Plenary Talk: Hydrodynamics of High Temperature Gas-Solid Fluidized Beds

Gas-solid fluidized beds have been widely employed in chemical industries, such as thermal conversion
of fuels, oxidation of hydrocarbons, the FCC process, ore processing, and gas-phase polymerization.
Hydrodynamic characteristics of these units directly influence the heat and mass transfer rates, reaction
progress, and the overall performance of fluidized bed reactors. As many of these units are operated under
elevated temperatures, it is essential to adequately predict and/or thoroughly characterize the
hydrodynamics of high temperature fluidized beds for proper design and performance evaluation. In some
industrial sectors, e.g., mining and petroleum industries, as well as fuel and power fields, the compositions
of feedstock are rapidly becoming more complex owing to the rarefaction of conventional resources. The
application of reduced quality feedstocks leads the corresponding fluidized bed based processes to operate
in the presence of cohesive interparticle forces (IPFs). This is while available hydrodynamic correlations,
which were developed based on experimental data collected at near-ambient conditions and discard the
contribution of IPFs, are typically adopted for the design and performance evaluation of these units under
elevated temperatures. This, however, results in dubious predictions, in particular when IPFs are present
in the bed.

Application of clean electricity with microwave heating (MWH) technique, which is a volumetric and
selective heating technique, would make a revolution in the chemical industry. For multiphase systems,
as the response of each component to microwaves is different owing to different dielectric and magnetic
characteristics of adopted materials, a very large temperature gradient can be adeptly created within the
system. For instance, in the case of gas-solid systems, the application of MWH can yield particles to have
temperatures very different from the gas temperature. This feature can assist in promoting the desired
reactions on the surface of particles, if they act as catalysts since most catalytic agents are highly effective
microwave-to-heat converters, while suppressing the secondary gas-phase reactions since the gas-phase
components have negligible interactions with the electromagnetic waves.

In my presentation, I will first review our recent research activities on hydrodynamic characterization of
gas-solid fluidized beds at high temperature in the virtual absence and presence of IPFs. Second, I will
present a simple approach that we recently developed for quantifying the magnitude of cohesive IPFs in
a high temperature gas-solid fluidized bed. Particle agglomeration originates when the magnitude of
cohesive IPFs reaches to a high level. Hence, I will then review the mechanisms of particle agglomeration
in a high temperature gas-solid fluidized bed and present a novel, simple, effective, and robust approach
that we recently developed for early detection of defluidization in a high temperature bubbling gas-solid
fluidized bed reactor. I will next compare the performance of this newly developed approach with other
leading approaches proposed in the literature. In a following part, I will present a defluidization map that
we recently developed to assist in the solid fuel formulations to avoid defluidization during co-combustion
of coal with waste in a fluidized bed reactor. I will then present an empirical correlation that we introduced
for estimating defluidization boundaries, and the results of our detailed study in identifying the most
effective counteractive or pre-emptive measures to delay or prevent defluidization. In the last part of the
presentation, I will review principles of MWH mechanism and present our recent inventions on enhancing
selected gas-solid, liquid-solid, and liquid-liquid reactions by application of MWH mechanism.