The oxidation of individually levitated char particles
An electrodynamic balance was constructed for use as a single particle thermogravimetric analyzer. The electrodynamic balance uses a vertical DC field to levitate an electrically charged particle. An AC voltage is applied to a ring electrode surrounding the particle between the DC electrodes. This A...
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| Format: | Others |
| Language: | en |
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1991
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| Online Access: | https://thesis.library.caltech.edu/2911/1/Wong_ba_1991.pdf Wong, Brian Alan (1991) The oxidation of individually levitated char particles. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/tm62-ax11. https://resolver.caltech.edu/CaltechETD:etd-07172007-090918 <https://resolver.caltech.edu/CaltechETD:etd-07172007-090918> |
| Summary: | An electrodynamic balance was constructed for use as a single particle thermogravimetric analyzer. The electrodynamic balance uses a vertical DC field to levitate an electrically charged particle. An AC voltage is applied to a ring electrode surrounding the particle between the DC electrodes. This AC field provides a restoring force if the particle is displaced from the center of the balance. A carbon dioxide laser was used to heat the particle. The temperature of the particle was measured by a dual-wavelength optical pyrometer. Two materials were the subject of oxidation studies, a porous synthetic carbon, Spherocarb and char made from PSOC 1451 bituminous coal. Two studies were performed, an ignition study, and a low temperature oxidation study. In the ignition study, a suspended particle was heated by a series of 500 millisecond pulses from the laser, at increasing oxygen concentrations. The particle temperature trace shows the ignition delay as predicted by Semenov's thermal explosion theory. A simple isothermal sphere model was applied with literature values for the physical parameters. A reasonably good match of the data to the model was found. In the low temperature experiments char particles were heated in air to a temperature of about 600°C. Some of the particles did not react at constant diameter, as expected. In particular, Spherocarb shrank or densified, as noted by others. The char particles formed from a narrow size cut of PSOC 1451 bituminous coal devolatilized at 1200K also shrank in size as it reacted. However the char formed at 1600K did not shrink, but oxidized at constant diameter. The densification phenomenon, then, is dependent on the devolatilization process and charring temperature. Simple char oxidation models will not accurately predict the size changes of these shrinking chars.
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