Electrostatic charging is a widely known natural phenomenon that has been observed sinceancient times. This phenomenon is also reported in solids handling and processing industrieswith varying extent of its interference in established processes and operations. Particlecollisions lead to electrostatic charge generation through triboelectrification. Sustainedcharging leads to particle agglomeration and adhesion, or even explosions. Hence, the presenceof charged particles are seen as a hindrance and a risk in certain processes. The focus of thisthesis is directed at gas-solid fluidization and pneumatic conveying where this holds true.Polyethylene is commonly manufactured in catalytic gas-solid fluidized bed reactors. Theinsulative nature of the polymer particles, the catalyst particles and the surrounding gas set upa conducive environment for electrostatic charge generation. Charged particles adhere on tonearby surfaces forming fused masses of polymer sheets. Presence of sheets in the reactorhinders the reactor productivity, thus warranting reactor shutdown and maintenance. On theother hand, catalyst introduction into the polyethylene reactor is performed through pneumaticconveying systems. In general, solids pneumatic conveying is known to cause the largestdegree of triboelectrification among many gas-solid systems. Therefore, the charging ofcatalyst particles may also contribute to operational challenges faced by this industry.Numerous studies have attributed particle characteristics, system variables, and operatingparameters as probable sources contributing to electrostatic charging in both fluidizationprocess and pneumatic conveying systems. However, a comprehensive consensus explainingparticle charging in real-world scenarios and suitable methods to mitigate or prevent chargingstill require further investigation. Thus, desirable control of charging in affected industrialsectors is still not present.Beyond the scope of fluidization and pneumatic conveying, certain studies have investigatedthe influence of dielectric strength of gases on the charging behaviour of solids. The worksclaim that gases with low dielectric strength perform better in minimizing electrostatic chargeof solids in controlled environments due to gas discharge and subsequent charge dissipation.Thus, applicability of such gases in dynamic processes like fluidization and pneumaticconveying must be investigated in hopes of reproducing similar observations. The principalaim of this thesis was to uncover a functional method to limit charging and particle adhesionin fluidization and other solids handling systems. As a means of accomplishing this, theobjective of this thesis was directed to study the efficacy of argon, which has a low dielectricstrength, against nitrogen in reducing triboelectrification of polyethylene particles influidization and pneumatic conveying operations.A stainless-steel fluidization apparatus was used to study the charging behaviour of acommercially produced polyethylene resin at atmospheric pressure. Results were drawn forpure argon and compared against pure nitrogen. Aiming to minimize the quantity of argonwhile simultaneously retaining as much efficacy as possible, binary mixtures of nitrogen andargon were also tested along with successive fluidization trials. Pure argon resulted in 90%reduction in fouling compared to pure nitrogen. Even binary mixture of 10 vol % argon showeda reduction of 50% in fouling values. Successive fluidization resulted in fouling valuescomparable to pure argon trials. Multiple pulse pneumatic conveying was carried out in astainless-steel tube with dehydrated amorphous silica that is a commonly used catalyst base inpolyethylene process. The net specific charge of the particles and the fouling inside the tubewere smaller under argon in the first injections. Subsequent injections were not as significant.Results from the above operations were validated through bench-scale shake tests performedunder controlled gaseous environment. Single large polyethylene particle charging was firsttested in nitrogen and argon atmosphere followed by multiple smaller particles. Bench-scaleshake tests showed argon influenced the saturation charges, reducing it and reaching it earliercompared to nitrogen. However, the degree of charge and fouling reduction was not assignificant as observed in fluidization trials.The thesis concludes that argon is indeed influential in reducing particle charge and particleadhesion in applicable systems. Influence of argon was observed in all operations withfluidization exhibiting the greatest degree of reduction in charging and fouling values.Furthermore, even small quantities of argon can make a non-linear impact on said parameters.The results also suggest that the majority of gas discharge and subsequent charge dissipationoccurs in areas of considerable electric fields. These are observed to entertain large number ofparticles contact and separation, providing plenty of opportunities for gas molecules to ionize.

A wide range of industrial processes involve multiphase granular flows. These include catalytic reactions in fluidized beds, the pneumatic conveying of raw materials and gas-particle separators. Due to the complex nature of multiphase flows and the lack of fundamental understanding of the phenomena in a multiphase system, appropriate design and optimized operation of such systems has remained a challenging field of research. Design of these processes is hampered by difficulties in upscaling pilot scale results, the difficulties involved in experimental measurements and in finding reliable numerical modelling methods. Significant work has been carried out on numerical modelling of multiphase systems but challenges remain, notably computational time, appropriate definition of boundary conditions, relative significance of effects such as lift and turbulence and the availability of reliable model validation. The work presented in this thesis encompasses experimental and numerical investigations of horizontal pneumatic conveying. In the experimental work, carefully controlled experiments were carried out in a 6.5 m long, 0.075 m diameter horizontal conveying line with the aid of the laser Doppler anemometry (LDA). Initially, LDA measurements were performed to measure the gas velocity in clear flow. Good agreement was observed between the theory and experimental measurements. For two-phase experiments, spherical and non-spherical particles with different sizes and densities were used to study the effect of particle size and solid loading ratio on the mean axial particle velocity. Three different sizes of spherical glass beads, ranging from 0.9 mm to 2 mm and cylindrical shaped particle of size 1x1.5 mm were employed. It was found that by increasing the particle size and solid loading ratios, the mean axial particle velocity decreased. Turbulence modulation of the carrier phase due to the presence of spherical particles was also investigated by measuring fluctuating gas velocity for clear gas flow and particle laden flow with different particle sizes and solid loading ratios. Results suggested that for the size ranges of particles tested, the level of gas turbulence intensity increased significantly by adding particles, and the higher the solid loading ratio, the higher the turbulence intensity. With the rapid advancement of computer resources and hardware, it is now possible to perform simulations for multiphase flows. For a fundamental understanding of the underlying phenomena in pneumatic conveying, the coupled Reynolds averaged Navier-Stokes and discrete element method (RANS-DEM) was selected. The aim of the modelling section of this study was to evaluate the abilities of coupled RANSDEM to predict the phenomena occurring in a research-sized pneumatic conveying line. Simulations for both one-way and two-way RANS-DEM coupling were performed using the commercial coupled software FLUENT-EDEM in an Eulerian- Lagrangian framework, where the gas is simulated as a continuum medium, while solid phase is treated as a discrete phase. In one-way coupling simulations, a considerable discrepancy in mean axial particle velocity was observed compared to the experimental results, meaning two-way coupling was required. It was further found that the inclusion of Magnus lift force due to particle rotation was essential to reproduce the general behaviour observed in the experiments. Turbulence modulation also was investigated numerically. Experimental and simulation results of gas and particle velocities were compared showing that the RANS-DEM method is a promising method to simulate pneumatic conveying. However, some discrepancy between simulation and experimental results was observed. Most studies in two-phase flow fields have focused on spherical particles. However the majority of particles encountered in industry involve non-spherical granules which show considerably different transportation behaviour compared with spherical particles. Further modelling of cylindrical particles was conducted using a multisphere model to represent cylindrical particles in the DEM code. Drag and lift forces and torque equations were modified in the code to take the effect of particle orientation into account. The framework developed was evaluated for two test cases, indicating a good agreement with the analytical and experimental results. The transportation of isometric (low-aspect-ratio) non-spherical particles in pneumatic conveying was also modelled. The simulation results of mean axial particle velocity agreed well with the experimental measurements with the LDA technique.

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

The rotary valve is a widely used mechanical device in many solids-handling industrial processes. However, it may also be responsible for most of the attrition effects occurring in a typical process. In this study, the attrition effects occurring in a rotary valve operating as a stand-alone device and as part of a pneumatic conveying system were investigated. In the former case granular attrition was carried out at three different rotary valve speeds and the experimental results obtained were found to be in good agreement with the Gwyn correlation. In the latter case three typical air flow rates were used in the pneumatic conveying system. The size distribution of the attrition product obtained at the lowest air flow rate used was not adequately described by the Gwyn correlation. The attrition process and mechanisms involved were analysed and the minimum size of the attrition product obtained from both modes of operations was found to be similar. / Singapore-MIT Alliance (SMA)

No description available.

Thesis (M.S.)--Ohio University, August, 2001. / Title from PDF t.p.

Thesis (M.S.)--University of Akron, Dept. of Electrical and Computer Engineering, 2006. / "December, 2006." Title from electronic thesis title page (viewed 12/31/2008) Advisor, Shivakumar Sastry; Committee members, Nathan Ida, James E. Grover; Department Chair, Alex De Abreu Garcia; Dean of the College, George K. Haritos; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

Abstract This study deals with optimal design of cantilevered fluid-conveying pipes. The aim is to maximize the critical flow speed of the fluid by means of additional masses, supporting springs or dampers along the length of the pipe. The optimization problem was formulated by modelling the pipe by FEM, using Euler-Bernoulli beam elements. The locations of the additional masses, springs and dampers and the properties of these elements (mass, spring constant and damping constant) were chosen as design parameters. The maximization problem for the critical fluid flow speed was solved by the sequential quadratic programming (SQP) technique. In addition to the presentation of the optimal values obtained for the design parameters, some aspects of the sensitiveness of the systems to variations in these parameters and the robustness of the optimum designs with respect to the stability of the system are studied. Although a considerable increase in the critical flow velocity of the fluid can be achieved in the example cases studied here, a marked sensitivity of the system to the location and properties of the additional elements in the optimum designs was observed. Also, the margin with respect to stability seems to be relatively small in some of the optimum designs considered. Non-linear numerical analysis confirmed the findings of the linear analysis with respect to the sensitivity of the optimum designs to the properties of the additional elements and revealed a very rich post-critical dynamic behaviour in the optimized structures.

M.Ing. (Engineering Management) / In a tender bid to energy and chemical company Sasol, a request to offer a technical solution for a two-flight overland conveyor system whose function is to transport coal from a 15 000 tonne bunker into an external stockpile storage facility in the plant was made. This conveyor consisted of two conveyor flight sections of lengths 18 423m and 8 537m each. The prospect of combining the two flights of conveyors to form one, super-efficient conveyor structure with additional cost saving benefits was identified. It was found that this occurrence was not unique to the individual project as other researching engineers have been faced with similar problems before [18]. This then lead the researcher into believing that there could be some advantage in investigating the possible benefits to the overall cost, maintainability and scheduling of the fabrication and erection activities for the entire project of combining the multiple flight conveyors into a single-flight conveyor. It is also the conviction of the researcher that the achieved outcomes will prove beneficial to the bulk materials handling industry as a whole. The problem is traditionally short, multiple flight conveyors have always been used for performing the function of transporting bulk material from one location in a mining plant to another hence; long, single-flight overland conveyors of lengths exceeding 26 km have not been commonly installed. In this dissertation the possibility of employing a single-flight overland as opposed to a two-flight conveyor in the Sasol Impumelelo coal plant is investigated. This is done against the work of other researchers who have conducted similar studies in the field as well as by utilizing project-specific data using applicable industry standards as well as Engineering Management course theory. By employing actual project procurement and engineering design data; the investigation is done by calculating and comparing the individual capital and operational costs that encompass the total cost of ownership (TCO) for both conveyor systems as well as the two systems’ reliability, availability and maintainability to establish each system’s complete life cycle costs. It is the opinion of the researcher that the investigation method is valid as it is in line with the guidelines given by The Miami University of Ohio [24] as well as J Hanek [25] and thus provides the researcher with a plausible technique for establishing which between the single-flight overland conveyor and two-flight overland conveyor configurations is overall the more superior system to install. It was found that even though its initial capital and operational costs are higher; the single-flight conveyor system is more reliable, readily available and cheaper to run and sustain over the 30 year expected life-span of the plant. It also is less labour intensive to perform maintenance on, yields less material degradation and results in less material spillage because of the elimination of additional transfer points and transfer towers. These results can be taken as valid on a global scale, for any mining plant, not restricted to any specific material as they are not subject to South African temperature, altitude or seismic conditions nor are they constrained to the type of bulk material being mined.

An air conveying system uses pressurized air as a propelling force to lift and move articles. It is supplied by a fan into a plenum with a top surface that is a flat perforated plate. Air escapes through the openings, creating a layer that supports and drives the articles along. This thesis provides information on the lifting and moving forces. It summarizes the results of both analytical and experimental studies. Most of the effort is focused on an experimental procedure for measuring the actual forces on the objects being conveyed and data are used to verify the analytical models. The experiments are limited to straight holes and louvers located under the bottom of aluminum concave-bottom cans. In some tests, a flat disc has been fixed to the bottom of the cans. Measurements are made of the can motion on an actual section of conveyor. / Master of Science