Bibliography: leaves 234-252. The devolution times of seven coals were determined by measuring the centre temperature response for single particles held stationary in a bench scale atmospheric fluidised-bed reactor.

Understanding the trajectories of particulate solids inside a flow-through reactor, such as the riser of a recirculating fluidized bed, is a basic requisite to accurately modelling the reactor. However, these trajectories, which are complicated by gross internal recirculation, are not readily measurable. Conventional means of measuring the residence time distribution can be applied to closed boundaries, such as the exit of the riser. Doing so, however, does not directly provide the details of the trajectories within the riser. In order to determine these trajectories, meaningful measurements must be made at the open boundaries between the adjacent axial regions which, in total, make up the riser. Transient tracer concentration measurements at open boundaries are ambiguous because, as tracer material recirculates past the sensor, its concentration is repeatedly recorded, with no distinction as to which region (above or below the boundary) it has just resided in. A method designed to eliminate this ambiguity at open boundaries is reported in this thesis. By repeatedly introducing single tracer particles into the riser, and measuring the time of passage through each axial region, the residence time distributions for each region can be obtained from the frequency density of these times. The crux of this approach is being able to sense individual tracer particles. The major thrust of this investigation has been to find a practical means to this end. The final sensor considered in this investigation is based on electromagnetic induction: a magnetic primary field induces an eddy current in a conductive tracer particle, and the resulting secondary field is sensed, indicating the presence of the tracer particle in the sensing volume. Noise, resulting from direct coupling between transmitter and receiver coils, electrostatics, and vibrations, determines the sensitivity of the device. The final prototype sensor is limited in sensitivity to relatively large tracer particles, and it is incapable of measuring tracer velocity. Nevertheless, the trajectory of large particles is of practical significance for circulating fluidized beds. Limited tests were conducted in a 0.15 m ID x 9.14 m tall acrylic riser where the tracer particles were injected opposite the solids re-entry point, and were sensed by a single sensor located at an open boundary 7.5 m downstream. At each of the two superficial gas velocities considered, and above a threshold solids flux, the time-of-flight frequency density between the injector and the sensor for these large tracer particles does not change with increasing flux of the fine solids. This result is incongruous with obvious changes in the macro-flow structure occurring in the riser. Recommended changes in the sensor would allow measurement of the direction and speed of the tracer, as it passes by the sensor, as well as potentially reducing noise. With these improvements, it would be useful to install multiple sensors along the full length of the riser. The information obtainable from such a configuration would greatly enhance understanding of the detailed trajectories within the riser. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Fluidized bed reactor studies were performed on the Claus reaction, ie. 2H₂S + S0₂<->3/n S[sub=n]n + 2H₂0. The basic objective was to determine whether the performance of the Claus process could be improved by replacing conventional fixed bed reactors with fluidized bed reactors. A computational procedure was developed which, unlike previous methods, does not require the user to specify the initial values for the iterative solution of the equilibrium equations. It is therefore possible to achieve, consistently, significant reductions in computer time and cost. The computer programme was used to simulate various idealized Claus plants. The results of the equilibrium calculations indicated that, for feed gases consisting of pure H₂S, sulphur conversions in excess of 99% are attainable by using a Claus furnace and two fluidized bed reactors in series. To substantiate the theoretical predictions, experimental studies were performed using a single fluidized bed reactor (0.1 m ID). The effects of temperature (150 - 300°C), flow rates (15 - 30 1/min), feed composition (0.06<H₂S<18%, 0.03<S0₂<9%, 73<N₂<99.91%) and bed height (0.12, 0.25 m) on the sulphur conversion were examined. The experimental results showed the same general trends as the theoretical predictions. However, the measured sulphur conversions exceed the theoretical values by up to 8%. Reasons for these discrepancies are discussed. Based on the theoretical and experimental studies, fluidized bed reactors appear to be technically superior to the conventional fixed bed devices. However, a proper commercial evaluation has to await longer term studies with larger fluidized beds. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

<p> The spontaneous oscillations of a fluidized bed with a variable volume below the bed support are investigated.</p> <p> The pressure vs. time dependence of the fixed bed is determined for glassbeads of 3 size ranges and for hematite.</p> <p> For each case several different bed masses were employed. For the oscillating bed the influence on the frequency of the oscillations of the materials fluidized, the size of the particles, the chamber volume and the superficial gas velocity are studied.</p> <p> Models of five different authors have been reviewed and a model to describe the relationship between the frequency and various parameters such as chamber volume, bed mass, gas velocity and the pressure drop characteristic (Δp vs. μ) is derived. The latter together with three other models have been evaluated by means of the experimental data.</p> / Thesis / Master of Engineering (MEngr)

No description available.

No description available.

No description available.

Graduation date: 1995

No description available.

No description available.