The separation efficiency of a triboelectrostatic separation (TES) for fine coal cleaning depends profoundly on the surface charges of the particles involved. In general, the larger the difference between the charges of the particle to be separated, the higher the separation efficiency. The premise that coal and mineral matter can be triboelectrically charged differently serves as a basis for the TES process. In order to improve the separation performance, it is apparent that a highly efficient charger is needed for the TES unit, as well as the information on the triboelectrification mechanisms of the coal and mineral matter. Tribo- or contact electrification is a phenomenon in which electrical charge is usually transferred form one material to another, when two dissimilar materials are brought into rubbing or contact. In the present work, the triboelectrification mechanisms of coal, quartz, and pyrite were investigated in an in-line static mixer charger. A new in-situ charge-measuring device has been developed, in which an in-line mixer charger is located in side a Faraday cage. This makes it possible to observe the charging mechanisms of the particles when they pass through the mixer. This device was used to study the tribocharging mechanisms of coal, quartz, and pyrite as functions of the air velocity, particle feed rate, particle size, temperature, ash content, and the work functions of the materials that make up the in-line mixer. Evidence suggests that the charge transfer mechanisms of coal and mineral matter be due to electrons. A new turbocharger designed and developed in the present study has been tested and used to investigate the triboelectrification mechanisms of coal and quartz. The charge measurements were conducted using a developed on-line charge-measuring device, which is based on the principle of the Faraday cage. The tribocharging mechanisms of coal and quartz were investigated as functions of the particle feed rate, particle size, rotor-blade rotation speed, ash content, and the type of the materials used to construct the turbocharger. The information on the charging mechanisms of the coal and quartz will be useful for improving the triboelectrification process and subsequently the design of a TES unit. / Ph. D.

No description available.

Ultrafine particles (UFPs) with diameters smaller than 100 nm are omnipresent in ambient air. They are important sources for fine particles produced through the agglomeration and/or vapor condensation. With their unique properties, UFPs have also been manufactured for industrial applications. But, from the toxicological and health perspective, ultrafine particles with high surface-to-volume ratios often have high bio-availability and toxicity. Many recent epidemiologic studies have evidence UFPs are highly relevant to human health and disease. In order to better investigate UFPs, better instrumentation and measurement techniques for UFPs are thus in need. The overall objective of this dissertation is to advance out current knowledge on UFPs generation and measurement. Accordingly, it has two major parts: (1) ultrafine particle generation for laboratory aerosol research via electrospray (ES), and (2) ultrafine particle measurement for ambient aerosol monitor and personal exposure study via the development of a cost-effective and compact electrical mobility particle sizer. In the first part, to provide monodisperse nanoparticles, a new single capillary electrospray with a soft X-ray photoionizer as a charge reduction scheme has been developed. The soft X-ray effects on electrospray operation, particle size distribution and particle charge reduction were evaluated. To generate ultrafine particles with sufficient mass concentration for exposure/toxicity study, a TSE twin-head electrospray (THES) was evaluated, as well. The configuration and operational variables of the studied THES has been optimized. Three different nanoparticle suspensions were sprayed to investigate material difference. In the second part, to develop a miniature electrical mobility based ultrafine particle sizer (mini e-UPS), a new mini-plate aerosol charger and a new mini-plate differential mobility analyzer (DMA) have been developed. The performances of mini-plate charger and mini-plate DMA were carefully evaluated for ultrafine particles, including intrinsic/extrinsic charging, extrinsic charge distribution, DMA sizing accuracy and DMA transfer function. A prototype mini e-UPS was then assembled and tested by laboratory generated aerosol. Also a constrained least square method was applied to recover the particle size distribution from the current measured by a mini Faraday Cage aerosol electrometer.

No description available.

In gas-solid fluidized beds, the generation of electrostatic charges due to continuous contacts between fluidizing particles, and the particles and the fluidization vessel wall, is unavoidable. Industrial operations, such as the production of polyethylene, are susceptible to significant operational challenges caused by electrostatics including reactor wall fouling, a problem known as “sheeting”. The formation of particle sheets can require shutdown periods for clean-up which results in significant economic losses. To gain a better understanding of the underlying mechanisms of electrostatic charging in gas-solid fluidized beds, in an attempt to eliminate or minimize this problem, a pilot-scale pressurized gas-solid fluidization system was designed and built, housing an online electrostatic charge measurement technique consisting of two Faraday cups. The system permits the study of the degree of particle wall fouling at pressures and temperatures up to 2600 kPa and 100°C, respectively, and gas velocities up to 1 m/s (covering a range including turbulent flow regime). The system also allowed, for the first time, the measurement of the fluidizing particles’ mass, net charge and size distribution in various regions of the bed, especially those related to the wall coating under the industrially relevant operating conditions of high pressures and gas velocities. Experimental trials were carried out using polyethylene resin received from commercial reactors to investigate the influence of pressure and gas velocity on the bed hydrodynamics and in turn, the degree of bed electrification. Mechanisms for particle charging, migration and adherence to the column wall were proposed. The size distribution of the gas bubbles shifted towards smaller bubbles as the operating pressure was raised. Thus, higher pressures lead to greater mixing within the bulk of the bed and resulted in a higher degree of particle wall fouling. Moreover, the extent of wall fouling increased linearly with the increase in gas velocity and as the bed transitioned to turbulent regime, due to the increase in particle-wall contacts. Bipolar charging was observed especially within the wall coating with smaller particles being negatively charged. Overall, particle-wall contacts generated negatively charged particles resulting in a net negative charge in the bed, whereas particle-particle contacts generated positively and negatively charged particles resulting in no net charge when entrainment was negligible. The formation of the wall layer and its extent was influenced by the gravitational and drag forces balancing the image force and Coulomb forces (created by the net charge of the bed and the metallic column wall as the attraction between oppositely charged particles).