Fume, sub-micron aerosal particles in the combustion gases, have been identified
as a cause of extensive plugging and fouling in the heat transfer section of a kraft
recovery boiler in kraft pulp mills. After the deposition on the heat transfer surface,
fume deposits will undergo the sintering process which causes densification and
hardening, making them hard to remove. There has been relatively little information
available on the kinetics of the sintering of fume particles, and no information on the
modeling of the sintering process of this particular material. No conclusion about the
effect of chloride species on the sintering of fume particles has been made.
A series of sintering tests in air at various temperatures were conducted using
dense pellets made from a specific fume dust which contains a low amount of chlorides.
Each pellet was heated at a constant temperature, ranging from 300��C to 550��C, for a
different time interval. By the study of the microstructural change of each sintered
specimen, the initial stage, intermediate stage, and final stage of sintering were
identified. By the presence of an empirical constant K���, the relative linear shrinkage data
in the initial stage sintering fit well with the model proposed by Kingery and Berg��� when
volume diffusion is the controlling mechanism. By the presence of an empirical constant
K2 and the application of grain growth data, the porosity-time data in the intermediate
stage sintering fit well with the model proposed by Coble����� when volume diffusion is the
controlling mechanism. The apparent activation energy obtained from the initial stage
sintering is equal to 54.5 �� 27.7 kcal/mol which is in good agreement with the apparent
activation energy obtained from the intermediate stage sintering which is equal to
56.0 �� 31.3 kcal/mol. A semi-empirical model for the sintering process of this particular
well-packed fume dust was formulated. The model does not apply well to the loosely packed
fume dust due to some unidentified factors
The same experiment was carried out for the other fume dust which contains a
high amount of chloride. By the use of the fractional density, the qualitative comparison
of the sintering of the low chloride and high chloride dusts was made. At low
temperatures, the sintering rate of the high chloride fume dust is lower than that of the
low chloride fume dust. At high temperatures, both dusts have the same sintering rate
and can sinter close to the theoretical density. It is postulated here that the retarded
grain growth rate for the high chloride dust can improve the densification process in the
intermediate stage sintering. / Graduation date: 1996
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/34899 |
| Date | 04 October 1995 |
| Creators | Techakijkajorn, Udom |
| Contributors | Frederick, William James |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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