No description available.

A fluidized bed gasification (FBG) pilot plant was designed and constructed at the University of Saskatchewan Chemical Engineering Department Fluidization Laboratory. FBG is a thermo-chemical method for converting solid biomass to a gaseous fuel, termed syngas. Several instrumentation and control issues were particularly challenging with this pilot plant, including development of the fuel feeding system, pressure measurement of high temperature fluids, and metering of steam as a process reactant.<p> The fuel feeding system was tested using MBM (meat and bone meal) to determine the output rate stability, and predictability and measurability of the system as the components in the fuel feeding system were integrated. The fuel feeding system that was tested included a 150 mm primary metering screw conveyor, a 150 mm rotary airlock, and a 50 mm secondary injection screw conveyor. Each component of the system was fitted with a 3-phase electric motor and a variable speed drive to allow for a variable output rate. The weighing system that was integral to the metering conveyor was tested as well, but upon pressurizing the metering conveyor and hopper, the weighing system sustained an unreasonable amount of noise. Integrating a pneumatic injection nozzle with the injection conveyor was found to work effectively both under ambient temperatures and hot FBG conditions up to 725oC. Above 725oC, it was found that the test fuel would char and coat the nozzle, causing it to plug. Testing of the feeding system with the injection nozzle removed illustrated that the system could work well without it. It was determined that the injection conveyor speed to metering conveyor speed ratio that should be used for this system was 1:110 for absolute rotational speeds, or 1:1 of the full conveyor speeds. The complete system, including the injection nozzle, was analyzed and determined to produce a fuel output rate (FS) for % speeds from 5-25%, which roughly corresponded to the desired plant fuel feed rate of 1-5 g/s.<p> Techniques for remote pressure measurement of fluidized beds were examined as well, including the use of long tubes to cool hot gases and filters for blocking solid particles. The pressure measurement delay of these techniques was examined in comparison to a direct local measurement. This was conducted by comparing the pressure readings from two identical sensors; one mounted directly to a manifold, and the other mounted via a variable assembly (comprised of a variable length of 6.35 mm (1/4") PE tubing and a porous plate filter). Assemblies without a porous plate were found to have a minimal delay of up to 0.303 seconds for 30 m length of PE impulse tubing. More significant delays were found for systems using both a 10 media grade porous plate filter and impulse tubing; a 3 m tube length with filter has a delay of up to 0.221 s, and a 30 m impulse tube combined with the filter has a measurement delay of up to 1.915 s, a significant delay in cases where high-frequency analysis of pressure is used for bed agglomeration prediction, or systems where fast response is required to changing pressure conditions.<p> Additionally, a steam flow measurement system using an orifice plate and differential pressure sensor was installed and calibrated. By collecting time-based steam samples and process data, the physical system coefficients were determined for this system, allowing for steam flow measurement, accurate within 5% over a flow range of 0.5 to 2.0 g/s.

A fluidized bed gasification (FBG) pilot plant was designed and constructed at the University of Saskatchewan Chemical Engineering Department Fluidization Laboratory. FBG is a thermo-chemical method for converting solid biomass to a gaseous fuel, termed syngas. Several instrumentation and control issues were particularly challenging with this pilot plant, including development of the fuel feeding system, pressure measurement of high temperature fluids, and metering of steam as a process reactant.<p> The fuel feeding system was tested using MBM (meat and bone meal) to determine the output rate stability, and predictability and measurability of the system as the components in the fuel feeding system were integrated. The fuel feeding system that was tested included a 150 mm primary metering screw conveyor, a 150 mm rotary airlock, and a 50 mm secondary injection screw conveyor. Each component of the system was fitted with a 3-phase electric motor and a variable speed drive to allow for a variable output rate. The weighing system that was integral to the metering conveyor was tested as well, but upon pressurizing the metering conveyor and hopper, the weighing system sustained an unreasonable amount of noise. Integrating a pneumatic injection nozzle with the injection conveyor was found to work effectively both under ambient temperatures and hot FBG conditions up to 725oC. Above 725oC, it was found that the test fuel would char and coat the nozzle, causing it to plug. Testing of the feeding system with the injection nozzle removed illustrated that the system could work well without it. It was determined that the injection conveyor speed to metering conveyor speed ratio that should be used for this system was 1:110 for absolute rotational speeds, or 1:1 of the full conveyor speeds. The complete system, including the injection nozzle, was analyzed and determined to produce a fuel output rate (FS) for % speeds from 5-25%, which roughly corresponded to the desired plant fuel feed rate of 1-5 g/s.<p> Techniques for remote pressure measurement of fluidized beds were examined as well, including the use of long tubes to cool hot gases and filters for blocking solid particles. The pressure measurement delay of these techniques was examined in comparison to a direct local measurement. This was conducted by comparing the pressure readings from two identical sensors; one mounted directly to a manifold, and the other mounted via a variable assembly (comprised of a variable length of 6.35 mm (1/4") PE tubing and a porous plate filter). Assemblies without a porous plate were found to have a minimal delay of up to 0.303 seconds for 30 m length of PE impulse tubing. More significant delays were found for systems using both a 10 media grade porous plate filter and impulse tubing; a 3 m tube length with filter has a delay of up to 0.221 s, and a 30 m impulse tube combined with the filter has a measurement delay of up to 1.915 s, a significant delay in cases where high-frequency analysis of pressure is used for bed agglomeration prediction, or systems where fast response is required to changing pressure conditions.<p> Additionally, a steam flow measurement system using an orifice plate and differential pressure sensor was installed and calibrated. By collecting time-based steam samples and process data, the physical system coefficients were determined for this system, allowing for steam flow measurement, accurate within 5% over a flow range of 0.5 to 2.0 g/s.

Made available in DSpace on 2014-10-09T12:37:02Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:56:31Z (GMT). No. of bitstreams: 1 04495.pdf: 1601893 bytes, checksum: e55704a48b48bc206869a88930e54240 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:37:02Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:56:31Z (GMT). No. of bitstreams: 1 04495.pdf: 1601893 bytes, checksum: e55704a48b48bc206869a88930e54240 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Microwave heating is implemented in various fields such as drying, material processing, and chemical reactors. Microwaves offer several advantages over conventional heating methods: 1) microwaves deposit heat directly in the material without convection or radiation, 2) microwave heating is easy and efficient to implement, and 3) microwave processes can be controlled.In order to understand how to use microwaves more efficiently, we must understand how they affect the material with which they interact.This requires the ability to predict the temperature distribution that is achieved within the material.In recent years packed and fluidized beds have been used as chemical reactors to achieve various tasks in industry.Recent studies have shown that microwave heating offers the potential to heat the bed particles to a higher temperature than that of the fluid.This results in enhanced reaction rates and improves the overall efficiency of the reactor.T he focus of this work is to determine the temperature distributions within the packed and fluidized beds, and to determine whether the catalyst particles can be heated to a higher temperature than the gas in catalytic reactions. The beds are modeled with multiphase flow equations.The gas velocity profiles along with the solid and gas temperature profiles for packed and fluidized beds are provided. F or the fluidized beds, the hydrodynamics is modeled using FLUENT and the solid velocity profiles are also determined. / Ph. D.

Computational fluid dynamics (CFD) modeling was used to predict the gas-solid hydrodynamics of fluidized beds. An Eulerian-Eulerian multi-fluid model and granular kinetic theory were used to simulate fluidization and to capture the complex physics associated therewith. The commercial code ANSYS FLUENT was used to study two-dimensional single solids phase glass bead and walnut shell fluidized beds. Current modeling codes only allow for modeling of spherical, uniform-density particles. Owing to the fact that biomass material, such as walnut shell, is abnormally shaped and has non-uniform density, a study was conducted to find the best modeling approach to accurately predict pressure drop, minimum fluidization velocity, and void fraction in the bed. Furthermore, experiments have revealed that all of the bed mass does not completely fluidize due to agglomeration of material between jets in the distributor plate. It was shown that the best modeling approach to capture the physics of the biomass bed was by correcting the amount of mass present in the bed in order to match how much material truly fluidizes experimentally, whereby the initial bed height of the system is altered. The approach was referred to as the SIM approach. A flow regime identification study was also performed on a glass bead fluidized bed to show the distinction between bubbling, slugging, and turbulent flow regimes by examining void fraction contours and bubble dynamics, as well as by comparison of simulated data with an established trend of standard deviation of pressure versus inlet gas velocity. Modeling was carried out with and without turbulence modeling (k-ϵ), to show the effect of turbulence modeling on two-dimensional simulations. / Master of Science

Gas fluidised beds are important components in many process industries, e.g. coal combustors and granulators, but not much is known about the movement of the solids. Positron Emission Particle Tracking (PEPT) enables the movement of a single, radioactive tracer particle to be followed rapidly and faithfully. Experiments were carried out in columns sized between 70 and 240mm diameter, operating in the bubbling regime at ambient process conditions using particles of group B and D (Geldart Classification). Particle motion was tracked and the data applied to models for particle movement at the gas distributor as well as close to other surfaces and to models for particle circulation in beds of cohesive particles. In the light of these data, models for particle and bubble interaction, particle circulation, segregation, attrition, erosion, heat transfer and fluidised bed scale-up rules were reassessed. Particle motion is directly caused by bubble motion, and their velocities were found to be equal for particles travelling in a bubble. PEPT enables particle circulation to be measured, giving a more accurate correlation for future predictions. Particle motion follows the scale-up rules based on similarities of the bubble motion in the bed. A new group of parameters was identified controlling the amount ofattrition in fluidised beds and a new model to predict attrition is proposed.

Pas de résumé / Fluidized beds are a particular hydrodynamic configuration in which a pack (either dense or loose) of particles laid inside a container is re-suspended as a result of an upward oriented imposed flow at the bottom of the pack. This kind of system is widely used in the chemical engineering industry where catalytic cracking or polymerization processes involve chemical reactions between the catalyst particles and the surrounding fluid and fluidizing the bed is admittedly beneficial to the efficiency of the process. Due to the wide range of spatial scales and complex features of solid/solid and solid/fluid interactions in a dense fluidized bed, the system can be studied at different length scales, namely micro, meso and macro. In this work we focus on micro/meso simulations of fluidized beds. The workflow we use is based on home made high-fidelity numerical tools: GRAINS3D (Pow. Tech., 224:374-389, 2012) for granular dynamics of convex particles and PeliGRIFF (Parallel Efficient LIbrary for GRains In Fluid Flows, Comp. Fluids, 38(8):1608-1628,2009) for reactive fluid/solid flows. The objectives of our micro/meso simulations of such systems are two-fold: (i) to understand the multi-scale features of the system from a hydrodynamic standpoint and (ii) to analyze the performance of our meso-scale numerical model and to improve it accordingly. To this end, we first perform Particle Resolved Simulations (PRS) of liquid/solid and gas/solid fluidization of a 2000 particle system. The accuracy of the numerical results is examined by assessing the space convergence of the computed solution in order to guarantee that our PRS results can be reliably considered as a reference solution for this problem. The computational challenge for our PRS is a combination of a fine mesh to properly resolve all flow length scales to a long enough physical simulation time in order to extract time converged statistics. For that task, High Performance Computing and highly parallel codes as GRAINS3D/PeliGRIFF are extremely helpful. Second, we carry out a detailed cross-comparison of PRS results with those of locally averaged Euler- Lagrange simulations. Results show an acceptable agreement between the micro- and meso-scale predictions on the integral measures as pressure drop, bed height, etc. However, particles fluctuations are remarkably underpredicted by the meso-scale model, especially in the direction transverse to the main flow. We explore different directions in the improvement of the meso-scale model, such as (a) improving the inter-phase coupling scheme and (b) introducing a stochastic formulation for the drag law derived from the PRS results. We show that both improvements (a) and (b) are required to yield a satisfactory match of meso-scale results with PRS results. The new stochastic drag law, which incorporates information on the first and second-order moments of the PRS results, shows promises to recover the appropriate level of particles fluctuations. It now deserves to be validated on a wider range of flow regimes.

Biomass is an alternative to fossil fuels that has a lower impact on the environment and is thus of great interest to replace fossil fuels for energy production. There are several technologies to convert the stored energy in biomass into useful energy and this thesis focuses on the process of gasification. The purpose of this thesis is to investigate how the prediction accuracy of gas composition in a kinetic model for fluidized bed gasifier is affected when hydrodynamic parameters are introduced into the model. Two fluidized bed gasifier models has therefore been set up in order to evaluate the affects: one model which only considers the kinetics of a gasifier and a second model which includes both the kinetics and the hydrodynamic parameters for a bubbling fluidized bed. The kinetic model is represented by an already existing kinetic model that is originally derived for a downdraft gasifier which has quite similar biomass gasification processes as fluidized bed gasifiers. Gas residence time differs between the two gasifier types and the model has thus been calibrated by introducing a time correction factor in order to use it for fluidized bed gasifiers and get optimum results. Two sets of experimental data were used for comparison between the two models. The models were compared by comparing the results of the predicted gas composition yield and the amount of unreacted carbon after the reactor at various equivalence ratios (ER). The result shows that the model that only considers reaction kinetics yields best agreement with the experimental data that have been used. One reasons as to why the kinetic model gives a better prediction of gas composition is due to the fact that there are higher reactant concentrations available for chemical reactions in the kinetic, in comparison to the combined model. Less reactant concentrations in the combined model is a result of the bed in the combined model consisting of two phases, according to the two-phase theory of fluidization that have been adapted. Both phases contain gases but the bubble phase is considered solid free, chemical reactions occur therefore only in the emulsion phase since the kinetic model is based on gas-solid reactions. The model that only contains reaction kinetics considers only one phase and all concentrations are available for chemical reactions. Higher char conversion is thus achieved in the model that only contains reaction kinetics and higher gas concentrations are produced.