Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Dr. Cedric Briens & Dr. Franco Berruti

Abstract

Fluidized beds are widely used for a variety of processes such as food, pharmaceutical, petrochemical and energy production. As a typical application of fluidized beds, the fluid coking process uses thermal cracking reactions to upgrade heavy oils and bitumen from oil sands. In order to maintain a well fluidized bed and a satisfactory operation, a series of supersonic nozzles are used to inject high pressure steam in the bed to maintain the coke particle within an optimal range. Currently, the attrition nozzles consume a large florwrate of high pressure and superheated steam, which accounts for about 40 % of the total energy consumption in fluid coking reactors. Improving the efficiency of the attrition process would increase energy efficiency and reduce sour waste water production, reducing the environmental impact of heavy oil upgrading. Therefore, the main objective of the present thesis is an experimental and numerical study of particle attrition with supersonic nozzles in high temperature fluidized beds. The specific objective is to improve particle grinding efficiency and reduce the steam consumption in the fluid coking process.

To achieve the research objective, the primary investigations focused on the solids entrainment and penetration of jets issuing from supersonic nozzles, which have significant effects on particle attrition. Novel measuring techniques, therefore, were developed to accurately measure the flowrate of solids entrained into the jet and its penetration length. The numerical and experimental studies reveal that the jet penetration lengths are related to the two-phase Froude number. A new correlation was developed to predict the penetration length of jets issuing from supersonic nozzles in high temperature fluidized beds, based on Benjelloun’s correlation and the Froude number. The attrition experimental results demonstrate that larger scale nozzles, operating with a high flowrate of a low molecular weight gas at high temperature provide the highest grinding efficiency.

A jet-induced attrition model in fluidized beds at high temperature has been proposed and developed. The model is a coupled Eulerian-Eulerian multiphase model with a population balance method. The particle-particle interactions are described with the kinetic theory of granular flow. Experimental results were used to determine and modify the critical parameters of the model. The best prediction was obtained using the Ghadiri breakage kernel, generalized daughter size distribution function, and discrete solution method.

Finally, the research focused on the enhancement of jet-induced attrition in fluidized bed. A twin-jet nozzle gave a grinding efficiency that is about 35% higher than with a single nozzle. The benefits of the twin-jet nozzle seem stronger at higher nozzle pressures and high temperature. It is likely that the twin-jet nozzle entrains more solids into the jets when compared with a single nozzle with the same gas flowrate.


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