Doctor of Philosophy
Chemical and Biochemical Engineering
Dr. Cedric Briens
Dr. Franco Berruti
The performance of several important industrial processes, such as fluid coking or fluid catalytic cracking, is dependent on the good distribution of liquid feed sprayed into a fluidized bed of hot inert or catalytic particles, respectively.
Liquid injected into a fluidized bed is distributed in three different ways: (i) free moisture, or liquid coating individual particles; (ii) wet micro-agglomerates, which are fluidized; and (iii) wet macro-agglomerates, which settle to the bottom of the bed. This study develops and evaluates various methods for the determination of this moisture.
In the study using electrical techniques, two different kinds of electrodes geometries are considered, one single rod electrode and 5 separate plate wall electrodes. Several nozzles are used to spray water into a gas-solid fluidized bed: scaled-down versions of regular industrial nozzles and a nozzle (HALR) that uses an exceptionally high flowrate of atomization gas to provide a nearly perfect dispersion of the injected liquid on fluidized particles. Since the HALR nozzle does not form agglomerates, it is ideal to calibrate various methods for the measurement of the free moisture.
The properties of the wet agglomerates that are formed during injection are determined with a method that is only suitable for small beds. A sugar solution as a binder is injected into a fluidized bed, and the bed is defluidized to preserve the initial agglomerates until the entire bed dries out. The agglomerates are collected, sorted in different size cuts, and their initial liquid content is estimated from their sugar concentration.
The bed conductance is shown to provide an accurate measurement of the free moisture in both small and large fluidized beds. While plate wall electrodes provide the most accurate results, both experimental measurements and modeling results show how rod electrode geometry could provide reliable estimates of the free moisture. The rod electrode is applied in a large fluidized bed with commercial-scale spray nozzles to determine the best nozzle premixer and the best nozzle type.
Finally, a model is developed for predicting the bed conductance, using COMSOL Multiphysics and considering the collected agglomerates properties. The model is fully validated with experimental data.
Farkhondehkavaki, Masoumeh, "Developing Novel Methods to characterize Liquid Dispersion in a Fluidized bed" (2012). Electronic Thesis and Dissertation Repository. 444.