle Image Velocimetry (PIV) and Digital Image Analysis (DIA) techniques, to characterize the flow in a two-dimensional experimental facility. In particular, the DIA technique is employed for the interpretation of images taken with a high-speed camera for different operating conditions. A clear difference between the dense phase and the bubble phase is established, thereby enabling different bubble parameters such as equivalent diameter, bubble mass center and bubble velocity to be quantified. In addition, the selected DIA technique allows us to detect and characterize dynamical bubble phenomena including bubble formation, growth and coalescence. In addition, to characterize the in fluence of the bubbles on the dense phase, the dense phase velocity has been measured with use made of the PIV technique. This PhD thesis reports relevant results with the aim to a better understanding of the dense and bubble phases interaction for different operation conditions, distributor design, fixed bed height, particle size and bed thickness. As a novel result, the circulation time was obtained, yielding an order-of-magnitude estimate for the mixing degree within the reactor. The present work also analyzes the effect of the bed thickness in the minimum uidization velocity, since this value is one of the most important parameters for reactor-design purposes. The influence regions promoted by the bubbles in the dense phase have been calculated, identifying and measuring the upwards and downwards solid movement regions around the bubble. The bubble size and the bubble velocity have been correlated with the volumetric dissipation of kinetic energy in the dense phase, providing information about the attrition phenomena responsible of the mechanical stress which leads to the gradual degradation of the individual bed particles, which in turn affects the fluidized bed behavior. Also, the influence of the grid configuration has been investigated. It has been proved that two uniform multi-orifice distributors, having the same pressure drop but different grid configurations yield the same dynamical bubble pattern and global bed behavior when the beds are operated at the same fluidization conditions. Consequently for the fluidization conditions covered, the overall bed dynamics for uniform gas distribution, do not depend on the grid configuration.---------------------------------------------------------------------------------------------------------------------------------------------