Doctor of Philosophy
Chemical and Biochemical Engineering
Geldart Group C particles become increasingly attractive in industry because of their small particle sizes and large specific surface areas. The main challenge in the flow and fluidization of Geldart Group C particles is their cohesive nature due to strong interparticle forces. The “nanoparticle modulation” technique was adopted to reduce the interparticle forces of Group C particles and thus significantly improved their flow and fluidization quality. Group C+ particles, a new type of fine particles with drastically reduced or insignificant interparticle forces, were created using the nano-modulation technique.
Fundamental studies provided a comprehensive understanding of the fluidization quality of Group C+ particles. Group C+ particles exhibited revolutionary advancements in fluidization, which enabled its pseudo-particulate fluidization over a wide range of operating gas velocities, up to 200%-300% times that of bed expansion. Group C+ particles also exhibited much higher dense phase expansion than Group A particles, indicating more gas holdup in the dense phase available for intimate gas-solid contact. Bubbling behaviors for Group C+ particles were further fully characterized, showing that bubbles were smaller in diameter, lower in rise velocity, and had a longer residence time in the Group C+ fluidized bed in comparison with the Geldart Group A fluidized bed. With more gas flow through the dense phase for Group C+ particles, the correction factor Y that accounts for increased dense phase gas flow in the modified two-phase theory was correlated to characterize the division of gas flow between the two phases for Group C+ particles, based on the experimental results. A theoretical method for predicting the dense phase voidage for Group C+ particles was also proposed. Furthermore, Group C+ particles were used as catalysts in a fluidized bed reactor (C-plus FBR) to evaluate the reaction performance and were compared to that using Group A particles. C-plus FBR achieved a much higher reaction conversion, up to 235% of that using Group A particles, and a higher contact efficiency, being 330% more than that for Group A particles.
In summary, Group C+ particles exhibited extremely higher dense phase expansion, smaller bubbles and less bubble holdups, more gas flow through the dense phase, etc. enhancing the gas-solid contact and thus improving the reactor performance. Therefore, Group C+ fluidized bed reactor is expected to cause a significant “splash” in industrial processes, especially for gas-phase catalytic reactions.
Summary for Lay Audience
Fluidization is an important operation which solid particles are transferred into a fluidlike state through suspension in a gas or liquid. This unique method of contacting has some unusual characteristics, such as uniform temperature distribution, high heat/mass transfer rate, and particularly more solid surface area for gas reactant and thus better gas-solid contact efficiency, etc., making fluidized beds as the most popular reactors for multi-phase reactions, especially for gas-phase catalytic reactions.
The degree of gas-solid contact is one most important factor determining the performance of a conventional fluidized bed reactor. Geldart Group C particles which have small particle size (+particles, exhibited good flowability and fluidization quality.
A bubbling fluidized bed contains two phases, the bubble phase and the dense phase. Bubbles go through the bed quickly with little gas-solid contact, while the dense phase provides a close gas-solid contact. The fluidized bed of Group C+ particles showed much higher dense phase expansion, smaller bubbles and less bubble holdup, and higher gas flowrate through the dense phase than the bed of Group A particles, indicating more gas has the opportunity to contact with particles and contributing to better gas-solid contact. Furthermore, Group C+ particles were used as catalysts in a fluidized bed reactor and exhibited much higher reaction conversion than Group A particles as catalysts, due to the higher gas holdup in the dense phase and the larger gas-solid interfacial area. Conclusively, Group C+ particles with superior fluidization quality and reaction performance do have huge potential in gas-phase catalytic reactions.
Zhou, Yandaizi, "Fluidization Characteristics of Group C+ Particles: Fine Powder with Nanoparticle Modulation" (2020). Electronic Thesis and Dissertation Repository. 7135.
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