Effects of Low-temperature Oxidation on Caking Property of Coal
H Ota and T Takarada Gunma University Department of Biological
and Chemical Engineering, Japan
Low-temperature oxidation is a well-known but important process to
change the caking property of coal. In this paper, we aim at investigating
the mechanism of coal oxidation and the effect of oxidation treatment on
the caking property. Particle size of coal sample showed a pronounced effect
on the oxidation reaction. The oxidation reaction occurred more severely
in the outer layer of coal particles than inside the coal particles. FT-ir
was used to characterize the oxidized samples, and it was observed that
carbonyl functional group (C=O and COOH) and ether functional group ( -O-
) were the main products formed during the oxidation. The isotope 18O2
was used to trace the dynamics of the oxygen inherent in coal and that
absorbed during oxidation. It was found that during the oxidation treatment,
not only the oxygen adsorption occurred on the coals but also the reaction
took place between oxygen and the hydrogen in coal with the release of
H2O (m/z=20), and the two interactions may change the chemical bonds and
the amount of hydrogen in coal and thus affect the caking property of coal.
Coal Petrography by Low Cost Imaging
B Jenkins Jenkins-Kwan Technology Brisbane; G O’Brien, H Beath,
and J Esterle CSIRO Exploration and Mining and CSIRO Minerals, Brisbane
A new coal petrography technique is being developed to characterise
coking and thermal coals. It involves the analysis of micrographic
images of coal to produce a characteristic reflectance signature or ‘fingerprint’
called a full phase maceral reflectogram. This can be used for several
purposes: to qualitatively compare coals, to quantify maceral group proportions,
to determine rank from vitrinite reflectance distributions, and to provide
utilisation modelling parameters. A low cost system has been designed
to retro-fit to existing petrographic microscopes. Similar to manual
techniques, a petrographer is required to calibrate the illumination system
and manually collect images which takes about 45 minutes. The calibration
data is stored to assist with the image processing which takes a further
45 minutes offline. A reflectogram and report are generated in MS Excel.
Current developments and testing are aimed at expanding the rank range
for quantitative analyses (0.4 – 2.2 at present) and determination of blend
proportions.
Factors Affecting the Coking Properties of Blends
R Sakurovs, E Gawronski and L Burke CSIRO Division of Energy Technology,
Sydney
The aim of this work was to determine which of a number of factors
suspected to affect coke properties do in fact affect them.
Eleven Australian coals were used to prepare eight blends, which where
coked in a 400 kg Research Coke Oven. The blend compositions were
chosen such that effective rank and fluidity of the blends were the same
but other factors were allowed to vary. The strength, abrasion resistance
and reactivity of the cokes were examined
It was found that cokes prepared to the same effective rank and fluidity
had similar overall quality though the variation in some coke properties
was significant. Tow factors that some consider responsible for the
variations in coke quality had no effect on any coke property: variations
in reflectance (or V-step) distribution and the presence of high volatile
poorly-coking coals, even at additions as great as 25% wt.
One source of variation was due to the presence of one low-volatile
coal. When this coal was present in the blend there was a marked
decrease in the resistance to abrasion as measured by severe abrasion tests
although no other indices were significantly affected. It is hypothesized
that the cokes containing this coal tend to flake on extended abrasion,
owing to the relatively large domain sizes in the coke generated by this
coal, but that this form of abrasion has no effect on strength or reactivity.
There were significant variations in D1150/15 that were not due to
rank, rank distributions or fluidity of the blend and remained unexplained.
Additionally, the significant variations in CRI and CSR were observed that
were not due to variations in the elemental composition of the ash.